| 1. |
- Lundgren, Jonas, 1993-
(författare)
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Internal Cooling Design Using Multiphysics Topology Optimization
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis investigates topology optimization (TO) as a tool for designing optimal internal cooling configurations in components subjected to external hot gas streams. The work is motivated by the challenge of simultaneously considering objectives from multiple physics domains, and the rapid development of additive manufacturing (AM) in the industry, which makes it possible to realize highly complex TO designs. Against this background, a multi-physics TO approach is employed, involving the following physics domains: • Fluid mechanics: describes the flow of the coolant • Heat transfer: describes the coolant and component temperatures • Solid mechanics: describes the structural behaviour of the component Density-based TO is used to parametrize the design, such that the interpolation between solid and fluid material properties is governed by a spatially varying design variable. Temperature measures are considered as objectives in the non-convex optimization problems, and coolant mass flow and structural stiffness measures are considered as constraints. The design process is iterative: for a given design, the flow velocities are computed and used to calculate the temperature distribution, which in turn influences the domain’s structural response. These three equilibrium state problems are solved sequentially, followed by solving corresponding adjoint problems in reversed order, to acquire first-order sensitivity information used by the gradient-based optimization solver. Numerical simulations are carried out for geometries of varying degrees of complexity, resembling gas turbine guide vanes. The simulations cover a range of fidelity levels: from simpler 2D setups to more complex 3D setups with fine resolution, intended for execution on high-performance computing (HPC) clusters. Low-fidelity flow models are utilized in the TO process, while more advanced flow models are employed for design comparisons, and flow and heat response comparisons for given TO designs. The thesis consists of two parts: the first provides the theoretical framework, and the second includes appended papers. In Paper I, only the heat problem is included when modelling convection on internal boundaries identified using the design gradient. Fluid and solid mechanics are introduced in Paper II, where a conjugate heat transfer problem is augmented with a structural model coupled through thermal strains, with numerical examples in 3D. In Paper III, the simultaneous consideration of flow and heat objectives is formulated as a mathematical game between two players trying to minimize the average temperature in the domain and the coolant mass flow through the domain, respectively, with examples in 2D and 3D. The flow problems are the computational bottlenecks, and therefore, Paper IV demonstrates a 3D implementation investigating two different numerical techniques for solving the flow problem, with a voxelization approach for efficient meshing of complex geometries. Paper V presents an efficient, massively parallel HPC implementation for three-field flow-heat-structural models, and addresses further implementation details. This thesis highlights challenging aspects of large-scale multiphysics TO considering fluid mechanics, heat transfer, and solid mechanics.
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| 2. |
- Lundgren, Jan, 1977-
(författare)
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Behavioral Level Simulation Methods for Early Noise Coupling Quantification in Mixed-Signal Systems
- 2005
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, noise coupling simulation is introduced into the behavioral level. Methods and models for simulating on-chip noise coupling at a behavioral level in a design flow are presented and verified for accuracy and validity. Today, designs of electronic systems are becoming denser and more and more mixed-signal systems such as System-on-Chip (SoC) are being devised. This raises problems when the electronics components start to interfere with each other. Often, digital components disturb analog components, introducing noise into the system causing degradation of the performance or even introducing errors into the functionality of the system. Today, these effects can only be simulated at a very late stage in the design process, causing large design iterations and increased costs if the designers are required to return and make alterations, which may have occurred at a very early stage in the process. This is why the focus of this work is centered on extracting noise coupling simulation models that can be used at a very early design stage such as the behavioral level and then follow the design through the various design stages. To realize this, SystemC is selected as a platform and implementation example for the behavioral level models. SystemC supports design refinement, which means that when designs are being refined and are crossing the design levels, the noise coupling models can also be refined to suit the current design. This new way of thinking in primarily mixed-signal designs is called Behavioral level Noise Coupling (BeNoC) simulation and shows great promise in enabling a reduction in the costs of design iterations due to component cross-talk and simplifies the work for mixed-signal system designers.
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| 3. |
- Lundgren, Jan, 1977-
(författare)
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Simulating Behavioral Level On-Chip Noise Coupling
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, noise coupling simulation is introduced into the behavioral level. Methods andmodels for simulating on-chip noise coupling at the behavioral level in a design flow are presentedand verified for accuracy and validity. Today, designs of electronic systems are becoming denserand more and more mixed-signal systems such as System-on-Chip (SoC) are being devised. Thisraises problems when the electronics components start to interfere with each other. Often, digitalcomponents disturb analog components, introducing noise into the system causing degradation ofthe performance or even introducing errors into the functionality of the system.Today, these effects can only be simulated at a very late stage in the design process, causinglarge design iterations and increased costs if the designers are required to return and makealterations, which may have occurred at a very early stage in the process.This is why the focus of this work is centered on extracting noise coupling simulation modelsthat can be used at a very early design stage, such as at the behavioral level and then follow thedesign through the various design stages. To achieve this, SystemC is selected as a platform andimplementation example for the behavioral level models. SystemC supports design refinement,which means that when designs are being refined and are crossing the design levels, the noisecoupling models can also be refined to suit the current design.This new method of thinking in primarily mixed-signal designs is called Behavioral levelNoise Coupling (BeNoC) simulation and shows great promise in enabling a reduction in the costsof design iterations due to component cross-talk and simplifies the work for mixed-signal systemdesigners.
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| 4. |
- Matinrad, Niki, 1986-
(författare)
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An Operations Research Approach for Daily Emergency Management
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Emergency services play a vital role in society by providing help to affected people and minimizing damage to public and private assets as well as the environment during emergencies. However, these organizations deal with problems of increasing demand uncertainty and resource shortage over time. These problems lead to the creation of many other problems, such as longer response times, lower survivability of victims and patients, and more severe damage to properties and the environment. Acquiring more information about future emergency demand, such as factors affecting this demand, can contribute to reduction of the effects of increasing demand uncertainty. The introduction of volunteers as a new type of emergency resource, which has gained attention in the past few years, can be a solution to the problem of increasing resource shortage.The aim of this thesis is to provide operations research-based models and methods that can assist medical emergency services in daily emergency management. The aim is supported by two objectives: 1) to develop a forecasting model and 2) to develop models for the dispatch of volunteers. Three separate studies with a focus on these objectives are conducted, and the results are described in three papers.In the first paper, a forecasting model for predicting the volume of ambulance calls per hour and geographic location for three counties in Sweden is presented. The model takes into consideration geographical zones with few or no population and very low call frequency. Comparative results based on the real data of ambulance calls show that the proposed model performs better than the model that is currently used in some parts of Sweden for operational and tactical planning of emergency medical services. In addition to performance improvement, the proposed model provides information about the factors affecting ambulance demand.In the second paper, the use of volunteers in response to out-of-hospital cardiac arrest (OHCA) cases is considered, and a deterministic optimization model for their dispatch is provided. The model benefits from a survival function for determining dispatch decisions. The effect of arrival times of volunteers on the survivability of patients is also considered. The results show that, in terms of achieved survivability of patient based on the applied survival function, the proposed model performs better than simple decision rules used today.The third paper presents a probabilistic method for the dispatch of volunteers to OHCA cases. This method considers the uncertainties associated with the actions of volunteers once they are assigned a task. The proposed method uses a survival function as the objective of dispatch decisions. The results of the method are compared to the static dispatch method that is currently used in an operational system in Sweden for the utilization of volunteers in OHCA cases. Comparative results based on real data show that, with respect to used survival function, the proposed method contributes to higher survivability of OHCA patients than the static dispatch method.The models and method in this thesis focus on solving real-world problems and use real data for that purpose when available. Some simplifications were considered in the development process. Nevertheless, these models and method have the potential to be beneficial for medical emergency services in practice and can be used as a base for dynamic resource management systems. Such systems can be helpful for both tactical and operational planning of emergency resources.
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| 5. |
- Matinrad, Niki, 1986-
(författare)
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Models for Dispatch of Volunteers in Daily Emergency Response
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Sufficient emergency resources are essential for emergency services to provide timely help to affected people and to minimize damage to public and private assets and the environment. Emergency services, however, face resource shortages and increasing demand over time. As a result, their response times increase, resulting in lower survival chances of affected people and more severe damage to properties and the environment. Thus, emergency services need to utilize and effectively manage all their available resources. These can be divided into traditional resources, such as ambulances, and new and emerging resources, such as volunteers. Models and methods developed using operations research (OR) methodologies can facilitate the management of these resources. However, despite a rich literature on OR-based models and methods focusing on traditional resources, the literature on new and emerging resources, and specifically volunteers, is scarce.The aim of this thesis is to develop models and methods for task assignment and dispatch of volunteers to daily medical emergencies. This also includes forecasting models for future emergencies. The developed models and methods consider volunteer programs in Sweden and the Netherlands, employing real historical data.The aim has been addressed through three studies, one main study and two sub-studies, the results of which are presented in the six included papers. The main study focuses on the development of models, methods, and strategies for task assignment and dispatch of volunteers to out-of-hospital cardiac arrest (OHCA) cases using OR. To evaluate the survival rates of these patients, the most important health outcome of a response process, survival functions have been used in the development of these models and strategies. The results of this study are presented in Papers II–V. The first sub-study investigates different types of new and emerging resources used in daily medical emergency response, and the results are presented as an overview of the literature in Paper I. The second sub-study focuses on the forecast of medical emergency demand, and its outcomes are presented in Paper VI.The overall conclusion is that the use of OR-based models and methods can contribute to improved outcomes and increased survival probabilities compared to the strategies and techniques used in the existing systems.
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| 6. |
- Ulander, Anna
(författare)
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Optimization Based Decision Support Tools for Fire and Rescue Resource Planning
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- When accidents occur, it is essential that fire and rescue service respond quickly and efficiently to the accident site to reduce suffering and save lives and property. Planning and coordinating of fire and rescue resources is therefore important in order to maintain a safe society. Firefighters in Sweden have by tradition worked in teams of five, and they have been allocated to fire stations strategically located in populated areas. However, this working approach has recently started to change and the fire and rescue services have started to deploy smaller groups of firefighters. These smaller units can be, for example, strategically located near high-risk areas or roads, or used for preventive work. The complexity of the resource planning process thus increases since the decision makers have to keep track of a large number of small units spread over the area. The new way of working has resulted in an increased need of support tools that can help the fire and rescue services in decisions regarding the resource management.In this thesis, optimization based decision support tools are developed in order to to support the fire and rescue service so they can efficiently manage, coordinate and dispatch fire and rescue resources with respect to the present demand for service.To find appropriate strategic and tactical locations for different types of response units, an optimization model that minimizes the response time to expected accidents is developed. The model considers both the response time for the first responding unit as well as the response time for the last responding unit. Furthermore, the model is flexible enough to incorporate any type of accidents or resources. The results show that the model can be used to produce practical support for various types of location decisions.To support the more complex operational planning, three optimization based decision support tools are developed. The tools can help the fire and rescue service to always maintain an adequate level of preparedness for handling accidents. To evaluate the preparedness, a quantitative measure has been defined and serves as the basis for the tools. The first tool can help illustrate the preparedness, the second tool to select appropriate vehicles and firefighters to dispatch to accidents, and the third tool to suggest how resources can be relocated to maintain an adequate preparedness for new accidents.The developed decision support tools are evaluated through tests and experiments with fire and rescue services in Sweden. Results from the experiments indicate that the three tools can support the fire and rescue service in operational decisions and in maintaining an adequate preparedness for handling accidents, but also that the planning time seems to increase when using the support tools. However, the participants’ experiences of the tools were in general positive, and they thought the tools were useful and that the tools could support their daily work. The perception of preparedness, which usually varies quite a bit among individuals, also seems to become more uniform with access to the tools.
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| 7. |
- Elyasi-Pour, Roya, 1969-
(författare)
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Simulation Based Evaluation of Advanced Driver Assistance Systems
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Road transportation is an essential element of mobility in most countries and we can observe an increasing demand for both goods and passenger traffic. There are however important societal and economical problems related to road transportation in terms of congestions, traffic safety and environmental effects. During the last decades vehicles have increasingly been equipped with different types of Advanced Driver Assistance Systems (ADAS). These systems can to some extent compensate for human behaviour and errors that cause congestions, accidents and air pollution. Most studies conducted to evaluate ADAS have focused on ADAS impacts on the driver or on the vehicle. Since an ADAS might influence not only driving behaviour and vehicle dynamics, but also the interaction between equipped and non-equipped vehicles, it is also important to consider the resulting effect on the traffic system. A reliable and realistic evaluation approach needs to include estimations of drivers’ decisions in different traffic situations with respect to the ADAS functionality and how such decisions affect the traffic system as a whole.The overall aim of the thesis is to develop a simulation based evaluation framework for investigations of impacts of different types of cruise controllers on the traffic system. The objective is also to apply the framework to evaluate a fuel minimizing cruise controller for trucks, the Look Ahead Cruise Control (LACC). The framework developed consists of a combination of a microscopic traffic simulation model, and a vehicle and ADAS simulation model. When applied for a specific ADAS, as for example the LACC, the framework needs to be complemented with a driver model that captures the changes in driving behaviour due to the system of interest. In this thesis a driver model for LACC equipped trucks was developed based on results from a driving simulator experiment, a field operational test, and a focus group study. Simulation experiments were carried out to observe the LACC impacts on the traffic system with respect to penetration rate, traffic density, and variation in the desired speed. Environmental effects were estimated using emission calculations.
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| 8. |
- Johnsson, Inger W, 1973-
(författare)
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Long-term metabolic effects of a high birth weight
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The intrauterine environment influences foetal growth as well as future response to risk factors for disease. This occurs partly through epigenetic mechanisms. Thus, birth weight is a possible risk marker of adult disease. Low birth weight is a well-known risk factor for adult disease, particularly when associated with obesity and a U-shaped relationship between birth weight and several metabolic diseases has been suggested.In this thesis we investigated associations between a high birth weight and risk of adult disease, e.g. obesity, cardiovascular disease, type 2 diabetes and gestational diabetes.By analyses of national register data on 759 999 subjects up to the age of 37 years, we could demonstrate an increased risk of type 2 diabetes in males, but not in females, with a high birth weight (>2 SDS). The increase was particularly pronounced in males with a birth weight >3 SDS. There was an association between high birth weight and obesity in males and females, but no such relation was seen for hypertension or serum lipid abnormalities.In a clinical study, 27 cases with a birth weight ≥4 500 grams were compared with 27 controls with normal birth weight, regarding risk factors for cardiovascular disease and diabetes. The cases had a greater radial artery intima thickness and intima:media ratio compared with the controls indicating early atherosclerotic changes. Body mass index, body composition, insulin sensitivity, lipid profiles, blood pressure, resting energy expenditure and respiratory quotient did not differ between cases and controls, but females with a high birth weight had a more disadvantageous distribution of body fat.In order to investigate associations between birth weight and pregnancy outcomes, register data on 305 893 females was analysed. The results demonstrated an association between the female´s own birth weight and offspring birth weight. A high maternal birth weight was associated with increased risk of obesity. The risk of gestational diabetes was increased in females with a low, but not a high birth weight.In conclusion, subjects with a moderately high birth weight did not differ substantially from those with a normal birth weight regarding risk factors for cardiovascular disease. However, differences in arterial wall dimensions were demonstrated in a clinical investigation, and there were differences in BMI and risk of type 2 diabetes on a population level. Since risks are most pronounced in subjects with a birth weight >3 SDS, this group is in particular need of follow up and disease preventive measures.
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| 9. |
- Khoshniyat, Fahimeh
(författare)
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Optimization-Based Methods for Revising Train Timetables with Focus on Robustness
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With increase in the use of railway transport, ensuring robustness in railway timetables has never been this important. In a dense railway timetable even a small disturbance can propagate easily and affect trains' arrival and departure times. In a robust timetable small delays are absorbed and knock-on effects are prevented effectively. The aim of this thesis is to study how optimization tools can support the generation of robust railway traffic timetables. We address two Train Timetabling Problems (TTP) and for both problems we apply Mixed Integer Linear Programming (MILP) to solve them from network management perspectives. The first problem is how robustness in a given timetable can be assessed and ensured. To tackle this problem, a headway-based method is introduced. The proposed method is implemented in real timetables and evaluated from performance perspectives. Furthermore, the impact of the proposed method on capacity utilization, heterogeneity and the speed of trains, is monitored. Results show that the proposed method can improve robustness without imposing major changes in timetables. The second problem addressed in the thesis is how robustness can be assessed and maintained in a given timetable when allocating additional traffic and maintenance slots. Different insertion strategies are studied and their consequences on capacity utilization and on the properties of the timetables are analyzed. Two different insertion strategies are considered: i) simultaneous and ii) stepwise insertion. The results show that inserting the additional trains simultaneously usually results in generating more optimal solutions. However, solving this type of problem is computationally challenging. We also observed that the existing robustness metrics cannot capture the essential properties of having more robust timetables. Therefore we proposed measuring Channel Width, Channel Width Forward, Channel Width Behind and Track Switching.Furthermore, the experimental analysis of the applied MILP model shows that some cases are computationally hard to solve and there is a need to decrease the computation time. Hence several valid inequalities are developed and their effects on the computation time are analyzed.This thesis contains three papers which are appended. The results of this thesis are of special interests for railway traffic planners and it would support their working process. However, railway traffic operators and passengers also benefit from this study.
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| 10. |
- Lundgren, Lars, 1973-
(författare)
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Culture and Transmission : The Technological and Cultural Reach of International Syndicated Radio
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this dissertation is to study the technological and cultural reach of internationally syndicated radio from the vantage point of the radio programme Solid Steel between 2000 and 2006. Solid Steel is a weekly two-hour music show originally produced and aired in London but today also broadcast by a large number of stations around the world, as well as via the Internet. The theoretical interest of the study lies in the tension and separation between communication as transmission and communication as ritual, as distribution in space and maintenance in time. This separation produces a number of subsequent conceptual pairs; technology and culture, material and symbolic, space and time, etc. Based upon these pairs the study explores the spatial and temporal organization of Solid Steel.As a first step in the analysis the original context of production in London is studied, noticing a shift from being a local production to an international syndication, as well as from a live studio production to a pre-produced show. The stations syndicating Solid Steel are then mapped according to their geographical location as well as their organizational form. Next, the themes and values enunciated in relation to the programme are examined, both as expressed by the producers in interviews and by texts published on the programme’s website. The programme is then analysed with these values in mind, with particular focus on the temporal organization of the music played, employing the concepts of flow and changing same. This part of the analysis is carried out on two levels, first the programme structure and then the actual sequences of sounds and songs making up the music mix. The final chapter returns to the opening concerns over culture and transmission, suggesting that new forms of radio, here exemplified by Solid Steel, may help us further our understanding of time and space in relation to international media productions.
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| 11. |
- Olstam, Johan, 1979-
(författare)
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Simulation of Surrounding Vehicles in Driving Simulators
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Driving simulators and microscopic traffic simulation are important tools for making evaluations of driving and traffic. A driving simulator is de-signed to imitate real driving and is used to conduct experiments on driver behavior. Traffic simulation is commonly used to evaluate the quality of service of different infrastructure designs. This thesis considers a different application of traffic simulation, namely the simulation of surrounding vehicles in driving simulators.The surrounding traffic is one of several factors that influence a driver's mental load and ability to drive a vehicle. The representation of the surrounding vehicles in a driving simulator plays an important role in the striving to create an illusion of real driving. If the illusion of real driving is not good enough, there is an risk that drivers will behave differently than in real world driving, implying that the results and conclusions reached from simulations may not be transferable to real driving.This thesis has two main objectives. The first objective is to develop a model for generating and simulating autonomous surrounding vehicles in a driving simulator. The approach used by the model developed is to only simulate the closest area of the driving simulator vehicle. This area is divided into one inner region and two outer regions. Vehicles in the inner region are simulated according to a microscopic model which includes sub-models for driving behavior, while vehicles in the outer regions are updated according to a less time-consuming mesoscopic model.The second objective is to develop an algorithm for combining autonomous vehicles and controlled events. Driving simulators are often used to study situations that rarely occur in the real traffic system. In order to create the same situations for each subject, the behavior of the surrounding vehicles has traditionally been strictly controlled. This often leads to less realistic surrounding traffic. The algorithm developed makes it possible to use autonomous traffic between the predefined controlled situations, and thereby get both realistic traffc and controlled events. The model and the algorithm developed have been implemented and tested in the VTI driving simulator with promising results.
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| 12. |
- Steins, Krisjanis
(författare)
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Towards Increased Use of Discrete-Event Simulation for Hospital Resource Planning
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Health care systems in many countries are experiencing a growing demand while their resources remain limited. The discrepancy between demand and capacity creates many problems – long waiting times for treatment, overcrowding in hospital wards, high workload, etc. More efficient delivery of health care services can be achieved by better planning of its resources so that the mismatch between demand and capacity is minimized. Planning health care resources, including hospital resources, is difficult due to system complexity and variability in both resource availability and demand. Discrete-event simulation and other operational research methods can be used for solving planning problems in health care, and have been gaining increased attention from researchers during recent decades. Despite the growing number of academic publications, simulation appears to be less used in health care than in other application areas and only a small proportion of simulation studies is actually implemented.The aim of this thesis is to contribute to increased use of discrete-event simulation in hospital resource planning. The separate studies regarding intensive care unit capacity planning, operating room allocation strategies and the management of emergency patient flow in a radiology department highlight both the possibilities and the requirements for practical application of discrete-event simulation in hospital resource planning. The studies are described in five papers.In the first paper, the relationship between intensive care unit (ICU) occupancy and patient outcomes was investigated and the results showed that risk adjusted mortality was higher in the group of patients who were treated during high levels of occupancy. This indicates that appropriate planning of ICU resources is necessary to avoid adverse effects on patient outcomes.In the second paper, analysis of a relatively simple care chain consisting of two hospital departments – emergency and radiology – revealed a process that was not very well defined and measured. Investigation into data availability uncovered disparate information systems storing incompatible and fragmented data. It suggests that the current degree of process orientation and the current IT infrastructure does not enable efficient use of quantitative process analysis and management tools such as simulation.In the third paper, the value and possibilities of using simulation modelling in hospital resource planning were examined through the development and use of a simulation model for improved operating room time allocation and patient flow in a hospital operating department. The model was initially used for studying overcrowding in a post-anaesthesia care unit. Advanced planning logic implemented in the model enabled evaluation of several different scenarios aiming to improve the utilization of operating room resources. The results showed that it is possible to achieve slightly better and more even resource utilization, as well as provide greater flexibility in scheduling operations.In the fourth paper, a generic ICU model was developed and validated using data from four different hospital ICUs. The model was adapted and calibrated stepwise in order to identify important parameters and their values to obtain a match between model predictions and actual data. The study showed that in presence of high quality data and well defined process logic it is possible to develop a generic ICU simulation model that could provide accurate decision support for planning critical care resources.In the fifth paper, a number of factors that can contribute to successful implementation of simulation results in health care were identified. The timing of the simulation study must be right to support a critical decision, the benefit from implementation should clearly outweigh the cost of making the necessary changes and the model should be thoroughly validated to increase the credibility of the results. Staff involvement in simulation modelling activities, availability of good quality data, as well as proper incentives to improve the system contribute to implementation as well. These findings can help in establishing the conditions for successful implementation in future applications of simulation modelling in health care.
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| 13. |
- Tapani, Andreas, 1978-
(författare)
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Traffic Simulation Modelling of Rural Roads and Driver Assistance Systems
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Microscopic traffic simulation has proven to be a useful tool for analysis of varioustraffic systems. This thesis consider microscopic traffic simulation of rural roads andthe use of traffic simulation for evaluation of driver assistance systems.A traffic simulation modelling framework for rural roads, the Rural Traffic Simulator(RuTSim), is developed. RuTSim is designed for simulation of traffic on singlecarriageway two-lane rural roads and on rural roads with separated oncoming trafficlanes. The simulated traffic may be interrupted by vehicles entering and leaving themodelled road at intersections or roundabouts.The RuTSim model is applied for analysis of rural road design alternatives.Quality-of-service effects of three alternatives for oncoming lane separation of anexisting Swedish two-lane road are analysed. In another model application, RuTSimis used to simulate traffic on a Dutch two-lane rural road. This application illustratesthat the high level of model detail of traffic micro-simulation may call for use of differentmodelling assumptions regarding driver behaviour for different applications,e. g. for simulation of traffic in different cultural regions.The use of traffic simulation for studies of driver assistance systems facilitateimpact analyses already at early stages of the system development. New and additionalrequirements are however then placed on the traffic simulation model. It isnecessary to model both the system functionality of the considered driver assistancesystem and the driver behaviour in system equipped vehicles. Such requirements canbe analysed using RuTSim.In this thesis, requirements on a traffic simulation model to be used for analysisof road safety effects of driver assistance systems are formulated and investigatedusing RuTSim. RuTSim is also applied for analyses of centre line rumble stripson two-lane roads, of an overtaking assistant and of adaptive cruise control. Thesestudies establish that the assumptions made regarding driver behaviour are crucialfor traffic simulation based analyses of driver assistance systems.
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| 14. |
- Tsanakas, Nikolaos, 1987-
(författare)
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Data-Driven Approaches for Traffic State and Emission Estimation
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Traffic congestion is one of the most severe problems in modern urban areas. Besides the amplified travel times, traffic congestion intensifies the amount of emitted pollutants impacting human health and the environment. By making the appropriate interventions in traffic, transportation planners can mitigate congestion and enhance the performance of a traffic system. One crucial step in traffic planning and management is the estimation of the current or historical traffic state of a network. The estimation of the traffic state variables (traffic flow, density and speed) reveals the problematic parts of a network, namely, the parts associated with severe congestion and high emission rates. Traffic-related observations and traffic models constitute two core elements of a traffic state estimation approach. While the available observation data explicitly or implicitly provide partial information on the traffic state, traffic models define the traffic behaviour and contribute to estimating the variables when they are not directly observable. The estimated traffic state variables form the input to the so-called emission models, which estimate the mass of the emitted pollutants.The type and availability level of the observation data play a key role in traffic state and emission estimation. Traditionally, the primary source of traffic-related field data are stationary detectors (loop detectors, radar sensors or cameras). Today, following the late advances in communication systems, a vast amount of traffic-related data from mobile sources (GPS or cellular networks) is available. Such high data availability may give transportation planners new insights into understanding traffic behaviour. Appropriate exploitation of data coming from mobile sources can improve the existing approaches for estimating the traffic state and emissions.The broad aim of this thesis is to enhance the quality of traffic state and emission estimation. A special focus is given to the development of methods for exploiting the growing availability of traffic-related field data. By combining traffic data and models, the thesis proposes data-driven approaches for traffic state and emission estimation.The first part of the thesis (Paper I and Paper II) focuses on improving the current approaches for network-wide emission estimation. Traditionally, network-wide emission estimations rely on a static traffic-modelling framework. In Paper I, we suggest an alternative emission estimation approach, which is based on a quasi-dynamic traffic model. To evaluate our approach, we perform field experiments on a 19 km long highway stretch in Stockholm. The results show that our method can improve the spatiotemporal distribution of the estimated emissions. In Paper II, the approach suggested in Paper I is applied to a more extensive network covering the city of Norrköping. The results indicate that our approach yields a realistic spatial layout of emissions.The second part of the thesis (Paper III and Paper IV) suggests novel data-driven approaches for estimating network-wide traffic flows and demand. More specifically, in Paper III, we develop a data-driven traffic-flow propagation approach by utilising traveltime observations. Our method is based on a piecewise linear approximation of the travel time function, which allows the use of an efficient event-based structure for propagating the traffic flow. We evaluate our approach through simulation-based experiments, and the results provide proof of the concept. In Paper IV, we exploit the approach suggested in Paper III to develop an efficient data-driven scheme for estimating the traffic demand. The results of the simulation-based experiments indicate that our approach might lead to more accurate estimations compared to other data-driven estimation approaches suggested in the literature.Finally, the last part of the thesis (Paper V) focuses on the estimation of fuel consumption and emissions at a vehicle level. In paper V, we propose a novel method for generating virtual vehicle trajectories by fusing data from different sources. Our approach provides a detailed description of vehicle kinematics, and thus, it permits the use of the underlying virtual vehicle trajectories to vehicle dynamics-sensitive applications, such as emission modelling. The results of our experiments show that the advanced modelling of vehicle kinematics can enhance the accuracy of the estimated emissions.
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| 15. |
- Åsa, Weinholt
(författare)
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Exploring Collaboration Between the Fire and Rescue Service and New Actors : Cost-efficiency and Adaptation
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The emergency services serves an important purpose in society by ensuring that people in need, regardless of their geographical location, receives help when they fall victims to undesirable incidents. Existing resources are however often limited and concentrated to urban areas making travel distances to remote areas long. Local authorities are also facing budget constraints and clients are becoming more demanding. This means that the emergency services need to do more, but with less resources. Collaboration with new actors has therefore been proposed as a solution. There exist several actors with basic knowledge in both fire suppression or medical treatment that might be able to contribute at an early stage in order to reduce response time and provide help to citizens in need. However, little research has been dedicated to investigating the possibilities and the potential of new collaborative practices in every day accidents.In this thesis collaboration between new actors and the fire and rescue service (FRS) in Sweden is studied. The aim is to analyze whether collaborative practices leads to an increased cost-efficiency, for the FRS and society as a whole. The thesis also aims to analyze how traditional actors and new actors adapt to collaborative practices.For evaluating cost-efficiency in the FRS stochastic frontier analysis is used and for analyzing the societal effects cost-benefit analysis is applied. In total three cases are studied; (1) security officers assisting the FRS in fire alarms (2) home care nurses collaborating with the FRS in medical alarms and (3) citizens responding to FRS-alarms through SMS.The results do not show that collaboration have led to increased cost-efficiency in the FRS during the studied time period. However, despite that no evidence for increased cost-efficiency is found in the FRS, there are several societal gains from collaborating related to e.g. equity, quality and effectiveness. And the costs for implementing collaborative arrangements are relatively low. It is however argued that to be able to get the most out of collaboration more emphasis should be put on building common platforms, where the different organizations and actors can communicate, share experiences, organize joint training sessions and actually collaborate. Today interaction outside the rescue site hardly exist between the collaborative partners; the actual collaboration between the FRS and the new actors is limited only to the response phase. Also, the FRS do not adapt their bureaucratic structures to collaborate with the new actors. Instead the changes associated with collaboration affect mainly the new actors, as an addition to their regular duties. Factors related to discretion, professional identity and personal motivation are identified as important for understanding how new actors adapt to collaboration.
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| 16. |
- Allström, Andreas
(författare)
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Highway Traffic State Estimation and Short-term Prediction
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Traffic congestion is increasing in almost all large cities, leading to a number of negative effects such as pollution and delays. However, building new roads is not a feasible solution. Instead, the use of the existing road network has to be optimized, together with a shift towards more sustainable transport modes. In order to achieve this there are several challenges that needs to be addressed. One challenge is the ability to provide accurate information about the current and future traffic state. This information is an essential input to the traffic management center and can be used to influence the choices made by the travelers. Accurate information about the traffic state on highways, where the potential to manage and control the traffic in general is very high, would be of great significance for the traffic managers. It would help the traffic managers to take action before the system reaches congestion and limit the effects of it. At the same time, the collection of traffic data is slowly shifting from fixed sensors to more probe based data collection. This requires an adaptation and further development of the traditional traffic models in order for them to handle and take advantage of the characteristics of all types of data, not just data from the traditionally used fixed sensors.The objective of this thesis is to contribute to the development and implementation of a model for estimation and prediction of the current and future traffic state and to facilitate an adaptation of the model to the conditions of the highway in Stockholm. The model used is a version of the Cell Transmission Model (CTM-v) where the velocity is used as the state variable. Thus, together with an Ensemble Kalman Filter (EnKF) it can be used to fuse different types of point speed measurements. The model is developed to run in real-time for a large network. Furthermore, a two-stage process used to calibrate the model is implemented. The results from the calibration and validation show that once the model is calibrated, the estimated travel times corresponds well with the ground truth travel times collected from Bluetooth sensors.In order to produce accurate short-term predictions for various networks and conditions it is vital to combine different methods. We have implemented and evaluated a hybrid prediction approach that assimilates parametric and non-parametric short-term traffic state prediction. To predict mainline sensor data we use a neural network, while the CTM-v is ran forward in time in order to predict future traffic states. The results show that both the hybrid approach and the CTM-v prediction without the additional predicted mainline sensor data is superior to a naïve prediction method for longer prediction horizons.
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| 17. |
- Andersson, Emma V.
(författare)
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Assessment of Robustness in Railway Traffic Timetables
- 2014
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A tendency seen for the last decades in many European railway networks is a growing demand for capacity. An increased number of operating trains has led to a delay sensitive system where it is hard to recover from delays, where even relatively small delays are easily propagating to other traffic.The overall aim of this thesis is to analyse the robustness of railway traffic timetables; why delays are propagating in the network and how the timetable design and dispatching strategies influence the delays. In this context we want to establish quantitative measures of timetable robustness. There is a need for measures that can be used by the timetable constructors. Measures that identify where and how to improve the robustness and thereby indicating how and where margin time should be inserted. It is also important that the measures can capture interdependencies between different trains.In this thesis we introduce the concept of critical points, which is a practical approach to identify robustness weaknesses in a timetable. In contrast to other measures, critical points can be used to identify specific locations in both time and space. The corresponding measure, Robustness in Critical Points (RCP) provides the timetable constructors with concrete suggestions for which trains that should be given more runtime or headway margin. The measure also identifies where the margin time should be allocated to achieve a higher robustness.In a case study we show that the delay propagation is highly related to the operational train dispatching. This study shows that the current prioritisation rule used in Sweden results in an economic inefficiency and therefore should be revised. This statement is further supported by RCP and the importance of giving the train dispatchers more flexibility to efficiently solve conflict situations.
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| 18. |
- Backåker, Lars, 1984-
(författare)
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The Influence of Customer Agreements and Planning Principles on Rail Freight Performance
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Rail freight transportation is recognized worldwide as a suitable transportation mode when it comes to long haul transportation of heavy commodities. The industry is also known to be capital intensive, highly dependent on infrastructural developments and requires thorough planning of operations. Despite intensive planning of operations, great challenges remain in how to make best use of existing resources. Especially uncertainties related to up-coming daily freight volumes stand as central causes behind such planning challenges. This thesis focuses on rail freight carload transportation and concerns how customer commitments influence operational performance as well as potentials for improvements of operational planning principles. Problem statements are addressed using three separate studies and all experiments involve quantitative approaches. The first study investigates effects of a potential Volume Variation Allowance (VVA) policy through simulation. The policy dictates how much freight volumes are allowed to vary by day of week. Results indicate that effects of the policy are relatively small, but an overall decrease in transportation times is observed. The study also identifies improvement potentials with respect to the current operational planning principles used within Swedish railways. The second study proposes a new optimization-based approach for trip plan generation. The approach, including a number of extensions, is evaluated against the current industry practice. Results confirm the potentials for reduced transportation times, shunting activities as well as service frequencies. All experiments satisfy existing customer commitments. The third study explores effects of a Fixed Carload Capacity (FCC) concept which partially allows capacity reservation on services. The study adopts an extension of the previously developed optimization approach. Results confirm the hypothetical trade-off between customer groups and the dependency on capacity reservation levels, but indicate that the concept has relatively small effects with respect to regular carload customers. On the other hand, benefits in terms of guarantee of service and reliability in transportation times can be observed for the customer under the agreement.
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| 19. |
- Brugés, Javier Mauricio
(författare)
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Surface characterization methods for quality assessment of polyethylene-coated paperboard
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In manufacturing processes, the quality of a product often depends on its surface, and careful control of surface properties is critical to meet customer requirements. A thin layer of polyethylene (PE) is applied to paperboard to increase barrier functionality and high optical quality of the product. For PE-coated paperboard, product quality inspection is performed at the end of the manufacturing process by taking a portion of the reel to the laboratory for quality inspection. These associated offline characterization methods are destructive and time consuming and are representative of only a small portion of the product.The overall goal of this thesis is to provide new methods to characterize the Surface properties of PE-coated paperboard. Specifically, to determine imaging techniques for measuring surface parameters that affect its barrier functionality and surface roughness.In this thesis, two methods for surface characterization of PE-coated paperboard are presented to quantify the two most important product-related quality parameters, i.e. barrier functionality and optical quality, which are affected by the presence of defects in the coating and by the surface roughness of the product, respectively. First, a full-Stokes imaging polarimeter (FSIP) is used to detect the presence of PE-coated material and to distinguish between coated and uncoated samples at the pixel level. Second, a three-dimensional scanning electron microscope (3D SEM) is employed to calculate the Surface roughness of PE-coated paperboard. These surface characterization techniques offer an advantage over the industry standard due to the high speed and non-contact nature of the measurement, while increasing the throughput of the sample surface parameters studied.A classification accuracy of 99, 74% is achieved using a FSIP to distinguish between PE- and non-PE-coated paperboard at pixel level. Using the 3D SEM technique to measure the topography of PE-coated samples results in a faster method that is comparable in accuracy to a chromatic confocal microscope (CCM). The surface roughness measured with the 3D SEM differs from the standard method by up to 6% and good agreement with statistical parameters is found.In general, surface analysis of PE-coated is often a complex and difficult task for imaging techniques and suitable methods need to be evaluated for their sensitivity to measure the desired surface parameters. The presented characterization techniques inspect larger areas of PE-coated paperboard compared to current industry standards. These methods provide a quantitative solution for surface characterization to inspect the surface parameters necessary to assure the product’s quality.
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| 20. |
- Ekström, Joakim, 1980-
(författare)
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Designing Urban Road Congestion Charging Systems : Models and Heuristic Solution Approaches
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The question of how to design a congestion pricing scheme is difficult to answer and involves a number of complex decisions. This thesis is devoted to the quantitative parts of designing a congestion pricing scheme with link tolls in an urban car traffic network. The problem involves finding the number of tolled links, the link toll locations and their corresponding toll level. The road users are modeled in a static framework, with elastic travel demand.Assuming the toll locations to be fixed, we recognize a level setting problem as to find toll levels which maximize the social surplus. A heuristic procedure based on sensitivity analysis is developed to solve this optimization problem. In the numerical examples the heuristic is shown to converge towards the optimum for cases when all links are tollable, and when only some links are tollable.We formulate a combined toll location and level setting problem as to find both toll locations and toll levels which maximize the net social surplus, which is the social surplus minus the cost of collecting the tolls. The collection cost is assumed to be given for each possible toll location, and to be independent of toll level and traffic flow. We develop a new heuristic method which is based on repeated solutions of an approximation to the combined toll location and level setting problem. Also, a known heuristic method for locating a fixed number of toll facilities is extended, to find the optimal number of facilities to locate. Both heuristics are evaluated on two small networks, where our approximation procedure shows the best results.Our approximation procedure is also employed on the Sioux Falls network. The result is compared with different judgmental closed cordon structures, and the solution suggested by our method clearly improves the net social surplus more than any of the judgmental cordons.
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| 21. |
- Ekström, Joakim, 1980-
(författare)
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Optimization Approaches for Design of Congestion Pricing Schemes
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In recent years, there has been a growing interest in congestion pricing as a tool for solving traffic congestion problems in urban areas. However, the transportation system is complex and to design a congestion pricing scheme, i.e. to decide where and how much to charge the road users, is not trivial. This thesis considers congestion pricing schemes based on road tolls, and the efficiency of a pricing scheme is evaluated by a social welfare measure. To assist in the process of designing congestion pricing schemes, the toll design problem (TDP) is formulated as an optimization problem with the objective function describing the change in social welfare. In the TDP, the road users are assumed to be distributed in the traffic network according to a Wardrop equilibrium. The TDP is a non-convex optimization problem, and its objective function is non-smooth. Thus, the TDP is considered as a hard optimization problem to solve.This thesis aims to develop methods capable of optimizing both toll locations and their corresponding toll levels for real world traffic networks; methods which can be used in a decision support framework when designing new congestion pricing schemes or tuning already implemented ones. Also, this thesis addresses the global optimality of the TDP. 'In this thesis, a smoothening technique is applied which approximates the discrete toll location variables by continuous functions (Paper I). This allows for simultaneous optimization of both toll locations and their corresponding toll levels, using a sensitivity analysis based ascent algorithm. The smoothening technique is applied in a Stockholm case study (Paper II), which shows the potential of using optimization when designing congestion pricing schemes.Global optimality of the TDP is addressed by piecewise linear approximations of the non-linear functions in the TDP (Papers III and IV), resulting in a mixed integer linear program (MILP). The MILP can be solved to global optimality by branch and bound/cut methods which are implemented in commercially available software.
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| 22. |
- Furukawa, Toshi A., et al.
(författare)
-
Dismantling, optimising, and personalising internet cognitive behavioural therapy for depression : a systematic review and component network meta-analysis using individual data
- 2021
-
Ingår i: Lancet psychiatry. - London, United Kingdom : Elsevier. - 2215-0374 .- 2215-0366. ; 8:6, s. 500-511
-
Forskningsöversikt (refereegranskat)abstract
- Findings We identified 76 RCTs, including 48 trials contributing individual participant data (11 704 participants) and 28 trials with aggregate data (6474 participants). The participants' weighted mean age was 42.0 years and 12 406 (71%) of 17 521 reported were women. There was suggestive evidence that behavioural activation might be beneficial (iMD -1.83 [95% credible interval (CrI) -2.90 to -0.80]) and that relaxation might be harmful (1.20 [95% CrI 0.17 to 2.27]). Baseline severity emerged as the strongest prognostic factor for endpoint depression. Combining human and automated encouragement reduced dropouts from treatment (incremental odds ratio, 0.32 [95% CrI 0.13 to 0.93]). The risk of bias was low for the randomisation process, missing outcome data, or selection of reported results in most of the included studies, uncertain for deviation from intended interventions, and high for measurement of outcomes. There was moderate to high heterogeneity among the studies and their components. 511
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| 23. |
- Grumert, Ellen
(författare)
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Cooperative Variable Speed Limit Systems : Modeling and Evaluation using Microscopic Traffic Simulation
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- During the last decades the road traffic has increased tremendously leading to congestion, safety issues and increased environmental impacts. As a result, many countries are continuously trying to find improvements and new solutions to solve these issues. One way of improving the traffic conditions is by the use of so called intelligent transport systems, where information and communication technologies are being used for traffic management and control. One such system commonly used for traffic management purposes are variable speed limit systems. These systems are making use of signs to show speed limits adjusted to the prevailing road or traffic conditions. The rapid development in telecommunication technologies has enabled communication between vehicles, and between vehicles and the infrastructure, so called cooperative systems. This opens up for the possibility to further improve the performance of a standard variable speed limit system by adding cooperative system features.The overall aim of this thesis is to investigate the potential benefits of incorporating infrastructure to vehicle communication and autonomous control to an existing variable speed limit system. We show how such a cooperative variable speed limit system can be modeled and evaluated by the use of microscopic traffic simulation. Results from the evaluation indicate increased flow harmonization in terms of narrowing of the acceleration rate distribution and reduced exhaust emissions.Further, we compare four control algorithms for deciding on speed limits in variable speed limit systems. Differences in the resulting traffic performance between the control algorithms are quantified by the use of microscopic traffic simulation. It is concluded that the dened objective for the algorithms have a decisive influence on the effects of the variable speed limit system.The results from this thesis are useful for further development of variable speed limit systems, both with respect to incorporating cooperative features and by improving the speed setting control algorithms.
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| 24. |
- Grumert, Ellen F., 1983-
(författare)
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Using Connected Vehicles in Variable Speed Limit Systems: : System Design and Effects
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Motorway traffic management systems are useful for improving the traffic conditions on urban motorways. One of the most common motorway traffic management systems are variable speed limit systems. These systems adapt the speed limits based on the prevailing traffic conditions measured by roadside detectors and recommended or compulsory speed limits are shown on variable message signs installed on gantries over the road.Thesystems consist of three parts; the control algorithm used to determine which speed limit to be displayed, a method for estimating the traffic conditions to be used as input for the control algorithm and the infrastructure for application of the variable speed limits. The goal of the systems is often to increase safety or efficiency.Recent development in the field of connected vehicles have opened up for a new type of data source, as the status of a connected vehicle and its surroundings can be communicated at arbitrary locations. Hence, by the use of connected vehicles in variable speed limit systems there is a potential of reducing the amount of roadside equipment. It is even possible to control the connected vehicles towards the current speed limit without the use of variable message signs. This allows for the application of variable speed limits at arbitrary locations.The aim of this thesis is to examine how connected vehicles can be used to improve the efficiency of variable speed limit systems. The thesis contribute with new and improved methods using connected vehicles in all three parts of a variable speed limit system. The suggested methods are evaluated by microscopic traffic simulation. The overall conclusion is that the use of connected vehicles in variable speed limit systems can contribute to improvements in traffic efficiency compared to existing systems.The six papers included in the thesis can be summarized as follows. First, it is shown that traditional variable speed limit systems can be effective for improving the traffic conditions on the motorway and the results can be comparable to more costly alterations by reconstruction of the infrastructure to increase the capacity. Next, the usefulness of connected vehicles for application and control of the speed limits in an existing variable speed limit system is investigated. It is concluded that the design of the control algorithm and the accuracy of the estimated traffic conditions have a great effect on the final outcome of the system. The design of the control algorithm is then examined by evaluation of a number of control algorithms with respect to safety, efficiency and environmental impacts. The main benefits and drawbacks of the algorithms are highlighted and desirable characteristics to include when designing a control algorithm are identified. In two studies, methods making use of connected vehicles for estimating the traffic conditions are proposed. The results show that connected vehicles are useful for improving the accuracy of the estimated traffic conditions through the inclusion of more detailed information and information at locations where detector measurements are not available. Finally, a variable speed limit system is proposed in which connected vehicles play a central role in the estimation of the traffic conditions, as well as in the control algorithm and for application of the speed limit. The system is shown to be useful for improving traffic efficiency during an incident at an arbitrary location along the controlled road.
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| 25. |
- Gunnarsson Lidestam, Helene, 1968-
(författare)
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Supply chain optimization in the forest industry
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The scope of this thesis is modelling and solving large-scale planning problems in the supply chain within the forest industry. Five research papers are included, the first three of which focus on the modelling, and the last two on the solution methods. All problems included are tactical multi-commodity problems expressed as mixed integer programming (MIP) models. The work has been done in collaboration with two Swedish companies within the forest industry.In Paper I, a problem concerning the supply chain of forest fuel for Sydved Energileveranser AB is modelled and solved. We study the problem of deciding when and where forest residues are to be converted into wood chips, and how the residues and chips are to be transported and stored in order to satisfy energy demand at heating plants. The company has long-term contracts with forest owners and saw mills. Decisions in the model include whether or not additional harvest areas and saw mills are to be contracted and which terminals to use. The planning horizon is one year and monthly time periods are used.Papers II--V are based on planning problems at Södra Cell AB. The planning horizon is normally one year. Papers II--III consider only one time period. In Paper II the supply chain from pulp mills to customers is modelled and the combined problem of deciding terminal locations and which ship routes to use is studied. Shipping vessels chartered on short or long term are used to transport products to terminals in Europe. From each terminal, the products are transported to customers by truck, train, or a combination of both. In addition, trains and trucks can be used for transports directly to customers from mills. In Paper III the entire supply chain, from harvest areas to customers, is considered. Decisions included are transportation of raw materials, production mix, the distribution of pulp products, and the selection of potential orders and their quantities at customers. The ship routes are considered as flow links.In Papers IV--V the problems in Papers II--III are combined into one model and several time periods are used. Lagrangian heuristics based on Lagrangian decomposition are used as solution methods in both papers. In Paper IV, the approach leads to subproblems for each time period, whereas in Paper V, another approach that results in subproblems for different parts of the supply chain is developed.All models are based on real data from the companies. The models are detailed and describe the problems accurately. The solution methods are developed such that the solution time is kept within practical limits. Results from Papers II--III have been used by Södra Cell AB to support the change of the terminal structure as well as in budget planning.
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| 26. |
- Johansson, Fredrik
(författare)
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Microscopic Modeling and Simulation of Pedestrian Traffic
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Walking is an environmentally friendly and important mode of transportation. It constitutes the first and last part of almost any trip, regardless of what the main mode of transport is, and is especially important in connection to public transport trips.When designing public transport stations, and similar facilities with large and varying volumes of pedestrian traffic, it is advantageous to be able to predict the traffic conditions at the facility before it is built; discovering too late that the traffic at the facility is inefficient and perceived as uncomfortable may be very costly. To make these predictions we need accurate quantitative models of pedestrian traffic.The foundation of this thesis is the development of a microsimulation platform for pedestrian traffic, the Pedestrian Traffic Simulation Platform (FTSP). The platform is based on the Social Force Model (SFM) and intended for evaluation of proposed designs of pedestrian facilities. A contribution of this thesis is a thorough documentation of the implementation of the FTSP.An extensive literature review of previous research on the SFM revealed gaps in the methodology used to study the properties of the SFM and to interpret its results. This thesis proposes local performance measures to fill this gap. These measures are based on properties of the SFM, and enable quantitative analyses of the quality of service at pedestrian facilities. The proposed measures are applied to the simulation results of some basic scenarios, which reveal previously unknown properties of the SFM. These properties can be used to test the accuracy of the SFM.Another gap in the literature was how to include waiting behavior in the SFM. This thesis shows that accurate modeling of waiting pedestrians is important for the accuracy of the simulation results, and proposes three different extensions to the SFM to model waiting behavior.
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| 27. |
- Johansson, Fredrik, 1983-
(författare)
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Microscopic Simulation of Pedestrian Traffic
- 2016
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- There has recently been a renewed interest in planning for pedestrian traffic, primarily in connection to public transport interchange stations, since these are important for public transport to constitute an attractive alternative to car usage. This thesis concerns microscopic simulation of pedestrian traffic, which is a promising tool for analyzing and predicting the traffic situation in a given pedestrian facility; particularly powerful when the traffic is congested. Important applications of microscopic simulation include comparison of possible infrastructure designs such as proposed interchange stations, and evaluations of various traffic management solutions, for example information systems.The purpose of this thesis is to advance the capabilities of pedestrian microsimulation toward a level at which it can be reliably applied for quantitative analysis by practitioners in the field. The work is based on an established microscopic model of pedestrian dynamics, the Social Force Model (sfm), and the advances are made in a number of different areas.To be able to evaluate and compare simulated traffic situations suitable performance measures are needed. A set of local performance measures are proposed that quantifies the local delay rate density and estimates the discomfort perceived by the pedestrians.The sfm is extended to include waiting pedestrians through the introduction of a waiting model, demonstrated to be stable and free from oscillations. The inclusion of waiting pedestrians in the model is critical for accurate modelling of public transport interchange stations, where large groups of waiting pedestrians may hinder passing pedestrians if the design of the station is poor.The relaxation time of the adaptation to the preferred velocity is an important parameter in force based models of pedestrian traffic since it affects several behaviors of the simulated pedestrians, two of which are linear acceleration and turning movements. A comparison of observations of accelerating pedestrians reported in the literature and new observations of turning pedestrians indicates that no value of the relaxation time can give model behavior consistent with both sets of observations. This indicates that modifications of the model is needed to accurately reproduce the observed behavior.An important input to simulations is the preferred speed of the simulated pedestrians. The common assumption that the preferred speed distribution at a location does not vary during the day is tested through observations of pedestrian traffic at Stockholm Central Station. The results demonstrate that the preferred speeds are lower in the afternoon than in the morning, implying that the preferred speed should be treated as a source of uncertainty when applying pedestrian microsimulation.Finally, a sensitivity analysis of a simulation of the lower hall of Stockholm Central Station is performed to find the most important sources of uncertainty in the model predictions, given the available data. The results indicate that the uncertainty related to calibration is the largest of the considered potential error sources.
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| 28. |
- Kristoffersson, Ida, 1980-
(författare)
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Incorporation of Departure Time Choice in a Mesoscopic Transportation Model for Stockholm
- 2009
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Travel demand management policies such as congestion charges encourage car-users to change among other things route, mode and departure time. Departure time may be especially affected by time-varying charges, since car-users can avoid high peak hour charges by travelling earlier or later, so called peak spreading effects. Conventional transport models do not include departure time choice as a response. For evaluation of time-varying congestion charges departure time choice is essential.In this thesis a transport model called SILVESTER is implemented for Stockholm. It includes departure time, mode and route choice. Morning trips, commuting as well as other trips, are modelled and time is discretized into fifteen-minute time periods. This way peak spreading effects can be analysed. The implementation is made around an existing route choice model called CONTRAM, for which a Stockholm network already exists. The CONTRAM network has been in use for a long time in Stockholm and an origin-destination matrix calibrated against local traffic counts and travel times guarantee local credibility. On the demand side, an earlier developed departure time and mode choice model of mixed logit type is used. It was estimated on CONTRAM travel times to be consistent with the route choice model. The behavioural response under time-varying congestion charges was estimated from a hypothetical study conducted in Stockholm.Paper I describes the implementation of SILVESTER. The paper shows model structure, how model run time was reduced and tests of convergence. As regards run time, a 75% cut down was achieved by reducing the number of origin-destination pairs while not changing travel time and distance distributions too much.In Paper II car-users underlying preferred departure times are derived using a method called reverse engineering. This method derives preferred departure times that reproduce as well as possible the observed travel pattern of the base year. Reverse engineering has previously only been used on small example road networks. Paper II shows that application of reverse engineering to a real-life road network is possible and gives reasonable results.
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| 29. |
- Lidén, Tomas, 1961-
(författare)
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Concurrent planning of railway maintenance windows and train services
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Efficiency in public and freight transportation systems is of great importance for a society. Railways can other high capacity and relatively low environmental impact, but require that several technical systems are tuned and operate well. Specifically there is a tight interdependency between infrastructure and trains. The consequences are that all subsystems must be maintained and that the coordination of infrastructure activities and train operations is essential.Railway infrastructure maintenance and train services should ideally be planned together, but practice and research about railway scheduling has historically focused mainly on train operations and timetabling while maintenance planning has received less attention | and little research have considered the joint scheduling of both types of activities. Instead the traditional approach has been a sequential and iterative planning procedure, where train timetabling often has precedence over infrastructure maintenance.This thesis studies how maintenance windows, which are regular time windows reserved for maintenance work, can be dimensioned and jointly scheduled with train services in a balanced and efficient way for both maintenance contractors and train operators. Mathematical methods are used, with the aim of advancing the knowledge about quantitative methods for solving such coordination problems.The thesis contributes with new optimization models that jointly schedule maintenance windows and train services, investigates the solving efficiency of these models, and studies crucial extensions of the planning problem | primarily for the consideration of maintenance resources. Furthermore, the models are applied to, verified and validated on a demanding real-life problem instance. The main results are that integrated and optimal scheduling of maintenance windows and train services is viable for problems of practical size and importance, and that substantial maintenance cost savings can be achieved with such an integrated approach as compared to a traditional sequential planning process.The thesis consists of an introduction and overview of the research, followed by six papers which present: (1) A cost benefit model for assessment of competing capacity requests at a single location; (2) An optimization model for integrated scheduling of both maintenance windows and train services; (3) Mathematical reformulations that strengthen the optimization model; (4) Extensions for handling resource considerations and cyclic schedules; (5) A case study for a major single track line in Sweden; and (6) A mathematical study of length-restricted sequences under cyclic conditions.
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| 30. |
- Lidén, Tomas
(författare)
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Towards concurrent planning of railway maintenance and train services
- 2016
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Efficiency in the public and freight transportation systems is of crucial importance for a society. Railways can offer high capacity and relatively low environmental impact, but require that several technical systems are tuned and operate well. Specifically there is a very tight interdependency between infrastructure and trains, which distinguishes railways from other transportation modes. Thus maintenance of all the subsystems is needed.Railways do also have some specific and complicating properties that influence maintenance and operations: Most activities need exclusive access to the infrastructure and - due to the geographic layout, safety requirements and partitioning of the subsystems - large portions of the network will be affected by each activity. Furthermore, several organisational units and resources are involved, ranging from governments and regulatory bodies, over operators and contractors to suppliers, technical experts and work forces. Thus railway maintenance is complicated to organize and consumes large budgets.This thesis treats the planning and scheduling problems that concern railway infrastructure maintenance and the coordination with train traffic. Mathematical methods and optimization are studied and used, with the aim of advancing the knowledge about models for solving such problems.The thesis contains three papers and presents: (1) A survey regarding railway maintenance activities, the major planning problems and the conducted research so far; (2) A model for quantitative comparison and assessment of competing capacity requests from train operations and maintenance; (3) An optimization model for integrated scheduling of both maintenance windows and train services.The work can be helpful for practitioners as well as researchers who want to take further steps in this interesting and challenging area. Based on the results that have been obtained, future research directions are presented that may lead towards practical use of concurrent planning of railway maintenance and train services.
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| 31. |
- Lindberg, Therese, 1986-
(författare)
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Discrete Event Simulation of Bus Terminals
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Public transport is important to society as it provides spatial accessibility and reduces congestion and pollution in comparison to other motorized modes. To assure a high-quality service, all parts of the system need to be well-functioning and properly planned. One important aspect for the system's bus terminals is their capacity. This needs to be high enough to avoid congestion and queues and the delays these may lead to. During planning processes, various suggested designs and solutions for a terminal need to be evaluated. Estimating capacity and how well the suggestions will function is a challenging problem, however. It requires analysis of complex interactions and behaviour of the vehicles. This sort of analyses can preferably be carried out using microsimulation. Furthermore, a discrete event simulation approach can make use of the fact that the path of a vehicle through a terminal can readily be described by a sequence of events (such as arriving, starting to drive to a stop etc.).The overall aim of this thesis is to investigate how discrete event simulation can be used to evaluate bus terminal design and traffic control policies. The main contribution is the development of a method for bus terminal simulation. As a first step, a discrete event simulation model of a combined bus and tram stop is formulated. The model is tested on a real system where the current design is compared to an alternative one. The test shows that a model developed with a discrete event approach can be used to evaluate the situation at a stop and compare design alternatives. In the next step, a general discrete event simulation model of bus terminals is formulated. A modular approach is introduced, where a terminal can be constructed from a set of module building blocks. Another important contribution of the model is its spatial resolution that allows for queues and blockages to occur throughout the terminal. By applying the simulation model in a case study, it is shown that the model can be used to evaluate and compare various scenarios related to the layout, number of passengers and the outside traffic situation. Lastly, the bus terminal simulation model is used in a second case study in order to compare model output with empirical data. This study identified a number of factors that may have had an influence on differences between observations and simulation results and that is of interest to look further into. This includes the actual adherence to terminal rules and the effects of model parameters.
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| 32. |
- Lindström, Thomas, 1991-, et al.
(författare)
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Accounting for anisotropic, anisothermal, and inelastic effects in crack initiation lifing of additively manufactured components
- 2023
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Ingår i: Fatigue & Fracture of Engineering Materials & Structures. - : Wiley. - 8756-758X .- 1460-2695. ; 46:2, s. 396-415
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Tidskriftsartikel (refereegranskat)abstract
- The crack initiation life of a ductile additively manufactured nickel-based superalloy is studied and modeled for low-cycle fatigue and thermomechanical fatigue conditions up to 600 degrees C. Isothermal experiments were performed on smooth specimens at temperatures up to 600 degrees C with different applied strain ranges. Additionally, thermomechanical fatigue experiments at 100-450 degrees C and 100-600 degrees C were performed on smooth specimens under in-phase and out-of-phase conditions. A life prediction model accounting for the anisotropy was developed, where the temperature cycle is accounted with a Delta T$$ \Delta T $$-functionality, generating good agreements with the experiments. The model was also validated on notched specimens undergoing thermomechanical fatigue conditions at 100-500 degrees C using simplified notch correction methods.
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| 33. |
- Lundgren, Magdalena, 1973-
(författare)
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Interplay between hormones, nutrients and adipose depots in the regulation of insulin sensitivity : an experimental study in rat and human adipocytes
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Obesity and specifically central obesity is related to insulin resistance, type 2 diabetes and other components of the so-called metabolic syndrome. The aim of this study was to elucidate the interplay between hormones, nutrients and adipose depots in normal and insulin-resistant fat cell metabolism.High levels of free fatty acids (FFAs) induce insulin resistance in muscle and liver in vivo. In the present study, rat adipocytes were treated with high physiological levels of oleic or palmitic acid in vitro for 4-24 h. This treatment had no effect on basal or insulin-stimulated glucose uptake capacity in these cells, neither did it affect the levels of the insulin signalling proteins; insulin receptor substrate (IRS)-1 or –2, phosphatidylinositol 3-kinase (PI3-K), protein kinase B (PKB) or glucose transporter (GLUT) 4, or the regulation of lipolysis rate.Visceral adiposity is considered to be more harmful than peripheral adiposity with respect to metabolic and cardiovascular complications. In adipose biopsies from subjects undergoing abdominal surgery, we found that glucose uptake capacity was elevated in omental as compared to subcutaneous adipocytes. The sensitivity (EC50) or maximum relative response to insulin, measured as % of basal, did however not differ between the depots. In women, subcutaneous adipocytes displayed a higher lipolysis rate following cAMP-stimulation than omental adipocytes, whereas there was a tendency towards the opposite in adipocytes from men. No differences were found between depots or sexes in the ability of insulin to inhibit lipolysis or in the levels of the lipolysis regulating proteins, i.e. protein kinase A (PKA), hormone sensitive lipase (HSL) and perilipin.Glucocorticoids, e.g. cortisol, exert pronounced insulin-antagonistic effects and are associated with redistribution of fat from peripheral to central fat depots in humans. Treatment of human subcutaneous and omental adipocytes in vitro, with the cortisol analogue dexamethasone, resulted in a dose dependent down-regulation of basal and insulin-stimulated glucose uptake capacity in omental, but not in subcutaneous cells. Concomitantly, the levels of IRS-1 and PKB were decreased only in omental adipocytes after dexamethasone treatment. The relative effect of insulin to stimulate glucose uptake was however not altered by dexamethasone treatment. The cAMP-stimulated lipolysis rate was elevated by dexamethasone treatment in cells from the subcutaneous depot in women and tended to be elevated in omental cells from men. No alterations however, were seen in the levels of the assessed lipolysis regulating proteins.Subcutaneous as well as omental fat cell size correlated negatively to insulin action in subcutaneous fat cells in vitro after adjusting for age, sex and body fat parameters in non-diabetic, but not in type 2 diabetic, subjects. Large subcutaneous fat cell size was strongly related to plasma leptin levels in non-diabetic and in type 2 diabetic subjects.We conclude that 1) adipocytes seem to be less vulnerable to elevated levels of fatty acids than muscle and liver cells, 2) the interactions between glucocorticoids and insulin in the regulation of glucose uptake differ between adipose depots, 3) depot specific hormonal lipolysis regulation differs between sexes and 4) fat cell size is related to insulin action in subcutaneous fat cells and to circulating levels of leptin.
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| 34. |
- Luttens, Andreas, et al.
(författare)
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Ultralarge Virtual Screening Identifies SARS-CoV-2 Main Protease Inhibitors with Broad-Spectrum Activity against Coronaviruses
- 2022
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 144:7, s. 2905-2920
-
Tidskriftsartikel (refereegranskat)abstract
- Drugs targeting SARS-CoV-2 could have saved millions of lives during the COVID-19 pandemic, and it is now crucial to develop inhibitors of coronavirus replication in preparation for future outbreaks. We explored two virtual screening strategies to find inhibitors of the SARS-CoV-2 main protease in ultralarge chemical libraries. First, structure-based docking was used to screen a diverse library of 235 million virtual compounds against the active site. One hundred top-ranked compounds were tested in binding and enzymatic assays. Second, a fragment discovered by crystallographic screening was optimized guided by docking of millions of elaborated molecules and experimental testing of 93 compounds. Three inhibitors were identified in the first library screen, and five of the selected fragment elaborations showed inhibitory effects. Crystal structures of target-inhibitor complexes confirmed docking predictions and guided hit-to-lead optimization, resulting in a noncovalent main protease inhibitor with nanomolar affinity, a promising in vitro pharmacokinetic profile, and broad-spectrum antiviral effect in infected cells.
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| 35. |
- Nie, Yali
(författare)
-
Deep Learning Approaches towards Skin Lesion Classification with Dermoscopic Images
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Melanoma is a skin cancer that tends to be deadly. The incidence of melanoma is currently at the highest level ever recorded in Europe, North America and Oceania. The survival rate can be significantly increased if skin lesions are identified in dermoscopic images at an early stage. In the other hand, the classification of skin lesions is incredibly challenging. Skin lesion classification using deep learning approaches has provided better results in classifying skin diseases than those of dermatologist, which is lifesaving in terms of diagnosis.This thesis presents a review of our research articles on classifying skin lesions using deep learning. Regarding the research, I have four goals concerning research frontier work, small datasets, data imbalance, and improving accuracy. In this thesis, I discuss how deep learning can classify skin diseases, summarizing the problems that remain at this stage and the outlook for the future.For the above goals, I first studied and summarized more than 200 highguality articles published over five years. I then used three versions of You only look once (Yolo) to detect skin lesions. Although there were only 200 pictures, the test was very effective for detection. I applied the five-fold algorithm to Vgg_16, trained five models, and fused them so solve the small data problem. To improve the accuracy, I also tried to combine the traditional machine learning method, i.e., the seven-point checklist, with three different backbones. Since the learning rate. Then, I also tried to use the hybrid model, combining convolutional neural networks (CNN) and transformer to train the dataset, and applied focal loss to balance the extremely unbalanced weight of the data.In addition to high-quality data sets and high-performance computers being extremely important in the research and application of deep learning, the optimization of machine learning algorithms for skin lesions can be endless
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| 36. |
- Peterson, Anders, 1976-
(författare)
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The Origin-Destination Matrix Estimation Problem : Analysis and Computations
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- For most kind of analyses in the field of traffic planning, there is a need for origin--destination (OD) matrices, which specify the travel demands between the origin and destination nodes in the network. This thesis concerns the OD-matrix estimation problem, that is, the calculation of OD-matrices using observed link flows. Both time-independent and time-dependent models are considered, and we also study the placement of link flow detectors.Many methods have been suggested for OD-matrix estimation in time-independent models, which describe an average traffic situation. We assume a user equilibrium to hold for the link flows in the network and recognize a bilevel structure of the estimation problem. A descent heuristic is proposed, in which special attention is given to the issue of calculating the change of a link flow with respect to a change of the travel demand in a certain pair of origin and destination nodes.When a time-dimension is considered, the estimation problem becomes more complex. Besides the problem of distributing the travel demand onto routes, the flow propagation in time and space must also be handled. The time-dependent OD-matrix estimation problem is the subject for two studies. The first is a case study, where the conventional estimation technique is improved through introducing pre-adjustment schemes, which exploit the structure of the information contained in the OD-matrix and the link flow observations. In the second study, an algorithm for time-independent estimation is extended to the time-dependent case and tested for a network from Stockholm, Sweden.Finally, we study the underlying problem of finding those links where traffic flow observations are to be performed, in order to ensure the best possible quality of the estimated OD-matrix. There are different ways of quantifying a common goal to cover as much traffic as possible, and we create an experimental framework in which they can be evaluated. Presupposing that consistent flow observations from all the links in the network yields the best estimate of the OD-matrix, the lack of observations from some links results in a relaxation of the estimation problem, and a poorer estimate. We formulate the problem to place link flow detectors as to achieve the least relaxation with a limited number of detectors.
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| 37. |
- Posada, Marcus
(författare)
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Models and algorithms for integrated special transport services
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An essential challenge for all societies is to provide efficient and effective means of transporting people. Transport systems and transport infrastructure play an integral part in society both by providing a basis for social and economic development and as the physical structure which defines our environment. As our societies become increasingly interconnected and complex, the demand for personal mobility increases.There is an ongoing trend towards flexible public transport services— in part driven by meeting the flexibility of private automobile use, in part by rapid technological development. Despite this trend, there are segments of the population that have problems with, or are unable to, use the general public transport. One such segment is comprised of people who have impaired mobility due to disabilities or age. Special transport services provide mobility to such people, who would otherwise have difficulties moving around in society, albeit at a high cost to either the users or society.One proposed way of decreasing these high operational costs is that of implementing an integrated special transport service. In an integrated service, certain passengers can perform segments of their trips with the fixed-route public transport. For these passengers, the special transport service vehicles will service the first and last legs of their trips, while the bulk of their trips will be performed with the fixed-route public transport.When implementing or evaluating an integrated special transport service, one aspect crucial to the efficiency and effectiveness of the same is the issue of how to best make use of the available vehicle fleet. This thesis concerns the modelling, evaluation, and operational planning of such services. The thesis contains introductory chapters and three papers, and presents: mathematical models for the routing problem of an integrated service; planning algorithms for both static and dynamic instances of the problem; and evaluations of the suitability of integrated special transport services in both rural and urban environments.The work herein can be helpful for researchers as well as practitioners studying, or wishing to implement, integrated transport services, regardless of whether those services are aimed at the general public or specific segments of the population. Based on the research conducted, potential directions for future research are presented.
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| 38. |
- Steins, Krisjanis, 1971-
(författare)
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Discrete-Event Simulation for Hospital Resource Planning : Possibilities and Requirements
- 2010
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The delivery of health care services has been under pressure due to limited funding and increasing demand. This has highlighted the need to increase not only the effectiveness but also the efficiency of health care delivery. Discrete-event simulation has been suggested as an analysis tool in health care management to support the planning of health care resources.The overall purpose of this thesis is to investigate the possibilities and requirements for using discrete-event simulation in analyzing and planning the use of hospital resources. This is achieved by three case studies that focus on improvements in patient flow of emergency patients that require a radiology examination, intensive care unit capacity planning and operating room allocation strategies, respectively.The first case investigates the current stage of digitization and process orientation in hospital care as a prerequisite for efficient process simulation and analysis. The study reveals an emergency-radiology patient flow process that is not very well measured and uncovers disparate information systems storing incompatible and fragmented data. These results indicate that the current degree of process orientation and the current IT infrastructure does not enable efficient use of quantitative process analysis and management tools like simulation.In the second case the possibilities to develop generic hospital unit simulation models by building and validating a generic intensive care unit (ICU) model are explored. The results show that some of the modeling approaches described in literature cannot replicate the actual behavior observed in all studied ICUs. It is important to identify patient groups for different admission priorities, to account for over-utilizations in the model logic, and to discover and properly model dependencies in the input data. The research shows that it is possible to develop a generic ICU simulation model that could realistically describe the performance of different real ICUs in terms of occupancy, coverage and transfers.The value of simulation modeling in health care management is examined in the third case through the development and use of a simulation model for optimal resource allocation and patient flow in a hospital operating department. The goal of the simulation modeling in this case was to identify bottlenecks in the patient flow and to try different alternatives for allocation of operating room capacity in order to increase the utilization of operating room resources. The final model was used to evaluate four different proposed changes to operating room time allocation.
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| 39. |
- Svedberg, Victoria, 1988-
(författare)
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Towards optimal railway track utilization based on societal benefit
- 2018
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Infrastructure managers in railway systems are striving to have as efficient track utilization as possible. There are no unanimous interpretation of efficiency in terms of track utilization, but the aim of the Swedish Transport Administration is to allocate track capacity such that societal benefit is maximized. This means that the tracks should be used by as much traffic as possible and by traffic that provides as much benefit for the society as possible.To allocate track capacity such that the track utilization is optimal would be an easy task if the track capacity were not a scarce resource. Today, many train operators share railway network and there are cases when two or more operators want to use the same track capacity at the same time. The infrastructure manager must then make priorities and reject some operators, and the question is which operators to reject. The guiding principle is to grant the operators that provide the highest societal benefit access to the tracks. However, the question would then change into how to know which operator that provides the highest societal benefit.In this thesis, the societal benefit of publicly subsidized traffic is estimated using social cost-benefit analysis. Mathematical models and methods are developed for quantifying and computing the number of departures for the publicly subsidized traffic and their distribution in time, i.e. a train timetable, that provides the maximal societal benefit in a social cost-benefit analysis setting. The societal benefit of commercial traffic is estimated using the market value for their requested train timetables. The market value is set using dynamic pricing. A suggestion of a dynamic pricing process that can be used in the train timetabling process is described. Mathematical models and methods for calculating the supply and demand of a track access request are developed and tested, which enables the use of a dynamic pricing process on track capacity
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| 40. |
- Tsanakas, Nikolaos, 1987-
(författare)
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Emission estimation based on traffic models and measurements
- 2019
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Traffic congestion increases travel times, but also results in higher energy usage and vehicular emissions. To evaluate the impact of traffic emissions on environment and human health, the accurate estimation of their rates and location is required. Traffic emission models can be used for estimating emissions, providing emission factors in grams per vehicle and kilometre. Emission factors are defined for specific traffic situations, and traffic data is necessary in order to determine these traffic situations along a traffic network. The required traffic data, which consists of average speed and flow, can be obtained either from traffic models or sensor measurements.In large urban areas, the collection of cross-sectional data from stationary sensors is a costefficient method of deriving traffic data for emission modelling. However, the traditional approaches of extrapolating this data in time and space may not accurately capture the variations of the traffic variables when congestion is high, affecting the emission estimation. Static transportation planning models, commonly used for the evaluation of infrastructure investments and policy changes, constitute an alternative efficient method of estimating the traffic data. Nevertheless, their static nature may result in an inaccurate estimation of dynamic traffic variables, such as the location of congestion, having a direct impact on emission estimation. Congestion is strongly correlated with increased emission rates, and since emissions have location specific effects, the location of congestion becomes a crucial aspect.Therefore, the derivation of traffic data for emission modelling usually relies on the simplified, traditional approaches. The aim of this thesis is to identify, quantify and finally reduce the potential errors that these traditional approaches introduce in an emission estimation analysis. According to our main findings, traditional approaches may be sufficient for analysing pollutants with global effects such as CO2, or for large-scale emission modelling applications such as emission inventories. However, for more temporally and spatially sensitive applications, such as dispersion and exposure modelling, a more detailed approach is needed. In case of cross-sectional measurements, we suggest and evaluate the use of a more detailed, but computationally more expensive, data extrapolation approach. Additionally, considering the inabilities of static models, we propose and evaluate the post-processing of their results, by applying quasi-dynamic network loading.
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| 41. |
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| 42. |
- Yu, Cheng-Han, 1992-, et al.
(författare)
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Anisotropic behaviours of LPBF Hastelloy X under slow strain rate tensile testing at elevated temperature
- 2022
-
Ingår i: Materials Science & Engineering. - : ELSEVIER SCIENCE SA. - 0921-5093 .- 1873-4936. ; 844
-
Tidskriftsartikel (refereegranskat)abstract
- To improve the understanding of high temperature mechanical behaviours of LPBF Ni-based superalloys, this work investigates the influence of an elongated grain structure and characteristic crystallographic texture on the anisotropic tensile behaviours in LPBF Hastelloy X (HX) at 700 °C. Two types of loading conditions have been examined to analyse the anisotropy related to the building direction (BD), including the vertical loading (loading direction//BD) and the horizontal loading (loading direction ⊥ BD). To probe the short-term creep behaviours, slow strain rate tensile testing (SSRT) has been applied to address the strain rate dependent inelastic strain accumulation. In-situ time-of-flight neutron diffraction upon loading was performed to track the anisotropic lattice strain evolution in the elastic region and the texture evolution in the plastic region. Combined with the post microstructure and fracture analysis, the anisotropic mechanical behaviours are well correlated with the different microstructural responses between vertical and horizontal loading and the different strain rates. A better creep performance is expected in the vertical direction with the consideration of the better ductility and the higher level of texture evolution.
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