| 1. |
- Lundgren, Jonas, 1993-
(author)
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Internal Cooling Design Using Multiphysics Topology Optimization
- 2024
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Doctoral thesis (other academic/artistic)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-
(author)
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Behavioral Level Simulation Methods for Early Noise Coupling Quantification in Mixed-Signal Systems
- 2005
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Licentiate thesis (other academic/artistic)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-
(author)
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Simulating Behavioral Level On-Chip Noise Coupling
- 2007
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Doctoral thesis (other academic/artistic)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-
(author)
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An Operations Research Approach for Daily Emergency Management
- 2019
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Licentiate thesis (other academic/artistic)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-
(author)
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Models for Dispatch of Volunteers in Daily Emergency Response
- 2022
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Doctoral thesis (other academic/artistic)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
(author)
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Optimization Based Decision Support Tools for Fire and Rescue Resource Planning
- 2015
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Licentiate thesis (other academic/artistic)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-
(author)
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Simulation Based Evaluation of Advanced Driver Assistance Systems
- 2015
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Licentiate thesis (other academic/artistic)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-
(author)
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Long-term metabolic effects of a high birth weight
- 2019
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Doctoral thesis (other academic/artistic)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
(author)
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Optimization-Based Methods for Revising Train Timetables with Focus on Robustness
- 2016
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Licentiate thesis (other academic/artistic)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-
(author)
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Culture and Transmission : The Technological and Cultural Reach of International Syndicated Radio
- 2008
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Doctoral thesis (other academic/artistic)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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