| 1. |
- Amiryarahmadi, Nata
(författare)
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A Virtual Design Studio for Low-Frequency Sound from Walking in Lightweight Buildings
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In recent years there has been a growing interest for building lightweight multistorey woodenresidential buildings in countries like Sweden with large and renewable forests. While positive aspectsof these buildings, such as sustainability, ease of construction and lightness, motivate building more inwood, poor acoustic performance is a risk which concerns the wooden-building industry.Low-frequency impact sound from walking of the neighbors upstairs is the main source of complaintsabout the acoustic performance of these buildings. The disturbance caused by walking sounds,transmitted through lightweight wooden floors, results in acoustic discomfort and impairs theperceived quality of the building; sometimes even when the building has fulfilled an acoustic classhigher than minimum requirement, according to the national standard on sound classification and itssingle number ratings. The standard methods for objective evaluation of impact sound insulation offloors cannot predict, at a satisfactory level, the walking sound annoyance that the inhabitants ofwooden buildings experience. This causes an uncertainty about the resulting perceived quality of thesebuildings, which greatly concerns the building manufacturers and demotivates them from choosinglightweight wooden elements over heavyweight building materials such as concrete. This uncertaintycan be overcome by evaluating the perceived acoustic quality of the building prior to its construction.One solution is to build test houses where the subjective acoustic performance of floor samples can beevaluated in advance to the building construction. However, building a test house is expensive;besides, for evaluating the effect of every design modification on the experienced acoustic comfort ofthe building, a real floor sample has to be built and installed in the house, which would be timeconsumingand costly. An alternative solution is to use virtual acoustic test facilities.In this thesis a virtual design studio for impact sound is developed. It is a tool that facilitates creatingand listening to the acoustic field generated by impact forces such as footsteps on lightweight floors. Italso provides the possibility to evaluate the acoustic performance of floor elements in an early designphase, and to investigate the correlation between design parameters and the perceived impact soundinsulation of the floor. The tool is demonstrated and a very first listening test shows that one can obtainresults which are in good agreement with the results in literature. Loudness, reverberation andthumping are shown to influence the annoyance. It is also shown that there is a difference in judgementof walking sounds by persons who have experience with lightweight floors at home and by those whodo not have that experience.
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| 2. |
- Edh Mirzaei, Nina, 1984
(författare)
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Involving individuals in the manufacturing strategy formation: Strategic consensus among workers and managers
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Decisions made and actions taken by individuals in the operations function impact the formation of a company’s manufacturing strategy (MS). Therefore, it is important that the MS is understood and agreed on by all employees, that is, strategic consensus among the individuals in the operations function is essential. This research contributes to the current body of knowledge by including a workers’ perspective on MS formation. It is the workers on the shop floor who bring the MS to life in the actual operations through their daily decisions and actions. The MS falls short if the priorities outlined do not materialise in practice as intended. The purpose of this research is to investigate how the individuals in the operations function perceive the MS in order to understand how these individuals are involved in the MS formation. The research is based on five studies, differing by evidence, as follows: one theoretical, three qualitative in the setting of small and medium-sized enterprises (SMEs), and one quantitative at a large company. Based on the findings presented in the six appended papers, the results show that empirically and conceptually, workers have been overlooked or given a passive role in the MS formation. Empirically, it is seen that workers and managers do not have a shared understanding of the underlying reasons for strategic priorities; hence, the level of strategic consensus is low. Furthermore, the level of strategic consensus varies among the different MS dimensions depending on their organisational level. Moreover, the empirical findings reveal that internal contextual factors influence the individuals’ perceptions of the MS and the possibilities for strategic consensus. Regarding the external context, the results show that major customers’ strategies influence the subcontractor SMEs’ MS formation. The usage of means of communication in the operations function has also shown to be of importance for how the MS is perceived. Conceptually, the findings indicate that the MS literature tends to treat individuals in the operations function in a deterministic manner; individuals on the shop floor are regarded as manufacturing resources. To ensure a successful MS formation process, where the patterns of the decisions made by the individuals in the operations function forms the MS, the view on human nature within the MS requires a more voluntaristic approach. This research suggests to view the MS formation as an iterative “patterning process” which builds on a reciprocal relationship between workers and managers. The introduction of the patterning process contributes to the research on MS formation by explaining the perception range within the hierarchical levels, by re-defining the hierarchical levels included in the MS formation and by detailing the activities in the MS formation.
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| 3. |
- Sandin, Gustav
(författare)
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Life cycle assessment in the development of forest products : Contributions to improved methods and practices
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The prospect of reducing environmental impacts is a key driver for the research and development (R&D) of new forest products. Life cycle assessment (LCA) is often used for assessing the environmental impact of such products, e.g. for the purpose of guiding R&D. The aim of this thesis is to improve the methods and practices of LCA work carried out in the R&D of forest products. Six research questions were formulated from research needs identified in LCA work in five technical inter-organisational R&D projects. These projects also provided contexts for the case studies that were used to address the research questions. The main contributions of the research are as follows:Regarding the planning of LCA work in inter-organisational R&D projects, the research identified four characteristics that appear to be important to consider when selecting the roles of LCAs in such projects: (i) the project’s potential influence on environmental impacts, (ii) the degrees of freedom available for the technical direction of the project, (iii) the project’s potential to provide required input to the LCA, and (iv) access to relevant audiences for the LCA results.Regarding the modelling of future forest product systems, it was found that (i) it is important to capture uncertainties related to the technologies of end-of-life processes, the location of processes and the occurrence of land use change; and (ii) the choice of method for handling multi-functionality can strongly influence results in LCAs of forest products, particularly in consequential studies and in studies of relatively small co-product flows.Regarding the assessment of environmental impacts of particular relevance for forest products, it was found that using established climate impact assessment practices can cause LCA practitioners to miss environmental hot-spots and make erroneous conclusions about the performance of forest products vis-à-vis non-forest alternatives, particularly in studies aimed at short-term impact mitigation. Also, a new approach for inventorying water cycle alterations was developed, which made it possible to capture catchment-scale effects of forestry never captured before.To connect the LCA results to global challenges, a procedure was proposed for translating the planetary boundaries into absolute product-scale targets for impact reduction, e.g. to be used for evaluating interventions for product improvements or for managing trade-offs between impact categories.
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| 4. |
- Steinmetz, Erik M, 1984
(författare)
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Communication and Positioning Uncertainties in Cooperative Intelligent Transportation Systems
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The current road transport system has problems with both safety and efficiency. Future intelligent transportation systems (ITS) are envisioned to alleviate these problems. In particular, cooperative ITS, where vehicles are connected to each other and the cloud, will allow vehicles to collaborate and share both sensor and control information. This will significantly expand the possibilities of optimizing traffic flow and increasing safety. However, as both communication and sensing are unreliable, a key challenge in cooperative ITS is how to accommodate for communication and sensing impairments. This requires an understanding of what the limitations of communication and sensing systems are, and how their uncertainties affect the control and coordination task. The contribution of this thesis lies on the intersection of the fields of communication, sensing, and control, and can be summarized as follows. First of all, through the use of stochastic geometry, we analyze the impact of interference in vehicular networks, and propose a general procedure to analytically determine key performance metrics such as packet reception probabilities and throughput. Along with this procedure, we provide a model repository that can be used to adapt to both rural and urban propagation characteristics, and different medium access control protocols. The procedure can be used to gain fundamental insights about the performance of vehicular communication systems in a variety of scenarios of practical relevance. Secondly, when it comes to sensing uncertainties, we use Fisher information theory to provide bounds on the achievable performance of cooperative positioning solutions. We thereby characterize how the composition of the vehicle fleet, and the penetration rate of vehicles with extensive sensing capabilities affects positioning and mapping performance. While the analysis is generally applicable, we present simulation results from a multi-lane freeway scenario, which indicate that introducing a small fraction of cooperating vehicles with high-end sensors significantly improves the positioning quality of the entire fleet, but may not be enough to meet the stringent demands posed by safety-critical applications. Finally, we study how communication and sensing uncertainties impact cooperative intersection coordination. We show that the requirements on control, communication and sensing are stringent if they are treated separately and that they could be relaxed if the individual systems are made aware of each other. This awareness is explored in two ways: we provide a communication system analysis for a centralized intersection coordination scheme using stochastic geometry, which can be used to provide guidelines on how to design the communication system to guarantee a control-dependent communication quality. We also propose a collision aware resource allocation strategy, which proactively reduces channel congestion by only assigning communication resources to vehicles that are in critical configurations, i.e., when there is a risk for future collisions. This thesis, through the use of several mathematical tools, thus sheds new insights into the communication, sensing and control performance of cooperative ITS.
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| 5. |
- Walander, Tomas, 1986-
(författare)
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Influences of temperature, fatigue and mixed mode loading on the cohesive properties of adhesive layers
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis concerns some aspects that have influence on the strength of adhesive layers. The strength is determined by the stress deformation-relation of the layer. This relation is also referred to as cohesive law. The aspects having influence on the cohesive laws that are studied in this work are temperature, fatigue, multi-axial fatigue and mixed mode loading.For each aspect, a model is developed that can be used to describe the influence of the aspects on the cohesive laws numerically, e.g. by using the finite element method. These models are shown to give good agreement with the experimental results when performing simulations that aims at reproducing the experiments. For the aspect of temperature, a FE-model is suggested that can be used to simulate the mechanical behaviour in pure mode loadings at any temperature within the evaluated temperature span. Also, a damage law for modelling high cycle fatigue in a bonded structure in multi-axial loading is presented. Lastly, a new experimental set-up is presented for evaluating strength of adhesives during mixed mode loading. The set-up enables loading with a constant mode-mix ratio and by the experimental results, a potential model for describing the mechanical behaviour of the evaluated adhesive is presented.
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| 6. |
- Krook Riekkola, Anna Cecilia, 1971
(författare)
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National Energy System Modelling for Supporting Energy and Climate Policy Decision-making: The Case of Sweden
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Energy system models can contribute in evaluating impacts of energy and climate policies. The process of working with energy system models assists the understanding of the quantita-tive relationships between different parts of the energy system and between different time periods, under various assumptions. With the aim of improving the ability of national energy system models to provide robust and transparent input to the decision-making process, a three-step energy modelling process is introduced based on the literature on system analysis and energy modelling. This process is then used to address five different research questions, which are based on (but not identical to) six embedded papers. In the first step (step 1) the ‘real’ system is simplified and conceptualised into a model, where the main components and parameters of a problem are represented. In order to attain robust results, it is important to focus not only on what needs to be included in the model, but also on what can be left out. In order not to add noise to the analysis, there is a trade-off between what is desired and what can be included in terms of data. In the second step (step 2), all assumptions are sorted within a mathematical model and the algorithms solved. The structure of the model is found crucial for the possibility to trace the results back to the assumptions (transparency). In the last step (step 3), the model results are interpreted together with aspects not captured in the model (e.g. non-economic preferences, institutional barriers), and discussed in relation to the direct assumptions provided to the model (step 1) and to the implicit assumptions due to the choice of model (step 2). All three steps are essential in order to achieve robust and transparent policy analyses, and all three steps contribute to the learning about the ‘real’ system.The embedded papers (Paper I-VI) deal with issues of particular relevance for long-term analysis of the Swedish energy system. The results of Paper I illustrate the importance of capturing the seasonal and daily variations when representing cross-border trade of electricity in national models; a too simplified representation will make the model overestimate the need for installed power capacity in Sweden. Paper II presents a methodology for estimating the ‘useful demand’ for heating and cooling based on national statistics, which is useful as most energy system models are driven by ‘useful demand’, while national statistics are based on the measurable ‘final energy consumption’. Paper III compares the technical potential of com¬bined heat and power (CHP) from different approaches and calculates the economic potential of CHP using a European energy system model (EU-TIMES). The comparison the technical potential of the different approaches reveals differences in definitions of the potential as well as in the system boundary. The resulting economic potential of CHP in year 2030 is shown to be significantly higher compared to today’s level, even though conservative assumptions regarding district heating were used. Paper IV assesses the impacts of district heating on the future Swedish energy system, first by a quantitative analysis using TIMES-Sweden and then by discussing aspects that cannot be captured by the model. Paper V compares different climate target scenarios and examines the impacts on the resulting total system cost with and without the addition of ancillary benefits of reductions in domestic air-pollution. The results reflect the fact that carbon dioxide emission reductions abroad imply a lost opportunity of achieving substantial domestic welfare gains from the reductions of regional and local environmental pollutants. Paper VI presents and discusses an iteration procedure for soft-linking a national energy system model (TIMES-Sweden) with a national CGE model (EMEC). Some aspects of the way in which we perform the soft-linking are not standard in the literature (e.g., the use of direction-specific connection points). By applying the iteration process, the resulting carbon emissions were found to be lower than when the models are used separately.
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| 7. |
- de Blanche, Andreas
(författare)
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A Slowdown Prediction Method to Improve Memory Aware Scheduling
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Scientific and technological advances in the area of integrated circuits have allowed the performance of microprocessors to grow exponentially since the late 1960's. However, the imbalance between processor and memory bus capacity has increased in recent years. The increasing on-chip-parallelism of multi-core processors has turned the memory subsystem into a key factor for achieving high performance. When two or more processes share the memory subsystem their execution times typically increase, even at relatively low levels of memory traffic. Current research shows that a throughput increase of up to 40% is possible if the job-scheduler can minimizes the slowdown caused by memory contention in industrial multi-core systems such as high performance clusters, datacenters or clouds. In order to optimize the throughput the job-scheduler has to know how much slower the process will execute when co-scheduled on the same server as other processes. Consequently, unless the slowdown is known, or can be fairly well estimated, the scheduling becomes pure guesswork and the performance suffers. The central question addressed in this thesis is how the slowdown caused by memory traffic interference between processes executing on the same server can be predicted and to what extent. This thesis presents and evaluates a new slowdown prediction method which estimates how much longer a program will execute when co-scheduled on the same multi-core server as another program. The method measures how external memory traffic affects a program by generating different levels of synthetic memory traffic while observing the change in execution time. Based on the observations it makes a first order prediction of how much slowdown the program will experience when exposed to external memory traffic. Experimental results show that the method's predictions correlate well with the real measured slowdowns. Furthermore, it is shown that scheduling based on the new slowdown prediction method yields a higher throughput than three other techniques suggested for avoiding co-scheduling slowdowns caused by memory contention. Finally, a novel scheme is suggested to avoid some of the worst co-schedules, thus increasing the system throughput.
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| 8. |
- Hagqvist, Petter
(författare)
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Non-intrusive instrumentation and estimation : Applications for control of an additive manufacturing process
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- For integration of additive manufacturing into industrial production, there is a need for capable yet robust automation solutions. Such solutions are to ensure consistent process outputs, both with regard to deposit geometry and material properties. In this thesis, instrumentation and control solutions have been investigated for the laser metal wire deposition additive manufacturing process. This particular process is promising with regard to e.g. high deposition rates and negligible material waste. However, due to its inherent dynamics, it requires automatic control in order to prove competitive. A large number of process parameters affect the resulting quality of the deposit. Successful control of these parameters is crucial for turning laser metal wire deposition into an industrially tractable process. This requires relevant and reliable process information such as the temperature of the deposit and the positioning of the tool relative to the workpiece. Due to the particular requirements of instrumenting the process, only non-intrusive measurement methods are viable. In this thesis, such measurement solutions are presented that advance automatic control of the laser metal wire deposition. In response to the need for accurate temperature measurements for the process, a new temperature measurement method has been developed. By adopting the novel concept of temporal, rather than spectral, constraints for solving the multispectral pyrometry problem, it opens up for temperature measurements which compensates for e.g. an oxidising deposit. For maintaining a good deposition process in laser metal wire deposition, control of tool position and wire feed rate is required. Based on measurements of resistance through the weld pool, a simple yet well performing control system is presented in this thesis. The control system obtains geometrical input information from resistance measurements made in-situ, and feeds this information to an iterative learning controller. This results in a robust, cheap and practical control solution for laser metal wire deposition, which is suitable for industrial use and that can easily be retrofitted to existing equipment.
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| 9. |
- Javidi Shirvan, Alireza
(författare)
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Modelling of cathode-plasma interaction in short high-intensity electric arc : Application to Gas Tungsten Arc Welding
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In arc welding the quality of the weld is strongly influenced by the thermal history of the workpiece which is itself governed by the electric arc heat source. The models for predicting weld properties thus need a good evaluation of the distribution of the heat input from thearc to the workpiece. To have a predictive model of arc heat source it is necessary to take into account the cathode and its coupling with the plasma. The coupling allows to calculate the temperature and current density distributions along the cathode surface rather than prescribing them. This thesis focuses on the arc-cathode coupling for a plasma assumed to be in local thermal equilibrium. A self-consistent coupling boundary model for high-intensity electric arc on a refractory cathode (thoriated tungsten) was developed accounting for the physics of the sub-layers of the cathode layer and the non-uniformity of the cathode surface physical state. The cathode layer model accounts for the non-equilibria in the cathode layer. It was tested in one-dimensional calculations and then extended to a cathode-plasma coupling boundary condition for gas tungsten arc implemented in OpenFOAM. Different modelling assumptions commonly used for developing the model were questioned and investigated. It was checked that the secondary electron emission is negligible compared to the effect of emitted electrons and ions. It was verified that it is justified to neglect the space charge of emitted electron when calculating the cathode surface electric field. It was verified that Richardson-Dushman electron emission law supplemented with Schottky correction is used within its domain of validity in GTA applications even for low work function emitters. It was shown that the radiative absorption of the cathode surface is not negligible compared to the radiative emission. The cathode layer model was also further developed to take into account the in homogeneity of the cathode material. It was shown that the cathode in homogeneityhas a significant effect on the size of the arc attachment and consequently on the cathode surface and the plasma temperature. Good agreement was obtained with the measured cathode surface and plasma temperatures without imposing any adjustable parameters. The results showed that the proposed model, which is only based on physical principles, is ableto predict the trends observed experimentally.
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| 10. |
- Liwång, Hans
(författare)
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Risk-based ship security analysis : a decision-support approach
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The protection of shipping does not come without hazards and threats for military forces, individual civilian ship operators and crews. With particular focus on security threats, this thesis is about how to prepare for such operations without introducing unnecessary risks, i.e., supporting conscious risk-taking related to ship security. It examines both civilian and military aspects of maritime security and therefore draws from the experience of both fields.Maritime safety regulations, guidelines and methods have a history and culture of systematic research, development and implementation. In contrast, international security is highly politicised and therefore less transparent. Unfortunately, comprehensive studies of ship security risk are rare. Moreover, applying risk-based approaches to security areas requires special considerations, and the limited research in this field has led to a knowledge gap.To reduce the identified challenges with respect to security risk analysis, the goal of this thesis is to improve security decision support by defining an approach to ship security analysis. To increase overall safety, this approach must facilitate compromises between traditional maritime safety and maritime security. Accordingly, the objective is to develop an approach that is both systematic and gives the decision maker an appropriate picture of the security risks. To examine the requirements for a security decision-support approach, the work in the appended papers studies both threats to naval vessels and the security threat posed to commercial vessels by pirates. The results of the studies can be used to further develop military doctrines and civilian guidelines.This study shows that the description and quantification of the (concept of) operation in the risk analysis is central for implementing both security and naval ship survivability. In addition, the crew’s risk perception, procedural safeguards and how the implemented risk controls are perceived have an important role not only in risk analysis but also in deciding the effectiveness of implemented controls. It is also concluded that only using expected values—not collecting and using uncertainties—in the analysis can lead to misleading results. Therefore, the uncertainty treatment offered by a quantitative approach is crucial for risk understanding, especially if the aim is to find robust control options or to support the development of a resilient culture.
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