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| 2. |
- Abugabbara, Marwan
(författare)
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Modelling and Simulation of the Fifth-Generation District Heating and Cooling
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- District heating and cooling are efficient systems for distributing heat and cold in urban areas. They are a key solution for planning future urban energy-efficient systems due to their high potential for integrating renewable energy sources. The systems also play an important role in community resilience, which makes them a multidisciplinary research topic. The continuous development of these systems has now reached the fifth-generation whereby end-customers can benefit from the intrinsic synergies this generation offers. A typical Fifth-Generation District Heating and Cooling (5GDHC) system consists of connected buildings that together have simultaneous heating and cooling demands. Local heat pumps and chillers in decentralised substations modulate the low network temperature to the desired building supply temperatures. The demands are potentially balanced by the means of recovering local waste heat from chillers, while also utilising heat pumps to provide direct cooling. The heat carrier fluid in the distribution pipes can therefore flow in either direction in the so-called bidirectional low-temperature network. A balancing unit is incorporated to compensate for network energy imbalances. The exchange of energy flows is realised at different stages within the individual building and across connected buildings. Numerous factors influence the quantity and quality of the exchanged energy flows. Demand profiles in each building, the efficiency of building energy systems, and control logics of system components are some examples of these factors. Investigating this generation using traditional computational tools developed using imperative programming languages is no longer suitable due to system complexity, size variability, and changes adopted in different use cases. Modelica is a free open-source equation-based object-oriented language used for the modelling and simulation of multi-domain physical systems. Models are described by differential-algebraic and discrete equations. The mathematical relations between model variables are encapsulated inside an icon that represents the model. Different component models interface variables through standardised interfaces and connection lines. Large complex systems are composed by the visual assembly of components in a Lego-like approach. Models developed in Modelica can be easily inherited for rapid virtual prototyping and/or edited to adopt changes in the model use. This dissertation has a fourfold objective. Firstly, it demonstrates the development of a simulation model for an installed 5GDHC system located in Lund, Sweden. Secondly, it characterises the components that constitute a 5GDHC system. Thirdly, it unravels the exchange of energy flows at different system levels and describes, in a logical progression, the modelling of 5GDHC with Modelica. Fourthly, it presents ethical risk analyses of the different role-combinations that may arise in 5GDHC business models. The developed model is used in performing annual simulations and to evaluate the system performance under two different substation design cases. The results indicate that adding a direct cooling heat exchanger in each substation can reduce the electric energy consumption at both substation and system levels by about 10 and 7 %, respectively. Moreover, the annual waste heat to ambient air can be decreased by about 17 %. The dissertation fosters an ethical discourse that engages the public and all who take part in the multidisciplinary research on 5GDHC to guarantee safe operation and appropriate services. Future research will build on the models presented in this dissertation to investigate different network temperature and pressure control strategies, in addition to adopting several design concepts for balancing units and thermal energy storage systems.
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| 3. |
- Adham, Kristi
(författare)
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Growth and Characterization of Core-Branch Nanowire Structures
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis investigates growth of III – V semiconductor nanowire (NW) arrays, in a core- branch architecture, with the aim to develop diffusion driven light emitting diodes (LED) on NWs. Diffusion driven LEDs are based on the concept of decoupling the active region from the p-n junction. The carriers are injected by diffusion in the active region, because of the bandgap difference between the pn junction and the active region. This concept can be used in NW structures where tree structures are grown with high bandgap cores and low bandgap branches. The small diameter of the branches facilitates light extraction and removes the limitation of total internal reflection. The first part of the thesis focuses on studying the deposition parameters of Au particles on the sidewalls of the core NWs. These particles act as catalysts for branch growth. The second part of the thesis focuses on the growth of branches from homostructures (InP-InP) and heterostructures (InGaP-InGaP) where the Ga content in the core is higher than in the branches. We demonstrate high density branch growth distributed along the entire core length. Finally, we present some results from photoluminescence measurements in heterostructure core-branch NWs. The results presented in this thesis are intended to contribute to the development of a new and promising LED architecture.
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| 4. |
- Agner, Felix
(författare)
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On Hydraulic Constraints in Control of District Heating Systems
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- District heating systems make an important puzzle piece in the energy system of both today and tomorrow. When designing, simulating and controlling these systems, hydraulics play a vital role. The pressure generated by pumps has to drive sufficient flow throughout the system to satisfy the requirements of customers. Ensuring that the system is sufficiently pressurized is a challenging task already in current systems, and may become even more challenging in the transition to the 4th generation of district heating. In the first paper of this thesis, a demand response framework is suggested, which distributes the available flow to customers in a fair way. The framework aims to make it so that when the available pressure in the network is low, the buildings in the periphery should still be able to satisfy their heating needs. The second paper of this thesis extends previous methods for identifying greybox parameters for hydraulic district heating models. Previous methods of this type rely on more measurement points, and do not include the influence of the control valves situated in customer substations. These model parameters can then be used for simulation or control purposes. Together, the results presented in this thesis provide tools for better dealing with the hydraulic limitations in district heating systems. At the end, future work is outlined which may further pave the way for improved control that takes hydraulic limitations into account.
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| 5. |
- Akbarian, Fatemeh
(författare)
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Attack Resilient Cloud-based Industrial Control Systems
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Industrial control systems (ICSs) are a significant part of industry and they play an important role in monitoring and controlling industrial processes. Traditionally, ICSs have been isolated from the Internet, and thereby secured from various Internet-based security threats. In recent years, since the cloud can provide huge advantages regarding storage and computing resources, industry has been motivated to move industrial control systems to the cloud. However, when ICSs are moved to the cloud, they are inevitably exposed to increasing security threats, which can lead to severe degradation of the system performance or system failures. Moving control systems to the cloud can enable attackers to infiltrate the system and establish an attack that can lead to damages and disruptions with potentially catastrophic consequences. Therefore, some security measures are necessary to detect these attacks in a timely manner and mitigate the impact of them. In the work presented in this thesis, we mainly explore the security challenges of cloud-based industrial control systems and we propose a security framework for these systems that can make them resilient against attacks. Our proposed framework includes attack detection methods that can detect attacks in a timely manner. Also, the framework includes mitigation methods that can mitigate the impact of the attack on the system when an attack has been detected. So, by using this framework, an industrial plant can be maintained operational with an acceptable performance during an attack. Our solutions are validated on a real testbed, where the capabilities are evaluated by subjecting the system to a set of attacks.
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| 6. |
- Alm, Karin
(författare)
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Butikens roll för hållbar konsumtion : Ett marknadsorienterat perspektiv på hållbar sortimentsutveckling i dagligvarukedjan
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Sustainability is an increasingly important topic across the world, and awareness of it has been growing since the publication of the UN sustainable development goals (SDGs). Seeing an escalating societal interest in sustainability, consumer demand for sustainable products in retailer’s assortments. Making the retail store manager a key player for implementing Corporate Social Responsibility (CSR) in retail store assortment. The aim of the study is to use a market-oriented perspective to understand information management between different levels in the grocery retail chain and how the store manager as a key person could affect the growth of CSR products in the store assortment. This study uses a market-orientated information perspective to generate knowledge about the dissemination of information between retail managers at central level and retail store managers. The empirical data is based on interviews with managers in retail buying at central level and at store level in three Swedish food retail chains.Based on the framework by Jaworski and Kohli (1993) five market-oriented factors were identified from which 10 propositions was developed. The propositions contribute to an understanding on how market-oriented factors affect market-oriented activities in retail stores. Weber’s ideal types (Weber, 1983) where the individual is the subject for interpretation of driving forces for CSR in retail store assortment contributes to an understanding of forces, such as authority, power, and rationality from an unspoken and informal point of view. Through the weberian analysis ideal types has been identified among store managers. An analytical reasoning about how social structures operates in organisations, the understanding of substructures and their relationships with each other, became the impetus for the results of this study. Therefore, these ideal types contribute to an understanding for how information management in retail buying could improve the dynamics of internal market orientation that might reduce the gap between consumer demand for CSR and actual sustainable consumption.
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| 7. |
- Andersson, Linus
(författare)
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Reduced order modeling in structural dynamics : Consideration of local nonlinearities
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A structural design process may include various load cases for which a sufficient load-bearing capacity must be demonstrated. In addition to static load cases, a verification of dynamic loads, e.g. accidental loads such as blast and impact loading, may be required. To this end, the response may be estimated using a computational model representing an idealized structure. Particularly in the conceptual design phase, a time-efficient and straightforward modelingapproach can be of great utility, allowing for an interactive design process where alternative designs may be tested. Furthermore, a dynamic response analysis often requires some form of time (or frequency) discretization and can therefore become computationally expensive compared to the corresponding static analysis. The balance between performance and accuracy as well as the purpose, i.e. the output quantities of interest, are thus important aspects in a dynamic response analysis.A structural dynamics analysis typically requires a model being accurate as well as computationally efficient. The model accuracy is particularly important in a verification of structurescharacterized by brittle failure modes, i.e. that do not deform plastically before failure. Furthermore,to avoid a too conservative design and to ensure sufficient accuracy, it can be necessary to consider the nonlinear response of a structure, e.g. due to contact interactions or nonlinear material behavior. However, a nonlinear structural dynamic problem often requires computationallyexpensive solution methods. Consequently, there is a need for modeling strategies that enable time-efficient, accurate analyses and a straightforward modeling approach, appropriate in a structural design process. To achieve this, a reduced order model can be established providing an accurate prediction of important output quantities.Dynamic substructuring turns out to be an important aspect in the process of developing reduced order models. By subdivision of the structure into substructures, dynamic substructuring can be employed to effectively adjust the level of accuracy for different parts of the structure. For example, substructures that remain linear elastic can typically be modeled using mode-superposition methods whereas substructures which exhibit a nonlinear behavior can berepresented by a refined submodel.In the dissertation, strategies for reduced order modeling are investigated on the basis of structural engineering applications within two different areas, namely concrete structures subjected to blast loading and glass structures subjected to soft-body impact. Interestingly, however, some of the challenges with regard to the structural dynamics problems are similar. In particular, the response of higher order modes may be of importance and, moreover, an accuraterepresentation of the structural behavior may necessitate a model considering local nonlinearities.By means of dynamic substructuring, computationally efficient analysis techniques are developed for evaluating concrete structures subjected to blast loading, appropriate for use in a structural design process. In particular, a comparison to commonly used modeling strategies, using equivalent single-degree-of-freedom systems, suggests that the developed models providean increased accuracy of the shear force. Brittle failure modes such as shear failure are typically critical for concrete structures subjected to blast loading.Furthermore, reduced order models are established for verification of glass panels subjected to soft-body impact. In particular, a non-linear viscous single-degree-of-freedom system is proposed for reduced modeling of the standardized EN 12600 impactor. Further, the response of higher order modes is considered using a set of load-dependent mode shapes. The developed models are validated by experimental tests of impact on glass panels.Finally, a review of various reduced order modeling techniques is presented which, in a broader perspective, provide a basis for developing reduced order models in various structural engineering applications.
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| 8. |
- Annby-Andersson, Björn
(författare)
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A General Formalism for Continuous Feedback Control in Quantum Systems
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis devolops a general formalism for continuous feedback control in quantum systems. The main result is a quantum Fokker-Planck master equation describing the joint dynamics of a quantum system and a detector with finite bandwidth. For a fast detector, this equation can be reduced to a Markovian master equation for the system dynamics. In particular, the formalism is amenable to analytical treatments of feedback protocols that depend nonlinearly on the measured signal. Previously, only numerical methods were available for this. We apply the formalism on two toy models to highlight its usefuleness. We find that the formalism provides insight into the connection between thermodynamics and information theory.
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| 9. |
- Arve, Kristin
(författare)
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Unga och tramadol : Berättelser om droganvändningens förlopp och om att försöka sluta
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Non-medical use of prescription opioids, such as tramadol, is a major global health concern. In Sweden, tramadol use among young people is widely recognized and highlighted as a novel drug use pattern. The overall aim of this licentiate thesis is to explore drug use trajectories and the process of attempting to quit drugs among young people with experiences of problematic tramadol use. 24 qualitative interviews were conducted with 13 young people (aged 19–24) with self-reported experiences of problematic tramadol use.Paper 1 explores the drug use trajectories of the young people, including changes in drug use patterns and motivations for their use of tramadol and other drugs. The results indicate that most of the young people quickly started to use tramadol regularly and eventually expanded their drug use repertoire to include more substances. Overall, there was a progression to more severe drug use over time, where self-medication and experiences of dependence, as well as peer influence and other environmental factors playing significant roles.Paper 2 addresses the young people’s accounts of attempting to quit tramadol and other drugs. The results demonstrate conflicting emotions towards drug use along with a significant external pressure to quit, but also difficulties in quitting due to experiences of dependence and mental health issues. For most participants, however, an increasing autonomous will and ability to abstain from drugs gradually developed, with the support from trusted relationships playing a crucial role.The study demonstrates how aspects related to the drugs’ effects, personal circumstances, and the social environment interact in young people’s drug use trajectories, as well as in their process of attempting to quit drugs. By highlighting the young people’s perspective, the study can contribute to a deeper understanding of problematic tramadol use that may be helpful in improving both preventive and therapeutic measures for this target group.
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| 10. |
- Arvidsson, Magnus
(författare)
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Water mist fire protection systems : The development of testing procedures for marine and heritage applications
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Modern, commercial water mist fire protection system technology evolved at the beginning of the 1990s due a need to replace halon fire-extinguishing systems and improve fire safety on passenger ships. This thesis documents the unknown water mist system development work by two Swedish companies during the 1970s and 1980s. It also documents the development of the first international installation recommendations and fire test procedures for marine applications.Several of these fire test procedures needed revisions. A research project in the thesis showed that those for machinery space protection can be significantly improved by using simple and inexpensive measurements and performance measurement parameters. In another research project, tests simulating fire on a ro-ro cargo space of a ship was conducted. The results indicate that large water droplets are required for fire suppression, but smaller water droplets cool the fire gases well. For the protection of heritage buildings, a field study suggests that functional testing is essential to maintain the function of a system. Testing using commercial nozzles indicate that exposure of sensitive wall paintings to water spray could cause significant damage under real-life conditions, even if the flow rate is low.Future research should focus on improving fire test procedures based on experience as well on a theoretical understanding of the mechanisms of water mist. Long-term field experience is also desired for continual improvements of the performance and reliability of systems. In order to convince authorities, insurers, fire protection consultants and end-users on using water mist, these issues need to be dealt with in a systematic manner.
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