Examensarbeten för masterexamen

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    Numerical study of condensation and conjugated heat transfer from flow in a heat exchanger
    (2024) Peyvandi, Ehsan; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Chalmers University of Technology / Department of Mechanics and Maritime Sciences; Sasic, Srdjan; Johansson, Klas
    There are many industrial and nonindustrial fields where Plate heat exchangers, PHE, are utilized for their efficient heat transfer ability. Some fields in which PHEs are commonly used include HVAC (Heating, Ventilation, and Air Conditioning), Power Generation, and Refrigeration. The compact size, high heat transfer efficiency, ease of maintenance, and cleaning make them a popular option across various sectors. Hence, it is essential to study and understand the flow and heat transfer in plate heat exchangers to optimize the usage of these systems. Alfa Laval develops (design, analyze, and manufacture) a wide range of heat exchangers, including gasketed, brazed, and welded plate models. This Master’s thesis concentrated on investigating and laying the groundwork for conducting Computational Fluid Dynamics (CFD) simulations to study heat transfer during the phase change (condensation) process on the primary side, involving the full condensation of propane as it transitions from a gaseous to a liquid state. The procedure followed in this thesis is as follows: Initially, a Pipe flow, as a first test case, is simulated to gain an understanding of the various parameters involved in Computational fluid dynamics (CFD) analysis. Then, as a second test case, to develop and validate a multiphase flow modeling where a full condensation of the gaseous phase occurs, the Kuhn (1995) [12] experiment is adopted. The numerical simulation models were created using Ansys Discovery Modeling. Subsequently, the meshing and simulations were carried out using Ansys- Meshing and Fluent (2023R1). The hydrodynamics of the two-phase flow have been solved using both the Mixture- and Volume of Fluid (VoF) methods separately. Mass and heat transfer resulting from phase change (condensation) were handled through the Lee condensation model.
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    Minimize the aerodynamic effect of a strut on the wing
    (2023) Santor Blair, Andres Felipe; Utku, Mert; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Chalmers University of Technology / Department of Mechanics and Maritime Sciences; Xisto, Carlos; Antunes, Alexandre
    The field of aircraft design is continuously advancing through the utilization of scientific techniques and empirical methods. The incorporation of computational methods has facilitated the design process of new and complex aircraft, enabling more efficient conceptual design and optimization. These advancements have the potential to significantly reduce fuel consumption and emissions, making a positive impact on the environment, a critical global concern. The development of battery-electric airplanes represents a significant step towards creating a more sustainable aviation sector. Among the various emerging concepts, the Strut-Braced Wing (SBW) has shown great promise in enhancing aerodynamic efficiency while reducing wing weight. However, the implementation of new concepts and technologies also presents new challenges and limitations that must be addressed, particularly the impact of aerodynamics on the aircraft’s range, which can impose limitations on its maximum travel distance. The primary objective of this thesis is to minimize the aerodynamiceffects of a strut and wing configuration by reducing total drag and increasing the Oswald efficiency of the Strut-Braced Wing during the conceptual design phase. To achieve this goal, Sequential Quadratic Programming (SQP) and Genetic Algorithm (GA) optimization algorithms are employed, utilizing low-fidelity Computational Fluid Dynamics (CFD) methods. The airfoil data utilized in the study is obtained from the XFOIL tool, which provides important viscous aerodynamic characteristics. By implementing these methodologies, it is anticipated that the aerodynamic performance of the Strut-Braced Wing configuration can be optimized, leading to improved efficiency and weight reduction. The results obtained from this research will contribute to the advancement of aircraft design and promote the development of more environmentally friendly and efficient aircraft during the conceptual design phase.
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    Torque vectoring using e-axle configuration for 4WD battery electric truck: Utilizing control allocation for motion control and steer by propulsion
    (2022) Fahlgren, Emil; Söderberg, Daniel; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Chalmers University of Technology / Department of Mechanics and Maritime Sciences; Jonasson, Mats; Laine, Leo; Janardhanan, Sachin
    With the rise of electric drives in vehicle applications, configurations of new powertrain design are emerging. In recent years, this trend has shifted to include heavy vehicles as well. In this thesis, a concept 4x4 battery electric truck with a distributed powertrain is investigated. By using four individual motors on two separate e-axles, different coordination possibilities are available for motion control of the truck. This thesis focuses on using torque vectoring as a principle to allocate the requested global torque. Furthermore, a novel method mentioned to as steer by propulsion (SBP) is proposed, where the steering of the vehicle can be controlled solely by using the electric machines on the front axle. Investigations are conducted to explore the effectiveness of this method on vehicle performance and energy consumption. To distribute the control requests across the available actuators, control allocation (CA) is used. Here, the problem is formulated as a quadratic programming (QP) problem. High level controllers provide the requested global forces as an input to the control allocation, which in turn allocates torques to the separate wheel controllers. Furthermore, different formulations of the control allocator and motion controller are presented and compared. The control system is simulated with a vehicle model provided by Volvo, and the results indicate that steer by propulsion is able to follow a reference path with a lateral offset of a magnitude of an acceptable level. Furthermore, the simulations show that SBP can repeat this behavior at high speeds as well with an oscillatory behavior. Therefore, the method is recommended to use mainly at vehicle speeds below 50 km/h. Finally, simulations show that SBP increases the energy consumption by 2-4 %. Considering that the consumption is on par with using power steering, SBP will be viable for redundancy with some limitations.
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    Transmission loss analysis for boat propulsion unit noise shield
    (2023) Cruz Sánchez, Constanza Montserrat; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Chalmers University of Technology / Department of Mechanics and Maritime Sciences; Johansson, Håkan; Brauer, Samuel
    The transition from a diesel engine to an electric engine represents a significant step towards achieving greater sustainability in maritime vessels. However, this conversion can expose tonal noise from the Integrated Propulsion System (IPS) component of a boat propulsion system. Therefore, the main objective of this thesis project is to develop a methodology for assessing sound transmission loss (TL) in components that incorporate absorbent materials as passive noise control measures. The TL model was constructed using Actran software. The model consisted of a twolayered system composed by wood and foam in combination with a monopole source. Simulations were conducted in a semi-anechoic chamber setup. Two mathematical models, namely the Johnson-Champoux-Allard (JCA) model and the Miki model, were employed to study sound propagation in porous media and evaluate their impact on defining acoustic parameters. In order to determine the flow resistivity of any material when the acoustic properties are unknown, sound absorption and impedance theories were employed within an impedance tube model. The results demonstrated that accurately defining the complete acoustic parameters in the JCA model is crucial for obtaining reliable results. Furthermore, for accurate prediction of flow resistivity using either sound absorption or impedance values as inputs, impedance measurements must be performed utilizing the Miki model. The TL results exhibited a good correlation between the physical measurements and the simulations conducted in Actran, using both the Miki Model and JCA model. However, it should be noted that since the Miki model has only one material parameter, it is more sensitive to changes in flow resistivity compared to the JCA model. Consequently, variations in flow resistivity can have a substantial impact on the results and must be carefully considered in the analysis and in the design process.
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    Adaptive Traction for Optimal Mobility for Heavy Duty Vehicles
    (2023) Choudhary, Mukesh; Mapari, Aditya; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Chalmers University of Technology / Department of Mechanics and Maritime Sciences; Jacobson, Bengt; Oscarsson, Christian; Hjelte Ulmehag, Robert
    This thesis addresses the critical need for developing prediction-based control allocation strategies for autonomous or manually operated vehicles within low-speed application area such as construction and mining sites. A prediction horizon focused in this thesis is approximately 50 meters. In the pursuit of safe and energy-efficient control, it is essential to harness the potential of multiple traction actuators, which traditionally operate re-actively. This project seeks to optimize these systems using predictive algorithms, given that drivers often lack the knowledge required to operate them effectively. Furthermore, the timely responsiveness of actuators is of critical importance in demanding situations. The current practice involves manual control of traction actuators, such as differential locks and electronically controlled air suspension, based on drivers’ real-time observations. However, this approach is often sub-optimal, as it does not fully utilize the capabilities of these systems. To address this issue, the thesis centers on automating these traction actuators, leveraging predictive road data. It assumes the availability of upcoming road data, including road profile and predicted friction data for the next 50 meters. The primary objective is to develop an optimal control strategy that maximizes traction while ensuring adequate steering margin. To achieve this, the thesis initially delves into understanding how these actuators influence traction and steering. Subsequently, a rule-based control allocation model is developed in MATLAB and Simulink, which is then tested with a comprehensive vehicle simulation model across various test cases. The research also extends to practical implementation. The control allocation logic is transferred to real-world conditions using real-time systems, specifically the MicroAutoBox II, on a physical truck. Impressively, the developed control function provides results in almost real-time, with a response time of only approximately 1000 milliseconds. While this computational time may be considered too high for safety-critical functions in some contexts, it remains adequate for the specific function under scrutiny, which is focused on predicting the upcoming 50- meter road conditions. In conclusion, the thesis presents a comprehensive approach to enhance traction using differential locks and axle load distribution strategy. By automating traction actuators based on predictive road data and optimizing control strategies, this research contributes to realizing safer, more energy-efficient autonomous driving systems.