Examensarbeten för masterexamen

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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.
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    Developing a three stream, mixed flow variable cycle engine in NPSS
    (2023) Larsson, Vincent; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Chalmers University of Technology / Department of Mechanics and Maritime Sciences; Grönstedt, Tomas; Nilsson, Patrick
    One of the more important areas of improvement in aircraft engines is fuel efficiency for economicas well as environmental reasons. While modern civil turbofan engines are primarily designed with fuel efficiency in mind, thus having very high bypass ratios, military engines need to uphold high specific thrust requirements in order to reach supersonic speeds as well as perform the manoeuvres sometimes necessary in a combat scenario. Modern military aircraft engines are therefore designed as low-bypass turbofans capable of producing significant specific thrust, but at the cost of having a high specific fuel consumption even at lower speeds in comparison to their civil counterparts. The variable cycle engine, or adaptive cycle engine, is an engine concept for which the engine cycle can be modified in-flight to better fulfil different mission requirements. The type of variable cycle engine of interest for this thesis is a so called three stream, double bypass, mixed-flow variable cycle engine, in which a low-bypass turbofan engine has had an additional outer bypass duct added to it. This third stream can be independently modulated to vary the bypass ratio of the engine during flight, increasing the airflow through the bypass duct during subsonic flight for better fuel efficiency and increasing the flow through the engine core during supersonic flight for higher thrust. For the thesis, the Numerical Propulsion System Simulation software (NPSS) was used to both model and simulate two variable cycle engines with differing design bypass ratios. In order to evaluate the models, a baseline model representing a generic, standard low-bypass turbofan engine was also modelled for comparison. The primary area of study for the models was the effect of increased bypass ratio on thrust specific fuel consumption at different altitudes and speeds, as well as the total fuel savings during a simulated mission. The results showed that overall, the variable cycle engines had an advantage over the standard engine with regard to fuel consumption during dry-thrust. The mission analysis performed showed possible fuel savings of ca. 11 and 14 % compared to the base model for the two VCE designs respectively. This came however at the expense of a lower maximum net thrust when operating at wet-thrust settings.
  • Post
    Wurster fluidized bed coating: Integrative validation of coarse-grained CFD-DEM
    (2023) Kjaer Jepsen, Philip; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Chalmers University of Technology / Department of Mechanics and Maritime Sciences; Sasic, Srdjan; Martin De Juan, Luis