Examensarbeten för masterexamen // Master Theses

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1D Modeling and Simulations of Soot Oxidation in Diesel Particulate Filters and Monoliths using GT-POWER
(2016) Lerdmaleewong, Chanin; Luong, Staffan; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied Mechanics
Diesel particulate filter (DPF) is part of the exhaust aftertreatment system for diesel engines. The DPF’s main function is to trap particulate matter (soot) from the exhaust stream. The trapped soot is removed by regeneration of the filter. The regeneration process involves soot oxidation via oxygen and nitrogen dioxide. Simulations on kinetics and pressure drop are widely used in the assessment of the DPF. In this work detailed kinetic models of soot oxidation (by oxygen) were investigated and implemented in a flow-through monolith model and also in a DPF model using GT-POWER. The detailed kinetic models and data origins from previously published data. The DPF model consists of a number of interrelated sub-models soot oxidation by NO2 , NO oxidation and pressure drop. These sub-models were developed by using semi-steady state and transient engine data on a catalyzed DPF. Kinetics and pressure drop analysis were found to be the key in finding parameters for the models. The implementation of these models into GT-POWER required some special techniques due to rigid built-in model structure. The detailed kinetics was adequate to predict the low temperature experiment, in general, the detailed kinetic model was able to reduce the residual by approximately 25% compared to global kinetics model.
1D Simulation Modeling for an Exhaust Aftertreatment System SCR Calibration Modeling in GT-SUITE
(2021) Ramanjaneyalu, Puneeth; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Sjöblom, Jonas; Sjöblom, Jonas; Yitbarek, Zemichael
The Euro legislative regulations are imposed successively to hold back toxic elements that are harmful to the environment. Carbon monoxide (CO), hydrocarbons (HC) and nitric oxide (NOx) are the major toxic elements that cause serious health hazards for the living species. From many research works, selective catalytic reduction (SCR) is the most promising technology to address NOx. The objective of this project is to develop a surface reaction mechanism model, reaction rate calibration for SCR catalyst and validation. Firstly, building the SCR catalyst and surface reaction mechanism model in GTSUITE. The reaction rate calibration or characterization is performed for six reaction rate expressions with 18 unknown parameters by applying physical properties of the catalyst for example diameter and area of the catalyst. Furthermore, the digital laboratory Simulink black-box is utilized to produce the target reaction rate curves for all chemical reactions to calibrate the parameters then to compare with simulated GT-model results. Finally, validation for steady state or urea stairs, US, conditions and transient driving cycle conditions against WHTC (world harmonized transient driving cycles) for the Euro V regulations using tail pipe, engine-out emissions, mass flow rate and temperature traces experiments data. Overall, chemical kinetics modeling for SCR catalyst in GT-SUITE was successfully implemented and have reasonable results for urea stair cases, but the outcome can be further improved for transient cycles by extract information from 3D CFD to 1D in the future. Inevitably, simulations analysis is the best possible way to validate the results in quick time with low cost and it is a key factor during the development process.
1D Transient Simulation of Heavy Duty Truck Cooling system – HDEP 16 DST, Euro 6
(2012) Raghavan, Ganesh; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied Mechanics
In future and also in the present time, with the focus on minimizing environmental impacts, the truck industry faces a big technological challenge in terms of meeting statutory emission legislations and also on satisfying the ever increasing demand of customers in terms of minimizing the fuel consumption. There are other challenges in terms of having a short development time and reducing the overall development cost. All the above stated challenges requires measures in terms of how computer simulations can be used to better represent a system, how different concepts can be tested, how the overall system can be tested in particular system working environment which ultimately will give a short development time with minimum cost. This thesis work basically answers the above questions in a holistic manner by considering how the truck cooling system be modeled using different CFD tools like AMESim and GT Cool to understand how different performance parameters of a cooling system vary for a steady and transient driving cycle. In this thesis work, the cooling system model has been developed for an ongoing project in Volvo Powertrain AB. The model has been developed for 16L DST, 750 Hp, Euro 6 heavy duty truck engine with other auxiliary components like, air compressor, transmission oil cooler, cab heater, urea heater to mention a few. The model has been developed such that it can run on both steady and transient cycles by changing few elements in terms of how the input is given to the model. One of the aims of this thesis work was to evaluate the two tools mentioned above in terms of workability, implementability and reliability. Results in terms of pressure drop, mass flow rate, heat transfer rate, thermostat valve fluctuation etc. have been compared for above mentioned tools. It is pointed out that since the model has been developed for an ongoing project, the validation of the model by performing actual tests couldn’t be performed because of the unavailability of the engine. In the end certain conclusions have been drawn out in terms of cooling system performance and how effective the tools were in simulating the cooling system.
3-D object tracking through the use of a single camera and the motion of a driverless car
(2021) Ovnell, Andreas; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Benderius, Ola; Benderius, Ola
There has been a very large increase in interest and development of partially or fully driverless cars in recent years. For these driverless cars to function, they need to be able to navigate to their destination while avoiding nearby objects. This can be done using simultaneous localisation and mapping (SLAM). SLAM is the task of simultaneously creating a map of the surrounding objects while keeping track of the car’s position within this map. This thesis will look into the feasibility of using a single camera attached on a driverless car to perform SLAM on cones detected by the real-time object detection system You only look once (YOLO). Three different methods were tested. All of these require a calibrated camera that is capable of determining horizontal and vertical angles from the pixel positions. The first ‘triangulation’ method uses that the distance travelled and rotation between two frames is known. The second ‘plane projection’ method is an optimisation problem which consists of finding the variables which result in lowest error, and through this determine the cone distances and car speed. The map of the surrounding cones is moved according to the estimated velocity and rotation of the car such that the car is always placed at the origin, allowing for use of multiple detections to improve accuracy. The third ‘distance from cone height’ method works by using the size of the cone detections in order to determine the approximate distance of each cone, use this to determine the approximate angle of the camera and then use the median angle to make the final distance estimates. The triangulation method was shown to be completely unsuitable for mono-camera use. The plane projection method was shown to be unreliable, likely due to a relatively small number of visible cones and a too large noise amplitude of detections from YOLO. The distance from cone height method was shown to be the best out of the tested methods, as it was simple, fast and quite reliable. However, this method still had an error approximately 1.4 times larger than what is advertised by commercial stereo camera systems.
3D modelling of plane-strain fracture toughness tests using ansys wokbench
(2020) Wester, Filip; Gunnarsson, Eric; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Ekberg, Anders
This thesis shows the possibilities of modeling and recreating the fracture toughness test E399 using available test data. It also adds to the conclusion that for a excessive amount of plasticity the 95% secant can not be used to derive KIC as the crack has not propagated at that point. Further it has been shown that for limited amount of plasticity the J-integral can be used to calculate the linear elastic stress intensity factor. The thesis also discusses the validity of adding friction between the specimen and the pin to increase the stiffness in the simulation to match the test data and compare this approach to other methods. Finally, ways of using FE modelling to get information from invalid tests are discussed.
3D thermal modeling of a battery cell on a test jig fixture using CFD
(2023) Daneshvari, Reza; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Chalmers University of Technology / Department of Mechanics and Maritime Sciences; Sebben, Simone; Andersson, Ingemar; Arvani, Maedeh; Ramesh Babu, Anandh
The thermal conditioning of battery cells plays a crucial role in ensuring their safety and maximizing the driving range of electric vehicles. To gain a comprehensive understanding of battery cell performance under various conditions, testing is conducted within controlled chambers that replicate real-world scenarios. While battery packs and modules can function independently during testing, individual cells require mechanical support. This is where the jig comes into play, serving as a robust support structure that enables current conduction and facilitates effective liquidbased thermal conditioning. The objective is to achieve optimal cell climatization and maintain it at a suitable temperature. In order to comprehend the thermal properties of the jig when exposed to the heat generated by the battery cell, Computational Fluid Dynamics (CFD) simulations are employed. These simulations provide insights into the underlying physics of the phenomena and aid in the identification of potential enhancements for the jig design or testing conditions to prevent cell damage. The model can be adjusted to simulate different temperature scenarios, allowing for a comprehensive evaluation of the jig’s response under varying conditions.
7DCT Transmission efficiency optimization: Design and simulation of oil traps that reduce the churning los
(2020) Forsström, Birk; Minar, Matus; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Andersson, Sven B; Johansson, Robert
The automotive industry is undergoing a big change when switching from building combustion engine cars to electric powered cars. With the big limitation of range that comes with using battery to store energy there is an even greater need in finding ways to improve the efficiency. Together with CEVT (China Europe Vehicle Technology), this master’s thesis purpose is to make an improvement of the gearbox that lower the torque that is required to rotate it. To verify the results a prototype is built with materials available in the company’s workshop and investigated if it can withstand a test in a testing rig. With the use of CFD-analysis (Computational Fluid Dynamics) the lubricant of the gears is investigated through a simulation of a benchmark. The aim was to find areas where reduction of churning losses can be made with the use of a new part that is created in CAD (Computer Aided Design). Inspiration for these improvements is found in previous studies made by employees at CEVT and at rival companies. The process of creating a new part is iterative and performed with rough simulations before a comprehensive simulation is made that can be compared with the benchmark. Through the benchmark simulation it was concluded that the differential gear stands for most of the churning losses along with the output shaft above it. A new part was created that protects the top shaft from being hit by incoming oil transported by the differential, it also collects the oil in two containers for further redistribution. These changes resulted in a decrease in drag torque generated by the oil of 16.3% at 50km/h and a trend of larger reduction at higher speeds. For a prototype build, experimental tests were conducted on the ABS-plastic available at the company. It was concluded that the plastic would withstand the heat and oil inside of the gearbox and afterwards a prototype was built for future testing. In the end of the study it was concluded that oil can be collected in the upper regions of the gearbox by taking care of the splash from gears. This along with protecting gears from splash that hit them in the opposite direction of speed can reduce the churning losses by around 16%. With this knowledge a future work would be to investigate how to distribute this oil from these regions to where it is needed. By doing so, future development of gearboxes can be made around how oil is being transported by gears to benefit from these possibilities.
A booklet for the mandatory Crowd and Crisis Management course – according to the STCW ’95 Convention
(2010) Magnusson, Tobias; Lewenhaupt, Ian; Chalmers tekniska högskola / Institutionen för sjöfart och marin teknik; Chalmers University of Technology / Department of Shipping and Marine Technology
Problem: Only compendiums are used in the CCM courses. There is a lot of literature on crisis management and human behaviour, but the authors did not find any book combining these two subjects. Existing literature is either too extensive or not fully relevant for seafarers. Purpose: The purpose of this master thesis is to study theories related to crowd and crisis management and discuss them with course providers, course participants, authorities and specialists in the area. Further, the purpose is also, to use the result of the above mentioned study as a launch pad to start a writing process towards a booklet in Swedish on crowd and crisis management for seafarers. Completion of the writing process is outside the aim of this essay. The aim is that the booklet later on can be useful for students and seagoing personnel. Method: Interviews, literature studies and case studies. Results: The mandatory requirements for the Crowd and Crisis Management course are found in the Swedish Transport Agency (STA) TSFS 2010:20 Annex 18. In Sweden course providers have to be authorized by STA. At the time for this research there were six providers approved by STA. Through literature studies relevant theories in crisis management were found: Diffusion of innovations and emergency preparedness, The Situational Leadership model, the Fundamental Interpersonal Relations Orientation model, Wilfred Bion’s theories on group dynamics, Geert Hofstede’s Cultural Dimensions and Recognition-primed decisions (RPD). The interviews showed that most of the course providers discussed situational leadership in their courses in one way or another. Course participants asked for more education in leadership and clear authoritative leadership, some of the interviewees asked for military inspired leadership training. There were also a demand for communication theories and theories on human behaviours. When the course providers were asked what they think a book about CCM shall include, they answered: stress and crisis reactions, International Safety Management (ISM) for preparedness, mental preparedness, reaction during an accident, awareness for group dynamics, human behaviour, communication and procedures for tactical thinking during stress. The views of the providers are thus more or less the same as the course curriculum provided by the Swedish Transport Agency.
A CFD Investigation of Sailing Yacht Transom Sterns
(2014) Allroth, Jens; Wu, Ting-Hua; Chalmers tekniska högskola / Institutionen för sjöfart och marin teknik; Chalmers University of Technology / Department of Shipping and Marine Technology
The objective of this thesis was to investigate whether the hydrodynamic performance of the wide, box-shaped transoms that have become very popular on modern performance cruisers is better than the performance of the more conventional, less wide, rounder transoms. The investigation of the hydrodynamic performance was evaluated with the aid of computational fluid dynamics using the Reynolds Average Navier-Stokes (RANS) viscous solver SHIPFLOW 5.0 with Volume of Fluids method surface capturing (VOF). First part of the study was to conduct verification of the software using the Least Square Root method. Second part was to make a validation of the software where Computational Fluid Dynamics (CFD) results were compared to experimental data from towing tank tests of Delft Systematic Yacht Hull Series (DSYHS) hulls. In the third part an average modern performance cruiser was designed to later be used as a base line for a systematic transom geometry variation study. Twelve hulls were created with varying transom size and shape. Each hull was tested in four conditions; upright and heeled condition at Froude numbers 0.35 and 0.60. Finally the results from the CFD computations were used to set up a simple upwind-downwind race to distinguish which hull that had the best overall performance. In the upwind-downwind race the round transoms performed best for the three fastest transom sizes. The fastest hull around the course has an immersed transom ratio (At/Ax) of 0.16 and it is 1.9 % faster with round transom than with boxy. The study has led to better understanding of the relation between hydrostatic and hydrodynamic resistance at high Froude numbers where the gain from a big immersed transom area is larger than the loss from increased transom resistance. Also, the influence on wave resistance from the curvature of the water and buttock lines has been clearly illustrated. For low Froude numbers, where the transom is wetted, the effect from viscous pressure resistance, base drag, has been pinpointed.
A CFD Investigation of SailingYacht Forebodies in Head Seas
(2015) Kostalas, Konstantinos; Pluto, Adam; Chalmers tekniska högskola / Institutionen för sjöfart och marin teknik; Chalmers University of Technology / Department of Shipping and Marine Technology
The objective of this thesis is to investigate the hydrodynamic performance of a modern 41 feet sailing yacht by comparing the performance values acquired from simulations for different forebody geometry designs on the yacht. The particulars such as length, beam, displacement and prismatic coefficient are kept as similar as possible for all hulls. The resistance of the different designs are tested in flat water and in tests with waves. The set up for the waves is made with data taken from Svenska Björn; which is a caisson lighthouse in the Baltic Sea. The wave lengths tested in this study includes lengths of 12.5m, 25m and 34.5m and the yachts are run in straight head sea. The encounter frequency for the 25m wave matches the natural pitch frequency of the yachts. To evaluate realistic upwind condition, for cruising and racing, tests with a heel angle of 20o are additionally performed. All hulls are tested at Froude number 0.35 in the conditions described in the previous paragraph. This investigation is made with the aid of CFD using Unsteady Reynolds Averaged Navier-Stokes (U-RANS) equations integrated in the solvers provided in Star CCM+ software. Also, Volume of Fluids method for surface capturing is used. At the start of the study a verification of the software is made with the use of Least Square Root method. Then, a validation of the CFD results from the software is done by a comparison with data from towing tank tests from Delft Systematic Yachts Hull Series hull. In total three hulls are tested with a systematic forebody geometry variation of shape. The main result of this study is a better understanding of how the forebody design of a sailing yacht affects the performance. The study is done at high Froude number, where the gain from having a sharp and pointed entry angle and then diving into the water is larger than having volumes in the lower part of the bow. Having a tumblehome design that prevents the yacht from diving into waves gives calmer motions but higher resistance. However it is important to conclude that the drag, pitch and heave for all yachts are close and a definite winner hull is difficult to name because some of the three yachts are better than the other in certain conditions. Nevertheless, the best design overall is the hull with sharp entry angle and flare.
A combined numerical and statistical approach to crack propagation modeling and prediction of crack propagation rates
(2012) Rembeck, Martin; Sjöblom, Anders; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied Mechanics
A Comparative Study on Alternative Marine Fuels: Economic, Technology, Environmental and Safety Issues
(2024) Nasir, Hamza; Tian, Tian; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Chalmers University of Technology / Department of Mechanics and Maritime Sciences; Li, Zhiyuan; Brynolf, Selma; Lindmark, Olle; Li, Zhiyuan
Transitioning to sustainable energy sources in the maritime industry is imperative for mitigating environmental impacts and achieving long-term sustainability goals. This master thesis explores the feasibility and potential of hydrogen as an alternative marine fuel, comparing it with other options such as liquefied natural gas, methanol, and ammonia. The study addresses several key questions: What are the technological, economic, environmental, and safety implications of adopting hydrogen as a marine fuel? & How does hydrogen compare to other alternative fuels in terms of these criteria? The authors employ a multidimensional analysis approach, incorporating methodologies such as the Analytical Hierarchy Process (AHP) and a Case Study of MV Venta Maersk to evaluate the performance of alternative fuels. The study begins by examining the technological landscape through a literature review, highlighting the challenges and opportunities associated with hydrogen production, storage, transportation, and utilization. It concludes that Carbon Capture and Storage technology, critical for blue hydrogen production, faces challenges related to stringent requirements and consistent natural gas supply. Conversely, green hydrogen production poses formidable hurdles due to cost implications and necessitates advancements in electrolysis technology and supportive governmental policies. In assessing the environmental impact, this study emphasizes the significance of greenhouse gas emissions and marine pollution. Hydrogen emerges as a promising option, offering zero emissions during combustion and minimal environmental impact. However, the inherent characteristics of hydrogen pose technical and safety challenges. While LNG also demonstrates commendable environmental performance, generating minimal NOx and Particulate Matter emissions during use, it remains the top priority among alternative fuels due to its early adoption and relatively mature infrastructure. The AHP results from surveys have revealed a priority on safety and environmental concerns as critical criteria in the evaluation of alternative fuels. Methanol and ammonia rank lower in the comprehensive assessment due to their inherent challenges and safety considerations. Despite their potential, further research and development efforts are warranted to address technical and safety challenges and harness their full potential as viable fuel options. The study concludes by providing insights on limitations and suggests future research directions, emphasizing the need for technological innovation, supply chain optimization, and policy interventions to facilitate the adoption of alternative fuels.
A comparative study on the modeling of matrix cracking in fiber-reinforced polymer laminates under transverse compression - XFEM versus a smeared crack approach
(2016) Pourbahaaddini, Ershad; Simonsson, Philip; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied Mechanics
As the number of applications for fiber-reinforced polymers (FRP) is growing, the importance of understanding the failure behavior of this material is rising. This is merely conceivable by developing precise computational material models, which saves time, material, and energy. In general, the polymer matrix is the constitute with the lowest strength against failure in a FRP; hence the matrix requires additional attention especially under transverse compression where it is considered as the principal load carrying component of the FRP. In the present work, a comparative study on the modeling of matrix cracking in FRP laminates under transverse compression is carried out. To do so, an eXtended Finite Element Method (XFEM) approach is developed for discrete crack modeling, and the conventionally used smeared crack approach is applied via an existing Abaqus/Explicit implementation for continuum crack modeling. The comparison of the results illustrates that despite different kinematics behind the models, they both successfully predict a near identical material degradation and energy dissipation in the material response, but with differing predictions when considering frictional tractions and the predicted maximum stress levels. XFEM is established to be mesh-objective and the smeared crack method predicts the material response optimally when the mesh discretization is one element per ply with reduced integration excluding non-linear geometry effects. Moreover, the wedge effect described by geometrical deformation is distinctly represented as cracks are studied explicitly in XFEM, which provides the possibility of further study for inter-laminar effects such as delamination, crack propagation and crack migration. Key words: XFEM, smeared crack model, progressive damage analysis, transverse compression, friction, fiber-reinforced polymer
A comparison of elastic mooring systems for floating wave energy converters
(2020) Chen, Ho-Ann; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Ringsberg, Jonas; Ringsberg, Jonas
Wave energy is a widespread and abundant source of renewable energy, yet the technology of harnessing energy from waves is still in the pre-commercial stage. One of the key challenges in the development of wave energy converters (WEC) technology is to ensure the long-term performance and reliability of the mooring system, which must be designed to survice under cyclic loading, not fail due to fatigue, at a commercially competitive cost. This thesis takes WaveEL, a heaving point-absorbing WEC developed by Waves4Power, as the reference case to investigate the performance of WEC systems with different elastic mooring systems in regards to fatigue life and power absorption. As the electricity production of the heaving point-absorber WEC relies on the cyclic heave motion of the WEC device, the long-term deployment of the WEC systems under irregular ocean loads poses high fatigue damage on the mooring lines. The snap loads that act on the mooring lines also decrease the mechanical life of the mooring system. Studies have shown that by adding tether components to the mooring system, the fatigue life of the system can be increased, thus making the WEC systems more commercially feasible. A tether component is a mechanical system that reduces the responding force range and absorb the snap loads in mooring lines. It is this thesis’ objective to develop numerical models to represent tether components, and to evaluate its impact on the WEC performance by integrating the elastic tether component into the mooring system. This thesis investigates two mooring configurations: a 3-leg mooring system with floating buoys between the WEC device and the anchor to decreases the stress loading on the mooring lines, and a 2-leg mooring system with a deeper design water depth so that the system can benefit from the elasticity of the mooring lines. Comparisons are made between the two original mooring configurations and the same mooring setup with the tether component implemented. Coupled hydrodynamic-structural simulations are carried out with different mooring configurations under operational loads. The heave motions of the WEC device and the force response in the mooring lines under operation conditions are obtained from the simulation results and used to calculate the fatigue life of the mooring system and the absorbed power of the WEC system. It was found that the tether component greatly improves the fatigue life of the mooring system, whilst not negatively affecting the power absorption.
A comparison of finite element formulations for analysis of the converting process of packaging materials
(2015) Lindberg, Susanna; Sandvik, Patrik; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied Mechanics
A Computational Approach to Include the Effects of Elevated Temperatures in Finite Element Simulations
(2010) Brommesson, Rebecka; Ipsen, Nils; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied Mechanics
A Computational Investigation of Wheel and Underbody Flow Interaction
(2013) Koitrand, Sofie; Rehnberg, Sven; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied Mechanics
The use of moving ground and rotating wheels (MVG&RW) when testing road vehicles in wind tunnels have previously been shown to largely affect the results, however it is still not the standard test prodecure for many manufacturers. This also means that simulations are set up to match the static behaviour of the experimetal tests. However, when most companies today turn their efforts to the underbody of the vehicle in an effort to improve aerodynamics, stationary conditions are no longer adequate. This report aims at investigating how the rotation of the front and rear wheels in combination of moving ground influence the local, as well as the global, flow fields and especially the wake behind the vehicle, by the use of Computational Fluid Dynamics (CFD). Two different vehicle models based on the same platform, namely the Jaguar XF Saloon and Sportbrake, are used to set up eight different cases for each vehicle. The research has been set up to enable comparison with earlier experimental research. The results are divided into three groups giving the results due to the addition of a moving ground, rotating front wheels and rotating rear wheels. By adding a moving ground the drag and front lift increase noticeably, whereas the rear lift decreases significantly. The addition of front wheel rotation has little effect on the global results, whereas the addition of rear wheel rotation largely decreases both the drag and the rear lift. By adding these three groups up largely the same results are achieved as when comparing the fully stationary cases to the cases with MVG&RW conditions, namely that the addition of MVG&RW conditions noticeable reduces the drag and the rear lift, whereas front lift hardly changes.
A computational model of a ground vehicle with engine mounted on rigid chassis
(2009) Göbel, Felix; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied Mechanics
A Cooperative Function with Cloud Communication for Avoiding Collisions with Occluded Pedestrians - Concept Development and Feasibility Evaluation
(2017) Stolt, Caroline; Fahlin Strömberg, Jeanna; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied Mechanics
Annually, there are 1.25 million fatalities in traffic accidents around the world. In EU, 21 % of the road fatalities are pedestrians. Without action, road traffic crashes are predicted to be the 7th leading death cause by 2030. The safety of vehicles have improved over the past decades, during which, traditionally the focus has been on passive safety, reducing the injuries from a collision. During the last decade, however, active safety which focuses on preventing or mitigating collisions, have become increasingly important. Active safety functions, such as collision warning and avoidance systems, are common features in today’s vehicles. However, in several common scenarios, today’s active safety systems are not enough to avoid or mitigate a collision. The aim of the thesis was to develop a concept of a cooperative active safety function which avoids or mitigates a collision between an occluded pedestrian and a following vehicle whose view is compromised by a vehicle in the adjacent lane. Within this thesis, we establish the potential benefit, limitations and feasibility of such function by extending existing active safety systems with cloud communication. In this thesis, a concept of an occluded pedestrian warning and collision avoidance function was developed and evaluated in simulation. The function is cooperative and utilizes sensors in the occluding and following vehicle as well as cloud communication between them. The simulation was conducted in an ideal simulation environment with and without communication latency as well as in a cloud test bench. The developed concept yielded a large benefit for a wide set of parameter combinations and even for long latency of several hundred ms. Nevertheless, latency proved to be a limitation and should be limited to 100-200 ms considering the uncertainties. To conclude, a benefit for our cooperative function was shown for a wide range of parameters and scenarios. Long latencies limit the effectiveness of such system but benefit can still be observed. The current function can yield benefits for the type of scenarios which were tested. With soon expected technology shifts, the benefit of our function in more complex scenarios would increase.
A coupled multibody and discrete element approach for roller compaction dynamics
(2020) Göransson Axås, Joar; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Lidberg, Mathias; Quist, Johannes
This thesis presents a novel compaction simulation method, where a multibody dynamics model of a vibratory roller is coupled to the discrete element method (DEM) for unbound granular materials. A multibody dynamics solver is developed, and an analysis of the roller mechanical system is performed to construct a rigid body model of the machine. Further, a method for bed initialisation is developed, and a uniaxial strain test is used to calibrate the multisphere DEM material parameters. Then, compaction simulation is made possible by implementation of a coupling server, that runs the DEM and multibody solvers simultaneously at different timesteps. Such simulations are compared to full-scale experiments and compaction theory. The machine response to beds of varying stiffness agrees with experience from compaction practice, and characteristic behaviour, such as double jumps, is observed. The stresses in the bed agree with experiments if the particle Young's modulus is kept low. However, the roller penetration of the bed is higher than in experiments due to insufficient shear resistance in the DEM model. At the same time, no increase in bulk density is achieved. Further analysis shows that the lack of shear resistance is likely related to the multisphere model of the particle geometry, and the lack of compaction may be due to a particle size distribution that is too narrow. On the other hand, such simplifications are necessary, because large computational costs impose limits on the particle size distribution, particle discretisation, and domain size. The function of the solver coupling and machine model is verified, but in order to enhance agreement with full-scale experiments, improvements are needed in terms of both the particle modelling and computational performance capacity.

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