Projektarbeten // Project Reports

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CFD investigation of a generic vehicle side-view mirror
(2020) Ibáñez, Cristóbal; Palm, Richard; Rahani, Ramin; Shao, Xinyuan; Chalmers tekniska högskola // Institutionen för mekanik och maritima vetenskaper; Johansson, Håkan
Electric automobiles are becoming more common in today’s society. Since interior car noise can have negative mental health effects for the driver and passengers, it becomes relevant to find out how it is being generated. One important source of noise is the surface pressure fluctuations caused by shear layer impingement and turbulence from the flow around a side-view mirror. Even though many studies about the flow past a side-view mirror have been done, there is not sufficient research for lower speed cases at which electric cars drive at. The purpose of this project is therefore to study the flow around a generic side-view mirror and investigate how it generates noise for some of these cases. The computational fluid dynamics (CFD) software STAR-CCM+, running both steady and unsteady Reynolds-Averaged Navier Stokes (RANS) simulation models is used. Three cases at different freestream speeds of 20, 30 and 40 m/s are simulated. To ensure accurate results, a mesh independence study is carried out for the 40 m/s case with steady RANS simulation. The final mesh is then used to simulate the 20 and 30 m/s cases as well. The steady flow fields were obtained using the realizable k −" model and later used as initialization fields for the unsteady cases, were SST k − ! model is used. Pressure fluctuations data series of specific sensors placed on the surfaces of the mirror and window where analyzed for their power spectral density (PSD) in the frequency domain. For sensors placed in the back of the mirror and on the window inside the recirculation region, noticeable peaks at 500-1300 Hz in the signal’s power were observed. Comparison of the PSD’s against the Strouhal number revealed that the power peaks are due to coherent structures in the free shear layer developed from the mirror edges. Those PSD peaks will generate tonal noise which is of 500-1300 Hz. Measures should be taken to prevent drivers and passengers from hearing this kind of noise. The present study is also a fundamental step to provide hydrodynamic pressure fluctuation data for a future acoustic wave simulations.
Variables extraction and trajectory reconstruction for modelling driver behaviour
(2020) Hamdy Shams El Din, Ahmed; Takkoush, Mohamed; Pettersson, Nicklas; Hulkunte Gopinath, Sriranga; Chalmers tekniska högskola // Institutionen för mekanik och maritima vetenskaper; Sjöblom, Jonas; Bärgman, Jonas; Bianchi Piccinini, Giulio
Active safety and autonomous driving are two booming words in the automotive industry of today. Most, if not all, companies are in a race to provide a safe environment for driving and are thriving to reach their goals in producing autonomous vehicles. The general goal of this project is to develop a human driver model for critical lane-changing manoeuvres. Annotation of such data was done manually on videos acquired from dash-cam footage from a naturalistic driving study (NDS) by identifying di erent events in time, such as time of lane crossing and relative distance between vehicles. A semi-automatic tool to aid the annotation of the NDS footage was developed and several methods for range calculation are discussed such as the pixel width method and the triangulation method, which are also used for calculating the heading angle and the lateral o set of the lead vehicle. The results were found to be relatively accurate considering the simplicity of the tool. As for the tracking of the lead vehicles and the lanes, the most accurate method was found to be through interpolating between user inputs.
Deformations in welded panels
(2020) Selvaraj, Srikannan; Pamfil, Bogdan; Hård, Daniel; Gurram, Shivaprasad; Chalmers tekniska högskola // Institutionen för mekanik och maritima vetenskaper; Johansson, Håkan; Josefson, Lennart; McDill, Moyra
Welded panels are commonly used for ships hull manufacturing, and in order to lighten the hull the stiffened panel thickness tends to be reduced, thus increasing the distortion effects due to welding. This project will be part of Chalmers contribution to the benchmark exercise in a specialist committee, Material and Fabrication Technology, for the International Ship and Offshore Structures Congress (ISSC) 2021 conference. The project’s purpose is to compute the deformation for the ISSC2021v.3 benchmark [1] geometry of a stiffened welded panel which comprises of a stiffener 1000 x 100 x 5 mm DH36 plate which is initially tack welded on one side to a 1000 x 400 x 5 mm DH36. The welding procedure consists of a first weld fillet being deposited on one side of the stiffener, followed by a cooling time, and then another weld fillet being deposited on the other side and followed by a second cooling time before the welded panel is finally unclamped. To achieve that, both thermal and mechanical analyses are carried out by relying on the nonlinear Finite Element Analysis (FEA). The commercial FEA program ABAQUS is used for analyses in this project. Those simulations are however performed for a shorter plate and stiffener of length 200mm. The material properties were implemented in ABAQUS input file form, for both the weld and the plate and stiffener. Nonlinear thermal and mechanical properties were taken into account. The specific heat and thermal conductivity were implemented for the DH36 steel, however other properties such as thermal expansion coefficient, Poisson’s ratio etc., were implemented for a similar steel, S355. The weld material and the plate and stiffener are altogether modelled as being the same material except regarding the hardening modulus and the yield stress. When compared to the plate and stiffener material, the weld material itself has been modelled as having a higher yield stress and higher hardening modulus at room temperature. Two thermal models are considered with each having 1000 C as the heat source temperature of the weld. First, the fillet weld is activated simultaneously and in the second, the fillet weld material is activated sequentially by dividing the weld into segments. After each weld pass the model is allowed to cool down for 200 seconds so that the welded panel has cooled to around 50 C at the end of the simulation. The thermal simulations are coupled to mechanical simulations. In mechanical simulations, different clamping sequences are carried out. One with fully fixed and two with sliding clamps. In total six configurations are considered, since there are two thermal models and three clamping conditions for the mechanical simulations. Clamping is taken care of by taking the top and bottom nodes of the plate at designated locations. The same mesh model was used for both the thermal and mechanical simulations, and it consists of linear 8-node hexahedral and linear 4-node tetrahedral solid elements. The linear hexahedral elements are used to model the plate and stiffener and the welding joint is modelled by linear tetrahedral elements. Prior to choosing vi a final mesh a mesh convergence study was conducted by monitoring the temperature variation at a location close to the weld. The resulting mesh had 31200 nodes and elements with an aspect ratio lower than 10 to avoid complications with the mechanical simulations. The results of this project showed that the type of heating source and the clamping conditions have definite effects on the behaviour of the model. The displacements results for the mechanical simulations indicated that the sequential heating results were closer to the intended ones than for the simultaneous heating case. Also, the extent of clamping conditions, i.e., either fully clamped or sliding clamps, along with the methods used to prevent rigid body motions for a sliding clamp are all factors which have an effect on the behaviour of the model. And these differences in the thermal and mechanical loading configurations will be magnified when they are applied to the full length of 1000 mm for the plate and stiffener as per the ISSC2021v.3 benchmark.
Aerodynamic investigations of a bus under high side wind conditions conditions
(2020) Hellsten, Oskar; Pettersson, Oskar; Minár, Matús; Gefors, Hugo; Forsström, Birk; Ravindra, Nithin Bharadwaj; Chalmers tekniska högskola // Institutionen för mekanik och maritima vetenskaper; Sjöblom, Jonas; Sebben, Simone; Vdovin, Alexey
The Norwegian Public Roads Administration (NPRA) is looking for different solutions on how to shorten the travel time for road vehicles between Bergen and Trondheim. The main reason for the long traveling time is due to the amount of fjords that needs to be crossed by ferries when traveling by the coast. Because of this several alternatives to ferries are explored and one of these alternatives is using floating bridges. Since side winds affect the stability of the floating bridge coverage of the sides will be minimal and therefore all vehicles will be fully exposed to side winds. Larger vehicles like buses and trucks are the main concern in regards to sudden instability or a rollover. To prevent accidents it has been decided that a vehicle dynamic model will be made to evaluate the wind speed threshold for when the bridge should be closed or the vehicle speed should be limited. The magnitude of the side forces on long vehicles during high wind conditions is needed as an input to create this vehicle dynamic model. By using CFD together with wind tunnel testing with a scale model an investigation of these forces has been performed. A scale model of the Volvo 9700 series coach bus was 3D printed to be used for wind tunnel testing. Because of a predetermined available mounting area as well as with regards to wind tunnel blockage ratio a scale of 1:18 was chosen. The model was then printed in 9 different parts excluding the wheels because of print volume limitations. To be able to try different design configurations the model was made modular. The front and rear were attached using neodymium magnets while the other parts were either permanently attached using epoxy based glue or screws together with threaded inserts that were melted in to fuse with the plastic. To get a good surface finish for added accuracy in the wind tunnel the model was covered with body filler, sanded, then covered in spray filler and lastly painted black. The wind tunnel testing of yaw angles covered a complete 360 sweep with increments of 5 up to 90 and then increments of 10 for the rest. The results were mainly used as reference to the CFD results since the wind tunnel setup did not include rotating wheels and boundary layer suction. Visualization of the airflow around the bus was achieved by using tufts, smoke and thermal camera. A steady state incompressible RANS equations(Reynolds Averaged Navier Stokes) are numerically solved in StarCCM+ to determine forces and moments. These forces were determined by running simulations for a changing yaw angle from 0 to 90 in 5 steps. Non-dimensional co-efficients of drag force, lift force, side force, yaw moment, roll moment and pitch moment are calculated to compare the data from wind tunnel. This is done as the wind tunnel testing is obtained for a scaled model and in CFD the actual size of the bus is used. Results show that the trends observed in CFD follow the trends from wind tunnel test data. It was observed that coefficient of side force and roll moment increases with the increasing yaw angle and reaches a maximum value at 90 yaw. This shows the importance of the effect of cross winds on vehicles with large side area. This data can be further used in a vehicle dynamic model to evaluate the impact on vehicle stability.
Driver influence on vehicle track-ability on floating bridges
(2020) Balakrishna Bhat, Abhishek; Naik, Akshay; Adithya Reddy, Chintalapudi; Pishey, Kushaal; Manikanta, Venkatesh; Nishanth, Bharadwaj; Chalmers tekniska högskola // Institutionen för mekanik och maritima vetenskaper; Bengt, Jacobson; Sekulic, Dragan; Johansson, Ingemar
Thinking from a traveler’s perspective, it can be said that it is important to reduce travel time. The Norwegian Public Roads Administration (NPRA) is working on a long term project to extend the coastal highway route E39 as a continuous stretch of road between Kristiansand and Trondheim. The road has a number of ferry crossings over fjords. Due to the depth in the fjords, it is not possible to build conventional bridges. Thus, the objective is to reduce the travel time by implementing a series of connections (e.g.submerged floating tunnels, subsea road tunnels and floating bridges). One such fjord crossing is the Bjørnafjorden bridge which spans for a length of over 5000 m. The floating bridge will be exposed to a number of varied weather conditions of different intensities. It is important to assess the vehicle handling and how the driver is experiencing the moving road surface in these conditions. The bachelor thesis which was proposed on the same topic, established a method to simulate the weather conditions in the CASTER driving simulator at Chalmers. The Automotive Engineering project (AEP) aims at evaluating the driving comfort and handling, when driving over the bridge in different weather conditions. The main approach adopted is to simulate the driving conditions in CASTER driving simulator, using the weather data provided by NPRA. Further, driving trials are conducted for a combination of different weather conditions and vehicle speeds for car and bus models. The results obtained from the trials are analyzed both subjectively using the driver feedback and objectively using the data obtained from the driving simulator, to make suitable conclusions and recommendations regarding the safe operating conditions of the bridge. The project further concludes the correlation between the weather conditions and drivability through both subjective and objective data analysis. The weather conditions were varied from no wind condition to a 100-year storm condition. Also, the most frequently occurring 1-year storm condition was studied in detail with only wind on the vehicle, sea swell and wind due to the wave conditions. A total of 157 driving trials were conducted with different vehicle speeds (70 kmph, 90 kmph and 110kmph) and different maneuvers like lane change and overtaking were performed to analyze the handling and stability of the car and bus. Straight line driving is also simulated to determine the operating conditions of bridge, to check the safe speed limit and ability of the driver to stay in lane. Another deliverable of the project is to develop a driver model to perform a greater number driving trials to test more conditions. Due to the lack of time and complexity of the weather data, a basic driver model has been developed and a thorough literature survey has been done to make suitable suggestions for the existing basic driver model as a future scope of the project. To sum it up, the vertical and lateral dynamics of the vehicles driving over the bridge are assessed in a virtual environment. A detailed analysis is done with the help of the data obtained in order to make suitable recommendations for safe driving on the bridge at different weather conditions.
Development of environments to test driver assist functions for reversing an A-double combination vehicle
(2021) Parshetti, Vikram; Keshava Reddy, Lohith Reddy; Prabhu, Anand; Ashok, Nrupathunga; Jain, Pratham; Srinivas, Akhil; Chalmers tekniska högskola // Institutionen för mekanik och maritima vetenskaper; Sjöblom, Jonas; Jonasson, Mats
transportation efficiency. These vehicles have multiple trailers pulled by a single tractor and the A-double is an example of such a vehicle. Although A-doubles improve transportation efficiency, they are extremely difficult to manoeuvre in the reverse direction. The work done in the project aims to develop a rapid prototype environment that reduces development time and cost of controllers used to assist drivers in reversing the A-double. The assist functions developed using these environments help improve loading and unloading time while also reducing the stress levels of the driver(s). The testing and validation of the controller is done in two tiers. The first tier is a virtual environment to test the basic functionality and the second tier is a scaled environment to test the robustness and performance of the controller. Two control strategies have been developed to validate the test environments and their performance has been discussed. The performance of the test environments and possible improvements have been discussed.
A study of the influence of vertical tyre force on rolling resistance coefficient and lateral slip stiffness coefficient using truck tyre model
(2021) Govardhan Raju, Bharath; Nobeling, Nicholas; Rajopadhye, Chirag; Tota, Pranay Damodhar; Chalmers tekniska högskola // Institutionen för mekanik och maritima vetenskaper; Sjöblom, Jonas; Jacobson, Bengt; Bruzelius, Fredrik; Fröjd, Niklas; Romano, Luigi
Tyres are an important component that affect the energy consumption and performance of all vehicles, including trucks. The vital properties of the tyre realising these phenomena are the rolling resistance and lateral slip stiffness, respectively. This project aims to investigate and understand the influence of vertical load on the rolling resistance coefficient and lateral slip stiffness and based on these investigations, evaluate the possibility of creating simple and physically interpretable yet tune-able tyre models. The lateral slip stiffness investigation involves modelling a physical tire model based on the brush model with parabolic pressure distribution and a curve-fit model based on the ’openPBS’ tool non-linear tyre model. These models are tuned to match the data extracted from the VTI experiments of test performed with a truck tyre on the tyre testing facility. The lateral slip stiffness generated using both models is compared with the experimental test data, and found that the curve-fit model presents a better approximation of the test data. However, dense measurement data in terms of more data sets for varying vertical loads as well as more number of measured lateral force vs. slip points for each vertical load data set will be required to confirm this conclusion. The variation of RRC with lifted and non-lifted axles is studied using test data availed from a report by Lennart Cider, discussing the rollout tests of two different trucks with lifted and non-lifted axles. A proposition of load independent wheel bearing torque loss is considered as an alternate explanation for the varying rolling resistance and a study conducted for the same shows that the friction losses in the wheel bearings could approximately account for around only 13.5% of the estimated change in rolling resistance. Hence this cause solely is an unlikely explanation of the difference in rolling resistance. A finite element study of the tyre contact patch and the vertical load offset could aid the understanding of this phenomena better.
Aerodynamic investigations of a simplified truck under high yaw wind conditions
(2021) Dineff, Athanasia; Upadhyaya, Avaneesh; Nagaraja Rao, Kaushik; van Hoorn, Philip; Gudihal, Vinay; Chalmers tekniska högskola // Institutionen för mekanik och maritima vetenskaper; Sjöblom, Jonas; Sebben, Simone; Vdovin, Alexey
The Norwegian Public Roads Administration (NPRA) are investigating the impact of side winds on vehicles travelling over a floating bridge that they wish to construct to shorten travel time. To mitigate the movement of the floating bridge due to high crosswinds, the bridge will be designed in a way that it does not obstruct the wind as much; resulting in high wind impacts on the commuting vehicles. The tractor-trailer combination is a large bluff body and experiences large side wind forces. Due to these forces, it may affect its lateral stability and might result in rollover at high crosswind speeds. This automotive engineering project aims to investigate the forces and moments acting on the truck during strong side winds and design a generic modular model for research use in the road vehicle aerodynamics course. The force investigations were performed numerically using STAR-CCM+ and experimentally through the closed-loop wind tunnel test facility at the Chalmers University of Technology. SOLIDWORKS was used to design a simplified model of a truck that can be used for research purposes. To accommodate the option of add-ons and to increase the ease of add-ons interchangeability during the wind tunnel testing, the truck design was made modular. The customization could be, for example, the addition of roof fairing, boat tailing or even an American-nose. The down-scaled model was printed and then sanded down and spray-painted for a smoother surface finish and better aesthetics. Assembly of the parts was done using epoxy, super glue and magnets. This model was tested in the wind tunnel, where a sweeping study was performed at a constant wind speed of 30 m/s for varying yaw angles between 0 and 90 . The modular design made it easy to test different configurations, such as different gap sizes between tractor and trailer, and the addition of a roof fairing. Multiple computational fluid dynamics (CFD) simulations were performed on the 1:1 model to mimic open road conditions and cross-validate the wind tunnel test. STAR-CCM+ software was used to mesh, analyze and post-process the CFD data. A steady-state approach and the k-e turbulence model were used to solve the Reynolds- Averaged Navier-Stokes (RANS) equations. A mesh independence study was performed to ensure the validity of the mesh used for the sweep study. The sweep study tested different relative wind directions between 0 and 90 for the same domain and mesh. A simulation is said to have converged when the force coefficients averaged over 750 iterations lie within 2 drag counts for 750 iterations. A comparison between the CFD and wind tunnel results validate the results as the forces and moments acting on the models follow a similar trend for varying yaw angles. The slight discrepancies in the comparison occurred due to the absence of a moving ground, varying boundary conditions and the mounting struts that act as a flow obstruction
Advanced Combustion Analysis: The development of an advanced combustion analysis tool
(2021) Ahmed, Aijaz; Edholm, Oskar; Lutimath, Ajanish; Raj, Avanish; Tagesson, Filip; Chalmers tekniska högskola // Institutionen för mekanik och maritima vetenskaper; Sjöblom, Jonas; Sjöblom, Jonas; Koopmans, Lucien; Ahmed, Ahfaz
The main purpose of this project is to study and investigate advanced combustion analysis in compression-ignited (CI) and spark-ignited (SI) engines. A MATLAB code will be developed as the major deliverable, which will calculate the (apparent and real) rate of heat release with the provision of different, effective intake valve closing, heat transfer models, blow-by loss and gas properties with automatic polytropic coefficient detection. This code will also be used to compare and validate the different zero level corrections with commercial data acquisition software by Dewesoft (stakeholder for this project). For the study a 6-cylinder CI engine and am SI engine at Chalmers is used to record the in-cylinder pressure. Measurements of the in-cylinder pressure accurately plays an important role in pressure trace analysis. In this project, the experimental data like raw cylinder pressure and crank angle degree is recorded with the Dewesoft data acquisition system. Along with the recorded data, data from other test cells were also collected which was further analyzed and processed through the MATLAB code developed. After the investigation, the common assumption of constant values of certain parameters, such as IVC effective, constant polytropic coefficient, temperature at IVC, wall temperature, heat transfer loss and blow-by loss was found to skew the data significantly, thus giving incorrect results. Further, in-depth analysis for each of the above parameters is done and function scripts were developed and integrated into the main MATLAB program. The major findings are that the commercial combustion analyzer software’s usually considers a constant polytropic coefficient and also performs an apparent rate of heat release, thus neglecting the heat transfer and blow-by losses. But in reality, the polytropic coefficient varies and the heat transfer and blow-by loss do contribute and affect the amount of heat energy liberated during combustion. The results from the analysis of the data’s influence on the heat release is presented in the report.
Model of a standing bus passenger: Modelling Safety for Non-Impact Collisions
(2021) Gurram, Shivaprasad; Gebel, Till Rune; Niranjan Poojary, Yash; Chalmers tekniska högskola // Institutionen för mekanik och maritima vetenskaper; Sjöblom, Jonas; Thomson, Robert; Boyraz Baykas, Pinar
Public transport has been an efficient and convenient mode of transport for diverse population, though they are considered safe, but considerable injuries to passengers occur even due to non-crash related incidents. Evasive maneuvers, sudden accelerations or braking influence the posture of a standing passengers and result in them loosing balance. This project aims at developing a model to simulate the motion of a standing passenger influenced by distinct acceleration profiles and predict the time of when the passenger’s foot is off the ground. Extreme limits for imbalance is decided based on the position of the center of mass with respect to the ankle to find the instance for the event to occur. In order to capture the passenger response during these incidents a mathematical model is designed based on Single inverted pendulum (SIP) with a torsion spring at the ankle. The SIP models the motion of the standing passenger. In the model the torques acting on the ankle are two different kinds, one due to the center of mass and the other due to the muscle influence. A feedback controller consisting of a proportional and a predictive part is designed to control the torque influence due to the muscle actions. The stiffness of the ankles are calculated based on the combined torques due to the muscles and the center of mass. The output i.e. the predicted time for imbalance is influenced by various factors such as the acceleration jerk, amplitude and duration along with the reaction time of the person. The results obtained can be further used in the implementation of passenger safety features in the transportation industry as the model in this project can help in detailed study of the factors affecting the posture during standing and the prediction of the time for imbalance. Knowledge of the passenger’s state of balance can be an input signal to activate a safety feature. The model developed also has a lot of applications in the development of complex Human Body Models (HBM).
Developing a Solution to Utilize Vehicle Dynamics Simulation Tools with a Motion Driving Simulator
(2021) Madhava Prakash, Ajit Kumar; Garje Mohankumar, Anup; Misquith, Clive Rahul; Ganatra, Diler Paresh; Soudagar, Irfan Ahmed Khan; Johnsson, Jonas; Chalmers tekniska högskola // Institutionen för mekanik och maritima vetenskaper; Sjöblom, Jonas; Johansson, Ingemar; Jacobson, Bengt
The project develops a method to integrate a CAE software (IPG CarMaker) vehicle model into the CASTER driving simulator. The vehicle dynamics performance is assessed by comparing CarMaker (CM) simulation data against the driving simulator data. First, a baseline generic passenger SUV was modeled on CM with K&C parameters that resemble a real-world vehicle. Then, the driving scenarios and maneuvers such as steady state cornering [6] and double lane change [5] were modeled on CM. Alongside this, IPG Movie and CM for Simulink were used to create real driving scenarios with accurate driving views. Next, the baseline vehicle was simulated in CM and driven on the simulator for both maneuvers. Driver input signals from the driving simulator were fed into CM through CM for Simulink to run the physics of the vehicle model. The output signals computed by CM were fed to the driving simulator to provide motion, audio and visual cues. The integration tool was developed to introduce it in the early phase of vehicle development. The software simulation provides good objective data but no subjective assessment. The use of DIL-simulator is a good method to add subjective assessment in vehicle dynamics development. After every maneuver run, driver’s subjective assessment and rating was recorded. A statistical and graphical comparison of objective data between CM simulation and driving simulator drivers. Analysis of this data showed there is good correlation between results from CM simulations and the driving simulator. Then, vehicle parameter variations were made to understand the vehicle dynamics performance objectively and subjectively. For each model variation, a CM simulation and driving simulator test was carried out by multiple drivers. The vehicle specification variations were designed to produce changes in the steering feel and controllability. This indicates that the driving simulator is a viable supplement to prototype testing, however, further studies must be made to validate the preliminary conclusion. In reality, vehicle evaluations are performed by highly skilled test drivers with accurate subjective assessments. The project yields a tool to develop and evaluate the vehicle dynamics performance. In the hands of a professional driver, this will produce good subjective assessment that ties in with the objective metrics, thus validating it’s use as a cost effective and time efficient tool to develop vehicles.
Deformations and Stresses in Welded Panels: Development and analysis of a simulation procedure for two-pass fillet welding of a stiffener to a plate
(2021) Boominathan, Thangam; Pujari, Aditya; Sjödin, Wilhelm; Stoyanova, Monika; Chalmers tekniska högskola // Institutionen för mekanik och maritima vetenskaper; Johansson, Håkan; Josefson, Lennart; McDill, Moyra
This project is a part of the Masters programme Applied Mechanics at Chalmers and will also be a contribution to a benchmark exercise in a Specialist Committee, V.3 Material and Fabrication Technology for the International Ship and Offshore Structures Congress (ISSC) 2022 Conference. The goal of this project is to further develop and analyse an existing simulation procedure for two-pass fillet welding of a stiffener to a plate with the aim to find what simplifications that can be made in the modelling. The results from finite element simulations (FE-simulations) are then compared to analytical solutions and experimental data for validation. The FE-simulations are carried out with the commercial FEA-software ABAQUS using forward-coupled thermal-mechanical FE-simulations with geometrical and material nonlinearities included. The analysis is first performed on a shorter plate (200 mm) to draw faster conclusions by saving computational time. Once the analysis for the shorter plate has been conducted, a longer plate (1000 mm) representing the benchmark geometry is analysed. To verify that a simplified model of the heat input can be used, FE-simulations on the short plate are used to calculate the cooling time between 800˚C and 500˚C at a node on the weld. This data is then used to compare with analytical solutions for the cooling time in this interval, valid for the weld parameters specific to this benchmark project. By adapting the weld speed and maximum temperature of the weld, the optimal cooling time, and parameters for the heat input, are found. The simplified heat source model then gives the same behaviour as a real weld. With the thermal simulation settings validated by analytical solutions, the results from the mechanical part of the FE-simulations are analysed for the short plate. Here different sequences of releasing mechanical boundary conditions are studied, and how they affect the residual deformations after the two-pass fillet welding. This is achieved in ABAQUS by changing simulation steps and compiling the deformation fields for different configurations. Furthermore, different methods for preventing rigid body motion (RBM) are analysed and their influence on the residual deformations. Mechanical contact between a table beneath the plate is modelled using Lagrange multipliers creating a hard contact. The effect of this contact modelling on the residual deformations is also investigated, whether it is necessary or not since a removal of contact conditions will reduce computational cost considerably. One conclusion that can be drawn is that the release of mechanical boundary conditions is mainly elastic, and thus they can be modelled as removed at the same time. Furthermore, it is seen that the mechanical contact modelling is necessary to obtain reasonable results for some methods of preventing RBM. The long plate is then studied, where the complete benchmark geometry is modelled. Using Chalmers Centre for Computation Science and Engineering (C3SE) one complete simulation is run in a reasonable time of 12 hours on 24 CPUs. The residual stresses and deformations are then extracted and compared to experimental data on angular distortion and deformations. It is found that the simplified modelling approach used can give good agreement for the residual stresses and for the shape of the residual deformations. The magnitudes of the residual deformations, though, are harder to predict.
Liquid Hydrogen Tanks for Low-Emission Aircraft
(2021) Sjöberg, Jacob; Smith, Joshua; Haglund Nilsson, Olle; Emanuelsson, Per; Otlu, Sena; Chalmers tekniska högskola // Institutionen för mekanik och maritima vetenskaper; Johansson, Håkan; Asp, Leif
Hydrogen power shows high potential in reducing emissions of greenhouse gases from aircraft, which has led to companies investing more of their resources into developing this technology. One of the main issues of this technique is the storing of the liquid hydrogen within the airplane without adding too much weight. This has lead to a demand for designing tanks in carbon bre reinforced plastics (CFRP). This project has therefore been structured as a pre-study to further increase the knowledge available on the design of liner-less composite pressure vessels. It was discovered that a liner-less pressure vessel made out of thin-ply composite material is a concept of great potential. The two sections of the proposed tank, the tube, and the two endcaps were constructed di erently. In terms of stress and strain, they both indicated potential complying to limits set on the material, both in terms of ultimate values and thermal fatigue. Connecting the two main parts through a single scarf joint, currently common within the aerospace industry, the overall weight of the tank was decreased with a factor of over 85% compared to a steel tank. In conclusion, the design of a liner-less composite tank shows great potential and it is of interest to conduct further research in this area.
Finite element study of pressure distribution under tyre during low speed for explaining rolling resistance
(2021) Aalto, Robin; Johansson Sundblad, Lucas; Kareti, Priyatham Reddy; Olofsson, Nils; Subramanian, Vignesh; Chalmers tekniska högskola // Institutionen för mekanik och maritima vetenskaper; Johansson, Håkan; Jacobson, Bengt
Road transports are necessary as they are very flexible, and are essential for the logistics of today, though this requires sustainable solutions for environmentally stable transportation. Trucks are immense machines that are heavily affected by resistance, in both air and rolling resistance. In this report, the main focus will be to gain a better understanding of how the pressure distribution under a tyre influences the rolling resistance. In order to achieve a clearer perception of this phenomena, a 2D finite element model was defined. Two separate concepts were constructed, a more advanced model in ANSYS and a more simplified, yet more controllable, model in MATLAB. A hypothesis was formulated, wherein it is described that the pressure distribution is thought to be offset in the rolling direction. This would be the driving mechanism in creating rolling resistance, and the FE-models were made in order to try and capture this behaviour. The models were created with two layers, one for the sidewall and one for the belt. The boundary conditions were different between the models, in ANSYS the force was prescribed while in MATLAB, the deformation was prescribed. The simulations do show an offset for the pressure distribution beneath the tyre, which was thought to be the case. Though the simulation show that the offset would be in the other direction, something that was hard to explain. The two different model do however show a similar pattern, which was encouraging, though no unambiguous tendency was found. A varying vertical load, and the effects of that variation would be a desired factor to test, though since the project was short on time, this was not examined. Finally, there is more work to do in order to better understand the subject, which could be made by testing the model further or by developing a more complex model in either 2D or 3D.
Increasing freight transport capacity
(2022) Carlsson, Johan; Edberg, Marcus; Gullberg, Viktor; Nieswand, Niklas; Chalmers tekniska högskola // Institutionen för mekanik och maritima vetenskaper; Kabo, Elena; Ekberg, Anders
The main objective of this report is to investigate how freight train capacity can be increased to enable transportation related to carbon capture and storage (CCS) on the Swedish railway system in order to achieve the carbon dioxide climate target. The increased need for sustainable transport will create a large demand on the existing railway network. To meet these demands, several measures need to be taken. To investigate this further, literature study, interviews, a case study and analysis of the current network were conducted. As the railway network is a complex system, a range of measures is suggested to counter a high capacity utilization within both shorter and longer time frames. In the report several line segments limiting the system capacity were identified. Several measures were suggested with regards to both railway infrastructure and train set-up. It is concluded that additional investments have to be made to handle ccs transportation.
Model Exchange for Virtual SIL/MIL Verification of Passenger Cars with Electric Axles
(2022) Tsobanoglou, Christian; Jayanna Kundur, Ganesh; Siam Siraj, Mohammad; Anil Kumar Nikkam, Nitesh; Tsobanoglou, Simon; Ramakrishnan Bharadwaj, Varun; Chalmers tekniska högskola // Institutionen för mekanik och maritima vetenskaper; Sjöblom, Jonas; Jacobson, Bengt J H
In the present day, stiff competition in the automotive industry and shorter timelines for introduction of new passenger vehicles has forced vehicle manufacturers and component suppliers to cut down on development time. Virtual simulations help in bringing down this time drastically and are a critical phase in the design and development of new vehicles. Multiple subsystems make up a vehicle and these subsystems need to be tested before being used in production. In the case of system development in electric vehicles, virtual verification of subsystems early in the project phase is important given the platform modularity of the driveline in such a scenario. It also helps if the simulation models are modular, since model exchange between vehicle manufacturer and subsystem suppliers have to take place to build virtual prototypes. This report explores the modelling and simulation of such type of modular drivetrain for electric passenger vehicles. The modelling of drive axle as a subsystem is a key aspect in this project. Three types of drive axles, i.e., Torque Vectoring Dual Clutch (TVDC), Electric Torque Vectoring (e-TV) and an Open Differential axles are considered. Modelling the powertrain, specifically the motor, is done to determine the energy consumption of this driveline. Modellica language uses an equation-based modelling approach which has a higher flexibility when compared to the library-based modelling. For this reason, the open-differential model was modelled in Modellica and was exported as a Functional Mockup Unit (FMU). The TVDC model and the e-TV model is given as inputs by the concerned stakeholders from the project. Further, these models were integrated with a control model and a vehicle model in a VVE, namely, IPG CarMaker. To establish a comparison between these different models, vehicle performance and energy consumption of these drivelines were studied. Validation and verification of the developed models were carried out as a precursor to simulation in the project. Sanity check of the model was done to make sure that the given vehicle does not run off the desired path. This ticks off the basic physics involved in the models. This was an iterative process based on the validation results of the models. Further, to draw a comparison between the different powertrains, the models were simulated with an open diff at the rear wheel (RWD) as a reference. Plots for dynamic variables and energy were used to analyze the results and compute measures like vehicle performance and energy consumption. AWD, as expected, performed the best in terms of vehicle stability. However, the interesting comparison was between e-TV and the TVDC models. To establish a comparison for the RWD configurations, the open differential at the rear axle is taken as a reference. Apart from the deduced results, the most relevant aspect of the project, i.e., the modularity of the subsystems (specifically, the drive axles) was achieved. i
Pilot Naturalistic Riding Study (NRS) with VOI e-scooters to improve traffic safety
(2022) Schmidt, Daniel; Lindelöw, Fredrik; Gunashekara, Gowtham; Pai, Rahul Rajendra; Chalmers tekniska högskola // Institutionen för mekanik och maritima vetenskaper; Sjöblom, Jonas; Bianchi Piccinini, Giulio; Dozza, Marco; Dankert, André
Increase in traffic and emissions resulting from the rise in vehicle population and the first/last mile issue associated with the use of public transport has led to a rise in the micro-mobility market. The e-scooters take a major share of this market and can be attributed to the e-scooter rental service. Introduction of e-scooters into the traffic environment has resulted in new traffic conflicts hence, possible hazards that can lead to new types of near-crashes or crashes. To better understand how e-scooters interact with other road users and identify underlying risk factors that may lead to a crash, naturalistic data collection is a suitable tool for proactive traffic safety work. In fact, the naturalistic data offer the unique opportunity to understand the cause of crashes and the genuine road user behaviour in critical situations. In the past, naturalistic data has been collected mainly from motorized vehicles. In this pilot project an e-scooter has been equipped with a data logger that is connected to cameras and numerous on-board sensors. The sensors provide kinematic information of the e-scooter while the cameras provide a visual representation of the ride environment. Each of the hardware components is placed in a casing developed with additive manufacturing technologies. The data collected is stored locally and then can be transferred to a computer for data analysis. The data collection has been carried out in two stages with the initial one being to identify any vulnerability of the system. The second set of data collection include participant-based riding data. Graphical User Interface (GUI) has been developed to enable easier analysis and visualisation of the data. Several other tools required for data processing along with the GUI have been developed using MATLAB. These tools will enable frame by frame analysis of the ride and aid in the understanding of the cause of every critical event recorded. This thereby enables detection of the causation mechanism behind the safety-critical scenarios. The project has proven that it is fully possible to equip an e-scooter with instrumentation for naturalistic data collection. A GUI has been proven to be a necessary asset when it comes to evaluating the logged data. The results from this pilot study may be the basis for a large naturalistic data collection, that may cast light on safety of e-scooters.
Flow uniformity characterization in catalytic converters under turbulent inlet conditions
(2022) Tylén, Oskar; Larsson, Jacob; Murali, Aravind; Rangaswamy, Sunil; Peyvandi, Ehsan; Larsson, Axel; Chalmers tekniska högskola // Institutionen för mekanik och maritima vetenskaper; Johansson, Håkan; Ström, Henrik; Sjöblom, Jonas; Nagarajan, Pratheeba Chanda
In the sectors utilizing the combustion of fossil fuels, catalytic converters are commonly employed to reduce dangerous gases generated by combustion engines. For greater efficiency, it is critical to understand the exhaust flow homogeneity inside the converter. This work attempts to evaluate the added value of using Detached Eddy Simulation (DES) simulation over Reynolds-Averaged Navier-Stokes (RANS) simulation for analysis of turbulent flow inside catalytic converters. The meshing and simulation of the domain was carried out using ANSYS FLUENT and ANSYS Workbench. Initially a RANS simulation with k-ω SST turbulence model was carried out for a specific case to understand the behavior of the time averaged flow field with modeled turbulence and its effect on uniformity index. The results from the RANS simulation were, together with definitions of turbulent length scales, used to develop a mesh for DES simulation. In this process it was found that in order to resolve a sufficient amount of turbulence upstream of the monolith inlet, the DES simulation required a considerably finer grid than the RANS simulation. The DES simulation with k-ω SST model was used to simulate multiple retention times, attempting to achieve a quasi steady flow with resolved velocity fluctuations. However due to constraints on computational power, simulating until statistical convergence was not possible. The time averaged quantities were extracted from the DES simulation in order to make a fair comparison with RANS results. The uniformity indices of RANS and DES were then compared throughout the monolith of the catalytic converter. A difference of ∼1-1.5% in uniformity index was found from this comparison. Further more it was found that the resolved turbulence in the DES generates fluctuations of ∼3-6% in the uniformity index based on instantaneous quantities. The work concludes that for the exact case simulated, the possibility of increased accuracy when predicting uniformity index with DES instead of RANS does not outweigh the increased computational cost. However for different flow conditions, with larger mean velocity magnitude and less uniform flow, the measured difference between RANS and DES could make a larger difference for prediction of catalytic conversion efficiency. Hence in these cases it is possible that DES simulations are worth their computational cost. Whether this is the case or not would have to be examined through further research before coming to any definitive conclusions.
Handling increased need of maintenance to meet future freight demands: Deterioration and effective maintenance strategies for track system and rail vehicles
(2022) Mattsson, Klara; Lee, Jaseung; Ligmajer, Oskar; Chalmers tekniska högskola // Institutionen för mekanik och maritima vetenskaper; Kabo, Elena; Ekberg, Anders
This report addresses future increased demands of freight on the Swedish railways. To achieve an increase in total freight, different forms of operations can be utilized like increasing the axle load, speed, or frequency which are all scenarios that will be evaluated in the report. The impact caused by those measures will affect both deterioration and the need for efficient maintenance regarding rail vehicles and track systems. Different methods of maintenance, both currently used and newly developed methods are discussed in this report to be able to evaluate how it is possible to become more efficient. The deterioration that occurs during the operation of freight trains is described in the report since an understanding is needed to address the problems and possible solutions. What also plays a vital role in the maintenance plan is to detect faults efficiently. To get an idea about how all of these issues are handled in the industry, interviews have been held with professional staff at four large companies in Sweden. Together with literature studies, this forms the foundation of this report.
Project in railway technology: Damage from electric discharge in axle bearings on trains
(2023) Möslinger, Tobias; Ali, Aboobakkar Nakeeb; Thomson, Oskar; Chalmers tekniska högskola // Institutionen för mekanik och maritima vetenskaper; Chalmers University of Technology / Department of Mechanics and Maritime Sciences; Ekberg, Anders; Ekberg, Anders
A summary of known information on damage in bearings due to electrical currents, with a special focus on railway applications is provided. The process of inspection of a possibly damaged bearing is described. Results are compiled, also providing some suggestions on handling the damage. Finally, all results are connected with each other. Some proposals for solutions of the current problem are given and some points of interest for further research are highlighted.

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