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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.
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 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 joint model of heavy truck, tyres, and operating environment for tyres selection
(2015) Kolár, Petr; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied Mechanics
Improving fuel efficiency is one of the core targets when minimizing the transport cost of a vehicle combination. Hence, it is crucial to optimize the design and selection of all vehicle components, including tyres. Volvo Group Trucks Technology (GTT) and Chalmers University of Technology run a common research project TyreOpt—Fuel consumption reduction by tyre drag optimization. This master thesis is supporting the TyreOpt research project by verification of a computationally efficient model for an evaluation of the operating costs by a newly developed joint model of the vehicle, environment, and tyres, which is based on one of the existing tools within Volvo GTT. Selection of the proper Volvo GTT analysis tool, which serves as a base for the newly developed joint model, was supported by Volvo experts’ experience. Theory of tyre was reviewed in order to support modelling of the transientlinear tyre model and implementation of the rolling resistance model, which was developed within the TyreOpt research project. Representation of the computationally efficient model of the operational cycle and all relevant parameters was transformed to the newly developed model. Simple driver and power-train models were developed in order to evaluate vehicle performance for selected operational environments. Feasability of constraining events implementation to the high-fidelity model is discussed and candidates for new constraints are proposed. Verification of the computationally efficient model concludes performance and limitations of this computationally efficient model, developed within the TyreOpt research project. The tyre model is parameterised in tyre design parameters, such as tyre width, radius and pressure. The computationally efficient and the newly developed model are investigated in qualitative manner in order to list differences in behaviour under various specification parameters of the vehicle, the tyres and the operating environment. Improvements of the computationally efficient model are proposed. Sensitivity analysis aims to investigate energetic behaviour of both models with respect to changing tyre design variables. Results proved considerable influence of different fidelity of the model on transport costs, mainly due to inverse kinematic principle of computationally efficient model, which can not cope with velocity transients and different control strategies. Trends of the energy consumption for different tyre design variables are compared with the rolling resistance theory, which was summarized in the literature review.
A Methodology for Identification of Magic Formula Tire Model Parameters from In-Vehicle Measurements
(2016) Jonson, Axel; Olsson, Eric; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied Mechanics
Accurate tire modeling is of key importance to the development of modern vehicles. Traditional Flat-Trac testing of tires is expensive and time consuming. In order to increase the efficiency of the vehicle development process, a new method for identifying Magic Formula tire model parameters has been investigated. By driving specific maneuvers with a vehicle instrumented with sensors to measure wheel forces and angles, tire model parameters can be estimated by use of a global optimization algorithm. Full vehicle simulations were made in order to identify the test procedures necessary to provide a representative range of data for a tire. A tire model parameter fitting tool was developed and validated with Flat-Trac datasets. Physical testing was carried out to reproduce the simulated driving maneuvers on a car equipped with wheel force transducers, an inertial measurement device, and a high-speed camera system to measure wheel angles and displacements. Results of estimating the pure slip lateral tire model parameters from the in-vehicle measurements shows good correlation to the original tire model. Furthermore, the tire model parameters identified by this method more accurately represent the behavior of the tire on the test vehicle, without the need to modify scaling parameters. This indicates that this newly proposed method can produce accurate tire model parameters that require less tuning of scaling parameters to accurately represent vehicle behavior.
A modular Torque Vectoring System for a 4WD Electric Performance Vehicle
(2018) Schaaf, Aldo; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Chalmers University of Technology / Department of Mechanics and Maritime Sciences
This master’s thesis proposes a modular torque vectoring system for an electric performance vehicle with four independent motor-generator units (MGU). The implemented system is subdivided into three subsystems, consisting of a vehicle motion reference formulation, a chassis force control algorithm and a control allocation algorithm, where the former two belong the outer-loop and the latter belongs to the inner-loop of a cascaded control structure. The vehicle motion reference is based on three derivations of the states governing a single track model and its influence is studied on stability critical maneuvers. Gain scheduled PI control is used for yaw moment control, where the computational performance gain of a dynamic saturation is evaluated. A non-linear constrained optimization problem is solved in the control allocation subsystem, where the influence of weighing factors in the cost function is analyzed. The whole system performance is simulated in a software-in-the-loop (SIL) environment for different maneuvers, varying the control configurations and respective parameters.
A novel approach to a two-stroke dual stage expansion engine concept
(2016) Srinivasa, Kiran Subrahmanya Banavathy; Shankaregowda, Prajwal Kagganagadde; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied Mechanics
The SICO engine concept was proposed by Per-Arne Sigurdsson. The engine comprises of two main cylinders for combustion implementing a two-stroke cycle operation and a single help cylinder running at twice the engine speed. At the end of combustion, the burned gases from the main cylinder are transferred to the help cylinder where the second stage expansion occurs simultaneously along with the main cylinder. The cylinders are considered to be thermally insulated and along with the parallel expansion cylinder aims to derive a higher engine efficiency. The charged induction of air is done by means of a compressor cylinder/radial compressor. The engine concept is evaluated for a power generation application where the engine efficiency at a single operating speed is essential. Consequently, the scavenging and friction models were augmented to better suit the model. Different aspects like the heat insulation, valve timings, cylinder dimensions, cylinder phasing, compression ratio of the main and help cylinders, charged induction using a radial compressor and compression cylinder were evaluated and optimized for the necessary application. Additionally, the SICO concept was compared with existing concepts that implement similar strategies such as the five-stroke engine concept that aims in utilizing exhaust energy for a four stroke cycle operation. The final SICO engine model is a 3.14L engine, producing a peak power of 81.5kW at 1500rpm. At this operating point the engine runs at an efficiency of 41.3%. Simulations show that the implementation of the help cylinder contributes to around a 7% brake efficiency increase and the effect of heat insulation is not of large significance for the break efficiency. Based on the preliminary evaluation of the concept by means of simulations, the engine efficiency of the concept is comparable to existing modern diesel engines and thus the SICO concept’s operation and implementation can be further pursued.
A novel approach to the design of rear airfoil pylons on high performance car
(2020) Hellsten, Oskar; Pettersson, Oskar; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Löfdahl, Lennart; Urquhart, Magnus; Riccio, Ugo; Sepe, Vincenzo
The continuous improvement of every aspect of the car is what makes Lamborghini one of the leading super sports car manufacturers of the world. One of the areas that is to be investigated is the pylon, which attaches the rear wing to the car body. There are two main aerodynamic components of the pylon that could help to increase the performance of the car; the reduction of drag on the pylon and the ability to create a lateral force that could help while the car is cornering. This thesis aims to make an initial aerodynamic investigation of the shape of the airfoil that makes up the pylon to see what benefits that could be gained. At the start of the thesis, it was concluded that the pylon should be symmetric to be able to handle oncoming wind from different directions and that the investigated wind attack angle should span from 0 deg to 15 deg with a focus on the 0 deg to 5 deg region. A base airfoil shape was developed using an optimization method and CFD to test many different shapes efficiently and find the best one out of those. With the base shape set, different geometrical features were added to the base to see if that could improve the airfoil performance. One of the concepts had slots that went through the base airfoil, another one was a double airfoil that consists of two smaller sections. The same optimization method was used for the slots respectively the shape of the two airfoil sections. The result of the thesis shows potential for the three investigated airfoil designs, though it has also been concluded that a closed single airfoil is a good design to begin with. In the focus span of 0 deg to 5 deg some open configurations were tested. When generating a lateral force the closed airfoil was the best one.
A Refined Vehicle Dynamic Model for Driving Simulators
(2013) Obialero, Emanuele; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied Mechanics
Driving simulators play an important role in the automotive field, especially in the research about human factors and in the development of driving assistance systems. For this reason, driving experience should be as close as possible to reality. The mathematical model, describing vehicle dynamics, plays a fundamental part in providing this “reality feel”, since it is used by the simulator to compute vehicle motion. This Master´s thesis has the aim of refining an existing vehicle dynamic model for a driving simulator, developed in Modelica ® programming language, in order to make the driving experience closer to reality. In particular, this work is focused into two areas: the first concerns the development of vertical dynamics, in order to extend the degrees of freedom of the vehicle model from ten to fourteen. The second is related to the development of a more accurate steering system model, for both improving the steering feel and the steering dynamics. The vehicle model has been validated through different steps. First of all, its response to different manoeuvres has been compared with the one provided by a real car. This comparison has been made by confronting the model data with the real vehicle ones, coming from test track measurements. Then the model has been tested in the simulator by different drivers, who had to evaluate its behaviour
A report on Objective Development of Damper Specification
(2018) Adisesh, Ashrith; Agarwal, Rohit; Chalmers tekniska högskola / Extern; Chalmers University of Technology / External
Damping of the sprung and un-sprung masses of a vehicle through a suspension damper is crucial to obtain good comfort and handling characteristics. Damper tuning, which is predominantly based on subjective feedback and experience from engineers takes up a large amount of time and resources. Preliminary knowledge of the influence of dampers in different operating regions can provide a good starting point in the damper tuning process. This research thesis aims to develop objective metrics related to the response of simplified vehicle models and could provide information regarding the modifications in the damper specifications to achieve the desired response. Quarter-car models with linear, asymmetric and non-linear damper curves are simulated in the Matlab environment for step and swept sine inputs. The responses are further investigated to identify metrics of interest, by which the behaviour of the vehicle can be understood. For linear damper models, the poles of the system are analyzed and pole placement method is used to understand the behaviour of sprung and un-sprung masses when suspension parameters are varied. For asymmetric dampers, metrics which could help decide the required degree of asymmetricity between compression and rebound damping are presented. Finally, for non-linear dampers, the effect of damping force in different regions of operation is studied. A sensitivity analysis (Design of Experiments) is performed to identify the most influential variables corresponding to these metrics. With these results, the response of the model is studied to obtain the metrics of interest which can be attributed to the behaviour of the vehicle. Comparisons are presented to visualize the effects of different damper specifications by which an initial prediction could be made for the damper specifications. This outcome can potentially enhance the preliminary knowledge of the effects of damper tuning and thereby providing a better starting point for the damper development process.
A study of sitting posture and belt position in a travelling car: How do passengers sit in a travelling car?
(2019) Hansson, Annika; Lysén, Emma Nilsson; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Chalmers University of Technology / Department of Mechanics and Maritime Sciences
To improve the future design of restraint systems, it is important to know how passengers’ sitting postures change over time and how the passengers interact with the restraint systems. This master thesis at Chalmers University of Technology, focuses on pelvis rotation, slouching and belt position while travelling in a front seat of a car on regular roads. The information was collected during normal drive in the passenger seat of a regular car, while the volunteers perform activities such as; resting, e-socializing and conversing. Twenty volunteers, ten male and ten female, participated in the study. Volunteers were seated in the front row passenger seat, because this sitting posture is probably similar to how passengers will sit in future autonomous cars. The inertial motion measurement system MTw Awinda from Xsens, in total eight sensors, were used in the study. They were placed on the volunteer’s sacrum, sternum, C7, T3, L5, forehead and car. The data from the sacrum sensor, that corresponds with pelvis rotation are mainly presented and discussed in this report. In addition, a surface pressure sensing array (Tekscan mat) was placed on the car seat cushion. The data from selected volunteers was analyzed with the TEMA to determine degree of slouching. Photo analysis was carried out to assess belt positions before and after the test. Additionally, the rotation of pelvis and sternum when changing seat back angle in intervals of 5° between 23° and 48° were also investigated. The results show that pelvis rearward rotation increases by average 10° when riding in the car for about 45 minutes. Comparing the activities, the volunteers had similar average pelvis rotation. Slouching could be measured only for three volunteers out of 20 and it seemed to increase on average 3 cm during the ride. The belt position of initial and final sitting posture indicates that the diagonal belt moved less than the lap belt. To investigate the dynamic belt position, future video analysis is needed. Increasing seat back angle appeared to have a correlation with increasing sacrum and sternum pitch.
A study on engine efficiency and performance improvements through hybrid turbocharging assisting
(2014) Dobre, Alin-Gabriel; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied Mechanics
Engine efficiency and transient performance carry a major importance in the automotive industry as they incorporate the two major requirements: fuel consumption and drivability. A major inconvenience for turbochargers constitutes the low response in the low speed region of the engine creating the so called “turbo lag” affecting drivability. Also a large portion of the fuel energy is lost through exhaust gas in a SI engine affecting engine efficiency, fuel consumption implicitly. A hybrid turbocharging assist system is a promising technology for improving both transient response and engine efficiency. This paper studies the possibility of implementing a hybrid turbocharging assisting system on a VEP 2.0 L SI engine. Two modules are studied: electrically assistance for the turbocharger which regards the transient performance and exhaust gas energy recovery which regards the engine efficiency. An electric machine is connected to turbocharger’s shaft through a planetary gear, enabling two operating modes: motor in electrical assistance and generator in energy recovery mode. Transient simulations are performed for the electrical assistance module having three configurations: a standard and a bigger compressor (HP Compressor) and a bigger turbine (HP Turbine). Steady state simulations are performed for the exhaust gas energy recovery module at full load and part load conditions having two turbine configurations: standard turbine and bigger turbine (HP turbine). As a last step of the thesis, a take-off simulation where both modules work together is done for the Volvo XC90. All the modelling and simulations are carried within the framework of GT-Suite. Results from the electrically assistance module show that transient performance is improved by 30% at 1400 rpm, 20 % at 1600 rpm and 16% at 1800 rpm by using the standard compressor configuration. When using the exhaust gas energy recovery system the engine efficiency is significantly improved by using a bigger turbine configuration.
A truck dynamics model for driving simulators
(2016) Sedran, Stefano; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied Mechanics
Driving simulators provide important opportunities to study interaction between the drivers and vehicle in a wide variety of situations and scenarios. A vehicle dynamics model in the simulator calculates the motion of the simulated vehicle based on the inputs of the driver, in real time. The Swedish National Road and Transport Research Institute (VTI) has a need for an open and in-house developed truck model for its driving simulators. Currently, the truck dynamics models used so far were developed, operated and owned by an OEM. This has obvious restrictions for its use and publicity. This thesis presents the development of a truck dynamics model to be used in the VTI’s driving simulators, keeping the OEM model as a reference. The aim of this project is the development of an open model, with a high level of readability and flexibility for future understanding, modification and use. The model is written in the programming language Modelica in the software Dymola. The chosen strategy is using basic code, even though a library structure is designed. The thesis objective is to investigate the required level of detail for the modelling of trucks for driving simulators. An A-double combination is selected, focusing on the context of normal driving at almost constant speed on dry road. The model complexity is gradually increased, focusing, in each step, on what is believed to be the main contributing phenomena to the trajectory of the vehicle. The model validation consists of two parts. At first, desktop simulations aim at comparing each step of the developed model with the OEM model, using an ISO lane change maneuver. The importance of roll steer, torsional flexibility of the tractor chassis frame, axle dynamics, friction in the fifth wheel, nonlinearity of tyres is investigated. Afterwards, a further comparison is carried out by performing experiments in the VTI’s driving simulator with a few test drivers.
Accelerated road load simulation - Road load data for fatigue analysis in concept phase
(2016) Liu, Jianqiao; Ramnath, Vijay; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied Mechanics
Active aerodynamics of an autonomous car
(2023) Malali Obaiah, Samarth; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Chalmers University of Technology / Department of Mechanics and Maritime Sciences; Benderius, Ola; Benderius, Ola
Autonomous cars are one of the nascent technologies being focused on by many of the major automobile manufacturing companies. These new smarter cars allow for new possibilities in terms of integrated systems such as powertrain and safety. In the same way, manufacturers are trying to integrate vehicle aerodynamics into this smart ecosystem, making the car even more efficient and with improved performance. The first step towards smart aerodynamics can already be seen in present vehicles with features like active grille shutters, an extending tail section, and, in higher-end vehicles, the change in the angle of attack for the rear spoiler. The advantage of introducing smart aerodynamics into an autonomous Formula student car is very beneficial as the system already knows the path that the car is going to take. The basic function of the system is to feed the upcoming driving trajectory into the smart aerodynamics system, which in turn adjust aerodynamic character of the vehicle for example with help of wing profiles. As a result, the car will be ready to traverse the track in a more efficient manner. The objective of this thesis is to develop a control system for the aerodynamics of the car to alter its track characteristics to best suit the needs of track topology and for other performance enhancements. Furthermore, the methods that are implemented to the car will is backed up with numerical simulation using fluid simulation software and validated through the results obtained. Various techniques have been employed to enhance the aerodynamic characteristics with combinations of rear wing and front wing angle of attack manipulation. As a result, the improvements in terms of drag and lift are achieved.
Active Muscle Control in Human Body Model Simulations - Implementation of a feedback control algorithm with standard keywords in LS-DYNA
(2013) Andersson, Samuel; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied Mechanics
Simulation of occupant responses in scenarios involving low load levels requires the addition of active muscles to add posture control and muscular response to the human body. A model for active muscle control has previously been implemented in the Chalmers Active Human Body Model using subroutines written in the FORTRAN programming language. In order to decrease conflicts with future software updates and increase the usability of the model, the possibility to build the model using standard LS-DYNA keywords has been investigated in this thesis. The keywords need to perform signal retrieval, addition of a time delay, implementation of feedback control algorithms and solution of differential Equations for activation dynamics. In addition to the approach already existing as a subroutine to LS-DYNA, alternative ways to implement the areas of functionality has been reviewed in literature and scientific papers. A proposed solution using standard keywords called the Load Curve Method has been developed. For basic mathematical operations *DEFINE_CURVE_ FUNCTION keyword and its built in functions are used. To solve differential Equations a mechanical representation of the Equations together with the ability in LS-DYNA to simulate kinetic and kinematic properties of single and multiple nodes is proposed. All areas of functionality except a true time delay have been implemented using standard LS-DYNA keywords. Since it is not possible to retrieve data from earlier time steps a first order low pass filter has been implemented to model the effect of a time delay. Even though it does not exactly replicate the input signal, the filter provides a phase shift and can be used to model closed loop instability. The standard keyword solution has been implemented with the Chalmers Active Human Body Model (Chalmers AHBM) as well as on an elbow joint model using LS-DYNA V971, R5.1.1 or 6.1.0 standard binary. It has been validated against the implementation that uses a sub-routine to LS-DYNA; the elbow joint model in a situation similar to the ARMANDA haptic equipment (de Vlugt et al., 2003) and Chalmers AHBM in a seated position under influence of gravity and 1G forward acceleration. In simulations with the Chalmers Active Human Body Model a decrease in computational time of about 14% has been seen for the standard keyword solution compared to the FORTRAN sub-routine.
Advanced Control of Future Electric Propulsion Systems for Passenger Vehicles
(2018) Subbiah, Vignesh Arumugam; Nandivada, Yashasvi; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Chalmers University of Technology / Department of Mechanics and Maritime Sciences
Electric Vehicles (EVs) have been around since the 19th century,in fact the EVs were quite popular in that time period and a good number of them were sold during the 1900s but due to the advancement of gasoline engines and the invention of the electric starters for gasoline engines, vehicles powered with internal combustion engines began to dominate the market, thereby the trend for EVs declined until the early 2000s. From the early 2000s on-wards the market share of EVs has begun to rise due to the price rise of gasoline, enactment of stringent environmental policies and advent of cost effective manufacturing capabilities for EVs. The increased demand and environmental benefits of EVs are pushing the automotive companies to invest in the research and development for the Electric Vehicles to initiate the mitigation of global warming. As the technology is moving towards EVs there is also an increased need to set goals to mitigate the road accidents and improve the vehicle and traffic safety. As a matter of fact it could be stated that Electric propulsion systems have advantages over the conventional propulsion systems since the former has a high-power density, short response time and a better controllability. However, with the ongoing trends, for future vehicles with more sophisticated safety functions, the demand for controllability will be higher. Also new driving cycles used for energy consumption, correlating better with normal driving, will put higher demands on drive-train control. Thus the main objective of this thesis is to study and implement potential measures to improve controllability of electric drivetrains, in the view of ongoing development trends. As part of addressing the objective, it is envisioned to analyse the strengths and weaknesses in the present and future systems & the possibility of developing principles, methods and solutions to improve the control accuracy, response time, predictability and reliability is investigated. The first phase of the thesis majorly involved developing a state of the art drive-train based on the electric propulsion technology available in the current market. This model, developed in SIMULINK, is then validated against the real world data. This part of the thesis also involves establishing use cases and sub-system performance targets for a comparative study at a later point of the thesis. The second phase of the thesis involves establishing a relation between the control parameters and sub system performance targets, which would then be the principles of improvement. Subsequently, based on the ndings from the technology trends, a Future Drive-train is also proposed during this phase. The third phase involves developing the Future Drive-train and implementing the proposed principles, via a design of experiments approach, on the Future Drive-train to obtain an Optimised Future Drive-train. On carrying out the process of optimisation on the Future drive-train an Optimised Future drive-train consisting of a Switched Reluctance Motor (SRM) of 93 kW is obtained. The power of the developed SRM is within 7% of the state of the art motor. In terms of acceleration performance (rise time from 0 to 90% of reference velocity) the developed Optimal Future drive-train lags with respect the state of the art drive-train by 2%. This speed dependent characteristic is observed for a 0-35 kmph Step Reference Input. In terms of performance on drive cycles the Optimal Future drive-train, at worst, has a 3% greater deviation from reference velocity when compared to the state of the art drive-train due to its falling power characteristics at higher speeds. In terms of acceleration performance on a transient friction surface, the Optimal Future drive-train performs better on all counts due to the reduction of reflected load inertia stemming from a higher gear ratio.The developed principles of improvement are inline with the expectations to tackle the controllability issue of the future drive-trains.
Aerodynamic Optimization of Ground Vehicles with the Use of Fluent’s Adjoint Solver
(2013) Zaya, Johan; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied Mechanics
Like all other areas of the automotive development, environmental issues and fuel efficiency is one of the main driving forces for aerodynamic engineers where the aerodynamic drag force is the dominating resistance force at higher velocities. By improving the shape of a vehicle with respect to aerodynamic performance, the drag force can be reduced hence the fuel consumption can be reduced. The use of Computational Fluid Dynamics is a widely used methodology to carry out simulations that describes the flow in and around a vehicle. With these simulations, aerodynamic engineers can gather information about the aerodynamic performance Of the vehicle and make changes that can improve the performance. However, due to the many variables involved, this can become very computer demanding process and require a high number of design optimization cycles to finally reach valuable stage. Recently, a new procedure used for optimization purposes, named the Adjoint Solver, has been the focus of researchers and engineers. The Fluent Adjoint solver compute derivatives of chosen engineering observation, such as drag, with respect to all inputs and provides a more direct guidance for optimal modifications to improve performance. The Adjoint Solver accomplishes to calculate the derivative data by running only one single computation, very similar to basic CFD computations, and by that providing valuable engineering insight that can both improve and reduce the number for design optimization cycles. The main goal of this master thesis is to state if the Adjoint Solver is ready to be incorporated into Volvo Cars Aerodynamic development process. This project has been carried out as an Master Thesis together with Volvo Cars and Chalmers University of Technology, in a close relationship with Ansys which are the developers of Fluent. Fluent's Adjoint Solver has been tested on its computation abilities, robustness, computer requirements and functionality. The tests are done on four different vehicle models provided by Volvo Cars and simulations are computed in wide variation of different case setups. Based on the results from the simualtions, the conclusion is that Fluent Adjoint Solver is at the moment not at a stage where it is ready to be incorporated as a part of the development process. It is proven that the one can gain valuable engineering insight that surely can improve the development process, however, for external aerodynamics, the Adjoint Solver is not yet ready. Ansys will now continue to develop and improve the Adjoint Solver, with the issues discovered in this project in mind.
Aerodynamic optimization of pylons to improve rear wing performance using passive and active systems
(2021) Upadhyaya, Avaneesh; Nagaraja Rao, Kaushik; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Sebben, Simone; Urquhart, Magnus; Riccio, Ugo; Sepe, Vincenzo
In collaboration with Automobili Lamborghini S.p.A, an aerodynamic investigation was carried out on a dual pylon rear wing assembly to improve cornering stability of a car at high speeds. The pylon's primary purpose is to provide structural support to the wing. However, this project aimed at improving the performance of Aventador SV's rear wing using aerodynamically optimized pylons that not only boosted its downforce generating capabilities, but also generated large side forces at higher yaw angles. The project goals were fulfilled in two phases. The first phase involved development of pylon airfoils that would keep the flow attached within a range of ±15 yaw angles, without augmenting the drag when compared to NACA0010. A surrogate based model was used to generate these airfoils. 2D simulations were performed on the airfoils along with passive and active systems to achieve attached flow around the pylons, thus, generating more downforce by improving suction under the wing. Single slot approach was used to create passive slots that improved flow on one side of the design at the expense of the other. The active flow control was implemented in two ways, blowing and suction. Throughout this study, active blowing has held precedence due to energy constraints. Three airfoils with better performance than NACA0010 at higher yaw angles were selected for next phase. In the second phase, airfoils from 2D study were used to carry out 3D simulations using RANS solver on several wing and pylon combinations, without a car body, in a quest to find the optimum performing pylon. A study was conducted to analyse the effect of different pylon positions, sizes, and profiles along with passive and active systems on the air flow around the wing. With the profiles generated in 2D study, an improvement in the performance of the wing was achieved at higher yaw angles. Wherever the flow detached over the pylon, passive and active systems showed signs of improvement.

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