Studentarbeten // Student Theses

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A combined numerical and statistical approach to crack propagation modeling and prediction of crack propagation rates
(2012) Rembeck, Martin; Sjöblom, Anders; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied Mechanics
A comparative study on the modeling of matrix cracking in fiber-reinforced polymer laminates under transverse compression - XFEM versus a smeared crack approach
(2016) Pourbahaaddini, Ershad; Simonsson, Philip; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied Mechanics
As the number of applications for fiber-reinforced polymers (FRP) is growing, the importance of understanding the failure behavior of this material is rising. This is merely conceivable by developing precise computational material models, which saves time, material, and energy. In general, the polymer matrix is the constitute with the lowest strength against failure in a FRP; hence the matrix requires additional attention especially under transverse compression where it is considered as the principal load carrying component of the FRP. In the present work, a comparative study on the modeling of matrix cracking in FRP laminates under transverse compression is carried out. To do so, an eXtended Finite Element Method (XFEM) approach is developed for discrete crack modeling, and the conventionally used smeared crack approach is applied via an existing Abaqus/Explicit implementation for continuum crack modeling. The comparison of the results illustrates that despite different kinematics behind the models, they both successfully predict a near identical material degradation and energy dissipation in the material response, but with differing predictions when considering frictional tractions and the predicted maximum stress levels. XFEM is established to be mesh-objective and the smeared crack method predicts the material response optimally when the mesh discretization is one element per ply with reduced integration excluding non-linear geometry effects. Moreover, the wedge effect described by geometrical deformation is distinctly represented as cracks are studied explicitly in XFEM, which provides the possibility of further study for inter-laminar effects such as delamination, crack propagation and crack migration. Key words: XFEM, smeared crack model, progressive damage analysis, transverse compression, friction, fiber-reinforced polymer
A comparison of finite element formulations for analysis of the converting process of packaging materials
(2015) Lindberg, Susanna; Sandvik, Patrik; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied Mechanics
A coupled multibody and discrete element approach for roller compaction dynamics
(2020) Göransson Axås, Joar; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Lidberg, Mathias; Quist, Johannes
This thesis presents a novel compaction simulation method, where a multibody dynamics model of a vibratory roller is coupled to the discrete element method (DEM) for unbound granular materials. A multibody dynamics solver is developed, and an analysis of the roller mechanical system is performed to construct a rigid body model of the machine. Further, a method for bed initialisation is developed, and a uniaxial strain test is used to calibrate the multisphere DEM material parameters. Then, compaction simulation is made possible by implementation of a coupling server, that runs the DEM and multibody solvers simultaneously at different timesteps. Such simulations are compared to full-scale experiments and compaction theory. The machine response to beds of varying stiffness agrees with experience from compaction practice, and characteristic behaviour, such as double jumps, is observed. The stresses in the bed agree with experiments if the particle Young's modulus is kept low. However, the roller penetration of the bed is higher than in experiments due to insufficient shear resistance in the DEM model. At the same time, no increase in bulk density is achieved. Further analysis shows that the lack of shear resistance is likely related to the multisphere model of the particle geometry, and the lack of compaction may be due to a particle size distribution that is too narrow. On the other hand, such simplifications are necessary, because large computational costs impose limits on the particle size distribution, particle discretisation, and domain size. The function of the solver coupling and machine model is verified, but in order to enhance agreement with full-scale experiments, improvements are needed in terms of both the particle modelling and computational performance capacity.
A DEM Study to investigate the influence of ice particle adhesion on the angle of repose
(2020) Sai Tanneru, Yeswanth; Chalmers tekniska högskola / Institutionen för kemi och kemiteknik; Rasmuson, Anders; Eidevåg, Tobias; Kallin, David
A method for characterization of elastic in-plane material properties of continuous fiber reinforced polymer tubes
(2020) Bredenberg, Tobias; Borenius, John; Chalmers tekniska högskola / Institutionen för industri- och materialvetenskap; Blinzler, Brina; Fagerström, Martin
As fiber reinforced polymers are becoming commonplace in more and more industries every year, the need for accurate engineering tools connected to these materials arises. In several industries tubular composites are a staple, however the manufacturing methods used for tubular laminated composites do not transfer well into making test coupons for traditional material testing. This creates the need for a method where material properties can be derived from testing of tubular specimen. This thesis therefore aims to create a method for characterizing the elastic in-plane material properties of a tubular fiber reinforced composite. The method uses physical tests of two specific lay ups in order to isolate and derive the in-plane material properties one by one. The results of this thesis shows that the material properties derived from the test data is within close proximity of other material systems using the same fibers, which suggests that a promising first step has been taken. However, there is a need for validation in order to finalize the accuracy of the model. Furthermore a number of practical suggestions are made to reduce error sources for future testing.
A natural language processing approach for identifying driving styles in curves
(2016) McNabb, Eric; Kalander, Marcus; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied Mechanics
A machine able to autonomously recognise driving styles has numerous applications, of which the most straightforward is to recognise risky behaviour. Such knowledge can be used to teach new drivers with the goal of reducing accidents in the future and increasing traffic safety for all road users. Furthermore, insurance companies can incentivise safe driving with lower premiums, which in turn can motivate a more careful driving style. Another application is within the field of autonomous vehicles where learning about driving styles is imperative for autonomous vehicles to be able to interact with other drivers in traffic. The first step towards identifying different driving styles is being able to recognise and distinguish between them. The aim of this thesis is to identify the indicators of aggressive driving in curves from a large amount of naturalistic driving data. The first step was finding curve sections to analyse within trips and the second step was reducing the data to become more manageable. Symbolic representations were used for the second preprocessing step, which in turn allowed the use of Natural Language Processing techniques for the analysis. We categorise drivers into different groups depending on their perceived tendency towards aggressive driving styles. This categorisation is used to compare the drivers and their driving style with each other. The tendencies used were Speeding, Braking, Jerky curve handling and Rough curve handling. Some general trends among the analysed drivers are also identified. It is possible to reuse the categorisation to include more drivers in the future or to use what we have learned about the features and drivers for further research.
A new generation humanoid robot platform
(2011) Magnus, Wahlstrand; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied Mechanics
There are many tasks that humans for different reasons are unwilling or unfit to do. Examples are, for instance, dangerous tasks such as handling toxic waste or monotonous tasks, like working in assembly lines. The hope is that robots one day can do tasks like these for us. Even though a lot of progress has been made in robotics in the last few decades, it is clear that a lot of work and research remains for this goal to be fulfilled. This master thesis describes a process of upgrading Kondo, a small humanoid robot, from a basic robot with no sensory capabilities to a more advanced robotic platform. The hope is that the improved platform can be used to facilitate further research in several fields of robotics such as human-robot interaction, adaptive control and evolutionary robotics. In order to perform this upgrade, the servo controller of existing platform was replaced by a new programmable servo controller. Furthermore, a sensor module with an accelerometer and distance sensors was designed and added to the platform, giving Kondo sensory capabilities. To complete the system, a two part software interface was created. This included a graphical user interface to directly control the robot and create motion sequences and a Python class interface for prototyping and more advanced programs. The resulting platform was tested in order to ensure that it fulfilled the objectives stipulated in the project. The tests included hardware testing, i.e. testing the actual motion of the robot and the communication between to and from the electronic modules. The platform’s configurability was also tested by implementing three common robotic features, including automated fall recovery and wall avoidance. The results of these tests indicate that the basic functionality of the new platform, such as walking and standing, is rather robust. The speed of the developed gait however, can be improved. The platform is relatively easy to extend and modify therefore can be used in education or in robotic research. A weakness of the current platform is the number of connections needed to power and communicate with the electronic boards. Decreasing this number is something that could be worked on in future projects in order to increase the robot’s autonomy.
A Stochastic Approach for Parameter Relevance Estimation in Vehicle Interior Simulations of Frontal Impacts
(2019) Hübinette, William; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Chalmers University of Technology / Department of Mechanics and Maritime Sciences
The evaluation of frontal crash performance of vehicles is mainly performed using standardized barrier tests and the safety system is designed against these. Innovation has led to improved technologies such as more accurate simulation models enabling us to improve how the safety system can work in a variety of scenarios. Thus, virtual crash tests using finite elements (FE) have almost replaced the physical tests among vehicle manufactures. The combination of faster computers and more accurate models has led to the possibility to simulate the variability in the system performance using stochastic simulations. If stochastic simulations are performed, which allows for testing of different design options and variability, information can be gathered as how to create a balanced and optimized safety system where all components work together at their best. In this thesis, simulations and physical tests of a currently used car platform are studied in full-frontal crash tests in order to determine which components need to be represented in the stochastic simulations. Based on the discovered behavior in theses tests, a list of relevant input and output parameters for the stochastic simulation is defined. Input parameters are sorted into three different types; production, design and real life, and both risk injury criteria and kinematics of a crash test dummy are used as output. Furthermore, a simplified and parameterized FE model of a vehicle interior for frontal impacts is developed and validated. Passenger airbag and knee airbag are simplified as unfolded airbags and a curve fitting function that measured the root mean square error between the reference airbag pressure and the simplified airbags is used to reproduce the behavior of the studied airbags. Floor and windscreen are modeled as rigid surfaces and the seat is simplified by removing parts of the backrest and prestensioned bolt connections are changed to rigid. The validation show that the simplified model deviates slightly compared to the studied tests, but it is approximately 14 times faster compared to the reference. Further, stochastic simulations are performed with geometrical, impact and airbag parameters varied. The statistical information such as mean, standard deviation and correlation between parameters is evaluated. The results produced from the simplified model follows the existing trends in the reference model making it possible to draw trend-based conclusions from the stochastic simulations. The stochastic simulations indicates that a crash pulse with low Vehicle Pulse Index is to strive for when developing a car to get low values of the risk indicators in full frontal impact. In general, the linear correlation matrix is a valuable tool to see the influence a variation of the input parameters have on the risk injury criteria and dummy kinematics. Lastly, different ways to present the data, i.e. scatter plots and history curves based on time data are visualized. In summary, the methodology developed offers an approach for using stochastic vehicle interior simulations in frontal impact, which can lead to a deeper understanding of the safety system and the opportunity to optimize and make it more robust.
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
Accurate Prediction of the Flow Around a Truck and the Asymmetry of a Notchback Ahmed Body
(2016) Mattsson, Joacim; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied Mechanics
Partially Averaged Navier Stokes is a turbulence model purported to seamlessly shift between RANS and LES solution to achieve an accurate solution in a cost effective manner. The simulations were carried out in the commercial software AVL FIRE. The purpose of this thesis was to show that PANS can be used to achieve results in good comparison to the references. The flow around a generic truck, consisting of to boxes connected by two cylinders, was simulated at a Reynolds number of 510 000 based on the height of the trailer of the truck, using Partially Averaged Navier Stokes. The simulated flow turned steady after some simulated physical time. This was not expected to happen for such a blunt body, neither did it happen in the reference Large Eddy Simulation of the same body. Different numerical schemes, sizes of meshes, boundary conditions, and even workstations were used but all configuration gave these perplexing results. Also the flow around a fully detailed half scale truck from VOLVO AB in a wind tunnel were meant to be simulated at a Reynolds number of 4:5 106. However due to some computational difficulties no meaningful results could be found. These difficulties included problems saving data files, which is theorized to be due to memory running out on the computational cluster. Lastly a notchback Ahmed Body was simulated to try to reproduce the asymmetry of the wake that earlier has been seen in experiments. The flow was simulated at a Reynolds number of 1:9 106 based on the length of the body. No asymmetry of the flow was seen in the current work which contradicts the reference.
Active Flow Control for Reduction of Aerodynamic Drag on a Simplified Truck Model with side mirror
(2017) Tatchanamoorthy, Vijaikrishna; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied Mechanics
These days consumption of fuel plays the major role in automotive industry. Major plans are made to reduce fuel consumption and to cut the cost and emissions of the vehicle there should be reduction in the drag force. Recently based on research, use of Active Flow Control (AFC) has reduced the drag force. In this thesis AFC is introduced in the form of synthetic jet actuator at the A-pillar of the simplified truck along with the side mirrors and the amount of reduction in drag will be discussed in detail. In this thesis majorly 2 simulations are carried out one with the normal reference case without actuation of AFC and compared with the one with the case with actuation of AFC at the frequency, amplitude values are based on the research paper [1]. The unsteady turbulent simulations are carried out using the Partially-Averaged Navier-Stokes (PANS) turbulence model.
Actuator turbine models and trailing edge flow: implementation in an in-house code
(2015) Matsfelt, Johanna; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied Mechanics
To be able to simulate a trailing edge flow in CALC some modifications needs to be done in the code. The main reason for this is that CALC only can handle a computational domain consisting of one block. Modifications are made both in the multigrid solver that solves the pressure field and the flow solver. Some of the modifications that are made in the multigrid solver can be recognized from the implementations in the flow solver but the multigrid solver uses 1D arrays compared to 3D arrays in the flow solver. This implementation allows CALC to run a flat plate simulation and this was one of the validating cases run. One laminar flow and one turbulent flow using the Reynolds Averaged Navier Stokes (RANS) turbulent model and the results showed good agreement. One more validating RANS case was used here representing an airfoil instead of a flat plate. This simulation showed that the flow fulfilled the no slip condition at the surface of the airfoil which was the focus of the validation. The second part of this master thesis consisted of implementing two Actuator turbine models named Actuator disk model (ADM) and Actuator line model (ALM). The implementation of ADM which is the less accurate model of the two was validated by an axisymmetric flow using the 5-MW National Renewable Energy Laboratory (NREL) wind turbine. The ALM model was validated using the same turbine but with a 3D flow due to its 3D behaviour. The results were acceptable when comparing to the NREL data and results in [1]. The results from the ADM simulation obtained by restricting the "i variable in the Gaussian function showed that more consistent predictions of the rotor thrust and power between different meshes could be obtained.
Aero-validation of CFD Methods for Turbine rear structures using experimental data
(2019) Nilsson, Mattias; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Chalmers University of Technology / Department of Mechanics and Maritime Sciences
Secondary flow effects in an axial turbine are highly complex and have a significant impact on the performance of an aircraft engine. Understanding the flow in the engine is essential to improve the design and increase engine efficiency. In order to increase understanding of the aerodynamics in a Turbine Rear Structure (TRS) tests are conducted at experimental facilities. The resulting test data provides valuable input in improving the prediction tools used in the design of the TRS. The aim of this study is to use computational fluid dynamics (CFD) simulations to increase the understanding of differences between prediction method results and experimental data. The CFD predictions are compared to test data from a turbine test facility capable of reproducing realistic engine conditions. The same operating conditions as in the test facility are used on the same geometry to produce the numerical results. Comparisons of blade loading, swirl angle and total pressure profiles are made for design and off-design conditions using different turbulence models. For some cases, a heat transfer investigation is also conducted. The results show how steady state simulations can be used to reproduce a close approximation of the experimental measurements for both design and off-design conditions.
Aeroacoustic sound sources around the wheels of a passenger car - A Computational Fluid Dynamics study using steady state models to evaluate main sources of flow noise
(2017) Ringwall, Emil; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied Mechanics
When speaking about wheel noise most people think about the contact noise from wheel and road interaction. Previous experimental studies in wind tunnels show there is an apparent aerodynamic noise source near the front wheels. New legislative demands force car manufacturers to reduce the noise emitted and the wheel noise cannot be ignored anymore. The study has used broadband noise source models incorporated into the commercial software Star CCM+ to locate and analyze sources generated by dipoles and quadrupoles within the ow around the wheels of a DrivAer car model. The methods used are the Curle acoustic analogy, to approximate the dipole sources at the surface, Proudman acoustic analogy, to approximate the quadrupoles generated in the turbulent ow and the Lilley method, approximates the turbulent shear ow sources. Four cases have been studied comparing stationary and rotating wheels as well as open and closed rims. All cases studied show signi cant sources of noise at the front wheels and the simulations have shown a clear dependence of both rim geometry and rotation of the wheels. It is shown that wheel rotation gives a signi cant increase in aeroacoustic noise in both dipole and quadrupole sources while geometry dependence only could be noted in the quadrupole sources.
Aeroacoustic study on the roofbar of a truck using CFD
(2013) Johansson, Erik; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied Mechanics
Aeroacoustic CFD-simulations around a roofbar on a Volvo FH-series truck were performed with the purpose to find a method of how to perform an aeroacoustic simulation. The simulations included incompressible approaches using Detached Eddy Simulation (DES) with the SST k-! turbulence-model and Spalart-Allmaras turbulence-model as RANS-models, and Large Eddy Simulation (LES) but also a compressible approach using SST-DES. Turbulence models and compressibility effects were the main scopes of the project. The domain that was used proved to be unsuitable for both the compressible and the incompressible approach. The compressible case suffered from severe unphysical phenomena and the incompressible approach which removed the phenomena seemed to be too affected by stiff boundary conditions. Widening the domain could have mitigated the effects. The incompressible DES-cases proved to predict the ow separation point on the roofbar completely different compared to the incompressible LES. Also, turbulent scales could not be entirely developed downstream of the roofbar for the incompressible DES-cases which had a large impact on the acoustic surface sources for these cases. Presumably, the LES separation point could be explained by high turbulent viscosity. The behavior of the separation point cannot be unambiguously explained since measurements have not been done. It is therefore not clear which one of DES or LES that gave the best results, however, future recommendations are based on LES as the reference case. Among the realistic results only broadbanded noise sources were found. There were no major differences between SA-DES and SST-DES, however SSTDES showed somewhat closer results to LES and is therefore recommended to be used although it took relatively longer time to perform.
Aerodynamic Databank Modeling for Development of a Short-Haul Electric Airliner
(2022) Johansson, Anna; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Davidson, Lars; Gama de Almeida, André
To the support development of a new airplane, an aerodynamic databank model was developed. The airplane’s performance, stability, control, and handling qualities are analyzed by using a six degrees of freedom airplane model. One of the subsystems to this flight simulation model is the aerodynamic databank model which provides the aerodynamic forces and moments acting on the airplane. Essentially, the aero dynamic databank model is composed of different contributions to the six total aerodynamic coefficients which determine the loads on the airplane. This compo nent buildup method gives a modular architecture of the databank model and makes it easy to add aerodynamic effects to specific airplane components and aerodynamic coefficients. The total aerodynamic coefficients are the aggregate of the coefficient contributions of individual airplane components due to the relevant aerodynamic effects. In general, the aerodynamic coefficients are functions of a large number of variables, including the angle of attack, side slip angle, speed, deflection of flaps and control surfaces, deployment of landing gear, and proximity to the ground. To cover an entire arbitrary flight, the computational fluid dynamics (CFD) data is combined with mathematical, semi-empirical, and empirical methods for modeling additional aerodynamic effects which were not considered in the CFD simulations. In the design phase of the airplane, this approach is particularly advantageous as it reduces the computational cost related to CFD and allows for rapid evaluations of design updates.
Aerodynamic Evaluation of Nacelles for Engines with Ultra High Bypass Ratio
(2017) Petrusson, Andreas; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied Mechanics
The aim in this project is to gain deeper understanding of nacelle drag for engines with ultra high bypass ratio. 2D axisymmetric nacelles with different fan cowl thickness and length are studied to investigate how these parameters affect the nacelle drag. Some different fan pressure ratios is also investigated. Furthermore, the drag for an aircraft fuselage with a fan and fan cowl at the rear that ingest the boundary layer of the fuselage is studied. This is the last part of the project and therefore this work still requires further study. First the geometries of the nacelles are designed. The fan cowl and inlet profiles of the nacelle are designed using a CST method, based on fourth order Bernstein polynomials. This allows for specifying the initial curvature radius of the profile, along with maximum radius and trailing edge position and slope. A core engine cowl and a bypass channel are also designed using these curves, but the internal parts of the core engine are not included in this project and the core nozzle is only considered as an outlet boundary. These geometries are simulated in an axisymmetric section using CFX, and the drag was computed from the flow state and pressure forces on the nacelle surfaces. The geometries of the boundary layer ingestion cases are constructed in a similar manner to the nacelles. For these cases, a whole aircraft fuselage is placed in front of a nacelle, with the rear of the fuselage going into the inlet of the nacelle. The fan diameter is varied to study the effect on drag, which means that different portions of the boundary layer are ingested by the fan. It is concluded that only shortening the fan cowl does not lower nacelle drag, since the aft core cowl should also be considered to contribute to the drag. Redesigning the aft core cowl could give a lower drag for the shorter and thinner cowl that are investigated, but the designs in this project does not take this into account. For the boundary layer ingestion cases, the drag is decreased more if a larger portion of the boundary layer is ingested. However, it could be more efficient if only some part of the boundary layer is ingested.
Aerodynamic Optimization of High Speed Propellers
(2016) Montero Villar, Gonzalo; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied Mechanics
The fact that fuel costs accounts for 29% of all airlines cost [1] and the increase in environmental awareness is driving the aviation industry to reach for more efficient engines. One of the promising technologies to tackle this problem is the open-rotor, which combines the fuel efficiency of turboprops together with the high cruise Mach number of turbofans. More specifically, counter rotating open-rotors (CROR), which are expected to bring fuel savings in the order of 20% − 35% [2]. A new type of propeller blades was invented by Richard Avellán and Anders Lundbladh, the Boxprop (patent filed in 2009 [3]). Its highly 3 dimensional geometry together with the complexity of the flow, make the optimization challenging for conventional design methods, thus necessitating a different approach. In this thesis work a generic optimization framework in Python that can handle both single-objective and multi-objective optimization problems by means of genetic algorithms is presented. Moreover, the parametrization of the Boxprop is also carried out, together with the automation of the geometry creation and mesh generation processes using Python and ICEM CFD scripting.
Aerodynamics Around Wheels and Wheelhouses
(2017) Cavusoglu, Ömer Faruk; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied Mechanics
The aerodynamic drag of an EV is the major energy consuming vehicle attributes, an EV requires less cooling flow, and can have a flat underbody, which potentially can improve the overall aerodynamics of the vehicle. The flow around the wheels and in the wheelhouses is a significant part of the total aerodynamic drag. Different aerodynamics concept vehicles have been studied in the past and shown in the automotive industry, the flow around wheels is managed and smoothen. They key for success is to manage the flow and keep the car functional and attractive. This master thesis project combines a through study of the historical and current aerodynamics concept cars regarding wheelhouse flows, comparing different rim designs, quantifying different features around the wheels or improvements in terms of drag reduction and range increase and finally a CFD study of DrivAer with implementing features/improvements.

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