Publications

@mastersthesis{pereira2019development,
title = {Development of a Harvester Machine Simulator in Virtual Reality},
author = {Pereira Jr João},
url = {https://trepo.tuni.fi/bitstream/handle/10024/115646/Pereira.pdf?sequence=2},
year = {2019},
date = {2019-01-01},
school = {Faculty of Engineering and Natural Sciences, Tampere University},
abstract = {Computer-aided design (CAD) software is used in the product design and development to design complex and detailed prototypes. It provides good assistance and solid data generation to designers and engineers. In order to remain competitive, industry is always seeking for higher process efficiency and product quality enhancement in the shortest period of time. Continuous research keeps going to make it possible.

Virtual reality has been one of the research focus in the recent years. It is studied and applied to be used as an assistant tool in the product lifecyle management, particularly in facilitating the development phase. However, the implementation process from CAD to virtual reality remains a challenge due to time consumption and technology complexibility.

In this work a real-time virtual reality harvester simulator was developed. The start point was a 3D harvester CAD model. It was used the CAD simulator AGX Momentum, a game engine Unity
and the physics engine AGX Dynamics to create dynamics simulation, to design a virtual forest environment and to enable physical controllers interact with the model.

With the capabilities of AGX Momentum, it was added dynamics motion directly in the CAD software, creating fast CAD simulations. A virtual scene was designed with Unity to simulate an environment and the immersion of the user on it with Oculus Rift device. The harvester model was imported to the Unity scene with AGX Dynamics.

In the end it was obtained a real size virtual prototype, with the possibility of interacting and control it using physical controllers. The user can visualise the scene in real-time through a head mounted display, providing him the experience of a real machine operator. Driving the harvester in a simulated forest, allowed to test the model in a hypothetical real scenario.

The process of implementing the CAD model in virtual reality used in this work, revealed to be efficient and intuitive. However, because it is a complex and large model, it was necessary to remove certain bodies (without dynamics effect) and reduce the number of contact points between components in order to balance the speed and performance of the simulator.

Following the same method used in this work, Other CAD models can be imported to virtual reality and be dynamically simulated.},
keywords = {External},
pubstate = {published},
tppubtype = {mastersthesis}
}

@mastersthesis{Syren2019,
title = {A method for introducing flexibility in rigid multibodies from reduced order elastic models},
author = {Ludvig Syrén},
url = {http://urn.kb.se/resolve?urn=urn%3Anbn%3Ase%3Aumu%3Adiva-160417
https://umu.diva-portal.org/smash/get/diva2:1326569/FULLTEXT01.pdf
},
year = {2019},
date = {2019-01-01},
school = {Department of Physics, Umeå University},
abstract = {In multibody dynamics simulation of robots and vehicles it is common to model the systems as being composed of mainly rigid bodies with articulation joints. With the trend to more lightweight robots, however, the structural flexibility of the robots link’s needs to be considered for realistic dynamic simulations. The link’s geometries are complex and finite element models (FEM) are required to compute the deformations. However, FEM includes too many degrees of freedom for time-efficient dynamics simulation. A popular method is to generate reduced order models from the FE models, but with much fewer degrees of freedom, for fast and precise simulations. In this thesis a method for introducing reduced order models in rigid multibody systems was developed. The method is to divide a rigid body into two rigid bodies. Their relative movement is described by a six degree of freedom restoration force, determined with a reduced order model from Guyan reduction (static condensation). The method was validated for quasistatic deformation of a homogenous beam, a robot link arm with a more complex geometry and in multibody dynamics simulations. Finally the method was tested in simulation of a complete ABB robot with joint actuators, and any significant differences in the motion of the robot tool centre point due to replacing a rigid link arm by a flexible one was demonstrated.The method show good results for computing deformations of the homogenous beam, of the link arm and in the multibody simulation. The differences observed in simulation of a complete robot was expected and demonstrated the method to be applicable in robotic simulations.},
keywords = {Algoryx},
pubstate = {published},
tppubtype = {mastersthesis}
}

@mastersthesis{Lundkvist2018,
title = {Fatigue analysis - local geometry optimization},
author = {Anna Lundkvist},
url = {http://www.diva-portal.org/smash/get/diva2:1251131/FULLTEXT01.pdf
http://urn.kb.se/resolve?urn=urn%3Anbn%3Ase%3Aumu%3Adiva-152084},
year = {2018},
date = {2018-07-09},
abstract = {The cause of fatigue failure is repeated loads, that cause cracks to appear and grow even if the loads are far below the static load that would make a structure fail. High-cycle fatigue, which this project will focus on, is characterized by linear elastic stress and only fails after a large amount of loading cycles. While fatigue is the most common cause of failure in structures, it is not feasible to calculate fatigue damage analytically. The aim of this project was to develop, implement and test a workflow that unifies the wide range of physical scales and transient features that are relevant to fatigue analysis of complex dynamic machinery. The workflow should take both system-level and local aspects into account. The goal was to address both the global and local while still keeping practical feasibility and simulation performance in mind. The resulting unified fatigue analysis method was then used on several test cases and illustrated from a local geometry optimization perspective.

The workflow contains the following steps: First the model is to be simulated in order to get the load history. Then the finite element method (FEM) is used to make a submodel of the component that is to be analyzed. The submodel is subjected to forces and moments, and then the stress is extracted from the areas of interest in the model. Thus, a linear relation for the stress can be calculated. The stress history is calculated by putting the load history into the stress relation. Using established fatigue analysis methods like rainflow counting and the Palmgren-Miner rule the fatigue life is then calculated.

This project only had its focus on the FEM submodel part of the fatigue workflow. The geometry of the submodel should then be able to be optimized for the longest fatigue life.

The workflow was tested on several test cases. The first one was a simple upsidedown T-shaped component that was made by welding the parts together. The same component but with no weld, as if it had been moulded, was the next case. The final case was a component from the base of a crane. Two things were analyzed on this case. The first was the fatigue life around a hole in which a shaft was welded. The other was optimizing to find the best position for a hook to be welded onto the surface on the component.
},
keywords = {Algoryx},
pubstate = {published},
tppubtype = {mastersthesis}
}

@mastersthesis{lenerand2018component,
title = {Component-Based Simulator for Modelling the Design and Dynamics of Modular Robots},
author = {Torstein Sundnes Lenerand},
url = {http://hdl.handle.net/11250/2581432
https://ntnuopen.ntnu.no/ntnu-xmlui/bitstream/handle/11250/2581432/Lenerand%2c%20Torstein%20S.%202018.pdf?sequence=1&isAllowed=y},
year = {2018},
date = {2018-01-01},
abstract = {This project presents the design of a component-based simulator used for modelling the design and movement of chain-based modular robots. This work is in collaboration with NTNU Ålesund and implemented in the Unity® game engine with Algoryx® Dynamics for physics calculations. The focus is on Modular robots, along with techniques for simulator creation and software development such as Component-Based Software Engineering and Design. The Unified Process is used for prototyping and research, while the finished design is verified using tests, reviews, and use-case studies. This thesis discusses the impact of using Component-Based Design in a relatively small project, and the advantages/disadvantages of this decision. The goal is to provide the optimum tool for students to learn about, and researchers to develop, customized modular robots.},
keywords = {External},
pubstate = {published},
tppubtype = {mastersthesis}
}

@mastersthesis{Markgren2018,
title = {Fatigue analysis - system parameters optimization},
author = {Hanna Markgren},
url = {https://umu.diva-portal.org/smash/get/diva2:1247557/FULLTEXT01.pdf
http://urn.kb.se/resolve?urn=urn%3Anbn%3Ase%3Aumu%3Adiva-151755},
year = {2018},
date = {2018-01-01},
school = {Department of Physics, Umeå University},
abstract = {For a mechanical system exposed to repeated cyclic loads fatigue is one of the most common reasons for the system to fail. However fatigue failure calculations are not that well developed. Often when fatigue calculations are made they are done with standard loads and simplified cases.

The fatigue life is the time from start of use until the system fails due to fatigue and there does exist some building blocks to calculate the fatigue life. The aim for this project was to put these building blocks together in a workflow that ca be used for calculations of the fatigue life.

The workflow was built so that it should be easy to follow for any type of me- chanical system. The start of the workflow is the load history of the system. This is then converted into a stress history that is used for the calculations of the fatigue life. Finally the workflow was tested with two test cases to see if it was possible to use.

In Algoryx Momentum the model for each case was set up and then the load history was extracted for each time step during the simulation. To convert the load history to stress history FEM calculations was needed, this was however not a part of this project so the constants to convert loads to stress was given. Then with the stress history in place it was possible to calculate the fatigue life.

The results from both test cases were that it was possible to follow every step of the workflow and by this use the workflow to calculate the fatigue life. The second test also showed that with an optimization the system was improved and this resulted in a longer lifetime.

To conclude the workflow seems to work as expected and is quite easy to follow. The result given by using the workflow shows the fatigue life, which was the target for the project. However, to be able to evaluate the workflow fully and understand how well the resluts can be trusted a comparison with empiric data would be needed. Still the results from the tests are that the workflow seem to give reasonable results when calculating fatigue life.},
keywords = {Algoryx},
pubstate = {published},
tppubtype = {mastersthesis}
}

@mastersthesis{Sihlberg2017,
title = {Rendering Of Physically Simulated Wires},
author = {Jimmy Sihlberg},
url = {https://umu.diva-portal.org/smash/get/diva2:1258642/FULLTEXT01.pdf
http://urn.kb.se/resolve?urn=urn%3Anbn%3Ase%3Aumu%3Adiva-152811},
year = {2017},
date = {2017-01-01},
school = {Department of Computing Science, Umeå University, Sweden},
abstract = {Simulating deformable continious objects such as wires requires some discretization method. In this project we look at how to render simulated multiresolution lumped element wires in real time and the challenges that come with it. First we look how to create a 3D wire geometry on they from a set of constantly changing points. By utilising the idea of extrusion, the geometry can be built from a 2D shape. Special care must be taken to avoid twisting artifacts. To get a smooth curvature, we look at cubic spline methods to integrate the wire elements. We illustrate that the Catmull-Rom curve with Chordal parameterization produces well behaved curves for lower curvatures and for non-equidistant control points. Sharp curvatures proves to be a challenging task, we use the Catmull-Romcurve with Centripetal parameterization together with Cardinal spline and show its limitations. Finally we look at how to render wires with more realism by adding texture to it. Many wires have a symmetric pattern, we illustrate how to make use of this by repeating a symmetric pattern image along the wire. The physical stretching of the wire is also considered when applying texture.},
keywords = {Algoryx},
pubstate = {published},
tppubtype = {mastersthesis}
}

@mastersthesis{Forsberg2017,
title = {Automatic lumped element discretization of curved beams with variable sectional area},
author = {Hampus Forsberg},
url = {http://urn.kb.se/resolve?urn=urn%3Anbn%3Ase%3Aumu%3Adiva-145058
http://umu.diva-portal.org/smash/get/diva2:1184054/FULLTEXT01.pdf},
year = {2017},
date = {2017-01-01},
school = {Department of Physics, Umeå University},
abstract = {Calculations on stress, strain and deformation are typically made using finite element methods (FEM). An alternative to this is a rigid bodydynamics approach also called lumped element method (LEM). LEM implements deformation by replacing single rigid bodies with multiple subbodies, which are in turn connected with joints (also called constraints) that allow movement between the sub-bodies. If instead of FEM, a lumped element method is used to simulate deformable objects, sufficient accuracy can be obtained at a much lower cost, complexity-wise. A lumped element method-approach could for example achieve real-time simulationspeed.

The purpose of this thesis is to expand upon previous work into LEM, analyzing how the rigid bodies and constraints should be configured to produce accurate results for a wider range of objects. Specifically, beams of varying cross section and curved beam axis, as well as other test cases. The simulated values are compared with the analytic predictions given by Euler-Bernoulli beam theory.

These simulations are implemented using the AGX Dynamics physics engine from Algoryx Simulation AB.

One intended application area of LEM is crane arms. This motivates the focus on analyzing how LEM behaves when simulating beams, as they represent the most basic version of crane arms. Simulation and testing of full crane objects was unfortunately not accomplished, partly due to a lack of convenient testing data. Further work is needed to confirm that LEM behaves well for these expanded cases as well.

In addition to the analysis section above, the purpose is also to implement a pipeline for automatic conversion of a CAD-model to a lumped element version in AGX. Specifically, a CAD-model given in the 3D-modeling software SpaceClaim.},
keywords = {Algoryx},
pubstate = {published},
tppubtype = {mastersthesis}
}

@mastersthesis{Tornqvist2016,
title = {Simulation in the Control Loop: Control and Collision Detection for Collaborative Robots},
author = {Martin Törnqvist},
url = {https://www.algoryx.se/mainpage/wp-content/uploads/2021/04/Törnqvist_Simulation-in-the-Control-Loop-Control-and-Collision-Detection-for-Collaborative-Robots.pdf},
year = {2016},
date = {2016-03-18},
address = {Stockholm, Sweden},
school = {Electrical Engineering, KTH},
abstract = {Control and simulation are two areas heavily utilized in robotics research, and simulation is often used as a way to test and optimize control algorithms. Some controllers are even able to perform simulations, as is the case with ABB's virtual controller. Despite many similarities in the dynamics of model based controllers and physics simulation, using a simulation to perform dynamics calculations for controllers remains relatively uncharted territory. This report presents a general simulation-based controller that integrates simulation into every part of the control loop: from motion planning to model-based control and collision detection. The controller is implemented and tested on the ABB Yumi collaborative robot.},
keywords = {Algoryx},
pubstate = {published},
tppubtype = {mastersthesis}
}

@mastersthesis{he2016virtual,
title = {Virtual Winch Prototyping-Design, Modeling, Simulation and Testing of A Marine Hydraulic Winch System with Active Heave Compensation.},
author = {Dahai He},
url = {https://ntnuopen.ntnu.no/ntnu-xmlui/bitstream/handle/11250/2417673/He%2c%20D.%202016.pdf?sequence=1&isAllowed=y
https://ntnuopen.ntnu.no/ntnu-xmlui/handle/11250/2417673
http://hdl.handle.net/11250/2417673},
year = {2016},
date = {2016-01-01},
abstract = {This thesis is to develop a standard virtual prototyping system for hydraulic winch system including developing a library of standard sub-models of hydraulic system, mechanical system and control system (AHC), and visualizing the simulation and operation of the virtual winch prototyping system. To be more specific:

Chapter 1. Motivation and background of winch prototyping is introduced so as to break down the problems and formulate the objectives of this projects.

Chapter 2. Theoretical background is shown in this part. It contains the briefly descriptions of the important theory applied in virtual prototyping winch system.

Chapter 3. Methodology is shown in this part. It contains the detailed theory basis applied in the modelling of hydraulic and mechanical sub-systems of winch system.

Chapter 4. This chapter describes the implementation of mechanical sub-system. 3D modelling, parameterization and visualization are implemented by using WebGL technology with three.js library. The outcome of the mechanical part can be easily integrated into the virtual prototyping framework.

Chapter 5. This chapter elaborates the method and the process of hydraulic and control (AHC) sub-model modelling. Bond graph theory is applied during the modelling process. Different alternatives of hydraulic system structure are analysed and compared to finalize a better solution of hydraulic system structure.

Chapter 6: This chapter explains the integration method of virtual prototyping winch system framework.

Chapter 7: Results of mechanical modelling, hydraulic with control modelling and co-simulation of integrated virtual prototyping winch system are shown and discussed to evaluate the performance of virtual prototyping system.

Chapter 8: This part makes conclusions, modelling alternatives and future work for the virtual prototyping winch system.},
keywords = {External},
pubstate = {published},
tppubtype = {mastersthesis}
}

@mastersthesis{Sundling2016,
title = {Validation Toolbox for a Physics Engine},
author = {Emma Sundling},
url = {http://umu.diva-portal.org/smash/get/diva2:935814/FULLTEXT01.pdf
http://urn.kb.se/resolve?urn=urn%3Anbn%3Ase%3Aumu%3Adiva-121972},
year = {2016},
date = {2016-01-01},
school = {Department of Physics, Umeå University},
abstract = {Physics engines become more and more common due to the rapid development and increasing demand of simulations. With this comes a need of testing the engine, a way to measure its performance, not only its speed but also its accuracy and stability. The purpose of this thesis has been to create a set of benchmark tests. They aim to check the physical aspects, especially mechanics, of the engine. A strategy and export functions for the test results in order to automate the testing have also been developed.

The resulting tests became a beam on piles which analyses constraint stability, an overdetermined system consisting of a static door on multiple hinges, a falling object investigating the accuracy of the integrator, a box on an inclined plane for testing the friction model, a single pendulum as well as a multibody pendulum checking constraint accuracy and energy conservation, the Earth orbiting around the Sun which tests the stability of the integrator and finally a cantilever beam that is a static test of a real scenario. After the tests are performed the results are presented on an HTML-page. A prototype of a Web application is also established as well as a set of scalar tests that can be performed continuously, in order to follow trends or compare the engine's performance from time to time.

This thesis was initialized by Algoryx Simulation AB which also provided the engine, AgX Dynamics, with the numerical method called SPOOK. It mainly performed well on all tests. In order to build a fully general toolbox more tests need to be added such as material interactions, scalable test with thousands of bodies, torque tests as well as more complex scenarios, for example a scissor lift and robots. The work can also be extended with more developed export functions, both to the Web and to documents. Hopefully this thesis can be seen as a complement to the earlier efforts done in creating a general set of benchmarks and automation framework for continuous integration and testing.},
keywords = {Algoryx},
pubstate = {published},
tppubtype = {mastersthesis}
}

@mastersthesis{Agvik2015,
title = {A deformable terrain model in multi-domain dynamics using elastoplastic constraints: An adaptive approach},
author = {Simon Agvik},
url = {http://urn.kb.se/resolve?urn=urn%3Anbn%3Ase%3Aumu%3Adiva-108328
http://umu.diva-portal.org/smash/get/diva2:852371/FULLTEXT01.pdf},
year = {2015},
date = {2015-01-01},
school = {Department of Physics, Umeå University},
abstract = {Achieving realistic simulations of terrain vehicles in their work environment does not only require a careful model of the vehicle itself but the vehicle's interactions with the surroundings are equally important. For off-road ground vehicles the terrain will heavily affect the behaviour of the vehicle and thus puts great demands on the terrain model.

The purpose of this project has been to develop and evaluate a deformable terrain model, meant to be used in real-time simulations with multi-body dynamics. The proposed approach is a modification of an existing elastoplastic model based on linear elasticity theory and a capped Drucker-Prager model, using it in an adaptive way. The original model can be seen as a system of rigid bodies connected by elastoplastic constraints, representing the terrain. This project investigates if it is possible to create dynamic bodies just when it is absolutely necessary, and store information about possible deformations in a grid.

Two methods used for transferring information between the dynamic bodies and the grid have been evaluated; an interpolating approach and a discrete approach. The test results indicate that the interpolating approach is preferable, with better stability to an equal performance cost. However, stability problems still exist that have to be solved if the model should be useful in a commercial product.},
keywords = {Algoryx},
pubstate = {published},
tppubtype = {mastersthesis}
}

@mastersthesis{Pettersson2015,
title = {Analysis and implementation of the Smooth Discrete Element Method in AGX},
author = {Thomas Pettersson},
editor = {Thomas Pettersson},
url = {http://liu.diva-portal.org/smash/get/diva2:856766/FULLTEXT02.pdf
http://urn.kb.se/resolve?urn=urn%3Anbn%3Ase%3Aliu%3Adiva-121563},
year = {2015},
date = {2015-01-01},
school = {Faculty of Science & Engineering, Linköping University},
abstract = {We encounter granular materials on a daily basis. We walk up a gravel path or we eat our breakfast cereals. When handling granular materials on an industrial scale it is important to do so efficiently, to avoid unnecessary energy losses, wear and tear. To help designing efficient tools for handling these materials engineers uses numerical simulations.

This project investigates the difference between the two main approaches to simulation of granular materials, the Smooth- and Non-smooth Discrete Element Methods by implementing the Smooth method into AgX dynamics were the Non-smooth method already is implemented, and then setup and execute a range of experiments to investigate their differences.

The investigation shows both advantages and weaknesses for both methods. The result of simulations with smooth discrete element method are more consistent than with the nonsmooth discrete element method with respect to choice of time step and other parameters that can be chosen for the simulation. Smooth discrete element method have problems when it comes to extreme situations.

The relative simulation time for system as large as treated by this project (more than1000) can not be shown to depend on the size of the system.},
keywords = {Algoryx},
pubstate = {published},
tppubtype = {mastersthesis}
}

@mastersthesis{Sandqvist2015,
title = {Collision detection using boundary representation, BREP},
author = {Jonas Sandqvist},
url = {http://urn.kb.se/resolve?urn=urn%3Anbn%3Ase%3Aumu%3Adiva-102531
http://umu.diva-portal.org/smash/get/diva2:808317/FULLTEXT01.pdf
},
year = {2015},
date = {2015-01-01},
school = {Department of Physics, Umeå University},
abstract = {This thesis treats how to generate collision information for multibody simulations in AgX Dynamicswhere the geometries are described with the data structure boundary representation, BREP. BREP is adata structure that contains the exact mathematical description of each individual surface. To describecomplex surfaces exact and efficient non uniform rational basis spline, NURBS, is used and for trivialsurfaces like planes or spheres simpler equations is used. Since all surfaces in a BREP is described veryaccurate, the accuracy for the collision information can be set high without affecting the amount of dataneeded to describe the geometries.To make AgX Dynamics able to calculate forces in a multibody simulation, collision informationabout were and how much two geometries are intersecting is required. The collision information containswere the overlap between two geometries is, how much the objects have penetrated each other and thedirection for which the objects have to separate. To find the penetration depth and the overlap theNewton Raphson method were used. The experiments conducted, showed that it is possible to useBREPs as a description of geometries to produce the collision information needed for the physics engineused by AgX Dynamics to handle collisions. A comparison between trimesh and BREP for producingthe collision information, shows that data usage is much lower for the representation of geometries withBREPs than trimesh. The results also shows that the accuracy can be significantly higher than fortrimesh as the data usage for trimesh becomes non practical to handle when the required accuracy ishigh. With the high accuracy and with the smooth surfaces used with the BREP the artificial friction isalmost negligible except for cases were intersection points could not be found all around the intersectioncurves due to limitations in the algorithm.},
keywords = {Algoryx},
pubstate = {published},
tppubtype = {mastersthesis}
}

@mastersthesis{ostman2014collision,
title = {Collision detection for trimming curves and BREPs},
author = {Alexander Östman},
url = {http://umu.diva-portal.org/smash/record.jsf?searchId=2&pid=diva2:718124
http://umu.diva-portal.org/smash/get/diva2:718124/FULLTEXT01.pdf},
year = {2014},
date = {2014-01-01},
school = {Department of Computing Science, Umeå University, Sweden},
abstract = {This report treats the implementation of collision detection algorithms for Boundary representations (BREPs) consisting of connected trimmed surfaces, mainly Non Uniform Rational Basis Spline (NURBS) surfaces. Using the OpenNurbs software package, complicated geometries created in CAD program Space Claim were imported to the physics engine AgX, where dynamic simulations were carried out. Collision detection algorithms for the geometry pairs BREP-line, BREP-plane and BREP-sphere have been developed and investigated. In the case of BREP-sphere collision detection, experiments have been carried out which show that BREP-shape representation exceeds trimesh-shape representation both in computational performance and in collision accuracy. The conclusion is that BREP representation has the potential to replace trimesh representation for some complex geometries with higher computational performance and more accurate simulations as a result.},
keywords = {Algoryx},
pubstate = {published},
tppubtype = {mastersthesis}
}

@mastersthesis{Sandberg2014,
title = {Interactive simulation of hydrodynamics for arbitrarily shaped objects},
author = {Sandra Ålstig Sandberg},
url = {http://urn.kb.se/resolve?urn=urn%3Anbn%3Ase%3Aumu%3Adiva-90060
http://umu.diva-portal.org/smash/get/diva2:725897/FULLTEXT02.pdf},
year = {2014},
date = {2014-01-01},
school = {Department of Physics, Umeå University},
abstract = {Simulating hydrodynamics can require extensive calculations which becomes a problem when doing interactive simulations. This thesis investigates an efficient method for hydrodynamic simulations with the effects of buoyancy, drag, lift and added mass that is implementedand tested with the help of AgX Dynamics using triangulated meshes.

For buoyancy, drag and lift a method of numerical integration over triangles was used to calculate the forces and torques acting on each triangle of a mesh. For added mass a large part of the calculations could be done before the simulation starts using a Boundary Element Method (BEM). The final value for the added mass was calculated each time step based on how the object was submerged.

The method of triangle integration produced results that were close to the analytical values with a certain mesh dependence. The results had an increasing accuracy when the mesh had a more exact representation of the object. The drag and lift coefficients could however be better adjusted. The added mass results also had a mesh dependence, but with accuracy increasing with number of triangles even for shapes that already had an exact representation, e.g. a cube. For a fully submerged sphere with 4900 triangles the maximum error for the added mass was 0.65%.

The time required for precalculations using BEM had a rapid growth with increasing number of triangles due to the factorization of a dense matrix that has a complexity of O(n3). For the hydrodynamic calculations done each time step the time requirement increased linearly with number of triangles.},
keywords = {Algoryx},
pubstate = {published},
tppubtype = {mastersthesis}
}

@mastersthesis{Ronnbäck2014,
title = {Parallel implementation of the projected Gauss-Seidel method on the Intel Xeon Phi processor – Application to granular matter simulation},
author = {Emil Rönnbäck},
url = {http://urn.kb.se/resolve?urn=urn%3Anbn%3Ase%3Aumu%3Adiva-93299
http://umu.diva-portal.org/smash/get/diva2:747201/FULLTEXT01.pdf},
year = {2014},
date = {2014-01-01},
school = {Department of Computing Science, Umeå University, Sweden},
abstract = {Being able to simulate granular matter is important, because they are ubiquitous both in nature and in industry. Some examples of granular materials are ore, sand, coffee, rice, corn, and snow. Research and development of new, more accurate, and faster methods to simulate even more complex materials with millions of particles are needed. In the work of this thesis a typical scene containing thousands of particles has been used for analysing simulation performance using the iterative Gauss-Seidel method adapted to the specifications and capabilities of the Intel Xeon Phi coprocessor. The work began with analysing the performance (wall-clock time and speedup) of a method developed by Algoryx Simulation. The work continued with finding the parts in the code causing bottlenecks and implementing improvements such as a distributed task scheduler and vectorization of operations. In the end, this resulted in shorter execution time and linear speedup using more than 40 threads, compared to 20 in the initial state. We also investigated the benefit of other techniques, such as cache prefetching and usage of huge page sizes, but found no performance gain from these. It is well known that the Xeon Phi coprocessor performs well when executing highly parallel applications, but overload may occur if excessive amount of data is requested by many threads simultaneously. To tackle this issue, the convergence rate of the Gauss-Seidel method during simulation has been measured and suggested modifications of the method decreasing data flow have been implemented and analysed.},
keywords = {Algoryx},
pubstate = {published},
tppubtype = {mastersthesis}
}

@mastersthesis{Sundberg2014,
title = {Parallel projected Gauss-Seidelsolver for large-scale granular matter: Examining the physics of the parallel solver and development of a multigrid solver},
author = {Johan Sundberg},
url = {http://urn.kb.se/resolve?urn=urn%3Anbn%3Ase%3Aumu%3Adiva-85831
http://www.diva-portal.org/smash/get/diva2:695410/FULLTEXT01.pdf
},
year = {2014},
date = {2014-01-01},
school = {Department of Physics, Umeå University},
abstract = {Granular matter is found everywhere in nature and some examples include sand, rice,coee beans and iron ore pellets. Many dierent methods exists for simulating granularmatters using computers. In the scope of this thesis a physics engine called AgX Dynamicsfrom Algoryx Simulation AB is used to investigate and further develop methodsinvolving the discrete element method. During the rst half of 2013 a parallel solverfor the projected Gauss-Seidel method was implemented in AgX in order to speed upthe simulation time of simulations involving granular materials. In this thesis projectit is shown that the behaviour of the physics of this parallel solver is identical to theserial solver. Secondly this thesis works on the development of a multigrid solver forthe Gauss-Seidel method. Multigrid in this context means that the particle systemis partitioned in space. Each partition is then merged into a rigid body and contactforces between these rigid bodies is solved to machine precision using a direct solver.The forces from this direct solve is then used when solving the internal part of thepartitions using an iterative projected Gauss-Seidel method. The motivation for developinga multigrid method is to achieve faster convergence and even more speed-upof the solver. Numerical experiments has been performed on a 1D column and a 3Dsilo. The results show high potential of the method and the one-dimensional columnbehaves closer to a direct solver than an iterative solver. The thesis was done for UMIT Research Lab, Umea University and Algoryx Simulation AB.},
keywords = {Algoryx},
pubstate = {published},
tppubtype = {mastersthesis}
}

@mastersthesis{Lindberg2014,
title = {Remote rendering of physics simulations and scalability aspects in web applications},
author = {Lars Lindberg},
url = {http://urn.kb.se/resolve?urn=urn%3Anbn%3Ase%3Aumu%3Adiva-90042
https://umu.diva-portal.org/smash/get/diva2:725806/FULLTEXT01.pdf},
year = {2014},
date = {2014-01-01},
school = {Department of Computing Science, Umeå University, Sweden},
abstract = {This thesis, assigned by Algoryx Simulation AB, explores the concept of implementing a web application for managing Algoryx based physics simulations. The application enables users to get access to the Algoryx simulation software by providing a user interface for clients to submit scenes files to be simulated, and to view a 3D visualization of the finished simulations rendered directly in the web browser. This allows clients to do away with the work of performing the compute intensive physic simulations locally and instead hand over that responsibility to the web service, while the client only needs to handle the actual rendering. Applications made available through a web browser allows users to get easy access to applications that does not require any installation procedures. For that reason the clients do not need any simulation software or any plugin installed to access the service. This makes it easy to share results of simulations to customers by just giving out a link that can be accessed through a browser.

This paper also includes a theoretical study on scalability in web applications. The theory explains different ways of scaling, and common techniques and methods used to help achieving scalability that can be useful when designing and building scalable web system.},
keywords = {Algoryx},
pubstate = {published},
tppubtype = {mastersthesis}
}

@mastersthesis{Häggström2013,
title = {Collision detection with NURBS},
author = {Martin Häggström},
year = {2013},
date = {2013-02-26},
school = {Department of Computing Science, Umeå University, Sweden},
keywords = {Algoryx},
pubstate = {published},
tppubtype = {mastersthesis}
}