Lokomotorische Interaktion Planetarer Explorationssystememit weichen Sandböden - Modellbildung und Simulation

Kurzfassung

In everydays life, locomotion on soft, sandy soils is well known to us. Anyway this interaction with granular matter is one of the least understood and only partially modeled phenomena in our world. While on Earth locomotion systems can be directly recovered and interacted with, planetary Exploration arises further problems, like non-accessibility of the systems. State of the art modeling techniques cover the interaction insufficiently, only. Thus this thesis aims to enhance the Discrete Element Method and to make it usable for the development of systems for the exploration of our solar system. In order to cover the shear failure in granular matter, both correctly and efficient, a method using 2D-rotation planes to cover the grain shape is applied. Thereby the spherical particle shape for contact detection is maintained. In order to cover forces acting on the particles, contact models are adapted in order to cover frictional effects, as well as cohesion. But to utilize those particle models a parameter identification method is needed. This need is addressed by a novel identification method using sufficient constraints, microscopic pictures and a look-up table in order to determine the Parameters without calibration simulations. Hence the process is very fast and is carried out in less than 5 s instead of up to 5000 CPU-hours. Verification of the method is carried out using the bevameter test for two different soils. These advanced modeling techniques are then implemented in the framework DEMETRIA based on Pasimodo and are used for two applications. The first System is the HP3-Mole penetrator for Mars, for which less than 16% error compared to Penetration depth measurements were achieved. Using these validated models in optimization, the final depth of 5m was reached and the number of needed strokes was decreased to 25% of the original value. Thereby the HP3-Mole uses less than 5W of input power for locomotion. For the second application, planetary rover wheels, general effects of the interaction as well as soil Deformation are investigated and verified qualitatively using real tests. These comparisons yielded in good correlation and enabled to show the ability for wheel optimization using the proposed modeling techniques.