Impact Characterization of Earth Entry Vehicle for Terminal Landing (on Soil)
| dc.contributor.author | Shorts, Daniel Calvert | en |
| dc.contributor.committeechair | Bayandor, Javid | en |
| dc.contributor.committeemember | Battaglia, Francine | en |
| dc.contributor.committeemember | Perino, Scott Victor | en |
| dc.contributor.department | Mechanical Engineering | en |
| dc.date.accessioned | 2019-02-20T07:00:28Z | en |
| dc.date.available | 2019-02-20T07:00:28Z | en |
| dc.date.issued | 2017-08-28 | en |
| dc.description.abstract | In order to more accurately predict loads subjected to the EEV (Earth Entry Vehicle) upon impact with a variety of materials, finite element simulations of soil/EEV impact were created using the program LS-DYNA. Various modeling techniques were analyzed for accuracy through comparison with physical test data when available. Through variation of numerical methods, mesh density, and material definition, an accurate and numerically efficient representation of physical data has been created. The numerical methods, Lagrangian, arbitrary Lagrangian-Eulerian (ALE), and spherical particle hydrodynamics (SPH) are compared to determine their relative accuracy in modeling soil deformation and EEV acceleration. Experimentally validated soil material parameters and element formulations were then used in parametric studies to gain a perspective on effects of EEV mass and geometry on its maximum acceleration across varying soil moisture content. Additionally, the effects of EEV orientation, velocity, and impact material were explored. Multi-material arbitrary Lagrangian-Eulerian (MMALE) formulation possess the most effective compromise between its ability to: accurately display qualitative soil behavior, accurately recreate empirical test data, be easily utilized in parametric studies, and to maintain simulation stability. EEV acceleration can be minimized through increase of EEV mass (with constant geometry), allowing for maximum penetration depth, and longest deceleration time. A critical orientation was discovered at 30⁰ from normal, such that maximum EEV surface area impacts the soil surface instantaneously, resulting in maximum acceleration. Off-nominal impact with concrete is predicted to increase acceleration by up to 630% from impact with soil. | en |
| dc.description.abstractgeneral | As part of a larger effort to return Martian soil samples to Earth, the creation of a vehicle (Earth Entry Vehicle, EEV) to carry those samples from Mars, to the surface of Earth is underway. The EEV is designed to enter Earth’s atmosphere and decelerate using its geometry to slow itself during descent, and the crushing of the soil to absorb impact energy upon collision with Earth. Paramount in concern is the containment of the soil samples during the EEV’s impact. As part of the design process with respect to this concern, computer simulations are built in this work which are compared to collected physical test data, and used to predict impact forces on the EEV under various impact conditions. Impact conditions considered are the variation of the mass, orientation relative to vertical, geometry of the EEV, the moisture content of the soil, and the impact material. Through the testing of a variety of different numerical techniques, the optimal method for each case is determined based on the ability of each technique to accurately predict EEV acceleration, its ability to maintain computational stability during simulation, and its ease of use between various testing scenarios. It was determined through this process that more massive EEVs show a lower peak acceleration during impact due to their ability to penetrate the surface of the soil, extending the time of impact, and lowering the force applied by the soil per unit time. There was found to be a critical EEV orientation at 30⁰ from vertical such that the largest possible surface area of the EEV impacts the soil at one instant, resulting in a large spike in acceleration upon impact. Additionally, it was predicted that more massive EEVs be made into smaller, more sharply pointed geometries and less massive EEVs use larger geometries in order to minimize peak acceleration. Impact with concrete was estimated to increase acceleration by up to 650% when compared to soil impact acceleration. This work is intended to serve as an exploratory study into the validity of various impact simulation techniques, to be used in future in higher fidelity impact models. | en |
| dc.description.degree | MS | en |
| dc.format.medium | ETD | en |
| dc.identifier.other | vt_gsexam:12578 | en |
| dc.identifier.uri | http://hdl.handle.net/10919/87727 | en |
| dc.publisher | Virginia Tech | en |
| dc.rights | In Copyright | en |
| dc.rights.uri | http://rightsstatements.org/vocab/InC/1.0/ | en |
| dc.subject | Mars Sample Return | en |
| dc.subject | Earth Entry Vehicle | en |
| dc.subject | Soil Impact | en |
| dc.subject | Finite element method | en |
| dc.title | Impact Characterization of Earth Entry Vehicle for Terminal Landing (on Soil) | en |
| dc.type | Thesis | en |
| thesis.degree.discipline | Mechanical Engineering | en |
| thesis.degree.grantor | Virginia Polytechnic Institute and State University | en |
| thesis.degree.level | masters | en |
| thesis.degree.name | MS | en |
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