Mechanical and Civil Engineering Seminar

Abstract: Our curiosity and spirit for exploration has fueled advancements towards visiting Earth's neighbors in the solar system. Environments outside of Earth are extreme, however, and it is far from guaranteed that landing and operating on the surface of these bodies is an easy task. Conditions such as reduced gravity, extreme temperatures and sparse atmospheres play a role in the compressive, shear and tensile strength of a surface. These environmental factors make experiments that work to inform design decisions for spacecraft-surface interaction difficult and expensive. In order to better ensure successful mission operations in the future, this defense focuses on the development of a platform of numerical modeling for planetary surface interaction.

Dry granular matter and water ice are two surface materials that are pervasive in the solar system. For each the mechanical properties are heavily reliant on features at the micro scale that are insufficiently modeled using current methods. The first part of the defense will focus on crushable dry regolith. Here, a novel modeling capability for capturing both highly irregular particle shapes and breakage in granular matter will be developed. This will be followed by the validation of this method on a crushable sand sample experiment. This model demonstrates excellent predictive capability for the constitutive relationship, the evolution of particle sizes and the evolution of particle shape in the sample.

Unlike dry regolith, distinct neighboring water ice particles will sinter together over time at varying rates depending on their environment. This leads to a large amount of the water ice surfaces, that are of interest to future missions, having a highly varied and many times unknown levels of strength. The contact interaction between water ice particles at the microscale will be handled the same as regolith, however a modification was added to account for sintering. The strong cohesiveness sintering generates is modeled by placing massless bonds where sinters would form. The bonds used are breakable in order to capture the crushable nature of porous ice. Comparisons show that the model can produce similar stresses and qualitative features observed in the experiment. Further, the landing of a footpad on the surface of Enceladus is modeled. The model predicts that a lack of sintering could result in catastrophic sinkage, however even moderate sintering provides enough strength to support a lander. Also the model predicts landing on inclined surfaces and shows that landing could be possible at angles as high as 20 degrees.

Please virtually attend this thesis defense:

Zoom link: https://caltech.zoom.us/j/83712749006?pwd=K25ja2RJdWl4LytML2pGQVZrbWsxZz09