Dissertation Defense: Validating FSI Simulations in LS-DYNA 971

Committee

• Professor Amos Gilat, Chair (ME)
• Professor Brian Harper (ME)
• Professor Chia-Hsiang Menq (ME)
• Professor Herman Shen (ME)

Abstract

Analytical solutions to fluid-structure interaction (FSI) problems provide a powerful design tool that has many applications within the automotive industry. The interaction of body panels with various fluid flows is of interest. Automotive panels that are made too thin become susceptible to a phenomenon known as oil-canning. The deformation can be temporary, or if the loading is large enough the panel can snap through resulting in permanent deformation. One common occurrence of oil-canning is when going through the dryer section of an automatic car wash. If the roof panel is made too thin it is susceptible to oil-canning. For small deformations the panel can shift between various unstable elastic configurations resulting in loud popping noises within the passenger compartment. Large deformations can result in permanent deformation and pitting of the roof panel. Automotive underbody panels are susceptible to water shock loadings that can be generated when driving over a puddle at high speeds. Panels that are made too thin can be permanently deformed or even fail in some cases when the water shock loading is strong enough. Accurate simulations of these scenarios are of interest since thinning body panels provides an easy way to realize significant weight reduction and increase fuel economy. An experimental program is introduced where full size automotive roof panels are subjected to air blast loading. The panels are stamped from thin alloy sheet steel. Concurrent simulations will be performed and compared to the experimental data from this study to assess the validity of the numerical results. Roof panels are loaded into a custom test rig and clamped along the weld flanges. The air blast is generated using a commercial air compressor and a 35.1mm pipe. Force imparted on the panel by the air jet is measured by three load cells and full-field displacement data is captured using three-dimensional digital image correlation (DIC). The flow field is characterized using piezo-resistive pressure transducers placed in a sensor bar apparatus that can be swept across the flow field to generate pressure maps. Water jet experiments are performed on automotive underbody panels stamped from thin aluminum sheet. The panels are bolted into a custom test rig and the water jet loading is generated with a commercial pressure washer. The force on the panels is measured with four load cells and full-field displacement data is obtained from the back side of the panel using three-dimensional digital image correlation. The flow field is characterized using a commercial pressure measurement system consisting of a thin tactile membrane sensor and software to record the resulting pressure contours in real time. The flow field is also characterized through the use of high speed cameras mounted orthogonally to obtain jet velocity measurements and qualitative properties. Additional experiments are performed on the underbody panels using a water cannon that fires a slug of water contained within a latex balloon at high velocity in an effort to permanently deform the underbody panels.