Aerospace Engineering Ph.D. Dissertation Proposal: Development of Adaptive Granular Crystals Immersed in Active Fluids for Impact Mitigation by Hrachya Kocharyan

Friday, February 09, 2018
2:00 pm to 3:30 pm
Floor/Room #: 

Hrachya Kocharyan
Ph.D. Dissertation Proposal
Aerospace Engineering


Numerous numerical and experimental efforts in literature have extensively investigated the wave propagation through cohesion-less dry granular media. However, wave propagation through wet granular media has not garnered adequate attention. The cohesion-less nonlinear elastic interactions in dry granular media are well understood, whereas the influence of cohesive forces at inter-particle contacts along with dissipative effects complicate wave dynamics of wet granular media.  A drop-tower based experimental setup was developed to investigate wave propagation through 2D assembly of cylindrical particles completely submerged in a secondary fluid medium. The submerged granular assemblies of polyurethane cylinders of approximately 1ʺ in length and 1/2ʺ in diameter were arranged into two different 2D configurations: cubic and hexagonal. These granular assemblies were subject to impact loading using a rigid impactor at a velocity of around 6 m/s. The deformation of the granular assemblies under impact loading was recorded by a high-speed camera at frame rates around 4000-8000 fps. The kinematics and the strain fields in each individual particle were computed using digital image correlation (DIC). Subsequently, the experimental strain and kinematic measurements in each particle in conjunction with a Granular Element Method (GEM) based mathematical framework was employed to infer the inter-particle forces at each contact in granular assembly. However, a conventional GEM method cannot describe the influence of secondary fluid medium around the individual particles and hence a modified mathematical framework is needed to account the additional force and viscous effects experienced by each particle as a result of the local fluid pressure. The aforementioned experimental and numerical techniques were utilized to investigate the wave propagation through granular assembly submerged in fluids of different viscosities under impact loading. These impact loading experiments were also supplemented by some vibration experiments on submerged granular media using an electrodynamic shaker and laser scanning vibrometer. Moreover, the role of defects on wave propagation in granular materials as well as defect interactions were investigated. With non-Newtonian fluids like shear-thickening fluids and magnetorheological fluids, controlled defects were introduced to investigate and develop metamaterials to control acoustic waves in granular materials. The goal of this research is to develop adaptive granular crystals immersed in active fluids for impact mitigation.

Prof. Michael Demetriou