Meeting Abstract

107.6  Saturday, Jan. 7  physical model of the feeding strike of the mantis shrimp COX, Suzanne M*; MODARRES-SADEGHI, Yahya; PATEK, Sheila; University Of Massachussettes, Amherst; University Of Massachussettes, Amherst; University Of Massachussettes, Amherst

The goal of this study is to combine physical and mathematical modeling in conjunction with measures of live animal performance to probe the mechanical design of the mantis shrimp’s extremely fast feeding appendage while also measuring the fluid dynamic effects of these movements, particularly focusing on the production of cavitation bubbles. Our physical model is driven in similar environmental conditions to our laboratory aquaria and is powered by a latch-released spring that maintains the radial motion, scale, maximum velocity and acceleration that closely approximate a mantis shrimp’s strike (Gonodactylaceus smithii"). We varied spring constant, force and delivery time while holding appendage dimensions constant as an aluminum cylinder that is similarly sized to the study animals. We developed and applied a mathematical model based on spring mechanics, beam theory and linkage mechanics and used it to hone the spring design and linkages of the physical model. Velocity and acceleration were calculated from high speed images (30,000 fps) of the model and live mantis shrimp as were cavitation presence, absence, and onset speed. Ten strikes from each of 5 animals were analyzed with an average velocity of 18 m/s and acceleration of 2x104 m/s2. The model produced velocities up to 29 m/s and accelerations to 3x104 m/s2. Our key findings were that G. smithii appendages cavitate on impact and rarely cavitate in forward motion. The model cavitates on impact, but it also cavitates in forward motion at speeds where none was seen in animals. This indicates that one or more of the model's simplifications are fluid dynamically relevant for cavitation onset and suggests exploration of the relevance of the of shape, material and surface properties of the appendage.