Design and Analysis of Soft Structures for Underwater Applications

Traditional engineering structures are made of rigid structures with simple geometry, such as ship hulls and wind turbine blades. In contrast, recent advancements in manufacturing open the door to designing and manufacturing soft structures with programmable and unconventional functionalities. An optimal and efficient design of these soft structures interacting with external loads, such as fluids, remains challenging. In this talk, I will discuss how a combined physics-based modeling and machine-learning approach can help tackle the challenges. 

The key challenges involve the extraordinarily large structural design space and large structural deformation that are not amenable to conventional analytical tools. I will introduce a symmetry-constrained machine learning technique, combining Variational Autoencoder and Bayesian Optimization, to design soft composite shells of targeted functionalities. These soft composites – without rigid springs and hinges - are manufactured by combining kirigami and pre-stretch and can be scalably fabricated on a 2D plane. Despite fully planar fabrication, they can be programmed to assume a prescribed 3D shape without any external stimulus. We extended the design to structures with multistability. We demonstrate its effectiveness using soft grippers that gently grasp delicate objects of different shapes and sizes. 

Furthermore, we explore the snap-through buckling process of these bistable structures driven by fluid flows, modeling the fluid-structure interaction coupling via the Arbitrary Lagrangian-Eulerian method. We find additional design factors, such as the Cauchy number, must be considered when these soft bistable structures interact with fluid flows. A predictive model for the dimensionless strain energy as a function of the Cauchy number is proposed. We also find that bistable structures exhibit larger steady-state deformation than mono-stable structures in the same flow conditions. The research could provide insight into designing morphable marine energy devices and lightweight bioinspired propulsion systems.