Experimental study of cavity evolution and deformation during water entering into hyperelastic sphere

Abstract

Hyperelastic materials, which have strong nonlinear mechanical properties, are commonly used in the engineering field. The application of hyperelastic materials to the water entry problem is a new interdisciplinary research topic. Unlike the water entering into a traditional rigid sphere, the hyperelastic sphere is very easy to deform during water entry. In order to explore the fluid-structure coupling problem with large deformations during water entry, a high-speed camera is used to study the problem of vertical water entering into hyperelastic sphere in this paper. Based on the experimental results, the effects of the material properties and impacting conditions on the cavity flow and sphere deformation behaviors during water entry are compared and analyzed. The experimental results show that the formation of the nested cavity after impacting a free surface of the hyperelastic sphere needs large enough impact conditions and small material shear modulus. The time for the nested cavity to be formed and retained during water entry is related to the material shear modulus and sphere diameter. The sphere displacement and length of cavity formed by the hyperelastic sphere increase with the increase of the impact velocity and material shear modulus, but decrease with the increase of the diameter of the sphere. The increase of the impacting velocity can only aggravate the deformation behaviors of the hyperelastic sphere, but does not affect the formation moment of the nested cavity. In addition, the characteristics for the deformation behaviors of the hyperelastic sphere to vary with the Froude number and the dimensionless ratio of material shear modulus to impacting hydrodynamic pressure are described and studied.