Stress control of cylinders during water entry based on the characteristics of bi-material interfaces

This paper is devoted to stress control of cylinders during water entry based on the characteristics of bi-material interfaces. Firstly, the influence factors on dynamic stress are studied from the view of elastic mechanics and wave mechanics. It is found that the dynamic stress depends on the material parameters, material layout, natural frequency and deformation. On this basis, a sandwich scheme is proposed to reduce the stress level of the cylinder entering water. Then a sandwich cylinder, two bi-layer cylinders and two monolithic cylinders during water entry are investigated by coupling of smoothed particle hydrodynamics (SPH) and finite element method (FEM). It is found that when the material parameters are given, the deformation and natural frequency of the sandwich cylinder are moderate, but its stress level is significantly lower than that of other cylinders under the same initial conditions, attributing to its unique material layout. Accordingly, the limit velocity of the sandwich cylinder colliding with water is much higher than that of other cylinders. Therefore, the stress control scheme is expected to reduce the possibility of strength failure of cylindrical structure during water entry.