Elastic Bottom Effects on Ocean Water Wave Scattering by a Composite Caisson-Type Breakwater Placed Upon a Rock Foundation in a Two-Layer Fluid

The association of oblique surface gravity waves with a caisson-type multi-chamber porous breakwater fitted with a perforated front wall in a two-layer fluid is studied in finite ocean depth with an elastic bottom. This study focuses on the influence of porous parameters of the interface-piercing structure on wave attenuation in surface and interfacial modes. The flexural gravity wave motion establishes the influence of the elastic bottom. The reflection coefficients for waves in both modes are evaluated to show their effects on the free surface and interface elevations and the waveloads. Consequently, the appropriateness of various configurations of the structure on the wave scattering is studied. Due to wave dissipation by the structure, less waveload is detected on the stiff wall and less elevation is noticed in the porous zone. The structure’s multi-chamber division allows it to have more dissipative and reflective properties. Adjustment of the structure’s height, breadth, and porous parameter leads to achieving good amount of wave reflection and maximum energy dissipation. An optimal width can be determined for a suitable configuration of the structure so that a breakwater can be built with an acceptable level of reflection and dissipation characteristics. The shear force and bottom deflection show how elastic parameters of the sea-floor affect wave scattering.

Sound diffraction on an elastic spheroidal shell

Object and purpose of research. This paper obtains solutions and performs estimations of characteristics of sound reflection and scattering by ideal and elastic bodies of various shapes (analytical and non-analytical) near media interface, or underwater sonic channel, or in a planar waveguide with a solid elastic bottom. Materials and methods. The harmonic signals are investigated with the method of normal waves based on the phase velocity of signal propagation, and impulse signals related to the energy transfer are studied using the method of real and imaginary sources and scatterers based on the group velocity of propagation. Main results. The scattered sound field is calculated for ideal spheroids (elongated and compressed) at fluid – ideal medium interface. The spectrum of a scattered impulse signal is calculated for a body placed in a sonic channel. First reflected impulses are found for an ideal spheroid in a planar waveguide with anisotropic bottom. Conclusion. In the studies of diffraction characteristics of bodies at media interfaces it was found that the main contribution to scattered field is given by interference of scattered fields rather than interaction of scatterers (real or imaginary). It is shown that at long distances the spectral characteristics of the channel itself have a prevalent role. When impulse sound signals in the planar waveguide are used, it is necessary to apply the method of real and imaginary sources and scatterers based on the group velocity of sound propagation.

Experimentally Measured Hydroelastic Effects on Impact-Induced Loads during Flat Water Entry and Related Uncertainties

Extensive water entry experiments were performed to identify uncertainties associated with measured impact-induced loads acting on flat bottom ship structures. Of primary concern was the influence of air trapping on elastic structural deformations. The experimental measurements supplied benchmark data suitable to validate CFD predictions. Two bodies were tested. One body was fitted with stiffened, rigid bottom plating; the other body, with thin elastic plating. A large number of 30 repetitive runs recorded bottom pressures and forces acting on the flat bottom plating and monitored impact-induced elastic bottom strains. For each test case, high-speed videos of water entry sequences were evaluated. The resulting average peak values standard deviations quantified the uncertainty of these measurements.