Fully Nonlinear Slamming Investigation Of A Floating Body Freely Falling Into Wave With Three Degrees Of Freedom

In the field of ship and ocean engineering,the problem of water entry is very common.For example,the bow entry,the installation of the offshore platform,the seawater bump and torpedo launching are also closely related to the problem of water entry.Due to the strong non-linearity of waves and the transient process between the object and waves,there are few researches on the slamming of waves entry.In view of this,based on time-domain higher-order boundary element,present thesis adaptes the numerical simulation method to establish a fully nonlinear model of an object into the wave,focusing on regular wave and solitary wave slamming response mechanism.In addition,a floating body with air cavity is studied under the condition of wave invironment.In this thesis,a higher order boundary element model of wedge entrying into regular wave is established.In order to avoid the calculation error caused by mesh division,the stretching coordinate system is used for mesh division,and the vertical displacement of the wedge-shaped weight center is chosen as the stretching proportion.When the mesh is divided,the non-uniform mesh is adopted.The larger the mesh is away from the object surface,and the maximum value of the mesh is set.The grid and velocity potential are updated under the mixed Eulerian-Lagrange framework,in other words,the distance and bottom are updated with Eulerian coordinates,and the free surface is updated with Lagrange coordinates.The acceleration of wedge is solved by the method of auxiliary function.Since the wedge is assumed to be of infinite width,the coordinate of the liquid surface on the object surface is updated by using the rotating coordinate system to avoid the fluid particles from or invading the object surface.When simulation model runs over time,the mesh will produce sawtooth,and then the five-point smoothing method is used for smoothing processing.Verify the different minimum grids and select the moderate grid as the basis for the following calculation.From this,the influences of the parameters such as amplitude,wavelength,wedge heel angle,fixed angle and initial entry speeds on the water slamming and the law are studied.Secondly,the wave environment is expanded from regular waves to extreme waves,which adopt representative solitary wave.Solitary wave are simulated by using the third order analytical solution of Korteweg-de Vries equation as incident boundary conditions.Since the solitary wave is more nonlinear than the regular wave,the convergence of the grid is further verified.Thereafter,the the parameters influence of solitary wave,wedge and initial entry velocity on the slamming of wedge into solitary wave is studied.Finally,a floating body with cavitation is studied when it enters water and the wave is still a regular wave.Since the cross section is a semicircle,the flow will be separated along the bend angle.When the water on the left and right sides come into contact,the air will be enveloped,and the air will be enclosed by the semicircle below and surrounding water to form a closed cavitation.The effect of cavitation on slamming is studied.The process of cavitation closure is treated by double local stretch coordinate system.The fluid-solid-gas three-phase slamming problem involving air is preliminarily studied,which lays a foundation for further study of three-phase slamming problem.