Study On Coupling Numerical Simulation Method Of Freely Water Entry Of Plate Frame Structure

Slamming of water entry is very common in the field of ship and ocean engineering.In order to predict slamming load of hull into water accurately,various numerical calculation methods emerge at the historic moment,and boundary element method based on potential flow theory is one of the most widely used numerical methods.When the plate-frame structure enters the water,the plate-frame structure will generate high-frequency elastic vibration under the slamming load of the water.Previous studies did not consider the coupling between this high-frequency elastic vibration and hydrodynamic force,but regarded the water-entry structure as a rigid body.In order to explore the influence of high-frequency elastic vibration on the fluid force when the plate frame enters the water,and considering that the traditional potential flow method can't capture the high-frequency change characteristics of the fluid force,this paper studies the fluid slamming force considering the high-frequency elastic vibration of the plate frame by Fortran programming based on the Double Asymptotic Approximation method(DAA)which takes into account the fluid compressibility,and uses ABAQUS to calculate the high-frequency elastic vibration of the plate frame under the fluid slamming force,and establishes an interface to achieve the fluid-structure coupling calculation.The main research contents of this paper are as follows:(1)The experimental study on slamming of rigid and elastic wedge-shaped plate frame structure was carried out.The results show that the elastic vibration of the structure may reduce the peak value of slamming pressure,which provides the experimental basis for numerical simulation;(2)Based on the potential flow theory,a method for solving the rigid body water entry problem is proposed.The water entry process of the rigid wedge is solved by the fully nonlinear boundary element method,which is in good agreement with the experimental results of the rigid wedge,and the slamming pressure peak is predicted accurately.Through the sensitivity analysis of the factors influencing the slamming pressure peak value and the slamming pressure coefficient k;(3)Considering the influence of the response speed of the structure,fully nonlinear boundary element method is coupled with the response speed of the elastic wedge-shaped plate frame structure ABAQUS solves,and the results are compared with the experimental results,the numerical results are in good agreement on the extremum,and the sensitivity analysis of the extremum of the longitudinal bone stress response is studied;(4)The potential flow theory can solve the problem of considering the local response speed of the structure,but there are defects in the problem of considering the local acceleration of the structure.Therefore,it is suggested that the local acceleration of the structure should be considered and the compressibility of the fluid should be considered.The double asymptotic approximation method is derived by the delay potential equation considering compressibility,and the feasibility and accuracy of the double asymptotic approximation method are verified by comparing the numerical results with the analytical results of jet impinging on a flat plate;(5)The double asymptotic approximation method is applied to the water entry problem of two-dimensional elastic wedge,and a method is proposed to solve the water entry slamming problem of elastic structures.The influence of different difference forms on the solution process is studied.The influence of different influence factors on the slamming pressure peak and slamming pressure coefficient of the structure is analyzed,and the same law as the potential flow theory is obtained;(6)The doubly asymptotic approximation method is used to solve the problem of jet impacting wedge plate problem,and the effect of stiffness on the structural response is studied.It is found that with the increase of elastic modulus,moment of inertia and the stronger of structural constraints,the larger the response pressure,the shorter the response time of the structure are produced,and the earlier the stable vibration stage is reached.