Analysis And Research On Water Entry Problem And Its Application In Ship And Ocean Engineering

Water entry problem is of concern in practical application and an important research topic in marine and ocean engineering field. Because of its moving solid boundary and free surface, the water enty model is very difficult to be numerically simulated. In free surface capturing method, this paper presents the incompressible Euler equations for a variable density fluid system as governing equations, and the free surface is captured as a contact discontinuity in density field. Furthermore, due to its convience for treating moving solid boundary by updating a few cut cells locally, Cartesian cut cell mesh system is taken to discrete computational domain. On this basis, a centered finite volume method is adopted for numerical calculation. Therein, Roe's approximate Riemann solver is used to obtain numerical flux on edge of fluid cell, where fluid variables are reconstructed by a piecewise linear expression. Then a least-square method is employed to calculate variable gradients, and limiter is introduced to restrict the false vibration near discontinuity solution. Besides this, the flux on solid boundary is computed by using exact Riemann discontinuous solution. Splitting scheme is used to eliminate the effect of discontinuity of static pressure variable on the calculation of pressure gradient. Dual-time stepping technique with artificial compressibility method is applied for time advancing. A full body-fluid coupled method is taken into account for extending the method to the free-falling water entry problem of rigid body. Four test cases (2D rigid wedge and circle section entering water with a constant velocity, and free-falling water entry models for wedge and ship section) are calculated to verify the efficiency and applicability of the above method.By the present method, synchronous water entry model of twin cylinders is solved. The results show that the interaction of twin cylinders has obvious influence on pressure distribution and hydrodynamic. Futhermore, it can be found that radius, distance and entry velocity of twin cylinders can affect the interaction. Then according to the three parameters, various different numerical tests for synchronous water entry of twin cylinders are designed. At different water entry phases, analytical expressions of Normal and Weibull distribution are numerically fitted to estimate the additional hydrodynamic on a cylinder. Finally, two arbitrary water entry models of twin cylinders are created to verify the analytical expressions and the results are satisfactory in engineering precision, thus the analytical expressions can be applied in the evaluation of additional hydrodynamic in practical water entry problem of twin cylinders. The above way can also be applied in the water entry problem of multi-bodies.In combination with the theories of a piston-type wave-making and sponge damping wave-absorbing, the present method of this paper is used to implement numerical wave flume. Then the effect of wave parameters (wave height, wave period, wave phase versus cylinder touching free surface, and so on) on the hydrodynamic is analyzed. By introducing the influence of wire tension into the motion equation of cylinder, water entry model of cylinder in wave by lifting operation is numerically simulated. Finally, according to various parameters of cylinder and wave, the tension variation of wire and motion characteristic of cylinder under different working conditions are mainly studied.In this section, finite element theory about rigid frame structure is taken to analyze the structural response. On the other hand, the present method is applied in calculation of fluid variables. Futhermore, the above two methods are combined by single-direction coupled method to deal with the hydroelastic problems. Free-falling water entry models of elastic wedge are numerically computed and the results are compared with experimental data to show the feasibility and validaty of the above method. Finally, the effects of different water entry parameters on global motion and local deformation of elastic wedge are discussed.In order to dynamicly simulate longitudinal gravity launching of a hull along a slipway, CFD software Fluent is used to calculate fluid variables. On the basis, the VC codes about 3D motion equations of ship launching are programmed for secondary development.159 000t oil carrier is taken for numerical example, and it can be found from the results that current method is available and feasible for the calculation of ship launching. Finally, based on the forebody of 298 OOOt oil ship launching from H3 slipway, the influence of various parameters of slipway and hull on motion of ship is studied and some meaningful conclusions are proposed to guide the practical engineering design.