Frequency domain wave equation forward modeling using gaussian elimination with static pivoting

Frequency domain wave equation forward modeling is a problem of solving large scale linear sparse systems which is often subject to the limits of computational efficiency and memory storage. Conventional Gaussian elimination cannot resolve the parallel computation of huge data. Therefore, we use the Gaussian elimination with static pivoting （GESP） method for sparse matrix decomposition and multi-source finite-difference modeling. The GESP method does not only improve the computational efficiency but also benefit the distributed parallel computation of matrix decomposition within a single frequency point. We test the proposed method using the classic Marmousi model. Both the single-frequency wave field and time domain seismic section show that the proposed method improves the simulation accuracy and computational efficiency and saves and makes full use of memory. This method can lay the basis for waveform inversion.

Wash Waves Generated by High Speed Displacement Ships

It is difficult to compute far-field waves in a relative large area by using one wave generation model when a large calculation domain is needed because of large dimensions of the waterway and long distance of the required computing points. Variation of waterway bathymetry and nonlinearity in the far field cannot be included in a ship fixed process either. A coupled method combining a wave generation model and wave propagation model is then used in this paper to simulate the wash waves generated by the passing ship. A NURBS-based higher order panel method is adopted as the stationary wave generation model; a wave spectrum method and Boussinesq-type equation wave model are used as the wave propagation model for the constant water depth condition and variable water depth condition, respectively. The waves calculated by the NURBS-based higher order panel method in the near field are used as the input for the wave spectrum method and the Boussinesq-type equation wave model to obtain the far-field waves. With this approach it is possible to simulate the ship wash waves including the effects of water depth and waterway bathymetry. Parts of the calculated results are validated experimentally, and the agreement is demonstrated. The effects of ship wash waves on the moored ship are discussed by using a diffraction theory method. The results indicate that the prediction of the ship induced waves by coupling models is feasible.

WAVE EQUATION MODEL FOR NUMERICAL SOLUTIONS OF ADVECTION－DOMINANT HEAT TRANSFER

In this paper the wave equation model (WEM) [1] is extended to solve advection-dominant heat transfer problems in multi-dimensional space. Based on the operator-splitting method the heat transfer equation is divided into an advection equation and a diffusion equation which are solved separately. In advection stage the first order advection equation is transferred to a second order wave equation first, than the wave equation is solved by FEM with mass lumping. The diffusion equation can be solved accurately without many difficulties. A number of numerical examples of multi-dimensional advection are presented in which the advection velocities are non-uniform in space and unsteady in time. The numerical results are quite accurate in comparison with the exact solutions.The mass lumping saves computational effort greatly.

MASS CONSERVATION BEHAVIOR OF WAVE EQUATION MODEL FOR SOLVING SHALLOW WATER EQUATIONS

Wave equation model (WEM) first developed by Lynch and Gray [2] is one of accurate and effective numerical methods to resolve shallow water equations. This paper shows the numerical consistency of the second-order wave equation and the first-order continuity equation, analyzes the error between them. This paper also shows that the numerical friction factor τ0 appearing in wave equation is of key importance to the numerical solutions and mass conservation of wave equation model. Numerical calculations of M2 tidal waves in rectangular harbor and a quarter annular harbor are made to demonstrate that it is possible to find a proper numerical friction factor To with which accurate solutions and satisfactory mass conservation can be achieved by wave equation model.

RATIONAL FORM SOLITARY WAVE SOLUTIONS FOR SOME TYPES OF HIGH ORDER NONLINEAR EVOLUTION EQUATIONS

In this paper, three types of nonlinear evolution equations such as (2n + 1)th order KdV equation, etc, are studied. And their solitary wave solutions of rational form obtained are available and possess the simplest form so far. At last, the Hamiltonian form of (2n + 1)th order general KdV equation is generalized.

THE LONG WAVE OSCILLATIONS IN HARBORS WITH ABSORBING BOUNDARY CONDITIONS

This paper employs finite element method to solve shallow water equations with absorbing boundary conditions(the third kind,mixed boundary conditions).It is of practical importance in the cases that the land boundaries of the coastal area are made of porous medium allowing sea water flow in or out.The absorbing boundary conditions are treated as natural boundary conditions in wave equation finite element model.The numerical results for rectangu- lar and quarterly annular harbors indicate that the numerical solutions agree very well with ana- lytic solutions,which are also given in this paper.It is found that the land boundary absorbabili- ty may be significant to long wave oscillations,such as tidal waves in coastal harbors.