A high order accurate difference scheme for complex flow fields

A high order accurate finite difference method for direct numerical simulation of coherent structure in the mixing layers is presented. The reason for oscillation production in numerical solutions is analyzed, It is caused by a nonuniform group velocity of wavepackets. A method of group velocity control for the improvement of the shock resolution is presented. In numerical simulation the fifth-order accurate upwind compact difference relation is used to approximate the derivatives in the convection terms of the compressible N-S equations, a sixth-order accurate symmetric compact difference relation is used to approximate the viscous terms, and a three-stage R-K method is used to advance in time. In order to improve the shock resolution the scheme is reconstructed with the method of diffusion analogy which is used to control the group velocity of wavepackets. (C) 1997 Academic Press.

Effect of nonlinear wave-current interaction on flow fields and hydrodynamic forces

A fifth-order theory for solving the problem of interaction between Stokes waves and exponential profile currents is proposed. The calculated flow fields are compared with measurements. Then the errors caused by the linear superposition method and approximate theory are discussed. It is found that the total wave-current field consists of pure wave, pure current and interaction components. The shear current not only directly changes the flow field, but also indirectly does sx, by changing the wave parameters due to wave-current interaction. The present theory can predict the wave kinematics on shear currents satisfactorily. The linear superposition method may give rise to more than 40% loading error in extreme conditions. When the apparent wave period is used and the Wheeler stretching method is adopted to extrapolate the current, application of the approximate theory is the best.

Experimental investigation on low-temperature fatigue crack propagation in offshore structural steel A131 under random sea ice loading

An apparatus of low-temperature controlling for fatigue experiments and its crack measuring system were developed and used for offshore structural steel A131 under conditions of both low temperature and random sea ice. The experimental procedures and data processing were described, and a universal random data processing software for FCP under spectrum loading was written. Many specific features of random ice-induced FCP which differed with constant amplitude FCP behaviours were proposed and temperature effect on ice-induced FCP was pointed out with an easily neglected aspect in designing for platforms in sea ice emphasized. In the end, differences of FCP behaviours between sea ice and ocean wave were presented.