Numerical Simulation Of Steep Waves Based On New Wave Theory

In order to predict the loads and the responses of offshore structures accurately in various sea states, especially in extreme conditions, wave-model tests are often performed in the laboratory, including tank tests and numerical simulation. It is known establishing the appropriate wave model is the crucial part of this process.The "new wave" theory was originally proposed by Tromans in the 1990s. In summary, the "new wave "theory combines the probability theory and random wave theory by introducing conditional probability to determine the amplitudes η_n and phase angles φ_n,which makes it possible to obtain the target waves with greatest amplitude or steepness at specific location and time. In the meantime, it provides theoretical foundation for establishing new wave model. In the new wave theory, the random ocean surface can still be described by superimposing a series of regular wave components in the same way as do in random wave. However, compared with the random wave theory, the new method can avoid the disadvantages and obtain the desired extreme waves.It has been hold that the amplitude of wave is the major concern when computing forces the offshore structures experience. But the data reveals that waves with great steepness can cause strong nonlinear effects, leading to the damage, slamming.In this paper, the new wave theory is extended to establish steep wave model, which results in the wave shape with asymmetric surface. Based on new wave theory, consider a transformation function (?). When this transformation is applied to the wave height, it produces a combination of the wave height and the wave steepness, then, the wave spectrum is transformed to attain amplitudes and phase angles of each regular wave that constitutes the wave surface. The calculated results are compared with those obtained by experiments. Velocity and acceleration of water particles in wave field are calculated and analyzed, as well as the pressure profile .Then these parameters are compared when steepness coefficient takes different values .It can be seen that the "new wave" has great potential in numerical simulation of extreme waves from the outcome of comparison, which presents an effective and economical method to the simulation of extreme sea states on computer.