浅谈近岸、浅海海域波浪对船舶的危害——A轮沉没引发的思考

近岸、浅海海域的波浪与深海海域的波浪性质相异 ,航海驾驶人员必须特别重视 ,以防其造成船舶的浪损或更严重的海事发生。

A simplified model for extreme-wave kinematics in deep sea

Based on the fifth-order Stokes regular wave theory, a simplified model for extreme-wave kinematics in deep sea was developed. In this model, from the wave records the average of two neighboring wave periods for the extreme crest or trough was defined as the period of the Stokes wave by the up and down zero-crossing methods. Then the input wave amplitude was deduced by substituting the wave period and extreme crest or trough into the expression for the fifth-order Stokes wave elevation. Thus the corresponding formula for the wave velocity can be used to describe kinematics beneath the extreme wave. By comparison with the published numerical models and experimental data, the proposed model is validated to be able to calculate the extreme wave velocity rather easily and accurately.

A relationship between wave steepness and wave age for wind waves in deep water

Studying the relationship between wave steepness and wave age is important for describing wind wave growth with energy balance equation of significant waves. After invoking the dispersion rela- tion of surface gravity wave in deep water, a new relationship between wave steepness and wave age is revealed based on the “3/2-power law” (Toba, 1972), in which wave steepness is a function of wave age with a drag coefficient as a parameter. With a given wave age, a larger drag coefficient would lead to larger wave steepness. This could be interpreted as the result of interaction between wind and waves. Comparing with previous relationships, the newly proposed one is more consistent with observational data in field and laboratory.

Modification on Lynett and Liu’s model for internal solitary wave propagation over variable bathymetry

A two-dimensional, depth-integrated model proposed by Lynett and Liu (2002) was checked carefully, and several misprints in the model were corrected after detailed examination on both the theory and the numerical program. Several comparisons were made on wave profile, system energy and maximum wave amplitude. It is noted that the modified model can simulate the propagation of the internal solitary waves over variable bathymetry more reasonably to a certain degree, and the wave pro-files obtained based on the modified model can better fit the experiment data reported by Helfrich (1992) than those from original model.

Equilibrium scour depth at offshore monopile foundation in combined waves and current

Unlike the pier scour in bridge waterways,the local scour at offshore monopile foundations should take into account the effect of wave-current combination.Under the condition of wave-current coexistence,the water-soil interfacial scouring is usually coupled with the pore-pressure dynamics inside of the seabed.The aforementioned wave/current-pile-soil coupling process was physically modeled with a specially designed flow-structure-soil interaction flume.Experimental results indicate that superimposing a current onto the waves obviously changes the pore-pressure and the flow velocity at the bed around the pile.The concomitance of horseshoe vortex and local scour hole around a monopile proves that the horseshoe vortex is one of the main controlling mechanisms for scouring development under the combined waves and current.Based on similarity analyses,an average-velocity based Froude number(Fra)is proposed to correlate with the equilibrium scour depth(S/D)at offshore monopile foundation in the combined waves and current.An empirical expression for the correlation between S/D and Fra is given for predicting equilibrium scour depth,which may provide a guide for offshore engineering practice.