Multi-directional Irregular Waves Research Articles

Second-order wavemaker theory for multidirectional waves

The present paper develops the complete second-order wavemaker theory for the generation of multidirectional waves in a semi-infinite basin. The theory includes superharmonics and subharmonics and is valid for a rotational as well as a translatory serpent-type wave-board motion. The primary goal is to obtain the second-order motion of the wave paddles required to get a prescribed multidirectional irregular wave field correct to second order, i.e. to suppress spurious free-wave generation. The wavemaker theory is a 3D extension of the full second-order wavemaker theory for wave flumes by Schäffer (1996).

Numerical modeling of multi-directional irregular waves incorporating 2-D numerical wave absorber and subgrid turbulence

In this paper, a finite difference scheme with an efficient 2-D numerical wave absorber for solving the extended Boussinesq equations as derived by Nwogu (Nwogu, O., 1993. Alternative form of Boussinesq equations for nearshore wave propagation. J. Waterway, Port, Coastal and Ocean Engineering, ASCE 119, 618–638) is proposed. The alternate direction iterative method combined with an efficient predictor-corrector scheme are adopted for the numerical solution of the governing differential equations. To parameterize the contribution of unresolved small-scale motions, the philosophy of the large eddy simulation is applied on the horizontal plane. The proposed method is verified by two test cases where experimental data are available for comparison. The first case is wave diffraction around a semi-infinite breakwater studied by Briggs et al. (Briggs, M.J., Thompson, E.F., Vincent, C.L., 1995. Wave diffraction around breakwater. Journal of Waterway, Port, Coastal, and Ocean Engineering, ASCE 121, 23–35). The other case is wave concentration by a navigation channel as reported by Yu et al. (Yu, Y.-X., Liu, S.-X., Li, Y.S., Wai, O.W.H., 2000. Refraction and diffraction of random waves through breakwater. Ocean Engineering 27, 489–509). Numerical results agree very well with the corresponding experimental data in both cases.

Numerical modelling of multi-directional irregular waves through breakwaters

A numerical model based on the time domain solution of the Boussinesq equations using the finite element method is described in this paper. The propagation of multi-directional irregular waves in water of varying depth can be simulated using the present model and there are no limitations on the form of incident waves. The validity of the model had been demonstrated by Li et al. (cf. Y.S. Li et al., Numerical modelling of Boussinesq equations by finite element method, Coastal Engineering 37 (1999) 97–122) using several test cases where the incident wave is sinusoidal. In this paper, the propagation of multi-directional irregular wave over an elliptical shoal was first modelled to demonstrate the versatility of the finite element method. The multi-directional irregular wave diffraction around a semi-infinite breakwater and through a breakwater gap is then simulated to further validate the numerical model. Good agreements are observed between the numerical and experimental results. The results also show that the directional spreading of the incident waves has a significant effect on the wave diffraction and leads to a distinct diffraction contour compared with that of unidirectional waves. The computed results show that the model can be applied to solve practical engineering problems involving multi-directional irregular waves.

Estimation method of slowly varying wave drift force acting on very large floating structures

It is necessary to estimate slowly varying drift forces on very large floating structures (VLFS) for their safety. The aim of our research is to develop an estimation method of such forces on VLFS in the real seas, i.e. in multidirectional irregular waves. We knew such a method for rigid bodies, but it seems to be complicated to extend the method for VLFS directly because of their hydroelastic behavior. Thus, in the previous report, we presented an easy but legitimate estimation method in which we can evaluate slowly varying drift forces by means of the integration of the squared relative wave height and also we validated our method with model tests in long crested irregular waves. In this 2nd report, we carried out a numerical calculation with various flexural rigidities of VLFS, incident angles, and incident wave periods to validate our method more generally. We also validated our method with model tests in short crested irregular waves so that we can demonstrate our method can be applied for VLFS in multidirectional irregular waves.

Estimation method of slowly varying wave drift force acting on very large floating structures

It is necessary to estimate slowly varying drift forces on very large floating structures (VLFS) for their safety. The aim of our research is to develop an estimation method of such forces on VLFS in the real seas, i.e. in multidirectional irregular waves. We knew such a method for rigid bodies, but it seems to be complicated to extend the method for VLFS directly because of their hydroelastic behavior. Thus, in the previous report, we presented an easy but legitimate estimation method in which we can evaluate slowly varying drift forces by means of the integration of the squared relative wave height and also we validated our method with model tests in long crested irregular waves. In this 2nd report, we carried out a numerical calculation with various flexural rigidities of VLFS, incident angles, and incident wave periods to validate our method more generally. We also validated our method with model tests in short crested irregular waves so that we can demonstrate our method can be applied for VLFS in multidirectional irregular waves.

Consideration of the Phase Plane of the “Directional” Grouping Wave

Goda and Longuet-Higgins originally reviewed the grouping wave. However, we can find few studies on the grouping wave in the literature after them. It has been known that the grouping wave is strongly related to the break of mooring lines of a vessel in a port. In the mega-float case, especially, this problem will become a severe one due to no past experience in real design. This paper discusses the characteristics of the grouping wave. The directional grouping wave is defined from the multi-directional regular wave and also the complex grouping wave is reduced from the multi-directional irregular wave.

Effectiveness of an Array of Offshore Breakwaters for Irregular Waves

Wave transformation by an array of offshore breakwaters is examined in multi-directional irregular waves. Especially, concerning the ratio of an array pitch length to a representative wave length, plane wave interactions with the arrayed breakwaters are examined extensively. It is pointed out that the wave height variation behind the breakwater array changes from a long-crested pattern to a shortcrested one with increasing a pitch length of periodically arrayed breakwaters as compared to a wave length.

Experimental Study on Breaking Wave Deformation and Current of Short-Crested Waves on the Slope

Shoaling deformation of short-crested waves acting on the slope is investigated experimentally. Power and direction-al spectra, wave height and steady current velocity on the slope are compared among regular, uni- and multi-directional irregular waves. The application of the conventional formula proposed based on long-crested wave experiments is also discussed.

波向の定義に着目した多方向不規則波浪の波別解析法の検討

波向の定義に着目した多方向不規則波浪の波別解析法の検討

多方向不規則波の造波信号発生法に関する検討

多方向不規則波の造波信号発生法に関する検討