Near Trapping Effect on Wave-Power Extraction by Linear Periodic Arrays

Near trapping is a kind of strong hydrodynamic interaction phenomenon in a regular array under specific incident wave conditions, which causes the excitation force on the structures in the array to change suddenly. In this paper, based on linear potential flow theory, the effects of near trapping on the hydrodynamic interaction and wave-power extraction characteristics of linear periodic arrays composed of the oscillating float type wave energy converters are studied by using the higher-order boundary element method in a frequency domain. The parameters considered include the separation spacing, number of devices, and incident wave direction. It is found that the near trapping significantly reduces the overall wave-power extraction, especially for the cases with a large number of devices, and changes the trend of the power distribution. The occurrence of the near trapping phenomenon depends on the ratio of the separation spacing to the wavelength and the incident wave direction. The results highlight the effective layout of linear arrays under the influence of near trapping, which not only ensures the total production power, but also reduces the power difference among wave energy converters.

Homogeneous near-perfect invisible ground and free space cloak

A general approach to design near perfect invisible ground and free space cloaks is introduced in this paper. The proposed method which is based on the optical transformation theory, leads to homogeneous constitutive parameters for the cloaks without any singularities. Moreover, the single-step mapping process with linear relations achieves an uncomplicated designing process. Invisibility performance obtained by using this approach does not depend on the incident wave direction, also. The simplicity and design flexibility of the introduced approach with the homogeneity of extracted parameters greatly facilitate the design and fabrication processes of the both proposed ground and free space invisible cloaks. The numerical simulations prove the capability and universality of the proposed design approach.

Numerical Study of Wave Diffraction with Four Cylinders

By taking the 3D Laplace equation as the basic governing equation, a mathematical model with respect to the interaction between linear waves and arbitrary 3D structures was founded. With an example of wave action with four cylinders, numerical results show that when incident wave direction is 22.5°, wave force Fx on 1# cylinder and 2# cylinder is the biggest and when incident wave direction is 0°, wave force Fx on 3# cylinder and 4# cylinder is the biggest; wave force Fy and the wave height on origin point increases with incident wave direction increasing for the given layout and incident wave conditions.

PREDICTION OF DEVELOPMENT OF SAND SPITS AND CUSPATE FORELANDS WITH RHYTHMIC SHAPES CAUSED BY SHORELINE INSTABILITY USING BG MODEL

The BG model (a three-dimensional model for predicting beach changes based on Bagnold’s concept) was used to simulate the shoreline evolution caused by the high-angle wave instability discussed by Ashton et al. Three calculations were carried out: the wave direction was assumed to be obliquely incident from 60˚ counterclockwise (Case 1) or from the directions of ±60˚ with probabilities of 0.5:0.5 (Case 2) and 0.65:0.35 (Case 3), while determining the incident wave direction from the probability distribution at each step. The three-dimensional development of multiple sand spits and cuspate forelands with rhythmic shapes was successfully explained using the BG model. The results of the previous study conducted by Ashton et al. were reconfirmed and reinforced.

Hydrodynamic Analysis of Oil Storage Vessels for National Strategic Petroleum Reserve

This paper expatiates hydrodynamic time-domain analysis on strategic oil storage vessels in free floating condition or with dolphin-fender mooring system by means of AQWA numerical software. The results indicate that motion responses of the oil storage vessel with dolphin-fender mooring have improved significantly. The time-history of wave diffraction forces in incident wave direction are basically consistent between the free floating and moored condition. However, in vertical direction of incident wave, the diffraction wave force of the oil storage vessel in free floating condition is obviously different from that with mooring system, which is the result of the coupling interaction between dolphin and vessels. Mooring forces include fender reaction and cable tension, as for which dominate, it depend on evocable motion responses about incident wave direction.

Wave Interaction With a Rectangular Pit

A Green function approach is utilized to investigate wave interaction with a rectangular pit of finite dimensions in water of otherwise constant depth. The fluid domain is divided into two regions: an interior region which is finite in extent and represents the pit itself, and an exterior region consisting of the remainder of the fluid domain. An integral equation solution utilizing an appropriate Green function in the exterior region is linked to an interior solution in the form of a Fourier expansion containing unknown potential coefficients through matching conditions at the imaginary interface between the two regions. Discretizing the integral equation leads to a matrix system for these potential coefficients which may be solved using standard matrix techniques. Numerical results are presented for several example geometries which illustrate the effect of pit characteristics and incident wave direction on the water surface elevation.