Semi-analytical solution for the water wave diffraction by arrays of truncated circular cylinders in front of a vertical wall

The present study investigates the combined wave field that is induced by the continuous interaction of plane waves with an array of truncated circular cylinders in front of a rigid wall. The long-term goal of the study is the investigation of possible increase in the efficiency of cylindrical Wave Energy Converters (WECs) by putting in the vicinity of the array a barrier to propagation, a wall, that could assist the reflection of the incoming waves. The main task is to develop a generic solution method that is free of conceptual simplifications employed, e.g. by the method of images and the assumption of “pure” wave reflection. To cope with the set task, the proposed method relies on the semi-analytical formulation of the velocity potentials, while the solution is sought by combined expressions that involve polar and elliptical harmonics. The wall is represented as an elliptical cylinder with zero semi-minor axis. This assumption has eventually a beneficial effect to the underlying formulation given that it simplifies significantly the expansions of the involved diffraction potentials.     

四川雪宝顶W-Sn-Be矿床中矿物化学组成及矿床成因

雪宝顶矿床位于四川省的松潘甘孜造山带中,以出产大颗粒含W-Sn-Be-F-P的矿物而闻名,前人对该矿床已经开展了大量的研究,但缺乏对粗粒矿物的主次痕量元素研究.本次研究采用X射线荧光光谱(XRF)、电子探针(EMPA)和电感耦合等离子体质谱(ICP-MS)技术对矿床中各矿物的主次痕量元素进行测试分析.结果显示,雪宝顶矿...     

Wave diffraction and near-trapping by a multi-column gravity-based structure

This paper is concerned with the diffraction of water waves by offshore structures, with the ultimate aim of proposing tools for guiding airgap design. The diffraction of monochromatic waves by an array of four bottom mounted cylinders and a gravity-based structure is studied in detail using linear and second order theory. The phenomenon of near-trapping is investigated, allowing guidelines for airgap design to be established. When contemplating airgap design, however, it is crucially important that consideration is given to the largest waves in a sea state. Therefore, in this study a design wave, called NewWave, is proposed as a realistic model for large ocean waves and is used as the incident wave field in the wave-structure diffraction analysis.     

The phase difference effects on 3-D structure of wave pressure acting on a composite breakwater

In designing the coastal structures, the accurate estimation of the wave forces on them is of great importance. In this paper, the influences of the phase difference on wave pressure acting on a composite breakwater installed in the three-dimensional (3-D) wave field are studied numerically. We extend the earlier model [Hur, D.S., Mizutani, N., 2003. Coastal Engineering 47, 329–345] to simulate 3-D wave fields by introducing 3-D Navier–Stokes solver with the Smagorinsky's sub-grid scale (SGS) model. For the validation of the model, the wave field around a 3-D asymmetrical structure installed on a submerged breakwater, in which the complex wave deformations generate, is simulated, and the numerical solutions are compared to the experimental data reported by Hur, Mizutani, Kim [2004. Coastal Engineering (51, 407–420)]. The model is then adopted to investigate 3-D characteristics of wave pressure and force on a caisson of composite breakwater, and the numerical solutions were discussed with respect to the phase difference between harbor and seaward sides induced by the transmitted wave through the rubble mound or the diffraction. The numerical results reveal that wave forces acting on the composite breakwater are significantly different at each cross-section under influence of wave diffraction that is important parameter on 3-D wave interaction with coastal structures.     

Crystallographic and NMR studies on sterols from green alga Chaetomorpha basiretorsa Setchell

Chemical investigation of the ethanol extract of the marine green alga Chaetomorpha basiretorsa Setchell led to the isolation of a new sterol stigmast-4,28-dien-3α,6β-diol 1 in addition to the five known sterols of β-lawsaritol 2, saringosterol 3, 24-hydroperoxy-24-vinyl - cholesterol 4, β-stigmasterol 5, 29-hydroxystigmasta-5, 24 （28） -dien-3β-ol 6. Compounds were isolated by normal phase silica gel and Sephadex LH - 20 gel colum chromatography, reverse phase HPLC and recrystalization. Their structures were elucidated by spectroscopic methods including MS, IR 1D/2D NMR and X-ray analysis. Cytotoxicity of compounds was screened by using the standard MTF method. All these compounds were isolated from the green alga Chaetomorpha basiretorsa Setchell for the first time and they were inactive （50% inhibitory concentration was greater than 10 μg/cm^3） against KB, Bel -7402, PC - 3M, Ketr 3 and MCF-7 cell lines.     

非线性效应对浅水水波变形的影响

本文采用波数矢量无旋和波能守恒方程建立了一个考虑非线性作用的浅水水波变形数值模型,模型中采用Ｂａｔｔｊｅｓ关系与波数矢量无旋,波能守恒方程一起来求解波浪在浅水中变形的波浪要素,在波能守恒方程中考虑了底摩擦的影响。利用本文提出的数值模型对一个斜坡浅滩水域波浪折射绕射现象进行了验证,验证计算中用一个非线性经验弥散关系近似浅水水波变形的非线性效应并与用线性弥散关系的计算结果进行了比较,结果说明使用非线性     

Nonlinear Effect of Wave Propagation in Shallow Water

—In this paper,a nonlinear model is presented to describe wave transformation in shallow wat-er with the zero-vorticity equation of wave-number vector and energy conservation equation.Thenonlinear effect due to an empirical dispersion relation(by Hedges)is compared with that of Dalrymple＇sdispersion relation.The model is tested against the laboratory measurements for the case of a submergedelliptical shoal on a slope beach,where both refraction and diffraction are significant.The computation re-sults,compared with those obtained through linear dispersion relation.show that the nonlinear effect ofwave transformation in shallow water is important.And the empirical dispersion relation is suitable for re-searching the nonlinearity of wave in shallow water.     

不同因素对人工岛波浪绕射影响研究

为研究人工岛尺度变化和波浪方向分布对人工岛绕射波浪的影响,基于MIKE21-BW模型应用数值方法模拟人工岛波浪绕射过程。数值结果与Briggs等的物理试验结果的对比表明两者吻合较好,验证了模型的适用性。在规则波条件时,圆形人工岛绕射波浪的数值结果与线性波浪绕射理论解基本一致;采用该模型分别模拟了6种尺度的圆形人工岛、单向不规则波和9种方向分布θ_(max)、4种谱峰周期条件时绕射波浪分布情况。分析结果表明,圆形人工岛绕射系数随着尺度的增加,掩护区绕射系数随之减小;θ_(max)在10°~45°范围内,随着θmax的增大,绕射系数随之增大,θ_(max)在45°~75°内绕射系数变化较小;随着谱峰周期的增加,绕射系数随之增大。研究成果既为相关规范的完善提供了基础,也为相关工程设计提供了参考。     

折射/谐衍射红外双波段成像光谱仪系统研究

为了获取足够的目标信息,充分利用中波红外和长波红外的光谱信息,建立了谐衍射中、长波红外超光谱成像系统.利用谐衍射元件独特的色散特性,将谐衍射透镜应用于中、长波红外超光谱成像系统中,使系统在中波红外3.7—4.8 μm和长波红外8—12 μm的2个红外大气窗口内获取数百个光谱图像.设计结果表明,中波红外波段,在18对线/mm处光学系统的调制传递函数(MTF)大于0.55;长波红外波段,在13对线/mm处光学系统的MTF大于0.5;光学系统的衍射环绕能,在中波红外波段30 μm半径范围内大于85%,在长波红外     

Improvement of photorefractive properties in Hf:Fe:LiNbO3 crystals with various [Li]/[Nb] ratios

Photorefractive properties of Hf:Fe:LiNbO₃ crystals with various [Li]/[Nb] ratios have been investigated at 488 nm wavelength based on the two-wave coupling experiment. High diffraction efficiency and large recording sensitivity are observed and explained. The decrease in Li vacancies is suggested to be the main contributor to the increase in the photoconductivity and subsequently to the induction of the improvement of recording sensitivity. The saturation diffraction efficiency is measured up to 80.2%, and simultaneously the recording sensitivity of 0.91 cm/J is achieved to in the Hf:Fe:LiNbO₃ crystal grown from the melt with the [Li]/[Nb] ratio of 1.20, which is significantly enhanced as compared with those of the Hf:Fe:LiNbO₃ crystal with the [Li]/[Nb] ratio of 0.94 in melt under the same experimental conditions. Experimental results definitely show that increasing the [Li]/[Nb] ratio in crystal is an effective method for Hf:Fe:LiNbO₃ crystal to improve its photorefractive properties.