Wave diffraction and near-trapping by a multi-column gravity-based structure   总被引：1，自引：0，他引：1  

D.A.G. Walker  R. Eatock Taylor  P.H. Taylor  J. Zang   《Ocean Engineering》2008,35(2):201-229

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.  相似文献   

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

D.-S. Hur  K.-H. Lee  G.-S. Yeom   《Ocean Engineering》2008,35(17-18):1826-1841

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.  相似文献   

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

SHI Dayong  XU Feng  HE Juan  SHI Jiangong  FAN Xiao  HAN Lijun 《海洋学报(英文版)》2008,27(1):147-151

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.  相似文献   

Analysis of the extreme wave elevation due to second-order diffraction around a vertical cylinder     

《Applied Ocean Research》2019

Statistical analysis of nonlinear random waves is important in coastal and ocean engineering. One approach for modeling nonlinear waves is second-order random wave theory, which involves sum- and difference-frequency interactions between wave components. The probability distribution of the non-Gaussian surface elevation can be solved using a technique developed by Kac and Siegert [21]. The wave field can be significantly modified by wave diffraction due to a structure, and the nonlinear diffracted wave elevation can be of interest in certain applications, such as the airgap prediction for an offshore structure. This paper investigates the wave statistics due to second-order diffraction, motivated by the scarcity of prior research. The crossing rate approach is used to evaluate the extreme wave elevation over a specified duration. The application is a bottom-supported cylindrical structure, for which semi-analytical solutions for the second-order transfer functions are available. A new efficient statistical method is developed to allow the distribution of the diffracted wave elevation to be obtained exactly, accounting for the statistical dependency between the linear, sum-frequency and difference-frequency components. Moreover, refinements are proposed to improve the efficiency for computing the free surface integral. The case study yields insights into the problem. In particular, the second-order nonlinearity is found to significantly amplify the extreme wave elevation, especially in the upstream region; conversely, the extreme elevation at an oblique location downstream is attenuated due to sheltering effects. The statistical dependency between the linear and sum-frequency components is also shown to be important for the extreme wave statistics.  相似文献   

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

《Applied Ocean Research》2019

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.  相似文献   

硬X射线成像仪量能器测试系统的设计与实现          下载免费PDF全文

陈娇龙  张永强  张岩  郭建华 《天文学报》2024,65(3):31

硬X射线成像仪(Hard X-ray Imager, HXI)是先进天基太阳天文台(Advanced Space-based Solar Observatory, ASO-S)的3大载荷之一, 其中量能器作为其重要组成部分, 承担着观测30--200keV能段的太阳硬X射线的任务. 在卫星发射之前, 需要开展大量的测试工作, 以确保HXI量能器的各项功能和性能满足设计需求. HXI量能器通道数众多, 内含99个溴化镧探测器, 分别由8块相同的前端电子学板控制. 除了对各个通道的性能进行测试外, 地检系统还需模拟量能器在轨面对不同太阳活动时的运行情况, 对量能器进行全面完备的测试. 此外, 地检系统还需足够稳定, 能满足量能器在单机测试、环境试验、热真空与振动等多个不同测试项目的长时间测试需求. 为此, 设计了地检板与上位机软件, 结合放射源、直流电源、高压模块等组成一套HXI量能器的地检系统, 对8块前端电子学板实现同步配置与管理, 能高效完成指令发送与数据接收, 满足量能器最大数据输出带宽400Mbps的需求. 利用该系统, 在地面完成了HXI量能器的功能、性能验证, 获得了量能器的线性、死时间、能量分辨率等各项性能指标, 为HXI量能器的在轨高性能运行提供了保障.  相似文献   

慧眼-HXMT观测到的黑洞双星系统中的W-K 关系          下载免费PDF全文

马宾远  杨孜旭  廖进元  屈进禄 《天文学报》2024,65(3):25

通过几十年的观测研究, 黑洞X射线双星(X-Ray Binary, XRB)部分特征被揭示. 然而, 吸积盘结构尚不确定. 黑洞XRB功率密度谱的截断频率与准周期振荡(Quasi Periodic Oscillation, QPO)的相关性质(W-K关系)可以限制吸积盘结构. 利用慧眼-HXMT (Hard X-ray Modulation Telescope)观测到的5个黑洞XRB的数据, 对黑洞XRB的W-K关系进行了研究, 结果表明在慧眼-HXMT观测的3个探测器能段中W-K关系成立. 此外在MAXI J1535-571之中存在截断频率和吸积盘内半径的相关关系, 这和截断的吸积盘结构一致. 如果观测到的功率密度谱来自质量吸积率的扰动传播, 可以推测吸积盘内半径接近最内圆形稳定轨道, 此黑洞可能是高自旋系统.  相似文献   

岩石显微构造分析现代技术——EBSD技术及应用   总被引：10，自引：0，他引：10  

曹淑云  刘俊来 《地球科学进展》2006,21(10):1091-1096

EBSD技术的发展,为岩石显微构造分析开辟了一个全新的领域。它与现代扫描电子显微镜和能谱分析等设备配合,可以同时对块状样品进行晶体结构与成分分析,从而使显微构造、微区成分与结晶学数据分析有机结合起来。 EBSD技术可以精确、快速定量标定包括各种晶系晶体颗粒的晶格方位和描述晶体颗粒的边界、形态等特征,对于具有低角度边界的晶体颗粒提供精确数据,为阐述岩石变形机制提供重要约束,并为高级晶族和不透明矿物结晶学组构与变形机制研究提供了有效的手段。EBSD尤其使获取微米级甚至纳米级尺度上颗粒（亚颗粒）或相之间的定向差别（达到20 nm的空间分辨率和0.3度角度分辨率）成为可能。EBSD技术在矿物相鉴定、亚微域内的应变分析、矿物出溶作用等方面的应用,进一步证明了这一新技术在显微构造分析及相关领域的应用前景。其广泛应用必将带来岩石显微构造研究的新突破,也将成为未来岩石变形机制与岩石圈流变学研究取得飞速发展不可或缺的技术手段。  相似文献   

基于走时的保幅偏移方法   总被引：5，自引：4，他引：1       下载免费PDF全文

张平平  常旭  桂志先 《地球物理学进展》2006,21(4):1186-1191

振幅随偏移距变化是描述储层特征的重要方法之一,保幅偏移方法就是使偏移剖面能够反映出振幅随偏移距的变化.本论文中的保幅偏移是以走时为基础,主要的方法是采用走时的双曲线展开法,通过走时的二阶空间导数来确定波前曲率.该方法通过建立在大网格上的走时表来确定插值系数,将大网格插值成为较为精细的网格,这样就节省了数据的存储空间.对于相同的网格密度,通过插值来计算走时表比采用程函方程有限差分法直接计算走时要节省5至6倍的时间.走时的插值系数还可以用来计算几何扩散因子、权函数,不仅提高了成像质量,还大大节省了计算时间.  相似文献   

The additional radiation of Cyg X-1 at primary minimum     

I. Voloshina  V. M. Lyuty 《Astronomische Nachrichten》1995,316(2):85-90

New UBV-photoelectric observations of the well-known massive X-ray binary system Cyg X-1/V 1357 Cyg are obtained near the primary minimum. The detailed analysis of these observations confirms the existence of additional blue radiation which appears as a narrow peak with an amplitude of 0.01–0.02 mag near phase 0.00 on the light curve (the superior conjunction of the relativistic component), firstly detected by Lyuty (1985). This emission does not appear at every orbital cycle. The appearance of this narrow peak of additional blue radiation on the light curve of Cyg X-1 can be explained as the radiation of relativistic electrons in the disturbed magnetic field of the optical star in frames of the model proposed by Ikhsanov and Fabrika (1990).  相似文献