Poisson-Logistic二元复合极值模型在平台甲板标高设计中的应用     

刘德辅宋艳  李晓冬 《海洋工程》2003,21(4):35-40

考虑到平台所在海区台风出现的频次及其诱发之风、浪、潮、流极端海况联合出现的概率特性，本文推导出Poisson—Logistic二元复合极值模式，并以平台甲板标高进行实例计算。新模式增加了概率模型的物理内涵，解决了Logistic模型阈值选取的任意性。对海洋工程极端海况荷载组合预测具有广泛的应用前景。  相似文献   

WWATCH模式模拟南海海浪场的结果分析   总被引：25，自引：3，他引：25       下载免费PDF全文

齐义泉  朱伯承  施平  毛庆文  范辰五 《海洋学报》2003,25(4):1-9

利用美国NOAA/NCEP环境模拟中心海洋模拟小组近年新开发的一个准业务化的海浪数值模式WAVEWATCH Ⅲ(以下简称WWATCH),以每天4次的NOAA/NCEP再分析风场资料为输入,模拟了1996年的南海海域的海面风浪场,通过分析TOPEX/Poseidon(以下简称T/P)高度计的上升和下降轨道在南海海域的交叉点位置处的风、浪观测资料与NCEP风场和WWATCH模式模拟的有效波高大小,可以看出,NCEP风场基本与T/P高度计的风速观测结果一致,相应的模式模拟的有效波高也基本与卫星高度计的有效波高观测结果相一致,但从空间上看,在计算区域中心附近海域的结果一致性较好,靠近计算边界附近海域的结果相对较差,但这种因边界而影响模拟结果的范围很有限;从时间上看,冬季风期间的结果一致性较好,而夏季风期间的结果偏小的趋势明显,并且这种偏小主要出现在夏季风期间的极小风速值附近。  相似文献   

Wave run-up and overtopping on smooth and rough slopes of coastal structures     

N. J. Shankar  M. P. R. Jayaratne 《Ocean Engineering》2003,30(2):221-238

A series of hydraulic model tests has been carried out in a glass wave flume to investigate the influences of wave height, wave period, wave steepness, surf similarity parameter, roughness, layer thickness and porosity on wave run-up and overtopping of 1:2 sloped impermeable and permeable breakwaters fronted by a 1:10 gentle, smooth beach slope. The analysis of results involves the correlation between the overtopping energy transfer with the relative wall height and the relationship between wave run-up and overtopping rate. Further, measured wave run-up and overtopping rates are compared with the results given in the Shore Protection Manual (1984), Automated Coastal Engineering System (1992)and results of other investigators.  相似文献   

Spectral Analysis of Nonlinear Drag Forces     

马汝建  李桂喜赵东 《中国海洋工程》2005,19(2):325-332

The spectral properties of nonlinear drag forces of random waves on vertical circular cylinders are analyzed in this paper by means of nonlinear spectral analysis. The analysis provides basic parameters for estimation of the characteristic drag forces. Numerical computation is also performed for the investigation of the effects of nonlinearity of the drag forces.The results indicate that the wave drag forces calculated by linear wave theory are larger than those calculated by the third order Stokes wave theory for given waves. The difference between them increases with wave height. The wave drag forces calculated by use of hnear approximation are about 5% smaller than their actual values when measured in the peak values of spectral densities. This will result in a safety problem for the design of offshore structures. Therefore, the nonlinear effect of wave drag forces should be taken into comidemtion in design and application of important offshore structures.  相似文献   

Imaging of Buried Archaeological Materials: The Reflection Properties of Archaeological Wood   总被引：1，自引：0，他引：1  

Stephanie H.L. Arnott  Justin K. Dix  Angus I. Best  David J. Gregory 《Marine Geophysical Researches》2005,26(2-4):135-144

Effective marine archaeological site management demands detailed information on not only the spatial distribution of artefacts but also the degradation state of the materials present. Although sonar methods have frequently been used in an attempt to detect buried wooden shipwrecks they are currently unable to indicate their degradation state. To assess the sensitivity of acoustic measurements to changes in the degradation state of such material, and hence the potential for sonars to quantify degradation, laboratory measurements of compressional wave velocity, as well as bulk density for oak and pine samples, in varying states of decay, were undertaken. These data enabled the calculation of theoretical reflection coefficients for such materials buried in various marine sediments. As wood degrades, the reflection coefficients become more negative, resulting in the hypothesis that the more degraded wood becomes, the easier it should be to detect. Typical reflection coefficients of the order of −0.43 and −0.52 for the most degraded oak and pine samples in sand are predicted. Conversely, for wood exposed to seawater the predicted reflection coefficients are large and positive for undegraded material (0.35 for oak, 0.18 for pine) and decrease to zero or slightly below for the most degraded samples. This indicates that exposed timbers, when heavily degraded, can be acoustically transparent and so undetectable by acoustic methods. Corroboration of these experimental results was provided through comparison with high resolution seismic reflection data that has been acquired over two shipwrecks.  相似文献   

新型波浪采集系统平台设计     

刘世萱  王孝坤  牟长青 《海洋技术学报》2004,23(2):90-92

主要介绍了新型波浪采集系统的设计思想与主要参数，采集、存储、运算和电源控制部分的结构与组成，以及各部分的特点和关键技术。  相似文献   

Variations in wave direction estimated using first and second order Fourier coefficients     

V. Sanil Kumar  N. M. Anand 《Ocean Engineering》2004,31(17-18):2105-2119

In most design applications such as alignment of the berthing structure and breakwater alignment, it becomes necessary to determine the direction of design wave. There are two different approaches to determine wave direction. One involves the use of first order Fourier coefficients (mean wave direction) while the other uses second order Fourier coefficients (principal wave direction). Both the average wave direction over the entire frequency range (0.03–0.58 Hz) and the direction corresponding to the peak frequency are used in practice. In the present study, comparison is made on wave directions estimated based on first and second order Fourier coefficients using data collected at four locations in the west and east coasts of India. Study shows that at all locations, the mean and principal wave directions for frequencies ranging from 0.07 to 0.25 Hz (±0.5 times peak frequency) co-vary with a correlation coefficient of 0.99 but at lower and higher frequencies, difference between the parameters is large. Average difference between the mean wave direction at peak frequency and the average over the frequency related to spectral energy more than 20% of maximum value is less, around 13°. Study shows that average difference in the sea and swell directions is around 39°.  相似文献   

Dynamic analysis of a vertical plate exposed to breaking wave impact     

M. Salih Kirkgoz  A. Kamil Tanrikulu  Cengiz Dündar 《Ocean Engineering》2004,31(13):2308-1635

From the experimental studies in recent years, it has become known that when a wave breaks directly on a vertical faced coastal structure, high magnitude impact pressures are produced. The theoretical and experimental studies show that the dynamic response of such structures under wave impact loading is closely dependent on the magnitude and duration of the load history. The dynamic analysis and design of a coastal structure can be succeeded provided the design load history for the wave impact is available. Since these types of data are very scarce, it is much more convenient to follow a method which is based on static analysis for the dynamic design procedure. Therefore, to facilitate the dynamic design of a vertical plate that is exposed to breaking wave impact, a multiplication factor called “dynamic magnification factor” is herein presented which is defined as the ratio of the maximum value of the dynamic response to that found by static analysis. The computational results of the present study show that the dynamic magnification factor is a useful ratio to transfer the results of static analysis to the dynamic design of a coastal plate for the maximum impact pressure conditions of p_max/γH₀≤18.  相似文献   

Freely floating-body simulation by a 2D fully nonlinear numerical wave tank     

Weoncheol Koo  Moo-Hyun Kim 《Ocean Engineering》2004,31(16):221-2046

Nonlinear interactions between large waves and freely floating bodies are investigated by a 2D fully nonlinear numerical wave tank (NWT). The fully nonlinear 2D NWT is developed based on the potential theory, MEL/material-node time-marching approach, and boundary element method (BEM). A robust and stable 4th-order Runge–Kutta fully updated time-integration scheme is used with regriding (every time step) and smoothing (every five steps). A special φ_n-η type numerical beach on the free surface is developed to minimize wave reflection from end-wall and wave maker. The acceleration-potential formulation and direct mode-decomposition method are used for calculating the time derivative of velocity potential. The indirect mode-decomposition method is also independently developed for cross-checking. The present fully nonlinear simulations for a 2D freely floating barge are compared with the corresponding linear results, Nojiri and Murayama’s (Trans. West-Jpn. Soc. Nav. Archit. 51 (1975)) experimental results, and Tanizawa and Minami’s (Abstract for the 6th Symposium on Nonlinear and Free-surface Flow, 1998) fully nonlinear simulation results. It is shown that the fully nonlinear results converge to the corresponding linear results as incident wave heights decrease. A noticeable discrepancy between linear and fully nonlinear simulations is observed near the resonance area, where the second and third harmonic sway forces are even bigger than the first harmonic component causing highly nonlinear features in sway time series. The surprisingly large second harmonic heave forces in short waves are also successfully reproduced. The fully updated time-marching scheme is found to be much more robust than the frozen-coefficient method in fully nonlinear simulations with floating bodies. To compare the role of free-surface and body-surface nonlinearities, the body-nonlinear-only case with linearized free-surface condition was separately developed and simulated.  相似文献   

A method to estimate the forces exerted by internal solitons on cylindrical piles   总被引：1，自引：0，他引：1  

Shuqun Cai  Xiaomin Long  Zijun Gan 《Ocean Engineering》2003,30(5):673-689

Internal soliton is the large amplitude wave existing in the pycnocline, induced by internal tide in the condition of special bottom topography. During its propagation process, the induced disturbance can bring about strong convergence of sea water and sudden strong current (wave-induced-current), which can cause severe threat to the ocean engineering structures, such as oil drilling platform and pipeline. In this paper, Morison’s empirical method, modal separation and regression analyses are introduced to estimate the forces and torques exerted by internal soliton on cylindrical piles. As an example, a limited set of observational data recording a passage of the internal soliton near Dongsha Islands is used to estimate the horizontal velocity and its acceleration in a vertical section for computing the force and torque on a supposed pile, and the estimation results are reasonable. It is shown that, the higher number of the modes retained in the calculation, the better the estimation of velocity profile fits the observational one. A better overall approximation to the real solution can be reached if there are more observational current data acquired in a whole vertical profile.  相似文献