Diffraction–radiation of multiple floating structures in directional waves     

S. A. Sannasiraj  R. Sundaravadivelu  V. Sundar 《Ocean Engineering》2001,28(2):106

The dynamics of multiple floating structures have been studied using the finite element method. The emphasis is on the hydrodynamic behaviour of multiple bodies under a multi-directional wave field. A two-dimensional numerical model has been adopted to evaluate hydrodynamic coefficients and forces in an oblique wave field. The responses in sway, heave and roll modes are reported. The linear filter technique is then used to extrapolate the responses under directional waves. The effect of mean wave direction and directional homogeneity on the hydrodynamic behaviour of the structure is studied. Based on the present study, it is found that the two-dimensional model is applicable to investigate the wave-structure interaction problems of the type herein considered.  相似文献   

Statistical estimation of extreme ocean environments: The requirement for modelling directionality and other covariate effects     

Philip Jonathan  Kevin Ewans  George Forristall   《Ocean Engineering》2008,35(11-12):1211-1225

With increasing availability of good directional data, provision of directional estimates of extreme significant wave heights, in addition to the omni-directional estimates, is more common. However, interpretation of directional together with omni-directional design criteria is subject to inconsistency, even in design guidelines. In particular, omni-directional criteria are usually estimated ignoring directional effects. In this article, for data which exhibit directional effects, we show that a directional extreme value model generally explains the observed variation significantly better than a model which ignores directionality, and that omni-directional criteria developed from a directional model are different from those generated when directionality is not accounted for. We also show that omni-directional criteria derived from a directional model are more accurate and should be preferred in general over those based on models which ignore directional effects. We recommend use of directional extreme value models for estimation of both directional and omni-directional design criteria in future, when good directional data are available. If effects of other covariates (e.g. time or space) are suspected, we similarly recommend use of extreme value models which adequately capture sources of covariate variability for all design analysis.  相似文献   

Spectral characteristics of the nearshore waves off Paradip,India during monsoon and extreme events     

V. M. Aboobacker  P. Vethamony  K. Sudheesh  S. P. Rupali 《Natural Hazards》2009,49(2):311-323

Spectral and statistical wave parameters obtained from the measured time series wave data off Paradip, east coast of India during May 1996–January 1997 were analysed along with MIKE 21 spectral wave model (SW) results. Statistical wave parameters and directional wave energy spectra distinctly separate out the wave conditions that prevailed off Paradip in the monsoon, fair weather and extreme weather events during the above period. Frequency-energy spectra during extreme events are single peaked, and the maximum energy distribution is in a narrow frequency band with an average directional spreading of 20°. Spectra for other seasons are multi-peaked, and energy is distributed over a wide range of frequencies and directions. The NCEP re-analysis winds were used in the model, and the results clearly bring out the wave features during depressions. The simulated wave parameters reasonably show good match with the measurements. For example, the correlation coefficient between the measured and modelled significant wave height is 0.87 and the bias −0.25.  相似文献   

Directional Wavelets and a Wavelet Variogram for Two-Dimensional Data     

E. H. Bosch  A. P. González  J. G. Vivas  G. R. Easley 《Mathematical Geosciences》2009,41(6):611-641

This paper describes two new approaches that can be used to compute the two-dimensional experimental wavelet variogram. They are based on an extension from earlier work in one dimension. The methods are powerful 2D generalizations of the 1D variogram that use one- and two-dimensional filters to remove different types of trend present in the data and to provide information on the underlying variation simultaneously. In particular, the two-dimensional filtering method is effective in removing polynomial trend with filters having a simple structure. These methods are tested with simulated fields and microrelief data, and generate results similar to those of the ordinary method of moments variogram. Furthermore, from a filtering point of view, the variogram can be viewed in terms of a convolution of the data with a filter, which is computed fast in O(NLogN) number of operations in the frequency domain. We can also generate images of the filtered data corresponding to the nugget effect, sill and range of the variogram. This in turn provides additional tools to analyze the data further.  相似文献   

水平定向钻无套管双管回托工艺研究     

周立峰 《岩土钻凿工程》2009,(3):19-21

本文结合单根管道水平定向钻穿越回托力计算,对无套管双管回托力计算方法进行了理论分析,并通过工程实例对计算公式进行了修正,得出了无套管双管回托力计算方法,以期为同类工程实践提供理论参考。  相似文献   

FHD 磁力仪分量线圈装置误差对磁偏角观测的影响分析   总被引：1，自引：1，他引：0  

冯志生  夏忠  梅卫萍  张秀霞  庄明龙  沈红会  张晓勇 《地震》2003,23(4):97-103

根据FHD 磁力仪观测磁偏角的原理, 计算了分量线圈不水平导致的磁偏角观测值误差,发现分量线圈仅在EW 方向的倾斜对磁偏角观测产生误差。文中将理论分析结果与实际观测结果进行了对比分析, 发现由于分量线圈底座水平的长期漂移, 仪器的垂直分量及磁偏角观测误差也会发生长期漂移, 长期漂移变化的周期约2 ~ 4 个月, 对垂直分量其幅度约3.5~ 11.0nT, 而磁偏角的幅度约0.1′~ 1.0′, 因此认为在将该仪器观测值用作绝对观测值进行地震异常分析时, 应注意回避这种长期漂移变化。  相似文献   

Analysis of directional wave fields using X-band navigation radar   总被引：7，自引：0，他引：7  

J. C. Nieto Borge  C. Guedes Soares   《Coastal Engineering》2000,40(4)

The aim of this work is to present an approach to describe complex sea states including the ones consisting of superpositions of swell and wind sea components, using a nautical radar in X-band as a remote sensing technique. In the present article, the inversion method to obtain the spectral representation of the wave fields is described. The method is applied to analyse data obtained from simulation techniques, as well as from measurements obtained during oceanographic campaigns in the Bay of Biscay and North Sea.  相似文献   

方向导数迹变换面波压制          下载免费PDF全文

聂鹏飞  李月  曾谦  林洪波  吴宁 《地球物理学报》2012,55(6):2035-2043

面波是地震勘探中常见的一种相干干扰,它的存在严重的影响着地震记录的信噪比.由于面波和有效波具有相关性且面波的频带和有效波的频带总有重叠的部分,在时域或频域二者不能明显分开,因此在时域或频域采用切除法压制面波会造成子波畸变和有效信息的损失.本文提出一种利用方向导数迹变换压制面波的新方法.文中推导了方向导数迹变换的反变换公式.地震记录的方向导数迹变换(Directional Derivative Trace Transform,DDTT)由两部分组成,一部分主要体现面波,能量集中;另一部分主要体现反射有效波,能量相对分散.根据这两部分能确定压制面波的阈值,通过这一阈值在正变换中压制面波后,再通过反变换返回时-空域就可达到压制面波的目的.理论和实际数据的处理都取得了令人满意的效果,表明了本文提出方法的可行性和有效性.  相似文献   

基于目标区的局部角度域方向照明分析及其在偏移成像中的应用          下载免费PDF全文

耿瑜  毛剑  吴如山  高静怀 《地球物理学报》2012,55(3):981-990

叠前深度偏移已成为近年来地震偏移成像领域广泛应用的技术之一,其中复杂盐丘下方目标区域结构的成像始终是偏移成像中较难解决的问题.局部角度域波场分解可以提供在空间和方向上的双重局部化信息,因而这一技术被广泛地应用在方向照明分析、成像振幅校正等方面.本文在采用局部指数标架小波束进行角度域方向照明分析的基础上,研究采集系统对复杂盐丘下部层状结构成像质量的影响;同时通过分析目标区对应于相对地表采集系统分布的照明能量,确定叠前炮集数据中对盐下目标区成像起重要贡献的部分,并将这些数据用来对目标区成像,从而达到提高盐下结构成像质量的目的.本文将二维SEG-EAGE盐丘模型中盐下反射体作为目标区,分别计算其照明分析和由照明能量分布确定的炮集数据对目标区的偏移成像结果,同时通过与成像振幅校正前后的成像结果对比,说明了该方法对提高目标区结构成像质量的有效性.  相似文献   

Seismic directional random noise suppression by radial‐trace time–frequency peak filtering using the Hurst exponent statistic          下载免费PDF全文

Chao Zhang  Hongbo Lin  Baojun Yang 《Geophysical Prospecting》2016,64(3):571-580

Radial‐trace time–frequency peak filtering filters a seismic record along the radial‐trace direction rather than the conventional channel direction. It takes the spatial correlation of the reflected events between adjacent channels into account. Thus, radial‐trace time–frequency peak filtering performs well in denoising and enhancing the continuity of reflected events. However, in the seismic record there is often random noise whose energy is concentrated in certain directions; the noise in these directions is correlative. We refer to this kind of random noise (that is distributed randomly in time but correlative in the space) as directional random noise. Under radial‐trace time–frequency peak filtering, the directional random noise will be treated as signal and enhanced when this noise has same direction as the signal. Therefore, we need to identify the directional random noise before the filtering. In this paper, we test the linearity of signal and directional random noise in time using the Hurst exponent. The time series of signals with high linearity lead to large Hurst exponent value; however, directional random noise is a random series in time without a fixed waveform and thus its linearity is low; therefore, we can differentiate the signal and directional random noise by the Hurst exponent values. The directional random noise can then be suppressed by using a long filtering window length during the radial‐trace time–frequency peak filtering. Synthetic and real data examples show that the proposed method can remove most directional random noise and can effectively recover the reflected events.  相似文献