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131.
Acoustic plane-wave scattering from a rough surface overlying a fluid half-space with a sound-speed distribution subject to a small random variation is considered. Under the assumption that the surface roughness and medium randomness are statistically independent, the scattered field may be derived by first solving for the mean field in the medium, and then incorporating with boundary-perturbation method to obtain the total mean field and the power spectral density of the scattered field. The employed algorithm is compatible to the analysis available in the existing literature so that the formulations are conveniently integrated. The results for the power spectral density have shown that the effects of medium inhomogeneities on the rough surface scattering are limited in a spectral regime where the scattered components have shallow grazing angles. The distribution of the power spectral density over the space is primarily governed by the power spectrum and correlation lengths of the rough surface. 相似文献
132.
双层局部开孔板沉箱对波浪反射的理论研究 总被引:1,自引:0,他引:1
提出了一种用于研究由双层开孔板和一个不透水后板的开孔结构对斜向波反射率的理论分析方法。整个流域被分成三个子域,在每个子域内应用特征函数展开法以得到该域内包含未知展开系数的势函数的表达式,在速度势的展开中,考虑了非传播模态波浪的影响。通过匹配开孔板处的边界条件可以求解待定的展开系数,继而求解双层开孔板防波堤结构对斜向波的反射率。数值计算结果与试验结果进行了比较,符合较好。并进一步讨论了几个重要因素对反射系数的影响。 相似文献
133.
非常规管节点疲劳寿命分析与计算 总被引:6,自引:1,他引:6
对非常规管节点的疲劳寿命进行了分析研究,用SESAM计算疲劳载荷,应用精细有限元分析计算热点应力,用规范的S—N曲线计算管节点的疲劳寿命。通过实例计算表明,这些处理对非常规管节点疲劳寿命分析与计算是很有效的。 相似文献
134.
Jeom Kee Paik Anil K. Thayamballi P. Terndrup Pedersen Young Il Park 《Ocean Engineering》2001,28(8):51
For a ship hull with large deck openings such as container vessels and some large bulk carriers, the analysis of warping stresses and hatch opening deformations is an essential part of ship structural analyses. It is thus of importance to better understand the ultimate torsional strength characteristics of ships with large hatch openings. The primary aim of the present study is to investigate the ultimate strength characteristics of ship hulls with large hatch openings under torsion. Axial (warping) as well as shear stresses are normally developed for thin-walled beams with open cross sections subjected to torsion. A procedure for calculating these stresses is briefly described. As an illustrative example, the distribution and magnitude of warping and shear stresses for a typical container vessel hull cross section under unit torsion is calculated by the procedure. By theoretical and numerical analyses, it is shown that the influence of torsion induced warping stresses on the ultimate hull girder bending strength is small for ductile hull materials while torsion induced shear stresses will of course reduce the ship hull ultimate bending moment. 相似文献
135.
136.
长江口区风浪要素计算的探讨 总被引:2,自引:0,他引:2
本文以长江口区波浪实测资料为依据,对目前国内外常用的风浪要素计算方法进行了比较分析,认为就目前资料条件下,最适用于长江口区的、能满足工程设计等要求的风浪要素计算方法为莆田试验站方法(莆田公式)。 相似文献
137.
138.
A polar method for obtaining wave resonating quadruplets {K1, K2, K3, K4} in the computation of nonlinear wave–wave interaction source term of the wave model is presented with results for both deep and finite water depths. The method first determines the end radial points of the locus equation for K2, for each set of input wave vectors (K1, K3) on the symmetry. The locus of K2 (and hence K4) is then traced in the anti-clockwise direction starting with the maximum radial point on the line of symmetry. It is shown that when k3>k1, the number of points on the locus varies when the orientations of the input wave vectors are changed and reduces when the difference in the magnitude of the input wave vectors is increased. A significant advantage in this method is that the angular increment on the locus for K2 can be kept constant. 相似文献
139.
作为海洋环境预报公益服务的窗口自开播至今,经历了20年的风风雨雨,海洋电视节目的内容从单一性的项目到海浪、海温、海冰、风暴潮、海水浴场综合性预报,电视视频信号从复合、分量信号到数字信号,通过光缆采用基带的方式传送视频信号到中央电视台. 相似文献
140.
Hitoshi Kawabata Hisashi Narita Koh Harada Shizuo Tsunogai Masashi Kusakabe 《Journal of Oceanography》2003,59(5):651-661
Thirteen vertical profiles of 226Ra and 222Rn in the near-surface water were obtained in the western North Pacific in winter, and the gas transfer velocities across
the air-sea interface were estimated. The transfer velocities found by applying a steady state model varied widely from 2.1
to 30.2 m day−1 with a mean of 9.4 m day−1. The mean value is almost 5 times higher than that in summer in other oceans, and the maximum value is a record high for
world oceans. This is partly due to the inadequacy of the steady state model, which overestimates when stronger winds blow
in more recent days than the 222Rn half-life of about 4 days. In fact, a strong low pressure zone passed through the station about 2 days earlier, which was
one of the low pressure zones that with a period of develop once a week or so in the northwestern North Pacific in winter.
Instead of steady-state removal, if half of the radon removal occurred sporadically every 7 days, and the last removal took
place two days before the observation, the transfer velocity would be 26 m day−1. Our mean transfer velocity, which is less than 20% different from the steady state value including both overestimated and
underestimated values, 9.4 ± 4.8 m day−1, seems to represent the mean state of this region in winter. This suggests that the gas exchange fluxes under extremely rough
conditions in the open ocean are larger than those estimated by using a transfer velocity equation with a linear or quadratic
relationship with wind speed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献