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101.
J. H. Cushman B. X. Hu 《Stochastic Environmental Research and Risk Assessment (SERRA)》1997,11(4):297-302
A recursive perturbation solution to the eulerian transport problem for a conservative solute in a random conductivity field
is reported. The stochastic concentration is given to arbitrary order inσ
ν, the variance of fluctuating velocity. The result gives the stochastic concentration as a perturbation to the deterministic
concentration for constant mean flow. The closed form solution is easy to implement numerically via FFT. 相似文献
102.
The diffraction of linear waves by a uniform vertical cylinder with cosine-type radial perturbations
The interaction of linear waves with a uniform, bottom-mounted, surface-piercing cylinder whose diameter exhibits a cosine-type variation is investigated. Two solution methods are presented. One method is based on a perturbation theory, using a perturbation parameter defined in terms of the surface geometry of the cylinder. The analysis includes terms up to the first-order in this parameter, where the zeroth-order solution corresponds to a circular cylinder. The velocity potentials at the zeroth and first orders are expressed as eigenfunction expansions involving unknown coefficients that are subsequently determined through the cylinder boundary conditions. The second method is based on Green's theorem and gives rise to an integral equation for the fluid velocity potential on the cylinder surface. A comparison between the results of these two methods has proved that they are in good agreement for small values of the perturbation parameter. Numerical results are presented that illustrate the influence of the magnitude and frequency of these perturbations on the resulting hydrodynamic force and the wave runup on the cylinder. 相似文献
103.
Computation of wave-making resistance of a catamaran in deep water using a potential-based panel method 总被引:1,自引:0,他引:1
This paper presents a potential-based boundary element method for solving a nonlinear free-surface flow problem for a Wigley catamaran moving with a uniform speed in deep water. Since the interior flow of each monohull of the catamaran is different from the exterior flow, both monohulls must be considered as lifting bodies. The pressure Kutta condition is imposed at the trailing-edge of the lifting body by determining the dipole distribution, which generates required circulation on the lifting part. The effects of wave interference and hull separation on the hydrodynamic characteristics of the catamaran hull are analyzed and the validity of the computer scheme is examined by comparing the wave resistance with the numerical results of others. The present method could be a useful design tool for screening the suitable combinations of hull parameters and hull spacing at the preliminary design stage of catamaran hull. 相似文献
104.
105.
106.
Scattering theory, a form of perturbation theory, is a framework from within which time‐lapse seismic reflection methods can be derived and understood. It leads to expressions relating baseline and monitoring data and Earth properties, focusing on differences between these quantities as it does so. The baseline medium is, in the language of scattering theory, the reference medium and the monitoring medium is the perturbed medium. The general scattering relationship between monitoring data, baseline data, and time‐lapse Earth property changes is likely too complex to be tractable. However, there are special cases that can be analysed for physical insight. Two of these cases coincide with recognizable areas of applied reflection seismology: amplitude versus offset modelling/inversion, and imaging. The main result of this paper is a demonstration that time‐lapse difference amplitude versus offset modelling, and time‐lapse difference data imaging, emerge from a single theoretical framework. The time‐lapse amplitude versus offset case is considered first. We constrain the general time‐lapse scattering problem to correspond with a single immobile interface that separates a static overburden from a target medium whose properties undergo time‐lapse changes. The scattering solutions contain difference‐amplitude versus offset expressions that (although presently acoustic) resemble the expressions of Landro ( 2001 ). In addition, however, they contain non‐linear corrective terms whose importance becomes significant as the contrasts across the interface grow. The difference‐amplitude versus offset case is exemplified with two parameter acoustic (bulk modulus and density) and anacoustic (P‐wave velocity and quality factor Q) examples. The time‐lapse difference data imaging case is considered next. Instead of constraining the structure of the Earth volume as in the amplitude versus offset case, we instead make a small‐contrast assumption, namely that the time‐lapse variations are small enough that we may disregard contributions from beyond first order. An initial analysis, in which the case of a single mobile boundary is examined in 1D, justifies the use of a particular imaging algorithm applied directly to difference data shot records. This algorithm, a least‐squares, shot‐profile imaging method, is additionally capable of supporting a range of regularization techniques. Synthetic examples verify the applicability of linearized imaging methods of the difference image formation under ideal conditions. 相似文献
107.
本文在前期局地扰动位能理论工作基础上,进一步着眼于扰动位能与大气环流异常的关系和机理问题,采用奇异值分解(SVD)方法分析了扰动位能与高、中、低层大气动能的耦合相关模态以及年际变率情况,同时考察它与作为大气质量分布的海平面气压之间的相关关系,并从物理上初步探讨了扰动位能与大气动能以及质量的相关机理问题.结果表明,扰动位能自身变率的第一模态同时也是与大气环流异常场耦合变化的主要模态,与之相对应的大气动能和质量场的主模态也是其自身变率的支配模态,说明它们之间存在相互制约的物理机制.而且,热带外地区大气环流主模态特征的形成,与扰动位能兼具全球尺度纬向对称结构和局地尺度纬向非对称性密不可分.另外,冬季南北半球环状模指数与扰动位能的前两阶矩存在非常好的相关关系,而在夏季这种关系明显削弱,仅存在于南半球. 相似文献
108.
以先进的波动理论为基础的波动方程保幅地震偏移成像是在给出正确位置的同时也给出真实振幅的一种特殊完善.作者从保幅单程波动方程的非稳态相移公式出发,基于反问题求解中常用的摄动理论,利用单平方根算子的渐进展开,从而推导出保幅叠前深度偏移方程的高阶广义屏形式;针对散射波场计算项对于横向变速介质的不稳定性,通过数学近似提出一个有效提高稳定性的策略,应用到波场递归外推过程中,从而得到一种稳定的保幅高阶广义屏叠前深度偏移算子.理论模型试算和实际资料处理表明,该方法不但可以更精确地使散射能量聚焦、归位,提高成像精度;而且可以输出正确反映地下反射系数的振幅信息,使AVO响应更加清晰,提高了AVO资料的分析精度. 相似文献
109.
早三叠世是地球发展史上的特殊时期,代表了古、中生代过渡时期的生态重建与复苏.随着各种“异常环境事件”信息在近年陆续被揭示,早三叠世地质学研究成为地学界新的热点领域.海相碳酸盐碳同位素组成记录了碳循环的变化,是理解重大突变期的生态环境事件和地球过程的重要切入点.最近10年的研究表明,过去集中在二叠纪/三叠纪界线附近发现的“负漂移”现象只能代表海洋化学持续了约5 Ma的动荡局面的开始,直到中三叠世才趋于平稳,高频率、大幅度的整体演变型式已很难用过去提出的机制进行解释.全球范围内缺乏可精确对比性以及高达+8‰的正向极值的成因等,都是值得深入思考的问题. 相似文献
110.
The interaction between the typhoons Fengshen and Fung-wong over the Western Pacific in 2002 is studied with the Conditional Nonlinear Optimal Perturbation (CNOP) method. The study discovered that the CNOP method reveals the process of one-way interaction between Fengshen and Fung-wong. Moreover, if the region of Fung-wong was selected for verification, the sensitivity area was mainly located in the region of Fengshen and presented a half-ring structure; if the region of Fengshen was selected for verification, most of the sensitivity areas were located in the region between the Fengshen and the subtropical high, far away from Fung-wong. This indicated that Fung-wong is mainly steered by Fengshen, but Fengshen is mainly affected by the subtropical high. The sensitivity experiment showed that the initial errors in the CNOP-identified sensitive areas have larger impacts on the verification-area prediction than those near the typhoon center and their developments take a large proportion in the whole domain. This suggests that the CNOP-identified sensitive areas do have large influence on the verification-area prediction. 相似文献