共查询到20条相似文献，搜索用时 31 毫秒
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P. A. A. Laura 《Ocean Engineering》1995,22(3)
Lord Rayleigh proposed his now classical method (based on a one-term deflection function) in 1870. On the other hand, he suggested in 1894 the possibility of optimizing the eigenvalues (natural frequencies or buckling loads) by minimizing them with respect to an exponential parameter contained in the coordinate function. This optimization approach has become increasingly popular in the last decade and it has been extended to other variational methods and bounding techniques. The present paper reviews recent developments in this area which consists, essentially, in a nonlinear optimization process of the coordinate functions in a global sense. The technique is applicable in a large variety of applied mechanics problems of considerable interest to ocean engineers dealing with the analysis of mechanical systems. 相似文献
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Offshore fouling: investigation methods 总被引：2，自引：0，他引：2
On the hasis of the reason that the offshore oil development areas in the northem South China Sea are at greater depth, more hazardous conditions and distance from shore, the methods and technologies used in coastal waters are not feasible because of the higher risk of losing investigation equipment or facilities. A series of methods and technologies for offshore fouling investigation that have been successfully applied is given in detail and it is hoped that the experience can be helpful for further studies. 相似文献
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A.F. Bennett 《Progress in Oceanography》1985,15(2):129-156
The generalized inverse method of Bennett and McIntosh (1982) is used to assess the efficiency of instrument arrays with observe deterministic fields. The arrays considered are combinations of points at which bottom pressures are observed (Cartwright, 1978), plus paths along which averaged barotropic velocities are observed, by the acoustic tomography technique of reciprocal shooting (Munk and Wunsch, 1982a,b). The barotropic M2 tide is used as an example of a field which is being observed by the array, and for which an interpolation or smoothing is required. The treatment of observations of individual inter-annual events would be similar.It is shown that the generalized inverse method for the objective analysis of deterministic fields is formally identical to the Gandin (1965) method for the objective analysis of random fields.Construction of the generalized inverse requires the inversion of an Hermitian positive definite matrix. Array efficiency is characterized by the number of significant eigenvalues of the matrix.The admission of errors in the observations and dynamics necessitates the choice of weights in a variational principle. The choice is made by prior estimation of the relative error variances. It is also necessary to choose locally singular weighting functions for the dynamics, in order to ensure non-singular interpolating or smoothing fields. The dominant array modes are defined and constructed. These are the interpolating fields which make the most stable contribution to the generalized inverse.An example of inversion is carried out using simulated data. 相似文献
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A review is made of linear slender-body methods for predicting the squat of a ship in shallow open water, dredged channels or canals. The results are summarized into a general formula based on Fourier transforms, and the method is extended to cater to stepped canals. An approximate solution for canals of arbitrary cross-section is proposed. 相似文献
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This work discusses developments related to the generation and measurement of directional wave spectra in multi-directional wave tank using deterministic waves. The details of the generation method, based on the single summation method described by Jefferys (1987), are given and the capacity of the Edinburgh curved wave tank to generate such waves is assessed. The Maximum Likelihood Method (MLM) and one of its derivative, The Modified Maximum Likelihood Method (MMLM) (Isobe and Kondo, 1985), are adapted to the characteristics of deterministic waves. The methods are assessed both with simulated waves and real wave elevations from the Edinburgh curved tank. Both methods show very satisfactory results with very stable angular spreading estimates and good tracking of mean directions of propagation across frequencies. The adapted MLM compares favourably with the industry standard, the Bayesian Directional Method, while only taking a fraction of the time needed to the BDM to produce its spectral estimates. 相似文献
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对沉积物源判别的地球化学方法进行了分类总结，并分析了各类方法中存在的问题，进一步给出了应用建议，以期更加实用。综合分析表明，常量元素（组分）主要用于表征化学风化程度和判断源岩类型；微量元素组成不仅可以示踪物源区，还可以判别构造环境，其中蛛网图和三角图是最有效的判别图解，Ce异常是判断古海洋氧化还原环境的常用指标，Eu异常常用于区分基性岩和热液流体与酸性岩和陆源物质；直接指示物源的同位素指标以Sr、Nd、Pb同位素组成及其特征值最为有效，不仅可用于追踪沉积物源，还可用于确定沉积物的年龄、划分沉积地层和反映区域性或全球性的地质事件。古气候变化是影响生物碎屑碳酸盐中C、O同位素组成变化的重要因素，而古气候直接影响物源供给。因此，生物碎屑碳酸盐中C、O同位素组成可以间接反映物源供给情况。此外，石英δ18O对于河流、沙漠、黄土和风尘等沉积物的物源分析以及陆海源汇效应的研究具有重要意义。在利用地球化学方法进行物源分析时，运用单一方法往往存在一定的局限性，应当充分利用各类方法的优势，考虑各种造成误判的因素，利用多种方法综合分析，必要时还应考虑沉积环境的其他要素。 相似文献
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Subrata K. Chakrabarti 《Ocean Engineering》1989,16(4)
The design and performance of an offshore structure depends largely upon the response of the structure to the environmental loading such as waves. The extreme response chosen for the design of a structure should meet its lifetime response, operational response as well as the fatigue damage. The failure of the structural member may be caused by the maximum instantaneous stress experienced by the member due to a given environment. This is considered short-term as opposed to long-term or fatigue damage. The short-term response statistics are obtained on the basis of one particular seastate. Since this seastate is invariably high, nonlinearity in the excitation and response of the structure is almost invariably present. The general nonlinear problem in the extreme response prediction is largely unsolved. Response characteristics are often obtained from the perturbation methods and equivalent linearization techniques. Unlike nonlinear problems, these methods greatly simplify the analysis for extreme values. This paper reviews the available approximation techniques in the response computation and the limits of their applicability in a design situation. Results are illustrated so that a designer may evaluate the suitability of a method in a particular design condition. 相似文献
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壳聚糖硫酸酯制备方法 总被引：8，自引：0，他引：8
壳聚糖是甲壳素脱乙酰基的产物,本身可生物降解,具有良好的生物相容性。经过硫酸化引入SO4^2-基团。给予化合物重要生理功能,使其具有增强机体免疫力,抑制肿瘤,抑制病毒,降糖降脂,抗凝血,防治血栓,治疗溃疡和肾衰等方面的作用,国内外对其开发十分活跃,作者就壳聚糖硫酸酯的理化性质和几种制备方法进行介绍。 相似文献
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In this paper, we use matched-field inversion methods to estimate the geoacoustic parameters for three synthetic test cases from the Geoacoustic Inversion Techniques Workshop held in May 2001 in Gulfport, MS. The objective of this work is to use a sparse acoustic data set to obtain estimates of the parameters as well as an indication of their uncertainties. The unknown parameters include the geoacoustic properties of the sea bed (i.e., number of layers, layer thickness, density, compressional speed, and attenuation) and the bathymetry for simplified range-dependent acoustic environments. The acoustic data used to solve the problems are restricted to five frequencies for a single vertical line array of receivers located at one range from the source. Matched-field inversion using simplex simulated annealing optimization is initially used to find a maximum-likelihood (ML) estimate. However, the ML estimate provides no information on the uncertainties or covariance associated with the model parameters. To estimate uncertainties, a Bayesian formulation of matched-field inversion is used to generate posterior probability density distributions for the parameters. The mean, covariance, and marginal distributions are determined using a Gibbs importance sampler based on the cascaded Metropolis algorithm. In most cases, excellent results were obtained for relatively sensitive parameters such as wave speed, layer thickness, and water depth. The variance of the estimates increase for relatively insensitive parameters such as density and wave attenuation, especially when noise is added to the data. 相似文献
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Chapman N.R. Chin-Bing S. King D. Evans R.B. 《Oceanic Engineering, IEEE Journal of》2003,28(3):320-330
Inversion methods have been developed over the past decade to extract information about unknown ocean-bottom environments from acoustic field data. This paper summarizes results from the Office of Naval Research/Space and Naval Warfare Systems Command (SPAWAR) Geoacoustic Inversion Techniques Workshop, which was designed to benchmark present-day inversion methods. The format of the workshop was a blind test to estimate unknown geoacoustic profiles by inversion of synthetic acoustic field data. The fields were calculated using a high-angle parabolic approximation and verified using coupled normal modes for three range-dependent shallow-water test cases: a monotonic slope; a shelf break; and a fault intrusion in the sediment. Geoacoustic profiles were generated to simulate sand, silt, and mud sediments in these environments. Several different approaches for inverting the acoustic field data were presented at the workshop: model-based matched-field methods; perturbation methods; methods using transmission loss data; and methods using horizontal array information. An effective inversion must provide both an estimate of the bottom parameters and a measure of the uncertainty of the estimated values. New methods were presented at the workshop to formalize the measure of uncertainty in the inversion. Comparisons between the different inversions are discussed in terms of a metric-based transmission loss calculated using the inverted profiles. The results demonstrate the effectiveness of present-day inversion techniques and indicate the limits of their capabilities for range-dependent waveguides. 相似文献
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深水水下管汇安装方法研究与进展 总被引：1，自引：0，他引：1
水下生产系统由于其在开发深水油气田和边际油气田时具有明显的综合经济优势,已被世界上很多国家作为油田开发的一种重要方式广泛研究和应用。基于大量水下生产系统开发方案和工程实例的调研,针对其中水下管汇安装的工程实例,在安装方法的确定、设计和应用方面进行了深入研究,总结了适应不同要求下的多种安装方法,列举和比较各自的优点和限制条件。为油气田开发尤其是深水油气田采用水下生产系统的开发方式时,选择合适的安装方法给出了参考和建议。 相似文献
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When fluid flow passes a cylinder, the drag crisis phenomenon occurs between the sub-critical and the super-critical Reynolds numbers. The focus of the present studies was on the numerical prediction of the drag crisis based on CFD methods. In this work, block structured meshes with refined grids near the cylinder surface and in the downstream were employed. Both 2D and 3D simulations were performed using various turbulence models, including the SST k − ω model, the k − ϵ model, the SST with LCTM, the DES model, and the LES model. In the convergence studies, the effects of the grid size, the time step, the first grid size and the aspect ratio (for 3D simulations) on the solutions were examined. The errors due to spatial and time discretizations were quantified according to a V&V procedure. Validation studies were carried out for various Reynolds numbers between Re = 6.31 × 104 and 7.57 × 105. The averaged drag force, the RMS of lift force and the Strouhal number were compared with experimental data. The studies indicated that standard 2D and 3D RANS methods were inadequate to capture the drag crisis phenomenon. The LES method however has the potential to address the problem. 相似文献
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海洋产油真菌的简便初筛 总被引：1，自引：0，他引：1
选取分离自大洋、深海的28株酵母和143株霉菌，采用在培养基中添加尼罗红比较表观荧光强度的方法来筛选出酵母2株和霉菌7株，但菌体呈红色的酵母（17株）及菌丝为黑色的霉菌（28株）不适用于此法；通过单位DD鲫荧光强度的高低筛选出1株菌落为微红色的酵母，产油性能好于用第一种方法挑选出的2株酵母，且菌体颜色对结果并无影响，但只适合筛选酵母．通过上述2种方法筛选出高油脂菌株，大多来源于深海． 相似文献