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1.
- To characterize the uncertainty and fuzziness in offshore structural inspection, probability of detection (POD) must be determined. This paper presents the expressions for the POD of four different damage forms mainly existing in offshore structures. The fuzzy-set theory is applied to estimate human errors through the definition of inspection quality. Expressions of inspection quality are achieved. To verify the validity and correctness of the expressions, the data from an offshore platform field inspection of evaluation results of human errors affecting inspection quality are used to estimate the parameters of the POD. The results show that the present models can provide basis for further study of ofTshore structural inspection reliability. 相似文献
2.
提出了基于风险的海洋结构物无损检测功能分级方法，采用检测概率、错误识别概率和裂纹出现概率度量检测功能，并修正了错误识别概率的取值范围。根据风险值对无损检测功能进行了分级，研究了风险值随检测概率、错误识别概率和裂纹出现概率的变化规律，分析了风险值对检测费用、维修费用及失效费用的敏感性。在此基础上，将基于风险的海洋结构物无损检测功能分级方法应用于优化检测策略，用算例证明了文中所提方法的有效性。 相似文献
3.
Development of efficient global damage detection techniques for offshore structures is of great importance. The present paper applies the iterative modal strain energy (IMSE) method to locate and quantify the damage for three dimensional frame structures, when limited, spatially incomplete modal data are available. One theoretical development is a new procedure to directly incorporate the spatially-incomplete mode shapes in the algorithm, where slave degrees of freedom iterative updating procedure (SDUP) is developed for evaluating the damage indicator and damage severity. The merits of this new method are that both the modal frequencies and spatially incomplete mode shapes can be used. Also, the modal frequencies do not need to pair the mode shapes one by one. To demonstrate the feasibility and effectiveness of the developed algorithm, numerical studies are conducted for a 3D offshore platform based on data generated from finite element models. Numerical results demonstrate that the present method is effective for the damage assessment of a 3D frame structures when limited, spatially incomplete modal data are available. After considering more practical factors, it is expected to be more applicable in structural damage assessment. 相似文献
4.
A robust damage detection method developed for offshore jacket platforms using modified artificial immune system algorithm 总被引：1，自引：0，他引：1
Mojtahedi A. Lotfollahi Yaghin M.A. Hassanzadeh Y. Abbasidoust F. Ettefagh M.M. Aminfar M.H. 《中国海洋工程》2012,26(3):379-395
Steel jacket-type platforms are the common kind of the offshore structures and health monitoring is an important issue in their safety assessment.In the present study,a new damage detection method is adopted for this kind of structures and inspected experimentally by use of a laboratory model.The method is investigated for developing the robust damage detection technique which is less sensitive to both measurement and analytical model uncertainties.For this purpose,incorporation of the artificial immune system with weighted attributes(AISWA) method into finite element(FE) model updating is proposed and compared with other methods for exploring its effectiveness in damage identification.Based on mimicking immune recognition,noise simulation and attributes weighting,the method offers important advantages and has high success rates.Therefore,it is proposed as a suitable method for the detection of the failures in the large civil engineering structures with complicated structural geometry,such as the considered case study. 相似文献
5.
海洋平台结构超声相控阵检测成像技术的发展及应用 总被引：1，自引：0，他引：1
介绍了超声相控阵检测成像技术的基本原理及其在海洋平台结构检测中的最新进展。超声相控阵技术采用区域划分法将焊缝分成垂直方向的若干区,由扫查器携带超声相控阵探头运动,对其分区进行电子扫查,检测结果以图像形式显示。探讨了超声相控阵技术用于海洋平台结构管节点焊缝检测时存在的一些问题,提出解决方法,指出其在海洋平台结构、压力容器、航空航天等工业无损检测领域将具有应用前景。 相似文献
6.
《Applied Ocean Research》2007,29(1-2):1-16
Offshore structures are exposed to random wave loading in the ocean environment and hence the probability distribution of the extreme values of their response to wave loading is of great value in the design of these structures. Wave loading on slender members of bottom-supported jacket or jack-up structures is frequently calculated by Morison’s equation. Due to nonlinearity of the drag component of Morison wave loading and also due to intermittency of wave loading on members in the splash zone, the response is often non-Gaussian; therefore, simple techniques for derivation of their extreme response probability distribution are not available. Finite-memory nonlinear systems (FMNS) are extensively used in establishing a simple relationship between the output and input of complicated nonlinear systems. In this paper, it will be shown how the response of an offshore structure exposed to Morison wave loading can be approximated by the response of an equivalent finite-memory nonlinear system. The approximate models can then be used to determine the probability distribution of response extreme values with great efficiency. Part I of this paper is devoted to the development of an efficient FMNS model for offshore structural response while part II is devoted to the validation of the developed models. 相似文献
7.
The degree of bending (DoB) characterizing the through-the-thickness stress distribution has a profound effect on the fatigue behavior of tubular joints commonly found in steel offshore structures and the determination of DoB values is essential for improving the accuracy of fatigue life estimation. Probability density functions of the involved random variables are necessary for the fatigue reliability analysis of offshore structures. The objective of present research was the derivation of probability density function (PDF) for the DoB in tubular KT-joints commonly found in jacket-type offshore platforms. A total of 162 finite element (FE) analyses were carried out on 81 FE models of KT-joints subjected to two types of axial loading. Generated FE models were validated using experimental data, previous FE results, and available parametric equations. Based on the results of parametric FE study, a sample database was prepared for the DoB values and density histograms were generated for respective samples based on the Freedman-Diaconis rule. Thirteen theoretical PDFs were fitted to the developed histograms and the maximum likelihood (ML) method was applied to evaluate the parameters of fitted PDFs. In each case, the Kolmogorov-Smirnov test was used to evaluate the goodness of fit. Finally, the Generalized Extreme Value model was proposed as the governing probability distribution function for the DoB. After substituting the values of estimated parameters, six fully defined PDFs were presented for the DoB in tubular KT-joints subjected to two types of axial loading. 相似文献
8.
The load and corrosion caused by the harsh marine environment lead to the severe degradation of offshore equipment and to their compromised security and reliability. In the quantitative risk analysis, the failure models are difficult to establish through traditional statistical methods. Hence, the calculation of the occurrence probability of small sample events is often met with great uncertainty. In this study, the Bayesian statistical method is implemented to analyze the oil and gas leakages of FPSO internal turret, which is a typical small sample risk but could lead to severe losses.According to the corresponding failure mechanism, two Bayesian statistical models using the Weibull distribution and logarithmic normal distribution as the population distribution are established, and the posterior distribution of the corresponding parameters is calculated. The optimal Bayesian statistical model is determined according to the Bayesian information criterion and Akaike criterion. On the basis of the determined optimal model, the corresponding reliability index is solved to provide basic data for the subsequent risk assessments of FPSO systems. 相似文献
9.
The design of fixed or floating offshore structures requires accurate information of the met-ocean data at the intended offshore site. In the design process it is recognized that this environmental data is modified in the near-field by the interaction with the particular geometrical configuration of the offshore structure. This transformation of the incident wave field around and beneath an offshore structure presents a challenge for ocean engineers when specifying the wave gap elevation to avoid impact loads on the underside of the deck and inundation of the topsides. Thus, the accurate estimation of the wave crest distributions from measurements at various locations near and under the offshore structure during model test studies is essential. A semi-empirical approach is presented herein that builds upon the findings of previous studies and introduces the Method of L-moments. A three parameter model for a wave crest probability distribution function is presented and explicit relationships between the parameters of the distribution and its’ first three L-Moments are established. Furthermore, three narrow-band models from earlier research studies are reviewed and compared with the new model. Wave measurements from a mini-TLP model test program are used as the basis for comparison of the four distributions. The root-mean-square error is used as a metric to quantify the overall fit of the data and its accuracy in the high end tail of the data. The L-Moment model is shown to be more robust in representing the data in both the far-field and beneath the deck of the mini-TLP where the wave field demonstrates increased non-linear behavior. 相似文献
10.
Corrosion and fatigue cracks are major threats to the structural integrity of aging offshore platforms.For the rational estimation of the safety levels of aging platforms,a global reliability assessment approach for aging offshore platforms with corrosion and fatigue cracks is presented in this paper.The base shear capacity is taken as the global ultimate strength of the offshore plaffoms,it is modeled as a random process that decreases with time in the presence of corrosion and fatigue crack propagation.And the corrosion and fatigue crack growth rates in the main members and key joints are modeled as random variables.A simulation method of the extreme wave loads which are applied to the structures of offshore platforms is proposed too.Furthermore,the statistics of global base shear capacity and extreme wave loads are obtained by Monte Carlo simulation method.On the basis of the limit state equation of global failure mode,the instantaneous reliability and time dependent reliability assessment methods are both presented in this paper.Finally the instantaueous reliability index and time dependent failure probability of a jacket platform are estimated with different ages in the demonstration example. 相似文献
11.
Extreme dynamic, non-linear response of fixed platforms using a complete long-term approach 总被引：2，自引：0，他引：2
The general theoretical basis for application of the direct long-term approach to offshore structures with non-Gaussian response is outlined. The key to the method is the determination of the short-term response distribution. Special considerations should be taken, depending on the application, and the Weibull distribution with a special fitting procedure is suggested as a short-term probability model for fixed offshore platforms. The efficiency of the method is improved by introducing smoothing functions for the variation of the Weibull parameters with the seastate.
The method is applied to a jacket and jackup platform. The results show that smoothing functions increase the efficiency considerably. The design storm method compares well with the long-term results for the selected structures, but only the long-term approach yields realistic estimates of the design extreme response when both extreme and resonant seastates contribution to the 100-year response. 相似文献
12.
A model is given for the planning of the inspection and maintenance operations of a system: an application to an offshore structure is described. The objectiveis to minimize the total cost of inspections and consequences of failures, subject to an upper boundon the total failure probability of the system. An incremental algorithm is defined for the approximate solution of the problem, and a method is described for the evaluation of the quality of any feasible solution in terms of bounds of the optimal objective value. The incremental algorithm solves the problem parametrically for certain values of the system reliability. The model has been applied to obtain an optimal inspection plan against the consequences of gross errors, accidental events, fatigue and corrosion in terms of input describing element importance values, element reliability values, error detection probabilities, error detection costs and error repair costs for parametrical variations of the structural reliability. 相似文献
13.
Crack detection procedures by different modal parameters are analyzed for identitying a crack and its location and magnitude in a jacket plafform. The first ten natural frequencies and modal shapes of the jacket models are obtained by numerical experiments based on NASTRAN Code. A crack at different locations and of different magnitudes is imposed in the model at the underwater beams. Then, the modal evaluation parameters are calculated numerically, to illustrate the evaluation of modal parameter criteria used in jacket crack detection. The sensitivities of different modal parameters to different cracks are analyzed. A new technique is presented for predicting the approximate location of a breakage in the absence of the data of an intact model. This method can be used to detect a crack in underwater menbers by use of incomplete mode shapes of the top members of the jacket. 相似文献
14.
《Applied Ocean Research》2007,29(1-2):17-36
Finite-memory nonlinear systems (FMNS) are extensively used in establishing a simple relationship between the output and input of complicated nonlinear systems. In Part I of this paper, it was shown how the response of an offshore structure exposed to (random) Morison wave loading can be approximated by the response of an equivalent finite-memory nonlinear system. The approximate FMNS models can then be used to determine, with great efficiency, the probability distribution of response extreme values. Part I of this paper was devoted to the development of FMNS models for offshore structural response. In this part, the validity of the developed models has been investigated by examining the response of three test structures under different environmental conditions. The results are promising. 相似文献
15.
The development of robust techniques for early damage detection for offshore structures is crucial to avoid the possible catastrophe caused by structural failures. This article applies the cross-model cross-mode (CMCM) method for damage detection that is capable of identifying the damage to individual members of offshore jacket platforms, when limited, spatially incomplete modal data is available. Basically, the CMCM method is classified as a direct, physical property adjustment model updating method. Implementing this method requires only a few modes measured from the damaged structure. In dealing with spatial incompleteness, this paper investigates both model reduction and modal expansion techniques. Specifically, either Guyan (static condensation) or SEREP (system equivalent reduction expansion process) transformation matrix, between the master and slave degrees-of-freedom, is employed in the model reduction or modal expansion process. One theoretical development is an iterative procedure to compute the transformation matrix associated with the (unknown) damaged structure. Numerical studies are conducted for a jacket platform with multiple damaged members based on synthetic data generated from finite-element models. The results suggest that (i) Guyan scheme always outperforms SEREP, (ii) model reduction is always better than modal expansion, and (iii) the CMCM method in conjunction with iterative Guyan reduction approach yields the best damage location and severity estimate. 相似文献
16.
V. Sundar 《Ocean Engineering》1989,16(2)
Ocean waves and forces induced by them on offshore structures are random in nature. Experience has shown that short term statistics of wave heights can be described by the Rayleigh distribution for narrow band spectra (Longuet-Higgins, 1952) and that the long term statistics or the evaluation of design wave is based on certain well known extreme value distribution such as mixed Frechet distribution (Thom, 1973a, b).This paper presents a new application of the double bounded probability density function to describe the ocean wave statistics. The prime importance is to estimate the most probable maximum wave height for offshore structural designs. 相似文献
17.
海洋钻修井装置作业前检验,是海上钻修井作业过程中的重要环节。做好作业前检验工作,使作业装置满足作业和安全的要求,是后续作业顺利、安全、高效进行的重要保障。文章根据南海西部近5年来海洋钻修井装置作业前检验工作的现状,从管理、技术层面对作业前检验存在的问题进行剖析,并给出了相关建议。如：作业前检验全生命周期管理的流程及强化措施;保持验船人员的公用机制;引进、培养一支固定的验船队伍;制定验船标准化手册;增加验船技术手段等。为进一步提高海洋钻修井装置检验质量及海上钻修井作业保驾护航。 相似文献
18.
Probability models for offshore structural response due to Morison wave loading Part I: Drag-only response 总被引：1，自引：0，他引：1
Offshore structures are exposed to random wave loading in the ocean environment and hence the probability distribution of their response to wave loading is a minimum requirement for efficient probabilistic analysis of these structures. Due to nonlinearity of Morison wave loading and also due to intermittency of wave loading on members in the splash zone, the response is often non-Gaussian. Analysis of simulated data has, however, shown that neither of the two probability models proposed in the literature can accurately predict the tails of the response distribution. New probability models are therefore required to overcome this deficiency. This paper is composed of two parts: Part I is devoted to the development and validation of a new probability model for drag-only responses (i.e. responses due to the drag component of Morison wave loading), while Part II is devoted to the development and validation of new probability models for both inertia-only and total responses. 相似文献
19.
基于模型相似度拟合的海杂波统计方法 总被引：1，自引：0，他引：1
本文提出一种基于模型相似度拟合的海杂波统计方法。首先根据合成孔径雷达(SAR)图像计算瑞利分布、对数正态分布、韦布尔分布、K分布、G0分布5种经典的海杂波分布的概率密度函数,然后根据模型间的相似度准则拟合得到新的海杂波分布模型。文章利用四景不同类型的真实SAR数据对算法的拟合性能进行了评价,结果显示利用该算法得到的拟合模型与真实SAR数据的平均Kullback-Leibler距离仅为0.015 84,远优于其他分布模型。基于该拟合模型的恒虚警率舰船检测算法对四景SAR数据的平均检测精度达到95.75%,在控制虚警和漏检方面均优于采用其他模型的同类方法。 相似文献
20.
Kerry Gallagher Karl Charvin Soren Nielsen Malcolm Sambridge John Stephenson 《Marine and Petroleum Geology》2009
We present an overview of Markov chain Monte Carlo, a sampling method for model inference and uncertainty quantification. We focus on the Bayesian approach to MCMC, which allows us to estimate the posterior distribution of model parameters, without needing to know the normalising constant in Bayes' theorem. Given an estimate of the posterior, we can then determine representative models (such as the expected model, and the maximum posterior probability model), the probability distributions for individual parameters, and the uncertainty about the predictions from these models. We also consider variable dimensional problems in which the number of model parameters is unknown and needs to be inferred. Such problems can be addressed with reversible jump (RJ) MCMC. This leads us to model choice, where we may want to discriminate between models or theories of differing complexity. For problems where the models are hierarchical (e.g. similar structure but with a different number of parameters), the Bayesian approach naturally selects the simpler models. More complex problems require an estimate of the normalising constant in Bayes' theorem (also known as the evidence) and this is difficult to do reliably for high dimensional problems. We illustrate the applications of RJMCMC with 3 examples from our earlier working involving modelling distributions of geochronological age data, inference of sea-level and sediment supply histories from 2D stratigraphic cross-sections, and identification of spatially discontinuous thermal histories from a suite of apatite fission track samples distributed in 3D. 相似文献