Reliability-Based Full-Life Cycle Optimum Design of Offshore Jacket Platform

Based on the consideration of operation environment and structural property, an optimnm design model of offshore jacket platform is developed in this paper, namely, the reliability-based full-life cycle optimum design model. In this model, the time-dependent reliability assessment method for structural members is established by combination of the decrease, of sectional size and performance deterioration of material. The initial investment, maintenance cost and failure loss cost are assembled into the model. The total cost of the platform structure system in its full service period is chosen as the objective function, and the initial reliabilities of the layer elements partitioned in advance are taken as the design variables. Different models are obtained, depending on whether the system reliability eonstraint is considered or not. This optimum design model can result in the lowest full-life cost and the optimal initial layer reliability of an offshore jacket platform in the design of marine structures. The feasibility of this model is illustrated with an actual jacket platform in the Liaodong Gulf as an example.     

Categorisation and Harmonisation of Probabilistic Earthquake Hazard Assessments with Respect to Statistic Representation of Input Data

Probabilistic hazard calculations were tested with respect to input data uncertainties. Statistical approximations of input data allow the regression coefficients and their standard deviations to be determined. Since inaccuracies of the regressions closely depend on the input data uncertainties, the standard deviations of the individual coefficients were used as a measure of input data parametrisation. Differences in the hazard outputs, caused only by various combinations of the regression coefficients and their standard deviations determined for the cumulative recurrence graph and the attenuation law, were studied. It was concluded that the hazard calculation conditions should be (a) strictly defined and always quoted with every hazard assessment, and (b) standardized in order to establish a common liability of earthquake hazard calculations. The established categorisation of the earthquake hazard assessments divides the probabilistic hazard calculations according to their reliability and helps users to apply them in earthquake engineering practice. The credible hazard assessments corresponding to 90% probability can be recommended for common structures whereas the maximum credible hazard assessments coinciding with 95% probability yield values close to hazard assessments of important structures, hospitals, bridges, etc.     

THE EFFECTS OF INACCURATE INPUT PARAMETERS ON DEPOSITION OF SUSPENDED SEDIMENT

I.~OntjcnONEngineeringPredictionsofsedimenttransPOrtinopen-Channelsystems,especiallyifunsteadyflowconditionmustbeconsidered,isfraughtwithambigUityduetospatialandtemporalvariability,measurementerrors,lumtedsamplingoftheParameters,bounceandscallconditionS,andsink/sourcetenns.Duringrecentyearsmanysophisticatedmathematicalmodelshavebecomeavailabletocalculateunsteadyflowinone,tWoorthreedimensionS.ThesemodelswillbecoupledwithtranSportequationSforbedloadorsuSpendedloadtocalculateforexamplelongt…     

随机时变抗风结构动力可靠性分析

研究了随机时变结构特性，提出了随机时变强度的衰减表达式；在随机动力荷载作用下，用振型分解法分析了时变参数结构的动力响应，得到了此类结构的动力响应谱与数字统计式；给出了确定时变界限的方法；在若干基本假设下，得到了时变结构的可靠度计算公式；提出了在役结构时变可靠度的分析方法，以及结构在设计使用期与预计使用期限内可靠度评估公式     

Application of a wind-driven hydrodynamic model for the quantification of transport in an open boundary canal-lakes system in sw Friesland,The Netherlands

The south western lake district is a part of the boezem, a system of interconnected lakes and canals in the province of Friesland. The lake district has open boundaries with the other part of the boezem system. However, discharges in the boundary canals are unknown. These discharges are needed for modelling the phosphorus dynamics in the study area. Incidental water flow measurements gave a good indication of the complex water transport in the study area, but continuous water flow recording was not possible. Consequently, discharges could not be measured directly. In order to quantify the discharges, the water transport in the area was modelled by the application of a detailed wind-driven hydrodynamic model. In the model hourly mean values of wind data and water levels at the boundary locations were used as forcing functions. Model tuning was done by comparing observed and computed water levels of three stations within the system. This approach is new in surface water systems in The Netherlands. Therefore, a sensitivity analysis was done and it was verified whether the model results were reliable.The sensitivity analysis showed that the sensitivity was low for modifications of the wind exponent value and rather high for the bottom roughness coefficient. Simulations with daily or weekly mean wind and water level data resulted in an undesirable loss of detail. The sensitivity for noise at the imposed water levels at the boundary locations was moderate. The calculated discharges were used as forcing functions for a chloride mass balance model. Calculated chloride concentrations coincided with measured concentrations in three lakes, during three periods. From this it was concluded that the discharges were reliable. The simulations also lead to the quantification of the water balance and water residence times in the lakes.     

Time-Dependent Reliability Analysis of Offshore Structures

During the life of an offshore structure,its structural strength declines due to various kinds ofdamages related to the time factor.In this paper,four major kinds of damages,including damages causedby fatigue,dent,corrosion and marine life,are discussed.Based on these analyses,formulas for theevaluation of the damaged structure reliability are derived.Furthermore the computer program ISM forthe analysis of structural reliability is developed by the use of Advanced First Order Second Moment meth-od and Monte-Carlo Importance Sampling method.The reliability of a turbular joint and a beam are stu-died as numerical examples.The results show that the theory and the analysis method given in this paperare reasonable and effective.     

Determination of Partial Factors of Breast Wall on Top of Sloping Breakwater

- By applying the theory of structural reliability, reliability analyses for the stability of a breast wall on the top of a sloping breakwater are carried out. Based on the analyses, the method for determining partial action / load factors and partial resistance factors of breast walls is expounded, and the design expressions with partial factors are given. The values of partial action / load factors and partial resistance factors are recommended preliminarily according to the computation for breast walls with typical cross-sections.     

结构模糊可靠性指标的遗传算法

本文基于哈索弗－林德提出的结构可靠性指标β的定义，通过改进的遗传算法，建立了考虑变量服从多种概率发布与相关性及其模糊性的广义随机空间内可靠性指标的计算方法，并且通过结构可靠性指标分析与可靠性优化的实例，验证了算法的可行性与可靠性     

Time-Variant Reliability Analysis of FPSO Hull Girder Considering Corrosion Based on Statistics

FPSO is a kind of important exploitation platform used in ocean oil and gas industry, which has the unique character of mooring at outsea for a long time. Since it can not be inspected and maintained thoroughly at dock like other kinds of ships, the reliability of FPSO hull girder during the whole service should be focused. Based on latest corrosion database and rational corrosion model, the ultimate strength of one FPSO is calculated under the conditions of slight, moderate and severe corrosion. The results not only provide the reliability under different corrosion conditions, but also do well for further inspection and maintenance research. The results provide necessary foundation for deciding inspection intervals and maintenance measures, which has practical sense to improve the general safety level of ocean engineering.     

等幅疲劳三参数P—S—N曲线族最优拟合法

对于给定的等幅疲劳成组试验数据 ,利用三参数幂函数方程来描述P -S -N等幅曲线。通过线性拟合相关系数的最优化来确定其中三个系数 ,采用割线法进行最优化求解。该方法具有迭代收敛快、拟合精度高的特点