基于模糊故障树方法的脐带缆可靠性分析研究

脐带缆作为水下生产系统的“神经生命线”,是水下生产系统的关键一环,其可靠性问题越来越受到关注。影响脐带缆可靠性的事件具有随机性,目前缺乏对这些随机事件发生概率的统计,难以直接对其可靠性进行定量分析。基于模糊数理论和故障树结合的方法对脐带缆可靠性进行分析,首先获得引起脐带缆失效的40个最小割集及底事件重要度排序。其次采用基于模糊集理论的定量分析对脐带缆故障树系统中的底事件进行统计计算,得到各底事件的失效概率,最终计算出顶事件概率,并得出导致脐带缆失效的主要因素依次为护套/铠装失效、钢管失效、电缆失效,为脐带缆的安全运行提出适当的建议。     

海洋平台结构系统可靠性分析

本文研究了对三维模型的导管架平台结构系统可靠性评估方法。在极值载荷条件下，分别以极限冲剪应力及屈曲临界应力作为管节点及杆件的极限强度，采用增量载荷法建立失效模式安全余量方程。同时研究了求取结构系统主要失效模式的自动算法及计算系统失效概率的方法。作为一个算例，运用作者开发的计算机程序，对一固定式导管架平台进行了可靠性分析，验证了本文方法对开展三维模型平台结构系统可靠性评估是可行的。     

海上消防系统风险分析探讨

平台消防系统可靠与否直接影响到平台及平台操作人员的安全。文章在采用故障树方法对平台消防系统发生失效的路径及可能性进行分析。针对有些事件的发生频率极小但危险性极大的问题,引入危险度的概念,对可靠性进行量化,即计算产生概率,同时提出了计算模糊事件概率期望值的方法。为有效评估油气生产系统的安全性,以及建立起稳定可靠的功能服务系统提供了理论依据。     

基于重点抽样法的固定式平台结构风险评价研究

在建立海上油气设施的风险分析系统时,对由台风引发的极端海况造成的结构失效进行风险评估是1个十分重要的问题。为了建立实用可靠的风险评价方法,本文使用基于重点抽样法的随机模拟技术,对渤海海域CB12-C井组平台结构进行了全概率法失效概率计算,并在此基础上进行了平台结构的风险评价。该方法是1种适用于固定式海洋平台的定量风险评价方法,充分考虑了平台结构风险分析过程中各种不确定性的影响,极大提高了定量风险评价结果的可靠性。     

防波堤风险分析研究框架

介绍了防波堤风险分析研究的内容、方法和目前的研究进展。防波堤风险分析包涵四个主要方面:防波堤风险辨识、防波堤风险估计、防波堤风险评价和防波堤风险控制。具体内容包括:防波堤系统正常使用极限状态和承载力极限状态的界定,波浪不确定性的识别和描述,防波堤失效模式的探讨,单一模式失效概率和系统失效概率的计算,两种极限状态失效后果的量化,成本-获益分析,效用分析,可接受风险准则和降低风险的措施。防波堤风险分析的目的在于为决策者明确工程中存在的诸多不确定性因素,提供充足信息,实现项目的决策优化。     

QSF3—1型声学应答释放器的可靠性分析

本文就海洋监测系统中用到的一种仪器－ＱＳＦ３－１型声学应答释放器进行了可靠性分析。采用了迄今为止，在国外被公认的对复杂系统进行可靠性分析的最好方法－失效树分析法。详细地介绍了建树过程及各基本事件概率的计算方法，给出了ＱＳＦ３－１型声学应答释放器的可靠性指标。最后对提高释放器的可靠性途径进行了讨论。     

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     

钢悬链线立管强度可靠性计算研究

在钢悬链线立管分析中,材料性能、载荷参数、计算方法等都存在着大量不确定性。为考虑不确定性因素造成的影响,采用作用效应-抗力半随机过程构建可靠性模型,并采用极小化变换转化为静态可靠性问题。选用物理含义较为明确的屈服判定准则建立功能函数,通过单样本K-S检验对载荷随机过程的概率特性进行极值统计,提出载荷转化的方法以实现与目标可靠性指标的比对,并引入模型和主观不确定性随机变量。在此基础上采用改进的一次二阶矩法,对立管的强度可靠性进行了计算。结果表明此方法与利用系数方法能够相互印证,可以为立管的可靠性计算提供参考。     

海洋导管架平台抗震可靠性分析方法

以渤海湾的两座典型海洋导管架平台为研究对象,运用非线性逐步破坏分析方法,提出了在环境荷载作用下海洋导管架平台结构抗震可靠性的分析方法,并计算了相应的可靠度.计算与分析结果表明,本例的海洋导管架平台的抗震可靠度较大,即失效概率很小,而且该分析方法是一种较为简单、实用和可靠的分析方法.     

直接积分法在防波堤可靠性分析中应用

防波堤是港口工程的重要组成部分,在港口工程总投资中占有较大的比重。准确地计算防波堤的可靠性具有重大的理论和经济意义。随着数理统计理论的快速发展,直接积分法在结构可靠性计算中的应用逐渐得到重视。应用直接积分法计算直立式防波堤的可靠性,概率意义明确,计算精度高。以秦皇岛典型直立堤为算例,采用直接积分法对直立式防波堤进行可靠性分析时,将无限积分区域转换成有限积分区域,分析选择了波浪力和浮托力的联合密度函数,采用数值积分的办法计算失效概率,并将计算结果与独立变量JC法和相关变量JC法的计算结果进行了对比。结果表明:直接积分法和相关变量JC法计算结果相近,而比独立变量JC法计算结果偏低。     

Risk Analysis of Breakwater Caisson Under Wave Attack Using Load Surface Approximation

A new load surface based approach to the reliability analysis of caisson-type breakwater is proposed. Uncertainties of the horizontal and vertical wave loads acting on breakwater are considered by using the so-called load surfaces, which can be estimated as functions of wave height, water level, and so on. Then, the first-order reliability method（FORM） can be applied to determine the probability of failure under the wave action. In this way, the reliability analysis of breakwaters with uncertainties both in wave height and in water level is possible. Moreover, the uncertainty in wave breaking can be taken into account by considering a random variable for wave height ratio which relates the significant wave height to the maximum wave height. The proposed approach is applied numerically to the reliability analysis of caisson breakwater under wave attack that may undergo partial or full wave breaking.     

Effect of various surface-height-distribution properties on acoustic backscattering statistics

A problem of interest to underwater acousticians is understanding the relationship between ocean-bottom characteristics and acoustic backscattering statistics. This experimental work focused on examining surface roughness characteristics that cause backscattering strength statistics to deviate from the Rayleigh distribution. Several different scattering surfaces with known height distributions were designed for this study. The surfaces were modeled using a technique that allowed for different height-distribution functions and correlation lengths to be prescribed. Isotropic and anisotropic surfaces were fabricated having both Gaussian and non-Gaussian surface-height distributions. Many independent backscattering measurements were made for different aspects of each surface using a computer-controlled transducer-positioning system. Acoustic backscattering statistics were non-Rayleigh for the anisotropic surfaces when combining measurements from different aspects. Mean scattering strength was found to be dependent on both the surface-height distribution and correlation length. In addition, backscattering strength showed a dependence on the surface-height power distribution.     

Comparative Study on Response Surfaces for Reliability Analysis of Spatially Variable Soil Slope

This paper focuses on the performance of the second-order polynomial-based response surfaces on the reliability of spatially variable soil slope. A single response surface constructed to approximate the slope system failure performance function G(X) (called single RS) and multiple response surfaces constructed on finite number of slip surfaces (called multiple RS) are developed, respectively. Single RS and multiple RS are applied to evaluate the system failure probability pf for a cohesive soil slope together with Monte Carlo simulation (MCS). It is found that pf calculated by single RS deviates significantly from that obtained by searching a large number of potential slip surfaces, and this deviation becomes insignificant with the decrease of the number of random variables or the increase of the scale of fluctuation. In other words, single RS cannot approximate G(X) with reasonable accuracy. The value of pf from multiple response surfaces fits well with that obtained by searching a large number of potential slip surfaces. That is, multiple RS can estimate G(X) with reasonable accuracy.     

Comparative Study on Response Surfaces for Reliability Analysis of Spatially Variable Soil Slope

This paper focuses on the performance of the second-order polynomial-based response surfaces on the reliability of spatially variable soil slope.A single response surface constructed to approximate the slope system failure performance function G(X)(called single RS) and multiple response surfaces constructed on finite number of slip surfaces(called multiple RS) are developed,respectively.Single RS and multiple RS are applied to evaluate the system failure probability pf for a cohesive soil slope together with Monte Carlo simulation(MCS).It is found that pf calculated by single RS deviates significantly from that obtained by searching a large number of potential slip surfaces,and this deviation becomes insignificant with the decrease of the number of random variables or the increase of the scale of fluctuation.In other words,single RS cannot approximate G(X) with reasonable accuracy.The value of pf from multiple response surfaces fits well with that obtained by searching a large number of potential slip surfaces.That is,multiple RS can estimate G(X) with reasonable accuracy.     

Estimation of the Effect of Lateral Flow on Piled Bridge Abutments in Soft Ground Considering Piled Slabs as a Countermeasure of the Abutments

The effectiveness of a simple method to estimate the lateral movement of piled bridge abutments due to lateral flow from the safety factor (Fs) of slope stability analysis was studied. This was accomplished through the construction and measurement of actual piled bridge abutments and its backfill, with and without piled slabs as a countermeasure. To do this, a computer program SLOPILE (VER 3.0) considering the lateral earth pressure acting on a row of piled bridge abutment was developed. SLOPILE (VER 3.0) can calculate the slope stability for both planar failure surfaces in infinite slopes and arc failure surfaces based on Fellenius or Bishop simplified methods. SLOPILE (VER 3.0) was utilized to design the piled bridge abutment reinforced by a piled slab at a real site. The piled slab can effectively prevent the lateral flow of soft ground and satisfy not only the safety factor of a slope but also the allowable bearing capacity of piles. To verify the design method, an instrumentation system was adapted. The instrumentation results from a case study clearly showed that the piled slab effectively resisted the lateral movement of a bridge abutment due to placement of backfill. Also, the surcharge loads due to backfill were supported by the piled slab and transmitted to the bedrock through the piled slab.     

Ocean acoustic field matching: normal mode filtering andnon-Gaussian sources

Two qualitative results concerning statistical sonar signal processing and acoustic field matching are obtained. First, normal-mode field predictions are integrated with statistical signature analysis by constructing a boundary-value problem in the acoustic waveguide. From this construction it is found that the normal-mode filter is the unique acoustic preprocessor which does not confound deterministic waveguide correlation structure with stochastic source covariance structure. Second, the origin of deterministic, Gaussian, and non-Gaussian source signatures is investigated by associating physical parameters with the classical Lindeberg central limit conditions. From construction it is found that there are important objects that are not adequately represented either by infinitesimal points or by infinite surfaces. If receiver resolution is inadequate to resolve source complexity, these objects will exhibit a non-Gaussian acoustic signature via an entirely linear progression from internal excitation, to source radiation, through waveguide propagation, and finally to reception     

基于辛几何算法的高斯束叠前深度偏移

辛几何算法是专门针对动力学过程设计的算法,以提高动力学问题求解的精度与效率。高斯束偏移过程中的运动学与动力学射线追踪,从物理上讲是一个动力学过程,可以利用辛几何算法对其进行优化。本文将基于辛几何算法的运动学射线追踪引入高斯束叠前深度偏移中,并在推导了动力学射线追踪方程组的辛差分格式基础上,实现了基于辛几何算法的高斯束叠前深度偏移。模型实验表明,基于辛几何算法的运动学射线追踪,其效率与精度相比常规算法都具有一定优势,而基于辛几何算法的高斯束叠前深度偏移方法能够对复杂构造模型精确成像。     

Asymptotic analysis of the interaction between linear long waves and a submerged floating breakwater of wavy surfaces

In this work, we carried out an asymptotic analysis, up to the second order in a regular expansion, of the interaction of linear long waves with an impermeable, fixed, submerged breakwater composed of wavy surfaces. Below the floating breakwater, there is also a step with a wavy surface. The undulating surfaces are described by sinusoidal profiles. The effects of three different geometric parameters — the amplitude of the wavy surfaces and the submerged length and width of the structure — on the reflection and transmission coefficients are analyzed. The hydrodynamic forces are also determined. The governing equations are expressed in dimensionless form. Using the domain perturbation method, the small wavy surfaces of the breakwater are linearized. The wavy surfaces of the breakwater generate larger values of the reflection coefficient than those obtained for breakwaters with flat surfaces, and the largest values of this coefficient are obtained when the length of the breakwater is of the same order of magnitude as the wavelength. The asymptotic solution is compared with the theoretical solutions that have been reported in the specialized literature and with a numerical solution. The present mathematical model can be used as a practical reference for the selection of the geometric configuration of a submerged floating breakwater under shallow flow conditions.     

A panel-free method for time-domain analysis of the radiation problem

A panel-free method (PFM), based on the desingularized Green’s formulae proposed by Landweber and Macagno, has been developed to solve the radiation problem of a floating body in the time domain. The velocity potential due to a non-impulsive velocity is obtained by solving the boundary integral equation in terms of source strength distribution. The singularity in the Rankine source term of the time-dependent Green function is removed. The geometry of a body surface is mathematically represented by NURBS surfaces. The integral equation can be globally discretized over the body surface by Gaussian quadratures. No assumption is needed for certain degree of approximation of distributed source strength on the body surface. The accuracy of PFM was demonstrated by its application to a classical problem of uniform flow past a sphere. The response function of a hemisphere at zero speed was then computed by PFM. The computed response function, added-mass and damping coefficients are compared with other published results.     

Checking vulnerability to pure loss of stability in long crested following waves: A probabilistic approach

This paper presents a probabilistic methodology for the analysis of the vulnerability of a ship to the risk of inception of pure loss of stability events. A pure loss of stability failure is modelled as the persistence of the metacentric height below a critical level for a too long time. The metacentric height is modelled as a stationary Gaussian process with a spectrum obtained from the sea elevation spectrum. The time dependent failure index is obtained under the assumption of filtered Poisson process for the occurrence of critical events. The analysis separates cases where the fluctuation of the metacentric height is narrow-band from those where the bandwidth of the spectrum is wide, with an intermediate blending. In case of narrow-band processes appropriate approximate solutions to the problem are provided, while in the wide-band cases an exponential distribution for the persistence time below the critical level is employed. A rational development for the critical persistence time is also provided considering an approximation of the roll dynamics during periods of time where the metacentric height is negative. Monte Carlo simulations are performed to check the developed approximate distributions for the persistence time, and examples of application are provided for a sample ship.