斜坡式防波堤的可靠性分析

对港口工程中常用的可靠度计算方法进行阐述,给出了斜坡堤护面块体稳定性可靠性分析的功能函数,介绍了港口工程中常用的单变量极值分布。以秦皇岛水文观测数据为基础,统计换算斜坡堤护面块体的质量,采用极值分布理论对护面块体的计算质量进行分布拟合,对比得出对数正态分布可以对护面块体质量分布进行较好的适线。从算例计算结果对比中可以发现,Monte Carlo模拟的可靠度指标计算结果比验算点法的计算结果低。两种方法计算的可靠度指标均比规范要求的低。利用Monte Carlo模拟计算结构可靠度,选择合理的模拟次数即可。     

箱筒型基础防波堤的结构尺寸对其稳定性的影响分析

利用基于极限平衡法的箱筒型基础防波堤稳定性分析方法,分析了不同结构尺寸对这种结构稳定性的影响。结果表明基础筒高的变化对抗滑稳定性安全系数的影响最大;倾覆极限状态时和竖向承载力极限状态时转动点位置对应的无量纲量l/L分别在0.5和0.9附近。     

船用柴油机进气道类型及结构参数对流通性能的影响

以船用柴油机进气道为研究对象,用经试验验证的数值模拟方法研究了不同类型进气道的流通特性及串联进气道主要结构参数对气道流通性能的影响。研究结果表明,不同类型气道中,并联气道进气能力较串联气道要大,但并联气道形成的涡流比很弱;串联气道流量系数比对称型并联气道稍小,但能形成一定的涡流比;在进气道喉口面积一定的情况下,气道进口面积大小是影响气道流量系数最明显的结构参数,其余结构参数对气道流量系数影响都很小;进气道各结构参数对气道涡流比都有影响,其中气阀座高对涡流比影响最大,气道进口高度对涡流比影响也比较明显;气道出口处气流分布情况影响进气涡流大小,沿缸套周向速度分量越大,形成进气涡流的能力越大。     

鳍结构对SWATH船纵向稳定性及运动性能的影响

针对保持SWATH船纵向运动稳定鳍的结构尺寸难以确定的特点，从实船对鳍的展长和弦长取值的约束条件出发，利用计算机仿真出SWATH船在40kn的航速范围内保持纵向运动稳定的鳍结构尺寸的变化范围，然后，从这一范围内确定出不同航速且具有一定运动性能要求的鳍尺寸变化范围。以此为基础仿真出了对应于不同航速SWATH船在静水中的升沉和纵摇运动性能指标的变化范围。结果表明，此方法直观、有效，能初步确定稳定鳍尺寸并分析静水中鳍尺寸对SWATH船运动性能影响。     

船舶可修指数分布单元的可靠性评定

文章推导出可修小子样指数分布单元的Bayes方法稳态可用度下限,并在其基础上进行Monte Carlo仿真。评定方法有效地解决了船舶动力系统的可修小子样指数产品可靠性评定问题。     

显式和隐式方法求解防波堤可靠度的差异分析

半圆形防波堤具有稳定性高、结构简单、便于施工等优点。以往对其进行可靠度计算时,根据波高与周期,计算防波堤受到的荷载作用,将荷载作为随机变量,估计其概率分布模型,建立显式的极限状态方程,再进行求解。计算得到的波浪荷载序列对于最优分布线型的离散程度较差。采用基于隐式功能函数的防波堤可靠度分析方法,将波高和周期作为随机变量,无需计算波浪荷载这一中间序列,规避了误差的产生,简化了计算流程。分别采用隐式与显式两种方法对半圆形防波堤进行了可靠性分析。结果表明,两种方法得出的可靠度指标存在差异,这种差异是由于波浪荷载拟合时所产生的误差造成的。     

A reliability approach to fatigue crack propagation analysis of ship structures in polar regions

Fatigue is a common failure mode in ship structures. For structures with an initial crack, the fatigue crack propagation behavior needs to be considered. The purpose of this study is to establish a procedure for analysis of fatigue crack propagation of ship structures in combination with reliability methods. The stress intensity factor (SIF) and geometry correction factor are calculated by means of finite element analysis. Validation for the SIF calculation is achieved by comparing the computed results with those based on related solutions. Since fatigue damage usually occurs in weld areas, the effect of such components on the fatigue crack propagation behavior was also considered in this work. The Paris law in combination with the Monte Carlo technique are employed for the fatigue crack propagation analysis in this study. Reliability updating based on inspection for cracks is also carried out. A computer program was developed for the purpose of fatigue crack propagation analysis within the framework of reliability methods. An application example of fatigue crack propagation in relation to the hull of the icebreaker Xuelong 2 is presented. The sensitivity of the procedure to key analysis parameters (sample size, initial crack size) is also considered. Finally, the effect of low temperatures on the computed results is also analyzed.     

基于BP神经网络-Monte Carlo法的结构可靠性分析

  目的  船舶结构极限承载能力不足会导致海损事故,为此提出改进AK-MCS法,用于船舶结构极限强度可靠性研究。  方法  通过引入信息熵中的学习函数H对样本点进行二次寻优,以提高最佳样本点的质量,从而提高Kriging模型的精度和更新效率;采用K折交叉验证替代AK-MCS法的迭代停止准则,解决原本迭代停止准则过于保守的问题,以有效避免发生过学习和欠学习状态,从而以较少的样本点训练Kriging模型,实现对极限状态函数的高度拟合。使用非线性振荡器数学模型进行验证,并将改进AK-MCS法应用于船舶板架的极限强度可靠性研究。  结果  仿真结果表明,改进AK-MCS法调用有限元模型的次数比原方法减少了38%,验证了改进AK-MCS法的求解效率和精度。应用结果表明,该方法的计算精度最高,且调用有限元仿真次数比原方法减少32%,验证了改进AK-MCS法在船舶板架极限强度可靠性研究中的适用性和高效性。  结论  使用改进AK-MCS法研究船舶板架极限强度的可靠性,可评估船舶实际航行中局部结构尤其局部较危险结构的失效概率。     

超大型集装箱船绑扎桥数值模拟及结构优化

  目的  对超大型集装箱船绑扎桥结构而言,复杂的设计结构和恶劣的载荷环境对其可靠性提出了更高的要求。针对大型船舶结构可靠性分析时计算效率低、计算精度差等问题,提出基于改进梯度提升决策树—蒙特卡罗（GBDT-MC）方法。  方法  首先,通过Python库建立改进梯度提升决策树（GBDT）的近似模型,根据实验生成较少的样本点,并筛选位于失效面附近的样本点;接着,运用SMOTE算法合成新的样本点并参与有限元计算,进而结合原有的样本点形成训练集;然后,采用已训练的近似模型预测蒙特卡罗（MC）方法所产生的样本点信息,完成结构的可靠性分析;最后,运用算例验证改进GBDT-MC方法的可行性和准确性,并将其应用于超大型集装箱船绑扎桥结构的可靠性分析。  结果  计算结果表明：案例中超大型集装箱船绑扎桥在静态绑扎力作用下的失效概率误差为 3.5%,改进GBDT-MC方法的计算耗时为2.55 h,而MC方法则需要416.7 h,可见在允许的计算误差范围内,改进GBDT-MC方法可以大为缩减可靠性分析的计算时间。  结论  改进GBDT-MC方法能显著提高计算精度并缩短计算时间,可为结构可靠性的优化设计提供支持。     

A multi-criteria decision method for the analysis of the Motorways of the Sea: the application to the case of France and Spain on the Atlantic Coast

Despite European Union (EU) political support to identify the most feasible Motorways of the Sea, the final decision can only be made by Private Shipping Companies, which are operators of a unique stretch of the intermodal chain. This paper provides a multi-criteria decision method to identify the most suitable Motorways of the Sea taking into account the competitiveness of whole intermodal routes versus the alternative of road transport from the loader’s perspective. The analysis is carried out assuming a ‘many-to-many’ transport model. Firstly indexes of time and cost were defined and evaluated for every available route in the model in accordance with a multi-criteria decision matrix. Secondly, through a Monte Carlo simulation a sensitivity analysis was carried out in order to evaluate the influence on the results of the forecast assumed to construct the matrix. The results obtained are not only quantitative, but also qualitative. The development of intermodal routes via Motorways of the Sea is especially relevant for the peripheral EU countries. Due to the relevance of the freight flow between France and Spain and the congestion of their connections through the Pyrenees, the method proposed was applied to the analysis of this particular case