基于非线性设计波的船体结构强度直接计算研究

针对规范公式不适用于小方形系数Cb0.6的船舶以及线性设计波法不能反映波浪载荷非线性特征的情况,使用非线性设计波法研究了一艘小方形系数船的波浪载荷长期预报极值和波浪载荷与波高非线性变化规律,给出了非线性设计波参数的选取办法。根据参数,用非线性设计波法计算了船舶的波浪附加弯矩,并与线性设计波和规范公式两种方法得到的波浪附加弯矩进行了比较分析。分析结果表明,非线性设计波法能够反映出波浪幅值较大时波浪载荷随波高非线性变化的规律,以及中拱、中垂状态下舯剖面波浪附加弯矩的非对称特征,较线性方法更为合理。     

内河船舶可靠性分析中的波浪弯矩统计与极值分布

以内河A级航区波浪散布图与波浪谱为环境参数,基于三维势流水动力程序对43艘内河船舶进行波浪弯矩长期预报,获得样本船波浪弯矩长期Weibull概率分布的形状参数、尺度参数和10-8超越概率的预报值。将波浪弯矩预报值与静水弯矩进行对比,根据Turkstra载荷组合规则,确定船体梁总纵强度可靠性分析中的载荷组合形式。在此基础上采用序列统计法对波浪弯矩极值分布进行分析,极值分布近似服从Gumbel分布,即I型极值分布。     

船舶波浪弯矩短期预报研究

采用两种方法（一是利用WALCS软件，基于三维频域线性水动力理论；二是利用3小时波浪弯矩有义值MS，根据极值I型理论）进行船舶波浪弯矩短期预报，并分别计算得到16艘船舶（6艘散货船、10艘油船）的短期波浪弯矩。经比较发现，根据极值I型理论得到的短期波浪弯矩与WALCS软件短期波浪弯矩偏差较小，在工程实践中具有一定参考价值。     

UR S11A对船体梁波浪载荷长期极值的影响研究

2016年7月1日起生效的新版UR S11A以提升集装箱船结构安全为目标,替代了之前的版本UR S11。论文对UR S11A和UR S11中关于船体梁波浪载荷长期极值的计算公式和技术背景进行了比较。以已经交付运营或正在建造中的14型不同尺度集装船为分析数据库,对这两个规范在确定波浪载荷长期极值中的应用进行对比研究。然后以一型超大型集装船为算例,用基于线性波浪载荷的谱分析法、基于非线性波浪载荷的等效设计波法和非线性等效设计海况法等三种长期极值预报方法,对船舯区域垂向波浪弯矩进行计算,并分析它们与规范值之间的差异。总结UR S11A对船体梁的波浪载荷长期极值的影响,也为集装箱船波浪载荷设计极值的确定提供参考和建议。     

舰船总体结构的可靠性分析

本文首先介绍了三个水平等级可靠性分析方法的概况，随后详述了船体波浪诱导弯矩极值和甲板屈曲极限变矩统计参数的计算过程。最后根据第二水平法以现役五型舰船为计算对象，在分析综合的基础上推荐舰船设计的目标安全指数。     

航速对大型半潜船波浪载荷影响研究

基于三维势流理论,采用考虑航速的波浪载荷预报方法,对一艘10万t级半潜运输船在0航速及设计航速下的船体梁波浪弯矩及波浪剪力进行预报,结果表明,设计航速下船体波浪弯矩极值较0航速时增加约9%,波浪剪力极值增加约18%。为10万吨级大型半潜船设计提供参考。     

船舶横摇非线性运动最大值预报

横摇运动振幅渐近分布属于指数型分布，根据应用Markov过程理论得到的极值分布推导了最大值分布公式，同时提出了最大值预报方法。计算表明用此方法预报的最大值与实际统计的最大值非常接近，它比用线性理论预报的最大值误差要小，证明本文提出的最大值预报方法是可行的。     

用线性规划求船舶静水弯矩极值和剪力极值

本文将求解静水弯矩极值和剪力极值化为在一组约束条件下求线性泛函极值的问题,并用线性规划方法进行求解。不仅减少了计算的工作量,也为船舯剖面最优设计提供了求弯矩和剪力极值的方法。本文以16000吨散货船为例作了计算,并与常规方法的计算结果作了比较。本文方法还能用于在装载量一定时,求出最小弯矩和剪力的配载。     

船舶波浪弯矩1周短期预报研究

当船舶在海上发生碰撞、搁浅、泄漏等事故后,需在1周之内进行救助,所以有必要研究船舶1周短期波浪弯矩的预报方法。本文介绍2种方法:一是利用WALCS软件,基于三维频域线性水动力理论,计算后得到16艘船舶(6艘散货船、10艘油船)的1周短期波浪弯矩,记为1周软件波浪弯矩预报值;二是根据极值I型理论,通过公式推导,利用已知3小时波浪弯矩有义值M S,计算后得到了16艘船舶的1周短期波浪弯矩,记为1周极值I型波浪弯矩预报值。经比较发现二者预报结果高度一致,认为采用极值I型理论进行船舶波浪弯矩1周短期预报准确可靠,且该方法耗时更短,简便易行,值得推广。     

海浪统计资料对船舶波浪弯矩设计值的影响

对船舶,特别是超规范船舶,进行结构的直接计算设计时,首先要知道波浪弯矩设计值。 要确切地做到这一点,设计人员应合理地选择船舶航行海域的海浪长期统计资料,然后根据船 舶的装载工况和实际可能达到的航速,借用线性理论或非线性理论进行波浪弯矩的长期预报 来确定设计值。本文就一艘大型集装箱船舶,按五个典型海域的海浪统计资料,对波浪弯矩及 波浪合成弯矩作了长期预报计算,并与 ＩＡＣＳ的统一纵强度要求ＵＲ—Ｓ１１的结果作了比较和 分析,给出了对船舶结构直接计算设计有指导意义的几点结论。     

一种新型海洋能发电轮机水动力特性研究

摘 要：海洋发电轮机所处的海上作业环境恶劣，设备易发生故障且维修困难。基于三维势流理论，并结合ANSYS-AQWA软件，对风、浪、流荷载联合作用下的海洋能发电轮机的水动力特性进行研究，得出了发电轮机在工作工况及极限工况下的运动响应特性。结果表明，浮体运动响应幅值的最大值分别发生在遭遇艏斜浪和横浪时；其中极限工况下的运动响应幅值是工作工况下的3-10倍。该装置经过循环改型后水动力性能良好，能够满足实际的工程应用，本文提出的计算方法可以作为一种快速预报装置水动力特性的校核手段，满足工程设计阶段的需求。     

Discussion on the parameters of design waves

In order to respond the discredit on the design wave standard and to recommend new consideration on design wave parameters, based on the long-term distribution of statistic characteristics of waves and the short-term probability properties of sea state defined by giving the return period, the calculation of the return period, the height, the period, and the oceanic wave parameters of the design wave and the forecasting methods are discussed in this paper. To provide references for the operation reliability of floating structures in the extreme sea state, the method of determining the design wave parameters is resurveyed. A proposal is recommended that the design wave, which can be either significant wave with 500-year of the return period, or the maximum wave with 1/N of exceeding probability, 100-year of the return period, can be applied in the engineering design practice.     

船体主要载荷效应的随机组合

基于静水载荷的时间变异性，导出了一种静水载荷效应与波浪载荷效应组合的新方法，同基于FBC（Ferry Borges Castenbete）模型或随机过程的上跨率的组合形式相比较，此方法的概念更清晰，计算更容易实施，考虑到规范中给定的最大允许静水载荷效应对应的普遍接受的超越概率水平，以及静水载荷过程跨越某一固定水平的概率的上界特性，规定静水载荷过程超越二十年最大允许载荷效应的概率为确珲载荷效应特征值的概率水平，经过这样处理，避免了载荷效应特征值的过高估计，通过数值分析检验方法的有效性，结果表明本文的方法可以得到级合载荷效应特征极值的一致估计。     

集装箱船等效设计波法中疲劳载荷概率系数的确定

为了在应用等效设计波方法时将船体梁载荷规范包络值、运动包络值、加速度包络值转换为疲劳评估载荷,需得到疲劳载荷概率系数这一重要参数。采用基于三维势流理论的水动力计算软件,分析多型集装箱船不同航速及超越概率的载荷长期预报值,得到用于疲劳评估的疲劳载荷概率系数的直接计算值。对直接计算值进行回归分析,拟合出各载荷的概率系数简化公式。结果表明,简化公式比较理想。     

波浪弯矩设计值与长期预报理论计算值的比较

本文分析了国际船级社协会（ＩＡＣＳ）纵向强度标准Ｓ１中，波浪弯矩值成采用ＩＡＣＳＷＰ／Ｓ委员会推荐的海浪谱和海况统计资料条件下的长期预报理论计算值的关系，大量计算实践表明后者总体上要比前者大１．５倍。文中建议为了把长期技术应用于船体波浪弯的直接设计计算，对上述预报过程可取１０概率水平时地长期预报值作为船体波浪湾矩设计值。     

Design safety margin of a 10,000 TEU container ship through ultimate hull girder load combination analysis

Assessment of the ultimate longitudinal strength of hull girders under combined waveloads can be of particular importance especially for ships with large deck openings and low torsional rigidity. In such cases the horizontal and torsional moments may approach or exceed the vertical bending moment when a vessel progresses in oblique seas. This paper presents a direct calculation methodology for the evaluation of the ultimate strength of a 10,000 TEU container ship by considering the combined effects of structural non-linearities and steady state wave induced dynamic loads on a mid ship section cargo hold. The strength is evaluated deterministically using non-linear nite element analysis. The design extreme values of principal global wave-induced load components and their combinations in irregular seaways are predicted using a cross-spectral method together with short-term and long-term statistical formulations. Consequently, the margin of safety between the ultimate capacity and the maximum expected moment is established.     

Evaluation of expected maximum values of forces acting on containers and lashing rods on a container ship

The appearance of a number of large container ships in the 8000 TEU range raises the importance of a plan for container lashing arrangements on deck in relation to the design of the ship. Therefore, it is expected that a new method for evaluating the lashing arrangements on deck will be introduced which is applicable regardless of the ship's size and the lashing pattern, instead of using the standards of several different societies, as happens at present. To evaluate the lashing arrangements on deck, the expected maximum values of the forces acting on the containers and lashing rods should be evaluated. This paper presents a new method of evaluating the container lashing arrangements on a container ship using an "acceleration ellipsoid." The applicability of the acceleration ellipsoid to an evaluation of the expected maximum values of the forces was examined by comparing the expected maximum values of the forces calculated by the long-term distribution calculation known as the "Fukuda method," to those calculated using the acceleration ellipsoid. By comparing these results, it was confirmed that the expected maximum values of the forces calculated using the acceleration ellipsoid were not less than those calculated through by the long-term distribution calculation. It is concluded that the acceleration ellipsoid can be used to evaluate the expected maximum values of the forces acting on containers and lashing rods. Received: December 14, 2000 / Accepted: March 22, 2001     

Estimation of nonlinear long-term extremes of hull girder loads in ships

This paper deals with a estimation of long-term extreme value for a given return period, say D=100 yr. In principle, this response is obtained by combining the response in all the sea states. The long-term response for a linear system can be effectively obtained by determining the response for each sea state, specified by the significant wave height, H_s, and the peak period, T_p, in the frequency domain. However, if the response is nonlinear, time domain simulation and a long time series would be required, to limit statistical uncertainty. Therefore, the long-term analysis becomes rather complicated and time consuming. For the long-term analysis, it is crucial to introduce ways to improve the efficiency in the calculation. In this work, it is shown that, the long-term extremes can be estimated by considering only a few short-term sea states. A long-term analysis based on identifying the most important sea state, defined by the coefficient of contribution, using linear analysis is applied. An iteration procedure is thereafter used to find the nonlinear long-term extreme values. It is concluded that only a limited number of sea states is necessary to get an acceptable estimate of the nonlinear D-year response as long as the most important sea states are included, i.e., the sea state with the maximum coefficient of contribution.     

Comparing different contour methods with response-based methods for extreme ship response analysis

Environmental contours are often applied in probabilistic structural reliability analysis to identify extreme environmental conditions that may give rise to extreme loads and responses. They facilitate approximate long term analysis of critical structural responses in situations where computationally heavy and time-consuming response calculations makes full long-term analysis infeasible. The environmental contour method identifies extreme environmental conditions that are expected to give rise to extreme structural response of marine structures. The extreme responses can then be estimated by performing response calculations for environmental conditions along the contours.Response-based analysis is an alternative, where extreme value analysis is performed on the actual response rather than on the environmental conditions. For complex structures, this is often not practical due to computationally heavy response calculations. However, by establishing statistical emulators of the response, using machine learning techniques, one may obtain long time-series of the structural response and use this to estimate extreme responses.In this paper, various contour methods will be compared to response-based estimation of extreme vertical bending moment for a tanker. A response emulator based on Gaussian processes regression with adaptive sampling has been established based on response calculations from a hydrodynamic model. Long time-series of sea-state parameters such as significant wave height and wave period are used to construct N-year environmental contours and the extreme N-year response is estimated from numerical calculations for identified sea states. At the same time, the response emulator is applied on the time series to provide long time-series of structural response, in this case vertical bending moment of a tanker. Extreme value analysis is then performed directly on the responses to estimate the N-year extreme response. The results from either method will then be compared, and it is possible to evaluate the accuracy of the environmental contour method in estimating the response. Moreover, different contour methods will be compared.