海洋平台设计中的风浪参数选取标准

以我国渤海某区1970年至1993年风暴过程的后报资料为基础,提出了泊松二维冈贝尔逻辑分布,并将其用于风暴过程中伴生的风速与波高的联合概率计算,给出了美国石油协会(API)行业标准有关环境条件三种设计标准的具体做法.基于新的统计模式,同时提出了联合概率法设计标准.比较了多种标准所得设计参数的差异,给出了适合工程所在海区的环境荷载参数.计算结果表明,新的统计模式适用于遭受风暴影响的海洋工程结构设计,特别是边际油田的开发建设.     

外海轻型码头结构环境荷载的统计分析

对外海轻型码头结构的波浪荷载和海流荷载进行了统计分析。给出一个波浪周期内,波浪荷载的均值系数和变异系数随相位角的变化,进而得出50年设计基准期内波浪荷载的均值系数和变异系数。使用Monte-Carlo方法研究了波浪荷载的概率分布类型。利用海洋平台已有的研究成果,给出了50年设计基准期内海流荷载的均值系数和变异系数。结果表明:对于外海轻型码头结构,可认为波浪荷载和海流荷载均服从极值I型分布;50年基准期波浪荷载的均值系数为1.166,变异系数为0.263,海流荷载的均值系数为1.269,变异系数为0.142。     

吉布提LNG厂址波浪极值推算

在吉布提LNG厂址的设计过程中,由于当地可用水文资料缺乏,现场观测活动起步晚、持续时间短(仅1 a),无法满足多年重现期设计波浪要素推算的需求,给后续工作带来了较大的困难。以CCMP风场数据作为驱动,基于波作用量平衡方程建立印度洋大范围波浪数学模型、嵌套的亚丁湾中等范围模型及工程区小范围模型,在现场实测资料的基础上,结合同期的Jason卫星轨道资料对模型进行验证对比,模型验证结果良好。在此基础上,计算了1988—2017年的逐时波浪要素过程,并据此构建出年极值波浪序列,利用P-III型分布函数推算工程区深水处的各重现期波浪极值,结合不同水文条件计算得出工程区的设计波浪要素。     

Numerical and experimental investigations into the application of response conditioned waves for long-term nonlinear analyses

The coefficient of contribution method, in which the extreme response is determined by considering only the few most important sea states, is an efficient way to do nonlinear long-term load analyses. To furthermore efficiently find the nonlinear short-term probability distributions of the vessel responses in these sea states, response conditioned wave methods can be used. Several researchers have studied the accuracy of response conditioned wave methods for this purpose. However, further investigations are necessary before these can become established tools. In this paper we investigate the accuracy by comparing the short-term probability distributions obtained from random irregular waves with those from response conditioned waves. We furthermore show how response conditioned wave methods can be fitted into a long-term response analysis. The numerical and experimental investigations were performed using a container vessel with a length between perpendiculars of 281 m. Numerical simulations were done with a nonlinear hydroelastic time domain code. Experiments were carried out with a flexible model of the vessel in the towing tank at the Marine Technology Centre in Trondheim. The focus was on the probability distributions of the midship vertical hogging bending moments in the sea states contributing most to the hogging moments with a mean return period of 20 years and 10 000 years. We found that the response conditioned wave methods can very efficiently be used to accurately determine the nonlinear short-term probability distributions for rigid hulls, but either accuracy or efficiency is to a large effect lost for flexible hulls, when slamming induced whipping responses are accounted for.     

大连长兴岛北港区波浪条件数值模拟研究

利用国际通用的MM5风场模式和SWAN浪场模式,通过推算影响工程海域的台风和寒潮大风天气过程,得到工程海域-30 m等深线处不同重现期设计波要素,然后采用MIKE 21 NSW和BW波浪数学模型,对工程规划方案设计波要素和港内波况进行了计算。结果表明:工程受N向和NNE向风浪影响相对较大,外海波浪传播至防波堤处无明显衰减;设计高水位重现期50 a时防波堤处最大H1%约7.3 m;防波堤对港内围堰掩护较好,建成后港内波浪条件明显改善。     

印尼ADIPALA海域较长周期波浪谱分析

波浪谱是进行海岸工程设计的重要基础,不同海区、不同周期的波浪谱特性不同,因此有必要对于实际海上观测波浪的谱特性进行分析研究。针对在印尼海岸观测的较长周期波浪数据进行了波浪谱分析,给出谱特征参数与海浪统计特征值之间的关系。并基于JONSWAP谱型,对实测波浪谱进行拟合,得出适用于该海域的波浪谱公式,研究成果可为实际工程设计提供重要的参考。     

Extreme hawser tension assessment for FPSO vessel during offloading operation in Bohai bay

The Floating Production Storage and Offloading Unit (FPSO) is an offshore vessel that produces and stores crude oil prior to tanker transport.Robust prediction of extreme hawser tensions during Floating Production Storage and Offloading (FPSO) operation is an important safety concern. Excessive hawser tension may occur during offloading operations, posing an operational risk. In this paper, AQWA has been used to analyze vessel response due to hydrodynamic wave loads, acting on a specific FPSO vessel under actual sea conditions. Experimental validation of numerical results has been discussed as well.This paper advocates methodology for estimating extreme response statistics, based on simulations (or measurements). The modified ACER (averaged conditional exceedance rate) method is presented in brief detail. Proposed methodology provides an accurate extreme value prediction, utilizing all available data efficiently. In this study the estimated return level values, obtained by ACER method, are compared to the corresponding return level values obtained by Gumbel method. Based on the overall performance of the proposed method, it is concluded that the improved ACER method can provide more robust and accurate prediction of the extreme hawser tension.Data declustering issue has been addressed. Paper highlights ability of ACER method to account for a set of varying sea state probabilities, as required in engineering long term statistical analysis.Described approach may be well used at the vessel design stage, while defining optimal vessel parameters that would minimize potential FPSO hawser tension.     

海浪动态仿真研究

对海面波浪的特点进行分析,提出了用合成波加细碎波的方法进行海浪的动态仿真,着重分析利用对合成波参数进行修正的方法来增强模拟风浪的真实效果,海浪模拟图例说明了该仿真方法可行。     

Required test durations for converged short-term wave and impact extreme value statistics–Part 2: Deck box dataset

In the assessment of wave-in-deck loads for new and existing maritime structures typically model tests are carried out. To determine the most critical conditions and measure sufficient impact loads, a range of sea states and various seeds (realisations) for each sea state are tested. Based on these measurements, probability distributions can be derived and design loads determined. In air gap model testing usually only few, if any, impact loads occur per 3-hour seed. This can make it challenging to derive reliable probability distributions of the measured loads, especially when only a few seeds are generated. In addition wave impact forces, such as greenwater loading, slamming, or air gap impacts are typically strongly non-linear, resulting in a large variability of the measured loads. This results in the following questions: How many impacts are needed to derive a reliable distribution? How is the repeatability of individual events affecting the overall distribution? To answer these questions wave-in-deck model tests were carried out in 100 x 3-hour realisations of a 10,000 year North Sea sea state. The resulting probability distributions of the undisturbed wave measurements as well as the measured wave-in-deck loads are presented in this paper with focus on deriving the number of seeds and exposure durations required for a reliable estimate of design loads.The presented study is Part 2 of a combined study on guidance for the convergence and variability of wave crests and impact loading extreme values. The data set of Part 1 ([1]) is based on greenwater loads on a sailing ferry and the data set of Part 2 on wave-in-deck loads on a stationary deck box.     

坡度对波浪统计特征的影响

为了明确坡度对不同波浪统计特征的影响,利用数值模型对波浪在不同坡度斜坡上的传播进行模拟,分析波浪的非线性参数和波高分布等,比较不同坡度下波浪的传播特性。结果表明,在相同条件下,随着波浪在斜坡地形上传播,波高会随着水深的变浅逐渐增大;坡度对于波浪的波高分布具有较大影响,当坡度较大时,波浪传播至斜坡较浅水深时的波高分布接近瑞利分布,当坡度逐渐减小时,相同波高的发生概率逐渐减小;而Ursell参数则不会随着坡度的变化有明显的变化。     

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.     

基于船舶运动信息的航行海域海浪特性预报

以船舶自身为波浪测量仪,致力于采集方便而又尽可能少的船舶运动信号以提取航行海域实时海浪特性.由于估计中不依赖原始理论计算的传递函数,不需要附带波浪采集装置,而仅利用航行中船舶运动的观测序列完成海浪谱反演,故该海浪测量方法可适应船舶自身运动参数的变化.另一方面,由于反演估计的船舶运动频率响应特性,与事先计算或以其它实验方法得到的船舶运动频率响应特性得以比较,可以深化、修正对许多不易实时测量的海浪激励状态与船舶运动响应关系的认识,并积累船舶工程研究设计所必需的相关海域海浪谱信息.     

允许越浪条件下海堤越浪量可靠度分析*

基于可靠度理论,进行了允许越浪条件下海堤越浪量的可靠度分析,建立了允许越浪条件下海堤越浪量的极限状态方程。以青岛某斜坡式海堤为例,将有效波高和谱峰周期作为基本随机变量进行越浪量可靠度分析。首先对有效波高和谱峰周期进行Log-normal、Gumbel分布拟合,根据拟合结果,二者均采用Log-normal分布,然后采用Monte Carlo模拟计算了该海堤越浪量的可靠性指标。计算结果表明:进行允许越浪条件下海堤越浪量的可靠度分析是可行的,并且海堤越浪量的可靠性指标概率意义明确,比允许越浪量标准更合理。     

中国内海台风浪传播和演化过程数值模拟

基于波作用量守恒方程建立我国内海台风浪生成与传播的模型。用谱峰周期来界定涌浪,通过对全区域的典型台风浪过程的模拟计算,分析了内海台风浪时、空分布特征和演化过程。研究表明:台风登陆后,从能量扩散速度判断,应经历能量由高频向低频转化的过程(易形成长周期波浪),均可传播到渤海海域。生成长周期波浪后,波能衰减速度显著减慢,长周期波浪可在我国北方海域生存2 d以上。涌浪在台风登陆之后的传播速度很快,为50～60 km/h,涌浪传播速度在我国内海可以达到台风中心运动速度的2倍左右。     

半潜式海洋平台的周期内波载荷分析

基于半潜式海洋平台基本结构参数和南海海洋环境条件参数,建立海洋周期内波作用下的半潜式平台内波载荷计算模型。采用解析方法,分别给出波长、波高和密度跃层位置等对周期内波载荷的影响及作用力特点,并分析了相位差的影响。对半潜式平台存在较大威胁的海洋周期内波主要是波长较长、振幅较大且密度跃层位置接近于水面的内波;密度跃层位置对平台受力影响较大,相位差对周期内波载荷的影响可以忽略。     

大连海域波浪特征研究

根据大连及其附近海域11个站的波浪实测资料,研究分析了大连海域不同岸线段的波浪基本特征,包括常浪向、强浪向及其频率等,绘制了波浪玫瑰图;根据有关文献,对大连海域不同岸线外海深水波浪要素特征进行了分析研究,给出了50a一遇强浪向的波高和周期.结果表明:大连海域在渤海侧强浪向主要为偏北向,黄海侧海域的强浪向主要是偏南向.     

Efficient estimation of extreme long-term stresses by considering a combination of longitudinal bending stresses

Longitudinal stresses due to combined horizontal and vertical bending moments in ships, corresponding to a return period of 20 years, are estimated by linear response analysis. In principle, the stress should be obtained by combining the stress in all sea states that can occur over a long-term period. A method to determine the desired long-term extreme stress by considering only a few short-term sea states is presented. The sea states have a certain probability of occurrence, and are each identified by a contour line in the (H _s, T _p)-plane. This approach makes it possible to estimate the extreme loads on the vessel in a practical and accurate manner. Moreover, it is shown that the long-term stress can be estimated by combining the individual long-term extreme stresses due to vertical and horizontal bending moments by using the sum-of-squares approach and accounting for the correlation between stresses. It was found that the correlation coefficient can be taken as the largest of the ones calculated along the contour line. It is shown that this correlation coefficient can even be approximated by the normalized phase angle at the wave length where the dominant response has its peak value. A comparison with the results obtained using well-known combination rules is presented. While linear analysis has been used here, it is believed that the approach can be generalized to stresses with nonlinear behavior, and hence represent a significant improvement in calculation efficiency. Received: September 18, 2001 / Accepted: December 18, 2001     

不同方法对南黄海重现波高计算值的影响

采用SWAN波浪模型对江苏南黄海地区1979~2018年共40 a的波况进行模拟及验证,将模拟结果与实测资料进行比对,吻合良好。百年重现波高分布通过基于年极值和月极值的广义极值分布函数(GEV)和超阈值取值方法(POT)的广义帕累托分布模型(GP)计算得出。计算结果表明,不同方法的计算结果在辐射沙洲北部地区差别最大,采用月极值所得重现波高偏小,采用年极值计算的重现波高在辐射沙洲南北外围地区最大,其余地区则以POT方法为大值。在分别采用不同数据长度计算重现波高的试验中得出,取月极值的GEV分布计算结果对时间跨度的改变不敏感,而取年极值受之影响最大,POT方法介于两者之间。     

Splash zone lowering analysis of a large subsea spool piece

Lifting operation though the wave splash zone is challenging. Careful numerical analysis in the design phase is needed to minimize associated risks. This study addresses numerical modeling and analysis of the splash zone lowering of a large subsea spool. A typical offshore construction vessel is used for the operation. The objective is to compare the effects from different numerical methods and parameters on the allowable sea states and the operability. These methods and parameters include wave short-crestedness, shielding effects from the vessel, wave direction and wave seed number. A coupled numerical model of the spool-vessel system is established in SIMO program, which is a simulation tool for marine operations. Slamming and submergence-dependent loads on the spool during the transient lowering process are calculated. A large number of time-domain simulations has been performed to derive the allowable sea states. The operational criteria for assessment of the sea states include slack sling, snap loads in wires and clearance between spool and the vessel. Operability analysis of the operation at one reference site in the Barent Sea is established using 50-year hindcast data. The influences from different methods on the allowable sea states and the operability are compared and discussed in detail.     

中国海与西北太平洋波浪长期统计的导算方法

为了满足船舶与海洋工程对波侯数据的需要，本文回顾了以往出版的几种图集资料并分析了其不足之处，着重介绍了当前国际上较新的英国波峰综合模式（NMIMET）和美国海军风浪后报模式（SOWM）及两者的结果图集。为获得中国海与西北太平洋海域更可靠的数据，在对日本气象厅的器测浮标站长期资料的统计结果与相应的船舶报资料按各种方法处理的结果比较基础上，进一步改进了NMIMET模式。这主要是在波高与周期联合概率分布导算方法上，采用一种新的更灵活的联合分布模式以代替原来所用的由Ochi建议的二维对数正态模式；同时对于在模式中需要确定的有关周期的参数，根据新的资料和计算结果对原用的回归公式作出了改进。用改进后的模式导算得到的波高、周期分布与器测浮标站结果更为接近。