Estimation of fatigue damage and extreme response for a jack-up platform

Results from four different methods for stochastic dynamic response analysis of a proposed jack-up platform are compared. This structure exhibits both significant dynamic amplification and non-linear transfer of sea elevation into load effects. Both estimation of extreme response and fatigue damage are considered. The most complex procedure based on time-domain simulation and step-by-step integration is employed as a benchmark for assessment of three simplified methods. The simplifications consist of various types of linearization in conjunction with transfer function approximations. Applicability of the methods to structures with increasingly non-linear behaviour and dynamic amplification is briefly discussed.     

极端环境条件下TLP平台的应力校核

计算校核了某TLP平台垂向肘板在极端环境条件下的应力响应.该垂向肘板为TLP立柱与张力支撑系统(TSS)间的连接件,是TLP平台强度评估的关键部位.根据通用的业界标准,平台的环境载荷计算采用三维线性理论,结构分析使用有限元方法.应力数值计算与处理与实测应变片的位置和方向完全一致.平台在位监测的数据使用FFT技术进行了处理,得到了不同时段统计下各浪向的应力谱密度(RAO).数值计算与平台在位实测对比表明,数值模拟的应力谱密度与实测数据吻合较好,业界的分析方法可以在极端条件下对TLP的关键部位进行有效的强度分析.     

Contribution of supposed wave condition on the long-term distribution of a wave-induced load

This report is concerned with the statistical analysis of the long-term distribution of a wave-induced load, and examines which factors influence the long-term distribution of the load level, e.g., the significant wave height, the mean wave period of the supposed wave condition, and the relative angle between the ship's course and the wave direction. The long-term distribution is broken down into these factors, and a contribution rate analysis method for each factor in each load level in the long-term distribution is introduced. Based on the method used, the contribution rate of a specific mean wave period and a wave angle encountered is clarified, when the long-term distribution is larger than other wave periods and wave angles. The specific mean wave period and wave angle encountered are defined as the wave condition which governs the long-term distribution. The maximum wave-induced load in the vicinity of a probability of exceedance of around 10⁻⁸ in the long-term distribution is decided by the most severe short-term wave condition which has the largest significant wave height with a specific mean wave period. Based on S–N curves and Miner's rule, the relation between the fatigue damage and the supposed wave condition is examined. The contribution rate analysis method for fatigue damage is introduced. The governing wave condition and the most severe short-term wave condition also have an important effect on the fatigue damage. A simple estimation method for the long-term distribution, described by the Weibull distribution from the statistical properties of the most severe short-term wave condition, is introduced. Several examples show the applicability of the estimation method. Received: November 22, 2001 / Accepted: January 9, 2002     

等效波的散货船舱口角疲劳评估应力组合方法(英文)

The stress combination method for the fatigue assessment of the hatch corner of a bulk carrier was investigated based on equivalent waves.The principles of the equivalent waves of ship structures were given,including the determination of the dominant load parameter,heading,frequency,and amplitude of the equivalent regular waves.The dominant load parameters of the hatch corner of a bulk carrier were identified by the structural stress response analysis,and then a series of equivalent regular waves were defined based on these parameters.A combination method of the structural stress ranges under the different equivalent waves was developed for the fatigue analysis.The combination factors were obtained by least square regression analysis with the stress ranges derived from spectral fatigue analysis as the target value.The proposed method was applied to the hatch corner of another bulk carrier as an example.This shows that the results from the equivalent wave approach agree well with those from the spectral fatigue analysis.The workload is reduced substantially.This method can be referenced in the fatigue assessment of the hatch corner of a bulk carrier.     

Experimental and numerical analysis of a tanker side panel laterally punched by a knife edge indenter

The paper presents finite element simulations of a small-scale stiffened plate specimen quasi-statically punched at the mid-span by a rigid indenter, in order to examine its energy absorbing mechanisms and fracture. The specimen, scaled from a tanker side panel, is limited by one span between the web frames and the stringers. The paper provides practical information to estimate the extent of structural damage within ship side panels during collision accidents. Moreover, the results of this investigation should have relevance to evaluate grounding scenarios in which the bottom sustains local penetration. This is possible since the structural arrangement of the double hull and the double bottom of tanker vessels is very similar. The experimentally obtained force–displacement response and shape of the deformation show good agreement with the simulations performed by the explicit LS-DYNA finite element solver. The numerical analysis includes aspects of particular relevance to the behaviour of ship structures subjected to accidental loads which could give rise to difficulties in interpreting finite element calculations. In particular, the paper comments on the material nonlinearities, the importance of specifying the precise boundary conditions and the joining details of the structure. The considerable practical importance of these aspects has been the focus of attention in previous publications of the authors which evaluate the experimental-numerical impact response of simple ship structural components, such as beams and plates. Therefore, this paper uses the definitions proposed in those references to evaluate its applicability in the scaled tanker side panel, as an example of a more complex ship structure.