Investigation of Allowable Stresses for Fatigue Design of Fixed Offshore Platforms

Fatigue design method is usually used for estimating whether a platform structure meets the requirements of fatigue resistance. It is described in API RP-2A and ZC rules for fixed offshore platforms, in which the allowable stresses for fatigue design are defined. In this paper discussed are the allowable stresses related factors, such as wave climate, structural response, fatigue behaviour of structural members.     

Optimal Design for Main Dimensions of a 75000t Floating Production and Storage Vessel

The basis, process and results of the demonstration of the main dimensions of a 75000t floating production and storage vessel are discussed in this paper. A simple but reliable orthogonal design method is applied in the main dimension optimization. The ideas of gradual approximation and feedback from various aspects are put into effect. During the demonstration, in order to make the model tally with the actual situation, the draft design is closely related to the computational analysis, so that the demonstration model can be verified at any time; the handling of the overall system is closely related to the research of each item, which is beneficial not only to the mastery of various regularities, but also to the balance of decisions. Finally, according to the computational results and the regularities obtained from analysis, the main dimensions are determined.     

浮式生产储油轮船艏结构疲劳分析

由单点平台系泊的浮式生产储油轮的船脂结构承受着交变系泊力作用。通过详细的脂部结构有限元模型，进行了应力分析，应用S—N曲线和Miner线性疲劳累积损伤原理，进行了疲劳分析，预报了焊缝疲劳寿命。     

An Integrated Approach to Fatigue Life Prediction of Whole System for Offshore Platforms

The failure of one or even more components usually does not lead to the collapse of the whole structure. Most of the analysis of fatigue is centered on only a single component which the researchers are interested in or much attention should be paid to. However, the collapse of a structure is the result of failure of a series of components in a specific order or path. This paper proposes an integrated approach to fatigue life prediction of whole structural system for offshore platforms, mainly describing the basic principles and prediction method. A method is presented for determining the failure path of the whole structure system and calculating the fatigue life in the determined failure path. The corresponding final collapse criteria for the whole structure system are discussed. A simple method of equivalent fatigue stress range calculation and a mathematical model of structural component fatigue life estimation in consideration of sea wave and sea ice loads are provided. As an application of the propo     

Reliability Analysis of Ice-Induced Fatigue and Damage in Offshore Engineering Structures

—In Bohai Gulf,offshore and other installations have collapsed by sea ice due to the fatigueand fracture of the main supporting components in the ice environments.In this paper presented are someresults on fatigue reliability of these structures in the Gulf by investigating the distributions of iceparameters such as its floating direction and speed,sheet thickness,compressive strength,ice forces on thestructures,and hot spot stress in the structure.The low temperature,ice breaking modes and componentfatigue failure modes are also taken into account in the analysis of the fatigue reliability of the offshorestructures experiencing both random ice loading and low temperatures.The results could be applied to thedesign and operation of offshore platforms in the Bohai Gulf.     

An Improved Formulation for the Ultimate Static Strength of Tubular Joints subjected to Combined Loads

"The effect of interaction of loads on the ultimate static strength of tubular joints of offshore fixed platforms, is a practical problem. But there is still absence of rigorous theory to explain available experimental data and empirical criteria for the static strength of tubular joints. The idea of yield at hot spot of tubular joints is introduced in this paper. The interaction equations of plastic capacity for the tubular joints under combined loads (two and three different kinds) are derived. Thereafter the Yura's test data and empirical criteria of ultimate static strength for the tubular joints can be explained. The idea of classification of category of loads in accordance with experimental data and the present theory is suggested. Finally, the improved ultimate capacity equations for tubular joints are recommended. The physical significance of the coefficient of plastic reservation Qp is discussed.     

Fuzzy Fatigue Reliability Analysis of Offshore Platforms in Ice-Infested Waters

1 .IntroductionTheBohaiGulfisinfestedbyiceinthewholewinter,andoffshorestructuresthereexperiencenotonlywind ,waves ,currentsandearthquake ,butalsoiceloadswhicharecomplicatedbecauseofthedynamicinteractionbetweenicesheetsandstructures.Duanetal.( 2 0 0 0 )hadacomprehensivere viewofthelatestadvancesonice inducedvibration ,fatigueandfractureofoffshorestructures ,payingmuchattentiontothedifferencesinicebreakingmodeanddynamicsofstructuresindifferentice in festedwaters .Theypresentedcriticallythelates…     

新型多柱桁架式Spar平台疲劳寿命分析

利用谱分析方法对新型多柱桁架式Spar平台的关键点进行了疲劳寿命分析计算.首先建立平台的有限元计算模型,并在频域内进行动力分析;然后利用热点应力法求出关键点应力传递函数,根据应力传递函数得到每个短期海况的应力谱和应力谱参数;最后采用Miner线性累积损伤准则计算出关键点的疲劳寿命,计算结果表明关键点疲劳寿命符合规范要求.     

Concept Design and Coupled Dynamic Response Analysis on 6-MW Spar-Type Floating Offshore Wind Turbine

Tower, Spar platform and mooring system are designed in the project based on a given 6-MW wind turbine. Under wind-induced only, wave-induced only and combined wind and wave induced loads, dynamic response is analyzed for a 6-MW Spar-type floating offshore wind turbine (FOWT) under operating conditions and parked conditions respectively. Comparison with a platform-fixed system (land-based system) of a 6-MW wind turbine is carried out as well. Results demonstrate that the maximal out-of-plane deflection of the blade of a Spar-type system is 3.1% larger than that of a land-based system; the maximum response value of the nacelle acceleration is 215% larger for all the designed load cases being considered; the ultimate tower base fore-aft bending moment of the Spar-type system is 92% larger than that of the land-based system in all of the Design Load Cases (DLCs) being considered; the fluctuations of the mooring tension is mainly wave-induced, and the safety factor of the mooring tension is adequate for the 6-MW FOWT. The results can provide relevant modifications to the initial design for the Spar-type system, the detailed design and model basin test of the 6-MW Spar-type system.     

Dynamic Responses of A Semi-Type Offshore Floating Wind Turbine During Normal State and Emergency Shutdown

This paper addresses joint wind-wave induced dynamic responses of a semi-type offshore floating wind turbine (OFWT) under normal states and fault event conditions. The analysis in this paper is conducted in time domain, using an aero-hydro-servo-elastic simulation code-FAST. Owing to the unique viscous features of the reference system, the original viscous damping model implemented in FAST is replaced with a quadratic one to gain an accurate capture of viscous effects. Simulation cases involve free-decay motion in still water, steady motions in the presence of regular waves and wind as well as dynamic response in operational sea states with and without wind. Simulations also include the cases for transient responses induced by fast blade pitching after emergency shutdown. The features of platform motions, local structural loads and a typical mooring line tension force under a variety of excitations are obtained and investigated.     

软刚臂单点系泊系统静力特性分析

软刚臂系泊系统是一种利用压载质量为浮式生产储油装置(FPSO)提供回复力的单点系泊方式。为快速准确地评估多铰接组成的软刚臂系统的受力状态,避免应用高复杂度的有限元软件,进而快速完成优化设计等任务,建立一种静力计算方法十分有必要。因此,针对由刚臂(YOKE)、柔性系泊腿和压载舱组成的刚柔多体系统,以分解组合的方式,提出一种二维静力计算方法,用以研究FPSO软刚臂系泊系统的静力特性。该方法主要依靠软刚臂的几何构型,在有限铰接约束下,形成非线性静力平衡方程,建立了压载舱式水上软刚臂单点系泊系统二维静力平衡计算算法。采用OrcaFlex、SESAM等软件开展了理论和数值对比分析,同时与系泊试验结果开展验证分析。对比结果表明,文中所提方法计算精度较高,可为软刚臂单点系泊系统的研究提供可靠支持。     

System Reliability Analysis of Offshore Strctures and Component Safety Rank Assessment

Offshore structures will encounter serious environmental load,so it is important to study thestructural system reliability and to evaluate the structural component safety rank.In this paper,thebracnch-and-bound method is adopted to search the main failure path,and the Ditlevsen bound method isused to calculate the system failure probability.The structure is then assessed by the fuzzy comprehensiveassessment method,which evaluates the structural component safety rank.The ultimate equation of the tu-bular cross-section is analyzed on the basis of ultimate stregnth analysis.The influence of effectcoefficients on the structural system failure probability is investigated,and basic results are obtained.Ageneral program for spatial frame structures by means of the above method is developed,and verified bythe numerical examples.     

Analysis of Collision Protection for Ocean and Offshore Structures

1 .Introduction Many accidents of ocean and offshore structuresinvolve impact loadings .Some famous ship colli-sion cases arethe Tj rn Bridge (Sweden) ,the West Bridge of the Great Belt Link (Denmark) andtheMaracaibo Bridge (Venezuela) . Most studies usedthe Hertzian contact law(Zukaset al .,1982) tocalculate the impact force and analyze structures subjectedtoimpact loadings .Other alternative meth-ods such as the spring-dashpot and momentumbalance methods utilizedthe coefficient of rest…     

风、浪荷载作用下海上风机单桩结构灌浆连接段疲劳性能评价

灌浆连接段的疲劳性能对于海上风机单桩支撑结构至关重要。基于385种工况下的某实际5 MW单桩风机支撑结构在风、浪荷载作用下的动力响应分析,获取了灌浆连接段荷载边界条件时程。建立灌浆连接段精细化有限元子模型,将荷载边界条件转化为应力时程。对于剪力键采用"热点应力"方法进行疲劳性能评价。对于灌浆材料,选取剪力键附近灌浆材料单元积分点处的第三主应力进行疲劳性能评价。采用Palmgren-Miner线性损伤累计准则和雨流计数方法进行疲劳损伤的累计。在某实际灌浆连接段20年的设计寿命周期内,最大剪力键总疲劳损伤为1.35×10~(-10);最大灌浆材料总疲劳损伤为1.54×10~(-3)。由此可见,灌浆连接段的疲劳性能由灌浆材料控制,且损伤值远小于限值1/3,在现有的荷载条件下,灌浆连接段不会发生疲劳破坏。分析产生损伤较大的几种工况可知,风速对现有单桩结构灌浆连接段疲劳的损伤起控制作用。     

Fatigue Behavior of Plain Concrete Under Biaxial Compression: Experiments and Theoretical Model

The effects of different lateral confinement stress on the fatigue behavior of and cumulative damage to plain concrete are investigated experimentally. Eighty 100 mm x 100 mm x 100 mm specimens of ordinary strength concrete are tested under constant- or variable-amplitude fatigue loading and lateral confinement pressure in two orthogonal directions. A fatigue equation is developed by modifying the classical Aas-Jakobsen S-N equation for taking into account the effect of the confined stress on fatigue strength of plain concrete. The results of variable-amplitude fatigue tests indicate that the linear damage theory proposed by Palmgren and Miner is unreasonable in the biaxial stress state. A nonlinear cumulative damage model that could model the effects of the magnitude and sequence of variable-amplitude fatigue loading and lateral confinement pressure is proposed on the basis of the evolution laws of the residual strains in the longitudinal direction during fatigue tests. The residual fatigue life predic     

山东近岸黄海海域初级生产力的时空分布变化研究

于2006年8月(夏季)、2006年12月(冬季)、2007年4月(春季)、2007年10月(秋季)对山东黄海近岸初级生产力的分布进行了4个航次的调查,并对其时空分布特征进行了分析.结果显示:(1) 调查海域春、夏、秋、冬4个航次的初级生产力平均值分别为808.798,372.23,324.717和246.146 mg·m-2·d-1,春季的初级生产力最高,冬季的最低.(2) 春、夏、秋季初级生产力的变化在水平方向上总体呈现出近岸高于远岸的分布特征,而冬季的变化趋势正好相反;在垂直分布上,4个航次初级生产力均以相对海平面光强30%～10%的水层为最高,其中夏季初级生产力分层现象明显,春、秋、冬季各水层间的差异不显著.(3) 环境因子的变化对初级生产力的作用不同,利用同化指数法求得的初级生产力比14C同位素示踪法测得的数值高出1～70倍.     

压弯载荷下焊趾表面裂纹工程萌生寿命预测

首先定义焊趾处从无裂纹到检测到表面裂纹长度达到 1.5mm时对应的循环次数为裂纹“工程萌生寿命”。给出了基于修正Neuber法并考虑焊接残余应力等影响的焊接结构焊趾裂纹工程萌生寿命计算方法。用成一定角度对接焊板试件和轴向加载获得压弯组合应力 ,以 980钢板焊接件为试件 ,在压弯组合应力的作用下 ,对焊趾表面裂纹萌生寿命进行了实验研究 ,确定了焊趾处的疲劳缺口系数。该结果可用于疲劳热点部位的受力特征为压弯组合应力的潜艇耐压壳、压力容器等的某些重要焊接结构疲劳计算