软土地基围堤外侧桩基础施工时机*

在软土地基上修筑港口工程时,外侧栈桥桩基础的施工时机和工程安全直接受到围堤填筑加载过程的制约和影响。依托某一级渔港工程,通过围堤加载过程中软土地基侧向变形分析及深层水平位移跟踪监测数据的多元回归拟合,分析预测了地基水平位移随围堤加载过程的变化规律和发展趋势,在此基础上通过ANSYS三维建模分析围堤加载过程中灌注桩的内力及变形,最终确定了外侧灌注桩基础的施工时机。研究表明：该软土地基在加载过程中的侧向变形符合指数函数变化规律;围堤加载而导致软土地基产生的侧向变形对外侧灌注桩位移的影响作用比对其自身内力影响要大;当地基土体上部产生最大水平位移150 mm时,灌注桩混凝土的屈服应力安全度仍较大,据此可提出外侧栈桥灌注桩基础的施工时机,该方法可供类似工程设计与施工借鉴。     

圆筒型FPSO上部模块支撑结构疲劳分析

与船型FPSO相比,圆筒型FPSO没有明显的总纵弯曲,上部模块与船体结构之间通常采用刚性支墩来连接,水平运动所产生的弯矩和装/卸载引起的船体垂向变形对模块支撑结构的影响较为显著。因此,以“希望6号”圆筒型FPSO上部模块支撑结构为研究对象,基于DNVGL船级社规范,介绍一种简化疲劳分析方法。以FPSO运动加速度和船体变形载荷作为载荷输入条件,利用SESAM/GeniE软件进行有限元分析,得到结构在所有组合工况下应力的扫描计算结果。根据作业海域各个方向波浪发生的概率,运用简化疲劳分析方法计算得到所关注节点的疲劳损伤和各个工况对结构节点疲劳损伤度的贡献。结果表明,所关注节点的疲劳强度均满足设计疲劳强度要求;同一节点的疲劳损伤对不同浪向的敏感度不一样。该简化疲劳分析方法同样适用于承受周期性载荷的FPSO上部模块主结构和其他型式海洋结构物的疲劳分析。     

Structural analysis of an offshore vertical axis wind turbine composite blade experiencing an extreme wind load

The vertical axis wind turbine (VAWT) configuration has many advantages for an offshore wind turbine installation. The VAWT is omnidirectional and its rotating mechanical components can be placed close to sea level. In this paper, the structural analysis of a VAWT blade structure subject to a critical load case was investigated with two methods, an analytical model and a finite element (FE) model. It was shown that the utilisation of a composite blade topology can resist the induced flapwise loading and the material strains were contained within their allowable limits. The analytical approach was demonstrated to be a quick and accurate technique to compute the composite blade strain distribution when compared to the FE model results.     

超深水钻井船钻台支撑结构设计与强度评估

针对某新型钻井船钻台支撑结构,基于DLA全船有限元分析结果,采用子模型方法,对钻台支撑结构关键区域进行网格细化,综合考虑钻井船生命周期内全部装载和作业工况,对钻台支撑结构进行结构设计和强度评估。分析了各计算工况下的控制载荷,探索了相应的结构优化方向,总结了钻井船钻台支撑结构的设计要点。     

特征载荷下海工管状结构屈曲临界载荷分析

圆柱形管状结构在海洋工程领域中应用较多,在进行结构设计时,需重点关注其侧向受载时的屈曲强度问题。通过理论分析和数值模拟,对比研究径向线性载荷变化下圆柱壳的屈曲行为,以经典的Donnell壳体理论为基础,得到圆柱壳的屈曲控制方程,并通过本征值分析方法得到结构屈曲的临界条件。采用有限元软件ABAQUS对线性变化径压下圆柱壳的屈曲进行数值仿真。分析得出径厚比是径向线性分布载荷下圆柱壳屈曲临界载荷的主要影响因素,三角形径压下屈曲临界载荷值约为均布径压下屈曲临界载荷值的2倍。     

Strain estimation for offshore wind turbines with jacket substructures using dual-band modal expansion

Structural fatigue is a design driver for offshore wind turbines (OWT). In particular, the substructures, like jackets, are strongly affected by fatigue. Monitoring the fatigue progression in the welds is vital for the maintenance and a potential lifetime extension. However, inspections of critical locations are costly due to the limited accessibility of the mostly submerged jacket. Considering the high number of potentially critical welds, it is regarded as economically unfeasible to equip all fatigue hot spots with sensors. Thus, an indirect method to monitor the fatigue progress of the structure and point out critical locations is desirable. For a consistent support of ongoing maintenance, it has to yield reliable results for varying operational and environmental conditions. This paper applies a virtual sensing approach to jacket substructures. From a small set of sensors on the tower, fatigue at every desired location of the jacket is estimated using dual-band modal expansion. Simulations using the OC4 jacket design are performed to show potentials and limitations of the method. Namely fatigue progress on leg welds of K-joints is predicted with high accuracy over a wide range of load cases. However, some difficulties in fatigue prediction of X-joints due to the occurrence of local modes and limitations in the extrapolation of wave loading have to be resolved in future work.     

液化天然气B型独立液货舱结构低周疲劳研究

基于某B型独立液货舱为研究对象,开展液化天然气(LNG)船码头装卸货工况下的结构应力和温度场热应力分析,重点针对液货舱水平强框处连接节点计算其因装卸货受力和温度变化所引起的疲劳累积损伤。研究结果表明,部分研究疲劳节点由装卸货产生的低周疲劳损伤在整个结构疲劳累积损伤中的占比较大,对结构疲劳损伤起主导作用,需要在液货舱疲劳强度分析中予以重点关注。因此,对此类B型独立液货舱进行结构设计必须考虑低周疲劳的影响。     

沉管隧道垄沟碎石基床工程特性试验研究

通过室内大型载荷模型试验研究沉管隧道带垄沟碎石基床的力学特性。试验碎石基床的加载方法包括满铺碎石、压拢顶、压垄沟3种,模型宽1. 2 m,高0. 8 m,长2. 0 m。试验过程中测量竖向荷载、表面沉降和位移、垄沟空间变化、混凝土加载梁的钢筋应力发展以及试验槽侧移。结果表明:直至750 kPa的荷载压力下,3种碎石基床试验中沉降和荷载呈线性变化,说明碎石基床处于压密的弹性阶段;加载过程中,垄沟空间随荷载增加呈线性减小,并被逐渐压平;带垄沟碎石基床与满铺碎石基床的荷载沉降曲线基本一致,最终沉降基本一致,可以认为垄沟对基床力学性质无显著影响,但在工程中应计入由于垄沟存在导致接触面积差异,试验还发现带垄沟碎石基床的混凝土加载梁钢筋应力较满铺碎石基层情况下增加20%～30%;建立了带垄沟碎石基床数值模拟方法,模拟结果表明:满铺、压垄沟碎石基床的荷载沉降曲线基本一致,也证明2种基床的变形和承载力一致。     

Numerical weight function method for the structural analysis of ships: a speedy direct calculation with condensed structural information

The weight function method was originally derived for crack problems to calculate stress intensity factors for arbitrary loading conditions. In this article, a numerical weight function method has been extended to formulate the structural response analyses of two-dimensional elasticity, plate-bending, and three-dimensional plate-structures by using the finite-element method. The solution procedure is based on the well-known Maxwell–Betti reciprocal theorem, which is applied to the original and properly defined auxiliary problems. The present numerical weight function may be considered as a finite-element version of a Green’s function in an integral equation solution scheme. Although ship structures are certainly analysed by the finite-element method in a practical design procedure, the weight function approach has not yet been realized. The method is very useful for the analysis of structures subjected to a vast range of loading conditions, because structural responses can simply be calculated by the inner product of the universal weight function and load vectors. The validity and convergence characteristics of the present method are investigated by two-dimensional elastic and plate-bending problems, respectively. Finally, the method is applied to the calculation of the response amplitude operator of a stress component at a critical structural detail of a double-hull tanker, and the speed and efficiency of the method are quantitatively discussed based on the practical results.     

46000DWT内贸散货船舱段结构强度有限元计算

随着国内航运市场的旺盛,满足国内近海航区及南京以下长江各港口的国内贸易散货船应运而生。国内贸易散货船的受力工况和装载工况不同于常规CSR散货船,结构要求也有所不同。以46000DWT国内贸易散货船舱段结构的FEM直接计算分析为例,简单介绍了有限元分析计算过程中波浪载荷的选取、模型的建立和加载、分析的伞讨程．以及绎计算后对原结构的优化调整。     

大侧斜螺旋桨强度校核探讨

针对大侧斜螺旋桨复杂的几何外形和载荷分布,为准确解决其强度校核问题,介绍了两种螺旋桨强度校核方法,传统的悬臂梁法和有限元法。前者视桨叶为变截面的悬臂梁,按正车最大航速时的静态负荷来进行校核;采用有限元法在全速正车和紧急倒车状态时计算叶片的应力应变,重点介绍了紧急倒车过程中作用在桨叶上最大水动力载荷的确定方法。最后通过算例分析,比较两种方法校核同一螺旋桨强度的结果,指出有限元法更适合用于大侧斜螺旋桨的强度校核。     

基于剪流分布规律的节点力加载方式在船体结构有限元分析中的应用

船体结构强度评估是船舶建造与设计过程中的重要环节.本文在总结研究现有的船体结构有限元分析加载方式的基础上,提出基于剪流分布规律的节点力加载方式.对于为模拟船体梁载荷而在各剖面处施加的集中力以及为进行强度计算需在各剖面处施加的调整载荷,使用本文方法将其离散至单元网格节点处并于与加载,得到的结果符合船体梁弯曲时的应力分布规律,这对于正确进行船体结构强度评估具有重要意义.给出适用于计算机实施的规格化加载过程,以实现船体结构有限元分析的自动加载过程.     

Wave-in-deck loading on fixed steel jacket decks

For quite some years, wave-in-deck loading has been an issue of concern for engineers dealing with the performance of offshore structures. The topic is particularly relevant for reassessment of existing structures located in subsiding areas. One agrees that wave-in-deck loading is of dynamic nature, and that structural analyses should reflect this. There is, however, no general consensus on the size of the load and the shape of the load time history to be used for such analyses.In this paper focus has been on finding realistic load time histories for wave-in-deck loading on jacket platforms in the North Sea. A (normalised) time history shape and a simple expression to calculate a reference load (maximum load) to quantify the time history is presented.The presented ‘recipe’ for time histories is based on experimental data and is supported by results reported in the literature, comprising relevant computer simulations and model experiments of wave-in-deck loads on fixed offshore structures.The recommended load time history is intended for analyses where detailed information on the deck load for a given structure is unavailable, and where a simplified ‘rough-but-reasonable’ estimate can be accepted.     

码头沉箱变形的离心模型试验和数值分析

以某重力式码头沉箱结构为研究对象，进行了基于此码头的两种方案的离心模型试验，研究了不同条件下重力式码头的变形情况；利用非线性有限元程序ABAQUS，建立了挡土墙．砂垫层．地基体系固结问题的数值模型，然后分别以典型重力式码头的离心模型试验和工程原型为计算对象，以离心加速度增长和码头高度增长为加荷方式，对离心模型试验过程和码头的施工过程进行了数值模拟。综合对比了多种条件下码头和地基的变形情况，并探讨了地基土模量、淤积土的开挖深度对变形的影响，分析了施工过程中和竣工后的超静孔隙压水压力的变化和变形规律。     

多用途船集装箱装载工况直接计算分析

多用途船的货舱内装载集装箱的固定形式与普通集装箱船不同,船级社及船舶的设计、建造方对此类船舶结构强度的安全性和可靠性投入更多的关注。为此,参照中国船级社钢质海船入级规范的要求,研究提出了舱内载荷的模拟方法,以某多用途船舱段结构强度有限元计算分析为例,分析研究集装箱横向运动和垂向运动惯性力对船体结构强度的影响。为多用途船装载集装箱工况的结构设计提供准确的分析方法。     

Local structural response to seakeeping and slamming loads

A common approach to investigate the response of a structural detail such as a hatch corner is to compute the seakeeping loads using a linear 3D Boundary Element Method (BEM) and transfer the seakeeping loads to a Finite Element (FE) model of the ship structure. This approach is suitable for computations of the fatigue loading of structural details near amidships because a majority of the fatigue loading will occur in mild sea-states where the loading may be assumed linear. However, the linear seakeeping model may not hold when one investigates the ultimate response of the local bow structure of a ship which is designed to remain operational in severe conditions, for example, a frigate. A linear seakeeping analysis will significantly underpredict the loading at the bow because both the impulsive slamming loads and the non-linearities in the non-impulsive wave loads will contribute significant to the structural loading.The non-linear loads require one to first derive a short-term distribution of the local structural response before the ultimate value of the response can be derived. A method to compute the short-term distribution of a structural detail is presented in this paper. The first step is to perform seakeeping analyses which includes slamming, non-linear Froude-Kryloff and hydrostatic loads. The short-term distribution of the total hydrodynamic loading at the structural detail is obtained by simulating the seakeeping response for several hours. The response of the local structure is computed for the most severe impacts found in the seakeeping simulation. The hydrodynamic loading, including the non-linear contributions, is transfer to the structural model and the structural response is computed using the FE-method. The results of the structural analyses allow one to transform the short-term distribution of the structural loading to a short-term distribution of the response of the structural detail. A designer can obtain the ultimate structural response by entering the probability at which one accepts overloading of the structure in the short-term distribution of the response of the structural detail.     

船体梁静水载荷效应统计预报

船体梁静水剪力、弯矩等是由装载状态决定的载荷效应。营运船舶装载记录表明，实际装载状态具有不确定性，由此导致载荷效应发生变异，其统计特性可利用回归公式或随机模拟原理进行估算或预报。通过对油船、散货船、滚装船及集装箱船约2000种随机工况所作的统计分析，表明其静水弯矩等随装载偏差的变化近似于正态分布律，并具有比船体中剖面模数或钢材屈服极限更为显著的变异性。在船舶结构可靠性分析或理性设计中，合理估算并预报这种及异性是必要的。     

自升式钻井平台桩靴结构分析

以某自升式钻井平台的桩靴为研究对象,建立了结构分析模型,给出了结构分析的载荷及边界条件,并对各工况下的计算结果进行分析和评估,为此类结构的设计提供参考方法。     

基于非线性理论的船舶结构稳定性研究

本文以结构的线性分析为基础，对船舶结构的线性稳定性分析方法进行了改进。同时，采用基于特征值分析的线性稳定性分析方法得到了船舶结构的临界载荷，从该载荷值可以预测出实际结构临界载荷的上限并能较好地反映船舶结构线性性能对其稳定性的影响，据此得出船舶结构的失稳位形。在非线性稳定性分析中，采用NEWTON—ROPHSON方法及弧长法求解考虑非线性时船舶结构的临界载荷，并详细讨论了结构缺陷对稳定性的影响，提出考虑结构缺陷时船舶结构稳定性计算方法。通过不同类型的算例进行分析比较，总结出船舶结构边界条件、几何缺陷变化与船舶结构稳定性之间关系，验证了本文稳定性分析方法的正确性、有效性及对现役散货船船体结构的适用性。     

Research on short-term dynamic ice cases for dynamic analysis of ice-resistant jacket platform in the Bohai Gulf

Jacket platforms in the Bohai Gulf are often victims of random ice-induced vibrations. Their design originally did not account for dynamic ice loading on the jacket structures and significant ice-induced vibrations have been observed during winters. So it is urgent to find out as to how to consider the dynamic ice loading in the design stage of an ice-resistant jacket platform in the Bohai Gulf. In this paper, based on the state-of-art developments of dynamic ice load and ice–structure interaction, the authors proposed two different approaches to determine the short-term dynamic ice cases for dynamic analysis of ice-resistant jacket platform in the Bohai Gulf, named as the failure probability-based approach and the expected loss-based approach. Considering the variation of the ice environments and the variability of ice-resistant structure's properties, the random ice spectrum and the pseudo-excitation method (PEM) are employed to improve the efficiency of the procedure. Through finite element method (FEM) modeling of the real ice-resistant jacket platforms in the Bohai Gulf, such as MSW, MUQ and NW, the characteristics of the two proposed approaches have been investigated and compared. This paper provides an open and universal framework to assist designers and owners for determining the short-term dynamic ice cases in the Bohai Gulf, in which more information can be considered in the procedure to update and modify the results if available.