顺应式垂直通路立管的动力响应优化研究

海洋立管的动力响应优化要考虑复杂的环境载荷,如波浪、流以及浮体运动,有时还需考虑立管与海床的耦合作用,这个过程需要执行大量耗时较大的有限元分析,从而使动力优化的工作进展困难。针对此问题,本文将近似模型技术运用到FPSO的顺应式垂直通路立管（CVAR）的动力响应优化问题。优化以壁厚、管径等几何参数作为变量,优化目标是使总重量最小及等效应力在许用应力水平之下。研究给出了3种近似模型方法的比较分析,使得优化结果更具有可靠性。结果表明,3种近似模型方法的优化效果和效率彼此都非常接近,并且都能在CVAR的优化效果和减小耗时方面有出色表现。     

Integrated reliability and sizing optimization of a large composite structure

In this paper, we present the application of probabilistic design modeling and reliability-based design optimization (RBDO) methodology to the sizing optimization of a composite advanced submarine sail structure under parametric uncertainty. With the help of probabilistic sensitivity analysis, the influence of individual random variables on each structural failure mode is examined, and the critical modes are treated as probabilistic design constraints under consistent lower bounds on the corresponding reliability indices. Whereas the failure modes are evaluated for structural components in the solution of the RBDO problem, the overall system reliability is also evaluated as a post-optimization step. The results indicate that in comparison to a deterministic-optimum design, the structural mass of the probabilistic optimum design is slightly higher when consistent probabilistic constraints are imposed, and the overall structural stiffness is found to be more critical than individual component laminate ply thicknesses in meeting the specified design constraints. Moreover, the post-optimality analysis shows that the overall system failure probability of the probabilistic optimum design is more than 50% lower than that of the deterministic optimal design with less than 5% penalty in structural mass.     

Optimal base motion to compensate for the influence of sea currents during riser re-entry

One of the difficult operations, which consists in moving the riser and placing its end relatively close to a desired position, is the re-entry operation. Complex dynamic behavior of risers under different sea conditions requires efficient modelling methods. The model used in this paper applies a modification of the segment method using joint coordinates, in which it is possible to analyze only one selected deformation while neglecting the others. This enables a very high computational efficiency of the method to be achieved. The models developed take into account the impact of the environment in which the risers work. The model is validated by comparison of the authors' own results with those presented by other researchers and the simulations are concerned both with statics and dynamics of spatial risers. The numerical effectiveness of the method presented enables it to be applied in the solution of dynamic optimization problems, one of which is presented by the example of the re-entry process. The process of moving the riser is useful in emergency situations (evacuation) when it is necessary to disconnect the riser from the wellhead and move it together with the platform. This optimization task is a 3D problem due to the sea currents acting at different angles on the riser in relation to the direction defined by beginning and final positions of the bottom end of the riser. The calculations are carried out for a hang-off riser, and the optimal motion of the base for different conditions of the sea is defined. The influence of the LMRP (Lower Marine Riser Package) on this movement is also examined.     

基于动态罚因子的多学科协同优化算法及其在船舶设计中的应用

针对标准协同优化算法求解复杂系统工程问题的缺陷,提出了一种改进的协同优化算法,并将其应用于油船总体概念设计阶段。改进协同优化算法将系统级一致性约束最优化问题通过罚函数方法转化为一个无约束优化问题。同时,给出了两种不同的基于差异信息的动态可调罚系数,以保证在优化初期,系统级设计变量与学科级共享变量相差较大时,惩罚力度也大,促使一致性差异在总目标函数中占主导地位,则一致性差异将迅速下降。随着优化的进行,罚系数变小,惩罚力度减轻,目标函数的收敛加快。通过对MDO测试函数算例与标准协同优化和其他典型的改进协同算法的比较,验证了该方法在优化结果的可靠性和稳定性等方面有优势。最后,应用改进的协同优化算法求解以油船造价为系统级目标协同浮性与稳性、快速性等4个子学科的多学科优化问题以体现其工程实用性。     

An integrated methodology for the design of mooring systems and risers

Traditionally, the design of mooring lines and risers of floating production systems (FPS) has been performed separately, by different teams, employing uncoupled analysis tools that do not consider the nonlinear interaction between the platform hull and the mooring lines and risers. Design processes have been focused on fulfilling the design criteria of the respective component (mooring/riser) alone, with few or no consideration to the other component, and little interaction between the design teams. Nowadays the importance of employing analysis tools based on coupled formulations is widely recognized, and analysis strategies have been proposed to consider feedback between mooring lines and risers within their respective design processes.In this context, this work details a proposal of one single and fully integrated design methodology for mooring systems and risers for deep-water FPS. In this methodology, the design stages of both risers and mooring lines are incorporated in a single spiral, allowing the full interaction of different teams; mooring design implicitly considers the riser integrity, and vice-versa, leading to gains in efficiency and cost reduction.Different analysis strategies are employed, taking advantage of uncoupled and coupled numerical models. The models generated at the initial/intermediate design stages can be reused in subsequent stages: simpler models are used in the initial stages, and more refined models are gradually introduced, to reach an ideal balance between computational cost and accuracy of results. In the advanced stages, the exchange of information between mooring/riser also allows the definition of criteria for the selection of governing/critical loading cases to be revised and verified in detail. This leads to the reduction of the original loading case matrix, allowing a feasible use of time-consuming fully coupled analysis.Results of a case study illustrating the application of some of the main processes of the methodology are included.     

深海立管参激振动研究综述

由于浮式平台升沉运动的影响,导致立管在水平方向上发生参激振动。参激振动可以引起立管平衡位置的不稳定性,此外,参激振动与涡激振动联合作用会改变立管振动响应特性,加剧立管疲劳破坏。为对深海立管参激振动进行深入研究,通过总结国内外立管参激振动研究的主要成果,介绍了立管参激振动的主要特点和动力学模型,归纳了深海立管参激振动研究的主要方向,并就研究中较为薄弱的一些环节,提出了一些建议。     

Hull-form optimization using parametric modification functions and particle swarm optimization

The focus of this paper is on devising designer-friendly hull-form variations coupled with optimization algorithms. Hull-form variations are carried out through parametric modification functions. Two kinds of representative optimization algorithms are considered here. One is the well-known sequential quadratic programming which is the derivative based. The other is particle swarm optimization which is the derivative free. The results applying these two algorithms to typical hull-form optimization problems are discussed in the paper. The technique using the parametric modification functions has been developed for modifying the ship’s geometry according to the widely recognized naval architect’s design practice. An original geometry can be easily deformed through the change of the variables of the modification functions; and useful information about the effect of the parameters is immediately obtained. Moreover, the variables of the modification functions can be considered as the design variables in the formulation of the optimization problem. For the performance prediction of the hull form, WAVIS version 1.3 is used for the potential-flow and RANS solver. Computational results for both single- and multi-objective problems are presented.     

Rigid finite element method in applications to dynamic optimization of motion of a riser in reentry

Overloading of a riser, with possible subsequent damage, can be caused when the bottom end of the suspended riser encounters an obstacle during its relocation realized in reentry. Such collisions can be avoided by appropriate horizontal and vertical displacements of the riser, which can be realized by planning the motion of the base or use of Heave Compensation Systems − HCS. Simulation tasks concerned with this problem can be solved by use of numerically effective models of a riser's dynamics and optimization methods. The model of dynamics of a riser presented in this paper and formulated by means of the rigid finite element method (RFEM) is validated against experimental measurements and calculation results presented by other researchers. Due to its very good numerical effectiveness, the model is then applied to the solution of two optimization problems. The first optimization task consists in choosing the horizontal displacements of the upper end of the riser so that the bottom end of the riser is positioned as closely as possible to the final position with reduced vibrations at the end of the base motion. In the second task the upper end of the riser is moved vertically in such a way that the bottom end of the riser stays at a safe distance from an obstacle during riser relocation. The results of optimization simulations for a number of cases are presented and discussed.     

Optimization of mooring systems in the context of an integrated design methodology

This work describes an enhanced mooring optimization procedure, oriented towards recent floating production systems (FPS) for oil & gas exploitation in ultra-deep-water scenarios, which may present a large number of risers in an asymmetric layout. Acknowledging that the risers are the key component of an FPS, the optimization procedure is associated to an integrated mooring-riser design methodology; thus, instead of simply minimizing the platform offsets and/or the costs of the mooring system itself, one of the main objectives is to obtain a mooring configuration that ensures the integrity of the risers. Other highlights of the optimization procedure include the following aspects: Enhancements in the modeling of the optimization problem (including the definition of design variables, objective function and constraints that are relevant for such actual applications); The use of the PSO optimization algorithm associated to the ε-constrained method to efficiently handle the constraints; Enhancements in the evaluation of candidate solutions, by full nonlinear time-domain dynamic Finite Element simulations with coupled models; and the implementation in a parallel computing environment to deal with the high associated computational costs. A case study considering an FPS representative of actual applications in deepwater scenarios is presented to illustrate the practical application of the optimization tool.     

Efficient optimization design method of jacket structures for offshore wind turbines

With the gradual implementation of offshore wind energy production, the future tendency is to expand into the deeper water. The jacket foundations will take the place of the present monopile foundations when the water depth increases. The foundations account for the majority of the construction cost for offshore wind farms, and the structural optimization of jackets will bring lucrative economic benefits. Structural optimization is a complex iterative process that requires huge computing costs. Therefore, this paper proposes a structural optimization method based on surrogate models to solve this problem effectively and swiftly obtain optimized design schemes of lightweight jackets for offshore wind turbines. The structural responses of jacket wind turbine systems under the equivalent static extreme loads with a recurrence period of 50 years are mainly considered in structural optimization design, and the key optimization variables of jackets are determined by parameter sensitivity analysis. The finite element models of jackets are transformed into surrogate models, and the genetic algorithm is employed to optimize the surrogate models directly. The optimized jackets are additionally verified through coupled dynamic analysis, besides, buckling strength and fatigue life are also checked. And local refined optimizations are carried out for the failure members. According to the optimized design schemes of lightweight jackets for 30 m, 50 m and 70 m water depths, it is demonstrated that the structural optimization design method is adequate and efficient for jackets of wind turbines. Parameter sensitivity analysis can cut the number of optimization variables in half to improve the optimization efficiency. Furthermore, the application of surrogate models can significantly speed up the optimization process by saving about 98.61% of the original time consumed. The optimization design method of the jackets for offshore wind turbines proposed in this paper is suitable for practical engineering, with high precision and efficiency.     

Mechanical model and characteristics of deep-water drilling riser-wellhead system under internal solitary waves

Internal solitary waves with a huge amount of energy easily trigger the large dynamic responses of riser-wellhead system and threaten its structural safety. However, previous studies have only focused on the dynamic response of the riser under internal solitary waves. The riser may experience excessive traction from the platform, especially from the mooring platform, in response to the arrival of internal solitary waves. The bottom of the riser connects to the wellhead system, which in turn exerts a reaction force on the riser. To address this problem, a coupled dynamic model of deep-water drilling mooring platform-riser-wellhead system under internal solitary waves is developed in this paper. A dynamic response analysis method based on the fourth-order Runge-Kutta method and finite element method is also proposed for the mooring platform-riser-wellhead system. A dynamical solver for the coupled system is then developed using MATLAB. The dynamic response characteristics of the riser-wellhead system under internal solitary waves are calculated. Results show that the displacement and bending moment of the system initially increases and then decreases along with the propagation of internal solitary waves, and finally reach equilibrium position. The displacement and bending moment reach their peak before the trough of internal solitary waves passes through the riser-wellhead system. The dynamic responses of the riser-wellhead system under the influence of internal solitary wave loads are much larger than those without the effect of internal solitary wave loads. The riser system experiences shearing loads at the interface of internal solitary waves, which trigger a step-like bending moment variation. The bending moment of the conductor under the mudline is greatly increased by the internal solitary waves.     

Influence of seabed trench formation on fatigue performance of steel catenary risers in touchdown zone

The subsea survey results using remote operating vehicles (ROV) show that trenches with a depth of several riser diameters can be developed underneath the steel catenary risers (SCR). Therefore, an important question in respect of the riser–seabed interaction is, how the trench formation beneath the riser affects the riser fatigue performance in the touchdown zone. A common methodology reported in literature to study the impact of trench formation on riser fatigue life is the insertion of an artificial mathematical expression of the riser profile into the seabed. This study shows that such methodology can be inconsistent and leading to contradictory results. The current paper has employed ABAQUS finite element software and coded a non-linear soil hysteretic model to automatically simulate the variable seabed stiffness and the gradual trench development through the touchdown zone. In this method, the seabed model parameters are initially adjusted to extreme values allowing trench with desired depth to be developed over a moderate number of displacement cycles of the SCR. The design wave scatter diagram is then applied, simulating a generic Spar system, after switching the model parameters to values with normal range. The paper presents the impact of trenches of different depths on the fatigue performance of SCRs in the touchdown zone.     

超深水钻井隔水管动力分析理论研究与数值模拟

随着钻井作业向深水(500～1 500m)和超深水(1 500m以上)发展,在交变海洋环境载荷波浪力、海流力和浮式钻井平台运动的共同作用下,隔水管的动态响应更加显著.文中探讨了隔水管侧向振动的数学模型、动态特性分析中的结构与环境载荷建模技术及其非线性动力分析方法,研究并对比了不同分析方法在计算效率、计算精度和工程适用性等方面的差异.介绍了时域内应用ABAQUS软件进行超深水钻井隔水管非确定性动力分析的算法与详细流程,算例比较了不同边界条件对深水钻井隔水管动态特性的影响.研究表明,时域非确定性分析最为精确但需要时间最长,且只能采用线性AIRY波浪理论;理论上,海流主要引起隔水管动态响应的时不变部分,但该时不变部分不等同于海流引起的隔水管静态响应,一种简化方法只将海浪与钻井船运动作为动载荷而不考虑海流对动态响应的贡献;钻井船运动和波浪载荷是隔水管动态响应分析主要的动载荷,对于超深水隔水管来说,钻井船运动是首要的动载荷,其慢漂运动对隔水管性能有重要影响,而波浪仅对隔水管局部产生作用.     

基于多维多项式混沌展开法的船舶不确定性优化设计

以船舶不确定性优化设计为对象,分析考虑多个随机变量对优化目标和约束的影响,提出一种基于多维多项式混沌展开法(PCE)的船舶不确定性优化设计,并将其应用于散货船工程优化实例中,保证船舶的稳健性和可靠性。     

基于工艺可行性的离散变量结构动力特性设计优化

基于船舶工艺可行性分析,建立了使用自适应模拟退火算法的多工况下船体结构动力特性设计优化模型;并给出了相应的设计流程。模型使用矩阵描述由板材厚度和骨材型号构成的离散变量集合,同时将全体设计变量处理为共享设计变量。将模型应用于某集装箱船艉部结构的动力特性设计优化中,优化后的结构不仅减轻了自重,而且增加了频率储备。实例分析表明该模型能应用于工程结构的实际优化设计。     

缓波型柔性立管构型优化及敏感性分析

针对缓波型柔性立管存在的波型较陡和浮子段张力较大的问题,对其进行优化,将单波构型优化为双波构型,运用集中质量法对改进前后的2种结构形式进行分析,确认双波构型在静力和动力响应下的张力及弯曲特性更优。在此基础上,对双波型柔性立管进行敏感性分析。在静力状态下,悬挂点和第2段浮子段末端对浮子段间隔和浮子段长度敏感;在动力响应下,悬挂段到第1段浮子段的张力变化和最小弯曲半径对浮子段间隔和大悬挂角非常敏感。研究得到的敏感性参数结论可作为缓波型柔性立管总体布置设计的参考。为提升缓波型柔性立管的性能,可合理增加浮子段与浮子段的间隔和悬挂角,但同时要满足规范的要求,避免关键部位动力响应过大。     

深水缓波型刚性立管的设计方法

缓波型刚性悬链线立管由于其良好的力学性能和较低的成本,适用于深水油气田开发。本文详述了缓波型刚性悬链线立管的设计准则和设计流程,给出了分布式浮块的设计方法和等效原则,推导了等效水动力参数的计算公式。通过静力分析,得到了不同浮块的布置位置和浮力系数对立管形态、顶端张力、弯矩分布的影响;通过动力分析,得到了沿管等效应力响应的分布规律,为缓波型刚性悬链线立管的设计提供了有益的参考。     

缓波型非粘接柔性立管的干涉敏感性

针对非粘接柔性立管在波浪和海流作用下易发生立管干涉的问题,以我国南海某油田输油立管和相邻锚链为例,分别对拖曳力系数、管道单位长度质量、外径、内部介质密度、立管抗拉弯扭刚度和悬挂角度等参数进行敏感性分析,得出不同参数的敏感性情况,并在此基础上提出一些建议供实际工程设计参考.     

考虑声辐射特性的船舶板架结构动力优化设计

提出了一种基于导纳法和遗传算法的船舶板架结构动力优化设计方法,将板架结构分解成由薄板与梁在相应连接节点处耦合的组合结构,利用其导纳公式推导出带有隔振系统的板架结构在任意位置简谐力激励下的弯曲振动响应,并与边界元法相结合,分析计算板架结构的声辐射特性。数值计算表明,只需取较少的耦合节点即可得到较好的计算精度,避免了大量的有限元计算。在此算法的基础上,使用遗传算法进行考虑声辐射特性的板架结构动力优化设计。为提高优化收敛速度,针对船舶板架结构的特点,选取纵桁和强横梁剖面惯性矩作为设计变量,减少了设计变量的个数,并建立满足构件剖面尺寸搭配关系要求的、经过优选的剖面尺寸方案库,便于获得满足约束条件的离散优化解。一个船舶板架结构的动力优化实例验证了方法的有效性。     

船舶最小回转半径

本文确定了动稳定船舶的最小定常回转半径,进而就可把最优化方法应用于船舶操纵性设计中去。 基于线性化操纵运动方程,在优化过程中,把船体诸形状参数和舵面积作为设计变量,把回转性指数的倒数作为目标函数,把动稳定准则c′作为优化的约束条件。 根据计算结果,本文清晰地阐明了船体某些形状参数及舵面积的变化对最小回转半径的影响。