Dynamic analysis of vessel/riser/equipment system for deep-sea mining with RBF neural network approximations

Abstract

Deep-sea mining (DSM) is an advanced technology. This article is focused on the dynamic analysis of a coupled vessel/riser/equipment system of a DSM based on radial basis function (RBF) neural network approximations while considering vessel dynamic positioning (DP) and active heave compensation (AHC). A coupled model including the production support vessel (PSV), lifting riser, and slurry pump is established containing simulated DP and AHC models. Furthermore, dynamic simulations are implemented to obtain the results of the vessel motions, thruster forces, pump motions and riser tensions. Using optimal Latin hypercube sampling, an RBF neural network approximation model is established, the input includes environmental factors and the output includes the dynamic responses of the pump motion and riser tension. Calculations are performed using RBF network approximations instead of a coupled model. The obtained results show that the PSV wave frequency (WF) motions have significant influence on the dynamic responses of the subsea system. Moreover, the current load affects the compensation effect. The RBF network approximation model can be used to reduce the required calculation time.     

Coupled dynamic analysis of deep-sea mining support vessel with dynamic positioning

Deep-sea mining (DSM) is an advanced concept. A simulation method of coupled vessel/riser/body system in DSM combined with dynamic positioning (DP) is proposed. Based on the three-dimensional potential flow theory, lumped mass method, and Morison’s equations the dynamic models of the production support vessel, riser and slurry pump are established. A proportion integration differentiation (PID) controller with a nonlinear observer and a thrust allocation unit are used to simulate the DP system. Coupled time domain simulation is implemented with the vessel operated in two DP modes. Results of the vessel and pump motions, riser tension, and thruster forces are obtained. It shows that the pump will be lifted by the riser when the vessel is chasing the next set point. Riser tension is influenced by the wave frequency motions of the vessel in positioning mode and low-frequency motions in tracking mode. The proposed simulation scheme is practical to study the DSM operation.     

Lateral Vibration Behavior Analysis and TLD Vibration Absorption Design of the Soft Yoke Single-Point Mooring System

Mooring system is the key equipment of FPSO safe operation. The soft yoke mooring system is regarded as one of the best shallow water mooring strategies and widely applied to the oil exploitation in the Bohai Bay in China and the Gulf of Mexico. Based on the analysis of numerous monitoring data obtained by the prototype monitoring system of one FPSO in the Bohai Bay, the on-site lateral vibration behaviors found on the site of the soft yoke subject to wave load were analyzed. ADAMS simulation and model experiment were utilized to analyze the soft yoke lateral vibration and it was determined that lateral vibration was resonance behaviors caused by wave excitation. On the basis of the soft yoke longitudinal restoring force being guaranteed, a TLD-based vibration damper system was constructed and the vibration reduction experiments with multi-tank space and multi-load conditions were developed. The experimental results demonstrated that the proposed TLD vibration reduction system can effectively reduce lateral vibration of soft yoke structures.     

平台运动下深水钻井隔水管非线性动力响应研究

建立深水钻井隔水管在波、流和平台运动的联合作用下的运动方程,模拟1 000 m深水钻井隔水管的非线性动力响应.分析在波、流作用下钻井液密度和顶部张力比等因素对隔水管振动频率的影响,研究平台的静偏移和动态运动对隔水管最大弯矩分布的影响.结果表明,平台运动对深水钻井隔水管的动力响应有较大影响,使隔水管上部最大弯矩峰值增加了1倍多.     

基于神经网络优化算法的海洋动态缓波型立管设计

柔性立管连接海上平台和水下生产系统,缓波型构型可以减轻其受到的顶部张力和疲劳损伤,触地点处系链对于固定水下立管起着重要作用,然而加装系链的缓波型立管系统设计更为复杂。通过缓波型基本理论计算出合理的立管初始状态,之后使用立管分析软件OrcaFlex,在充分考虑环境因素、船体结构、立管材料和线型以及重力块、浮力块、系链等配置参数的情况下,建立缓波型立管系统有限元模型,通过静动态分析验证其满足设定的关于立管构型、张力、弯曲半径,系链张力和FPSO偏移量5个约束条件。结合神经网络优化算法和遗传算法制定出针对文中立管系统的优化算法并通过MATLAB编程将浮力块数量优化至最少,之后基于L-M算法构建神经网络模型,通过迭代训练提升精度,得到最终参数优化结果。通过对比优化前后静动态分析结果可知：优化后浮力块数量大幅减少,立管最大有效张力大幅减小,而悬挂段最低点深度有一定程度的增大,整体构型更趋向于合理的缓波型构型。     

Dynamic response of marine risers by single wave and spectral analysis methods

This paper uses the Galerkin method in the solution of the marine riser differential equation and compares the dynamic bending stresses in a tension-leg-platform riser calculated by the linearised single wave and linearised spectral analysis methods.The results show that it is possible to make some rational assessment of approximate peak values of bending stress in the spectral method.The analysis methods are applicable to any riser system subject to horizontal exciting forces due to fluid and vessel motion.     

Coupled analysis of floating production systems

Fully coupled global analysis of Floating Production Systems, including the vessel, the mooring system and the riser system is described. Design of the system can be a daunting task, involving more than 1000 load cases for global analysis. The primary driver for the mooring system and for the riser system is motion of the vessel. Vessel motions are driven by environmental forces, but are restrained by forces from the mooring and riser systems. Numerical models and procedures that provide accurate and efficient global modeling of the Floating Production System are presented. Both Time Domain and Frequency Domain procedures are included. The accuracy and efficiency of the procedures are illustrated in an example: a large semi with 16 mooring lines and 20 risers. The procedures provide the accuracy and efficiency for use of fully coupled analysis in design of Floating Production Systems from concept selection to final design, installation and operation.     

Dynamic and static analysis of a marine riser

A frequency domain normal mode solution is presented for the dynamic response of an unbuoyed marine riser subjected to periodic excitation from a surface vessel in the direction of wave propagation. The variable tension beam-column equation is solved in terms of normal modes of free vibration of the riser and the rigid body displacement. Drag forces on the riser are represented by Morison's formula taking account of the velocity of the riser and wave-induced fluid velocity. A periodic solution for the flexural motion of the riser and the bending stress is then obtained by means of an iterative solution of the frequency response function. The drag force induced stresses arising from a linearly varying current are also determined. The results presented compare favourably with those obtained by other methods.     

深海采矿立管在波流载荷下的弯矩响应分析

采矿立管是深海采矿系统的重要组成部分，立管的弯矩分析是确保立管正常使用的重要指标。立管所处海洋环境复杂，且立管底部的自由边界条件使得立管弯矩特性难以分析。本文基于波浪理论，使用Abaqus 有限元软件建立海洋采矿立管的模型，运用Abaqus中的AQUA海洋工程模块，考虑立管在轴向力、自重、浮力、波浪载荷、海流载荷及模拟海上平台水平和升沉运动共同作用下，对采矿立管进行弯矩分析，计算了提升泵不同安装位置、不同中继仓重量变化对弯矩的影响，结果表明：提升泵会增大安装位置的弯矩幅度，且安装在不同位置对立管弯矩会产生叠加影响；中继仓重量的增加提高了立管整体稳定性，但会使提升泵处弯矩波动产生向中部延伸的不利影响。     

Nonlinear Dynamic Analysis of Deepwater Drilling Risers Subjected to Random Loads

Excited by ocean currents, random wave and vessel motion, deepwater drilling risers exhibit significant dynamic response. In time domain, a method is proposed to calculate the nonlinear dynamic response of deepwater drilling risers subjected to random wave and dynamic large displacement vessel motion boundary condition. Structural and functional loads, external and internal pressure, free surface effect of irregular wave, hydrodynamic forces induced by current and wave, as well as wave and low frequency (drift) motion of the drilling vessel are all accounted for. An example is presented which illustrates the application of the proposed method. The study shows that long term drift motion of the vessel has profound effect on the envelopes of bending stress and lateral displacement, as well as the range of lower flex joint angle of the deepwater riser. It can also be concluded that vessel motion is the principal dynamic loading of nonlinear dynamic response for the deepwater risers rather than wave force.     

LNG-FSRU在软刚臂系泊下水动力特性研究

针对35万立方米超大型LNG-FSRU,采用软刚臂单点系泊系统定位方式,运用模型试验与数值计算两种技术手段开展风、浪、流联合作用下水动力研究。软刚臂系泊系统各构件间的连接方式及Yoke重量模拟是数值计算与模型试验的关键,数值计算对构件间的铰接方式与Yoke重量进行模拟,模型试验同样模拟了系泊系统的相似性,并将数值计算结果与模型试验结果进行对比分析。结果表明,软刚臂系泊系统刚度曲线呈非线性,试验结果与数值结果吻合良好,表明对于软刚臂系泊系统的两种模拟是合理的,反映了LNG-FSRU在风、浪、流联合作用下的运动特性,建立的研究方法可用于软刚臂系统的水动力研究。     

驳船横荡运动下海洋立管的动力响应

海洋浮式生产系统下立管的受力情况复杂,国内的研究大多集中于两端固支或简支的情况。本文则以水面驳船的横荡运动作为立管上端的动力边界条件,将Matteo Luca Facchinetti的尾流振子模型与考虑外流涡激振动作用下海洋立管运动微分方程相结合,得到管道与流体的耦合振动方程,用Hermit插值函数将方程进行有限元离散,并用Newmark时程分析法及迭代法求解,得到管道各点的位移时程曲线。结果表明:立管的振动频率主要由上端驳船的运动频率所确定,随着驳船运动频率的增加,立管中点的位移幅值先增加后减小;在有动边界存在的条件下,改变外流流速对立管中点的位移幅值影响不大。     

Nonlinear Static Finite Element Stress Analysis of Pipe-in-Pipe Risers

Owing to the complexity of the pipe-in-pipe (PIP) riser system in structure, load and restraint, many problems arise in the structural analysis of the system. This paper presents a new method for nonlinear static finite element stress analysis of the PIP riser system. The finite element (FE) model of the PIP riser system is built via software AutoPIPE 6.1. According to the specialties of a variety of components in the PIP riser system, different elements are used so as to model the system accurately. Allowing for the complication in modeling the effects of seabed restraint, a technique based on the bilinear spring concept is developed to calculate the soil properties. Then, based on a pipeline project, the entire procedure of stress analysis is discussed in detail, including creation of an FE model, processing of input data and analysis of results. A wide range of loading schemes is investigated to ascertain that the stresses remain within the acceptable range of the pipe material strength. Finally, the effects of the location of flanges, the thermal expansion of submarine pipelines and the seabed restraint on stress distribution in the riser and expansion loop are studied, which are valuable for pipeline designers.     

波频和慢漂组合作用下钢悬链线立管疲劳损伤研究

为了有效地考虑浮体慢漂运动对钢悬链线立管疲劳损伤的影响,提出了波频和慢漂运动组合作用下钢悬链线立管疲劳损伤简化计算的位置组合叠加法。其核心是:基于浮体慢漂运动概率分布选取若干典型慢漂位置,进行波频运动作用下钢悬链线立管动力响应分析;根据钢悬链线立管运动位置变化特征,截取若干慢漂位置对应的波频应力时程叠加到慢漂应力时程上,得到波频和慢漂运动的组合应力时程;编写基于雨流计数法的MATLAB程序处理立管各节点应力,采用海水环境下Do E.E型S-N曲线和Palmgren-Miner累积损伤准则计算立管各节点疲劳损伤。应用位置组合叠加法对某海域500 m水深的立管进行了疲劳分析,并与全耦合法、权重组合叠加法以及波频和慢漂疲劳损伤简单相加法的结果进行了对比,结果表明该方法具有较高的精度和效率。此外,进行了区域设定系数、波浪高度、波浪周期和土壤表面剪切强度等参数对组合作用下立管疲劳损伤的敏感性分析。     

Nonlinear control of an active heave compensation system

Heave motion of a vessel or a rig has an adverse impact on the response of a drill-string or a riser. To compensate for heave motion, passive and active devices are usually used. Active heave compensators, in which a control system is an essential part, allow conducting operations under more extreme weather conditions than passive ones. This paper presents a constructive method to design a nonlinear controller for an active heave compensation system using an electro-hydraulic system driven by a double rod actuator. The control system reduces the effect of the heave motion of the vessel on the response of the riser by regulating the distance from the upper end of the riser to the seabed. The control development is based on Lyapunov's direct method and disturbance observers. The paper also includes a method to select the control and disturbance observer gains such that actuator saturations are avoided. Stability of the closed loop system is carefully examined. Simulation results illustrate the effectiveness of the proposed control system.     

内孤立波作用下顶部张紧式立管动力特性

基于内孤立波mKdV理论,采用考虑内流的细长杆动力学方程,结合改进的Morison公式,研究两层流体中内孤立波与顶张立管的相互作用问题。针对东沙群岛南部海域附近某实测内孤立波特征参数,计算分析在该内孤立波作用下某顶张立管的内孤立波载荷与运动响应,以及立管横截面弯矩及其应力的变化特性。研究表明,内孤立波不仅会对顶张立管产生突发性的冲击载荷以及大幅度水平变形,而且还会使其横截面弯矩及其应力显著增大。因此在深海立管的设计与应用中,内孤立波的影响是不可忽视的。     

Stress Wave Propagation Analysis on Vortex-Induced Vibration of Marine Risers

To analyze the stress wave propagation associated with the vortex-induced vibration (VIV) of a marine riser, this paper employed a multi-signal complex exponential method. This method is an extension of the classical Prony''s method which decomposes a complicated signal into a number of complex exponential components. Because the proposed method processes multiple signals simultaneously, it can estimate the "global" dominating frequencies (poles) shared by those signals. The complex amplitude (residues) corresponding to the estimated frequencies for those signals is also obtained in the process. As the signals were collected at different locations along the axial direction of a marine riser, the phenomena of the stress wave propagation could be analyzed through the obtained residues of those signals. The Norwegian Deepwater Program (NDP) high mode test data were utilized in the numerical studies, including data sets in both the in-line (IL) and cross-flow (CF) directions. It was found that the most dominant component in the IL direction has its stress wave propagation along the riser being dominated by a standing wave, while that in the CF direction dominated by a traveling wave.     

超深水钻井作业隔水管顶张力确定方法

对于深水和超深水钻井作业,确定钻井隔水管系统顶张力是钻前设计非常重要的工作。研究三种隔水管系统顶张力确定方法,分别是理论方法、基于隔水管系统底部残余张力方法和基于下放隔水管系统的最大钩载方法。算例计算与超深水钻井实践对比表明,在相同的隔水管系统配置下,三种方法计算结果都接近于实际钻井作业时的顶张力设定值。但研究认为,基于下放最大钩载的顶张力计算方法简单实用,推荐作为优选方法。     

基于能量竞争载荷模型的海洋立管双向涡激振动时域预报方法研究

海洋立管是深海油气开发中用于连接海底井口和水面浮体的唯一通道。立管在洋流作用下极易发生涡激振动（vortex-induced vibration,简称VIV）,发展快速经验性涡激振动时域预报方法对立管的安全设计具有重要意义。通过柔性立管模型试验,结合载荷重构方法和最小二乘法,识别建立了能量竞争载荷模型下的经验水动力载荷系数模型。应用识别建立的经验水动力载荷系数模型,发展形成了海洋立管顺流向及横流向双向涡激振动时域预报方法。将预报结果与试验结果对比,结果表明：基于能量竞争载荷模型的海洋立管双向涡激振动预报方法能够有效预报海洋立管涡激振动主导模态、主导频率、流向平均位移响应和涡激振动位移响应等力学行为特性。研究成果对发展更为有效的涡激振动预报手段具有有益参考。