非灌浆导管架平台异常振动的测试分析及故障诊断

通过对平台在风浪作用下的振动测试分析,发现了直立式非灌浆桩腿导管架平台在海底冲刷条件下发生异常振动的原因是导管架与桩之间存在较大的相对运动,以至于在风浪较大时发生碰撞。因而,结构的动力特性和动态响应都与设计结果不一致。在非极值海况条件下,平台的振动超出了设计预测值,并提出了治理和设计建议。     

渤海导管架平台的冰激振动响应分析

为研究渤海海域海冰撞击导管架海洋平台的冰振响应,基于锥体冰力函数,本文建立了渤海海域的冰力作用模型。采用ANSYS有限元软件对导管架平台与海冰的相互作用进行数值模拟,开展了海冰作用下抗冰平台的静力分析及平台动力响应分析。通过与静力分析结果对比,验证了动冰力对结构响应的动力放大效应。在此基础上通过改变冰厚、冰速等海冰参数,研究了不同冰力作用周期下导管架平台的冰振响应。研究表明,海冰厚度及海冰流动速度是影响平台动力响应的主要因素,为导管架平台结构的动力优化设计提供了研究基础。     

Adaptive Predictive Inverse Control of Offshore Jacket Platform Based on Rough Neural Network

The offshore jacket platform is a complex and time-varying nonlinear system,which can be excited of harmful vibration by external loads.It is difficult to obtain an ideal control performance for passive control methods or traditional active control methods based on accurate mathematic model.In this paper,an adaptive inverse control method is proposed on the basis of novel rough neural networks (RNN) to control the harmful vibration of the offshore jacket platform,and the offshore jacket platform model is established by dynamic stiffness matrix (DSM) method.Benefited from the nonlinear processing ability of the neural networks and data interpretation ability of the rough set theory,RNN is utilized to identify the predictive inverse model of the offshore jacket platform system.Then the identified model is used as the adaptive predictive inverse controller to control the harmful vibration caused by wave and wind loads,and to deal with the delay problem caused by signal transmission in the control process.The numerical results show that the constructed novel RNN has advantages such as clear structure,fast training speed and strong error-tolerance ability,and the proposed method based on RNN can effectively control the harmfid vibration of the offshore jacket platform.     

Optimal Active Control of Wave-Induced Vibration for Offshore Platforms

An obvious motivation of this paper is to examine the effectiveness of the lateral vibration control of a jacket type offshore platform with an AMD control device, in conjunction with H2 control algorithm, which is an optimal frequency domain control method based on minimization of H2 norm of the system transfer function. In this study, the offshore platform is modeled numerically by use of the finite element method, instead of a lumped mass model. This structural model is later simplified to be single-degree-of-freedom (SDOF) system by extracting the first vibration mode of the structure. The corresponding "generalized" wave force is determined based on an analytical approximation of the first mode shape function, the physical wave loading being calculated from the linearized Morison equation. This approach facilitates the filter design for the generalized force. Furthermore, the present paper also intends to make numerical comparison between H2 active control and the corresponding passive control using a T     

Structural monitoring of offshore platforms using impulse and relaxation response

Monitoring offshore platforms, long span bridges, high rise buildings, TV towers and other similar structures is essential for ensuring their safety in service. Continuous monitoring assumes even greater significance in the case of offshore platforms, which are highly susceptible to damage due to the corrosive environment and the continuous action of waves. Also, since a major part of the structure is under water and covered by marine growth, even a trained diver cannot easily detect damage in the structure. In the present work, vibration criterion is adopted for structural monitoring of jacket platforms. Artificial excitation of these structures is not always practicable and ambient excitation due to wind and waves may not be sufficient for collecting the required vibration data. Alternate methods can be adopted for the same purpose, for example, the application of an impact or a sudden relaxation of an applied force for exciting the structure. For jacket platforms, impact can be applied by gently pushing the structure at the fender while relaxation can be accomplished by pulling the structure and then suddenly releasing it using a tug or a supply vessel in both cases. The present study is an experimental investigation on a laboratory model of a jacket platform, for exploring the feasibility of adapting vibration responses due to impulse and relaxation, for structural monitoring. Effects of damage in six members of the platform as well as changes in deck masses were studied. A finite element model of the structure was used to analyze all the cases for comparison of the results as well as system identification. A data acquisition and analysis procedure for obtaining the response signatures of the platform due to the impulse and relaxation procedure was also developed for possible adoption in on-line monitoring of offshore platforms. From the study, it has been concluded that both impulse and relaxation responses are useful tools for monitoring offshore jacket platforms. The present work forms the basis for the development of an automated, on-line monitoring system for offshore platforms, using neural networks.     

Wave-induced vibration control of offshore jacket platforms through SMA dampers

Since permanent wave-induced vibrations of offshore jacket platforms reduce the service life of the jacket structure and deck equipment and increase the fatigue failure of the welded connections, this research has used SMA (shape memory alloy) dampers to control the jacket platform oscillations. Superelasticity, high durability, and energy dissipation capability make SMA elements good nominees for the design of vibration control devices. In this research, to model the force-displacement hysteretic behavior of SMA elements their idealized multi-linear constitutive model has been implemented and the time history responses of vibration equations have been evaluated by direct integration method. To analyze the SMA damper effects on the vibration suppression of the jacket platforms, a 90 (m) high jacket located 80 (m) deep in water has been selected as a case study. Numerical results have shown that optimized SMA dampers with constant-geometry SMA bars will improve the dynamic behavior of the jacket platform under the action of an extreme regular wave. However, under the action of two irregular waves, SMA dampers with varying-geometry SMA bars will cause significant reduction in the dynamic responses of the jacket platform. The power spectral density function of the deck displacements have shown that the previously mentioned SMA dampers avoid resonance by shifting the natural frequencies of the jacket structure away from the excitation frequencies.     

南海某导管架海洋平台倒塌分析

针对在役老龄导管架平台进行倒塌计算分析,确定极限承载力进而评估老龄导管架的安全裕度。采用非线性有限元方法,考虑平台的波流载荷及桩-土的非线性相互作用,利用SACS软件建立导管架整体三维有限元计算分析模型,并用逐步加载的方式,对南海某导管架平台进行了全过程非线性倒塌分析。计算分析表明,该导管架平台极限强度很高,具有较大的安全裕度;导管架倒塌过程呈逐步破坏形式,先是撑杆屈服,造成局部结构破坏,然后是钢桩发生屈服,降低结构承载力,最后节点逐步失效,造成结构倒塌。揭示了导管架平台结构失效倒塌的机理,给出了倒塌分析的可行方法和步骤。     

冰激振动下简易平台的动态优化设计

简易平台是边际油田开发的主要结构形式,由于平台结构形式简单,受到动力荷载作用响应比较大。采用动态设计可以合理优化平台结构形式,达到降低平台动力响应的效果。文中以JZ20-2NW简易平台为原型,运用ANSYS有限元分析软件对其进行冰激振动下的动态优化设计。结果表明,动态设计减振效果明显,可供设计人员参考。     

Topology optimization design for offshore platform jacket structure

Offshore jacket platform is widely used as production or oil recovering platform in the shallow sea, and is also applied to the offshore wind turbine supporting structure in the recent years. The jacket structures are normally designed to be conservative and bulky according to various design codes. In this work, a structural optimization design method for jacket platform structure has been developed based on topology optimization theory. The topology optimization method is applicable at an early design stage, which can determine the initial structure and force transmission path. The whole design space is chosen as design variables, and the goal is to maximize the structural stiffness. A set of constraints based on multi-criteria design assessment is applied according to standard requirements, which includes stress, deformation, vibration and design variable constraints. The optimization results are compared with the original platform for static performance, dynamic performance and Ultimate Carrying Capacity (UCC). Results show that the optimized structure show a 13.7% reduction in the global mass, 46.31% reduction in the maximum equivalent stress, and large ultimate carrying capacity ability under the same environmental loads. It is demonstrated that the proposed topology optimization method is capable of effectively determining the optimal design of jacket platform structures.     

Reliability-Based Design for Jacket Platform Under Extreme Loads

In this paper, reliability analysis for the offshore jacket platform with the interaction of structure- pile- soil under extreme environmental loads is carried out. The inherent uncertainties of the environmental load, foundation soil, platform itself, and calculating models are evaluated. The action of extreme loads on the offshore platform is modeled as a function of extreme wave height. The system capacity of the whole platform is determined by nonlinear pushover analysis, and the relevant probability property is obtained by the simulation method. The reliability model for the whole jacket platform is described as the relationship between the load and resistance based on the offshore design codes. The reliability of whole platform is calculated by the analytical method and the importance sampling method on the basis of a case study for a tripod jacket platform.     

考虑流固耦合时的海洋平台结构非线性动力分析

采用非线性的Morison方程,建立了考虑流固耦合时的海洋平台非线性动力方程及其时程分析方法.以一固定式导管架平台为算例,计算了考虑流固耦合时的海洋平台浪致振动响应,比较了考虑流固耦合和不考虑流固耦合时海洋平台动力响应的差异.算例表明：在较大的波浪条件下,不考虑流固耦合时的计算结果明显小于考虑流固耦合时的计算结果,因此,偏于不安全.分析认为,在极端海况条件下,考虑流固耦合的分析方法更符合实际情况.     

Reliability-Based Load and Resistance Factors Design for Offshore Jacket Platforms in the Bohai Bay： Calibration on Target Reliability Index

The target reliability index has been effectively used as the best solution to deal with the relationship between the structural safety and the optimal economy in any structural design.However,the target reliability index for offshore jacket platforms based on different sea areas in China has never been calibrated.This paper presents an approach for its calibration,and suggests many kinds of associated load cases.The uncertainties of loads and structural resistance are mainly investigated.The target reliability index for structural components,tubular joints and piles of offshore jacket platforms are discussed respectively in detail.Finally,through the calibrated results from the offshore jacket platforms of QK18-1,JZ20-2,SZ36-1 and BZ28-1 in the Bohai Bay,it is proposed to adopt 2.8 as the target reliability index of offshore jacket platforms in the Bohai Bay for a 25-year design period.The results provide significant reference for the design of offshore jacket platforms.     

Reliability-Based Load and Resistance Factors Design for Offshore Jacket Platforms in the Bohai Bay: Calibration on Target Reliability Index

The target reliability index has been effectively used as the best solution to deal with the relationship between the structural safety and the optimal economy in any structural design. However, the target reliability index for off-shore jacket platforms based on different sea areas in China has never been calibrated. This paper presents an approach for its calibration, and suggests many kinds of associated load cases. The uncertainties of loads and structural resistance are mainly investigated. The target reliability index for structural components, tubular joints and piles of offshore jacket platforms are discussed respectively in detail. Finally, through the calibrated results from the offshore jacket platforms of QK18-1, JZ20-2, SZ36-1 and BZ28-1 in the Bohai Bay, it is proposed to adopt 2.8 as the target reliability index of offshore jacket platforms in the Bohai Bay for a 25-year design period. The results provide significant reference for the design of offshore jacket platforms.     

基于实测的导管架海洋平台振动对人员安全评价

目前我国的海洋工程结构中,导管架式海洋平台占有很大比重,动荷载作用下导管架式海洋平台的振动问题日益突出。随着石油开发向深海进军,平台结构柔性更大,振动问题更为显著,可能对结构、设备及人员造成一定的安全隐患。基于现场监测获得的导管架平台振动响应,结合相关规范给出振动对人体的影响,提出人员感受评价流程。最后,以渤海、南海海域的导管架平台为例,基于现场监测,分析了结构的振动特性及作业人员在相应振动环境下的感受。此方法对导管架平台上部作业人员的工作与安全保障提供了科学依据。     

锥体导管架海洋平台冰激振动的DEM-FEM耦合分析及高性能算法

在寒区海域,冰荷载是影响海洋平台安全运行的主要环境荷载之一,由其引起的冰激振动给平台结构及其上部设备带来了严重危害。为分析不同冰况下平台的振动响应,本文建立了导管架海洋平台冰激振动的离散元（DEM）-有限元（FEM）耦合模型。采用具有黏接-破碎性能的等粒径球体离散单元对海冰的破碎特性进行模拟,通过由梁单元构建的海洋平台有限元模型获得结构的振动响应。在离散元与有限元的接触区域中实现了两个模型间计算参数的传递。为提高该耦合模型的计算效率和规模,发展了基于动力子结构方法的DEM-FEM耦合模型。为验证该耦合模型的有效性和可行性,将不同冰况下得到的冰荷载与ISO19906和JTS 144-1-2010标准进行了对比。结果表明,计算得到的冰荷载与标准相近,且冰厚与冰荷载呈二次非线性关系。同时,从冰速和冰厚两方面对比了渤海四桩腿JZ20-2 MUQ锥体导管架平台冰激振动加速度的数值结果和现场实测数据,发现冰速与振动加速度呈线性关系,冰厚与振动加速度呈二次非线性关系,并且振动加速度与冰速和冰厚平方的乘积呈线性关系。     

Inverse vibration technique for structural health monitoring of offshore jacket platforms

In this paper a new approach is introduced for structural health monitoring of offshore jacket platforms. The procedure uses the measured ambient vibration responses and the corresponding readable natural frequencies and mode shapes of the structural system. Since offshore platforms are composed of heavy topsides supported by jacket structures, participation of the first mode is dominant in each direction in the response of the structure under field excitations. Moreover, ambient vibrations such as wave loads and boat impacts only excite the first modes of the structure. Therefore, it is difficult to find higher modes and the pertinent frequencies by use of accelerometers data. The introduced innovative method in this research uses the first few fundamental frequencies and mode shapes of the structure. The algorithm employs the inverse vibration technique to develop a simple two and three dimensional reference model for monitoring health of the structure. To show the efficiency of the proposed procedure, a case study is carried out on the models of a jacket-type platform in the Persian Gulf, namely SPD2. Finally, an uncertainty analysis is performed, due to the existence of noises and uncertainties in input data collected by accelerometers. Results indicate that the proposed method has the ability to detect the induced damages by a high level of accuracy considering probable sources of error.     

海洋导管架平台的极限强度分析

海洋导管架平台的极限分析是一项较新的研究课题，随着海上采油事业的飞速发展，它已越来越受到海洋工程设计及维修部门的重视。其研究成果不仅能用于设计结构的应力校核，尚可用于现有平台结构的整体安全估算。本文利用非线性模拟技术及线性分析程序的完美结合。成功地分析计算了受集中哉茶作用的空间框架结构，及受静载荷和环境载荷作用下的真实导管架平台极限强度。     

Passive control of offshore jacket platforms

The wave-induced dynamic force is one of the most important excitations to be dealt with in the design of offshore structures. In order to perform a reliable design of an offshore structure, it is important to obtain an exact evaluation of its dynamic response but also to examine the ways of reducing the response. This paper presents the response of offshore jacket platforms installed with energy dissipation devices such as viscoelastic, viscous and friction dampers under wave loading. The offshore jacket platforms are modeled as multi-degrees-of-freedom system provided with dampers at each floor location. The wave forces are modeled as per Morison's equation. The governing equations of motion of the jacket platform with dampers are derived and their solution in the frequency domain is presented. The uni-directional random wave loading is expressed by the Pierson-Muskowitz spectrum. The response of the jacket platform with viscoelastic, viscous and friction dampers is compared with the corresponding response without dampers in order to investigate the effectiveness of the passive control systems. It is observed that the additional dampers add substantial damping to structure and thus favorably control the response of platform structure. Among the various energy dissipation devices used for study, the viscoelastic dampers perform better in comparison to the other dampers. This is due to the fact that the added viscoelastic dampers contribute to increased viscous damping as well as lateral stiffness which reduces the response of the offshore jacket platforms significantly.     

Investigation on Cutting Stability of Jacket in Decommissioning Process

Jacket cutting operation is one of the most complicated and highest risk operations in the process of decommissioning offshore piled platform, the security and stability of which must be assured. In this paper, the current research on offshore structure removal and jacket cutting is introduced, on the basis of which the types of load along with the load calculation method are determined. The main influences on the stability of a jacket in cutting are analyzed. The experiment test plan is drawn by using orthogonal testing method, and the formula of critical load during the cutting procedure is deduced by differential evolution algorithm. To verify the method and results of this paper, an offshore piled platform to be decommissioned in the South China Sea is taken for an example, and the detailed schedule for jacket cutting is made with the three-dimensional finite element model of the jacket established. The natural frequency, stress, strain and stability of the jacket during cutting process are calculated, which indicates that the results of finite element analysis agree well with that of the deduced formula. The result provides the scientific reference for guaranteeing the safety of jacket in cutting operation.     

Energy Anaiysis for TMD-Structure Systems Subjected to Impact Loading

This paper investigates the characteristics of reduction of the lateral vibration by use of a Tuned Mass Damper (TMD) for offshore jacket platforms under impact loading. Unlike traditional analysis, the present analysis focuses on the energy concept of TMD/structure systems. In this study, a time domain is taken. The platform is modeled as a simplified single-degree-of-freedom (SDOF) system by extraction of the first vibration mode of the structure and the excited force is assumed to be impact loading. The energy dissipation and energy transmission of the structure-TMD system are studied. Finally, an optimized TMD design for the modeled platform is demonstrated based on a new type of cost function - maxi-mum dissipated energy by TMD. Results indicate that TMD control is effective in reducing the Standard deviation of the deck motion but less effective in reducing the maximum response under impact loading.