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.     

Long-Term Effect of TMD on Vibration Control of An MDOF Offshore Fixed Platform

A three-dimensional fixed offshore platform in deep water modeled by the finite element method is studied in this paper. Analysis of the dynamic response of the MDOF structure is realized taking the non-linearity of the wave drag force and the wave-structure interaction into account. The structural response statistics, which have Gaussian distributions, are used to evaluate the vibration effect of the structure without TMD and with TMD. And an optimal method to design TMD controlling the first mode of the multi-mode structure is proposed. Moreover, the probabilities of occurrence of sea states at the platform site are considered for prediction of the long-term effect of a TMD. Simulation results demonstrate that the long-term effect of a well-designed TMD is good and the practical use is possible due to the good stability of its optimal parameters under different sea states.     

Mitigation of Ice-Induced Vibrations for Offshore Platforms Using Tuned Mass Damper

The problems of ice-induced vibration have been noticed and concerned since the 1960s, but it has not been well resolved. One reason is that the dynamic interaction between ice and structure is so complicated that practical ice force model has not been developed. The recent full-scale tests conducted on jacket platforms in the Bohai Sea presented that ice could cause intense vibrations which endanger the facilities on the deck and make discomfort for the crew. In this paper, the strategy of mitigation of ice-induced offshore structure vibration is discussed. Based on field observations and understanding of the interaction between ice and structure, the absorption mitigation method to suppress ice-induced vibration is presented. The numerical simulations were conducted for a simplified model of platform attached with a Tuned Mass Danlper （TMD） under ice force function and ice force time history. The simulation results show that TMD can fa- vorably reduce ice-induced vibrations, therefore, it can be considered to be an alternative approach to utilize. Finally, the application possibilities of utilizing TMDs on other miniature offshore structures in ice-covered areas of marginal oil fields are discussed.     

调谐质量阻尼器对海洋平台的减振效果分析

目前调谐质量阻尼器(TMD)的研究和设计多数是依据结构的第一阶模态进行的,忽略了TMD对结构其它模态的影响。为了明确TMD是否会对结构的高阶模态造成不利的影响以及影响的程度,论文采用模态分析法将海洋平台-TMD系统进行模态分解,推导出系统各阶模态的状态空间方程。并以一海洋平台为算例,讨论TMD针对结构的某一摸态进行设计时对各阶模态响应的减振效果,仿真的结果表明TMD对设计的模态有较好的减振效果,但对平台的其它模态响应的减振幅度有限,甚至产生不利影响,使某些模态的振动响应增幅较大。     

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.     

Energy Analysis 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 focnses on theenergy concept of TMD/structure systems. In this study, a time domain is taken. The platform is modeled as a simplifiedsingle-degree-of-freedom (SDOF) system by extraction of the first vibration mode of the structure and the excited force isassumed 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 thedeck motion but less effective in reducing the maximum response under impact loading.     

考虑流固耦合时的海底管道悬跨段非线性动力分析

通过对管道的涡激振动试验,提出了考虑流固耦合的非线性涡激升力表达式,并用该式进行了海底管线悬跨段非线性动力响应时程分析。对考虑流固耦合与未考虑流固耦合情况下得到的管道动力响应时程进行对比,算例表明:当管外流场流速与管道顺流向振动速度值较接近时,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。分析认为,在管外流场流速与管道顺流向振动速度值较接近的情况下,管道的涡激振动计算宜采用非线性涡激力模型。     

Dynamic modeling and vibration suppression for an offshore wind turbine with a tuned mass damper in floating platform

The worldwide demand for renewable energy is increasing rapidly. Wind energy appears as a good solution to copy with the energy shortage situation. In recent years, offshore wind energy has become an attractive option due to the increasing development of the multitudinous offshore wind turbines. Because of the unstable vibration for the barge-type offshore wind turbine in various maritime conditions, an ameliorative method incorporating a tuned mass damper (TMD) in offshore wind turbine platform is proposed to demonstrate the improvement of the structural dynamic performance in this investigation. The Lagrange's equations are applied to establish a limited degree-of-freedom (DOF) mathematical model for the barge-type offshore wind turbine. The objective function is defined as the suppression rate of the standard deviation for the tower top deflection due to the fact that the tower top deflection is essential to the tower bottom fatigue loads, then frequency tuning method and genetic algorithm (GA) are employed respectively to obtain the globally optimum TMD design parameters using this objective function. Numerical simulations based on FAST have been carried out in typical load cases in order to evaluate the effect of the passive control system. The need to prevent the platform mass increasing obviously has become apparent due to the installation of a heavy TMD in the barge-type platform. In this case, partial ballast is substituted for the equal mass of the tuned mass damper, and then the vibration mitigation is simulated in five typical load cases. The results show that the passive control can improve the dynamic responses of the barge-type wind turbine by placing a TMD in the floating platform. Through replacing partial ballast with a uniform mass of the tuned mass damper, a significant reduction of the dynamic response is also observed in simulation results for the barge-type floating structure.     

Torsional Response of the Offshore Platform with TMD

It is pointed out in this paper that the offshore platform could be controlled by means of the Tuned Mass Damper (TMD) if there is torsional vibration in the system. The effectiveness of the location of TMD is quantified with the help of the response ratio between the peak responses of the system in the presence and in the absence of TMD. In addition, the parameters of frequency and damping ratio of TMD are optimized.     

Vibration Control of Multi-Tuned Mass Dampers for An Offshore Oil Platform

The purpose of this study is to investigate the effectiveness of multi-tuned mass dampers (MTMD) on mitigating vi-bration of an offshore oil platform subjected to ocean wave loading. An optimal design method is used to determine the optimal damper parameters under ocean wave loading. The force on the structure is determined by use of the linearized Morison equation. Investigation on the deck motion with and vvithout MTMD on the structure is made under design condi-tions. The results show that MTMD with the optimized parameters suppress the response of each structural mode. The sensitivity of optimum values of MTMD to characteristic wave parameters is also analyzed. it is indicated that a single TMD on the deck of a platform can have the best performance, and the small the damping value of TMD, the betler the vibration control.     

弯曲柔性立管举升气液两相流时的流固耦合效应研究

海洋油气混输时,气液两相流与混输立管之间的双向流固耦合作用机理十分复杂.针对柔性立管与气液两相流的流固耦合响应问题,在气液两相循环试验装置中开展了不同流型两相流流动特性及柔性立管振动响应的测试,利用高速摄像非介入测试技术同步捕捉了柔性立管的振动位移与管内的流型演变过程,对比了不同流型气液两相流诱导的立管振动响应特性,通过对比固定和振动立管内的气液两相流动特性,辨析了振动对管内两相流动的影响.结果表明:柔性立管中出现了泡状流、泡状—段塞流、段塞流、段塞—搅拌流和搅拌流五种流型,不同流型的气液两相流诱导立管振动的机理不同,在段塞—搅拌流作用时立管的振动响应最剧烈.与固定立管相比,强烈的振动不同程度地改变了气液两相流的流动特性,振动立管中部分两相流流型转变的临界条件有明显地调整,相对而言,振动对搅拌流和泡状流的影响较小.     

内孤立波与深海立管相互作用数值模拟

提出了一种对内孤立波与深海立管相互作用耦合数值模拟方法。流场采用内孤立波数值水槽方法进行模拟,结构响应采用基于薄壳理论的有限元方法进行计算,采用一种将流场和结构响应数据进行实时传输的方法,实现了流体与固体之间的耦合数值模拟。对内孤立波作用下某长径比为1 200的深海立管载荷及其动力响应特性进行了数值模拟与分析。结果表明内孤立波不仅会对深海立管产生突发性剪切载荷作用,而且还会使立管产生大幅度变形响应现象,因此在深海立管设计与应用中,内孤立波的影响是不可忽视的。研究表明,该方法为研究内孤立波作用下深海立管动力特性及其工程预报相关问题提供了一种有效的手段。     

The Optimal Design of TMD for Offshore Structures

This paper presents the optimal design procedure of Tuned Mass Damper(TMD)for re-ducing vibration of an actual steel jacket offshore platform excited by random wave loading.In this study,a frequency domain is taken.The force on the structure is determined by use of the linearized Morisonequation for an input Power Spectral Density(PSD)of wave elevation.The sensitivity of optimum valuesof TMD to characteristic parameters of random wave spectrum is analyzed.An optimized TMD designfor the modeled platform is given based on design conditions and the findings of the study.     

Dynamic Analysis of A 5-MW Tripod Offshore Wind Turbine by Considering Fluid–Structure Interaction

Fixed offshore wind turbines usually have large underwater supporting structures. The fluid influences the dynamic characteristics of the structure system. The dynamic model of a 5-MW tripod offshore wind turbine considering the pile–soil system and fluid structure interaction (FSI) is established, and the structural modes in air and in water are obtained by use of ANSYS. By comparing low-order natural frequencies and mode shapes, the influence of sea water on the free vibration characteristics of offshore wind turbine is analyzed. On basis of the above work, seismic responses under excitation by El-Centro waves are calculated by the time-history analysis method. The results reveal that the dynamic responses such as the lateral displacement of the foundation and the section bending moment of the tubular piles increase substantially under the influence of the added-mass and hydrodynamic pressure of sea water. The method and conclusions presented in this paper can provide a theoretical reference for structure design and analysis of offshore wind turbines fixed in deep seawater.     

Dynamic Analysis of A 5-MW Tripod Offshore Wind Turbine by Considering Fluid–Structure Interaction

Fixed offshore wind turbines usually have large underwater supporting structures.The fluid influences the dynamic characteristics of the structure system.The dynamic model of a 5-MW tripod offshore wind turbine considering the pile–soil system and fluid structure interaction(FSI) is established,and the structural modes in air and in water are obtained by use of ANSYS.By comparing low-order natural frequencies and mode shapes,the influence of sea water on the free vibration characteristics of offshore wind turbine is analyzed.On basis of the above work,seismic responses under excitation by El-Centro waves are calculated by the time-history analysis method.The results reveal that the dynamic responses such as the lateral displacement of the foundation and the section bending moment of the tubular piles increase substantially under the influence of the added-mass and hydrodynamic pressure of sea water.The method and conclusions presented in this paper can provide a theoretical reference for structure design and analysis of offshore wind turbines fixed in deep seawater.     

考虑流固耦合效应的单桩式海上风电机组结构响应模拟

针对海上风电整机系统,建立了一体化流固耦合分析方法。在模拟过程中,采用浸入边界法解决风机叶片旋转引起的静动干涉问题,利用改进的守恒式 level set（简称 ICLS）方法捕捉海浪自由面,并使用交错迭代法求解流固耦合方程。通过构建 “风机—塔架—基础”一体化流固耦合数值模拟方法,能够在一次仿真计算中实现海上风电整机系统的全过程数值模拟,准确求解多荷载耦合作用下“风机—塔架—基础”的整体结构动力响应。以某单桩式海上风电工程为例,验证了本方法能够实现对海上风电整体系统的一体化分析。     

Similarity method for modelling hydroelastic offshore platforms

Similarity methods provide a very powerful technique for modelling offshore platforms. Such methods are preferable for situations where the wave-structure interaction process is complex, and its modelling cannot be expressed by rigorous mathematical formulations.In modelling the interaction between waves and an offshore platform, the dynamic properties of the wave and structure must be considered together to determine the similitude parameters. The paper gives details of such an investigation using a frequency response function approach. Three different models, which are termed general, distorted and nondistorted Froudian models, are developed. From the general model, it was found that the velocity scales of the wave and structure could be treated differently. Internal and external force scales could also be different. It is observed then that a restrictive modelling criterion is used when the velocity scale of a structure is obtained from Froudian scale modelling. Furthermore, detailed scales for practical use are developed. The model parameters for an acrylic plastic tripod tower platform with length scales of 1/50 and 1/70 are given, and the accuracy involved among the three models determined for these scales. The sensitivity of the results to slight variations in thickness and Young's modulus are also discussed.     

Dynamic Response Analysis of Interaction System of R.C. Gravity Single-Leg Platform

In this paper, the responses of the interaction system of R.C. gravity single-leg platform to seismic excitation are mainly analysed. A set of nonlinear equations for the interaction system are established by using the wave, one is the soil-structure interaction and the other is the fluid-structure interaction. The seismic response of the interaction system is analysed for the influence of the asymmetric structure, fluid action, etc. with the input of seismic SH waves in any direction. The numerical results are given for a simple example.     

Response mitigation on the offshore floating platform system with tuned liquid column damper

In this study a typical tension-leg type of floating platform incorporated with the tuned liquid column damper (TLCD) device is studied. The purpose is to find an effective and economic means to reduce the wave induced vibrations of the floating offshore platform system. The floating offshore platform has been widely applied for the offshore exploitation such as operation station, cross-strait bridges, floating breakwater and complex of the entertainment facilities. For offshore platform being employed as a public complex the stability and comfort to stay will be the major concern besides the safety requirement. Therefore, how to mitigate the vibration induced from waves and similar environmental loading becomes an important issue. The TLCD system utilizing the water sloshing power to reduce the vibration of the main structure, a newly developed device that could effectively reduce the vibrations for many kinds of structure is the first-time employed in the floating platform system. In both the analytical and experimental results it is found that the accurately tuned TLCD system could effectively reduce the dynamic response of the offshore platform system in terms of the vibration amplitude and the resonant frequency.     

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.