Optimum geometry of tuned liquid column-gas damper for control of offshore jacket platform vibrations under seismic excitation

In this study, the effectiveness of a tuned liquid column-gas damper, TLCGD, on the.suppression of seismic-induced vibrations of steel jacket platforms is evaluated. TLCGD is an interesting choice in the case of jacket platforms because it is possible to use the structural elements as the horizontal column of the TLCGD. The objective here is to find the optimum geometric parameters, namely orientation and configuration of vertical columns, length ratio, and area ratio of the TLCGD, considering nonlinear damping of the TLCGD and water-structure interaction between the jacket platform and sea water. The effects of different characteristics of ground motion such as PGA and frequency content on the optimum geometry are also investigated and it is observed that these features have some influence on the optimum area ratio. Finally it is observed that pulse arrangement of ground acceleration is one of the most important parameters affecting the efficiency of a TLCGD. In other words, it is found that the TLCGD＇s capability to reduce the RMS responses depends only on the frequency content of the ground acceleration, but its capability to reduce the maximum responses depends on both the frequency content and the pulse arrangement of the ground acceleration.

Semi-Active Control of Wave-Induced Vibration for Offshore Platforms by Use of MR Damper

The objective of the present research is to examine the effectiveness of the lateral vibration control of wave-excited response of offshore platforms with magneto-rheological (MR) damper. In this study, the offshore platform is simplified to be a singled degree-of-freedom (SDOF) system by extracting the first vibration mode of the structure. The external 'generalized' wave force is determined with a white noise via a designed filter. A semi-active control method based on optimal control theory is proposed considering that the yield stress of the MR damper can he varied continuously within a certain range. The dynamics of SDOF structure coupled with the MR damper is investigated. Numerical simulation demonstrates that the MR damper with this control strategy can significantly reduce the maximum responses and the root-mean-square (RMS) values.

Seismic Response Control of Offshore Platform Structures with Shape Memory Alloy Dampers

In this study, the seismic response control of offshore platform structures with Shape Memory Alloy (SMA) dampers is investigated. A new SMA damper and its restoring force model are introduced for the calculation of seismic response reduction. Based on an actual platform structure and its mechanical model, the parameters which may affect the rate of shock absorption are analyzed, such as the number, position and characteristics of the SMA dampers and the condition of the site where the platform is located. The results show that the SMA damper is an effective control device for offshore platforms and satisfactory control can be achieved by proper selection of the parameters.

Suppression of Wave-Excited Vibration of Offshore Platform by Use of Tuned Liquid Dampers

This paper describes experimental and theoretical investigations of Tuned Liquid Damper (TLD) characteristics for suppressing the wave-excited structural vibration. The structural model for the experiments is scaled according to a full size offshore platform by matching their dynamic properties. Rectangular TLDs of different sizes with partially filled liquid are examined. By observing the performance and behavior of TLDs through laboratory experiments, the Study investigates the influence of a number of parameters, including container size, container shape, frequency ratio, and incident wave characteristics. In an analytical study, a mathematical model that describes the nonlinear behavior of liquid in TLD and the interaction of TLD and structure is prerequisite. The validity of the model is evaluated and simulating results can reasonably match the corresponding experimental results.

Seismic Response Reduction for Fixed Offshore Platform by Tuned Liquid Damper

An approach to seismic response reduction for offshore platforms by the use of the tuned liquid damper is presented in this paper. First of all, the effects of the tuned frequency ratio and excited frequency ratio on the seismic response reduction of the platform structure are investigated. Based on the results, a mechanical model and equation of motion for the TLD-platform system are established. And then effectiveness of the appraoch is verified by numerical calculation.

Torsionally Coupled Response Control of Offshore Platform Structures Using Circular Tuned Liquid Column Dampers

In this paper, the control performance is investigated of Circular Tuned Liquid Column Dampers (CTLCD) over torsional response of offshore platform structures excited by ground motions. Based on the equation of motion for the CTLCD-structure system, the optimal control parameters of CTLCD are given through some derivations on the supposition that the ground motion is a stochastic process. The influence of systematic parameters on the equivalent damping ratio of the structures is analyzed with purely torsional vibration and translational-torsional coupled vibration, respectively. The results show that the Circular Tuned Liquid Column Damper (CTLCD) is an effective torsional response control device.

Real-time hybrid simulation of structures equipped with viscoelastic-plastic dampers using a user-programmable computational platform

A user-programmable computational/control platform was developed at the University of Toronto that offers real-time hybrid simulation （RTHS） capabilities. The platform was verified previously using several linear physical substructures. The study presented in this paper is focused on further validating the RTHS platform using a nonlinear viscoelastic-plastic damper that has displacement, frequency and temperature-dependent properties. The validation study includes damper component characterization tests, as well as RTHS of a series of single-degree-of-freedom （SDOF） systems equipped with viscoelastic-plastic dampers that represent different structural designs. From the component characterization tests, it was found that for a wide range of excitation frequencies and friction slip loads, the tracking errors are comparable to the errors in RTHS of linear spring systems. The hybrid SDOF results are compared to an independently validated thermal- mechanical viscoelastic model to further validate the ability for the platform to test nonlinear systems. After the validation, as an application study, nonlinear SDOF hybrid tests were used to develop performance spectra to predict the response of structures equipped with damping systems that are more challenging to model analytically. The use of the experimental performance spectra is illustrated by comparing the predicted response to the hybrid test response of 2DOF systems equipped with viscoelastic-plastic dampers.

基于柔性包袋阻尼器的蜂窝芯子暴露平台降冲击研究

暴露平台作为搭载火工分离装置和载荷适配器等精密仪器的构件是航天飞行器中重要组成部分,暴露平台在火工冲击环境下会产生高频、瞬态和高量级特点的火工冲击响应。高量级的火工冲击易对星载设备中的敏感元器件造成损伤从而产生难以估量的损失,故有效地控制星箭暴露平台在火工环境下的高频冲击对航空航天领域具有巨大的意义。该研究运用蜂窝芯子式的柔性包袋阻尼技术对暴露平台进行降冲击研究,通过对柔性包袋阻尼系统模型进行离散元耗能仿真设计,分析粒子材质、粒径、填充率及包袋膜厚度对柔性包袋阻尼器降冲击性能的影响,获取柔性包袋阻尼器的最优特征参数。通过冲击试验得出安装不同参数柔性包袋阻尼器暴露平台的冲击响应谱并与仿真结果进行对比,验证了模型的正确性和柔性包袋阻尼技术的有效性。仿真和试验结果表明,柔性包袋阻尼器降冲击性能最佳的粒子材质为铁基合金,最优粒径为2.0 mm,最优填充率为95%,最优膜厚为0.2 mm。最优参数的柔性包袋阻尼器降冲击效果达到了58.13%,达到了梦天载荷仓暴露平台的降冲击要求。

Optimal Design of TMD Under Long-Term Nonstationary Wave Loading

Traditionally, the use of a tuned mass damper (TMD) is to improve the surviability of the primary structure under extraordinary loading environment while the design loading condition is described by either a harmonic function or a stationary random process that can be fully characterized by a power spectral density (PSD) function. Aiming at prolonging the fatigue life of an offshore platform, this study considers an optimal design of TMD for the platform under long-term nonstationary loading due to long-term random sea waves characterized by a probabilistic power spectral density (PPSD) function In principle, a PPSD could be derived based on numerous ordinary PSD functions; and each of them is treated as realization of the corresponding PPSD. This study provides a theoretical development for the optimal TMD design by minimizing the cost function to be the mean square value of the expected long term response. A numerical example is presented to illustrate the developed design procedure.

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.

Semi-Active TLCD Control of Fixed Offshore Platforms Using Artifical Neural Networks

In this paper, the control method for fixed offshore platforms using semi-active tuned liquid column damper (TLCD) is presented. The equation of motion for the platform-TLCD control system is given and the semi-active control strategy is established. A back propagation artificial neural network (ANN) is used to adjust the orifice opening of TLCD because of the nonlinear motion of liquid in TLCD. The effectiveness of the control method is verified by numerical examples.

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.

Experimental Study on the Effectiveness of TLDs under Wave Loading

The objective of this study is to experimentally investigate the effectiveness of Tuned Liquid Dampers (TLDs) for suppressing the dynamic response of a platform structure subjected to wave loading and to explore the applicability of TLDs for suppressing the structural vibration of fixed offshore platforms. The experimental model is scaled according to a full size platform by matching its dynamic properties. Rectangular and circular TLDs of various sizes and water depths are examined. The experiments were performed in a 2-D wave flume. The effectiveness of TLDs is evaluated based on their response reduction. By observing the performance and the behavior of TLDs through laboratory experiments, the effects of a number of parameters including container shape, container size, number of dampers, frequency ratio, mass ratio, and incident wave characteristics are investigated.

调谐液体阻尼器对多层多模态平台结构的运动控制研究

基于双向流固耦合理论,建立了调谐液体阻尼器(tuned liquid damper,TLD)与多层多模态平台结构的数值模型,系统性研究TLD减振频率和安装高度对多层结构前两阶共振模态的影响,通过数值方法将阻尼力做功定量化,结合晃荡波、平台运动的相位延滞关系,分析TLD对多层多模态平台结构的阻尼特性。研究表明,TLD不同安装位置的控制效果与结构对应模态的最大振型相关,晃荡过程中产生的倍频激励可拓宽TLD的减振频带。此外,保持2%的质量比不变,多TLD联合减振系统对多层结构的减振效果更为稳定,无局部负面激励,两个共振点处的平均减振率均高于其他方案。

漂浮式风机运动抑制方法综述

通过可靠可控的技术手段,实现浮式风机系统支撑平台的运动抑制,对保障浮式风机的安全性与可靠性具有重要意义。综述各类主要浮式风机运动抑制方法与技术,介绍各种方法的基本原理、技术特点、研究现状和应用情况,以期为相关领域研究人员提供技术参考和研究思路。

一种利用液体阻尼器减小单桩基础海洋平台在地震载荷下位移的新方法

The efficiency of a tuned liquid damper(TLD)in controlling the dynamic responses of offshore monopile platforms underseismic excitation has been investigated in this paper.Damping is performed by applying a type of reservoir inside a tower,which is designed optimally via seawater and a monopile body.Hydrodynamic forces due to water surface oscillation inthe reservoir act as resistant forces against structure vibration and displacement.Using ANSYS finite element(FE)software,a monopile structure with the same dimensions as the samples in the Persian Gulf climate was modeled and thenanalyzed in this research using the transient time history analysis related to the records of El-Centro,Kobe,and Tabasearthquakes for seismic investigation.The dynamic responses of the monopile platform with and without TLD werecompared after the completion of FE results.Findings show that using the mentioned TLDs reduced structure displacementby more than 50%based on the earthquake frequency content.

带缘板阻尼结构转子叶片振动特性的影响参数分析

针对转子叶片缘板阻尼结构设计需求。根据简化模型定性分析了缘板阻尼结构接触作用对刚度和阻尼带来的非线性影响;采用考虑正压力的分布形式和局部滑移现象的分布式摩擦力学模型,通过数值计算叶片非线性振动响应,获得了缘板阻尼结构关键参数对叶片振动特性的影响规律。研究结果表明:阻尼块质量是缘板阻尼结构设计的最关键参数,应根据最佳压紧力值确定阻尼块质量。

机载光电侦察平台复合减振设计

为减小振动对机载光电侦察平台成像质量和稳定精度的影响,对光电平台进行了复合减振设计。分析了复合减振原理,针对以往单级隔振系统存在的缺点在平台内框架和外框架之间设计了二级减振系统,更加有效地隔离了外框架传递到内框架上的振动。采用二维参数优化方法计算出了复合减振系统的最优固有频率比fopt为1.43,最优阻尼比ζopt为0.243。最后,通过振动试验验证了光电平台复合减振效果。与以往单级隔振系统相比,复合减振系统的最大振动传递率降低了50%,振动传递率小于1的频率范围更宽,高频时传递率的衰减程度也大大优于单级隔振系统。得到的结果表明了光电平台复合减振设计的合理性和有效性。

缘板干摩擦阻尼器叶片减振实验研究

为了减小叶片振动,在叶片缘板部位设置干摩擦阻尼器,以引入外加阻尼。本文介绍缘板干摩擦阻尼器叶片减振实验研究方法;针对带阻尼器的单叶片、双叶片,在3种激振力、9种正压力情况下,进行1阶弯曲、1阶扭转、2阶弯曲强迫振动实验;对试验结果进行分析,获得阻尼器对不同振型下振动响应和谐振频率的基本影响规律。实验结果表明:干摩擦阻尼器对1阶弯曲、1阶扭转振动有一定的减振效果;对2阶弯曲振动没有减振作用。