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

This paper describes experimenlal and theoretical investigations of Tuned Liquid Damper (TLD) characteristics tor suppressing the wave-excited structural vibration. The structural model lor 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.     

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.     

Multiaxial Fatigue Analysis on Reeled Deepwater Steel Catenary Risers with Girth Weld Defects

In the present study, we simulated the reel-lay installation process of deepwater steel catenary risers (SCRs) using the finite element method and proposed multiaxial fatigue analysis for reeled SCRs. The reel-lay method is one of the most efficient and economical pipeline installation methods. However, material properties of reeled risers may change, especially in the weld zone, which can affect the fatigue performance. Applying finite element analysis (FEA), we simulated an installation load history through the reel, aligner, and straightener and analyzed the property variations. The impact of weld defects during the installation process, lack of penetration and lack of fusion, was also discussed. Based on the FEA results, we used the Brown-Miller criterion combined with the critical plane approach to predict the fatigue life of reeled and non-reeled models. The results indicated that a weld defect has a significant influence on the material properties of a riser, and the reel-lay method can significantly reduce the fatigue life of SCRs. The analysis conclusion can help designers understand the mechanical performance of welds during reel-lay installation.     

复指数方法降噪技术及其试验研究

实测信号中的噪声,以及模型阶次的不确定性给模态参数的准确识别带来困难。以提高模态参数识别精度为目标,提出基于模型定阶和信噪分离的复指数模态参数识别方法。该方法借助奇异值分解技术确定模型阶次,采用结构低秩逼近方法进行信噪分离。在此基础上,利用复指数法进行模态参数识别。分别选取一维的悬臂梁模型和二维的悬挂板模型进行物理模型实验,结果表明:该方法提高模态参数的识别精度,尤其是阻尼比的识别精度,具有较好的工程应用前景。     

复指数方法降噪技术及其试验研究

实测信号中的噪声,以及模型阶次的不确定性给模态参数的准确识别带来困难.以提高模态参数识别精度为目标,提出基于模30-定阶和信噪分离的复指数模态参数识别方法.该方法借助奇异值分解技术确定模型阶次,采用结构低秩逼近方法进行信噪分离.在此基础上.利用复指数法进行模态参数识别.分别选取一维的悬臂梁模型和二维的悬挂板模型进行物理模型实验,结果表明:该方法提高模态参数的识别梢度,尤其是阻尼比的识别精度,具有较好的工程应用前景.     

Prediction of Extreme Significant Wave Height from Daily Maxima

For prediction of the extreme significant wave height in the ocean areas where long term wave data are not available, the empirical method of extrapolating short term data (1-3 years) is used in design practice. In this paper two methods are proposed to predict extreme significant wave height based on short-term daily maxima. According to the da-a recorded by the Oceanographic Station of Liaodong Bay at the Bohai Sea, it is supposed that daily maximum wave heights are statistically independent. The data show that daily maximum wave heights obey log-normal distribution, and that the numbers of daily maxima vary from year to year, obeying binomial distribution. Based on these statistical characteristics, the binomial-log-normal compound extremum distribution is derived for prediction of extreme significant wave heights (50-100 years). For examination of its accuracy and validity, the prediction of extreme wave heights is based on 12 years' data at this station, and based on each 3 years' data respectively     

海洋平台磁流变阻尼器半主动控制研究

基于现代最优控制理论建立海洋平台磁流变 (MR)半主动控制系统的数学模型 ,采用白噪声过程通过滤波器来近似随机波浪力谱。以典型导管架平台为算例 ,对磁流变阻尼器进行了参数设计。分析了 MR阻尼器对海洋平台振动控制的有效性 ,仿真结果表明 ,采用磁流变阻尼器对海洋平台进行半主动控制能够有效的减小平台的动态响应。     

发动机排气余热吸附式制冷机性能及其热力学机理的研究(英文)

分析一台以6缸柴油机排气余热为热源的吸附式制冷机的性能和热力机理。研制了一台以CaCl2为吸附剂，NH3为工质的8KW冷量吸附式制冷机。该制冷机的工作特性表明在不变蒸发温度时，制冷机冷量随发动机排气功率变化。对吸附制冷单管的热力试验研究表明；CaCl2介质中的热／质迁移是相互作用的。建立了以非平衡态热力学为基础的数值模型来描述这些热力过程。     

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     

随机波浪作用下海洋平台主动控制的时滞补偿研究

基于预测控制理论，研究了适用于海洋平台的时滞补偿控制算法。该方法借助于随机波浪力的近似公式和卡尔曼滤波原理，推导出了随机波浪力向前一步预测公式，同时采用卡尔曼滤波方程，实现了对状态向量向前一步预测。利用随机波浪力及状态向量的实时在线预测公式，推导出最优控制力向前一步预测的表达式。在此基础上，发展了不仅适用于反馈控制系统而且适用于前馈-反馈控制系统的时滞补偿算法。采用一典型海洋平台为数值算例，计算结果表明，该方法在一定时滞范围内对海洋平台主动控制中时滞的补偿效果是显著的。