海洋平台基于隔振锥体装置的减振效应研究

针对导管架式海洋平台结构型式与特点,利用冲击隔振理论,将冰锥体与隔振技术结合起来,提出一种能有效降低冰荷载激励的"两级柔性隔振锥体"设计方案。建立了两极隔振锥体简化计算模型,确定了系统振动传递系数参数之间的关系。通过建立海洋平台有限元模型,采用有限元程序,进行了模拟冰荷载激励下的振动响应分析,并对安装隔振装置的小比例模型结构进行了冲击荷载下的减振试验。结果表明采用"两级柔性隔振锥体"能有效降低传递给海洋平台的冰力极值,减小海洋平台冰激励的响应。     

Experimental Investigation on Vortex-Induced Vibration of Steel Catenary Riser

Steel catenary riser (SCR) is the transmission device between the seabed and the floating production facilities. As developments move into deeper water, the fatigue life of the riser can become critical to the whole production system, especially due to the vortex-induced vibration (VIV), which is the key factor to operational longevity. As a result, experimental investigation about VIV of the riser was performed in a large plane pool which is 60 m long, 36 m wide and 6.5 m deep. Experiments were developed to study the influence of current speed and seabed on VIV of SCR. The results show that amplitudes of strain and response frequencies increase with the current speed both in cross-flow (CF) and in-line (IL). When the current speed is high, multi-mode response is observed in the VIV motion. The amplitudes of strain in IL direction are not much smaller than those in CF direction. The seabed has influence on the response frequencies of riser and the positions of damage for riser.     

子母管结构中海缆涡激振动特性研究

采用流固耦合分析方法,对某海洋石油开采项目采用的子母管结构进行涡激振动特性研究,并与相同海缆在自由悬跨状态下振动特性进行比较。数值仿真结果显示,受母管影响,子母管中海缆由于涡街效应产生的升力振幅随时间变化不一致,而单根海缆升力幅值稳定;子母管中海缆产生的拖曳力高出单根海缆65%,振动幅值加大,并且沿整根海缆尾流中湍动能分布呈现随机性,导致水动力沿整根海缆分布不均匀。提取海缆升力与垂直水流方向振幅进行比较,发现涡激升力是导致垂直方向振动的主要原因。子母管中海缆在水流阻力和涡激升力共同作用下产生较大的位移和应变,应进一步调整夹具间距和剩余张力来减缓海缆疲劳损伤。     

3种附属管排布方式对主管路水动力特性的影响

【目的】研究均匀流多管束干涉流动下圆柱受迫振动的水动力特性。【方法】基于SSTκ-ω模型,在亚临界雷诺数下(Re=1×10⁵)对多管束共振强迫的涡激振动问题进行二维数值模拟,比较与分析三种典型附属管排布方式对主管路流体动力学特征的影响。【结果与结论】采用模型3下的附属管排布方式可在较大范围的振幅比下(A_y/D=0.1~0.8)有效改善主管路水动力特性:1)有效降低主管路上平均升力系数的幅值;2)抑制在单管路系统中出现的脉动升力系数突变衰减。同时,由于多管束对流动产生干涉效应,主管路上表现的尾迹涡度随着振动幅度的增大而呈现出不同的模式。此外,功率谱密度分析发现,多管束系统相较于单圆柱系统,在频率比为1时,模型2与模型3的共振“锁定”状态得到改善。     

QN control method for building vibration caused by periodic excitation acting on intermediate story

It has been proved in the authors' latest paper that the effective location of active control devices for building vibration caused by periodic excitation acting on intermediate story is the adjacent three floors to the vibration source. However, in terms of the Discrete‐Optimizing control method, the control forces are on‐line calculated step‐by‐step and time‐delay must exist. The degradation of control effect caused by time‐delay can not be avoided. In this paper, QN control method is proposed in order to resolve this practical problem. Since the external excitations which the building structure would experience are supposed to be periodic to some degree, Quasi‐Newton method is applied into the close‐loop Linear–Quadratic optimal control method and the new control method is called the ‘QN control method’. In this new control method, instead of solving the Riccati equation, the feedback gain matrix is determined by optimizing the quadratic performance index of the structure with the Quasi‐Newton method, one of the most commonly used minimization of functions. The new control law can easily be implemented for time‐delay problems, the degradation can be greatly improved with compensated feedback gain matrix. As a result, the QN control method is proved to be an efficient method to determine the feedback gain matrix. Copyright © 2000 John Wiley & Sons, Ltd.     

One‐year monitoring of the Z24‐Bridge: environmental effects versus damage events

When using the analysis of vibration measurements as a tool for health monitoring of bridges, the problem arises of separating abnormal changes from normal changes in the dynamic behaviour. Normal changes are caused by varying environmental conditions such as humidity, wind and most important, temperature. The temperature may have an impact on the boundary conditions and the material properties. Abnormal changes on the other hand are caused by a loss of stiffness somewhere along the bridge. It is clear that the normal changes should not raise an alarm in the monitoring system (i.e. a false positive), whereas the abnormal changes may be critical for the structure's safety. In the frame of the European SIMCES‐project, the Z24‐Bridge in Switzerland was monitored during almost one year before it was artificially damaged. Black‐box models are determined from the healthy‐bridge data. These models describe the variations of eigenfrequencies as a function of temperature. New data are compared with the models. If an eigenfrequency exceeds certain confidence intervals of the model, there is probably another cause than the temperature that drives the eigenfrequency variations, for instance damage. Copyright © 2001 John Wiley & Sons, Ltd.     

System identification of linear MDOF structures under ambient excitation

This paper introduces the eigenspace structural identification technique for tall buildings subjected to ambient excitations that are stationary and where only the response time histories are measured. Based on the forward innovation model of the Kalman filter sequence, the actual response can be constructed as a function of the measured response time history with contamination of either displacement or velocity. The response time history is decomposed into subspace matrices using QR decomposition and Quotient Singular Value Decomposition (QSVD) techniques. These are then substituted into the least-square formulation to obtain the solution which is non-unique. Similarity transformation is applied to arrive at the desired solution employing the fact that eigenvalues of self-similar systems are identical. The advantages of this eigenspace technique are that it is non-iterative, initial estimates of the parameters to the identified are not required, well-established numerical algorithm of the decomposition techniques employed are available, and the method can handle MDOF systems efficiently. Copyright © 1999 John Wiley & Sons, Ltd.     

Aseismic roof isolation system: analytic and shake table studies

Presented are the features of a roof isolation system that is proposed as a device to reduce the seismic response of buildings. Presented also are the details of and results from analytical and experimental studies conducted with a small-scale laboratory model to assess the feasibility and effectiveness of such a device. The roof isolation system entails the insertion of flexible laminated rubber bearings between a building’s roof and the columns that support this roof, and the installation of viscous dampers that are connected to the roof and a structural element below the roof. It is based on the concept of a damped vibration absorber and on the idea of making the roof, rubber bearings, and viscous dampers respectively constitute the mass, spring, and dashpot of such an absorber. The model considered in the analytical and experimental studies is a 2·44-m high, five-storey, moment-resisting steel frame, with a fundamental natural frequency of 2·0 Hz. In the experimental study the frame is tested with and without the proposed roof isolation system on a pair of shaking tables under a truncated version of one of the accelerograms from the 1985 Mexico City earthquake. In the analytical study, the frame is also analysed with and without such a system and under the same ground motion except that the ground motion accelerations are properly magnified to study the effec tiveness of the roof isolation system when the frame is stressed beyond its linear range of behavior. It is found that the suggested device effectively reduces the seismic response of the frame, although the extent of this reduction depends on how large its non-linear deformations are. Based on these findings, it is concluded that the proposed roof isolation system has the potential to become a practical and effective way to reduce earthquake damage in low- and medium-rise buildings. Copyright © 1999 John Wiley & Sons, Ltd.     

DYNAMIC INVESTIGATION OF A REPAIRED CABLE-STAYED BRIDGE

The theoretical and experimental investigation of a cable-stayed bridge after major repair is described in this paper. Strengthening mainly involved the suspension system (originally with prestressed concrete stays) which was retrofitted by means of external tendons. Full-scale tests were conducted to measure the dynamic response of the repaired system; the experimental program included both traffic-induced and free vibration measurements. A total of 16 vertical frequencies and mode shapes were identified in the frequency range of 0–10 Hz. In the theoretical study, vibration modes involving deck, towers and cables were determined by using finite element models which accounted for the strengthening effects. Two- and three-dimensional models were used so that the importance of three-dimensional modes was estimated as well. The experimental results were compared to natural frequencies and mode shapes computed using theoretical models. For most modes the measured and predicted modal parameters compare well, especially for the vertical modes involving in-phase motion of the stays. © 1997 by John Wiley & Sons, Ltd.     

基于S-变换的面波压制技术

对得到信噪比和分辨率较高的地震记录,做好地震资料的地质构造解释十分必要,而压制面波是提高信噪比和分辨率的一项重要技术,本文提出用S-变换来压制面波的方法,该方法是将时间域地震信号变换到时频域,在时频域去除面波,再变换回时间域,其结果是滤掉面波的地震信号。针对这种技术,给出实施流程,并将其应用于含有面波的理论模型和实际资料中。理论模型和实际应用效果表明,该方法能有效地压制面波,并保持了地震记录的其他特征,其结果不会出现空间假频的现象：同时,还具有适应性强、效果好等特点。