共查询到20条相似文献，搜索用时 51 毫秒
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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. 相似文献
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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. 相似文献
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Farhad HOSSEINLOU 《中国海洋工程》2021,(1):96-106
The identification of variations in the dynamic behavior of structures is an important subject in structural integrity assessment.Improvement and servicing of offshore platforms in the marine environment with constant changing,requires understanding the real behavior of these structures to prevent possible failure.In this work,empirical and numerical models of jacket structure are investigated.A test on experimental modal analysis is accomplished to acquire the response of structure and a mathematical model of the jacket structure is also performed.Then,based on the control theory using developed reduction system,the matrices of the platform model is calibrated and updated.The current methodology can be applied to prepare the finite element model to be more adaptable to the empirical model.Calibrated results with the proposed approach in this paper are very close to those of the actual model and also this technique leads to a reduction in the amount of calculations and expenses.The research clearly confirms that the dynamic behavior of fixed marine structures should be designed and assessed considering the calibrated analytical models for the safety of these structures. 相似文献
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海洋平台磁流变阻尼器控制技术研究 总被引：3，自引：0，他引：3
为了更有效地减小海洋平台动力响应,采用基于模糊控制算法的磁流变阻尼器对海洋平台的振动进行控制.以海洋平台位移响应误差和误差变化为输入变量,以最优控制力为输出变量,优化设计出模糊控制器.考虑实际磁流变阻尼器输出控制力上限存在限制,采用半主动控制算法计算接近于最优控制力的半主动控制力.以一固定式海洋平台为算例研究磁流变阻尼器的振动控制效果及其模糊性,仿真结果表明模糊磁流变控制器对于平台的振动可以实现非常有效的控制,且控制效果对结构阻尼和环境的不确定性具有较好的模糊性. 相似文献
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The purpose of this paper is to investigate the static structural response of a new type of composite stiffener containing a viscoelastic insert. The introduction of this material has proven benefits in terms of noise and vibration attenuation across the joint. House, 1997 describes the use of this material in sonar dome/hull connections — equipment sensitive to noise and vibration. Structural stiffeners incorporating this material would have positive implications for not only marine and ocean structures but for structural applications in general. The effects of introducing this new material on the structural response of the joint are numerically examined by using a progressive damage model. Application of this method allows the initiation and progression of failure and ultimate failure load to be predicted. Experimental results show good qualitative and quantitative agreement with the predictive damage model. 相似文献
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Qian Lingxi Zhong Wanxie Zhang Hongwu Professor Dalian University of Technology Dalian
Associate Professor Dalian University of Technology Dalian 《中国海洋工程》1993,(1)
In this paper, the foundation soil of offshore structure is simulated as a two phase saturated porous medium. The dynamic equations of porous medium and finite element formulation are given. For structural analysis, the technique of multilevel substructure is used, and the saturated soil analysis is set in the highest level substructure model. Based on these theories a dynamic finite element analysis program DIASS for the analysis of interaction between two phase ocean soil foundation and platform structures has been developed. A numerical example is given here to illustrate the influence of the pore water in soil on the structural response of an ocean platform. 相似文献
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《中国海洋工程》2020,(4)
Vortex-induced vibration(VIV) for flexible cylinders under combined uniform and oscillatory flow is a challenging and practical issue in ocean engineering. In this paper, a time domain numerical model is adopted to investigate the characteristics of cross-flow VIV response and fatigue damage under different combined flow cases. Firstly, the adopted VIV model and fatigue analysis procedure are validated well against the published experimental results of a4-m cylinder model under pure oscillatory flows. Then, forty-five combined flow cases of the same cylinder model are designed to reveal the VIV response characteristics with different non-dimensional oscillation period T* and combined ratio r. The combined flow cases are classified into three categories to investigate the effect of r on cylinder's dynamic response, and the effect of T* is described under long and short period cases. Finally, fatigue analysis is carried out to investigate how the structural fatigue damage varies with the variations of r and T*. The captured characteristics of structural response and fatigue damage are explained through the VIV mechanism analysis. 相似文献
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A robust damage detection method developed for offshore jacket platforms using modified artificial immune system algorithm 总被引：1，自引：0，他引：1
Mojtahedi A. Lotfollahi Yaghin M.A. Hassanzadeh Y. Abbasidoust F. Ettefagh M.M. Aminfar M.H. 《中国海洋工程》2012,26(3):379-395
Steel jacket-type platforms are the common kind of the offshore structures and health monitoring is an important issue in their safety assessment.In the present study,a new damage detection method is adopted for this kind of structures and inspected experimentally by use of a laboratory model.The method is investigated for developing the robust damage detection technique which is less sensitive to both measurement and analytical model uncertainties.For this purpose,incorporation of the artificial immune system with weighted attributes(AISWA) method into finite element(FE) model updating is proposed and compared with other methods for exploring its effectiveness in damage identification.Based on mimicking immune recognition,noise simulation and attributes weighting,the method offers important advantages and has high success rates.Therefore,it is proposed as a suitable method for the detection of the failures in the large civil engineering structures with complicated structural geometry,such as the considered case study. 相似文献
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Suppression of Wave-Excited Vibration of Offshore Platform by Use of Tuned Liquid Dampers 总被引：3，自引：0，他引：3
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. 相似文献
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针对水下系泊监测平台在水流涡激作用下的稳定性问题,考虑了浮体在振动过程中的变形,建立了其流固耦合的非线性动力学方程,利用谐波平衡法进行了非线性特性定性分析,Melnikov方法进行稳定性判据研究及影响因素分析,以系统出现混沌状态为稳定性控制条件,重点研究了系泊缆支撑间距对稳定性的影响,并计算出支撑间距的临界值。结果表明,系统稳定性随支撑间距增加而降低,当支撑间距超过临界值后,稍微增加都可能导致系泊监测平台振动偏离振动轨道而造成局部失稳甚至结构破坏。为保证监测平台的稳定性,应增加支撑数量,且支撑的间距不能超过系统发生失稳的临界值。 相似文献
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The flexible riser top connection is a critical region for lifetime assessment due to large tension/curvature variations and modeling uncertainties. The bend stiffener polyurethane mechanical response not only presents a nonlinear loading rate and temperature dependency but is also subjected to weather ageing during operation, which may affect its mechanical behavior over time. The top tension, employed for riser local cross-section stress calculation, is usually obtained from global dynamic analyses performed under selected environmental conditions, if direct measurement is not available. As a consequence, both the bend stiffener effect on the curvature distribution and the top tension time series present inherent uncertainties for riser lifetime (re)assessment. In the present work, a proposed monitoring approach composed by gyrometers installed along flexible riser/bend stiffener top connection system length combined with an inverse problem methodology is numerically investigated to estimate the following parameters: (i) polyurethane hyperelastic response and (ii) effective top tension. The top connection system is modeled using a large deflection beam bending model and the parameters are estimated using a damped least-square minimization approach with the Levenberg–Marquardt algorithm. For the preliminary feasibility investigation, the gyrometer experimental data is numerically estimated through Monte Carlo simulations. A case study is carried out to investigate the influence that the number of sensors, sensors arrangement, loading conditions and top connection model have on the inverse parameters estimation. The results indicate that the proposed monitoring approach and inverse parameter estimation methodology may effectively reduce flexible riser lifetime calculation uncertainties. 相似文献
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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 相似文献
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Dynamic analysis of tension leg platform for offshore wind turbine support as fluid-structure interaction 总被引：2，自引：1，他引：1
Tension leg platform (TLP) for offshore wind turbine support is a new type structure in wind energy utilization.The strong-interaction method is used in analyzing the coupled model,and the dynamic characteristics of the TLP for offshore wind turbine support are recognized.As shown by the calculated results:for the lower modes,the shapes are water’s vibration,and the vibration of water induces the structure’s swing;the mode shapes of the structure are complex,and can largely change among different members;the mode shapes of the platform are related to the tower’s.The frequencies of the structure do not change much after adjusting the length of the tension cables and the depth of the platform;the TLP has good adaptability for the water depths and the environment loads.The change of the size and parameters of TLP can improve the dynamic characteristics,which can reduce the vibration of the TLP caused by the loads.Through the vibration analysis,the natural vibration frequencies of TLP can be distinguished from the frequencies of condition loads,and thus the resonance vibration can be avoided,therefore the offshore wind turbine can work normally in the complex conditions. 相似文献
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应用ANSYS软件建立了平台和冰相互作用的有限元模型,构建了自升式平台的冰激振动模型,并计算基于2种冰力模型的自升式平台的动力响应。此动力分析方法具有建模方便和计算精度高的特点。以某自升式平台为例,计算了冰和平台结构相互作用的耦合效应,为自升式平台冰激振动安全评估提供了参考依据。 相似文献
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当结构物产生损伤时,结构的动力特性会发生变化,从而引起结构振动响应产生相应的变化。小波变换是奇异性信号的良好检测工具,可以用于识别结构损伤的发生。建立了某海洋平台有限元模型,得到了随机海浪作用下不同损伤工况的结构振动响应。基于小波变换损伤检测,针对不同类型杆件损伤、不同位置杆件损伤、不同程度的噪声污染以及不同方向振动响应信号情况下,分别研究了海洋平台结构的损伤检测问题,得到了一些有用的结论。 相似文献