【作者】 张力；

【导师】 岳前进； 张文首；

【作者基本信息】 大连理工大学 ， 工程力学， 2008， 博士

【摘要】 本文工作是结合国家“十五·863”高技术研究发展计划-新型平台抗冰振技术项目(项目编号:2001AA602015)完成的。针对我国渤海冰区边际油田的现役抗冰导管架平台的冰激振动,通过比较不同的减振策略,选择合理、有效、可行的减振装置对现役平台进行减振控制,并试图通过对柔性抗冰平台的冰激振动减振研究,为大型复杂柔性结构在环境荷载作用下的振动减振研究提供一套新的思路和途径。本文研究内容主要包括以下几方面:第一章介绍了本文研究的背景、意义,对柔性结构在环境荷载作用下的振动及其减振策略进行概括,主要对柔性抗冰导管架平台的冰激振动及其相关研究现状进行阐述。第二章以渤海抗冰导管架平台作为研究对象。借助于抗冰平台现场监测对抗冰平台的结构特点、冰荷载特性以及平台的冰激振动响应特性进行分析,进一步明确了抗冰平台冰激振动危害以及对抗冰平台采取冰激振动减振措施的必要性。基于现场原型监测的冰荷载及冰激振动分析是开展抗冰平台减振的基础。第三章介绍了当前土木工程应用中较成熟的减振策略,如耗能减振、端部隔振以及动力吸振等减振策略在海洋平台冰激振动减振中应用的可行性。基于现场原型监测,认为采用调谐质量阻尼器(Tuned Mass Damper-TMD)对现役抗冰平台进行冰激振动减振是较优的选择。本章同时对TMD的参数优化、不同外激励作用下TMD减振效果进行了分析。第四章针对目前土木工程应用中TMD减振效果无法准确评估的问题,依据TMD的减振机理并基于TMD与结构相互作用位置产生对结构的作用力的实质提出的时域相位分析方法。该方法区别于以往在频域或采用附加阻尼的宏观效果评价方法,为从机理上研究TMD减振效果提供了参考。第五章主要研究TMD在抗冰平台冰激振动减振中应用的可行性。研制了可应用于实际抗冰平台减振的大比尺、单向、滑动式TMD装置,并对该装置的概念设计及详细设计进行介绍。同时针对该减振装置进行实验研究,建立了一套可对大型复杂结构进行减振、控振实验研究的半仿真实验系统(Semi-Simulation experimental testing system)。该实验系统由仿真部分和物理部分组成。仿真部分为实测响应数据(或通过计算机中建立的数学模型计算得到的结构响应)通过计算机控制的伺服作动器系统输出:物理部分为实物减振装置。该实验系统的建立为大型复杂结构的减振、控振实验研究提供了参考,该系统具有较大的实际工程意义。第六章介绍了一种用于测试TMD装置等效作用力的测量方法。TMD减振机理和要依靠装置运动过程中对结构产生的作用力,然而针对该作用力的测试和研究还不多。本章在研究TMD装置在海洋平台冰激振动减振效果时,提出了一种可以直接测量结构安装TMD装置时产生的作用力,并通过实验验证了该等效作用力测试的准确性。利用该测试系统检验了冰荷载作用下TMD对抗冰平台减振的减振效果,结果表明TMD能有效降低平台的动力响应。第七章提出了一种用于测量调谐液体阻尼器(Tuned Liquid Damper-TLD)等效阻尼力的测试方法。利用该方法可以实时测量TLD液体水箱晃动过程中对结构产生的作用力,从而解决了由于液体晃动剧烈时的强烈非线性而无法采用理论计算得到TLD对结构作用力计算的难题。为了从机理上研究TLD的减振效果并为实际应用中TLD减振效果评估提供依据,从TLD基本晃动特性分析出发,对设计制作的小比尺TLD减振装置进行共振情况下等效阻尼力的识别。第八章基于海洋平台结构复杂、某些物理参数不确定等因素,考虑系统参数不确定性影响的H_∞控制方法对海洋平台的冰激振动进行主动控制研究。导管架平台动力学模型的自由度数较多,但研究表明平台的振动主要集中在前几阶模态,甚至是第一阶模态起主导作用。本文采用模态空间平衡降阶法对平台动力学模型进行降阶,进而构造了H_∞控制器和H_∞模态观测器,并利用主动质量阻尼器(Active Mass Damper-AMD)作为控制装置对抗冰平台的冰激振动进行仿真分析。最后,对全文工作进行总结,并提出了需要进一步研究的内容。更多还原

【Abstract】 This study was performed under the financial support of the National High-tech Research Development Program named Key Problems Study of the New Ice-Resistant Platform (No. 2001AA602015). The research subjects are the existing steel jacket offshore platforms in the Bohai Sea, Liaodong Gulf. The main goals are to find the optimal mitigation strategy to reduce ice-induced vibrations and to provide the instructive suggestions for the other flexible structures vibration mitigation under environmental loads.In section one, a summary of vibration induced by environmental loads of flexible structures are presented, especially for the ice-resistant offshore platforms as well as state-of-art of ice-induced vibration.In section two, analysis are conducted on ice forces features、dynamic characteristic of platform and features of dynamic deck response of offshore platform based on field measurements. Therefore, effective measures have to be introduced to reduce the vibration level down to acceptable limits. In others words, field observations are the basis of carrying out dynamic analysis and ice-induced vibration of offshore platforms.In section three, commonly used vibration mitigation strategies, like vibration dissipation, top isolation and dynamic vibration absorption that have already been implemented in civil engineering are introduced. According to the understanding of field observations as well as characteristics of environmental load, the geometric features of platforms, features of dynamic response, mitigation objectives, it is believed that adding an auxiliary device is an optimal choice.In section four, based on the mechanism of the Tuned Mass Damper (TMD) and the fact that the interaction force generated between the relative position of the TMD and structure, time-domain and phase analysis for the vibration reduction of the TMD system is presented. Due to the stochastic characteristic of environmental excitation the motions between the structure and the TMD cannot lock in when out of phase, causing the sharp vibration reduction. In order to analyze the vibration reduction of the TMD from the mechanism, it is critical to conduct the analysis from the relative movement between structure and itself. The evaluation criteria for the performance of the TMD are given based on relative movement analysis between structure and itself. Experimental study and simulation analysis conducted demonstrated the reliability of the proposed criteria.In section five, to investigate the feasibility that the TMD can indeed mitigate the vibrations induced by ice forces on offshore steel jacket platforms, a large scale TMD device was designed and manufactured with respect to an offshore oil platform. Large scale testing is expensive and the requirements for model similarity in model scale testing are hard to meet. Thus, an experimental technique that focuses on the control device itself and emulates the behavior of the structure with a simulator is presented. This novel experimental system consists of a virtual part and a tangible part called semi-experimental testing system (also can be called Hybrid Experimental Testing system). The virtual parts include scaled external load and a scaled simplified platform model. The tangible parts include the TMD device and a moving table, which is controlled by a hydraulic actuator.In section six, to assess the effectiveness of the TMD to mitigate ice-induced vibrations of platforms, the method of measurement of the equivalent damping force of the TMD based on semi-simulation experimental testing system is presented. The interaction force between the TMD and the structure can be measured directly by this system. In this chapter, the principle and method to measure force is introduced. The force comparison between experimental and calculated values is made under sinusoidal displacement inputs. Experimental results show that the force measured from load cell is almost equal to the inertial force of the TMD. Therefore, the feasibility of using this system to measure equivalent damping forces of the TMD was confirmed. The vibration reduction performance of the TMD was carried out by incorporating its equivalent damping force. Experimental results show that the TMD is quite effective to mitigate ice-induced vibration.In section seven, to study the physical principle of TLD (Tuned Liquid Damper) device and provide references for evaluating the performance of TLD. A small scale rectangular TLD device was manufactured. A method to measure the equivalent damping force of the TLD device based on the semi-simulation experimental testing system is presented. Harmonic displacement input was used to identify the resonant frequency of the TLD device as well as the damping force. The experimental force results agree with the theoretical. So the feasibility of the testing system was verified.In section eight, H_∞method has been used extensively in many control systems designed for structural applications due to its stability and robustness. H_∞control of the critical modes of vibration of an offshore platform under ice loads is studied. The control is applied to a platform via an active tuned mass damper (AMD) located at the top of the platform. An algorithm combining the H_∞method together with a balanced reduction scheme in modal space is used for control design. The solution for ice-induced vibration response of the system is derived in terms of the pseudo-excitation method. With the derived solution, extensive parametric studies can be carried out. The optimal parameters of H_∞, controllers for achieving the maximum vibration response reduction of the platform can be identified. The effectiveness of H_∞controllers for this particular application is evaluated in this study. The results show that the ice-induced vibration response of the platform can be considerably reduced if the parameters of H_∞controllers are selected appropriately.At last, some concluding remarks are stated. Suggestions and directions on the further research and applications of structural control for offshore platforms are presented.更多还原