【作者】 刘福顺；

【导师】 李华军；

【作者基本信息】 中国海洋大学 ， 港口、海岸及近海工程， 2008， 博士

【摘要】 目前,我国已有相当数量的海洋平台接近或即将达到其设计寿命,但为了开发相邻地区新发现的石油储量,往往需要这些平台超龄服役。另外,还有一些油田的部分平台其服役期限虽然还未达到设计寿命,但这些平台由于设计施工不当或使用过程中受到腐蚀、疲劳、碰撞以及恶劣环境载荷的作用,各构件出现不同程度的损伤,致使平台结构的整体安全性和完整性受到威胁。因此,如何合理评价这些平台的健康状况成为迫切需要解决的问题。为更好的保证服役中及需超期服役海洋平台的安全服役,针对目前大部分模型修正与损伤诊断方法未考虑阻尼特性及在处理实测模态不完备性方面的不足,本文在阻尼矩阵识别、结构损伤诊断及试验模型边界条件修正三个方面进行基础性的研究工作;同时,开展新方法——动力等效子结构法的前期的研究工作;接下来在实验室中通过一钢质悬臂梁模型验证理论方法的正确性;最后,通过对埕北22B井组平台海上动力测试,探讨测试方案的可行性及获取其低阶动力特性的可能性。本文在理论上将交叉模型交叉模态(CMCM)方法从无阻尼体系推广到阻尼体系,解决应用空间不完备的低阶实测模态进行模型修正与损伤诊断的问题。在阻尼矩阵识别方面,文中提出两种阻尼矩阵识别方法——整体阻尼矩阵识别方法与单元阻尼矩阵识别方法。前者适用于复杂结构,后者适用于相对简单的结构,并且两种方法均可处理实测模态空间不完备问题。在损伤识别方面,直接应用CMCM方法的修正系数α_n作为损伤诊断指标适用于实测模态测试误差较小的情况,新发展的损伤定位指标MSECI_n较α_n在刚度损伤定位方面具有更好的鲁棒性,并且发展的复合指标诊断方法能充分发挥上述两种损伤指标的优势,推动了CMCM方法的实际工程应用。当模型实验精度要求较高时,为充分考虑地基对模型的约束程度,文中提出基于边界条件的试验模型修正方法,通过调整物理模型与地基的边界条件,实现修正后的有限元模型与真实模型在低阶动力特性上一致或尽可能吻合的要求,该方法不仅适用于实测模态空间不完备的情形,而且所选用的初始估计矩阵的形式具有常规性,工程意义明显。文中还探讨新的动力子结构方法——动力等效子结构方法,其数值结果证实,当子结构选取比较合理时,可以实现子结构与整体结构在低阶模态上的动力等效。钢质悬臂梁物理模型实验亦证实基于边界条件的试验模型修正方法、复合指标诊断方法及动力等效子结构方法均具有较好的工程应用前景。埕北22B井组平台海上动力测试结果表明,所采用的海洋平台动力测试方案切实可行,具有较好的通用性,而且可以比较精确的获得平台的低阶频率,但识别的振型其精度需待提高。Friswell在其书中提到,在现有模型修正领域有三个公认的难题:其一是实测模态与理论模态的配对问题;其二是实测模态与理论模态的比例问题;最后是结构的阻尼模拟问题。本文的研究成果不仅可考虑结构的阻尼特性,甚至可将阻尼模拟为非比例阻尼,而且该方法既不要求实测模态与理论模态配对,也不要求二者的比例问题。可以说本文在一定程度上解决了模型修正领域的三个难题,理论创新性明显;所进行的物理模型实验及海洋平台现场动力测试推动了文中方法在海洋平台中的应用,工程意义明显。其研究成果虽然主要服务于海洋平台的模型修正与损伤诊断,但也可应用于航空航天、土木工程以及汽车工程结构的同类问题。更多还原

【Abstract】 Though most platforms close to their service life, they have to be used continuously even out of their service life for the new exploitation of oil in the nearby areas. In some oil fields, there are portion platforms whose safty and integraty are threatened by damages in some members, which may be caused for lots of reasons, such as improper design and construction, corrosion, fatigue, collision and abominable environment loads, though these platforms have not finished their service life. Then how to evaluate the health level of these platforms become emergent issues. Therefore, to assure the safety of these platforms and to overcome the drawbacks of model updating and damage detection methods at present on damping simulation and spatial incompleteness consideration, foundamental studies on the damping matrix identification, the damage detection and the experiment model updating based on interface modification are performed; and a new method, i.e., dynamically equivalent substructures is proposed, and foundamental studies are performed as well. Then the correctness and feasibility of above methods are demonstrated using a steel cantilever beam. Finally, dynamic test for the CB22B platform is performed, and the feasibility of test scheme and the possibility of obtaining the first few dynamic properties are discussed as well.In theory, this thesis extends the Cross Model Cross Mode (CMCM) method from undamped systems to damped systems employing few spatially incomplete measured data for model updating and damage detection. For damping identification, two methods, i.e., global damping matrix indentification and local damping matrix identification are proposed. The former one can be used for complex structures, the latter one is suitable for simple structures, and the above two damping matrix identification methods can both solve the spatial incompleteness of measured data. For damage detection, using correction coefficientsα_n as damage indicators is available only when the measurement errors are very small, and the robustness of developed indicator, i.e., the magnified idicator MSECI_n is better thanα_n in damage localization; thus the proposed damage detection method, i.e., composite indicator method, can synthesize the advantages of above two indicators, and the achievements can contribute to the application of the CMCM method in engineering. When the required precision of experiment is strict, the thesis proposes experiment model updating method based on interface modification, which can match a few measured modal data. This method is suitable to spatial incompleteness and the initial damping matrix is common, thus engineering meaning is obvious. In addition, the thesis studies the new dynamic substructure method, i.e., dynamically equivalent substructure method, and numerical studies reveal that if the selected substructure is proper, the modified substructure is dynamically equivalent or close to the whole structure in a few measured modal data. From the experiment of a steel cantilever beam, one concludes that the composite indicator method, the experiment model updating method based on interface modification and the dynamically equivalent substructure method display the promising application in engineering. Dynamic test for CB22B platform indicates, the adopted scheme is feasible and universal, and the first few frequencies can be measured reasonably, while the accuracy for mode shapes identification should be improved in the future work.Friswell mentioned in his book that there are three challenges for model updating, that is pairing, scaling between measured and analytical modal, and damping simulation. One side, achievements in this thesis doesn’t require pairing and scaling; and on the other hand is that damping properties can be considered. In other words, three challenges are solved at a certain level, thus theoretical innovation is obvious. In addition, the experiment and dynamic test on CB22B platform improved the application of proposed methods in engineering. In general, achievements can be applied not only to offshore platforms, but also to aviation and spaceflight, civil engineering and automobile engineering.更多还原