【作者】 韩东颖；

【导师】 李子丰；

【作者基本信息】 燕山大学 ， 机械设计及理论， 2008， 博士

【摘要】 准确分析含有损伤缺陷的井架钢结构的静动态力学行为,定量评价井架钢结构的承载能力,能够提高石油天然气开采过程中的安全性,充分利用现有资源的使用价值和提高生产效率。课题在此背景下,深入研究了井架钢结构的损伤缺陷识别方法和有限元模型修正理论,确定了对井架钢结构损伤缺陷敏感的参数及损伤缺陷与物理参数之间的定量关系,建立了井架钢结构的有限元模型直接修正数学模型和模型局部反演修正数学模型,提出了一套定量评价大型复杂井架钢结构的安全性和极限承载力的新方法。应用有限元法对井架钢结构的线弹性、几何非线性、材料非线性、双重非线性、动力特性和稳定性进行了分析,得到了位移、应力、固有频率、振型以及动力响应等力学参数和行为特征,为开展井架钢结构损伤识别、模型修正、安全评价和极限承载力预测奠定了理论基础。开展了井架钢结构损伤缺陷的识别研究。针对井架钢结构的特点和形式,应用当量损伤系数作为判别损伤缺陷是否存在与程度大小的统一量化指标。基于该指标和静/动力测试技术,提出了当量损伤系数直接识别法、基于应变应力的识别法、基于频率变化比或频率平方变化比的识别法和基于单位载荷变形差值曲率的识别法。通过数值算例验证了这几种方法的正确性和可行性。研究了井架钢结构有限元模型的修正理论。提出了两种修正方法:直接修正法和模型局部反演修正法。对井架钢结构普遍存在的几种损伤缺陷情况,如截面锈蚀、杆件初弯曲、整体初弯曲、载荷偏心、节点刚性降低以及支座沉陷,用直接修正法,直接建立相应的损伤修正数学模型;以灵敏度分析技术为基础,以静/动力测试获得的应变、应力、频率和振型等为参考指标,以主要承载杆件的设计参数为修正对象,建立井架钢结构模型局部修正数学模型,应用直接解析或迭代求解的方法求得修正参数。用这种方法解决了井架钢结构测试数据不完备的问题。对井架钢结构测试理论及模型实验进行了研究。根据井架钢结构的激振特点,推导了在有量测输入和输入未知条件下的模态参数识别公式;制作了井架钢结构相似比例模型,进行了逐级动载实验、安全与极限承载实验,验证了模型局部修正理论和直接修正理论的正确可行性,得出了可以依据在安全承载内的修正的数值模型对极限承载性能进行预测的结论;进行了井架钢结构简易模型的载荷与动力特性关系实验,得到了载荷与动力特性的关系,为探讨以动力特性为基准的评价理论提供了参考。在上述研究的基础上,构建了基于静力和动力测试数据的井架钢结构安全和极限承载力评价的新体系。基于静力测试的评定理论主要是以可靠性理论和API Spec 4F规范为基准。基于动力测试的评定理论则是以振动频率为基准直接预测或依据动力测试参数建立的动力有限元模型综合评定。在现场井架钢结构上的成功应用表明该评价新体系能实现安全承载力的评价和极限承载力的预测。更多还原

【Abstract】 To correctly analyze the static and dynamic mechanical behavior and quantitatively evaluate the load-capacity of derrick steel structures with damage and deficiencies can improve the security and production efficiency in the process of extraction of oil and gas, and make available resources being full use of. In the background, this paper has reseached the methods of damage identification and the updated theory of finite element model. The sensitive parameters and quantitative relations between physical parameters and damage have been determined. The direct updating and patial model updating mathematical model of the finite element model for derrick steel structures are established. Then, a novel approach is proposed to quantitatively evaluate the safety and ultimate load-carrying capacity.The linear elastic mechanics, geometric nonlinearity, material nonlinearity, double nonlinearity, dynamic characteristics and stability of derrick steel structures are analyzed using finite element method. The mechanical characteristics as displacement, stress, natural frequency, modal shapes and dynamic response are acquired. The results offers foundation for damage identification, model updating and forecast of safety and ultimate loading-capacity.Damage identification for derrick steel structures has been researched. According to the feature and character of the structure, equivalent damage coefficient is taken as the unite index to identify the existence and degree of damage. Based on the index and static and dynamic test technology, four approaches of damage identification methods are proposed. The first is named as direct identification method, and the other three methods are presented respectively combined with strain or stress, frequency variation ratio or the square of frequency variation ratio, deformation difference curvature in unit load. The four theoretical methods are proved to be correct and effective by simulation analysis.Finite element updating theories of derrick steel structures have been studied. Two kinds of updating methods are proposed. One is direct updating method, and the other is partial model updating method. Applying the former method, the revising mathematical models of corresponding damage are constructed according to the general existing damage and deficiencies such as corrosion of section, initial flexural deformation of member bars, initial flexural deformation of integral structure, eccentric acting load, the decrease of rigidity of knock-off joints, and base sinkage. Based on sensitivity analysis, partial model updating mathematical models are constructed, in which, strain, stress, frequency, mode shapes obtained from static and dynamic measurement are taken as the key referenced indicators, while the relevant design parameters as the input updating objects. The updating parameters are acquired by direct analytic or iterative approach. The problem of incomplete testing data is solved by using the latter method.Testing theory and model experiment of derrick steel structures have been studied. According to the shock exciation mode, the formulas are deduced for identifying modal parameters in the condition of measuring input and unknown input. The similar scale models of derrick steel structures were made, and dynamic grading load test, safety load test and detruction test were performed on them. The experimental results are compared with the simulative values and an agreement between both is very satisfactory, which proved the correctness and feasibility of patial model updating theory and direct updating theory. From the above analysis, it can be concluded that the the ultimate bearing capacity can be obtained by analyzing the updating simulation model from safety load test. In addition, the relations between load and dynamic characteristics of simple model are achieved from dynamic test with load fluctuation. The experimental results also offer the reference for the evaluation theory based on dynamic characteristics.On the foundation of previous research, a novel evaluation system for forcasting safety and ultimate load-carrying capacity of derrick steel structures is established on the basis of static test data and dynamic parameters. The former is constructed on the reliability theory and the criterion of API Spec 4F, while the latter is based on natural frequency to forecast directly, or relies on the updated finite element model which is obtained according to dynamic measurement parameters to evaluate synthetically. The novel evaluation system is applied successfully in forcasting the safety load-capacity and ultimate bearing capacity of in-service derrick steel structures.更多还原