深海顶张力立管在多频参数激励下的稳定性分析和可靠性评估

发布时间：2018-07-15 12:21

【摘要】：顶张力立管作为海洋油气开发的重要设备，其稳定性尤为重要。参数激励的不稳定性是实际立管面临的一大挑战，一旦被激发将使立管极度不稳定，影响海洋油气开发的正常开展，严重时将带来重大经济损失和环境污染。有效预测此立管稳定性，并指导工程设计是避免灾难发生的关键。当前研究预测参量激励的不稳定性大都基于规则波进行探讨，即假定实际参数激励为单频谐波激励。然而，实际海洋环境具有很大随机性，波浪对于海洋平台的激励是多频叠加的随机载荷，导致立管中张力随机性波动，，因此以单频激励预测张力波动形态不符合实际，其预测结果的准确性会受到很大影响。与此同时，由于海洋环境即波浪和洋流作用力的随机性，以及立管本身的结构尺寸和材料特性存在的随机性，立管的参量稳定性设计存在很大的不确定性，而传统方法大都基于确定性参数进行研究，因此其预测得到的稳定性受到现实随机性的严峻挑战。此外，工作于随机海洋环境下的顶张力既受到海洋表面波浪力作用又受到洋流绕流立管产生周期性涡激励力作用，仅考虑前者作用将导致参量共振，仅考虑后者作用将导致涡激振动。而实际海洋环境下，立管可能同时受到两种周期性作用而使立管不稳定，因此有必要考虑周期性波浪和涡同时作用下立管的动力稳定性。为解决以上问题，本文从以下三个方面展开，对顶张力立管在随机海洋环境下的稳定性进行深入研究: 1.基于线性波浪理论和P-M海浪谱，预测实际海洋环境中的波浪载荷得到多频参数激励，推导多频激励下立管的参量稳定性Hill方程，运用Bubnov Galerkin法求解相应方程得到Hill稳定性图。探讨多频激励预测立管系统参量稳定性特点，对比多频激励产生的Hill稳定性图和传统采用单频激励产生Mathieu稳定性图，分析传统方法研究存在的不足。基于Hill稳定性图预测实际海洋环境下立管的参量稳定性，并提出抑制或消除不稳定性的方法。 2.考虑海洋环境、结构设计和材料特性存在的不确定性，对影响立管参量稳定性的随机性因素进行敏感性分析，确定对参量稳定性影响较大的关键因素。建立代理模型模拟不确定因子和输出响应之间的关系,以及进行随后的可靠性分析。计算在关键因素影响下立管参量稳定的可靠度，并分析每个因素对可靠度影响的规律。结合可靠性分析，提出抑制和消除不稳定性的方法。 3.考虑参数和涡同时作用于顶张力立管，推导相应的动力学方程，并计算其动力响应，比较其与参量共振和涡激振动之间的差异。在参数和涡共同激励作用下，深入分析各相关变量对立管动力稳定性的影响。分别分析涡和参数激励对共同激励不稳定性的影响规律。讨论减弱或避开不稳定性的措施。
[Abstract]:As an important equipment for offshore oil and gas development, the stability of top tension riser is particularly important. The instability of parametric excitation is a great challenge to the actual riser. Once excited, the riser will be extremely unstable, which will affect the normal development of offshore oil and gas development, and will bring serious economic losses and environmental pollution. Effectively predicting the stability of the riser and guiding the engineering design is the key to avoid the disaster. At present, the instability of prediction parameter excitation is mostly discussed based on regular wave, that is to say, the actual parameter excitation is assumed to be single frequency harmonic excitation. However, the actual marine environment has a lot of randomness, and the wave excitation to the offshore platform is a random load of multi-frequency superposition, which leads to the random fluctuation of tension in riser, so the prediction of tension fluctuation pattern by single frequency excitation is not in line with the reality. The accuracy of the prediction results will be greatly affected. At the same time, due to the randomness of ocean environment, namely wave and ocean current forces, and the randomness of structural size and material characteristics of riser itself, the parametric stability design of riser is very uncertain. However, the traditional methods are mostly based on deterministic parameters, so the stability of the prediction is severely challenged by the randomness of reality. In addition, the top tension working in random marine environment is not only subjected to the wave force on the ocean surface but also to the periodic vortex excitation force produced by the ocean current around the current riser. Only considering the former action will lead to parametric resonance. Only considering the latter effect will lead to vortex-induced vibration. In the actual marine environment, the riser may be unstable by two periodic actions at the same time, so it is necessary to consider the dynamic stability of riser under the simultaneous action of periodic waves and vortices. In order to solve the above problems, the stability of top tension riser in random marine environment is studied in the following three aspects: 1. Based on the linear wave theory and P-M wave spectrum, the multi-frequency parametric excitation is obtained by predicting the wave loads in the actual marine environment. The Hill equation of parametric stability of risers under multi-frequency excitation is derived, and the Hill stability diagram is obtained by using the Bubnov Galerkin method. The characteristics of parametric stability prediction of riser system by multi-frequency excitation are discussed. Compared with Hill stability diagram generated by multi-frequency excitation and Mathieu stability diagram generated by traditional single-frequency excitation, the shortcomings of traditional method are analyzed. Based on Hill stability diagram, the parametric stability of riser in real marine environment is predicted, and a method to suppress or eliminate instability is proposed. 2. Considering the uncertainty of marine environment, structural design and material characteristics, the random factors affecting the parametric stability of risers are analyzed, and the key factors affecting the parametric stability are determined. An agent model was established to simulate the relationship between the uncertainty factor and the output response, and the subsequent reliability analysis was carried out. The reliability of riser parametric stability is calculated under the influence of key factors, and the regularity of each factor on reliability is analyzed. Combined with reliability analysis, the method of restraining and eliminating instability is put forward. Considering that the parameters and vortices act on the top tension riser at the same time, the corresponding dynamic equations are derived, and the dynamic responses are calculated, and the differences between them and parametric resonance and vortex-induced vibration are compared. Under the joint excitation of parameters and vortices, the influence of each related variable on the dynamic stability of the tube is analyzed in depth. The effects of vortex and parametric excitation on the instability of common excitation are analyzed respectively. Discuss measures to reduce or avoid instability.
【学位授予单位】：上海交通大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：P742;P756.2

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