【作者】 董汝博；

【导师】 周晶； 李昕；

【作者基本信息】 大连理工大学 ， 防灾减灾工程及防护工程， 2008， 博士

【摘要】 随着海洋油气资源的开发,海底管道成为海洋油气集输的最重要方式,在海上油气田的生产、精炼、储存及到用户的全过程中发挥着重要作用,成为海上油气田的生命线。海底管道的安全性成为海洋油气开发的关键问题。我国渤海海域为地震多发区,地震荷载和工作荷载的组合成为该地区管道设计的控制条件。此外,由于地球介质构造的复杂性(各向异性,不均匀性),一次地震时在各空间点上的地震动在幅值、相位角、频率等方面存在差异,这种差异直接影响管道的地震反应。因此,研究海底管道在多点地震动输入下的计算模型和破坏机理具有重大理论意义和实用价值。提出了一种一定程度上符合实际地震动传播特点的多点地震动合成方法。在前人方法的基础上进行改进,通过修正随机相位角,使生成的多点地震动满足地震动传播机制,给出了未知和已知相位差谱统计规律两种情况下非平稳多点地震动的合成方法,进一步提出了基于实际地震纪录的空间相关多点地震动合成方法。采用本文方法进行了基于美国Northridge地震和我国集集地震的多点地震动模拟研究,结果表明本文方法能较好符合实际地震动传播的一些特性,可用于大尺度结构的多点输入分析。建立了海底悬跨管道多点输入非线性分析模型,该模型考虑了管材和土体的非线性本构模型,以及几何非线性特性。据此推导了多点输入运动方程,并进行了海底悬跨管道三维多点输入地震时程反应分析。结果表明,在进行海底悬跨管道多点输入地震响应分析时,对于管道和土体应采用非线性本构模型;当管道的悬空段较长时,必须考虑几何非线性特征。在此基础上,比较了海底悬跨管道在不同地震输入模型(多点输入、行波输入、一致输入)作用下的地震响应。同时进一步分析了模型计算长度、悬跨长度、管道外径、钢管壁厚、混凝土配重层厚度以及海床坡度等因素对海底悬跨管道多点输入非线性反应的影响。分析结果显示地震动的空间变化特性能显著增大海底管道的地震反应,其他因素也在不同程度上对海底管道多点输入地震反应产生影响。采用一种能考虑内压作用的管单元对海底悬跨管道在复杂荷载作用下的响应进行了有限元分析。分析中同样考虑了管道和土体的非线性特征及结构的几何非线性效应,同时考虑了多点地震动、内压和工作温度等荷载的作用。首先验证了利用管单元考虑内压作用的有效性,并进一步研究了内压、温度及两者之间的耦合作用对海底悬跨管道多点输入地震响应的影响。利用水下振动台进行了海底悬跨管道动力模型试验,研究了地震动输入方向对管道所受动水作用力的影响。基于模型试验工况,建立管-水耦合系统的三维有限元模型进行数值分析,数值结果与试验结果符合得较好。结合海底悬跨管道动力模型试验,在传统的Morison模型和Wake模型的基础上分别提出了能够考虑不同地震动输入方向的动水作用力模型。与试验对比的结果表明,采用地震时Morison模型和地震时Wake模型能够较好地模拟海底管道在地震作用下所受到的动水作用力。最后比较了不同动水作用力模型对海底悬跨管道多点输入地震响应的影响。更多还原

【Abstract】 With the marine exploration and production of oil and gas submarine pipelines as the most important way to collect and transport offshore hydrate play an important role in the producing, refining, and storing of oil and gas and are regarded as the lifelines of offshore oil and gas fields. The security and integrity of submarine pipelines become the issue of marine resource development. The Bohai Sea is a seismically active region in China. The combination of seismic load and working loads is the critical case in the design of the submarine pipelines in the area. Moreover, due to the anisotropy and inhomogeneity of geologic structure the seismic ground motions can vary significantly in magnitude, phase angle and frequency along pipelines routes. The distinction of ground motions in different stations is a key factor that affects the seismic response of the submarine pipelines. It is of great significance to study the dynamic response and failure mechanism of submarine pipelines subjected to spatially varying earthquake ground motions and other loads.An improved method for simulating multiple-station ground motions was presented. The method proposed by modifying the random phase angle can synthesize multi-station earthquake ground motions satisfying seismic propagation mechanism. The synthetic methods for non-stationary multi-station earthquake ground motions are introduced under the conditions of known phase-difference spectrum and unknown phase-difference spectrum respectively. Further a method for synthesizing the time histories of multi-station ground motions on the base of actual earthquake records is derived. The proposed method is applied to simulate the multi-station ground motions recorded from the Northridge earthquake and the ChiChi earthquake. The results indicate that the multi-station ground motions synthesized by the proposed method accord with propagating characteristics of the real earthquake wave. Therefore, the method can be used for multi-support excitation analysis of large scale structures.A three-dimensional (3D) finite element model of buried submarine pipelines with free span subjected to spatially variable ground motions was established. The model took account of nonlinear constitutional relationships of pipe steel and soil, and geometry nonlinearity. The motion equations of the pipeline were derived and nonlinear multi-support input time-history analysis was performed. The results show that nonlinear material models related to soil and pipe should be introduced in the multi-support input seismic analysis of submarine pipelines. The large displacement should be considered in nonlinear seismic analysis for long-span submarine pipelines. Furthermore, seismic response of submarine pipelines was compared with different input method such as the multi-station input, traveling wave input and identical input. Some factors including pipe length, free span length, outside diameter of the pipe, wall thickness of the pipe, concrete coating thickness, and seabed slope were studied in the sensitivity analysis. The numerical results display that the spatial variation of ground motions can significantly increase the seismic response of submarine pipelines. Meanwhile, the other factors also influence on the response of the submarine pipelines under multiple-station earthquake ground motions to some extents.FE analysis of submarine pipelines with free span under complex loads was performed with the aid of a pipe element considering internal pressure effect. The nonlinear material models of the pipe and the soil as well as the large displacement effect were also considered. The spatially varying earthquake ground motions, the internal pressure and the thermal loading were imposed on FE model. Firstly, validation of the pipe element was carried out. Then, the effects of internal pressure, thermal loading and the interaction between pressure and temperature on the multi-support input response of the submarine pipelines were studied.Model tests of free spanning submarine pipeline were performed on an underwater shaking table in the Sate Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology. Hydrodynamic forces imposed on the span of submarine pipeline due to different direction excitations are studied in detail. The pipe-water interaction was simulated using a 3D FE model and the numerical results were compared with the experimental results.Based on Morison equation and Wake model two improved hydrodynamic force models considering the effects of seismic exciting directions were derived. Finite element method on the base of improved Morison equation and improved Wake model were employed to analyze the dynamic response of free spanning submarine pipelines subjected to earthquakes. FE models were established to simulate the above experimental conditions. The numerical results considering sine wave inputs and simulated El Centro earthquake inputs were obtained. Then a conclusion can be drawn that the improved hydrodynamic force models could satisfactorily predict the hydrodynamic force on the free span of submarine pipelines due to earthquakes. Finally, the effects of different hydrodynamic force models on the seismic response of submarine pipeline with free span subjected to spatially varying earthquake ground motions were studied.更多还原