IMECH-IR  > 流固耦合系统力学重点实验室
Alternative TitleDisintegration and evolution of internal solitary waves and their impact on flexible risers
Thesis Advisor周济福
Degree Grantor中国科学院大学
Place of Conferral北京
Degree Discipline流体力学







Other Abstract

Oceanic internal solitary waves are the key factor linking large scale ocean currents and small scale eddy motions. The flow field induced by internal solitary waves is special in that water motion occurs in the whole water depth and the upper-layer flow is generally opposite to the lower-layer flow making strong shear near the pycnocline. Thus, internal solitary waves play a significant role in marine ecosystem, sediment transportation and energy transfer. They also act as a great potential threat to the typical marine structures, such as piles, risers, mooring chains, etc. Therefore, it is of great scientific significance and practical importance to investigate the evolution of internal solitary waves and their impact on flexible risers. In this thesis, we carry out research on the disintegration of internal solitary waves and the dynamic response of flexible risers to internal solitary waves via theoretical analysis and numerical simulations in combination with observation data.

Firstly, the extension form of weakly nonlinear KdV model is used to study shoaling and friction effects on the evolution of internal solitary waves. Based on theoretical analysis and in situ measurements, the Chezy friction coefficient is proved to be inversely proportional to the initial amplitude of an internal solitary wave. Moreover, a dimensionless parameter defining the relative importance of shoaling and friction is presented. This parameter is used to investigate the amplitude variation of internal solitary waves in the South China Sea. According to the variation of amplitude along the propagation path, the evolution law of internal solitary waves in the deep basin, slope shelf, shelf break and continental shelf is obtained.

Secondly, a revised density profile model is proposed, which is validated by the data of different seas at different time. It is proved more accurate and more widely used. Then, the disintegration law of internal solitary waves over a sharply varied bathymetry and the distribution of their disintegrated solitons are explored with the KdV equation, a method is proposed to forecast the number and amplitudes of disintegrated solitons just by the amplitudes of the leading two solions in a wave packet. And the distribution of mass and energy of each soliton and the secondary tail wave are obtained. Furthermore, a transformation is derived to turn the general eKdV equation into a standard KdV equation.

Thirdly, the dynamic response of a top tensioned riser under internal solitary waves is investigated. The analytical solution to the dynamic response of a simply supported beam under internal solitary waves is acquired with the mode superposition method. By using ABAQUS, a finite element model for analyzing the dynamic response of a top tensioned riser under internal solitary waves is established. It is demonstrated that the displacement and moment of a top tensioned riser reach their maxima near the pycnocline, and they approximately increase linearly with the amplitude of internal solitary waves. The stress at the bottom of the riser experiences a significant increase as internal solitary waves pass by.

Finally, a three dimensional finite element model is established for analyzing the dynamic response of a steel catenary riser to internal solitary waves. Two cases with water depth of 300m and 3000m are considered to represent shallow and deep water, respectively. It is demonstrated that the axial distribution of stress is distinctly different in shallow and deep water. The odd and even vibration modes behave differently. The odd and even frequencies vary independently, and the odd and even modes are found to be “hybrid” in some frequency range. Under the same amplitude internal solitary waves, the displacement of the riser in shallow water is larger than in deep water, but the variation of stress is smaller. Moreover, when the incident internal solitary wave is perpendicular to the plane of the catenary riser, the displacement of the riser reaches its maximum, but the variation of stress reached minimum. When the incident internal solitary wave is in the plane of the catenary riser, the displacement of the riser reaches its minimum, but the stress reaches its maximum.

Call NumberPhd2019-019
Document Type学位论文
Recommended Citation
GB/T 7714
檀大林. 内孤立波的分裂演化及其对柔性立管作用机理研究[D]. 北京. 中国科学院大学,2019.
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