Method for determining time-domain pulsating drag force of deepwater riser

Abstract

The invention relates to a research method of an ocean deepwater riser, in particular to a method for determining a time-domain pulsating drag force of the deepwater riser. According to the method, viscous drag and an added mass force caused by vibration velocity and accelerated speed of the deepwater riser are introduced into the calculation of the pulsating drag force, and the time-domain pulsating drag force is calculated by adopting an iterative approach, so that a complete computational method of the fluid structure interaction time-domain pulsating drag force is established. Due to the addition of the viscous drag and the added mass force caused by the vibration velocity and the accelerated speed of the deepwater riser, compared with an existing method, the method provided by the invention is more in line with the stress state of downstream vortex induced vibration of a cylinder.

Description

technical field [0001] The invention relates to a research method of a marine deepwater riser, in particular to a method for determining the time-domain fluctuating drag force of a deepwater riser. Background technique [0002] The pulsating drag force is an alternating fluid load on the cylinder in the direction of fluid flow. Since the flow velocity of the fluid is constant, the pulsating drag force is caused by the vortex discharge at the wake of the cylinder. For elastic cylinders, the pulsating drag will cause the cylinder to vibrate in the direction of fluid flow. While for a rigid cylinder, the pulsating drag force does not cause the cylinder to vibrate. That is to say, whether the cylinder vibrates or not, the pulsating drag always exists. [0003] The alternating frequency of the pulsating drag force is related to the frequency of the vortex discharge, and the frequency of the vortex discharge depends on the velocity of the fluid flowing through the cylinder, and ...

AI Technical Summary

Problems solved by technology

Therefore, the calculated deepwater riser vibration frequency is low;

[0007] (2) The velocity effect of the down-flow vibration of the deep-water riser is not considered, and the viscous resistance caused by the relative velocity change between the deep-water riser and the fluid is ignored, so the calculation result is too small;

[0008] (3) The variation of the pulsating drag force along the axial direction of the deepwater riser cannot be calculated, that is, the change of the pulsating drag force caused by the fluid-solid coupling at different axial positions of the deepwater riser cannot be considered;

[0009] (4) The frequency change of the pulsating drag force in the locked area and the unlocked area is not considered, and only the frequency of the locked area is used

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