Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Numerical simulation and model test of VIM of full depth mooring TLP
Wen Jia Hu, Shi Sheng Wang and Jing Rui Zhao

Engineering Design Institute,CNOOC Research Institute Co.,Ltd,
Beijing, China

ABSTRACT.
Aiming at the VIM of traditional TLP and the VIV of tension leg andriser, the VIM of full depth mooring TLP is studied by combining
numerical simulation with basin model test. According to the main
scale parameters of TLP, the basin test model is made according togeometric similarity,and under the conditions of motion similarity anddynamic similarity, the model tests were carried out in cases of
uniform flow, profile flow and wave current combined. The model test
results are compared with the numerical simulation results to verify theconsistency of the two. The results show that the lock-in range of VIMfor TLP is 5.5 < Ur < 8.5, the incoming angle has a great influence onthe VIM, and the wave has a certain weakening effect on the VIM anda strengthening effect on surge. The lift standard deviation and dragstandard deviation of fixed flow increase with the increase of reducedvelocity. The Research of paper can provide reference for the researchand design of TLP.

KEY WORDS: TLP; VIM; Model test; Numerical simulation;
Uniform flow; Profile flow; Wave current combination

INTRODUCTION
TLP is a deep-water floating platform moored with tension legs, whichbears external loads such as wind, wave and current during service.
When the flow passes through the TLP, discontinuous vortex sheddingoccurs. When the vortex shedding frequency of the vortex is close tothe natural vibration frequency of the platform, resonance will occur,
which will induce large dynamic response of the platform and cause
serious fatigue damage to the structure. The dynamic response of theplatform is the superposition of the VIM of the floating body and theVIV response of the tension leg and the riser. They affect each otherand have a complex nonlinear coupling relationship. The researchmethods of VIM mainly include numerical simulation and model test.
Numerical simulation is based on the theory of viscous fluid mechanics.
This method is convenient for parameter adjustment. Compared withmodel test,it has high accuracy and low cost. It is an important
supplementary means of model test. Kim and Dusan(2015) investigatednumerical sensitivity of the VIM response. The results show that
applying the delayed separation eddy simulation(DDES) method canobtain more accurate prediction of VIM response amplitude. Chen andChen(2016) used the finite-analytic Navier-Stokes (FANS) numerical

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method for the simulations of VIM of a deep draft semi-submersible.
All the simulations and experiments indicate the peak nominaltransverse amplitude at a reduced velocity of 6-7. Hu, Zhang, Li You（ 2021 ） used the Improved Delayed Separation Vortex Method tonumerically simulate the VIM of a deep-draft semi-submersible
platform.The results show that lock-in range of transverse motion under
22.5° and 45° flow angles is 6.0<Ur<8.0，and The lock-in area underthe 0° flow angle is relatively lagging behind. The model test generally
scales the real object in a certain proportion according to the geometricsimilarity, and the motion similarity and dynamic similarity between
the testing conditions and the actual working conditions shall be met as
far as possible to obtain similar results. Hong, Choi, Lee and Kim(2008)
Completed the deep-draft semi-submersible(DDS) platform model test
to assess the global motion performance in wind, wave and current
environments. Model test results showed that a DDS may experiencesignificant VIM in the direction normal to the current. At present, theTLP model tests carried out at China and other countries in the world
are basically towed pool model tests. Li, Huang, Chang, Zhang, andXie(2019) studied inline and transverse VIM of TLP based on theVIM experiment.The results show that the frequency of VIM is related
to the location of the structure in the current in lock-in region. Whenthe structure shape is symmetric along inline direction, the frequency ofinline vibration is twice of that in transverse. While the structure shapeis asymmetric along inline direction, the frequency of inline vibration isequal to that in transverse. Tian, Liu, Wang,and Xiao(2020,2021)
studied the VIM characteristics of the TLP under typical flow direction
angles through numerical simulation and Drag pool test. The researchshows that the lateral motion response of the tension leg platform is themost significant at a flow angle of 0°, and the lateral motion responseof the tension leg platform is the smallest at a flow angle of 45°.The
test model does not include mooring and riser systems. Only thevertical bearing system is used to simulate the load ,or the truncatedstudy is used to calculate the mooring motion response.
Mooring and riser systems are important components of tension leg
platforms. The draft and system stiffness of the platform can besimulated by using the simulation method of equivalent transverse
mooring and applying vertical ballast. If this method is applied to theVIM test of tension leg platform, the VIM response of floating bodycan be obtained, but the VIV response of tension leg and riser itself can
not be obtained. The full depth mooring TLP test model includes
floating body, tension leg and riser model. In the model system,