Comparative studies of hydrodynamic force models for flexible pipe in an oscillatory flow

Abstract

The objective of this comparison study is to verify and clarify whether the energy competitive force model has significant benefits in eliminating the influence of certain factors on the hydrodynamic coefficient. The typical cases with the smaller Keulegan–Carpenter (KC) number (KC = 31) and larger KC number (KC = 178) under the maximum reduced velocity of 6.5 with the prominent VIV responses are selected for analysis. The characteristics of the ortex-induced vibration (VIV) response, the hydrodynamic force, and the corresponding spatiotemporal coefficients in typical cases are revealed, compared, and discussed. The results suggest that the energy competition force model cannot avoid spatial-temporal distribution characteristics of the hydrodynamic coefficients. Drag and excitation coefficients with energy roles under Sarpkaya's and energy competitive force models are affected by the VIV response and wake effects in an oscillatory flow. The larger coefficients are witnessed under the smaller KC number. When the KC number increases from 31 to 178, the mean drag coefficients decrease from 2.25 to 1.73, and the mean excitation coefficients in in-line (IL) and cross-flow (CF) directions decrease from 1.42 and 1.44 to 0.60 and 0.81, respectively, under the energy competition force model. Changes in wake effects under a larger KC number lead to distinctive differences in drag and excitation coefficients during the acceleration and deceleration phases. Through a quantitative comparative analysis, the current identified drag and excitation coefficients under the energy competition force model can obtain a more accurate prediction result. The present work shows that there exists the blindness in the selection of coefficients within the framework of the energy competition force model.