This paper aimed at describing numerical simulations of vortex-induced vibrations（VIVs） of a long flexible riser with different length-to-diameter ratio（aspect ratio） in uniform and shear currents. Three aspect ra...This paper aimed at describing numerical simulations of vortex-induced vibrations（VIVs） of a long flexible riser with different length-to-diameter ratio（aspect ratio） in uniform and shear currents. Three aspect ratios were simulated： L/D= 500, 750 and 1 000. The simulation was carried out by the in-house computational fluid dynamics（CFD） solver viv-FOAM-SJTU developed by the authors, which was coupled with the strip method and developed on the OpenFOAM platform. Moreover, the radial basis function（RBF） dynamic grid technique is applied to the viv-FOAM-SJTU solver to simulate the VIV in both in-line（IL） and cross-flow（CF） directions of flexible riser with high aspect ratio. The validation of the benchmark case has been completed. With the same parameters, the aspect ratio shows a significant influence on VIV of a long flexible riser. The increase of aspect ratio exerted a strong effect on the IL equilibrium position of the riser while producing little effect on the curvature of riser. With the aspect ratio rose from 500 to 1 000, the maximum IL mean displacement increased from 3 times the diameter to 8 times the diameter. On the other hand, the vibration mode of the riser would increase with the increase of aspect ratio. When the aspect ratio was 500, the CF vibration was shown as a standing wave with a 3-（rd） order single mode. When the aspect ratio was 1 000, the modal weights of the 5-（th） and 6-（th） modes are high, serving as the dominant modes. The effect of the flow profile on the oscillating mode becomes more and more apparent when the aspect ratio is high, and the dominant mode of riser in shear flow is usually higher than that in uniform flow. When the aspect ratio was 750, the CF oscillations in both uniform flow and shear flow showed multi-mode vibration of the 4-（th） and 5-（th） mode. While, the dominant mode in uniform flow is the 4-（th） order, and the dominant mode in shear flow is the 5-（th） order.展开更多
Effects of depth and forward speed on hydrodynamic coefficients of ships are presented in this paper. A modified simple Green function technique was used to calculate 2D coefficients while strip theory was used to cal...Effects of depth and forward speed on hydrodynamic coefficients of ships are presented in this paper. A modified simple Green function technique was used to calculate 2D coefficients while strip theory was used to calculate 3D coefficients. Numerical results are provided for hydrodynamic coefficients of parabolic hull ship. It is found out that both depth and forward speed have considerable effects on hydrodynamic coefficients of ship.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51490675,51379125,11432009 and 51579145)
文摘This paper aimed at describing numerical simulations of vortex-induced vibrations（VIVs） of a long flexible riser with different length-to-diameter ratio（aspect ratio） in uniform and shear currents. Three aspect ratios were simulated： L/D= 500, 750 and 1 000. The simulation was carried out by the in-house computational fluid dynamics（CFD） solver viv-FOAM-SJTU developed by the authors, which was coupled with the strip method and developed on the OpenFOAM platform. Moreover, the radial basis function（RBF） dynamic grid technique is applied to the viv-FOAM-SJTU solver to simulate the VIV in both in-line（IL） and cross-flow（CF） directions of flexible riser with high aspect ratio. The validation of the benchmark case has been completed. With the same parameters, the aspect ratio shows a significant influence on VIV of a long flexible riser. The increase of aspect ratio exerted a strong effect on the IL equilibrium position of the riser while producing little effect on the curvature of riser. With the aspect ratio rose from 500 to 1 000, the maximum IL mean displacement increased from 3 times the diameter to 8 times the diameter. On the other hand, the vibration mode of the riser would increase with the increase of aspect ratio. When the aspect ratio was 500, the CF vibration was shown as a standing wave with a 3-（rd） order single mode. When the aspect ratio was 1 000, the modal weights of the 5-（th） and 6-（th） modes are high, serving as the dominant modes. The effect of the flow profile on the oscillating mode becomes more and more apparent when the aspect ratio is high, and the dominant mode of riser in shear flow is usually higher than that in uniform flow. When the aspect ratio was 750, the CF oscillations in both uniform flow and shear flow showed multi-mode vibration of the 4-（th） and 5-（th） mode. While, the dominant mode in uniform flow is the 4-（th） order, and the dominant mode in shear flow is the 5-（th） order.
文摘Effects of depth and forward speed on hydrodynamic coefficients of ships are presented in this paper. A modified simple Green function technique was used to calculate 2D coefficients while strip theory was used to calculate 3D coefficients. Numerical results are provided for hydrodynamic coefficients of parabolic hull ship. It is found out that both depth and forward speed have considerable effects on hydrodynamic coefficients of ship.
