In the present paper,two-and three-dimensional numerical simulations of the flow interference between four cylinders in an in-line square arrangement at Re = 200 are performed.Assisted with the two-dimensional(2-D) nu...In the present paper,two-and three-dimensional numerical simulations of the flow interference between four cylinders in an in-line square arrangement at Re = 200 are performed.Assisted with the two-dimensional(2-D) numerical simulation,the mean and fluctuating forces,Strouhal number(St) and vortex shedding pattern in the wake for each cylinder were analyzed with the spacing ratio(L /D) ranging from 1.5 to 6.0.It was found that,four different vortex modes(viz.,flip-flopping,shielding anti-phase-synchronized,in-phasesynchronized and anti-phase-synchronized) gradually appear with the increase of the L/D ratio.The average drag coefficient of the upstream cylinders is larger than that of the downstream cylinders,while the downstream cylinders usually undergo serious fluctuating forces.When the L/D ratio ranges from 3.0 to 4.0,the dominant frequency of the drag coefficient is equal to the value of St of upstream cylinders.This indicates that a simultaneous resonance in the in-flow and cross-flow directions may occur for some single structures of a multi-body oscillating system.For the 3-D numerical simulation,the L/D and aspect ratios are kept constant as 5.0 and 10,respectively.It was found that some vortices are formed in the wake of the upstream cylinders.Besides,with the same spacing ratio,the calculated drag coefficient and lift coefficient fluctuation are slightly larger than the 2-D results,but with a phase difference.展开更多
Pulsating flow is a common condition for under water manipulators in Bohai Bay.This study aimed to investigate the effects of pulsation frequency and amplitude on the hydrodynamic characteristics of an underwater mani...Pulsating flow is a common condition for under water manipulators in Bohai Bay.This study aimed to investigate the effects of pulsation frequency and amplitude on the hydrodynamic characteristics of an underwater manipulator with different postures using the user-defined function (UDF) method. The lift coefficient (C_(L)), drag coefficient (C_(D)), and vortex shedding of the underwater manipulator in single-and dualarm forms were obtained. Results indicated that the maximum increase in the lift and drag coefficients subjected to the pulsation parameters was 24.45%and 28%, respectively, when the fluid flowed past a single arm. Compared with the single arm, the lift and drag coefficients of the arms were higher than those of the single arm when arm 2 was located upstream. Additionally, the pulsation frequency had no obvious effect on the manipulator, but the C_(L) and C_(D) of arm 2 showed an obvious increasing trend with an increase in pulsation amplitude. Meanwhile, when arm 2 was located downstream, the C_(L) and C_(D) of arm 2 were reduced by 16.38%and 1.15%, respectively, with an increase in the pulse frequency,and the maximum increase in the lift and dragcoefficients was 33.33%and 16.78%,respectively,with increasing pulsation amplitude.Moreover, the downstream wake morphology changed significantly, and a combined vortex phenomenon appeared. Finally, a theoretical basis for examining the hydrodynamic characteristics of marine engineering equipment was established to aid future marine resource exploitation.展开更多
In order to verify the flow interference at the fracture intersections, a group of hydraulic simulations of crossing flow was carried out. The manifold interference effects at the intersection of fractures on water fl...In order to verify the flow interference at the fracture intersections, a group of hydraulic simulations of crossing flow was carried out. The manifold interference effects at the intersection of fractures on water flow has been confirmed extensively either in the normal or in the oblique intersected tubes as well as in the intersected tubes of either equal or variant diameters. Consequently, suggest that the fissure network can no longer be taken as a set of solitary fractures, but as a set of elementary intersected fractures. The deflection effect at fracture intersections on the water flow should be taken into consideration when is dealt with any theory related to the water migration in fractures.展开更多
Winds on the earth are commonly strong enough to erode transport and deposit sediment. The modes of sand transport by the wind are greatly different from those by water flow. On the other hand wind-blown sands are of...Winds on the earth are commonly strong enough to erode transport and deposit sediment. The modes of sand transport by the wind are greatly different from those by water flow. On the other hand wind-blown sands are of a material circulation process of the earth surface. They affect wind-sand transport flux and sand ejection of a flux, the damage of grains formed cannot be neglected in engineering. Because of the complexity of windblown sand flux system, the understanding of its basic mechanics is not yet clear. The key forces in sand salutation mainly includes： the valid gravity, air drag force ＇Magnus force＇ Saffman force ＇Basset force＇ additional quality force and scatter force among grains. The most important force in sand salutation is the air drag force. Computation of the single sphere drag coefficient and double spheres drag coefficient is presented for the distance between two spheres being smaller than twelve times of the sphere diameter and the spheres being at different angular positions. The flow interference of two spheres was investigated for the distance s = 0.08 d to 12d, angular position 0 = 0 to 360 and Reynolds number 15≤Re≤1000.展开更多
Analysis of model test results was carried out to investigate the hydrodynamic interaction between a pair of elastically-supported rigid cylinders of dissimilar diameters in a water flume. The two cylinders are placed...Analysis of model test results was carried out to investigate the hydrodynamic interaction between a pair of elastically-supported rigid cylinders of dissimilar diameters in a water flume. The two cylinders are placed in tandem with one situated in the wake of the other. The diameter of the upstream cylinder is twice as large as that of the downstream cylinder. The spacing between the two cylinders ranges from 1 to 10 times the larger cylinder diameter. The Reynolds numbers are within the sub-critical range. The cylinders are free to oscillate in both the in-line and the cross-flow directions. The reduced velocity ranges from 1 to 10 and the low damping ratio of the model test set-up at 0.006 gives a combined mass-damping parameter of 0.02. It is found that the lift on and the cross-flow motion of the downstream cylinder have the frequency components derived from the upstream cylinder＇s vortex shedding as well as from its own vortex shedding, and the relative importance of the two sources of excitation is influenced by the spacing between the two cylinders. The downstream cylinder＇s VIV response appears to be largely dependent upon the actual reduced velocity of the cylinder.展开更多
基金Sponsored by the National Natural Science Foundation of China(Grant No.50538020)
文摘In the present paper,two-and three-dimensional numerical simulations of the flow interference between four cylinders in an in-line square arrangement at Re = 200 are performed.Assisted with the two-dimensional(2-D) numerical simulation,the mean and fluctuating forces,Strouhal number(St) and vortex shedding pattern in the wake for each cylinder were analyzed with the spacing ratio(L /D) ranging from 1.5 to 6.0.It was found that,four different vortex modes(viz.,flip-flopping,shielding anti-phase-synchronized,in-phasesynchronized and anti-phase-synchronized) gradually appear with the increase of the L/D ratio.The average drag coefficient of the upstream cylinders is larger than that of the downstream cylinders,while the downstream cylinders usually undergo serious fluctuating forces.When the L/D ratio ranges from 3.0 to 4.0,the dominant frequency of the drag coefficient is equal to the value of St of upstream cylinders.This indicates that a simultaneous resonance in the in-flow and cross-flow directions may occur for some single structures of a multi-body oscillating system.For the 3-D numerical simulation,the L/D and aspect ratios are kept constant as 5.0 and 10,respectively.It was found that some vortices are formed in the wake of the upstream cylinders.Besides,with the same spacing ratio,the calculated drag coefficient and lift coefficient fluctuation are slightly larger than the 2-D results,but with a phase difference.
基金the National Natural Science Foundation of China (No. 51905211)China Postdoctoral Science Foundation (Grant No. 2020M672128)+1 种基金University of Jinan Research Startup and Discipline Construction Fund (Grant No.1009435)a Project of the “20 Regulations for New Universities” funding program of Jinan (No.202228116)。
文摘Pulsating flow is a common condition for under water manipulators in Bohai Bay.This study aimed to investigate the effects of pulsation frequency and amplitude on the hydrodynamic characteristics of an underwater manipulator with different postures using the user-defined function (UDF) method. The lift coefficient (C_(L)), drag coefficient (C_(D)), and vortex shedding of the underwater manipulator in single-and dualarm forms were obtained. Results indicated that the maximum increase in the lift and drag coefficients subjected to the pulsation parameters was 24.45%and 28%, respectively, when the fluid flowed past a single arm. Compared with the single arm, the lift and drag coefficients of the arms were higher than those of the single arm when arm 2 was located upstream. Additionally, the pulsation frequency had no obvious effect on the manipulator, but the C_(L) and C_(D) of arm 2 showed an obvious increasing trend with an increase in pulsation amplitude. Meanwhile, when arm 2 was located downstream, the C_(L) and C_(D) of arm 2 were reduced by 16.38%and 1.15%, respectively, with an increase in the pulse frequency,and the maximum increase in the lift and dragcoefficients was 33.33%and 16.78%,respectively,with increasing pulsation amplitude.Moreover, the downstream wake morphology changed significantly, and a combined vortex phenomenon appeared. Finally, a theoretical basis for examining the hydrodynamic characteristics of marine engineering equipment was established to aid future marine resource exploitation.
文摘In order to verify the flow interference at the fracture intersections, a group of hydraulic simulations of crossing flow was carried out. The manifold interference effects at the intersection of fractures on water flow has been confirmed extensively either in the normal or in the oblique intersected tubes as well as in the intersected tubes of either equal or variant diameters. Consequently, suggest that the fissure network can no longer be taken as a set of solitary fractures, but as a set of elementary intersected fractures. The deflection effect at fracture intersections on the water flow should be taken into consideration when is dealt with any theory related to the water migration in fractures.
基金supported by National Natural Science Foundation (10532030)
文摘Winds on the earth are commonly strong enough to erode transport and deposit sediment. The modes of sand transport by the wind are greatly different from those by water flow. On the other hand wind-blown sands are of a material circulation process of the earth surface. They affect wind-sand transport flux and sand ejection of a flux, the damage of grains formed cannot be neglected in engineering. Because of the complexity of windblown sand flux system, the understanding of its basic mechanics is not yet clear. The key forces in sand salutation mainly includes： the valid gravity, air drag force ＇Magnus force＇ Saffman force ＇Basset force＇ additional quality force and scatter force among grains. The most important force in sand salutation is the air drag force. Computation of the single sphere drag coefficient and double spheres drag coefficient is presented for the distance between two spheres being smaller than twelve times of the sphere diameter and the spheres being at different angular positions. The flow interference of two spheres was investigated for the distance s = 0.08 d to 12d, angular position 0 = 0 to 360 and Reynolds number 15≤Re≤1000.
文摘Analysis of model test results was carried out to investigate the hydrodynamic interaction between a pair of elastically-supported rigid cylinders of dissimilar diameters in a water flume. The two cylinders are placed in tandem with one situated in the wake of the other. The diameter of the upstream cylinder is twice as large as that of the downstream cylinder. The spacing between the two cylinders ranges from 1 to 10 times the larger cylinder diameter. The Reynolds numbers are within the sub-critical range. The cylinders are free to oscillate in both the in-line and the cross-flow directions. The reduced velocity ranges from 1 to 10 and the low damping ratio of the model test set-up at 0.006 gives a combined mass-damping parameter of 0.02. It is found that the lift on and the cross-flow motion of the downstream cylinder have the frequency components derived from the upstream cylinder＇s vortex shedding as well as from its own vortex shedding, and the relative importance of the two sources of excitation is influenced by the spacing between the two cylinders. The downstream cylinder＇s VIV response appears to be largely dependent upon the actual reduced velocity of the cylinder.
