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Flexible cylinders, such as marine risers, often experience sustained vortex-induced vibration (VIV). Both helical strakes and fairings are demonstrated to be effective in suppressing VIV, while, helical strakes result in large drag, which increases the rotational angle and bending moment at the riser hang-off location and, fairings are cumbersome...
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... low Reynolds number (Re = 200) flow field is simulated using the commercial software AN-SYS FLUENT. Cylinders with two different shapes of crosssection are studied: (a) circular cylinders with an outer diameter of D as the reference case; and (b) cylinders with a cactusshaped cross-section with 20 ribs (or called "ridges"). As shown in Fig. 2, the inscribed circle of the cactus-shaped cross-section is D which is the same as the outer diameter of the cross-section of the circular cylinder. The shapes of ridges and grooves are obtained by spline-curve-fitting of semi-circles with a radius of 0.04D, i.e., the radial distance from the highest point of ridges to the lowest point ...
Context 2
... single stationary cylinder with a circular cross-section in a two-dimensional low Reynolds number (Re = 200) flow field was simulated first; and the lift coefficient, C l , drag coefficient, C d , and Strouhal number, St, were calculated. Then, a single stationary cylinder with the cactus-shaped cross-section (as shown in Fig. 2) in the flow field with the same current speed was simulated. Recall that the outmost diameter of the cactus-shaped cross-section is 1.08D which is 8% larger than the diameter of the circular cross-section. The Reynolds number of the flow filed containing the cactus-shaped cross-section is a little bit larger than that for the case of ...
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Pakistan is blessed with an intricate irrigation system typically comprising a wide network of canals, minors, distributaries, and watercourses. A huge amount of flowing water from irrigation channels is lost by seepage, which is the cause of waterlogging, salinity, and affects the conveyance efficiency of water to the field. This potential menace...
Citations
... Talley et al. [16] conducted an experimental study of cactus-like cylinders with different grooved depths, and the results show that the drag forces acting on the cylinder decrease as the grooved depth increases for Reynolds number in the range 2 × 10 4~2 × 10 5 . Wang et al. [17] numerically studied flow past a cylinder with a fixed surface bulge. The forces acting on the cylinder and Strouhal number are smaller than that of a smooth cylinder. ...
Inspired by the cactus in nature, a cactus-like cross-sectional structure was proposed to achieve the VIV suppression. The VIV of the elastically mounted cylinder was realized based on the ANSYS Fluent and User Defined Function (UDF). The dynamic motion of the cylinder was solved by the single-step time integration algorithms Newmark-β
method. The in-house code was first validated by studying the 2DOF VIV of a circular cylinder with small mass ratio over the range U∗=2~13
, and the results agree well with the published literature. Then, the performance of surface bulge on VIV suppression was studied and four different coverage ratios (CR) were considered, i.e., 0%, 20%, 33%, and 40%. The VIV of a bulged cylinder can be effectively suppressed. CR20 performs the best in VIV suppression and the suppression efficiency in streamwise and transverse direction are 44.6% and 63.1%, respectively. The mechanism of surface bulge on the VIV suppression is the shift of separation point of the shear layer and vortices form between the surface bulges.
... In a previous study of authors (Wang et al., 2018), vortexshedding from a stationary cylinder of a cactus-shaped cross section in a two-dimensional (2D) flow field was simulated using ANSYS FLUENT. Results showed that cactus-shaped cylinders might have smaller lift and drag coefficients. ...
... In a previous work of authors (Wang et al., 2018), steady current flows past a stationary cylinder were numerically simulated to investigate the influence of cylinder's cross-sectional shape on flow patterns and vortex-sheddings. Twenty cactus-shaped cross sections were considered with the number of ridges varying from 8 to 24 and the height of ridges varying from 0:02D to 0:08D (D is the diameter of the counterpart circular cylinder). ...
... The results showed that the cactus-shaped cylinders investigated in this study reduced VIV responses with no cost of significant increase of drag. The observations were consistent with the results of numerical simulations conducted by the authors (Wang et al., 2018). ...
Vortex-Induced Vibration (VIV) is a major contributor to the fatigue damage of marine risers which are often arranged in an array configuration. In addition to helical strakes and fairings, studies have been strived in searching for possible VIV suppression techniques. Inspired by giant Saguaro Cacti, flexible cylinders of different cactus-shaped cross sections were tested in a water tunnel facility, and test results showed that cactus-like body shapes reduced VIV responses of a cylinder at no cost of significant increase of drag. A series of experiments were conducted on a pair of two tandem-arranged flexible cylinders and an array of four cylinders in a square configuration to investigate the effects of wake on the dynamic responses of cylinders and the VIV mitigation effectiveness of the cactus-like body shape. Results showed that the cylinders in a square configuration, either at the upstream or downstream positions, might have larger dynamic responses than those of a single cylinder. The cactus-like body shape could mitigate VIV responses of cylinders at upstream positions in an array configuration; however, similar to helical strakes, the mitigation efficiency was reduced on downstream cylinders. Note that the cactus-like cross-sectional shape investigated was not optimized for VIV suppression. The present study indicates that the modification of the cross-sectional shape of a cylinder to a well-designed cactus-like shape may be used as an alternative technique to mitigate the VIV of marine risers.
The present investigation set out to assess the influence of the surface roughness on the flow and thermal mean quantities, around the heated corrugated cylinder in the laminar steady flow. The current investigation has been devoted to a numerical analysis of a two-dimensional steady flow and forced convection heat transfer characteristics over a heated longitudinal sinusoidal shape grooved cylinder, immersed in an unconfined Newtonian fluid. The number of the grooved cavities was chosen to be 10, 20 and 30 grooves, equally distributed around the cylinder circumference with wavelength and wave amplitude of 1/50 and 1, respectively. Moreover, the thermal boundary condition effect has been analyzed by imposing a uniform heat flux and constant temperature on the cylinder periphery as a thermal boundary condition, over a Reynolds number range of ([Formula: see text]) and a fixed Prandtl number of 0.715. The numerical procedure is based on the finite volume method. The findings indicate that with increasing groove number, the total drag coefficient of the grooved cylinder reduces markedly compared to the smooth one. This trend is more pronounced as the Reynolds number increases. The effect of the groove number on the pressure coefficients is limited, where the profiles of the grooved cylinder coincide with that of the smooth one over the Reynolds number range. When the Reynolds number varies from 0.1 to 40, the average Nusselt number enhances noticeably by about 86% for the smooth and grooved cylinders. Moreover, the groove number affects significantly the average Nusselt number, where the increased groove number results in a gradual reduction in the average Nusselt number. This attenuation is more pronounced as the Reynolds number increases. To predict the average Nusselt number, a correlation has been proposed.
