Maximum Drag Coefficient Research Articles

Enhancing savonius rotor model with additional grooves on hydrokinetic turbine performance

Hydrokinetic turbines use different rotors for technological and economic reasons. Even though it performs poorly, vertical-axis hydrokinetic turbines use the Savonius rotor. The object of research is a Savonius rotor model with additional grooves. The study addresses the need to improve the efficiency and overall performance of Savonius rotor models in hydrokinetic turbines, which are widely used for harnessing energy from flowing water currents. The problem involves understanding how different groove configurations affect the aerodynamic behavior and energy extraction efficiency of the Savonius rotor in hydrokinetic turbine applications. The test results revealed that incorporating grooves led to notable improvements in efficiency (ɳ) and coefficient of drag (CD). Grooved blades exhibited a maximum efficiency of 30.97 % and a maximum drag coefficient of 2.71. Notably, blades with a groove width of 12.5 mm emerged as the optimal model, demonstrating an efficiency peak of 35.66 % and a drag coefficient 3.08. This indicates a substantial increase in efficiency by 4.69 % and a corresponding rise in the drag coefficient by 0.37 for grooved blades. The grooves on grooved blades increase friction, improving performance. Grooved rotor blades improve turbine performance significantly. Savonius rotor models in hydrokinetic turbines extract more energy by optimizing groove width and arrangement to maximize drag coefficient and efficiency. This research affects hydrokinetic turbine design and optimization for renewable energy generation. Engineers and designers can improve the performance and efficiency of the Savonius rotor model in hydrokinetic turbine applications by applying this study’s findings

Material Extrusion Additive Manufacturing of the Composite UAV Used for Search-and-Rescue Missions

The additive processes used in the manufacture of components for unmanned aerial vehicles (UAVs), from composite filaments, have an important advantage compared to classical technologies. This study focused on three-dimensional design, preliminary aerodynamic analysis, fabrication and assembly of thermoplastic extruded composite components, flight testing and search-rescue performance of an UAV. The UAV model was designed to have the highest possible structural strength (the fuselage has a structure with stiffening frames and the wing is a tri-spar), but also taking into account the limitations of the thermoplastic extrusion process. From the preliminary aerodynamic analysis of the UAV model, it was found that the maximum lift coefficient of 1.2 and the maximum drag coefficient of 0.06 were obtained at the angle of attack of 12°. After conducting flight tests, it can be stated that the UAV model, with components manufactured by the thermoplastic extrusion process, presented high stability and maneuverability, a wide range of speeds and good aerodynamic characteristics. The lack of this type of aircraft, equipped with electric motors, a traffic management system, and a thermal module designed for search-and-rescue missions, within the additive manufacturing UAV market, validates the uniqueness of the innovation of the UAV model presented in the current paper.

Aerothermodynamic analysis and rear wake assessment of shock wave interference over blunt leading edge at Mach 6.5

A detailed numerical study of shock-wave interference on a cylindrical blunt leading edge in hypersonic flow is carried out to reveal the effect of shock-shock interaction on peak heating and blunt body aerodynamics. This study is unique in that it examines the effect of interactions on rear wake formation and aerodynamic forces acting on the blunt body. Six different shock wave interference patterns described by Edney are studied for a freestream Mach number of 6.5. Compressible Reynolds-averaged Navier–Stokes equations are solved using finite volume method to obtain accurate prediction of the flowfield and aerodynamic loads. Hugoniot jump conditions are imposed in the inlet boundary to realize oblique shock of desired strength to interact with the detached shock at specific location. Numerical predictions are in good agreement with reported experimental measurements. The results obtained in this study reveals that the type of shock-shock interaction pattern can significantly alter the characteristics of the rear wake. Comparisons to undisturbed flow conditions reveal that Type II to VI interactions lead to an increase in wake size, whereas Type I interaction shows a marginal reduction. These changes in wake size are attributed to modifications in the forebody boundary layer induced by the shock-shock interactions. In the case of Type I interaction, however, the transmitted wave interacting with the rear wake is found to be responsible for the marginal reduction in wake size. This study also shows that changes to the rear wake structure caused by the change in interaction type can affect aerodynamic loads. Type VI interaction recorded a maximum drag coefficient of 2.96, whereas Type IV interaction yielded a maximum lift coefficient of 0.992. These findings demonstrate the potential for dynamically adjusting the control forces of a flying body by manipulating shock interference.

Numerical analysis of the buoy design to extract the effective kinetic wave energy

In many countries, sea wave energy is becoming more widely recognized as a significant and hopeful resource. The objective of this research is to evaluate the impact of alterations in buoy shape on the efficacy of the wave model by utilizing Computational Fluid Dynamics (CFD) to assess modifications in the buoy's dynamic behavior. The buoy's behavior is simulated using ANSYS Fluent, the volume of fluid approach, the open channel flow module, and 5th order Stokes wave models. To further investigate the wave sensitivity in challenging circumstances, Stokes waves were applied in the shallow domain at high wave steepness. The validation process consisted of a comparative analysis between the practical and mathematical results. The outcomes of a numerical fluid dynamical computation were compared, and laboratory observations were modified. For various configurations of underwater buoyancy, the drag and lift characteristics of numerical results were analyzed. The aim of this study was to identify the optimum buoy shape. The selection of this shape was based on several factors, of which the most significant were the least entropy, as well as the maximum lift and drag coefficient. Ideal shape was determined to be a spherical shape (shape B).

Numerical simulation of subsonic and transonic water entry with compressibility effect considered

The purpose of this study is to analyze the subsonic and transonic water entry of the axisymmetric body with compressibility effect considered. The water-entry processes of axisymmetric body are numerically investigated, with Tait state equation and energy equation used to describe the compressibility of the liquid. Reasonable agreement has been obtained between the numerical results and the experimental measurements of trajectory, velocity and acceleration. The cavity evolution and dynamic characteristics of subsonic cases are investigated for vertical and oblique water-entry. The results show that the maximum drag coefficient of the oblique water entry is lower, and it is affected by a large moment which causes pitch angle and trajectory inclination angle to change significantly. In the oblique transonic conditions, the effect of compressibility of the liquid on the dynamic flow characteristics is analyzed. On this basis, the influence of entry angle on the hydrodynamic characteristics is investigated. It is concluded that the water-entry angle has a more significant influence on the trajectory characteristics.

Numerical investigation of aerodynamic performance of an axial fan blade equipped with vortex generators

Delay in the onset of static stall via passive vortex generators (VGs) results in more efficient equipment. Nevertheless, most studies of VGs are conducted on wind turbine blades rather than other turbomachinery devices like axial fan blades. This study is feasibility research to see whether the aerodynamic performance of axial fan blades improves in the presence of VGs. Therefore, the VGs' effect of a static blade with an elliptical profile having a maximum thickness of 8% chord length and without a twist angle is investigated. Fully resolved RANS (Reynolds-averaged Navier–Stokes) simulation with the shear stress transport k–ω turbulence model at Re = 1 × 105 is used to discover the blade flow characteristics with VGs for two types of fan, eight and twelve blades. It is shown that, in both fans, not only can implementing VGs improve the aerodynamic performance of the blade effectively but also the separation phenomenon is delayed. Furthermore, it is concluded that installing VGs performed better in the 8-blade fan, with up to a 3° separation delay, a 9.88% increase in the maximum lift coefficient, and a 48.15% decrease in the maximum drag coefficient with respect to the clean blade. Analyzing the aerodynamic performance of real axial fans considering rotary blades with twist angles equipped with VGs will be feasible in future research.

Contribution of debris and substructures to hydrodynamic forces on bridges

The frequency and intensity of recent flood events demonstrate the need for investigating the forces exerted on inundated bridges. The hydrodynamic force coefficients for bridge superstructures are well established in the literature, but they can be significantly affected by the accumulation of debris upstream and the presence of substructures (e.g., piers, bent caps). The aim of this study is to evaluate the effects of debris-damming and substructures on hydrodynamic forces exerted on bridge superstructures. For this purpose, a series of laboratory experiments on the small-scale bridge and debris models was performed, and the lift and drag forces and overturning moments on bridge decks with debris and substructures were measured and compared to the hydrodynamic forces generated by the flow on superstructures without blockages. The total streamwise and vertical forces and overturning moment were used to investigate the effects of debris and substructures on superstructure forces. Results are also presented on drag, lift, and moment coefficients, as they revealed a considerable change in the hydrodynamic force and moment coefficients because of the additional flow blockages created by debris and substructures. Maximum drag coefficients were observed for a flat plate debris model, combined bridge model (i.e., superstructure, debris, and superstructure), partially submerged model, and a substructure-superstructure model of a fully submerged bridge. Maximum lift and moment coefficients occurred for the substructure and wedge debris models, respectively.

Dynamic stall characteristics of wind turbine airfoil in sand-wind environment

Although the traditional dynamic stall has been well studied, the effect of sand particle on dynamic stall characteristics is seldom considered in the previous studies. Therefore, a research about dynamic stall of the S809 airfoil is accomplished under a sand-wind environment. The unsteady CFD method and the discrete phase model (DPM) are adopted in this research to simulate the dynamic stall characteristic of the S809 airfoil. The influence of different sand particle diameters and different particle concentrations on airfoil dynamic stall characteristics is studied respectively. The simulated results indicate that the maximum lift coefficient and drag coefficient with particle diameter of 10 μm decrease about 2.18% and 2.52% respectively compared with that of the clear air. Meanwhile, the maximum lift coefficient decreases about 6.93% for the case of particle concentration with 62.6 g/m3. The simulated results also indicate that the lift coefficient and drag coefficient decreasing are enlarged with particle concentration increasing. This tendency indicated that the efficiency of a wind turbine would be reduced in sand storm weather.

Hydrodynamic loads of the bridge decks in wave-current combined flows

This work uses a Large Eddy Simulation (LES) model and the Volume of Fluid (VOF) scheme to investigate the hydrodynamic loads on submerged rectangular decks in wave-current combined flows. The influences of current velocity, wave height, deck length, and blockage ratio on the wave loads are examined, and a modified Morison equation is used to predict the hydrodynamic forces on the deck. The simulation results demonstrate that the wave loads are linearly proportional to wave height H when H ≤ 0.4h, h is the water depth. By setting the reference velocity as Ur = (gH)1/2 for wave-induced flow, the hydrodynamic loads can be separated into a steady term (current-induced load) and an acceleration term (wave-induced load). The crucial hydrodynamic load comes from the surface pressures on the upper side of the decks, owing to the deck length being much larger than the deck thickness. In addition, the drag coefficient is independent of the wave height H, aspect ratio L/D, and the Keulegan-Carpenter number KC; while the lift coefficient depends on the submergence ratio S/D. Bridge engineers could easily use the modified Morison equation and the maximum drag coefficient CD = 2.73, lift coefficient CL = −2.05, the inertia coefficients CMx = 0.95 and CMz = 2.53 to compute the maximum loads against wave-current combined flows.

Numerical investigation on drag characteristics of the truncated hemispherical-nose projectile in vertical water entry

ABSTRACT In this study, the feasibility of the ALE algorithm in analyzing the drag of a rigid truncated hemispherical-nose projectile at the initial stage of vertical water entry is examined. The water entry process is simulated under the conditions of different dilated half-angles of the head plane (DHAHPs) and muzzle velocities (u 0). The drag coefficient is obtained by dimensionless processing of the drag. The maximum (Cd max) drag coefficients of the initial stage are fitted to obtain the generalised impact laws of water entry. The results show that the larger the DHAHP, the smaller is u 0 and the higher is Cd max. The bivariate fitting formula for Cd max of the truncated hemispherical-nose projectile has high prediction accuracy and wide applicability. The average (Cd ave) drag coefficients of the projectile changes significantly after DHAHP of approximately 40°. This change is related to the wet state of the head.

Bulirsch-Stoer computations for bioconvective magnetized nanomaterial flow subjected to convective thermal heating and Stefan blowing: a revised Buongiorno model for theranostic applications

Theranostics is a novel procedure that integrates therapy and diagnosis in a single platform. For its application in theranostic and photothermal therapy for melanoma skin cancer, the hydromagnetic bioconvective flow of a nanomaterial over a lengthening surface is investigated. Realistic nanomaterial modeling is achieved by incorporating passive control of the nanoparticles at the boundary. The impact of the Newtonian heating and Stefan blowing constraints are also accounted. Apposite transformations are employed and then transmuted nonlinear ODEs are resolved using the Bulirsch-Stoer and Newton-Raphson methods. The influence of Stefan blowing parameter , the magnetic field parameter , and the Biot number on the heat transfer rate has been scrutinized and optimized utilizing the response surface methodology (RSM). The sensitivity of heat transport rate is computed. It is found that the Newtonian thermal condition intensifies the nanomaterial temperature that serves as a crucial role in the termination of cancerous cells or tumors. The maximum drag coefficient is experienced for the insignificant intensity of the magnetic field and Stefan blowing. Further, the heat transfer rate is maximum when the Stefan blowing and Biot numbers are at a high level and the Hartmann number is at a low level.

Experimental Investigation of Flow Separation Control over Airfoil by Upper Surface Flap with a Gap

This paper focused on the effects of the flap with a tiny gap on the flow separation over the NPU-WA-180 airfoil. The effects of the geometric parameters of the flaps, such as the flap gap height, angle, and position, were investigated. The study showed that the flap can significantly improve the stall features of airfoil in a limited phase of angle of attack (AoA), and increase lift and reduce drag at a high AoA. It can increase the lift coefficient and drag coefficient in the case of high AoAs, and the angle range of the lift augmentation and drag reduction can reach more than 9°. Furthermore, an excessively large gap is not conducive to the improvement of the airfoil stall performance. The flap angle plays a key role in the airfoil stall characteristic. As the flap angle decreases, the angle range of improving airfoil stall characteristics becomes larger, the pitching moment increment becomes smaller. However, the maximum lift increment and the effect of the drag reduction will decrease. And the effects of the position of the flap on the airfoil performance were also studied. Considering the maximum lift coefficient and drag coefficients in large AoA, the Type1 installed at the 0.7c position has the best effect; from the perspective of delayed stall, the Type1 installed at the 0.6c position has the best delay effect. These results can provide the data and theoretical support for the flap application in engineering.

Assessment of physical and aerodynamic properties of corn kernel (KSC 704)

AbstractPhysical and aerodynamic properties of agricultural products have been used to precision design of the machinery and different postharvest operations. In this study, some physical and aerodynamic properties of corn kernels were investigated as a function of size at three levels of small, medium, and large (8.41 mm, 9.60 mm, and 11.62 mm, respectively) and moisture content in the range of 10 to 25% (wet basis). According to results, with increasing the moisture content from 10 to 25%, the length; width; thickness; geometric mean diameter; mass; and volume of the small, medium, and large kernels linearly increased by 2.22%, 2.40%, and 1.68%; 3.76%, 1.82%, and 1.55%; 3.98%, 2.49%, and 2.67%; 3.29%, 2.23%, and 1.93%; 8.44%, 7.38%, and 8.12%; and 11.32%, 10.71%, and 10.21%, respectively. In this regard, the projection area of the specimens increased nonlinearly by 6.06%, 4.26%, and 3.26%, respectively; whereas, true density decreased nonlinearly by 2.65%, 2.91%, and 1.90%, respectively. The maximum terminal velocity (12.41 m/s) and Reynolds number (6,037.44) were observed in large kernels and the moisture content of 25%; whereas, the minimum terminal velocity (8.32 m/s) and Reynolds number (3,016.55) were observed in small kernels and the moisture content of 10%. Maximum and minimum drag coefficients (1.014 vs. 0.302) were observed in small kernels at the moisture of 10% and large kernels at the moisture of 25%, respectively. The polynomial model was chosen as a suitable model in order to foretell the terminal velocity, Reynolds number, and drag coefficient of kernels as a function of moisture content and size.Practical ApplicationsMechanical damages to seeds at harvesting, transporting, and threshing are major concerns for farmers and farming experts. All the processes of wind transfer, flotation, and seed removal from seed mixture and the stalks and husks depend on the behavior of the seeds in the wind flow. Therefore, it is crucial to determine the physical and aerodynamic properties of various crops to analyzing their behavior during transport, processing, and precise design of farm equipment and machines to minimize wastes.

Study of wind loading and flow characteristics on an array of parabolic trough collectors

Wind loads and structure of the flow field around an array of parabolic trough collectors (PTCs) were investigated using Delayed Detached Eddy Simulation (DDES) method. A scaled three-dimensional (3D) model was adopted and simulated using the ANSYS-Fluent software. Several pitch angles, including θ = 0°, 45°, 135°, and 180° and the stow mode with the pitch angle, θ = 90°, and flow Reynolds number of 2×105, are considered for numerical solutions. For validation of the numerical model, the mean wind load coefficient on a stand-alone PTC and an array model of PTCs were simulated and compared with the wind tunnel data. Detailed analysis of wind characteristics and wind loading on an array for five-pitch angles was provided. Results demonstrated that except for the stow mode, the first PTC in the array experienced the maximum mean pressure in the upwind side of the PTCs model and corresponded to the maximum mean drag coefficient. Besides, the minimum mean drag coefficient belongs to the second row in the array except for the stow mode. A comparison between flow patterns around the PTCs revealed the high vorticity concentration in front of the collectors for pitch angles θ = 0° and θ = 180°.

Effect of cable surface geometry and ice accretion shapes on the aerodynamic behaviour of inclined stay cables

A wind-tunnel study has been conducted to evaluate changes in the aerodynamic behaviour of stay cables of a bridge due to ice accretion from freezing rain and, due to different cable surface geometries. Numerical simulations were performed to predict the three-dimensional ice shapes resulting from freezing rain for a variation of environmental conditions: wind speed, wind direction, air temperature, velocity of precipitation and duration of precipitation. Stay-cable models were fabricated using laser selective sintering for three different surface geometries (double helical fillet, concentric rings, and double helical strakes) with ice formed under the same environmental conditions. Additional models with the helical fillet geometry were fabricated to evaluate the effect of the air temperature at which ice was formed, the effect of wind direction during the precipitation event and the effect of the duration of the precipitation. The aerodynamic drag and lift forces acting on the models were measured for different wind speeds and cable-wind angles. The overall study evaluated the mean aerodynamic force coefficients of ten models in smooth flow, and two of the models were also tested in turbulent flow. The critical Reynolds number regime for the models of stay cable with ice accretion shapes occurred at a lower Reynolds number (below 100,000) than for the un-iced cables and the drag coefficient was less sensitive to increases in Reynolds numbers than the equivalent un-iced cables. These effects were attributed to the combined role of the ice-shape in determining the separation point combined with the higher surface roughness of the ice. An important observation was that for the three surface geometries and the range of test conditions that were considered, the maximum drag coefficients for ice-accreted models ranged from approximately 1.1 to 1.3, and were up to 50% greater than those observed without ice. The model with helical strakes and ice accretion exhibited the highest drag coefficient and exhibited more variation in lift coefficient with changes in Reynolds number than the other two cable surface geometries. The aerodynamic forces of an ice-accreted model followed similar trends in smooth and turbulent flow, but the drag coefficients were greater in turbulent flow. The presence and shape of the ice appeared to have a more dominant effect on the separation behaviour of the models than the presence of turbulence (for an ice-accreted model). The aerodynamic coefficients did not change greatly between the cases where ice was accreted at −0.5°C and −1.5°C due to the similar ice shape and thickness near the separation locations. The ice shape formed at −5°C was thicker but more localized and resulted in drag and lift coefficients that had greater variation with changes in the cable-wind plane. The effect of ice duration from 10 h to 20 h resulted in a increased variation in mean lift coefficient behaviour due to the asymmetric shape that resulted from the ice accretion parameters.

Suppression of vortex-induced vibration of a cactus-inspired cylinder near a free surface

Bionic ribs inspired by those of a cactus are adopted in order to suppress the vortex-induced vibration (VIV) responses of cylinders located near free surfaces. The VIV responses of cactus-inspired cylinders located near free surface are investigated numerically. The range of the Reynolds number is 8.0 × 103 ≤ Re ≤ 5.6 × 104, and the range of the Froude number is 0.08 ≤ Fr ≤ 0.56. The distance between the cylinder and the free surface is 2D (D is diameter of the cylinder), and the cactus-inspired ribs with height ratios (Ks/D, where Ks is the height of the ribs) include 0.0 (M1), 0.025 (M2), 0.05 (M3), and 0.1 (M4). The VIV response of a smooth cylinder (M0) far from a free surface is used as a reference. Different ribs with height ratios have different effects on the VIV responses of cylinders located near free surfaces. The suppression effect of the bionic ribs on the VIV response is largest when Ks/D = 0.1 (M4). The maximum cross-flow amplitude ratio, the maximum in-line amplitude ratio, and the maximum mean drag coefficient of the cactus-inspired cylinder (M4) are 53.57%, 53.13%, and 49.21% lower than that of the smooth cylinder (M1). The cactus-inspired cylinders are easier to desynchronize from the lock-in region. The free surface causes the vortex phase transition to happen earlier. The free surface has a better suppression effect on VIV response in the high Froude number range. When the rib height ratio is small (M2, Ks/D = 0.025), the free surface enhances the VIV response. However, the VIV response is mainly affected by the ribs when the rib height ratio exceeds a certain value (Ks/D ≥ 0.05). When the cactus-inspired rib with height ratio increases, the critical Reynolds number of the vortex phase transition decreases. The free surface and the cactus-inspired ribs are conducive to dissipation of wakes and lead to decreases in the wake turbulence intensity. Because the cactus-inspired ribs can cause the separation line to develop away from the cylinder wall and effectively control the wake intensity, the VIV response of the cactus-inspired cylinder is suppressed effectively. For the cactus-inspired cylinder, galloping responses can be avoided in high-Reynolds-number range, and boundary-layer separation occurs at the top of the ribs. Unlike the boundary-layer separation process of the smooth cylinder (M1), the ribs of the cactus-inspired cylinder destroy the boundary layer, causing smaller vortices to be produced.

Experimental and numerical study on the aerodynamic characteristics of steel tubular transmission tower bodies under skew winds

A study of the aerodynamic characteristics of circular steel tubular lattice tower bodies in an ultrahigh-voltage direct-current transmission tower under skew winds is presented. The objective of the study, which was based on experimental and numerical methods, was to investigate the aerodynamic coefficients of tower bodies under both yaw and tilt angles. Scaled rigid models of tower bodies with a scale ratio of 1:30 were tested, and the influence of the wind velocity and turbulence intensity on the aerodynamic coefficient was examined. Furthermore, a modified formula for the skewed wind load factor is proposed and compared with different standards. The aerodynamic coefficients of tower bodies with different solidity ratios and tilt angles were obtained via numerical simulation. Additionally, a recommended calculation formula of tilted wind load factor is proposed. The results show that the drag coefficients calculated by standards for different yaw angles were significantly underestimated and that the wind direction corresponding to the predicted maximum drag coefficient was inconsistent with observed wind direction. The formulas proposed in this study accurately describe the characteristics of wind load factor under different yaw and tilt angles. In particular, the influence of the tilt angle on the drag coefficient cannot be ignored.

Investigation of flow characteristics for triangular grooved shape cylinder at different heights in shallow water

This study is an investigation and comparison of the flow characteristic around triangular grooved and bare cylinders, positioned horizontally in shallow water using Particle Image Velocimetry (PIV). Throughout the experiment, Reynolds number, Froude number and water height have been selected as 5000, 0.27 and 90 mm, respectively. To observe the effect of height (h) on the flow structure, cylinder is positioned at h: 0 mm, 15 mm, 22.5 mm, 30 mm, 37.5 mm, 45 mm, 52.5 mm and 60 mm. Moreover, grooved angle (a) has been changed from 0°, 80°, 85°, 90° and 95° in shallow water to investigate the effect of grooved angle. The results show that the vortex forms vary according to the groove angle. It is seen that the vortex, the cylinders especially positioned at h: 0 mm and h: 60 mm, are affected owing to the surface and bottom effect. Furthermore, the largest Reynolds stress is observed at the h: 37.5 mm while the largest wake region is observed at the h: 52.5 mm. Also, the maximum Drag Coefficient (Cd) and Turbulence Kinetic Energy (TKE) are observed at h: 0 mm, a: 90° for grooved cylinder and at h: 37.5 mm for bare cylinder, respectively.

Numerical simulations of wind loading on the floating photovoltaic systems

This study analyses the fluid dynamics of wind loadings on the floating photovoltaic (PV) system using computational fluid dynamics. The two representative models of pontoon-type and a frame-type with a panel angle of 15° to the ground were investigated. The simulation was performed using the steady solver and incompressible Reynolds-Averaged Navier–Stokes equations with a shear stress transport $$k$$ – $$\omega$$ turbulence model. Inlet condition was 45 m/s steady wind, and outlet condition was set to atmospheric pressure. The results confirmed that wind blowing from the backside of floating PV systems increases drag, lift, and pressure on the first row of the PV panels. The maximum drag and lift coefficient of frame-type PV panels were 0.85 and 0.79, respectively, while that of pontoon-type were 0.81 and 0.65, respectively. The maximum drag and lift coefficient of pontoon-type PV panels with a floating body are 0.29 and 0.25, respectively. Adding the floating body reduced the wind loadings by 70%. Additionally, the blocking back space of the PV panel effectively reduced the maximum drag and lift by 75%, as it prevented the flow impingement.

Study on the hydrodynamic characteristics of a marine riser under periodic pulsation disturbance

In this paper, the hydrodynamic forces and vortex distributions of a riser subjected to a non-uniform flow generated by an upstream oscillating wing structure are simulated using high-precision code Incompact3d combined with immersed boundary method. The effects of in-line and transverse positions, oscillating frequency and amplitude on riser performance have also been discussed. It is found that with the increase of in-line spacing or the decrease of oscillation frequency and transverse positions, the time-averaged drag coefficient of riser changes from the negative values to positive values. The time-averaged lift coefficient of riser is generally insensitive to oscillation frequency. However, it shows a large shift when changing the transverse positions or the amplitude of the wing is larger than π/6. Moreover, for various in-line positions, oscillating frequency and amplitude, the vortex shedding of the rigid riser, indicated by the main frequency of lift force, is always locked by the oscillating wing. However, when the transverse position is changing, the ratio of main frequency of lift coefficient to the swing frequency does not still remain 1:1. More concretely, the maximum time-averaged drag coefficient and lift coefficient Root-mean-square value of 0.559 and 1.629 is obtained in the simulation respectively.