Hamid Ghafari - Academia.edu (original) (raw)

Papers by Hamid Ghafari

Research paper thumbnail of Novel concept of hybrid wavestar- floating offshore wind turbine system with rectilinear arrays of WECs

Research paper thumbnail of Numerical study on the hydrodynamic interaction between two floating platforms in Caspian Sea environmental conditions

Ocean Engineering, 2019

h i g h l i g h t s • Ship-ship interaction in shallow water is investigated by a high-order pane... more h i g h l i g h t s • Ship-ship interaction in shallow water is investigated by a high-order panel method. • Interaction hydrodynamic forces during meeting and overtaking are predicted. • The method is validated by comparing the numerical results with experimental data. • Computations are conducted at different water depth, ship-ship distance and ship speed. • The influences of water depth, ship-ship distance and ship speed are demonstrated.

Research paper thumbnail of Power matrix and dynamic response of the hybrid Wavestar-DeepCwind platform under different diameters and regular wave conditions

Research paper thumbnail of Hydrodynamic performance and the power production of the tidal turbine by new profiles at the leading-edge tubercles

Ships and Offshore Structures

In this work, two new profiles at the leading-edge tubercles of the tidal turbine have been propo... more In this work, two new profiles at the leading-edge tubercles of the tidal turbine have been proposed to predict the hydrodynamic performance and obtain more power production than the original blade with a smooth leading edge. A computational method based on the Reynolds-Averaged Navier-Stokes (RANS) is employed for predicting the hydrodynamic performance of the tidal turbine. The turbulent model of the k − v SST (shear stress transport) has been used. A three-bladed tidal turbine with the NREL's S814 foil section is selected. The numerical results of the power coefficient against tip speed ratio (TSR) show a good agreement in comparison with the experimental data. Then, two new profiles of tubercles, namely zigzag (ZZ) and absolute sinus (AS), at the leading-edge with 0.1 chord length height at each section, are proposed. The results of the power and torque coefficients are significantly increased, especially at higher TSRs.

Research paper thumbnail of Power production of the counter-rotating tidal current turbine, including duct effect

Ships and Offshore Structures, 2022

Research paper thumbnail of Numerical study of the Wavestar wave energy converter with multi-point-absorber around DeepCwind semisubmersible floating platform

Ocean Engineering, 2021

Abstract The presented paper numerically studies on the Wavestar wave energy converter (WEC) with... more Abstract The presented paper numerically studies on the Wavestar wave energy converter (WEC) with multi-point-absorber around the DeepCwind semisubmersible floating platform. The Wavestar concept is selected as suitable point absorbers in conduction with floating wind turbine supported by DeepCwind semisubmersible. The effects of the Wavestars mechanism on the power extraction and DeepCwind semisubmersible movement were investigated using the potential flow-based boundary element method (BEM) in ANSYS/AQWA software in time domain for two different wave incident angles. The DeepCwind semisubmersible floating wind turbine design was simulated, and the results were compared with the available experimental data. Uncoupled simulations in which the response amplitude operator (RAO) motions and fairlead tensions are prescribed according to the experimental data show relatively good agreement in fairlead tensions. Finally, various numbers of the Wavestars WEC of point absorbers are mounted around the DeepCwind semisubmersible. The numerical results of the surge, heave and pitch motions, absorbed power and wave contour under multi-point-absorber are presented and discussed.

Research paper thumbnail of Hydrodynamic Analysis of 3D Hydrofoil Using Nonuniform Rational B-Spline and Boundary Element Method

Mathematical Problems in Engineering, 2021

In this paper, two different 3D hydrofoils with profiles NACA0012 are simulated in the potential ... more In this paper, two different 3D hydrofoils with profiles NACA0012 are simulated in the potential flow. Boundary element method (BEM) and nonuniform rational B-spline (NURBS) are coupled to reduce error and increase accuracy. The computer code is developed in different submergence depths (d), flow velocities (U), and various angles of attack (AoA), and the pressure is obtained by NURBS formulation. The pressure on a 3D hydrofoil with NACA412 profile iscompared with other existing methods. The validity of result is revealed. The accuracy of the results is acceptable. The competition of the two models’ results indicates that the increasing chord length leads to increase in C p min , and the decrease in depth and angle of attack leads to the growing value of C p min . Moreover, when the flow velocity is changed, the changes of potential and pressure coefficient distribution do not follow the specific trend. NURBS is a basic equation in different CAD packages because it is able to mesh s...

Research paper thumbnail of Numerical Study on the Tandem Submerged Hydrofoils Using RANS Solver

Mathematical Problems in Engineering, 2021

This paper is presented on the tandem two-dimensional hydrofoils with profiles NACA4412 in single... more This paper is presented on the tandem two-dimensional hydrofoils with profiles NACA4412 in single-phase and two-phase flow domains for different submergence depths and different distances in a various angle of attack (AoA). Also, supercavitation is studied at σ = 0.34 by the Zwart cavitation model. Reynolds-averaged Navier–Stokes (RANS) with the shear stress transport (SST) K-ω is employed as a turbulence model in transient analysis of Ansys FLUENT software. The numerical results show that, by increasing depth, the drag coefficient increases for both hydrofoils 1 and 2 as well as the lift coefficient. The drag coefficient of hydrofoil 2 is bigger than hydrofoil 1 for all depths; moreover, it was found that the flow pressure behind the hydrofoil 1 had affected the upper and the lower surface of the hydrofoil 2 at each distance or AoA. These effects are observed in the hydrofoil 2 lift coefficient as well as the flow separation. However, the maximum lift-to-drag ratio is observed at A...

Research paper thumbnail of Power production of the hybrid Wavestar point absorber mounted around the Hywind spar platform and its dynamic response

Journal of Renewable and Sustainable Energy, 2021

This article presents the novel hybrid Wavestar–Hywind concept that combines a floating wind turb... more This article presents the novel hybrid Wavestar–Hywind concept that combines a floating wind turbine with a number of Wavestar point-absorbers on a shared OC3-Hywind spar platform. The effect of increasing Wavestar number on the wave power production and platform motions has been investigated using both time and frequency domains. Simulations were carried out with the boundary element method using the three-dimensional diffraction/radiation theory, which is employed by the ANSYS AQWA software. Regular Airy wave under different wave periods from 4 to 16 s and constant wave height (1.2 m) was considered as an environmental condition. The results of the response amplitude operator (RAO) motions of the platform show that increasing wave periods cause an increase on the surge, heave, and pitch RAO. Moreover, in higher periods as Wavestar numbers increase, the heave motion decreases, while it does not significantly affect the surge and pitch motions. Due to Wavestar resonance, the maximum capture width ratio occurs in wave periods 5 and 6 s for all case studies, that means higher Wavestar power and lower platform motion due to increasing radiation damping force. Furthermore, the result shows that the angle between Wavestar arm and wave direction and its location are two main factors that influence the power production. The maximum power absorbed by Wavestar occurs in the wave periods 6 s and makes 46, 103, 160, and 210 kW power for 3, 6, 9, and 12 WS, respectively.

Research paper thumbnail of Novel concept of hybrid wavestar- floating offshore wind turbine system with rectilinear arrays of WECs

Research paper thumbnail of Numerical study on the hydrodynamic interaction between two floating platforms in Caspian Sea environmental conditions

Ocean Engineering, 2019

h i g h l i g h t s • Ship-ship interaction in shallow water is investigated by a high-order pane... more h i g h l i g h t s • Ship-ship interaction in shallow water is investigated by a high-order panel method. • Interaction hydrodynamic forces during meeting and overtaking are predicted. • The method is validated by comparing the numerical results with experimental data. • Computations are conducted at different water depth, ship-ship distance and ship speed. • The influences of water depth, ship-ship distance and ship speed are demonstrated.

Research paper thumbnail of Power matrix and dynamic response of the hybrid Wavestar-DeepCwind platform under different diameters and regular wave conditions

Research paper thumbnail of Hydrodynamic performance and the power production of the tidal turbine by new profiles at the leading-edge tubercles

Ships and Offshore Structures

In this work, two new profiles at the leading-edge tubercles of the tidal turbine have been propo... more In this work, two new profiles at the leading-edge tubercles of the tidal turbine have been proposed to predict the hydrodynamic performance and obtain more power production than the original blade with a smooth leading edge. A computational method based on the Reynolds-Averaged Navier-Stokes (RANS) is employed for predicting the hydrodynamic performance of the tidal turbine. The turbulent model of the k − v SST (shear stress transport) has been used. A three-bladed tidal turbine with the NREL's S814 foil section is selected. The numerical results of the power coefficient against tip speed ratio (TSR) show a good agreement in comparison with the experimental data. Then, two new profiles of tubercles, namely zigzag (ZZ) and absolute sinus (AS), at the leading-edge with 0.1 chord length height at each section, are proposed. The results of the power and torque coefficients are significantly increased, especially at higher TSRs.

Research paper thumbnail of Power production of the counter-rotating tidal current turbine, including duct effect

Ships and Offshore Structures, 2022

Research paper thumbnail of Numerical study of the Wavestar wave energy converter with multi-point-absorber around DeepCwind semisubmersible floating platform

Ocean Engineering, 2021

Abstract The presented paper numerically studies on the Wavestar wave energy converter (WEC) with... more Abstract The presented paper numerically studies on the Wavestar wave energy converter (WEC) with multi-point-absorber around the DeepCwind semisubmersible floating platform. The Wavestar concept is selected as suitable point absorbers in conduction with floating wind turbine supported by DeepCwind semisubmersible. The effects of the Wavestars mechanism on the power extraction and DeepCwind semisubmersible movement were investigated using the potential flow-based boundary element method (BEM) in ANSYS/AQWA software in time domain for two different wave incident angles. The DeepCwind semisubmersible floating wind turbine design was simulated, and the results were compared with the available experimental data. Uncoupled simulations in which the response amplitude operator (RAO) motions and fairlead tensions are prescribed according to the experimental data show relatively good agreement in fairlead tensions. Finally, various numbers of the Wavestars WEC of point absorbers are mounted around the DeepCwind semisubmersible. The numerical results of the surge, heave and pitch motions, absorbed power and wave contour under multi-point-absorber are presented and discussed.

Research paper thumbnail of Hydrodynamic Analysis of 3D Hydrofoil Using Nonuniform Rational B-Spline and Boundary Element Method

Mathematical Problems in Engineering, 2021

In this paper, two different 3D hydrofoils with profiles NACA0012 are simulated in the potential ... more In this paper, two different 3D hydrofoils with profiles NACA0012 are simulated in the potential flow. Boundary element method (BEM) and nonuniform rational B-spline (NURBS) are coupled to reduce error and increase accuracy. The computer code is developed in different submergence depths (d), flow velocities (U), and various angles of attack (AoA), and the pressure is obtained by NURBS formulation. The pressure on a 3D hydrofoil with NACA412 profile iscompared with other existing methods. The validity of result is revealed. The accuracy of the results is acceptable. The competition of the two models’ results indicates that the increasing chord length leads to increase in C p min , and the decrease in depth and angle of attack leads to the growing value of C p min . Moreover, when the flow velocity is changed, the changes of potential and pressure coefficient distribution do not follow the specific trend. NURBS is a basic equation in different CAD packages because it is able to mesh s...

Research paper thumbnail of Numerical Study on the Tandem Submerged Hydrofoils Using RANS Solver

Mathematical Problems in Engineering, 2021

This paper is presented on the tandem two-dimensional hydrofoils with profiles NACA4412 in single... more This paper is presented on the tandem two-dimensional hydrofoils with profiles NACA4412 in single-phase and two-phase flow domains for different submergence depths and different distances in a various angle of attack (AoA). Also, supercavitation is studied at σ = 0.34 by the Zwart cavitation model. Reynolds-averaged Navier–Stokes (RANS) with the shear stress transport (SST) K-ω is employed as a turbulence model in transient analysis of Ansys FLUENT software. The numerical results show that, by increasing depth, the drag coefficient increases for both hydrofoils 1 and 2 as well as the lift coefficient. The drag coefficient of hydrofoil 2 is bigger than hydrofoil 1 for all depths; moreover, it was found that the flow pressure behind the hydrofoil 1 had affected the upper and the lower surface of the hydrofoil 2 at each distance or AoA. These effects are observed in the hydrofoil 2 lift coefficient as well as the flow separation. However, the maximum lift-to-drag ratio is observed at A...

Research paper thumbnail of Power production of the hybrid Wavestar point absorber mounted around the Hywind spar platform and its dynamic response

Journal of Renewable and Sustainable Energy, 2021

This article presents the novel hybrid Wavestar–Hywind concept that combines a floating wind turb... more This article presents the novel hybrid Wavestar–Hywind concept that combines a floating wind turbine with a number of Wavestar point-absorbers on a shared OC3-Hywind spar platform. The effect of increasing Wavestar number on the wave power production and platform motions has been investigated using both time and frequency domains. Simulations were carried out with the boundary element method using the three-dimensional diffraction/radiation theory, which is employed by the ANSYS AQWA software. Regular Airy wave under different wave periods from 4 to 16 s and constant wave height (1.2 m) was considered as an environmental condition. The results of the response amplitude operator (RAO) motions of the platform show that increasing wave periods cause an increase on the surge, heave, and pitch RAO. Moreover, in higher periods as Wavestar numbers increase, the heave motion decreases, while it does not significantly affect the surge and pitch motions. Due to Wavestar resonance, the maximum capture width ratio occurs in wave periods 5 and 6 s for all case studies, that means higher Wavestar power and lower platform motion due to increasing radiation damping force. Furthermore, the result shows that the angle between Wavestar arm and wave direction and its location are two main factors that influence the power production. The maximum power absorbed by Wavestar occurs in the wave periods 6 s and makes 46, 103, 160, and 210 kW power for 3, 6, 9, and 12 WS, respectively.