Figure 1 - uploaded by Am Ghasemi

Content may be subject to copyright.

Source publication

Ocean wave energy represents a vast renewable energy resource which is mostly untapped. With the current focus on renewable energy, the ability to accurately test wave energy converter (WEC) designs is gaining importance both in research and in industry. The numerical testing of WEC geometry, in place of multiple scale experimental model testing sa...

## Similar publications

Assessment of the performance of a shallow water model with closure using a linear k-ε turbulence model is made for various obstruction-induced discontinuous flows. The monotone upwind scheme of conservative laws (MUSCL) - Hancock scheme is used, together with the Harten Lax van Leer (HLL) approximate Riemann solver in the discretization of the fin...

Abstract In this study, an analysis of the flow properties around an isolated sphere under isothermal conditions for flows with high Mach numbers and low Reynolds numbers is conducted via direct numerical simulation (DNS) of the three-dimensional compressible Navier–Stokes equations. The calculations are performed with a boundary-fitted coordinate...

In this paper, Direct Numerical Simulations (DNS) are carried out in order to capture the flow instabilities and transition to turbulence occurring on a Savonius style wind turbine (SSWT) blade. Simulations are conducted with the open source code Nek5000, solving the incompressible Navier-Stokes equations with a high order, spectral element method....

Turbulent secondary flow in straight open ducts with rectangular cross-section are studied numerically by means of pseudo-spectral direct numerical simulation (DNS). Similarly to the corresponding closed duct flows, the mean streamwise vorticity pattern in turbulent open duct flows were found to be the statistical footprint of the most probable loc...

This study presents a two-dimensional (2D) direct numerical simulation (DNS) of the effects of bed slope and sediment settling on the dynamic behaviors of lock-exchange turbidity currents. The 2D DNS model is first validated against existing DNS solutions and experimental data. Afterwards, a series of numerical case studies on the effect of bed slo...

## Citations

... Viscous fluid motion near the stagnation region of a solid body has motivated many researchers for more decades, where ''body" corresponds to either fix or moving surfaces [1][2][3] in a fluid. This multidisciplinary concept has frequent applications in, thrust bearings, thermal oil recovery, wave energy converters and air condensers [4,5]. ...

This paper studies a steady two-dimensional stagnation-point flow of nanofluids over a nonlinearly stretching/shrinking sheet in the presence of blowing/suction. The effects of different nanoparticle materials, namely copper, alumina and titania on the flow and heat transfer rate are investigated. Employing similarity variables, the governing partial differential equations including continuity, momentum and energy have been reduced to ordinary equations and are solved numerically via Runge-Kutta-Fehlberg scheme. It is shown that two solutions exist for shrinking sheets in both blowing and impermeable cases, while an additional solution appears in the case of suction (there are three solutions). Moreover, the effects of nonlinearly parameter β, blowing/suction S, and solid volume fraction ϕ(symbol) on the heat and fluid flow characteristics are investigated in details.

... At the upstream end of domain, a constant velocity is specified for the current flow and the fluid is allowed to flow out at the downstream of the domain. The pressure gradient at the downstream end of the domain is assumed to be zero [26][27][28]: ...

In this paper, a numerical simulation of tether undersea kites (TUSK) used for power generation is undertaken. The effect of varying key design parameters in these systems is studied. TUSK systems consist of a rigid-winged kite, or glider, moving in an ocean current. One proposed TUSK concept uses a tethered kite which is connected by a flexible tether to a support structure with a generator on a surface buoy. The numerical simulation models the flow field in a three-dimensional domain near the rigid undersea kite wing by solving the full Navier-Stokes equations. A moving computational domain method is used to reduce the computational run times. A second-order corrector-predictor method, along with Open Multi-Processing (OpenMP), is employed to solve the flow equations. In order to track the rigid kite, which is a rectangular planform wing with a NACA 0021 airfoil, an immersed boundary method is used. The tension force in the elastic tether is modeled by a simple Hooke's law, and the effect of tether damping is added.
PID control methods are used to adjust the kite pitch, roll and yaw angles during power (tether reel-out) and retraction (reel-in) phases to obtain the desired kite trajectories. During the reel-out phase the kite moves in successive cross-current motions in a figure-8 pattern, the tether length increases and power is generated. During reel-in the kite motion is along the tether, and kite hydrodynamic forces are reduced so that net positive power is produced.
The effects of different key design parameters in TUSK systems, such as the ratio of tether to current velocity, and tether retraction velocity, are then further studied. System power output, kite trajectories, and vorticity flow fields for the kite are also determined.

... The governing equations are solved using the two step projection method as defined in Ref. [43] with using OpenMP. The OpenMP is explained in detail in Ref. [44]. ...

... Enough discretization of complex and moving geometries while reducing the computational time is one of the difficulties of the computational fluid dynamics methods (Kozak, 2014). This means that grids have to be coarse enough so that the calculation is low-cost, but also fine enough, so that each important physical feature is captured and simulated (Gosselin et al., 2013 andGhasemi, 2013). The most important factor to identify a good grid resolution is the ability to predict the time and place of flow separation around the turbine blades (Kozak, 2014). ...

Unlike horizontal axis turbines, the Darrieus-type wind turbines have less efficiency and suffer from the self-starting inability. The effects of fixed and variable blade pitch angle as an idea for improving the performance of Darrieus turbine have been investigated using the CFD analysis, and a pitching system (variable pitch Darrieus-type wind turbine) has been proposed that can reduce both the blades oscillating motion and the magnitude of angle of attack in one revolution compared to that of the Darrieus-type wind turbines. In this study, the method of computational fluid dynamics with moving mesh has been used for analyzing the unsteady two-dimensional flow simulation. The numerical results show that the SST k-x turbulence model matches well with the experimental results and can capture the flow separation phenomenon at low tip speed ratios. Also, it was observed that a small negative fixed pitch angle of �3� can delay the separation and improve the performance of wind turbine. The numerical simulation also
showed that the variable-pitch blade turbine can reduce or eliminate the flow separation on its blades at a lower tip speed ratios than that of the fixed pitch blades.This result increases the starting torque and obtaining high efficiency with decreasing in torque ripple on blades during the turbine operation compared to that of the fixed-pitch blade Darrieus turbine.

... The numerical interaction of a solid and fluid flow is widely studied in Refs. [19][20][21][22][23][24][25], and here, we use the fictitious domain-immersed boundary method to simulate the interaction of the kite with the flow. TUSK system kites generally fly across the current along three-dimensional paths, and our final goal is to simulate these complex motions. ...

The dynamic motion of tethered undersea kites (TUSK) is studied using numerical simulations. TUSK systems consist of a rigid winged-shaped kite moving in an ocean current. The kite is connected by tethers to a platform on the ocean surface or anchored to the seabed. Hydrodynamic forces generated by the kite are transmitted through the tethers to a generator on the platform to produce electricity. TUSK systems are being considered as an alternative to marine turbines since the kite can move at a high-speed, thereby increasing power production compared to conventional marine turbines. The twodimensional Navier-Stokes equations are solved on a regular structured grid to resolve the ocean current flow, and a fictitious domain-immersed boundary method is used for the rigid kite. A projection method along with open multiprocessing (OpenMP) is employed to solve the flow equations. The reel-out and reel-in velocities of the two tethers are adjusted to control the kite angle of attack and the resultant hydrodynamic forces. A baseline simulation, where a high net power output was achieved during successive kite power and retraction phases, is examined in detail. The effects of different key design parameters in TUSK systems, such as the ratio of tether to current velocity, kite weight, current velocity, and the tether to kite chord length ratio, are then further studied. System power output, vorticity flow fields, tether tensions, and hydrodynamic coefficients for the kite are determined. The power output results are shown to be in good agreement with the established theoretical results for a kite moving in two dimensions.

... At the upstream end of domain, a constant velocity is specified for the current flow and the fluid is allowed to flow out at the downstream of the domain. The pressure gradient at the downstream end of the domain is assumed to be zero [30], ...

... Gomes et al. [16] performed a numerical simulation of an OWC submitted to the wave climate of Rio Grande city using Fluent package, employing the multiphase Volume of Fluid (VOF) model for tracking the water free surface [17]. Zhang et al. [18] developed a 2D NWT based on a two-phase level set immersed boundary method to predict the hydrodynamic efficiency of a fix OWC. ...

... Gomes et al. [16] performed a numerical simulation of an OWC submitted to the wave climate of Rio Grande city using Fluent package, employing the multiphase Volume of Fluid (VOF) model for tracking the water free surface [17]. Zhang et al. [18] developed a 2D NWT based on a two-phase level set immersed boundary method to predict the hydrodynamic efficiency of a fix OWC. ...

In the current study, a fully nonlinear two-dimensional numerical wave tank is developed using the commercial CFD software, Ansys Fluent 15.0, in order to study the absorption characteristics of an OWC at linear and highly nonlinear steep waves. The two-phase Volume-Of-Fluid (VOF) method is employed to predict the water free surface evolution. The numerical results are first validated against the available analytical data in the literature. The good agreement between the numerical results and those of analytics, revealed the capability of the developed numerical tank to study the performance of the OWC. Next, the simulations are performed for strongly nonlinear waves, up to the wave steepness of 0.069 (H/L=0.069), where H is the wave height and L is the wave length. The optimum pneumatic damping of the air turbine at such strongly steep and nonlinear waves is determined. Results show that the absorption efficiency of the OWC decreases considerably as the wave height increases. Moreover, the maximum wave energy absorption efficiency for the highly nonlinear waves occurs at a pneumatic damping coefficient lower than that of the linear theory.
Copyright © 2016 by ASME Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature
Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal

... A second-order essentially non-oscillatory (ENO) method and a simple second order centered difference approximation were used to discretized the advection and viscous terms, respectively. The two step projection method is defined as [37]: ...

1 Abstract A numerical method is developed to capture the interaction of a solid object with two-phase flow with high density ratios. The full two-dimensional Navier-Stokes equations are solved on a regular structured grid to resolve the flow field. Level set and immersed boundary methods 1

Purpose
A numerical method is developed to capture the interaction of solid object with two-phase flow with high density ratios. The current computational tool would be the first step of accurate modeling of wave energy converters in which the immense energy of the ocean can be extracted at low cost.
Design/methodology/approach
The full two-dimensional Navier–Stokes equations are discretized on a regular structured grid, and the two-step projection method along with multi-processing (OpenMP) is used to efficiently solve the flow equations. The level set and the immersed boundary methods are used to capture the free surface of a fluid and a solid object, respectively. The full two-dimensional Navier–Stokes equations are solved on a regular structured grid to resolve the flow field. Level set and immersed boundary methods are used to capture the free surface of liquid and solid object, respectively. A proper contact angle between the solid object and the fluid is used to enhance the accuracy of the advection of the mass and momentum of the fluids in three-phase cells.
Findings
The computational tool is verified based on numerical and experimental data with two scenarios: a cylinder falling into a rectangular domain due to gravity and a dam breaking in the presence of a fixed obstacle. In the former validation simulation, the accuracy of the immersed boundary method is verified. However, the accuracy of the level set method while the computational tool can model the high-density ratio is confirmed in the dam-breaking simulation. The results obtained from the current method are in good agreement with experimental data and other numerical studies.
Practical/implications
The computational tool is capable of being parallelized to reduce the computational cost; therefore, an OpenMP is used to solve the flow equations. Its application is seen in the following: wind energy conversion, interaction of solid object such as wind turbine with water waves, etc.
Originality/value
A high efficient CFD approach method is introduced to capture the interaction of solid object with a two-phase flow where they have high-density ratio. The current method has the ability to efficiently be parallelized.