Beom-Soo Hyun

EXPERIMENTAL AND NUMERICAL STUDY FOR HYDRODYNAMIC CHARACTERISTICS OF AN OSCILLATING HYDROFOIL

The present article reports the experimental Particle Image Velocimetry (PIV) investigation and the corresponding numerical simulation results about the water flow over the oscillating hydrofoil and its unsteady dynamic characters. The experimental study focuses on the effect of mean angles of attack. The comparison between the PIV results and numerical prediction about the flow field using Fluent well demonstrates the capability of CFD on the simulation of the water flow around the pitching hydrofoil. The numerical results indicate that the forced oscillating frequencies have evident effects on the flow separation and vortex shedding. The simulations about the hydrodynamic drag and lift coefficients were also performed.

Numerical Prediction for Overtopping Performance of OWEC

Overtopping wave energy converter is an offshore wave energy converter for collecting the overtopping waves converting the water pressure head into electric power through the hydro turbines. This paper presents a numerical wave tank based on the commercial CFD code Fluent. The Reynolds averaged Naiver-Stokes and VOF model is utilized to generate the 2D numerical linear propagating waves, which has been validated by the analytical solutions. Several incident wave conditions and shape parameters are calculated in the optimal designing investigation of the overtopping characteristics and discharge for the overtopping wave energy converter.

Unsteady flow around a two-dimensional section of a vertical axis turbine for tidal stream energy conversion

The two-dimensional unsteady flow around a vertical axis turbine for tidal stream energy conversion was investigated using a computational fluid dynamics tool solving the Reynolds-Averaged Navier-Stokes equations. The geometry of the turbine blade section was NACA653-018 airfoil. The computational analysis was done at several different angles of attack and the results were compared with the corresponding experimental data for validation and calibration. Simulations were then carried out for the two-dimensional cross section of a vertical axis turbine. The simulation results demonstrated the usefulness of the method for the typical unsteady flows around vertical axis turbines. The optimum turbine efficiency was achieved for carefully selected combinations of the number of blades and tip speed ratios.

Practical Simulation of Oscillating Water Column Chamber for Wave Energy Conversion

Oscillating water column (OWC) device has been widely employed in the wave energy conversion. In the present paper, a numerical wave tank (NWT) using two-phase volume of fluid (VOF) model is utilized to simulate the generation and propagation of incident regular waves, and water column oscillation inside the chamber. The NWT consists of the continuity equation, the Reynolds-averaged Navier-Stokes equations, and the two-phase VOF functions. The standard k-ϵ turbulence model, the finite volume method, NITA-PISO algorithm, and dynamic mesh technique are employed to generate 2 Dimensional (2D) regular waves. The numerical results are compared and validated with corresponding experimental data. Effects of incident wave conditions and several structure parameters on the operating performance of OWC chamber are investigated numerically.

Production & Performance Assessment of Composite Material Flexible Propeller

The researches on the development of composite material underwater vehicle propeller have been actively attempted for the reduction of radiation noise with outstanding damping effects. Composite material propellers have almost been designed and produced by the foreign experts, and it is difficult to obtain the related info rmations about their flow, vibration, material characteristics because they are treated as the secrets with close relationship to the military technology, especially in the case of underwater vehicles. For the security of domestic manufacture of composite material propeller and the comparison and examination of its performance and radiation noise characteristics with those of German CONTUR composite material propeller, two propellers were self-produced according to the fiber weaving and array using compressible molding process and their self performances and radiation noise characteristics were measured. The mean fluctuations of blade tip of self-produced composite material propeller were increased and the radiation noises in the low frequency band were reduced compared to those of CONTUR, which could be estimated as the change of material characteristics and also be thought to be used for the future research informations.

Review of Application of VOF-Based NWT on Integrated OWC System

Abstract - Oscillating water column is the most widely used ocean energy converting systems all over theworld. The operating performance is influenced by the efficiencies of the two converting stages in the OWCchamber-turbine integrated system. In order to consider the effects of the turbine, the orifice model are carriedout. The VOF based Numerical Wave Tank (NWT) is utilized to simulate the water column oscillation insidethe chamber and the results are compared with corresponding experimental data. This paper reviews the stateof the art in interaction among wave elevation inside the chamber and air flow rate in the duct, which are con-sidered the turbine effects. Effects of incident wave conditions and several shape parameters on the operatingperformance of OWC chamber are investigated numerically. The effects of the impulse turbine on the integratedsystem and interaction among the wave elevation, pressure and air flow velocities variations are investigated.Keywords: Integrated System(통합시스템), Numerical Wave Tank(수치조파수조), Orifice(오리피스),Oscillating Water Column(진동수주 ), Wave Energy Conversion(파력에너지변환 )

Experiments on the magnetic coupling in a small scale counter rotating marine current turbine

Modern economies are dependent on energy consumption to ensure growth or sustainable development. Renewable energy sources provide a source of energy that can provide energy security and is renewable. Tidal energy is more predictable than other sources or renewable energy like the sun or wind. Horizontal axis marine current turbines are currently the most advanced and commercially feasible option for tidal current convertors. A dual rotor turbine is theoretically able to produce more power than a single rotor turbine at the same fluid velocity. Previous experiments for a counter rotating dual rotor horizontal axis marine current turbine used a mechanical oil seal coupling that caused mechanical losses when water entered through small gaps at the shaft. A new magnetic coupling assembly eliminates the need for a shaft to connect physically with the internal mechanisms and is water tight. This reduces mechanical losses in the system and the effect on the dual rotor performance is presented in this paper.

Effects of Damping Plate and Taut Line System on Mooring Stability of Small Wave Energy Converter

Ocean wave energy can be used for electricity supply to ocean data acquisition buoys. A heaving buoy wave energy converter is designed and the damping plate and taut line system are used to provide the mooring stability for better operating conditions. The potential flow assumption is employed for wave generation and fluid structure interactions, which are processed by the commercial software AQWA. Effects of damping plate diameter and taut line linking style with clump and seabed weights on reduction of displacements in 6 degrees of freedom are numerically studied under different operating wave conditions. Tensile forces on taut lines of optimized mooring system are tested to satisfy the national code for wire rope utilization.

Parametric Numerical Study on the Performance of Helical Tidal Stream Turbines

Abstract − The characteristics of a helical turbine to be used for tidal stream energy conversion have beennumerically studied with varying a few design parameters. The helical turbines were proposed aiming atmitgating the well known poor cut-in characteristics and the structural vibration caused by the fluctuatingtorque, and the basic concept is introducing some twisting angle of the vertical blade along the rotation axisof the turbine. Among many potential controling parameters, we focused, in this paper, on the twisting angleand the height to diameter ratio of the turbine, and, based on the numerical experiment, We tried to proposea configuration of such turbine for which better performance can be expected. The three-dimensional unsteadyRANS equations were solved by using the commercial CFD software, FLUENT with k- ω SST turbulencemodel, and the grid was generated by GAMBIT. It is shown that there are a range of the twisting angleproducing better efficiency with less vibration and the minimum height to diameter ratio above which the efficiencydoes not improve considerably.Keywords: Vertical Axis Tidal Stream Turbine(수직축 조류발전 터빈), Computational Fluid Dynamics(전산유체역학), Twisting Angle(비틀림각), Height to Diameter Ratio(길이 직경 비), Tip-Speed Ratio(날개속도비), Helical Turbine(헬리컬 터빈)

Analysis of Flow Field Including Bodies Steadily Moving Around the Free-surface by FLUENT-VOF Method

VOF method is known as one of the most effective numerical techniques handling two-fluid domains of different density simultaneously. Present study deals with the numerical analysis of flow field around bodies steadily moving near free-surface using FLUENT-VOF method. Validations were made by applying to three typical examples ; 2-D submerged hydrofoil, 3-D surface piercing body and container ship. It was found that the commercial software, FLUENT, is useful in practical use, and VOF method is capable of handling free-surface around moving bodies although discussions are limited to the analysis in qualitative sense.