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Choi H.-J.,Korea University | Zullah M.A.,Green and Industrial Technology Center | Roh H.-W.,IVAIGD3 Ltd. | Ha P.-S.,K water Resources Corporation | And 2 more authors.
Renewable Energy | Year: 2013

Conventionally assessing of turbine performance was done by conducting model experiments which at times become costly and time consuming for several design alternatives in design optimization. Recently, computational fluid dynamics (CFD) has become a more cost effective tool for predicting detailed flow information in turbine space to enable the selection of the best design. With the growth of computational mechanics, the virtual hydraulic machines are becoming more and more realistic to get minor details of the flow, which are not possible in model testing. The inverse design technique and fully 3-dimensional flow simulations were performed early to manufacture the newly developed runner. It allows a quick and efficient improvement and optimization of turbine components. The system has been applied to the optimization of a Francis turbine runner for a turbine replacement project. In present work, 3D turbulent real flow analyses in hydraulic Francis turbine have been carried out at four guide vane opening at constant rotational speed using Ansys CFX computational fluid dynamics (CFD) software. The newly developed runner from reverse engineering and CFD results show an enhanced performance. The average values of flow parameters like velocities and flow angles at the inlet and outlet of runner, guide vane and stay vane of turbine are computed to derive flow characteristics. The aim was to analyze the flow behavior and pressure distribution to further fine-tune the whole numerical experiment to achieve the level of accuracy necessary for the concept design of a revitalized turbine. The obtained results are in good agreement with the in site experiments, especially for the characteristic curve. © 2012.

Kim S.-J.,Mokpo Maritime University | Kim S.-K.,Seoul National University of Science and Technology | Park J.-C.,Green and Industrial Technology Center
Transactions of Nonferrous Metals Society of China (English Edition) | Year: 2012

To improve the durability of underwater rotating products, the corrosion characteristics in harsh marine environment were evaluated through various electrochemical experiments on the Al2O3-3TiO2 and CoNiCrAlY coating layers by atmospheric pressure plasma spray coating process. By evaluating the corrosion resistance of these materials, their applicability to environmentally friendly power generation equipment such as blades of tidal current turbines was examined. According to the Tafel analysis for micro-areas including the coating layer, the coating/metal interlayer and the base metal, the Al2O3-3TiO2 coating layer and the CoNiCrAlY coating layer show markedly lower corrosion current density than the base metal. The corrosion current density of the CoNiCrAlY coating layer (9.75316×10-8 A/cm2) is about 1.6 times more than that of the Al2O3-3TiO2 coating layer (6.13139×10-8 A/cm2). © 2012 The Nonferrous Metals Society of China.

Kim B.,Green and Industrial Technology Center | Kim W.,Green and Industrial Technology Center | Lee S.,Green and Industrial Technology Center | Bae S.,Green and Industrial Technology Center | Lee Y.,Korea University
Renewable Energy | Year: 2013

In this research, we developed software for designing the optimum shape of multi-MW wind turbine blades and analyzing the performance, and it features aerodynamic shape design, performance analysis, pitch-torque analysis and shape optimization for wind turbine blades. In order to verify the accuracy of the performance analysis results of the software developed in this research, we chose the 5 MW blade, designed by NREL, as the comparison model and compared with the analysis results of well known commercial software (GH-Bladed). The calculated performance analysis results of GH-Bladed and our software were consistent in all values of CP in all λ ranges. Also, to confirm applicability of the optimum design module, the optimum design of the new 5 MW blade was performed using the initial design data of the comparison model and found that solidity was smaller in our design even though it produced the same output and efficiency. Through optimization of blade design, efficiency increased by 1% while the thrust coefficient decreased by 7.5%. © 2012 Elsevier Ltd.

Lee K.-S.,Green and Industrial Technology Center | Park R.-S.,University of Ulsan
International Journal of Offshore and Polar Engineering | Year: 2012

The main object of this research is to minimize the shock effects which frequently result in fatal damage to the windmeasuring met mast after impact with a service boat. The collision between wind-measuring met mast and service boat is generally a complex problem, and it is often impractical to perform rigorous finite element analyses to include all effects and sequences during the collision. This paper focuses on the structural behaviors of the wind-measuring met mast. A significant part of the collision energy is dissipated in terms of strain energy, and the contribution from the elastic strain can normally be neglected. On applying the impact force of a service boat to the wind-measuring met mast, the maximum acceleration, internal energy and plastic strain are calculated for each load case using the finite element method. LS-dyna, a commercial explicit finite element code from ANSYS software, is used to produce a finite element model and analyze the nonlinear responses of the met mast due to the service boat collision. A parametric study is carried out by changing design variables of the service boat's velocity and the thickness of the wind-measuring met mast. Three types of materials for rubber fenders are taken into account where Mooney-Rivlin coefficients are determined based on the experimental data. It is assumed that the effect of the wave-induced vertical motion of a service boat is negligible. It is concluded that this paper provides a designing process used for rubber fenders considering a service boat impact. © The International Society of Offshore and Polar Engineers.

Kim B.-H.,Korea Maritime and Ocean University | Wata J.,Korea Maritime and Ocean University | Zullah M.A.,Green and Industrial Technology Center | Ahmed M.R.,University of The South Pacific | Lee Y.-H.,KMOU
Renewable Energy | Year: 2014

Experiments and several numerical studies were done on a power-take off system of a novel floating wave energy convertor. The wave energy convertor utilizes the changes in surface elevation of the waves to cause a column of water to rise and fall periodically in the caisson which creates a bi-directional flow. A cross flow turbine within the device uses this bi-directional flow to rotate in one direction. A 6 DOF ocean simulator was used to conduct experiments on the PTO system at a model to prototype scale of 1:3, for no-load conditions and loaded conditions. In the experiment, the parameters like pitching angles of the device, moment of inertia on the shaft, wave periods and rotational speeds of the turbine were varied. It was found that for all pitching angles, the device had optimum response at a wave period of 3s. A moment of inertia of 0.053kgm2 was found to be appropriate for all test cases. Peak hydraulic efficiencies between 35% and 45% were obtained for the range of 40-50RPM for most test cases. Particle image velocimetry (PIV) tests then done to document and investigate the flow around the turbine and the inlet and exit nozzles. A commercial CFD software was used to carry out the numerical calculations and to observe the internal flow. Finally, a floating body simulation was conducted on to calculate the motion of the device at sea and thus calculate the overall performance of the device. © 2014.

Bang H.-J.,Korea Institute of Energy Research | Kim H.-I.,Korea Advanced Institute of Science and Technology | Lee K.-S.,Green and Industrial Technology Center
International Journal of Precision Engineering and Manufacturing | Year: 2012

This paper introduces a fiber Bragg grating (FBG) based arrayed sensor system for use in the measurement of strain and bending deflection of an 1. 5 MW wind turbine tower, and describes the results of field tests of structural monitoring of turbine start and feathering load conditions. A wavelength division multiplexing (WDM) FBG interrogator was developed with a spectrometer-type demodulator based on a linear photo detector for high-speed strain sensing. Real-time shape estimation of the wind turbine tower was accomplished using strain data gathered by surface mounted fiber Bragg grating sensors. The finite element model of the wind turbine tower was created and the displacement-strain transformation (DST) matrix on the basis of the modal approach was obtained. To monitor the dynamic structural behavior of the wind turbine, 10 FBG sensors were arrayed and installed on the inner surface of the tower located at the primary wind direction. The time histories of the strain were gathered using the FBG sensors and the deflections of the tower top position were simultaneously transformed using the DST matrix. Finally, the full deflection shapes of the tower were successfully estimated using arrayed FBG sensors. © 2012 Korean Society for Precision Engineering and Springer-Verlag Berlin Heidelberg.

Lee K.-S.,Green and Industrial Technology Center | Bang H.-J.,Korea Institute of Energy Research
International Journal of Precision Engineering and Manufacturing | Year: 2012

A method to evaluate the structural safety of lateral buckling load is presented, using FEM analysis for a wind turbine tower with a thin circular wall. Europe, the U.S., and Japan already have long histories of research into wind power due to its high efficiency. The tower structure that supports a wind turbine is one important research area. There are three types of tower that vary by structural composition: a cylindrical tower with a circular cross-section, a jacket tower with a truss structure, and a hybrid tower. This paper investigates an accident involving a 600kW wind turbine that occurred in JeJu, Korea in October of 2010. The results from a numerical analysis are compared with the actual collapse mode observed at the accident. Some buckling modes and wind speeds at which non-linear buckling response occurs are predicted via the arc-length method for a land-based cylindrical stationary tower. The evaluation method is used accident (experiment), analytical, linear and nonlinear finite element method (beam and shell) to analyze the result of predicted buckling load of tower. The result of nonlinear FEM shell model was found to exhibit similar behavior to the accident situation during buckling. It is concluded that this paper provides buckling analysis process and method used for the slender shell structures: the predicted buckling load and analysis methodology. In this paper, The results from the numerical estimation show good agreement with those of the analytical calculation, indicating that the arc-length method effectively improved the convergence. We found out buckling limit load of the accident wind turbine tower and wind speed at buckling point. The result of nonlinear FEM shell model was found to exhibit similar behavior to the actual accident (experiment) situation during buckling. The presented buckling evaluation method will be useful for both static design and dynamic performance evaluation of land-based wind turbines, as well as sea-based wind turbines. © KSPE and Springer 2012.

Kim B.-S.,Green and Industrial Technology Center | Bae S.-Y.,Green and Industrial Technology Center | Kim M.-K.,Green and Industrial Technology Center | Kim W.-J.,Green and Industrial Technology Center | Lee S.-L.,Green and Industrial Technology Center
Proceedings of the International Offshore and Polar Engineering Conference | Year: 2012

This research represents the results of performance prediction and structural safety evaluation of 50-KW tidal turbine rotor assembly. Unsteady CFD simulation of the rotor assembly was performed to predict the performance of rotor assembly, and a cavitation model was applied with consideration of underwater operating conditions. Flow analysis result showed that the average power was 47.87kW at an extreme tidal velocity of 6 m/s. Moreover, creations and destructions of rotating cavitations were also observed near the blade. The structural safety of the rotor assembly was evaluated by unidirectional FSI method. The analysis results showed that the minimum safety factor of the rotor assembly was 3.76. From the result, it was concluded that the rotor assembly had sufficient structural safety at an extreme operating condition. Copyright © 2012 by the International Society of Offshore and Polar Engineers (ISOPE).

Ahn N.,Sejong University | Lee K.,Green and Industrial Technology Center
Structural Engineering and Mechanics | Year: 2011

Sandwich elements have high flexural rigidity and high strength per density. They also have excellent anti-vibration and anti-noise characteristics. Therefore, they are used for structures of airplanes and high speed ships that must be light, as well as strong. In this paper, the Reissner-Mindlin's plate theory is studied from a Hamilton's principle point of view. This theory is modified to include the influence of shear deformation and rotary inertia, and the equation of motion is derived using energy relationships. The theory is applied to a rectangular sandwich model which has isotropic, asymmetrical faces and an isotropic core. Investigations are conducted for five different plate thicknesses. These plates are identical to the sandwich plates currently used in various structural elements of surface effect ships (SES). The boundary conditions are set to simple supports and fixed supports. The elastic and shear moduli are obtained from the four-point bending tests on the sandwich beams.

Kim B.,Green and Industrial Technology Center | Kim W.,Green and Industrial Technology Center | Bae S.,Green and Industrial Technology Center | Park J.,New Products R and D Team | Kim M.,Green and Industrial Technology Center
Journal of Mechanical Science and Technology | Year: 2011

The rotor blade is an important device that converts kinetic energy of wind into mechanical energy. It affects power performance, efficiency of energy conversion, load and dynamic stability of a wind power generation system. This paper presents an aerodynamic design of 3 MW class blade using BEM and confirms that the design satisfies the initial design target by BEM and CFD analysis. To investigate the effects of radial flow at the inboard region, the result of static BEM analysis was compared with the result of CFD analysis. The result of quantitative comparison among thrust force, power coefficient and mechanical power depending on wind speed change is presented. Furthermore, design reference data such as pressure, streamline, torque and thrust force distribution on the blade surface is presented as well. © 2011 The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.

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