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Acharya N.,Korea Maritime and Ocean University | Kim C.-G.,Korea Maritime and Ocean University | Thapa B.,Kathmandu University | Lee Y.-H.,KMOU
Renewable Energy | Year: 2015

Exploitation of small hydropower sources requires the use of small turbines that combine efficiency and economy which can conveniently cater the power needs of rural and small communities. Cross-flow turbines are used widely in such micro hydropower plants due to their simple design, easier maintenance, low initial investment and modest efficiency. Also, because of their suitability under low heads, their efficient operation under a wide range of flow variations and ease of fabrication, cross-flow turbines have been extensively employed. The primary objective of this study is to numerically analyze the characteristics and the fluid flow in a cross-flow hydro turbine and to optimize its performance by geometrically modifying the several parameters. During the process, a base model was chosen, the design was modified simultaneously by varying the nozzle shape, changing the guide vane angle, varying the number of runner blades and simulations were carried out individually. Two phase (air & water at 25°C), steady state with SST turbulence model was selected in the commercial CFD code ANSYS CFX 13.0 for the numerical simulation. The design parameters included 10m head, 0.1m3/s flow rate and 642rpm rotational speed. The results obtained showed that the best efficiency obtained from the base nozzle was 63.67% which was geometrically modified that improved the turbine performance and the efficiency reached 76.60% (increase by 12.93%). Velocity distribution, pressure contours, output torque within the flow domain were also characterized. It was observed that the re-circulating flow region was reduced and also its pattern was varied. © 2015 Elsevier Ltd.

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.

Ahn J.-K.,MAN Group | So G.-B.,Korea Maritime and Ocean University | Lee J.-Y.,Korea Advanced Institute of Science and Technology | Lee Y.-H.,Korea Port Training Institute | And 2 more authors.
Journal of Institute of Control, Robotics and Systems | Year: 2014

In many industrial processes and operations, such as power plants, petrochemical industries and ships, shell and tube heat exchangers are widely used and probably applicable for a wide range of operating temperatures. The main purpose of a heat exchanger is to transfer heat between two or more medium with temperature differences. Heat exchangers are highly nonlinear, time-varying and show time lag behavior during operation. The temperature control of such processes has been challenging for control engineers and a variety of forms of PID controllers have been proposed to guarantee better performance. In this paper, a scheme to control the outlet temperature of a shell and tube heat exchanger system that combines the PID controller with feedforward control and anti-windup techniques is presented. A genetic algorithm is used to tune the parameters of the PID controller with anti-windup and the feedforward controller by minimizing the IAE (Integral of Absolute Error). Simulation works are performed to study the performance of the proposed method when applied to the process. © ICROS 2014.

Lee N.J.,Korea Maritime and Ocean University | Kim I.C.,Korea Maritime and Ocean University | Hyun B.S.,KMOU | Lee Y.H.,KMOU
Proceedings of the International Offshore and Polar Engineering Conference | Year: 2014

Global warming is one of the issues in the world mainly due to the burning of fossil fuels and so alternative energy is now paramount in the 21st century. In Korea, the tidal currents in the South western sea has a large range of currents that are available for tidal current power generation. Single rotor turbines can obtain a theoretical maximum power coefficient of 59.3%, whereas dual rotor can obtain a maximum of 64%. In this study, we investigated the performance and efficiency of a Counter-rotating current turbine by different front and rear blade angle by water velocity by using CFD and experimental methods. Copyright © 2014 by the International Society of Offshore and Polar Engineers (ISOPE).

Kim S.Y.,Korea Maritime and Ocean University | Kim B.H.,Korea Maritime and Ocean University | Lee Y.H.,KMOU
IET Conference Publications | Year: 2014

Wave power generator uses the surface water displacement as an energy source. The pitching motion of the device causes a column of water to rise and fall periodically in the double-hull housed caisson, creating a bi-directional flow. A cross-flow turbine uses this bi-directional flow for self-start and causes the rotation of turbine in a single direction. The turbine does not have direct contact with sea water, as the working fluid used is fresh water. So, the system is free from bio-fouling and hence easier to maintain. A small opening is provided in the system which serves to check the pressure built up inside the double-hull due to water motion. The power conversion system in this device is a buffered system in which the working fluid uses the wave energy to rotate the turbine, and then transfers energy to the generator. As we know, the numerical analysis using CFD requires a lot of time and resources thus to compensate this, MATLAB was used. Using predictable inner flow model, results obtained from both CFD and MATLAB were analyzed and compared. Similarly, PTO performance of the wave-power generator was also analyzed and compared for both CFD and MATLAB. The results obtained from this analysis can be further applied for various scale models.

Park J.-H.,Korea Maritime and Ocean University | Kim B.-J.,Korea Maritime and Ocean University | Lee N.-J.,Korea Maritime and Ocean University | Lee Y.-H.,KMOU
IET Conference Publications | Year: 2014

Renewable energy sources which are gaining popularity over conventional resources mostly produce intermittent power as they fall under the influence of natural phenomena as daily cycle or weather conditions. However, worldwide remarkable growth of electricity generation from renewable resources in the recent years has resulted in the decentralized production posing network load stability problems, which requires proper energy storage. Therefore, energy storage system can make more efficient utilization of renewable energies available and hence it will be more practical in application. This research work discusses about the energy storage system which comprises the concepts of combined pumped-storage hydro electricity and compressed air energy storage. The system consists of two tanks, one open tank to the air and one closed tank which stores water and compressed air using multistage pump. The energy of compressed air will be released to drive water which passes through the hydro turbine resulting in the generation of electricity when the grid power is insufficient. This study focuses on the CFD analysis on the closed tank of energy storage system during discharge.

Lee N.J.,Korea Maritime and Ocean University | Kim I.C.,Korea Maritime and Ocean University | Kim C.G.,KMOU | Hyun B.S.,KMOU | Lee Y.H.,Korea Maritime and Ocean University
Renewable Energy | Year: 2015

Among the various ocean energy resources in Korea, the tidal currents in the South western sea have a large potential for development tidal current power generation. The biggest advantage of tidal power is that it is not dependent on seasons or weather and is always constant. This makes power generation predictable and makes tidal power a more reliable energy source than other renewable energy sources. Marine current turbines convert the kinetic energy in tidal currents for power production. Single rotor turbines can obtain a theoretical maximum power coefficient of 59.3%, whereas dual rotor can obtain a maximum of 64%. Therefore by optimizing the counter rotating turbines, more power can be obtained than the single rotor turbines. In this study, we investigated the effect of varying the distance between the dual rotors on the performance and efficiency of a counter-rotating current turbine by using computational fluid dynamics (CFD) and experimental methods. It was found that the dual rotor produced more power than the single rotor. In addition, the blade gap distance affects the flow on the rear rotor blades as well as power output and performance of the turbine. The distance can be used a parameter for counter rotating turbine design. Finally, the numerical setup used for this study can be further used to evaluate the design of larger counter rotating blade designs. © 2014 Elsevier Ltd.

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