• 한국연소학회:학술대회논문집
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• 한국연소학회 2005년도 제31회 KOSCO SYMPOSIUM 논문집
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• pp.85-92
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• 2005

Oil-fired power plants usually use several burners and the combustion air is supplied to each burner through the complicated duct which is called windbox. A windbox should be designed to supply combustion air to each burner evenly but, due to the complicated duct shape, flow distribution in the windbox is unbalanced and uneven supplies of combustion air to each burner are induced by these unbalanced flow distribution in the windbox. These flow patterns tend to make flame unstable, increase the formation of pollutants and lower the overall combustion efficiency. To prevent these disadvantages, flow patterns in the windbox should be investigated for the uniform flow distribution. In this study, computational simulation method was used to investigate the flow distribution in the windbox and measured the velocities at the exit of burners in the real windbox to compare with CFD results. The results show two significant flow patterns. One is that the flow rates of each burner are different from each other and this means that all burners operate in different conditions of air to fuel ratio. The other is that the flow distribution at the exit of each burner is not axi-symmetric although the burner shape is axi-symmetric and this increases the pollutant products like CO.

• International Journal of Naval Architecture and Ocean Engineering
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• 제8권1호
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• pp.73-82
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• 2016

In order to extend the operational life of Underwater Moored Platforms (UMPs), a horizontal axis water turbine is designed to supply energy for the UMPs. The turbine, equipped with controllable blades, can be opened to generate power and charge the UMPs in moored state. Three-dimensional Computational Fluid Dynamics (CFD) simulations are performed to study the characteristics of power, thrust and the wake of the turbine. Particularly, the effect of the installation position of the turbine is considered. Simulations are based on the Reynolds Averaged Navier-Stokes (RANS) equations and the shear stress transport ${\kappa}-{\omega}$ turbulent model is utilized. The numerical method is validated using existing experimental data. The simulation results show that this turbine has a maximum power coefficient of 0.327 when the turbine is installed near the tail of the UMP. The flow structure near the blade and in the wake are also discussed.

• Journal of Power Electronics
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• 제17권1호
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• pp.76-87
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• 2017

Finite-set predictive current control (FS-PCC) is advantageous for power converters due to its high dynamic performance and has received increasing interest in multilevel inverters. Among multilevel inverter topologies, the cascaded H-bridge (CHB) inverter is popular and mature in the industry. However, a main drawback of FS-PCC is its large computational burden, especially for the application of CHB inverters. In this paper, an FS-PCC method based on a deadbeat solution for three-phase zero-common-mode-voltage CHB inverters is proposed. In the proposed method, an inverse model of the load is utilized to calculate the reference voltage based on the reference current. In addition, a cost function is directly expressed in the terms of the voltage errors. An optimal control actuation is selected by minimizing the cost function. In the proposed method, only three instead of all of the control actuations are used for the calculations in one sampling period. This leads to a significant reduction in computations. The proposed method is tested on a three-phase 5-level CHB inverter. Simulation and experimental results show a very similar and comparable control performance from the proposed method compared with the traditional FS-PCC method which evaluates the cost function for all of the control actuations.

• 한국전기전자재료학회논문지
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• 제21권10호
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• pp.954-960
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• 2008

The effects of elastic modulus coefficient and linear expansion coefficient of overhead distribution power line(ACSR $58 mm^2$) on sag behavior in distribution line have been investigated to clarify the difference between specification and experimental level. The elastic modulus coefficients of Al wire and steel wire were $5,182.6 kgf/mm^2,\;18,348.8 kgf/mm^2$, respectively Therefore, the computational composition elastic modulus coefficient of the power line was $7,063.5 kgf/mm^2$, while that of experimentally measured was $7681.1 kgf/mm^2$. As a result, we found that elastic modulus coefficient which was experimentally measured was higher than that of computational by 8.7 %. However, when planner designs the sag of disoibution line, the elastic modulus coefficient of power line $8,400 kgf/mm^2$ should be generally adopted. These two different using values lead to the sag difference of 0.62 m. The other results will be discussed.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2010년 춘계학술대회논문집
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• pp.155-162
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• 2010

Recently, due to high oil prices and environmental pollution issues, interest of alternative energy development increases and the related research is widely conducted. Among those research activities the tidal stream power generation utilizes the tidal flow as its mechanical power resource and less depends on the environmental condition for installation and operation than other renewable energy resources. Therefore the amount of power generated is quite consistent and straightforward to predict. However, research on the tidal stream energy conversion turbine is rarely found. In the present study, two numerical methods were developed and compared for the open water Momentum Theory, which is widely used for wind turbines, was adopted. The moving reference frame method for Computational Fluid Dynamis solver were also used. Hybrid meshing was used for the complex geometry of turbines. The analysis results using each method were compared to figure out a better method for the performance prediction.

• 한국전산유체공학회지
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• 제15권4호
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• pp.1-8
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• 2010

This article describes the numerical investigation of turbulent blood flow in the stenosed artery bifurcation under periodic acceleration of the human body. Numerical analyses for turbulent blood flow were performed with different magnitude of periodic accelerations using a modified turbulence model which was considering drag reduction of non-Newtonian fluid. The blood was considered to be a non-Newtonian fluid which was based on the power-law viscosity. In order to validate the modified $k-{\varepsilon}$ model, numerical simulations were compared with the standard $k-{\varepsilon}$ model and the Malin's low Reynolds number turbulence model for power-law fluid. As results, the modified $k-{\varepsilon}$ model represents intermediate characteristics between laminar and standard $k-{\varepsilon}$ model, and the modified $k-{\varepsilon}$ model showed good agreements with Malin's verified power law model. Moreover, the computing time and computer resource of the modified $k-{\varepsilon}$ model were reduced about one third than low Reynolds number model including Malin's model.

• 동력기계공학회지
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• 제18권3호
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• pp.59-65
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• 2014

The computational fluid dynamics was carried out to evaluate turbulent models on the swirling flow of a gun-type gas burner(GTGB) according to the mesh size. The commercial SC/Tetra software was used for a steady-state, incompressible and three-dimensional numerical analysis. In consequence, the velocity magnitude from the exit of a GTGB and the flowrate predicted by the turbulent models of MP k-${\varepsilon}$, Realizable k-${\varepsilon}$ and RNG k-${\varepsilon}$ agree with the results measured by an experiment very well. Moreover, the turbulent kinetic energy predicted by the turbulent model of standard k-${\varepsilon}$ with mesh type C only agrees with the experimental result very well along the radial distance. On the other hand, the detailed prediction of the information of swirling flow field near the exit of a GTGB at least needs a CFD analysis using a fairly large-sized mesh such as a mesh type C.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2002년도 춘계 학술대회논문집
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• pp.140-145
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• 2002

The purpose of this 3-D numerical simulation is to calculate and examine a 500 kW Horizontal Axis Wind Turbine (HAWT) power performance and compare to calculation data(BEM method) from Delft University. The experimental approach, which has been the main method of investigation, appears to be reaching its limits, the cost increasing relate with the size of wind turbines. Hence, the use of Computational Fluid Dynamics (CFD) techniques and Navier-Stokes Solvers are considered a very serious contender. We has used the CFD software package CFX-TASC flow as a modeling tool to predict the power performance of a wind turbine on the basis of its geometry and operating data. The wind turbine with 40m diameters rotor, it was scaled to compare with the calculation data from delft university. The HAWT, which has eight-rpm variations are investigated respectively. The pitch angle is $+0.5^{\circ}$ and wind speed is fixed at 5m/s. The tip speed ratio (TSR) of the HAWT ranging from 2.89 to 9.63.

• 한국전산유체공학회지
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• 제16권3호
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• pp.75-81
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• 2011

The turbo blowers having large power capacity are generally composed of the variable inlet guide vane, the impeller and the variable diffuser. In the present study, the effect of the stagger angles on the aerodynamic performances has been investigated by CFD methods. The design specifications of the reference model having 400kW power were given as 7.43kg/s of mass flow rate, 1.66 of pressure ratio with 12000rpm of impeller rotating speed. As the first simulation parameter, the diffuser vane angle was varied in the range of ${\pm}$20 degree from the initial-design point. The inlet guide vane angles, as the second one, was changed in the range of ${\pm}$40 degree from the initial-design point. The commercial Navier-Stokes solver, ANSYS-CFX, was applied to solve the three-dimensional unsteady flow fields inside the turbo blower. Through the numerical results, the desirable setting angles were proposed to fit the best performance to the variation of the operating conditions.

• Journal of Power Electronics
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• 제19권6호
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• pp.1429-1439
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• 2019

Buck-Boost LLC (BBLLC) converters based on a PWM + phase control strategy are good candidates for high efficiency, high power density and wide input range applications. Nevertheless, they suffer from large computational complexity when it comes to calculating the optimal phase for ZVS of all the switches. In this paper, a method is proposed for a microcontroller unit (MCU) to calculate the optimal phase quickly and accurately. Firstly, a 2-D lookup table of the phase is established with an index of the input voltage and output current. Then, a bilinear interpolation method is applied to improve the accuracy. Meanwhile, simplification of the phase equation is presented to reduce the computational complexity. When compared with conventional curve-fitting and LUT methods, the proposed method makes the best tradeoff among the accuracy of the optimal phase, the computation time and the memory consumption of the MCU. Finally, A 350V-420V input, 24V/30A output experimental prototype is built to verify the proposed method. The efficiency can be improved by 1% when compared with the LUT method, and the computation time can be reduced by 13.5% when compared with the curve-fitting method.