• Proceedings of the KIEE Conference
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• 1995.07a
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• pp.171-173
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• 1995

Slot field harmonics exist in air gap due to inevitable slot constructure of induction motors. They give rise to noise by the electromagnetic vibration and mechanical pulsation. We calculate the slot field harmonics for varying the ratio of slot width vs teeth pitch using the carter's coefficent. We computate the flux density in air gap by FEM(Finite Element Method) and analyze it in frequency domain using DFT(Discrete Fourier Transform). We develop the new algorithm mixing FEM with DFT.

• Applied Chemistry for Engineering
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• v.35 no.2
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• pp.107-114
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• 2024

In order to produce high-yield pitch-based activated carbon, pitch was synthesized by blending pyrolysis fuel oil (PFO) and coal-tar. Pitch was synthesized by varying the amount of coal-tar from 0~20% compared to PFO and reacting at 380~420 ℃ for 3 h. The synthesized pitch had a softening point between 80 and 260 ℃, and yields ranged from 10 to 40%. At all synthesis temperatures, as the coal-tar blending ratio increased, the yield increased and the softening point decreased. After considering the selected pitches (softening points: 230~260 ℃), pitches containing coal-tar were more volatile at a low boiling point and had a higher residual carbon content. This is a difference in the composition of coal-tar and PFO, and it was con- firmed that coal-tar has a lot of aromatics and PFO has a lot of aliphatics. The selected pitch was heated to 950 ℃ in a tubular reactor and physically activated with steam for 1 hour. Activated carbon containing coal-tar showed higher yield and microporosity compared to only PFO. In this study, the effect of increasing activated carbon yield by blending pitch raw materials was confirmed, and the physical activation characteristics according to the coal-tar mixing ratio were examined.

• Journal of Advanced Marine Engineering and Technology
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• v.34 no.1
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• pp.76-83
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• 2010

The Characteristics of the flow field through cylinders with in-line and staggered arrangements were calculated by vortex method. Vortex distributions and velocity profiles around the cylinders with in-line and staggered arrangements were simulated at the pitch ratio of Pt/D=1.25~2.0 and Reynolds number of Re=$4.0{\times}10^1{\sim}4.0{\times}10^4$. As the results the vortices of clockwise at the upper separation point cylinder and the vortices of anticlockwise at the lower separation point of each cylinder were generated at both in-line and staggered arrangements. The generation of the reverse flow in the rear region of the cylinders was caused by the pitch ratio and Reynolds number, the boundary region was at the pitch ratio of Pt/D=1.5 and Reynolds number of Re=$4.0{\times}10^2{\sim}4.0{\times}10^3$ in case of in-line arrangement and was at the pitch ratio of Pt/D=1.4 and Reynolds number of Re=$4.0{\times}10^1{\sim}4.0{\times}10^2$ in case of staggered arrangement.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.6
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• pp.1603-1612
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• 1990

An experimental study is conducted to investigate the fluid flow and heat transfer around tubes arranged in line. All measurements are performed at Reynolds number 1.58*10$^{4}$ with varing tube spacings from the small pitch ratio(L/D=1.25) to the large pitch ratio(L/D=3.0). Mean static pressures and mean temperatures of the surface of tubes and mean velocities and turbulent intensities in tube banks are measured. The flow patterns and the characteristics of heat transfer are strongly influenced by the tube spacings. Especially, in the case of very small spacings(L/D=1.25), the flow between neighboring tubes becomes very stagnant and the heat transfer decreases. In the case of each tube spacing, the characteristics of heat transfer around the 3rd, the 4th and the 5th tubes are nearly similar to one another, because the flow around tubes becomes stable at the 3rd tubes. The local heat transfer has the peak value near the reattachment point which has the peak value of pressure, but the local heat transfer for the 2nd tube of L/D=1.25 without reattaching has the peak value at .theta.=75.deg.. For each pitch ratio, the mean heat transfer increases gradually toward the downstream tubes, because the oncoming flow through neighboring tubes comes closer to the forward and rear surfaces of the tube and the turbulent intensity becomes larger in the downstream direction.

• Ocean Systems Engineering
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• v.8 no.1
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• pp.79-99
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• 2018

The effects of BPC (blade pitch control) on FOWT (floating offshore wind turbine) motions and generated power are investigated by using a fully-coupled turbine-floater-mooring simulation program. In this regard, two example FOWTs, OC4-5MW semi-submersible FOWT and KRISO four-3MW-units FOWT, are selected since the numerical simulations of those two FOWTs have been verified against experiments in authors' previous studies. Various simulations are performed changing BPC natural frequency (BPCNF), BPC damping ratio (BPCDR), and wind speeds. Through the numerical simulations, it was demonstrated that negative damping can happen for platform pitch motions and its influences are affected by BPCNF, BPCDR, and wind speeds. If BPCNF is significantly larger than platform-pitch natural frequency, the pitch resonance can be very serious due to the BPC-induced negative-damping effects, which should be avoided in the FOWT design. If wind speed is significantly higher than the rated wind velocity, the negative damping effects start to become reduced. Other important findings are also given through systematic sensitivity investigations.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.8 no.1
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• pp.120-139
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• 1996

Experiment was performed to study the heat transfer characteristics in 27 kinds of 15 : 1 scale models of multi-louverred fin heat exchangers with a wide range of variables(R $e_{Lp}$ =100~1, 800, $L_p$/F$p$=0.3~0.9, $\theta$=20$^{\circ}$~40$^{\circ}$). Thermofoil heaters were used to heat the louver fins and the local average Nusselt number for each louver in the louver array was obtained at constant wall temperature conditions. Correlations are developed to predict the heat transfer characteristics and drag coefficients. Generally, the heat transfer characteristics in the multi-louvered fins is shown to be similar to those of the laminar heat transfer on a flat plate. As the Reynolds number, the louver pitch to fin pitch ratio$L_p$/F$p$and the louver angle($\theta$) increase respectively, the average Nusselt number increases, but the variation of average Nusselt number as a function of the louver angle is smaller than that as a function of the louver pitch to fin pitch ratio. In case of$L_p$/F$p$ <0.5, the average Nusselt number of the 3rd louver is especially lower than the others, it is expected that it is due to the flow structure such as a recirculation flow and a flow separation.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.5
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• pp.40-45
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• 1995

The kinematical relationship of bevel gearsets lies at the root of the gear design. As the demand on precision bevel gears is increased in the related industries, the kinematic analysis of a pair of sperical involute bevel gears needs to be exactly evaluated for the computer aided design. Pitch cone angles of bevel gearsets have been calculated under the assumption that the geared system is equivalent to a coned roller system without slipping. But this kinematical model involves some errors in the value of the ratio of angular velocity. In this paper, the ratio of the angular velocity is exactly derived, based on the perfect involute tooth surface. Four nonlinear equations representing the kinematical relationships are numerically solved to obtain the pitch and base cone angles. The ratios of angular volocities according to pressure and shaft angles are calculated and compared with those of the approximate gear model.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.3
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• pp.375-383
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• 2008

This paper deals with reduction and analysis of cogging torque for permanent magnet synchronous generators with multi-pole rotor for wind power applications. Open-circuit field solutions are derived using a magnetic vector potential and a two-dimensional (2-d) polar coordinate systems. On the basis of derived open-circuit field solutions and 2-d permeance functions, we also derive open-circuit field solutions considering stator slotting effects. By using open-circuit field solutions considering stator slotting effects and energy variation methods, this paper analytically predicts the cogging torque considering skew effects. All analytical results are shown in good agreement with those obtained from finite element (FE) analyses. In order to reduce the cogging torque, by predicting the variation of the cogging torque according to pole arc/pitch ratio using analytical and FE methods, pole arc/pitch ratio which makes the cogging torque minimum are determined. However, we confirm that measured value for cogging torque of the PMG with determined pole arc/pitch ratio is twice higher than predicted value. Therefore, the reason for an error between measured and predicted cogging torque is discussed in terms of a shape of PMs and is proved experimentally.

• Journal of the Korean institute of surface engineering
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• v.50 no.6
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• pp.516-522
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• 2017

We report the growth of carbon nanotubes (CNT) on Invar-42 plates using coal tar pitch (CTP) by chemical vapor deposition (CVD) method. The solid phase CTP is used as an inexpensive carbon source since it produces a bunch of hydrocarbon gases such as $CH_4$ and other $C_xH_v$ by thermal decomposition over $450^{\circ}C$. The Invar-42 is a representative Ni-based ferrous alloy and can be used repetitively as a substrate for CNT growth because Ni and Fe are used as very active catalytic elements. We changed mixing ratio of carrier gases, argon and hydrogen, and temperature of growth region. It was found that the optimum gas ratio and temperature for high quality CNT growth are $Ar:H_2=400:400$ sccm and $1000^{\circ}C$, respectively. In addition, the carbon nanoball (CNB) was also obtained by just changing the mixing ratio to $Ar:H_2=100:600$ sccm. Finally, CTP can be employed as a versatile carbon source to produce various carbon-based nanomaterials, such as CNT and CNB.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.53 no.11
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• pp.753-759
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• 2004

This paper presents a modeling and simulation of a fuzzy controller for maximum power extraction of a grid-connected wind energy conversion system with a link of a rectifier and an inverter. It discusses the maximum power control algorithm for a wind turbine and proposes, in a graphical form, the relationships of wind turbine output, rotor speed, power coefficient, tip-speed ratio with wind speed when the wind turbine is operated under the maximum power control. The control objective is to always extract maximum power from wind and transfer the power to the utility by controlling both the pitch angle of the wind turbine blades and the inverter firing angle. Pitch control method is mechanically complicated, but the control performance is better than that of the stall regulation method. The simulation results performed on MATLAB will show the variation of generator's rotor angle and rotor speed, pitch angle, and generator output.