• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.9
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• pp.826-834
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• 2007

A 7K60MC-S low speed diesel engine in a power plant has frequently experienced high vibration since the unit completed construction works. Up to date, no fundamental vibration solutions were reached. Hence, several vibration tests and analyses were conducted to identify the root cause of this high vibration and to suggest the optimal countermeasures for diesel engine. The 9.25 Hz and 25.4 Hz vibrations have been observed on main body during operation. The magnitude of engine upper structural vibration is generally similar in horizontal transverse direction. However, differences in the 'Fore' and 'After' vibration magnitude with the same vibration phase angle at 9.25 Hz occur due to the explosion pulsations of 7 cylinders and the Inertia momentum added by the SCR (selective catalytic reduction) duct system. It was analyzed that the excess structural vibration occurred when the natural frequency of engine body is affected by the exciting sources due to the explosion pressure and the discharge pulsation of the seven cylinders in resonance range.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.591-595
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• 1997

In analysis of piping vibration of petrochemical plant, the forcing functions mainly depend upon the equipment working mechanism and vibration resources in the piping systems. In general, harmonic function is used for the system with rotary equipments. Mechanical driving frequencies, wave functions, and response spectrum are used for reciprocating compressors, surge vibration of long transfer piping, and seismic/wind vibration, respectively. In this study, for the spray injection case inside the pipe, forcing function was modeled, in which two different fluids are distributed uniformly. To confirm the results, the scheme used for the forcing function was applied for real piping system. The vibration mode of the real system was consistent with the 4th mode obtained by simulation using the forcing function formulated in this study.

• Journal of the Korea Society for Simulation
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• v.10 no.4
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• pp.1-10
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• 2001

For the simulation of piping vibrations in petrochemical plants, forcing functions mainly depend upon the equipment working mechanism and vibration resources in the piping systems. In general, harmonic function is used to simulate rotary equipment. Mechanical driving frequencies, wave functions, and response spectrum are used to simulate reciprocating compressors, surge vibration of long transfer piping, and seismic/wind vibration, respectively. In this study, the general suggestions for forcing functions were reviewed and proposed the forcing function to simulate the spray injection system inside the pipe in which two different fluids are distributed uniformly. To confirm the results, the scheme was applied for a real piping system. The vibration mode of the real system was consistent with the 4th mode (26.725 Hz) obtained by simulation using the forcing function presented in this study.

• Korean Journal of Optics and Photonics
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• v.17 no.6
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• pp.548-555
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• 2006

We investigate the effect of the reflectivity of both facets and the phase of a phase tuning section on the self-pulsation (SP) characteristics of multisection index-coupled (IC) DFB lasers composed of two index-coupled DFB sections and a phase tuning section between them in terms of yield. In the case of weak coupling strength, as the reflectivity of both facets increases, the effect of reflected fields from both facets and the other DFB section on the mode characteristics of one DFB section increases. Thus the number of mode hoping increases and yield decreases for the variation of phases of both facets. In the case of strong coupling strength, as the reflectivity of both facets increases, the spatial hole burning effect increases, so that the yield decreases. The maximum yield and the range of the phase of a phase tuning section with yield more than 40% decrease as the facet reflectivity increases irrespective of coupling strength. As the coupling strength increases, the variation of yield for the variation of the phase of a phase tuning section increases and the variation of the phase of a phase tuning section with the maximum yield for the variation of the reflectivity of both facets decreases. The yield characteristics of the cases with the coupling strengths of 2 and 3 are better than those with the coupling strengths of 1.2 and 4.

• Journal of Astronomy and Space Sciences
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• v.19 no.3
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• pp.187-196
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• 2002

We performed CCD photometric observations of the eclipsing binary Y Cam with a pulsating component, for 16 nights from November 2000 to May 2001 using a V filter attached to the 61-cm reflector at Sobaeksan Optical Astronomy Observatory. Our V light curve and Broglia & Marin's (1974) BV ones were analyzed with Mode 2 for a detached Roche model as well as Model 5 for a semi-detached one in the Wilson-Devinney code. From the analysis, we found the following results: 1) It is hardly discernible from only light curve synthesis which model between the detached and semi-detached ones is a real Roche model of Y Cam. 2) There exist the third light of about 2% and 3% in B and V light curves of Y Cam, respectively. 3) The light curve solution is immune from the light variation due to the pulsation of the primary component of Y cam. However, the detached model rather than the semi-detached one has slightly better fitted to the observations which were get rid of the pulsation effect. 4) The absolute dimensions of Y Cam were calculated for two Roche models.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.453-458
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• 2000

The paper describes a study of the variation of the NO production emitted from turbulent propane flames established on a practical combustor where a primary and a secondary fuel lines are installed. The flowrate of the secondary fuel is pulsated or added in addition to that of the primary fuel which constrantly flows to the nozzle of the burner. Two modes depending on the positions of supplying the secondary fuel are performed; one is for its position to be placed at the center of the primary fuel tube and the other around the stabilization baffle. The mean concentrations of gas species, $O_2,\;Co\;CO_2,\;NO$, and HC(unburnt hydrocarbones) have been measured at the exit of the combustor. As equivalence ration $({\Phi})$ is increased the profile of the NO concentration on the latter mode rises slowly less than that on the former one. In the range of ${\Phi}=0.5$ to 0.54 the NO production is reduced by about 35% more on the latter mode than on the former one. The influence of pulsating the secondary fuel on the variation of the NO concentration doesn't appear at both modes.

• Journal of The Korean Astronomical Society
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• v.23 no.1
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• pp.1-13
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• 1990

New uvby photoelectric photometry was carried out for a $\delta$ Scuti variable, HR1170. By applying the Fourier method and the linear least square method, three frequencies were derived: $f_1=10.06134c/d$ ($P_1=0.^d0994$). $f_2=11.91754c/d$ ($P_2=0.^d0839$). $f_3=18.96776c/d$ ($P_3=0.^d0527$). From the observed pulsational constants and from the phase difference and amplitude ratios for color(b-y) and magnitude y. three different pulsation modes (n, l) of $f_1(0,0)$, $f_2(1,2)$, $f_3(3,2)$ are deduced, indicating the existence of nonradial mode in HR1170. Some physical parameters indicate that HR1170 is evolving at the stage of H-shell burning.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.51 no.12
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• pp.676-681
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• 2002

This paper presents the implementation and experimental investigation of sensorless speed control for a variable-speed PMSM(Permanent Magnet Synchronous Motor) in super-high speed compressor operation. The proposed control scheme consists of two different sensorless algorithms to guarantee the reliable starting operation in low speed region and full torque characteristics using the vector control in high speed region. An automatic switching technique between two control modes is proposed to minimize the speed and torque pulsation during the switching instant of control mode. A testing system of 3.3㎾ PMSM has been built and 90% load test results at 7000r/min are presented to examine the feasibility of proposed sensorless control scheme.

• Korean Journal of Optics and Photonics
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• v.18 no.5
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• pp.323-332
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• 2007

The effect of the reflectivity of both facets and the phase of a phase tuning section on the self-pulsation (SP) characteristics of multisection complex-coupled (CC) DFB lasers is investigated in terms of yield. The lasers are composed of two CC DFB sections and a phase tuning section between them. As the coupling strength and the coupling ratio (CR) decrease, the effect of the reflected fields from both facets and the other DFB section on the mode characteristics of one DFB section increases, so that the yield decreases. As the facet reflectivity increases, the maximum yield and the range of the phase of a phase tuning section with yield more than 60% decrease independent of the coupling strength and CR. The yield characteristics of CR=0.2 are better than those of CR=0.1 with the same coupling strength due to the larger complex coupling effect. The case with ${\mid}{\kappa}L{\mid}=3$ and CR=0.2 shows best yield characteristics among the cases considered in this work.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.311-315
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• 2000

A numerical investigation is made of time-dependent buoyant convection in a square of a non-Boussinesq fluid. The density-temperature$({\rho}-T)$ relation is modeled by a quadratic function, with the maximum density ${\rho}_M$ at temperature $T_M$. The horizontal walls of the square are insulated, and a pulsating temperature $T_H=T_M+{\Delta}T'\;sin({\omega}{\tau})$ is imposed on the hot vertical sidewall. The temperature at the cold wall $T_c$ is constant. Extensive numerical solutions to the governing Navier-Stokes equations are portrayed. Resonance is identified by monitoring the amplitude of the mid-plane Nusselt number, $A(Nu^*)$. The primary resonance frequency is found by matching ${\omega}$ to the nondimensional basic mode $N_1$ of internal gravity oscillations. Due to the quadratic$({\rho}-T)$ relationship, the effective pulsation frequency for density, $2{\omega}$, is meaningful, which brings forth the secondary resonance frequency, i.e., $2{\omega}=N_1$