• 전기의세계
• /
• v.14 no.5
• /
• pp.20-27
• /
• 1965

There are several methods of speed control in induction motors. One of which is to change the frequency of source but was not used frequently because of the difficulty of frequency-change. Then, the development of frequency changer using semiconductor enables the method useful. In this paper the speed characteristics of mechanical output, secondary input torque and secondary power factor are described when the frequency of source and voltage which is proportional to the frequency of source in order to make the flux in the air gap in constant, are changed. The above characteristics are searched on the basis of the rated characteristics of the motor. Because the ratio of these is proportional to that of the secondary current or the square value of it. To get the ratio of the secondary current, a current circle diagram is introduced, and the magnitude of the ratio from this diagram is accurate and simple. Experimental results are in good agreement with theoretical predictions.

• The Transactions of the Korean Institute of Electrical Engineers B
• /
• v.49 no.8
• /
• pp.529-535
• /
• 2000

In this paper, a current control system of a single phase PWM AC/DC converter using a reduced-order Luenberger observer without source voltage sensors is proposed. The sinusoidal input current and unity input power factor are realised based on the estimated source voltage performed by the reduced-order Luenberger observer using actual currents and DC link voltage. The poles of the reduced-order Luenberger observer are placed in the left half plane of s-plane by the pole-placement method in order to acquire the stability of the observer. The magnitude and the phase of the estimated source voltage are used to accomplish the unity power factor. The proposed method is implemented by DSP(Digital Signal Processor). Experimental Results verify that the reduced-order observer estimates the source voltage without the estimation error and the control system accomplishes the unity power factor, and constant DC link voltage.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.16 no.8 s.113
• /
• pp.806-813
• /
• 2006

An important factor of vibration test using MAST(multi axial simulation table) system is the reliance of input excitation source. Generally the generation of input excitation source is obtained by the measured data on special road in proving ground. The measured data on special road have more exciting energy than the data of real fields, therefore the time and expense for test can be reduced. But the magnitude of input excitation source must be defined by comparison with the excited energy on real field. The object of this paper makes the data base of domestic roads for the definition of input excitation source which is obtained by the measured data on special road in proving ground. These real field data on domestic roads are analyzed by the power spectral density and interrelationship index.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2005.11a
• /
• pp.637-640
• /
• 2005

We propose a sound source localization method using the Head-Related-Transfer-Function (HRTF) to be implemented in a given platform. HRTFs contain not only the information regarding proper time delays but also phase and magnitude distortions due to diffraction and scattering by the shading object. Therefore, a set of HRTFs for any given platform provides a substantial amount of information as to the whereabouts of the source. In this study, we introduce new phase criterion in order to find the sound source location in accordance with the HRTF database empirically obtained in an anechoic chamber with the given platform. Using this criterion, we analyze the estimation performance of the proposed method in a household environment.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.12 no.5
• /
• pp.899-906
• /
• 2017

This paper proposes an inter-floor noise prevention system using an open-source controller. In the proposed system, Arduino which is a widely used open source controller analyzes sound signals and vibration signals with fast fourier transform. When the magnitude of the band-passed signal excesses the noise reference considering transmission loss of a panel or a wall, the system displays warning messages on an LCD module and a mobile device for users to be aware of the noise condition. In the experiment, the system has succeeded extracting and processing the band-passed signals between 130 Hz ~ 1040 Hz. When the magnitude of the extracted signal that is subtracted from the transmission loss exceeds 45 dB, the system has displayed the warning message on an LCD module and a mobile devicefor noise reduction.

• Journal of Environmental Science International
• /
• v.12 no.1
• /
• pp.23-34
• /
• 2003

Urban air quality is usually worse than that of rural counterpart. The contrasting atmospheric properties seem to be direct result of different urban-rural air pollutant emission. Hence, the emission estimation of air pollutants plays an important role to the atmospheric environmental management. The main purpose of this study is to find out the temporal and spatial distribution of air pollutant emission in Daegu area. For the study, the Daegu statistical yearbook and data of waste facilities and the report on traffic survey issued by Daegu metropolitan city and the statistical yearbook on the road capacity issued by the ministry of construction and transportation are used. Each item for the emission estimation is $SO_2$, CO, HC, $NO_x$, PM-10 from point, line and area source. The result were as follow; (1) The air pollutants with the highest amount of emission from the emission source is CO followed by $NO_x$, $SO_2$, PM-10, HC in descending order of magnitude. (2) The annually totaled air pollutant emission consists of 81%(73,185 ton/year) of line, 11%(9,589% ton/year) of area and 8%(7,445 ton/year) of point source in Daegu. Air polluant emission was mainly due to line sources. (3) High-emission of the air pollutants of line source appeared ariond Bukgu, Dalseonggun, Dongu and Seogu ; the areas with highway networks.

• The Journal of the Acoustical Society of Korea
• /
• v.34 no.5
• /
• pp.351-359
• /
• 2015

Typical underwater acoustic transducers detect only the magnitude of an acoustic pressure and they have the limitation of not being able to recognize the direction of the sound signal. Hence, the authors of this paper proposed a new vector sensor structure based on Tonpilz transducers that could detect both the magnitude and the direction of a sound pressure. In the proposed structure, the piezoceramic ring was divided into four segments, and proper combination of the output voltages of the segments in response to the external sound pressure could provide the information on the orientation of the sound source. In this paper, a Tonpilz transducer has been fabricated to have the proposed structure and its characteristics has been measured to confirm the validity of the proposed structure.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.17 no.6
• /
• pp.231-237
• /
• 2007

For an aspect ratio (transport length-to-width) of 5, Pr=3.34, Le=0.078, Pe=4.16, Cv=1.01, $P_B=50$ Torr, only thermally buoyancy-driven convection ($Gr=4.83{\times}10^5$) is considered in this study in spite of the disparity in the molecular weights of the component A ($Hg_2Cl_2$) and B which would cause thermally and/or solutally buoyancy-driven convection. The crystal growth rate and the maximum velocity vector magnitude are decreased exponentially for $3{\le}Ar{\le}5$, for (1) adiabatic walls and (2) the linear temperature profile, with a fixed source temperature. This is related to the finding that the effects of side walls tend to stabilize convection in the growth reactor. The rate for the linear temperature profiles walls is slightly greater than for the adiabatic walls far varied temperature differences and aspect ratios. With the imposed thermal profile, a fixed source region, both the rate and the maximum velocity vector magnitude increase linearly with increasing the temperature difference for $10{\le}{\Delta}T{\le}50K$.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.33 no.3
• /
• pp.257-263
• /
• 2013

Acoustic nonlinearity of surface waves is an effective method to evaluate the micro damage on the surface of materials. In this method, the $A_1$ (magnitude of the fundamental wave) and $A_2$ (magnitude of the second-order harmonic wave) are measured for evaluation of acoustic nonlinearity. However, if there is another source of second-order harmonic wave other than the material itself, the linear relationship between $A_1{^2}$ and $A_2$ will not be guaranteed. Therefore, the second-order harmonic generation by another source should be fully suppressed. In this paper, we investigated the initial second-order harmonic generation in narrowband surface waves by multi-line laser beams. The spatial profile of laser beam was considered in the cases of Gaussian and square-like. The temporal profile was assumed to be Gaussian. In case of Gaussian spatial profile, the generation of the initial second-order harmonic wave was inevitable. However, when the spatial profile was square-like, the generation of the initial second-order harmonic wave was able to be fully suppressed at specific duty ratio. These results mean that the multi-line laser beams of square-like profile with a proper duty ratio are useful to evaluate the acoustic nonlinearity of the generated surface waves.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
• /
• v.8 no.2
• /
• pp.55-60
• /
• 2012

In many cases, geothemal wells will not be opened up a geothermal reservoir under such conditions that an extraction of geothermal energy is economically viable without any further measures. Geothermal wells often have to be stimulated, in order to increase productivity. For the non-volcanic area, such as Korea, the hydraulic stimulation is necessary to complete geothermal power plant. The analysis of induced seismic event showed that the thermal resource might have a much wider extent and a much higher generation potential than previously assumed. In order to record compressional and shear waves emitted during fracture stimulation, three-component geophones are placed in a seismometer. The recorded data from one seismometer is the convolution of the source magnitude, the transmission media, and the sensitivity of the instrument.