• 천문학회지
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• 제27권1호
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• pp.1-11
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• 1994

We have observed the emission of $HC_3N$ J=4-3, 5-4,10-9 and 12-11 transitions toward the Sgr B2 central region in an area of $150'\times150'$ with resolutions of 16'-48'. The intensities and central velocities of line profiles show significant variations with positions. In contrast to the intensities of the low J-level transitions which gradually increase from the central source toward the outside region, the $HC_3N$ emission of the high J-level transition become stronger toward 'the central radio continuum source MD5. Systematic change in the radial velocity of each line profile occurs along north-south direction. There are a few peaks in most line profiles, and these indicate that there are multiple velocity components along the line of sight. Distributions of excitation temperature and column density which were estimated from the excitation calculations show the existence of a small $(1\times2pc),\;hot\;(T_{ex}>50K)$ core which contains two temperature peaks at-15' east and north of MD5. The column density of $HC_3N\;is\;(1-3)\times10^{14}cm^{-2}$ Column density at distant position from MD5 is larger than that in the central region. We have deduced that this 'hot-core' has a mass of 105M 0, which is about an order of magnitude larger than those obtained by previous studies.

• 한국소음진동공학회논문집
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• 제24권6호
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• pp.483-492
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• 2014

Uncomfortable feelings of occupants by indoor floor impact noise in a residential building are not accurately represented by the floor impact noise from a standard impact source. It is due to the characteristics of standard impact sources, which are different from the impact forces produced by occupants. It varies significantly by impact source, and it is not easy to be replicated for testing. As a result, the indoor floor impact noise under different acoustic conditions cannot be directly compared. Using frequency response function(FRF), which represents the input-output relationships of a dynamic system, it is possible to examine the characteristics of the system. Especially, FRF can predict the response of a linear dynamic system subjected to various excitation. To determine the relationship between impact force and the corresponding response of dynamic system in residential building, the acceleration response of a concrete slab and the floor impact noise in the living room, produced by bang-machine and rubber-ball excitation, were measured. The test results are compared to the estimates based on FRF and impact force spectrum.

• 디지털융복합연구
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• 제13권7호
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• pp.177-182
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• 2015

유성음원과 무성음원을 사용하는 멀티펄스 음성부호화 방식(MPC)에 있어서, 유성음의 파형에서 일그러짐이 발생한다. 이러한 문제를 해결하기 위해, 재생파형의 일그러짐이 감소하도록 피치구간 마다 멀티펄스의 진폭과 위치를 보정하는 APC-MPC를 제안하였다. 또한 융복합 시스템의 8kbps 부호화 조건에서 APC-MPC의 SNRseg를 검토하고 부호화 시스템으로 구현하였다. APC-MPC의 SNRseg를 평가한 결과, APC-MPC의 남자음성에서 14.3dB, 여자음성에서 13.9dB 임을 확인할 수 있었다. 본 방법은 셀룰러폰이나 스마트폰과 같이 Low Bit Rate의 음원을 사용하여 음성신호를 부호화하는 방식에 활용할 수 있을 것으로 기대된다.

• 한국소음진동공학회논문집
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• 제23권6호
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• pp.527-536
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• 2013

In order to predict structural vibration and radiated noise of high-voltage transformer in operation, it is necessary to precisely find the excitation force generated by the coils and core. However, finding the excitation force through experiments of high voltage transformer in operation is not possible. Therefore, this paper deals with identifying the excitation force by using the acceleration data measured through experiments and the transfer function estimated through finite element model. A method to predict structural vibration and radiated noise was also proposed. Three-phase windings and the core are the source of high-voltage transformer. The excitation forces were identified using the acceleration data and the transfer function of the surface of the tank. Structural vibration and radiated noise from the surface of the tank was predicted by using the identified excitation force. As a result of the interpretation of the experimental and computational analysis of structural vibration from the surface of the tank and radiated noise from the field point, the interpretation of the computational analysis showed relatively good accordance with the experiment.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2010년도 학술대회 초록집
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• pp.27-27
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• 2010

There have been several studies about empirical relation between seismic source parameters(e.g., focal mechanisms, depths, magnitudes, etc.) and T-wave observation. In order to delineate the relation, numerical and theoretical approaches to figure out T-wave excitation mechanism are required. In an attempt to investigate source radiation and wave scattering effects in the oceanic crust on T-wave envelopes, we perform three-dimensional numerical modeling to synthesize T-wave envelopes. We first calculate seismic P- and SV-wave energy on the seafloor using the Direct Simulation Monte Carlo based on the Radiative Transfer Theory, which enables us to take into account both realistic seismic source parameters and wave scattering in heterogeneous media, and then estimate excited T-wave energy by normal mode computation. The numerical simulation has been carried out considering the following different conditions: source types (strike and normal faults), source depths (shallow and deep), and wave propagation through homogeneous and heterogeneous Earth media. From the results of numerical modeling, we confirmed that T-wave envelopes vary according to spatial seismic energy distributions on the seafloor for the various input parameters. Furthermore, the synthesized T-wave envelopes show directional patterns due to anisotropic source radiation, and the slope change of T-wave envelopes caused by focal depth. Seismic wave scattering in the oceanic crust is likely to control the shape of envelopes.

• Journal of Power Electronics
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• 제13권5호
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• pp.841-853
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• 2013

An application of doubly-fed induction generator (DFIG), which is one of adjustable speed generators, to a gas engine cogeneration system has been investigated. To operate during a blackout as an emergency power supply is one of important roles for the gas engine cogeneration system. However, the DFIG requires initial excitation for startup during a blackout because the DFIG has no excitation source. In this paper, we propose the "blackout start" as a new excitation method to generate a rated voltage at the primary side during a blackout. In addition, a stand-alone operation following a blackout has been investigated by using experimental setup with a real gas engine. Power flows in the generating set with the DFIG at the stand-alone operation have been investigated experimentally. Experimental investigation of the power flow suggests that the generating set with DFIG has optimal speed in minimizing whole system losses.

• 한국해양환경ㆍ에너지학회지
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• 제18권4호
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• pp.304-309
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• 2015

해양에서 기름 유출 사고로 인한 오염도를 정량적으로 평가하기 위해서, 사고 현장에서 기름을 직접 탐지할 수 있는 센서의 적용이 필요하다. 여러 형태의 기름 탐지 센서 중에서, 기름 성분에 의한 형광 현상(fluorescence)을 탐지 원리로 하는 센서는 해수 중에 존재하는 기름의 농도를 측정할 수 있으므로 효용성이 높은 장점을 갖고 있다. 그러나 이런 종류의 센서는 기름의 형광 현상을 야기시키기 위해서, 수은 램프(mercury lamp)와 같은 자외선 광원(ultraviolet light source)이 필요하고 다양한 종류의 광학 필터와 광전증배관(photomultiplier tube, PMT)과 같은 광학 센서가 주로 사용된다. 이러한 이유로 형광 측정을 기반으로 하고 있는 센서는 측정 플랫폼의 크기가 크기 때문에 현장에서 원활히 사용하기에 한계가 있으며, 고가의 부품들이 집적되어 있어, 센서의 가격이 높은 단점을 갖고 있다. 이러한 단점을 극복하기 위해서, 본 논문에서는 소형의 크기와 가격 경쟁력을 갖고 있는 형광 광도계 기반의 기름 탐지 센서를 설계하는 방법에 대해서 제시하였다. 형광 광도계의 설계 인자를 파악하기 위한 방법으로, 본 연구에서는 5종의 원유 샘플과 3종의 정제유를 이용하여, 기름의 여기 스펙트럼(excitation spectrum)과 발광 스펙트럼(emission spectrum)을 측정하였다. 여기 스펙트럼과 발광 스펙트럼의 측정을 위해서는 형광 분광기(fluorescence spectrometer)를 이용하였고, 측정된 스펙트럼 자료를 분석하여 형광 광도계(fluorimeter) 설계에 필요한 유종에 따른 공통 스펙트럼 파장 대역을 도출하였다. 본 실험을 통해서 모든 종류의 기름 샘플의 경우, 여기 스펙트럼과 발광 스펙트럼의 최고 값을 갖는 파장의 차이는 약 50 nm인 것으로 파악되었다. 실험 중에서, 여기광의 파장을 365 nm와 405 nm로 고정하였을 경우, 280 nm와 325 nm로 고정하였을 경우에 비해서 최대 발광(emission)의 세기가 작아지는 것을 확인할 수 있었다. 따라서 형광 광도계의 광원 파장을 365 nm 또는 405 nm로 사용할 경우, 광학 센서의 민감도(sensitivity)가 발광되는 빛의 세기를 측정할 수 있도록 설계에 반영해야 할 것으로 판단된다. 본 연구의 실험에서 도출된 결과를 통해서, 기름 탐지를 위한 형광 광도계의 광원, 광학 센서 그리고 광학 필터의 유효 파장 대역을 선택하는데 필요한 설계 인자를 파악할 수 있었다.

• 한국조명전기설비학회지:조명전기설비
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• 제9권4호
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• pp.78-85
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• 1995

This paper covers stability and stabilization of Multi-Excited Induction Motor used in numberous electric equipment system of industrial field. The induction motor with multi-excitation has tow sets of three-phase system : One is connected to the AC source to supply most power required at the load, and the other is to the inverter for variable frequency and/or magnitude of voltage. The conventional induction motor is operated under single excitation mode only, that is called induction mode. But in multi-excited induction motor both the induction mode and the synchronous mode are possible, and the proposed multi-excited induction motor can be driven as a synchronous motor by the extra three-phase input. At the synchronous mode the efficiency is improved so higher than that at induction mode or conventional induction motor. The rating of the inverter used for speed control of numberous electric equipment system can be reduced upto one-tenth of that for conventional induction motor. Also the cost and maintenance fee of multi-excited induction motor can be reduced compared to any other motor.

• 산업기술연구
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• 제25권B호
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• pp.141-147
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• 2005

A target of this paper is to get some elementary experimental data on the energy harvesting using a piezoelectric material. A THUNDER series piezo material (TH7-R), which has been developed by NASA engineer is selected for this study. In order to provide a mechanical energy to the piezoelectric material, a mechanical motion vibrator and its driving electronics are designed. Using a simple PWM control, the excitation frequency of vibrating mechanical motion is varied. The generated electric power as a function of the excitation frequency is monitored and analyzed. This initial experiment shows a possible energy source using a piezoelectric material for the application to low-power consumed small electronic devices such as RFID, MEMS, and etc.

• 전기학회논문지
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• 제62권10호
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• pp.1397-1402
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• 2013

This study researched cause of resonance noise for BLDC motor used in the refrigerator. it is difficult to measure dynamic characteristics for small sized fan & rotor system with conventional excitation method. Therefore this study performed electric exiting method and natural frequency method using microphone instead of conventional excitation and showed validity of these methods. Study result showed that tortional vibration frequency of fan & rotor system and natural bending frequency of the fan were matched with exciting frequency of BLDC motor caused by commutating ripple torque. And this frequency match caused resonance of the system. The study analyzed main parameters of this phenomenon and suggested alternative solution.