• 천문학회보
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• 제41권1호
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• pp.44.2-44.2
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• 2016

The solar wind electrons are made of three or four distinct components, which are core Maxwellian background, isotropic halo, and super-halo (and sometimes, highly field-aligned strahl component which can be considered as a fourth element). We put forth a steady-state model for the solar wind electrons by considering both the steady-state particle and wave kinetic equations. Since the steady-state solar wind electron VDFs and the steady-state wave fluctuation spectrum are related to each other, we also investigate the complete fluctuation spectra in the whistler and Langmuir frequency ranges by considering halo- and superhalo-like model electron VDFs. It is found that the energetic electrons make important contributions to the total emission spectrum. Based on this, we complete the steady-state model by considering both the whistler and Langmuir fluctuations. In particular, the Langmuir fluctuation plays an important role in the formation and maintenance of nonthermal electrons.

• Smart Structures and Systems
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• 제1권2호
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• pp.121-140
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• 2005

This paper presents a systematic investigation of the effect of sensor location on the data quality and subsequently, on the effectiveness of machine health monitoring. Based on an analysis of the signal propagation process from the defect location to the sensor, numerical simulations using finite element modeling were conducted on a bearing test bed to determine the signal strength at several representative sensor locations. The results showed that placing sensors closely to the machine component being monitored is critical to achieving high signal-to-noise ratio, thus improving the data quality. Using millimeter-sized piezoceramic plates, the obtained results were evaluated experimentally. A comparison with a set of commercial vibration sensors verified the developed structural dynamics-based sensor placement strategy. It further demonstrated that the proposed shock wave-based sensing technique provided an effective alternative to vibration measurement, while requiring less space for sensor installation.

• 대한기계학회논문집B
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• 제33권8호
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• pp.589-595
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• 2009

The instability wave formed near nozzle region grows to vortex with large scale in downstream region of spray. It plays an important role in the fuel-air mixing, combustion process and engine exhaust emissions in direct injection diesel engine. The objective of this study is to analyze effect of variant parameters (injection pressure, ambient gas density, etc.) and fuel properties on spray instability near nozzle region. Spray structure near nozzle region was investigated using a magnification photograph. A pulsed Nd-YAG laser was used as a light source, and image was taken by CCD camera. The following conclusions are drawn from this experimental analysis. In low ambient density, the effect of fuel properties on spray instability near nozzle region is dominant. In high ambient density, the effect of ambient gas on spray instability near nozzle region is dominant. High jet velocity has strong influence on spray instability.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2001년도 전력전자학술대회 논문집
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• pp.638-641
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• 2001

Connectorless power transmission and supply are the power transfer device revealed by resonant inverter or transformer using inductant device. Recently, on power supply have been going on frequently, so several power supply circuit forms are announced. But Compared with the circuit of previous paper, instead of the circuit composed of a simple sylinder Ferrit, I was manufacture in a sylinder that It was a double overlab to a sylinder and I was followed a double flux in inner flux path. Above all, for practicalization, supply circuit operation character analysis and development of controller should be preceded. According to this paper, power transmission and supply analyze characters and design control circuit like the analysis of general resonant inverter for power transmission. They compose the circuit to get sinusoid wave output voltage using pulse width modulation control mode. For Supply, output wave form through power track and power pick-up of magnetic inductance includes ripper component. So I intend to design the controller including filter and regulator, compare analyze theoretical result with real measurement value and then show you their practicality

• 한국항해학회지
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• 제5권2호
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• pp.41-47
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• 1981

Many new radar techniques have appeared on the electronic scene in recent years, such as a variety of automatic computer processing. However, even with the advent of these sophisticated radar techniques, an old problem continues to plague all radars: the problem of transmission line losses. With the higher performance required today, the Waveguide testing and trouble-shooting techniques remain essentially unchanged in principle. This paper dealt with the rf pulse "Time-domain Reflectometry" to inspect radar wave-guide system and compared with the conventional methods. During the investigation, it was verified that the pulsed TDR for wave-guide is superior to the conventional methods; 1. Disassembling is not needed to locate the discontinity points and measure the reflections of trobled points. 2. The results of the data are more precise. 3. The condition of individual component is able to the photographed and recorded permanently. 4. Since rf pulse TDR is based on the well-known basic radar principle, such a test set requires the minimum of training to operate. With the level of transmission line problems, the prospect of increasing complexity of equipment, and no relief in sight, the benifits must be emphasizied to adopt such a testing procedure.procedure.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2003년도 추계 학술발표회논문집
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• pp.74-81
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• 2003

During the 1995 Hyogoken-Nambu earthquake, many caisson-type quay walls in Kobe Port moved several meters towards the seaside due to liquefaction and subsequent ground flow, To investigate the mechanism of quay wall damage, we carried out the numerical simulation using the 2-D effective stress analysis. Input earthquake motions used for the analyses are original Dip wave and the component wave in each compact support of wavelet transformation. The results suggested that the shear failure occurred in the foundation soil underneath the caisson type quay wall due to the deformation of the caisson type quay wall.

• Structural Engineering and Mechanics
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• 제82권4호
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• pp.459-467
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• 2022

We investigated the influence of variable thermal conductivity on waves propagating through the elastic medium. Infinitesimal deformation results in generation of thermal signal, and is analyzed by using dual phase lag heat (DPL) conduction model. The medium considered is homogenous, isotropic and bounded by thermal shock. The elastic waves propagating through the medium are considered to be harmonic in nature, and expressions for the physical variables are obtained accordingly. Analytically, we obtained the expressions for displacement components, temperature, micro-temperature component and stresses. The theoretical results obtained are computed graphically for the particular medium by using MATLAB.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2000년도 춘계 학술발표회 논문집 Proceedings of EESK Conference-Spring
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• pp.63-69
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• 2000

Korea Institute of Geology Mining and Materials(KIGAM) cooperating with Southern Methodist University(SMU) has been operating seismo-acoustic array in Chul-Won area to discriminate man-made explosions from natural earthquakes since at the end of July 1999. In order to characterize propagation parameters of detected seismo-acoustic signal and to associate these signals as a blast event accompanying seismic and acoustic signals simultaneously it is necessary to understand infrasound wave propagation in the atmosphere. Two comparable Effective Sound Velocity Structures(ESVS) in atmosphere were constructed by using empirical model (MSISE90 and HWM93) and by aerological observation data of Korea Meteorological Administration (KMA) at O-San area. Infrasound propagation path computed by empirical model resulted in rare arival of refracted waves on ground less than 200km from source region. On the other hand Propagation paths by KMA more realistic data had various arrivals at near source region and well agreement with analyzed seismo-acoustic signals from Chul-Won data. And infrasound propagation in specific direction was very influenced by horizontal wind component in that direction. Linear travel time curve drawn up by 9 days data of the KMA in autumn season showed 335.6m/s apparent sound velocity in near source region. The propagation characteristics will be used to associate seismo-acoustic signals and to calculate propagation parameters of infrasound wave front.

• 한국해양공학회지
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• 제1권1호
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• pp.57-64
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• 1987

Methods of nonlinear stochastic analysis of guyed towers are studied in this paper. Two different kinds of nonlinearities are considered. They are the nonlinear restoring force from the guying system and the nonlinear hydrodynamic force. Analyses are carried out mainly in the frequency domain using linearization techniques. Two methods for the linearization of the nonlinear stiffness are presented, in which the effects of the steady offset and the oscillating component of the structural motion can be adequately analyzed. those two methods are the equivalent linearization method and the average stiffness method. The linearization of the nonlinear drag force is also carried out considering the effect of steady current as well as oscillatory wave motions. Example analyses are performed for guyed tower in 300m water. Transfer functions and the expected maximum values of the deck displacement and the bending moment near the middle of the tower are calculated. Numerical results show that both of the frequency domain methods presented in this paper predict the responses of the sturcture very reasonably compared with those by the time integration method utilzing the random simulations wave particla motions.

• 한국전기전자재료학회논문지
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• 제26권4호
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• pp.309-314
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• 2013

This paper dealt with the radiated electromagnetic wave detection of partial discharge (PD) in oil for insulation diagnostics of oil-immersed transformers. Three types of electrode system were fabricated to simulate the insulation defects that could occur in oil-immersed transformers. Frequency components of radiated electromagnetic wave in oil was measured by broadband bi-conical antennas of 300 MHz~2 GHz and a spectrum analyzer of 9 kHz~3 GHz. Frequency component of electromagnetic waves from PD in oil were highly distributed at 500 MHz. From the result, a narrow-band monopole antenna with the center frequency of 500 MHz was fabricated. We could detect PD signal in insulation oil without an influence of external noise by a measurement system which consists of the prototype monopole antenna, a LNA (Low Noise Amplifier), an oscilloscope and a spectrum analyzer.