• The Journal of the Acoustical Society of Korea
• /
• v.17 no.2
• /
• pp.56-62
• /
• 1998

전기-기계변환효율이 좋은 PZT를 송신용으로, 대역특성이 우수한 PVDF를 수신용 으로한 PZT/PVDF 복합구조 수중초음파 트랜스듀서를 제안하고, 외부는 PZT, 내부는 PVDF로 된 동심원형의 트랜스듀서를 설계·제작하여, 그 특성을 이론적, 실험적으로 파악 하였다. 삽입손실과 임펄스 응답파형에 대한 등가회로해석 및 측정결과로부터 제안한 트랜 스듀서의 특성, 특히, 대역폭이 종래의 PZT 단일소자에 의한 트랜스듀서보다 향상될 수 있 음을 알았다.

• Proceedings of the IEEK Conference
• /
• 1999.11a
• /
• pp.301-304
• /
• 1999

밀리미터파 대역의 아날로그 광전송을 위한 진행파형 (travel ing wave, TW) 전계흡수 광변조기 (electroabsorption modulator, EAM)와 광수신기의 설계에 대해 발표하고자 한다. TW EAM 및 TW 광수신기의 일반적인 형태인 ridge-type의 co-planar waveguide (CPW)구조에서의 마이크로파의 전송특성을 3차원 FDTD로 분석하여 광파와 전파의 속도 정합 등을 이루는 최적화 구조를 설계하였다. TW EAM의 경우 광세기 변조의 비선형 응답특성에 있어서 마이크로파 손실과 소자길이가 RF 신호의 혼변조 왜곡 (intermodulation distortion)과 SFDR (spurious free dynamic range)성능에 미치는 영향도 이론적으로 조사하였다. TW PIN 광수신기의 경우 광파와 마이크로파의 속도정합의 영향과 이전에는 고려되지 않았던 photo-generated 전송자의 진성 영역에서의 transit time이 광수신기의 밴드 폭에 미치는 영향을 분석하여 최적화 설계하였다.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.21 no.2
• /
• pp.495-504
• /
• 1996

In this paper, series-fed mirostrip array anteenas with coupling-slots are prposed and their operating characteristics are analyzed based on analyzed based on analytical and experimental results. An accurate analysis method for the slot-coupled feed structure is based on using both circuit coupling between anteenas and full-wave analysis which use travling wave mode and non-traveling wave mode on feed line. The basis functions that used for the numerical analysis bas been determined depending upon the accuracy, convergence properties of the solution, and the computation time:The patch uses 3 EB mode, the slot uses 1PWS mode, and feeders use 5 PWS mode. Series-fed array antennas have been designed, built, and tested in a standing-wave configuration. Using the results of the full-wave analysis, the chebyshev array antennas consisting of 8 elements are designed and fabricated changing the amount excited to each array element by adjusting slot length and by the slot position relative to the feeder. Experiment results show that the series-fed array antenna designed by adjusting the slot position relative to the feeder is superior to that designed by slot length.

• The Journal of the Acoustical Society of Korea
• /
• v.25 no.6
• /
• pp.282-290
• /
• 2006

This paper proposes a new Digital Reverberator that models Analog Helical Coil Spring Reverberator for guitar amplifiers. While the conventional digital reverberators are proposed to provide better sound field mainly based on room acoustics, no algorithm or analysis of digital reverberators those model Helical Coil Spring Reverberator was proposed. Considering the fact that approximately $70{\sim}80$ percent of guitar amplifiers are still with Helical Coil Spring Reverberator, research was performed based not on Room Acoustics but on Helical Coil Spring Reverberator itself as an effector. After performing simulations with proposed algorithm, it was confirmed that the Digital Reverberator by proposed algorithm provides perceptually equivalent response to the conventional Analog Helical Coil Spring Reverberators.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.13 no.5
• /
• pp.23-29
• /
• 2009

On December 13, 1996, an earthquake with local magnitude (M$_L$) 4.5 occurred in the Yeongwol area of South Korea. The epicenter was 37.2545$^{\circ}$N and 128.7277$^{\circ}$E, which is located inside the Okcheon Fold Belt. The waveform inversion analysis was carried out to estimate source parameters of the event according to the filtering bandwidth of seismic data. Using 0.02$\sim$0.2 Hz filtering bandwidth, focal depth and seismic moment were estimated to be 6 km and 1.3$\times$10$^{16}$ N$\cdot$m, respectively. This seismic moment corresponds to the moment magnitude (M$_W$) 4.7. The focal mechanism by the waveform inversion and P wave first motion polarity analysis is a strike slip faulting including a small thrust component, and the direction of P-axis is ENE-WSW. The moment magnitude estimated by spectral analysis was 4.8, which is similar to that estimated by waveform inversion. Average stress drop was estimated to be 14.3 MPa.

• Proceedings of the KIPE Conference
• /
• 2016.11a
• /
• pp.9-10
• /
• 2016

최근 급속한 산업 발달로 인하여 기존의 수 MW급 대용량 인버터가 산업용 팬, 컴프레서, 고속 철도 시스템 등 여러 분야에 사용되면서 이와 관련된 대용량 인버터 연구가 활발히 진행 중이다. 이런 대용량 인버터는 고효율과 직병렬의 구성된 전력용반도체 소자를 동시다발적으로 제어되어야하기 때문에 멀티레벨 인버터의 구조가 가장 적합하다. Cascaded H-bridge 멀티레벨 인버터는 커패시터와 다이오드를 사용하지 않고 스위치만으로 구성하며, 필터를 따로 구성하지 않아도 정현파와 유사하게 전압을 출력할 수 있다. 이로 인해 고주파 감소 및 각 셀을 직렬로 연결하여 입력전압보다 높은 출력전압을 얻을 수 있다. 또한, 스위칭 방법에 따라 동일한 Cascaded H-bridge 멀티레벨인버터 토폴로지에서도 각 THD와 온도에 따른 손실이 달라질 수 있다. Cascaded H-bridge 멀티레벨 인버터에서 이용하는 스위칭 방식은 첫 번째로 유니폴라 방식을 기본으로 한 Phase-shift가 있다. 이는 180도 위상차를 갖는 2개의 레퍼런스 파형과 위상천이가 된 캐리어 파형의 비교로 PWM (Pulse Width Modulation) 을 수행한다. 두 번째 방식으로는 Level-shift가 있다. 이는 캐리어 파형을 IPD (In-Phase Disposition) 방식으로 수직적으로 대역폭이 연속적이게 나열하여 레퍼런스 파형과 비교하는 PWM방식이다. 본 논문에서는 Phase-shift와 Level-shift 방식에 따른 Cascaded H-bridge 인버터와 NPC (Neutral Point Clamped) 인버터를 결합한 토폴로지에서의 온도에 따른 손실을 분석하고, 시뮬레이션을 통하여 비교 분석하였다.

• Computational Structural Engineering
• /
• v.1 no.1
• /
• pp.123-133
• /
• 1988

A method to calculate maximum dynamic deflection, which is close to the measured deflection, was proposed by comparing the real deflection with the claculated one in three span continuous highway steel bridge. From this, the pattern of variation of impact factors depending an vehicle speeds and weights was studied in simple and continuous bridges. From the numerical analysis, it was known that the maximum dynamic deflection which is close to the measured one could be obtained by using the transformed flexural rigidity of a bridge, and the factors are generally increased with increasing vehicle speed. However, it was thought that there are some problems in the code specification about the impact factors of the continuous bridges.

• Journal of the Korean Society for Advanced Composite Structures
• /
• v.6 no.1
• /
• pp.38-44
• /
• 2015

In this paper, a finite element dynamic simulation study was performed to gain an insight about the blast wall test details for the offshore structures. The simulation was verified using qualitative and quantitative comparisons for different materials. Based on in-depth examination of blast simulation recordings, dynamic behaviors occurred in the blast wall against the explosion are determined. Subsequent simulation results present that the blast wall made of high energy absorbing high manganese steel performs much better in the shock absorption. In this paper, the existing finite element shock analysis using the LS-DYNA program is further extended to study the blast wave response of the corrugated blast wall made of the high manganese steel considering strain rate effects. The numerical results for various parameters are verified by comparing different material models with dynamic effects occurred in the blast wall from the explosive simulation.

• Journal of computational fluids engineering
• /
• v.17 no.2
• /
• pp.93-99
• /
• 2012

The present study focuses on the case of developing flow with in a channel containing a long array of sinusoidal waves (2a/${\lambda}$=0.1, ${\lambda}$=h, ${\lambda}$ is the wavelength, 2a is the wave height, h is the mean channel depth) at the bottom wall. The Reynolds number defined with channel height, h and the mean velocity, U, is Re=6,700. The channel is sufficiently long such that transition is completed and the flow is fully developed over the downstream half of the channel. For the case of an incoming steady flow with no resolved turbulence, the instantaneous flow fields in the transition region are characterized by the formation of arrays of highly-organized large-scale hairpin vortices whose dimensions scale with that of the roughness elements. The paper explains the mechanism for the formation of these arrays of hairpin vortices and shows these eddies play the primary role in the formation of the large-scale streaks of high and low velocity over the wavy wall region. The presence of resolved turbulence in the incoming flow, reduces the streamwise distance needed for the streaks to develop over the wavy region, but does not affect qualitatively the transition process. In the fully-developed region, isolated and trains of large-scale hairpins play an important role in the dynamics of the streaks over the wavy wall.

• Journal of The Institute of Information and Telecommunication Facilities Engineering
• /
• v.3 no.1
• /
• pp.56-74
• /
• 2004

본 논문에서는 기존의 여러 가지 무선 홈 네트워크에 대해 개괄하고 새로운 표준인 Binary CDMA (Code Division Multiple Access)를 이용한 Koinonia 시스템을 제안한다. 제안된 시스템은 멀티 코드 CDMA 시스템을 고속의 멀티미디어 전송을 위해 변형한 형태이다. 멀티코드 사용 시 송신 신호 파형이 멀티 레벨로 나타나게 되어 시스템의 구조가 복잡해지고 가격이 비싸지는 단점이 존재한다. 이러한 기술적 문제점을 해결하기 위해 멀티레벨의 신호를 부호화 블록을 통해 정진폭으로 변환해 전송한다. 이를 통해서 복잡한 멀티 레벨의 신호가 간단히 나타나므로 전송되는 신호의 파형이 간단히 표현되어지고 수신기의 구조가 간단해진다. 그리고, 제안된 시스템은 멀티 코드 방식을 기반으로 하기 때문에 디지털 가전기기나 3세대 이동통신과, WPAN과 관련된 무선 네트워크 응용과 같은 미래의 고속의 무선 멀티미디어 서비스를 지원하기에 적합하다.