• 대한조선학회논문집
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• 제55권1호
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• pp.56-65
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• 2018

Pressure oscillation caused by the compressibility of entrapped air in dam break flow is analyzed using an open source code, which is a two-phase compressible code for non-isothermal immiscible fluids. Since compressible flows are computed based on a pressure-based method, the code can handle the equation of state of barotropic fluid, which is virtually incompressible. The computed time variation of pressure is compared with other experimental and computational results. The present result shows good agreements with other results until the air is entrapped. As the entrapped air bubbles pulsate, pressure oscillations are predicted and the pressure oscillations damp out quickly. Although the compressibility parameter of water has been varied for a wide range, it has no effects on the computed results, because the present equation of state for water is so close to that of incompressible fluid. Grid independency test for computed time variation of pressure shows that all results predict similar period of pressure oscillation and quick damping out of the oscillation, even though the amplitude of pressure oscillation is sensitive to the velocity field at the moment of the entrapping. It is observed that as pressure inside the entrapped air changes quickly, the pressure field in the neighboring water adjusts instantly, because the sound of speed is much higher in water. It is confirmed that the period of pressure oscillation is dominated by the added mass of neighboring water. It is found that the temperature oscillation of the entrapped air is critical to the quick damping out of the oscillations, due to the fact that the time averaged temperature inside the entrapped air is higher than that of surrounding water, which is almost constant.

• 전자공학회논문지C
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• 제35C권11호
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• pp.76-88
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• 1998

강화 학습은 이산적인 공간을 가상하여 많은 연구가 행해졌지만, 많은 실제적인 제어 문제는 연속적인 공간에서 이루어진다. 평가 함수와 행동 함수를 연속함수로 하면 강화 학습 구조를 연속 공간에서 사용할 수 있다. 그러나 이 경우 두 가지 고려해야 할 점이 있다. 하나는 어떤 종류의 함수 표현 법을 사용할 것인가 하는 문제고, 다른 하나는 첨가하는 잡음의 양을 결정하는 것이다. 평가 함수와 정책 함수(제어기)에는 신경회로를 사용하였다. 강화 예측기로 다음 순간의 강화 신호를 예측하고, 아울러 첨가하는 잡음의 양도 결정하였다. 제안된 강화 학습 구조를 사용하여 차량의 횡 방향 제어 모의 실험에서 온라인 학습의 특성을 확인하였다. 제안된 구조를 실차 실험에도 적용하여 유용성과 타당성을 검증하였다.

• 드라이브 ㆍ 컨트롤
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• 제13권3호
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• pp.24-31
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• 2016

The performance characteristics of a dynamic control system are evaluated according to the transient and steady-state responses. The transient performance is the controllability of the output for the tracking of the reference or the ability to reduce or reject the effects of unwanted disturbances; alternatively, the steady-state performance is represented by the magnitude of the control error at the steady state. As the effects of the two performances on each other are reciprocal, a controller design that shows a zero steady-state error for the ramp input is uncommon because of the challenge regarding the achievement of an acceptable transient response. This paper proposes a PI+double-integral controller for the elimination of the steady-state error for the ramp input while a sound transient performance is maintained. The control-gain design procedure is described by the second-order response for the step input and the response of the error dynamics for the ramp input. The PI+double-integral controller is designed for the first-order transfer function that is derived from a system identification with the open-loop experiment data of the dc-motor. The simple structure of the proposed controller enables the adoption of a low-end microcontroller for the implementation of a real-time control. The experiment results show that the control performance is as effective as that of the simulation analysis for the operating point of linear system; furthermore, the PI+double-integral controller can be conveniently applied to the control system, which is desirable for the improvement of the steady-state error.

• 한국음향학회지
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• 제32권6호
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• pp.455-471
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• 2013

능동소나는 일반적으로 천해에서 존재하는 표적을 탐지하기 위해 사용된다. 신호가 송신되고 표적으로부터 반향되어 되돌아올 때, 표적 반향신호는 다중경로, 거친 해저면 또는 해수면에 의한 산란 그리고 음속구조에 의한 굴절과 같은 다양한 음파전달 특성에 의해 왜곡 되어 수신되며, 이는 표적 탐지를 어렵게 만든다. 그러므로 능동소나의 운용성능 체계에서 표적 신호 모의 시 음파전달 특성을 고려하는 것이 필요하다. 본 논문에서는 단상태 능동소나 시스템을 고려하였으며, 표적 반향, 잔향음 그리고 주변소음은 각각 시계열 함수로 모의되었다. 마지막으로 전체 수신 신호를 모의하기 위해 위 신호들을 합하였다. 표적의 특징(형태, 위치, 자세각 등)을 반영한 3차원 대표반향점 모델은 음원과 표적 사이에 각각의 다중경로를 고려하여 표적 반향 신호를 모의하였다. 본 논문의 결과는 표적 신호 모의 시 직접파만을 고려한 알고리즘의 결과와 비교하였다.

• 한국군사과학기술학회지
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• 제14권2호
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• pp.222-231
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• 2011

In this paper, we have proposed a method which can make it possible to stably transmit and receive data like the ARC-164 radio frequency hopping environment as a S/W packet modem with PSK modulation. This is a method that the S/W packet modem with PSK digital modulation and the use of PC sound cards change over from data to voice signals and then transmit/receive data. We confirmed not only that it is possible to solve the slow speed communication with the use of sending data through multi-channels and PSK modulation that has the ability to methodically improve transmission rates, but also that it is possible to send the state of frequency hopping stably. In conclusion, we've confirmed both tactical values that though the transmission rate may be a tad slow, a state of frequency hopping of more than 94% confidence plus voice and data can be sent via radio at the same time. In this paper, the proposed S/W packet modem is only an implemented S/W component, so when we apply it to aircraft that we don't consider EMC problems with, then we have the advantage of a wider use of conventional UHF/VHF/HF radio that is possible to voice communication. If we recognize these operational requirements, we can apply for a lot of field equipment efficiently.

• 한국재료학회지
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• 제27권5호
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• pp.276-280
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• 2017

This study was carried out to evaluate the developed microstructures and mechanical properties of friction welded A6063 alloy. For this work, specimens were prepared at a size of 12 mm ${\O}{\times}80mm$, and friction welding was carried out at a rotation speed of 2,000 RPM, friction pressure of $12kgf/cm^2$ and upset pressure of $25kgf/cm^2$. To perform an analysis of the grain boundary characteristic distributions, such as the grain size, orientation and misorientation angle distributions, the electron back-scattering diffraction method was used. In addition, in order to identify the dispersed intermetallic compounds of the base and welded materials, transmission electron microscopy was used. The experimental results found that the application of friction welding on A6063 led to significant grain refinement of the welded zone relative to that of the base material. Besides this, intermetallic compounds such as AlMnSi and $Al_2Cu$ were found to be dispersed with more refined size relative to that of the base material. This formation retains the mechanical properties of the welds, which results in the fracture aspect at the base material zone. Therefore, based on the developed microstructures and mechanical properties, the application of friction welding on A6063 could be used to obtain a sound weld zone.

• 대한의용생체공학회:의공학회지
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• 제23권2호
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• pp.165-170
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• 2002

본 연구는 감각-운동 통합의 관점에서 다양한 시각 자극에 의하여 생체 내에 입력된 각기 다른 감각 정보가 운동 기능에 미치는 영향을 정량적으로 분석하기 위하여 수행되었다. 특히 보색 관계의 시각 자극이 이에 대한 운동의 반응시간에 어떠한 영향을 주는지에 관심을 두었다. 실험은 20세에서 25세 사이의 20대 성인 남녀 각각 10명을 대상으로 자체 제작한 방음 암실에서 수행하였다. 실험 장치는 디스플레이 판넬, 시각 자극을 위한 고휘도 LED 그리고 자극에 대한 반응시간 검출을 위한 키보드 스위치로 구성하였다. 지금까지의 많은 연구들은 감각 정보의 차이가 인식에 미치는 영향에 대한 평가나 색채 자극에 의한 감각 수용기의 반응의 강도의 차이를 연구하는데 머무르고 있으며 색채 환경에서의 감각-운동 협응에 대한 연구는 미흡한 실정이다. 따라서 본 실험에서는 다양한 시각 자극 환경에서 운동의 반응 시간을 계측함으로써 감각과 운동의 관계를 정량적으로 분석하였다. 그 결과 보색 관계의 시각 자극에 대한 반응시간이 동일한 색채 환경 하에서의 반응시간 보다 빠르고 동일 색채 자극 환경에서는 빛의 파장의 크기에 반비례하여 반응속도가 나타나는 결과를 얻었으며 통계적 분석(p<0.05)을 통해서 유의성도 검증되었다.

• 말소리와 음성과학
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• 제1권3호
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• pp.151-154
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• 2009

The external ear generates resonance gain because of anatomical characteristics. The ear canal resonance is influenced by the length and volume of the ear canal, the pinna, the concha cavity, the body trunk, and the speed of sound wave. This study is focus on the influence of the volume of ear canal. 17-healthy-adult (32 ears) were participated. They did not have any medical and ear disease history. The maximum resonance frequency of the ear canal was 2675 (${\pm}265$) Hz at azimuth $0^{\circ}$ and 2784 (${\pm}268$) Hz at azimuth $45^{\circ}$. The resonance gain was 18.1 (${\pm}3.9$) dB at azimuth $0^{\circ}$ and 17.9 (${\pm}3.8$) dB at azimuth $45^{\circ}$, respectively. The ear canal volume was 0.78 (${\pm}0.2$) cc and 1.32 (${\pm}0.8$) cc including static compliance. The ear canal resonance was changed depending on the ear canal volume. It was also statistically correlated at azimuth $0^{\circ}$ (p=0.038) and $45^{\circ}$ (p=0.013), respectively. The resonance gain was not correlated with the ear canal volume. The change of resonance frequency according to the ear canal volume will be useful information in the field of audiological rehabilitation especially for hearing aids fitting. In addition, we expected this study can provide the basic information for the study of the external ear resonance characteristics.

• 한국통신학회논문지
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• 제42권4호
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• pp.848-854
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• 2017

최근 경찰서 등과 같은 관공서로 허위 신고를 하는 경우가 줄지 않고 있는 실정이다. 이로 말미암아 실제 신속한 출동과 대응이 필요한 강력 범죄나 화재가 발생하였을 경우 이를 제때에 가지 못하여 이에 따른 인명 피해 등이 발생할 수 있게 된다. 또한 허위 신고로 말미암은 경찰력과 행정력의 낭비 또한 매우 심각한 문제를 야기할 수 있다. 이를 위해 본 논문에서는 경찰서에 신고 된 실제 음원을 기반으로 실제 신고와 허위 신고의 음성 차이가 무엇 인지를 규명해 내는 연구를 수행하고자 한다. 아울러 향후 이를 기반으로 거짓 신고와 실제 신고를 판별해 내는 허위 신고 판별 시스템을 개발하고자 한다.

• International Journal of Advanced Culture Technology
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• 제3권1호
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• pp.61-67
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• 2015

The application of SS400 carbon steel and AISI430 ferritic stainless steel joint has been increased in industries because of the advantage of both metals was able to increase the service lifetime of the important structures. Therefore, a fusion welding process that could produce a sound weld and good joint properties should be optimized. This research is aimed to weld a butt joint of SS400 carbon steel and AISI430 ferritic stainless steel using Gas Metal Arc Welding (GMAW) welding process and to study the effects of welding parameters on joint properties. The experimental results were concluded as follows. The optimized welding parameter that produced the tensile strength of 448 MPa was the welding current of 110A, the welding speed of 400 mm/min and the mixed gas of $80%Ar+20%CO_2$. Increase of the welding current affected to increase and decrease the tensile strength of the joint, respectively. Lower welding current produced the incomplete bonding of the metals and indicated the low tensile strength. Microstructure investigation of the welded joint showed a columnar grain in the weld metal and a coarse grain in the heat affected zone (HAZ). The unknown hard precipitated phases were also found at the grain boundaries of the weld metal and HAZ. The hardness profile did not show the difference of the hardness on the joint that was welded by various welding currents but the hardness of the weld metal was higher than that of the other location.