• Smart Structures and Systems
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• 제26권5호
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• pp.619-629
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• 2020

Solar towers, which often has a large aspect ratio and low fundamental natural frequency, were extremely prone to large amplitude of wind-induced vibrations, especially Vortex-Induced Vibration (VIV). A tiny Tuned Mass Damper (TMD) with conveniently adjustable eddy current damping was specially designed and manufactured for elastic wind tunnel tests of a solar tower. A series of numerical simulations by using the COMSOL software were conducted to determine three key parameters, including the thickness of the back iron plate and the conductive plate (T_b and T_c), the distance between the magnet and the conductive plate (T_d). Based on the results of numerical simulations, a tiny TMD was manufactured and its structural parameters were experimentally identified. The optimized values of the tiny TMD can be conveniently realized. The tiny TMD was installed at the top of the elastic test model of a 243-meter-high solar tower, and a series of wind tunnel tests were carried out to examine the effectiveness of the TMD in suppressing wind-induced responses of the test model. The results showed that the wind-induced responses could be obviously reduced by the TMD, especially in the cross-wind direction. The cross-wind RMS and peak responses at the critical wind velocity can be reduced by about 86% and 75%, respectively. However, the maximum reduction of the responses at the design wind velocity is about 45%, obviously less than that at the critical wind velocity.

• 한국음향학회지
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• 제13권1호
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• pp.71-83
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• 1994

본 논문은 한국어 문어면환(TTS : Text-to-Speech) 시스템내에서의 음성합성시 음질 및 자연성 개선을 위한 연구 결과이다. 합성방법으로는 단음절단위의 파형을 시간영역에서 분석(표1)하여 규칙합성에 필요한 매개변수(표2)를 추출하여 규칙합성시켰다. 실험에 사용된 음절은 한국어 발음 대사전의 빈도순위에 따라 V형 19개, CV형 80개, VC형 30개, CVC형 100개등 총 229음절을 선정하여 규칙합성시켰다. 규칙합성음의 평가방법으로는 229개의 규칙합성음중 음절 유형별로 15개씩 무작위로 추출한 합성음을 사전지식이 없는 임의의 그룹을 선정하여 이해도, 명료도, 잡음감, 자연성등 4가지 항목에 대하여 주관적인 오피니온 평가를 수행하였다. 실험결과, 합성음의 음질은 대단히 명료한 수준이었으며, 운율요소의 제어결과는 지속시간(장단)과 악센트(강약)의 제어(그림 9, 그림 10)가 가능하였으며, 피치주기(억양)의 제어도 Lagrange 보간법을 사용함으로써 가능하였다(그림 11, 그림 12).

• The Korean Journal of Physiology
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• 제13권1_2호
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• pp.41-50
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• 1979

The activation mechanism of K-induced contracture was studied in renal vascular muscle which does not generate an action potential readily and in taenia coli which generates a spike potential spontaneously. Helical strips of arterial muscle from rabbit renal arteries and longitudinal strips of taenia coli from guinea-pig's colons, respectively, were prepared. All experiments were performed in Tris-buffered Tyrode solution which was aerated with 100% $O_2$ and kept $35^{\circ}C$. Renal arterial muscles developed the contracture rapidly, which was composed of a small phasic and a large tonic components, when exposed to a 40 mM K-Tyrode solution. In the absence of external $Ca^{++}$, however, no K-contracture appeared. The contracture induced by K-depolarization was abolished by the treatment with verapamil, which is known to be a selective $Ca^{++}-blocker$ through potential-sensitive $Ca^{++}-channel$. K-contracture of taenia coli showed the contracture composed of a large phasic and a small tonic components. In the $Ca^{++}-free$ Tyrode solution, only the tonic component was abolished and almost no change in the phasic component was observed. The amplitude of tonic component was dependent on the external $Ca^{++}$; The tonic component increased dose-dependently by a stepwise increase of the external $Ca^{++}$, and this component decreased in parallel with the increase of verapamil in the external medium. The results of this experiment suggest that K-contracture of rabbit renal artery is the direct result of the influx of the external $Ca^{++}$, while that of taenia coli is the result of both $Ca^{++}$ influx and the release of sequestered $Ca^{++}$.

• 천문학회보
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• 제36권2호
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• pp.141.1-141.1
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• 2011

New CCD BVR light curves of BD And are presented. Our light curves with nearly equal depths for both primary and secondary eclipses show well-defined photometric waves outside eclipse for all of BVR bandpasses. The orbital period is greatly revised as $0.^d92580519$ which is twice longer than that known previously. Sixteen timings from our observations and thirteen ones from the SuperWASP measurements were calculated. All available timings over 76 years, including ours, were analyzed to figure out the dynamical behavior of the system. It was found that the recent CCD O-C residuals varied in a cyclical way with a period of $9.^y18$ and a semi-amplitude of $0.^d0046$. The secondary period of $9.^y18$ is the most shortest one among those which have been ever found in the short period RS CVn binary stars. The periodic variation most likely arises from the light-travel time effect due to a low-mass ($m_3{\sim}0.88\;M_{\odot}$) tertiary companion moving in an orbit with an large eccentricity ($e_3$=0.70) and a low inclination ($i_3{\sim}28^{\circ}$). The Applegate mechanism could not operate properly in both components because the model parameters require too much large luminosity changes of ${\Delta}L/L_{p,s}$ > 10. The new light curves were synthesized using the 2003 version of Wilson-Divinney code. It was found useful to model two huge spots on the surface of the hotter star and a third-light in order to minimize the residuals from the observations. Astronomical basic parameters were deduced from our photometric solution.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 춘계학술대회논문집
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• pp.719-724
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• 2003

The present experimental study deals with noise reduction and improvements in cooling performance in a plasma display panel(PDP) television (TV). To reduce the noise, the effects of installation parameters are studied. The experimental parameters under investigation are the distance between the fan and the rear case of a PDP TV, position of the strut on the fan, and the fan RPM. The variance of RPM is the most significant facto., and a 250 RPM decrease from 910 RPM causes about 4㏈(A) reduction in the system noise. To increase performance, flow characteristics are investigated by using a visualization technique and measuring the volume flow rate. The visualized results show that a radial direction flow due to large system resistance is significant, and an axial velocity oscillation is observed from the measurement of the volume flow rate. To prevent both a radial direction flow and an axial velocity oscillation, sponges are inserted in the space between f3n and the rear case. Inserted sponges improve the volume flow rate of cooling fans up to 32% since they convert a radial direction flow to an axial direction flow. Also an axial velocity oscillation with large amplitude and low RPM disappears. Increasing volume flow rate causes the PDP TV to improve its cooling performance. Additionally the same volume flow rate can be obtained with a decreased fan speed due to the inserted sponge. Noise reductions of 4.2 ㏈(A) at the rear and 1.1 ㏈(A) at the front of the TV are obtained by the decreased RPM. An increase of 10% of the volume flow rate is also achieved by inserting sponges.

• 한국통신학회논문지
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• 제19권5호
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• pp.822-832
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• 1994

DSC-HDTV 시스템은 영상에 존재하는 공간, 시간, 진폭의 중복성을 제거하기위하여 변환 부호화, 움직임 보상 예측 부호화, 적응 양자화를 이용한다. 본 논문에서는 장면 변화와 전송 잡음으로부터 신속히 화질을 복원하는데 이용하는 누설요소의 적용 방법과 인간 시각 시스템을 이용한 인식하중치를 구하여 적응 양자화하는 방법을 제안한다. 인식하중치는 대비 민감도, 시공간 매스킹과 주파수 민감도에 따라 구한다. 적응 양자화는 인식하중치와 버퍼이력상태로부터 얻은 전체 왜곡 레벨을 이용하고 그에 따른 잉여 비트량은 다음 프레임의 화질 개선에 이용된다. 장면이 변할 경우 복원된 영상은 큰 양자화 오차를 포함하기 때문에 움직 보상 예측 부호화에서 구한 변위프레임 차신호가 큰 값이 되어 비트량이 증가하고 버퍼의 상태가 불안정하게 된다. 그러므로 본 논문에서는 누설요소를 장면이 변할 경우 0으로 하고 그이후의 프레임에서의 15/16으로 고정하여 전체왜곡레벨을 표준편차를 이용하여 조절한다. 실험결과 제안된 방법의 영상의 화질은 수 프레임내에 복원되고 버퍼상태도 신속히 안정화된다.

• 한국음향학회지
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• 제39권4호
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• pp.371-377
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• 2020

종횡비(Length/Diameter, L/D)가 크고, 실린더-슬롯형 그레인을 적용한 고체로켓모터의 연소시험에서 연소불안정 현상이 발생하였다. 압력섭동을 스펙트럼 분석한 결과 중심축 길이방향 주파수가 지배적임이 확인되어, 음향노드와의 일치를 해소하기 위해 실린더 파트의 길이를 증가시켰다. 또한 고체로켓모터에서 발생하는 유동 구조에 의한 불안정성 발생 원인을 분석하기 위하여 음향모드해석과 유동해석을 수행하였다. 설계 변경 전후 그레인 형상을 이용하여 연소실 내 압력 진동 크기 및 주파수에 대해 정량적 비교를 통해 연소불안정이 저감됨을 확인하였다. 최종적으로 연소시험을 수행하여 해석결과와 같이 연소불안정 현상이 사라짐을 확인하였다.

• International Journal of Fluid Machinery and Systems
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• 제6권4호
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• pp.200-205
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• 2013

In order to investigate the characteristics of unsteady flow in a mixed flow pump guide vane under the small flow conditions, several indicator points in a mixed flow pump guide vane was set, the three-dimensional unsteady turbulence numerical value of the mixed flow pump which is in the whole flow field will be calculated by means of the large eddy simulation (LES), sub-grid scale model and sliding mesh technology. The experimental results suggest that the large eddy simulation can estimate the positive slope characteristic of head & capacity curve. And the calculation results show that the pressure fluctuation coefficients of the middle section in guide vane inlet will decrease firstly and then increase. In guide vane outlet, the pressure fluctuation coefficients of section will be approximately axially symmetrical distribution. The pressure fluctuation minimum of section in guide vane inlet is above the middle location of the guide vane suction surface, and the pressure fluctuation minimum of section in which located the middle and outlet of guide vane. When it is under the small flow operating condition, the eddy scale of guide vane is larger, and the pressure fluctuation of the channel in guide vane being cyclical fluctuations obviously which leads to the area of eddy expanding to the whole channel from the suction side. The middle of the guide vane suction surface of the minimum amplitude pressure fluctuation to which the vortex core of eddy scale whose direction of fluid's rotation is the same to impeller in the guide vane adhere.

• 한국항공우주학회지
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• 제50권6호
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• pp.413-422
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• 2022

본 논문에서는 중대형 위성용 '제어모멘트자이로'의 고속회전체인 모멘텀 휠의 고장 분석에 대해 기술하였다. 고장 분석을 위해 변조된 신호에서 주기적으로 발생되는 충격신호를 찾기 위해 힐베르트 변환 기법과 신호 복조 기법을 사용한 포락선 스펙트럼 분석을 하였다. 이를 통해 높은 신호의 크기를 가지는 특정 주파수 밴드에서 회전주파수의 조화 성분과 베어링 결함 주파수가 있는지 분석하여 모멘텀 휠의 고장을 진단하였다.

• 반도체디스플레이기술학회지
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• 제22권3호
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• pp.28-35
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• 2023

Moiré patterns emerge due to the interference between the non-emission area of the LED screen and the grid line in an image sensor of a video recording device when taking a video in the presence of the LED screen. To reduce the moiré intensity, we have fabricated an anti-moiré filter using hollow glass microspheres (HGMs) by slot-die coating. The LED screen has a large non-emission area because of a large pitch (distance between LED chips), causing more severe moiré phenomenon, compared with a display panel having a very narrow black matrix (BM). It is shown that HGMs diffuse light in such a way that the periodicity of the screen is broken and thus the moiré intensity weakens. To quantitatively analyze its moiré suppression capability, we have calculated the spatial frequencies of the moiré fringes using fast Fourier transform. It is addressed that the moiré phenomenon is suppressed and thus the amplitude of each discrete spatial frequency term is reduced as the HGM concentration is increased. Using the filter with the HGM concentration of 9 wt%, the moiré fringes appeared depending sensitively on the distance between the LED screen and the camera are almost completely removed and the visibility of a nature image is enhanced at a sacrifice of luminance.