• ETRI Journal
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• 제29권1호
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• pp.8-17
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• 2007

In this paper, we present a time domain combined field integral equation formulation (TD-CFIE) to analyze the transient electromagnetic response from dielectric objects. The solution method is based on the method of moments which involves separate spatial and temporal testing procedures. A set of the RWG functions is used for spatial expansion of the equivalent electric and magnetic current densities, and a combination of RWG and its orthogonal component is used for spatial testing. The time domain unknowns are approximated by a set of orthonormal basis functions derived from the Laguerre polynomials. These basis functions are also used for temporal testing. Use of this temporal expansion function characterizing the time variable makes it possible to handle the time derivative terms in the integral equation and decouples the space-time continuum in an analytic fashion. Numerical results computed by the proposed formulation are compared with the solutions of the frequency domain combined field integral equation.

• 대한건축학회논문집:구조계
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• 제34권2호
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• pp.3-10
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• 2018

Damage location and extent of structure could be detected by the inverse analysis on dynamic response properties such as frequencies and mode shapes. In practice the measured difference of natural frequencies represent the stiffness change reliably, however the measured mode shape is insensitive for stiffness change, but provides spatial information of damage. The damage detection index on shear building structures is formulated in this study. The damage detection index could be estimated from mode shape and srory stiffness of undamaged structure and frequency difference between undamaged and damaged structure. For the verification of the observed damage detection method, the numerical analysis of Matlab and MIDAS and shacking table test were performed. In results, the damage index of damaged story was estimated so higher than undamaged stories that indicates the damaged story apparently.

• Geomechanics and Engineering
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• 제32권3호
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• pp.307-319
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• 2023

Ground fissures have a huge effect on the integrity of surface structures. In high-intensity ground fissure regions, however, land resource would be wasted and city building and economic development would be limited if the area avoiding principle was used. In view of this challenge, to reveal the seismic response and seismic failure characteristics of ground fissure sites, a shaking table test on model soil based on a 1:15 scale experiment was carried out. In the test, the spatial distribution characteristics of acceleration response and Arias intensity were obtained for a site exposed to earthquakes with different characteristics. Furthermore, the failure characteristics and damage evolution of the model soil were analyzed. The test results indicated that, with the increase in the earthquake acceleration magnitude, the crack width of the ground fissure enlarged from 0 to 5 mm. The soil of the hanging wall was characterized by earlier cracking and a higher abundance of secondary fissures at 45°. Under strong earthquakes, the model soil, especially the soil near the ground fissure, was severely damaged and exhibited reduced stiffness. As a result, its natural frequency also decreased from 11.41 Hz to 8.05 Hz, whereas the damping ratio increased from 4.8% to 9.1%. Due to the existence of ground fissure, the acceleration was amplified to nearly 0.476 m/s², as high as 2.38 times of the input acceleration magnitude. The maximum of acceleration and Arias intensity appeared at the fissure zone, which decreased from the main fissure toward both sides, showing hanging wall effects. The seismic intensity, duration and frequency spectrum all had certain effects on the seismic response of the ground fissure site, but their influence degrees were different. The seismic response of the site induced by the seismic wave that had richer low-frequency components and longer duration was larger. The discrepancies of seismic response between the hanging wall and the footwall declined obviously when the magnitude of the earthquake acceleration increased. The research results will be propitious to enhancing the utilizing ratio of the limited landing resource, alleviation of property damages and casualties, and provide a good engineering application foreground.

• 대한토목학회논문집
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• 제29권3B호
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• pp.269-279
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• 2009

대유역에서 계획홍수량 추정은 ARF, 강우 시공간분포 및 강우-유출 모형의 매개변수 등에서 많은 불확실성이 발생한다. 과거 동시 강우사상을 이용한 계획홍수량의 추정은 이들 불확실성을 개선할 수 있다. 본 연구는 과거 동시 강우사상과 저류 함수모형을 이용하여 대유역의 홍수량을 추정하는 방법을 제시하였다. 과거 동시 강우사상의 시공간분포를 이용하여 계획 강우량과 강우의 시공간분포를 산정하였고 비선형 강우-유출 반응을 재현할 수 있는 저류함수모형을 이용하여 홍수량을 추정하였다. 추정된 계획홍수량은 실측홍수량에 의한 빈도분석 결과와 비교하여 본 연구에서 제시한 홍수량 추정기법의 적용성을 평가하였다. 본 연구의 결과는 실측홍수량의 빈도해석과 비슷한 결과를 얻었으며 이는 대유역의 홍수량 추정에서 본 연구의 홍수량 추정과정을 충분히 이용할 수 있음을 보여준다.

• Wind and Structures
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• 제14권4호
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• pp.301-319
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• 2011

The full-scale measurements are compared with the wind tunnel test results for the long-span roof latticed spatial structure of Shenzhen Citizen Center. A direct comparison of model testing results to full-scale measurements is always desirable, not only in validating the experimental data and methods but also in providing better understanding of the physics such as Reynolds numbers and scale effects. Since the quantity and location of full-scale measurements points are different from those of the wind tunnel tests taps, the weighted proper orthogonal decomposition technique is applied to the wind pressure data obtained from the wind tunnel tests to generate a time history of wind load vector, then loads acted on all the internal nodes are obtained by interpolation technique. The nodal mean wind pressure coefficients, root-mean-square of wind pressure coefficients and wind pressure power spectrum are also calculated. The time and frequency domain characteristics of full-scale measurements wind load are analyzed based on filtered data-acquisitions. In the analysis, special attention is paid to the distributions of the mean wind pressure coefficients of center part of Shenzhen Citizen Center long-span roof spatial latticed structure. Furthermore, a brief discussion about difference between the wind pressure power spectrum from the wind tunnel experiments and that from the full-scale in-site measurements is compared. The result is important fundament of wind-induced dynamic response of long-span spatial latticed structures.

• 한국공간구조학회논문집
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• 제7권5호
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• pp.57-65
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• 2007

철골조 고층건물을 대상으로 풍응답계측을 실시하여, 감쇠율과 고유진동수의 진폭의존성을 검토하였다. 진폭의존성의 검토를 위하여 RD법을 사용하였다. RD법에 의한 진동특성을 하프파워법에 의한 진동특성과 비교하여 두 방법 사이의 상관관계를 분석하였다. 또한 일본, 캐나다기준에 의한 강풍시의 사용성평가를 통하여 두 가지 방법의 적용성을 검토하였다. RD법에 의하여 감쇠율의 진폭의존성을 확인하였으며, 고유진동수의 진폭의존성은 공학적인 의미에서 상대적으로 매우 작은 것을 확인하였다. 또한 계측건물은 사용성을 만족하였으며, 일본기준이 캐나다기준보다 더욱 엄격함을 확인하였다.

• 한국통신학회논문지
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• 제24권7B호
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• pp.1370-1377
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• 1999

본 논문에서는 움직임에 따른 인간시각 시스템의 인지 특성을 이용하여 동영상을 효과적으로 압축할 수 있는 기법을 제안한다. 비디오 신호에 대한 인간 시각 인지 특성을 분석하여 큰 이득을 주지 못하는 성분, 즉 인간의 눈에 민감하지 않은 부분을 감축 내지는 제거함으로써 인지 능력에서 볼 때 주관적 화질의 저하 없이 비디오 신호를 낮은 비트율로 압축할 수 있다. 제안된 기법은 움직임이 발생되는 정도와 크기에 매우 의존적으로, 움직임이 많은 비디오 신호에 더욱 적합하나 움직임이 작은 경우에도 적합한 움직임 보상을 통해 높은 이득을 얻기 때문에 모든 영상에 대해서 적용 가능한 방법이다. 몇 가지 영상을 대상으로 한 컴퓨터 시뮬레이션 결과, 프레임당 21-30:1 정도의 압축하에서 높은 재생화질을 얻을 수 있다.

• Korea-Australia Rheology Journal
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• 제21권1호
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• pp.17-25
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• 2009

We studied the flow characteristics of the polymer melt in the injection molding process with ultrasonic vibration by using the numerical analysis. To minimize the error between the experimental data and numerical result, we presented a methodology using the design of experiments and the response surface method for reverse engineering. This methodology can be applied to various fields to obtain a valid and accurate numerical analysis. Ultrasonic vibration is generally applied between an extruder and the entrance of a mold for improvement the flow rate in injection molding. In comparison with the general ultrasonic process, the mode shape of the mold must be also considered when the ultrasonic vibration is applied on the mold. The mode shape is defined as the periodic and spatial deformation of the structure owing to the effect of the vibration, and it varies greatly according to vibration conditions such as the forcing frequency. Therefore, we considered new index and found the forcing frequency for obtaining the highest flow rate within the range from 20 to 60 kHz on the basis of the index. Ultimately, we presented the methodology for not only obtaining a valid and accurate numerical analysis, but also for finding the forcing frequency to obtain the highest flow rate in injection molding using ultrasonic vibration.

• 한국전자파학회논문지
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• 제15권3호
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• pp.278-283
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• 2004

위성통신에서 있어서 주파수 할당 및 빔 커버리지가 다양해지고 복잡해짐에 따라 주파수상에서 인접하지 않은 여러 개의 채널 신호가 하나의 고출력 증폭기에 의해서 증폭되어져 안테나를 통하여 지상으로 송출되는 경우가 있다. 본 논문에서는, 이러한 위성통신 시스템에 적용이 가능한 두 개의 통과대역을 갖는 위성 중계기용 이중모드 정규(canonical) 구조 필터를 제시하였다. 필터의 무게와 부피를 줄이기 위하여 이중모드 설계기법을 사용하였으며, 최대한 많은 수의 전달영점 구현이 가능한 정규 구조로 필터를 설계하였다. 두 개의 통과대역을 갖는 Ka대역 위성 중계기용(30/20 ㎓) 6차 이중모드 정규 구조 필터의 구현을 통하여 설계기법을 검증하였다.

• Nuclear Engineering and Technology
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• 제55권6호
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• pp.1999-2010
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• 2023

Undesirable flapping motion of discs can cause the failure of swing check valves in nuclear passive safety systems. Time-resolved particle image velocimetry (PIV) was employed to investigate the flow characteristics around a free-to-rotate plate and the motion response, with the Reynolds numbers, based on the hydraulic diameter of the channel, from 1.32 × 10⁴ to 3.95 × 10⁴. Appreciable flapping motion (±3.52°) appeared at the Reynolds number of 2.6 × 10⁴ with the frequency of 5.08 Hz. In the low-Reynolds-number case, the plate showed negligible flapping. In the high-Reynolds-number case, the deflection angle increased with reduced flapping amplitude. The torque from the fluid determined the flapping amplitude. In the low-Reynolds-number case, Karman vortices were absent. With increasing Reynolds numbers, Karman vortices developed behind the plate with larger deflection angles. Strong interaction between the wake flow from the leading and trailing edge of the plate was observed. Based on power spectrum density (PSD) analysis, the vortex shedding frequency coincided with the flapping frequency, and the amplitude was positively correlated to the strength of the vortices. Proper orthogonal decomposition (POD) modes evince that, in the case of appreciable motion, coherent structures exhibited a larger spatial scale, enhancing the magnitude of the external torque on the plate.