• Nuclear Engineering and Technology
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• 제54권3호
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• pp.926-939
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• 2022

The area of this study will cover the location-wise seismic response variation of an electrical cabinet in nuclear power point (NPP) based on classical reliability analysis. The location-based seismic ground motion (GM) selection is carried out with the help of probabilistic seismic hazard analysis using PSHRisktool, where the variation of reliability analysis can be understood from the relation between the reliability index and intensity measure. Two different approaches such as the first-order second moment method (FOSM) and Monte Carlo Simulation (MCS) are helped to evaluate and compare the reliability assessment of the cabinet. The cabinet is modeled with material uncertainty utilizing Steel01 as the material model and the fiber section modeling approach is considered to characterize the section's nonlinear reaction behavior. To verify the modal frequency, this study compares the FEM result with recorded data using Least-Squares Complex Exponential (LSCE) method from the impact hammer test. In spite of a few investigations, the main novelty of this study is to introduce the reader to check and compare the seismic reliability assessment variation in different seismic locations and for different earthquake levels. Alongside, the betterment can be found by comparing the result between two considered reliability estimation methods.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2004년도 전력전자학술대회 논문집(1)
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• pp.87-91
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• 2004

In this paper, the paralleled forward converter, that is generally used as the power supply for the low voltage, high current load, is described. The proposed forward converter for battery charging could be provided the power without failure not only in steady state but also in the transient period by the step load variation or the unexpected faults among the converter modules. Each converter nodule designed is operated alone with the self closed controller for the elevation of stability, performance, reliability, and maintainability. The frequency response of the designed converter module is analyzed, and the stability is confirmed in analytic method. And the experiments of the paralleled battery charger are carried out in steady state, in the step load variation.

• 한국정보통신학회논문지
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• 제3권3호
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• pp.617-626
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• 1999

주파수 응답 특성이 부하 변동에 따라 변화되는 채널에서의 고속, 고신뢰의 데이터 전송을 위하여 CSK방식의 신호전송 특성을 컴퓨터 시뮬레이션 방법을 통하여 알아보았다. 특히, 간단한 구조의 Roll-off 필터를 등화기로 사용함으로써 극히 낮은 S/(I+N) 환경하에서도 BER을 크게 향상시키는 결과를 얻었다. 컴퓨터 시뮬레이션 결과 S/I=2, S/N=2 즉, S(I+N)=1에서 에러없는 데이터 전송이 이루어지는 것을 확인하였다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2003년도 하계종합학술대회 논문집 I
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• pp.418-421
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• 2003

In this thesis, a new channel estimation technique is proposed for orthogonal frequency division multiplexing (OFDM) over time varying channels. The channel estimation algorithm exploits the fact that the estimated channel impulse response (CIR) by using pilot signal is the average value of the CIR variation within an OFDM symbol period. With this fact, the CIR variation is simply estimated through lowpass interpolation of the CIRs of the adjacent OFDM symbols. For signal detection, a time domain equalizer is used in this thesis. Simulation results show that the proposed system improves the bit error rate (BER) over time varying channels.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.442-448
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• 2008

This paper presents an approach to define an optimal piezoactuator length to actively control structural vibration. The optimal ratio of the piezoactuator length against beam length when a pair of piezoceramic actuator and accelerometer is used to suppress unwanted vibration with direct velocity feedback (DVFB) control strategy is not clearly defined so far. It is well known that direct velocity feedback (DVFB) control can be very useful when a pair of sensor and actuator is collocated on structures with a high gain and excellent stability. It is considered that three different collocated pairs of piezoelectric actuators (20, 50 and 100 mm) and accelerometers installed on three identical clamped-clamped beams (300 * 20 * 1 mm). The response of each sensor-actuator pair requires strictly positive real (SPR) property to apply a high feedback gain. However the length of the piezoactuator affects SPR property of the sensor-actuator response. Intensive simulation and experiment shows the effect of the actuator length variation is strongly related with the frequency range of SPR property. A shorter actuator gave a wider SPR frequency range as a longer one had a narrower range. The shorter actuator showed limited control performance in spite of a higher gain was applied because the actuation force was relatively small. Thus an optimal length ratio (actuator length/beam length) was suggested to obtain relevant performance with good stability with DVFB strategy. The result of this investigation could give important information in the design of active control system to suppress unwanted vibration of smart structures with piezoelectric actuators and accelerometers.

• 한국정보통신학회논문지
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• 제18권8호
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• pp.1818-1826
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• 2014

해면 상태의 변화는 수중 음향 통신 수신 신호에 전방 산란 및 도플러 확산을 야기하여 수신 신호의 진폭, 주파수 및 위상은 시간적으로 변화한다. 따라서 통신채널의 일관성 대역폭과 페이딩 변화에 의해 고속 동기식 디지털 통신 성능은 장애를 받게 된다. 본 논문에서는 2가지의 해면 상태에서 QPSK의 성능을 평가하였다. 해면 산란이 성능에 미치는 영향은 LFM 신호를 이용하여 구한 채널의 임펄스 응답과 시간 일관성을 기반으로 해석하였다. 잔잔한 해면보다 거친 해면 상태의 임펄스 응답은 불안정하고 일관성 시간은 짧다. 이러한 결과와 수신 신호의 포락선, 진폭 및 위상과의 관계를 해석하여 QPSK의 비트 오류율이 해면 상태와 직접적으로 관계되는 것을 확인하였다.

• 대한조선학회논문집
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• 제59권3호
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• pp.134-140
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• 2022

Ship local structure sometimes experiences severe vibration due to the resonance with an excitation force generated by the propulsion system. In that case, the installation of dynamic vibration absorber such as Tuned Mass Damper (TMD) on the structure can be considered as an effective alternative countermeasure to reduce the troublesome vibration if structural modification or change of excitation frequencies is difficult. Meanwhile, the conventional optimal design method of TMD premises the target structure exposed on an excitation force without the constraint of its magnitude and frequency range. However, the frequencies of major ship excitation forces due to propulsion system are normally bounded and its magnitude is varied according to its operation speed. Hence, the optimal design of TMD to reduce the resonant vibration of ship local structure should be differently approached compared with the conventional ones. For the purpose, this paper proposes an optimal design method of TMD considering maximum frequency and magnitude variation of a target harmonic excitation component. It is done by both lowering the resonant response at the 1st natural frequency and locating the 2nd natural frequency over maximum excitation frequency for the idealized 2 degree of freedom system consisted of the structure and the TMD. For the validation of the proposed method, a numerical design case of TMD for a ship local structure exposed on resonant vibration due to a propeller excitation force is introduced and its performance is compared with the conventionally designed one.

• 감성과학
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• 제4권1호
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• pp.61-67
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• 2001

This paper described the effect of subjective approach in case of the human sensibility experiments. The procedure is proceeded subjectively. Human faces are selected as the image presentation media. Pleasant and unpleasant images are selected directly by examiner, And also the image presentation system, which is executed with a computer and has the square-type black box monitor equipment, is manufactured. Images are presented with the step-variation time interval technique. questionnaire test and EEG signal detection data are analyzed. The analysis parameters are a “frequency band integral value” and a “band differential variation ratio”. he results show the high sensibility and fast response. The fact that image presenting repetition alleviates is verified.

• 한국추진공학회지
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• 제9권2호
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• pp.32-39
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• 2005

액체 연료 로켓의 연료 공급 라인을 모사 한 시스템에 대해, PSD가 시스템의 응답에 미치는 영향을 살펴보았다. 주관의 유량 변화에 대한 주관 압력 변화의 비(시스템 응답)를 PSD 내의 기체 체적$((0\~2)\times10^{-3}m^3)$과 PSD 배플의 직경(5, 50, 115 mm)을 변화시키며 살펴보았다. PSD 내에 기체가 있을 경우, 시스템의 고유진동 주파수가 작아짐을 확인하였다. 그리고 기체의 체적이 클수록 시스템 고유진동 주파수가 작아졌으나, 그 변화는 그리 크지 않았다. 또한 PSD 내 기체량이 많은 경우, 주관 내 압력 및 유량 변화의 진폭이 많이 감소함을 확인할 수 있었다. PSD 배플의 직경이 작아질수록 시스템 고유 진동 주파수가 작아졌으나 그 변화는 작았다. 또한 PSD 배플의 저항이 클 때, PSD 내 압력은 주관의 압력 크기보다 작고, 지연된 파형이 관찰되었다.

• Structural Engineering and Mechanics
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• 제34권1호
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• pp.61-84
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• 2010

Presented in this paper is the behaviour of asymmetric building isolated by the double variable frequency pendulum isolator (DVFPI). The DVFPI is an adoption of single variable frequency pendulum isolator (VFPI). The geometry and coefficient of friction of top and bottom sliding surfaces can be unequal. The governing equations of motion of the building-isolation system are derived and solved in incremental form. The analysis duly considers the interaction of frictional forces in the two principal directions developed at each sliding surface of the DVFPI. In order to investigate the behaviour of the base isolation using the DVFPI, the coupled lateral-torsional response is obtained under different parametric variations for a set of six far-fault earthquake ground motions and criterion to optimize its performance is proposed. Further, influences of the initial time period, coefficient of friction and frequency variation factors at the two sliding surfaces are investigated. The numerical results of the extensive parametric study help in understanding the torsional behaviour of the structure isolated with the double sliding surfaces as in the DVFPI. It is found that the performance of the DVFPI can be optimized by designing the top sliding surface initially softer and smoother relative to the bottom one.