• 한국소음진동공학회논문집
• /
• 제26권5호
• /
• pp.501-510
• /
• 2016

Capabilities of several beamforming techniques are compared for estimating the position of a moving source. Beamforming has enabled to widen our perspective of aeroacoustics in wind tunnel experiments and has provided useful approach in array measurements. Meanwhile beamforming techniques have been developed in a way to improve estimation accuracy and to save ing effort at the same time. In order to achieve reasonable outcome from aeroacoustic measurement, it is important to identify the spectral characteristics of source and to select an appropriate beamformer. Though aeroacoustic sources normally generates broadband noises, many array signal processing have been focused on narrowband processing which makes calculation numerically efficient. However, calculation in frequency-domain requires selection of single frequency of interest which affects spatial resolution and sidelobe level as a consequence. To be able to localize broadband noise source, it is proposed to use broadband beamforming. The formulas implements the deletion of diagonal term from cross spectral matrix. In this study, trajectory of flying source emitting broadband noise was simulated and several beamformers are applied.

• 한국전자파학회논문지
• /
• 제11권2호
• /
• pp.186-196
• /
• 2000

본 논문에서는 이중통신용 안테나 시스템을 위한 변형된 사각 루프 주파수 선택 반사기를 제안하고, 그 특성 을 해석하였다 변형된 사각 루프 주파수 선택 반사기를 해석함에 있어서 유전체의 영향과 주기적 배열구조임을 고려하기 워하여 파수 영역 방법(Spectral Domain Method)과 Floquet 이론을 도입하였으며, 수치해석 방법으로 는 rooftop basis function을 이용한 모멘트법을 적용하였다 해석결과로는 기존의 사각 루프와 변형된 사각 루프 의 전송 특성플 비교하였으며. 변형된 사각 루프의 경우 입사각과 편파 변화에 따른 전송 특성도 제시하였다. 수 치해석 방법의 타당성을 검증하기 위해 변형된 사각 루프 주파수 선택 반사기를 실제 제작 및 측정하여 수치해 석 결파와 비교하였다. 측정결과는 수치해석 결과와 비교적 잘 일치함을 보였다

• Current Applied Physics
• /
• 제18권11호
• /
• pp.1327-1337
• /
• 2018

This paper investigates the vibration behavior of pristine and defected triangular graphene sheets; which has recently attracted the attention of researchers and compare these two types in natural frequencies and sensitivity. Here, the molecular dynamics method has been employed to establish a virtual laboratory for this purpose. After measuring the different parameters obtained by the molecular dynamics approach, these data have been analyzed by using the frequency domain decomposition (FDD) method, and the dominant frequencies and mode shapes of the system have been extracted. By analyzing the vibration behaviors of pristine triangular graphene sheets in four cases (right angle of 45-90-45 configuration, right angle of 60-90-30 configuration, equilateral triangle and isosceles triangle), it has been demonstrated that the natural frequencies of these sheets are higher than the natural frequency of a square sheet, with the same number of atoms, by a minimum of 7.6% and maximum of 26.6%. Therefore, for increasing the resonance range of sensors based on 2D materials, nonrectangular structures, and especially the triangular structure, can be considered as viable candidates. Although the pristine and defective equilateral triangular sheets have the highest values of resonance, the sensitivity of defective (45,90,45) triangular sheet is more than other configurations and then, defective (45,90,45) sheet is the worst choice for sensor applications.

• IEIE Transactions on Smart Processing and Computing
• /
• 제2권6호
• /
• pp.350-356
• /
• 2013

Single Carrier Frequency Domain Multiple Access (SC-FDMA) has proven to be the best long term evolution for uplink multiple access because of its low Peak to Average Power Ratio (PAPR), a feature that leads to low power consumption. This is achievable only if the resource allocation is performed in a contiguous manner. This paper proposes a new approach with an improvement in the global resources allocation. The new approach presented utilizes the gain function, which adopts some of the procedures deduced from the older Recursive Maximum Expansion (RME) algorithm. The experiment proved that the new approach is better than the original RME algorithms and in most cases, is closer to the optimal solution.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제12권3호
• /
• pp.1224-1242
• /
• 2018

Aiming at motion analysis and compensation, it is essential to conduct motion detection with images. However, motion detection and tracking from low-altitude images obtained from an unmanned aerial system may pose many challenges due to degraded image quality caused by platform motion, image instability and illumination fluctuation. This research tackles these challenges by proposing a modified joint transform correlation algorithm which includes two preprocessing strategies. In spatial domain, a modified fuzzy edge detection method is proposed for preprocessing the input images. In frequency domain, to eliminate the disturbance of self-correlation items, the cross-correlation items are extracted from joint power spectrum output plane. The effectiveness and accuracy of the algorithm has been tested and evaluated by both simulation and real datasets in this research. The simulation experiments show that the proposed approach can derive satisfactory peaks of cross-correlation and achieve detection accuracy of displacement vectors with no more than 0.03pixel for image pairs with displacement smaller than 20pixels, when addition of image motion blurring in the range of 0~10pixel and 0.002variance of additive Gaussian noise. Moreover,this paper proposes quantitative analysis approach using tri-image pairs from real datasets and the experimental results show that detection accuracy can be achieved with sub-pixel level even if the sampling frequency can only attain 50 frames per second.

• 융합신호처리학회 학술대회논문집
• /
• 한국신호처리시스템학회 2005년도 추계학술대회 논문집
• /
• pp.302-305
• /
• 2005

Recently, many methods to analyze signal have been proposed and representative methods are the Fourier transform and wavelet transform. In these methods, the Fourier transform represents signal with combination cosine and sine at all locations in the frequency domain. However, it doesn't provide time information that particular frequency occurs in signal and denpends on only the global feature of the signal. So, to improve these points the wavelet transform which is capable of multiresolution analysis has been applied to many fields such as speech processing, image processing and computer vision. And the wavelet transform, which uses changing window according to scale parameter, presents time-frequency localization. In this paper, we proposed a new approach using a wavelet of cosine and sine type and analyzed features of signal in a limited point of frequency-time plane.

• 지구물리와물리탐사
• /
• 제15권3호
• /
• pp.129-135
• /
• 2012

동시 송신원 전파형 역산 기법은 계산량을 획기적으로 줄여 전파형 역산의 적용성을 높여준다. 그러나 다수의 송신원 모음 자료를 동시에 모델링하여 사용하기 때문에 관측 자료의 수진기 위치가 송신원에 따라 다른 경우, 나머지(residual) 파동장에 불필요한 값을 생성하게 되고 이는 파형역산의 수렴성을 저해하게 된다. 특히, 제한된 벌림 거리(offset)를 갖는 스트리머 방식의 탐사자료는 동시 송신원 기법을 적용하기에 가장 어려운 자료 형태이다. 이러한 문제점을 극복하기 위해 최근에 global correlation에 기반한 목적함수가 제안되었고, 시간영역 전파형 역산에 성공적으로 적용되었다. 그러나 이 기법은 변형된 목적함수를 사용하기 때문에 나머지 파동장이 왜곡되고 경우에 따라 역산 결과에 부정적인 영향을 주기도 한다. 또한, 여러 가지 장점을 갖고 있는 주파수 영역 파형역산에 적용된 사례는 아직 보고된 적이 없다. 본 논문에서는 이러한 나머지 파동장의 왜곡을 최소화하기 위해 global correlation 계산 시 사용하는 자료에 진폭감쇠 기법을 적용한다. 진폭감쇠를 적용한 자료는 global correlation의 특성을 최적화하여 나머지 파동장의 왜곡을 줄이고 파형역산 결과를 향상시킨다. 시간 영역에서 구한 나머지 파동장을 주파수 영역에서 역전파시킴으로써 global correlation기법을 주파수 영역에서 구현한다. 스트리머 방식의 합성 탐사자료를 이용한 예제를 통해 본 논문에서 제안한 기법이 기존의 global correlation 목적함수에 기반한 동시 송신원 전파형 역산보다 향상된 결과를 얻을 수 있음을 보여준다.

• Computers and Concrete
• /
• 제30권4호
• /
• pp.277-287
• /
• 2022

Due to the scarcity of extortionate experimental data, fatigue failure of the reinforced concrete (RC) element might be achieved economically adopting nonlinear finite element (FE) analysis as an alternative approach. However, conventional implicit dynamic analysis is expensive, quasi-static method overlooks interaction effects and inertia, direct cyclic analysis computes stabilized responses. Apart from this, explicit dynamic analysis may provide a numerical operating system for factual long-term responses. The study explores the fatigue behavior based on a simplified explicit dynamic solution employing nonlinear time domain analysis. Among fourteen RC beams, one beam is selected to validate under static loading, one under fatigue with the experimental study and other twelve to check the detail fatigue behavior. The SWOT (Strength, Weakness, Opportunities, Threats) analysis has been carried out to pinpoint the detail scenario in the adoption of numerical approach as an alternative to the experimental study. Excellent agreement of FE and experimental results is seen. The 3D nonlinear RC beam model at service fatigue limits is truthful to be used as an expedient contrivance to envisage the precise fatigue behavior. The simplified analysis approach for RC beam under fatigue offers savings in computation to predict responses providing acceptable accuracy rather than the complicated laboratory investigation. At higher frequency, the flexural failure occurs a bit earlier gradually compared to the repeated loading case of lower frequency. The deflection increases by 6%-10% at the end of first cycle for beams with increasing frequency of cyclic loading. However, at the end of fatigue loading, greater deflection occur earlier for higher load range because of more rapid stiffness degradation. For higher frequency, a slight boost in concrete compressive strains at an initial stage of loading has been seen indicating somewhat stepper increment. Stiffness degradation in larger loading cycle at same duration escalates the upsurge of the rate of strain in case of higher frequency.

• 대한전자공학회논문지TC
• /
• 제39권4호
• /
• pp.201-208
• /
• 2002

본 논문에서는 3 차원 임의 형태 도체의 지연 산란 응답을 얻기 위한, 새로운 시간영역 전장 적분방정식(Time-Domain Electric Field Integral Equation: TD-EFIE)을 제안한다. 자기 벡터 전위의 시간 미분항은 중앙 차분으로, 전기 스칼라 전위는 시간에 대한 평균을 취한 두 개의 항으로 근사하였다. 이로부터 도체에 의한 산란 지연 응답 해의 산출시, 기존의 방법보다 정확하고 더욱 안정된 해를 얻을 수 있었다. 제안된 방법의 자세한 정식화 과정을 보였으며, 주파수 영역에서의 이산 푸리에 역변환 (Inverse Discrete Fourier Transform: IDFT) 결과치와 제안된 방법에 의한 수치해를 각각 비교하였다.

• Wind and Structures
• /
• 제17권2호
• /
• pp.227-244
• /
• 2013

Non-stationary extreme winds such as thunderstorm downbursts are responsible for many structural damages. This research presents a time domain approach for estimating along-wind load effects on tall buildings using multiple wind speed time history samples, which are simulated from evolutionary power spectra density (EPSD) functions of non-stationary wind fluctuations using the method developed by the authors' earlier research. The influence of transient wind loads on various responses including time-varying mean, root-mean-square value and peak factor is also studied. Furthermore, a simplified model is proposed to describe the non-stationary wind fluctuation as a uniformly modulated process with a modulation function following the time-varying mean. Finally, the probabilistic extreme response and peak factor are quantified based on the up-crossing theory of non-stationary process. As compared to the time domain response analysis using limited samples of wind record, usually one sample, the analysis using multiple samples presented in this study will provide more statistical information of responses. The time domain simulation also facilitates consideration of nonlinearities of structural and wind load characteristics over previous frequency domain analysis.