• 한국산학기술학회논문지
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• 제15권8호
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• pp.4769-4775
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• 2014

본 논문은 다관절 붐의 선단이 구조물과 충돌할 때 발생하는 각 붐의 동응력에 대해서 논하고자 한다. CATIA를 이용하여 3D 모델을 작성하고, ADAMS와 ANSYS를 이용하여 메쉬작업을 수행 후 응력데이터를 포함한 다관절 붐의 MNF를 만든다. 이 두가지 모델을 가지고 ADAMS에서 FFT해석을 수행하여 각각 모델의 타당성을 알아본다. ADAMS에서 타당성이 검증된 모델을 이용하여 붐 선단의 충돌해석에 따른 동특성 해석을 수행한다. ADAMS Durability를 이용하여 다관절 붐과 구조물의 충돌시 각 붐에 응력이 크게 발생하는 지점을 알아보고자 한다.

• 한국통신학회논문지
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• 제29권10C호
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• pp.1378-1386
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• 2004

본 논문에서는 oversampling에 의하여 BER 성능을 개선할 수 있는 OFDM 변복조 방식을 제안하였다. 제안된 OFDM 변복조 방식은 사용하는 반송파 개수 N과 동일한 개수의 0 데이터를 삽입하여 2N point IFFT하여 전송한다. 수신단에서는 두 배 높은 주파수로 샘플링하여 2N point FFT하여 신호를 복조한다. 본 논문에서는 AWGN 환경에서 제안된 방식이 기존의 방식에 비하여 SNR에서 3 dB 성능 개선이 이루어진다는 것을 수학적인 증명을 시도하였다. 또한 컴퓨터 시뮬레션을 통하여 AWGN 채널 환경에서 기존의 방식과 제안된 방식의 BER 성능을 분석하였다. 시뮬레이션 결과 동일 에러 확률 성능을 얻기 위한 Eb/No이 3 dB 개선됨을 보였다.

• 대한기계학회논문집A
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• 제25권8호
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• pp.1253-1260
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• 2001

Transient thermal analysis of a three-dimensional axisymmetric automotive disk brake is presented in this paper. Temperature fields are obtained using a hybrid FFT-FEM scheme that combines Fourier transform techniques and finite element method. The use of a fast Fourier transform algorithm can avoid singularity problems and lead to inexpensive computing time. The transformed problem is solved with finite element scheme for each frequency domain. Inverse transforms are then performed for time domain solution. Numerical examples are presented for validation tests. Comparisons with analytical results show very good agreement. Also, a 3-D simulation, based upon an automotive brake disk model is performed.

• 제어로봇시스템학회논문지
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• 제16권7호
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• pp.720-725
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• 2010

In AGPS method, user position can be obtained even in the shadow region by improving signal sensitivity. A hybrid long integration scheme employing both coherent and non-coherent integration method is commonly used in AGPS receivers. Because coherent loss increases as residual frequency become large, residual frequency should be minimized to maximize coherent integration gain. This paper presents performance analysis of residual frequency estimator using FFT in fine-time assistance AGPS method. Considering the hardware complexity and the estimation accuracy, optimal length of FFT is proposed for GPS L1 C/A signal. Signal sensitivity for estimating the residual frequency is also analysed. By field experimental results, it is found that the residual frequency can be successfully estimated using 1 second snap-shot data when GPS signal strength is larger than -150 dBm and its RMS error is 3Hz.

• Journal of Power Electronics
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• 제11권3호
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• pp.360-368
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• 2011

This paper proposes an active frequency with a positive feedback in the d-q frame anti-islanding method suitable for a robust phase-locked loop (PLL) algorithm using the FFT concept. In general, PLL algorithms for grid-connected PV PCS use d-q transformation and controllers to make zero an imaginary part of the transformed voltage vector. In a real grid system, the grid voltage is not ideal. It may be unbalanced, noisy and have many harmonics. For these reasons, the d-q transformed components do not have a pure DC component. The controller tuning of a PLL algorithm is difficult. The proposed PLL algorithm using the FFT concept can use the strong noise cancelation characteristics of a FFT algorithm without a PI controller. Therefore, the proposed PLL algorithm has no gain-tuning of a PI controller, and it is hardly influenced by voltage drops, phase step changes and harmonics. Islanding prediction is a necessary feature of inverter-based photovoltaic (PV) systems in order to meet the stringent standard requirements for interconnection with an electrical grid. Both passive and active anti-islanding methods exist. Typically, active methods modify a given parameter, which also affects the shape and quality of the grid injected current. In this paper, the active anti-islanding algorithm for a grid-connected PV PCS uses positive feedback control in the d-q frame. The proposed PLL and anti-islanding algorithm are implemented for a 250kW PV PCS. This system has four DC/DC converters each with a 25kW power rating. This is only one-third of the total system power. The experimental results show that the proposed PLL, anti-islanding method and topology demonstrate good performance in a 250kW PV PCS.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 춘계학술대회논문집
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• pp.27-33
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• 2003

In closed-die forging process, blocker has been used to fill and distribute metal well in finisher die. Generally, the blocker shape was determined by an expert with many experiences. However, the manual blocker design process takes much time and efforts, so various automatic methods for the blocker design process have been suggested for the last three decades. The method with filtering in FFT (Fast Fourier Transform) for the blocker design provides general solution than other methods. But, due to the properties of FFT in time-frequency domain, this method has some drawbacks such as long calculation time, difficulty of local control and additional boundary process after filtering. In this study, DWT (Discrete Wavelet Transform), which is more flexible and is more wildly used than FFT, is applied to the blocker design. The method with filtering in DWT is very proper to design blocker in both 2-D and 3-D shapes. To verify the efficiency of this method, blockers of some models are designed and the results show that blocker design with DWT is effective fer the blocker designs

• 소성∙가공
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• 제12권4호
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• pp.277-283
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• 2003

In a closed-die forging process, blocker has been used to fill and distribute metal well in finisher die. Generally, the blocker shape was determined by an expert with many experiences. However, the manual blocker design process takes much time and efforts, so various automatic methods for the blocker design process have been suggested for the last three decades. The method with filtering in FFT (Fast Fourier Transform) for the blocker design provides general solution than other methods. But. due to the properties of FFT in time-frequency domain, this method has some drawbacks such as long calculation time, difficulty of local control and additional boundary process after filtering. In this study. DWT (Discrete Wavelet Transform), which is more flexible and is more wildly used than FFT, is applied to the blocker design. The method with filtering in DWT is very proper to design blocker in both 2-D and 3-D shapes. To verify the efficiency of this method, blockers of some models are designed and the results show that blocker design with DWT is effective for the blocker designs.

• 대한건축학회논문집:계획계
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• 제36권4호
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• pp.41-49
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• 2020

The purpose of this study was to investigate the use of the Deep Neural Networks(DNN) model to classify user's emotions, in particular Electroencephalography(EEG) toward Virtual-Reality(VR) based 3D design alternatives. Four different types of VR Space were constructed to measure a user's emotion and EEG was measured for each stimulus. In addition to the quantitative evaluation based on EEG data, a questionnaire was conducted to qualitatively check whether there is a difference between VR stimuli. As a result, there is a significant difference between plan types according to the normalized ranking method. Therefore, the value of the subjective questionnaire was used as labeling data and collected EEG data was used for a feature value in the DNN model. Google TensorFlow was used to build and train the model. The accuracy of the developed model was 98.9%, which is higher than in previous studies. This indicates that there is a possibility of VR and Fast Fourier Transform(FFT) processing would affect the accuracy of the model, which means that it is possible to classify a user's emotions toward VR based 3D design alternatives by measuring the EEG with this model.

• 한국정보통신학회논문지
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• 제25권3호
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• pp.427-432
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• 2021

본 논문에서는 미상의 통신신호에 대한 자동 변조 인식을 위하여 심층신경망인 딥뉴럴네트워크를 적용하여 변조 형태를 식별하고 그 성능을 분석하였다. 신경망 입력 데이터는 변조된 신호의 시간영역 디지털샘플 데이터, FFT(Fast Fourier Transform)를 적용한 주파수영역 데이터, 시간 및 주파수영역 혼합데이터를 사용하여 각각의 변조인식 성능을 확인하였다. 아날로그 변조 및 디지털 변조 신호 11종에 대하여 -20~18 dB 까지 다양한 SNR(Signal to Noise Ratio) 환경에서 변조인식 성능을 확인하고 그 성능을 분석하였으며, 입력 데이터의 종류에 따른 학습 속도를 확인함으로써 제안한 방법이 실제적인 자동변조 인식 시스템 구축에 효과적인 방법임을 확인 하였다.

• 전자공학회논문지CI
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• 제48권5호
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• pp.55-63
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• 2011

본 논문은 방위각 및 고저방향으로 카메라 움직임이 있는 감시장치의 비디오 프레임 연속영상을 1)각각 $N{\times}M$ 개의 서브블록으로 나눈 후 각각의 서브블록에 대해 FFT 위상상관 기법을 적용하여 이동표적 위치를 구하고, 2)연속영상을 정합 후 차영상을 구하여 적응 문턱 값을 적용해서 표적후보군을 구하였으며, 3)두 기법을 적용하여 클러터를 제거하는 새로운 표적탐지기법을 제안하였다. 블록 내 다양한 크기의 영상 움직임이 있을 경우 FFT 위상상관 기법은 적용하여 움직임을 구하면 큰 영상의 움직임이 가장 큰 위상상관 값으로 나타나는 특성을 이용하여 배경환경에 강인한 이동표적 위치(블록)탐지를 하였다. 또한, 차영상을 영상분리하기 위한 적응 문턱 값은 카메라 움직임 등 배경환경 변화를 고려한 학습가중치를 이용하여 구하였다. 제안된 알고리즘 성능입증은 다양한 배경환경에서 카메라 이동/정지조건에서 다양한 이동표적에 대해 탐지 가능함을 시뮬레이션을 통해 확인하였으며 탐지성능은 ROC 커브를 통해 확인하였다.