• 제목/요약/키워드: Fourier-Based Optimization

검색결과 32건 처리시간 0.023초

Neural Network Based Expert System for Induction Motor Faults Detection

  • Su Hua;Chong Kil-To
    • Journal of Mechanical Science and Technology
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    • 제20권7호
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    • pp.929-940
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    • 2006
  • Early detection and diagnosis of incipient induction machine faults increases machinery availability, reduces consequential damage, and improves operational efficiency. However, fault detection using analytical methods is not always possible because it requires perfect knowledge of a process model. This paper proposes a neural network based expert system for diagnosing problems with induction motors using vibration analysis. The short-time Fourier transform (STFT) is used to process the quasi-steady vibration signals, and the neural network is trained and tested using the vibration spectra. The efficiency of the developed neural network expert system is evaluated. The results show that a neural network expert system can be developed based on vibration measurements acquired on-line from the machine.

스펙트럼을 이용한 피로손상도 계산과정 최적화 연구 (Study on Optimization of Fatigue Damage Calculation Process Using Spectrum)

  • 김상우;이승재;최솔미
    • 한국해양공학회지
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    • 제32권3호
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    • pp.151-157
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    • 2018
  • Offshore structures are exposed to low- and high-frequency responses due to environmental loads, and fatigue damage models are used to calculate the fatigue damage from these. In this study, we tried to optimize the main parameters used in fatigue damage calculation to derive a new fatigue damage model. A total of 162 bi-modal spectra using the elliptic equation were defined to describe the response of offshore structures. To calculate the fatigue damage from the spectra, time series were generated from the spectra using the inverse Fourier transform, and the rain-flow counting method was applied. The considered optimization variables were the size of the frequency increments, ratio of the time increment, and number of repetitions of the time series. In order to obtain optimized values, the fatigue damage was calculated using the parameter values proposed in previous work, and the fatigue damage was calculated by increasing or decreasing the proposed values. The results were compared, and the error rate was checked. Based on the test results, new values were found for the size of the frequency increment and number of time series iterations. As a validation, the fatigue damage of an actual tension spectrum found using the new proposed values and fatigue damage found using the previously proposed method were compared. In conclusion, we propose a new optimized calculation process that is faster and more accurate than the existed method.

바로서기 동작 시 EEG와 역학변인 간 동작 예측의 탐구 (Exploration of Motion Prediction between Electroencephalography and Biomechanical Variables during Upright Standing Posture)

  • Kyoung Seok Yoo
    • 한국운동역학회지
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    • 제34권2호
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    • pp.71-80
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    • 2024
  • Objective: This study aimed to explore the brain connectivity between brain and biomechanical variables by exploring motion recognition through FFT (fast fourier transform) analysis and AI (artificial intelligence) focusing on quiet standing movement patterns. Method: Participants included 12 young adult males, comprising university students (n=6) and elite gymnasts (n=6). The first experiment involved FFT of biomechanical signals (fCoP, fAJtorque and fEEG), and the second experiment explored the optimization of AI-based GRU (gated recurrent unit) using fEEG data. Results: Significant differences (p<.05) were observed in frequency bands and maximum power based on group and posture types in the first experiment. The second study improved motion prediction accuracy through GRU performance metrics derived from brain signals. Conclusion: This study delved into the movement pattern of upright standing posture through the analysis of bio-signals linking the cerebral cortex to motor performance, culminating in the attainment of motion recognition prediction performance.

맞춤형 BCI시스템을 위한 STFT와 PSO를 이용한 ERS특징 추출 (ERS Feature Extraction using STFT and PSO for Customized BCI System)

  • 김용훈;김준엽;박승민;고광은;심귀보
    • 한국지능시스템학회논문지
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    • 제22권4호
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    • pp.429-434
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    • 2012
  • 본 논문에서는 사지가 마비되어 신체를 움직이지 못하지만 뇌의 기능은 정상적인 대 마비 환자들을 위한, 생각만으로 외부의 장치를 제어할 수 있도록 하는 BCI(Brain-Computer Interface) 시스템 제어기술을 연구하였다. 사지를 움직이는 상상을 할 경우, 뇌의 운동 감각 피질 영역에서 발생하는 뮤리듬(${\mu}8$-12Hz)에서 증가되는 신호의 패턴인 Event-Related Synchronization (ERS)를 Short-Time Fourier Transform (STFT)과 Particle Swarm Optimization (PSO)를 이용하여 검출 하는 방법을 시도 하였다. ERS는 사람마다 다른 주파수 영역에서 발생하며, 본 논문에서는 ERS가 가장 많이 발현되고 전압이 큰 주파수를 검출하기 위해 8-12Hz 주파수영역의 EEG평균에서 PSO를 이용하여 가장 큰 진폭을 가지는 주파수를 확인 한 후, 해당 주파수를 사용하여 C3, C4채널에서 동작 상상 시 나타나는 ERS의 특징을 PSO를 이용하여 찾는 것이며. 개개인 마다 다른 주파수 영역에서 나타나는 ERS의 특징을 가장 많이 발현되는 주파수영역으로 고정하여 움직임 분석을 시도 하였다. 실험 결과에 사용된 data는 BCI competition IV data set의 실험자 b data를 사용 하였고, 하나의 주파수 대역만을 사용한 결과 왼손 40%, 오른손 38% 검출 정확도를 보였다.

균일 밝기 랜덤 도트 어레이 생성을 위한 이진 회절광학소자 설계 및 제작 (Design and Fabrication of Binary Diffractive Optical Elements for the Creation of Pseudorandom Dot Arrays of Uniform Brightness)

  • 이수연;이준호;김영광;이혁교;이문섭
    • 한국광학회지
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    • 제33권6호
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    • pp.267-274
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    • 2022
  • 쉴리렌 이미징을 위한 랜덤 도트 배열 투영용 이진 회절광학소자를 설계하고 제작하였다. 이 연구에서 적용된 회절광학소자는 단 두 단계의 위상 및 10 ㎛의 피치를 갖는 이진 위상 회절 격자로, 제작 단가 및 제작 공정의 용이성을 위하여 선택되었다. 회절광학소자의 설계는 최종 패턴의 밝기 정보를 목적 함수로 사용하는 iterative Fourier transform algorithm을 적용하였다. 먼저 균일 밝기의 랜덤 도트 이미지를 생성하였고, 이를 최종 목표 이미지(패턴)로 적용한 결과, 위치(시야)에 따른 랜덤 도트의 밝기 변화를 확인하였다. 이를 해결하기 위하여 최종 목표 패턴에 가우시안 가중치를 적용한 개선 설계를 적용하였고, 그 결과 패턴 밝기 균일도를 52.7%에서 90.8%까지 향상시켰다. 이후, 바이너리 회절 소자 및 이를 적용한 빔 투사기를 제작하여 설계 결과를 검증하였다. 검증 결과 투사 거리 5 m에서 설계 목표인 430 mm × 430 mm 투광면적, 10,000개 이상의 랜덤 도트 패턴의 생성을 확인하였다. 측정된 균일도는 시뮬레이션에서 예상되었던 균일도보다 다소 적은 84.5%이나, 이는 회절 격자 형상, 특히 모서리 뭉개짐 및 간격 오류에 의한 것으로 추정된다.

압축 영상의 블록화 제거를 위한 적응적 고속 영상 복원 필터 (An Adaptive Fast Image Restoration Filter for Reducing Blocking Artifacts in the Compressed Image)

  • 백종호;이형호;백준기;윈치선
    • 한국방송∙미디어공학회:학술대회논문집
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    • 한국방송공학회 1996년도 학술대회
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    • pp.223-227
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    • 1996
  • In this paper we propose an adaptive fast image restoration filter, which is suitable for reducing the blocking artifacts in the compressed image in real-time. The proposed restoration filter is based on the observation that quantization operation in a series of coding process is a nonlinear and many-to-one mapping operator. And then we propose an approximated version of constrained optimization technique as a restoration process for removing the nonlinear and space varying degradation operator. We also propose a novel block classification method for adaptively choosing the direction of a highpass filter, which serves as a constraint in the optimization process. The proposed classification method adopts the bias-corrected maximized likelihood, which is used to determine the number of regions in the image for the unsupervised segmentation. The proposed restoration filter can be realized either in the discrete Fourier transform domain or in the spatial domain in the form of a truncated finite impulse response (FIR) filter structure for real-time processing. In order to demonstrate the validity of the proposed restoration filter experimental results will be shown.

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Optimization of Reaction Conditions for High Yield Synthesis of Carbon Nanotube Bundles by Low-Temperature Solvothermal Process and Study of their H2 Storage Capacity

  • Krishnamurthy, G.;Agarwal, Sarika
    • Bulletin of the Korean Chemical Society
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    • 제34권10호
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    • pp.3046-3054
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    • 2013
  • Synthesis of Carbon Nanotube bundles has been achieved by simple and economical solvothermal procedure at very low temperature of $180^{\circ}C$. The product yield obtained was about 70-75%. The optimization of reaction conditions for an efficient synthesis of CNTs has been presented. The CNTs are obtained by reduction of hexachlorobenzene in the presence of Na/Ni in cyclohexane. The X-ray diffraction, Fourier transform infrared and Raman spectral studies have inferred us the graphene structure of the products. The CNTs formed as the bundles were viewed on scanning electron microscope, transmission electron microscope and high-resolution transmission electron microscope. These are the multiwalled CNTs with outer diameter of 5-10 nm, the inner diameter 2-4 nm and cross sectional diameter up to 5 nm. Brunauer-Emmett-Teller (BET) based $N_2$ gas adsorption studies have been made to obtain BET surface area and $H_2$ storage capacity. Effect of the experimental variables such as reaction temperature, amount of catalyst and the amount of carbon source were investigated. It is found that they affect significantly on the product nature and yield.

Regularized Multichannel Blind Deconvolution Using Alternating Minimization

  • James, Soniya;Maik, Vivek;Karibassappa, K.;Paik, Joonki
    • IEIE Transactions on Smart Processing and Computing
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    • 제4권6호
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    • pp.413-421
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    • 2015
  • Regularized Blind Deconvolution is a problem applicable in degraded images in order to bring the original image out of blur. Multichannel blind Deconvolution considered as an optimization problem. Each step in the optimization is considered as variable splitting problem using an algorithm called Alternating Minimization Algorithm. Each Step in the Variable splitting undergoes Augmented Lagrangian method (ALM) / Bregman Iterative method. Regularization is used where an ill posed problem converted into a well posed problem. Two well known regularizers are Tikhonov class and Total Variation (TV) / L2 model. TV can be isotropic and anisotropic, where isotropic for L2 norm and anisotropic for L1 norm. Based on many probabilistic model and Fourier Transforms Image deblurring can be solved. Here in this paper to improve the performance, we have used an adaptive regularization filtering and isotropic TV model Lp norm. Image deblurring is applicable in the areas such as medical image sensing, astrophotography, traffic signal monitoring, remote sensors, case investigation and even images that are taken using a digital camera / mobile cameras.

Design method of computer-generated controller for linear time-periodic systems

  • Jo, Jang-Hyen
    • 제어로봇시스템학회:학술대회논문집
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    • 제어로봇시스템학회 1992년도 한국자동제어학술회의논문집(국제학술편); KOEX, Seoul; 19-21 Oct. 1992
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    • pp.225-228
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    • 1992
  • The purpose of this project is the presentation of new method for selection of a scalar control of linear time-periodic system. The approach has been proposed by Radziszewski and Zaleski [4] and utilizes the quadratic form of Lyapunov function. The system under consideration is assigned either in closed-loop state or in modal variables as in Calico, Wiesel [1]. The case of scalar control is considered, the gain matrix being assumed to be at worst periodic with the system period T, each element being represented by a Fourier series. As the optimal gain matrix we consider the matrix ensuring the minimum value of the larger real part of the two Poincare exponents of the system. The method, based on two-step optimization procedure, allows to find the approximate optimal gain matrix. At present state of art determination of the gain matrix for this case has been done by systematic numerical search procedure, at each step of which the Floquet solution must be found.

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Novel Superabsorbent Hydrogel Based on Natural Hybrid Backbone: Optimized Synthesis and its Swelling Behavior

  • Pourjavadi, Ali;Soleyman, Rouhollah;Bardajee, Ghasem Rezanejade;Ghavami, Somayeh
    • Bulletin of the Korean Chemical Society
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    • 제30권11호
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    • pp.2680-2686
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    • 2009
  • The synthesis of a novel superabsorbent hydrogel with natural hybrid backbone via graft copolymerization of acrylamide (AAm) onto kappa-carrageenan (kC, as a polysaccharide) and gelatin (as a protein) under classic thermal conditions is described. The Taguchi method as a strong experimental design tool was used for synthesis optimization. A series of hydrogels were synthesized by proposed conditions of Qualitek-4 Software. Considering the results of 9 trials according to analysis of variance (ANOVA), optimum conditions were proposed. The swelling behavior of optimum hydrogel was measured in various solutions with pH values ranging from 1 to 13. In addition, swelling kinetics, swelling in various organic solvents, various salt solutions and On–Off switching behavior were investigated. The hydrogel formation was confirmed by Fourier transform infrared spectroscopy (FTIR) and thermogravimetrical analysis (TGA). Surface morphology of the synthesized hydrogels was assessed by scanning electron microscope (SEM).