FFT Method Research Articles

Numerical Simulation of Rough Surface with Crossed Texture

To meet the demands for rough surfaces data in the research of surface engineering, contacts characteristic and so on, a new numerical simulation of rough surface is proposed. Based on FFT method, rough surface with single direction texture is simulated with circular cosine-exponent autocorrelation function (ACF), and the generated surface is rotated of different given angles respectively by rotation of reference system, then the rough surface with multi-direction texture is created by synthesizing the rotated surfaces. The simulation results show that, the ACF curves of generated surface is periodic fluctuation decay, and has a good fitting result with the predetermined ACF. The contrast result between simulated surface and measured surface shows the available of the proposed method.

Failure Diagnosis of Large Cooling Tower Fan Based on FFT and EMD Analysis Method

Large cooling tower fan mainly used in petroleum, chemical, electric power industry, carries industrial water circulating cooling function and its operational status directly affects the industrial production. The blades are the important parts of the fan. The modal analysis is used to find the distribution of blade vibration frequency, and then the acquisition and analysis of vibration parameters of running large cooling tower fan blades are done using the EMD methods. Finally, compare with the modal analysis to find out safety hazards of fan blades. This method can eliminate the failures of the cooling tower fan blades, shorten the repair cycle, ensure the smooth production of the enterprise and improve economic efficiency.

Synthesis of the speech signals by using autocorrelation function

The running autocorrelation function (r-ACF) is obtained by the FFT method based on the Wiener–Khinchine theorem after obtaining the power density spectrum for a signal. This study attempted to reconstruct the original speech signal by using a part of its r-ACF. First, the stationary part of the vowel signals were investigated to determine until which delay time of the ACF (maximum time lag) is necessary to recognize the reconstructed signals as the original ones. Then, the continuous speech signals were investigated to determine the appropriate integration interval as well as the maximum time lag.

Erratum for “Fast Bayesian FFT Method for Ambient Modal Identification with Separated Modes” by Siu-Kui Au

Erratum for “Fast Bayesian FFT Method for Ambient Modal Identification with Separated Modes” by Siu-Kui Au

3D space charge code with the FFT method

Precise and fast 3D space-charge calculations have become important for high intensity hadron accelerator design. The PIC method is most frequently used due to its efficiency. This paper introduces a 3D-PIC code that computes the potential of the bunch in the rest frame by means of Poisson's equation. FFT is applied as Poisson solvers. The details and the results are presented as well as error analysis.

Signal processing using a statistical algorithm for vibration measurement with a self‐coupling effect sensor

AbstractIn this paper, signal processing using a statistical algorithm for vibration measurement is reported. The algorithm uses the statistical features of the standard deviation of sinusoidal vibration and is capable of accuracy superior to the peak‐to‐peak method. Additionally, the algorithm achieves accuracy as good as or better than the FFT method with less hardware. This method gave good results in simulations and actual measurement values. The method is widely applied in self‐coupling effect sensors and other vibration sensors. © 2013 Wiley Periodicals, Inc. Electron Comm Jpn, 96(3): 9–16, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.11454.

A Multilevel FFT Method for the 3-D Capacitance Extraction

We present a new multilevel fast Fourier transform (MLFFT) method and its application for the 3-D structures capacitance extraction. The multilevel octree structure, multilevel interpolation/projection, and subdomain FFTs techniques are employed in the MLFFT. Distinctions between the MLFFT and the conventional FFT-based methods are discussed carefully. Numerical results demonstrate that the MLFFT is more efficient than conventional FFT based methods, especially when analyzing inhomogeneous problems.

Flow Characterization of Dense-Phase Pneumatic Conveying System of Pulverized Coal through Electrostatic Sensor Arrays

Experiments are performed in a dense-phase pneumatic conveying system of pulverized coal, and electrostatic signals and coal particle distribution images over cross-section of the pipeline at superficial gas velocities of 5.7 m/s, 6.9 m/s, and 8.1 m/s are obtained through use of electrostatic sensor arrays (ESA) and electrical capacitance tomography (ECT), respectively. In combination with ECT imaging results, the output signals of the ESA are analyzed by FFT and approximate entropy method. Results show that characteristic of particles motion and its change with increasing superficial gas velocity are different in the dense and dilute phase region of the pipe. With increasing the superficial gas velocity, the peak frequency of the electrostatic signal increases linearly in dense-phase region, while that in dilute phase region is nonlinear, implying that the increase of the axial particles velocity is the main dynamic change, while in dilute phase regions, the particles velocity fluctuation in the radial direction cannot be ignored. The ApEn value of the electrostatic signal in dense phase region is larger than that in dilute phase region. When the ApEn value difference of the electrostatic signals is smaller, the pulverized coal particles are better suspended.

Modal Parameter Identification of a Rigid Frame-Continuous Girders Bridge under Ambient Excitation by Fast Bayesian FFT Method

Bayesian theory is adopted in modal parameter identification, finite element model updating and residual capacity evaluation of the structures recently. Fast Bayesian FFT modal identification approach provides a rigorous way to obtain modal parameters and well-separated modes using the fast Fourier transform under ambient excitation. Moreover, it avoids choosing the modal order or removing false modes based on the stable diagram and has its obvious advantages. In this paper, modal parameters of a rigid frame-continuous girders bridge under ambient excitation are identified by this approach. Comparison with stochastic subspace identification (SSI) method indicates that Fast Bayesian FFT is a good approach to identify the modal parameters even for a large number of measurement channels.

A Method for InSAR Baseline Refinement Based on CR

Interferometric baseline plays a very important role in InSAR data processing, and it will directly affect the accuracy of interferometric result. Shuping area is covered by all of vegetation, so the coherence is very low. In Shuping area, it is very difficulty to generate clearly residue stripe to use the FFT method and to find natural coherence pixels points as GCP to refine the baseline to meet the need of monitoring the deformation accurately. But through CR stability phase information can be got. So It is also highlights to the apply CR in this region to refine the baseline parameters. In this article, the baseline got from coarse orbit file is regarded as initial value, and that got from precise orbit file is regarded as True. By comparing and analyzing the parameters of refined baseline with that of the precise baseline, it can be concluded that the refined method based on CRs is correct and feasible.

Fast Detection of Chatter in End-Milling Using Pseudo Auto-Correlation Function

The chatter vibrations cause problems, such as the reduction of tool life, tool fracture, and a deterioration in the quality of the machined surface. This paper presents a fast detection method for expected chatter in high-speed end-milling. In this study, a pseudo auto-correlation function is applied to tool vibration data sampled at intervals as the spindle rotated at a constant angle. The calculation time for the pseudo auto-correlation function is expected to be shorter than that of the FFT method. As a result, it was indicated that detection reliability under the proposed method was approximately equal to the detection reliability by the previous methods by using tool vibration data sampled at constant intervals of time.

FFT Based Sum-Product Algorithm for Decoding LDPC Lattices

LDPC lattices were introduced by Sadeghi et al. in [13] and have a good performance under generalized minsum and sum-product algorithms. The high complexity of these algorithms is mainly due to the search for local valid codewords in each check node process. In addition, when the dimension of such lattices is increased, these decoding algorithms are very time-consuming. In this paper, we propose an FFT based sum-product algorithm to decode LDPC lattices. In the check node process, using the FFT method reduces the check node complexity from O(dcg2) to O(dcg log g) where dc is the degree of a check equation and g is the alphabet size of an LDPC lattice. As a result, with almost the same complexity cost, we have a significant improvement over the performance of the minsum based decoding 2-level LDPC lattices with the symbol error probability smaller than 10-5 at SNR = 1.5 dB.

Spectra of L-band ionospheric scintillation over Nanjing

We report the spatiotemporal statistical characteristics of amplitude scintillation over Nanjing. A FFT method for computing scintillation intensity power spectra is briefly described. Using this method, the data with ISATM in Nanjing is analyzed. Spectra characteristic is presented and the irregularities property is discussed preliminarily. The results reveal that the power spectra obtained for Nanjing is consistent with theoretical modeling. At frequencies below the Fresnel frequency, the power density plotted on log-log scale is almost constant whereas above it asymptotes to a straight line. The spectral index ranges from 1.71 to 1.92, which has positive correlation with the S 4 index. Finally, the average drift velocity of irregularities is computed assumably and compared with that obtained for Xinxiang and Haikou.

Two algorithms to compute Hansen-like coefficients with respect to the eccentric anomaly

Considering a point of polar coordinates (r,ν) on an elliptic orbit of semi-major axis a, we set up and compare two algorithms based on recurrence relations to compute the Hansen-like coefficients Zsn,m, which are the coefficients of the expansion of (r/a)nexpimν in Fourier series of the eccentric anomaly. Both Hansen-like coefficients and their derivatives with respect to the eccentricity are considered, with a special focus on the case 0⩽|m|⩽n arising in the expression of the gravity potential due to a body external to the elliptic orbit. We provide two efficient algorithms to compute a table of coefficients with a simple recursive process. One algorithm uses some recurrence relations linking directly to the Zsn,m whereas the other algorithm involves the generalized Laplace coefficients bp,rk (Laskar, 2005). Numerical behavior of the algorithms is investigated for low and high eccentricities. Both algorithms provide a relative accuracy better than 10-14 for n⩽30. Also, they are at least 10 time faster than an algorithm based on the FFT method (Klioner et al., 1997).

Phoneme recognition using zerocrossing interval distribution of speech patterns and ANN

The speech signal is modeled using zerocrossing interval distribution of the signal in time domain. The distributions of these parameters are studied over five Malayalam (one of the most popular Indian language) vowels. We found that the distribution patterns are almost similar for repeated utterances of the same vowel and varies from vowel to vowel. These distribution patterns are used for recognizing the vowels using multilayer feed forward artificial neural network. After analyzing the distribution patterns and the vowel recognition results, we realize that the zerocrossing interval distribution parameters can be effectively used for the speech phone classification and recognition. The noise adaptness of this parameter is also studied by adding additive white Gaussian noise at different signal to noise ratio. The computational complexity of the proposed technique is also less compared to the conventional spectral techniques, which includes FFT and Cepstral methods, used in the parameterization of speech signal.

Analysis of turbulence and tilt by in-situ measurements inside the codend of a shrimp beam trawl

The turbulence flow inside the codend and tilt of the codend in a shrimp beam trawl was measured with a Nortek Vector and the towline tension during five fishing operations; data collected for turbulence intensity with codend tilt was analysed under towing speeds. The turbulence intensity at a point in the posterior upper part of the codend ranged from 5 to 40% and decreased significantly by mean flow velocity (0.1–0.9ms−1) inside the codend. Simultaneously, the shorter periods of the turbulence flow in the towing or perpendicular direction were located between 2 and 8s by the FFT method and the Morlet wavelet method. Pitch and roll of the codend also varied each other within S.D<±6° and their shorter period was shown mostly as 3s around. However, turbulence flow velocities inside the codend were not related to tilt changes or towline tension, which increased significantly with towing speed. As a result, turbulence intensity and periodicity in the codend could affect the manoeuvring of fish swimming and the application of active stimulating devices.

Studying The Effect of Window Type on Power Spectrum Based on Mat Lab

The representation that describes signal’s frequency behavior can be divided into two categories: linear representation such as the Fourier-transform and quadratic representation such as power spectrum. Power spectrum characterizes the signal’s energy distribution in the frequency domain, and can answer whether most of the power of the signal resides at low or high frequencies. By performing spectral analysis, some important features of signals can be discovered that are not obvious in the time waveform of the signal. One problem with spectrum analysis is that the duration of the signals is finite, although adjustable. Applying the FFT method to finite duration sequences can produce inadequate results because of “spectral leakage”, to reduce the spectral leakage FFT window function is applied. Power spectrum parameters are window size, window type, window over lap and number of FFT. The aim of this work is to demonstrate the effect of varying window type on the power spectrum using Mat Lab software. Five windows have been compared to study their effect on the spectrum of a typical data.

The Research on Bispectrum Detection of Underwater Target in Frequency Domain

As the non-Gaussianity of ship-radiated noise reduces fast when the Signal-to-Noise Ratio (SNR) becomes low, a bispectrum detector in the frequency domain is proposed to ease the problem. First, FFT method is applied on the received data to calculate the power spectrum. Second, the non-Gaussianity of the power spectrum series is tested by Hinich-Wilson Gaussian Test rule. Last, the bispectrum detector based on non-Gaussianity is used to determine whether there are ship-radiated signals. The bispectrum detector in frequency domain is applied to detect simulated noise and real ship-radiated noise. The results are compared with the detector which is in the signal’s time domain. The comparison illustrates that the bispectrum detector based on the power spectrum series(in frequency domain) is much better in detecting low SNR signals, which is very valuable in far distance detection.

Detection of a static eccentricity fault in a closed loop driven induction motor by using the angular domain order tracking analysis method

In this study, a new method was presented for the detection of a static eccentricity fault in a closed loop operating induction motor driven by inverter. Contrary to the motors supplied by the line, if the speed and load, and therefore the amplitude and frequency, of the current constantly change then this also causes a continuous change in the location of fault harmonics in the frequency spectrum. Angular Domain Order Tracking analysis (AD-OT) is one of the most frequently used fault diagnosis methods in the monitoring of rotating machines and the analysis of dynamic vibration signals. In the presented experimental study, motor phase current and rotor speed were monitored at various speeds and load levels with a healthy and static eccentricity fault in the closed loop driven induction motor with vector control. The AD-OT method was applied to the motor current and the results were compared with the traditional FFT and Fourier Transform based Order Tracking (FT-OT) methods. The experimental results demonstrate that AD-OT method is more efficient than the FFT and FT-OT methods for fault diagnosis, especially while the motor is operating run-up and run-down. Also the AD-OT does not incur any additional cost for the user because in inverter driven systems, current and speed sensor coexist in the system. The main innovative parts of this study are that AD-OT method was implemented on the motor current signal for the first time.

이동평균 영상처리기법을 이용한 금속판재 표면품질 정밀 측정시스템 연구

산업자동화를 위한 영상처리기술을 활용하여 금속 표면 검사 공정의 육안 검사를 대체하기 위한 장치개발이 요구된다. 본 논문에서는 압연 공정의 금속 판재 표면의 결함을 탐지하기 위하여 이동평균 영상처리기법을 적용한 정밀측정시스템을 제안하였다. 금속 판재의 압연 처리 과정에서 발생하는 표면 패턴이 결함으로 판정될 수 있다. 이러한 경우에 대하여 제안한 시스템을 적용하여 금속 판재 표면의 실제 결함의 수를 측정할 수 있었고 FFT방법에 의한 측정치에 비하여 양호한 결과를 얻었다. It has been highly required to develope an automatic metal surface inspection system, specifically using image processing techniques, which can replace the visual inspection method in the steel industry. In this paper, we propose a precisional surface measurement system using the moving average image processing technique. When the surface patterns which are generated in the rolling process of metal plates are recognized as defects, the proposed system can measure the actual number of defects. It has been proved that our system shows better results than the conventional FFT method.