Papers by Keyword: Fast Fourier Transform (FFT)

Abstract: To realize the automatic transmission for present digital image capture test system, a new system which consists of laptop computer, camera, fixing device and mechanical testing machine was presented and designed. The Monitor software, which was developed using MATLAB to realize automatic transmission function for the system, includes slow and high speed. The general stage and key stage for quasi-brittle materials can be effectively captured by the software. With MATLAB, the digital image correlation software (DIC) was developed. In DIC the first image is used as the base image. The images are sorted by photographing time (or file name), and the listing file is generated. The grid is drawn on the base image to divide the area into ‘facets’, the size of which can be adjusted between 1pixel and 100 pixels. Based on fast Fourier transform and convolution algorithm, the image comparison is realized and the deformation of the material is calculated. The designed system is applied to the compression test of a concrete specimen, and the results show that the system realizes automatic transmission image capture, and calculates accurate displacement. The displacement distribution is uniform in linear elastic stage, and varies in yielding stage. This is mostly due to localized failure and displacement discontinuity.

Abstract: During clinical operation in root canals, NiTi endodontic rotary instruments are subjected to alternating tension and compression and are prone to accidental fracture without prior warning. Once broken, extracting the fractured part from the canal is difficult and is annoying to both the patient and the dentist. Warning of an imminent fracture during clinical use will be a great help to avoid medical and legal complications. To this end, a monitoring technique that involves the picking up and analysis of the stress wave signals due to the cutting and rubbing at the canal wall-instrument blade interface was investigated. Both the stress wave conducted through solid and the sound wave conducted in air were monitored. The former was picked up by a Fiber Bragg Grating (FBG) and the latter with a microphone. When cracking developed in a rotary instrument, we expect the natural vibration frequency of the instrument as well as the characteristics of cutting/rubbing with the canal wall change. From the raw signal intensity history, it is possible to differentiate whether the instrument is operating but there is no clue when a fatigue crack has initiated. By employing Fast Fourier Transform (FFT) on the signal, we can reveal the energy associated with different frequencies. With characteristic frequency we refer to the frequency that is associated with the highest signal intensity. It was found that the energy intensity of the characteristic frequency varied in a well-defined pattern during the process of fatigue testing of the rotary instrument. Towards the end of fatigue life, a large intensity spike of the characteristic frequency was observed and this was shown to be associated with the occurrence of a fatigue crack. It is hoped that with this information, the fatigue failure of rotary instruments can be closely monitored to avoid/alleviate the occurrence of unexpected fracture during clinical use.

Abstract: Based on the fast fourier transform (FFT) and flexibility matrix method, the effects of the FFT and flexibility matrix method on the distribution of oil film pressure, elastic deformation in the steady load and the journal center orbit of the connecting rod big-end bearings in the dynamic load are investigated. The results are shown that when the eccentricity ratio is more than 1, the maximum oil film pressure obtained by FFT method is bigger on both ends of the journal bearing and on its intermediate position is smaller. To the connecting rod big-end bearing, under the dynamic load condition, there is the same trend of the journal center orbit with two methods. However, with FFT method, the journal is largely deviated from bearing center.

Abstract: Synchronized Phasor Measurement Unit with CAN bus can be used to phasor acquisition and real-time dynamic monitoring of ship power system. As it is known to all, traditional CAN communication is based on event-triggered mechanism. Message transmission will be delayed when there are a lot of messages in CAN bus. This paper used TTCAN protocol to synchronize the master and slave clock nodes based on STM32 microcontrollers. A Fast Fourier transform of AD samples was been done and transferred to host computer through CAN bus which reflects the real-time running status of system well.

Abstract: Based on the fast fourier transform（FFT） and flexibility matrix method, the study is presented for journal bearing elastohydrodynamic lubrication. The effects of FFT and flexibility matrix method on the distribution of oil film pressure and elastic deformation in the steady load are investigated. The results are shown that the difficulty of the EHL for journal bearings in the case of high eccentricity ratios or heave loads can be effectively solved by the FFT method. When the eccentricity ratio is smaller, the magnitude and distribution of the oil film pressure are basic agreement by FFT method and flexibility matrix method. When the eccentricity ratio enhances, the maximum oil film pressure obtained by FFT method is bigger on both ends of the journal bearing and on its intermediate is smaller.

Abstract: In this paper, a design method of high-speed, real-time digital pulse compression module based on Xilinx FPGA devices and Monbit receiver is introduced. A novel changeable-points of 256 or 1024 for three channels Digital Pulse Compression(DPC) with realizing FFT , complex-multiplication and IFFT function are presented which is accomplished by FPGA. A top-down flow has been used in the system. The whole design, which characters high stability, small logic resource occupation, low power consumption, is implemented with only one chip of FPGA XC2V500-5 for one channel. It takes 73.31us to complete a 1024-point DPC. Compared with the MATLAB simulation results, our module can accomplish function of 32k points digital pulse compression of 200MSPS throughput.

Abstract: Based on the unified Reynolds equation model and fast Fourier transform (FFT) method, the lubrication performance of the piston pin bearing for high power density diesel engine was studied by numerical simulation. First of all, through the coupled solving of a unified Reynolds equation and elastic deformation equation, the orbit of journal center for piston pin bearing is investigated. The eccentricity ratio of the piston pin bearing in vertical direction of the piston stroke is smaller, however it is much larger in the downward direction of the piston stroke, which indicate that the below area of the piston pin bearing bears greater load and occurs larger deformation. This is consistent with the reality that the below area of the piston pin bearing is prone to damage and wear. Secondly, the influence of the different bearing clearances and width on the minimum oil film thickness is discussed, The results show that the minimum oil film thickness is increased, while the width of piston pin bearing is increased or the clearance of piston pin bearing is decreased.

Abstract: Based on the unified Reynolds equation model and fast Fourier transform (FFT) method, the lubrication performance of the piston pin bearing for high power density diesel engine was studied by numerical simulation. First of all, through the coupled solving of a unified Reynolds equation and elastic deformation equation, the influence of the viscous-pressure effect on the maximum film pressure and the minimum oil film thickness for piston pin bearing are investigated. The results show that, after considering the viscosity-pressure effect, the minimum oil film thickness and the maximum film pressure of semi-floating piston pin bearings for high power density increase, and the elastic deformation decreases in greatest load position. It confirms that the bearing capability is greatly enhanced while the viscosity- pressure effect is considered. Secondly, The eccentricity ratio of the piston pin bearing in vertical direction of the piston stroke is smaller, however it is much larger in the downward direction of the piston stroke, which indicate that the below area of the piston pin bearing bears greater load and occurs larger deformation. This is consistent with the reality that the below area of the piston pin bearing is prone to damage and wear

Abstract: Diagnosis measurement of vibration and noise, should allow monitoring of equipment defects, through a system of preventive maintenance, predictive. Automatic diagnosis of machinery and equipment was made in order to ensure a higher reliability of these and how to obtain a more extended life cycle without the occurrence of defects. Vibrations are always measured in analog format (time domain) and must be transformed into the frequency domain. Therefore Fast Fourier Transform (FFT) method is used to evaluate vibration Almega AX-V6 robot. The application of preventive and predictive maintenance management supports enterprise, because it proves effective, the information you provide in making decisions.

Abstract: In this paper, we come up with the idea of using frequency shift method to strip carrier when acquiring the GPS signal. The RF uses the quadrature demodulator and dual channel to sample the signal, forming the IF digital signal in I channel and Q channel. The paper derivates the mathematical formula of the frequency shift method, and compares the trigonometric function method with it from the aspect of schematic diagram and calculating. Also, we make simulation of the two schemes using Matlab for both true signal and analog signal. And it comes out that the frequency shift method has got a much greater correlation peak than the trigonometric function method. So we come to the conclusion that it is better using the frequency shift method to acquire signal in low signal intensity.