FFT Processing Research Articles

Study on the formation and characteristics of unstable sheet cavitation on hydrofoils

Hydrofoils, as fundamental components of hydraulic machinery, directly influence the performance of such machinery. This study conducted an analysis of the cavitation characteristics of hydrofoils at a + 4° angle of attack under various cavitation numbers using numerical simulation and experimental research methods. The focus of the research was to explore the phenomenon of unstable sheet cavitation and its causes, as well as to reveal the characteristics of the re-entrant jet. The large eddy simulation method was employed to calculate the cavitation morphology under three different cavitation numbers. The method is highly consistent with the experimental results in simulating the small-scale detachment at the tail of unstable sheet cavitation and the large-scale shedding of cloud cavitation. The study found that the detachment of unstable sheet cavitation is closely related to the re-entrant jet, which exhibits transient and abrupt characteristics during the unstable sheet cavitation phase. Furthermore, by applying FFT processing to the distribution of maximum reverse velocity and the spatiotemporal changes of Ux on characteristic lines, eigenfrequency of the detachment of unstable sheet cavitation were identified. The research results indicate that cavitation mainly show as sheet cavitation when the cavitation closure point does not exceed the zero-slope point. Beyond this point, it transitions to cloud cavitation. This study provides new insights into the cavitation phenomenon of hydrofoils and offers quantitative research on the phenomenon of unstable sheet cavitation.

Investigating and Improving the Efficiency of Space-time Codes in Visible light Communication Systems based on a Multi-input-multi-output Channel Model

Background: Visible light communication (VLC) is a new communication method for transmitting information through semiconductor lighting devices. One of the applicable methods to improve the spectral efficiency of the system is the multi-input-multiple-output (MIMO) structure. Also, carrierless amplitude-phase (CAP) modulation is a high-dimensional modulation technique that can be used to improve the data transmission rate in modern communication systems. Methods: In this paper, carrierless amplitude-phase method is introduced in indoor optical communication systems to improve the performance of multi-input multi-output (MIMO) structures. The CAP modulation is considered a suitable method due to its low complexity and is introduced and studied in two structures with one carrier or CAP and multiple carriers or m-CAP. Results: In this study, the target system is simulated in m-CAP structures and the improvement is measured in the MIMO structure using this modulation. The results show that by using this method, the PAPR of the system was reduced compared to other research with the MIMO-OFDM structure. In addition, by not using FFT blocks, the computational and processing complexity was also reduced. Conclusion: It has been shown that the use of m-CAP increases the data transfer rate and improves the spectral efficiency of the system. In addition to CAP, spatial modulation schemes can also help improve the spectral efficiency and power efficiency of the system. Moreover, the space-time code is combined with m-CAP modulation and it is shown that this idea improves the efficiency of the MIMO system.

Effect of Tip Clearance on the Cavitation Performance of High-Speed Pump-Jet Propeller

To investigate the impact of tip clearance variation on the cavitation performance of a high-speed pump-jet propeller, Fluent software was employed for simulation calculations. The study utilized the RNG k-ε turbulence model and ZGB cavitation, conducting three-dimensional numerical simulations under both steady and transient conditions. A pump-jet propeller with a rated speed of 20,000 r/min was used to set three kinds of clearance for simulation, and the simulation proved to be reliable by comparison with the experiment. Initially, the analysis examined the effect of tip clearance on cavitation characteristics and cavitation volume under steady-state conditions, while also studying the distribution patterns of cavitation. Subsequently, the radial force and pressure pulsation of the jet propeller are analyzed by FFT processing, aiming at the influence of tip clearance on the structural strength of the pump-jet propeller. Under the design conditions, the smaller tip clearance shows better performance, while the larger tip clearance shows stronger anti-cavitation ability than the smaller clearance. In addition, the greater the tip clearance, the greater the radial force and pressure pulsation, which will adversely affect the pump-jet structure. The research results provide some references for further research on the effect of high-speed pump-jet propeller structures on performance.

Design of Multi-channel Real-time Signal Acquisition System

In order to improve the accuracy of the real-time signal acquisition, a real-time signal acquisition system based on high speed ADC and FPGA is proposed in this paper. AD9208 is used to realize high speed acquisition and DDC processing of original signal. FPGA 7V690T is used to realize digital channelization and fine FFT processing. This system can realize massive data storage and real-time signal display. The test results show that this system can effectively realize real-time signal acquisition and processing, and has strong anti-interference ability.

Nonlinear distortion signal generation and THD measuring device

In order to generate nonlinear distortion when the amplifiers work in the nonlinear region, the system uses the transistor amplifiers to combine the analog switch and MCU to realize nonlinear distortion signal generation and THD(Total Harmonic Distortion) measurement device. The system is mainly composed of fixed gain amplifier circuit, multi-type signal selection circuit, class A and B complementary symmetric circuit, analog switch and microcontroller. The input signal is fixed as a 1KHz, 20mVp-p sinusoidal signal. Based on the influence of quiescent operation point on the common emitter amplifier circuit and the characteristics of Type B push-pull circuit, the analog switch is turned on or off by pressing the button of MCU to adjust the static working point and circuit structure to realize output of different types of signals. THD was calculated by sampling ADC inside MCU and FFT processing. The experimental results show that the system can successfully output sinusoidal signals and four kinds of nonlinear distortion signals (top distortion, bottom distortion, bidirectional distortion and cross-over distortion), and the peak-to-peak values are all greater than 2Vp-p. THD measurement error is less than 0.6%, which can achieve a more accurate measurement of total harmonic distortion.

Research on the underwater noise radiation of high pressure water jet propulsion

High pressure water jet propulsion is a new type of propulsion, which has the characteristics of simple system structure, small energy loss in the water inlet duct, easy vectored control, without additional drag force and so on. Underwater jet noise radiation of high pressure waterjet propulsion is an important factor that would directly determine the stealth performance of underwater vehicles. A co-simulation method combining the CFD (Computational Fluid Dynamics) and CAA (Computational Aeroacoustics) was used in this paper to study and analyze the underwater jet noise radiation characteristics of high pressure water jet propulsion. The Realizable k-ε turbulence model was used to numerically simulate the flow field of waterjet. And the FFT processing of the flow field results were implemented by use of the Actran iCFD module in order to obtain the sound source of the waterjet radiation. Then, the Lighthill acoustic analogy theory was utilized to achieve the underwater jet noise radiation characteristic. Consequently, the effects of inlet velocity on the underwater jet noise radiation characteristics of high pressure waterjet propulsion were researched. The results indicated that the underwater jet noise radiation of high pressure water jet propulsion mainly comes from the mixing area where is the 8–10 times diameter away from the nozzle outlet, and the increase of the inlet flow velocity would enlarge the sound pressure level of the underwater jet noise radiation. In addition, the underwater noise jet radiation is directional and mainly propagates in the axial direction. However, the inlet velocity has little influence on the frequency domain characteristics of underwater jet noise radiation and the underwater jet noise radiation has high energy below the frequency 200 Hz. The research provides theoretical guidance for reducing the underwater jet noise radiation of high pressure waterjet propulsion and improving the stealth performance of underwater vehicles.

Development of adhesion force evaluation equipment for nano diamond coated tool using shear method

In this study, we have developed a thin film adhesion evaluation system for diamond coating tool, which is mainly used for CFRP processing. CFRP is widely used in aviation and automobile industries. Because of the high surface hardness of the diamond coating tool, it is difficult to evaluate the adhesive strength of the tool, and it is difficult to quantitatively evaluate the existing adhesion force evaluation method and it is costly. This study has developed an evaluation method to measure the adhesive force based on the data of the grinding process using a low-cost polishing pad. When the frictional force and the shearing force are applied to the specimen by the sanding belt, friction is continuously generated between the coating layer and the belt, and peeling occurs at the moment when a specific load is applied. Acceleration, load, and torque values that occur during each experiment are collected through acceleration sensors, load cells, and torque sensors. The data obtained through the experiments are subjected to FFT processing and analysis. As a result, the peeling point and the critical load value at this point are identified and referred to as the adhesion force of the coating layer.

Digital zenith camera accuracy analysis scheme based on digital image processing

This article uses a digital zenith camera to perform field measurements to obtain high-precision astronomical longitude and latitude data. To identify the photographed stellar markers, we utilize FFT and digital image processing methods to do CCD star image matching, the establishment of a numerical fit model for star matching, and then the astronomical coordinates of the station against the table decomposition, and finally the use of astronomical geodesy to calculate the vertical deviation of the station and the error in cyclic observation, to test the instrument in the Sensitivity in both directions, astronomical longitude and astronomical latitude.

Line Spectrum Enhancement of Underwater Acoustic Signals Using Kalman Filter

To detect weak underwater acoustic signals radiated by submarines and other underwater equipment, an effective line spectrum enhancement algorithm based on Kalman filter and FFT processing is proposed. The proposed algorithm first determines the frequency components of the weak underwater signal and then filters the signal to enhance the line spectrum, thereby improving the signal-to-noise ratio (SNR). This paper discussed two cases: one is a simulated signal consisting of a dual-frequency sinusoidal periodic signal and Gaussian white noise, and the signal is received after passing through a Rayleigh fading channel; the other is a ship signal recorded from the South China Sea. The results show that the line spectrum of the underwater acoustic signal could be effectively enhanced in both cases, and the filtered waveform is smoother. The analysis of simulated signals and ship signal reflects the effectiveness of the proposed algorithm.

OFDM comparison with FFT and DWT processing for DVB-T2 wireless channels

Introduction: Recent studies on the FFT processing (Fast Fourier Transform) or DWT (Discrete Wavelet Transform) of the OFDM signal (Orthogonal Frequency Division Multiplexing) have shown pros and cons for DVB-T2 (Digital Video Broadcasting-Second Generation Terrestrial) radio communications; however, the benefits of both types of processing have yet to be compared for the same scenario.
 Objective: The objective of this research is to compare the response of the wireless channel with AWGN noise (Additive White Gaussian Noise Channel) and Rayleigh and Rician fading in the UHF (Ultra High Frequency) band.
 Methodology: The transmission of DVB-T2 information with OFDM modulation and FFT and DWT processing was simulated in Matlab®, specifically in Simulink.
 Results: The results of the study proved to be more efficient for DWT system than FFT system, due to the low rate of erroneous bits, spectral efficiency and reduction of the Peak-to-Average Power Ratio (PAPR), for Eb / No relations greater than 10dB.
 Conclusions: In this article, we present the designs of both systems and the results of the research experience; likewise, the practical applicability of these systems is discussed, and improvements are suggested for future work.

Collision Detection Method Using Self Interference Cancelation for Random Access Multiuser MIMO

This paper proposes an interference detection method for multiuser-multiple input multiple output (MU-MIMO) transmission, which utilizes periodical preamble signals in the frequency domain and the concept of full-duplex transmission when assuming idle antennas at the access point (AP) in MU-MIMO. In the propose method, collision detection (CD) of MU-MIMO is achieved by utilizing asynchronous MU-MIMO called random access MU-MIMO. In random access MU-MIMO, several antennas that are not used for the transmission exist, due to asynchronous MU-MIMO. Hence, idle antennas at the AP can receive preamble signals while the transmit antennas at the AP transmit the preamble signals: this procedure is regarded as full-duplex transmission, which cancels the self-interference between AP antennas. The interference can be detected by subtracting the short preamble signal, which is multiplied by the estimated channel response using the received signal after the FFT processing. Moreover, we utilize dual polarization to reduce the mutual coupling between transmit and receive antennas at the AP. Through a computer simulation, it is shown that the proposed method can successfully detect collision from other user terminals (UTs) with OFDM signals when the interfering power from the interfering user terminal (IT) is greater than the noise power. In addition, the interfering power from IT at the AP and the desired user terminal (DT) is measured in an actual indoor environment, and the possibility of using the proposed method at the AP is discussed by using the measurement results.

Modal dispersion characterization of few-mode fiber based on electrical spectral interferometry with optical frequency comb

Abstract We experimentally demonstrate a novel method based on electrical spectral interferometry with optical frequency comb for characterizing the modal dispersion between the higher-order modes and fundamental mode in a 1-km four-mode few-mode fiber (FMF). In this method, an optical frequency comb (OFC) is used to generate many subwavelengths with the same frequency interval to improve the measurement accuracy and speed. Based on the electrical spectral interferometry, the differential mode group delay (DMGD) and modal dispersion of the tested FMF are obtained by applying the simple FFT processing. The measured DMGD and modal dispersion within the whole C-band are about (3.2032–3.3033) ps/m, (2.5573–4.2085) ps/nm.km and (5.5055–5.7057) ps/m, (−11.2112–−4.1486) ps/nm.km and (11.1111–11.3113) ps/m, (−10.2454–−14.1332) ps/nm.km for LP11, LP21 and LP02 modes respectively. Meanwhile, we achieved a precision of ±0.002 ps/m for DMGD measurement. Compared with previous methods, our method has the advantage of high measurement accuracy, simple configuration and fast speed. The experimental results show that the demonstrated method could be a good solution to the characterization of a long FMF used in large capacity mode-division-multiplexing transmission systems.

Radar Sensor Signal Acquisition and Multidimensional FFT Processing for Surveillance Applications in Transport Systems

The design and test of a radio detection and ranging (Radar) sensor signal acquisition and processing platform is presented in this paper. The Radar sensor operates in real time and is suited for surveillance applications in transport systems. It includes a front-end with a continuous-wave frequency-modulated transceiver operating in X-band, with a single transmitter and multiple receivers, and a multichannel high-speed A/D converter. Sensor signal processing and data communication tasks with external hosts are managed by a field-programmable gate array. The signal processing chain includes region of interest selection, multidimensional fast Fourier transform, peak detection, alarm decision logic, data calibration, and diagnostic. By configuring the Radar sensing platform in low-power mode (7-dBm transmitted power), it is possible to detect still and moving targets with a covered range up to 300-m and 30-cm resolution. The measuring range can be increased up to 2 km by adding an extra 34.5-dBm power amplifier. The Radar sensing platform can be configured for a maximum detected speed of 200 km/h, with a resolution of 1.56 km/h, or a speed up to 50 km/h with a resolution of 0.4 km/h. The cross-range resolution depends on the number of receiving channels; a tradeoff can be found between cross-range resolution of the Radar sensor and its complexity and power consumption. With respect to the state of the art of surveillance Radar sensors and light detection and ranging, the proposed solution stands for its high configurability and for the better tradeoff that can be found in terms of covered distance and power consumption.

Near infrared spectro-interferometer using femtosecond laser written GLS embedded waveguides and nano-scatterers.

Guided optics spectrometers can be essentially classified into two main families: based on Fourier transform or dispersion. In the first case, an interferogram generated inside an optical waveguide and containing the spectral information is sampled using spatially distributed nanodetectors. These scatter quasi-non-perturbingly light into the detector that is in contact with the waveguide, helping to reconstruct the stationary wave. A dedicated FFT processing is needed in order to recover the spectrum with high resolution but limited spectral range. Another way is to directly disperse the different wavelengths to different pixels, either introducing differential optical path in the same propagation plane (multiple Mach-Zehnder interferometers or Arrayed Waveguides Gratings), or using a periodic structure to perpendicularly extract the optical signal confined in a waveguide (photonic crystals or surface gratings), and by means of a relay optics, generate the spectrum on the Fourier plane of the lens, where the detector is placed. Following this second approach, we present a laser-fabricated high-resolution compact dispersive spectro-interferometer (R>2500, 30nm spectral range at λ = 1560nm), using four parallel waveguides that can provide up to three non-redundant interferometric combinations. The device is based on guided optics technology embedded in bulk optical glass. Ultrafast laser photoinscription with 3D laser index engineering in bulk chalcogenide Gallium Lanthanium Sulfide glass is utilized to fabricate large mode area waveguides in an evanescently-coupled hexagonal multicore array configuration, followed by subsequent realization of nanoscaled scattering centers via one dimensional nanovoids across the waveguide, written in a non-diffractive Bessel configuration. A simple relay optics, with limited optical aberrations, reimages the diffracted signal on the focal plane array, leading to a robust, easy to align instrument.

High performance refractive index sensor based on low Q-factor ring resonators and FFT processing of wavelength scanning data.

We extend our previous simulation study and we present experimental results regarding our Fast Fourier Transform method for the calculation of the resonance shifts in biosensors based on micro-ring resonators (MRRs). For the simulation study, we use a system model with a tunable laser at 850 nm, an MRR with 1.5∙104 quality factor, and a detection system with 50 dB maximum signal-to-noise ratio, and investigate the impact on the system performance of factors like the number of the resonance peaks inside the scanning window, the wavelength dependence of the laser power, and the asymmetry of the transfer functions of the MRRs. We find that the performance is improved by a factor of 2 when we go from single- to four-peak transfer functions, and that the impact of the wavelength dependence of the laser power is very low. We also find that the presence of asymmetries can lead to strong discontinuities of the transfer functions at the edges of the scanning window and can significantly increase the measurement errors, making necessary the use of techniques for their elimination. Using these conclusions, we build a system with sensing MRRs on TriPleX platform, and we experimentally validate our method using sucrose solutions with different concentrations. Involving techniques in order to exclude the noise originating from the microfluidic system, we achieve a wavelength resolution close to 0.08 pm, when the system operates with 0.5 pm scanning step. In combination with the sensitivity of the MRRs, which is measured to be equal to 93.7 nm/RIU, this wavelength resolution indicates the possibility for a limit of detection close to 8.5·10-7 RIU, which represents to the best of our knowledge a record performance for this type of optical sensors and this level of scanning steps.

APOFDM system design based on all phase FFT technology

The traditional OFDM system as an important part of current wireless communication technology, its advantages are obvious, but one of shortcoming is easily affected by the frequency deviation. An effective solution is to improve data signal processing technology in the front of the system, thus can reduce the effects of system faults and improve the performance of the system. All phase data processing under the research idea of it is in this, after 20 years of research and development, now all phase FFT technology has been applied to image processing, signal processing, signal spectrum analysis, wireless communication transmission, etc. In this paper, using all phase FFT processing technology and detailed the APOFDM, Finally, using MATLAB simulation tools to analyze its advantages.

The Influence on Modal Parameters of Thin Cylindrical Shell under Bolt Looseness Boundary

The influence on modal parameters of thin cylindrical shell (TCS) under bolt looseness boundary is investigated. Firstly, bolt looseness boundary of the shell is divided into two types, that is, different bolt looseness numbers and different bolt looseness levels, and natural frequencies and mode shapes are calculated by finite element method to roughly master vibration characteristics of TCS under these conditions. Then, the following measurements and identification techniques are used to get precise frequency, damping, and shape results; for example, noncontact laser Doppler vibrometer and vibration shaker with excitation level being precisely controlled are used in the test system; “preexperiment” is adopted to determine the required tightening torque and verify fixed constraint boundary; the small-segment FFT processing technique is employed to accurately measure nature frequency and laser rotating scanning technique is used to get shape results with high efficiency. Finally, based on the measured results obtained by the above techniques, the influence on modal parameters of TCS under two types of bolt looseness boundaries is analyzed and discussed. It can be found that bolt looseness boundary can significantly affect frequency and damping results which might be caused by changes of nonlinear stiffness and damping and in bolt looseness positions.

Optofluidic multi-measurement system for the online monitoring of lubricant oil

We show a detection system that simultaneously allows absorbance (ABS), laser-induced fluorescence (LIF) and scattering detection excited by two different laser sources at 405 nm and 450 nm. The heart of the system consists of a mass manufacturable polymer optofluidic chip. The chip is mounted in an optical detection assembly that aligns the chip to the rest of the system, seals the chip from leakage, fixes the position and connects the channels to the rest of the fluidic system. The fluidics exhibit a reduced susceptibility to perturbations caused by air bubbles, this is accomplished by making use of a serpentine channel layout. For coumarin 480, detection limits of 100 nM and 10 pM are observed for ABS and LIF respectively. An effective detection range of 4000 down to 1 nephelometric turbidity units is shown for the detection of scattered light. The viscous behaviour of the sample is analysed by a secondary FFT processing step of which the result is further processed by multivariate data analysis. This allows the identification of samples and prediction of their quality parameters. We apply this system for the monitoring of lubricant oil, demonstrating its ability to compete with spectroscopic detection techniques. The low-cost approach and multi-measurement architecture shown in this paper pave the way for miniaturized on-line monitoring of liquids in an industrial environment.

A high performance hardware accelerator for dynamic texture segmentation

The major contribution of this paper is the development of a hardware (FPGA) software (CPU) co-design architecture for accelerating the application of Dynamic Texture Segmentation.This work presents a FPGA implementation of FFT processing sub-system including FFT/IFFT processors, read/write control modules, and memory/FIFO modules, as well as memory optimization using local FIFOs to minimize external RAM access. Such FPGA implementation fully exploits the hardware acceleration technique. All FFT and related operations are executed in hardware which should run orders of magnitude faster than the software implementation.This paper demonstrates that the FPGA-CPU based solution is 37.3 times faster in data processing time and 5.9 times faster in total run time, compared to the CPU (CPU-GPU) based solution. Hardware accelerators such as general-purpose GPUs and FPGAs have been used as an alternative to conventional CPU architectures in scientific computing applications, and have achieved good speed-up results. Within this context, the present study presents a heterogeneous architecture for high-performance computing based on CPUs and FPGAs, which efficiently explores the maximum parallelism degree for processing video segmentation using the concept of dynamic textures. The video segmentation algorithm includes processing the 3-D FFT, calculating the phase spectrum and the 2-D IFFT operation. The performance of the proposed architecture based on CPU and FPGA is compared with the reference implementation of FFTW in CPU and with the cuFFT library in GPU. The performance report of the prototyped architecture in a single Stratix IV FPGA obtained an overall speedup of 37x over the FFTW software library.

КОНВЕЙЕРНАЯ ОБРАБОТКА СИГНАЛОВ С ВЫСОКОЙ ТОЧНОСТЬЮ ИЗМЕРЕНИЯ В ЧАСТОТНОЙ И ВРЕМЕННОЙ ОБЛАСТЯХ

An algorithm for real time signal processing with high accuracy of determining both frequency and time characteristics of RF signals is proposed. The algorithm provides frequency resolution through FFT processing and pulse width measurement in time domain. The algorithm is developed for real-time systems, for example in laboratory measurement devices or in radioemission monitoring applications. Keywords: signal processing, frequency measurement, pulse width measuring, real-time processing Manuscript submitted 17.04.2015 Radio phys. radio astron. 2015, 20(2): 180-186 REFERENCES 1. TSUI, J. B., 2004. Digital techniques for wideband receivers. Raleigh, NC, USA: SciTech Publishing Inc. DOI: https://doi.org/10.1049/sbra005e 2. TSUI, J. B., 1986. Microwave Receivers With Electronic Warfare Applications. New York, USA: Wiley-Interscience. 3. NAMGOONG, W., 2003. AChannelized Digital Ultrawideband Receiver. IEEE Trans. Wireless Commun . vol. 2, no. 3, pp. 502–510. DOI: https://doi.org/10.1109/TWC.2003.811177 4. ZAHIRNIAK, D. R., SHARPIN, D. L. and FIELDS, T. W., 1998. AHardware-Efficient, Multirate, Digital Channelized Receiver Architecture. IEEE Trans. Aerosp. Electron. Syst . vol. 34, no. 1, pp. 137–152. DOI: https://doi.org/10.1109/7.640270 5. FIELDS, T. W., SHARPIN, D. L. and TSUI, J. B., 1994. Digital Channelized IFM Receiver. In: Microwave Symposium Digest IEEEMTT-S International . San Diego, CA, USA, 23-27 May 1994, vol. 3, pp. 1667–1670. 6. LOPEZ-RISUENO, G., GRAJAL, J. and SANZ-OSORIO, A., 2005. Digital Channelized Receiver Based on Time-Frequency Analysis for Signal Interception. IEEE Trans. Aerosp. Electron. Syst . vol. 41, no. 3, pp. 879–898. DOI: https://doi.org/10.1109/TAES.2005.1541437