Perform Frequency Domain Analysis Research Articles

Research on Response Characteristics of GPR Method for Detecting Phreatic Lines in Embankments

The excessive elevation of the phreatic lines under continuous high-water levels is the cause of many dangerous situations in embankments. Therefore, accurately understanding the dynamic changes in the infiltration characteristics of embankments is of great significance for judging and evaluating the stability of engineering. This study conducted indoor model experiments and used ground penetrating radar to detect the phreatic lines of soil. By comparing the radar detection results with the measured position of the phreatic lines, it was determined that the phreatic lines appeared as a continuous strong reflection surface with similar shapes in the radargram, and the reflection below the reflection surface became weaker. Through time-domain analysis of the single waveform at different time points, it was found that the amplitude of the reflected wave at the saturation line was larger, and the energy attenuation below the saturation line was faster, resulting in a rapid decrease in amplitude; perform Fourier transform on a single channel signal to obtain a spectrogram, and perform frequency domain analysis on it. The main frequency is around 600MHz, and the second main frequency is around 900MHz. As the saturation line rises, the main frequency gradually shifts towards lower frequencies.

Research And Analysis Of Three Degree Of Freedom Drivetrain Model For Wind Turbine

According to the characteristics of the drivetrain shaft system of large-scale wind turbines, a three-degree-of-freedom wind turbine drivetrain dynamic model is established using Lagrangian equations and dynamic equations, and the drivetrain torsion mathematical model and multi-mass simplified model are extended to Three-degree-of-freedom multi-body dynamics mathematical model. Using this mathematical model can effectively carry out theoretical analysis on the vibration model of wind power generators, and provide a theoretical reference for the design and simulation of the drivetrain. Taking this three-degree-of-freedom mathematical model as a prototype, a three-degree-of-freedom(3-DOF) rigid-flexible coupling multi-body dynamics simulation model is established in Simpack. Perform frequency domain analysis in the dynamic equilibrium state of the drivetrain model to obtain frequency characteristics such as the natural frequency and energy distribution of the drivetrain. According to the frequency characteristics, the potential resonance frequency is identified, and the dynamic response characteristics of the transmission chain are analyzed to determine the dangerous resonance frequency of the dynamic model.

Inter- and Intra-subject Template-Based Multivariate Synchronization Index Using an Adaptive Threshold for SSVEP-Based BCIs

The steady-state visually evoked potential (SSVEP) has been widely used in brain-computer interfaces (BCIs). Many studies have proved that the Multivariate synchronization index (MSI) is an efficient method for recognizing the frequency components in SSVEP-based BCIs. Despite its success, the recognition accuracy has not been satisfactory because the simplified pre-constructed sine-cosine waves lack abundant features from the real electroencephalogram (EEG) data. Recent advances in addressing this issue have achieved a significant improvement in recognition accuracy by using individual calibration data. In this study, a new extension based on inter- and intra-subject template signals is introduced to improve the performance of the standard MSI method. Through template transfer, inter-subject similarity and variability are employed to enhance the robustness of SSVEP recognition. Additionally, most existed methods for SSVEP recognition utilize a fixed time window (TW) to perform frequency domain analysis, which limits the information transfer rate (ITR) of BCIs. For addressing this problem, a novel adaptive threshold strategy is integrated into the extension of MSI, which uses a dynamic window to extract the temporal features of SSVEPs and recognizes the stimulus frequency based on a pre-set threshold. The pre-set threshold contributes to obtaining an appropriate and shorter signal length for frequency recognition and filtering ignored-invalid trials. The proposed method is evaluated on a 12-class SSVEP dataset recorded from 10 subjects, and the result shows that this achieves higher recognition accuracy and information transfer rate when compared with the CCA, MSI, Multi-set CCA, and Individual Template-based CCA. This paper demonstrates that the proposed method is a promising approach for developing high-speed BCIs.

Deagglomeration of Ultrafine Hydrophilic Nanopowder Using Low-Frequency Pulsed Fluidization.

Low-frequency flow pulsations were utilized to improve the hydrodynamics of the fluidized bed of hydrophilic ultrafine nanosilica powder with strong agglomeration behavior. A gradual fluidization of unassisted fluidized bed through stepwise velocity change was carried out over a wide range of velocities followed by a gradual defluidization process. Bed dynamics in different regions of the fluidized bed were carefully monitored using fast and sensitive pressure transducers. Next, 0.05-Hz square-wave flow pulsation was introduced, and the fluidization behavior of the pulsed fluidized bed was rigorously characterized to delineate its effect on the bed hydrodynamics by comparing it with one of the unassisted fluidized bed. Flow pulsations caused a substantial decrease in minimum fluidization velocity and effective agglomerate diameter. The frequencies and amplitudes of various events in different fluidized bed regions were determined by performing frequency domain analysis on real-time bed transient data. The pulsations and their effects promoted deagglomeration and improved homogeneity of the pulsed fluidized bed.

Lightweight architected hollow sphere foams for simultaneous noise and vibration control

Phononic metamaterials, composed of periodically topological structures and materials dispersions, can manipulate acoustic or elastic wave propagation, but not concurrently in most cases. Here we report a new type of three-dimensional (3D) architected hollow sphere foams that can attenuate acoustic and elastic waves synchronically. Our numerical simulation results reveal that the acoustic wave attenuation is attributed to local resonances in the drilled hollow spheres, which act as Helmholtz resonators. The elastic wave mitigation stems from Bragg scatterings in the 3D architected periodic hollow sphere foams. The numerically predicted acoustic and elastic wave band gaps are further validated against the corresponding transmission spectra, which are obtained by performing frequency domain analysis. Notably, elastic wave band gap properties can be decoupled from acoustic wave and independently tuned by tailoring the connectivity among the hollow spheres. The findings reported here offer new opportunities to design lightweight architected metamaterials to simultaneously control undesired noise and vibration over a wide frequency range.

Frequency Domain Analysis of Multiwavelength Photoacoustic Signals for Differentiating Tissue Components

The feasibility of differentiating tissue components by performing frequency domain analysis of photoacoustic images acquired at different wavelengths was studied in this paper. Firstly, according to the basic theory of photoacoustic imaging, a brief theoretical model for frequency domain analysis of multiwavelength photoacoustic signal was deduced. The experiment results proved that the performance of different targets in frequency domain is quite different. Especially, the acoustic spectrum characteristic peaks of different targets are unique, which are 2.93 MHz, 5.37 MHz, 6.83 MHz, and 8.78 MHz for PDMS phantom, while 13.20 MHz, 16.60 MHz, 26.86 MHz, and 29.30 MHz for pork fat. The results indicated that the acoustic spectrum of photoacoustic imaging signals is possible to be utilized for tissue composition characterization.

Evaluation of Frequency Domain Analysis of a Multiwavelength Photoacoustic Signal for Differentiating Malignant From Benign and Normal Prostates: Ex Vivo Study With Human Prostates.

The purpose of this study was to investigate the feasibility of differentiating malignant prostate from benign prostatic hyperplasia (BPH) and normal prostate tissue by performing frequency domain analysis of photoacoustic images acquired at 2 different wavelengths. We performed multiwavelength photoacoustic imaging on freshly excised human prostate specimens taken from a total of 30 patients undergoing prostatectomy for biopsy-confirmed prostate cancer. Histologic slides marked by a genitourinary pathologist were used as ground truth to define regions of interest (ROIs) in the photoacoustic images. Primarily, 3 different prostate tissue categories, namely malignant, BPH, and normal, were considered, while a fourth category named nonmalignant was formed by combining the ROIs corresponding to BPH and normal tissue together. We extracted 3 spectral parameters, namely slope, midband fit, and intercept, from power spectra of the radiofrequency photoacoustic signals corresponding to the 3 primary tissue categories. We analyzed data from 53 ROIs selected from the photoacoustic images of 30 patients. According to the histopathologic analysis, 19 ROIs were malignant, 8 were BPH, and 26 were normal. All the 3 spectral parameters and C-scan grayscale photoacoustic image pixel values were found to be significantly different (P < .01) between malignant and nonmalignant prostate as well as malignant and normal prostate. Preliminary results of our ex vivo human prostate study suggest that spectral parameters obtained by performing frequency domain analysis of photoacoustic signals can be used to differentiate between malignant and nonmalignant prostate.

Dynamic response of a frame-foundation-soil system: a coupled BEM–FEM procedure and a GPU implementation

Graphics processing units have experienced an increasing demand for general-purpose computer applications such as engineering, science, finance, among other areas. This study uses such devices to analyze the performance of a code designed to evaluate the dynamic response of frame-foundation-soil system. In the present article, a direct version of the boundary element method (BEM) is applied to synthesize the 3D dynamic compliance matrix of a rigid and massless foundation interacting with unbounded soil profiles. The foundation compliance matrix is coupled to a frame, modeled by the finite element method (FEM) leading to the dynamic response of a coupled frame-foundation-soil system. The direct version of the 3D boundary element method is built based on the stationary fundamental solution of an elastic full-space. Viscoelastic effects are incorporated by means of the elastic–viscoelastic correspondence principle. The article describes the methodology applied to couple rigid bodies with the BEM mesh. The soil-foundation interaction result is given in terms of a dynamic compliance matrix for a rigid and massless foundation. The frame structural analysis is based on FEM where bar and beam elements are coupled. This strategy allows performing frequency domain analysis of such structural systems. The performance analysis is done by comparing two codes: one was exclusively developed in C language and the other one in CUDA C (Compute Unified Device Architecture). The level of speedup was achieved by implementing some functions in the frame model, i.e., on the FEM based code.

Dynamic analysis of cracks using the SGBEM for elastodynamics in the Laplace-space frequency domain

Abstract Dynamic analysis of a system can be carried out either in the time or frequency domains. Time responses/histories of this system may be directly obtained using time-domain formulations. In the frequency domain, analysis can be performed in either the Fourier or Laplace spaces. The symmetric-Galerkin boundary element method (SGBEM) for 2-D elastodynamics in the Fourier-space frequency domain has been previously reported in the literature. In this paper, the SGBEM for elastodynamics in the Laplace-space frequency domain using the standard continuous quadratic element and its application to dynamic analysis of cracks is presented for the first time. The technique developed is employed together with the fast Laplace inverse transform by Durbin to obtain time-dependent results for several typical examples including both crack and non-crack problems. These results are highly accurate when compared to those obtained from other numerical techniques. It is shown in this work that the very same boundary element code can be utilized to perform frequency domain analysis in either the Fourier or Laplace spaces. However, if time responses are required, the accuracy and computational effectiveness of the analysis may depend on the type of space selected as it determines the type of transforms (inverse Fourier/Laplace transforms) needed for converting frequency solutions to the desired time responses.

A multi-sensor approach to the monitoring of end milling operations

The application of multi-sensor systems for the monitoring of machining processes is becoming more common-place to improve productivity, automation and reliability. The sensors employed in such systems possess signal- and information-ability for enhancing the monitoring and control of machining processes. Although measuring force, power and acoustic emission (AE) signals has been commonly used for the monitoring of turning and drilling operations, their application to the milling process has not been well developed, perhaps due to the complexity of the process. In order to enhance knowledge in this area of applications, a multi-sensor system was developed and installed for the monitoring of end milling operations. The signals acquired and analyzed by the system include force, torque and AE under different machining conditions. The measured signal data was used to perform frequency domain analysis. The results indicate the feasibility of using the frequency peaks of the AE RMS and the torque power spectra for the monitoring of end milling operations.

A Linear Electronic Circuit Analysis Progam

A general purpose program for analysing arbitrary linear electronic circuits is described. The program is capable of performing frequency domain analysis of any circuit consisting of linear components, such as resistors capacitors inductors transistors and operational amplifiers, and independent sources, i.e. voltage and current sources. This program is developed on a widely used 8 bits microcomputer. The ease of using the program and various useful features of the program make the program useful as a teaching aid for beginners such as university students and as a design tool for experts in analog circuit design. The program is highly suitable for users who cannot afford the relatively high cost of minicomputers.