Journal of Engineering and Thermal Sciences
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Numerical simulation for machining S-tube by abrasive flow with various particle volume fractions
Get PDFAbrasive flow machining has become an economical and efficient ultra-precision process for machining complex-shaped pipe parts, and processing effect is exceedingly subject to particle volume fraction. In this paper, aiming at uncovering the influence of various particle volume fractions on the machining result of abrasive flow finishing, based on fluid mechanics theory, mixed phase model and discrete phase model were conducted, FLUENT software was resorted to simulate the numerical characteristics of the solid-liquid two-phase flow field in the inner channel of S-tube with different-particle-volume-fraction abrasive flows, the mechanism of erosion and wear of particles was uncovered, which provides a theoretical basis for abrasive flow machining S-tube structured components
EEMD-Based cICA method for single-channel signal separation and fault feature extraction of gearbox
Get PDFThis paper proposes a novel fault feature extraction method with the aim of extracting the fault feature submerged in the single-channel observation signal. The proposed method integrates the strengths of the constrained independent component analysis (cICA) extracting only the signals of interest (SOIs) with the advantage of ensemble empirical mode decomposition (EEMD) alleviating the mode mixing. The method, which is named EEMD-based cICA, not only enables gear fault feature extraction but also offers a new independent component analysis (ICA) mixing model with source noise and measured noise for the single-channel observation signal. The efficiency of the proposed method is tested on simulated as well as real-world vibration signals acquired from a multi-stage gearbox with a missing tooth and a chipped tooth, respectively
Analysis of nonlinear suspension power harvest potential
Get PDFBecause the power consumption of a controlled suspension is huge, the power harvest potential of a nonlinear controlled suspension is analyzed. Instead of simplifying the suspension to a linear model or adopting some control strategies to solve the problem, this paper investigates the effect of the nonlinear characteristics on the power harvesting potential. A mathematic model is introduced to calculate the nonlinear vibration, and the amount of harvested power was obtained using the multi-scale method. A numerical validation is carried out at the end of this study. The results show that the investigated mechanical parameters affect both the vibration amplitude and the induced current, while the electric parameters only affect the induced current. The power harvesting potential of the nonlinear suspension is generally greater than the linear suspension because the frequency band of the actual pavement also contains bandwidth surrounding the body resonance point. The only exception occurs if the vehicle travels on a road with a particular profile, e.g. a sine curve. To optimize harvested power, it is better to consider the nonlinear characteristics rather than simplifying the suspension to a linear model
Three-dimensional operational modal analysis based on self-iteration principal component extraction and direct matrix assembly
Get PDFThis paper proposes a self-iteration principal component extraction (SIPCE) and direct matrix assembly method for three-dimensional structures. Different from calculating principal components (PCs) by matrix decomposition in traditional principal component analysis (PCA), SIPCE extracts PCs one by one through self-iteration, so SIPCE has lower space-time complexity. Besides that, it avoids singular-value and ill-posed problems of matrix decomposition. The previous method of solving three-dimensional structures is using modal coordinate response back general reversion of least square algorithm, while the new matrix assembly method calculates three-dimensional modal shapes at one time. So, the new matrix assembly method has less calculation error. The numerical simulation results in a cylindrical shell demonstrate that this method can be practically and effectively applied in operational modal analysis (OMA) of three-dimensional structures. The new method is also robust to noise, and has higher identification accuracy and lower space-time consumption than previous method
Study on active vibration isolation system using neural network sliding mode control
Get PDFIn this paper, an active vibration isolation system based on hybrid algorithm is presented in a wide frequency band. Initially, a nonlinear magnetostrictive actuator model is used to establish the appropriate parameters by experiments, which make the actuator using in vibration isolation system work in a better linear dynamic performance, then the sliding mode algorithm modified by neural network, a hybrid algorithm is proposed as the active control controller, and its stability is also analyzed by Lyapunov theory. Furthermore, a dynamic virtual prototype model of active vibration isolation is established to carry out the co-simulation with Adams and Matlab/Simulink, and the results show that under the difference excitations, the neural network sliding mode controller exhibits a good control performance, and the active vibration isolation can effectively improve the vibration isolation effect, reduce the force transmitted to the base and broaden the vibration isolation bandwidth
Efficient FPGA-based FIR – architecture and its significance in ultrasonic signal processing
Get PDFThe presented work demonstrates the most suitable architecture for the FPGA-based signal processing which makes available various real-time filtering algorithms, such as band pass, high pass, low pass, and band-reject for FIR filters. The processor was implemented with the fixed-point arithmetic using VHDL, which can be downloadable on FPGA device. The FPGA device can be interfaced with an analog-to-digital converter (ADC), digital-to-analog converter (DAC) and a personal computer with MATLAB for the user interface and feeding coefficients and order of the filter. The core part of this paper was to find the reconfigurable and efficient architecture of the processor with only one multiplier which can work for Finite Impulse response (FIR) filter with the best- suited structure. The system will be used for automatic generation of fixed-point FIR filters. The model was also implemented in MATLAB script and the verification of results in the case of low-pass filtering confirmed that both models in MATLAB and VHDL matched to each other. All components of architecture in VHDL were designed using generics which allow changing its structure and behavior by generic values. Therefore, it is a universal filter platform where user can process the data while changing the filter parameters as per the requirement of applications. The complete design was verified by taking the example of audio signal frequency, but parameterized components of system architecture can also facilitate its applicability at ultrasonic frequencies by changing the algorithm. The significance and applicability of FPGAs in ultrasonic signal processing were also studied and reviewed
Study on acoustic target strength characteristics of underwater composite rudder
Get PDFIn order to investigate the acoustic behavior of composite material, in this paper, the acoustic target strength (TS) of rudders is obtained by combining the finite element method with the automatically matched layer technique. However, besides the composite material mentioned above, the considered materials of rudder models also include steel. In addition, the results of abeam direction and other angles are computed. Finally, the magnitude of abeam TS versus frequency shows that the acoustic scattering property of composite model is better than that of steel one when the frequency is higher than 1600 Hz. Moreover, the acoustic scattering properties are totally different when frequency is lower than 600 Hz for models with composite and steel materials. As for directivity patterns, the TS of composite model in each direction is lower than that of steel model at 3800 Hz, which matches the conclusions mentioned above
Analysis acoustic target strength of anechoic coatings in low frequency based on equivalent parameter inversion
Get PDFIt’s generally different to predict the acoustic target strength of a submarine with anechoic coatings by conventional finite element method (FEM). Parameter inversion is a common method to solve this problem. Some researchers have studied the parameter inversion about normal incidence of anechoic coatings. In this paper, the FEM of impedance tube is used to obtain acoustic reflection coefficient of anechoic coatings. Then the genetic algorithm is applied to acquire the physical parameters of viscoelastic material which is equivalent to anechoic coatings. The LMS Virtual Lab is used to construct finite element model of the anechoic coatings to validate the parameter inversion with normal incidence
Research on mobile robot path planning based on improved artificial potential field
Get PDFArtificial potential field method is one of the commonly used path planning methods. This paper introduces the defects of U-shaped obstacle problem, narrow channel, Local minimum, GNRON. Repulsive force field reconstruction is used to reduce the U-shaped obstacles and to solve the problem that cannot pass narrow channel, using “change target point as the target line” to solve the local minimum problem, for GNRON we use “Reverse repulsion force field” to solve. The feasibility of the algorithm is proved by simulation and analysis
Study on coupling effect between the time-varying gear backlash and the different time-varying mesh parameters on the gear system
Get PDFThe vibration excitation of the rolling mill mainly comes from the gearbox in the process of rolling strip, and the meshing excitation is the main excitation factor of the gearbox. And the gear backlash plays an important role in the meshing excitation. However, the backlash is inevitable in the process of designing the gear system. Therefore, it is important to select the appropriate gear backlash to reduce the vibration amplitude of the gearbox, to improve the rolling speed and the quality of the steel strip. So, in this paper, the effect of the different variation amplitudes for the time-varying gear backlash (TVGB) on the vibration characteristics of the gear system under various mesh parameters is studied. A new formulation for calculating nonlinear damping and time varying meshing stiffness is applied in this coupling model. The results show that increasing of the load torque, the damping ratio, the system parameter or decreasing the directional rotation radius variation or kinematic transmission error caused the effects of variation amplitudes for the (TVGB) on the dynamic characteristics of the gear system to decrease. Test data from a gearbox experimental table verifies the accuracy of the model. The model is shown to be capable of simulating the mutually coupled effect between the backlash and the different parameters on the gear system. So, the new coupled model can be used as guide to select the appropriate gear backlash values for the rolling mill under different operating conditions