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Numerical analysis of aerodynamic features of porosity-optimized wind barriers and running safety of train
Get PDFA 2-D model-bridge with different porosity barriers is simulated with CFD to explore the windbreak mechanism. The accuracy of simulation is verified by a wind tunnel test. The porosity of the barriers is optimized by analyzing the aerodynamic features of the train-bridge system subjected to cross winds. It is found that wind velocity on the windward track changes greater than that on the leeward track. The train rolls towards the barrier when porosity is lower than 10 % and away from barrier when porosity is higher than 30 %, and the rolling moment is minimized when porosity is 30 %. The dynamic response of running train with and without wind barrier is compared, from which the windbreak effect of barrier is identified
Rolling element bearings fault diagnosis based on correlated kurtosis kurtogram
Get PDFFind optimum frequency band which contains strong impulsive signal is very critical for bearing fault diagnosis. Recently developed kurtogram method is an effective method to determine optimum frequency band for envelope analysis. However, most of kurtograms and its improvements are based on kurtosis criteria. A limitation of kurtosis is that high kurtosis value will be acquired even if the signal has only a single impulse. This will lead to error frequency band selection when the signal contains some impulse like noise. So, this paper uses correlated kurtosis as a criterion to construct kurtogram. Correlated kurtosis is superior to traditional kurtosis for detecting the periodic impulses produced by bearing fault. Finally, a real bearing outer race fault experiment is used to demonstrate the method’s effectiveness
Research on dynamic performance and motion control of robot manipulator
Get PDFAmongst the robotics and autonomous systems, robot manipulators have proven themselves to be of increasing importance and are widely adopted to substitute for human in repetitive and/or hazardous tasks. In this paper, the purpose is to research on dynamic performance and motion control of robot manipulator for the more precise, crucial and critical tasks in industry. Firstly, the forward and inverse kinematics was accurately described by obtaining the link transformation matrices from each joint in robot manipulator. To find admissible solutions along the path, the workspace of the manipulator was determined by joint limit condition and validated by actual measurement. And then, the dynamic performance of robot manipulator is researched by using the forming flexible multi-body system. Furthermore, the frequency response curves are obtained by exciting vibration simulation based on vibration model, which the predicted method was validated by comparing simulation and experimental results. Finally, the control system architecture was given and the grasping process was conducted by gripper based on motion trajectory control in the workspace
Conversion of inhomogeneous robin boundary conditions into virtual sources for wave motions and heat conduction
Get PDFIn vibration engineering, the differential equations of wave motions and heat conduction are usually accompanied by inhomogeneous boundary conditions in practice. Boundary inhomogeneity makes the dynamics essentially nonlinear, which prevents Hilbert space from being applied for modal decomposition. To deal with this difficulty, this paper does not treat boundary inhomogeneity as a “condition”, but almost converts it into a virtual source in conjunction with homogeneous boundary. This conversion counts mostly on the Laplace-Galerkin transform, a functional tool developed in previous works. We also explore boundary topology of this virtual-source conversion, and find that its strategy is to zero the environment and simultaneously create a spatially impulsive source on the homogeneous boundary, yielding almost the same solution. In one-dimensional region, such a boundary source takes the form of Dirac delta function usually combined by its derivatives. In a sense, this paper catches how Nature really handles boundary conditions
Comparison of the noise level and the skid resistance of asphalt pavement mixtures on road surface
Get PDFTraffic noise is a major environmental source of pollution both in developed and in developing countries. Pavement surface texture affects many vehicle and road characteristics; therefore, efforts are needed to develop more advanced techniques for evaluating pavement texture. The selection of an appropriate pavement as the best method to control the main cause of road noise, the sound absorption resulting from contact wheel vehicles and pavement is proposed. In this study skid resistance of porous asphalt and conventional asphalt were measured. The correlation R2 and P value of the linear regression was used for skid resistance and noise. Various pavement characteristics were measured and their effects on noise levels were evaluated using principal components regression, in addition to ordinary least-squares regression. This research confirmed that open graded pavements exhibit reduced tire noise compared to dense and gap graded mixes and quantified this reduction for typical mixes in Tehran. Correlation between Skid resistance of asphalt pavements and noise levels were determined using the statistical program
Destructive energy impact to the myocard damage: between technological advantages and risk
Get PDFBackground: The aim of the study was to evaluate and compare destruction effect to different heart structures using RF, cryo and laser methodology in animal (pig) model. Methods: Ablation procedure was performed on right and left pulmonary veins area, free wall of right and left atrias, and free wall of ventricles positioning ablation electrode from endocardial side. Ablation electrodes were inserted through an incision in right/left auricle. The effects of ablation were observed visually and using thermography for temperature control. Results: Standard recommended parameters for both of used destruction energies were possible to evoke quick critical scar formation and rupture. Temperature in cardiac surface differs from 34.5 till 70.2 °C, and directly depends from electrode compression level, time of application and energy power. We express dissent from the general view, what destruction in cardiac structures is point like. We observed enough high range of temperature dispersion, especially in ventricles. Conclusions: Usage of thermography enable to estimate peculiarities and borders of destruction site, optimize parameters of ablation, allows us to avoid or minimize undesirable effects, save structures and improve clinical outcomes
Research on flow-sound separation algorithm of aerodynamic noise based on immersed boundary method
Get PDFWith the development of theoretical models, numerical algorithms and available computational power, numerical aero-acoustics presents a huge prospect for solving the actual problems of aerodynamic noises. Under low Mach number, structures with a complicated geometric shapes were selected as the research objects to analyze their aerodynamic noises by means of flow-sound separation algorithm based on immersed boundary method. Firstly, the incompressible complicated flow field was solved on the basis of immersed boundary method, and the flow field parameters were obtained as the input values. Then, the linear compressible perturbation equation was solved to simulate generation and travel of acoustic waves. This method was used to predict the noise of flow past two circular cylinders in tandem arrangements and the aerodynamic noise of the rudimentary landing gear. The numerical simulation was then compared with the corresponding experiments, and results were consistent. That showed the algorithm proposed was feasible
The roller bearing fault diagnosis methods with harmonic wavelet packet and multi-classification relevance vector machine
Get PDFRoller bearings are widely used elements in rotary machines. How to monitor the working conditions of roller bearings are focus study in the world. Monitoring the vibration signals of roller bearings is important indirect mean for that they reveal the characteristics and feature of roller bearing faults. Therefore, monitor the vibration signals and diagnose the working states of roller bearings are widely used to ensure the safety operation of the machines. This paper studies a novel roller bearing faults discrimination method with harmonic wavelet packet and Multi-classification Relevance Vector Machine (MRVM). Indeed, the fault discrimination is a pattern recognition process including feature extraction and faulty patterns recognition. Therefore, this paper collects vibration signals and decomposes them with harmonic wavelet packet. After the wavelet coefficients of each node are available, compute the vector energy by corresponding coefficients. The feature vector is prepared after the vector energy has been standardized. With MRVM, the paper proposes three fault discrimination methods in order to identify good bearing, bearing with inner race fault, bearing with outer race fault and bearing with roller fault. The Decision Tree (DT) model, One Against Rest (OAR) model and One Against One (OAO) model are used to propose the classification methods respectively. The proposed OAO model is simplified in order to improve the computation efficiency and simplify the architecture of the model. Finally, capture the vibration signal from the roller bearing stand of electric engineering lab and the roller bearing fault simulation stand QPZZ-II to illustrate the proposed methods. The proposed feature extraction method with harmonic wavelet packet is compared with conventional wavelet packet. With the previous feature vectors, the accuracy and efficiency of the three fault discrimination methods are compared. The accuracy and efficiency of three fault discrimination methods are compared under different conditions including developing faults, noise involving and several faults developing simultaneously. Experiment results show that the proposed feature extraction method is more effective than conventional method and the simplified OAO-RVM model possess the best fault discrimination accuracy and DT-RVM model possesses the better computation efficiency
Modal analysis for a complex military trucks structure
Get PDFThe artillery weapon system muzzle disturbance is influenced largely by the carrier vibration through firing. In case of military trucks carrying cannons, the longitudinal bending vibration is the most important factor affects the muzzle disturbance. The corner stone of this article is the modal and sensitivity analysis of a chosen military truck carrying cannon in order to investigate how much the longitudinal bending natural frequencies of this truck deviated from the nominal value as a result of truck components layout or position variation and some system design parameters variations. This deviation is examined to clarify the most sensitive parameters that affect the longitudinal bending natural frequency. The dynamic characteristics of the truck, such as the natural frequencies and the mode shapes, are determined by using finite element method in order to create the truck flexible system. Via intermediate file, the flexible truck model is imported into commercial FE code “ABAQUS” software for modal analysis whose solutions agree well with an experimental data. This study shows a complete and deep investigation of the dynamic response calculations for a complex flexible military truck. In addition, the sensitivity analysis compels the designer to identify the critical variables which affect the longitudinal bending vibration beside obtain additional information about weapon system dynamics
A contrast between classical method and finite element method for calculating strength in impeller of centrifugal pump
Get PDFIn order to calculate accurately the stress and the deformation conditions of the closed impeller of centrifugal pumps in the flow field, “direct-calculation method” and the ANSYS Workbench-based finite element method are separately used to calculate the maximum stress that the impeller bears and the strength check of it have been proceed. This paper has made a comparative analysis between the two methods, and it is shown that the finite element analysis method can more comprehensively show the stress concentration, whereas the traditional method is more focused on the average of checking. Therefore, in terms of the results, it is suggested that in addition to the traditional direct-calculation method, modern simulation software such as the finite element method should be used for the proofread of the impeller in the industry, in order to improve the running safety and the reliability of the closed impeller of centrifugal pumps