Showing papers in "Journal of Vibroengineering in 2014"

Application of the discrete wavelet transform and probabilistic neural networks in IC engine fault diagnostics

Abstract: Around the world are continued attempts to use the vibroacoustic phenomena for purposes of diagnosis of machine condition. Particularly important becomes non-invasive methods including methods based on vibration and acoustic signals. Vibroacoustic phenomena, which relates to the working of technical objects, includes all necessary information connected with the technical condition. The biggest difficulty is the transformation of registered vibroacoustic signals and creation on their basic measures, which will be non-sensitive to any type of interference occurring during the operation of objects and recording signals. To the group of technical objects, for which are already conducted numerous studies all over the world, connected with use of vibroacoustic phenomena for diagnostic purposes which relates to the automotive drive systems, including combustion engines. Combustion engines during its working generate a whole range of vibroacoustic phenomena bringing information on the proper operation of the engine, as well as on condition of each of its elements. In a combustion engine, there are many sources of vibroacoustic phenomena, which contributes to the disruption of diagnostic information. The development of appropriate methods for vibroacoustic signal processing and complete diagnostic systems may allow future extension of the on-board diagnostics OBD system – currently in used cars. The most interesting would be the development of complex system for diagnosing the condition of the individual elements of the car engine operating by basing on information from vibroacoustic signals. In this article are shown results of research, which aim is to diagnose damages of mechanical elements of car combustion engine using vibration signals and artificial neural networks.

Identification of structure and directional distribution of vibration transferred to car-body from road roughness

Abstract: The article presents results of the research on identification of structure and directional distribution of vibration transferred to car-body from road roughness. It is the case study of multiple sources of vibration interacting on vehicle and vibration transfer into driver and passengers. During the research the passenger car was driven on special test track. It were recorded the vibration signals in 3 orthogonal axes. The sensors were mounted at the floor panel in locations where the vibration are transferred into the human organism. For the purpose of analysis of vibration transfer in term of human perception it is necessary to correlate the vibration energy, frequency and time of exposition. It allows to evaluate exposure on vibration in frequency bands close to natural frequency of chosen human organs. The analysis of time-frequency distribution of the vibration allow to separate the main components of the signal. The paper presents the results of comparison of RMS value of vibration for different axes in measurement points on floor panel.

Diagnostics of the tram track shape with the use of the global positioning satellite systems (GPS/Glonass) measurements with a 20 Hz frequency sampling

Abstract: Satellite geodetic measurements used in the diagnosis of railway tracks require professional receivers and a very high frequency rate of data processing. It stems from a significant speed (10 km/h) kinematic measurements carried out during the passage of a measuring platform. The survey results (positions) of deformed railroad track have waveforms nature requiring additional processing methods and approximations. Due to the announcement in 2011 of the operating status for the Russian Global Navigation System (Glonass) and launching a commercial geodetic satellite network SmartNet in northern Poland (2012) created for the first time a possibility of carrying out measurements using two satellite systems (GPS/GLONASS) which significantly increase the accuracy of measurements on a rail. A paper presents a possibility of using two-system satellite receivers to measure the deformation of the tram track on the example of the measurement line in Gdansk (October 2013). The studies used rarely encountered in geodesy a very high position frequency rate (20 Hz), which entails the use of wave processing methods.

Design and analysis of a quasi-zero stiffness isolator using a slotted conical disk spring as negative stiffness structure

Abstract: This paper concerns the characteristics of a novel quasi-zero stiffness (QZS) isolator developed by parallelly combining a slotted conical disk spring with a vertical linear spring. The static characteristics of the slotted conical disk spring as well as the QZS isolator are presented. The configurative parameters are optimized to achieve a wide displacement range around the equilibrium position for which the stiffness has a low value and changes slightly. The overload and underload conditions are taken into account, resulting in a Helmoholtz-Duffing equation. The primary resonance response of the nonlinear system composed by a loaded mass and the QZS isolator are determined by employing the Harmonic Balance Method (HBM) and confirmed with the results of numerical simulation. The frequency response curves (FRCs) are obtained for both force and displacement excitations. The force transmissibility, the absolute displacement and acceleration transmissibility are defined and investigated. The study shows that the overloaded or underloaded system can exhibit linear stiffness, softening stiffness, softening-hardening stiffness and hardening stiffness with the increasing excitation amplitude. The response and the resonance frequency of the system are affected by the excitation amplitude and the offset displacement to the position at which the dynamic stiffness is zero. To enlarge the isolation frequency range and improve the isolation performance, the loaded mass and the excitation amplitude should be suitably controlled.

Nonlocal thermoelastic vibrations for variable thermal conductivity nanobeams due to harmonically varying heat

Abstract: This article constructs a new model of nonlocal thermoelasticity beam theory with phase-lags considering the thermal conductivity to be variable. A nanobeam subjected to a harmonically varying heat is considered. The nonlocal theories of coupled thermoelasticity and generalized thermoelasticity with one relaxation time can be extracted as limited and special cases of the present model. The effects of the variable thermal conductivity parameter, the nonlocal parameter, the phase-lags and the angular frequency of thermal vibration on the lateral vibration, the temperature, the displacement, and the bending moment of the nanobeam are investigated.

Assessment of the vibroactivity level of SI engines in stationary and non-stationary operating conditions

Abstract: Combustion engines are one of the main sources of vibration and noise in vehicles. The level of engine vibroactivity is affected by aspects such as rotational speed and technical condition. Tests were carried out as part of the research, designed to assess the level of vibroactivity of SI engines in stationary and non-stationary conditions. During the bench tests, the engine’s rotational speed and its technical condition were changed by simulating a slightly enlarged valve clearance. As a result of the experiments it was determined that local changes in the amplitude of engine vibrations caused by the combustion process, clearances or misfire can be used as diagnostic information about the condition of the engine. It has been shown that the local level of vibration is dependent on the point of measurement, the angle of the crankshaft rotation and valve timing, and that for diagnostic tests, measurements performed in stationary engine operating conditions are more useful. The tests have also shown how the change of engine condition affects the level of noise and vibration generated, and how these levels change during the acceleration of the engine.

Diagnostics of buggy vehicle transmission gearbox technical state based on modal vibrations

Abstract: This paper presents a diagnostics technique of beach buggy gearbox technical state based on the measurement of modal vibrations. It is well known that the vibration level of machine elements can be correlated to the technical state of the machine. The frequency analysis of vibration signals can be effectively used for the monitoring of the fault origination and development in rotating machinery. The proposed technique uses gearbox modal vibration data to identify and monitor developing faults in the buggy vehicle.

Testing polymer rollers memory in the context of passenger lift car comfort

Abstract: The article presents the authors’ own studies on the application of polymer materials with different physical and chemical properties for vibro-insulation of lifting appliances. The studies were performed on a static test stand, which was made as part of works on the examined polymers, as well as on a dynamic test stand. We analyzed the effect of various polymer materials upon the phenomenon of susceptibility and possibility of returning to primary shape after the load disappears. We determined susceptibility characteristics for examined polyurethane materials. Study results are important from the point of view of improving the comfort and operation of lifting appliances.

An improved spline-local mean decomposition and its application to vibration analysis of rotating machinery with rub-impact fault

Abstract: A troublesome problem in application of local mean decomposition (LMD) is that the moving averaging process is time-consuming and inaccurate in processing the mechanical vibration signals. An improved spline-LMD (SLMD) method is proposed to solve this problem. The proposed method uses the cubic spline interpolation to compute the upper and lower envelopes of a signal, and then the local mean and envelope estimate functions can be derived using the envelopes. Meanwhile, a signal extending approach based on self-adaptive waveform matching technique is applied to extend the raw signal and overcome the boundary distortion resulting from the process of computing the upper and lower envelopes. Subsequently, this paper compares SLMD with LMD in four aspects through a simulative signal. The comparative results illustrate that SLMD consumes less computation time and produces more accurate decomposed results than LMD. In the experimental part, SLMD and LMD are respectively applied to analyze the vibration signals resulting from a rotor-bearing system with rub-impact fault. The results show that SLMD can more efficiently and accurately extract the important fault features, which demonstrates that SLMD performs better than LMD in analyzing the mechanical vibration signals.

Interference model of conical pick in cutting process

Abstract: The load on conical pick is affected by many factors such as pick geometry and installation angle. In order to decrease the wear and vibration of pick in the cutting process by choosing proper impact angle, the interference mathematical models of straight and revolving cutting were established according to coal cutting theory. Based on this, coal cutting experiment was carried out with different impact angles β, different head face radii of pick body R and different cutting depths d to verify the mathematical model. The results indicate that the picks cutting into coal with a certain installed angle are prone to interfere with coal in the cutting progress. There is a crsitical impact angle, and it is different under different cutting conditions. The critical impact angle decreases with the head face radius of pick body R and cutting depth d. On the condition of given pick geometry and movement parameters, the cutting force of picks or cutting torque of cutting header decreases with the impact angle. When the impact angle of the pick is larger than the critical angle, the load on pick will increase prominently.

Bearing performance degradation assessment and prediction based on EMD and PCA-SOM

Abstract: Bearings are used in a wide variety of rotating machineries. Bearing vibration signals are non-stationary signals. According to the non-stationary characteristics of bearing vibration signals, a bearing performance degradation assessment/prediction and fault diagnosis method based on empirical mode decomposition (EMD) and principal component analysis (PCA)-self organizing map (SOM) is proposed in this paper. First, vibration signals are decomposed into a finite number of intrinsic mode functions, after which the EMD energy feature vector, which is composed of all the IMF energy, is obtained. PCA is then introduced to reduce the dimension of feature vectors. After that, the reduced feature vectors are selected as input vectors of the SOM neural network for performance degradation and fault diagnosis. Finally, the degradation trend of bearing is predicted by Elman neural network. The analysis results from bearings with different fault degrees or degradation trend and fault patterns show that the proposed method can assess and predict the degradation of bearing suitably and achieve a fault recognition rate of over 95 % for various bearing fault patterns.

Free transverse vibrations of orthotropic thin rectangular plates with arbitrary elastic edge supports

Abstract: A so-called Spectro-Geometric Method (SGM) is presented for the free transverse vibration analysis of orthotropic thin rectangular plates with arbitrary elastic supports along each of its edges, a class of problems which are rarely attempted in the literature. Regardless of boundary conditions, the displacement function is invariably and simply expressed, in spectral form, as a trigonometric series expansion with an accelerated polynomial rate of convergence as compared with the conventional Fourier series. All the unknown expansion coefficients are treated as the generalized coordinates, and determined using the Rayleigh-Ritz technique. This work allows a capability of modeling a wide spectrum of orthotropic thin rectangular plate under a variety of boundary conditions, and changing the boundary conditions as easily as modifying the material properties or dimensions of the plates. The accuracy and reliability of the SGM prediction are demonstrated though numerical examples. The SGM prediction can be readily and directly extended to other more complicated boundary conditions involving non-uniform restraints, point supports, partial supports and their combinations.

Computational considerations of 3-D finite element method models of railway vibration prediction in ballasted tracks

Abstract: The study of vibrations induced by a passing train is of utmost importance to understand better this phenomenon and to design efficient mitigation measures. Within all the techniques used to model vibrations, finite element methods allow introducing in the model detailed characteristics of the real vehicle-train-soil system. However, the accuracy of the results is linked to how detailed the real elements implemented in the model are and consequently, with the computing time. In this paper a three-dimensional finite element method to predict vibrations is developed and validated with real field-measured data. Then, different scenarios are represented to assess the efficiency of the model linking the quality of the results obtained with the calculation time required in each case. Finally, a reflection regarding the constitutive model of the materials when working with finite element models is done.

Theoretical study on self-synchronization of two homodromy rotors coupled with a pendulum rod in a far-resonant vibrating system

Abstract: The objective of this paper is to investigate the self-synchronization of two homodromy rotors coupled with a pendulum rod in a far-resonant vibrating system. Using the average method and revisionary small parameters, we derive the dimensionless equation of the self-synchronization criterion and synchronous stability of the vibrating system. Meanwhile, to prove the correctness of the theoretical analysis, the diversity feature of the vibrating system is simulated numerically. Both results of theoretical analysis and numerical simulation show that increasing the length of the pendulum rod or decreasing the mass of the rotor connected with pendulum rod can ensure the self-synchronization and synchronous stability of two homodromy rotors in the vibrating system.

Practical formula to calculate tension of vertical cable with hinged-fixed conditions based on vibration method

Abstract: Vertical cables are widely used in the tied-arch bridges and suspension bridges as the vital components to transfer load. It is very important to accurately estimate the cable tensions in the cable supported bridges during both construction and in-service stages. Vibration method is the most widely used method for in-situ measurement of cable tensions. But for the cables with hinged-fixed boundary conditions, no analytical formulas can be used to describe the relationship between the frequencies and the cable tension. According to the general solution of the vibration equation and based on its numerical computational results, practical formula to calculate tensions of vertical cables by multiple natural frequencies satisfying hinged-fixed boundary conditions is proposed in this paper. The expression of the practical formula is the same as the solution derived from an axially loaded beam with simple supported ends and can use the first 10 order frequencies to calculate the cable tension conveniently and accurately. Error analysis showed that when using the fundamental frequency to estimate cable force, the estimated tension errors of the cables with its dimensionless parameter ξ≥ 2.8 are less than 2 %. It contained nearly all of the vertical cables used in bridge engineering. In addition, with multiple natural frequencies being measured, bending stiffness of the cable can be identified by using the formulas presented in this paper with an iterative method. At last, the practical formula in this paper is verified to have high precision with several numerical examples, and can be conveniently applied to field test for cable-supported bridges.

Nonlinear behavior of a spur gear pair transmission system with backlash

Abstract: In order to investigate the nonlinear characteristics of gear transmission system under the action of external and internal excitations, a dynamic model of a spur gear pair was established involving the backlash, damping, transmission error and the meshing stiffness. Based on the incremental harmonic balance method (IHBM), the general forms of the periodic solution with arbitrary precision are deduced. The vibration response obtained by IHBM compare very well with the results obtained by New-Mark method, which verifies the accuracy and electiveness of the analytical methodology (IHBM) and provide information on the dynamic characteristic of spur gear. The simulation results revealed that several types of steady-state periodic solution are identified and determined by employing the IHBM. Due to the effect of backlash, the nonlinear characteristics of jump discontinuity phenomena and multiple stable solutions coexist and the meshing impact phenomenon are obvious. In addition, the influences of the system damping, transmission error and excitation amplitude on the amplitude frequency characteristic are illustrated by a series of diagrams. The results implicate that increasing the external excitation amplitude and system damping can effectively decrease the system resonant amplitude and control the nonlinear vibration response of the gear system and the effect of hardening spring behavior becomes weaker. The transmission error excitation amplitude variation also tends to worse the degree of nonlinearity. Therefore, it presents some useful information to reduce the vibration and noise of gear system.

Determination method of the structure size interval of dynamic similar models for predicting vibration characteristics of the isotropic sandwich plates

Abstract: A method is studied for determining the structure size interval of dynamic similar models of the isotropic sandwich plates. Firstly, a comparison between the two theories of plates, the Resineer theory and the Hoff theory, is conducted, including their governing equations and the ANSYS analytic solutions of frequency. The Resineer theory is chosen as the basic theory of this paper finally. Secondly, the scaling laws between the model and prototype of isotropic sandwich plate are established by combining the dimensional analysis and governing analysis. Both complete and incomplete geometric similarity conditions are discussed. Thirdly, the determination method of the structure size interval of the models is proposed. The nature vibration mode keeps the same and the nature frequency and harmonic response keep in proportion with the prototype of the sandwich plate. At last, the flow step of the intervals determination method is given.

A novel semi-active suspension design based on decoupling skyhook control

Abstract: A semi-active suspension design based on the traditional method of skyhook control is not capable of effectively controlling the attitude of the vehicle. However, an innovative approach called decoupling skyhook control allows the attitude of the vehicle body and its vibration characteristics to be effectively controlled. In this paper, a new decoupling skyhook controller for semi-active suspension is presented. Vehicle body motions in the three directions of vertical, pitch, and roll have been adopted to develop three skyhook controllers and directly control the vehicle body attitude. Furthermore, three orientation skyhook control forces are converted into actual damping forces of four adjustable dampers through the input decoupling transformation. The simulation results show that the developed controller is more effective than the traditional skyhook control in improving ride comfort.

An effective diagnosis method for single and multiple defects detection in gearbox based on nonlinear feature selection and kernel-based extreme learning machine

Abstract: Gear transmissions have been widely used in most of today’s manufacturing and production industries; however, they often suffer from deteriorations and damages on gear pairs. Severe damages of the machinery caused by the failures of gears account for 48 %, leading to significant economic losses. Therefore it is crucial to implement fault diagnosis procedure for gearboxes. The gear meshing motion is a kind of typical strong nonlinear movement, and the related vibration signals are the nonlinear mixtures of different kinds of vibration source, leading to great difficulty in the fault feature extraction and fault detection. In order to improve the fault detection of gearboxes, a new method based on the nonlinear fault feature selection and intelligent fault identification is proposed in this work. The blind source separation (BSS) procedure was firstly employed to eliminate the influence of noise signal sources. The useful information related to the fault vibration was hence separated by the independent component analysis (ICA). Then the spectral regression (SR) was used as a nonlinear feature selection technique for the separated vibration sources. Hence, distinct fault features can be obtained. Lastly, the kernel-based extreme learning machine (KELM) was applied for the pattern recognition of single and multiply faults of the gearbox. The fault vibration data acquired from a gearbox fault experimental tester was used to valuate the proposed diagnostic method. The experiment results show that useful fault vibration signals can be separated by the new method, and the fault detection rate of the proposed method is superior to the existing approaches with an increase of 4.4 % or better. Hence, this new development will produce considerable savings by reducing unplanned outages of machinery so a company can get the full benefit from condition monitoring.

Nonlinear characteristics and stability optimization of rotor-seal-bearing system

Abstract: A nonlinear rotor-seal-bearing system model, including the Muszynska nonlinear seal force model and nonlinear oil-film force model based on short bearing assumption, is proposed in this paper. The non-dimensional dynamic motion equations of the system are also established and solved by fourth order Runge-kutta method. The nonlinear dynamic characteristics of the system are analyzed with the help of bifurcation diagrams, spectrum waterfall diagrams, axis orbit diagrams, Poincare maps and amplitude spectrums. The effect of rotor speed, seal clearance, seal length and seal radius on the nonlinear characteristics of the system is also explored. The genetic algorithm (GA) is applied to optimize the stability of the system. The numerical results demonstrate that the rotor-seal-bearing system contains many motion forms, such as periodic, multi-periodic and quasi-periodic motions. Lower rotor speed, proper seal clearance and seal radius, larger seal length are of benefit to the stability of rotor-seal-bearing system. The minimum instability rotor speed changing from 1970 rad/s to 2110 rad/s indicates the GA is an effective optimization method of improving the stability of rotor-seal-bearing system.

Nonlinear backstepping design for the underactuated TORA system

Abstract: The nonlinear feedback cascade model of the underactuated translational oscillators with rotating actuator is obtained through a collocated partial feedback linearization and a global change of coordinates. A nonlinear controller is designed with the backsteping technology, which treats the state variables as virtual control inputs to design the virtual controllers step by step. The system stability is proved with the Lyapunov stability theorem. The simulation results show the system under any initial states can be asymptotically stabilized to the origin and the controller has a good control performance.

An improved longitudinal vibration model and dynamic characteristic of sucker rod string

Abstract: Considering the influence of the nonlinear characteristics of plunger load and the friction of sucker rod string (SRS) on the SRS’s longitudinal vibration, an improved simulation model of SRS’s longitudinal vibration is derived. In the details, based on the flow characteristic of non-Newtonian power law fluid (NNPLF), a velocity model of NNPLF between pump plunger and pump barrel is established. Then the law of the velocity distribution is solved out with Lagrange multiplier method. Therefore, with the law of the velocity distribution of NNPLF, the computing models of nonlinear friction of pump plunger and clearance leakage between pump plunger and barrel are derived. Taking account of the influence of some parameters on the plunger load, such as plunger friction, hydraulic loss of pump and clearance leakage, an improved simulation model of plunger load is derived. The dynamic response is solved out with fourth order Runge-Kutta method. Comparing experiment results with simulated results, good agreement is found, which shows the simulation model is feasible. The influences of the different parameters on pump pressure and pump plunger load are analyzed, such as stroke number, power law exponent, consistency coefficient and gap between plunger and pump barrel. Simulation result indicates that the opening time of standing valve and traveling valve is affected by the parameters, and the maximum and minimum loads of pump plunger are affected by stroke number. In addition, the influence of SRS absorber on SRS’s longitudinal vibration is analyzed.

Fractional order generalized thermoelasticity with variable thermal conductivity

Abstract: In this work, the consideration of variable thermal conductivity as a linear function of temperature has been taken into account in the context of fractional order generalized thermoelasticity (Youssef’s model). The governing equations have been derived and used to solve the one-dimensional problems of an elastic half-space. The solution has been induced in the Laplace transform domain and applying for thermal shock half-space on the bounding plane when it is rigid. The numerical inversion of the Laplace transform has been calculated numerically by using Tzou method and the results have been represented in figures with some comparisons to stand on the effect of the fractional order parameter and the variability of the thermal conductivity on all the studied fields.

Flexible supporting and fixing method for hybrid ultrasonic motor using longitudinal and torsional vibration modes

Abstract: A new flexible supporting and fixing method for hybrid ultrasonic motor using longitudinal and torsional vibration modes is presented. A motor base is used to support and fix the motor, which has dual concentric bearings in opposite shell sides and a fixing slot. The axis of the motor has two extended parts outside the both sides of the motor. Once the motor has been assembled completely, the two extended parts of the motor axis will be inserted into the concentric bearings, which support the motor and restrict several degrees of freedom (DOFs) of the motor, such as the translational DOFs along X and Y axes, the rotational DOFs around X and Y axes. The motor has a flexible fixing sheet which placed near the piezoelectric ceramics, and the flexibility of the fixing is discussed by analyzing the thickness and the foot length of fixing sheet. The fixing sheet is fixed on the fixing slot with glue, which restricts the translational DOF along Z axis and rotational DOF around Z axis of the stator. The experiment results show that there is little influence on the motor working performance by using this supporting and fixing method; the motor can work smoothly and steadily and the maximum speed of the motor can exceed 2000 r/min.

Health assessment of rotary machinery based on integrated feature selection and Gaussian mixed model

Abstract: Bearing failure is the most common failure mode of all rotary machinery failures, and can interrupt the production in a plant causing unscheduled downtime and production losses. A bearing failure also has the potential to damage machinery causing soaring machinery repair and/or replacement costs. In order to prevent unexpected bearing failure, a health assessment method is proposed in this paper. It employs an integrated feature selection approach and Gaussian mixture model (GMM). Firstly, the integrated feature selection approach, which combines empirical mode decomposition (EMD), singular value decomposition (SVD) and Principal Component Analysis (PCA), processes nonlinear and non-stationary vibration signals of a bearing and extracts features for health assessment. Then, GMM is utilized to evaluate and track the health degradation of the bearing in terms of confidence values (CV). This method, which is notable for bearing health tracking and detect the defect at its incipient stage, can be used without the need for failure datasets in applications. Finally, the feasibility and efficiency of this method was validated by two datasets of different bearing experiments.

Quantification and minimization of sensor effects on modal parameters of lightweight structures

Abstract: This paper aims to quantify the adverse effects of contact type sensors on modal parameters of lightweight structures and to present a practical way for identification of modal parameters of structures with minimal sensor effects. The adverse effects of a contact type sensor on natural frequencies, damping levels and mode shapes are explored using the theoretical model of a typical beam-like sample carrying a sensor and a controlled experimental study based on measurement of frequency response functions using non-contact excitation and response sensors. The half-power and circle fit modal identification methods are used to extract modal parameter from measured data. The experimental and theoretical modal analysis results are evaluated, and a practical methodology based on classical acoustic and vibration frequency response functions is suggested to identify modal loss factors and natural frequencies of lightweight structures with minimal sensor effects.

Stability analysis and response of nonlinear rotor-seal system

Abstract: In this paper, we study the stability of the nonlinear rotor-seal system using Liapunov’s first method The mathematical solutions using multiple scales up to and including second order approximations is investigated We extract all resonance cases from analytical solution and investigated It is quite clear that some of the simultaneous resonance cases are undesirable in the design of such system as they represent some of the worst behavior of the system The effects of various parameters on the behavior of the system and stability of the system are investigated numerically by response curve Poincare maps are used to determine stability and plot bifurcation diagrams

Fault diagnosis of rolling bearing based on relevance vector machine and kernel principal component analysis

Abstract: In order to improve the speed and accuracy of rolling bearing fault diagnosis on small samples, a method based on relevance vector machine (RVM) and Kernel Principle Component Analysis (KPCA) is proposed Firstly, the wavelet packet energy of the vibration signal is extracted with the wavelet packet transform, which is used as fault feature vectors Secondly, the dimension of feature vectors is reduced in order to weaken the correlation between the features The important principal components are selected using KPCA as the new feature vectors under the criterion that the cumulative variance is greater than 95 % Finally, the faults of rolling bearing are diagnosed through combining KPCA with RVM Simulation experimental indicates the advantages of the presented method Moreover, the proposed approach is applied to diagnoses rolling bearing fault The results show that wavelet packet energy can express rolling bearing fault features accurately, KPCA can reduce the dimension of feature vectors effectively and the proposed method has better performance in the speed of fault diagnosis than the method based on support vector machine (SVM), which supplies a strategy of fault diagnosis for rolling bearing In this paper, the performance of the proposed method is also compared with other diagnostic methods

Closed-form solution of curved beam model of elastic mechanical wheel

Abstract: Based on the Timoshenko curved beam theory, a novel and feasible closed-form solution was proposed to deal with the internal mechanics characteristics of mechanical elastic wheel (MEW). With the Laplace transformation and boundary conditions, the governing differential equations was reduced to a single equation in regard to the rotation angle of curved beam, so as to reveal the relationship among the radial deformation, the tangential deformation and the curved angle. Furthermore, by adopting the Frobenius theory and the Green function, six normalized solutions of equations, the general solution and the free vibration of system equations were obtained. In the end, structure mechanics and vibration modal experiments were carried out and the results show that the analytical model is applicable for the experimental results.

Numerical calculation and finite element calculation on impeller of stainless steel multistage centrifugal pump

Abstract: In order to save energy and materials, some mechanical structures are very thin. Aiming to study the influence of impeller blade thickness on the performance of stainless steel multistage centrifugal pump, the whole flow field of stainless steel multistage centrifugal pump with different blade thickness were calculated based on ANSYS Fluent. The relationship between the impeller blade thickness and the overall performance of the pump was analyzed. To further study the reliability of the impeller structure for stainless steel multistage centrifugal pump, based on the ANSYS Workbench, the final stage impeller of the pump with different blade thickness were calculated by using the finite element method. Results indicate that with the increase of blade thickness, the maximum stress and deformation of the impeller gradually decreased, while the stability of the impeller structure increased.