In order to accurately establishing helical gear dynamic model, and well knowing vibration characteristics of helical gear system, meshing stiffness calculation method is put forward based on load tooth contact analysis and considering shaft torsional deformation. Analyzing the helical gear dynamics models established by the decomposition of the mesh stiffness in major domestic literature, and illustrating it’s violation of theoretical mechanics. Based on decomposition of the force and vibration displacement, helical gear vibration model is established consdering meshing stiffness excitation and corner mesh impact excitation. Take the helical gear transmission system as an example, the results consistently indicate that the method based load tooth contact analysis can easily and accurately calculate the teeth meshing stiffness. The dynamic response of literature[8] are significantly different from theory of actual. The results based on decomposition of the force and vibration displacement are good agreement with the theoretical actual.
Appling the numerical simulation method, the characteristics of underwater explosion loading in port were investigated. At first, the numerical method was proved by compared with the empirical formula and the results of experiments, then the propagation of shock wave of underwater explosion and the laws of bubble expansion were also analyzed. The result showed that: the loading of bubble expansion in an underwater explosion in port couldn’t be ignored. If the loading are scaled by impulse, the loading of bubble expansion is larger than the loading of shock wave in most area. The loading of bubble expansion and shock wave are influenced observably by the water surface, the closer to the water surface, the smaller the impulse of both. But the attenuation of the loading of bubble expansion is faster than shock wave, the impulse of bubble expansion even is less than the impulse of shock wave. Water bottom have less influence to the loading of bubble expansion, but have greater influence to the loading of shock wave. The acting time of shock wave would be shortened due to the influence of reflection of water bottom, thereby the impulse of shock wave reduced rapidly. On the condition of sludge bed in existence, the reflection of shock wave on the interface between sludge bed and water are not remarkable, most of the reflection wave is from the interface between sludge bed and rock.
The hydropower station is coupling field of the vibration of water turbine generator set and power house, which shows the superimposed and coupled signals of multiple vibration sources. In this paper, the time-delayed transfer entropy is proposed to identify the transport directionality and path of the vibration information. Firstly, the identifying method for the information transfer in hydropower station based on the transfer entropy is studied by a simulated model. Next, with the field experiments, the actual paths of different vibration sources are identified and analyzed. The paper presents a new time-field identifying method and findings for the study of vibration regularity, location and inherence in the hydropower station.
Chongqing 400044,China)
Abstract: To improve the precision of extracting feature and efficiency of classification and recognition from heart sound, the method of Discrete Wavelet Transform Mel Frequency Cepstrum Coefficients (DWPTMFCC) combined with improved Gaussian Mixture Model (GMM) is used for classification and recognition of heart sound. Firstly, the new feature parameter is formed by using wavelet packet transform instead of Fourier transform and Mel filter group on the basis of the extraction method of MFCC; Secondly, to overcome the shortcoming of K-means algorithm which is used in the parameters initialization process of traditional GMM, Weighted Optional Fuzzy C-Means (WOFCM) algorithm is proposed; Finally, the feature parameters are input into improved GMM for recognition. The clinical data experimental diagnosis and test results show that the method not only can effectively extract heart sound feature, but also have better recognition performance compared with traditional GMM.
In order to get a more accurate finite element analysis model of the bolt-ball shell for health monitoring, the element in adjustable stiffness model is used to reveal the semi-rigid characters of the node. Then, the neural network technology is introduced, by forming network input parameter CPFM with limited measuring point information. A new method of the recognition of the rigid factor, in consideration of the semi-rigid character of the joint reasonably, is put forward by the combination of the elements. A single-layer latticed cylindrical shell with 157 nodes and 414 elements experiment model was used for shaking table test. Based on the basic model and measured modal data, a finite element model updating is done. The result shows that the true dynamic characters of the shell structure can be reflected better, at the same time the neural network can be simplified by applying step-by-step correction algorithm. The result shows that the method can be used for model updating of the bolt-ball shell and certain value in engineering practice.
Finite element models of a bus and a barrier were established. By means of mathematical operation, one special type of traffic accident, a bus rolling over and colliding with barrier, was simulated successfully. In both national standard GB/T 17578-1998 and EU’s ECE R66, strength of the top of bus was stipulated. However, simulation made in this paper indicated that the severity of this kind of accident is far more beyond the experiment. To reduce the loss of accident, new material and increased thickness were used for side post of this vehicle, and a following simulation proved its effectiveness, although only to some extent. The results of this paper could be referred by automotive vehicle designers.
The mechanical system vibration signals effectively reflect the characteristics of the system, its blind deconvolution can provide the possibility of separation of source signals from the mixed signals. Firstly,this paper proposes the convolution model of the mechanical system vibration; Secondly, this paper combines the Multi-Channel Blind Least Mean Squares with the Deflation Source .it is called as the MBLMS-TDS algorithm. For verifing the reasonableness of the algorithm, it is applied in the blind deconvolution of simulation mixed sources.Finally, This paper extracts the diesel engine piston-slap signal and combustion signal from the mixed vibration signal on the surface of the diesel engine piston by the MBLMS-TDS algorithm.
A HHT-based vibration monitoring system, consisting both of the software and the hardware system, was designed and implemented according to the non-stationary nature of the vibration signal from NC spindle. The hardware system concerns with the development of the data acquisition module based on FPGA and PC104 bus, and the software system includes both the monitoring module of time domain wave and the counterpart of the characteristic data. The function of characteristic data monitoring is divided into two parts, i.e., the spectrum distribution monitoring and the time-frequency distribution monitoring. In order to reflect the non-stationary characteristic of the vibration signal from NC spindle more accurate, a data analysis approach, named the Hilbert-Huang Transform (HHT), was introduced into the developed system. Test and analysis of the vibration signal show that the vibration monitoring system not only can characterize the time domain wave and the spectrum distribution, but also can implement the tracing of the time-frequency distribution through HHT’s superiority in characterizing instantaneous frequency.
The inverse matrix of frequency response function is a common method for load identification in practice. The key point of the method is to solve the ill-conditioned problem, which was dealt with Tikhonov regularization and singular value decomposition (SVD) in the paper. Simulation of a plate was carried out to compare the load identification accuracy of the two methods under different ill-conditions, which were evaluated by the condition number of the normal matrix of frequency response function. Conclusions show that Tikhonov regularization is more suitable when the condition number is greater than 1000 and SVD method is better for other situations. What’s more, a novel method is proposed to identify loads with the combination of the two methods based on the condition number. Comparing with SVD and Tikhonov regularization methods through results of simulation and experiment, the novel method can obviously improve the load identification accuracy, and provides a certain guide for practical engineering.
A general method to design ISD structure was introduced in this paper. Twenty-one kinds of new suspension structures feasible in engineering application were built by the method of putting energy storage elements, supporting elements and damper elements in different position. The general dynamic model of these structures was built then. The optimization of acceleration of sprung mass and dynamic tyre load was used to obtain the parameters of mechanical elements. By the comparison of the new and traditional suspension, twelve kinds of new structures were proved to be more excellent. The analysis of typical structures indicated that the method based on dynamic model and parameter optimization was general and universal to design ISD suspension structure.
The width and height of the main powerhouse at the Xiangjiaba Hydropower Station are 31.4 m and 88.2 m, respectively. The structural stability of powerhouse is influenced by the spread of seismic wave and vibration effect, which is induced by blasting construction. The safety of powerhouse is controlled by the structural stability during the excavation process. In this paper, the response of blasting vibration for the rock masses of powerhouse during the excavation process is simulated by the dynamical finite element method (FEM). The simulated results show that, the particle vibration velocity and tensile stress at the feet of top arch is very large, and rapidly decreased with the increasing height. The tensile stress at bottom or top of the rock anchor beam is also large, and has a good correlation with the horizontal particle vibration velocity. The particle vibration velocity and tensile stress of the sidewall are decreased with increasing of height difference. Combined with simulated results and field monitoring data, we suggest that the safe particle vibration velocity for surrounding rock mass and anchor concrete are 15 cm/s and 10 cm/s respectively.
The railway turnout is a vital component of the rail-track structure. The structural performance and safety condition of the railway turnout has a significant impact on the running safety and operation quality of the trains, especially the high-speed trains, and it is therefore of great importance to conduct the research of damage detection and crack monitoring for the railway turnout. This paper proposes a fiber Bragg grating (FBG) sensing technology-based method for damage detection of turnout rail-tracks with the aid of the characteristics of reflection spectra of the FBG sensors. The FBG sensors are installed on the turnout rail-track with cracks, and the static and dynamic experiments in the laboratory are carried out to verify the method of damage detection by analyzing the structure of reflection spectra of the FBG sensors. The experimental results show that the proposed damage identification method based on the characteristics of FBG reflective spectra can effectively identify the cracks on the turnout rail-tracks.
In order to screen out which design parameters have significant effects on the vertical vibration model of the railway vehicle, so as to simplify the parameter optimization design of the vehicle model, a global sensitivity analysis method–extended Fourier amplitude sensitivity test (EFAST) is introduced and applied to the parameter sensitivity analysis of a typical railway vehicle vertical model. The analysis results show that, the variations of the secondary suspension parameters and the primary suspension damping parameters have a greater influence on the car body’s bounce motion than the primary suspension stiffness; car body’s pitch motion can be improved considerably by adjusting the length between bogie pivot centers; the interaction between design parameters in the model is small-scale. The research methods and conclusions proposed in this paper have a certain reference value and engineering significance in the vibration characteristics and parameter optimization design of railway vehicle model.
Extended minimal control synthesis with good ability of nonlinear control is used to suppress the panel vibration. In order to solve the problem of its controller saturation, a saturation compensator minimal control synthesis including adaptive compensation gain based on erf function is put forward. The stability of control system is verified by popov’ s criterion. Simulation and experimental results show that this method has better robustness compared with EMCS algorithm under multi-mode sine mixed broadband random disturbance. Especially the saturation caused by integrator and sign function mutation can be suppressed effectively by this method.
A general inflow turbulence synthetic method for large eddy simulation (LES) involved in parallel calculation was proposed. Firstly, fluctuating velocities of some main grid points on the inflow boundary were generated adopting POD based spectral representation method. Secondly, velocity timeseries of all grid points on the inflow panel were spatially interpolated, adopting the finite element shape functions. The synthesized velocities were then read in commercial code Fluent by user-defined-functions (UDF) program with special consideration of parallel calculation. In order to verify the efficiency of the present method, the flow around a single square section tall building with width to height aspect ratio of 1:6 was numerically simulated by adopting the present inflow turbulence generation method for LES. The simulated wind profiles, wind spectra, statistics, self-spectra, and coherence of wind pressure coefficients, were compared with both the experimental and numerical results of existing works in detail. The present inflow turbulence generation method for LES was verified as being applicable to a certain extent in both simulating turbulent wind field and predicting wind loads on buildings.
Finite element models of reinforced concrete slab impacted by the engine at different speeds were established. Using results of those simulations, material models and related parameters were calibrated. The mesh size effect was also analyzed. A large commercial aircraft at 200m/s impacting to steel concrete nuclear power plant structure is discussed utilizing nonlinear material model, the result of the crash was analyzed compared by rigid and elastic model, regularity of aircraft impact load with different structure stiffness was proposed,and the applicability of the common method --Riera method used in aircraft impact force calculation in the preliminary design of nuclear power plant was discussed.
Centrifugal compressor is key equipment for process industry such as petroleum refinery and chemical. As the capacity and compress ratio as well as the efficiency increase, instability of rotor-bearing system become the major obstacle for it operation in a long period without shutdown. Based on the mechanism and affect factors research, the paper investigate the control strategy for improving the stability of rotor bearing system. After introducing a case study about a centrifugal compressor with several instable faults, transient response investigation is conducted to find the effect of rotating speed and cross coupling stiffness of seal on the stability of rotor. Then force can be exerted on rotor by controller through displacement feed-back or velocity feed-back strategy. By displacement feed-back, the controller functions as spring with cross-coupling stiffness opposite to seal. While, it function as a damper when velocity feed-back strategy is adopted. Results of the research indicate that both of the strategy can depress the vibration caused by instable of the rotor. Furthermore, displacement feed-back strategy has high efficiency because of it consume lower power. Results of this paper can provide new insight and feasibility for control or upgrade the stability of compressor rotor-bearing system.
The structural difference between floating shock platform and real ship makes it difficult to establish the corresponding relations of shock environment between the two. In order to make the device impact ability getting from the floating shock platform at different working conditions can react to the impact resistance of ship equipment from different positions and different displacement, the vertical filtering effect of four different displacement ships subjecting to the underwater explosion shock wave is studied firstly. Then, the discriminant analysis of spectral parameters where floating shock platform connects to the device and the inside and outside bottom of the ship is analyzed using the Fisher method. The rationality of the method is validated finally. The results show that filtering effect is more obvious for the larger displacement hull. The shock environment of deck 1 with no superstructure is more serious than deck 2 and deck 3. The Discrimination method of multivariate statistical analysis can establish a correspondence for shock environment of equipment assessment between real ship and floating shock platform. The result has a certain guiding significance for the assessment of ship equipment in engineering applications.
A new method of detecting short track defects from in-service vehicles is developed using successive impact of the leading and rear wheels on short track defects. The initial moment and the end moment as a rotation of wheel, which are determined through integration of the operational velocity of train, are used to truncate and divide the time history of leading and rear axle vertical accelerations. The truncated acceleration signals between initial moment and the end moment were transformed by frequency sliced wavelet transform (FSWT) to get the time-frequency characteristic of wheel-rail impact. The time axis was replaced by displacement axis signifying wheel circumference in the time-frequency figures to achieve time-frequency feature locations as a rotation of wheel. The model of detecting short track defects was constructed by comparing the location of wavelet energy peak in continuous three circles. The effectiveness of way has been proved through much dynamics simulation data, with high real-time, high accuracy and a good engineering applicability.
Based on the time-dependent matrix fraction polynomial model of transfer functions, the time-frequency-domain parametric model of linear time-varying structures is presented in this article. Furthermore, based on the time-frequency-domain parametric model, through adapting the current popular least square complex frequency-domain method of modal parameter estimation for linear time-invariant structures into the time-frequency domain, a matrix fraction polynomial model-based least square estimation method of modal parameters for linear time-varying structures in the time-frequency domain is presented. In addition, to reduce the unacceptably computational consumption of the time-frequency least squares, this article presents a reduced normal equation-based solution for the least square problem. Finally, the two 3-DOF simulation examples with the varying mass illustrate the influence of the constraints on the unknown parameters to the estimation results, discuss the characteristics of the proposed method and validate the proposed method itself and its potential applications.
The study of seismic damage control was carried out for large-span space truss structures by placing viscous dampers at different locations on the roof. Time history analyses were performed with three-dimensional earthquake ground motion inputs for a gymnasium building. Taking the displacement, acceleration on the horizontal direction, member forces in the roof structure as the targets of the vibration control, the analytical results indicated that the seismic responses were effectively controlled via installing the dampers on the space truss structure. Uniformly placement of viscous dampers showed better performance when compared with that of centralized placement. The efficiency of the seismic response reduction was not linearly increasing with the damping coefficient enhancement, while there was an optimal value existing. The viscous dampers had obvious effects on vibration control of space truss structure under different earthquake intensity. The energy dissipation hysteresis curves of viscous dampers were full under different seismic waves input, and displayed the classic characteristic of velocity-dependent dampers. This study provided a valuable reference to applying the viscous dampers for seismic damage control in the long-span space structure.
Modal parameters of power transformer winding are closely related to the vibration feature, dynamic optimal design and winding vibration fault diagnosis. Consequently, it is of importance to accurately identify the modal parameter of power transformer winding. In the paper, the complex Morlet wavelet is applied to analyze the free vibration signal according to the results of the axial excitation experiment of some 10kV power transformer winding. The improved Crazy Climber algorithm is designed and presented to extract the wavelet ridge of time-frequency spectrogram. Then the first four natural frequencies and its corresponding damping ratio are obtained successfully. The calculated results are also compared with the identification results calculated by the frequency domain identification method of PolyMAX which is currently widely used to illustrate the effectiveness of the proposed method. It is shown that the proposed method can accurately identify the initial fourth order natural frequency, and the distribution of signal energy with time and frequency can be displayed more clearly. Furthermore, It is illustrated that the proposed method has strong anti-interference feature and could be applied effectively to identify the modal parameters of power transformer winding.
The piles of bridge built on soft clay foundation produce additional settlement due to cyclic loading of moving trains, which affects the operation safety of the train. Dynamic model of vehicle-bridge system and settlement model of pile foundation-soil system are established. Reaction force induced by the moving vehicle is got from dynamic model, firstly, which is taken as excavation of settlement model to study the train-induced cumulative settlement. Then, the additional track irregularity induced by settlement pier is overlaid to original track irregularity, and consider the influence of the vertical centrifugal force induced by settlement pier, which influences on running safety of train is studied by dynamic model. Calculation is performed with German ICE3 train running on the 32 m three-span simple-supported beam. The calculated results show that most cumulative settlement occurs in the range of 10 m below the pile bottom. Relative camber of the bridge induced by adjacent pile settlement is more dangerous to running safety of the train, because the train bears vertical centrifugal force in the direction opposite to the settlement direction, when it runs on the bridges with camber.
Based on analyzing the disadvantages of traditional adaptive stochastic resonance, for example, optimizing only one parameter which ignores the interaction between parameters and the convergence speed of genetic algorithm slowing down with the increasing population, a new adaptive stochastic resonance method is proposed. With a wide range of initial value and parameter setting, the proposed method adaptively realizes the optimal stochastic resonance system matching input signals, utilizing the ability of parallel processing and the characteristics that the algorithm has faster convergence speed with the increasing of the number of artificial fish. The analysis of the simulation data and the bearing fault data shows that the new adaptive stochastic resonance method effectively realizes the weak signal detection and early fault diagnosis.
A theoretical method of calculating multiple scattering of P and SV waves by arbitrarily arranged and circular cross-section multi-row elastic piles barrier is presented, which has covered the shortage that single scattering hypothesis is reasonable only under the cross-section size is negligible compared with the incident wave length, and this method is considered interference phenomenon as well. It is defined first order scattering of P and SV waves by an arbitrary elastic pile s, the second order scattering is regarded as the first scattering waves induced, thus all scatterers and successive orders follow this multiple scattering process. Every order of scattering satisfies stress and displacement continuity conditions at pile-soil interface and an iteration relationship of wave functions is obtained. Total scattering wave field is achieved by composing all orders scattering by scatterers. It is investigated the influences of scattering orders, separations of piles, distances of pile-rows and shear modulus ratio of pile and soil etc. on isolation effectiveness of pile barriers, which are some of referred basis in practical engineering vibration isolation design.
In order to improve vehicle ride comfort and decrease dynamic tire load on road, a 4-DOF pneumatic suspension model for a half vehicle model was established. Based on this model, a general genetic algorithm was used to solve the multi-objective optimization problem. Besides, an improved adaptive multi-objective genetic algorithm (MOGA) was proposed and applied to optimize the suspension parameters of heavy vehicle. Compared with the former, the effective value of the vehicle body's vertical acceleration and the front/rear-wheel dynamic load decreases by 10%, and the improvement of objective value decreases remarkably by 57.03%. It is shown that using this method proposed in this paper not only enhance the ride stability but also reduce dynamic tire load on ground, which further verify the effectiveness and feasibility of the improved adaptive MOGA.
Nonlinear normal modes of infinitely long functionally graded cylindrical thin shells with internal resonance in thermal environments were studied. The internal resonance condition was obtained. The nonlinear modulation equations with internal resonance were established using multiple scale method. The effects of gradient exponent, temperature and vibration energy on the frequency response of nonlinear normal modes were discussed. It is found that the nonlinear normal modes of system will undergo bifurcations with variation of detuning parameter, and the bifurcation value of detuning parameter depends on gradient exponent, temperature and vibration energy.
Gear pitting fault causes change in non-Gaussian components of vibration signals. This change can be quantitatively described by higher order spectral analysis. Measured vibration signals of the gearbox, and made study on the development process of gear pitting fault in depth. At first retained the sideband components and the random components of vibration signals by using Gabor filter. Secondly analyzed the bispectral results and researched the change of nonlinear non-Gaussian characteristics of vibration signals, then extracted the non-Gaussian intensity characteristic values. At last made the fault trend analysis and set fault threshold value by ‘3σ criterion’. The results show that the non-Gaussian intensity characteristic value is sensitive to gear pitting fault, and it can reveal the trend of fault development. It’s conducive to the failure alarm and life prediction of gears, and has practical significance to condition monitoring and fault diagnosis for gear transmission system.
The nonlinear vibration characters of the bistable piezoelectric power generation system were investigated. Adopting the harmonic balance method, the equation of amplitude-frequency was derived. The effects of different nonlinear coefficient, the impedance parameters and excitation were analyzed. With changing of frequency and force amplitude, the jump and multiple solutions phenomenon were observed. The minimum unstable area was obtained by varying the nonlinear coefficient and the impedance parameters. Then, the influence of excitation on the power was analyzed, with the nonlinear coefficient and impedance parameters increase, the output power first increase and then decrease, the maximum power was get by adjusting the magnetization and the load impedance. At last, the voltage frequency response curves and the power resistance response curves obtained through experiments verify the system’s nonlinear characters. The results provide theory evidence for engineering application.
Dynamic bifurcation buckling of an elastic straight rod under stress wave were studied. Numerical method, which unifies both the idea of twin-characteristic-parameters method and method of the preferred mode, was established. The method can be used to solve buckling of rod under time-varying load, with a unified buckling discriminate form for dynamic buckling under stress wave caused by both step load and time-varying load. Calculation results predicted by this method are in good agreement with the experimental results.
The sonic echo test is a regular nondestructive test, and the applications are mainly limited by piles with high length-to-diameter ratio, high soil shear modulus, small defect areas or with an inaccessible head condition. Wavelet transform (WT), however, has good time frequency characteristics, which is suitable for identifying the singularities of pile testing signals. Three-dimensional axial symmetric finite element models were used to simulate the testing, and wavelet transform was employed to deal with the simulated signal data. It was found that for piles with accessible head condition, wavelet transform can identify weak wave reflected from pile bottom or defects, then reduce the limitation of length-to-diameter ratio, soil shear modulus, defect areas; For pile with inaccessible head condition, pile bottom can be identified by plate-excitation if the plate is within certain effective sizes.
For the vibration of the flexible modular crane in a workshop tending to have large amplitudes and slow degradation during lifting of the workpiece, field vibration tests were carried out on the whole lifting system. Via the tests, the reinforcement schemes were proposed to reduce the vibration amplitude of the system by improving the dynamic stiffness. Finite element models were developed to simulate the whole lifting system and to investigate the dynamic response of the system under an inertial impact load caused by a sudden pause happening during the lifting of a workpiece, The effect on vibration reduction of the system was verified through simulation analysis, which can provide references for installation and solving vibration problems of such cranes.
Based on one masonry structures in Shanghai adjacent to the subway,setted up a detailed numerical model. The measured vibration acceleration was carried out to be the input excitation and model parameters was calibrated by the measured vibration response. Through numerical analysis , Study on variation regularity of vibration with the floor, the same floor in different floor structure, different room size and other factors had an effect on the vibration response distribution. The results show that: when the subway passed, the vertical vibration at larger mid-span was 1~3dB higher than the corner of walls. The vertical vibration arrangement of precasted slab room was greater than the castplate room. The vertical vibration at the ash between the precasted slabs, had a certain amplification effect;the room depth parameters had a small effect on the vibration, can be neglected;the relationship with the room depth and the vibration intensity related with the size of the width and depth of the room. the width of room had a big effect on the vertical vibration, the bigger of the width of the room, the higher of the vibration. vibration intensity has great relationship with floor corner and the surrounding constraint conditions.
An optimum installation method of viscous dampers in tall buildings is proposed based on relative fitness genetic algorithm, which considering different seismic waves and different optimal objectives. Compared with standard genetic algorithm (SGA), relative fitness genetic algorithm constructs fitness function based on the relative objective function value, which can fully embody the fitness difference in the population, and, promote effective evolution, obtain the global optimal solution as a result. Various coefficient combinations of the objective function were discussed. The objective function was normalized and different seismic waves were considered. The method is used to optimize damper installations in a 20 layers frame structure. The result demonstrated the efficiency and applicability of the method proposed in this paper.