The phenomenon of Doppler distortion in the acoustic signal of moving acoustic source acquired with a microphone leads to the difficulty for signal analysis. In this paper, a Doppler distortion removal method based on energy centrobaric method is proposed to solve this problem, and applied in the fault diagnosis of train bearings. Firstly, the instantaneous frequency (IF) estimation (IFE) based on energy centrobaric method is applied to attain the IF vector. According to the Morse acoustic theory, the data fitting is then carried out to achieve the fitting IFs with which the re-sampling sequence can be established as the re-sampling vector in time domain. Through the resample, the Doppler distortion effect could be removed. Finally, a simulation and an experiment with practical acoustic signals of train bearings with a defect on the outer race and the inner race had been carried out in this paper, and the results verified the effectiveness of this method.
Since the response of a spindle with sudden unbalance shows non-stationary characteristics, it cannot be extracted by signal processing methods using traditional Fourier transform. To tackle this problem, a new signal extracting method combining wavelet de-noising technique and the short time Fourier transform method is proposed in this paper. Firstly, the non-stationary signal of the spindle is filtered and reconstructed by the wavelet de-noising technique. Then, the amplitude of the unbalance response is acquired by the short time Fourier transform method. Finally, the feasibility and the accurately of the proposed method is verified by numerical simulation and practical experiment.
In order to predict the fatigue life of rubber isolator, the prediction model is proposed on the basis of experimental data by using the dumbbell-shaped rubber sample, thereby coming up with a corresponding prediction scheme. The fatigue tension experiment of the dumbbell-shaped rubber sample is devised, and then the experimental data is observed. Additionally, the prediction model in the form of power function is fitted by the least square method. Thereafter, three common evaluation parameters, i.e. Logarithmic principal strain, Cauchy principal stress and strain energy density, for fatigue life are computed by the finite element method. Lastly, a comparison is made between the prediction and experimental data. It is concluded that all three parameters can be effectively fitted by that prediction model in the same power function form when the fatigue failure criterion declined to the 25 percent of stiffness. Specifically, the prediction value of logarithmic principal strain closes to the observation; likewise, the prediction magnitude of principal strain density is approximately double of the observation; and the reliability coefficient of fatigue life for Cauchy principal stress is approaching to 5. In addition, the shape of all three fitting curves is similar.
The pipeline fatigue by fluid induced oscillation frequently takes place in the large scale centrifugal compressor. This paper investigates the main failure source of centrifugal compressor by fluid induced oscillation analysis. One of pipeline fatigue failure mechanism which could be original from acoustic resonance is investigated. Simulation for the pipeline cavity is analyzed in the test lab. With LMS acoustic finite element method software, the acoustic mode of pipeline is determined. The vibration level will increase typically when the blade passing frequency is the close to the acoustic mode frequency for the reason of acoustic resonance according to experiment analysis. It can give clear demonstration for the pipeline vibration with fluid induced oscillation. A practical centrifugal compressor pipeline vibration control is used to verify the effectiveness by acoustic resonance analysis according to the theory analysis. The research will contribute to development for reduction on centrifugal compressor pipeline damage based on high cycle fatigue.
The existing empirical formulae on gas explosion overpressure often ignore the influence of obstructions and barriers. Overpressures of series methane gas explosions occurred in a confined space were researched in logarithmic coordinates based on CFD method. The results indicated that the relation between the overpressure and the scaled distance is linear in logarithmic coordinates. Formulae on overpressure, combustion heat of the methane gas and distance from the centre of the combustible gas cloud were raised. This research can be used in calculations of explosion engineering, scientific research and others on methane gas explosion.
SRC frame-bent hybrid structure is a new type of main building system for thermal power plants, and reasonable arrangement of shear walls can make the structure have three anti-seismic lines. ABAQUS finite element software is used to analyze the elastic-plastic seismic response of the structure under 8 degree minor earthquake, 8 moderate earthquake, 8 major earthquake and 9 degree major earthquake, to acquire the base shear, lateral displacement, inter-story drift and damage evolutionary character of the structure under different earthquake intensities. The results show that: the shear wall is damaged firstly under strong earthquake, which can be the first anti-seismic line, and this can enhance the earthquake resistance of the structure effectively; as the earthquake intensity increase, the weak part of the structure is down from coal hopper floor to operation floor and to bottom two stories, and the lateral displacement curve is shifting from shear-moment-type toward shear-type; the deformation performance of the whole structure is well, which can make the structure meet the requirement of “no collapse under severe earthquake”. Finally, the reasonable arrangement and seismic tectonic measure of shear wall under different earthquake intensities and different site category are advised through calculation analysis, which could be referred by engineering design.
Based on the design proposal of twin balancer shafts system in some type of 4-cylinder in line internal combustion (IC) engine, a multiple body dynamical model of engine powerplant is constructed using a famous commercial software of AVL Excite PU to estimate noise and vibration of powerplant. The influence of mating force between crankshaft gear and balancer shaft gear on rotate speed and impact force acting on journal bearing is analyzed, and then the comparison of vibration response of engine block between the case of with balancer shaft and the case of without it is carried out. Finally, Based on the translate path analysis (TPA), the effect of balancer shafts on 2nd order vibration of engine powerplant mount and 2nd order vehicle interior noise is investigated. The simulation results shown the fact that it is helpful to improve the NVH ability of powerplant and to reduce interior sound pressure level by installing twin balancer shafts system into IC engine.
For diesel vibration isolation nonlinear system, curve fitting method based on Hammerstein model is proposed, which can discuss how nonlinearity affects features of vibration system and can obtain linear structural dynamical features by implementing mode test. Generalized Frequency Response Functions (GFRFs) is established based on Hammerstein model, and (the 1st generalized) FRF of the system is extracted when considering fundamental frequency harmonic GFRFs’ impact on fundamental frequency response. (The 1st generalized) FRF is estimated by employing curve fitting method in frequency-domain, and linear structural dynamical feature is identified. The experimental result of mode parameters identification showed that the proposed method was valid and feasible to estimate linear mode parameters of diesel vibration isolation nonlinear system. When carrying out curve fitting based on Hammerstein model, one can eliminate nonlinearity effects on features of vibration system, and can obtain linear structural dynamical feature of nonlinear system.
Micro-Electro Mechanical Systems (MEMS) based inertial sensors are low-cost but their performances are also degraded because of the large uncertainties in their output and the effects caused by vibrations. To estimate the attitude using the MEMS inertial sensors, a pretreatment method to mitigate the noise of the inertial sensors is proposed based on the singular spectrum analysis (SSA). SSA belongs to the general category of PCA methods. With the so-called lagged covariance matrix of this approach, the trend and periodic components are separated by SSA. As a result, the true attitude signal is contained in the trend component, while the vibrations are contained in the periodic components. Then, the trend component is extracted by the use of the number of zero-crossing. Finally, the true attitude measurements pretreated by the SSA are utilized as the measurement input of the fusion filter for accurate attitude estimation. The car tests verified the feasibility and the capacity of the method to improve the accuracy of the attitude estimation effectively.
The precision of fault feature extraction and damage locating by AE signal is determined by its propagation characteristics in different structures. In this paper, a two-dimensional explicit finite difference method is extended in AE signal model building of shaft, stepped shaft and stepped shaft with too withdraw groove; the constitutive behavior of the shafts under impact load is analyzed; the experiments of three different structural shafts are conducted. The results of the simulations and the experiments reveal that the propagation characteristics-reflection, transmission, attenuation-of AE signal in shaft, stepped shaft and stepped shaft with too withdraw groove are simulated correctly by using the model of AE signal built through the explicit finite difference method.
Dynamic responses and bearing capacity of members under blast loadings are directly affected by different boundary restraints. In this paper, both elastic and plastic analytical methods for a beam with general flexible supports and restraints under blast loadings are proposed, and the effects of vertically elastic and damping support, horizontal supporting stiffness, rotational constraint, loading characteristics and the dynamically intensifying coefficient of yielding bending moment on responses are analyzed. The results show that the inertia forces owing to vertically elastic support and damping support can decrease the dynamic coefficient of deflection of the beam markedly in elastic-plastic stages. Horizontal supports, which exert transverse pressure on section during the deformation process, and rotational restraints, which confine the rotation of rigid body directly, both have great effects on dynamic responses mainly in plastic range in terms of reducing the dynamic coefficient of displacement and increasing the resistance of the beam accordingly. On the condition with the same constraints and peak load, the dynamic coefficient of displacement of a beam under rectangular pulse loads is always higher than the one under triangular pulse loads, which implies longer duration of pulse loads is negative for bearing capacity. In addition, potential anti-explosion resistance of beams can be improved by taking intensifying coefficient of yielding bending moment into account.
In order to study the nonlinear interaction between CWR(continuously welded rail) and continuous beam carrying high-speed railway under traveling wave effect, the beam element with rigid elements was used to simulate the beam, the nonlinear bar element was used to simulate the longitudinal interaction between beam and tracks. The track-structure interaction model was established for the first time with considering the longitudinal and vertical seismic traveling wave effect. Taking a (60 +100 +60) m continuous beam on the Shanghai-Kunming line as a case, it was analyzed that the track made an impact on the seismic response of the beam and pier, the force characteristics of the track and pier was studied under the longitudinal and vertical traveling wave effect. Studies have shown that the track can improve the system natural frequency and reduce the seismic response of the continuous beam; the maximum longitudinal stress on the track under the traveling wave effect is up to 1.2 times under the uniform excitation; calculating the track stress, the impact of the vertical traveling wave effect on the track should be also considered.
In basis of the classical plate theory, a laminated damping plate model is built. Regarding the plate inlaid in an infinite rigid baffle, the acoustical power and its sensitivity of the structure are obtained using the Rayleigh integral. The topology optimization model for placement of constraint damping material is established with objective function defined as the minimum of acoustical power under the exciting force of the first mode frequency or frequency band, and the design constraint defined as the volume fraction of damping material. According to the evolutionary structural optimization (ESO) method, the topology optimization of damping plate is conducted and the optimal placement of damping material under the volume requirement is found. Compared with the acoustic radiation of plates without constraint damping material and with full constraint damping material, it is concluded that the optimization method adopted in this paper has an effective control on the acoustic radiation of structure in condition of less damping material usage, and provides a crucial theory reference and technical means for the low noise design of structure.
The identification method of viscoelastic dynamic parameters based on the reflection coefficient measurement of viscoelastic layer in a acoustic-pipe has been developed. Two different types of layers, where one is solid and the other contains cylindrical-hole, will be utilized in the parameter identification. The complex longitudinal speed of viscoelastic material can be obtained through the reflection coefficient measurement of solid sample. Besides of the coefficient measurement of cylindrical-hole sample, the solving of the characteristic equation of viscoelastic-tube should be included in the identification of the complex transverse of viscoelastic material. Then, the complex Young’s modulus and the complex Poisson’s ratio can be calculated easily. Finally, a rubber sample has been tested in the acoustic-pipe, and the identification results of viscoelastic dynamic parameters have been analyzed and discussed.
The specimens with supplemental structural damping at both sides are frequently used in the measurement of viscoelastic material’s mechanics parameters through flexural resonating cantilever beam method(FRCBM). Appropriate design of specimens decides the accuracy of experimental results. Though sensitivity analysis, influence coefficient was proposed and used in the analysis of experimental results which were affected by the measurement accuracy of thickness ratio, resonance frequency ratio, density ratio and loss factor of the specimen, and some significant technical specifications were proposed to help design the specimens. Finally, the applicability of the specimens damped both sides used in the measurement of mechanics parameters through FRCBM was analyzed.
Ducted fan noise attenuation method using Herschel–Quincke Tube (HQ Tube) placed on both sides of ducted fan is studied by theoretical and experimental method. The results show that the insertion loss of the system is zero when the effective length of the bypass duct is odd times of half wave length. However, the sound attenuation performance is good when it’s even times. Different from usual HQ Tube, the insertion loss of the system shown in this paper is not zero when the frequency is approaching zero because dipole noise is the main part of the ducted fan noise. The insertion loss of the system when the frequency is approaching zero depends on the length ratio and area ratio between bypass duct and main duct. Comparison to the theoretical method, simulation method and experimental method show that the results are agree with each other at low frequency, but have small differences at middle and high frequency range , the reason is plane wave is not the only wave in the duct .
Aiming at the mathematical expressions of amplitude probability density functions of non-Gaussian vibrations, a Gaussian mixture model based probability density function (PDF) is proposed that is available for non-Gaussian vibra-tion signals. Firstly, the estimators of the higher-order moments of the non-Gaussian vibration process is obtained from the sample time history. Secondly, based on the quantitative relations of the even order moments of a given Gaussian process, along with the Gaussian mixture model, an equations set for evaluating the parameters in Gaussian mixture model is obtained. Lastly, based on the evaluated weighting factors and variances of the Gaussian elements, the mathe-matical model of non-Gaussian probability density function is obtained. Finally, the examples of simulated signals and measured signals have verified the validity of the presented method.
Based on the theories and methods of underground anti-explosion, a simplified calculation method for the dynamic response of segment lining subjected to blast loading was proposed. The lining was composed of a number of rigid arch segments, ignoring the deformation of segments. The dynamic interaction between the segments and the bolts, and the interaction between tunnel lining segment and soil-structure can be properly simulated with the method. As an example, the calculation of the shield section of Nanjing tunnel subjected to blast loading was discussed. The time-history curves of displacement and speed of some key points of section lining were obtained. Furthermore, the influences of the parameters of the segments on dynamic response of tunnel lining were investigated. The result indicates that the simplified method of blasting response analysis can reflect the response of structure subjected to blast loading accurately. It is a simple, convenient and practical calculation method. The results will be a reference for antiknock design of tunnel lining.
The vibration model of Mechanical Rapping Ash Removal Devices was built based on the one-dimensional wave equation. According to special boundary conditions of the stricken rod, accurate analytical expressions of displacement, velocity, stress distribution as well as the impact duration time, when the stricken rod was impacted by transitive rod, were deduced. Furthermore, the obtained analytical expressions was verified by the simulated results by finite element software ansys/ls-dyna under actual operation conditions of rapping devices, and a good agreement was found.
Based on the improvement of threshold denoising method of morphological component analysis (MCA), a new method for the fault diagnosis of rolling bearings based on MCA is proposed. According to the morphological difference of each component, different sparse dictionaries are built by MCA to separate each component from the signal. When a rolling bearing is locally damaged, its vibration signal is often composed of harmonic component with system characteristics of the rolling bearing,impulse component with fault information and random noise. The harmonic component represents the smooth part of the vibration signal, while the impulse component represents the detail part of the vibration signal, therefore, the two kinds of components can be separated according to the morphological difference. The harmonic component, impulse component and random noise component are separated from the vibration signal of a fault rolling bearing by using the MCA, and the fault diagnosis of rolling bearing is carried out according to the time interval of impulses in the impulse component. The simulation and application examples have proved that the proposed method is effective in extracting the fault impulse component from the vibration signal of a local damaged rolling bearing.
With the prosperous development of the railway and urban rail transit engineering in recent years in China, the integrated station-bridge structures have been the predominant structure types for the key stations. Owing to the lack of the special code for these structures, the seismic design for the integrated station-bridge structure must be catering to the existing Code for Seismic Design of Buildings and Code for Seismic Design of Railway Engineering simultaneously. But the design philosophy of the two codes above mentioned is essentially different. In this paper, taking the main structure of Beijing South railway station as an example, based on the universe software of Midas/Gen and Sap2000, the global structure model considering the multiple modes effect resulted from upper truss and the corresponding simplified model were constructed, respectively. The rationality of the simplified model was verified by comparing the results from the analysis of the natural vibration characteristics, spectral analysis and the dynamics analysis of time history. The plastic yielding mechanism and the seismic performance were researched in detail by the Pushover analysis (considering the multiple patterns of the lateral loading) and the incremental dynamic analysis (IDA) respectively. It was shown that the proposed simplified model could essentially reflect the behavior of the main structure under the designated earthquake. The Pushover analysis method based on the improved lateral loading pattern considering the multiple modes combination could be applied to evaluate the seismic performance of the integrated station-bridge structures.
Referring to excessive longitudinal impulse of heavy haul trains in practice when trains make emergency brake at a complex longitudinal section, by using of air braking system and train longitudinal joint simulation system, studied on heavy haul train longitudinal impulse level through the ramp. And the influence of the braking start position、the ramp slope size and train braking velocity on the train longitudinal impulse. The results show: The impulse level is same when heavy haul trains make emergency brake completely at the same ramp uphill or downhill compared with it is at a flat track. It will generate coupler force significantly when heavy haul trains make emergency brake at a complex longitudinal section (such as flat add uphill or downhill add flat ) , For ten thousand tons trains the most dangerous braking position is the fortieth freight car of the train on the ramp. The brake synchronism and the slope of the ramp are the two main factors that influence the longitudinal impulse occurs on grade change point .The ramp slope is smaller, the smaller the train longitudinal impulse level.Increase brake synchronism will reduce longitudinal impulse significantly.
To investigate the vibration effect on setting wind-resistant bearing at isolation layer when the structure locates at large wind pressure area. Taking an actual base-isolated structure as background, goals were setted which structural horizontal damping coefficient is less than 0.53 and 0.40. setting or no-setting wind resistant bearing isolated models were established, though dynamic time-history analysis it is compared about structural seismic response. The results show that seismic response of the two isolation models is significantly decreased compared with seismic structure. For no setting wind resistant bearing model, LRB number is increased to meet the wind design requirements, but seismic effect is reduced. While for setting wind resistant bearing model, LRB number is reduced, which benefits seismic effect. Under normal operation and small earthquake, wind resistant bearing functions and isolation layer does not yield, when the structure suffers fortification earthquake , the wind resistant bearing shall yield and destroy and be out of work, which dose not affect the upper structure seismic effect.
Selection of ground motion records forms the basis for incremental dynamic analysis ( IDA ) . In order to study the influence of spectral characteristics and duration of ground motions on the results from IDA, four conventional methods to calculate the characteristic period of ground motions are introduced, by which the record groups of ground motion are selected, compared with the response spectrum . IDA is carried out in accordance with the selected inputs of ground motions, then the IDA curves and fragility curves are discussed. On this basis, the influnece of earthquake duration on IDA is analysed according to two duration principles. It is shown from the results that the Spectral characteristics of ground motions influences evidently not only the values but also the degree of dispersion of IDA, and sufficient duration time is good for the stability results of IDA.
Multi-ribbed slab structure (MRSS) is a new type of composite structure with specific characteristics which is composed of prefabricated multi-ribbed composite wall slab, cast-in-place floor slab and cast-in-suit concealed outer frame. In this paper, according to the basic components and construct characteristic of MRSS, the ultra low yield strength steel panels are used in the multi-ribbed composite wall slab, seismic response control of the multi-ribbed slab structures using the ultra low yield strength steel was explored. The nonlinear dynamic time-history analysis of the MRSS seismic control systems under horizontal earthquakes waves were carried out. The earthquake responses and energy dissipation mechanisms of the control structures were investigated. The effects of vibration reduction of the ultra low yield strength steel panel were discussed. The computing results show that the ultra low yield strength steel panel has obvious seismic mitigation effects, which a simple and effective seismic energy dissipation measures is provided for the multi-ribbed slab structure.
Lifting wavelet packet decomposing algorithm based on optimal basis was applied to de-noising and analysis of energy distribution in the paper, in order to ensure accuracy and efficiency of engineering blasting network monitoring and forecasting system. Based on lifting wavelet packet multi-scale transform, improved search algorithm for optimal basis was used which can meet online processing of complicated signals. In application examples, noise was filtered by lifting wavelet packet decomposing algorithm, and energy distribution of every frequency band was acquired precisely. Application of the algorithm to analysis of blasting vibration signal can provide research basis and technique supports for studying and controlling of blasting vibration hazards, and it has a good application prospect.
To achieve comprehensive assessment of motorcycle frame fatigue reliability indoor under the impact of moving load in real road, the acquisition method of road load spectrum based on the finite element analysis of the frame was firstly established, and the collection and analysis of the road load spectrum was then completed.A multi-axial,multi-channel road simulation test platform for motorcycle frame was designed and built based on the practical driving load analysis of motorcycle frame,combined with the remote parameter control (RPC) technology , American MTS hydraulic servo actuator and the control system . And the force - displacement mixed control simulation iterative method of road load spectrum was put forward.Combined with the acquired road load spectrum of the motorcycle frame and the mixed loading control mode—force loading control and inertial loading control , road load spectrum of motorcycle frame was efficiently and accurately simulated indoor and a multi axial multi channel road simulation test method of motorcycle frame was established ,providing an effective indoor method for the fatigue reliability test for the motorcycle frame.
The problem of dynamic responses of partially sealed lining with a deep buried circular tunnel in the saturated transversely isotropic fractional derivative viscoelastic soil is studied in the frequency domain. Regarding the soil skeleton as transversely isotropic viscoelastic medium with fractional derivative constitutive behavior because of the soils have the anisotropic characteristics in the long-term deposition, and based on the theory of saturated porous medium and elastic, the analytical expressions of the displacement, stress and pore water pressure of saturated transversely isotropic viscoelastic soil and lining subjected to the harmonic load are respectively derived by the stress coordination on the inner boundary of lining and the stress and displacement continuous at the interface between soil and lining. The parameter for saturated viscoelastic soil and lining under the three conditions of saturated classical elastic soil, saturated fractional derivative viscoelastic soil and saturated classical viscoelastic soil is investigated. It is reveal that the influences of the elastic modulus of transversely isotropic surface and the lining thickness on the system responses are relation to the order of fractional derivative and viscosity of the soil skeleton; the system has obvious resonance phenomena when the permeability coefficient is small. In addition, the dynamic responses of the partially lining have obvious difference in the three conditions.
For the research of characteristics about penetrating runway obliquely by projectile of anti-runway series warhead, which was at the situation of holding in advance by warhead of former stage, the penetrative process of the tandem warhead was simulated by the finite element code LS-DYNA3D, which considered the different influences about speed, attack angle and medium interface. The conclusion also got the validation of live ammunition experiments. The results of simulation have reference value for design of anti-runway projectile.
A theoretical solving approach of the multiple pounding forces taken place in bridge under near-fault vertical earthquakes is presented by the consideration of the rubber bearing. The bridge is simplified by a continuous model of beam-spring-rod, and solved by the expansion of transient wave functions in a series of eigenfunctions and the transient internal force method by the use of contact interfacial force of combined body. The numerical results show that the presented approach can solve reasonably the multiple pounding forces between deck and rubber bearing. The calculations of pounding forces and number of pounding in different vertical earthquake spectra, vertical earthquake periods, vertical earthquake amplitudes and span lengths of bridge, illustrates that the vertical pounding phenomenon can take place under near-fault vertical earthquakes, and damages the bridge before the horizontal earthquakes reaches. The present investigation exposes possibly the two conditions that may result in vertical poundings. One is when vertical earthquake periods is close to natural period of bridge. The other one is when the amplitude of vertical earthquake exceeds some threshold. In addition, the vertical pounding force varies in highly non-linearity with vertical earthquake periods, vertical earthquake amplitudes and span lengths of bridge.
High-frequency vibrations excited by the high-speed rotor of the cantilever Single Gimbal Control Moment Gyroscope (SGCMG) have many negative effects on the attitude stability and other performances of some spacecrafts,for instance, an agile small satellite. And the severe jitter includes some complex frequency components and reveals complicated dynamic characteristics, rendering it difficult to suppress thoroughly and to perceive exactly. Firstly, under the linear assumption, the exciting sources for high-speed rotor vibration were analyzed, who derive from the static unbalance and dynamic unbalance and the geometrical errors of preloading bearing rolling elements. Secondly, the vibration dynamics models of the cantilever high-speed rotor in the SGCMG were established based on its structure using the analytic mechanics theory- a set of coupled second order ordinary differential equations. Finally, the facts that the analysis is reasonable and these models are feasible were verified by comparing the results of the numerical simulation based on the models and the vibration test for a high-speed rotor of a cantilever SGCMG.