A design of an equal stress ultrasonic horn for high amplitude is presented. Based on the longitudinal vibration theory, ANSYS modal and harmonic response analysis, an equal stress horn of required frequency is obtained. The dynamic characteristics of four kinds of typical horns are also simulated and compared to verify the accuracy of the design. The designed horn is then manufactured and tested, the results show that a peak-to-peak vibration amplitude reached 148 um at the driving voltage of 198Vp-p.
The tower-line finite element model of the transmission test line is set up by means of ABAQUS software. Galloping of the six bundle conductors with D-shaped ice model in the line is numerically simulated, and the dynamic response of displacements, galloping orbit, galloping modes and frequencies are obtained. The numerical simulation results are consistent with those measured on the transmission test line, which verifies the numerical model and simulation method. The established finite element model and the numerical method can be employed to investigate galloping behavior and assessment of anti-galloping techniques.
The vortex-induced vibration is a kind of common phenomenon of fluid-structure interaction. When the vibration of structure is substantial, it can be used to extract energy from ocean or river currents. A numerical method using fully coupling between fluid and structure was presented for simulating the vortex-induced vibration of spring mounted cylinder in uniform currents. In order to analysis the influence of mass ratio m*, damping ratio ζ, mass-damping ratio m*ζ and natural frequency fn on the energy conversion efficiency η, four groups of cases were computed. The results reveals that η is influenced by the above parameters and there is an optimum value of m*ζ where the η presents a maximum. The conclusion is considered as a reference to the design of vibration system which based on the present concept.
The formation mechanism of process damping and the influence of process damping on milling system stability is analyzed. The process damping results from plough effect, which was caused by interference between flank face and machined surface. The paper calculate the indentation area and resistance caused by interference and build nonlinear model which consider process damping. The simulation results indicate that stability limitation at low speed can be improved significantly relative to linear model, the phenomenon also be verified by milling experiment.
After taking the characteristic of embedded system into consideration, the traditional method based on the convolution for digital frequency weighting was analyzed. As the requirement of high precision and long filter coefficient, the calculation will increase dramatically. A novel method based on overlapping and adding DFT result was introduced. Analyzing and comparing the total computation of each kind of method. Simulation with MATLAB simulink toolbox and experiment on embedded system were implemented later. The result shows that both kinds of methods get the same result. The one based on overlapping and adding DFT result has better performance while the filter coefficient become longer and the selection principle was acquired for the situation the length of filter coefficient is known and both the length of filter coefficient and the length of frame are decided.
From acoustic point of view, the characteristics of the submarine are numerous vibration and noise sources, the serious coupling among them and the complex transmission path. Hierarchy diagnosis resolves the problem of the vibration and noise source separation and quantification by constructing hierarchical structure, and the dominance relationship is formed from top to bottom. By means of scale, the vibration and noise source’s contribution is obtained by pairwise comparison. According to the decibel addition principle, the AHP comparison scale is adjusted for physical significance, and the result of the hierarchy diagnosis is the measure with actual physical significance. The hierarchy diagnosis procedure of the submarine is divided into two links: they are from the equipment to the shell and the shell to the underwater acoustic field. The results are fused by weighted averages method and D-S evidence theory. The feasibility of this method is validated by simulation and cabin test.
A fast algorithm for computing one dimensional manifold of a hyperbolic fixed point of a map is presented. The new algorithm uses a variant of the standard approach of iterating a fundamental domain; we prove that parallel computing could be realized by subdividing the local manifold, at the same time, the implementation details are discussed. Curvature constraint and distance control are used to ensue the accuracy and efficiency of the algorithm.
As the number of elevated bridge of high-speed railway grows, the possibility of the bad effect on the running safety of trains caused by the collision between motors and bridge piers also increases. A model test based on the equipment of vehicle-track-bridge coupling system is carried to analyze the variation of bridge and vehicle’s running safety under lateral collision force. The collision force's time history, dynamic strain on the bottom of pier, dynamic displacement and acceleration time history on the top of pier, the dynamic displacement at 1/4, 1/2 and 3/4 span of the bridge beam, and the tri-direction acceleration time histories of the vehicle are obtained. The vibration characteristics such as pier natural frequencies are also calculated. The results show that the lateral collision greatly increases the dynamic responses of the bridge, which may dramatically affect the running safety of vehicles. According to the collision time history, the methods of calculating equivalent static forces are discussed and verified in this field, which may provide a reference for engineering design.
Piezoelectric stack actuators have great potential in structural vibration control and other applications, and it is critical to build a mathematic model that can depict important physical behavior of the actuators. An impedance-based model that can describe the electromechanical coupling characteristics of the actuators is developed in this paper. Short circuit mechanical impedance matrix, electric impedance and transduction coefficients are derived based on a rod model and the constitutive relationships of piezoelectric materials. Transduction equations in matrix form that represent the electric-mechanical interaction of the actuators are introduced by taking advantage of these three parameters. Numerical simulations are also conducted to verify the theoretical derivation. Both theoretical analysis and simulation results show that the impedances of external structures attached to the actuators have a significant influence on these parameters. The resonance frequency for the electric impedance and transduction coefficients is the highest when the two external impedances are exactly equal, and decreases for other cases. The influences of external impedances need to be considered to get a satisfactory control.
A numerical model has been developed which allows the vibration of rotational plate with particle dampers to be evaluated numerically. The model is based on the combination FEM with DEM. The simulation results indicate that the coupling simulation algorithm is remarkably effective over a wide frequency range. The results also indicate the damping performance of the rotating plate with particle damper has a strong relation with its rotating velocity.A higher rotating velocity results in the increase of the r.m.s. of the plate vibration response at the first and the second mode, that is, the decrease of the damping of the rotating plate. And at the third mode, the displacement of the rotating plate first goes down to its minimum level as the rotating velocity reaches then goes up gradually until the rotating velocity of about 1000 rpm, afterward keeps at a stable level.
According to the structure characteristics of herringbone gear transmission, the dynamic response of the gear box is researched in consideration of the excitation (such as: time-varying mesh stiffness, gear errors and inertial force), herringbone gears axial positioning and sliding bearing. The model is solved by using the Newmark integrals method, then the time history of system dynamic force is obtained. Taking bearing force as excitations the gearbox noise radiation characteristics are researched. The distribution of sound pressure and frequency spectrum for noise of the field points are obtained, then the spatial distribution and frequency components of the noise are analyzed. The effects of the connection stiffness of left and right sides of herringbone gears and axial support stiffness on the noise radiation characteristics are discussed. The study provides useful theoretical guideline to the design of the gear box.
Based on MB fractal model and its modified model, on the foundation of elastic and plastic regime, and considering the elastoplastic regime, an elastoplastic fractal model of normal contact stiffness of rough surfaces, which is continuous for critical contact parameters and considers the influence of domain extension factor, was proposed. Numerical simulation results show elastoplastic regime has an obvious effect on normal contact stiffness and dimensionless normal contact stiffness of elastoplastic fractal model is much more than that of only considering elastic and plastic regime; dimensionless normal contact stiffness increases with the increment of dimensionless normal load but the varying tendency is convex nonlinear(when fractal dimension D=1.1~1.4) or near linear(when fractal dimension D=1.4~1.9), increases(when fractal dimension D=1.1~1.5) or decreases(when fractal dimension D=1.5~1.9) with the increment of fractal dimension, decreases with the increment of fractal roughness, and increases with the increment of plastic index.
The axially moving beam is a simplified model for many aircraft structures. The elasticity is patently obvious with slenderness increased and quality reduced, and the velocity has significant effect on vibration characteristics at the same time. The dynamic equation of transverse vibration of axially moving beam, subjected to a transverse excitation is derived from Hamilton’s principle. At first, dimensionless method and complex modal analysis method are applied to simplify the equation as there is an axial force or not respectively, also the frequency equation and modal function can be determined, which can be calculated using numerical method. Then, the decoupling method is used to simplify the control equation into a set of differential equations, the displacement response of transverse vibration is yielded after solving that equations. Finally, random response’s correlation function is calculated by using the method of mathematical statistics, and the random response spectrum is given via Fourier transform. The numerical example illustrates that velocity could affect vibration characteristics and random response significantly.
The dynamic failure characteristics of sandstone with different axial static pressures (0 ~ 72MPa) and impact energy,are investigated by the improved split Hopkinson pressure bar (SHPB) with axial static pressure and confining pressure. Combining the fractal theory and energy principle, the distribution rule of rupture fragmentation of sandstone specimens and its correlation with strain energy transformation are investigated. The results showed that the dynamic compression strength of sandstone increases with increase in impact energy when the axial static pressure is a constant; when the critical failure of sandstone, the impact strength first increases and then decreases as the axial static pressure increases; rock takes compression-shearing damage as the principal failure mode. The nonlinear relation of fractal dimension and impact energy, it is demonstrated that the elastic potential energy release leads to increase in the degree of crushing of samples when the energy of impact load is low under coupled static and dynamic loads with high stress.
Aimed at the complexity for the corresponding relation between fault characteristics and fault categories of rotating machinery, a twelve channel fault information set for a double span rotor system is constructed, a new method about the feature extraction based on weighted KPCA is proposed. At first, the time domain, frequency domain, time and frequency domain for a single channel vibration signal is extracted, and the original fault feature set is obtained from the twelve channel of the monitoring system. Secondly, a sensitive feature subset of fault is screened from the original feature set by using multiple criterion of feature selection method. And then, a fusion feature vector is obtained by fusing the sensitive feature subset. Finally, the main components of fusion feature are extracted by using the weighted kernel principal component analysis. Experiment result shows that this method can search a sensitive feature subset, the kernel main components can show the gap between the different fault categories effectively.
Effective vibration control technology for stay cables is extremely critical to safe operations of cable-stayed bridges. This paper mainly foucs on a new vibration control technology based on an electromagnetic damper for stay cables. First, both mechanical and electrical performance of a rotary electromagnetic damper was tested. On this basis, a test platform consisting of an electromagnetic damper and a model cable was established in the laboratory to evaluate control performance of the cable, where different damper locations and transmission ratios between linear and rotation motion were investigated. The test results shows that the proposed vibration control system can greatly improve modal damping ratios in each of first five modes of the cable. The control performance of the cable is propotional to the installation height of the damper and transmission ratios. It it further demonstated that excellent control performance of the electromagnetic damper is mainly due to two aspects: one is that it can work as a linear viscous damper, and the other is it can realize negative stiffness control.
Using multiple tuned mass dampers (MTMD) has already been proved as an effective way to reduce the pedestrian-induced excessive floor vibrations. However, the optimization of MTMD parameters based on FEM software is very time-consuming, if not impossible, due to the temporal-spacial variation feature of pedestrian’s walking loads. To tackle this problem, this paper proposes a hybrid calculation approach in which the dynamic properties of the floor are first determined by FEM software and the floor’s responses are then calculated using the modal decomposition theory with consideration of the walking loads. Based on this efficient calculation approach, the optimal frequencies and damping ratios of the MTMD can be determined through the genetic algorithm optimization method. Taking an existing long span concrete floor as an example, the optimal MTMD parameters, i.e. number of TMD, locations, frequencies and damping ratios, have been studied. The MTMD off-tuning effect due to variation of floor’s natural frequencies and damping ratios has also been investigated. The results show that the suggested approach greatly improves the computation efficiency and the resulting MTMD parameters are reliable and robust to variation of structural properties.
Based on the principle of energy conservation in the cylinder test and the empirical formula of cylinder expansion velocity at feature distances, a simple method for calculating the parameters of JWL EOS of detonation products of CHNO explosives was presented. If density and detonation velocity of the explosive were given, the parameters of JWL EOS of detonation products could be obtained by this method. It does not require cylinder test and is more economical, convenient and accurate. Using this method, four kinds of common explosive have been studied. By comparing to the P-V curve of JWL EOS given by cylinder test and numerical simulation, we showed that this method has a high precision and meets the need of explosion mechanics application.
The damping of composite cylindrical shells using the wave propagation approach was theoretically studied. The vibration equations of the cylindrical shells were derived based on the Love’s 1st order shell theory. The wave propagation method was applied to solve the equations in order to establish the damping model of cylindrical shells. The theoretical results obtained by the model met well with the solutions obtained by the finite element analysis. In this paper the damping of composite cylindrical shells with and laminations was studied on three boundary conditions: SS-SS (simply supported- simply supported), C-F (champed- free) and C-C (champed-champed), furthermore the influence of orientations and geometry was also discussed.
Based on the theory of incremental dynamic mechanics, longitudinal dynamic response of initially homogeneous isotropic saturated soil under the influence of borehole pressure is investigated theoretically. Firstly,the radial inhomogeneity of soil medium is deduced. Then,longitudinal dynamic governing equation of each annular is deduced based on the plain strain assumption. The analytical solution is also arrived. Finally,the influence of inhomogeneous initial stress field caused by borehole pressure on the longitudinal impedance of soil is analyzed,and available solution is presented for a comparison of present solution.
The mechanical model of shock waves propagation is investigated when linear charge explosive in blasting chamber. The model is thought about many influence factors such as the length of linear charge, detonation velocity and air pressure that affect the flow field of blasting.
The reflection of blast pressure on the inner face of chamber is computed based on this mechanical and computation value is in good with experimental value.
The reliability of ship structure subjected to inner explosion is important both in theory and in practice. In this paper, the destroy probability of general structure ships and box girder structure ships are calculated, with random variables taken into consideration. Then the effect of box girder structure in improving structural reliability is analyzed based on comparison. The Monte-Carlo Method combined with the Maximum Entropy Method is used in this paper. Simulations of structural responses of the ship subjected to cabin inner explosion are done by MSC-Dytran, taking the fluid-structure-interaction into consideration. The results indicate that the box girder structure can significantly reduce the deformation of the 01 deck under inner explosion longitudinally and transversally.
Base isolation structures with general rubber bear will impact with adjacent buildings easily for the excessive horizontal displacement under strong earthquake.In this paper,using nonlinearity pounding element,the pounding model of adjacent isolated structures with prestressed rubber bears is built, and the pounding dynamic equation is deduced.On this basis,the influence of prestressed rubber bear to the pounding of adjacent structures is studied, and the influencing factor of pounding is analysed.The results show that:Compared to general RB,PRB can reduce effectively the horizontal displacement of isolated structures, and minish the pounding responses of adjacent structures.
Air flow in wind tunnel usually results in large vibration of model support system, which can influence the accuracy and reliability of wind tunnel test. Therefore, it is crucial to study and accomplish the vibration control technique of model support system. Based on electromechanical coupling characteristics of piezoelectric material and active vibration control principle the piezoelectric package embedded model support system was designed. Meanwhile, according to rigid-flexible coupling dynamics theory the structure vibration simulation model of model support system was built. Furthermore, associated with classic PID control arithmetics the integrated structural and control simulation model of model support system was built for simulating active vibration control. Finally, considered nonlinear contact factor the finite element model of piezoelectric package embedded model support system was built for inspecting contact strength and optimizing embedding style. These simulation results show that the piezoelectric package embedded model support system has fine vibration control capability and structural safety, which can be applied to actual engineering efficiently.
Numerical simulation is an effective way to analyze blast response of underground protective arches. The efficiency of the numerical method is weakened when a three-dimensional (3D) structure is simplified as a two-dimensional (2D) structure. A comparative study of blast response of buried arches with 2D and 3D models was carried out. In 2D model, restraints to the arch are strengthened by the model and responses, including strains, stresses and vibration velocities, should be under-estimated. It is found that the computer results for the free field and structure responses by 2D and 3D model could agree well just on the condition when the blast scaled distance beyond a range. To the buried arches, the critical scaled distance is 2.76 m/kg1/3.
Numerical simulations were carried out based on the software Sysnoise and Fluent.And it also puts forward a muffler structure of impedance, raises methods to calculate the property of a muffler through which the medium is the mixture of gas and water, and forecasts the transmission loss and flow resistance of the muffler and then prove it by verification test. Experiment results fit the calculations very well in low frequency. Uniform mixing of gas and liquid makes the noise reduction frequency higher, thus the property of the muffler become worse in low frequency. Water held up on the surface of the inner tube makes the muffler function well in low frequency.
Strength and ductility data for Q235B steel from 20 ℃ to 950 ℃ was obtained from tension tests with smooth cylindrical specimens (SCSs). The strain rate sensitivity was studied by conducting Split-Hopkinson Tension Bar (SHTB) test and uniaxial tension test on SCSs, while the influence of stress triaxiality on ductility was revealed by conducting upsetting tests on cylinder specimens, tension tests on pre-notched cylinder specimens and torsion tests on SCSs. Slightly modified versions of the two Johnson-Cook (J-C) models describing flow stress and fracture strain are presented to characterize the properties of Q235B steel as function of strain rate, temperature and stress triaxiality. Corresponding model parameters were calibrated based on the test data and with the help of finite element calculation. The validity of the model parameters was verified by Taylor test.
The accuracy of load identification is often hindered by the inversion of an ill-conditioned transfer function matrixs at frequencies near the structural resonances. To overcome this inversion instability, total least squares (TLS) method is a successful approach for linear problems is introduced. Tikhonov regularization of the TLS leads to an optimization problem of minimizing the sum of fractional quadratic and quadratic functions. Then, a conjunction gradient(CG) method is proposed for solving the tikhonov TLS optimization problem, called CG-TLS algorithm, whose advantages are more simple to implement,smaller storage capacity, better convergence performance and that can consider not only vibration response but the transfer matrix is contaminated by noise. The ill-conditioned reasons of transfer function matrix are investigated by numerical simulations and test of load identification, then choosing the locations of vibration response optimally with condition number. Finally, The CG-TLS regularization algorithm and other two methods are used to identify vibration load in different noise levels. The results demonstrate that the CG-TLS regularization algorithm outperforms general regularization methods showed the best performance, which also has lower noise sensitivity. Therefore the new algorithms established in this paper has broad prospect of engineering application.
The coupled relationship of optimize algorithm and dynamic simulation was established based on launch dynamics simulation model of Multiple Launch Rocket System(MRLS).The launch dynamics simulation and optimization were performed,the best launch time sequence and corresponding support stiffness and damping were obtained and vibration performance was calculated also,all of these verified the valid of optimized parameters.Moreover,the influence of random launch time on initial perturbation was analyzed.The methods and conclusions can be used as a theoretical foundation for development and revise of new MRLS.
The workpiece mass varies greatly due to large material removal rate when machining aeronautical thin-walled structure. The driving force of transmission system also changes greatly, which can affect the transmission system dynamics. In order to obtain the time-varying dynamics of machine tool transmission system, a dynamics model of the transmission system was established using the lumped parameter method considering load variation and friction characteristics of the slide block. The equivalent damping coefficient in feed direction was theoretically analyzed with the load variation. And the evolution of natural frequency and vibration response of transmission system is studied as well under different loads. The results show that a time-varying dynamics of transmission system is found when machining large material removal rate. The equivalent damping coefficient decreases as the load decreases, while the natural frequency and vibration amplitude increase as the load decreases. Finally, modal testing is performed to validate the theoretical analysis.
New attenuation relationships of vertical strong ground-motion parameters of rock sites in Western U.S. are presented in this paper, which are regressed using high-quality digital strong motion records from NGA (Next Generation Attenuation) database. The new attenuation relationships focus on vertical PGA (peak ground acceleration), PGV (peak ground velocity) and 5% damped spectral acceleration (period from 0.04 to 6.0s). Ratio of vertical to horizontal component of spectral acceleration is calculated with another attenuation relationship, which was regressed using the same regression procedure and strong-motion data, and characteristics of how V/H ratio varies with period, magnitude and distance are studied in this paper. The new vertical attenuation relationships are recommended to be used with surface wave magnitude ranged from 5.0 to 8.0, and epicenter distance ranged from 0 to 200km.
Quantitative identification of bearing fault severity is the basis of condition-based maintenance. The vibration signals will exhibit nonstationarity and nonlinearity in the presence of bearing faults. On the base of the multi-scale entropy, a new index quantitatively describing bearing fault severity is constructed which takes into account the mean value and the variations of the entropies over multiple scales. The new index is termed Partial Mean of Multi-scale Entropy (PMME). Simulation and experimental results show that the new index is able to detect incipient bearing fault and trend the fault development well.
To the problem of time delay difference(TDD) estimation of unknown frequency, the paper
describes that a time delay difference estimation method with time delay difference variance weighted. First, the received signals are processed using Fast Fourier Transform(FFT). Then the cross-correlation of every frequency unit is processed by using a pilot signal in frequency domain. The final TDD is obtained by calculating statistically the TDD results of every frequency unit, as TDD of noise frequency unit is random, and TDD of target are nearly consistent. The theoretical analysis and experiment results show that the method is valid and the signal-to-noise ratio tolerance of the method is much better than the cross-correlation of frequency domain method. A reference idea is provided for the time delay difference of weak line spectrum target.
In this paper, author analyzed the mechanism of vibration control of composite blasting cut with high load relieving groove technology comprehensively based on the energy theory, numerical results, the measured vibration results and engineering practice. First of all, this technology can adjust and control the tower body’s stress state, increase the disintegration failure degree and speed in the tower collapsed process, then reduce the tower kinetic energy when it touchdown the ground. Secondly, it can increase the disintegration failure energy of the shock structure, and reduce the vibration wave energy. Once more, it can change the impact forms and the impact process of tower body, disperse the ground shock energy, extend the touchdown impact time, and decrease the impact strength of tower body.