Frequency Of Forced Vibration Research Articles

Deformation criterion of the prefracture state of truss-structure elements and an acoustic-emission resonance technique on their basis

The results of theoretical and experimental studies of the prefracture state of truss-structure elements with a cut determined by finite-element analysis of the resonance frequencies and modes of forced vibrations, which are associated with the time history of the acoustic-emission parameters, are given. The natural frequencies of plane vibration modes of a delta-shaped truss-structure element most sensitive to changes in the geometrical dimensions (the depth and angle of opening) of a cut are determined. A relationship between the angle of the cut opening and the value of displacements (accelerations) at the truss-structure model points adjacent to the cut is formulated. It is shown that the angle of the cut opening, calculated using this relationship, is completely a deformation criterion of the prefracture state of structures. The values of resonance frequencies of forced vibrations of structure elements at which the critical angle is reached and over which intense cracking begins are found.

215 振動ふるいに起こる自励振動

This paper describes an experimental study on self-excited vibration of a vibrating screen. We investigate the motions of granular material, the effects of frequency of forced vibration and mass flow rate of granular material from the vibrating screen. Consequently, self-excited vibration is observed, when the acceleration of vibrating screen is more than 1 g. Fluctuation of flow rate of granular material causes a self-excited vibration.

Application of FFT-Based Signal Analysis to Micro-Scratch Testing for Adhesion Strength Measurement of Thin Films and Measured Results Based on Different Measurement Parameters

An FFT-based signal processing method for the micro-scratch test, proposed by Baba was compared with a conventional micro-scratching method to quantitatively evaluate the suitability of the technique. Original scratch signals from a micro-scratch system were first digitized by a 16-bit analog-to-digital converter with a sampling frequency of 44.1 kHz, which were fed into a personal computer. Then, the FFT-based method and the conventional method were used to process the signals according to their individual algorithms. The output results from the two methods were compared, showing that the FFT-based method effectively reduces unnecessary signals arising from the micro-scratching mechanism, and that the output level of the unnecessary signals for the FFT-based method is about 50% lower than that observed in the conventional method. The FFT-based method was implemented into a micro-scratch tester for actual application and critical loads of various thin films were measured using various measurement parameters. The results showed that the critical load increases with increasing stylus radius, or increasing thickness of the film, whereas it decreases with increasing frequency of forced vibration. It is also shown that the amplitude of the forced vibration has only little effect on the critical load.

2901 振動ふるいに起る自励振動(G10-1 機械力学・計測制御(1) 非線形・複雑システム,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

This paper describes an experimental study on self-excited vibration of a vibrating screen. We investigate the motions of granular material, the effects of frequency of forced vibration and mass flow rate of granular material of the vibrating screen. Consequently, self-excited vibration is observed.

FORCED AND FREE VIBRATIONS OF RECTANGULAR SANDWICH PLATES WITH PARAMETRIC STIFFNESS MODULATION

An active control of the resonant vibrations of a rectangular sandwich plate performed by the parametric stiffness modulation is analyzed. The controlled vibrations are those of the dominantly flexural type excited by the transverse force acting at the first resonant frequency of dominantly flexural vibrations. The stiffness modulation is performed at a comparatively high frequency identified by the resonance of a mode of the dominantly shear type. The method of direct partition of motions is used that predicts an existence of the modal interaction between these two modes of vibrations due to the parametric stiffness modulation. It is shown that such a parametric control can provide a significant shift of the first eigenfrequency of a controlled plate (the one subjected to the stiffness modulation) from its nominal value for an uncontrolled plate. Heavy fluid loading conditions are accounted for as well as the energy dissipation in the material of a plate. It is demonstrated that although heavy fluid loading reduces resonant frequencies of forced vibrations, the suggested mechanism of control remains valid in these cases. Dynamics of an elementary two-degree-of-freedom model mechanical system is considered to illustrate the mechanism of modal interaction, which is involved in the suggested way of an active control of vibrations of sandwich plates.

Modeling Vibratory Drilling Dynamics

The dynamic behavior of deep-hole vibratory drilling is analyzed. The mathematical model presented allows the determination of axial tool and workpiece displacements and cutting forces for significant dynamic system behavior such as the engagement and disengagement of the cutting tool into the workpiece material and tool breakthrough. Model parameters include the actual rigidity of the tool and workpiece holders, time-varying chip thickness, time lag for chip formation due to tool rotation and possible disengagement of drill cutting edges from the workpiece due to tool and/or workpiece axial vibrations. The main features of this model are its nonlinearity and inclusion of time lag differential equations, which require numeric solutions. The specific cutting conditions (feed, tool rotational velocity, amplitude and frequency of forced vibrations) necessary to obtain discontinuous chips and reliable removal are determined. Calculated bifurcation diagrams make it possible to derive the relevant domain of user-specified system parameters along with the determination of optimal cutting conditions.

The active control of vibrations of composite beams by parametric stiffness modulation

The paper addresses an active control of the resonant vibrations of composite beams performed by a parametric stiffness modulation. A sandwich beam composition with the continuous core is considered. The stiffness modulation is introduced by some fairly small changes in an orientation of elements of the microstructure of a core ply. The controlled vibrations are those of the dominantly flexural type excited by a transverse force acting at a low resonant frequency, whereas the stiffness modulation is performed at a comparatively high frequency identified by the resonance of a mode of the dominantly shear type. This difference in time scales of the controlled vibrations and the input signal facilitates a use of the method of direct partition of motion that predicts an existence of the modal interaction between the low-frequency and the high-frequency motions due to so-called vibrational forces. It is shown that such a parametric control can provide a significant favourable shift of the first eigenfrequency of a controlled beam (the one subjected to the stiffness modulation) from its nominal value for an uncontrolled beam. Heavy fluid loading conditions are accounted for as well as material losses in a structure. Then instead of analysis of eigenfrequencies, a problem of forced vibrations is posed and the forced frequency–amplitude response is analysed. It is demonstrated that although heavy fluid loading reduces resonant frequencies of forced vibrations, the suggested mechanism of control remains valid in these cases.

Effects of the Aspect Ratio of Vibrated Enclosures on the Thermal Convection Field and Chaotic Characteristics.

In this paper the time-dependent characteristics of the thermal convection field in rectangular enclosures with large aspect ratio exposed vertical vibration were numerically examined and the results were compared with the ones of square enclosure. In the computation the Prandtl number, the Rayleigh number and the vibration Grashof number were held constant of 0.71, 104 and 106 respectively. The normalized angular frequency of forced vibration was changed in the range between 10 and 7680. As a result, it was ascertained that the five regimes with respect to the angular frequency proposed by Fu and Shieh for the square enclosure captured the change of surface-average Nusselt number when the chaotic characteristics were considered. It was also revealed that the vortices in the enclosure aligned to the vertical direction in the enclosure with large aspect ratio determined the characteristics of the surface-average Nusselt number on hot and cold side walls.

The effect of travelling seismic waves on the dynamic response of earth dams

A theoretical investigation of the dynamic response of earth dams to the travelling seismic waves is presented. The earth dam is simplified as a truncated two-dimensional elastic wedge. The dam body consists of an isotropical linear viscoelastic material with homogeneous elastic modulus and density. The seismic waves travel along the longitudinal direction of the earth dam. The numerical calculations show the following. (i) For the longitudinal mode of vibration, the greater the ratio ( H L ) of the height to the lenght of the complete wedge, the more the natural transverse period of vibrational of the two-dimensional wedge is less than that of the one-dimensional wedge. Especially for the first two natural transverse period, this influence is large. The decrease of the ratio of the natural transverse period for a two-dimensional wedge to that for a one-dimensional wedge with the ratio H L is rapid for the higher than for the lower longitudinal modes. (ii) Comparing with the one-dimensional wedge, the natural transverse periods for the two-dimensional case in the complete wedge are lower, and they will increase as the coefficient of truncation, h H increases. (iii) When the frequency of forced vibration is less than the natural transverse frequency for one-dimensional wedge, the amplification is less for a two-dimensional wedge than for a one-dimensional wedge. (iv) When the phase difference of ground motion at both ends of the dam equals π, the amplification for a two-dimensional wedge is less than that for a one-dimensional wedge, but when the phase difference equals nπ, ( n > 1), the situation is reversed. (v) As the coefficient of truncation, h/H, increases, the displacement model partecipations decrease monotically. (vi) In general, the displacement caused by an earthquake is greater for a one-dimensional wedge than for a two-dimensional wedge when considering the seismic waves travelling, but the acceleration response of a two-dimensional wedge with long length of dam to travelling seismic waves with long dominant period is greater than that of a one-dimensional wedge. When the length of the dam is short enough, the response of a two-dimensional wedge without considering the influence of travelling seismic waves always gives the greatest value.

Vortex shedding controlled by the transverse vibration of three in-line elliptic cylinders in a uniform flow

An experimental study has been conducted on the vortex shedding frequency from three in-line elliptic cylinders with one of them undergoing forced transverse vibration in a uniform flow at frequencies up to 4 times the natural vortex shedding frequency. The possibility that the vortex shedding from each elliptic cylinder can be controlled by the vibrating cylider is examined by FFT analyses. It is shown that the locking-on characteristics of each cylinder depend on the arrangement of the elliptic cylinders, the amplitude and frequency of forced vibration, the uniform flow Reynolds number and the location of the vibratinf cylinder.

加振式グリッパの試作研究

The theory of grasping method of object with the most suitable force, by which an object could be grasped in no slip condition nor over grasped condition, had been reported already. The purpose of this paper is to describe the details of the vibration gripper applied this theory. The most distinctive point of this gripper, is in the compact vibration roller constructed by Harmonic Gear, by which forced vibration and correction for slipping could be able easily. The second special point is in the control circuit of grasping force, in which the circuit is divided in two sections : one is the grasping motor circuit operated at low response, and another is piezoelectric actuator circuit operated at high response. By the result of experiment, it has been cleared that this gripper had ability to grasp the object with the most suitable force as mentioned above constantly, and, in addition, safety factor for this grasping force could be controlled to adequate value, by regulating the frequency of forced vibration. Also, band width for the control circuit of grasping force has been improved up to 116.5 Hz by the piezoelectric actuator circuit inserted for this purpose.

Experimental investigations of the elastic moduli of the soil in a lateral fill

1. The shape of the distribution of the elastic moduli of the soil over the height of a lateral fill conforms to a curvilinear law. The distribution curve of the elastic moduli can be assumed parabolic for low frequencies of forced vibrations, and triangular for high frequencies.

Determining the resonance frequencies of forced vibrations of turbogenerators with foundations

The model method for determination of dynamic properties of framed foundations on plastic scale models is elaborated. Position shifting of resonance peaks has been found by evaluation of different response curves, measured on models. Theoretical and experimental analysis of forced vibrations of complex damped mechanical system with several degrees of freedom has shown that resonance peaks, measured at different points of the same system, correspond to various frequencies of exciting force. To locate eigen frequencies and dangerous resonances from results of measurements, it is necessary to plot the envelope of the set of curves and to determine the positions of its peaks, or, at least, to find the concentration of resonance maxima of all individual curves.