Electrodynamic Vibration Research Articles

Substantiation of Improved Efficiency of Electrodynamic Excitation of Vibration in Fatigue Testing of Machine Structural Components

The paper presents the results of investigation aimed at substantiating the approaches to choosing a scheme of fastening structural components to be fatigue tested on the movable table of an electrodynamic vibration exciter. It is demonstrated that an improvement of efficiency of electrodynamic excitation of vibration is achievable in the case of antiphase vibrations of the test component and one of the elements of the component-fastening vibrating system, as well as in the case of a simultaneous optimal mismatch of their natural frequencies.

Energy Regenerative and Active Control of Electro Dynamic Vibration Damper

Active vibration control is introduced to an electrodynamic regenerative vibration damper. It is intended to improve vibration reduction capability using the regenerated energy. An electrodynamic actuator is used as an energy regenerative damper and active control actuator. This idea is applied to a moving mass type vibration absorber and vibration control is performed. In the case of energy regenerative control, a PWM step-up chopper is used to solve the dead zone problem. Active control signal is also controlled by other PWM chopper from the power supply. However, energy regenerative and active control mode can not operate at the same time. A new control law is introduced to switch control mode and to follow the ideal force. The ideal force is calculated using the LQ control theory. Experimental setup is mode to confirm the proposed technique and the damping capability is tested.

225 エネルギ回生・アクティブ制御を用いた振動ダンパの研究

225 エネルギ回生・アクティブ制御を用いた振動ダンパの研究

On the Force Drop Off Phenomenon in Shaker Testing in Experimental Modal Analysis

The Electrodynamic Vibration Exciter (shakers) has been one of the most employed excitation sources in modal tests. The shaker is an electromechanical device that provides a mechanical motion due to the input signal sent to its coil. Despite being widely used, it is well known that the shaker interacts with the structure under test. In particular, when the structure passes through a given resonance, the force delivered by the shaker abruptly decreases, causing the so called drop off phenomenon. This paper aims to study this force drop off phenomenon in the single shaker modal testing. Analytical models are developed to help in understanding the physical principles involved in the interaction between the shaker and the structure under test. Experimental analyses are performed using different shakers as well as excitation signals, in order to evaluate the effects of the input signal, as well as the power amplifier operational modes, on the structure dynamics. Preliminary tests revealed that significant distortions might occur during vibration tests using shakers and these distortions significantly affect the determination of the structure response.

Sh-3 Shinken's New Technology for Electro-dynamic Vibration Generators (VGs)

Sh-3 Shinken's New Technology for Electro-dynamic Vibration Generators (VGs)

Evaluation of whole-body road traffic vibration in building.

Level fluctuating vibration has been evaluated by the cumulative index L10, but some investigators suggest that the L10 cannot represent an adverse comment on vibration. In order to clarify the compliant, various factors involving vibration need to be analysed together by statistical methods, for instance factor analysis or quantum theory. The authors investigated the relationship between an evaluation index and human sensation of vibration in a subjective experiment in a wooden house. The subjects were exposed to vertical road traffic vibration reproduced with an electrodynamic vibrator placed near the house. The range of vibration levels at surfaces in contact with the subjects were from 50dB to 70dB in root mean square of frequency weighted acceleration level, i.e. the vibration level. Numbers assigned by the subjects and evaluation indices of the vibration level were analysed by applying the Stevens power law. The results showed that L10 or Leq (55) could become an effective index for the assessment of subjective perception of level fluctuating vibration in a wooden house.

Characterizing, simulating, and eliminating vibration-induced counts in measurement-while-drilling gamma ray detectors

A measurement-while-drilling (MWD) gamma ray tool will report a higher than actual count rate if its scintillation crystal package produces vibration-induced light pulses. The scintillation crystal is used as a transducer that measures the count rate of gamma rays coming from naturally occurring radioisotopes in downhole shales. Each gamma ray causes the crystal to emit a number of visible light photons that are converted into an electrical pulse by a photomultiplier tube. The pulse is shaped and digitized by tool electronics and registers as a count if it is above some threshold energy. The harsh shock and vibration conditions MWD gamma detectors experience can cause a crystal package to emit spurious light pulses which typical tool electronics cannot distinguish from genuine gamma counts, so the detector will report a higher than actual count rate. For ‘geosteering’ applications a higher count rate typically will indicate that the drill string trajectory must be changed to remain within a reservoir because such a response is indicative of a shale reservoir boundary; therefore vibration-induced counts will provide a false control input, making it difficult to steer correctly. This could cause the trajectory of the drill string to exit the reservoir. Measurements of vibration-induced counts from MWD scintillation packages were made using an electrodynamic vibration table, gamma ray spectroscopy electronics, and a digitizing oscilloscope. It was found that a scintillation package will produce counts as a function of the input g-level if the Rigid body resonant frequency of the crystal in its support structure is within the bandwidth of the operational vibration environment. These measurements provided the basis for computer simulations of MWD gamma ray logging that showed the detrimental effect of vibration-induced counts on log accuracy. It was concluded that stiffening the scintillation crystal mechanical support and, therefore, moving the rigid body resonant frequencies of the system outside the operational vibration bandwidth ensures the scintillation package will not produce vibration-induced counts in a specified bandwidth.

The ESS Muddle: Physics vs. Relics

This paper examines the history and evolution of environmental stress screening (ESS) to show how uncoordinated initiatives from each military service contributed to the current state of array in the ESS community. The lack of a common vision for ESS is examined as a continuing handicap in efforts to integrate ESS more fully into the hardware development process. Common areas of confusion regarding effective ESS procedures and facilities are discussed, including: temperature air change rate vs. hardware thermal response; the number of vibration axes needed; simultaneous vibration in combined axes vs. sequential vibration in each; and pneumatic vs. electrodynamic vibration facilities. A "checklist" of considerations to apply in developing a successful ESS program is presented. The June, 1994, DoD initiative regarding possible elimination or replacement of military specifications and standards with commercial standards is reviewed with respect to ESS.

A fast iterative finite element model for electrodynamic and magnetostrictive vibration absorbers

This paper presents a finite element model for simulating electrodynamic and magnetostrictive vibration absorber systems. The model employs a decoupled formulation to compute motion induced voltages in a magnetomechanical coupled system. The model is first validated by comparison with experimental measurements. An application of the model for optimization of the system damping performance using model predictions, is presented. The model is also used to calculate the frequency response of a magnetostrictive actuator.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Reciprocity assessment of single transducers

Although most conventional transducers are usually regarded as reciprocal at nominal signal level, it is still necessary to ascertain that the presumed reciprocal transducer is indeed reciprocal or possesses sufficient reciprocity in reciprocity calibration practice. A conventional reciprocity check involves a system comprised of the two transducers and the gaseous, liquid, or solid medium and its boundaries. This paper tries to give an absolute method for reciprocity assessment without the need of any other auxiliary transducer. The principle is that if the imaginary part of the electrical impedance of a transducer (i.e., the capacitance for piezoelectric‐type or the inductance for electrodynamic‐type transducers) varies linearly with its mass load impedance, the transducer is reciprocal. So, the linear correlation coefficient could be considered as a reciprocity index. The theory is applied to evaluate the reciprocity of a piezoelectric and an electrodynamic vibration generator. The coefficients are determined as 0.9915 (at 10 kHz) and 0.9773 (at 1 kHz), respectively. With the data processed by a complex least‐square‐fitting code [L.‐F. Ge, J. Acoust. Soc. Am. 91, 2326 (1992)], the relevant coefficients are adjusted to 0.9987 and 0.9724. Thereupon, the transducers can be regarded as reciprocal at their respective working frequencies. The assessment has been verified by the accurate calibration results.

Microstructural changes associated with vibratory prepared weldments

The solidification of grey cast irol~L [1] under imposed vibration shows a varying microstructure. Kou and Le [2] showed experimentally that under lowfrequency vibration there is improvement in the microstructure and mechanical properties of aluminium weldments. Researchers [3-6] have proved that solidification of castings under vibratory conditions shows a refinement in grain size, metaUographic refinement and reduction in various casting defects. This letter pertains to the microstructure of the weldments prepared under stationary and vibratory conditions. Micrographs show an appreciable improvement in the grain refinement of the weldments prepared under vibratory conditions. Two mild steel workpieces were clamped with the help of C-clamps and angle iron pieces on a vibrating table (Fig. 1). The vibrating table rested on shafts which were supported on bearings. This table was rigidly coupled to an electrodynamic vibrator. A three-phase a.c. transformer and futile-coated mild steel electrodes were used for welding. A oscillator/ power amplifier and vibration meter were used for

A three-parameter model for the behavior of transducers.

Owing to the limitation of materials and technology, it is significant to determine the behavior of a transducer as a whole by experiments. The impedance method is one of the most important methods. In previous works, a four-parameter model was established to relate the mechanical load impedance to its input electrical impedance. The characterized parameters of the transducer were then determined from the model parameters. [L.-F. Ge, J. Acoust. Soc. Am. Suppl. 1 87, S129 (1990); J. Acoust. Soc. Am. 89, 1860 (1991)]. But, results obtained by the model vary more or less with different beginning values calculated even from proper three-pair impedance data. In this paper, a three-parameter model is presented, and a complex least-squares fitting code is developed to fit the model to more than three pairs of data; thereby, a definite and more accurate solution has been obtained. The model is formulated as ZE=A*(ZL−B*)/(ZL−C*), where ZE is the electrical impedance, ZL is the load impedance, and the multiplier A*, pole point C*, and zero point B* are the three parameters to be determined. Exactly, A* is equal to the mechanically blocked electrical impedance and C* is equal and opposite to the electrically blocked mechanical impedance. The new model has been successfully used to determine the characterized parameters, motional impedance, and sensitivity of both piezoelectric and electrodynamic vibration generators, and then the sensitivity of accelerometers.

Automatic refabrication and quality control of fuel elements for the BOR-60 reactor in the USSR

The USSR and the former GDR pursued the common objective in a contract about scientific cooperation in order to project, to erect and to take in operation an automated pilot plant for the refabrication of fuel elements for the fast reactor BOR-60. The layout of the plant was determined mainly by the radioactivity and toxicity of the U/Pu oxide fuel and by the application of the procedure of electrodynamic vibration to densify the fuel. For vibrocompacting non-spherical granular U/Pu oxide fuel with a definite spectrum of particle sizes and a sufficient flowability was prepared. Relations between particle size mixture, the density and the axial density distribution of the vibrocompacted fuel column is presented by elected examples. For the quality assurance the fuel elements was controlled during the technological process and by irradiation of 11000 fuel rods fabricated between 1977 and 1986 for the reactor BOR 60.

Experiments on a compressed air loudspeaker

This work describes the development, construction, theoretical analysis and experimental evaluation of a novel type of electropneumatic sound source. The source has been specifically developed with a view to its application in active noise control systems applied in hostile environments, such as those found in the exhaust systems of gas turbines and internal combustion engines. This need arises in view of the relative fragility and large physical size of conventional loudspeakers and the high degree of non-linearity of existing electropneumatic transducers. In the new design a gas bearing is used to support the friction free motion of a sliding plate which is used to modulate the supply of compressed air. The sliding plate is driven by an electrodynamic vibrator. Experimental results demonstrate that this arrangement reduces harmonic distortion to at least 20 dB below the fundamental driving frequency for most operating conditions. In a companion paper a theoretical analysis of the transducer is presented by Chapman and Glendinning which enables predictions to be made of the acoustic volume velocity (source strength) produced by the transducer as a function of the upstream pressure and displacement of the sliding valve. The predictions of this theoretical model are found to be in good agreement with experimental results.

Automatic system of programmed control of parameters of vibration and thermal tests of gas turbine engine blades (ASPC VTT)

The article describes the automated system of programmed control of the parameters of vibration and thermal tests of gas turbine engine blades, designed at the Special Design and Technological Bureau of the Institute of the Strength of Materials, Academy of Sciences of the Ukrainian SSR, and intended for the control of different types of electrodynamic vibration test stands and heating installations; they make it possible to test the life and the ultimate state of turbine blades under conditions of the simultaneous effect of cyclically changing vibration and thermal loads in a broad range of vibration frequencies of blades.

Subjective Assessment of the Vibration Discomfort Produced by Different Hand Held Machines

A subjective method of paired comparisons was developed to compare the discomfort caused by the vibration from hand-held power tools with the predictions obtained using the procedures recommended by standards for the evaluation of human exposure to hand-transmitted vibration. Fiteen trained subjects were exposed in the laboratory to seven different vibration exposures produced by five hand-held tools (one of the tools was used in two positions) and an electrodynamic vibrator. The good agreement observed between and within subjects shows that they can reliably rank vibration dicomfort produced by different hand-held tools. For five vibration exposures out of seven, the rank deduced from the subjective assessments was in accord with the rank of the predicted evaluations derived from the frequency-weighted acceleration values measured. An exposure with highly impulsive vibration was rated as being much more annoying than it was foreseen by the current procedures of evaluation. The operator's position proved to be an important factor in the perception of the discomfort.

Working standard of units of length, speed, and acceleration in vibratory motion of solids

UDC 53.089.68:531.3 At the All-Union Research Institute of Gauges and Standards (VNIIMS) a working standard (WS) of units of length, speed, and acceleration in vibratory motion of solids was devised; it is intended for checking reference and accurate working means of measuring vibration parameters [i ]. The introduction of this instrument in checking practice will make it possible to use methods of checking and calibration on a broader scale; these methods are based on measuring the amplitude of translation by direct comparison with the wavelength of laser radiation, and thereby they improve the level of metrological provisions in the field of vibrometry. The working standard is a complex of means of presetting mechanical vibrations, and also of measuring the amplitude and frequency of these vibrations. In accordance with the government checking arrangement [i] the WS has the following technical and metrological characteristics: range of vibratory translation 2.0"10-8-5.0"10 -3 m; range of vibratory speeds 1.0"i0-~-i.0"i0 -l m/sec; range of vibratory accelerations 1.0-10-3-5.0"103 m/sec2; total error SZ, determined by the rms deviation of the result of measurement in the comparison of WS with a primary standard and by the noneliminated systematic error, no more than 5.0"10 -3 in the frequency range 2.0-10 -I- 1.0-i0 s Hz and no more than 1.5"10 -2 in the frequency ranges 3.0"10-i-2.0"101 and 1.0"i03-2.0"i0 ~ Hz. The following serve as means of presetting the mechanical vibrations: a piezoelectric vibrator in the range of amplitudes of vibratory translations 2.0"i0-s-2.0"i0 -7 m and of frequencies 3.0"i0-i-2.0"I04 Hz, an electrodynamic vibrator in the range of amplitudes of vibratory translations 2.0"10-7-5.0"10 -3 m and frequencies 3.0"10-I-103 Hz, a tuning fork vibrator in the range of amplitudes of vibratory accelerations up to 5.0"103 m/sec 2 at the frequency of 1.35"103 Hz. The amplitude of the vibratory translations is measured with the aid of two small twoway and one multiway laser interferometers. The former two operate jointly with the electrodynamic and the tuning fork vibrators, the latter with the piezoelectric vibrator. The measurement of small and ultrasmall vibrations is based on the method of "zeros" of a Bessel function, which in turn is a modification of the method of narrow-band filters. Amplitudes of translation above 0.2 ~m are determined by the method of counting interference bands. We will deal with each of the mentioned methods of measurement. The method of counting interference bands. In the WS two modifications of the mentioned method are realized: the method of unidirectional count and the method using a frequency meter. It is known [2] that the double amplitude of the vibrations 2S0 in measurements by the method of unidirectional count is correlated with the number of interference bands by the relation

Self-modulation and recurrence phenomena in vibrator-induced, steady-state sinusoidal ground vibration

Results of an experimental investigation of the evolution of vibrator-induced, steady-state sinusoidal ground vibration are reported and interpreted as suggesting the nonlinear wave phenomenon known as Fermi-Pasta-Ulam recurrence. Uniform-amplitude (unmodulated) sinusoidal wavetrains were generated by a 4441 N electrodynamic vibrator, the vertical force being used, and the evolution of the wavetrains was monitored on the ground surface by eight vertical seismometers. Two locations, 6 m apart, were used to install the vibrator. The seismometers were aligned along three profiles: two for the first location of the vibrator (30 and 60 m long) and one for the second (73 m long). The wavetrain carrier frequency was varied from 7 to 14.65 Hz; its amplitude measured from 0.015 to 0.6 cm s −1 at 1 m from the source. Whenever a wavetrain was generated with a Mach number below some critical value (∼ 10 −5 at 1 m from the vibrator), it evolved in a recurrent manner. The Fourier spectra of the records show that, during the initial stage of evolution, an instability developed resulting in a dramatic growth of the second and third harmonics, whose appearance is attributed to ground nonlinearity ( harmonic generation), and their lower sideband components. As the instability effects reached their peak levels, the wavetrain seemed to be losing its coherence, often becoming strongly modulated ( self-modulation). With increasing propagation distance, however, the energy gradually returned to the carrier component, and the wavetrain demodulated, recovering its original (uniform and coherent) form ( recurrence). Despite some important peculiarities, the unstable wavetrain evolution observed is believed to belong to the class of nonlinear wave phenomena known as Fermi-Pasta-Ulam recurrence. Since, by theory, recurrence involves solitons, the results also imply the existence of seismic solitons.

A Technique to Predict the Acoustic Radiation Characteristics of an Automobile Tire

Abstract A technique to predict the acoustic radiation characteristics of the predominant structural modes of an automobile tire is presented. A stationary tire is excited by an electrodynamic vibrator and, through conventional modal analysis methods, a description of the surface velocity is obtained. With this information, and a representation of the tire geometry, numerical procedures are used to predict the acoustic surface intensity and field pressure, for a given frequency of interest, based on a Helmholtz integral formulation. Predicted far field sound pressure levels are in close agreement with experimental measurements taken in an anechoic chamber. This provided the necessary validation of the technique.

Influence of Vibrations on Weld Characteristics

The influence of longitudinal vibration on certain weld characteristics have been studied in the present paper. Longitudinal vibration have been imposed by electrodynamic vibrator in the frequency range of 40Hz to 10Hz and amplitude .0005 cm. to .0025 cm. during experimentation with the mild steel work pieces. It has been observed that hardness of the weldment increase due to increase in frequency and amplitude of vibration. Increase of frequency affects more than amplitude increase on hardness. Percentage elongations of the specimens decrease with increase in frequency and amplitude of vibration. Porosity is reduced at higher frequency and amplitude.