Study on Vibration Reduction Due to Pile-Raft Foundation for High-Tech Lab Based on Frequency Sweep Test

Evaluation of the vibration reduction of piled-slab is of great significance for the layout of process and power equipment in high-tech facilities. In-situ measurement was performed to study the vibration reduction of the piled-slab of a high-tech lab. Slab vibrations with frequencies of 10 Hz to 60 Hz with steps 5 Hz were induced by an electromagnetic vibration exciter. INV3062U data acquisition device and 941B sensor were used to measure the velocities in the vertical direction at six measurement locations on the slab surface. For single frequency, the measurement results showed that the peak values of the slab vibration velocities generally decayed nonlinearly as the distance increased, however, the attenuations of 25 Hz, 35 Hz, 40 Hz, 50 Hz and 60 Hz slab vibrations were not monotonically.

Substantiation of amplitude-frequency characteristics and design parameters of vibration exciter in volume oscillation separator

The main effects of the developed design for vibratory separator: the increased driving force in the process of bulk material separation in this work, achieved by providing the working cylindrical-conical container with vibrational motion; improving the conditions for the passage of product particles through openings, achieved by providing the sieve surface with volume oscillations; reduction of energy consumption and improvement of operating conditions for support nodes during the operation of the designed vibrating screen, achieved due to the installation of additional elastic elements between the separator body and bearing assemblies of the vertical drive shaft in vibration exciter. Providing the working bodies of the designed vibrating screen with volume oscillating motion allows increasing the performance and quality of the separation process of solid bulk materials. To determine the rational parameters for vibration screening process, the equations of motion of working bodies as a conical sieve surface were obtained using the method of the Lagrange equations of the second order. When applying solutions of the Cauchy problem for linear nonhomogeneous differential equations, the solution of the latter was obtained. The obtained dependences of oscillation amplitudes, vibration velocity and vibration acceleration, and the intensity of oscillating motion allowed us to perform a mathematical analysis for power and energy parameters of vibration drive in the developed separator. The inclined placement of the conical sieve surface allows for spatial gyration or circular translational motion, which makes it possible to realize the advantages of volumetric separation of bulk materials. The results of the conducted analytical study made it possible to substantiate the optimal inclination angle for working sieve surface. Based on our analysis, the design parameters of vibration exciter were substantiated and clarified, and the design of this technical system was demonstrated.

Determining the energy efficiency of a resonance single-mass vibratory machine whose operation is based on the Sommerfeld effect

This paper reports determining the energy efficiency of a vibratory machine consisting of a viscoelastically fixed platform that can move vertically, and a vibration exciter whose operation is based on the Sommerfeld effect. The body of the vibration exciter rotates at a steady angular speed while there are the same loads in the form of a ball, a roller, or a pendulum inside it. The load, being moved relative to the body, is exposed to the forces of viscous resistance, which are internal within the system. It was established that under the steady oscillatory modes of a vibratory machine's movement, the loads are tightly pressed to each other, thereby forming a combined load. Energy is productively spent on platform oscillations and unproductively dissipated due to the movement of the combined load relative to the body. With an increase in the speed of the body rotation, the increasing internal forces of viscous resistance bring the speed of rotation of the combined load closer to the resonance speed, and the amplitude of platform oscillations increases. However, the combined load, in this case, increasingly lags behind the body, which increases unproductive energy loss and decreases the efficiency of the vibratory machine. A purely resonant motion mode of the vibratory machine produces the maximum amplitude of platform oscillations, the dynamic factor, the total power of viscous resistance forces. In this case, the efficiency reaches its minimum value. To obtain vigorous oscillations of the platform with a simultaneous increase in the efficiency of the vibratory machine, it is necessary to reduce the forces of viscous resistance in supports with a simultaneous increase in the internal forces of viscous resistance. An algorithm for calculating the basic dynamic characteristics of the vibratory machine's oscillatory motion has been built, based on solving the problem parametrically. The accepted parameter is the angular speed at which a combined load gets stuck. The effectiveness of the algorithm has been illustrated using a specific example

DYNAMICS FEATURES OF A VIBRATING MACHINE WITH ELASTIC ELEMENT HAVING EXPONENTIAL CHARACTERISTIC OF RESILIENT FORCE

The article analyzes the possibility of using nonlinear elastic elements as a suspension of the working element of resonant vibrating machines with two unbalance vibration exciters is analyzed. The elastic characteristic of the suspension is described by an exponential law, which ensures that the natural frequency remains unchanged regardless of the system mass. Static characteristics of the vibration exciter motors are taken into account. A system of differential equations describing movement of the system depending on the processed material mass is obtained. Amplitude-frequency characteristics depending on the power supply voltage, as well as on the debalance rotational speed are obtained for different values of material mass. The stability of the obtained periodic solutions is analyzed. The constancy of resonant amplitude and frequency of the working element vibrations at various values of material mass is shown. The results obtained confirm the advisability of using an equalfrequency suspension of the working element for resonant vibrating machines.

SLOW OSCILLATIONS IN DRIVES OF MACHINE ASSEMBLIES

Machine assembly with additional degrees of freedom is considered. The method of direct separation of motions was used for research. It was shown that the braking vibration moment occurring by the reason of resonance effects in the driven object can lead to excitation of rotor oscillations of the assembly with a occurrence of slow oscillations of the vibration exciter rotor is demonstrated. frequency lower than the rotation frequency. Slow rotor oscillations represent a transient process to the stationary motion mode, which is established when an additional load torque occurs. Moreover, the maximum oscillation amplitudes will be relatively large. By the example of a vibration machine with an inertial drive, the occurrence of slow oscillations of the vibration exciter rotor is demonstrated.

A Vibration Sensor-Based Method for Generating the Precise Rotor Orbit Shape with General Notch Filter Method for New Rotor Seal Design Testing and Diagnostics

Verification of the behaviour of new designs of rotor seals is a crucial phase necessary for their use in rotary machines. Therefore, experimental equipment for the verification of properties that have an effect on rotor dynamics is being developed in the test laboratories of the manufacturers of these components all over the world. In order to be able to compare the analytically derived and experimentally identified values of the seal parameters, specific requirements for the rotor vibration pattern during experiments are usually set. The rotor vibration signal must contain the specified dominant components, while the others, usually caused by unbalance, must be attenuated. Technological advances have made it possible to use magnetic bearings in test equipment to support the rotor and as a rotor vibration exciter. Active magnetic bearings allow control of the vibrations of the rotor and generate the desired shape of the rotor orbit. This article presents a solution developed for a real test rig equipped with active magnetic bearings and rotor vibration sensors, which is to be used for testing a new design of rotor seals. Generating the exact shape of the orbit is challenging. The exact shape of the rotor orbit is necessary to compare the experimentally and numerically identified properties of the seal. The generalized notch filter method is used to compensate for the undesired harmonic vibrations. In addition, a novel modified generalized notch filter is introduced, which is used for harmonic vibration generation. The excitation of harmonic vibration of the rotor in an AMB system is generally done by injecting the harmonic current into the control loop of each AMB axis. The motion of the rotor in the AMB axis is coupled, therefore adjustment of the amplitudes and phases of the injected signals may be tedious. The novel general notch filter algorithm achieves the desired harmonic vibration of the rotor automatically. At first, the general notch filter algorithm is simulated and the functionality is confirmed. Finally, an experimental test device with an active magnetic bearing is used for verification of the algorithm. The measured data are presented to demonstrate that this approach can be used for precise rotor orbit shape generation by active magnetic bearings.

Vibration Perception Thresholds of Skin Mechanoreceptors Are Influenced by Different Contact Forces

Determining vibration perception thresholds (VPT) is a central concern of clinical research and science to assess the somatosensory capacity of humans. The response of different mechanoreceptors to an increasing contact force has rarely been studied. We hypothesize that increasing contact force leads to a decrease in VPTs of fast-adapting mechanoreceptors in the sole of the human foot. VPTs of 10 healthy subjects were measured at 30 Hz and 200 Hz at the heel of the right foot using a vibration exciter. Contact forces were adjusted precisely between 0.3 N–9.6 N through an integrated force sensor. Significant main effects were found for frequency and contact force. Furthermore, there was a significant interaction for frequency and contact force, meaning that the influence of an increasing contact force was more obvious for the 30 Hz condition. We presume that the principles of contrast enhancement and spatial summation are valid in Meissner and Pacinian corpuscles, respectively. In addition to spatial summation, we presume an effect on Pacinian corpuscles due to their presence in the periosteum or interosseous membrane.

Low and High Frequency Vibration Perception Thresholds Can Improve the Diagnosis of Diabetic Neuropathy

Recent studies demonstrate neuropathic changes with respect to vibration sensitivity for different measurement frequencies. This study investigates the relationship between vibration perception thresholds (VPTs) at low and high frequencies at two plantar locations and diabetic peripheral neuropathy (DPN) severity in diabetes mellitus (DM) subjects with DPN. We examine differences of VPTs between participants with DM, with DPN, as well as healthy controls. The influence of anthropometric, demographic parameters, and DM duration on VPTs is studied. Thirty-three healthy control group subjects (CG: 56.3 ± 9.9 years) and 33 with DM are studied. DM participants are subdivided into DM group (DM without DPN, n = 20, 53.3 ± 15.1 years), and DPN group (DM with DPN, n = 13, 61.0 ± 14.5 years). VPTs are measured at the first metatarsal head (MTH1) and heel (30 Hz, 200 Hz), using a customized vibration exciter. Spearman and Pearson correlations are used to identify relationships between VPTs and clinical parameters. ANOVAs are calculated to compare VPTs among groups. Significant correlations are observed between DPN severity (by fuzzy scores) and VPTs at both locations and frequencies (MTH1_30 Hz vs. fuzzy: r = 0.68, p = 0.011; Heel_30 Hz vs. fuzzy: r = 0.66, p = 0.014; MTH1_200 Hz vs. fuzzy: r = 0.73, p = 0.005; Heel_200 Hz vs. fuzzy: r = 0.60, p = 0.032). VPTs in CG and DM groups are significantly smaller than the DPN group, showing higher contrasts for the 30 Hz compared to the 200 Hz measurement. The correlations between fuzzy scores and VPTs confirm the relevance of using low and high frequencies to assess a comprehensive foot sensitivity status in people with DM.

The dynamics of a resonance single-mass vibratory machine with a vibration exciter of targeted action that operates on the Sommerfeld effect

This paper reports a study into the dynamics of a vibratory machine composed of a viscoelastically-fixed platform that can move vertically and two identical inertial vibration exciters. The vibration exciters' bodies rotate at the same angular velocities in opposite directions. The bodies host a single load in the form of a ball, roller, or pendulum. The loads' centers of mass can move relative to the bodies in a circle with a center on the axis of rotation. The loads' relative movements are hindered by the forces of viscous resistance. It was established that a vibratory machine theoretically possesses the following: – one to three oscillatory modes of movement under which loads get stuck at almost constant angular velocity and generate total unbalanced mass in the vertical direction only; – a no-oscillation mode under which loads rotate synchronously with the bodies and generate total unbalanced mass in the horizontal direction only. At the same time, only one oscillatory mode is resonant and exists at the above-the-resonance speeds of body rotation, lower than some characteristic speed. At the bodies' rotation speeds: ‒ pre-resonant; there is a globally asymptotically stable (the only existing) mode of load jams; ‒ above-the-resonance, lower than the characteristic velocity; there are locally asymptotically stable regimes ‒ both the resonance mode of movement of a vibratory machine and a no-oscillations mode; ‒ exceeding the characteristic velocity: there is a globally asymptotically stable no-oscillations mode. Computational experiments have confirmed the results of theoretical research. At the same time, it was additionally established that it would suffice, to enter a resonant mode of movement, to slowly accelerate the bodies of vibration exciters to the above-the-resonance speed, less than the characteristic speed. The results reported here could be interesting both for the theory and practice of designing new vibratory machines

SYNTHESIS OF THE LOW-FREQUENCY VIBRATION EXCITER

The article is devoted to synthesis of the low-frequency vibration exciter for checking of sensors of acceleration. In many areas of the modern equipment sensors of acceleration working in very low range of frequencies are widely used. For checking and graduation of such sensors the vibration exciter capable to provide rectilinear horizontal harmonic oscillations of the calibrated accelerometer in so low range of frequencies are required. Low frequencies of fluctuations cause the necessity of creation of big amplitudes of movements for ensuring the acceptable values of amplitudes of accelerations. The low-frequency electrodynamic vibration exciter with a magnetic suspension of mobile part which is a component of the National Standard of the vibration movement of the Russian Federation is so far created. However, development of the modern equipment demands expansion of frequency ranges to the area of ultralow frequencies. One of requirements shown to the vibration exciter working in the ultralow range of frequencies is increase in amplitude of horizontal movements of a mobile part as with small amplitudes the speed and acceleration of the harmonious law of the movements proportional according to the frequency of fluctuations and a square of this frequency, will have small amplitude values. One of problems of realization of a control system of the electric drive of the vibration exciter consists in that a mobile part possesses indifferent position of balance. The centre of fluctuations of a mobile part is not defined and can be in any point on magnetic conductor length. That fluctuations had the steady centre in an average point of a magnetic conductor without use of a mechanical spring, the drive is supplied with an additional control system of fluctuations, or a so-called electromagnetic spring.