Absolute Vibration Research Articles

A multi-level model correlation approach for low-frequency vibration transmission in wood structures

The main challenge in predicting structure-borne sound in wood buildings is to accurately model the vibration transmission between the source and the receiving room. Large variations in model parameters make it difficult to predict absolute vibration levels and to make conclusions regarding the relative effects of different designs. A step towards establishing reliable models is to investigate the possibilities and limitations of using deterministic methods, which requires correlations between simulations and measurements. In this paper, we present a multi-level model correlation approach for low-frequency vibration transmission in wood buildings. We apply the proposed approach to a scaled-size experimental structure representing a part of a two-storey wood building, and we evaluate the results for frequencies up to 100 Hz. We perform correlations between simulations and measurements four different levels: structural components (viz. beams and boards), planar structures (viz. floor, ceiling and walls), room structures and the complete structure. The results indicate that the dynamic behaviour of the experimental structure was to a great extent captured by the developed model. Based on the observations made in the multi-level correlations, we discuss important model parameters and propose modelling guidelines. We conclude that it is possible to employ deterministic methods in order to simulate the low-frequency vibration transmission in wood buildings provided that measurement data for calibration purposes are available. The developed numerical model can be used as a reference model for investigations on the effects of variations and uncertainties in the modelling.

The dynamic parameters correlation assessment of the textile machine high-speed bearings in changed technological conditions

The paper describes the correlation of the changed manufacturing and technological conditions of the spinning device applicable in the textile industry with the change of the dynamic parameters of the spinning rotor bearings. Special ball bearings for textile machines are designed for high rotational speeds and relatively low loads. They are characterized by high dimensional accuracy and reliable running, which guarantees their great utility value. In the diagnostics of the spinning machine spindle high-speed bearings, absolute vibrations were measured according to the recommendation of STN ISO 10816-3 norm. The conducted experiments focused primarily on the assessment of the impact of the unstable technological process on the change of the monitored dynamic parameters. The measurements showed a statistical increase of the measured dynamic parameters by 50% when the spinning machine spindle rotor speed was increased by 15%. The measured vibration values showed that technological instability (rotor clogging by fiber during combing and subsequent braking and speed deceleration, a signal from a damaged drive belt, variable dynamic imbalance of the rotor, and at the same time an uneven bowl wear caused by the fiber friction) had a noticeable impact.

Vibration measurement with nonlinear converter in the presence of noise

Conventional vibration measurement methods use the linear properties of physical converters. These methods are strongly influenced by nonlinear distortions, because ideal linear converters are not available. Practically, any converter can be considered as a linear one, when an output signal is very small. However, the influence of noise increases significantly and signal-to-noise ratio decreases at lower signals. When the output signal is increasing, the nonlinear distortions are also augmenting. If the wide spectrum vibration is measured, conventional methods face a harmonic distortion as well as intermodulation effects. Purpose of this research is to develop a measurement method of wide spectrum vibration by using a converter described by a nonlinear function of type f(x), where x =x(t) denotes the dependence of coordinate x on time t due to the vibration. Parameter x(t) describing the vibration is expressed as Fourier series. The spectral components of the converter output f(x(t)) are determined by using Fourier transform. The obtained system of nonlinear equations is solved using the least squares technique that permits to find x(t) in the presence of noise. This method allows one to carry out the absolute or relative vibration measurements. High resistance to noise is typical for the absolute vibration measurement, but it is necessary to know the Taylor expansion coefficients of the function f(x). If the Taylor expansion is not known, the relative measurement of vibration parameters is also possible, but with lower resistance to noise. This method allows one to eliminate the influence of nonlinear distortions to the measurement results, and consequently to eliminate harmonic distortion and intermodulation effects. The use of nonlinear properties of the converter for measurement gives some advantages related to an increased frequency range of the output signal (consequently increasing the number of equations) that allows one to decrease the noise influence on the measurement results. The greater is the nonlinearity the lower is noise. This method enables the use of the converters that are normally not suitable due to the high nonlinearity.

Development of elements of the condition monitoring system of turbo generators of thermal power stations and nuclear power plants

The rationale is given for the improvement of the regulatory framework for the use of shaft sensors for the in-service condition monitoring of turbo generators and the development of control systems of shaft surfacing and misalignments of supports. A modern concept and a set of methods are proposed for the condition monitoring of the “shaft line–thrust bearing oil film–turbo generator supports” system elements based on the domestic COMPACS® technology. The system raw data are design, technology, installation, and operating parameters of the turbo generator as well as measured parameters of the absolute vibration of supports and mechanical quantities, relative displacements and relative vibration of the rotor teeth in accordance with GOST R 55263-2012. The precalculated shaft line assembly line in the cold state, the nominal parameters of rotor teeth positions on the dynamic equilibrium curve, the static and dynamic characteristics of the oil film of thrust bearings, and the shaft line stiffness matrix of unit support displacements have been introduced into the system. Using the COMPACS-T system, it is planned to measure positions and oscillations of rotor teeth, to count corresponding static and dynamic characteristics of the oil film, and the static and dynamic loads in the supports in real time. Using the obtained data, the system must determine the misalignments of supports and corrective alignments of rotors of coupling halves, voltages in rotor teeth, welds, and bolts of the coupling halves, and provide automatic conclusion if condition monitoring parameters correspond to standard values. A part of the methodological support for the proposed system is presented, including methods for determining static reactions of supports under load, the method for determining shaft line stiffness matrices, and the method for solving the inverse problem, i.e., the determination of the misalignments of the supports by measurements of rotor teeth relative positions in bearing housings. The procedure for calculating misalignments of turbo generator shaft line supports is set out.

Determining the vibrations between sensor and sample in SQUID microscopy

Vibrations can cause noise in scanning probe microscopies. Relative vibrations between the scanning sensor and the sample are important but can be more difficult to determine than absolute vibrations or vibrations relative to the laboratory. We measure the noise spectral density in a scanning SQUID microscope as a function of position near a localized source of magnetic field and show that we can determine the spectra of all three components of the relative sensor-sample vibrations. This method is a powerful tool for diagnosing vibrational noise in scanning microscopies.

A six-direction absolute displacement sensor for time-delayed control based on quasi-zero-stiffness property

A novel six-direction sensor for absolute vibration motion is proposed in this study for the measurement of absolute motions by employing multi-direction quasi-zero-stiffness property. Scissor-like structures with pre-deformed springs are applied symmetrically in the proposed sensor. Based on the mathematical modeling of the proposed six-direction sensor, it is shown that the stiffness and damping properties of the sensor are adjustable nonlinear functions which are dependent on the structural parameters of scissor-like structures. And then, by utilizing bifurcation theory and perturbation method, the structural parameters are optimized for the improvement of measurement accuracy. For the realization of the approximate fixed point for a moving vibration object, the vibration from measurement object to the sensor is isolated, and thus the sensor could obtain the absolute motions. Utilizing the signals obtained by the proposed sensor directly, better vibration/suppression effectiveness is achieved. The results provide a novel and significant six-direction absolute motion measurement method by utilizing multi-direction quasi-zero-stiffness property with noticeable isolation performance only with passive elements.

Design of a quasi-zero-stiffness based sensor system for the measurement of absolute vibration displacement of moving platforms

This study presents the analysis and design of a novel sensor system for measuring the absolute vibration displacement of moving platforms based on the concept of quasi-zero-stiffness (QZS). The sensor system is constructed using positive- and negative-stiffness springs, which make it possible to achieve an equivalent QZS and consequently to create a broadband vibration-free point for absolute vibration displacement measurement in moving platforms. Theoretical analysis is conducted for the analysis and design of the influence of structure parameters on system measurement performance. A prototype is designed which can avoid the drawback of instability in existing QZS systems with negative stiffness, and corresponding data-processing software is developed to fulfill time domain measurements. Both the simulation and experimental results verify the effectiveness of this novel sensor system.

Vibrational stability of a cryocooled horizontal double-crystal monochromator.

The vibrational stability of a horizontally deflecting double-crystal monochromator (HDCM) is investigated. Inherently a HDCM will preserve the vertical beam stability better than a `normal' vertical double-crystal monochromator as the vibrations of a HDCM will almost exclusively affect the horizontal stability. Here both the relative pitch vibration between the first and second crystal and the absolute pitch vibration of the second crystal are measured. All reported measurements are obtained under active cooling by means of flowing liquid nitrogen (LN2). It is found that it is favorable to circulate the LN2 at high pressures and low flow rates (up to 5.9 bar and down to 3 l min(-1) is tested) to attain low vibrations. An absolute pitch stability of the second crystal of 18 nrad RMS, 2-2500 Hz, and a relative pitch stability between the two crystals of 25 nrad RMS, 1-2500 Hz, is obtained under cryocooling conditions that allow for 1516 W to be adsorbed by the LN2 before it vaporizes.

Harmonic Mistuning of Blisks

AbstractThe paper describes a new method to calculate the maximum amplificationof blade vibrations of a bladed disk or blisk subject to manufacturing tolerances. Two effects of mistuned blisks are analyzed in this paper. The separation of two orthogonal nodal diameters are shown and described in detail. Furthermore, the excitation of more than one nodal diameter by only one engine order is discussed. If the eigenfrequencies of these nodal diameters are close together, the vibration amplitude of some blades increases. Based on a lumped‐mass model, it is shown which maximum amplitude can occur. The idea is to use a harmonic mistuning pattern to get the highest influence at small tolerances for one single nodal diameter. This influence is not exceeded by a randomly mistuned system and limits the maximum amplitude. The given analysis is validated by a common Monte‐Carlo simulation. On the other hand, a description of the excitation of other nodal diameters is given. Using these two effects, an absolute vibration maximum for a given mistuning limit can be calculated. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Experimental test of static and dynamic characteristics of tilting-pad thrust bearings

The axial vibration in turbine machine has attracted more and more interest. Tilting-pad thrust bearings are widely used in turbine machines to support the axial load. The dynamic properties generated by oil film of the thrust pad have important effects on the axial vibration of the rotor-bearing system. It is necessary to develop the method to test the dynamic characteristics of thrust bearings. A new rig has been developed. The facility allows a complete set of bearing operating parameters to be measured. Parameters measured include oil temperatures, oil-film thickness, and pressure. The static load and dynamic load can be added on the thrust bearing in the vertical direction at the same time. The relative and absolute displacement vibrations of the test experimental bearing with the changes of dynamic force are measured, and the dynamic characteristics of the test bearing are obtained. The experimental results show clearly that the operating conditions influence largely on the pad static and dynamic characteristics.

Vibration measurements of high-heat-load monochromators for DESY PETRA III extension.

The requirement for vibrational stability of beamline optics continues to evolve rapidly to comply with the demands created by the improved brilliance of the third-generation low-emittance storage rings around the world. The challenge is to quantify the performance of the instrument before it is installed at the beamline. In this article, measurement techniques are presented that directly and accurately measure (i) the relative vibration between the two crystals of a double-crystal monochromator (DCM) and (ii) the absolute vibration of the second-crystal cage of a DCM. Excluding a synchrotron beam, the measurements are conducted under in situ conditions, connected to a liquid-nitrogen cryocooler. The investigated DCM utilizes a direct-drive (no gearing) goniometer for the Bragg rotation. The main causes of the DCM vibration are found to be the servoing of the direct-drive goniometer and the flexibility in the crystal cage motion stages. It is found that the investigated DCM can offer relative pitch vibration down to 48 nrad RMS (capacitive sensors, 0-5 kHz bandwidth) and absolute pitch vibration down to 82 nrad RMS (laser interferometer, 0-50 kHz bandwidth), with the Bragg axis brake engaged.

The Improvement Modification of Rotor Unbalance Verification Technique in Monitoring Systems and Automatic Diagnostics

The purpose of this paper is to present make establish create define automatic technique превышение remainder disbalance of rotors in power devices power unit running both for general purpose and for special one as well. The technique supposed takes into account individual dynamic properties опор, rotor's weight and the norm of remainder disbalance in the whole range of working rotation frequencies. The point is it is reported that the requirements of up-to-date IS industry standard ГОСТ and standards ISO International Standardization Organization towards remainder absolute vibration support for dynamically rigid stand are essentially underestimated. But these requirements are underestimated for yielding stand. The technique proposed is recommended to use in automatic monitoring systems and diagnostics for continuum verification of rotors exceeding remainder disbalance

Scoping prediction of re-radiated ground-borne noise and vibration near high speed rail lines with variable soils

This paper outlines a vibration prediction tool, ScopeRail, capable of predicting in-door noise and vibration, within structures in close proximity to high speed railway lines. The tool is designed to rapidly predict vibration levels over large track distances, while using historical soil information to increase accuracy. Model results are compared to an alternative, commonly used, scoping model and it is found that ScopeRail offers higher accuracy predictions. This increased accuracy can potentially reduce the cost of vibration environmental impact assessments for new high speed rail lines.To develop the tool, a three-dimensional finite element model is first outlined capable of simulating vibration generation and propagation from high speed rail lines. A vast array of model permutations are computed to assess the effect of each input parameter on absolute ground vibration levels. These relations are analysed using a machine learning approach, resulting in a model that can instantly predict ground vibration levels in the presence of different train speeds and soil profiles. Then a collection of empirical factors are coupled with the model to allow for the prediction of structural vibration and in-door noise in buildings located near high speed lines. Additional factors are also used to enable the prediction of vibrations in the presence of abatement measures (e.g. ballast mats and floating slab tracks) and additional excitation mechanisms (e.g. wheelflats and switches/crossings).

Vibration Analysis of Gas Turbine SIEMENS 162MW- V94.2 Related to Iran Power Plant Industry in Fars Province

Vibration analysis of most critical equipment is considered as one of the most challenging activities in preventive maintenance. Utilities are heart of the process in big industrial plants like petrochemical zones. Vibration analysis methods and condition monitoring systems of these kind of equipment are developed too much in recent years. On the other hand, there are too much operation factors like inlet and outlet pressures and temperatures that should be monitored. In this paper some of the most effective concepts and techniques related to gas turbine vibration analysis are discussed. In addition, a gas turbine SIEMENS 162MW- V94.2 vibration case history related to Iran power industry in Fars province is explained. Vibration monitoring system and machinery technical specification are introduced. Besides, absolute and relative vibration trends, turbine and compressor orbits, fast Fourier transform (FFT) in absolute vibrations, vibration modal analysis, turbine and compressor start up and shut down conditions, bode diagrams for relative vibrations, Nyquist diagrams and waterfall or three-dimensional FFT diagrams in startup and trip conditions are discussed with relative graphs. Furthermore, Split Resonance in gas turbines discussed in details. Moreover, some updated vibration monitoring system, blade manufacturing technique and modern damping mechanism are discussed in this paper.

Developments and Thoughts on Operational Reliability Assessment of Mechanical Equipment

Operational reliability assessment of the specified mechanical equipment is an individual problem. The average reliability, obtained by using probability statistics method with large sample data, cannot fulfil requirements of operating reliability evaluation for individual equipment.The emerged problems are summarized when the traditional reliability theory is applied to operational reliability assessment of mechanical equipment, and corresponding improved methods are reviewed. The theoretical basis and technical connotation of operational reliability assessment for individual equipment, which is based on dynamic modelling, fault mechanism analysis, signal processing and fault feature extraction, are expounded. Then, a new concept of operational reliability is given and the degree of operational reliability is defined. An operational reliability assessment approach based on running condition information of mechanical equipment is proposed. Mapping models between running condition and operational reliability is established for mechanical equipment to calculate the degree of operational reliability. Based on ISO3945, absolute vibration values which are used to evaluate running condition of rotating machinery are transformed to reliability degree. The proposed method is applied to a turbogenerator set with bearing bush looseness before/after repair, and rolling bearings which degrade from normal to failure state under continuous running condition. Good results are achieved, which validate the method. The unsolved problems for operational reliability assessment of mechanical equipment are brought up, which may provide reference for the further research.

Active Vibration Isolation Using a Voice Coil Actuator with Absolute Velocity Feedback Control

This paper describes the active vibration isolation using a voice coil actuator with absolute velocity feedback control for highly sensitive instruments (e.g., atomic force microscopes) which suffer from building vibration. Compared with traditional isolators, the main advantage of the proposed isolation system is that it produces no isolator resonance. The absolute vibration velocity signal is acquired from an accelerator and processed through an integrator, and is then input to the controller as a feedback signal. The controller output signal then drives the voice coil actuator to produce a sky-hook damper force. In practice, the phase response of the integrator at low frequencies (2~6 Hz) deviates from 90 degree which is the exact phase difference between the vibration velocity and acceleration. Therefore, an adaptive filter is used to compensate for the phase error. Analysis of this active vibration isolation system and comparison of model predictions to experimental results indicate that the proposed method significantly reduces transmissibility at resonance without incurring increased transmissibility at higher frequencies.

Experience in the design and adaptation of vibration control and vibromonitoring equipment for turbines installed at Sayano-Shushenskaya HPS

We consider the problems of measuring the vibration of the supporting parts in hydro-turbine manufacturing, for example of the Sayano-Shushenskaya Hydro Power Station (SS HPS). It was explore the concepts of vibration control system (VCS) of hydro units. The analysis of the main types of vibration sensors, as the most important elements of the vibration control system of the hydro units. The main results of comparative tests of sensors that measure absolute vibration are given. It is proposed the optimization of the algorithms VCS of the units, including taking into account the seismic area of the hydropower station.

On the relationship between wave based control, absolute vibration suppression and input shaping

The modeling and control of continuous flexible structures is one of the most challenging problems in control theory. This topic gains more interest with the development of slender space structures, light weight aeronautical components or even traditional gears and drive shafts with flexible properties. Several control schemes are based on the traveling wave approach, rather than the more common modal methods. In this work we investigate the relationships between two of these methods. The Absolute Vibration Suppression (AVS) controller, which was developed for infinite dimension systems, is compared to Wave Based Control (WBC) which was designed primarily for lumped systems. The WBC was first adjusted to continuous systems and then the two controllers, whose algorithms seem different, are compared. The investigation shows that for the flexible shaft these two control laws are actually the same. Furthermore, when converted into an equivalent open loop controller they appear as an extension to continuous systems of the Input Shaping (IS) methodology.

DAMPING TRANSVERSAL VIBRATIONS OF THE OFFSET CYLINDER OF THE OFFSET PRESS / RULONINĖS OFSETINĖS MAŠINOS OFSETINIO CILINDRO SKERSINIŲ VIRPESIŲ SLOPINIMAS

Investigation into the influence of a dynamic vibration damper on the intensity of the absolute forced transversal vibrations of the blanket cylinder of the web printing offset press was performed. The analytical and numerical examination of the dynamic model of the cylinder was done. The obtained results have disclosed that the application of the damper decreases the intensity of printing cylinder vibrations. Santrauka Analiziniu ir skaitmeniniu būdu ištirtas dinaminio virpesių slopintuvo efektyvumas slopinant priverstinius periodinius ofsetinio spausdinimo įrenginio ofsetinio cilindro skersinius virpesius, bloginančius atspaudų kokybę. Atliktas ofsetinio cilindro ir virpesių slopintuvo modeliavimas „Matlab“ programa. Sudarytos „Simulink“ diagramos. Pateiktos amplitudinės dažninės charakteristikos. Parodyta, kad naudojant virpesių slopintuvus galima efektyviai mažinti spausdinimo įrenginio cilindrų skersinius virpesius.

Application of Active Base Isolation System Using Absolute Vibration Control Technology

An active base isolation system, which uses absolute vibration control technology, has been applied to the real full scale building, Obayashi Corporation Technical Research Institute Main Building ‘Techno-Station’. This building is the first active base isolation building all over the world. The absolute vibration control is an active vibration control method for base isolated structures to stay in the absolute space and to have vibration free environment, by applying control forces through actuators during earthquakes. Four 1100kN hydraulic actuators, two in each horizontal direction, are installed in the Techno Station to reduce the seismic response to 1/10 of the conventional passive base isolation system. When applying active control to a real full scale building, it is necessary to install fail safe mechanism in case that actuators are over-loaded by input ground motion of more than expected level or unstable control condition. As fail safe mechanism for this absolute vibration control, the trigger system using friction dampers has been developed and is installed between actuators and reaction foundations.