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Non-iterative mode shape expansion for three-dimensional structures based on coordinate decomposition
Get PDFThe direct mode shape expansion method is an iterative technique, one can conclude that the convergence performance maybe challenged when applied to three-dimensional structures. In addition, mode shape values at different DOFs (degrees-of-freedom) sometimes are not in a same order of magnitude, which will produce much error for the estimation of small values of unmeasured mode components. Therefore this paper proposed a non-iterative mode shape expansion method based on coordinate decomposition technique. The advantage of coordinate decomposition is that the unmeasured components of mode shape values could be estimated with different weighting coefficients, even in a physical meaningful interval. Numerical studies in this paper are conducted for a 30-DOF cantilever beam with multiple damaged elements, as the measured modes are synthesized from finite element models. The numerical results show that the approach can estimate unmeasured mode shape values at translational and rotational DOFs in x, y and z directions with different weighting coefficients, respectively; and better mode shape expansion results can be obtained when proper constraints are employed. A numerical three dimensional structure is also investigated, and results indicate that the estimation of unmeasured components can be improved by imposing reasonable constraints based on the coordinate decomposition technique, even only translational DOFs of two diagonal nodes of the first floor are measured
Prognostics of vibration induced risk to operators of agricultural machinery
Get PDFFrequent use of vibrating hand-held tools and operation of machinery can result in various chronic diseases. Operators of machinery are often afflicted with peripheral and systematic disorders. The statistical data collected over several decades clearly indicate the lack of operator’s safety from exposure to vibrations. The causes and impacts of vibration effects on humans are reviewed in annual reports by health and safety experts in many countries. One of the most common occupational diseases that has been frequently reported is the musculoskeletal disorder due to extended exposure to mechanical vibrations. The influence of vibrations during time period τ can be described by vibro-energy load aτ2·τ. If this load value over a specified time period does not exceed the permissible level a2·T0, it will not induce negative effects on human health. This approach was used in the present study for the prediction of hands and whole body vibration effects on operators of various vibration inducing machinery. Agricultural operators were selected as test subjects, since agricultural tractors and other mobile machinery emit high levels of vibration. Vibration data were obtained from statistical reports developed in the time period from 1988 to 2008. It was found that majority of agricultural machinery does not guarantee proper vibration safety. Thus organizational prevention methods should be developed and implemented. Reduction of vibrations by various technical methods and/or reduction of vibration exposure could be costly, but they are needed in order to provide effective solutions in reducing vibration risk to operators
Determining the torsional natural frequency of underframe of off-road vehicle with use of the procedure of operational modal analysis
Get PDFThe paper presents the example of use of the operational modal analysis procedure (OMA) to set the torsional natural frequency of underframe of off-road vehicle. Determining the natural frequency for the object of this shape is possible with the output-only data and using the peak picking technique
Investigation of dissipative properties of liquid crystalline lubricant layer
Get PDFThis work aims to investigate vibration behavior of rotating roller - a fixed segment friction pair lubricated with pure motor oil and motor oil containing liquid crystal (cholesteryl oleate) additive. Experiments were performed under boundary friction conditions. Mechanical vibrations were registered through the processing and analysis of radial vibration data of the segment, obtained for each lubricant composition under constant roller speed. It is established that vibration level of the segment is reduced at the presence of liquid crystal additive. Theoretical investigations of load-carrying properties of individual layered liquid crystal in a lubricating gap of the film lubrication bearing show a strong increase in load as compared with the equivalent viscous lubricant
Introduction to synthesis of the torsional vibrating discrete-continuous mechatronic systems by means of the hypergraphs and structural numbers method
Get PDFIn this paper the modeling by a different category graphs and an analysis of vibrating clamped – free mechatronic system by the approximate method called Galerkin's method has been presented. The frequency - modal analysis and assignment of amplitude -frequency characteristics of the mechatronic system is considered. The aim was to nominate the relevance or irrelevance between the characteristics obtained by exact - only for shaft - and approximate method. Such formulation especially concerns the relevance of the natural frequencies - poles of characteristics both of mechanical subsystem and the discrete – continuous clamped – free vibrating mechatronic system. This approach is a fact, that approximate solutions fulfill all conditions for vibrating mechanical and/or mechatronic systems and can be an introduction to synthesis of these systems modeled by different category graphs. Using the hypergraph methods of modeling and synthesis methods of torsionally vibrating bars to the synthesis of discrete-continuous mechatronic systems is originality of such formulation of problems
Structural determinants maximising wear resistance of friction joints
Get PDFThe paper addresses the issue of maximising resistance of tribological system elements against wear in the conditions of dry friction. A method of virtually multiplying wear resistance of solid bodies, particularly metals, has been found. This effect appears where the temperature of a friction area is equal to the characteristic temperature, and thus markedly different than temperatures applied in typical tribological experiments. Increased wear resistance of a system of bodies is effected by a system transfer of material between surfaces of rubbing bodies and stabilisation of the friction coefficient. Resistance to abrasive wear in conditions of dry friction and oxidational wear was tested in selected frictional systems (specimens from steels C45 and counter-specimens from 145Cr6, in different structural states of the material). In order to identify composition and structure of the friction products and the types of ferrous compounds arising from friction present on the surface of rubbing components, especially secondary oxide structures, Mössbauer spectral analysis was applied. The wear testing required construction of an original test device to measure wear in conditions of formation and regulation of the isothermic limit of temperature variation at a precisely determined distance from a contact of rubbing bodies by means of release (by cooling) or supply (by heating) of heat energy
A quantitative study of the blade passing frequency noise of a centrifugal fan
Get PDFTonal noise constitutes the major part of the overall fan noise, particularly the blade passing frequency (BPF) noise, which is generally the most annoying component. This paper quantitatively studies the BPF tonal noise of a centrifugal fan, including casing aerodynamic noise, blade aerodynamic noise and casing structural noise. Firstly, fan noise generation and propagation is discussed and the measured spectra of fan noise and casing vibration are presented. Secondly, a fully 3-D transient simulation of the internal flow field of the fan is performed. Flow interactions between the impeller and the volute casing result in the periodic pressure fluctuations on solid walls of the impeller and casing. This pressure fluctuation, in the aeroacoustic study, is modeled as aeroacoustic dipole source according to the Lighthill’s acoustic analogy theory. With the inhomogeneous wave equations solved by the boundary element method, the BPF casing and blade aerodynamic noise radiation is obtained. Finally, in the casing structural noise study, the casing structural vibration under the excitation of BPF pressure fluctuation is calculated by the finite element method and sound radiation is solved by the boundary element method subsequently. Results demonstrate that the casing aerodynamic noise is the main contribution to the centrifugal fan noise with the sound power level of 103 dB followed by the blade noise (91 dB), and the casing structural noise is 79 dB
Entropy-based fault detection approach for motor vibration signals under accelerated aging process
Get PDFThe purpose of this study is to analyze motor vibration signals due to the bearing fault, which is artificially generated by aging process. Vibration signal data recorded by the experimental setup has been conditioned by a high-pass filter (Butterworth type) to reach the regarding frequency components of the bearing failure. Spectral analysis has been applied to realize the degradation on the bearing and the power spectral density figures revealed that the magnitudes of frequency components between 1.5-4 kHz bandwidth increased after every aging cycle. Vibration signals were investigated statistically by examining four main statistical parameters: mean value, standard deviation, skewness and kurtosis. Evaluation of these parameters indicated that significant variance occurred on standard deviation. At this point Shannon entropy became an approach to analyze the variance on the standard deviation. The probability of the aging cycles has been defined as a function of standard deviation values for each aging cycle. Entropy definition, which is a function of probability, determines the uncertainty level on the data and it has been examined to identify the effect of the aging progress on the bearing by examining the transferred entropy amount between aging cycles
Vibrodiagnostics and dynamic behaviour of aggregates in small hydroelectric power plants
No full textThe presentation introduces the solution for the vibroactivity problems in small hydroelectric power plants, based on original stationary vibromonitoring and diagnostic systems as well as their application to solve various problems. Dynamic behaviour of hydromachinery and causes of increased vibrations are analysed taking into account structural, design- and construction-related issues. It is demonstrated that condition monitoring and analysis of vibrations enable identification of causes of large vibrations in hydromachiner
Investigation of vibrations of line scale calibration systems
Get PDFThe paper treats the issue of embedding the traceable length metrology directly into technological process by performing precise dynamic measurements of line scale in real industrial environment. It addresses the error-related problems specific to line scale calibration in dynamic mode of operation that are caused primarily by static and dynamic loads as well as geometrical deviations of the calibration system components. Introducing the dynamic regime of calibration leads to the dynamic calibration error originating due to vibration sources in the structure. This term should be considered and implicated in the measurement uncertainty budget. A new 3D finite element model has been developed in order to both investigate the influence of dynamical excitations of a long stroke comparator structure and evaluate possible influence of vibrations on geometrical dimensions of the line scale. The experiments have been conducted on the new interferometer-controlled comparator setup with a moving microscope in order to evaluate the performance of the precision scale calibration proces