1,721,009 research outputs found
Measuring the Performance of Underplatform Dampers for Turbine Blades by Rotating Laser Doppler Vibrometer
Full text linkUnderplatform friction dampers are commonly used to control the vibration level of turbine blades in order to prevent high-cycle fatigue failures. Experimental validation of highly non-linear response predictions obtained from FEM bladed disk models incorporating underplatform dampers models, has proved to be very difficult so as the assessment of the performance of a chosen design. In this paper, the effect of wedgeshaped underplatform dampers on the dynamics of a simple bladed disk under rotating conditions is measured and the effect of the excitation level on the UPDs performances is investigated at different number of the engine order excitation nearby resonance frequencies of the 1st blade bending modes of the system. The measurements are performed with an improved configuration of a rotating test rig, designed with a noncontact magnetic excitation and a non-contact rotating SLDV measurement syste
Development of a Comprehensive Mathematical Model for Simulating the Effects of Misalignments in Vibration Measurements using Scanning LDV Measurement Systems
No full textSix degrees of freedom measurement with continuous scanning laser Doppler vibrometer
No full textThe dynamicresponseofastructurecanconsistofuptosixdegreesoffreedom(DOF).
Not allofthemmaybepresentatalltimesinastructure,butforadetailedfinite
elementmodelvalidationitisimportanttoprovideasmuchinformationaspossible.
CurrentcontacttransducerscanpickupacombinationofsomeofthementionedDOFs,
but arenotabletoprovideallsixDOFsfromasingletransducer.Severalcontact-less
transducers,suchasaScanningLaserDopplerVibrometer(SLDV),canbecombinedtoa
single measurementsystemthatallowsthedeterminationofuptothreetranslational
degreesoffreedomatapoint,buttheyarestillnotprovidingrotationalinformationas
the laserbeamisfixedtoapoint.ContinuouslyScanningLaserDopplerVibrometer
(CSLDV)methodscanpartlyovercomethisissuebytravellinginsmallcirclesaroundthe
measurementlocationandthusalsosensingtherotationaroundthethreeaxesata
point.AnintroductionofCSLDVmethodsformeasuringDOFsatapointisgiven,
focussingonamethodforcapturingupto5DOFsusingalens.However,thelenscan
make themeasurementofthein-planerotationverydifficultandimpractical.Thispaper
presentsanewtypeofscanningdevicewhichallowsmeasuringallsixdegreesof
freedomatameasurementlocationwithasinglesetupandasinglepointLDV,by
combiningvariablesmallcirclescans.Experimentalvalidationofthescanningheadis
presentedandthemeasurementofthelastDOF,thein-planerotation,isdemonstrated
Dealing with harmonics and noise for advanced dynamic identification using in-flight helicopter data
No full textIn the framework of the HC-AG19 Garteur Action Group, novel methodologies and procedures are proposed and analyzed to improve finite element models of helicopters through in-flight dynamic data. Thus, the development of methods allowing accurate modal parameter estimation is essential to provide reliable reference data to the model updating process. Recently, a complete GVT test was performed by NLR, University of Bristol and Agusta Westland on a commercial helicopter, including shaker excitation with both random and pseudo-random signals, as well as acceleration profiles recorded during specific flight maneuvers. These provide an ideal data-set for method validation and development, in particular to verify the efficiency of Operational Modal Analysis versus standard Experimental Modal Analysis techniques. An additional challenge of the data set is that the recorded in-flight data contain both the harmonic contribution coming from the rotor as well as the noise which inevitably contaminate the data when measuring in operating conditions. In this paper, harmonic removal techniques and advanced identification methods will be applied on the data. The modal models will be firstly identified using Experimental Modal Analysis to obtain a reference dataset for validation. Operational Modal Analysis is then performed on the same data but neglecting the input force to validate the methods. Different harmonic removal techniques are also applied and their efficient in removing these components from the signals compared. Finally, the simulated in-flight GVT tests were repeated using as input recorded accelerations from different maneuvers (constant speed flight, hovering, landing and rotor stop). The results in some of these conditions will also be discussed
Deflection shape reconstructions of a rotating five-blade helicopter rotor from SLDV measurements
No full textRecovery of Operational Deflection Shapes from noise-corrupted measurement data from CSLDV: comparison between polynomial and mode filtering approaches
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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