2Structural Dynamic Testing Term differentiating it from Static Analysis and TestingModal Analysis and Modal TestingOperational Deflection ShapesObjectivesWhat is Modal TestingWhy do Modal TestingHow to do Modal TestingBrüel & Kjær Solution to Modal TestingWith the advent of the aircraft industry, it was not only necessary to test structures for their static load capabilities, but also to investigate their behaviour under dynamic loading to verify the design parameters of the structures. The field of Structural Dynamic Testing as it was then called, has developed both theoretically and experimentally over the years, and is widely used today in all advanced industries under the terminology – Modal Analysis and Modal Testing.The purpose of this lecture is to describe what is Modal Testing, explain why we do Modal Testing and illustrate how Modal Testing is carried out in practice. Finally, the features incorporated in Brüel & Kjær instrumentation to facilitate Modal Testing will be highlighted.
3Structural Dynamic Testing Modal Analysis vs Operational Deflection ShapesModal Analysisartificial excitation (hammer, 1 or more shakers)input force is well known (“under our control”)Operational Deflection Shapesinvestigation (visualisation) of structure behaviour under “running conditions”input forces not known and complicated to describeOutputInputWith the advent of the aircraft industry, it was not only necessary to test structures for their static load capabilities, but also to investigate their behaviour under dynamic loading to verify the design parameters of the structures. The field of Structural Dynamic Testing as it was then called, has developed both theoretically and experimentally over the years, and is widely used today in all advanced industries under the terminology – Modal Analysis and Modal Testing.The purpose of this lecture is to describe what is Modal Testing, explain why we do Modal Testing and illustrate how Modal Testing is carried out in practice. Finally, the features incorporated in Brüel & Kjær instrumentation to facilitate Modal Testing will be highlighted.
4Introduction to Modal Testing Present day demandsIncreasing speed in transportationHigher fuel economyBoth demands achieved by reducing the mass of structuresConsequencesStructures become inherently weakResonances move down into frequency regions of excitation forcesStructures fail because of dynamic loadsStatics studied for over a centuryThe ever increasing demands for higher speeds in all forms of transportation, coupled with the insatiable desire for better fuel economy, entices design engineers to use the obvious solution – to reduce the mass of their structures. An inevitable consequence of this, is that structures become inherently weak, i.e. the resonance frequencies move down in the frequency range to where the excitation frequencies of the structure during operation are present. Thus structures fail under dynamic loading if the resonances excited during operation are not sufficiently damped. These problems, however, can be avoided if the structure is so designed that the excitation frequencies neither coincide with, or are in the immediate vicinity of the resonances.Today structures fail rarely due to static loads as this field has been studied for over a century and reached a sufficient level of sophistication.
5What Modal Testing Why How Brüel & Kjær Solution This section answers the question: what is Modal Testing
6Definition of Modal Testing To construct a mathematical model of the vibrational properties and behaviour of a structure by experimental meansNatural FrequencyModal DampingResiduesOnce the design of a structure has been accepted, a prototype is produced to carry out modal tests to verify the dynamic parameters – natural frequencies, modal damping and residues which are the components of the mode shapes – predicted for the design.The experimentally determined parameters which rarely agree with those predicted, can nevertheless be used to make a mathematical model for structural dynamic modifications and for investigating the dynamic behaviour of the structure.
7Modal Parameters Theoretician Experimentalist Eigenvalue Percent DampingEigenvectorExperimentalistNatural FrequencyLoss FactorMode ShapeAmplitudeFirstModeDistanceSecondModeThirdModeTo understand what modal parameters are, consider a simple free-free beam excited at one end by a random force. If the imaginary part of the response (i.e. motion, be it acceleration, velocity or displacement) is measured at different points on the beam as a function of frequency, a set of curves would be obtained as shown in the 3D plot in the diagram.The first three natural (resonance) frequencies, where the amplitudes start building up, are clearly seen along the frequency axis. By connecting the peaks at each of the natural frequencies the corresponding mode shapes can be traced out. Furthermore, if the 3 dB bandwidths at each of the resonances are determined, the loss factor can be calculated which gives the amount of modal damping for each of the modes. (In practice these are determined through curve fitting the frequency response curves)Using structural mechanics (FE method), the theoretician can calculate system stiffnesses and masses and with this eigenvalues and eigenvectors that are simply the undamped natural frequencies and the corresponding undamped mode shapes, because damping is generally not taken into account in the design at this stage.Although these values can be mathematically related to the measured values, they rarely agree in practice.From the 3D plot it can be seen that information about the dynamic properties of the structure lies at the natural frequencies and in their vicinity. Thus by determining the 3 above mentioned parameters experimentally for the first 10 modes, for example, a mathematical model can be built up in a computer.FrequencyBeamModalDomainViewFrequency Domain ViewForce
8Why Modal Testing What How Brüel & Kjær Solution On account of the large investments needed to carry out these tests it is necessary to explain why we do modal testing.
9Trouble Shooting Frequency Response Function High responses One of the most widely used applications of modal testing is in the field of trouble shooting. The figure on top is the frequency response function of a plate when excited at a point using a hammer and the response measured at some other relevant point. The fact that the plate has two resonances as can be seen in the diagram is not a problem in itself. The problem only arises, if the plate is excited at a resonance frequency during operation, for example, at 1.2 kHz. In this case the amplitude at this point would be rather high as shown in the bottom diagram.To avoid this problem, one can either change the operation of the machine such that the excitation frequency is moved away from the resonance frequency, or modify the plate such that its resonance frequency is moved further up or down in the frequency range.Vibration responseduring operation
10SDM and FRS (Assumes validated Modal Model) What if … scenariosStructural Dynamics ModificationMassStiffnessTuned absorberMove resonance frequencyIn the example of the plate, the resonance frequency was moved down to approximately 1.15 kHz by mounting an additional mass on the plate. It can be seen from the bottom diagram that the response of the plate under excitation is therefore now significantly reduced at 1.2 kHz.Similarly, the resonance frequencies can be moved to higher frequencies by attaching a stiffener to a structure. In some cases moving the frequencies may not result in enough attenuation, and the only solution left would be to add a tuned absorber.To avoid such trial and error methods of adding and removing masses and stiffeners, a more professional approach can be implemented using the Structural Dynamics Modification’ program. This program utilises the mathematical model of the structure, synthesised from the measured modal parameters described previously. This software can not only predict the response of the structure when such changes are made, but could also be used to indicate optimum positions on the structure, where such modifications should be implemented.The ‘Forced Response Simulation’ software makes use of the mathematical model to predict the response of the structure at any point when excited by a variety of forces.Thus investigating potential design changes by computer modelling can dramatically reduce the time and cost of understanding and solving troublesome vibration problems.High responseLow responseForced Response SimulationHow will a structure behave when one or more forces are applied?Previousresponse
11Why do Modal Testing Trouble shooting FE-modelling To reduce excessive vibration levelsFE-modellingTo ensure resonances are away from excitation frequencyValidation by testing on prototypesRefinement of the mathematical model through inclusion of dampingPrerequisite in aircraft industryToday also commonly used in automotive industryStructural assembly analysisTo predict the dynamic behaviour of assembled sub-componentsSimulation of “what if” scenariosDetermination of forcesResponse to complex excitationThe most widely used application of modal testing is in trouble shooting to reduce excessive vibration levels.Major industries normally design their structures on computers and often have an analytical model of their structure. The dynamic properties calculated from their model need to be validated through modal testing on their prototype. Additionally modal testing gives some information about the damping in the structure, which can be utilised for the refinement of their analytical model.Although this is a prerequisite in the aircraft industry, it is now also widely used in other major industries.If the dynamic properties at the connection points of sub-structures are known, they can be used to predict the properties of the complete structure.In ‘what if’ scenarios, the forces exciting the structure can be predicted, if the mathematical model is reasonably complete and accurate, and the responses are measured at a sufficient number of points on the structure during operation. Similarly, the responses at various points can also be predicted for known force inputs.
12How Modal Testing What Why Brüel & Kjær Solution Next we will answer the question: how is modal analysis realised.We will describe the techniques including the requirements for measuring equipment and the different signal processing tools.
131 2 3 4 How to do Modal Testing Modeling Measurements Curve fitting GeometryDegree of Freedom definitionX or XYZ direction1MeasurementsFrequency Response FunctionsHammer or shaker excitationCoherence Function for validation2Curve fittingFrequencyDampingResidues3The Four steps of Modal Testing areModelling An important step in modal testing is to make the optimal test model. The first step is to create a geometrical model in the computer. The second is to define DOFs for the measurements. A DOF (degree of freedom) is a point with associated directions. One point can consist of up to 6 DOF’s (three directions and three rotations).Measurements The FRFs must be measured for the Modal Post processing. Often other functions such as Autospectra and coherence are measured for the validation of data.Curve fitting is the process which extracts the modal parameters from the measured set of FRFs.Validation is important to do before the data are used for Simulation or comparison with FEM data. Validation takes place both after the measurements e.g. by evaluating the coherence function, as well as after the curve fitting by evaluating functions as:MAC (othogonality of mode shapes)Modal Confidence factor (Validation of the mode being a physical rather than a computational mode).Phase Scatter (complexity of mode shapes)ValidationMAC (Modal Assurance Criteria)Modal Confidence FactorPhase Scatter4
14System Analysis Determination of the inherent properties of the system Excitation of the system by a known forceMeasurement of the OutputRelating the Output to the InputInputOutputFrequency Response Function:ExcitationResponseForceMotionInputOutputH(w) ==The goal of system analysis is to determine the inherent properties of the device under test. This is done by excitation of the structure by means of a known force, and measurement of an output.Different algorithms are used for relating the output to the input in order to indicate the properties of the structure.The aim of these algorithms is to calculate a quantity, which is independent of the excitation signal in order to extract information about the structure itself and not about the external environment.A simple way could be to divide the output by the input. Provided linearity of the input relationship when the input doubles the output will also double, so in this case the quantity becomes independent of the input.The excitation is most often measured by means of a force transducer mounted on the tip of a hammer or on an exciter.The response can be measured by different means, but a very popular way is to measure this with an accelerometer.The FRF shows the inherent properties of a dynamic system — independent of the excitation force and type
15Frequency Response Function FFTFrequency DomainTime DomainOutputInverseFFTInputFrequencyResponseFunctionImpulseResponseFunctionLet us follow the measurements through the analysis chain.In the figures shown above are typical signals obtained when using the impact of a hammer as excitation.The signal from the hammer is ideally a single pulse, and the response, as measured by an accelerometer, is a decaying signal depending both on the excitation signal (hammer impact) and the dynamic properties of the structure under test.Having recorded the time signals, they are processed by means of a Fast Fourier Transform (FFT), and the outcome is typically a very broad spectrum from the excitation signal, and the response spectrum is somehow weighted by the dynamics of the structure.Dividing the two spectra will create the Frequency Response Function which then is the estimator of the properties of the structure itself, rather than properties of the external environment.To optimise the measurements, such as reducing influence of noise in the measurements, averaging of the FFT signals is most often used.For the same reason the simple division of input and output is most often replaced with cross spectrum calculations the so called H1 and H2 etc.If it for some reason is preferable to carry out the processing in the time domain, the frequency response function can be processed in an inverse FFT and the Impulse response function calculated.For large structures the hammer is most often substituted by one or more shakers to which different signal types are supplied from a generator.FFTExcitationResponseForceMotionInputOutputH(w) ==
16Natural Frequency and Modal Damping Modal Model – Global ParametersNatural Frequency and Modal DampingFrequency DomainTime Domain13 dB bandwidth= 2 Decay Rate3dBs =tTimeFrequencytw0TThe aim of the modal model is to describe the very often complex response of the excited structure by the properties for each resonance namely the resonance frequency, damping and the modeshape, which can be expressed as the characteristic vibration pattern for a particular resonance.The transformation from frequency to modal domain is known as curvefitting. The curvefitting process will for each mode fit a SDOF model in the Frequency response function.Often time domain is used, then we use the impulse response function.The frequency and damping are considered as global parameters, this means, that they are of the same value independent of where on the structure they are measured.Above is a simple example of curve fitting. In frequency domain the peak of the FRF is an indicator of the resonance frequency and the bandwidth an indicator of the damping. Higher damping means larger bandwidth. Frequency is indicated in Hz and damping most often is expressed as a fraction of critical damping.In the time domain, frequency is determined by the oscillation, and damping by the decay rate. The faster decay the higher damping.Natural Frequency:w0 = 2pf0Natural Frequency:Damping Ratio:Damping Ratio:
17The Driving point Residue scales the Mode Shape Modal Model – Local ParametersResiduesResidue: The “strength” of the modeH(w0)2 AmplitudeFirstModeDistanceSecondModeThirdModew0FrequencyResidue: R = H(w0) · sFrequencyThe third modal parameter is the residue. The residue can be explained as a quantity describing the strength of the mode. Although it has no direct physical meaning, it is somehow related to the height of the FRF peak at a resonance.In our example, the beam, it can be seen that the amplitude is dependent on where we measure. So, whereas frequency and damping are global parameters, the residue is a local parameter.ModalDomainViewDriving point Residue: Riir = a · yir2General Residue: Rijr = a · yir · yjrFrequency Domain ViewBeamForceThe Driving point Residue scales the Mode Shape
18Excitation Technique Hammer excitation Shaker excitation Excitation movedMultichannel response orresponse points may be movedInOutInOutSmall homogenous structuresQuick Polyreference techniqueFast method - no fixtures requiredLarge or complex structuresVarious excitation signals possibleTime consuming - installation work to be doneNormally we talk about two different types of excitation techniques, shaker and hammer excitation.Using hammer excitation, the hammer is moved from DOF to DOF and the response normally measured at one of the DOFs.The hammer excitation is easy to use, and free from leakage.Using shaker excitation, a shaker need to be attached to the structure, and all DOFs measured at the same time or one by one moving the accelerometers from DOF to DOF.The shaker excitation is more cumbersome but can take advantage of the different generator signals in PULSE. Some of these signals are leakage free like hammer excitation.
19Curve Fitting Single Degree of Freedom (SDOF) Simple structureFew and widely spaced modesMulti Degree of Freedom (MDOF)Multiple modesMany and close modesLocalBased upon one single DOFGlobalBased upon multiple DOF’sPolyreferenceSymmetric structures exhibit multiple modes at the same frequencyOne single peak does not necessarily mean one modeCurve fitting is the tool for the transformation from frequency to modal domain by estimating the modal parameters.Multiple techniques have been developed in the history of modal analysis. Many based on the mathematics of Least Square Polynomial curve fitting.Either time- or frequency domain data are used for the curve fitting.The simplest type of curve fitters are the SDOF types. They operate assuming only one mode per resonance peak in the FRF. They are useful for simple objects for educational training and for the first rough estimates of the modal model.The MDOF curve fitters must be used for most practical structures, where modes are influencing each other.Often in highly symmetrical structures the problem appears, that several modes occur at the same frequency. This problem is known as multiple modes. For solving this problem the polyreference technique is used.The input data needs to have more than one reference i.e. excitation at several points on the structure.
20How to do Modal Testing Modeling Measurements Curve fitting Validation GeometryDegree of Freedom definitionX or XYZ directionMeasurementsFrequency Response FunctionsHammer or shaker excitationCurve fittingFrequencyDampingResiduesTo recap on the process of modal analysis we talk about 4 steps.1. The creation of the modal test model. Often a computerised geometry model already in existence prior to the test. The task is then to define which of the points on the structure to measure at, and in which direction measurements are to be made.This step of the process is very important, because the goal is to limit the number of measurements, and not to do unnecessary, time consuming, installation work. But on the other hand, to choose the right points to create a useable modal model.Often a part of an FEM model is used, and the advantage is that the FEM analysis gives a lot valuable information for creating the best Modal test model.2. The measurement is often the most time consuming step. What takes time is the installation of the transducers and their set-up, which can often be 80% of the complete test time.As discussed, the FRF is used for the curve fitting, but often other functions are important for validation. We can mention Coherence, Autospectrum etc.3. Many software packages have a wide variety of curve fitters, so it is important to choose the right one for the job.4. Validation is important to do before the data are used for Simulation or comparison with FEM data. Validation takes place both after the measurements e.g. by evaluating the coherence function, as well as after the curve fitting by evaluating functions as:MAC (othogonality of mode shapes)Modal Confidence factor (Validation of the mode being a physical rather than a computational mode).Phase Scatter (complexity of mode shapes)ValidationMAC (Modal Assurance Criteria)Modal Confidence FactorPhase Scatter
21Brüel & Kjær Solution Modal Testing What Why How The next part is a description of an example of instrumentation for Modal testing.The Brüel & Kjær PULSE Modal solution: The Modal Test Consultant bases its concept on the experience that in modal testing the installation and set-up time is often 80% and the post-processing is only 20%.The Modal Test Consultant bases its functionality on cutting down the 80% and being open to all major modal post processing packages.
22The Brüel & Kjær Solution PULSEinsideModal TestConsultantVibrationDataModalSoftwarePULSEFileTransferThe Modal Test Consultant is an application shell on top of PULSE. It assists the user in setting up the measurement, performing the measurement and organises the vibration data before they are transferred to a Modal Application for postprocessing.In practice, the Modal Test Consultant, a true native Windows NT application, is installed on a computer together with the Multi Analyzer Software PULSE and a Modal Application. The solution uses the PULSE system including the Noise and Vibration Analysis Package type 7700 but the whole operation is controlled from the user interface of the Modal Test Consultant.The Modal Test Consultant is a must in any sound and vibration analysis toolbox.
23Brüel & Kjær Solution PULSE Software Predefined projects for typical hammer, shaker testsContains predefined measurement setuptrigger conditions, weighting functions, multi-bufferEasy data display using workbook layoutsTime, Autospectra, FRF H1, H2, H3, CoherenceFRF Display of Magnitude and Phase, Real and Imaginary, Nyquist plotThe PULSE system takes advantage of the predefined projects. They contain all information of the analyser set-up for reuse next time a similar measurement has to be performed.Data of Autospectra, FRFs etc. can be exported in many different formats.
24PULSE Modal Test Consultant Features and BenefitsGeometry driven measurementwith the option of importing geo-metry from CAD dataIntuitive graphic control of analyzer parametersCuts your setup and measurement time in halfModal data acquisition your waycomprehensive choice of Modal Post-processing packagesFeedback from many people working with Modal Testing has concluded that 80% of the time is spent on installation and set-up and only 20% on Modal Analysis post processing.As the Modal Test Consultant attacks the 80% of the work, the total testing and analysis time can can be drastically reduced.Modal testing your way. The Modal Test Consultant is by default delivered as an icon-driven application providing a logical sequence for performing the test. The user interface is based around the latest windows interface as used in the MS Windows® environments (e.g. MS® Outlook and Frontpage).But incase items such as geometry, analyzer set-up etc. have to be reused, the sequence is customisable. This makes the Modal Test Consultant versatile and dedicated at the same time.
25PULSE Modal Test Consultant The Modal Test Consultant based on PULSE gives the user:OpennessScalabilityModularityProductivityEase of useModal Test Consultant enforces the issues of PULSE includingOpenness to all major Modal Analysis Post-processing packages.Scalability: handles all from the smallest hammer excitation jobs up to big shaker excitation of big structures.Modularity: the Modal Test Consultant is the first application using the new PULSE container concept, which makes PULSE at the same time the optimal choice for both versatile and dedicated test jobs.Productivity: Modal Test Consultant saves time and therefore money for the usersEase of useIntuitive de-facto standard user interfaceMeasurements driven by a geometry modelIntuitive graphical supported setting of analyzer parameters such as time weightingEasy data transfer between PULSE and modal post-processing packages.OLE AutomationBrüel & Kjær PULSETM
26PULSE Modal Test Consultant Mountingthe transducerSetting up measurementsTransducer mounting guided by geometry model on screenGraphic supported set-up of measurement parametersAudio and visual notification of measurement statusAutomatic DOF labelinglabel while measuringGeometry modelon screenDedicated practical tools for transducer mounting makes installation and correct alignment easy. Free alignment of transducers can save much time on creation of the geometry model.The attachment of the various transducers to the structure is guided by means of the geometry on the screen. First the transducers are connected to the frontend according to the hardware setup table. Hereafter they are excited either by means of a calibrator or just simply by shaking them in the hand while symbols on the geometry are flashing indicating where to mount the activated transducer.Various analyzer parameter settings are supported by graphical tools. An example is the setting of time weighting. Both the weighting and the signal is visible on the screen, so the weighting can be optimised for the signal by simple mouse dragging.The PULSE notification system is used intensively for indication of the measurement status. As an example, the overload information both goes to the geometry model and to an indicator, which can be resized enabling visibility from a distance. Also audible status information is provided.The above means that the Modal Test Consultant provides the full data information such as DOF annotation fitted for the modal post processing tool.Time weightingOverload indication
27Easy Scaling and Set-up of Hammer Excitation Hit the test object in a number of different places and …..1 Autorange or select Input Range2 Select Trigger LevelFor a typical hammer test four parameters need to be set:Input RangeTrigger LevelTime WeightingPre-triggerTo set up the input range and trigger level the analyser is set to run in a free-run mode while the structure is excited in different DOF’s. The result is a time function, where two cursors appear one for Input Level and one for Trigger Level.The Input Level cursor should then be set to a value higher than the maximum impact, and the Trigger Level to a level smaller than the smallest.The trigger is now set, so the next step is creating an impulse using the trigger settings just made.The weighting can now be graphically adjusted around the impulse directly on the screen by dragging the beginning and the end of the weighting using the computer cursor.Hit the test object once and …..3 Choose Time Weighting4 Set Pre-trigger
28PULSE Modal Test Consultant Create Test Model from geometryGeometry creationImport geometry via DXF and UFF file formatEasy-to-use geometry drawing toolsTest ModelAssign DOFs to geometryExportGeometry modelDOF informationThe geometry model can be created by means of tools in the Modal Test Consultant or imported from the modal analysis or FEM software.After having been used in the Modal Test Consultant the geometry model can be exported into the modal analysis software. This process ensures, that the same model is used both for the testing and for the analysis.The model can also be imported from CAD packages as AutoCAD as it supports also the .DXF format. This ensures that the correct model is also reused from the rest of the design process.If an FEM or CAD model is used, the first task in defining the test model is to select a subset of points for the testing and in cases where animation is to be used, a simplified geometry model based on these points.
29PULSE Modal Test Consultant Measurements are guided by a geometrical modelA time consuming issue in modal testing is the bookkeeping. Here we are talking about the channel- transducer information and settings as well as their their position on the physical object under test.The Modal Test Consultant makes use of geometry driven measurements and sensible tabular overviews of relevant information. Geometry driven measurements is the technique whereby information for any given DOF can be accessed by just clicking on the computer model (geometry) DOF onscreen. This makes the whole process very intuitive as physical setup and response parameters are related directly to the onscreen geometry.The Geometry Model is also used for the detailed planning of the measurement sequence.
30PULSE Test Consultant for Modal Set up of signal parameters using tables*Table forms are intensively used throughout the Modal Test Consultant. These give a good overview of the set-up giving the user a comfortable sense of not having done any of the myriad's of settings wrong.The tables can be customizer to suit individual needs.* The tables can be customizer to suit individual needs
31PULSE Test Consultant for Modal Set up Measurement conditionsAuto-ranging signalsusing graphic supportTrigger conditionsTrigger level (impact test)Pre-triggerTime weightingTransientExponentialHanning, ...Analyzer set up is also done using graphical support.Settings such as:Trigger levelTime weighting typePre-triggerare visualized together with the signal ensuring optimal setting of all parameters.This is especially of importance when hammer excitation is used because this is often causing problems.Warnings such as overload are clearly indicated on the screen, and can be maximized for increased visibility at a distance.Automated TransducerCalibration
32PULSE Modal Test Consultant Data transfer to modal softwareData transfer ofgeometry model and DOF informationmeasurement dataVia file transferUniversal File ASCIIUniversal File BinaryStar BinarySDFVia OLE automationAutomatic transfer to ME´scopeData transfer to modal analysis packages of :Geometry modelMeasurement data: Time, Auto spectra, FRF etc.Via file transfer to most standard modal analysis packages andvia OLE automation to packages which support this, such as ME’scope.
33Measurement data transfer to modal software Via file transferUniversal File ASCIIUniversal File BinaryStar BinarySDFVia OLE automationAutomatic transfer to ME´scope(Bridge to ME’scope)Data transfer to modal analysis packages of :Geometry modelMeasurement data: Time, Auto spectra, FRF etc.Via file transfer to most standard modal analysis packages andvia OLE automation to packages which support this, such as ME’scope.
34PULSE Modal Test Consultant Automatic Data Transfer to modal softwareBefore data transfer the user must decide:which type of functions to be used by the modal analysis softwarewhat data format to use in the transferMost modal analysis packages support the UFF format, but also STAR, Star binary and ME’scope format is supported by the Modal Test Consultant.The settings made here are stored together with the project so there is no need to define this for every single test.
35PULSE Modal Test Consultant The Modal Test Consultant link PULSE to major modal analysis post processing toolsReuse of existing softwarePost-processing of modal data as an integral part of Modal TestingFileTransferBrüel & Kjær PULSETMOLE AutomationME’scopeTMOLEAutomationSTAR, I-DEASTMAs Modal Test Consultant being a true native Windows NT® application, it supports OLE Automation also called ACTIVE-X.The direct advantage is, that modal packages like ME’scope also supporting this, can integrate Modal testing and analysis in one single PULSE environment.
36PULSE Modal Test Consultant Geometry driven reliable Modal Testing resultsCreate test model from geometrySet up measurement conditionsPerform measurementsTransfer data to modal softwareWe have described how the Modal Test Consultant assists in performing Structure Dynamic measurements in a safe and easy way.It has been shown how PULSE equipped with this application provides assistance:Creating test model from geometryProviding set-up measurement conditionsPerforming the measurementsTransfer data to modal post processing software
37Brüel & Kjær PULSETM ME’scopeTM PULSE Bridge to ME’scope The PULSE Bridge to ME’scope makes PULSE and ME'scope an integrated environment from the measurements to the result of the modal analysis: the modal model. It provides fast and efficient data transfer throughout the entire process. This means that the correct results will be achieved in a much shorter time compared to using data transfer between different software packages.Brüel & Kjær PULSETMME’scopeTM
38Automatic Measurement Data Transfer To use PULSE Bridge to ME’scope, you activate the program directly from Windows via its icon. By clicking the “Load PULSE Project” button you automatically get the PULSE Open dialogue box. Here you can select the project with the required measurement data. On selecting a project, the contents of its Function Organiser appear showing the Function Groups in the PULSE Bridge to ME’scope program window. You simply check the box next to the data you wish to transfer to ME’scope, and click on the Export to ME’scope button.It must be noticed, that the functionality of the Bridge is included in the Modal Test Consultant.The Bridge is an Active-X based software. This gives the option, in addition to direct data transfer via a UFF file, of having operation of software and data transfer done in one step.The Bridge can also be inserted as an object in a PULSE Worknote.Load PULSE ProjectExport to MEScope
39Modal Software Available through Brüel & Kjær: STAR (Spectral Dynamics)The STAR SystemTM Modal and Structural Analysis - Type 7750ME’scopeTM (Vibrant Technology, Inc)Brüel & Kjær ME’scope - Type 7754I-DEASTM Master Series (MTS)I-DEAS TestThe following modal post processing packages are available through Brüel&KjærSTAR (Spectral Dynamics)ME’scopeTM (Vibrant Technology, Inc)I-DEASTM Master Series (MTS)These packages are fully supported by the Brüel & Kjær solution specialists.A lot of other modal analysis packages can also work with the Modal Test Consultant, the only requirement is that the package should support the UFF file format, which all major packages do.The advantage of the architecture where PULSE, Modal Test Consultant, and 3rd party modal software are combined is that:The PULSE Modal solution is always open to the latest developments in modal analysisExisting modal users can still use the modal package they already have.Openness to other software:ICATS (Imperial College, London)LMS
40Modal Analysis software Beyond Modal TestingObtain modal parametersNatural FrequencyModal DampingResidues (Mode shape)Validate modal parametersPhase ScatterMACModal Confidence FactorSimulationsAdd massChange stiffnessTuned absorbersBeyond the modal testing comes the stages where users get the advantage of having done the Modal Testing.First the extraction of the modal parameters which is covered by this material.The important part is the validation of the modal parameters.Only when this is done to a level of satisfaction, can the user get on with the tasks where the time spent on the testing is repayed, the simulation and the validation against the finite element model.Validate FEM Models
41Conclusion to Modal Testing WhatObtain Modal ModelTrouble shooting, FE Modeling, Structural assembly analysis, SDM and FRSModeling, System Analysis Measurements,Curve fitting, Validation of Modal ModelPULSE Modal Bridge to ME’scopeModal Test ConsultantWhyHowResuméBrüel & Kjær Solution
42Operational Deflection Shapes Investigation (visualisation) of structure behaviour under “running conditions”Powerfull trouble-shooting toolPhase information neededData to be measured:phase assigned spectra (f.ex.between response point and tacho (reference))orFRF between response point / reference pointCross spectraNo Curve - fittingWith the advent of the aircraft industry, it was not only necessary to test structures for their static load capabilities, but also to investigate their behaviour under dynamic loading to verify the design parameters of the structures. The field of Structural Dynamic Testing as it was then called, has developed both theoretically and experimentally over the years, and is widely used today in all advanced industries under the terminology – Modal Analysis and Modal Testing.The purpose of this lecture is to describe what is Modal Testing, explain why we do Modal Testing and illustrate how Modal Testing is carried out in practice. Finally, the features incorporated in Brüel & Kjær instrumentation to facilitate Modal Testing will be highlighted.
43Measurement data transfer to ODS /modal sw Via file transferUniversal File ASCIIUniversal File BinaryStar BinarySDFVia OLE automationAutomatic transfer to ME´scope(Bridge to ME’scope)Data transfer to modal analysis packages of :Geometry modelMeasurement data: Time, Auto spectra, FRF etc.Via file transfer to most standard modal analysis packages andvia OLE automation to packages which support this, such as ME’scope.
44Literature for Further Reading Frequency Analysis by R.B.Randall(Brüel & Kjær Theory and Application Handbook BT )Modal Analysis of Large Structures - Multiple Exciter Systems by K. Zaveri(Brüel & Kjær Theory and Application Handbook BT )Modal Testing: Theory and Practice by D.J. Ewins(Brüel & Kjær Theory and Application Handbook BT )Dual Channel FFT Analysis by H. Herlufsen(Brüel & Kjær Technical Review No. 1 & 2, 1984)Structural Testing, Part 1: Mechanical Mobility Measurement by O. Døssing(Brüel & Kjær Theory and Application Booklet BR )Structural Testing, Part 2: Modal Analysis and Simulation by O. Døssing(Brüel & Kjær Theory and Application Booklet BR )