Tutorial at SURVISHNO

Error characterization in modal analysis and model updating. An overview of tools and procedures using the Structural Dynamics Toolbox.

will be presented by Etienne Balmès at the SURVISHNO conference in Lyon on July 8, 2019. This tutorial will mix theoretical considerations and applications using SDT (animations https://www.youtube.com/channel/UCy5PHLw70NqfDDvg24tXJWg , presentation www.sdtools.com/pdf/Vishno19_Tutorial.pdf )

Experimental modal analysis seeks to extract shape and resonance properties from test data. While identification algorithms have been well documented for a long time, at least under the assumption linear behavior, significant differences continue to exist in the implementation details. In particular, non-linear optimization of poles and work by sub-bands is an often overlooked necessity to avoid bias. Once modal data available, the next step is to obtain test/analysis correlation. This requires topology correlation which brings its share of errors, which despite being usually small should be addressed. Global correlation criteria, such as the MAC, are introduced next but for efficient use should be complemented by a set of procedures to localize measurement, topology and correlation errors. While the simple evaluation of correlation is often an industrial objective, the best exploitation of test results is achieved using hybrid approaches combining test with a model, which does not need to be exact to usefully complement the measurements. In particular, expansion methods estimating the full Finite Element responses from data measured at sensors are particularly useful. Energy based criteria on the model side (Minimum Dynamic Residual Expansion or the various variants of Error in Constitutive Relation) have been long known to provide excellent solutions but deployment has been scarce due to an important numerical cost. Simple model reduction strategies are shown to give excellent results for industrial models and open the way for model error localization and updating.

The tutorial is illustrated using standard procedures implemented in the Structural Dynamics Toolbox which provides experimental modal analysis, finite element modeling, model reduction and correlation tools in the MATLAB environment. A main brake squeal application serves a red line and is complemented by illustrations from other industries.

SDT 7.1 released

SDT 7.1 is the only version fully compatible with MATLAB 9.4 (2018b) to 9.6 (2019a) mostly due to changes in the representation of complex numbers in MATLAB. Key changes of this release are

    • A continued effort in making the experimental modal analysis part of SDT section 2.2 fully accessible without any script is nearly complete. Functions however obviously remain accessible from the command line to users will to learn how to use them. The associated docks Id (for experimental modal analysis see section 2.2), CoTopo (topology correlation see section 3.1) and CoShape (test/FEM correlation see section 3.2) have been extended and tutorials have been introduced.
    • A major effort was put on the documentation. The new structuration of demos into tutorials helps training. You can for example see tutorials in various files with d_mesh(‘tuto’), gartid(‘tuto’), d_cor(‘tuto’), d_cms(‘tuto’), …. Equations are now shown as SVG files which improves readability, but may pose problems on some older versions of MATLAB where the help browser does not support SVG.
    • We are still working with the MathWorks on improving reliability of the help browser. To bypass some bugs, you may have to change default location where the help is shown using sdtdef(‘browser-SetPref’,‘-helpbrowser’) or sdtdef(‘browser-SetPref’,‘-webbrowser’). For clickable areas of SVG figures, use Ctrl-Click to open in a new window or right-click and select Open in a new tab.

Outside improved robustness of the GUI, key changes for FEMLink are

    • ans2sdt extended BDF reading in particular for orthotropic materials and substructure export (to ease superelement import). Job submission integration is now supported as a consulting project feature.
    • nasread compatibility with NX Nastran BGSET and BSURFS cards. Documentation of superelement (see d_cms(‘TutoNasCb’)). Performance of MAT9 and set reading.
    •  abaqus significant .inp reading improvements *distribution,*hyperelastic, set handling, … Performance of large .fil reading. Robustness and performance enhancements of resolve commands. Introduction of a .dat reading framework for customer use, with complex modes output reading support.

You can download SDT 7.1 from www.sdtools.com/faq/Release.html

Keynote lecture of Etienne Balmès, CEO of SDTools, at the ISMA conference

Etienne Balmès, CEO of SDTools was invited as a keynote speaker at the ISMA (International Symposium on Modal Analysis) conference in Leuven, Belgium on September 17, 2018.

ISMA 2018 is the 28th international conference in a series of annual courses and biennial conferences on structural dynamics, modal testing and noise and vibration engineering, organised by the Department of Mechanical Engineering of the KU Leuven., and is a reference in the field of structural dynamics and vibro-acoustics.

Shapes & DOF: on the use of modal concepts in the context of parametric non-linear studies

copy of the slides (pdf)

Physical responses tend to lie within restricted subspaces even for parametric problems. For a given subspace, the choice of a basis defines Degree Of Freedom (DOF) and this choice may give interesting meaning to the associated amplitudes. Classical modal analysis builds subspaces combining modeshapes and static responses. Parametric loads for non-linear, damped, variable, … structures are discussed to extend the theory and illustrated for test and simulation cases. Challenges in shape extraction and basis generation techniques are then detailed. Introducing the ability to manipulate models with variable junction properties, component material and geometry, load and operating conditions, … opens new questions on the quantification and tracking of changes and objectives throughout design exploration. The definition of a reference linear system and the use of global and/or local modal DOF are shown to provide an interesting perspective.

SDT 7.0 released

SDT 7.0 is now released.

SDT 7.0 is the only version compatible with MATLAB 9.2 (2017a), 9.3 (2017b) and 9.4 (2018b) mostly due to ongoing improvements of MATLAB graphics. Key changes of this release are

  • A full rewrite and major extension of modal analysis graphical interfaces and documentation detailed in section 2.2. Step-by-step tutorials, such as  section 2.2.1, include buttons of the form Run which you can use to execute a step. LSCF and stabilization diagrams are now supported.
  • The new notion of docks corresponds to MATLAB docks where multiple figures are combined for a typical use. Currently supported docks are
    • Id : for experimental modal analysis see section 2.2
    • TestFEM : topology correlation see section 3.1
    • MAC : test/FEM correlation see ii_mac.
  • A major update of SDT GUI with most existing tabs ported to Java mode and necessary in docks. You can set the default tab to Java mode using sdtdef(‘JavaUI’,1) or turn it off with sdtdef(‘JavaUI’,0). User documentation of tabs can be found in section 8.2. Developer level documentation of GUI functions is now included in section 8.
  • Use sdtweb(‘feplot’,‘webbrowser’) to bypass the not yet fixed MATLAB bug where the links within pages are not called appropriately.

Key changes for FEMLink are

  • ans2sdt improved import of .cdb and support of contacts.
  • nasread Direct import of EXTESOUT output to SDT superelement format. Continued enhancements of bulk and op2 reading. Initial support of .op2 format writing of responses.
  • abaqus continued enhancements of .INP reading in particular for composites and superelements, contact, … Significant writing enhancements.
  • GUI import of models is supported with the FEMLink tab, section 8.2.2.

You can download SDT 7.0 from www.sdtools.com/faq/Release.html