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  • Users: Xtina
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  1. Xtina

    Multiple regression with 2 categorical variables

    Hi all! I would like to know how to obtain a regression model to make predictions about the value of a dependant variable if the independent variables are categorical.I read about transforming them into Dummy variables, but I don't know how to do it in Statgraphics. I would like to estimate the...
  2. Xtina

    Modal Shape from Experimental FRF

    The experimental data behaves in the same way as the numerical model, that is, it also provides FRFs which real parts are maximum at resonance instead of zero. So my experimental data also contradicts the theory... My objective is to create a model that behaves as the real beam, and the way of...
  3. Xtina

    Modal Shape from Experimental FRF

    And here the FRF plot. ¡ Thanks for your attention !http://files.engineering.com/getfile.aspx?folder=72773756-0f28-4dee-a183-d33f37f787a0&file=FRF_receptance.JPG
  4. Xtina

    Modal Shape from Experimental FRF

    Here is the pdf of the modal shape formulae.http://files.engineering.com/getfile.aspx?folder=a6763814-8a7e-4b70-9cd7-5844be1fc203&file=Modal_shape.pdf
  5. Xtina

    Modal Shape from Experimental FRF

    Thanks Greg for your help. You can find attached the plot of my FRF and also an excel with the accelerations measured in case you can process them. I have to say that my acceleration data have been obtained from a transient analysis in ANSYS, in which I impacted the simply supported concrete...
  6. Xtina

    Modal Shape from Experimental FRF

    Yes, it sounds wrong but I drew my modal shapes from the real parts (as they do in the thesis) and it seems to be correct, I obtained the typical bending shapes of a simply supported beam... I found the first and second bending shapes at the first and second frequencies and the third bending...
  7. Xtina

    Modal Shape from Experimental FRF

    No, I measure accelerations and obtain the accelerance, but then I get the receptance (as if I had taken displacements) with the expression: H(w)=Ha(w)/(-w^2) where H(w) is the receptance, Ha(w) the accelerance, and w the frequencies. In both cases, accelerance or receptance, the real part...
  8. Xtina

    Modal Shape from Experimental FRF

    Thanks electricpete for your explanations. The way I am using to obtain the mode shapes is explained very simply and fast in this pdf: http://macl.caeds.eng.uml.edu/umlspace/aug99.pdf It says that the imaginary part of the FRF is directly related to the residues, and the residues to the modal...
  9. Xtina

    Modal Shape from Experimental FRF

    I correct: "so I can observe peaks in the real part that provide the correct modal shapes and values of zero in the *imaginary* part for the resonant frequencies"
  10. Xtina

    Modal Shape from Experimental FRF

    Hi all, I am performing an experimental modal analysis of a beam and I am trying to get the mode shapes from the FRF measured. I have read in many articles and books that the mode shapes (unscaled) may be obtained from the peak amplitudes of the imaginary part of the FRF, as in lightly damped...
  11. Xtina

    Modal analysis ANSYS Simply supported beam

    Thank you for your respones. The fact is that the measured spectra in laboratory is very clear and eigen frequencies can be obtained using the accelerations without problems, but the model does not provide the same results... and then was when I tried to run the modal analysis without...
  12. Xtina

    Modal analysis ANSYS Simply supported beam

    Hi all, i am performing a modal analysis of a beam in ANSYS. In the laboratory, the beam is supported on transversal steel bars, so vertical positive displacements are allowed when I hit it with the hammer, and the bars are fixed to the ground. If I model the supports as typical rigid supports...
  13. Xtina

    Modal analysis ANSYS-Simply supported beam

    Hi all, i am performing a modal analysis of a beam in ANSYS. In the laboratory, the beam is supported on transversal steel bars, so vertical positive displacements are allowed, and the bars are fixed to the ground. I tried with contact surfaces between the beam and the steel bars with standard...

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