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Recent content by fetraining

  1. fetraining

    short cut to fixed cell definition input type $A$1

    I have been shown in the past how to use a built in hot key or function key to make any cell reference in an equation a fixed reference, on the fly. However I have forgotten how and can't find any reference in the help documentation. So instead of clicking on cell A1 when building an equation...
  2. fetraining

    Scaled modal analysis?

    Adubeng, thinking about this some more: The usual way to do a fatigue analysis using a real vibration environment is to use a random vibration analysis. That is a 'full blown harmonic' analysis as you describe it, followed by a PSD factorization to get an output PSD and then RMS stress levels...
  3. fetraining

    Scaled modal analysis?

    All, The stresses from a normal modes analysis are in general meaningless in their own right, but there are some ways they can be interpreted and used after some manipulation. One of these is via the Modal Effective Mass (MEM) concept. This is the basis for shock response methods and an outline...
  4. fetraining

    Objective value to compare the vibration of two (similar) systems

    Tralala, The RMS calculation would be a way to compare motors, but it might be misleading. If the distribution of acceleration in the time history is 'normal' in a statistical sense then the RMS value is the standard deviation (or 1 sigma) of the acceleration - there is approximatly a 68%...
  5. fetraining

    Keeping zero as a real value in the Concatenate Function

    ElectricPete my original intention was to just avoid integer 0's. But you guys have opened my eyes to all sorts of options - thanks! Just to make it more interesting, the actual format is an 8 column field, a real number must have a decimal in it. This means in practice that it is a compromise...
  6. fetraining

    Keeping zero as a real value in the Concatenate Function

    electricpete, thanks - the sample spreadsheet you uploaded is very useful for experimenting with, regards, Tony Tony Abbey www.fetraining.com
  7. fetraining

    Response Spectrum to PSD?!

    TomEME, I thought about it some more and read the abstract of the reference paper more carefully. It seems there may be a route through this, but I don't know what the assumptions are behind it. I think that most certification authorities would view it as a bit radical to do a random analysis...
  8. fetraining

    Keeping zero as a real value in the Concatenate Function

    electricpete, thanks for the tips on TEXT and formating via a named range. That has given a very neat solution. I experimented with the the data to go in the range. I am not clear what the implication of *;*;0.000 is. Now you have given me the hint I have read up on named ranges and format...
  9. fetraining

    Keeping zero as a real value in the Concatenate Function

    I use the Concatenate function a lot to group data into a comma deliminated string to paste into various FEA input files. A simple example is to calculate x,y,z grid coordinates, say (23.4,45.6,78,9) stored in A2:A4 and then produce a string such as: " GRID,23,23.4,45.6,78,9" where GRID is...
  10. fetraining

    Harmonic analysis with ANSYS and damping ratio

    crisbunget, I think the rteason for the apparent resonant frequency shift in the frequency response analysis is beacuse you are changing the boundary conditions in several of the loading caes. If the longitudinal natural frequency of 18525 Hz is found from a free-free normal modes analysis...
  11. fetraining

    Response Spectrum to PSD?!

    TomEME, This is a long reply – but the topic is complicated! The bottom line is I don’t know a way of taking an SRS input curve and turning it into a PSD input curve. In many industries structures have to be qualified by analysis against both an SRS loading specification, and a PSD curve...
  12. fetraining

    Finite element meshing

    longisland, a triangular shaped element with three nodes will generally have an inferior performance to a quadrlateral shaped element with four nodes. This manifests itself in poor internal mappping of the stress distribution in stress gradient regions and a tendancy to be over stiff. Different...
  13. fetraining

    Simple beam bending FEM vs. theory comparison error

    rb1957, thanks for spotting that - yes I mislabeled it as $ rectangular solid 10 by 8 select PBEAM 3 It should read ' 10 by 10 ' just to confirm the model file and hand calcs are for a 10 by 10. regards, Tony
  14. fetraining

    Simple beam bending FEM vs. theory comparison error

    Raymond, I'm new to the forum so this is my attempt to upload the Nastran file. it is called 'beam_shear_test.nas'. Both beam property types (I and rectangular) are in the deck, plus annotated comment/uncomment lines for k. regards, Tony...
  15. fetraining

    Simple beam bending FEM vs. theory comparison error

    Raymond, I am still convinced the shear stiffness term missing from Roark is the culprit. Particularly as you have a short stubby beam where this is an important term. I set up a nastran beam model with length L = 60 ins, center load W = 10,000 lbs. I beam 10 ins deep , 8 ins wide. E = 1.07e7...
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