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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...

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...

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...

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%...

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...

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

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...

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...

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...

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...

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...

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...

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

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...

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...

Raymond, if the beams are showing greater deflection than Euler theory, then I still suspect the missing shear term in the theory. One way to test this is to manually increase the shear stiffness factor on the beams. The idea is that if you set this to a very high value it replicates the...

Raymond, I worked in tech support for several nastran providers and this came up every once in a while. The finite element models will include bending stiffness terms and shear stiffness terms, whether they are created using beams, shells or solids. (more later on relative accuracies). Euler...