What numerical engine do commercial FEA codes use for modal transient analysis? The Newmark-beta method?
I have posted a paper on a ramp invariant digital recursive filtering relationship for modal analysis at:
http://www.vibrationdata.com/ramp_invariant/force_ramp_invariant.pdf
Please let...
I am uncertain about the formula in your reference.
But here is a tutorial which derives natural frequency formulas for various beam configurations.
http://www.vibrationdata.com/tutorials2/beam.pdf
Tom Irvine
Yes, ten sources with the same Sound pressure level (SPL) will and have a combined SPL that is 10 dB greater than just one source.
Here is a Matlab script that can be used to demonstrate the calculation:
disp(' ');
disp(' add_dB.m ver 1.0 February 9, 2010');
disp(' by Tom Irvine ');
%
disp('...
A Fourier transform and a shock response spectrum are two different calculations. Yes, there are some roundabout, indirect, relationships between the two functions; but please consider them separate for now.
I have posted a shock response spectrum tutorial at...
I have written a paper called: Shaker Table Seismic Testing of Equipemnt using Historical Strong Motion Data Scaled to Satisfy a Shock Response Spectrum
It is posted at:
http://www.vibrationdata.com/quake_syn.pdf
I hope to present it at a conference although I have not selected one yet.
I...
Can someone recommend a reference that gives formulas for analyzing the centrifugal twisting moment of a propeller blade with variable pitch?
Thank you,
Tom Irvine
Kyle,
This idea is not ready for SolidWorks. It first needs to be tried out using a subscale prototype made from hardware store parts. Thanks for your offer of help anyway.
Jim,
This idea is very similar to a Hopinkson's bar. The excitation source is different as you noted.
One of the...
Certain electronic components must be subjected to shock response spectrum testing, particular if the component must survive a pyrotechnic shock event while in service. (Refer to MIL-STD-1540, 810, etc.)
I have an idea for a new type of shock test machine...
A time history can be synthesized to satisfy a shock response spectrum. (The time history will not be unique.)
Then you can perform a modal transient in FEA.
Tom Irvine
www.vibrationdata.com
I have posted a tutorial with some very basic information on the "added mass effect" at:
http://www.vibrationdata.com/tutorials2/added_mass_fluid.pdf
Tom Irvine
http://www.vibrationdata.com
NEWS ALERT!
Avionics components in missiles may be subjected to high-amplitude, high-frequency pyrotechnic shock pulses. The components must thus be qualified to these shock levels per MIL-STD-1540D, 810F, etc.
The qualification levels often have so much margin that the tests must be...
One approach is to synthesize a time history to satisfy the shock response spectrum.
Then use the time history as a base input to modal transient analysis.
Tom Irvine
www.vibrationdata.com
I perform random vibration finite element analyses via a modal analysis which yields frequency response functions(FRFs) for the nodes of interest.
Then I develop my own power transmissbility functions from the FRF functions, outside of the FEA software.
Then I apply a base input PSD (or...
I agree that you need to gather you own field measurements.
You may want to search out the references that MIL-STD-810F gives, but clear answers regarding the origins of test levels are sometimes hard to come by.
MIL-STD-810F gives some duration guidelines. For example, the exposure duration...
As an aside, there are some special cases where a sine sweep actually represents an expected vibration environment.
Certain solid rocket motors, for example, have cavity pressure oscillations that produce sinusoidal excitation that sweeps downward in frequency with time. Avionics must be...
The shock response spectrum gives the peak acceleration response for a single-degree-of-freedom system subjected to base excitation. The natural frequency of the item is the independent variable.
You can readily determine the item's peak acceleration for a given natural frequency from the SRS...
The generic assumption in mechanical engineering is 5%. Some "large structures" are as low as 1%.
So you run the analysis with both values.
Ultimately, damping cannot be predicted. It can only be measured.
Tom Irvine
www.vibrationdata.com
