Calculating Natural Frequency in English Units

To calculate natural frequency in English units, you have to
1) convert the weight of the unit into slugs
2) convert stiffness from (lb/in) into (lb/ft), b/c slugs is in (lbf*s^2/ft)

Also, don't forget to multiply by (1/(2*pi)) to get natrual frequency in Hz!

Ex:

k = 1000; %lb/in
m = 30; %lb

k = k*12; %convert stiffness into lbf/ft
m = m*0.031081; %convert lb into slugs (lbf*s^2/ft)
wn = (1/(2*pi))*sqrt(k/m); %natrual frequency

Docushare

To get to Moog's Docushare system:

http://docushare.moog.com

username: jfox2
password: regular password

Q factor

The q factor determines how underdamped a system is.

Q = 1/(2*zeta)

More can be found in:

http://en.wikipedia.org/wiki/Q_factor

EZ Analyst - On saving/exporting data

To do averaging in EZ Analyst,

1) Click on "continuous measurement" button.

2) Take the data. (settings are under configuration menu)
NOTE: if taking time histories, the #avgs specified is irrelavent. It will take data for as long as you tell it to.

3) Save data. Go to "save multiple data set".

4)Exporting data...this is done in two steps. ONE, you have to go to the export menu to enter in all your settings (what you want file to be named, what you want to export, etc.). TWO, you have to actually export the data. This is done under the "control" menu.

WHAT IT EXPORTS: For awhile I was unsure if EZ Analyst exported the AVERAGED FRF or just a single FRF from the last time window (because when exporting multiple data set data, EZ Analyst only saves time history data from last time window if you are doing a continuous measurement instead of recording time history). Despite this, EZ Analyst DOES export the AVERAGED FRF. I did a self check and found this to be the case!!

Checking out equipment in Atrax

Log in using regular user name and password.

Go to Check out/ return equipement.

Double click the CSA logo to allow editing of check out log.

If checking out, scan each item.

If returning, just enter the return date in the proper field.

I-deas not working

if I-deas loads up alright, but does not take data, it could be because the address scheme for the input modules is flipped (aka reading the last module first and first last). To change this, go to:

UGS\NXI5\tda\hpvxi-1432

This is the setup file for ideas. Scroll down to the "flip 1" option and change it.

Ideas
flip
not taking data

Good Modal Extraction

To get good modal extraction from tap tests and the like, You should have at least 5 (better to have 10) spectral lines within the modal bandwidth.

Modal Bandwidth: the area between the half power points of the mode

Half Power Points: take the peak of the mode, normalize it to 1, come down to .707 on either side. Whatever width that is is the modal bandwidth. (.707 because you are looking at an FRF, a linear scale. If you were looking at a PSD it would be 0.5)