B. Bland, J. Kissel, R. Lane, J. O'Dell, N. Roberston, T. Sadecki

Over the weekend, I took a two vertical transfer functions, at high frequency (15-50 Hz) and at low frequency (0.05-0.3 Hz), using swept sine DTT (as opposed to the white noise excitations that have been performed in the past) just to begin to get a feel for what would be excitation levels will be needed to get good coherence for Matlab transfer functions. However, in the process, I discovered that there was a good deal of cross-coupling between vertical and roll (with a little bit of transverse -- see first attachment). This cross-coupling is completely unexpected, but our best guess was that it had to do with the recently re-adjusted blade spring tip heights -- in that one side of blades, or even a particular blade was higher that the opposing side. 

So, taking advantage of the newly arrived Joe O'Dell, we went in and re-assessed and re-adjusted all four blade spring tip heights, such that they "better" matched the nomimal 26.6mm from blade spring tip height to M1 base plate (see description of measurement in Saturday's aLOG). After a few more lessons from Joe on how best to align the OSEMs (use CAM tools instead of just fingers -- see second attachment), we sat down for another round of transfer functions. Retook the 15 -50 Hz Vertical transfer function (because it was quick), and the cross-coupling has *changed* but *not improved.* 

Both Joe and Norna recommended a pitch transfer function to diagnose whether we've got the blade tip heights correct. 

Attached (fourth attachment) are the results of the (white noise) transfer function, compared with two models. The first, blue, "d1 = Nominal" model uses the same parameter set that was used for the BSFM's final design review (see T1000724), except that I've removed the damping by turning the damping gains to 0.0, to recreate a free model. This is what the M1, Pitch to Pitch transfer function *should* look like. The second, green "d1 = Nominal - 3 mm" model uses the exact same parameter set, except for subracting 3 mm from the d1 parameter (the distance between the vertical suspension break off points of the M1 blade springs and the M1 center of mass). This is the same as *raising* the blade spring tip heights by 3 mm.

One can see that the "d1 = Nominal - 3 mm" model matches first two measured resonances exactly -- the first mode at 0.41 Hz is a L mode. The second mode, at 0.44 Hz (nominally at 0.48 Hz) is the pitch mode that we're trying to nail (see M080134 for reasoning). Again, this implies that the blade spring tip heights are *too high* by 3 mm. 

So, tomorrow we will readjust the blade spring tip heights such that our fiducial measurement reads 23.6 mm (the distance between the blade spring tip and the M1 base plate).





The DTT files for the attachments can be found here:
~/SusSVN/sus/trunk/BSFM/X1/BSFM01/BUILD02/SAGM1/Data
(First Attachment)
110617_X1SUSBSFM01_SweptSine_V_15to50Hz.xml
110617_X1SUSBSFM01_SweptSine_V_0p05to0p3.xml -- This one's cycles and averages are ridiculous, if you want to use it again (and have it *not* take all weekend, then reduce the number of cycles / averages / points)

(Second Attachment)
110620_X1SUSBSFM01_OSEMDiagonalization_VtoLFRT_1p1Hz.xml
110620_X1SUSBSFM01_OSEMDiagonalization_YtoF2F3_1p4Hz.xml

(Third Attachment)
110620_X1SUSBSFM01_SweptSine_V_15to50Hz.xml

(Fourth Attachment)
110620_X1SUSBSFM_WhiteNoise_P_0p005to50Hz.xml
(Exported as 110620_X1SUSBSFM_WhiteNoise_P_0p005to50Hz_F1F2F3LFRTSDLTVRPY_{tf,coh}.txt)

The Matlab script to process the Pitch transfer function is
plot_110620_X1SUSBSFM01_WhiteNoise_P_0p005to50Hz.m
(which uses the BSFM model and parameter files in ~/trunk/BSFM/Common/MatlabTools/BSFM_Model_Production/, which are edited versions (as described above) of T1000724)