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Obtained some results on ground and HAM table-top yaw analysis with e2e. To make the analyses realistic, the following procedure was taken. First created calibrated platform U, V (translational displacement in X and Y) motions and Yaw motion using horizontal seismic position sensor DAQ signals (e.g., L1:SEI-MC1_POS_H1_INMON, etc). The resultant platform's U, V and Yaw time series were fed into the e2e HAM stack box input ports to compute small optics (SOS) OSEM Yaw signal. This OSEM signal was compared with the corresponding DAQ signal recorded at the same time as the seismic position sensor DAQ
signals.
The analyses were made based on two different HAM table Yaw models. In the first model (called the model A), only the platform's Yaw motion was used as input to the HAM stack box, and the resultant HAM table top Yaw motion was fed
into the SOS box placed on top of HAM stack box. In other words, the stack's Yaw-to-Yaw coupling only was considered.
In the second model (model B), the platform's U, V, and Yaw were all fed into the HAM stack U, V, and Yaw input ports, respectively, and the table top U, V, and Yaw motions were computed based on the stack's U-to-U, V-to-V and Yaw-to-Yaw couplings. Then, additional table top Yaw was computed as dV/dx-dU/dy (where U and V are the table top translational motions computed by the stack box and x and y are the coordinate on the table) and this table top Yaw was added to the table top yaw based on the Yaw-to-Yaw coupling (the same as model A) to compute the total table Yaw, which was fed into the SOS box in turn.
The additional table top Yaw in model B was computed to consider the following effect. At the bottom of different stacks of the same table (say, for example, the north stack and south stack of HAM 1) the platform experiences east-west translational displacement with a certain phase delay. (This phase delay causes the platform's Yaw motion mentioned above.) Then if the north stack and south stack transfers the east-west displacement at a different rate (i.e., the transferring speed of the displacement is different for the north and south stacks), the phase delay will be enhanced at the table top; in other words, the phase delay associated with the difference in the transferring speed between the south and north is added to the initial phase delay existing at the bottom of the stacks.
Results of the computation show that the model B is closer to the OSEM Yaw DAQ signals in the overall shape of the power spectrum. The DAQ OSEM Yaw spectrum has two broad peaks around 1.5 Hz and 2.8 Hz, which can be identified as the
stack's translational-translation first and second resonances, respectively. The computed spectrum based on model A shows only one peak around 1.5 Hz, while the computed spectrum based on model B shows two peaks around 1.5 Hz and 2.5 Hz. This indicates the above-mentioned effect of phase delay introduced by asymmetric stack response is a possible cause for the HAM table Yaw.
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