Data Acquisition and Reduction Methodology

• The present interest is in data acquisition of carriage speed U_c, ship model motions (x, y, z, f, q, y), and forces and moments (F_x, F_y, F_z, M_x, M_y, M_z) for static and dynamic PMM tests. 

• All variables are acquired as time histories through each carriage run. 

• Static test variables (F_x, F_y, M_z) are time-averaged whereas dynamic test variables (y, y, F_x, F_y, M_z) are treated with harmonic analysis in the data reduction phases. 

• z and q are measured to compute sinkage and trim for free-condition tests. 

• Although not used in the data-reduction equations (DRE’s), x, f, F_z, M_x, M_y, are also measured to monitor operation of the mount and loadcell. 

• The measurement details for U_c are presented in Longo and Stern, (2005). 

• F_X, F_Y, and M_Z are measured longitudinal and transverse forces and yaw moments, respectively.
• In general  for conventional marine vessels, but it is assumed to be non-zero for the purpose of uncertainty assessment in a later part of this report.  
• Equation (24) can be non-dimensionlized using water density , advance speed , mean draft , and ship model length L_PP. 

• They can be simplified considerably by dropping the inertia terms for the case of the static tests.

• For static tests, average values of surge and sway forces and yaw moment are computed from the time histories.
• For the dynamic tests, first the inertia forces and moment are subtracted from the measured forces and moment, respectively.
• Then, the resultant time histories of the forces and yaw moment are reconstructed with a 6th-order Fourier-series (FS) equation as per the following expression

• where X(t) can be any force or moment, n is the order of the FS, f is the PMM frequency, and f_n is the nth-order phase.