Force Pulse Testing of Ship Models 



model tests are conducted at forward speeds, quantities such as pitch, heave, 

 and surge force are in general not zero, even in a steady state translation. The 

 actual records of a transient pulse test, as analyzed, are necessarily truncated, 

 and thus have the form of an oscillatory pulse superimposed upon a rectangular 

 pulse of length equal to the record. See Fig. 6. The recorded signal can be con- 

 sidered as part of function, 



f(t) 



fi(t) 



- CO < t < +00 



where fg is a constant and fjCt) is the pulse excitation or response. The func- 

 tion f(t) has no Fourier transform unless f^ is zero, but our only interest is 



the transform of f i(t). 

 treated, can be written 



The truncated signal, f'''"(A) , which is the one actually 



fT(t) = fo + fi(t) < t < T 



= 



elsewhere 



This function does have a Fourier transform. If f i(t) is zero outside the in- 

 terval (o,t) the transform of f^(t) will be equal to the transform of f ^(t) plus 

 the transform of a rectangular pulse of height fo and length T. However, the 



Fig. 6a - The recorded signal f(t) 



Fig. 6b - The analyzed signal f^(t) 



Fig. 6c - The analyzed signal imbedded in a periodic function 



447 



