Gerritsma and Beiikelman 



Table 1 

 Main Particulars of the Shipmodel 



integration the first harmonics of the in- phase and quadrature components can 

 be found with distortion due to vibration noise. In some details the electronic 

 circuit differs somewhat from the description in [11]. In particular synchro re- 

 solvers are used instead of sine-cosine potentiometers, because they allow 

 higher rotational speeds. 



The accuracy of the instrumentation proved to be satisfactory which is im- 

 portant for the determination of the quadrature components, which are small in 

 comparison with the in-phase components of the measured forces. 



Throughout the experiments only first harmonics were determined. It 

 should be noted that non-linear effects may be important for the sections at the 

 bow and the stern where the ship is not wall- sided. The forced oscillation tests 

 were carried out for frequencies up to oj = 14 rad/sec and four speeds of ad- 

 vance were considered, namely: Fn = 0.15, 0.20, 0.25 and 0.30. Below a fre- 

 quency of CO = 3 to 4 rad/sec the experimental results are influenced by wall 

 effect due to reflected waves generated by the oscillating model. 



The motion amplitudes of the shipmodel covered a sufficiently large range 

 to study the linearity of the measured values (heave ~4 cm, pitch -4.6 degrees). 

 An example of the measured forces on section 2, when the combination of the 

 seven sections performs a pitching motion, is given in Fig. 4. 



222 



