INGENIEUR
test are rotating speed , drift angle , water density , sway force and centrifugal force .
PLANAR MOTION MECHANISM TEST
The planar motion mechanism test is also carried out in a special manoeuvring tank or in a large towing tank using model ships to determine all the hull derivatives with respect to velocity and acceleration . The model is fitted with full appendages and is towed and swung either by pure sinusoidal sway or yaw as shown in Figures 7 and 8 . In a pure sinusoidal sway motion test the model is towed along the tank with constant velocity , frequency and amplitude .
As the model is swung sideway following a sinusoid path , the motion changes the drift angle sinusoidally whereas the drift angle acceleration is 90 ° out of phase . By varying the amplitude of acceleration and drift angle for every run , the sway forces and yaw moments can be measured and subsequently the first derivatives of sway force and yaw moment with respect to non-dimensional sway acceleration can be determined .
A pure sinusoidal yaw motion test is similar to that of pure sinusoidal sway motion test except that the model is turned to follow the direction of motion of the sinusoidal path as shown in Figure 8 . The drift angle is zero all along the way of the motion , however the rate of yaw and the yaw acceleration change sinusoidally . The quantities measured in the test are sway force , yaw moment , drift angle , water density and temperature . Both the pure sinusoidal sway and yaw motion tests generate the first derivatives of sway force , yaw moment with respect to rate of yaw and yaw acceleration .
Figure 7 : Pure Sinusoidal Sway Motion Test
Figure 8 : Pure Sinusoidal Yaw Motion Test
WILLIAMSON TURN TEST
The ship response with respect to rudder deflection can also be evaluated or studied by performing the Williamson turn test in which the ship ’ s characteristics i . e . the distances A , B and C as shown in Figure 9 are determined . The test commences with the model moving steadily in a straight direction with constant velocity . The model
Figure 9 : Williamson Turn Test
54 VOL 83 JULY-SEPTEMBER 2020