4.2 HPMM System

　

 KRISO has recently updated HPMM to be able to measure hydrodynamic coefficients required for simulating maneuvering motion of four degrees of freedom. The force measuring system was changed to be able to measure roll moments as well as horizontal forces and moments. And, a roll motion driving system was added for pure roll motion tests. It is also possible to lock the model ship at a desired heel angle on carrying out model tests such as drift with heel test and yaw with heel test.

　

 Force measuring system is composed of six one-component gages to measure four component forces as shown in Fig. 2. Surge and sway forces are measured by summation of two X-gages and Y-gages located fore and aft respectively. Using the measured forces of two Y-gages and Z-gages, yaw and roll moments can be also calculated.

　

　

　

4.3 HPMM Test Conditions

　

 HPMM tests were carried out at the towing tank of KRISO with 1/72 scaled model ship of 9000TEU container ship, the same model ship that was used for free running tests. The tests were conducted at both full load and ballast conditions.

　

 The test program was designed to get enough hydrodynamic data to obtain hydrodynamic coefficients for a mathematical model of four degrees of freedom described in the foregoing. The ranges of test variables were determined to cover full range of standard maneuvering motions. Table 5 summarizes the test program. Here, Uo/U means the ratio of design speed to test speed. Free roll test was conducted to estimate the roll damping coefficients from the decay of roll.

　

 During tests, the model was free in heave and pitch but it was constrained in roll. All the tests were carried out with fully appended model at the ship propulsion point. Forces acting on the rudder were measured and they were used to separate the bare hull forces from the forces acting on a fully appended ship. Fig. 4 shows the view of drift and heel tests.

　

　

　

4.4 HPMM Test Results

　

 Hydrodynamic coefficients(rudder and propeller effects are included) and stability indices obtained from HPMM test are summarized in Table 5 for full load and ballast conditions. Here, all coefficients are nondimensonalized by length of ship and design speed. The ship has a positive value of dynamic lever(lv') at ballast condition but she has negative one at full load condition. It is understood that the ship has a good directional stability at ballast condition but she does not at full load condition.

　

　

 zH in equation (2) was obtained from the static drift test. Fig. 5 shows the relation between side forces and roll moments measured from static drift test at full load condition. Linear relationship is clearly seen up to large drift angles(20 degrees). Estimated vertical center of hydrodynamic forces from this curve is located at 0.76d below from the waterline. Similar curve was also obtained from pure yaw tests but the data were not adopted because of a little large scattering. Instead, vertical center of hydrodynamic forces acting on the hull is estimated from static drift test data.

　

　

 Fig. 6 shows the data from drift with heel tests. Effects of heel on yaw moments are clearly. But heel seems not to affect side forces so much. Anyway, force modeling of equation (2) fits experimental data very well.