3.4 Stopping Test

　

 Time history of propeller revolution for both full load and ballast conditions are illustrated in Fig. 11. Rudder angle was hold amidship during the test. Definition of track reach RT and final state heading angle ΨST are shown in Fig. 12, Track reach RT and final state heading angle ΨST in stopping test are shown in Fig.13 for both full load and ballast conditions. Measurement was carried out two times for each wavelength and wave encounter angle condition.

　

　

　

　

 Wave effect on track reach RT can be seen mainly in beam and head wave conditions for both full load and ballast conditions. In these test conditions wave makes track reach RT shorter than that in calm water condition. Shorter track reach in head wave of 1.0 wavelength ratio in full load condition is considered to be attributed to the same reason of large speed drop in straight running test in the same wave condition, large added resistance due to large pitching and heaving motion. While in beam wave conditions of short wavelength drift force due to wave reflection on hull surface is estimated dominant.

　

 Final state heading angle ΨST in beam and head wave conditions is smaller than that in calm water. This is understood as effect of wave drift moment that tends to make ship direct toward wave propagating direction as explained in section 3.1 for straight running test. Large negative value of final state heading angle ΨST in beam wave of 1.0 wavelength ratio for full load condition is corresponding to the fact that negative counter rudder angle δC in straight running test in the same wave condition.

　

 Note that since final state heading angle ΨST in calm water is caused solely by asymmetric forces and moment due to propeller reversing, tendency shown in Fig. 13 is not directly applied to negative initial wave encounter angle χi conditions symmetrically.

　

 Theoretical calculations of manoeuvring motion of ships in waves are not so many. Hirano et al. [2] proposed calculation procedure using experimental data of wave drift forces and moment at zero forward speed. Kijima et al. [4] calculated manoeuvring motion of a ship in waves using Newman's method [5] for predicting wave drift forces and moment. Newman's method calculates wave drift forces and moment originating in ship's periodic motions in waves at zero ship speed. Ueno et al. [6, 7, 8] proposed calculation method of wave drift forces and moment originating in wave reflection on hull surface. This method takes effect of ship speed, oblique angle and yaw rate together with water plane form upon wave drift forces and moment into consideration.

　

　

　

 Fig. 14 shows an example of calculation of -35deg turning in wave of 0.4 wavelength ratio in full load condition for the model ship comparing measured data. Wave drift forces and moment are calculated using Ueno's method. Origin of the ship trajectory graph in Fig. 14 is taken at steering point. Ship trajectory indicates large difference of drifting distance and drifting direction. However, time histories of yaw rate, ship speed, oblique angle and heading angle explain measured data qualitatively. This comparison implies that some improvement must be needed for practical application of Ueno's method to predict wave drift forces and moment.

　

 Free-running model test using a VLCC model ship was carried out in regular waves. Wave effect on manoeuvring motion of the model ship in straight running test, zigzag test and stopping test are reported. Effect of loading condition is also shown experimentally.

　

 An example of theoretical calculation of 35deg turning of the model ship in wave is compared with corresponding measured data.

　

 These experimental data is considered valuable not only for better understanding of manoeuvring characteristics in waves but also for development of practically applicable prediction method of wave drift forces and moment acting on ships manoeuvring in waves.

　

[1] Ueno M., Nimura T., Fujiwara T., Nonaka K., "Evaluation of RTK-OTF Positioning System for Free Running Manoeuvrability Test of a Model Ship", Journal of the Kansai Society of Naval Architects, Japan, No.228, pp. 113-121, 1997.

[2] Hirano M., Takashina J., Takaishi Y., Saruta T., "Ship Turning Trajectory in Regular Waves", Transactions of the West-Japan Society of Naval Architects, No.60, pp. 17-31, 1980.

[3] Nimura T., Haraguchi T., Nonaka K., Yoshino Y., "Turning and Straight Running Test in Waves", Proceedings of General Meeting of National Maritime Research Institute, No.56, pp. 108-112, 1990.

[4] Kijima K., Furukawa Y., "Ship Manoeuvring Performance in Waves", Contemporary Ideas on Ship Stability Elsevier Science Ltd., pp. 435-448, 2000.

[5] Newman J.N., "The Drift Force and Moment on Ships in Waves", Journal of Ship Research, Vol.11, No.1, pp. 51-60, 1967.

[6] Ueno M., Nimura T., Miyazaki H., Nonaka K., "Steady Wave Forces and Moment Acting on Ships in Manoeuvring Motion in Short Waves", Journal of the Society of Naval Architects of Japan, No.188, pp. 163-172, 2000.

[7] Ueno M., Nimura T., Miyazaki H., Nonaka K., "On Steady Horizontal Forces and Moment due to Short Waves Acting on Ships in Manoeuvring Motion", Proceedings of the PRADS 2001 (The Eighth International Symposium on Practical Design of Ships and Other Floating Structures), Elsevier Science Ltd., pp. 671-677, 2001.

[8] Ueno M., Nimura T., Miyazaki H., "Prediction of Steady Short Wave Forces and Moment Acting on Ships in Manoeuvring Motion", Proceedings of Mini Symposium on Prediction of Ship Manoeuvring Performance, Japan Marine Dynamics Research Sub-Committee, The Society of Naval Architects of Japan, pp. 93-102, 2001.

　

1984; Researcher in Hydro-elasticity Section, Ship Dynamics Division, Ship Research Institute, Ministry of Transport, Japan: 1985; Researcher in Wave Force Section, Ship Dynamics Division, Ship Research Institute, Ministry of Transport: 1992; Senior Researcher, Ship Dynamics Division, Ship Research Institute, Ministry of Transport: 1993-1994; Visiting Associate, California Institute of Technology, U.S.A.: 1994-1995; Special Assistant, Technology and Safety Division, Ministry of Transport, Japan: 2001; Senior Researcher, Ship Dynamics Division, National Maritime Research Institute, Japan: 2002; Head, Manoeuvring and Control Group, Department of Maritime Safety, National Maritime Research Institute, Japan