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 Secondly, the wave height of even 2[m] (corresponding to the unity wave amplitude) is essential. The wave height of 4[m] is absolutely 'destructive' for the turning manoeuvre- the surge velocity vx goes below zero (for such a reason, Fig. 9 does not contain the drift angle β in that case). A very interesting issue is that the yaw velocity ωz, is very resistant to the wave second order impact, also in situations of higher wave heights. Notwithstanding some oscillations, the yaw velocity is generally like in calm water - even large alterations in drift angle (contributing also to hull and rudder forces) do not have a higher impact here.
 
Fig.7 Turning tracks in waves
 
Fig.8 Surge velocity during turning in waves
 
Fig.9 Drift angle during turning in waves
 
Fig.10 Sway velocity during tunring in waves
 
Fig.11 Yaw velocity during turning in waves
 
 Though the model presented above is not extremely accurate (it reflects in a certain way the status of the ship manoeuvring hydrodynamics science) as relying still upon not fully validated assumptions (hypotheses), it seems to have enough properties to test the wave impact within the stated research objectives.
 
3. FINAL REMARKS
 The regular waves, though justified from a theoretical point of view (being simple to investigate analytically and/or experimentally and enabling gathering input data for irregular wave case) are not however representative for simulating the ship manoeuvring behaviour in waves, at least with regard to the wave second order forces. Two major motives lie under such a conclusion.
 
 The first one is that the ship manoeuvring motion is very sensitive on small wave amplitudes of order even 1[m] if associated with low wave/ship length ratios (λ/L less than e.g. 0.6). Depending of course upon the sea spectrum parameters (significant wave height and modal frequency) and additionally upon the spectrum discretisation while transforming it into harmonic (regular) components, those wave amplitudes and lengths are sometimes hardly to be achieved in, a real-world. A short wave/ship length ratio could be easier reached in a seaway by very long ships. Though the ship analysed in the paper belongs to somewhat shorter ones, and due to her freeboard 〜2[m] (as a rough criterion of manoeuvring motion sensitivity upon the wave amplitude) being subject already to small wave amplitudes, it could be considered a bit not illustrative in real-world conditions. However, a quite similar and true response seems to be experienced if the ship and the wave height are proportionally scaled up to higher dimensions - the case of e.g. a big tanker is obtained.
 
 The second aspect concerns the wave to wind dependence. This relationship (actually there are many formulas more or less widely adopted) exists only in relation to irregular waves- e.g. the wind velocity 15[m/s] produces a fully developed random waves of the significant wave height ca. 5 [m]. Thus to have an adequate simulation under combined wind and wave conditions, the only accepted is the ship manoeuvring in irregular waves like in e.g. [13]. However, the ready-to-use formulations (strictly lookup tables) by [13] for second order forces are of no advantage as they are computed for one particular sea spectrum. The latter is strongly linked to the wave significant height, which in turn is affected by the wind velocity.
 
 The wave first or second order forces and the frequency dependence of added masses and hull derivatives are not the only aspect of the wave action. Of some importance appears the propeller, wake, and rudder performance in waves (as usual with any interactions)- a great progress has been made here so far. Moreover, a higher interest is returning lately with reference to modelling the wave forces in restricted waterways (including the bank proximity) e.g. [32].
 
SYMBOLS
AR -rudder area m66 -yaw added inertia
B - ship beam Mz -yaw moment
cB -block coeff. n -propeller revs
cD -rudder drag coeff. P/D -pitch ratio
cL -rudder lift coeff. vPS -slipstream velocity
cm -m22 corrective ratio vx -surge velocity
cTh -thrust load coeff. vy -sway velocity
D -propeller drameter α -rudder incidence angle
FDR -rudder drag force β -ship drift angle
FnL -Froude number βR -rudder local drift angle
FLR -rudder lift force γWV -wave direction
Fx -surge force γWVrel -wave incidence angle
Fy -sway force δ -rudder angle
g -gravity acceleration ζo -wave amplitude
h -wave height λ -wave length
H -ship height λR -rudder aspect ratio
Jz -inertia moment ρ -water density
k11 -m11 ratio Ψ -ship course
k22 -m22 ratio ω -wave frequency
L -ship length ωE -wave encountered freq.
m -ship mass ωz -yaw velocity
m11 -surge added mass Ωm -modified relative yaw velocity
m22 -sway added mass  
subscripts:
'H'- hull, 'P'-propeller, 'R'-rudder
'WD'-wind, 'WV'- wave
'WV1'-(wave) first order excitations
'WV2'-(wave) second order excitations
'F-K'-(wave) Froude-Krylov component
'D'-(wave) diffraction component
 
REFERENCES
[1] Artyszuk J. "Full scale Trials and Rudder Hydrodynamics of a Schilling Rudder Ship", HYDRONAV 2001, 14th International Conference on Hydrodynamics in Ship Design, Sep 27-29, Technical University of Szczecin, Szczecin-Miedzyzdroje, pp. 123-133, 2001
[2] Artyszuk J. "Wind Effect in Ship Manoeuvring Motion MM - a Review Analysis", International Scientific-Technical Conference EXPLOSHIP '2002 ('Operation Problems of Floating Objects and Harbour Facilities'), May 21-23, Szczecin-Kopenhagen, Scientific Bulletin no. 65, Maritime University of Szczecin, pp. 21-32, 2002
[3] Bailey P.A., Price W.G., Temarel P. "A Unified Mathematical Model Describing the Manoeuvring of a Ship Travelling in a Seaway", RINA Trans vol. 140, pp. 131-149, 1998
[4] Boese P. "On Safety Increase of a Ship in the Following Waves in Relation to the Controllability", Schiff&Hafen (S&H), vol. 22, no.2, pp. 109-118, 1970 (in German)
[5] Faltinsen O.M., Kjaerland O., Liapis N., Walderhaug H. "Hydrodynamic Analysis of Tankers at Single-Point-Mooring Systems", BOSS'79, 2nd International Conference on Behaviour of Off-Shore Structures, London, Aug 28-31, vol. 1, pp. 177-206, 1979
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[12] Journee J.M.J. "Motions and Resistance of a Ship in Regular Following Waves", Report no. 440, University of Technology/Ship Hydromechanics Laboratory, Delft, 1976
[13] Kalicinski J. "Numerical Simulation of Ship Manoeuvring Tests with Wind, Wave and Shallow Water Effects Taken into Account", Scientific Proceedings (Zeszyty Problemowe), B-047, CTO, Gdansk, 1990
[14] Kashiwagi M. "Added Resistance, Wave-Induced Steady Sway Force and Yaw Moment on an Advancing Ship", Ship Technology Research (Schiffstechnik), vol. 39, no. 1, pp. 3-16, 1992
[15] Kijima K., Tanaka S., Furukawa Y., Hori T. "On a Prediction Method of Ship Manoeuvring Characteristics", MARSIM '93 Proc., vol. 1, International Conference on Marine Simulation and Ship Manoeuvrability, Sep 26-Oct 2, St. John's, pp. 285-294, 1993
[16] Kim C.H., Chou F. "Prediction of Drifting Force and Moment on an Ocean Platform Floating in Oblique Waves", International Shipbuilding Progress (ISP), Oct, pp. 388-401, 1973
[17] Kim S.E., Hirayama T. "Speed Loss and Maneuverability of a Full Ship in Directional Spectrum Waves", 6th International Symposium on Practical Design of Ships and Mobile Units (PRADS'95). Sep 17-22, Seoul, pp. 1.357-1.368, 1995
[18] Loukakis T.A., Chryssostomidis C. "Seakeeping Standard Series for Cruiser-Stern Ships", Trans. SNAME, vol. 83, pp. 67-127, 1975
[19] Loukakis T.A., Sclavounos P.D. "Some Extensions of the Classical Approach to Strip Theory of Ship Motions, Including the Calculation of Mean Added Forces and Moments", Journal of Ship Research (JSR), vol. 22, no.1 (Mar), pp. 1-19, 1978
[20] Martin L.L. "Ship Maneuvering and Control in Wind", SNAME Trans., vol. 88, pp.257-281, 1980
[21] Meijing L., Xiuheng W. "Simulation Calculation and Comprehensive Assessment on Ship Maneuverabilities in Wind, Wave, Current and Shallow Water", MARSIM & ICSM '90 Proc., Jun 4-7, SNAJ, Tokyo, pp. 403-411, 1990
[22] Newman J.N. "Second-order, Slowly-varying Forces on Vessels in Irregular Waves", International Symposium on the Dynamics of Marine Vehicles and Structures in Waves, pp. 182-186, 1974
[23] Ohkusu M. "Prediction of Wave Forces on a Ship Running in Following Waves with Low Encounter Frequency", Naval Architecture and Ocean Engineering, vol. 25, pp. 67-79, 1987
[24] Papanikolaou A., Zaraphonitis G. "On an Improved Method for the Evaluation of Second-Order Motions and Loads on 3D Floating Bodies in Waves" Schiffstechnik, vol. 34, no. 4, pp. 170-211, 1987
[25] Pawlowski M. "Linear Model of Ship Motions In Irregular Wave", PRS Technical Report no. 41, Gdansk, 2001 (in Polish)
[26] Pinkster J.A. "Low Frequency Second Order Wave Exciting Forces on Floating Structures", Ph.D. Thesis, Technical University, Delft, 1980
[27] Salvesen N. "Second-order Steady-state Forces and Moments on Surface Ships in Oblique Regular Waves", International Symposium on the Dynamics of Marine Vehicles and Structures in Waves, pp. 212-226, 1974
[28] Strom-Tejsen J., Yeh H.Y.H., Moran D.D. "Added Resistance in Waves", Trans. SNAME, vol. 81, pp. 109-143, 1973
[29] Szifrin L.S. "Approximate Calculation of Ship Added Resistance in Regular Wave", Sudostroenie, no.12, pp. 5-7, 1973 (in Russian)
[30] Vojtkunskij J.I. (ed.) "Ship Theory Handbook in 3 Volumes, Vol. 1, Sudostroenie, Leningrad, 1985 (in Russian)
[31] Wichers J.E.W. "The Prediction of the Behaviour of Single Point Moored Tankers", Workshop on Floating Structures and Offshore Operations, Nov 19-20, ('Floating Structures and Offshore Operations', series: Developments in Marine Technology, vol. 4, ed. Oortmerssen, van G. Elsevier, Amsterdam), Wageningen, pp. 125-142, 1987.
[32] Xia J., Krokstad J.R. "Wave Forces on a Body in Confined Waters", 14th Australian Fluid Mechanics Conference, Dec 10-14, Adelaide, 2001
 
AUTHOR'S BIOGRAPHY
 Jaroslaw Artysznk, Ph.D. in sea navigation, Assistant Professor at Szczecin Maritime University (Poland), Faculty of Navigation. Multiyear service at sea on big tankers (chief officer rank). Educational experience: lectures and simulator training on ship manoeuvring and handling. Scientific interest: ship manoeuvring mathematical model identification and ship manoeuvring simulation.







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