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Influence of propulsion system configuration on the manoeuvring performances of a surface twin-screw ship
9th IFAC Conference on Control Applications in Marine Systems The International Federation of Automatic Control September 17-20, 2013. Osaka, Japan
Influence of propulsion system configuration on the manoeuvring performances of a surface twin-screw ship S.Mauro CNR-I.N.S.E.A.N. (Istituto Nazionale per Studi ed Esperienze di Architettura Navale) Via di Vallerano 139 00143 Rome (Italy) [email protected] Abstract: Propulsion system can experience large power absorption fluctuations during tight maneuvers. In the case of a turning circle manoeuvre for a twin-screw ship, the power required by the two shaft lines can be completely different; in case of non conventional propulsion system, like cross-connect configurations, a compromise must be met in order to design a safe control system without affecting dramatically the vessel's manoeuvring performance. In this work, a series of free running model tests on a unmanned surface twin screw ship model have been carried out in order to investigate the influence of different propulsion system operation settings on the vessel's manoeuvring characteristics. Keywords: Unmanned self-propelled free running surface model tests, propulsion system control, asymmetric propeller loads, propeller loads measurements, maneuverability/controllability performances 1. INTRODUCTION
This kind of propulsion plant, despite not very common, has been recently proposed as a solution for particular applications, such as fast naval ships (patrol vessels, frigates). In these cases, automation plant needs to monitor carefully these effects, in order to avoid any possible problems. Moreover, large asymmetrical shaft power during the maneuvers might result in different maneuvering behavior of the ship, with effects on both the transient and the stabilized phases. Another aspect that can have an important effects on the turning ability characteristics of the vessel is the strategy adopted by the automation plant (i.e. constant RPM, constant power or constant torque strategy).
Marine propulsion plants can experience large power fluctuations during tight manoeuvres. During these critical situations, dramatic increases of shaft torque are possible, up to and over 100% of the steady values in straight course. In the case of a twin-screw ship turning circle, the two shaft lines dynamics can be completely different in terms of required power and torque. A preliminary work was performed in last years analyzing turning circle maneuvers at different speeds and rudder angles carried out during sea trials for a series of twin screw naval ships. Results of this analysis allowed to underline a common trend for asymmetrical shaft power increase despite significant differences in ships considered (Viviani et al. 2007 and 2008) (figure 1 and 2). On the basis of the outcomes of this analysis, it is clear that this phenomenon, if not correctly considered, could be potentially dangerous, especially for propulsion plants with two shaft lines powered via a unique reduction gear (figure 3), which can be subject to significant unbalances.
Fig. 2. Internal shaft power increase
Fig. 3. External shaft power increase Fig. 1. Cross connect propulsion system power plant 1.1 Work's purpose
978-3-902823-52-6/2013 © IFAC
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10.3182/20130918-4-JP-3022.00003
IFAC CAMS 2013 September 17-20, 2013. Osaka, Japan
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IFAC CAMS 2013 September 17-20, 2013. Osaka, Japan
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IFAC CAMS 2013 September 17-20, 2013. Osaka, Japan
Fig. 7. Model’s kinematic and propulsion measured data It can be evidenced that, after the rudder is acted, thrust and torque experience a marked increase differently on both shafts: in particular, on the external shaft thrust and torque increase by 80% and 60% with respect the value in the approach phase, respectively; on the other hand, propeller on the internal side is lightly overloaded (thrust 20%, torque 10%). At the highest speed (FN=0.38) internal shaft does not experience an increase in torque/thrust demanding, otherwise external propeller experiences an increase in torque (40% and thrust 70%). This behaviour confirms qualitatively trends reported in figure 1 and 2 in terms of torque absorption; asymmetrical loads demanding are strictly related to the asymmetric wake developing during the combined sway-yaw motion of the vessel in a turn. It has to be emphasized that at full scale, at the highest speed the two shaft lines are connected via the unique reduction gear; it is evident that discrepancies among the internal and the external shaft are critical for this component and the action of the automation control system is demanded in order to alleviate the magnitude of pulsating loads. In table 2 non dimensional thrust (KT) and torque (KQ) percentage increase are summarized for the maximum rudder angle (35°) at both F N for the constant RPM tests. Table 2. Thrust and Torque percentage increase INTERNAL EXTERNAL FN=0.26 KT KQ KT KQ RPM 9% 7.3% 80.61% 58.5% FN=0.38 RPM
INTERNAL KT KQ 5.8% 3.4%
EXTERNAL KT KQ 55.9% 51.9% Fig. 8. Propulsion system behavior at different control configuration
In figure 8 propulsion system behaviour at constant torque and power settings in terms of ratio of shaft revolutions, torque, and thrust with respect the value in the approach phase are compared to the constant RPM configuration; for the sake of brevity, only turning circle at lowest FN, at maximum rudder angle is considered. It can be evidenced that, after the manoeuvre is started, the control device acts in order to maintain torque/power to the same value recorded in the approach phase.
5. PROPULSION SYSTEM CONFIGURATION INFLUENCE ON MANEUVRING CAPABILITIES In figure 9 trajectory (advance, transfer, tactical diameter and final diameter) and kinematics parameters (speed drop) for the turning circle tests at the both FN at the maximum rudder angle for the different propulsion system setting considered in this study are summarized. It can be evidenced that, moving from constant propeller revolution mode to controlled settings 176
IFAC CAMS 2013 September 17-20, 2013. Osaka, Japan
177
IFAC CAMS 2013 September 17-20, 2013. Osaka, Japan
Research in the framework of the National Research Program 2011-2013. Table 4. Zig-Zag tests results
d [°] 20.00 10.00
d [°] 20.00 10.00
d [°] 20.00 10.00
REFERENCES
RPM = CONSTANT 18 knots 26 knots 1st overshoot 2nd overshoot 1st overshoot 2nd overshoot 13.73 12.96 17.51 16.31 5.19 5.62 5.54 7.59
Altosole, M., Bagnasco, A., Benvenuto, G., Campora, U., Figari, M., D’Arco, S., Giuliano, M., Giuffra, V., Spadoni, A., Michetti, S., Ratto, A., Zanichelli, A., “Real Time Simulation of the Propulsion Plant Dynamic Behaviour of the Aircraft Carrier Cavour”, Proceedings INEC 2008, Hamburg, Germany, 2008 Benvenuto, G., Brizzolara, S., Carrera, G., (2003) “Ship Propulsion Numerical Simulator: Validation of the Manoeuvrability Module”, Proceedings NAV 2003, Palermo G. Dubbioso, A. Coraddu, M. Viviani, M. Figari, S.Mauro, R. Depascale, A.Menna, A.Manfredini (2010), “Investigation of asymmetrical shaft power increase during ship manoeuvres by means of simulation techniques” Proceedings 11th International Symposium on Practical Design of Ships and Other Floating Structures (PRADS 2010), Rio De Janeiro, 19-24 September 2010-vol.1 – pag. 172-181, ISBN 978-85-285-0140-7 Dubbioso, G., Mauro, S., Viviani, M. (2011), “Off-Design Propulsion Power Plant Investigations by Means of Free Running Manoeuvring Ship Model Test and Simulation Techniques” Proceedings of the Twenty-first (2011) International Offshore and Polar Engineering Conference, p.943-950, Maui, Hawaii, USA, June 19-24, 2011, ISBN 978-1-880653-96-8 (Set); ISSN 1098-6189 (Set) M. Viviani, C. Podenzana Bonvino, S. Mauro, M. Cerruti, D. Guadalupi, A. Menna, (2007) “Analysis of Asymmetrical Shaft Power Increase During Tight Manoeuvres”, 9th International Conference on Fast Sea Transportation (FAST2007), Shanghai, China, September 2007 M.Viviani, M.Altosole, M.Cerruti, A.Menna, G.Dubbioso (2008) “Marine Propulsion System Dynamics During Ship Manoeuvres”, 6th International Conference On HighPerformance Marine Vehicles (Hiper 2008) , 18/19/09/2008 – Naples, ISBN: 8890117494, p.81-93
TORQUE = CONSTANT 18 knots 26 knots 1st overshoot 2nd overshoot 1st overshoot 2nd overshoot 10.55 14.93 15.53 17.76 4.33 5.62 8.62 3.82 POWER = CONSTANT 18 knots 26 knots 1st overshoot 2nd overshoot 1st overshoot 2nd overshoot 13.04 11.41 15.19 16.05 3.99 5.45 7.77 5.36
6. CONCLUSIONS In this works principal results of free running model tests carried out at different prime mover configurations have been presented and discussed. Measurements of propellers thrust and torque provide a detailed insight into off-design propulsion system, in particular those met during tight maneuver; moreover, it has been evidenced that when the propulsion system is set to deliver prescribed value of torque/power, maneuvering performance is not affected at all. A general trend for unsteady maneuvers (zig-zag) was difficult to assess, probably due to slight external disturbances (wind). Further work is necessary for improving the experimental setup also for this kind of maneuvers. These results are very important for the development of a “full mission” maneuvering mathematical model, i.e. those mathematical models which include an hydrodynamic description of the ship including the propulsion system and the control device. The measurements of propeller thrust and torque is extremely useful for the improvement of propeller models adopted in standard maneuvering mathematical models in order to describe more accurately the overloading and unbalancing phenomena for a twin/multi screw vessel. The improvement of these simulators is of paramount importance, since they can be used as a useful tool for a deeper and broad analysis of either propulsion system and the most reliable control system strategy since the preliminary vessel’s design stages. Further work is needed in order to characterize propeller behavior during off design conditions; in particular, in addition to thrust and torque, also in-plane loads, namely lateral and vertical forces, must be monitored in order to better modeling such a complicated phenomenon propelled marine vehicles. AKNOWLEDGEMENTS This work has been carried out in the framework of project RITMARE coordinated by CNR - National Research Council and founded by the Italian Ministry of Education and 178
Influence of propulsion system configuration on the manoeuvring performances of a surface twin-screw ship S.Mauro CNR-I.N.S.E.A.N. (Istituto Nazionale per Studi ed Esperienze di Architettura Navale) Via di Vallerano 139 00143 Rome (Italy) [email protected] Abstract: Propulsion system can experience large power absorption fluctuations during tight maneuvers. In the case of a turning circle manoeuvre for a twin-screw ship, the power required by the two shaft lines can be completely different; in case of non conventional propulsion system, like cross-connect configurations, a compromise must be met in order to design a safe control system without affecting dramatically the vessel's manoeuvring performance. In this work, a series of free running model tests on a unmanned surface twin screw ship model have been carried out in order to investigate the influence of different propulsion system operation settings on the vessel's manoeuvring characteristics. Keywords: Unmanned self-propelled free running surface model tests, propulsion system control, asymmetric propeller loads, propeller loads measurements, maneuverability/controllability performances 1. INTRODUCTION
This kind of propulsion plant, despite not very common, has been recently proposed as a solution for particular applications, such as fast naval ships (patrol vessels, frigates). In these cases, automation plant needs to monitor carefully these effects, in order to avoid any possible problems. Moreover, large asymmetrical shaft power during the maneuvers might result in different maneuvering behavior of the ship, with effects on both the transient and the stabilized phases. Another aspect that can have an important effects on the turning ability characteristics of the vessel is the strategy adopted by the automation plant (i.e. constant RPM, constant power or constant torque strategy).
Marine propulsion plants can experience large power fluctuations during tight manoeuvres. During these critical situations, dramatic increases of shaft torque are possible, up to and over 100% of the steady values in straight course. In the case of a twin-screw ship turning circle, the two shaft lines dynamics can be completely different in terms of required power and torque. A preliminary work was performed in last years analyzing turning circle maneuvers at different speeds and rudder angles carried out during sea trials for a series of twin screw naval ships. Results of this analysis allowed to underline a common trend for asymmetrical shaft power increase despite significant differences in ships considered (Viviani et al. 2007 and 2008) (figure 1 and 2). On the basis of the outcomes of this analysis, it is clear that this phenomenon, if not correctly considered, could be potentially dangerous, especially for propulsion plants with two shaft lines powered via a unique reduction gear (figure 3), which can be subject to significant unbalances.
Fig. 2. Internal shaft power increase
Fig. 3. External shaft power increase Fig. 1. Cross connect propulsion system power plant 1.1 Work's purpose
978-3-902823-52-6/2013 © IFAC
173
10.3182/20130918-4-JP-3022.00003
IFAC CAMS 2013 September 17-20, 2013. Osaka, Japan
174
IFAC CAMS 2013 September 17-20, 2013. Osaka, Japan
175
IFAC CAMS 2013 September 17-20, 2013. Osaka, Japan
Fig. 7. Model’s kinematic and propulsion measured data It can be evidenced that, after the rudder is acted, thrust and torque experience a marked increase differently on both shafts: in particular, on the external shaft thrust and torque increase by 80% and 60% with respect the value in the approach phase, respectively; on the other hand, propeller on the internal side is lightly overloaded (thrust 20%, torque 10%). At the highest speed (FN=0.38) internal shaft does not experience an increase in torque/thrust demanding, otherwise external propeller experiences an increase in torque (40% and thrust 70%). This behaviour confirms qualitatively trends reported in figure 1 and 2 in terms of torque absorption; asymmetrical loads demanding are strictly related to the asymmetric wake developing during the combined sway-yaw motion of the vessel in a turn. It has to be emphasized that at full scale, at the highest speed the two shaft lines are connected via the unique reduction gear; it is evident that discrepancies among the internal and the external shaft are critical for this component and the action of the automation control system is demanded in order to alleviate the magnitude of pulsating loads. In table 2 non dimensional thrust (KT) and torque (KQ) percentage increase are summarized for the maximum rudder angle (35°) at both F N for the constant RPM tests. Table 2. Thrust and Torque percentage increase INTERNAL EXTERNAL FN=0.26 KT KQ KT KQ RPM 9% 7.3% 80.61% 58.5% FN=0.38 RPM
INTERNAL KT KQ 5.8% 3.4%
EXTERNAL KT KQ 55.9% 51.9% Fig. 8. Propulsion system behavior at different control configuration
In figure 8 propulsion system behaviour at constant torque and power settings in terms of ratio of shaft revolutions, torque, and thrust with respect the value in the approach phase are compared to the constant RPM configuration; for the sake of brevity, only turning circle at lowest FN, at maximum rudder angle is considered. It can be evidenced that, after the manoeuvre is started, the control device acts in order to maintain torque/power to the same value recorded in the approach phase.
5. PROPULSION SYSTEM CONFIGURATION INFLUENCE ON MANEUVRING CAPABILITIES In figure 9 trajectory (advance, transfer, tactical diameter and final diameter) and kinematics parameters (speed drop) for the turning circle tests at the both FN at the maximum rudder angle for the different propulsion system setting considered in this study are summarized. It can be evidenced that, moving from constant propeller revolution mode to controlled settings 176
IFAC CAMS 2013 September 17-20, 2013. Osaka, Japan
177
IFAC CAMS 2013 September 17-20, 2013. Osaka, Japan
Research in the framework of the National Research Program 2011-2013. Table 4. Zig-Zag tests results
d [°] 20.00 10.00
d [°] 20.00 10.00
d [°] 20.00 10.00
REFERENCES
RPM = CONSTANT 18 knots 26 knots 1st overshoot 2nd overshoot 1st overshoot 2nd overshoot 13.73 12.96 17.51 16.31 5.19 5.62 5.54 7.59
Altosole, M., Bagnasco, A., Benvenuto, G., Campora, U., Figari, M., D’Arco, S., Giuliano, M., Giuffra, V., Spadoni, A., Michetti, S., Ratto, A., Zanichelli, A., “Real Time Simulation of the Propulsion Plant Dynamic Behaviour of the Aircraft Carrier Cavour”, Proceedings INEC 2008, Hamburg, Germany, 2008 Benvenuto, G., Brizzolara, S., Carrera, G., (2003) “Ship Propulsion Numerical Simulator: Validation of the Manoeuvrability Module”, Proceedings NAV 2003, Palermo G. Dubbioso, A. Coraddu, M. Viviani, M. Figari, S.Mauro, R. Depascale, A.Menna, A.Manfredini (2010), “Investigation of asymmetrical shaft power increase during ship manoeuvres by means of simulation techniques” Proceedings 11th International Symposium on Practical Design of Ships and Other Floating Structures (PRADS 2010), Rio De Janeiro, 19-24 September 2010-vol.1 – pag. 172-181, ISBN 978-85-285-0140-7 Dubbioso, G., Mauro, S., Viviani, M. (2011), “Off-Design Propulsion Power Plant Investigations by Means of Free Running Manoeuvring Ship Model Test and Simulation Techniques” Proceedings of the Twenty-first (2011) International Offshore and Polar Engineering Conference, p.943-950, Maui, Hawaii, USA, June 19-24, 2011, ISBN 978-1-880653-96-8 (Set); ISSN 1098-6189 (Set) M. Viviani, C. Podenzana Bonvino, S. Mauro, M. Cerruti, D. Guadalupi, A. Menna, (2007) “Analysis of Asymmetrical Shaft Power Increase During Tight Manoeuvres”, 9th International Conference on Fast Sea Transportation (FAST2007), Shanghai, China, September 2007 M.Viviani, M.Altosole, M.Cerruti, A.Menna, G.Dubbioso (2008) “Marine Propulsion System Dynamics During Ship Manoeuvres”, 6th International Conference On HighPerformance Marine Vehicles (Hiper 2008) , 18/19/09/2008 – Naples, ISBN: 8890117494, p.81-93
TORQUE = CONSTANT 18 knots 26 knots 1st overshoot 2nd overshoot 1st overshoot 2nd overshoot 10.55 14.93 15.53 17.76 4.33 5.62 8.62 3.82 POWER = CONSTANT 18 knots 26 knots 1st overshoot 2nd overshoot 1st overshoot 2nd overshoot 13.04 11.41 15.19 16.05 3.99 5.45 7.77 5.36
6. CONCLUSIONS In this works principal results of free running model tests carried out at different prime mover configurations have been presented and discussed. Measurements of propellers thrust and torque provide a detailed insight into off-design propulsion system, in particular those met during tight maneuver; moreover, it has been evidenced that when the propulsion system is set to deliver prescribed value of torque/power, maneuvering performance is not affected at all. A general trend for unsteady maneuvers (zig-zag) was difficult to assess, probably due to slight external disturbances (wind). Further work is necessary for improving the experimental setup also for this kind of maneuvers. These results are very important for the development of a “full mission” maneuvering mathematical model, i.e. those mathematical models which include an hydrodynamic description of the ship including the propulsion system and the control device. The measurements of propeller thrust and torque is extremely useful for the improvement of propeller models adopted in standard maneuvering mathematical models in order to describe more accurately the overloading and unbalancing phenomena for a twin/multi screw vessel. The improvement of these simulators is of paramount importance, since they can be used as a useful tool for a deeper and broad analysis of either propulsion system and the most reliable control system strategy since the preliminary vessel’s design stages. Further work is needed in order to characterize propeller behavior during off design conditions; in particular, in addition to thrust and torque, also in-plane loads, namely lateral and vertical forces, must be monitored in order to better modeling such a complicated phenomenon propelled marine vehicles. AKNOWLEDGEMENTS This work has been carried out in the framework of project RITMARE coordinated by CNR - National Research Council and founded by the Italian Ministry of Education and 178