Impulse propulsion

Abstract

The present invention relates to providing impulse propulsion for a ship. In a preferred embodiment, impulse propulsion is provided by increasing the rotational speed of a propeller in real time.

Description

[Technical Field]

[0001] The present invention relates to providing impulse propulsion for a ship. In a preferred embodiment, impulse propulsion is provided by increasing the rotational speed of a propeller in real time. [Background technology]

[0002] Ships typically have one or more propellers that provide propulsion. While propellers have provided propulsion for decades, they have evolved into thrusters such as rim-driven azimuth thrusters and rim-driven tunnel thrusters, which have proven to be more versatile than conventional propeller configurations. This versatility is particularly evident in the automatic positioning and / or low-speed maneuvering of ships.

[0003] The operation of propellers, particularly thrusters, during automatic position holding and / or low-speed maneuvering is focused on achieving precision in automatic position holding and / or low-speed maneuvering, with little or no attention paid to power consumption during such operation.

[0004] This lack of attention to power consumption may stem from the common teaching that changes in propeller rotation speed must be made in a sufficiently slow manner so that the water flow through the propeller reaches a hydrodynamically stable state while the propeller rotation speed is increasing or decreasing.

[0005] Therefore, while the current operation of the propeller enables the ship to maintain its precise automatic position and / or to maneuver at low speeds, the power consumption during such operation is typically considerable.

[0006] Therefore, improved methods for operating propellers, especially thrusters, would be advantageous, particularly for more energy-efficient operation. [Overview of the project] [Problems that the invention aims to solve]

[0007] An object of the present invention is to provide an improved method for operating propellers, particularly thrusters, during automatic ship positioning and / or low-speed operation, though not necessarily limited to this method.

[0008] A further object of the present invention is to provide a more energy-efficient method for operating propellers, particularly thrusters, during automatic position holding and / or low-speed operation, though not necessarily limited to these methods.

[0009] A further object of the present invention is to provide an alternative to the prior art. [Means for solving the problem]

[0010] Therefore, the above-mentioned objectives and several other objectives are intended to be achieved by providing a method for providing impulse propulsion to a vessel by a propulsion system, in a first aspect of the present invention.

[0011] The propulsion system is preferably, A propulsion device having a rotatable propeller and generating thrust of a magnitude corresponding to the rotational speed of the propeller, • An electric motor coupled to the propeller and providing the rotational speed, A control unit, such as a propulsion control system, is configured to receive a thrust request representing the thrust required from the propulsion device, and to control the electric motor to rotate the propeller at a rotational speed corresponding to the thrust request. It is equipped with.

[0012] Preferably, this method includes the control unit controlling the electric motor so that, upon receiving a thrust request from the control unit, the rotational speed of the propeller increases or decreases in real time to a rotational speed corresponding to the thrust request.

[0013] The terms used herein are used in the ordinary sense to those skilled in the art. Some of the terms used are defined below.

[0014] Impulse propulsion refers to the supply of impulses to water by a propulsion system. The impulses supplied to the water are provided by the thrust supplied to the water by the propulsion system, which in turn provides the propulsion system with a reaction force to move the vessel. Impulse propulsion is characterized in particular by the real-time increase in the rotational speed of the propeller that assists in supplying impulses to the water. When using impulse propulsion, the movement of a vessel utilizing impulse propulsion may be carried out with the propeller operating intermittently at a high rotational speed, preferably with a dwell time in between, during which the propeller is either not rotating or rotating at a considerably low RPM.

[0015] As used herein, “ship” means a vessel equipped with one or more propulsion systems having propellers that provide thrust for propelling the vessel. A vessel may be a submersible such as a submarine, a displacement (floating) vessel, a planing boat, and / or a vessel equipped with one or more hydrofoils.

[0016] "RPM" and "propeller rotation speed" are used interchangeably in this specification.

[0017] Impulse propulsion with dwell time has the potential to significantly reduce the power consumption of the propulsion system.

[0018] As used herein, "in real time," for example in relation to "increasing or decreasing the rotational speed of the propeller in real time," preferably means that the increase or decrease is performed as quickly as possible by the electric motor and propulsion system. In some embodiments utilizing permanent magnet rim-driven thrusters, "real time" is provided by the thruster's ability to provide a rapid increase and high value of the force acting on the rim and, consequently, the propeller blades.

[0019] "Dwell time" preferably refers to a period during which the rotational speed is less than 20%, preferably less than 15%, for example less than 10% of the maximum rotational speed of the propeller. In some embodiments, the rotational speed during the dwell time is substantially zero, such as when the propeller is in an idle state. In other embodiments, the rotational speed of the propeller is zero.

[0020] By operating the propeller with an increase and decrease in RPM, preferably including the dwell time after the decrease, a vortex ring can be generated downstream of the propeller during the RPM increase. Such a vortex ring is generated because the water downstream and outside of the propeller has a lower velocity than the water flowing out from the propeller, creating a shear layer that is drawn into the vortex ring. The vortex ring typically starts at the outer downstream end of the casing surrounding the propeller (relative to the propeller and the flow), and the vortex moves downstream (relative to the forward movement of the propeller) with the water flow. The generation of the vortex ring is particularly prominent in rim-driven azimuth thrusters, rim-driven tunnel thrusters, and the like. Without being bound by theory, the inventors have surprisingly found that the formation of the vortex ring improves the efficiency of the propulsion device. Since generally vortices may be considered to consume energy, such an improvement in efficiency may seem counterintuitive. However, with respect to impulse propulsion, the presence of the vortex ring is suggested to enhance the ability of the propeller to impart an impulse to the water, presumably because the vortex ring provides backpressure or flow resistance to the water directly below the propeller. Such backpressure of the flow resistance dissipates over time as the vortex moves further downstream of the propeller. However, in impulse propulsion where the RPM is repeatedly increased and decreased, the generation of the vortex ring near the propeller allows the effect of the backpressure or flow resistance to be utilized in a positive way with respect to efficiency. The inventors further hypothesized that during the alternating increase and decrease of the rotational speed, a velocity decrease occurs due to the periodic vorticity on the pressure side of the thruster, resulting in an increase in the local pressure on the pressure side (downstream). This is thought to increase the total thrust and, if the power to the propeller is constant, increase the efficiency.

[0021] In one aspect, the present invention is a computer program product comprising at least one computer to which data storage means is connected and configured to control the propulsion system disclosed herein, for example, a computer program product including instructions that cause a computer to execute the method according to the first aspect of the present invention when executed by the computer. In some embodiments, the computer program is a thruster allocation routine. Such a thruster allocation routine can be configured to perform automatic ship position holding and / or low-speed maneuvering of a ship, and during its execution, the routine distributes the thrust vector so that the force by the thrust vector (direction and magnitude) cancels out the environmental force. The thruster allocation routine typically receives positioning inputs based on GPS, motion sensors, and / or gyrocompasses. Further, wind force may be included as an input to the thruster allocation routine.

Brief Description of the Drawings

[0022] Hereinafter, the present invention, particularly its preferred embodiments, will be described in more detail with reference to the accompanying drawings. The drawings illustrate the method of implementing the present invention, and these drawings should not be construed as limiting other possible embodiments falling within the scope of the appended claims. [Figure 1] Schematically shows a method of providing impulse propulsion to a ship in the first embodiment of the present invention. [Figure 2] [[ID=1​​​​​The temporal thrust response during increasing rotational speed, generated by a method according to a preferred embodiment of the present invention, is shown, and the results shown are provided by a computational fluid dynamics model. [Figure 4B] The temporal thrust response during increasing rotational speed, generated by a method according to a preferred embodiment of the present invention, is shown, and the results shown are provided by a computational fluid dynamics model. [Modes for carrying out the invention]

[0023] Referring to Figure 1, a preferred embodiment of a method for providing impulse propulsion to a vessel using propulsion system 1 will be described in detail.

[0024] As shown in Figure 1, the propulsion system 1 according to the first preferred embodiment includes a propulsion device 1. The propulsion device 1 should have a rotatable propeller 2, as the rotatable propeller 2 plays a role in generating hydrodynamic force through rotation, although it may differ from the propulsion device shown in Figure 1. However, since the rotatable propeller 2 works in cooperation with the shape surrounding the propeller, the propulsion device 1 is said to generate thrust when the propeller 2 rotates.

[0025] The magnitude of the thrust generated by the propulsion system depends, in particular, on the rotational speed of propeller 2. One schematic example of such a dependency within the schematicly shown control unit 4 is shown in Figure 1. As shown, the generated thrust depends on the rotational speed (RPM), and this dependency can in some cases be approximated as follows:

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[0026] To provide the rotational speed of the propeller, an electric motor 3 is provided and coupled to the propeller 2. In the embodiment shown in Figure 1, where the propulsion system is a permanent magnet rim-driven thruster, also known as a rim-driven azimuth thruster (RD-AZ), the electric motor is provided, in particular, by magnets positioned on a rim to which the tips of the propeller blades are coupled, and by a number of coils positioned in a fixed part of the thruster, such that the rim and, by extension, the propeller blades rotate when power is supplied to the coils.

[0027] A detailed description of preferred embodiments will be made with reference to rim-driven azimuth thrusters, but other propulsion systems such as rim-driven tunnel thrusters (RD-TT) may also be used.

[0028] A control unit 4 is provided, which may generally be called a propulsion control system. The control unit 4 is configured to receive a thrust request Tr representing the thrust required by the propulsion device. The meaning of the required thrust is that although the thrust curve provides a one-to-one correspondence between thrust and RPM, the actual conditions under which the thruster operates may deviate from the conditions under which the thrust curve is obtained, meaning that the actual thrust generated by the thruster may deviate from what is shown by the thrust curve.

[0029] Using the thrust request Tr received by the control unit 4, the control unit 4 determines the propeller's RPM based on the thrust curve. In the case of RD-AZ, the RPM of propeller 2 and the RPM of the electric motor are the same, but this may not be the case in other propulsion systems that involve transmitting the rotation of the electric motor to the propeller via a gear connection with a gear mechanism that deviates from a 1:1 ratio for the propeller's rotation. However, in such cases, there is a one-to-one relationship between the rotation of the electric motor and the rotation of the propeller, and it is possible to rotate the electric motor at a rotational speed that gives the propeller rotation according to the thrust curve.

[0030] It should be noted that the present invention is not limited to the use of thrust curves, as other relationships between RPM and rotational speed are also available.

[0031] Based on the thrust request Tr, the control unit 4 determines the corresponding propeller rotation speed, and the control unit 4 is further configured to control the electric motor 3 to rotate the propeller 2 at the rotation speed corresponding to the thrust request Tr.

[0032] In a preferred embodiment, the method includes the step of increasing or decreasing the rotational speed of the propeller, and such step preferably includes the following:

[0033] The control unit receives a thrust request Tr, and upon receiving the thrust request Tr, the control unit 4 controls the electric motor 3 to increase or decrease the rotational speed of the propeller 2 in real time to the rotational speed corresponding to the thrust request (Tr). Increasing the rotational speed occurs when the actual rotational speed of the propeller is lower than that corresponding to the thrust request, and decreasing it occurs when the actual rotational speed of the propeller is higher than that corresponding to the thrust request. Therefore, in a preferred embodiment, the control unit 4 maintains a record of the actual rotational speed of the propeller in order to determine whether to increase or decrease the rotational speed.

[0034] The increase and decrease are performed in real time, which preferably means that no time delay is introduced during the increase and decrease. The rate at which the rotational speed is increased and decreased (dRPM / dt) is typically determined by the propulsion system's ability to respond to the change. In the RD-AZ, the force F (see Figure 2) and moment F·a (see Figure 2) acting on the propeller are already high at zero RPM, enabling a fast response by the propeller when power is supplied to the electric motor.

[0035] This high-speed response allows the propeller's rotational speed to increase rapidly, thus enabling a high amount of momentum to be quickly transferred to the fluid.

[0036] From a power consumption standpoint, it may be beneficial to control the rotational speed between two extremes: maximum RPM and zero RPM. However, a preferred embodiment of the present invention is achieved by operating the RPM so that it falls within the following limits.

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[0037] In other words, the thrust request Tr for an increase corresponds to at least 60% of the propeller's maximum rotational speed, for example, at least 80%. And the thrust request for a decrease corresponds to at most 20% of the propeller's maximum rotational speed, for example, at most 10%. In some embodiments, RPM is reduced to substantially zero RPM, for example, zero RPM. Substantially zero RPM may refer to a situation where the propeller is idle and the flow of water can induce some rotation of the propeller. In some embodiments, the thrust request comes from a thruster allocation routine.

[0038] Figure 1 also shows a preferred embodiment at the bottom of Figure 1, in which the rotational speed corresponding to the thrust requirement for increase is maintained for the duration of the operating time Ot. After the operating time ends, the rotational speed is reduced to the rotational speed corresponding to the thrust requirement for decrease. As shown, the operating time Ot has different durations, but the present invention is not limited to such different durations. During the operating time Ot, the rotational speed is typically constant, but may vary.

[0039] A preferred embodiment of impulse propulsion according to the present invention may involve a gradual increase or decrease in rotational speed. For example, a first thrust request for increasing rotational speed up to 50% of the maximum rotational speed may be followed by a second thrust request for increasing rotational speed up to 80% of the maximum rotational speed. Similarly, a thrust request for decrease may be, for example, a request to decrease to 40% of the maximum rotational speed, followed by a request to decrease to 10% of the maximum rotational speed. Thus, the increase and / or decrease may be performed in stages. Operating time may be included between changes in rotational speed.

[0040] It has also been found that it is beneficial for power consumption for the dwell time Dw to continue after the reduction is executed. However, the duration of the dwell time may have a longer duration in some cases, but the dwell time may not reach a period longer than the time it takes to set up the propulsion device to start increasing, which basically means that an increase can continue immediately after the reduction in rotational speed.

[0041] As shown in Figure 1, the rotational speed of the propeller can be constant during the dwell time. However, the rotational speed may be increased and / or decreased, or may be a combination of constant, increasing, and / or decreasing.

[0042] In the embodiment shown in Figure 1, the rotational speed during the dwell time Dw is less than 10%, and in some cases, 0. In other embodiments, the rotational speed of the propeller is less than 20% of the maximum rotational speed of the propeller during the dwell time Dw, preferably less than 15%, for example less than 10%.

[0043] In a preferred embodiment, the rotational speed of the propeller is substantially zero or zero during the dwell time. Here, "substantially zero" typically refers to a situation where the propeller is in an idle state. In a preferred use case, the method includes providing a number of consecutive alternating thrust requests, which are typically a number of thrust requests as exemplified herein: ···Tr inc ,Tr dec ,Tr inc ,Tr dec ,Tr inc ,Tr dec ,Tr inc ,Tr dec ···

[0044] Here, Tr inc is a thrust request to increase the rotational speed, and Tr dec is a thrust request to decrease the rotational speed. Tr may be stepwise as described above. Tr inc, Tr dec The combination is considered to represent alternating thrust requirements.

[0045] In a preferred embodiment involving such alternating thrust requirements, the thrust requirements for increase are of different magnitudes for at least a number of the alternating thrust requirements, for example, two, three, four, five, or more. As an example, in the embodiment shown in Figure 1, the thrust requirement for increasing the first alternating thrust requirement corresponds to a rotational speed of 100% magnitude, the thrust requirement for decreasing the second alternating thrust requirement is of 80% magnitude, the third is of 100% magnitude, and the fourth is of -100% magnitude.

[0046] In a preferred embodiment, for at least a number of the alternating thrust requests, e.g., two, three, four, five, or more, the thrust requests for the increase are of the same magnitude. This could be a thrust request corresponding to a 10% increase in rotational speed.

[0047] In other embodiments, the thrust requirements for reduction have different magnitudes for at least a number of the alternating thrust requirements, for example, two, three, four, five, or more. One such example is shown in Figure 1, where the thrust requirement for reduction of the first alternating thrust requirement corresponds to a rotational speed of 5%, the thrust requirement for reduction of the second alternating thrust requirement has a magnitude of 8%, the third has a magnitude of 3%, and the fourth has a magnitude of 0%.

[0048] In some preferred embodiments, the thrust requirements for the increase may be the same magnitude for at least a number of the alternating thrust requirements, for example, two, three, four, five, or more.

[0049] As shown in Figure 1, the rotational speed may be kept constant after reaching the rotational speed corresponding to the thrust request. In a preferred embodiment, such an operating time is used in combination with the number of alternating thrust requests, where for at least a number of the alternating thrust requests, e.g., two, three, four, five, or more, the rotational speed corresponding to the thrust request for increase is maintained for the operating time Ot, and thereafter the rotational speed is reduced to the rotational speed corresponding to the thrust request for decrease.

[0050] In a preferred embodiment, the duration of the operating time Ot is of a different magnitude for at least a number of the alternating thrust requests, for example, two, three, four, five, or more. An example of such a case is shown in Figure 1, where it is clear that the operating times Ot are different from one another.

[0051] In a preferred embodiment, at least a number of alternating thrust requests, e.g., two, three, four, five, or more, are time-spaced by dwell times. In a preferred embodiment, at least some dwell times have different durations. In the example shown in Figure 1, all dwell times are different from each other, but the present invention is not limited to such differences.

[0052] The right side of Figure 2 conceptually illustrates how a preferred embodiment of the present invention can consume less power than a prior art method. The thruster shown in Figure 2 is a rim-driven tunnel thruster, but the present invention is not limited to such thrusters. In the embodiment shown in Figure 2, the objective is to maintain a ship at a fixed position. In the prior art method, this is done by keeping the propeller running continuously, but the force F(t) applied to rotate the propeller in Figure 2 fluctuates over time, as shown by the dotted line.

[0053] On the right side of Figure 2, the temporal change of force F(t) in a preferred embodiment is also plotted and labeled "impulse propulsion".

[0054] Assuming an ideal, lossless hydrodynamic model, the amount of impulse supplied to the seawater by the propulsion system can be expressed as follows:

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[0055] Therefore, by rapidly increasing F(t), a greater change is achieved in the impulse to seawater compared to a slower increase in F(t). This can be symbolically expressed in an unrestricted manner.

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[0056] It should be noted that propellers can typically rotate in both forward and reverse directions. In preferred embodiments, therefore, RPM does not impart direction to rotation. Since the blades are hydrodynamically designed for rotation in one direction, the thrust generated in reverse rotation may be smaller. In rim-driven azimuth thrusters, the azimuth function can be used to prevent reverse rotation, and in rim-driven tunnel thrusters, it can be assumed that the design can provide maximum RPM and thrust in both rotation directions.

[0057] On the right side of Figure 2, F(t) is plotted to vary between zero and higher values ​​for clarity. Since the energy consumption of the propulsion system is proportional to the area under the dotted line, it is clear from the visual inspection that impulse propulsion has lower energy consumption than prior art.

[0058] As shown in Figure 2, a preferred embodiment of impulse propulsion involves the propulsion system being operated intermittently, with a thrust request Tr for increasing RPM followed by a thrust request for decreasing RPM. That is, in a preferred embodiment, the RPM decreases immediately after it has increased. Impulse propulsion may include a dwell time, as shown in Figure 2.

[0059] Since a preferred embodiment of the present invention lies in the rapid increase of RPM, it may be preferable that the electric motor and propeller be configured to provide the propeller 2 with maximum rotational force when power is supplied to the electric motor. Such a configuration is particularly evident in embodiments involving rim drives, such as RD-AZ and RD-TT, where the magnet and coil configuration provides a large force to the rim even at zero RPM.

[0060] Impulse propulsion may include a period during which the rotational speed is maintained substantially constant after being increased or decreased in real time. An example of this is shown in Figure 3, where the modified RPM is maintained at a substantially constant value before the change was made to the RPM. Figure 3 also shows that the RPM can be less than zero, meaning the propeller can rotate in both clockwise and counterclockwise directions. Maintaining a substantially constant RPM after an increase or decrease in RPM may result in impulse propulsion falling into what could be called conventional propulsion, although the favorable effects of impulse propulsion can still be obtained during the increase in RPM. The upper part of Figure 3 is for a rim-driven tunnel thruster, and the lower part is for a rim-driven azimuth thruster.

[0061] In Figure 3, the following abbreviations are used. ·“ThrustAft” Stern thrust • "Tp" Propeller thrust, "TpAft" Stern propeller thrust, "TpFore" Bow propeller thrust, "Tp BB(N)" Port propeller thrust (Newtons), "Tp SB(N)" Starboard propeller thrust (Newtons) • "ThrustFore Monitor (N)" Bow monitor thrust (Newtons) • "Thrust BB (N)" Port thrust (Newtons) • "Thrust SB (N)" Starboard thrust (Newtons) • "HullFY": Hull thrust, "HullFy (N)": Hull thrust (Newtons) • "TotFY" Total lateral thrust (Tp + HullFY) • "RPM aft" - Stern rotation speed • "RPM Fore" Bow rotation speed • "RPM BB" Port rotation speed • "RPM SB" Starboard rotation speed • "Monitor" is a data term referring to a value that has been calculated and displayed.

[0062] The dashed ellipse indicates the region where the total transverse thrust (TotFY) changes rapidly. Tunnel thrusters generate thrust from the propeller, which creates a pressure field on the hull, and the sum of the resulting forces provides a force in the same direction as the propeller thrust. Typically, the Tp / TotFY relationship is approximately 70 / 30.

[0063] The upper part of Figure 3 is achieved by two tunnel thrusters (RD-TT), one at the bow and one at the stern. The lower part of Figure 3 is achieved by two azimuth thrusters (RD-AZ), both located at the stern, one on the starboard side and one on the port side.

[0064] Figures 4A and 4B show examples of real-time RPM increase. The results are provided by a computational fluid dynamics model, and the thrusters are two tunnel thrusters (rim-driven tunnel thrusters) located at the bow of the ship. Figure 4A shows the total thrust acting on the hull when the thrusters are "boosted," i.e., when they provide the maximum thrust response. The temporal change in RPM of the two thrusters is also shown in Figure 4A. Note that in Figures 4A and 4B, "fore" refers to the forward thruster and "aft" refers to the thruster located behind the forward thruster, towards the stern.

[0065] Figure 4B shows the power consumption over the same period as in Figure 4A.

[0066] Figure 4A shows that maximum thrust is reached in a time slightly greater than 1 second (approximately 1.33 seconds). Figure 4B shows that approximately 200 kW is required for maximum thrust. This appears to be in stark contrast to the virtually steady state reached after about 2 seconds (see Figure 4A - total force), where the power consumption is approximately 1100 kW and the thrust generated is lower than that of the maximum thrust.

[0067] From the perspective of the present invention, at least the portion of Figure 4A up to the point of reaching maximum thrust can be considered an example of impulse propulsion. Therefore, the power in the thrust / power consumption relationship is more power-efficient than in the steady state.

[0068] The propulsion system can be virtually any type of device equipped with a propeller, but preferred embodiments of the present invention utilize thrusters such as azimuth thrusters and / or tunnel thrusters. In preferred embodiments, the thruster can be a rim-driven azimuth thruster and / or a rim-driven tunnel thruster. Such thrusters can typically have propeller blades coupled to the rim at the tip, so that there is no gap between the blade tips and the rim. Such a zero-gap configuration results in higher hydrodynamic efficiency of the propeller compared to an open-propeller configuration because tip vortices are not generated. Such tip vortices would otherwise arise from the flow of water from the high-pressure side to the low-pressure side of the propeller blade, but such water passage is prevented due to the zero gap.

[0069] While tunnel thrusters can generally be used as general-purpose thrusters, in preferred embodiments of the present invention, tunnel thrusters are used to provide only basic lateral thrust, such as when used as bow thrusters.

[0070] In a preferred embodiment where a thruster is used, the thruster can be a permanent magnet rim-driven thruster. In such a thruster, permanent magnets are positioned on a rim 8 from which the propeller blades 6 of the propeller 2 extend toward the thruster's hub 7. One such example is shown in Figure 1, which represents an azimuth thruster. By integrating the propeller blades 6 into the thruster, there is no gap between the tips of the propeller blades 6 and the rim 8, and there is no gap between the roots of the propeller blades 6 and the hub 7. Thus, the thruster has a zero-gap configuration.

[0071] Instead of rim-driven thrusters, a shrouded propeller is used in a preferred embodiment. Such a shrouded propeller can also be considered a zero-gap configuration, and the propeller is typically driven by a central shaft connected to an electric motor.

[0072] Since the motor that provides the rotational speed of the propeller is electric, the motor is supplied with power. Several options are available for supplying power, and in some preferred embodiments, the power supplied to the electric motor 3 for the rotation of the propeller 2 is supplied at least partially, for example, entirely, by a power storage device such as one or more batteries. Thus, in some embodiments, all of the power is supplied by the power storage device, and in other embodiments, the power storage device is an additional power supply to another power source.

[0073] Another power source that can be a standalone power source may be a combustion-electric drive system, such as a diesel-electric drive system or an Otto-electric drive system. In such embodiments, a combustion engine drives a generator, which generates electricity. In embodiments with a combustion-electric drive system, the drive system may also include a power storage device, such as a battery, which is electrically charged by a generator driven by the combustion engine of the drive system, and the electricity supplied to the electric motor is supplied at least partially, for example, entirely, by the power storage device. A configuration of a combustion-electric drive system with a power storage device may have the advantage that, in relation to impulse propulsion, the combustion engine can be rated to provide less effect than what is required to drive the propeller at maximum RPM. This is because the combustion engine charges the power storage device when the RPM is low, and the power storage device is discharged at high RPM.

[0074] In a preferred embodiment, the electric motor 3 is an AC motor, and the power supplied to the electric motor for the rotation of the propeller 2 is supplied via a frequency converter. Such a frequency converter is configured to supply alternating current at a controllable frequency. In such an embodiment, the frequency of the alternating current controls the rotational speed of the electric motor 3. Thus, by controlling the frequency of the alternating current, control of the rotational speed of the propeller is provided. Therefore, in a preferred embodiment, the thrust request Tr is converted to the rotational speed of the propeller (as detailed with respect to Figure 4), and this rotational speed is then converted to a frequency to be delivered by a frequency control device.

[0075] In a preferred embodiment, the frequency converter is configured to provide real-time increases or decreases in RPM by ramping up and ramping down the frequency of the AC. The ramp-up or ramp-down can preferably be performed at a rate of change greater than 10 Hz per second (dHz / dt), for example, greater than 20 Hz per second and less than 30 Hz per second.

[0076] Furthermore, by changing the rate of change (dHz / dt), that is, d 2 Hz / dt 2 Since it can be advantageous for d to be different from zero, the rate of change (dHz / dt) does not necessarily have to be constant during ramp-up or ramp-down. For example, because a propeller has a considerable moment of inertia, d does not necessarily have to be constant with respect to accelerating and decelerating a rotating propeller. 2 Hz / dt 2 It may be advantageous to choose to increase it over time when RPM is increasing and decrease it over time when RPM is decreasing.

[0077] One of the highly advantageous effects of applying impulse propulsion is provided in the automatic positioning of a vessel, during which the vessel is required to maintain its position, such as maintaining a position defined by coordinates, for example, GPS coordinates. In such embodiments, the vessel typically comprises at least two propulsion devices 1, as otherwise disclosed herein.

[0078] In a preferred embodiment, the propulsion system may consist of two azimuth thrusters at the stern of the vessel and one or more tunnel thrusters at the bow of the vessel. Each of these propulsion systems 1 is configured to provide impulse propulsion in the manner of a preferred embodiment disclosed herein.

[0079] A preferred embodiment of automatic ship positioning utilizes a thruster assignment routine that provides a set of thrust requests Tr to the control unit 4 to maintain the ship in a substantially fixed position. Such a thruster assignment routine is computer-implemented, and the input to the routine is the actual GPS position provided by the GPS system. The thruster assignment routine calculates what may be called a position correction based on the actual GPS position and a specified GPS position, and converts the position correction into thrust requests to the propulsion system.

[0080] The present invention can be implemented by hardware, software, firmware, or any combination thereof. Some aspects of the present invention or its features can also be implemented as software running on one or more data processors and / or digital signal processors.

[0081] Individual elements of embodiments of the present invention can be implemented in any suitable physical, functional, and logical manner, such as in a single unit, in multiple units, or as part of multiple other functional units. The present invention can be implemented in a single unit or physically and functionally distributed among multiple different units and processors.

[0082] While the present invention has been described in relation to specific embodiments, it should not be construed as being limited to the examples presented. The scope of the present invention should be interpreted in light of the accompanying set of claims. In the context of the claims, the terms “comprising” or “comprises” do not exclude other possible elements or processes. Nor should references such as “a” or “an” be construed as excluding plurals. Nor should the use of reference numerals for elements shown in the figures in the claims be construed as limiting the scope of the present invention. Furthermore, individual features mentioned in different claims may, in some cases, be advantageously combined, and references to these features in different claims do not preclude the possibility or benefit of combining features. [Explanation of Symbols]

[0083] 1. Propulsion System 2-rotatable propeller 3 Electric motor 4. Control Unit 5. Power supply unit (of the propulsion system) 6 propeller blades 7 Hubs Tr thrust requirement Dw Dwell time Ot operating time

Claims

1. A method for providing impulse propulsion to a ship by a propulsion system (1), wherein the propulsion system is - A propulsion device (1) having a rotatable propeller (2) and generating thrust of a magnitude corresponding to the rotational speed of the propeller (2), - An electric motor (3) coupled to the propeller (2) and providing the rotational speed, - A control unit (4) such as a propulsion control system, which is configured to receive a thrust request (Tr) representing the thrust required from the propulsion device (1), and to control the electric motor (3) to rotate the propeller (2) at a rotational speed corresponding to the thrust request, Equipped with, The aforementioned method, - When the control unit (4) receives the thrust request (Tr), the control unit (4) controls the electric motor (3) to increase or decrease the rotational speed of the propeller (2) in real time to the rotational speed corresponding to the thrust request (Tr). Methods that include...

2. - The thrust requirement (Tr) for the increase corresponds to at least 50%, for example at least 60%, for example at least 80%, of the maximum rotational speed of the propeller, and / or - The thrust requirement for the reduction corresponds to at most 20%, for example, at most 10%, of the propeller's maximum rotational speed, or the reduction corresponds to a rotational speed at which it is substantially zero, for example, zero. The method according to claim 1.

3. The method according to claim 1 or 2, wherein the rotational speed corresponding to the thrust request for the increase is maintained for an operating time (Ot), and thereafter the rotational speed is reduced to the rotational speed corresponding to the thrust request for the decrease.

4. The method according to any one of claims 1 to 3, wherein the propulsion device is operated intermittently, and the thrust request for an increase (Tr) is followed by the thrust request for a decrease.

5. The method according to any one of claims 1 to 4, wherein a dwell time (Dw) follows after the reduction is performed.

6. The method according to claim 5, wherein during the dwell time, the rotational speed of the propeller is constant, increased, and / or decreased.

7. The method according to claim 5 or 6, wherein during the dwell time, the rotational speed of the propeller is less than 20%, preferably less than 15%, for example less than 10%, of the maximum rotational speed of the propeller.

8. The method according to claim 5, wherein during the dwell time, the rotational speed of the propeller is substantially zero or zero.

9. It comprises a number of consecutive alternating thrust requests, each including the thrust request (Tr) for increasing thrust and the subsequent thrust request (Tr) for decreasing thrust, wherein for at least a number of the alternating thrust requests, for example two, three, four, five, or more, the thrust requests for increasing thrust have different magnitudes. The method according to any one of claims 1 to 8.

10. The method according to claim 9, wherein for at least a number of the alternating thrust requests, for example two, three, four, five, or more, the thrust requests for the increase are of the same magnitude.

11. The method according to claim 9, wherein for at least a number of the alternating thrust requests, for example two, three, four, five, or more, the thrust requests for reduction are of different magnitudes.

12. The method according to any one of claims 9 to 11, wherein for at least a number of the alternating thrust requests, for example two, three, four, five, or more, the thrust requests for the increase are of the same magnitude.

13. The method according to any one of claims 9 to 12, wherein for at least a number of the alternating thrust requests, for example two, three, four, five, or more thrust requests, the rotational speed corresponding to the thrust requests for increase is maintained for an operating time (Ot), and thereafter the rotational speed is reduced to the rotational speed corresponding to the thrust requests for decrease.

14. The method according to claim 13, wherein the duration of the operating time (Ot) is of a different magnitude for at least a number of the alternating thrust requests, for example, two, three, four, five, or more thrust requests.

15. When dependent on claim 4, for at least a number of the alternating thrust requests, for example two, three, four, five, or more, the alternating thrust requests are time-separated by the dwell time, preferably at least some of the dwell times having different durations. The method according to any one of claims 9 to 14.

16. The method according to any one of claims 1 to 15, wherein the electric motor and the propeller are configured to provide the propeller (2) with maximum rotational force when power is supplied to the electric motor.

17. The method according to any one of claims 1 to 16, wherein the rotational speed, after being increased or decreased in real time, is kept substantially constant.

18. The method according to any one of claims 1 to 17, wherein the propulsion device (1) is a thruster such as an azimuth thruster and / or a tunnel thruster.

19. The method according to claim 18, wherein the thruster is a permanent magnet rim-driven thruster, the magnets are arranged on the rim (8), the propeller blades (6) of the propeller (2) extend from the rim (8) toward the hub (7) of the thruster, there is no gap between the tip of the propeller blade (6) and the rim (8), and there is no gap between the base of the propeller blade (6) and the hub (7).

20. The method according to any one of claims 1 to 17, wherein the propulsion device is a shrouded propeller, a ducted propeller, or a nozzle propeller.

21. The method according to any one of claims 1 to 20, wherein the power supplied to the electric motor (3) for the rotation of the propeller (2) is at least partially, for example, fully supplied by one or more power storage devices such as batteries.

22. The method according to any one of claims 1 to 21, wherein the power supplied to the electric motor (3) for the rotation of the propeller (2) is at least partially, for example, fully, supplied by a combustion electric drive system such as a diesel electric drive system or an Otto electric drive system, the drive system includes a power storage device such as a battery, the power storage device is electrically charged by a generator driven by the combustion engine of the drive system, and the power supplied to the electric motor is at least partially, for example, fully supplied by the power storage device.

23. The method according to any one of claims 1 to 22, wherein the electric motor (3) is an AC motor, the power supplied to the electric motor for the rotation of the propeller (2) is supplied via a frequency converter that supplies alternating current, and the frequency of the alternating current controls the rotational speed of the electric motor (3) and, consequently, the rotational speed of the propeller.

24. The method according to claim 23, wherein the frequency converter is configured to increase (ramp up) and decrease (ramp down) the frequency of the AC at a rate of change (dHz / dt) of more than 10 Hz per second, for example, more than 20 Hz per second and less than 30 Hz per second, thereby providing the increase or decrease in real time.

25. A method for automatically maintaining the position of a vessel, wherein the vessel comprises at least two propulsion devices (1), for example, two azimuth thrusters at the stern of the vessel and one or more tunnel thrusters at the bow of the vessel, each of the propulsion devices (1) is configured to provide impulse propulsion in accordance with the method of any one of claims 1 to 24, and a thruster assignment routine provides the thrust requests to the control unit (4) to maintain the vessel in a substantially fixed position.

26. A propulsion system that provides impulse propulsion to a ship by propulsion system (1), wherein the propulsion system is - A propulsion device (1) having a rotatable propeller (2) and generating thrust of a magnitude corresponding to the rotational speed of the propeller (2), - An electric motor (3) coupled to the propeller (2) and providing the rotational speed, - A control unit (4) such as a propulsion control system, which is configured to receive a thrust request (Tr) representing the thrust required from the propulsion device (1), and to control the electric motor (3) to rotate the propeller (2) at a rotational speed corresponding to the thrust request, Equipped with, The propulsion system is - When the control unit (4) receives the thrust request (Tr), the control unit (4) controls the electric motor (3) to increase or decrease the rotational speed of the propeller (2) in real time to the rotational speed corresponding to the thrust request (Tr). A propulsion system that is configured in such a way.

27. The propulsion system according to claim 26, configured to perform the method described in any one of claims 1 to 25.

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