Pile gripper positioning system, dynamic positioning system, monopile installation vessel, and corresponding methods

BACKGROUND OF THE INVENTION

The invention relates to the installation of monopiles as part of the installation process of wind turbines, in particular offshore wind turbines. In a known method for installing an offshore wind turbine, the foundation, in the form of a monopile, is installed first by driving the monopile into the sea bottom after which the wind turbine is installed on the monopile, either by installing the wind turbine at once as a whole or by assembling the wind turbine in parts on the monopile.

There is a trend towards larger wind turbines and a desire to install offshore wind turbines at locations with larger water depths than currently encountered. Both result in larger and heavier foundations. Hence, it is expected that soon monopiles need to be installed that are larger than 100 meters, possibly 120 meters or larger. The weight of such monopiles may be larger than lOOOmt, possibly 1300mt or above.

To save time during the installation process, the use of floating vessels is preferred over jack-up type vessels. Such floating vessels typically include a lifting crane to suspend the monopile from, and a pile gripper to engage with the monopile, wherein the lifting crane and the pile gripper cooperate to lower the monopile into the sea using, amongst others, a pile gripper positioning system. Generally, the vessels further include a dynamic positioning system to position the vessel during the lowering of the monopile.

When the dynamic positioning system and the pile gripper positioning system function independently from each other, stability issues may arise in which the dynamic positioning system becomes unstable.

To solve these and other issues, it has been proposed in international patent publication WO2020/145825 to interconnect control systems of different actuators of the vessel, such as for example the dynamic positioning system and the pile gripper positioning system. One of the disclosed interconnections is to use an instruction for motive action, i.e. a signal directly or indirectly sent to an actuator by the pile gripper positioning system, to determine a force intended to be applied to the vessel, to subsequently determine a compensation action, and to control the dynamic positioning system to apply the compensation action. This is also known as feedforward control.

However, it has been found by the applicant that this type of feedforward control is insufficient to provide stability in all desired operating situations.

SUMMARY OF THE INVENTION

In view of the above it is an object of the invention to improve stability of a monopile installation method using a floating vessel with dynamic positioning system and pile gripper positioning system.

According to a first aspect of the invention, there is provided a pile gripper positioning system for a pile gripper that is configured to be provided on a vessel to engage with a monopile during a monopile installation method, wherein the pile gripper positioning system comprises: an actuator system for applying forces to the pile gripper to position the pile gripper relative to the vessel, a measurement system for determining a position of the monopile in the pile gripper relative to the vessel, and a pile gripper control unit for driving the actuator system in dependency of a desired position and an actual position of the monopile as measured by the measurement system, wherein the pile gripper control unit is configured to receive a signal representative for a position of the vessel, wherein, during at least a portion of the monopile installation method, the pile gripper control unit is configured to determine a drive signal for the actuator system to compensate at most a portion of a deviation of the position of the vessel from a desired position of the vessel, and wherein, during said at least a portion of the monopile installation method, the pile gripper control unit for driving the actuator system is configured to drive the actuator system in dependency of a desired position and an actual position of the monopile as measured by the measurement system, and the drive signal to compensate at most a portion of a deviation of the position of the vessel from a desired position of the vessel.

The invention according to the first aspect of the invention is based on the insight that stability issues may arise when the pile gripper and corresponding pile gripper positioning system are configured to fully compensate motion of the vessel as the full compensation is likely to exert relatively large forces to the vessel urging the vessel away from its desired position thereby requiring even more compensation. During at least some portions of the monopile installation method this may cause instable behavior. By only partially compensating for the vessel's motion, and thus allowing a deviation of the position of the monopile from its desired position, the forces applied to the vessel by the pile gripper can be limited to prevent instable behavior.

Hence, by only partially compensating for the vessel's motion, the setpoint for the pile gripper (and thus the monopile) is deliberately changed from a desired position to an adjusted position and the pile gripper control unit is then configured to control the actuator system using this changed setpoint. However, there is always some kind of setpoint and the pile gripper control unit is always urging the actual position to be identical to the position represented by the setpoint, whether this position is the desired position or a position deliberately chosen to be different from the desired position. The skilled person will recognize that this deliberate change of the setpoint is not linked to any unwanted deviation or tolerance that may inherently exist in a control system nor to measures to reduce applied forces and prevent damage. These measures may be applied as an addition to the current invention but do not change the fact that the control system has a different setpoint for the position of the pile gripper and is trying to meet this setpoint within the boundaries that may have been set by force limitation loops and not the original desired setpoint. The invention is further not related to the absence of control when the pile gripper is within a certain desired positional range. It is explicitly noted that the position of the monopile in the pile gripper may alternatively or additionally refer to a position of a part of the monopile and/or an orientation of the monopile or a part thereof.

It is further noted here that the position of the vessel may alternatively or additionally refer to a position of a part of the vessel and/or an orientation of the vessel or part thereof.

It is also explicitly noted that the determination of a drive signal for the actuator system to compensate at most a portion of a deviation of the position of the vessel from a desired position of the vessel means that at least a non-zero portion of the deviation of the position of the vessel from a desired position is directly or indirectly ignored or discarded either by multiplication with a factor smaller than 1 or by subtraction of a nonzero value.

The mentioned monopile installation method may include a plurality of phases, including but not limited to: a suspension phase, in which the monopile is suspended from the lifting crane above water level and engaged by the pile gripper, a lowering phase, in which the monopile is suspended from the lifting crane and engaged by the pile gripper, and a lower end of the monopile is in the water, but above the seabed, a seabed penetration phase, in which the monopile is suspended from the lifting crane and engaged by the pile gripper, and a lower end of the monopile has penetrated the seabed, a driving phase, in which the monopile is engaged by the pile gripper and driven into the seabed using a hammer or the like.

In an embodiment, the at least a portion of the monopile installation method includes at least a portion of the seabed penetration phase. In an embodiment, the at least a portion of the monopile installation method includes at least a portion of the lowering phase, for instance the portion of the lowering phase just before the seabed penetration phase, where the lower end of the monopile is just above the seabed to penetrate the seabed.

In an embodiment, a ratio is defined between the to be compensated portion of the deviation of the position of the vessel from a desired position of the vessel and the deviation of the position of the vessel from a desired position of the vessel, i.e. the full deviation of the position of the vessel from the desired position of the vessel.

In an embodiment, said ratio or the to be subtracted non-zero value is dependent on one or more of the following parameters: a weight of the monopile, a length of the monopile, an inclination of the monopile relative to the vertical, a length of hoisting wire between lifting crane and monopile, an orientation of the hoisting wire between lifting crane and monopile, a length of monopile below the pile gripper, a length of monopile above the pile gripper, a length of monopile between the pile gripper and sea bottom, a water depth, i.e. a distance between the sea bottom and the water surface, a distance between the location where the hoisting line leaves the lifting crane and the pile gripper, a distance between a lower end of the monopile and the sea bottom, a distance between the location where the hoisting line leaves the lifting crane and the sea bottom, a distance between the pile gripper and the sea bottom, a ratio between a length of monopile below the pile gripper and a length of monopile above the pile gripper, a ratio between a length of monopile above the pile gripper and a length of monopile between the pile gripper and sea bottom, a position of a center of gravity of the monopile, and a tension in the hoisting wire between lifting crane and monopile.

In an embodiment, during at least a portion of the seabed penetration phase, the pile gripper control unit is configured such that said ratio is increasing with increasing penetration depth of the lower end of the monopile, or the to be subtracted non-zero value is decreasing with increasing penetration depth of the lower end of the monopile.

In an embodiment, during at least a portion of the seabed penetration phase, the pile gripper control unit is configured such that said ratio has a linear relationship with the penetration depth of the lower end of the monopile.

In an embodiment, during at least a portion of the lowering phase, the pile gripper control unit is configured such that said ratio is set to the distance between the location where the hoisting line leaves the lifting crane divided by the distance between the location where the hoisting line leaves the lifting crane and the sea bottom.

According to a second aspect of the invention, there is provided a dynamic positioning system for a vessel, wherein the vessel comprises a pile gripper for engaging with a monopile during a monopile installation method, wherein the dynamic positioning system comprises: an actuator system for applying forces to the vessel to position the vessel, a measurement system for measuring a position of the vessel, and a dynamic positioning control unit for driving the actuator system in dependency of a desired position and an actual position of the vessel as measured by the measurement system, wherein the dynamic positioning control unit is configured to determine a signal representative for a difference between the desired position and the actual position of the vessel, and wherein, during at least a portion of the installation method, the dynamic positioning control unit is configured to output a signal that is representative for at most a portion of said difference. It is noted explicitly here that said difference between the desired position and the actual position of the vessel may alternatively be referred to as a deviation of the position of the vessel from a desired position of the vessel.

It is further noted here that the position of the vessel may alternatively or additionally refer to a position of a part of the vessel and/or an orientation of the vessel or part thereof.

It is also explicitly noted that a portion of the difference between the desired position of the vessel and the actual position of the vessel means that at least a non-zero portion of said difference is directly or indirectly ignored or discarded either by multiplication with a factor smaller than 1 or by subtraction of a non-zero value.

The mentioned monopile installation method may include a plurality of phases, including but not limited to: a suspension phase, in which the monopile is suspended from the lifting crane above water level and engaged by the pile gripper, a lowering phase, in which the monopile is suspended from the lifting crane and engaged by the pile gripper, and a lower end of the monopile is in the water, but above the seabed, a seabed penetration phase, in which the monopile is suspended from the lifting crane and engaged by the pile gripper, and a lower end of the monopile has penetrated the seabed, a driving phase, in which the monopile is engaged by the pile gripper and driven into the seabed using a hammer or the like.

In an embodiment, the at least a portion of the monopile installation method includes at least a portion of the seabed penetration phase.

In an embodiment, the at least a portion of the monopile installation method includes at least a portion of the lowering phase, for instance the portion of the lowering phase just before the seabed penetration phase, where the lower end of the monopile is just above the seabed to penetrate the seabed.

In an embodiment, a ratio is defined between the outputted difference and the full difference between the desired position and the actual position of the vessel.

In an embodiment, said ratio or the to be subtracted non-zero value is dependent on one or more of the following parameters: a weight of the monopile, a length of the monopile, an inclination of the monopile relative to the vertical, a length of hoisting wire between lifting crane and monopile, an orientation of the hoisting wire between lifting crane and monopile, a length of monopile below the pile gripper, a length of monopile above the pile gripper, a length of monopile between the pile gripper and sea bottom, a water depth, i.e. a distance between the sea bottom and the water surface, a distance between the location where the hoisting line leaves the lifting crane and the pile gripper, a distance between a lower end of the monopile and the sea bottom, a distance between the location where the hoisting line leaves the lifting crane and the sea bottom, a distance between the pile gripper and the sea bottom, a ratio between a length of monopile below the pile gripper and a length of monopile above the pile gripper, a ratio between a length of monopile above the pile gripper and a length of monopile between the pile gripper and sea bottom, a position of a center of gravity of the monopile, and a tension in the hoisting wire between lifting crane and monopile.

In an embodiment, during at least a portion of the seabed penetration phase, the dynamic positioning control unit is configured such that said ratio is increasing with increasing penetration depth of the lower end of the monopile, or the to be subtracted non-zero value is decreasing with increasing penetration depth of the lower end of the monopile.

In an embodiment, during at least a portion of the seabed penetration phase, the dynamic positioning control unit is configured such that said ratio has a linear relationship with the penetration depth of the lower end of the monopile.

In an embodiment, during at least a portion of the lowering phase, the dynamic positioning control unit is configured such that said ratio is set to the distance between the location where the hoisting line leaves the lifting crane divided by the distance between the location where the hoisting line leaves the lifting crane and the sea bottom.

According to a third aspect of the invention, there is provided a vessel to carry out a monopile installation method, comprising: a hull, a pile gripper arranged on the hull for engaging a monopile, a dynamic positioning system for positioning the vessel, and a pile gripper positioning system for positioning a monopile with the pile gripper, wherein the dynamic positioning system is configured to determine a position of the vessel, and wherein, during at least a portion of the monopile installation method, the vessel is configured to operate the pile gripper positioning system for at most partially compensating a deviation of the determined position of the vessel from a desired position of the vessel.

In an embodiment, the dynamic positioning system is configured to provide the determined position of the vessel to the pile gripper positioning system, wherein the pile gripper positioning system is a pile gripper positioning system according to a first aspect of the invention. In an embodiment, the dynamic positioning control unit is a dynamic positioning control unit according to a second aspect of the invention, wherein the pile gripper positioning system is configured to receive the signal that is representative for at most a portion of said difference in order to at most partially compensating a deviation of the determined position of the vessel from a desired position of the vessel.

In an embodiment, the vessel comprises an overall control unit, wherein the pile gripper positioning system is configured to is configured to receive a signal representative for a position of the vessel from the dynamic positioning system, to determine a drive signal for the actuator system to compensate at most a portion of a deviation of the position of the vessel from a desired position of the vessel, and to output said drive signal to the pile gripper positioning system in order to at most partially compensating a deviation of the determined position of the vessel from a desired position of the vessel.

According to a fourth aspect of the invention, there is provided a method to install monopiles, wherein use is made of a vessel comprising a dynamic positioning system to position the vessel, and a pile gripper to engage with the monopile, and wherein the method comprises the following steps: a. lowering a monopile towards or into a seabed while engaging the monopile with the pile gripper, b. determining a deviation of the position of the vessel from a desired position of the vessel, and c. at most partially compensating said deviation with the pile gripper.

In an embodiment, the vessel comprises a lifting crane to suspend the monopile therefrom.

In an embodiment, the method is carried out when the monopile is suspended by the lifting crane.

In an embodiment, the method is carried out during a portion of the monopile installation method. In an embodiment, the method is carried out during at least a portion of the seabed penetration phase in which the monopile is suspended from a lifting crane and engaged by the pile gripper, and a lower end of the monopile has penetrated the seabed.

In an embodiment, the method is carrier out during at least a portion of the lowering phase in which the monopile is suspended from a lifting crane and engage by the pie gripper, and a lower end of the monopile is in the water, but above the seabed.

According to a fifth aspect of the invention, there is provided a dynamic positioning system for a vessel, wherein the vessel comprises a lifting crane for lifting a monopile and a pile gripper for engaging with a monopile, said lifting crane and pile gripper being configured to cooperate in lowering the monopile into a sea, wherein the dynamic positioning system comprises: an actuator system for applying forces to the vessel to position the vessel, a measurement system for measuring a position of the vessel, a dynamic positioning control unit for driving the actuator system in dependency of a desired position and an actual position of the vessel as measured by the measurement system, wherein the dynamic positioning control unit is configured to receive a signal representative for a force exerted by the pile gripper to the vessel, and wherein the dynamic positioning control unit is configured to use a portion of said signal as a feedforward signal to drive the actuator system.

The invention according to the fifth aspect is based on the insight that an obvious improvement over WO2020/145825 by using the actual force exerted by the pile gripper to the vessel instead of the desired force to be exerted by the pile gripper is insufficient to improve stability in all circumstances, but that by using a portion of the actual force exerted by the pile gripper as feedforward signal does improve stability. It is noted explicitly here that the position of the vessel may alternatively or additionally refer to a position of a part of the vessel and/or an orientation of the vessel or part thereof.

It is further noted explicitly that the use of a portion of the signal representative for a force exerted by the pile gripper to the vessel means that at least a non-zero portion of the signal is ignored or discarded either by multiplication with a factor smaller than 1 or by subtraction of a non-zero value.

In an embodiment, a ratio between the used portion of the signal as feedforward signal and the received full signal is between 0.4 to 0.9, preferably between 0.5 and 0.7, e.g. 0.6.

The monopile installation method may include a plurality of phases, including but not limited to: a suspension phase, in which the monopile is suspended from the lifting crane above water level and engaged by the pile gripper, a lowering phase, in which the monopile is suspended from the lifting crane and engaged by the pile gripper, and a lower end of the monopile is in the water, but above the seabed, a seabed penetration phase, in which the monopile is suspended from the lifting crane and engaged by the pile gripper, and a lower end of the monopile has penetrated the seabed, a driving phase, in which the monopile is engaged by the pile gripper and driven into the seabed using a hammer or the like.

In an embodiment, the ratio between the used portion of the signal as feedforward signal and the received full signal or the to be subtracted non-zero value is dependent on the phase of the monopile installation method.

In an embodiment, the use of only a portion of the signal representative for a force exerted by the pile gripper to the vessel, e.g. a ratio below 1 or the to be subtracted non- zero value, is applied only during the lowering phase and/or the seabed penetration phase.

In an embodiment, the ratio between the used portion of the signal as feedforward signal and the received full signal or the to be subtracted non-zero value is dependent on one or more of the following parameters: a weight of the monopile, a length of the monopile, an inclination of the monopile relative to the vertical, a length of hoisting wire between lifting crane and monopile, an orientation of the hoisting wire between lifting crane and monopile, a length of monopile below the pile gripper, a length of monopile above the pile gripper, a length of monopile between the pile gripper and sea bottom, a ratio between a length of monopile below the pile gripper and a length of monopile above the pile gripper, a ratio between a length of monopile above the pile gripper and a length of monopile between the pile gripper and sea bottom, a position of a center of gravity of the monopile, and a tension in the hoisting wire between lifting crane and monopile.

In an embodiment, the ratio between the used portion of the signal as feedforward signal and the received full signal is dependent on a length of the monopile below the pile gripper or a length of the monopile between the pile gripper and sea bottom, and on a length of the monopile above the pile gripper. In an embodiment, this dependency may only apply during the seabed penetration phase.

In an embodiment, during the seabed penetration phase, the dynamic positioning system is configured to determine a ratio a between the used portion of the signal as feedforward signal and the received full signal using the following equation: a = a / (a + b) with a being the length of the monopile above the pile gripper, and b being the length of the monopile below the pile gripper or being the length of the monopile between the pile gripper and the sea bottom.

In an embodiment, the dynamic positioning system is configured to receive input allowing to determine parameters a and b. This input may include one or more of the following information: a measurement signal representative for parameter a, a measurement signal representative for parameter b, a total length of the monopile handled, a measurement signal representative for a (vertical) position of a hoisting hook from which the monopile is suspended, and a(n) (average) water depth.

According to a sixth aspect of the invention, there is provided a pile gripper positioning system for a pile gripper that is configured to be provided on a vessel to engage with a monopile suspended by a lifting crane of the vessel, wherein the pile gripper positioning system comprises: an actuator system for applying forces to the pile gripper to position the pile gripper relative to the vessel, a measurement system for determining a position of the monopile in the pile gripper, a pile gripper control unit for driving the actuator system in dependency of a desired position and an actual position of the monopile as measured by the measurement system, wherein the measurement system is further configured to determine a force exerted by the pile gripper to the vessel, and wherein the pile gripper control unit is configured to output a signal that is representative for a portion of the force exerted by the pile gripper to the vessel as measured by the measurement system. It is noted explicitly here that the position of the pile gripper may alternatively or additionally refer to a position of a part of the pile gripper and/or an orientation of the pile gripper or part thereof. Further, the position of the monopile in the pile gripper may alternatively or additionally refer to a position of a part of the monopile and/or an orientation of the monopile or a part thereof.

It is further noted explicitly that outputting a portion of the signal representative for a force exerted by the pile gripper to the vessel means that at least a non-zero portion of said signal is ignored or discarded either by multiplication with a factor smaller than 1 or by subtraction of a non-zero value.

In an embodiment, a ratio between the outputted signal and a signal representative for the force exerted by the pile gripper to the vessel as measured by the measurement system is between 0.4 to 0.9, preferably between 0.5 and 0.7, e.g. 0.6.

In an embodiment, the ratio between the outputted signal and a signal representative for the force exerted by the pile gripper to the vessel as measured by the measurement system or the to be subtracted non-zero value is dependent on the phase of the monopile installation method as described above for the fifth aspect of the invention.

In an embodiment, outputting only a portion of a signal representative for the force exerted by the pile gripper to the vessel as measured by the measurement system, e.g. a ratio below 1 or the to be subtracted non-zero value, is applied only during the lowering phase and/or the seabed penetration phase.

In an embodiment, the ratio between the outputted signal and a signal representative for the force exerted by the pile gripper to the vessel as measured by the measurement system or the to be subtracted non-zero value is dependent on one or more of the following parameters: a weight of the monopile, a length of the monopile, an inclination of the monopile relative to the vertical, a length of hoisting wire between lifting crane and monopile, an orientation of the hoisting wire between lifting crane and monopile, a length of monopile below the pile gripper, a length of monopile above the pile gripper, a length of monopile between the pile gripper and sea bottom, a ratio between a length of monopile below the pile gripper and the length of monopile above the pile gripper, a ratio between a length of monopile above the pile gripper and a length of monopile between the pile gripper and sea bottom, a position of a center of gravity of the monopile, and a tension in the hoisting wire between lifting crane and monopile.

In an embodiment, the ratio between the outputted signal and a signal representative for the force exerted by the pile gripper to the vessel as measured by the measurement system or the to be subtracted non-zero value is dependent on a length of the monopile below the pile gripper or a length of the monopile between the pile gripper and sea bottom, and on a length of the monopile above the pile gripper. In an embodiment, this dependency may only apply during the seabed penetration phase.

In an embodiment, during the seabed penetration phase, the dynamic positioning system is configured to determine a ratio a between the outputted signal and a signal representative for the force exerted by the pile gripper to the vessel as measured by the measurement system using the following equation: a = a / (a + b) with a being the length of the monopile above the pile gripper, and b being the length of the monopile below the pile gripper or being the length of the monopile between the pile gripper and the sea bottom.

In an embodiment, the dynamic positioning system is configured to receive input allowing to determine parameters a and b. This input may include one or more of the following information: a measurement signal representative for parameter a, a measurement signal representative for parameter b, a total length of the monopile handled, a measurement signal representative for a (vertical) position of a hoisting hook from which the monopile is suspended, and a(n) (average) water depth.

According to a seventh aspect of the invention, there is provided a vessel to install monopiles, comprising: a hull, a lifting crane provided on said hull for suspending a monopile therefrom, a pile gripper for engaging a monopile, a dynamic positioning system for positioning the vessel, a pile gripper positioning system for positioning a monopile with the pile gripper, wherein the pile gripper positioning system is configured to determine a force exerted by the pile gripper to the vessel, wherein the vessel is configured to use a portion of the determined force as feedforward signal to the dynamic positioning system to position the vessel.

It is noted explicitly here that the position of the vessel may alternatively or additionally refer to a position of a part of the vessel and/or an orientation of the vessel or part thereof. Further, the position of the monopile may alternatively or additionally refer to a position of a part of the monopile and/or an orientation of the monopile or part thereof.

In an embodiment, the pile gripper positioning system is configured to provide a signal to the dynamic positioning system that is representative for the force exerted by the pile gripper to the vessel, and the dynamic positioning system is a dynamic positioning system according to a fifth aspect of the invention.

In an embodiment, the pile gripper positioning system is a pile gripper positioning system according to the sixth aspect of the invention, and the pile gripper positioning system provides a signal to the dynamic positioning system that is representative for a portion of the force exerted by the pile gripper to the vessel as determined by the pile gripper positioning system.

In an embodiment, the vessel comprises an overall control unit, wherein the pile gripper positioning system is configured to provide a signal to an overall control unit that is representative for the force exerted by the pile gripper to the vessel, and wherein the overall control unit is configured to use a portion of the signal received from the pile gripper positioning system to determine a feedforward signal to be provided to the dynamic positioning system by the overall control unit.

It is noted explicitly that the use of a portion of the signal representative for a force exerted by the pile gripper to the vessel means that the overall control unit is configured to ignore or discard at least a non-zero portion of the signal either by multiplication with a factor smaller than 1 or by subtraction of a non-zero value.

According to an eighth aspect of the invention, there is provided a method to install monopiles, wherein use is made of a vessel comprising a dynamic positioning system to position the vessel, a lifting crane to suspend monopiles therefrom, and a pile gripper to engage with the monopile during lowering thereof, and wherein the method comprises the following steps: a. lowering a monopile towards or into a seabed while engaging the monopile with the pile gripper, b. determining a force exerted by the pile gripper to the vessel during lowering, and c. using a portion of said determined force as feedforward signal to the dynamic positioning system to position the vessel.

In an embodiment, the method is carried out when the monopile is suspended by the lifting crane.

It is explicitly mentioned here that embodiments and/or features described in relation to one aspect of the invention may readily be applied in other aspects of the invention where appropriate. As an example, the pile gripper positioning system according to the first aspect of the invention may be combined with the pile gripper positioning system according to the sixth aspect of the invention:

A pile gripper positioning system for a pile gripper that is configured to be provided on a vessel to engage with a monopile during a monopile installation method, wherein the pile gripper positioning system comprises: an actuator system for applying forces to the pile gripper to position the pile gripper relative to the vessel, a measurement system for determining a position of the monopile in the pile gripper relative to the vessel, and a pile gripper control unit for driving the actuator system in dependency of a desired position and an actual position of the monopile as measured by the measurement system, wherein the pile gripper control unit is configured to receive a signal representative for a position of the vessel, wherein, during at least a portion of the monopile installation method, the pile gripper control unit is configured to determine a drive signal for the actuator system to compensate at most a portion of a deviation of the position of the vessel from a desired position of the vessel, and wherein, during said at least a portion of the monopile installation method, the pile gripper control unit for driving the actuator system is configured to drive the actuator system in dependency of a desired position and an actual position of the monopile as measured by the measurement system, and the drive signal to compensate at most a portion of a deviation of the position of the vessel from a desired position of the vessel, wherein the measurement system is further configured to determine a force exerted by the pile gripper to the vessel, and wherein the pile gripper control unit is configured to output a signal that is representative for a portion of the force exerted by the pile gripper to the vessel as measured by the measurement system. As a further example, the dynamic positioning system according to the second aspect of the invention may be combined with the dynamic positioning system according to the fifth aspect of the invention:

A dynamic positioning system for a vessel, wherein the vessel comprises a lifting crane for lifting a monopile and a pile gripper for engaging with a monopile, said lifting crane and pile gripper being configured to cooperate in lowering the monopile into a sea during a monopile installation method, wherein the dynamic positioning system comprises: an actuator system for applying forces to the vessel to position the vessel, a measurement system for measuring a position of the vessel, and a dynamic positioning control unit for driving the actuator system in dependency of a desired position and an actual position of the vessel as measured by the measurement system, wherein the dynamic positioning control unit is configured to determine a signal representative for a difference between the desired position and the actual position of the vessel, and wherein, during at least a portion of the installation method, the dynamic positioning control unit is configured to output a signal that is representative for at most a portion of said difference, wherein the dynamic positioning control unit is configured to receive a signal representative for a force exerted by the pile gripper to the vessel, and wherein the dynamic positioning control unit is configured to use a portion of said signal as a feedforward signal to drive the actuator system.

As another example, the vessel according to the third aspect of the invention may be combined with the vessel according to the seventh aspect of the invention:

A vessel to carry out a monopile installation method, comprising: a hull, a pile gripper arranged on the hull for engaging a monopile, a dynamic positioning system for positioning the vessel, and a pile gripper positioning system for positioning a monopile with the pile gripper, wherein the pile gripper positioning system is configured to determine a force exerted by the pile gripper to the vessel, wherein the vessel is configured to use a portion of the determined force as feedforward signal to the dynamic positioning system to position the vessel, wherein the dynamic positioning system is configured to determine a position of the vessel, and wherein, during at least a portion of the monopile installation method, the vessel is configured to operate the pile gripper positioning system for at most partially compensating a deviation of the determined position of the vessel from a desired position of the vessel.

Alternatively, the vessel may also be described as:

A vessel to carry out a monopile installation method, comprising: a hull, a pile gripper arranged on the hull for engaging a monopile, a dynamic positioning system for positioning the vessel, and a pile gripper positioning system for positioning a monopile with the pile gripper, wherein the dynamic positioning system is a dynamic positioning system according to the second aspect of the invention and the pile gripper positioning system is a pile gripper positioning system according to the sixth aspect of the invention, and/or wherein the dynamic positioning system is a dynamic positioning system according to the fifth aspect of the invention and the pile gripper positioning system is a pile gripper positioning system according to the first aspect of the invention.

As a further example, a method according to the fourth aspect of the invention may be combined with a method according to the eighth aspect of the invention:

A method to install monopiles, wherein use is made of a vessel comprising a dynamic positioning system to position the vessel, and a pile gripper to engage with the monopile, and wherein the method comprises the following steps: a. lowering a monopile towards or into a seabed while engaging the monopile with the pile gripper, b. determining a deviation of the position of the vessel from a desired position of the vessel, c. at most partially compensating said deviation with the pile gripper, d. determining a force exerted by the pile gripper to the vessel during lowering, and e. using a portion of said determined force as feedforward signal to the dynamic positioning system to position the vessel.

It is explicitly mentioned there that throughout the specification, a signal may refer to its signal value where appropriate. Hence, the term "signal" may be replaced by the term "signal value" throughout this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in a non-limiting way by reference to the accompanying drawings in which like parts are indicated by like reference symbols, and in which:

Fig. 1 schematically depicts a vessel according to an embodiment of the invention,

Fig. 2 schematically depicts a portion of the vessel of Fig. 1 during upending of a monopile,

Fig. 3 schematically a control scheme of a vessel according to an embodiment of the invention,

Fig. 4 schematically depicts a control scheme of a vessel according to another embodiment of the invention,

Fig. 5 schematically depicts a control scheme of a vessel according to a further embodiment of the invention,

Fig. 6 schematically depicts a monopile during a seabed penetration phase of a monopile installation method,

Fig. 7 schematically depicts a vessel lowering a monopile during a lowering phase of a monopile installation method,

Fig. 8 schematically depicts a control scheme of a vessel according to an embodiment of the invention,

Fig. 9 schematically depicts a control scheme of a vessel according to another embodiment of the invention, and

Fig. 10 schematically depicts a control scheme of a vessel according to a further embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION

Figs. 1 and 2 schematically depict a vessel 200 according to an embodiment of the invention. The vessel 200 comprises a deck 201. The deck 201 provides sufficient space to store, in this case, five monopiles 202 in a horizontal orientation. The monopiles 202 are stored such that their longitudinal axes are parallel to a longitudinal axis of the vessel 200.

In this embodiment, the vessel 200 is a monohull vessel, but alternatively, the vessel could be a semi-submersible.

At a stern of the vessel 200 is provided a lifting crane 203. The lifting crane 203 is arranged in a center of the deck 201 seen in transverse direction of the vessel 200 to be aligned with a center of gravity of the vessel 200. On one side of lifting crane a pile gripper 1 is arranged, and on an opposite side of the lifting crane 203, a pile driving mechanism 205, alternatively referred to as a pile hammer, is arranged at a corresponding storage location.

When the vessel 200 has sailed to an offshore installation site where a monopile 202 needs to be installed into the sea bottom, a monopile 202 is positioned in a pile holder 50 of the pile gripper 1. The pile holder 50 is in this embodiment pivotable between a vertical orientation, in which it can receive a monopile in a horizontal orientation, and a horizontal orientation as shown in Fig. 1, in which it is able to guide the lowering of the monopile into the sea towards or into the sea bottom. In this embodiment, the monopile is positioned in the pile holder 50 of the pile gripper 1 while the pile holder 50 is in the vertical position.

Arms 57, 58 of the pile holder 50 are moveable between an open position to allow a monopile 202 to pass the arms 57, 58, and thus to receive the monopile, and a closed position in which the pile holder 50 (and thus the pile gripper 1) engages with the monopile 202 to limit movement in a direction perpendicular to a longitudinal axis of the monopile 202. The pile holder 50 may be provided with a pile support 77 configured to engage with a lower end of the monopile 202. The monopile 202 can be brought into engagement by first bringing the pile support 77 into a desired position and subsequently translating the monopile along its longitudinal axis until the lower end of the monopile engages with the pile support 77. The pile support 77 is used to limit movement of the monopile 202 in a direction parallel to the longitudinal axis of the monopile 202, which is advantageous during upending of the monopile 202.

An upper end of the monopile 202 is then lifted using the lifting crane 203 with the lower side of the monopile 202 in the pile holder 50 thereby rotating the monopile 202 from a horizontal orientation to a vertical orientation. Fig. 2 shows the monopile in an intermediate oblique orientation between the horizontal orientation and the vertical orientation.

After rotating, the pile holder 50 is in the horizontal position, which may alternatively be referred to as lowering position, and the monopile 202 is located outside the contour of the vessel 202, i.e. overboard, seen from above to be lowered into the water as can be seen in Fig. 1.

Before lowering the monopile 202 into the water, the lower end of the monopile 202 needs to be disengaged from the pile support 77. The monopile 202 is in that case lifted first using the lifting crane 203 after which the pile support 77 can be moved out of the way. The monopile 202 can then be lowered into the water.

During the above operations, the vessel 200 is in floating condition, and the pile holder 50 is compensated for wave-induced motion of the vessel 200 to maintain a predetermined X-Y location independent of the wave-induced motion of the vessel 200 by operating a pile gripper positioning system of the pile gripper 1 in wave-induced motion compensation mode, which will be explained below in more detail by reference to the Figs. 3-10. To allow the pile gripper 1 to maintain a predetermined X-Y location, the vessel 200 must maintain its position within the working boundaries of the pile gripper 1. The vessel 200 is therefore provided with a dynamic positioning system to position the vessel 200, including maintaining or adjusting a position or orientation of the vessel 200. The dynamic positioning system includes an actuator system including for instance a multitude of thrusting modules 220 for applying forces to the vessel 200, preferably allowing to at least translate the vessel 200 in a horizontal X-Y plane and to rotate the vessel 200 about a Z-axis.

When the monopile 202 is lowered into the water and suspended from the lifting crane 203, the lifting crane 203 may be operated in wave-induced motion compensation mode so that the monopile 202 is compensated for wave-induced motion of the vessel 200 to maintain a predetermined Z location independent of the wave=induced motion of the vessel 200. This may also be referred to as heave compensation.

To lift the upper end of the monopile 202 to rotate the monopile 202 from a horizontal orientation to a vertical orientation, the lifting crane 203 may be provided with a pile clamping device 210 comprising a clamping part 211 to clamp the upper end of the monopile 202 and a connecting part 212 allowing to connect the pile clamping device to a load connector 213 of the lifting crane 203. The connecting part 212 is able to rotate freely relative to the clamping part 211 during lifting of the upper end, i.e. during rotating of the monopile 202.

Fig. 3 schematically depicts a control scheme of a vessel 200 according to an embodiment of the invention. The control scheme of Fig. 3 may be used to control the vessel 200 of Fig. 1.

Fig. 3 schematically depicts the vessel 200 and a dynamic positioning system 100 to position the vessel 200, and a pile gripper 1 with a pile gripper positioning system 150 to position a monopile with the pile gripper 1. Although the pile gripper 1 is shown as being part of the pile gripper positioning system 150, it is explicitly mentioned here that the pile gripper 1 is not part of the pile gripper positioning system 150. The pile gripper 1 includes the constructive elements, the pile gripper positioning system 150 includes all other components configured to position the constructive elements of the pile gripper 1.

The dynamic positioning system 100 includes an actuator system 220 for applying forces Fl to the vessel 200 to position the vessel 200. The dynamic positioning system 100 further includes a measurement system 105 to measure a position of the vessel 200, and a dynamic positioning control unit 110 for driving the actuator system 220 in dependency of a desired position 111 and an actual position 112 as measured by the measurement system 105.

The pile gripper positioning system 150 comprises an actuator system 170 for applying forces F2 to the pile gripper 1 to position the pile gripper 1 relative to the vessel 200. The pile gripper positioning system 150 further comprises a measurement system 155 for determining a position of the monopile in the pile gripper 1, and a pile gripper control unit 160 for driving the actuator system 170, using a drive signal 164, in dependency of a desired position 161 and an actual position 162 of the monopile as measured by the measurement system 155.

The dynamic positioning system 100 is configured to output a signal 112a representative for a position of the vessel 200. This signal 112a is provided to the pile gripper positioning system 150, where the pile gripper control unit 160 is configured to receive the signal 112a representative for the position of the vessel 200.

In this embodiment, at least during a portion of a monopile installation method, the pile gripper control unit 160 is configured to determine a drive signal 163 for the actuator system 170 to compensate at most a portion of a deviation of the position of the vessel 200 from a desired position of the vessel 200.

The signal 112a outputted by the dynamic positioning system 100 may be equal to the actual position 112 as measured by the measurement system 105. The deviation of the position of the vessel 200 from a desired position of the vessel 200 may then be determined by providing the desired position 111 of the vessel 200, via dashed line 111b, and allow the pile gripper control unit 160 to compare the actual position 112 with the desired position 111.

Alternatively, the deviation of the position of the vessel 200 from a desired position 111 of the vessel 200 may be determined in the dynamic positioning system, e.g. by comparing signal 112 with a signal Illa and outputting the comparison as signal 112a, which is now representative for the deviation of the position of the vessel 200 from the desired position 111 of the vessel.

Alternatively, the position outputted by the measurement system 105 may already be a relative measurement indicative for the deviation of the position of the vessel 200 from the desired position 111 of the vessel, so that no additional provision of the desired position is necessary. Due to the many possibilities, the signals Illa and 111b have been indicated using dashed lines.

The pile gripper control unit 160 is further configured, at least during said portion of the monopile installation method, to drive the actuator system 170 using the drive signal 164 in dependency of a desired position 161 and an actual position 162 of the monopile as measured by the measurement system 155, and the drive signal 163 to compensate at most a portion of a deviation of the position of the vessel from a desired position of the vessel.

In this embodiment, compensating at most a portion of a deviation of the vessel 200 from a desired position of the vessel is implemented by applying a factor a to the received signal 112a, and possibly the received signal lib as well, if present, which factor a<l. Alternatively, a non-zero value can be subtracted from the received signal(s).

Fig. 4 schematically depicts a control scheme of a vessel 200 according to another embodiment of the invention. The control scheme of Fig. 4 may be used to control the vessel 200 of Fig. 1. Fig. 4 schematically depicts the vessel 200 and a dynamic positioning system 100 to position the vessel 200, and a pile gripper 1 with a pile gripper positioning system 150 to position a monopile with the pile gripper 1. Although the pile gripper 1 is shown as being part of the pile gripper positioning system 150, it is explicitly mentioned here that the pile gripper 1 is not part of the pile gripper positioning system 150. The pile gripper 1 includes the constructive elements, the pile gripper positioning system 150 includes all other components configured to position the constructive elements of the pile gripper 1.

The dynamic positioning system 100 includes an actuator system 220 for applying forces Fl to the vessel 200 to position the vessel 200. The dynamic positioning system 100 further includes a measurement system 105 to measure a position of the vessel 200, and a dynamic positioning control unit 110 for driving the actuator system 220 in dependency of a desired position 111 and an actual position 112 as measured by the measurement system 105.

The pile gripper positioning system 150 comprises an actuator system 170 for applying forces F2 to the pile gripper 1 to position the pile gripper 1 relative to the vessel 200. The pile gripper positioning system 150 further comprises a measurement system 155 for determining a position of the monopile in the pile gripper 1, and a pile gripper control unit 160 for driving the actuator system 170, using a drive signal 164, in dependency of a desired position 161 and an actual position 162 of the monopile as measured by the measurement system 155.

The dynamic positioning system 100 is configured to output a signal 112a representative for a position of the vessel 200. This signal 112a is provided to the pile gripper positioning system 150, where the pile gripper control unit 160 is configured to receive the signal 112a representative for the position of the vessel 200.

The dynamic positioning system 100 is configured, at least during a portion of the installation method carried out, to output a signal 112a representative for at most a portion of a difference between the desired position Illa and the actual position 112 of the vessel 200. This signal 112a is provided to the pile gripper positioning system 150, where the pile gripper control unit 160 is configured to receive the signal 112a representative for a portion of the deviation in the position of the vessel 200.

Alternatively, the signal outputted by the measurement system 105 may already be a relative measurement indicative for the deviation of the position of the vessel 200 from the desired position Illa or 111 of the vessel 202, so that signal Illa may be omitted.

The pile gripper control unit 160 is further configured, at least during said portion of the monopile installation method, to drive the actuator system 170 using the drive signal 164 in dependency of a desired position 161 and an actual position 162 of the monopile as measured by the measurement system 155, and the signal 112a representative for the difference between the desired position and the actual position of the vessel 200 to compensate at most a portion of said difference.

In this embodiment, compensating at most a portion of a difference between the desired position and the actual position of the vessel 200 is implemented by applying a factor a to said difference, which factor a<l. Alternatively, a non-zero value can be subtracted from the difference.

Fig. 5 schematically depicts a control scheme of a vessel 200 according to a further embodiment of the invention. The control scheme of Fig. 5 may be used to control the vessel 200 of Fig. 1.

Fig. 5 schematically depicts the vessel 200 and a dynamic positioning system 100 to position the vessel 200, and a pile gripper 1 with a pile gripper positioning system 150 to position a monopile with the pile gripper 1. Although the pile gripper 1 is shown as being part of the pile gripper positioning system 150, it is explicitly mentioned here that the pile gripper 1 is not part of the pile gripper positioning system 150. The pile gripper 1 includes the constructive elements, the pile gripper positioning system 150 includes all other components configured to position the constructive elements of the pile gripper 1. The dynamic positioning system 100 includes an actuator system 220 for applying forces Fl to the vessel 200 to position the vessel 200. The dynamic positioning system 100 further includes a measurement system 105 to measure a position of the vessel 200, and a dynamic positioning control unit 110 for driving the actuator system 220 in dependency of an input signal 111 and an actual position 112 as measured by the measurement system 105.

The pile gripper positioning system 150 comprises an actuator system 170 for applying forces F2 to the pile gripper 1 to position the pile gripper 1 relative to the vessel 200. The pile gripper positioning system 150 further comprises a measurement system 155 for determining a position of the monopile in the pile gripper 1, and a pile gripper control unit 160 for driving the actuator system 170, using a drive signal 164, in dependency of an input signal 161 and an actual position 162 of the monopile as measured by the measurement system 155.

The input signals 111 and 161 are provided to the dynamic positioning control unit 110 and the pile gripper control unit 160, respectively, by an overall control unit 180. The overall control unit 180 is configured to receive one or more inputs and in dependency of these one or more inputs output the signals 111 and 161 allowing to use information from different systems in driving of the dynamic positioning system 100 and the pile gripper positioning system 150. Two examples of the one or more inputs to the overall control unit 180 are given, namely, a user input 181 and the measurement signal 112 from the measurement system 155.

The measurement signal 112 provided to the overall control unit 180 is thus representative for an actual position of the vessel 200. The overall control unit 180 is configured to compare this actual position of the vessel 200 with a desired position Illa of the vessel 200 and uses only a portion of the comparison result in unit 190 to determine a drive signal 163 to at most partially compensate for a deviation of the determined position of the vessel from a desired position of the vessel. The drive signal 163 is possibly combined with other signals to determine input signal 161 to be provided to the pile gripper control unit 160. To at most partially compensate for a deviation of the determined position of the vessel from a desired position of the vessel, a factor a is applied to the signals 112 and Illa. Alternatively, a non-zero value can be subtracted from the received signal.

By reference to the Figs. 1-5, a portion of a monopile installation method has already been described. In more detail, a monopile installation method may include a plurality of phases, including but not limited to: a suspension phase, in which the monopile is suspended from a lifting crane above water level and engaged by the pile gripper as for instance shown in Fig, 2 after completely rotating to the vertical orientation of the monopile, a lowering phase, in which the monopile is suspended from the lifting crane and engaged by the pile gripper, and a lower end of the monopile is in the water, but above the seabed, alternatively referred to as sea bottom throughout this specification, a seabed penetration phase, in which the monopile is suspended from the lifting crane and engaged by the pile gripper, and a lower end of the monopile has penetrated the seabed, and a driving phase, in which the monopile is engaged by the pile gripper and driven into the seabed using a hammer or the like.

Fig. 6 schematically depicts a monopile 202 during a seabed penetration phase of a monopile installation method. The monopile 202 is suspended from a lifting crane using a pile clamping device 210 comprising a clamping part 211 to clamp an upper end of the monopile 202 and a connecting part 212 allowing to connect the pile clamping device 210 to a load connector of the lifting crane. The connecting part 212 is able to rotate freely relative to the clamping part 211 about a rotation axis 251 thereby providing a suspension point. Alternatively, the clamping device 210 may only include a clamping part 211 that is configured to be connected directly to the load connector of the lifting crane thereby providing a suspension point 251 that allows some rotation of the clamping part 211 relative to the load connector. The connecting part 212 may then be the hoisting cable and load connector referred to using reference symbol 250 to clearly distinguish the two alternative suspension types.

During the seabed penetration phase, a lower end of the monopile 202 has penetrated a seabed SB, and the monopile 202 is engaged by a pile gripper for applying a force FG to the monopile using a pile gripper positioning system as for instance described above.

Different parameters can be defined: a for a length of monopile above the pile gripper, a' for a distance between pile gripper and suspension point, b for a length of monopile below the pile gripper, and b' for a length of monopile between pile gripper and seabed.

Alternatively, or additionally, the following parameters may be defined: c = a + b', i.e. a length of monopile above the seabed, and c' = a' + b', i.e. a distance between seabed and suspension point.

The ratios a described above in relation to the Figs. 3-5 may be determined during the seabed penetration phase using the following equation or an equivalent thereof: where L is equal to a length of the monopile, and 11 is a predetermined length of monopile above the seabed, i.e. L-ll is a predetermined length of monopile that has penetrated the seabed also referred to as penetration depth, corresponding to a situation in which control of the monopile is sufficiently stable to fully compensate the deviation of the actual position of the vessel from the desired position of the vessel using the pile gripper positioning system. Hence, for the duration of the seabed penetration phase when parameter c is in between L and L-ll, at most a portion of said deviation is compensated by the pile gripper positioning system. By only compensating a portion of the deviation, stability is improved at the cost of possible position loss of the monopile. However, at this stage of the monopile installation method, the position of the monopile can still be corrected for and large compensation forces due to the deviation in the vessel's position are prevented. When the penetration depth increases, stability of the monopile improves and larger forces can be exerted between monopile and vessel allowing to correct the monopile's position and thus fully compensate the deviation in vessel's position.

Although the above equation shows a linear relationship, it is explicitly noted here that other relationships, quadratic, hyperbolic, non-linear, etc. may also be used.

Fig. 7 schematically depicts a vessel 200 during a lowering phase of a monopile installation method as described for instance above. The vessel comprises a lifting crane 203 to suspend a monopile 202 therefrom using a hoisting line 215. The vessel 200 further includes a pile gripper 10 to engage with the monopile.

Fig. 7 includes the vessel 200 and monopile 202 in solid lines and in dashed lines. The solid lines version corresponds to a situation in which the monopile 202 is in a vertical orientation above a location LO where the monopile 202 should be installed in the seabed SB, and the vessel 200 is in a desired position.

The dashed lines version corresponds to a situation in which the vessel 200 has drifted away and thus there exists a deviation Ax of the position of the vessel 200 from the desired position (in solid lines) of the vessel 200.

Due to the deviation Ax of the position of the vessel 200, the location where the hoisting line 215 leaves the lifting crane 203 also has drifted away thereby in principle taking the monopile 202 along with it thus moving the monopile 202 away from the location LO.

In an embodiment, the pile gripper 10 can be operated, e.g. using one of the control systems of Figs. 3-5, to only compensate a portion a*Ax of the deviation Ax of the position of the vessel 200 from the desired position of the vessel 200, with a being defined by the ratio D1/(D1+D2), with DI being a distance between the location where the hoisting line 215 leaves the lifting crane 203 and the pile gripper 10, D2 being a distance between the pile gripper 10 and the seabed SB, and thus D1+D2 being the location where the hoisting line 215 leaves the lifting crane 203 and the sea bottom SB.

The advantage of defining a to be the ratio D1/(D1+D2) is that the monopile 202 maintains an orientation towards the intended installation location LO independent of the vessels motion thereby being able to easily land the monopile on the seabed SB at the location LO without any stability issues. After landing on the seabed, the seabed penetration phase commences, and the situation of Fig. 6 may apply.

In an embodiment, the equation for a described in relation to Fig. 6 may apply to the seabed penetration phase with the difference that always a minimum ratio defined by D1/(D1+D2) is applied in accordance with the embodiment of Fig. 7.

Fig. 8 schematically depicts a control scheme of a vessel 200 according to an embodiment of the invention. The control scheme of Fig. 3 may be used to control the vessel 200 of Fig. 1.

Fig. 8 schematically depicts the vessel 200 and a dynamic positioning system 100 to position the vessel 200, and a pile gripper 1 with a pile gripper positioning system 150 to position a monopile with the pile gripper 1. Although the pile gripper 1 is shown as being part of the pile gripper positioning system 150, it is explicitly mentioned here that the pile gripper 1 is not part of the pile gripper positioning system 150. The pile gripper 1 includes the constructive elements, the pile gripper positioning system 150 includes all other components configured to position the constructive elements of the pile gripper 1.

The dynamic positioning system 100 includes an actuator system 220 for applying forces Fi to the vessel 200 to position the vessel 200. The dynamic positioning system 100 further includes a measurement system 105 to measure a position of the vessel 200, and a dynamic positioning control unit 110 for driving the actuator system 220 in dependency of a desired position 111 and an actual position 112 as measured by the measurement system 105.

The pile gripper positioning system 150 comprises an actuator system 170 for applying forces F2 to the pile gripper 1 to position the pile gripper 1 relative to the vessel 200. The pile gripper positioning system 150 further comprises a measurement system 155 for determining a position of the monopile in the pile gripper 1, and a pile gripper control unit 160 for driving the actuator system 170 in dependency of a desired position 161 and an actual position 162 of the monopile as measured by the measurement system 155.

The measurement system 155 is further configured to determine a force F3 exerted by the pile gripper 1 to the vessel 200. The pile gripper positioning system 150 is further configured to output a signal representative for the measured force F3 and provide the signal to the dynamic positioning system 100.

The dynamic positioning system 100 is configured to only use a portion of the signal provided by the pile gripper positioning system 150 as a feedforward signal to the dynamic positioning control unit 110, in this embodiment by applying a factor a to the received signal, which factor a<l. Alternatively, a non-zero value can be subtracted from the received signal.

Fig. 9 schematically depicts a control scheme of a vessel 200 according to another embodiment of the invention. The control scheme of Fig. 9 may be used to control the vessel 200 of Fig. 1.

Fig. 9 schematically depicts the vessel 200 and a dynamic positioning system 100 to position the vessel 200, and a pile gripper 1 with a pile gripper positioning system 150 to position a monopile with the pile gripper 1. Although the pile gripper 1 is shown as being part of the pile gripper positioning system 150, it is explicitly mentioned here that the pile gripper 1 is not part of the pile gripper positioning system 150. The pile gripper 1 includes the constructive elements, the pile gripper positioning system 150 includes all other components configured to position the constructive elements of the pile gripper 1. The dynamic positioning system 100 includes an actuator system 220 for applying forces Fi to the vessel 200 to position the vessel 200. The dynamic positioning system 100 further includes a measurement system 105 to measure a position of the vessel 200, and a dynamic positioning control unit 110 for driving the actuator system 220 in dependency of a desired position 111 and an actual position 112 as measured by the measurement system 105.

The pile gripper positioning system 150 comprises an actuator system 170 for applying forces F2 to the pile gripper 1 to position the pile gripper 1 relative to the vessel 200. The pile gripper positioning system 150 further comprises a measurement system 155 for determining a position of the monopile in the pile gripper 1, and a pile gripper control unit 160 for driving the actuator system 170 in dependency of a desired position 161 and an actual position 162 of the monopile as measured by the measurement system 155.

The measurement system 155 is further configured to determine a force F3 exerted by the pile gripper 1 to the vessel 200. The pile gripper positioning system 150 is further configured to output a signal representative for a portion of the measured force F3, in this embodiment by applying a factor a to the measured signal, which factor a<l, and provide this reduced signal to the dynamic positioning system 100. Alternatively, a nonzero value can be subtracted from the measured signal to obtain a reduced signal.

The dynamic positioning system 100 is configured to use the reduced signal provided by the pile gripper positioning system 150 as a feedforward signal to the dynamic positioning control unit 110.

Fig. 10 schematically depicts a control scheme of a vessel 200 according to a further embodiment of the invention. The control scheme of Fig. 10 may be used to control the vessel 200 of Fig. 1.

Fig. 10 schematically depicts the vessel 200 and a dynamic positioning system 100 to position the vessel 200, and a pile gripper 1 with a pile gripper positioning system 150 to position a monopile with the pile gripper 1. Although the pile gripper 1 is shown as being part of the pile gripper positioning system 150, it is explicitly mentioned here that the pile gripper 1 is not part of the pile gripper positioning system 150. The pile gripper 1 includes the constructive elements, the pile gripper positioning system 150 includes all other components configured to position the constructive elements of the pile gripper 1.

The dynamic positioning system 100 includes an actuator system 220 for applying forces Fi to the vessel 200 to position the vessel 200. The dynamic positioning system 100 further includes a measurement system 105 to measure a position of the vessel 200, and a dynamic positioning control unit 110 for driving the actuator system 220 in dependency of input signal 111 and an actual position 112 as measured by the measurement system 105.

The pile gripper positioning system 150 comprises an actuator system 170 for applying forces F2 to the pile gripper 1 to position the pile gripper 1 relative to the vessel 200. The pile gripper positioning system 150 further comprises a measurement system 155 for determining a position of the monopile in the pile gripper 1, and a pile gripper control unit 160 for driving the actuator system 170 in dependency of an input signal 161 and an actual position 162 of the monopile as measured by the measurement system 155.

The input signals 111 and 161 are provided to the dynamic positioning control unit 110 and the pile gripper control unit 160, respectively, by an overall control unit 180. The overall control unit 180 is configured to receive one or more inputs and in dependency of these one or more inputs output the signals 111 and 161 allowing to use information from different systems in driving of the dynamic positioning system 100 and the pile gripper positioning system 150. Two examples of the one or more inputs to the overall control unit 180 are given, namely, a user input 181 and a measurement signal from the measurement system 155.

The measurement system 155 is further configured to determine a force F3 exerted by the pile gripper 1 to the vessel 200. The signal provided to the overall control unit is thus representative of the force F3. The overall control unit only uses a portion of this signal, determines a corresponding drive signal in unit 190, possibly combines the drive signal with other signals to determine input signal 111 to be provided to the dynamic positioning control unit 110. In this way, a portion of the force F3 can be used as a feedforward signal to drive the dynamic position system 100. Alternatively, the drive signal used as feedforward signal is provided as a separate input from the overall control unit 180 to the dynamic positioning control unit 110 next to the input signal 111. This may make it easier to use the separate inputs differently.

To only use a portion of the determined force F3, a factor a is applied to the by the overall control unit received signal, which factor a<l. Alternatively, a non-zero value can be subtracted from the received signal.

Referring to Fig. 6 again, the ratios a described above in relation to the Figs. 8-10 may be determined during the seabed penetration phase using the following equation: a = a / (a + b)

In an embodiment, a may be replaced by a' and/or b may be replaced by b'. When a (or a') is between b (or b') and 1.5 times b (or b') during the seabed penetration phase, a will be in between 0.5 and 0.6.