Patent Description:
It also deals with an assembly comprising the monopile.

Such monopile may serve as a support for an offshore wind mill.

Monopiles are huge steel structures, with a length up to <NUM> meters and more, including up to <NUM> meters in the seabed, and an external diameter up to <NUM> meters and more. Their mass may amount to <NUM> metric tonnes or more.

In known processes, at least one monopile is loaded on a regular transportation barge in a horizontal storage position. This regular transportation barge is carried near a heavy lift vessel or a jack-up platform located near the installation location. Using a crane mounted on the heavy lift vessel or the jack-up platform, the monopile is lifted and carried from the regular transportation barge to an upending barge or vessel having a tiltable upending tool, the monopile remaining approximately horizontal during carrying. Then the upending tool is tilted to put the monopile in a vertical position, wherein the monopile is partly immersed. Using the crane, the monopile is then disengaged from the upending tool, lowered and hammered into the seabed.

Such a process works well. However, it comprises many steps that are complex, due to the dimensions and mass of the monopile and as they are performed offshore. Also, the crane used to carry the monopile from the regular transportation barge to the upending barge or vessel has to withstand the full weight of the monopile, plus dynamic efforts due to relative movements of the monopile being carried. This is also time-consuming in crane revolving mode as subsequent ballasting operations are required in the meantime. As a consequence, such a crane is a huge, expensive piece of equipment.

<CIT> discloses an installation facility for installing a pile in a vertical orientation on a target pile position into a seabed, using an upending tool. <CIT> describes a similar installation. However, these installations are only adapted for monopiles having a rather small size, several of them being stored on board a transportation vessel prior to using the upending tool.

<CIT> describes a monopile having an internal volume filled with air. <CIT> describes several internal volumes initially filled with air.

<CIT> discloses a process of installing a monopile using an articulated upending tool adapted for clamping and lifting the monopile, the monopile sliding on a surface of the vessel while being lifted.

An aim of the invention is thus to reduce the cost of installing the monopile.

To this end, the invention proposes a method according to claim <NUM>.

In other embodiments, the method comprises one or several of the features corresponding to claims <NUM> to <NUM>.

The invention also deals with an assembly according to claim <NUM>.

In other embodiments, the assembly comprises one or several of the features corresponding to claims <NUM> and <NUM>.

The invention and its advantages will be better understood upon reading the following description, given solely by way of example and with reference to the appended drawings, in which:.

A method according to the invention will now be described with reference to <FIG>.

The methods aims at installing a monopile <NUM> (shown in <FIG> and <FIG>) in a seabed <NUM> at an installation location <NUM> (<FIG>).

The method comprises charging the monopile <NUM> on a transportation barge <NUM> in a harbor <NUM> (<FIG>), the transportation barge having a main body <NUM>, and an upending tool <NUM> mounted rotatable on the main body around a horizontal axis R, the monopile and the upending tool being in a transport position (<FIG>). The method comprises moving the transportation barge <NUM> from the harbor <NUM> to a vicinity of the installation location <NUM> (<FIG>), rotating the monopile <NUM> and the upending tool <NUM> together (<FIG>) from the transport position to a discharge position (<FIG>), and disengaging the monopile <NUM> from the upending tool <NUM>. The method comprises lowering the monopile <NUM> with respect to the transportation barge <NUM> (<FIG>) and hammering the monopile <NUM> into the seabed <NUM> (<FIG>).

The monopile <NUM> defines a longitudinal axis L. The monopile <NUM> has a length L1 for example comprised between <NUM> and <NUM> meters, and a maximum external diameter D1 for example comprised between <NUM> and <NUM> meters. The monopile mass is for example comprised between <NUM> and <NUM> tonnes.

The monopile <NUM> has a first longitudinal extremity <NUM> adapted to be pushed into the seabed <NUM>, so that the monopile can for example serve as a support for a wind mill (not shown), the longitudinal axis L being vertical. Once the monopile <NUM> is installed, it has a second longitudinal extremity <NUM>, opposite the first longitudinal extremity <NUM>, still above a body of water <NUM>, on which the wind mill can be fixed.

The monopile <NUM> for example comprises an external envelope <NUM> around the longitudinal axis L, the external envelope defining an internal volume <NUM> of the monopile.

During the step of charging the monopile <NUM>, the transportation barge <NUM> is for example near a quay <NUM> of the harbor <NUM>. Charging is for example performed using at least one crane <NUM> located on the quay <NUM>. The monopile <NUM> is for example carried in a horizontal position, in which the crane <NUM> withstands a full weight of the monopile, and deposited on the upending tool <NUM>.

As variants (not shown), charging is performed using a sheer leg (i.e. a pier floating crane), a heavy lift vessel available locally, or alternatively with self-propelled modular trailers from quay <NUM> to barge <NUM>.

In the transport position, the monopile <NUM> rests on a cradle <NUM> of the upending tool <NUM> and is for example approximately horizontal.

The upending tool <NUM> is advantageously mounted on a support structure <NUM> of the transportation barge <NUM>.

The upending tool <NUM> comprises a bottom part <NUM> located near the first longitudinal extremity <NUM> of the monopile <NUM>, and advantageously two longitudinal telescopic beams <NUM>, <NUM> located on either sides of the monopile along the horizontal axis R.

The bottom part <NUM> advantageously extends between distal extremities <NUM>, <NUM> of the telescopic beams <NUM>, <NUM>. The bottom part <NUM> is for example perpendicular to the longitudinal axis L in the transport position.

In the transport position, the cradle <NUM> of the upending tool <NUM> partly surrounds the monopile <NUM> around the longitudinal axis L (<FIG>), the cradle being under the monopile. Advantageously, the cradle <NUM> is semicircular.

As a variant (not shown), the upending tool <NUM> comprises one or several other cradles, for example analogous to the cradle <NUM>. The cradle <NUM> and the other cradles are distributed along the longitudinal direction L and support the monopile <NUM> in the transport position.

As a variant, a transportation vessel is used instead of the transportation barge <NUM>. A transportation vessel is self-propelled, whereas a transportation barge is not, and therefore is towed by a tug boat (not shown).

A tug or vessel (not shown) is used for moving the transportation barge <NUM> from the harbor <NUM> towards the installation location <NUM> in case the transportation barge <NUM> is not self-propelled. The transportation barge <NUM> is then located near a heavy lift vessel <NUM>.

As a variant (not shown), the transportation barge <NUM> is located near a jack-up platform equipped with a lifting crane.

Before rotating the monopile <NUM> and the upending tool <NUM> together (<FIG>), the monopile is advantageously equipped at its second longitudinal extremity <NUM> with an internal lifting tool <NUM> shown in <FIG>.

The internal lifting tool <NUM> is adapted for being attached to a crane <NUM> mounted on the heavy lift vessel <NUM> (or a jack-up platform). The internal lifting tool <NUM> at least partly extends in the internal volume <NUM> of the monopile <NUM> and advantageously comprises a plurality of pads <NUM> (<FIG>) distributed around the longitudinal axis L and adapted to press on a radially inner surface <NUM> of the envelope <NUM>, so as to stick to the monopile thanks to shear friction.

The internal lifting tool <NUM> for example comprises an air tight joint <NUM> extending around the longitudinal axis L and in contact with the envelope <NUM>, and advantageously an air vent <NUM>.

Rotating the monopile <NUM> and the upending tool <NUM> is obtained by lifting the second longitudinal extremity <NUM> of the monopile. Therefore, the crane <NUM> is connected to the second longitudinal extremity <NUM>, advantageously to the internal lifting tool <NUM>, and pulls the monopile. The monopile <NUM> and the upending tool <NUM> rotate together around the axis R to come to the discharge position, in which the monopile is vertical and has its first longitudinal extremity <NUM> resting on the bottom part <NUM> of the upending tool <NUM>.

Still using the crane <NUM>, the monopile <NUM> is disengaged from the upending tool <NUM> and for example put in a gripper system <NUM> (<FIG>) while it is being lowered with respect to the transportation barge <NUM> till the monopile <NUM> self penetrates and rests on the seabed <NUM>. The monopile <NUM> is guided by the gripper system <NUM>.

Then the internal lifting tool <NUM> is withdrawn, and the monopile <NUM> is hammered into the seabed <NUM> (<FIG>), for example using a hammer <NUM> carried by the crane <NUM>.

Advantageously, during at least part of said rotating the monopile <NUM> and the upending tool <NUM> and/or said disengaging, the method comprises providing a chamber <NUM> containing an amount of air, the chamber <NUM> providing additional buoyancy to the monopile <NUM>.

The monopile <NUM>, being partly immersed, receives a moderate buoyancy force due to the volume of the envelope <NUM> displacing water. The chamber <NUM> provides additional buoyancy because it displaces more water. Hence the crane <NUM> does not have to withstand the full weight in air of the monopile <NUM>. As a consequence, the crane <NUM> can have a maximum lifting capacity smaller than said full weight in air, and smaller than the weight of the monopile <NUM> in water without the chamber <NUM>.

For example, said additional buoyancy amounts to several hundreds of tonnes, and advantageously more than <NUM>% or even <NUM>% of the monopile mass. For example, if the monopile mass is <NUM> tonnes, the additional buoyancy brought by the chamber <NUM> may reach <NUM> tonnes.

For example, the chamber <NUM> extends within the internal volume <NUM> and is delimited downwards by a surface of free water <NUM> located under a waterline <NUM> of the monopile. Advantageously, the internal lifting tool <NUM> forms an upper limit of the chamber <NUM>, thanks to the air tight joint <NUM>.

Advantageously, the method comprises using a system <NUM> for adjusting the amount and the pressure of air in the chamber <NUM>.

For example, the system <NUM> includes the air vent <NUM> of the internal lifting tool <NUM> for letting part of said amount of air exit from the chamber <NUM>. This allows raising the surface of free water <NUM> with respect to said waterline <NUM>, thereby decreasing the additional buoyancy brought by the chamber <NUM>.

For example, the system <NUM> comprises at least one air pump <NUM> configured for injecting air into the chamber <NUM>. This allows lowering the surface of free water <NUM> with respect to said waterline <NUM>, thereby increasing the additional buoyancy brought by the chamber <NUM>.

The air pump <NUM> is preferably an air compressor, and more preferably a centrifugal one.

The internal lifting tool <NUM> advantageously comprises an aperture, for example the air vent <NUM>, for introducing compressed air provided by the air pump <NUM>.

Among air compressors, centrifugal compressors are particularly preferred, since they allow high volume throughput with appropriate pressure, typically ranging from <NUM> to <NUM> barg. "Barg" stands for measured pressure in bar relative to the atmospheric pressure. For instance, if the atmospheric pressure is one bar and the pressure that is delivered at compressor outlet is <NUM>,<NUM> barg, then the absolute pressure at compressor outlet is <NUM>,<NUM> bar.

The air monitoring in the chamber <NUM> may be directly measured using conventional means, such as pressure gauge, optical or ultrasound sensor, and/or indirectly measured using weight sensor positioned on the lifting crane <NUM>.

Commercial centrifugal compressors of sufficient throughput and pressure are suitable for use in the instant invention without specific design modification.

Compressor outlet may provide compressed air through a pipe connected to the chamber <NUM>, ideally through a dedicated aperture in the internal lifting tool <NUM> or through the air vent <NUM>. The pipe diameter is adapted to the compressor capacity and the working pressure that has been selected based on the monopile size and a desired buoyancy during the installation. Buoyancy may be adapted at each step of the installation of the monopile. It is advisable to install at least one air valve on the pipe anywhere between the compressor outlet and the chamber <NUM>.

A large range of compressors is available in the industry, for example with a <NUM> to <NUM> barg working pressure and a <NUM>-<NUM> m3/minute capacity, and selection may be fine-tuned to the application option. A centrifugal compressor, for instance, could be appropriate for monopiles having a diameter of a magnitude of <NUM> and a length of about <NUM>.

Altogether, the monopile <NUM>, the internal lifting tool <NUM> and the chamber <NUM> form an assembly <NUM> according to the invention.

Thanks to the above described features, the cost of installing the monopile <NUM> is reduced.

Indeed, as the monopile <NUM> is installed on the transportation barge <NUM> (or on a vessel) on the upending tool <NUM> in a harbor <NUM> and not in the vicinity of the installation location <NUM>, the number of steps performed offshore is reduced.

Besides, the crane <NUM> can have a maximum lifting capacity smaller than the full weight in air of the monopile <NUM>. Such a crane is much less expensive, as there are more potential providers.

The optional step of providing a chamber <NUM> containing air further reduces the maximum lifting capacity that is needed. Besides, such a chamber <NUM> is for example easily obtained using the internal lifting tool <NUM> as an upper limit.

In case several monopiles are to be installed, the installation schedule can be improved at equivalent installation cost by mobilizing several low cost heavy lift vessels or jack-up platforms rather than one more expensive.

The above described method makes it possible to use jack-up platforms which usually have lower craneage than large heavy lift vessels.

The method allows installing large monopiles in shallow waters, as jack-up platforms have limited draft and can access shallow waters, which is not the case for heavy lift vessels.

With reference to <FIG>, a method according to a first variant of the invention will now be described. The first variant is analogous to the method shown in <FIG>. The similarities will not be described again. Only the differences will be described in detail here after.

In the first variant, the chamber <NUM> extends within the internal volume <NUM>, and is delimited downwards by a sacrificial membrane <NUM> or a diaphragm fixed on a lower end <NUM> of the monopile <NUM>. The chamber <NUM> is not delimited by a surface of free water in fluid communication with the body of water <NUM>.

The membrane <NUM> surrounds the lower end <NUM> around the longitudinal direction L.

The membrane <NUM> is watertight. When the monopile <NUM> is partly immersed in the body of water <NUM>, the envelope <NUM> and the membrane <NUM> work as a hull defining the chamber <NUM>.

The membrane <NUM> is called "sacrificial", as it can be torn apart when the monopile <NUM> penetrates into the seabed <NUM>.

Before this happens, the amount of air in the chamber <NUM> may be reduced by allowing some water to flow in it in between the membrane <NUM> and the envelope <NUM> or by pumping water in (towards) the chamber <NUM>.

In this variant, the internal lifting tool <NUM>, if present, does not have to be air tight.

With reference to <FIG>, a method according to a second variant of the invention will now be described. The second variant is analogous to the method shown in <FIG>. The similarities will not be described again. Only the differences will be described in detail here after.

In the second variant, the chamber <NUM> comprises an inflatable member <NUM> located in the internal volume <NUM> and attached to the monopile <NUM>. The inflatable member <NUM> is attached to the first longitudinal extremity <NUM> of the monopile by peripheral hooks <NUM>.

When inflated with air, the inflatable member <NUM> operates as an "underwater lifting parachute", the monopile <NUM> being partly immersed. Water from the body of water <NUM> can freely circulate around the inflatable member <NUM>.

The amount of air in the inflatable member <NUM>, hence buoyancy, can advantageously be adjusted.

The inflatable member <NUM> is advantageously connected towards the second longitudinal extremity <NUM> by a link <NUM> allowing to help deploying the inflatable member <NUM> in the internal volume <NUM> and/or connecting the inflatable member to an air source, for example the pump <NUM> shown in <FIG>.

The inflatable member <NUM> is advantageously recovered before the monopile <NUM> penetrates into the seabed <NUM>.

In this variant, the internal lifting tool <NUM>, if present, does not have to be air tight, but could be, so as to provide additional buoyancy.

An air compressor, such as the ones described above, may be used to inflate the inflatable member <NUM>, possibly via the internal lifting tool <NUM>.

With reference to <FIG>, a method according to a third variant of the invention will now be described. The third variant is analogous to the first variant shown in <FIG>. The similarities will not be described again. Only the differences will be described in detail here after.

In the third variant, the chamber <NUM> is delimited downwards by an inflatable plugging element <NUM> located in the internal volume <NUM> and pressing against the envelope <NUM>. The chamber <NUM> comprises the plugging element <NUM>, and advantageously a part <NUM> of the internal volume <NUM> located above the plugging element <NUM> when the monopile <NUM> is in the discharge position.

The plugging element <NUM> maintains itself in a given longitudinal position with respect to the envelope <NUM> by friction, and advantageously prevents water from invading the part <NUM>.

The longitudinal position can advantageously be selected before inflating the plugging element <NUM>, which allows adjusting the additional buoyancy. In <FIG>, two positions are represented.

The plugging element <NUM> is advantageously recovered before the monopile <NUM> penetrated into the seabed <NUM>.

An air compressor, such as the ones described above, may be used to inflate the plugging element <NUM>, possibly via the internal lifting tool <NUM>.

In the method and its above variants, the external envelope <NUM> may define an orifice <NUM> intended to form a passage for at least one electric cable <NUM> (shown in <FIG>) from the internal volume <NUM> towards outside the monopile <NUM>.

Such a cable is for example used to electrically connect a wind turbine (not shown) fixed to the monopile <NUM> to a network (not shown), once the monopile is installed (even if, for simplicity, the cable is shown in <FIG>, in which the monopile is not yet installed).

The passage is intended to be located above the seabed <NUM> once the monopile <NUM> is installed.

The method and its variants, in particular the first and third ones, may further comprise closing the orifice <NUM> with a temporary closing member <NUM>, such as a plugging pin device, while the monopile <NUM> is being installed, in order to prevent water from flowing into the chamber <NUM>.

In the third variant (<FIG>), the longitudinal position of the plugging element <NUM> can advantageously be chosen such that the plugging element actually forms the closing member <NUM>.

Once the closing member <NUM> is removed, the cable <NUM> can be installed via the orifice <NUM>. The similarities will not be described again. Only the differences will be described in detail here after.

In the second variant, the chamber <NUM> comprises an inflatable member <NUM> located in the internal volume <NUM> and attached to the monopile <NUM>. For example, the inflatable member <NUM> is attached to the first longitudinal extremity <NUM> of the monopile by peripheral hooks <NUM>.

Claim 1:
A method of installing a monopile (<NUM>) in a seabed (<NUM>) at an installation location (<NUM>), comprising:
- in a harbor (<NUM>), charging the monopile (<NUM>) on a transportation barge (<NUM>) or vessel having a main body (<NUM>), and an upending tool (<NUM>) mounted rotatable on the main body (<NUM>) around a horizontal axis (R), the monopile (<NUM>) and the upending tool (<NUM>) being in a transport position in which the monopile (<NUM>) rests on at least one cradle (<NUM>) of the upending tool (<NUM>), the cradle (<NUM>) partly surrounding the monopile (<NUM>) around a longitudinal axis (L) defined by the monopile (<NUM>),
- moving the transportation barge (<NUM>) or vessel from the harbor (<NUM>) to a vicinity of the installation location (<NUM>),
- rotating the monopile (<NUM>) and the upending tool (<NUM>) together from the transport position to a discharge position, in which the monopile (<NUM>) is vertical, partly immersed in a body of water (<NUM>) and has a first longitudinal extremity (<NUM>) resting on a bottom part (<NUM>) of the upending tool (<NUM>), by pulling a second longitudinal extremity (<NUM>) of the monopile (<NUM>) opposite the first longitudinal extremity (<NUM>), using a crane (<NUM>) mounted on a heavy lift vessel (<NUM>) or on a jack-up platform, and connected to the second longitudinal extremity (<NUM>),
- disengaging the monopile (<NUM>) from the upending tool (<NUM>) using the crane (<NUM>), and
- lowering the monopile (<NUM>) with respect to the transportation barge (<NUM>) or vessel and hammering the monopile (<NUM>) into the seabed (<NUM>).