EP4355647A1

EP4355647A1 - Method and device for estimating the probability of damage caused by the sloshing of a liquid load during an operation of transferring said liquid load between two floating structures

Info

Publication number: EP4355647A1
Application number: EP22732209.6A
Authority: EP
Inventors: Erwan CORBINEAU; Arnaud DUMAIL; Alaric SIBRA; Florent OUVRARD
Original assignee: Gaztransport et Technigaz SA
Current assignee: Gaztransport et Technigaz SA
Priority date: 2021-06-15
Filing date: 2022-06-09
Publication date: 2024-04-24
Also published as: CN117500721A; FR3123962B1; CA3221239A1; WO2022263267A1; KR20240022547A; FR3123962A1

Abstract

The invention relates to a method (300) for estimating the probability of damage caused by the sloshing of a liquid load during an operation of transferring said liquid load from a first floating structure (1) to a second floating structure (40), the first floating structure (1) and the second floating structure (40) being connected with one another during the transfer operation so that the first floating structure (1) and the second floating structure (40) are oriented with a shared heading (99). The method comprises the steps of estimating (307) the probability of damage of at least one tank of at least one of the first and second floating structures (1, 40) and of supplying a user (308) with an indication dependent on the probability of damage thus estimated.

Description

Method and device for estimating a probability of damage due to the sloshing of a liquid load during a transfer operation of said liquid load between two floating structures

The invention relates to operations for transferring a liquid load between two floating structures. More particularly, the invention relates to a method and a device for estimating a probability of damage due to the sloshing of a liquid load during a transfer operation of said liquid load from a first floating structure to a second floating structure.

Technology background

In the field of floating structures capable of transporting a liquid load, it is known to carry out operations for transferring the liquid load from a first floating structure, such as a liquid carrier vessel, to a second floating structure.

Such liquid cargo transfer operations are commonly implemented in particular for liquefied natural gas (LNG or LNG) cargoes. For such cargoes, in a known manner, an LNG carrier ship, such as an LNG carrier (also known by the acronym LNGC for "LNG Carrier" in English), can approach a floating storage and regasification unit for liquefied natural gas (also known as FSRU for "Floating Storage and Regasification Unit" in English). The FSRU is for example located offshore and moored to an underwater buoy or to a turret mooring system allowing the structure to orient itself freely according to the constraints applied to it (waves, wind, current, etc.) . The LNGC then docks with the FSRU, and flexible lines are installed between the LNGC and the FSRU to transfer LNG between the LNGC and the FSRU. Such an LNG transfer operation is known as such, under the acronym STS for "Ship-to-Ship Transfer". It can also take place between an LNGC and another floating installation, such as a floating liquefied natural gas production unit (also known by the acronym FLNG for "Floating Liquid Natural Gas" in English).

However, during such an operation, the LNGC and FSRU tanks intended to contain the LNG are partially filled. It is known that in such a situation, the LNG contained in the tanks is agitated under the effect of the waves. The agitation of the liquid, generally referred to as "sloshing" or sloshing, creates stresses on the walls of the tank which can affect the integrity of the tank. However, the integrity of the tank is particularly important in the context of a tank intended to contain LNG, due to the flammable or explosive nature of the transported liquid and the risk of a cold spot on the steel hull of the floating structure. .

In addition, an operation of this type is likely to take a long time, of the order of several tens of hours when it involves an LNGC and a large capacity FSRU or a floating liquefied natural gas production unit (FLNG ). However, the longer the time required for the operation, the more climatic conditions likely to cause sloshing of the LNG in the tanks are likely to occur.

In view of the above, it would be useful to have processes and systems available to help limit or even eliminate the risk of damage to the tanks due to sloshing.

Summary

An idea underlying the invention is to take advantage of meteorological and oceanographic forecasts relating to the geographical position of the liquid load transfer operation, for a planned duration of said transfer operation, to estimate a probability of damage at least one tank of at least one of the floating structures involved in the transfer operation. Another idea underlying the invention is to provide a user with an indication according to the probability of damage thus estimated.

According to an embodiment in accordance with a first variant, the invention provides a method for estimating a probability of damage due to the sloshing of a liquid load during a transfer operation of said liquid load from a first floating structure to a second floating structure, the first floating structure and the second floating structure being associated with each other during said transfer operation such that the first floating structure and the second floating structure are oriented along a common heading, said process comprising:
- obtain a planned geographical position of said transfer operation;
- obtaining meteorological and oceanographic forecasts relating to said geographical position for a plurality of time periods, said time periods together covering an expected duration of said transfer operation, said forecasts comprising, for each time period, a state of the swell , wherein the swell condition includes a swell direction, a significant swell height and a swell period;
- for each time period: obtain the common course of the first and second floating structures; determining at least one projected filling level of at least one tank of at least one of said first and second floating structures intended to contain all or part of said liquid load; determining a swell angle of incidence, which is an angle between said common course of the first and second floating structures and the direction of the swell; and estimating at least one probability of damage to said at least one tank as a function of the angle of incidence of the swell thus determined, of the significant height of the swell, of the period of the swell and of the forecast filling level of the said tank; and
- provide a user with an indication based on said at least one probability of damage thus estimated.

Thanks to such a method, a user such as a crew member can take any necessary measure to limit the risk of damage to the tanks of the floating structure(s), such as for example modifying the heading common to the two floating structures and/or modify a parameter of the transfer operation, for example a liquid loading transfer rate and/or a filling level of the tank(s) (between the tanks of the same floating structure and/or between the tanks of the two floating structures).

According to embodiments, such a method may comprise one or more of the following characteristics.

According to one embodiment, the period of the swell is a peak period of the swell, that is to say a period of time between the passage of two successive peaks of the swell. According to one embodiment, the period of the swell is an average period of the swell, that is to say a period of time between three successive passages of the swell at the average height of the sea; this average period is commonly denoted T _z .

The provisional filling level of the tank can be estimated in various ways. According to one embodiment, said at least one predicted filling level is determined from a liquid loading transfer scenario, the liquid loading transfer scenario defining an evolution of the filling level of said tank as a function of time.

Such a liquid load transfer scenario can in particular be entered by the user at the start of the transfer operation.

According to one embodiment, for each period of time, two predicted filling levels of said tank are determined, the two predicted filling levels including a predicted low filling level and a predicted high filling level, and a probability of damage of said tank is estimated for each of the two forecast filling levels.

In this way, the estimation of the probability of damage can take into account the fact that the sloshing of the liquid load is different depending on the filling level of the tank.

According to one embodiment, the predicted low filling level and the predicted high filling level are determined in advance during a preliminary step consisting in searching, for example by simulation and/or by experimental tests, for two filling levels of the tank which are most likely to lead to a risk of damage to the tank due to sloshing.

The probability of damage can be estimated in various ways. According to one embodiment, the probability of damage is estimated by consulting a database previously established for said tank, said database comprising data relating to sloshing as a function of an angle of incidence of the swell, a significant height of the swell, the period of the swell and a current filling level of said tank,
the sloshing data being determined by experimental measurements, and
the probability of damage being relative to a probability density of encountering a pressure on an internal surface of the tank greater than an internal resistance of the tank as a function of the angle of incidence of the swell, of the significant height of the swell, the period of the swell and the current filling level of said tank.

According to one embodiment, said indication comprises information representing the probability of damage estimated as a function of said periods of time. In particular, according to one embodiment, said indication comprises a visual indication of the probability of damage estimated as a function of said periods of time.

According to one embodiment, the first floating structure and the second floating structure are anchored to an anchor point during said transfer operation.

According to one embodiment, said forecasts further comprise a wind sea state, the wind sea state comprising a significant wind sea height and/or a wind sea period and/or a wind sea direction wind.

According to one embodiment, the wind sea period is a wind sea peak period, that is to say a period of time between the passage of two successive peaks of the wind sea. According to one embodiment, the period of the swell is an average period of the wind sea, that is to say a period of time between three successive passages of the wind sea at the average height of the sea; this average period is commonly denoted T _z .

According to one embodiment, the probability of damage to said at least one tank is also estimated according to the sea state of the wind.

The common heading of the first and the second floating structures can simply be provided in advance for each time period, for example by the user. Alternatively, according to one embodiment, for each period of time, said common heading of the two floating structures is obtained by:
- calculating, for a plurality of theoretical headings, a resultant of the forces undergone by the first and second floating structures as a function of the state of the swell and a moment relative to the anchor point of said resultant;
- selecting, among said plurality of theoretical headings, a common heading which minimizes the absolute value of the moment with respect to the anchor point of said resultant.

According to one embodiment, the resultant of the forces undergone by the first and second floating structures is also calculated according to the sea state of the wind.

According to one embodiment, said forecasts further comprise a state of the wind, the state of the wind comprising a wind speed and/or a wind direction, and the resultant of the forces undergone by the first and second floating structures is furthermore calculated according to the state of the wind.

According to one embodiment, said forecasts further comprise a state of the current, the state of the current comprising a speed of the current and/or a direction of the current, and the resultant of the forces undergone by the first and second floating structures is furthermore calculated according to the state of the current.

According to one embodiment, said indication comprises information representing the probability of damage estimated as a function of said plurality of theoretical headings.

According to one embodiment, the method further comprises a step for decision support intended to reduce the estimated probability of damage.

According to one embodiment, the decision support step comprises providing the user with:
- a proposal to change the common course, and/or
- a proposed modification of at least one parameter of the transfer operation.

According to one embodiment, the proposal for modifying at least one parameter of the transfer operation comprises a proposal for modifying a liquid loading transfer rate and/or a filling level of the tank(s) (between the tanks of the same floating structure and/or between the tanks of two floating structures).

Thus, the user is enabled to take the necessary measures, on the basis of these proposals, in order to reduce the risk of damage to the tanks.

The method is applicable to floating structures transporting any type of liquid load. However, it finds particular application in floating structures carrying a load of a cold liquid product.

According to one embodiment, the liquid load is a load of liquefied gas, in particular a load of liquefied petroleum gas (LPG) or a load of liquefied natural gas (LNG).

According to one embodiment, the at least one tank is a sealed and/or thermally insulating tank.

According to one embodiment, the first floating structure is a liquefied natural gas carrier ship (LNGC), and the second floating structure is a floating storage and regasification unit (FSRU) for liquefied natural gas or a floating production unit for liquefied natural gas (FLNG).

According to one embodiment, the invention also provides a device for estimating a probability of damage due to the sloshing of a liquid load during a transfer operation of said liquid load from a first floating structure to a second floating structure. , the first floating structure and the second floating structure being associated with each other during said transfer operation such that the first floating structure and the second floating structure are oriented on a common heading, the device comprising a processor configured to implement the method according to any of the embodiments described above.

Such a device has the same advantages as those described above in relation to the method.

According to one embodiment, the invention also provides a floating structure comprising a device as described above.

The principles described above are also applicable to a floating structure carrying a liquid load and anchored to an anchor point. Indeed, the liquid load of such a floating structure is also likely to be agitated under the effect of the waves, which can also lead to a phenomenon of sloshing which is likely to harm the integrity of the tanks containing the liquid load.

Thus, according to an embodiment in accordance with a second variant, the invention provides a method for estimating a probability of damage due to the sloshing of a liquid load of a floating structure, the floating structure being moored to an anchor point relative to the seabed while being free to pivot around said anchor point, said method comprising:
- obtain a geographical position of the floating structure moored to the anchor point;
- obtaining meteorological and oceanographic forecasts relating to said geographical position for a plurality of time periods, said forecasts comprising, for each time period, a swell condition, wherein the swell condition comprises a swell direction , a significant wave height and a wave period;
- for each time period: obtain a bearing of the floating structure; determining at least one projected filling level of at least one tank of said floating structure intended to contain said liquid load; determining a swell angle of incidence, which is an angle between said heading and the direction of the swell; and estimating at least one probability of damage to said at least one tank as a function of the angle of incidence of the swell thus determined, of the significant height of the swell, of the period of the swell and of the forecast filling level of the said tank; and
- provide a user with an indication based on said at least one probability of damage thus estimated.

Thanks to such a method, a user such as a crew member can take any measure necessary to limit the risk of damage to the tank(s) of the floating structure, such as for example modifying the heading of the floating structure , being reminded that the floating structure is free to pivot around its anchor point.

According to one embodiment, the period of the swell is a peak period of the swell, that is to say a period of time between the passage of two successive peaks of the swell. According to one embodiment, the period of the swell is an average period of the swell, that is to say a period of time between three successive passages at the average height of the sea; this average period is commonly denoted T _z .

According to one embodiment, the probability of damage is estimated by consulting a database previously established for said tank, said database comprising data relating to sloshing as a function of an angle of incidence of the swell, a significant height of the swell, the period of the swell and a current filling level of said tank,
the sloshing data being determined by experimental measurements, and
the probability of damage being relative to a probability density of encountering a pressure on an internal surface of the tank greater than an internal resistance of the tank as a function of the angle of incidence of the swell, of the significant height of the swell, the period of the swell and the current filling level of said tank.

According to one embodiment, the wind sea period is a wind sea peak period, that is to say a period of time between the passage of two successive peaks of the wind sea. According to one embodiment, the period of the swell is an average period of the sea of the wind, that is to say a period of time between three successive passages at the average height of the sea; this average period is commonly denoted T _z .

The heading of the structure can simply be provided in advance for each time period, for example by the user. Alternatively, according to one embodiment, for each period of time, said common heading of the floating structure is obtained by:
- calculating, for a plurality of theoretical headings, a resultant of the forces undergone by the floating structure as a function of the state of the swell and a moment relative to the anchor point of said resultant;
- selecting, among said plurality of theoretical headings, a common heading which minimizes the absolute value of the moment with respect to the anchor point of said resultant.

According to one embodiment, the resultant of the forces undergone by the floating structure is also calculated according to the sea state of the wind.

According to one embodiment, said forecasts further comprise a state of the wind, the state of the wind comprising a wind speed and/or a wind direction, and the resultant of the forces undergone by the floating structure is further calculated by depending on the wind condition.

According to one embodiment, said forecasts further comprise a state of the current, the state of the current comprising a speed of the current and/or a direction of the current, and the resultant of the forces undergone by the floating structure is further calculated by depending on the state of the current.

According to one embodiment, the decision support step comprises providing the user with:
- a proposal to change the heading of the floating structure, and/or
- a proposal for modifying a filling level of at least one of the tanks of the floating structure.

Thus, the user is enabled to take the necessary measures, on the basis of these proposals, in order to reduce the risk of damage to the tank(s) of the floating structure.

According to one embodiment, the floating structure is a liquefied natural gas carrier vessel (LNGC), a floating liquefied natural gas storage and regasification unit (FSRU) or a floating liquefied natural gas production unit (FLNG) .

According to one embodiment, the invention also provides a device for predicting the estimation of a probability of damage due to the sloshing of a liquid load of a floating structure, the floating structure being moored to a point of anchoring relative to the seabed while being free to pivot around said anchoring point, the device comprising a processor configured to implement the method according to any of the embodiments described above.

Brief description of figures

The invention will be better understood, and other aims, details, characteristics and advantages thereof will appear more clearly during the following description of several particular embodiments of the invention, given solely by way of illustration and not limiting, with reference to the accompanying drawings.

The is a schematic representation in longitudinal section of a floating structure, in this case a ship, comprising a plurality of tanks comprising a liquid load.

. The is a diagram representing two floating structures, in this case a ship and a floating unit, associated with each other during a liquid load transfer operation, and from a wind sea state, from a state of swell, a state of the current and a state of the wind to which the two floating structures may be subjected.

The is a flowchart representing a method for estimating a risk of damage due to the sloshing of a liquid load during an operation of transferring said liquid load from a first floating structure to a second floating structure.

The is a detail of the organization chart of the representing a variant of the process.

The represents a device for predicting the sloshing of a liquid load during a transfer operation of said liquid load from a first floating structure to a second floating structure.

The shows an example of a visual indication of the estimated probability of damage to a tank of a floating structure as a function of time periods.

The is a diagram representing a floating structure moored to an anchor point relative to the seabed while being free to pivot around said anchor point, and a sea state of the wind, a swell state, d a state of the current and a state of the wind to which the floating structure may be subjected.

The is a flowchart representing a method for estimating a risk of damage due to the sloshing of a liquid load of the floating structure of the .

The figures are described below in the context of a ship 1 comprising a double hull forming a supporting structure in which are arranged a plurality of watertight and thermally insulating tanks. Such a carrier structure has for example a polyhedral geometry, for example of prismatic shape.

Such sealed and thermally insulating tanks are provided for example for the transport of liquefied gas. The liquefied gas is stored and transported in such tanks at a low temperature, which requires thermally insulating tank walls in order to maintain the liquefied gas at this temperature. It is therefore particularly important to maintain the integrity of the walls of the tanks intact, on the one hand to preserve the tightness of the tank and avoid leaks of liquefied gas from the tanks and, on the other hand, to avoid degradation of the insulating characteristics. of the tank in order to maintain the gas in its liquefied form.

Such watertight and thermally insulating tanks also comprise an insulating barrier anchored to the double ship hull and carrying at least one watertight membrane. By way of example, such tanks can be made using technologies of the Mark III® type, as described for example in FR 2 691 520 A1, of the NO96® type as described for example in FR 2 877 638 A1, or other as described for example in WO 2014/057221 A2.

The illustrates a ship 1 comprising four watertight and thermally insulating tanks 2 . On such a ship 1, the tanks 2 are interconnected by a cargo handling system (not shown) which may include many components, for example pumps, valves and pipes so as to allow the transfer of liquid from the one of the tanks 2 to another tank 2.

On the , the ship 1 has been shown associated with a stationary floating structure 40, in order to carry out a transfer operation (“Ship-to-Ship Transfer” or STS) of the LNG contained in the four tanks 2 of the ship 1 towards sealed tanks and thermally insulating (not shown) that comprises the stationary floating structure 40. The stationary floating structure 40 is here a floating storage and regasification unit (FSRU) of liquefied natural gas, but it could also be a unit floating liquefied natural gas (FLNG) production vessel, another LNG transport vessel similar to vessel 1, or more generally any floating structure, stationary or otherwise, comprising sealed and thermally insulated tanks for receiving LNG.

The stationary floating structure 40 is here located offshore and moored to an anchor point 90 relative to the seabed, such as an underwater buoy anchored to the seabed or a turret mooring system. The vessel 1 is associated with the stationary floating structure 40 using several mooring lines 92, typically located at the bow and stern of the vessel 1 and the stationary floating structure 40. Floats 91 can be arranged between the stationary floating structure 40 and the ship 1 in order to avoid an accidental collision between them. At least one flexible pipe 93 is installed in order to transfer the LNG contained in the four tanks 2 of the ship 1 to the tanks of the stationary floating structure 40.

During the LNG transfer operation, the ship 1 and the stationary floating structure are oriented along the same heading 99, hereinafter referred to as the common heading 99. It is however specified that the common heading 99 can be modified during the transfer operation, which can last several hours or even several tens of hours.

The ship 1 typically arrives near the stationary floating structure 40 with its four tanks 2 almost completely filled with LNG. However, as the LNG is transferred, the tanks 2 are gradually emptied. The four tanks 2 present on the a partially full state. A first tank 3 is filled to approximately 60% of its capacity. A second tank 4 is filled to approximately 35% of its capacity. A third tank 5 is filled to approximately 35% of its capacity. A fourth tank 6 is filled to approximately 40% of its capacity.

This partial filling of the tanks 3, 4, 5, 6 can generate significant risks of damage to said tanks 3, 4, 5, 6 during the LNG transfer operation. Indeed, when it is at sea, the ship 1 is subject to many movements related to climatic conditions.

In particular, ship 1 is subject to wind sea excitation represented by axis 10, swell excitation represented by axis 12, current excitation 14, and wind excitation 16. The wind sea is created by the excitation of the wind 16 which prevails in the vicinity of the ship 1, and induces waves having a wind sea direction parallel to the axis 10, a significant wind sea height and a period of windy sea peak. The swell is created by wind excitation away from ship 1, and causes waves with a swell direction parallel to axis 12, a significant swell height and a peak swell period. The meeting of the waves induced by the swell and the sea of the wind causes movements of the vessel 1. The vessel 1 is furthermore subject to the movements due to the current, the current having a direction parallel to the axis 14 and a speed of the current. Finally, the ship 1 is subject to the excitation of the wind, the wind having a direction parallel to the axis 16 and a wind speed. These movements of the vessel 1 affect the liquid contained in the tanks 3, 4, 5, 6 which, consequently, is subject to sloshing in the tanks 3, 4, 5, 6 by producing impacts on the walls of the tanks . When the sloshing exceeds the capacity of the vessel walls to absorb or disperse the sloshing, the impacts on the vessel walls 3, 4, 5, 6 can degrade the vessel walls 3, 4, 5, 6. However, it is important to preserve the integrity of the walls of the tanks 3, 4, 5, 6 to preserve the tightness and the insulation characteristics of the tanks 3, 4, 5, 6. It is therefore important to estimate a probability of damage due to sloshing in order to avoid such damage.

Obviously, the risk of degradation of the walls of the tanks 3, 4, 5, 6 of the ship 1 is just as present for the walls of the tanks of the stationary floating structure 40, which is also subject to the sea excitation of the wind 10, wave excitation 12, and current excitation 14.

A process 300, shown in , can be implemented in order to predict a probability of damage to the tanks of the ship 1 and/or of the stationary floating structure 40.

The method 300 first comprises a step 301 in which a forecast geographical position of the LNG transfer operation is obtained. This geographical position can be entered by a user, or else be acquired automatically by an on-board system of the ship 1 or of the stationary floating structure 40, for example in the form of GPS coordinates.

After step 301, the method 300 passes to a step 302 in which meteorological and oceanographic forecasts relating to the geographical position obtained in step 301 are obtained. Such forecasts are for example transmitted by a means of communication such as radio or satellite by a weather and oceanographic forecast provider. The forecasts are obtained for a plurality of time periods which together cover an expected duration of the LNG transfer operation, which expected duration may be entered by a user.

For each time period, the forecast includes at least one wave state. They preferably further comprise a sea state of the wind or a current state or a wind state, more preferably several of these states, and even more preferably all of these states.

After step 302, method 300 further comprises the following steps:
- a step 303A in which one extracts from the forecasts obtained in step 302, for each period of time, a direction of the swell (represented on the by the direction of the axis 12) and a significant height of the swell, and a peak period of the swell;
- if applicable, a step 303B in which one extracts, from the forecasts obtained in step 302, for each period of time, a significant wind sea height and/or a wind sea peak period and/or a sea direction of the wind (shown on the by the direction of the axis 10);
- where appropriate, a step 303C in which one extracts, from the forecasts obtained in step 302, for each period of time, a current speed and/or a current direction (represented on the by the direction of the axis 14);
- if applicable, a step 303D in which one extracts, from the forecasts obtained in step 302, for each period of time, a wind speed and/or a wind direction (represented on the by the direction of axis 16).

The method 300 then comprises the following steps, which are repeated for each of the time periods:
- A step 304 in which the common heading 99 of the ship 1 and of the stationary floating structure 40 is obtained;
- A step 305 in which at least one forecast filling level of at least one tank of at least one of the ship 1 and of the stationary floating structure 40 is determined;
- a step 306 in which a swell angle of incidence is determined, that is to say an angle between the common heading 99 and the direction of the swell (shown on the by the direction of the axis 12);
- a step 307 in which at least one probability of damage to the tank, the provisional filling level of which was determined in step 305, is estimated as a function of: the angle of incidence of the swell determined in step 306; the significant wave height and the wave peak period extracted in step 303A; and the at least one provisional filling level of the tank in question determined in step 305.

Step 305 can be performed in various ways. According to a variant, one or more forecast filling levels of the tank are determined from a liquid loading transfer scenario, the liquid loading transfer scenario defining an evolution of the filling level of said tank as a function of time. Such a liquid load transfer scenario can be determined in advance, and for example be entered by the user prior to the transfer operation.

Several predicted filling levels of the tank can be determined in step 305, a probability of damage to the tank being estimated in step 307 for each predicted filling level of the tank determined in step 305. According to a As a variant, in step 305, two forecast filling levels of the tank are determined, the two forecast filling levels including a low forecast filling level and a high forecast filling level. According to a particular variant, the low forecast filling level and the high forecast filling level are forecast filling levels determined in advance: step 305 then simply consists of reading - for example in the database mentioned above - below in relation to step 307 - the values of the low forecast filling level and the high forecast filling level. The predicted low filling level and the predicted high filling level can be determined in advance during a preliminary step (not shown in the drawings) consisting in searching, for example by simulation and/or by experimental tests, two levels filling the tank which are most likely to lead to a risk of damage to the tank due to sloshing.

When several tanks of the ship 1 and/or of the stationary floating structure 40 are taken into consideration, steps 305 and 307 are implemented for each of these tanks. It is also possible to choose to consider only some of the tanks of the ship 1 and/or of the stationary floating structure 40, for example one or some of the tanks of the ship 1 and/or of the stationary floating structure 40 which have been determined by prior analysis that they are most at risk of damage due to sloshing.

Step 307 can be carried out by consulting a database previously established for the vessel considered, as the case may be, of the ship 1 or of the stationary floating structure 40. Such a database includes data relating to the sloshing in as a function of an angle of incidence of the swell, of a significant height of the swell, of a peak period of the swell, and of a current filling level of said tank, the data relating to the sloshing being determined by experimental measurements. The probability of damage being relative to a probability density of encountering a pressure on an internal surface of the tank greater than an internal resistance of the tank as a function of the angle of incidence of the swell, of the significant height of the swell, the peak period of the swell and the filling level of said tank.

The common heading 99 obtained in step 304 can be defined in advance. According to a variant, the common heading 99 can be entered by a user, for each period of time or even for all the periods of time considered. According to an advantageous variant, for each period of time, this common heading 99 is obtained so as to take into account the forces undergone by the ship 1 and the floating structure 40 due to the state of the swell, and preferably the sea state, wind and/or current state.

The shows an example of such an implementation of step 304, wherein:
- in a first step 304-1, the forces undergone by the ship 1 and the floating structure 40 are calculated due to the state of the swell, and preferably the sea state of the wind and/or the the state of the current and/or the state of the wind;
- in a second step 304-2, a resultant of the forces determined in step 304-1 is calculated;
- in a third step 304-3, a moment of the resultant determined in step 304-2 is calculated around the anchor point 90.
Steps 304-1, 304-2, 304-3 are implemented for a plurality of theoretical headings, that is to say a plurality of possible values of the common heading 99. For example, steps 304-1, 304-2, 304-3 are implemented for increments of values of the common heading 99, these increments being 5 degrees, 2 degrees or even 1 degree. Next, in a step 304-4, a common heading 99 is selected from among said plurality of theoretical headings which minimizes the absolute value of the moment determined in steps 304-3.

After step 307, the method 300 proceeds to a step 308 in which an indication is provided to a user based on the probabilities of damage estimated in step 307.

This step 308 can simply consist of providing a visual and/or audible alarm to the user when the probability of damage to one of the tanks exceeds a predetermined threshold. In addition or alternatively, the indication provided at step 308 may comprise the fact of providing the user with at least one visual indication of the damage probabilities estimated at step 307, as a function of another quantity.

The represents by way of example a visual indication of the probabilities of damage estimated at step 307 as a function of the time periods to which they relate. In this figure, the visual indication comprises a box corresponding to each of the time periods. An absence of hatching indicates that the probability of damage is zero or less than a low threshold. Simple hatching indicates that the probability of damage is between a low threshold and a high threshold. Double hatching indicates that the probability of damage is above a high threshold. It is understood that instead of different hatching, different colors according to a color code or any other representation can be used. It is also understood that a different number of damage probability thresholds can be used.

Preferably, after step 308, the method 300 passes to a step 309 of decision support intended to reduce the probability or probabilities of damage estimated in step 307. This step 309 of decision support can including including providing the user with:
- a proposal to change the common heading 99, and/or
- a proposal for modifying at least one parameter of the transfer operation, for example a liquid loading transfer rate and/or a filling level of the tank or tanks (between the tanks of the vessel 1 and/or between the tanks of the stationary floating structure 40 and/or between the tanks of the ship 1 and the tanks of the stationary floating structure 40).

Thanks to this step 309, the user is enabled to take the necessary measures, on the basis of these proposals, in order to reduce the risk of damage to the tanks.

The illustrates a device 100 for determining sloshing that can be embarked on ship 1. This device 100 comprises a central unit 110 configured to carry out the different steps of method 300 to estimate the probability of damage to a tank of ship 1 and/or of the stationary floating structure 40.

The central unit 110 is connected to a plurality of on-board sensors 120 making it possible to obtain the various quantities indicated above. Thus, the sensors 120 comprise, for example and in a non-exhaustive manner, a filling level sensor 121 of each tank, and other sensors 122, 123 capable of providing at the output quantities indicative of the state of the swell, and preferably sea state, wind and/or current state and/or wind state.

The device 100 further comprises a man-machine interface 140. This man-machine interface 140 comprises a display means 41 enabling an operator of the ship 1 to obtain various information, for example the probabilities of damage estimated by implementing the steps of the method 300, the indication or indications generated in step 308, the decision aid generated in step 309, the quantities obtained by the sensors 120, the state of loading of the ship or even meteorological information .

The man-machine interface 140 further comprises an acquisition means 42 enabling the operator to manually supply quantities to the central unit 110, typically to supply the central unit 110 with data which cannot be obtained by sensors because the ship 1 does not have the necessary sensor or because the latter is damaged. For example, in one embodiment, the acquisition means 42 allows the operator to enter information on the sea state of the wind and/or the state of the swell.

The device 100 comprises a database 150. This database 316 comprises for example certain quantities obtained in the laboratory or during measurement campaigns on board at sea. For example, the database 150 can comprise, for a given tank, data relating to sloshing as a function of an angle of incidence of the swell, of a significant height of the swell, of a peak period of the swell and of a current filling level of said tank.

The device 100 also comprises a communication interface 130 allowing the central unit 110 to communicate with remote devices, for example to obtain weather forecasts, ship position data or other.

Certain elements represented, in particular the central unit 110, can be produced in different forms, in a unitary or distributed manner, by means of hardware and/or software components. Material components that can be used are specific integrated circuits ASIC, programmable logic networks FPGA or microprocessors. Software components can be written in different programming languages, for example C, C++, C#, Java (registered trademark) or VHDL. This list is not exhaustive.

In the description above, reference has been made to a wave peak period, i.e. a period of time between the passage of two successive wave peaks. As a variant, instead of the peak period of the swell, one can consider the mean period of the swell, that is to say a period of time between three successive passages of the swell at the mean height of the wave. sea.

Similarly, instead of the peak wind sea period, we can consider the mean wind sea period, i.e. a period of time between three successive passages of the wind sea at mean sea level.

On the , we have thus represented the ship 1 of the , moored by one or more mooring lines 92 to an anchor point 90 relative to the seabed, such as an underwater buoy anchored to the seabed. The ship 1 is free to pivot around the anchor point 90, and can thus adopt any heading due to its pivoting around the anchor point 90. The heading of the ship 1 here bears the reference 190.

As previously described in connection with the , the ship 1 is here also subject to a sea excitation of the wind represented by the axis 10, to an excitation of the swell represented by the axis 12, to an excitation of the current 14, and to an excitation of the wind 16. The movements of the vessel 1 affect the liquid contained in the tanks 3, 4, 5, 6 which, consequently, is subject to sloshing in the tanks 3, 4, 5, 6 by producing impacts on the walls of the tanks . When the sloshing exceeds the capacity of the vessel walls to absorb or disperse the sloshing, the impacts on the vessel walls 3, 4, 5, 6 can degrade the vessel walls 3, 4, 5, 6. However, it is important to maintain the integrity of the walls of the tanks 3, 4, 5, 6 to maintain the tightness and the insulation characteristics of the tanks 3, 4, 5, 6. It is therefore, here too, important to estimate a probability of damage due to sloshing in order to avoid such damage.

A 1300 process, shown in , can be implemented in order to predict a probability of damage to the tanks of ship 1.

The method 1300 first comprises a step 1301 in which a geographical position of the vessel 1 moored at the anchor point 190 is obtained. This geographical position can be entered by a user, or else be acquired automatically by an on-board system of the vessel 1 , for example in the form of GPS coordinates.

After step 1301, the method 1300 passes to a step 1302 in which meteorological and oceanographic forecasts relating to the geographical position obtained in step 1301 are obtained. Such forecasts are for example transmitted by a means of communication such as radio or satellite by a weather and oceanographic forecast provider. The forecasts are obtained for a plurality of time periods which together cover an expected duration of the LNG transfer operation, which expected duration may be entered by a user.

After step 1302, method 1300 further comprises the following steps:
- a step 1303A in which one extracts from the forecasts obtained in step 1302, for each period of time, a direction of the swell (represented on the by the direction of the axis 12) and a significant height of the swell, and a peak period of the swell;
- if applicable, a step 1303B in which one extracts, from the forecasts obtained in step 1302, for each time period, a significant wind sea height and/or a wind sea peak period and/or a sea direction of the wind (shown on the by the direction of the axis 10);
- if applicable, a step 1303C in which one extracts, from the forecasts obtained in step 1302, for each period of time, a speed of the current and/or a direction of the current (represented on the by the direction of the axis 14);
- where applicable, a step 1303D in which one extracts, from the forecasts obtained in step 1302, for each period of time, a wind speed and/or a wind direction (represented on the by the direction of axis 16).

Method 1300 then includes the following steps, which are repeated for each of the time periods:
- a step 1304 in which the heading 190 of the ship 1 is obtained;
- A step 1305 in which at least one provisional filling level of at least one tank of the vessel 1 is determined;
- a step 1306 in which a swell angle of incidence is determined, that is to say an angle between the heading 190 of the ship 1 and the direction of the swell (shown on the by the direction of the axis 12);
- a step 1307 in which at least one probability of damage to the tank, the provisional filling level of which was determined in step 305, is estimated as a function of: the angle of incidence of the swell determined in step 1306; the significant height of the swell and the peak period of the swell extracted in step 1303A; and the at least one forecast filling level of the tank in question determined in step 1305.

When several tanks of ship 1 are taken into consideration, steps 1305 and 1307 are implemented for each of these tanks. It is also possible to choose to consider only some of the tanks of ship 1, for example one or some of the tanks of ship 1 which it has been determined by a prior analysis that they are the most subject to a risk of damage due to sloshing.

Step 1307 can be performed by consulting a database previously established for the considered tank of the ship 1. Such a database includes data relating to sloshing as a function of an angle of incidence of the swell, d a significant height of the swell, a peak period of the swell and a current filling level of said tank, the data relating to the sloshing being determined by experimental measurements. The probability of damage being relative to a probability density of encountering a pressure on an internal surface of the tank greater than an internal resistance of the tank as a function of the angle of incidence of the swell, of the significant height of the swell, the peak period of the swell and the filling level of said tank.

The heading 190 obtained in step 1304 can be defined in advance. According to a variant, the heading 190 can be entered by a user, for each period of time or even for all the periods of time considered. According to an advantageous variant, for each period of time, this course of the ship 190 is obtained so as to take into account the forces undergone by the ship 1 due to the state of the swell, and preferably the sea state of the wind and/or current conditions.

The shows an example of such an implementation of step 1304, wherein:
- in a first step 1304-1, the forces undergone by the ship 1 are calculated due to the state of the swell, and preferably the sea state of the wind and/or the state of the current and/ or the state of the wind;
- in a second step 1304-2, a resultant of the forces determined in step 1304-1 is calculated;
- in a third step 1304-3, a moment of the resultant determined in step 1304-2 is calculated around the anchor point 90.
Steps 1304-1, 1304-2, 1304-3 are implemented for a plurality of theoretical headings, that is to say a plurality of possible values of heading 190. For example, steps 1304-1, 1304 -2, 1304-3 are implemented for increments of values of heading 190, these increments being 5 degrees, 2 degrees or even 1 degree. Then, in a step 1304-4, one selects, from among said plurality of theoretical headings, a heading 190 which minimizes the absolute value of the moment determined in steps 1304-3.

After step 1307, the method 1300 proceeds to a step 1308 in which an indication is provided to a user based on the probabilities of damage estimated in step 1307.

This step 1308 can simply consist of providing a visual and/or audible alarm to the user when the probability of damage to one of the tanks exceeds a predetermined threshold. In addition or alternatively, the indication provided in step 1308 may comprise the fact of providing the user with at least a visual indication of the probabilities of damage estimated in step 1307, as a function of another quantity. This visual indication may be analogous to that described above in relation to the .

Preferably, after step 1308, the method 1300 passes to a step 1309 of decision support intended to reduce the probability or probabilities of damage estimated in step 1307. This step 1309 of decision support can including including providing the user with:
- a proposal to change course 190, and/or
- a proposal to modify a filling level of at least one of the tanks of vessel 1.

Thanks to this step 1309, the user is enabled to take the necessary measures, on the basis of these proposals, in order to reduce the risk of damage to the tanks.

The different steps of the method 1300 can be implemented by the central unit 110 of the device 100 already described above in relation to the .

Although the invention has been described in connection with several particular embodiments, it is obvious that it is in no way limited thereto and that it includes all the technical equivalents of the means described as well as their combinations if these fall within the scope of the invention.

Moreover, it is quite obvious that a characteristic or a combination of characteristics described in relation to a process applies equally to a corresponding system, and vice versa.

The use of the verb "comport", "understand" or "include" and its conjugated forms does not exclude the presence of other elements or other steps than those set out in a claim.

In the claims, any reference sign in parentheses cannot be interpreted as a limitation of the claim.

Claims

Method (300) for estimating a probability of damage due to the sloshing of a liquid load during an operation of transferring said liquid load from a first floating structure (1) to a second floating structure (40), the first floating structure (1) and the second floating structure (40) being associated with each other during said transfer operation such that the first floating structure (1) and the second floating structure (40) are oriented according to a common cap (99), said method (300) comprising:
- obtaining (301) a predicted geographical position of said transfer operation;
- obtaining (302) meteorological and oceanographic forecasts relating to said geographical position for a plurality of time periods, said time periods together covering an expected duration of said transfer operation, said forecasts comprising, for each time period, a state swell, wherein the swell condition includes a swell direction, a significant swell height and a swell period;
- for each period of time: obtaining (304) the common course (99) of the first and of the second floating structures (1, 40); determining (305) at least one projected filling level of at least one tank of at least one of said first and second floating structures (1, 40) intended to contain all or part of said liquid load; determining (306) a swell angle of incidence, which is an angle between said common heading (99) of the first and second floating structures and the direction of the swell (12); and estimating (307) at least one probability of damage to said at least one tank as a function of the angle of incidence of the swell thus determined, the significant height of the swell, the period of the swell and the said at least a forecast filling level of said tank; and
- providing a user (308) with an indication as a function of said at least one probability of damage thus estimated.
Method (300) according to claim 1, in which the said at least one forecast filling level is determined (305) from a liquid loading transfer scenario, the liquid loading transfer scenario defining a change in the filling level of said tank as a function of time.
Method (300) according to any one of Claims 1 to 2, in which for each period of time, two forecast filling levels of the said tank are determined (305), the two forecast filling levels including a low forecast filling level and a forecast high filling level, and a probability of damage to said tank is estimated (307) for each of the two forecast filling levels.
Method (300) according to any one of Claims 1 to 3, in which the said at least one probability of damage is estimated (307) by consulting a database previously established for the said vessel, the said database comprising data relating to sloshing as a function of an angle of incidence of the swell, a significant height of the swell, the period of the swell and a current filling level of said tank,
the sloshing data being determined by experimental measurements, and
the probability of damage being relative to a probability density of encountering a pressure on an internal surface of the tank greater than an internal resistance of the tank as a function of the angle of incidence of the swell, of the significant height of the swell, the period of the swell and the current filling level of said tank.
A method (300) according to any of claims 1 to 4, wherein said indication includes information representative of the probability of damage estimated as a function of said periods of time.
A method (300) according to any one of claims 1 to 5, wherein said forecast further comprises a wind sea state, the wind sea state comprising a significant wind sea height and/or a period of wind sea and/or a wind sea direction (10), and the probability of damage to said at least one tank is further estimated based on the wind sea state.
A method (300) according to any of claims 1 to 6, wherein the first floating structure (1) and the second floating structure (40) are anchored to an anchor point (90) during said transfer operation, and for each period of time, said common heading (99) of the two floating structures (1, 40) is obtained (304) by:
- calculating (304-2, 304-3), for a plurality of theoretical headings, a resultant of the forces undergone by the first and second floating structures as a function of the state of the swell and a moment relative to the anchor point (90) of said resultant;
- selecting (304-4), among said plurality of theoretical headings, a common heading (99) which minimizes the absolute value of the moment with respect to the anchor point of said resultant.
Method (300) according to claim 6 and claim 7 taken in combination, in which the resultant of the forces undergone by the first and second floating structures (1, 40) is further calculated (304-2) as a function of the state sea wind.
A method (300) according to claim 7 or 8, wherein said forecast further comprises a wind condition, the wind condition including wind speed and/or wind direction (16), and wherein the resultant of the forces experienced by the first and second floating structures is further calculated according to the state of the wind.
A method (300) according to any of claims 7 to 9, wherein said predictions further comprise a current state, the current state comprising a current velocity and/or a current direction (14), and in wherein the resultant of the forces experienced by the first and second floating structures (1, 40) is further calculated as a function of the state of the current.
Method (300) according to any one of claims 7 to 10, in which said indication comprises information representative of the probability of damage estimated as a function of said plurality of theoretical headings.
A method (300) according to any of claims 1 to 11, further comprising a decision support step (309) for reducing the estimated probability of damage.
A method (300) according to claim 12, wherein the decision support step (309) comprises providing the user with:
- a proposal to change the common heading (99), and/or
- a proposed modification of at least one parameter of the transfer operation.
A method (300) according to any one of claims 1 to 13, wherein the liquid feed is a liquefied gas feed, in particular a liquefied petroleum gas feed or a liquefied natural gas feed.
A method (300) according to claim 14, wherein the liquid cargo is a liquefied natural gas cargo, the first floating structure is a liquefied natural gas carrier vessel (1), and the second floating structure is a floating storage and liquefied natural gas regasification unit (40) or a floating liquefied natural gas production unit.
Device (100) for estimating a probability of damage due to the sloshing of a liquid load during an operation of transferring said liquid load from a first floating structure (1) to a second floating structure (40), the first floating structure (1) and the second floating structure (40) being associated with each other during said transfer operation such that the first floating structure and the second floating structure are oriented on a common heading (99), the device (100) comprising a processor (110) configured to implement the method (300) according to any one of claims 1 to 15.
Floating structure (1, 40) comprising a device (100) according to claim 16.