Method and device for estimating the probability of damage caused by sloshing of a liquid load during the transfer of this liquid between two floating structures

Description

Domaine technique

[0001] 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 an operation for transferring said liquid load from a first floating structure to a second floating structure. Arrière-plan technologique

[0002] In the field of floating structures capable of transporting a liquid cargo, it is known to carry out operations of transferring the liquid cargo from a first floating structure, such as a liquid transport vessel, to a second floating structure.

[0003] Such liquid cargo transfer operations are commonly implemented for liquefied natural gas (LNG) cargoes. For such cargoes, as is well known, an LNG carrier, such as an LNG carrier (also known as LNGC), can be used in conjunction with a floating liquefied natural gas storage and regasification unit (FSRU). The FSRU is, for example, located offshore and moored to an underwater buoy or a turret mooring system allowing the structure to freely orient itself according to the constraints applied to it (waves, wind, current, etc.). The LNGC then docks with the FSRU, and flexible pipes 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 a Ship-to-Ship Transfer (STS). It can also be carried out between an LNGC and another floating facility, such as a floating liquefied natural gas production unit (FLNG).

[0004] However, during such an operation, the LNGC and FSRU tanks intended to contain LNG are partially filled. It is known that in such a situation, the LNG contained in the tanks is agitated by the effect of waves. The agitation of the liquid, generally referred to as "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 liquid transported and the risk of cold spots on the steel hull of the floating structure.

[0005] Furthermore, such an operation is likely to take a significant amount of time, in the order of several dozen hours when it involves an LNGC and a large-capacity FSRU or a floating liquefied natural gas (FLNG) production unit. The longer the time required for the operation, the more likely it is that climatic conditions that could cause sloshing of the LNG in the tanks will occur.

[0006] WO 2018 / 064598 A1 describes a method taking into account, among several factors, the sloshing in the tanks, to optimize the transfer operations, by adjusting the orientation of the floating structures so as to avoid any situation which could hinder the filling operations.

[0007] 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 tanks due to sloshing. Résumé

[0008] An idea underlying the invention is to take advantage of meteorological and oceanographic forecasts relating to the geographical position of the liquid cargo transfer operation, for an expected duration of said transfer operation, to estimate a probability of damage to 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 based on the probability of damage thus estimated.

[0009] 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 an operation of transferring 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 method comprising: obtaining an expected 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 wave state, wherein the wave state comprises a wave direction, a significant wave height and a wave period; for each time period: obtaining the common heading of the first and second floating structures; determining at least one forecast 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 cargo; determining a wave incidence angle, which is an angle between said common heading of the first and second floating structures and the wave direction;and estimate at least one probability of damage to said at least one tank as a function of the wave incidence angle thus determined, the significant height of the wave, the period of the wave and the predicted filling level of said tank; and provide a user with an indication as a function of said at least one probability of damage thus estimated.;

[0010] By means of such a method, a user such as a crew member can take any necessary measures to limit the risk of damage to the tanks of the floating structure(s), such as, for example, modifying the common course of the two floating structures and / or modifying 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).

[0011] According to embodiments, such a method may comprise one or more of the following features.

[0012] According to one embodiment, the swell period is a peak swell period, i.e. a period of time between the passage of two successive swell peaks. According to one embodiment, the swell period is an average swell period, i.e. a period of time between three successive passages of the swell at the average sea height; this average period is commonly denoted T z .

[0013] The predicted 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 load transfer scenario, the liquid load transfer scenario defining a change in the filling level of said tank as a function of time.

[0014] Such a liquid cargo transfer scenario can be entered by the user at the start of the transfer operation.

[0015] According to one embodiment, for each time period, two forecast filling levels of said tank are determined, the two forecast filling levels including a low forecast filling level and a high forecast filling level, and a probability of damage to said tank is estimated for each of the two forecast filling levels.

[0016] 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.

[0017] According to one embodiment, the predicted low filling level and the predicted high filling level are determined in advance during a preliminary step consisting of searching, for example by simulation and / or by experimental tests, two filling levels of the tank which are most likely to lead to a risk of damage to the tank due to sloshing.

[0018] 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 data relating to sloshing 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, the significant height of the swell, the period of the swell and the current filling level of said tank.

[0019] According to one embodiment, said indication comprises information representative of the probability of damage estimated as a function of said time periods. In particular, according to one embodiment, said indication comprises a visual indication of the probability of damage estimated as a function of said time periods.

[0020] According to one embodiment, the first floating structure and the second floating structure are anchored to an anchoring point during said transfer operation.

[0021] 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.

[0022] According to one embodiment, the wind sea period is a wind sea peak period, i.e. a period of time between the passage of two successive peaks of the wind sea. According to one embodiment, the swell period is an average wind sea period, i.e. a period of time between three successive passages of the wind sea at the average sea height; this average period is commonly denoted T z .

[0023] According to one embodiment, the probability of damage to said at least one tank is further estimated as a function of the sea state of the wind.

[0024] The common heading of the first and 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 time period, said common heading of the two floating structures is obtained by: calculating, for a plurality of theoretical headings, a resultant of the forces experienced by the first and second floating structures as a function of the state of the swell and a moment relative to the anchoring point of said resultant; selecting, from among said plurality of theoretical headings, a common heading which minimizes the absolute value of the moment relative to the anchoring point of said resultant.

[0025] According to one embodiment, the resultant of the forces experienced by the first and second floating structures is further calculated as a function of the sea state of the wind.

[0026] According to one embodiment, said forecasts further comprise a wind state, the wind state comprising a wind speed and / or a wind direction, and the resultant of the forces experienced by the first and second floating structures is further calculated as a function of the wind state.

[0027] 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 experienced by the first and second floating structures is further calculated as a function of the state of the current.

[0028] According to one embodiment, said indication comprises information representative of the probability of damage estimated as a function of said plurality of theoretical headings.

[0029] According to one embodiment, the method further comprises a decision support step intended to reduce the estimated probability of damage.

[0030] According to one embodiment, the decision support step comprises providing the user with: a proposal to change the common course, and / or a proposal to modify at least one parameter of the transfer operation.

[0031] According to one embodiment, the proposal to modify at least one parameter of the transfer operation comprises a proposal to modify 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).

[0032] The user is thus able to take the necessary measures, based on these proposals, to reduce the risk of damage to the tanks.

[0033] The process is applicable to floating structures transporting any type of liquid cargo. However, it finds particular application to floating structures transporting a load of a cold liquid product.

[0034] According to one embodiment, the liquid cargo is a liquefied gas cargo, in particular a liquefied petroleum gas (LPG) cargo or a liquefied natural gas (LNG) cargo.

[0035] According to one embodiment, the at least one tank is a sealed and / or thermally insulating tank.

[0036] According to one embodiment, the first floating structure is a liquefied natural gas (LNGC) carrier vessel, and the second floating structure is a liquefied natural gas floating storage and regasification unit (FSRU) or a liquefied natural gas floating production unit (FLNG).

[0037] According to one embodiment, the invention also provides a device for estimating a probability of damage due to sloshing of a liquid load during an operation of transferring 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, the device comprising a processor configured to implement the method according to any of the embodiments described above.

[0038] Such a device has the same advantages as those described above in relation to the method.

[0039] According to one embodiment, the invention also provides a floating structure comprising a device as described above.

[0040] The principles described above are also applicable to a floating structure carrying a liquid cargo and anchored to an anchor point. Indeed, the liquid cargo of such a floating structure is also likely to be agitated by the effect of waves, which can also lead to a sloshing phenomenon which is likely to harm the integrity of the tank(s) containing the liquid cargo.

[0041] 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 anchoring point relative to the seabed while being free to pivot around said anchoring point, said method comprising: obtaining a geographical position of the floating structure moored at 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 wave state, in which the wave state comprises a wave direction, a significant wave height and a wave period; for each time period: obtaining a heading of the floating structure; determining at least one forecast filling level of at least one tank of said floating structure intended to contain said liquid cargo; determining a wave incidence angle, which is an angle between said heading and the wave direction;and estimate at least one probability of damage to said at least one tank as a function of the wave incidence angle thus determined, the significant height of the wave, the period of the wave and the predicted filling level of said tank; and provide a user with an indication as a function of said at least one probability of damage thus estimated.;

[0042] By means of such a method, a user such as a crew member can take any necessary measures to limit the risk of damage to the tank(s) of the floating structure, such as, for example, changing the course of the floating structure, it being remembered that the floating structure is free to pivot around its anchor point.

[0043] According to embodiments, such a method may comprise one or more of the following features.

[0044] According to one embodiment, the swell period is a peak swell period, i.e. a period of time between the passage of two successive swell peaks. According to one embodiment, the swell period is an average swell period, i.e. a period of time between three successive passages at the average sea height; this average period is commonly denoted T z .

[0045] 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 data relating to sloshing 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, the significant height of the swell, the period of the swell and the current filling level of said tank.

[0046] According to one embodiment, said indication comprises information representative of the probability of damage estimated as a function of said time periods. In particular, according to one embodiment, said indication comprises a visual indication of the probability of damage estimated as a function of said time periods.

[0047] 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.

[0048] According to one embodiment, the wind sea period is a wind sea peak period, i.e. a period of time between the passage of two successive peaks of the wind sea. According to one embodiment, the swell period is an average wind sea period, i.e. a period of time between three successive passages at the average sea height; this average period is commonly noted T z .

[0049] According to one embodiment, the probability of damage to said at least one tank is further estimated as a function of the sea state of the wind.

[0050] 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 time period, said common heading of the floating structure is obtained by: calculating, for a plurality of theoretical headings, a resultant of the forces experienced by the floating structure as a function of the state of the swell and a moment relative to the anchoring point of said resultant; selecting, from said plurality of theoretical headings, a common heading which minimizes the absolute value of the moment relative to the anchoring point of said resultant.

[0051] According to one embodiment, the resultant of the forces experienced by the floating structure is further calculated as a function of the sea state of the wind.

[0052] According to one embodiment, said forecasts further comprise a wind state, the wind state comprising a wind speed and / or a wind direction, and the resultant of the forces experienced by the floating structure is further calculated as a function of the wind state.

[0053] 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 experienced by the floating structure is further calculated as a function of the state of the current.

[0054] According to one embodiment, the resultant of the forces experienced by the floating structure is further calculated as a function of the sea state of the wind.

[0055] According to one embodiment, said forecasts further comprise a wind state, the wind state comprising a wind speed and / or a wind direction, and the resultant of the forces experienced by the floating structure is further calculated as a function of the wind state.

[0056] 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 experienced by the floating structure is further calculated as a function of the state of the current.

[0057] According to one embodiment, said indication comprises information representative of the probability of damage estimated as a function of said plurality of theoretical headings.

[0058] According to one embodiment, the method further comprises a decision support step intended to reduce the estimated probability of damage.

[0059] According to one embodiment, the decision support step comprises providing the user with: a proposal to change the course of the floating structure, and / or a proposal to modify the filling level of at least one of the tanks of the floating structure.

[0060] The user is thus able to take the necessary measures, on the basis of these proposals, to reduce the risk of damage to the tank(s) of the floating structure.

[0061] The process is applicable to floating structures transporting any type of liquid cargo. However, it finds particular application to floating structures transporting a load of a cold liquid product.

[0062] According to one embodiment, the liquid cargo is a liquefied gas cargo, in particular a liquefied petroleum gas (LPG) cargo or a liquefied natural gas (LNG) cargo.

[0063] According to one embodiment, the at least one tank is a sealed and / or thermally insulating tank.

[0064] According to one embodiment, the floating structure is a liquefied natural gas (LNGC) carrier vessel, a liquefied natural gas floating storage and regasification unit (FSRU) or a liquefied natural gas (FLNG) floating production unit.

[0065] 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 an anchoring point 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.

[0066] Such a device has the same advantages as those described above in relation to the method.

[0067] According to one embodiment, the invention also provides a floating structure comprising a device as described above. Brief description of the figures

[0068] 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 for illustrative and non-limiting purposes, with reference to the accompanying drawings. [ Fig. 1 ] There figure 1 is a schematic representation in longitudinal section of a floating structure, in this case a ship, comprising a plurality of tanks containing a liquid cargo. Fig. 2 ]. There figure 2 is a diagram representing two floating structures, in this case a ship and a floating unit, associated with each other during a liquid cargo transfer operation, and a sea state of wind, a wave state, a current state and a wind state to which the two floating structures may be subjected. Fig. 3A ] There figure 3A is a flowchart representing a method for estimating a risk of damage due to sloshing of a liquid cargo during an operation of transferring said liquid cargo from a first floating structure to a second floating structure. Fig. 3B ] There figure 3B is a detail of the organization chart of the figure 3A representing a variant of the process. [ Fig. 4 ] There figure 4 represents a device for predicting the sloshing of a liquid load during an operation of transferring said liquid load from a first floating structure to a second floating structure. Fig. 5 ] There figure 5 represents an example of a visual indication of the estimated probability of damage to a tank of a floating structure as a function of periods of time. Fig. 6 ] There figure 6 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 wind, a wave state, a current state and a wind state to which the floating structure may be subjected. Fig. 7A ] There figure 7A is a flowchart representing a process for estimating the risk of damage due to the sloshing of a liquid load of the floating structure of the figure 6 . [ Fig. 7B ] There figure 7B is a detail of the organization chart of the figure 7A representing a variant of the process. Description des modes de réalisation

[0069] The figures are described below in the context of a ship 1 comprising a double hull forming a load-bearing structure in which a plurality of sealed and thermally insulating tanks are arranged. Such a load-bearing structure has, for example, a polyhedral geometry, for example a prismatic shape.

[0070] Such sealed and thermally insulating tanks are intended, for example, for the transport of liquefied gas. 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 tank walls intact, on the one hand to maintain the tank's tightness and prevent liquefied gas from leaking out of the tanks and, on the other hand, to prevent damage to the tank's insulating characteristics in order to maintain the gas in its liquefied form.

[0071] Such sealed and thermally insulating tanks also comprise an insulating barrier anchored to the double hull of the ship and carrying at least one sealed membrane. For example, such tanks may be produced using Mark III ®< type technologies, as described for example in FR 2 691 520 A1, NO96 ®< type technologies as described for example in FR 2 877 638 A1, or other technologies as described for example in WO 2014 / 057221 A2.

[0072] There figure 1 illustrates a ship 1 having four watertight and thermally insulating tanks 2. On such a ship 1, the tanks 2 are connected to each other by a cargo handling system (not shown) which may include numerous components, for example pumps, valves and pipes so as to allow the transfer of liquid from one of the tanks 2 to another tank 2.

[0073] On the figure 2 , the ship 1 is represented 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 to sealed and thermally insulating tanks (not represented) which comprise 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 floating production unit of liquefied natural gas (FLNG), another LNG transport ship similar to the ship 1, or more generally any floating structure, stationary or not, comprising sealed and thermally insulating tanks for receiving LNG.

[0074] 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 ship 1 is associated with the stationary floating structure 40 using several mooring lines 92, typically located at the bow and stern of the ship 1 and the stationary floating structure 40. Floats 91 may be arranged between the stationary floating structure 40 and the ship 1 in order to avoid 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.

[0075] During the LNG transfer operation, vessel 1 and the stationary floating structure are oriented along the same heading 99, hereinafter referred to as the common heading 99. However, it is specified that the common heading 99 may be modified during the transfer operation, which may last several hours or even several dozen hours.

[0076] Vessel 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 figure 1 a partial filling 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.

[0077] This partial filling of tanks 3, 4, 5, 6 may cause significant risks of damage to said tanks 3, 4, 5, 6 during the LNG transfer operation. Indeed, when at sea, ship 1 is subject to numerous movements linked to climatic conditions.

[0078] In particular, the vessel 1 is subject to a wind sea excitation represented by the axis 10, a swell excitation represented by the axis 12, a current excitation 14, and a wind excitation 16. The wind sea is created by the wind excitation 16 prevailing in the vicinity of the vessel 1, and induces waves having a wind sea direction parallel to the axis 10, a significant wind sea height and a peak wind sea period. The swell is created by a wind excitation away from the vessel 1, and causes waves having a swell direction parallel to the axis 12, a significant swell height and a peak swell period. The meeting of the waves induced by the swell and the wind sea causes movements of the vessel 1. The vessel 1 is further subject to movements due to the current, the current having a direction parallel to the axis 14 and a current speed.Finally, the ship 1 is subject to wind excitation, the wind having a direction parallel to the axis 16 and a wind speed. These movements of the ship 1 are reflected on 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 tank walls. When the sloshing exceeds the capacity of the tank walls to absorb or disperse the sloshing, the impacts on the tank walls 3, 4, 5, 6 can degrade the tank walls 3, 4, 5, 6. However, it is important to maintain the integrity of the tank walls 3, 4, 5, 6 to maintain the sealing and 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 degradation.

[0079] Obviously, the risk of degradation of the walls of 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 sea excitation from the wind 10, to excitation from the swell 12, and to excitation from the current 14.

[0080] A 300 process, shown in the figure 3A , can be implemented in order to predict a probability of damage to the tanks of the ship 1 and / or the stationary floating structure 40.

[0081] The method 300 firstly comprises a step 301 in which an expected 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 the stationary floating structure 40, for example in the form of GPS coordinates.

[0082] After step 301, the method 300 proceeds 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 communication means such as radio or satellite by a meteorological 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, this expected duration being able to be entered by a user.

[0083] For each time period, the forecasts include at least one swell state. They preferably further include a wind sea state or a current state or a wind state, more preferably several of these states, and even more preferably all of these states.

[0084] After step 302, the method 300 further comprises the following steps: a step 303A in which a swell direction (represented on the) is extracted from the forecasts obtained in step 302, for each time period. figure 2 by the direction of axis 12) and a significant swell height, and a peak swell period; where appropriate, a step 303B in which, from the forecasts obtained in step 302, for each time period, a significant wind sea height and / or a peak wind sea period and / or a wind sea direction (represented on the figure 2 by the direction of axis 10); where appropriate, a step 303C in which, from the forecasts obtained in step 302, for each time period, a current speed and / or a current direction (represented on the figure 2 by the direction of axis 14); where appropriate, a step 303D in which a wind speed and / or a wind direction (represented on the) are extracted from the forecasts obtained in step 302, for each time period. figure 2 by the direction of axis 16).

[0085] 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 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 the stationary floating structure 40 is determined; a step 306 in which a wave incidence angle is determined, i.e. an angle between the common heading 99 and the direction of the wave (represented on the figure 2 by the direction of axis 12); a step 307 in which at least one probability of damage to the tank whose forecast filling level was determined in step 305 is estimated, as a function of: the wave incidence angle determined in step 306; the significant wave height and the wave peak period extracted in step 303A; and the at least one forecast filling level of the tank in question determined in step 305.

[0086] Step 305 can be carried out in various ways. According to a variant, one or more predicted filling levels of the tank are determined from a liquid load transfer scenario, the liquid load transfer scenario defining a change in 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.

[0087] Several predicted tank fill levels may be determined in step 305, a probability of damage to the tank being estimated in step 307 for each predicted tank fill level determined in step 305. According to a variant, in step 305, two predicted tank fill levels are determined, the two predicted fill levels including a predicted low fill level and a predicted high fill level. According to a particular variant, the predicted low fill level and the predicted high fill level are predicted fill levels determined in advance: step 305 then simply consists of reading - for example in the database mentioned below in connection with step 307 - the values of the predicted low fill level and the predicted high fill 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 of 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.

[0088] 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 a prior analysis to be most subject to a risk of damage due to sloshing.

[0089] Step 307 can be carried out by consulting a database previously established for the tank in question, depending on the case, of the ship 1 or of the stationary floating structure 40. Such a database includes data relating to sloshing as a function of an angle of incidence of the swell, a significant height of the swell, a period of peak swell, and a current filling level of said tank, the data relating to 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, the significant height of the swell, the period of peak swell and the filling level of said tank.

[0090] 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 of the wind and / or the state of the current.

[0091] There figure 3B represents an example of such an implementation of step 304, wherein: in a first step 304-1, the forces experienced 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 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.

[0092] Steps 304-1, 304-2, 304-3 are implemented for a plurality of theoretical headings, i.e. 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 1 degree. Then, 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.

[0093] After step 307, the method 300 proceeds to a step 308 in which an indication is provided to a user based on the damage probabilities estimated in step 307.

[0094] This step 308 may 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 as an alternative, the indication provided in step 308 may comprise providing the user with at least one visual indication of the damage probabilities estimated in step 307, as a function of another quantity.

[0095] There figure 5 represents, as an example, a visual indication of the damage probabilities estimated in 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 damage probability is zero or less than a low threshold. Single hatching indicates that the damage probability is between a low threshold and a high threshold. Double hatching indicates that the damage probability is greater than a high threshold. It is understood that instead of different hatching, different colors following a color code or any other representation may be used. It is further understood that a different number of damage probability thresholds may be used.

[0096] Preferably, after step 308, the method 300 moves to a decision support step 309 intended to reduce the probability or probabilities of damage estimated in step 307. This decision support step 309 may in particular comprise providing the user with: a proposal to change the common course 99, and / or a proposal to modify at least one 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 ship 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).

[0097] Thanks to this step 309, the user is able to take the necessary measures, on the basis of these proposals, in order to reduce the risk of damage to the tanks.

[0098] There figure 4 illustrates a device 100 for determining sloshing that can be embarked on the ship 1. This device 100 comprises a central unit 110 configured to carry out the different steps of the method 300 to estimate the probability of damage to a tank of the ship 1 and / or the stationary floating structure 40.

[0099] 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 for each tank, and other sensors 122, 123 capable of providing output quantities indicative of the state of the swell, and preferably of the sea state of the wind and / or the state of the current and / or the state of the wind.

[0100] The device 100 further comprises a human-machine interface 140. This human-machine interface 140 comprises a display means 41 allowing an operator of the ship 1 to obtain various information, for example the estimated probabilities of damage by implementing the steps of the method 300, the indication(s) generated in step 308, the decision aid generated in step 309, the quantities obtained by the sensors 120, the loading state of the ship or even meteorological information.

[0101] The human-machine interface 140 further comprises an acquisition means 42 allowing the operator to manually provide quantities to the central unit 110, typically to provide the central unit 110 with data that cannot be obtained by sensors because the ship 1 does not have the necessary sensor or 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.

[0102] The device 100 comprises a database 150. This database 316 comprises, for example, certain quantities obtained in the laboratory or during measurement campaigns carried out at sea. For example, the database 150 may comprise, for a given tank, data relating to sloshing as a function of an angle of incidence of the swell, a significant height of the swell, a period of peak swell and a current filling level of said tank.

[0103] 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 the like.

[0104] Some elements shown, in particular the central unit 110, can be implemented in different forms, in a unitary or distributed manner, by means of hardware and / or software components. Usable hardware components 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.

[0105] In the above description, reference has been made to a peak swell period, i.e. a period of time between the passage of two successive swell peaks. Alternatively, instead of the peak swell period, the mean swell period can be considered, i.e. a period of time between three successive passages of the swell at the mean sea height.

[0106] Similarly, instead of the peak wind height period, we can consider the mean wind height period, that is, a period of time between three successive passages of the wind height at the mean sea height.

[0107] The principles described above are also applicable to a floating structure carrying a liquid cargo and anchored to an anchor point. Indeed, the liquid cargo of such a floating structure is also likely to be agitated by the effect of waves, which can also lead to a sloshing phenomenon which is likely to harm the integrity of the tank(s) containing the liquid cargo.

[0108] On the figure 6 , we thus represented ship 1 of the figure 1 , 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.

[0109] As previously described in connection with the figure 2 , the ship 1 is here also subject to a sea excitation of the wind represented by the axis 10, to a swell excitation represented by the axis 12, to a current excitation 14, and to a wind excitation 16. The movements of the ship 1 are reflected on 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 tank walls. When the sloshing exceeds the capacity of the tank walls to absorb or disperse the sloshing, the impacts on the tank walls 3, 4, 5, 6 can damage the tank walls 3, 4, 5, 6. However, it is important to maintain the integrity of the tank walls 3, 4, 5, 6 to maintain the sealing and 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.

[0110] A 1300 process, shown in the figure 7A , can be implemented to predict a probability of damage to the tanks of ship 1.

[0111] The method 1300 firstly comprises a step 1301 in which a geographical position of the ship 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 ship 1, for example in the form of GPS coordinates.

[0112] After step 1301, the method 1300 proceeds to a step 1302 in which meteorological and oceanographic forecasts are obtained relating to the geographical position obtained in step 1301. Such forecasts are for example transmitted by a communication means such as radio or satellite by a meteorological 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, this expected duration being able to be entered by a user.

[0113] For each time period, the forecasts include at least one swell state. They preferably further include a wind sea state or a current state or a wind state, more preferably several of these states, and even more preferably all of these states.

[0114] After step 1302, method 1300 further comprises the following steps: a step 1303A in which a swell direction (represented on the) is extracted from the forecasts obtained in step 1302, for each time period. figure 6 by the direction of axis 12) and a significant swell height, and a peak swell period; where appropriate, a step 1303B in which, from the forecasts obtained in step 1302, for each time period, a significant wind sea height and / or a peak wind sea period and / or a wind sea direction (represented on the figure 6 by the direction of axis 10); where appropriate, a step 1303C in which, from the forecasts obtained in step 1302, for each time period, a current speed and / or a current direction (represented on the figure 6 by the direction of axis 14); where appropriate, a step 1303D in which a wind speed and / or a wind direction (represented on the) are extracted from the forecasts obtained in step 1302, for each time period. figure 6 by the direction of axis 16).

[0115] The method 1300 then comprises 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 forecast filling level of at least one tank of the ship 1 is determined; a step 1306 in which a wave incidence angle is determined, i.e. an angle between the heading 190 of the ship 1 and the direction of the swell (represented on the figure 6 by the direction of axis 12); a step 1307 in which at least one probability of damage to the tank whose forecast filling level was determined in step 305 is estimated, as a function of: the wave incidence angle determined in step 1306; the significant wave height and the wave peak period extracted in step 1303A; and the at least one forecast filling level of the tank in question determined in step 1305.

[0116] When several tanks of the ship 1 are considered, 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 the ship 1, for example one or some of the tanks of the ship 1 which have been determined by a prior analysis to be most subject to a risk of damage due to sloshing.

[0117] Step 1307 may be performed by consulting a database previously established for the tank in question of the ship 1. Such a database includes data relating to sloshing as a function of an angle of incidence of the swell, a significant height of the swell, a period of peak swell and a current filling level of said tank, the data relating to 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, the significant height of the swell, the period of peak swell and the filling level of said tank.

[0118] 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 heading 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 the state of the current.

[0119] There figure 7B represents an example of such an implementation of step 1304, wherein: in a first step 1304-1, the forces experienced 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.

[0120] Steps 1304-1, 1304-2, 1304-3 are implemented for a plurality of theoretical headings, i.e. 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 1 degree. Then, in a step 1304-4, a heading 190 is selected from among said plurality of theoretical headings, which minimizes the absolute value of the moment determined in steps 1304-3.

[0121] After step 1307, the method 1300 proceeds to a step 1308 in which an indication is provided to a user based on the damage probabilities estimated in step 1307.

[0122] This step 1308 may 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 as an alternative, the indication provided in step 1308 may comprise providing the user with at least one visual indication of the damage probabilities estimated in step 1307, as a function of another quantity. This visual indication may be analogous to that described above in relation to the figure 5 .

[0123] Preferably, after step 1308, the method 1300 moves to a decision support step 1309 intended to reduce the probability(s) of damage estimated in step 1307. This decision support step 1309 may in particular comprise providing the user with: a proposal to change course 190, and / or a proposal to change the filling level of at least one of the tanks of the vessel 1.

[0124] Thanks to this step 1309, the user is able to take the necessary measures, based on these proposals, to reduce the risk of damage to the tanks.

[0125] 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 figure 4 .

[0126] In the above description, reference has been made to a peak swell period, i.e. a period of time between the passage of two successive swell peaks. Alternatively, instead of the peak swell period, the mean swell period can be considered, i.e. a period of time between three successive passages of the swell at the mean sea height.

[0127] Similarly, instead of the peak wind height period, we can consider the mean wind height period, that is, a period of time between three successive passages of the wind height at the mean sea height.

[0128] Furthermore, it is quite obvious that a characteristic or combination of characteristics described in connection with a method applies equally to a corresponding system, and vice versa.

[0129] The use of the verb "comprise", "comprise" or "include" and its conjugated forms does not exclude the presence of other elements or other steps than those set out in a claim.

[0130] In the claims, any reference sign in parentheses cannot be interpreted as a limitation of the claim.

Claims

1. A method (300) for estimation of a probability of damage caused by sloshing of a liquid load during an operation to transfer 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 one another during said transfer operation so that the first floating structure (1) and the second floating structure (40) are oriented with a common bearing (99), said method (300) including: - obtaining (301) a forecast geographical position of said transfer operation; - obtaining (302) meteorological and oceanographic forecasts relating to said geographical position for a plurality of periods of time, said periods of time together covering a forecast duration of said transfer operation, said forecasts including, for each period of time, a swell state, in which the state of the swell includes a direction of the swell, a significant height of the swell and a period of the swell; - for each period of time: obtaining (304) the common bearing (99) of the first and second floating structures (1, 40) ; determining (305) at least one forecast filling level of at least one tank of at least one of said first or second floating structures (1, 40) intended to contain all or part of said liquid load; determining (306) an angle of attack of the swell, which is an angle between said common bearing (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 attack of the swell determined in this way, of the significant height of the swell, of the period of the swell and of said at least one forecast filling level of said tank; and - supplying (308) information to a user as a function of said at least one probability of damage estimated in this way.

2. The method (300) as claimed in claim 1 wherein said at least one forecast filling level is determined (305) from a liquid load transfer scenario defining an evolution of the filling level of said tank as a function of time.

3. The method (300) as claimed in either one of claims 1 or 2 in which, for each period of time, two forecast filling levels of said tank are determined (305), the two forecast filling levels including a low forecast filling level and a high forecast filling level, and a probability of damage to said tank is estimated (307) for each of the two forecast filling levels.

4. The method (300) as claimed in any one of claims 1 to 3 in which said at least one probability of damage is estimated (307) by consultation of a database established beforehand for said tank, said database including data relating to sloshing as a function of an angle of attack of the swell, of a significant height of the swell, of the period of the swell and of a current filling level of said tank, the data relating to sloshing being determined by experiment, and the probability of damage being related to a density of probability of encountering a pressure on an internal surface of the tank above an internal strength of the tank as a function of the angle of attack of the swell, of the significant height of the swell, of the period of the swell and of the current filling level of said tank.

5. The method (300) as claimed in any one of claims 1 to 4 in which said information includes information representing the probability of damage estimated as a function of said periods of time.

6. The method (300) as claimed in any one of claims 1 to 5 in which said forecasts further include a wind sea state including a significant wind sea height and / or a wind sea period and / or a wind sea direction (10) and the probability of damage to said at least one tank is further estimated as a function of the wind sea state.

7. The method (300) as claimed in any one of claims 1 to 6 in which 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 bearing (99) of the two floating structures (1, 40) is obtained (304) by: - calculating (304-2, 304-3), for a plurality of theoretical bearings, a resultant of the forces to which the first and second floating structures are subjected as a function of the swell state and of a moment relative to the anchor point (90) of said resultant; - selecting (304-4) from said plurality of theoretical bearings a common bearing (99) that minimizes the absolute value of the moment relative to the anchor point of said resultant.

8. The method (300) as claimed in claim 6 and claim 7 in combination in which the resultant of the forces to which the first and second floating structures (1, 40) are subjected is further calculated (304-2) as a function of the wind sea state.

9. The method (300) as claimed in claim 7 or 8 in which said forecasts further include a wind state including a speed of the wind and / or a direction of the wind (16) and in which the resultant of the forces to which the first and second floating structures are subjected is further calculated as function of the wind state.

10. The method (300) as claimed in any one of claims 7 to 9 in which said forecasts further include a current state including a speed of the current and / or a direction (14) of the current and in which the resultant of the forces to which the first and second floating structures (1, 40) are subjected is further calculated as a function of the current state.

11. The method (300) as claimed in any one of claims 7 to 10 in which said information includes information representing the probability of damage estimated as a function of said plurality of theoretical bearings.

12. The method (300) as claimed in any one of claims 1 to 11 further including a step (309) of assisting the decision intended to reduce the estimated probability of damage.

13. The method (300) as claimed in claim 12 in which the step (309) of assisting the decision includes supplying to the user: - a proposal to change the common bearing (99), and / or - a proposal to modify at least one parameter of the transfer operation.

14. The method (300) as claimed in any one of claims 1 to 13 in which the liquid load is a liquefied gas load, in particular a liquefied petroleum gas load or a liquefied natural gas load.

15. The method (300) as claimed in claim 14 in which the liquid load is a liquefied natural gas load, the first floating structure is a liquefied natural gas carrier ship (1) and the second floating structure is a liquefied natural gas floating storage and regasification unit (40) or a liquefied natural gas floating production unit.

16. A device (100) for estimation of a probability of damage caused by sloshing of a liquid load during an operation to transfer 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 one another during said transfer operation so that the first floating structure and the second floating structure are oriented with a common bearing (99), the device (100) including a processor (110) configured to execute the method (300) as claimed in any one of claims 1 to 15.

17. A floating structure (1, 40) including a device (100) as claimed in claim 16.