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

Abstract

The invention relates to a method (300) for estimating a probability of damage caused by sloshing of a liquid load during a transfer operation of said liquid load from a first floating structure (1) to a second floating structure (40), said first floating structure (1) and said second floating structure (40) being related to each other during said transfer operation such that said first floating structure (1) and said second floating structure (40) are oriented in a common orientation (99). The method comprises a step (307) of estimating at least one probability of damage to said at least one tank and a step (308) of providing information to a user as a function of said estimated probability of at least one damage.

Description

[Technical field]

[0001] The present invention relates to an operation of transferring a liquid load between two floating structures. In particular, the present invention relates to a method and an apparatus for estimating the probability of damage caused by sloshing of a liquid load during an operation of moving said liquid load from a first floating structure to a second floating structure. [Background technology]

[0002] In the field of floating structures capable of carrying a liquid load, it is known to perform operations to transfer the liquid load from a first floating structure, such as a liquid carrier, to a second floating structure.

[0003] This type of liquid load transfer operation is commonly employed, especially for liquefied natural gas (LNG) loads. For such loads, in a known manner, an LNG carrier vessel, such as a methane tanker (also known as an LNG Carrier (LNGC)), can be moved closer to a floating storage and regasification unit (FSRU) for liquefied natural gas. The FSRU is, for example, located offshore and moored to a subsea buoy or moored to a turret mooring system that allows the structure to be free to orient itself according to forces applied to the structure (by waves, wind, currents, etc.). The LNGC is then moored to the FSRU, and flexible pipes are installed between the LNGC and the FSRU to transfer the LNG between the LNGC and the FSRU. This type of LNG transfer operation is known as ship-to-ship transfer (STS). This operation can also be performed between an LNGC and another floating structure, such as a floating liquefied natural gas production unit (FLNG).

[0004] However, during this type of operation, the tanks of LNGCs and of FSRUs intended to contain LNG are partially filled. In such situations, it is known that the LNG contained in the tanks is disturbed by the effects of high waves. The disturbance of the liquid, commonly known as sloshing, generates forces on the tank walls that have the potential to compromise the tank's integrity. Currently, the integrity of tanks intended to contain LNG is of particular importance, given the flammable or explosive nature of the liquids transported and the risk of cold spots on the steel hull of floating structures.

[0005] Additionally, operations involving large-capacity LNGCs, high-capacity FSRUs, or floating liquefied natural gas (FLNG) production units are likely to take tens of hours. Currently, the longer the operation takes, the greater the risk of climatic conditions occurring that are conducive to sloshing of LNG in the tanks.

[0006] In view of the above circumstances, methods and systems that help limit or eliminate the risk of tank damage caused by sloshing would be useful. Summary of the Invention

[0007] One idea behind the invention is to estimate the probability of damage to at least one tank of at least one of the floating structures involved in the transfer operation, utilizing meteorological and hydrographic forecasts related to the geographic location of the liquid load transfer operation, for the expected duration of said transfer operation. Another idea behind the invention is to provide the user with information as a function of the probability of damage thus estimated.

[0008] A first variation of the invention according to one embodiment provides a method of estimating a probability of damage caused by sloshing of a liquid load during a transfer operation of the liquid load from a first floating structure to a second floating structure, the first and second floating structures being associated with each other during the transfer operation such that the first and second floating structures are oriented in a common orientation, the method comprising the steps of obtaining a predicted geolocation of the transfer operation, obtaining meteorological and oceanographic forecasts for the geolocation for a number of time periods, the number of time periods together covering a predicted duration of the transfer operation, the forecasts including swell conditions for each period, the swell conditions including swell direction, significant wave height of the swell and swell period, and for each of the number of time periods The method includes the steps of obtaining the common orientation of the first floating structure and the second floating structure; determining a predicted filling level of at least one tank of at least one of the first floating structure and the second floating structure, which accommodates all or a portion of the liquid load; determining a swell angle of attack, which is the angle between the common orientation of the first floating structure and the second floating structure and the swell direction; estimating a probability of at least one damage to the at least one tank as a function of the determined angle of attack of the swell, the significant wave height of the swell, the swell period, and the at least one predicted filling level of the at least one tank of the tanks; and providing information to a user as a function of the estimated probability of at least one damage.

[0009] Thanks to this method, a user such as a crew member can take any measures necessary to limit the risk of damage to the tanks of the floating structures, such as, for example, changing the common orientation of the two floating structures and / or changing the parameters of the transfer operation, such as the liquid load transfer flow rate (between tanks of the same floating structure and / or between tanks of two floating structures) and / or the filling bells of the tanks.

[0010] Some embodiments of this type of method may have one or more of the following features.

[0011] According to one embodiment, the swell period is the peak period of the swell, i.e. the time period between two successive peak passes of the swell. According to one embodiment, the swell period is the mean period of the swell, i.e. the time period between three passes of the swell at the mean sea height, which period is generally equal to T z This is expressed as:

[0012] The predicted filling level of a tank can be estimated in different ways: According to one embodiment, at least one predicted filling level is determined from a liquid load transfer scenario defining the evolution over time of the filling level of said tank as a function of time.

[0013] Such liquid load transfer scenarios may be entered by the user specifically at the start of a transfer operation.

[0014] According to one embodiment, for each time period, two predicted filling levels of the tank are determined, comprising a low predicted filling level and a high predicted filling level, and for each of the two predicted filling levels, a probability of damage is estimated for the tank.

[0015] In this way, the estimate of the probability of damage can take into account that the sloshing of the liquid load varies with the tank's filling level.

[0016] According to one embodiment, the low and high predicted filling levels are pre-determined in a preliminary step which involves investigating, for example, by simulation and / or experiment, the two filling levels of the tank which have the highest probability of resulting in a risk of damage to the tank due to sloshing.

[0017] The probability of damage can be estimated in different ways. According to one embodiment, the probability of damage is estimated by referring to a database pre-built for the tank, said database comprising data on sloshing determined by experiment as a function of the angle of attack of the swell, the significant wave height of the swell, the period of the swell and the current filling level of the tank. The probability of damage is related to the probability density of encountering a pressure on the inner surface of the tank exceeding the internal strength of the tank as a function of the angle of attack of the swell, the significant wave height of the swell, the period of the swell and the current filling level of the tank.

[0018] According to one embodiment, the information comprises information representative of an estimated probability of damage as a function of the plurality of time periods, in particular according to one embodiment, the information comprises a visual indication of the estimated probability of damage as a function of the plurality of time periods.

[0019] According to one embodiment, during the transfer operation, the first floating structure and the second floating structure are moored to an anchor point.

[0020] According to one embodiment, the prediction further comprises wind wave conditions including significant wind wave height and / or wind wave period and / or wind wave direction.

[0021] According to one embodiment, the period of the wind waves is the peak period of the wind waves, i.e. the time period between two successive peak passes of the wind waves. According to one embodiment, the period of the wind waves is the mean period of the wind waves, i.e. the time period between three successive passes of the wind waves at the mean height of the sea, this mean period being generally equal to T z This is expressed as:

[0022] According to one embodiment, the probability of damage to the at least one tank is further estimated as a function of wind and wave conditions.

[0023] The common orientation of the first and second floating structures can be provided in advance, for example, by the user, in each of the plurality of time periods. Alternatively, according to one embodiment, the common orientation of the two floating structures is obtained by performing the steps of: calculating a resultant force acting on the first and second floating structures for a plurality of theoretical orientations, the resultant force being a function of the swell state and a moment of the resultant force with respect to the anchor point; and selecting, from the plurality of theoretical orientations, the common orientation that minimizes the absolute value of the moment of the resultant force with respect to the anchor point.

[0024] According to one embodiment, the resultant force acting on the first and second floating structures is further calculated depending on said wind and wave conditions.

[0025] According to one embodiment, the prediction further includes wind conditions including wind speed and / or wind direction, and the resultant of the forces acting on the first floating structure and the second floating structure is further calculated as a function of the wind conditions.

[0026] According to one embodiment, the prediction further includes ocean current conditions including the speed and / or direction of the ocean current, and the resultant of the forces acting on the first floating structure and the second floating structure is further calculated as a function of the ocean current conditions.

[0027] According to one embodiment, the information comprises information representative of an estimated probability of the damage as a function of the plurality of theoretical orientations.

[0028] According to one embodiment, the method further comprises a step of aiding the decision to reduce the estimated probability of damage.

[0029] According to one embodiment, the step of assisting a decision to reduce the estimated probability of damage includes providing the user with suggestions to change the common orientation and / or suggestions to change at least one parameter of the transport operation.

[0030] According to one embodiment, the proposal to change at least one parameter of the transfer operation comprises a proposal to change the liquid load transfer flow rate (between tanks of the same floating structure and / or between tanks of two floating structures) and / or the filling level of a tank.

[0031] Users can thus take the necessary measures based on these suggestions to reduce the risk of damage to the tank.

[0032] The method is applicable to floating structures transporting any type of liquid load, although it finds one particular application to floating structures transporting cryogenic liquid product loads.

[0033] According to one embodiment, said liquid load is a liquefied gas load, in particular a liquefied petroleum gas (LPG) load or a liquefied natural gas (LNG) load.

[0034] According to one embodiment, the at least one tank is a sealed tank and / or an insulated tank.

[0035] According to one embodiment, the first floating structure is a liquefied natural gas carrier (LNGC) 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).

[0036] According to one embodiment, the present invention further provides an apparatus for estimating the probability of damage caused by sloshing of a liquid load during a transfer operation of the liquid load from a first floating structure to a second floating structure, wherein the first floating structure and the second floating structure are associated with each other during the transfer operation such that the first floating structure and the second floating structure are oriented in a common orientation, and the apparatus comprises a processor configured to perform the method described in any one of the above embodiments.

[0037] This type of device has the same advantages as the method described above.

[0038] According to one embodiment, the present invention further provides a floating structure comprising the device described above.

[0039] The above principles are applicable to floating structures carrying a liquid load and moored to an anchor point, the liquid load of which is in fact subject to disturbances also by the effects of waves which may result in sloshing phenomena that may impair the integrity of the tanks containing the liquid load.

[0040] Thus, in a second variant of the invention according to one embodiment, a method is provided for estimating the probability of damage caused by sloshing of a liquid load on a floating structure, the floating structure being moored to an anchor point relative to the seabed whilst being free to rotate around the anchor point. The method comprises the steps of obtaining a geographical position of a floating structure moored to the anchor point; obtaining meteorological and oceanographic forecasts for said geographical position over a number of time periods, said forecasts including swell conditions for each time period, including swell direction, significant wave height of the swell and swell period; obtaining, for each of the number of time periods, an orientation of the floating structure, determining a predicted filling level of at least one tank of the floating structure intended to accommodate the liquid load, determining a swell angle of attack as the angle between the orientation and the swell direction, estimating a probability of damage to the at least one tank as a function of the swell angle of attack, significant wave height of the swell, swell period and predicted filling level of the tank thus determined; and providing information to a user which is a function of the probability of at least one damage thus estimated.

[0041] Thanks to this type of method, a user such as a crew member can carry out all the necessary measures to limit the risk of damage to the tanks of the floating structure, such as correcting the orientation of the floating structure, remembering that the floating structure is free to rotate around its anchor point.

[0042] Embodiments of this type of method have one or more of the following features.

[0043] According to one embodiment, the swell period is the peak period of the swell, i.e. the time period between two successive peak passes of the swell. According to one embodiment, the swell period is the mean period of the swell, i.e. the time period between three passes of the swell at the mean sea height, which period is generally equal to T z This is expressed as:

[0044] According to one embodiment, the probability of damage is estimated by referring to a database previously constructed for the tank, said database comprising data on sloshing determined by experiment as a function of the angle of attack of the swell, the significant wave height of the swell, the period of the swell and the current filling level of the tank, said probability of damage being related to the probability density of encountering a pressure on the inner surface of the tank exceeding the internal strength of the tank as a function of the angle of attack of the swell, the significant wave height of the swell, the period of the swell and the current filling level of the tank.

[0045] According to one embodiment, the information comprises information representative of an estimated probability of damage as a function of the plurality of time periods, in particular according to one embodiment, the information comprises a visual indication of the estimated probability of damage as a function of the plurality of time periods.

[0046] According to one embodiment, the prediction further comprises wind wave conditions including significant wind wave height and / or wind wave period and / or wind wave direction.

[0047] According to one embodiment, the period of the wind waves is the peak period of the wind waves, i.e. the time period between two successive peak passes of the wind waves. According to one embodiment, the period of the wind waves is the mean period of the wind waves, i.e. the time period between three successive passes of the wind waves at the mean height of the sea, this mean period being generally equal to T z This is expressed as:

[0048] According to one embodiment, the probability of damage to the at least one tank is further estimated as a function of wind and wave conditions.

[0049] The orientation of the floating structure can be provided in advance, for example, by the user, in each of the plurality of time periods. Alternatively, according to one embodiment, the orientation of the floating structure is obtained by performing the steps of: calculating a resultant force acting on the floating structure for a plurality of theoretical orientations, the resultant force being a function of the swell state and a moment of the resultant force with respect to the anchor point; and selecting, from the plurality of theoretical orientations, the orientation that minimizes the absolute value of the moment of the resultant force with respect to the anchor point.

[0050] According to one embodiment, the resultant force acting on the floating structure is further calculated depending on the wind and wave conditions.

[0051] According to one embodiment, the prediction further comprises wind conditions including wind speed and / or wind direction, and the resultant of the forces acting on the floating structure is further calculated as a function of the wind conditions.

[0052] According to one embodiment, the prediction further includes current conditions including the speed and / or direction of the current, and the resultant of the forces acting on the floating structure is further calculated as a function of the current conditions.

[0053] According to one embodiment, the resultant force experienced by the floating structure is further calculated as a function of the wind and wave conditions.

[0054] According to one embodiment, the prediction further comprises wind conditions including wind speed and / or wind direction, and the resultant of the forces acting on the floating structure is further calculated as a function of the wind conditions.

[0055] According to one embodiment, the prediction further includes current conditions including the speed and / or direction of the current, and the resultant of the forces acting on the floating structure is further calculated as a function of the current conditions.

[0056] According to one embodiment, the information comprises information representative of an estimated probability of the damage as a function of the plurality of theoretical orientations.

[0057] According to one embodiment, the method further comprises a step of aiding the decision to reduce the estimated probability of damage.

[0058] According to one embodiment, the step of assisting a decision to reduce the estimated probability of damage includes providing the user with suggestions to change the common orientation and / or suggestions to change at least one parameter of the transport operation.

[0059] Users can therefore take the necessary measures based on these suggestions to reduce the risk of damage to the tanks of the floating structure.

[0060] The method is applicable to floating structures transporting any type of liquid load, although it finds one particular application to floating structures transporting cryogenic liquid product loads.

[0061] According to one embodiment, said liquid load is a liquefied gas load, in particular a liquefied petroleum gas (LPG) load or a liquefied natural gas (LNG) load.

[0062] According to one embodiment, the at least one tank is a sealed tank and / or an insulated tank.

[0063] According to one embodiment, the floating structure is a liquefied natural gas carrier (LNGC), a liquefied natural gas floating storage and regasification unit (FSRU) or a liquefied natural gas floating production unit (FLNG).

[0064] According to one embodiment, the invention further provides an apparatus for estimating the probability of damage caused by sloshing of a liquid load of a floating structure moored to an anchor point relative to the seabed while freely rotating around said anchor point, said apparatus comprising a processor configured to perform the method described in any one of the above embodiments.

[0065] This type of device has the same advantages as the method described above.

[0066] According to one embodiment, the present invention further provides a floating structure comprising the device described above.

[0067] The present invention, as well as other objects, details, features and advantages thereof, will become more apparent in the following description of specific embodiments of the invention, taken in conjunction with the following non-limiting drawings and the accompanying figures, in which: [Brief description of the drawings]

[0068] [Figure 1] FIG. 1 is a longitudinal section through a floating structure, in this example a ship, including a number of tanks containing a liquid load. [Diagram 2] FIG. 1 shows two floating structures, in this example a ship and one floating structure, associated with each other in a liquid load transfer operation, and the wind wave conditions, swell conditions, ocean current conditions and wind conditions acting on the two floating structures. [Figure 3A] 13 is a flow chart showing a method for estimating the risk of damage due to sloshing of a liquid load during an operation of transferring the liquid load from a first floating structure to a second floating structure. [Figure 3B] FIG. 3B shows a detail of the flow chart of FIG. 3A illustrating one variation of the method. [Figure 4] FIG. 1 is a diagram of an apparatus for predicting sloshing of a liquid load during the operation of transferring the liquid load from a first floating structure to a second floating structure. [Diagram 5] FIG. 13 is a diagram illustrating an example of a visual display of the estimated probability of damage to a tank of a floating structure as a function of period. [Figure 6] This is a schematic diagram showing a floating structure that is moored to an anchor point on the seabed and can freely rotate around the anchor point, and the wind wave conditions, swell conditions, ocean current conditions, and wind conditions acting on the floating structure. [Figure 7A] 7 is a flowchart showing a method for estimating the risk of damage due to sloshing of a liquid load of the floating structure of FIG. 6. [Figure 7B] FIG. 7B shows a detail of the flow chart of FIG. 7A illustrating one variation of the method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0069] These figures are described below in the context of a ship 1 including a double hull forming a support structure in which a number of sealed insulated tanks are arranged. This type of support structure has, for example, a prismatic polyhedral shape.

[0070] The above-mentioned kind of sealed insulated tanks are designed for example for the transportation of liquefied gas, which is stored and transported at low temperatures, and therefore requires a highly insulating tank wall to maintain the temperature of the liquefied gas. Therefore, it is particularly important to keep the tank wall intact, on the one hand, in order to keep the tank tight and prevent the liquefied gas from leaking out of the tank, and on the other hand to prevent the deterioration of the tank's insulation, in order to keep the gas in a liquefied state.

[0071] A sealed and thermally insulating tank of the above kind is secured to the double hull of the ship and comprises an insulating barrier carrying at least one sealing membrane. By way of example, this kind of tank can be manufactured using technologies of the Mark III type, for example as described in patent application FR 2 691 520, of the NO 96 type, for example as described in patent application FR 2 877 638, or of other kinds, for example as described in WO 2014 / 057221.

[0072] Figure 1 shows a vessel 1 comprising four sealed, insulated tanks 2. In this type of vessel 1, the tanks 2 are interconnected by a cargo handling equipment (not shown) which may include a number of components, e.g. pumps, valves and pipes, allowing the transfer of liquid from one of the tanks 2 to another tank 2.

[0073] In Figure 2, the vessel 1 is shown in association with a stationary floating structure 40 for performing a ship-to-ship (STS) operation to transfer LNG contained in four tanks 2 of the vessel 1 to a sealed, thermally insulated tank (not shown) of the stationary floating structure 40. Here, the stationary floating structure 40 is a Liquefied Natural Gas Floating Storage and Regasification Unit (FSRU), but may equally be a Liquefied Natural Gas Floating Production Unit (FLNG), another LNG carrier similar to the vessel 1, or more generally a stationary or non-stationary floating structure including sealed and thermally insulated tanks for receiving LNG.

[0074] Here, the stationary floating structure 40 is located offshore and is moored to an anchor point 90 relative to the seabed, such as a submerged buoy or turret mooring system moored to the seabed. The vessel 1 is associated with the stationary floating structure 40 by means of a number of mooring lines 92, typically located at the bow and stern of the vessel 1 and to the stationary floating structure 40. A float 91 may be placed between the stationary floating structure 40 and the vessel 1 to prevent accidental collision between them. At least one flexible pipe 93 is provided for transferring the LNG contained in the four tanks 2 of the vessel 1 to the tanks of the stationary floating structure 40.

[0075] During the LNG transfer operation, the vessel 1 and the stationary floating structure are oriented in the same heading 99, hereinafter referred to as the common heading 99. Nevertheless, it is provided that the common heading 99 may be corrected during the transfer operation, which may last for several hours or even tens of hours.

[0076] The vessel 1 typically arrives in the vicinity of the stationary floating structure 40 with its four tanks 2 almost completely filled with LNG. However, as the LNG is transferred, the tanks 2 gradually empty. In FIG. 1, the four tanks 2 have partially filled states. The first tank 3 is filled to about 60% of its capacity. The second tank 4 is filled to about 35% of its capacity. The third tank 5 is filled to about 35% of its capacity. The fourth tank 6 is filled to about 40% of its capacity.

[0077] Such partial filling of tanks 3, 4, 5, 6 may pose a high risk of damage to tanks 3, 4, 5, 6 during LNG transfer operations. Indeed, when at sea, the vessel 1 is subject to weather conditions and undergoes numerous movements.

[0078] In particular, the vessel 1 is subjected to wind wave excitation represented by axis 10, swell excitation represented by axis 12, current excitation 14, and wind excitation 16. Wind waves are created by wind excitation 16 close to the vessel 1 and generate waves with a wind wave direction, a significant wave height, and a peak period of the wind waves parallel to axis 10. Swells are created by wind excitation far from the vessel 1 and generate waves with a swell direction, a significant wave height, and a peak period of the swell parallel to axis 12. The encounter of the swell excited waves with the wind excited waves causes the vessel 1 to move. The vessel 1 is also caused to move by a current with a direction and current speed parallel to axis 14. Finally, the vessel 1 is subjected to wind excitation by wind with a direction and current speed parallel to axis 16. These movements of the vessel 1 are transferred to the liquid contained in the tanks 3, 4, 5, 6, resulting in sloshing in the tanks 3, 4, 5, 6 and impacts on the tank walls. If the sloshing exceeds the tank walls' ability to absorb or disperse the impacts on the tank walls 3, 4, 5, 6, the impacts on the tank walls 3, 4, 5, 6 may deteriorate the tank walls 3, 4, 5, 6. It is then important to maintain the integrity of the tank walls 3, 4, 5, 6 so as to maintain their sealing and insulating properties. It is therefore important to estimate the probability of damage caused by sloshing in order to prevent such damage.

[0079] Obviously, the probability of damage for tank walls 3, 4, 5, 6 of a ship 1 is similar for tank walls of a stationary floating structure 40 which are also subjected to wind wave excitation 10, swell excitation 12 and ocean current excitation 14.

[0080] The method 300 shown in FIG. 3A may be used to predict the probability of damage to tanks of a vessel 1 and / or a stationary floating structure 40.

[0081] The method 300 comprises a first step 301 in which a predicted geolocation of the LNG transfer operation is obtained. This geolocation may be input by a user or may be obtained automatically by a system on-board the vessel 1 or the stationary floating structure 40, for example in the form of GPS coordinates.

[0082] After step 301, method 300 proceeds to step 302 where meteorological and hydrographic forecasts are obtained for the geographic location obtained in step 301. Such forecasts may be transmitted, for example, by a communication means such as radio or satellite, by a provider of meteorological and hydrographic forecasts. These forecasts are obtained for multiple time periods that together cover the expected time of the LNG transfer operation, which may be input by a user.

[0083] The predictions for each time period include at least one swell condition, and preferably these predictions further include wind wave conditions or current conditions or wind conditions, more preferably a plurality of these conditions, even more preferably all of these conditions.

[0084] After step 302, the method 300 further includes the following steps: a step 303A of extracting for each time period the swell direction (represented in FIG. 2 by the direction of axis 12), the significant wave height of the swell and the peak period of the swell from the prediction obtained in step 302; Optionally, a step 303B of extracting, for each time period, the wind wave direction (represented in FIG. 2 by the direction of axis 10), the wind wave significant height, and the wind wave peak period from the prediction obtained in step 302; a step 303C of extracting, optionally for each time period, the current speed and / or the current direction (represented in FIG. 2 by the direction of axis 14) from the prediction obtained in step 302; Optionally, for each time period, the wind speed and / or wind direction (represented in FIG. 2 by the direction of axis 16) is extracted from the prediction obtained in step 302, step 303D.

[0085] Thereafter, the method 300 further includes the following steps repeated for each time period: Step 304, in which a common orientation 99 of the vessel 1 and the stationary floating structure 40 is obtained; A step 305 in which a predicted filling level of at least one of the at least one tanks of the ship 1 and / or the stationary floating structure 40 is determined; Step 306, where the swell angle of attack is determined as the angle between the common heading 99 and the direction of the swell (represented in FIG. 2 by the direction of axis 12); Step 307 estimates a probability of at least one damage for a tank having at least one predicted filling level determined in step 305 as a function of the swell angle of attack determined in step 306, the swell significant wave height and the swell peak period determined in step 303A, and the at least one predicted filling level of the tank determined in step 305.

[0086] Step 305 can be performed in various ways. In one variant, the predicted filling level of at least one of the tanks is determined from a liquid load transfer scenario that defines the change over time of the filling level of said tank as a function of time. Such a liquid load transfer scenario may be determined in advance and entered by a user, for example, before the transfer operation.

[0087] A number of predicted filling levels of the tank can be determined in step 305 and for each predicted filling level determined in step 305 a damage probability of the tank can be determined in step 307. In one variant, two predicted filling levels of the tank are determined in step 305, comprising a low predicted filling level and a high predicted filling level. In one particular variant, the low predicted filling level and the high predicted filling level are pre-determined. Step 305 can then be read, for example, as simply having values ​​of the low predicted filling level and the high predicted filling level in a database in step 307, which will be described later. The values ​​of the low predicted filling level and the high predicted filling level can be pre-determined in a preliminary step (not shown) in which, for example, the two filling levels of the tank that have the highest probability of causing a risk of damage to the tank caused by sloshing are investigated by simulation and / or experiment.

[0088] If several tanks of the vessel 1 and / or the stationary floating structure 40 are considered, steps 305 and 307 are performed for each of these tanks. This selection may consider only a portion of the tanks of the vessel 1 and / or the stationary floating structure 40, for example only one or more tanks of the vessel 1 and / or the stationary floating structure 40 which are at the highest risk of tank damage caused by sloshing, as determined by means of a preliminary analysis.

[0089] Step 307 can be performed by referring to a pre-built database for the relevant tank of the ship 1 or stationary floating structure 40. Such a database contains data related to sloshing as a function of the swell angle of attack, the significant wave height of the swell, the peak period of the swell and the current filling level of the tank, the data related to sloshing being determined by experiment. The probability of damage is related to the probability density of encountering a pressure on the inner surface of the tank exceeding the internal strength of the tank as a function of the swell angle of attack, the significant wave height of the swell, the peak period of the swell and the filling level of the tank.

[0090] The common orientation 99 obtained in step 304 may be predefined. According to a variant, the common orientation 99 may be entered by a user for each time period or for all time periods to be considered. In an advantageous variant, this common orientation 99 is obtained taking into account the forces experienced by the vessel 1 and the floating structure 40 due to swell conditions, more preferably wind wave conditions and / or current conditions.

[0091] FIG. 3B depicts an illustration of such an implementation of step 304. In a first step 304-1, the forces experienced by the vessel 1 and the floating structure 40 due to swell conditions, more preferably due to wind wave conditions and / or current conditions and / or wind, are calculated. In a second step 304-2, the resultant of the forces determined in step 304-1 is calculated. In a third step 304-3, the moment of the resultant forces determined in step 304-2 is calculated about anchor point 90. Steps 304-1, 304-2, 304-3 are performed for a plurality of theoretical orientations, i.e., a plurality of possible values ​​of the common orientation 99. For example, steps 304-1, 304-2, 304-3 are performed in increments of 5 degrees, 2 degrees, or 1 degree for increments of the common orientation 99. Thereafter, in step 304-4, the orientation that minimizes the absolute value of the moment determined in step 304-3 is selected as the common orientation 99 from the plurality of theoretical orientations.

[0092] After step 307, method 300 proceeds to step 308, where information is provided to a user that is a function of the probability of damage estimated in step 307.

[0093] This step 308 may simply consist of providing a visual and / or audio alarm to the user if the probability of damage to one of the tanks exceeds a predefined threshold. Additionally or alternatively, the information provided in step 308 may include providing the user with at least one visual indication of the probability of damage estimated in step 307 as a function of some other amplitude.

[0094] FIG. 5 represents, by way of example, a visual indicator of the damage probabilities estimated in step 307 as a function of the time periods to which they relate. In this figure, this visual indicator comprises a box corresponding to each time period. No hatching indicates that the damage probability is zero or lower than a low threshold. Single hatching indicates that the damage probability is between the low and high thresholds. Double hatching indicates that the damage probability is higher than the high threshold. It is clear that instead of different hatchings, different colors according to a color code or any other representation may be adopted. Furthermore, different numbers of damage probability thresholds may be used.

[0095] After step 308, the method 300 preferably proceeds to a decision support step 309 intended to reduce the probability of damage estimated in step 307. This decision support step 309 may comprise in particular providing the user with the following: a proposal to change the common orientation 99, and / or a proposal to modify at least one parameter of the transfer operation, such as the liquid load transfer flow rate (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 vessel 1 and the tanks of the stationary floating structure 40), and / or the fill level of the tanks or tanks.

[0096] Thanks to this step 309, the user can carry out the necessary measures based on these suggestions in order to reduce the risk of damage to the tank.

[0097] 4 shows a sloshing determination device 100 that can be mounted on the vessel 1. The device 100 includes a central unit 110 configured to execute the various steps of the method 300 to estimate the probability of damage to a tank of the vessel 1 and / or the stationary floating structure 40.

[0098] The central unit 110 is connected to a number of on-board sensors 120, making it possible to obtain numerical values ​​of the various magnitudes mentioned above. The sensors 120 thus include, for example, but not inexhaustibly, a sensor 121 for the filling level of each tank, and other sensors 122, 123 capable of providing as magnitudes of their output the state of the swell, and preferably the state of wind waves and / or the state of the current and / or the state of the wind.

[0099] The apparatus 100 further comprises a human machine interface 140 comprising display means 41 enabling personnel on board the vessel 1 to obtain various information, for example the probability of damage estimated using the steps of the method 300, the information generated in step 308, the decision aid generated in step 309, the magnitude of the values ​​obtained by the sensors 120, and the loading state of the vessel or meteorological information.

[0100] The human machine interface 140 further comprises acquisition means 42 enabling an operator to manually input the values ​​of each magnitude into the central unit 110, typically because the vessel 1 is not equipped with the necessary sensors or the latter are damaged. For example, according to one embodiment, the acquisition means 42 allows an operator to input information regarding wind wave conditions and / or swell conditions.

[0101] The device 100 includes a database 150. This database 150 contains several magnitude values ​​obtained, for example, during measurement campaigns carried out in a laboratory or at sea. For example, for a given tank, the database 150 may contain data related to sloshing as a function of the swell angle of attack, the swell significant wave height, the swell peak period, and the current filling level of the tank.

[0102] The device 100 also includes a communication interface 130 that enables the central unit 110 to communicate with remote devices, for example to obtain data relating to meteorological forecasts and ship position or other data.

[0103] In particular, some elements in the central unit 110 can be produced in various forms by hardware and / or software components, in a unitary or distributed manner. Possible hardware components include application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), and microprocessors. Software components can be written in various programming languages, such as C, C++, C#, Java, and VHDL. This list is not exhaustive.

[0104] In the present description, it is defined with reference to the peak period of the swell, i.e. the time period between two successive peak passes of the swell. In a variant, instead of the peak period of the swell, the mean period of the swell is considered, i.e. the time period between three successive passes of the swell at the mean sea height.

[0105] Similarly, instead of the peak period of the wind waves, the mean period of the wind waves is considered, i.e. the time period between three successive passes of the wind waves at the mean sea height.

[0106] The above-mentioned principles are applicable to floating structures carrying liquid loads and moored to an anchor point. Indeed, the liquid loads of this type of floating structure are also susceptible to being disturbed by the effects of waves, which may result in the phenomenon of sloshing that may impair the integrity of the tanks that contain them.

[0107] Thus, in Figure 6 the vessel 1 according to Figure 1 is shown moored by one or more mooring lines 92 to an anchor point relative to the seabed, such as an undersea buoy moored to the seabed. The vessel 1 is free to rotate about the anchor point 90 and can therefore adopt any heading by rotating about the anchor point 90. The heading of the vessel 1 here is towards reference numeral 190.

[0108] As mentioned above with reference to figure 2, the vessel 1 is now also subjected to wind wave excitation represented by axis 10, swell excitation represented by axis 12, current excitation 14 and wind excitation 16. The motions of the vessel 1 are transferred to the liquid contained in the tanks 3, 4, 5, 6, which gradually cause sloshing in the tanks 3, 4, 5, 6, resulting in impacts on the tank walls. If the sloshing exceeds the capacity of the tank walls to absorb or disperse the impacts of the sloshing, the impacts on the walls of the tanks 3, 4, 5, 6 may damage the walls of the tanks 3, 4, 5, 6. It is then important to preserve the integrity of the walls of the tanks 3, 4, 5, 6 and to preserve the sealing and insulating properties of the tanks 3, 4, 5, 6. It is therefore also important to estimate the probability of damage caused by sloshing in order to prevent such damage.

[0109] The method 1300 shown in FIG. 7A may be employed to predict the probability that a tank of a vessel 1 will be damaged.

[0110] The method 1300 comprises a first step 1301 in which the geographical position of the vessel 1 moored at the anchor point 190 is obtained. This geographical position may be entered by a user or may be obtained automatically by a system on board the vessel 1, for example in the form of GPS coordinates.

[0111] After step 1301, method 1300 proceeds to step 1302 where meteorological and hydrographic forecasts are obtained for the geographic location obtained in step 1301. Such forecasts may be transmitted, for example, by a communication means such as radio or satellite, by a provider of meteorological and hydrographic forecasts. These forecasts are obtained for multiple time periods that together cover a forecasted period of the LNG transfer operation, which may be input by a user.

[0112] The predictions for each time period include at least one swell condition, which preferably further include wind wave conditions or current conditions or wind conditions, more preferably include a plurality of these conditions, and even more preferably include all these conditions.

[0113] After step 1302, the method 1300 further includes the following steps: Step 1303A of extracting, for each time period, from the predictions obtained in step 1302, the swell direction (represented by the direction of axis 12 in FIG. 6), the significant wave height of the swell, and the peak period of the swell; Optionally, a step 1303B of extracting for each time period from the predictions obtained in step 1302 the wind wave direction (represented by the direction of axis 10 in FIG. 6 ), the wind wave significant height and / or the wind wave peak period and / or the wind wave direction; Optionally, a step 1303C of extracting, for each time period, from the predictions obtained in step 1302, the current speed and / or the current direction (represented by the direction of axis 14 in FIG. 6 ); Optionally, step 1303C extracts, for each time period, the wind speed and / or wind direction (represented by the direction of axis 16 in FIG. 6) from the predictions obtained in step 1302.

[0114] The method 1300 then includes the following steps, which are repeated for each of the periods: A step 1304 of obtaining a heading 190 of the vessel 1; A step 1305 of determining at least one predicted filling level for at least one tank of the vessel 1; A step 1306 of determining the angle of attack of the swell, i.e. the angle between the heading 190 of the vessel 1 and the direction of the swell (represented by the direction of axis 12 in FIG. 6 ); Step 1307 estimates a probability of at least one damage for a tank having at least one predicted fill level extracted in step 1305 as a function of the swell angle of attack determined in step 1306, the swell significant wave height and the swell peak period extracted in step 1303A, and the at least one predicted fill level of the tank extracted in step 1305.

[0115] If multiple tanks of vessel 1 are being considered, steps 1305 and 1307 are performed for each of those tanks. This selection is similarly made when considering only a portion of the tanks of vessel 1, for example one or several tanks of vessel 1 that have been determined by a previously performed analysis to be most susceptible to risk of damage caused by sloshing.

[0116] Step 1307 may be performed by referring to a pre-built database for the relevant tank of the vessel 1. Such a database contains data relating to sloshing as a function of the swell angle of attack, the swell significant wave height, the swell peak period and the current filling level of the tank, the data relating to sloshing being determined by experiment. The probability of damage is related to the probability density of encountering a pressure on the inner surface of the tank exceeding the internal strength of the tank as a function of the swell angle of attack, the swell significant wave height, the swell peak period and the filling level of the tank.

[0117] The orientation 190 obtained in step 1304 may be predefined. In one variant, the orientation 190 may be input by a user and for all time periods considered. In a further variant, this orientation 190 of the vessel is obtained so as to take into account, for each time period, the forces experienced by the vessel 1 due to swell conditions, and preferably wind, wave and / or current conditions.

[0118] FIG. 7B illustrates an example of the execution of step 1304, as follows: In a first step 1304-1 the forces experienced by the vessel 1 due to swell conditions, preferably due to wind, wave and / or current and / or wind conditions, are calculated; In a second step 1304-2, the resultant force of the forces determined in step 1304-1 is calculated, In a third step 1304-3, a moment about anchor point 90 is calculated for the resultant force determined in step 1304-2. Steps 1304-1, 1304-2, 1304-3 are performed for a plurality of theoretical orientations, i.e., a plurality of possible values ​​of orientation 190. For example, steps 1304-1, 1304-2, 1304-3 are performed in increments of 5 degrees, 2 degrees, or 1 degree for increments of orientation 190. Then, in step 1304-4, the orientation that minimizes the absolute value of the moment determined in step 1304-3 is selected from the plurality of theoretical orientations as common orientation 190.

[0119] After step 1307, the method 1300 proceeds to step 1308, where information is provided to a user as a function of the probability of damage estimated in step 1307.

[0120] This step 1308 may consist only of providing a visual and / or audio alarm to the user if the probability of damage for one of the tanks exceeds a predetermined threshold. Additionally or alternatively, the information provided to the user in step 1308 may include at least one visual indication of the probability of damage estimated in step 1307 as a function of some other magnitude. This visual indication may be similar to that described above in connection with FIG. 5.

[0121] After step 1308, the method 1300 preferably proceeds to step 1309 of decision support intended to reduce the probability of damage estimated in step 1307. This decision support step 1309 may in particular comprise providing to the user: suggestions to change the heading 190 and / or suggestions to modify the filling level of at least one tank of the vessel 1.

[0122] Thanks to this step 1309, the user can carry out the necessary measures based on these suggestions in order to reduce the risk of damage to the tank.

[0123] The various steps of the method 1300 may be performed by the central unit 110 of the apparatus 100 already described with reference to FIG.

[0124] The above explanation is defined with reference to the peak period of the swell, i.e. the time period between two successive peak passes of the swell. In a variant, instead of the peak period of the swell, the mean period of the swell is considered, i.e. the time period between three successive passes of the swell at the mean sea height.

[0125] Similarly, instead of the peak period of the wind sea, one may consider the mean period of the wind waves, i.e. the period between three successive passes of the wind waves at the mean sea height.

[0126] As described above, the present invention has been described using specific embodiments. However, it is clear that the present invention is not limited to these embodiments, and it is clear that the scope of the present invention includes all technical equivalents of the described means and combinations thereof.

[0127] Furthermore, it will be apparent that a feature or combination of features described in connection with a method applies equally to the corresponding system, and vice versa.

[0128] Use of the terms "comprise" or "include" and their conjugations does not exclude the presence of other elements or steps in addition to those stated in a claim.

[0129] In the claims, any reference signs placed between parentheses shall not be construed as construing as limiting the claim.

Claims

1. A method (300) for estimating a probability of damage caused by sloshing of a liquid load during a transfer operation of said liquid load from a first floating structure (1) to a second floating structure (40), said first floating structure (1) and said second floating structure (40) being associated with each other during said transfer operation such that said first floating structure (1) and said second floating structure (40) are oriented in a common orientation (99), said method (300) comprising: Obtaining a predicted geolocation of the transport operation (301); obtaining (302) meteorological and oceanographic forecasts for the geolocation for a plurality of time periods, the plurality of time periods together covering a forecast duration of the transfer operation, the forecasts including swell conditions for each period, the swell conditions including swell direction, significant wave height, and swell period; Each of the plurality of time periods includes: Obtaining (304) the common orientation (99) of the first floating structure (1) and the second floating structure (40); Determining (305) a predicted filling level of at least one tank of at least one of said first floating structure (1) and said second floating structure (40) that contains all or a part of said liquid load; Determining (306) an angle of attack of a swell, the angle being an angle between the common orientation (99) of the first floating structure (1) and the second floating structure (40) and the direction (12) of the swell; and estimating (307) a probability of at least one damage to the at least one tank as a function of the determined angle of attack of the swell, the significant wave height of the swell, the period of the swell, and the at least one predicted filling level of the at least one tank of the tanks, providing (308) information to a user as a function of the estimated probability of the at least one damage; 1. A method (300), comprising:

2. 2. The method (300) of claim 1, characterized in that the at least one predicted filling level is determined (305) from a liquid load transfer scenario defining a progression of the filling level of the tank as a function of time.

3. Each of the plurality of time periods includes: determining (305) two predicted filling levels, including a low predicted filling level and a high predicted filling level; A method (300) according to claim 1 or 2, characterized in that it comprises a step (307) of estimating the probability of damage to the tank for each of the two predicted filling levels.

4. The probability of the at least one damage is estimated (307) by referring to a pre-established database for the tank; the database having data regarding sloshing determined by experiment as a function of the angle of attack of the swell, the significant wave height of the swell, the period of the swell, and the current filling level of the tank; 3. The method (300) according to claim 1 or 2, characterized in that the probability of damage is related to the probability density of encountering a pressure on the inner surface of the tank that exceeds the internal strength of the tank as a function of the angle of attack of the swell, the significant wave height of the swell, the period of the swell and the current filling level of the tank.

5. The method (300) of claim 1 or claim 2, characterized in that the information comprises information representative of the probability of the damage estimated as a function of the plurality of time periods.

6. The prediction further includes wind wave conditions including significant wind wave height and / or wind wave period and / or wind wave direction (10); 3. The method (300) of claim 1 or 2, characterized in that the probability of damage to the at least one tank is further estimated as a function of the wind and wave conditions.

7. During the transfer operation, the first floating structure (1) and the second floating structure (40) are moored to an anchor point (90); For each of the plurality of time periods, the common orientation (99) of the first floating structure (1) and the second floating structure (40) is Calculating a resultant force acting on the first floating structure (1) and the second floating structure (40) for a plurality of theoretical orientations, the resultant force being a function of the swell condition and a moment of the resultant force relative to the anchor point (90); selecting (304-4) the common orientation (99) that minimizes the absolute value of the moment of the resultant force relative to the anchor point (90) from the plurality of theoretical orientations; The method (300) according to claim 1 or 2, characterized in that it comprises the step (304) of obtaining by performing:

8. The prediction further includes wind wave conditions including significant wind wave height and / or wind wave period and / or wind wave direction (10); The probability of damage to the at least one tank is further estimated as a function of the wind and wave conditions; The method (300) of claim 7, characterized in that the resultant of the forces acting on the first floating structure (1) and the second floating structure (40) is further calculated (304-2) as a function of the wind and wave conditions.

9. the prediction further includes wind conditions including a speed of the wind (16) and / or a direction of the wind (16); 8. The method (300) of claim 7, characterized in that the resultant of the forces acting on the first floating structure (1) and the second floating structure (40) is further calculated as a function of the wind conditions.

10. the prediction further includes current conditions including a speed of the current and / or a direction of the current (14); 8. The method (300) of claim 7, characterized in that the resultant of the forces acting on the first floating structure (1) and the second floating structure (40) is further calculated as a function of the ocean current conditions.

11. The method (300) of claim 7, wherein the information comprises information representative of an estimated probability of the damage as a function of the plurality of theoretical orientations.

12. The method (300) of claim 1 or claim 2, further comprising the step of assisting (309) in making a decision to reduce the estimated probability of damage.

13. The method (300) according to claim 12, characterized in that the step (309) of assisting in a decision to reduce the estimated probability of damage comprises providing the user with suggestions to modify the common orientation (99) and / or suggestions to modify at least one parameter of the transfer operation.

14. 3. The method (300) according to claim 1 or 2, characterized in that the liquid load is a liquefied gas load, in particular a liquefied petroleum gas load or a liquefied natural gas load.

15. the liquid load is the liquefied natural gas load; The first floating structure (1) is a liquefied natural gas carrier, 15. The method (300) of claim 14, characterized in that the second floating structure (40) is a LNG floating storage and regasification unit or a LNG floating production unit.

16. An apparatus (100) for estimating the probability of damage caused by sloshing of a liquid load during a transfer operation of the liquid load from a first floating structure (1) to a second floating structure (40), wherein the first floating structure (1) and the second floating structure (40) are associated with each other during the transfer operation such that the first floating structure (1) and the second floating structure (40) are oriented in a common orientation (99), and the apparatus (100) comprises a processor (110) configured to perform the method (300) described in claim 1 or claim 2.

17. A floating structure (1, 40) comprising the device (100) according to claim 16.

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