EP3966101B1 - Method and device for determining sloshing - Google Patents

Description

Technical area

The invention relates to the field of methods and device for determining the sloshing, in particular for determining the sloshing of the liquid loading of ships.

Technology background

During its storage and/or its transport, the liquid contained in a tank is subjected to various movements. In particular, the movements at sea of a ship comprising the tank, for example under the effect of climatic conditions such as the state of the sea or the wind, cause agitation of the liquid in the tank. The agitation of the liquid, generally referred to as "sloshing" or sloshing, generates 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 an LNG tank due to the flammable or explosive nature of the transported liquid and the risk of a cold spot on the steel hull of the floating unit.

We know a method described by US8643509 to determine a risk of damage to the tank caused by the sloshing of the liquid and to alert a ship's operator when the risk of damage exceeds a predetermined threshold. The method determines the risk of damage caused by sloshing according to the sea states to which the ship is subjected, which are determined from the climatic and oceanic conditions, and from a numerical model of the ship.

Summary

The present inventors have observed that precise consideration of the sea states is complex to implement in a numerical model given the large number of possible sea states, in particular the existence of multimodal sea conditions in certain circumstances.

An idea underlying the claimed invention is to determine the sloshing of the liquid contained in the vessel by a method that is relatively economical in terms of calculation time and calculation resources. For this, another idea underlying this invention is to provide a less complex method for determining sloshing by determining a sea state in order to reduce the calculation time without reducing the reliability of sloshing determination.

• une étape de détermination d'une excitation monomodale en fonction d'un état de la houle et d'un état de mer du vent auxquels est soumis ledit navire,
• une étape de détermination d'une donnée relative au ballotement dudit chargement en fonction de l'excitation monomodale.

According to one embodiment, the invention provides a method for determining the sloshing of a liquid cargo from a ship, said method comprising:

• a step of determining a monomodal excitation as a function of a state of the swell and a sea state of the wind to which said ship is subjected,
• a step of determining data relating to the sloshing of said load as a function of the monomodal excitation.

The method is advantageous in that it determines a monomodal excitation equivalent to a multimodal excitation comprising the swell state and the sea state of the wind. The sloshing is thus determined for an equivalent monomodal excitation and not from the multimodal excitation, which would be much more complex to model by calculation or by experience. The method is thus less greedy in computational resources and requires less computation time compared to the state of the art.

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

The step of determining the sloshing can be carried out in different ways. According to one embodiment, the datum relating to the sloshing is determined as a function of the monomodal excitation by consulting a previously established database comprising data representing the sloshing as a function of the monomodal excitation. The database can include sloshing levels obtained experimentally in the laboratory or during on-board measurement campaigns at sea as a function of monomodal excitation. According to another embodiment, the datum relating to the sloshing is determined by a previously established numerical modeling expressing the sloshing as a function of the monomodal excitation.

The state of the swell and/or the sea state of the wind define environmental data of the ship. According to one embodiment, the state of the swell comprises a significant height of the swell and/or a peak period of the swell and/or a direction of the swell with respect to a longitudinal axis of the vessel. According to one embodiment, the wind sea state comprises a significant wind sea height and/or a wind sea peak period and/or a wind sea direction with respect to a longitudinal axis.

According to one embodiment, the state of the swell and/or the sea state of the wind are determined in real time by sensors provided in the ship and configured to measure a significant height of the swell and/or a period of swell peak and/or swell direction and significant wind sea height and/or wind sea peak period and/or wind sea direction.

According to one embodiment, the state of the swell and/or the sea state of the wind are determined indirectly from the meteorological and oceanic conditions.

According to one embodiment, the state of the swell and/or the sea state of the wind are determined by weather prediction.

Monomodal excitation can be determined in different ways. According to one embodiment, the swell state includes a significant swell height and the wind sea state includes a significant wind sea height, and the single-mode excitation has a total significant height equal to a root mean square said significant swell height and said significant wind sea height.

• une première consultation de base de données, par exemple données acquises par l'expérimentation, pour déterminer un premier ballotement engendré par la période de pic de la houle ,
• une deuxième consultation de base de données pour déterminer un deuxième ballotement engendré par la période de pic de mer de vent, et
• une détermination du ballotement le plus sévère parmi le premier ballotement et le deuxième ballotement.

In one embodiment, the swell state includes a swell peak period and the wind sea state includes a wind sea peak period, and the single-mode excitation has an equal total peak period to one of the peak swell period and the peak sea wind period selected as the period causing the most severe load sloshing. In this case, the method may comprise a step for selecting the total peak period from among the swell peak period and the wind sea peak period by:

• a first database consultation, for example data acquired by experimentation, to determine a first sloshing generated by the peak period of the swell,
• a second database consultation to determine a second sloshing generated by the peak sea wind period, and
• a determination of the most severe sloshing among the first sloshing and the second sloshing.

According to one embodiment, the swell state includes a swell direction and the wind sea state includes a wind sea direction, and the single-mode excitation has a total direction equivalent to one of the direction of the swell and the sea direction of the wind closest to a direction perpendicular to the longitudinal axis of the ship.

According to one embodiment, the method comprises a step of determining a probability of damage to a tank of the ship comprising all or part of the load as a function of the data relating to the sloshing and of a filling level of said tank. In particular, the probability of damage is 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 datum relating to the sloshing and the filling level of the tank. .

In particular, the filling level of the tank can be determined by filling level sensors arranged in said tank.

According to one embodiment, the method comprises a step of emitting an audible or visual signal for an operator of the ship when the datum relating to the sloshing is greater than a predetermined threshold.

• la hauteur significative de la houle et de la hauteur significative de mer du vent sont non nulles, et
• une différence entre la direction de la houle et de la direction de mer du vent est supérieure à 15°, et
• la hauteur significative de la houle et la hauteur significative de mer du vent sont inférieures à 85% d'une moyenne quadratique de la hauteur significative de la houle et de la hauteur significative de mer du vent.

According to one embodiment, the method further comprises a step consisting in detecting that the ship is subjected to a significantly multimodal excitation. In this case, a significantly multimodal excitation is detected when:

• the significant wave height and the significant wind sea height are non-zero, and
• a difference between the direction of the swell and the direction of the sea wind is greater than 15°, and
• the significant wave height and the significant wind sea height are less than 85% of a quadratic mean of the significant wave height and the significant wind sea height.

According to this embodiment, the method comprises following the detection that the ship is subjected to a significantly multimodal excitation, a step of determining a datum relating to the sloshing according to the sea state of the wind and the state of significantly multimodal arousal swell. The method may further comprise, in response to the detection that the ship is not subjected to a significantly multimodal excitation, a step of determining the datum relating to the sloshing of the load as a function of a recombined monomodal excitation corresponding to the swell state and wind sea state. In this case, the recombined single-mode excitation is provided by meteorological or oceanic services.

According to one embodiment, the liquid is a liquefied gas, for example liquefied natural gas.

According to another aspect of the invention, there is proposed a device for determining the sloshing of a liquid load of a ship, said device comprising a processor configured to implement the aforementioned method.

Such a device or method for determining sloshing can be installed in a floating, coastal or deep-water structure, in particular an LNG carrier, a floating storage and regasification unit (FSRU), a floating production and remote storage unit ( FPSO), a barge and others. In addition, such a device or method for determining the sloshing can be implemented for the dimensioning of the floating structure, in particular the dimensioning of a tank of a ship or of said ship according to the data relating to the sloshing of the load determined by a such device or process. Such a device or method for determining sloshing can also be implemented to determine navigation instructions, for example a speed of the ship, a direction, to be executed automatically or by a driver of the ship, in order to reduce or avoid a level of sloshing of the ship.

According to another aspect of the invention, a ship is proposed, for example for the transport of a cold liquid product such as liquefied natural gas, comprising at at least one tank comprising a load and the device for determining the aforementioned sloshing.

Brief description of figures

• [Fig.1] la figure 1 est une représentation schématique en coupe longitudinale d'un navire comportant une pluralité de cuves comprenant un chargement liquide.
• [Fig.2] la figure 2 est une représentation schématique d'un état de mer du vent et d'un état de houle auxquels peut être soumis le navire de la figure 1.
• [Fig.3] la figure 3 est une représentation schématique d'un procédé de détermination du ballotement du navire de la figure 1.
• [Fig.4] la figure 4 est une représentation schématique d'un dispositif de détermination du ballotement du navire de la figure 1.

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

• [ Fig.1 ] the figure 1 is a schematic representation in longitudinal section of a ship comprising a plurality of tanks comprising a liquid load.
• [ Fig.2 ] the picture 2 is a schematic representation of a sea state of the wind and of a swell state to which the ship of the figure 1 .
• [ Fig.3 ] the picture 3 is a schematic representation of a method for determining the ship's sloshing from the figure 1 .
• [ Fig.4 ] the figure 4 is a schematic representation of a device for determining the sloshing of the ship of the figure 1 .

Description of embodiments

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

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

Such watertight and thermally insulating tanks also comprise an insulating barrier anchored to the double ship hull and carrying at least one watertight membrane. By way of example, such tanks can be made according to Mark III ^® type technologies, as described for example in FR2691520 , of the NO96 ^® type as described for example in FR2877638 , or other as described for example in WO14057221 .

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

The four tanks 2 present on the figure 1 an initial filling state. In this initial state, the tanks are partially filled. A first tank 3 is filled to about 60% of its capacity. A second tank 4 is filled to about 35% of its capacity. A third tank 5 is filled to about 35% of its capacity. A fourth tank 6 is filled to approximately 40% of its capacity.

This partial filling of the tanks 3, 4, 5, 6 can lead to significant risks of damage to said tanks 3, 4, 5, 6 when the ship 1 is sailing at sea. Indeed, when it is at sea, the ship 1 is subject to many movements related to navigation conditions.

In particular, the ship 1 is subject on the one hand to a first sea excitation of the wind represented by the axis 10 and to a second excitation of the swell represented by the axis 12 on the Fig.2 . The wind sea induces waves having a wind sea direction parallel to the axis 10 with respect to a longitudinal axis 16 of the ship 1, a significant wind sea height and a peak wind sea period. Similarly, the swell causes waves having a swell direction parallel to the axis 12 with respect to the longitudinal axis 16, a significant swell height and a peak swell period. The meeting of the waves induced by the swell and the sea of the wind generates a multimodal excitation of the ship 1 causing the movements of the ship 1. 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 walls of the tanks. When the sloshing exceeds the capacity of the vessel walls to absorb or disperse the sloshing, the impacts on the vessel walls 3, 4, 5, 6 can degrade the vessel walls 3, 4, 5, 6. However, it is important to preserve the integrity of the walls of the tanks 3, 4, 5, 6 to preserve the tightness and the insulation characteristics of the tanks 3, 4, 5, 6. It is therefore important to determine the sloshing in order to avoid such damage.

For this, a method 200, represented on the Fig.3 , for determining the sloshing can be implemented by the ship 1 to estimate a monomodal excitation represented by the axis 14 on the Fig.2 equivalent to the total excitation of the ship 1 caused by the meeting of the sea excitation of the wind 10 and the excitation of the swell 12.

• étape 202 : acquisition d'un état de mer du vent comprenant la hauteur significative de mer du vent Hs_windsea, la période de pic de mer du vent Tp_windsea et la direction de mer du vent Hg_windsea par rapport à l'axe longitudinal 16,
• étape 204 : acquisition d'un état de la houle comprenant la hauteur significative de la houle Hs_swell, la période de pic de la houle Tp_swell et la direction de la houle Hg_swell par rapport à l'axe longitudinal 16,
• étape 206 : détermination de l'excitation monomodale par détermination d'une hauteur totale Hs_tot, la période de pic totale Tp_tot et la direction totale Hg_tot' en fonction de l'état de mer du vent et de l'état de la houle,
• étape 208 : détermination d'une donnée relative au ballotement du liquide compris dans le navire 1 en fonction de l'excitation monomodale déterminée à l'étape 206.

Method 200 includes the following steps:

• step 202: acquisition of a wind sea state comprising the significant wind sea height Hs _windsea , the wind sea peak period Tp _windsea and the wind sea direction Hg _windsea with respect to the longitudinal axis 16 ,
• step 204: acquisition of a state of the swell comprising the significant height of the swell Hs _swell, the peak period of the swell Tp _swell and the direction of the swell Hg _swell with respect to the longitudinal axis 16,
• step 206: determination of the monomodal excitation by determining a total height Hs _tot , the total peak period Tp _tot and the total direction Hg _tot' as a function of the sea state of the wind and the state of the swell,
• step 208: determination of a datum relating to the sloshing of the liquid included in the vessel 1 as a function of the monomodal excitation determined in step 206.

According to one embodiment, steps 202 and 204 are performed by acquiring measurements relating to the sea state, wind and swell state by sensors deployed in the ship 1. Alternatively, steps 202 and 204 are carried out by acquiring predictions of the state of the swell and the sea state of the wind previously determined.

According to one embodiment, the total height Hs _tot is determined in step 206 by solving the following equation:
$${\mathit{hs}}_{\mathit{early}}=\sqrt{{{\mathit{hs}}_{\mathit{windsea}}}^2+{{\mathit{hs}}_{\mathit{swell}}}^2}$$

According to one embodiment, the total peak period Tp _tot is determined in step 206 by determining the peak period from among those of the swell Tp _swell and of the wind sea Tp _windsea causing the most severe load sloshing in monomodal excitation, for example by consulting a database or by numerical calculation.

According to one embodiment, the total direction Hg _tot is determined in step 206 by determining the direction among the direction of the swell Hg _swell and the sea direction of the wind Hg _windsea closest to a direction perpendicular 18 to the longitudinal axis 16 of the ship 1. In a case where these two directions are symmetrical with respect to the perpendicular direction 18, the excitation which comes from the front of the ship is retained.

Step 208 can be carried out by consulting a database previously established for the ship 1 or by digital calculation from a previously established digital model expressing the sloshing as a function of the monomodal excitation 14.

avec SC étant un niveau de ballotement engendré par la donnée relative au ballotement pour le niveau de remplissage fl de la cuve,

• Prob_tk représente la densité de probabilité de rencontrer une pression Pres_surf sur une surface interne de la cuve supérieure à la résistance Res_surf de ladite surface interne de la cuve en fonction du niveau de ballotement SC(f l),
• surf est la surface interne de la cuve impactée par le liquide, et t_ope est la durée d'opération de navigation du navire 1 soumis à l'état de mer du vent et la houle engendrant le niveau de ballotement SC(f l) pour le niveau de remplissage fl.

According to one embodiment, the method 200 comprises a step 210 of determining a risk of damaging Risk _ope a tank 2 as a function of the data relating to the sloshing determined in step 208 and the filling level of said tank 2. In particular, the risk of damage Risk _ope is determined by the equation next :
$${\mathit{Risk}}_{\mathit{open}}={\displaystyle \underset{0}{\overset{{\mathit{surf}}^{\mathrm{you}}}{\int }}{\displaystyle \underset{0}{\overset{\mathit{open}}{\int }}{\mathit{problem}}_{\mathit{tk}}\left({\mathit{Close}}_{\mathit{surf}}>{\mathit{Res}}_{\mathit{surf}},\mathit{CS}\left(\mathit{fl}\right)\right).\mathit{dt}.\mathit{dsurf}}}$$

with SC being a level of sloshing generated by the datum relating to sloshing for the filling level fl of the tank,

• Prob _tk represents the density of probability of encountering a pressure Pres _surf on an internal surface of the tank greater than the resistance Res _surf of said internal surface of the tank as a function of the level of sloshing SC(fl),
• surf is the internal surface of the tank impacted by the liquid, and to _ope is the duration of navigation operation of the ship 1 subjected to the sea state of the wind and the swell generating the level of sloshing SC(fl) for the fill level fl.

The law prob _tk is a statistical law for example of the GEV, Weibull, Pareto, Gumbel type. One, several or all of the parameters of this law are for example defined from monomodal tests of liquid movement in the laboratory or monomodal measurement campaigns at sea.

The figure 4 illustrates a device 300 for determining the sloshing that can be embarked on the ship 1. This device 300 comprises a central unit 302 configured to carry out the different steps of the method 200 to determine the data relating to the sloshing of the ship and/or the risk of damage of a tank 2 of the ship 1.

The central unit 302 is connected to a plurality of on-board sensors 304 making it possible to obtain the various quantities indicated above. Thus, the sensors 304 comprise, for example and in a non-exhaustive manner, a filling level sensor 306 of each tank, various sensors 308 (accelerometer, strain gauge, strain gauge, sound, light) allowing the central unit 302 via a dedicated algorithm to detect the impacts linked to the movements of the liquid in the tanks 3, 4, 5, 6, etc.

The device 300 further comprises a man-machine interface 310. This man-machine interface 310 comprises a display means 312 allowing an operator of the ship 1 to obtain the various information, for example information on the data relating to the sloshing determined by implementing the steps of the method 200, the risk of damage to one of the tanks 2 of the ship 1, the quantities obtained by the sensors 308 such as the intensity of the movements of liquid in the tanks, information on the impacts linked to these movements of liquid, the movements of the ship, the state of loading of the ship or even meteorological information.

The man-machine interface 310 further comprises an acquisition means 314 enabling the operator to manually supply quantities to the central unit 302, typically to supply the central unit 302 with data which cannot be obtained by sensors because the vessel does not have the required sensor or the sensor is damaged. For example, in one embodiment, the acquisition means allows the operator to enter information on the sea state of the wind and/or the state of the swell.

The device 300 comprises a database 316. This database 316 comprises, for example, certain quantities obtained in the laboratory or during measurement campaigns on board at sea. For example, the database 316 can comprise data relating to sloshing according to monomodal excitation. In particular, the database can store data representative of the global or local stresses exerted on the vessel wall, for each value of amplitude, frequency and incidence of the monomodal excitation. These data representative of the stresses exerted on the vessel wall may for example be a distribution of the pressure exerted on the vessel wall, namely the function P _surf .

In one embodiment, the calculations of the risk of damage are also pre-established and the database can directly store data representative of the risk of damage Risk _ope for each value of the significant height, peak period and direction of monomodal excitation.

The device 300 also comprises a communication interface 318 enabling the central unit 302 to communicate with remote devices, for example to obtain meteorological data, ship position data or other.

According to one embodiment, the central unit 302 is configured to determine a navigation datum, for example a course of the ship, a speed, etc., as a function of the datum relating to the sloshing and/or the risk of damage.

Certain elements represented, in particular the central unit 302, can be produced in different forms, in a unitary or distributed manner, by means of hardware and/or software components. Material components that can be used are specific integrated circuits ASIC, programmable logic networks FPGA or microprocessors. Software components can be written in different programming languages, for example C, C++, Java or VHDL. This list is not exhaustive

Although the invention has been described in connection with several particular embodiments, it is quite obvious that it is in no way limited thereto.

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

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

Claims (11)

1. A method (200) for determining the sloshing of a liquid loading of a vessel (1), implemented by a device (300) for determining the sloshing of a liquid loading of a vessel, said method (200) comprising:

   a step (206) of determination of a monomodal excitation as a function of a multimode excitation to which said vessel is subjected, the multimodal excitation comprising a state of the swell and a wind sea state, wherein the state of the swell comprises a direction of the swell and the wind sea state comprises a wind sea direction, and wherein the monomodal excitation exhibits a total direction equivalent to one out of the direction of the swell and the wind sea direction closest to a direction at right angles to the longitudinal axis of the vessel,

   a step (208) of determination of a datum relating to the sloshing of said loading as a function of the monomodal excitation, wherein the datum relating to the sloshing is determined as a function of the monomodal excitation through consultation of a previously established database, said database comprising data relating to the sloshing expressing the sloshing as a function of the monomodal excitation, wherein the data relating to the sloshing are determined by experimental measurements, and a step (210) of determination of a probability of damage to a tank (2) of the vessel (1) comprising all or a part of the loading as a function of the datum relating to the sloshing and of a level of filing of said tank,

   wherein the probability of damage is relative to a density of probability of encountering a pressure on an internal surface of the tank greater than an internal resistance of the tank as a function of the datum relating to the sloshing and of the level of filling of the tank.
2. The method (200) as claimed in claim 1, wherein the state of the swell comprises a significant height of the swell and/or a peak period of the swell and/or a direction of the swell with respect to a longitudinal axis of the vessel.
3. The method (200) as claimed in either one of claims 1 and 2, wherein the wind sea state comprises a significant wind sea height and/or a peak wind sea period and/or a wind sea direction with respect to a longitudinal axis.
4. The method (200) as claimed in any one of claims 1 to 3, wherein the state of the swell comprises a significant height of the swell and the wind sea state comprises a significant wind sea height, and
   wherein the monomodal excitation exhibits a total significant height equal to a root mean square of said significant height of the swell and of said significant wind sea height.
5. The method as claimed in any one of claims 1 to 4, wherein the state of the swell comprises a peak period of the swell and the wind sea state comprises a peak wind sea period, and
   wherein the monomodal excitation exhibits a total peak period equal to one out of the peak period of the swell and the peak wind sea period selected as the period generating the most severe sloshing of the loading.
6. The method as claimed in claim 5, comprising a step for selecting the total peak period out of the peak period of the swell and the peak wind sea period by:

   a first database consultation to determine a first sloshing generated by the peak period of the swell,

   a second database consultation to determine a second sloshing generated by the peak wind sea period, and

   a determination of the most severe sloshing out of the first sloshing and the second sloshing.
7. The method as claimed in any one of claims 1 to 6, further comprising a step consisting in detecting that the vessel is subjected to a significantly multimodal excitation.
8. The method as claimed in claim 7, wherein a significantly multimodal excitation is detected when:

   the significant height of the swell and of the significant wind sea height are non-zero, and

   the difference between the direction of the swell and of the wind sea direction is greater than 15°, and

   the significant height of the swell and the significant wind sea height are less than 85% of a root mean square of the significant height of the swell and of the significant wind sea height.
9. The method as claimed in any one of claims 1 to 8, comprising a step of transmission of an audio or visual signal for an operator of the vessel when the datum relating to the sloshing is above a predetermined threshold.
10. A device (300) for determining the sloshing of a liquid loading of a vessel, said device comprising a processor (302) configured to implement the method (200) as claimed in any one of claims 1 to 9.
11. A vessel (1) comprising a device (300) as claimed in claim 10.]

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