WO2010089463A1

WO2010089463A1 - Device and method for damping movements of a liquid in a vessel, such as a tank of a liquid natural gas tanker, and such a vessel

Info

Publication number: WO2010089463A1
Application number: PCT/FR2009/000132
Authority: WO
Inventors: Jean-Michel Simon
Original assignee: Jean-Michel Simon
Priority date: 2009-02-05
Filing date: 2009-02-05
Publication date: 2010-08-12

Abstract

The invention relates to a device and to a method for damping movements of a liquid in a closed vessel in order to protect the wall thereof from potentially harmful consequences of said movements, and such a vessel containing said liquid and provided with said device. Said damping device (201) is intended for being at least partially submerged in a liquid contained in a closed vessel (4) in order to protect the wall (4a) of the vessel by damping the movements of said liquid, said device comprising a three-dimensional arrangement of elements (202) freely mobile on and/or in said liquid. According to the invention, said elements are externally defined, either individually in a first case in which said elements are separated, or together with one another in a second case in which said elements are connected, by a partition (205) which is deformable by said movements, which defines a sealed inner space and which is pervious to the liquid so as to dissipate part of the kinetic energy of the liquid flowing through said partition as heat, said elements withstanding cryotemperatures, for example of around -162°C for liquid methane.

Description

DEVICE AND METHOD FOR DAMPING MOVEMENTS OF A LIQUID IN A TANK, SUCH AS A METHANIER TANK,

AND SUCH A TANK.

The present invention relates to a device and a method of damping the movements of a liquid in a closed vessel to preserve its wall of the potentially harmful consequences of these movements, and such a tank containing this liquid and equipped with this device. The invention applies in particular to large land tanks or LNG tankers containing a cryogenic liquid, such as liquid methane at a temperature of about -162 ° C, and in particular under conditions of partial filling of these tanks.

Various techniques exist to design the tanks of LNG carriers which are the seat of very particular constraints compared to the tanks used to transport other liquids. The very low temperature of the transported liquid is the determining parameter in the design of these tanks. With the increase of the size of the LNG carriers (typically from 150,000 m ³ to 260,000 m ³ ), the so-called "membrane" technique is the most used to protect the tank wall, which is formed by the double hull of the vessel and is provided with an insulation layer and two cryogenic liquid sealing barriers respectively primary and secondary. The primary barrier in contact with the liquid is metallic, usually being made of embossed stainless steel sheet to absorb the thermal contractions between + 20 ° C and -162 ° C, or of Invar alloy which is a stable alloy in expansion at these temperatures. In both cases, the membrane is thin (around the mm) and is therefore relatively fragile vis-à-vis shocks.

However, a disadvantage of this membrane technique lies in the difficulty of preventing or at least damping the movements of liquid in the tanks in partial filling situations. It is indeed very difficult with this technique to design anchor points the anchorages are even more difficult to mount for ships already built.

Thus, the damping of the movements of liquid in the tanks of LNG tankers represents a critical and still unsolved problem despite the considerable studies carried out on this subject by the shipping companies.

Classification, shipyards or shipbuilding companies LNG carriers. It is probable that the non-resolution of this problem could one day lead to serious damage in these ships related to the damage, or even the breakage of the primary barrier of these tanks, with massive contact of liquid methane with the secondary containment barrier and, in the event of even minor damage in this secondary barrier, also the possibility of cold-setting the vessel's double hull with unforeseeable and potentially very serious consequences.

Given the failure of the experimental prediction of the violent and singular impacts of cryogenic liquids on the tank walls and the lack of reliable numerical simulation, the currently known technical solutions are few and can be summarized as follows: the size of the vessels and therefore the vessels, in particular their length, so that the critical frequency of the liquid mass is statistically significantly shifted from the excitation frequencies, limiting the free surface of the liquid, for example by imposing tanks with blanks cut larger, or prohibit partial fillings, which is undesirable and would not solve the problem for current ships, and solutions with creation of "bubble curtains" that have shown their effectiveness in other cases , but are subjected for the application to the LNG carriers to the same hazards and disadvantages as the damping partitions voiced above, namely anchor points of the "bubbler" pipes in the very expensive structure and delicate to achieve, causing very large thermal leakage doubled in this case of energy input into the tank by the compressed gas (nitrogen for example); moreover, the anchors and the compressed gas would lead to significant evaporation of the liquid, which is difficult to accept for the operation of the ships.

It is also known that the known devices for absorbing energy at ambient temperature are for the most part inoperative at cryotemperatures (ie less than about -160 ° C.), as is the case for viscous liquids at ambient temperature and elastomers. which at these cryotemperatures are respectively solid and brittle.

JP-A-2007 191183 and JP-A-2007 191174 disclose the use in oil tanks anti-sloshing devices ("anti-sloshing" in English) in the event of an earthquake. These devices consist of a perforated wall which is arranged under a floating cover of the tank and which limits the amplitude of the movements of the oil. Mention may also be made of document KR-A-2003 0050314 which teaches the use of perforated partitions carried by a lattice anchored in the wall of the tank. It should be noted that such partitions are difficult to use in LNG tanks whose wall is of membrane type, given the extremely strong anchoring points that should be implanted in the insulation, the difficulty of anchoring these partitions. without creating thermal bridges detrimental to the energy balance of the tank and the very high additional cost inherent in the installation of these partitions.

It is also known from JP-A-03 000684, still for oil tanks anti-sloshing in the event of an earthquake, to float on the entire surface of the oil several layers of aggregates for example plastic or wood that dissipates energy by rubbing on each other. These layers of aggregates are not suitable for satisfactorily preserving the wall of a LNG tank operating in rough or rough seas, liquid methane movements being extremely violent with liquid velocities of up to 25 m / s such movements being difficult to absorb through this single dissipation of energy by friction. On the other hand, the aggregates projected on the wall of such a tank would damage it for sure and the large volume occupied by these aggregates would be lost for the cargo, which is unacceptable for the operation of an LNG carrier.

An object of the present invention is to provide a damping device intended to be at least partly immersed in a liquid contained in a closed vessel to preserve the wall of the tank by damping the movements of this liquid (for example by protecting locally the wall of a direct jet at high speed of the liquid against this wall), this device comprising a three-dimensional arrangement of freely movable elements on and / or in this liquid whose lost volume for the cargo remains extremely low and overcomes the aforementioned drawbacks .

For this purpose, a device according to the invention is such that these elements are delimited externally, or each of them in a first case where they are separated from each other or with each other in a second case where they are interconnected , by a partition which defines a closed internal volume and which is permeable to the liquid so as to dissipate in heat all or part of the kinetic energy of the liquid flowing through this partition, these elements being able to withstand cryotemperatures, for example about -162 ° C for liquid methane. In other words, the device according to the invention comprises in the first case as many permeable external partitions as moving elements and, in the second case, a single permeable external partition which connects the movable elements between them. In both cases, it should be noted that the or each partition considered and has a closed three-dimensional geometry, preferably at least partly convex, and is adapted to receive the liquid to somehow be filled by imprisoning, and to expel the deformation of the partition following a shock against the wall of another element or against the wall of the tank, thus permitting permanent circulation of the liquid in both directions from its crossing of this partition.

It will further be noted that these mobile elements of the device according to the invention may be identical or different (for example according to sizes and / or different geometries), and they are devoid of any means of attachment to the wall of the tank, unlike the straight partitions of the aforementioned prior art, in particular.

According to another characteristic of the invention, the or each permeable partition is deformable by said movements and can advantageously define a mesh (ie a perforated structure) which has a multitude of orifices preferably capable of rolling the liquid and which is formed by at least one layer of a flexible fabric or knit fabric, preferably a glass, carbon or metal fabric (eg stainless steel, aluminum alloy or titanium). As a variant, this mesh may be obtained by a glass fabric comprising metal wires, for example made of stainless steel that are stubborn with the aforementioned cryotemperatures.

When the device according to the invention conforms to said first case, said separated elements are intended to form one or more superimposed layers on and / or in the liquid while being substantially in contact with each other so that the mutual friction between these elements contribute to the heat dissipation of the kinetic energy of the liquid, the partition of each element having a symmetry of revolution and surrounding at least one float which is formed by a metal or composite shell optionally filled with a filling material, such as that a material of the cellular polyurethane type.

The porosity or size of the orifices of this mesh may vary according to the locations of the or each partition, with, for example, wider openings on the bases or ends of the partition than on the sides, in the case of a cylindrical or ovoid partition. , as shown below.

In addition, it is advantageous to provide the outer surface of the partition of each movable member of a friction type friction coating to further increase the friction between elements.

Said float shell may advantageously be made of aluminum or of any other low density metal material, and the filling material is chosen to be of low density, such as, for example, polyurethane foam. According to this first case of the invention, each element may have a substantially cylindrical geometry with rounded ends (ie for example hemispherical) or an ovoid geometry, so as to have a minimized drag coefficient in the liquid, the or each float each element being then substantially tubular and arranged in relation to the center of gravity of the element so that the latter has a free floating position:

substantially vertical, this or these floats being preferably arranged above said center of gravity, or substantially horizontal.

In the example of an external cylindrical geometry (or forming part of a cylinder) for these elements, the latter may for example each have a partition diameter of between 10 cm and 200 cm and a slenderness factor of between 1 and 10. Alternatively, each element may have a spherical or substantially spherical external geometry (eg in an ellipsoid of revolution or inscribed in a sphere), with for example a partition diameter of between 10 cm and 200 cm.

It will be noted that the above-mentioned geometries for each mobile element of the device of the invention make it possible to promote lateral friction between the partitions of these elements.

According to another characteristic of this first case of the invention, the or each float of each element may be mounted integral with the corresponding partition by resilient and resiliently flexible connecting means, such as sheets or sheaths of fabric and / or cables for example provided with metal springs, these connecting means being able, on the one hand, to deform without breaking during impacts on the wall of the vessel, for example at a speed of 20 m / s and, on the other hand, to dampen these shocks by reducing the maximum impact force of the or each float projected with the corresponding element against said wall.

These connecting means may advantageously comprise substantially radial cables connecting the partition to said or each float at regular intervals over the height of the latter, the or each float being centered on a longitudinal axis of symmetry of each corresponding element and being formed of said shell which has a tubular shape and is filled with said filling material. According to another characteristic of the invention, the total volume of a damping device according to the invention is greater than 50 times and preferably 100 times the volume of said floats, which are dimensionally stable and impervious to liquid and each have a mass preferably of less than 200 g for a mass of each element less than 5 kg, so as to maximize the dissipation of energy while minimizing the volume and the mass of these floats to preserve said wall (ie not to damage it during impacts).

It should be noted that the closed geometry defined by the partition associated with each float or group of floats defines a much larger volume (in a factor of up to 1000) than the volume of the floats themselves. This characteristic is very important for increasing the efficiency of the energy damping because it allows, without penalizing the cargo capacity carried, considerably increase the rolling and friction surfaces. Incidentally, the additional cost related to these partitions is reduced compared to the amortization performance obtained.

Finally, it should be noted that these means that increase the efficiency of the energy dissipation are also used - this is particularly important in the case of LNG tankers equipped with a diaphragm tank wall - for damping the shocks of said elements of the tank. device against the wall so as not to damage it. Indeed, in the hypothesis to be chosen as a precaution of an unmortized local violent movement, the highest speeds (which may exceed 20 m / s) are usually in the corners or corners (by focusing energies) and could damage the membrane, which would not be the case with the displacements of a damping device according to the invention because it occupies on several thicknesses all the free surface of the liquid (hence the interest of 'a very small mass and means shock absorption). In other words, the device according to the invention is interposed in the manner of a screen between the membrane of the wall and the direct flow of the liquid which must pass through the permeable partitions of said elements before reaching the membrane, allowing to "spread" the energy and avoid a destructive shock too concentrated.

According to another characteristic of this first case of the invention, the partition of each element may comprise said reinforced fabric or knitted fabric on its internal and / or external face by elastic reinforcing means at said cryotemperatures (for example formed of blades or metal springs in stubborn materials, small diameter fibers or cables, without limitation), so as to protect the or each float shocks on the tank wall by damping the kinetic energy transmitted by the liquid while allowing the partition to resume its original shape after deformation, which reinforcement means may further contribute by internal friction to their structure to the heat dissipation of the kinetic energy of the liquid. These elastic reinforcing means may comprise longitudinal stiffeners regularly spaced around the perimeter of this partition and, optionally, transverse stiffeners preferably annular regularly spaced along the height of the partition. As will be detailed below, each partition can be stiffened by such flexible multilayer stiffeners (non-brittle steel at these cryotemperatures or composite for example carbon-epoxy) which maintain the geometry of the corresponding element by damping the shocks against the wall and which also dissipate the energy by rubbing the layers together during the deformation of each partition and its return to its original shape. Finally, these partitions can dissipate energy by their friction between adjacent elements and / or by the rupture of magnetic bonds integral with these partitions.

Advantageously, said connecting means and / or said elastic reinforcing means (both for the transverse and longitudinal stiffeners) can be made, in particular for elements generally in the form of oblong cylinders: - A hardened stainless steel with high elastic limit ("HLE" abbreviated, preferably characterized by an elastic limit exceeding 700 MPa), a titanium or aluminum alloy preferably assembled in several thin layers advantageously separated from each other by friction interfaces (or provided with these interfaces, which are for example formed by pins or embossings of their surfaces or by glass or carbon fabrics) stuck on the inside of the thin layers, contributing to increase the damping during friction between elements, or - a composite material with several thin layers for example based on an epoxy resin reinforced with carbon fibers or glass.

It will be noted, however, that only preformed longitudinal stiffeners having a suitable shape (for example equivalent to a half-ellipse or an arc-shaped shape) slid and fixed inside each cylindrical partition through an opening in a duct formed in this partition (for example a duct sewn into the glass fabric or metal fabric thereof). It will be further noted that the fabric or knit forming each partition could advantageously be obtained by winding a composite of threads at an angle of approximately 54 ° with the axis of symmetry of the corresponding element, which makes it possible to obtain a state optimum balance of this winding, particularly resistant to the pressure to which the partition is subjected.

When the device according to the invention conforms to said second case, said elements can be connected to one another in a spaced manner by flexible means of preferably elastic connection, such as cables, and being intended to form a three-dimensional network of floats and weights having respectively lower and higher densities than those of the liquid, each float being formed by a metal shell optionally filled with a filling material, such as a cellular polyurethane.

According to this second case, these elements may alternatively be interconnected spaced apart by magnetic bonds intended to be broken by the movements of the liquid, each element being previously magnetized or incorporating magnetic means preferably located on the inner face said permeable partition delimiting externally each element or in floats contained therein.

A closed vessel according to the invention, which contains a liquid and is capable of being subjected to multidirectional displacements, in particular a terrestrial storage tank or a tank of a vessel which is at least partially filled with the liquid and whose wall is formed by the double hull of the ship, such as a methane vessel containing liquid methane at a temperature of about -162 ° C, is characterized in that at least partly immersed in this liquid a damping device as defined above, which preferably has an immersed volume equal to or greater than 85%. According to a first embodiment of the invention, the mobile elements that comprise this device have, in whole or in part, a positive buoyancy in this liquid defined by a relative density of these elements which is preferably between 0.7 and 0.95 relative to that of the liquid (these elements may, in the preferential case where they are substantially cylindrical, ovoid or more generally oblong, have a natural position of floating either horizontal or vertical).

According to a second embodiment of the invention, the mobile elements that comprise this device have, in whole or in part, a negative buoyancy in this liquid defined by a relative density of these elements which is greater than 1 relative to that of the liquid (these elements can then rest on the bottom of the tank). A damping method according to the invention of the movements of a liquid contained in a closed vessel, in particular a cryogenic liquid contained in a vessel tank, to preserve the wall of the tank from the harmful effects of these movements, comprises a dissipation in heat of all or part of the kinetic energy of the liquid moving in the tank by a permanent circulation of this liquid through at least one partition of a three-dimensional arrangement of freely movable elements on and / or in this liquid, these elements being delimited externally, or each of them in a first case where they are separated from each other or with each other in a second case where they are interconnected, by this partition which defines a closed internal volume being permeable to the liquid and which is preferably deformable by these movements to achieve this circulation by capture and expulsion of the latter under deformation. According to another characteristic of the invention, this heat dissipation of the energy of the liquid can be further achieved:

by mutual friction between said elements which are substantially in contact with each other, and / or

by hydrodynamic vortices generated in the liquid by the rotation of the elements themselves, for example because of their asymmetrical or helical geometry (in particular by a suitable shape of said connecting or reinforcing means or the float itself) , thus creating an improved energy dissipation by these vortices and increased friction on the other elements.

Other characteristics, advantages and details of the present invention will emerge on reading the following description of several examples of embodiment of the invention, given by way of nonlimiting illustration, this description being made with reference to the accompanying drawings, among which : FIG. 1 is a diagrammatic view in vertical section of a LNG tank equipped with a positive buoyancy damping device according to an example embodiment of said first case of the invention, FIG. 2 is a schematic vertical sectional view. of this reservoir equipped with a positive buoyancy damping device corresponding to a variant according to the invention of this first case, Figure 3 is a schematic view from above of this tank equipped with a damping device according to this first case, illustrating the movable elements constituting it according to one embodiment of the invention, Figure 4 is a schematic vertical sectional view of this tank equipped with a negative buoyancy damping device according to another embodiment of the invention Referring to the first case and the elements of Figure 3, Figure 5 is a schematic vertical cross-sectional view of a positive buoyant movable element. according to another example of the invention relating to this first case, Figure 6 is a cross-sectional view of a float according to the invention used in each of the movable elements according to this first case, in particular in relation to that of Figure 5, FIG. 7 is a cross-sectional view of a movable element that can be used in a damping device according to this first case; FIG. 8 is a detailed schematic view illustrating the multilayer structure of said elastic reinforcement means used to reinforce each movable element according to this first case of the invention, in particular with reference to FIGS. 7 and 9 to 13, FIG. 9 is a diagrammatic view in vertical longitudinal section showing a mobile element of oblong shape and with positive buoyancy, according to this first case of the invention as illustrated in FIG. 3, FIGS. 10, 11 and 12 schematically illustrate in longitudinal section three respective embodiments of FIG. the arrangement of the floats and elastic reinforcing means of FIG. 9, FIG. 13 schematically illustrates in longitudinal section another alternative embodiment of the element of FIG. 9 with several floats connected to each other, FIG. 14 is a schematic cross-sectional view of the element of FIG. 13 according to plane XIV. FIG. 15 is a partial schematic view in vertical section of a positive buoyancy damping device according to an exemplary embodiment of said second case of the invention, FIG. 16 is a partial diagrammatic sectional view. vertical line of a damping device according to a variant of Figure 15, according to this second case, Figure 17 is a medallion illustrating in section a detail of the device of Figure 16, Figure 18 is a schematic perspective view of a damping device according to this second case, corresponding to a variant of FIG. 16, and FIG. 19 is a schematic sectional view of a part of a damping device according to a another embodiment showing one of its floats provided with means attached to the surface of the float which increase the frictional forces between floats and which can be magnetized to create magnetic bonding forces between floats, and FIG. 20 is a view schematic sectional view of a portion of a damping device according to another embodiment of said first case, showing the internal structure of a movable element with a spherical shell forming a partition and associated floats, the shell being provided with means for increase the frictional forces between elements and which can be magnetized to create magnetic bonding forces between them.

The damping devices 1 and 101 according to the first case of the invention, which are respectively illustrated in FIGS. 1 and 2, each form a three-dimensional arrangement with n layers of moving elements 2 and

102 (n being for example between 2 and 10) floating at the free surface 3 a cryogenic liquid partially filling a tank 4, such as a tank of a LNG tanker whose wall 4a, formed by the double hull of the vessel coated with its insulation system, is filled with liquid methane at a temperature of -162 ° C. Each element 2, 102 is delimited externally by a partition or perforated wall 5, 105, which is formed by a flexible fabric (eg metal or a glass or carbon fabric) of spherical shape in the examples of FIGS. 2, and which surrounds at least one internal float 6, 106 connected to this partition 5, 105 via flexible and sturdy cables 7 (preferably metal, only visible in Figure 1). According to the invention, the circulation of the liquid in motion through each perforated partition 5, 105, combined with the mutual friction of the elements 2, 102 provided by the permanent contact between these resiliently deformable partitions 5, 105 makes it possible to dissipate a significant part of the heat. of the kinetic energy of the liquid and thus to minimize the impact forces of the latter on the wall 4a of the tank 4.

As will be explained in more detail below, it will be noted that each perforated and deformable partition 5, 105 may advantageously have a plurality of thin layers of fabric (preferably of the single-ply type for each thin layer), the passage through which two directions by the liquid preferably promotes by rolling the dissipation of this kinetic energy and which further increase this dissipation by the friction provided at the mutual interfaces of these thin layers.

As visible in these figures, these elements 2, 102 float in contact with each other not only on the liquid surface, but also and especially below the free surface 3 of the liquid, thus being mainly immersed in the latter. For this purpose, the overall buoyancy of the device 1, 101 (ie its difference in density with the liquid) is in these examples chosen slightly positive, this excess buoyancy representing only a small part (20% maximum of the total weight) of so that the thrust of the floats 6, 106 immersed from the lower plies does not cause the elements 2, 102 to come out of the upper plies out of the liquid. For example for such elements 2, 102 spherical weighing in the air according to a force of 5 daN, it is necessary that the net thrust of the floats 6, 106 immersed in the liquid methane (density close to 500 kg / m ³ ) is for example 5.15 daN, so that with n = 4 webs of movable elements 2, 102, those of the upper web have a height emerging out of the liquid equal to about 40% of their diameter. The device

1, 101 is thus immersed substantially more than 80% in the liquid.

The device 201 of FIG. 3, illustrated in a rolling situation for the LNG vessel incorporating it in its tank 4, differs from those of FIGS. 1 and 2, in that each of the mobile elements 202 that it comprises has a cylindrical shape with rounded ends delimited externally by a perforated partition 205 similar to that mentioned above, to which is connected at least one float 206 by radial cables 207 such as those mentioned above. In the example of FIG. 3, the elements 202 also have a slightly positive buoyancy and float in a substantially vertical position on the surface 3 of the liquid. FIG. 3 represents only one layer of elements 202 but, depending on the chosen length of the mobile elements 202, one or more layers of elements may be present on the surface of the liquid. For example with a length of 1.5 m and a diameter of 0.7 m, one could have three layers of moving elements 202 is a total height of about 4 m.

As for the device 201 'of FIG. 4, it differs essentially from that of FIG. 3 in that its mobile elements 202' have a negative buoyancy, resting substantially on the bottom 4b of the tank 4 by weighting means 208 ' . In general, it will be noted that the movable elements of a damping device according to the invention each have a geometry capable of preventing any accumulation by interlocking, winding, agglomeration or stacking of elements in a zone of the tank at detrimental to other areas thereof, so that substantially the entire free surface of the liquid and / or a whole horizontal section of the tank below this surface is occupied by these movable elements. FIGS. 5 and 6 illustrate an embodiment of each spherical element 302 similar to those of the device 1 of FIG. 1, with thin elastic connecting cables 307 which connect in the manner of springs the float 306 to the perforated and deformable partition 305 (it will be noted that this intrinsic elasticity of the cables 307 could be replaced by springs interposed between the connecting cables and the partition 305). Each float 306, which is as light as possible, is advantageously composed of an aluminum or aluminum-magnesium alloy shell or, as illustrated in FIG. 6, a composite structure comprising a thin metal strip 306a (for example an aluminum foil approximately equal to 500 μm thick) applied to a central body 306b of rigid cellular foam such as a polyurethane foam of 80 kg / m ³ density. This float 306 may be externally protected by one or more tissue layers 306c. Each float 306 is thus extremely light (about 450 g for a float 1 m long and 50 mm in diameter), and the kinetic energy acquired by each element 302 remains relatively small, even at 25 m / s, and can be absorbed by the device incorporating these elements 302.

In the embodiment illustrated in FIG. 7, the movable elements 402 with positive buoyancy which are in this spherical contour example contain, inside the perforated partition 405 and elastically deformable, several floats 406 housed in an upper compartment of each element 402 separated from the rest of the latter by a net or diaphragm 409 for example made of reinforced glass fabric or stainless steel mesh. The partition 405 is reinforced by elastic reinforcing means 410 and 411, so as to protect the element 402 (and in particular its floats 406) from impacts on the tank wall 4a by damping the kinetic energy transmitted by the liquid while allowing the partition 405 to return to its original shape after deformation. These partition reinforcing means 410 and 411 comprise, on the one hand, two flexible rings 410 fixed to the outer face of the partition 405 in parallel and symmetrically relative to each other with respect to each other. at the equatorial plane of this partition 405 and, secondly, by several (for example six) evenly spaced circumferential reinforcements 411 in contact with the internal face of the partition 405 and preferably connected to the rings 410 at the crossing points of the reinforcement 411 with the latter, such that these reinforcing means 410, 411 are held in position on the partition 405.

As illustrated in FIG. 8, the outer rings 410 and the internal armature 411 are each constituted by very thin multilayer structures 412 made of steel "HLE" that are stubborn at very low temperatures or in composite, for example carbon-epoxy (for example with respective orientations of 80% and 20% of the fibers), which are designed to prevent these reinforcing means 410, 411 from plastically deforming or even breaking under very small radii of curvature. The internal reinforcement 411 may consist of strips (of section 15 mm × 0.5 mm for example) which are individually integral and which each have a length equal to for example three times the circumference of the partition 406, about 7.5 m. Each strip is advantageously introduced inside the partition 406 by sliding it through an opening thereof in a closed fabric duct sewn into this partition 405 and which is all around it (at the end of the winding, this strip is in three thicknesses in the example above). Alternatively, the internal armatures 411 may be constituted directly of a multilayer assembly of strips introduced in the same way into the wall 405 and "spliced" by a suitable connection system placed at each end. The external reinforcing rings 410 may also be constituted by a simple fabric reinforcement sewn on the partition 405, itself made of fabric, or knitted with this partition 405 during its manufacture.

The spherical elements 402 of FIG. 7 may for example be divided into 4 or 5 layers on the surface 3 of the liquid, and their respective partitions 405 may have a diameter of 0.5 m and advantageously be made of glass fabrics. As for the floats 406, they can be formed of ten cylinders or closed alloy spheres of aluminum, stainless steel or titanium alloy (in the horizontal position in the example of FIG. 7, each float 406 being for example 50 mm in diameter, 150 mm in length and 0.5 mm in 1 mm d 'thickness).

The generally cylindrical movable member 202 of FIG. 3 is illustrated in detail in FIGS. 9 to 12 which show, in a nonlimiting manner, several variants that can be combined with one another.

The reinforcement means 510 to 710 and 211, 511 to 711 may be predominantly longitudinal, such as those 211 of FIG. 9 or longitudinal members 511 to 711 and transverse members 510 to 710 in FIGS. 10, 11 and 12. The reinforcement means 211 of FIG. element 202 "according to Figure 9 are preferably preformed in a shape that resembles that of an arc As previously described for Figure 7, they are regularly spaced and preferably multilayered and introduced into the partition 205" in conduits reserved for this purpose. These reinforcing means 510 to 710, 511 to 711 comprise, in the example of FIGS. 10, 11 and 12:

- optionally transverse stiffening rings

510 to 710 mounted at regular intervals on the height of the external and / or internal face of the partition 505 to 705 according to the direction of the cylinder formed by it, and

- necessarily a reinforcement of longitudinal stiffeners

511 to 711 mounted on the entire height of the internal and / or external face of the partition 505 to 705 according generatrices regularly spaced from the cylinder formed by it, and preferably completed by an internal transverse ring fixed in the immediate vicinity of the upper end of the partition 505 to 705 (on the inner face of the cap formed by this end).

These reinforcing means 510 to 710 and 211, 511 to 711 made of "HLE" steel, aluminum alloy, titanium alloy or a composite (carbon-epoxy for example), are designed to impart an elastic stiffness of shape to the partition 205 ", 505 to 705, allowing it to regain its original shape after having been deformed and to dampen the energy kinetics taken by the floats 206 ", 506, 606, 706, 706a so as to minimize the impacts on the tank wall 4a.

These floats 206 ", 506 to 706a are preferably cylindrical or spherical, numerous (about ten for example) with very small individual masses of the order of a few tens of grams.They are held together and connected to the partition 205" 505 to 705 by a sock or a kind of elastic fabric bag 209 in the case of Figure 9, or mechanically linked to the wall 505 in the example of Figure 10 or trapped in a compartment limited by a diaphragm in fabric 609 closing transversely the upper end of the cylindrical portion of the partition 605 (the case of FIG. 11), or else distributed between a portion of floats 706 trapped in a compartment limited by two diaphragms 709a and 709b and a vertical cylindrical float 706a (case of Figure 12). The or each diaphragm 609, 709a, 709b of separation of this upper compartment is advantageously made of a metal fabric, glass or carbon, like the corresponding partition 605, 705.

More specifically, in connection with the example of FIG. 9, the internal flexible stiffeners 211 are arranged along generatrices of the generally cylindrical surface of the partition 205 "and are preferably made of" HLE "or carbon or glass composite multilayers. These stiffeners 211 are slid into "passers" or "sliding" sewn into the fabric partition 205 "so as to maintain the shape of each element 202" despite shocks and to dampen shocks on the vessel wall 4a. The floats 206 "housed in each element 202" may be spherical, for example being made of stainless steel, aluminum or foam / stainless steel or aluminum composite, while the ends 212a and 212b of each element 202 "are used to fixing the stiffeners 211 on the partition 205 ", the upper end 212a being closed to receive the floats 206" while the lower end 212b is open e. These two ends 212a and 212b may be made of a material similar to that of the floats 206 "(for example stainless steel or aluminum), it being specified that the end 212a is preferably made of a shock-absorbing material such as for example a cellular polyurethane coated with a stainless steel strip.

Moreover, the elastic reinforcing means 510 to 710, 511 to 711 are similar to those mentioned above in relation to FIGS. 7 or 9.

The float 706a of Figure 12 may advantageously comprise in its lower part a ballast which will give it a better vertical stability. This float 706a is connected to its wall 705 perforated and deformable by thin flexible and sturdy connecting cables 707, this wall 705 of cylindrical type with rounded ends (shaped substantially hemispherical caps) being provided on its outer and inner faces with means The cables 707 extend transversely between the float 706a and the partition 705 forming two broken lines in zigzags at angles close to 45 °.

The cables 707 between the float 706a and the partition 705 pass for example in guides or cable glands (not shown) which are integral with the float 706 or resilient reinforcing means 710, 711. Springs (not shown) can be interposed in series in these cables 707 to give them some elasticity.

To understand the advantage of the partitions 205 ", 505 to 705 attached to the floats 206", 506 to 706, 706a, consider for example the case of the movable elements 202 ", 502 to 702 such as those of FIGS. 9 to 12 which are In this geometry, in order to set the orders of magnitude, it is envisaged to set for a 200,000 m ³ LNG carrier, individual oblong elements 202 ", 502 to 702, for example 0.7 m in diameter, and 1.5 m long over three layers, ie about 4 m high (the total height depends on the vertical imbrication of the cylinders between them). The horizontal projected surface of the liquid in a LNG tanker being of the order of 5300 m ² , the characteristics of a device according to the invention incorporating these elements 202 ", 502 to 702 are:

• volume occupied by the device: approximately 21,000 m ³ (more than 15% of the total liquid volume for a partial filling rate of the LNG tanker of 70% and 52% for a filling of 20% - these are very high rates which guarantee to oppose considerably the development of resonances of excessive liquid movements;

Number of elements 202 ", 502 to 702: about 36,000;

• mass of an element 202 ", 502 to 702: 1, 5 kg or an apparent" density "of 3 kg / m ³ which is extremely low (in comparison, a thermal insulation for the building typically has a density of order of 20 kg / m ³ ), which is a very important data to avoid damaging the fragile wall 4a of the tanks 4;

The floats 206 ", 506 to 706a in each oblong element 202", 502 to 702 are, for example, spheres 70 mm in diameter and 14 floats per element, the individual weight of which is a few tens of grams, which is also very important not to damage the structure of the wall 4a;

The friction surfaces are very large: approximately 30,000 m ² of the contact surface of the elements 202 ", 502 to 702 between them and more than 200,000 m ² of frictional contact between the layers of the stiffeners 510 to 710 and 211, 511 at 711 partitions 205 ", 505 to 705 therebetween; and

• The rolling surfaces of the liquid through the openings of the fabrics of partitions 205 ", 505 to 705 are also very important (more than 150,000 m ² ).

In conclusion, the permeable partitions according to the invention make it possible to delimit a very important space around each group of floats which thus makes it possible to imprison a considerable volume of the liquid (21,000 m ³ ) for a minimum loss of capacity (the loss of capacity being the volume of the damping device which is not permeable to the liquid, namely essentially the volume of the floats (less than 100 m ³ in total here, less than one hundredth of the volume occupied by the entire apparatus and less than 1/2 ^000th the volume of the cargo).

The permeable partitions according to the invention therefore make it possible to enormously increase the rolling surfaces of the liquid and friction without penalizing the loss of capacity. Thus, starting from about 70 000 individual floats of 70 mm in diameter which would occupy 65% of the total surface of the liquid if they were alone and thus would not cause any damping of the movements, one reaches occupied volumes higher than 21 000 m ³ , friction surfaces greater than 150,000 m ² and liquid rolling surfaces also greater than 150,000 m ² .

The embodiment of FIGS. 13 and 14 only illustrates, in addition to that of FIG. 9, the fact that it is possible to use several floats 806 aligned within the same mobile element 802 that is elongated and intended to float. in a substantially horizontal position. These floats 806 are connected, on the one hand, to the partition 805 (which is reinforced by resilient reinforcing means 810, 811 in the form of longitudinal stiffeners and transverse rings similar to those mentioned above) by the flexible connecting cables 807 and, on the other hand, two by two between them by these same cables 807 which are fixed to these reinforcing means 810. In this version, each element 802 can have high dimensions, for example 1 m diameter D over 10 m of length L or more, so that the velocity field of the liquid is different from one end of the element 802 to the other, thus creating shear of the liquid related to the velocity gradient in the length and a more high efficiency in the dissipation of the kinetic energy of the liquid.

In general, with reference to the mobile elements 202 to 802 of FIGS. 7 to 14, the transverse stiffeners 210 to 810 (optional) and longitudinal stiffeners 211 to 811 comprise, as previously mentioned, an assembly of several thin layers (for example three layers "HLE" steel strip or equivalent material 0.7 mm thick or five layers of 80/20 single-ply carbon-epoxy composite 0.25 mm thick) which have the advantage of being less fragile with respect to shocks and severe flexures. In addition, the surfaces of the different layers of strip or composite are able to "rub" against each other during the deformation of these stiffeners under the effect of the movements of the liquid, which still dissipates energy by friction and contributes additionally to the damping of these movements. In the particular case of the use of metal strips for these longitudinal stiffeners 211 to 811 and optionally transverse

210 to 810, one can furthermore: - "to graining" the respective surfaces of these strips to increase the dissipation of energy generated by frictional contact, or else

glue a glass or carbon fabric on each side of these thin layers of strips that have been previously perforated so that the adhesive layers used for the bonding of the tissues are intimately bonded, the two tissues facing each other; assembly interface between thin layers rubbing against each other (it being specified that the friction area at the interfaces of the stiffeners is considerable, greater than that of the moving elements 202 to 802 between them).

Note also that one can advantageously increase the friction of the movable elements 202 to 802 between them by equipping the outer surface of their partitions 205 to 805 of "brushes" for example metal or fiberglass.

Still with reference to the movable elements 202 to 802 according to the invention, it will be further noted that the perforated fabrics forming their respective partitions 205 to 805 which emerge out of the liquid advantageously make it possible to "trap" micro-bubbles of gas, which contributes still to dampen the movements of this liquid.

FIGS. 15 to 18 illustrate exemplary embodiments of said second case according to the invention, where the damping device 901 (FIG. 15),

901 '(FIG. 16), 1001 (FIG. 18) comprises a multitude of moving elements

902, 1002 consisting of small floats 1006 and possibly 1008 weights which are interconnected by elastic cables 907, 1007 for example of steel or composite, themselves joined by a same deformable outer partition and openwork 1005 (not visible in Figures 18 and 19) for the entire device 901, 1001 This partition 1005 is made of a fabric such as the one mentioned above with reference to the partitions 5 to 805 of said first case. As for the elements 902, 1002, they may comprise (see medallion of FIG. 17) friction amplification means 912 in the form of "metal barbs", spikes, or surface corrugations. As can be seen in FIG. 18, the device 1001 preferably comprises a plurality of floats 1006 located on at least its highest row, and a greater number of ballasts 1008 located on the rest of its lower rows.

In the example of FIG. 19, the spherical floats 1106 forming the moving elements 1102, for example made of stainless steel, are each provided at their periphery with a multitude of metal cables 1107 protecting them (for example about twenty cables 1107 in float stainless steel 1106) which can be magnetized at their ends with + and - poles thereby creating magnetic bonds with adjacent floats 1106 to be broken by the movements of the liquid. By way of indication, each float 1106 may have a diameter of 100 mm and a thickness of 0.5 mm, and each cable 1107 may have a length of 10 cm to 30 cm and a diameter of 1.5 mm. The movements of the floats 1106 are thwarted by the mutual friction of the cables 1107, which dissipate heat and thus contribute to damping part of the kinetic energy of the moving liquid.

In particular with reference to Figures 15, 16, 17 and 19 above, it will be noted in general that the or each partition of a damping device according to the invention may not be permeable and then be designed to dispel the kinetic energy of the liquid not by rolling, but by friction and / or by magnetization breaks. In the example of FIG. 20, the spherical hulls 1205 associated with the floats 1206 form the partitions of the movable elements 1202 which have a slightly positive buoyancy. The shells 1205 are made of ferritic steel "HLE" or aluminum or composite carbon or glass. In the case where shells 1205 are made of ferritic steel, they comprise magnets in the form of inserts 1213 (about ten for example) associated with as many "patches" 1214 of stainless steel which are welded or fixed on each shell 1205 and on which magnets 1213 are attached. In the case where the hulls 1205 are made of aluminum or composite, they comprise, as in the previous case, magnets in the form of inserts 1213 associated with aluminum "patches" 1214 alternating with "patches" (not shown) that are identical. to the previous magnet + "patch" assembly, but made of ferritic steel. In this way, the magnets 1213 of a movable member 1202 will attract the ferritic steel "patches" 1214 from the adjacent movable member 1202, if the shells 1205 are of aluminum or composite, or the ferritic structure of this adjacent element 1202, if the shells 1205 are made of ferritic steel.

In addition, these shells 1205 have numerous recesses 1205a (for example 80% of recesses 1205a) which allow the liquid to flow through the permeable partitions 1205 thus formed for the moving elements 1202. Thus, the energy of the movements of liquid will be dissipated by the friction shells 1205 between them, by the rupture of the magnetic bonds between hulls 1205 and the turbulence of the liquid passing through them. Note that the magnets 1213 are not essential and that one could have on the same principle spherical shells for example aluminum with a bumpy outer surface, pins or "brushes" to increase the friction between the elements and therefore the dissipation of energy. In general, for all the damping devices according to the invention, it will also be noted that the most external of the or each partition could be advantageously interchangeable, in the manner of a bag mounted removably.

Claims

1) damping device (1 to 1001) intended to be at least partly immersed in a liquid contained in a closed vessel (4) to preserve the wall (4a) of the tank by damping the movements of this liquid, this device comprising a three-dimensional arrangement of movable elements (2 to 1202) freely on and / or in this liquid, characterized in that these elements are delimited externally, or each of them in a first case where they are separated from each other or with the others in a second case where they are interconnected by a partition (5 to 1205) which defines a closed internal volume and which is permeable to the liquid so as to dissipate all or part of the kinetic energy of the liquid into heat circulating through this partition, these elements being able to withstand cryotemperature for example of about -162 ° C for liquid methane.

2) damping device (1 to 1001) according to claim 1, characterized in that said or each permeable partition (5 to 1005) is deformable by said movements and defines a mesh which has a plurality of orifices capable of rolling the liquid and which is formed by at least one layer of a flexible fabric or knit, preferably a glass fabric, carbon fabric, a metal fabric or a glass fabric having metal wires.

3) damping device (1 to 801) according to claim 1 or 2, characterized in that it conforms to said first case, said elements (2 to 802) separated being intended to form one or more layers superimposed on and / or in the liquid being substantially in contact with each other so that the mutual friction between these elements contributes to the heat dissipation of the kinetic energy of the liquid, said partition (5 to 805) of each element having a symmetry of revolution and surrounding at least one float (6 to 806) which is formed by a hull metal or composite (306a) optionally filled with a filler (306b), such as a cellular polyurethane.

4) damping device (1 to 801) according to claim 3, characterized in that each element (2 to 802) has a substantially cylindrical geometry with rounded ends or an ovoid geometry, so as to have a drag coefficient minimized in the liquid, said one or more floats (6 to 806) of each element being arranged in relation to the center of gravity of this element so that the latter has a free float position:

substantially vertical, this or these floats being preferably arranged above said center of gravity, or else

- substantially horizontal.

5) damping device (1 to 801) according to the claim

3 or 4, characterized in that the or each float (6 to 806) of each element (2 to 802) is mounted integral with said corresponding partition (5 to 805) by flexible connection means (409 to 709a, 709b and 7 to 807) preferably elastic, such as webs or fabric sheaths and / or cables for example provided with metal springs, these connecting means being able, on the one hand, to deform without breaking during shocks on said wall (4a) tank (4) for example at a speed of 20 m / s and, secondly, to dampen these shocks by reducing the maximum force of impact of the or each float projected with the corresponding element against said wall

6) damping device (1 to 801) according to one of claims 3 to 5, characterized in that its total volume is greater than 50 times and preferably 100 times the volume of said floats (6 to 806), which are indeformable and each preferably has a mass less than 200 g for a mass of each element (2 to 802) less than 5 kg, so as to maximize the energy dissipation while minimizing the volume and mass of these floats so as to preserve said wall. 7) A damping device (1 to 801) according to claim 2 and one of claims 3 to 6, characterized in that said partition (5 to 805) of each element (2 to 802) comprises said reinforced fabric or knit on its inner and / or outer face by resilient reinforcing means to said cryotemperatures (210, 211 to 810, 811) so as to protect the or each float (6 to 806) against shocks on said vessel wall (4a) (4 ) by damping the kinetic energy transmitted by the liquid while allowing the partition to resume its original shape after deformation, which reinforcement means contribute by internal friction to their structure to the heat dissipation of the kinetic energy of the liquid.

8) damping device (1 to 801) according to claims 5 and 7, characterized in that said elastic reinforcing means (210, 211 to 810, 811) comprise longitudinal stiffeners (211 to 811) regularly spaced around the periphery of this partition (5 to 805) and, optionally, transverse stiffeners (210 to 810) preferably annular regularly spaced along the height of said partition.

9) damping device (1 to 801) according to the claim

7 or 8, characterized in that said connecting means (7 to 807) and / or said elastic reinforcing means (210, 211 to 810, 811) are made:

- a hardened stainless steel with a high elastic limit, in a titanium or aluminum alloy with several thin layers (412) preferably separated from each other by frictional interfaces bonded to the inside of the thin layers, thus contributing to increasing the damping during the deformations of said elements (2 to 802), or

- A composite material with several thin layers (412) for example based on an epoxy resin reinforced with carbon fibers or glass. 10) Device (901, 1001) according to claim 1 or 2, characterized in that it conforms to said second case, said elements (902, 1002) being connected together spaced by flexible connecting means (907, 1007) preferably elastic, such as cables, and being intended to form a three-dimensional network of floats (1006) and weights (1008) respectively presenting densities lower and higher than those of the liquid, each float being formed by a metal shell (306a) optionally filled with a filler (306b), such as a cellular polyurethane.

11) Device according to claim 1 or 2, characterized in that it conforms to said second case, said elements (1102, 1202) being interconnected spaced apart by magnetic connections provided to be broken by the movements of the liquid, each element being previously magnetized or incorporating magnetic means (1107) preferably located on the inner face of said permeable partition (1205) delimiting externally each element or in floats (1206) contained therein.

12) Closed vessel (4) containing a liquid and capable of being subjected to multidirectional displacements, in particular an earth storage tank or a tank of a ship which is at least partially filled with the liquid and whose wall (4a) is formed by the double hull of the ship, such as a LNG tanker containing liquid methane at a temperature of approx. -162 ° C, characterized in that is at least partially immersed in the liquid a device (1 to 1001) according to one of the preceding claims, which preferably has a submerged volume equal to or greater than 85%.

13) tank (4) according to claim 12, characterized in that said movable elements (2 to 1002) that comprises this device (1 to 1001) have, in whole or in part, a positive buoyancy in this liquid defined by a relative density of these elements which is preferably between 0.7 and 0.95 relative to that of the liquid.

14) tank (4) according to claim 12, characterized in that said movable elements (2 to 1002) that comprises this device (1 to 1001) have, in whole or in part, a negative buoyancy in the liquid defined by a density relative of these elements which is greater than 1 with respect to that of the liquid.

15) A method of damping the movements of a liquid contained in a closed vessel (4), in particular a cryogenic liquid contained in a vessel tank, to preserve the wall (4a) of the tank from the harmful effects of these movements, characterized in that it comprises a dissipation in heat of all or part of the kinetic energy of the liquid moving in the tank by a permanent circulation of this liquid through at least one partition (5 to 1005) of a three-dimensional arrangement elements (2 to 1002) freely movable on and / or in this liquid, these elements being delimited externally, or each of them in a first case where they are separated from each other or with each other in a second case where they are interconnected by this partition which defines a closed internal volume being permeable to the liquid and which is preferably deformable by these movements to achieve this circulation by capture and expulsion of the liquid under deformation.

16) damping method according to claim 15, characterized in that this heat dissipation of the kinetic energy of the liquid is further achieved:

by mutual friction between said elements (2 to

1002) which are substantially in contact with one another, and / or - by hydrodynamic vortices generated in the liquid by the rotation on themselves of said elements, for example because of their asymmetric or helical geometry.