EP3728020A1

EP3728020A1 - Method for controlling the buoyancy of a submarine vehicle

Info

Publication number: EP3728020A1
Application number: EP18808366.1A
Authority: EP
Inventors: Christophe Borel; Eric Rouvier; Cyril BOUYER
Original assignee: Thales SA
Current assignee: Thales SA
Priority date: 2017-12-19
Filing date: 2018-11-29
Publication date: 2020-10-28
Anticipated expiration: 2038-11-29
Also published as: FR3075163B1; US11167828B2; WO2019120926A1; FR3075163A1; EP3728020C0; CA3085422A1; SG11202003033QA; EP3728020B1; US20200361583A1; AU2018389953A1

Abstract

A method for controlling the buoyancy of a submarine vehicle (1) such that it substantially has a predetermined target buoyancy Fc when it is submerged in a volume of liquid delimited by a first surface and a second surface along a vertical axis (z), the method comprising: - starting from an initial buoyancy of the vehicle which maintains the vehicle at the level of the first surface (S), a first step (100) of modifying the density of the vehicle (1) such that it approaches the second surface, the first step being implemented until a second step (200) of detecting the crossing, by the vehicle (1), of a predetermined non-zero distance threshold (SD) with respect to the first surface (S), along the vertical axis, then a third step of modifying the density of the vehicle (1) until the vehicle has substantially the target buoyancy.

Description

METHOD FOR ADJUSTING THE FLOATABILITY OF A SUB-VEHICLE

MARINE

The field of the invention is that of submarine vehicles. These vehicles are able to have a negative buoyancy, that is to say able to be totally immersed. It relates more particularly to unmanned underwater vehicles, also known as UUVs in reference to the English expression "Unmanned Underwater Vehicles", which may be autonomous vehicles also called AUVs with reference to the Anglo-Saxon expression (" Autonomous Underwater Vehicle ") or non-autonomous vehicles also known as ROVs in reference to the English expression" remotely operated vehicle "or vehicles commonly called fish when they are devoid of thrusters.

Buoyancy is the force acting on the underwater vehicle is the result of the difference between buoyancy and the weight of the craft. This force can be directed from bottom to top (positive buoyancy, weight less than buoyancy) or from top to bottom (negative buoyancy, higher weight than buoyancy).

An underwater vehicle must classically have a positive buoyancy when it is launched. Thus, the vehicle naturally floats on the surface of the water when it is only subject to the pressure of Archimedes and its weight. This allows recovery from a surface platform when the vehicle no longer has energy for propulsion. This also allows the underwater vehicle to communicate with a surface platform by means of radio communication means of the underwater vehicle which are then emerged. It also allows the subsea vehicle to be powered from a surface platform without consuming energy for propulsion. Once the submarine vehicle is launched, it is conventionally intended to perform underwater missions, for example inspection, so that it is led to dive, by means of a thruster, to join positions of great depth before going to the surface, for example, to refuel, to communicate with a large transmission rate, to be recovered from a surface platform. However, in order to dive underwater to perform its mission and maintain its submerged position, the underwater vehicle which has a positive buoyancy must overcome forces all the more important as its buoyancy is important. It can thus be unable to dive under water or consume, to dive, an energy all the more important as its buoyancy is important which has the effect of limiting its endurance and the duration of its mission . When its positive buoyancy is too high, the vehicle may also have difficulty diving due to disturbances caused by the sea surface condition which partially and randomly discovers the actuators of the craft, such as its propellant, becoming ineffective. out of water. The adjustment of the buoyancy of the vehicle (or balancing by adjusting its buoyancy) is therefore essential and this step must be performed with great precision.

Underwater vehicles can also be balanced with negative buoyancy when they are launched. This allows to be in a configuration where the underwater vehicle will naturally come to rest on the seabed and thus be invisible from the surface. During his mission, the submarine vehicle will be brought up to the surface punctually or to the surface. However, in order to go up to the surface the underwater vehicle which has a negative buoyancy, must overcome forces all the more important that its negative buoyancy is low, that is to say, has a high absolute value. It can thus be unable to go back up or have to consume, to go back, an energy all the more important that its negative buoyancy is low which has the effect of limiting its autonomy and the duration of its mission.

It therefore appears that to achieve its mission optimally, the underwater vehicle must be able to adjust its buoyancy according to the stages of the mission: positive buoyancy at launch, neutral during the diving phases and negative to be discreet.

One solution for regulating the buoyancy of underwater vehicles is to carry out static weighing before launching in order to substantially balance the weight and buoyancy of Archimedes. Flaws in this solution are that this setting is fixed for the duration of the mission (buoyancy can not be controlled) and that this setting is not robust to local variations in water density (the vehicle initially weighed for being slightly floating in seawater can become flowing when coming into the water soft) or the variations of mass of the underwater vehicle, for example when a shell or an alga is fixed on its hull, or to the variations of volume of the body of the vehicle, for example, by compression of the hull under the effect of pressure.

Another solution consists in equipping the underwater vehicle with means for varying its density of the underwater vehicle. A method of adjusting the buoyancy of an underwater vehicle during its implementation conventionally consists of manually controlling the means for varying the density. The vehicle initially has a positive buoyancy that is not precisely known, an operator controls the means to vary the density to slowly increase the density of the underwater vehicle so that its buoyancy decreases continuously until the vehicle achieves lower positive target buoyancy. This solution is long, delicate and difficult to automate. For example, a small variation in the mass of the underwater vehicle can vary the buoyancy of the underwater vehicle significantly, so the buoyancy adjustment of the underwater vehicle must be done with great accuracy and very slowly. to prevent the underwater vehicle from sinking which can prevent the operator from recovering the vehicle.

An object of the invention is to limit at least one of the above disadvantages.

For this purpose, the subject of the invention is a method for adjusting the buoyancy of an underwater vehicle so that it substantially has a predetermined target buoyancy when it is immersed in a defined volume of liquid along an axis vertical, by a first surface and a second surface, the method comprising:

from an initial buoyancy of the vehicle holding the vehicle at the first surface, a first step of modifying the density of the vehicle so that it approaches the second surface, the first step being implemented until a second step of detecting the crossing, by the vehicle, of a threshold of predetermined non-zero distance with respect to the first surface, along the vertical axis,

and then a third step of modifying the density of the vehicle until the vehicle has substantially the target buoyancy. Advantageously, the variation of the density of the vehicle during the third step is predetermined.

Advantageously, the first step is implemented so that the vehicle has a predetermined buoyancy during the detection of crossing the threshold.

Advantageously, the target buoyancy is of the same sign as the initial buoyancy and of absolute value less than the absolute value of the initial buoyancy.

Advantageously, during the implementation of the method, the vehicle moves, along the vertical axis, solely under the effect of a variation of its buoyancy.

Advantageously, the first surface is the surface of the liquid, that is to say its upper surface, and the initial buoyancy is positive, the first step of modifying the density being a step of increasing the density of the vehicle , the distance threshold being an immersion threshold.

Advantageously, the first surface is a bottom of the liquid volume, the initial buoyancy is negative, the first density modification step being a density reduction step, the distance threshold being an altitude threshold relative to at the first surface.

Advantageously, during the first step and during the third step, the mass of the vehicle, at constant volume of the underwater vehicle, is varied and / or the volume of the constant mass constant mass vehicle of the vehicle is varied. submarine.

Advantageously, the vehicle comprises a first variable density tank, the density variation of which varies the density of the vehicle, disposed near a first longitudinal end of the vehicle, and a second tank of variable density, whose density variation varies the density of the vehicle and which disposed near a second longitudinal end of the vehicle, wherein, in the first step, the density of a single predetermined reservoir is varied, taken from the first tank and the second tank.

Advantageously, the invention also relates to a balancing method comprising the method of adjusting the buoyancy followed by method of adjusting the buoyancy according to the invention and a step of adjusting the longitudinal attitude of the vehicle.

The invention also relates to a buoyancy adjustment device for adjusting the buoyancy of the underwater vehicle and comprising means for varying the density of the underwater vehicle and at least one sensor for detecting the crossing, by the vehicle, a threshold of predetermined non-zero distance with respect to a first surface delimiting, in a vertical direction, the volume of a liquid in which the vehicle is immersed, the buoyancy adjustment device being configured to a method comprising the following steps when a buoyancy adjustment condition is verified:

from an initial buoyancy maintaining the vehicle at the first surface; a first step of modifying the density of the vehicle by the means for varying the buoyancy, so that the vehicle approaches a second surface also defining the volume of liquid in the vertical direction, the first step being implemented until a second step of detection, by the sensor, of crossing of the distance threshold by the vehicle,

and then a third step of modifying the density of the vehicle, by the means for varying the buoyancy, until the vehicle has substantially the target buoyancy.

Advantageously, the variation of the density during the third step is predetermined.

The invention also relates to a vehicle comprising the buoyancy adjustment variation device according to the invention. The invention will be better understood by studying a few embodiments described by way of non-limiting examples, and illustrated by appended drawings in which:

FIGS. 1a, 1b and 1c represent different situations of an underwater vehicle during the implementation of the method according to the invention,

FIG. 2 diagrammatically represents an example of means for adjusting the buoyancy of a marine machine according to the invention.

From one figure to another, the same elements are designated by the same numerical references.

In the present patent application, the vertical and horizontal directions are defined in a terrestrial reference system. The upper and lower positions being determined along a vertical axis z of the terrestrial reference.

The invention relates to a method of adjusting the buoyancy of the underwater vehicle 1 so that it has a final buoyancy substantially equal to a target buoyancy.

The underwater vehicle 1 initially has a so-called initial float, such that it maintains the underwater vehicle 1 at a so-called initial surface S, delimiting the volume of liquid in which the underwater vehicle is immersed for example water E, for example seawater or fresh water, in a vertical direction (defined in a terrestrial reference). The vehicle 1 is maintained at the initial S surface only by its buoyancy.

This initial surface is, for example, the upper surface of the volume of the liquid, for example the surface of the water S. The initial buoyancy of the underwater vehicle 1 is then positive and the underwater vehicle initially floats on the surface of the the water.

The volume of liquid in which the underwater vehicle is immersed is delimited, in the vertical direction z, by two surfaces spaced from each other in the vertical direction, the upper surface and a lower surface. In the case of a vehicle immersed in seawater, this volume is delimited by the surface of the water S (upper surface) and by the seabed Fd (lower surface). The initial surface may alternatively be the lower surface of the volume of the liquid, that is to say the bottom of the volume of the liquid, for example the seabed. The initial buoyancy of the vehicle is then negative and the vehicle is initially placed on the lower surface of the volume of the liquid, that is to say on the ground or the seabed.

In Figure 1a, there is shown a submarine vehicle 1 initially having a positive buoyancy. The underwater vehicle 1, in its initial situation shown in Figure 1a, floats on the surface of the water S. Alternatively, the underwater vehicle 1 initially has a negative buoyancy so as to be held against the bottom Fd marine.

Typically, the positive initial buoyancy of the vehicle is of the order of 5% of its weight. The purpose of the method is to give the underwater vehicle a final buoyancy closest to 0 while remaining positive. It is typically desired to achieve a target buoyancy of between 0.05% and 0.01% of the weight of the vehicle. For a vehicle of 1000 kg, this amounts to having to balance the vehicle with an accuracy of 100 g. When the underwater vehicle has a very low positive buoyancy, its recovery to the surface, in case of failure of its thruster, is ensured and its energy consumption to dive to the seabed is minimal. The fact that the buoyancy setpoint is positive gives a margin of buoyancy that ensures that the final buoyancy of the submarine vehicle at the end of the implementation of the process is positive.

The method comprises the steps shown in Figures 1a to 1c.

This method comprises a first step 100 of modifying the density of the vehicle 1 so that it moves away from the initial surface S by approaching the other surface delimiting the volume of liquid. Thus, the vehicle moves in the vertical direction. The variation of the density of the vehicle varies the buoyancy of the vehicle. In the example of FIGS. 1a to 1c, this step 100 is a step of increasing the density of the underwater vehicle 1 so that the underwater vehicle 1 sinks, that is to say away from the surface of the water S or approaches the seabed Fd. In the case where the underwater vehicle has a negative initial buoyancy, this step is a step of reducing the density of the underwater vehicle 1 so that the underwater vehicle 1 rises to the surface of the water S , that is to say, moves away from the seabed Fd. The first step 100 of modifying the density is carried out until a second step 200.

During the first step 100, the attitude of the vehicle can vary under the effect of the variation of the density, which does not impact the method of adjusting the buoyancy according to the invention.

This second step 200 is a step of detecting the crossing, by the underwater vehicle 1, of a predetermined non-zero distance threshold SD with respect to the initial surface S, along a vertical axis z. In the case where the initial surface S is the surface of the water, the distance threshold SD is an immersion threshold or distance threshold with respect to the surface of the water. In cases where the initial surface S is the seabed, the distance threshold SD is an altitude threshold, that is to say distance from the seabed along the z axis.

The first step 100 is stopped upon detection 200 of the passage of the threshold SD by the vehicle 1.

The method then comprises a third step 300 of modifying the density of the underwater vehicle 1 until the buoyancy of the underwater vehicle 1 is substantially equal to the target buoyancy.

The density of the vehicle 1 advantageously varies in one direction during the third step 300. In other words, the buoyancy of the vehicle only varies in one direction during the step 300.

When the underwater vehicle 1 crosses the distance threshold SD, it has a known or determinable buoyancy. When the vehicle crosses the predetermined distance threshold SD, it always has the same buoyancy, whatever its initial buoyancy, if conditions of variation of the buoyancy, in the first step 100, are the same for the same initial longitudinal attitude. This buoyancy serves as a reference. Once this reference is available, it is possible to determine a density variation that will make it possible to reach the target buoyancy during step 300 whatever the initial buoyancy. It is then sufficient to evaluate once only this variation of density.

For example, for a vehicle of about 1000 kg that is weighed down by a pump with a chosen flow rate, and an immersion trigger threshold at 1 m, will cross the threshold with always the same buoyancy. An example of buoyancy crossing the threshold of - 20N corresponds to about -20 / (1000 ^* 10) = 0.2% of the vehicle weight for a newton constant rounded to 10 N m ² kg ² . If the target buoyancy is 0.05% of the weight of the vehicle, then, once the threshold is exceeded, the vehicle must be lightened by (0.05 + 0.2) / 100 ^* 1000 = 2.5 kg.

The method according to the invention requires a relative adjustment accuracy of the buoyancy of the vehicle, easier to obtain than an absolute precision of buoyancy of the vehicle. It is independent of the initial buoyancy of the vehicle and is therefore reproducible.

This method can be implemented at any time, that is to say, the launching of the vehicle or during a mission or during a reconfiguration of the underwater vehicle (adding or removing sensors, for example).

This process can be easily automated because its stages are few and sequential, so it adapts well to unmanned vehicles UUV and does not require the intervention of an outside operator.

The method according to the invention is independent of the mass and / or volume of the underwater vehicle 1. It makes it possible to achieve the target buoyancy even if one of these two parameters varies, for example in the case of addition or withdrawal. voluntary or not of components or particles especially in case of loss of a pale propeller propeller after its launching.

The process according to the invention is much faster than a series of weighings carried out by an operator in a water having a certain density, making it possible to calculate the quantity of ballast to be added or removed on the vehicle.

This solution only requires an immersion or pressure sensor to detect crossing the threshold. This type of sensor is simple and cheap.

In summary, the proposed solution is inexpensive, simple to implement and makes it possible to balance the underwater vehicle in a reliable, repeatable and easily automatable way (simple algorithm simply requiring an immersion sensor).

In the example of FIGS. 1 a to 1c, the initial buoyancy is positive, the target buoyancy is positive and lower than the initial buoyancy and the buoyancy of the vehicle when it crosses the threshold SD is negative. In other words, it makes the vehicle slightly flowing for a short period of time, it then moves away from the surface of the water S, before making it floating again. The buoyancy of the underwater vehicle increases during the third stage 300 until a positive buoyancy, it then rises to the surface S of the water where it floats during the third step 300. Alternatively, the final buoyancy is negative or zero.

In this embodiment, the buoyancy varies in one direction during step 100 and in the opposite direction during step 300 but, alternatively, the variation of the density during these steps could be such that the buoyancy varies in the same direction. meaning during these two stages.

Alternatively, the initial buoyancy is negative, the buoyancy at crossing the threshold is positive and the target buoyancy is positive. Alternatively, the final buoyancy is negative or zero.

Advantageously, the target buoyancy has an absolute value lower than the absolute value of the initial buoyancy.

For example, the target buoyancy is negative and of absolute value lower than the absolute value of the initial negative buoyancy and the buoyancy at the crossing of the threshold is positive. This limits the energy required for the vehicle to go up later on the surface under the effect of its propulsion. This process is faster than a continuous variation of the vehicle and avoids an unexpected rise of the vehicle on the surface. This process is also more reliable than static weighing.

During steps 100 and 300, the density of the underwater vehicle 1 is varied by varying its constant volume mass of the underwater vehicle and / or by modifying its constant mass volume of the underwater vehicle.

The change in the density of the vehicle during step 300, that is to say the variation of mass or volume of the vehicle during step 300, depends on the buoyancy of the vehicle when the crossing of the threshold is detected. .

The variation of the density during step 300 depends on the distance threshold SD and the target buoyancy Fc.

Advantageously, the method is implemented so that the vehicle 1 has a predetermined buoyancy during the detection of crossing the threshold, that is to say at the end of the first step 100.

This makes it possible to improve the accuracy of the final buoyancy adjustment of the underwater vehicle 1 and to simplify the process. It is sufficient to determine once only the variation of mass or volume then necessary to reach the target buoyancy during step 300. In other words, the variation of mass or volume necessary to achieve the target buoyancy during step 300 is predetermined.

The variation of the density or mass or volume during step 300 is predetermined. It depends on the buoyancy of the vehicle when the crossing of the threshold is detected.

This variation during step 300 therefore depends on the initial conditions and the conditions of realization of step 100. It is the same for the same initial conditions and the conditions of realization of step 100.

The density variation necessary to reach the target buoyancy during step 300 can be obtained beforehand iteratively or by trial and error. For example, the process according to the invention is carried out several times with predetermined initial conditions and predetermined density variation conditions in step 100 and, once the crossing of the threshold is detected and the Step 100 stopped, the volume (or mass) of the vehicle is varied. During different implementations of the method, the volume of different values is varied and each time the final buoyancy is compared with the target buoyancy. This comparison step can be performed by measuring a magnitude representative of the final buoyancy and comparing this value with the value that this magnitude should present for the target buoyancy. This is for example a distance, taken in the vertical direction, of the vehicle relative to a predetermined surface of the liquid. Alternatively, it is possible to determine the volume variation necessary, during step 300, to reach the target buoyancy by varying the volume of the vehicle little by little until reaching the target buoyancy.

The buoyancy of the vehicle at the time of detection of the passage of the distance threshold SD or the stopping of the first step depends on adjustable conditions of variations of the density of the vehicle during step 100 which have an influence on the buoyancy of the underwater vehicle 1 when the crossing of the threshold is detected. For example, if the vehicle 1 has several tanks whose density can be varied independently to vary that of the vehicle, the choice of tank has an influence on the buoyancy of the vehicle when crossing the threshold as the speed of variation the mass or volume of the vehicle (that is, the rate of change of mass or volume of each tank). These parameters are predetermined so that the vehicle 1 has a predetermined buoyancy during the detection of crossing the threshold, that is to say at the end of the first step 100.

Alternatively, variations in mass or volume to be applied to the vehicle during step 300 to achieve the target buoyancy Fc or different target buoyancy can be determined prior to the implementation of the method for different values of these parameters and the target buoyancy and listed in a table as explained previously. The method advantageously comprises, prior to step 300, a step of determining the variation of mass or volume to be applied to the vehicle during step 300 to reach the target buoyancy Fc from the value of at least one parameter, for example by consulting a table.

The parameters may also include a density of the liquid volume. The variation of mass or volume can be determined for several densities. The method may then comprise a step of determining a density of the liquid in which the vehicle is immersed, for example from a salinity measurement of the water obtained from a salinity sensor 35. In a variant, the density is predetermined.

Advantageously, at least one initial condition of implementation of step 100 having an influence on the buoyancy of the underwater vehicle at the time of detection of the threshold is predetermined, such as, for example, the initial longitudinal attitude of the undercarriage. predetermined initial marine, for example zero or of a different value.

The method may then comprise, prior to step 100, a step of adjusting the attitude of the vehicle so that the vehicle has a predetermined longitudinal attitude, if the attitude of the vehicle is different from the predetermined longitudinal attitude.

Alternatively, the change in mass or volume is determined independently of this initial condition.

Advantageously, during the implementation of the method, the speed of the underwater vehicle along the vertical axis is only induced by a variation of its buoyancy by calm sea state.

Advantageously, the vehicle 1 has a substantially zero speed, relative to the liquid in which it is immersed, in a horizontal plane. This makes it possible to avoid the disturbances generated by the hydrodynamic lift on the buoyancy of the vehicle when crossing the threshold and therefore on the final buoyancy of the vehicle.

Advantageously, the initial speed of the vehicle relative to the liquid in which it is immersed is zero.

As shown in the figures, the underwater vehicle 1 may comprise a thruster 22 for propelling the marine vehicle 1. Advantageously, the thruster 22 is stopped throughout the implementation of the buoyancy adjustment method. Alternatively, the vehicle is devoid of propellant.

FIG. 2 shows means 10 for adjusting the buoyancy of the vehicle 1 according to the invention being able to implement the method according to the invention. These means are advantageously configured to implement the steps of the method when a buoyancy adjustment condition is verified.

The vehicle 1 comprises detecting means DET crossing the distance threshold SD to verify if the vehicle exceeds the distance threshold. These means comprise at least one sensor 2, also shown in FIGS. 1a to 1c, capable of measuring a magnitude representative of the distance separating the vehicle from the initial surface along the z axis. This sensor is for example an immersion or pressure sensor. The detection means DET also comprise a comparator COMP making it possible to verify whether a distance of the vehicle 1, with respect to the surface S, determined from this measurement is equal to the distance threshold SD. The sensor 2 is fixed relative to the body 3 of the vehicle 1.

The underwater vehicle 1 comprises an adjustment device REG of the buoyancy of the underwater vehicle 1 for regulating the buoyancy of the underwater vehicle 1.

The adjustment device REG comprises means VAR for varying the density of the vehicle 1 and a control member 26 for controlling these means so as to implement the method according to the invention. Advantageously, the control member is configured to control the VAR means for implementing the method according to the invention.

The means VAR for varying the density comprise at least one reservoir 20 or 21 of variable density, that is to say of variable mass and fixed volume (as in the example of Figures 1 to 1c) and / or at least one tank of variable volume and fixed mass, and means for varying the mass or volume controllable by the control member 26.

The tanks 20, 21 are able to communicate with the medium in which the underwater vehicle is immersed so that liquid in which the underwater vehicle 1 is immersed can circulate between these tanks and the marine environment so as to fill or empty the tanks of this liquid. This medium is for example the marine environment but can be any other liquid. In the rest of the text, reference will be made to the marine environment, but the invention is of course applicable to any other liquid.

The tanks 20, 21 are able to communicate with the marine environment by respective hydraulic circuits 24, 25 which can be opened or closed by respective front and rear valves 22, 23, the circulation of the water from the marine environment to the tanks 20 , 21 (or vice versa) being caused by a pump 29 actuated by an actuator 30, for example, a motor. The actuator 30 and the valves AV and AR are controlled by the control member 26 to vary the masses of the tanks 20 and 21 by varying the volume of water contained in these tanks 20 and 21 (by rejecting the water contained in the tank in the marine environment or vice versa) during the steps 100 and 300. The control member 26 can also make it possible to control the actuator and the valves to vary the conditions of variation of the density (flow rate of the pump, distribution of mass variations between the tanks.) Alternatively, these conditions are fixed.

In this example, the mass of reservoirs varying and remaining fixed volume, buoyancy thrust acting on the underwater vehicle is fixed during the implementation of the process (if we consider that the portion of the vehicle located out of water is negligible when the submarine vehicle floats) while its weight varies.

After detection of the crossing of the distance threshold SD, the weight variation (in Newton) necessary for the buoyancy of the underwater vehicle to reach the target buoyancy Fc is constant and depends on the immersion threshold SD and the buoyancy setpoint Fc . For a reference buoyancy of 10 N and a buoyancy of the submarine vehicle 1 of -15 N at the detection of the crossing of the threshold, the variation of weight that the underwater vehicle to achieve the set buoyancy is 25 Newton.

It is then necessary to vary the mass of the tanks of Dm = DP / g = 25 / 9.81 = 2, 548 kg, where g is the acceleration of gravity (9.81 ms ² ). This represents a variation in volume of water DV = Dm / d where d is the density of the liquid in which the underwater vehicle is immersed. In the case of seawater, d = 1.025 kg / L. Then DV = 2.548 / 1.025 = 2.486 L.

This means that 2,486 L of seawater must be removed from the tanks to lighten the vehicle so that the buoyancy is set.

On the non-limiting embodiment of the figures, the tanks 20 and 21 are spaced along an axis x of the underwater vehicle 1 which is, in the nonlimiting example of the figures, a longitudinal axis according to which the underwater vehicle extends longitudinally. The two tanks 20, 21 are then placed each close to one end of the underwater vehicle 1. The tank 21 is placed near the front end AV and the tank 20 of the rear end AR of the vehicle under -marine. Alternatively, the means for varying the buoyancy comprise a single tank or more than two tanks. The vehicle is intended to move mainly along the longitudinal axis in the direction of the rear end AR towards the front end AV.

Alternatively or additionally, the means VAR for varying the density comprise at least one so-called external reservoir of variable volume arranged so that a variation in the volume of the reservoir causes a change in the volume of the underwater vehicle 1. This tank for example with an internal tank disposed inside the body of the underwater vehicle via a valve so as to allow a fluid to pass from one of the tanks to another or block the passage of this fluid between the two tanks, a pump causing the circulation of the fluid via the valve. An actuator, for example a motor, is provided to actuate the pump. The valve and the pump are controlled by a controller receiving measurements from an immersion sensor for measuring an immersion of the underwater vehicle and controlling the valve to vary the volume of the external reservoir so that the vehicle submarine has a set immersion received by the controller. This solution causes less corrosion and reliability problems than the previous solution at the expense of the vehicle submarine. Two tanks may be provided, one at each longitudinal end of the underwater vehicle.

In this case, the weight of the underwater vehicle is constant but the Archimedes thrust varies during the implementation of the method. For a reference buoyancy of 10 N and a buoyancy of the underwater vehicle of -15 N at the initiation of the step 200, the Archimedes DA thrust variation which the underwater vehicle must undergo to reach the target buoyancy is of 25 Newton. It is therefore necessary to increase the volume of the submarine vehicle by DV = DA / (g ^* d) = 25 / (9.81 ^* 1.025) = 2.486 L.

The control member 26 triggers the implementation of the method when the condition for adjusting the buoyancy is verified. The buoyancy adjustment condition can be verified when the control member receives a buoyancy adjustment setpoint C. Alternatively, the method comprises a verification step of checking whether the condition of adjusting the buoyancy is verified, this step being implemented by the control member. This step can be performed from a measurement of the density of the liquid. The buoyancy adjustment set point is for example verified when the density of the water passes below or above a certain threshold or for example when a variation of the volume or mass of the underwater vehicle exceeds a certain threshold (for example when seashells have invested the hull of the underwater vehicle or during the installation of new equipment).

Advantageously, during step 100, the density of a single predetermined reservoir is modified, among the two tanks 20 and 21. This makes it possible to obtain a faster dive of the underwater vehicle 1 and therefore, the crossing of the immersion threshold occurs after adding a smaller amount of water than when filling both tanks simultaneously. The process is therefore faster (the amount of water to be withdrawn from the tanks during step 200 is also less important) and requires less energy.

In the embodiment in which the volume of the underwater vehicle 1 is modified during the step 100, it is possible to modify the volume of only one of the two variable-volume tanks located at one end of the underwater vehicle so as to make vary the volume of the underwater vehicle only near this end. Advantageously, the reservoir whose density is varied during step 100 is the reservoir 20 located near an end (here AR) opposite another longitudinal end AV of the vehicle near which are arranged a sensor or a vehicle radio wave transmitter for use when the sensor or detector is emerging for the vehicle to communicate with a sensor / detector outside the vehicle. This helps to maintain a longer communication of the vehicle with the outside when it comes to dive.

Alternatively, during step 100, the density of the tanks is changed according to a predetermined order of the tanks. For example, the reservoir 21 and the reservoir 20 are first filled when the reservoir 21 is filled.

The invention also relates to a balancing method comprising the buoyancy adjustment method described above and a step of adjusting the longitudinal attitude so that the vehicle has, at the end of the process, a longitudinal pitch attitude. .

For this purpose, the underwater vehicle 1 advantageously comprises means for adjusting the longitudinal attitude of the body 11 of the underwater vehicle 10.

These means for adjusting the longitudinal attitude of the body 11 comprise means for varying the longitudinal attitude of the body of the underwater vehicle comprising, in the nonlimiting example of Figure 2, the two tanks 20, 21 spaced according to the longitudinal axis x and placed respectively close to the rear end AR and the front end AV of the body 11. The means for varying the longitudinal attitude of the body 10 comprise a hydraulic circuit 36 through which the tanks 21 communicate with each other. one with the other so that the passage of a fluid from one to the other is possible via a valve 37 that can close the hydraulic circuit 36 or open to allow or not this fluid communication. A second pump 38 circulates the liquid between the two tanks via the valve 37 and a second associated actuator 39 for actuating the pump 38.

Alternatively, the same pump can be used for the variation of the longitudinal attitude and the buoyancy. A distributor or one or more additional valves are then provided to connect the pump to one of the two hydraulic circuits. The distributor or each valve is controlled by means of the control member.

The means for adjusting the longitudinal attitude also comprise a control member making it possible to control the means making it possible to vary the longitudinal attitude as a function of a longitudinal attitude of reference and of measurements of a attitude sensor 40, allowing measuring the longitudinal attitude of the underwater vehicle, comprising for example immersion sensors disposed at two respective longitudinal ends of the underwater vehicle or a gravity sensor measuring the verticality of the underwater vehicle or an inertial unit. This control member is the control member 26 of the buoyancy control means in Figure 2 but may be another control member.

Adjusting the buoyancy and the longitudinal attitude by the same tanks as shown in the figure allows pooling these means which limits the volume dedicated to these settings and the number of elements dedicated to these settings.

The means for adjusting the longitudinal attitude are advantageously configured so that the step of adjusting the longitudinal attitude of the underwater vehicle consists of transferring water (or other liquid) from a reservoir arranged near the one end of the underwater vehicle, for example the tank 21, to the other tank disposed near the other longitudinal end of the underwater vehicle, for example the tank 20. Thus the buoyancy is not changed, only the plate varies.

Other types of controllable internal means can be used to vary the attitude of the underwater vehicle such as moving masses in translations along the x axis, an example of which is described in document GB 2 335 888, but this system requires an additional and dedicated actuator.

Alternatively, the tanks 20, 21 are replaced by variable volume tanks as described above. Alternatively, the vehicle comprises both types of tanks.

Each controller and the comparator may each comprise one or more dedicated electronic circuits or a general purpose circuit. Each electronic circuit may comprise a machine for reprogrammable calculation (a processor or a microcontroller for example) and / or a computer executing a program comprising a sequence of instructions and / or a dedicated calculation machine (for example a set of logic gates such as an FPGA, a DSP or an ASIC , or any other hardware module).

Claims

A method of adjusting the buoyancy of a submarine vehicle (1) substantially having a predetermined target buoyancy Fc when immersed in a liquid volume delimited by a first surface and a second surface, along a vertical axis (z), the method comprising:

from an initial buoyancy of the vehicle holding the vehicle at the first surface (S), a first step (100) of modifying the density of the vehicle (1) so that it approaches the second surface the first step being carried out until a second step (200) for detecting the crossing by the vehicle (1) of a predetermined non-zero distance threshold (SD) with respect to the first surface (S), along the vertical axis, the first step being implemented so that the vehicle has, when crossing the threshold, a predetermined buoyancy during the detection of crossing the threshold, and a third step (300) for modifying the mass the volume of the vehicle (1) until the vehicle has substantially the target buoyancy, the variation of the density in the third step being predetermined,

the target buoyancy being of the same sign as the initial buoyancy and of absolute value less than the absolute value of the initial buoyancy.

2. Method according to the preceding claim, wherein during the implementation of the method, the vehicle moves, along the vertical axis, only under the effect of a variation of its buoyancy.

A method according to any one of the preceding claims, wherein the first surface is the liquid surface and the initial buoyancy is positive, the first density modifying step being a step of increasing the density of the vehicle. , the distance threshold being an immersion threshold.

4. A method according to any of claims 1 to 2, wherein the first surface is a bottom of the liquid volume, the initial buoyancy is negative, the first density modifying step being a step of reducing the density, the distance threshold being an altitude threshold with respect to the first surface.

5. A method according to any one of the preceding claims, wherein during the first step (100) and in the third step (300), the vehicle mass is varied at constant volume of the underwater vehicle, and / or the volume of the constant mass constant-weight marine vehicle of the underwater vehicle is varied.

6. Method according to any one of the preceding claims, wherein the vehicle (1) comprises a first variable density tank, the density variation of which varies the density of the vehicle (1), arranged in the vicinity of a first longitudinal end of the vehicle (1), and a second variable density tank whose density variation varies the density of the vehicle (1) and disposed near a second longitudinal end of the vehicle (1), wherein, in the first step (100), the density of a single predetermined reservoir taken from the first reservoir and the second reservoir is varied.

7. A balancing method comprising the buoyancy control method according to any one of the preceding claims followed by a step of according to any one of the preceding claims and a step of adjusting the longitudinal attitude of the vehicle (1 ).

8. Device for regulating the buoyancy of a submarine including buoyancy variation means making it possible to vary the density of the underwater vehicle and at least one sensor making it possible to detect the crossing by the vehicle of a threshold of predetermined non-zero distance with respect to a first surface delimiting, in a vertical direction, the volume of a liquid in which the vehicle is immersed, the buoyancy adjustment device being configured to implement a method comprising the following steps when a buoyancy adjustment condition is verified:

from an initial buoyancy maintaining the vehicle at the first surface; a first step of modifying the mass the volume of the vehicle by the buoyancy variation means, so that the vehicle approaches a second surface defining the volume of liquid in the vertical direction, the first step being implemented to a second step (200) detecting, by the sensor, the crossing of the distance threshold by the vehicle, the first step being implemented so that the vehicle has a predetermined buoyancy during the detection of crossing the threshold,

then a third step (300) of modifying the density of the vehicle (1), by the means of variation of the buoyancy, until the vehicle has substantially the target buoyancy, the variation of the density during the third step being predetermined,

9. Underwater vehicle comprising the buoyancy adjustment device according to the invention.