FR3161040A1 - METHOD AND SYSTEM FOR REDUCING AERODYNAMIC LOADS EXERCISED ON AN AIRCRAFT BY ATMOSPHERIC TURBULENCE. - Google Patents

Abstract

The present disclosure relates to a system and method for reducing aerodynamic loads exerted on an aircraft (100) in flight by atmospheric turbulence. The method comprises detecting atmospheric turbulence by: receiving information representative of a current vertical wind speed (u(t)) and comparing it to a predetermined threshold (S), and determining the presence of atmospheric turbulence if said speed is greater than this threshold (S). The method comprises, when said speed is greater than the predetermined threshold (S), reducing aerodynamic loads by: estimating a first derivative of said current vertical wind speed (u(t)), and calculating and providing, from at least the first derivative, a control surface command to deflect at least one control surface. It is thus possible to reduce the aerodynamic load factor and achieve a gain in the structural mass of the aircraft while improving passenger comfort. Figure to be published with the abstract: Fig. 2

Description

METHOD AND SYSTEM FOR REDUCING AERODYNAMIC LOADS EXERCISED ON AN AIRCRAFT BY ATMOSPHERIC TURBULENCE.

The present invention relates to a method and a system for reducing loads exerted on an aircraft by atmospheric turbulence, and in particular gusts of wind.

STATE OF PRIOR ART

During flight, aircraft often encounter atmospheric turbulence (e.g., wind shear, wind gradients, free air turbulence, wake turbulence, air pockets, etc.). Atmospheric turbulence can include vertical and horizontal wind shear or wind gusts.

Wind gusts generate aerodynamic loads on the aircraft structure, particularly the wing structure (i.e., the aircraft’s wings). In particular, wind gusts cause mechanical stress on the aircraft structure, as well as discomfort for passengers (e.g., buffeting felt when the aircraft passes through a wind gust zone) and a reduction in its aerodynamic performance in flight.

For economic and environmental reasons, reducing fuel consumption is a factor that must be taken into account when designing aircraft. To achieve this, the aircraft structure must be able to withstand the aerodynamic loads exerted by gusts of wind while being light enough to limit fuel consumption.

One solution to achieve a compromise between reducing the load factor (i.e., increasing the resistance of the aircraft structure to wind gusts) and reducing the aircraft weight is the application of Gust Loads Alleviation (GLA) strategies. One strategy for alleviating wind loads consists of using aircraft sensors to provide control commands allowing the deflection of aircraft control surfaces (e.g., internal or external ailerons, elevators) taking into account wind conditions. More specifically, sensors (e.g., air data sensors, accelerometers, etc.) placed on the aircraft body or on its wings detect wind conditions and provide information on the aerodynamic loads exerted on the aircraft. This information is then transmitted to an aircraft avionics system to trigger the deflection of the control surfaces at a specific angle depending in particular on wind conditions. This makes it possible to create the aerodynamic forces and moments necessary to mitigate the additional aerodynamic load induced by wind gusts. The control surfaces are then used as control surfaces to mitigate the aerodynamic loads induced by wind gusts.

Control surface orders for wind gust load alleviation can be established according to various well-known control surface control laws. For example, a control surface control law is known based on an estimation of the wind angle of attack using an angle of attack probe placed at the nose of the aircraft. An elevator and aileron order is then developed based on the wind angle of attack to reduce wind gust loads on the aircraft, mainly at the wing root of the aircraft.

However, it is desirable to provide a solution that improves the effectiveness of existing wind gust load alleviation strategies. In particular, it is desirable to provide a wind gust load alleviation strategy that optimizes load factor reduction and improves passenger comfort.

There is provided herein a method for reducing aerodynamic loads exerted on an aircraft in flight by atmospheric turbulence, said method being implemented by an aerodynamic load reduction system in the form of electronic circuitry, said method comprising:
(i) a detection of atmospheric turbulence, and
(ii) a reduction in aerodynamic loads,
said detection comprising the following steps:
- receive information from a measuring system representing a current vertical wind speed,
- compare the said current vertical wind speed to a predetermined threshold,
- determine the presence of atmospheric turbulence if said current vertical wind speed is greater than a predetermined threshold,
said reduction of aerodynamic loads comprising:
- estimate a first derivative of said current vertical wind speed,
- calculate a steering order at least from the first derivative of said current vertical wind speed,
- provide said control command for a deflection of at least one control surface of the aircraft according to said control command,
said reduction of aerodynamic loads being carried out when said current vertical wind speed is greater than the predetermined threshold, otherwise said detection is repeated.

Advantageously, it is possible to reduce the aerodynamic load factor exerted on the aircraft. By thus reducing the load factor, it is possible to obtain a gain on the structural mass of the aircraft, but also to improve the comfort of the passengers when the aircraft passes through a zone of atmospheric turbulence.

According to a particular embodiment, said steering order is expressed according to the following equation:
With :
- K _wind representing a gain for an optimization of the reduction of the wind gust load factor;
- corresponding to a moment gradient in effect of variation of pitch speed of the complete aircraft expressed at an aerodynamic focus in effect of incidence;
- corresponding to a moment gradient in effect of pitch speed of the complete aircraft expressed at the aerodynamic focus in effect of incidence;
- corresponding to a gradient of moment in effect of variation of incidence of the complete aircraft expressed at the aerodynamic focus in effect of incidence;
- corresponding to a gradient of moment in effect of steering of said at least one control surface of the complete aircraft expressed at the aerodynamic focus in effect of incidence;
- V representing a real speed of the aircraft;
- corresponding to a reference length;
- representing a travel time of the wind from the nose of the aircraft to the aerodynamic focus in effect of incidence;
- u(t) corresponding to the current vertical wind speed at time t ;
- corresponding to the first derivative of the current vertical wind speed u(t);
- corresponding to a second derivative of the current vertical wind speed u(t).

According to a particular embodiment, the gain K _wind is expressed according to the following equation:
and the optimized steering order is then expressed according to the following equation:
.

According to a particular embodiment, said detection of the presence of atmospheric turbulence and said reduction of aerodynamic loads are repeated according to a predetermined frequency ( Δt ).

According to a particular embodiment, the measurement system comprises a light detection and telemetry system configured to obtain said information representative of the current vertical wind speed.

According to a particular embodiment, the measurement system comprises a set of incidence probes configured to measure an angle of incidence of the wind from which said information representative of the current speed of the vertical wind is obtained.

Also proposed herein is a system for reducing aerodynamic loads exerted on an aircraft in flight by atmospheric turbulence, said system comprising electronic circuitry configured to:
(i) perform atmospheric turbulence detection, and
(ii) implement a reduction in aerodynamic loads,
said detection comprising the following steps:
- receive information from a measuring system representing a current vertical wind speed,
- compare the said current vertical wind speed to a predetermined threshold,
- determine the presence of atmospheric turbulence if said current vertical wind speed is greater than a predetermined threshold,
said reduction of aerodynamic loads comprising:
- estimate a first derivative of said current vertical wind speed,
- calculate a steering order at least from the first derivative of said current vertical wind speed,
- provide said control command for a deflection of at least one control surface of the aircraft according to said control command,
said reduction of aerodynamic loads being carried out when said current vertical wind speed is greater than the predetermined threshold, otherwise said detection is repeated.

Also provided herein is an aircraft comprising an aerodynamic load reduction system as described above according to one embodiment.

Also provided is a computer program product, comprising instructions causing a processor to execute the method described above according to any of its embodiments, when said instructions are executed by the processor. Also provided is a storage medium storing such instructions.

The above-mentioned features of the invention, as well as others, will appear more clearly on reading the following description of at least one exemplary embodiment, said description being made in relation to the attached drawings, among which:

FIG. 1 schematically illustrates, in side view, an aircraft equipped with an aerodynamic load reduction system, according to one embodiment;

FIG. 2 schematically illustrates the aerodynamic load reduction system, according to one embodiment;

FIG. 3 schematically illustrates an example of a hardware platform for implementing, in the form of electronic circuitry, the aerodynamic load reduction system according to one embodiment; and

FIG. 4 schematically illustrates the steps of a method for reducing aerodynamic loads exerted on an aircraft, executed by the aerodynamic load reduction system, according to one embodiment.

DETAILED PRESENTATION OF IMPLEMENTATION METHODS

The general principle of the following disclosure relates to a method and a system for reducing aerodynamic loads exerted on an aircraft by atmospheric turbulence, and in particular wind gusts. For this, information representative of the vertical wind speed is obtained in real time from a measurement system comprising sensors positioned on the aircraft. This information is then transmitted to the aerodynamic load reduction system for calculating a control command from a first derivative and, optionally, a second derivative of the vertical wind speed. This control command thus calculated allows real-time deflection of the control surfaces (e.g., elevators and/or ailerons) to reduce the aerodynamic loads by a “nose-down” or “pitch-up” action of the aircraft to counter the effects of the gust.

There FIG. 1 schematically illustrates, in side view, an aircraft 100 equipped with an aerodynamic load reduction system 101, according to one embodiment.

Depending on the method of implementation of the FIG. 1 , the aerodynamic load reduction system 101 (also subsequently called load reduction system 101) is electronic equipment on board the aircraft 100. For example, the load reduction system 101 is part of an electronic circuit of the avionics of the aircraft 100. For example, the load reduction system 101 is integrated into a flight control computer, denoted CCV.

The load reduction system 101 is schematically and generally illustrated in the FIG. 2 , according to one embodiment.

The load reduction system 101 is configured to receive information representative of the vertical wind speed. This information is transmitted by a measurement system SYS_MES of the aircraft 100 comprising sensors configured to measure wind conditions (e.g., vertical wind speed, angle of incidence, etc.). In one example, the sensors are a set of incidence probes positioned at the nose of the aircraft 100 and/or a light detection and ranging system, also called LIDAR (“ Light Detection and Ranging ” in English).

The load reduction system 101 is further configured to estimate a first derivative and, optionally, a second derivative of the vertical wind speed obtained from said information to calculate a control command. The load reduction system 101 is further configured to provide this control command to the flight control controller CCV. The flight control controller CCV is configured to control the movement, via actuators (not shown in the FIG. 2 ), control surfaces of the aircraft 100, such as the two external ailerons (denoted SC1 and SC2), the two internal ailerons (denoted SC3 and SC4) and/or the two elevators (denoted SC5 and SC6). In particular, the flight control controller CCV is configured to transmit the control order calculated by the load reduction system 101 to the actuators which then deflect one or the other, or a combination of the control surfaces SC1 to SC6 according to a particular angle.

The load reduction system 101 is also configured to receive various other information from other avionics systems of the aircraft 100 (not shown in the FIG. 2 ). This information is, for example, information concerning the altitude of the aircraft 100, the actual speed of the aircraft 100 (i.e., speed of the aircraft relative to the ground), etc.

There FIG. 3 schematically illustrates an example of a hardware platform making it possible to implement, in the form of electronic circuitry, the load reduction system 101, according to one embodiment.

The hardware platform comprises, connected by a communication bus 310, a processor or CPU ( Central Processing Unit ) 301; a random access memory (RAM) 302; a read-only memory 303, for example of the ROM ( Read Only Memory ) or EEPROM (Electrically Erasable Programmable ROM ) type, such as a Flash memory; a storage unit, such as a hard disk (HDD) 304, or a storage media reader, such as an SD ( Secure Digital ) card reader; and a COM interface manager 305.

The COM interface manager 305 allows the load reduction system 101 to interact with other avionics systems of the aircraft 100 such as for example the SYS_MES measurement system.

The processor 301 is capable of executing instructions loaded into the RAM 302 from the ROM 303, an external memory, a storage medium (such as an SD card), or a communications network. When the hardware platform is powered on, the processor 301 is capable of reading instructions from the RAM 302 and executing them. These instructions form a computer program causing the implementation, by the processor 301, of all or part of the steps or methods or more broadly of the operating sequences of the aircraft described in the present description.

All or part of the steps, methods and operations described herein may thus be implemented in software form by executing a set of instructions by a programmable machine, for example a DSP ( Digital Signal Processor ) type processor or a microcontroller, or be implemented in hardware form by a machine or a dedicated electronic component ( chip ) or a set of dedicated electronic components ( chipset ), for example an FPGA ( Field Programmable Gate Array ) or ASIC ( Application Specific Integrated Circuit ) component. In general, the load reduction system 101 comprises electronic circuitry adapted and configured to implement all or part of the operations, methods and steps described herein.

It is presented in connection with the FIG. 4 , in the form of a diagram the steps of a method for reducing aerodynamic loads exerted on the aircraft 100 by atmospheric turbulence, such as gusts of wind, according to one embodiment. All or part of this method for reducing aerodynamic loads is implemented by the load reduction system 101 described above.

The process of reducing aerodynamic loads includes:
- a detection of atmospheric turbulence, such as gusts of wind. This detection of atmospheric turbulence comprises steps 401 and 402;
- a reduction of aerodynamic loads comprising steps 403 to 405.

From the start of the flight of the aircraft 100, during step 401, the load reduction system 101 receives, in real time, from a measurement system SYS_MES information representative of the current vertical wind speed, noted u( t ), at time t in a particular geographical area. This particular geographical area corresponds to a measurement range area of the sensors of the measurement system SYS_MES.

According to one embodiment, the measurement system SYS_MES transmits to the load reduction system 101 the information representative of the current vertical wind speed u( t ) according to a predetermined frequency. In one example, this frequency is less than 500 ms.

In one embodiment, the measurement system SYS_MES comprises a plurality of sensors corresponding to a set of incidence probes positioned at the nose of the aircraft 100. Atmospheric turbulence, and in particular a gust of wind, has the effect of varying the angle of incidence measurement of these incidence probes. The current vertical wind speed u( t ) is then determined by a wind estimating device, also included in the measurement system SYS_MES, from the angle of incidence measured at time t by the incidence probes and the actual speed of the aircraft 100.

According to this embodiment, the geographic area corresponds to the measurement range area of the incidence probes, i.e. the area corresponding to the current position of the aircraft 100 during flight.

Alternatively or additionally, the SYS_MES measurement system comprises a sensor corresponding to a LIDAR which directly measures the current vertical wind speed u( t ) as described in the Applicant's patent application FR2 883 983. In particular, the LIDAR directly measures the current vertical wind speed u( t ) in a geographical area corresponding to a measurement range area located on the trajectory of the aircraft 100 in flight, upstream of the current position of the aircraft 100, in the direction of movement thereof. It is thus possible to anticipate the aerodynamic load which will be exerted on the aircraft 100 by the gusts of wind present in this geographical area when the aircraft 100 has reached said area.

The load reduction system 101 also obtains from other avionics systems of the aircraft 100, information representative of the actual speed of the aircraft 100, denoted V.

During a step 402, the load reduction system 101 compares the value of the current vertical wind speed u( t ) with a predetermined threshold, denoted S. If the value of the current vertical wind speed u( t ) is greater than the predetermined threshold S, then the load reduction system 101 repeats step 401 (step 402, with result “no”), otherwise, a step 403 is carried out (step 402, with result “yes”). The application of this threshold makes it possible to avoid any triggering of an aerodynamic load reduction for weak wind gusts.

When reducing aerodynamic loads, in a step 403, the load reduction system 101 estimates a first derivative noted and, optionally a second derivative noted of the current vertical wind speed u( t ).

Indeed, according to one embodiment, it is possible to consider the second derivative of the current vertical wind speed u( t ) as negligible (i.e., approximation according to which the second derivative is substantially zero) in order to simplify the calculation of equation EQ1 below.

The load reduction system 101 calculates during a step 404, a control command, providing a steering angle of a control surface. This control command is calculated from the first derivative and advantageously of the second derivative of the current wind speed u( t ) in order to deflect one or the other or a combination of the control surfaces SC1 to SC6 by an appropriate deflection angle to reduce the aerodynamic loads. Furthermore, the deflection angle is adapted to the nature of the control surface. Indeed, the control order depends on the nature of the control surface, that is to say it is different if the control surface corresponds to an internal aileron, or an external aileron or an elevator.

This steering order, noted is expressed according to equation EQ1 below:

with :

representing a gain allowing an optimization of the reduction of the wind gust load factor;

corresponding to the gradient of the “moment in effect of variation of pitch speed” of the complete aircraft 100 expressed at the “aerodynamic focus in effect of incidence”. The aerodynamic focus in effect of incidence (or “ neutral point ” in English) being the point of reduction of the forces in effects of incidence.
corresponding to the gradient of “moment in effect of pitch speed” of the complete aircraft 100 expressed at the “aerodynamic focus in effect of incidence”, without dimension.
corresponding to the gradient of “moment in effect of variation of incidence” of the complete aircraft 100 expressed at the “aerodynamic focus in effect of incidence”, without dimension.
corresponding to the gradient of “moment in effect of deflection of a given control surface” of the complete aircraft 100 expressed at the “aerodynamic focus in effect of incidence”, without dimension.
V representing the actual speed of aircraft 100, that is to say the speed of aircraft 100 relative to the ground and expressed in meters per second.
corresponding to the reference length. This parameter is classically used in the equations of flight mechanics and is expressed in meters.
representing the travel time of the wind from the nose of the aircraft 100 to the “aerodynamic focus of incidence” and is expressed in seconds.
The term u( t ) is the vertical wind speed at time t , expressed in meters per second.
The term is the first derivative of the vertical wind speed u( t ). This is the vertical wind expressed in meters per second squared, at time t .
The term is the second derivative of the vertical wind speed u( t ). This is the vertical wind expressed in meters per second cubed, at time t .

This equation EQ1 of the steering order as a function of the first derivative and, optionally, the second derivative of the vertical wind speed at time t results from a coupling between a lift equation and aerodynamic moments of a quasi-static linear model of flight mechanics. By performing this coupling, this makes it possible to arrive at a single equation expressed as a function of the vertical wind speed at time t as input data and the control surfaces (i.e., elevator and/or internal ailerons and/or external ailerons). It turns out that by performing this coupling, the direct component of the vertical wind disappears, leaving only the components corresponding to the first derivative and, where appropriate, to the second derivative of the vertical wind speed at time t . Indeed, as described above, in a particular embodiment, it is possible to approximate the second derivative and to consider it as negligible.

In order to optimize the reduction of the wind gust load factor and thus improve passenger comfort, the gain K _wind is applied to equation EQ1 above. Indeed, by writing the expression of the load factor with respect to the vertical wind speed, it is possible to demonstrate that there is a particular gain or an optimal gain, which makes it possible to cancel the static gain of the transfer function with respect to the vertical wind speed at time t , which has the effect of reducing the load factor at the center of gravity of the aircraft 100.

In a particular embodiment, the reduction of the wind gust load factor is optimized in order to improve passenger comfort. For this, the gain K _wind must be greater than or equal to one. Thus, in order to minimize the maximum value of the wind gust load factor in the low frequency domain of the wind gusts, the gain K _wind is expressed according to the following equation EQ2:

Thus, the optimized steering order, noted can be expressed according to equation EQ3 below:

Initial simulations show a significant effect on the reduction of the wind gust load factor at the center of gravity of the aircraft 100, of the order of 30% for discrete gusts. Using the expression for the optimal gain K _wind mentioned above, this reduction goes up to 70%, still for discrete gusts, but with an increase in the control surface order (i.e., an increase in the absolute value of the steering angle of the control surfaces SC1 to SC6).

During a step 405, the load reduction system 101 provides the flight control computer CCV in real time with the control command calculated according to the equation EQ1 or the optimized control command calculated according to the equation EQ3. The flight control computer CCV then controls actuators of the control surfaces SC1 to SC6 to deflect one or the other or a combination of these control surfaces SC1 to SC6 according to a deflection angle depending on the current vertical wind speed u( t ) and the nature of the control surface to be deflected.

In a particular embodiment, when the measurement system SYS_MES comprises a LIDAR, it is possible for the load reduction system 101 to transmit the steering command before the aircraft 100 encounters wind gusts detected in the geographical area located on the trajectory of the aircraft 100, upstream of the aircraft 100 in the direction of its movement. This steering command is sent at a predetermined activation time taking into account the current position, the mass and the inertia of the aircraft 100. In addition, this predetermined activation time also takes into account the transmission delays within the various avionics systems of the aircraft 100, so that the steering command does not produce the opposite effect to that sought, namely the reduction of the load factor. This makes it possible to perform steering of one or the other or a combination of the control surfaces SC1 to SC6 in an anticipated and smoother manner, which improves passenger comfort.

According to one embodiment, at the end of step 405, the load reduction system 101 repeats the detection of atmospheric turbulence, then, if necessary, the reduction of atmospheric loads, as described previously. In other words, the calculation of the control order is carried out iteratively by a control loop of predetermined frequency, noted Δt (for example Δt < 500 ms). Thus, at each of the instants t ₀ , t ₀ + Δt , t ₀ + 2 Δt , t ₀ + 3 Δt … the load reduction system 101 calculates the control orders. When the vertical wind speed u( t ) is lower than the predetermined threshold S, then the control order making it possible to counter the gust is zero (i.e., no deflection of the control surfaces SC1 to SC6).

Claims (10)

A method of reducing aerodynamic loads exerted on an aircraft (100) in flight by atmospheric turbulence, said method being implemented by an aerodynamic load reduction system (101) in the form of electronic circuitry, said method comprising:
(i) a detection of atmospheric turbulence, and
(ii) a reduction in aerodynamic loads,
said detection comprising the following steps:
- receive information from a measuring system (SYS_MES) representing a current vertical wind speed (u( t )),
- compare said current vertical wind speed (u( t )) to a predetermined threshold (S),
- determine the presence of atmospheric turbulence if said current vertical wind speed (u( t )) is greater than a predetermined threshold (S),
said reduction of aerodynamic loads comprising:
- estimate a first derivative of said current vertical wind speed (u( t )),
- calculate a steering order at least from the first derivative of said current vertical wind speed (u( t )),
- providing said control command for a deflection of at least one control surface of the aircraft (100) as a function of said control command,
said reduction of aerodynamic loads being carried out when said current vertical wind speed (u( t )) is greater than the predetermined threshold (S), otherwise said detection is repeated. The method of claim 1, wherein said steering order is expressed according to the following equation (EQ1):
With :
- K _wind representing a gain for an optimization of the reduction of the wind gust load factor;
- corresponding to a moment gradient in effect of variation of pitch speed of the aircraft (100) complete expressed at an aerodynamic focus in effect of incidence;
- corresponding to a moment gradient in effect of pitch speed of the aircraft (100) complete expressed at the aerodynamic focus in effect of incidence;
- corresponding to a moment gradient in effect of variation of incidence of the aircraft (100) complete expressed at the aerodynamic focus in effect of incidence;
- corresponding to a gradient of moment in effect of steering of said at least one control surface of the complete aircraft (100) expressed at the aerodynamic focus in effect of incidence;
- V representing a real speed of the aircraft (100);
- corresponding to a reference length;
- representing a travel time of the wind from a nose of the aircraft (100) to the aerodynamic focus in effect of incidence;
- u(t) corresponding to the current vertical wind speed at time t ;
- corresponding to the first derivative of the current vertical wind speed u(t);
- corresponding to a second derivative of the current vertical wind speed u(t). The method of claim 2, wherein the gain K _wind is expressed according to the following equation (EQ2):
and the optimized steering order is then expressed according to the following equation (EQ3):
. A method according to any one of claims 1 to 3, wherein said detection of the presence of atmospheric turbulence and said reduction of aerodynamic loads are repeated at a predetermined frequency ( Δt ). Method according to any one of claims 1 to 4, wherein said measuring system (SYS_MES) comprises a light detection and ranging system (LIDAR) configured to obtain said information representative of the current vertical wind speed (u( t )). Method according to any one of claims 1 to 5, wherein said measuring system (SYS_MES) comprises a set of incidence probes configured to measure an angle of incidence of the wind from which said information representative of the current speed of the vertical wind (u( t )) is obtained. A system for reducing aerodynamic loads exerted on an aircraft (100) in flight by atmospheric turbulence, said system comprising electronic circuitry configured to:
(i) perform atmospheric turbulence detection, and
(ii) implement a reduction in aerodynamic loads,
said detection comprising the following steps:
- receive information from a measuring system (SYS_MES) representing a current vertical wind speed (u( t )),
- compare said current vertical wind speed (u( t )) to a predetermined threshold (S),
- determine the presence of atmospheric turbulence if said current vertical wind speed (u( t )) is greater than a predetermined threshold (S),
said reduction of aerodynamic loads comprising:
- estimate a first derivative of said current vertical wind speed (u( t )),
- calculate a steering order at least from the first derivative of said current vertical wind speed (u( t )),
- providing said control command for a deflection of a control surface of the aircraft (100) as a function of said control command,
said reduction of aerodynamic loads being carried out when said current vertical wind speed (u( t )) is greater than the predetermined threshold (S), otherwise said detection is repeated. Aircraft (100) comprising an aerodynamic load reduction system (101) according to claim 7. Computer program product, comprising instructions causing the execution, by a processor, of the method according to any one of claims 1 to 6, when said instructions are executed by the processor. Storage medium, storing a computer program comprising instructions causing the execution, by a processor, of the method according to any one of claims 1 to 6, when said instructions are read and executed by the processor.