METHOD FOR MAPPING AN INSPECTION AREA COMPRISING A MOVING FLUID MEDIUM, DEVICE, COMPUTER PROGRAM AND ASSOCIATED STORAGE MEDIA
The method simulates acoustic wave propagation in a virtual inspection area with a moving fluid medium to accurately map acoustic reflectors, addressing the limitations of existing methods in dynamic environments.
Patent Information
- Authority / Receiving Office
- FR · FR
- Patent Type
- Applications
- Current Assignee / Owner
- COMMISSARIAT A LENERGIE ATOMIQUE ET AUX ENERGIES ALTERNATIVES
- Filing Date
- 2024-12-19
- Publication Date
- 2026-06-26
AI Technical Summary
Existing acoustic mapping methods are ineffective in inspection areas containing moving fluid media due to the assumption of a static or low-speed environment, leading to inaccurate determination of acoustic reflectors.
A method involving the simulation of acoustic wave propagation in a virtual inspection area with a moving fluid medium, using time-reversed simulations to generate a topological energy map that compensates for fluid flow, allowing accurate mapping of acoustic reflectors regardless of fluid speed.
Enables accurate mapping of acoustic reflectors in areas with high-speed fluid media by simulating wave propagation and convolution, providing precise determination of reflector positions and shapes.
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Abstract
Description
Title of the invention: METHOD FOR MAPPING AN INSPECTION AREA COMPRISING A MOVING FLUID MEDIUM, DEVICE, COMPUTER PROGRAM AND ASSOCIATED STORAGE MEDIA technical field
[0001] The technical field of the invention relates to a method for mapping an inspection area comprising a moving fluid medium. The technical field also relates to a device, a computer program, and a storage medium for implementing such a method.
[0002] The invention finds particularly advantageous applications in the development of passive heat extraction systems, industrial processes requiring the characterization of fluid flow (detection of leaks, particles or bubbles in the fluid, etc.), and in the medical, geophysical, and nuclear fields. PRIOR TECHNOLOGY
[0003] Acoustic mapping of an inspection area allows visualization of variations in acoustic impedance within that area. This makes it possible to determine, non-destructively, whether a solid part has a defect such as a crack. Acoustic mapping is also commonly used on inspection areas containing a fluid medium, such as a liquid pipeline or the seabed.
[0004] There are two commonly used approaches for performing acoustic mapping. In both cases, an incident acoustic wave is generated in the inspection area and a measurement of the reflected waves is taken. The differences between the two approaches lie in the processing of the incident and reflected waves.
[0005] According to a first approach, a so-called "time-of-flight" calculation between the incident wave and the reflected waves allows for triangulation of the position of each object on which the incident wave has been reflected. This approach is also called "delay and sum" in English, commonly abbreviated "DaS". The accuracy of the position or shape of the objects can be well determined. However, it is sometimes necessary to send several inspection waves (and therefore reduce the acquisition rate) to obtain a good signal-to-noise ratio. DaS methods are relatively efficient and are now widely used in non-destructive testing (NDT).
[0006] A second approach, called the "time-reversal" approach, is based on the time and space reciprocity of the equation for the propagation of acoustic waves in a static, infinite, and homogeneous medium. According to this approach, each reflected wave is reversed in time. Thus, each reversed wave corresponds to a wave that backpropagates in the fluid medium, focusing towards the source object of the reflection. This approach therefore makes it possible to determine the exact position and shape of the source object of the reflection.
[0007] The document [“Time domain topological gradient and time reversal analogy: an inverse method for ultrasonic target detection”, N. Dominguez et al., Wave Motion, vol. 42, Issue 1, 2005, pages 31-52] describes a mapping method in an inspection area based on this second approach. Each measured reflected wave is time-reversed and back-propagated in a virtual inspection area.
[0008] The mapped quantity is the topological gradient and accounts for a variation in impedance associated with the presence of an acoustic reflector (such as a hole or a hard object).
[0009] While this mapping method makes it possible to determine the position and shape of objects in the inspection zone, it cannot be applied to an inspection zone containing a moving fluid medium. Indeed, the inspection zone must be static or have a velocity negligible compared to the wave speed. In this way, the propagation of acoustic waves in the inspection zone is considered equivalent to propagation in a static medium.
[0010] This method is therefore not applicable in the case where the inspection area includes a fluid medium in motion with a speed that is not very low compared to the speed of propagation of acoustic waves, or even a fluid medium with a high speed (for example close to the acoustic speed of said fluid medium).
[0011] There is therefore a need to provide a method for mapping an inspection area comprising a moving fluid medium that is neither static nor at very low speed, and that remains accurate even when the fluid medium's speed is high. SUMMARY
[0012] To solve the aforementioned problems, the invention provides a method for mapping an inspection area comprising a moving fluid medium, the method comprising the following steps: a. In the presence of at least one acoustic reflector in the inspection area: i. Generate a first acoustic wave, called the "inspection wave" ", in the inspection area, by means of a first multi-element ultrasonic transducer controlled by a first plurality of electrical control signals; ii. acquire a plurality of electrical signals, called "measurement signals", by means of a second multi-element ultrasonic transducer receiving a second acoustic wave, called "reflected wave", resulting from a reflection of the inspection wave on said at least one acoustic reflector; b. determine a second plurality of control signals from the time-returned measurement signals; c. from a digital model of the inspection area without an acoustic reflector, forming a virtual inspection area comprising a virtual fluid medium in motion: i. simulate the propagation of inspection background in the virtual inspection zone, generated by means of a first virtual multi-element ultrasonic transducer controlled by the first plurality of electrical control signals, so as to obtain a first time-dependent mapping of a first pressure field, called the "direct field"; ii. to simulate the propagation of a third acoustic wave, called a "focusing wave", in the virtual inspection zone, generated by means of a second virtual multi-element ultrasonic transducer controlled by the second plurality of control signals, so as to obtain a second time-dependent mapping of a second pressure field, called an "adjunct field"; and d. temporally convolve the first and second direct and adjoint field maps in order to obtain a topological energy map of the virtual inspection area.
[0013] The process is remarkable in that: a. The simulation of the propagation of the inspection wave in the virtual inspection zone is carried out with the virtual fluid medium exhibiting a velocity field t) where X is a position in the virtual inspection zone and t is time; and in that b. The simulation of the propagation of the focusing wave in the virtual inspection zone is carried out with the virtual fluid medium exhibiting a velocity field _ y(x, -t)-
[0014] The method makes it possible to obtain a topological energy map of the virtual inspection area. By considering the virtual inspection area as representative of the actual inspection area, the method makes it possible to obtain a topological energy map of the actual inspection area.
[0015] Topological energy is a quantity representing the contribution of discontinuities or structural variations in a medium to the acoustic field measured by a probe. It highlights the origin and intensity of acoustic variations (primary or secondary sources). Topological energy differs from the topological gradient (also called the Fréchet derivative), which highlights the areas of greatest probability of variation of a specific acoustic parameter in the medium. Since acoustic sources are generally characterized by breaks in acoustic properties relative to the inspection medium, the two quantities are generally considered to be similar, although they do not measure the same amount.
[0016] The simulations of the inspection wave and focusing wave propagation take into account the flow velocity of the fluid medium. In particular, the focusing wave propagation simulation takes into account the time-reversed velocity of the fluid medium. The simulations thus compensate for the fluid flow, regardless of the flow velocity. Consequently, the determination of the position and shape of the reflectors remains accurate regardless of the fluid medium velocity, even if the latter is close to the acoustic speed of the fluid medium.
[0017] The invention further relates to a device comprising: a. a first multi-element ultrasonic transducer, preferably piezoelectric, configured to generate a first acoustic wave, called the "inspection wave", in an inspection zone from a first plurality of electrical control signals; and b. a second multi-element ultrasonic transducer, preferably piezoelectric, configured to convert a second acoustic wave, called the "reflected wave," into a plurality of electrical signals, called "measurement signals"; and c. a control and processing device configured to implement the steps of the process according to the invention.
[0018] The invention also relates to a computer program comprising instructions which lead the device according to the invention to perform the steps of the process according to the invention.
[0019] The invention finally relates to a computer-readable storage medium on which the computer program according to the invention is recorded. BRIEF DESCRIPTION OF THE FIGURES
[0020] Fig. 1 schematically represents an implementation of a mapping process according to the invention.
[0021] Figs. 2, 3, 4, 5, and 6 schematically represent five examples of steps in the process of Fig. 1.
[0022] Fig. 7 schematically represents an example of a complementary step in the process of Fig. 1.
[0023] Figures [Fig.8] and [Fig.9] represent maps obtained for two modes of implementation of the process of [Fig.1].
[0024] The figures are given by way of example and are not limiting to the invention. They constitute schematic representations of the principle intended to facilitate understanding of the invention and are not necessarily to scale with practical applications. In particular, Figures 1 to 9 are not representative of reality. DETAILED DESCRIPTION
[0025] Before proceeding to a detailed review of embodiments of the invention, optional features that may be used in combination or alternatively are listed below:
[0026] Advantageously, the numerical model of the inspection zone 100' includes an equation describing the propagation of an inspection wave i) and a focusing wave f(x. i) in the virtual fluid medium 110', said equation being self-adjoint.
[0027] An equation is said to be self-adjoint for a scalar product < ' ) for an operator L (allowing the equation in question to be summarized by Lu = S where u is the field considered (a scalar) and S a source term (also a scalar)) if for any two fields u and v, {u - Lv) — (v ■ Lu). The scalar product U ) is preferably the so-called "usual" scalar product, corresponding to the integral over space of the product of quantities.
[0028] For example, the equation describing the wave propagation of inspection and focusing waves (t), f(x. i) in the virtual fluid medium 110' is: 100291 I p'=-^ IhQw) -iv-(pV0)=O
[0030] with [00311 2 =
[0032] with p a velocity potential, $ a quantity derived from the acoustic pressure, P the density of the virtual fluid medium etc the acoustic speed in the fluid medium.
[0033] According to one development, process 200 comprises the additional steps of: a. In the absence of an acoustic reflector 120 in the inspection zone 100: i. generate the inspection wave J^x, t) again in the inspection zone 100 using the first ultrasonic transducer b. multi-element 310 controlled by the first plurality of electrical control signals; ii. acquire 212 a plurality of additional electrical signals jref0' * reference signals », by means of the second multi-element ultrasonic transducer 310 receiving the reflected wave j(x, t) resulting from a reflection of the inspection wave J^X. t) without an acoustic reflector 120; and subtract 230 the reference signals yefQ from the measurement signals, the determination 240 of the second plurality of control signals being carried out from the measurement signals M subtracted from the signals of
[0034]
[0035]
[0036]
[0037]
[0038]
[0039]
[0040]
[0041]
[0042]
[0043]
[0044] reference^). Advantageously, the movement of the liquid medium 110 satisfies the condition: where Ax is a detection accuracy, L is a characteristic distance of the inspection area 100, vo is the standard of a fluid medium velocity 110 etc is the acoustic speed in the fluid medium 110. Advantageously, the first and second multi-element ultrasonic transducers form a single multi-element ultrasonic transducer 310. Advantageously, the simulation steps and the convolution step are performed in Fourier space. Advantageously, the 120 acoustic reflectors are microbubbles formed by injecting a gas into the fluid medium. Advantageously, the process 200 includes, before the generation 211 of the inspection wave J^x, in the presence of at least one acoustic reflector 120 in the inspection zone 100, a step of introducing the acoustic reflectors 120 into the fluid medium. The step of generating the inspection wave ^x, t) in the absence of acoustic reflector 120 in the inspection zone 100 can then be carried out before the step of introducing the acoustic reflectors 120 into the fluid medium, or after the disappearance of the acoustic reflectors 120 in the fluid medium. Advantageously, the fluid medium 110 is a metal or a mixture of metals in liquid phase. Advantageously, fluid medium 110 is liquid metallic sodium. Advantageously, inspection zone 100 is a forced conduit.
[0045] Preferably, the forced conduit is made of metal, plastic or glass.
[0046] Advantageously, the inspection zone is a penstock, for example for liquid sodium.
[0047] In one embodiment of the device, the first and second multi-element ultrasonic transducers form only one and the same multi-element ultrasonic transducer.
[0048] The term "acoustic reflector" means any object presenting a break in acoustic impedance with the inspection medium.
[0049] The term "conduit" means a tube, channel or closed or semi-closed structure containing a moving fluid medium.
[0050] An "acoustic wave" is understood to be a mechanical oscillation or wave that propagates through a medium (such as a solid or a fluid) in the form of longitudinal and / or transverse pressure waves. These waves are generated by the vibration of a sound source, creating successive zones of compression and rarefaction in the medium.
[0051] The invention aims to provide a technical solution, in particular a method 200, for mapping an inspection area 100. This solution is remarkable in that it is compatible with an inspection area 100 comprising a moving fluid medium 110, without constraint on the speed of the fluid medium 110. The invention also relates to a device configured to implement this method 200.
[0052] The inspection zone 100 can be a volume or a section of a volume.
[0053] In particular, inspection zone 100 may be a penstock. The middle Fluid 110 can be a liquid such as water or liquid sodium. The penstock has a characteristic dimension, for example, a diameter, between 50 mm and 500 mm, for example, 200 mm. The velocity of the fluid 110 in the penstock can be greater than 50 m / s and, for example, between 50 m / s and 1000 m / s, or even between 150 m / s and 700 m / s. At such velocities, the assumptions of a static or very low-velocity fluid do not apply. Acoustic waves propagating in the liquid 110 can then be displaced. As a reminder, the speed of sound, also called the "speed of sound," is approximately 1500 m / s in water.
[0054] The fluid medium 110 can be homogeneous or inhomogeneous. It can be a mixture of fluids or a suspension of one fluid (for example, gas bubbles or microparticles) in another (for example, a liquid).
[0055] The inspection zone 100 may have a large characteristic dimension. It may be a seabed to be mapped. A characteristic dimension of the inspection zone 100, for example the depth of the liquid medium 110, may be between 10 m and 4000 m, for example between 10 m and 500 m. The velocity of the fluid medium 110 is not high in itself, since it can be on the order of 1 m / s, or even less. On the other hand, the path that can be traveled by an acoustic wave in such a volume can prove to be large enough that the acoustic wave is significantly deflected by the movement of the fluid during a measurement.
[0056] The ratio of the offset of an acoustic wave with respect to the distance traveled can be determined to be equal to (v / c)², where v is the magnitude of the velocity of the fluid medium 110, and c is the acoustic speed in the fluid medium. The characteristic distance L of the inspection zone 110 is the distance that the acoustic wave must travel in the fluid medium 110. It corresponds, for example, to the depth of a reservoir, a lake, or an inlet, or to the diameter of a penstock. The application of the method 200 according to the invention is therefore particularly advantageous when one seeks to obtain a mapping accuracy Ax satisfying the following inequality: [° 057 ] G) 2 £ <ax
[0058] The flow can be any type, laminar or turbulent.
[0059] Figure 1 schematically represents one embodiment of process 200 according to the invention. Different steps of process 200 of Figure 1 are shown in Figures 5 to 7.
[0060] Figures 2, 3, and 7 show an example of an inspection zone. In this example, the inspection zone corresponds, for instance, to a section of a sub-part of a larger inspection domain (e.g., a lake). The inspection zone 100 comprises a fluid medium 110, for example, water, moving with a velocity field θ(t) where θ is a position vector and θ is time. In Figures 2, 3, and 7, the inspection zone 100 also includes acoustic reflectors 120. These can be objects such as bubbles or particles. They form a discontinuity in acoustic impedance and are therefore capable of reflecting an incident acoustic wave. These reflectors 120 have, for example, been introduced into the inspection zone just before carrying out the steps in Figures 2, 3, or 7.
[0061] The inspection zone 100 includes a boundary 101. This is an interface between the fluid medium 110 and another medium such as air or a solid (for example, a multi-element transducer). The inspection zone 100 may include other boundaries.
[0062] Figures 2, 3, and 7 also depict an embodiment of a device 300 according to the invention, enabling the implementation of the mapping process 200. In the illustrated embodiment, the device 300 comprises a multi-element ultrasonic transducer 310. This is, for example, a transducer comprising N active elements capable of: a. to deform when an electrical voltage (for example, an electrical control signal $^0) is applied to them; and / or b. generate an electrical voltage (for example an electrical measurement signal yj$ when a deformation is applied to them.
[0063] The elements of the transducer 310 are, for example, piezoelectric elements.
[0064] The transducer 310 is located at the boundary 101 of the inspection zone. 100. It can thus generate an acoustic wave capable of propagating in the inspection zone 100 from a plurality of electrical control signals ^0 and generate electrical measurement signals yNÙ) when it receives an acoustic wave.
[0065] The device 300 includes a control circuit 320, configured to generate the electrical control signals $^0 on the elements of the 310 multi-element transducer and acquire electrical measurement signals / A from these elements. Thus, the Control circuit 320 allows the transducer 310 to be controlled to emit or measure an acoustic wave.
[0066] The device 300 also includes the processing circuit 330, such as a computer, configured to communicate with the control circuit 320 and perform calculations from the electrical control signals and the measured electrical signals.
[0067] The device 300 may include an additional multi-element ultrasonic transducer, which may be disposed at another boundary of the inspection zone. This multi-element ultrasonic transducer may comprise a plurality of M active elements (M being equal to or different from / V). The two transducers may then be configured in a complementary manner such that: a. one of the two transducers generates an acoustic wave at a boundary of the inspection zone 100; and b. the other of the two transducers measures an acoustic wave (for example reflected) at the level of another boundary of the inspection zone 100.
[0068] The two ultrasonic transducers can be interfaced with the same control circuit 320 or with separate control circuits. In all cases, the device 300 comprises only one computer 330 to perform the processing on the various electrical signals. In Figures 2, 3, and 7, a single transducer 310 performs all of these operations.
[0069] Figure 2 shows an example of a first step 211 of the process of Figure 1. In this step, a first acoustic inspection wave &(x, called the "inspection wave", is generated 211 by the transducer 310, at the boundary 101 of inspection zone 100. The inspection wave k(x, t) is represented by arrows showing the direction of wave propagation. In the illustrated example, the arrows are perpendicular to the boundary 101 of inspection zone 100. In other words, the inspection wave is a plane wave propagating normally to the boundary 101, and in particular, towards the acoustic reflectors 120. The inspection wave k(x, t) can also be a spherical wave.
[0070] To generate the inspection wave, a first plurality of A control signals ^0 is sent to the N elements of the transducer 310. Each element of the transducer 310 thus emits a spherical acoustic wave from a point on the boundary 101 of the inspection zone 100, with an amplitude and a delay (relative to the other spherical waves) allowing it to form, by superposition with the other spherical waves, a plane wave or a spherical wave (convergent or divergent) or a wave with a wavefront of arbitrary shape.
[0071] The boundary 101 against which the transducer 310 is in contact may be curved. The inspection zone 100 is, for example, a penstock. The curvature of the boundary 101 can be compensated to generate an inspection wave k(x, t) exhibiting a planar wavefront.
[0072] Figure 3 shows an example of a second step 212 of the process of Figure 1. In this step, a plurality of A electrical signals yN(t), emitted by the transducer 310, are acquired by the control circuit 320. Each of the electrical signals yN(t), called the "measurement signal", corresponds to the measurement of a reflected acoustic wave j(x, t) at a point on the boundary 101 of the inspection zone 100. This reflected wave j(x, t) results, for example, from the reflection of the inspection wave k(x, t) on an object such as an acoustic reflector 120. This reflected wave j(x, t) can also correspond to the superposition of several waves reflected by several different objects such as several acoustic reflectors 120.
[0073] The method of Figure 1 also includes a calculation step 240 of a second plurality of electrical control signals called "focusing control signals" or "focusing signals". Each of the focusing signals zM is based on the time reversal of one of the measurement signals ZAN. In other words, considering that the acquisition time for the measurement signals is r, the focusing signals are, for each element ' among the A elements: [00741
[0075] Figures 4 and 5 schematically represent a digital model of an inspection zone 100' forming a virtual inspection zone 100'. This virtual zone 100' aims to correspond to the real inspection zone 100 of Figures 2, 3 and 7.
[0076] The virtual inspection zone 100' includes, for example, a virtual fluid medium 110'. For this purpose, the numerical model includes, for example, a set of equations describing the behavior of the fluid medium 110 in the real zone 100, as well as equations of motion describing the flow of the fluid medium 100. For this reason, it is preferable that the type of flow of the fluid medium 110 be known and modelable. The numerical model may also include a set of equations describing the propagation of acoustic waves in the fluid medium 100.
[0077] In order for the virtual inspection zone 100' to best reflect the actual inspection zone 100, it is preferable that the implemented equations best describe the flow of the fluid medium 110 and the propagation of acoustic waves in this medium. For this reason, it is preferable that the velocity field of the fluid medium 110 in the actual inspection zone 100 be able to be studied and modeled. This could, for example, be a laminar or turbulent flow.
[0078] The digital model of the real zone 100 can also include a two- or three-dimensional mock-up of the real inspection zone 100. The virtual inspection zone 100' has, for example, the same shape and dimensions as the real inspection zone 100. It also includes at least one boundary 101', which corresponds, for example, to the boundary 101 of the real inspection zone 100 and against which the transducer 310 of Figures 2 and 3 rests.
[0079] The digital model of the actual zone 100 may also include a model of the multi-element ultrasonic transducer(s). These virtual multi-element transducers are, for example, modeled by a boundary condition, for example at the boundary 101' of the virtual inspection zone 100'. In this way, a wave generated or received at the boundary 101 of the actual inspection zone 100 corresponds to a wave generated or received at the boundary 101' of the virtual zone 100'.
[0080] Unlike the actual area 100 in Figures 2 and 3, the virtual inspection area 100' does not include acoustic reflectors 120.
[0081] The method 200 includes a simulation step 260 of the generation of the inspection wave ^x, t) in the virtual zone 100'. This step is illustrated by [Fig.4].
[0082] The inspection wave i) is, for example, generated by means of a model of the real transducer 310. The generation is, for example, carried out from the boundary 101' of the virtual inspection zone 100'. The control signals sN(t) considered The parameters used to generate the inspection wave k(x, t) are preferably identical to those used to generate the inspection wave k(x, t) in the actual inspection zone 100.
[0083] This first simulation 250 allows the inspection wave t) to propagate in the virtual inspection zone 100' in the same way as in the actual inspection zone 100. Thus, for any time F, a map of a first pressure field idx, t) associated with the propagation of the inspection wave and called the "direct field" is obtained. This map corresponds to a variation over time of the pressure field across the entire study area.
[0084] The method 200 includes a simulation step 260 of the generation of a focusing wave f[x. t) in the virtual zone 100'. This step is illustrated by [Fig.5].
[0085] The focusing wave f(x, t) can also be generated by means of a model of the actual transducer 310 (or of an additional transducer if two transducers are implemented for the first steps). The generation of the focusing wave f(x, t) can also be carried out from the boundary 101' of the virtual inspection zone 100'. Unlike the inspection wave z), the control signals considered for generating the focusing wave f(x, t) are the focusing control signals
[0086] In other words, the focusing wave f(x, t) is generated based on the previously acquired measurement signals yN(t) that have been time-reversed. The focusing wave f(x, t) therefore corresponds to the reflected wave j⇌x, t) back-propagating in the virtual inspection zone 100', with the focusing wave then focusing on the position of the acoustic reflectors that gave rise to the reflected wave. By "back-propagation," we mean the propagation of a wave in reverse. In simpler terms, the wave moves backward instead of forward.
[0087] At the end of this simulation 260, for all times*, a map of a second pressure field u^X, t) associated with the focusing Fonde propagation and called the "adjoint field" is obtained. This map corresponds to a variation over time of the pressure field over the entire study area.
[0088] Unlike prior art mapping methods, the method 200 according to the invention takes into account the velocity field f) of the fluid medium 110. The velocity field is notably integrated into the simulation steps 250, 260 allowing the direct and adjoint fields to be obtained.
[0089] In particular, in simulation 250 of the propagation of inspection Fonde idx, the virtual fluid medium 110' follows the same flow as the real fluid medium 110. In other words, it follows the same velocity field y(xt) as the real fluid medium 110.
[0090] In the simulation 260 of the propagation of a focusing wave f(x, t), said focusing wave corresponds to the reflected wave j(x, t) back-propagating in the fluid medium 110. To properly compensate for the effect of the flow of the fluid medium 110 on the propagation of the reflected wave j(x, t), the velocity field considered to simulate the flow of the fluid medium 110 is time-reversed and therefore corresponds to -v(x, -t). In fact, the acquisition time of the measurement signals is T. The reversed velocity field is then -V(x, T -t). Thus, during the simulation of the generation and propagation of the focusing wave, the virtual fluid medium 110' moves backward instead of forward.
[0091] The process 200 finally includes a time convolution step of the maps of the direct and adjoint fields ^(x. i)^ Ï^X, t) as follows:
[0092] £(x) T~i)dt
[0093] This convolution allows us to obtain a map 280 of the topological energy E(x) on the virtual inspection zone 100'. Considering that the behavior of the virtual inspection zone 100' is sufficiently close to the real inspection zone 100, we can consider that the map 280 of the topological energy E(x) on the virtual zone 100' corresponds to the map on the real inspection zone 100.
[0094] The adjoint field concentrates the energy at the positions of the reflectors 120, thanks to the refocusing properties of time reversal. The direct field adds temporal and spatial coherence because it intersects the adjoint field at the acoustic reflectors 120. Mapping the topological energy E(x) thus allows the position of the acoustic reflectors 120 within the actual inspection area 120 to be determined.
[0095] Figures 8 and 9 represent two results obtained using method 200. These figures represent, along the X and Y directions, a topological energy map e(x) corresponding to the inspection zone 100. In the first case, corresponding to Figure 8, the velocity field v(x, 0) was not taken into account in simulations 250, 260. In the second case, corresponding to Figure 9, the velocity field V(X, t) (and therefore -y(x, - θ)) was not taken into account in the Simulations 250 and 260 show that the topological energy peaks in [Fig. 8] do not correspond to the position of reflectors 120. In contrast, in [Fig. 9], the topological energy peaks do correspond to the position of the reflectors. The influence induced by the fluid velocity has been correctly compensated.
[0096] Advantageously, the simulation steps 250, 260 and the convolution step 270 can be performed in Fourier space. Numerical simulations as well as time convolutions are generally faster. A description of Simulation and convolution in Fourier space is described in the document [“Time domain topological gradient and time reversal analogy: an inverse method for ultrasonic target detection,” N. Dominguez et al., Wave Motion, vol. 42, Issue 1, 2005, pages 31–52]. It may be preferable to determine the impulse responses of the transducer(s), and in particular of each active element. While this step can be complex, it does improve the computational speed of the simulations.
[0097] The calculation of the topological energy is based on the principle of time reversal. The equations describing the propagation of acoustic waves in the fluid medium and the flow of the fluid medium are preferably chosen to be time reciprocal and preferably self-adjoint.
[0098] An example of equations for the propagation of acoustic waves in a moving fluid medium, respecting the aforementioned criterion, is as follows:
[0099] [n- î P~ ~Pnt D / 1 Dÿ \ n [ Df ( Cg Dr / " ~ 0
[0100] with [°101i
[0102] with p the acoustic pressure and 0 a quantity derived from the acoustic pressure called velocity potential, since it can also be defined by = Vv0 with ro the flow velocity.
[0103] The density P of the virtual fluid medium (110') preferentially approaches the density of the real fluid medium 110. The acoustic speed c of the virtual fluid medium 110' preferentially approaches the acoustic speed of the real fluid medium 110.
[0104] This equation, formulated by Pierce, assumes the propagation of a high-frequency acoustic wave (that is, the variation of the physical quantities characterizing the fluid, such as its velocity or density, is negligible over a distance corresponding to the wavelength of the acoustic wave).
[0105] In order to improve the accuracy of the mapping, the method 200 may include additional steps aimed at removing unwanted reflections, not originating from the acoustic reflectors 120. These are, for example, reflections on walls of the inspection area 100.
[0106] To eliminate unwanted reflections, a measurement, called a "reference" measurement, is taken in the absence of an acoustic reflector 120. When the reflectors are artificially added to the fluid medium 110 (for example, by adding gas bubbles), the source of the reflectors is stopped. A waiting period may be necessary to ensure the disappearance of the 120 reflectors. Alternatively, the reference measurement can be carried out before the introduction of the 120 reflectors.
[0107] In all cases, the method 200 includes, in the absence of an acoustic reflector 120, a generation step 211 of the inspection wave t) in the inspection zone 100. The inspection wave is preferably identical to the one previously generated or at least similar. The inspection wave k(x.t) is, for example, generated by means of the same multi-element ultrasonic transducer 310 controlled by the same first plurality of control signals.
[0108] The process 200 also includes a step 212 for acquiring a plurality of additional electrical signals ret / fl, called "reference signals". This step iV Vf is illustrated in Figure 7. Acquisition is preferably performed using the same multi-element ultrasonic transducer used for the step in Figure 3. The reflected wave jÇx, t) received by transducer 310 originates from a reflection on walls or extraneous elements that are independent of the presence of acoustic reflectors 120 or not.
[0109] Finally, the process 200 includes a subtraction step 230 between the signals of Measurement of Ifl and the reference signals flfl. yNv' yN VJ The determination of 240 signals Focusing z 0 is then done from the cleaned measurement signals / fl. Thus, n yV / The sources of parasitic reflection will not be taken into account in the simulation leading to the obtaining of the map of the adjoint field t)- The final map 280 then only includes the acoustic reflectors 120 specifically studied.
[0110] The results in Figures 8 and 9, for example, were obtained after removing spurious reflections.
[0111] The invention is not limited to the embodiments previously described and extends to all embodiments covered by the invention.< / ax>
Claims
Demands
1. A method for mapping (200) an inspection area (100) comprising a moving fluid medium (110), the method (200) comprising the following steps: in the presence of at least one acoustic reflector (120) in the inspection area: • generate (211) a first acoustic wave (k(x, t)\ called "inspection wave", in the inspection zone (100) by means of a first multi-element ultrasonic transducer (310) controlled by a first plurality of electrical control signals ($^0); • acquire (212) a plurality of electrical signals (M), called "measurement signals", by means of a •^AA / second multi-element ultrasonic transducer (310) receiving a second acoustic wave (j(x, t)\ called the "reflected wave", resulting from a reflection of the inspection wave (J^x, t)) on said at least one acoustic reflector (120); determine (240) a second plurality of signals control based on measurement signals temporally returned; from a digital model of the inspection zone (100) without acoustic reflector (120), forming a virtual inspection zone (100') comprising a virtual fluid medium (110') in motion: • simulate (260) the propagation of the inspection background (k(x. / )) in the virtual inspection zone (100'), generated by means of a first virtual multi-element ultrasonic transducer controlled by the first plurality of electrical control signals (^0), so as to obtain a first mapping as a function of the time of a first pressure field (ifa, called "direct field"; • simulate (250) the propagation of a third acoustic wave (fÇx. t)), called "focusing wave", in the virtual inspection zone (100'), generated by means of a second virtual multi-element ultrasonic transducer controlled by the second plurality of control signals Qv0), so as to obtain a second time-dependent map of a second pressure field (j^x, i)\ called "adjoint field"; and • temporally convolve the first and second maps of the direct and adjoint fields (u(x„ tjlx. / )) so as to obtain a map of the topological energy (E(x) ) of the virtual inspection zone (100'), the method (200) being characterized in that: • the simulation (260) of the propagation of the inspection field (k(x. / )) in the virtual inspection zone (100') is carried out with the virtual fluid medium (110') presenting a velocity field i) °where X is a position in the virtual inspection zone (100') and' is time; and • the simulation (250) of the propagation of the focusing Fonde (f(x. ?)) in the virtual inspection zone (100') is carried out with the virtual fluid medium (110') presenting a velocity field _ -t)-.
2. A method (200) according to the preceding claim, wherein the numerical model of the inspection zone (100') includes an equation describing the propagation of the inspection background and the focusing wave ( / {(x, f(x, / )) in the virtual fluid medium (110'), said equation being self-adjoint.
3. A method (200) according to any one of the preceding claims, wherein the equation describing the propagation of the inspection wave and the focusing wave (J^x, f(x, i)) in the virtual fluid medium (110') is:
4. f P=-PÜ IDZ 1 D0 \ 1 „ z „ , xn l DM c2 DZ / " P^ ' - 0 with 5 = tyv, with p a velocity potential, 0 a quantity derived from the acoustic pressure, P the density of the virtual fluid medium etc the acoustic speed in the fluid medium. A method according to any one of the preceding claims, comprising the additional steps of:
5. • in the absence of an acoustic reflector (120) in the inspection area (100): • generate (211) again the inspection wave (k(x, / )) in the inspection zone (100) by means of the first multi-element ultrasonic transducer (310) controlled by the first plurality of electrical control signals (s^)); • acquire (212) a plurality of additional electrical signals („^*1), called “signals of ■ vv / reference », by means of the second multi-element ultrasonic transducer (310) receiving reflected Fonde ( t)) resulting from a reflection of the inspection wave (k[x, z]) without acoustic reflector (120); and • subtract (230) the reference signals (re^\) from the JN measurement signals (ZA), the determination (240) of the second plurality of control signals Q ^) being realized from the measurement signals ( / A) to which ■W / are subtracted from the reference signals y N V7 Method (200) according to any one of the preceding claims, wherein the movement of the liquid medium (100) satisfies the condition:
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15. where Ax is a detection accuracy, L is a characteristic distance of the inspection area (100), vo is the norm of a fluid medium velocity (110) etc is the acoustic speed in the fluid medium (110). Method (200) according to any one of the preceding claims, wherein the first and second multi-element ultrasonic transducers form only one and the same multi-element ultrasonic transducer (310). A method according to any one of the preceding claims, wherein the simulation steps (250, 260) and the convolution step (270) are carried out in Fourier space. A method according to any one of the preceding claims, wherein the acoustic reflectors (120) are microbubbles formed by injecting a gas into the fluid medium (110). A method according to any one of the preceding claims, comprising, before the generation (211) of the inspection wave ()), in the presence of at least one acoustic reflector (120) in the inspection zone (100), a step of introducing the acoustic reflectors (120) into the fluid medium. A method according to any one of the preceding claims, wherein the fluid medium (110) is a metal or a mixture of metals in liquid phase. A method according to the preceding claim, wherein the fluid medium (110) is liquid metallic sodium. A method according to any one of the preceding claims, wherein the inspection zone (100) is a penstock. A method according to the preceding claim, wherein the penstock is made of metal, plastic or glass. A method according to any one of the preceding claims, wherein the fluid medium is homogeneous. Device including: A first multi-element ultrasonic transducer (310), preferably piezoelectric, configured to generate a first acoustic wave (k(x. / )), called the "inspection wave", in an inspection zone (100) from a first plurality of electrical control signals; and
16. • A second multi-element ultrasonic transducer (310), preferably piezoelectric, configured to convert a second acoustic wave (y(x, / )), called a "reflected wave", into a plurality of electrical signals ( ZA), called "measurement signals"; and • A control and processing device (320, 330) configured to implement the steps of the process (200) according to any one of the preceding claims. Device according to the preceding claim, wherein the first and second multi-element ultrasonic transducers (310) form only one and the same multi-element ultrasonic transducer (310).