Device for measuring variations in force, mechanical deformations, hydrostatic pressures and temperature, and associated measurement method

Abstract

A non-intrusive method and device for measuring a variation in longitudinal force, other than exerted by hydrostatic pressure, and / or a variation in hydrostatic pressure, relating to a host structure of interest, comprising: - a sensor (3) including at least one optical waveguide (7) installed on one of the surfaces or in the wall of a cylindrical test body (9), deforming within its elastic range, each optical waveguide locally describing a circular helix and carrying at least one orientation-sensitive transducer (11) configured to perform a selective measurement of a first primary variable, and a second primary variable, - a computer (17) configured to selectively calculate the local variation of a longitudinal force δF, other than exerted by hydrostatic pressure,applied to the test specimen and / or the local variation of hydrostatic pressure ΔP applied to the test specimen (9) as a function of the true relative variations of the measurements of said first and / or second primary variables. Figure for the abbreviation: Figure 1.

Description

Title of the invention: Device for measuring variations in force, mechanical deformations, hydrostatic pressures and temperature, and associated measurement method technical field

[0001] The present invention relates to a non-intrusive device for selectively measuring a change in force, other than that exerted by hydrostatic pressure, and / or a change in hydrostatic pressure, as well as a change in temperature, and an associated measurement method. The invention is applicable to the field of instrumentation, and more specifically to the measurement of force, mechanical deformations, hydrostatic pressures, and temperature, on the surface or within a deformable mechanical structure. PREVIOUS STATE OF THE ART

[0002] There is, particularly in environments subject to significant constraints, such as certain structures, especially tanks or pressurized pipes, a need to carry out measurements of mechanical deformations, hydrostatic pressures and / or temperatures, particularly for monitoring purposes, to ensure their structural mechanical integrity during their operation, but also for predictive maintenance purposes.

[0003] Measurements within structures using in situ sensors are particularly difficult to carry out when temperatures, mechanical deformations, or hydrostatic pressure are likely to vary simultaneously, due to the cross-sensitivity in temperature, mechanical deformation and hydrostatic pressure of the transducers generally used.

[0004] This problem is all the more delicate because these quantities can vary significantly. For example, the temperature can vary from several tens of degrees Celsius in the most common applications, and in extreme conditions, up to several hundred degrees Celsius.

[0005] By way of example, the temperature of gaseous molecular hydrogen H2 can reach 70°C at 700 bar during the filling process of a tank, with a hydrostatic pressure difference of several hundred bar between its internal and external walls, and mechanical deformations of up to 0.6% (6000 qm / m) at 700 bar in the case of a type IV carbon-epoxy resin matrix tank.

[0006] However, the effect of temperature on the measurement provided by a sensor is generally sufficient on its own to bias any measurement of mechanical deformation that may in result if it is not perfectly compensated, in addition to the fact that hydrostatic pressure can also interfere.

[0007] Thus, for example, a thermal compensation error of the order of 0.038°C is sufficient on its own to lead to a measurement error of 1 bar in pressure for a metal pipe of 102.3 mm external diameter for a wall thickness of 13.49 mm according to a standardized standard.

[0008] In addition to the lack of thermal compensation, there are those of mechanical forces; thus, a variation of 600 N of a force applied longitudinally to this same pipe is responsible for a measurement error of 1 bar of its internal hydrostatic pressure, or even a measurement error of the order of 0.72 qm / m of its longitudinal mechanical deformation.

[0009] It is therefore advantageous for a sensor whose transducers (housed within or on the surface of a deformable structure) are sensitive to the effects of temperature, hydrostatic pressure and longitudinal mechanical deformation applied to them, to be able to separate each of these three effects, in order to provide, independently of each other, the measurement of the variations of each of these three effects acting on the instrumented structure, relative to an arbitrary reference state.

[0010] Currently, there exists a measurement technique based on the use of an ellipsoidal, preferably spherical, test body made of a homogeneous, elastic material with known mechanical properties, intended to be embedded in a host structure. This technique uses a strain measurement fiber, mechanically attached to the test body, so as to transmit the deformations of the host structure to the fiber (document WO 2014 / 140496). The three-dimensional measurement of the deformations of the host structure then relies on the Eshelby embedding problem to determine the deformation field of the host structure as it would exist in the absence of the inclusion of this test body within the host structure.Besides the fact that this sensor does not compensate for the thermal effects acting on each of the transducers (in this case Bragg gratings), the inclusion of a foreign body several tens of millimeters in diameter within a host structure remains problematic, as it very often causes local weakening, which can ultimately lead to the collapse of the structure.

[0011] Document FR 3 117 582 B1 is an improvement of the solution proposed in document WO 2014 / 140496 in order to reduce its intrusive effect, with a tangential rather than through arrangement of the transducers with respect to the spheroidal inclusion: the problem of compensating for the thermal effects on each of the transducers, allowing a purely mechanical measurement to be provided in a variable temperature field, is however still not solved by this approach.

[0012] Furthermore, there are also measurement techniques based on the use of an optical fiber exhibiting birefringence created by the residual mechanical deformations of the structure, within which the sensor is integrated.

[0013] Such a technique is described, for example, in US patent 5,591,965. This technique relies on the use of a birefringent optical fiber with several Bragg gratings photo-inscribed at distinct Bragg wavelengths. These Bragg gratings are positioned at the same location in the optical fiber, and therefore subjected to the same temperature, which makes it possible to reconstruct the components of the local mechanical strain tensor independently of temperature effects, since it involves the pairwise differences of the raw measurements performed by each transducer.

[0014] According to this state-of-the-art technique, variations in hydrostatic pressure and longitudinal forces act mutually. Thus, this technique does not intrinsically allow one to eliminate undesirable mechanical effects such as variations in external longitudinal forces (when a hydrostatic pressure measurement is sought) or variations in hydrostatic pressure (when a measurement of external longitudinal forces, independent of the mechanical effects of hydrostatic pressure, is sought), since the number of physical quantities to be separated (temperature, hydrostatic pressure and longitudinal mechanical deformation) is greater than the number of equations governing the problem.

[0015] Another technique is described in US patent 5,841,131. It also relies on the use of a birefringent optical fiber, primarily dedicated to measuring the variation of the hydrostatic pressure applied to it, independently of temperature variations. The principle consists of exploiting the separation of the Bragg peak under the effect of hydrostatic pressure, which accentuates the birefringence effect. However, this principle alone does not allow for the separation of the two mechanical effects of longitudinal deformation and hydrostatic pressure, independently of temperature effects, applied to the optical fiber, because, here again, the problem is poorly formulated (the number of unknowns to be determined is greater than the number of equations) to separate the three physical quantities in question independently of one another.

[0016] The solutions described in applications FR 3 125 875 and FR 3 125 879 do indeed make it possible to overcome the effects of temperature, independently of the effects of hydrostatic pressure applied to a pressurized pipe that is hermetically sealed at its ends, but they remain dependent on the variation of the longitudinal forces ôF, which are generally unknown, that are applied to it.

[0017] The solution described in document FR 3 125 878 provides a partial answer to the measurement of the variation ΔF of the longitudinal forces applied to the pressurized pipe, independently of the effects of hydrostatic pressure. However, it requires that the measurement technique used be itself intrinsically compensated for the effects of temperature (such as, for example, the Brillouin reflectometry measurement technique described in document EP 3 232 165), or that the effects of temperature remain negligible (an assumption that can be verified in the case of very rapid phenomena, for example in detonation, provided that the transducer remains within its elastic deformation range and that heat exchange with the surrounding structure remains negligible), or that the temperature remains constant, under the limiting assumption that the transducer is not sensitive to the hydrostatic pressure applied to it.

[0018] No combination of the solutions described in documents FR 3 125 875, FR 3 125 878 and FR 3 125 879 can solve the problem on its own, because the different configurations in terms of radial positions (on internal or external surfaces, or in the wall of the structure) and angular orientations of the transducers are largely incompatible with each other.Moreover, none of these solutions takes into account, once again, the pressure sensitivity kp of the transducers, which must necessarily be corrected when the wall experiences a non-zero pressure differential Pext-Pint between its internal and external faces, since when a transducer is positioned within the thickness of the wall, it is subjected to a hydrostatic pressure that depends on the variations of the internal pressure Pint and external pressure Pext, which must necessarily be taken into account in order not to introduce a significant measurement bias on each of the three effects that we are trying to separate, something that none of the three aforementioned documents considers so far.

[0019] Finally, despite the possibility of performing a measurement using optical fiber that is intrinsically uncorrelated with temperature effects (for example, using Brillouin reflectometry, as described in document EP 3 232 165), the problem of calibrating such a measurement remains for the implementation of the solution described in document FR 3 125 878. This measurement natively provides a purely mechanical measurement only for the optical fiber itself. At a minimum, it is necessary to take into account the additional mechanical effects exerted on the fiber by differential expansion with the host structure, which is not always possible to achieve with sufficient accuracy, particularly if the thermal behavior of the instrumented structure is not known with sufficient precision in the temperature range considered.Besides this effect of differential expansions, the sensitivity kp in hydrostatic pressure of such a measurement technique must, again, . to be taken into account, since the optical fiber is positioned in the wall or on the surface of the structure, which neither document FR 3 125 878, nor document EP 3 232 165, deal with satisfactorily.

[0020] The object of the present invention is to propose a device and a method for measuring variations in force (other than that exerted by hydrostatic pressure) and mechanical deformation, hydrostatic pressures, and temperature to which a structure is subjected, remedying the aforementioned drawbacks, allowing for a selective measurement of the three components of temperature variation AT, hydrostatic pressure AP (internal APint and / or external APext) and longitudinal force ôF, independently of each other, provided that the conditions for achieving this are met. Description of the invention

[0021] To this end, the invention relates to a non-intrusive (or minimally intrusive) measuring device for measuring a variation in force along a predetermined orientation, other than that exerted by hydrostatic pressure, and / or a variation in hydrostatic pressure relating to a host structure of interest, comprising:

[0022] - a sensor comprising at least one optical waveguide installed in a attached to one of the surfaces or in the wall of a cylindrical test body, of circular cross-section, hollow and hermetically sealed at its ends, deforming in its elastic domain, each optical waveguide locally describing a circular helix positioned at a radius r around the axis of revolution of the test body, and locally oriented at a predetermined angle 0(r) with respect to a plane normal to said axis of revolution, each waveguide carrying at least one transducer whose mechanical component of the measurement is sensitive to orientation and configured to perform a selective measurement of a first primary variable, whose true relative variation is representative of a local variation of hydrostatic pressure applied to the test body or of a second primary variable, whose true relative variation is representative of a local variation of longitudinal force, other than exerted by a hydrostatic pressure,applied to the test specimen, the selectivity of one or the other mechanical effect (hydrostatic pressure vs. longitudinal force), through the true relative variations of the first and second primary variables, being ensured by the angular orientation ¢) of each waveguide, and ,

[0023] - a calculator configured to selectively calculate the local variation of the effort longitudinal ôF, other than exerted by hydrostatic pressure, and / or the local variation of hydrostatic pressure AP applied to the test body, as a function of the true relative variations of the measurements of said first and / or second primary variables.

[0024] This device makes it possible to separate the two mechanical effects exerted by a hydrostatic pressure and a longitudinal force (distinct from that exerted by a hydrostatic pressure) applied to the test body, independently of each other, independently of the shear erz (according to its radius r and its axis of revolution (zz)) that this test body may undergo.

[0025] It should be noted that the expression “waveguide carrying a transducer” means, according to the embodiment of the invention, that a transducer is inscribed in the waveguide or that the waveguide itself carries or has the function of a transducer.

[0026] Advantageously, the calculator is further configured to calculate the local variation of the temperature AT as a function of the true relative variations of the measurements of said first and / or second primary variables, provided that the primary measurement is sensitive to the effects of temperature.

[0027] Thus, the device makes it possible to separate the temperature, in addition to the two mechanical effects of hydrostatic pressure and longitudinal force, other than exerted by a hydrostatic pressure.

[0028] Advantageously, the calculator is configured to calculate the local variation of the longitudinal mechanical deformation Asme^ of the test body as a function of the local variation of the longitudinal force ôF (other than exerted by hydrostatic pressure) and the local variation of hydrostatic pressure AP applied to the test body, as well as the physical parameters of the test body.

[0029] Advantageously, the device comprises at least one pair of optical waveguides oriented locally in a circular helix around the axis of revolution of the test body and carrying at least one pair of transducers, the optical waveguides of each pair being positioned along two distinct radii ri and r2 around the axis of revolution of the test body, and oriented locally along a pair of predetermined angles with respect to a plane normal to said axis of revolution.

[0030] Thus, the device has a selective character in measuring the variation of hydrostatic pressure and / or the variation of longitudinal forces, other than those exerted by hydrostatic pressure, independently of the effects of temperature, with the additional provision of the indication of the local variation of temperature as soon as the primary measurement provided by each transducer is itself sensitive to temperature.

[0031] Moreover, the local circular helix orientation of the transducers ensures, by design, that they are totally insensitive to erz type shears (i.e.: along the radius r and the axis of revolution (zz)) suffered by the test body, as can for example be the case when this test body is housed within a deformable host structure, which makes it possible to ensure, in this way, a particularly robust measurement of the variation of the longitudinal forces ôF.

[0032] According to a first embodiment, the device comprises first and second optical waveguides oriented locally in a circular helix around the axis of revolution of the test specimen at distinct first and second angles (φc(φr2π) with respect to a plane normal to the axis of revolution. The first optical waveguide is dedicated to measuring the variation of the hydrostatic pressure AP, while the second optical waveguide is dedicated to measuring the variation of the longitudinal force ΔF, other than that exerted by hydrostatic pressure, applied to the test specimen. This can be achieved by using a continuously sensitive, intrinsically temperature-compensated distributed measurement technique, such as, for example, the Brillouin reflectometry measurement technique based on the Landau-Placzek ratio, described in document EP 3 232 165 B1 or in article doi: 10.1109 / 3.663443, with a hydrostatic pressure sensitivity kp now taken into consideration, which is new compared to previous approaches (notably FR 3 125 875, FR 3 125 878 and FR 3 125 879).

[0033] According to variants of the first embodiment, the device comprises first and second optical waveguides oriented locally in a circular helix around the axis of revolution of the test body according to the same family of angles J OR Vgp(r2w)} with respect to a plane normal to the axis of revolution of the test body, the first family of angles being dedicated to the selective measurement of the variation of hydrostatic pressure AP, while the second family of angles is dedicated to the selective measurement of the variation of the longitudinal force ôF, other than exerted by a hydrostatic pressure, applied to the test body.

[0034] More particularly, according to a variant of the first embodiment, the device comprises first and second optical waveguides oriented locally in a circular helix around the axis of revolution of the test body, at first and second angles and ) with respect to a plane normal to the axis of revolution of the test specimen, these two angles being equal if the waveguides are both positioned within the wall of the test specimen or positioned on its internal and external surfaces, the said first and second optical waveguides being dedicated to measuring the variation of hydrostatic pressure AP (internal APint or external APext) within the test specimen. The angles take on a first identical and constant value within the wall of the test specimen and a second identical and constant value on the internal and external surfaces of the test specimen, the first and second angle values ​​being distinct.

[0035] According to another variant of the first embodiment, the device comprises first and second optical waveguides oriented locally in a circular helix around the axis of revolution of the test body, according to first and second angles <PÔF(riSF) et (PSF(r2SF) distincts par rapport à un plan normal à l’axe de révolution du corps d’épreuve, lesdits premier et deuxième guides d’ondes optiques étant dédiés à la mesure de la variation de l’effort longitudinal ôF, autre qu’exercé par une pression hydrostatique, appliqué de manière externe au corps d’épreuve.

[0036] According to a second embodiment, the device comprises first and second pairs of optical waveguides positioned locally in a circular helix around the axis of revolution of the test body along a first pair of distinct rays rUp, r2AP, and a second pair of distinct rays rkr, the two waveguides of the first pair are positioned locally along first and second angles (p^p ( r) and <PAp ( ) par rapport à un plan normal à l’axe de revolution, these two angles being equal if the waveguides are both positioned in the wall of the test body or positioned on internal and external surfaces, while the two waveguides of the second pair are positioned locally at two distinct angles and <PÔF ( rzSF ) par rapport à un plan normal à the axis of revolution, the first pair of waveguides being dedicated to measuring the variation of the hydrostatic pressure AP (internal APint or external APext), while the second pair of waveguides is dedicated to measuring the variation of the longitudinal force ôF, other than exerted by a hydrostatic pressure, applied externally to the test body.

[0037] This allows the simultaneous selective measurement of the two mechanical effects of variation of hydrostatic pressure AP (internal APint or external APext) and variation of longitudinal forces ôF, other than exerted by a hydrostatic pressure, applied externally to the test body with respect to an arbitrary reference state, as well as the local variation of temperature AT of the test body as long as the primary measurement provided by each transducer is itself sensitive to temperature.

[0038] According to a third embodiment, the device comprises a single optical waveguide positioned at a predetermined radius in the elastic wall of the test body or on its internal or external surface, and locally oriented in a circular helix around the axis of revolution of the test body at a predetermined angle with respect to a plane normal to the axis of revolution, the optical waveguide being dedicated to the measurement of the variation of hydrostatic pressure AP (internal APint or external APext) or to the measurement of the variation of the longitudinal force ôF, other than exerted by a hydrostatic pressure, applied externally to the test body, by exploiting a continuously sensitive and temperature-compensated distributed measurement technique, such as, for example, the Brillouin reflectometry measurement technique based on the Landau-Placzek ratio, described in document EP 3 232 165 B1.

[0039] According to a fourth embodiment, the device comprises first, second and third optical waveguides oriented locally in a circular helix around the axis of revolution of the test body with first, second and third radii rb r2 and r3 of which at least two of them are distinct, and with first, second and third angles which are arbitrary but in absolute value distinct modulo ir for at least two of them, 0(ri), 0(r2) and 0(r3), with respect to a plane normal to the axis of revolution, the first, second and third optical waveguides being dedicated to the selective measurement of the variation of hydrostatic pressure AP (internal APint or external APext) and of the variation of the longitudinal force ôF, other than exerted by a hydrostatic pressure, applied to the test body.

[0040] Advantageously, according to a first aspect of the present invention, each optical waveguide carries a Bragg grating transducer for performing distributed measurements (equivalent English term: quasi-distributed measurements), suitable for performing very localized measurements, this Bragg grating being able to be of high order (for example greater than 500) in order to present in the spectral domain a comb in frequencies, and thus conduct a more precise measurement by simple averaging of the frequency shift of each of its resonances.

[0041] Advantageously, according to another aspect of the present invention, each optical waveguide carries a transducer according to a continuously sensitive reflectometric technique of the Brillouin type, OFDR (Optical Time Domain Reflectometer, “optical frequency domain reflectometer”) Rayleigh, or even phase-OTDR (0-OTDR (Optical Frequency Domain Reflectometer, “optical time domain reflectometer”) or DAS (Dynamic Acoustic Sensing “dynamic acoustic sensing”) adapted to perform distributed measurements along the optical waveguide.

[0042] Advantageously, according to a first particular aspect of the present invention, the sensor comprises said cylindrical test body, of circular cross-section, delimiting a sealed cavity. The sensor is intended to be installed in any host structure, the variation of the external hydrostatic pressure APext applied to the test body, and the temperature variation ATi of the test body associated with this hydrostatic pressure variation, as well as the variation of the longitudinal force 5F&p, other than exerted by a hydrostatic pressure, applied to the test body, and the temperature variation AT2 of the test body associated (ATi = AT2 when the assumptions of the underlying model are met) with this longitudinal force variation, being defined according to the following equations:

[0043]

[0044]

[0045] [Math.l] ■ A Ti = — [Math.2] A Tq — K — 1 A Pext ~ A^rf-AT^ int (AVrA¥2yfr^(l-2v)A^ ^Eext (rHXC ^ir^pE) l-2v E Ks Kp)^int A^^AT^ (A^r^ / l-2v 1a» rfô " (r j-rÿ.a^ + \ Ë~ Ke ' KP / ^ùa where AW = 111 ( 1 + “ ) is a true relative variation of the raw value 4* (j,e, : primary measurement performed by the transducer) between its reference value and its current value: = Wo+ A 'F, E is the Young's modulus of the test specimen, v is the Poisson's ratio of the test specimen, kp, Ks and Kr are respectively the sensitivities in hydrostatic pressure, in longitudinal mechanical strain and in temperature of the transducer attached to the host structure (equation (46) of the article doi: 10.3389 / fsens.2022.835140) for the measurement technique considered, APint is the variation of the internal hydrostatic pressure of the test body, and r0i„t, r(Et are respectively the internal and external radii of the test body in its reference state.

[0046]

[0047]

[0048]

[0049] Advantageously, the test body is a micro-structured optical fiber forming a micro-capillary that is hermetically sealed at its ends. Advantageously, the test body is covered with a deformable mechanical sheath of polymer type, for example, but not limited to, polyimide or polyacrylate, and more generally, with a sheath capable of transmitting the stresses of the host structure to the transducers attached to the test body. Advantageously, the sensor is configured to exploit a birefringence effect of the optical waveguide. Advantageously, according to a second particular aspect of the present invention, the host structure has a cylindrical shape, a circular cross-section, is hollow, and is hermetically sealed at its ends, itself acting as a test specimen. The variations in internal hydrostatic pressures APint and external hydrostatic pressures APext, the variations in associated longitudinal forces &F&pM and ÔF&p, other than those exerted by hydrostatic pressure, and the associated local temperature variations ATB AT2, AT3, AT4 applied to it (ATi = AT2 = AT3 = AT4 when the assumptions of the underlying model are met), are defined according to the following equations, provided that the structure deforms within its elastic range, with transducers positioned in the wall with rays ri and r2:

[0050] [Math.3] AP lut — A Pext (A^-AV^ -ti ^E

[0051] [Math.4] A — kt

[0052] [Math.5] (ATrA^2)r2r|((] <h^^^ rrr? + rljr'l-^ APm (rcrÿ^\-2v')Ke-KpE) (V2v (rj-rÿ((1-2^-jCpE) +\ E Ke~Kp)aPext &Pext = int (A'P rA^2)r l-2v>e-Kp£) ( E Ke Kp ) APif#

[0053] [Math.6] 2Eea (^2)(( Ï^K^KpE) A^-AT^ (A^-AT^r^y^ r^-r^ (rj-rf)((l-2v)fce-KpE) Kp ) ^P 'mt

[0054] where AT = ln(l + ^) is the true relative variation of the gross value (i A primary measurement performed by the transducer) between its reference value and its current value: 'F = Wo+ A 'F, E is the Young's modulus of the structure, v is the Poisson's ratio of the structure, kp, Ks and kt are respectively the Sensitivities to hydrostatic pressure, longitudinal mechanical deformation, and temperature of the transducer, integral with the host structure for the measurement technique considered (e.g., Bragg grating), APint is the pressure variation internal hydrostatic, APext is the variation of the external hydrostatic pressure, and r%a, r°i:xt are respectively the internal and external radii of the cylindrical structure in its reference state.

[0055] The invention also relates to an installation comprising:

[0056] - a structure whose pressure and / or mechanical deformation and / or temperature are things to watch out for, and

[0057] - a measuring device according to any one of the above characteristics.

[0058] Advantageously, according to a first particular aspect of the present invention, the The structure of the installation has a cylindrical shape, with a circular cross-section, hollow and closed at its ends. This structure then acts as the sensor's proof body.

[0059] Advantageously, according to a second particular aspect of the present invention, the structure has any shape, and the sensor, comprising a cylindrical test body, of circular cross-section, hollow and sealed at its ends, is housed in a perfectly secure manner within the structure or on its surface.

[0060] The invention also relates to a non-intrusive method for measuring a variation in longitudinal force (other than exerted by hydrostatic pressure) and / or a variation in hydrostatic pressure relating to a host structure of interest, comprising the following steps:

[0061] - position at least one optical waveguide locally describing a helix circular on one of the surfaces or in the wall of a cylindrical test body, of circular cross-section, hollow and hermetically sealed at its ends, each optical waveguide being positioned at a radius r around the axis of revolution of the test body and being locally oriented at a predetermined angle 0(r) with respect to a plane normal to said axis of revolution, each waveguide carrying at least one orientation-sensitive transducer,

[0062] - to perform a selective measurement using the primary measurement of said transducer of a first mechanical quantity representing a local variation of hydrostatic pressure applied to the test specimen or of a second mechanical quantity representing a local variation of longitudinal force, other than exerted by hydrostatic pressure, applied to the test specimen, the selectivity of one or the other of the first and second mechanical quantities being ensured by the orientation of each waveguide, and

[0063] - selectively calculate the local variation of the mechanical deformation longitudinal of the test body and / or the local variation of the hydrostatic pressure applied to the test body as a function of the measurement of said first and / or second primary measurements. Brief description of the drawings

[0064] The invention will be better understood with the aid of the following description, given solely by way of non-limiting example, and made with reference to the accompanying drawings in which:

[0065] Figure 1 illustrates a minimally intrusive measuring device for measuring a variation in a longitudinal force (along the orientation k of the axis of revolution (zz) of the sensor's test body), other than that exerted by hydrostatic pressure, and / or a hydrostatic pressure variation relative to a host structure of interest, according to an embodiment of the invention;

[0066] Figs [2A], [Fig.2B], [Fig.2C], [Fig.2D], [Fig.2E] and [Fig.3A], [Fig.3B] each illustrate a low-intrusive measuring sensor intended to measure a variation of a longitudinal force (according to the orientation k of the axis of revolution (zz) of the sensor's test body), other than exerted by a hydrostatic pressure, and / or a variation of hydrostatic pressure relating to a host structure of interest, according to different embodiments of the invention;

[0067] Fig. 4 is a flowchart illustrating the steps of a low-intrusive measurement process of a longitudinal mechanical deformation (i.e., along the orientation k of the axis of revolution of the sensor's test body) and / or a hydrostatic pressure variation relating to a structure of interest, according to the embodiments of Figs. 1, 2A-2E and 3A-3B;

[0068] Fig. 5 is a flowchart illustrating the steps of a low-intrusive method for measuring a longitudinal mechanical deformation (i.e., along the orientation k of the axis of revolution of the sensor's test body) and / or a variation of hydrostatic pressure relating to any structure of interest, according to a particular embodiment of the invention;

[0069] Fig. 6 is a flowchart illustrating the steps of a low-intrusive method for measuring a longitudinal mechanical deformation (i.e., along the orientation k of the axis of revolution of the sensor's test body) and / or a pressure variation relating to any structure of interest, according to another particular embodiment of the invention;

[0070] Figs. 7A and 7B each illustrate a low-intrusive measuring sensor intended to measure a variation of a longitudinal force (according to the orientation k of the axis of revolution of the sensor's test body), other than exerted by a hydrostatic pressure, and / or a variation of hydrostatic pressure relating to a host structure of interest, according to different embodiments of the invention;

[0071] Figs. 8A and 8B each illustrate a low-intrusive measuring sensor intended to selectively measure, with or without exploitation of birefringence, the variation of hydrostatic pressure AP (internal APint and / or external APext) and the variation of the longitudinal force ôF (according to the orientation k of the axis of revolution (zz) of the sensor's test body), other than exerted by hydrostatic pressure, applied to the test body, according to particular modes of the invention. DETAILED DESCRIPTION

[0072] The concept underlying the invention is based on the selectivity of mechanical effects by means of the specific orientations of the transducers, the mechanical component of which of the primary measurement is sensitive to orientation, coupled to their radial positions in the wall or on the surface of the test specimen, making it possible to eliminate one or the other mechanical effect depending on the orientation in question, thus reducing the complexity of the underlying thermomechanical problem (and consequently of the associated solutions) to the resolution of only two independent equations, requiring the implementation of only two transducers since their measurement is sensitive to temperature, since in the most general case where the orientation of the transducers is arbitrary, the problem is described by three independent equations, then requiring the implementation of three transducers (the two mechanical effects of hydrostatic pressure and longitudinal force, other than that exerted by a hydrostatic pressure, being then obtained simultaneously,in addition to temperature information (provided the measurement supplied by the transducers is sensitive to this parameter).

[0073] Fig. 1 illustrates a non-intrusive measuring device for measuring a variation of a longitudinal force, other than exerted by hydrostatic pressure, and / or a variation of hydrostatic pressure relating to a host structure of interest, according to an embodiment of the invention.

[0074] Such a measuring device 1 is particularly suitable for measuring variations in hydrostatic pressure, mechanical force, and temperature in installations with pressurized structures, such as, for example, fluid tanks or pressurized pipes. The device is also suitable for measuring variations in hydrostatic pressure, mechanical force other than that exerted by hydrostatic pressure, and temperature in certain structures of turbomachinery, power plants, nuclear power plants, etc.

[0075] The measuring device 1 comprises a sensor 3 and an optoelectronic module 5. The sensor 3 includes at least one optical waveguide 7 intended to be rigidly mounted on one of the surfaces or in the wall of a cylindrical test body 9, with a circular cross-section, hollow and sealed at its ends, deforming within its elastic range, and extending along an axis of revolution (zz) (i.e., orientation along J). Only one optical waveguide 7 is shown in the example in [Fig. 1], but of course, the measuring device 1 can include several (see the other figures). Each optical waveguide 7 locally describes a circular helix positioned at a radius r around the axis of revolution (zz) of the test body and locally oriented at a predetermined angle 0(r) with respect to a plane normal to the axis of revolution (zz).Note that an angle equal to ± ir / 2 (modulo jt) is synonymous with orientation along this axis of revolution (zz).

[0076] Each optical waveguide 7 carries at least one transducer (not shown) whose mechanical measurement component is orientation-sensitive. According to a first aspect of the invention, the optical waveguide 7 carries at least one transducer of A Bragg grating type, adapted for distributed measurements. According to a second aspect of the invention, the optical waveguide 7 carries at least one transducer using a continuously sensitive reflectometric technique of the Brillouin type (including the measurement technique described in document EP 3 232 165), Rayleigh OFDR, or phase-OTDR (0-OTDR) or DAS (Dynamic Acoustic Sensing), adapted for distributed measurements along the optical waveguide. According to this second aspect, the optical waveguide 7 itself acts as a transducer.

[0077] Thus, according to a first aspect, the transducer can be inscribed in the optical waveguide 7 such as a Bragg grating. According to a second aspect, the transducer is intrinsically supported by the optical waveguide 7 to perform measurements by Brillouin reflectometry (according to the measurement technique described in document EP 3 232 165), Rayleigh OFDR, or even <j)-OTDR ou DAS, etc.

[0078] Each transducer is configured to perform a selective measurement of a mechanical effect according to a first primary measurement 'P' whose true relative variation is representative of a variation of hydrostatic pressure applied to the test body 9 or of a second primary measurement VF2 whose true relative variation is representative of a variation of a longitudinal force, other than exerted by a hydrostatic pressure, applied to the test body 9. The selectivity of one or the other of the first and second mechanical effects (hydrostatic pressure vs. longitudinal force), via the true relative variations of the first and second primary variables, being ensured by the orientation of each waveguide 7.

[0079] Advantageously, according to a particular aspect of the present invention, any cylindrical host structure, of circular cross-section, under hydrostatic pressure, hermetically sealed and deforming within its elastic range, such as a storage tank or a pressurized pipe, can be considered as a test body 9. In this case, each optical waveguide 7 carrying the transducer is positioned in the wall of the host structure or on one of its surfaces, which is then itself considered as the sensor 3.

[0080] Furthermore, if the deformable host structure is not cylindrical, then, according to another particular aspect of the present invention, the sensor 3 intrinsically comprises a cylindrical, circular-section, hollow, and hermetically sealed test body 9, deforming within its elastic range. Advantageously, the test body 9 is a microstructured optical fiber having, within the thickness of its wall, at least one optical waveguide 7, preferably single-mode, locally oriented in a circular helix around its axis (zz), at the predetermined angle θ) with respect to a plane normal to the axis (zz) of the optical fiber. The transducer can then be photo-inscribed in the waveguide 7. In this case, the sensor 3, deforming within its elastic range, can then be integrated in a solid manner at the very heart of the host structure (within its wall) or on one of its surfaces. It should be noted that the watertight seal of the test body 9 can be achieved, at least at one of its ends, by the instrumented host structure in question when the sensor 3 is embedded in its wall.

[0081] The optoelectronic module 5 comprises a light source 13, an optical spectrometer 15, and a computer 17. The light source 13 is advantageously of the broadband type, including the interrogation wavelength ranges for each transducer. The optical spectrometer 15 is adapted to detect and characterize (in terms of power, wavelength, and, if necessary, phase) the signal reflected or backscattered by the transducers 11.

[0082] The computer 17 is configured to control the light source 13 and the optical spectrometer 15, and to query and retrieve (digitize) the signals from the transducers.

[0083] The calculator 17 is configured to selectively calculate the local variation of the longitudinal force ΔF, other than that exerted by hydrostatic pressure, applied to the test body 9 and / or the local variation of hydrostatic pressure (internal and / or external) applied to the test body 9 as a function of the true relative variations of the first and / or second primary measurements. The calculator 17 is also configured to calculate the local temperature variation from the true relative variations of the first and / or second primary measurements, provided that these are temperature-sensitive.

[0084] In addition, the calculator 17 is configured to calculate the local variation of the longitudinal mechanical deformation A «mcccap of the test body 9 as a function of the local variations of the longitudinal force ôF (other than exerted by hydrostatic pressure) and of the hydrostatic pressure AP applied to the test body 9, as well as the physical parameters of the test body 9.

[0085] Advantageously, the calculator 17 determines, from a formal model, the variations of longitudinal mechanical deformations, hydrostatic pressures and temperatures applied to the test body 9, thus allowing an easy calculation of these quantities.

[0086] Figs. 2A-2E and 3A-3B each illustrate a non-intrusive measuring sensor for measuring a variation in longitudinal force (depending on the orientation of the sensor's test body), other than that exerted by hydrostatic pressure, and / or a variation in hydrostatic pressure relative to a host structure of interest, according to different embodiments of the invention. Figs. 2A-2E illustrate a first embodiment, while Figs. 3A-3B illustrate a second embodiment, according to different variants.

[0087] It should be noted that the watertight closure of the test body is effective in all embodiments, even if, for simplification, it is not represented on the diagrams.

[0088] These different embodiments each relate to a sensor 3 comprising at least one pair of optical waveguides 7a, 7b locally oriented in a circular helix around the axis of revolution (zz) of the test body 9. Each optical waveguide 7a, 7b is positioned along a distinct radius around the axis of revolution (zz) of the test body 9, and locally oriented at predetermined angles with respect to a plane normal to said axis of revolution.

[0089] The test body 9 has an empty space inside its wall, and can receive a fluid under pressure in the variant where the structure plays the role of test body 9.

[0090] More particularly, [Fig.2A] illustrates a first embodiment in which the test body 9 (micro-structured fiber, or even a tank or pressurized pipe) has, in the thickness of its wall, a pair of optical waveguides 7a, 7b carrying a pair of transducers 1la, 11b.

[0091] The first and second optical waveguides 7a, 7b are locally oriented in a circular helix around the axis of revolution at angles 0(rAP) and ¢(¾) respectively with respect to a plane normal to the axis of revolution (zz) of the test body 9. The two optical waveguides 7a, 7b are positioned respectively at rAP and rÔF in the elastic wall and / or on the surface of the test body 9.

[0092] The measurement technique then implemented makes it possible to provide a primary measurement of a purely mechanical nature, which can be achieved in at least three configurations:

[0093] - provided that the temperature remains constant or varies negligibly, so that its effect on the primary measurement performed by the transducer remains negligible compared to the desired mechanical effect,

[0094] - during very rapid events, such as in detonation, as soon as the transducer remains within its elastic deformation range, and the heat exchange with the surrounding structure has effects that can be considered negligible compared to the desired mechanical effect.

[0095] - or when the measurement technique is intrinsically self-compensated in temperature, to provide separately from a single transducer, a measurement of longitudinal mechanical strain and temperature, such as, for example, the Brillouin reflectometry measurement based on the Landau-Placzek ratio.

[0096] It is recalled that the test body 9 is a hollow cylinder, with a circular cross-section, closed at its ends to form a sealed cavity (micro-structured fiber in the case of an optical fiber, or even a pressurized tank or pipe, provided that they have a circular cross-section), deforming within its elastic range.

[0097] The measurement of mechanical deformation performed by each transducer 1a, 11b is sensitive to their orientation according to the two specific angle families 0AP and 4>sf, as well as to their radial position in the wall or on the surface of the test specimen 9. These angles depend on the mechanical deformation and hydrostatic pressure sensitivities of the transducers 1a, 11b, and possibly on their radial position in the wall or on the surface of the test specimen. However, the orientation of the transducers 1a, 11b, according to each of the two angle families, is in no way dependent on the temperature sensitivity of the transducer.This orientation is solely dependent on the mechanical (Young's modulus and Poisson's ratio) and geometric (internal and external radii) characteristics of the test specimen, where applicable, the radial position of the transducer (in the wall or on the surface), as well as the sensitivities of the transducer to longitudinal mechanical deformations and, where applicable, to hydrostatic pressure.

[0098] Depending on whether one wishes to carry out a measurement of variation of hydrostatic pressure or of longitudinal force, other than exerted by a hydrostatic pressure, the two waveguides lia, 11b are positioned according to two angles at 0AP and 0ÔF distinct in absolute value modulo ir (0AP ± 0ÔF mod ji) with respect to the axis (zz) of the test body 9.

[0099] The properties of the test body 9 (i.e., cylindrical, circular in cross-section, hollow, and hermetically sealed at its ends) give it such behavior (in response to hydrostatic pressure and longitudinal forces, distinct from those exerted by hydrostatic pressure, applied to it) that a directional measurement, performed by transducers 1a, 11b which are thermomechanically attached to it, does not exhibit the same sensitivity to these two effects depending on the orientation of these transducers and their radial position in the wall or on the surface of the test body. The selectivity of one or the other of these two mechanical effects (in other words, obtained independently of each other) is ensured by the choice of the angle (0A P or 0OF) in question, the residual sensitivity to the desired mechanical effect (hydrostatic pressure vs.longitudinal force (other than exerted by hydrostatic pressure) being mainly obtained by the distinct radial positions of the two transducers.

[0100] The selectivity of the mechanical effects is thus the result of the specific orientations of the transducers 1a, 11b, allowing one effect or the other to be eliminated depending on the direction in question. This selectivity relies on the exploitation of the Poisson transverse contraction effect. It is this Poisson effect that explains why the component of the mechanical deformation of the test body 9 changes sign. from the direction of application of the longitudinal force applied to it (which we seek to eliminate) to its perpendicular direction, since it passes, by continuity, through a remarkable intermediate angle where its value is zero. It is this remarkable angle that is used to selectively measure the hydrostatic pressure applied to the test specimen 9 on the one hand, and its complementary angle to selectively measure the longitudinal force, distinct from that exerted by a hydrostatic pressure, applied to it on the other hand.

[0101] The intrinsic compensation of the effects of temperature, when the measurement technique used is not itself temperature self-compensated, is the result of the difference of the true relative variations of two primary measurements obtained from two transducers oriented according to the same family of angles and positioned at two distinct radii, within the wall or on the surface of the test body, since by hypothesis and construction, the two transducers are subjected to the same temperature.

[0102] Also, the local variation of the temperature AT is an additional information provided by the sensor 3 in all embodiments, provided that the transducers have a non-zero sensitivity to temperature, or that the measurement technique implemented is itself temperature self-compensated, since it generally provides in a dual manner, the temperature or its variation with respect to an arbitrary reference for the transducer considered (as is the case, for example, for the Brillouin reflectometry measurement technique based on the Landau-Placzek ratio, described in document EP 3 232 165).

[0103] Furthermore, in the case of a sensor 3 integrable in the heart of a structure of any geometry, the hydrostatic pressure, by the gradient of mechanical deformations that it creates in the thickness of the wall, induces a birefringence effect which can also be exploited for the selective measurement of variations in hydrostatic pressure and longitudinal forces, other than those exerted by a hydrostatic pressure.

[0104] Fig. 2B is a variant of the first embodiment illustrating a sensor intended to measure, with or without exploitation of birefringence, the variation of hydrostatic pressure AP applied to the sensor.

[0105] The sensor 3, according to this second embodiment, comprises first and second optical waveguides 7a, 7b oriented locally in a circular helix around the axis of revolution (zz) of the test body 9 at an angle 4>AP with respect to a plane normal to the axis of revolution of the test body 9, the value of which depends on their radial position (on the surface - internal or external - or within the thickness of the test body). The two optical waveguides 7a, 7b are positioned respectively at the radii rUp and in the elastic wall of the test body 9 and / or on its surfaces. The two optical waveguides 7a, 7b carry two transducers lia, 11b, respectively of the Bragg grating type.

[0106] The two transducers 1la, 11b are preferably positioned at the same curvilinear abscissa along the axis of revolution of the test body 9 so as to be subjected to the same temperature variation in the case where there is a temperature gradient along the test body.

[0107] The specific orientation of the two transducers, according to this angle 4>AP, allows them to remain insensitive to variations in longitudinal forces ôF, other than those exerted by hydrostatic pressure, applied to the test body 9, while their sensitivity to mechanical deformation, under the effect of the variation of the hydrostatic pressure AP, is mainly modulated by their distinct radial positions in the wall of the test body.

[0108] The difference in true relative variations, with respect to an arbitrary reference state, between the two primary measurements of the transducers, subjected by hypothesis to the same temperature, then eliminates the effect of temperature variations, with a result of a purely mechanical nature, in direct relation to the variation of hydrostatic pressure AP, which makes it possible to ensure the selective nature of their measurement, independently of the effects of temperature, and by extension, of any other phenomenon of a non-mechanical nature such as the effects of ionizing radiation.

[0109] And since the transducers have a non-zero sensitivity to temperature, the local temperature variation AT is additional information provided by the sensor 3, since temperature is the only non-mechanical phenomenon to which the transducers are subjected, obtained jointly during the formal resolution of the underlying thermomechanical problem.

[0110] The [Fig.2C] is another variant of the first embodiment, also for selectively measuring, with or without exploitation of birefringence, the variation of the hydrostatic pressure AP applied to the sensor 3.

[0111] According to this variant, the two waveguides 7a, 7b are exploited by a distributed fiber optic measurement reflectometric technique, sensitive to both temperature and mechanical deformation, such as Brillouin, OFDR Rayleigh, phase-OTDR (0-OTDR) or DAS (Dynamic Acoustic Sensing) techniques.

[0112] Fig. 2D is yet another variant of the first embodiment illustrating a sensor intended to selectively measure, with or without exploitation of birefringence, the variation of the longitudinal force ôF, other than exerted by a hydrostatic pressure, according to the orientation & of the sensor.

[0113] The sensor 3 according to this third embodiment comprises first and second optical waveguides 7a, 7b locally oriented in a circular helix around the axis of revolution (zz) of the test body at distinct angles (PSF() and (PgF(r2SF) with respect to a plane normal to the axis of revolution of the test body 9. The two optical waveguides 7a, 7b are positioned respectively at distinct radii r W- and r26P in the elastic wall of the test body 9. The two optical waveguides 7a, 7b carry Bragg grating transducers lia, 11b.

[0114] The two transducers 1la, 11b are preferably positioned at the same curvilinear abscissa along the axis of revolution of the test body 9 so as to be subjected to the same temperature variation in the case where there is a temperature gradient along the test body.

[0115] The specific orientation of the two transducers, according to the angles ) and <PSF( f2ep ), leur permet de rester insensible aux variations de la pression hydrostatique AP appliquée au corps d’épreuve 9, alors que leur sensibilité en déformation mécanique, sous l’effet de la variation des efforts longitudinaux ôF (distincts de ceux exercés par une pression hydrostatique), est quant à elle modulée par leurs positions radiales distinctes dans la paroi ou en surface du corps d’épreuve.

[0116] The difference in true relative variations, with respect to an arbitrary reference state, between the two primary measurements of the transducers, subjected by hypothesis to the same temperature, then eliminates the effect of temperature variations, with a result of a purely mechanical nature, in direct relation to the variation of the longitudinal forces ôF (distinct from those exerted by a hydrostatic pressure), which makes it possible to ensure the selectivity of their measurement, independently of the effects of temperature, and by extension, of any other phenomenon of a non-mechanical nature such as the effects of ionizing radiation.

[0117] And since the transducers have a non-zero sensitivity to temperature, the local temperature variation AT is additional information provided by the sensor 3, since temperature is the only non-mechanical phenomenon to which the transducers are subjected, obtained jointly during the formal resolution of the underlying thermomechanical problem.

[0118] Fig. 2E is yet another variant of the first embodiment, also for selectively measuring, with or without exploitation of birefringence, the variation of longitudinal force ôF, other than exerted by hydrostatic pressure, according to the orientation J of the sensor.

[0119] According to this variant, the two optical waveguides 7a, 7b are exploited by a distributed fiber optical fiber reflectometric measurement technique, sensitive to both temperature and mechanical deformation, such as Brillouin, OFDR Rayleigh, phase-OTDR (0-OTDR) or DAS (Dynamic Acoustic Sensing) techniques.

[0120] Fig. 3A illustrates a second embodiment in which the test body (micro-structured fiber, tank, or pressurized pipe) has, in the thickness of its wall and / or on its surfaces, two pairs of optical waveguides 7a, 7b, 7c, 7d carrying two pairs of transducers 1a, 11b, 1le, 1Id.

[0121] More specifically, the sensor 3 comprises first 7a, 7b and second 7c, 7d pairs of optical waveguides locally describing two pairs of circular helices carrying two pairs of transducers 1a, 11b, and 1le, 1Id. A first pair of waveguides 7a, 7b is dedicated to measuring the variation of the hydrostatic pressure AP, while the second pair of waveguides 7c, 7d is dedicated to measuring the variation of the longitudinal force ôF, other than that exerted by hydrostatic pressure, applied to the test body 9, according to the orientation Σ of the sensor. This allows, with or without the use of birefringence, the selective measurement of the two mechanical components of the variation of the hydrostatic pressure AP and the variation of the longitudinal force ôF (other than that exerted by hydrostatic pressure) applied to the sensor 3.

[0122] The two waveguides 7a, 7b of the first pair, locally oriented in a circular helix, are positioned around the axis of revolution at the angle 4>AP with respect to a plane normal to the axis of revolution of the test body 9. The two waveguides 7c, 7d of the second pair of waveguides, locally oriented in a circular helix, are positioned around the axis of revolution at the angles (pSF(rî5r) and with respect to a plane normal to the axis of revolution. The first 7a, 7b and second 7c, 7d pairs of waveguides are positioned respectively at r2&p, and rkp, r2sr in the elastic wall of the test body 9, each carrying a Bragg grating transducer 1la, 11b, 1le, 1Id.

[0123] The combination of these two families of angles, using two pairs of transducers positioned within the same test body 9, allows the device 1 to perform a simultaneous selective measurement of the two mechanical effects of hydrostatic pressure variation AP (internal APint and / or external APext) and variation of longitudinal forces ôF, other than those exerted by hydrostatic pressure, applied to the test body. Subsequently, variations in longitudinal mechanical deformations A emeccq, according to the orientation k of the sensor, with respect to an arbitrary reference state, can be deduced.

[0124] Fig. 3B is a variant of the second embodiment also for measuring the variation of hydrostatic pressure AP applied to the sensor, as well as the variation of the longitudinal force ôF, according to the orientation k of the sensor.

[0125] According to this variant, the four waveguides 7a, 7b, 7c, 7d are used by a distributed fiber optic reflectometric measurement technique, sensitive to both the temperature and mechanical deformation, such as Brillouin, OFDR Rayleigh, phase-OTDR (0-OTDR) or DAS (Dynamic Acoustic Sensing) techniques.

[0126] Figs. 4, 5 and 6 illustrate the use by the computer of a thermomechanical model to calculate, from a formal model derived from this model, the variations of longitudinal mechanical deformations (according to the orientation k of the sensor), of hydrostatic pressures and of temperatures relative to the sensor according to different embodiments of the invention.

[0127] Fig. 4 is a flowchart illustrating the steps of a non-intrusive measurement process of a variation in mechanical deformation and / or a variation in hydrostatic pressure relating to a structure of interest, according to the embodiments of Figs. 1, 2A-2E and 3A-3B.

[0128] Step El relates to the instrumentation of the host structure with one or more measuring devices 1 each comprising at least one optical waveguide 7 according to the embodiments of Figs. 1, 2A-2E and 3A-3B.

[0129] The optical waveguides 7 are positioned within the test body 9 forming the sensor 3. If the host structure has a suitable cylindrical geometry and is hermetically sealed at its ends, it can itself act as a test body 9 as soon as it deforms within its elastic range. Alternatively, in the case of a host structure of arbitrary geometry, a test body 9 is rigidly integrated within the wall of the structure, or on one of its surfaces.

[0130] In step E2, the transducer of each optical waveguide 7 provides first primary measurements Tj and / or second primary measurements whose difference in the true relative variations ATj and AT2 with respect to an arbitrary reference state is selectively and exclusively representative of a local variation of a hydrostatic pressure AP (internal or external), or of a local variation of a longitudinal force θF, other than that exerted by a hydrostatic pressure, applied to the test specimen. The selectivity of one or the other mechanical effect (hydrostatic pressure AP vs. longitudinal force θF) achieved by first and / or second primary measurements is ensured by the orientation β) of the transducers concerned.

[0131] In the case where the measurement technique is sensitive to temperature, and the effect of temperature on the deformation measurement is not self-compensated (e.g., measurement by Bragg gratings) and the effect of temperature on the transducers cannot be neglected, the number of transducers is at least equal to two, and the true relative variations of the primary measurements A T j and A 'P, must be selective of the same mechanical effect (variation of hydrostatic pressure AP or, exclusively, of longitudinal force ôF, distinct from that exerted by a hydrostatic pressure), i.e. oriented along the same family of angles.

[0132] In the case where the mechanical deformation measurement technique is by nature insensitive to temperature (self-compensated measurement), such as for example the distributed measurement technique by Brillouin reflectometry based on the Landau-Placzek ratio, described in document EP 3 232 165, or where the effect of temperature on the transducer can be neglected, at least one waveguide (or transducer) is necessary, oriented according to its family of selective angle for the measurement of the mechanical effect considered, provided that the conditions for the application of such a measurement are met (the selective angle in question having to take a real value).

[0133] The calculator 17 queries each transducer and selectively calculates the local variation of the longitudinal force ôF (other than exerted by a hydrostatic pressure) applied to the test body 9, or the local variation of internal hydrostatic pressure APint or external hydrostatic pressure APext applied to the test body 9. The calculator 17 also calculates the local temperature variation AT of the test body 9 when the primary measurement is sensitive to temperature.

[0134] The variation of the longitudinal force ôF (other than exerted by a hydrostatic pressure) or the local variation of internal hydrostatic pressure APint or external hydrostatic pressure APext is determined as a function of the true relative variation A of the first primary measurement and / or the true relative variation A T2 of the second primary measurement ^2 according to the orientation ¢) of each transducer 7. This calculation is detailed further in relation to Figs. 5 and 6.

[0135] In step E3, the computer 17 determines the local variation of the longitudinal mechanical deformation Ammeccap of the test body 9 as a function of the longitudinal variations of the force ΔF (other than that exerted by hydrostatic pressure) and the variations of the internal hydrostatic pressures APint and external hydrostatic pressures APext applied to the test body 9, as well as the physical parameters of the latter. The variation of the longitudinal mechanical deformation Ammeccap of the sensor, and more particularly of the test body, is given by:

[0136] [Math.7] A 1 8F l-2v _rg r £ ,.2 \ 'Vx' -M' vfnr

[0137] E is the Young's modulus and v the Poisson's ratio (-1 < v < 0.5) of the test body, and r0iia, r°ext are respectively the internal and external radii of the test body 9 in its reference state.

[0138] In step E4, the computer 17 applies corrections to the variation in longitudinal mechanical deformation A (mecca), of the sensor 3 calculated in step E3 to match the nature of this measurement to that of the instrumented host structure. These corrections are based on taking into account the differential expansions between the test body 9 and the instrumented host structure, to determine the component of the mechanical deformation variation A smec5ttuct, according to the orientation k of the sensor, of the host structure in question, according to the following expression:

[0139] [Math. 8] A £mecstnlcl — A ^mcceap ■ Acc XAT

[0140] where AT is the measure of the local temperature variation, and Aa = (astruct - acap) is the difference in the coefficients of thermal expansion between the host structure and the test body 9. Of course, Aa = 0 in the case where the host structure acts as a test body 9.

[0141] Step E5 is a test to verify whether the host structure acts as a proof body or not. If so, we go to step E6. Otherwise, we go to step E8.

[0142] Step E6 concerns the case where the host structure is a pressurized tank or pipe, circular in cross-section, hermetically sealed at its ends, deforming within its elastic range. In this case, the calculator 17 considers the variation in mechanical deformation Amecstlucl to be its variation in longitudinal mechanical deformation, as calculated in step E3.

[0143] At step E7, the calculator 17 optionally determines the other local components of the variations in displacements, strain tensor and stress tensor for the host structure, which is assumed to have an overall isotropic behavior and is deforming in its elastic domain.

[0144] Step E8 concerns the case where the sensor 3 is embedded or positioned on the surface of the host structure of any kind. At this step, the computer 17 considers that the longitudinal mechanical deformation variation A £mecshurt calculated in step E4 is the local component of the mechanical deformation variation of the host structure, according to the orientation k of the sensor's test body, of the micro-structured optical fiber type.

[0145] In step E9, the computer 17 determines some values ​​of other local components. The calculation is performed by continuity between the local variations of the components relating to the sensor's test body and the host structure, on their common interface defined by the external surface of the sensor's test body.

[0146] It should be noted that the local equality by continuity is valid for the following quantities: temperature variation AT, variation of total displacements (mechanical + thermal) Au (radial component), Aw (longitudinal component), total longitudinal strain Atotcap (mechanical Atotcap + thermal AtLap) of the sensor Atotcap — Atotcap + A, with the component, according to the orientation k of the sensor's test body, of the variation of the local total strain Atotsmtrt of the host structure (Atotcap = Atot,t), and of the variation of the radial stress A0. (corresponding, up to the sign, to a variation of hydrostatic pressure) exerted on the external surface of the sensor (thus corresponding, up to the sign, to the variation of the internal hydrostatic pressure APint of the host structure, at the very place where the sensor is positioned).

[0147] The [Fig.5] is a flowchart illustrating the steps of a non-intrusive method for measuring a variation in mechanical deformation and / or a variation in hydrostatic pressure relating to any structure of interest, according to a particular embodiment of the invention.

[0148] This embodiment relates to the case of a sensor according to Figs. 1 to 3B in its version integrable at the heart of a structure of arbitrary geometry.

[0149] The Eli step concerns the configuration of sensor 3 and its integration into a host structure 19.

[0150] The sensor 3 comprises a sensing element 9 and at least two waveguides 7 oriented along the same family of angles. The sensing element 9 is cylindrical, with a circular cross-section, hollow, and hermetically sealed at its ends, deforming within its elastic range. The hermetically sealed closure can advantageously be provided, for at least one end, by the instrumented host structure 19 when the sensor 3 is embedded in its wall.

[0151] The test body 9 may be under internal pressure, or preferably, be at zero pressure (i.e., a vacuum). It should be noted that if the test body 9 is not under zero pressure, and if the temperature varies significantly with respect to the phenomenon being investigated, then the value of the internal pressure can be corrected using the ideal gas law, since temperature is one of the physical quantities measured by the sensor, provided that the transducers are themselves sensitive to temperature.

[0152] Advantageously, the test body 9 is a micro-structured optical fiber, thus forming a micro-capillary. The test body (optical fiber) is preferably made of silica, or even of sapphire A12O3 (the latter solution allowing the sensor to be used up to about 1800°C, with however an overall multimode behavior of the waveguide in most cases, but which can nevertheless still be exploited with a Bragg grating, with a measurement uncertainty however greater than within a single-mode optical guide).

[0153] Furthermore, the optical fiber-type test body 9 can advantageously be coated with a deformable mechanical sheath, for example made of polymer (polyimide, polyacrylate, etc.), and of low thickness (for example, a few tens of micrometers). This ensures its survival throughout the operating period of the structure and provides good transduction of the mechanical deformations of the instrumented host structure.

[0154] At least two optical waveguides 7 carrying transducers whose mechanical measurement component is sensitive to orientation (such as Bragg gratings in the case of distributed measurements, or simply two optical waveguides, preferably single-mode, if these are used in Brillouin reflectometry, Rayleigh OFDR, or even phase-OTDR (0-OTDR) or DAS (Dynamic Acoustic Sensing) in the case of distributed measurements), are positioned in the thickness of the test body 9 (for example in the wall of the microstructured fiber).

[0155] Advantageously, the microstructured fiber of sensor 3 can be manufactured by 3D nanoprinting to form an end component of an optical fiber, for example, a multi-core type, to which it can be connected. In such a case, the creation of locally circular helices with opposite sign angles is feasible. Combining (arithmetic mean) measurements taken with opposite sign angles makes it possible to eliminate, in a conventional manner, the effects of torsion on the sensor.

[0156] Alternatively, the microstructured fiber can be manufactured by drawing, on a fiber-drawing tower, a preform structured in such a way as to have optical waveguides to house the transducers. This preform, once drawn, can undergo, locally or not, one or more twisting operations so as to force the optical waveguides to conform locally into circular helices at the notable angles defined above or at any angles distinct in absolute value modulo ji, or alternatively, the preform can originally have optical waveguides in predefined orientations or at any angles distinct in absolute value modulo ji, thus limiting the number of subsequent local twisting operations.

[0157] Furthermore, in the case of Bragg grating transducers, their photo-inscription can be carried out point-by-point, by femtosecond laser, in each of the optical waveguides 7 arranged locally in a circular helix around the axis of the micro-structured optical fiber 9 (test body).

[0158] The sensor 3, according to the properties described above, allows the measuring device 1 to perform a selective measurement of the variation of hydrostatic pressure and / or longitudinal forces, other than those exerted by hydrostatic pressure, applied to the test body 9, and then of its longitudinal mechanical deformations.

[0159] Steps E12 to E17 relate to the determination of the variations of the internal hydrostatic pressure APint or external hydrostatic pressure APext, the local temperature AT and the longitudinal forces ôF (according to the orientation k of the sensor), other than those exerted by a hydrostatic pressure, as a function of the configuration of the transducers (positioned at the radii r according to the families of angles ¢).

[0160] In particular, steps E12 to E16 relate to selective measurements in the absence of birefringence (i.e.: without separation of the Bragg peak), while step E17 relates to selective measurements in the presence of birefringence.

[0161] Step E12 relates to the selective measurement of the variation of the hydrostatic pressure APext applying outside the sensor as well as the variation of the local temperature AT associated with the variation of the external hydrostatic pressure.

[0162] In this case, angles ¢1 and ¢2 are equal in absolute value to the absolute value of angle V&p modulo ji, defined according to their radial position (in the wall or on the surface of the test body) by the following relation: - if the transducer is in the wall of the test body:

[0163] [Math.9] (p. p - + 2 arccosi ” ( 1- v - / J mod / r - if the transducer is on the internal or external surface of the test body:

[0164] [Math. 10] = ±4arccos(-£; ) mod / r

[0165] where E is the Young's modulus of the optical fiber test body, kp and K( are respectively the hydrostatic pressure and longitudinal mechanical strain sensitivities of the transducer, attached to the test body, for the measurement technique considered (for example of Bragg grating type), and v is the Poisson's ratio of the test body.

[0166] For example, for a germanosilicate type optical fibre: Esiiice 72 GPa, visiiice - 0.17, and for a Bragg grating transducer: Kp ~ - 2 87 X 10° MPa'! ct Kg“0.78.

[0167] The variation of the external hydrostatic pressure APext is then a linear function f of the difference between the true relative variations: ATa - AT of the primary measurements: Ta and Tb, the true relative variation: AT of the primary measurement: T being defined as follows:

[0168] [Math. 11] AT = In ( 1 + )

[0169] where AT is the variation of the raw value T: primary measurement carried out by the transducer) between its reference value To and its current value T: AT = T-T0).

[0170] It should be noted that for a Bragg grating transducer 7, the raw value or primary measurement T corresponds to its Bragg wavelength: XBragg. For a measurement For Brillouin reflectometry on an optical fiber (the measurement being distributed in this case, with the transducer being the waveguide of the optical fiber itself), the primary measurement corresponds to its Brillouin frequency. For a Rayleigh OFDR reflectometry measurement on an optical fiber (the measurement also being distributed in this case, with the transducer being the waveguide of the optical fiber itself), the primary measurement T corresponds to its Rayleigh frequency VR. For any other optical fiber reflectometry measurement technique (e.g., phase-OTDR (0-OTDR) or DAS (Dynamic Acoustic Sensing)), sensitive to temperature and mechanical deformation, the primary measurement is the value of its characteristic quantity Vc.

[0171] The variation of the hydrostatic pressure APext applied to the external surface of the sensor is given by the following relation:

[0172] [Math. 12] AP^

[0173] By making the above formula explicit, the variation of the hydrostatic pressure AP ext as well as the calculation of the corresponding variation of the local temperature AT are expressed as a function of the configuration of the transducers, in the following way: - if the two transducers are positioned at radii ri and r2 in the wall of the test specimen:

[0174] [Math. 13] A Pext =

[0175] [Math. 14] [ 'A'V / j-A'Pjri (A'PfA'tyririft 1-2\'')Ke-KpE) + (1f■Ke-Kp)^Pint if the transducers are positioned on surfaces internal to the radius roin! and external to the radius roext of the test specimen:

[0176]

[0177] [Math. 15] K(+KpE [Math. 16] E Ke~ Kp) ^Pjnt if the first transducer is positioned at radius ri in the wall and the second transducer on the external surface at radius r

[0178] [Math. 17] A p _ ap , eXt

[0179] [Math.18] A T - 1 [ AW . - rT if the first transducer is positioned on the internal surface at the radius and the second transducer at radius r2 in the wall of the test body:

[0180] [Math. 19] }E \ p — \ p ~ ~ "*• eXt

[0181]

[0182] [Math.20] 1 < 2(4^,-4^ / ¾1-vK kt _ int r'^^K^KpÉyry.Kf+KpE) where E is the Young's modulus of the proof body optical fiber, kp, Kf and kt are ​respectively the sensitivities in hydrostatic pressure, in longitudinal mechanical deformation, and in temperature of the transducer attached to the host structure for the measurement technique considered, APint is the variation of the internal hydrostatic pressure, and r%,t, r{Xxt are respectively the internal and external radii of the micro-structured optical fiber, acting as a test body, in its reference state, and are respectively the primary measurements of the transducers positioned on the internal surface at radius roiHt and on the external surface at radius roCxt, and and V? are respectively the primary measurements of the transducers positioned within the wall, to the ri and r2 rays.

[0183] Step E13 relates to the selective measurement of the variation of longitudinal forces ôF (other than exerted by hydrostatic pressure) applied to the test body as well as the calculation of the variation of the local temperature AT associated with this variation of longitudinal forces, other than exerted by hydrostatic pressure.

[0184] The angle 0; is, in absolute value, equal to the absolute value of the angle 0ÔF, modulo ji, defined by:

[0185] [Math.21] w=id^i modÆ'

[0186] In particular, for a selective measurement of the variation of longitudinal forces ÔF\p independently of APext, the angle 0; is, in absolute value, equal to the absolute value of the angle / \ modulo n, defined by the following relation: - if the two transducers are positioned at radii ri and r2 in the wall of the test specimen:

[0187] [Math.22] (r / ) = 2-J-(^ mod^ (VI,2) - if the transducers are positioned on surfaces internal to the radius r0M and external to the radius roext of the test specimen:

[0188] [Math.23] <PSFàP (ro,j = ±4arccos( -3^ ) mod / r ext

[0189] [Math.24] <Pw (r0 V ±~arccos -2---------1 mocbr T Or \ -axt J ~ I ( i+vjà... j

[0190] The variation of the longitudinal forces ÔF&p exerted on the test body is a linear function f8F of the difference of the true relative variations: A^-A^ of the primary measurements: and ;

[0191] [Math.25] exi

[0192] Explicitly, the variation of the longitudinal forces ÔF.\j>^t and the variation of the local temperature AT are equal to: - if the two transducers are positioned at radii ri and r2 in the wall of the test specimen:

[0193] [Math.26] (A^-A^^rg (rg -r^}E 0P “ (ry-ny

[0194] [Math.27] (A^ 1- AT2HJk4 KjÆ) d-ri " (r^rl\(_l-2v)Kt-KPE) + (kÿ-Ks-Kp)APint if the transducers are positioned on surfaces internal to radius r0;œ and external to radius ro<,Xi of the test body:

[0195] [Math.28] °F\Pexl~ ^-2^-Kf.E

[0196] [Math.29] AT- i X. j 'VL - if the first transducer is positioned at radius ri in the wall and the second transducer on the external surface at radius r <L« du corps d’épreuve :

[0197] [Math.30] - 3(^^)( l-2vK-(4r^-3(7^-r^pE

[0198] [Math.31] AT=^ \has" 'Vî '+ e ^-kp)APint if the first transducer is positioned on the internal surface at radius roM and the second transducer at radius r2 in the wall of the test specimen:

[0199] [Math.32] APaïf )(1-2^)^-(3^^^^

[0200] [Math.33] — — -, ^nt

[0201] Step E14 concerns the calculation of the variation in longitudinal mechanical deformation of the test body. Indeed, variations in internal hydrostatic pressure APint or external hydrostatic pressure APext on the test body 9, variations in external longitudinal forces ôF applied to the test body (other than those exerted by hydrostatic pressure), and variations in local temperature AT of the test body, lead to the calculation of the variation in longitudinal mechanical deformation A Emeccap of the sensor test body 9, according to the following equation:

[0202] [Math.34] A _ 1 BF l-2v A Pmeccap - E ^ 2 _r2 ) - E r? -ri

[0203] Step E15 concerns the calculation of the component of the variation of the mechanical strain Amstruct of the instrumented host structure 19 according to the orientation k of the optical fiber 9. In order to determine this component of the variation of the mechanical strain Amstruct of the host structure, the computer 17 corrects the effects of differential expansions between the host structure 19 and the sensor 3. This correction is based on the local measurement of the variation of the temperature AT (provided jointly by the sensor) and on the difference in the coefficients of thermal expansion Aa between the sensor acap and the host structure astruct: Aa = (acap - astruct). The component of the variation of the mechanical strain of the host structure: Amstruct is then defined by the following equation:

[0204] [Math.35] A £mec!talct — A PmeCcap ' A « X AT

[0205] Step E16 concerns the calculation of certain local values ​​of variations of radial displacements Au and longitudinal displacements Aw, of total deformations (mechanical + thermal) radial and longitudinal, and of radial stresses Ao^, by continuity on its common external interface with the host structure.

[0206] It should be noted that the thermomechanical properties (coefficients E, \ a) and the measurement sensitivities (*\ and Kr) correspond to those of the transducer 7 attached to the sensor 3 for the measurement technique considered. If the test body 9 is the micro-structured fiber (micro-capillary sealed at its ends), the sensor 3 is then formed from this sealed capillary and its transducers 7. This sensor 3 can then be integrated, in a fixed and minimally intrusive manner, within or on the surface of any host structure 19 to measure local variations in temperature, mechanical deformation (component depending on the orientation & of the sensor) and hydrostatic pressure, external to the sensor (corresponding to the variation of the hydrostatic pressure internal to the structure, at the position of the sensor).

[0207] Step E17 relates to selective measurements in the presence of birefringence, and therefore with a separation of the Bragg peak into two distinct wavelengths X2 and X3, along a first propagation axis (called ordinary axis or slow axis) and a second propagation axis (called extraordinary axis or fast axis).

[0208] This step illustrates the effect of birefringence on a Bragg grating carried by an optical fiber. The diagram shows the reflected intensity I(X) as a function of the wavelength X before and after the action of a hydrostatic pressure variation acting on the sensor.

[0209] Indeed, according to the configuration of a sensor 3 integrable within a structure 19 of arbitrary geometry, the hydrostatic pressure acting on the micro-structured optical fiber 9 naturally generates a deformation gradient in its wall, and therefore birefringence. This results in the separation of the original Bragg peak Xi into two distinct Bragg wavelengths X2 and X3 along the ordinary and extraordinary axes, respectively.

[0210] Hydrostatic pressure exerts, in a way, a "pinching" effect on the Bragg grating for this test body geometry, resulting in the generation or exacerbation of local birefringence (if the optical waveguide is initially highly birefringent). This birefringence is caused by the appearance of a deformation gradient in the test body wall when it is subjected to hydrostatic stress. In such a case, the positioning angles of the optical fiber 9 can be adapted for selective measurements of the mechanical contributions to the deformation of the test body, such as pressure variations.

[0211]

[0212]

[0213]

[0214]

[0215]

[0216]

[0217]

[0218]

[0219]

[0220]

[0221]

[0222]

[0223]

[0224] hydrostatic AP or longitudinal forces ôF, other than those exerted by hydrostatic pressure. In this case, for a selective measurement of the variation of the hydrostatic pressure applied inside APint or outside APext of the sensor 3, an angle equal, in absolute value, to the absolute value of the angle 0AP modulo ji, is defined for each of the wavelengths X2 and X3, according to the following relations. For the wavelength X2 relative to the ordinary axis, the angle 0AP is defined by: [Math.36] ir 2k i ±2 arccos L -1 + Ü7 J For the wavelength X3 relative to the extraordinary axis, the angle 0AP is defined by: [Math.37] (P^pin^ ± Iarccos [ -1 - ] mo <Vr On the other hand, for a selective measurement of the variation of longitudinal forces ôF (other than those exerted by hydrostatic pressure) exerted on the sensor 3, each of the angles ^SF^ and PdF^pt is defined, for each of the wavelengths X2 and X3, according to the following relations. For wavelength X2, the angles / and ( with i= 1,2, are expressed as ^ôFAp \ il ÔF\ O tntX f gKt\ > in the following way: [Math.38] ±4 arccos 3-- modr [Math.39] = ± 1 arccos 3-^(3Ke + ^Eh-^-) modyr For wavelength X3, the angles ( ) and [ ) are expressed in terms of PsFw \ri ^ÔF^p VV f, Al exi\ f in the following way: [Math.40] ■ rg (i+vY-r^KpE Vqf^M - ± 2arœos[ 1 + 2^^“ [Math.41] ^ôf^~ -ïarccos1 + mod / r mocfT These effects may, however, not be significant enough to lead to a clear separation of its spectral profile under the effect of this deformation gradient. Fig. 6 is a flowchart illustrating the steps of a non-intrusive measurement process of longitudinal mechanical deformation (according to the orientation k of the sensor) and / or a variation of hydrostatic pressure relating to a cylindrical structure, of circular cross-section, according to another particular embodiment of the invention.

[0225] This embodiment relates to the case of a sensor according to Figs. 1 to 3B in its version with waveguides (and therefore transducers) integrable into a host structure of cylindrical geometry, circular cross-section, hollow and sealed at its ends and deforming within its elastic range. Here, the host structure itself plays the role of the test body.

[0226] Step E21 relates to the configuration of the sensor 3 formed by optical waveguides 7 within the cylindrical host structure.

[0227] At least two optical waveguides 7 (carrying transducers), whose mechanical measurement component is orientation-sensitive, are positioned in the wall of the cylindrical section and / or on one of the surfaces of the host structure 19, but not on its ends, acting as watertight seals (the watertight seal at the ends being to be considered in a broad sense, meaning that it is not necessarily made directly on the structure: this concerns, for example, a pipe used for extracting hydrocarbons from the seabed, where the watertight seal can be considered by the well itself on the seabed side for the first end, and by the surface storage station at the other end). The transducers carried by the optical waveguides 7 are configured to measure the mechanical component of the total deformation (resulting from the sum of a mechanical deformation and a thermal deformation).For example, transducers are Bragg gratings within a single-mode optical fiber in the case of distributed measurements, or simply an optical fiber, preferably single-mode, if it is used for distributed measurements by Brillouin reflectometry, Rayleigh reflectometry, phase-OTDR (0-OTDR), or DAS (Dynamic Acoustic Sensing), etc. The optical fiber can advantageously be equipped with an elastically deformable protective sheath, for example, made of a polymer (polyimide, polyacrylate, etc.). Advantageously, the protective sheath is made of ceramic (e.g., boron nitride BN) or metal (e.g., copper, aluminum, gold) to withstand 3D printing processes where temperatures are likely to be high, particularly in the field of metal and ceramic 3D printing.

[0228] The two transducers carried by the waveguides 7 are locally oriented respectively along a circular helix with its axis aligned with that of the cylindrical host structure, which has a circular cross-section (acting as a test body). The orientation is defined by the same predetermined family of angles 4AP or 0F with respect to a plane normal to the axis of the structure, so as to be able to exclusively select one or the other mechanical effect (hydrostatic pressure or longitudinal force, other than that exerted by hydrostatic pressure). The two transducers are positioned at two radii distinct values ​​for ri and r2, either on the internal or external surface of the radius, allow for distinct sensitivities to mechanical deformations, while remaining subject to the same temperature variation. This eliminates the effects of temperature variations and, by extension, any other non-mechanical effects such as ionizing radiation on the transducers, simply by subtracting the true relative values ​​from their raw measurements.

[0229] It should be noted that conventional transducers can be used, provided that the mechanical component of the deformation measurement they enable is sensitive to the orientation of the transducer relative to the structure acting as the test specimen. Thus, with regard to Bragg gratings, the use of conventional single-mode optical fibers, whose optical guide is on their axis, is perfectly feasible, with a photo-inscription method for the Bragg gratings which can also be conventional (such as phase masks or Lloyd's mirrors), or even point-by-point with a femtosecond laser (e.g., type III Bragg gratings).

[0230] Depending on the temperature ranges envisaged, the optical fiber can be made in a conventional way in doped silica (case of germanosilicate type optical fibers), or even in sapphire A12O3, in order to withstand the most extreme temperatures, up to 1000°C continuously, and even beyond (1800°C being an upper limit temperature for sapphire).

[0231] The sensor can be considered as an end component (as in the case of Bragg grating transducers), or as a distributed measurement sensor (several components coupled in a daisy chain within the same optical fiber), or even as a distributed measurement sensor, sensitive over its entire length, for example usable by Brillouin reflectometry, Rayleigh OFDR, phase-OTDR (0-OTDR) or DAS (Dynamic Acoustic Sensing).

[0232] This sensor 3, formed by the structure 19 playing the role of the test body 9 with the transducers 7 positioned in its wall, allows for a selective measurement of variations in hydrostatic pressures or longitudinal forces (other than those exerted by a hydrostatic pressure).

[0233] Step E22 relates to the selective measurement of the variation of the hydrostatic pressure APint prevailing inside the host structure 19 and the determination of the variation of the local temperature AT associated with the variation of the internal hydrostatic pressure.

[0234] The angles ¢1 and 02 are equal, in absolute value, to the absolute value of the angle modulo ji, the value of which depends on the radial position, on the surface - internal or external - or within the wall of the structure acting as a test body.

[0235] In the case where the transducer is positioned on the internal surface at radius r®M or external at radius E\xt of the cylindrical structure, of circular cross-section (i.e.: test body), the angle ^np^ is defined by the following relation:

[0236] [Math.42] ^pJr^=VNP^ = Marccos(£;) mod^

[0237] However, in the case where the transducer is positioned in the wall of the cylindrical structure, with a circular cross-section (i.e.: test body), the angle (P^pM) is defined by the following relation:

[0238] [Math.43] 1 [ 1 / ? K pE \ 1 mod / r

[0239] where E is the Young's modulus of the structure, kp and Ks are respectively the hydrostatic pressure and longitudinal mechanical strain sensitivities of the transducer, for the measurement technique considered (for example of Bragg grating type), and v is the Poisson's ratio of the structure acting as the test body.

[0240] The variation of the internal hydrostatic pressure APint is a linear function f. „ &*inf of the difference of the true relative variations: AT^-A^ of the primary measurements: and The variation of the hydrostatic pressure APint prevailing inside the structure is given by the following relationship:

[0241] [Math.44] APint = f^.(^^ mt

[0242] Explicitly, the variation of the internal hydrostatic pressure APint and the variation of the local temperature AT associated with this variation of the internal hydrostatic pressure are expressed as follows: - when the transducers are positioned in the wall of the test body to rays ri and r2:

[0243] [Math.45] ext rlAJr^MKPE^

[0244] [Math.46] --77--+---77777—i—7--+ \~Ë~KP- Kp ) Ærexl 07 rüJrrrltKe--KPh) ' £ '■ ' ' exl

[0245] where kt is the temperature sensitivity of the transducer, attached to the host structure, for the measurement technique considered (for example of Bragg grating type). - when the transducers are positioned on surfaces internal to the radius and external to the radius of the test body:

[0246]

[0247]

[0248]

[0249]

[0250]

[0251]

[0252]

[0253]

[0254]

[0255] [Math.47] AP AP *mt ~ ext " Ke+KPE [Math.48] 'VL + Kp) APext - when the transducers are positioned in the wall at radius ri and on the external surface at radius rQext of the test specimen: [Math.49] AP. — AP mt ext [Math.50] 2(A^„rA'!',yf(lv);cf rLV KpÈyr^Ke+KPE) ext when the transducers are positioned on the internal surface at radius r%!t and in the wall at radius r2 of the test specimen: [Math.51] ^Pint = &Pext + rlJflJwAKpE}-r^ when the transducers are positioned on the internal surface at radius roiW and in the wall at radius r2 of the test body: [Math.52] 1 r A 1 “ M + rlJr^K^ 1-2? \ a t» — Ks-Kp)kPext Step E23 concerns the measurement of the variation of longitudinal forces ôF (other than those exerted by hydrostatic pressure) exerted on the structure acting as a test body and the variation of the associated local temperature AT. The angle ¢, (i.e., ¢1 or 02) is, in absolute value, equal to the absolute value of the angle / \ modulo ir: goose \ / [Math.53] modr i = 1, 2 In the case where the transducer is positioned on the internal surface of the cylindrical structure, with a circular cross-section (ze: test body), the angle (pSF, (row) is defined by the following relationship:

[0256]

[0257]

[0258]

[0259]

[0260]

[0261]

[0262]

[0263]

[0264]

[0265]

[0266] [Math.54] M = ±4arccos r%J- modr In the case where the transducer is positioned on the external surface of the cylindrical structure, with a circular cross-section (i.e., the test specimen), the angle (pSF, () is defined by the following relationship: [Math.55] V^p = ±4arccos( -3^) mod / r In the case where the transducer is positioned in the wall of the cylindrical structure (i.e., the test body), the angle (pSF t ( F; ), where rQint < ri < roeia and i = l, 2, is defined by the following relation: [Math.56] Vsf.p (ri) = ±2anxos motbr The variation of the longitudinal forces 5F&p exerted on the test body (i.e., the cylindrical structure with a circular cross-section) is a linear function fSF of the difference in the variations of the true relative values: ATo-AT^ of the primary measurements ^et^: [Math.57] int Explicitly, the variation in longitudinal forces 5F^p and the corresponding variation in local temperature AT are equal to: - when the transducers are positioned in the wall of the test body to rays ri and r2: [Math.58] ~ (r]-rQ(( 1-2 v)k,-kpE) [Math.59] r(-r( " (r|-r5)((l-2v)Kt-KPE) when the transducers are positioned on surfaces internal to the radius r%lt and external to the radius rve*t of the test specimen: [Math.60] (F2v)Ke-KpE

[0267] [Math.61] A^ ^^r^t^jK.+KpE) (rkrtJV~2^ + (^Ke-Kp)APext - when the transducers are positioned in the wall at radius ri and on the external surface at radius roext of the test specimen:

[0268] [Math.62] XA^rAM^J^ ^Pinl

[0269] [Math.63] AT = ; ' (A^rA^rr^3^ / ]-2v X 'Vî' when the transducers are positioned on the internal surface at radius rüM and in the wall at radius r2 of the test specimen:

[0270] [Math.64]

[0271] [Math.65] 1 [A^-A^ p_21. . 1

[0272] Steps E24-E25 represent a variant of measuring the variation of hydrostatic pressure, the variation of longitudinal forces (along the axis of the structure) and the variation of local temperature.

[0273] More specifically, in step E24, sensor 3 is configured to selectively measure the variation of the hydrostatic pressure APext prevailing outside of structure 19. In addition, the calculator determines the variation of the local temperature AT associated with the variation of external hydrostatic pressure.

[0274] In this case, the angles ¢1 and ¢2 are equal, in absolute value, to the absolute value of the angle (pAPeii modulo ji, whose value depends on the radial position, on the surface -internal or external - or in the wall of the structure acting as a test body.

[0275] In the case where the transducer is positioned on the internal surface at the radius or external surface at the radius r^ext of the cylindrical structure (i.e.: test body), the angle ^AP^ is defined by the following relation:

[0276] [Math.66] = PapJ^Ï = ±4arccos(fe) mod / r

[0277] However, in the case where the transducer is positioned in the wall of the cylindrical structure, with a circular cross-section (i.e.: test body), the angle V^p^ is defined by the following relation:

[0278] [Math.67] 1 [ 1 ( , 2 KpE 1 1 । =±2arccos[3^(lv-3—moajr

[0279] where E is the Young's modulus of the structure, kp and K; are respectively the hydrostatic pressure and longitudinal mechanical strain sensitivities of the transducer for the measurement technique considered (e.g. Bragg grating type), and v is the Poisson's ratio of the structure acting as the test body.

[0280] The variation of the external hydrostatic pressure APext is a linear function exî of the difference between the true relative variations: ATI(-AT / ; of the primary measurements: 'Fa and vFb. The variation of the hydrostatic pressure APext prevailing outside the structure is given by the following relation:

[0281] [Math.68]

[0282] Explicitly, the variation of the external hydrostatic pressure APext and the associated variation of the local temperature AT are expressed as follows: - when the transducers are positioned in the wall of the test body to rays ri and r2:

[0283] [Math.69]

[0284] [Math.70] (A^|-AW2y2r5((l-2i.^ / t2v 'H + + £ Ke when the transducers are positioned on surfaces both internal to the radius and external to the radius of the test specimen:

[0285] [Math.71] ^rext~ K.+KpE

[0286] [Math.72] i kt + ( E Ke - K p ) - when the transducers are positioned in the wall at radius ri and on the external surface at radius rol!St of the test specimen:

[0287] [Math.73] A p _ A p . eXt M

[0288] [Math.74] . ] [ ,1Tf A T - âÿ AT^ +----77-77—î—---- ^Ke-KP)APint when the transducers are positioned on the internal surface at radius r0fW and in the wall at radius r2 of the test body:

[0289] [Math.75] AP — AP. - ~ ~ ~ A ext uit rlJri_yK^KpEyr^Kt+Kt,E})

[0290] [Math.76] JL [ A w . kt _ int rüjKr3KpE\r^Kf+KpE) (E Ke~Kp)&Pint

[0291] Step E25 concerns the measurement of the variation of the longitudinal forces ôF (other than those exerted by hydrostatic pressure) applied to the structure acting as the test specimen. In addition, the calculator determines the variation of the local temperature AT associated with this variation of the longitudinal forces ôF.

[0292] The angle (i.e., ¢1 or ¢2) is, in absolute value, equal to the absolute value of the angle / \ modulo ir:

[0293] [Math.77] |^E Â / J r v| mod7r 2

[0294] In the case where the transducer is positioned on the internal surface of the cylindrical structure, with a circular cross-section (ze: test body), the angle (p$F (Fq. ) is defined by the following relation:

[0295] [Math.78] = ±|arccos( -3^ ) mod^ A* ext

[0296] In the case where the transducer is positioned on the external surface of the cylindrical structure, of circular cross-section (ze: test body), the angle cp^p _ (n)^) is defined by the following relation:

[0297] [Math.79] 1 [ L (i-2 vX-(r -rn \itpE ] (p*F (ro ,) = ±4arccos -2——777777""—- I mod / r

[0298]

[0299]

[0300]

[0301]

[0302]

[0303]

[0304]

[0305]

[0306]

[0307] z >. . 1 [ -. T / kp E 1-2 v \ i (ri) = ± 2arccos 2^- (—üt -TiT ) -1 L "int In the case where the transducer is positioned in the wall of the cylindrical structure (i.e., test body with circular cross-section), the angle (p5F()), where r0int < ri < roeW and i = 1, 2, is defined by the following relation: [Math. 80] modr The measure of the variation of the longitudinal forces ÔF^p exerted on the test body (i.e., the cylindrical structure with a circular cross-section) is a linear function of the difference of the true relative variations: AT„ - A^ of the primary measurements: and ^b: [Math.81] (A^-AW.) Explicitly, the variation of the longitudinal forces 5Fsf^p and the associated variation of the local temperature AT are given by: - when the transducers are positioned in the wall of the test body at the r1 and r2 radii: [Math. 82] (A'P]-A,P2)t^ -rp (E __ ' ~ l ™ ' ^r'xf ''irai ^Pext— (r^-r^(l-2v)Kf-KPE) [Math.83] A'^rl-A'M ( £ Ke-Kp)APint when the transducers are positioned on surfaces internal to the radius r0iK; and external to the radius roext of the test specimen: [Math. 84] Or AP,., ~ (1-2^-,,-k^E [Math.85] / l-2v \ ^a-di:^2^KpE) +\~^-Kp) àPint - when the transducers are positioned in the wall at radius ri and on the external surface at radius ro„. / of the test body: [Math. 86] 5F ,\p — ext / kv \.p «Vî ' EVfyj int when the transducers are positioned on the internal surface at radius roto and in the wall at radius r2 of the test specimen:

[0309] [Math.88]

[0310] [Math.89] M +k E Ke-Kp) int

[0311] It should be noted that the measurements according to steps E22-E25 (whether for the variation of internal or external hydrostatic pressure, or the variation of longitudinal forces or the variation of local temperature) can be applied to all radial position configurations of the transducers, in particular when at least one of them is positioned on the internal or external surface of the test body.

[0312] Step E26 concerns the calculation of the variation in longitudinal mechanical deformation of the test specimen A £mece»P. The variation in longitudinal mechanical deformation of the test specimen A gmeccap is defined by the following equation:

[0313] [Math.90] * _ 2 dF i-2 v A Êmeccap — £ ^2 _r2} ~ EA -1%

[0314] According to this configuration, the host structure 19 plays the role of the test body 9 and consequently, the component of the longitudinal mechanical strain variation A £mecstrud of the host structure is equal to the longitudinal mechanical strain variation of the test body A emeccap.

[0315] Step E27 concerns the calculation of the values ​​of the displacements and the components of the strain and stress tensors.

[0316] On the other hand, according to this configuration where the structure itself plays the role of the test body and standard single-mode optical fibers, provided for example with a polymer sheath, are used for the measurement, the birefringence effect created by the structure within the optical fiber can remain negligible, and consequently not be taken into account when exploiting the measurement (except in the case of using optical fibers that are already highly birefringent, in which case the birefringence of these optical fibers will then be exacerbated by the mechanical effects induced by the host structure).

[0317] It should be noted that the methods relating to Figs. 5 and 6 also apply to the embodiment of Figs. 3A and 3B in which the sensor 3 is advantageously formed of two pairs of transducers. These transducers are locally oriented at the angles | ; ), ) | and ( (ri^Ar ) ' (r2^r) ), and according to the distinct radii and r^F^.„. This allows us to measure simultaneously, according to an intrinsic selectivity, the two mechanical effects of variation of external hydrostatic pressure APext and of variation of longitudinal mechanical forces ôF applied to the test body (distinct from those exerted by a hydrostatic pressure), as well as the associated variations AT of the local temperature.

[0318] Advantageously, the methods described above provide complete calculation formulas corresponding to the vast majority of possible declinations in terms of combinations of radial positions and orientations of the transducers, provided that the calculations are possible (in particular concerning the notable angles, which must necessarily take a real value).

[0319] Figure [7A] illustrates a sensor intended to selectively measure the variation of hydrostatic pressure AP applied to the sensor, according to a third embodiment of the invention.

[0320] The sensor 3, according to this third embodiment, comprises a single optical waveguide 7 oriented locally in a circular helix around the axis of revolution of the test body 9 at an angle 4AP with respect to a plane normal to the axis of revolution of the test body. The optical waveguide 7 is positioned at a radius r within the elastic wall of the test body 9. In this example, the optical waveguide is intrinsically a transducer corresponding to an optical fiber, preferably single-mode, employing a continuously sensitive distributed reflectometric measurement technique, of the Brillouin type, based on the Landau-Placzek ratio to perform an intrinsic measurement of the hydrostatic pressure variation. The temperature information is generally additional information provided directly by the measurement technique in question (see document EP 3 232 165).

[0321] In such a case, the variation: - The internal hydrostatic pressure APint at the test body is given by:

[0322] [Math.91] ^hnt- ext + - The external hydrostatic pressure APext on the test body is given by: AP AP A Pext - A Pint - \^YKpE^+rlJ

[0324] where Aemec is the variation in mechanical deformation of the structure, according to the orientation of the optical fiber, achieved by the measurement technique in question between the current state and the reference state of the structure, and kp and Ks are respectively the sensitivities in hydrostatic pressure and in longitudinal mechanical deformation of the measurement technique considered for the waveguide in question.

[0325] The [Fig.7B] is a variant of the third embodiment in which the sensor 3 is intended to selectively measure the variation of the longitudinal force ôF (other than exerted by hydrostatic pressure) applied to the test body.

[0326] According to this embodiment, the single optical waveguide 7 is locally oriented in a circular helix around the axis of revolution of the test body 9 at an angle 00F with respect to a plane normal to the axis of revolution of the test body. The optical waveguide 7 is positioned at a radius r within the elastic wall of the test body 9. Here too, a continuously sensitive distributed reflectometric measurement technique of the Brillouin type is used, based on the Landau-Placzek ratio to achieve an intrinsic separation of longitudinal mechanical deformation and temperature.

[0327] In such a case, the variation of the longitudinal force ôF: - independent of the variation of the internal hydrostatic pressure APint applied to the test specimen, is given by:

[0328] [Math.93] - independent of the variation of the external hydrostatic pressure APext applied to the test specimen, is given by:

[0329] [Math.94]

[0330] where Aemec is the variation of mechanical deformation of the test body structure, according to the orientation of the waveguide, achieved by the measurement technique in question between the current state and the reference state of the structure, and kp and Kt are respectively the sensitivities in hydrostatic pressure and in longitudinal mechanical deformation of the measurement technique considered for the waveguide in question.

[0331] Figure 8A illustrates a sensor intended to selectively measure, with or without birefringence, the variation of the hydrostatic pressure AP and the variation of the longitudinal force ôF, other than exerted by hydrostatic pressure, applied to the test body, according to a fourth embodiment of the invention.

[0332] The sensor 3, according to this fourth embodiment, comprises first 7a, second 7b, and third 7c optical waveguides oriented locally in a circular helix around the axis of revolution of the test body 9. The three waveguides 7a, 7b, 7c are positioned in the elastic wall of the test body at arbitrary angles, but at least two of which are, in absolute value, distinct modulo r: 0(r1), 0(r2), and 0(r3), and along the radii: r2 and r3, at least two of which are distinct. Each of the three waveguides carries a Bragg grating transducer 1a, 11b, 11e. The three transducers 1la, 11b, 1le are preferentially positioned at the same curvilinear abscissa along the axis of revolution of the test body 9 so as to be subjected to the same temperature.

[0333] Thus, this sensor 3 makes it possible to selectively measure the variations of hydrostatic pressure AP (internal and / or external) and of longitudinal force ôF (other than exerted by a hydrostatic pressure), as well as the variation of temperature AT, thanks to the use of the formal solution of the underlying thermomechanical problem.

[0334] These solutions are given, for transducers positioned within the thickness of the test body (which represents the majority of application cases), by the following expressions: - when the formal problem is solved according to the 3 unknowns {APint, ôF, AT}: - Regarding the variation of internal pressure APint:

[0335] [Math.95] âPiat = Us*.(-2'taSh-AW (ri2—ra2} tl+vl j Cos {2q>3} + Cos (2$a) (n? (-2 (ÀV2-ÀV3) {) T33rs¾+ Îra2-r3*} (1+vï (r^-ri2) r32tl*v>Ca8-f?^* (rs^-ra2) (1+v) Cos ï + Cas (ra2 (2 Wfc-âVi) (rS -ri ) r^rs^-âSwiSMgr* r*. (n2-r32) (1+v) )- SF-ks-r 1 (ra^-rs2) (1+v)CosJ ) / (1+^) ( (ri^-rs2) r3%os (2^3) + Cos,{2çi) (ri^'ira2-??8} - (rs^-r^î Cos (2çi) )♦ Cost (2$2> (rs^Cra^-n2) -ri2■(ra2-^^) Case (2x) ) )} with respect to the temperature variation AT: AT = S&Ts^^ 'si^ 2^3⁄43⁄4..^3⁄45^ ;«a\a¥-3fiw|^!^ TT;;3 £^2^-3^3⁄4^ ..«3siç».*Kv-.^3⁄41⁄4 3AFs$$fÇrg. ..«S^s'a^ThipsJ—3ûP^-K*rç .r;W&is £2:^3 + -^.YsK^ ï' / e^SGos (2$,) + 3ÀT: k} r^Xi^os ^'J --SAP^K. h>. , ^« / ECm (:2^ − 3AT; ft\fj; ^'« / ECos t2:^3 s (2^) + SATs K* rft / rj'EC'&s C2^j3 — {2^} - S^ViXjs^- J 2:^3 ) '” SATs Kpr^Ki'' (2s} 13⁄43 ss'E^Cos (2^2^ - UtM* (Ms) * (Ms) “If You Are Wrong” (Ms) " or (Ms) - iw^w©» Ws) *imw^ of " SAÇwj^r^ïrrsM*^ CS>sHS&^*^^ tWw) <l*vM^I§*^ s (&w ( * wtf<HL*$ WA»S (* “S v > -^3⁄4^ ( - n® ( ~ âta8 '{My (dL*^^ rsl-M (KMrr (l~MMr|^ (â-M *W flw) Ihh 33⁄43⁄4.^ (£1^1 >ëss (Mîth H > (:Wos|y|^ IW^ î s- f kwl . «s*WW“ 'AVi-.xw- v £;•:> *— '"j'.ïf ^\^sister|^ s^KErl^ry^ / Bv-ïâM^ry'sW 33⁄4^. (^r / ><l*v> )©and” (M » M ^L <«**“* / > U*VE * (â$M.) J Cm (M4 j > / x F s 1^> ( ( n*~r^in*€m ( Ws) * Cv'Â U'M m* (r / ~r^ - (n$;^8) h%« (2^) *rr tna~r / >c^ (Ms) > * Sm <:2M <^s~r?) "M (rsM^*> Cw (Ms) ) I > when the formal problem is solved according to the 3 unknowns { APext, ôF, AT}: with respect to the variation of the external pressure APext: AiW = (r? (2 (H −4} n2r?E+ {ri )Things î2^ * Cos {2ci} <ria{2 (fi^s-Afaî âPüwi ri (rz^-rs^Hl+vn-APiat^^ ri (^1^-^)^(1+^)0^(2^2) + wv^xx '"cw “crtr wa'v- APiat^rg^^^ (1+v)Cos(2$2)}+ Cos (2^) {^(-2(^-1⁄2) C^-n2 JC ) Cos (2ts) 1 ) / ÎKs'rl^.^ (1+v) {(riz-rzz) r^os (2¢3) + Cos (2>i) (r / -( r^-ra2) r^Cos (21⁄43⁄4) +raz (13⁄42^2)Cos(2^) ) + Cos (2^s) (Fs2 (r^-ri2) -n2 (r^-r / ) Cos (2ç3)} ) ) - concerning the temperature variation AT:

[0338] [Math.98] AT = Fi^ra^B-SAViK'fï^ ri^a^E- JuliKFF^r^ta^^Z&Wîapr^r^rz2!?*^ 2â¥aKpr&. r^rs^-ESSAYMst^ SÆfiJQr^ 1-13⁄4.3⁄4^ -a&ÇsKjr^rx^^v - SâPistKirl rj^rs^os (2®sî -3APiatRiri. . r^sVCos (2®.$} ♦ <'X'X<>w '■'üiS. xx-w-xx '"■jrtÿ ^i^rl^ra^s^Cos (2®3) -3»2^-r|.w(2^) + 3ATiKÆrgx.^ (2^3> (2ç3) - SüysKfFg rs^rs^ECuos (2$sJ+SâP^AfKpf^rz2^^^ (2^3) * (2^3} -fiOTa^ra^a^s^ECos (2£M “ 2AViKpr|,%<.ri-2r2ïE%os (2|f3>+2&WaK|srg ri^'S^os (293} -SA^iK^ï'^ï^^E^Cos ( .^Çi^2a) Ms -S^inîKfr^^ (2^3) (2$s) - M¥aKfr& ri2rs^Cos (2^3) +3^3⁄4^3⁄4^^3⁄4 (21⁄43⁄4} + (21⁄4¼} -3A^a^€Kjpr| ra^ £2$3} - 3^3113⁄4^ 3⁄423⁄4^^ (21⁄43⁄4) (2 <M - IZâ.Çi^ri^rs^^'aCos (2^} +12^83^33⁄42^3⁄4 (21⁄43⁄4) - T^rs^v^s (2^3) rz^s^y^os (21⁄43⁄4) ♦ Cqs {2çï} (3APi$tJ^rg^ (1+v) ( ^2+.81^(2^-1)) + E (A¥j F32 ( - 2Kpria (ri +33⁄42) E+ 6«f Ts2r22 (1-2^ ) +3KErn, ( - Ta2 ( - 1+v) +r22 (1+vj}} + (2kp trf ♦3raa) rsaÉ-3Ks (2^3⁄42 (l-2v) (ra2 (1-v)+F22-(1+v]( J ) ) ) + 3^^^12¾2¾2) (!♦*}} Cos(2^) ) + Case (2^0 ( 3 3&¥2«rFfl ri'r / g-SâPiatMf^- r?rÆ»- WiKfri'rî'b^-fiâl^nW.^^ .r / tÆ2* SAWsKprl 13⁄43⁄43⁄4^ 613⁄4^3⁄42 3£^$KrR>r| ^l3⁄43⁄4y-3â3⁄4«3⁄4r^.Fa2F33⁄4y+ .3^3⁄43⁄4r|K itfnïv-iî^nWr^W^ ^3⁄43⁄4^ fiûPjuœKjïl r^W^+SâP^jsi»^ ri2 r 33⁄43⁄4^ {r^-ra2) f32 Ù+v) (-Û^E+A]^ (2v-l)} Cos<2^ - Fa2 (fi2-F32) (ï+v) {-&7aB+âP^KpE+d&^^ (2v-l} ) Cos {2^3$ ) ) / (3«t«ï4, E (1+v) ( (Fî'-fz2) f / Cos [2qM + 'W Cbs {2^1} (fj2 (ra*-rs2)' - (Fi2-!*2) rs^Cos (2ç2) +¾2 {Fi2-Fa2 J Cos (2^3) ) + Cos (2«M' (Fz2 (Fss-Fis) -Fi* (Fa2-Fa2) Cos (2^3} )} )

[0339] The formula leading to the variation of the longitudinal force ôF is identical according to the two methods of solving the formal problem:

[0340] [Math.99] 5F = -((2b (ri -ri 3 E (^a^A^J-ra^Cos (2^1) - rvWCos (2^K+â^ - ÛFaFi^^Cos (2^3) ) ) / ( »«• (1+v ) ( (ri2-rz2} Fs^Cos (2fa) + Cos (2$i) (Ba2 (F22-F32) - (Ba2-F®2) F3SCos-(2ça-J +Ba2(rs.2-raa)Cos (2 <p3}) + Cos (2^2) (Fa2 (Fa2-!!2) -n2 (rZ-Fa2) Cos Ws) ) ) ) )

[0341] It should be noted that the procedure described in Fig. 4, which allows, among other things, obtaining a measurement of the variation of the longitudinal mechanical deformation of the test body A gmeccap and of the variation of the mechanical deformation A £mecstr„ct of the host structure according to the orientation of the sensor, applies in the same way.

[0342] The [Fig.8B] is a variant of the fourth embodiment also for selectively measuring, with or without exploitation of birefringence, the variations of the hydrostatic pressure AP and the longitudinal force ôF, other than exerted by a hydrostatic pressure, applied to the test body.

[0343] According to this variant, the three waveguides 7a, 7b, 7c are used by a distributed fiber optic reflectometric measurement technique, sensitive to both the temperature and mechanical deformation, such as Brillouin, OFDR Rayleigh, phase-OTDR (0-OTDR) and DAS (Dynamic Acoustic Sensing) techniques.

[0344] Thus, the sensor 3, according to the various embodiments of the present invention, makes it possible to separate the effects of temperature, hydrostatic pressure, and longitudinal mechanical deformation, in order to provide, independently of each other, provided that the transducers implemented within the sensor are sensitive to these three effects, the local measurement of the variations of each of these three effects relative to an arbitrary reference state. This is valid whether in the case of a microstructured fiber or in the case of a structure acting as a test body which itself acts as a sensor (e.g., a tank or a pressurized pipe).

[0345] The provision of formal expressions in hydrostatic pressure variation and longitudinal mechanical deformation variation according to a given orientation (the axis (zz) of the sensor) is a real added value, in the sense that they can allow the experimenter to do without calibration for his measurement, provided that the thermomechanical properties of the test body, in the temperature ranges considered, and its reference state, are known with sufficient precision.

[0346] None of the non-intrusive (or minimally intrusive) solutions in the state of the art make it possible to separate the two mechanical effects (pressure and longitudinal force) from non-mechanical effects such as temperature and / or the effects of ionizing radiation, independently of each other, whether or not the sensor is embedded in a deformable structure.

[0347] In addition, it is possible to simultaneously provide information on hydrostatic pressure variation and longitudinal mechanical deformation variation along a given orientation by combining two separate sensors, each based on its family of angles for intrinsic selectivity of measurements, in which case 2x2=4 transducers are used if the measurement technique implemented does not allow for intrinsic separation of mechanical effects from non-mechanical effects (such as temperature and / or the effects of ionizing radiation).

[0348] It should be noted that it is also possible to use only three transducers if the families of notable angles, allowing selectivity for one or the other mechanical effect (hydrostatic pressure or longitudinal force), are not used. In this case, the solution allowing their formal expression is more complex, as shown by the expressions in the absence of birefringence cited earlier in this document, and consequently more subject to measurement uncertainties. The use of three transducers nevertheless has the major advantage of always providing a practical solution, as the angles can be arbitrary, although at least two of them must be distinct in absolute value modulo ji. This facilitates the implementation of the sensor on the one hand, and allows the use of radii of curvature of the waveguides large enough not to lead to excessive optical losses on the other hand.

[0349] And although it is not its main characteristic, the sensor, in each of its variants, makes it possible to provide the additional information of local temperature variation as soon as the measurement technique implemented, for the transducers considered, is itself sensitive to temperature, as soon as temperature is the only non-mechanical phenomenon to which the transducers are subjected.

[0350] The sensor can be used for the instrumentation of type IV composite tanks for the high-pressure storage of gaseous molecular hydrogen (H2), so as to monitor their condition throughout their operational life. This is particularly advantageous during filling phases where the tank is subjected to both significant temperature variations (temperature rise up to +70°C) and significant variations in stress (700 bar at operating pressure) and deformation (0.6% elongation at operating pressure, and up to 2% at the tank's rupture limit), where the risk of bursting is therefore highest.

[0351] The simultaneous use of a pressure measurement in contact with the fluid within the tank then makes it possible to construct a tank damage parameter which can be used to detect the moment from which it must be scrapped due to a high risk of bursting.

[0352] Such a sensor, in a configuration with Bragg grating transducers, would thus make it possible to provide the state of health of the reservoir in real time, unlike an OFDR Rayleigh type measurement technique which remains sensitive to vibrations, and moreover to the effects of temperature (see L. Maurin et al. “OFDR Distributed Strain Measurements for SHM of Hydrostatic Stressed Structures: An Application to High Pressure Hydrogen Storage Type IV Composite Vessels - H2E Project”. <hal-01021252>).

[0353] More generally, the sensor can be used for instrumentation at the heart of any deformable structure for its in situ monitoring, during its use, in particular composite structures, since the optical fiber fits perfectly into it without generating additional defects that could lead to local embrittlement.

[0354] Other types of structures (metallic, ceramic, polymer, composite) can be considered provided that the sensor can be inserted into them, for example when these structures are manufactured by additive manufacturing. Surface instrumentation is also perfectly feasible.

[0355] The host structure can be made of composite material (the preferred material for optical fibers, which are inserted into it quite easily without generating additional structural defects, provided that it is oriented in the same direction as the fibers of reinforcement). This is the typical case of type IV tanks for the high-pressure storage of gaseous molecular hydrogen (H2). The host structure can be made of any other material, for example metal, plastic, or ceramic (the structure can be composite, i.e., formed of materials of various kinds), the sensor then being able to be inserted within the part to be instrumented during its manufacture.

[0356] The present invention has industrial applications in any sector where the measurement of directional mechanical deformations, as well as the measurement of hydrostatic pressures within a deformable mechanical structure, is of interest. In particular, for taking measurements during the manufacturing process of an instrumented part, for example to validate calculation codes, or to improve the manufacturing process in question, through in-situ measurements, and once the part is manufactured, the invention makes it possible to ensure its structural integrity throughout its entire lifespan.

[0357] Any installation comprising a pressurized structure can be instrumented. Thus, the invention is also suitable for pressurized pipes provided that it is possible to insert the sensor (in its micro-structured fiber version) or to insert optical measurement fibers (as is the case with composite material pipes, such as the flexible hoses used for transporting hydrocarbons from the seabed) in cases where the pipe itself acts as the test specimen. It should be noted that a pipe can generally be considered, during its use, to be hermetically sealed at its ends.

Claims

1.

2. Demands A non-intrusive measuring device intended to measure a variation in longitudinal force, other than that exerted by hydrostatic pressure, and / or a variation in hydrostatic pressure relating to a host structure of interest, comprising: -a sensor (3) comprising at least one optical waveguide (7) fixedly installed on one of the surfaces or in the wall of a cylindrical test body (9), of circular cross-section, hollow and sealed at its ends, deforming in its elastic domain, each optical waveguide locally describing a circular helix positioned at a radius r around the axis of revolution of the test body (9) and locally oriented at a predetermined angle 0(r) with respect to a plane normal to said axis of revolution, each waveguide (7) carrying at least one transducer (11) whose mechanical measurement component is sensitive to orientation and configured to perform a selective measurement of a first primary variable, whose true relative variation with respect to a reference state is representative of a local variation of hydrostatic pressure applied to the test body (9) or of a second primary variable,whose true relative variation with respect to a reference state is representative of a local variation of longitudinal force, other than exerted by hydrostatic pressure, applied to the test body, the selectivity of one or the other mechanical effect via the first and second primary variables being ensured by the orientation of each waveguide, and, - a calculator (17) configured to selectively calculate the local variation of the longitudinal force ôF, other than exerted by a hydrostatic pressure, applied to the test body and / or the local variation of the hydrostatic pressure AP applied to the test body (9) as a function of the true relative variations of the measurements of said first and / or second primary variables. Device according to claim 1, characterized in that the calculator (17) is further configured to calculate the variation of the local temperature as a function of the true relative variations of the measurements of said first and / or second primary variables.

3. Device according to claim 1 or 2, characterized in that the calculator (17) is configured to calculate the local variation of the longitudinal mechanical deformation A smcccap of the test body (9) as a function of the local variation of the longitudinal force ôF, other than exerted by a hydrostatic pressure, and of the local variation of the hydrostatic pressure AP applied to the test body, as well as of the physical parameters of the test body (9).

4. Device according to any one of the preceding claims, characterized in that it comprises at least one pair of optical waveguides (7a, 7b) locally oriented in a circular helix around the axis of revolution of the test body (9) and carrying at least one pair of transducers (lia, 11b), the optical waveguides forming each pair being positioned along two distinct radii ri and r2 around the axis of revolution of the test body (9) and locally oriented along a pair of predetermined angles with respect to a plane normal to said axis of revolution.

5. Device according to any one of the preceding claims, characterized in that it comprises first and second optical waveguides oriented locally in a circular helix around the axis of revolution of the test body at first and second angles and distinct with respect to a plane normal to the axis of revolution, the first optical waveguide being dedicated to measuring the variation of the hydrostatic pressure AP, the second optical waveguide being dedicated to measuring the variation of the longitudinal force ôF, other than exerted by a hydrostatic pressure, applied to the test body.

6. Device according to any one of claims 1 to 4, characterized in that it comprises first and second optical waveguides (7a, 7b) oriented locally in a circular helix around the axis of revolution of the test body in the same family of angles (^(^),^(^)) or ( <PSF(rlgp), ) par rapport à un plan normal à l’axe de révolution, la première famille d’angles étant dédiée à la mesure sélective de la variation de pression hydrostatique AP, tandis que la deuxième famille d’angles est dédiée à la mesure sélective de la variation de l’effort longitudinal ôF, autre qu’exercé par une pression hydrostatique, appliqués au corps d’épreuve.

7.

8.

9. Device according to claim 6, characterized in that it comprises first and second optical waveguides (7a, 7b) oriented locally in a circular helix around the axis of revolution of the test body, with respect to first and second angles Ç'A / >(riAP) and fPAP( rZv) with respect to a plane normal to the axis of revolution of the test body, these angles taking a first identical and constant value in the wall of the test body and a second identical and constant value on the internal and external surfaces of the test body, the first and second angle values ​​being distinct, said first and second optical waveguides being dedicated to the selective measurement of the variation of hydrostatic pressure AP.Device according to claim 6, characterized in that it comprises first and second optical waveguides (7a, 7b) oriented locally in a circular helix around the axis of revolution of the test body, at first and second angles and <PSF(r29F ) distincts par rapport à un plan normal à l’axe de révolution du corps d’épreuve, lesdits premier et deuxième guides d’ondes optiques étant dédiés à la mesure de la variation de l’effort longitudinal ôF, autre qu’exercé par une pression hydrostatique, appliqué au corps d’épreuve. A device according to any one of claims 1 to 4, characterized in that it comprises first and second pairs of optical waveguides (7a, 7b, 7c, 7d) positioned locally in a circular helix around the axis of revolution of the test body (9) along distinct radii r^p, r^p, rkp, and r^p, the two waveguides of the first pair being positioned at first and second angles<PAp(rh / > ) and V'^pi ^2^,) with respect to a plane normal to the axis of revolution of the test body, these angles taking a first identical and constant value in the wall of the test body and a second identical and constant value on the internal and external surfaces of the test body, the first and second angle values ​​being distinct, while the two waveguides of the second pair are positioned at two distinct angles (pSF) and with respect to a plane normal to the axis of revolution, the first pair of waveguides being dedicated to measuring the variation of hydrostatic pressure AP, while the second pair of waveguides is dedicated to measuring the variation of the longitudinal force ôF, other than exerted by hydrostatic pressure, applied to the test body.

10. Device according to any one of claims 1 to 3, characterized in that it comprises a single optical waveguide (7) positioned at a predetermined radius in the elastic wall of the test body and locally oriented in a circular helix around the axis of revolution of the test body (9) at a predetermined angle with respect to a plane normal to the axis of revolution, the optical waveguide being dedicated to the measurement of the variation of hydrostatic pressure AP or to the measurement of the variation of the longitudinal force ôF, other than exerted by a hydrostatic pressure, applied to the test body, by exploiting a continuously sensitive distributed measurement technique of the Brillouin reflectometry type, based on the Landau-Placzek ratio.

11. A device according to any one of claims 1 to 3, characterized in that it comprises first, second, and third optical waveguides (7a, 7b, 7c) oriented locally in a circular helix around the axis of revolution of the test specimen (9) with first, second, and third radii rb, r2, and r3, at least two of which are distinct, and with first, second, and third angles θ(r1), θ(r2), and θ(r3) with respect to a plane normal to the axis of revolution, at least two of which are, in absolute value, distinct modulo θ, the first, second, and third optical waveguides being dedicated to measuring the variation of hydrostatic pressure AP and the variation of longitudinal force θF, other than that exerted by hydrostatic pressure, applied to the test specimen, as well as the local variation of temperature AT, provided that no other non-mechanical effect other than The temperature factor does not affect the transducers.and that the raw measurement performed by each transducer is itself sensitive to temperature.

12. Device according to any one of the preceding claims, characterized in that each optical waveguide (7) carries a transducer (11) according to a Bragg grating type technique adapted to perform distributed measurements.

13. A device according to any one of claims 1 to 10, characterized in that each optical waveguide (7) carries a transducer according to a continuous reflectometry-type technique

14. Brillouin, OFDR Rayleigh, phase-OTDR or DAS, adapted to perform measurements distributed along the optical waveguide. Device according to any one of claims 1 to 5, 7 to 10, 12 and 13, characterized in that the sensor (3) comprises said cylindrical test body (9) of circular cross-section delimiting a sealed cavity, and in that it is intended to be installed in any host structure (19), the external hydrostatic pressure variation APext and the temperature variation ATi associated with the hydrostatic pressure, as well as the variation of the longitudinal force ÔF other than exerted by a hydrostatic pressure, and the temperature variation AT2 associated with the calculation of the longitudinal force being defined according to the following equations, provided that the test body deforms within its elastic range: [Math.1] (AWrAVAnl -rtj yWE int A7I * / [ + r^-r^K^KpE) +\ E Ke-Kp)APinl [Math.2] (d -rl \E 011 ^xt ~ 1-2 v^y-KpE) A^-AMy? (a^at^Jk^^ ,b2v x rtrl ' + t E Ke-Kp)^int where A1!7 is the true relative variation of the raw value 'F corresponding to the primary measurement made by the transducer between its reference value To and its current value E is the Young's modulus of the test body, v is the Poisson's ratio of the test body, kp, Ke and kt are respectively the sensitivities in hydrostatic pressure, in longitudinal mechanical strain and in temperature of the transducer attached to the host structure for the measurement technique considered (for example of Bragg grating type), APint is the variation of the internal hydrostatic pressure, r°M, rQexi are respectively the internal and external radii of the optical fiber in its reference state, and r\ are respectively the radii corresponding to the positioning of the first and second transducers.

15.

16.

17.

18. Device according to claim 14, characterized in that the test body (9) is a micro-structured optical fiber forming a micro-capillary sealed at its ends. Device according to claim 14 or 15, characterized in that the test body (9) is covered with a deformable mechanical sheath of polymer type. Device according to any one of the preceding claims, characterized in that the sensor (3) is configured to exploit a birefringence effect within the optical waveguide. Device according to any one of claims 1 to 5, 7 to 10, and 12 to 17, characterized in that the host structure has a cylindrical shape, a circular cross-section, is hollow and hermetically sealed at its ends, thus acting as a test body (9), the variations of internal hydrostatic pressures APint and external hydrostatic pressures APext, the variations of associated longitudinal forces ÔF&p and ÔF&p, other than those exerted by hydrostatic pressure, and the variations of associated temperatures ATb AT2, AT3, AT4 being defined according to the following equations, when the structure deforms in its elastic range, with transducers positioned in the wall of the structure, at radii ri and r2: [Math.3] (ÀWrA'J'A^ -rl y^E 44 + rlJrtrlixAK^ +VE Ke-Kp}^Pext [Math.4] at2=4 [Math.5] 44" 44X42 > E Kg-Kpj&rçxi , (A^AT^-rg^ ext int+ rljlJryrîfa^K^ _ J_r A^,4A^ (Ay + r^Jrj-rli^KpE) + (^Ke-Kp)&Pint [Math.6] &?exi (rj-rÿ^l-2v)K^KpE) AT4 = i ' (r^E^ / c^pE) +\ E Ke-KP)Ar!nf where AT is the true relative variation of the raw value (i.e.: primary measurement made by the transducer) between its reference value To and its current value T, E is the Young's modulus of the structure, v is the Poisson's ratio of the structure, kp, Kc and K? are respectively the sensitivities in hydrostatic pressure, in longitudinal mechanical strain and in temperature of the transducer attached to the host structure for the measurement technique considered (e.g. Bragg grating type), and r0i„t, r^ext are respectively the internal and external radii of the cylindrical structure in its reference state, and ri, r2 are respectively the radii corresponding to the positioning of the first and second transducers.

19. Device according to any one of claims 1 to 12, characterized in that the structure (19) has any shape and in that the cylindrical test body (9) of circular cross-section is housed in the structure.

20. Installation characterized in that it comprises: - a structure whose hydrostatic pressure and / or longitudinal mechanical deformation and / or temperature are to be monitored, and - a measuring device (1) according to any one of claims 1 to 16.

21. A non-intrusive method for measuring a variation in longitudinal force and / or a variation in hydrostatic pressure relative to a host structure of interest, comprising the following steps: - positioning at least one optical waveguide (7) locally describing a circular helix on one of the surfaces or in the wall of a cylindrical test body (9) of circular cross-section, hollow and hermetically sealed at its ends, each optical waveguide being positioned at a radius r around the axis of revolution of the test body and being locally oriented at a predetermined angle <])(r) with respect to a plane normal to said axis of revolution, each waveguide carrying at least one transducer (11) whose mechanical component of the primary measurement is sensitive to orientation, - to perform, by means of at least one of said transducer (11), a selective measurement of a first primary variable, the true relative variation of which with respect to a reference state is representative of a local variation of hydrostatic pressure applied to the test specimen, or of a second primary variable, the true relative variation of which with respect to a reference state is representative of a local variation of longitudinal force, other than that exerted by hydrostatic pressure, applied to the test specimen, the selectivity of one or the other of the first and second primary variables being ensured by the orientation of each waveguide, and - selectively calculate the local variation of the longitudinal mechanical deformation of the test body and / or the local variation of hydrostatic pressure applied to the test body as a function of the true relative variations of the measurements of said first and / or second primary variables.

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