High-pressure shell temperature-strain monitoring method based on distributed acoustic sensor

Abstract

The invention relates to the technical field of structural deformation sensing and monitoring in extreme environments such as high-temperature and high-pressure conditions, in particular to a high-pressure shell temperature-strain monitoring method based on a distributed acoustic sensor, which comprises the following steps: designing a cascade distributed measurement fiber bragg grating acoustic sensor; the method comprises the following steps: arranging a cascaded distributed measurement fiber grating acoustic sensor on a high-voltage shell, carrying out heating and pressurizing experiments, and recording two wavelength offsets measured at each measurement point in the cascaded distributed measurement fiber grating acoustic sensor; and based on the two wavelength offsets of each measuring point, obtaining an actual strain value of the measuring point. According to the invention, the influence of temperature change on the measurement of the cascaded distributed measurement fiber grating acoustic sensor is eliminated, the deformation of the solid space engine shell under extreme temperature and pressure conditions is accurately monitored, and the rapid change of the strain of the shell is captured and accurately measured.

Description

Technical Field

[0001] This invention relates to the field of structural deformation sensing and monitoring technology under extreme environments such as high temperature and high pressure, and specifically to a high-pressure shell temperature-strain monitoring method based on distributed acoustic sensors. Background Technology

[0002] Solid rocket motor casings are a critical component of the overall spacecraft structure, and also one of the weakest points in the spacecraft's structure. Timely diagnosis and inspection of the casing's health status and assessment of engine reliability are essential to ensuring the safe and stable operation of aerospace equipment.

[0003] Strain response parameters are crucial indicators for assessing the structural integrity of aerospace engine casings. Traditional surface-mounted strain sensors have significant limitations in aerospace engine casing inspection: firstly, the sensors require power to operate, while the propellant inside the engine is flammable and explosive, posing a major safety hazard; secondly, current casting processes make it difficult to embed the sensors within the propellant grains. Fiber optic sensors, as a novel type of sensor, offer advantages such as resistance to electromagnetic interference, small size, and suitability for distributed sensing, and therefore have attracted widespread attention in the field of aerospace engine casing strain detection.

[0004] Therefore, there is a need to provide a high-pressure housing temperature-strain monitoring method based on distributed acoustic sensors to solve the above problems. Summary of the Invention

[0005] This invention provides a method for monitoring the temperature and strain of a high-pressure housing based on a distributed acoustic sensor, in order to solve existing problems.

[0006] The present invention provides a high-pressure housing temperature-strain monitoring method based on distributed acoustic sensors, which adopts the following technical solution, including: Design a cascaded distributed measurement fiber Bragg grating acoustic sensor. The cascaded distributed measurement fiber Bragg grating acoustic sensor includes: an optical fiber, on which multiple measurement points are evenly distributed. Each measurement point corresponds to a first fiber Bragg grating and a second fiber Bragg grating. The first fiber Bragg grating is directly attached to the surface of the measurement point on the optical fiber, and the second fiber Bragg grating is attached to the surface of the measurement point after encapsulation. The fiber Bragg grating is used to selectively filter light coupled into the optical fiber at specific wavelengths. The optical fiber of the cascaded distributed measurement fiber Bragg grating acoustic sensor is wound around a high-pressure housing, and the high-pressure housing is heated and pressurized. The two wavelength offsets measured at each measuring point in the cascaded distributed measurement fiber Bragg grating acoustic sensor are recorded. The actual strain value of each measuring point is obtained based on the two wavelength offsets of each measuring point.

[0007] A further technical solution of the present invention is that a specific wavelength satisfies:

[0008] In the formula, For a specific wavelength; The period of the fiber grating; The effective refractive index of the cascaded fiber Bragg grating.

[0009] A further technical solution of the present invention is that the relationship between the wavelength shift of the first fiber Bragg grating and the applied temperature and strain is expressed as follows:

[0010] In the formula, This represents the wavelength offset of the first fiber Bragg grating; For a specific wavelength; is the optical elastic coefficient of the fiber Bragg grating; The axial strain change experienced by the fiber of the first fiber Bragg grating; The coefficient of thermal expansion of a fiber Bragg grating; The thermo-optic coefficient of the fiber Bragg grating; This represents the temperature change around the fiber Bragg grating. The strain sensitivity coefficient; This is the temperature sensitivity coefficient.

[0011] A further technical solution of the present invention is that the relationship between the wavelength shift of the second fiber Bragg grating and the applied temperature is as follows:

[0012] In the formula, This represents the wavelength offset of the second fiber Bragg grating; The coefficient of thermal expansion of a fiber Bragg grating; The thermo-optic coefficient of the fiber Bragg grating; This represents the temperature change around the fiber Bragg grating. This is the temperature sensitivity coefficient.

[0013] A further technical solution of the present invention is that the second fiber Bragg grating is pasted onto the surface of the measuring point after being encapsulated as follows: the second fiber Bragg grating is encapsulated using a high-temperature resistant ceramic tube, and the encapsulated structure is pasted onto the surface of the measuring point.

[0014] A further technical solution of the present invention is that, during the process of winding the optical fiber of the cascaded distributed measurement fiber Bragg grating acoustic sensor on the high-pressure housing: the first fiber Bragg grating of each measuring point on the optical fiber is attached to the high-pressure housing.

[0015] A further technical solution of the present invention is that the expression for the actual strain value of the measuring point is:

[0016] In the formula, This represents the actual strain value at the measuring point; This represents the wavelength offset of the first fiber Bragg grating; This represents the wavelength offset of the second fiber Bragg grating; This is the strain sensitivity coefficient.

[0017] The beneficial effects of this invention are: This invention establishes multiple measurement points on a single optical fiber, with two fiber Bragg gratings (FBGs) arranged at each point. The first FBG at the same measurement point is directly bonded to the surface of the measurement point, while the second FBG is encapsulated and adhered to the surface of the measurement point, forming a cascaded distributed measurement fiber Bragg grating acoustic sensor. Specifically, by employing different configurations for different FBGs at the same measurement point, this invention ensures that the encapsulated second FBG does not directly contact the surface of the high-pressure housing, only measuring the temperature of the high-pressure housing. Then, based on the compensation offset of the second FBG, temperature compensation is applied to the wavelength offset measured by the first FBG, eliminating the influence of temperature changes on the measurement of the cascaded distributed measurement fiber Bragg grating acoustic sensor. This accurately monitors the deformation of the solid rocket motor housing under extreme temperature and pressure conditions, enabling the capture and precise measurement of rapid changes in housing strain. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram showing the distribution of various measuring points on the cascaded distributed measurement fiber optic grating acoustic sensor designed in this invention; Figure 2 This is a schematic diagram of the structure of FBG-1 and the packaging of FBG-2 at each measuring point of the present invention; Figure 3 This is a schematic diagram of the high-voltage housing after the cascaded distributed measurement fiber optic grating acoustic sensor is installed. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] This invention provides an embodiment of a high-pressure vessel temperature-strain monitoring method based on distributed acoustic sensors. This embodiment addresses the problem that high-pressure vessels are prone to significant deformation under load, leading to excessive stretching and structural failure, which seriously threatens equipment reliability and production safety. This method maintains stable measurements over a wide temperature range (-60℃ to 320℃), and the acrylic coating on the fiber optic surface can increase its strain limit to 20,000 microstrains (με), which is of great significance for improving the service quality and safety of solid rocket motors. The method includes: S1, Design of Cascaded Distributed Measurement Fiber Bragg Grating Acoustic Sensor Specifically, the cascaded distributed measurement fiber Bragg grating acoustic sensor includes: an optical fiber, with multiple measurement points evenly distributed on the optical fiber, each measurement point corresponding to a first fiber Bragg grating and a second fiber Bragg grating. The first fiber Bragg grating is directly attached to the surface of the measurement point on the optical fiber, and the second fiber Bragg grating is attached to the surface of the measurement point after encapsulation. The fiber Bragg grating is used to selectively filter light coupled into the optical fiber at specific wavelengths.

[0022] For example, in one specific embodiment, such as Figure 1 As shown, the optical fiber deployed outside the high-voltage housing is approximately 0.54m long, with 11 measuring points set up, each spaced 45mm apart. Figure 2 As shown, each measurement point corresponds to two fiber Bragg gratings (FBGs): FBG-1 and FBG-2. FBG-1 is directly bonded to the fiber surface. FBG-2 is encapsulated in a high-temperature resistant ceramic tube before being bonded to the fiber surface, ensuring that FBG-2 does not directly contact the high-voltage housing surface. Figure 2 As shown, the second fiber Bragg grating FBG-2 is configured to measure only the temperature of the high-pressure housing.

[0023] For example, in one specific embodiment, a particular wavelength satisfies:

[0024] In the formula, For a specific wavelength; The period of the fiber grating; The effective refractive index of the cascaded fiber Bragg grating.

[0025] For example, in one specific embodiment, when external temperature and strain are applied to the first fiber Bragg grating (FBG-1), it will cause a shift in the reflected wavelength of the first fiber Bragg grating (FBG-1). The relationship between the wavelength shift of the first fiber Bragg grating (FBG-1) and the applied temperature and strain is as follows:

[0026] In the formula, This represents the wavelength offset of the first fiber Bragg grating; For a specific wavelength; is the optical elastic coefficient of the fiber Bragg grating; The axial strain change experienced by the fiber of the first fiber Bragg grating; The coefficient of thermal expansion of a fiber Bragg grating; The thermo-optic coefficient of the fiber Bragg grating; This represents the temperature change around the fiber Bragg grating. The strain sensitivity coefficient; This is the temperature sensitivity coefficient.

[0027] For example, in one specific embodiment, since a second fiber Bragg grating (FBG-2) encapsulated in a high-temperature resistant ceramic tube is installed at the measuring point where the first fiber Bragg grating (FBG-1) is installed, the high-temperature resistant ceramic tube isolates the influence of the high-pressure shell deformation. That is, the second fiber Bragg grating directly measures the temperature of the high-pressure shell. Therefore, the relationship between the wavelength shift of the second fiber Bragg grating (FBG-2) and the applied temperature is as follows:

[0028] In the formula, This represents the wavelength offset of the second fiber Bragg grating; The coefficient of thermal expansion of a fiber Bragg grating; The thermo-optic coefficient of the fiber Bragg grating; This represents the temperature change around the fiber Bragg grating. This is the temperature sensitivity coefficient.

[0029] S2. The optical fiber of the cascaded distributed measurement fiber optic grating acoustic sensor is wound around the high-pressure housing. The high-pressure housing is subjected to heating and pressurization experiments, and the two wavelength offsets measured at each measuring point in the cascaded distributed measurement fiber optic grating acoustic sensor are recorded. For example, in this embodiment, such as Figure 3As shown, the cylindrical high-pressure housing model representing the solid rocket motor casing has a radius of 0.02m, a length of 0.2m, a wall thickness of 2mm, and a fiber diameter of 500μm. The fiber is uniformly wound around the surface of the high-pressure housing with 3 turns, and the axial distance between the fibers is 0.065m. During the deployment process, it is necessary to ensure that the first fiber Bragg grating (FBG-1) at each measuring point is firmly attached to the high-pressure housing. Then, heating and pressurizing experiments can be performed on the high-pressure housing, and the wavelength shift corresponding to the first and second fiber Bragg gratings (FBG-2) during the experiment can be recorded.

[0030] S3. Based on the two wavelength offsets of each measuring point, obtain the actual strain value of the measuring point.

[0031] For example, in one specific embodiment, the data obtained by monitoring the second fiber Bragg grating FBG-2 is used to perform temperature compensation on the first fiber Bragg grating FBG-1, and the expression for the actual strain value of the measuring point is:

[0032] In the formula, This represents the actual strain value at the measuring point; This represents the wavelength offset of the first fiber Bragg grating; This represents the wavelength offset of the second fiber Bragg grating; This is the strain sensitivity coefficient.

[0033] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for high pressure shell temperature-strain monitoring based on distributed acoustic sensors, characterized in that, The application relates to a cascaded distributed measurement fiber grating acoustic sensor, which comprises an optical fiber, a plurality of measuring points are uniformly arranged on the optical fiber, each measuring point corresponds to a first fiber Bragg grating and a second fiber Bragg grating, wherein the first fiber Bragg grating is directly pasted on the surface of the measuring point of the optical fiber, and the second fiber Bragg grating is pasted on the surface of the measuring point after encapsulation; the fiber Bragg grating is used for selectively filtering specific wavelengths of light coupled into the optical fiber. The optical fiber of the cascaded distributed measurement fiber grating acoustic sensor is wound on a high-pressure shell, the high-pressure shell is subjected to temperature rising and pressure increasing experiments, and the two wavelength shift amounts measured by each measuring point in the cascaded distributed measurement fiber grating acoustic sensor are recorded. Based on the two wavelength shift amounts of each measuring point, the actual strain value of the measuring point is obtained. The specific wavelength satisfies the following conditions:

2. The method of claim 1, wherein, The relationship between the wavelength shift amount of the first fiber Bragg grating and the temperature and strain borne by the first fiber Bragg grating is as follows: wherein is a specific wavelength; is a fiber grating period; is an effective refractive index of the cascaded fiber Bragg grating.

3. The method of claim 1, wherein, The relationship between the wavelength shift amount of the second fiber Bragg grating and the temperature borne by the second fiber Bragg grating is as follows: In the formula, is a wavelength shift of the first fiber Bragg grating; is a specific wavelength; is a photoelastic coefficient of the fiber Bragg grating; is a change in the axial strain of the fiber of the first fiber Bragg grating; is a thermal expansion coefficient of the fiber Bragg grating; is a thermo-optic coefficient of the fiber Bragg grating; is a change in the temperature around the fiber Bragg grating; is a strain sensitivity coefficient; is a temperature sensitivity coefficient.

4. The method of claim 1, wherein, The step of pasting the second fiber Bragg grating on the surface of the measuring point after encapsulation is as follows: the second fiber Bragg grating is encapsulated by using a high-temperature-resistant ceramic tube, and the encapsulated structure is pasted on the surface of the measuring point. In the formula, is a wavelength shift amount of the second fiber Bragg grating; is a thermal expansion coefficient of the fiber Bragg grating; is a thermo-optic coefficient of the fiber Bragg grating; is a temperature change amount around the fiber Bragg grating; is a temperature sensitivity coefficient.

5. The method of claim 1, wherein, During the process of winding the optical fiber of the cascaded distributed measurement fiber grating acoustic sensor on the high-pressure shell, the first fiber Bragg grating of each measuring point on the optical fiber is attached to the high-pressure shell.

6. The method of claim 1, wherein, The expression of the actual strain value of the measuring point is as follows:

7. The method of claim 1, wherein, ​ In the formula, is the actual strain value of the measuring point; is the wavelength shift of the first fiber Bragg grating; is the wavelength shift of the second fiber Bragg grating; is the strain sensitivity coefficient.

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