Solid fuel sedimentation monitoring method based on implanted optical fiber and wireless passive sensing

Abstract

The present invention relates to the technical field of sensing and monitoring, and provides a method for monitoring the settlement of solid fuel based on the cooperation of implanted optical fibers and wireless passive sensors. The present invention uses fiber Bragg grating sensors implanted in the inner surface layer of solid fuel to calibrate a wireless passive sensor array, enabling the wireless passive sensors to have accurate strain monitoring capabilities. The present invention uses a wireless passive sensor array that has been strictly calibrated and encapsulated to monitor the settlement of solid fuel, avoiding the problem of low accuracy of the settlement amount obtained through simulation. The present invention does not require drilling holes and laying wires on the solid engine housing, overcoming the damage to the engine structure caused by conventional wired and active methods, and having a high safety factor. The implanted fiber Bragg grating calibration method used in this invention has the advantages of being easy to implant, small in size, high in precision, simple in wiring, and not requiring disassembly after calibration compared with other electrical sensors. During the calibration process of the present invention, mutual interference between signals is avoided, and the system measurement is more accurate.

Description

Technical Field

[0001] The invention relates to the field of sensor monitoring technology, and in particular to a solid fuel sedimentation monitoring method that cooperates with implanted optical fiber and wireless passive sensing. Background Art

[0002] Solid fuel in solid engines is a viscoelastic substance. During long-term storage, it is prone to stratification, debonding, cracking, etc. due to internal and external factors. Especially under long-term vertical storage conditions, solid fuel is prone to sedimentation, which brings great harm to the engine. Specifically, large sedimentation will directly change the inner hole profile of the solid fuel, causing the gas channel to be blocked or causing the shape of the solid fuel combustion surface to change, thereby changing the internal ballistic performance of the engine, and the engine is at risk of explosion.

[0003] There are two main methods for monitoring settlement. One is to obtain the settlement amount through simulation calculation, and the other is to monitor it through mounting sensors. For the former, due to the large number of environmental factors, it is difficult to take all factors into account in simulation, so it is difficult to obtain accurate settlement. For the latter, taking conventional mounting resistance strain gauges as an example, there are the following defects:

[0004] (1) The elastic modulus of the resistance strain gauge does not match that of the solid fuel being measured, resulting in local stress concentration and large strain measurement errors.

[0005] (2) When using conventional methods such as resistance strain gauges for measurement, power supply, signal conditioning circuits, etc. are required, and cable connections are required. For large-area array monitoring of the internal fuel of large solid engines, a large number of cables need to be arranged on the solid fuel, which affects the gas channel space.

[0006] (3) A large number of cables are used for transmitting electrical signals, which poses a safety risk when combined with solid fuel.

[0007] (4) More importantly, the connection between the cable and the external equipment requires drilling holes in the engine casing for wiring, which damages the engine structure, poor operability, and poses a safety hazard.

[0008] Therefore, whether it is possible to find an effective way to monitor settlement and overcome the above-mentioned defects has become an urgent problem to be solved. Summary of the invention

[0009] In order to solve the problems existing in the background technology, the present invention provides a solid fuel sedimentation monitoring method by integrating implanted optical fiber and wireless passive sensing, which comprises the following steps:

[0010] S1: After encapsulating the optical fiber containing several grating sensors with silicone rubber, the encapsulated optical fiber is implanted into the inner surface of the hollow cylindrical solid fuel;

[0011] S2: using EPDM rubber to encapsulate a number of wireless passive sensors, and attaching the encapsulated wireless passive sensors to the inner surface of the solid fuel, so that each wireless passive sensor corresponds to the grating sensor in the optical fiber one by one, and is maintained in the same radial direction of the solid fuel cylinder;

[0012] S3: setting the spatial coordinates of each wireless passive sensor, and setting a unique radio frequency reflection peak signal code for each wireless passive sensor, and uniquely corresponding each code to the spatial coordinates of the wireless passive sensor;

[0013] S4: Calibrate the fiber grating sensor array and the wireless passive sensor array implanted on the inner surface of the solid fuel;

[0014] S5: Use the radio frequency reading and writing device to read the strain information of the wireless passive sensor array, combine the spatial coordinates and the strain at the corresponding point, and construct the three-dimensional situation of the solid fuel sedimentation to realize the monitoring of the solid fuel sedimentation.

[0015] The specific process of step S3 includes:

[0016] n fiber grating sensors are implanted at designated positions on the inner surface of a cylindrical solid fuel, and each fiber grating sensor is set to have its own unique spatial coordinates;

[0017] Fiber Bragg grating sensors are used in a wavelength division multiplexing manner, and n fiber Bragg gratings are set with different central wavelengths, namely λ 1 ... n , and the center wavelengths are far apart, so that when strain occurs, the wavelength change of the fiber Bragg grating is less than the spacing between the center wavelengths of adjacent fiber Bragg gratings, so that the changes in the center wavelengths of gratings at different positions will not overlap, ensuring that the spatial coordinates of each fiber Bragg grating sensor form a unique corresponding relationship with its center wavelength.

[0018] Furthermore, the specific process of step S3 also includes:

[0019] By changing the size of n wireless passive sensors to change their resonant frequencies, each passive wireless sensor has a specific resonant frequency to avoid crosstalk between them. The n wireless passive sensors are set with different resonant frequencies, which are f 1 ……f n .

[0020] Further, the specific process of step S4 includes:

[0021] Step A: Calibrate the strain measurement of the fiber Bragg grating sensor:

[0022] Fiber Bragg grating sensors measure strain by wavelength variation. Ignoring the influence of temperature, the calculation method is:

[0023]

[0024] Among them, λ 0 is the central wavelength of the fiber Bragg grating, is a known fixed value for each grating, Δλ is the wavelength change caused by the deformation of the fiber Bragg grating, P e is the elastic-optic coefficient (constant), and ε is the strain value; it can be seen from the above formula that the wavelength change Δλ of the fiber Bragg grating is proportional to the strain ε, so the strain can be measured by the change in wavelength;

[0025] The specific calibration operation is: applying a known gradient strain value to the fiber Bragg grating sensor, measuring its wavelength change, and after multiple measurements and fitting, the coefficient of the proportional relationship between the two can be obtained, thus completing the calibration of the fiber Bragg grating sensor for measuring strain;

[0026] Step B: Strain measurement calibration of wireless passive sensors:

[0027] After the fiber grating sensor completes the strain measurement calibration, it is used as the basis for strain measurement, and then the wireless passive sensor strain monitoring is calibrated; the wireless passive sensor used in the present invention determines the change of strain by the change of resonant frequency, and the relationship between the two is as follows:

[0028] Δf=k·ε+c

[0029] Among them, ε is the strain monitored by the wireless passive sensor, Δf is the change of the resonant frequency of the passive wireless sensor, k and c are constants, so the relationship between the change of the resonant frequency and the strain can be obtained through calibration.

[0030] Further, the specific process of step S5 includes:

[0031] P1: By measuring the frequency shift of each wireless passive sensor, the strain ε1…εn at the corresponding position is obtained. Combined with the thickness of the wireless passive sensor, the curvature of each sensing point can be obtained;

[0032] P2: Based on the fact that the deformation of solid fuel mainly occurs in the axial and radial directions and the distortion is small, the curves of sensors in the same row on the solid fuel are equivalent to two-dimensional curves;

[0033] P3: A two-dimensional rectangular coordinate system is established for each curve, and the curvature calculated above is interpolated to convert the entire curve into several small arcs of equal length. Then, the change in the horizontal / vertical coordinates of each point on the curve compared to the previous point is derived one by one using the curvature value, curvature radius, bending angle, arc length, etc. That is, the coordinate change is added to the initial coordinate point, and the coordinates of all discrete points on the curve can be derived one by one. All discrete points are connected by fitting to complete the reconstruction of a single curve.

[0034] P4: After reconstructing several curves where the sensors on the inner surface of the solid fuel are located, the shape of the inner surface of the solid fuel can be reconstructed through fitting, and the spatial coordinates of each sensor point can be obtained;

[0035] P5: After settlement, the spatial coordinates of the sensor point have changed compared with the spatial coordinates during installation and calibration. The settlement information is obtained by comparing the spatial position of the sensor point during installation with the spatial position obtained after shape reconstruction.

[0036] The beneficial effects achieved by the present invention are:

[0037] First, the present invention uses a strictly calibrated and packaged wireless passive sensor array to monitor solid fuel sedimentation, thereby avoiding the problem of low accuracy of sedimentation obtained through simulation.

[0038] Second, the present invention does not require holes to be drilled in the solid engine casing for wiring, thus overcoming the damage to the engine structure caused by conventional wired active methods and having a high safety factor.

[0039] Third, the entire solid fuel monitoring area of ​​the present invention has no cables, no transmission of electrical signals and no power supply, which solves the potential safety hazard problem in the environment of flammable and explosive materials. At the same time, the use of traditional electrical sensor arrays to monitor sedimentation requires a large number of cables to be laid out, affecting the gas channel space. The method used by this invention solves this problem.

[0040] Fourthly, the elastic modulus of the wireless passive sensor and fiber grating sensor packaging materials of the present invention are well matched with the elastic modulus of the solid fuel, which solves the problem of inaccurate strain measurement caused by local stress concentration and can achieve large strain and high-precision measurement.

[0041] Fifth, by using the collaborative detection of implanted optical fiber and wireless passive sensing, the quasi-in-situ calibration of wireless passive sensing is achieved, and the measurement accuracy is higher. Compared with other electrical sensors, the implanted fiber grating calibration method used in this invention has the advantages of easy implantation, small size, high accuracy, simple wiring, and no need to disassemble after calibration. At the same time, the two belong to optical means and electrical means respectively, and mutual interference between signals is avoided during the calibration process, and the system measurement is more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a schematic diagram of the packaging results of the fiber Bragg grating sensor;

[0043] Figure 2 It is a schematic diagram of the packaging result of wireless passive sensor;

[0044] Figure 3 Side view of the mounting structure of the grating sensor, the wireless passive sensor and the solid fuel;

[0045] Figure 4 This is a schematic diagram of the sensor point layout and engine solid fuel sedimentation monitoring in Example 1;

[0046] Figure 5 yes Figure 4 Schematic diagram of the expansion;

[0047] Figure 6 is a flow chart of solid fuel sedimentation monitoring by integrating implanted optical fiber and wireless passive sensing in Example 1;

[0048] Figure 7 It is a schematic diagram of the monitoring results of Example 1. DETAILED DESCRIPTION

[0049] To facilitate those skilled in the art to understand the present invention, specific implementations of the present invention are described below with reference to the accompanying drawings.

[0050] Reference Figure 1-Figure 3 The present invention provides a solid fuel sedimentation monitoring method that integrates implanted optical fiber and wireless passive sensing. The first step includes encapsulating an optical fiber containing a plurality of grating sensors with silicone rubber, and then implanting the encapsulated optical fiber into the inner surface of a hollow cylindrical solid fuel. The process can be specifically implemented by the following steps:

[0051] A long straight hollow cylindrical mold with holes at both ends is used, and an injection hole is opened at the top of the mold. When packaging, first pass a whole optical fiber engraved with a fiber grating sensor through the holes at both ends of the mold, and after pre-stretching and fixing, inject liquid silicone rubber from the injection hole. After the silicone rubber solidifies, separate it from the outer mold to complete the production of the fiber grating sensor based on silicone rubber packaging.

[0052] The second step includes encapsulating a plurality of wireless passive sensors with EPDM rubber, and attaching the encapsulated wireless passive sensors to the inner surface of the solid fuel, so that each wireless passive sensor corresponds to the grating sensor in the optical fiber one by one and is maintained in the same radial direction of the solid fuel cylinder; this process can be specifically implemented by the following steps:

[0053] First, make a rectangular mold with an openable top, pour the heated and melted liquid EPDM rubber into the mold, wait for the EPDM rubber base to solidify when the liquid level reaches half the height of the mold, then place the wireless passive sensor in the center, pour liquid EPDM rubber into the mold to fill it, remove the mold after it is completely solidified, and complete the production of the wireless passive sensor based on EPDM rubber encapsulation.

[0054] In the packaging process of the above two sensors, in order to avoid bubbles inside the silicone rubber and EPDM rubber after solidification, reduce the mechanical properties, and affect the measurement accuracy, the vulcanization temperature is appropriately increased and the vulcanization time is extended. The present invention sets the vulcanization temperature to 230°C and the vulcanization time to 8 hours. The surface of the mold to be made needs to be smooth and clean, and the guide angle of the mold can have a certain curvature to reduce the possibility of bubbles stored in the right-angle groove.

[0055] The third step includes setting the spatial coordinates of each wireless passive sensor, and setting a unique radio frequency reflection peak signal code for each wireless passive sensor, and uniquely corresponding each code to the spatial coordinates of the wireless passive sensor;

[0056] The fourth step includes calibrating the fiber grating sensor array and the wireless passive sensor array implanted on the inner surface of the solid fuel;

[0057] The fifth step includes using a radio frequency reader to read the strain information of the wireless passive sensor array, combining the spatial coordinates and the strain at the corresponding points to construct a three-dimensional picture of the solid fuel sedimentation, thereby realizing the monitoring of the solid fuel sedimentation.

[0058] Embodiment 1,

[0059] The third, fourth and fifth steps of the present invention are described below in conjunction with specific embodiments. In this embodiment, the monitored object is a cylindrical solid fuel in the engine casing. The wireless passive sensor uses a high temperature resistant sensor with a temperature resistance of not less than 300°C. The sensor is encapsulated with EPDM rubber whose elastic modulus is similar to that of the solid fuel. The encapsulated sensor has a thickness of 5mm and a length and width of 20mm. Taking the solid fuel height of 100cm and the circumference of 160cm as an example, the fiber grating sensor and the wireless passive sensor are both 8×8 layout structures, the 8 columns of sensors are equally spaced at 20cm, and the intervals of the 8 rows of sensors from top to bottom are 5cm, 5cm, 5cm, 10cm, 15cm, 20cm, and 30cm.

[0060] In this embodiment, the packaged fiber grating sensor is used to calibrate the packaged wireless passive sensor. The diameter of the entire fiber grating sensor after packaging and integration with silicone rubber is 1 mm. The packaged shape is a long cylinder. The elastic modulus of silicone rubber is similar to that of solid fuel.

[0061] The specific operation process includes burying the fiber Bragg grating sensor based on silicone rubber encapsulation into the inner surface of the hollow cylindrical solid fuel, and the closest distance between the silicone rubber surface and the inner surface of the solid fuel is constant at 3mm. The wireless passive sensor based on EPDM rubber encapsulation is attached to the inner surface of the solid fuel facing the fiber Bragg grating sensor, and the two correspond one to one and are kept in the same radial direction of the solid fuel cylinder. Figure 4-Figure 5 The sensor point layout diagram and the engine solid fuel sedimentation monitoring situation are shown. Due to gravity, the solid fuel sedimentation of solid engines under vertical storage conditions generally shows a trend of gradually decreasing from top to bottom. In order to obtain more effective data, a sensor point layout method with dense top and sparse bottom is selected.

[0062] During the calibration of the fiber grating sensor array and the wireless passive sensor array implanted on the inner surface of the solid fuel, the fiber grating sensor and the wireless passive sensor are quasi-in-situ measured on the solid fuel. During the calibration, vertical downward tension is applied to the solid fuel. The strain value measured by the fiber grating sensor is used as the standard value to calibrate the wireless passive sensor. The strain measurement sensitivity of the wireless passive sensor can be obtained through the calibration test. The specific process also includes:

[0063] 64 fiber Bragg grating sensors are installed at designated positions on the inner surface of a cylindrical solid fuel, and each fiber Bragg grating sensor is set to have its own unique spatial coordinates;

[0064] The fiber grating sensors are used in a wavelength division multiplexing manner, and the 64 fiber grating sensors are set with different central wavelengths, namely λ 1 ... n , and the center wavelengths are far apart, so that when strain occurs, the wavelength change of the fiber Bragg grating is less than the spacing between the center wavelengths of adjacent fiber Bragg gratings, so that the changes in the center wavelengths of gratings at different positions will not overlap, ensuring that the spatial coordinates of each fiber Bragg grating sensor form a unique corresponding relationship with its center wavelength.

[0065] Then, the resonant frequency of the 64 wireless passive sensors is changed by changing their sizes, so that each passive wireless sensor has a specific resonant frequency to avoid crosstalk between them. The 64 wireless passive sensors are set with different resonant frequencies, which are f 1 ……f n .

[0066] The process of calibrating the strain measurement of a fiber Bragg grating sensor includes:

[0067] Fiber Bragg grating sensors measure strain by wavelength variation. Ignoring the influence of temperature, the calculation method is:

[0068]

[0069] Among them, λ 0 is the central wavelength of the fiber Bragg grating, is a known fixed value for each grating, Δλ is the wavelength change caused by the deformation of the fiber Bragg grating, P e is the elastic-optic coefficient (constant), and ε is the strain value; it can be seen from the above formula that the wavelength change Δλ of the fiber Bragg grating is proportional to the strain ε, so the strain can be measured by the change in wavelength;

[0070] The specific calibration operation is: applying a known gradient strain value to the fiber Bragg grating sensor, measuring its wavelength change, and after multiple measurements and fitting, the coefficient of the proportional relationship between the two can be obtained, thus completing the calibration of the fiber Bragg grating sensor for measuring strain;

[0071] The process of strain measurement calibration for wireless passive sensors includes:

[0072] After the fiber grating sensor completes the strain measurement calibration, it is used as the basis for strain measurement, and then the wireless passive sensor strain monitoring is calibrated; the wireless passive sensor used in the present invention determines the change of strain by the change of resonant frequency, and the relationship between the two is as follows:

[0073] Δf=k·ε+c

[0074] Among them, ε is the strain monitored by the wireless passive sensor, Δf is the change of the resonant frequency of the passive wireless sensor, k and c are constants, so the relationship between the change of the resonant frequency and the strain can be obtained through calibration.

[0075] After the calibration is completed, a set of wireless radio frequency reading and writing devices is installed outside the 64 wireless passive sensor arrays. After the calibration of the wireless passive sensors is completed, the fiber optic Bragg grating sensor cables remaining outside the solid fuel are removed, leaving only the part implanted inside the solid fuel, and the engine casing is closed. In this way, the wireless passive sensor can monitor the solid fuel in the enclosed space inside the solid engine in real time.

[0076] The object monitored in this embodiment is the cylindrical segment of solid fuel in the solid engine, which is generally in a relatively regular cylindrical shape in its initial state. During long-term storage, the solid fuel is affected by internal and external factors, especially the deadweight load and aging. The geometric shape of the solid fuel changes and sedimentation occurs, which is especially significant for long-term vertical storage. After sedimentation occurs, the appearance shape often changes. Therefore, monitoring the sedimentation of solid fuel is of great significance for evaluating the health status of the engine. The specific process of the present invention for monitoring the sedimentation of solid fuel in the closed space inside the engine is referred to in the following. Figure 6, the strain values ​​of 64 layout points are measured by wireless passive sensors. Combined with the thickness of wireless passive sensors, the curvature of each sensing point can be obtained. Since the deformation of solid fuel mainly occurs in its axial and radial directions, the distortion is small and negligible. Therefore, the curve where the sensors in the same column on the solid fuel are located can be equivalent to a two-dimensional curve. A two-dimensional rectangular coordinate system is established for each curve, and the curvature calculated above is interpolated to make the entire curve equivalent to several small arcs of equal length. Then, the curvature value, curvature radius, bending angle, arc length and other values ​​are used to derive the change in the horizontal / vertical coordinates of each point on the curve compared to the previous point. That is, the coordinate change is added to the initial coordinate point, and the coordinates of all discrete points on the curve can be derived one by one. All discrete points are fitted and connected to complete the reconstruction of a single curve. After reconstructing the 8 curves where the sensors on the inner surface of the solid fuel are located, the shape of the inner surface of the solid fuel is reconstructed after fitting, as shown in the figure. Figure 7 As shown. The spatial coordinates of each sensor point are obtained. The spatial coordinates of the sensor point after settlement have changed compared with the spatial coordinates during installation and calibration. The settlement information can be obtained by comparing the spatial position of the sensor point during installation with the spatial position obtained after the shape reconstruction.

[0077] The above embodiments of the present invention do not constitute a limitation on the protection scope of the present invention. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. Solid fuel sedimentation monitoring method based on implanted optical fiber and wireless passive sensing, It is characterized in that It includes the following steps: S1: After encapsulating the optical fiber containing several grating sensors with silicone rubber, the encapsulated optical fiber is implanted into the inner surface of the hollow cylindrical solid fuel; S2: using EPDM rubber to encapsulate a number of wireless passive sensors, and attaching the encapsulated wireless passive sensors to the inner surface of the solid fuel, so that each wireless passive sensor corresponds to the grating sensor in the optical fiber one by one, and is maintained in the same radial direction of the solid fuel cylinder; S3: setting the spatial coordinates of each wireless passive sensor, and setting a unique radio frequency reflection peak signal code for each wireless passive sensor, and uniquely corresponding each code to the spatial coordinates of the wireless passive sensor; S4: Calibrate the fiber grating sensor array and the wireless passive sensor array implanted on the inner surface of the solid fuel; the specific process of step S4 includes: Step A: Calibrate the strain measurement of the fiber Bragg grating sensor: Fiber Bragg grating sensors measure strain by wavelength variation. Ignoring the influence of temperature, the calculation method is: in, is the central wavelength of the fiber Bragg grating, is a known fixed value for each grating, is the wavelength change caused by the deformation of the fiber Bragg grating, is the elastic-optical coefficient (a constant), is the strain value; From the above formula, it can be seen that the wavelength change of the fiber Bragg grating With strain is proportional to the wavelength, so the strain can be measured by the change in wavelength; The specific calibration operation is: applying a known gradient strain value to the fiber Bragg grating sensor, measuring its wavelength change, and after multiple measurements and fitting, the coefficient of the proportional relationship between the two can be obtained, thus completing the calibration of the fiber Bragg grating sensor for measuring strain; Step B: Strain measurement calibration of wireless passive sensors: After the fiber Bragg grating sensor completes the strain measurement calibration, it serves as the benchmark for strain measurement, and then calibrates the strain monitoring of the wireless passive sensor; the wireless passive sensor judges the change of strain by the change of the resonance frequency, and the relationship between the two is as follows: Among them, is the strain value, is the change of the resonance frequency of the passive wireless sensor, and k and c are both constants. Therefore, the relationship between the change of the resonance frequency and the strain can be obtained through calibration; S5: Use the radio frequency reading and writing device to read the strain information of the wireless passive sensor array, combine the spatial coordinates and the strain at the corresponding point, and construct the three-dimensional situation of the solid fuel sedimentation to realize the monitoring of the solid fuel sedimentation.

2. The solid fuel sedimentation monitoring method using implanted optical fiber and wireless passive sensing according to claim 1, Features: The specific process of step S3 includes: n fiber grating sensors are implanted at designated positions on the inner surface of a cylindrical solid fuel, and each fiber grating sensor is set to have its own unique spatial coordinates; Fiber Bragg grating sensors are used in a wavelength division multiplexing manner, and n fiber Bragg gratings are set with different central wavelengths, namely λ 1 ... n , and the center wavelengths are far apart, so that when strain occurs, the wavelength change of the fiber Bragg grating is less than the spacing between the center wavelengths of adjacent fiber Bragg gratings, so that the changes in the center wavelengths of gratings at different positions will not overlap, ensuring that the spatial coordinates of each fiber Bragg grating sensor form a unique corresponding relationship with its center wavelength.

3. The solid fuel sedimentation monitoring method using implanted optical fiber and wireless passive sensing according to claim 1, Features: The specific process of step S3 also includes: By changing the size of n wireless passive sensors to change their resonant frequencies, each passive wireless sensor has a specific resonant frequency to avoid crosstalk between them. The n wireless passive sensors are set with different resonant frequencies, which are f 1 ……f n .

4. The solid fuel sedimentation monitoring method using implanted optical fiber and wireless passive sensing according to claim 1, Features: The specific process of step S5 includes: P1: By measuring the frequency shift of each wireless passive sensor, the strain at the corresponding position is obtained … ,Combined with the thickness of wireless passive sensor, the curvature of each sensing point can be obtained; P2: Based on the fact that the deformation of solid fuel mainly occurs in the axial and radial directions and the distortion is small, the curves of sensors in the same row on the solid fuel are equivalent to two-dimensional curves; P3: A two-dimensional rectangular coordinate system is established for each curve, and the curvature calculated above is interpolated to convert the entire curve into several small arcs of equal length. Then, the change in the horizontal / vertical coordinates of each point on the curve compared to the previous point is derived one by one using the curvature value, curvature radius, bending angle, arc length, etc. That is, the coordinate change is added to the initial coordinate point, and the coordinates of all discrete points on the curve can be derived one by one. All discrete points are connected by fitting to complete the reconstruction of a single curve. P4: After reconstructing several curves where the sensors on the inner surface of the solid fuel are located, the shape of the inner surface of the solid fuel can be reconstructed through fitting, and the spatial coordinates of each sensor point can be obtained; P5: After settlement, the spatial coordinates of the sensor point have changed compared with the spatial coordinates during installation and calibration. The settlement information is obtained by comparing the spatial position of the sensor point when it was installed with the spatial position obtained after the reconstructed shape.

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