A stress monitoring method suitable for special-shaped wind tunnel pressure shell

Abstract

A stress monitoring method suitable for a special-shaped wind tunnel pressure shell belongs to the field of stress analysis and testing technology. It is to solve the problem of safety in the operation and use of special-shaped wind tunnels. The present invention establishes a finite element simulation model of the special-shaped wind tunnel pressure shell based on the structure of the special-shaped wind tunnel pressure shell, performs static structural calculations, obtains finite element calculation results of the special-shaped wind tunnel pressure shell, selects stress monitoring points, and marks stress monitoring points at corresponding positions of the special-shaped wind tunnel pressure shell; welds and installs strain gauges on the stress monitoring points marked on the special-shaped wind tunnel pressure shell, connects the strain gauges to the collection box, and connects the collection box to the control box of the strain data acquisition instrument. During the operation of the wind tunnel, the strain data acquisition instrument collects the strain measurement values of the strain gauges and converts them into stress values of the stress monitoring points; the strain data acquisition instrument control box is connected to the host computer via Ethernet, and the host computer monitors the stress values in real time. The monitoring of the present invention is accurate.

Description

Technical Field

[0001] The present invention belongs to the technical field of stress analysis and testing, and in particular relates to a stress monitoring method applicable to a special-shaped wind tunnel pressure shell. Background Art

[0002] A wind tunnel is a device that uses a power unit to drive a controlled airflow within a designed piping system to conduct various aerodynamic tests based on the principles of relativity and similarity of motion. The pressure hull, the main structure of a large-scale wind tunnel, is the primary pressure-bearing structure for aerodynamic loads. Depending on the requirements of the wind tunnel design, the pressure hull must be designed with various cross-sectional forms. To facilitate the use and maintenance of wind tunnel test equipment, a large number of mounting openings and manholes are required. To ensure the safe operation and use of special-shaped wind tunnels, stress safety monitoring of the pressure hull is essential during operation. Summary of the Invention

[0003] The problem to be solved by the present invention is the safety of operation and use of a special-shaped wind tunnel. The present invention proposes a stress monitoring method suitable for the pressure shell of a special-shaped wind tunnel.

[0004] To achieve the above object, the present invention is implemented through the following technical solutions:

[0005] A stress monitoring method applicable to a special-shaped wind tunnel pressure shell comprises the following steps:

[0006] S1. Establish a finite element simulation model of the special-shaped wind tunnel pressure shell based on its structure. Apply corresponding loads for different working conditions, calculate the stress distribution of the special-shaped wind tunnel pressure shell under different working conditions, select the maximum stress value points, stress alternation points, stress concentration points, and structural mutation positions of the special-shaped wind tunnel pressure shell under each working condition, analyze the stress state at each position, and mark stress monitoring points at the corresponding positions of the special-shaped wind tunnel pressure shell;

[0007] S2. Weld and install strain gauges at the stress monitoring points marked on the pressure shell of the special-shaped wind tunnel in step S1, connect the strain gauges to a collection box, and connect the collection box to a control box of a strain data acquisition instrument. During the operation of the wind tunnel, the strain data acquisition instrument collects strain measurements of the strain gauges and converts them into stress values at the stress monitoring points.

[0008] S3. The strain data acquisition instrument control box is connected to the host computer via Ethernet to monitor the stress value of the stress monitoring point in real time.

[0009] Furthermore, the specific implementation method of step S1 includes the following steps:

[0010] S1.1. Simplification of the pressure shell structure of the special-shaped wind tunnel: The pressure shell structure of the special-shaped wind tunnel is simplified into a thin shell structure for modeling. At the same time, the observation holes in the pressure shell of the wind tunnel are analyzed, and the threaded holes and pin holes that do not affect the accuracy of the calculation results are simplified and omitted;

[0011] S1.2. Geometric model construction and meshing of the special-shaped wind tunnel pressure shell: The special-shaped wind tunnel pressure shell is constructed as a shell structure composed of curved surfaces, and the geometric model is meshed using surface elements. The tie rod structure is constructed as a linear structure, and the geometric model is meshed using beam elements.

[0012] S1.3. Boundary conditions and load application of the special-shaped wind tunnel pressure shell: When applying boundary conditions of the special-shaped wind tunnel pressure shell, different degrees of freedom constraint forms are selected according to the form of the supports, and corresponding internal pressure loads are applied according to the different working pressure conditions of each section of the special-shaped wind tunnel pressure shell;

[0013] S1.4. Perform static structural calculations on the finite element model of the wind tunnel pressure shell completed in step S1.3. Based on the finite element calculation results, select stress monitoring points in the stress range of 115 MPa to 172.5 MPa, and analyze the stress states of the stress monitoring points.

[0014] Furthermore, in step S1.2, the surface element adopts the shell181 element, which is a 4-node element, and each node has 6 degrees of freedom: displacement freedom in the x, y, and z directions and rotation freedom around the X, Y, and Z axes; the beam element adopts the beam188 element, which is a two-node three-dimensional linear beam element, and each node has 6 degrees of freedom, namely, displacement freedom along the x, y, and z directions and rotation freedom around the X, Y, and Z axes.

[0015] Furthermore, the node displacement {x} in the static structural calculation in step S1.4 is solved by the following matrix equation:

[0016] K]{x}={F}

[0017] K] is a stiffness matrix, {F} is a list of external loads, and {x} is the node displacement;

[0018] The shape function {x} of the shell181 element shell181 for:

[0019]

[0020] [s,r] are the coordinates of the symmetric parameterized unit; h i [s,r] is the shape function of the 4-node element, {x} i is the node coordinate array of node i;

[0021] The shape function {x} of the beam188 element beam188 for:

[0022]

[0023] x a 、x b are the node coordinates of node a and node b respectively, and x is the node coordinate of any point.

[0024] Furthermore, the specific implementation method of step S2 includes the following steps:

[0025] S2.1. Select the 0-degree, 45-degree, and 90-degree rosette arrangements based on the stress state of the stress monitoring point to monitor the stress state and stress direction of the stress monitoring point.

[0026] S2.2. Install the welded strain gauge. Clean the surface of the welding area of the special-shaped wind tunnel pressure shell and perform spot welding with a spot welder, controlling the weld spot diameter to 0.8 mm.

[0027] S2.3. After installing the strain gauge, begin wiring and routing. Connect the strain gauge data acquisition cable to the acquisition box. Connect the strain data acquisition instrument control box and the acquisition box via connectors for communication and power supply. Once connected, enter the bridge mode, wire resistance, strain gauge sensitivity coefficient, elastic modulus, and Poisson's ratio of the special-shaped wind tunnel pressure shell material to automatically correct the measurement results.

[0028] S2.4. When the wind tunnel is running, the strain data acquisition instrument collects the strain measurement values of the strain gauge in real time and converts them into stress values at the stress monitoring points.

[0029] Furthermore, the specific implementation method of step S2.2 includes the following steps:

[0030] S2.2.1. Grind the locations where the special-shaped wind tunnel pressure shell is to be welded with 300-450 grit sandpaper, and grind the back and upper edges of the strain gauge metal base with 300-450 grit sandpaper;

[0031] S2.2.2. Marking: At the location where the pressure shell of the special-shaped wind tunnel is to be measured, use a hard pencil or a scriber to mark a visible mark along the pre-installation direction as a positioning mark;

[0032] S2.2.3. Clean the surface of the area to be welded with acetone or anhydrous ethanol;

[0033] S2.2.4, Test Welding: Use the welding test piece to weld to the metal component to be tested, and prepare for strain gauge installation;

[0034] S2.2.5. With the strain gauge facing upward, align the strain gauge's positioning mark with the strain gauge's installation position's positioning line. Use tape to secure the strain gauge to the stress monitoring position to be measured. Then use a spot welder to spot weld one positioning weld point to initially secure the position. Remove the tape after the position is secured.

[0035] S2.2.6 Formal spot welding: The starting point is close to the center of the strain gauge edge, and then spot welding is carried out according to the welding spot marks as shown by A1, A2, A3, A4, A5, A6, A7, A8 and the direction of the arrow. The spacing between the welding spot marks is uniform and the welding spot diameter is 0.8mm.

[0036] S2.2.7. Check the strain gauge resistance, insulation resistance, sealing layer, protective layer, and lead wires to complete the strain gauge installation.

[0037] Furthermore, the specific implementation method of step S3 includes the following steps:

[0038] S3.1. The strain data acquisition instrument control box converts the principal stress collected at the stress monitoring point into the von Mises stress at the stress monitoring point. The specific formula is as follows:

[0039]

[0040] σ e is the von Mises stress, σ1 is the first principal stress of the stress monitoring point, σ2 is the second principal stress of the stress monitoring point, and σ3 is the third principal stress of the stress monitoring point;

[0041] S3.2. The strain data acquisition instrument control box compares the calculated von Mises stress with the allowable stress of the stress monitoring point, converts the comparison result into a system signal and transmits it to the host computer via Ethernet, so that the host computer can monitor the stress value in real time.

[0042] Beneficial effects of the present invention:

[0043] The present invention describes a stress monitoring method suitable for the pressure shell of a special-shaped wind tunnel. The pressure shell of a large-sized metal structure wind tunnel cannot be designed according to the pressure vessel standard. Finite element method is used for auxiliary design. Since the ratio of the shell thickness of each section of the wind tunnel to the inner diameter of the circular ring of its corresponding cross-section is very small, it can be simplified as a thin shell structure for modeling. At the same time, the observation hole structure in the wind tunnel pressure shell that has little effect on the accuracy of the calculation results is analyzed, and this part of the structure is appropriately simplified and omitted.

[0044] The stress monitoring method for the pressure shell of a special-shaped wind tunnel described in the present invention can accurately evaluate the stiffness and strength of the pressure shell of the special-shaped wind tunnel and calculate the accurate stress distribution of the pressure shell of the special-shaped wind tunnel; the stress of the pressure shell of the special-shaped wind tunnel is collected in real time by the control box of the strain data acquisition instrument, and the principal stress conditions of the key measuring points are compared and checked at any time; and the safety of the pressure shell of the special-shaped wind tunnel is monitored in real time by the upper computer to ensure the normal operation of the test equipment and the life safety of the users. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a finite element calculation and analysis model diagram of a special-shaped wind tunnel pressure shell according to the present invention;

[0046] Figure 2 Schematic diagram of the spot welding sequence of the strain gauge according to the present invention;

[0047] Figure 3 Schematic diagram of the stress monitoring connection relationship of the special-shaped wind tunnel pressure shell according to the present invention;

[0048] Figure 4 A comparison chart of stress monitoring test results of the special-shaped wind tunnel pressure shell according to the present invention;

[0049] Figure 1 Middle: 1-first corner section, 2-second corner section, 3-pull rod mechanism, 4-second diffusion section, 5-heat exchanger, 6-third corner section, 7-fourth corner section, 8-stable section, 9-stationary room door, 10-stationary room, 11-diffusion section. DETAILED DESCRIPTION

[0050] In order to make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain the present invention and are not intended to limit the present invention. That is, the specific embodiments described herein are only some embodiments of the present invention, not all embodiments. Generally, the components of the specific embodiments of the present invention described and illustrated in the drawings herein can be arranged and designed in various different configurations, and the present invention can also have other embodiments.

[0051] Therefore, the following detailed description of the specific embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but is merely representative of selected specific embodiments of the present invention. All other specific embodiments obtained by those skilled in the art based on the specific embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0052] In order to further understand the content, features and effects of the present invention, the following specific embodiments are given as examples, and the attached Figure 1-4 The detailed instructions are as follows: Specific implementation method one:

[0054] A stress monitoring method applicable to a special-shaped wind tunnel pressure shell comprises the following steps:

[0055] S1. Establish a finite element simulation model of the special-shaped wind tunnel pressure shell based on its structure. Apply corresponding loads for different working conditions, calculate the stress distribution of the special-shaped wind tunnel pressure shell under different working conditions, select the maximum stress value points, stress alternation points, stress concentration points, and structural mutation positions of the special-shaped wind tunnel pressure shell under each working condition, analyze the stress state at each position, and mark stress monitoring points at the corresponding positions of the special-shaped wind tunnel pressure shell;

[0056] Furthermore, the specific implementation method of step S1 includes the following steps:

[0057] S1.1. Simplification of the pressure shell structure of the special-shaped wind tunnel: The pressure shell structure of the special-shaped wind tunnel is simplified into a thin shell structure for modeling. At the same time, the observation holes in the pressure shell of the wind tunnel are analyzed, and the threaded holes and pin holes that do not affect the accuracy of the calculation results are simplified and omitted;

[0058] S1.2. Geometric model construction and meshing of the special-shaped wind tunnel pressure shell: The special-shaped wind tunnel pressure shell is constructed as a shell structure composed of curved surfaces, and the geometric model is meshed using surface elements. The tie rod structure is constructed as a linear structure, and the geometric model is meshed using beam elements.

[0059] Figure 1 This is a finite element calculation and analysis model diagram of a special-shaped wind tunnel pressure shell according to this embodiment. In the figure, 1 is the first corner section, 2 is the second corner section, 3 is the pull rod mechanism, 4 is the second diffuser section, 5 is the heat exchanger, 6 is the third corner section, 7 is the fourth corner section, 8 is the stable section, 9 is the stationary chamber door, 10 is the stationary chamber, and 11 is the diffuser section.

[0060] Furthermore, in step S1.2, the surface element uses the shell181 element, which is a 4-node element with 6 degrees of freedom at each node: displacement degrees of freedom in the x, y, and z directions and rotation degrees of freedom around the X, Y, and Z axes; the beam element uses the beam188 element, which is a 2-node 3D linear beam element with 6 degrees of freedom at each node: displacement degrees of freedom along the x, y, and z directions and rotation degrees of freedom around the X, Y, and Z axes;

[0061] S1.3. Boundary conditions and load application of the special-shaped wind tunnel pressure shell: When applying boundary conditions of the special-shaped wind tunnel pressure shell, different degrees of freedom constraint forms are selected according to the form of the supports, and corresponding internal pressure loads are applied according to the different working pressure conditions of each section of the special-shaped wind tunnel pressure shell;

[0062] Furthermore, there are three types of wind tunnel supports: fixed supports, unidirectional sliding supports, and multidirectional sliding supports. Fixed supports are the main load-bearing supports of the wind tunnel and must be fully constrained, i.e., they must constrain the six degrees of freedom on the interface with the foundation. Unidirectional sliding supports are generally used to release the displacement constraints of the wind tunnel in a certain direction and must constrain the remaining five degrees of freedom in the wind tunnel except for that direction. Multidirectional sliding supports only bear the gravity load of the wind tunnel itself, i.e., they constrain the degrees of freedom in the gravity direction.

[0063] S1.4. Perform static structural calculations on the finite element model of the wind tunnel pressure shell completed in step S1.3. Based on the finite element calculation results, select stress monitoring points within the stress range of 115 MPa to 172.5 MPa, and analyze the stress states of the stress monitoring points.

[0064] Furthermore, the node displacement {x} in the static structural calculation in step S1.4 is solved by the following matrix equation:

[0065] K]{x}={F}

[0066] [K] is a stiffness matrix, {F} is a list of external loads, and {x} is the node displacement;

[0067] The shape function {x} of the shell181 element shell181 for:

[0068]

[0069] [s,r] are the coordinates of the symmetric parameterized unit; h i [s,r] is the shape function of the 4-node element, {x} i is the node coordinate array of node i;

[0070] The shape function {x} of the beam188 element beam188 for:

[0071]

[0072] x a 、x b are the node coordinates of node a and node b respectively, and x is the node coordinate of any point.

[0073] S2. Weld and install strain gauges at the stress monitoring points marked on the pressure shell of the special-shaped wind tunnel in step S1, connect the strain gauges to a collection box, and connect the collection box to a control box of a strain data acquisition instrument. During the operation of the wind tunnel, the strain data acquisition instrument collects strain measurements of the strain gauges and converts them into stress values at the stress monitoring points.

[0074] The specific implementation method of step S2 includes the following steps:

[0075] S2.1. Select the rosette arrangement of 0, 45, and 90 degrees according to the stress state of the stress monitoring point to monitor the stress state and stress direction of the stress monitoring point;

[0076] S2.2. Install the welded strain gauge. Clean the surface of the welding area of the special-shaped wind tunnel pressure shell and perform spot welding with a spot welder, controlling the weld spot diameter to 0.8 mm. Figure 2 Schematic diagram of the spot welding sequence of the strain gauge according to this embodiment; it can be seen from the figure that the strain gauge is fixed to the stress monitoring position to be measured with tape, and the spot welding sequence of the spot welding machine is set as A1, A2, A3, A4, A5, A6, A7, and A8;

[0077] Furthermore, the specific implementation method of step S2.2 includes the following steps:

[0078] S2.2.1. Grind the locations where the special-shaped wind tunnel pressure shell is to be welded with 300-450 grit sandpaper, and grind the back and upper edges of the strain gauge metal base with 300-450 grit sandpaper;

[0079] S2.2.2. Marking: At the location where the pressure shell of the special-shaped wind tunnel is to be measured, use a hard pencil or a scriber to mark a visible mark along the pre-installation direction as a positioning mark;

[0080] S2.2.3. Clean the surface of the area to be welded with acetone or anhydrous ethanol;

[0081] S2.2.4, Test Welding: Use the welding test piece to weld to the metal component to be tested, and prepare for strain gauge installation;

[0082] S2.2.5. With the strain gauge facing upward, align the strain gauge's positioning mark with the strain gauge's installation position's positioning line. Use tape to secure the strain gauge to the stress monitoring position to be measured. Then use a spot welder to spot weld one positioning weld point to initially secure the position. Remove the tape after the position is secured.

[0083] S2.2.6 Formal spot welding: The starting point is close to the center of the strain gauge edge, and then spot welding is carried out according to the welding spot marks as shown by A1, A2, A3, A4, A5, A6, A7, A8 and the direction of the arrow. The spacing between the welding spot marks is uniform and the welding spot diameter is 0.8mm.

[0084] S2.2.7. Check the strain gauge resistance, insulation resistance, sealant, protective layer, and lead wires, and complete the strain gauge installation;

[0085] S2.3. After the strain gauge is installed, begin wiring and routing. Connect the strain gauge data acquisition cable to the acquisition box. Connect the strain data acquisition instrument control box and the acquisition box via connectors for communication and power supply. After the connection is complete, enter the bridge mode, wire resistance, strain gauge sensitivity coefficient, elastic modulus and Poisson's ratio of the special-shaped wind tunnel pressure shell material for automatic correction of the measurement results.

[0086] S2.4. Run the wind tunnel, and the strain data acquisition instrument collects the strain measurement values of the strain gauge in real time and converts them into stress values at the stress monitoring points;

[0087] S3, the strain data acquisition instrument control box is connected to the host computer via Ethernet, and the host computer monitors the stress value in real time; Figure 3 Schematic diagram of the stress monitoring connection relationship of the special-shaped wind tunnel pressure shell according to this embodiment. Figure 3 The diagram shows that strain gauges numbered 3#-8# are connected to collection box A to measure the position of the heat exchanger of the special-shaped wind tunnel pressure shell; strain gauges numbered 9#-16# are connected to collection box B to measure the positions of the third corner section, fourth corner section, and stable section of the special-shaped wind tunnel pressure shell; strain gauges numbered 17#-24# are connected to collection box C to measure the positions of the stationary chamber and the stationary chamber door of the special-shaped wind tunnel pressure shell; strain gauges numbered 25#-29# are connected to collection box D to measure the positions of the tie rods of the special-shaped wind tunnel pressure shell; and strain gauges numbered 30#-36# are connected to collection box E to measure the position of the diffuser section of the special-shaped wind tunnel pressure shell.

[0088] The specific implementation method of step S3 includes the following steps:

[0089] S3.1. The strain data acquisition instrument control box converts the principal stress collected at the stress monitoring point into the von Mises stress at the stress monitoring point. The specific formula is as follows:

[0090]

[0091] σ e is the von Mises stress, σ1 is the first principal stress of the stress monitoring point, σ2 is the second principal stress of the stress monitoring point, and σ3 is the third principal stress of the stress monitoring point;

[0092] S3.2. The strain data acquisition instrument control box compares the calculated von Mises stress with the allowable stress of the stress monitoring point, converts the comparison result into a system signal and transmits it to the host computer via Ethernet to monitor the stress value in real time.

[0093] The measurement data of some monitoring points at a fixed time in the pressure holding state during the wind tunnel pressure test were extracted and compared with the finite element calculation results. The results are shown in Table 1 and Figure 4 As shown:

[0094] Table 1 Comparison of measured and calculated stress values of the cavern / MPa

[0095]

[0096] Table 1 is a comparison table of the measured stress values and the calculated stress values of the cave. The data in Table 1 show that the measured stress values of the cave are basically consistent with the calculated stress values, and the stress values of each measuring point in the cave are all less than the yield limit of the material.

[0097] Figure 4 This is a comparison chart of the stress monitoring test results of the special-shaped wind tunnel pressure shell described in this embodiment. Figure 4 The measured point number and Figure 3 The strain gauge numbers in the figure correspond to each other. Strain gauges 3#-8# measure the position of the heat exchanger of the special-shaped wind tunnel pressure shell, strain gauges 9#-16# measure the positions of the third corner section, the fourth corner section, and the stable section of the special-shaped wind tunnel pressure shell, strain gauges 17#-24# measure the positions of the stationary room and the door of the special-shaped wind tunnel pressure shell, strain gauges 25#-29# measure the positions of the tie rods of the special-shaped wind tunnel pressure shell, and strain gauges 30#-36# measure the positions of the diffusion section of the special-shaped wind tunnel pressure shell. It can be seen from the figure that the measured stress values of the measured points are basically consistent with the calculated stress values. The calculated stress value curve and the actual measured stress value curve cross and float up and down within a certain range. The difference between the tested stress value and the calculated stress value is about 5MPa, and the difference between the tested stress value and the calculated stress value is not much.

[0098] It should be noted that relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus comprising the element.

[0099] Although the present application has been described above with reference to specific embodiments, various modifications may be made thereto and components may be substituted with equivalents without departing from the scope of the present application. In particular, as long as there are no structural conflicts, the various features of the embodiments disclosed herein may be combined with each other in any manner, and the omission of an exhaustive description of these combinations in this specification is solely for the sake of space and resource conservation. Therefore, the present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions within the scope of the claims.

Claims

1. A stress monitoring method for a special-shaped wind tunnel pressure shell, characterized by: The steps include: S1. Establish a finite element simulation model of the special-shaped wind tunnel pressure shell based on its structure. Apply corresponding loads for different working conditions, calculate the stress distribution of the special-shaped wind tunnel pressure shell under different working conditions, select the maximum stress value points, stress alternation points, stress concentration points, and structural mutation positions of the special-shaped wind tunnel pressure shell under each working condition, analyze the stress state at each position, and mark stress monitoring points at the corresponding positions of the special-shaped wind tunnel pressure shell; The specific implementation method of step S1 includes the following steps: S1.

1. Simplification of the pressure shell structure of the special-shaped wind tunnel: The pressure shell structure of the special-shaped wind tunnel is simplified into a thin shell structure for modeling. At the same time, the observation holes in the pressure shell of the wind tunnel are analyzed, and the threaded holes and pin holes that do not affect the accuracy of the calculation results are simplified and omitted; S1.

2. Geometric model construction and meshing of the special-shaped wind tunnel pressure shell: The special-shaped wind tunnel pressure shell is constructed as a shell structure composed of curved surfaces, and the geometric model is meshed using surface elements. The tie rod structure is constructed as a linear structure, and the geometric model is meshed using beam elements. S1.

3. Boundary conditions and load application of the special-shaped wind tunnel pressure shell: When applying boundary conditions of the special-shaped wind tunnel pressure shell, different degrees of freedom constraint forms are selected according to the form of the supports, and corresponding internal pressure loads are applied according to the different working pressure conditions of each section of the special-shaped wind tunnel pressure shell; S1.

4. Perform static structural calculations on the finite element model of the wind tunnel pressure shell completed in step S1.

3. Based on the finite element calculation results, select stress monitoring points within the stress range of 115 MPa to 172.5 MPa, and analyze the stress states of the stress monitoring points. S2. Weld and install strain gauges at the stress monitoring points marked on the pressure shell of the special-shaped wind tunnel in step S1, connect the strain gauges to a collection box, and connect the collection box to a strain data acquisition instrument control box. During the operation of the wind tunnel, the strain data acquisition instrument collects strain measurements of the strain gauges and converts them into stress values at the stress monitoring points. S3. The strain data acquisition instrument control box is connected to the host computer via Ethernet to monitor the stress value of the stress monitoring point in real time.

2. The stress monitoring method for a special-shaped wind tunnel pressure shell according to claim 1, characterized in that: In step S1.2, the surface element uses the shell181 element. The shell181 element is a 4-node element, and each node has 6 degrees of freedom: displacement freedom in the x, y, and z directions and rotation freedom around the X, Y, and Z axes; the beam element uses the beam188 element. The beam188 element is a two-node three-dimensional linear beam element, and each node has 6 degrees of freedom, namely, displacement freedom along the x, y, and z directions and rotation freedom around the X, Y, and Z axes.

3. The stress monitoring method for a special-shaped wind tunnel pressure shell according to claim 2, characterized in that: The node displacements {x} in the static structural calculation in step S1.4 are solved by the following matrix equation: [K]{x}={F} [K] is a stiffness matrix, {F} is a list of external loads, and {x} is the node displacement; The shape function {x} of the shell181 element shell181 for: [s,r] are the coordinates of the symmetric parameterized unit; h i [s,r] is the shape function of the 4-node element, {x} i is the node coordinate array of node i; The shape function {x} of the beam188 element beam188 for: x a 、x b are the node coordinates of node a and node b respectively, and x is the node coordinate of any point.

4. The stress monitoring method for a special-shaped wind tunnel pressure shell according to claim 3, characterized in that: The specific implementation method of step S2 includes the following steps: S2.

1. Select the 0-degree, 45-degree, and 90-degree rosette arrangements based on the stress state of the stress monitoring point to monitor the stress state and stress direction of the stress monitoring point. S2.

2. Install the welded strain gauge. Clean the surface of the welding area of the special-shaped wind tunnel pressure shell and perform spot welding with a spot welder, controlling the weld spot diameter to 0.8 mm. S2.

3. After the strain gauge is installed, begin wiring and routing. Connect the strain gauge data acquisition cable to the acquisition box. Connect the strain data acquisition instrument control box and the acquisition box via connectors for communication and power supply. After the connection is complete, enter the bridge mode, wire resistance, strain gauge sensitivity coefficient, elastic modulus and Poisson's ratio of the special-shaped wind tunnel pressure shell material for automatic correction of the measurement results. S2.

4. When the wind tunnel is running, the strain data acquisition instrument collects the strain measurement values of the strain gauge in real time and converts them into stress values at the stress monitoring points.

5. The stress monitoring method for a special-shaped wind tunnel pressure shell according to claim 4, characterized in that: The specific implementation method of step S2.2 includes the following steps: S2.2.

1. Grind the locations where the special-shaped wind tunnel pressure shell is to be welded with 300-450 grit sandpaper, and grind the back and upper edges of the strain gauge metal base with 300-450 grit sandpaper; S2.2.

2. Marking: At the location where the pressure shell of the special-shaped wind tunnel is to be measured, use a hard pencil or a scriber to mark a visible mark along the pre-installation direction as a positioning mark; S2.2.

3. Clean the surface of the area to be welded with acetone or anhydrous ethanol; S2.2.4, Test Welding: Use the welding test piece to weld to the metal component to be tested, and prepare for strain gauge installation; S2.2.

5. With the strain gauge facing upward, align the strain gauge's positioning mark with the strain gauge's installation position's positioning line. Use tape to secure the strain gauge to the stress monitoring position to be measured. Then use a spot welder to spot weld one positioning weld point to initially secure the position. Remove the tape after the position is secured. S2.2.6 Formal spot welding: The starting point is close to the center of the strain gauge edge, and then spot welding is carried out according to the weld mark. The spacing between the weld marks is uniform and the weld spot diameter is 0.8mm. S2.2.

7. Check the strain gauge resistance, insulation resistance, sealing layer, protective layer, and lead wires to complete the strain gauge installation.

6. The stress monitoring method for a special-shaped wind tunnel pressure shell according to claim 5, characterized in that: The specific implementation method of step S3 includes the following steps: S3.

1. The strain data acquisition instrument control box converts the principal stress collected at the stress monitoring point into the von Mises stress at the stress monitoring point. The specific formula is as follows: σ e is the von Mises stress, σ1 is the first principal stress of the stress monitoring point, σ2 is the second principal stress of the stress monitoring point, and σ3 is the third principal stress of the stress monitoring point; S3.

2. The strain data acquisition instrument control box compares the calculated von Mises stress with the allowable stress of the stress monitoring point, converts the comparison result into a system signal and transmits it to the host computer via Ethernet to monitor the stress value in real time.

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