Deformable test device for modal test of plane tensile membrane structure

Abstract

The invention discloses a plane tensile membrane structure modal test deformable test device, which comprises a main body frame structure used for vibration tests of plane tensile membrane structures with different shapes and sizes; the membrane material tensioning mechanism is used for tensioning the membrane material and collecting and adjusting the pretension of the membrane material test piece; the vibration test module is used for exciting the diaphragm surface so that the diaphragm surface is forced to vibrate within a certain frequency range; and the data acquisition module is used for acquiring the displacement time history data of the membrane surface and the numerical value of the tension and compression sensor. According to the invention, the modal test of the tensile membrane structures with different plane shapes and sizes can be met at low cost, the device can be flexibly adjusted according to the structures with different shapes and sizes, and can be disassembled and secondarily assembled, so that the occupied field area is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of modal test of plane tensioned membrane structure, and in particular relates to a vibration modal test device of a deformable plane tensioned membrane structure. Background Art

[0002] Tensile membrane structure is a flexible space structure, which is mainly formed by applying a certain pre-tension to the membrane material. It is widely used in the fields of construction engineering and aerospace engineering due to its light weight, high surface-to-mass ratio, high space utilization rate, and easy folding. These characteristics also make the tensile membrane structure more sensitive to the influence of vibration. When the structure is excited, studying the influence of its modal vibration shape and modal frequency on the structure will help to optimize and improve the structure.

[0003] For vibration tests on planar tensile membrane structures, the most common test device currently used is a rectangle. Although the modal identification technology is relatively mature and can obtain relatively accurate test data, there are still the following problems: (1) The test devices currently used are basically for conducting relevant tests on structures of specific shapes, such as squares, and cannot adjust the shape of the structure. In addition, the device size is large, and most of them use steel as the main material, and the overall mass is heavy. (2) A few test devices for other shapes, such as hexagons, cannot flexibly adjust the size of the specimens and can only conduct relevant tests on pre-set sizes. Summary of the invention

[0004] The purpose of the present invention is to provide a deformable test device for modal tests of planar tensile membrane structures, which can meet the modal tests of planar tensile membrane structures of different plane shapes and sizes, and can be flexibly adjusted according to structures of different shapes and sizes. While ensuring the structural rigidity, the overall quality and use cost of the device are reduced, and the device can be dismantled and reassembled after the test is completed, reducing the site area occupied by the device.

[0005] The technical solution to achieve the purpose of the present invention is:

[0006] A deformable test device for modal test of a plane tensile membrane structure, comprising:

[0007] The main frame structure is used to adjust the assembly shape according to the different shapes of membrane specimens and to fix the membrane specimens;

[0008] The membrane material tensioning mechanism is located in the main frame structure and is used to tension the membrane material specimen and collect and adjust the pre-tension of the membrane material specimen;

[0009] The vibration test module is used to apply an external excitation to the membrane surface so that it undergoes forced vibration within a set frequency range;

[0010] Data acquisition module, used to collect displacement time history data of membrane surface vibration and pre-tension data of each side of the membrane specimen;

[0011] The data processing module is used to process the collected membrane surface vibration displacement time history data, perform modal identification on the data, and obtain the modal frequency and modal vibration shape of the structure respectively.

[0012] Compared with the prior art, the present invention has the following significant advantages:

[0013] The present invention can be flexibly adjusted and deformed according to planar tensile membrane structures of different planar shapes and sizes, and the overall mass is light. Not only can the assembled device be moved more conveniently as a whole, but it can also be flexibly disassembled and reassembled after the test is completed. In addition, the exciter driving device in the present invention adopts a panel-type signal generator and an independent power amplifier, which is small in size and cheap in price. Under the premise of low cost, it meets the modal test requirements of planar tensile membrane structures of different shapes and sizes. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is the overall structure diagram of the deformable test device.

[0015] Figure 2 This is the main frame structure diagram.

[0016] Figure 3 It is a structural diagram of an independent side of the main frame.

[0017] Figure 4 This is the structural diagram of the membrane tensioning mechanism.

[0018] Figure 5 This is a schematic diagram of the assembly of the membrane tensioning mechanism and the main frame.

[0019] Figure 6 This is the structural diagram of the vibration test module and data acquisition module. DETAILED DESCRIPTION

[0020] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0021] As attached Figure 1-5 As shown, the present invention provides a deformable test device for modal test of a plane tensioned membrane structure, including a main frame structure, a membrane tensioning mechanism, a vibration test module, and a data acquisition module;

[0022] The main frame structure includes: a support frame 1 of 40×80mm aluminum alloy profile, a connecting piece 2 of 90×50×5mm U-shaped slot aluminum, an equipment supporting angle 3, M6 bolts 4, M6 washers 5, M8 bolts and nuts 6, 5mm thick spacers 7, and a fixing piece 8 of 30×30mm aluminum alloy profile.

[0023] A support frame 1 and two connectors 2 are assembled into an independent side of the main frame. A connector 2 is provided at each end of the support frame 1. The connector 2 is sleeved on the support frame 1 and fixed with two M6 bolts 4 and M6 washers 5. When installing the connector 2 at one end of the support frame 1, a 5mm thick pad 7 is required. Figure 3 As shown. According to the shape of the specimen, assemble the corresponding number of independent sides, use M8 bolts and nuts 6 to connect and assemble into the main frame structure in the reserved holes of the connector 2, and overlap the adjacent sides with one end with a gasket and one end without a gasket respectively, so as to ensure that the sides of the entire frame after installation remain at the same horizontal height; install a 30mm×30mm aluminum alloy profile fixing 8 on the adjacent sides to fix the main frame structure to prevent deformation, and use two equipment support angles 3 on each side to be installed on the 40×80mm aluminum alloy profile to support the main structure of the frame, as shown. Figure 1 As shown; the main frame can be flexibly adjusted into a polygonal structure according to the shape and size of the specimen, such as Figure 2 The following uses the square, regular triangle and regular hexagon as examples.

[0024] The membrane tensioning mechanism is located in the main frame structure, and includes a support plate 9 with a C-shaped groove aluminum alloy profile, a tension and compression sensor 10, an M6 screw 11, an M6 nut 12, and a connecting rod 29 made of an ABS round rod. The number of sides of the membrane tensioning mechanism is the same as the number of sides of the main frame structure, that is, the number of support plates 9 is the same as the number of support frames 1, and they are correspondingly arranged on the inner side of the support frame 1; each support plate 9 is connected to the tension and compression sensor 10 through an M6 screw 11, two tension and compression sensors 11 are installed on each side, and the M6 ​​screw 11 is fixed with an M6 nut 12, and the loading arm reserved on each side of the membrane is installed in the C-shaped groove of the support plate 9, and the membrane is fixed with a connecting rod 27 to assemble into a membrane tensioning mechanism, such as Figure 3 As shown; install M6 screws 11 on the two tension and compression sensors on each side, install the assembled membrane tensioning mechanism on the main frame through the installation space reserved on the main frame support frame 1, connect each tension and compression sensor to the data acquisition box 19, the acquisition box has a built-in acquisition card, the interface between the tension and compression sensor 10 and the data acquisition box 19 uses an aviation plug, the data acquisition box 19 is connected to the computer 22 via a double-headed USB data cable, read the readings of the tension and compression sensors 10 in the computer 22, adjust the length of the M6 ​​screw 11 by tightening or loosening the M6 ​​nut 12 to adjust the pre-tension of each side of the membrane material, so that the readings of the two tension and compression sensors 10 on each side are basically the same, to ensure that the pre-tension of the membrane material is uniform.

[0025] The vibration test module includes an exciter 13, a 24V DC transformer 14, a 100W power amplifier 15, a signal generator 16, and a cooling fan 17. The above devices, except the exciter, are placed in a box, and a cooling fan 17 is provided in the box for heat dissipation. The exciter is placed under the membrane specimen and is bonded and fixed to the membrane surface by a push rod. The connection point between the push rod and the membrane surface is called the excitation point, and the excitation point is generally set near the edge of the membrane specimen. The output end of the signal generator 16 is connected to the input end of the power amplifier 15 through a signal line. The power amplifier 15 is powered by a matching 24V DC transformer 14. The output end of the power amplifier 15 is connected to the exciter 13. The signal generator 16 can output waveforms of different frequency amplitudes. The waveform, amplitude and other parameters need to be set by yourself before use. After amplification by the power amplifier 15, the exciter 13 can be driven to vibrate within the set frequency range.

[0026] The data acquisition module includes a 5V and 24V switching power supply 18, a data acquisition box 19, a mounting beam 23 made of a 30×30mm aluminum alloy profile, a 30mm×30mm corner piece 24, a reflective target 25, and a laser displacement meter 26. The reflective target 25 is set on the membrane material specimen. The mounting beam 23 and the corner piece 24 are assembled into a laser displacement meter placement rack that can span the top of the main frame. Multiple laser displacement meters 26 are fixed to the side of the upper mounting beam 23 using double-sided tape, connected to the data acquisition box 19, and the 5V and 24V power supply 15 are turned on. The position of the laser point is adjusted to fall within the range of the observation point marked with the reflective target 25 on the membrane surface.

[0027] The computer is used as a data processing module to process the collected membrane surface vibration displacement time history data. The fast Fourier transform (FFT) method and the random subspace analysis (SSI) method are used in the computer to perform modal identification on the data to obtain the modal frequency and modal vibration shape of the structure respectively.

[0028] The specific test methods are as follows:

[0029] The first step is to determine the test plan, determine the type, size, plane shape, pre-tension and other parameters of the membrane material, select the material to make the test piece, and paste the reflective target on its surface as the observation point of the subsequent laser displacement meter. According to the shape and side length of the membrane material, the side length of each side of the main frame is designed, and the main frame is assembled according to the designed size so that the internal space can meet the installation, tensioning and subsequent pre-tension adjustment of the membrane material. The equipment support feet are installed on the lower side of the profile on each side of the frame, leaving enough space under the frame to arrange the exciter.

[0030] The second step is to assemble the membrane tensioning mechanism and install the membrane specimen. A circular loading arm is reserved on each side of the specimen during production, and an ABS round bar is placed in the middle to fix the membrane while ensuring the uniformity of the pre-tension. Install the assembled membrane on the main frame, connect the tension and compression sensors, read the real-time readings of the tension and compression sensors on the computer, and adjust the pre-tension of each side of the membrane by loosening or tightening the bolts so that the readings of the two tension and compression sensors on each side are basically consistent to avoid uneven tensioning of the membrane.

[0031] The third step is to assemble the laser displacement meter stand. The laser displacement meter stand needs to be adjusted according to the shape of the structure. Taking the square structure test as an example, the laser displacement meter is connected to the data acquisition box, and the height and position of each laser displacement meter are adjusted so that its laser point falls within the observation point range marked with the reflective target and is within the working range of the laser displacement meter.

[0032] The fourth step is to determine the position of the exciter, bond the exciter to the membrane surface with a push rod, assemble the vibration test module, connect the signal generator, power amplifier, and exciter in sequence, set the output waveform, frequency range, amplitude, sweep mode, sweep speed and other parameters in the signal generator, and the vibration test using the exciter as the excitation generally uses a sweep mode to drive the exciter to vibrate within the set range. The sweep mode is divided into linear sweep and logarithmic sweep.

[0033] The fifth step is to record the laser displacement meter data in the computer, start recording, then drive the vibrator to make the membrane specimen vibrate, record the displacement time history data of the membrane surface during vibration, and stop the vibrator vibration and stop recording the displacement time history data after obtaining enough data.

[0034] In the sixth step, the recorded displacement time-history data is processed in MATLAB software. The modal frequency of this test is identified by fast Fourier transform (FFT) processing data. The modal vibration shape and modal frequency of this test are identified by random subspace method (SSI). The modal vibration shape at the corresponding frequency identified by SSI method is found in combination with the modal frequency identified by FFT.

Claims

1. A deformable test device for modal test of a plane tensile membrane structure, characterized in that: include: The main frame structure is used to adjust the assembly shape according to the different shapes of membrane specimens and to fix the membrane specimens; The membrane material tensioning mechanism is located in the main frame structure and is used to tension the membrane material specimen and collect and adjust the pre-tension of the membrane material specimen; The vibration test module is used to apply an external excitation to the membrane surface so that it undergoes forced vibration within a set frequency range; Data acquisition module, used to collect displacement time history data of membrane surface vibration and pre-tension data of each side of the membrane specimen; The data processing module is used to process the collected membrane surface vibration displacement time history data, perform modal identification on the data, and obtain the modal frequency and modal vibration shape of the structure respectively.

2. The deformable test device for modal test of planar tensile membrane structure according to claim 1, characterized in that: The main frame structure includes a support frame, a connecting piece, a support angle, and a cushion block; The two ends of the support frame are respectively sleeved with connecting pieces to form an independent side of the main frame structure, and a pad is provided between one end of the support frame and the connecting piece; adjacent support frames are connected to form a polygonal structure by connecting pieces, and the two adjacent sides are overlapped using an end with a pad and an end without a pad respectively to ensure that the sides of the assembled main frame are at the same level; the main frame structure is supported by multiple supporting legs.

3. The deformable test device for modal test of planar tensile membrane structure according to claim 2, characterized in that: The membrane material tensioning mechanism includes a support plate with a C-shaped groove, a tension and compression sensor, a screw and a connecting rod; the number of the support plates is the same as the number of the support frames, and they are installed on the inner side of the support frames. The C-shaped groove is used to load the loading arms reserved on each side of the membrane material specimen; the connecting rod is used to fix the loading arms reserved on each side of the membrane material specimen in the C-shaped groove; each support plate is connected to two tension and compression sensors through a screw, which are used to connect the membrane material specimen to the support frame, and the tension and compression sensors are connected to the data acquisition module.

4. The deformable test device for modal test of planar tensile membrane structure according to claim 1, characterized in that: The vibration test module includes an exciter, a DC transformer, a power amplifier, and a signal generator; the output end of the signal generator is connected to the input end of the power amplifier, the power amplifier is powered by the DC transformer, the output end of the power amplifier is connected to the exciter, the exciter is placed under the membrane specimen, and the excitation position is close to the edge of the membrane specimen.

5. The deformable test device for modal test of planar tensile membrane structure according to claim 1, characterized in that: The data acquisition module includes a data acquisition box, a laser displacement meter placement rack, a reflective target, and a laser displacement meter; the reflective target is set on the film material specimen; the laser displacement meter placement rack spans above the main frame, and is provided with multiple laser displacement meters, the laser displacement meters are connected to the data acquisition box, and the laser point position of the laser displacement meter falls within the observation point range marked by the reflective target.

6. The deformable test device for modal test of planar tensile membrane structure according to claim 5, characterized in that: The test method is as follows: The first step is to determine the test plan: determine the size, shape and pre-tension parameters of the membrane specimen, select the material to make the membrane specimen, and attach a reflective target on its surface as the observation point of the subsequent laser displacement meter; determine the size of the main frame structure so that the internal space can meet the installation, tensioning and subsequent pre-tension adjustment of the membrane specimen; The second step is to assemble the membrane tensioning mechanism, the number of sides of which is the same as that of the main frame structure, install the membrane specimen between the membrane tensioning mechanism and the main frame structure, and adjust the pre-tension of the membrane specimen on each side to be consistent; The third step is to arrange the laser displacement meter according to the position of the reflective target point reserved on the film surface, and adjust the height and position of each laser displacement meter so that the laser point falls within the range of the observation point marked with the reflective target point and is within the working range of the laser displacement meter; The fourth step is to assemble the vibration test module, determine the excitation position and bond it to the membrane surface using a push rod. The excitation position is close to the edge of the membrane specimen. The fifth step is to record the data of the laser displacement meter, start recording, drive the vibration test module to drive the membrane specimen to vibrate, record the displacement time history data when the membrane surface vibrates, stop the vibration of the exciter after obtaining the set amount of data, and stop recording the displacement time history data; The sixth step is to process the recorded displacement time history data in MATLAB software, identify the modal frequency of this test through fast Fourier transform processing data, identify the modal vibration shape and modal frequency of this test through random subspace method, and find the modal vibration shape at the corresponding frequency in combination with the modal frequency.

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