Device and method for measuring hail impact load of membrane structure

Abstract

The present application discloses a device and method for measuring the hail impact load of a membrane structure, and relates to the technical field of tensioned membrane structures. The device for measuring the hail impact load of a membrane structure includes a frame, a tensioning mechanism, a hail emission mechanism, and a signal acquisition mechanism; the tensioning mechanism is installed on the frame, and the tensioning mechanism is used to tension the membrane structure to be measured and form a membrane surface with a stable pre-tension; the hail emission mechanism is connected to the frame and is placed above the membrane surface, and the hail emission mechanism is used to emit hail onto the membrane surface; the signal acquisition mechanism is connected to the frame, and the signal acquisition mechanism includes a laser displacement sensor, and the laser displacement sensor is placed below the membrane surface. The device for measuring the hail impact load of a membrane structure can conduct an in-depth study on the dynamic response of the membrane structure under the action of hail impact load, and provide a theoretical basis for the impact resistance design of the membrane structure. The method for measuring the hail impact load of a membrane structure is convenient and fast, has a wide range of applications, and is highly accurate.

Description

Technical Field

[0001] The present application relates to the technical field of tensioned membrane structures, and in particular to a device and method for measuring hail impact loads on membrane structures. Background Art

[0002] As a new type of spatial structure, membrane structure represents the development level of current architectural technology and material science, and is a perfect combination of art and technology. Membrane structure is widely used in large-span spatial structures due to its superior architectural characteristics, excellent structural characteristics and suitable economy. Engineering practice shows that membrane structure buildings are light in weight, fast in construction, strong in spanning capacity, good in mechanical properties, rich in architectural shapes, moderate in light transmittance, simple in appearance, light and stretchable, dynamic, foldable, easy to disassemble and transport, and suitable for industrial production.

[0003] As the application of membrane structures becomes more and more extensive, more and more engineering accidents occur in membrane structures. A large number of engineering accident analyses show that the impact of hail and other factors causes the membrane structure to vibrate significantly, resulting in large relaxation deformation and greatly reducing the pretension in the membrane. Therefore, although the membrane structures in actual projects have undergone strict wind resistance design, many of them still fail when the actual wind speed is far less than the design critical wind speed for instability, indicating that the adverse effects of impact loads such as hail on membrane structures cannot be ignored. The only domestic regulation on membrane structure design, the "Technical Regulation for Membrane Structures" (CECS 158:2015), stipulates: "The design of membrane structures should be based on the loads that may occur simultaneously on the structure during use, and the load combinations should be carried out according to the ultimate limit state of bearing capacity and the limit state of normal use, and the most unfavorable effect combination should be taken for design." However, this regulation does not include the impact dynamic loads generated by hail in the load effect combination. Summary of the invention

[0004] The present application provides a device and method for measuring the hail impact load of a membrane structure, which can conduct in-depth research on the dynamic response of the membrane structure under the hail impact load. The measurement is convenient and fast, has a wide range of applications, and is highly accurate, providing a theoretical basis for the impact-resistant design of the membrane structure. The method for measuring the hail impact load of the membrane structure is convenient and fast, has a wide range of applications, and is highly accurate.

[0005] In a first aspect, a device for measuring the hail impact load of a membrane structure is provided, the device for measuring the hail impact load of a membrane structure comprising a frame, a tensioning mechanism, a hail transmitting mechanism and a signal acquisition mechanism; the tensioning mechanism is installed on the frame, the tensioning mechanism is used to tension the membrane structure to be measured and form a membrane surface with a stable pre-tension; the hail transmitting mechanism is connected to the frame and placed above the membrane surface, the hail transmitting mechanism is used to transmit hail onto the membrane surface; the signal acquisition mechanism is connected to the frame, the signal acquisition mechanism comprises a laser displacement sensor, and the laser displacement sensor is placed below the membrane surface.

[0006] In the above technical solution, the tensioning mechanism is used to tension the membrane structure to be tested and form a membrane surface with a stable pre-tension, thereby simulating the stress state of the membrane structure to be tested when it is actually used; the hail launching mechanism is used to launch hail onto the membrane surface, thereby simulating the motion state of hail actually impacting the membrane surface; the laser displacement sensor monitors the displacement of the membrane surface in the vertical direction, thereby reflecting the first moment when the hail just touches the membrane surface and the second moment when the membrane surface reaches the maximum displacement under the impact of the hail. The hail impact load measuring device of the membrane structure only needs to measure the data of the first moment and the second moment when the membrane structure to be tested is impacted by hail to complete the entire test detection, so as to calculate the impact load of the hail on the membrane structure to be tested, thereby laying a foundation for in-depth research on the dynamic response of the membrane structure to be tested under the impact load of hail.

[0007] In combination with the first aspect, in a first possible implementation of the first aspect of the present application, the frame is a cross-shaped tensioning frame, and the frame is formed with four installation ends that are symmetrically arranged at intervals; and the four tensioning mechanisms are respectively installed on the four installation ends.

[0008] In the above technical solution, the frame adopts a cross-shaped tension frame, which can more accurately simulate the state of biaxial force along two orthogonal directions of the membrane structure to be measured during actual use, so that the measurement result is more accurate.

[0009] In combination with the first possible implementation method of the first aspect, in a second possible implementation method of the first aspect of the present application, the tensioning mechanism includes a clamping device and an electro-hydraulic push-pull rod; the clamping device is used to clamp the membrane structure to be tested, and the electro-hydraulic push-pull rod is installed at the installation end; the electro-hydraulic push-pull rod is used to drive the clamping device to move, so that the clamping device tensions the membrane structure to be tested and forms a membrane surface with a stable pre-tension.

[0010] In the above technical solution, the clamping device is used to fix the membrane structure to be measured, and the electro-hydraulic push-pull rod drives the clamping device to move. The four electro-hydraulic push-pull rods can accurately control the tension force in four directions of the membrane surface in real time, and can simultaneously perform tensioning operations in four directions, thereby minimizing the force instability during the tensioning process of the membrane structure to be measured. Finally, after the electro-hydraulic push-pull rod stops, the clamping device forms a membrane surface with stable pre-tension for the membrane structure to be measured, ensuring the accuracy of the measurement.

[0011] In combination with the second possible implementation of the first aspect, in a third possible implementation of the first aspect of the present application, the clamping device includes an upper clamping plate and a lower clamping plate; the upper clamping plate is detachably connected to the lower clamping plate, and the membrane structure to be tested is placed between the upper clamping plate and the lower clamping plate; the electro-hydraulic push-pull rod is connected to the lower clamping plate.

[0012] In the above technical solution, the upper clamping plate and the lower clamping plate cooperate to clamp the membrane structure to be tested in a detachable connection, which is convenient for fixing the membrane structure to be tested. The electro-hydraulic push-pull rod is connected to the lower clamping plate, and the membrane structure to be tested can be tensioned by pushing and pulling the lower clamping plate.

[0013] In combination with the first aspect, in a fourth possible implementation of the first aspect of the present application, the hail launching mechanism includes a bracket, a hail launcher and an air compressor; the bracket is connected to the frame, the hail launcher is connected to the bracket and is placed directly above the center position of the frame, and the air compressor is connected to the hail launcher.

[0014] In the above technical solution, the hail launcher uses high-pressure air generated by an air compressor to drive the hail projectiles, thereby minimizing the damage to the hail during the acceleration process.

[0015] In combination with the fourth possible implementation of the first aspect, in a fifth possible implementation of the first aspect of the present application, the hail launcher includes a hail launching tube, the air compressor is connected to the hail launching tube, and a micro speed measuring device is installed in the hail launching tube.

[0016] In the above technical solution, before conducting the test, the emission speed of hail is first detected by a micro speed measuring device, so as to adjust the air compressor and finally set the output air pressure of the air compressor to obtain the speed at which the hail launcher is driven to emit the simulated hail that actually impacts the membrane structure.

[0017] In combination with the fifth possible implementation of the first aspect, in a sixth possible implementation of the first aspect of the present application, the signal acquisition mechanism further includes a signal processing module, and the signal processing module is electrically connected to the laser displacement sensor.

[0018] In the above technical solution, the signal processing module is used to read the data of the first moment and the second moment when the membrane structure to be measured is impacted by hail measured by the laser displacement sensor, and analyze and calculate the action time of the hail impacting the membrane surface.

[0019] In combination with the third possible implementation of the first aspect, in a seventh possible implementation of the first aspect of the present application, the frame is formed with a fixing frame, the fixing frame is located below the mounting end, and the laser displacement sensor is connected to the fixing frame.

[0020] In the above technical solution, the fixing bracket is located below the center of the mounting end and is used to mount the laser displacement sensor.

[0021] In combination with the fifth possible implementation manner of the first aspect, in an eighth possible implementation manner of the first aspect of the present application, the micro speed measuring device is a speed sensor.

[0022] The above technical solution detects the speed of hail emission through a speed sensor.

[0023] In a second aspect, a method for measuring the hail impact load of a membrane structure is provided, and the method for measuring the hail impact load of a membrane structure comprises the following steps:

[0024] Cutting and fixing the membrane structure to be measured to the hail impact load measuring device of the membrane structure in the first aspect or any possible implementation of the first aspect;

[0025] The membrane structure to be tested is tensioned by a tensioning mechanism to form a membrane surface with a stable pre-tension;

[0026] The hail is launched onto the membrane surface at a speed of V by the hail launching mechanism.

[0027] Where V is given by the empirical formula It is calculated that ρ is the hail density, and ρ = 0.9 × 10 3 kg / m 3 , d is the diameter of the hail, g is the acceleration due to gravity, ρ a is the density of air at 20°C;

[0028] C D is the drag coefficient. For smooth spherical hailstones,

[0029] When 0.5cm≤d≤5cm, C D =0.41d 0.185 ; When 5cm≤d≤7.5cm, C D =0.575-0.0208(d-4) 2 ; When 6.4cm≤d≤16cm, C D =0.109d 0.253;

[0030] The first moment t1 when the hailstone contacts the membrane surface and the second moment t2 when the membrane surface reaches the maximum displacement under the impact of the hailstone are obtained by the signal acquisition mechanism, so as to obtain the action time τ=t2-t1 of the hailstone impacting the membrane surface;

[0031] The action time τ = t2-t1 and Substitute into the formula for measuring impact load Thus, the impact load F of hail on the membrane structure is obtained.

[0032] The above technical solution only needs to obtain the first moment t1 when the hailstone contacts the membrane surface and the second moment t2 when the membrane surface reaches the maximum displacement under the impact of the hailstone through the signal acquisition mechanism, and obtain the action time τ=t2-t1 of the hailstone impacting the membrane surface, and then calculate the action time τ=t2-t1 and the empirical formula Substitute the calculated hail velocity V into the formula for measuring impact load The impact load F of hail on the membrane structure can be obtained. The parameters required to be measured are few and easy to measure. The whole measurement process is convenient and has high accuracy. Tests can be carried out on hail of different sizes. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0034] Figure 1 This is a schematic structural diagram of a device for measuring hail impact loads on a membrane structure in an optional embodiment of the present application;

[0035] Figure 2 This is a schematic diagram of the structure of a rack in an optional embodiment of the present application;

[0036] Figure 3 This is a structural schematic diagram of a tensioning mechanism in an optional embodiment of the present application;

[0037] Figure 4 This is a structural schematic diagram of the cooperation between the frame and the tensioning mechanism in an optional embodiment of the present application;

[0038] Figure 5 Schematic diagram of the theoretical calculation model for measuring impact loads on membrane structures.

[0039] Icons: 10- device for measuring hail impact load of membrane structure; 20- membrane structure to be measured; 100- frame; 110- mounting end; 112- mounting plate; 114- mounting column; 120- fixing frame; 200- tensioning mechanism; 210- upper clamping plate; 220- lower clamping plate; 230- electro-hydraulic push-pull rod; 240- connecting hole; 300- hail launching mechanism; 310- bracket; 320- hail launcher; 330- air compressor; 400- signal acquisition mechanism; 410- laser displacement sensor; 420- signal processing module. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations.

[0041] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for which protection is sought, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0042] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0043] In the description of this application, it should be noted that the terms "inner", "lower", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the application is usually placed when in use, which is only for the convenience of describing this application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0044] In the description of this application, it should also be noted that, unless otherwise clearly specified and limited, the terms "disposed" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0045] In the present application, unless otherwise clearly specified and limited, a first feature being above or below a second feature may include the first and second features being in direct contact, or may include the first and second features not being in direct contact but being in contact through another feature between them. Moreover, a first feature being above, above, and above a second feature includes the first feature being directly above and obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being below, below, and below a second feature includes the first feature being directly below and obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0046] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application may be combined with each other.

[0047] An optional embodiment of the present application provides a hail impact load measuring device 10 for a membrane structure. The hail impact load measuring device 10 for a membrane structure can accurately simulate and measure the impact load of the membrane structure under the impact of hail, and then conduct an in-depth study on the dynamic response of the membrane structure under the actual hail impact load based on the impact load.

[0048] Please refer to Figure 1-Figure 4 , Figure 1 The specific structure of a hail impact load measuring device 10 for a membrane structure provided by an optional embodiment of the present application is shown. Figure 2 The specific structure of a rack 100 provided in an optional embodiment of the present application is shown. Figure 3 The specific structure of the tensioning mechanism 200 provided in an optional embodiment of the present application is shown. Figure 4 The specific structure of the frame 100 and the tensioning mechanism 200 provided in an optional embodiment of the present application is shown.

[0049] like Figure 1 As shown, the hail impact load measuring device 10 of the membrane structure includes a frame 100 , four tensioning mechanisms 200 , a hail launching mechanism 300 and a signal collecting mechanism 400 .

[0050] Since the stress state of the membrane structure during actual use is a biaxial stress state, and the stress is in two orthogonal directions, in order to be closer to the actual situation, in the embodiment of the present application, the frame 100 adopts a cross-shaped tension frame. It should be noted that the embodiment of the present application does not limit the specific form of the frame 100. In some other optional embodiments, the frame 100 can also adopt a circular tension frame or a square tension frame.

[0051] Please also refer to Figure 2The cross-shaped tension frame is made of 50×50mm square steel pipes welded together, and as a whole includes three parts: horizontal support (not marked in the figure), vertical support (not marked in the figure) and diagonal support (not marked in the figure). The upper end of the horizontal support of the frame 100 is formed with four mounting ends 110 symmetrically arranged at intervals of 90°, and the four mounting ends 110 constitute the four tensioning directions of the cross-shaped tension frame. The mounting end 110 includes two first side frames (not marked in the figure) arranged at intervals and a second side frame (not marked in the figure) connected between the two first side frames, wherein two mounting columns 114 are arranged at intervals on the second side frame, and the two mounting columns 114 on the two second side frames arranged oppositely are arranged symmetrically based on the center of the frame 100. At the bottom end of the center position surrounded by the four mounting ends 110, the frame 100 is horizontally supported to form a fixed frame 120.

[0052] It should be noted that in the embodiments of the present application, the words such as "upper end" that describe the positional relationship are determined based on the positional relationship in the drawings of the specification and will not be repeated in the following text.

[0053] Please continue to refer to Figure 3 and Figure 4 The tensioning mechanism 200 includes a clamping device and a straight electro-hydraulic push-pull rod 230. The electro-hydraulic push-pull rod 230 is a hydraulically driven mechanical device that integrates mechanics, electricity, and hydraulics, and is suitable for places where reciprocating push-pull linear motion is required. It consists of an actuator (oil cylinder), a control mechanism (hydraulic control valve group) and a power source (oil pump motor, etc.). The power supply controls the forward and reverse rotation of the motor to drive the bidirectional hydraulic pump to output pressure oil in both directions, which is sent to the oil cylinder through the hydraulic control valve to realize the reciprocating motion of the piston rod. The clamping mechanism includes an upper clamping plate 210 and a lower clamping plate 220. The four tensioning mechanisms 200 are respectively installed on the four mounting ends 110 (please refer to Figure 1 shown).

[0054] The lower clamping plate 220 is convex, and is made of two parts, a long plate (not marked in the figure) and a short plate (not marked in the figure), which are integrally formed. The size of the long plate is the same as that of the upper clamping plate 210, and the length of the long plate is equal to the distance between the two first side frames of the mounting end 110. The long plate and the upper clamping plate 210 are both provided with two connecting holes 240, and the two connecting holes 240 are arranged at both ends of the long plate and the upper clamping plate 210, so that when the upper clamping plate 210 is covered on the long plate, the four connecting holes 240 are connected in pairs. When installing, the upper clamping plate 210 and the lower clamping plate 220 are detachably connected by passing the connecting piece through the two connecting holes 240 located at the same position. When in use, the membrane structure 20 to be tested (please refer to Figure 1The upper clamping plate 210 and the lower clamping plate 220 are respectively fixed to the membrane structure 20 to be tested by clamping the membrane structure 20 to be tested in a detachable manner.

[0055] It should be noted that the connection hole 240 can be set as a threaded hole, and correspondingly, the connecting piece can be a stud equipped with a nut. After the stud is passed through the two connection holes 240 located at the same position, the nut is tightened to achieve the connection between the upper clamping plate 210 and the lower clamping plate 220.

[0056] A threaded hole is provided at the center of the short plate of the lower clamping plate 220, and the piston rod of the electric hydraulic push-pull rod 230 is connected to the threaded hole by bolts, and the other end of the electric hydraulic push-pull rod 230 is installed on two mounting posts 114 through the mounting plate 112. The middle part of the mounting plate 112 is an arc shape that fits the circumference of the other end of the electric hydraulic push-pull rod 230, and the two ends of the mounting plate 112 are horizontal, and mounting holes are provided at both ends of the mounting plate 112. The other end of the electric hydraulic push-pull rod 230 is placed between the two mounting posts 114 of the mounting end 110, and then the mounting plate 112 is clamped on the electric hydraulic push-pull rod 230, so that the two mounting holes are connected to the mounting posts 114, wherein the mounting hole can be a threaded hole, and the mounting post 114 can be a bolt post.

[0057] The reciprocating motion of the piston rod of the electro-hydraulic push-pull rod 230 drives the clamping device to reciprocate, and the clamping device can be driven to tension the membrane structure 20 to be tested by pushing and pulling the lower clamping plate 220, thereby achieving the effect of controlling the tension of the membrane structure 20 to be tested. The power lines of the four electro-hydraulic push-pull rods 230 are connected in parallel, and a main power switch is set, and the four electro-hydraulic push-pull rods 230 are controlled by the main power switch. The four electro-hydraulic push-pull rods 230 perform tensioning operations in four directions at the same time, and the tensioning with the same force is achieved by setting the same motor speed. When the electro-hydraulic push-pull rod 230 is in a state where the piston rod is stable and motionless, the membrane structure 20 to be tested can form a membrane surface with stable pre-tension, thereby simulating the force situation of the membrane structure 20 to be tested when it is actually used. The four electro-hydraulic push-pull rods 230 can accurately control the tensioning force in the four directions of the membrane surface in real time, and can simultaneously perform tensioning operations in the four directions, thereby minimizing the instability of the force during the tensioning process of the membrane structure 20 to be tested, and ensuring the accuracy of the measurement.

[0058] Please continue to refer to Figure 1As shown, the hail launching mechanism 300 includes a bracket 310, a hail launcher 320 and an air compressor 330, and the hail launcher 320 includes a hail launching tube (not shown in the figure). The bracket 310 is L-shaped, and the bracket 310 is vertically placed on a horizontal plane and connected to the vertical support of the frame 100, so that the far end of the bending section of the bracket 310 is located above the center position of the membrane structure 20 to be tested. The hail launcher 320 is connected to the far end of the bending section of the bracket 310, and the pipe mouth of the hail launching tube points to the center of the membrane surface of the membrane structure 20 to be tested. The hail launching tube can be replaced according to the adaptation of hail of different diameters. The hail launcher 320 is connected to the air compressor 330 through a pressure pipe, and the speed of hail launching is adjusted by the air pressure output by the air cylinder of the air compressor 330.

[0059] A micro speed measuring device (not shown) is installed in the hail launch tube, and the micro speed measuring device is a speed sensor. The speed sensor is electrically connected to the control processor to realize data transmission or interaction, and the electrical connection can be realized through one or more communication buses or signal lines. The control processor can be an integrated circuit chip with signal processing capabilities; the control processor can also be a general-purpose processor, including a central processing unit (CPU), a network processor (NP), etc.; it can also be a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components. The general-purpose processor can be a microprocessor or the processor can also be any conventional processor, etc. The emission speed of hail is detected by the speed sensor, and the emission speed of hail is changed by adjusting the air pressure of the air compressor 330, and finally a terminal speed that can simulate the actual impact of hail on the membrane structure is set, so that the hail impacts the membrane surface after being launched from the hail launcher 320 at this terminal speed. Since the distance between the hail launcher 320 and the membrane surface is short, the instantaneous speed of the hail impacting the membrane surface is considered to be consistent with the speed when it is launched from the hail launcher 320.

[0060] The hail launcher 320 uses the high-pressure air generated by the air compressor 330 to drive the hail projectiles, so as to minimize the damage to the hail during the acceleration process. Before the test, the launch speed of the hail is first detected by a micro speed measuring device, so as to adjust the air compressor 330, and finally set the output air pressure of the air compressor 330 to obtain the speed at which the hail launcher 320 is driven to launch the simulated hail that actually impacts the membrane structure.

[0061] Please continue to refer to Figure 1 As shown, the signal acquisition mechanism 400 includes a laser displacement sensor 410 and a signal processing module 420. The laser displacement sensor 410 is connected to the fixing frame 120 so that the laser sensor is located directly below the membrane surface. The laser displacement sensor 410 is electrically connected to the signal processing module 420 to realize data transmission and interaction, and the electrical connection can be realized through one or more communication buses or signal lines. In the present application, the signal processing module 420 is a computer. It should be noted that the embodiment of the present application does not limit the specific form of the signal processing module 420. In some other optional embodiments, the signal processing module 420 can be an integrated circuit chip with signal processing capabilities. The signal processing module 420 can also be other general-purpose processors, including network processors (Network Processor, referred to as NP), etc.; it can also be a digital signal processor (Digital Signal Processor, referred to as DSP), an application specific integrated circuit (Application Specific Integrated Circuit, referred to as ASIC), a field programmable gate array (Field-Programmable Gate Array, referred to as FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components. The laser displacement sensor 410 can characterize the moment of the hail impacting the membrane surface according to the displacement change of the membrane surface in the vertical direction, so as to reflect the first moment when the hail just touches the membrane surface and the second moment when the membrane surface reaches the maximum displacement under the impact of the hail. The signal processing module 420 is used to read the data of the first moment and the second moment when the membrane structure 20 to be tested is impacted by the hail measured by the laser displacement sensor 410, and analyze and calculate the action time of the hail impacting the membrane surface, and at the same time perform the next step of calculating the impact load (see the following description for details).

[0062] The hail impact load measuring device 10 of the membrane structure only needs to measure the data of the first moment and the second moment when the membrane structure 20 to be tested is impacted by hail to complete the entire test detection, so as to calculate the impact load of the hail on the membrane structure 20 to be tested, thereby laying a foundation for in-depth research on the dynamic response of the membrane structure 20 to be tested under the hail impact load.

[0063] Another embodiment of the present application provides a method for measuring the hail impact load of a membrane structure. The method for measuring the hail impact load of a membrane structure uses the hail impact load measuring device 10 of a membrane structure provided in the previous embodiment to simulate the actual impact of hail of different sizes on the membrane structure, and obtains the impact load of the hail on the membrane structure. The parameters required to be measured are few and easy to measure, and the entire measurement process is convenient and fast with high accuracy.

[0064] Please refer to Figure 5 As shown, Figure 5 The schematic diagram of the theoretical calculation model for the impact load measurement of membrane structure is shown in Figure 2. Based on the large deflection theory of membrane, it is assumed that the side length in the x direction of the orthogonal anisotropic rectangular membrane structure with four sides fixed is a, the side length in the y direction is b, and the initial tension in the x direction is N. ox , the initial tension in the y direction is N oy , the impact load is a hailstone incident perpendicular to the membrane surface (represented by a small ball in the figure), its mass is M, the final velocity of the hailstone impacting the membrane surface is V, and the impact time of the hailstone in contact with the membrane surface is τ. Then, according to the law of conservation of momentum, we can get:

[0065]

[0066] Where f(t) is the hail impact vector, v is the hail velocity vector, and the impact force of the hail on the membrane surface during the contact time τ is F(τ):

[0067]

[0068] Assuming the hailstone is a sphere, then M = ρπd 3 / 6, where ρ is the hail density and d is the hail diameter, the impact force is:

[0069]

[0070] Once the impact force is known, the impact load F can be calculated as long as the contact area A between the hailstone and the membrane surface is known:

[0071]

[0072] According to experimental experience, the contact range between hail and the membrane surface is one-fourth of the height of the spherical crown of the contact surface, so A=πdh, where the height of the spherical crown of the contact surface is h=d / 4.

[0073] By arranging the above formulas, the formula for measuring the impact load F is:

[0074]

[0075] V in formula (1) is calculated by the following formula (2):

[0076]

[0077] Formula (2) is an empirical formula, which represents the semi-empirical relationship of the hail resistance coefficient and the approximate formula of the terminal velocity. In formula (2):

[0078] V is the final velocity of hail (m / s); ρ is the hail density, ρ = 0.9 × 10 3 kg / m 3 ; d is the diameter of the hail (m), and the test can be carried out on hail of different diameters; g is the acceleration due to gravity, g = 9.8m / s 2 ρ a is the density of air at room temperature (20°C), take ρ a =1.205kg / m 3 ;

[0079] C D is the drag coefficient. For smooth spherical hailstones,

[0080] When 0.5cm≤d≤5cm, C D =0.41d 0.185 (d is the diameter of the hail (cm)); when 5cm≤d≤7.5cm, C D =0.575-0.0208(d-4) 2 (d is the diameter of the hail (cm)); when 6.4cm≤d≤16cm, C D =0.109d 0.253 (d is the diameter of the hail (cm)).

[0081] From the above analysis, it can be seen that when hail of a certain diameter impacts the membrane structure to be tested 20 (please refer to Figure 1 In the test shown in FIG. 1 , only the signal acquisition mechanism 400 (see FIG. 1 ) is required. Figure 1 As shown in the figure, the first moment t1 when the hailstone contacts the membrane surface and the second moment t2 when the membrane surface reaches the maximum displacement under the impact of the hailstone are obtained, and the action time τ=t2-t1 of the hailstone impacting the membrane surface is obtained. Then, the action time τ=t2-t1 and the empirical formula are used to calculate the maximum displacement of the membrane surface. Substitute the calculated hail velocity V into the formula for measuring impact load The impact load F of hail on the membrane structure can be obtained. Figure 1-Figure 4 , the method for measuring the hail impact load of the membrane structure includes the following steps:

[0082] The membrane structure 20 to be tested is cut and fixed to the hail impact load measuring device 10 of the membrane structure provided in the previous embodiment;

[0083] The membrane structure 20 to be tested is tensioned by the tensioning mechanism 200 to form a membrane surface with a stable pre-tension;

[0084] Turn on the power switch of the air compressor 330, start the air compressor 330 to start pressurizing to the required air pressure level, then start the switch of the hail launcher 320, and launch hail onto the membrane surface at a speed of V through the hail launching mechanism 300, where V is given by the empirical formula Calculated;

[0085] The laser displacement sensor 410 in the signal acquisition mechanism 400 obtains the first moment t1 when the hailstone contacts the membrane surface and the second moment t2 when the membrane surface reaches the maximum displacement under the impact of the hailstone, so that the signal processing module 420 calculates the action time τ=t2-t1 of the hailstone impacting the membrane surface;

[0086] The action time τ = t2-t1 and Substitute into the formula for measuring impact load (This step is automatically performed by the signal processing module 420), thereby obtaining the impact load F of the hail on the membrane structure.

[0087] It should be noted that before carrying out the above-mentioned method for measuring the hail impact load of the membrane structure, the following preparatory work before the test measurement is required:

[0088] 1. Install four straight electro-hydraulic push-pull rods 230 on the mounting ends 110 of the frame 100 respectively, and connect them to the lower clamping plate 220, connect the power lines of the four straight electro-hydraulic push-pull rods 230 in parallel, set the main power switch, and debug the hydraulic system of the electro-hydraulic push-pull rods 230.

[0089] 2. Turn on the main power switch of the hydraulic system of the electro-hydraulic push-pull rod 230, adjust the tensioning force to the design level, and start the motors of the four straight electro-hydraulic push-pull rods 230 at the same time to start tensioning the membrane structure 20 to be tested. After the membrane surface of the membrane structure 20 to be tested is tensioned in place, lock the straight electro-hydraulic push-pull rods 230 to keep the membrane surface tension unchanged.

[0090] 3. Install the laser displacement sensor 410 on the fixing frame 120 and align it with the measuring point.

[0091] 4. Use a wire to connect the laser displacement sensor 410 to the signal processing module 420, reset the laser displacement sensor 410 to zero, and debug the laser displacement sensor 410.

[0092] 5. Install the hail launcher 320 and the bracket 310, align the hail launch tube with the center of the membrane surface, and use the empirical formula The launch speed V of the hail is calculated.

[0093] 6. Install an air pressure pipe to connect the air compressor 330 and the hail launcher 320. According to the launching speed V of the hail, adjust the air compressor 330 and the hail launcher 320 to obtain the air pressure level of the air compressor 330 that can launch the hail at this speed.

[0094] 7. Before the hail is emitted, the signal processing module 420 is turned on, the corresponding sensor software is started, and the membrane surface displacement data is monitored.

[0095] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A device for measuring hail impact load of membrane structure, characterized in that: include: frame; A tensioning mechanism, the tensioning mechanism is installed on the frame, and the tensioning mechanism is used to tension the membrane structure to be tested and form a membrane surface with a stable pre-tension; A hail launching mechanism, which is connected to the frame and placed above the membrane surface, and is used to launch hail onto the membrane surface; and A signal collection mechanism, the signal collection mechanism is connected to the frame, the signal collection mechanism comprises a laser displacement sensor, and the laser displacement sensor is placed below the membrane surface; The frame is a cross-shaped tension frame, and the frame is formed with four installation ends that are symmetrically arranged at intervals; The four tensioning mechanisms are respectively installed on the four installation ends; The tensioning mechanism comprises a clamping device and an electro-hydraulic push-pull rod, the power lines of the electro-hydraulic push-pull rods of the four tensioning mechanisms are connected in parallel, and a main power switch is provided, and the electro-hydraulic push-pull rods of the four tensioning mechanisms are controlled by the main power switch; The clamping device is used to clamp the membrane structure to be tested, and the electro-hydraulic push-pull rod is installed at the installation end; The electro-hydraulic push-pull rod is used to drive the clamping device to move, so that the clamping device tensions the membrane structure to be tested and forms a membrane surface with a stable pre-tension; The mounting end includes two first side frames arranged at intervals; The clamping device comprises an upper clamping plate and a lower clamping plate; The upper clamping plate is detachably connected to the lower clamping plate, and the membrane structure to be tested is placed between the upper clamping plate and the lower clamping plate; The electro-hydraulic push-pull rod is connected to the lower clamping plate; The lower clamping plate is convex, and comprises a long plate and a short plate, wherein the length of the long plate is equal to the distance between the two first side frames at the mounting end; The signal acquisition mechanism further includes a signal processing module, which is electrically connected to the laser displacement sensor, and is used to read the first moment t1 when the hailstone contacts the membrane surface and the second moment t2 when the membrane surface reaches the maximum displacement under the impact of the hailstone, and obtain the action time τ=t2-t1 of the hailstone impacting the membrane surface through the first moment t1 and the second moment t2; The action time τ = t2-t1 and Substitute into the formula for measuring impact load Thus, the impact load F of hail on the membrane structure is obtained, where ρ is the hail density, d is the diameter of the hail, g is the gravitational acceleration, and ρ is a is the density of air at 20°C, the C D is the drag coefficient of smooth spherical hail.

2. The hail impact load measuring device for membrane structures according to claim 1 is characterized in that: The hail launching mechanism comprises a bracket, a hail launcher and an air compressor; The bracket is connected to the frame, the hail launcher is connected to the bracket and is placed just above the center of the frame, and the air compressor is connected to the hail launcher.

3. The hail impact load measuring device for membrane structures according to claim 2 is characterized in that: The hail launcher comprises a hail launch tube, the air compressor is connected to the hail launch tube, and a micro speed measuring device is installed in the hail launch tube.

4. The hail impact load measuring device for membrane structures according to claim 1 is characterized in that: The frame is formed with a fixing frame, the fixing frame is located below the center of the mounting end, and the laser displacement sensor is connected to the fixing frame.

5. The hail impact load measuring device for membrane structures according to claim 3 is characterized in that: The micro speed measuring device is a speed sensor.

6. A method for measuring hail impact load on membrane structures, characterized in that: The following steps are involved: Cutting and fixing the membrane structure to be tested to a hail impact load measuring device for the membrane structure according to any one of claims 1 to 5; The membrane structure to be tested is tensioned by the tensioning mechanism to form a membrane surface with a stable pre-tension; The hail-emitting mechanism emits hail onto the membrane surface at a speed of V. Where V is given by the empirical formula It is calculated that ρ is the hail density, and ρ = 0.9 × 10 3 kg / m 3 , d is the diameter of the hail, g is the acceleration due to gravity, ρ a is the density of air at 20°C; C D is the drag coefficient. For smooth spherical hailstones, When 0.5cm≤d≤5cm, C D =0.41d 0.185 ; When 5cm≤d≤7.5cm, C D =0.575-0.0208(d-4) 2 ; When 6.4cm≤d≤16cm, C D =0.109d 0.253 ; The signal acquisition mechanism is used to obtain a first moment t1 when the hailstone contacts the membrane surface and a second moment t2 when the membrane surface reaches a maximum displacement under the impact of the hailstone, thereby obtaining an action time τ=t2-t1 of the hailstone impacting the membrane surface; The action time τ = t2-t1 and Substitute into the formula for measuring impact load Thus, the impact load F of hail on the membrane structure is obtained.

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