CN113188745B - Method and device for testing wind load of crown of standing tree - Google Patents
Method and device for testing wind load of crown of standing tree Download PDFInfo
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Abstract
The invention discloses a method for testing the wind load of a crown of a standing tree and a detection device thereof, wherein the method comprises the following steps: (1) measuring parameters such as height, breast diameter and crown area of the standing tree to be measured, calculating inertia moment and obtaining elastic modulus, and measuring a first distance between a wind power concentration action point on the standing tree to be measured and the ground; (2) installing a strain sensor to obtain a second distance from the sensor to the ground; (3) obtaining a strain measurement; (4) and obtaining the equivalent wind load according to the tree height, the elastic modulus, the section inertia moment, the first distance and the second distance of the standing tree to be tested. The invention discloses a mechanical model obtained based on the relation between the strain at the bottom of a trunk and the wind load of a crown. The mechanical model is packaged in the detection device provided by the invention, and under the action of external wind force, the wind load of the tree crown can be obtained without using other measurement devices.
Description
Technical Field
The invention belongs to the field of nondestructive detection of forestry, and particularly relates to a method and a device for testing wind load of a crown of a standing tree.
Background
Living stumps refer to uncut trees and bamboo grown in the ground. With the increase of age, the growth tendency of the tree is weakened, the capability of resisting external natural disasters is also reduced, and the damage phenomena of trunk breakage, tree root connection pulling, branch breakage and the like are easy to occur under the action of strong wind. In order to protect the tree and avoid the above-mentioned damage phenomena, it is necessary to perform an appropriate safety assessment of the tree. At present, the safety evaluation of the standing tree is mainly carried out by means of nondestructive detection technologies such as stress wave detection, ultrasonic detection, X-ray detection, micro-drilling resistance detection, inclined-pulling method detection and the like, and the maximum bearing capacity of the trunk and the crown is evaluated, so that the tree with insufficient stability is reinforced and protected in a targeted manner, and damage is avoided.
Wind force acts on the crown of the standing tree, the formed torque is transmitted to the root of the tree, and when the torque exceeds the bearing limit of the root, trunk breakage or tree root connection pulling-up and other damages can occur. Therefore, measuring the crown wind load is the basis for evaluating the stability of the tree. The existing method for measuring the wind load of the crown of the standing tree is a diagonal pulling method, namely, a certain lateral tension is applied to the tree to be measured to simulate the wind load, and the inclination angle and the strain of the trunk are measured simultaneously. However, the method has some disadvantages in the implementation process, such as the need of using devices such as a winch and a steel cable to perform side pulling, the devices are heavy, the requirement on the use site is high, and the measurement work is difficult to perform in a complex environment; in addition, the existing sensor is expensive, the endurance time is short, the internal storage data export process is complicated, and the universality is poor.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a method for testing the wind load of the crown of the standing tree and a detection device thereof. The invention provides a method for testing the wind load of a crown of a standing tree, which is a mechanical model obtained based on the relationship between the strain at the bottom of a trunk and the wind load of the crown. The mechanical model is packaged in the detection device provided by the invention, and under the action of external wind force, the wind load of the tree crown can be obtained without using other measurement devices. The detection device comprises a strain sensor suitable for strain measurement of the standing tree and auxiliary mounting devices such as a mounting steel needle and a sensor mounting positioning hole limiting handle. The strain sensor is provided with a specially-made shell, a circuit board, a grating ruler, a lithium ion battery and other components are installed inside the strain sensor, the sensor is installed at a proper position of a trunk by using a nut to pre-tighten a steel needle in an installation hole, and measurement of tree strain and storage of measurement results can be achieved. The installation steel needle be length 10cm, diameter 4 mm's cylindrical steel nail, the spacing handle of installation locating hole be a cross-section for the cuboid of square, both ends have with the round hole of installation steel needle isodiametric, and the distance in two holes is the same with the interval of strain sensor installation locating hole.
The technical scheme of the invention is as follows:
the invention provides a method for testing the wind load of a crown of a standing tree, which comprises the following steps:
s1, measuring the height, crown area and breast height of a standing tree to be measured, obtaining elastic modulus according to the species of the standing tree to be measured, obtaining section moment of inertia according to the crown area and the breast height, and measuring a first distance between a wind power concentration action point on the standing tree and the ground;
s2, mounting a detection device, namely a strain sensor, on the standing timber to be detected, and obtaining a second distance between the strain sensor and the ground;
s3, detecting a strain measurement value through the strain sensor according to the following formula:
X＝[(Sum1×65535+Count1)-(Sum2×65535+Count2)]×0.25 (1)
wherein, X is a strain measurement value, Sum1 is the overflow number of the first timer, Sum2 is the overflow number of the second timer, Count1 is the current value of the first timer Count register, and Count2 is the current value of the second timer Count register;
and S4, obtaining the equivalent wind load size according to the strain measurement value, the length, the elastic modulus and the section inertia moment of the standing tree to be measured, the first distance and the second distance.
The invention provides a method for testing the wind load of a crown of a standing tree, which is based on a mechanical model for calculating the wind load of the crown of the standing tree under the action of wind power, and the equivalent wind load can be obtained according to the mechanical model. The model is characterized in that: the area of a crown of a tree in nature is far larger than the surface area of a trunk, under the action of the same wind force, the stress of the crown is far larger than that of the trunk, the measured trunk is equivalent to a constant-height polished rod inserted in the ground, namely, a cantilever beam structure, and the total length of the tree, namely, the height of the tree is H; the position of the crown is high, a large lever moment is generated on the tree when the tree is subjected to wind power, the large lever moment is a main influence factor of tree toppling, the wind power borne by the tree is set as a concentrated load, the equivalent wind load is P, the equivalent wind load acts on a proper position a away from the top of the polished rod in a concentrated mode, and the distance between a sensor mounting point and the ground is K; the distance L between the sensor installation positioning holes is small, and the tree is high, namely L < < H, so that the bending deformation of the sensor fixing section is small when the tree is blown by wind, the sensor fixing section is still straight after being bent and deformed, and the horizontal displacement of the lower fixing end is small and approximately zero. According to the factors, the complex acting force of the wind on the surface of the trunk can be ignored, and only the wind load generated by the wind acting on the tree crown is considered.
Detection device install the bottom of trunk near the suitable position department on ground, the wind power is spent, the deflection in detection device mounted position department is very little, its deformation and the original upright position can be approximately equivalent into right angled triangle, according to equivalent right angled triangle's pythagorean theorem:
from the flexible line equation:
wherein: x is the stretching amount of the tree root when stretching or compressing deformation occurs, m is the deflection of the sensor mounting point when bending occurs, E is the elastic modulus, I is the section inertia moment, and lambda is an error compensation coefficient which is usually 1.0-1.6, and different compensation coefficients are required to be selected according to different tree species. According to the above equation, the equivalent wind load P at the crown a can be determined by the sensor dependent variable X.
The invention provides a method for testing the crown wind load of a standing tree, wherein a strain sensor is arranged on the standing tree to be tested, and the method specifically comprises the following steps:
and S21, determining whether the working state of the strain sensor is normal, checking the state of the strain sensor, ensuring that the battery power is sufficient, the residual space of the memory card is sufficient, and the external stretching measuring scale can enable the readings to change synchronously, so that the strain sensor can run normally. If the sensor can not work normally, the reset key of the sensor is used for resetting, or the power supply of the sensor is turned off for clearing and troubleshooting.
S22, if the sensor status is normal, one fiftieth of the tree height is typically selected for measurement. And drawing a mounting line at a set position of the measured trunk, and nailing a mounting steel needle into the mounting steel needle by using a mounting positioning hole limiting handle.
S23, after the steel needle penetrates into the mounting holes at the two ends of the sensor, the bolt and the nut are screwed to firmly mount the sensor on the trunk, and the strain sensor is tightly attached to the trunk during mounting.
The invention also provides a detection device suitable for measuring the strain of the standing tree, wherein the strain sensor hardware in the detection device mainly comprises a grating ruler, a quadruple frequency circuit, a data acquisition and storage module, a sensor shell, an interaction module, a power supply module and a 20000mAh lithium ion battery.
The grating ruler reading head outputs pulses to be connected to the input end of the quadruple frequency circuit, quadruple frequency pulse signals are output to the data acquisition and storage module to carry out pulse counting acquisition, the data acquisition and storage module obtains dependent variables according to a formula (1) by the calculation method, the interaction module is connected with the data acquisition and storage module to carry out dependent variable display and key control signal transmission, and the power module is matched with the lithium ion battery to provide electric power for the grating ruler, the quadruple frequency circuit, the data acquisition and storage module and the interaction module.
The data acquisition and storage module consists of an STM32F407 single chip microcomputer and a Mini TF Card female seat. And a first pin and a second pin of the STM32F407 single chip microcomputer are respectively connected with two output ends of the quadruple frequency circuit, the output pulses of the quadruple frequency circuit are accumulated by using ETR functions of a first timer and a second timer in the STM32 single chip microcomputer, and the dependent variable measured by the current sensor is calculated according to a formula (1). And the STM32F407 singlechip forms a data packet by the strain data and the real-time and writes the data packet into a data file of the memory card. The storage card module is connected with the microcontroller, the microcontroller establishes an FATFS file system on the external storage card, and a group of measured dependent variable data is written in at intervals in the measurement process. In addition, the data acquisition and storage module can be connected with a computer through a USB Type-C interface in the power module and performs data transmission.
The grating ruler is used for generating A, B paths of pulse outputs with the phase difference of 90 degrees, and the 1 pulse output represents that the grating reading head generates 0.5 mu m displacement relative to the grating of the ruler; when the reading head of the grating ruler moves, the indicating grating in the reading head and the grating of the ruler form an interlacing, and the output pulse changes.
The quadruple frequency circuit consists of a 4-channel JK trigger and a one-out-of-four data selector, A, B-phase pulses output by the grating ruler are respectively connected with 1 channel and 3 channels of the JK trigger, the outputs of the 1 channel and the 3 channel are respectively connected with 2 channel and 4 channel inputs, the output of the 2 nd channel of the JK trigger is connected with 1 channel 0 bit and 2 channel 1 bit of the data selector, the 3 rd channel output of the JK trigger is connected with 1 channel 3 bit and 2 channel 2 bit of the data selector, the outputs of the 1 channel and the 3 channel of the JK trigger are respectively connected with the input end of the data selector A, B, and the 4-channel output of the JK trigger is connected with 1 channel 2 bit and 2 channel 0 bit of the data selector; the four-frequency circuit can carry out frequency multiplication subdivision processing on pulses output by the grating scale A, B two phases, judge the moving direction of the reading head of the grating scale, improve the measurement precision of the grating scale to 2 pulses output, and represent that the reading head of the grating produces 0.5 mu m relative displacement, thereby improving the precision.
The power supply module comprises elements such as a battery management chip sp4522b, a USB Type-C interface and protocol chip IP2721, a direct-current converter chip, a coulometer chip bq40z52 and the like; the power module is connected with a lithium ion battery in the sensor, and can acquire electric energy from the battery and provide required voltage for each element in the sensor; the USB Type-C interface CC1 and the CC2 interface are connected with 5.1K pull-down resistors and then are respectively connected with IP2721 CC1 and CC2 interfaces, the VBUS pin of the USB Type-C interface is connected with the S pole of an NMOS tube, the DP + and DP-of Type C are connected with the PA11 and PA12 pins of an STM32F407 singlechip to complete a data USB transmission function, the D pole of an NMOS is connected with the vin pin of a power management chip sp4522b, the G pole of the NMOS is connected with the VBUSG pin of the IP2721, the capacity of a built-in lithium ion battery of the sensor is 20000mAh, the direct current converter chip has 93% conversion efficiency, the working current of the sensor is less than 80mA, so that the sensor has longer endurance time, and the power module calculates the current residual battery capacity through a coulometer bq40z 52.
The interactive module consists of an OLED screen and four function keys, wherein the function keys are respectively a starting up key, a starting measurement key, an OLED display switch and a reset key; the interaction module is connected with the power supply module to obtain corresponding voltage; the interactive module supports a key awakening function and can display the electric quantity information, the measurement data, the time and date and other sensor state information of the lithium battery on an OLED screen; the starting key is connected with a starting pin of a power management chip sp4522b and is used as a main switch of the sensor; the start measurement, reset and OLED display switch key is connected to pins PD4, 5 and 6 of STM32F407, and when the key is pressed down, the single chip microcomputer processes low-level external interrupt to realize corresponding functions; the measuring start key selects a relative displacement zero point for starting measurement, so that the flexibility of data measurement is improved; the reset key clears the data in the RAM of the singlechip and returns to the initial state of electrifying the sensor; the OLED display switch key controls the OLED screen to be turned off and normally on, the screen can be turned off when measurement data do not need to be displayed, and electric quantity is saved.
The invention provides a detection device suitable for measuring the strain of a standing tree, which comprises a strain sensor and an auxiliary installation device, wherein a strain sensor shell consists of a sensor top shell, a sensor bottom shell, a sensor front shell, a sensor rear shell, a sensor left shell, a sensor right shell, a rear side fixing piece threaded cylinder, a front side fixing connecting piece bolt, a front side fixing connecting piece adjusting nut, an installation fixing frame and an L-shaped connecting piece.
The sensor top shell and the sensor bottom shell are respectively provided with four mounting holes on two long sides and four mounting holes on short sides, the mounting holes respectively correspond to the eight mounting holes of the left sensor shell and the right sensor shell and the two mounting holes on the front sensor shell and the rear sensor shell, and the top sensor shell, the bottom sensor shell and the left sensor shell are assembled and fixed through connecting screws.
Sensor drain pan and sensor top shell all process have with the groove of lithium cell and circuit board equidistance, place battery and circuit board in the groove, with the sensor about the shell use the screw accomplish with the assembly of sensor top shell and drain pan, can accomplish spacing fixed action well to lithium cell and circuit board after the assembly is accomplished. The installation mount be L type sheet metal connector, the bottom surface of installation mounting passes through the screw and installs the sensor drain pan, the perpendicular installation of installation mounting the sensor circuit board.
The upper right side of the left shell of the sensor is provided with an OLED display screen slotted hole which is used for installing a display screen and displaying measurement data and a sensor state; an interactive key interface is arranged on the left lower side of the left shell of the sensor, and a key signal cable penetrates through the interactive key interface to be connected to an interface of the circuit board.
The grating of the scale plate of the grating ruler is fixedly arranged in the mounting groove of the bottom shell through a bolt; the right side of the reading head of the grating ruler is connected with the L-shaped connecting piece and the outward extending measuring ruler through screws; the extended measuring scale is of a flat cuboid structure, so that the grating scale reading head is not damaged by rotation in the sensor, and the transmission of the measured strain can be completed; the upper part of the reading head of the grating is connected with the inner slide block of the guide rail through an L-shaped connecting piece in a threaded fit manner; the L-shaped connecting piece can ensure that the grating ruler reading head can only slide in a given direction without generating movement in other directions, and the grating ruler reading head and the linear guide rail are integrated; the utility model discloses a grating ruler, including overhanging dipperstick, front side fixed connector bolt, front side fixed connector adjusting nut, front side fixed connector gasket, overhanging dipperstick one end accomplish the cooperation through threaded connection and grating ruler reading head, the other end have the hole of the same diameter size with front side fixed connector bolt, the screw thread part of front side fixed connector bolt have the mounting hole of installation steel needle diameter size, the mounting hole of front side fixed connector bolt is passed perpendicularly and is assembled by the installation steel needle overhanging dipperstick one side, the opposite side is accomplished the cooperation through front side fixed connector adjusting nut and front side fixed connector gasket, provides the pretightning force through screwing front side fixed connector adjusting nut and will install the steel needle and press from both sides tightly.
The sensor rear shell and the center of the grating ruler reading head are provided with circular slotted holes, and a rear side fixing piece threaded cylinder of the sensor is connected to the sensor rear shell through threads, so that the rear end mounting fixing piece and the sensor shell form a whole.
The threaded cylinder of the rear side fixing piece is a metal rod with threads, one end of the threaded cylinder is connected with the rear shell of the sensor, the other end of the threaded cylinder is provided with a mounting hole with the same diameter as that of a mounting steel needle, and the threads of the outer ring can be assembled to complete the fixture device; the clamp device consists of a rear side fixing piece nut, a rear side fixing piece adjusting nut, a rear side fixing piece fixing screw and a rear side fixing piece end stop nut; the rear side mounting nut is a knurled round nut, a fixing steel needle penetrates through the mounting hole at the other end of the rear side mounting threaded cylinder, the rear side mounting fixing screw and the rear side mounting adjusting nut are located on one side of the mounting hole, the rear side mounting nut is located on the other side of the mounting hole, pre-tightening force can be applied to the clamp through screwing the rear side mounting nut, and therefore the fixing steel needle in the mounting hole is clamped tightly.
The invention provides a detection device suitable for measuring the strain of standing trees. The installation steel needle be length 10cm, diameter 4 mm's cylindrical steel nail, the spacing handle of installation locating hole be the cuboid of a cross-section for the square, both ends have with the round hole of installation steel needle isodiametric, and the distance in two holes is the same with the interval of strain sensor installation locating hole.
The invention provides a detection device which uses an overhanging measuring scale, an L-shaped connecting piece and a linear guide rail to finish the transmission of the measured strain amount. A linear guide rail is arranged on the central line of the inner wall of the sensor top shell, a sliding block is arranged in the guide rail, and a reading head of the grating is connected with the sliding block in the guide rail through an L-shaped connecting piece in a threaded fit manner; the L-shaped connecting piece can ensure that the grating ruler reading head can only slide linearly in a given direction without generating movement in other directions, and the grating ruler reading head and the linear guide rail are integrated; the overhanging measuring scale is a stainless steel connecting rod with a rectangular cross section, one end of the overhanging measuring scale is connected with the grating reading head through threaded connection, and the other end of the overhanging measuring scale is matched with a front side fixed connecting piece bolt and an adjusting nut to transmit the measured strain to the grating reading head.
After the sensor shell is assembled, sealant needs to be poured into gaps of the assembling interfaces, and a transparent waterproof sealing rubber layer covers the sensor, so that the sensor can be waterproof and moistureproof, has high reliability, and can perform long-time stable measurement under severe meteorological conditions.
The invention provides a method for testing the wind load of a crown of a standing tree, which is a mechanical model obtained based on the relationship between the strain at the bottom of a trunk and the wind load of the crown. The mechanical model is packaged in the detection device provided by the invention, and under the action of external wind force, the wind load of the tree crown can be obtained without using other measurement devices.
Drawings
FIG. 1 is a schematic diagram of a mechanical model for calculating wind load of standing trees
FIG. 2 is a schematic view of a strain sensor
FIG. 3 is a flow chart of a test using sensors
1. Sensor drain pan 2, installation mount 3, circuit board
4. OLED display screen slotted hole 5, mutual key interface 6, sensor left shell
7. Grating ruler scale grating 8, lithium battery 9 and sensor rear shell
10. Rear side fixing member nut 11, rear side fixing member adjusting nut 12, rear side fixing member fixing screw
13. Rear fastener end stop nut 14, rear fastener threaded cylinder 15, rear fastener connector
16. Sensor top shell 17, linear guide rail 18 and L-shaped connecting piece
19. Grating ruler reading head 20, sensor right shell 21 and front side fixed connecting piece gasket
22. Front side fixed connector adjusting nut 23, overhanging measuring scale 24, front side fixed connector bolt
25. Sensor front shell
Detailed Description
In order to make the technical scheme of the invention clearer, the invention is clearly and completely described below with reference to the specific embodiments of the attached drawings.
The method for testing the wind load of the crown of the standing tree is based on a mechanical model, the relation between the bottom strain of the trunk and the wind load of the crown is obtained, the mechanical model only depends on the action of external wind force, and the wind load of the crown can be obtained by matching with the detection device provided by the invention without using other measurement devices.
As shown in FIG. 1, the deformed front line segment AB is the equivalent polished rod of the tree, the length of the equivalent polished rod is H, and K is the distance from the sensor mounting point to the ground. The equivalent load of the tree is P, the distance between a centralized action point and the bottom is a, X is the expansion amount of the tree root when the tree root is stretched or compressed, namely the strain value, m is the deflection of a sensor mounting point when the tree is bent, and when the tree is subjected to wind force, the tree is bent from the AB position to the AB position
In a local area of the bottom of the trunk, the trunk changes from an initial position CD to a position
The distance L between the sensor installation positioning holes is that the bottom of the trunk is bent and stretched into (L + X), and E is an elastic dieQuantity, I is the section moment of inertia.
According to the deformed equivalent right triangle Pythagorean theorem:
from the flexible line equation:
in the formula, lambda is an error compensation coefficient, the value of lambda is usually 1.0-1.6, and different error compensation parameters should be selected according to different tree species. According to the above equation, the crown wind load can be determined by the sensor displacement X.
As shown in fig. 2, the invention provides a detection device suitable for strain measurement of standing trees, wherein a strain sensor in the detection device is provided with a specially-made shell, a circuit board 3, a grating ruler (composed of a grating ruler scale grating 7 and a grating ruler reading head 19), a lithium battery 8 and other components are arranged in the detection device, a front side fixed connecting piece adjusting nut 22 and a rear side fixed piece nut 10 are adjusted, steel needles in front and rear end mounting holes are pre-tightened, the sensor is mounted at a proper position of a trunk, and the data acquisition and storage module realizes acquisition processing of tree strain and storage of measurement results.
The upper right side of the sensor left shell 6 is provided with an OLED display screen slot hole 4 for installing a display screen and displaying measurement data and a sensor state; an interactive key interface 5 is arranged on the lower left side of the sensor left shell 6, and a key signal cable penetrates through the interactive key interface 5 to be connected to an interface of the circuit board 3.
The grating ruler consists of two parts, namely a grating ruler grating 7 and a grating ruler reading head 19, the grating interval is 0.5 mu m, and the grating ruler reading head 19 outputs A, B two-phase pulses with the phase difference of 90 degrees; when the grating scale reading head 19 moves, the indication grating in the reading head and the scale grating form interleaving, and output pulses are changed; the grating 7 of the grating ruler scale is fixedly arranged in the mounting groove of the bottom shell 1 through a bolt; the right side of the grating ruler reading head 19 is connected with the L-shaped connecting piece 18 and the outward extending measuring ruler 23 through screws; the overhanging measuring scale 23 is a flat cuboid structure, which not only ensures that the grating scale reading head 19 does not rotate and damage in the sensor, but also can complete the transmission of the measured strain; the upper part of a reading head 19 of the grating is connected with an inner sliding block of the linear guide rail 17 through an L-shaped connecting piece 18 by thread matching; the L-shaped connecting piece 18 can ensure that the grating ruler reading head 19 can only slide in a given direction without generating movement in other directions, and the grating ruler reading head 19 and the linear guide rail 17 are integrated; one end of the overhanging measuring scale 23 is matched with the grating scale reading head 19 through threaded connection, the other end of the overhanging measuring scale 23 is provided with a hole with the same diameter as the front side fixed connecting piece bolt 24, the threaded part of the front side fixed connecting piece bolt 24 is provided with a mounting hole with the same diameter as the mounting steel needle, the mounting hole of the front side fixed connecting piece bolt 24 is vertically penetrated by the mounting steel needle and assembled at one side of the overhanging measuring scale 23, the other side of the overhanging measuring scale is matched with the front side fixed connecting piece gasket 21 through the front side fixed connecting piece adjusting nut 22, and the mounting steel needle is clamped tightly through screwing the front side fixed connecting piece adjusting nut 22 to provide pretightening force.
A linear guide rail 17 is installed on the central line of the inner wall of the sensor top shell 16, and a sliding block is installed in the linear guide rail 17. The sensor rear shell 9 and the grating ruler reading head 19 are provided with circular slotted holes at corresponding positions, a rear side fixing piece threaded cylinder 14 of the sensor is connected with the sensor rear shell 9 and a rear side fixing connecting piece 15 through threads, and the fixing connecting piece 15 is assembled with the upper part of the sensor rear shell 9 through screws, so that the rear end mounting fixing piece and the sensor shell form a whole. The rear side fixing piece threaded cylinder 14 is a metal rod with threads, one end of the metal rod is connected with the sensor rear shell 9, the other end of the metal rod is provided with a mounting hole with the diameter equal to that of a mounting steel needle, the threads of the outer ring can be assembled into a fixture device, the fixture device is composed of a rear side fixing piece nut 10, a rear side fixing piece adjusting nut 11, a rear side fixing piece fixing screw 12 and a rear side fixing piece end stop nut 13, the rear side fixing piece nut is a knurled round nut, the fixing steel needle penetrates through the mounting hole at the other end of the rear side fixing piece threaded cylinder 14, the rear side fixing piece fixing screw 12 and the rear side fixing piece adjusting nut 11 are located on one side of the mounting hole, the rear side fixing piece nut 10 is located on the other side of the mounting hole, pre-tightening force can be applied to the fixture through screwing the rear side fixing piece nut 10, and therefore the fixing steel needle in the mounting hole is clamped tightly.
As shown in fig. 3, the invention provides a method for testing the wind load of the crown of a standing tree, which comprises the following steps:
s1, measuring the length H, the crown area and the breast height of the standing tree to be measured, obtaining the elastic modulus E according to the tree species of the standing tree to be measured, and obtaining the section moment of inertia I according to the crown area and the breast height; and measuring a first distance a between a wind power concentration action point on the standing timber and the ground.
And S2, mounting a strain sensor on the standing timber to be measured, and obtaining a second distance K between the strain sensor and the ground.
Whether sensor operating condition is normal is confirmed at first to the installation sensor, and the inspection sensor state ensures that battery power is sufficient, memory card residual space is enough, tensile external dipperstick can make the registration synchronous change, can normal operating. If the sensor can not work normally, the reset button of the sensor is used for resetting, or the power supply of the sensor is closed for clearing, so that faults can be eliminated. Wherein the appropriate position is typically selected to be one fiftieth of the tree height.
And then, if the state of the sensor is normal, drawing a mounting line at the set position of the measured trunk, and nailing a mounting steel needle according to the distance between the mounting positioning holes at the two ends of the sensor.
And finally, after the steel needle penetrates into the mounting holes at the two ends of the sensor, the bolt and the nut are screwed to firmly mount the sensor on the trunk, and the strain sensor is tightly attached to the trunk during mounting.
S3, detecting a strain measurement value through the strain sensor according to the following formula:
X＝[(Sum1×65535+Count1)-(Sum2×65535+Count2)]×0.25 (3)
wherein, X is a strain measurement value, Sum1 is the overflow number of the first timer, Sum2 is the overflow number of the second timer, Count1 is the current value of the first timer Count register, and Count2 is the current value of the second timer Count register;
and S4, obtaining the equivalent wind load size according to the strain measurement value, the length H, the elastic modulus E and the section inertia moment I of the standing tree to be measured, and the first distance a and the second distance K.
Specifically, the equivalent wind load magnitude is obtained according to the following formula:
wherein, P is equivalent wind load, L is the length of the strain sensor, E is the elastic modulus of the standing tree to be tested, I is the inertia moment of the standing tree to be tested, a is a first distance, K is a second distance, X is a strain measurement value, and lambda is an error compensation coefficient.
Claims (4)
1. A method for testing the wind load of the crown of a standing tree is characterized by comprising the following steps:
s1, measuring the length, crown area and breast height of the standing tree to be measured, obtaining elastic modulus according to the tree species of the standing tree to be measured, and obtaining section moment of inertia according to the crown area and the breast height; measuring a first distance between a wind power concentration action point on the standing tree and the ground;
s2, mounting a strain sensor on the standing timber to be measured, and obtaining a second distance between the strain sensor and the ground; the strain sensor includes: the system comprises a grating ruler, a quadruple frequency circuit, a data acquisition and storage module, an interaction module, a power module and a lithium ion battery;
the grating ruler comprises a grating ruler grating and a grating ruler reading head; the grating ruler reading head is used for connecting the generated output pulse to the input port of the quadruple frequency circuit;
the quadruple frequency circuit is used for connecting a frequency doubling pulse signal output to the first pin and the second pin of the data acquisition and storage module for pulse counting acquisition;
the data acquisition and storage module is used for calculating and obtaining the dependent variable;
the interaction module is connected with the data acquisition and storage module to display the dependent variable and transmit the key control signal;
the power supply module is matched with the lithium ion battery to supply power to the grating ruler, the quadruple frequency circuit, the data acquisition and storage module and the interaction module;
the data acquisition and storage module consists of an STM32F407 single chip microcomputer and a MiniTFCard mother seat, external pulse acquisition pins of the STM32F407 single chip microcomputer are respectively connected with two output ends of a quadruple frequency circuit, the output pulses of the quadruple frequency circuit are accumulated by using ETR functions of a first timer and a second timer in the STM32F407 single chip microcomputer, and a strain measurement value is obtained by calculation according to the corresponding relation among the pulse number, the motion direction and the displacement; the STM32F407 single chip microcomputer also writes a data packet consisting of the strain data and the real-time into a data file of the mobile storage medium;
s3, detecting a strain measurement value through the strain sensor according to the following formula:
X＝[(Sum1×65535+Count1)-(Sum2×65535+Count2)]×0.25
wherein, X is a strain measurement value, Sum1 is the overflow number of the first timer, Sum2 is the overflow number of the second timer, Count1 is the current value of the first timer Count register, and Count2 is the current value of the second timer Count register;
s4, calculating according to the strain measurement value, the length of the standing timber to be measured, the elastic modulus, the section moment of inertia, the first distance and the second distance to obtain an equivalent wind load according to the following formula,
wherein, P is equivalent wind load, L is the length of the strain sensor, E is the elastic modulus of the standing tree to be measured, I is the inertia moment of the standing tree to be measured, a is a first distance, K is a second distance, X is a strain measurement value, and lambda is an error compensation coefficient.
2. The method according to claim 1, wherein installing a strain sensor on the standing timber to be tested specifically comprises:
s21, determining whether the working state of the sensor is normal, checking the electric quantity and the storage space of the sensor, and checking whether the test data is changed;
s22, if the sensor is in a normal state, drawing a mounting line at the set position of the measured trunk, and nailing a mounting steel needle according to the distance between the mounting positioning holes at the two ends of the sensor;
s23, after the steel needle penetrates through the mounting holes at the two ends of the sensor, the bolt and the nut are screwed to install the sensor on the trunk, and the strain sensor is tightly attached to the trunk during installation.
3. The test method of claim 1,
the grating ruler is used for generating A, B paths of pulse outputs with the phase difference of 90 degrees, and 1 pulse output represents that the reading head of the grating ruler generates 0.5 mu m displacement relative to the grating of the ruler;
the quadruple frequency circuit consists of a 4-channel JK trigger and a one-out-of-four data selector, A, B-phase pulses output by the grating ruler are respectively connected with 1 channel and 3 channels of the JK trigger, the outputs of the 1 channel and the 3 channel are respectively connected with 2 channel and 4 channel inputs, the output of the 2 nd channel of the JK trigger is connected with 1 channel 0 bit and 2 channel 1 bit of the data selector, the 3 rd channel output of the JK trigger is connected with 1 channel 3 bit and 2 channel 2 bit of the data selector, the outputs of the 1 channel and the 3 channel of the JK trigger are respectively connected with the input end of the data selector A, B, and the 4-channel output of the JK trigger is connected with 1 channel 2 bit and 2 channel 0 bit of the data selector; a, B two-phase output pulses of the grating ruler reading head are subjected to frequency multiplication subdivision processing through a quadruple frequency circuit, the moving direction of the grating ruler reading head is judged, the precision is improved to 2 pulses to output, and the relative displacement of 0.5 mu m generated by the grating ruler reading head is represented.
4. The test method of claim 1, wherein the strain sensor further comprises a top case, a linear guide, an overhanging measurement scale, and an L-shaped connector;
the linear guide rail is arranged on the central line of the inner wall of the top shell, a sliding block is arranged in the linear guide rail, and the reading head of the grating ruler is connected with the sliding block in the linear guide rail through an L-shaped connecting piece in a threaded fit manner;
the L-shaped connecting piece is used for ensuring that the grating ruler reading head can only slide linearly in a given direction without generating movement in other directions, and the grating ruler reading head and the linear guide rail are integrated;
the overhanging measuring scale is a stainless steel connecting rod with a rectangular cross section, one end of the overhanging measuring scale is connected with the grating scale reading head through threads, and the other end of the overhanging measuring scale is matched with a front side fixed connecting piece bolt and an adjusting nut to transmit the measured strain to the grating scale reading head.
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| CN113504025B (en) * | 2021-09-13 | 2021-12-14 | 中国航天空气动力技术研究院 | Dynamic load testing method for wind tunnel with large attack angle and low frequency structure |
| CN115290867A (en) * | 2022-05-12 | 2022-11-04 | 北京林业大学 | Method and device for detecting trunk strength of standing tree |
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