Suspension bridge sling force rapid identification method based on unmanned aerial vehicle photogrammetry

Abstract

The invention relates to a suspension bridge sling force rapid identification method based on unmanned aerial vehicle photogrammetry, and the method comprises the steps: collecting the point cloud data of a suspension bridge through arranging a three-dimensional laser scanner on the suspension bridge, carrying out the point cloud splicing and point cloud processing of the collected point cloud data, and obtaining the coordinates of an intersection point of a main cable and a sling, and the form of the main cable; the method comprises the following steps: acquiring an intersection point coordinate, performing temperature correction on the acquired intersection point coordinate, and then expanding the corrected intersection point coordinate according to a relation between pixel precision and a distance from an unmanned aerial vehicle to a main cable to obtain an unmanned aerial vehicle waypoint so as to complete planning of an unmanned aerial vehicle route; then, obtaining side lines of the main cable and the sling by adopting an image processing method, obtaining coordinates of an intersection point of the main cable and the sling, obtaining a sling force calculation parameter, and calculating the sling force according to a sling force calculation formula. According to the suspension bridge sling force rapid identification method based on unmanned aerial vehicle photogrammetry, daily sling force detection of a suspension bridge can be faster and more accurate.

Description

Technical Field

[0001] The invention relates to the technical field of bridge engineering, and in particular to a method for quickly identifying the cable forces of a suspension bridge based on unmanned aerial vehicle photogrammetry. Background Art

[0002] Suspension bridges are widely used in long-span bridges. As the important force transmission component between the main cable and the main beam, the fast and accurate identification of the cable force plays an important role in the safety of the suspension bridge. The existing methods for measuring the cable force of suspension bridges mainly include frequency method, oil pressure method, magnetic flux method and sensor method.

[0003] The frequency method is the most frequently used measurement method at present. Its principle is to artificially excite the sling to make it vibrate, identify the vibration frequency by using acceleration and other methods, and calculate the sling force based on the relationship between frequency and tension. However, due to the coupling of various factors such as boundary conditions and sag, it is inevitable to cause errors in the identification of cable force. In addition, the string vibration model is not suitable for short slings, and the measured short sling force is obviously deviated from the true value.

[0004] The principle of the oil pressure method for measuring cable force is to tension the cable through a hydraulic jack at the anchor position of the cable, but it is only applicable to the construction stage and is difficult to use for daily cable force monitoring;

[0005] The principle of the magnetic flux method is to identify the change of magnetic flux inside the electromagnetic sensor on the cable, and then identify the cable force based on the relationship between the change of magnetic flux and the cable force and temperature. However, the magnetic permeability of the cable is affected by factors such as the material properties and temperature of the cable, and the influence of these factors is variable and difficult to control. Under long-term monitoring, the monitoring results of the cable force will be affected by factors such as the sensor and temperature, resulting in insufficient reliability of the measurement results.

[0006] The sensor method measures the strain, stress and other parameters of the sensor installed on the cable, and monitors the cable force based on the relationship between stress, strain and cable force. The sensor has the characteristics of complex installation and high cost, and the life span problem has not yet been solved, making it difficult to use it for long-term cable force monitoring and measurement.

[0007] The above commonly used cable tension measurement methods are affected by many factors, resulting in limitations in their measurement accuracy and applicability. Currently, there is an urgent need for a fast and accurate cable tension measurement method to facilitate daily cable tension testing of suspension bridges. Summary of the invention

[0008] The technical problem to be solved by the present invention is to provide a method for quickly identifying the cable tension of a suspension bridge based on drone photogrammetry in response to the above-mentioned defects, which can quickly and accurately measure the cable tension of the suspension bridge.

[0009] The technical solution adopted by the present invention to solve the technical problem is: to provide a method for quickly identifying the cable force of a suspension bridge based on drone photogrammetry, comprising the following steps:

[0010] S1. Arrange multiple 3D laser scanner stations according to the design drawings of the suspension bridge, collect multiple sets of point cloud data through multiple stations, calculate the number of stations and the distance between adjacent stations, and obtain high-precision point clouds;

[0011] S2. splicing the collected point cloud data to obtain point cloud data of the suspension bridge and establish a point cloud model, segmenting the point cloud model to obtain point clouds of a single suspension cable and point clouds of a main cable segment between two adjacent cable clamps;

[0012] S3, the main cable segment and the sling are divided into multiple micro-segments, the centroid coordinates of each micro-segment are calculated, and the centroid coordinates of each micro-segment on the main cable segment and the sling are fitted using a standard catenary and a straight line, respectively, to obtain the axis equations of the main cable segment and the sling and solve them simultaneously, thereby obtaining the intersection coordinates of the main cable and the sling;

[0013] S4, performing temperature correction on the obtained intersection coordinates;

[0014] S5. Expand the corrected intersection coordinates according to the relationship between the pixel accuracy and the distance between the UAV and the main cable surface, obtain the UAV waypoints, connect the UAV waypoints in order, generate an accurate UAV route, and take orthophoto images of the main cable of the suspension bridge through the UAV;

[0015] S6. Processing the captured orthophoto to obtain the edge lines of the main cable and the sling, thereby obtaining the axis equations of the main cable and the sling, solving the axis equations of the main cable and the sling simultaneously, obtaining the coordinates of the intersection of the main cable and the sling, and calculating the horizontal distance and vertical distance between two adjacent intersections;

[0016] S7. Substituting the horizontal distance and vertical distance between two adjacent intersection points into the cable force calculation formula, the cable force of the suspension bridge can be calculated.

[0017] As a preferred embodiment of the present invention, the method for calculating the station spacing in S1 comprises the following steps:

[0018] S101, arrange the 3D laser scanner on the center line of the suspension bridge deck, set the height of the 3D laser scanner to h, the limit incident angle to α, the overlap rate between two adjacent measuring stations to ν, the bridge deck width to 2H, obtain the height B of the main cable intersection point A relative to the suspension bridge deck, substitute the above data into formula (1), and calculate the distance D between adjacent measuring stations.

[0019] D=d(1-ν)=2 cosβtanαH(1-ν) (1)

[0020] In the formula, D represents the spacing when the overlap rate between adjacent measuring stations is considered, and d represents the spacing when the overlap rate between adjacent measuring stations is not considered. Then the number of measuring stations to be arranged is calculated according to the bridge length and the spacing D between adjacent measuring stations.

[0021] As a preferred embodiment of the present invention, the method of dividing the main cable segment and the sling in S2 comprises the following steps:

[0022] S201, rotating the point cloud model so that the axis of the main beam is parallel to the X-axis, the cross section of the main beam is parallel to the Y-axis, and the Z direction is the elevation direction;

[0023] S202, projecting the rotated point cloud model onto the YOZ plane, dividing the projected two-dimensional point cloud into blocks with a width of 2 m along the Y direction, counting the number of point clouds in each block, and the two point clouds with the largest number of point clouds are the locations of the main cable surface;

[0024] S203, projecting the segmented point clouds of the main cable and the sling onto the XOY plane respectively, dividing them into blocks with a width of 2 m along the X direction, counting the number of point clouds in each block, and the n point clouds with the largest number of point clouds are the locations of the slings, where n is the number of slings on a single cable plane.

[0025] As a preferred embodiment of the present invention, the method for obtaining the main cable segment and the sling axis equation in S3 comprises the following steps:

[0026] S301, deleting the auxiliary facility point cloud around the main cable segment point cloud to obtain an accurate point cloud of the main cable segment;

[0027] S302, split the main cable segment point cloud into multiple micro segments of equal length along the X direction, project each micro segment along its vertical direction to obtain the projected point cloud coordinates (X, Y, Z), randomly select 3 points from the projected point cloud for circle fitting, and traverse all the points in turn, and fit the calculated circle center coordinates (X i , Y i , Z i ) and radius R i Statistically, the radius R0 with the highest probability of occurrence is obtained. The center of the circle corresponding to this radius is the centroid coordinate (X0, Y0, Z0) of the main cable of this micro-segment. The above operation is performed on all micro-segments to obtain the centroid coordinate (X0, Y0, Z0) of each micro-segment. i0 , Y i0 , Z i0 );

[0028] S303. Fit all centroid coordinates using a standard catenary curve to obtain the axis equation of the main cable segment, as shown in formula (2):

[0029]

[0030] In the formula, q is the concentration of the main cable's deadweight along the main cable's length, U is the horizontal component of the main cable's axial force, li is the horizontal distance between the i-th intersection and the i+1 intersection, and hi is the vertical distance between the i-th intersection and the i+1 intersection;

[0031] S304, using the same method to calculate the centroid coordinates (X d0 , Y d0 , Z d0 ), all centroid coordinates are fitted with straight lines to obtain the axis equation of the sling, as shown in formula (3):

[0032] y(x)=ax+b (3)

[0033] S305, combine the two axis equations and solve to obtain the coordinates of the main cable intersection point (x i ,y i , z i ).

[0034] As a preferred embodiment of the present invention, the method for temperature correction of the main cable intersection coordinates in S4 comprises the following steps:

[0035] S401, the elevation change δf of the main cable mid-span intersection caused by the temperature change of the main cable in the mid-span 01x make corrections;

[0036] S402, the elevation change δf of the main cable mid-span intersection caused by the temperature change of the side span main cable 02x make corrections;

[0037] S403, the elevation change δf of the main cable mid-span intersection caused by the temperature change of the bridge pier 03x As a preferred embodiment of the present invention, the elevation change δf of the main cable mid-span intersection in S401 is 01x The calculation is performed according to the catenary theory, as shown in formula (4):

[0038]

[0039] In the formula, S represents the length of the stressed cable in the bridge state, q refers to the main cable deadweight load, H refers to the main cable horizontal force under the bridge state, θ C is the main cable expansion coefficient, ΔT C is the temperature change of the main cable, L0 refers to the calculated span of the mid-span main cable, C n As shown in formula (5),

[0040]

[0041] In the formula, n represents the span ratio;

[0042] The elevation change δf of the main cable mid-span intersection in S402 02x Calculate as shown in formula (6):

[0043]

[0044] Where L1 and L1 refer to the spans of the left and right side spans of the suspension bridge, respectively, and H1 and H2 refer to the heights of the left and right piers;

[0045] The elevation change δf of the main cable mid-span intersection in S403 03x Calculate as shown in formula (7):

[0046]

[0047] In the formula, θ P is the linear expansion coefficient of the main tower;

[0048] Thus, the elevation change of the main cable intersection point in the span under temperature change is obtained, as shown in formula (8):

[0049] δf 0x =δf 01x +Δf 02x +Δf 03x (8)

[0050] According to the change of the main cable mid-span intersection point, the coordinates of the main cable mid-span intersection point after temperature change (x0, y0 + Δf0) are obtained and combined with the tower top coordinates to establish a new parabolic equation y i ′, and then calculate the coordinates of all the intersection points of the main cables in the main span, as shown in formula (9):

[0051]

[0052] In the formula, x i is the x-coordinate of the ith sling.

[0053] As a preferred embodiment of the present invention, the method for generating a drone route in S5 comprises the following steps:

[0054] S501, using a thermometer to obtain the temperature when the drone collects the image of the suspension bridge, and making a difference with the temperature when the point cloud data is collected to correct the temperature of the main cable intersection;

[0055] S502, calculating the position of the UAV from the main cable surface according to the pixel accuracy and the shooting range, as shown in formula (10), expanding the main cable intersection outward to obtain the UAV waypoint;

[0056]

[0057] Where D represents the shooting range, D = 2L + 2δ = 2L + 2, where δ represents half of the cable clamp width, which is 1m, d represents the imaging sensor width, and L represents the cable spacing;

[0058] S503, using line segments to connect the UAV waypoints in order, setting the UAV flight speed, yaw angle and gimbal angle, generating a precise UAV route, and using the UAV to take orthophoto images of the main cable segment of the suspension bridge.

[0059] As a preferred embodiment of the present invention, the method for obtaining the main cable and the sling edge line in S6 comprises the following steps:

[0060] S601, marking the orthophoto taken by the drone, establishing a deep learning training set for training, and segmenting the images of the main cable and the sling from the image;

[0061] S602: Using the obvious grayscale gradient between the main cables and slings and the background edge, the edge lines of the main cables and slings are set by calculating the grayscale gradient.

[0062] As a preferred embodiment of the present invention, the method for obtaining the coordinates of the intersection of the main cable and the sling in S6 comprises the following steps:

[0063] S603, the upper and lower edges of the main cable are fitted with a quadratic parabola, y1 = ax 2 +bx+c and y2=ex 2 +fx+g, for the fitted edge line y i =q i x+p i Generate multiple straight lines along the span direction in its normal direction, and the edge lines intersect the normal lines at points ((x 11 ,y 11 ),(x 21 ,y 21 ))、((x 12 ,y 12 ),(x 22 ,y 22 ))...((x1i,y1i),(x2i,y2i)) and then 11 ,y 11 ),(x 21 ,y 21 ))、((x 12 ,y 12 ),(x 22 ,y 22 ))...((x 1i ,y 1i ),(x 2i ,y 2i)) The corresponding intersection point is the midpoint of the ball, and the point on the main cable axis is obtained. The point on the main cable axis is fitted with a parabola to obtain the main cable axis equation, y zi =A I x 2 +B I x+C I ;

[0064] S604, use the same method to perform straight line fitting on the edge of the sling to obtain the axis equation of the sling, y di =B dI x+C dI ;

[0065] S605, solve the two axis equations simultaneously to obtain the main cable intersection coordinates (x i ,y i ), calculate the horizontal distance L between adjacent main cable intersections i and vertical distance H i .

[0066] As a preferred embodiment of the present invention, the horizontal distance and vertical distance between adjacent main cable intersections are substituted into the calculation formula of the suspension bridge cable force, as shown in formula (12),

[0067] P i =U sinh(α i )-U sinh(2β i-1 -α i-1 ) (12)

[0068] In the formula,

[0069] Calculate the cable forces in a suspension bridge.

[0070] Compared with the existing technology, the benefits of this solution are as follows: by deploying a three-dimensional laser scanner on the suspension bridge to collect point cloud data of the suspension bridge, the collected point cloud data is subjected to point cloud stitching and point cloud processing to obtain the intersection coordinates of the main cable and the sling and the main cable shape, and the obtained intersection coordinates are temperature corrected, and then the corrected intersection coordinates are expanded according to the relationship between the pixel accuracy and the distance of the drone from the main cable to obtain the drone waypoints, thereby completing the drone route planning, and collecting orthophotos of the main cable segment by the drone, and then using image processing methods to obtain the main cable and sling edge lines, obtain the intersection coordinates of the main cable and the sling, obtain the cable force calculation parameters, and calculate the sling force according to the cable force calculation formula, which can make the daily cable force detection of the suspension bridge faster and more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Figure 1 Schematic diagram of the structure of the station distance calculation principle in this embodiment.

[0072] Figure 2 It is the projection density distribution map on the XOY plane.

[0073] Figure 3 It is the YOZ plane projection density distribution map.

[0074] Figure 4 Schematic diagram of the structure of main cable segment slices in the main cable intersection identification flow chart.

[0075] Figure 5 Schematic diagram of the structure of slice projection in the main cable intersection point identification flow chart.

[0076] Figure 6 Schematic diagram of the structure of three-point circle fitting in the main cable intersection point identification flow chart.

[0077] Figure 7 Schematic diagram of the structure of probability density statistics in the main cable intersection point identification flow chart.

[0078] Figure 8 Schematic diagram of the structure of the main cable ancillary facility point cloud elimination in the main cable intersection identification flow chart.

[0079] Fig. 9 Schematic diagram of the structure of the main cable segment axis fitting in the main cable intersection identification flow chart.

[0080] Fig.10 Simplified model diagram of a suspension bridge.

[0081] Fig.11 Simplified model diagram of the main span catenary.

[0082] Fig.12 Simplified model diagram for edge span.

[0083] Fig.13 Schematic diagram of the waypoint extension distance calculation principle.

[0084] Fig.14 This is the main cable route planning diagram for the suspension bridge.

[0085] Fig.15 Schematic diagram of the calculation principle of sling force. DETAILED DESCRIPTION

[0086] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described below are only used to explain the present invention and will not limit the protection scope of the present invention.

[0087] The terms "first", "second" and the like in the specification, claims and embodiments of the present application are used to distinguish similar objects rather than to describe a specific order or sequential sequence.

[0088] The present invention is further described in detail below through preferred specific embodiments:

[0089] The method for quickly identifying the cable force of a suspension bridge based on drone photogrammetry in this embodiment includes the following steps:

[0090] As attached Figure 1 As shown:

[0091] S1. Arrange multiple 3D laser scanner measuring stations according to the design drawings of the suspension bridge, collect multiple groups of point cloud data through the multiple measuring stations, calculate the number of measuring station arrangements and the distance between adjacent measuring stations, and obtain high-precision point clouds. Specifically, the method for calculating the measuring station distance in S1 includes the following steps:

[0092] S101, arrange the 3D laser scanner on the center line of the suspension bridge deck, set the height of the 3D laser scanner to h, the limit incident angle to α, the overlap rate between two adjacent measuring stations to ν, the bridge deck width to 2H, obtain the height B of the main cable intersection point A relative to the suspension bridge deck, substitute the above data into formula (1), and calculate the distance D between adjacent measuring stations.

[0093] D=d(1-ν)=2 cosβtanαH(1-ν) (1)

[0094] In the formula, D represents the spacing when the overlap rate between adjacent measuring stations is considered, and d represents the spacing when the overlap rate between adjacent measuring stations is not considered. Then the number of measuring stations to be arranged is calculated according to the bridge length and the spacing D between adjacent measuring stations.

[0095] As attached Figure 2 and attached Figure 3 As shown:

[0096] S2. Splicing the collected point cloud data to obtain point cloud data of the suspension bridge and establish a point cloud model. Segmenting the point cloud model to obtain point clouds of a single sling and point clouds of a main cable segment between two adjacent cable clamps. Specifically, the method of segmenting the main cable segment and the sling in S2 includes the following steps:

[0097] S201, rotating the point cloud model so that the axis of the main beam is parallel to the X-axis, the cross section of the main beam is parallel to the Y-axis, and the Z direction is the elevation direction;

[0098] S202, projecting the rotated point cloud model onto the YOZ plane, dividing the projected two-dimensional point cloud into blocks with a width of 2 m along the Y direction, counting the number of point clouds in each block, and the two point clouds with the largest number of point clouds are the locations of the main cable surface;

[0099] S203, projecting the segmented point clouds of the main cable and the sling onto the XOY plane respectively, dividing them into blocks with a width of 2 m along the X direction, counting the number of point clouds in each block, and the n point clouds with the largest number of point clouds are the locations of the slings, where n is the number of slings on a single cable plane.

[0100] As attached Figures 4 to 9 As shown:

[0101] S3, the main cable segment and the sling are divided into multiple micro-segments, the centroid coordinates of each micro-segment are calculated, and the centroid coordinates of each micro-segment on the main cable segment and the sling are fitted with a standard catenary and a straight line, respectively, to obtain the axis equations of the main cable segment and the sling and solve them simultaneously, so as to obtain the coordinates of the intersection of the main cable and the sling. Specifically, the method for obtaining the axis equations of the main cable segment and the sling in S3 includes the following steps:

[0102] S301, deleting the auxiliary facility point cloud around the main cable segment point cloud to obtain an accurate point cloud of the main cable segment;

[0103] S302, split the main cable segment point cloud into multiple micro segments of equal length along the X direction, project each micro segment along its vertical direction to obtain the projected point cloud coordinates (X, Y, Z), randomly select 3 points from the projected point cloud for circle fitting, and traverse all the points in turn, and fit the calculated circle center coordinates (X i , Y i , Z i ) and radius R i Statistically, the radius R0 with the highest probability of occurrence is obtained. The center of the circle corresponding to this radius is the centroid coordinate (X0, Y0, Z0) of the main cable of this micro-segment. The above operation is performed on all micro-segments to obtain the centroid coordinate (X0, Y0, Z0) of each micro-segment. i0 , Y i0 , Z i0 );

[0104] S303. Fit all centroid coordinates using a standard catenary curve to obtain the axis equation of the main cable segment, as shown in formula (2):

[0105]

[0106] In the formula, q is the concentration of the main cable's deadweight along the main cable's length, U is the horizontal component of the main cable's axial force, li is the horizontal distance between the i-th intersection and the i+1 intersection, and hi is the vertical distance between the i-th intersection and the i+1 intersection;

[0107] S304, using the same method to calculate the centroid coordinates (X d0 , Y d0 , Z d0), all centroid coordinates are fitted with straight lines to obtain the axis equation of the sling, as shown in formula (3):

[0108] y(x)=ax+b (3)

[0109] S305, combine the two axis equations and solve to obtain the coordinates of the main cable intersection point (x i ,y i , z i ).

[0110] As attached Figures 10-12 As shown:

[0111] S4, performing temperature correction on the obtained intersection coordinates, including the following steps:

[0112] S401, the elevation change δf of the main cable mid-span intersection caused by the temperature change of the main cable in the mid-span 01x To make corrections, specifically, the following steps are included:

[0113] The calculation is performed according to the catenary theory, as shown in formula (4):

[0114]

[0115] In the formula, S represents the length of the stressed cable in the bridge state, q refers to the main cable deadweight load, H refers to the main cable horizontal force under the bridge state, θ C is the main cable expansion coefficient, ΔT C is the temperature change of the main cable, L0 refers to the calculated span of the mid-span main cable, C n As shown in formula (5),

[0116]

[0117] In the formula, n represents the span ratio;

[0118] S402, the elevation change δf of the main cable mid-span intersection caused by the temperature change of the side span main cable 02x To make corrections, specifically, as shown in formula (6),

[0119]

[0120] Where L1 and L1 refer to the spans of the left and right side spans of the suspension bridge, respectively, and H1 and H2 refer to the heights of the left and right piers;

[0121] S403, the elevation change δf of the main cable mid-span intersection caused by the temperature change of the bridge pier 03x To make corrections, specifically, as shown in formula (7):

[0122]

[0123] In the formula, θ P is the linear expansion coefficient of the main tower;

[0124] Thus, the elevation change of the main cable intersection point in the span under temperature change is obtained, as shown in formula (8):

[0125] δf 0x =δf 01x +Δf 02x +Δf 03x (8)

[0126] According to the change of the main cable mid-span intersection point, the coordinates of the main cable mid-span intersection point after temperature change (x0, y0 + Δf0) are obtained and combined with the tower top coordinates to establish a new parabolic equation y i ′, and then calculate the coordinates of all the intersection points of the main cables in the main span, as shown in formula (9):

[0127]

[0128] In the formula, x i is the x-coordinate of the ith sling.

[0129] As attached Fig.13 As shown:

[0130] S5. Expand the corrected intersection coordinates according to the relationship between the pixel accuracy and the distance between the UAV and the main cable surface, obtain the UAV waypoints, connect the UAV waypoints in order, generate an accurate UAV route, and use the UAV to take orthophotos of the main cable of the suspension bridge. Specifically, the steps include:

[0131] S501, using a thermometer to obtain the temperature when the drone collects the image of the suspension bridge, and making a difference with the temperature when the point cloud data is collected to correct the temperature of the main cable intersection;

[0132] S502, calculating the position of the UAV from the main cable surface according to the pixel accuracy and the shooting range, as shown in formula (10), expanding the main cable intersection outward to obtain the UAV waypoint;

[0133]

[0134] Where D represents the shooting range, D = 2L + 2δ = 2L + 2, where δ represents half of the cable clamp width, which is 1m, d represents the imaging sensor width, and L represents the cable spacing;

[0135] S503, using line segments to connect the UAV waypoints in order, setting the UAV flight speed, yaw angle and gimbal angle, generating a precise UAV route, and using the UAV to take orthophoto images of the main cable segment of the suspension bridge.

[0136] As attached Fig.14 As shown:

[0137] S6. Processing the captured orthophoto to obtain the edge lines of the main cable and the sling, thereby obtaining the axis equations of the main cable and the sling, solving the axis equations of the main cable and the sling simultaneously, obtaining the coordinates of the intersection of the main cable and the sling, and calculating the horizontal distance and vertical distance between two adjacent intersections. Specifically, the process includes the following steps:

[0138] S601, marking the orthophoto taken by the drone, establishing a deep learning training set for training, and segmenting the images of the main cable and the sling from the image;

[0139] S602, using the obvious grayscale gradient between the main cable and the sling and the background edge, and setting the edge lines of the main cable and the sling by calculating the grayscale gradient;

[0140] S603, the upper and lower edges of the main cable are fitted with a quadratic parabola, y1 = ax 2 +bx+c and y2=ex 2 +fx+g, for the fitted edge line y i =q i x+p i Generate multiple straight lines along the span direction in its normal direction, and the edge lines intersect the normal lines at points ((x 11 ,y 11 ),(x 21 ,y 21 ))、((x 12 ,y 12 ),(x 22 ,y 22 ))...((x1i,y1i),(x2i,y2i)) and then 11 ,y 11 ),(x 21 ,y 21 ))、((x 12 ,y 12 ),(x 22 ,y 22 ))...((x 1i ,y 1i ),(x 2i ,y 2i )) The corresponding intersection point is the midpoint of the ball, and the point on the main cable axis is obtained. The point on the main cable axis is fitted with a parabola to obtain the main cable axis equation, y zi =A I x 2 +B I x+C I ;

[0141] S604, use the same method to perform straight line fitting on the edge of the sling to obtain the axis equation of the sling, y di =B dI x+C dI ;

[0142] S605, solve the two axis equations simultaneously to obtain the main cable intersection coordinates (x i ,y i ), calculate the horizontal distance L between adjacent main cable intersections i and vertical distance H i .

[0143] As attached Fig.15 As shown:

[0144] S7. Substituting the horizontal distance and vertical distance between two adjacent intersection points into the cable force calculation formula, the cable force of the suspension bridge can be calculated, as shown in formula (12):

[0145] P i =U sinh(α i )-U sinh(2β i-1 -α i-1 ) (12)

[0146] In the formula,

[0147] The preferred implementation modes of the present application are described in detail above in conjunction with the accompanying drawings. Typical known structures and common knowledge technologies in the preferred implementation modes are not described in detail here. Ordinary technicians in the relevant field can improve and implement the technical solutions of the present invention based on their own abilities under the inspiration given by the present implementation modes. Some typical known structures, known methods or common knowledge technologies should not become obstacles for ordinary technicians in the relevant field to implement the present application.

[0148] The scope of protection required by this application shall be based on the contents of its claims, and the contents recorded in the invention content, specific implementation methods and drawings of the specification shall be used to interpret the claims.

[0149] Within the technical concept of the present application, several modifications may be made to the specific implementation methods of the present application, and these modified specific implementation methods should also be regarded as within the protection scope of the present application.

Claims

1. A method for quickly identifying the cable force of a suspension bridge based on drone photogrammetry, characterized in that: The following steps are involved: S1. Arrange multiple 3D laser scanner stations according to the design drawings of the suspension bridge, collect multiple sets of point cloud data through multiple stations, calculate the number of stations and the distance between adjacent stations, and obtain high-precision point clouds; S2. splicing the collected point cloud data to obtain point cloud data of the suspension bridge and establish a point cloud model, segmenting the point cloud model to obtain point clouds of a single suspension cable and point clouds of a main cable segment between two adjacent cable clamps; S3, the main cable segment and the sling are divided into multiple micro-segments, the centroid coordinates of each micro-segment are calculated, and the centroid coordinates of each micro-segment on the main cable segment and the sling are fitted using a standard catenary and a straight line, respectively, to obtain the axis equations of the main cable segment and the sling and solve them simultaneously, thereby obtaining the intersection coordinates of the main cable and the sling; S4, performing temperature correction on the obtained intersection coordinates; S5. Expand the corrected intersection coordinates according to the relationship between the pixel accuracy and the distance between the UAV and the main cable surface, obtain the UAV waypoints, connect the UAV waypoints in order, generate an accurate UAV route, and take orthophoto images of the main cable of the suspension bridge through the UAV; S6. Processing the captured orthophoto to obtain the edge lines of the main cable and the sling, thereby obtaining the axis equations of the main cable and the sling, solving the axis equations of the main cable and the sling simultaneously, obtaining the coordinates of the intersection of the main cable and the sling, and calculating the horizontal distance and vertical distance between two adjacent intersections; S7. Substituting the horizontal distance and vertical distance between two adjacent intersection points into the cable force calculation formula, the cable force of the suspension bridge can be calculated.

2. The method for rapid identification of cable forces of a suspension bridge based on drone photogrammetry according to claim 1 is characterized by: The method for calculating the station spacing in S1 includes the following steps: S101, arrange the 3D laser scanner on the center line of the suspension bridge deck, set the height of the 3D laser scanner to h, the limit incident angle to α, the overlap rate between two adjacent measuring stations to ν, the bridge deck width to 2H, obtain the height B of the main cable intersection point A relative to the suspension bridge deck, substitute the above data into formula (1), and calculate the distance D between adjacent measuring stations. D=d(1-ν)=2cosβtanαH(1-ν) (1) In the formula, D represents the spacing when the overlap rate between adjacent measuring stations is considered, and d represents the spacing when the overlap rate between adjacent measuring stations is not considered. Then the number of measuring stations to be arranged is calculated according to the bridge length and the spacing D between adjacent measuring stations.

3. The method for rapid identification of cable forces of a suspension bridge based on drone photogrammetry according to claim 1 is characterized in that: The method for dividing the main cable segment and the sling in S2 comprises the following steps: S201, rotating the point cloud model so that the axis of the main beam is parallel to the X-axis, the cross section of the main beam is parallel to the Y-axis, and the Z direction is the elevation direction; S202, projecting the rotated point cloud model onto the YOZ plane, dividing the projected two-dimensional point cloud into blocks with a width of 2 m along the Y direction, counting the number of point clouds in each block, and the two point clouds with the largest number of point clouds are the locations of the main cable surface; S203, projecting the segmented point clouds of the main cable and the sling onto the XOY plane respectively, dividing them into blocks with a width of 2 m along the X direction, counting the number of point clouds in each block, and the n point clouds with the largest number of point clouds are the locations of the slings, where n is the number of slings on a single cable plane.

4. The method for rapid identification of cable forces of a suspension bridge based on drone photogrammetry according to claim 1 is characterized in that: The method for obtaining the main cable segment and the sling axis equation in S3 includes the following steps: S301, deleting the auxiliary facility point cloud around the main cable segment point cloud to obtain an accurate point cloud of the main cable segment; S302, split the main cable segment point cloud into multiple micro segments of equal length along the X direction, project each micro segment along its vertical direction to obtain the projected point cloud coordinates (X, Y, Z), randomly select 3 points from the projected point cloud for circle fitting, and traverse all the points in turn, and fit the calculated circle center coordinates (X i , Y i , Z i ) and radius R i Statistically, the radius R0 with the highest probability of occurrence is obtained. The center of the circle corresponding to this radius is the centroid coordinate (X0, Y0, Z0) of the main cable of this micro-segment. The above operation is performed on all micro-segments to obtain the centroid coordinate (X0, Y0, Z0) of each micro-segment. i0 , Y i0 , Z i0 ); S303. Fit all centroid coordinates using a standard catenary curve to obtain the axis equation of the main cable segment, as shown in formula (2): In the formula, q is the concentration of the main cable's deadweight along the main cable's length, U is the horizontal component of the main cable's axial force, li is the horizontal distance between the i-th intersection and the i+1 intersection, and hi is the vertical distance between the i-th intersection and the i+1 intersection; S304, using the same method to calculate the centroid coordinates (X d0 , Y d0 , Z d0 ), all centroid coordinates are fitted with straight lines to obtain the axis equation of the sling, as shown in formula (3): y(x)=ax+b (3) S305, combine the two axis equations and solve to obtain the coordinates of the main cable intersection point (x i ,y i , z i ).

5. The method for rapid identification of cable forces of a suspension bridge based on drone photogrammetry according to claim 1 is characterized in that: The method for performing temperature correction on the main cable intersection coordinates in S4 comprises the following steps: S401, the elevation change δf of the main cable mid-span intersection caused by the temperature change of the main cable in the mid-span 01x make corrections; S402, the elevation change δf of the main cable mid-span intersection caused by the temperature change of the side span main cable 02x make corrections; S403, the elevation change δf of the main cable mid-span intersection caused by the temperature change of the bridge pier 03x Make corrections.

6. The method for rapid identification of cable forces of a suspension bridge based on drone photogrammetry according to claim 5 is characterized in that: The elevation change δf of the main cable mid-span intersection in S401 01x The calculation is performed according to the catenary theory, as shown in formula (4): In the formula, S represents the length of the stressed cable in the bridge state, q refers to the main cable deadweight load, H refers to the main cable horizontal force under the bridge state, θ C is the main cable expansion coefficient, ΔT C is the temperature change of the main cable, L0 refers to the calculated span of the mid-span main cable, C n As shown in formula (5), In the formula, n represents the span ratio; The elevation change δf of the main cable mid-span intersection in S402 02x Calculate as shown in formula (6): Where L1 and L1 refer to the spans of the left and right side spans of the suspension bridge, respectively, and H1 and H2 refer to the heights of the left and right piers; The elevation change δf of the main cable mid-span intersection in S403 03x Calculate as shown in formula (7): In the formula, θ P is the linear expansion coefficient of the main tower; Thus, the elevation change of the main cable intersection point in the span under temperature change is obtained, as shown in formula (8): δf 0x =δf 01x +Δf 02x +Δf 03x (8) According to the change of the main cable mid-span intersection point, the coordinates of the main cable mid-span intersection point after temperature change (x0, y0 + Δf0) are obtained and combined with the tower top coordinates to establish a new parabolic equation y′ i , and calculate the coordinates of all intersection points of the main cables in the main span, as shown in formula (9): In the formula, x i is the x-coordinate of the ith sling.

7. The method for rapid identification of cable forces of a suspension bridge based on drone photogrammetry according to claim 1 is characterized in that: The method for generating a drone route in S5 includes the following steps: S501, using a thermometer to obtain the temperature when the drone collects the image of the suspension bridge, and making a difference with the temperature when the point cloud data is collected to correct the temperature of the main cable intersection; S502, calculating the position of the UAV from the main cable surface according to the pixel accuracy and the shooting range, as shown in formula (10), expanding the main cable intersection outward to obtain the UAV waypoint; Where D represents the shooting range, D = 2L + 2δ = 2L + 2, where δ represents half of the cable clamp width, which is 1m, d represents the imaging sensor width, and L represents the cable spacing; S503, using line segments to connect the UAV waypoints in order, setting the UAV flight speed, yaw angle and gimbal angle, generating a precise UAV route, and using the UAV to take orthophoto images of the main cable segment of the suspension bridge.

8. The method for rapid identification of cable forces of a suspension bridge based on drone photogrammetry according to claim 1 is characterized in that: The method for obtaining the main cable and the sling edge line in S6 includes the following steps: S601, marking the orthophoto taken by the drone, establishing a deep learning training set for training, and segmenting the images of the main cable and the sling from the image; S602: Using the obvious grayscale gradient between the main cables and slings and the background edge, the edge lines of the main cables and slings are set by calculating the grayscale gradient.

9. The method for rapid identification of cable forces of a suspension bridge based on drone photogrammetry according to claim 8 is characterized in that: The method for obtaining the coordinates of the intersection of the main cable and the sling in S6 comprises the following steps: S603, the upper and lower edges of the main cable are fitted with a quadratic parabola, y1 = ax 2 +bx+c and y2=ex 2 +fx+g, for the fitted edge line y i =q i x+p i Generate multiple straight lines along the span direction in its normal direction, and the edge lines intersect the normal lines at points ((x 11 ,y 11 ),(x 21 ,y 21 ))、((x 12 ,y 12 ),(x 22 ,y 22 ))...((x1i,y1i),(x2i,y2i)) and then 11 ,y 11 ),(x 21 ,y 21 ))、((x 12 ,y 12 ),(x 22 ,y 22 ))...((x 1i ,y 1i ),(x 2i ,y 2i )) The corresponding intersection point is the midpoint of the ball, and the point on the main cable axis is obtained. The point on the main cable axis is fitted with a parabola to obtain the main cable axis equation, y zi =A I x 2 +B I x+C I ; S604, use the same method to perform straight line fitting on the edge of the sling to obtain the axis equation of the sling, y di =B dI x+C dI ; S605, solve the two axis equations simultaneously to obtain the main cable intersection coordinates (x i ,y i ), calculate the horizontal distance L between adjacent main cable intersections i and vertical distance H i .

10. The method for rapid identification of cable forces of a suspension bridge based on drone photogrammetry according to claim 1 is characterized in that: Substitute the horizontal distance and vertical distance between the adjacent main cable intersections into the calculation formula of the suspension bridge cable force, as shown in formula (12): P i =U sinh(α i )-U sinh(2β i-1 -α i-1 ) (12) In the formula, Calculate the cable forces in a suspension bridge.

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