CN112284509A - Bridge structure vibration mode measuring method based on mobile phone video - Google Patents
Bridge structure vibration mode measuring method based on mobile phone video Download PDFInfo
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- CN112284509A CN112284509A CN202011042730.XA CN202011042730A CN112284509A CN 112284509 A CN112284509 A CN 112284509A CN 202011042730 A CN202011042730 A CN 202011042730A CN 112284509 A CN112284509 A CN 112284509A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06V—IMAGE OR VIDEO RECOGNITION OR UNDERSTANDING
- G06V10/00—Arrangements for image or video recognition or understanding
- G06V10/40—Extraction of image or video features
- G06V10/44—Local feature extraction by analysis of parts of the pattern, e.g. by detecting edges, contours, loops, corners, strokes or intersections; Connectivity analysis, e.g. of connected components
Abstract
The invention discloses a bridge structure vibration mode measuring method based on single mobile phone photography, which comprises the following steps: recording a bridge video through a mobile phone camera to obtain a video sample; selecting a bridge vibration contour line with large color difference from a video sample as an identification object of the bridge vibration mode; identifying an upper contour line and a lower contour line of a video sample, and obtaining a static balance curve of the video sample through the upper contour line and the lower contour line; obtaining an original vibration mode sample of the video sample through the upper contour line and the static balance curve; and obtaining the bridge vibration mode through the original vibration mode sample. The vibration mode measurement of the bridge structure can be completed by using one mobile phone to shoot, the structural characteristics of the surface of the structure to be measured, such as texture, pattern background and the like of the target surface, are directly utilized as a measurement area, so that the method has the advantages of simple and convenient experiment operation, low requirement on video quality, low cost, convenience in popularization, wide video acquisition source, no need of professional training and the like.
Description
Technical Field
The invention belongs to the field of bridge structure health monitoring, and particularly relates to a bridge structure vibration mode measuring method based on a mobile phone video.
Background
The measurement of the vibration information of the bridge structure is the essential content for the health monitoring of the bridge structure. The vibration information of the structure reflects the overall safety performance of the bridge and is an important data source for identifying the structural damage of the bridge and evaluating the safety state. The vibration information of the structure comprises key parameters such as natural vibration frequency, vibration mode, damping coefficient and the like. At present, a mature method for measuring the natural vibration frequency and the damping coefficient is available, but the natural vibration frequency and the damping coefficient have poor effects on structural damage identification and safety state evaluation.
The method for measuring the vibration mode of the bridge structure can be divided into a contact type measuring method and a non-contact type measuring method. The contact measuring method mainly adopts sensors of the types of an accelerometer, an inclinometer, a displacement meter, a GPS, a differential pressure transmitter and the like to measure. The contact type measuring method has the advantage of relatively high accuracy of measured data. However, the existing method has the following disadvantages: (1) the number of the measuring points is very limited, and a high-order vibration mode cannot be obtained. (2) An external power supply and data acquisition and transmission equipment are required. (3) The sensor and the acquisition instrument thereof have high equipment cost and high installation difficulty. (4) The synchronism of the data of each measuring point is not high.
The non-contact measuring method mainly includes a laser scanning method, a method based on machine vision, and the like. The laser scanning method is high in cost, the laser array is not strong in synchronism, the weather influence is large, and binocular measurement is generally needed. In the existing measuring method based on machine vision, in order to obtain a vibration time-course curve of a preset measuring point, a high-definition video image must be acquired, and at the moment, an industrial high-speed camera must be adopted. However, such a camera is too costly, and requires a certain number of operators, and the processing of image data needs to be completed by the cooperation of a highly configured computer.
Disclosure of Invention
The invention belongs to a non-contact vibration mode measuring method based on machine vision. The invention provides a bridge structure vibration mode measuring method based on single mobile phone photography, aiming at the defects of the traditional bridge vibration mode measuring method. The measuring method adopts a machine vision dynamic tracking method based on mobile phone photography.
The invention achieves the purpose through at least one of the following technical schemes.
A bridge structure vibration mode measuring method based on single mobile phone photography comprises the following steps:
recording a bridge video through a mobile phone camera to obtain a video sample;
selecting a bridge vibration contour line with large color difference from a video sample as an identification object of the bridge vibration mode;
identifying an upper contour line and a lower contour line of a video sample, and obtaining a static balance curve of the video sample through the upper contour line and the lower contour line;
obtaining an original vibration mode sample of the video sample through the upper contour line and the static balance curve;
and obtaining the bridge vibration mode through the original vibration mode sample.
Further, a conventional mobile phone lens is adopted for video recording. The invention needs to acquire the contour of the bridge instead of the accurate structural displacement, has low requirement on the image precision, can meet the requirement by a conventional mobile phone camera without a professional camera or an industrial camera, can effectively reduce the cost and is convenient to use.
Further, the obtaining the video sample specifically includes: and acquiring a video capable of identifying the vibration profile of the bridge structure as a video sample.
Further, a single mobile phone is adopted for video recording.
Further, environmental stimuli are used during the measurement process, including but not limited to vehicle loads or wind loads.
Further, the upper contour line and the lower contour line of the video sample are identified through a video image contour identification technology.
Further, the identification of the upper contour line and the lower contour line of the video sample, and the obtaining of the static balance curve of the video sample through the upper contour line and the lower contour line specifically include:
respectively identifying the upper contour line f of each bridge vibration contour lineGo up i(x) And lower contour line fLower i(x) I.e. the position where the amplitude is maximal;
calculating the upper contour line and the lower contour line of the video sample according to the following formula to obtain a static balance curve f of the bridge structure in the video sampleBalance i(x)；
fBalance i(x)＝[fGo up i(x)+fLower i(x)]/2
Further, the obtaining of the original mode shape sample of the video sample through the upper contour line and the static balance curve specifically includes: by the upper contour f of the video sampleGo up i(x) And static equilibrium curve fBalance i(x) Obtaining the original mode shape sample fi(x) The formula is as follows:
fi(x)＝fgo up i(x)-fBalance i(x)
Further, the bridge video is recorded through a mobile phone camera, n video samples are obtained from the obtained video samples, and the value range of the video samples is that n is more than or equal to 10 and less than or equal to 20.
Further, the obtaining of the bridge vibration mode through the original vibration mode sample specifically includes:
for the ith original mode shape sample fi(x) Performing normalization operation to obtain vibration mode sample for arithmetic mean
The concrete formula is
Where max (f)i(x) Is the original vibration mode sample fi(x) The maximum observed value of (a);
performing arithmetic mean operation on the sample
And obtaining the final bridge vibration mode f (x).
Compared with the prior art, the invention can realize the following beneficial effects:
(1) the method solves the defect that the traditional bridge dynamic characteristic identification method needs to artificially apply excitation to the bridge, and the structural vibration mode measurement of the invention adopts environment excitation such as vehicle load, wind load and the like, does not need additional excitation sources, does not need to manage and process traffic on the bridge in the measurement process, and does not have adverse effect on the bridge.
(2) The vibration mode measurement of the bridge structure can be completed by using one mobile phone to shoot, and the problem that the high-order vibration mode cannot be obtained due to limited measuring points in the traditional measurement method is solved.
(3) The bridge structure vibration testing method solves the problem of testing errors caused by direct connection of an acceleration sensor and the like with a tested structure in field wiring, secondary integration, remote transmission, electromagnetic interference and the like in the traditional bridge structure vibration testing method, and the bridge structure vibration testing method takes a mobile phone camera as a measuring device to realize remote non-contact dynamic displacement monitoring of the bridge structure.
(4) The traditional measuring method firstly measures the displacement of the designated index points on the bridge structure accurately, and then connects the displacement of a series of index points into the vibration mode curve of the structure. The mark point may be blurred or the recognition resolution may be degraded due to the change in weather conditions. The conventional method has extremely strong light sensitivity, even needs extra supplementary lighting to finish measurement, and influences the measurement result with slight interference. The method for recognizing the vibration contour of the structure does not need to designate a mark point or recognize the displacement of the mark point, so that the method is insensitive to the influence of weather factors. The method and the device identify the vibration contour of the structure, and even if double images appear in the image or the bridge structure is partially shielded, the contour of the bridge structure can be identified according to the observed information. The problem of measuring the misalignment caused by weather reasons is solved, for example, fog, rain or other light changes can cause the camera can't effectively reliably to the target point go on discerning the problem.
(5) The method solves the problem that the damage identification and the safety state evaluation can be carried out only by obtaining the real vibration mode of the structure under a real world coordinate system through coordinate transformation in the traditional vision vibration mode measurement method. According to the method, coordinate transformation is not needed to be carried out on the measurement result, and the vibration mode measurement result before and after the bridge is damaged can be directly analyzed under the condition that the position of a mobile phone camera is basically unchanged, so that key information such as the damage position and the damage degree can be obtained.
(6) The invention solves the problem that additional characteristic points need to be arranged on the tested structure in the traditional testing method based on the machine vision technology, and the invention directly utilizes the structural characteristics of the surface of the tested structure, such as the texture, the pattern background and the like of the target surface, as the measuring area, thereby ensuring that the experiment operation is simple and convenient and the requirement on the video quality is lower.
(7) The method and the device avoid the problem of high cost of high-speed cameras, acceleration sensors, GPS and other equipment, and can completely realize low-cost measurement of the bridge vibration mode. And the method for recording the video by the conventional mobile phone has the advantages of low cost, convenience in popularization, wide video acquisition source, no need of professional training and the like. Compared with other measuring methods, the measuring method has the advantages of low cost, simple operation, convenience in carrying and controllable precision.
(8) And a single mobile phone is adopted for video recording, and multi-lens collaborative recording is not needed. The monocular video recording is adopted, the problem of synchronism of multi-view photography is avoided, the trouble that the real vibration mode can be obtained only by performing visual correction on a multi-view lens is avoided, the operation is convenient, and the problem that sampling time of each measuring point is asynchronous in various contact vibration mode measuring methods is fundamentally solved.
(9) And multiple times of contour recognition is adopted, the recognition result is subjected to arithmetic average to eliminate the measurement error, and the measurement precision is improved.
(10) The measuring method does not need to comprehensively observe the whole bridge structure, only selects the local part of the bridge to obtain the vibration mode of the observed part, and can carry out the next structural damage identification and safety state evaluation work by utilizing the measured vibration mode. The method can effectively solve the problem that the valuable vibration mode of the bridge structure can be obtained only by selecting a favorable observation angle and an observation place in the conventional vision measurement method, and particularly the situation that the shelters cannot be avoided.
(11) The measurement method can be used for respectively carrying out structural damage identification and safety state evaluation on videos of the same bridge at different visual angles. The obtained result can be cross-verified, so that the measurement precision is improved, and the reliability of the result is also improved. The traditional contact method can only obtain a unique group of mode shape data, and corresponding measuring point data can be completely lost if a measuring instrument is damaged. The invention can measure the same bridge from different observation places and multiple angles. The comprehensive analysis of the result of the invention can obviously improve the applicability of the measuring method and the reliability of the measuring result.
Drawings
Fig. 1 is a measurement flowchart of a bridge structure vibration mode measurement method based on single mobile phone photography according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating the relationship between the error in the arithmetic mean and the number of measurements according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.
Referring to fig. 1, a bridge structure vibration mode measurement method based on single mobile phone photography according to the present embodiment includes the following steps:
s1, selecting a shooting place, wherein the measuring device comprises a common mobile phone, and adjusting the lens of the mobile phone to enable the whole bridge main body structure or part of the bridge main body structure to appear in the camera view. Of course, in other embodiments, the mobile phone can be directly held by hand to shoot without being erected.
In this embodiment, a single mobile phone is used for video recording. The mobile phone camera is used as a measuring device, so that the remote non-contact vibration mode measurement of a bridge structure can be realized, the problem that sampling time of each measuring point is asynchronous in various contact vibration mode measurement methods is fundamentally solved, the synchronization problem of multi-view photography is avoided by adopting monocular video recording, the trouble that real vibration modes can be obtained only by performing vision correction on a multi-view lens is avoided, and the operation is convenient.
And S2, recording the bridge video by using the mobile phone to obtain a video sample.
Specifically, a video capable of identifying the vibration profile of the bridge structure is obtained as a video sample. In this embodiment, n views are selectedThe frequency sample is observed for n times, and according to the measurement error analysis theory, the independent observation is assumed to be carried out for n times with the same precision for a certain quantity, and the observed values are L respectively1,L2,L3,...,LnError in each observation is equal to σLTaking the arithmetic mean of the n observations as the final result of the quantity, i.e.
At this time
Namely, it is
According to the formula, the number of the selected samples satisfies that n is more than or equal to 10 and less than or equal to 20, so that the measurement precision can be improved, and the reduction of data processing efficiency caused by overlarge data volume can be avoided. The number of samples satisfying the interval 10. ltoreq. n.ltoreq.20 is the result after the preference.
According to the method, the whole bridge structure does not need to be comprehensively observed, the vibration mode of the observed part can be obtained only by selecting the local bridge position, the video of the local bridge position is selected as the video sample, and then the bridge vibration mode can be finally obtained according to the following steps. The method can effectively solve the problem that the valuable vibration mode of the bridge structure can be obtained only by selecting a favorable observation angle and an observation place in the conventional vision measurement method, and particularly the situation that the shelters cannot be avoided.
And S3, selecting the bridge vibration contour lines with large color difference from each video sample as the identification objects of the bridge vibration modes.
Specifically, bridge vibration contour line identification objects with large color difference are determined according to the background or bridge color characteristics, and a plurality of contour line identification objects can be selected from each video sample. For example, the bridge construction is not of the same colour, such as the body of the concrete structure is grey, and the background may be blue in the sky, or the colour of the outer walls of the surrounding building. If the difference of the color numbers of the colors RGB (for example, the range of red R is 0 to 255) of the image is distinguished, the difference of the color numbers of the colors RGB is more than 50, and the difference of the colors RGB can be completely considered as large.
And S4, identifying the upper contour line and the lower contour line of each video sample through a video image contour identification technology, and respectively obtaining the static balance curve of each video sample through the upper contour line and the lower contour line.
The outline recognition of the image is a relatively mature technology, and a subprogram can be called conveniently in programs such as matlab and C language for processing. Edge identification of images is often divided into two steps: (1) locations where the pixel characteristics change dramatically are identified. The pixel change has two properties of direction and amplitude, and the pixel change is generally gentle along the direction of the edge and violent along the direction perpendicular to the edge. (2) And (4) connecting discontinuous edge pixel points by utilizing mathematical transformations such as Hough transformation and the like to obtain a boundary curve. In the present embodiment, the "differential operator-based image contour recognition method" is used to recognize the upper contour line and the lower contour line.
Specifically, the upper contour line f of each bridge vibration east contour line is respectively identified for the ith video sampleGo up i(x) And lower contour line fLower i(x) I.e. the position where the amplitude is maximal;
f is respectively carried out on the upper contour line and the lower contour line of each video sampleBalance i(x)＝[fGo up i(x)+fLower i(x)]Performing/2 operation to correspondingly obtain a static balance curve f of the bridge structure in each video sampleBalance i(x)。
S5, passing the corresponding upper contour line f in each video sampleGo up i(x) And static equilibrium curve fBalance i(x) And respectively obtaining an original mode shape sample of each video sample. The specific formula is as follows:
fi(x)＝fgo up i(x)-fBalance i(x)
And S5, obtaining the bridge vibration mode through the original vibration mode sample. The method comprises the following specific steps:
s51, carrying out normalization operation on each original mode sample according to the following formula to obtain the mode sample for arithmetic mean
Wherein, max (f)i(x) Is the original vibration mode sample fi(x) Is measured.
S52, according to the following formula, each mode sample
And (4) performing arithmetic mean operation to obtain the final bridge vibration mode f (x).
The contour lines in the video samples are identified, the original vibration mode samples are obtained respectively, then the measurement error can be effectively reduced by carrying out arithmetic mean on the original vibration mode samples in the video samples, and the measurement precision is improved.
The non-contact measurement method provided by the embodiment is used for completing the vibration mode measurement of the bridge structure by adopting a single mobile phone to shoot, coordinate transformation of a measurement result is not needed, and key information such as a damage position, a damage degree and the like can be obtained only by directly analyzing the vibration mode measurement result before and after the bridge damage under the condition that the position of a camera is basically unchanged.
When the measuring method of the embodiment is used, the bridge structure vibration mode under the excitation of the environment such as vehicles and environmental wind is measured without an additional excitation source, the traffic on the bridge is not required to be managed and processed in the measuring process, and the bridge is not adversely affected.
It should be understood that the above-described embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the claims of the present invention.
Claims (10)
1. A bridge structure vibration mode measuring method based on single mobile phone photography is characterized by comprising the following steps:
recording a bridge video through a mobile phone camera to obtain a video sample;
selecting a bridge vibration contour line with large color difference from a video sample as an identification object of the bridge vibration mode;
identifying an upper contour line and a lower contour line of a video sample, and obtaining a static balance curve of the video sample through the upper contour line and the lower contour line;
obtaining an original vibration mode sample of the video sample through the upper contour line and the static balance curve;
and obtaining the bridge vibration mode through the original vibration mode sample.
2. The bridge structure vibration mode measurement method based on single mobile phone photography according to claim 1, characterized in that: and recording videos by adopting a conventional mobile phone lens.
3. The bridge structure vibration mode measurement method based on single mobile phone photography according to claim 1, wherein the obtaining of the video sample specifically comprises: and acquiring a video capable of identifying the vibration profile of the bridge structure as a video sample.
4. The bridge structure vibration mode measurement method based on single mobile phone photography according to claim 1, characterized in that: and recording videos by adopting a single mobile phone.
5. The bridge structure vibration mode measurement method based on single mobile phone photography according to claim 1, characterized in that: environmental stimuli are used during the measurement process, including but not limited to vehicle loads or wind loads.
6. The bridge structure vibration mode measurement method based on single mobile phone photography according to claim 1, characterized in that: and identifying the upper contour line and the lower contour line of the video sample by a video image contour identification technology.
7. The bridge structure mode vibration measuring method based on single mobile phone photography according to claim 1, wherein the upper contour line and the lower contour line of the video sample are identified, and the static balance curve of the video sample is obtained through the upper contour line and the lower contour line, specifically:
respectively identifying the upper contour line f of each bridge vibration contour lineGo up i(x) And lower contour line fLower i(x) I.e. the position where the amplitude is maximal;
calculating the upper contour line and the lower contour line of the video sample according to the following formula to obtain a static balance curve f of the bridge structure in the video sampleBalance i(x)；
fBalance i(x)＝[fGo up i(x)+fLower i(x)]/2 。
8. The bridge structure mode shape measuring method based on single mobile phone photography according to claim 1, wherein the original mode shape sample of the video sample is obtained through an upper contour line and a static balance curve, and specifically comprises the following steps: by the upper contour f of the video sampleGo up i(x) And static equilibrium curve fBalance i(x) Obtaining the original mode shape sample fi(x) The formula is as follows:
fi(x)＝fgo up i(x)-fBalance i(x) 。
9. The bridge structure vibration mode measuring method based on single mobile phone photography according to any one of claims 1 to 8, characterized in that: the bridge video is recorded through the mobile phone camera, n video samples are obtained from the video samples, and the value range of the video samples is that n is larger than or equal to 10 and smaller than or equal to 20.
10. The bridge structure vibration mode measurement method based on single mobile phone photography according to claim 9, wherein the bridge vibration mode is obtained through an original vibration mode sample, specifically:
for the i (i ═ 1,2, 3.., n) th original mode shape sample fi(x) Performing normalization operation to obtain vibration mode sample for arithmetic mean
The concrete formula is
Where max (f)i(x) Is the original vibration mode sample fi(x) The maximum observed value of (a);
(7) performing arithmetic mean operation on the sample
And obtaining the final bridge vibration mode f (x).
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