CN114383874A - Large-scale structure modal testing method - Google Patents
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Abstract
The invention provides a large-scale structure modal testing method, and belongs to the field of vibration testing. The method comprises the steps of optimizing and analyzing the position of the sensor, fixing sensor equipment, establishing the relation between the position direction of the sensor and a geometric model, acquiring and recording data, processing the data, identifying modal parameters and the like. The invention adopts the sensor with wireless transmission function to measure, thus reducing the experiment preparation time; the three-way micro-electromechanical acceleration sensor integrating the inclinometer and the positioning device is adopted, so that the cost is low, and the connection with a geometric model is conveniently established; and a step excitation method is adopted, so that the implementation difficulty is low.
Description
Technical Field
The invention relates to a large-scale structure modal testing method, and belongs to the field of mechanical structure and vibration testing.
Background
The modality information includes three elements: natural frequency, modal damping ratio, and mode shape. The modal information reflects the inherent vibration characteristics of the structure itself, and is an important index that must be considered in the design, processing and manufacturing of large structures. In practical engineering, besides applying computer simulation technology, determining the mode of a large-scale structure by an experimentally measured method is also an essential important means.
Modal testing can be roughly divided into three forms according to the excitation form: sine sweep frequency, pulse excitation and step excitation. The sine sweep is a single frequency excitation of the structure by a vibration exciter or a vibration table, and the excitation is in a sine wave form, and the excitation frequency changes along with time. When the excitation frequency is close to the natural frequency of the structure, the structure resonates, the response amplitude is obviously increased, and the relevant modal parameters can be determined. Pulsed and stepped excitation is achieved by hammering or displacing a boundary change to elastically deform the structure and then releasing abruptly to obtain a free response of the structure. The structural modal parameters are obtained by the free response of the structure. In modal testing, the structural response may be displacement, velocity, acceleration, strain, and the like. Acceleration response is often used in practical engineering applications.
For a large structure, large excitation equipment is needed by adopting sweep frequency excitation, and displacement boundary conditions of the structure need to be properly constrained, so that the implementation difficulty is high, the cost is high, and the experimental period is long. The structure can be effectively excited by adopting a pulse or step excitation mode, but a large-scale space structure usually pays attention to vibration characteristics in all directions, so that a three-way sensor is needed. The traditional test method needs acquisition equipment with a large number of channels, so that the cost is high; the three-way sensor has more wire harnesses, is easy to be interfered, and has longer experiment preparation period.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides the large structure modal testing method, which can test the natural frequency of large structures in various forms, and has the advantages of low cost and easy implementation.
In order to achieve the purpose, the invention adopts the technical scheme that:
a large-scale structure modal test method comprises the following steps:
(1) carrying out modal analysis on a large-scale structure to be tested to obtain initial natural frequency and vibration mode;
(2) according to the preliminary vibration mode obtained in the step (1), determining the installation position of the sensor by comparing vibration mode results in the concerned frequency, and installing the sensor at a position with a large amplitude in the vibration mode; a three-axis acceleration sensor, an inclinometer, a positioning device and a wireless connecting device are arranged in the sensor;
(3) establishing a relation between the sensor position direction and the geometric model;
(4) step excitation is applied to the large-scale structure, the amplitude of acceleration response is monitored through the information processing computer, excitation is performed again when the acceleration response is attenuated, the excitation is repeated for multiple times, and response data of each sensor is recorded through the information processing computer;
(5) and processing the data according to the response data of the sensor and the relation between the sensor position direction and the geometric model to obtain the modal parameters of the large-scale structure.
Further, the specific mode of the step (3) is as follows:
(301) establishing a global coordinate system in an information processing computer, and importing a geometric model of a large-scale structure;
(302) determining the position coordinate and the attitude direction of the sensor by utilizing a positioning device and an inclinometer which are arranged in the sensor;
(303) and establishing a relation between the sensor position direction and the large-scale structure geometric model, wherein the relation comprises the specific position of the sensor measuring point in the large-scale structure geometric model and a rotation matrix from a sensor coordinate system to a whole coordinate system.
Further, in the step (4), firstly, time synchronization is carried out on each sensor by utilizing the time service function of the positioning device; the specific way of applying the step excitation is to excite the large-scale structure in three directions respectively, and at least 10 times of effective free attenuation is recorded in each excitation direction; and after the data recording of each direction is completed, the excitation of the next direction is carried out.
Further, the specific mode of the step (5) is as follows:
(501) obtaining the acceleration response of the sensor under the global coordinate system according to the rotation matrix from the sensor coordinate system to the global coordinate system:
in the formula, RnGIs a rotation matrix, vector, from the sensor coordinate system to the global coordinate system
For the acceleration response of the sensor in the global coordinate system,
the acceleration response of the sensor under the coordinate system of the sensor is obtained;
(502) selecting a sensor as a reference sensor according to the initial natural frequency obtained in the step (1), so that a power spectrogram of the response data of the reference sensor comprises natural frequency components of each order; carrying out Fourier transform on the response data of the reference sensor, wherein each extreme point corresponds to the inherent frequency of different orders;
(503) decomposing response data of the reference sensor to obtain modal responses of all orders, enveloping the modal responses of all orders and carrying out exponential curve fitting to obtain modal damping ratios of different orders; wherein the form of the exponential curve is as follows:
x＝Ae-σt＝Ae-2πfξt
xe＝Ae-σt＝Ae-2πfξte＝Ae-σt＝Ae-2πfξt
in the formula, xeExtracting envelope data on acceleration response, wherein A is a signal amplitude, f is the natural frequency of the order, and xi is a modal damping ratio to be solved;
(504) decomposing the response data of each sensor to obtain concerned modal responses of each order; averaging root mean square values obtained by the same sensors, the same direction, the same order and different excitation orders according to the excitation orders to obtain vibration mode components of the corresponding sensors, the corresponding directions and the corresponding orders; and carrying out maximum value normalization on the vibration mode components of different sensors and the same order to obtain the vibration modes of different orders of the large-scale structure.
Compared with the prior art, the invention has the beneficial effects that:
1. the invention aims at the characteristic of large scale of a large structure, adopts the sensor with the wireless transmission function to carry out measurement, can realize wireless measurement and automatically acquire the position and the direction of the sensor, is easy to implement in the test process, does not need wiring and wire arrangement, and can obviously reduce the test time.
2. Aiming at the problem that a large structure requires attention to vibration modes in three directions, the three-direction micro-electromechanical acceleration sensor integrating the inclinometer and the positioning device is adopted, so that the cost is low, and the connection with a geometric model is conveniently established.
3. Aiming at the problem that a large-scale structure is difficult to excite by a vibration exciter, the invention adopts displacement step to excite, and the excitation form is simple and easy to realize.
Drawings
Fig. 1 is a schematic structural diagram of a large-scale structural modal testing system according to an embodiment of the present invention.
Fig. 2 is a schematic view of the installation position of the sensor in the embodiment of the present invention.
Fig. 3 is a graph of the acceleration response spectrum of the sensor at the ball node 4 in the X direction according to the embodiment of the present invention.
Fig. 4 is a graph of the X-direction acceleration response envelope of the sensor at the ball node 4 in an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings and specific embodiments, wherein the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not meant to limit the present invention.
A large-scale structural mode testing method, a testing system thereof is shown in fig. 1, the testing system comprises:
the smart sensor device 1. The sensor equipment is internally provided with a three-axis acceleration sensor, an inclinometer, a GPS or Beidou positioning device, a WiFi or Bluetooth or other wireless connection devices. The intelligent sensor equipment is internally provided with related software which can carry out data acquisition and data preprocessing on the sensor and send the sensor data to the wireless connection switch through a built-in wireless device according to a wireless protocol.
A wireless connection switch 2. The device provides a wireless connection convergence function, and converges the structural response information acquired by the sensor to the information processing computer through the network. The wireless network switch wireless connection protocol needs to be compatible with the sensor wireless connection protocol.
An information processing computer 3. The computer is connected with the wireless network switch and can receive the data of each sensor gathered by the switch. And the information processing computer is provided with special software for processing the sensor data and identifying the large-scale structure modal parameters.
The method mainly comprises the following steps:
(1) and (5) optimizing and analyzing the position of the sensor. And carrying out modal analysis on the structure to be tested by finite element mechanical analysis software or a theoretical method to obtain initial natural frequency and vibration mode.
(2) The sensor device is fixed. And determining the installation position of the sensor by comparing the vibration mode results in the concerned frequency, and fixing the sensor equipment to the corresponding position of the structure. The sensor mounting position should be avoided from being mounted at a vibration mode node position, a vibration mode amplitude smaller position, and a position with larger structural rigidity is selected as far as possible. The fixing mode of the sensor is firm and reliable, the tool can be designed independently for clamping and fixing the sensor, and the tool can be mounted on the structure through bolts, hoops and the like.
The method adopts wireless sensor equipment, adopts a wireless transmission mode for data transmission, and can automatically report the posture and the position of the wireless sensor equipment by arranging an inclinometer and a positioning device in the wireless sensor equipment.
(3) And establishing the relation between the position direction of the sensor and the geometric model of the large-scale structure to be measured according to the attitude direction and the position information reported by the sensor. Firstly, an overall coordinate system is established in an information processing computer, a structural geometric model is imported, then the position coordinates and the attitude direction of a sensor are determined by utilizing special software preinstalled in the information processing computer and a positioning device and an inclinometer which are built in the sensor, and finally the relationship between the position direction of the sensor and the structural geometric model is established. The relationship includes the specific location of the sensor measurement points in the structural geometric model and the rotation matrix of the sensor coordinate system to the global coordinate system. Wherein, the rotation matrix from the sensor coordinate system to the global coordinate system can be a transformation matrix in Euler or Kaldo form.
(4) And (6) data acquisition and recording. The method comprises the steps of firstly synchronizing the time of sensors by using the time service function of a GPS or Beidou positioning device, then recording the acceleration data of each sensor by using special software preinstalled in an information processing computer, applying step excitation to a mechanism while recording the data and adding the amplitude of acceleration response in the software, exciting again when the acceleration response is attenuated, and repeating for many times.
Preferably, recording is stopped after more than 10 effective free decay responses have been recorded. The excitation direction was changed and the recording of the sensor acceleration response was resumed, stopping after 10 effective free decay responses were reached. The above steps are repeated until the structure has been excited in all three directions.
(5) Data processing and modal parameter identification. After obtaining the acceleration response of each sensor in three directions, obtaining the acceleration response of the sensor in the global coordinate system according to the rotation matrix between the coordinate system of each sensor and the global coordinate system obtained in the step (3), wherein a specific transformation formula is as follows:
in the formula, RnGIs a rotation matrix, vector, from the local coordinate system of the sensor to the global coordinate system
For the acceleration response of the acceleration sensor under the global coordinate system,
is the acceleration response of the sensor in its own coordinate system.
Selecting sensor data as reference data, wherein the power spectrogram of the sensor response data comprises natural frequency components of each order, and the reference value of the modal frequency can refer to the natural frequency obtained by the modal analysis in the step (1). And carrying out Fourier transform on the reference sensor data, wherein each extreme point corresponds to the natural frequency of different orders of the structure.
And decomposing the response data of the reference sensor to obtain modal responses of all orders, and enveloping and carrying out exponential curve fitting on the modal responses of all orders to obtain modal damping ratios of different orders of the structure. The exponential curve is of the form:
x＝Ae-σt＝Ae-2πfξt
xe＝Ae-σt＝Ae-2πfξte＝Ae-σt＝Ae-2πfξt
wherein x iseAnd extracting envelope data on the acceleration response, wherein A is a signal amplitude, f is a natural frequency of the order, and xi is a modal damping ratio to be solved.
And decomposing the response data of each sensor to obtain concerned modal response of each order. According to the excitation sequence, averaging the root mean square values obtained by the same sensor, the same direction, the same order and different excitation sequences to obtain the vibration mode components of the sensor, the direction and the order. And performing the same processing on all sensor data to obtain vibration mode components of all sensors, all directions and the concerned order. And maximum value normalization is carried out on the vibration mode components of different sensors and the same order, so that the vibration modes of different structures and different orders can be obtained.
In the step (5), when the data of each sensor is decomposed, the calculation parameters are ensured to be consistent, and the modal responses of each order obtained by decomposition are equal in quantity; the algorithm used for the sensor data decomposition can be empirical mode decomposition, variational mode decomposition, wavelet decomposition and the like; when the root mean square value is solved for the modal responses of the same order of different sensors, the number of the selected data points is ensured to be the same.
Preferably, the sensor reference data amplitude in step (5) should not be too low.
In the following, a large structure is taken as an example, and the large structure is shown in fig. 2 and is a space truss structure. The modal testing method of the structure is as follows:
(1) modal analysis is carried out on the truss structure through finite element mechanical analysis software to obtain initial natural frequency and vibration mode, and installation positions of the sensors are determined to be positions of the ball nodes 4, 5 and 6 in the diagram 2 through the analysis.
(2) The sensor device is fixed. And (3) fixing the sensor equipment to the corresponding position of the structure according to the determined sensor installation position in the step (1).
(3) Sensor position coordinates are established. And importing a truss structure geometric model into computer special software, and establishing an overall coordinate system. The position coordinates and the orientation of the sensor are determined by using special software pre-installed in an information processing computer and a positioning device and an inclinometer built in the sensor, for example, the sensor at the ball node 4 has the coordinates of [ -3232,1179, -3232] in the space, and the coordinates are basically coincident with the ball node in the geometric model, so that the response of the sensor can be used for representing the response of the ball node in the geometric model. The included angle of the sensor and the Y-axis is 45 degrees.
(4) The acceleration data of each sensor is recorded by using special software pre-installed in an information processing computer, and step excitation is applied to the mechanism while the data is recorded, so that the effective excitation is carried out for 10 times in total.
(5) And (4) obtaining acceleration responses of the three sensors under the global coordinate system according to the transformation matrix between the coordinate system of each sensor and the global coordinate system obtained in the step (3) after obtaining the acceleration responses of the sensors. Taking the sensor at the ball node 4 as an example, the euler X-Y-Z coordinate rotation transformation matrix corresponding to the sensor is an expression, so that the sensor responds as follows under the overall coordinate system:
the sensor at the ball node 4 is selected as a reference, and the X-direction response Fourier transform spectrum of the sensor is shown in FIG. 3. As can be seen from the figure, the first three natural frequencies are 1.67 Hz, 3.18 Hz and 6.04Hz respectively. The X-direction data of the sensor is decomposed to obtain the first three-order modal responses, and the first order is taken as an example, and the single step response is shown in fig. 4. Obtaining an exponential envelope curve expression x according to response fitting in the graphe＝Ae-σt＝Ae-2πfξt＝e-2π×1.67×0.0098×tTherefore, the first-order modal damping ratio is 0.98%.
And decomposing the response data of each sensor to obtain concerned modal response of each order. According to the excitation sequence, solving the root mean square value of the modal response of the same order of the three sensors, and averaging the root mean square values obtained by the same sensors, the same direction, the same order and different excitation sequences to obtain the vibration mode components of the sensor, the direction and the order. The same processing is carried out on all three sensor data, and vibration mode components of all sensors, all directions and the concerned orders are obtained. And maximum value normalization is carried out on the vibration mode components of the three sensors and the same order, so that the vibration modes with different orders of structures can be obtained.
In this example, the first order mode matrix is
The matrix has a first row of X-direction component, a second row of Y-direction component, and a third row of Z-direction component, wherein the first row is sensor mode component at ball node 4, the second row is sensor mode component at ball node 5, and the third row is sensor mode componentIs the sensor mode shape component at the ball node 6.
In a word, the invention adopts the sensor with the wireless transmission function to measure, thus reducing the experiment preparation time; the three-way micro-electromechanical acceleration sensor integrating the inclinometer and the positioning device is adopted, so that the cost is low, and the connection with a geometric model is conveniently established; and a step excitation method is adopted, so that the implementation difficulty is low.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only illustrative of the present invention and are not intended to limit the scope of the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (4)
1. A large-scale structure modal testing method is characterized by comprising the following steps:
(1) carrying out modal analysis on a large-scale structure to be tested to obtain a primary natural frequency and a primary vibration mode;
(2) according to the preliminary vibration mode obtained in the step (1), determining the installation position of the sensor by comparing vibration mode results in the concerned frequency, and installing the sensor at a position with a large amplitude in the vibration mode; a three-axis acceleration sensor, an inclinometer, a positioning device and a wireless connecting device are arranged in the sensor;
(3) establishing a relation between the sensor position direction and the geometric model;
(4) step excitation is applied to the large-scale structure, the amplitude of acceleration response is monitored through the information processing computer, excitation is performed again when the acceleration response is attenuated, the excitation is repeated for multiple times, and response data of each sensor is recorded through the information processing computer;
(5) and processing the data according to the response data of the sensor and the relation between the sensor position direction and the geometric model to obtain the modal parameters of the large-scale structure.
2. The large-scale structure modal testing method according to claim 1, wherein the specific manner of the step (3) is as follows:
(301) establishing a global coordinate system in an information processing computer, and importing a geometric model of a large-scale structure;
(302) determining the position coordinate and the attitude direction of the sensor by utilizing a positioning device and an inclinometer which are arranged in the sensor;
(303) and establishing a relation between the sensor position direction and the large-scale structure geometric model, wherein the relation comprises the specific position of the sensor measuring point in the large-scale structure geometric model and a rotation matrix from a sensor coordinate system to a whole coordinate system.
3. The large-scale structure modal testing method according to claim 1, wherein in the step (4), firstly, the time service function of the positioning device is utilized to perform time synchronization on each sensor; the specific way of applying the step excitation is to excite the large-scale structure in three directions respectively, and at least 10 times of effective free attenuation is recorded in each excitation direction; and after the data recording of each direction is completed, the excitation of the next direction is carried out.
4. The large-scale structural modal testing method according to claim 1, wherein the specific manner of the step (5) is as follows:
(501) obtaining the acceleration response of the sensor under the global coordinate system according to the rotation matrix from the sensor coordinate system to the global coordinate system:
in the formula, RnGIs a rotation matrix, vector, from the sensor coordinate system to the global coordinate system
For the acceleration response of the sensor in the global coordinate system,
the acceleration response of the sensor under the coordinate system of the sensor is obtained;
(502) selecting a sensor as a reference sensor according to the initial natural frequency obtained in the step (1), so that a power spectrogram of the response data of the reference sensor comprises natural frequency components of each order; carrying out Fourier transform on the response data of the reference sensor, wherein each extreme point corresponds to the inherent frequency of different orders;
(503) decomposing response data of the reference sensor to obtain modal responses of all orders, enveloping the modal responses of all orders and carrying out exponential curve fitting to obtain modal damping ratios of different orders; wherein the form of the exponential curve is as follows:
xe＝Ae-σt＝Ae-2πfξt
in the formula, xeExtracting envelope data on acceleration response, wherein A is a signal amplitude, f is the natural frequency of the order, and xi is a modal damping ratio to be solved;
(504) decomposing the response data of each sensor to obtain concerned modal responses of each order; averaging root mean square values obtained by the same sensors, the same direction, the same order and different excitation orders according to the excitation orders to obtain vibration mode components of the corresponding sensors, the corresponding directions and the corresponding orders; and carrying out maximum value normalization on the vibration mode components of different sensors and the same order to obtain the vibration modes of different orders of the large-scale structure.
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