Wall structure damage identification method and equipment based on random excitation signal

Abstract

The invention provides a wall structure damage identification method and equipment based on a random excitation signal, and the method comprises the steps: arranging a plurality of sensors on the surface of a to-be-detected wall, and forming a sensor array covering a wall region; randomly selecting a plurality of positions on the surface of the wall body for knocking so as to generate random excitation signals; collecting a vibration signal generated by each time of knocking through a sensor array; based on the vibration signals, the propagation velocity of vibration waves in the wall is determined through the receiving time difference of the sensor array, and the intensity and phase change of reflected waves are extracted to construct a wave velocity field; and carrying out wave velocity field inversion, and positioning the internal damage position of the wall body. The internal damage of the wall structure can be quickly and accurately identified, and the specific position of the damage is determined, so that a scientific basis is provided for health monitoring and maintenance of a building.

Description

Technical Field

[0001] The present invention relates to the technical field of wall structure testing, and particularly relates to a method and device for identifying wall structure damage based on random excitation signals. Background Art

[0002] The health status of the wall structure is directly related to the safety and durability of the building. During long-term use, the wall may suffer internal damage (such as hollowing, leakage, etc.) due to factors such as material aging, load changes, or environmental erosion. If these hidden damages are not detected in time, they may pose potential structural safety hazards and even lead to the failure of the building's functions. Therefore, developing efficient and accurate wall damage detection technology is of great significance for ensuring building safety.

[0003] Traditional wall damage detection methods, such as visual inspection, infrared thermography, etc., often have problems such as low efficiency, high cost, or insufficient accuracy. The results of visual inspection largely depend on the experience and judgment of the inspector, so there may be subjectivity, and usually only surface damages of the wall, such as cracks, stains, etc., can be found, while hidden damages inside the wall, such as hollowing, leakage, etc., are difficult to detect. For large-area walls, visual inspection requires checking one by one, which is time-consuming and has low efficiency. Infrared thermography equipment is usually expensive and may be difficult for general building inspection companies or individuals to afford. Infrared thermography detection requires professional technical personnel for operation and analysis, and has high requirements for operation techniques. If the operator is not proficient or lacks experience, it may lead to errors in the detection results. The results of infrared thermography detection may also be affected by environmental factors, such as temperature, humidity, wind speed, etc. These factors may cause changes in the temperature distribution on the wall surface. Although infrared thermography technology can detect the temperature difference on the wall surface, it cannot directly show the specific type and degree of damage. Summary of the Invention

[0004] The present invention proposes a method and device for identifying wall structure damage based on random excitation signals to solve the technical problems that the prior art is difficult to balance detection efficiency, cost, and accuracy, and lacks the ability to accurately locate the damage position.

[0005] To solve the above technical problems, the present invention provides a method for identifying wall structure damage based on random excitation signals, including the following steps:

[0006] Step S1: Arrange a plurality of sensors on the surface of the wall to be detected to form a sensor array covering the wall area;

[0007] Step S2: Randomly select multiple positions on the wall surface for knocking to generate random excitation signals;

[0008] Step S3: Collect the vibration signals generated by each knock through the sensor array;

[0009] Step S4: Based on the vibration signals, determine the propagation speed of the vibration wave inside the wall through the reception time difference of the sensor array, and extract the intensity and phase changes of the reflected wave to construct a wave speed field;

[0010] Step S5: Perform wave speed field inversion to locate the damage position inside the wall.

[0011] Preferably, in step S1, the sensor array adopts a rectangular arrangement layout, and in step S2, the excitation source knocks on the upper and lower or left and right sides of the sensor array.

[0012] Preferably, preprocess the collected vibration signals, including denoising processing and signal normalization.

[0013] Preferably, the denoising processing includes low-pass filtering, band-pass filtering, and wavelet transform methods.

[0014] Preferably, the method for determining the wave speed through the reception time difference of the sensor array in step S4 includes:

[0015] Step S411: Discretize the area of the wave speed field to be inverted into n grids, and determine the coordinates of each knock and the coordinates of the sensor array;

[0016] Step S412: Construct m emission-reception pairs and determine the wave travel time of each emission-reception pair;

[0017] Step S413: Through the fast marching method (FMM) of ray tracing algorithm and the multi-template fast marching method (MSFM), obtain the condition that the propagation time T(x,y) at the corresponding grid position (x, y) satisfies:

[0018]

[0019] In the formula, v represents the calculation template serial number; represents the included angle of the calculation template; Δh represents the distance between two adjacent calculation points; T v represents the wavefront propagation time of the corresponding template serial number; s represents the wavefront slowness.

[0020] Preferably, in step S5, the wave speed field inversion adopts an inversion algorithm based on wave speed difference or a numerical simulation method combined with finite element analysis.

[0021] Preferably, in step S2, a force hammer is used as the excitation source for knocking.

[0022] Preferably, when the wall to be detected is a rigid wall, the hammer head of the impact hammer is made of a material with a contact stiffness ratio with the wall greater than 1.5 times; when the wall to be detected is a flexible wall, the hammer head of the impact hammer is made of a material with a contact stiffness ratio with the wall not greater than 1.2 times.

[0023] The present invention also provides an electronic device, including: a memory, a processor, and a computer program, characterized in that: the computer program is stored in the memory and is configured to be executed by the processor to implement the above method.

[0024] The beneficial effects of the present invention at least include: The present invention adopts a method for identifying damage to the wall structure by a random excitation signal, and evaluates the structural damage by measuring and analyzing the wave propagation speed in the wall, without the need for destructive sampling or drilling of the wall, thereby protecting the integrity of the wall. Through precise wave speed measurement and data processing, the wave speed field inversion technology can accurately locate the damage area in the wall and evaluate the severity of the damage. This high precision makes the present invention an important tool for wall structure damage assessment.

[0025] The present invention can cover the entire area of the wall, not limited to surface damage, but also able to detect hidden damage inside the wall. This comprehensiveness helps to comprehensively evaluate the structural safety of the wall. And it is applicable to various types of wall structures, including concrete walls, brick walls, etc. This makes the technology have a wide application prospect and can meet the detection needs of different building structures.

[0026] Through the present invention, potential problems can be discovered at the initial stage of wall structure damage. Early discovery of wall structure damage and taking repair measures and reinforcement measures can significantly reduce the maintenance cost, improve the overall safety of the building, avoid further deterioration of the damage, and have significant advantages and positive effects in wall structure damage assessment, providing a strong guarantee for the safety and durability of building structures.

[0027] In summary, through the random excitation signal method, the present invention can efficiently and accurately identify the damage inside the wall and accurately locate the damage position. Compared with traditional detection methods, the present invention has low cost and strong applicability, and is particularly suitable for various types of building wall structures. This method can provide a fast and non-destructive detection means, significantly improving the efficiency and reliability of wall health monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a schematic flow chart of the method according to an embodiment of the present invention;

[0029] Figure 2 is a schematic structural diagram of the excitation signal and sensor arrangement according to an embodiment of the present invention;

[0030] Figure 3 Schematic diagram of wave velocity field inversion according to an embodiment of the present invention. Detailed implementation manners

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0032] As Figure 1 shown, an embodiment of the present invention provides a method for identifying damage to a wall structure based on a random excitation signal, including the following steps:

[0033] Step S1: Arrange a plurality of sensors on the surface of the wall to be detected to form a sensor array covering the wall area.

[0034] Specifically, a plurality of sensors are arranged on the surface of the wall to be detected for collecting vibration signals generated by knocking. The sensors can be accelerometers or other sensing devices suitable for measuring vibration signals. The positions of the sensors are arranged to ensure coverage of the entire wall area, and a certain distance is maintained between the sensors to obtain vibration responses in different areas.

[0035] In the embodiment of the present invention, the arrangement of the sensors preferably adopts a rectangular arrangement layout. The entire array of sensors is arranged in a rectangle, with the excitation sources on the left and right or top and bottom sides, and the middle part is the entire column of sensors. It is also possible to independently design the excitation source and the sensor array. This design can collect the change trend in a fixed direction and can collect a large amount of data at the same time. Compared with discrete sensors, the array can provide higher sensitivity and accuracy, thereby more accurately detecting and analyzing physical phenomena.

[0036] Step S2: Randomly select a plurality of positions on the surface of the wall for knocking to generate a random excitation signal.

[0037] Specifically, in the embodiment of the present invention, a force hammer is used as the excitation source, and a plurality of positions on the surface of the wall are randomly selected for knocking. Each knock generates an instantaneous vibration signal, which propagates within the wall structure. The purpose of random excitation is to cover different areas of the wall and ensure that the vibration signal can comprehensively reflect the internal structure state of the wall.

[0038] A force hammer, also known as a hand hammer, is a vibration excitation device commonly used in experimental modal analysis. It has two structural forms. It consists of several main components such as a hammer head, a hammer body, and a force sensor. When the force hammer strikes a test piece, the force sensor measures the magnitude and waveform of the impact force, which is then recorded by an amplification and recording device. Therefore, the force hammer is actually a handheld impact vibration excitation device. By using different hammer cap materials, force pulses with different pulse widths can be obtained, and the corresponding force spectra are also different.

[0039] Common hammer cap materials include rubber, nylon, aluminum, steel, etc. When using different hammer cap materials, the bandwidth of the force spectrum of the force hammer is different. Generally, the bandwidth of the rubber hammer cap is relatively narrow, while that of the steel cap is relatively wide. Therefore, when using a force hammer to excite a structure, different hammer cap materials should be selected according to the structure and the analysis frequency band.

[0040] Common force hammers weigh from a few tens of grams to several tens of kilograms, and the impact force can reach tens of thousands of Newtons. Due to the simple structure of the force hammer, easy manufacturing, and very convenient use, it avoids a large amount of work caused by using expensive vibration excitation equipment and installing exciters, and is widely used in field and indoor excitation tests.

[0041] Before selecting a force hammer, one factor to consider is the frequency bandwidth. The basis of using a force hammer for modal testing is to apply an impact to the test piece, thereby generating vibrations over a wide frequency bandwidth. The frequency bandwidth of the excited vibration depends on the impact duration. The narrower the pulse width (τ), the higher the excited frequency. The impact duration can be changed by installing special force hammers with different stiffnesses. When striking the test piece with the same energy, force hammers with different hammer heads can excite multiple frequency widths. The softer the hammer head, the wider the pulse, and the narrower the excited frequency bandwidth.

[0042] In some cases, the pulse duration also depends on the stiffness of the sample being struck. When using a hard force hammer, the impact energy is distributed over a wide frequency bandwidth, which means that in some cases the excited power spectral density may be very low, or even too low to excite the vibration modes / resonances of the sample. In this case, we can try to strike the structure being tested with the force hammer more forcefully, by making a larger swing or installing a hammer head increment to increase the weight of the force hammer. However, it should be noted that this method may also increase the risk of force sensor saturation. Therefore, in some cases, it may be considered to switch to a force hammer with a larger measurement range. Another option is to use a soft hammer head, which will concentrate the impact energy at lower frequencies.

[0043] In the detection of wall structures, the selection of the materials for the hammer head, hammer rod, and hammer handle of the force hammer is crucial, and different materials are suitable for different types of walls, which will be introduced in detail below.

[0044] Hammer head material selection. For rigid walls, the strength and stiffness of the wall are relatively high, and a relatively large impact force is required to excite its vibration. The ratio of the contact stiffness between the hammer head and the wall needs to be greater than 1.5 to avoid pulse energy leakage. The force spectrum bandwidth needs to cover more than 1.5 times the first three modal frequencies. For example, if the first three frequencies are 500 Hz, 1200 Hz, and 2800 Hz, then the bandwidth needs to be ≥ 4200 Hz. Verification of the energy coupling coefficient. By collecting the wall response signal through an acceleration sensor, calculate that the signal-to-noise ratio SNR of the signal is greater than 25 dB to ensure that high-frequency signals can be identified.

[0045] Therefore, in this embodiment, a cemented carbide or steel hammer head is selected, that is, the elastic modulus of the hammer head is about 200 - 210 GPa, and the elastic modulus of the wall is about 30 - 35 GPa, so as to ensure that the contact time is extremely short, τ ≤ 0.3 ms. A narrow pulse τ = 0.1 - 0.3 ms is realized through a hard hammer head to excite high-frequency modes to cover the 0 - 5 kHz frequency band, so that the energy is concentrated in the 0 - 5 kHz range, and the high-frequency attenuation rate ≤ 2 dB / oct. The peak of the force spectrum usually appears at 2.5 - 3.5 kHz, corresponding to more than 1.5 times the first three modal frequencies of the wall.

[0046] The diameter of the hammer head is set to 10 - 15 mm, and the contact stress ≤ 0.3σ_ult, that is, the ultimate compressive strength of the wall. The impact energy is 0.3 - 0.8 J, and the energy density ≥ 0.1 J / cm 3 , and the energy density is based on the contact volume of the hammer head.

[0047] Correspondingly, in this embodiment, when setting the sensor, considering damping compensation, a -4 dB / oct pre-emphasis filter is configured to compensate for high-frequency energy attenuation. The sampling rate ≥ 20 kHz, and the flat-top window is selected as the window function to suppress spectrum leakage.

[0048] For flexible walls, such as lightweight block walls or light steel keel gypsum board walls, their strength and stiffness are relatively low, and their ability to withstand impact force is weak. The ratio of hammer head-wall contact stiffness ≤ 1.2, and the contact time is extended to enhance low-frequency energy transfer. The force spectrum bandwidth needs to cover more than 1.2 times the first three modal frequencies. For example, if the first three frequencies are 100 Hz, 250 Hz, and 550 Hz, the bandwidth needs to be ≥ 660 Hz, SNR ≥ 15 dB, to meet the requirements of low-frequency signal analysis. Therefore, nylon or rubber hammer heads are usually selected. The elastic modulus of nylon or rubber materials is about 3 - 5 GPa. The stiffness of the hammer head needs to be close to or slightly lower than the wall stiffness to extend the contact time τ ≥ 1.5 ms, excite the low-frequency mode, and cover the 0 - 800 Hz frequency band. A wide pulse τ = 1.5 - 3.0 ms is achieved through a soft hammer head, and the energy distribution is smoother. The energy is concentrated in the 0 - 800 Hz range, and the high-frequency attenuation rate ≤ 8 dB / oct. The peak of the force spectrum usually appears at 300 - 500 Hz, which is more than 1.2 times the first three modal frequencies of the wall. The diameter of the hammer head is 25 - 30 mm, and the contact area ≥ 500 mm 2 , ensuring that the energy coupling coefficient ≥ 0.7. The impact energy is 2.0 - 4.0 J, and the energy density ≥ 0.05 J / cm 3 , and the energy density is based on the contact volume of the hammer head.

[0049] Correspondingly, in this embodiment, when setting up the sensor, considering damping compensation, a -12 dB / oct pre-emphasis filter is configured to increase the proportion of low-frequency energy. The sampling rate ≥ 5 kHz, and the window function selects an exponential window to smooth the low-frequency signal.

[0050] For the selection of the hammer rod material, whether for rigid or flexible walls, a high-strength aluminum alloy hammer rod is an ideal choice. It has a small density, can reduce the overall weight of the impact hammer, is easy to operate, and at the same time has high strength and stiffness, and can effectively transmit the impact force. Taking the detection of multi-story brick-concrete structure walls as an example, the impact hammer with an aluminum alloy hammer rod can not only ensure the effective transmission of the impact force, but also reduce the labor intensity of the operator and improve the detection efficiency. Carbon fiber composite materials have a higher strength and stiffness-to-weight ratio than aluminum alloy. For the testing of some wall structures with high requirements for testing accuracy, especially the walls in large and complex structures, the carbon fiber composite material hammer rod can reduce the influence of the vibration of the hammer rod itself on the test results and improve the test accuracy. For example, when performing modal testing on the walls of a large industrial factory building, the impact hammer with a carbon fiber composite material hammer rod can more accurately excite the modal vibration of the wall and obtain more accurate modal parameters.

[0051] Hammer handle material selection: A wooden handle offers a pleasant grip and a certain degree of elasticity, reducing the reaction force on the operator's hand and making it suitable for routine testing of various wall structures. For example, when performing routine inspections on ordinary residential walls, a hammer with a wooden handle provides a more comfortable grip and reduces hand fatigue. An engineering plastic handle offers advantages such as high strength, corrosion resistance, and insulation. In some challenging environments, such as humid environments or locations with electrical interference, a hammer with an engineering plastic handle is safer and more reliable. For example, when inspecting the walls of chemical plants, an engineering plastic handle can prevent damage to operators and test equipment due to corrosion or electrical problems.

[0052] Step S3: collecting the vibration signal generated by each tapping through the sensor array.

[0053] At each hammer strike, the sensors placed on the wall surface begin to collect vibration response signals. The collected data includes the time domain and frequency domain information of the vibration. Through multiple excitations and signal collection, the vibration wave propagation at different locations can be obtained. Its structure is as follows: Figure 2 shown.

[0054] Then, in the embodiment of the present invention, the collected vibration signal is pre-processed, including denoising and signal normalization.

[0055] Denoising removes external noise interference through low-pass filtering, band-pass filtering, or wavelet transforms to extract effective vibration signals related to wall damage. Signal normalization normalizes the amplitude of the vibration signal to ensure effective comparison of signal characteristics under different impact intensities.

[0056] Step S4: Based on the vibration signal, the propagation speed of the vibration wave inside the wall is determined through the reception time difference of the sensor array, and the intensity and phase change of the reflected wave are extracted to construct the wave velocity field; the wave velocity field is inverted to locate the damage position inside the wall.

[0057] Specifically, a hammer is used to apply random excitation to the wall, and the propagation, transmission, and reflection characteristics of the collected vibration signals in the wall are used to identify damage and characterize the internal state of the wall. The specific steps are as follows:

[0058] 1) Wave velocity information extraction and damage correlation analysis: For the vibration signals generated by the impact hammer at various knocking positions on the wall, calculate the propagation speed of the vibration wave. By accurately measuring the time difference when the vibration wave is received by the sensor, that is, the time difference, the propagation speed of the vibration wave in the internal medium of the wall is determined. In principle, if there is a damaged area in the wall, the material in this area will show discontinuity, which will change the propagation path and characteristics of the vibration wave, resulting in a decrease in the propagation speed of the vibration wave in this area compared to the normal area. This difference in propagation speed will be one of the important bases for us to identify the location and degree of wall damage.

[0059] As Figure 3 shown, in the wall area to be identified for damage, discretize it into n grid units for refined analysis of the internal state of the wall. Among them, the red and blue marked points represent the emission device and the receiving device of the random excitation signal respectively, and they together form m emission-reception combination pairs. The propagation time (wave travel time) of the vibration wave between each emission-reception combination pair is known, and the coordinate positions of each emission and receiving device in the wall space are also clearly determined. These known information will provide basic data support for subsequent analysis of wall damage based on the propagation characteristics of the vibration wave.

[0060] When the wave propagates in a two-dimensional medium, the mathematical form of the evolution of its wavefront is expressed by the following eikonal equation:

[0061]

[0062] In the formula, T represents the wavefront propagation time, s represents the wavefront slowness, and x and y represent the positions of the knocking point in the horizontal and vertical coordinates of the grid.

[0063] Use an efficient and high-precision ray tracing algorithm FMM and a multi-template fast marching method MSFM to perform wave velocity field inversion, taking into account the information of points in the axial and diagonal directions, and obtain that the propagation time T(x, y) at the position (x, y) satisfies the following equation:

[0064]

[0065] In the formula, v represents the calculation template number; represents the included angle of the calculation template; Δh represents the distance between two adjacent calculation points; T v represents the wavefront propagation time corresponding to the template number; s represents the wavefront slowness.

[0066] After that, analyze the reflected wave. By analyzing the reflected wave of the vibration signal, especially the intensity and phase changes of the reflected wave, judge whether there is damage. In a normal wall structure, the reflected wave is weak and propagates evenly; while in the damaged area, the reflected wave will be significantly enhanced.

[0067] According to the inversion results of the wave velocity field, further locate the specific positions of the internal damage of the wall. The inversion method in this embodiment can adopt an inversion algorithm based on wave velocity differences, or a numerical simulation method such as finite element analysis, which will not be elaborated here. By calculating the wave velocity changes at the positions of each sensor, a wave velocity distribution map inside the wall is drawn, as Figure 3 . The damaged area usually shows an area where the wave velocity is significantly reduced. Combining with the intensity change of the reflected wave, the damage position can be accurately located.

[0068] In this embodiment, the damage detection results can also be visualized to generate a damage position distribution map. Through this distribution map, the internal damage situation of the wall can be intuitively understood, and the damage position, range, and possible damage types can be obtained. In addition, a detection report can be provided for the user, detailing the detection process and results, and putting forward corresponding repair suggestions.

[0069] The present invention also provides an electronic device, including: a memory, a processor, and a computer program. The computer program is stored in the memory and is configured to be executed by the processor to implement the above method.

[0070] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. Only the preferred embodiments of the present invention are expressed. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the present invention. As long as the combination of these technical features does not conflict, it should be considered as within the scope described in this specification.

[0071] It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the appended claims.

Claims

1. A method for identifying damage to a wall structure based on a random excitation signal, characterized in that: Including the following steps: Step S1: Arrange a plurality of sensors on the surface of the wall to be detected to form a sensor array covering the wall area; Step S2: Randomly select multiple positions on the wall surface for knocking to generate random excitation signals; Step S3: Collect the vibration signals generated by each knocking through the sensor array; Step S4: Based on the vibration signals, determine the propagation speed of the vibration wave inside the wall through the reception time difference of the sensor array, and extract the intensity and phase changes of the reflected wave to construct a wave speed field; Step S5: Perform wave speed field inversion to locate the damage position inside the wall.

2. The method for identifying damage of a wall structure based on a random excitation signal according to claim 1, characterized in that: In Step S1, the sensor array adopts a rectangular arrangement layout, and in Step S2, the excitation source knocks on the upper and lower or left and right sides of the sensor array.

3. A method for identifying damage to a wall structure based on a random excitation signal according to claim 1, characterized in that: Preprocess the collected vibration signals, including denoising processing and signal normalization.

4. A method for identifying damage to a wall structure based on a random excitation signal according to claim 3, characterized in that: The denoising processing includes low-pass filtering, band-pass filtering, and wavelet transform methods.

5. A method for identifying damage to a wall structure based on a random excitation signal according to claim 1, characterized in that: The method for determining the wave speed through the reception time difference of the sensor array in Step S4 includes: Step S411: Discretize the wave speed field area to be inverted into n grids, and determine the coordinates of each knocking and the coordinates of the sensor array; Step S412: Construct m transmit-receive pairs and determine the wave travel time of each transmit-receive pair; Step S413: Through the ray tracing algorithm FMM and the multi-template fast marching method MSFM, obtain the condition that the propagation time T(x,y) at the corresponding grid position (x,y) satisfies: In the formula, v represents the calculation template serial number; represents the included angle of the calculation template; Δh represents the distance between two adjacent calculation points; T v represents the wavefront propagation time corresponding to the template serial number; s represents the wavefront slowness.

6. A method for identifying damage to a wall structure based on a random excitation signal according to claim 1, characterized in that: In Step S5, the wave speed field inversion adopts an inversion algorithm based on wave speed difference or a numerical simulation method combined with finite element analysis.

7. A method for identifying damage to a wall structure based on a random excitation signal according to claim 1, characterized in that: In Step S2, a force hammer is used as the excitation source for knocking.

8. A method for identifying damage to a wall structure based on a random excitation signal according to claim 7, characterized in that: When the wall to be detected is a rigid wall, the hammer head of the force hammer is selected from a material with a contact stiffness ratio with the wall greater than 1.5 times; when the wall to be detected is a flexible wall, the hammer head of the force hammer is selected from a material with a contact stiffness ratio with the wall not greater than 1.2 times.

9. An electronic device, comprising: A memory, a processor, and a computer program, characterized in that: the computer program is stored in the memory and is configured to be executed by the processor to implement the method according to any one of claims 1 to 8.

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