Method for batch detection of quality of test point results in modal test

Abstract

The invention discloses a method for batch detection of test point result quality in modal testing, which belongs to the technical field of modal testing, and comprises the following steps of: after all test points in the modal testing are tested, selecting a constant coherence function test result drop area proportion of one test point as a judgment condition; and when the test result does not pass the judgment, that is, the coherence of multiple tests of a certain test point is poor, and the test needs to be retested. According to the invention, the test results of all test points in a test project can be rapidly detected in batches, modal test points needing to be retested are automatically screened, and the time for manually judging and detecting the test result data of all test points one by one is saved; the method has the advantages that human judgment experience instability factors caused by frequent coherence and frequency response functions when an engineer observes test results of each test point one by one are reduced, the labor and time cost is reduced, the test efficiency is improved, and the objectivity and accuracy of evaluation results are guaranteed through uniform and fixed judgment condition evaluation.

Description

Technical Field

[0001] The present invention belongs to the technical field of modal testing, and particularly relates to a method for batch detection of the quality of measurement point results in modal testing. Background Art

[0002] With the progress of society and the development of technology, modal testing, as an engineering testing method widely used in the fields of mechanical engineering, civil engineering, aerospace engineering, power systems, etc., obtains the frequency response function of the measurement points of the structure through experimental measurement, extracts modal parameters from the frequency response function, and is used for modal identification and evaluation of the actual structure, analyzes the modal characteristics of the system, and predicts and improves the system performance.

[0003] At present, the quality of all measurement point result data in modal testing is judged by test engineers observing the coherence function and frequency response function of the test results of each test point one by one; this judgment method has problems such as unstable human judgment experience, high time cost of manual judgment, and low practicality of test efficiency. Summary of the Invention

[0004] In order to solve the deficiencies of the prior art and achieve the purpose of batch detection of the quality of measurement point results in the modal testing of structures, the present invention adopts the following technical solutions:

[0005] A method for batch detection of the quality of measurement point results in modal testing includes the following steps:

[0006] Step S1: Conduct modal testing on the structural member to obtain the modal testing results of each measurement point of the structural member;

[0007] Step S2: Set a non-range difference threshold for the modal testing results of the measurement points, select reference measurement points whose modal testing results are better than the non-range difference threshold from the measurement points, and set judgment conditions based on the reference measurement points;

[0008] Step S3: Judge whether the modal testing structures of each measurement point meet the judgment conditions. If all meet, execute Step S4; otherwise, execute Step S5;

[0009] Step S4: The modal testing results of each measurement point are judged to pass;

[0010] Step S5: Retest the measurement points that do not meet the judgment conditions to obtain the modal testing structure, and return to Step S3.

[0011] Further, in step S2, a non-extreme difference threshold is set for the constant coherence function in the modal test results of the measurement points. The reference measurement points that are better than the non-extreme difference threshold of the constant coherence function are selected from the measurement points. The total area is constructed based on the start frequency, end frequency, upper amplitude limit, and lower amplitude limit of the constant coherence function of the reference measurement points. The ratio of the drop area to the total area in the total area is obtained to get the drop area ratio, and the drop area ratio is used as the drop ratio limit for condition determination.

[0012] Further, the modal test in step S1 is to obtain the frequency response function of the structure measurement points through measurement, and extract the modal parameters from the frequency response function; the constant coherence function in step S2 is used to judge the degree of linear correlation between the current test frequency response function of the measurement point and the average test result of the frequency response functions obtained from multiple previous tests, so as to evaluate the quality of the frequency response function of the modal test result of the measurement point through the constant coherence function of the measurement point.

[0013] Further, the formula for the constant coherence function in step S2 is as follows:

[0014]

[0015] where represents the constant coherence function at frequency , ranging between [0, 1], represents and the cross-power spectral density of and respectively represent and the auto-power spectral densities of , if , it means that and are completely linearly correlated at frequency , if , it means that and have no linear relationship at frequency , if is the median value between 0 and 1, it means that and are partially linearly correlated at frequency represents the value of the current test frequency response function of the measurement point, represents the average value of the frequency response functions obtained from multiple previous tests of the measurement point.

[0016] Further, in step S3, the ratio of the drop area generated by each measurement point based on the constant coherence function is compared with the drop ratio limit. If the ratio of the drop area of each measurement point is less than or equal to the drop ratio limit, step S4 is executed; otherwise, step S5 is executed. In step S5, the measurement points with a drop area ratio greater than the drop ratio limit are determined to be unqualified, and the unqualified measurement points are redirected to step S3 for retesting until the modal test results of all measurement points are determined to be qualified.

[0017] Further, the modal test in step S1 is to obtain the frequency response function of the structure measurement points through measurement and extract the modal parameters from the frequency response function. In step S2, significant features are set for the frequency response function of the measurement points, and the selected measurement points that meet the significant features are selected from the measurement points, with the frequency value where the significant features of the frequency response function of the selected measurement points are located as the judgment condition. In step S3, a judgment frequency interval is set for the frequency value. If the frequency response functions of each measurement point also have significant features within the judgment frequency interval of the frequency value, the judgment condition is met and step S4 is executed; otherwise, step S5 is executed.

[0018] Further, in step S2, the identification frequency band of the peak points of the frequency response function is set based on the distribution of the peak points of the frequency response function of the measurement points, and the condition judgment of the measurement points is carried out within the identification frequency band.

[0019] Further, in step S2, the significant features include the peak point frequency. The frequency value where the peak point of the frequency response function of the selected measurement points is located is used as the judgment frequency point, and a judgment frequency interval is set for the judgment frequency point. If the frequency response functions of each measurement point also have peak points within the judgment frequency interval, the judgment condition is met.

[0020] Further, the formula for the judgment condition is as follows:

[0021]

[0022]

[0023]

[0024] Where is an intermediate variable representing the frequency where the maximum peak point of the measurement point is located and the frequency where the peak point of the selected measurement point is located is the absolute value of the difference, represents the judgment frequency interval, represents and is the ratio of, i represents the index of the judgment frequency point, and the selected measurement points include a set of judgment frequency points. It indicates that the judgment condition is met, there is a peak point at the measurement point within the judgment frequency range, the measurement point is judged qualified, and the modal test result is qualified. Otherwise, there is no peak within the judgment frequency range of the peak point, the judgment condition is not met, and the measurement point needs to be manually judged whether it is qualified and whether retesting is required.

[0025] Further, in step S3, for the measurement points that do not meet the judgment condition, manual judgment is performed. For the measurement points that fail the manual judgment, retesting is performed through step S5 to obtain the modal test result, and then return to step S3 for re-judgment; the basis for manual judgment: in modal testing, when it is difficult to excite the measurement points at the modal vibration mode nodes at a certain natural frequency (i.e., a peak point in the frequency response function), this is due to the inherent property of the measured structural member, rather than poor test quality of the measurement point. Therefore, in this case, retesting is not required. Otherwise, retesting is required.

[0026] The advantages and beneficial effects of the present invention are as follows:

[0027] The present invention selects any measurement point with a normal coherence function that is not extremely poor among all the modal test results of the measurement points, and uses the proportion of the coherence function drop area in the modal test result of this measurement point as the judgment condition to batch and uniformly judge the results of all measurement points, ensuring the objectivity and accuracy of the judgment results and avoiding the unstable factors of human judgment experience; the present invention quickly judges the quality of all measurement point test results by batch comparing the proportion of the coherence function drop area of all measurement point modal test results with the judgment condition at one time, accurately screens out the measurement points with unqualified test result quality for retesting and re-judgment, improves the quality of the modal test results, saves the time cost of human judgment and screening of the modal test results by test engineers, and enhances the practicality of the modal test efficiency. Description of the Drawings

[0028] Figure 1 is the flowchart of the method in an embodiment of the present invention.

[0029] Figure 2 is a schematic diagram of using the coherence function at the measurement points of a structural member in an embodiment of the present invention as the judgment condition.

[0030] Figure 3 is the flowchart of the method in another embodiment of the present invention.

[0031] Figure 4 is a schematic diagram of using the frequency response function at the measurement points of a structural member in another embodiment of the present invention as the judgment condition. Detailed Embodiments

[0032] The following will describe the detailed embodiments of the present invention in conjunction with the drawings. It should be understood that the detailed embodiments described herein are only for explaining and illustrating the present invention, and are not used to limit the present invention.

[0033] As Figure 1 shown, a method for batch detection of the quality of measurement point results in modal testing includes the following steps:

[0034] Step S1: Conduct modal testing on the structural member to obtain the modal testing results of all measurement points;

[0035] Step S2: In modal analysis, the ordinary coherence function is used to evaluate the strength of the linear relationship between two signals. Select any measurement point with a non-extreme ordinary coherence function from the modal testing results of all measurement points, and use the proportion of the falling area of the ordinary coherence function in the modal testing results of this measurement point as the judgment condition, where the judgment condition can be set, that is, quality inspection setting;

[0036] Select a certain measurement point of the structural member as the reference measurement point, and conduct quality inspection setting on the ordinary coherence function of this reference measurement point. The quality inspection setting can select the range of the ordinary coherence function of the measurement point used as the judgment condition. This range is formed by the starting frequency of ordinary coherence function judgment, the ending frequency of ordinary coherence function judgment, the upper limit of ordinary coherence function judgment amplitude, and the lower limit of ordinary coherence function judgment amplitude, as Figure 2 shown:

[0037] L1: Set the "starting frequency line of ordinary coherence function judgment";

[0038] L2: Set the "ending frequency line of ordinary coherence function judgment";

[0039] L3: Set the "upper limit line of ordinary coherence function judgment amplitude";

[0040] L4: Set the "lower limit line of ordinary coherence function judgment amplitude";

[0041] S 阴1 : The area formed by L1, L2, L3, and L4;

[0042] S 阴0 : The falling area of the ordinary coherence function of the reference measurement point in S 阴1 ;

[0043] Select the proportion of the falling area of the ordinary coherence function of the measurement point used as the judgment condition, and automatically set it as the falling ratio limit value. This falling ratio limit value can also be manually changed and set.

[0044] Modal testing obtains the frequency response function of the measurement points of the structure through experimental measurement, so as to extract modal parameters from the frequency response function for modal identification and evaluation of the actual structure, analyze the modal characteristics of the system, and predict and improve the system performance. Therefore, as the measurement point result data of modal testing, the quality of the frequency response function plays a decisive role in the ultimate goal of modal testing.

[0045] The coherence function is obtained by dividing the square of the magnitude of the cross-spectrum by the product of the auto-spectra, representing the degree of linear correlation between two signals. Among them, when it is the real number "0", it indicates no linear correlation, and when it is the real number "1", it indicates complete linear correlation. In modal testing, the coherence function is usually used to judge the linear relationship between the system response signal and the excitation signal, or to evaluate the influence of measurement noise. In the present invention, the coherence function is used to evaluate the frequency response function of the average test result obtained from multiple tests at each measurement point, that is, to judge the degree of linear correlation between the current test frequency response function of the measurement point and the average test result of the frequency response function obtained from multiple previous tests. Therefore, the quality of the frequency response function of the modal test result of the measurement point can be evaluated by the coherence function of the measurement point.

[0046] The calculation formula is as follows:

[0047]

[0048] Among them, represents the coherence function value at frequency , and the range is between [0, 1]. represents and 's cross-power spectral density. and respectively represent and 's auto-power spectral density. If , it means and are completely linearly correlated at frequency . If , it means and have no linear relationship at frequency . If is the median value between 0 and 1, it means and are partially linearly correlated at frequency . represents the current test frequency response function value of the measurement point. represents the average value of the frequency response functions obtained from multiple previous tests at the measurement point.

[0049] Step S3: Judge whether the coherence functions of the test results of all measurement points are within the set drop area ratio. If so, execute Step S4; otherwise, execute Step S5.

[0050] The judgment method is to check whether the ratio of the drop area of the coherence functions of the test results of all measurement points within the judgment range to the area of the judgment range exceeds the drop ratio limit; specifically:

[0051] The proportion of the drop in the coherence function of the reference measurement points of the selected structural members is A0, and this value is set as the limit value of the structural member drop ratio. A0 satisfies:

[0052] A0 = S 阴0 / S 阴1

[0053] The proportion of the drop in the coherence function of the modal test results of any measurement point of the structural member is A X , A X satisfies:

[0054] A x = S 阴x / S 阴1

[0055] where S 阴X represents the drop area of the coherence function of any measurement point in S 阴1 ;

[0056] Compare the proportion of the drop in the coherence function A X of the modal test results of any measurement point of the structural member with the drop ratio limit value A0 to determine whether all measurement points satisfy:

[0057] A X ≤ A0

[0058] If all measurement points satisfy A X ≤ A0, that is, the proportion of the drop area of the coherence function of the test results of all measurement points is within the set drop area proportion, then execute step S4. If not all measurement points satisfy A X ≤ A0, that is, the proportion of the drop area of the coherence function of the test results of not all measurement points is within the set drop area proportion, then execute step S5.

[0059] Step S4: The modal test results of all measurement points are judged to pass;

[0060] Step S5: Screen out the measurement points that are not within the set drop area proportion and judge them as not passing; Retest the measurement points with unqualified test results and re-obtain the modal test results. Because the coherence function drops significantly, it means that most of them are not 1 and the linear correlation degree is weak. That is to say, it indicates that the correlation degree of the frequency response functions obtained from multiple tests of this measurement point is weak. In this case, this measurement point needs to be retested to exclude the situation where the frequency response of a certain or multiple tests of this measurement point is not measured well. Then, jump to step S3 and judge again whether the coherence function of the test results of all measurement points is within the set drop area proportion until the modal test results of all measurement points are judged to pass.

[0061] In the modal test of a certain structural member in this embodiment, a test method for batch detection of the quality of all measurement point results defines the judgment conditions for the modal test results of the measurement points of the structural member, that is, the quality inspection setting scheme. It can batch, quickly, and accurately judge the quality of the modal test results of all measurement points of the structural member, screen out the measurement points with unqualified test results for retesting and rejudgment, improve the quality of the test results of the modal test, save the time cost of manual judgment and screening of the test results of the modal test by test engineers, and enhance the practicality of the test efficiency of the modal test.

[0062] In another embodiment, it directly judges whether the test result of the measurement point is qualified from the perspective of the frequency response function of the measurement point. As Figure 3 shown, the specific steps are as follows:

[0063] Select the frequency response function of a certain measurement point, and require that the frequency response function is smooth and has obvious peaks. Set the identification frequency band of the peak point of the frequency response function; use the frequency value of the peak point of the selected frequency response function of the measurement point as the judgment frequency point, and set the judgment frequency interval for the judgment frequency point; require that the frequency response functions of other measurement points also have peaks within the peak point judgment frequency interval; otherwise, screen out the non-compliant measurement points for manual judgment, and retest the measurement points that fail the manual judgment.

[0064] As a frequency response function of a measurement point of the structural member used as a judgment condition, as Figure 4 shown.

[0065] L1: The line of the "starting point of the peak point judgment frequency band of the frequency response function" set;

[0066] L2: The line of the "ending point of the peak point judgment frequency band of the frequency response function" set;

[0067] The lines L1 and L2 determine the peak point identification frequency band F of the frequency response function (the non-gray section in Figure 4 , and there are 6 judgment frequency points in F). Set the peak point judgment frequency interval as ∆f, and compare the maximum peak point f in ∆f imax (because there may be multiple peak points in the peak point identification frequency interval) with the peak f of the measurement point used as the judgment condition i to judge whether it is within the identification interval:

[0068]

[0069]

[0070]

[0071] When all the frequency response functions θ of the measurement points i meet the conditions, there are peaks within the peak point judgment frequency interval, and the measurement point is judged to be qualified, and the modal test result is qualified; when there are θ in the frequency response function of the measurement point iWhen the conditions are not met, there is no peak value within the peak point judgment frequency range, and manual judgment is required for this measurement point to determine whether it is qualified and whether retesting is needed.

[0072] Basis for manual judgment: In modal testing, the measurement points at the modal vibration mode nodes are difficult to be excited at a certain natural frequency (i.e., a certain peak point in the frequency response function). This is due to the inherent properties of the structure under test, rather than poor test quality of the measurement points. Therefore, retesting is not required in this case.

[0073] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for batch detection of the quality of measurement points in modal testing, characterized in that It includes the following steps: Step S1: Conduct a modal test on the structural member to obtain the modal test results of each measuring point of the structural member; Step S2: Set a non-range difference threshold for the modal test results of the measuring points, select reference measuring points from the measuring points whose modal test results are better than the non-range difference threshold, and set a judgment condition based on the reference measuring points; Step S3: Judge whether the modal test results of each measuring point meet the judgment condition. If all meet, execute Step S4; otherwise, execute Step S5; Step S4: The modal test results of each measuring point are judged to pass; Step S5: Retest the measuring points that do not meet the judgment condition to obtain the modal test results, and return to Step S3.

2. The method for batch detection of the quality of measurement point results in a modal test according to claim 1, wherein: In Step S2, set a non-range difference threshold for the coherence function in the modal test results of the measuring points, select reference measuring points from the measuring points that are better than the non-range difference threshold of the coherence function, construct a total area based on the start frequency, end frequency, amplitude upper limit, and amplitude lower limit of the coherence function of the reference measuring points, and obtain the proportion of the drop area in the total area by the ratio of the drop area in the total area to the total area. Use the proportion of the drop area as the drop ratio limit for condition judgment.

3. A method for batch detection of the quality of measurement point results in modal testing according to claim 2, characterized in that: In the modal test in Step S1, the frequency response function of the measuring points of the structure is obtained through measurement, and the modal parameters are extracted from the frequency response function; the coherence function in Step S2 is used to judge the degree of linear correlation between the current measured frequency response function of the measuring point and the average test results of the frequency response functions obtained from multiple previous tests.

4. A method for batch detection of the quality of measurement point results in modal testing according to claim 3, characterized in that: In the coherence function in Step S2, the cross-power spectral density of the current measured frequency response function value of the measuring point and the average value of the frequency response functions obtained from multiple previous tests of the measuring point, and the auto-power spectral density of each of them are obtained. Divide the square of the absolute value of the cross-power spectral density by the auto-power spectral density of each of them to obtain the coherence function value at the corresponding frequency; if the coherence function value is equal to one, it means that the current measured frequency response function value of the measuring point and the average value of the frequency response functions obtained from multiple previous tests of the measuring point are completely linearly correlated at the corresponding frequency; if the coherence function value is equal to zero, it means that there is no linear relationship between the current measured frequency response function value of the measuring point and the average value of the frequency response functions obtained from multiple previous tests of the measuring point at the corresponding frequency; if the coherence function value is the median value between zero and one, it means that the current measured frequency response function value of the measuring point and the average value of the frequency response functions obtained from multiple previous tests of the measuring point are partially linearly correlated at the corresponding frequency.

5. A method for batch detection of the quality of measurement point results in modal testing according to claim 2, characterized in that: In Step S3, compare the proportion of the drop area generated by each measuring point based on the coherence function with the drop ratio limit. If the proportion of the drop area of each measuring point is less than or equal to the drop ratio limit, execute Step S4; otherwise, execute Step S5; in Step S5, judge the measuring points with the proportion of the drop area greater than the drop ratio limit as not passing, and jump to Step S3 to retest the non-passing measuring points.

6. A method for batch detection of the quality of measurement point results in modal testing according to claim 1, characterized in that: The modal test in step S1 is to obtain the frequency response function of the structure's measurement points through measurement and extract modal parameters from the frequency response function; in step S2, significant features are set for the frequency response function of the measurement points, and selected measurement points that meet the significant features are selected from the measurement points, with the frequency value where the significant feature of the frequency response function of the selected measurement points is located as the judgment condition; in step S3, a judgment frequency interval is set for the frequency value. If the frequency response functions of each measurement point also have significant features within the judgment frequency interval of the frequency value, the judgment condition is met and step S4 is executed; otherwise, step S5 is executed.

7. A method for batch detection of the quality of measurement point results in modal testing according to claim 6, characterized in that: In step S2, an identification frequency band for the peak points of the frequency response function is set based on the distribution of the peak points of the frequency response function of the measurement points, and the condition determination of the measurement points is carried out within the identification frequency band.

8. A method for batch detection of the quality of measurement point results in modal testing according to claim 6, characterized in that: In step S2, the significant features include the peak point frequency. The frequency value where the peak point of the frequency response function of the selected measurement points is located is used as the judgment frequency point, and a judgment frequency interval is set for the judgment frequency point. If the frequency response functions of each measurement point also have peak points within the judgment frequency interval, the judgment condition is met.

9. A method for batch detection of the quality of measurement point results in modal testing according to claim 8, characterized in that: The judgment condition is to take the absolute value of the difference between the frequency where the maximum peak point of the measurement point is located and the frequency where the peak point of the selected measurement point is located as an intermediate variable, and obtain the ratio of the intermediate variable to the judgment frequency interval. If the ratio is greater than or equal to zero and less than one, the judgment condition is met, and the measurement point has a peak point within the judgment frequency interval; otherwise, the judgment condition is not met.

10. A method for batch detection of the quality of measurement point results in modal testing according to claim 6, characterized in that: In step S3, for the measurement points that do not meet the judgment condition, manual judgment is carried out. The measurement points that fail the manual judgment are retested through step S5 to obtain the modal test result, and then returned to step S3 for re-judgment; the basis for manual judgment: in modal testing, when it is difficult to excite a certain peak point in the frequency response function of the measurement points at the modal vibration mode nodes, retesting is not required; otherwise, retesting is required.

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