CN112161785A - Ocean engineering structure micro-damage judgment method - Google Patents

Ocean engineering structure micro-damage judgment method Download PDF

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CN112161785A
CN112161785A CN202010960246.9A CN202010960246A CN112161785A CN 112161785 A CN112161785 A CN 112161785A CN 202010960246 A CN202010960246 A CN 202010960246A CN 112161785 A CN112161785 A CN 112161785A
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王树青
蒋玉峰
徐明强
郭建
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Ocean University of China
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Abstract

The invention discloses a method for judging tiny damage of an ocean engineering structure, which comprises the following steps: (1) carrying out vibration test on a perfect ocean engineering structure in an actual operation environment to obtain a perfect frequency matrix of the structure; (2) carrying out vibration test on the damaged ocean engineering structure in the actual operation environment to obtain a frequency matrix to be tested of the structure; (3) solving the projection direction with the optimized classification performance of intact and to-be-tested frequencies by carrying out linear discriminant analysis on the frequency matrix to obtain the frequency residual error of the intact and to-be-tested structures; (4) and carrying out structural damage judgment on the intact frequency residual error and the frequency residual error to be detected by a hypothesis testing technology. According to the scheme, the original frequency matrix is processed by using a linear discriminant analysis method, the influence of environmental factor change on the structural vibration characteristic is effectively eliminated, the frequency residual capable of reflecting structural health information is obtained, the accurate judgment on the micro damage state of the structure is realized by using an effective statistical hypothesis testing technology in a matching manner, and the method has certain guiding significance on early warning and maintenance reinforcement decision of the structure.

Description

Ocean engineering structure micro-damage judgment method
Technical Field
The invention relates to the field of ship and ocean engineering, in particular to a method for judging tiny damage of an ocean engineering structure under the conditions of environmental factors and noise interference.
Background
Ocean engineering structures such as ocean platforms and offshore wind turbines are basic facilities for ocean oil gas and wind energy resource development, and are in severe ocean environments for a long time, fatigue accumulation damage is easy to occur, structure failure is caused, and huge economic loss is caused. Therefore, the method is very important for carrying out damage detection on the ocean engineering structure.
The common method for detecting the structural damage of the ocean engineering at the present stage can be summarized into local detection and overall detection, wherein the local detection method starts earlier and develops relatively mature; for example, magnetic particle inspection, ray inspection, ultrasonic guided wave inspection and the like are adopted, but the method is only limited to a local area of the structure and is difficult to reflect the whole state information of the structure; in addition, the local detection position needs to be determined in advance, and the detection efficiency is extremely low when the damage position is unknown. In contrast, the integral detection method based on the structural vibration characteristics can completely reflect the integral state information of the structure, can provide enough structural performance evolution and degradation information, is particularly suitable for monitoring the ocean engineering structure in real time, and can provide certain guiding significance for the structure life evaluation and maintenance reinforcement decision. The basic principle is as follows: the damage of the structure can cause the change of the physical characteristics of the structure, thereby changing the modal parameters of the structure; and the overall state information of the structure is inverted by obtaining the modal parameters reflecting the physical characteristics of the structure. Common modal parameters are frequency, mode shape, damping ratio, and multi-parameter derivatives.
With the rapid improvement of computer level and data acquisition capability, the overall detection method based on modal parameters is greatly developed. It is noted that most of these methods do not consider the influence of changes in marine environmental factors on the performance of damage detection. The change of the marine environmental factors such as temperature, marine organism attachment, basic scouring and the like can also cause the change of the physical characteristics of the structure, influence the change of the modal parameters of the structure, and even cover the change of the modal parameters caused by the real damage of the structure, especially for early/micro damage. The detection of the tiny damage of the ocean engineering structure considering environmental factors and noise pollution is a difficult problem to be solved urgently at present.
The early detection and diagnosis of the early/small damage of the structure are carried out, the effective structural operation state evaluation is carried out, and the method has important practical value for the safe operation guarantee of the ocean engineering structure.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a method for judging the micro-damage of the ocean engineering structure, which realizes the judgment of the micro-damage of the ocean engineering structure under the environment and noise pollution and has certain guiding significance for early warning and maintenance reinforcement decision of the structure.
The invention is realized by adopting the following technical scheme: a method for judging tiny damage of an ocean engineering structure comprises the following steps:
step A, carrying out vibration test on an intact ocean engineering structure in an actual operation environment to obtain an intact frequency matrix of the structure;
b, performing vibration test on the ocean engineering structure to be tested in the actual operation environment to obtain a frequency matrix to be tested of the structure, wherein whether the ocean engineering structure to be tested is damaged or not is unknown;
step C, performing linear discrimination analysis on the intact frequency matrix and the frequency matrix to be detected obtained in the step A and the step B, and solving the projection direction with optimized classification performance of the intact frequency matrix and the frequency matrix to be detected to obtain an intact frequency residual error and a frequency residual error to be detected of the ocean engineering structure;
and D, judging structural damage of the perfect frequency residual error and the frequency residual error to be detected based on a hypothesis testing technology.
Further, the frequency matrix of the intact ocean engineering structure obtained in the step a is specifically obtained by the following method:
(1) in an actual operation environment, measuring complete dynamic response time-course data of the ocean engineering structure by using an acceleration sensor or a displacement sensor;
(2) acquiring the first n-order modal frequency of the ocean engineering structure based on a modal parameter identification method, wherein the ith-order modal frequency is obtained by the jth measurement
Figure RE-GDA0002750496210000021
Represents;
(3) and (3) performing m vibration tests in total, combining the frequencies obtained by the tests to construct a complete frequency matrix omega of the structureh
Figure RE-GDA0002750496210000022
Further, in the step B, the same principle as that of the step a is adopted:
the method comprises the steps of carrying out m-time vibration test on an ocean engineering structure to be tested to construct a frequency matrix omega to be tested of the structurec
Figure RE-GDA0002750496210000023
Wherein the first n-th order modal frequency obtained by the jth measurement is calculated by
Figure RE-GDA0002750496210000024
And (4) showing.
Further, in the step C, the specific process of obtaining the intact frequency residual error and the frequency residual error to be measured of the ocean engineering structure is as follows:
(1) respectively carrying out equalization processing on the intact frequency matrix and the frequency matrix to be measured of the structure, wherein
Figure RE-GDA0002750496210000025
And
Figure RE-GDA0002750496210000026
modal frequency matrix omega representing intact ocean engineering structure and ocean engineering structure to be measuredhAnd ωcAverage of row i;
Figure RE-GDA0002750496210000031
(2) analyzing to obtain the frequency matrix of the intact ocean engineering structure and the intra-class variance and S of the frequency matrix of the ocean engineering structure to be detectedwWherein
Figure RE-GDA0002750496210000032
And
Figure RE-GDA0002750496210000033
the intra-class variance is expressed as a modal frequency matrix of the intact ocean engineering structure and the ocean engineering structure to be tested;
Figure RE-GDA0002750496210000034
Figure RE-GDA0002750496210000035
Figure RE-GDA0002750496210000036
(3) calculating to obtain the optimal classification performance projection vector P of the intact frequency matrix and the frequency matrix to be measured;
P＝Sw -1(mh-mc) (7)
(4) projecting and dimensionality-reducing the intact frequency matrix and the frequency matrix to be detected of the ocean engineering structure through the projection vector P to obtain corresponding intact frequency residual error and frequency residual error to be detected;
Figure RE-GDA0002750496210000037
Figure RE-GDA0002750496210000038
wherein, formula (8) is the perfect frequency residual, and formula (9) is the frequency residual to be measured.
Further, in the step D, when the structural damage is determined, the following method is adopted:
(1) assuming the mean of the intact frequency residual and the to-be-measured frequency residual is equal to the original hypothesis H0The average values are assumed to be unequal H1；
H0：μh＝μc(10)
H1：μh≠μc(11)
(2) Calculating a statistical hypothesis test magnitude, t, where μ and σ represent the mean and standard deviation of the frequency residuals;
Figure RE-GDA0002750496210000039
(3) determining a confidence level alpha, calculating a hypothesis testing quantity threshold t*；
P(t＜t*)＝1-α/2 (13)
(4) Comparing the hypothesis test magnitude | t | with a test magnitude threshold t*Judging whether the ocean engineering structure is damaged or not;
Figure RE-GDA00027504962100000310
Figure RE-GDA00027504962100000311
the judgment criterion is as follows: if the hypothesis testing magnitude is larger than the threshold value, rejecting the original hypothesis and considering that the structure is damaged; otherwise, the structure is considered not to be damaged.
Compared with the prior art, the invention has the advantages and positive effects that:
according to the scheme, the original frequency matrix is processed by using a linear discriminant analysis method, so that the influence of environmental factor change on the structural vibration characteristic is effectively eliminated, a frequency residual capable of reflecting structural health information is obtained, and the accurate judgment on the tiny damage state of the structure is realized by using an effective statistical hypothesis testing technology in a matching manner;
moreover, only the vibration response of the structure needs to be measured, the current environmental factors do not need to be measured, only the intact ocean platform and the damaged ocean platform need to be measured in a short term respectively, and long-term continuous monitoring is not needed; the damage judgment process can be completed by only arranging one sensor, so that the difficulty of damage detection is greatly reduced, and the cost is saved;
the method realizes judgment of the micro damage of the ocean engineering structure under environmental and noise pollution, is beneficial to finding the early damage/micro damage of the structure, and has certain guiding significance for early warning and maintenance reinforcement decision of the structure.
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FIG. 1 is a schematic diagram of a finite element model of an offshore wind turbine structure according to an embodiment of the present invention; (a) numbering schematic diagrams of structural nodes of the offshore wind turbine, (b) numbering schematic diagrams of structural units of the offshore wind turbine, (b) in 14, a diagonal unit and 10, a cross-brace unit;
FIG. 2 is a diagram showing the result of the determination of the small damage under the influence of no noise and environmental factors;
fig. 3 is a diagram showing the result of the determination of the micro damage under the influence of 0.15% noise and environmental factors.
Detailed Description
In order to make the above objects, features and advantages of the present invention more clearly understood, the present invention will be further described with reference to the accompanying drawings and examples. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, however, the present invention may be practiced in other ways than those described herein, and thus, the present invention is not limited to the specific embodiments disclosed below.
A method for judging tiny damage of an ocean engineering structure comprises the following steps:
firstly, carrying out vibration test on a perfect ocean engineering structure in an actual operation environment to obtain a perfect frequency matrix of the structure;
secondly, performing vibration test on the ocean engineering structure to be tested in the actual operation environment to obtain a frequency matrix to be tested of the structure, wherein whether the ocean engineering structure to be tested is damaged or not is unknown;
thirdly, solving the projection direction with optimized classification performance of the intact frequency matrix to be detected and the frequency matrix to be detected by carrying out linear discrimination analysis on the intact frequency matrix and the frequency matrix to be detected to obtain an intact frequency residual error and a frequency residual error to be detected of the ocean engineering structure;
the fourth step: and carrying out structural damage judgment on the intact frequency residual error and the frequency residual error to be detected by a hypothesis testing technology.
Specifically, the following describes the determination method in detail with reference to specific embodiments:
in the first step, a vibration test is carried out on an intact ocean engineering structure in an actual working environment, and the specific steps of obtaining a frequency matrix of the intact ocean engineering structure are as follows:
(1) in an actual operation environment, measuring complete dynamic response time-course data of the ocean engineering structure by using an acceleration sensor and a displacement sensor;
(2) acquiring the first n-order modal frequency of the ocean engineering structure based on a modal parameter identification method, wherein the ith-order modal frequency is obtained by the jth measurement
Figure RE-GDA0002750496210000051
Represents;
(3) and (3) performing m vibration tests in total, combining the frequencies obtained by the tests to construct a complete frequency matrix omega of the structureh
Figure RE-GDA0002750496210000052
In the second step, the marine engineering structure to be tested in the actual operation environment is subjected to vibration test, and the specific steps of obtaining the frequency matrix to be tested of the marine engineering structure are as follows:
the method comprises the steps of carrying out m-time vibration test on a damaged ocean engineering structure, and constructing a frequency matrix omega of the ocean engineering structure to be tested according to the step of obtaining the frequency vibration mode of the intact structure of the ocean engineeringc
Figure RE-GDA0002750496210000053
Wherein the first n-th order modal frequency obtained by the jth measurement is calculated by
Figure RE-GDA0002750496210000054
And (4) showing.
In the third step, the interference of environmental factors is eliminated by performing linear discrimination analysis on the intact frequency matrix and the frequency matrix to be detected, and the concrete steps of obtaining the intact frequency residual error and the frequency residual error to be detected are as follows:
(1) respectively carrying out equalization processing on the intact frequency matrix and the frequency matrix to be measured, wherein
Figure RE-GDA0002750496210000055
And
Figure RE-GDA0002750496210000056
modal frequency matrix omega representing intact ocean engineering structure and ocean engineering structure to be measuredhAnd ωcAverage of row i;
Figure RE-GDA0002750496210000057
(2) analyzing to obtain the frequency matrix of the intact ocean engineering structure and the intra-class variance and S of the frequency matrix of the ocean engineering structure to be detectedwWherein
Figure RE-GDA0002750496210000058
And
Figure RE-GDA0002750496210000059
the intra-class variance is expressed as a modal frequency matrix of the intact ocean engineering structure and the ocean engineering structure to be tested;
Figure RE-GDA00027504962100000510
Figure RE-GDA0002750496210000061
Figure RE-GDA0002750496210000062
(3) calculating to obtain the optimal classification performance projection vectors of the intact frequency matrix and the frequency matrix to be measured;
P＝Sw -1(mh-mc) (7)
(4) projecting and dimension-reducing the frequency matrix of the intact ocean engineering structure and the frequency matrix of the ocean engineering structure to be detected through the projection vector P to obtain corresponding intact frequency residual error and frequency residual error to be detected;
Figure RE-GDA0002750496210000063
Figure RE-GDA0002750496210000064
wherein, formula (8) is the perfect frequency residual, and formula (9) is the frequency residual to be measured.
And in the fourth step, judging the structural damage of the intact frequency residual error and the frequency residual error to be detected by a hypothesis testing technology, and specifically comprising the following steps of:
(1) falseAssuming the mean of the intact frequency residual and the to-be-measured frequency residual is equal to the original hypothesis H0The average values are assumed to be unequal H1；
H0：μh＝μc (10)
H1：μh≠μc (11)
(2) Calculating statistical hypothesis test magnitudes, where μ and σ represent the mean and standard deviation of the frequency residuals;
Figure RE-GDA0002750496210000065
(3) determining a confidence level alpha, calculating a hypothesis testing quantity threshold t*；
P(t＜t*)＝1-α/2 (13)
(4) Comparing the hypothesis test magnitude | t | with a test magnitude threshold t*Judging whether the ocean engineering structure is damaged or not;
Figure RE-GDA0002750496210000066
Figure RE-GDA0002750496210000067
the judgment criterion is as follows: if the hypothesis testing magnitude is larger than the threshold value, rejecting the original hypothesis and considering that the structure is damaged; otherwise, the structure is considered not to be damaged.
To verify the effectiveness of the above method, a typical marine offshore wind turbine structure is illustrated as follows:
firstly, establishing a finite element model:
as shown in fig. 1, the marine wind turbine structure under simulation study in this embodiment is composed of a support structure and a tower structure, and includes 18 nodes and 20 units. And (3) writing a finite element program by using MATLAB software, and establishing a finite element model by using a computer to serve as a reference finite element model of an intact ocean platform. And then, simulating different damage working conditions under different working environments to obtain the modal frequency simulating actual measurement. The method simulates various damage working conditions, including damage at different positions and damage in different degrees.
Second, simulation of structural damage and environmental conditions
When the ocean engineering structure is damaged, the overall rigidity of the material is lost, and the material is uniformly simplified into that the elastic modulus on a damaged unit is uniformly weakened. Meanwhile, the overall rigidity of the structure is also affected by changes of environmental conditions, wherein the most typical environmental conditions include temperature, basic scouring and the like, and in the embodiment, temperature factors are selected for simulation. The change of temperature generally causes the change of the elastic modulus of the material, and further influences the rigidity of the ocean platform, and experimental research shows that the elastic modulus and the temperature present a strong linear relationship
E(Tt)＝E(T0)+τ(Tt-T0) (16)
Wherein E (T)0) For the value of the modulus of elasticity in the reference state, the temperature is usually set to 10 ℃ and the corresponding modulus of elasticity is 2.06X 1011Pa; tau is the coefficient of variation of the elastic modulus of steel with temperature and is taken as 1 x 108Pa/℃。
The method is characterized in that the intact and damaged offshore wind turbine structure is supposed to be tested for 1000 times, the temperature difference between the seawater and the air is considered, the temperature in the air is supposed to be subjected to standard normal distribution with the mean value of 10 ℃ and the standard deviation of 8 ℃, and the temperature in the seawater is supposed to be subjected to standard normal distribution with the mean value of 15 ℃ and the standard deviation of 4 ℃.
Thirdly, analyzing damage judgment result
The scheme of the invention is utilized to judge the micro damage of the offshore wind turbine structure, and four working conditions are considered as follows: the working condition I is as follows: the bracing unit is damaged by 1%; working conditions are as follows: 1% of damage to the cross brace unit; working conditions are as follows: the bracing unit is damaged by 3%; working conditions are as follows: 3% of damage to the cross brace unit; each working condition adopts 50 times of repeated tests, and the accuracy of judging the tiny damage is calculated;
as shown in fig. 3, under the influence of no noise, the test statistic of the four damage conditions is assumed to be much larger than the test statistic threshold (1.96), so that the damage determination accuracy of the four damage conditions is 100%; under the influence of 0.15% noise, only 7 times (working condition one) are judged to be healthy by mistake, other 193 times of repeated tests can accurately judge the micro damage of the structure, and the micro damage judgment accuracy rate is 96.5%.
The above description is only a preferred embodiment of the present invention, and not intended to limit the present invention in other forms, and any person skilled in the art may apply the above modifications or changes to the equivalent embodiments with equivalent changes, without departing from the technical spirit of the present invention, and any simple modification, equivalent change and change made to the above embodiments according to the technical spirit of the present invention still belong to the protection scope of the technical spirit of the present invention.

Claims (5)

1. A method for judging tiny damage of an ocean engineering structure is characterized by comprising the following steps:
step A, carrying out vibration test on an intact ocean engineering structure in an actual operation environment to obtain an intact frequency matrix of the structure;
b, performing vibration test on the ocean engineering structure to be tested in the actual operation environment to obtain a frequency matrix to be tested of the structure, wherein whether the ocean engineering structure to be tested is damaged or not is unknown;
step C, performing linear discrimination analysis on the intact frequency matrix and the frequency matrix to be detected obtained in the step A and the step B, and solving the projection direction with optimized classification performance of the intact frequency matrix and the frequency matrix to be detected to obtain an intact frequency residual error and a frequency residual error to be detected of the ocean engineering structure;
and D, judging structural damage of the perfect frequency residual error and the frequency residual error to be detected based on a hypothesis testing technology.
2. The method for determining the micro damage of the oceaneering structure according to claim 1, wherein: the frequency matrix of the intact ocean engineering structure obtained in the step A is specifically obtained by the following method:
(1) in an actual operation environment, measuring complete dynamic response time-course data of the ocean engineering structure by using an acceleration sensor or a displacement sensor;
(2) acquiring the first n-order modal frequency of the ocean engineering structure based on a modal parameter identification method, wherein the ith-order modal frequency is obtained by the jth measurement
Figure FDA0002680286670000013
Represents;
(3) and (3) performing m vibration tests in total, combining the frequencies obtained by the tests to construct a complete frequency matrix omega of the structureh
Figure FDA0002680286670000011
Wherein the first n-th order modal frequency obtained by the jth measurement is calculated by
Figure FDA0002680286670000014
And (4) showing.
3. The method for determining the micro damage of the oceaneering structure according to claim 2, wherein: in the step B, the same principle as the step A is adopted:
the method comprises the steps of carrying out m-time vibration test on an ocean engineering structure to be tested to construct a frequency matrix omega to be tested of the structurec
Figure FDA0002680286670000012
Wherein the first n-th order modal frequency obtained by the jth measurement is calculated by
Figure FDA0002680286670000015
And (4) showing.
4. The method for determining the micro damage of the oceaneering structure according to claim 3, wherein: in the step C, the specific process of obtaining the intact frequency residual error and the frequency residual error to be measured of the ocean engineering structure is as follows:
(1) respectively carrying out equalization processing on the intact frequency matrix and the frequency matrix to be measured of the structure, wherein
Figure FDA0002680286670000028
And
Figure FDA0002680286670000029
modal frequency matrix omega representing intact ocean engineering structure and ocean engineering structure to be measuredhAnd ωcAverage of row i;
Figure FDA0002680286670000021
(2) analyzing to obtain the frequency matrix of the intact ocean engineering structure and the intra-class variance and S of the frequency matrix of the ocean engineering structure to be detectedwWherein
Figure FDA00026802866700000210
And
Figure FDA00026802866700000211
the intra-class variance is expressed as a modal frequency matrix of the intact ocean engineering structure and the ocean engineering structure to be tested;
Figure FDA0002680286670000022
Figure FDA0002680286670000023
Figure FDA0002680286670000024
(3) calculating to obtain the optimal classification performance projection vector P of the intact frequency matrix and the frequency matrix to be measured;
P＝Sw -1(mh-mc) (7)
(4) projecting and dimensionality-reducing the intact frequency matrix and the frequency matrix to be detected of the ocean engineering structure through the projection vector P to obtain corresponding intact frequency residual error and frequency residual error to be detected;
Figure FDA0002680286670000025
Figure FDA0002680286670000026
wherein, formula (8) is the perfect frequency residual, and formula (9) is the frequency residual to be measured.
5. The method for determining the micro damage of the oceaneering structure according to claim 4, wherein: in the step D, when the structural damage is determined, the following method is adopted:
(1) assuming the mean of the intact frequency residual and the to-be-measured frequency residual is equal to the original hypothesis H0The average values are assumed to be unequal H1；
H0：μh＝μc (10)
H1：μh≠μc (11)
(2) Calculating a statistical hypothesis test magnitude, t, where μ and σ represent the mean and standard deviation of the frequency residuals;
Figure FDA0002680286670000027
(3) determining a confidence level alpha, calculating a hypothesis testing quantity threshold t*；
P(t＜t*)＝1-α/2 (13)
(4) Comparing the hypothesis test magnitude | t | with a test magnitude threshold t*Judging whether the ocean engineering structure is damaged or not;
Figure FDA0002680286670000031
Figure FDA0002680286670000032
the judgment criterion is as follows: if the hypothesis testing magnitude is larger than the threshold value, rejecting the original hypothesis and considering that the structure is damaged; otherwise, the structure is considered not to be damaged.
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