Hanhang NTS.LAB Link correlation analysis software module - building a bridge between finite element simulation and experiment

Hanspace

Hanhang NTS.LAB Link correlation analysis software module - building a bridge between finite element simulation and experiment [Copy link]

1. Basic principles of modal correlation analysis

Modal correlation analysis usually includes two aspects: model matching (which can be called model correlation analysis) and modal vibration type correlation analysis (modal correlation analysis for short). In addition, in order to meet the needs of frequency response function sensitivity analysis in model modification, frequency response function correlation analysis is also included. Among them:

(1) Model matching refers to aligning the test geometry model and the finite element mesh model through coordinate transformation methods such as rotation and scaling, and searching for vertex numbers and coordinates close to the measurement points in the finite element mesh model through least squares, geometric topology and other algorithms;

(2) Modal correlation analysis refers to the use of modal correlation coefficients between modal vibration modes of test and finite element analysis to characterize the similarity of modal vibration modes between two models based on model matching. The modal coefficient vibration correlation coefficient is also called the Modal Assurance Criterion (MAC). Its basic idea is to assume that the structural mass is approximately uniformly distributed, and the vibration modes of the structure have unweighted orthogonality.

The mode correlation coefficient is a scalar between 0 and 1. When the MAC value is 1, it means that the two modes are completely correlated and are the same mode; when the MAC value is 0, it means that the two modes are linearly independent. In engineering applications, when the diagonal elements of the MAC matrix are ≥ 70% and the non-diagonal elements are ≤ 10%, it can be considered that there is a good correlation between the two models.

(3) Frequency response function correlation analysis has the ability to quantify the overall and local differences between the corresponding frequency response functions of simulation analysis and experimental testing. Commonly used frequency response function correlation evaluation indicators include the frequency response function shape correlation coefficient (FSAC) and the frequency response function amplitude correlation coefficient (FAAC). The definitions of the shape correlation coefficient and amplitude correlation coefficient of the frequency response function are similar to the definitions of the modal confidence criterion and modal scale factor in the modal vibration shape correlation analysis, and are specifically defined as follows:

2. Related analysis module of China Airlines NTS.LAB Link

The correlation analysis module of NTS.LAB Link software includes model correlation analysis, modal correlation analysis and frequency response function correlation analysis. Model correlation analysis (model matching) is the prerequisite for the latter two analysis methods.

(1) Model correlation analysis

NTS.LAB Link supports four coordinate transformation methods: rotation, scaling, translation, and coordinate mapping to complete model alignment and node matching between the test model and the finite element model, as shown in Figures 1 and 2.

Figure 1. Scaling and translation parameter settings in model matching

Figure 2 Rotation and coordinate mapping parameter settings in model matching

NTS.LAB Link has a complete model matching result chart display function, through which the node correspondence between the test model and the finite element model can be clearly viewed.

Figure 3: Model matching result chart display

(2) Modal correlation analysis

NTS.LAB Link supports both automatic and manual modal matching modes, and has a unique modal shape matching algorithm for centrosymmetric models.

Figure 4 Modal manual matching dialog box

In addition to providing the modal frequency matching and vibration type correlation coefficients of each order test-finite element, NTS.LAB Link also has an excellent 3D vibration type comparison display function, making the advantages and disadvantages of modal correlation clear at a glance.

Figure 5: Modal shape matching comparison display

(3) Frequency response correlation analysis

NTS.LAB Link supports amplitude correlation analysis and shape correlation analysis of frequency response functions.

Figure 6. Cloud diagram of modal frequency points in frequency response function correlation analysis

3. The significance and application background of correlation analysis

Due to the uncertainty of boundary conditions, material properties and connections, there are inevitably differences between the finite element model calculation results and the experimental test results. If the difference between the two is large, the calculation results of the finite element model are considered unreliable. Correlation analysis is an important means to measure this difference.

Modal correlation analysis quantifies the finite element modeling error by calculating the deviation between the test and finite element modal frequencies and the degree of matching between the vibration modes, thereby checking the quality of the finite element calculation results. Therefore, the main engineering applications of modal correlation analysis are:

(1) To verify and confirm the credibility of the finite element model, engineers often use modal correlation analysis to check whether the calculation results of the finite element model can "match" the test results;

(2) Due to its function of quantifying finite element modeling errors, modal correlation analysis is also an indispensable part of model correction and model modification technology.

Experimental modal analysis has a wide range of practical value. Modal analysis can help designers determine modal parameters such as the natural frequency and vibration mode of the structure, provide improvement directions to avoid structural resonance, and guide engineers to predict the vibration form under different loads.

• Verify the accuracy of the finite element model
• Evaluating the dynamic characteristics of existing structures
• Predict dangerous parts of the structure

Experimental modal analysis is widely used. One of its important applications is to provide accurate structural dynamics test data for finite element model modification. Whether the finite element model needs to be modified and how to modify it requires modal correlation analysis.