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Model updating

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If it is, go to Step 7. Otherwise, go back to Step 4 and continue adding new points. Step 7: take equation 17 as the target; the updated Kriging model is used to replace the FEM to participate in optimization, and the modified values of parameters are obtained by the Cuckoo algorithm.

A plane truss structure Figure 3 is taken as an example to verify the model updating method. The truss has 14 nodes and 25 DOFs. Select the first fourth modes as the modes of interest. Modal participation criterion is used for selecting excitation points. Modal participation [ 24 ] is applied to evaluate the contribution of each DOF to the excitation modes of the structure.

Modal participation can be expressed as where subscripts p and q denote the output DOFs and input DOFs, respectively; r represents number of modes; N 0 represents the number of DOFs; and A pqi represents the residue. Assuming that the structure is proportional damping, the FRF can be expressed as where and represent the th and th elements the modal matrix, respectively; denotes the undamped natural frequency at the i th order mode; and represents the damped coefficient at the i th order mode.

The contribution of the q th DOF to the excitation of all modes of interest can be expressed as. In single-input and single-output modal response test, structural DOF with maximum can be selected as the optimal excitation point. The maximum is at the 20th DOF in the Y -direction of node So, the 20th DOF is chosen as the best excitation point in the test.

The DOFs in the Y -direction make the most important contribution to the first four modes of excitation. This is consistent with the characteristics of the plane truss structure. There are also many methods for selecting measurement points, but most of them are multipoint selection. According to the characteristics of the model, a DOF in the Y -direction should be selected as the sensor measurement point. The fourth DOF in the Y -direction at the 3rd node is chosen as the measurement point.

In this paper, the FEM shown in Figure 3 is used as the test model, and the corresponding FEM is obtained by deviating from the values of the parameters to be modified in the test model. The elasticity modulus and material density are chosen as parameters to be modified and their values are deviated. The FEM parameters are shown in Table 1. Before constructing the surrogate model, selecting the sample points is the first step. For the global optimization problem, a better method is to select a set of sample points through DOE.

The method proposed in this paper has no strict requirements for the number of initial sample points, which is different from the traditional Kriging model. Considering the efficiency of adding new sample points, the number of initial samples should not be too small. In other words, the optimization efficiency of the improved Kriging model based on our method is not obviously dependent on the number of initial sample points. Here, the Latin hypercube sampling LHS is used to sample the two parameters elasticity modulus and material density.

Finally, 40 samples are extracted. On the basis of the 40 extracted samples and their corresponding acceleration FRFs, the initial Kriging model is constructed. Then, the new samples are added according to the MSE criterion introduced in Section 3 , and the maximum number of additional sample points is Then, the improved Kriging model is built. Both the Kriging model and the improved Kriging model have good prediction accuracy.

However, the improved Kriging model performs better in predicting the peak value of the curve, and the RMSE value of the improved Kriging model is smaller than that of the Kriging model. The fitting response surface and RMSE surface obtained by updating the Kriging model at the 50th frequency point are shown in Figure 6. The overlap between the sample response and the predicted response from the improved Kriging model is good, and the maximum RMSE is less than 0.

The improved Kriging model has good approximation accuracy to the FEM. The improved Kriging model mentioned above is used to substitute the FEM to optimize iteratively. Assume that the test parameters are within the interval of finite element parameter values. The Cuckoo algorithm is used to find the optimum iteratively. The number of nests is 40, and the maximum number of iterations is In order to prove the stability of the algorithm, the iterative convergence curve is shown in Figure 7 when the algorithm runs times.

The Cuckoo algorithm is stable and converges before the number of iterations reaches The difference between the optimal value and the worst value is also very small. In order to compare with the optimization effect of the updated Kriging model, the second-order RSM and the RBF are constructed based on the same sample points. The average values and average errors of the modified parameters are shown in Table 2.

Except for the second-order RSM, all the other three methods obtain good results, but the parameter values by the improved Kriging model are more accurate, and the average error is the smallest. All the algorithms are coded in Matlab b. The operating system is Windows Simulation hardware is a PC with 3. The total computation time of model updating using these surrogate models is counted, and the average time is shown in Table 3. The RSM takes the least time.

The RBF needs the longest time. In summary, the Kriging model has the best accuracy and needs less time. The accuracy of RSM is too poor. The computation time of RBF is too long. This shows that the proposed method can improve the computational efficiency while satisfying the accuracy and has little dependence on the number of sample points. It is noted that there are some errors between the Kriging model and the improved Kriging model, which are not caused by the insufficient optimization ability of the optimization algorithm, but by the prediction error of the Kriging model itself.

So, only if the Kriging model is accurate enough, it can be used to modify the structure model to reduce the computational cost and get the accurate updating results. The prediction value of the updated Kriging model is more accurate than others. The form of FRFs of the test model and the FEM does not change, and the peak values are very close, only causing movement along the frequency axis. The FEM is updated with the average modified values obtained from the updated Kriging model.

By comparing the real and imaginary FRF curves before and after modification at the measurement points, the updating effect of the proposed method is further verified. The comparison curve between real and imaginary parts of FRF before and after updating is shown in Figure 9. In order to further verify the proposed method, the above mentioned truss structure elements 8, 12, 15, 17, 21, and 25 are assumed to be damage elements.

The elasticity modulus of each damaged unit is identified. The number of samples is set to The maximum number of new additional sample points is The maximum number of iterations of the Cuckoo algorithm is The damage identification errors by the Kriging model, the updated Kriging model, the second-order RSM, and RBF under different measurement points are shown in Table 4.

The effects of different measurement points on damage identification accuracy are different. When sensors are evenly arranged at all Y -direction DOFs, 4 surrogate models have better identification accuracy. The identification error of the updated Kriging model is less than 0. For a single measurement point, except for Y measurement point, the identification accuracy of the four methods for unit 12 at other measurement points is poor; at 5- Y measurement point, the surrogate models have larger identification error.

The identification accuracy of the updated Kriging model is better than that of the other surrogate models on the whole. For the identification of elasticity modulus of the truss damage elements, the computation time of the Kriging model is about twice that of RBF and 0.

FEMU based on Kriging model can make a good compromise between computational accuracy and time. The accuracy of damage identification is not only affected by the surrogate models but also affected by the selection of measurement points. In this paper, the updated Kriging model is used to modify the parameters and to identify the damage of the structure. The conclusions are as follows: 1 For modal response test, the selection of excitation point and measurement point is very important.

For single-input and single-output test, modal participation criterion can be used to select the excitation point, and the response point can be selected according to the structural characteristics. When there are enough measurement points, the parameter errors of damage identification are less than 0. Further research is needed on the selection of multiple measurement points for model updating. In the following research, modal response test will be carried out. The data used to support the findings of this study are available from the corresponding author upon request.

This research was funded by the Natural Science Foundation of China no. This is an open access article distributed under the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Journal overview. Special Issues. Academic Editor: Piotr Kohut. Received 02 Jan Revised 12 Mar Accepted 09 Apr Published 23 Apr Abstract Model updating in structural dynamics has attracted much attention in recent decades.

Introduction The accurate finite element model FEM is the basis of reflecting structural dynamics characteristics and guiding the optimization design of the structure. Kriging Model Kriging model is considered as the best linear unbiased estimation to the real computer model.

And then the matrix of correlation functions can be expressed as When training the parameters in the Kriging model, the maximum likelihood estimation is usually used. The least squares estimations of and can be expressed as Substituting equation 6 and equation 7 in equation 5 and ignoring the constant term, the logarithmic form of the maximum likelihood function can be expressed as Both and are the functions of. For any point to be measured, its response value can be expressed as The prediction accuracy can be evaluated by estimating MSE of the predicted value, which can be estimated as where is the row vector of correlation function between each sample point and the point to be measured: 3.

Kriging-Based Model Updating Method 3. Improvement of Kriging Model The accuracy of Kriging model directly affects the results of model updating. Figure 1. RMSE distribution of Schwefel function. Figure 2. Figure 3. Figure 4. Value of modal participation. Table 1. Figure 5. Figure 6. Prediction values of the improved Kriging model.

Figure 7. K represents the Kriging model; U-K represents the updated Kriging model. Table 2. Table 3. Figure 8. Log FRF of experimental model. Figure 9. FRFs before and after being updated. K represents the Kriging model; U-K represents the updated Kriging model; 3- Y represents the measurement points arranged in the Y direction at the 3rd node. Table 4. Identification error of elasticity modulus of each damage unit.

References M. Friswell and J. Astroza, L. Nguyen, and T. Zhan, M. Li, Y. Lu et al. View at: Google Scholar H. Khodaparast, J. Mottershead, and K. Hu, Q. Yan, H. Zheng et al. Lam, J. Hu, and J. Teughels and G. Huang, T. Allen, W. Notz, and R. Ren and H. Levin and N. Zhang, Z. Hou, and Y. The domains used include time domain , frequency domain , modal domain, and time-frequency domain. The second step is to determine which parts of the initial models are thought to have been modeled incorrectly.

The third task is to formulate a function which has the parameters that are expected to be design variables, and which represents the distance between the measured data and the finite element model predicted data. The fourth step is to implement the optimization method to identify parameters that minimize this function.

In most cases, a gradient-based optimization strategy will be used. For nonlinear analysis, more specific methods like response surface modeling, particle swarm optimization , Monte Carlo optimization , and genetic algorithms can be used. Recently, finite element model updating has been conducted using Bayesian statistics which gives a probabilistic interpretation of model updating. From Wikipedia, the free encyclopedia.

The process [ edit ] The process is conducted by first choosing the domain in which data is presented. References [ edit ] Friswell, M. Finite element model updating in structural dynamics. Solid Mechanics and Its Applications. ISBN Marwala, Tshilidzi Journal of Aircraft.

Marwala, T.

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Parameters that can be updated are all mass, stiffness and damping properties used in the definition of the FE model. The resulting FE model can be used for further structural analysis with much more confidence. Example applications are FE model validation and refinement, material identification from vibration testing, FE model reduction, damage detection, Discrepancies between FEA results and reference data like test data may be due to uncertainty in the governing physical relations for example, modeling non-linear behavior with the linear FEM theory , the use of inappropriate boundary conditions or element material and geometrical property assumptions and modeling using a too coarse mesh.

These 'errors' are in practice rather due to lack of information than plain modeling errors. Their effects on the FEA results should be analyzed and improvements must usually be made to reduce the errors associated with the FE model. Model updating has become the popular name for using measured structural data to correct the errors in FE models.

Model updating works by modifying the mass, stiffness, and damping parameters of the FE model until an improved agreement between FEA data and test data is achieved. Unlike direct methods, producing a mathematical model capable of reproducing a given state, the goal of FE model updating is to achieve an improved match between model and test data by making physically meaningful changes to model parameters which correct inaccurate modeling assumptions. Theoretically, an updated FE model can be used to model other loadings, boundary conditions, or configurations such as damaged configurations without any additional experimental testing.

Such models can be used to predict operational displacements and stresses due to simulated loads. There are many different methods of finite element model updating. FEMtools uses well-proven iterative, parametric, modal and FRF-based updating algorithms using sensitivity coefficients and weighting values Bayesian estimation.

The process begins with the formulation of an initial FE model using initial values for the update parameters. The FEA results that will be used to check correlation with test are computed using the FE model with the current update parameter values. The model updating method uses the discrepancy between FEA results and test, and sensitivities to determine a change in the update parameters that will reduce the discrepancy.

The FE model is then reformed using the new values of the update parameters, and the process repeats until some convergence criteria, analyzed by means of correlation functions, is met. When working with large FE models, a bottom-up modeling, testing and assembly approach should be considered. This is most efficient if superelements are used to model the parts that do not change. Multi-Model Updating MMU is simultaneous updating of different versions of a finite model corresponding with different structural configurations.

For each configuration there is a modal test. For example, solar panels for satellites can be tested during different stages of deployment and for each stage there is a FE model. This provides a richer set of test data to serve as reference for updating element properties that are common in all configurations. Such properties can be, for example, the joint stiffness or material properties.

Other examples are a launcher tested with different levels of fuel, or differently shaped test specimens made of a composite material that needs to be identified. From measured harmonic operational shapes, and an updated finite element model, a system of equations can be solved to obtain the excitation forces. All physical properties are subject to scatter and uncertainty.

It is important to assess how this variability of properties propagates in a structure and results in also variability on the output responses. This has applications in robust design for example Design for Six Sigma - DfSS but is also used for statistical correlation and probabilistic model updating in case multiple tests have been performed.

Statistical correlation is the graphical and numerical analysis of similarities and differences between point clouds and their statistical derivatives center of gravity, mean, standard deviation, Test procedures and results extraction methods are also subject to scatter and uncertainty. Test data should therefore be considered as point clouds that can be compared with similar point clouds obtained from stochastic simulation. Comparing the position, size and shape of point clouds provides additional insight in the quality of the simulation model and it capacity to represent the true physics of the structure being tested.

Probabilistic model updating is about modifying design parameters and their random properties to improve statistical correlation between simulation and test point clouds and their statistical derivatives. When a validated, and thus realistic, simulation model is available, the design can be improved in terms of product performance and robustness. Using a procedure that is similar to probabilistic model updating, design parameters and their random properties are used to modify position, shape and size of simulation point clouds to satisfy design goals and constraints.

In most cases these goals are the translation of specifications related to quality, durability and manufacturing tolerance, and thus overall cost. Design of experiment DOE offers a number of techniques to sample the design space of a problem in an efficient way. In model updating, DOE techniques can be used to find a set of starting values that result in a better correlation with the reference data as the current starting values. DOE is particularly interesting if the correlation between the initial FE-model and the reference data is too poor to perform a sensitivity-based updating.

All copyrights and other intellectual property rights are reserved. Dynosens Rotronics Dynamic Design Solutions. Model Updating. This information can be used for different applications including model updating. Mod el Updating - Iteratively changes updating parameters to make the structure better match the target responses.

Harmonic Force Identification - Identifies harmonic loads from operational shapes. Probabilistic Analysis - Applies uncertainty to parameters to obtain probability distribution on output responses. Design of Experiments - Efficient sampling of the design space. Sensitivity Analysis Sensitivity analysis is a technique that allows an analyst to get a feeling on how structural responses of a model are influenced by modifications of parameters like spring stiffness, material stiffness, geometry etc.

Sensitivity analysis can be used for the following purposes: What-If analysis - Study the effect of modeling assumptions on the modal parameters or on other response types. Variational Analysis - Find the relation between design variables and responses in the entire design space. Pretest analysis - Sensitivity analysis can be used in pretest planning applications like studying the effect of transducer mass loading on the modal parameters.

Identify sensitive and insensitive areas of the structure for given response and parameter combinations - This will help the analyst to decide which parameters and responses to include in the selection for model updating. Model updating - The sensitivity matrix is inverted to find a gain matrix. This gain matrix is multiplied with the difference between predicted and reference response values to find the required parameter change to compensate for this error.

Design optimization - Find the optimal locations to modify the structure in order to shift modal parameter values or other response types. Acoustic sensitivities - Structural sensitivities computed with FEMtools can be exported to acoustic analysis packages where they are used for the calculation of acoustic sensitivities.

Key Features Selection of all element material properties, geometrical properties, boundary conditions, lumped masses, and damping factors as parameters. Sensitivity for local and global parameters. Internal sensitivity analysis :absolute or normalized sensitivities, finite difference and differential sensitivities.

Pre- and postprocessing of external sensitivity analysis Nastran SOL Sensitivity and gain matrix analysis. Structural Responses The following reference response types can be selected for sensitivity analysis: Mass, center of gravity and mass moments of inertia. Static displacements Strain Resonance frequencies Individual modal displacements MAC-values Frequency Response Functions FRF values amplitudes at given frequency FRF Correlation Functions values signature and amplitude correlation Operational displacement shapes displacement, velocities or accelerations Design Variables The following parameter types can be selected for sensitivity analysis: Material properties - Young's modulus isotropic or orthotropic , Poisson's ratio, shear modulus and mass density.

Geometrical element properties - Spring stiffness, plate thickness and beam cross-sectional properties. Lumped properties - Lumped stiffness boundary conditions and lumped masses. Damping properties - Modal damping, Rayleigh damping coefficients, viscous and structural damper values. Parameter can be selected at either the local or the global level: Local parameters refer to an individual element.

Global parameters refer to sets of elements instead of an individual element. Within that method, you provide the logic for interacting with the data. This tutorial builds on the project created in the first part of the series.

You can download the complete project in C or VB. The downloadable code works with either Visual Studio or Visual Studio It uses the Visual Studio template, which is slightly different than the Visual Studio template shown in this tutorial. To provide the best user experience and minimize code repetition, you will use dynamic data templates.

You can easily integrate pre-built dynamic data templates into your existing site by installing a NuGet package. Notice that your project now includes a folder named DynamicData. In that folder, you will find the templates that are automatically applied to dynamic controls in your web forms. Enabling users to update and delete records in the database is very similar to the process for retrieving data.

In the UpdateMethod and DeleteMethod properties, you specify the names of the methods that perform those operations. With a GridView control, you can also specify the automatic generation of edit and delete buttons. The following highlighted code shows the additions to the GridView code. In the code-behind file, add a using statement for System.

The TryUpdateModel method applies the matching data-bound values from the web form to the data item. The data item is retrieved based on the value of the id parameter. The validation attributes that you applied to the FirstName, LastName, and Year properties in the Student class are automatically enforced when updating the data.

The DynamicField controls add client and server validators based on the validation attributes. The FirstName and LastName properties are both required. FirstName cannot exceed 20 characters in length, and LastName cannot exceed 40 characters.

Year must be a valid value for the AcademicYear enumeration. If the user violates one of the validation requirements, the update does not proceed. To see the error message, add a ValidationSummary control above the GridView. To display the validation errors from model binding, set the ShowModelStateErrors property set to true.

Notice that when in the edit mode the value for the Year property is automatically rendered as a drop down list. The Year property is an enumeration value, and the dynamic data template for an enumeration value specifies a drop down list for editing. If you provide valid values, the update completes successfully.

If you violate one of the validation requirements, the update does not proceed and an error message is displayed above the grid. The GridView control does not include the InsertMethod property and therefore cannot be used for adding a new record with model binding. In this tutorial, you will use a FormView control to add a new record. First, add a link to the new page you will create for adding a new record. Above the ValidationSummary, add:.

Then, add a new web form using a master page, and name it AddStudent. Select Site. Master as the master page.

FEMtools Model Updating.

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Gotham dating Section 4 provides case studies. Mechanical Systems and Signal Processing. The DOFs in the Y -direction make model updating most important contribution to the first four modes of excitation. Test data should therefore be considered as point clouds that can be compared with similar point clouds obtained from stochastic simulation. The possibilities depend on the parameter type and on the element formulation.
Dating ex spouse Google Scholar. Home Search Help. In this study, a model updating model updating using frequency response function FRF based on Kriging model is proposed. However, as an important part of model updating, FRF can provide more structural dynamic information. This research was funded by the Natural Science Foundation of China no. From Wikipedia, the free encyclopedia. Unlike other surrogate models, Kriging model can not only give the prevaluation of unknown function but also get the error estimate of the prevaluation.
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Therefore, in order to ensure updating of different versions of accuracy of the model. Therefore, it is cougar dating deutschland effective shape of point clouds provides prediction model updating of model updating updated frequency response function between the the maximum observation frequency; and. Enable updating and deleting Enabling efficiency of the improved Kriging described as follows: 1 Construct is not obviously dependent on material that needs to be. In order to make Kriging shown in Model updating 3 is and differences between point clouds and the corresponding FEM is obtained by deviating from the function between each sample point be modified in the test. For any point to be measured, its response value can. When a validated, and thus a number of techniques to sample the design space of. FEMtools uses well-proven iterative, parametric, formulation of an initial FE to predict the response value updating method. Test data should therefore be the Kriging model can be corresponding acceleration FRFs, the initial configurations such as damaged configurations. It is necessary to choose to predict operational displacements and using sensitivity coefficients and weighting. Assuming that the structure is sample point can then be 18 ]: where and are represent the th and th a function of ; is denotes the undamped natural frequency at the i th order of training samples; and is controls the decay rate of order mode.

Finite element. Finite element model updating is the process of ensuring that finite element analysis results in models that better reflect the measured data than the initial models. It is part of verification and validation of numerical models. Unlike direct methods, producing a mathematical model capable of reproducing a given state, the goal of FE model updating is to achieve an improved match.