| 1. |
- Chen, Yousheng, 1985-, et al.
(författare)
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Frequency Response Calculations of a Nonlinear Structure a Comparison of Numerical Methods
- 2014
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Ingår i: Nonlinear Dynamics, Volume 2. - Cham : Springer. - 9783319045221 - 9783319045221 ; 2, s. 35-44
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Konferensbidrag (refereegranskat)abstract
- Mechanical systems having presence of nonlinearities are often represented by nonlinear ordinary differential 5 equations. For most of such equations, exact analytic solutions are not found; thus numerical techniques have to be used. 6 In many applications, among which model calibration can be one, steady-state frequency response functions are the desired 7 quantities to calculate. 8 The objective of this paper is to compare the performance of computations of nonlinear frequency response functions 9 (FRFs) calculated directly within the frequency domain, using the Multi-Harmonic Balance method, with the time-domain 10 methods Runge–Kutta, Newmark and Pseudo Force in State Space (PFSS). The PFSS method is a recently developed state- 11 space based force feedback method that is shown to give efficient solutions. 12 The accuracy and efficiency of the methods are studied and compared using a model of a cantilever beam connected to a 13 non-linear spring at its free end.
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| 2. |
- Chen, Yousheng, 1985-, et al.
(författare)
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Model calibration of locally nonlinear structures using information from sub and super harmonic responses
- 2012
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Ingår i: International Conference on Noise and Vibration Engineering 2012 (ISMA 2012). - Leuven : Katholieke Universiteit Leuven, Department of Mechanical Engineering. - 9781622768257 ; , s. 2451-2464
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Large linear finite element models are commonly used in industry to represent global structural behavior and such models are often validated by use of data from vibrational tests. The validated models serve to predict the structural responses due to dynamic loads. Hence, it is important to have models that are able to represent the structural dynamics within the given operating envelope. When test data show proof of non linear behavior, a linear model may not be able to represent the dynamics well enough and thus a modification of the model is required. The main part of the structure may have a linear characteristic whereas localized physical processes can be sources of the observed nonlinearities. Model calibration of such locally nonlinear structures is studied in this paper. Specifically, the calibration process including the selection of appropriate data to be used for calibration of the model parameters chosen is treated. Here, synthetic test data stemming from a model of the Ecole Centrale de Lyon (ECL) nonlinear benchmark are used.
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| 3. |
- Johansson, Anders, 1982, et al.
(författare)
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Model calibration and uncertainty of A600 wind turbine blades
- 2014
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Ingår i: Model Validation and Uncertainty Quantification, Volume 3. - Cham : Springer. - 2191-5644 .- 2191-5652. - 9783319045511 ; , s. 215-227
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Konferensbidrag (refereegranskat)abstract
- Recently, a lot of work has been made on modeling, testing and calibrating Ampair 600W wind turbine blades, owing to the use of that turbine as a test bed structure for the Dynamic Substructuring Focus Group within the Society of Experimental Mechanics. In Sweden alone, more than 20 blades have been tested for dynamical properties, geometrical differences and material properties as was presented in several papers at IMAC XXXI. The quantity of blades, originating from different manufacturing batches, makes them ideal for investigations of component variability.In this paper, measurement variability predominantly stemming from the difference between individual blades is propagated backwards to model parameters, using model calibration techniques, in an effort to quantify their uncertainties. The coupling between spread in structural properties such as mass, center of gravity together with blade twist angles and spread in the resulting blade dynamics is shown.
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| 4. |
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| 5. |
- Yaghoubi Nasrabadi, Vahid, 1985, et al.
(författare)
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Locally Non-Linear Model Calibration Using Multi Harmonic Responses : Applied on Ecole de Lyon Non-Linear Benchmark Structure
- 2013
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Ingår i: Topics in Nonlinear Dynamics, Volume 1. - New York, NY : Springer. - 9781461465690 ; 1, s. 113-123
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In industry, linear FE-models commonly serve to represent global structural behavior. However, when test data are availa-ble they may show evidence of nonlinear dynamic characteristics. In such a case, an initial linear model may be judged being insufficient in representing the dynamics of the structure. The causes of the non-linear characteristics may be local in nature whereas the major part of the structure is satisfactorily represented by linear descriptions. Although the initial model then can serve as a good foundation, the parameters needed to substantially increase the model’s capability of representing the real structure are most likely not included in the initial model. Therefore, a set of candidate parameters controlling nonlinear effects, opposite to what is used within the vast majority of model calibration exercises, have to be added. The selection of the candidates is a delicate task which must be based on engineering insight into the structure at hand.The focus here is on the selection of the model parameters and the data forming the objective function for calibration. An over parameterized model for calibration render in indefinite parameter value estimates. This is coupled to the test data that should be chosen such that the expected estimate variances of the chosen parameters are made small. Since the amount of information depends on the raw data available and the usage of them, one possibility to increase the estimate precision is to process the test data differently before calibration. A tempting solution may be to simply add more test data but, as shown in this paper, the opposite could be an alternative; disregarding low excessive data may make the remaining data better to dis-criminate between different parameter settings.Since pure mono-harmonic excitation during test is an abnormality, the excitation force is here designed to contain sub and super harmonics besides the fundamental one. Further, the steady-state responses at the side frequencies are here shown to contain most valuable information for the calibration process of models of locally nonlinear structures.Here, synthetic test data stemming from a model representing the Ecole Centrale de Lyon (ECL) nonlinear benchmark are used for illustration. The nonlinear steady state solutions are found using iterative linear reverse path state space calculations. The model calibration is here based on nonlinear programming utilizing several parametric starting points. Candidates for starting points are found by the Latin Hypercube sampling method. The best candidates are selected as starting points for optimization.
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