| 1. |
- Chen, Yousheng, 1985-, et al.
(författare)
-
A Pretest Planning Method for Model Calibration for Nonlinear Systems
- 2016
-
Ingår i: Model Validation and Uncertainty Quantification, Volume 3. - Cham : Springer. - 2191-5644 .- 2191-5652. - 9783319297538 - 9783319297545 ; , s. 371-379
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- With increasing demands on more flexible and lighter engineering structures, it has been more common to take nonlinearity into account. Model calibration is an important procedure for nonlinear analysis in structural dynamics with many industrial applications. Pretest planning plays a key role in the previously proposed calibration method for nonlinear systems, which is based on multi-harmonic excitation and an effective optimization routine. This paper aims to improve the pretest planning strategy for the proposed calibration method. In this study, the Fisher information matrix (FIM), which is calculated from the gradients with respect to the chosen parameters with unknown values, is used for determining the locations, frequency range, and the amplitudes of the excitations as well as the sensor placements. This pretest planning based model calibration method is validated by a structure with clearance nonlinearity. Synthetic test data is used to simulate the test procedure. Model calibration and K-fold cross validation are conducted for the optimum configurations selected from the pretest planning as well as three other configurations. The calibration and cross validation results show that a more accurate estimation of parameters can be obtained by using test data from the optimum configuration.
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| 2. |
- Khorsand Vakilzadeh, Majid, 1984, et al.
(författare)
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Approximate Bayesian Computation by Subset Simulation for Parameter Inference of Dynamical Models
- 2016
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Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. - 9783319297538 ; 3, s. 37-50
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Konferensbidrag (refereegranskat)abstract
- A new multi-level Markov chain Monte Carlo algorithm for Bayesian inference, ABC-SubSim, has recently appeared that combines the principles of Approximate Bayesian Computation (ABC) with the method of subset simulation for efficient rare-event simulation. ABC-SubSim adaptively creates a nested decreasing sequence of data-approximating regions in the output space. This sequence corresponds to increasingly closer approximations of the observed output vector in this output space. At each stage, the approximate likelihood function at a given value of the model parameter vector is defined as the probability that the predicted output corresponding to that parameter value falls in the current data-approximating region. If continued to the limit, the sequence of the data-approximating regions would converge on to the observed output vector and the approximate likelihood function would become exact, but this is not computationally feasible. At the heart of this paper is the interpretation of the resulting approximate likelihood function. We show that under the assumption of the existence of uniformly-distributed measurement errors, ABC gives exact Bayesian inference. Moreover, we present a new optimal proposal variance scaling strategy which enables ABC-SubSim to efficiently explore the posterior PDF. The algorithm is applied to the model updating of a two degree-of-freedom linear structure to illustrate its ability to handle model classes with various degrees of identifiability.
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| 3. |
- Rahrovani, Sadegh, 1981, et al.
(författare)
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Bayesian Treatment of Spatially-Varying Parameter Estimation Problems via Canonical BUS
- 2016
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Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. - 9783319297538 ; 3, s. 1-13
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Konferensbidrag (refereegranskat)abstract
- The inverse problem of identifying spatially-varying parameters, based on indirect/incomplete experimental data, is a computationally and conceptually challenging problem. One issue of concern is that the variation of the parameter random field is not known a priori, and therefore, it is typical that inappropriate discretization of the parameter field leads to either poor modelling (due to modelling error) or ill-condition problem (due to the use of over-parameterized models). As a result, classical least square or maximum likelihood estimation typically performs poorly. Even with a proper discretization, these problems are computationally cumbersome since they are usually associated with a large vector of unknown parameters. This paper addresses these issues through Bayesian approach, via a recently developed stochastic simulation algorithm, called Canonical BUS. This algorithm is considered as a revisited formulation of the original BUS (Bayesian Updating using Structural reliability methods), that is, an enhancement of rejection approach that is used in conjunction with Subset Simulation rare-event sampler. Desirable features of the method and its performance to treat real-world applications has been investigated. The studied industrial problem originates from a railway mechanics application, where the spatial variation of ballast bed is of particular interest.
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| 4. |
- Abrahamsson, Thomas, 1956, et al.
(författare)
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Calibration and Validation of a Car Subframe Finite Element Model Using Frequency Responses
- 2015
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. - 9783319152516 ; 10, s. 9-22
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Konferensbidrag (refereegranskat)abstract
- A finite element model of a car front subframe has been calibrated against test data. Stepped-sine testing has been used to give frequency response function estimates on an ensemble of seemingly identical subframes. Therefore, the deviation between test data and simulation results can be compared in a meaningful way by the outcome of model calibration and cross-validation. Emphasis has been put on the preparation of the test pieces for high fidelity testing and on bettering the chances of getting a calibration outcome that provides insight into the physical processes that govern the subframe dynamics. The front subframe model has more than 200,000 degrees-of-freedom and 17 model calibration parameters. The efficiency of the calibration procedure under these conditions is reported. To achieve efficiency, a calibration with a smooth deviation metric is used together with a damping equalization method that eliminates the need for matching of experimental and analytical eigenmodes. The method is combined with surrogate model frequency response evaluation based on model reduction for increased speed. The Matlab based open-domain software tool FEMcali that employs the Levenberg-Marquardt minimizer with randomized starts has been used for calibration and an unregularized Gauss-Newton minimizer has been used in the cross-validation.
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| 5. |
- Abrahamsson, Thomas, 1956, et al.
(författare)
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FEM calibration with FRF damping equalization
- 2014
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. - 9783319007670 ; 3, s. 265-278
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Konferensbidrag (refereegranskat)abstract
- A finite element model calibration procedure that uses frequency response function data and relies on damping equalization is presented. In this, the dampings of the finite element model and the corresponding experimental model are set equal before calibration. The damping equalization is made to avoid the mode pairing problem that normally needs to be solved in other model updating procedures. It is demonstrated that one particular use of frequency response data gives a calibration deviation metric that is smooth in the variation of model parameters and give a large radius of convergence to the calibration minimum. The method is combined with model reduction for increased speed and employs a minimizing procedure that employs randomized multiple starting points in the parameter space to get to the calibration solution. The performance of the calibration procedure is demonstrated by two numerical examples. © The Society for Experimental Mechanics, Inc. 2014.
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| 6. |
- Abrahamsson, Thomas, 1956, et al.
(författare)
-
What Is Normal About Normal Modes?
- 2016
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Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. ; 10, s. 97-110
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Konferensbidrag (refereegranskat)abstract
- A normal mode of a vibrating system is a mode that is orthogonal to all other normal modes of that system. The orthogonality is in a weighted sense. For an undamped discretized linear mechanical system, the orthogonality is defined with respect to stiffness and mass such that normal modes are mutually stiffness and mass orthogonal. Another commonly used definition of an oscillating normal mode is that it is a pattern of motion in which all parts of the system vibrate harmonically with the same frequency and therefore with fixed relative phase relations between parts. The normality of a mode is thus not in a statistical sense. For lightly damped linear systems, a normal observation, i.e. one very common observation in the statistical sense, is that the phase relation between the motion of different parts of the system deviates very little from zero or pi. However, this normally occurring behavior should not lead us to think that that always has to be the case. Here it is shown by example that the normal modes of an undamped system may have arbitrary phase relations. One such mode of vibrationmay then possess the property of moving nodal lines, which is often attributed to non-proportionally damped or nonself-adjoint systems. The proper normalization of such modes is discussed and their relation to the well-known modal mass and MAC concepts and also to state-space based normalizations that are usually being used for complex-valued eigenmodes.
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| 7. |
- Brewick, P., et al.
(författare)
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Hybrid Time/Frequency Domain Identification of Real Base-Isolated Structure
- 2016
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Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. - 9783319297514 ; 2, s. 303-311
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Konferensbidrag (refereegranskat)abstract
- This paper presents a case study using hybrid time-and frequency-domain identifications in a synergistic manner to develop models of a full-scale experimental base-isolated structure. This four-story reinforced-concrete building on an isolation layer (of rubber bearings, elastic sliding bearings, passive metallic yielding dampers, and controllable oil dampers) was designed and constructed at the large-scale Japanese NIED E-Defense earthquake engineering laboratory. A variety of sensors, including accelerometers, were mounted within the structure to measure building response to shake table excitations. While the building was ultimately subjected to historical and synthetic ground motions, the recorded table and building accelerations during a number of random excitation tests are used to identify the structure's natural frequencies, damping ratios and mode shapes. The substantial damping provided by the isolation layer necessitates adopting a hybrid time-and frequency-domain approach for identification. The modes of the structure are separated by frequency content wherein lower frequency modes are identified using time domain approaches from the subspace identification family of methods and higher frequency modes are identified using frequency response functions. Individually, neither approach is able to successfully identify all of the desired modes but, through their combination, the modal properties of the structure are successfully characterized.
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| 8. |
- Chen, Yousheng, 1985-, et al.
(författare)
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An Efficient Simulation Method for Large-Scale Systems with Local Nonlinearities
- 2016
-
Ingår i: Special topics in structural dynamics, 34th IMAC. - Cham : Springer. - 2191-5644 .- 2191-5652. - 9783319299105 - 9783319299099
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In practice, most mechanical systems show nonlinear characteristics within the operational envelope. However, the nonlinearities are often caused by local phenomena and many mechanical systems can be well represented by a linear model enriched with local nonlinearities. Conventional nonlinear response simulations are often computationally intensive; the problem which becomes more severe when large-scale nonlinear systems are concerned. Thus, there is a need to further develop efficient simulation techniques. In this work, an efficient simulation method for large-scale systems with local nonlinearities is proposed. The method is formulated in a state-space form and the simulations are done in the Matlab environment. The nonlinear system is divided into a linearized system and a nonlinear part represented as external nonlinear forces acting on the linear system; thus taking advantage in the computationally superiority in the locally nonlinear system description compared to a generally nonlinear counterpart. The triangular-order hold exponential integrator is used to obtain a discrete state-space form. To shorten the simulation time additionally, auxiliary matrices, similarity transformation and compiled C-codes (mex) to be used for the time integration are studied. Comparisons of the efficiency and accuracy of the proposed method in relation to simulations using the ODE45 solver in Matlab and MSC Nastran are demonstrated on numerical examples of different model sizes.
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| 9. |
- Chen, Yousheng, 1985-, et al.
(författare)
-
Frequency Response Calculations of a Nonlinear Structure a Comparison of Numerical Methods
- 2014
-
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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| 10. |
- Chen, Yousheng, 1985-, et al.
(författare)
-
Model Calibration of a Locally Non-linear Structure Utilizing Multi Harmonic Response Data
- 2014
-
Ingår i: Nonlinear Dynamics, Volume 2. - Cham : Springer. - 2191-5644 .- 2191-5652. - 9783319045221 - 9783319045214 ; , s. 97-109
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Konferensbidrag (refereegranskat)abstract
- Model correlation and model calibration using test data are natural ingredients in the process of validating computational models. Here, model calibration for the important sub-class of non-linear systems consisting of structures dominated by linear behavior having presence of local non-linear effects is studied. The focus is on the selection of uncertain model parameters together with the forming of the objective function to be used for calibration. To give precise estimation of parameters in the presence of measurement noise, the objective function data have to be informative with respect to the parameters chosen. Also, to get useful data the excitation force is here designed to be multi-harmonic since steady-state responses at the side frequencies are shown to contain valuable information for the calibration process. In this paper, test data from a replica of the Ecole Centrale de Lyon (ECL) nonlinear benchmark together with steady-state solutions stemming from calculations using the Multi-Harmonic Balancing method are used for illustration of the proposed model calibration procedure.
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| 11. |
- Gibanica, Mladen, 1988, et al.
(författare)
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Calibration, Validation and Uncertainty Quantification of Nominally Identical Car Subframes
- 2016
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. ; 3, s. 315-326
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Konferensbidrag (refereegranskat)abstract
- In this paper a finite element model, with over half a million degrees-of-freedom, of a car front subframe has been calibrated and validated against experimental MIMO data of several nominally identical components. The spread between the individual components has been investigated and is reported. Sensor positioning was performed with an extended effective independence method, using system gramians to reject sensors with redundant information. The Fisher information matrix was used in the identification of the most significant model calibration parameters. Validation of the calibrated model was performed to evaluated the difference between the nominal and calibrated model, and bootstrapping used to investigate the validity of the calibrated parameters. The parameter identification, calibration, validation and bootstrapping have been performed using the open-source MATLAB tool FEMcali.
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| 12. |
- Gibanica, Mladen, 1988, et al.
(författare)
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Experimental-Analytical Dynamic Substructuring of Ampair Testbed: A State-Space Approach
- 2014
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. ; 1, s. 1-14
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Konferensbidrag (refereegranskat)abstract
- The Society for Experimental Mechanics (SEM) Substructuring Focus Group has initiated a research project in experimental dynamic substructuring using the Ampair 600W wind turbine as a testbed. In this paper, experimental as well as analytical models of the blades of said wind turbine are coupled to analytical models of its brackets. The focus is on a state-space based substructuring method designed specifically for experimental-analytical dynamic substructuring. It is shown a) theoretically that the state-space method gives equivalent results to the second order methods under certain conditions, b) that the state-space method numerically produces results equivalent to those of a well-known frequency-based substructuring technique when the same experimental models are used for the two methods and c) that the state-space synthesis procedure can be translated to the general framework given by De Klerk et al.
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| 13. |
- Gibanica, Mladen, 1988, et al.
(författare)
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Parameter Estimation and Uncertainty Quantification of a Subframe with Mass Loaded Bushings
- 2017
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. ; 3, s. 61-76
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Konferensbidrag (refereegranskat)abstract
- In the automotive industry components are often connected through rubber bushings. The bushingsʼ material properties are usually not well known. In computational models these properties are parametrised and their spread can be considerable. A good estimate of these parameters is important in various applications, including substructuring, and for uncertainty quantification of systems with connected components. This paper deals with the calibration of an industrial size finite element model of a car subframe with parametrised bushing models. Mass loading is used on the bushings to bring local bushing modes to a lower frequency region and impose a more realistic boundary condition in component testing. The model parameters can be calibrated in different ways. In this paper two approaches are considered. They are based on two test configurations, one with and one without mass loaded boundaries. In the first case only the bushing parameters are considered for the mass loaded boundary configuration. In the second case, consisting of two steps, the configuration without mass loaded boundaries is considered in which the bushing parameters are first fixed and other model parameters considered, and in the last step a subset of all parameters is considered. The calibration, validation and uncertainty quantification, using bootstrapping, have been performed using the open-source MATLAB tool FEMcali.
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| 14. |
- Gibanica, Mladen, 1988, et al.
(författare)
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Redundant Information Rejection in Sensor Localisation Using System Gramians
- 2016
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. ; 10, s. 325-333
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Konferensbidrag (refereegranskat)abstract
- Sensors placement is important in vibration testing. The method of effective independence, recently extended to account for triaxial sensors, is widely used for this purpose in case a finite element model of the structure is available. In this paper a criteria is added to reject redundant information that usually arises in symmetric structures or finite element models with high candidate sensor density. A sensor placement strategy is proposed in which, initially, the method of effective independence is used to select the best sensors from a candidate set by maximising the Fisher information matrix determinant. Next, the gramians of a balanced realisation is used to compare the information between systems consisting of only previously added sensors to the final set with systems of the previous and candidate sensors. Sensors with redundant information will have negligible effect on the gramian and can be rejected. The method is fast, as gramians of systems with only one or two outputs are evaluated. It is sub-optimal in the sense that all possible sensor placement combinations are not evaluated for optimality. A test case, consisting of a rectangular plate, is presented, but the method has been used on a large scale industrial model with good results.
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| 15. |
- Gibanica, Mladen, 1988, et al.
(författare)
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Residual States for Modal Models Identified from Accelerance Data
- 2019
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Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. ; 9, s. 195-206
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Konferensbidrag (refereegranskat)abstract
- Residual stiffness and mass terms are often employed in frequency response synthesis to compensate for outside band eigenmodes in the identification of modal models from test data. For structures that have strongly participating modes above the test frequency band, it has been observed that in particular direct accelerances with strong outside-band modal contribution tend to render modal models that give poor fit to test data. For such problems it may be insufficient to just add residual mass and stiffness terms to the accelerance modal series to get a sufficiently improved fit. For accelerance, such residual terms are constant and quadratic in frequency. Another, residual term that is quasi-linear over the frequency range of interest has been found to augment the identified model. In this paper that complementary term is added to the constant and quadratic terms in a state-space model identification with a subspace state-space identification method. A comparison is performed to an alternative residualisation method. The methods' results are compared on simulated finite element test data from of an automotive component.
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| 16. |
- Irfan, Muhammad, 1986, et al.
(författare)
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Dynamics and Pareto Optimization of a Generic Synchronizer Mechanism
- 2016
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. - 9783319300849 ; 8, s. 417-425
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Konferensbidrag (refereegranskat)abstract
- Transmission systems for passenger cars and trucks are equipped with synchronizer mechanism. It has a great impact on driving comfort and transmission efficiency. A synchronizer mechanism as a key component of a transmission system must be able to prevent gears from shocking and reduce the noise. Gear shifting improvement with respect to smooth, quick and energy efficient synchronizer's performance is still an important issue for automotive industry. This contribution studies the kinematics and dynamics of a generic synchronizer consisting of sleeve, blocker ring and gearwheel constituting a mechanical system with a set of time-varying constraints describing frictional contacts between system's components. The dynamic response is modelled using constrained Lagrangian formalism. Pareto optimization problem is stated and optimized the rate of the applied sleeve force, coefficient of friction and cone angle are found to attain a minimal synchronization time as well as speed difference between sleeve and gearwheel. One outcome of the study is that the obtained Pareto solution is characterized by the minimal admissible value of the cone angle of the synchronizer.
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| 17. |
- Johansson, Anders, 1982, et al.
(författare)
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Improving test rig performance using passive components
- 2012
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Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - New York, NY : Springer New York. - 2191-5644 .- 2191-5652. - 9781461424185 ; 6, s. 437-442
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Konferensbidrag (refereegranskat)abstract
- The Time Waveform Replication (TWR) algorithm is presently used in industry for calculating the input force needed to replicate reference sensor outputs in a dynamic test rig. The feasible range of that input force is restricted by power supply and forcing rate limitations. If the force transfer paths of the reference test cannot be replicated in the test rig, lack of state controllability may cause unnecessarily large input forces and an increased remaining output error. We advocate the use of passive components to improve output tracking and limit input force demands of dynamic test rigs in the case that controllability is lacking. A method for introducing such passive components is described in this paper. It uses a virtual testing model of the test system with genetic algorithm optimization and TWR in the loop to calculate the position and dynamic properties of the proposed passive component.
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| 18. |
- 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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| 19. |
- Khorsand Vakilzadeh, Majid, 1984, et al.
(författare)
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Development of simplified models for wind turbine blades with application to NREL 5MW offshore research wind turbine
- 2014
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. - 9783319007700 ; 1, s. 389-402
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Konferensbidrag (refereegranskat)abstract
- Integration of complex models of wind turbine blades in aeroelastic simulations places an untenable demand on computational resources and, hence, means of speed-up become necessary. This paper considers the process of producing simplified rotor blade models which accurately approximate the dynamics of interest. The novelty, besides applying an efficient model updating procedure to the wind turbine blade, is to challenge the conventional beam element formulation utilized in the majority of aeroelastic codes. First, a 61.5 m blade, previously reported by the National Renewable Energy Laboratory, is selected as a case study and a verified industry-standard three dimensional shell model is developed based on its actual geometry. Next, given the reported spanwise cross sectional properties of the blade, a calibrated beam model is developed, using an efficient model updating process, that shows an excellent agreement to the low frequency dynamics of the baseline model in terms of mode shapes, resonance frequency and frequency response function. The simulation study provides evidence that a beam model cannot capture all the important features found in a large-scale 3D blade. This motivates a departure from conventional beam element formulation and suggests addressing the problem of producing simplified models in the framework of model reduction techniques. A modified modal truncation algorithm is applied to the baseline model to produce a simpler model which accurately approximates its input-output behavior in a given frequency range. It is concluded that besides the computational efficiency of the reduction algorithm, the resulting approximation error is guaranteed to be bounded and the yielded low-order model can, in turn, be served in wind turbine design codes.
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| 20. |
- Khorsand Vakilzadeh, Majid, 1984, et al.
(författare)
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Modal Reduction Based on Accurate Input-Output Relation Preservation
- 2014
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - New York, NY : Springer New York. - 2191-5644 .- 2191-5652. - 9781461465843 ; 45:7, s. 333-342
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Konferensbidrag (refereegranskat)abstract
- An eigenmode based model reduction technique is proposed to obtain low-order models which contain the dominanteigenvalue subspace of the full system. A frequency-limited interval dominancy is introduced to this technique to measure the output deviation caused by deflation of eigenvalues from the original system in the frequency range of interest. Thus, the dominant eigensolutions with effective contribution can be identified and retained in the reduced-order model. This metric is an explicit formula in terms of the corresponding eigensolution. Hence, the reduction can be made at a low computational cost. In addition, the retained low-order model does not contain any uncontrollable and unobservable eigensolutions. The performance of the created reduced-order models, in regard to the approximation error, is examined by applying three different input signals; unit-impulse, unit-step and linear chirp.
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| 21. |
- Khorsand Vakilzadeh, Majid, 1984, et al.
(författare)
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Sequential gauss-newton MCMC algorithm for high-dimensional bayesian model updating
- 2017
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Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. ; 3 Part F2, s. 303-314
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Konferensbidrag (refereegranskat)abstract
- Bayesian model updating provides a rigorous framework to account for uncertainty induced by lack of knowledge about engineering systems in their respective mathematical models through updates of the joint probability density function (PDF), the so-called posterior PDF, of the unknown model parameters. The Markov chain Monte Carlo (MCMC) methods are currently the most popular approaches for generating samples from the posterior PDF. However, these methods often found wanting when sampling from difficult distributions (e.g., high-dimensional PDFs, PDFs with flat manifolds, multimodal PDFs, and very peaked PDFs). This paper introduces a new multi-level sampling approach for Bayesian model updating, called Sequential Gauss-Newton algorithm, which is inspired by the Transitional Markov chain Monte Carlo (TMCMC) algorithm. The Sequential Gauss-Newton algorithm improves two aspects of TMCMC to make an efficient and effective MCMC algorithm for drawing samples from difficult posterior PDFs. First, the statistical efficiency of the algorithm is enhanced by use of the systematic resampling scheme. Second, a new MCMC algorithm, called Gauss-Newton MCMC algorithm, is proposed which is essentially an M-H algorithm with a Gaussian proposal PDF tailored to the posterior PDF using the gradient and Hessian information of the negative log posterior. The effectiveness of the proposed algorithm for solving the Bayesian model updating problem is illustrated using three examples with irregularly shaped posterior PDFs.
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| 22. |
- Khorsand Vakilzadeh, Majid, 1984, et al.
(författare)
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Towards an Automatic Modal Parameter Estimation Framework: Mode Clustering
- 2015
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. - 9783319152509 ; 10, s. 243-259
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Konferensbidrag (refereegranskat)abstract
- The estimation of modal parameters from a set of measured data is a highly judgmental task, with user expertise playing a significant role for distinguishing between physical and spurious modes. However, it can be very tedious especially in situations when the data is difficult to analyze. This study presents a new algorithm for mode clustering as a preliminary step in a multi-step algorithm for performing physical mode selection with little or no user interaction. The algorithm commences by identification of a high-order model from estimated frequency response functions to collect all the important characteristics of the structure in a so-called library of modes. This often results in the presence of spurious modes which can be detected on the basis of the hypothesis that spurious modes are estimated with a higher level of uncertainty comparing to physical modes. Therefore, we construct a series of data using a simple random sampling technique in order to obtain a set of linear systems using subspace identification. Then, their similar modes are grouped together using a new correlation criterion, which is called Modal Observability Correlation (MOC). An illustrative example shows the efficiency of the proposed clustering technique and also demonstrates its capability to dealing with inconsistent data.
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| 23. |
- Larsson, Karl-Johan, 1985, et al.
(författare)
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Calibration and cross-validation of a car component model using repeated testing
- 2015
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. ; 3
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- © The Society for Experimental Mechanics, Inc. 2015. Repeated testing has been made both in the sense of testing multiple test pieces of the same type and in the sense of repeated tests on the same test piece by 13 testers at different occasions. Between the individual tests, the test subject has been dismounted from the test stand and the sensors have been re-calibrated. Statistical evaluation of these tests gives information about the spread that can be expected in modal tests. The SIMO test data and data statistics are used for traditional validation and cross-validation of a finite element model of the car component under test. Planning of the sensor layout has been made prior to testing with the use of the nominal finite element model. A model calibration is made prior to the model validation. The finite element model size is over 20,000 degrees-of-freedom and involves two calibration parameters. The work has been made as part of a structural dynamics model validation Master’s course. An open-source Matlab application has been used for calibration, validation and cross-validation
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| 24. |
- Liljerehn, A., et al.
(författare)
-
Experimental-analytical substructure model sensitivity analysis for cutting machine chatter prediction
- 2012
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - New York, NY : Springer New York. - 2191-5644 .- 2191-5652. - 9781461424215 ; 2, s. 11-20
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Konferensbidrag (refereegranskat)abstract
- Process reliability and dynamic stability is a growing customer demand in the metal machining industry. A limiting factor in process stability is regenerative vibrations which may damage the machined component, the cutting tool and even the machine tool. Spindle speed optimization to ensure process stability and enable larger cutting depths is based on the machine tool and cutting tool assembly's frequency response at the tool-tip. The traditional procedure to retrieve the tool-tip frequency response is to conduct dynamic testing of each machine tool mounted cutting tool. This methodology is normally very time-consuming. In an attempt to reduce testing time, receptance coupling substructure analysis (RCSA) has been proposed by a number of researchers. The objective with this approach is to measure the machine tool structure once and then couple a finite element based substructure representation of the cutting tool of interest. The accuracy of the predicted tool-tip frequency response is then dependent on the quality of measured data. This paper details the state-space based sub-structure coupling technique that is used and presents a sensitivity analysis. This analysis distinguishes key considerations for the machine tool component test and it quantifies the parameter influence on the process stability predictions of the coupled system.
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| 25. |
- Linderholt, Andreas, 1968-, et al.
(författare)
-
A Comparison of the Dynamic Behavior of Three Sets of the Ampair 600 Wind Turbine
- 2015
-
Ingår i: Dynamics of Coupled Structures. - Cham : Springer. - 2191-5644 .- 2191-5652. - 9783319152080 ; , s. 99-110
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The Ampair 600 wind turbine assembly has been modified to suit as a benchmark structure in the pursuit of finding best practices for experimental substructure coupling of structural dynamic systems. Seven such systems have been assembled in test laboratories in Europe and in the USA. We scrutinize the dynamic behavior of the total assembly of three of those by vibration testing and compare the test outcome from seemingly identical assemblies. The aim is to support future component synthesis activities with high fidelity data and support future model validation. Comparisons are made by evaluating deviations of measured frequency response functions, the differences of identified structural eigenfrequencies and the correlation between eigenvector estimates. The testing is made in two parts. First, a partly assembled system, not including the hub and blades, is tested. This constitutes one possible and logical subsystem splitting that is likely to appear in future substructure synthesis efforts. In the second part, the full system assembly is tested. The test procedure, the test setup, the obtained test data and test data statistics are presented.
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| 26. |
- Linderholt, Andreas, 1974, et al.
(författare)
-
Finding local non-linearities using error localization from model updating theory
- 2012
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - New York, NY : Springer New York. - 2191-5644 .- 2191-5652. - 9781461424154 ; 3, s. 323-334
-
Konferensbidrag (refereegranskat)abstract
- Within the aerospace industry, linear finite element models are traditionally used to describe the global structural dynamics of an aircraft. Ground vibration test data serve to facilitate the validation of models which are then used to characterize the aeroelastic behavior of the aircraft and to predict the responses due to dynamic loads. Thus, it is vital that the models contain the essential dynamics of the aircraft. Observed nonlinearities are judged to be local in nature whereas the main part of the structure behaves linearly under normal loading. In this work we focus on the identification of nonlinear effects and do that based on model updating theory. That includes methods for error localization with proper selection of candidate error parameters. The nonlinearities are treated as local modeling errors not considered in the linear system model. The error localization behavior is studied using synthetic test data from a simple system, known as the ECL Benchmark, with known nonlinear properties.
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| 27. |
- Mousavi Bideleh Seyed, Milad, 1985, et al.
(författare)
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Pareto Optimization of a Nonlinear Tuned Mass Damper to Control Vibrations in Hand Held Impact Machines
- 2019
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. ; 1, s. 27-44
-
Konferensbidrag (refereegranskat)abstract
- Large amplitude vibrations from hand held impact machines might bring serious health problems for users in long term. Here, a vibration absorber which works based on the nonlinear tuned mass damper concept is applied to mitigate unpleasant vibrations in a hand held impact machine. A global sensitivity analysis is carried out using multiplicative dimensional reduction method to scrutinize the effects of different components on the hand held impact machine dynamics response and attenuate the number of input parameters for optimization. Based on the global sensitivity analysis results, the nonlinear tuned mass damper components are chosen as the design parameters subject to optimization. A multiobjective optimization problem is formulated and solved using genetic algorithm to reduce vibrations and total weight of the machine. The Pareto optimized solutions are robust against the exciting force amplitude and frequency. The global sensitivity analysis results revealed that it is possible to run the simulations with a constant exciting force amplitude and extend the obtained solutions for the case with a variable exciting force amplitude while the same order of accuracy in the results can be observed. This significantly reduced the computational burden of the optimization. Closed form expressions for the optimal values of the tuned mass damper parameters as well as system response in terms of the auxiliary mass are developed by using the nonlinear least squares method. The results revealed that the proposed technique can significantly suppress the vibrations induced by the hand held impact machine. This makes it possible for users to operate the machine for a longer time period with lower health risks.
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| 28. |
- Okhovat, Reza, 1984, et al.
(författare)
-
Dynamic Equations for an Anisotropic Cylindrical Shell
- 2014
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - New York, NY : Springer New York. - 2191-5644 .- 2191-5652. - 9781461465843 ; 45:7, s. 731-741
-
Konferensbidrag (refereegranskat)abstract
- Dynamic equations for an anisotropic cylindrical shell are derived using a series expansion technique. First the displacement components are expanded into power series in the thickness coordinate relative to the mid-surface of the shell. By using these expansions, the three-dimensional elastodynamic equations yield a set of recursion relations among the expansion functions that can be used to eliminate all but the six of lowest order and to express higher order expansion functions in terms of these of lowest orders. Applying the boundary conditions on the surfaces of the cylindrical shell and eliminating all but the six lowest order expansion functions give the shell equations as a power series in the shell thickness. These six differential equations can in principle be truncated to any order. The method is believed to be asymptotically correct to any order. For the special case of a ring, the eigenfrequencies are compared with exact two-dimensional theory, generally with a good correspondence.
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| 29. |
- Okhovat, Reza, 1984, et al.
(författare)
-
Dynamic equations for an isotropic spherical shell using power series method and surface differential operators
- 2015
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. - 9783319069883 ; 6, s. 29-36
-
Konferensbidrag (refereegranskat)abstract
- Dynamic equations for an isotropic spherical shell are derived by using a series expansion technique. The displacement field is split into a scalar (radial) part and a vector (tangential) part. Surface differential operators are introduced to decrease the length of the shell equations. The starting point is a power series expansion of the displacement components in the thickness coordinate relative to the mid-surface of the shell. By using the expansions of the displacement components, the three-dimensional elastodynamic equations yield a set of recursion relations among the expansion functions that can be used to eliminate all but the four of lowest order and to express higher order expansion functions in terms of these of lowest orders. Applying the boundary conditions on the surfaces of the spherical shell and eliminating all but the four lowest order expansion functions give the shell equations as a power series in the shell thickness. After lengthy manipulations, the final four shell equations are obtained in a more compact form which can be represented explicitly in terms of the surface differential operators. The method is believed to be asymptotically correct to any order. The eigenfrequencies are compared to exact three-dimensional theory and membrane theory.
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| 30. |
- Rahrovani, Sadegh, 1981, et al.
(författare)
-
A Metric for Modal Truncation in Model Reduction Problems Part 1: Performance and Error Analysis
- 2014
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - New York, NY : Springer New York. - 2191-5644 .- 2191-5652. - 9781461465843 ; 7:7, s. 781-788
-
Konferensbidrag (refereegranskat)abstract
- The strength of the modal based reduction approach resides in its simplicity, applicability to treat moderate-size systems and also in the fact that it preserves the original system pole locations. However, the main restriction has been in the lack of reliable techniques for identifying the modes that dominate the input-output relationship. To address this problem, an enhanced modal dominancy approach for reduction of second-order systems is presented. Briefly stated, a modal reduction approach is combined with optimality considerations such that the difference between the frequency response function of the full and reduced modal model is minimized in H2 sense. A modal ranking process is performed without solving Lyapunov equations. In the first part of this study, a literature survey on different model reduction approaches and a theoretical investigation of the modified modal approach is presented. The error analysis of the proposed dominancymetric is carried out. Furthermore, the performance of the method is validated for a lightly damped structure and the results are compared with other dominancy metrics. Finally the optimality of the obtained reduced model is discussed and the results are compared with the optimum solution.
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| 31. |
- Rahrovani, Sadegh, 1981, et al.
(författare)
-
A Metric for Modal Truncation in Model Reduction Problems Part 2: Extension to Systems with High-Dimensional Input Space
- 2014
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - New York, NY : Springer New York. - 2191-5644 .- 2191-5652. - 9781461465843 ; 7:7, s. 789-796
-
Konferensbidrag (refereegranskat)abstract
- In the first part of this study, a theoretical investigation of an improved modal approach and a complete error analysis of the proposed modal dominancy metric were presented. In this part the problem of metric non-uniqueness for systems with multiple eigenvalues is described and a method to circumvent this problem based on spatial distribution of either the sensors or the actuators is proposed. This technique is implemented using QR factorization without solving Lyapunov equations. Moreover, the method is improved such that it is able to use the information extracted from spectral properties of the input. Also in order to make the method more effective, information extracted from the input internal structure is incorporated in the modal ranking process. It is shown that this improvement is particularly effective in problems with high-dimensional input and/or output space such as in distributed loading and moving load problems. Finally the performance of the method is validated for a high order system subjected to a high-dimensional input force. That originates from a railway track moving load problem.
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| 32. |
- Rahrovani, Sadegh, 1981, et al.
(författare)
-
An Efficient Exponential Integrator for Large Nonlinear Stiff Systems Part 1: Theoretical Investigation
- 2014
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. - 9783319045214 ; 2, s. 259-268
-
Konferensbidrag (refereegranskat)abstract
- In the first part of this study an exponential integration scheme for computing solutions of large stiff systems isintroduced. It is claimed that the integrator is particularly effective in large-scale problems with localized nonlinearity when compared with the general purpose methods. A brief literature review of different integration schemes is presented and theoretical aspect of the proposed method is discussed in detail. Computational efficiency concerns that arise in simulation of large-scale systems are treated by using an approximation of the Jacobian matrix. This is achieved by combining theproposed integration scheme with the developed methods for model reduction, in order to treat the large nonlinear problems.In the second part, geometric and structural properties of the presented integrator are examined and the preservation of these properties such as area in the phase plane and also energy consistency are investigated. The error analysis is given through small scale examples and the efficiency and accuracy of the proposed exponential integrator is investigated through a large-scale size problem that originates from a moving load problem in railway mechanics. The superiority of the proposedmethod in sense of computational efficiency, for large-scale problems particularly system with localized nonlinearity, has been demonstrated, comparing the results with classical Runge–Kutta approach.
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| 33. |
- Rahrovani, Sadegh, 1981, et al.
(författare)
-
An Efficient Exponential Integrator for Large Nonlinear Stiff Systems Part 2: Symplecticity and Global Error Analysis
- 2014
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. - 9783319045214 ; 2, s. 269-280
-
Konferensbidrag (refereegranskat)abstract
- In the first part of this study an exponential integration scheme for computing solutions of large stiff systems was presented. It was claimed that the integrator is particularly efficient in large-scale problems with localized nonlinearity when compared to general-purpose methods. Theoretical aspects of the proposed method were investigated. The method computational efficiency was increased by using an approximation of the Jacobian matrix. This was achieved by combining the proposed integration scheme with the developed methods for model reduction, in order to treat the large nonlinear problems. In this second part geometric and structural properties of the presented integration algorithm are examined and preservation of these properties such as area in the phase plane and also energy consistency are investigated. The error analysis is given through small scale examples and the efficiency and accuracy of the proposed exponential integrator is investigated through a large-scale size problem that originates from a moving load problem in railway mechanics. The superiority of the proposed method in sense of computational efficiency, for large-scale problems particularly system with localized nonlinearity, has been demonstrated, comparing the results with classical Runge–Kutta approach.
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| 34. |
- Rahrovani, Sadegh, 1981, et al.
(författare)
-
On Gramian-Based Techniques for Minimal Realization of Large-Scale Mechanical Systems
- 2014
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - New York, NY : Springer New York. - 2191-5644 .- 2191-5652. - 9781461465843 ; 45:7, s. 797-805
-
Konferensbidrag (refereegranskat)abstract
- Abstract In this paper, a review of Gramian-based minimal realization algorithms is presented, several comments regarding their properties are given and the ill-condition and efficiency that arise in balancing of large-scale realizations is being addressed. A new algorithm to treat non-minimal realization of very large second-order systems with dense clusters of close eigenvalues is proposed. The method benefits the effectiveness of balancing techniques in treating of non-minimal realizations in combination with the computational efficiency of modal techniques to treat large-scale problems.
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| 35. |
- Rahrovani, Sadegh, 1981, et al.
(författare)
-
Stability Limitations in Simulation of Dynamical Systems with Multiple Time-Scales
- 2016
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. - 9783319152219 ; 1, s. 93-105
-
Konferensbidrag (refereegranskat)abstract
- This paper focuses on the stability properties of a recently proposed exponential integrator particularly in simulation of highly oscillatory systems with multiple time-scales. The linear and nonlinear stability properties of the presented exponential integrator have been studied. We illustrate this with the Fermi–Pasta–Ulam (FPU) problem, a highly oscillatory nonlinear system known as a test benchmark for multi-scale time integrators. This example is also illustrative when studying the numerical resonance and algorithmic instability in the multi-time-stepping (MTS) methods, such as in exponential and/or trigonometric integration schemes, since it has no external input force and therefore no real physical resonance.
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| 36. |
- Ronasi, Hamed, 1980, et al.
(författare)
-
Identification of wheel-rail contact forces based on strain measurement and finite element model of the rolling wheel
- 2012
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - New York, NY : Springer New York. - 2191-5644 .- 2191-5652. - 9781461424185 ; 6, s. 169-177
-
Konferensbidrag (refereegranskat)abstract
- In railway mechanics, the wheel-rail contact force is an important measure in the analysis of different kinds of rolling contactfatigue as well as being used for track condition monitoring. As the contact force cannot be measured directly in the field, oneapproach is to measure the strain at certain points on an instrumented wheel and upon employing signal processing techniques,extract an estimation of the contact force. However, the obtained force is restricted in terms of frequency content, i.e. the resultsare not accurate close to certain resonance frequencies of the wheel, [2]. In order to investigate and overcome the experiencedproblems, a 3-D Finite Element model of the wheel is used in an inverse identification procedure [7], whereby the proper dynamicsof the system is taken into account. The method of signal processing using two Wheatstone bridges is compared withthe inverse identification scheme by means of synthetic data.
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| 37. |
- Scheel, Maren, 1990, et al.
(författare)
-
State-Space Substructuring with Transmission Simulator
- 2016
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. ; 4, s. 91-103
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The dynamic substructuring focus group of SEM organizes sessions on experimental substructuring each IMAC conference and has been doing so for a number of years. Over the last decade, the use of so-called transmission simulators has trended within the community. Transmission simulators are well-modeled parts that fit to the interface of the substructures to be coupled to allow distributed interfaces and relaxation of the coupling conditions by the transmission simulator’s analytical modes at the cost of adding a decoupling step to the substructuring problem. In this paper, the transmission simulator concept is adapted to state-space substructuring. Experimental-analytical substructuring of the focus group benchmark structure, the Ampair A600 wind turbine, is used to verify the methodology.
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| 38. |
- Yaghoubi Nasrabadi, Vahid, 1985, et al.
(författare)
-
A Parallel Solution Method for Structural Dynamic Response Analysis
- 2015
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. ; 4, s. 149-161
-
Konferensbidrag (refereegranskat)abstract
- With the continuous improvements of technology in and around multi-core CPU:s and GPU:s there is a strong desire to exploit this technology in its full potential. For structural dynamics problems, the domain decomposition is a very mature technique that is well adapted to parallel computations in multi-core machines as it is almost trivially parallelizable. However, competing alternatives with model reduction without parallel computation has also reached an extremely high level of maturity and are thus highly competitive. In this paper, a domain decomposition method, in a procedure named the split-stitch-spread (S3) procedure, is proposed to do transient analysis of large finite element models in parallel. In the method, the structure splits into model substructures with elastic interfacial substructures coupling them together. Each of them can be sent to different computer cores to do time discretization. The model substructures stitch to each other by using interfacial forces and as a result, the systems’ state sequence will be obtained. The solution can then be spread into the substructures and response quantities can be evaluated in parallel processing. The method is applied to a multi-story building subjected to earthquake loading and the results are compared with mode displacement method as a model reduction method with focus on computational efficiency.
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| 39. |
- Yaghoubi Nasrabadi, Vahid, 1985, et al.
(författare)
-
An efficient simulation method for structures with local nonlinearity
- 2014
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. - 9783319045214 ; 2, s. 141-149
-
Konferensbidrag (refereegranskat)abstract
- In general, simulating the nonlinear behavior of systems needs a lot of computational effort. Since researchers in different fields are increasingly targeting nonlinear systems, attempts toward fast nonlinear simulation have attracted much interest in recent years. Examples of such fields are system identification and system reliability. In addition to efficiency, the algorithmic stability and accuracy need to be addressed in the development of new simulation procedures. In this paper, we propose a method to treat localized nonlinearity in a structure in an efficient way. The system will be separated by a linearized part and a nonlinear part that is considered as external pseudo forces that act on the linearized system. The response of the system is obtained by iterations in which the pseudo forces are updated. Since the method is presented in linear state space model form, all manipulations that are made on these, like similarity transformations and model reduction, can easily be exploited. To do numerical integration, time-stepping schemes like the triangular hold interpolation can be used to the advantage. We demonstrate the efficiency, stability and accuracy of the method on numerical examples.
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| 40. |
- Yaghoubi Nasrabadi, Vahid, 1985, et al.
(författare)
-
Automated modal analysis based on frequency response function estimates
- 2012
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - New York, NY : Springer New York. - 2191-5644 .- 2191-5652. - 9781461424246 ; 5, s. 9-18
-
Konferensbidrag (refereegranskat)abstract
- Given measured data as estimated frequency responses of a quasi-linear system, there is a variety of system identification methods that identify a state-space model that gives good correlation to the data. Such methods are the N4SID and the PolyMAX methods. Using these methods, a key problem is to select the proper model order. In this work we investigate a method for the automatic detection of proper model order. The method is based on the statistical evaluation of an ensemble of state-space models all identified from the same basic set of frequency response functions, but with different realizations based on a bootstrapping scheme. We apply the method to real test data.
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| 41. |
- Yaghoubi Nasrabadi, Vahid, 1985, et al.
(författare)
-
Automated Modal Analysis Based on Statistical Evaluation of Frequency Responses
- 2014
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - New York, NY : Springer New York. - 2191-5644 .- 2191-5652. - 9781461465843 ; 45:7, s. 479-486
-
Konferensbidrag (refereegranskat)abstract
- This paper presents a newly developed method for obtaining the modal model with a proper model order from experimental frequency response functions (FRF). The method is a multi-step procedure which commences with the identification of a high-order state-space model, Exhaustive Model (EM), using the full FRF data set. Then, modal states that give small contribution to the output, quantified by a metric associated to the observability grammian, are rejected from the EM resulting in a Reference Model (RM). Competing models, with the same model order as the RM, are then found by bootstrapping realization using same-size fractions of the full FRF. Eigensolutions of the Bootstrapping Models (BMs) are then paired by the eigensolutions of the RM based on high Modal Observability Correlation (MOC) indices. In a second reduction stage, the modal states with low MOC index are rejected from the BMs. Final model is found by an averaging through BMs. Only one threshold quantity, related to observability grammians need to be set by the user. The method thus requires very little user interaction. The method is applied to experimental data used in a previous IMAC Round Robin exercise for experimental modal analysis evaluation. © The Society for Experimental Mechanics 2014.
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| 42. |
- Yaghoubi Nasrabadi, Vahid, 1985, et al.
(författare)
-
Locally Non-Linear Model Calibration Using Multi Harmonic Responses : Applied on Ecole de Lyon Non-Linear Benchmark Structure
- 2013
-
Ingår i: Topics in Nonlinear Dynamics, Volume 1. - New York, NY : Springer. - 9781461465690 ; 1, s. 113-123
-
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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| 43. |
- Yaghoubi Nasrabadi, Vahid, 1985, et al.
(författare)
-
Stochastic Finite Element Model Updating by Bootstrapping
- 2016
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. ; 3, s. 117-130
-
Konferensbidrag (refereegranskat)abstract
- This paper presents a new stochastic finite element model calibration framework for estimation of the uncertainty in model parameters, which combines the principles of bootstrapping with the technique of FE model calibration with damping equalization. The bootstrapping allows to quantify the uncertainty bounds on the model parameters by constructing a number of resamples, with replacement, of the experimental data and solving the FE model calibration problem on the resampled datasets. To a great extent, the success of the calibration problem depends on the starting value for the parameters. The formulation of FE model calibration with damping equalization gives a smooth metric with a large radius of convergence to the global minimum and its solution can be viewed as the initial estimate for the model parameters. In this study, practical suggestions are made to improve the performance of this algorithm in dealing with noisy measurements. The performance of the proposed stochastic calibration algorithm is illustrated using simulated data for a six degree-of-freedom mass-spring model.
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| 44. |
- Yaghoubi Nasrabadi, Vahid, 1985, et al.
(författare)
-
The Modal Observability Correlation as a Modal Correlation Metric
- 2014
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - New York, NY : Springer New York. - 2191-5644 .- 2191-5652. - 9781461465843 ; 45:7, s. 487-494
-
Konferensbidrag (refereegranskat)abstract
- The historical development of the Modal Assurance Criterion (MAC) originated from the need of a correlation metric for comparingexperimental modal vectors, estimated from measured data, to eigenvectors that have been determined from finite element calculation. For systems with well separated eigenvalues with many system degrees-of-freedom (DOF) represented in the eigenvectors it is normally easy to distinguish eigenvectors associated to different eigenvalues by low MAC correlation numbers. However, for eigenvectors with a sparse DOF sampling it may be hard to distinguish between vectors by MAC correlation numbers. To reduce the problem of distinguishing between eigensolutions, this paper advocates the use of a new correlation metric based on the observability matrix of the diagonal state-space realization. This is instead of using a metric based on the eigenvectors only. © The Society for Experimental Mechanics 2014.
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| 45. |
- Johansson, Anders, 1982, et al.
(författare)
-
Modeling and Calibration of Small-scale Wind Turbine Blade
- 2014
-
Ingår i: Topics in Experimental Dynamic Substructuring, Volume 2, Proceedings of the 31st IMAC, A Conference on Structural Dynamics, 2013. - New York, NY : Springer New York. - 2191-5644. ; 36:2, s. 51-58
-
Konferensbidrag (refereegranskat)abstract
- The SEM Substructuring Focus Group has chosen an Ampair 600W wind turbine to be used as a test bed in the continued efforts to further experimental and experimental-analytical substructure coupling techniques. To assess such coupling techniques, validated models of the parts, the substructures considered, play a crucial role. This paper describes the modeling, calibration and validation of a Finite Element (FE) model of a blade for the test bed turbine. State-of-the-art composite material modeling is used to set up the model, which is calibrated and validated based on results from an ambitious measurement campaign including both nondestructive testing for dynamic properties and dedicated destructive tests for deduction of material properties. The measurement campaign is carefully described in the paper.
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| 46. |
- Johansson, Anders, 1982, et al.
(författare)
-
Selecting Appropriate Analytical Mode Basis for SEREP-expansion of Experimental Modes
- 2011
-
Ingår i: Proceedings of the 29th IMAC, A Conference on Structural Dynamics, 2011. - 2191-5644. - 9781441992987 ; 3
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Since being introduced in 1986, the System Equivalent Reduction ExpansionProcess (SEREP) has been used to expand experimental eigenvector elementsto the number of degrees-of-freedom of an associated FE-model. In fact, expansionfor interpolation and extrapolation was its original purpose. Since then, studies ofSEREP and other reduction/expansion methods have been abundant. A remarkablenumber of these have concentrated on the selection of master degrees of freedomfor model reduction. Few have however considered the modal basis best used whenSEREP is used for expansion.Expanded experimental modes are expected to correlate well with their analyticalsiblings. However, we argue that the degree of global correlation should only be inparity with the local correlation between the analytical and experimental modes atlocations where measurements are made. Since SEREP is a method which basicallyapproximates a measured mode by a linear combination of analytical modes, perfectagreement between the expanded experimental and analytical modes is easilyachieved, e.g. by simply using only one single mode for expansion. Of course, inthis way the expanded mode normally has very little in common with the measuredmode. On the other hand, using too many modes may result in something similarto the well known problem of fitting a high-order polynomial to noisy data: Perfectagreement at measurement locations is achieved at the expense of unrealisticdeviations and large curvatures between these. To make sure that the experimentalmode has been expanded in a manner faithful to the actual measurements, it is thereforereasonable to use a correlation based criterion in the selection of the expansionbasis. Such a criterion is presented in the present paper.
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| 47. |
- Negreira, Juan, et al.
(författare)
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Numerical Prediction Tools for Low-Frequency Sound Insulation in Lightweight Buildings
- 2015
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Ingår i: Experimental Techniques, Rotating Machinery, and Acoustics. - Cham : Springer International Publishing. - 2191-5644. ; 8, s. 85-95
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Bokkapitel (refereegranskat)abstract
- Lightweight wooden-framed constructions have steadily increased their market share in Sweden during the last two decades. Achieving acoustic and vibration comfort in wooden-based buildings is, however, still a challenging task. Wood is high in both strength and stiffness in relation to its weight, but its variability has repercussions on how sound propagates, this triggering sound insulation problems. Even if buildings comply with present-to-day regulations, complaints amid residents often arise due to low frequency noise, as it is outside the scope of the standards (where no analyses are performed below 50 Hz). In this investigation, laboratory acoustic sound insulation measurements carried out on a facade element according to the current standards, are intended to be reproduced and calibrated by means of the finite element method. In doing so, the first steps of a numerical predictive tool mimicking the real specimen, from 0 to 100 Hz, are presented. This will enable further research about phenomena occurring in the far low end of the frequency range, which is believed to be the cause of most nuisances reported by residents. Reliable predictive tools for addressing acoustic issues during the design phase avoid additional costs of building test prototypes and ensure a better acoustic performance.
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| 48. |
- Sjövall, Per, 1977, et al.
(författare)
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Indirect Vibration Sensing and Optimal Sensor Placement
- 2008
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Ingår i: 26th Conference and Exposition on Structural Dynamics 2008, IMAC-XXVI; Orlando, FL; United States; 4 February 2008 through 7 February 2008. - 2191-5652. - 9781605600666
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Konferensbidrag (refereegranskat)abstract
- The problems to estimate the response of a flexible structure using indirect sensors and to select the best possible locations for these measurements are addressed. The sensor placement problem and the indirect sensing problem are simultaneously approached by considering the Kalman filter. For linear systems exposed to Gaussian white process and measurement noise the Kalman filter provides the optimal estimate of the internal states. The state estimate can be used to map the measured response to the desired response of the structure. A sensor placement index is derived which addresses the statistical properties of the response estimate and a sensor set expansion procedure is formulated. The sensor of the candidate set that maximizes the performance of the Kalman filter is added to the selected set by recursion. This constitutes a computationally inexpensive but sub-optimal procedure. The method can be generalized to treat different types of sensors and response quantities in a straightforward manner. In particular the application to modal state tracking is illustrated. A numerical example which demonstrate the procedure is given. Comparisons between this sub-optimal procedure and the globally optimal sensor placement are made. Furthermore, the predictive ability of the method is satisfactory in the example.
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| 49. |
- Sturesson, Per-Olof, et al.
(författare)
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Structural dynamics teaching example: A linear test analysis case using open software
- 2013
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Ingår i: Special Topics in Structural Dynamics. - New York, NY : Springer. - 2191-5644. ; 6, s. 143-154, s. 143-154
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Konferensbidrag (refereegranskat)abstract
- Teaching the topic of structural dynamics in any engineering field is a true challenge due to the wide span of the underlying subjects like mathematics, mechanics (both rigid body and continuum mechanics), numerical analysis, random data analysis and physical understanding.With the increased availability of computers many engineering problems in practice are evaluated by means of numerical methods. The teaching task within the field of structural dynamics thus has to include analytical models in order to create a theoretical basis but also has to include computational techniques with its approximations, and knowledge about their limitations. Equally important is for students to have knowledge of the experimental verification of the obtained models. This paper describes a teaching example where a simple plate structure is modeled by shell elements, followed by a model calibration using experimental modal analysis data. By using open software, based on MATLAB®1 as a basis for the example, the applied numerical methods are made transparent to the student. The example is built on a combination of the free CALFEM®2 and ABRAVIBE toolboxes, and thus all code used in this paper is publically available as open source code.
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