Nonlinear dynamic model upgrading and updating using sine-sweep vibration data

2019 ◽  
Vol 475 (2229) ◽  
pp. 20190166
Author(s):  
T. Dossogne ◽  
L. Masset ◽  
B. Peeters ◽  
J. P. Noël
Keyword(s):  
Dynamic Modelling ◽  
Element Model ◽  
Nonlinear Behaviour ◽  
Nonlinear Dynamic Model ◽  
Vibration Data ◽  
Computational Environment ◽  
Acceleration Time Histories ◽  
Time Histories ◽  
Wing Tips ◽  
Sine Sweep

Dynamic modelling is a core activity in mechanical engineering towards supporting system and control design. It is typically carried out in a computational environment, involving idealizing assumptions of diverse kinds. The most notable assumption commonly adopted in the field is the excitation-to-response linearity of the mechanical vibrations. This common practice contrasts with the day-to-day experience of test engineers, who are ever more confronted with nonlinearities when dynamically testing modern mechanical structures. A nonlinear behaviour may result from various physical mechanisms, the most recurrent being the existence of dynamic boundary conditions in the direct vicinity of structural joints and interfaces. In this paper, a coherent set of techniques is described to locate, characterize and model nonlinearities using sine-sweep vibration data, with the purpose of upgrading a pre-existing linear numerical model into a reliable nonlinear one. A constant thread in this set of techniques is the analysis of sensor measurements in phase space. The presented tools are illustrated using acceleration time histories measured at multiple forcing amplitudes on a full-scale F-16 aircraft. Nonlinear stiffness and damping elements, modelling a loosened attachment at one of the aircraft wing tips, are identified and introduced in a linear finite-element model, leading to accurate response predictions in a strongly nonlinear regime of motion.

Validation of FMVSS201 Featureless Headform Finite Element Model for Rotational Acceleration

2001 ◽  
Author(s):  
Saeed D. Barbat
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Element Model ◽  
Fe Model ◽  
Rotational Acceleration ◽  
Acceleration Time ◽  
Acceleration Time Histories ◽  
Time Histories ◽  
Drop Tests ◽  
Constitutive Parameters

Abstract This paper demonstrates an application of the nine linear accelerometer scheme, proposed by (Padgaonkar et al., 1975), to the development and validation of a finite element model of a deformable featureless headform for rotational accelerations. Steps and procedures involved in the development and calibration of the model are also described. A set of tri-axial accelerometers was mounted at the headform center of gravity, C.G., which is located at the origin of the local coordinate axes of the headform. Three bi-axial accelerometers were also mounted at the front, left, and top of the headform’s aluminum skull and on the local coordinate axes of the physical headform. Nine linear accelerations were measured at the headform in drop tests against a rigid plate at impact speeds of 2.68, 4.0, 5.36, and 6.71 m/s (6, 9, 12, and 15 mph). The rotational accelerations of the headform were then calculated from the nine linear acceleration measurements. In the finite element (FE) model of the featureless deformable headform, a visco-elastic material law, available in the non-linear dynamic explicit code PAM-CRASH, was used to simulate the vinyl skin response during impact. The constitutive parameters of the headform’s skin material were calibrated through comparison of the headform drop simulations at various impact speeds with the corresponding tests. Headform responses, such as, resultant acceleration time histories at the headform C.G. and the rotational acceleration time histories obtained from the FE predictions of the headform responses during the drop tests simulations correlated very well with those obtained from experiments. Validation of the headform model for rotational accelerations provided higher level of confidence in the prediction capability of the model when used for interior head impact simulations with vehicle upper interior as specified by the Federal Motor Vehicle Safety Standard FMVSS 201.

scholarly journals Seismic Analysis of AP1000 Nuclear Island Structure by Using the Finite Element Software ANSYS

2017 ◽  
Vol 20 (K2) ◽  
pp. 14-23
Author(s):  
Kien Dinh Nguyen ◽  
Dong Lam Vu
Keyword(s):  
Finite Element ◽  
Seismic Analysis ◽  
Element Model ◽  
Relative Displacement ◽  
Maximum Displacement ◽  
Acceleration Time ◽  
Island Structure ◽  
Finite Element Software ◽  
Acceleration Time Histories ◽  
Time Histories

Seismic analysis of AP1000 nuclear island structure by using the commercial finite element software ANSYS is presented. Using the ANSYS Workbench, a sophisticated threedimensional finite element model of the structure is created and employed in the analysis. Dynamic response of the structure to both the one-directional and three-directional acceleration time histories are considered in the analysis. The time histories for the relative displacement, velocity and absolute acceleration of the structure are obtained for various earthquakes, including American El Centro, Japanese Kobe and Vietnamese Dien Bien earthquakes. The numerical results show that the dynamic characteristics obtained by using one-directional and thee-directional acceleration time histories are different, and the three three-directional acceleration time histories should be employed in the seismic analysis. The result also reveals that the nuclear island is safer in Dien Bien earthquake that it is in El Centro and Kobe earthquakes. The distribution of the von Mises stresses of the structure according to the maximum displacement at the top point is also examined and highlighted.

Metrics for the Comparison of Acceleration Time Histories

2017 ◽  
Author(s):  
Nithyagopal Goswami ◽  
Mourad Zeghal ◽  
Majid Manzari ◽  
Bruce Kutter
Keyword(s):  
Acceleration Time ◽  
Acceleration Time Histories ◽  
Time Histories

Influence of Pedestrian Number on Vibration Serviceability of Footbridge

2014 ◽  
Vol 1049-1050 ◽  
pp. 378-382
Author(s):  
Ju Bing Zhang ◽  
Shao Xia Zhang ◽  
Ying Zou
Keyword(s):  
Finite Element ◽  
Flow Simulation ◽  
Steel Structure ◽  
Element Model ◽  
Simulation Software ◽  
Force Model ◽  
Social Force ◽  
Vibration Data ◽  
Finite Element Software ◽  
Vibration Serviceability

In recent years, the problem of the human-induced bridge vibration has attracted more and more concerns. In this paper , a steel structure footbridge named Shuang'an East in Beijing was taken as the example to collect the whole bridge vibration data and build the finite element model with the finite element software. In addition, this research changes the limitation of considering the pedestrian load as a whole with a traffic flow simulation software, which is based on social force model, applying to reflect the pedestrians' locations during walking. Comparing the simulation data with the the measured data, the vibration serviceability of footbridge will decrease with the increasing of the number of the pedestrians. The analysis results will provide reference for the dynamic characteristic of similar structures.

Selection and Scaling Time History Records for Performance-Based Design

2017 ◽  
pp. 1-35
Author(s):  
Yasin M. Fahjan ◽  
F. İlknur Kara ◽  
Aydın Mert
Keyword(s):  
Ground Motion ◽  
Strong Ground Motion ◽  
Time History ◽  
Design Code ◽  
Uniform Hazard Spectra ◽  
Acceleration Time ◽  
Acceleration Time Histories ◽  
Recent Developments ◽  
Time Histories ◽  
Strong Ground

Recent developments in performance-based analyses and the high performance of computational facilities have led to an increased trend for utilizing nonlinear time-history analysis in seismic evaluation of the performance of structures. One of the crucial issues of such analysis is the selection of appropriate acceleration time histories set that satisfy design code requirements at a specific site. In literature, there are three sources of acceleration time histories: 1) recorded accelerograms in real earthquakes scaled to match design code spectrum/uniform hazard spectra/conditional mean spectrum, 2) artificial records generated from white noise spectra to satisfy design code spectrum, and 3) synthetic records obtained from seismological models. Due to the increase of available strong ground motion database, using and scaling real recorded accelerograms is becoming one of the most contemporary research issues in this field. In this study, basic methodologies and criteria for selecting strong ground motion time histories are discussed. Design code requirements for scaling are summarized for ASCE/SEI-7-10, EC8 and Turkish Seismic Codes. Examples for scaling earthquake records to uniform hazard spectra are provided.

scholarly journals Earthquake Ground Motion Matching on a Small Electric Shaking Table Using a Combined NN-PDFF Controller

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Selma H. Larbi ◽  
Nouredine Bourahla ◽  
Hacine Benchoubane ◽  
Khireddine Choutri ◽  
Mohammed Badaoui
Keyword(s):  
Control Function ◽  
Coupling Effect ◽  
Experimental Tests ◽  
Shaking Table ◽  
Earthquake Ground Motion ◽  
Feedback Signal ◽  
Linear Motors ◽  
Acceleration Time Histories ◽  
Time Histories ◽  
Acceleration Tracking

Replicating acceleration time histories with high accuracy on shaking table platforms is still a challenging task. The complex interference between the components of the system, the inherent nonlinearities, and the coupling effect between the specimen and the shaking table are among other reasons that most affect the control performance. In this paper, a neural network- (NN-) based controller has been developed and experimentally implemented to improve the acceleration tracking performance of an electric shaking table. The latter is a biaxial shaking table driven by linear motors and controlled by a proportional-derivative-feedforward (PDFF) controller that is very efficient in reproducing displacement waveforms on the detriment of the simulation of the prescribed acceleration ground motions. In order to bypass this shortcoming, a control scheme combining the PDFF as a basic control function with a NN controller which filters the shaking table feedback signal and acts on the drive signal by compensating for acceleration distortions is proposed in this study. Several experimental tests have been carried out to build a database for offline training, validating, and testing of the proposed NN control model. Subsequently, the well-trained NN is implemented in the inner control loop of the shaking table to compensate, in parallel with the PDFF controller, the distortions during the replication of acceleration signals. Results of tests using earthquake records showed an enhancement in signal matching when integrating the NN model for both bare and loaded conditions of the shaking table. The tracking errors, estimated using the relative root-mean-square error, between the measured and the desired signal, are significantly reduced in time and frequency domains with the additional NN online controller.

Identification of cracks in an Euler–Bernoulli beam using Bayesian inference and closed-form solution of vibration modes

2020 ◽  
pp. 146442072096971
Author(s):  
Tianyu Wang ◽  
Mohammad Noori ◽  
Wael A. Altabey
Keyword(s):  
Finite Element ◽  
Bayesian Inference ◽  
Finite Element Model ◽  
Crack Detection ◽  
Closed Form Solution ◽  
Element Model ◽  
Form Solution ◽  
Vibration Modes ◽  
Vibration Data ◽  
The Finite Element Model

Over the past two decades, extensive research has been carried out in the field of structural health monitoring for damage detection in structural systems. Some crack detection methods are based on the finite element model of a beam and use vibration data are developed. These methods identify the crack by updating of the finite element model according to the vibration data of structure. This paper proposes a novel method for crack detection in Euler–Bernoulli beams based on the closed-form solution of mode shapes using Bayesian inference. The expression of vibration modes is derived analytically with the crack parameters as unknown variables. Subsequently, the Bayesian inference is used to obtain the probability density function of crack parameters and to evaluate the uncertainty of the modes. Finally, the method is applied to a series of numerical examples, including a beam with a single-crack and multi-cracks, to verify the effectiveness of this method.

Pilot and Observer Performance in Simulated Low Altitude High Speed Flight

1965 ◽  
Vol 7 (3) ◽  
pp. 257-265 ◽  
Author(s):  
Ben Schohan ◽  
Harve E. Rawson ◽  
Stanley M. Soliday
Keyword(s):  
Atmospheric Turbulence ◽  
High Speed ◽  
Target Identification ◽  
Observer Performance ◽  
Acceleration Time ◽  
Acceleration Time Histories ◽  
Time Histories ◽  
Low Altitude ◽  
Vertical Accelerations

Responses of experienced pilots and aerial observers were studied in simulated low-altitude, high-speed (LAHS) flight. The pilots “flew” three-hour surveillance missions at airspeeds of .4M and .9M in different degrees of simulated atmospheric turbulence. Flying ability decreased from .4 to .9M; however, intensity of vertical accelerations did not seem to affect flying ability except at the most severe levels. Target identification was unimpaired by either turbulence or airspeed. The observers also flew three-hour missions while experiencing acceleration time histories recorded from the pilot's flights. Target identification deteriorated as airspeed increased from 0.4 to 0.9 Mach. Gust intensity did not affect performance of any of their tasks. Performance efficiency on all tasks did not deteriorate from beginning to end of the missions of both pilots and observers.

An Improved Stochastic Finite-Fault Method Based on Energy

2015 ◽  
Vol 744-746 ◽  
pp. 878-883
Author(s):  
Ju Fang Zhong ◽  
Jun Wei Liang ◽  
Zhi Peng Fan ◽  
Luo Long Zhan
Keyword(s):  
Ground Motion ◽  
Amplification Factor ◽  
Response Spectrum ◽  
Near Field ◽  
Energy Accumulation ◽  
Accumulation Curve ◽  
Finite Fault ◽  
Acceleration Time Histories ◽  
Time Histories ◽  
Finite Fault Method

Owing to the simulated ground motion energy distribution by stochastic finite-fault method is not reasonable, near-field bedrock strong ground motion acceleration time histories are used to study. Fourier transform is adapted to analysis the variation of the energy accumulation curve with frequency. The results show that the record energy accumulation curve is a steep rise curve, 80% of total energy of the vertical ground motion is concentrated on the 2.5-15Hz, while the horizontal is mainly concentrated on the 2-11Hz. An improved stochastic finite-fault method is proposed by multiplying an amplification factor in some frequency. The results show that multiplying an amplification factor, the simulated acceleration energy accumulation curve matches to the record acceleration energy accumulation curve, and the peak of simulated acceleration response spectrum tends to the record acceleration value.

Spectrographic Analysis for the Modal Testing of Nonlinear Aeroelastic Systems

2006 ◽  
Author(s):  
Catharine C. Marsden ◽  
Stuart J. Price
Keyword(s):  
Nonlinear System ◽  
Time History ◽  
Modal Testing ◽  
System Response ◽  
Spectrographic Analysis ◽  
Input Frequency ◽  
Frequency Content ◽  
Aeroelastic System ◽  
Time Histories ◽  
Sine Sweep

The spectrograph is a signal processing tool often used for the frequency domain analysis of time-varying signals. When the signal to be analyzed is a function of time, the spectrograph represents the frequency content of the signal as a sequence of power spectra that change with time. In this paper, the usefulness of the technique is demonstrated in its application to the analysis of the time history response of a nonlinear aeroelastic system. The aeroelastic system is modeled analytically as a two-dimensional, rigid airfoil section free to move in both the bending and pitching directions and possessing a rigid flap. The airfoil is mounted by torsional and translational springs attached at the elastic axis, and the flap is used to provide the forcing input to the system. The nonlinear system is obtained by introducing a freeplay type of nonlinearity in the pitch degree-of-freedom restoring moment. The airfoil is immersed in an aerodynamic flow environment, modeled using incompressible thin airfoil theory for unsteady oscillatory motion. The equations of motion are solved using a fourth-order Runge-Kutta numerical integration technique to provide time-history solutions of the response of the airfoil in the pitch and plunge directions. Time-histories are obtained for the nonlinear responses of the linear and nonlinear aeroelastic systems to a sine-sweep input. The time-histories are analyzed using the spectrographic technique, and the frequency content of the response is plotted directly as a function of the input frequency. Results show that the combination of the sine-sweep input with the spectrographic analysis permits a unique insight into the behaviour of the nonlinear system with a minimum of testing. It is shown that the frequency of the nonlinear system response is a function of the input frequency and one other characteristic frequency that can be associated with the limit cycle oscillations of the same nonlinear system subject to a transient input.

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