Characterization of Nonlinear Coupled Dynamics in Sandwich Structures

2008 ◽  
Author(s):  
Ioannis T. Georgiou
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Geometric Nonlinearity ◽  
Sandwich Structures ◽  
Normal Modes ◽  
Element Model ◽  
Nonlinear Normal Modes ◽  
High Fidelity ◽  
Coupled Dynamics ◽  
Nonlinear Normal

In this work, the nonlinear coupled dynamics of a sandwich structure with hexagonal honeycomb core are characterized in terms of Proper Orthogonal Decomposition modes. A high fidelity nonlinear finite element model is derived to describe geometric nonlinearity and displacement and rotation fields that govern the coupled dynamics. Contrary to equivalent continuum models used to predict vibration properties of lattice and sandwich structures, a high fidelity finite element model allows for a quite detailed description of the distributed complicated geometric nonlinearity of the core. It was found that the free dynamics excited by a blast load and the forced dynamics excited by a harmonic force posses POD modes which are localized in space and time. The processing of the simulated dynamics by the Time Discrete Proper Transform forms a means to study the nonlinear coupled dynamics of sandwich structures in the context of nonlinear normal modes of vibration and reduced order models.

Characterizing the Dynamics of 3-D Elastic Nonlinear Continua Using the Method of Proper Orthogonal Decompositions

2005 ◽  
Author(s):  
Ioannis Georgiou ◽  
Dimitris Servis
Keyword(s):  
Finite Element ◽  
Three Dimensional ◽  
Normal Modes ◽  
Element Model ◽  
Nonlinear Normal Modes ◽  
Modes Of Vibration ◽  
Nonlinear Normal ◽  
Proper Orthogonal Decompositions ◽  
Nonlinear Finite Element Model ◽  
Proper Orthogonal

A novel and systematic way is presented to characterize the modal structure of the free dynamics of three-dimensional elastic continua. In particular, the method of Proper Orthogonal Decomposition (POD) for multi-field dynamics is applied to analyze the dynamics of prisms and moderately thick beams. A nonlinear finite element model is used to compute accurate approximations to free motions which in turn are processed by POD. The extension of POD to analyze the dynamics of three-dimensional elastic continua, which are multi-field coupled dynamical system, is carried out by vector and matrix quantization of the finite element dynamics. An important outcome of this study is the fact that POD provides the means to systematically identify the shapes of nonlinear normal modes of vibration of three-dimensional structures from high resolution finite element simulations.

scholarly journals Prediction of Isolated Resonance Curves Using Nonlinear Normal Modes

2015 ◽  
Author(s):  
R. J. Kuether ◽  
L. Renson ◽  
T. Detroux ◽  
C. Grappasonni ◽  
G. Kerschen ◽  
...  
Keyword(s):  
Normal Modes ◽  
Resonance Curve ◽  
Element Model ◽  
Nonlinear Normal Modes ◽  
Initial Guess ◽  
Forced Response ◽  
Numerical Continuation ◽  
Continuation Algorithm ◽  
Resonance Curves ◽  
Nonlinear Normal

Isolated resonance curves are separate from the main nonlinear forced-response branch, so they can easily be missed by a continuation algorithm and the resonant response might be underpredicted. The present work explores the connection between these isolated resonances and the nonlinear normal modes of the system and adapts an energy balance criterion to connect the two. This approach provides new insights into the occurrence of isolated resonances as well as a method to find an initial guess to compute the isolated resonance curve using numerical continuation. The concepts are illustrated on a finite element model of a cantilever beam with a nonlinear spring at its tip. This system presents jumps in both frequency and amplitude in its response to a swept sinusoidal excitation. The jumps are found to be the result of a modal interaction that creates an isolated resonance curve that eventually merges with the main resonance branch as the excitation force increases. Excellent insight into the observed dynamics is provided with the NNM theory, which supports that NNMs can also be a useful tool for predicting isolated resonance curves and other behaviors in the damped, forced response.

Damage quantification in foam core sandwich composites via finite element model updating and artificial neural networks

2020 ◽  
Vol 234 (21) ◽  
pp. 4288-4304
Author(s):  
Ali Mardanshahi ◽  
Masoud Mardanshahi ◽  
Ahmad Izadi
Keyword(s):  
Neural Networks ◽  
Finite Element ◽  
Artificial Neural Networks ◽  
Finite Element Model ◽  
Model Updating ◽  
Sandwich Structures ◽  
Element Model ◽  
Foam Core ◽  
Damage Quantification ◽  
Artificial Neural

The main idea of this paper is to propose a nondestructive evaluation (NDE) system for two types of damages, core cracking and skin/core debonding, in fiberglass/foam core sandwich structures based on the inverse eigensensitivity-based finite element model updating using the modal test results, and the artificial neural networks. First, the modal testing was conducted on the fabricated fiberglass/foam core sandwich specimens, in the intact and damaged states, and the natural frequencies were extracted. Finite element modeling and inverse eigensensitivity-based model updating of the intact and damaged sandwich structures were conducted and the parameters of the models were identified. Afterward, the updated finite element models were employed to generate a large dataset of the first five harmonic frequencies of the damaged sandwich structures with different damage sizes and locations. This dataset was adopted to train the machine learning models for detection, localization, and size estimation of the core cracking and skin/core debonding damages. A multilayer perceptron neural network classification model was used for detection of types of damages and also a multilayer perceptron neural network regression model was fitted to the dataset for automatically estimation of the locations and dimensions of damages. This intelligent system of damage quantification was also used to make predictions on real damaged specimens not seen by the system. The results indicated that the extracted natural frequencies from the accurate finite element model, in coordination with the experimental data, and using the artificial neural networks can provide an effective system for nondestructive evaluation of foam core sandwich structures.

Contact Stress and Linearized Modal Predictions of As-Built Preloaded Assembly

2020 ◽  
Vol 142 (5) ◽  
Author(s):  
Adam R. Brink ◽  
Robert J. Kuether ◽  
Matthew D. Fronk ◽  
Bryan L. Witt ◽  
Brendan L. Nation
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Contact Area ◽  
Element Model ◽  
High Fidelity ◽  
Vibration Modes ◽  
Low Level ◽  
Pressure Sensitive ◽  
Sensitive Film ◽  
Pressure Sensitive Film

Abstract The member stiffness and pressure distribution in a bolted joint is significantly influenced by the contact area of the mechanical interface under a prescribed preload force. This research explores the influence of as-built surface profiles for nominally flat interfaces of a C-Beam assembly with two well-defined contact regions. A high-fidelity finite element model is created such that the model uncertainty is minimized by updating and calibrating the piece parts prior to the preload assembly procedure. The model is then assembled and preloaded to evaluate the contact stresses and contact area for both nominally flat and perturbed non-flat surfaces based on three-dimensional surface topography measurements. The predicted pressures are validated with digitized pressure-sensitive film measurements. The high-fidelity modeling reveals how the compliance and thickness of the pressure-sensitive film alter the measured pressures, leading to incorrect evaluations of the stresses and contact area in the joint. The resulting low-level dynamic behavior of the preloaded assembly is shown to be sensitive to the true contact area by linearizing the nonlinear finite element model about the preloaded equilibrium and performing a computational modal analysis. The resonant frequencies are validated with experimental measurements to demonstrate the effect of the contact area on the modal characteristics of the bolted assembly. Vibration modes and loading patterns exhibit varying levels of sensitivity to the contact area in the joint, leading to an improved physical understanding of the influence of contact mechanics on the low-level linear vibration modes of jointed assemblies.

Finite Element Model of Schallamach Waves in Belt-Drives

2019 ◽  
Author(s):  
Mohammed Khattab ◽  
Tamer Wasfy
Keyword(s):  
Finite Element ◽  
Friction Coefficient ◽  
Finite Element Model ◽  
Wave Phenomenon ◽  
Coulomb Friction ◽  
Element Model ◽  
Belt Drive ◽  
High Fidelity ◽  
Stick Slip ◽  
Belt Drives

Abstract The objective of this study is to investigate if a high-fidelity finite element model can predict the Schallamach wave phenomenon in belt-drives. To this end a computational model which closely mimics a recently developed one-pulley experimental belt-drive apparatus, was created. The dynamic response predicted by the model is compared to the experiment results in order to demonstrate that the model can be used to predict the Schallamach wave phenomenon. Furthermore, the model is used to investigate the roles of Coulomb friction coefficient, adhesion, and torque direction on stick-slip instability effects.

A study on the crack detection in beams using linear and nonlinear normal modes

2019 ◽  
Vol 23 (7) ◽  
pp. 1305-1321
Author(s):  
Yildirim Serhat Erdogan
Keyword(s):  
Normal Mode ◽  
Crack Detection ◽  
Normal Modes ◽  
Element Model ◽  
Nonlinear Normal Modes ◽  
Crack Identification ◽  
Crack Location ◽  
Linear And Nonlinear ◽  
Nonlinear Normal ◽  
Cracked Beams

Linear and nonlinear normal mode motions may provide promising information about the condition of mechanical structures under small and large amplitude vibrations, respectively. In this view, this study investigates the nonlinear dynamics of cracked beams through use of the nonlinear mode motion and extends the crack identification methods that utilize the linear characteristics to nonlinear vibrating structures. At first, the nonlinear normal modes of the intact and cracked beams are calculated by a continuation algorithm. A finite element model of a geometrically nonlinear prismatic beam was created based on crack stress intensity. Subsequently, a method based on normal mode motion and minimization of strain energy, which is valid for linear and nonlinear vibrating beams, was developed as an optimization problem. To this end, hybrid optimization was also used due to its capability in finding global minimum along with its computational efficiency. It was shown that the proposed crack detection technique is applicable to beams vibrating in linear and/or nonlinear regimes and well capable of detecting both crack location and severity.

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