scholarly journals Variable Modal Parameter Identification for Non-Linear Mdof Systems. Part II: Experimental Validation and Advanced Case Study

2000 ◽  
Vol 7 (4) ◽  
pp. 229-240 ◽  
Author(s):  
Y.H. Chong ◽  
M. Imregun
Keyword(s):  
Modal Analysis ◽  
Experimental Validation ◽  
Element Model ◽  
Force Level ◽  
Friction Damper ◽  
Modal Parameter ◽  
Mdof Systems ◽  
Non Linear ◽  
Linear Friction

The purpose of Part II is to provide an experimental validation of the methodology presented in Part I and to consider a representative engineering case, the study of which requires a relatively large numerical model. A beam system with cubic stiffness type non-linearity was used in the experimental study. The non-linear response was measured at three locations and the underlying linear system was obtained via linear modal analysis of low-excitation response data. The non-linear parameter variations were obtained as a function of the modal amplitude and the response of the system was generated for other force levels. The results were found to agree very well with the corresponding measurements, indicating the success of the non-linear modal analysis methodology, even in the presence of true experimental noise. An advanced numerical case study that included both inherent structural damping and non-linear friction damping, was considered next. The linear finite element model of a high-pressure turbine blade was used in conjunction with three local non-linear friction damper elements. It was shown that the response of the system could be predicted at any force level, provided that that non-linear modal parameters were available at some reference force level. The predicted response levels were compared against those obtained from reference simulations and very good agreement was achieved in all cases.

scholarly journals Variable Modal Parameter Identification for Non-Linear Mdof Systems. Part I: Formulation and Numerical Validation

2000 ◽  
Vol 7 (4) ◽  
pp. 217-227 ◽  
Author(s):  
Y.H. Chong ◽  
M. Imregun
Keyword(s):  
Modal Analysis ◽  
Numerical Study ◽  
Modal Parameters ◽  
Modal Parameter ◽  
Modal Parameter Identification ◽  
Linear Mode ◽  
Analysis Technique ◽  
Mdof Systems ◽  
Non Linear ◽  
Modal Amplitude

This paper deals with the formulation of a frequency domain modal analysis technique that is applicable to weakly non-linear multi-degree of freedom (MDOF) systems with well-separated modes. The concept of linear modal superposition is combined with the normal non-linear mode technique, an approach that allows the formulation of a system identification procedure in terms of variable modal parameters. The numerical study was focused on a 4-DOF system with cubic stiffness non-linearity, and the modal parameters were obtained as functions of the modal amplitude. It was shown that the methodology was well suited to the study of practical cases for which the underlying linear model may be approximate. Similarly, the technique was found to be robust in the presence of measurement noise, though some adverse effects were observed for high noise levels. Once the variable modal parameters were extracted at some given force level, the non-linear responses were predicted at other force levels via synthesis of normal non-linear modes. The same responses were also obtained using a harmonic balance approach and very good agreement was obtained between the two sets of results. The procedure is well suited to the study of industrial cases because of its compatibility with existing finite element methods and linear modal analysis techniques.

scholarly journals Uncertainty in vision based modal analysis: probabilistic studies and experimental validation

ACTA IMEKO ◽  
2016 ◽  
Vol 5 (4) ◽  
pp. 37 ◽  
Author(s):  
Alberto Lavatelli ◽  
Emanuele Zappa
Keyword(s):  
Modal Analysis ◽  
Experimental Validation ◽  
Experimental Approach ◽  
Motion Blur ◽  
Actual Behavior ◽  
Resonant Frequencies ◽  
Blob Analysis ◽  
Structural Excitation ◽  
Made In

This paper analyses the issues related with the application of photogrammetric methods in the context of modal analysis. In this field of mechanical testing, the vibrations of the measurand are monitored. The possibility to measure displacement of several monitored points without directly instrumenting those, pushes the interest toward the application of an image based measurement system. However, the process of acquiring a moving target with a camera is complex due to the motion blur phenomenon. The effects of this particular phenomenon on uncertainty generation and propagation are discussed in parallel with Monte Carlo simulation and experimental approach. The case study here proposed focuses on the estimation of the main modal parameters (first two resonant frequencies and amplitudes) of a structure with the help of 2D Blob Analysis, with particular focus in comparing the performances of photogrammetry with the ones of classic motion transducers. The results of both the approaches confirm that the choice of using photogrammetry as an input for modal analysis should be made carefully, since the actual behavior of a structure can be distorted. Nonetheless, the results show that particular care should be made in the choice of structural excitation when using vision based techniques.

scholarly journals Seismic Assessment in a Historical Masonry Minaret by Linear and Non-linear Seismic Analyses

2020 ◽  
Author(s):  
Emin Hökelekli ◽  
Ali Demir ◽  
Emre Ercan ◽  
Halil Nohutçu ◽  
Abdurrahman Karabulut
Keyword(s):  
Finite Element ◽  
Modal Analysis ◽  
Dynamic Properties ◽  
Ground Motions ◽  
Element Model ◽  
Operational Modal Analysis ◽  
Finite Element Models ◽  
Non Linear ◽  
Concrete Damage ◽  
Historical Masonry

Operational Modal Analysis (OMA) method is frequently used in order to determine dynamical properties of historical masonry structures. In this study, damage pattern of historical Alaca minaret which is selected as application is investigated under different ground motions by updating finite element models (FEM) depending on operational modal analysis test. Initial Finite element model was prepared in ABAQUS V10 program and numerical dynamic characteristics of minaret were determined. In addition, experimental dynamic properties of minaret were provided by operational modal analysis. Initial numerical model of brick masonry structure was calibrated via OMA method. Then, linear and non-linear seismic analyses of calibrated FEM of historical minaret were performed by using different earthquakes acceleration records that occurred in Turkey. Concrete Damage Plasticity model was taken into account in non-linear seismic analyses. As a result of the analyses, it is concluded that the stresses obtained with linear analyses aren’t as realistic as the non-linear analyses results and the earthquakes can cause some damages in the minaret.  

Dynamic Simulation and Experimental Modal Analysis of Large Vibratory Feeder

2010 ◽  
Vol 139-141 ◽  
pp. 2423-2426
Author(s):  
Lian Wan Zhang ◽  
Zhong Jun Yin ◽  
Bing Chen ◽  
Zhi Chao Tang ◽  
Zheng Tian
Keyword(s):  
Finite Element ◽  
Modal Analysis ◽  
Element Model ◽  
Experimental Modal Analysis ◽  
Modal Parameters ◽  
Modal Parameter ◽  
Element Analysis ◽  
Dynamic Design ◽  
Vibratory Feeder ◽  
Modal Damping

The LMS Test.Lab system was used to carried out experimental modal analysis of large vibratory feeder, the PloyMAX method was employed to estimate and identify the modal parameter of vibratory feeder and the modal parameters such as modal frequencies, modal damping ratios and mode shape at concerned band were got; Compared the results of experimental modal analysis to the results of finite element method, the results show that the experimental modal analysis and finite element analysis was consistent to some extent, verified the correctness of finite element model; the bias between experimental and theoretical is inevitable, the experimental results are more reliable relative to the actual and better reflect the dynamic characteristics of vibratory feeder, which will be provided as the reference for dynamic design and dynamic improvement of the vibratory feeder.

scholarly journals Evaluation of Moisture and Decay Models for a New Design Framework for Decay Prediction of Wood

Forests ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 721
Author(s):  
Jonas Niklewski ◽  
Philip Bester van Niekerk ◽  
Christian Brischke ◽  
Eva Frühwald Hansson
Keyword(s):  
Service Life ◽  
Wood Decay ◽  
Element Model ◽  
Digital Design ◽  
Design Guideline ◽  
Digital Performance ◽  
Detail Design ◽  
Non Linear ◽  
Service Life Design ◽  
Life Design

Performance-based, service-life design of wood has been the focus of much research in recent decades. Previous works have been synthesized in various factorized design frameworks presented in the form of technical reports. Factorization does not consider the non-linear dependency between decay-influencing effects, such as between detail design and climate variables. The CLICKdesign project is a joint European effort targeting digital, performance-based specification for service-life design (SLD) of wood. This study evaluates the feasibility of using a semi-empirical moisture model (SMM) as a basis for a digital SLD framework. The performance of the SMM is assessed by comparison against a finite element model (FEM). In addition, two different wood decay models (a logistic, LM, and simplified logistic model (SLM)) are compared. While discrepancies between the SMM and FEM were detected particularly at high wood moisture content, the overall performance of the SMM was deemed sufficient for the application. The main source of uncertainty instead stems from the choice of wood decay model. Based on the results, a new method based on pre-calculated time series, empirical equations, and interpolation is proposed for predicting the service life of wood. The method is fast and simple yet able to deal with non-linear effects between weather variables and the design of details. As such, it can easily be implemented as part of a digital design guideline to provide decision support for architects and engineers, with less uncertainty than existing factorized guidelines.

scholarly journals Bi-objective design-for-control of water distribution networks with global bounds

2021 ◽  
Author(s):  
Aly-Joy Ulusoy ◽  
Filippo Pecci ◽  
Ivan Stoianov
Keyword(s):  
Water Distribution ◽  
Distribution Networks ◽  
Water Distribution Networks ◽  
Mixed Integer ◽  
Global Optimality ◽  
Linear Programs ◽  
Design For Control ◽  
Non Linear ◽  
Feasible Solutions

AbstractThis manuscript investigates the design-for-control (DfC) problem of minimizing pressure induced leakage and maximizing resilience in existing water distribution networks. The problem consists in simultaneously selecting locations for the installation of new valves and/or pipes, and optimizing valve control settings. This results in a challenging optimization problem belonging to the class of non-convex bi-objective mixed-integer non-linear programs (BOMINLP). In this manuscript, we propose and investigate a method to approximate the non-dominated set of the DfC problem with guarantees of global non-dominance. The BOMINLP is first scalarized using the method of $$\epsilon $$ ϵ -constraints. Feasible solutions with global optimality bounds are then computed for the resulting sequence of single-objective mixed-integer non-linear programs, using a tailored spatial branch-and-bound (sBB) method. In particular, we propose an equivalent reformulation of the non-linear resilience objective function to enable the computation of global optimality bounds. We show that our approach returns a set of potentially non-dominated solutions along with guarantees of their non-dominance in the form of a superset of the true non-dominated set of the BOMINLP. Finally, we evaluate the method on two case study networks and show that the tailored sBB method outperforms state-of-the-art global optimization solvers.

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