Experimental Quantification and Validation of Modal Properties of Geometrically Nonlinear Structures by Using Response-Controlled Stepped-Sine Testing

Karaagacli, T.
Özgüven, Hasan Nevzat
Background Various nonlinear system identification methods applicable to distributed nonlinearities have been developed over the last decade. However, many of them are not eligible to accurately quantify a high degree of nonlinearity. Furthermore, there exist few studies that actually validate the identified nonlinear properties. Objective The main objective of this paper is the validation of a novel nonlinear system identification framework recently developed by the authors on a double-clamped thin beam structure that exhibits continuously distributed strong geometrical nonlinearity due to large amplitude oscillations and considerable damping nonlinearity due to micro-slip in the beam-base connections. Methods The identification framework consists of response-controlled stepped-sine testing (RCT) and the harmonic force surface (HFS) concept. The framework is implemented by using standard hardware and software in modal testing. The RCT approach is based on keeping the displacement amplitude of the driving point constant throughout the frequency sweep and its basic assumptions are well-separated modes and no internal resonance. Constant-force frequency response curves and backbone curves of the first nonlinear normal mode (NNM) are identified at multiple measurement points from HFSs constructed by using measured harmonic excitation force spectra. The NNM shapes of the first mode at various vibration levels are then constructed from the identified NNM backbone curves. On the other side, the response level-dependent modal parameters are identified by applying standard linear modal analysis techniques to frequency response functions (FRFs) measured at constant displacement amplitude levels throughout RCT. Results The RCT-HFS framework quantifies about a 20% shift of the natural frequency and an order of magnitude change of the modal damping ratio (from 0.5% to 4%) for the first mode of the double-clamped beam, which indicates a considerably high degree of stiffness and damping nonlinearities in the vibration range of interest. The identified nonlinear modal parameters are successfully validated by comparing near-resonant constant-force frequency response curves synthesized from these parameters with the ones measured by constant-force stepped-sine testing and with the ones extracted from the HFSs. The HFSs are determined for the first time in an experiment at multiple measurement points other than the driving point. The NNM shapes determined from HFSs are also validated by comparing them with the ones obtained from the identified nonlinear modal constants. Conclusions The RCT-HFS framework is successfully validated for the first time on a structure that exhibits continuously distributed geometrical nonlinearity. This study is a humble contribution towards making nonlinear experimental modal analysis a standard engineering practice.


Analysis of Face Recognition Algorithms for Online and Automatic Annotation of Personal Videos
Yılmaztürk, Mehmet; Ulusoy Parnas, İlkay; Çiçekli, Fehime Nihan (Springer, Dordrecht; 2010-05-08)
Different from previous automatic but offline annotation systems, this paper studies automatic and online face annotation for personal videos/episodes of TV series considering Nearest Neighbourhood, LDA and SVM classification with Local Binary Patterns, Discrete Cosine Transform and Histogram of Oriented Gradients feature extraction methods in terms of their recognition accuracies and execution times. The best performing feature extraction method and the classifier pair is found out to be SVM classification...
Experimentally driven verification of synthetic biological circuits
Yordanov, Boyan; Appleton, Evan; Ganguly, Rishi; Aydın Göl, Ebru; Carr, Swati B; Bhatia, Swapnil; Haddock, Traci; Belta, Calin; Densmore, Douglas (2012-04-03)
We present a framework that allows us to construct and formally analyze the behavior of synthetic gene circuits from specifications in a high level language used in describing electronic circuits. Our back-end synthesis tool automatically generates genetic-regulatory network (GRN) topology realizing the specifications with assigned biological "parts" from a database. We describe experimental procedures to acquire characterization data for the assigned parts and construct mathematical models capturing all po...
Experimental Analysis and FPGA Implementation of the Real Valued Time Delay Neural Network Based Digital Predistortion
Yesil, Soner; Sen, Cansu; Yılmaz, Ali Özgür (2019-01-01)
This paper presents an FPGA implementation of the Real Valued Time Delay Neural Network (RVTDNN) based digital predistortion with a very low resource utilization and high throughput. The implementation exploits efficient utilization of FPGA primitives and approximation of activation functions that can be realized with simple logic operations. The proposed modifications and constraints on the algorithms have been decided and verified based on a closed-loop adaptive hardware setup including RFHIC RWP03040-1H ...
Parametric Identification of Hybrid Linear-Time-Periodic Systems
Uyanik, Ismail; Saranlı, Uluç; Morgul, Omer; Ankaralı, Mustafa Mert (2016-06-24)
In this paper, we present a state-space system identification technique for a class of hybrid LTP systems, formulated in the frequency domain based on input-output data. Other than a few notable exceptions, the majority of studies in the state-space system identification literature (e.g. subspace methods) focus only on LTI systems. Our goal in this study is to develop a technique for estimating time-periodic system and input matrices for a hybrid LTP system, assuming that full state measurements are availab...
Numerical study on effects of computational domain length on flow field in standing wave thermoacoustic couple
MERGEN, SÜHAN; Yıldırım, Ender; TÜRKOĞLU, HAŞMET (Elsevier BV, 2019-03-01)
For the analysis of thermoacoustic (TA) devices, computational methods are commonly used. In the computational studies found in the literature, the flow domain has been modelled differently by different researchers. A common approach in modelling the flow domain is to truncate the computational domain around the stack, instead of modelling the whole resonator to save computational time. However, where to truncate the domain is not clear. In this study, we have investigated how the simulation results are aff...
Citation Formats
T. Karaagacli and H. N. Özgüven, “Experimental Quantification and Validation of Modal Properties of Geometrically Nonlinear Structures by Using Response-Controlled Stepped-Sine Testing,” EXPERIMENTAL MECHANICS, pp. 0–0, 2021, Accessed: 00, 2021. [Online]. Available: https://hdl.handle.net/11511/94068.