Experimental Dynamics

The aim of the study is to maintain the desired period-1 rotation of the parametric pendulum over a wide range of the excitation parameters. Here the Time-Delayed Feedback control method is employed to suppress those bifurcations, which lead to loss of stability of the desired rotational motion. First, the nonlinear dynamic analysis is carried out numerically for the system without control. Specifically, bifurcation diagrams and basins of attractions are computed showing co-existence of oscillatory and rotary attractors. Then numerical bifurcation diagrams are experimentally validated for a typical set of the system parameters giving undesired bifurcations. Finally, the control has been implemented and investigated both numerically and experimentally showing a good qualitative agreement.

An original parametric model is presented to describe the modal interactions characterizing the linearized free dynamics of a cable-beam system. The structural system is composed by two vertical cantilever beams, connected by a suspended nonlinear cable. A closed form solution is achieved for the linear eigenproblem governing the undamped small-amplitude vibrations. The eigensolution shows a rich scenario of frequency crossing and veering phenomena between global modes, dominated by the beam dynamics, and local modes, dominated by the cable vibrations. Veering phenomena are accompanied by modal hybridization processes. The role played by different parameters is discussed, with focus on the resonance regions. The discussion allows the identification of an updated set of parameters, which offers a satisfying explanation of some unexpected dynamic interactions, observed in the experimental behavior of the masonry walls of the Basilica of Collemaggio, a historic structure heavily damaged by the 2009 L'Aquila earthquake.

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

The role of structure and dynamics in mechanisms for RNA becomes increasingly important. Computational approaches using simple dynamics models have been successful at predicting the motions of proteins and are often applied to ribonucleoprotein complexes but have not been thoroughly tested for well-packed nucleic acid structures. In order to characterize a true set of motions, we investigate the apparent motions from 16 ensembles of experimentally determined RNA structures. These indicate a relatively limited set of motions that are captured by a small set of principal components (PCs). These limited motions closely resemble the motions computed from low frequency normal modes from elastic network models (ENMs), either at atomic or coarse-grained resolution. Various ENM model types, parameters, and structure representations are tested here against the experimental RNA structural ensembles, exposing differences between models for proteins and for folded RNAs. Differences in performance are seen, depending on the structure alignment algorithm used to generate PCs, modulating the apparent utility of ENMs but not significantly impacting their ability to generate functional motions. The loss of dynamical information upon coarse-graining is somewhat larger for RNAs than for globular proteins, indicating, perhaps, the lower cooperativity of the less densely packed RNA. However, the RNA structures show less sensitivity to the elastic network model parameters than do proteins. These findings further demonstrate the utility of ENMs and the appropriateness of their application to well-packed RNA-only structures, justifying their use for studying the dynamics of ribonucleo-proteins, such as the ribosome and regulatory RNAs.

G-quadruplex DNA (GqDNA) structures act as promising anticancer targets for smallmolecules (ligands). Solvation dynamics of a ligand (DAPI: 4′,6-diamidino-2-phenylindole) inside antiparallel-GqDNA is studied through direct comparison of time-resolved experiments to molecular dynamics (MD) simulation. Dynamic Stokes shifts of DAPI in GqDNA prepared in H 2 O buffer and D 2 O are compared to find the effect of water on ligand solvation. Experimental dynamics (in H 2 O) is then directly compared with the dynamics computed from 65 ns simulation on the same DAPI-GqDNA complex. Ligand solvation follows power-law relaxation (summed with fast exponential relaxation) from ∼100 fs to 10 ns. Simulation results show relaxation below ∼5 ps is dominated by water motion, while both water and DNA contribute comparably to dictate long-time power-law dynamics. Ion contribution is, however, found to be negligible. Simulation results also suggest that anomalous solvation dynamics may have origin in subdiffusive motion of perturbed water near GqDNA.

G-quadruplex DNA (GqDNA) structures act as promising anticancer targets for smallmolecules (ligands). Solvation dynamics of a ligand (DAPI: 4′,6-diamidino-2-phenylindole) inside antiparallel-GqDNA is studied through direct comparison of time-resolved experiments to molecular dynamics (MD) simulation. Dynamic Stokes shifts of DAPI in GqDNA prepared in H 2 O buffer and D 2 O are compared to find the effect of water on ligand solvation. Experimental dynamics (in H 2 O) is then directly compared with the dynamics computed from 65 ns simulation on the same DAPI-GqDNA complex. Ligand solvation follows power-law relaxation (summed with fast exponential relaxation) from ∼100 fs to 10 ns. Simulation results show relaxation below ∼5 ps is dominated by water motion, while both water and DNA contribute comparably to dictate long-time power-law dynamics. Ion contribution is, however, found to be negligible. Simulation results also suggest that anomalous solvation dynamics may have origin in subdiffusive motion of perturbed water near GqDNA.

The aim of the study is to maintain the desired period-1 rotation of the parametric pendulum over a wide range of the excitation parameters. Here the Time-Delayed Feedback control method is employed to suppress those bifurcations, which lead to loss of stability of the desired rotational motion. First, the nonlinear dynamic analysis is carried out numerically for the system without control. Specifically, bifurcation diagrams and basins of attractions are computed showing co-existence of oscillatory and rotary attractors. Then numerical bifurcation diagrams are experimentally validated for a typical set of the system parameters giving undesired bifurcations. Finally, the control has been implemented and investigated both numerically and experimentally showing a good qualitative agreement.

In this paper, a new model updating scheme is introduced to adjust the system matrices of a finite-element model by using experimental operating deflection shapes (ODS). An ODS is defined here as the response vector when the system is driven at a given degree of freedom with a unit force of fixed frequency. The proposed algorithm adjusts the numerical model in an iterative way. The matrix equilibrium equation is solved by first taking into account the frequency shift that appears between the non-updated finite element model and the experimental structure. In this way, numerical instabilities observed in state-of-the-art methods are avoided. We present results on two well-known numerical and experimental benchmark cases. They show the good convergence properties of the proposed approach.

Frequency Response Functions (FRFs) residues have been widely used in time to update Finite Element models [2, 3, 4, 5, 6, 11, 12, 14, 15, 16]. Major reasons for this is that FRFs are very sensitive to damping properties at resonance peaks, local modes influence is included and no modal analysis is required. Nevertheless, it is well known that due to their nature, the frequency responses may change its order of magnitude very rapidly for small parameter or frequency changes. This situation may cause serious discontinuities in the topology of the objective function, causing the updating strategy to diverge or to find a local non-physical minimum [5, 15, 18]. A primary tool for the correlation of FRFs is the Frequency Domain Assurance Criterion [19]. This technique introduces the concept of frequency shift between the frequency response shapes of a reference model (the experimental structure) and a perturbed model (an initial non-updated FE model). Such a concept opens the way for using residues at different frequencies. For instance, in reference [6] the residue is composed by point FRFs at anti-resonances. This paper introduces a general FRF-based model-updating technique, which is focused in using stable residues during the interactive optimization procedure. A benchmark case from the Cost F3 action is used to assess the goodness of the method compared to other well known methods.

A finite element model updating method is proposed for damage detection in mechanical structures using frequency measurements. The cost function is made up of a frequency residual formulated by the gradient of a correlation function in the frequency domain. An optimization algorithm is proposed for the resolution of the numerical problem. The suggested technique is applied to simulated structures considering the effect of noisy measurements. The simulation tests results show the effectiveness of this new damage identification technique. Mathematical and algorithmic analyses highlight very interesting characteristics of the proposed optimization algorithm. The updating method thus obtained has application in structural damage detection and finite elements models validation. It allows also a structural health monitoring of large mechanical structures.

In this paper, a new model updating scheme is introduced to adjust the system matrices of a finite-element model by using experimental operating deflection shapes (ODS). An ODS is defined here as the response vector when the system is driven at a given degree of freedom with a unit force of fixed frequency. The proposed algorithm adjusts the numerical model in an iterative way. The matrix equilibrium equation is solved by first taking into account the frequency shift that appears between the non-updated finite element model and the experimental structure. In this way, numerical instabilities observed in state-of-the-art methods are avoided. We present results on two well-known numerical and experimental benchmark cases. They show the good convergence properties of the proposed approach. r (R. Pascual).

Up to now, existent FRF based model updating methods use the differences between measured and analytical FRFs at a fixed frequency, as residual to minimize. This approach does not take into account that FRFs between a reference model (experimental) and a perturbed one (a finite elements model not yet updated), displace in two axes : amplitude and frequency. A more physical correlation, then, uses also the frequency shift . The problem is how to find it.

In this paper, a new model updating scheme is introduced to adjust the system matrices of a finite-element model by using experimental operating deflection shapes (ODS). An ODS is defined here as the response vector when the system is driven at a given degree of freedom with a unit force of fixed frequency. The proposed algorithm adjusts the numerical model in an iterative way. The matrix equilibrium equation is solved by first taking into account the frequency shift that appears between the non-updated finite element model and the experimental structure. In this way, numerical instabilities observed in state-of-the-art methods are avoided. We present results on two well-known numerical and experimental benchmark cases. They show the good convergence properties of the proposed approach.

Frequency Response Functions (FRFs) residues have been widely used in time to update Finite Element models . Major reasons for this is that FRFs are very sensitive to damping properties at resonance peaks, local modes influence is included and no modal analysis is required. Nevertheless, it is well known that due to their nature, the frequency responses may change its order of magnitude very rapidly for small parameter or frequency changes. This situation may cause serious discontinuities in the topology of the objective function, causing the updating strategy to diverge or to find a local non-physical minimum . A primary tool for the correlation of FRFs is the Frequency Domain Assurance Criterion . This technique introduces the concept of frequency shift between the frequency response shapes of a reference model (the experimental structure) and a perturbed model (an initial non-updated FE model). Such a concept opens the way for using residues at different frequencies. For instance, in reference [6] the residue is composed by point FRFs at anti-resonances. This paper introduces a general FRF-based model-updating technique, which is focused in using stable residues during the interactive optimization procedure. A benchmark case from the Cost F3 action is used to assess the goodness of the method compared to other well known methods.