Dynamic Response Pattern Research Articles

Lyapunov stability of suspension bridges in turbulent flow

In the era of sleek, super slender suspension bridges, facing the issue of stability against dynamic wind actions represents an increasingly complex challenge. Despite the significant progress over the last decades, the impact of atmospheric turbulence on bridge stability remains partially not understood, evoking the need for innovative research approaches. This study aims to address a gap in current research by investigating the random flutter stability associated with variations in the angle of attack due to turbulence, which has not formally been addressed yet. The present investigation employs the 2D rational function approximation model to express self-excited forces in a turbulent flow. The application of this type of models to bridge dynamics yields a viscoelastic coupled dynamic system characterized by memory effects and driven by broad-band long-time-scale noise, described here by a linear homogeneous time-variant differential equation, which shows apparent nonlinear features, and which has rarely been matter of research. Utilizing a Monte Carlo methodology, this work innovates in applying the largest Lyapunov exponent (LE) and the moment Lyapunov exponents (MLE) to study bridge random flutter stability. The calculation of LE and MLE under diverse turbulent wind conditions uncovers lower flutter stability than without turbulence effects. In most cases, sample and low-order p-th moment stability thresholds closely align with the bridge dynamic response pattern; therefore, the flutter critical wind speed is unequivocal. However, under certain turbulence scenarios, it is necessary to resort to MLE for a complete description of stability, evoking some additional consideration of which statistical moments should be considered for the engineering assessment of the flutter limit. Finally, this work provides a qualitative insight into the instability mechanisms by approximating the random parametric excitation with a sinusoidal gust and evaluating the time-periodic system stability via Floquet theory.

Mathematical Complexities in Modelling Damage in Spur Gears

Analytical modelling is an effective approach to obtaining a gear dynamic response or vibration pattern for health monitoring and useful life prediction. Many researchers have modelled this response with various fault conditions commonly observed in gears. The outcome of such models provides a good idea about the changes in the dynamic response available between different gear health states. Hence, a catalogue of the responses is currently available, which ought to aid predictions of the health of actual gears by their vibration patterns. However, these analytical models are limited in providing solutions to useful life prediction. This may be because a majority of these models used single fault conditions for modelling and are not valid to predict the remaining life of gears undergoing more than one fault condition. Existing reviews related to gear faults and dynamic modelling can provide an overview of fault modes, methods for modelling and health prediction. However, these reviews are unable to provide the critical similarities and differences in the single-fault dynamic models to ascertain the possibility of developing models under combined fault modes. In this paper, existing analytical models of spur gears are reviewed with their associated challenges to predict the gear health state. Recommendations for establishing more realistic models are made especially in the context of modelling combined faults and their possible impact on gear dynamic response and health prediction.

Dynamic response of GFRP/Nomex honeycomb sandwich panels subjected to multiple hail impacts – An experimental study

AbstractNowadays, more and more aircraft components are made of composite sandwich structures, and ice impacts are prone to cause internal damage to composite sandwich structures, so it is crucial to study the impact of hail on composite sandwich structures. Since hail impacts may occur several times at a single point, an experimental approach was used to investigate the dynamic response of GFRP/Nomex honeycomb sandwich panels under multiple hail impacts. The dynamic response of the structure was investigated in terms of response rate and deflection‐profile curves using 3D digital image correlation methods, and the effects of impact energy, hail size, and number of impacts on the impact resistance of the honeycomb sandwich structure were explored. The results show that the dynamic response process of sandwich panels can be categorized into the ball‐and‐crown phase, the rebound phase, and the vibration phase. Under the same impact energy, the impact of small‐sized hailstones is more threatening to honeycomb sandwich panels. As the number of impacts increases, the maximum deflection value of the back panel first increases uniformly, and when the layered damage area reaches the threshold value, fiber stripping occurs, and the increment of the maximum deflection value increases significantly.Highlights Since hail impacts may occur several times in real situations, this study conducted multiple impact experiments for one impact site. The dynamic response and damage pattern of the GFRP/Nomex honeycomb sandwich panels under multiple hail impacts were also investigated. The dynamic response process of GFRP/Nomex honeycomb sandwich panels was categorized into three phases: ball‐crown stage, rebound stage, and vibration stage. With the increase of the number of impacts, fiber stripping and fiber break damage began to occur when the layered damage area of the panel reached the threshold value. The honeycomb core has three main failure modes: cell wall folds, cell wall fracture, and cell wall debonding at the TGPW interface. Small‐diameter hails pose a more significant threat of damage to honeycomb sandwich panels at the same impact energy.

Nonlinear dynamic response of stone masonry minarets under harmonic excitation

In this paper three historical masonry minarets in Istanbul, Turkey, are assessed for the dependency between the input harmonic motion and structural response parameters. Their heights are 40, 73 and 74 m, while the slenderness is 12, 6 and 12, respectively. The discrete element method is used in dynamic nonlinear analyses. Models were calibrated with measured natural frequencies. A series of sine-wave excitations is created for different frequency-amplitude pairs varying between 0.4 and 10 Hz, and between 0.1 and 1 m/s. From the results of dynamic simulations, a general trend was observed for masonry minarets. Especially, slenderness and wall thickness play an important role on their dynamic response and damage pattern. Dynamic behavior of these minarets cannot reliably be estimated by static non-linear analysis. Two engineering demand parameters (EDPs) are defined to characterize the displacement of the minaret top and the inter-ring shear displacements along the minaret body. Damage performance criteria for minarets are proposed based on four damage states and tentative limit values are given. We were able to identify the occurrence of those limit states as a function of frequency and amplitude of sinusoidal input motion.

Dynamics of a circular cylinder with an attached splitter plate in laminar flow: A transition from vortex-induced vibration to galloping

Flow-induced vibration (FIV) of a circular cylinder with an attached splitter plate in a laminar flow with Re = 100 is studied numerically. First, the mechanical model along with mathematical formulations is proposed to describe the fluid-structure interaction (FSI) between the elastically supported cylinder–plate body and the surrounding flow. Subsequently, an FSI solution procedure is developed based on the characteristic-based split finite element method, and its accuracy and stability are validated using vortex-induced vibrations (VIVs) of a plain circular cylinder with benchmark solutions. Finally, using FSI simulations, effects of the plate length (L), reduced velocity, mass ratio and damping coefficient on the dynamic response, fluid load, and flow pattern of the cylinder–plate assembly are investigated in detail. As the plate length increases from L/D = 0–1.5 (D is the cylinder diameter), three FIV modes are observed successively: VIV, coupled VIV and galloping, and separated VIV and galloping, along with three vortex modes in the wake: 2S (two separated vortices in one cycle), P+S (a vortex pair and a separated vortex in one cycle), and 2P (two vortex pairs in one cycle). Moreover, it is found that the lift components generated from the splitter plate and the cylinder behave, respectively, as the driving force and the suppressing force of galloping, and the transition from VIV to galloping can be taken as a result of the competition between them. The cylinder–plate model presented could be taken as a benchmark model demonstrating the VIV-galloping interaction and applied to the design of novel FSI-based energy harvesters.

Dynamic response pattern of gold prices to economic policy uncertainty

Abstract Based on a time-varying parameter structural vector autoregression with stochastic volatility (TVP-SVAR-SV) model, the time-varying effects and country differences of economic policy uncertainty (EPU) on gold prices from August 2006 to December 2017 were examined. The results show that the effects of global economic policy uncertainty (GEPU) shock on gold prices change over time. The changes were positive during 2006−2008 and 2013−2017, while the impacts were negative during 2009−2012, implying that the efficiency of gold as a safe haven is not stable and depends on economic conditions. There are significant country differences regarding the impact of EPU on the price of gold, particularly during the international financial crisis, European debt crisis and Trump election. During the international financial crisis, EPU exerts a positive impact on gold prices in most countries. During the European debt crisis, the impact of EPU on gold prices is mainly negative in the examined countries. While during the Trump election, the impact displays positive and negative alternating in most countries.

Large deformation and failure analysis of river embankments subjected to seismic loading

A numerical model based on the theory of mixtures is proposed for the nonlinear large deformation and failure analysis of river embankments subjected to large earthquakes. The governing equations are discretized using the finite element method in large deformation regime with the updated Lagrangian description. A cyclic elasto-viscoplastic model is used for describing the rate-dependent behavior of clayey soils, while a cyclic elasto-plastic model is adopted for sand. The nonlinear kinematic hardening and softening due to structural degradation of soil particles are taken into account in the constitutive relations. Efforts have been made to model the failure modes and damage patterns of river embankments observed in the 2011 Tohoku Earthquake. The effects of ground profile, water table, and earthquake motion on the dynamic response and damage pattern of river embankments are particularly emphasized.

Exposure time relevance of response to nitrite exposure: Insight from transcriptional responses of immune and antioxidant defense in the crayfish, Procambarus clarkii

To understand the toxic effects of nitrite exposure on crayfish, expression of genes involved in the immune system, the antioxidant defense, and the heat shock protein 70 (HSP70) was measured after 12, 24, and 48 h of different nitrite concentrations exposure in the hepatopancreas and hemocytes of Procambarus clarkii. Nitrite exposure up-regulated mRNA levels of cytoplasmic Mn superoxide dismutase (cMn-SOD), catalase (CAT), glutathione peroxidase (GPx), and glutathione-S-transferase (GST), after 24 h nitrite exposure. At 48 h, nitrite exposure decreased the mRNA levels of mitochondrial MnSOD (mMn-SOD), CAT, and GPx. High concentrations of nitrite at 48 h of exposure decreased expression of β-1,3-glucan-bingding protein in the hepatopancreas, and lysozyme expression in hemocytes. Nitrite exposure caused little effect on the heat shock protein 70 (HSP70) in hemocytes. Through overall clustering analysis, we found that 24 h of nitrite exposure caused stronger transcriptional responses. Our study indicated that the response of P. clarkii to acute nitrite exposure was exposure time-dependent. These results will help to understand the dynamic response pattern of crustaceans to nitrite pollution, and improve our understanding of the toxicological mechanisms of nitrite in crustaceans.

Correlation between habituation of visual-evoked potentials and magnetophosphene thresholds in migraine: A case-control study.

In migraine most studies report an interictal deficit of habituation of visual-evoked potentials (VEP-hab) and reduced thresholds for phosphene induction (PT) by transcranial magnetic stimulation (TMS). We searched for a possible correlation between VEP-hab and PT in migraine patients and healthy controls to test whether they reflect the same pathophysiological abnormality. We assessed PT and VEP-hab measured as the percentage change of N1/P1 amplitude over six blocks of 100 responses in 15 healthy volunteers (HV) and in 13 episodic migraineurs without aura (MO) between attacks. Results were compared using Mann-Whitney U test. Interrelationships were examined using Spearman's correlation. In MO patients VEP-hab was reduced compared to HV (p = 0.001), while PT were not significantly different between HV and MO. There was no correlation between PT and VEP-hab in either group of participants. We confirm that in interictal migraine VEP habituation is deficient, but magnetophosphene threshold normal. VEP-hab and PT were not correlated with each other in healthy controls or in migraineurs. This finding suggests that they index different facets of cortical excitability in migraine, i.e. a punctual normal measure of the cortical activation threshold for PT and a dynamic response pattern to repeated stimuli for VEP habituation.

Correlation between Habituation of Visual Evoked Potentials and Magnetophosphene thresholds in migraine

Event Abstract Back to Event Correlation between Habituation of Visual Evoked Potentials and Magnetophosphene thresholds in migraine Anna Ambrosini1*, Aliaksei Kisialiou2, Ennio Iezzi1, Armando Perrotta1, Andrea Nardella1, Alfredo Berardelli3, Francesco Pierelli3 and Jean Schoenen4 1 IRCCS Neuromed, Pozzilli (Isernia), Italy, Italy 2 University of Glasgow, United Kingdom 3 University "La Sapienza", Italy 4 CHR CItadelle - University of Liège, Belgium Introduction: An interictal habituation deficit of visual evoked potentials (VEP) and a reduced threshold (PT) of magnetophosphenes have been reported in migraine in separate studies. While the habituation deficit was attributed to reduced preactivation level of the visual coretx, the reduced PT likely indicates cortical hyperexcitability. Both phenomena have not yet been explored in the same patients. Methods: We assessed PT by transcranial magnetic stimulation (TMS) in 15 healthy volunteers (HV) and in 13 episodic migraineurs without aura between attacks (MO), whereafter we recorded pattern-reversal VEP (6 blocks of 100 responses) and measured habituation. Results were compared using Mann-Whitney U test. Interrelationships were examined using Spearman’s correlation. Results: Phosphene thresholds was not significantly different between HV and MO. By contrast, MO patients had a reduced VEP habituation compared to HV (p=0.001). There was no correlation between PT and habituation in neither group of subjects . Conclusion: this study confirmed that migraineurs present interictally a deficit of VEP habituation, but failed to find decreased PT in these patients. VEP habituation and phosphene threshold values are not reciprocally correlated in healthy volunteers or in migraine patients, which suggest that they index different aspects of cortical excitability, i.e. a punctual measure of cortical activation threshold for PT, as opposed to a dynamic response pattern to repeated stimuli for VEP habituation. Keywords: Migraine Disorders, migraine pathophysiology, Evoked Potentials, Visual, transcranial magnetic stimulation cortical, phosphene threshold Conference: Belgian Brain Council 2014 MODULATING THE BRAIN: FACTS, FICTION, FUTURE, Ghent, Belgium, 4 Oct - 4 Oct, 2014. Presentation Type: Poster Presentation Topic: Clinical Neuroscience Citation: Ambrosini A, Kisialiou A, Iezzi E, Perrotta A, Nardella A, Berardelli A, Pierelli F and Schoenen J (2014). Correlation between Habituation of Visual Evoked Potentials and Magnetophosphene thresholds in migraine. Conference Abstract: Belgian Brain Council 2014 MODULATING THE BRAIN: FACTS, FICTION, FUTURE. doi: 10.3389/conf.fnhum.2014.214.00071 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 02 Jul 2014; Published Online: 16 Aug 2014. * Correspondence: Dr. Anna Ambrosini, IRCCS Neuromed, Pozzilli (Isernia), Italy, Pozzilli, Isernia, Italy, anna.ambrosini@neuromed.it Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Anna Ambrosini Aliaksei Kisialiou Ennio Iezzi Armando Perrotta Andrea Nardella Alfredo Berardelli Francesco Pierelli Jean Schoenen Google Anna Ambrosini Aliaksei Kisialiou Ennio Iezzi Armando Perrotta Andrea Nardella Alfredo Berardelli Francesco Pierelli Jean Schoenen Google Scholar Anna Ambrosini Aliaksei Kisialiou Ennio Iezzi Armando Perrotta Andrea Nardella Alfredo Berardelli Francesco Pierelli Jean Schoenen PubMed Anna Ambrosini Aliaksei Kisialiou Ennio Iezzi Armando Perrotta Andrea Nardella Alfredo Berardelli Francesco Pierelli Jean Schoenen Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Research on Computing Method of Similarity Scale of Dynamic Model Test Concerning Fluid-Structure Coupling for Water-Conveyance Tunnel

Based on the research of numerical simulation of model experiment of water-conveyance tunnel in under soft soil, and three basic types of similarity relation ship between the prototype and the model for dynamic structural model test and dynamic rupture model test was proposed, and the situation where various similarity relation ship is applicable and the technique to ensure similarity for the different goal (to study dynamic behavior, elastic response or damage pattern) was discussed, the similarity relation and the technique is proposed according to specific selection of material of model test . At one time the similarity relation and the technique is validated to pass a example. The results of numerical simulation show: in the specific thing, the similarity relation completely from data of the model test transfer to the prototype. Some new ideas to keep the similarity of the embankment structures are introduced.

Two Patterns of Dynamic Responses of Single‐Free‐Surface Slope and Their Threshold Height

AbstractIn this paper, the dynamic responses of slopes with single‐free‐surface are grouped into two classes according to their distribution pattern, one is high slope dynamic response pattern and the other is low slope dynamic response pattern. Influencing factors on the threshold height (Hthre) of low and high slope response patterns are studied by dimensional analysis. The result shows that Hthre is propotional to the ratio square root of the dynamic elastic moduli Ed to the density ρ, at the same time, it is proportional to period T of the dynamic input if slope material is under elastic condition. According to elastic wave propagation theory and the results of a large quantity of numerical simulations, a formula of Hthre is reached by statistic method. The formula tells that for a slope, if its height is larger than one fifth of the wavelength, its response will be the high slope dynamic response pattern; otherwise, its response will be the low slope dynamic response pattern.

An experimental study of pre-notched clamped beams under impact loading

Experiments were conducted aiming to systematically investigate the failure behavior of clamped beams with one pre-notch or two pre-notches under impact loading from a projectile strike. High-speed digital video photography was successfully applied in the structural impact tests to record in real time the hasty scenario of the specimens' deformations and failures. It is observed that even a minor pre-notch in a beam may dramatically alter its dynamic response and failure behavior by making it much easier to break. That is, with the presence of pre-notches, the beam' dynamic response pattern would switch from a large global ductile plastic deformation to a local strength-failure, which evolves from crack initiation and extension to a breakage. In this case, much more plastic dissipation is localized at the pre-notched cross-section(s) and the breakage is caused basically by a Mode I crack extension. The effect of pre-notch is found to be strongly location-dependent and surface-dependent.

On the purchasing power parity puzzle

A puzzle concerning purchasing power parity is examined: Although the immense exchange rate volatility suggests a likely major role of nominal shocks under sticky prices, the observed half-life persistence of the real exchange rate seems excessively high to be rationalized by price stickiness. This study analyzes carefully the adjustment dynamics of real exchange rates through impulse response analysis. Half-life estimates are found to have substantial imprecision. Moreover, the dynamic response pattern suggests that the shock response is initially amplified before dissipating and that such non-monotonic dynamics can contribute to more than one-third of the observed persistence of real exchange rates.

International Transmission of Stock Market Movements

This paper investigates the international transmission mechanism of stock market movements by estimating a nine-market vector autoregression (VAR) system. Using simulated responses of the estimated VAR system, we (i) locate all the main channels of interactions among national stock markets, and (ii) trace out the dynamic responses of one market to innovations in another. Generally speaking, a substantial amount of multi-lateral interaction is detected among national stock markets. Innovations in the U.S. are rapidly transmitted to other markets in a clearly recognizable fashion, whereas no single foreign market can significantly explain the U.S. market movements. Also, the dynamic response pattern is found to be generally consistent with the notion of informationally efficient international stock markets.

Physiological properties of muscle spindles in dorsal neck muscles of the cat

1. Single-fiber recording was used to examine the properties of 107 spindle endings in cat biventer cervicis (BC) and complexus (CM) muscles. Responses of receptors were examined following muscle contraction and ramp and hold stretch. Twenty-two endings in splenius (SP) were also examined, but their responses could not be quantitated because the anatomy of SP prevented the application of appropriate stretches. 2. Conduction velocitites of spindle afferents ranged from 13 to 90 m/s. Endings with primary response patterns usually had faster conduction velocities than secondary endings, but there was overlap in the conduction velocity ranges of the two subgroups. 3. Most neck spindle afferents could be classified as either primary or secondary by a constellation of physiological criteria including dynamic response pattern, dynamic index, and variability of resting discharge frequency. However, 22 of 107 endings from BC and CM had responses with characteristics intermediate between primary and secondary responses. The possible sources of these characteristics are discussed. 4. Despite the similarity in properties between spindles of different neck muscles, the length sensitivities of CM spindles were high compared to those of BC spindles. CM spindles showed length-related modulation of firing frequency over a more restricted range of initial muscle lengths than did BC spindles. 5. Eight Golgi tendon organs (GTO) were identified by their characteristics responses. Conduction velocities obtained for five GTO afferent nerves ranged from 50 to 67 m/s. Recordings were also made from receptros in deep muscles surrounding the vertebrae. These receptors had properties characteristic of muscle spindles.