Transient Deflection Research Articles

Performance analysis of input shaped model reference adaptive control for a single-link flexible manipulator

Motion control for flexible link manipulators will have a great influence on their overall performance. Conventional control systems have the problem that they cannot compensate for the presence of uncertainty due to a variety of factors such as a change in the system itself-payload variations, degradation and modelling uncertainty. In addition, the underdamped structure of these systems entails motion-induced transient deflection and residual vibration. On the contrary, adaptive control, in particular Model Reference Adaptive Control (MRAC), has therefore been proposed to handle problems of this type dealing with other systems such as cranes, steering stability control for ground vehicles, airplanes and so on. This study presents a review and discussion on the MRAC and some individual issues of MRAC for these flexible link manipulators are addressed to specify: the state tracking error, the limitation of the adaptation values corresponding to the control gains and the control effort. Dealing with the last one, this work proves that shaping the command input to a Model Reference Adaptive Control (IS-MRAC) reduces the control effort necessary for the plant to follow the reference model and also mitigates the detrimental effects of flexibility. The IS-MRAC is implemented in a Single-Link Flexible Manipulator whose natural frequencies, experimentally and analytically estimated using the Transfer Matrix Method plus symbolic computation, vary significantly depending on payload mass and position. To this structured or parametric uncertainty, the proposed Lyapunov control law using the states associated with the low mode is designed for asymptotic stability and accommodates correctly. The state tracking, vibration suppression and control effort reduction performances of the proposed IS-MRAC combined controller are analysed via numerical simulations and experiments.

An exploratory framework for accelerated airport pavement testing using the geotechnical centrifuge

ABSTRACT Full-scale Accelerated Pavement testing (APT) has been regarded as an essential step to bridge the gap between research and practice for pavement design because it can fully mimic a large number of heavy wheel loading on pavements. Despite being able to test pavements in an accelerated manner compared to Long-term Performance Monitoring (LTPM), conducting one full-scale APT experiment is still demanding in terms of monetary cost, space, time, etc., and the accessibility to APT facilities is only available in a few countries nowadays. In this study, an exploratory APT study with a down-scaled pavement model in a high-g environment created by geotechnical centrifuge was performed with up to half a million simulated aircraft load repetitions. Through this test, it was proved that the centrifuge APT can reproduce the full-scale airfield pavement responses, including rutting, cracking, material fatigue, etc. The transient and permanent deflection of the pavement surface, variations in stress and strain states within the pavement structure over its lifespan can be well captured for analysis. This framework of centrifuge APT provides a new methodology for pavement testing and can significantly save the current cost and time of full-scale APT.

Effects of the launch parameters on trans-phase stability performance and mechanism for submarine-launched missiles model

The impact of missile head shape, launch angle, and Fr number on the stability of trans-phase missiles was investigated, providing both experimental and theoretical support for designing diverse ballistic trans-phase weapons and aircraft. Through water-to-air trans-phase experiments and numerical calculations of missiles, deflection angle, velocity, and trajectory are obtained, while statistical and flow-field analyses reveal associated stability mechanisms. The research results indicate a good agreement between the experimental and numerical results. As the Fr number increases for the same head shape, the variations in transient deflection angle decrease. The deflection angle shows notable variations for different head shapes under the same Fr number. Specifically, the flat head demonstrates the highest deflection angle, followed by the 120° conical head, the 90° conical head, and finally the round head shape. Different head shapes lead to varying water film deformations and turbulent kinetic energy dissipations, resulting in differences in shedding vortex intensity and frequency. Launch angles cause variable component wall shear forces and fluid resistances, while changing the Fr number affects initial kinetic energy and energy dissipation, leading to missile model stability differences.

Ultrafast Coupling of Optical Near Fields to Low-Energy Electrons Probed in a Point-Projection Microscope.

We report the first observation of the coupling of strong optical near fields to wavepackets of free, 100 eV electrons with <50 fs temporal resolution in an ultrafast point-projection microscope. Optical near fields are created by excitation of a thin, nanometer-sized Yagi-Uda antenna, with 20 fs near-infrared laser pulses. Phase matching between electrons and near fields is achieved due to strong spatial confinement of the antenna near field. Energy-resolved projection images of the antenna are recorded in an optical pump-electron probe scheme. We show that the phase modulation of the electron by transverse-field components results in a transient electron deflection while longitudinal near-field components broaden the kinetic energy distribution. This low-energy electron near-field coupling is used here to characterize the chirp of the ultrafast electron wavepackets, acquired upon propagation from the electron emitter to the sample. Our results bring direct mapping of different vectorial components of highly localized optical near fields into reach.

Transient response and performance of prestressed concrete deep T-beams with large web openings under impact loading

Abstract This study reports testing results of the transient response of T-shape concrete deep beams with large openings due to impact loading. Seven concrete deep beams with openings including two ordinary reinforced, four partially prestressed, and one solid ordinary reinforced as a reference beam were fabricated and tested. The effects of prestressing strand position and the intensity of the impact force were investigated. Two values for the opening’s depth relative to the beam cross-section dimensions were inspected under the effect of an impacting mass repeatedly dropped from different heights. The study revealed that the beam’s transient deflection was increased by about 50% with greater amplitudes for response oscillations due to impact loading as the impact force increased twice. The results showed that the transient strains in the reinforcement and concrete increased when increasing the opening depth with higher amplitudes for the response oscillations, whereas it had a minimal effect on the beam’s transient deflection. The reinforcement and concrete strain results indicated a higher damping for the strains as the prestressing strands were introduced. Comparison with solid deep beam response showed remarkable increase in the beam deflection and strains with greater amplitudes for response oscillations when large openings were introduced in the web.

Multiphasic value biases in fast-paced decisions

Perceptual decisions are biased toward higher-value options when overall gains can be improved. When stimuli demand immediate reactions, the neurophysiological decision process dynamically evolves through distinct phases of growing anticipation, detection, and discrimination, but how value biases are exerted through these phases remains unknown. Here, by parsing motor preparation dynamics in human electrophysiology, we uncovered a multiphasic pattern of countervailing biases operating in speeded decisions. Anticipatory preparation of higher-value actions began earlier, conferring a 'starting point' advantage at stimulus onset, but the delayed preparation of lower-value actions was steeper, conferring a value-opposed buildup-rate bias. This, in turn, was countered by a transient deflection toward the higher-value action evoked by stimulus detection. A neurally-constrained process model featuring anticipatory urgency, biased detection, and accumulation of growing stimulus-discriminating evidence, successfully captured both behavior and motor preparation dynamics. Thus, an intricate interplay of distinct biasing mechanisms serves to prioritise time-constrained perceptual decisions.

Geometric control of myosin II orientation during axis elongation.

The actomyosin cytoskeleton is a crucial driver of morphogenesis. Yet how the behavior of large-scale cytoskeletal patterns in deforming tissues emerges from the interplay of geometry, genetics, and mechanics remains incompletely understood. Convergent extension in Drosophila melanogaster embryos provides the opportunity to establish a quantitative understanding of the dynamics of anisotropic non-muscle myosin II. Cell-scale analysis of protein localization in fixed embryos suggests that gene expression patterns govern myosin anisotropy via complex rules. However, technical limitations have impeded quantitative and dynamic studies of this process at the whole embryo level, leaving the role of geometry open. Here, we combine in toto live imaging with quantitative analysis of molecular dynamics to characterize the distribution of myosin anisotropy and the corresponding genetic patterning. We found pair rule gene expression continuously deformed, flowing with the tissue frame. In contrast, myosin anisotropy orientation remained approximately static and was only weakly deflected from the stationary dorsal-ventral axis of the embryo. We propose that myosin is recruited by a geometrically defined static source, potentially related to the embryo-scale epithelial tension, and account for transient deflections by cytoskeletal turnover and junction reorientation by flow. With only one parameter, this model quantitatively accounts for the time course of myosin anisotropy orientation in wild-type, twist, and even-skipped embryos, as well as embryos with perturbed egg geometry. Geometric patterning of the cytoskeleton suggests a simple physical strategy to ensure a robust flow and formation of shape.

Dynamic deflection behaviour of plant fibre reinforced laminated composite plate structure using simulation model

In this work, a finite element model has been developed for the transient deflection analysis of plant fibre reinforced laminated composite flat panel using commercial finite element software platform. The plate model has been discretised using eight noded SHELL 281 serendipity element in ANSYS parametric design language (APDL) platform and the responses in time domain are obtained using Newmark time integration algorithm. The accuracy and performance of the present simulation model have been checked via reference literature. Further, the model is extended to analyse the influence of geometrical parameters and support condition on time dependent responses of plant fibre reinforced composite plate structure.

Low-velocity impact analysis of functionally graded porous circular plate reinforced with graphene platelets

ABSTRACT In this study, the low-velocity impact analysis of functionally graded (FG) porous circular plate reinforced with graphene platelets based on the first-order shear deformation theory is presented for the first time. The governing equations are derived using Hamilton's principle. A modified Hertzian contact law is used to model the contact force between the annular plate and the impactor. FEM approach in conjunction with the Picard method is employed to solve the governing equations of the plate under low-velocity impact. The results of the present study are compared with previous studies, and a good agreement can be seen between the results. The effects of different parameters such as porosity distribution and porosity coefficients, various GPL patterns and the weight fractions of Nano-filler on the contact force and transverse displacement of the circular plate are investigated. The results show that the effect of porosity distribution on the time history of contact force and transient central deflection of the structure is more than other parameters.

Impulse saturation in metal plates under confined blasts

The phenomenon of impulse saturation is revisited for metal plates subjected to confined blasts through a combination of experiments, numerical simulations, and analytical modeling. Internal blast experiments were performed on the fully-clamped aluminium square plate where its transient inelastic (mode I) response was recorded using three-dimensional digital image correlation (DIC). A methodology was proposed to idealise the confined blast induced pulse-pressure through a validated numerical model. An analytical model was developed to predict the transient central deflection of the aluminium plate under the idealised pulse pressure, where the predictions were shown to be in reasonable agreement with the DIC measurements. Parametric studies were performed to elucidate the effect of standoff distance and confinement geometry on the saturation duration, saturated impulse and deflection. It was found that both the pulse-shape and saturated impulse strongly influence the saturated deflection during internal blast loadings.

Large-Scale Fire Tests on Sliding Doors for Building Applications

The performance of fire doors is essential for the fire safety in buildings. In the present study, a series of large-scale fire tests on sliding doors is performed in the facilities of the Danish Institute of Fire and Security Technology. The test specimens comprise typical and commercially available door solutions for building applications. Similar doors of approximate dimensions 3 m × 3 m and 5 m × 3 m (width × height) are examined, while separate tests are conducted for each side of door exposed to fire. In all cases, the test specimens are mounted on appropriate wall frames of aeriated concrete as used in practice. The test results are compared in terms of transient temperature and deflection measurements. Findings reveal that the examined sliding doors exhibit satisfactory fire performance meeting the classification requirements. The overall fire performance is not affected by the width opening of door, while the fire resistance rating is significantly influenced by the side of exposure to fire. Finally, the failure characteristics are discussed, and the fire behavior of sliding doors is evaluated.

Numerical Simulation On the Perforation Response of Pressurized Pipe Elbows Under Destructive Impact Loading

Abstract Pipe elbows are essential connection components between the storage terminal and conveying pipelines in the petrochemical industry, which are prone to rupture and perforation under various potential impact loads. In this paper, the rupture and perforation responses of pressurized pipe elbows subjected to transverse impact loads were systematically investigated. Perforation phenomena of pipe elbows were qualitatively analyzed to identify the failure modes and features. Perforation mechanisms of mode transition, transient deflection, velocity variation, energy transfer, and stress distribution were systematically discussed. Extensive parametric studies were performed to investigate the deflection and mechanical responses. Parametric equations were established to describe the critical impact resistance. These results revealed the perforation phenomena and impact limits of pipe elbows subjected to impact loads, which are informative for protection design and damage assessment of pressurized pipe elbows.

Geometrically nonlinear dynamic analysis of variable stiffness composite laminated and sandwich shell panels

The nonlinear free and forced vibration analyses of variable stiffness composite laminated (VSCL) and sandwich shell panels having curvilinear fibres, not yet reported in literature, are conducted based on a higher-order theory. The present structural model considers a third-order shear deformation theory incorporating Murakami zig-zag effects. The analyses are performed using C0 nine-noded isoparametric element with thirteen degrees of freedom and geometrical nonlinearity is included through von Kármán nonlinear strain–displacement relations. The free and forced vibrational responses of the VSCL are established using the eigenvalue solutions and Newmark’s time integration technique, respectively. The results obtained using the present finite element formulation are compared with the available three-dimensional exact and two-dimensional analytical and numerical solutions for establishing the validity of the model. The fundamental frequencies and nonlinear transient deflections of VSCL and sandwich spherical and cylindrical shell panels are evaluated considering the effects of curvilinear fibre path, curvature ratio, number of layers and lamination configuration.

Sparse-Denoising Methods for Extracting Desaturation Transients in Cerebral Oxygenation Signals of Preterm Infants.

Preterm infants are at high risk of developing brain injury in the first days of life as a consequence of poor cerebral oxygen delivery. Near-infrared spectroscopy (NIRS) is an established technology developed to monitor regional tissue oxygenation. Detailed waveform analysis of the cerebral NIRS signal could improve the clinical utility of this method in accurately predicting brain injury. Frequent transient cerebral oxygen desaturations are commonly observed in extremely preterm infants, yet their clinical significance remains unclear. The aim of this study was to examine and compare the performance of two distinct approaches in isolating and extracting transient deflections within NIRS signals. We optimized three different simultaneous low-pass filtering and total variation denoising (LPF-TVD) methods and compared their performance with a recently proposed method that uses singular-spectrum analysis and the discrete cosine transform (SSA-DCT). Parameters for the LPF-TVD methods were optimized over a grid search using synthetic NIRS-like signals. The SSA-DCT method was modified with a post-processing procedure to increase sparsity in the extracted components. Our analysis, using a synthetic NIRS-like dataset, showed that a LPF-TVD method outperformed the modified SSA-DCT method: median mean-squared error of 0.97 (95% CI: 0.86 to 1.07) was lower for the LPF-TVD method compared to the modified SSA-DCT method of 1.48 (95% CI: 1.33 to 1.63), P<0.001. The dual low-pass filter and total variation denoising methods are considerably more computational efficient, by 3 to 4 orders of magnitude, than the SSA-DCT method. More research is needed to examine the efficacy of these methods in extracting oxygen desaturation in real NIRS signals.Clinical relevance- Early and precise identification of abnormal brain oxygenation in premature infants would enable clinicians to employ therapeutic strategies that seek to prevent brain injury and long-term morbidity in this vulnerable population.

Experimental verification of multi-fibre hybridization influence on dynamic deflection and stress values of curved composite panel

The finite-element time-dependent deflection and stress responses of the shallow composite panels subjected to variable mechanical loadings (uniformly distributed load and sinusoidally distributed load) are reported in this article. The study reveals the influence of the advanced fibre hybridization (glass–carbon–kevlar) on the dynamic responses and establishes the accuracy of the numerical responses by comparing them with the experimental values. The numerical steady-state deflections of the hybrid composite structure are evaluated using a generic mathematical model derived through Reddy's third-order shear deformation in conjunction with the finite-element technique and Newmark's time integration scheme. The experimentally evaluated mechanical properties of the fabricated composites are utilized in the computations. The validity of the computed solutions is ascertained with in-house experimental (transient deflection) results. Besides, the numerical model is extended to assess the parametric dependence (aspect ratio, thickness ratio, curvature ratio, geometry, hybrid schemes and support conditions) of the dynamic deflection/stress responses of hybrid composite shallow shell panels subjected to variable mechanical loading types.

Numerical and experimental analysis of temperature field and mechanical analysis for the multi-layer Cr3C2-NiCr coating deposited by HVOF

Cr3C2-NiCr coating has been extensively applied on the surface of components to resist high temperature oxidation, hot corrosion and erosion. The service properties of multi-layer Cr3C2-NiCr coatings deposited by HVOF are highly correlated with cyclic heating and cooling effects and subsequent residual stress distribution during the coating deposition process. A finite element model of the HVOF spraying process was developed based the superposition of double Gauss heat sources to study the thermal and mechanical evolutions of the specimen. The stacking of the coating is accomplished by the activation of each layer by using the birth-death element method. The heat transferred from sprayed particles and flame flow to the substrate is considered by using the superposition of two heat fluxes with a Gaussian distribution. The results show that the model can be used to analyze the transient heating stress state and deflection of the specimen during coating deposition and cooling. The reduction of heat flux can reduce the temperature accumulation of the specimen from the initial stage. Also, different convection coefficients on the coating surface are adopted to simulate different heat dissipation conditions during the coating deposition. The increase of the convection coefficient can effectively reduce the final deflection of the specimens and the final residual stress of the coating. Finally, the surface temperature variation and the final deflection of the specimen predicted by the numerical model are consistent with the measured values. This work provides an effective computational approach to analyze and optimize the HVOF spraying process.

Cortical Localization of the Sensory-Motor Transformation in a Whisker Detection Task in Mice

Responding to a stimulus requires transforming an internal sensory representation into an internal motor representation. Where and how this sensory-motor transformation occurs is a matter of vigorous debate. Here, we trained male and female mice in a whisker detection go/no-go task in which they learned to respond (lick) following a transient whisker deflection. Using single unit recordings, we quantified sensory-related, motor-related, and choice-related activities in whisker primary somatosensory cortex (S1), whisker region of primary motor cortex (wMC), and anterior lateral motor cortex (ALM), three regions that have been proposed to be critical for the sensory-motor transformation in whisker detection. We observed strong sensory encoding in S1 and wMC, with enhanced encoding in wMC, and a lack of sensory encoding in ALM. We observed strong motor encoding in all three regions, yet largest in wMC and ALM. We observed the earliest choice probability in wMC, despite earliest sensory responses in S1. Based on the criteria of having both strong sensory and motor representations and early choice probability, we identify whisker motor cortex as the cortical region most directly related to the sensory-motor transformation. Our data support a model of sensory encoding originating in S1, sensory amplification and sensory-motor transformation occurring within wMC, and motor signals emerging in ALM after the sensory-motor transformation.

Time-Dependent Deflection Responses of Porous FGM Structure Including Pattern and Porosity

The transient deflections of the functionally graded structure considering various types of patterns (power-law, sigmoid and exponential) are computed in this paper numerically using a higher-order shear deformation model. Also, the model includes variable distribution of porosity, i.e., the even and the uneven types, through the thickness direction ([Formula: see text]-axis) of the graded panel. The transient deflection data are obtained computationally via a customized computer code prepared in MATLAB in association with Newmark’s constant acceleration-type time-integration technique. The model accuracy is checked by comparing the present time-dependent data with the published transient deflection values and the simulated results (modeled through a commercial package, ANSYS). Further, the effects of several design parameters (aspect ratio, thickness ratio, power exponent, porosity index, type of porosity, geometry and end-support conditions) on the transient deflection responses of the graded structure are computed through the derived numerical model.

Effective aspect ratio of helices in shear flow.

We report the results of simulations of rigid colloidal helices suspended in a shear flow, using dissipative particle dynamics for a coarse-grained representation of the suspending fluid, as well as deterministic trajectories of non-Brownian helices calculated from the resistance tensor derived under the slender-body approximation. The shear flow produces nonuniform rotation of the helices, similarly to other high aspect ratio particles, such that more elongated helices spend more time aligned with the fluid velocity. We introduce a geometric effective aspect ratio calculated directly from the helix geometry and a dynamical effective aspect ratio derived from the trajectories of the particles and find that the two effective aspect ratios are approximately equal over the entire parameter range tested. We also describe observed transient deflections of the helical axis into the vorticity direction that can occur when the helix is rotating through the gradient direction and that depend on the rotation of the helix about its axis.

Nonlinear dynamic analysis of piezoelectric-bonded FG-CNTR composite structures using an improved FSDT theory

In the present work, a geometrically nonlinear finite shell element is first presented to predict nonlinear dynamic behavior of piezolaminated functionally graded carbon nanotube-reinforced composite (FG-CNTRC) shell, to enrich the existing research results on FG-CNTRC structures. The governing equations are developed via an improved first-order shear deformation theory (FSDT), in which a parabolic distribution of the transverse shear strains across the shell thickness is assumed and a zero condition of the transverse shear stresses on the top and bottom surfaces is imposed. Using a micro-mechanical model on the foundation of the developed rule of mixture, the effective material properties of the FG-CNTRC structures, which are strengthened by single-walled carbon nanotubes (SWCNTs), are scrutinized. The effectiveness of the present method is demonstrated by validating the obtained results against those of other studies from literature considering shell structures. Furthermore, some novel numerical results, including the nonlinear transient deflection of smart FG-CNTRC spherical and cylindrical shells, will be presented and can be considered for future structure design.