scholarly journals Surprising simplicity in the modeling of dynamic granular intrusion

2021 ◽  
Vol 7 (17) ◽  
pp. eabe0631
Author(s):  
Shashank Agarwal ◽  
Andras Karsai ◽  
Daniel I. Goldman ◽  
Ken Kamrin
Keyword(s):  
Dynamic Impact ◽  
Free Surfaces ◽  
Reduced Order ◽  
Physical Mechanisms ◽  
Order Relations ◽  
Resistive Force Theory ◽  
Rapid Modeling ◽  
Unified Description ◽  
Potential Use ◽  
The Continuum

Granular intrusions, such as dynamic impact or wheel locomotion, are complex multiphase phenomena where the grains exhibit solid-like and fluid-like characteristics together with an ejected gas-like phase. Despite decades of modeling efforts, a unified description of the physics in such intrusions is as yet unknown. Here, we show that a continuum model based on the simple notions of frictional flow and tension-free separation describes complex granular intrusions near free surfaces. This model captures dynamics in a variety of experiments including wheel locomotion, plate intrusions, and running legged robots. The model reveals that one static and two dynamic effects primarily give rise to intrusion forces in such scenarios. We merge these effects into a further reduced-order technique (dynamic resistive force theory) for rapid modeling of granular locomotion of arbitrarily shaped intruders. The continuum-motivated strategy we propose for identifying physical mechanisms and corresponding reduced-order relations has potential use for a variety of other materials.

scholarly journals Cluster-based reduced-order modelling of a mixing layer

2014 ◽  
Vol 754 ◽  
pp. 365-414 ◽  
Author(s):  
Eurika Kaiser ◽  
Bernd R. Noack ◽  
Laurent Cordier ◽  
Andreas Spohn ◽  
Marc Segond ◽  
...  
Keyword(s):  
Markov Process ◽  
State Space ◽  
Transition Matrix ◽  
Bluff Body ◽  
Mixing Layer ◽  
The State ◽  
Lorenz Attractor ◽  
Reduced Order ◽  
Physical Mechanisms ◽  
Reduced Order Modelling

AbstractWe propose a novel cluster-based reduced-order modelling (CROM) strategy for unsteady flows. CROM combines the cluster analysis pioneered in Gunzburger’s group (Burkardt, Gunzburger & Lee,Comput. Meth. Appl. Mech. Engng, vol. 196, 2006a, pp. 337–355) and transition matrix models introduced in fluid dynamics in Eckhardt’s group (Schneider, Eckhardt & Vollmer,Phys. Rev. E, vol. 75, 2007, art. 066313). CROM constitutes a potential alternative to POD models and generalises the Ulam–Galerkin method classically used in dynamical systems to determine a finite-rank approximation of the Perron–Frobenius operator. The proposed strategy processes a time-resolved sequence of flow snapshots in two steps. First, the snapshot data are clustered into a small number of representative states, called centroids, in the state space. These centroids partition the state space in complementary non-overlapping regions (centroidal Voronoi cells). Departing from the standard algorithm, the probabilities of the clusters are determined, and the states are sorted by analysis of the transition matrix. Second, the transitions between the states are dynamically modelled using a Markov process. Physical mechanisms are then distilled by a refined analysis of the Markov process, e.g. using finite-time Lyapunov exponent (FTLE) and entropic methods. This CROM framework is applied to the Lorenz attractor (as illustrative example), to velocity fields of the spatially evolving incompressible mixing layer and the three-dimensional turbulent wake of a bluff body. For these examples, CROM is shown to identify non-trivial quasi-attractors and transition processes in an unsupervised manner. CROM has numerous potential applications for the systematic identification of physical mechanisms of complex dynamics, for comparison of flow evolution models, for the identification of precursors to desirable and undesirable events, and for flow control applications exploiting nonlinear actuation dynamics.

IMPURITY INDUCED WRINKLING PATTERNS IN METAL FILMS DEPOSITED ON SOFT ELASTIC SUBSTRATES

2017 ◽  
Vol 24 (03) ◽  
pp. 1750034 ◽  
Author(s):  
YONG-JU ZHANG ◽  
SEN-JIANG YU ◽  
MIAO-GEN CHEN ◽  
PING-GEN CAI ◽  
HONG ZHOU
Keyword(s):  
Atomic Force Microscopy ◽  
Structural Characteristics ◽  
Metal Films ◽  
Force Microscopy ◽  
Physical Mechanisms ◽  
Linear Defects ◽  
Atomic Force ◽  
Elastic Substrates ◽  
Direct Current Sputtering ◽  
The Continuum

Metal (iron and nickel) films have been deposited on soft elastic polydimethylsiloxane (PDMS) substrates by direct current sputtering technique and the impurity induced wrinkling patterns are investigated by using optical microscopy and atomic force microscopy. It is found that the metal films can spontaneously form disordered wrinkles due to the isotropic compressive stress. In the vicinity of film impurities such as extraneous particles, linear defects, cracks and thickness-gradient film edges, the stress field becomes anisotropic owing to symmetry breaking and thus complex wrinkling patterns including straight stripes, herringbones, crossings, labyrinths and their transitions can be observed. The morphological evolutions, structural characteristics and physical mechanisms of the impurity induced wrinkles have been discussed and analyzed based on the continuum elastic theory.

The Continuum Energy Distribution of the Old-Nova GK Per (1901)

1983 ◽  
Vol 72 ◽  
pp. 127-131
Author(s):  
A. Bianchini ◽  
F. Sabbadin
Keyword(s):  
Magnetic Field ◽  
Energy Distribution ◽  
White Dwarf ◽  
Late Type ◽  
X Ray ◽  
Physical Mechanisms ◽  
Continuum Energy ◽  
Field Lines ◽  
The Continuum ◽  
Standard Disc

ABSTRACTThe observed X-ray to IR continuum energy distribution of the old-nova GK Per, corrected for the contribution of the late-type secondary and for i.s. extinction,is found to be consistent with the model of an accreting magnetic white dwarf. Furthermore, we discuss plausible modifications of the standard disc structure caused by the presence of magnetic field lines threading the disc and evaluate the contribution to the observed radiation field from several physical mechanisms.

Validated Reduced Order Models for Simulating Trajectories of Bio-Inspired Artificial Micro-Swimmers

2010 ◽  
Author(s):  
Ahmet Fatih Tabak ◽  
Serhat Yesilyurt
Keyword(s):  
Rigid Body Dynamics ◽  
The Body ◽  
Reduced Order Model ◽  
Control Input ◽  
Body Frame ◽  
Order Model ◽  
Reduced Order ◽  
Resistive Force ◽  
Resistive Force Theory ◽  
Good Agreement

Autonomous micro-swimming robots can be utilized to perform specialized procedures such as in vitro or in vivo medical tasks as well as chemical surveillance or micro manipulation. Maneuverability of the robot is one of the requirements that ensure successful completion of its task. In micro fluidic environments, dynamic trajectories of active micro-swimming robots must be predicted reliably and the response of control inputs must be well-understood. In this work, a reduced-order model, which is based on the resistive force theory, is used to predict the transient, coupled rigid body dynamics and hydrodynamic behavior of bio-inspired artificial micro-swimmers. Conceptual design of the micro-swimmer is biologically inspired: it is composed of a body that carries a payload, control and actuation mechanisms, and a long flagellum either such as an inextensible whip like tail-actuator that deforms and propagates sinusoidal planar waves similar to spermatozoa, or of a rotating rigid helix similar to many bacteria, such as E. Coli. In the reduced-order model of the micro-swimmer, fluid’s resistance to the motion of the body and the tail are computed from resistive force theory, which breaks up the resistance coefficients to local normal and tangential components. Using rotational transformations between a fixed world frame, body frame and the local Frenet-Serret coordinates on the helical tail we obtain the full 6 degrees-of-freedom relationship between the resistive forces and torques and the linear and rotational motions of the swimmer. In the model, only the tail’s frequency (angular velocity for helical tail) is used as a control input in the dynamic equations of the micro-swimming robot. The reduced-order model is validated by means of direct observations of natural micro swimmers presented earlier in the literature and against; results show very good agreement. Three-dimensional, transient CFD simulations of a single degree of freedom swimmer is used to predict resistive force coefficients of a micro-swimmer with a spherical body and flexible tail actuator that uses traveling plane wave deformations for propulsion. Modified coefficients show a very good agreement between the predicted and actual time-dependent swimming speeds, as well as forces and torques along all axes.

Multiscale Modeling of Point Defects and Free Surfaces in Semi-infinite Solids

2002 ◽  
Vol 731 ◽  
Author(s):  
V.K. Tewary
Keyword(s):  
Green’S Function ◽  
Multiscale Modeling ◽  
Green's Function ◽  
Point Defects ◽  
Extended Defects ◽  
Free Surfaces ◽  
Lattice Statics ◽  
Surfaces And Interfaces ◽  
Macroscopic Continuum ◽  
The Continuum

AbstractA Green's function method is described for multiscale modeling of point defects such as vacancies and interstitials at the atomistic level and extended defects such as free surfaces and interfaces at the macroscopic continuum level in a solid. The point defects are represented in terms of Kanzaki forces using the lattice-statics Green's function, which can model a large crystallite containing a million atoms without excessive CPU effort. The lattice-statics Green's function reduces to the continuum Green's function in the asymptotic limit which is used to model the extended defects by imposing continuum- model boundary conditions. Numerical results are presented for the displacement field on the free surface due to a vacancy in semi-infinite fcc copper.

Model Synthesis for Design of Switched Systems Using a Variable Structure System Formulation

2003 ◽  
Vol 125 (4) ◽  
pp. 618-629 ◽  
Author(s):  
Javier A. Kypuros ◽  
Raul G. Longoria
Keyword(s):  
Switched Systems ◽  
Variable Structure ◽  
Reduced Order Models ◽  
Bond Graphs ◽  
Reduced Order ◽  
Structure System ◽  
Physical Mechanisms ◽  
Variable Structure System ◽  
Optimizing Design ◽  
Efficient Power

A Variable Structure System (VSS) formulation and bond graph approach are used to develop a novel scheme for synthesizing reduced order models of switched systems. Switches are physical mechanisms that discontinuously redirect power, and switched systems employ switches for more efficient power conversion and/or to incorporate a control structure. A variety of power converters including electronic converters, hydraulic pumps, and clutched transmissions/differentials employ switches. It is shown how reduced order models can be derived using bond graphs and a VSS formulation to provide insight for optimizing design of switched systems. Experimental results are presented to validate this utility.

scholarly journals The GALAH survey: characterization of emission-line stars with spectral modelling using autoencoders

2020 ◽  
Vol 500 (4) ◽  
pp. 4849-4865
Author(s):  
Klemen Čotar ◽  
Tomaž Zwitter ◽  
Gregor Traven ◽  
Joss Bland-Hawthorn ◽  
Sven Buder ◽  
...  
Keyword(s):  
Emission Line ◽  
Rarefied Gas ◽  
Signal To Noise Ratio ◽  
Emission Spectra ◽  
High Signal ◽  
Physical Mechanisms ◽  
Repeated Observation ◽  
Hα Emission ◽  
The Continuum

ABSTRACT We present a neural network autoencoder structure that is able to extract essential latent spectral features from observed spectra and then reconstruct a spectrum from those features. Because of the training with a set of unpeculiar spectra, the network is able to reproduce a spectrum of high signal-to-noise ratio that does not show any spectral peculiarities, even if they are present in an observed spectrum. Spectra generated in this manner were used to identify various emission features among spectra acquired by multiple surveys using the HERMES spectrograph at the Anglo-Australian telescope. Emission features were identified by a direct comparison of the observed and generated spectra. Using the described comparison procedure, we discovered 10 364 candidate spectra with varying intensities (from partially filled-in to well above the continuum) of the Hα/Hβ emission component, produced by different physical mechanisms. A fraction of these spectra belong to the repeated observation that shows temporal variability in their emission profile. Among the emission spectra, we find objects that feature contributions from a nearby rarefied gas (identified through the emission of [N ii] and [S ii] lines) that was identified in 4004 spectra, which were not all identified as having Hα emission. The positions of identified emission-line objects coincide with multiple known regions that harbour young stars. Similarly, detected nebular emission spectra coincide with visually prominent nebular clouds observable in the red all-sky photographic composites.

scholarly journals On Singular Perturbations of Flexible and Variable-Speed Wind Turbines

2012 ◽  
Vol 2012 ◽  
pp. 1-12 ◽  
Author(s):  
R. Oulad Ben Zarouala ◽  
C. Vivas ◽  
J. Á. Acosta ◽  
L. El Bakkali
Keyword(s):  
Singular Perturbations ◽  
Time Scale ◽  
Reduced Model ◽  
Physical Parameters ◽  
Scale Separation ◽  
Reduced Order ◽  
Physical Mechanisms ◽  
Time Scale Separation ◽  
Successful Approach ◽  
Mechanical Dynamics

A model for the mechanical dynamics of a wind turbine is developed, which is the composition of three physical mechanisms: flexion, torsion, and rotational dynamics. A first contribution is the identification of the essential physical parameters that provide a time-scale separation of these three mechanisms. Under the assumption of singular perturbations the time-scale separation allows to work with a reduced model of order one. This reduction has been essential for the control of this system allowing to control designers to take into account only the reduced-order model. A second contribution consists in employing a measurement of the fore-aft nacelle acceleration with the reduced model, together with a Kalman filter to estimate the flexible DOFs of the system (tower and average blade deflection). The successful approach is tested on high-order nonlinear aeroelastic simulator (FAST).

scholarly journals Are there bound states in the continuum in a dielectric ring?

2021 ◽  
Vol 2015 (1) ◽  
pp. 012017
Author(s):  
D V Bochek ◽  
N S Solodovchenko ◽  
K B Samusev ◽  
M F Limonov
Keyword(s):  
Electromagnetic Waves ◽  
Bound States ◽  
Basic Research ◽  
Destructive Interference ◽  
Field Zone ◽  
Physical Mechanisms ◽  
Photonic States ◽  
Quality Factor Q ◽  
Dielectric Structures ◽  
The Continuum

Abstract Trapping and confining electromagnetic waves is important in both basic research and a variety of applications. For these purposes, various physical mechanisms are exploited including bound states in the continuum, which have been actively investigated recently. Bound states in the continuum have been observed in various objects consisting of both one and a number of dielectric structures. In particular, these photonic states were observed in high-contrast dielectric cylinders in the regime of strong eigenmode coupling, which leads to destructive interference in the far-field zone. In this article, we present the results of a study of bound states in a continuum in a dielectric ring, i.e. cylinder with coaxial air hole. The dependence of the quality factor Q on the normalized diameter of the hole is discussed.

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