165,743 research outputs found
DESIGN, MODELING, AND CONTROL OF SOFT DYNAMIC SYSTEMS
Soft physical systems, be they elastic bodies, fluids, and compliant-bodied creatures, are ubiquitous in nature. Modeling and simulation of these systems with computer algorithms enable the creation of visually appealing animations, automated fabrication paradigms, and novel user interfaces and control mechanics to assist designers and engineers to develop new soft machines. This thesis develops computational methods to address the challenges emerged during the automation of the design, modeling, and control workflow supporting various soft dynamic systems. On the design/control side, we present a sketch-based design interface to enable non-expert users to design soft multicopters. Our system is endorsed by a data-driven algorithm to generate system identification and control policies given a novel shape prototype and rotor configurations. We show that our interactive system can automate the workflow of different soft multicopters\u27 design, simulation, and control with human designers involved in the loop. On the modeling side, we study the physical behaviors of fluidic systems from a local, collective perspective. We develop a prior-embedded graph network to uncover the local constraint relations underpinning a collective dynamic system such as particle fluid. We also proposed a simulation algorithm to model vortex dynamics with locally interacting Lagrangian elements. We demonstrate the efficacy of the two systems by learning, simulating and visualizing complicated dynamics of incompressible fluid
LightGCNet: A Lightweight Geometric Constructive Neural Network for Data-Driven Soft sensors
Data-driven soft sensors provide a potentially cost-effective and more
accurate modeling approach to measure difficult-to-measure indices in
industrial processes compared to mechanistic approaches. Artificial
intelligence (AI) techniques, such as deep learning, have become a popular soft
sensors modeling approach in the area of machine learning and big data.
However, soft sensors models based deep learning potentially lead to complex
model structures and excessive training time. In addition, industrial processes
often rely on distributed control systems (DCS) characterized by resource
constraints. Herein, guided by spatial geometric, a lightweight geometric
constructive neural network, namely LightGCNet, is proposed, which utilizes
compact angle constraint to assign the hidden parameters from dynamic
intervals. At the same time, a node pool strategy and spatial geometric
relationships are used to visualize and optimize the process of assigning
hidden parameters, enhancing interpretability. In addition, the universal
approximation property of LightGCNet is proved by spatial geometric analysis.
Two versions algorithmic implementations of LightGCNet are presented in this
article. Simulation results concerning both benchmark datasets and the ore
grinding process indicate remarkable merits of LightGCNet in terms of small
network size, fast learning speed, and sound generalization.Comment: arXiv admin note: text overlap with arXiv:2307.0018
Microstructure and Velocity of Field-Driven SOS Interfaces: Analytic Approximations and Numerical Results
The local structure of a solid-on-solid (SOS) interface in a two-dimensional
kinetic Ising ferromagnet with single-spin-flip Glauber dynamics, which is
driven far from equilibrium by an applied field, is studied by an analytic
mean-field, nonlinear-response theory [P.A. Rikvold and M. Kolesik, J. Stat.
Phys. 100, 377 (2000)] and by dynamic Monte Carlo simulations. The probability
density of the height of an individual step in the surface is obtained, both
analytically and by simulation. The width of the probability density is found
to increase dramatically with the magnitude of the applied field, with close
agreement between the theoretical predictions and the simulation results.
Excellent agreement between theory and simulations is also found for the
field-dependence and anisotropy of the interface velocity. The joint
distribution of nearest-neighbor step heights is obtained by simulation. It
shows increasing correlations with increasing field, similar to the skewness
observed in other examples of growing surfaces.Comment: 18 pages RevTex4 with imbedded figure
Density-Temperature-Softness Scaling of the Dynamics of Glass-forming Soft-sphere Liquids
The principle of dynamic equivalence between soft-sphere and hard-sphere
fluids [Phys. Rev. E \textbf{68}, 011405 (2003)] is employed to describe the
interplay of the effects of varying the density n, the temperature T, and the
softness (characterized by a softness parameter {\nu}^{-1}) on the dynamics of
glass-forming soft-sphere liquids in terms of simple scaling rules. The main
prediction is that the dynamic parameters of these systems, such as the
{\alpha}-relaxation time and the long-time self-diffusion coefficient, depend
on n, T, and {\nu} only through the reduced density n^\ast \equiv
n{\sigma}^{3}_{HS}(T, {\nu}),where the effective hard-sphere diameter
{\sigma}_{HS}(T, {\nu}) is determined, for example, by the
Andersen-Weeks-Chandler condition for soft-sphere-hard-sphere structural
equivalence. A number of scaling properties observed in recent simulations
involving glass-forming fluids with repulsive short range interactions are
found to be a direct manifestation of this general dynamic equivalence
principle. The self-consistent generalized Langevin equation (SCGLE) theory of
colloid dynamics is shown to accurately capture these scaling rule
Metastability at the Yield-Stress Transition in Soft Glasses
We study the solid-to-liquid transition in a two-dimensional fully periodic
soft-glassy model with an imposed spatially heterogeneous stress. The model we
consider consists of droplets of a dispersed phase jammed together in a
continuous phase. When the peak value of the stress gets close to the yield
stress of the material, we find that the whole system intermittently tunnels to
a metastable "fluidized" state, which relaxes back to a metastable "solid"
state by means of an elastic-wave dissipation. This macroscopic scenario is
studied through the microscopic displacement field of the droplets, whose time
statistics displays a remarkable bimodality. Metastability is rooted in the
existence, in a given stress range, of two distinct stable rheological branches
as well as long-range correlations (e.g., large dynamic heterogeneity)
developed in the system. Finally, we show that a similar behavior holds for a
pressure-driven flow, thus suggesting possible experimental tests.Comment: 13 pages, 11 figure
Real-time Error Control for Surgical Simulation
Objective: To present the first real-time a posteriori error-driven adaptive
finite element approach for real-time simulation and to demonstrate the method
on a needle insertion problem. Methods: We use corotational elasticity and a
frictional needle/tissue interaction model. The problem is solved using finite
elements within SOFA. The refinement strategy relies upon a hexahedron-based
finite element method, combined with a posteriori error estimation driven local
-refinement, for simulating soft tissue deformation. Results: We control the
local and global error level in the mechanical fields (e.g. displacement or
stresses) during the simulation. We show the convergence of the algorithm on
academic examples, and demonstrate its practical usability on a percutaneous
procedure involving needle insertion in a liver. For the latter case, we
compare the force displacement curves obtained from the proposed adaptive
algorithm with that obtained from a uniform refinement approach. Conclusions:
Error control guarantees that a tolerable error level is not exceeded during
the simulations. Local mesh refinement accelerates simulations. Significance:
Our work provides a first step to discriminate between discretization error and
modeling error by providing a robust quantification of discretization error
during simulations.Comment: 12 pages, 16 figures, change of the title, submitted to IEEE TBM
Soft versus Hard Dynamics for Field-driven Solid-on-Solid Interfaces
Analytical arguments and dynamic Monte Carlo simulations show that the
microstructure of field-driven Solid-on-Solid interfaces depends strongly on
the dynamics. For nonconservative dynamics with transition rates that factorize
into parts dependent only on the changes in interaction energy and field
energy, respectively (soft dynamics), the intrinsic interface width is
field-independent. For non-factorizing rates, such as the standard Glauber and
Metropolis algorithms (hard dynamics), it increases with the field.
Consequences for the interface velocity and its anisotropy are discussed.Comment: 9 pages LaTex with imbedded .eps figs. Minor revision
DynamO: A free O(N) general event-driven molecular-dynamics simulator
Molecular-dynamics algorithms for systems of particles interacting through
discrete or "hard" potentials are fundamentally different to the methods for
continuous or "soft" potential systems. Although many software packages have
been developed for continuous potential systems, software for discrete
potential systems based on event-driven algorithms are relatively scarce and
specialized. We present DynamO, a general event-driven simulation package which
displays the optimal O(N) asymptotic scaling of the computational cost with the
number of particles N, rather than the O(N log(N)) scaling found in most
standard algorithms. DynamO provides reference implementations of the best
available event-driven algorithms. These techniques allow the rapid simulation
of both complex and large (>10^6 particles) systems for long times. The
performance of the program is benchmarked for elastic hard sphere systems,
homogeneous cooling and sheared inelastic hard spheres, and equilibrium
Lennard-Jones fluids. This software and its documentation are distributed under
the GNU General Public license and can be freely downloaded from
http://marcusbannerman.co.uk/dynamo
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