5,661 research outputs found
Reasoning About Liquids via Closed-Loop Simulation
Simulators are powerful tools for reasoning about a robot's interactions with
its environment. However, when simulations diverge from reality, that reasoning
becomes less useful. In this paper, we show how to close the loop between
liquid simulation and real-time perception. We use observations of liquids to
correct errors when tracking the liquid's state in a simulator. Our results
show that closed-loop simulation is an effective way to prevent large
divergence between the simulated and real liquid states. As a direct
consequence of this, our method can enable reasoning about liquids that would
otherwise be infeasible due to large divergences, such as reasoning about
occluded liquid.Comment: Robotics: Science & Systems (RSS), July 12-16, 2017. Cambridge, MA,
US
Amorphous silica between confining walls and under shear: a computer simulation study
Molecular dynamics computer simulations are used to investigate a silica melt
confined between walls at equilibrium and in a steady-state Poisseuille flow.
The walls consist of point particles forming a rigid face-centered cubic
lattice and the interaction of the walls with the melt atoms is modelled such
that the wall particles have only a weak bonding to those in the melt, i.e.
much weaker than the covalent bonding of a Si-O unit. We observe a pronounced
layering of the melt near the walls. This layering, as seen in the total
density profile, has a very irregular character which can be attributed to a
preferred orientational ordering of SiO4 tetrahedra near the wall. On
intermediate length scales, the structure of the melt at the walls can be well
distinguished from that of the bulk by means of the ring size distribution.
Whereas essentially no structural changes occur in the bulk under the influence
of the shear fields considered, strong structural rearrangements in the ring
size distribution are present at the walls as far as there is a slip motion.
For the sheared system, parabolic velocity profiles are found in the bulk
region as expected from hydrodynamics and the values for the shear viscosity as
extracted from those profiles are in good agreement with those obtained in pure
bulk simulations from the appropriate Green-Kubo formula.Comment: 23 pages of Late
Supercooled Liquids Under Shear: Theory and Simulation
We analyze the behavior of supercooled fluids under shear both theoretically
and numerically. Theoretically, we generalize the mode-coupling theory of
supercooled fluids to systems under stationary shear flow. Our starting point
is the set of generalized fluctuating hydrodynamic equations with a convection
term. A nonlinear integro-differential equation for the intermediate scattering
function is constructed. This theory is applied to a two-dimensional colloidal
suspension. The shear rate dependence of the intermediate scattering function
and the shear viscosity is analyzed. We have also performed extensive numerical
simulations of a two-dimensional binary liquid with soft-core interactions
near, but above, the glass transition temperature. Both theoretical and
numerical results show: (i) A drastic reduction of the structural relaxation
time and the shear viscosity due to shear. Both the structural relaxation time
and the viscosity decrease as with an exponent , where is the shear rate. (ii) Almost isotropic dynamics
regardless of the strength of the anisotropic shear flow.Comment: 14 pages, 14 figure
To Stir or Not to Stir:Online Estimation of Liquid Properties for Pouring Actions
Our brains are able to exploit coarse physical models of fluids to solve
everyday manipulation tasks. There has been considerable interest in developing
such a capability in robots so that they can autonomously manipulate fluids
adapting to different conditions. In this paper, we investigate the problem of
adaptation to liquids with different characteristics. We develop a simple
calibration task (stirring with a stick) that enables rapid inference of the
parameters of the liquid from RBG data. We perform the inference in the space
of simulation parameters rather than on physically accurate parameters. This
facilitates prediction and optimization tasks since the inferred parameters may
be fed directly to the simulator. We demonstrate that our "stirring" learner
performs better than when the robot is calibrated with pouring actions. We show
that our method is able to infer properties of three different liquids --
water, glycerin and gel -- and present experimental results by executing
stirring and pouring actions on a UR10. We believe that decoupling of the
training actions from the goal task is an important step towards simple,
autonomous learning of the behavior of different fluids in unstructured
environments.Comment: Presented at the Modeling the Physical World: Perception, Learning,
and Control Workshop (NeurIPS) 201
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