1,777,177 research outputs found
Scalable partitioning for parallel position based dynamics
We introduce a practical partitioning technique designed for parallelizing Position Based Dynamics, and exploiting
the ubiquitous multi-core processors present in current commodity GPUs. The input is a set of particles whose
dynamics is influenced by spatial constraints. In the initialization phase, we build a graph in which each node
corresponds to a constraint and two constraints are connected by an edge if they influence at least one common
particle. We introduce a novel greedy algorithm for inserting additional constraints (phantoms) in the graph
such that the resulting topology is q-colourable, where ˆ qˆ ≥ 2 is an arbitrary number. We color the graph, and
the constraints with the same color are assigned to the same partition. Then, the set of constraints belonging to
each partition is solved in parallel during the animation phase. We demonstrate this by using our partitioning
technique; the performance hit caused by the GPU kernel calls is significantly decreased, leaving unaffected the
visual quality, robustness and speed of serial position based dynamics
Position-Based Multi-Agent Dynamics for Real-Time Crowd Simulation (MiG paper)
Exploiting the efficiency and stability of Position-Based Dynamics (PBD), we
introduce a novel crowd simulation method that runs at interactive rates for
hundreds of thousands of agents. Our method enables the detailed modeling of
per-agent behavior in a Lagrangian formulation. We model short-range and
long-range collision avoidance to simulate both sparse and dense crowds. On the
particles representing agents, we formulate a set of positional constraints
that can be readily integrated into a standard PBD solver. We augment the
tentative particle motions with planning velocities to determine the preferred
velocities of agents, and project the positions onto the constraint manifold to
eliminate colliding configurations. The local short-range interaction is
represented with collision and frictional contact between agents, as in the
discrete simulation of granular materials. We incorporate a cohesion model for
modeling collective behaviors and propose a new constraint for dealing with
potential future collisions. Our new method is suitable for use in interactive
games.Comment: 9 page
Robust position control of a tilt-wing quadrotor
This paper presents a robust position controller for a tilt-wing quadrotor to track desired trajectories under external wind and aerodynamic disturbances. Wind effects are modeled using Dryden model and are included in the dynamic model of the vehicle. Robust position control is achieved by introducing a disturbance observer which estimates the total disturbance acting on the system. In the design of the disturbance observer, the nonlinear terms which appear
in the dynamics of the aerial vehicle are also treated as disturbances and included in the total disturbance. Utilization of the disturbance observer implies a linear model with nominal parameters. Since the resulting dynamics are linear, only PID type simple controllers are designed for position and attitude
control. Simulations and experimental results show that the performance of the observer based position control system is quite satisfactory
Geometrical phase effects on the Wigner distribution of Bloch electrons
We investigate the dynamics of Bloch electrons using a density operator
method and connect this approach with previous theories based on wave packets.
We study non-interacting systems with negligible disorder and strong spin-orbit
interactions, which have been at the forefront of recent research on
spin-related phenomena. We demonstrate that the requirement of gauge invariance
results in a shift in the position at which the Wigner function of Bloch
electrons is evaluated. The present formalism also yields the correction to the
carrier velocity arising from the Berry phase. The gauge-dependent shift in
carrier position and the Berry phase correction to the carrier velocity
naturally appear in the charge and current density distributions. In the
context of spin transport we show that the spin velocity may be defined in such
a way as to enable spin dynamics to be treated on the same footing as charge
dynamics. Aside from the gauge-dependent position shift we find additional,
gauge-covariant multipole terms in the density distributions of spin, spin
current and spin torque.Comment: 12 pages, 3 figure
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