14,499 research outputs found
Direct Coupling Method for Time-Accurate Solution of Incompressible Navier-Stokes Equations
A noniterative finite difference numerical method is presented for the solution of the incompressible Navier-Stokes equations with second order accuracy in time and space. Explicit treatment of convection and diffusion terms and implicit treatment of the pressure gradient give a single pressure Poisson equation when the discretized momentum and continuity equations are combined. A pressure boundary condition is not needed on solid boundaries in the staggered mesh system. The solution of the pressure Poisson equation is obtained directly by Gaussian elimination. This method is tested on flow problems in a driven cavity and a curved duct
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The role of the scale and the frequency bandwidth of steering wheel vibration on road surface recognition
Automobile drivers are regularly exposed to vibrational stimuli in their vehicle. Of the automobile
subsystems, the steering wheel is one of the most important due to its role in controlling the vehicle. In
particular, the steering wheel plays an important role in transmitting information about the road and about
the vehicle to the driver. This paper investigates the effect of steering system feedback gain and steering
system feedback bandwidth on the human interpretation of the driving information transmitted by the
steering wheel. Human recognition of road surface type was found to be highly dependent on the feedback
gain and the feedback bandwidth of the steering wheel vibration. The results provide some basic guidelines for designing the control logic of steer by wire systems
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A study of the human ability to detect road surface type based on steering wheel vibration feedback
A study was performed to investigate the human ability to detect road surface type based on the
associated steering wheel vibration feedback. Tangential direction acceleration time histories
measured during road testing of a single mid-sized European automobile were used as the basis
for the study. Scaled and frequency filtered copies of two base stimuli were presented to test
subjects in a laboratory setting during two experiments which each involved 25 participants. Theory
of signal detection (TSD) was adopted as the analytical framework and the results were
summarised by means of the detectability index d’ and as receiver operating curve (ROC) points.
The results of the experiment to investigate the effect of scaling suggested monotonic relationships
between stimulus level and detection for both road surfaces. Detection of the tarmac surface
improved with reductions in acceleration level while the opposite was true of the cobblestone
surface. The ROC points for both surfaces were characterised by gradual increases in detection as
a function of acceleration level, obtaining hit rates of nearly 100% at optimum. The results of the
experiment to investigate the effect of frequency bandwidth suggested a monotonically increasing
relationship between detectability and the bandwi\dth of the vibration stimuli. Detection of both road
surfaces improved with increases in bandwidth. Average hit rates exceeded 80% for stimuli
covering the frequency range from 0 to 80 Hz. Human detection of road surface type appears to
depend on the long term memory model, or cognitive interpretation mechanism, associated with
each surface. The complexity of the measured response suggests the need to categorise and
classify incoming data before an optimal choice of feedback stimuli can be made in automotive
steering systems
Collisional Dynamics of Half-Quantum Vortices in a Spinor Bose-Einstein Condensate
We present an experimental study on the interaction and dynamics of
half-quantum vortices (HQVs) in an antiferromagnetic spinor Bose-Einstein
condensate. By exploiting the orbit motion of a vortex dipole in a trapped
condensate, we perform a collision experiment of two HQV pairs, and observe
that the scattering motions of the HQVs is consistent with the short-range
vortex interaction that arises from nonsingular magnetized vortex cores. We
also investigate the relaxation dynamics of turbulent condensates containing
many HQVs, and demonstrate that spin wave excitations are generated by the
collisional motions of the HQVs. The short-range vortex interaction and the
HQV-magnon coupling represent two characteristics of the HQV dynamics in the
spinor superfluid.Comment: 7 pages, 6 figure
Statistical Analysis of the Metropolitan Seoul Subway System: Network Structure and Passenger Flows
The Metropolitan Seoul Subway system, consisting of 380 stations, provides
the major transportation mode in the metropolitan Seoul area. Focusing on the
network structure, we analyze statistical properties and topological
consequences of the subway system. We further study the passenger flows on the
system, and find that the flow weight distribution exhibits a power-law
behavior. In addition, the degree distribution of the spanning tree of the
flows also follows a power law.Comment: 10 pages, 4 figure
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