1,482 research outputs found
Complex numerical modeling of dynamics and crashes of wing-in-ground vehicles
The Wing-In-Ground craft (WIG), a vehicle flying in
the ground effect, is a promising transportation means
of the near future. This paper describes mathematical
modeling of WIG motion in all regimes, such as
planing, take-off, transition to flight, and flight itself.
The model, which includes nonlinear hydroaerodynamics,
serves as a base for simulation of
motion. The theory developed here enhances the
process of designing WIG vehicles; its advantages and
disadvantages are discussed. The results of numerical
modeling are compared with experimental data
obtained for planing and flight regimes of motion. The
model is applied for studying emergency problems in
WIG operation
Free Malcev algebra of rank three
We find a basis of the free Malcev algebra on three free generators over a
field of characteristic zero. The specialty and semiprimity of this algebra are
proved. In addition, we prove the decomposability of this algebra into
subdirect sum of the free Lie algebra rank three and the free algebra of rank
three of variety of Malcev algebras generated by a simple seven-dimensional
Malcev algebra
Interfacial dynamics in transport-limited dissolution
Various model problems of ``transport-limited dissolution'' in two dimensions
are analyzed using time-dependent conformal maps. For diffusion-limited
dissolution (reverse Laplacian growth), several exact solutions are discussed
for the smoothing of corrugated surfaces, including the continuous analogs of
``internal diffusion-limited aggregation'' and ``diffusion-limited erosion''. A
class of non-Laplacian, transport-limited dissolution processes are also
considered, which raise the general question of when and where a finite solid
will disappear. In a case of dissolution by advection-diffusion, a tilted
ellipse maintains its shape during collapse, as its center of mass drifts
obliquely away from the background fluid flow, but other initial shapes have
more complicated dynamics.Comment: 5 pages, 4 fig
Domain evolution of BaTiO3 ultrathin films under electric field: a first-principles study
A first-principles-derived method is used to study the morphology and
electric-field-induced evolution of stripe nanodomains in (001) BaTiO3 (BTO)
ultrathin films, and to compare them with those in (001) Pb(Zr,Ti)O3 (PZT)
ultrathin films. The BaTiO3 systems exhibit 180o periodic stripe domains at
null electric field, as in PZT ultrathin films. However, the stripes alternate
along [1-10] in BTO systems versus [010] in PZT systems, and no in-plane
surface dipoles occur in BTO ultrathin films (unlike in PZT materials).
Moreover, the evolution of the 180o stripe domains in the BaTiO3 systems, when
applying and increasing an electric field along [001], involves four regions:
Region I for which the magnitude of the down dipoles (i.e., those that are
antiparallel to the electric field) is reduced, while the domain walls do not
move; Region II in which some local down dipoles adjacent to domain walls
switch their direction, resulting in zigzagged domain walls - with the overall
stripe periodicity being unchanged; Region III in which nanobubbles are
created, then contract along [110] and finally collapse; and Region IV which is
associated with a single monodomain. Such evolution differs from that of PZT
ultrathin films for which neither Region I nor zigzagged domain walls exist,
and for which the bubbles contract along [100]. Discussion about such
differences is provided.Comment: 19 pages, 4 figures, 27 references, submitted to Phys. Rev.
Ultrathin films of ferroelectric solid solutions under residual depolarizing field
A first-principles-derived approach is developed to study the effects of
uncompensated depolarizing electric fields on the properties of Pb(Zr,Ti)O
ultrathin films for different mechanical boundary conditions. A rich variety of
ferroelectric phases and polarization patterns is found, depending on the
interplay between strain and amount of screening of surface charges. Examples
include triclinic phases, monoclinic states with in-plane and/or out-of-plane
components of the polarization, homogeneous and inhomogeneous tetragonal
states, as well as, peculiar laminar nanodomains.Comment: REVTeX, 7 pages, 2 figures, fig 2 in colo
Analysis of the unsteady wake of a full bottomed ship in shallow water
The paper is devoted to the analysis of the unsteady hydrodynamic processes
taking place in the ship wake under shallow water conditions. The motivation of the
research is the determination of the reasons for the rise of strong vibration in the stern of
inland cruise ships in the waterways with considerable depth restriction.
As a research tool the hybrid URANS/LES approach of Kornev et al. [1] is selected in
order to capture the influence of nonstationary vortical structures on the velocity
oscillations in the propeller plane. As it will be shown, URANS method cannot reproduce these flow
features.
The flow is studied in a single-phase and in a two-phase formulation. Influence of the free
surface, depth Froude number and depth to draft ratio on the wake is analyzed. The adverse
pressure gradient in the stern region causes massive separations of the boundary layer. On account
of the separations the velocity oscillations in the wake are turned out to be strongly dependent on
the under keel clearance.
On the other hand, it is shown, that at high F rH the wave pattern can significantly
influence the viscous wake and cause the suppression of the velocity oscillations due
to the decrease of the water level. Possible effect of the wake unsteadiness on the propeller
performance in such circumstances is discussed
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