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

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$_3$ 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

Vortex particle intensified large eddy simulation - VπLES

This paper presents a novel Large Eddy Simulation approach with a direct resolution of the subgrid motion of fine concentrated vortices. The method, proposed first by [10], is based on combination of a grid based and the grid free computational vortex particle (VPM) methods. The large scale flow structures are simulated on the grid whereas the concentrated structures are modeled using VPM. Due to this combination the advantages of both methods are strengthened whereas the disadvantages are diminished. The procedure of the separation of small concentrated vortices from the large scale ones is based on LES filtering idea. The flow dynamics is governed by two coupled transport equations taking two-way interaction between large and fine structures into account. The fine structures are mapped back to the grid if their size grows due to diffusion. Algorith- mic aspects specific for three dimensional flow simulations are discussed. Validity and advantages of the new approach are illustrated for a well tried benchmark test of the decaying homogeneous isotropic turbulence using the experimental data of [4] and free turbulent jet flow using experiments of [8, 2, 15]