Rarefaction

About: Rarefaction is a research topic. Over the lifetime, 1852 publications have been published within this topic receiving 26943 citations.

Shelf solutions and dispersive shocks in a discrete NLS equation: Effects of nonlocality

Abstract: We study shelf-like breathers and dispersive shock phenomena in a discrete nonlinear Schrodinger (DNLS) equation with a nonlocal nonlinearity. The system models laser light propagation in waveguide arrays made from a nematic liquid crystal substratum. Shelf-like breathers are studied in the regime of small linear intersite coupling, and we report some new theoretical existence and stability results. We also study numerically the evolution from nearby dam-break and more general jump initial conditions for stronger linear intersite coupling. In the defocusing case, we see rarefaction and shock wave profiles, superposed with oscillations. Some of the hyperbolic features of the observed profiles are described approximately by continuous NLS hydrodynamics. Nonlocality is seen to lead to some smoothing of the rapid oscillations seen in the local DNLS.

Numerical investigation of rarefied vortex loop formation due to shock wave diffraction with the use of rorticity

Abstract: When compressed gas is ejected from a nozzle into a low-pressure environment, the shock wave diffracts around the nozzle lip and a vortex loop will form. The phenomenon has been widely investigated in the continuum flow regime, but how the shock diffraction and vortex behave under rarefied flow conditions has not received as much attention. It is necessary to understand this transient flow in rarefied environments to improve thrust vector control and avoid potential contamination and erosion of spacecraft surfaces. This work provides numerical results of the vortex loop formation caused by shock wave diffraction around a 90° corner using the direct simulation Monte Carlo method and the compressible Navier–Stokes equations with the appropriate Maxwell velocity slip and the von Smoluchowski temperature jump boundary conditions. The Mach number and rarefaction effects on the formation and evolution of the vortex loop are discussed. A study of the transient structures of vortex loops has been performed using the rorticity concept. A relationship of mutual transformation between the rorticity and shear vectors has been discovered, demonstrating that the application of this concept is useful to understand vortex flow phenomena.

A note on experimental and theoretical comparisons of conical shock-shock interactions.

Abstract: lated beyond their range of validity, when applied to the present experimental conditions. A rough estimate yielded a value of Mm/Rem> .T ~ 0.1 as a criterion for the occurrence of rarefaction effects in the heat-transfer experiment. More experimental evidence is needed to substantiate the findings reported in this note. Also, it would be interesting to investigate the dependence of the numerical value of the rarefaction parameter upon wedgeand cone-angle.

Effect of Environmental Conditions on Quality Factors of MEMS Cantilever Beam Resonator in Gas Rarefaction

Abstract: This paper discussed the effect of environmental conditions (moisture and temperature) on the quality factors (Q-factor) of micro-electro-mechanical systems (MEMS) cantilever beam resonators in wide range of gas rarefaction (pressure (p), and accommodation coefficients (ACs)), and flexural mode of resonator. The modified molecular gas lubrication (MMGL) equation is applied for modeling the dominant squeeze film damping (SFD) problem on the quality factor of MEMS cantilever beam resonators to discuss the effect of environmental conditions. The external SFD and the internal structure damping (thermoelastic damping) and support loss) are accurately taken into account. Effective viscosity, which is ratio of dynamic viscosity and Poiseuille flow rate of moist air, is utilized to modify the MMGL equation to consider the environmental effects of moisture and temperature in gas rarefaction. In low pressures, mean free path changes more significantly with relative humidity and temperature than that of dynamic viscosity of moisture in gas rarefaction. Thus, effect of environmental conditions such as moisture and temperature must be discussed to improve Q-factors of MEMS cantilever beam resonators in wide range of gas rarefaction (p and ACs) and flexural modes of resonator. The results showed that Q-factor of SFD decreases significantly as moisture and temperature increase at higher gas rarefaction (lower p, and ACs), while Q-factor of SFD decreases and then increases slightly as moisture and temperature increase at lower gas rarefaction (higher p, and ACs). The total Q-factor is highly sensitive to the relative humidity and temperature in higher gas rarefaction (lower p and ACs) and lower flexural modes of resonator.

Formation mechanism of cavitating spalls

Abstract: The dynamics of formation of cavitation zones in a liquid upon reflection of a shock pulse from the free surface is studied numerically in a one-dimensional formulation using the Iordanskii-Kogarko-van Wijngaarden two-phase model. It is shown that the formation of a system of cavitation zones (clusters) with a dynamically increasing volume concentration of the gas phase near the free surface is due to oscillations of the structure of the rarefaction wave profile. The fast relaxation of tensile stresses in the cavitation zone ends in the formation of a quasistationary mass-velocity field, which provides for almost unbounded growth of cavitation bubbles in subsurface clusters and explains the occurrence of the spall layers observed in experiments.