We consider a reaction-diffusion system of activator-inhibitor type which is subject to Turing's diffusion-driven instability. It is shown that unilateral obstacles of various type for the inhibitor, modeled by variational inequalities, lead to instability of the trivial solution in a parameter domain where it would be stable otherwise. The result is based on a previous joint work with I.-S. Kim, but a refinement of the underlying theoretical tool is developed. Moreover, a different regime of parameters is considered for which instability is shown also when there are simultaneously obstacles for the activator and inhibitor, obstacles of opposite direction for the inhibitor, or in the presence of Dirichlet conditions.
This paper is aimed at differences in designs of spiral case and impeller of mixed flow pump with regard to suppression of Y-Q characteristic curves instability, pressure pulsations and especially to achieving necessary delivery head. The differences between new and old conception will be explained. The reasons of these differences with regard to flow in pump interior, hydraulic losses, static pressures and velocities will be explained as well.
The article presents a liquid film instability model designed using results of the set of CFD simulations. The governing equations of the model are derived using a linear equation of motion. The stability analysis is carried out by imposing a liquid surface disturbance which growth rate is investigated in dependence on the geometrical and physical configuration. The gas effect parameters, which are decisive variables in the model, are derived using results of the set of CFD simulations of turbulent flow in channel with wavy surface. The agreement between predicted and measured critical gas velocities and wavelengths in dependence on the liquid film thickness is very good. and Obsahuje seznam literatury