Different models of self-excited oscillators which are four-dimensional extensions of the van der Pol system are reported. Their symmetries are analyzed. Three of them were introduced to model the release of vortices behind circular cylinders with a possible transition from a symmetric to an antisymmetric Bénard-von Karman vortex street. The fourth reported self-excited oscillator is a new mode...

A modeling method for the modal analysis of cantilever plates undergoing accelerated in-plane motion is presented in this paper. Von Karman strain measures are employed to derive the in-plane and the lateral equations of motion. In-plane strain measures of the accelerated plates are obtained from the in-plane equations and substituted into the lateral equations to obtain the linear equations fo...

Long wavelength optical phonons of quartz were analyzed by a Born-Von Karman model not previously used. It was found that only one force constant associated with the turning of the Si-0 bonds has a critical effect on the softmode frequency and the a-p transition in quartz. The square of the soft-mode frequency was found to depend linearly on this force constant which has the temperature depende...

Using the geometrical optics approximation, a theoretical prediction of the deflection angle correlation of a laser beam propagating in a hot turbulent jet is found as a functional form of the turbulent spectrum of the refractive index fluctuations. By applying the modified Von Karman model and Tatarskii model, the structure coefficient of the refractive index and the deflection angle correlati...

We simulate turbulence in a plane Couette geometry by a spectral method intermediate between full resolution and the complete elimination of small modes common in large eddy simulations. The wave number grid is sparse in spanwise and downstream direction, with a total number of modes proportional to Re(3/4) lnRe. At a Reynolds number of 2000 we could suppress more than 80% of the modes and stil...

We discuss the stability of icosadeltahedral shells subjected to a uniform external load in the form of an isotropic pressure. We demonstrate that there exists a universal critical buckling pressure scaling form that defines a locus of buckling instabilities. The parameter that uniquely determines this scaling form is shown to be the Föppl-von Karman number of nonpressurized shells. Numerical r...