When placed in a crowded environment, a semiflexible tube is forced to fold so as to make a more compact shape. One compact shape that often arises in nature is the tight helix, especially when the tube thickness is of comparable size to the tube length. In this paper we use an excluded volume effect to model the effects of crowding. This gives us a measure of compactness for configurations of ...

In this paper we discuss some design issues for a helical undulator which covers the energy range between 500-3000 eV at an electron energy of 23 GeV. The design is based on the technology of the BESSY II helical devices. Other technologies might be also applicable but will not be considered here. At BESSY II two helical double undulators are already in operation and 2 more helical devices are ...

Abstract We performed Large-eddy simulations of the flow in a model air Francis turbine range low-load regimes with swirler rotating at fixed frequency. All investigated revealed presence coherent helical vortex structure draft tube: precessing core. identified frequency this instability and obtained mean velocity fields to be utilized further works.