Vortex Structures and Electron Beam Dynamics in Magnetized Plasma

We investigate the formation of vortex structures at the refl ection of an electron beam from the double layer of the Jupiter ionosphere. The infl uence of these vortex structures on the formation of dense upward electron fl uxes accelerated by the double layer potential along the Io flux tube is studied. The phase transition to the cyclotron superradiance mode becomes possible for these electrons. The conditions of the formation of vortex perturbations are considered. The nonlinear equation that describes the vortex dynamics of electrons is constructed, and its consequences are studied.

Numerical Method for Modeling the Turbofan Engine Tonal Fan BPF Noise Generation and Propagation Accounting the SAS Complex Acoustic Impedance

Noise reduction issues in the developed world receive an increasing attention, which is reflected in a great tightening of the noise level requirements. For the practical solution of this problem authors propose a new high-performance numerical modeling method of three-dimensional tonal noise acoustic field generated by the fan as a bladed machine. The method is based on solving a boundary value problem for Fourier transformed convective wave equation with complex variables in a Cartesian coordinate system in the arbitrary domain with impedance boundary conditions by finite volume method. The noise source is set in the form of sound power on the surface near the rotor that bounds the area of the vortex perturbations (pseudosound). Sound power is determined by acoustic-vortex method. There are shown examples of the method validation and application.

Learning From the Fins of Ray-Finned Fish for the Propulsors of Unmanned Undersea Vehicles

Advanced propulsors are required to help unmanned undersea vehicles (UUVs) overcome major challenges associated with energy and autonomy. The fins of ray-finned fish provide an excellent model from which to develop propulsors that can create forces efficiently and drive a wide range of behaviors, from hover to low-speed maneuvers to high-speed travel. Although much is known about the mechanics of fins, little is known about the fin’s sensorimotor systems or how fins are regulated in response to external disturbances. This information is crucial for implementing propulsive and control systems that exploit the same phenomena as the biological fins for efficiency, effectiveness, and autonomous regulation. Experiments were conducted to evaluate the in vivo response of the sunfish and its pectoral fins to vortex perturbations applied directly to the fish and to the fins. The fish and the fins responded actively to perturbations that disturbed the motion of the fish body. Surprisingly, perturbations that deformed the fins extensively did not cause a reaction from either the fins or the body. These results indicate that the response of the pectoral fins to large deformations is not reflexive and that fin motions are regulated when it is necessary to correct for disturbances to the motion of the fish. The results also demonstrate a benefit of compliance in propulsors, in that external perturbations can disturb the fins without having its impact be transferred to the fish body.