Axial-Symmetric Diffraction Radiation Antenna with a Very Narrow Funnel-Shaped Directional Diagram

The paper is focused on reliable modeling and analysis of axially symmetric radiators with a very narrow (throat) funnel-shaped radiation pattern. When such a diagram is formed, a wave analogue of Smith–Purcell coherent radiation is realized—the surface wave of a radial dielectric waveguide ‘sweeps out’ with its exponentially decaying part a concentric periodic grating, the fundamental spatial harmonic of which, propagating without attenuation in a direction close to the symmetry axis of the structure, generates a radiation field with the required characteristics.

DIFFRACTION RADIATION OF PARTICLE PASSING BY IMPEDANCE WEDGE

The diffraction radiation field generated by the charged particle passing by the perfectly conductive or impedance wedge is considered. With perfect conductivity, the wedge rotation around the edge fixed along with the straight particle motion line, does not change the total radiated energy. When the motion to the edge is almost parallel to a face of wedge then an increase of impedance from zero increases the radiated energy.

Reduction of wave-induced pitch motion of a semi-sub wind platform by balancing heave excitation with pumping between floats

It is desirable to control pitch motion of semi-submersible wind platforms to reduce turbine hub acceleration and increase structural fatigue life. This is achieved by balancing the moment on the platform due to heave float excitation by generating a differential internal head of water between the floats though a pump. This is demonstrated with an experimentally validated linear diffraction-radiation-drag model of an idealised platform. Different scales of platform are considered corresponding to 5, 10 and 20 MW turbines. The pitch angles and hub accelerations generally reduce as scales increase. Pumping reduces hub accelerations by up to about 40% for larger sea states. The power required for pumping would be small with a hybrid pump also operating as a turbine to store energy for the pumping operation. Without storage the power requirement is still small relative to the turbine capacity except for very high wind speeds.

RADIATION OF CHARGE PASSING BY IMPEDANCE WEDGE

The diffraction radiation generated by a charge passing by a plasma wedge is considered in impedance approximation. In the perfect conductivity limit, the total radiated energy is not varying with the wedge rotation around the edge fixed along with the charge motion line. The impedance increase may lead to the total radiated energy increase, due to effective surface wave generation, when the charge motion to the edge is almost parallel to a face of wedge.