Feedback control is used to suppress oscillations in the subsonic flow past a rectangular cavity. A heuristic feedback law is introduced into 2D direct numerical simulations, using zero-net-mass forcing at the leading edge of the cavity and a pressure sensor at the wall, and the oscillations are reduced by −13dB. Reduced-order models are obtained from fullorder direct numerical simulations, and...

Since the direct numerical simulation (DNS) of aeroacoustic noise requires the numerical solution of the compressible Navier-Stokes equations in a large computational domain, it is computationally too demanding to solve computational aeroacoustics (CAA) applications using this technique only. In this paper a number of different hybrid approaches, where the computational domain is split into a s...

This paper investigates the reduction of backscatter radar cross section (RCS) for a rectangular cavity embedded in the ground plane. The bottom of the cavity is coated by a thin, multilayered radar absorbing material (RAM) with possibly different permittivities. The objective is to minimize the backscatter RCS by the incidence of a plane wave over a single or a set of incident angles. By formu...

We will present the results of experimental studies of the elastic enhancement factor W and the nearest neighbors spacing distribution P(s) for microwave rectangular and rough cavities simulating two-dimensional quantum billiards in a transient region between regular and chaotic dynamics [1] and in a pure chaotic dynamics region, respectively. The analogy between microwave cavities and quantum ...

In this paper measurement of real part of permittivity and loss tangent of (1-x) Zn.xMg.TiO3 (ZMT) material in powder form in S-band of microwave frequencies is presented and the associated accuracy estimated. This approach is based on the measurement of transmitted power from the cavity at and off resonance. Details of the design and fabrication of the rectangular cavity and the input and outp...

We show analytically that the presence of a hard diffracting object inside an optical cavity, for example an aperture or a waveguide, reduces the symmetry of the system from cylindrical to rectangular. As a consequence, patterns with concentric rings of bright or dark spots made up by modes whose azimuthal indexes are not multiples of one another, appear when the zero field solution becomes uns...

Experiences from using a higher order accurate finite difference multiblock solver to compute the time dependent flow over a cavity is summarized. The work has been carried out as part of a work in a European project called IDIHOM in a collaboration between the Swedish Defense Research Agency (FOI) and University of Linköping (LiU). The higher order code is based on Summation By Parts operators...