Search

Three-dimensional unsteady numerical simulations are performed to investigate the fluctuating pressure environment around a Mars entry capsule under the forced oscillation. The forced oscillation of the capsule is simulated numerically by coupling and solving the unsteady compressible Navier-Stokes equations and Euler equation of the rigid-body dynamics. Based on the dynamic-mesh, the fluctuating pressure characteristics at different wall locations are obtained and analyzed. The research shows that the forced oscillation of the capsule aggravates the fluctuating pressure during the supersonic entry. When the inflow Mach number is 1.2, the forced oscillation of the capsule has little effect on the detached shock. The detached shock intensity is weak and the shape change is small, but the distance between the detached shock and the point alters periodically with the angle of attack changed. The fluctuating pressure on the windward side of the capsule is mainly affected by the angle of attack. When the inflow Mach number is 3, the detached shock oscillates intensely, leading to a severe fluctuating pressure environment around the capsule base and the windward of the trim-flap, and the spectrum of the fluctuating energy induced by the shock oscillation is concentrated at around 30 Hz. [ABSTRACT FROM AUTHOR]

To characterize physical properties of a scattering object, a steady and fast algorithm of super-resolution SAR imaging is proposed based on attribute scattering center in this paper. An improved Orthogonal Matching Pursuit (OMP) algorithm is utilized to estimate the parameters of simplified attribute scattering center model. Based on the model parameters, two-dimensional spectrum extrapolation is preformed in signal reconstruction to achieve super-resolution SAR imaging. The method has fast computational efficiency and can accurately describe the physical structure compared with the traditional super-resolution algorithm based on the point scattering model. In addition, the initial orientation angle can be used to achieve a better focusing performance. The simulation results validate the superiority of the proposed algorithm. [ABSTRACT FROM AUTHOR]

In modern electronic warfare, for the direction finding of multiple wideband coherent radiation sources under the background of decoys, the algorithms for signal number estimation and direction finding of multiple wideband coherent radiation sources are presented based on single baseline in this paper. Firstly, new signals are created by using conjugate multiplication of signal spectrums received by two antenna arraies. According to the spectrum architectural feature of new signals, the number of radiation sources can be estimated. In case the number of sources is given, by using the fractional time delay estimation algorithm based on the wideband signal phase spectrum, the time delays between radiation source signals received by two antennas can be got indirectly. So the directions of these radiation sources can be found according to the time delays. The algorithms have the feature of simple equipment and only the single baseline composed of two antennas is required. The simulation results show that the number of multiple wideband coherent radiation sources can be estimated accurately and directions of multiple radiation sources can be found accurately under certain condition. [ABSTRACT FROM AUTHOR]