With the increasing threat of attacks and reconnaissance on surface targets, in addition to radar and infrared measures, visible light camouflage measures for surface targets are receiving more and more attention. Camouflage measures such as camouflage color have been widely used in small surface targets in recent years. However, since the meteorological conditions on the sea are different from those on the land and in the sky, how to determine the design distance of visible light camouflage on surface targets through scientific analysis still needs to be solved. To this end, this paper establishes a calculation method of visible light transmittance on the sea through Modtran, combined with human visual characteristics and Johnson’s criteria, to calculate the camouflage standard design distance of different target sizes under different contrasts on the sea, and solve the problem of camouflage design distance selection under human eye observation conditions.
At present, water spray cooling is widely used in the fields of fire prevention and cooling as an economical and convenient method. In recent years, surface ships have been using water curtains for surface cooling and infrared stealth, which is becoming more and more common. The LECHLER nozzle used in the infrared stealth field of ships adopts the built-in type, featuring a mounting surface flush with the shell plate, which is suitable for ship stealth. It has a water pressure of 0.5Mpa and a water volume of 4m3/h, and the water spray covers a diameter of 7m. However, through observing the inside, the author found that there is a total pressure loss existing in many structures in the nozzle, which generally results in a loss of flow energy inside the nozzle, thereby reducing the spray coverage of the nozzle. In this paper, the structural optimization research of the nozzle is carried out, and the dual control conditions of inlet water pressure and water supply are proposed. The pressure loss and the coverage of water spray are analyzed by numerical simulation. The calculation shows that the total pressure loss is reduced from the original 47.5% to 10% with the optimized design. Under the premise of controlling the inlet water pressure and flow, the spray coverage is increased by 86.6%.
In this paper, a new method to suppress both barrage jamming and deceptive jamming is proposed based on spaceborne azimuth multichannel synthetic aperture radar (AMSAR). The relationship between signals received over arbitrary channel and reference channel is obtained by analyzing the signal models of the jammed AMSAR. Based on this relationship, a system of equations, whose solution contains SAR echo and all jamming signals, is established. In order to obtain high-precision solutions, the system noise has to be removed and accurate direction of arrival (DOA) estimation of jammers is required. For this purposes, a singular value decomposition (SVD) based method for noise reduction and a least square method for the two-dimensional locations of jammers are put forward. By solving the equations, SAR echoes can be recovered. Finally, several simulation experiments are provided to illustrate the effectiveness of the proposed method.
The symplectic multi-resolution time-domain(SMTD) scheme with cylindrical grids is developed for electromagnetic simulation. Based on Daubechies' scaling functions and sympletic propagation technique, equations are implemented. In cylindrical coordinates, some singular areas are analyzing and solving. In different stencil sizes, the stability and dispersion property is investigated and it turns out that SMTD is better than FDTD for stability restriction and medium discretization. Perfectly matched layer(PML) absorbing boundary conditions (ABC's) are derived for cylindrical SMTD grids. The numerical simulations validate that SMTD and PML are effective, so this paper may provide a new solution for electromagnetic simulation of cylindrical objects.