2012 Vol. 41, No. 6
2012, 41(6): 1401-1404.
Abstract: For the prediction of aero-optical effects in engineering application, the influence of turbulent vortex structure on optical transmission cannot be simulated because RANS method does not provide details of the turbulent vortex structure. A random phase screen method based on the sphere vortex model was improved, which uses sphere with different diameter and density to simulate the instantaneous vortex. The improvement connects the sphere parameters with the local characteristic of the flow fields. For example, the sphere diameter is determined by the correlation scale and the sphere density is determined by the root mean square of the flow density. The simulations of the image distortion in the compressible shear layers show that the improved random screen method is in line with the results from direct integration of the intensity and the accuracy is much higher than the original method.
In the radar and infrared(IR) sensor compound guidance under strong counterwork condition, intermittent working of radar can reduce the enemy missile interception probability and electronic support measures(ESM) lock probability. A radar/IR sequential filtering fusion algorithm was proposed in radar/IR compound guidance with radar under intermittent-working state. The algorithm used sequential centralized multisensor fusion method for target tracking considering that the measurement of radar and infrared sensor was non-synchronous. Sequential filtering fusion algorithm based on interacting multiple model and extended Kalman filter(IMM-EKF) was used for target tracking. The algorithm used the comparison of the state estimation covariance and the measurement error variance to control radar under intermittent-working state. The algorithm can automatically adapt to radar under intermittent-working state, need not switch over single sensor tracking mode and dual sensor tracking mode. The influence of the sensors data rate and radar under intermittent-working state on radar/IR compound tracking precision was analyzed.
2012, 41(6): 1411-1415.
The space cryogenic shield is a device of phase-change refrigeration used to wrap the high-speed spacecraft up, which aims at improving penetration of near-earth high-speed spacecraft, and preventing being discovered and intercepted by infrared detector in near-earth orbit. In order to realize the effect of infrared stealth of ballistic missiles in the midcourse flight, a prototype of cryogenic shield was developed by adopting the phase-changed refrigeration of the cryogenic refrigerant. An experimental study on the surface temperature distribution and weight change of the prototype was carried out, and an empirical model was presented to make quantitative analysis. The result indicates that the prototype of space cryogenic shield may lower the surface temperature of ballistic missiles to less than 100 K, and reduce the infrared radiation of the surface to 0.15 W/m2 in 30 minutes. This cryogenic shield can meet the requirements of cryogenic infrared radiation in the space.
Linear frequency modulation infrared thermal-wave imaging(LFMITWI) is an active infrared thermography based on linear frequency modulation thermal-wave signal processing, which makes up for the disadvantage of traditional lock-in thermography that only detects the limited depth of subsurface defects by using a single frequency modulation thermal-wave. The theory, mathematics analysis and experiments in support of the LFMITWI for nondestructive subsurface defects detection in solids were described. The finite element modeling was used to analyze the thermal-wave behavior generated by linear frequency modulation chirp heat flux. The cross correlation peak value and its time were calculated by the use of cross correlation between surface temperature signal and reference chirp signal, and the peak value image and its time image were obtained. In experimental study, the law of chirp modulated halogen lamp was used as active heat source into metal flat-bottom holes sample, and the thermal-waveimage sequences were collected with Jade MWIR 550 FPA infrared camera. The cross correlation processing of time field and Fourier transform scanning of frequency field were used to obtain the peak value image, peak value time image and phase image respectively. The experimental results show that the peak value image and phase image are helpful to identify the geometric characteristic of different depths defects under the condition of given chirp thermal stimulation.
