| In hypersonic environments,optical domes are used as the optical window of infrared detection systems,and they are at the forefront of hypersonic infrared precision-guided weapons(PGWs).Because of aero-optic effects,the optical and aerodynamic performances of optical domes are directly correlated with the guidance precision,speed,range,maneuverability,and penetration capacity of hypersonic infrared PGWs.In addition,in their image processing,blurred,dithered,and shifted images are generated,and intense background thermal noises are introduced into infrared detection systems,causing serious limitations to target detection,identification,and tracking.As a result,the proper design of optical domes is regarded as a critical factor in the combat capability of hypersonic infrared PGWs.Due to their higher air drag coefficients,traditional hemispheric optical domes with good optical performance are unable to meet the development needs of hypersonic infrared PGWs for higher speeds,and thus conformal optical domes with streamlined surface design have been proposed.The von Karman curve was applied to conformal optical dome design in this dissertation,and various characteristics of von Karman domes were studied.Thus,a design method for optical domes based on von Karman surface was proposed.This method takes into account the aerodynamic,geometric,aberration,and aerooptic characteristics of von Karman domes,which have a positive effect on the combat capability of hypersonic infrared PGWs.The following are the primary findings of this dissertation:A fluid domain simulation model for conformal optical domes with all contours according to aerodynamic theory was established in the research on aerodynamic characteristics of von Karman domes using the finite element method.The heat flux density simulation results for conformal optical domes with three typical contours were obtained using this model and compared to the wind tunnel test results.The comparison results for conformal optical domes demonstrated the reliability of the fluid domain simulation,and the air drag coefficient and peak heat flux density were proposed as aerodynamic performance evaluation indexes of conformal optical domes.Furthermore,the aerodynamic performance of von Karman domes in hypersonic environments was simulated and evaluated,and the ability to reduce the air drag coefficient by 32.2% was demonstrated as an aerodynamic advantage of von Karman domes over traditional hemispheric domes.Furthermore,the influence laws of the dome length-todiameter ratio and the flying speed and altitude of hypersonic infrared PGWs on the aerodynamic performance of von Karman domes were discovered.According to differential geometric theory,a curvature formula for von Karman surface was derived in the research on geometric and aberration characteristics of von Karman domes.This formula was used to calculate the curvature radius difference between the meridian and sagittal directions,as well as the intersection angle between the visual axis and the surface normal for von Karman domes under different visual angles.The influencing laws of the dome length-to-diameter ratio and the rotation center position of internal imaging systems for these parameters were summarized.Furthermore,the spot diagram for target rays on the imaging surface and the Zernike coefficient for wavefront aberration at the exit pupil were obtained for infrared detection systems based on the von Karman dome under different visual angles using the ray tracing principle and Zemike aberration theory,and the influence laws of the dome length-todistance ratio,material and thickness,entrance pupil diameter,and rotation center position of internal imaging systems were determined.In the research on aero-optic characteristics of von Karman domes,an aerooptic effect simulation model was established based on fluid and structural mechanics,heat transfer,and optic theories,and a space-time coupling strategy was proposed among the fluid domain,aerodynamic heat transfer,structure domain,and image domain in the aero-optic effect simulation process.The wavefront aberration at exit pupil,spot spread function,and peak signal-to-noise ratio of distorted images were proposed as image quality assessment indexes of infrared detection systems under aero-optic effects.Furthermore,an imaging process simulation and assessment model for infrared detection systems in hypersonic environments was developed,and the imaging process was simulated,and the image quality was evaluated for infrared detection systems based on von Karman domes under aero-optic effects and in time-varying speed conditions.Besides this,the influencing laws of the aerodynamic optical transmission and thermal radiation effects,as well as the overall aero-optic effect,were revealed for the imaging process of von Karman dome-based infrared detection systems.The influencing laws of dome length-to-diameter ratio,thickness,and material were analyzed in the design of conformal optical domes based on von Karman surface for the overall image quality of infrared detection systems based on von Karman dome,and a design method for assembled conformal optical domes was proposed in view of the aerodynamic,geometric,aberration,and aero-optic characteristics of von Karman domes,including a contour assembly method based on genetic algorithm and a material assembly method based on material substitution.Furthermore,the design results for assembled conformal optical domes based on the von Karman curve were obtained and compared to those for traditional hemispheric domes.The comparison results show that the air drag coefficient of the optical dome can be reduced by up to 39.5% after the design,while the peak signal-to-noise ratio of the distorted image obtained by the infrared detection system can be improved by up to 9.6%,demonstrating the design method proposed in this paper can improve the comprehensive performance of the optical domes. |
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