| With the rapid development of military technology,modern wars are supposed to lauched all-weather and all-time.Thus,the requirements of all-weather combat capability of military weapon are of great urgency.To find out the infrared characteristics of ground targets and backgrounds in complicated meteorological environments accurately is one of the important technologies for all-weather detection,recognition,attack and infrared stealth evaluation of ground targets.Research on the effects of the droplets and particles on the radiative characteristics of vehicles is of great significance to the acquirement of the infrared characteristics of ground targets and backgrounds in complicated meteorological environments.Based on the test datas of thermal radiation of ground targets,the creditability of the thermal radiation model,which takes the uncertainties of the parameters into account,can be evaluated,providing a robust application evidence in the field of target stealth design,stealth evaluation,target detection and identification.Therefore,researchon the effects of the droplets and particles on thethermal radiative characteristics of vehicles in complicated meteorological environments and the credibility evaluation methodof the thermal radiation model exhibit a substantial prospect.A common infrared model of vehicles was summarized in this work.With the investigation of the effects of the droplets and particles in complicated meteorological environments on the radiation transmission and heat transfer characteristics of surfaces,the thermal radiation model of vehicles and backgrounds in complicated meteorological environments was established,and thus the influence of the droplets and particles on the radiative characteristics of vehicles was evaluated.Thereafter,the creditability evaluation method of the infrared model was proposed.Finally,the infrared simulation software for vehicles has been developed.The main works of this paper include:1.Effect of the rain and fog on the radiation transmissionOn the basis of summarizing the physical characteristics of rain and fog,the method of the atmosphric transmittance was theoretically founded combined the Bouguer-Lambert law with the MIE theory.With this method,the infrared attenuation characteristics of the rain and fog were invetigated.Furthermore,the empirical calculation model for the sky longwave radiation under the rainy and foggy weather was established based on the literature results.Then,by means of the nonlinear fitting of amounts of measured data,the empirical calculation model for the solar radiation under the rainy and foggy weather was also prop.osed.2.Effect of the droplets and particles on the heat transfer characteristics of surfacesThe targets’ surfaces may be covered or deposited with the water film,ramdonly-distributed droplets or dust deposits due to the falling of the rain drops,adsorption of the fog drops,or deposition of the dust particles in complicated meteorological environments,thereby resulting in the impacts on the surfaces’ radiative properties and convection heat transfer.Therefore,both the effects of droplets and solid particles on the surfaces’ heat transfer characteristics were investigated.Firstly,the factors impacting the apparent absorption properties of particle deposit were found out through the analysis of the physical structure and absorption mechanism of particle deposit.A general approach combining the effective medium theory with RTM-DRE was presented to simulate the apparent spectral absorptance of surfaces covered with particulate deposit and evaluate the effects of the particles on the radiative properties of the surface.Then,the apparent absorption features of surfaces with dust deposit were experimentally explored.Moreover,the impacts of the deposit thickness,size distribution,particulate bulk fraction,coverage,chemical content,H2O content,and substrate reflectance on the radiative properties of the surface were quatitatively investigated.Secondly,based on the transfer-matrix method,the prediction model of the apparent absorption characteristics of surfaces with randomly-distributed droplets was developed,in which the multi reflection and absorption inside the liquid film or droplet as well as the randomness of the droplets were considered.The effects of droplets mean height,coverage fraction and temperature difference on the equivalent absorptance were investigated.Both the prediction models of the apparent absorption characteristics were validated through the comparison of the experiment datas.Finally,taking into account the heat and mass transfer processes of the rain and fog on the surfaces,including the adsorption,evaporation,condensation and rainwash heat transfer,the surfaces’ convection heat transfer model was developed.The surfaces’ temperatre variation characterstics as well as the impact factors under the rainy and foggy weather were analyzed.Thus,the impacts of the rain and fog on the surfaces’ heat transfer characteristics were theoretically revealed.3.Analysisof the effects of the droplets and particles on the thermal radiation properties of vehiclesConsidering the effects of the rain and fog on the radiation transmission,imapcts of the droplets and particles on the surfaces’ radiative properties and convection hear transfer,the thermal radiation characteristics of the typical vehicles and backgrounds were investigated based on the common thermal radiation model of vehicles.Furthermore,with the theoretical models,the temperature and infrared characteristics of the vehicles and backgrounds under the impact of droplets and particles were investigated.The significant differences of the vehilces’ infrared feature in different meteorological environments were then summarized.Finally,the effect of droplets and particles on vehicle’s infrared characteristics was revealedbased on the point detection features of the vehicles.4.Research on the creditability evaluation method for thermal radiation model of vehiclesThe sensitivity analysis method for the thermal model of vehicles was established by the system sensitivity theory and system error statistical theory.The temperature sensitivities of typical parameters were then particularly investigated.Based on the orthogonal method,the sensitivity factors were eventually found out.Afterwards,the estimation method for the total infrared error was proposed,wherein the calculation errors generated from the theoretical model deviation,parameter uncertainty of the sensitive factors,and numerical calculation process were considered.Moreover,two forms of the creditability evaluation method for the thermal radiation model were presented:(1)Analysis method for the confidence interval of the calculation error with the given confidence level;and(2)Analysis method for the model creditability confidence interval with the threshold value to determine if the results were credible.Finally,the creditability of the simulation results of the simple tetragonal cavity and typical vehicle was estimated.For the typical vehicle modeled with large geometric error,the confidence intervals at a confidence level of 0.95 of the infrared calculation error in the wavebands of 3-5μm and 8-14μm were(9.48%10.79%)and(3.84%±0.32%),respectively,which adequately validated the reliability of the thermal radiation model of vehicles.5.Development of integrated software for the infrared radiation analysis of vehiclesBased on the principles and methods of software engineering,the integrated software for thermal radiation simulation of vehicles was developed for Windows System.With the modularization of the heat flux boundary under complicated environment and utilizing the FLUENT as the backstage temperature solver,both the temperature and infrared simulation can be carried out.The necessary inputs and settings for targets and backgrounds were accomplished in the software’s interface,which was compiled via MFC visual programming language.Finally,the infrared scene of targets and backgrounds was rendered by OPENGL graphics library. |
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