A simulation method of aircraft plumes for real-time imaging

Real-time infrared simulation technology can provide a large number of infrared images under different conditions to support the design, test and evaluation of a system having infrared imaging equipment with very low costs. By synthesizing heat transfer, infrared physics, fluid mechanics and computer graphics, a real-time infrared simulation method is proposed based on the method of characteristics to predict the infrared feature of aircraft plumes, which tries to obtain a good balance between simulation precision and computation efficiency. The temperature and pressure distribution in the under-expansion status can be rapidly solved with dynamically changing flight statuses and engine working states. And a modified C–G (Curtis–Godson) spectral band model that combines the plume streamlines with the conventional C–G spectral band model was implemented to calculate the non-uniformly distributed radiation parameters inside a plume field. The simulation result was analyzed and compared with the CFD++, which validates the credibility and efficiency of the proposed simulation method.     

A real-time infrared imaging simulation method with physical effects modeling of infrared sensors

Infrared imaging simulation technology can provide infrared data sources for the development, improvement and evaluation of infrared imaging systems under different environment, status and weather conditions, which is reusable and more economic than physical experiments. A real-time infrared imaging simulation process is established to reproduce a complete physical imaging process. Our emphasis is put on the modeling of infrared sensors, involving physical effects of both spatial domain and frequency domain. An improved image convolution method is proposed based on GPU parallel processing to enhance the real-time simulation ability with ensuring its simulation accuracy at the same time. Finally the effectiveness of the above methods is validated by simulation analysis and result comparison.     

A fast-saliency method for real-time infrared small target detection

Infrared small target detection plays an important role in applications including military reconnaissance, early warning and terminal guidance. In this paper, we present a fast method, called fast-saliency, with very low computational complexity, for real-time small target detection in single image frame under various complex backgrounds. Different from traditional algorithms, the proposed method is inspired by a recent research on visual saliency detection indicating that small salient signals could be well detected by a gradient enhancement operation combined with Gaussian smoothing, which is able to delineate regions of small targets in infrared images. Concisely, there are only four simple steps contained in fast-saliency. In order, they are gradient operation, square computation, Gaussian smoothing and automatic thresholding, representing the four procedures as highpass filtering, target enhancement, noise suppression and target segmentation, respectively. Especially, for the most crucial step, gradient operation, we innovatively propose a 5 × 5 facet kernel operator that holds the key for separating the small targets from backgrounds. To verify the effectiveness of our proposed method, a set of real infrared images covering typical backgrounds with sea, sky and ground clutters are tested in experiments. The results demonstrate that it outperforms the state-of-the-art methods not only in detection accuracy, but also in computation efficiency.     

考虑太阳辐射影响的飞机实时红外探测成像仿真

针对飞行器红外探测过程的成像仿真,有助于红外隐身效能的评估,进而提高应对红外探测的反侦察能力。建立了飞机红外成像仿真模型,并针对不同的飞行姿态、速度以及不同的探测时间,求解其蒙皮温度与红外辐射亮度,结果表明当飞机从低速到高速运行时,太阳辐射条件与气动加热层温度分布分别成为影响其成像结果的主要因素。建模方法及仿真结果对飞行器的隐身设计具有指导意义,为飞机实时红外成像场景的生成提供理论基础     

A novel accurate and expandable infrared radiation transmission effect computing service

In infrared imaging simulation system, the infrared radiation transmission is significantly affected by natural environment. Attenuation and blurring are introduced by atmospheric environment impacts on the transmission process from zero sight infrared radiation to the detector. The classic IR transmission calculation methods have been intensively studied and many applicable approaches are proposed. The novel IR transmission effect computing service introduced in this paper could render accurate and expandable IR simulation result based on synthetic natural environment, especially concerning the atmosphere effects imposed on the IR transmission process. A simulation architecture is constructed and supports an infrared imaging simulation system for the IR transmission process calculation. The environment representation approach and the transmission effect calculation method were elaborated. Simulation experiment was carried out and the result was shown to be more accurate than that of conventional MODTRAN based atmosphere transmission simulation results. The two results are both compared with the physically captured image. The comprehensive simulation experiment results are implied to be competent and offered an applicable solution for the infrared imaging simulation system. Furthermore, this interdisciplinary simulation method can be extended to other synthetic natural environment supported military simulation and further serve the large-scale distributed collaborative combat simulation.     

Analysis of a thermal imaging method for landmine detection, using infrared heating of the sand surface

The detection of a buried surrogate land mine is investigated by use of a pulsed thermographic method driven by a high powered infrared heater. In this experimental and analytical investigation, the surface of the sand is initially heated by infrared lamps and is then cooled by natural convection, and during this second phase a dry layer of sand develops on the surface. The temperature distribution of the dry sand surface is influenced by the presence of the buried mine.

The experimental investigation was performed in a laboratory where a surrogate mine was buried at depths between 1 cm and 4 cm in dry sand, and sand which had initial water contents of 2.5%, 5% and 10%. The results show that an observable ‘hot spot’ develops on the sand surface above the mine, during the cooling phase of most tests. The water content of the sand was found to have a strong influence on the development of the hot spot. The surface temperature variation for dry sand tends to be less than that found for sands that contain water and the only test where the hot spot was not detected was in dry sand where the mine was buried at 4 cm. A one-dimensional finite difference model was used to describe the heat and mass transfer mechanisms and interpret the experimental results.     

气动光学头罩热辐射效应数值仿真研究

气动热环境下高速飞行器的光学头罩由于受气动热效应作用,其温度急剧升高,产生严重的气动热辐射效应。为评估气动热环境下高速飞行器光学头罩热辐射对探测系统性能的影响,采用有限光线代表连续辐射的方法,并引入热瞳概念建立了气动光学头罩热辐射传输计算模型并对气动光学头罩自身干扰辐射光线在光学系统内的传输进行了数值仿真,考察了光学头罩温度场为非均匀分布时其自身干扰辐射在探测器接收面的辐照度分布。研究结果表明:由头罩顶点求得的热瞳是光学头罩热辐射能的公共入口,它可将光线追迹的时间减小至追迹全部光线所需时间的十几分之一;根据探测器接受面干扰辐射随时间的变化趋势可知在飞行数秒后头罩干扰辐射将淹没目标信号,气动光学头罩热辐射效应不容忽视。     

空间目标红外辐射理论计算

建立了空间目标的热平衡方程,利用节点网络法求解其表面温度场分布;然后利用普朗克公式计算了空间目标的红外辐射强度;最后对大气层外某空间目标的表面温度场分布和红外辐射强度分布进行了数值计算。     

Simulation of the infrared radiation characteristics of high-temperature exhaust plume including particles using the backward Monte Carlo method

The analysis of the infrared radiation characteristics of high-temperature free-stream flow including particles is very significant for the field of target detection, combustion diagnosis and temperature measurement of flame. In this paper, the infrared radiation characteristics of high-temperature free-stream flow are calculated and analyzed using the backward Monte Carlo method, considering the effect of the directional radiation heat flux due to the particle scattering and the different boundary conditions. The calculation results of emitting, absorbing and anisotropically scattering media are compared with the forward Monte Carlo and finite-volume methods results, which shows the superiority on computational efficiency with the backward Monte Carlo method.     

Validation method of infrared imaging simulation based on recognition range北大核心CSCD

随着红外成像技术的发展和应用,红外系统成像仿真及验证技术越来越受到重视。现有仿真模型验证方法没有考虑到人眼视觉的影响,可能导致严重后果,为了解决这一问题,提出了基于识别距离的红外系统成像仿真模型验证方法。以识别距离作为红外系统成像仿真模型的准确度评价因子,考评仿真图像与实测图像在灰度分布、信噪比、分辨率、成像大小、人眼视觉等方面的综合差异。     

对激光等离子体中X射线的产生与辐射加热研究

利用一维辐射流体力学程序MULTI数值模拟研究了功率为1014Wcm2、脉冲宽度为300ps、波长为0.44μm的强激光辐照平面Au靶时产生X射线的过程,给出了X射线转换效率和能谱分布.通过将靶物质划分为对所产生的X射线光学薄的转化区和光学厚的再发射区,得到了作为黑体辐射热源的最佳靶厚度,并给出了辐射加热靶所产生的等离子体的密度和温度的空间分布. 关键词： 辐射流体力学 激光等离子体 X射线转换 辐射热波     

GPU-accelerated real-time IR smoke screen simulation and assessment of its obscuration

With the growing demand for the Battlefield Environment Simulation (BES), IR smoke screen, which is computationally expensive and absolutely indispensable, should be modeled true to life and correct in its thermal radiation characteristics. This paper analyzes the features of an IR smoke screen, and represents an IR smoke screen model based on light extinction, particle dispersion and temperature attenuation, which is calculated by GPU and rendered to screen in real time. Thus a method considering both the real-life in profile and the real-time in efficiency is presented. Additionally, the comparison between the simulated results and the measured data is made to verify the correctness of the smoke screen’s obscuration, which illustrates the effect of its interference feature in an infrared scene.     

利用蒙特卡洛法分析红外光学系统的杂散辐射

介绍了杂散辐射的概念及其对光学系统成像质量的影响。以一透视式红外系统为例,通过对系统的光机结构的合理简化,利用杂散辐射分析软件Light tools中已有的蒙特卡洛分析方法,对已建立的红外系统光机结构的三维模型进行光线追迹分析,得到了系统像面的照度分布结果。同时,基于辐射度学相关理论对该系统中各结构表面的热辐射进行了定量计算,分析了结构中不同组成部分对系统像面的杂散辐射影响,提出本文系统中前镜框内表面为主要杂散辐射源。针对分析结果,探讨了红外系统的杂散辐射抑制方法,提出的方法可为后续设计提供参考。     

Estimation of thermophysical properties by an inverse method with experimentally determined heating region of a thin-layer heater

This paper deals with the problem of estimation of thermophysical parameters by an inverse method. The thermal conductivity in radial and axial direction of a cylindrical sample and the heat capacity were simultaneously estimated using the Levenberg–Marquardt method of minimizing a mean square functional. As heat sources the thin-layer heater KHR 2/10 of diameter  = 50 mm and thickness 0.20 mm made by OMEGA as well as the Kanthal resistance wire of diameter  = 0.1 mm in a form of semicircle were simultaneously used. The main aim of using these two heaters simultaneously, both placed at one of the sample interfaces, was to generate heat fluxes in axial and additionally in radial direction. However, measurements of temperature distribution on the main surface of the thin-layer heater by using the FLIR Systems (ThermaCAM SC 3000 infrared camera) revealed a spatial heterogeneity of its temperature field, and therefore it was necessary to determine the effective heating region of that heater indispensable for solving of the coefficient inverse problem of heat conduction.     

JEMS-FDTD软件在飞机HIRF仿真中的应用

高强辐射场防护逐渐受到重视,并成为飞机设计和机载设备装机的必要条件。将自主研发的大规模并行三维时域全波电磁模拟软件JEMS-FDTD应用于飞机高强辐射场(HIRF)仿真。数值模拟中为保证计算精度,采用了非均匀网格及共形网格技术。根据实验条件,平面波近似与实验条件差异较大,需考虑天线近场效应,故构建了球面波等效源。给出了平面波近似及球面波近似下的仿真结果与实验结果的对比,结果显示,球面波近似与实验结果更加吻合。在完成数值模拟的基础上,采用PFC方法对仿真结果与实验结果的吻合度进行了评估,评估等级与欧盟HIRF-SE项目定级相当。     

三维柱腔内辐射输运的一维模拟

在惯性约束聚变实验中,使用一维辐射流体力学程序模拟辐射在管壁约束的介质中的传输,因为无法考虑管壁辐射漏失等二维或三维边缘效应而引入了较大的误差.通过解析的视角因子公式和反照率定标公式来模拟X射线在管壁中的损失以及腔壁开口的漏失等边缘效应,对一维辐射流体力学程序MULTI的辐射输运计算进行了修改,成功模拟了X射线辐照下金等离子体的界面运动轨迹,比不考虑边缘漏失更接近实验测量结果,证明了该方法的有效性.     

背景辐射中负热容量系统的质量演化讨论及Runge-Kutta法数值模拟

以黑洞为例,在不考虑满足幺正性的情况下得到了在背景辐射中Schwarzschild黑洞的质量随时间变化的微分方程,并对该方程进行了必要的研究和讨论,作为对《新概念物理教程.力学》和《新概念物理教程.热学》中提到的负热容量系统的不稳定性的另一个注释.文章最后用Runge-Kutta法数值模拟了Schwarzschild黑洞的质量演化过程,使广大学生能够更直观地理解这一过程.     

脉冲X射线辐射效应时间能量联合数值模拟

在脉冲X射线辐射效应研究中,需要将时间维度信息结合到仿真模型中,进而实现基于时间能量联合方法的辐射效应数值模拟,同时也为瞬态脉冲辐照效应的仿真提供了一种思路。建立轫致辐射打靶模型,计算出射脉冲X射线能谱,得到脉冲X射线的时间能量联合谱,结合辐射对象的辐射效应仿真模型,获得氧化铝陶瓷试样在不同时间及不同入射深度处的能量沉积。     

A wide-FoV athermalized infrared imaging system with a two-element lens

For infrared imaging systems to achieve wide field of view (FoV), wide operating temperature and low weight, this work designs a wide-FoV athermalized infrared imaging system (AIIS) with a two-element lens. Its principle, design, manufacture, measurement and performance validation are successively discussed. The two-element lens contains four surfaces, where three aspheric surfaces are introduced to reduce optical off-axis aberrations and a cubic surface is introduced to achieve athermalization. The key coding mask containing an aspheric surface and a cubic surface is manufactured by nano-metric machining of ion implanted material (NiIM). Experimental results validate that our wide-FoV wavefront coding AIIS has a full FoV of 26.10° and an operating temperature over –20 °C to +70 °C.