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文章介绍了分形理论及分形维数,综述了分形维数在图像信息提取中的应用.分别应用分形维数和灰度共生矩阵方法,对遥感图像中的树种进行分类提取,通过对比两种方法分类精度可以看出,分形维数方法在图像信息提取中具有较好的效果. 相似文献
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针对自然界中实际多孔介质具有的分形特性和随机性,利用中点替代算法和二值化处理构造统计上具有分形特性的随机多孔介质。分析了所构造的多孔介质盒维数与Hurst指数之间的关系。基于随机分形构造的原理,对二维实际多孔介质图像进行了重构。利用两点相关函数,分析了重构图像的结构相关性,并与实际目标多孔介质的结构特征进行比较。在与解析解对比验证的基础上,将基于二元混合理论的格子Boltzmann模型(LBM)用于模拟多孔介质内流体扩散过程。通过计算不同分形特性的二维多孔介质的有效扩散系数,研究了重构多孔介质的分形维数与有效扩散系数的关系。利用热耦合LBM模型计算多孔介质内传热过程,分析了不同的分形特性对多孔介质蓄热过程的影响。 相似文献
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本文以NaCl为熔盐介质、镁橄榄石为原料制备了多孔镁橄榄石轻质材料,采用分形理论研究材料的微孔结构与材料物理性能的关系.对图像数据在预处理后用Image-Pro Plus软件进行二值化处理.利用分形理论确定线性关系式的相关系数R,以及用数学的方式来研究分形维数D.在烧成温度相同的条件下(1050℃,1100℃和1150℃),随试样中盐含量的增加,孔分形维数略有增加,当试样的烧成温度为1100℃,盐的含量为50%时,分形维数达到最大,即D=2.7.而在同一配比下,试样在1100℃时,孔分形维数较大,试样的孔结构趋于三维规则,烧成后试样的体积密度、显气孔率和常温耐压强度出现拐点.从而揭示了材料结构与性能之间的关系,即材料的分形维数越大,孔结构越趋于三维结构,材料的性能越优. 相似文献
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依据相似定理,通过二维水模型模拟顶吹转炉吹炼过程. 利用数码相机进行摄影,通过对图像的计算机处理,研究了依据相似定理,通过二维水模型模拟顶吹转炉吹炼过程. 利用数码相机进行摄影,通过对图像的计算机处理,研究了顶吹过程中炉渣与钢液母相边界的变化. 应用分形理论对其边界的织构分维数及无量纲长度进行了计算. 结果表明,吹炼过程中枪位、吹气流量及渣金比对炉渣与钢液母相边界的织构分维数影响较大,其中流量为主要影响因素. 得出了三者对织构分维数的影响及织构分维数对无量纲长度影响的经验关系式,渣金母相边界织构维数是评价二维渣金母相边界长度的重要依据. 分形理论可以为转炉吹炼过程中渣金母相边界的量化计算提供一种有效的方法. 相似文献
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Foaming properties of the three NC‐based (nitrocellulose‐based) propellants, namely, single‐base propellant, NG (nitroglycerine) propellant and TEGDN (triethylene glycol dinitrate) propellant were investigated in the batch foaming process by using supercritical CO2 as the physical foaming agent. Burning characteristics of the foamed NC‐based propellants were also investigated in this work. For this study, the CO2 desorption of the three NC‐based propellants were plotted by the gravimetric method. The morphology and burning characteristics of these foamed NC‐based propellants were characterized by scanning electron microscope (SEM) and closed vessel experiment. The test data revealed that the energetic plasticizer has a considerable effect on the pore formation in the NC matrix although it has little effect on the CO2 solubility in the NC‐based propellants. Moreover, the SEM images showed the foaming temperature also plays an important role in the pore parameters of foamed propellants. Furthermore, the data of closed vessel experiment indicated that the burning characteristics of foamed NC‐based propellants largely depend on the pore parameters, and the porous structure of foamed propellants would considerably increase the mass conversion rate. 相似文献
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为预估轻武器用钝感发射药在贮存过程中,因钝感剂迁移导致弹道性能变化而引起功能失效的问题,采用Fick第二定律和扩散系数与扩散活化能的关系,以发射药钝感层结构相同、其内弹道性能相同为前提,建立了轻武器用钝感发射药功能失效阈值预估方法。应用该方法,采用3种配方钝感发射药分别在75℃和85℃下长贮,计算出各发射药钝感剂药的扩散活化能,并以75℃为基准预测了3种配方钝感发射药65℃长贮下的膛压功能失效阈值,同时在65℃下对发射药进行长贮,通过内弹道试验实测出发射药在65℃长贮下膛压功能失效阈值。结果表明,应用该方法预估发射药膛压功能失效阈值与实测值偏差分别为10.3%、2.9%、7.9%。同时以65、75、85℃下平均扩散活化能,计算出不同温度下发射药功能失效阈值,并对3种配方钝感发射药要满足常规弹药17年的贮存寿命要求的最高贮存温度提出了要求。 相似文献
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化学推进剂及重要相关原材料发展回顾与展望(续前) 总被引:1,自引:1,他引:0
王新德 《化学推进剂与高分子材料》2010,8(5):4-5,19
<正>(续2010年第3期第7页)2化学推进剂国外研究进展2.1液体推进剂国外研究进展液体推进剂目前以美国、俄罗斯水平为最高,在大型运载火箭用液体推进剂领域,俄、美、法基本相当;但在巡航导弹、高超声速导 相似文献
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Prior to laser ignition tests, spectral absorption properties of three different solid motor propellants were analysed. The extruded double base (EDB) propellant exhibited >95 % absorption over the 250–550 nm wavelength band whereas, the cast double base (CDB) showed similar absorption over a wider band extending between 375–800 nm. The composite sample (CP) showed a uniform spectral absorption at about 90 % over 250–800 nm band. Ignition tests using an average of 500 nm output from an Ar‐ion laser showed that the double base propellants undergo deflagration prior to ignition due to the presence of carbon black material. Within the laser power density range of 24–125 Wċcm−2, the threshold laser energy densities for deflagration and ignition in the double base propellant were found to␣be between 2–2.5 Jċcm−2, and 40–215 Jċcm−2, respectively. No deflagration was observed for the composite propellant, and the threshold ignition energy was found to be within the range, 11–18 Jċcm−2 for the same range of laser power densities. From the ignition map for this propellant, the threshold energy for ignition at this wavelength was found to be approximately 18 Jċcm−2 and was practically independent of laser power density. In the near infrared wavelength (780 nm) the EDB propellant was not readily ignitable due to its comparatively much higher reflectance at this wavelength. The ignition threshold values were found to be between 19–23 Jċcm−2 for a similar power density level. The results indicate that the ignitability of propellants is enhanced through the promotion of deflagration. 相似文献
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Nettula Pandarinath Rao Chetan Solanke Bipin Kumar Bihari Praveen Prakash Singh Bikash Bhattacharya 《Propellants, Explosives, Pyrotechnics》2016,41(2):281-285
It is essential to evaluate the mechanical properties of propellants in a solid propellant rocket motor (SPRM) for structural integrity and its performance evaluation before the flight test. Conventionally, uni‐axial tensile testing on an universal testing machine (UTM) is used to evaluate the mechanical properties of solid propellant carton which is cast along with SPRM. Propellants in rocket motors experience various types of loading during storage, transportation, and environmental conditions over the period of time before actual flight whereas the propellant carton doesn’t experience the same as it is stored in magazine. At present, the mechanical properties of propellant cast in a carton are considered to be the mechanical properties of propellant in a rocket motor, which is not truly representative. Therefore, a non‐destructive indentation technique has been used to establish a method for evaluating the mechanical properties of solid propellants in rocket motors based on hydroxyl terminated polybutadiene. The test results obtained using the penetrometer indentation technique was analyzed comprehensively and compared with UTM results. The mathematical correlations were also developed using least square method and established by conducting the penetrometer indentation test on similar propellant composition. Further, the developed correlation was used to evaluate the mechanical properties of propellant in flight SPRM by penetrometer indentation technique. 相似文献
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The viscosity of composite solid propellant slurry is an important parameter in charging technical performance of solid rocket motors. It is affected not only by the liquid phase ingredients of propellants, but also by the size, content, shape and surface properties of solid fillers in propellants. This paper will present a prediction formula of viscosity of composite solid propellant and will also give a method for calculating the maximum packing volume fraction of solid in the formula. One can predict the viscosity of propellant slurry with the formula if the composition of the propellant is known. 相似文献
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Fractal Characteristics of Fracture Surfaces 总被引:2,自引:0,他引:2
George R. Baran Claude Roques-Carmes Dohloul Wehbi Michel Degrange 《Journal of the American Ceramic Society》1992,75(10):2687-2691
Quantitative fractography is often used to study material failure mechanisms. During calculation of surface or profile roughness parameters, the magnification used in obtaining fractographic data is found to influence the value of the parameters. Fractal geometry has been developed into a tool capable of defining surface and profile topography without sensitivity to magnification, and several studies have related fractal dimension ( D F ) to other physical or mechanical properties. In this study, we obtained the fractal dimension of profiled fracture surfaces of one glass and three proprietary dental porcelains. The fracture toughness ( K 1c ) of these materials was also measured using the indentation-strength method. Results show the surfaces to be fractal. No quantitative relationship between fractal dimension and toughness was found. Differences in K 1c were demonstrated between some materials. It is postulated that the size range within which fractal dimension can be defined as constant is dependent on the toughening mechanism, and that the relationship between K Ic and D F cannot be identical for all materials. 相似文献
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Composite solid propellants demand fine and stable mechanical properties, creep resistance and stress relaxation performance during their long storage and usage time. In this study, modified hyperbranched polyester (MHBPE) was prepared and introduced into HTPE/AP/Al/RDX (HTPE, hydroxyl‐terminated polyether; AP, ammonium perchlorate; RDX, cyclotrimethylenetrinitramine) solid propellant as an effective additive. The static tensile and dynamic mechanical properties of this propellant before and after the introduction of MHBPE were evaluated. The elevated interfacial interaction by using MHBPE between the binder and RDX fillers improved the toughness and elasticity of the propellant. The enhancement mechanisms were also confirmed by the influence on the fracture surface morphology of the binder which was investigated by SEM. In addition, some influence on the dynamic mechanical properties of HTPE/AP/Al/RDX propellant caused by MHBPE was investigated by dynamic mechanical analysis. The creep behaviors of the HTPE/AP/Al/RDX propellants with and without MHBPE were also investigated at different stresses and temperatures. Reduced creep strain rate and strain were obtained for the modified propellant, implying enhanced creep resistance performance. The creep properties were quantitatively evaluated using a six‐element model and the long‐term creep performance of the propellant was predicted using the time–temperature superposition principle. A creep behavior of nearly 106 s at 30 °C could be acquired in a short‐term experiment (800 s) at 30–70 °C. Moreover, the stress relaxation investigation of the propellants with and without MHBPE at ?40 °C, 20 °C and 70 °C suggested that MHBPE/HTPE/AP/Al/RDX propellant possessed better response ability to deformation. Thus, the application of MHBPE provides an efficient route of reinforcement to enhance the creep resistance and stress relaxation properties. © 2020 Society of Chemical Industry 相似文献