粉末药型罩的材料密度对聚能射流性能的影响

为研究粉末药型罩的材料密度对其所形成的聚能射流的影响,借助Birkhoff定常模型和Gurney压垮速度理论,计算了相同装药条件下药型罩密度与其所形成的聚能射流速度、射流微粒动量与动能的关系曲线。在相同装药结构下,对W、Cu质量配比分别为0.5∶0.5和0.4∶0.6的两种W-Cu粉末药型罩,进行了射流速度测定和破甲威力实验研究。计算结果与实验结果吻合较好,表明借助Birkhoff定常模型和Gurney压垮速度理论所计算的射流密度、射流微粒动量及动能与药型罩密度的关系曲线具有一定的参考价值,增大粉末药型罩密度可有效提高聚能射流的破甲威力。     

起爆方式对环向聚能射流成型影响的数值模拟

采用LS-DYNA有限元分析软件,对环向聚能装药在中心点起爆、端点起爆和两端对称起爆方式下的射流形成过程分别进行了数值模拟。计算结果表明:3种起爆方式下,两端对称起爆的射流头部速度最高,中心点起爆次之,端点起爆最小。起爆方式的不同,导致爆轰波阵面与药型罩母线的夹角不同;而夹角越小,罩微元受到的爆轰载荷越大,相应的压垮速度越高,形成的射流头部速度越大。在端点起爆的情况下,由于爆轰波形关于药型罩不对称,导致两侧罩微元的爆轰载荷和压垮速度不同,射流发生偏移。     

起爆偏心对聚能装药射流成型过程及威力参量的影响

为了研究起爆偏心对聚能射流的影响,运用有限元软件LS-DYNA模拟了不同起爆偏心量(0.025D_k～0.125D_k,D_k为装药直径)下射流成型及其破甲过程,探究了药型罩非对称压垮程度、射流形态以及横向速度的变化规律,建立了理论模型以分析不同偏心量下射流横向速度分布情况,并基于正交试验设计理论和方差分析法揭示了各因素对评价指标影响程度的显著差异。结果表明：药型罩非对称压垮程度及射流横向速度均与偏心量呈正相关变化趋势。偏心量为0.025D_k时,射流侵彻深度仅下降0.7%;偏心量为0.050D_k时,侵彻深度下降突跃为12.4%;随着偏心量的增加,侵彻深度继续下降。此外,适当增大壁厚、罩顶装药高度可削弱起爆偏心对射流横向速度的影响。     

药型罩材料的晶粒度对射流性能的影响

 通过对紫铜药型罩的静破甲威力实验和脉冲X射线照像，研究了药型罩材料的晶粒度对射流性能的影响。研究结果表明，药型罩材料的晶粒度对射流动态延伸特性有重要影响。罩材料的晶粒细化可以增加有效连续射流的长度，推迟射流断裂的时间，提高静破甲威力水平。最后讨论了晶粒度对射流性能影响的机理。     

辅助药型罩材料对线型聚能射流性能影响的数值仿真

为了提升线型聚能射流的性能,将截顶加辅助药型罩结构应用于线型聚能装药,应用三维有限元分析软件(LS-DYNA)对以紫铜为主体药型罩,Al、Cu和W作为辅助药型罩时形成的线型聚能射流进行了数值仿真,并将其与传统的线型聚能射流进行了对比分析。结果表明:截顶加辅助药型罩结构形成的射流性能更优,并随辅助药型罩材料密度等的增大,射流的延展性、速度及有效质量均有提高,且均优于传统的楔形罩结构;W作为辅助药型罩材料时形成的线型聚能射流,速度较传统的楔形罩结构提高约25.9%,射流的有效长度增加约145%。     

铅对粉末药型罩性能的影响

 为了研究铅粉对钨铜粉末药型罩性能的影响,在钨铜药型罩原配方的基础上,添加5%～20%的铅粉进行实验研究。实验结果表明：添加铅粉可以减少粉末药型罩的孔隙度;随着铅粉添加量的增加,射流的侵彻深度和入口孔径均增加,当铅含量为10%～15%时,侵彻深度和入口孔径达到最佳值,侵彻深度可以提高30%,再添加铅粉,侵彻深度和入口孔径均随之下降。从粉末药型罩成型以及射流的形成、拉伸及侵彻靶板等方面,对造成这种现象的原因进行了详细分析,获得了铅对粉末药型罩性能影响的一些机理认识。研究结果为铅粉代替铋粉添加到钨铜粉末药型罩以提高其侵彻性能提供了一定的理论依据。     

铝铜药型罩射流与侵彻数值模拟

为提高射流侵彻性能,根据聚能射流装置的射流形成特点,设计了爆炸复合铝铜金属体作为药型罩的聚能射流装置。此装置依据已有的锥角为42°的聚能装药紫铜药型罩改进而来。利用LS-DYNA软件中的MMALE多物质算法,对此装置的射流形成、侵彻金属靶体全过程进行数值模拟。在保持装药量不变的情况下,计算了当铝铜药型罩锥角分别为36°、38°、40°和42°时的射流形成及侵彻过程。结果表明:射流头部速度随着铝铜药型罩锥角的减小而增大;且锥角为38°时射流穿深最大。相比单纯金属铜药型罩情况,射流头部速度提高了13.2%,侵彻深度提高了14.5%。     

杆式射流对充液防护结构的毁伤机理及影响因素的数值模拟

运用ANSYS/LS_DYNA软件分析了聚能射流对充液结构的毁伤,初步获得了药型罩壁厚和材料等参数对聚能战斗部水下作用的影响特性。药型罩壁厚在0.04D_k~0.06D_k(D_k为装药直径)之间形成的射流对充液防护结构具有较优的侵彻性能;当δ<0.04D_k时,杆流成型结构较差,在水中的动能抗衰减性能较低;δ>0.06D_k时,射流的初始动能低,靶后效果差。药型罩可采用纯铁、紫铜和钽3种材料,其中纯铁射流的侵彻能力最高,钽射流在水中的动能抗衰减性能最好,紫铜射流具有较好的综合性能。     

贫铀合金药型罩聚能破甲性能实验研究

为分析贫铀合金药型罩的破甲性能,以某种结构的紫铜药型罩为比较对象,采取数值仿真的方法设计了贫铀合金药型罩结构,并分别以紫铜和铀铌合金为药型罩材料开展了静爆破甲效应实验,对比了两种材料药型罩形成的射流对45钢棒的侵彻能力。研究结果表明,在主药柱质量相当的情况下,贫铀合金药型罩形成的射流最高侵深较紫铜材料的平均侵深提高约33.4%。     

射流冲击泡沫金属流动液膜传热的实验研究

薄液膜蒸发由于其优良的传热特性而被广泛应用于工业领域。在流动液膜上表面覆盖铜质泡沫金属,并耦合空气射流冲击,能够进一步强化传热。多孔泡沫金属提供的毛细驱动力能够有效控制流动液膜的厚度以避免干涸,同时多孔材料特殊的固体骨架构造可以扩大固液、气液传热面积。为了研究射流冲击条件下多孔介质覆盖流动液膜的传热特性,本文通过实验方法,对包括液膜流速Vf、空气射流速度Va、液膜厚度δf和多孔介质孔隙率ε在内的影响因素进行分析,研究并对比这些因素对加热壁面温度Tw、表面传热系数hw以及传热系数提升率的影响。     

An atmospheric-pressure nitrogen-plasma jet produced from microdischarges in a porous dielectric

This report presents an atmospheric-pressure nitrogen-plasma jet generated from microdischarges in a porous dielectric. A plasma jet with a length of 42 mm was produced by feeding nitrogen gas through a porous alumina installed between an outer electrode and a hollow inner electrode and by applying 60 Hz sinusoidal voltage wave to the electrodes. Microdischarges in the porous alumina are ejected as a plasma jet from the outer electrode through a 1 mm hole by increasing the applied voltage, showing that the temperature of the jet decreases to a value close to room temperature. Even at a frequency as low as 60 Hz, the plasma that evolves from a large amount of microdischarge inside a porous dielectric can have characteristics that are similar to those generated at several hundreds of kilohertz. From the electrical measurements, it is expected that not only the steady generation but also the frequency of the pulses resulting from the microdischarges in the porous dielectric play an important role in obtaining a stable plasma jet. We also identified the various excited plasma species produced from the plasma jet by an optical emission spectroscopy.     

沉降分布孔隙率多孔介质模型及数值研究

研究沉降分布孔隙率多孔介质流动和传热,根据"O"形圈理论和现场测定确定孔隙率系数,建立坐标方向孔隙率分布函数;考虑流体密度变化,并引入Brinkman-Forchheimer的扩展Darcy模型,能量方程采用界面连续条件,建立沉降分布孔隙率多孔介质流动和传热求解模型.采用差分法对模型进行离散化,应用高斯-赛德尔方法迭代求解.数值分析表明:沉降分布孔隙率条件下多孔介质内流体流动速度在壁面附近较大,中心部位较小,壁面附近孔隙率的增大使得低流速区域减小,较高流速区域增大;当孔隙率小值时,温度按线性减小;当孔隙率大值时,温度在高低温壁面附近迅速减小,在中部减小较缓,热量按导热和对流共同传递;孔隙率增大能使平均怒谢尔数增大,对流换热作用增强.     

Underground Storage of Natural Gas in Hydrate State: Primary Injection Stage

The paper is devoted to simulation of the initial stage of natural gas hydrate underground storage: gas injection into aquifer just below permafrost rocks. It is based on the mathematical model of multiphase non-isothermal real gas and water flow in porous media. The model takes into account the transformation of gas and water into hydrate at certain temperature, which depends on gas flow pressure. The dynamics of hydrate and water saturation as well as the pressure and temperature fields in a reservoir with given porosity, permeability, and initial values of pressure, temperature and water saturation were studied. An implicit finite-difference scheme is used to approximate the original boundary-value problem. The finite-difference equations are solved using simple iteration and sweeping algorithms. Several examples of calculations corresponding to real cases are given. Calculations have revealed that the final result strongly depends on the combination of porosity and permeability of a reservoir.     

孔隙度数值反演计算

由渗流微分方程定解问题和Peaceman方程给出了网格压力、井底压力对网格孔隙度的导数,利用三维渗流方程压强数值解计算井底压力对网格孔隙度的导数;采用共轭梯度法实现孔隙度均匀(或分块均匀)分布油藏模型的反演计算.算例表明,经过8~10次迭代后反演结果与真值的最大相对误差在0.03%以内,反演收敛于真值.     

孔隙度敏感系数的数值计算

由渗流微分方程定解问题,利用格林互易定理导出了网格压力对孔隙度的敏感系数,再由Peaceman方程给出了井底压力对孔隙度的敏感系数.借助三维不均匀非稳定渗流场的压强数值解计算了井底压力对孔隙度的敏感系数,并用直接求解敏感系数的方法进行了验证.     

Simulation Study of Shock Reaction on Porous Material

Direct modeling of porous materials under shock is a complex issue. We investigate such a system via the newly developed material-point method. The effects of shock strength and porosity size are the main concerns. For the same porosity, the effects of mean-void-size are checked. It is found that local turbulence mixing and volume dissipation are two important mechanisms for transformation of kinetic energy to heat. When the porosity is very small, the shocked portion may arrive at a dynamical steady state; the voids in the downstream portion reflect back rarefactive waves and result in slight oscillations of mean density and pressure; for the same value of porosity, a larger mean-void-size makes a higher mean temperature. When the porosity becomes large, hydrodynamic quantities vary with time during the whole shock-loading procedure： after the initial stage, the mean density and pressure decrease, but the temperature increases with a higher rate. The distributions of local density, pressure, temperature and particle-velocity are generally non-Gaussian and vary with time. The changing rates depend on the porosity value, mean-void-size and shock strength. The stronger the loaded shock, the stronger the porosity effects. This work provides a supplement to experiments for the very quick procedures and reveals more fundamental mechanisms in energy and momentum transportation.     

多孔铁冲击温度的分子动力学模拟

 采用Matsui和Anderson提出的Morse型有效原子对势及导带电子热激发能贡献，通过分子动力学方法（MD）对多孔铁的冲击温度进行了数值模拟。计算时，采用了在一定冲击压力下多孔铁样品已转变为均匀介质的近似。多孔铁冲击温度的模拟结果与经合理修正后的热力学计算结果相一致。这个结果表明：在一定的冲击压力下，多孔材料样品确实存在一个热力学平衡状态下的温度值。以上结论可能也适用于更高孔隙率的样品，当然这一观点还需要更多的实验结果给予证实。     

Polymorphic transformations in nanostructured anatase (TiO2) under high-pressure shock compression

The action of dynamic pressure and temperature on polymorphic transformations in nanostructured (grain size of 8–20 nm) anatase (TiO₂) is studied. The dynamic pressure of a loading pulse (10–45 GPa) is measured with a manganin gauge. The temperature of shock-compressed specimens, which is varied by varying the initial temperature and initial porosity, is found to fall into the range 500–2500 K. It is shown that as the temperature and shock compression pressure rise, the nanostructured anatase turns into a nanoanatase-nanocolumbite or columbite-rutile mixture or into almost impurity-free (pure) nanocolumbite or impurity-free microcrystalline rutile.     

高温气冷堆堆芯球床流动与温度分布均匀性研究

由于燃料球的随机分布和球床的壁面效应,球床式高温气冷堆堆芯孔隙率分布会有一定的不均匀性。深入认识壁面漏流、随机孔隙率对球床温度分布均匀性的影响对进一步提高高温气冷堆冷却剂出口温度及其安全性具有重要意义。本文采用多孔介质模型实现了对堆芯球床壁面漏流、随机孔隙率效应的数值模拟。结果表明,由于壁面漏流效应,壁面附近局部区域冷却剂最大速度会比中心高50%,对球床温度影响则不大。中心区域局部极小、极大孔隙率只对很小区域内流速和温度有影响,但温度变化幅值很小。球床中心随机孔隙率使冷却剂速度波动小于13%,对球床温度影响很小。     

Influence of experimental parameters on physical properties of porous silicon and oxidized porous silicon layers

This paper reports physical properties of porous silicon and oxidized porous silicon, manufactured by anodisation from heavily p-type doped silicon wafers as a function of experimental parameters. The growth rate and refractive index of the layers were studied at different applied current densities and glycerol concentrations in electrolyte. When the current density varied from 5 to 100 mA/cm², the refractive index was between 1.2 and 2.4 which corresponded to a porosity range from 42 to 85%. After oxidation, the porosity decreased and was between 2 and 45% for a refractive index range from 1.22 to 1.46. The thermal processing also induced an increase in thickness which was dependent on the initial porosity. This increase in thickness was more important for the lowest porosities. Lastly, the roughness of the porous layer/silicon substrate interface was studied at different applied current densities and glycerol concentrations in solution. Roughness decreased when the current density or glycerol concentration increased. Moreover, roughness was also reduced by thermal oxidation.