A deep understanding of the internal ballistic process and the factors affecting it is of primary importance to efficiently design a gun system and ensure its safe management. One of the main goals of internal ballist...A deep understanding of the internal ballistic process and the factors affecting it is of primary importance to efficiently design a gun system and ensure its safe management. One of the main goals of internal ballistics is to estimate the gas pressure into the combustion chamber and the projectile muzzle velocity in order to use the propellant to its higher efficiency while avoiding over-pressure phenomena. Dealing with the internal ballistic problem is a complex undertaking since it requires handling the interaction between different constituents during a transient time lapse with very steep rise of pressure and temperature. Several approaches have been proposed in the literature, based on different assumptions and techniques. Generally, depending on the used mathematical framework, they can be classified into two categories: computational fluid dynamics-based models and lumped-parameter ones. By focusing on gun systems, this paper offers a review of the main contributions in the field by mentioning their advantages and drawbacks. An insight into the limitations of the currently available modelling strategies is provided,as well as some considerations on the choice of one model over another. Lumped-parameter models, for example, are a good candidate for performing parametric analysis and optimisation processes of gun systems, given their minimum requirements of computer resources. Conversely, CFD-based models have a better capacity to address more sophisticated phenomena like pressure waves and turbulent flow effects. The performed review also reveals that too little attention has been given to small calibre guns since the majority of currently available models are conceived for medium and large calibre gun systems.Similarly, aspects like wear phenomena, bore deformations or projectile-barrel interactions still need to be adequately addressed and our suggestion is to dedicate more effort on it.展开更多
Pursuing the green manufacturing (GM) of products i s very beneficial in the alleviation of environment burdens. In order to reap such benefits, green manufacturing is involved in every aspect of manufacturing proc es...Pursuing the green manufacturing (GM) of products i s very beneficial in the alleviation of environment burdens. In order to reap such benefits, green manufacturing is involved in every aspect of manufacturing proc esses. During the machining process, cutting fluid is one of the main roots of e nvironmental pollution. And how to make an optimal selection for cutting fluid f or GM is an important path to reduce the environmental pollution. The objective factors of decision-making problems in the traditional selection of cutting flu id are usually two: quality and cost. But from the viewpoint of GM, environmenta l impact (E) should be considered together. In this paper, a multi-object d ecision-making model of cutting fluid selection for GM is put forward, in which the objects of Quality (Q), Cost(C) and Environmental impact (E) are considered together. In this model, E means to minimize the environmental impact, Q means to maximize the quality and C means to minimize the cost. Each objective is anal yzed in detail too. A case study on a decision-making problem of cutting fluid selection in a gear hobbing process is analyzed, and the result shows the model is practical.展开更多
Wireless communication is easily disturbed by unfortunate factors which drive the wireless environment unstable and complicated. Therefore, it is essential to consider these factors in stability analysis of the wirele...Wireless communication is easily disturbed by unfortunate factors which drive the wireless environment unstable and complicated. Therefore, it is essential to consider these factors in stability analysis of the wireless network. However, wireless channel characteristics and packets collisions are neglected in the classical fluid model. A wireless TCP fluid model （WTFM） for stability analysis of wireless network is proposed based on cross layers, which not only makes the congestion control based on random early detection （RED） available for wireless network, but also provides a more accurate model to analyze the stability of wireless system theoretically. In the proposed model, active queue management, abnormality of wireless channels and packets collisions are taken into consideration. The comparisons between evaluating results from the WTFM and the practical performance from NS2 simulations validate the accuracy of the proposed WTFM in the perspectives of delay, dropping probability, throughput, sliding window size and queue length. A set of comparisons among the proposed WTFM, the classical fluid model and the convex optimization model are conducted. The results demonstrate that the proposed WTFM model performs better than other schemes in comprehensive aspects on capturing the characteristic of the wireless network and computing complexity.展开更多
针对复杂管道系统内水流冲击滞留气团现象,采用VOF模型(Volume of Fluid Model)进行了数值模拟计算,并与一维模型进行了比较计算分析,结果表明:系统的最大压力并不总是气团的最大压力,有可能还会叠加水体对管壁的撞击而形成的突然升高...针对复杂管道系统内水流冲击滞留气团现象,采用VOF模型(Volume of Fluid Model)进行了数值模拟计算,并与一维模型进行了比较计算分析,结果表明:系统的最大压力并不总是气团的最大压力,有可能还会叠加水体对管壁的撞击而形成的突然升高压力。与实验实测结果的比较分析表明:采用VOF模型,能够较精细地仿真水流冲击滞留气团现象的气团形态、流场结构以及压力分布等的变化过程,其压力数值计算结果与实验实测基本吻合,其计算误差明显小于现有一维模型的计算误差,是深入研究该复杂瞬变流现象的有效方法。展开更多
isoAdvector是一种新的几何VOF(Volume of Fluid)方法,虽然克服了传统几何VOF方法难以适用于三维空间任意多面体网格的缺点,但不能直接用来模拟涉及动网格技术的液舱晃荡.为此,引入了运动通量修正,并提出了面-界面交线运动修正,使得修...isoAdvector是一种新的几何VOF(Volume of Fluid)方法,虽然克服了传统几何VOF方法难以适用于三维空间任意多面体网格的缺点,但不能直接用来模拟涉及动网格技术的液舱晃荡.为此,引入了运动通量修正,并提出了面-界面交线运动修正,使得修正后的isoAdvector方法可以应用到液舱晃荡的模拟中.基于不同的VOF方法对非共振、共振受迫晃荡和单次冲击波面进行数值模拟,并将模拟结果与试验结果以及解析解进行了比较.结果表明:相对于代数VOF方法,采用修正后的isoAdvector方法获得的自由液面位置和整体水动力载荷精度更高;捕捉的波面没有褶皱,能够较好地模拟波面的翻卷和破碎.此外,提出了界面厚度的估计方法,分析了自由液面波高精度提高的原因.展开更多
结合长距离无压引水隧洞充水过程,建立了水气两相流耦合VOF(Volume of Fluid)法的k-ε紊流模型,近壁面采用考虑糙率影响的壁面函数,结合实际工程对长距离无压引水隧洞水气两相流进行了模拟。模拟结果表明:隧洞内水位随充水时间的增加逐...结合长距离无压引水隧洞充水过程,建立了水气两相流耦合VOF(Volume of Fluid)法的k-ε紊流模型,近壁面采用考虑糙率影响的壁面函数,结合实际工程对长距离无压引水隧洞水气两相流进行了模拟。模拟结果表明:隧洞内水位随充水时间的增加逐渐上升并趋于稳定;对隧洞充水过程中沿程典型断面的水气两相流进行了动态分析,结果表明进口流量为65 m3/s时水流能顺利通过隧洞;对某水库放水兼放空洞水深实测数据进行了验证对比,模拟结果与实验结果基本吻合。展开更多
基金the support provided by the Royal Higher Institute for Defence (RHID) of the Belgian Defence, which has contributed to the progress of this ongoing research.
文摘A deep understanding of the internal ballistic process and the factors affecting it is of primary importance to efficiently design a gun system and ensure its safe management. One of the main goals of internal ballistics is to estimate the gas pressure into the combustion chamber and the projectile muzzle velocity in order to use the propellant to its higher efficiency while avoiding over-pressure phenomena. Dealing with the internal ballistic problem is a complex undertaking since it requires handling the interaction between different constituents during a transient time lapse with very steep rise of pressure and temperature. Several approaches have been proposed in the literature, based on different assumptions and techniques. Generally, depending on the used mathematical framework, they can be classified into two categories: computational fluid dynamics-based models and lumped-parameter ones. By focusing on gun systems, this paper offers a review of the main contributions in the field by mentioning their advantages and drawbacks. An insight into the limitations of the currently available modelling strategies is provided,as well as some considerations on the choice of one model over another. Lumped-parameter models, for example, are a good candidate for performing parametric analysis and optimisation processes of gun systems, given their minimum requirements of computer resources. Conversely, CFD-based models have a better capacity to address more sophisticated phenomena like pressure waves and turbulent flow effects. The performed review also reveals that too little attention has been given to small calibre guns since the majority of currently available models are conceived for medium and large calibre gun systems.Similarly, aspects like wear phenomena, bore deformations or projectile-barrel interactions still need to be adequately addressed and our suggestion is to dedicate more effort on it.
文摘Pursuing the green manufacturing (GM) of products i s very beneficial in the alleviation of environment burdens. In order to reap such benefits, green manufacturing is involved in every aspect of manufacturing proc esses. During the machining process, cutting fluid is one of the main roots of e nvironmental pollution. And how to make an optimal selection for cutting fluid f or GM is an important path to reduce the environmental pollution. The objective factors of decision-making problems in the traditional selection of cutting flu id are usually two: quality and cost. But from the viewpoint of GM, environmenta l impact (E) should be considered together. In this paper, a multi-object d ecision-making model of cutting fluid selection for GM is put forward, in which the objects of Quality (Q), Cost(C) and Environmental impact (E) are considered together. In this model, E means to minimize the environmental impact, Q means to maximize the quality and C means to minimize the cost. Each objective is anal yzed in detail too. A case study on a decision-making problem of cutting fluid selection in a gear hobbing process is analyzed, and the result shows the model is practical.
基金supported by the National Natural Science Foundation of China(61106022)the Beijing Natural Science Foundation(4143066)
文摘Wireless communication is easily disturbed by unfortunate factors which drive the wireless environment unstable and complicated. Therefore, it is essential to consider these factors in stability analysis of the wireless network. However, wireless channel characteristics and packets collisions are neglected in the classical fluid model. A wireless TCP fluid model （WTFM） for stability analysis of wireless network is proposed based on cross layers, which not only makes the congestion control based on random early detection （RED） available for wireless network, but also provides a more accurate model to analyze the stability of wireless system theoretically. In the proposed model, active queue management, abnormality of wireless channels and packets collisions are taken into consideration. The comparisons between evaluating results from the WTFM and the practical performance from NS2 simulations validate the accuracy of the proposed WTFM in the perspectives of delay, dropping probability, throughput, sliding window size and queue length. A set of comparisons among the proposed WTFM, the classical fluid model and the convex optimization model are conducted. The results demonstrate that the proposed WTFM model performs better than other schemes in comprehensive aspects on capturing the characteristic of the wireless network and computing complexity.
文摘针对复杂管道系统内水流冲击滞留气团现象,采用VOF模型(Volume of Fluid Model)进行了数值模拟计算,并与一维模型进行了比较计算分析,结果表明:系统的最大压力并不总是气团的最大压力,有可能还会叠加水体对管壁的撞击而形成的突然升高压力。与实验实测结果的比较分析表明:采用VOF模型,能够较精细地仿真水流冲击滞留气团现象的气团形态、流场结构以及压力分布等的变化过程,其压力数值计算结果与实验实测基本吻合,其计算误差明显小于现有一维模型的计算误差,是深入研究该复杂瞬变流现象的有效方法。
文摘isoAdvector是一种新的几何VOF(Volume of Fluid)方法,虽然克服了传统几何VOF方法难以适用于三维空间任意多面体网格的缺点,但不能直接用来模拟涉及动网格技术的液舱晃荡.为此,引入了运动通量修正,并提出了面-界面交线运动修正,使得修正后的isoAdvector方法可以应用到液舱晃荡的模拟中.基于不同的VOF方法对非共振、共振受迫晃荡和单次冲击波面进行数值模拟,并将模拟结果与试验结果以及解析解进行了比较.结果表明:相对于代数VOF方法,采用修正后的isoAdvector方法获得的自由液面位置和整体水动力载荷精度更高;捕捉的波面没有褶皱,能够较好地模拟波面的翻卷和破碎.此外,提出了界面厚度的估计方法,分析了自由液面波高精度提高的原因.
文摘结合长距离无压引水隧洞充水过程,建立了水气两相流耦合VOF(Volume of Fluid)法的k-ε紊流模型,近壁面采用考虑糙率影响的壁面函数,结合实际工程对长距离无压引水隧洞水气两相流进行了模拟。模拟结果表明:隧洞内水位随充水时间的增加逐渐上升并趋于稳定;对隧洞充水过程中沿程典型断面的水气两相流进行了动态分析,结果表明进口流量为65 m3/s时水流能顺利通过隧洞;对某水库放水兼放空洞水深实测数据进行了验证对比,模拟结果与实验结果基本吻合。
