排序方式: 共有60条查询结果,搜索用时 15 毫秒
31.
前人应用开尔文冲量理论得到了判断固定边界上方气泡射流方向的Blake准则,但其预测精度在特定参数范围内不足。为此,通过考虑气泡内压力变化并引入边界效应,提出了改进的气泡射流方向判断准则,使用边界元方法模拟结果对其进行验证,比较了改进模型与传统Blake准则的预测结果,并分析了无量纲强度参数对改进模型预测结果的影响。研究表明,改进的模型比传统Blake准则具有更高的预测精度。改进的理论模型能够为水下爆炸、海底资源勘探等领域提供理论参考。 相似文献
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Su-wei Wang Xiu-duo Song Zong-kai Wu Lei Xiao Guang-pu Zhang Yu-bing Hu Ga-zi Hao Wei Jiang Feng-qi Zhao 《防务技术》2021,17(6):1954-1966
The frequent occurrence of safety accidents during the calendering process is caused by the flammable and explosive properties of composite modified double-base (CMDB) propellant. Optimization of process parameters with the aid of fluid simulation technology could effectively ensure the safety of the calendering process. To improve the accuracy of the simulation results, material parameters and model structure were corrected based on actual conditions, and adaptive grid technology was applied in the local mesh refinement. In addition, the rheological behavior, motion trajectories and heat transfer mechanisms of CMDB propellant slurry were studied with different gaps, rotational rates and temperatures of two rollers. The results indicated that the refined mesh could significantly improve the contour clarity of boundaries and simulate the characteristics of CMDB propellant slurry reflux movement caused by the convergent flow near the outlet. Compared with the gap, the increased rotational rate of roller could promote the reflux movement and intensify the shear flow of slurry inside the flow region by viscous shear dragging. Meanwhile, under the synergistic effect of contact heat transfer as well as convective heat exchange, heat accumulated near the outlet and diffused along the reflux movement, which led to the countercurrent heat dissipation behavior of CMDB propellant slurry. The plasticizing mechanism of slurry and the safety of calendering under different conditions were explored, which provided theoretical guidance and reference data for the optimization of calendering process conditions. Based on the simulation results, the safety of the CMDB propellant calendering process could be significantly improved with a few tests conducted during a short research and development cycle. 相似文献
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张士峰 《国防科技大学学报》2000,22(3):84-89
当应力、强度分别服从于正态分布、指数分布和Weibull分布时 ,分析了应力 -强度模型的可靠性评估 ,着重讨论了无信息验前下的Bayes可靠性评估。仿真结果表明 ,无信息验前下的评估结论可以很好地用频率学派的观点来解释。 相似文献
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研究了一种在更换时间有限的情况下 ,基于交替更新过程的双参数批更换系统的优化问题 ,这一问题的目标是平均费用率的极小化。给出了一种特殊情况的讨论结果。 相似文献
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高鲁棒性的动网格变形方法是求解包含运动边界的非定常流场问题的关键技术。基于经典的弹性体动网格方法,引入两种设计合理、评价效果较好的网格质量参数——Patrick参数和Baker参数,提出了一种基于网格质量反馈的改进弹性体动网格方法。结合二维NACA0012翼型、三维ONERA M6机翼大角度俯仰运动,对比研究改进方法与经典方法的变形能力,改进方法能够保持较好的网格质量,尤其在最大变形时,可以有效改善较差网格单元,具有更高的鲁棒性。计算了NACA0012翼型、ONERA M6机翼的俯仰振荡绕流,并与实验结果及文献进行对比,结果表明,基于网格质量反馈的改进弹性体法能够显著提高变形网格的鲁棒性,可为非定常流场问题的求解提供有力支撑。 相似文献
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高鲁棒性的动网格变形方法是求解包含运动边界的非定常流场问题的关键技术。基于经典的弹性体动网格方法,引入两种设计合理、评价效果较好的网格质量参数——Patrick网格质量参数和Baker网格质量参数,从网格质量反馈优化的角度对经典方法作出改进,提出了一种基于网格质量反馈的改进弹性体动网格方法。结合NACA0012翼型的大角度俯仰运动,对比研究改进方法与经典方法的变形能力,整个过程中改进方法均保持更好的平均/最小网格质量,尤其在大俯仰角90deg时,经典方法的平均、最小网格质量降幅均是改进方法的4倍之多,且机翼尾缘处的网格扭曲严重,而改进方法仍与初始网格保持了较好的一致性,具有更高的鲁棒性。作为例证,分别计算了二维NACA0012翼型、三维ONERA M6机翼的俯仰振荡绕流,并与实验结果及流场规律进行对比,结果表明:基于网格质量反馈的改进弹性体法能够显著提高变形网格的鲁棒性,在大幅度的变形下保持较高的网格质量,对多维流场的求解均可取得精确结果,可为非定常流场问题的求解提供有力支撑。 相似文献
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采用液相浸渍法结合反应熔渗法快速制备了改性C/C复合材料,研究其微观组织及在氧乙炔焰和高频等离子体风洞环境中的烧蚀行为。结果表明:改性C/C复合材料主要含有HfC、ZrC、TaC等高熔点陶瓷改性相,其密度为3.83g/cm3,开孔率仅为4.71%。氧乙炔焰烧蚀360s后,改性C/C复合材料表面形成一层主要由HfO2、ZrO2、Ta2O5组成的致密氧化物层,材料的线烧蚀率为0.00518mm/s。使用高频等离子体风洞考核改性C/C复合材料球头模型,在热流量3.5MW/m2、驻点温度2293℃的条件下考核180s后,模型表面生成致密光滑的氧化物保护层,与基体结合牢固,模型形状及尺寸无明显改变,去掉氧化物后测得其线烧蚀率为0.00172mm/s。 相似文献
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Ward Whitt 《海军后勤学研究》2007,54(5):476-484
One traditional application of queueing models is to help set staffing requirements in service systems, but the way to do so is not entirely straightforward, largely because demand in service systems typically varies greatly by the time of day. This article discusses ways—old and new—to cope with that time‐varying demand. © 2007 Wiley Periodicals, Inc. Naval Research Logistics, 2007 相似文献
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在多元先验信息条件下,运用Bayes理论讨论问题时,必然会遇到先验信息融合问题.文中提出了几种简化形式,并针对产品失效率的多个先验信息情形,结合实例与熵度量的拟合优度说明了该方法的合理性. 相似文献