• 主题
高级搜索  >
历史搜索 清空历史
首页> 外文学位 >Analyse de sensibilite dans les ecoulements instables complexes.
【24h】

Analyse de sensibilite dans les ecoulements instables complexes.

机译：复杂不稳定流动中的灵敏度分析。

获取原文
获取原文并翻译 | 示例
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

This project, suggested by the IMI of NRC focuses on the simulation of thermohydrodynamic instabilities causing manufacturing defects during metal powders injection molding processes. At present time, 30% of the manufactured parts are defective. We can found inhomogeneities, empty spaces or debilitating parts when operating conditions are poorly controlled or poorly known. An understanding of the phenomenon will enable manufacturers to reduce or even eliminate defects and improve their competitiveness. The elimination of these effects involves a study and a rigorous fundamental analysis based on CFD ("Computational Fluid Dynamics") and sensitivity analysis. We use a T-shape geometry, typical of injectors that are found in systems of metallic powders casting. The metallic powders is injected at the basis of the T, and then leave by the two ends of the T.;We modeled this problem by using the equations of motion (Navier-Stokes) coupled with the heat transfer equation and a generalized Newtonian viscosity model. Our equations are then solved by the finite elements method which provides the velocity (u and v), pressure and temperature as functions of space and time. The calculation of sensitivities will establish a causal relationship between the different ranges of parameter values that cause instability. The stability or instability depends on the value of two rheological parameters, the Graetz number (ratio of thermal conduction time to fill time) and B, a dimensionless ratio measuring the importance of the effects of temperature on the viscosity. For some values of Graetz and B numbers, the flow becomes unstable and asymmetrical. However, in some cases, this asymmetry is growing to the point where the fluid is forced to leave the injection channel by a single exit. This eventually lead to a complete cessation of the flow in one branch of the T, as if it was obstructed. The instabilities are due to changes in viscosity, itself driven by temperature gradients which can be found at the entrance to the injector. We can see an exponential growth in the temperature difference between the two exits (symmetrical point at the injectors exits). The sensitivity analysis will establish rigorously which of the two parameters trigger instability. Moreover, this analysis will indicate in what regions and at what times the parameters are critical to stability.;After assuring ourself that the implementation in the computer code has been verified by the method of manufactured solutions, we built with the help of numerical solutions the stability chart of the flow in terms of the dimensionless number Gz and B. The chart allows to define the border separating the region where the flow is stable from the one where the flow is unstable. Finally, in connection with the calculation of neighbouring solutions, sensitivity analysis shows that it is possible to anticipate and predict the behaviour of fluid when parameters of the flow (i.e. Gz et B) are disrupts. These results suggest that it is possible to control and even eliminate manufacturing defects in processes related to metal powders injection molding.
机译：由NRC的IMI建议的该项目着重于模拟在金属粉末注射成型过程中引起制造缺陷的热流体动力学不稳定性。目前，有30％的制造零件有缺陷。当操作条件控制不当或不为人所知时，我们会发现不均匀，空旷的地方或易损件。对这种现象的理解将使制造商能够减少甚至消除缺陷并提高竞争力。要消除这些影响，需要进行基于CFD（“计算流体动力学”）和灵敏度分析的研究和严格的基础分析。我们使用T形几何形状，这是金属粉末铸造系统中常见的喷射器。在T的基础上注入金属粉末，然后从T的两端离开;我们通过使用运动方程（Navier-Stokes），传热方程和广义牛顿粘度对这个问题进行建模模型。然后通过有限元方法求解我们的方程，该方法提供速度（u和v），压力和温度作为空间和时间的函数。灵敏度的计算将在引起不稳定的参数值的不同范围之间建立因果关系。稳定性或不稳定性取决于两个流变参数的值，即Graetz数（导热时间与填充时间之比）和B（无因次比），用于测量温度对粘度影响的重要性。对于Graetz和B数的某些值，流动变得不稳定且不对称。但是，在某些情况下，这种不对称性会增大到迫使流体通过单个出口离开喷射通道的程度。最终导致T的一个分支中的流动完全停止，就好像被阻塞了一样。这种不稳定性是由于粘度的变化所致，而粘度的变化本身是由温度梯度驱动的，该温度梯度可在喷射器的入口处发现。我们可以看到两个出口之间的温差（喷射器出口的对称点）呈指数增长。灵敏度分析将严格建立两个参数中哪个触发不稳定性。此外，此分析将指出参数在哪个区域和什么时间对稳定性至关重要。；在确保自己已通过制造解决方案的方法验证了计算机代码中的实现之后，我们借助数值解建立了用无因次数Gz和B表示流动的稳定性图表。该图表允许定义边界，以将流动稳定的区域与流动不稳定的区域分开。最后，结合邻近解的计算，敏感性分析表明，当流量参数（即Gz等B）受到破坏时，可以预测和预测流体的行为。这些结果表明，有可能控制甚至消除与金属粉末注射成型有关的工艺中的制造缺陷。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号