A vorticity budget investigation is performed using the output data from a numerical simulation of a typical MCV (mesoscale convectively generated votex) case in South China. Results suggest that the divergence caus...A vorticity budget investigation is performed using the output data from a numerical simulation of a typical MCV (mesoscale convectively generated votex) case in South China. Results suggest that the divergence caused by convection in the low troposphere is the main producer of positive vorticity, while vertical vorticity transferred by the tilting term from the horizontal vorticity compensates the upward output of cyclonic vorticity. Scale analyses of the vorticity equation suggest that the advection of planetary vorticity can be neglected owing to the low latitude, which is di?erent from the larger scale systems in high latitude areas. In addition, the distribution of relative vorticity tendency on pressure level is not uniform. A vortex will move along the vector from the negative to the positive vorticity tendency region. The mechanism of the phenomenon—that nearly all of the convectively ascending region is located southward/southeastward of the vortex center—is also discussed. Convergence with regard to latent heat release would be in favor of the spin-up of meso-vortex, however, the horizontal vorticity caused by wind shear is tilted by vertical motion due to convection. Consequently, the negative and positive vorticity tendencies are located symmetrically about the convective center, which suggests that the vortex southward movement is dynamically driven by convection.展开更多
The characteristics of a flow in spinning devices are one of the fundamental problems innew-type spinning.In this paper the vortex flow in interior of the shell-case was studied by usingexperimental methods,which incl...The characteristics of a flow in spinning devices are one of the fundamental problems innew-type spinning.In this paper the vortex flow in interior of the shell-case was studied by usingexperimental methods,which include flow visualization and laser doppler techniques.The flow sur-vey by measurement has been compared with that photographed by flow visualization method,andshows a fairly good conformity.The results of experiments are similar to those by numericalevaluation.展开更多
采用ZWICK 100 k N高温拉伸试验机在变形温度为750℃,应变速率为0.1 s^-1下对工业纯钛进行高温拉伸试验。将试验数据导入DEFORM-3D中拟合得到J-C本构模型。对已有的涡旋挤压模具进行改进,基于拟合的J-C本构模型进行数值模拟,研究改进模...采用ZWICK 100 k N高温拉伸试验机在变形温度为750℃,应变速率为0.1 s^-1下对工业纯钛进行高温拉伸试验。将试验数据导入DEFORM-3D中拟合得到J-C本构模型。对已有的涡旋挤压模具进行改进,基于拟合的J-C本构模型进行数值模拟,研究改进模具的晶粒细化效率及可行性。结果表明:挤出后,坯料轴向截面和径向截面等效应变均呈梯度分布,轴向截面最高等效应变值约为10.6,径向截面最高等效应变值约为14.5。整个挤出过程中,坯料扭曲部分等效应变累积量最高,外侧部分晶粒细化效率远高于心部。坯料挤出端平均等效应变大幅提高,采用改进的模具晶粒细化效率更高。在改进的模具中,坯料流动性较好,最大载荷显著降低,说明改进的坯料用于强化工业纯钛是可行的。展开更多
文摘A vorticity budget investigation is performed using the output data from a numerical simulation of a typical MCV (mesoscale convectively generated votex) case in South China. Results suggest that the divergence caused by convection in the low troposphere is the main producer of positive vorticity, while vertical vorticity transferred by the tilting term from the horizontal vorticity compensates the upward output of cyclonic vorticity. Scale analyses of the vorticity equation suggest that the advection of planetary vorticity can be neglected owing to the low latitude, which is di?erent from the larger scale systems in high latitude areas. In addition, the distribution of relative vorticity tendency on pressure level is not uniform. A vortex will move along the vector from the negative to the positive vorticity tendency region. The mechanism of the phenomenon—that nearly all of the convectively ascending region is located southward/southeastward of the vortex center—is also discussed. Convergence with regard to latent heat release would be in favor of the spin-up of meso-vortex, however, the horizontal vorticity caused by wind shear is tilted by vertical motion due to convection. Consequently, the negative and positive vorticity tendencies are located symmetrically about the convective center, which suggests that the vortex southward movement is dynamically driven by convection.
文摘The characteristics of a flow in spinning devices are one of the fundamental problems innew-type spinning.In this paper the vortex flow in interior of the shell-case was studied by usingexperimental methods,which include flow visualization and laser doppler techniques.The flow sur-vey by measurement has been compared with that photographed by flow visualization method,andshows a fairly good conformity.The results of experiments are similar to those by numericalevaluation.
文摘采用ZWICK 100 k N高温拉伸试验机在变形温度为750℃,应变速率为0.1 s^-1下对工业纯钛进行高温拉伸试验。将试验数据导入DEFORM-3D中拟合得到J-C本构模型。对已有的涡旋挤压模具进行改进,基于拟合的J-C本构模型进行数值模拟,研究改进模具的晶粒细化效率及可行性。结果表明:挤出后,坯料轴向截面和径向截面等效应变均呈梯度分布,轴向截面最高等效应变值约为10.6,径向截面最高等效应变值约为14.5。整个挤出过程中,坯料扭曲部分等效应变累积量最高,外侧部分晶粒细化效率远高于心部。坯料挤出端平均等效应变大幅提高,采用改进的模具晶粒细化效率更高。在改进的模具中,坯料流动性较好,最大载荷显著降低,说明改进的坯料用于强化工业纯钛是可行的。
