The stretch bending of L-section variable-curvature SUS301L stainless-steel roof bending beams for metro vehicles was numerically simulated.The causes of defects such as wrinkling,section distortion,and poor contour a...The stretch bending of L-section variable-curvature SUS301L stainless-steel roof bending beams for metro vehicles was numerically simulated.The causes of defects such as wrinkling,section distortion,and poor contour accuracy were analysed,and the corresponding control methods were proposed.The simulation results demonstrated that wrinkling in the small-arc segment could be eliminated by setting the die clearance and adjusting the elongation reasonably.Owing to the sidewall shrinkage of the profile in the process of stretch bending,the die groove depth was correspondingly reduced.Each section of the profile was effectively supported by the bottom of the die groove,and the section distortion could be controlled.Springback was the main reason for the poor contour accuracy,which could be compensated by modifying the die surface based on the springback value.Using the above defect control methods,forming experiments were performed on a new type of stretch bending die with variable die clearance and groove depth developed in this work.Finally,high-quality components were obtained,which verified the efficacy of the defect control methods.展开更多
以麝香百合系L型"新铁炮"和OT型"黄色风暴"百合植株的子房、花药为材料,在离体条件下采用不同的授粉方式进行L×OT和OT×L的组间杂交,期望获得兼有父母本优良特点的百合杂交种。其研究结果,获最佳的材料灭...以麝香百合系L型"新铁炮"和OT型"黄色风暴"百合植株的子房、花药为材料,在离体条件下采用不同的授粉方式进行L×OT和OT×L的组间杂交,期望获得兼有父母本优良特点的百合杂交种。其研究结果,获最佳的材料灭菌方法为先用酒精消毒0.5 m in再用升汞消毒6 m in;采用切割子房授粉的方式可获得较高的子房膨大率;筛选出MS+0.02 mg/L NAA的培养基为杂交种子最佳培养基,其所含的蔗糖浓度为6%。展开更多
文摘随着高温超导等低温技术的快速发展,脉动热管作为一种高效换热元件在液氮温区的应用逐渐受到关注。对于较长距离和冷热两端不共面的应用背景,本文利用计算流体力学(computational fluid dynamics,CFD)对脉动热管元件建立三维数值模型,并用流体体积(volume of fluid,VOF)方法模拟气液两相流。首先对绝热段长度分别为22mm、50mm和100mm的脉动热管在液氮温区的热性能进行对比研究,结果表明蒸发段和冷凝段长度不变,增加绝热段长度时,其表现出更高的热传导能力,同时潜热传热量也会增大。此外,针对绝热段长度为50mm脉动热管,分析了三种尺寸L形结构的运行特性,发现仅蒸发段水平放置,以及绝热段1/2与蒸发段一起水平放置时可成功启动;但蒸发段和绝热段全部水平放置时,管内始终处于下气上液分布状态,从而未能启动。研究结果为脉动热管在复杂环境中的应用提供了参考。
基金the National Natural Science Foundation of China(51101072)Technology Development Program of Jilin Province(20150307015GX and 20160204058GX).
文摘The stretch bending of L-section variable-curvature SUS301L stainless-steel roof bending beams for metro vehicles was numerically simulated.The causes of defects such as wrinkling,section distortion,and poor contour accuracy were analysed,and the corresponding control methods were proposed.The simulation results demonstrated that wrinkling in the small-arc segment could be eliminated by setting the die clearance and adjusting the elongation reasonably.Owing to the sidewall shrinkage of the profile in the process of stretch bending,the die groove depth was correspondingly reduced.Each section of the profile was effectively supported by the bottom of the die groove,and the section distortion could be controlled.Springback was the main reason for the poor contour accuracy,which could be compensated by modifying the die surface based on the springback value.Using the above defect control methods,forming experiments were performed on a new type of stretch bending die with variable die clearance and groove depth developed in this work.Finally,high-quality components were obtained,which verified the efficacy of the defect control methods.
文摘以麝香百合系L型"新铁炮"和OT型"黄色风暴"百合植株的子房、花药为材料,在离体条件下采用不同的授粉方式进行L×OT和OT×L的组间杂交,期望获得兼有父母本优良特点的百合杂交种。其研究结果,获最佳的材料灭菌方法为先用酒精消毒0.5 m in再用升汞消毒6 m in;采用切割子房授粉的方式可获得较高的子房膨大率;筛选出MS+0.02 mg/L NAA的培养基为杂交种子最佳培养基,其所含的蔗糖浓度为6%。
