The continuous extrusion forming process for producing large section copper concave bus bar under different extrusion wheel angular velocities was studied by three-dimensional finite element technology based on softwa...The continuous extrusion forming process for producing large section copper concave bus bar under different extrusion wheel angular velocities was studied by three-dimensional finite element technology based on software DEFORM-3D. The rigid-viscoplastic constitutive equation was employed in the model. The numerical simulation results show that the deformation body flow velocity in the die orifice increases gradually with the increase of the extrusion wheel angular velocity. But slippage between the rod and extrusion wheel occurs when the extrusion wheel angular velocity is high. The effective stress near the die orifice enhances gradually with increasing extrusion wheel angular velocity. High stress is concentrated in adjacent regions of the flash gap. The effective strain gradient is greater near the abutment than that near the die orifice. The effective strain of the product increases gradually with increasing extrusion wheel angular velocity. In the deformation process, the deformation body temperature increases remarkably due to friction and deformation. So the cooling is necessary in the region of the die and tools.展开更多
经典的哈希分级时间轮算法在管理大规模定时器时存在响应时间长、累积时延高等缺点。该文借鉴"高速缓存"思想,提出了一种时间轮改进算法(Cached And Timing Wheels,CTW),基于多线程和缓存机制,提前查找和存储即将超时的定时...经典的哈希分级时间轮算法在管理大规模定时器时存在响应时间长、累积时延高等缺点。该文借鉴"高速缓存"思想,提出了一种时间轮改进算法(Cached And Timing Wheels,CTW),基于多线程和缓存机制,提前查找和存储即将超时的定时器。该算法能够充分利用多核CPU的性能,优化开启、查找和停止定时器的操作,提升大规模定时器的管理效率。实践表明,CTW算法在管理大规模定时器时能够缩短响应时间,消除累积时延,提高定时器精度。展开更多
文摘The continuous extrusion forming process for producing large section copper concave bus bar under different extrusion wheel angular velocities was studied by three-dimensional finite element technology based on software DEFORM-3D. The rigid-viscoplastic constitutive equation was employed in the model. The numerical simulation results show that the deformation body flow velocity in the die orifice increases gradually with the increase of the extrusion wheel angular velocity. But slippage between the rod and extrusion wheel occurs when the extrusion wheel angular velocity is high. The effective stress near the die orifice enhances gradually with increasing extrusion wheel angular velocity. High stress is concentrated in adjacent regions of the flash gap. The effective strain gradient is greater near the abutment than that near the die orifice. The effective strain of the product increases gradually with increasing extrusion wheel angular velocity. In the deformation process, the deformation body temperature increases remarkably due to friction and deformation. So the cooling is necessary in the region of the die and tools.
文摘经典的哈希分级时间轮算法在管理大规模定时器时存在响应时间长、累积时延高等缺点。该文借鉴"高速缓存"思想,提出了一种时间轮改进算法(Cached And Timing Wheels,CTW),基于多线程和缓存机制,提前查找和存储即将超时的定时器。该算法能够充分利用多核CPU的性能,优化开启、查找和停止定时器的操作,提升大规模定时器的管理效率。实践表明,CTW算法在管理大规模定时器时能够缩短响应时间,消除累积时延,提高定时器精度。
文摘为研究车辆高速运行条件下钢轨焊接接头不平顺引起的轮轨动态响应规律,利用ABAQUS软件建立轮轨有限元接触模型,引入不同形状的焊接接头不平顺作为轨道子模型边界条件,并利用一高速铁路焊接接头不平顺及轮轨垂向力实测数据验证了模型的可靠性;利用模型仿真计算不同车辆运行速度和焊接接头不平顺幅值条件下的轮轨垂向力,并分析轮轨垂向力等势线分布特征。研究结果表明:轮轨垂向力受焊接接头不平顺幅值的影响程度随车辆运行速度的增加而增大;为使钢轨焊接接头不平顺引起的轮轨垂向力不大于170 kN,不同速度等级的线路应该限定相应的焊接接头不平顺幅值管理值;对于300~350 km/h速度等级的线路,凸型焊接接头不平顺幅值不应超过0.27 mm,凹型焊接接头短波不平顺幅值不应超过0.30 mm.
