分数导数型粘弹性阻尼器的动力学有限元方程及数值解

采用分数导数Kelvin固体模型建立粘弹性阻尼器在外力作用下的分数阶动力学有限元方程,并利用Newmark数值积分法得到数值解.结果表明,Zhang and Shimizu分数导数数值积分法能够很好地满足精度、收敛性和稳定性等要求,通过减小时间步长能够有效减小因引入Newmark而导致的周期误差,从而提高计算精度.     

高光谱遥感图像空谱联合分类方法研究

在遥感影像研究领域里,高光谱数据分类是一个热点问题。近年来,在这个问题上涌现出很多研究方法,然而,大多数方法都是用浅层的方法提取原始数据的特征。将深度学习的方法引入高光谱图像分类中,提出一种新的基于深信度网络(DBN)的特征提取方法和图像分类架构用于高光谱数据分析。将谱域-空域特征提取和分类器相结合提高分类精度。使用高光谱数据进行实验,结果表明该分类器优于当前的一些先进的分类方法。此外,本文还揭示了深度学习系统在高光谱图像分类研究中具有的巨大潜力。     

FE analysis of metal flow and weld seam formation in a porthole die during the extrusion of a magnesium alloy into a square tube and the effect of ram speed on weld strength

The present communication concerns a detailed analysis of metal flow into a porthole extrusion die to produce a thin-walled square magnesium tube by means of three-dimensional FE simulation in both the transient state and steady state. The research was aimed to get an insight into the longitudinal weld seam formation during extrusion through porthole dies and to evaluate the factors determining the quality of the weld seams. FE simulation revealed distinctive stages at the beginning of an extrusion cycle, corresponding to the changes in extrusion pressure during the process. It showed that the commonly observed defect at the extrudate head was due to entrapped air under the bridges in the upper part of the welding chamber. The dead metal zones existed at the corners between the container and die face and between the bottom and sidewall of the welding chamber. Because of the friction at the die bearing, the metal flow through the die bearing resembled laminar flow. Only the virgin metal from the interior of the billet flowed along the bridges and formed the welding seams. As ram speed increased, the mean stresses and temperatures on the welding plane in the welding chamber increased, which was reflected in the increases in extrusion pressure and extrudate temperature, being beneficial to the solid-state bonding at the weld seams. Tensile tests confirmed that extrusion at a higher ram speed led to enhanced transverse tensile strength and strain of the extruded square tube, as a result of improved bonding at the longitudinal weld seams.     

提高自由镦粗成形质量的工艺方法与有限元模拟

讨论各种提高镦粗成形质量的工艺方法,分析扭压复合加载成形过程,并比较这些方法的优缺点。扭压复合加载通过把摩擦力转化成促进金属流动的主动力,将提高金属流动性。运用DEFORM 3D软件模拟了Al2017在室温下的扭压复合加载变形过程,其结果证明此方法有利于减小镦粗鼓形和变形力,提高变形均匀性。     

焊缝管液压胀形模拟建模及变形规律的研究

基于周向显微硬度的分布及经验公式法,确立了STKM11A焊缝管热影响区的流动应力;通过对热影响区进行分片的方式,建立了包含焊缝和热影响区的焊缝管液压胀形的有限元模拟模型。基于该模型,模拟分析了STKM11A焊缝管液压胀形时的变形规律,如截面轮廓形状、周向壁厚分布和成形极限等,并与胀形实验结果进行对比。结果表明,液压胀形后焊缝管的截面轮廓形状不对称、壁厚分布不均匀,最小壁厚位于热影响区;包含焊缝及热影响区的有限元模型在预测焊缝管液压胀形的变形规律、极限载荷和潜在胀裂位置等方面,较其他常规模型更加精确。     

汽车覆盖件成形拉深筋的有限元模拟与优化

利用有限元法模拟某汽车高强钢横梁的成形过程,通过设置拉深筋作为材料流动控制手段。拉深筋的参数设置对成形结果影响很大,首先通过对简单形状零件拉深成形过程的模拟得出一些拉深筋参数对模拟结果的影响规律,然后对横梁拉深筋模型进行多次模拟和修改。通过比较采用等效拉深筋与真实拉深筋模型所得模拟结果,最终得出对于复杂冲压件,应该采用真实拉深筋模型进行模拟的建议。     

异型钢管辊挤成型过程的有限元模拟

利用非线性有限元分析软件MSC.Marc对方形异型钢管的无芯棒辊挤成型过程进行了有限元分析,得到了成型过程中应力与变形的分布与变化以及成型后异型管的结构形状。实验结果验证了有限元分析的正确性。研究结果为生产提供了有益的依据。     

The response of viscoelastic-frictionless bodies under normal impact

This paper presents a computational finite element model capable of simulation of the impact response of viscoelastic-frictionless bodies. The variational method is developed to drive the equations of motion. The Lagrange multiplier method is exploited to impose the nonholmonic contact constraints and convert the problem form constraint problem to unconstraint one. The constitutive equations are expressed in integral form. and involving relaxation moduli are adopted to describe the nonaging simple material. Generalized Standard Linear Solid (Wiechert) model is adopted to simulate the internal damping (viscoelastic) behavior of the structure. Wiechert model is exploited in order to drive a recursive relationship and thereby eliminate storage problem. Newmark constant average acceleration is proposed to integrate the governing equation numerically and transfer the problem into a static one for each time increment.