Genetic Algorithms to the Nesting Problem in the Leather Manufacturing Industry

The nesting problem in the leather manufacturing is the problem of placing a set of irregularly shaped pieces (called stencils) on a set of irregularly shaped surfaces (called leathers sheets). This paper presents a novel and promising processing approach. After the profile of leather sheets and stencils is obtained with digitizer, the discretization makes the processing independent of the specific geometrical information. The constraints of profile are regarded thoroughly. A heuristic bottom-left placement strategy is employed to sequentially locate stencils on sheets. The optimal placement sequence and rotation are deterimined by genetic algorithms (GA). A natural concise encoding method is developed to satisfy all the possible requirements of the leather nesting problem. The experimental results show that the proposed algorithm can not only be applied to the normal two-dimensional nesting problem, but also especially suitable for the placement of multiple twodimensional irregular stencils on multiple two-dimensional irregular sheets.     

计入弹性变形的水润滑轴承润滑性能

基于有限元软件ANSYS CFX对水润滑滑动轴承进行流固耦合分析,研究空化作用对水润滑滑动轴承水膜的影响,得到了水膜周向和轴向的压力分布以及轴瓦的弹性变形分布,进一步分析了轴瓦材料弹性模量、偏心率、转速对水膜压强分布以及对轴瓦弹性变形的影响规律。结果表明:计入轴瓦的弹性变形后,水膜的最大压强减小,水膜压力分布更加均匀;水膜最大压强随着偏心率、弹性模量、转速的增大而增大,而轴承弹性变形随着偏心率、转速的提高而增大,随着弹性模量的增大而减小;相同条件下,随着弹性模量的增大,水膜发生空化的位置提前。     

导水槽结构对水润滑滑动轴承水膜压强影响分析

导水槽是保证水润滑滑动轴承润滑性能的重要组成结构,而且其会对轴承的承载能力产生较大影响.通过仿真分析发现,导水槽会破坏稳定动压水膜的形成,造成水膜压强波动.通过对不同导水槽结构轴承的仿真与对比分析,发现导水槽对轴承承载能力产生的影响会随着导水槽尺寸及导水槽所在位置处压强的增大而增大.因此,在开设导水槽的轴承结构设计中,应尽量减小导水槽的尺寸,并避免将导水槽分布在轴承下方的主要承载区域.     

基于CFD的水润滑斜面推力轴承承载能力分析

基于计算流体动力学(CFD)理论,建立不同的水膜润滑模型并进行仿真计算,分析最小水膜厚度、瓦块倾斜角度、瓦斜面升高比及转速对某斜面推力轴承的承载能力的影响规律,为水润滑斜面推力轴承的设计提供理论依据.结果表明:最小水膜厚度和转速是影响轴承承载能力的重要因素;当最小水膜厚度和转速一定时,存在最优的瓦块倾斜角度或瓦斜面升高比使轴承承载能力最大,最优瓦斜面升高比为0.656,最优瓦块倾斜角度可以通过最小水膜厚度与最优瓦斜面升高比计算得到.