| Bionic nonsmooth effect is applied to the research of the lubrication mecha- nism about piston-cylinder friction pair in this dissertation. Aiming at the characteristic of oil storage lubrication which occurs in the micro-pits of piston surface, a mathematical model is built up in order to describe large-amplitude sloshing of the lubricating oil with the up-down motion of the piston. Then, this sloshing problem is solved by an ALE (Arbitrary Lagrange-Euler) finite element method. By an example,sloshing free surface and wave height are obtained and the effects of lubricating properties on wave height is analyzed. Meanwhile, a principle is provided for the design of the nonsmooth oil storage micro-pits. The main research achievements are as follows.(1) Biological nonsmooth phenomena and bionics application is introduced. Nonsmooth effect of earthworm's body surface excreting and storage slime is applied to the research of the lubrication about piston-cylinder friction pair. Reynolds lubrication model which described traditional smooth piston-cylinder friction pair is summarized, as well as average flow model, micro convex body contact model and mixed lubrication model considering surface roughness of piston-cylinder.(2) In order to describe the lubricating oil sloshing in nonsmooth micro-pits A mathematical model is built up based on the liquid velocity potential and free surface tracking theories, because lubricating oil film between piston and cylinder is uncontinuous and the scale of nonsmooth pits can not meet the hypothesis of Reynolds lubrication model.(3) Because the wave height of sloshing free surface is large displacement and large deformation, so an ALE finite element method is presented for the analysis of large-amplitude sloshing problems. The motion of the liquid is decomposed into the large displacement motion with the micro-pits and the large-amplitude sloshing relative to the micro-pits. By introducing ALE kinematical description in the micro-pits fixed local frame, a governing equation of large-amplitude sloshing problems is built up described by ALE method. Thus, the finite element mesh need only regenerate relatively to the micro-pits, so micro-pits wall do not need special algorithm to regenerate, but only free surface needs special regeneration algorithm to be designed. After introducing ALE kinematical description in the micro-pits fixed local frame, it can be concluded that y component of mesh velocity in the free liquid surface is ALE time derivative of free surface wave height, and x component of mesh velocity is not to be constrained, which can be arbitrarily prescribed. As a result the algorithm of free surface tracking becomes simple, convenience and accurate.(4) In order to numerically solve large-amplitude sloshing problems, a discrete ALE finite element equation is built up by principle of virtual work. Finite difference method is applied to the former equation for the time discretization, then a system of non-linear differential equations can be obtained. The predictor multic- orrector algorithm(PMA) is adopted for the iterative solution of the equations system. The effective control of the time integration step size can not only guarantee the numerical convergence and raise the iterative efficiency greatly based on iterative times and convergence condition during solving. All of these get finer effect.(5) By an example,sloshing free surface and wave height are obtained and the time of lubricating oil arriving at the inner surface of the cylinder is solved. Meanwhile, a principle is provided for the design of the nonsmooth oil storage micro-pits. Excessive distortion and winding of the mesh is avoided and the mesh-updating scheme is better.Finally, summarization and prospect are brought forth and future works to be done is presented. Oil storage effect of nonsmooth micro-pits is comparatively intuitively explained in this dissertation. In addition, some important and practical conclusions are obtained.
|
PDF Full Text Request