Ph.D Thesis


Ph.D StudentAdi Minikes
SubjectNon-Contacting Levitation and Transportation Using
Ultrasonic Vibrations-Analytical, Numerical
and Experimental Study
DepartmentDepartment of Mechanical Engineering
Supervisor Full Professors Bucher Izhak


Abstract

The squeeze-film levitation phenomenon (also referred as near-field acoustic levitation) is known to occur when a planar object is placed at close proximity to a vibrating surface. The normal oscillating motion can generate a gas film with an average pressure higher than the surrounding. Equilibrium of this load-carrying phenomenon is established through a balance between viscous flow forces and compressibility forces. Lateral motion accompanied with normal levitation occurs when the oscillatory motion between two surfaces, creates flexural traveling waves. Such a lateral motion is the result of wall shear stresses and the non-uniform lateral pressure gradients. The combination of normal and lateral forces could be used to transport planar objects without any direct contact with the driving surface. A study on the coupling effects between elastic and electro-static effects together with compressible fluid effects was advocated by a coupled numerical solver; verified experimentally. A novel analytical expression and a second order perturbation solution for the levitation force are suggested and are proved valid for a wider physical range of squeeze numbers and vibration amplitudes in comparison with existing solutions. The skin-friction force exerted on the planar surface in the presence of traveling waves was obtained analytically based on a first order perturbation solution. Energy leakages in the peripheries of the levitated object, not accounted for by the one-dimensional Reynolds equation was investigated by a two-dimensional CFD analysis of the compressible and viscous N.S equations. An original parametric method for tuning the excitation conditions to achieve pure transverse traveling waves has been developed and the non-contact levitation and transportation of planar objects was demonstrated experimentally on a dedicated prototype.