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Bearing Design in Machinery Episode 2 Part 2

Tham khảo tài liệu 'bearing design in machinery episode 2 part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Fig. 9-5 Foil bearing. 9.8 ANALYSIS of a foil bearing The following analysis is presented to illustrate the concept of the hydrodynamic foil bearing. The foil is stretched around a journal of radius R rotating at constant speed and resulting in a tangential velocity U at the journal surface. A vertical external load F is applied to the journal that is equal to the load capacity Wof the fluid film. The following assumptions are made for solving the load capacity Wof the foil bearing. 1. The foil sleeve is parallel to the journal surface constant clearance along the lower half of the journal due to its high flexibility. In turn there is no localized pressure concentration. Copyright 2003 by Marcel Dekker Inc. All Rights Reserved. 2. The contributions to load-carrying capacity of the converging and diverging ends are neglected. 3. The simplified equation for an infinitely long bearing can be applied. This problem is similar to that of the sled of Example problem 4-4. In the sled problem there is also a converging clearance between a flat plate and a cylinder. Let us recall that the film thickness in the converging region between a flat plate and a cylinder is given by the following equation see equation 4-24 h 0 h0 R 1 cos 0 9-1 Here 0 is measured from the line x 0. The expression for the film thickness h is approximated by see Sec. 4.10.1 h x h0 9-2 2R This approximation is valid within the relevant range of the converging region. The boundary conditions of lubricant pressure is p 0 at x 1. The Reynolds equation for an infinitely long bearing is dp 6 uV 9-3 dx h3 In the parallel region h h0. So it follows from Eq. 9-3 that dp dx 0 parallel region . This means that the pressure is constant within the parallel region. The pressure acting over the entire lower parallel region is constant and solely responsible for carrying the journal load. The force dW on an elementary area dA LR d0 is dW p0LR d0 9-4 This force is in the direction normal to the journal surface. The .