Print ISSN: 1681-6900

Online ISSN: 2412-0758

Keywords : Rotor

Optimum Design of Journal Bearings Dimensions for Rotating Machines

Tariq M. Hammza; Ehab N. Abas; Nassear R. Hmoad

Engineering and Technology Journal, 2020, Volume 38, Issue 10A, Pages 1481-1488
DOI: 10.30684/etj.v38i10A.1093

The values of Many parameters which involve in the design of fluid film journal bearings mainly depend on the bearing applied load when using the conventional design method to design the journal bearings, in this study, as well as applied bearing load, the dynamic response and critical speed have been used to calculate the dimensions of journal bearings. In the field of rotating machine, especially a heavy-duty rotating machines, the critical speed and response are the main parameters that specify bearing dimensions. The bearing aspect ratio (bearing length to bore diameter) and bearing clearance have been determined based on rotor maximum critical speed and minimum response displacement. The analytical solution of rotor Eq. of motion was verified by numerical solution via using ANSYS Mechanical APDL 18.0 and by comparing the numerical solution with the preceding study. The final study results clearly showed that the bearing aspect ratio has little effect on the critical speed, but it has a high effect on the dynamic response also the bearing clearance has little effect on the critical speed and considerable effect on the dynamic response. The study showed that the more accurate values of bearing aspect ratio to make the response of rotor as low as possible are about 0.65 - 1 and bearing percent clearance is about 0.15 - 0.2 for different rotor dimensions.

Improving the Stability and Critical Speed of Rotor Bearing System By Using External Damping Source

Tariq M. Hammza; Nassear R. Hmoad; Ehab N. Abas

Engineering and Technology Journal, 2020, Volume 38, Issue 3A, Pages 319-324
DOI: 10.30684/etj.v38i3A.344

Improving the essential factors of rotor bearing system are the aim of this study. In addition to the presence of two ball bearings to support the rotor, two additional fluid film journal bearings have been used as an external damping sources. The ANSYS Mechanical APDL 18.0 was used to model rotor bearing system with existence of two additional fluid film journal bearings. Matlab software has been used to achieve the analytical solution. The results clearly showed that the maximum response displacement strongly decreasing and the critical speed has been enhance by using an external damping source as well as the stability of rotor bearing system has been improved due to increasing damping of rotor system where the response displacement decreasing by 99% and critical speed increasing by 0.6% when using an external damping sources. The position of damping source has an important effect on the maximum response displacement and the more decreasing value of response displacement has been achieved when the damping source become as close as possible to the disk position.

Application of a Finite Element Package for Modeling Rotating Machinery Vibrations

Farouk O. Hamdoon

Engineering and Technology Journal, 2009, Volume 27, Issue 12, Pages 2268-2276

ANSYS has no module to analyze dynamics of rotor-bearing systems,
especially to calculate critical speeds. But it has element types, such as beam element
and matrix27 element, which can be modeled as stiffness, damping and mass matrix.
In this paper, BEAM4 element and MATRIX27 element are adopted to model the
shaft, rotating disks and bearings. Some ideas are presented to deal with critical speeds
calculation using ANSYS. The accuracy of the model and the solution technique have
been demonstrated by comparison with results of previous publications. Very good
agreement has been obtained.