API RP 684:2010 pdf download

API RP 684:2010 pdf download.API Standard Paragraphs Rotordynamic Tutorial: Lateral Critical Speeds, Unbalance Response, Stability, Train Torsionals, and Rotor Balancing.
Another example of the misapplication of the evacuated housing design is shown in Figure 3-14. In this case, [he oil is introduced with a single housing hole between each set of tilting pads at the pad’s axial centerline. The Pad length to diameter ratio is 1.0 resulting in a relatively long pad. The designer, desiring lower pad operating temperatures, used open end seals that resulted in a relatively low housing pressure of 1.3 psig. This low housing pressure coupled with the long pad caused oil starvation and a subsynchronous rotor vibration. The spray bar design shown in Figure 3-16 distributes the oil along the full axial length of the pad and was successful in eliminating the subsynchronous rotor vibration.
A final example of the misapplication of the evacuated housing design is shown in Figure 3-15. In this case, the oil is introduced with a mushroom orifice spray between each set of tilting pads at the pad’s axial centerline. Again, the pad length to diameter ratio is 1 .0 resulting in a relatively long pad. As before, lower pad operating temperatures were desired prompting the designer to used open end seals. Clearly from Figure 3-15, no oil is directly sprayed toward the pad’s axial ends resulting in a 1.9-in. oil free” zone at both pad ends. This again caused oil starvation and a subsynchronous rotor vibration. A spray bar similar to the one illustrated in Figure 3-16 again solved the problem.
While it may appear that these tilting pad bearings caused a rotor instability, it was the misapplication of the evacuated
Squeeze film dampers are widely applied in aircraft jet engines to supplement the otherwise negligible damping inherent in the rolling element bearings used in this type of machinery. Although their main purpose is to reduce rotor response amplitudes, they provide some improvement in the stability of the rotor system. Squeeze film dampers are also used in a variety of land-based machinery operating on oil film bearings. Of these applications, they are more frequently used in high-pressure centrifugal compressors to eliminate instability problems. although they are also used to reduce the critical speed response characteristics of machines with highly flexible rotors. A brief history of the development and early applications of squeeze film dampers along with a general discussion on theoretical models and design considerations is given in Zeidan, et al. [II.
Although tilting pad bearings are routinely used to avoid oil whirl instability problems. machines with flexible rotors supported on tilting pad journal bearings may be prone to instability if there exists an external destabilizing force of magnitude that exceeds the restoring damping of the beariiig. This instability may he avoided by either eliminating the destabilizing mechanism, raising the rotor’s first damped natural frequency, or by adding sutlicient external damping to raise the stability threshold. In cases where it is not possible to eliminate the instability mechanism or raise the natural frequency. the only practical solution is to add external damping. Since damping is also a dynamic stiffness, adding external damping to a rotor supported on relatively stiff.