Browsing by Author "Delgado-Marquez, Adolfo"
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Item A linear fluid inertia model for improved prediction of force coefficients in grooved squeeze film dampers and grooved oil seal rings(2009-05-15) Delgado-Marquez, AdolfoIn Squeeze Film Dampers, (SFD), grooves (deep or shallow) are used to feed oil into the damper and prevent oil starvation within the fluid film lands. In oil seals with film land of clearance c, short shallow grooves (depth ? 15c, length ? 30c) are machined to reduce the cross-coupled stiffness coefficients, and thus improve the seal stability characteristics. Moreover, test stands for these devices can also incorporate grooves or recesses as part of oil feeding/ discharge arrangements. A common assumption is that these grooves do not influence the test system forced response. However, unexpected large added mass coefficients are reported in these configurations and not adequately predicted. In the case of grooved oil seals, experimental results also show that circumferential grooves do aid to reduce cross-coupled force coefficients but to a lesser extent than predictions otherwise indicate. A linear fluid inertia model for analysis of multiple-groove SFD or oil seal configurations is advanced. A perturbation analysis for small motion about a journal centered and off-centered position yields zeroth and first order flow equations defined at each individual flow region (land and grooves) of constant clearance ( c ).The analysis considers both the circumferential and axial dynamic pressure variations across the groove and land regions. At the groove regions, an effective groove depth ( d? ) and effective clearance (c d c ? ? = + ) are defined based on qualitative observations of the laminar flow pattern through annular cavities. This depth differs from the actual physical groove depth. The boundary conditions at the inlet and exit plane are a function of the geometric configuration. Integration of the resulting dynamic pressure fields on the journal surface yields the force coefficients (stiffness, damping, and inertia). Comparisons between predicted and experimental force coefficients for a grooved oil seal and a SFD show excellent correlation over a narrow range of effective groove depths. The results confirm that large added mass coefficients are associated to the feed/discharge grooves in the scrutinized test configurations. Furthermore, predictions, benchmarking experimental data, corroborate that short inner land grooves in an oil seal do not isolate the pressure field of the adjacent film lands, and hence contribute greatly to the force response of the seal.Item Identification of force coefficients in a squeeze film damper with a mechanical seal(Texas A&M University, 2006-04-12) Delgado-Marquez, AdolfoSqueeze film dampers (SFDs) with low levels of external pressurization and poor end sealing are prone to air entrapment, thus reducing the damping capability. Furthermore, existing predictive models are too restrictive. Single frequency, unidirectional load and centered circular orbit experiments were conducted on a revamped SFD test rig. The damper journal is 1" in length and 5" in diameter, with nominal clearance of 5 mils (0.127 mm). The SFD feed end is flooded with oil, while the discharge end contains a recirculation groove and four orifice discharge ports to prevent air ingestion. The discharge end is fully sealed with a wave-spring that pushes a seal ring into contact with the SFD journal. The measurements conducted without and with lubricant in the squeeze film lands, along with a frequency domain identification procedure, render the mechanical seal dry-friction force and viscous damping force coefficients as functions of frequency and motion amplitude. The end seal arrangement is quite effective in eliminating side leakage and preventing air entrainment into the film lands. Importantly enough, the dry friction force, arising from the contact forces in relative motion, increases significantly the test element equivalent viscous damping coefficients. The identified system damping coefficients are thus frequency and amplitude of motion dependent, albeit decreasing rapidly as the motion parameters increase. Identified force coefficients, damping and added mass, for the squeeze film damper alone agree very well with predictions based on the full film, short length SFD model.