Browsing by Subject "Bearing"
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Item Experimental evaluation of wire mesh for design as a bearing damper(Texas A&M University, 2004-11-15) Choudhry, Vivek VaibhavWire mesh vibration dampers have been the subject of some very encouraging experiments at the Texas A&M Turbomachinery laboratories for the past several years and have emerged as an excellent replacement for squeeze film dampers. Their capability to provide damping for a wide range of temperatures (even cryogenic), fluid free operation and ability to perform even when soaked with lubricants makes them a suitable option as a bearing damper. Experiments were conducted to investigate the effect of design parameters like axial thickness and axial compression that influence the characteristics of wire mesh as a bearing damper. Two groups of wire mesh were tested to show that the stiffness and damping are directly proportional to the axial thickness, if all the other parameters are kept constant. Tests on four wire mesh donuts of different radial thickness showed that stiffness and damping vary inversely with radial thickness. Rigorous tests were also conducted to quantify the effects of axial compression, radial interference and displacement amplitude on stiffness and damping of the wire mesh. Another novel kind of mesh damper tested was comprised of two small segments instead of a whole donut. The results showed that wire mesh exhibited good damping characteristics even when used in small segments. Empirical expressions were developed using MathCADTM worksheets, and an existing ExcelTM design worksheet was modified to include these factors. The effect of frequency variation was also included to give a comprehensive design tool for wire mesh. A new design worksheet was developed that can predict rotordynamic coefficients for a wire mesh bearing damper having a different size as well as different installation and operational conditions.Item A fundamental approximation in MATLAB of the efficiency of an automotive differential in transmitting rotational kinetic energy(2012-05) Vaughn, James Roy; Matthews, Ronald D.; Bryant, Michael D.The VCOST budgeting tool uses a drive cycle simulator to improve fuel economy predictions for vehicle fleets. This drive cycle simulator needs to predict the efficiency of various components of the vehicle's powertrain including any differentials. Existing differential efficiency models either lack accuracy over the operating conditions considered or require too great an investment. A fundamental model for differential efficiency is a cost-effective solution for predicting the odd behaviors unique to a differential. The differential efficiency model itself combines the torque balance equation and the Navier-Stokes equations with models for gear pair, bearing, and seal efficiencies under a set of appropriate assumptions. Comparison of the model with existing data has shown that observable trends in differential efficiency are reproducible in some cases to within 10% of the accepted efficiency value over a range of torques and speeds that represents the operating conditions of the differential. Though the model is generally an improvement over existing curve fits, the potential exists for further improvement to the accuracy of the model. When the model performs correctly, it represents an immense savings over collecting data with comparable accuracy.Item Rotordynamic coefficients for a load-between-pad, flexible-pivot tilting pad bearing at high loads(Texas A&M University, 2006-10-30) Hensley, John EricThe dynamic and static performance of a flexure-pivot tilting pad bearing is presented at a load between pad configuration for various load and speed combinations. A similar work performed on the same bearing at lower loads ranging from 0-1 MPa (0-150 psi) by Al-Ghasem was tested, whereas the current work investigates effects in the load range between 1-2.2 MPa (150-320 psi). The bearing design parameters include: 4 pads with pad arc angle 72???? and 50% pivot offset, pad axial length 0.0762 m (3 in), pad radial clearance 0.254 mm (0.010 in), bearing radial clearance 190.5 ????m (0.0075 in), preload 0.25, and shaft nominal diameter of 0.11684 m (4.600 in). An important distinction between the two sets of tests is the difference in experimental bearing radial clearance, which for this case measured 208 ????m (0.00082 in), and for Al-Ghasem??????s was 165.1 ????m (0.0065 in). The rotordynamic coefficients are determined experimentally using a test rig equipped with motion and load sensors. The rig is modeled using Newton??????s laws, which is converted from the time to frequency domain using Fourier Transform to give complex dynamic stiffnesses. From the resulting complex dynamic stiffnesses the associated real and imaginary components are plotted as a function of excitation frequency and curve fitted via linear regression to give the rotordynamic coefficients. The primary objectives were to determine whether the real component of the complex dynamic stiffnesses could be better modeled with or without the mass coefficient and to contrast the rotordynamic coefficients with an analytical model. Only in the load range of 1 to 2.2 MPa were the unloaded direct mass coefficients near or at 0, which would allow for a [K][C] model to be used. The remaining real components are better represented with the mass term. The analytical model generally overpredicted the stiffness, damping and mass coefficients, especially for the direct components; the trends were generally consistent.Item Rotordynamic Performance of a Flexure Pivot Pad Bearing with Active and Locked Integral Squeeze Film Damper Including Predictions(2012-02-14) Agnew, Jeffrey ScottTests are performed on a flexure-pivot-pad tilting-pad bearing with a series integral squeeze film damper in load-between-pads configuration, with both active and locked damper. The damper effects are negated when locked, resulting in a flexure-pivot-pad bearing only. Experimental tests provide static performance data and dynamic stiffnesses from which rotordynamic coefficients are extracted. The following two excitation schemes are implemented: (1) multi-frequency, single direction excitation and (2) single-frequency, rotating load excitation (or "circular excitation"). The XLTRC2 Rotordynamics Software Suite provides stiffness and damping coefficient, eccentricity, and power loss predictions for the locked damper bearing. Test conditions include the rotor-speed range of 4000-12000 rpm and the unit-load range of 0-862 kPa (0-125 psi). Dynamic tests utilizing the multi-frequency excitation for the locked and active damper bearing configurations both show that the real portion of the dynamic stiffness is well modeled by a quadratic curve fit, and the imaginary portion representing the damping is a linear function of excitation frequency. This means that frequency independent coefficients can be obtained when an added mass term is included. While stiffness coefficients are lower for the active damper bearing, damping coefficients remain almost constant between the locked and active damper configurations. A simulation shows that, although the damping coefficients do not change significantly, the reduced stiffness provided by the damper results in greater effective damping. Static performance tests for the locked and active damper bearing indicate low cross-coupling, as shown by the eccentricity and low attitude angle measurements. Pad metal temperature measurements show a smaller temperature differential along the pad arcs for the active damper bearing, than observed for the locked damper case. Frictional power loss is estimated based on lubricant temperature rise and does not differ significantly for the two bearing configurations.Item Static and dynamic characteristics for a two-axial-groove bearing and a pressure-dam bearing(2009-06-02) Al Jughaiman, Bader K.This thesis compares experimental static and dynamic force characteristics for a two-axial-groove bearing and a pressure-dam bearing without a relief track. The thesis also compares experimental results to predictions from a numerical analysis. The tested pressure-dam bearing has s ?= 130?, ' k =3.4~4.2, and d L ? =0.75. The test results show that eccentricity for both bearings decreases as Sommerfeld number increases. However, the pressure-dam bearing maintains a minimum eccentricity of about 0.5 at high speeds. The results also show that the attitude angle for both bearings increases as Sommerfeld number increases. The maximum attitude angle for the axial-groove bearing is 90? at noload. However, the attitude angle for the pressure-dam bearing increases above 90? at no-load as speed increases. A dynamic test shows that the pressure-dam bearing has higher direct stiffness and damping at high Sommerfeld number because of the increase in eccentricity. However, as Sommerfeld number decreases, the difference between stiffness and damping coefficients of both bearings diminishes. The dynamic test also shows that both bearings have significant added mass coefficients in the laminar flow region that decrease as eccentricity increases. The estimated axial-groove bearing whirlfrequency ratio (WFR) from experimental results is 0.45. The WFR of the pressure-dam bearing reduces to 0.41 at high Sommerfeld numbers. Numerical analysis shows that the pressure-dam bearing can have lower WFR if the dam arc length is increased to 150?. Numerical analysis also shows that stability can be improved further by adding a relief track. Generally, the numerical analysis under predicts the bearings? eccentricity and dynamic force coefficients with better agreement at low Sommerfeld numbers.