This thesis presents the static and dynamic performance data for a 5 pad tilting pad bearing in both the load-on-pad (LOP) and the load-between-pad (LBP) configurations over a variety of different loads and speeds. The bearing tested was an Orion Advantage with direct lubrication exhibiting these specifications: 5 pads, .282 preload, 60% offset, 57.87° pad arc angle, 101.587 mm (3.9995 in) rotor diameter, .1575 mm (.0062 in) diametrical clearance, 60.325 mm (2.375 in) pad length. Dynamic tests were performed over a range of frequencies to observe any frequency effects on the dynamic stfffnesses. It was found that under most test conditions the direct real part of the dynamic stiffnesses could be approximated as quadratic functions of the excitation frequency. This frequency dependency is caused by pad inertia, pad flexibility, and fluid inertia. The observed frequency dependency can be accounted for with the addition of an added mass matrix to the conventional [K][C] matrix model to produce a frequency independent [K][C][M] model. This method eliminates the often debated question over whether a stability analysis should be performed at the running speed or at the first natural frequency. Substantially large added mass terms in the loaded direction were found that approached 60 kg. Some conditions for the LBP bearing exhibited unloaded direct mass coefficients that were at or near zero, which would lead to a frequency dependent [K][C] model to be used instead. The whirl frequency ratio was found to be zero at all test conditions. Static data were also recorded which included pad temperatures, attitude angle, eccentricity, static stiffness and power loss. Some cross coupling in the form of deviation from the loaded axis was evident from the locus plots; however, the cross coupled stiffness coefficients were found to be very small relative to the direct stiffness coefficients. Both static and dynamic experimental results were compared to theoretical predictions via a bulk flow analysis. Most parameters were modeled well including the static eccentricity e dynamic direct stiffness coefficients Kxx and Kyy, which were slightly over predicted. However, the direct damping coefficients Cxx and Cyy were significantly over predicted.

Oil-free microturbomachinery (MTM) are inevitably subjected to base or foundation excitations: multiple periodic load excitations from internal combustion (IC) engines in turbochargers, for example. Too large base excitations can produce severe damage, even failure, due to hard collision or rubbing contact between a rotor and its bearings. Therefore, it is paramount to evaluate the reliability of rotor-air bearing systems to withstanding base load excitations. In 2008, intermittent shock excitations, up to 30 g (pk-pk), were introduced to a test rig consisting of a rotor (0.825 kg) supported on two hybrid flexure pivot tilting pad gas bearings (FPTPBs). The experiments demonstrated the reliability of the gas bearings to withstanding external transient load excitations. Presently, a shaker delivers periodic load excitations to the base plate supporting the test rig. The whole system, weighing 48 kg, is supported on two soft coil springs and its lowest natural frequency is ~5 Hz. The rod connecting the shaker to the base plate is not affixed rigidly to the test rig base. The rod merely pushes on the base plate and hence the induced based motions are intermittent with multiple impacts and frequencies. As with most practical conditions, the base motion frequencies (5-12 Hz) are low respective to the operating speed of the rotor-bearing system. Rotor speed coast down tests evidence the rotor-bearing system natural frequency when the gas bearings are supplied with feed pressures increasing from 2.36 to 5.08 bar (ab). Shaker excitation induced rotor response, relative to the bearing housings, contains the main input frequency (5-12 Hz) and its super harmonics; and because of the intermittency of the base motions, it also excites the rotor-bearing system natural frequency, with smaller motion amplitudes than synchronous motion components. The excitation of the system natural frequency does not mean rotordynamic instability. With base induced motions, the rotor motion amplitude at the system natural frequency increases as the gas bearing feed pressure decreases, as the rotor speed increases, and as the shaker input excitation frequency increases (5-12 Hz). Hence, the test rotor-air bearing system is highly sensitive to base motions, intermittent in character, in particular when the gas bearings are supplied with a low feed pressure. Predicted rotor motion responses obtained from XLTRC2 and an analytical rigid rotor model, both including the (measured) periodic base motions, show good correlation with the measurements. The research results demonstrate further the applicability of gas bearings into oil-free high speed MTM.

Comprehensive modeling of gas foil bearings (GFBs) anchored to reliable test data will enable the widespread usage of GFBs into novel turbomachinery applications, such as light weight business aircraft engines, hybrid fuel cell-turbine power systems, and micro-engines recharging battery packs for clean hybrid electric vehicles. Pressurized air is often needed to cool GFBs and to carry away heat conducted from a hot turbine in oil-free micro turbomachinery. Side end pressurization, however, demonstrates a profound effect on the rotordynamic performance of GFBs. This dissertation presents the first study that devotes considerable attention to the effect of side end pressurization on delaying the onset rotor speed of subsynchronous motions. GFB performance depends largely on the support elastic structure, i.e. a smooth foil on top of bump strips. The top foil on bump strips layers is modeled as a two dimensional (2D), finite element (FE) shell supported on axially distributed linear springs. The structural model is coupled to a unique model of the gas film governed by modified Reynolds equation with the evolution of gas flow circumferential velocity, a function of the side end pressure. Predicted direct stiffness and damping increase as the pressure raises, while the difference in cross-coupled stiffnesses, directly related to rotor-bearing system stability, decreases. Prediction also shows that side end pressurization delays the threshold speed of instability. Dynamic response measurements are conducted on a rigid rotor supported on GFBs. Rotor speed-up tests first demonstrate the beneficial effect of side end pressurization on delaying the onset speed of rotor subsynchronous motions. The test data are in agreement with predictions of threshold speed of instability and whirl frequency ratio, thus validating the model of GFBs with side end pressurization. Rotor speed coastdown tests at a low pressure of 0.35 bar evidence nearly uniform normalized rotor motion amplitudes and phase angles with small and moderately large imbalance masses, thus implying a linear rotor response behavior. A finite element rotordynamic model integrates the linearized GFB force coefficients to predict the synchronous responses of the test rotor. A comparison of predictions to test data demonstrates an excellent agreement and successfully validates the rotordynamic model.

This thesis presents the static and dynamic performance data for a 5 pad tilting pad bearing in both the load-on-pad (LOP) and the load-between-pad (LBP) configurations over a variety of different loads and speeds. The bearing tested was an Orion Advantage with direct lubrication exhibiting these specifications: 5 pads, .282 preload, 60% offset, 57.87° pad arc angle, 101.587 mm (3.9995 in) rotor diameter, .1575 mm (.0062 in) diametrical clearance, 60.325 mm (2.375 in) pad length. Dynamic tests were performed over a range of frequencies to observe any frequency effects on the dynamic stfffnesses. It was found that under most test conditions the direct real part of the dynamic stiffnesses could be approximated as quadratic functions of the excitation frequency. This frequency dependency is caused by pad inertia, pad flexibility, and fluid inertia. The observed frequency dependency can be accounted for with the addition of an added mass matrix to the conventional [K][C] matrix model to produce a frequency independent [K][C][M] model. This method eliminates the often debated question over whether a stability analysis should be performed at the running speed or at the first natural frequency. Substantially large added mass terms in the loaded direction were found that approached 60 kg. Some conditions for the LBP bearing exhibited unloaded direct mass coefficients that were at or near zero, which would lead to a frequency dependent [K][C] model to be used instead. The whirl frequency ratio was found to be zero at all test conditions. Static data were also recorded which included pad temperatures, attitude angle, eccentricity, static stiffness and power loss. Some cross coupling in the form of deviation from the loaded axis was evident from the locus plots; however, the cross coupled stiffness coefficients were found to be very small relative to the direct stiffness coefficients. Both static and dynamic experimental results were compared to theoretical predictions via a bulk flow analysis. Most parameters were modeled well including the static eccentricity e dynamic direct stiffness coefficients Kxx and Kyy, which were slightly over predicted. However, the direct damping coefficients Cxx and Cyy were significantly over predicted.

A hybrid bearing designed for use in a next generation turbo-pump is evaluated for the performance of initial lift-off, referred to as start-transient. The radial test rig features a high-speed spindle motor capable of 20,000 rpm that drives a 718 Inconel rotor attached via a high-speed coupling. The drive end is supported by ceramic ball bearings, while the hybrid bearing supports the opposite end. A magnetic bearing delivers the applied loading along the mid-span of the rotor. Many parameters, including ramp rate [rpm/s] (drive torque), supply pressure at 15,000 rpm, magnitude of the applied load, and load orientation, are varied to simulate different start-transient scenarios. The data are recorded in .dat files for future evaluation of transient predictions. Analysis of the data includes an evaluation of hydrodynamic and hydrostatic liftoff, an assessment of rub from passing through a lightly damped critical speed, and observation of pneumatic hammer instability. Hydrodynamic lift-off occurs when the hydrodynamic pressure, resulting from the relative motion of two surfaces, overcomes the forces acting on the rotor; no indication of hydrodynamic lift-off is provided. Hydrostatic lift-off results from the external supply pressure (which for this test rig is speed dependent) overcoming the forces acting on the rotor as determined from rotor centerline plots. With 0.263 bar applied unit load in the vertical direction, hydrostatic lift-off occurs at 0 rpm and 2.08 bar supply pressure. With a much higher load of 1.53 bar, hydrostatic lift-off is at 12,337 rpm and 10.7 bar supply pressure. The required supply pressure for hydrostatic lift-off is approximately a linear function of the applied unit load. In a turbopump, hydrostatic lift-off depends on the speed because the supply pressure is proportional to the speed squared. With the load in the horizontal direction, hydrostatic lift-off occurs at lower speeds and pressures. The ramp rate did not affect the required supply pressure for hydrostatic lift-off. A lower supply pressure at 15,000 rpm lowered the required supply pressure for hydrostatic liftoff as well as the natural frequencies creating a rub. The hydrostatic lift-off speed should be minimized to avoid damage to the rotor/bearing surfaces due to contact.

Comprehensive modeling of gas foil bearings (GFBs) anchored to reliable test data will enable the widespread usage of GFBs into novel turbomachinery applications, such as light weight business aircraft engines, hybrid fuel cell-turbine power systems, and micro-engines recharging battery packs for clean hybrid electric vehicles. Pressurized air is often needed to cool GFBs and to carry away heat conducted from a hot turbine in oil-free micro turbomachinery. Side end pressurization, however, demonstrates a profound effect on the rotordynamic performance of GFBs. This dissertation presents the first study that devotes considerable attention to the effect of side end pressurization on delaying the onset rotor speed of subsynchronous motions. GFB performance depends largely on the support elastic structure, i.e. a smooth foil on top of bump strips. The top foil on bump strips layers is modeled as a two dimensional (2D), finite element (FE) shell supported on axially distributed linear springs. The structural model is coupled to a unique model of the gas film governed by modified Reynolds equation with the evolution of gas flow circumferential velocity, a function of the side end pressure. Predicted direct stiffness and damping increase as the pressure raises, while the difference in cross-coupled stiffnesses, directly related to rotor-bearing system stability, decreases. Prediction also shows that side end pressurization delays the threshold speed of instability. Dynamic response measurements are conducted on a rigid rotor supported on GFBs. Rotor speed-up tests first demonstrate the beneficial effect of side end pressurization on delaying the onset speed of rotor subsynchronous motions. The test data are in agreement with predictions of threshold speed of instability and whirl frequency ratio, thus validating the model of GFBs with side end pressurization. Rotor speed coastdown tests at a low pressure of 0.35 bar evidence nearly uniform normalized rotor motion amplitudes and phase angles with small and moderately large imbalance masses, thus implying a linear rotor response behavior. A finite element rotordynamic model integrates the linearized GFB force coefficients to predict the synchronous responses of the test rotor. A comparison of predictions to test data demonstrates an excellent agreement and successfully validates the rotordynamic model.

Magnetic bearings have been researched by the National Aeronautics and Space Administration (NASA) for a very long time to be used in wide applications. This research was to assemble and test an axial thrust electromagnetic bearing, which can handle 1000 lb-f of axial thrust load, when rotating at high speed, in a high temperature environment of 1000 0F. This high temperature magnetic bearing system would be used in high performance, high speed and high temperature applications like space vehicles, jet engines and deep sea equipment. An experimental procedure was developed to measure actual load capacity of the designed bearing in the test rig. All the results obtained from the experiment were compiled and analyzed to determine the relation between bearing force, applied current and temperature. The thesis incorporates the assembly, testing of the electromagnetic bearing at various speeds and temperatures and compare predicted to measured force vs. speed, current, gap and temperature. The results showed that the high temperature thrust magnetic bearing is capable of handling 1000 lb-f at 10000F and 5500 rpm.

Thesis (D. Min.)--Concordia Theological Seminary, Ft. Wayne, 1992. / Abstract. Includes bibliographical references (leaves 215-219).

Thesis (D. Min.)--Biblical Theological Seminary, 2001. / Includes bibliographical references (leaves 103-108).

This report was produced at the request of ABB Robotics and the work was conducted at their facilities in Västerås, Sweden. In the development of industrial robots the structures are slimmed to increase the accuracy and speed. When conducting finite element analysis on the robots the accuracy of the component modelling and definitions of the boundary conditions becomes more important. One such component is the ball bearing which consist of several parts and has a nonlinear behavior where the balls are in contact with the rings. The task given was to develop new methods to model roller bearings in Siemens finite element modelling software NX Nastran. Then conduct a strain measurement, to compare the methods to real experimental values. The goal with the report is to find one or more methods to model roller bearings, with accurate results, that can beused in their development work. The report was conducted by first doing a study on bearings and finite element modeling, and learning to use the software NX Nastran. Then the development of the methods were done by generating ideas for bearing models and testing them on simple structures. Nine methods was produced and a tenth, the method used to model bearings today, was used as a reference. The methods was used to build bearing models in a finite element model of a six axis robot wrist. Simulations were done on the models with different load cases and the results were compared to a strain measurement of the wrists real counterpart. Only six of the models were analyzed in the result, since four of the models returned results that were deemed unusable. When compiling the result data no model was found to accurately recreate the stresses in every load case. Three methods, that allow deformation, performed similarly. One of them is suggested to be used as modelling method in the future. Worst of the methods, according to the results compiled, was found to be the method used today. It fails to describe local stresses around the bearing. For continued work it is suggested that linear contact elements is studied further. Four out of five models constructed with linear contact elements failed to return satisfactory results.