Determination of Journal Bearing Stiffness and Damping at Hydropower Generators Using Strain Gauges

2005 ◽  
Author(s):  
Rolf K. Gustavsson ◽  
Mattias L. Lundstro¨m ◽  
Jan-Olov Aidanpa¨a¨
Keyword(s):  
Degrees Of Freedom ◽  
Journal Bearing ◽  
Displacement Velocity ◽  
Condition Numbers ◽  
Strain Gauges ◽  
Pull Force ◽  
Bearing Load ◽  
Bearing Stiffness ◽  
Bearing Loads ◽  
Stiffness And Damping

In hydropower generators, the measurement of bearing load, vibration and shaft displacement are wildly used methods for indication of maintenance demand and troubleshooting. When measurement of bearing load and shaft displacement is performed the collected data make it possible to determine the bearing properties, such as stiffness and damping. In this paper a method to determine the bearing stiffness and damping properties for generator journal bearing in hydropower units is presented. The majority of hydropower generators are, however, not equipped with facilities for measurements of bearing loads. To provide the bearings with load sensors it is necessary to reconstruct the bearings, which is associated with heavy expenditures. In this paper an alternative method to obtain the bearing load is utilize, in which strain gauges installed on the generator bearing brackets is used. The collected data in the experiment were obtained from measurements on a 238 MW hydropower generator connected to a Francis type runner. The bracket that holds the generator bearing consists of 18 spokes and each of these spokes has been provided with strain gauges for load measurements. The displacement of the shaft has been measured relative to the generator-bearing casing. The generator-bearing model has been described as a system with two degrees of freedom containing both bearing stiffness and damping matrix as well as displacement and displacement velocity vector. When the calculation of the bearing properties are based on measured data, the irregularity in the calculated stiffness and damping has to be eliminated. To eliminate the unrealistic values of the calculated damping and stiffness, the samples that cause high condition numbers of the displacement–velocity matrix are neglected. The results of the calculation of bearing stiffness and damping are presented in polar plots. This method determines the bearing properties for the generator bearing in a certain point, the point where the generator shaft has its stationary position. The stationary position for the generator shaft depends on the static magnetic pull force acting on the generator rotor and the influence from the turbine. The influence on the bearing characteristics of nonstationary loads as acting on the bearing can be investigated. The non-stationary loads can for instance be rotor unbalance force, influence of thermal expansion and dynamical magnetic pull force. It is thereby possible to evaluate different loads effect on the generator bearing and in which way the bearing properties are affected.

High Stiffness Gas Journal Bearing Under Harmonic Excitation

1994 ◽  
Author(s):  
Krzysztof Czolczynskl
Keyword(s):  
Degrees Of Freedom ◽  
Dynamic Models ◽  
Journal Bearing ◽  
Harmonic Excitation ◽  
Harmonic Load ◽  
High Stiffness ◽  
Bearing Stiffness ◽  
Stiffness And Damping ◽  
Gas Bearing ◽  
Gas Journal Bearing

This paper presents an analysis of the dynamic response of the high stiffness gas journal bearing to a harmonic load. The dependence between the frequency of the load, and the amplitude and phase angle of the shaft vibration are estimated from numerical simulation. Results of this simulation enable an attempt of identification of the high stiffness bearing as a linear system with two (or in simplification - one) degrees of freedom, to formulate simple dynamic models of the bearing. Stiffness and damping coefficients are calculated and compared with the simple gas journal bearing. The comparison suggests, that the investigated gas bearing retains high stiffness not only for slow changes of the load which appear in its application to grinding machines, but even when the frequency of the load is equal to several rad/s.

scholarly journals Improvement of Tilting-Pad Journal Bearing Operating Characteristics by Application of Eddy Grooves

Lubricants ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 18
Author(s):  
Eckhard Schüler ◽  
Olaf Berner
Keyword(s):  
High Speed ◽  
Journal Bearing ◽  
Load Capacity ◽  
Fluid Film ◽  
Operating Characteristics ◽  
Fluid Film Bearings ◽  
Tilting Pad ◽  
Bearing Load ◽  
Bearing Loads ◽  
Tilting Pad Journal Bearing

In high speed, high load fluid-film bearings, the laminar-turbulent flow transition can lead to a considerable reduction of the maximum bearing temperatures, due to a homogenization of the fluid-film temperature in radial direction. Since this phenomenon only occurs significantly in large bearings or at very high sliding speeds, means to achieve the effect at lower speeds have been investigated in the past. This paper shows an experimental investigation of this effect and how it can be used for smaller bearings by optimized eddy grooves, machined into the bearing surface. The investigations were carried out on a Miba journal bearing test rig with Ø120 mm shaft diameter at speeds between 50 m/s–110 m/s and at specific bearing loads up to 4.0 MPa. To investigate the potential of this technology, additional temperature probes were installed at the crucial position directly in the sliding surface of an up-to-date tilting pad journal bearing. The results show that the achieved surface temperature reduction with the optimized eddy grooves is significant and represents a considerable enhancement of bearing load capacity. This increase in performance opens new options for the design of bearings and related turbomachinery applications.

Tilting Pad Journal Bearings: A Discussion on Stability Calculation, Frequency Dependence, and Pad and Pivot Flexibility

2012 ◽  
Author(s):  
Jason C. Wilkes ◽  
Dara W. Childs
Keyword(s):  
Degrees Of Freedom ◽  
Journal Bearing ◽  
Operating Temperature ◽  
Excitation Frequency ◽  
Full Model ◽  
Stability Calculation ◽  
Damping Coefficients ◽  
Tilting Pad ◽  
Stiffness And Damping ◽  
Tilting Pad Journal Bearing

For several years, researchers have presented predictions showing that using a full tilting-pad journal bearing (TPJB) model (retaining all of the pad degrees of freedom) is necessary to accurately perform stability calculations for a shaft operating on TPJBs. This paper will discuss this issue, discuss the importance of pad and pivot flexibility in predicting impedance coefficients for the tilting-pad journal bearing, present measured changes in bearing clearance with operating temperature, and summarize the differences between measured and predicted frequency dependence of dynamic impedance coefficients. The current work presents recent test data for a 100 mm (4 in) five-pad TPJB tested in load on pad (LOP) configuration. Measured results include bearing clearance as a function of operating temperature, pad clearance and radial displacement of the loaded pad (the pad having the static load vector directed through its pivot), and frequency dependent stiffness and damping. Measured hot bearing clearances are approximately 30% smaller than measured cold bearing clearances and are inversely proportional to pad surface temperature; predicting bearing impedances with a rigid pad and pivot model using these reduced clearances results in overpredicted stiffness and damping coefficients that are several times larger than previous comparisons. The effect of employing a full bearing model versus a reduced bearing model (where only journal degrees of freedom are retained) in a stability calculation for a realistic rotor-bearing system is assessed. For the bearing tested, the bearing coefficients reduced at the frequency of the unstable eigenvalue (subsynchronously reduced) predicted a destabilizing cross-coupled stiffness coefficient at the onset of instability within 1% of the full model, while synchronously reduced coefficients for the lightly loaded bearing required 25% more destabilizing cross-coupled stiffness than the full model to cause system instability. The same stability calculation was performed using measured stiffness and damping coefficients at synchronous and subsynchronous frequencies. These predictions showed that both the synchronously measured stiffness and damping and predictions using the full bearing model were more conservative than the model using subsynchronously measured stiffness and damping, an outcome that is completely opposite from conclusions reached by comparing different prediction models. This contrasting outcome results from a predicted increase in damping with increasing excitation frequency at all speeds and loads; however, this increase in damping with increasing excitation frequency was only measured at the most heavily loaded conditions.

An Analytical Complete Model of Tilting-Pad Journal Bearing Considering Pivot Stiffness and Damping

2010 ◽  
Vol 133 (1) ◽  
Author(s):  
Zhiyong Yan ◽  
Yi Lu ◽  
Tiesheng Zheng
Keyword(s):  
Degrees Of Freedom ◽  
Journal Bearing ◽  
Local Coordinate System ◽  
Dynamical Behavior ◽  
Complete Model ◽  
Damping Coefficients ◽  
Tilting Pad ◽  
Generalized Force ◽  
Stiffness And Damping ◽  
Tilting Pad Journal Bearing

Considering the freedom of pad tilting and pad translation along preload orientation, an analytical complete model, as well as mathematical method, which contains 2n+2 degrees of freedom, is presented for calculating the dynamical characteristics of tilting-pad journal bearing. Based on the motion relationship of shaft and pad, the local coordinate system, the generalized displacement, and the generalized force vector are chosen. The concise transformation of generalized displacement, generalized force, and its Jacobian matrix between the local and global coordinate systems are built up in matrix form. A fast algorithm using the Newton–Raphson method for calculating the equilibrium position of journal and pads is proposed. The eight reduced stiffness and damping coefficients can be obtained assuming that the journal and all pads are subject to harmonic vibration. Numerical results show that the reduced damping coefficients and the threshold speed can be effectively enhanced by giving suitable pad pivot stiffness and damping simultaneously, and this analytical method can be applied to analyze dynamical behavior of the tilting-pad journal bearing rotor system.

Dynamic Characteristics of TEHD Tilt Pad Journal Bearing Simulation Including Multiple Mode Pad Flexibility Model

1993 ◽  
Author(s):  
Jinsang Kim ◽  
Alan Palazzolo
Keyword(s):  
Heat Transfer ◽  
Elastic Deformation ◽  
Degrees Of Freedom ◽  
Journal Bearing ◽  
Variable Viscosity ◽  
Global Analysis ◽  
Analysis Method ◽  
Stiffness And Damping ◽  
Modal Coordinates ◽  
Good Agreement

Abstract An approach for incorporating the heat transfer and elastic deformation effects into dynamic coefficient calculation is presented. A global analysis method is used, which finds the equilibrium pad tilt angles at each eccentricity position and includes cross-film variable viscosity, heat transfer effects in the lubricant, elastic deformation, heat conduction effects in the pads, and elastic deformation effect in the pivots. Deflection modes are used to approximate deformation of the top surface of the pads. The dynamic coefficients of a single pad are calculated at the equilibrium state of the bearing, based on numerical perturbation with respect to the bearing degrees of freedom. These include journal position, pad rotation, pivot deformation, and modal coordinates. The stiffness and damping coefficients are calculated and show very good agreement with experimental and numerical results from the existing literature.

Numerical Investigation for Characteristics and Oil-Air Distributions of a Tilting-Pad Journal Bearing Under Different Loads

2020 ◽  
Author(s):  
Aoshuang Ding ◽  
Xuesong Li
Keyword(s):  
Film Thickness ◽  
Journal Bearing ◽  
Viscosity Ratio ◽  
Cavitation Model ◽  
Tilting Pad ◽  
Sst Model ◽  
Bearing Load ◽  
Simulation Results ◽  
Bearing Loads ◽  
Tilting Pad Journal Bearing

Abstract This paper analyses the flow characteristics and oil-air distributions of oil flows in a tilting-pad journal bearing under different bearing loads. This titling-pad journal bearing is working at 3000 rpm rotation speed and its minimum film thicknesses have been measured under different loads from 180 kN to 299 kN. Based on the previous researches of this bearing under 180 kN, the gaseous cavitation and low-turbulence flow exists in this bearing flow. A suitable gaseous cavitation model and the SST model with low-Re correction are used in the film flow simulations. With the rotor and pads assumed to be rigid, the dynamic mesh and motion equations are applied to simulate the motions of the rotor and the rotations of the pads. Based on the simulation results under different bearing loads, the simulated minimum film thicknesses agrees well with the measured data. It indicates that the simulation results can catch the film geometries and flows correctly. With the load increasing, the rotor moves closer to the loaded pads and the minimum film thickness decreases. Taking the effect of boundary layers into consideration, the turbulence has a negative relationship with the film thickness and decreases in the loaded area under higher bearing load. It can be verified by the simulated lower turbulent viscosity ratio distributions in the loaded pads. In the unloaded area, both the film thickness and turbulence viscosity ratio are positively related to the bearing loads. Thus, the higher bearing load may lead the flow to be more different in the loaded and unloaded area, and the turbulence in the loaded pads may transfer to laminar in the end. As for the oil-air distributions, in the unloaded pads, with the bearing load increasing, the simulated air volume fraction increases in the unloaded pads with lower pressure. It should be caused by the higher film thickness of the unloaded pads under higher loads. In sum, the flow turbulence and cavitation process changes with the bearing load. With a higher load, the cavitation becomes more in the unloaded pads and the flow changes sharper from the high-turbulence unloaded area to the low-turbulence loaded area. As the simulation results is in good accordance with the experimental data, the SST model with low-Re correction and the gaseous cavitation model are verified to be suitable for bearing film simulations under different loads.

Measurement of Oil Aeration Effects in Journal Bearings

2002 ◽  
Author(s):  
J. L. Nikolajsen ◽  
D. Dong ◽  
M. J. Goodwin
Keyword(s):  
Journal Bearing ◽  
Load Capacity ◽  
Journal Bearings ◽  
Damping Capacity ◽  
Bearing Load ◽  
Bearing Stiffness

Preliminary measurements have been conducted to determine the effect of oil aeration on journal bearing performance. Oil aeration was observed to reduce the bearing load capacity and to increase the bearing stiffness. Also, the bearing damping capacity was improved significantly by oil aeration.

Measurement of Thermally Induced Loads in Back-to-Back Angular Contact Spindle Bearings Using Strain Gauges

2004 ◽  
Author(s):  
John E. Harder ◽  
Jeffrey L. Stein
Keyword(s):  
Metal Cutting ◽  
Strain Gauges ◽  
Future Research ◽  
Axial Loads ◽  
Thermally Induced ◽  
Outer Race ◽  
Repeatability Error ◽  
Bearing Load ◽  
Bearing Loads ◽  
Set Up

Thermally induced bearing loads can potentially create serious problems for metal cutting spindles when used at high speeds. Proper spindle bearing set-up can minimize, but cannot eliminate this problem. Measuring the thermally induced load can alert the user to a potential problem or can be used to control the load directly. The purpose of this paper is to describe the design of a thermally induced bearing load sensor using strain gauges placed around the outer race. A box spindle with strain gauges on a pair of angular contact ball bearings located in the front of the spindle is used in this analysis. In order to calculate the thermally induced bearing load, the outputs of the strain gauges were recorded over a one second interval, sampled at 7500 Hz from each strain gauge and the root mean square of the deviation of this data from its mean is calculated. This value is a measure of the ball load. This calculated output is calibrated by a quadratic regression of these data to applied axial loads over a range of 0 to 2800 N. Values for each bearing were averaged to yield a front and rear value. The repeatability error for the front bearing sensor is 1.36%, and its accuracy is 98.9%. The repeatability error for the rear bearing sensor is 2.17% and its accuracy is 98.3%. These relatively low repeatability errors are attributable in part to filtering that does reduce the sensors’ bandwidth, but not significantly for measuring the relatively slowly changing thermally induced loads. Sensor design improvements and potential avenues of future research are discussed.

Excitation Frequency Effects on the Stiffness and Damping Coefficients of a Five-Pad Tilting Pad Journal Bearing

1999 ◽  
Vol 121 (3) ◽  
pp. 517-522 ◽  
Author(s):  
Hyun Cheon Ha ◽  
Seong Heon Yang
Keyword(s):  
Frequency Ratio ◽  
Journal Bearing ◽  
Excitation Frequency ◽  
Shaft Speed ◽  
Frequency Effects ◽  
Damping Coefficients ◽  
Tilting Pad ◽  
Bearing Load ◽  
Stiffness And Damping ◽  
Tilting Pad Journal Bearing

An experimental study is performed to investigate the frequency effects of the excitation force on the linear stiffness and damping coefficients of a LOP (load on pad) type five-pad tilting pad journal bearing with the diameter of 300.91 mm and the length of 149.80 mm. The main parameter of interest in the present work is excitation frequency to shake the test hearing. The excitation frequency is controlled independently, using orthogonally mounted hydraulic exciters, as follows: 1) excitation frequency ratio in the x-axis direction νx = 0.5, 2) excitation frequency ratio in the y-axis direction νy = 0.6, 0.7, 0.8, 0.9. The magnitude of the excitation force is controlled to make sure that the test hearing has a linear behavior during the test. The relative movement between the bearing and shaft, and the acceleration of the bearing casing are measured as a function of excitation frequency using the different values of bearing load and shaft speed. Measurements show that the variation of excitation, frequency has quite a little effect on both stiffness and damping coefficients. The stiffness coefficients of the five-pad tilting pad journal bearing slightly decrease as the excitation frequency ratio increases, while the damping coefficients slightly increase with excitation frequency ratio, especially in the case of lower speed and higher load. Both direct stiffness and damping coefficients in the direction of bearing load decrease with an increase of shaft speed, but increase with the bearing load.

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