Identification of Structural Stiffness and Damping Coefficients of a Shoed Brush Seal

2005 ◽  
Author(s):  
Adolfo Delgado ◽  
Luis San Andre´s
Keyword(s):  
Energy Dissipation ◽  
Dry Friction ◽  
Single Frequency ◽  
Structural Stiffness ◽  
Rotor Spinning ◽  
Equivalent Damping ◽  
Shaft Rotation ◽  
Brush Seal ◽  
Lift Off ◽  
Energy Dissipated

The multiple-shoe brush seal, a variation of a standard brush seal, accommodates arcuate pads at the bristles free ends. This novel design allows reverse shaft rotation operation, and reduces and even eliminates bristle wear, since the pads lift off due to the generation of a hydrodynamic film during rotor spinning. This type of seal, able to work at both cold and high temperatures, not only restricts secondary leakage but also acts as an effective vibration damper. The dynamic operation of the shoed-brush seals, along with the validation of reliable predictive tools, relies on the appropriate estimation of the seal structural stiffness and energy dissipation features. Single frequency external load tests conducted on a controlled motion test rig and without shaft rotation allow the identification of the structural stiffness and equivalent damping of a 20-pad brush seal, 153 mm in diameter. The seal energy dissipation mechanism, represented by a structural loss factor and a dry friction coefficient, characterizes the energy dissipated by the bristles and the dry friction interaction of the brush seal bristles rubbing against each other. The physical model used reproduces well the measured system motions, even for frequencies well above the identification range.

Identification of Structural Stiffness and Damping Coefficients of a Shoed-Brush Seal

2007 ◽  
Vol 129 (5) ◽  
pp. 648-655 ◽  
Author(s):  
Adolfo Delgado ◽  
Luis San Andrés
Keyword(s):  
Energy Dissipation ◽  
Dry Friction ◽  
Single Frequency ◽  
Structural Stiffness ◽  
Rotor Spinning ◽  
Equivalent Damping ◽  
Shaft Rotation ◽  
Brush Seal ◽  
Lift Off ◽  
Energy Dissipated

The multiple-shoe brush seal, a variation of a standard brush seal, accommodates arcuate pads at the bristles’ free ends. This novel design allows reverse shaft rotation operation and reduces and even eliminates bristle wear, since the pads lift-off due to the generation of a hydrodynamic film during rotor spinning. This type of seal, able to work at both cold and high temperatures, not only restricts secondary leakage but also acts as an effective vibration damper. The dynamic operation of the shoed-brush seals, along with the validation of reliable predictive tools, relies on the appropriate estimation of the seal structural stiffness and energy dissipation features. Single-frequency external load tests conducted on a controlled motion test rig and without shaft rotation allow the identification (measurement) of the structural stiffness and equivalent damping of a 20-pad brush seal, 153mm in diameter. The seal energy dissipation mechanism, represented by a structural loss factor and a dry friction coefficient, characterizes the energy dissipated by the bristles and the dry friction interaction of the brush seal bristles rubbing against each other. The physical model used reproduces well the measured system motions, even for frequencies well above the identification range.

Rotordynamic Force Coefficients of a Hybrid Brush Seal: Measurements and Predictions

2009 ◽  
Author(s):  
Luis San Andre´s ◽  
Adolfo Delgado ◽  
Jose´ Baker
Keyword(s):  
Test System ◽  
Operating Conditions ◽  
Single Frequency ◽  
Viscous Damping ◽  
Domain Identification ◽  
Damping Coefficients ◽  
Brush Seal ◽  
Brush Seals ◽  
Lift Off ◽  
Stiffness And Damping

Brush seals effectively control leakage in air breathing engines, albeit only applied for relatively low-pressure differentials. Hybrid brush seals (HBS) are an alternative to resolve poor reliability resulting from bristle tip wear while also allowing for reverse shaft rotation operation. A HBS incorporates pads contacting the shaft on assembly; and which under rotor spinning, lift off due to the generation of a hydrodynamic pressure. The ensuing gas film prevents intermittent contact, reducing wear and thermal distortions. The paper presents rotordynamic measurements conducted on a test rig for evaluation of HBS technology. Single frequency shaker loads are exerted on a test rotor holding a hybrid brush seal and measurements of rotor displacements follow for operating conditions with increasing gas supply pressures and two rotor speeds. A frequency domain identification method delivers the test system stiffness and damping coefficients. The HBS stiffness coefficients are not affected by rotor speed though the seal viscous damping shows a strong frequency dependency. The identified HBS direct stiffness decreases ∼15% as the supply/discharge pressure increases Pr = 1.7 to 2.4. The HBS cross-coupled stiffnesses are insignificant, at least one order of magnitude smaller than the direct stiffnesses. A structural loss factor (γ) and dry friction coefficient (μ) represent the energy dissipated in a HBS by the bristle-to-bristle and bristle-to-pads interactions. Predictions of HBS stiffness and damping coefficients correlate well with the test derived parameters. Both model predictions and test results show the dramatic reduction of the seal equivalent viscous damping coefficients as the excitation whirl frequency increases.

Rotordynamic Force Coefficients of a Hybrid Brush Seal: Measurements and Predictions

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Luis San Andrés ◽  
José Baker ◽  
Adolfo Delgado
Keyword(s):  
Test System ◽  
Operating Conditions ◽  
Single Frequency ◽  
Viscous Damping ◽  
Domain Identification ◽  
Damping Coefficients ◽  
Brush Seal ◽  
Brush Seals ◽  
Lift Off ◽  
Stiffness And Damping

Brush seals effectively control leakage in air breathing engines, albeit only applied for relatively low-pressure differentials. Hybrid brush seals (HBS) are an alternative to resolve poor reliability resulting from bristle tip wear while also allowing for reverse shaft rotation operations. A HBS incorporates pads contacting the shaft on assembly; and which under rotor spinning, lift off due to the generation of a hydrodynamic pressure. The ensuing gas film prevents intermittent contact, reducing wear, and thermal distortions. This paper presents rotordynamic measurements conducted on a test rig for evaluation of HBS technology. Single frequency shaker loads are exerted on a test rotor holding a hybrid brush seal, and measurements of rotor displacements follow for operating conditions with increasing gas supply pressures and two rotor speeds. A frequency domain identification method delivers the test system stiffness and damping coefficients. The HBS stiffness coefficients are not affected by rotor speed though the seal viscous damping shows a strong frequency dependency. The identified HBS direct stiffness decreases ∼15% as the supply/discharge pressure increases Pr=1.7–2.4. The HBS cross-coupled stiffnesses are insignificant, at least one order of magnitude smaller than the direct stiffnesses. A structural loss factor (γ) and dry-friction coefficient (μ) represent the energy dissipated in a HBS by the bristle-to-bristle and bristle-to-pad interactions. Predictions of HBS stiffness and damping coefficients correlate well with the test derived parameters. Both model predictions and test results show the dramatic reduction in the seal equivalent viscous damping coefficients as the excitation whirl frequency increases.

Characterization of a Foil Bearing Structure at Increasing Temperatures: Static Load and Dynamic Force Performance

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Tae Ho Kim ◽  
Anthony W. Breedlove ◽  
Luis San Andrés
Keyword(s):  
Friction Coefficient ◽  
Dynamic Load ◽  
Material Properties ◽  
Dry Friction ◽  
Dynamic Stiffness ◽  
Excitation Frequency ◽  
Single Frequency ◽  
Viscous Damping ◽  
Structural Stiffness ◽  
Simple Physical Model

Oil-free turbomachinery relies on gas bearing supports for reduced power losses and enhanced rotordynamic stability. Gas foil bearings (GFBs) with bump-strip compliant layers can sustain large loads, both static and dynamic, and provide damping to reduce shaft vibrations. The ultimate load capacity of GFBs depends on the material properties and configuration of the underlying bump-strip structures. In high temperature applications, thermal effects, which change the operating clearances and material properties, can considerably affect the performance of the GFB structure. This paper presents experiments conducted to estimate the structural stiffness of a test GFB for increasing shaft temperatures. A 38.17 mm inner diameter GFB is mounted on a nonrotating hollow shaft affixed to a rigid structure. A cartridge heater inserted into the shaft provides a controllable heat source and thermocouples record the temperatures on the shaft and GFB housing. For increasing shaft temperatures (up to 188°C), increasing static loads (0–133 N) are applied to the bearing and its deflection recorded. In the test configuration, thermal expansion of the GFB housing, larger than that of the shaft, nets a significant increase in radial clearance, which produces a significant reduction in the bearing’s structural stiffness. A simple physical model, which assembles the individual bump stiffnesses, predicts well the measured GFB structural stiffness. Single frequency periodic loads (40–200 Hz) are exerted on the test bearing to identify its dynamic structural stiffness and equivalent viscous damping or a dry-friction coefficient. The GFB dynamic stiffness increases by as much as 50% with dynamic load amplitudes increasing from 13 N to 31 N. The stiffness nearly doubles from low to high frequencies, and most importantly, it decreases by a third as the shaft temperature rises to 188°C. In general, the GFB dynamic stiffness is lower than its static magnitude at low excitation frequencies, while it becomes larger with increasing excitation frequency due apparently to a bump slip-stick phenomenon. The GFB viscous damping is inversely proportional to the amplitude of the dynamic load, excitation frequency, and shaft temperature. The GFB dry-friction coefficient decreases with increasing amplitude of the applied load and shaft temperature, and increases with increasing excitation frequency.

Measurements of leakage, structural stiffness and energy dissipation parameters in a shoed brush seal

2005 ◽  
Vol 2005 (12) ◽  
pp. 7-10 ◽  
Author(s):  
Adolfo Delgado ◽  
Luis San Andrés ◽  
John F Justak
Keyword(s):  
Energy Dissipation ◽  
Structural Stiffness ◽  
Brush Seal

scholarly journals Estimation of Additional Equivalent Damping Ratio of the Damped Structure Based on Energy Dissipation

2019 ◽  
Vol 2019 ◽  
pp. 1-14
Author(s):  
Xiuyan Hu ◽  
Qingjun Chen ◽  
Dagen Weng ◽  
Ruifu Zhang ◽  
Xiaosong Ren
Keyword(s):  
Energy Dissipation ◽  
Damping Ratio ◽  
Theoretical Concept ◽  
Estimation Methods ◽  
External Excitation ◽  
Single Degree Of Freedom ◽  
Equivalent Damping ◽  
Seismic Motion ◽  
Practical Engineering ◽  
Energy Dissipation Capacity

In the design of damped structures, the additional equivalent damping ratio (EDR) is an important factor in the evaluation of the energy dissipation effect. However, previous additional EDR estimation methods are complicated and not easy to be applied in practical engineering. Therefore, in this study, a method based on energy dissipation is developed to simplify the estimation of the additional EDR. First, an energy governing equation is established to calculate the structural energy dissipation. By means of dynamic analysis, the ratio of the energy consumed by dampers to that consumed by structural inherent damping is obtained under external excitation. Because the energy dissipation capacity of the installed dampers is reflected by the additional EDR, the abovementioned ratio can be used to estimate the additional EDR of the damped structure. Energy dissipation varies with time, which indicates that the ratio is related to the duration of ground motion. Hence, the energy dissipation during the most intensive period in the entire seismic motion duration is used to calculate the additional EDR. Accordingly, the procedure of the proposed method is presented. The feasibility of this method is verified by using a single-degree-of-freedom system. Then, a benchmark structure with dampers is adopted to illustrate the usefulness of this method in practical engineering applications. In conclusion, the proposed method is not only explicit in the theoretical concept and convenient in application but also reflects the time-varying characteristic of additional EDR, which possesses the value in practical engineering.

Computed Effects of Rotor-Induced Swirl on Brush Seal Performance—Part 2: Bristle Force Analysis

1996 ◽  
Vol 118 (4) ◽  
pp. 920-926 ◽  
Author(s):  
M. C. Sharatchandra ◽  
D. L. Rhode
Keyword(s):  
Inclination Angle ◽  
Flow Direction ◽  
Flow Simulation ◽  
Companion Paper ◽  
Navier Stokes ◽  
Brush Seal ◽  
Swirl Flows ◽  
Lift Off ◽  
Square Configuration ◽  
Periodic Module

This paper analytically investigates the aerodynamic bristle force distributions in brush seals used in aircraft gas turbine engines. These forces are responsible for the onset of bristle tip lift-off from the rotor surface which significantly affects brush seal performance. In order to provide an enhanced understanding of the mechanisms governing the bristle force distributions, a full Navier-Stokes flow simulation is performed in a streamwise periodic module of bristles corresponding to the staggered square configuration. As is the case with a companion paper (Sharatchandra and Rhode, 1996), this study has the novel feature of considering the combined effects of axial (leakage) and tangential (swirl) flows. Specifically, the effects of intra-bristle spacing and bristle inclination angle are explored. The results indicate that the lifting bristle force increases with reduced intra-bristle spacing and increased inclination angle. It was also observed that increases in the axial or tangential flow rates increased the force component in the normal as well as the flow direction.

Two-Frequency Oscillation With Combined Coulomb and Viscous Frictions

2002 ◽  
Vol 124 (4) ◽  
pp. 537-544 ◽  
Author(s):  
Gong Cheng ◽  
Jean W. Zu
Keyword(s):  
Steady State ◽  
Dry Friction ◽  
Single Frequency ◽  
Friction Oscillator ◽  
One Stop ◽  
Frequency Excitation ◽  
Stop Motion ◽  
The One ◽  
Coulomb Dry Friction ◽  
Mass Spring

In this paper, a mass-spring-friction oscillator subjected to two harmonic disturbing forces with different frequencies is studied for the first time. The friction in the system has combined Coulomb dry friction and viscous damping. Two kinds of steady-state vibrations of the system—non-stop and one-stop motions—are considered. The existence conditions for each steady-state motion are provided. Using analytical analysis, the steady-state responses are derived for the two-frequency oscillating system undergoing both the non-stop and one-stop motions. The focus of the paper is to study the influence of the Coulomb dry friction in combination with the two frequency excitations on the dynamic behavior of the system. From the numerical simulations, it is found that near the resonance, the dynamic response due to the two-frequency excitation demonstrates characteristics significantly different from those due to a single frequency excitation. Furthermore, the one-stop motion demonstrates peculiar characteristics, different from those in the non-stop motion.

Analysis of Beam-Like Structures With Displacement-Dependent Friction Forces: Part I — Single-Degree-of-Freedom Model

1995 ◽  
Author(s):  
Wayne E. Whiteman ◽  
Aldo A. Ferri
Keyword(s):  
Dry Friction ◽  
Damping Ratio ◽  
Strong Dependence ◽  
Time Integration ◽  
Single Mode ◽  
Stick Slip ◽  
Friction Forces ◽  
Equivalent Damping ◽  
Damping Characteristics ◽  
Parameter Values

Abstract The dynamic behavior of a beam-like structure undergoing transverse vibration and subjected to a displacement-dependent dry friction force is examined. In Part I, the beam is modeled by a single mode while Part II considers multi-mode representations. The displacement dependence in each case is caused by a ramp configuration that allows the normal force across the sliding interface to increase linearly with slip displacement. The system is studied first by using first-order harmonic balance and then by using a time integration method. The stick-slip behavior of the system is also studied. Even though the only source of damping is dry friction, the system is seen to exhibit “viscous-like” damping characteristics. A strong dependence of the equivalent natural frequency and damping ratio on the displacement amplitude is an interesting result. It is shown that for a given set of parameter values, an optimal ramp angle exists that maximizes the equivalent damping ratio. The appearance of two dynamic response solutions at certain system and forcing parameter values is also seen. Results suggest that the overall characteristics of mechanical systems may be improved by properly configuring frictional interfaces to allow normal forces to vary with displacement.

In-Plane Vibration Damping of a U-Tube With Wet and Dry Flat-Bar Supports

2014 ◽  
Author(s):  
Paul A. Feenstra ◽  
Victor P. Janzen ◽  
Bruce A. W. Smith
Keyword(s):  
Energy Dissipation ◽  
Plane Motion ◽  
Test Facility ◽  
Vibration Energy ◽  
Test Rig ◽  
Two Phase ◽  
Support Conditions ◽  
Vibration Tests ◽  
Energy Dissipated ◽  
Steam Generator Tubes

Tests are being planned which will use AECL’s MR-3 Freon test facility and a Multi-Span U-Bend (MSUB) test rig to investigate the dynamics of tube vibration in two-phase flow, in particular those mechanisms that can cause excessive damage to steam-generator tubes. In preparation for the tests, free- and forced-vibration tests were conducted to measure the vibration energy dissipation (damping) of a single U-bend tube in air, with dry and wet anti-vibration bars, under a variety of tube-support conditions. This paper presents the relevant damping mechanisms and documents methods used to conduct the tests and to analyze the energy dissipated at the supports. Results indicate that for in-plane motion without tube-to-support contact, viscous damping related to wet AV B supports is much smaller than guidelines based on other types of supports suggest. To begin to examine the effects of the tube coming into contact with its supports, such as friction-related energy dissipation, the results of tests with light tube-to-support preloads are also presented.

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