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Research Papers: Other (Seals, Manufacturing)

A New Structural Dynamic Model for Pump Mechanical Seals Vibration Analysis Incorporating Squeeze Motion of O-Ring Seals and General Dynamic Motion of the Pump Housing and the Pump Shaft

[+] Author and Article Information
Dara Childs

Mechanical Engineering Department,
Texas A&M University,
College Station, TX 77843

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received January 2, 2017; final manuscript received October 10, 2017; published online July 3, 2018. Assoc. Editor: Mihai Arghir.

J. Tribol 140(6), 062201 (Jul 03, 2018) (10 pages) Paper No: TRIB-17-1002; doi: 10.1115/1.4038867 History: Received January 02, 2017; Revised October 10, 2017

New models are developed for flexibly mounted stator (FMS) and flexibly mounted rotor (FMR) mechanical seals that incorporate the radial reaction force components produced by supporting O-rings due to relative squeezing motion across the O-rings. Supporting data come from tests done in relation to O-ring supports for ball bearing races. The reaction-force model is linear but a nonlinear function of excitation frequency. The model accounts for the axial displacement doz of the O-ring from the mass center of the seal stator (FMS configuration) or seal rotor (FMR configuration), which couples the radial and pitch–yaw motion of the model's stiffness and damping matrices. Greens' coned-face-seal model is used to define the reaction moment arising across the seal faces via stiffness and damping matrices. The damping matrix does not coincide with Green's. His is constant; the matrix developed here contains terms that are harmonic at twice theprecession frequency. When averaged over one precession cycle, the new average damping matrix coincides with Green's result. When the averaged damping matrix is used, the resultant model is linear. However, because of the viscoelastic reaction-force and reaction-moment models used for the O-ring coefficients, most of the stiffness and damping matrices are strong functions of the assumed precession frequency. The new FMR model contains a skew-symmetric stiffness matrix due to the O-ring damping terms. In rotordynamics, skew symmetric stiffness matrices due to internal damping in the rotor can lead to rotordynamic instabilities.

FIGURES IN THIS ARTICLE
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Copyright © 2018 by ASME
Topics: Seals , Rotors , Stators , Yaw , Pumps , Damping
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References

Durham, M. , Williams, J. , and Goldman, D. , 1990, “ Effect of Vibration on Electric-Submersible Pump Failures,” SPE J. Pet. Technol., 42(2), pp. 186–190. [CrossRef]
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Green, I. , 1988, “ Gyroscopic and Damping Effects on the Stability of a Noncontacting Flexibly-Mounted Rotor Mechanical Seal,” ISROMAC II Conference, Honolulu, HI, Feb. 26–Mar. 2, pp. 153–174.
Green, I. , and Etsion, I. , 1985, “ Stability Threshold and Steady-State Response of Noncontacting Coned-Face Seals,” STLE Trans., 28(4), pp. 449–460. https://www.tandfonline.com/doi/abs/10.1080/05698198508981642
Green, I. , and Etsion, I. , 1984, “ Stiffness and Damping Characteristics of Elastomer O-Rings Secondary Seals Subjected to Reciprocating Twist,” Tenth International Conference on Fluid Sealing, BHRA, Innsbruck Austria, Apr. 3–5, pp. A2–A10.
Lebeck, A. , 1991, Principles and Design of Mechanical Seals, Wiley, New York, p. 636.
Smalley, A. , Darlow, M. , and Mehta, R. , 1978, “ The Dynamic Characteristics of O-Rings,” ASME J. Mech. Design, 100(1), pp. 132–138. [CrossRef]
Kimball, A. , 1925, “ Internal Friction as a Cause of Shaft Whirling,” Philos. Mag., Ser, 49(6), pp. 724–727. [CrossRef]
Green, I. , and Etsion, I. , 1986, “ Nonlinear Dynamic Analysis of Noncontacting Coned-Face Mechanical Seals,” ASLE Trans., 29(3), pp. 383–393. [CrossRef]
Wileman, J. , 2004, “ Dynamic Response of Eccentric Face Seals to Synchronous Shaft Whirl,” ASME J. Tribol., 126(2), pp. 301–309. [CrossRef]
Lebeck, A. , 2015, private communications.

Figures

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Fig. 4

Green's relative pitch angle γ locating the 1-2-3 coordinate system [5]

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Fig. 3

The Etsion–Green kinematic model for the seal's rotor and stator, after [5]

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Fig. 2

(a) Flexibly mounted stator and (b) FMR configurations, after [4]

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Fig. 1

Lifetime predictions for pump operations versus measured housing velocity, after [2]

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Fig. 5

Flexibly-mounted stator seal stator with the O-ring placed to the left of CM by dOZ.ThehousingsupportbaseliesthedistanceDOZ to the left of CM

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Fig. 6

O-ring x0−y0 coordinate system

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