The effects of surface roughness on the transient characteristics of hydrodynamic cylindrical bearings during startup

In order to study the dual-rotor system’s rubbing fault, a new dynamic model is established. The unbalance and the rubbing faults are modeled, respectively. Considering the softening characteristics of casing, the Lankarani–Nikravesh model is utilized to describe the impact force between the disk and fixed limiter. The numerical integral method is applied to obtain system’s dynamic behavior, and the characteristics of the rubbing faults are analyzed by time-domain waveform, 3D waterfall plot and spectrum cascades. The influences of rotational speed ratio, initial clearance, mass eccentricity and inter-shaft bearing stiffness on the dynamic characteristics are investigated. The vibration displacement of the low-pressure rotor is collected from the impact experiment performed on a dual-rotor test rig. The analysis result of simulation is identical with the experiment result. Consequently, this method can be used to study characteristics of rubbing faults of dual-rotor bearing system efficiently.

Vibration response analysis of rubbing faults on a dual-rotor bearing system

Fixed-point rubbing characteristic analysis of a dual-rotor system based on the Lankarani-Nikravesh model

Passive vibration control in rotor dynamics: Optimization of composed support using viscoelastic materials

This paper studies the effect of a number of smooth nonlinear energy sinks (NESs) on the vibration mitigation of a rotor supported by journal bearings with nonlinear suspensions under mass eccentricity force. The NESs have a linear damping and an essentially nonlinear stiffness. Two NESs in the perpendicular directions are located on the bearing body. The equations of motion are derived and numerically solved. In order to optimize the parameters of the NESs, a genetic algorithm is utilized. For different values of the system parameters, periodic, two-periodic (2T) and qusai-periodic motions, occur in the system. It is shown that the NESs reduce effectively vibration of the rotor-bearing system in an operating speed range. However, the type of motion does not change in the most rotational speeds of rotor. Furthermore, for lower values of damping, the NESs demonstrate a high performance.

Vibration attenuation of a rotor supported by journal bearings with nonlinear suspensions under mass eccentricity force using nonlinear energy sink

Noncontacting mechanical face seals are often described as unpredictable machine elements, gaining this moniker from numerous instances of premature and unexpected failure. Machine faults such as misalignment or imbalance exacerbate seal vibration, leading to undesirable and unforeseen contact between the seal faces. A hypothesis explaining the high probability of failure in noncontacting mechanical face seals is this undesired seal face contact. However, research supporting this hypothesis is heuristic and experiential and lacks the rigor provided by robust simulation incorporating contact into the seal dynamics. Here, recent developments in modeling rotor–stator rub using rough surface contact are employed to simulate impact phenomena in a flexibly mounted stator (FMS) mechanical face seal designed to operate in a noncontacting regime. Specifically, the elastoplastic Jackson–Green rough surface contact model is used to quantify the contact forces using real and measurable surface and material parameters. This method also ensures that the seal face clearance remains positive, thus allowing one to calculate fluid-film forces. The seal equations of motion are simulated to indicate several modes of contacting operation, where contact is identified using waveforms, frequency spectra, and contact force calculations. Interestingly, and for the first time, certain parameters generating contact are shown to induce aperiodic mechanical face seal vibration, which is a useful machine vibration monitoring symptom. Also for the first time, this work analytically shows a mechanism where severe contact precipitates seal failure, which was previously known only through intuition and/or experience. The utility of seal face contact diagnostics is discussed along with directions for future work. [DOI: 10.1115/1.4033366]

Impact Phenomena in a Noncontacting Mechanical Face Seal

https://itzhak.green.gatech.edu/rotordynamics/Rotordynamic_Analysis_Using_the_Complex_Transfer_Matrix__An_Application_to_Elastomer_Supports_Using_the_Viscoelastic_Correspondence_Principle.pdf

Rotordynamic analysis using the Complex Transfer Matrix: An application to elastomer supports using the viscoelastic correspondence principle

Rotating machines and associated triboelements are ubiquitous in industrial society, playing a central role in power generation, transportation, and manufacturing. Unfortunately, these systems are susceptible to undesirable contact (i.e., rub) between the rotor and stator, which is both costly and dangerous. These adverse effects can be alleviated by properly applying accurate real-time diagnostics. The first step toward accurate diagnostics is developing rotor–stator rub models which appropriately emulate reality. Previous rotor–stator rub models disavow the contact physics by reducing the problem to a single esoteric linear contact stiffness occurring only at the point of maximum rotor radial deflection. Further, the contact stiffness is typically chosen arbitrarily, and as such provides no additional insight into the contacting surfaces. Here, a novel rotor–stator rub model is developed by treating the strongly conformal curved surfaces according to their actual nature: a collection of stochastically distributed asperities. Such an approach is advantageous in that it relies on real surface measurements to quantify the contact force rather than a heuristic choice of linear contact stiffness. Specifically, the elastoplastic Jackson–Green (JG) rough surface contact model is used to obtain the quasistatic contact force versus rotor radial deflection; differences and similarities in contact force between the linear elastic contact model (LECM) and JG model are discussed. Furthermore, the linear elastic model’s point contact assumption is assessed and found to be inaccurate for systems with small clearances. Finally, to aid in computational efficiency in future rotordynamic simulation, a simple exponential curve fit is proposed to approximate the JG force–displacement relationship. [DOI: 10.1115/1.4032786]

Rough Surface Contact of Curved Conformal Surfaces: An Application to Rotor–Stator Rub

Undesirable rotor–stator rub is frequently observed in rotordynamic systems, and has been the subject of many investigations. Most of these studies employ a simple piecewise-smooth linear-elastic contact model (LECM), where the rotor switches between noncontacting and contacting operation once the clearance is exceeded (various complications have been incorporated, though the essential model premises endure). Though useful as a first step, the LECM relies on an arcane contact stiffness estimate, and therefore does not emulate the actual contacting surfaces. Consequentially, the LECM fails to elucidate how real surface parameters influence contact severity and surface durability. This work develops a novel model for rotor–stator rub which is commensurate with reality by treating the surfaces as a collection of stochastically distributed asperities. Specifically, the elastoplastic Jackson–Green (JG) rough surface contact model is used to calculate the quasistatic contact force as a function of rotor displacement, where bulk material deformation and surface cumulative damage are ignored. A simple exponential fit of the contact force is proposed to reduce computational burden associated with evaluating the JG rough surface contact model at each simulation time step. The rotor's response using the LECM and JG rough surface contact model is compared via shaft speed bifurcations and orbit analysis. Significant differences are observed between the models, though some similarities exist for responses with few contacts per rotor revolution.

/pdf/rotordynamic-analysis-of-rotor-stator-rub-using-rough-314x4vz1y3.pdf

Rotordynamic Analysis of Rotor–Stator Rub Using Rough Surface Contact

The goal of this work is to establish a condition monitoring regimen capable of diagnosing the depth and location of a transverse fatigue crack in a rotordynamic system The success of an on-line crack diagnosis regimen hinges on the accuracy of the crack model used The model should account for the depth of the crack and the localization of the crack along the shaft Negating the influence of crack location on system response ignores a crucial component of real cracks Two gaping crack models are presented; the first simulates a finite-width manufactured notch, while the second models an open fatigue crack An overhung rotordynamic system is modeled, imitating an available rotordynamic test rig Four degree-of-freedom equations of motion for both crack models are presented and discussed, along with corresponding transfer matrix techniques Free and forced response analyses are performed, with emphasis placed on results applicable to condition monitoring It is demonstrated that two identifiers are necessary to diagnose the crack parameters: the 2X resonance frequency and the magnitude of the 2X component of the rotor angular response at resonance First, a contour plot of the 2X resonant shaft speed versus crack depth and location is generated The magnitude of the 2X component of the rotor’s angular response along the desired contour is obtained, narrowing the possible pairs of crack location/depth to either one or two possibilities Practical aspects of the diagnosis procedure are then discussedCopyright © 2013 by ASME

Rotordynamic Crack Diagnosis: Distinguishing Crack Depth and Location

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