Material and Microslip Damping in a Rotor Taking Gravity and Anisotropic Bearings Into Account

2000 ◽  
Vol 123 (1) ◽  
pp. 30-35 ◽  
Author(s):  
Ha˚kan L. Wettergren
Keyword(s):  
Numerical Simulations ◽  
Rotational Frequency ◽  
Dissipated Energy ◽  
Viscous Damping ◽  
Internal Damping ◽  
Material Damping ◽  
Turbine Generator ◽  
Equivalent Viscous Damping ◽  
Sign Change ◽  
The Difference

The paper is concerned with material and microslip damping in a rotor. The horizontal rotor is carried by anisotropic bearings, which means that the shaft feels three different frequencies, the rotational frequency and the difference and the sum of the rotational and vibrational frequencies. When material damping is studied, these three frequencies lead to three different equivalent viscous damping constants and the dissipated energy can be solved analytically. The rotor slot wedges in a turbine generator are used as an example of microslip damping. In this case the damping is nonlinear and the results are obtained through numerical simulations. The results show that these two different internal damping sources give both similarities and dissimilarities. The sign change and different magnitude of the dissipated energy running sub- or supercritical are the same. However the dissipated energy for material damping is not affected by gravity which microslip damping is.

Material and Microslip Damping in a Rotor Taking Gravity and Anisotropic Bearings Into Account

1999 ◽  
Author(s):  
Håkan L. Wettergren
Keyword(s):  
Numerical Simulations ◽  
Rotational Frequency ◽  
Dissipated Energy ◽  
Viscous Damping ◽  
Internal Damping ◽  
Material Damping ◽  
Turbine Generator ◽  
Equivalent Viscous Damping ◽  
Sign Change ◽  
The Difference

Abstract The paper is concerned with material and microslip damping in a rotor. The horizontal rotor is carried by anisotropic bearings, which means that the shaft feels three different frequencies, the rotational frequency and the difference and the sum of the rotational and vibrational frequencies. When material damping is studied these three frequencies lead to three different equivalent viscous damping constants and the dissipated energy can be solved analytically. The rotor slot wedges in a turbine generator are used as an example of microslip damping. In this case the damping is non-linear and the results are obtained through numerical simulations. The results show that these two different internal damping sources give both similarities and dissimilarities. The sign change and different magnitude of the dissipated energy running sub- or supercritical are the same. However the dissipated energy for material damping is not affected by gravity which microslip damping is.

Dynamic Instability of a Turbine Generator due to Microslip

1999 ◽  
Vol 121 (2) ◽  
pp. 162-168 ◽  
Author(s):  
H. L. Wettergren ◽  
G. Csaba
Keyword(s):  
Vibrational Frequency ◽  
Normal Force ◽  
Dynamic Instability ◽  
Rotational Frequency ◽  
Circular Motion ◽  
Dissipated Energy ◽  
Nonlinear Phenomenon ◽  
Material Damping ◽  
Turbine Generator

The present paper is concerned with dynamic instability of a turbine generator due to friction between rotor slot wedges and the rotor. When the normal force on the wedge is constant the dissipated energy is of the same type as hysteretic material damping in the sense that for a circular motion excluding gravity it is independent of the rotational frequency, but changes sign when the rotational frequency exceeds the vibrational frequency. The magnitude of the dissipated energy will however depend on the rotational frequency as the normal force does. The transferred energy due to friction is a nonlinear phenomenon and approximately proportional to the amplitude cubed and may be much larger than material damping. It is also shown that when gravity is included or the motion is elliptical the energy transferred is larger than for a simple circular motion.

Thermodynamic Effects on Pressure Fluctuations of a Liquid Oxygen Turbopump

2021 ◽  
Author(s):  
Deyou Li ◽  
Zhipeng Ren ◽  
Yu Li ◽  
Boxuan Miao ◽  
Ruzhi Gong ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Pressure Fluctuations ◽  
Rotational Frequency ◽  
Liquid Oxygen ◽  
Rocket Engines ◽  
Cavitation Flow ◽  
Characteristic Frequencies ◽  
Thermodynamic Effects ◽  
The Difference

Abstract Liquid oxygen turbopumps are an important component of rocket engines. The instability induced by cavitation flow in turbopumps has received considerable attention because of thermodynamic effects. In this study, unsteady numerical simulations of a turbopump with thermodynamic effects were performed. The frequency composition and source of pressure fluctuations in a turbopump were analyzed, and the difference in pressure fluctuations with/without thermodynamic effects was revealed. The results showed that the pressure fluctuations were mainly caused by the interaction between the impeller and diffuser, and the thermodynamic effects slightly increased the amplitudes of the characteristic frequencies. In addition, in the inducer and impeller, three characteristic frequencies (4.089fn, 2.519fn, and 3.238fn, where fn is the rotational frequency) were confirmed. Analyses revealed that the 4.089fn was due to the periodic shedding of cavitation structures on the suction surfaces at the inducer outlet, 2.519fn was induced by the periodic occurrence and collapse of cavitation on the suction surfaces at the impeller inlet; and 3.238fn was from the periodic shedding of cavitation structures on the suction surfaces at the impeller middle blades. The existence of thermodynamic effects decreased the frequency of cavitation shedding and increased the frequency of the periodic occurrence and collapse of cavitation.

Modulation instability in nonlinear chiral fiber

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Demissie Jobir Gelmecha ◽  
Ram Sewak Singh
Keyword(s):  
Theoretical Model ◽  
Numerical Simulations ◽  
Pulse Propagation ◽  
Modulation Instability ◽  
Constitutive Relations ◽  
Gain Spectrum ◽  
Circularly Polarized ◽  
Left Handed ◽  
Simulation Results ◽  
The Difference

AbstractIn this paper, the rigorous derivations of generalized coupled chiral nonlinear Schrödinger equations (CCNLSEs) and their modulation instability analysis have been explored theoretically and computationally. With the consideration of Maxwell’s equations and Post’s constitutive relations, a generalized CCNLSE has been derived, which describes the evolution of left-handed circularly polarized (LCP) and right-handed circularly polarized (RCP) components propagating through single-core nonlinear chiral fiber. The analysis of modulation instability in nonlinear chiral fiber has been investigated starting from CCNLSEs. Based on a theoretical model and numerical simulations, the difference on the modulation instability gain spectrum in LCP and RCP components through chiral fiber has been analyzed by considering loss and chirality into account. The obtained simulation results have shown that the loss distorts the sidebands of the modulation instability gain spectrum, while chirality modulates the gain for LCP and RCP components in a different manner. This suggests that adjusting chirality strength may control the loss, and nonlinearity simultaneously provides stable modulated pulse propagation.

scholarly journals Outcomes of Femtosecond Laser Assisted Cataract Surgery Performed by Resident and Attending Surgeons

2021 ◽  
Vol 13 (01) ◽  
pp. e26-e31
Author(s):  
Spencer C. Cleland ◽  
Daniel W. Knoch ◽  
Jennifer C. Larson
Keyword(s):  
Visual Acuity ◽  
Femtosecond Laser ◽  
Cataract Surgery ◽  
Retrospective Chart Review ◽  
Dissipated Energy ◽  
Independent Practice ◽  
Postoperative Visual Acuity ◽  
Included Patient ◽  
Duration Of Surgery ◽  
The Difference

Abstract Objective The study aimed to evaluate the safety and efficacy of resident surgeons performing femtosecond laser assisted cataract surgery (FLACS). Methods A retrospective chart review was conducted at the University of Wisconsin-Madison from postgraduate year four residents performing FLACS between 2017 and 2019. Data were also collected from residents performing manual cataract surgery, and attending surgeons performing FLACS for comparison. Recorded data included patient demographics, pre- and postoperative visual acuity, pre- and postoperative spherical equivalent, nuclear sclerotic cataract grade, ocular and systemic comorbidities, intraocular lens, duration of surgery, cumulative dissipated energy (CDE), and intraoperative and postoperative complications. Results A total of 90 cases were reviewed with 30 resident manual cases, 30 resident FLACS cases, and 30 attending FLACS cases. Resident manual (25.5 ± 6.8 minutes) and resident FLACS (17.5 ± 7.1 minutes) cases took a significantly longer time to complete compared with attending FLACS cases (13.6 ± 4.4 minutes; p < 0.001). There was higher CDE in resident FLACS and resident manual cases compared with attending FLACS cases, but the difference was not statistically significant (p = 0.06). Postoperative visual acuity was not statistically different at 1-day and 1-month after surgery among the three groups. Resident FLACS complications, which included one case requiring an intraoperative suture to close the wound, two cases with intraoperative corneal abrasions, two cases with postoperative ocular hypertension, and one case with cystoid macular edema, were not significantly greater than attending FLACS complications (p = 0.30). Conclusion The FLACS performed by resident surgeons had comparable visual acuity outcomes to FLACS performed by attending surgeons, and to manual cataract surgery performed by resident surgeons. However, resident FLACS cases took significantly longer time to complete, and they were associated with a higher CDE and minor complication rate compared with attending FLACS cases. Introducing advanced technologies into surgical training curricula improves resident preparedness for independent practice, and this study suggests FLACS can be incorporated safely and effectively into resident education.

Design and structural performance measurements of a novel multi-cantilever foil bearing

2014 ◽  
Vol 229 (10) ◽  
pp. 1830-1838 ◽  
Author(s):  
Kai Feng ◽  
Xueyuan Zhao ◽  
Zhiyang Guo
Keyword(s):  
Dynamic Characteristics ◽  
Dynamic Load ◽  
Dynamic Stiffness ◽  
Excitation Frequency ◽  
Viscous Damping ◽  
Equivalent Viscous Damping ◽  
Foil Bearing ◽  
Load Tests ◽  
Stiffness And Damping ◽  
Motion Amplitude

With increasing need for high-speed, high-temperature, and oil-free turbomachinery, gas foil bearings (GFBs) have been considered to be the best substitutes for traditional oil-lubricated bearings. A multi-cantilever foil bearing (MCFB), a novel GFB with multi-cantilever foil strips serving as the compliant underlying structure, was designed, fabricated, and tested. A series of static and dynamic load tests were conducted to measure the structural stiffness and equivalent viscous damping of the prototype MCFB. Experiments of static load versus deflection showed that the proposed bearing has a large mechanical energy dissipation capability and a pronounced nonlinear static stiffness that can prevents overly large motion amplitude of journal. Dynamic load tests evaluated the influence of motion amplitude, loading orientation and misalignment on the dynamic stiffness and equivalent viscous damping with respect to excitation frequency. The test results demonstrated that the dynamic stiffness and damping are strongly dependent on the excitation frequency. Three motion amplitudes were applied to the bearing housing to investigate the effects of motion amplitude on the dynamic characteristics. It is noted that the bearing dynamic stiffness and damping decreases with incrementally increasing motion amplitudes. A high level of misalignment can lead to larger static and dynamic bearing stiffness as well as to larger equivalent viscous damping. With dynamic loads applied to two orientations in the bearing midplane separately, the dynamic stiffness increases rapidly and the equivalent viscous damping declines slightly. These results indicate that the loading orientation is a non-negligible factor on the dynamic characteristics of MCFBs.

Assessment of Internal Damping in Uniaxially Stressed Metals: Exponential and Autoregressive Methods

1998 ◽  
Vol 120 (2) ◽  
pp. 177-184 ◽  
Author(s):  
A. L. Audenino ◽  
E. M. Zanetti ◽  
P. M. Calderale
Keyword(s):  
Nonlinear Behavior ◽  
Least Square ◽  
Dissipated Energy ◽  
Exponential Fitting ◽  
Damping Capacity ◽  
Test Machine ◽  
Internal Damping ◽  
Cast Irons ◽  
Decay Signal ◽  
Specific Damping Capacity

When a metallic material is highly stressed, its internal specific damping capacity increases showing a nonlinear behavior. In spite of this, the most part of experimental methods employ nonhomogeneous stress fields measuring only a volumetric average, often called structural damping. To overcome this problem the procedure herein presented extends the applicability of the plain traction or compression methods to higher frequency range (up to 300 Hz). The introduced methodology corrects for elastic energy and dissipated energy relative to the test machine and to the fixtures. The experimental procedure is based on the acquisition of a decay signal when the test machine excitation force has been removed. Two different methods to extract the pattern of internal damping versus material strain have been compared: one is based on least square exponential fitting while the other employs an autoregressive model. Best results have been obtained combining the two techniques taking into account also the variation of Young’s modulus with strain. The resulting curves of the loss factor as a function of strain amplitude for three steels and two cast irons are presented.

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