scholarly journals Modelling rocking response via equivalent viscous damping

2019 ◽  
Vol 48 (11) ◽  
pp. 1277-1296 ◽  
Author(s):  
Umberto Tomassetti ◽  
Francesco Graziotti ◽  
Luigi Sorrentino ◽  
Andrea Penna
Keyword(s):  
Viscous Damping ◽  
Equivalent Viscous Damping ◽  
Rocking Response

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.

Experimental Evaluation of the Structure Characterization of a Novel Hybrid Bump-Metal Mesh Foil Bearing

2015 ◽  
Vol 138 (2) ◽  
Author(s):  
Kai Feng ◽  
Yuman Liu ◽  
Xueyuan Zhao ◽  
Wanhui Liu
Keyword(s):  
Excitation Frequency ◽  
Structure Characterization ◽  
Viscous Damping ◽  
Metal Mesh ◽  
Equivalent Viscous Damping ◽  
Foil Bearings ◽  
Damping Characteristics ◽  
Foil Bearing ◽  
Mesh Density ◽  
Load Tests

Rotors supported by gas foil bearings (GFBs) experience stability problem caused by subsynchronous vibrations. To obtain a GFB with satisfactory damping characteristics, this study presented a novel hybrid bump-metal mesh foil bearing (HB-MMFB) that consists of a bump foil and metal mesh blocks in an underlying supporting structure, which takes advantage of both bump-type foil bearings (BFBs) and MMFBs. A test rig with a nonrotating shaft was designed to estimate structure characterization. Results from the static load tests show that the proposed HB-MFBs exhibit an excellent damping level compared with the BFBs with a similar size because of the countless microslips in the metal mesh blocks. In the dynamic load tests, the HB-MFB with a metal mesh density of 36% presents a viscous damping coefficient that is approximately twice that of the test BFB. The dynamics structural coefficients of HB-MFBs, including structural stiffness, equivalent viscous damping, and structural loss factor, are all dependent on excitation frequency and motion amplitude. Moreover, they exhibit an obvious decrease with the decline in metal mesh density.

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.

Accuracy of expressing the effects of hysteretic energy in terms of equivalent viscous damping according to ATC 40 and FEMA 440

2021 ◽  
Vol 244 ◽  
pp. 112804
Author(s):  
Oscar D. Gaxiola-Camacho ◽  
Alfredo Reyes-Salazar ◽  
Mario D. Llanes-Tizoc ◽  
Federico Valenzuela-Beltran ◽  
Edén Bojorquez ◽  
...  
Keyword(s):  
Viscous Damping ◽  
Equivalent Viscous Damping ◽  
Hysteretic Energy

Under-Actuated Humanoid Model With Elastomeric Springs

2017 ◽  
Author(s):  
Christian Fry ◽  
Stanley Coram ◽  
Davide Piovesan
Keyword(s):  
Human Body ◽  
Equilibrium Position ◽  
Static Stability ◽  
Viscous Damping ◽  
Equivalent Viscous Damping ◽  
New Model ◽  
Design Iteration ◽  
Hysteretic Effect

This paper presents the mechanical modifications and simulation of a bipedal humanoid system actuated with linear springs to produce a standing equilibrium position. The original humanoid system is comprised of two leg assemblies connected by a hip bracket. Eleven pairs of springs were attached to the system in locations designed to simulate the muscles and tendons in a human body. The next evolution of the LUIGEE project is the inclusion of three servo motors per leg and a series of elastomeric springs. Although servo motors have been introduced, it is desired to maintain the passive, static aspect of the previous prototype. This paper reports on part modifications to accommodate servo motors and the introduction of polymeric springs that guarantee static stability. ABS plastic and photopolymer resin was used to produce the new model. Due to the size of the motors, some parts of the original robot were redesigned. The new design iteration was stimulated using SimWise 4D®, where the hysteretic effect of rubber was modelled with an equivalent viscous damping.

Force Behavior of Parallel Double Coupling Beams with Different Width

2014 ◽  
Vol 578-579 ◽  
pp. 707-710
Author(s):  
Ming Li ◽  
Ji Guang Chen ◽  
Wei Jian Zhao ◽  
Li Guo Wang
Keyword(s):  
Finite Element ◽  
Energy Dissipation ◽  
Damping Coefficient ◽  
Viscous Damping ◽  
Coupling Beams ◽  
Equivalent Viscous Damping ◽  
Dissipation Coefficient ◽  
Finite Element Software ◽  
Double Coupling ◽  
Energy Dissipation Coefficient

The force behavior of parallel double coupling beams (PDCB) with different width is analyzed, based on which the feasibility of this kind of beams is discussed. The loading process of the PDCB is simulated by using finite element software ABAQUS. By analyzing the hysteretic loops, skeleton curves, energy dissipation coefficient, equivalent viscous damping coefficient and ductility coefficient,the bearing capacity and seismic performance of the PDCB is studied. Through simulation, it shows that the hysteretic loops is plump, and the energy dissipation coefficient, equivalent viscous damping coefficient and ductility coefficient of this double beams is high. It can be concluded that the PDCB has good force behavior, and the beams of PDCB can work in coordination.

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