The Influence of Structural Damping on Internal Pressure During a Transient Pipe Flow

1991 ◽  
Vol 113 (3) ◽  
pp. 424-429 ◽  
Author(s):  
Dan D. Budny ◽  
D. C. Wiggert ◽  
F. J. Hatfield
Keyword(s):  
Fluid Pressure ◽  
Equation Model ◽  
Piping System ◽  
Viscous Damping ◽  
Structural Damping ◽  
Equivalent Viscous Damping ◽  
Transient Event ◽  
Frequency Components ◽  
Transient Pipe Flow ◽  
Poisson Coupling

A four equation model of axial wave propagation with Poisson coupling which includes viscous damping to account for structural energy dissipation is evaluated. Comparison of the predictions with experimental data indicates that the model can satisfactorily predict fluid pressure and structural velocity. The results show that structural damping reduces the pressure peaks during a transient event by eliminating the high frequency components. For the conditions studied, this reduction was 20 to 25 percent for a piping system with no axial constraints. A saddle-type support increases the equivalent viscous damping, and this increased damping can be modeled as either distributed damping or as an external damper.

An Experimental Study on the Influence of Structural Damping on Internal Fluid Pressure During a Transient Flow

1990 ◽  
Vol 112 (3) ◽  
pp. 284-290 ◽  
Author(s):  
D. D. Budny ◽  
F. J. Hatfield ◽  
D. C. Wiggert
Keyword(s):  
Experimental Study ◽  
Transient Flow ◽  
Traditional Approach ◽  
Dynamic Pressure ◽  
Fluid Pressure ◽  
Piping System ◽  
Internal Dynamic ◽  
Structural Damping ◽  
Pipe System ◽  
Internal Fluid

The traditional approach to designing a piping system subject to internal dynamic pressure is to restrain the piping as much as possible, and the approximation made in the analysis is to assume no contribution of structural energy dissipation. To determine the validity of this concept and approximation, an experimental study of a piping system was performed to measure the influence of structural damping. A pipe system was designed with a loop that could be turned so that its natural frequency would match that of the contained liquid. It was discovered that a properly sized damper on the piping loop greatly accelerates the decay of the fluid pressure transient. The damper absorbs some energy from the piping, reducing the resulting rebound fluid pressure. When the loop is subjected to forced steady-state vibration, there is a fluid pressure response. The amplitude of that pressure can be reduced by installing an external damper: the stiffer the damper the more effective it is in reducing dynamic pressure.

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.

Rayleigh Damping Effects on Global Analysis of Umbilicals

2011 ◽  
Author(s):  
Lauro Massao Yamada da Silveira ◽  
Rafael Loureiro Tanaka ◽  
Joa˜o Paulo Zi´lio Novaes
Keyword(s):  
Global Analysis ◽  
Time History ◽  
Systems Design ◽  
Hydrodynamic Drag ◽  
Viscous Damping ◽  
Structural Damping ◽  
Peak Period ◽  
Rayleigh Damping ◽  
Drag Forces ◽  
Offshore Industry

Despite global analysis of umbilicals is a well-known area in the offshore systems design, some topics are still opened for discussions. One of these topics refers to the structural damping. Obviously, the viscous damping caused by hydrodynamic drag forces is the major source of damping to the whole system. However, in some severe load cases, the host vessel dynamics may induce high snatch loads to the umbilical top end and these loads are more related to structural damping, specifically in tension–elongation hysteresis, than to viscous damping. The snatch loads must be taken into account in the whole design process, which leads to an umbilical designed to resist to higher tension loads and implies also, in most cases, in over-dimensioned accessories, such as the bending limiters. Actually, due to the high level of friction between layers, the umbilical presents some level of structural damping which is, in fact, related to hysteretic moment-curvature and tension-elongation relations. This intrinsic structural damping may in fact contribute to the reduction of the snatch loads and considering it may reduce the level of conservatism in the design. However, due to the complexity and diversity of umbilical designs, it is not straightforward to come up with general-use hysteretic curves. A simplification then is to apply classic Rayleigh damping. Typically, damping levels of 5% are accepted in the offshore industry when using stiffness-proportional Rayleigh damping (the 5% damping is a percentage of the critical damping and is accounted for at the regular wave period or irregular wave spectral peak period). The problem here is that stiffness-proportional Rayleigh damping increases linearly with the frequency and the damping level at 1Hz, for example, may get to 60%. This fact indicates that the high-frequency part of the response may be simply discarded from the results, which in turn may lead to an incorrect, over-damped analysis. The present work aims tackling the Rayleigh damping issue, evaluating its effects on tension levels and spectral density of the tension time history. A recommendation of how to apply Rayleigh damping is proposed.

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
Sign in / Sign up

Export Citation Format

Share Document