Closure to “Discussion of ‘Deceleration of an Unbalanced Rotor Through a Critical Speed’” (1967, ASME J. Eng. Ind., 89, p. 585)

1967 ◽  
Vol 89 (4) ◽  
pp. 585-586
Author(s):  
W. K. Bodger
Keyword(s):  
Critical Speed ◽  
Unbalanced Rotor

Deceleration of an Unbalanced Rotor Through a Critical Speed

1967 ◽  
Vol 89 (4) ◽  
pp. 582-585
Author(s):  
W. K. Bodger
Keyword(s):  
Critical Speed ◽  
Degree Of Freedom ◽  
Bending Stress ◽  
Rotor Speed ◽  
Single Degree Of Freedom ◽  
Closed Solution ◽  
Rotor Shaft ◽  
Single Degree ◽  
Unbalanced Rotor ◽  
Maximum Increment

The problem of a single-degree-of-freedom rotor decelerating slowly through its critica speed is solved by an energy approach; a closed solution is obtained. A small discontinuous downward jump of rotor speed across the critical speed is shown to be required, either with or without damping in the system. The maximum increment of deflection, hence bending stress, in the rotor shaft is shown to be small, provided the rotor is carefully balanced and/or the system is sufficiently damped.

The Effect of an Electromagnetic Damper on Vibrations in Rotating Machinery

1991 ◽  
Author(s):  
M. E. F. Kasarda ◽  
P. E. Allaire ◽  
R. R. Humphris ◽  
E. J. Gunter
Keyword(s):  
Critical Speed ◽  
Rotating Machinery ◽  
Response Mode ◽  
Unbalanced Rotor ◽  
Stiffness Properties ◽  
Vibration Problems ◽  
Bending Modes ◽  
Stiffness And Damping ◽  
Mass Test ◽  
Electromagnetic Damper

Abstract Compressors, turbines and other rotating machines often have long thin shafts which may cause vibration problems. An electromagnetic damper placed on the rotor of a machine represents one method of controlling high levels of vibrations. This paper discusses experimental results of an electromagnetic damper placed on a small three mass test rotor. Experimental data was taken for cases with the damper at three different locations on the highly unbalanced rotor to study the effectiveness of the damper in controlling vibrations at the first and second rotor bending modes and at a pedestal response mode. Reductions of vibrations up to 88%, 40%, and 19% were achieved for the first critical speed, second critical speed, and pedestal response mode, respectively. Values of magnetic damper stiffness and damping used to obtain these reductions were only a small fraction of the fluid film bearing damping and stiffness properties.

Reducing Lateral Vibration of a Rotor Passing Through Critical Speeds by Phase Modulating

2003 ◽  
Vol 125 (3) ◽  
pp. 766-771 ◽  
Author(s):  
S.-M. Wang ◽  
Q.-S. Lu ◽  
E. H. Twizell
Keyword(s):  
Vibration Amplitude ◽  
Critical Speed ◽  
Lateral Vibration ◽  
Constant Acceleration ◽  
Unbalanced Rotor ◽  
Acceleration Rate ◽  
Modulated Phase ◽  
Response Phase ◽  
Theoretical And Numerical Analysis ◽  
Rotor Model

A method is presented to reduce the lateral vibration amplitude of an unbalanced rotor accelerating or decelerating through its critical speed, by means of modulating the response phase with varying acceleration rate. Theoretical and numerical analysis on the amplitude and the phase characteristics of lateral vibration of a rotor model are made. Numerical results show that when the rotor passes through its critical speed with a modulated phase, the response amplitude can be reduced by 20% or so, compared with the nonmodulated (constant) acceleration case.

Formation of Standing Waves in Radial Tires

1984 ◽  
Vol 12 (1) ◽  
pp. 44-63 ◽  
Author(s):  
Y. D. Kwon ◽  
D. C. Prevorsek
Keyword(s):  
High Speed ◽  
Critical Speed ◽  
Unit Length ◽  
Standing Waves ◽  
Rolling Resistance ◽  
Damping Coefficient ◽  
Circular Membrane ◽  
Critical Speeds ◽  
Steel Cord ◽  
The Individual

Abstract Radial tires for automobiles were subjected to high speed rolling under load on a testing wheel to determine the critical speeds at which standing waves started to form. Tires of different makes had significantly different critical speeds. The damping coefficient and mass per unit length of the tire wall were measured and a correlation between these properties and the observed critical speed of standing wave formation was sought through use of a circular membrane model. As expected from the model, desirably high critical speed calls for a high damping coefficient and a low mass per unit length of the tire wall. The damping coefficient is particularly important. Surprisingly, those tire walls that were reinforced with steel cord had higher damping coefficients than did those reinforced with polymeric cord. Although the individual steel filaments are elastic, the interfilament friction is higher in the steel cords than in the polymeric cords. A steel-reinforced tire wall also has a higher density per unit length. The damping coefficient is directly related to the mechanical loss in cyclic deformation and, hence, to the rolling resistance of a tire. The study shows that, in principle, it is more difficult to design a tire that is both fuel-efficient and free from standing waves when steel cord is used than when polymeric cords are used.

Optimum Design of Journal Bearings Dimensions for Rotating Machines

2020 ◽  
Vol 38 (10A) ◽  
pp. 1481-1488
Author(s):  
Tariq M. Hammza ◽  
Ehab N. Abas ◽  
Nassear R. Hmoad
Keyword(s):  
Aspect Ratio ◽  
Dynamic Response ◽  
Numerical Solution ◽  
Critical Speed ◽  
Design Method ◽  
Considerable Effect ◽  
Journal Bearings ◽  
Rotating Machines ◽  
Bearing Clearance ◽  
Study Results

The values of Many parameters which involve in the design of fluid film journal bearings mainly depend on the bearing applied load when using the conventional design method to design the journal bearings, in this study, as well as applied bearing load, the dynamic response and critical speed have been used to calculate the dimensions of journal bearings. In the field of rotating machine, especially a heavy-duty rotating machines, the critical speed and response are the main parameters that specify bearing dimensions. The bearing aspect ratio (bearing length to bore diameter) and bearing clearance have been determined based on rotor maximum critical speed and minimum response displacement. The analytical solution of rotor Eq. of motion was verified by numerical solution via using ANSYS Mechanical APDL 18.0 and by comparing the numerical solution with the preceding study. The final study results clearly showed that the bearing aspect ratio has little effect on the critical speed, but it has a high effect on the dynamic response also the bearing clearance has little effect on the critical speed and considerable effect on the dynamic response. The study showed that the more accurate values of bearing aspect ratio to make the response of rotor as low as possible are about 0.65 - 1 and bearing percent clearance is about 0.15 - 0.2 for different rotor dimensions.

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