A new type of vibration damper for rotor systems was developed and tested. The damper contains electroviscous fluid which solidifies and provides Coulomb damping when an electric voltage is imposed across the fluid. The damping capacity is controlled by the voltage. The damper was incorporated in a flexible rotor system and found to be able to damp out high levels of unbalanced excitation. Other proven advantages include controllability, simplicity, and no requirement for oil supply. Still unconfirmed are the capabilities to eliminate critical speeds and to suppress rotor instabilities

Hoque, M. S.

Nikolajsen, Jorgen L.

English

NASA Technical Reports Server

AN ELECTROV I scous DAMPER' 
J.L.  Nikolajsen and M.S. Hoque 
Department o f  Mechanical Engineering 
Texas A&M University 
College Station, Texas 77843-3123, U . S . A .  
A new type of vibration damper for rotor systems has been developed 
and tested. The damper contains electroviscous fluid which solidifies and 
provides Coulomb damping when an electric voltage is imposed across the 
fluid. The damper has 
been incorporated in a flexible rotor system and found to be able to damp 
out high levels of unbalanced excitation. Other proven advantages include 
controllability, simplicity, and no requirement for oil supply. Still 
unconfirmed are the capabilities to eliminate critical speeds and to 
suppress rotor instabilities. 
The damping capacity is controlled by the voltage. 
INTRODUCTION 
Electroviscous fluids have been known for almost a century. In 1885, 
Koenig [l] tried unsuccessfully to demonstrate a viscosity change in a 
fluid due to an imposed voltage. Duff [2] and Quincke 131 succeeded in 
1896-97 with glycerin and other liquids. It has since been found that a 
wide variety of fluids and fluid/solid mixtures (e.g. starch in silicone 
oil) exhibit some level of electroviscosity [4],[5]. However, the effect 
remained too weak for practical applications until the early 1980's when 
advances in polymer research led to electroviscous or EV-fluids with 
sufficient strength to warrant patent protection, e.g. [ 6 ] .  
The main effect in the modern fluids is not the viscosity ch,ange but 
the creation of a solid consistency with an initial shear strength which 
must be overcome before the llfluidll will flow. 
terminology, the fluid turns into a Bingham plastic when subjected to a 
voltage, see Fig.1. Some important characteristics of the modern fluids 
are as follows: the composition is roughly a 1:l suspension of 10~1 DIA 
polymer particles in silicone oil; the optimum thickness of the fluid layer 
to be sheared is 1-2 mm; the required voltage for full activation is 
5,000-10,OOOV; the maximum current is less than 10 mA; the maximum yield 
strength obtainable is about 5-10 kPa; the fluid activation and 
deactivation time is less than 1 ms. The invention of the modern fluids 
led to a profusion of suggested applications in the early 1980's, e.g. [7], 
[ 8 ] ,  [9]. However, to the authors' knowledge, the damper proposed in this 
In fluid dynamics 
1. This work was supported by the TAMU Turbomachinery Research Consortium. 
The rig hardware was donated by John Crane-Houdaille, Inc., and the EV-fluid 
was donated by Castrol Research Laboratories, U . K .  
133  
https://ntrs.nasa.gov/search.jsp?R=19890013527 2020-03-20T03:08:41+00:00Z
paper represents the first application of EV-fluids to vibration control of 
rotor systems. 
THE EV-DAMPER PRINCIPLE 
The electroviscous, or EV-damper design is shown in principle in Fig. 
2.  A rotating shaft is supported by a bearing with the outer race 
connected to the damper housing via a so-called squirrel-cage which 
provides radial support flexibility. The outer bearing race also supports 
a non-rotating disk located inside the damper housing. The housing is 
filled with EV-fluid. Two annular rubber membranes seal the damper 
housing. The fluid films between the disk and the housing solidify when a 
DC voltage is applied between the disk and the housing. The solidified 
fluid provides Coulomb damping which impedes the radial motion of the disk, 
thereby attenuating the radial vibration of the shaft. The damping 
capacity is controlled by the applied voltage. 
THE EXPERIMENTAL APPARATUS 
Rig Hardware 
An EV-damper with six moving disks and five stationary disks was 
designed and built and incorporated in a simple flexible rotor system as 
shown in Figs. 3 and 4 .  The entire apparatus is made of steel. The design 
configuration simulates the low pressure shaft of a gas turbine engine with 
the rotating disk simulating the fan stage. This configuration was chosen 
to demonstrate the capability of the damper to attenuate the high load 
excitation that follows a fan blade loss. The rotor is driven by a small 
air-motor through a flexible rubber coupling. A small electric pump slowly 
circulates the EV-fluid through the damper to prevent the polymer particles 
from settling out. 
The multidisk damper configuration was designed to ensure that 
optimum system damping could be reached. 
damping C was found by rotor analysis to be about 4000 Ns/m. The total 
area A for fluid shearing in the damper was then estimated from 
The optimum equivalent viscous 
see [ l o ] ,  with Fo = PA. 
maximum shear strength of ?he EV-fluid; o is the rotational speed; x is 
the vibration amplitude; and b=uA/h is the viscous damping coefficient 
between the disks where u is the fluid viscosity and h is the fluid-film 
thickness. Thus, the total required area A of fluid shearing was estimated 
to be roughly 4000 cm2 with a fluid-film thickness h=1.6mm. The maximum 
possible radial rotor excursion at the damper location is 1 cm. 
F is the constant Coulomb damping force; p is the 
0 
134 
The squirrel-cage consists of three outer beams and three inner beams 
connected via an electrically insulating disk. 
Each beam is 4 . 8  cm long by 4 . 8  mm dia. 
insulated from the damper at the bearing outer race. 
electrically insulated from the base plate. 
The beams are 120' apart. 
The shaft is electrically 
The damper housing is 
EV-Fluid 
The EV-fluid used here has the following known characteristics: 
Composition: 12 IJ dia particles in silicone oil 
Max. yield strength: 
Viscosity: 
Density: 1110 kg/m at 25 C 
4 EPa at 3.5 kV/mm 
100 CP ajt 30 Co(deactivated) 
Damper Power Supply 
The circuit diagram of the damper power supply is shown in Fig. 5. 
The damping capacity is controlled manually via the variable transformer. 
Instrumentation 
Two perpendicular pairs of  inductive proximity probes pick up the 
shaft displacements near midspan and near the damper as shown in Figs. 3 
and 4 .  
circuits. The signals are then AID-converted and recorded on a 
micro-computer in the usual fashion. 
on an oscilloscope for critical speed identification and as a safety 
precaution. The rotational speed is derived from a photodiode facing a 
black and white painted stripe on the rotating disk. The speed signal is 
also recorded digitally and displayed live by a digital timer/counter. 
The DC-offsets of the probes are removed by standard op-amp summer 
The signals are also displayed live 
RESULTS 
Controllability 
The rotor system shown in Figs. 3 and 4 was run up to its first 
critical speed (rigid body pitching mode) at about 1400 rpm and voltage was 
applied to the damper. 
by a factor 4 as shown in Fig. 6. 
slightly smaller orbits which grew to the steady-state size shown within a 
few seconds. 
The shaft whirl orbit near the damper was reduced 
Rapid voltage application resulted in 
High Load Damping Capability 
The rotor was run up to about 2000 rpm and an 8040 g.mm balance weight 
was knocked of f  to simulate a blade loss. The rotor was then allowed to 
decelerate slowly down through its critical speed. Fig. 7 shows the 
135 
With the current damper, the response peaks could not be sufficiently 
separated because the residual damping, due to fluid viscosity and the 
rubber seals, is too large. The damper will be redesigned with fewer disks 
and better seals to demonstrate the critical speed elimination. It is 
expected that a reduction of the residual damping will also result in a 
more dramatic rate of reduction of the unbalance response than demonstrated 
in this paper. 
response, including the initial transient, with and without voltage 
application. The reduction of the response after voltage application is 
substantial. The critical speed is almost eliminated. 
CRITICAL SPEED ELIMINATION 
The EV-damper also has the potential capability to eliminate critical 
EV-fluid will solidify 
speeds as shown in Fig. 8. As the rotational speed approaches the critical 
speed Qcr maximum voltage is applied at R1. 
and i t  will remain solidified provided the yield strength of the "fluid" 
films exceeds the unbalance force transmitted through the damper. The 
effective rotor support stiffness will therefore increase so the critical 
speed will increase and the response curve will move to the dashed location 
in Fig. 8. The response at R1 will then drop as shown and the rotational 
speed can be increased to R The voltage is then disconnected and the 
response curve jumps back to its original position as the fluid relaxes. 
The fluid relaxation time is less than one millisecond which, for most 
applications, is too short f o r  any vibrations t o  build up. Thus, the 
critical speed has virtually been eliminated. Rotor deceleration is 
analogous. 
The 
2 '  
The minimum response that can be achieved is represented by the bottom 
point of the valley between the peaks. The elevation of this point depends 
on the sensitivity of the critical speed to changes in rotor support 
stiffness. It also depends on the bandwidth of the response peak which is 
a function of the residual damping with the EV-fluid relaxed. 
CONCLUSION 
A new type of rotor-damper has been built and tested f o r  the first 
time. The damper contains an electroviscous fluid which provides Coulomb 
damping at a variable rate controlled by a DC-voltage applied to the fluid. 
Widespread industrial application of  this damper is anticipated due to 
its simplicity, controllability, high-load damping capability and its 
potential capability to eliminate critical speeds. 
136 
REFERENCES 
1. Koenig, W., I1Bestimmung einiger Reibungscoefficienten und Versuche 
uber den Einfluss der Magnetisirung und Electrisirung auf die Reibung der 
Flussigkeiten," Annalen der Physik und Chemie, Vol. XXV, No. 8, 1885, pp. 
618-625. 
2. Duff, A.W., "The Viscosity of Polarized Dielectrics,'' Physical Review, 
Vol. 4 ,  NO. 1, 1896, pp. 23-38. 
3.  Quincke, G., "Die Klebrigkeit isolirender Flussigkeiten im constanten 
electrischen Felde," Annalen der Physik und Chernie, Vol. 62, No.9, 1897, 
pp. 1-13. 
4 .  Winslow, W.M., "Method and Means for Translating Electrical Impulses 
into Mechanical Force," U . S .  Patent No. 2,417,850, 1947, (filed 1942). 
5 .  Winslow, W.M., "Induced Fibration of Suspensions," Journal of Applied 
Physics, Vol. 20, No. 12,1949, pp. 1137-1140. 
6. Stangroom, J.E., "Electroviscous Fluids," U.S. Patent No. 4,502,973, 
1985. 
7. Kerr, J., "Freeze! A Solid Chance to Jam Liquid Flow Lines," The 
Engineer, July 1981, pp. 63 and 67. 
8. Brooks, D.A., "Electro-Rheological Devices," Chartered Mechanical 
Engineer, Sept. 1982, pp. 91-93. 
9. Scott, D., "Amazing Hardening Fluid," Popular Science, April 1984, pp. 
82-85. 
10. Den Hartog, J.P., "Mechanical Vibrations," 4th Ed., McGraw-Hill, 1956. 
137 
L 
Figure 1 EV-Fluid Behavior 
DC 
v o  
Figure 2 EV-Damper Principle 
138 
ORfGINAU PAGE 
BLACK AND WHITE PHOTOGRAPH 
a, 
L 
h o c ,  c, 
*r .r a, .r a, 
L 
W E  Q E 
0 *-a, I E .? a, 
c, x n > a  X Q  0 u) o o o w n  0 0  a, e m  E: 
-c L L  LL. - s L-r a aa n U'V a- L 
*I-- c, V - L ~ C L  o 
crcl mns a s  Lc, 
.!-a, 3 0  * r O  
- 
F 
S h a f t  1067mm long, 25.4mm d i a .  
Disk 25.4mm t h i c k ,  229mm d i a .  
F i g u r e  3 EV-Damper Test R i g  (Schemat i c )  
F i g u r e  4 EV-Damper Test Rig 
139 
119 
60Hz 
Locat ion  : 
Near Damper 
Var i a  b l  e 
Transformer 
Speed 1400rpm 
Unbal. 1270g.mm 
Damper 
DC Power 
0- 10, ooov 
max. lOmA 
r 
0-12ov 
F i g u r e  5 Damper Power Supply 
F i g u r e  6 Trace of S h a f t  W h i r l  
O r b i t s  Near Damper 
140 
+ 
A' 
A 
A 
4- ++- 
\A A 
&%A 
AA 
'\A. 
A A- 
+ 
F i g u r e  7 S imula t ed  Blade  Loss  Response as a Func t ion  of Vo l t age  
I I I I I 
*I Qr *2 Gr speed  (rpm> 
F i g u r e  8 C r i t i c a l  Speed Elimination (Schemat- ic)  
141 


An electroviscous damper

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