Research into the identification of potential passive damping concepts for use in very slender structural members was continued. The following damping concepts are under investigation: mass-string dampers; bright zinc chain; polyethylene tubing; external viscoelastic tape; brushes for electrostatic and frictional damping; suspended chambers with oil and discs; and hybrid concepts. Each of these concepts are briefly discussed

Razzaq, Z.

English

NASA Technical Reports Server

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33 
A 
DEPARTMENT OF CIVIL ENGINEERING 
SCHOOL OF ENGINEERING 
OLD DOMINION UNIVERSITY 
NORFOLK, V I R G I N I A  
t 
PASSIVE DAMPING CONCEPTS FOR SLENDER COLUMNS 
I N  SPACE STRUCTURES 
BY 
Z i a  Razzaq, Pr inc ipa l  I nves t i ga to r  
Progress Report 
For the  per iod  ending February 1, 1985 
Prepared f o r  the 
National Aeronautics and Space Admin is t ra t ion  
Langley Research Center 
Hampton, V i  r g i n i  a 23665 
Under 
Research Grant NAG-1-336 
Harold G. Bush, Technical Monitor 
SDD-Structural Concepts Branch 
Submitted by  the 
Old Dominion Un ive rs i t y  Research Foundation 
P. 0. Box 6369 
Norfolk, V i r g i n i a  23508 
February 1985, . 
. 4  
https://ntrs.nasa.gov/search.jsp?R=19870001745 2020-03-20T14:04:10+00:00Z
PASSIVE DAMPING CONCEPTS FOR SLENDER COLUMNS I N  SPACE STRUCTURES 
BY 
Z i a  Razzap 
A. FURTHER PASSIVE DAMPING EXPERIMENTS 
Research i n t o  the  i d e n t i f i c a t i o n  o f  p o t e n t i a l  passive danping concepts 
f o r  use i n  very slender s t r u c t u r a l  members i s  continuing. The f o l l o w i n g  
danping concepts are under cur ren t  inves t iga t ion :  
1. Mass-St r i  ng Dampers 
2. B r igh t  Zinc Chain 
3. Polyethylene Tubing 
4. 
5. Brushes f o r  E l e c t r o s t a t i c  and F r i c t i o n a l  Damping 
6.  Suspended Chmbers w i t h  O i l  and Discs 
7. Hybrid Concepts 
Extensive t e s t i n g  o f  t he  f i r s t  t h ree  concepts already has been con- 
ducted. Experiments are p resen t l y  being c a r r i e d  ou t  f o r  t h e  4 t h  and t h e  5 t h  
concepts. A comprehensive research r e p o r t  embodying t h e  experimental re -  
s u l t s  and t h e o r e t i c a l  comparisons f o r  t h e  f i r s t  t h ree  danping concepts i s  
being prepared and w i l l  be ready i n  March, 1985, f o r  an i n i t i a l  review. A 
b r i e f  d e s c r i p t i o n  o f  each of t h e  seven concepts, and an o u t l i n e  o f  t h e  r e -  
s u l t s  obtained fo r  t h e  f i r s t  f ou r  concepts, are given here. Each o f  t h e  
t e s t s  was conducted on a p a r t i a l l y  res t ra ined  t u b u l a r  member 12 ft. long, 
as used prev ious ly  f o r  t h i s  research p ro jec t .  For each t e s t  conducted, t h e  
member was i n i t i a l l y  plucked a t  mid-height by  0.366 i n .  and then released 
External V i  scoel a s t i c  Tape 
t o  induce na tura l  v ib ra t i on .  The damped na tu ra l  frequency f o r  a l l  t he  cases 
was observed t o  be genera l l y  about 3.8 Hz exper imental ly wh i l e  t h a t  found 
*Associate Professor, Department o f  C i v i l  Enqineering, 01 d Dominion Univers- 
i t y ,  Norfolk,  V i r g i n i a  23508 
f rom Eq. 28 o f  t he  NASA Memorandum was about 3.7 Hz w i t h  a r o t a t i o n a l  end 
sp r ing  s t i f f ness ,  K, o f  2,230 i nch-pound/rad. 
1. Mass-String Dampers 
The concept of lead masses attached t o  a s t r i p  suspended i n s i d e  the  
t u b u l a r  member as described i n  NASA Technical Memorandum 85697 has been 
explored extens ive ly .  Spec i f i ca l l y ,  t he  in f luence o f  t h e  nunber o f  lead 
shots, and connection f r i c t i o n  on dmping i s  studied. F iqure 1 shows t w o  
curves f o r  dmping  r a t i o ,  c ,  versus t h e  nunber o f  lead  shots, N, w i t h  and 
wi thout  j a m  nuts, respec t ive ly .  The lead shots are suspended a t  member mid- 
he igh t  and attached t o  a nylon s t r i n q  next t o  each other.  The nylon s t r i n g  
i s  attached a t  the  top  o f  the  tubular member i n t e r n a l l y .  The j a m  nuts  a r e  
used f o r  a considerable reduc t ion  o f  connection f r i c t i o n .  As i s  evident 
from these curves, t he  presence o f  jam nuts r e s u l t s  i n  a reduc t ion  o f  the  
dmp ing  r a t i o .  For example, with a t o t a l  o f  15 lead shots, t he  value of 5 
with j a m  nuts i s  about 86% o f  i t s  value wi thout  j a m  nuts. Approximately, 
t h e  same d i f f e rence  holds f o r  a l l  other N values. For N = 21, t h e  value o f  
? i s  0.0060 w i t h  jam nuts. The corresponding experimental de f lec t ion- t ime 
p l o t  f o r  t h i s  case i s  shown i n  Figure 2. 
I n  t h e  experiments with N = 21, t h e  value o f  5 was found t o  vary 
s l i g h t l y  w i th  time. This v a r i a t i o n  diminished as a decreasing nunber o f  
lead  shots was used. 
2. Br ight  Z inc Chain 
A " b r i q h t  z inc chain" weighing 0.05 pound/foot was suspended i n s i d e  the  
t u b u l a r  member by a nylon s t r i n g  t o  absorb the  v i b r a t i o n  energy through 
c o l l i s i o n s  as wel l  as f r i c t i o n a l  forces between the  chain l i n k s .  Chains o f  
1, 2, 3, 5, 7, 9, and 10 f o o t  lengths were tested. Each chain was s i t u a t e d  
synmetr ica l  l y  about the  member mid-height. Natural  v i b r a t i o n  t e s t s  were 
2 
conducted i n  the  presence o f  end jam nuts. F igure 3 describes a t y p i c a l  
de f lec t ion- t ime p l o t  w i th  a 10 f o o t  long chain. This  f i g u r e  shows t h a t  t he  
motion o f  the  tubu la r  member i s  completely f i n i s h e d  w i t h i n  about 7 seconds. 
A noteworthy c h a r a c t e r i s t i c  o f  t he  chain danping approach i s  t h a t  t he  
5 values obtained from i t  increase considerably w i t h  t ime as the  chain 
length  i s  increased, un l i ke  the  mass-string concept i n  which 5 remains 
constant.  F igure 4 shows the  time-dependence o f  5 f o r  var ious chain 
lengths i n  t h e  form o f  5 versus average t ime curves f o r  chains of var ious 
lengths.  Each o f  t he  curves i n  t h i s  f i g u r e  i s  p l o t t e d  by  using the  r 
values computed from the  experimental de f lec t ion- t ime r e l a t i o n s h i p s  f o r  an 
average time, ta, It i s  
c lea r  t h a t  t h e  5 values increase r a p i d l y  both w i t h  an increase i n  t h e  
chain l eng th  as we l l  as the  t ime o f  v ib ra t i on .  The best r e s u l t s  are obta in-  
ed fo r  t he  10 f o o t  long chain for which 5 increases with t ime almost 
exponenti  a1 ly. 
o f  0, 1, 2, 3, 4, 5, and 6 seconds, respec t ive ly .  
3. Polyethylene Tubing 
Three d i f f e r e n t  types o f  polyethylene tubes were used f o r  damping by 
i n s e r t i o n  i n t o  the  tubu la r  member f o r  t he  e n t i r e  length.  One se t  o f  t e s t s  
was conducted w i th  a polyethylene funed tube w i th  an outer d ianeter  o f  0.33 
i nch  approximately. A second se t  o f  t e s t s  was conducted w i t h  a l ess  s t i f f  
po lyethy lene tube w i t h  the  sane cross sec t iona l  dimensions. The t h i r d  set  
of t e s t s  was conducted by f i r s t  i nse r t i ng  a low s t i f f n e s s  polyethylene tube 
(ou ter  diameter = 0.25 inch, w a l l  thickness = 0.04 inch  approximately) i n t o  
t h e  fumed tube, and then i n s e r t i n g  the  r e s u l t i n g  assembly i n t o  the  tubu la r  
member under t e s t .  The second setup gave the  maximum amount o f  damping 
compared t o  the  other 
0.0023. This system, 
two polyethylene tube setups, w i th  a 5 value of 
therefore, d id not prove t o  be as e f f e c t i v e  as the  
3 
mass-str ing o r  t h e  b r i g h t  z inc chain damping systems. 
4. External  V iscoe las t ic  Tape 
A one-inch wide paper- th in v i scoe las t i c  tape was mounted on the  ex ter -  
na l  surface of the  tubu la r  member over i t s  e n t i r e  length.  The tape was 
f i r s t  s p i r a l  wound around the  member and then the  whole assembly was placed 
i n  a temperature-control led heat ing system, and heated t o  200°F f o r  about 
f i v e  minutes. The procedure was sugqested by  the  manufacturers of t h e  tape 
b u t  appears not t o  have worked wel l  i n  t h i s  case. Th is  i s  because c e r t a i n  
p o r t i o n s  o f  the  tape appeared t o  have become somewhat overheated and embr i t -  
t l e d .  The maximum c value observed was n e a r l y  0.0018, w i t h  a frequency of 
3.60 Hz. Further  exp lo ra t i on  of both ex terna l  and i n t e r n a l  danping t r e a t -  
ments i s  necessary before a r r i v i n g  a t  any conclus ive decis ions. 
5. Brushes f o r  E l e c t r o s t a t i c  and F r i c t i o n a l  Damping 
A major problem faced i n  e l e c t r o s t a t i c  and (unavoidable) f r i c t i o n a l  
danping concept has been the  i d e n t i f i c a t i o n  and se lec t i on  o f  appropr ia te 
d i s s i m i l a r  mater ia ls  f o r  i n s t a l l a t i o n  i n  t h e  r a t h e r  l i m i t e d  space ava i l ab le  
i n s i d e  o f  the  tubu la r  member. Presently, t w o  types o f  brush-type ma te r ia l s  
are under inves t iqa t ion .  One of these cons is ts  o f  nylon f i b e r  brushes 
( t r a d e  name: Qu ick ie  Percolator Brush manufactured by Qu ick ie  Manufacturing 
Corporation, P. 0. Box 156, Cinnaminson, NJ 08077). Each brush i s  about 3.5 
inches i n  length  and can be forced i n t o  t h e  tubu la r  member and placed any- 
where lengthwise by means o f  a nylon s t r i ng .  Several such brushes can be 
used a t  the  same t ime t o  cover various lengths along t h e  member l o n g i t u d i n a l  
ax is .  The e l e c t r o s t a t i c  and f r i c t i o n a l  e f f e c t s  due t o  the  i n t e r a c t i o n  o f  
t h e  brush b r i s t l e s  and the  i ns ide  wal ls  o f  t he  member may produce damping 
e f f e c t s .  A second mater ia l  being considered i s  a "weatherstr ip"  used t o  
s top  window r a t t l i n g  ( t rade  name: P i  l e  Weatherseal manufactured by  Elgar 
4 
Products, Inc., Cleveland, OH 44122), which i s  0.25 inches wide, has 0.1 
i nch  long h a i r - l i k e  syn the t ic  b r i s t l e s ,  and can be used i n  any length  i n s i d e  
of t h e  member. Presently, t h in  long brushes mounted on m e t a l l i c  o r  p l a s t i c  
stems are being sought which may be i nse r ted  along w i t h  the  weatherst r ip  
w i t h  in terconnect ing l ow-s t i f f ness  springs. The i n t e r a c t i o n  of t he  brushes 
w i t h  t h e  weatherst r ip  may prov ide the des i red danping e f fec ts .  
6. Suspended Chambers w i t h  O i l  and Discs 
F igure  5 shows a nunber o f  chanbers w i th  o i l  and t h i n  copper d iscs  
suspended i n s i d e  the  tubu la r  member by a nylon s t r i ng .  The e f f e c t  o f  the  
nunber o f  chambers, o i l  v iscos i ty ,  and the  nunber o f  d iscs  on danping w i l l  
be invest igated.  
7. Hybrid Concepts 
Besides ca r ry inq  out  a search f o r  s i n q l e  danping concepts, combinations 
o f  t he  most promising concepts w i l l  a lso be tested. F igure 6 shows an exam- 
p l e  o f  a hyb r id  concept i n  which t h e  suspended chambers w i th  o i l  and d iscs  
are i nterconnected w i th  chains. 
B. NATIONAL SCIENCE FOUNDATION DYNAMIC EQUIPMENT PROPOSAL 
A research equipment acqu is i t i on  proposal t i t l e d  'IDynamic Equipment f o r  
Space and L i f e l i n e  Structures" has been submitted t o  the  Nat ional  Science 
Foundation, Washington, D.C. i n  December, 1984 by Z i a  Razzaq and Leon R. L. 
Wang. A t o t a l  o f  $93,387 has been requested from NSF ( o f  which one- th i rd  
cos t  w i l l  be shared by ODU) f o r  the  acqu is i t i on  of devices needed t o  conduct 
pass ive damping t e s t s  on slender members f o r  space s t ruc tu res  as we l l  as t o  
conduct some earthquake engineering tes ts .  There i s  a h igh  p r o b a b i l i t y  o f  
r e c e i v i n g  t h i s  funding by  June, 1985. If granted, a p a r t  o f  t he  funds w i l l  
a l so  be used t o  develop support-frames f o r  mounting specimens f o r  dynamic 
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t es t i ng .  This  p a r t i c u l a r  grant  program o f  NSF does not provide any support 
for t h e  graduate students or t he  p r i n c i p a l  i n v e s t i q a t o r  and i s  s t r i c t l y  
r e s t r i c t e d  t o  research equipment requests on a h i g h l y  compet i t i ve  basis. 
6 
.008 
- 007 
.006 
,., .005 
0 2 .004 
2 
2 .003 
.rl 
.001 
0 I I I 1 I 1 I 1  I 1 1 1  I 1 I I I 1 I I 1  
0 2 4 6 8 10 12  1 4  16 18 20 
Number of Lead Shots, N 
Figure 1 Effect of Connection Fr ic t ion  on Damping Ratio versus N r e l a t ions  
7 
0.4 
0.3 
0.2 
VJ : 0.1 c 
rl 
n 
0 
c) -0.1 
-0.2 n 
-0.3 
d 
U 
al 
d 
rw 
I I I I I I I I 
6 7 1 2 3 4 5 0 
Time, Seconds 
Figure 2 Deflection-Time Relationship with Mass-String System 
0.4 
0.3 
0.2 
0.1 
c 0 
$ -0.1 
VJ 
c 
rl 
n 
0 
rl 
al 
d 
v-l 
n al -0.2 
-0.3 
c 
5 6 7 0 1 2 3 4 
Time, Seconds 
Figure 3 Deflection-Time Relationship with 10 ft. Chain 
8 
.04 
.03 
0 
H 
.O' 
AVERAGE TIME, ta 
Figure 4 Time-Dependence of Damping Ratio for Various Chain Lengths 
9 
-TUBULAR MEMBER 
NYLON STRING 
SUSPENDED CHAMBER WITH OIL AND DISCS 
F igure  5 Suspended Chambers with O i l  and Discs 
10 
-TUBULAR MEMBER 
CHAIN 
SUSPENDED CHAMBER WITH OIL AND DISCS 
Figure 6 Hybrid Concept 
11 


Passive damping concepts for slender columns in space structures

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