The development of a moire technique suitable for the analysis of object deflections in a cryogenically cooled, transonic wind tunnel is described. The operating environment for the wind tunnel has a temperature range of 77 to 3390 k, pressure to 91390 Kgs/sq m, and noise to 150 dB SPL. Efforts were made to accomplish the following: to demonstrate projection moire as it would be used to study structural deflections; to use optical processing to multiply the sensitivity of the moire; and to investigate a system design based on the requirements of the wind tunnel geometry

Harding, K. G.

Harris, J. S.

English

NASA Technical Reports Server

General Disclaimer 
One or more of the Following Statements may affect this Document 
 
 This document has been reproduced from the best copy furnished by the 
organizational source. It is being released in the interest of making available as 
much information as possible. 
 
 This document may contain data, which exceeds the sheet parameters. It was 
furnished in this condition by the organizational source and is the best copy 
available. 
 
 This document may contain tone-on-tone or color graphs, charts and/or pictures, 
which have been reproduced in black and white. 
 
 This document is paginated as submitted by the original source. 
 
 Portions of this document are not fully legible due to the historical nature of some 
of the material. However, it is the best reproduction available from the original 
submission. 
 
 
 
 
 
 
 
Produced by the NASA Center for Aerospace Information (CASI) 
https://ntrs.nasa.gov/search.jsp?R=19810017619 2020-03-21T12:04:48+00:00Z
UNIVERSITY OF DAYTON
RESEARCH INSTITUTE
DAYTON, OHIO 45469
EVALUATION OF MOIRE TECHNIQUES
FOR WIND TUNNEL METROLOGY
Interim Report,
J. S. Harris and K. G. Harding
Report Period 4/1/81 to 6/30/81
Grant No. NAG-1-143
June 1981
Prepared for
National Aeronautics and Space Administration
Langley Research Center (NASA/Langley)
Hampton, Virginia 23665
(NASA-CH-164477)
	 EVALUATICN CL MOI&L
	 N81-26155
TECHNI4JLS FOh BINC TUNNL•L METROLOGY
Interim Retort, 4 Jan. - 30 Jun. 1981
;Dayton Univ., Ohio.)
	 17 p HC AJ2/17F A01
	 Unclas
CSCL 148 G3/OS 20620
""?
JUL
'i flT
,iECEIVED
NASA STI FACILITY,
ACCESS DOd
•^	 i
UNIVERSITY OF DAYTON
t;
	
	 RESEARCH INSTITUTE
DAYTON, OHIO 45469
Evaluation Of Moire Techniques
For Wind Tunnel Metrology
1. Report Period
This report covers the period from 1 April 1981 to 30 June
1981 for work conducted under research grant number NAG-1-143
from the National Aeronautics and Space Administration, Langley
Research Center, Hampton, Virginia.
2. Study Objectives
The purpose of this program is to investigate the develop-
ment of a moire technique suitable for the analysis of object
deflections in the cryogenically coined, transonic wind tunnel at
NASA, Langley Research Center. The operating environment for the
new wind tunnel !ias a temperature range of 77 to 3,390°K (140 to
6100 R), pressure to 91,390 Kgs/sq. meter (130 psia), and noise to
150 de SPL. Expected object deflections of 75 millimeters (3
inches) need to be measured accurately to better than 1 part in
1,200. Contact methods provide only a limited number of data
points at the risk of disturbing the flow or mechanically
changing the response of the structure. The moire technique
under investigation provides a wide range of sensitivity with a
full-field, noncontact approach. The objectives of this study
are: (a) to demonstrate projection moire as it would be used to
study structural deflections, (b) to use optical pro-zessing to
multiply the sensitivity of the moire, and (c) to investigate a
system design based on the requirements of the moire technique
and the restrictions imposed by the wind tunnel geometry.
Y.
....v4..,:...,,. s.r}b•rc^i?aw+./_. ti'%2KA.e...•...^^'^stx
	 Y	 ^	 :"rrY1+.^p --... ..i:ti...
I3.	 R & D Status Report
Moire testing is a full-field, noncontact method of
measuring out-of-plane displacements of a structure. There are
five basic types of moire: shadow, reflection, projection,
contact, and holographic. Shadow moire is clearly the simplest,
requiring only that a grating be placed close to the test object
which is then illuminated by a point source. The shadow of the
grating on the object as viewed through the grating creates a
contour moire which maps the topography of the object. Because
of the sensitivity to surface topography and the requirement that
a grating be placed close to the object, shadow moire is not
suitable for testing in a wind tunnel and has not been pursued.
Reflection moire requires that the surface of the object be
specular. A grating can be reflected off the object and imaged
onto a reference grating. To accomplish this, the object must be
viewed at the specular angle. Because of these restrictions, this
approach is also not desirable for testing in a wind tunnel.
Projection moire provides greater versatility than shadow
or reflection moire. A grating is projected onto the test
object. This object grating is photographed at some angle other
than the projection angle and compared to a master reference
grating creating the moire. If the reference grating is made
photographically, directly from the image of the object grating,
the contour of the object will be subtracted out of the moire and
only displacements from the reference position will be measured.
Projection moire is a possible candidate for wind tunnel testing
if the physical facilities permit two suitable access angles.
Contact moire uses a grating applied directly to the
object. The grating can then be photographed directly and
compared to a reference master grating, which can be a photograph
of the object grating before it is deflected (thus subtracting
out the object topography). only one access angle is required
for this type of moire. As an alternate approach, a second
2
igrating can be projected onto the contacted grating which will
create a moire directly on the object. 4b subtract out the
object topography, this second grating would need to be made from
a photograph of the underformed contacted object grating.
Contact moire would be the most appropriate approach to wind tun-
nel testing, if only one access angle is available.
Holographic moire involves making a real-time or double-
pulsed hologram of the test object and comparing the high-fre-
quency holographic fringes with a reference grating or another
set of holographic fringes (such as in sandwich holography).
Because of the stability requirements of holography and the dif-
ficulty of interpreting the data, holographic moire is not seen as
a viable option for wind tunnel testing.
The above moire techniques are summarized in Table 1. The
systems being investigated are projection moire, contact moire,
and possible combinations of the projection and contact moire.
An appropriate system will be relatively insensitive to vibra-
tions of the system and capable of taking data quickly, probably
using a short pulse light source. A real-time visualization
would be possible, but to obtain high sensitivity in areas of
interest, optical processing will be required.
4.	 Results
As a demonstration of testing dynamic objects with projec-
tion moire, we have applied the technique to a ten-inch vibrating
steel plate driven at resonance. The object grating was produced
by imaging a ronchi ruling onto the plate so as to have approxi-
mately a 2-line-per-millimeter (50-line-per-inch) grating on the
object. The grating was photographed at various points in the
vibration cycle, using a Q-switched ruby laser to freeze the
motion of the plate. By taking two of the photographs 180
degrees apart in phase as referenced to the vibration cycle of
the plate and laying one over the other, we obtained the moire
pattern shown in Figure la. The sensitivity of this moire is
approximately 500 microns (0.02 inches) per moire fringe.
3
We then multiplied the sensitivity of this moire by optical
processing to obtain a sensitivity of 250 microns (0.01 inches)
and 125 microns (0.005 inches) per fringe as shown in Figures lb
and lc. The original photographs made with the ruby laser were
recopied using a high contrast process to obtain higher diffrac-
tion efficiency. The multiplication of sensitivity is
accomplished by selecting out specific diffracted orders in the
optical Fourier transform of the object photograph which
correspond to the spatial frequency sensitivity desired. The
moire is created between a master grating made in the optical
processor using one of the abject photographs and the image
created in the optical processor of the other photograph. The
direction of a deflection can be determined in the optical pro-
cessor by laterally translating the master grating relative to
the image of the test grating.
As an alternate approach, we made a double exposure pho-
tograph of the plate undergoing random vibrations using the ruby
laser as the light source. A section of the double-exposure pho-
tograph is shown in Figure 2a. The moire created in this fashion
is an additive moire which is inherently low contrast. By optic-
ally filtering out the frequency information relating to the
grating and leaving only the information relating to the moire
pattern, the moire pattern is effectively enhanced as shown in
Figure 2b. This approach permits changes on a short-time scale
to be recorded.
A technique similar to double-exposure moire is time-
average moire. To demonstrate time-average moire, we projected a
reference grating onto a ten-inch steel plate which had an object
grating glued onto its surface (using stripping film). The
period of the contacted object grating was 4 lines per millimeter
(100 lines per inch). The projected grating was made using an
Argon laser and a Wollaston prism. By mismatching the period of
the projected grating relative to the object grating, we
_.,tea	 ,=.acs .acnr.^413 .^ ,..
	 F	 -	 _	 -..
w a 1 nN`°	 ....	 '•.vpt'F^ NaLrnry	 "ih £N: V ^i'L"' 	 i"^ +} y'	c-Tn se	 •.. .c ... 4	 H'.+e
a (,
^Q
(.b	 t e
created a set of bias fringes with a period of 1 line per milli-
meter (25 lines per inch). The low-frequency bias fringe was
easy to record, since it did not require high-resolution optics,
yet the sensitivity was still determined by the projected grating
which was 5 lines per millimeter (125 lines per inch).
When the plate was driven at resonance, we obtained the low-
contrast, time-average moire shown in Figure 3a. This photograph
is similar to the double-exposure photograph made with the ruby
laser. By optically filtering the time average photograph we
obtained the moire pattern shown in Figure 3b. Time-average
moire would allow oscillatory motions to be integrated over a time
period and recorded using very little light.
An important technical consideration for any of these moire
approaches is the type of photographic film required. The pho-
tographic film should be high contrast and fast, with sufficient
resolution for the type of moire. We conducted a survey of some
possible films. The results are summarized in Table 2. Photo-
micrographs of a sinusoidal grating photographed with the various
films are shown in Figure 4.
Holographic film (Figure 4d) gives very high resolution,
high contrast, and relatively low noise. The only real limita-
tion of the holographic film is the relatively slow speed.
Technical Pan film (Figure 4c) was found to give a reasonable
trade-off between speed and resolution. At the ruby laser wave-
length the Technical Pan film was found to have the highest
sensitivity. Both the holographic plate copy and the
lithographic film copy of the Technical Pan film (Figure 4e and 4f)
showed higher contrast, thus higher diffraction efficiency, and
less noise. The holographic plate had the advantage of being on
a glass plate which introduced
the lithographic film.
5. Future Work
The demonstrated sensitivity of the pulsed moired to date
has been 125 microns (0.005 inches) per fringe, which would yield
a readable sensitivity of about 25 microns (0.001 inches) of
deflection. We will be further investigating the pulsed and con-
tact moire. These approaches can be scaled up to larger objects
using a lower frequency grating on the object. We will also be
investigating additional possible films.
The results of this investigation will depend on the physi-
cal limitations imposed by the wind tunnel and test objects on
the particular moire systems. Based upon this investigation, we
will identify what would be required to develop an appropriate
moire system for wind tunnel tests.
6. Overall Program Status
The present level of effort is expected to meet the program
objectives as stated.
6.1 Performance and Cost Report
Funds spent to date	 $10,318.61
Outstanding Commitments	 740.00
Percentage of total grant amount
spent to date (funds spent +
outstanding commitments/$29,374)
	 388
Remainder of grant funds 	 $18,315.39
6.2 Overall Cost Status
The remaining funds are sufficient to complete the
program.
6
N
c
v
cg
W
m
a N
z o+s ro
W C
E-4	 ro
ti]	 >
a m
O0 N•.1
S A
O
z
0
to
a
Q
y
O W
tT
ro
C •-I
U	 .+ V v	 W roC v N v •• + N	 v Vv L 0 4 JJ ^•-^	 I	 N •.+w	 O CL 7 41 L ro aJN O v O O CL L •.a .•1 C Ciw 4 C E C vO
L'OL vL Lm ti
ro
•^TL41
v avi ro 3 tr •°' >, 0 .0 c -Mtr
C C E W	 c W ro .0 r0 03: C
ro	 •M v v •-1 a E 041 y .4 •.1	 •.1
c N Nt>O daJ >, v m c •M 0 y NU •4 N •.+ v W V v >. •• 1 .r v
v.J^ vNU v W w'p 0040
•n ro V E00p O > V•.+ v CN700O MW E+CIG QNCfc ULVC^
C d
0
c
y
•'''1 >>1 E	 C C	 v •^.1 p
,1 V r °	 N W• to •	 •	 f .0	 rn m JI
> C v w	 3 tr A	 v c aJ c
..1 v r° w
•C JJ IAA 1>0 aJ N,,,1 V
N w v 01 tT E• U U ro E E
	 3•+ IT OC v L •r1 C •.•1 •'1 N • '1 W W o	 W tT •H JJ >1tY w N > ro .0 w C L 0 tT Q1
	
.0 r	 JJ
N 7 0 V 0 0+ v	 10 JJ •.1N E W W N .•1 •.4 ro N N	 > N v N '•1 >^p v ro ro v ro L W v, •'1 •'1 J.J v 7 •.1Cl W ,1J .•1 .i w to v ro C, ra w JJ 4J x V W 0 +1y •.4 U 7 7 V w JJ	 tU ./ V •'J ro v ..1 "J..
•.^ 7 v U V 7 •14 •.4 >. N 7 v tN	 •n 344 NEtT •n v v 014J AJ E ^4 '•1 0''n C w p pe w c
•. 1 v
.Z 99 m 04 04ONN v 04040 0 ••1 C 0zr10Gb v J7 v W Wa0N004 v •.a varON
C	 4% v	 041 v • v c
> 3N7.0 CNJ 1C0 >14
.1 •.1 E • 4 •.1 .4 iJ 041
JJ L C	 N 41 JJ 04 •.1 04J 0 •N O v '•I m 0 ad > .-I
C c°O+ C tJ W U C. •.4 C JJ N
••+ • v 0 0 •.+ C >1	 O •.•+	 v
^lC
EN a0 OL^4V cw•q	 rz• v •N w • '1 N	 O•.1 J.1 ,0 v ro vtd v •^1 JJ V 11 v '0
	
w V	 4J ••• 1 	 E N 01 N
ro 0 N tV	 • ro •-1 .J >r w •m UC4 a••+ N u .a v N 10
 0 0 .'1
	 0 t .c •^1E E w w C ro v •-1 v • .1 N E c w 0^	 JJ
V] y U L W	 7 av > Ar	 C. .-1 V ,0 W c 0
v
w
U	 4
7	 •H
N	 0
0	 X
Q1
W
•-+ U
r c c 04 _0 .1
°
o
14 vcxu a
Ai V W 4J3 C01 v C.•O.1	 v roO v v 0+ v
,O ^4 Si •n W .0 •'1 U yJ p w
ro w ..1 0 .^ V JJ 0 c .i •.1
av ^ 8004 SE
r-1 N M 4 1n ^p
TABLE 2. COMPARISON OF POSSIBLE FILMS FOR MOIRE PHOTOGRAPHS
Film Exposure Devel. Comments
1. 35 mm Litho- 9 sec Litho, 2 min High contrast,
graphic film noisy,	 (no ruby
sens).
2. Polaroid Pas/Neg - 50 sec Low contrast,
grainy
3. Litho Copy of High contrast,
Polaroid Pos./ - - sensitive to
Neg irregular orig.
4. Agfa Gaveart 1 sec HRP,	 10 min High contrast,
10 E56 very fine grain
Holographic
Plate
5. Technical Pan 1 sec D-19,	 6 min Med. contrast,
med. grain
6. Agfa Gaveart 4 sec HRP, 8 min High contrast,
10E75 copy of some noise from
Technical Pan Tech. Pan base
7. Litho copy of 0.4 sec Litho, 6 min High contrast,
Technical Pan Noise from base
8. Panatomic-X 2 sec D-19,	 4 min Low contrast,
grainy
e
k
F e
I(
8
i
e v-. w^.-..:	 .......	 .. .,..+-.:'SS,=W w'V}: s^	 N -.-3g^^.Ya 3<b' .e.Y..naa A...c	 .^ ^. r• _n...u.a.
f;
LIST OF FIGURES
Figure No.	 Title
1
	
	
Steel Plate Resonating at 60 Hz, Various
Sensitivities.
2a	 Double Exposure of Vibrating Steel Plate.
2b	 Double Exposure after Optical Filtering.
3a	 Time Average Moire Photograph of Resonant Plate.
3b	 Time Average Moire after Optical Filtering.
4a	 35 MM Lithographic Film Photo of Grating.
4b	 Polaroid Pos/Neg Photo of grating.
4c	 Lithographic Copy of Polaroid Pos/Neg Photo.
4d	 Holographic Plate (10E56) Photo of Grating.
4e	 Technical Pan Film Photo of Grating.
4f
	
	
Holographic Plate (10E75) Copy of Technical Pan
Photo.
4g Lithographic Copy of Technical Pan Photo
4h Panatomic-X Film Photo of Grating.
9
(a) 1X Multiplication
(c) 4X Multiplication
(b) 2X Multiplication
f I )' ;, ,
Fiaure 1. Steel Plate Resonating at 60 Hz, Various Sensitivities.
10
Figure ?.a. Double Exposure of Vibrating Steel Plate.
Figure 2b. Double Exposure After Optical Filtering.
11
Figure 3a. Time Average Moire Photograph of Resonant Plate.
I
i
Figure 3b. Time Average Moire After Optical F'ilterin?.
12
Figure 4a. 35 mm Lithographic Film Photo of Grziing.
Figure 4b. Polaroid Pos/Neg of Grating.
13
Fiqurc 4c. Lithooraphic Copy of Polaroid Pos/Neq Photo.
Fioure 4d. Holo g raphic Plate (10E W Photo of Gratino.
F
1.1
I.
Figure 4e. Technical Pan Film Photo of Grating.
Figure 4f. Holographic Plate (10E75) Copy of Technical Pan Photo.
15
Fi•iure 4g. Lithographic Cope of Technical Pan Photo.
Figure 4h. Panatomic-X Film Photo of Crating.
16


Evaluation of moire techniques for wind tunnel metrology

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server