Static analysis and a computer structural model for the large 64-m antenna pedestal are developed using the MSC version of the NASTRAN program. This improved pedestal model includes the launch areas and the actual pressure pattern of the oil under the hydrostatic bearing pad. The results obtained from the new improved model have indicated that the deflections due to pad loads are in good agreement with field measurements. The top surface deflection of the pedestal obtained from the NASTRAN model is used as an input to the oil film computer program to determine the minimum oil film thickness under the pad

Chian, C. T.

English

NASA Technical Reports Server

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N84 1 3 4 1 2  
TDA Progress Report 42-75 
NASTRAN Structural Model for the 
&Meter Antenna Pedestal, 
Part II - Improved Model 
C. T. Chian 
Ground Antennas and Facilities Engineering Section 
July - September 1983 
Large 
Static analysis and a computer structtrral model for the large 64-m antenna pedestal 
are developed using the MSC version of the NASTRAN program. This iniproved pedestal 
model includes the haunch areas and the actual pressure pattern of the oil under the 
hydrostatic bearing pad. The resulis obtained from the new improved model have indi- 
cated that the deflections due to pad loads are in good agreement with field measure- 
ments. The top surface deflection of the pedestal obtained from the NASTRAN model is 
used as an input to the oil film computer program to determine the minimum oil firm 
thickness under the pad, 
1. Introduction 
This article is the second in a series of reports on the static 
analysis and computer modeling performed for the large 64-m 
antenna pedestal. The pedestal is under pressure loadings at 
the three hydrostatic bearing pads. The pedestal computer 
model previously reported in Ref. 1 has been improved in 
order to better re? -esent the displacement and force distribu- 
tion throughout the pedestal, as well as to obtain the state of 
stress ant  strain. 
The deflections of the pedestal under the pad resulted 1,om 
the NASTRAN model are used as inputs to the oil film heir& 
program' to evaluate the corner oil film thickness between the 
pad and the runner. A minimum hydrostatic bearing oil film of 
'This is a modified version of the program initially developed by the 
Franklin Institbte, Ref. 3. 
0.13 mm (0.005 in.) is required to avoid any metal to metal 
contact between the pad and the runner and to  accommodate 
any runner malfunctioning and piacement tolerance. 
II. Description of the Improved Model 
The first computer structural model of the pedestal was 
reported in Ref. 1.  The assumptions made in this initial model 
are that ( I )  the pedestal is a cylinder of uniform wall thick- 
ness, thus ignoring the effect of the haunch; (2) the pedestal 
loading is uniform with 6.9 X IO6 N/m2 (1000 psi) pressure 
over the pad length and width;and (3) the modulus of elastic- 
ity of the entire pzdestal concrete is 2.8 X I O t o  N/m* (4.0 X 
lo6 psi). By symmetry, the pedestal could be modelled as one 
60 degree segment with two boundary conditions. ( 1 )  zero 
slope at the points representing the centerline of the pad, and 
105 
https://ntrs.nasa.gov/search.jsp?R=19840005344 2020-03-21T01:50:34+00:00Z
(3) zero slope at the points representing midposition between 
two pads 
In the present imoroved pedestal model, the first two as- 
sumpticns are modified IV include ( 1) the actual haunch con- 
tour in the pedesta! io provide additional stiffness on the 
pedestal wall. and (2) the actual pressure profile of the oil 
under the pad. The model was developed using the MSC ver- 
sion of the NXSTRAN structural program. 
The improved pedestal model consists of a wall. haunch, 
and top slab, as shown in Fig. 1. Figure 2 is a cross-sectional 
diagram of the pedestal. A cross-sectional diagram of the hy- 
drostatic bearing is shown in Fig. 3. Deflected shapes of the 
hydrostatic bearing pad and runner surface ;re illustrated in 
Fig. 4. Relative deflections within the hydrostatic bearing pad 
and within the runner surface from centerline to edge of pad 
are shown as Ap and A,, respectively. Design constraints re- 
quired that the mismatch of deflected surfaces, 6,  be within 
0.10 mm (0.004 in.). Part of this 0.10 mm (0.004 in.) total 
mismatch, a maximum mismatch of deflected shapes of 
0.08 mm (0.003 in.) was established as the limit for creep dur 
ing construction. hence before the bearing pads c3uld be 
moved. The remaining 0.025 mm (0.001 in.) was the design 
criteria for mismatch of elastic deformations (Ref. 2). If the 
creep strains are compensated for by releveling of the runner, 
then the total 6 of 0.10 mm (0.004 in.) might be tolerated for 
the elastic deformations portion alone. 
The actual pressure profile of the oil under the hydrostatic 
bearing pad is illustrated in Fig. 5. For simplicity, the pressure 
pattern of the oil under the pad is assumed to be symmetric 
with respect to the pad centerl..:e in the NASTRAN pedestal 
model. Therefore, pi = p 3  and p4 = p 6 .  Pad 3. wnich experi- 
ences the highst load among the three pads, is the one consid- 
ered in our mr del. The values of the pad recess pressures are 
given in Table I .  
Figure ', shows a typical deflection map of the top pedestal 
surfaci under pad load. This deflec!ion map is used as the 
input to the oil film height model to determine the minimum 
oil film thickness between the pad and the runner. 
111. Comparison with Field Measurements 
Field measured load-deformation relationships of the 
pedestal were obtained and used to calibrate the present 
NASTRAN pedestal model. The pad load tests can also be 
used to determine the spatial distribution of deteriorated con- 
crete in the haunch. 
The field measurements were conducted by JPL in coopera- 
tion with Construction Technology Laboratories (CTL) of 
Skokie, I!linois. (CTL is a division of the Portland Cement 
Association.) Figure 7 shows the locations of the gauges for 
deflection measuremen:s. Instrumer,. we!e ulled to mea. 
sure veitical deformations over a 1.27 m (50 in.) gauge length 
on the external surfxe of the haunch and the wall. Figure 8 i: 
a schematic of the instrumentation used. As sliown, snlall 
blocks were bonded to the ?rwture .,' thc preselected loca- 
tions. A direct current differe ransfornier (DCDT 
upper block. A H I I  mounted in a fixture was attache( 
from the spring-loaded plunger of JT w3s attached tb 
the lower block. The output of th, : # \ I ) I  was cantinuously 
recorded during the time required for antenna Pad 3 to be 
moved across the instrumented location. This time is approxi- 
mately 3 . iinutes. 
Figures9 and 10 show the good correlation between the 
field deflection ~ iea~urements  and the NASTRAN predicted 
values for two different. locations: azunuth 49" and zzimuth 
96'. 
IV. Conclusions 
The improved NASTRAN structural model for the large 
64-m antenna pedestal shows excellent correlation with the 
field deflection measurement. This new model incorporates 
improvements over the previous model of Ref. 1 which in- 
cludes the actual haunch areas in the pedestal and the actual 
pressure pattern of the oil under the hydrostatic bearing pzd. 
The maximum pad out-of-flatness and the minimum oil 
film thickness are important factors to evaluate the condition 
of the hydrostatic beaiing performance. The new pedestal 
computer model will be a useful tool in the large antenna bear- 
ing rehdbilitation and upgrade studies. A series of parametric 
studies using the improved NASTRAN pedestal model a.id the 
oil film thickness progrhi:l will be performed. For exarrple, the 
effects of varying moduli . elasticit) in different regions of 
the pedestal concrete, and tlie effects of increasing pad loads 
due to 64-m to 70-m extension will be investigated. 
Acknowledgment 
The author acknowledges the assistance giver: by F. Lansing, H. Phillips, A. Riewe, 
R. Oesterle and B. Morgan (both the last two with Construction Technology Laborato- 
ries) during the various execution steps of this work. 
References 
1. Chain. C. T., Katow, M. S.. and McGinness, H., “NASTKAN Structural Model for the 
Large W-m Antenna Pedestal, Part I,” TDA Progress Reporr 42-74. Jet Propulsion 
Laboratory, Pasadena, CA, August 15. 1983. 
2. TDA Technical Staff, “T..e NASA/JPL 64-Meter-Diameter Antenna at Goldstone. Cali- 
foinia: Project Report,” JPL Technicn. Memorandum 33-6 71, Jet Propulsion Labora- 
tory. Pasadena, CA, July 15,1974. 
3. Hinkle, J .  G., Castelli, V., Rippel, H. C.. and Zimmerman. C. D.. “A Computer Pro- 
ram for Hydrostatic Bearings Including Effects on Non-Uniform Film Thickness and 
Relative Velocity for Various Methods of Lubricant Supply,” The Franklin Institute. 
Final Technical Report F-B2099, Philadelphia, P.4, April. 1964. 
ORlGtNAL PAGE IS 
OF POOR QUALrrV 
N/m2 11,383,000 7,757,@00 10,859,000 9,480.000 
psi 1651 i12-5 1575 1375 
‘Assum. p, = p3 = ~ ( p ,  1 +p3)and p4 = p6 = - (p 1 +p6j.  2 4  
108 
OR!CfNAL PAGE IS 
OF POOR QUALITY 
I 
10 I 2005 RUNNER RAIN SHIELD 
1 GROUT 
SOLE PLATE 
HAUNCH \
CONCRETE 
Fig. 3. Cross s4ctkn d hydmrtlttc kulng 8ystOm 
109 
VERTICAL LOAD FROh ALIDADE n 
JL HYfXOSTATIC BEARING P A D 7  
RUNNER WRFACt 
OIL J 
8 = MISMATCH Of DEFLECTED SURFACES 
8 = A ,  - A p  
-- -i 1524 (@ 
P1 
f 254 
1 127 
110 
OA;G!SA\L PAGE IS 
OF POOR QUALITY 
3.7s 4 
LEVEL OF 
PRESENT 
ORIGINAL PAGE W 
OF POOR QUALITY 
Q 
SONISCOPE 
READ1 NGS 
LENGTH 
GAUGE T 
SECTION A-A 
I 
I 
171 
5.80 m (19 ft) 
112 
-0.005 
4.006 
-0.001 om 
- 1  - - 
DEFORMATION AT AZIMUTH 49* (STATION H2.1) 
2 = 20.5 in. 
I I I I I 
t f -0.m .- 
4.005 
-0.006 
51 I 2 4.003 
3 
CTL DATA 
.$ NASTRANDATA 
- " I 
DEFORMATION AT AZIMUTH 96O (STATION H3.1) 
~ I I I I I 
113 


NASTRAN structural model for the large 64-meter antenna pedestal. Part 2: Improved model

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