topsfield engineering service, inc. figure 1 thermoelastic analysis in design william bell &...
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Topsfield Engineering Service, Inc. Figure 1
Thermoelastic Analysis in Design
William Bell & Paul-W. YoungTopsfield Engineering Service, Inc.
John Stewart, Saber Design and Analysis Services, LLC.
Topsfield Engineering Service, Inc.
Slide 2
Purpose
This study explores the capability of Thermal Desktop to map temperatures
from a thermal model to a Nastran model to evaluate thermal stress and distortion
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Slide 3
Applications Rapid cool-down to cryogenic temperatures Differential thermal expansion causing
leakage, failure, galling, or seizing Electronics components Misalignment due to thermal distortion Time dependent and steady state conditions Space optics - optical alignment Gasket/seal seating - pressure containing Thermal contact joint design
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Slide 4
Tools Used
Thermal Desktop from C & R Technologies – Version 4.7 patch 16
FEMAP V8.3 and NX NASTRAN V2.0
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Slide 5
Study Assembly½” thick heated plate with a serpentine pipe 1/8” sch 40 pipe attached to the plate for temperature control
Heat Loads
20 watts/in2
15 watts/in2
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Slide 6
Thermal Model Development
Evolved from a early version of a Thermal Desktop model
Rebuilt using latest modeling objects without simplifying dimensions
Picked off dimensions from the Autocad drawing for creation of the Nastran model
Result - there were some discrepancies
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Slide 7
Thermal Study Conditions
Mass Flow cooling - Coolant – 100 lb/hr of Nitrogen gas at -200 F and 40 psig – built-in properties for Nitrogen
No Radiation Heat Transfer Plate is heated with 1150 watts Conduction within plate and pipe walls Built in convection equations for heat transfer from
pipe to Nitrogen Steady State Conditions (although Thermal Desktop
can solve time dependent cases and search for worst case conditions)
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Slide 8
Material Properties The structural and thermal properties used in
the analysis models are values commonly used for Stainless Steel, Aluminum, and the attachment techniques employed
The property data used can be found in the Nastran and Thermal Desktop model files
In a “real world” problem, the material data would be detailed out and agreed to prior to beginning any analysis. Due to the large temperature differences, temperature dependent properties would also be used
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Slide 9
Thermal Desktop Model Construction
Pipe with wall (1/8” nps - sch 40) built on a polyline
Lumps and paths within pipe
Ties representing the convective heat transfer from the pipe wall to the fluid lumps
Three brick objects with edge nodes merged for the plate except for Case D where the plate was created from the Nastran grooved plate. Plate is ½” thick
Heat flux applied to the bottom surface of two of the bricks
Contactor object to represent the pipe to plate bond. In the groove the bond thickness is 0.003”. The weld to the flat plate is an 1/8” fillet
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Slide 10
Cases evaluated in Nastran
A - Pipe bonded to grooved plate – Nastran pipe and plate from chexa elements
B - Pipe bonded to grooved plate – Nastran pipe from cquad4 elements and plate from chexa elements
C - Pipe welded to flat plate – Nastran pipe from cquad4 elements and plate from chexa elements
D - Pipe bonded to grooved plate – Nastran pipe and plate from chexa elements – TD plate from the Nastran plate
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Slide 11
Case Material Combinations
Case At1, Bt1, Dt1 - SS plate; SS pipe; easyflo braze
Case At2, Bt2 - Al plate; Al pipe; Al braze
Case At3, Bt3 - Al plate; SS pipe; epoxy bond
Case Ct1 - SS plate; SS pipe; SS weld
Case Ct2 - Al plate; Al pipe; Al weld
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Slide 12
Cases A and B
Pipe bonded to a groove in the plate.
Case B – pipe from cquad4 elements and plate from chexa elements
Case A – pipe and plate from chexa elements
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Slide 13
Case C
Pipe with cquad4 elements attached with chexa solid elements to the top surface of the solid plate of chexa solid elements.
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Slide 14
Case D
Pipe and Plate from chexa elements
Pipe bonded to a groove in the plate.
TD plate from Nastran plate above, with groove.
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Slide 15
Thermal Desktop Geometry
Cases A and B Thermal Model Geometry
Case C Thermal Model Geometry
Case D Thermal Model Geometry
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Slide 16
Thermal Desktop ties
Ties from the fluid lumps to the pipe wall
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Slide 17
Thermal Desktop contactors
Contactor connections – shown in yellow
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Slide 18
Case A & D Nastran Model Geometry
chexa elements thru pipe
Bond shown in yellow
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Slide 19
Case B Nastran Model Geometry
Pipe with cquad4 elements
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Slide 20
Case C Nastran Model Geometry
Weld bead shown in yellow
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Slide 21
Thermal model elements – Cases A & B
Pipe2448 TD/RC Nodes1 pipe1 contactor
Plate 1880 TD/RC Nodes 3 fdsolids 2 heat loads 1 contactor
12,038 conductors connecting plate and pipe
Fluid103 lumps
2 plenums 101 junctions
102 paths1 tie
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Slide 22
Thermal model elements – Case D
Pipe 2448 TD/RC Nodes 1 pipe 1 contactor
Plate 78,213 TD/RC Nodes 25,482 plates 65,240 solids 2 heat loads 1 contactor
909,152 conductors connecting plate and pipe
Fluid 103 lumps
2 plenums 101 junctions
102 paths 1 tie
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Slide 23
Nastran Model Construction
Plate and bond built with 95,480 chexa elements for Cases A, B, and D
Plate and weld built with 112,216 cquad4 elements for Case C
Pipe built with 70,908 chexa elements for Case A & D
Pipe built with 23,636 cquad4 elements for Case B & C
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Slide 24
Temperature Mapping Procedure
Step 1 – Temperatures from TD plate to Nastran plate
Step 2 - Temperatures from TD plate to Nastran bond, if required
Step 3 - Temperatures from TD pipe to Nastran pipe
This avoids mixing pipe and plate temperatures when mapping
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Slide 25
Mapping tolerances
Thermal Desktop plate to the Nastran plate and bond, if required – 1e-5”
Thermal Desktop pipe to Nastran pipe – 0.00025”
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Slide 26
Results – Case At1
TD Temperature
Nastran Temperature
Deflection Stres
s
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Slide 27
Results – Case Bt1
TD Temperature
Nastran Temperature
Deflection
Stress
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Slide 28
Results – Case Ct1
TD Temperature
Nastran Temperature
Deflection
Stress
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Slide 29
Results – Case Dt1
TD Temperature
Nastran Temperature
Deflection
Stress
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Slide 30
Results – Case At1 versus Dt1
Dt1 Stress
Dt1 Stress
At1 Stress
At1 Stress
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Slide 31
Results – Case At2
TD Temperature
Nastran Temperature
Deflection Stres
s
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Slide 32
Results – Case Bt2Nastran Temperature
Deflection
Stress
TD Temperature
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Slide 33
Results – Case Ct2
TD Temperature
Nastran Temperature
Deflection Stres
s
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Slide 34
Results – Case At3
TD Temperature
Nastran Temperature
Deflection
Stress
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Slide 35
Results – Case Bt3
TD Temperature
Nastran Temperature
Deflection
Stress
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Slide 36
Case At1 Thermal Results
Cross section for temperature and Nastran Results
Thermal model node numbers
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Slide 37
Case At1 Thermal ResultsTemperatures in TD plate
Temperatures in TD pipe
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Slide 38
Case Dt1 Thermal ResultsTemperatures in TD plate from Nastran model
Temperatures in TD pipe
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Slide 39
Case At1 Thermal Results
Temperatures in Nastran plate from TD model
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Slide 40
Nastran Results Summary
CasesMaximum Von Mises
Stress at Cross Section psi
Maximum Deflection -
inches
Maximum Temperature -
F
Case At1 47,149 0.02200 314
Case At2 5,532 0.00811 30
Case At3 30,574 0.03900 67
Case Bt1 39,968 0.02300 314
Case Bt2 11,879 0.01130 30
Case Bt3 24,110 0.01290 67
Case Ct1 36,762 0.04200 451
Case Ct2 17,648 0.01230 55
Case Dt1 88,310 0.02660 418
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Slide 41
Lessons Learned - thermal Spend some time reviewing thermal results:
Determining if nodalization is sufficient – distortion or stress
Choosing materials and material thermal properties Assuring convergence Getting separate files for each component of the model
and putting each component on a separate layer Plan out the combinations with the design team Carefully check to see if the temperature mapping
is accurate Let go of the fear of finite elements
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Slide 42
Lessons learned - structural Spend some time working with the thermal analyst:
Getting dimensions consistent Sorting out materials and structural properties up front Determining the mounting constraint Getting separate files for each component of the model
Plan out the combinations with the design team Carefully check to see if the temperature mapping
is accurate Do hand calculations as a check on stresses and
deflections