Thermoelastic Analysis in Design
William Bell & Paul-W. Young
Topsfield Engineering Service, Inc.
John Stewart, Saber Design and
Analysis Services, LLC.
Topsfield Engineering Service, Inc.
Figure 1
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
Topsfield Engineering Service, Inc.
Slide 2
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
Topsfield Engineering Service, Inc.
Slide 3
Tools Used
Thermal Desktop from C & R Technologies –
Version 4.7 patch 16
 FEMAP V8.3 and NX NASTRAN V2.0

Topsfield Engineering Service, Inc.
Slide 4
Study Assembly
½” thick heated plate
with a serpentine pipe
1/8” sch 40 pipe
attached to the plate
for temperature
control
20 watts/in2
15 watts/in2
Heat Loads
Topsfield Engineering Service, Inc.
Slide 5
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
Topsfield Engineering Service, Inc.
Slide 6
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)
Topsfield Engineering Service, Inc.
Slide 7
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
Topsfield Engineering Service, Inc.
Slide 8
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
Topsfield Engineering Service, Inc.
Slide 9
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
Topsfield Engineering Service, Inc.
Slide 10
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
Topsfield Engineering Service, Inc.
Slide 11
Cases A and B
Pipe bonded to a groove
in the plate.
Case A – pipe and plate from chexa
elements
Topsfield Engineering Service, Inc.
Case B – pipe from cquad4 elements
Slide 12
and plate from chexa elements
Case C
Pipe with cquad4 elements
attached with chexa solid elements
to the top surface of the solid plate
of chexa solid elements.
Topsfield Engineering Service, Inc.
Slide 13
Case D
Pipe bonded to a groove
in the plate.
Pipe and Plate from chexa elements
TD plate from Nastran plate above,
with groove.
Topsfield Engineering Service, Inc.
Slide 14
Thermal Desktop Geometry
Cases A and B Thermal Model Geometry
Case C Thermal Model Geometry
Topsfield Engineering Service, Inc.
Case D Thermal Model Geometry
Slide 15
Thermal Desktop ties
Ties from the fluid lumps to the pipe wall
Topsfield Engineering Service, Inc.
Slide 16
Thermal Desktop contactors
Contactor connections – shown in yellow
Topsfield Engineering Service, Inc.
Slide 17
Case A & D Nastran Model Geometry
chexa elements thru pipe
Bond shown in yellow
Topsfield Engineering Service, Inc.
Slide 18
Case B Nastran Model Geometry
Pipe with cquad4 elements
Topsfield Engineering Service, Inc.
Slide 19
Case C Nastran Model Geometry
Weld bead shown in yellow
Topsfield Engineering Service, Inc.
Slide 20
Thermal model elements – Cases A & B

Plate
1880 TD/RC Nodes
 3 fdsolids
 2 heat loads
 1 contactor
12,038 conductors
connecting plate and pipe



Pipe
2448
TD/RC Nodes
1 pipe
1 contactor

Fluid
103
lumps
2
plenums
 101 junctions
102
1
paths
tie
Topsfield Engineering Service, Inc.
Slide 21
Thermal model elements – Case D

Plate

78,213 TD/RC Nodes
 25,482 plates
 65,240 solids
 2 heat loads
 1 contactor
909,152 conductors
connecting plate and pipe
2448
TD/RC Nodes
1 pipe
1 contactor


Pipe

Fluid
103
lumps
2
plenums
 101 junctions
102
1
paths
tie
Topsfield Engineering Service, Inc.
Slide 22
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
Topsfield Engineering Service, Inc.
Slide 23
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
Topsfield Engineering Service, Inc.
Slide 24
Mapping tolerances

Thermal Desktop plate to
the Nastran plate and
bond, if required – 1e-5”

Thermal Desktop pipe to
Nastran pipe – 0.00025”
Topsfield Engineering Service, Inc.
Slide 25
Results – Case At1
Nastran Temperature
TD Temperature
Deflection
Stress
Topsfield Engineering Service, Inc.
Slide 26
Results – Case Bt1
Nastran Temperature
TD Temperature
Deflection
Stress
Topsfield Engineering Service, Inc.
Slide 27
Results – Case Ct1
Nastran Temperature
TD Temperature
Deflection
Stress
Topsfield Engineering Service, Inc.
Slide 28
Results – Case Dt1
Nastran Temperature
TD Temperature
Deflection
Stress
Topsfield Engineering Service, Inc.
Slide 29
Results – Case At1 versus Dt1
Dt1 Stress
At1 Stress
At1 Stress
Dt1 Stress
Topsfield Engineering Service, Inc.
Slide 30
Results – Case At2
Nastran Temperature
TD Temperature
Deflection
Stress
Topsfield Engineering Service, Inc.
Slide 31
Results – Case Bt2
Nastran Temperature
TD Temperature
Deflection
Stress
Topsfield Engineering Service, Inc.
Slide 32
Results – Case Ct2
Nastran Temperature
TD Temperature
Deflection
Stress
Topsfield Engineering Service, Inc.
Slide 33
Results – Case At3
Nastran Temperature
TD Temperature
Deflection
Stress
Topsfield Engineering Service, Inc.
Slide 34
Results – Case Bt3
Nastran Temperature
TD Temperature
Deflection
Stress
Topsfield Engineering Service, Inc.
Slide 35
Case At1 Thermal Results
Cross section for temperature
and Nastran Results
Thermal model node numbers
Topsfield Engineering Service, Inc.
Slide 36
Case At1 Thermal Results
Temperatures in TD plate
Temperatures in TD pipe
Topsfield Engineering Service, Inc.
Slide 37
Case Dt1 Thermal Results
Temperatures in TD plate from Nastran model
Temperatures in TD pipe
Topsfield Engineering Service, Inc.
Slide 38
Case At1 Thermal Results
Temperatures in Nastran plate from TD model
Topsfield Engineering Service, Inc.
Slide 39
Nastran Results Summary
Cases
Maximum 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
Topsfield Engineering Service, Inc.
Slide 40
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
Topsfield Engineering Service, Inc.
Slide 41
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
Topsfield Engineering Service, Inc.
Slide 42
Models
The Nastran and Thermal Desktop models are
available as a down load by going to the
following URL:
http://www.topeng.com/downloads
Topsfield Engineering Service, Inc.
Slide 43