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Thermoelastic Analysis in Design

William Bell & Paul-W. YoungTopsfield Engineering Service, Inc.

John Stewart, Saber Design and Analysis Services, LLC.

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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

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Slide 43

Models

The Nastran and Thermal Desktop models are available as a down load by going to the following URL:

http://www.topeng.com/downloads