mrd final presentation

8/4/2019 MRD Final Presentation

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THERMAL ANALYSIS OF THE

CAMERA HEAD OF THE ROVER

Saikumar Reddy


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MOTIVATION

Extreme thermal conditions on the Moon

Affects the smooth functioning of the vision

system, by overheating the cameras

i) In-turn affecting the 500m traverse detection and/or

ii) Quality of the images sent back

This calls for a careful heat transfer analysis, for predictingfailures and help design a better thermal casing


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TYPES OF FAILURES

Over-heating of electronic components (Cameras)

Failure due to thermal expansion

- Fatigue due to thermal cycling (expansion

during day and contraction during night)

- Pointing of the stereo cameras is affected

due to the thermal expansion of casing


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APPROACH

Test for Over-Heating Computational radiation and conduction analysis

using THERMAL DESKTOP

Test for Thermal -Expansion Coupled Thermal-Structural analysis using

ABAQUS (Finite Element Analysis)


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RESULTS

The temperature of the stereo cameras during

duty cycle, generating 2.5 W, on a typical hotlunar day came out to be in range of 500 to 600 C

Due to thermal expansion the relative

displacement between the stereo cameraschanges approximately by

r = Ux i + Uyj + Uz k

r = 0.78 i+ 0.27j+ 0.76 k

= 1.26 mm

r

r


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HEAT TRANSFER ANALYSIS IN THERMAL

DESKTOP (SET- UP)


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RESULTS (RAY-TRACE PLOT AND HEAT

FLUX PLOT)


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RESULTS(HEAT FLUX CONTOUR PLOT)


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RESULTS(TEMPERATURE CONTOUR PLOT)


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THERMAL-STRUCTURAL ANALYSIS SET-UP

Albedo (12% of Solar)

Solar radiation heat

(assumed Sun is directly above)

Casing is made of Pure Aluminum and is

Isotropic in nature, painted white, e = 0.85

Ambient temperature is 120 C

Loading Conditions

Assumptions


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Boundary Conditions

THERMAL-STRUCTURAL ANALYSIS SET-UP

Revolute Joint

Ux=Uy=Uz=0

CAD model of the Camera-HeadAnalogous fully enclosed casing of the

camera head


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RESULTS


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RESULTS


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RESULTS

Comparison of deformed and un-deformed shapes of the thermal

casing (scaled 10 times)

Stress plot

MPa

High stress points, with stress valuebeyond Yield point.

Filleting required


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SOLUTION

Try to design the camera head, in such a way that

the stereo cameras could be placed more close to

each other. Current design is good, but a better

design could be made.

Expansion can be avoided/reduced by choosing

better materials which have lower values of CTE.


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FLOW-CHART FOR ANALYSIS

New design

of thermal

casing

Develop similar CAD

model in Thermal

Desktop (TD)

PRE-PROCESSING

material properties, heat-

loads, orbital heating rates

Solve for heat flux

absorbed using Radks

solver in TD

Input the heat-flux results

obtained from radiation

analysis into SINDA solver

to solve for temperatures

Is camera

temperature

within

tolerable

limits?

Change design

parameters

(design topology,thickness, width

etc.,), choose new

materials

Perform thermal-

structural analysis

Develop an appropriate

CAD of the thermal casing

with cameras in ABAQUS/

ANSYS

Use heat-flux values obtained from

TD as loads provide boundary

conditions based on the assembly

Is the

pointing of

the cameras

affected?

YesNo

Post-Process the results toplot displacement and

stress contour plot

Change design parameters

(design topology, thickness, width

etc.,), choose new materials

No

Yes

Design

Okay!


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CONCLUSION

Approximately 45% - 50% temperature gradientexists between the ambient temperature(120 C)and the temperature of the cameras (50 C to 60C), which is towards a conservative side (worst

case temperature), as no heat pipes have yet beendesigned.

The cameras move a distance of ~ 1.26 mmrelatively from each other when a purealuminum casing is used. This could possiblyaffect the calibration of the cameras and theprecision of 500m traverse, depending upon thetolerance levels


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FUTURE WORK

Using heterogeneous (alloys/ composite

materials) to perform the heat transfer and

thermal-structural analysis

Design of heat pipe that conducts away the heat

generated by the stereo cameras

Once the casing design is finalized, its prototypecan be subjected experimental high and low

temperatures so as to observe if the structural

integrity of the casing is maintained.


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THANK YOU!

mrd final presentation

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