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# Spacecraft Thermal Analysis

Experimenter

Hi there!

I'm trying to do a thermal analysis of a spacecraft in low earth orbit using NX Space Systems Thermal.  My goal is to create an MLI insulation layer good enough to ensure the equipment on the inside stays between a certain temperature range.  My simplified spacecraft is a simple cylinder with a floor and boxes representing equipment on the inside.  I'm using 2D thin shells and 2D elements for all the objects  I'm using the Orbital Heating simulation object to simulate incoming radiation, the Radiation simulation object to make everything into a radiation enclosure, and the Thermal Load to simulate the heat load on the internal equipment.

To simulate the MLI on the outside of the spacecraft I'm using multi-layer non-uniform 2D shell elements with two layers.  The first layer is the MLI with the effective emissivity and the second layer is the main structural material.  The problem I'm having is setting up the convection constraints on the inside of my spacecraft.  I want to simulate heat transfer by convection between the inner walls and the equipment but I can't seem to pick the inside walls of the cylindrical shell when I input the free convection constraint (see below).  When I click the inside of the shell it always puts the convection constrain on the outside pointing towards outer space.

Does anyone know how I can get the convection constraint to point inward?  Also, doe anyone know if this is the best (simplest) way to model MLI on spacecraft (multi-layer non uniform shell)?  Any tips or suggestions would be greatly appreciated.  Thanks.

On a side note:  Does anyone know why the nanosat NX simulation tutorial used a thermal coupling with a heat transfer coefficient of 20000?  Doesn't the NX CAE take into account the conduction between elements that are touching based on their physical properties (material properties)?

3 REPLIES

# Re: Spacecraft Thermal Analysis

Solution Partner Phenom

Hello,

1.Does anyone know how I can get the convection constraint to point inward?

Yes. You can:

• flip the elements’ normal
• flip the order of the layers in the Stack Definition List
• use “bottom” side of the shells for radiation
• use “top” side of the shells for convection

Out of curiosity, what behavior are you trying to capture with the use of convection in an orbiting spacecraft model?

1. Any tips or suggestions would be greatly appreciated.

Regarding MLI, if you have simple geometry, it makes sense to use multi-layer shells for MLI since the wrapping follows the panels’ shape very closely. But for more complex geometry, you should create a null shell mesh that surrounds your geometry and define your MLI on this surrounding mesh.

1. Does anyone know why the nanosat NX simulation tutorial used a thermal coupling with a heat transfer coefficient of 20000?  Doesn't the NX CAE take into account the conduction between elements that are touching based on their physical properties (material properties)?

No, conduction will not be calculated automatically if the touching elements do not share nodes.

Phil

Philippe Tremblay
phillippe.tremblay.ext@siemens.com
www.mayahtt.com

# Re: Spacecraft Thermal Analysis

Experimenter

Hi Phil,

Thanks for the response!

Out of curiosity, what behavior are you trying to capture with the use of convection in an orbiting spacecraft model?

I'm trying to model air (and heat transfer through air) inside the spacecraft, so I put convection constraints on the inside walls of the spacecraft, on the floor, and on the equipment (the box).  I made the convection constraint with air at room temperature.  Is there a better way to simulate air inside my spacecraft?

No, conduction will not be calculated automatically if the touching elements do not share nodes.

So to clarify...I have a box representing a piece of equipment on the floor in my model.  I meshed the box and the floor separately and they are physically in contact in the model.  Does that mean they are not sharing nodes and that I need to specify a thermal coupling to model conduction?

Thanks!

# Re: Spacecraft Thermal Analysis

Community Manager

Wurst130,

Does that mean they are not sharing nodes and that I need to specify a thermal coupling to model conduction?

yes, this is correct. Thanks and sorry for the delayed response!

Regards,
Ganesh

Simcenter 3D Community Manager
Simulation and Test Solutions