Thermal Software Lab: Finite Element Analysis

Frances Zhu

7. Thermal Control

Thermal Software Lab: Finite Element Analysis

Part 1: Adding Thermal Characteristics to the Model

Download the artemis_thermal_lab files from GitHub and open artemis_thermal_lab.dwg with Thermal Desktop.

Let’s talk about navigating the environment!

You can use the middle button on your mouse to move the view. The hand icon may also be used.

Shift + middle button on your mouse can be used to rotate your view. The 3D orbit icon may be used to orbit your view.

These icons can be easily accessed on the toolbar.

We will use a Submodel Node Tree to navigate through the layers of the file.

To open the tree, go to Thermal, Common, and Model Browser.

First, we will edit the components inside of the structure.

In the submodel tree, right click and turn off visibility for NEGY, NEGY_SOLAR, NEGZ, NEGZ_SOLAR, POSY, POSY_SOLAR, POSZ, POSZ_SOLAR. This will allow us to view the internal boards. Items can be hidden by selection of the component, right-clicking, and selecting Turn Visibility Off.
Items may also be reshown by repeating the method but selecting Turn Visibility On instead of Turn Visibility Off.

After turning visibility off for the components outside of the structure, you should be left with the following model.

Before we apply values to heat loads, we must assign materials to our boards.

Go to Thermal -> Thermophysical Properties -> Edit Property Data
- Type in materials, conduction, density, specific heat, effective emissivity
Similarly, define Optical Properties in Thin Shell Data

Let’s assign values to the frame conductors. These conductors are in place to show contact between the frames and mid sections.

To assign a value to the frame conductors, right click the conductor, Thermal Desktop -> Edit
- For the aluminum corners, assign a value of 0.167 W/C
- For aluminum frame, assign a value of 0.0323 W/C

Repeat the assignments for all conductors in the model.

In the model, heat load can be assigned on a hot spot or surface. A hot spot indicates a point source of heat and a surface heat load would indicate a more evenly spread heat load on an entire surface.

For example, the EPS is assigned a surface heat load in this example as the components generating a heat load are mostly evenly spread on the EPS board.
Compared to the OBC, hot spots are used to indicate a point load of a heat load.

Let’s now take a look at the OBC.

Turn off visibility for EPS, BATT, BATTERY STACK, POSX_ANTENNA_BOARD to have a better view of of the OBC

There are 4 hotspots on the OBC: GPS and Radio are located in about the same spot, so we use one heat node to indicate both. There is also the IMU, RaspberryPi, and Teensy.

We will be assigning values to each of these hotspots. In this example we will be using the IMU. Right click the node and select Thermal Desktop -> Edit.

A heat load edit form will pop up. Input a name for the hotspot and value associated with the spot. These values can be found in the expected Artemis Thermal Collation and Expected Heat load sheet.

Select OK to confirm. Now repeat the heat load assignment for all other hotspots on the OBC Board. The following is an image that helps map out which heat loads are for which components on the OBC board.

Repeat this method with all other heat nodes found in the model. It must be noted that you will have to change the visibility of boards in the Submodel Node Tree to gain access to selection of some surfaces and hot spots. This includes the following “[Board] [Type of Heat Load] [Component] Heat Load”

Antenna Board RF Amp Hot Spot Heat Load, EPS Surface Total PDU Heat Load, Battery Surface Batteries Heat Load, Solar Panel Torque Coil Surface Heat Load, Camera Board Camera Hot Spot Heat Load

Now we will be assigning heat loads with time dependence. Some components will not be ON constantly. These modes can be found in the Artemis Power budget. For this example, we will be using the camera board.

Right click the camera hot spot located on the camera board and click Thermal Desktop -> Edit
Under Heat Load, select Time Dep…

Based on the Artemis Power Budget, we see that the camera is ON only in Data Collect mode. In the typical mode sequence (heat) tab, we can see that heat load values are only returned in data collect mode. To transfer this data into a csv file, which then can be pasted into the time dependance tabular input table

First, copy the seconds and heat load camera payload columns

Paste this into a notepad or text editor then delete the headings so only the numbers remain. Then save as a .csv file.

If you open the csv file and the text is not reformatted to have commas, we can do this manually.

Use command Ctrl+H and replace all tabs with commas. Save this file. You may paste this data directly into the Tabular Input table.

Most of the data has already been collected and has been converted into a csv file for you in the Software Thermal Lab Heat Load Folder. You will have to modify the radio payload data and create your own .csv file for your payload.

Part 2: Your Own Payload

Let’s edit the model to be more specific towards your payload.

First, let’s make sure we are in the right units.

Go to Preferences and click on the arrow next to it. This will display your units. Keep these units in mind while creating your model.

The pcb for your payload has already been added into the model.

If your payload does not have any large components, heat loads may be directly added onto the board, similar to the EPS and OBC board heat load assignments we did in part 1 and no additional objects will be required to model.

If your payload has components to be mounted on the board, similar to the batteries which are mounted onto the battery board, we must create an object to place onto the payload board to represent your payload

Turn off the visibility of the camera board so the payload board can be seen
In this example, an object with length 3 cm, width of 3 cm, and height of 1 cm will be modeled. Dimensions must be adjusted as required by your payload.

If referencing nodes to create your object, remove all other boards to avoid clicking other layered nodes.

Use command ORTHOMODE and type 1 to enable.

In this example, we will be creating a payload for the payload board that is 62 mm by 32 mm by 8 mm. The payload’s bottom right corner will be located 23 mm left on the x and 14 mm up on the y away from the bottom right node of the payload carrier board.

Use command RCFDBRICK. Use the rectangular coordinate system to indicate where the bottom right corner of the payload will be located. Input the height of the payload board (0.0284), 0.023, 0.014.

Then, bring your mouse to the left. Because we enabled ortho mode, the line should snap in place. Input the width of the payload. For 32 mm we input 0.032.

To get a better view of the solid being created, the view was rotated. Now we will set the depth of the payload to be 8mm represented by 0.008.

Finally we will set the height of the payload. 62 cm is represented as 0.062

This is the top view of the resulting payload from the previous instructions

Some commands that may be useful in orientation of your payload or boards may include:

MOVE

Displacement method – specify displacement
Two point method – Select base point and the second point of displacement

COPY

Same methods as move

ARRAYCLASSIC (Array)

Creates rectangular or polar arrays

ROTATE

Rotates objects about the z axis at specific X,Y locations

OFFSET

Creates a copy of an object some distance away

ALIGN

Performs translation, rotation, and scaling to align objects

As we have done in Part 1, we will have to create the materials for your payload. The PCB will likely use the same material as the other boards, but if your payload includes any other materials, you must input the data specific to your component’s materials.

Identify materials of components which will be used in the modeling engine to observe conduction
- Go to Thermal -> Thermophysical Properties -> Edit Property Data
  - Type in materials, conduction, density, specific heat, effective emissivity
  - For surfaces involved with coating and color, values are used for the radiative component of analysis
    - Thermal -> Optical Properties Database
      - Fill out solar absorptivity, emissivity, and alpha or epsilon data

As we have done in Part 1, we will be assigning heat loads to your payload. Determine the type of heat load your payload requires and assign your payload either a hot spot or head load surface and assign the heat load.

If necessary, remember to set up time dependence for the heat load of the component(s) on your payload. To do so, review the procedure in Part 1.

Part 3: Running the Simulation

Lets run our simulation for post process analysis. First we will set orbit related characteristics.

Select Thermal -> Orbit -> Edit Current Orbit

Fill out any necessary information
- Orbit inclination, RA, argument, sun parameters in degrees, altitude and eccentricity, any orientation parameters, how many positions you want represented in the orbit, parameters of external effects (such as earth), solar effects, albedo, planet shine, and fast spin

Now we can create an orbit.

Select Thermal -> Orbit -> Display Current Orbit

To check parameters to ensure they behave the way you want it to, animate the orbit, Select Thermal -> Orbit -> View Vehicle
- Select a scale factor of 2 for visibility
- Select animate and indicate a number of cycles and frame rate. This will show how the sun is seeing different faces of the cubesat and how that will impact the temperature

Now we can run the model.

Select Thermal -> Case Set Manager
- Set parameters for the run (Lloyd explains his method of setting case at 1:25:10)
  - Run a steady state (before transient) to get a more realistic view of the spacecraft to set what the temperature and distribution is likely going to be, then transient after.
- A window will pop up to show it is processing, which means you bypassed any errors and the basic structural components of your model works
  - See troubleshooting section for errors

We can animate the thermal characteristics over time.

Go to Thermal -> post processing -> Animate
- This will popup continuous cycle dialogue. Indicate number of cycles, start and end time, frame rate
- Dynamic changes as heat flows around the spacecraft should show

To find the maximum and minimum temperature at a specific time we can analyze the satellite and find the portion which looks like it has the greatest temperature. Find the side of the model which nodes look like they have the greatest temperature based on the temperature color scale.

To check temperature on a surface or node

Select surface or node and select Thermal -> post processing -> XY plot Data vs Time

In this example, a mid section frame has been selected. This does not include the nodes on the outer solar panel.

You will get a plot

Each period represents a cycle and in this case each cycle is an orbit of the temperature which a node is seeing
The maximum of the plot provides you with the maximum temperature and the minimum of the plot is the minimum temperature of all nodes selected

Notice the smaller oscillating lines. A thermal enclosure has been created for thermal components inside of the spacecraft. The data derived from the smaller oscillating lines may be used as the internal frames thermal behavior.

When removing the solar panel we can see where the low temperature nodes are located at this point of time.