This example is an introduction to Autodesk® Simulation's steady-state heat transfer analysis capabilities. The example will give step-by-step instructions to create a mesh and analyze a three-dimensional (3-D) model of a radiator. There are three sections:
Setting up the model – Open the model in the FEA Editor environment and create a mesh on the model. Add the necessary loads and define the model parameters. Visually check the model for errors with the Results environment.
Analyzing the model – Analyze the model using the steady-state heat transfer processor.
View the processor log file.
Reviewing the results – View the temperatures and heat fluxes graphically using the Results environment.
Use the archive file, Radiator.ach, located in the "Chapter 8 Example Model\Input File"
folder to create a simple model of the radiator (see Figure 8.1). This file may be copied to your computer from the class directory or the Solutions CD. The fluid at the left end of the model is 120°F. The tube and the ends of the radiator are insulated. The fins are convecting to an ambient temperature of 70°F with a coefficient of 0.04
F
solid parts are made of Steel (ASTM-A36). The thermal conductivity of the fluid is 600
⋅ . Analyze the model to determine the temperature profile of the fluid.
Chapter
8
Figure 8.1: Radiator Model Meshing the Model
"Start: All Programs:
Autodesk: Autodesk Algor Simulation 2012: Autodesk Simulation 2012"
Press the Windows "Start" button and access the "All Programs" pull-out menu. Select the "Autodesk" folder and then the "Autodesk Algor Simulation 2012" pull-out menu. Choose the "Autodesk Simulation 2012 software"
command.
"Getting Started: Launch:
Open"
Click on the "Open" button in the Launch panel.
Alternatively you select “Open” from the quick access toolbar or Application Menu.
"Autodesk Simulation Archive (*.ach)"
Select the "Autodesk Simulation Archive (*.ach)" option in the "Files of type:" drop-down box.
"Radiator.ach" Select the file Radiator.ach in the "Chapter 8 Example Model\Input File" directory.
"OK" Select the location on your hard drive where you want the model to be extracted and press the "OK" button.
The model will now appear in the FEA Editor environment. The analysis type will have already been set as "Steady-State Heat Transfer" and the units system set to "English (in.)".
"Mesh: Mesh: 3D Mesh Settings"
Select the "Mesh" tab. Click on the "3D Mesh Settings"
button in the "Mesh" panel.
"Mesh model" Press the "Mesh model" button to create a mesh using the default options.
"View: Navigate: Orbit"
Select the "View" tab. Click on the "Orbit" button in the
"Navigate" panel. Now inspect the mesh, rotating the model around by pressing the left mouse button and dragging the cursor across the screen.
<Esc> Press the <Esc> key to cancel the command.
Setting up the Model
Since you have created a solid mesh, the "Element Type" heading in the tree view has already set to "Brick" and the default "Element Definition" parameters have been applied.
Adding Loads
"View: Navigate: Back View"
Select the "View" tab. Click on the options button to the bottom of "Orientation" button in the "Navigate" panel.
Select "Back View" from the pull-out menu.
Mouse Click on the heading for Part 1 in the tree view.
<Ctrl> Mouse Holding down the <Ctrl> key, click on the heading for Part 2 in the tree view.
Mouse Right-click on one of the selected headings.
"Visibility" Select "Visibility" to hide the parts.
"Selection: Shape: Rectangle" Select the "Selection" tab. Click on the "Rectangle"
button in the "Shape" panel.
"Selection: Select: Surfaces" Also make sure the "Surfaces" button is selected in the
"Select" panel.
Mouse Click and drag a selection rectangle that fully encloses all of the fins but does not enclose the pipe fittings.
<Ctrl> Mouse
Holding down the <Ctrl> key, click and drag a selection rectangle that fully encloses all four holes in the fins but does NOT fully enclose any of the remaining fin surfaces. This will remove the inner surfaces of each hole from the selection set. These surfaces will not have the thermal load applied.
"Setup: Thermal Loads:
Convection"
Select the "Setup" tab. Click on the "Convection” button in the "Thermal Loads" panel.
0.04 Type "0.04" in the "Temperature Independent Convection Coefficient" field.
70 Type "70" in the "Temperature" field.
"OK" Press the "OK" button.
Mouse Right-click on the "Parts" heading at the top of the parts list in the tree view.
"Visibility of all Parts" Select "Visibility of all Parts ". You may need to select it again to see all parts.
Mouse Right-click on the heading for Part 17 in the tree view.
"Visibility" Select "Visibility" to hide the parts.
"View: Navigate: Top View"
Select the "View" tab. Click on the options button to the bottom of "Orientation" button in the "Navigate" panel.
Select "Top View" from the pull-out menu.
Mouse Draw a box enclosing the far left edge of the model (-X end, where the fitting has been hidden).
"Setup: Thermal Loads:
Controlled Temperature"
Select the "Setup" tab. Click on the "Controlled Temperature” button in the "Thermal Loads" panel.
120 Type "120" in the "Magnitude" field.
"OK" Press the "OK" button.
Mouse Right-click on the heading for Part 17 in the tree view.
" Visibility " Select the "Visibility " command.
Defining the Materials
Mouse Click on the heading for Part 1 in the tree view.
<Ctrl> <Shift> "M" Holding the <Ctrl> and <Shift> keys, press the keyboard’s
"M" key. This will collapse the parts list in the tree view.
<Shift> Mouse Holding down the <Shift> key, click on the heading for Part 18 in the tree view. All parts should now be selected.
<Ctrl> Mouse Holding down the <Ctrl> key, click on the heading for Part 2 in the tree view to deselect it.
Mouse Right-click on one of the selected headings.
"Edit: Material…" Select the "Edit" pull-out menu and select the
"Material…" command.
"Steel (ASTM-A36)"
Expand the Steel folder and then expand the ASTM folder.
Select "Steel (ASTM-A36)" within the Autodesk Simulation Material Library.
"OK" Press the "OK" button.
Mouse Right-click on the heading for Part 2 tree view.
"Edit: Material…" Select the "Edit" pull-out menu and select the
"Material…" command.
"Edit Properties" Press the "Edit Properties" button.
600 Type "600" in the "Thermal conductivity" field.
"OK" Press the "OK" button.
"OK" Press the "OK" button.
"Analysis: Analysis: Check Model"
Select the "Analysis" tab. Click on the "Check Model"
button in the "Analysis" panel.
"Details >> "
Click on the "Details >>" button to see the solid meshing progress log. This process will take some time to complete for all eighteen parts. The dialog will automatically close after solid meshing has been completed.
"Tools: Environments: FEA Editor"
Select the "Tools" tab. Press the "FEA Editor" button in the "Environments" panel.
Analyzing the Model
"Analysis: Analysis: Run Simulation"
Select the "Analysis" tab. Click on the "Run Simulation"
button in the "Analysis" panel.
"View: Orientation: Isometric View"
Select the "View" tab. Click on the options button to the bottom of "Orientation" button in the "Navigate" panel.
Select "Isometric View" from the pull-out menu.
Reviewing the Results
We want to view the temperature profile of the fluid part. In order to do this, we should hide the other parts.
"Results Options: View: Load and Constraint"
Click on the "Load and Constraint" button in the "View"
panel with the "Results Options" tab to hide the load and constraint symbols.
Mouse Click on the heading for Part 1 in the tree view.
<Shift> Mouse Holding down the <Shift> key, click on the heading for Part 18 in the tree view.
<Ctrl> Mouse Holding down the <Ctrl> key, click on the heading for Part 2 in the tree view to deselect it.
Mouse Right-click on one of the selected headings.
"Visibility" Select the "Visibility" command. The temperature profile for the fluid should appear as shown in Figure 8.2.
Figure 8.2: Temperature Profile of the Fluid
A completed archive with results (Radiator.ach) is located in the "Chapter 8 Example Model\Results Archive"
folder in the class directory or in the copy of the solutions folders on your computer.
Meshing Options
All of the basic meshing options in the FEA Editor environment are available for a steady-state heat transfer analysis. For more information on these options, refer to Chapter 5, Meshing.
Thermal Contact
One meshing option that is unique to thermal analysis of assembly models is thermal contact.
This can be applied in the FEA Editor environment. Thermal contact is used to represent imperfect contact between two parts. You will be able to define a resistance value for each contact pair in the assembly. This feature can also be used to model the effects of small parts without physically including them in the model. For example, a thin epoxy film can be represented by thermal contact between the parts that it connects. If this part were to be included in the analysis, it would result in a large number of elements because of its size relative to the rest of the model and the small elements that would be needed to mesh it.
There are four types of thermal contact available. These can be set up for individual pairs of parts or surfaces by selecting the appropriate headings in the tree view or display area and right-clicking. Select the "Contact" pull-out menu and select the appropriate contact type as described below. If you want certain contact parameters to be applied to every contact pair in the model, right-click on the "Contact" heading in the tree view and select the appropriate command for the default contact type desired.
Bonded
If the "Bonded" command is selected, the nodes on the surfaces in this contact pair will be matched. Heat will flow freely from one part to the other through the bonded surfaces and it will flow without resistance.
Welded
If the "Welded" command is selected, the nodes along the edges of the contact surfaces will be matched. These nodes will act the same as if the "Bonded" command were selected. The nodes along the interior of these surfaces will not be matched together. No heat will be transferred between these nodes.
Free/No Contact
If the "Free" command is selected, the nodes on the surfaces in this contact pair will not be matched. No heat will be transferred between these nodes.
Surface Contact
If the "Surface Contact" command is selected, the nodes on the surfaces in this contact pair will be matched. The difference between this command and the "Bonded" command is that you will be able to define a thermal contact resistance between the surfaces. This can be done by right-clicking on the heading for the contact pair and selecting the "Settings…"
command. You will be able to specify the total combined resistance in all of the surfaces involved in the selected contact pairs ("Total Resistance") or the amount of resistance per unit area ("Distributed Resistance") in the "Type:" drop-down box. Enter the appropriate value in the "Value:" field.
NOTE: If thermal results will subsequently be used as a load in a structural analysis in which surface contact is to be used, then this should be anticipated prior to running the heat transfer analysis. Thermal contact should be specified wherever surface contact is to be used later, even if no thermal resistance is to be imposed. This will ensure that the node numbering will be consistent between the two models or two design scenarios. Where two parts having surface or thermal contact meet, there will be sets of two nodes at each point where the meshes are matched. These will have the same coordinates and will be connected by zero-length gap elements (for structural analysis) or thermal contact elements (for heat transfer analysis). Otherwise, with bonded contact, the nodes for each part will be merged and only one node will exist at each point where the meshes are matched.
Element Options
There are five types of elements available for a steady-state heat transfer analysis. All of the element types share the same basic loading options that will be discussed later in this chapter.
Rod Elements
Rod elements are line elements that consist of 2 nodes. These elements can be created in the FEA Editor environment.
Rod elements are used to represent parts that have a constant cross-section that is small relative to the length. These elements can be used to represent wires. Since the cross-section is small, it is assumed that the entire cross-section at a specific point along the length is at a uniform temperature. The cross-sectional area and perimeter will be required. The perimeter will be used to calculate the surface area for convection and radiation to the environment.
Rod elements cannot be used in an enclosure for body-to-body radiation.
Rod elements have two material models available. The first material model is the
"Isotropic" material model. This material model is used for a material that has material properties that are constant with regards to the temperature. The second material model is the
"Temperature Dependent Isotropic" material model. This material model is used for a material that has different material properties at different temperatures. The material properties for each temperature will be entered into a spreadsheet. The temperatures that the model will experience must be between the low and high values of the spreadsheet.
2-D Elements
2-D elements are planar elements that are drawn in the Y-Z plane. Each element consists of an area enclosed by three or four lines. These elements are generally created by building and meshing Y-Z sketches in the FEA Editor environment. There are two geometry types available for 2-D elements—planar and axisymmetric. The planar geometry is used to model parts of a constant thickness that can be represented by a cross-section. The axisymmetric geometry is used to model parts that have a continuous cross-section that is revolved about a center axis. In Autodesk® Simulation, this axis of revolution must be the global Z axis and the cross-section must be drawn in the +Y half of the Y-Z plane.
2-D elements have four available material models. The first is "Isotropic." This model is used for materials that have identical thermal properties in all directions and at all temperatures. The second material model is "Orthotropic." This model is used for materials that have different thermal properties in different directions but the properties are assumed not to vary as the temperature changes. The third and fourth material models are
"Temperature Dependent Isotropic" and "Temperature Dependent Orthotropic." As the names imply, these are temperature dependent variants of the Isotropic and Orthotropic material models. Either one allows you to model materials that have different thermal conductivity or specific heat values at different temperatures. The material properties for each temperature will be entered into a spreadsheet within the "Element Material Specification" dialog. The temperatures that the FEA model will experience during the analysis must fall between the low and high values of the spreadsheet.
For an orthotropic material model, you will need to define two orthogonal material axes. The
"Principal Axis Transformation Angle" field on the "General" tab of the "Element Definition" dialog is used to accomplish this. The value in this field is measured counterclockwise from the positive Y axis and defines the direction of the principal material axis (also referred to as the "n" axis or the "r" axis). The "s" axis will be based on the same transformation angle but measured counterclockwise from the positive Z axis. The third material axis will always be the X axis for 2-D elements. Please note that the letters "n" and "r"
are used interchangeably when referring to the first material axis. For example, the conductivity in this direction may be referred to as "Thermal conductivity, Local Axis n" or as "Kr."
Plate Elements
Plate elements are 3-D area elements that consist of an area enclosed by three or four lines.
These elements can be created from CAD solid parts or assemblies by using the "Midplane"
mesh setting. They can also be manually created in the FEA Editor environment. Lastly, plate elements can be generated from CAD surface models (i.e. those models consisting of zero-thickness surface geometry, rather than solids). To do this, choose the "Plate/Shell"
mesh option.
These elements are used to represent parts that are thin relative to the other dimensions. Since these parts are thin, it is assumed that both the top and bottom of the plates are the same temperature. No temperature distribution will exist through the thickness. In the "General Controls and Parameters" section of the "General" tab of the "Element Definition"
dialog, you will be able to define a point in space (the "Element Normal" point) that will be used to define the top of the plate elements in this part. The top of the plate will face away from this point. The orientation of the plate is only used when considering the side of a plate involved in an enclosure for body-to-body radiation.
As is true for the 2-D elements discussed previously, plate elements have four available material models. The first is "Isotropic," used for materials that have identical thermal properties in all directions and at all temperatures. The second material model is
"Orthotropic," used when materials have different thermal properties in different directions but the properties are assumed not to vary with the temperature. The third and fourth material models are "Temperature Dependent Isotropic" and "Temperature Dependent Orthotropic." As the names imply, these are temperature dependent variants of the Isotropic and Orthotropic material models. Either one allows you to model materials that have different thermal conductivity or specific heat values at different temperatures. The material properties for each temperature will be entered into a spreadsheet within the "Element Material Specification" dialog. The temperatures that the FEA model will experience during the analysis must fall between the low and high values of the spreadsheet.
For an orthotropic material model, you will need to define the orientation of the three orthogonal material axes, "n," "s," and "t" (or "r," "s," and "t"). This is done in the
"Orientation" tab of the "Element Definition" dialog, which is shown in Figure 8.3. Please note that the letters "n" and "r" are used interchangeably when referring to the first material axis. For example, the conductivity in this direction may be referred to as "Thermal conductivity, Local Axis n" or as "Kr."
Figure 8.3: Orientation Tab of the Element Definition – Thermal Plate Dialog There are four options available for defining the n, s and t axes. These are found in the
Figure 8.3: Orientation Tab of the Element Definition – Thermal Plate Dialog There are four options available for defining the n, s and t axes. These are found in the