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Paulin Research Group
Mesh/PRO v.3.
User’s Guide
TABLE OF CONTENTS
1.0 INTRODUCTION
2.0 AXISYMMETRIC MODELS
2.1 OVERVIEW
2.2 EXAMPLE
2.2.1 Using Nozzle/PRO to Calculate a Film Coefficient 3.0 SHELL MODELS 3.1 OVERVIEW 3.2 SHELL REGIONS 3.3 EXAMPLE – IMPORT FROM FE/PIPE 3.4 EXAMPLE – EXPORT TO FE/PIPE 4.0 BRICK MODELS 4.1 OVERVIEW 4.2 EXAMPLE 4.2.1 Post-process stresses using StresPLOT
Addenda: Nozzle Intersection Models
1.0 INTRODUCTION
Mesh/PRO provides an interface between AutoCAD 2000/2005 and FE/Pipe. It allows Axisymmetric, Shell and Brick models to be created and modified in AutoCAD, and then analyzed in FE/Pipe. The following documentation provides an overview and an example for each model type. The input files and corresponding AutoCAD drawings can be found in the “\Models\MeshPRO” folder. The example drawings were made in AutoCAD 2005.
Generating FE/PIPE Quads
- Use AutoCAD’s 3DFACE entity to designate the quadrilateral. Note –
no other entity will work!
- Each 3DFACE should be assigned to a properly designated layer in AutoCAD. See table above.
- Curved Edges - Edges of quads may be curved by designating a circle or arc, then placing the quads edges along this circle or arc.
Edge Conditions (Thermal BC’s, Pressure and Fixities)
- These features may be included in the model by generating polylines with vertices (nodes) at the corners of each quad (3DFACE)
- The layer name convention given above must be used.
Stress Classification Lines
- SCL’s are generated by defining polylines from one corner of a quad to another.
- The SCL’s must be generated in AutoCAD using the naming convention in the table above.
File Export Procedure
- Save your AutoCAD file as a type DXF drawing. Remove all features such as dimensions, text, or other entities that are not to be included in the FE/PIPE model. It is best to not use SAVE AS to revise existing DXF files. Each DXF file generated should be a new file. Do not save over existing DXF files, as some previous data might remain inside the file.
- Open an FE/PIPE file using the Axisymmetric template. Existing files may be used, but when revised Mesh/PRO models are imported the user should delete all QUAD screens and all POINTS screens or error may occur.
- In Mesh/PRO, click Axisymmetric > Import DXF File.
- A file open dialog box will appear. Navigate to your DXF file and click OPEN.
- Mesh/PRO will begin to read in the data and the status bar will keep the user updated. The status box will close once the file is ready to be exported. Any errors should be noted and investigated.
- In Mesh/PRO, click Axisymmetric > Export to FE/PIPE.
- Follow the instructions given in each screen that will appear.
- You’re finished!
1. Add the quads The quads are laid out using the “3D Face” tool in AutoCAD. The layer must correspond to a material id #. For example, in this model, there will be one material, and we will assign it material id # 1. So we need to define a layer with the name “1” (see the layer name conventions in the table in section 2.1).
In Figure 2 we have started to define the quads, starting in the head. Note that it is very important that the quad corners are actually ON the arc. If they are not, then FE/Pipe will not know to curve the edges. We’ve made these quads about the size we want the elements to be in the model (note that by default, FE/Pipe will divide each quad into 4 actual elements. We could have also defined a larger quad, and set the number of elements for this quad in FE/Pipe. This is simply a user preference.
Figure 2 - Adding Quads to the Head
As shown in Figure 2, we’ve continued adding quads in the head and now we are getting close to the head and shell intersection. Let’s say that we are particularly concerned about the stress in this area and that we would like to double the number of quads though the thickness. Figure 3 shows how this is done. Note the transitions between one element and two elements through the thickness. We use transitions like this to avoid triangular elements. We should always have 4-sided elements.
Figure 3 - Transition Elements
Completing the quad layout, we add a large quad at the end of the shell that extends to the centerline (Figure 4). This will be used to apply boundary conditions.
Figure 4 - Completed Quad Layout
2. Thermal Boundary Conditions Thermal boundary conditions are added using the “Polyline” tool in AutoCAD. New layer will be added with the names “TB1” and “TB2” (see the layer name conventions in the table at the end of this section). Each vertex of the polyline must coincide with a vertex of a quad (Figure 5). Note how the hot boundary condition is applied to the end block. This ensures that the end will expand in a similar fashion to the rest of the model preventing artificial bending stresses from being created.
Figure 6 - Completed Thermal Boundary Conditions
3. Apply Pressure Pressure boundaries are defined by polylines as well. Again, a new layer must be added, however, with pressure, the actual pressure value must be part of the layer name. In this model, let’s say that there is an internal pressure of 200 psig. Thus the layer we will draw our polylines with will be named “PR200” (see the layer name conventions in the table at
Figure 5 - Applying Thermal Boundary Conditions
Figure 9 - Cleanup Text and Geometry Figure 10 - Leave Arcs
Axisymmetric models in FE/Pipe are always oriented vertically, and the centerline must be along the vertical line x = 0. In Figure 11, the model has been rotated vertically and then the bottom left of the base is moved to the coordinate 0,0,0.
6. Add Boundary Conditions Fixity boundary conditions can also be applied in the X, Y or XY directions, using a polyline and a layer with the name “X”, “Y” or “XY” (see the layer name conventions in the table at the end of this section). We will put a “Y” boundary condition at the bottom of the model (Figure 12).
Bottom left at coordinate 0,0,0.
Figure 11 - Model Orientation
Figure 12 - Boundary Conditions
Figure 13 - AutoCAD Model Ready for Import
Final Preparations
Finally, the model must be saved as an AutoCAD 2000 DXF type file. We also will run the “Purge All” command to make sure there is no extraneous data in the model that might cause errors. Figure 13 shows the completed model ready to export to Mesh/PRO.
Import the Model into Mesh/PRO
Now that the model is ready to be imported, we start Mesh/PRO. In the initial screen select “Axisymmetric” from the menu at the top. Then select “Import DXF File” from the Axisymmetric menu. A DXF Reader message box should appear as a reminder to purge the file and to use a new file name when saving the dxf file. Click “OK”. If there are no errors in the import, you should see a screen similar to Figure 14 (click View Database Grids from the View menu to see the tables). You can then use the Mesh/PRO radio buttons to view/edit different aspects of the model, i.e. edge conditions, SCLs, and so on.
Figure 16 Figure 17
Once the DXF has been imported successfully without errors, the model is ready to be exported to FE/Pipe.
Export the Model into FE/Pipe
The general procedure for exporting the model into FE/Pipe is as follows:
- Create an FE/Pipe Axisymmetric Template input file.
- Use the Export Wizard in Mesh/PRO.
- Make final model modifications/preparations in FE/Pipe.
Create an FE/Pipe Axisymmetric Template input file.
To create an input file, start PRGMAPS, and give your model a job name (Figure 18). In this example, we used “axisym” for the job name. Then click FE/Pipe -> New Job -> More -> Symetric Geometries. The Symetric template input screen should appear. Click “B-Save” and the input file will be created and the model is ready to be exported (Figure 19). Do not close the FE/Pipe input screen, as the export process is interactive between FE/Pipe and Mesh/PRO.
Figure 18 - PRG MAPS Screen Figure 19 - SYMETRIC Template Menu
Use the Export Wizard in Mesh/PRO
With your FE/Pipe model open, return to Mesh/PRO and select “Axisymmetric” -> “Export to FE/Pipe” from the menu at the top. The Mesh/PRO export wizard will appear and step through the export process. In general, Mesh/PRO writes out portions of the model data as text files, which FE/Pipe then reads in using the “TextIN” feature.
Step #1 – Locate FE/PIPE File (Figure 20) Click “Continue” and browse to the input file you saved (in this case it is “axisym.ifu”).
Figure 20
Step #4 – Export Quads (Figure 25) In this step, again with the ‘3-Geometry’ screen open, click ‘TEXT IN’ from the menu bar. You should see at the top the number of quads exported. In our example the number was 133 (Figure 26). At this point, it is a good idea to exit the Geometry screen and save the input.
Figure 25 Figure 26
Step #5 – Export Boundary Conditions (Figures 27 and 28) In this step, open the ‘6-Boundary Conditions’ screen and click ‘TEXT IN’ from the menu bar. When the boundary condition data appears, exit the boundary condition screen and click “Continue…” on the Mesh/PRO Export Wizard.
Figure 27 Figure 28
Step #6 – Export Point Locations (Figures 29 and 30) In this step, open the ‘8-Point Locations’ screen and click ‘TEXT IN’ from the menu bar. When the point data, exit the boundary condition screen and click “Continue…” on the Mesh/PRO Export Wizard.
Figure 29 Figure 30
Step #7 – Export Completed (Figure 31) The export process is complete; click “Continue…” on the Mesh/PRO Export Wizard. Before continuing to work with the model it is a good idea to save the input once again. If we click “Plot” now from the FE/Pipe menu, we should see the following plot of our model (Figure 32).
Figure 31 Figure 32
Make final model modifications/preparations in FE/Pipe.
While there may be other model specific adjustments that need to be made, every axisymmetric model after being imported from Mesh/PRO will need to have the material properties defined. Click ‘5-Properties’ from the FE/Pipe menu, and set the material properties for the model (Figure 33). Note that the property id # corresponds to the layer number chosen in AutoCAD to define the quads.
Our model also had thermal boundary conditions applied with 750 degrees F on the inside and ambient temperature outside. Thermal boundary conditions are applied in the ‘Thermal Boundary Conditions’ screen (Figure 34). Our first thermal boundary condition which was identified in AutoCAD with layer TB1, is the inside layer. Figure 34 shows how this entry is put in. Boundary type 3 is a contact boundary. The “0 750 1”
Using Nozzle/PRO to Calculate a Film Coefficient
- Start Nozzle/PRO. Under Base Shell Type select Hemihead and under Nozzle / Attachment Type select Straight (Fig. 35). These selections make Axisymmetric options available.
- Click Options
- In the Options screen select Axisymmetric Head and Skirts under Finite Element Type (Fig. 36).
- Click Axisymmetric Head and Skirt Options.
- In the Axisymmetric Model Data screen click Heat Transfer Data (Fig. 37).
- In the Axisymmetric Heat Transfer Data screen click the question mark “ ?” next to the Outside (Insulated) Film Coefficient field (Fig. 38).
- In the Insulated Outside Film Coefficients screen, the first field is (h) Outside Film Coefficient. An estimate for this value can be found by clicking the question mark “? ” next to the Outside (NOT- INSULATED) Film Coefficient field in the Axisymmetric Heat Transfer Data screen. From this, let’s use the value for still air which is 8.3E-7 Btu/sec/sq.in/degF (Fig. 39).
Figure 35 - Nozzle/PRO Main Screen
Figure 36 - Options Screen
Figure 37 - Axisymmetric Head and Skirt Options
Figure 38 – Axisymmetric Heat Transfer Data
- The next value in the Insulated Outside Film Coefficients screen is (k) Insulation Conductivity. Press the question mark “? ” next to this field to see a list of common conductivities for various common insulating materials (Figure 40). From this list we will use the value for mineral wool at 500F which is 9.64E- Btu/sec/in/degF.
- Finally, enter in the inside and outside radius of the insulation layer and click Find Outside Film Coefficient. A film coefficient is calculated (Figure 41), and this is the value we will put in our Thermal Boundary Conditions screen (Figure 42).
Figure 39 – NON-Insulated Film Coefficients Figure 40 - Insulation Conductivity
Figure 41 - Insulated Outside Film Coeffs Figure 42 – Completed Thermal BC
