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InventiumTM PreSysTM Tutorial: An Introduction to Modeling with PreSys

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PreSys Tutorial: An Introduction to Modeling with PreSys

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PreSys Tutorial: An Introduction to Modeling

with PreSys

This tutorial was created to familiarize PreSys users with the functions and techniques associated with the use of the PreSys for the construction of finite element models, and the associated features within the PreSys user environment. This tutorial will demonstrate the steps required to create and prepare a model for simulation using PreSys modeling tools.

Introduction to Finite Element Modeling with PreSys

Finite element modeling is a task that enables engineers to perform evaluations of their designs under simulated testing and operational conditions. This task, while sometimes tedious, is the foundation of a proper simulation. Without a proper model, using proper techniques and quality guides, is a possible source of a misleading finite element analysis results. This tutorial will provide you with the basic information and understanding of the tools available to the user for construction of quality finite element models. While the immense scope of all engineering problems keeps us from fully discussing all possible modeling scenarios, this tutorial should provide the knowledgeable user with the tools and techniques to apply to their problem. The user should consider this the ‘basics’ and look for techniques which may be applied to their specific application areas. This Tutorial is divided into 7 sections, each of which may be performed as a separate exercise: 1. Modeling Concepts: Basic info needed to create models (Page 2) 2. Basic Shell Modeling: CAD data import and semi-automated mesh creation methods (Page6) 3. Shell Automeshing: Using the Topology Automesher & mesh refinement tools (Page 11) 4. Mesh Repair and Enhancement Tools: Checking, Repairing and Improving Mesh (Page 13) 5. Solid Mesh Creation: Using PreSys’ solid mesh tools to generate hexa meshes (Page 17) 6. Automatic Tetra Mesh Generation: Using the Tetra Automesh Tool (Page 21) 7. Drag Mesh Creation of Solid Elements: Solid Mesh Creation Tools (Page 22)


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1. Modeling Concepts: Creating a Model with PreSys

The PreSys user interface can be configured in many different ways, for maximum flexibility. The default user interface is shown in Figure 1. The main areas of the interface are labeled, and will be referred to in this Guide. The TOOLBAR area is located at the top of the window, and contains selectable icons for all of the commands available in PreSys. The DROP DOWN MENUs are at the very top of the window allows users to access every command through an easy to use drop down menu system. The DISPLAY AREA is where all graphical data is displayed. The MESSAGE WINDOW displays information about the model and prompts the user if data is needed, as well as warning or error messages for the user. The MODEL EXPLORER allows the user to access a great deal of information about the model, control the display of data, edit the model data and view non-graphical data via ‘card’ images.

Figure 1: Default PreSys User Interface

Display Area

Message Window

Toolbars

Drop Down Menus

Model Explorer


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Function Keys

For quick access and to improve productivity, function keys may be assigned for any function. By default only the F1 and F3 function keys are assigned. These assignments may be modified by the user.

F1 F2 F3 F4 F5 F6 F7 F8 F9

On Line Help

open Import File

open open open open open open

Menu Bars and Icons Several rows of icons may be shown near the top of the PreSys window. Tool tips are displayed when the user places the mouse pointer over the icon. Functions are activated by clicking once on the icon using the mouse. In all cases, the functions which are accessed through the icons are also available for use through the menu system.

The icons shown below control the rotate about center, pan, zoom, fill screen and standard views of the model data.

The file open, save, and print functions can be accessed from these icons. Access to the PART ON/OFF function is available through the following icon. PreSys may occasionally highlight entities on the screen to identify them for review or selection. To remove this highlighting, or to re-draw the screen, the user may select the icons on the right.

NOTE: Please note that some images shown in this tutorial may make use of optional display

features including background colors, shading, and element outlines. These may be controlled through the VIEW Menu, and the OPTIONS CENTER.


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PreSys provides a set of tools which allow the user to identify entities and measure the distance between points, nodes, etc. These functions can be accessed by using the icons to the right.

Keyboard Controls Rotation, Pan and Zoom functions can be controlled through a combination of the mouse and keyboard. By selecting the right, center or left mouse button, and the CTRL key, the use can

access these functions. Users may dynamically rotate by pressing the left mouse button and the CTRL key. An added feature of PreSys is the ability to dynamically zoom the model using he mouse wheel. The zoom center will be at the location of the cursor. Rolling the mouse wheel toward you will zoom in, moving the model closer to the viewer, and rolling the mouse wheel away from the user will zoom out.

Parts The concept of PARTS in PreSys:

- All lines, surfaces and elements must be in a ‘part’. This is a convenient way to collect and display these entities

- Each ‘part’ can contain some or all of these entities - A physical part need not be contained in single PreSys ‘part’. In other words, a

component could be divided into several parts for easier manipulation. - A ‘part’ can contain some elements, some lines and some surfaces, but does not

necessarily need to contain all elements, all lines and all surfaces. For instance, a ‘part’ might contain a portion of the elements of a complete physical part as well as some of the geometry used in creation of the mesh.

- Nodes, Materials and Boundary Conditions do not belong to any ‘part’ - When entities are created, they are placed in the CURRENT PART. A part must be

made CURRENT to add any data to it.

Toolbars

++


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The user may turn on/off toolbars by right clicking the mouse in the area near the displayed toolbars. A list of available toolbars will be presented, and the user may select the toolbars they desire to display. This configuration will be saved in the configuration file when the user exits PreSys.

Windows The PreSys windows shown on Page 2, may be hidden/displayed by selecting Window from the drop down menus, The desired windows may be selected for display. It is recommended that the Message Window be displayed, since many messages are displayed regarding any errors which may occur during the modeling processes presented here. These messages will direct the user to select or input the proper data.

The PreSys Modeling Process The PreSys modeling process is one common to most commercial finite element modeling software. The user creates or imports geometry on which a discretized finite element mesh will be applied. The mesh then has physical properties associated with it, and boundary conditions applied. This data is then exported to an internal or external finite element solver where the data is interpreted and a solution is stored in a computer file for post processing.

PreSys Modeling Process

Open PreSys and Create a New Database

Check and Repair Mesh

Create Mesh using Automesh and Semi-automated Meshing Tools

Import or Create CAD Geometry

Create and Assign Materials

Create and Apply Boundary Conditions

Create and Assign Material Thickness

Define Simulation Parameters and Results Requests

Export Model for Execution


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2. Basic Shell Modeling Example The techniques used in creating a finite element model are varied and many times depend on the user’s preferences. However, there are some basic concepts that are useful for all users to implement in their modeling activities. This tutorial will focus on the basic steps used in creating shell model. The steps in reading a CAD data file, creating a mesh, checking the mesh and applying the material and boundary conditions, and ultimately exporting a analysis input file will be presented.

Shell Model Creation: A Step-by-Step Tutorial

A PreSys model can be created from existing geometry that you import or from data that you create using PreSys’ geometry creation tools. Also, existing finite element models in various formats may be imported into PreSys. Your PreSys installation comes with a sample file that we will use to quickly demonstrate how to import CAD data, create a mesh, create a material and element properties, and export that data. Images of the User Interface will be used to help guide you through this process.

Open a New PreSys Model Database

Select the PreSys icon on your desktop and open the software. Once PreSys has started, select NEW MODEL from the FILE Menu.

Importing CAD Data

PreSys imports many native CAD formats, using a common interface. IGES, STEP, CATIA V4 and V5, UG NX, ProE, SolidWorks VDA and Autodesk DXF file formats may be both imported and exported from PreSys. From the FILE drop-down menu, select IMPORT. A file selection window will open. Navigate to the PreSys Examples folder and select the IGES file ‘training_cad.igs’. This iges data will be imported and displayed. By default, the lines and surfaces in the Model Explorer are toggled ON. Take the opportunity to switch ON/OFF those options by clicking the green check boxes next to the LINES and SURFACES entries in the Model Explorer. If necessary, click on the plus (+) next to the entity name to expand the entity list. You can determine the number of surface and line entities


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currently in the model by reviewing the numbers next to the LINE and SURFACE entries in the Model Explorer. Rotate and explore the loaded CAD information by clicking the Rotate About Center icon in the VIEW toolbar. You can toggle the shading of the surfaces on/off by selecting the SHADING icon from the VIEW toolbar.

Meshing the CAD Data: 2 Line Mesh

The “Current Part” is the active part to which all new entities are assigned. All new lines, surfaces and elements will be automatically included in the current part. The current part is displayed at the lower right corner of the PreSys window, with its part color shown. Caution should be taken to make sure that the desired part is current before creating any new lines, surfaces, or elements. Using the PART ON/OFF function, turn OFF ALL PARTS, and select PID8; this will turn on PID8. Please note that the CURRENT PART, as designated by the PART NAME shown in the CURRENT PART field at the lower right of the PreSys, is not the part displayed (PID8). To set this as the CURRENT PART click on the name shown in the CURRENT PART field. This will open a Part List from which you may select the PID8. To begin creating a mesh on our CAD data, we will go to the Mesher menu by either selecting Mesher and the Area Mesh option from the Preprocess drop down menu menu, or by selecting


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the icon for Area Mesh from the Mesher Toolbar. If the Mesher Toolbar is not displayed, right-click near the existing toolbars and select the Mesher Toolbar for display. In the Preprocess/ Mesher/ Area Mesh menu the user is presented with the various options for creating and editing meshes. Select the option 2 LINE MESH. This option allows the user to select two lines to create a mesh between these two lines using a specified mesh pattern. Mesh created in this manner can include quadrilateral and triangular mesh.

First select the Number of Elements option on the Area Mesh Task Panel. This will then set the data requirements for the completion of the 2 Line Mesh. Select the first line of the 2 Line Mesh. Select the Line on the left, as shown the following figure. The line will be highlighted, indicating that it has been selected. A ‘1’ will be displayed near the center of the line, indicating this is ‘line 1’. Next, select the line on the right, which will be highlighted and designated ‘line 2’. PreSys will prompt the user to enter the number of elements they wish to have on N1, N2, N3, N4. For a 20 element mesh by 10 element mesh, the user would enter 20, 10. All four numbers are not required unless the user desires a different number of elements on each of the lines. PreSys will immediately create the mesh and display the elements on the geometry. If the user would like to regenerate the mesh using different mesh parameters, they may select the UNDO button in the

Meshing Process and Meshing Task Panels


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toolbar. They may then reselect the lines and enter a new mesh density.

4 Line Mesh Function We will now use another Area mesh option, 4 Line Mesh, to create another section of mesh in our example model Using the technique outlined above, turn on the Part PID9, and make that part CURRENT.

In order to illustrate several of the options available

in the 4 LINE meshing tool, we will make some modification to our CAD data. We will split the lines and delete some segments in order to show that the lines need not intersect or share common end points to be meshed. To split these lines, we will enter the Preprocess-- Line/Point menu, and the Split Line function.

Select Split from the Line/Point drop down menu or Line/Point toolbar. PreSys will prompt you to split the line at the selected cursor location on the line. Select each line at a location near the endpoint, as shown the following figure. Select Apply or press the middle mouse button to complete the split operation. PreSys will split the lines at these locations and create a point at the end of the new line segments. For this example, the split locations can be approximate.

Next, we will delete the end segments of these lines. Close the Split function and select Delete from the Line menu. Select the line segments near the ends of each line, as shown in the following figure, to delete these corner line segments. The resulting lines will have the end sections removed. From the Mesher toolbar or drop down menu, select the Area Mesh and the 4 LINE MESH option. As in the 2 LINE


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MESH, PreSys will prompt you to select the lines. The user should select the lines in a continuous, clockwise or counter-clockwise order. PreSys will internally calculate the endpoints of these lines at the intersection of the lines. It will then use these ‘temporarily lines’ to create the mesh. Enter a mesh of 20, 10 (in the N1, N2 fields), then select the 4 lines shown. The resulting mesh is shown below. This 4 Line Mesh technique may be used to create meshes on simple geometries and efficiently create models when line data is available. Please note that while the geometry shown here are simple lines, the 2 Line and 4 Line Mesh options can be used on any B-Spline geometry.


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3. Shell Automeshing Using the Surface Meshing tools in PreSys, the user may create meshes on complex geometry, as well as multiple surfaces and multiple parts simultaneously. The next exercise will familiarize the user with the surface meshing tools within PreSys. The surface mesher uses algorithms which are forgiving of poor quality surface data, and allows the user to neglect the steps related to CURRENT PART important to the other mesh generation techniques. The Surface Mesh function has controls which allow it to mesh over holes or gaps in the mesh and ignore some features of the CAD geometry. For example, we will work on a different part, PID4. Turn off all other parts and turn on PID4. The TOPOLOGY MESH are found in the Preprocess--Mesher Menu or via the Mesher Toolbar. The Topology Mesh option is the preferred tool for creating mesh on a single surface or many surfaces in many different parts. This will create a quad-dominant mesh using the parameters specified by the user. Select TOPOLOGY MESH and enter the surface meshing options. The user will be presented with several options for selection of the surface data. We will use the DISPLAYED option. This will select all of the surfaces displayed in our model (Parts that are turned ON). Please note that this will select the surfaces, even if they are not currently shown on the screen. The case where we are zoomed in and cannot see other displayed surfaces is an example of this condition. Once the surfaces have been selected, the Task Panel will allow the user to specify the various options for mesh creation. Select the In Original Part option to create the elements in their CAD data part. This panel also has default values which may be perfectly fine for your application. However, these should be reviewed for each specific modeling application. We will input new values for the IGNORE HOLE SIZE parameter, to mesh over the hole shown in our CAD surface. Enter 50 in this field. Verify that the ELEMENT SIZE field has a value of 5.00. This will generate a mesh of 5.0 distance units (nominally) for our surface. Select APPLY at the bottom of the Topology Mesh panel to accept the model parameters and create the mesh.


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After the meshing process is completed, the mesh will be displayed.

NOTE: “Mesh Quality” determines the parameters for the Auto Mesher and the criteria for triangle and quadrilateral elements to be created. Mesh Quality Parameters are controlled through the Tools drop down menu, and selecting the Options Center. Once there, select the PreProcess/Model Check to set the default modeling and model checking parameters.


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4. Mesh Repair and Enhancement Tools Once a user has created a mesh, it is necessary to check the quality of the mesh, since that may have a direct effect on the accuracy of the analysis results. PreSys has a collection of tools which allow the user to check and repair the mesh. These can work on a single aspect of the mesh, or on several mesh quality parameters, simultaneously. In this exercise, we will automatically generate a surface mesh, check the quality of that mesh, and use tools to repair the mesh. Open the PreSys database used in the previous examples. If you have not yet created a database and imported the CAD geometry, please go back to pages 6-7 of this document and follow the instruction on importing CAD geometry.

Use the PART ON/OFF function to turn on only the PID1 and PID5 parts. Select the ISOMETRIC VIEW from the icon bar to place the data in a convenient orientation. Make sure that the options ‘In Original Part’ so the elements will be placed in the corresponding CAD surface part. Also, reset the Hole Size option back to 1.0. Note that the mesh will not exactly match at the interface between the tube and the plate. This will be the focus of our exercise. Enter the Mesher menu and select the Surface Mesh option, and the Topology Mesh option to create a mesh on the surfaces shown. To do this, select the Displayed Surfaces and then accept all of the default meshing parameters. The resulting mesh should look like the image below. In order to identify the quality and connectivity problems in this mesh we will use the MODEL CHECK menu. This can be accessed either by selecting PREPROCESS/MODEL CHECK, or by using the toolbar icon. In the MODEL CHECK menu, the user will find many different options for evaluating the model.


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Note that even though the TOPOLOGY MESH tool has a set of mesh quality parameters which may be defined, these parameters are not an assurance that the entire model has these required mesh quality. Therefore, it is necessary to check these parameters and repair the model using the tools found in the MODEL CHECK menu. We will start by checking the boundary of our model to see if there are any unconnected elements. Select BOUNDARY DISPLAY from the MODEL CHECK menu. This function will find any free edges in our elements. The user may select individual parts, multiple parts or the entire model for this operation. After identifying the free edges in the model, PreSys will display these edges highlighted in a white color for the user’s review. The boundaries will be highlighted as shown in the following figure. Note that there are two boundaries shown at the interface of the tube and the plate, indicating that those elements are not connected. After finding the boundaries of our parts, PreSys offers several options to proceed. The user may CANCEL and the highlighting will not be removed. The user may generate lines or elements to visualize the boundaries and develop a repair strategy. Occasionally the above options are useful for model construction or for display purposes but the majority of the time the user will simply select OK. Cancelling will still keep boundary display highlighted until the user selects the clear function from the icon bar. From this MODEL CHECK operation we can see that the mesh is not properly connected. Connecting this mesh can be accomplished several ways: manual movement and deletion of the duplicate nodes, coincident node check and remeshing using additional options. Since this last option is the easiest and least labor intensive, we will use some options in the surface mesh operations to repair this mesh quality problem. To automatically fix this in the meshing operation, we will use a different tolerance in the Merge Boundary Gap field.

Model Check/Check Boundary Display

To check the boundary display for free edges, select Boundary Display from the model check menu. This command finds free edges on plate mesh and displays them as highlighted lines. Options: Create Lines: Will use the boundary lines to create geometric lines. Create Plotels: Uses the boundary lines to create PLOTEL elements. In New Part: This will create the lines/ plotels in a new part, as designated in the Task Panel


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Notes on Intersecting Mesh & Master Surface: In the case of 2( or more) surfaces intersecting where the surfaces do not touch, the master surface will be the one extrapolated to intersect the slave surface for high quality intersecting meshing results. In the case where 2 (or more) intersecting surfaces are in contact with each other, the master surface will be the one that the user intends the nodes to remain in place, and therefore the non master surface mesh will adjust itself, to stitch itself to the master surface.

Move back to the Mesher Menu and select a TOPOLOGY MESH/ SURFACES ON DISPLAY. When the meshing options windows opens, Enter 3.0 in the Intersection Gap field. This value will check for nodes within the defined tolerance for mesh repair. The result of this operation should be mesh which is connected at the intersection of the tube and plate.

Note: You do not need to remove or delete the current mesh, PreSys will replace an

existing mesh, if you select the surfaces for meshing.


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Using Enhance Mesh to Check the Model

After the mesh has been completed, the user should check the elements which were created, to assure that there are no cracks in the model, and that all elements meet the desired quality criteria. To perform this verification, the user selects Model Check from the Drop Down menu or from the Model Check toolbar. To perform a comprehensive model check and repair, it is recommended that the Enhance Mesh option be used. Once the Enhance Mesh Task Panel is opened, the user can select the model checking parameters that will be used to evaluate the mesh. The user may check/uncheck the desired boxes next to the parameter to enable or disable the model checking options. Enhance Mesh will check all quantities simultaneously and display the results using a color-coded scale. Elements failing any of the criteria will be displayed, filled with the color corresponding to the scale displayed on the right side of the Display Window. Elements which fail multiple criteria will be displayed in a red color. To execute the ENHANCE MESH function, select CHECK . This will display the elements which fail. Selecting AUTO REPAIR will initiate an action to repair any elements which fail, using the strategies selected in the OPTIONS section of the Task Panel. MANUAL REPAIR allows the user to select and dynamically move a node, to attempt to repair the mesh.

During a Manual Repair operation, you will be prompted to select a node to dynamically move. The effected element color will change from a ‘fail color’ to gray when the element meets the quality criteria.


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There are four repair and display options to aid the user in dynamically repairing the mesh. Toggling off the ‘Move Node in Origin Plane’ provides the user with more freedom in moving the nodes to meet the quality criteria. Please note that this may also allow the node to move out of plane.

Failed Elements Repaired Elements


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So far in this exercise we have either made parts ‘current’ to mesh or we insured that the newly created mesh would reside in its original part during the surface meshing function. Because of the differences between plate and solid elements in regards to materials/element properties, PreSys will not allow plate and solid elements to reside into the same part. So it becomes necessary to create a new part to house the solid elements if plate elements already exist in the intended solid part. PreSys will issue a warning: CANNOT CREATE SOLID ELEMENT IN PLATE PART

5. Solid Mesh Creation This exercise will explain several options for generating solid mesh – hexahedron and tetrahedron elements. It will also explain some of the solid element-specific model checking features in PreSys.

Open a NEW MODEL and IMPORT the training_cad.igs file once again. The model should appear like the image to the left.

Special Note to Users:

To start this exercise, use the PART ON/OFF function to turn on PIDs 7, 8 and 9. Place the data in an ISOMETRIC view. Creating solid elements in PreSys has some similarities with creation of shell meshes in PreSys. Both may use lines and/or surfaces to define a region to be meshed. Creating a solid mesh, however requires the additional step of defining the volume in some manner. While PreSys does not require a volume definition, per se, it does rely on the user to define the volume through multiple lines to establish the volume definition, or an enclosed shell mesh to define a volume.


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Please make PID7 as the CURRENT PART. This should be now displayed as the CURRENT PART in the lower right hand corner of the PreSys window. Enter the Mesher menu. Select the Volume Mesh/8 LINE MESH and the Density option. PreSys will prompt the user to select 4 lines on the BOTTOM and 4 lines on the TOP. Please note that the designation of TOP/BOTTOM is purely arbitrary and has no meaning other than to group the lines together for the meshing operation. Select the 4 lines which make up the bottom (PID9), by selecting the individual lines using the mouse. These lines should be highlighted as the user selects them. PreSys will also label each line (1, 2, 3, 4) so that the user may provide a similar selection order for the top lines. Now select the 4 lines which make up the TOP of the volume to be meshed, using a similar order in the selection of the lines. All 8 lines should be highlighted. PreSys now asks the user to define the mesh pattern; Enter the desired number of elements in the N1, N2, N3 fields of the Task Panel. The N1 value is the number of elements along line 1, N2 is the number of elements along line 2 and N3 is the number of elements between the bottom and top. Enter 20, 10 , 8. This will create 20 elements along line 1, 10 elements along line 2 and 8 elements between the top and bottom. A preview of the mesh will be displayed for the user, in a highlighted manner. Note that the elements do not follow the curved lines which connect the bottom and top sections of the mesh. Therefore, the 8 LINE MESH option is suitable only for top and bottom surface that are connected via straight lines. For our exercise, we will UNDO the meshing operation using the UNDO toolbar icon, and return to the VOLUME MESH menu. Select the 12 LINE MESH option. This will provide a way for us to follow the lines which connect these two surfaces.

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Just as in the 8 LINE MESH, the user selects a BOTTOM and TOP set of lines. In addition, the user now selects 4 lines which connect the BOTTOM and TOP. PreSys prompts the user to select the line which connects the vertex between line 1 and line 4, and continue the selection from that point. Once all the necessary data has been entered, select APPLY to generate the elements. The resulting mesh is displayed in a highlighted manner for the user to review before accepting the mesh.

Solid Element Quality Checking Next we will use some model checking tools to check our mesh, and use the results of this model check to generate the volume mesh using tetrahedron (tetra) elements. Enter the MODEL CHECK menu. Select the CHECK FREE SURFACE command. This command identifies any faces of elements which are not fully connected to adjacent elements (sharing at least one, but less than four nodes). This is useful because it identifies potential voids in the model, created during the meshing process. Once the free surface check has been completed, PreSys will display the free faces of the model. Note that if the model has any voids, crack or missed connections, PreSys will display a face, which may look like a shell element. If there are no voids, PreSys will still calculate a ‘skin’ on the model. At this point, this is still merely a visualization of the free faces. After the free faces are determined, PreSys allows the user to create shell elements from these free faces. This is extremely useful when there are model problems which need to be fixed, since the complexity of the interior of a solid element mesh may result in an extremely difficult problem to visualize. The figure on the right shows that there are no interior faces shown, indicating that the mesh has been created properly.


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Selecting the option Create Shell in Part - New Part, allows the user to generate the free surfaces as shell elements in a new part. The user can also enter a new part name, or accept the default part name that PreSys provides. Select OK to create the shell elements.

As an example of what a Check Free Surface result may look like if there are voids in the model, the following figure is provided.


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6. Automatic Tetrahedron Mesh Generation PreSys includes a function to fill an enclosed volume with a tetrahedron (tetra) mesh. These are 4-noded or 10-noded (mid-side nodes) solid elements. PreSys includes two methods for tetra mesh generation; filling an enclosed set of surfaces, or using an existing surface mesh. In each method, in order for PreSys to perform this function, it requires that the user define an enclosed volume. This means that there are no voids or cracks in the mesh or the surfaces should be make a completely enclosed volume. The user should verify this condition by performing the BOUNDARY check, as described in the preceding sections. Other suggested mesh quality parameters are an element warpage of less than 20 degrees, and an aspect ratio of less than 8-to-1. Meeting these requirements will provide a higher quality tetra mesh, and increase the chance that the automated meshing process will complete successfully. To perform an example tetra mesh, we will use the surface data. Enter the PART menu and select ON/OFF. Turn ON PID11 and TURN OFF all of the other parts. The model should appear like the image on the right. Now enter the Mesher Menu by selecting Preprocess / Mesher or by selecting the Tetra Mesh icon from the Mesher Toolbar. The user will be presented with the option to create 4 Noded Tetras or 10-Noded Tetras. Select 4 Noded Tetras for this example. Select the by Triangular Mesh option. The Triangular mesh option will automatically split quads into triangular elements for this operation, so the user may also select quad elements as the input for this operation. PreSys will automatically create a new part called TETRA000011, which corresponds to PID11) hence TETRA000011). This will also be made the current part, and will include the newly created tetra elements. Note that the tetrahedron elements created follow the node pattern established from the shell elements which are on the skin. Therefore, to create a finer or coarser tetrahedron element mesh, the user must control the element size on the exterior skin.


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7. Drag Mesh Creation of Solid Elements PreSys’s DRAG MESH function extrudes (‘drags’) a 1-D Mesh to create a 2-D Mesh or extrudes a 2-D Mesh into a 3-D Mesh. In other words, the user can use beam elements to drag into a shell mesh, and can use a shell mesh to drag into a hexahedron mesh. We will use this technique to extrude a shell mesh into a hexahedron mesh. First, we will delete any solid elements that we just created in our last example. If you are starting from this example, please just open a new database and import the example file CAD data, as described on Pges 6-7 of this tutorial. Alternatively, the user may select UNDO to restore just the CAD data. To delete the elements, go to the Element drop down menu, and select Delete. The user will open the Delete Task Panel, which provides options by which the user can delete individual or groups of elements. Select the DELETE function and then drag a window around the elements generated by the tetra mesh function. The elements will be highlighted. Select Apply, to complete the selection of elements. PreSys will provide the option to also delete the nodes that are associated with the selected elements. Select this option- PreSys will then delete all of the selected nodes and elements. Enter PART ON/OFF and turn on PID2 and PID7. Make PID7 part current by selecting the CURRENT PART field on the lower right corner of the PreSys window. To start our DRAG MESH operation, we will create a set of shell elements to extrude. Enter the SURFACE MESH, and create a mesh on the top surface, using an element size of 15.0. When the mesh preview is displayed, select YES to accept the mesh. The mesh should look like the following image.

The DRAG MESH function will allow us to generate a hexahedron mesh. The mesh will follow the mesh pattern established on the shell mesh, and will use a line or series of lines to control the extrusion of the mesh. The DRAG MESH menu is shown below. The various drag methods are explained below. The following steps illustrate how to use ONE LINE DRAG mesh, as well as 4 LINE DRAG, as they are the most commonly used. Normal Drag is also a commonly used option in PreSys but


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won’t be discussed, since they are quite easily understood from these examples.

One line drag mesh has a couple requirements prior to performing the Drag Mesh operation. The function assumes that the user has a shell mesh that can be extruded, such as a planar surface. An example of a mesh that could not be extruded would be an enclosed cube or sphere. The Drag Mesh function also needs a line which it uses to define the direction of the extrusion and the number of elements layers which will be created.

For our example, we will create a new line to use for our one line drag operation. Go to Preprocess menu and select the Line/Create option or use the Line Create icon from the Line Toolbar. Select Preprocess/ Line/Point and then Create function, then select the option Node and select node 1 as the start of the line. Then select the option POINT to tell PreSys that you are going to select a line data point rather than a node to create the line. Select point 2, and then select Close to complete the line definition.

The line direction will dictate the direction the drag mesh will follow. In order to determine the line direction, select Show line from the Line/Point menu and then select the newly created line. The line will be highlighted and an arrowhead will displayed at the end of the line.

DRAG MESH OPTIONS: Line Drag: Extrudes 1D elements to 2D and 2D elements to 3D along a selected line(s)

Translational Drag: Extrudes 1D elements to 2D and 2D elements to 3D along either a global Z or local W axis Normal Drag: Extrudes 2D elements to 3D in a normal direction Rotational Drag: Extrudes 1D elements to 2D about either the global Z or local W axis


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The line will display the new points as arrowheads. These points is the location of the solid elements which will be created using the DRAG MESH. EXIT the Line/Point MENU. Select the elements by window or by Displayed and select Apply to complete the selection of elements. Next, select the newly created line and select Apply to generate the Drag Mesh. The number of element layers has a default value of 10. Users should also note the options of deleting the source elements when the solid elements are created, and the option to reverse the Drag Mesh direction.


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Exporting a Model

When the modeling process is completed, the model may be exported. Select FILE from the drop down menu, or by select the EXPORT icon from the TOOLBAR. A FILE selection window will be displayed and the user can select the type of file to be exported and define the file name/location.

After the export file name is entered, the user will be provided with options of what data to export. The user may select to export only the displayed parts of the model, the complete model, or a selected set of parts of the model. The user also has the ability to preserve any include files, or to optionally combine all previously defined include files into a single input file. If the user would prefer, the default values will be printed in the input file, where no other values have been input. Finally, the user has the option to change the unit system of the model, prior to output.

presys tutorial - caesoft

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