Chapter 6 Concept Modeling 6-1
Contents Concept Modeling Creating Line Bodies Modifying i Line Bodies Cross Sections Cross Section Alignment Cross Section Offset Surfaces From Lines Surfaces From Sketches Edge Joints Workshop 6-1, Line and Surface Bodies 6-2
Concept Modeling The features in the Concept menu are used to create and modify line bodies and/or surface bodies which become FE beam or shell models. To begin Concept Modeling, you can either: Create line or surface bodies using the features in the Draw toolbox to design a 2D sketch and/or generate a 3D model Use the Import external geometry file feature Line bodies can be created using the concept modeling tools: Lines from points Lines from sketches Lines from edges Surface bodies can be created using the concept modeling tools: Surfaces from line bodies Surfaces from sketches Surfaces from 3d edges 6-3
Creating Line Bodies Lines From Points: Points can be any 2D sketch points, 3D model vertices or Point Feature (PF) points. A point segment is a straight line connecting two selected points. The feature can produce multiple Line Bodies, depending on the connectivity of the chosen point segments. The Operation field allows Add or Add Frozen choices for line bodies. 6-4
Creating Line Bodies Example of Line From Points using 2d points from a rectangular sketch. 2 points are chosen to define a diagonal line body. The green line indicates proposed line segment. Apply the selection then Generate. The Line body is displayed in blue. Line Body Point 1 Point 2 6-5
Creating Line Bodies Lines From Sketches: Line bodies created based on sketches and planes from faces Multiple Line Bodies may be created depending on the connectivity of the edges within the base objects Select sketches or planes in the feature tree then Apply in the detail window Multiple sketches, planes, and combinations of sketches and planes can be used as the base object for the creation of line bodies 6-6
Creating Line Bodies Example of Lines From Sketches. Sketch created as input for Line Body creation. Lines From Sketches is chosen: Highlight sketch in tree Apply as base object in Detail window 6-7
Creating Line Bodies Lines From Edges: Creates line bodies based on existing 2D and 3D model edges Can produce multiple line bodies depending on the connectivity of the selected edges and faces Can select edges and/or faces through two fields in the detail window then Apply 6-8
Creating Line Bodies Example of Lines From Edges. 3D solid created as input for Line Body creation. Lines From Edges is chosen: Select faces on model. Face boundaries will become line bodies (alternately select 3d edges directly). Apply as base object in Detail window Note: in this case 2 line bodies are created due to the edge connectivity. 6-9
Modifying Line Bodies Split Line Body: Splits line body edges into two pieces Split location is controlled by the Fraction property (e.g. 0.5 = split in half). Example: Selected line Fraction = 0.5 Fraction = 0.25 6-10
Cross Sections Cross Sections: Cross sections are attributes assigned to line bodies to define beam properties in the FE simulation In DM, cross sections are represented by sketches and are controlled by a set of dimensions Note: DesignModeler uses a different coordinate system for cross sections than the one used in the ANSYS environment (described later) 6-11
Cross Sections Cross sections are selected from the Concept menu A cross section branch is inserted in the tree where each chosen cross section is listed Concept menu Display Tree Cross Section menu 6-12
Cross Sections Highlight the cross section in the Tree to modify dimensions in the Details window Desig gnmodeler 6-13
Cross Sections Dimension Editing Cross section dimensions can be repositioned via a RMB and choosing Move Dimensions 6-14
Cross Sections Assigning a cross section to a line body: Highlight the line body in the Tree A cross section property appears in the detail window Click in this field and choose the desired cross section from the drop down list 6-15
Cross Sections A user integrated section can be defined in DM The cross section is not sketched, rather the cross section s properties are placed in the details window A = Area of section. Ixx = Moment of inertia about the x axis. Ixy = Product of inertia. Iyy = Moment of inertia about the y axis. Iw =Warping constant. J = Torsional constant. CGx = X coordinate of centroid. CGy = Y coordinate of centroid. SHx = X coordinate of shear center. SHy = Y coordinate of shear center. 6-16
Cross Section Alignment As shown below in DesignModeler the cross section lies in the XY plane: Cross section alignment is defined by: A local or cross section +Y direction Default alignment is with the global +Y direction unless that would result in an invalid alignment in which case +Z is used Note: In the ANSYS S Classic Environment, the cross section lies in the YZ plane and uses the X direction as the edge tangent. This difference in orientation has no bearing on the analysis. Y Cross Section Edge Tangent 6-17
Cross Section Alignment A color code is used to indicate cross section status for line bodies: Violet: no cross section assigned Black: cross section assigned with valid alignment Red: cross section assigned with invalid alignment The line body icons in the tree have similar visual aids: Green: cross section assigned with valid cross section alignment Yellow: no cross section assigned or default alignment Red: invalid cross section alignment 6-18
Cross Section Alignment Checking alignment can be done graphically using the View menu: Choose Show Cross Section Alignments Green arrow = +Y, blue arrow = edge tangent of cross section Or choose Cross Section Solids +Y Edge Tangent 6-19
Cross Section Alignment Because a default alignment is chosen cross section orientation will almost always need to be modified. There are 2 methods for cross section alignment, selection and vector: The selection method uses existing geometry (edges, points, etc.) as alignment reference The vector method uses input according to X, Y, Z coordinate directions For either method a rotation angle can be input and/or the orientation reversed Selection Method Vector Method 6-20
Cross Section Alignment Modifying the cross section orientation by vector: Switch to Vector alignment mode Enter the desired coordinate values Enter rotation ti angle if desired Reverse orientation if desired 6-21
Cross Section Alignment Modifying the cross section orientation by selection (several examples follow): 1. Select the line body to be aligned in graphics window 3. Select the geometry to be used for alignment 2. With Selection method active click in the alignment field 6-22
Cross Section Alignment Alignment using lines or axes. Line chosen for alignment Y Axis chosen for alignment Y Edge Tangent 6-23
Cross Section Alignment Alignment using face normal. Y Desig gnmodeler Alignment Faces Y 6-24
Cross Section Alignment Alignment using sketch points. Note: the order of point selection determines cross section alignment. 1 2D points 2 Selected Line Body Y Edge Tangent 6-25
Cross Section Offset Cross Section Offset: After assigning a cross section to a line body, the Detail property allows users to specify the type of offset to use with the cross section: Centroid: The cross section is centered on the line body according to its centroid (default) Shear Center: The cross section is centered on the line body according to its shear center Note the graphical display for centroid and shear center appear the same however, when analyzed, the shear center is used Origin: The cross section is not offset and is taken exactly as it appears in its sketch Examples next page 6-26
Cross Section Offset Origin offset (no offset) DesignModele er Line Body Line Body with cross section displayed Centroid/Shear Center offset 6-27
Surfaces From Lines Surfaces From Lines: Creates surface body using line body edges as the boundary Line body edges must form non-intersecting closed loops Each closed loop creates a frozen Surface Body The loops should form a shape such that a simple surface can be inserted into the model: Planes, cylinders, tori, cones, spheres and simple twisted surfaces Planar surface Twisted surface Details window: Flip surface normals Input thickness which will be transferred to the FE model 6-28
Surfaces From Lines Notes on surface from lines: A line body with no cross section can be used to tie together surface models. In this case the line body acts merely as a mechanism to insure a continuous mesh at the surface boundaries. 2S Surface Bodies Line Body (no cross section) Result is continuous FE mesh at surface interface 6-29
Surfaces From Sketches Surfaces From Sketches: Creates surface bodies using sketches as boundaries (single or multiple sketches are OK) Base sketches must be closed profiles which are not self intersecting May choose to Add or Add Frozen operations Can reverse normal direction No in Orient With Plane Normal field Can enter thickness which will be used in creating the FE model 6-30
Surfaces From Sketches 2 ways to identify sketch for operation Click in the Base Objects field Select the desired sketch from the tree then Apply Select a portion of the desired sketch in the graphics window then Apply 6-31
Surfaces From Edges Surfaces from Edges: Creates surfaces from existing body edges Can be solid or line body edges. Edges must produce non-intersecting closed loops. Example: Existing solid body edges are New, frozen, surface body generated selected for new surface boundary. (note, solid body is hidden). 6-32
Surfaces Patch Surface patching attempts to fill gaps in the model. Uses similar healing methods as face delete (natural and patch). Complex gaps may result in multiple surfaces being created to fill them. Example: 2 holes selected for patching Two patches created using multiple surfaces 6-33
Edge Joints Edge Joints are the glue that holds together bodies where a continuous mesh is desired. Creating surface and/or line multibody parts with coincident edges results in automatic creation of edge joints. Joints can be created manually where no coincident topology exists. 6-34
Edge Joints Edge Joints can be viewed by turning on the Edge Joints option in the View menu: Edge joints are displayed in either blue or red. Blue: edge joint is contained in properly defined multi-body part Red: edge joint not grouped into the same part No Edge Joint With Edge Joint 6-35
Line and Surface Bodies Workshop 6-1 6-36
Workshop 6-1, Line and Surface Bodies Goals: Create a sketch representing beams used to stiffen a panel. Create a line body from the sketch. Choose a beam cross section to be used and assign it to the line body. Create a surface model representing the panel. >File>New, or Start Page: Choose to create new geometry At the prompt, set the length unit to millimeter 6-37
Workshop 6-1, Line and Surface Bodies Create a rectangle [Sketch] > Rectangle 1. Place the cursor near the origin until P appears, click then drag to define the rectangle Click >Look At & >Zoom to Fit tool buttons, and Triad ISO Ball as desired. 1 6-38
Workshop 6-1, Line and Surface Bodies Dimension the rectangle 600X300 mm as shown [Sketch] > Dimension > General Horizontal = 600 mm Vertical = 300 mm Fit the sketch and move dimensions as necessary [Sketch] > Dimension > Move 6-39
Workshop 6-1, Line and Surface Bodies Add 2 vertical lines and dimension as shown [Sketch] > Draw > Line 2. Place the cursor near the top line until the C coincidence constraint appears. Move the cursor to the bottom line until the C appears and a V i indicating a vertical constraint. 3. Repeat for second line 2 3 Apply horizontal dimensions i as shown. [Sketch] > Dimension > Horizontal Adjust Details so all dimensions are as indicated 6-40
Workshop 6-1, Line and Surface Bodies Create a Line Body from Sketch1 [Main Menu] > Concept > Lines From Sketches 4. Select Sketch1 from the Tree (click the + near the XYPlane to expand that branch if necessary) and >Details>Apply it as the base object 5. Click >Generate 5 4 6-41
Workshop 6-1, Line and Surface Bodies Select a rectangular tube type cross section: [Main Menu] > Concept > Cross Section > Rectangular Tube After selection, the cross section is displayed with its dimensions. In this case we will use the default dimensions. If desired the cross section Details can be changed to modify the cross section. 6-42
Workshop 6-1, Line and Surface Bodies With a cross section selected we now need to associate it with our line body. 6. Highlight the line body in the tree and the details shows that no cross section is yet associated with it. [tree] > 1 Part, 1 Body > Line Body (at bottom of tree) 7. Click in the Cross Section field 6 8. Choose RecTube1 from the drop down list 7 8 6-43
Workshop 6-1, Line and Surface Bodies 9. After assigning the cross section to the line body the default display shows the line body with its cross section alignment (see right). We can also display the beam with the cross section displayed as a solid. [Main Menu] > View >Sh Show Cross Sections Solids 6-44
Workshop 6-1, Line and Surface Bodies The next step is to create the surfaces between the beams. These surfaces will be shell meshed in the FE simulation. 10. [Main Menu] > Concept > Surfaces From Lines Hold the control key and select the 4 lines shown at right. (or can hold down LMB and sweep mouse over lines to be group selected) 11. >Apply 10 11 6-45
Workshop 6-1, Line and Surface Bodies 12. >Generate the Surface Body. Note: a frozen surface body is created, bounded by the selected lines Repeat the previous steps to create two more surface bodies 12 >Generate as necessary 6-46
Workshop 6-1, Line and Surface Bodies The final modeling operation is to place all the bodies into a single part (multi-body yp part). We must do this to insure that, when meshed, each boundary recognizes its neighbor resulting in a continuous mesh. Set the Selection Filter to Bodies. In the graphics window right mouse click and choose >Select All 6-47
Workshop 6-1, Line and Surface Bodies With all bodies selected, again right click in the graphics window and choose Form New Part. By examining the Tree notice a single part has been formed which contains 4 bodies. 6-48
Workshop 6-1, Line and Surface Bodies Shown here we have moved to a Simulation environment in Workbench and meshed the geometry. By grouping all bodies into a common (single) part, nodal connectivity it is insured. 6-49