solid modeling module 9. training manual january 30, 2001 inventory #001441 9-2 solid modeling...
TRANSCRIPT
Solid Modeling
Module 9
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Solid Modeling
Overview
• Importing geometry is convenient, but sometimes you may need to create it in ANSYS. Some possible reasons:
– You may need to build a parametric model — one defined in terms of variables for later use in design optimization or sensitivity studies.
– The geometry may not be available in a format ANSYS can read.
– The Connection product you need may not be available on your computer platform.
– You may need to modify or add geometry to an imported part or assembly.
• ANSYS has an extensive set of geometry creation tools, which we will discuss in this chapter.
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Solid Modeling
...Overview
• Topics covered:
A. Definitions
B. Top-Down Modeling
• Primitives
• Working Plane
• Boolean Operations
C. Workshop
D. Bottom-Up Modeling
• Keypoints
• Coordinate Systems
• Lines, Areas, Volumes
• Operations
E. Workshop
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Solid Modeling
A. Definitions
• Solid Modeling can be defined as the process of creating solid models.
• Let’s review some earlier definitions:
– A solid model is defined by volumes, areas, lines, and keypoints.
– Volumes are bounded by areas, areas by lines, and lines by keypoints.
– Hierarchy of entities from low to high: keypoints lines areas volumes. You cannot delete an entity if a higher-order entity is attached to it.
• Also, a model with just areas and below, such as a shell or 2-D plane model, is still considered a solid model in ANSYS terminology.
Volumes
Areas
Lines &Keypoints
Keypoints
Lines
Areas
Volumes
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Solid Modeling
...Definitions
• There are two approaches to creating a solid model:
– Top-down
– Bottom-up
• Top-down modeling starts with a definition of volumes (or areas), which are then combined in some fashion to create the final shape.
add
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Solid Modeling
...Definitions
• Bottom-up modeling starts with keypoints, from which you “build up” lines, areas, etc.
• You may choose whichever approach best suits the shape of the model, and also freely combine both methods.
• We will now discuss each modeling approach in detail.
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Solid Modeling
B. Top-Down Modeling
• Top-down modeling starts with a definition of volumes (or areas), which are then combined in some fashion to create the final shape.
– The volumes or areas that you initially define are called primitives.
– Primitives are located and oriented with the help of the working plane.
– The combinations used to produce the final shape are called Boolean operations.
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Solid Modeling - Top-Down Modeling
Primitives
• Primitives are predefined geometric shapes such as circles, polygons, and spheres.
• 2-D primitives include rectangles, circles, triangles, and other polygons.
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Solid Modeling - Top-Down Modeling
...Primitives
• 3-D primitives include blocks, cylinders, prisms, spheres, and cones.
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Solid Modeling - Top-Down Modeling
...Primitives
• When you create a 2-D primitive, ANSYS defines an area, along with its underlying lines and keypoints.
• When you create a 3-D primitive, ANSYS defines a volume, along with its underlying areas, lines and keypoints.
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Solid Modeling - Top-Down Modeling
...Primitives
• You can create primitives by specifying their dimensions or by picking locations in the graphics window.
– For example, to create a solid circle:
• Preprocessor > -Modeling- Create > -Areas- Circle >
Instructions
Picker Pick the center and radiusin graphics window...
By picking
...Or enter values here
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...Primitives
– To create a block:
• Preprocessor > -Modeling- Create > -Volumes- Block >
Instructions
Picker
Pick the desired locationsin graphics window...
By picking
...Or enter values here
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Working Plane
• The “WP” in the prompts and in the picker stands for Working Plane — a movable, 2-D reference plane used to locate and orient primitives.
– By default, the WP origin coincides with the global origin, but you can move it and/or rotate it to any desired position.
– By displaying a grid, you can use the WP as a “drawing tablet.”
– WP is infinite despite the grid settings.
WX
WY
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X1Y2
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WP (X,Y)
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...Working Plane
• All working plane controls are in Utility Menu > WorkPlane.
• The WP Settings menu controls the following:
– WP display - triad only (default), grid only, or both.
– Snap - allows you to pick locations on the WP easily by “snapping” the cursor to the nearest grid point.
– Grid spacing - the distance between grid lines.
– Grid size - how much of the (infinite) working plane is displayed.
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...Working Plane
• You can move the working plane to any desired position using the Offset and Align menus.
– Offset WP by Increments…
• Use the push buttons (with increment set by slider).
• Or type in the desired increments.
• Or use dynamic mode (similar to pan-zoom-rotate).
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...Working Plane
– Offset WP to >
This simply “translates” the WP, maintaining its current orientation, to the desired destination, which can be:
• Existing keypoint(s). Picking multiple keypoints moves WP to their average location.
• Existing node(s).
• Coordinate location(s).
• Global origin.
• Origin of the active coordinate system (discussed later).
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...Working Plane
– Align WP with >
This reorients the WP.
• For example, Align WP with Keypoints prompts you to pick 3 keypoints - one at the origin, one to define the X-axis, and one to define the X-Y plane.
• To return the WP to its default position (at global origin, on global X-Y plane), click on Align WP with > Global Cartesian.
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...Working Plane
• Demo:
– Clear the database
– Display WP and create a few keypoints by picking. Note the coordinates displayed in the picker.
– Turn on the grid, change spacing, and activate snap.
– Create more keypoints. Note how the cursor snaps to grid points.
– Define 2 rectangles — one by picking corners and one by dimensions.
– Now offset WP to average of a few keypoints, then rotate in-plane by 30º.
– Define 2 more rectangles by picking and by dimensions. Note the change in rectangle orientation.
– Align WP with global origin, then define some 3-D primitives. Use picking as well as “By dimensions.”
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Boolean Operations
• Boolean operations are computations involving combinations of geometric entities. ANSYS Boolean operations include add, subtract, intersect, divide, glue, and overlap.
• The “input” to Boolean operations can be any geometric entity, ranging from simple primitives to complicated volumes imported from a CAD system.
add
Input entities Boolean operation Output entity(ies)
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...Boolean Operations
• All Boolean operations are available in the GUI under Preprocessor > -Modeling- Operate.
• By default, input entities of a Boolean operation are deleted after the operation.
• Deleted entity numbers become “free” (i.e., they will be assigned to a new entity created, starting with the lowest available number).
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...Boolean Operations
• Add
– Combines two or more entities into one.
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...Boolean Operations
• Glue
– Attaches two or more entities by creating a common boundary between them.
– Useful when you want to maintain the distinction between entities (such as for different materials).
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...Boolean Operations
• Overlap
– Same as glue, except that the input entities overlap each other.
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...Boolean Operations
• Subtract
– Removes the overlapping portion of one or more entities from a set of “base” entities.
– Useful for creating holes or trimming off portions of an entity.
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...Boolean Operations
• Divide
– Cuts an entity into two or more pieces that are still connected to each other by common boundaries.
– The “cutting tool” may be the working plane, an area, a line, or even a volume.
– Useful for “slicing and dicing” a complicated volume into simpler volumes for brick meshing.
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...Boolean Operations
• Intersect
– Keeps only the overlapping portion of two or more entities.
– If there are more than two input entities, you have two choices: common intersection and pairwise intersection
• Common intersection finds the common overlapping region among all input entities.
• Pairwise intersection finds the overlapping region for each pair of entities and may produce more than one output entity.
CommonIntersection
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...Boolean Operations
• Partition
– Cuts two or more intersecting entities into multiple pieces that are still connected to each other by common boundaries.
– Useful, for example, to find the intersection point of two lines and still retain all four line segments, as shown below. (An intersection operation would return the common keypoint and delete both lines.)
L1
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L3
L6
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...Boolean Operations
• Demo:
– “Drill” a hole by subtracting a circle from a rectangle (or a cylinder from a block)
– Create two overlapping entities, save db, and do the overlap operation. Now resume db and add the entities. Note the difference between the two operations. (Glue is similar to overlap.)
– Interesting model:
• block,-2,2, 0,2, -2,2
• sphere,2.5,2.7
• vinv,all ! intersection
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C. Workshop
• Refer to your Workshop Supplement for instructions on:
W6. Pillow Block
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D. Bottom-Up Modeling
• Bottom-up modeling begins with a definition of keypoints, from which other entities are “built up.”
• To build an L-shaped object, for example, you could start by defining the corner keypoints as shown below. You can then create the area by simply “connecting the dots” or by first defining lines and then defining the area by lines.
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Keypoints
• To define keypoints:
– Preprocessor > -Modeling- Create > Keypoints
– Or use the K family of commands: K, KFILL, KNODE, etc.
• The only data needed to create a keypoint is the keypoint number and the coordinate location.
– Keypoint number defaults to the next available number.
– The coordinate location may be provided by simply picking locations on the working plane or by entering the X,Y,Z values.
How are the X,Y,Z values interpreted? It depends on the active coordinate system.
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Coordinate Systems
Active Coordinate System
• Defaults to global Cartesian.
• Use CSYS command (or Utility Menu > WorkPlane > Change Active CS to) to change it to
– global Cartesian [csys,0]
– global cylindrical [csys,1]
– global spherical [csys,2]
– working plane [csys,4]
– or a user-defined local coordinate system [csys, n]
Each of these systems is explained next.
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...Coordinate Systems
Global Coordinate System
• The global reference system for the model.
• May be Cartesian (system 0), cylindrical (1), or spherical (2).
– For example, location (0,10,0) in global Cartesian is the same as (10,90,0) in global Cylindrical.
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...Coordinate Systems
Local Coordinate System
• A user-defined system at a desired location, with ID number 11 or greater. The location may be:
– At WP origin [CSWP]
– At specified coordinates [LOCAL]
– At existing keypoints [CSKP] or nodes [CS]
• May be Cartesian, cylindrical, or spherical.
• May be rotated about X, Y, Z axes.
X
Y
X11
Y11
X12
Y12
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...Coordinate Systems
Working Plane Coordinate System
• Attached to the working plane.
• Used mainly to locate and orient solid model primitives.
• You can also use the working plane to define keypoints by picking.
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...Coordinate Systems
• You can define any number of coordinate systems, but only one may be active at any given time.
• Several geometry items are affected by the coordinate system [CSYS] that is active at the time they are defined:
– Keypoint and node locations
– Line curvature
– Area curvature
– Generation and “filling” of keypoints and nodes
– Etc.
• The graphics window title shows the active system.
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Lines
• There are many ways to create lines, as shown here.
• If you define areas or volumes, ANSYS will automatically generate any undefined lines, with the curvature determined by the active CS.
• Keypoints must be available in order to create lines.
Create >
-Lines- Arcs
Create >
-Lines- Lines
Create >
-Lines- Splines
Operate >
Extrude / Sweep
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Areas
• Creating areas using bottom-up method requires keypoints or lines to be already defined.
• If you define volumes, ANSYS will automatically generate any undefined areas and lines, with the curvature determined by the active CS.
Create >
-Areas- Arbitrary
Operate > Extrude
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Volumes
• Creating volumes using bottom-up method requires keypoints or lines or areas to be already defined.
Create >
-Volumes- Arbitrary
Operate > Extrude
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Bottom-Up Modeling
• Demo:
– Clear the database
– Create 5 keypoints at (1,2), (3,2), (4,0), (1,1.5), (2.5,0)
– Switch to CSYS,1 and create a line “in active CS” between KP4 & KP5
– Switch back to CSYS,0 and create an area “through KP’s.” Notice that the remaining lines were automatically generated lines, all of them straight.
– Define two circles:
• 0.3R, centered at (2.25,1.5)
• 0.35R, centered at (3.0,0.6)
– Subtract the two circles from base area. (We have used a combination of bottom-up and top-down modeling.)
– Save as r.db
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Operations
• Boolean operations are available for entities created by both top-down and bottom-up modeling approaches.
• Besides Booleans, many other operations are available:
– Extrude
– Scale
– Move
– Copy
– Reflect
– Merge
– Fillet
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...Operations
Extrude
• To quickly create volumes from existing areas (or areas from lines, and lines from keypoints).
• If the area is meshed, you can extrude the elements along with the areas.
• Four ways to extrude areas:
– Along normal — creates volume by normal offset of areas [VOFFST] .
– By XYZ offset — creates volume by a general x-y-z offset [VEXT]. Allows tapered extrusion.
– About axis — creates volume by revolving areas about an axis (specified by two keypoints) [VROTAT].
– Along lines — creates volume by “dragging” areas along a line or a set of contiguous lines [VDRAG].
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...Operations
Scale
• Useful for conversion from one units system to another.
• Discussed in Chapter 4.
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...Operations
Move
• To translate or rotate an entity by specifying DX,DY,DZ offsets.
– DX,DY,DZ are interpreted in the active CS.
– To translate an entity, make the active CS Cartesian.
– To rotate an entity, make the active CS cylindrical or spherical.
– Or use the commands
• VGEN, AGEN, LGEN, KGEN
• Another option is to transfer coordinates to a different system.
– Transfer occurs from the active CS to a specified CS.
– This operation is useful when you need to move and rotate an entity at the same time.
– Or use the commands
• VTRAN, ATRAN, LTRAN, KTRAN
Transfer from csys,0 to csys,11
Rotate -30°
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Copy
• To generate multiple copies of an entity.
• Specify the number of copies (2 or greater) and the DX,DY,DZ offset for each copy. DX,DY,DZ are interpreted in the active CS.
• Useful to create multiple holes, ribs, protrusions, etc.
Copy inlocalcylindricalCS
Create outerareas byskinning
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...Operations
Reflect
• To reflect entities about a plane.
• Specify the direction of reflection:
– X for reflection about the YZ plane
– Y for XZ plane
– Z for XY plane
All directions are interpreted in the active CS, which must be a Cartesian system.
What is the direction of reflection in this case?
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Merge
• To attach two entities together by removing coincident keypoints.
– Merging keypoints will automatically merge coincident higher-order entities, if any.
• Usually required after a reflect, copy, or other operation that causes coincident entities.
Merge or gluerequired
Reflect
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Solid Modeling - Bottom-Up Modeling
...Operations
Fillet
• Line fillet requires two intersecting lines with a common keypoint at the intersection.
– If the common keypoint does not exist, do a partition operation first.
– ANSYS does not update the underlying area (if any), so you need to either add or subtract the fillet region.
• Area filleting is similar.Createfillet
Createarea
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...Operations
• Demo:
– Resume r.db (if necessary)
– Create two keypoints for the axis, at (0,0) and (0,1), then extrude the area by revolving about the axis 60º
– Resume r.db
– Make copies of the rib radially about the Y-axis:
• Create a local cylindrical CS at global origin, with THYZ = -90
• Generate 7 total copies (6 new ones) with DY=15
– Create the three outer “skin” areas using ASKIN,P
– Resume r.db
– Create a 0.5R fillet between the top and right lines. (Notice that the lines attached to the area have been modified. This is allowed in some cases.)
– Create the triangular fillet area by lines (AL,P), then subtract it from the main area.
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E. Workshop
• Refer to your Workshop Supplement for instructions on:
W7. Connecting Rod