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HEXAHEDRAL-MESHING PREPROCESSOR 3DSHOP 1 - 1

1 HEXAHEDRAL-MESHING PREPROCESSOR 3DSHOP

1.1 Introduction

3DShop is an optional program that can be used with the basic version of FLAC3D. A license for3DShop can be purchased at an additional cost. Contact Itasca for pricing information.

3DShop is a hexahedral-meshing preprocessor that enables the creation of complex meshes forFLAC3D. 3DShop can substantially reduce model creation time by uncoupling the model buildingfrom the meshing process; the model is built via a menu-driven graphical interface, and then meshedusing a fully automatic all-hexahedral mesh generator. 3DShop can be used to assist FLAC3D modelgeneration for a wide range of geotechnical problems, including intersecting tunnels and shafts,complex excavation shapes, and irregular geologic stratigraphies and structures. For example, anexisting three-dimensional geometry can be read into 3DShop from existing CAD models, or acomplex model grid can be created from scratch. Meshes produced by 3DShop are exported in a

format that can be read directly into FLAC3D.

3DShop has two components: the 3DShop solid modeler*, and the KUBRIXmesh generator**. The3DShop modeler component is used first to create the surface geometry representing the problemdomain surfaces. KUBRIX is then used to generate hexahedral zoning automatically, to fit withinthis geometry. Figure 1.1 shows an example after the 3DShop solid-model stage and the KUBRIXmesh stage.

* The 3DShop solid modeler is based on 3DShop ModelDesign, which is a copyrighted product ofC4W, S.A.

** The KUBRIX mesh generator is a copyrighted product of Simulation Works, Inc. KUBRIX is aregistered trademark of Simulation Works, Inc.

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1 - 2 Hexahedral-Meshing Preprocessor 3DShop

Figure 1.1 3DShop solid model (upper figure) and KUBRIX hexahedralmesh (lower figure) for intersecting circular and horseshoe tun-nels

The 3DShop solid modeler is capable of handling non-manifold surfaces (i.e., closed surfacescontaining internal surfaces). Non-manifoldsurfaces are common in geotechnicalapplications (e.g.,sequential excavations in tunnel construction). The KUBRIXcomponent features the capability ofdefining coinciding nodes at material boundaries, which facilitates the creation of interfaces inFLAC3D.

This chapter is a users guide for operating 3DShop. The installation and licensing instructions for

the program are given in Section 1.2. The recommended procedure to use 3DShop to build a modelfor FLAC3D is outlined in Section 1.3. Section 1.4 provides instructions to get you started using3DShop. General information and tips on applying 3DShop are given in Section 1.5, and simpleexample applications of3DShop are provided in Section 1.6 as a guide to users.

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1.2 Installation and Licensing of3DShop

1.2.1 Installation

3DShop is installed in Windows from the Itasca CD-ROM using standard Windows procedures.Insert the Itasca CD in the appropriate drive. If the autorun feature for the CD drive is enabled, amenu providing options for using the CD will appear automatically. If this menu does not appear,type [cd drive]:\start.exe at the command line ( START > RUN in Windows) to access theCD-ROM menu. The option to install 3DShop may be selected from this menu.

To install 3DShop, follow the installation procedure for FLAC3D. Select the 3DShop box in theSelect Components dialog to install 3DShop on your computer. Note that 3DShop can be installedseparately from FLAC3D if you wish to run FLAC3D and 3DShop on different computers.

When 3DShop is installed, the electronic version of this chapter will be made available via the3DSHOP Manual

shortcut in theItasca

group on the Start menu. All electronic volumes of the FLAC3D

manual (including the 3DShop manual) are PDF files that require the Adobe Acrobat Reader inorder to be viewed. The software is freely available from Adobe Systems Incorporated(http://www.adobe.com).

The 3DShop package can be uninstalled via the Add/Remove Programs icon in the Windows ControlPanel.

1.2.2 Licensing

To purchase this option, or to request a trial license, please contact your local Itasca office or agent.

CAUTION: The 3DShop option is notactivated through the FLAC3D hardware key; it is node-lockedto a specific computer. It is important to note that once 3DShop has been installed on a specificcomputer, it can only be operated from that computer.

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1.3 FLAC3D Model Creation with 3DShop

To build a model for FLAC3D using 3DShop, the following procedure is recommended:

1. Reading an Existing Geometry If an STL, DXF or VRML description of the geometryis available, read it into 3DShop. We recommend reading data in the STL or VRMLformats, as there are many types of DXF that are not compatible with 3DShop.

Often, an imported geometry contains extraneous entities that are irrelevant to meshgeneration. Remove extraneous data and, in order to ensure precision, make sure thatyour model is as centered as possible around the (0, 0, 0) coordinate.

An imported STL, DXF or VRML file is not a geometrical entity. You cannot cut or trimthese entities, nor use them in any Boolean operation. It is a triangular mesh entity, thevertices of which can be used in creating new geometrical entities.

2. Simplifying the Geometry An imported geometry may be very complex, andnot closed.

Using it directly may result is a very large mesh. It is recommended that you recreate anew and simplified geometry in which details unimportant to mesh generation have beenremoved. Create a simplified geometry from scratch, or using the points of the importedgeometry as a reference.

3. Creating a Model There are two approaches to solid modeling: surface-based andsolid-based.

In the surface-basedapproach, you create points, or use existing points, to create Edgesthat can be line segments, circular arcs or other smooth curves such as Bzier or B-splinecurves. You can extrude an Edge along another Edge to create a Face. A collection ofEdges is called a Wire. A collection of Faces that are sewn together is called a Shell.

You can extrude a Wire along another Wire to create a Shell. A Shell can be open orclosed. You can create a closed Shell by sewing several open Shells together.

In the solid-basedapproach, you use ready-made closed Shells called Primitives. Prim-itives can be parallelepipeds, cylinders, spheres, cone sections, etc. You can use Booleanoperations to subtract, add or intersect Primitives and closed Shells, in order to create amore complex closed Shell. Because of some limitations in the solid modeling libraryused in 3DShop, we do not recommend extensive use of Boolean operations, especiallywhen two Faces in two different Solids are tangent.

4. Final Checks of the Model Once a model is complete, it should be dissociated intofaces and checked with the Clean function to remove all double Faces. Furthermore, the

model itself should contain no free edges; in other words, it should be watertight. Youcan check for free edges using the Free boundaries function in the Analysis menuitem.

5. Model Discretization The faces of a solid model should be discretized into trianglesprior to automatic meshing. You can specify several parameters that control how closelytriangles approximate the geometry. Use the Discretize function to create a discretized

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surface. The discretized surface must be saved as an STL file prior to hexahedral meshgeneration.

6. Mesh Generation To generate an all-hexahedral mesh, you should read a closed

STL file, and select the automatic hexahedral mesh generation function. A number ofparameters can be set in this function to control the density and size distribution of theresulting mesh. The mesh is automatically saved as a .flac3d and a .wrl file. A.flac3d file can be directly read into FLAC3D by using the IMPGRID command. A .wrlfile can be read into 3DShop to visually examine the resulting mesh.

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1.4 Getting Started

The default installation procedure creates a C4W group with a 3DSHOP shortcut that can be used to startthe code. To start 3DShop, click on the 3DSHOP button. The 3DShop window opens.*

The 3DShop graphical user interface is composed of two panels. On the left is the Objects Explorerpanel, which is similar to the Windows Explorer.** On the right is the Graphic Window, in whichgeometrical entities listed in the Objects Explorer are displayed. Maximize the Graphic Windowby clicking on the Maximize icon at the top-right corner of the newly created window. The 3DShopwindow is shown in Figure 1.2.

Figure 1.2 The 3DShop window

In order to open a new document to start a new model in 3DShop, select the File/New menu item. Ablank document opens. Your current model appears as a folder Document in the Objects Explorerpanel with the name of the model in brackets. Clicking on the + sign to the left of each entry in

* If at start-up a dialog box inquiring about licenses of certain components of3DShop appears, clickon the button marked Cancel . If the dialog box inquires about a license for 3DShop itself, yourlicense is no longer valid. Copy and paste the character string appearing in the dialog box into anemail message and send this message to Itasca to renew the license see Section 1.2.2.

** If the Objects Explorerwindow is not displayed on start-up, select Display/Objects Explorer toopen the panel.

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the Objects Explorer opens its contents. You can see an entity entitled Document [Document 1].Clicking on the + sign to the left of Document opens a tree structure containing two entries: 2DWorldand 3D World.

To open the toolbars that are most used in 3DShop, right-click in the toolbar area at the top ofthe 3DShop window below the menu bar. Alternatively, you can select Display/Toolbars. TheToolbars dialog box opens, as shown in Figure 1.3. Click the Views, Construction, Objects, and3dprim entries, and click on the Close button to open these toolbars. The descriptions of these menuitems are given in Section 1.5.1.

Figure 1.3 3DShop toolbars

It is important to be familiar with the following features before creating models in 3DShop.

1.4.1 Online Help and Icons

Online help is available to access the operation instructions of3DShop through the Help menu item.In addition, by moving the cursor over any icon, its function is shown in a bubble.

1.4.2 Importing External Geometries and File Formats

You can Open or Insert VRML (Virtual Reality Markup Language), STL (StereoLythigraphy),and DXF (Data Exchange Format) files in 3DShop.

VRML files are in ASCII, and are mainly used to show solid models on the World Wide Web.Multiple mesh entities can exist in a VRML file, and entities can each have their own color andtransparency.

STL files are used in mechanical engineering and Computer-Aided Design (CAD) as a Rapid Proto-typing file format, and have emerged as a de facto, albeit awkward, standard for the representation oftriangulated surfaces. Some CAD systems refuse to produce STL files of non-manifold geometries(solids containing internal surfaces), but most allow it. An STL file can contain only one meshentity.

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DXF files are ASCII files used by AutoCad. There are several types of DXF, and not all of themare readable by 3DShop. However, the most common types are readable. A DXF file can containmultiple Mesh entities. After reading a DXF file, the entities appear in the Objects Explorer as

Mesh of Triangles. This entity is not immediately recognized as a mesh entity. To transform it into

a mesh entity, select it, and select Construction/Sew to turn it into a GL Triangle, which is theinternal representation of surface meshes in 3DShop.

1.4.3 Selecting Entities

To perform an operation on an object, it must first be selected. You can select an entity by left-clicking on it in either the Objects Explorer or the Graphic Window. When an entity is selected,its color changes to orange. Right-clicking on an entity lets you query properties and change thedisplay mode or color and transparency of the entity.

Use followed by to copy and paste entities, either in the same document orbetween several components, either in the Objects Exploreror the Graphic Window.

As in many Windows applications, in the Objects Explorer, you can select a range of componentsby holding down the key. Using the key instead of enables you toselect multiple noncontiguous components. lets you select all entities in your model.

A useful selection tool is Edit/Reverse the Selection, which allows you to select the oppositeof the selected item.

1.4.4 Keeping Track of Model Development

Every operation is recorded, and can be undone and redone with the Edit/Undo and Redo menu

items. You can also use to undo an operation, and to redo one. Youcan undo as many steps as you want, as long as the undo stack is long enough. You can set thelength of the undo stack in File/Preferences. You can also use several Undos to go to a paststate, copy something, Redo everything back to the present state, and paste those entities in yourdocument. Please note that hiding, displaying, changing view angles, etc., are not operations, andtherefore cannot be undone. If you want the redo/undo stack to be saved in your .opn files, checkFile/Preferences, put a check mark next to Save Redo/Undo stack , and set the number of lines to 1000or more.

1.4.5 Viewing and Changing Displays

Use the arrow keys to pan any view, and use your mouse wheel to zoom in at any time, even in themidst of using any of the geometry construction tools. If you have a numerical keypad, or afteractivating on your keyboard, you can rotate the view by increments of 5 degrees inall directions with the numerical keypad arrows.

In the Graphic Window, the X, Y and Z directions are shown with a small coordinate system symbolcolored in Red, Green and Blue representing X, Y and Z (RGB = XYZ).

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If you want to see through surfaces, and select objects behind surfaces, you can right-click on thesurfaces, select Display mode, check Curves , and uncheck everything else. You can also check

Wireframe instead of Curves . Both of these transparent modes allow you to reach through a surface toselect an object behind it.

You can also see through surfaces by right-clicking, selecting Attributes, and using the Transparency

cursor. But you will not be able to select an object behind a transparent surface.

If curves look jagged, it is due to a default representational setting, and has no bearing on accuracy.You can refine the representation of curves by selecting File/Preferences and then Display,setting the solid deflection value to approximately 1/100th of the smallest feature size in the model,and the minimum number of curve points to at least 30.

Clicking the XY , YZ , and XZ icons sets the view to the corresponding points of view. Clicking the Fit

icon, or right-clicking on the background and selecting Fit , maximizes the view to fit the screen.

You can permanently choose the Display mode of objects in 3DShop, in File/Preferences in

the 3D View dialog in the Display Mode section. Please note that the new display mode will applyto objects that will be created after changing the Preferences. If you want the changes to takeeffect immediately (and for all existing objects) after changing the Preferences, select everythingin the model, delete everything, then type to restore deleted entities. All objects willbe restored and displayed in accordance with the new preferences.

1.4.6 Operations on Geometric Entities

Aside from the Boolean operations that are reserved for closed Shells, other entities such as Edges,Wires, Faces and Shells can be cut and trimmed by Edges and Wires. Once a point of view ischosen, any Edge or Wire can be used as a knife to slice an object in the direction of sight. Edges,

Wires, Faces and Shells can also be sewn together to create more complex Wires and Shells.

Any entity can also be rotated, translated, mirrored, relocated and distorted.

Some operations involve using a Shell, and cannot be performed with a Face. To turn a Face into aShell, simply select it, and select Construction/Sew.

1.4.7 Saving Your Work

To avoid creating damaged files, save often, under different filenames, and at regular time intervals.Make sure to save your work as .opn files. These files also store the sequence of operations(undo/redo stack) used up to the point of saving, if Save Redo/Undo Stack is checked in Preferences.If at a later date you decide to read a saved file, you can use the saved Redo and Undo stack tonavigate the sequence of operations. Please be aware that sometimes a save operation may resultin the loss of the Redo/Undo stack.

Note that if you save a surface mesh as an STL file, it will be saved as one mesh entity. When yousave your model as an STL file, any mesh entity is saved as is, and any Shell or Face is discretizedby default and saved. All entities are saved as a single mesh entity. So, be aware that saving your

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1 - 1 0 Hexahedral-Meshing Preprocessor 3DShop

work as an STL file degrades it. You should always save your work in the default .opn file format;save it as an STL file only prior to hexahedral mesh generation.

When you use Applications/3Dmesh and select the Discretize option, you control the triangu-

lation of surfaces, and translate your Shells and Faces into a mesh entity, which you then save asan STL file.

1.4.8 Hexahedral Mesh Generation

Hexahedral meshing always produces 2 files: one with the extension .flac3d, which is directlyreadable in FLAC3D ; and another with the extension .wrl, which is a VRML (Virtual RealityMarkup Language) file readable in 3DShop. After generating a mesh, you can read the .wrl fileinto 3DShop to visually evaluate the resulting mesh.

To choose hexahedral meshing parameters, take the following steps:

1. Read in the STL file. Select Applications/Kubrix/Hexahedral Meshing to open theHexahedral Meshing dialog.

2. Click on the Default button to reset all parameters to their default values.

3. Click on Compute to launch the computation. When the computation is finished, the DOSwindow remains open.

4. Read the .wrl file into 3DShop, and verify that the block decomposition represents areasonable decomposition of your model into blocks. Please note that this is the coarsestpossible mesh produced by KUBRIX, and represents only the blocks of the mesh.

5. In 3DShop, close the .wrl file, click on the window containing the STL file, and openthe Hexahedral Meshing dialog again.

6. Enter a value for theMaximum allowable edge length equal to approximately 1/5 of whatis reported as the Maximum edge length in the KUBRIXscreen output, and click Compute .

7. Verify that the resulting .wrl file is approaching the mesh densities expected.

8. Close the .wrl file, activate the STL window, and open theHexahedral Meshing dialog.

9. To further limit the maximum size of the elements, note the maximum edge lengthreported in the screen output, and cut the maximum size to a third or less, if needed.

10. To improve the distribution of gridpoints throughout the mesh, set the Number of surfacesmoothing iterations to a higher number. Please note that, in some cases, fewer iterationsresult in a better mesh.

11. To increase the minimum number of elements used to capture details such as wall thick-ness, distances between consecutive walls, gap diameters, etc., set Resolution to 2 ormore.

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HEXAHEDRAL-MESHING PREPROCESSOR 3DSHOP 1 - 1 1

12. To make sure that the mesh follows the surface of the geometry more closely, look forthe Maximum edge offset reported in the screen output, and set the Maximum alloweddistance between the mesh surface and the input surface to a third of what was reportedin the output.

13. To better capture surface dihedral angles (wedges) and avoid smoothing over faint butimportant surface features, use a cut angle of 60 or less.

Please note that small cut angles force KUBRIXto attempt to mesh every surface detail,including those caused by bad or noisy triangulation. As a result, block decomposi-tion may be slow or produce a very large mesh. In some cases, the automatic blockdecomposition may not converge.

14. To better control mesh size near walls without dramatically increasing the total numberof elements in the mesh, add -wallsize in the New Keywords field. In order toavoid dramatic mesh density changes near walls, please choose a value of nosmaller than roughly half the Maximum allowable edge length.

15. To force meshing to follow a prescribed block decomposition, to concentrate meshesaround a particular feature, or to create a layer of vertices along a given line or surface,add internal surfaces to the input. Just make sure that you do not create any free edges.

16. To create a fully structured mesh where each element and each node is defined by aunique i , j , k-index, select 3 as the Structure of the mesh. Please note that the resultingnodes are elements numbered in increasing i-, then increasing j- and, finally, increasingk-order.

You can experiment with various mesh structures by selecting values of -structrangingfrom 0 to 4. Please note that some meshes look much better as a structured mesh.

17. To minimize aspect ratios, it is best, in general, to start by selecting a smaller Maximumallowable edge length and increasing the Number of surface smoothing iterations.

Use aspect ratio control as a last resort to get rid of stubbornly high aspect ratios. Inthe screen output, Maximum aspect ratio shows the highest aspect ratio. Set Maximumallowed aspect ratio to a third of what was reported and check the result.

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1.5 Using 3DShop

1.5.1 Useful Tools and Functions in 3DShop

The following tools are most useful in creating 3DShop models for FLAC3D.

The Objects menu item contains geometrical transformation operations such as Rotationand Translation.

The Construction menu item contains tools to create lines, as well as the Sew and Cuttools, which can be used on every geometrical entity.

The Analysis menu item contains two important functions: Free Boundaries detectsand extracts the free edges of Faces and Shells; the Measures function can be used tofind coordinates and distances.

The Applications menu item contains several important functions:

The Mesh menu item contains the following functions. Discretize discretizesa collection of Faces and Shells into a collection of triangles. Extractiondetects and extracts free and multiple edges of triangular mesh entities. Itis useful for checking whether an imported geometry is closed. The Cleanfunction removes all double Faces and double Edges in a selection; it is usedto ensure that no double Faces remain in the geometry prior to discretizationand final mesh generation. The Topographic Surface function helps youcreate a surface based on level lines.

The 3Dprim menu item contains all of the Primitives.

The 3Dsolid menu item contains all of the Boolean operations. In particular,the Split 2 solids operation can be used to compute all of the Shells resultingfrom the intersection, subtraction and addition of two closed Shells. Anotheruseful tool is the Split by half space operation, which cuts a closed Shell intwo with an open Shell. The 3Dsolid menu item also contains the Extrusionfunction, which works with an extrusion Wire. An extruded Wire is a Shell,and an extruded Shell is a closed Shell.

The 3Dsurf menu item contains all of the operations needed to create complexShells, starting from Points and Curves. In particular, the Shell menu itemcontains the Cap planar holes function, which creates a closed Shell.

The OpenScripting menu item runs scripts. In particular, select ScriptBarto open the Script Editor dialog box. Once in the Script Editor, choose theColorize script to colorize all selected objects in distinct colors.

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1.5.2 Modeling Tips

1.5.2.1 Construction Operations

To cancel any ongoing operations, press the or key.

When a Sew operation fails, try using a smaller Tolerance.

When adding several adjacent closed Shells to create one closed Shell, use the Boolean operationApplications/3dsolid/Add, not Sew. Sew is only used for open Shells.

When trying to Add two adjacent closed shells, the operation may fail if the two Shells do not clearlytouch, or if the interface is made of two different surfaces. If Add fails, dissociate each shell intofaces, trim common faces, and reassemble (Sew) the faces into a closed Shell.

In Extrusion operations, the direction of the extrusion depends on the orientation of the edge orwire along which the extrusion is performed. To change the direction of a Wire or Edge, use

Objects/Reverse.

1.5.2.2 Creating Line Segments

In 3DShop, there are two ways to create a line segment. The Construction/line tool creates aline between two existing points. The Construction/Polyline tool allows you to either selectexisting points or enter the exact coordinates of new points.

If after the creation of a Polyline an errant line follows your cursor, simply right-click in theGraphic Window to get rid of it.

To create a perfectly straight line segment passing through a given point, open Construction/Polyline

, click on the point, and hold down the , or key while you drag the mousein any direction. This will create a straight line along the x-, y-, or z-direction.

1.5.2.3 Colorizing Entities

It is sometimes difficult to distinguish one entity from another if all are shown with the same color.To automatically colorize a group of entities, select them and click on the Colorize icon or selectObjects/Colorize.

1.5.2.4 If Hexahedral Meshing Indicates Free Edges

Select Applications/3Dmesh and Discretize , and make sure that all Free Boundaries are removed. Ifyou cannot get rid of Free Boundaries with a reasonable tolerance, make sure that your geometry isindeed closed. If two Shells intersect visually without having been intersected through a geometricaloperation, they are not aware of each other, and they are not intersecting for the purpose of solidmodeling.

Make sure that if 3DShop sets the value of Chord Error in the Discretize dialog box, you do notoverride it with a smaller value, because this would result in the creation of Free Edges in the STLfile.

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1.5.2.5 If the Hexahedral Meshing Does Not Converge

If the KUBRIX computation remains stuck at 1 fuzzy-logic iteration, your model may containdouble Faces. If your model is a single material object, read the STL file, select the object, and

select Applications/3Dmesh and Extraction/Multiple Boundaries. This operation detectsboundaries where three or more faces join at one Edge. If this is the case at multiple boundaries,at least one of the faces is doubled, and may need to be deleted manually. In multiple materialobjects, read in the last .opn file you created prior to discretization. Dissociate your model intoits constitutive Faces, and look for double-faces using the Applications/3Dmesh, and select theClean function. It may sometimes be necessary to remove double Faces manually.

If the KUBRIX computation fails to converge during the fuzzy-logic block decomposition stage,try rerunning it with Refine set to 1. This option refines the coarse triangular surface mesh prior torunning KUBRIX, and may result in a faster convergence. You can also create a more controllableSTL mesh by using Applications/3Dmesh, selecting Regular Meshing, and rerunning KUBRIX.

1.5.2.6 If the Grid Layers are to follow a Prescribed Surface

Sometimes it may be useful for internal grid layers to be perfectly horizontal or follow a prescribedsurface. To do this, simply add the surface to the model as you would add a wall between twomaterial properties. The resulting mesh will contain two different groups that can be declared asone group when the material properties are set in FLAC3D.

1.5.2.7 If the Mesh Does Not Capture Certain Dihedral Angles on the Surface

Try a cut angle of less than 80 (the default value). (For example, use 60.) This will force theseparation of grid blocks along wedges that have dihedral angles greater than 60. Please note thatif your input surface mesh contains unintended 60 wedge angles as a result of coarse triangulation,

these wedges will be meshed. As a result, noisy triangulations may overly constrain the meshingprocedure and prevent convergence of the block decomposition.

1.5.2.8 If the Resulting Mesh is Too Coarse

Read the KUBRIX screen output and look for the maximum edge length. Rerun KUBRIX usinga maximum allowable element edge length equal to a third of what was reported in the KUBRIXoutput. If the output mesh contains elements that are too coarse near walls, add -wallsize L in theNew Keywords field provided in the Options section of the Hexahedral Meshing dialog box. Thisensures that the mesh thickness in the direction perpendicular to walls does not exceed L near thewalls.

If the output mesh does not depict geometric details such as boreholes and wall thicknesses withenough precision, try a higher mesh Resolution in the Mesh Parameters section of the Hexahedral

Meshing dialog box.

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1.5.2.9 Creating an i, j, k-Structured Mesh

Sometimes, it is desirable to create a mesh where all elements and vertices can be identified by an(i, j, k) triplet. To create such a mesh, set the Structure of the mesh to 3 in the Mesh Parameters

section of the Hexahedral Meshing dialog box.

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1.6 Simple Examples

Three simple examples are presented to illustrate the procedure for model building and meshgeneration using 3DShop. These examples are taken from the Examples volume.

1.6.1 Bathtub Model

In this tutorial, you will learn to create a solid model and mesh of a quarter section of an open pit.The height of the slope is 25 m, and the slope angle is 2 vertical to 1 horizontal, or approximately63. See Figure 1.4. This FLAC3D model is the same as that given in Section 1 in the Examplesvolume.

Figure 1.4 CAD model of bathtub-shaped open pit

Follow the steps below to create this model using 3DShop.

1. Start 3DShop and, using File/New, open a new document.

2. Using Applications/3dprim, create a Parallelepiped with the dimensions (80, 120, 40).

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3. Right-click on the parallelepiped and, in the Display Mode ..., select the Wireframerepresentation of the object so you can clearly see the origin and axes (Figure 1.5). UseObjects/Translation to translate the parallelepiped by a vector with the starting point(40, 60, 20) and the ending point (0, 40, 15).

Figure 1.5 Wireframe view of the parallelepiped

4. Using Applications/3dprim, create a cone section with the following dimensions:

Radius 1 = 12

Radius 2 = 24.5

Height = 25

Angle = 90

5. In the Objects Explorer, select both Shells and, using Edit/Dissociate, dissociate theminto their constitutive faces. The two Shells are deleted and replaced with 11 Faces (6resulting from the parallelepiped and 5 resulting from the cone section).

6. Faces are not distinguishable, because they are all shown in gray. To colorize them, Selectall Faces and the select Objects/Colorize, or click on the Colorize icon (Figure 1.6).This tool uses a circular color assignment scheme to distinctly colorize all selected items.

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Figure 1.6 The Colorize icon

7. The resulting colorized faces are shown in Figure 1.7.

Figure 1.7 All faces after colorization

8. Delete the two Faces of the parallelepiped facing the x < 0 and z > 0 directions to revealthe interior of the box. (Click on each face and select Edit/Delete.)

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9. Select Construction/Extract and Edge, and click on the inclined and lower horizontaledges of the cone face facing y < 0 (Figure 1.8). As a result, two edges are created inthe Graphic Window.

10. To project the two edges, select them, selectApplications

/3Dsurf

, and then selectCurves/Projection. The cursor symbol changes to the letter F. Move the cursor on theface of the parallelepiped facing the y < 0 direction to highlight it, then left-click toproject the edges on it (Figure 1.8).

Figure 1.8 Geometry after removal of two faces and edge projections

11. Delete the three Faces of the cone facing the x < 0, y < 0 and z > 0 directions, anddelete the face of the parallelepiped facing the y < 0 direction. In Figure 1.9, you can

now clearly see the extracted and projected edges.

Figure 1.9 Geometry after more faces have been removed

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12. Using Construction/Polyline, check Display Characteristic Points and create thesix line segments shown in Figure 1.10.

Figure 1.10 Six construction lines appear

13. Using Construction/Extract and Edge, extract the nine edges shown in Figure 1.11.Select all faces and hide them with Display/Hide. What remains visible are all of theedges that have been extracted, as well as those explicitly built in the previous steps(Figure 1.11).

Figure 1.11 Nine extracted edges representing the boundaries of the faces

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14. Select the six edges bounding the top face of the volume. Then select Applications/3dsurf and Surfaces/Fill Curves to create the top face of the volume, shown in grayin Figure 1.12.

Figure 1.12 Creation of the top face

15. Select the four edges bounding the sloping face, and then select Applications/3dsurfand Surfaces Fill Curves to create the sloping face, shown in gray in Figure 1.13.

Figure 1.13 Creation of the sloping face

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16. The two faces representing the conical surface and the base of the cone already exist(Figure 1.14). They were created as the result of the dissociation of the cone, but theyare currently hidden. Select them in the Objects Explorer, and select Display/Displayto make them visible again.

Figure 1.14 Remaining faces of the cone section

17. At this point there are still three faces to be built (light areas in Figure 1.14). Selectthe edges bounding each face, and create them using Applications/3dsurf and FillCurves (Figure 1.15). All of the Faces have now been built and you should have a totalof 10 faces.

Figure 1.15 Building the remaining faces

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18. In the Objects Explorer, select all faces, and select Edit/Reverse the Selection. Allobjects other than faces are now selected. Select Edit/Delete to delete them. Thereshould now be ten faces left.

19. SelectEdit

/Select All

, thenObjects

/Colorize

to colorize all faces (Figure 1.16).

Figure 1.16 Final geometry with colorized faces

20. Select File/Save As to open the Save As dialog box. Save your model under the namepl.opn.

21. Select all Faces, and select Applications/3dmesh and Discretize toopentheDiscretizedialog box (Figure 1.17). This tool transforms a solid model into a collection of triangles

enclosing a watertight volume.

Figure 1.17 The Discretize dialog box

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22. Enter 0.001 in the Chord error field, uncheck the Edges length Max field, and check theRemove initial object field.

23. Click on Create and OK . A triangulated surface is created (Figure 1.18).

Figure 1.18 Triangulated surface representing the geometry

24. Select File/Save As to open the Save As dialog box. Select STL Files in the Save astype field, and save your geometry under the name p1.stl.

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25. Close the current document. Select File/Open and open p1.stl. Select Applications/kubrix and Hexahedral Meshing to open the Hexahedral Meshing dialog box (Fig-ure 1.19).

Figure 1.19 Hexahedral Meshing dialog box

26. Click on Default and enter the following values in their respective fields:

10 Max. allowable element edge length

4 Structure of the mesh

5 Resolution

1000 Nb. of surface smoothing iterations

Press Compute to launch the automatic mesh generation.

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27. Read p1.wrl into 3DShop. You can adjust certain graphic properties of objects toimprove visibility. After you read the .wrl file in the Objects Explorer, right-click onthe entity marked prim triangle 1 , select Attributes and set its Transparency to 5. Next,select the entity marked prim line 1 , set its Color to yellow and its Line Width to 2 to obtain

Figure 1.20.

Figure 1.20 Final mesh for open pit model

The data file listed in Example 1.1 is similar to that in Section 1 in the Examples volume. Theonly difference is that the zoning is replaced by the command IMPGRID p1.flac3d.

Example 1.1 Bathtub model created with 3DShop

;-------------------------------------------------------------

; SL_3D_3DSHOP.DAT influence of slope curvature on stability

; of an open pit modeled using 3DShop

;-------------------------------------------------------------

; read in flac3d model created by 3DShop

impgrid p1.flac3d

; install water table

ini pp 0 grad 0 0 -1e4 range z -15.1 0

call water.fis

; assign Mohr Coulomb model and properties

mod mo

pro bulk 2e8 she 1e8 fric 45 coh 1e5 ten 1e5

; boundary conditions

fix x range x -.1 .1

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fix x range x 79.9 80.1

fix y range y -40.1 -39.9

fix y range y 79.9 80.1

fix x range z -15.1 -14.9

fix y range z -15.1 -14.9fix z range z -15.1 -14.9

; initialize density: saturated and unsaturated

def ini_dens

pnt = zone_head

loop while pnt # null

if z_pp(pnt) # 0.0 then

z_density(pnt) = 2600

else

z_density(pnt) = 2500

endif

pnt = z_next(pnt)

endloopend

ini_dens

s e t g 0 0 - 1 0

; initialize gravity stresses

ini syy -6.25e5 grad 0 0 2.5e4

ini sxx -6.25e5 grad 0 0 2.5e4

ini szz -6.25e5 grad 0 0 2.5e4

; histories

hist unbal

hist gp xdisp 24.5 -40 25

hist gp zdisp 24.5 -40 25

hist gp xdisp 24.5 0 25

hist gp ydisp 24.5 0 25

hist gp zdisp 24.5 0 25

hist gp ydisp 0 24.5 25

hist gp zdisp 0 24.5 25

; calculate fos

solve fos

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1.6.2 Mine Pillar Model

In this tutorial, you will learn to create a solid model and mesh for a mine room-and-pillar layer, asdescribed in Section 2 in the Examples volume. See Figure 1.21.

Figure 1.21 CAD model of mine pillar

1. Start 3DShop and, using File/New, open a new document.

2. Using Applications/3dprim, create a Parallelepiped with the dimensions (13, 7.5, 20).

3. Select the parallelepiped and use Objects/Translation to open the Direction Acquisi-tion dialog box. Click on Center to set the coordinates in the first column to those of thecurrent center of the object, and set the second column to (6.5, 3.75, 0). Click on OK

(Figure 1.22).

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Figure 1.22 View of the box

4. Hide the box and adopt an XZ point of view. Using Construction/Polyline, create aline from (2, 0, 0) to (2, 0, 0). Click on Next , and create a line segment going from (0,0, 0) to (0, 0, 2).

5. Select Construction/Arc 3Pts to open the Plane Acquisition dialog box. Check Dis-play Characteristic Points, then click on points (2, 0, 0), (0, 0, 2) and (2, 0, 0) to createa circular arc passing through these 3 points (Figure 1.23).

Figure 1.23 A circular arc passing through 3 points

6. Using Construction/Polyline, create a Polyline segment starting at (2, 0, 0), passingthrough (2, 0, 2) and (2, 0, 2), and ending at (2, 0, 0) (Figure 1.24).

Figure 1.24 Circular arc and rectangle

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7. Delete the two interior line segments. Select the circular arc and the remaining Polyline,and select Construction/Sew to create a closed Wire representing the tunnel cross-section. While in the XZ-view, select Display/Display All to display the box and thesection (Figure 1.25).

Figure 1.25 Single Wire representing the tunnel cross-section and the box

8. While in the XZ-view, select the box, and select Construction/Cut. The cursor symbolchanges to the letter E. Click on the wire representing the tunnel cross-section to cut thebox into 2 parts.

9. Delete the part inside the section (Figure 1.26).

Figure 1.26 What remains of the box when the tunnel is subtracted

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10. Adopt a perspective view (Figure 1.27).

Figure 1.27 Perspective view of the box

11. Select the Wire representing the tunnel section, and select Objects/Rotation to openthe Axis Acquisition dialog box. Click on the node at the center of the base of the tunnelsection. Next, click on the node located at the apex of the circular arc. Click OK , checkthe 90 button in the Angle dialog, and then check OK . Figure 1.28 shows the tunnelsection before the rotation, and Figure 1.29 after.

Figure 1.28 Rotating the tunnel section around a vertical axis, before

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Figure 1.29 Rotating the tunnel section around a vertical axis, after

12. Adopt a YZ-point of view, select the box, and select Construction/Cut. The cursorsymbol turns into the letter E. Click on the wire representing the tunnel section to cut thebox.

13. Delete both the portion of the box inside the section and the Wire itself, as it is nolonger needed. A perspective view of the excavated box is shown in Figure 1.30. SelectFile/Save As to open the Save As dialog box, and save your model under the namep2.opn.

Figure 1.30 Final model of the pillar

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14. Select the pillar, and select Applications/3dmesh/discretize to open the Discretizedialog box. This tool transforms a solid model into a collection of triangles enclosing avolume.

15. Enter 0.001 in the Chord error field, uncheck the Edges length: Max field, and check theRemove initial object field.

Click on Create and OK . A triangulated surface is created (Figure 1.31).

Figure 1.31 Triangulated surface representing the geometry


17. Close the current document. Select File/Open, and open p2.stl. SelectApplications/kubrix/Hexahedral Meshing to open the Hexahedral Meshing dialogbox (Figure 1.32).

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Figure 1.32 The Hexahedral Meshing dialog box


1.5 Max. allowable element edge length


5 Resolution


-wallsize 0.5 New keywords


19. Read p2.wrl into 3DShop. You can adjust certain graphic properties of objects toimprove visibility. Here, after you read the .wrl file, in the Objects Explorer, right-click on the entity marked prim line 1 , select Attributes, and set its Color to yellow andits Line Width to 2 to obtain Figure 1.33.

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Figure 1.33 Final mesh for pillar model

The data file needed to run this problem is shown in Example 1.2. It is similar to that in Section 2in the Examples volume. The only difference is that the zoning section has been replaced by thecommand IMPGRID p2.flac3d.

Example 1.2 Pillar model created with 3DShop

;-------------------------------------------------------------

; PILLAR_3DSHOP.DAT evolution of peak load

; in a rectangular pillar

;-------------------------------------------------------------

def parm

rat1=1.14

rat_1=1.0/rat1

end

parm

def s_base

pnt=gp_head

sum=0.0

loop while pnt # null

if gp_zpos(pnt)


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pnt=gp_next(pnt)

end_loop

s_base=sum/(13.0*7.5)

end

; read in flac3d model created by 3DShop

impgrid p2.flac3d

mo ss

fix y range y -.1 .1

fix y range y 7.4 7.6

fix x range x -.1 .1

fix x range x 12.9 13.1

fix z range z -10.1 -9.9

apply szz -17e6 range z 9.9 10.1

pro bulk 14.1e9 she 8.87e9 fric 35 coh 4e6 ten 5e5 ftab 1 ctab 2table 1 0 35 0.01 32 0.02 30 .5 30

table 2 0 4e6 0.01 0.5e6 0.02 0 .5 0

ini sxx -25e6

ini syy -30e6

ini szz -17e6

hist unbal

hist gp zdisp 0 0 2

hist gp xdisp 2 7.5 0

hist gp ydisp 13 2 0

;

step 4000

;

save pillar1.sav

fix z range z 9.9 10.1

ini zvel -1e-5 range z 9.9 10.1

hist gp zdisp 13 7.5 10

hist s_base

step 1740

save pillar2.sav

step 1645

save pillar3.sav

;

ret

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1.6.3 Tunnel Intersection Model

In this tutorial, you will learn to create a solid model and mesh for two equal size tunnels intersectingat 45. This FLAC3D model is the same as that given in Section 5 in the Examples volume. See

Figure 1.34.

Figure 1.34 CAD model of 45 tunnel intersection

1. Start 3DShop and, using File/New, open a new document

2. Adopt an XZ-view and, using Construction/Polyline, create a line segment from (1,0, 0) to (1, 0, 0). Use Zoom if you need to see the line better.

3. Select Construction/Circle to open the Circle dialog box. Select the Center, Radiustype of construction, click on the (0, 0, 0) point located in the middle of the line segment,and enter 1 in the Radius field (Figure 1.35). Click OK to create the circle.

Figure 1.35 The Circle dialog box

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4. With Construction/Polyline, create one line from (1, 0, 0) to (1, 0, 1), and asecond line from (1, 0, 1) to (1, 0, 0 ).

5. Select the circle, and select Construction/Trim. The cursor symbol changes to the letter

E. Click on the horizontal segment representing the diameter of the circle. To eliminatethe lower portion of the circle, click somewhere below the diameter (Figure 1.36).

Figure 1.36 The trimmed circle and lower rectangle

6. Delete the diameter, select the half-circle and the two vertical lines, and selectConstruction/Sew to create a single Wire representing the cross section of the tunnel(Figure 1.37).

Figure 1.37 Tunnel cross-section

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7. Adopt an Axonometric perspective view and, using Construction/Polyline, create aline segment from (1, 0, 1) to (1, 20, 1) (Figure 1.38).

Figure 1.38 Tunnel section and line representing the direction of tunnel ex-trusion

8. Select the tunnel section, and select Application/3Dsolid/Extrude/Along an Edge.The cursor symbol changes to the letter E. Click on the line representing the extrusiondirection to create the first tunnel (Figure 1.39).

Figure 1.39 First tunnel

9. Adopt an XY-point of view. Select the tunnel and, using Edit/Copy followed by Edit/Paste, create a copy of the tunnel. In the Objects Explorer, select one of the two tunnels,and select Objects/Rotation to open the Axis Acquisition dialog box.

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10. Click once on the button marked Center . The coordinates of the center of the tunnel areentered in the first column of the dialog box. Click once more on Center to enter the samecoordinates in the second column. The resulting axis of rotation is now a vector of length0. You must create a vertical axis of rotation. To do so, in the second column, replace

the present value of Z with 10 (Figure 1.40).

Figure 1.40 Rotation of a tunnel around a vertical axis passing through itscenter

11. Click on OK to open the Angle dialog box. Check the Other button and enter 45 in thefield next to it, then press OK to complete the rotation of the tunnel (Figure 1.41).

Figure 1.41 The rotated tunnel

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12. In the Objects Explorer, locate and delete the Edge and Wire. There are now two grayShells left. To colorize them, select them both, and then select Objects/Colorize(Figure 1.42).

Figure 1.42 The Colorize icon

13. Click on the background of the graphic window to see the colorized shells (Figure 1.43).

Figure 1.43 Intersecting tunnels

14. To intersect the two tunnels, first select one of the Shells. Select Applications/3Dsurf/Features/Intersection to open the Intersection dialog box. The name of the selected

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Shell already appears in the field marked First group of objects. Select the otherShell. Its name appears in the field marked Second group of objects. Click on OK

to create the entities representing the intersection of the two groups (Figure 1.44). TheObjects Explorernow includes a new folder called Intersection, containing 8 Edges.

Figure 1.44 Intersecting two tunnels

15. Hide both Shells, adopt a perspective view, and create two line segments connecting thebase of each of the two arcs (Figure 1.45).

Figure 1.45 Line segments joining arc bases

16. Select one of thehorizontal line segments youhave just created, andselect Objects/Scaleto open the Point acquisition dialog box. Click on Center to set the fixed point of the scal-ing to the center of the segment, then click OK to open the Scale dialog box. Enter 2 for

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the scale value and click OK to scale the segment by a factor 2. Similarly, scale up thesecond horizontal line segment by a factor 2 (Figure 1.46).

Figure 1.46 Scaling up two line segments

17. Delete all edges except the last two that you just scaled up. Select Display/Displayall and adopt an XY-point of view (Figure 1.47). You are now going to cut both tunnelsalong both lines to create 8 separate pieces.

Figure 1.47 Tunnels and cutting lines

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18. Hide the tunnel oriented in the y-direction. The select the angled tunnel, selectConstruction/ menuitemCut, and click on one of the cutting lines to cut the tunnel intwo (Figure 1.48).

Figure 1.48 Cutting one tunnel in two

19. Select both visible pieces of the tunnel, select Construction/Cut, and click on the otherline to cut the two pieces into four pieces. There are now four shells on your screen,but represented with just two colors. To colorize them distinctly, select the four visiblepieces and select Objects/Colorize (Figure 1.49).

Figure 1.49 The four pieces of the angled tunnel

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20. Hide all visible Shells, and display the remaining tunnel. Using a similar procedure, cutit into four pieces along the two cutting lines, and colorize the four shells (Figure 1.50).

Figure 1.50 The four pieces of the y-direction tunnel

21. Delete the two cutting lines, display all Shells and Colorize them. Please note that fourof the smaller Shells are hidden underneath the visible Shells (Figure 1.51).

Figure 1.51 Intersecting tunnels

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22. Delete the Shell pointing to the southwest (Figure 1.52). There are now 3 remainingsmaller Shells that need to be deleted.

Figure 1.52 Removing the southwest tunnel

23. Turn the model over, and delete the 3 internal Shells in order to create the final assemblyrepresenting the tunnel intersection (Figure 1.53).

Figure 1.53 The two tunnels after the removal of all unneeded Shells

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24. Select the four remaining Shells, select Construction/Sew and enter 104 for the sewingtolerance to create a single Shell representing the tunnel intersection. Use Construction/Line to create three line segments connecting the corners of the three arches representingthe three ends of the intersection (Figure 1.54).

Figure 1.54 Three line segments connecting the corners of the three arches

25. To cap the three arches, you must extract the Edges that describe them. Select Edge inthe Construction/ Extract menu. The cursor symbol changes to the letter E. As youhover the cursor along the edges of the model, you will notice that the Edges becomehighlighted. Carefully left-click the Edges of each arch, making sure not to forget orduplicate any. Hide the Shell to display only the Edges in the model (Figure 1.55).

Figure 1.55 Extracting the edges representing the three arches

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26. For each of the three arches, select all its edges and, in Applications/3Dsurf/Surfaces,select Fill Curves to create the Face spanning the arch (Figure 1.56).

Figure 1.56 Capping the 3 branch ends

27. Delete all Edges, select the Shell and Faces and select Display/Display all. Select theShell and the three capping Faces, and sew them together with Construction/Sew and

a tolerance of 104 (Figure 1.57). Please note that the floor of the tunnel is still missing.

Figure 1.57 The complete tunnel branch without the floor

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28. To build the floor, select the Shell and select Applications/3Dsurf/Shell/Cap planarholes (Figure 1.58). If you right-click the Shell and select Properties, you will noticethat the Shell is now closed.

Figure 1.58 Closed Shell representing the branching

29. Adopt an axonometric perspective view, and select the menu item Parallelepiped fromthe Applications/3Dprim menu to open the Parallelepiped dialog box. Enter (10, 14,10) for the dimensions, and click OK to create it (Figure 1.59).

Figure 1.59 The branching and a parallelepiped

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30. Using Objects/Translation, translate the parallelepiped from point (0, 0, 0) to (0, 13,0). Select the parallelepiped and the Shell representing the tunnel intersection, and selectApplications/3Dsolid/Split 2 solids to create all of the Shells resulting from theintersection of the tunnel intersection and the box (Figure 1.60).

Figure 1.60 The result of Split 2 solids

31. Look at the Objects Explorerand you will notice that there is an entity called Compound.This entity represents the two Shells sticking out of the box. It is called a Compoundbecause the Shells do not touch. Were you to Edit/Dissociate the Compound, youwould obtain two Shells. Here, simply delete the Compound.

32. Right-click the outer Shell, select Properties and set its transparency to 50% so you can

see the tunnel intersection inside (Figure 1.61).

Figure 1.61 The outer Shell is rendered transparent to show the branchinginside

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33. Each of the two Shells has its own outer Face. As a result, the Faces forming the tunnelare all doubled. To remove double-Faces, select both Shells and select Edit/Dissociateto dissociate the Shells into 35 constitutive Faces.

34. Select all Faces, selectApplications

/3Dmesh

/Clean

to open the Clean dialog box. Enter104 for the Tolerance and click on Analyse . 3DShop responds with number of objects =35, number of double objects = 13. Click on Clean to remove all double objects.

35. Select all Faces, select Applications/3Dmesh/Regular Meshing to open the RegularMeshing dialog box (Figure 1.62).

Figure 1.62 The Discretize dialog box

36. Enter 0.001 in the Chord error field, enter 1 in the Edges length Max field, and check theRemove initial object field.

Click on Create and OK . A triangulated surface is created (Figure 1.63).

Figure 1.63 Triangulated geometry

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38. Close the current document. Select File/Open and open p3.stl. Select the menu itemHexahedral Meshing

fromApplications

/kubrix

to open the Hexahedral Meshingdialog box.


3 Max. allowable element edge length


4 Resolution



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40. Read p3.wrl into 3DShop. You can adjust certain graphic properties of objects toimprove visibility. After you read the .wrl file, in the Objects Explorer, right-click onthe entity marked prim triangle 1 , select Attributes and set its Transparency to, say, 5.Next, select the entity marked prim line 1 , set its Color to yellow and its Line Width to 2

to obtain Figure 1.64.

Figure 1.64 Final mesh for intersecting tunnels model

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