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option in the pull-down menu for Type in the Properties window.

There is no requirement to set the region Type to anything other than FluidRegion as it has no effect on the meshing operations. However, setting thetype is a good reminder of what type of region each part of the domain isand what type of prism layer mesh should be allocated to this region. Theregion icon will also change to reflect the new type.

We can now proceed and define the boundary surfaces for each region.

Defining the Boundaries

The CAD import resulted in one boundary per region. CAD informationthat will distinguish one boundary surface from another is stored as patcheswithin STAR-CCM+. One of the easiest ways of splitting a boundary surfaceinto constituent boundaries is using this patch information. The reason forsplitting is that we need to identify the flow boundaries, plus the interfaceboundary that will be used to indicate which surface planes are common toboth regions and will require a conformal mesh condition.

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• Repeat the above operation for the other two boundary patches, usingthe names specified in the table.

• Press the Close button on the Boundary Patches dialog when done.

The completed list of boundaries for the fluid region is shown below:

The original boundary for the fluid region (Boundary 1) is now composedof surfaces that belong solely to the interface plane between the fluid andsolid regions. This will make the interface definition easier later on byhaving all the surfaces in one boundary.

Next we will rename the original boundary and set the boundary types foreach.

Renaming and Setting the Fluid Boundary Types

The following boundary types will be used for each boundary in the fluidregion:

Boundary Name Boundary Type

Boundary 1 (Interface) Wall

Inlet Velocity Inlet

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button to apply it.

The boundary types can now be set. For the Interface boundary node, thedefault Wall condition is appropriate and does not need to be changed. Toset the type for the Inlet boundary, do the following:

• Select the Inlet node in the simulation tree.

• Select the Velocity Inlet option in the pull-down menu for Type in theProperties window.

Repeat the above operation for the remaining boundary nodes in the table.The completed list of boundaries is shown below:

We can now proceed to extract the boundaries for the solid region.

Extracting the Solid Boundaries

The solid boundaries will be extracted using the same method as used forthe fluid ones.

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The completed list of boundaries for the solid region is shown below:

The original boundary for the solid region (Boundary 1) is now composed ofsurfaces that belong solely to the interface plane between the solid and fluidregions.

Next we will rename the original boundary and set the boundary types foreach.

Renaming and Setting the Solid Boundary Types

The following boundary types will be used for each boundary in the solidregion:

Rename the Boundary 1 boundary as previously done for the fluid region:

• Select the Solid body>Boundaries>Boundary 1 node in the simulation tree,right-click and select Rename from the pop-up menu.

Boundary Name Boundary Type

Boundary 1 (Interface) Wall

Inner cylinder wall Wall

Outer cylinder wall Wall

Symmetry Symmetry Plane

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Two new interface nodes will appear in the simulation tree, one for eachregion, as shown below:

These two new nodes compose the two halves of the in-place internalboundary interface between the fluid and solid regions.

Selecting the Meshing Models

The surface remesher and the polyhedral volume mesher will be used forthis example, along with the prism mesher so that we can generate prismlayers next to the walls of the fluid region. The generation of prism layersnext to solid region walls will be disabled.

• Right-click on the Continua>Mesh 1>Models node and select Select

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Setting the Reference Values

To view the global reference values required for the selected meshingmodels, open the Continua>Mesh 1>Reference Values node. The followingmesh inputs will be listed:

The following parameters will be used for this meshing tutorial:

Reference Node Name Property Name Value

Base Size Value 1.0 m(default)

Number of Prism Layers Number of Prism Layers 1

Prism Layer Stretching Prism Layer Stretching 1.5 (default)

Prism Layer Thickness>Abso-lute Size

Value 2.0 mm

Surface Curvature #Pts/circle 36 (default)

Surface Growth Rate Surface Growth Rate 1.3 (default)

Surface Proximity # Points in gap 4.0

Surface Proximity Search Floor 0.0 (default)

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• In the Properties window, set Value to 2.0 mm.

• Repeat this for the other nodes in the list using the values supplied inthe table.

Including Prism Layers on the Interface

The generation of an in-place interface between the fluid and solid regionsalso created a new node in the Interfaces node in the simulation tree. Thisnode can control the mesh conditions on either side of the interface. Bydefault, the option to grow prism layers on either side of the interface is setto off. In our case, we want prism layers on the fluid side only, since thereis no requirement to include layers for the solid material region. To achievethis, we will enable the prism layer generation option for the interface butdisable the generation of layers on the region level for the solid body.

• Select the Interfaces>In-place 1>Mesh Conditions>Interface Prism Layer

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node and set the Customize Prism Mesh option to Disable.

The generation of prism layers for the boundaries in the solid region is nowdisabled. However, if you decided to specify custom values for a boundarybelonging to this region then it would override the region levelspecification. There is no requirement to do this for this example.

Running the Surface Remesher

Since the surface remesher and volume mesher models have been selectedin tandem then we could proceed and generate both meshes in one go.However, for training purposes, we will first generate the surface remeshermesh and view it before proceeding with the volume meshing. To do this,either:

• Press the (Generate Surface Mesh) button in the Mesh Generationtoolbar; or

• Select Mesh>Generate Surface Mesh from the pull-down menu on the

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Manifold Surface Wrapping Tutorial

This tutorial demonstrates how to use the surface wrapper to extract theinternal fluid surface from a collection of parts representing an intakemanifold assembly. The wrapper is run several times in order to present thegeneral iterative nature of the tool when dealing with new or unfamiliargeometries. With each iteration, additional features and options areincluded in order to better improve the overall fidelity of the resultantwrapped surface. With experience, the user can utilize the wrapper and getthe desired result in one or two iterations on geometries that they arefamiliar with.

The geometry used in the tutorial is shown below.

The manifold assembly is composed of several parts, including the mainbody, mounting struts, air-flow sensor, control valve and directional flowbaffles. Most parts are in their original CAD form and have not yet beenprepared to be used for a CCM or CFD type of analysis.

One approach for preparing the geometry would be to do a lot of manual orhand fixing to remove unwanted surfaces and stitch together remainingones to form a closed volume geometry. For a simple case with only a fewparts this is sometimes a realistic solution. However, as the number of partsand overall complexity increases, manual repair becomes inefficient, if not

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The surface wrapper can be a very fast and efficient process of extractingboth internal and external surfaces from CAD type geometries. Thewrapper model has a wide range of options to deal with different startingscenarios, not all of which need to be used for a specific case. In this respect,successful use of the wrapper is (initially) somewhat of a black art due to theholistic approach taken and the numerous paths available. For example,tweaking some of the basic input values to deal with a particular feature cansometime have a big effect on the overall result. Repeated use of thewrapper however will build up a wealth of experience which can betransferred from one case to another and provide the user with a robustapproach to solving surface preparation problems.

Objectives

The general objectives of this tutorial are:

• Perform an internal surface wrap on an industrial type assemblystarting from CAD parts.

• Highlight best practises for wrapping and provide guidelines on how toidentify issues and resolve them using the surface wrapper tools.

• Provide alternative methods for dealing with certain issues.

• Provide a general methodology for tackling cases that require thesurface wrapper to be used.

• Demonstrate the robustness and efficiency of the surface wrapperwithin STAR-CCM+.

Specific tasks that are undertaken include:

• Importing multiple CAD files and combining regions.

• How to use the fill polygonal patch option to cap open boundaries.

• Setting the wrapper properties and reference values.

• How to use the leak detection tool.

• How and when to implement contact prevention.

• Surface refinement for a boundary.

It is assumed that the user has a general knowledge of STAR-CCM+ alreadyand has completed the earlier two meshing tutorial examples.

Importing the CAD Parts

Create a sub-directory for the tutorial called manifoldWrap. Copy thetutorial Parasolid Transmit files (which contains the geometry definition)

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Use the mouse buttons to rotate the model so that viewing direction shownbelow is seen:

The tessellation density is sufficient in this case for the surface wrapper tobe used and still extract a reasonably good surface definition.

Combining Regions and Identifying Important Boundaries

The import process created 11 new regions, labelled Body 1 throughBody 11. These can be seen by opening the Regions node in the simulationtree. The current surface wrapper implementation works only on one regionat a time so the individual regions must be combined before proceeding.

• In the Regions node, select Body 1 through Body 11, right-click and select

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Repeat the above process for the other boundaries listed in the table. Thecompleted list of updated boundaries is shown below:

Note that you can right-click on the Boundaries node and select Refresh tore-sort the list alphabetically.

Activating the Wrapper Model

The next step after organizing the boundaries is to close or “cap off” anyopen boundaries or large holes in the surface so that the wrapper candetermine what pertains to be inside the geometry and what is outside. Notall holes need to be closed at this time as the wrapping process can naturallyclose holes that are of approximately the same order as the specified targetsize for the surface.

To assist with the hole detection process, we will activate the surfacewrapper model now and specify initial surface sizes so that the leak detectorcan be invoked to check for any holes we may have missed. The leakdetection tool also contains a sub-set of the surface repair tools, which wecan use initially to close the gaps in the model.

• Right-click on the Continua > Mesh 1 > Models node and select

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Setting the Initial Reference Values

For the leak detector to be used, some initial first guess reference valuesneed to be specified for the surface minimum and target sizes. We will userelative size specification for this tutorial, using a base size of 0.1 m, whichis approximately the width of the main manifold body.

• Select the Continua > Mesh 1 > Reference Values > Base Size node.

• Set the base size Value in the Properties window to be 0.1 m.

The above setting is shown below:

The surface minimum and target size can be set next based on the base sizevalue. As initial guesses, we will take use one tenth of the base size for thetarget size and half of this value for the minimum size.

• Select the Reference Values > Surface Size > Relative Minimum Size node.

• Set the Percentage of Base value to be 5.0 (equivalent to 5 mm).

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surface without having to visit each value in turn. The default value of100.0% means that the original values are applied without alteration.

Decreasing the Percentage value will increase the resultant triangulationdensity in the wrapped surface.

Capping the Geometry

As we are extracting the internal volume of the manifold, then a mostlywatertight import surface must be supplied as a starting point. We canachieve this by capping-off the open inlet and outlet boundary areas in themanifold. The capping-off process does not need to be exact as small gapsand slits can be closed by the wrapping process itself.

Two different tools are available to help close off holes, namely thepolygonal patch fill and the hole filler. The polygonal patch filler is a quickand easy way of closing arbitrary shaped holes which may not have a closedloop definition and/or be planar. The process literally “patches” up thesurface by creating faces that cover the hole area completely. The hole filleris a more exact method of filling well defined holes by using a closed loop

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The result of the hole fill on the outlet pipes is shown below:

All the major holes in the geometry are now closed so we can proceed to runthe leak detector.

Running the Leak Detector

The surface wrapper is now ready to run and produce a wrapped surfacebased on the supplied reference values. As a pre-cursor to doing this, itssometimes a good idea to run the leak detection scheme prior to doing thefirst wrap so that any remaining holes that may have been missed duringsurface cleanup will come to light. Performing a leak detection before doinga wrap is possible as long as the appropriate Reference Values and modeloptions are set. Using these settings, it is possible to construct theunderlying octree matrix and detect whether holes larger than the wrappersurface sizes exist. If they do, then a leak will occur and the wrap will notproceed as expected. The source of the leak will be highlighted by the toolusing a path from the interior source point to the exterior target point. Notethat leaks are not desired because they cause an inversion in the wrappingprocess, which results in the incorrect volumes being wrapped.

To perform a leak detection, do the following:

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Note that if a hole was detected then you should use the polygonal patchfiller as described earlier to quickly patch the leak area as indicated by thetool. The leak detector can then be re-run by pressing theRecompute Template+Paths button again. Alternatively, the reference valuesand/or model options can be adjusted so that the wrapper closes anymarginal holes itself.

• Press the Close button on the dialog to close the tool.

Removing the Feature Curves

Feature curves for the manifold assembly were created during the importprocess, based on a sharp edge angle of 30 degrees. The surface wrappingprocess however normally does not require feature curves in the startingsurface as it will generate its own set of features based on the suppliedWrapper Feature Angle reference value (also 30 degrees by default). Thesenew feature curves will supersede any coincident ones in the input surface,so the original ones should be deleted in this instance. Leaving the featurecurves in could lead to double features being created very close together,resulting in artificial refinement areas for the wrapper.

The reason for generating feature curves during the import process was sothat they could be used during the hole filling process for surface repair.Note that feature curves pertaining to surface features on planar surfaceshould be kept if the feature is to be retained in the wrapper result (asopposed to those representing edges).

To delete the feature curves, do the following:

• Open the Regions > Body 1 > Feature Curves node, select all the featurecurves (1 through 1 11), right-click and select Delete from the pop-upmenu.

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Producing a Basic Wrap

By default, the surface wrapper will attempt to extract the largest internalvolume from the region definition. This specification is made via theRegions > Body 1 > Mesh Conditions > Volume of Interest Specification, shownbelow:

The other options available are External, Seed Point and Nth Largest, each ofwhich allow you to specify the eternal or specific internal volumes to bewrapped. The largest internal volume is the option we want for this case.

The surface wrapper can now be run based on the initial settings suppliedfor the reference values:

• Press the (Generate Surface Mesh) button in the Mesh Generationtoolbar; or

• Select Mesh > Generate Surface Mesh from the pull-down menu on themain display.

The output of the surface wrapper will be shown in the Output window andstatus shown in the status bar. When it is complete, the message SurfaceWrapper Completed will appear. To view the result:

• Right-click in the current scene and select Apply Representation >Wrapped Surface.

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In a similar way, the channels in the valve were also defeatured since thefeature size (approximately 2.5 mm wide) is much less than the target size.We would have to have a target size of the same order as the feature in orderto capture this detail (this will be described later in this tutorial).

We can easily improve on the first wrap result by tweaking the referencesettings and including additional options to deal with feature specificissues. The remainder of this tutorial will concentrate on improving eachgeometry feature in turn, identifying the issue and the solution to rectify theproblem. The following items will be covered:

• Improving the manifold body fidelity and curvature.

• Sensor definition.

• Capturing the channel details (if desired).

• Flange resolution.

• Valve area resolution in general.

• Baffle intersection and resolution.

Improving the Manifold Body Fidelity and Curvature

We will start by improving the general manifold body fidelity andcurvature, which is controlled via the reference surface target andminimum size. Reducing both of these values will have a significant impacton the general model fidelity immediately:

• Set the Percentage of Base value in Continua > Mesh 1 > Reference Values> Surface Size > Relative Minimum Size to be 2.5 (2.5 mm).

• Set the Percentage of Base value in Reference Values > Surface Size >Relative Target Size to be 8.0 (8.0 mm).

When changing the target size, it is sometimes prudent to re-run the leakdetector to check that the specified surface sizes haven’t decreased such thatholes that previously were automatically filled are now relatively largeenough to allow a leak. In this case we will proceed and re-run the surfacewrapper as before:

• Press the (Generate Surface Mesh) button in the Mesh Generationtoolbar; or

• Select Mesh > Generate Surface Mesh from the pull-down menu on themain display.

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Improving the Sensor Part Definition

The wrapped surface for the sensor area currently looks like this:

As can be seen, the sensor part is joined to the bottom surface of themanifold body, which is not desirable. This is happening because theclearance between the sensor and the base is approximately 2 mm, which isless than the current target surface size of 8 mm. In other words, thewrapper octree process is unable to detect or “see” the space between thetwo parts, since the triangle size it is using is much bigger than it. Oneobvious solution is to reduce the target size locally for both parts, but thiswould mean that the manifold base would have to be split into differentboundaries, which may not be possible given the coarseness of the importsurface. An easier solution, which does not involve splitting of boundaries,is the application of a contact prevention set to inform the wrapper that thetwo boundaries should not be joined together during wrapping.

Additionally, a floor value is set to indicate the triangle size that should beused in the space between the two parts, which will determine the octreerefinement in the area. A value smaller than the gap size will need to beused (typically one half or one quarter of the distance). Note however that,just because a search floor value has been set, doesn’t guarantee that the twoboundaries will not be joined. The floor value is simply a stopping size for

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Improving the Channels Definition

Based on the current reference target size of 8 mm, the three channels thatexist in the manifold cross pipe have been defeatured. The location of thechannels in the current wrap is shown below:

Depending on the requirements of the flow analysis, this may be a desirableresult, as it simplifies the geometry without adversely affecting the flowsolution. The defeaturing occurs as the channels themselves areapproximately 2.5 mm wide and the octree triangles in this area are basedon the target size, which means it cannot capture the detail. A localizedtarget size on the order of the channel width will be required if we are tomaintain this feature.

To improve the resolution of the channel we must first separate them outinto a different boundary so that boundary specific wrapper values can beapplied. Since we are modifying the underlying boundary arrangement, wehave to eliminate all but one of the surface representations. Since thewrapped surface is not complete yet, we will delete it and work on theoriginal import representation.

• Clear away the wrapped surface to leave the original importrepresentation by pressing the (Clear Generated Meshes) button.

• Click the Yes button in the Clear Generated Meshes dialog that appears.

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When the process is complete, right-click on the scene and selectApply Representation > Wrapped Surface in the pop-up menu. The scene willupdate the display with the new result.

As shown in the close-up above, the channels are now very well defined andhave sharp edges in the circumferential direction.

Improving the Flange Definition

There are two sets of flanges in the manifold assembly, one between theinlet pipe and manifold body and the second between the cross-pipe andthe manifold, which represent high curvature areas in close proximity toone another. The flange opposite parts are also not joined to one another.

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When the process is complete, STAR-CCM+ will update the display withthe new result.

As shown in the close-up above, the flanges are now well defined and havea sharp edges in the circumferential direction.

Improving the Valve Definition

The surface size used for the valve geometry is reasonable but due to theproximity to the cross pipe surface, the surface wrapper defeatures the gap

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When the process is complete, STAR-CCM+ will update the display withthe new result:

As can be seen, the valve is now well defined and does not intersect the sidewall of the cross-pipe.

Improving the Baffle Definition

The baffles within the geometry are initially represented as intersectingsurfaces which pass through the outlet pipes emerging from the manifoldbody. The surface wrapper can detect these surfaces and automatically“inflate” them, so that a small thickness is introduced into the shape of the

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Using the Built-in Wrapper Baffle Inflation with Contact Prevention

To improve the surface definition using the default built-in wrapper baffleinflation option depends simply on including a contact prevention set forthe baffle boundaries (which determines the resulting inflation thickness)and increasing the surface triangulation on the baffles themselves. This issimilar to the technique outlined earlier in the tutorial for improving thesensor definition.

An alternative method also exists for including thin baffles which will beexplained here but not presented in detail. If no inflation is required for thebaffle surface, then you should delete (or even better, don’t import in thefirst place) the baffle parts and proceed with the wrapping process asexplained up until this portion of the tutorial. In other words, perform asurface wrap without the baffle boundaries existing. Then, import the bafflesurfaces (which will create a new region) and combine this new region backwith the original one which is already wrapped. Next, use the boundaryintersection process to intersect the baffles with the wrapped surface anduse the manual surface repair tool to delete any superfluous faces that areexterior to the geometry. Finally, convert the baffle boundaries to interfaces.The surface is now ready to be used as the starting point for the surfaceremeshing step of the process, which will result in a high quality, zerothickness interior wall being created for the baffles.

To continue and use the surface wrapper to perform the baffle inflation,follow the instructions below.

A single group contact prevention can be used in this instance, since thebaffles all belong to one boundary and the manifold body to another. Asmall search floor value will need to be used due to curvature occurring intwo different directions at the intersection of the baffles and manifold pipes.The search floor will also have some influence over the thickness used forthe baffle inflation.

• Right-click on Regions > Body 1 > Mesh Values > Contact Prevention and

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A close up of the baffle intersection area is shown below:

Using the Offset Tool to Inflate the Baffles Manually

The surface preparation offset tool can be used to manually inflate surfacesso that they have a thickness associated with them. The inflation can takeplace in any specified direction and can be done on more than one boundaryat a time. By inflating the surfaces, the wrapper can then more easily dealwith the resultant closed body shape and incorporate the feature as part ofthe final surface while maintaining a good definition.

The baffle inflation will be performed directly on the import surface. Thecurrent wrapped surface representation is not needed so for this reason itwill be deleted to simplify the process:

• Clear away the wrapped surface to leave the original importrepresentation by pressing the (Clear Generated Meshes) button.

• Click the Yes button in the Clear Generated Meshes dialog that appears.

The current scene display will show the imported surface. The surfacepreparation tools can now be accessed:

• Right-click on the Representations > Import node and select

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A close up of the baffle intersection areas is shown below:

In this instance, the wrapper has incorporated the inflated body into themain geometry and left a well defined void to represent the baffle.

What To Do Next

The surface wrapper always provides a closed surface definition. If thefeatures of interest have been adequately captured by the wrapping processthen the next step is to improve the overall quality of the triangulation sothat a volume mesh can be made. This can be done by using the surfaceremesher model. As a starting point, the same surface sizes as used for thewrapper can be used for the remesher, but some boundaries may requiredifferent sizes in order to optimize the triangulation for the volumemeshing process.

To change boundary or reference sizes without invoking the surfacewrapper again, it is necessary to “break” the pipeline and both remove thesurface wrapper model and delete the original surface importrepresentation. This way, the wrapped surface becomes the starting pointfor the surface remeshing process.