Take Advantage of Repeatedly Used Components in CAD by Instance Meshing in ANSYS Mechanical

Repetitive meshing tasks can be a significant portion of the time a user spends setting up an FEA model for simulation. In cases where components are reused multiple times in an assembly, the meshing can be tedious.

Select 20 of the exact same face in a bolt circle to specify the number of elements on an annulus…

Select the 20 bodies that those 20 faces belong to for a mesh method…

What if the number of bodies/faces/even edges is larger? Continue reading

Design of Roll Over Protection Systems and Trailer Rear Impact Guards Using ANSYS Mechanical Energy Absorption Calculations

Many companies use ANSYS to reduce chance of injury and death when an accident occurs such as the overturning of a tractor or the rear impact crash of a car into the back of a trailer. An effective method to minimize danger to vehicle occupants during an accident is to ensure that that the structure absorbs sufficient energy through plastic deformation during the accident impact.

Many vehicles have Roll Over Protection Systems (ROPS) to reduce injury to operators. Figure 1 shows a Bobcat skid steer loader including its ROPS, which is the black cage structure surrounding the driver. Continue reading

The Impossible is Now Routine

Sometimes, during the course of doing what you might have thought was a routine simulation, you realize that you are doing something that didn’t used to be routine.  In fact, it may have been impossible without advances in software and hardware in recent years.

Recently, DRD was conducting stress simulation for a casting assembly from Davis Tool & Die of Fenton, MO. As the geometry was meshed and examined, small details of the casting continued to become evident and additional refinement was needed.  As seen in the images below, the model became quite large. Continue reading

Tricks for Producing Averaged Results for Surfaces or Volumes In ANSYS Mechanical

Occasionally it may be a requirement to report average values of stress or strain from an ANSYS Mechanical analysis. There are tricks to do this either for a group of nodes/elements on a face or elements within a specific volume.

Depending on the requirement, the goal may be to simply report either :

– “Average” stresses on a face (based on nodes)
– “Average” stresses on a face (based on elements)
– “Average” stresses on a volume (based on elements)

Technique 1 : Reporting weighted area average nodal stress Continue reading

Transferring Deformed Geometry Between ANSYS Applications

Often there is a need to export the deformed geometry from ANSYS Mechanical. Possibly to a 3D printer to show to customers, or maybe a new CAD geometry file is needed that can be used for drawings or further design evaluation. Starting with Release 17, Mechanical offers two options for users for doing this task.

Exporting STL (Standard Tessellation Language) files from the deformed results is one option. The STL file may be opened within ANSYS SpaceClaim Direct Modeler and reverse engineered to create deformed solid geometry from the STL facets. Continue reading

Determining the Interior Wall Direction in ANSYS Fluent

Boundaries in ANSYS Fluent can be broken into two groups: external boundaries and internal boundaries.  External boundaries appear on the outer boundary of meshed regions (inlets, outlets, interfaces, etc.), while internal boundaries exist within a conformal mesh (interiors, porous-jumps, fans, etc.).  Internal boundaries are not limited to only residing inside a cell zone (for example they can separate two different cell zones); instead their restriction is simply that the mesh be continuous across them.  There is one boundary type that can be used as either an external or internal boundary: walls.

While external walls are fairly self-explanatory, internal walls are called coupled walls (or two-sided walls) because they are actually formed by a pair of wall boundaries that are by default coupled together.  You most often see coupled walls separating Fluid and Solid cell zones, but they can also be used with as infinitely thin baffles with fluid on both sides.  Each coupled wall pair shows up in the boundary list as a zone and its shadow: one for each side of the wall.  Sometimes it is necessary to set different boundary conditions on either side of the coupled wall.

Continue reading

Boundary Condition Setup of Zero Thickness Baffles in ANSYS CFD

Last week we discussed the different ways to create and mesh infinitely thin baffles using the tools in ANSYS Workbench.  In this blog, we’ll discuss how to create and modify baffles using the two flagship ANSYS CFD programs: CFX and Fluent.

CFX:

In CFX, the method you use to specify your baffles depends on your modeling intent, but the way the baffles were meshed will affect some of our choices. The two methods are as a ‘baffle boundary condition’ or defining a ‘baffle interface’.

Baffle Boundary Condition

Baffle walls can be created by inserting a boundary condition into the surrounding domain and selecting the appropriate faces.

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Baffles created this way are for directing flow only!  Boundaries in CFX are always treated as leading to the exterior of the solved domain, which mean information cannot be passed from one side to the other (e.g. no heat transfer across the faces).

Baffle Interface

Alternatively, you can connect one side of a baffle face to the one facing the opposite direction by creating an Interface.

Face selection will depend on whether you made a conformal baffle (Default Method, Option 1, or Option 2 in Part 1 of this blog) or a nonconformal baffle (Option 3).  For nonconformal baffles, you can create Named Selections for each side of the baffle and then pick those from a list.  For conformal baffles, technically only 1 face exists for both sides in the Mesher, so the Named Selection can’t be used to specify side dependent locations.  That being said, conformal baffles will create 2 identical face IDs with different body IDs representing each side, and if you pick them for Side 1, CFX will automatically populate Side 2 with the appropriate pair.

bc2bc3

The interface will then need to be set as a wall, and additional interface models can be specified for the different equations.  For example, for Heat Transfer you can specify that the baffle provides a thermal resistance of a certain thickness of some defined material.

 

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Heat transfer in this case is purely through-thickness.  In other words, heat can flow through the thickness of a metal baffle, but a high temperature would not conduct along the length of the baffle; instead the heat would spread through the adjacent fluid (and then interact with the wall at that the next location).

Fluent:

In Fluent, the method you use to specify your baffles is controlled by how the baffles were meshed, but modelling intent will still affect some choices therein. These methods we will separate between Conformal and Non-Conformal.

Conformal Baffles

Baffles formed by conformal meshes within a Part (Default Method, described last week in this blog) will come into Fluent as a coupled wall, consisting of a boundary zone and its shadow.  These zones represent the two opposite-facing sides of the baffle.

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For the equations other than momentum, each side of the coupled wall can be treated individually or jointly.  For example, the default thermal behavior is to couple each side of the wall together using either a direct mapping of temperature (0 Wall Thickness) or using a specified thermal resistance (nonzero Wall Thickness), but you could instead set one side to have 0 Heat Flux and the other side to be a specific temperature.

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Much like CFX, entering a Wall Thickness will provide a thermal resistance in the through-thickness direction.  However, Fluent additionally has a model called Shell Conduction that allows for heat transfer along the baffle in addition to through it.

Non-Conformal Baffles

Baffles defined by non-conformally meshed faces (i.e. Option 3 in last week’s blog) require different actions depending on whether you are using them to direct flow only or to additionally pass information.

Non-conformal baffles are exterior faces in the mesher, so if you only need them to direct the flow, they will automatically do so without any user intervention (note that if you also have a non-conformal mesh across regions where there are no baffles, you will need to have an interface across those faces).

If you do need to pass information across the baffle (like heat flow), you must create a non-conformal interface using the coupled-wall option.

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This will create 4 addition zones: the Boundary Zones (Side 1 & 2) which are used to control the wall information for areas where the two sides do not line up, and the coupled wall Interface Wall Zones (Side 1 & Side 2) which are used to specify the wall behavior when there is overlap between the two sides.  From here, the coupled wall Interface Wall Zones can be set as described in the Conformal Baffles section, other than that Shell Conduction is not supported (through-thickness heat transfer is still allowed).

One important thing to remember here is that Fluent non-conformal interfaces regularly experience trouble with significant overpenetration between the two sides of the interface.  This typically occurs when there are different mesh sizes on either side of a curved interface.  To combat this, you can enable the Mapped Interface Option, which will use an alternative heat transfer calculation across the coupled wall that performs much better with excessive mesh penetration.

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