Elevate

The Elevate command provides tools for elevating and exporting high-order meshes from existing structured, unstructured, and voxel blocks.

Elevate, Elevate Tab
Use the tools in the Elevate panel to elevate and export high-order meshes.

The recommended starting point to use the Elevate command is a set of valid initialized structured, unstructured, and/or voxel blocks. Once this initial condition is met, the command is designed to elevate the linear (or Q1) mesh to the desired higher order, perform smoothing to ensure the quality of the curved high-order elements, and export the high-order mesh to the desired CAE formats.

 

Caution: Due to the nature of polynomial elevation (which adds additional mid-edge, mid-face, and mid-volume nodes to each cell), producing a high-order mesh can be a lengthy and computationally expensive process for larger grids.

After entering the command, you will be presented with the Elevate panel shown above. The panel is split into two tabs: Elevate and Export Options.

High-Order Elevation Overview

The elevation process consists of two primary phases, the curving phase and the weighted condition number (WCN) smoothing phase, which are intertwined. During the curving phase, the initial linear (or Q1) mesh is incrementally elevated one polynomial order at a time to the final desired polynomial order (Q2, Q3, Q4, or a mixture of Q1-Q4). For cells adjacent to database constrained domains, the high-order nodes of the constrained face are projected to the geometry.

Illustration of a curved and linearly interpolated high-order
                                           boundary face.
The high-order nodes are placed on the underlying database (shown in blue) or, if the domain is free, using linear interpolation (shown in red).
 

Tip: Minimize the Database Deviation and Relative Database Deviation examine metrics to reduce the total amount of curving required during high-order elevation.

Since cells within a viscous boundary layer are highly anisotropic, the curving phase typically causes the cells adjacent to the geometry to become self-intersecting. WCN smoothing is then performed after each order pass of the curving phase to restore these cells to a valid, high quality state.

AltText
After the high-order nodes are projected onto the geometry, some cells may either be self-intersecting (shown left in red) or may have edges that intersect the geometry (shown left in yellow). WCN smoothing is performed to return all cells to a valid, high quality state (shown right).

During WCN smoothing, each cell's quality is computed using a cost function which has both a weighted condition number component and a normalized Jacobian component. The weighted condition number component is used to preserve the shape of the linear cell in the high-order cell. The normalized Jacobian component ensures validity of the resulting high-order mesh and takes precedence if any Jacobians within that cell are negative. Each smoothing pass uses an incrementally more accurate approximation of the Jacobian across the high-order cell and there may be up to ten passes in total.

Once WCN smoothing finishes and all cells have positive Jacobians, the high-order mesh is exported to the CAE formats prescribed on the Export Options tab.

When elevating and exporting a high-order mesh, please note the following:

Troubleshooting

The table below shows some of the more common error and warning messages that may be encountered during the high-order elevation process and recommendations on how to address the issues.

 

Tip: The most common reason for mesh elevation and curving to fail is improper geometry association. Ensure that Pointwise domains on the model surface are fully associated with the geometry. For domains, this can be done from the Attributes tab in the unstructured domain and structured domain solvers. It is also recommended to use the Project Shape option in the Projection Control frame when projecting connectors

Type Message Recommendation
Error Domain is used in a baffle. The elevation process detected a domain that is used as a baffle. The elevation process does not currently support baffles. Remove all baffle domains from the mesh.
Error Domain is not fully constrained on its interior. The elevation process detected a domain that is only partially constrained to the geometry surface. Inspect the domain and either fully constrain it to the surface or split the domain so that the constrained and unconstrained portions are separate.
Error Domain is non-manifold. The elevation process detected that a domain is being referenced more than two times in the definitions of the selected blocks. This topology is non-manifold and is not allowed. Inspect the block selection and modify accordingly to ensure all block interfaces are manifold.
Warning Domain is unconstrained non-planar. The elevation process detected a domain that is non-planar in shape and is not constrained to the geometry. Inspect the domain and if curving is desired, constrain it to the surface. Otherwise, the mesh elevation process will retain the linear cell shape for all of the faces in the domain and no action is required.
Warning Locked # mesh faces due to geometry projection issues. A mesh face constrained to a geometry surface has a vertex which is excessively far from the surface. Inspect the linear mesh in the region of the geometry violation. If the linear mesh is acceptable, no action is required as the offending faces will be frozen to the linear shape in the curved mesh. If the linear mesh is unacceptable it should be corrected before attempting to elevate.
 

Tip: Another common issue encountered during high-order elevation is the use of models that have a large model assembly tolerance compared to the mesh element size. If the large model assembly tolerance cannot be avoided, consider splitting the domain to allow for a portion of the mesh to be unconstrained, and thus require no curving.

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