Checking and orienting the normals of 2D elements

Use the 2D Element Normals command to:

• Display the normals of 2D elements.

• Reverse the normals of 2D elements.

• Change the orientation of selected 2D elements to match the orientation of a specified seed element.

• Create a group of inconsistent 2D elements.

• Create groups of element subdomains

• Automatically align the normals of a selected set of elements.

Importance of consistent normals for 2D elements

All 2D elements have a normal (perpendicular) that establishes their top and bottom. Consistent elements normals help ensure the overall quality of your FE model.

For example, consistent normals are important for:

• Properly defining contact between surfaces.

• Modeling laminate composites.

• Post-processing stress or strain results for 2D elements.

• Checking the element normals of all 2D elements, which must be oriented outward in the direct BEM exterior acoustic solutions.

• Checking the element normals of all 2D elements, which must be oriented in the same direction either all outward or all inward in the indirect BEM acoustic and vibro-acoustic solutions.

The positive normal direction of an element is defined by the right-hand rule, following I, J, K, L nodal sequence as shown below:

Checking and reversing element normals

You can check the normals of:

• All displayed elements.

• Selected elements only.

The software displays an arrow symbol on each element or two different colors on element faces. The green elements represent the faces with outward-facing normals and the red elements represent the faces with inward-facing normals.

After you check the elements’ normals, you can use the Reverse Normals command in the 2D Element Normals dialog box to reverse the direction of the normals. When you click Reverse Normals, the software reverses the normals for all 2D elements on the selected face or within the selected mesh. When you reverse an element's normal, you reverse the connectivity of that element. For example, if the software created the element's nodes in the order of 1,2,3,4, the order becomes 4,3,2,1 when the connectivity is reversed.

Note:

If you reverse an element's normal, the software maintains that reversal across all mesh updates.

Creating a group of inconsistent element edges

You can use the Create Inconsistent Element-Edge Group button in the 2D Element Normals dialog box to create a group of the inconsistent 2D elements in your mesh. If two neighboring elements have a different orientation, these elements are considered inconsistent elements. The software creates an Inconsistent 2D Elements group in the Simulation Navigator under the Groups folder. This group might be useful if you want to inspect the element connectivity in more detail.

Creating a group of element subdomains

When you check element normals, the software internally groups the elements into different subdomains. A subdomain is a part of mesh that:

• Is bounded by free element edges.

• Is delimited by junctions, such as T-type junctions between faces.

• Can include non-manifold element edges.

For example, the software places elements that lie on non-contiguous faces, such as faces at non-manifold junctions, into different subdomains.

You can use the Create Subdomain Element Group button to have the software create permanent groups that contain the elements from each individual subdomain domain. The software creates the Subdomain_ groups in the Simulation Navigator under the Groups folder.

You can use the subdomain element groups, for example, to more easily apply boundary conditions in the Simulation file.

Automatically align 2D element normals

When you use the 2D Element Normals dialog box to orient 2D element normals, you can select Automatic from the Orientation Method menu to have the software orient the normals automatically. With the Automatic method, the software aligns the normals of all the 2D elements in a specified domain that:

• Is bounded by free element edges.

• Can include non-manifold element edges.

The Automatic method lets you accurately and efficiently align element normals, especially in complex models that include a high number of junctions. Proper alignment of 2D element normals is particularly important for the accuracy of Simcenter 3D Acoustics BEM analyses, which use the boundary element method (BEM) to solve interior and exterior acoustic and vibro-acoustic problems.

Inconsistent element normals	Automatically aligned, consistent element normals

Changing the orientation of element normals based on the normal of a seed element

Use the Orient Normals by Seed Element option to orient the normals of 2D elements to match the normal of a selected seed element. The seed element is an element whose orientation is in the desired direction.

You can use the Orient Normals by Seed Element option to quickly modify the normals of elements so that they are consistent.

Note:

If you want your selection to stop at the end of a non-manifold edge, you should first merge any coincident nodes before you use the Orient Normals by Seed Element option. To merge coincident nodes, use the Duplicate Nodes command.

Where do I find it?

Application	Pre/Post
Prerequisite	A FEM file or Simulation file as the work part and displayed part
Command Finder	2D Element Normals
Simulation Navigator	Right-click the 2D Collectors collector container→Check All→Element NormalsorRight-click the 2D mesh collector→Check→Element Normals

Learn more

Checking your finite element model

Checking for free and non-manifold element edges

Aligning the first edges of 2D elements

Checking and orienting the directions of 1D elements

Checking and orienting the normals of 3D element faces

Checking aerodynamic panel meshes

Checking for duplicate elements and nodes

Detecting interference and clearance issues between faces

Checking CAE model consistency

Checking the association of nodes to geometry

Checking the completeness of your model prior to a solve

Computing mechanical loads

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Checking and orienting the normals of 2D elements, Simcenter 3D 2021.1 Series

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