The reinforcing and direct-embedding workflows have the following primary differences:
In a reinforcing workflow, the stiffness of the embedded members is captured via reinforcing (REINF
nnn) elements.In a direct-embedding workflow, the stiffness of embedded members is captured via standard structural, thermal, or coupled-field elements (such as BEAM188, LINK33, and LINK228).
In a reinforcing workflow, the bonded connection between the embedded members and base material accounts for the degenerated geometry of the embedded members (such as lines and surfaces) only. The cross-sectional geometry of the embedded members is ignored.
In a direct-embedding workflow, the bonded connection is formed between the cross-sectional geometry of the embedded members and the 3D geometry of the base material.
The direct-embedding workflow makes full use of the options and capabilities of the standard elements when those elements are used for modeling the embedded members. Generally, this workflow leads to more accurate models and fewer restrictions on the loading and boundary conditions of the embedded members. Because direct embedding does not account for the removal of base material, embedded element material properties must be significantly stiffer than the base material so that the inclusion of redundant base material does not impact the overall solution accuracy. Improper choice of embedded element material properties could lead to inaccurate solution results. In contrast, the reinforcing workflow does not have this limitation.
Reinforcing elements generated in the reinforcing workflow represent the simplified structural or thermal stiffness of the embedded members. Reinforcing elements share the same degrees of freedom with the base elements. When simplified reinforcing stiffness (such as uniaxial, plane stress, unidirectional, or planer heat flow) is adequate to capture the primary mechanical or thermal properties of the embedded members, use the reinforcing workflow to reduce computational cost.
The direct-embedding workflow supports standard line elements for modeling the embedded members. The reinforcing workflow is required for thin embedded surfaces.
The direct-embedding workflow supports coupled-field elements as embedded and base elements.
The direct-embedding workflow accounts for the actual cross-section geometry of the embedded members in the member/base connection modeling. Load transfer from the embedded members to the base material is not sensitive to base mesh overloading.
Table 14.4: Detailed Comparison of Reinforcing and Direct-Embedding Workflows
| Reinforcing (Standard) | Reinforcing (Mesh-Independent) | Direct Embedding | |
|---|---|---|---|
| Reinforcing (REINF) section | Required | Required | Not required |
| Degrees of freedom (DOFs) for embedded members | No independent DOFs | No independent DOFs | Independent DOFs |
| Stiffness of embedded members | REINFnnn elements | REINFnnn elements | Standard structural, thermal, or coupled-field elements |
| Partially embedded members | Not supported | Not supported | Supported |
| Meshing of embedded members | -- | Independent | Independent |
| Element solution | Via REINFnnn elements | Via REINFnnn elements | Standard structural, thermal, or coupled-field elements |
| Cross-section geometry of embedded members | Area / Thickness | Area / Thickness | Sections supported by standard structural or thermal elements |
| Mesh overloading | Susceptible | Susceptible | None |
| Loading on embedded member | Limited | Limited | All loads allowed by standard structural, thermal, or coupled-field elements |
| Boundary condition (BC) | -- | -- | All BCs allowed by standard structural, thermal, or coupled-field elements |
| Overlapping base element material removal | Supported | Supported | Not supported |
| Computational cost | Low | Low | High |
To overcome solution accuracy issues due to base mesh overloading, the base mesh can be optimized according to the reinforcing requirements via the MSHOPTIM command. For more details about the requirements and limitations, refer to the MSHOPTIM command.
Standard Reinforcing — The location and orientation of embedded members can be easily defined with respect to the base elements. For example, 3D smeared reinforcing elements are embedded in 3D shell or layered solid elements.
Mesh-Independent Reinforcing — The embedded and base elements do not share any common patterns. The cross-section geometry of the embedded members can be adequately represented with the area or thickness of the cross-section.
Direct Embedding — The cross-section geometry of the embedded members must be fully accounted for to capture the essential stiffness (such as bending and torsional stiffnesses) of the embedded members or to properly model the embedded and base element interactions (such as heat generation load transfer from embedded members to the base).