Substructures moving as rigid bodies
Features tested
Substructure's ability to move as a rigid body. The substructures undergo large rotation motions in analyses that generate negligible strain/stress in the substructure. Both static and direct-integration implicit dynamic analyses are verified. Problem description
A rectangular substructure is formed. The substructure is subjected to boundary conditions and concentrated loads specified at the retained degrees of freedom that create negligible strain in the substructure but generate large rotations of the model. In the static analyses the substructure is constrained using springs to prevent numerical singularities. A second identical mesh is defined without substructures. The displacements, rotations, and reaction forces should be nearly identical between the two equivalent analyses. Results and discussion
All results in the substructure are nearly identical to the results in the regular mesh.
Small-deformation substructures in large rotations
Features tested
Substructures that are subject to elastic small-deformations but undergo large rotations. Both static and direct-integration implicit dynamic analyses are verified. Problem description
The modes to be used are specified, and a rectangular mesh is formed. The loading and boundary contions specified at the retained degrees of freedom are such that elastic small-strain-inducing defomations occur on top of large rotations of the substructure. In the static analyses additional springs are used to prevent numerical singularities. Results are then compared to results obtained from equivalent analyses that do not use substructures. Results and discussion
All results in the analyses using substructures are nearly identical to the results obtained in the analyses using a regular mesh.
User-specified rotation/mirroring and transformations
Features tested
User-rotated or mirrored substructures that also exhibit elastic small-strain deformation in addition to large rotations. Problem description
A rectangular mesh is formed. At the usage level the substructure is either translated and rotated or mirrored. A second identical mesh is defined without using substructures but accounting for the user-specified rotation/mirroring. The displacements, rotations, and stresses should be nearly identical between the two equivalent analyses. Results and discussion
All results in the substructure are nearly identical to the results in the regular mesh.
Multi-level substructures in large rotations
Features tested
Multi-level substructures that undergo large rotations. Problem description
Three levels of substructures are created for this particular analysis. The lowest level is a 2 × 2 mesh of CPE4 elements. The next level comprises two of the first-level substructures, and the third level is the actual structure. The use of unsorted retained degrees of freedom is tested during the creation levels. The loading and boundary conditions specified at the retained degrees of freedom are such that elastic small-strain-inducing defomations occur in addition to the large rotations of the substructure. A second identical mesh is defined without substructures and the results are compared. Results and discussion
All results in the substructure are nearly identical to the results in the regular mesh.
Substructures and gravity loads
Features tested
Substructures subjected to fixed direction gravity loads. Problem description
A rectangular substructure is formed. A gravity load is then applied by accounting for the substructure's gravity load vectors during generation and by specifying a distributed load type GRAV at the substructure usage level. The loading is such that the substructure undergoes large rotations. An equivalent regular mesh is also created, and the results are compared. Results and discussion
All results in the substructure are nearly identical to the results in the regular mesh.
Substructures, connector elements, Coupling constraints, and rigid body constraints
Features tested
Multiple substructures connected with connector elements and coupling constraints in large motions. Substructures included in a rigid body constraint in large rotations. How to switch quickly from a rigid body model of a part to a small-strain large-motion representation of the same part. Problem description
The common 4-bar mechanism is analyzed (see Overconstraint Checks). The two-dimensional rigid bodies are meshed using CPE4 elements. The coupling constraints are used to attach connection nodes to the ends of each bar, and connector elements are used to enforce the appropriate kinematic constraints between the bars. The bars are gravity loaded, and the mechanism is driven by prescribing the available components of relative motion in connector elements. Since the four bars are identical in shape, only one substructure is generated. The substructure is then translated, mirrored, and rotated at the usage level to create four copies of the substructure in the appropriate locations. Results from both static and direct-integration implicit dynamic analyses are verified against equivalent analyses that do not use substructures. In addition, at the usage level one of the substructures is turned into a rigid part. The attached input files illustrate how one can very efficiently switch from a rigid (faster to run) model (substr_4barrb_solid2d_sta.inp and nosubstr_4barrb_solid2d_sta.inp) to a small-deformation large-rotations efficient subtructure representation of the same model (substr_4bar_solid2d_sta.inp). The substructure analysis is typically significantly faster to run than the regular mesh models (nosubstr_4bar_solid2d_sta.inp). Results and discussion
All results in the substructure are nearly identical to the results in the regular mesh.
Substructures and contact
Features tested
Large rotation substructures and contact. Problem description
A rectangular substructure is formed. The applied loads and boundary conditions are such that the substructure exhibits large rotations. After a 45° rotation, impact with a rigid surface occurs. Results are compared with results from an equivalent model without substructures. Results and discussion
All results in the substructure are nearly identical to the results in the regular mesh.
Miscellaneous tests
Features tested
Substructures with large rotations with multi-point constraints, model change, prescribed initial conditions, and restart analysis. Problem description
Several input files are created to test various features with large rotation substructures. Results are compared with equivalent models that do not use substructures. Results and discussion
All results in the substructure are nearly identical to the results in the regular mesh. |