The context menu under “Shafts” or under groups allows to insert “3D elastic parts as shaft” or “3D elastic parts as housing”. A new part will then be shown in the shaft/group tree.
The 3D elastic parts combine the FEA beam model used for the usual shafts with 3D solid meshes. The stiffness of the 3D solids is reduced to a stiffness matrix, which is then considered in the solver for the beam model. On the first use of the 3D elastic part the reduced stiffness matrix is generated, which can take a while dependent on the size of the mesh. Afterwards the reduced stiffness is saved with the file and only needs to be regenerated if material, mesh or selections for faces are changed.
The 3D elastic parts are considered as stiffness and optionally by modal reduction. No mass is taken into account without modal reduction. Thermal expansion and weight are considered. A “3D elastic parts as shaft” must have the x-axis as rotation axis and a rotation speed can be defined. A “3D elastic parts as housing” can not rotate and should be fixed in space.
If the option “calculate displacements” for the 3D elastic parts is selected, the displacement field of the surface is calculated for each connected degree of freedom on initial calculation of reduced stiffness. This increases the initial calculation time and the file size, but allows to visualize the deformed shape afterwards. The same is valid for the option “calculate mode shapes”; this is used for visualization only, too.
In case modal analysis is supported, the displacement field and the mode shapes need to be calculated. Therefore options “calculate displacements” and “calculate mode shapes” won't affect the required time for reduction. They only affect the required file size.
If the option "use second order mesh" is activated quadratic shape functions are used instead of linear shape functions. An eight node hexahedral will get a 27-node hexahedral instead. As the number of nodes increase, reduction time and memory usage will increase too. Generally the second order mesh will be more accurate. It is better to use a larger mesh size and a second order mesh instead of a fine linear mesh.
On geometry import or generation an option "Generate second order mesh" in available at several locations. If this option is set, then a second order surface mesh will be generated. It will require approximately four times the memory compared to a linear mesh, but will lead to a better geometry approximation if "use second order mesh" is activated. The option at the import only affects the surface mesh while the option "use second order mesh" under "General" defined what type of 3D-mesh is used.
Selected faces are reduced to one node (or elastic bearing, gear or contact) and can be connected to a support element. Following options are available:
•An existing support can be selected. This support is then connected to the 3D-elastic part instead of the rigid environment
•A new support can be defined as possible for shafts. Only a subset of the available types in the shaft calculation is supported so far. It can be used to support an imported housing by a stiffness.
•A force can be added on the reduced node
•A shaft can be selected. This will lead to a connection to the shaft in all six degrees of freedom. It is the same as adding a weld-point to the shaft and connection this to the 3D-elastic part. The shaft can be selected for the reduction types 'rigid', 'average' or 'elastic contact'. In case of an 'elastic contact' the face will be kept cylindrical in each section but can deform over the axial position.
•"Set as fixed" is available for "3D-elastic parts as housing". This node will be connected to the rigid environment.
For the reduction of a face five options are available as connection type:
•average: The reaction force will be distributed on all nodes of the face and an average value of the displacement of the face will be used. This option will not stiffen the part.
•rigid: A rigid connection of the reduced node to all nodes of the face will be added. This will stiffen the part.
•elastic bearing: This option may only be connected to a roller bearing and will consider the elastic deformations of the part in the load distribution of the bearing. A license for the bearing calculation software including ring deformations is required. Currently an elastic outer ring is only permitted for axially fixed bearings.
•elastic gear: This option may only be connected to a cylindrical gear so far and will consider elastic deformations of a gear body. The shaft system option is required for this.
•elastic contact: This option may only be used with either a weld point or a cylindrical constraint for connection of faces in two parts both reduces as elastic contact. The dimensions of both contact faces have to be identical. In addition the connection to a shaft is possible.
