Skip to main content

REXS Specification

Assembly Groups

The following describes the modeling system for FE and CAD assemblies in the REXS interface.

Assembly groups | assembly_group

The assembly_group component can supplement a single analytical component (e.g., shaft, casing) or an assembly of analytical components (e.g., planet carrier).

The analytical components and their relations are retained. Each analytical component that is supplemented by an assembly_group ergänzt also has a "reference" relation to the assembly_group.

This assembly-group serves as a container for FE or CAD information on the assembly and has a position and orientation in space (local coordinate system).

  • If a .rexsz file is used, the "folder" attribute can assign a folder in the zip file to the assembly group

  • This folder (which may also contain a subfolder structure) contains the FE and CAD files which represent the assembly group

  • If coordinates are used in the files, they must refer to the local coordinate system of the assembly group

  • Connecting FE assembly groups to the analytical components (e.g., via reduced stiffness matrix) is described in the "connecting FE assemblies and analytical components" section.

Required components

XML syntax

Planetary stage

<component id="30" type="assembly_group"> ... </component>                        

Required relations

XML syntax

Reference relation

<relation id="45" type="reference">
	<ref id="2" role="origin" hint="gear_casing"/>
	<ref id="30" role="referenced" hint="assembly_group"/>

CAD components/groups

A *.stp/*.step format is expected for CAD representation of the assembly_group.

FE components/groups

In principle, any FE format can be saved in the corresponding folder for the assembly. The "fem_file_format" attribute is used to identify the FE format used.

All relevant files must be in the assembly_group folder (see "folder" attribute). Constraints, materials, reduction information, etc. are specified directly in the FE files in the respective format.

Associating FE assemblies and analytical components

So-called reduction points are used for the mechanical coupling of an FE assembly and analytical components. These form the interface between the FE assemblies (in which a node typically has a displacement of 3 degrees of freedom) and the analytical mechanical model (in which a node typically has a displacement and rotation of 3 degrees of freedom). Bearings, couplings, or external forces can be located at reduction points. "Free" reduction points that are not connected with the analytical model can also be defined.

The specific type of coupling between the reduction point and the nodes of the FE assembly is not included in the REXS file; this can only be stored in the FE files. The influence of a reduction point on another reduction point can be stored in the REXS model; for example, in the form of a reduced stiffness matrix.

Separate reduction_point components must be created for every reduction point in the assembly. This is associated with the assembly_group via an ordered_assembly relation. The "reduction_point" is also linked to connected (analytical) components (bearings, couplings, external loads) via a reference relation, unless it is not connected to the analytical model. A reduction_point also has a position in space (support_vector attribute).

For an assembly with n reduction points, the associated reduced stiffness matrix (for static calculations) can then be stored in the "reduced_static_stiffness_matrix" attribute. The dimensions of the matrix are 6n x 6n. The matrix entries are assigned to the reduction points as follows: the lines and columns of the matrix are divided into blocks of 6 for each reduction point. The order of the blocks corresponds to the "order" in the "ordered_assembly" relations between the assembly_group and the reduction points. In a block, the order of the degrees of freedom is always: dispU, dispV, dispW, rotU, rotV, rotW. The entries of the matrix are relative to the local coordinate system of the assembly_group. Sign (+/-) rules correspond to a right-handed, rightward-rotating coordinate system.

Reduction points | reduction_point

Required components

XML syntax

Reduction point

<component id="31" type="reduction_point"> ... </component>

Required relations

XML syntax

Ordered assembly relation

<relation id="45" type="ordered_assembly" order="1">
	<ref id="30" role="assembly" hint="assembly_group"/>
	<ref id="31" role="part" hint="reduction_point"/>

Reference relation

(only if the reduction point is coupled to analytical components)

<relation id="46" type="reference">
	<ref id="31" role="origin" hint="reduction_point"/>
	<ref id="35" role="referenced" hint="coupling"/>

FE casings and inertial system

A REXS model can contain multiple gear_casing components. A bearing in the (analytical) gear_casing corresponds to a bearing in the inertial system ("rigid casing"). Each gear_casing component can be extended by an assembly component to represent an FE (partial) casing. Specifically, an FE casing can be coupled with another gear_casing component via a coupling component (for example, to represent a soft coupling to the inertial system).