4.1. The Unidirectional Load-Transfer Method: Mechanical APDL to CFX

With this method, Mechanical APDL performs an analysis and writes out a profile file via the following command:

EXPROFILE, Ldtype, LOAD, VALUE, Pname, Fname, Fext, Fdir

The exported profile file contains both nodal coordinates and the load. The Ansys CFX preprocessor then reads the load profile and mesh files to set up a CFD analysis. EXPROFILE operates on the currently selected entities, and a sequence of steps is therefore required prior to issuing the command to ensure that necessary data are set and appropriate conditions are met. The following procedure outlines these steps:

  1. Create a component or assembly for the nodes where the loads will be exported.

    In the Mechanical APDL preprocessor (/PREP7), issue NSEL to select a subset of nodes, then issue CM to create a named component. If nodes from more than one component are to be exported into the profile file, issue CMGRP to group components into assemblies.

    NSEL, Type, Item, Comp, VMIN, VMAX, VINC, KABS
    CM, Name, Entity
    CMGRP, Aname, Cnam1, Cnam2, Cnam3, Cnam4, Cnam5, Cnam6, Cnam7, Cnam8

    When the mesh is created in Ansys Workbench, a named selection can similarly be created for a subset of nodes.

    Alternatively, Mechanical APDL also allows for load-transfer by flagging field surface and volume interfaces in the /PREP7 or /SOLU processor. Flagged surfaces sharing a common surface interface number will exchange surface load data; flagged volumes sharing a common volume interface number will exchange volume load data.

    For surface load-transfer across fields, use the following SF family of commands and the FSIN surface load label. Use the VALUE2, VAL2, and VALJ arguments to specify the surface interface number.

    SF, Nlist, FSIN, VALUE, VALUE2
    SFA, AREA, LKEY, FSIN, VALUE, VALUE2
    SFE, ELEM, LKEY, FSIN, KVAL, VAL1, VAL2, VAL3, VAL4
    SFL, LINE, FSIN, VALI, VALJ, VAL2I, VAL2J

    Following is a list of element types that support the SF family of commands for surface load-transfer with the field surface interface (FSIN) flag.

    Structural ElementsThermal Elements
    SOLID185SOLID70
    SOLID186SOLID87
    SOLID187SOLID90

    For volumetric load-transfer, issue BFE and the FVIN volume load label. Use VAL2 to specify the volume interface number.

    BFE, ELEM, FVIN, STLOC, VAL1, VAL2, VAL3, VAL4

    For additional information on FSIN and FVIN labels, see the SF family of commands and BFE.

  2. In the Mechanical APDL postprocessor, ensure that the Mechanical APDL database is the one saved after the solution and that the desired results are loaded into the database. Otherwise, issue RESUME to resume a database file into the program and then issue FILE to specify the data file corresponding to the desired results. For loads not specified directly via commands (such as SF or BF) and not yet loaded into the database (or not from the desired load step/substep), use SET or LCASE to read the data set at the desired load step/substep from the results file.

  3. Specify the unit labels for the transferred loads to be written in the file via EXUNIT, repeating the command for each unit label.

    EXUNIT, Ldtype, Load, Untype, Name

    The predefined units are:

    • Surface load Metric: SI

    • Volume load Metric: SI

    • Surface load English: FT

    • Volume load English: FT

    If the system of units is not the SI system, issue EXUNIT before the file is written (EXPROFILE); otherwise, the units written default to the SI system.

  4. Specify export options to include mesh connectivity and precision for the profile file (EXOPTION):

    EXOPTION, Ldtype, Option, VALUE

    Specify the mesh connectivity or precision for the surface load type, and the precision for the volume load type.

  5. Write the profile file for CFX by issuing (and reissuing for each load type) the following command in /POST1:

    EXPROFILE, Ldtype, LOAD, VALUE, Pname, Fname, Fext, Fdir

    Specify a surface or volume interface number (VALUE) for the load, field and file names for the profile file (Pname and Fname), and a profile file extension and directory (Fext and Fdir).

    If a surface or volume interface number (VALUE) is set to zero (default), the data for the selected subset of nodes is exported. You can issue CMSEL before issuing EXPROFILE, export previously defined nodes (CM or CMGRP), or use the named selection defined in Ansys Workbench.

    To export multiple loads, specify a unique file name for each load.

    EXPROFILE notes:

    • The nodes being exported must be selected. Loads on unselected nodes are not exported.

    • The underlying elements must also be selected.

    • All nodes of the element face must be selected; otherwise, all nodes on that face are ignored.

    • If higher-order elements are used in the model, the loads on midpoint nodes are properly redistributed to corner nodes if necessary so that only loads on corner nodes are exported.

    • For a cyclic symmetry analysis, select only the base nodes and elements, as the duplicate nodes are automatically selected by Mechanical APDL.

The following commands provide an example of exporting mass-average mode shapes from a modal analysis on previously defined nodes (ALLBLADESURFACE):

/post1
set,1,1                                    ! Load the results of interest
allsel,all                                 ! Select all entities
cmsel,s,ALLBLADESURFACE                    ! Select a subset of nodes for export

exunit,surf,disp,comm,si                   ! Specify standard SI unit for displacement
exunit,surf,mass,comm,si                   ! Specify standard SI unit for mass
exunit,surf,time,comm,si                   ! Specify standard SI unit for time

exoption,surf,precision,8                  ! Set 8 significant digits for the fractional part of real data 
exoption,surf,connectivity,on              ! Add face connectivity to the CSV profile file.
exprofile,surf,disp,0,'meshdisp',disp1,csv ! Export the mass-average mode shape
                                           ! to the CSV profile file (disp1.csv)