FLLWER

Bulk Data Entry Defines parameters for the calculation follower loads in large displacement nonlinear analysis.

Attention: Valid for Implicit and Explicit Analysis
Supported load types are:
Pressure load
PLOAD, PLOAD2, PLOAD4, PLOADSF, PLOADE1, PLOADX1 and PRSPENE
Concentrated load
FORCE1, FORCE2, MOMENT, MOMENT1, and MOMENT2

Format

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
FLLWER ID OPT              
The following continuation line is used to define another set of follower force parameters, which overrides the set of parameters above, for a specific follower (or DLOAD) load interface. It can be repeated as required.
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
+ LOADSET OPT LSID1 LSID2 LSID3 LSID4      
+ DLOADSET OPT LSID5 LSID6 LSID7 LSID8      

Example

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
FLLWER 99 2              
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
FLLWER 99                
+ LOADSET -1 8 12 13        
+ DLOADSET 1 9 14 15 16      
+ LOADSET 2 10 17 19 20 21    
+ 22 23 24            

Definitions

Field Contents SI Unit Example
ID Each FLLWER Bulk Data card must have a unique ID.

No default (Integer > 0)

  
OPT Options for the calculation for Follower Loads.
= -1, 0
Follower force calculation is not activated.
= 1 (Default)
Follower effect is activated. For a pressure load, both the element surface area and the load direction are involved to calculate the follower effect, and, the change in the z-coordinate is also considered if the type of the pressure is hydrostatic. For a concentrated force or moment, only the load direction is involved.
= 2
Follower effect is activated. For a hydrostatic pressure load, this option gives the same effect as the complete follower option FLLWER = 1. For other pressure loads, only the element surface area is involved. For a concentrated force or moment, only the load direction is involved (same as FLLWER = 1).
= 3
Follower effect is activated. For a hydrostatic pressure load, this option gives the same effect as the complete follower option FLLWER = 1. For other pressure loads, only the load direction is involved. For a concentrated force or moment, only the load direction is involved (same as FLLWER = 1).
  
LSIDi
LOADSET
The identification number of
  • a LOAD(ADD) Bulk Data Entry directly referenced by the LOAD in the Subcase Information section, or
  • a load set consists of supported Bulk Data Entries (FORCE, PLOAD4, etc.).
DLOADSET
The identification number of
  • a DLOAD Bulk Data Entry, or
  • a TLOAD1/TLOAD2 Bulk Data Entry.

No default (Integer > 0)

  

Comments

  1. The FLLWER Bulk Data Entry is selected by the Subcase Information command FLLWER = option.
  2. Follower options for concentrated loads (static and dynamic) and the hydrostatic pressure are currently only supported for large-displacement nonlinear static and large displacement nonlinear transient analysis subcases.
  3. Continuation (by use of entry CNTNLSUB) of a nonlinear solution from a preceding nonlinear subcase is supported. However, if a load set is applied in both subcases, the FLLWER option of the load set must be exactly the same in the two subcases.
  4. If for a subcase a load set is referenced by a LOAD and by a dynamic LOAD simultaneously, the follower option of this load set should be unique.
  5. Hash assembly is used for follower effect calculation by default.
  6. Follower load stiffness is generally un-symmetric. OptiStruct supports both symmetric solvers and un-symmetric solvers for the follower load case. The un-symmetric solver is activated using PARAM,UNSYMSLV,YES.
  7. Unsymmetric equation solver (PARAM,UNSYMSLV,YES) is recommended for better convergence in large displacement implicit nonlinear analysis with follower loads.
  8. The available follower options are listed below with the precedence being from low to high:
    • PARAM,FLLWER entry
    • OPT on the first line of FLLWER Bulk Data Entry
    • OPT assigned to an LSIDi, which is a top-level LOAD(ADD) or DLOAD entry (as in, the one directly referenced by the LOAD or DLOAD entry in the Subcase Information Entry section).
    • OPT assigned to an LSIDi, which is a loadset ID with label LOADSET or, a TLOAD1/TLOAD2 ID with label DLOADSET.

    An option with a high precedence would overwrite a lower one. Also, an LOAD(ADD) entry can reference another LOAD(ADD) entry, but the LSIDi of intermediate LOAD(ADD) entries are not supported.

  9. Follower effect is calculated by default for pressure loading even if PARAM,FLLWER, FLLWER Subcase Information Entry, or the FLLWER Bulk Data Entry are not specified for a large displacement (LGDISP) subcase.
  10. The follower effects of FORCE1, FORCE2, MOMENT1, and MOMENT2 are based on the vectors formed by the user-specified nodes, while that of FORCE/MOMENT is based on the rotation of the nodes.
  11. To activate the follower effect for FORCE/MOMENT, an additional flag, ROT is required. For more details, refer to the FORCE/MOMENT Bulk Data Entries.
  12. In case of Nonlinear Explicit Analysis (NLEXPL), follower loads are supported with DLOAD/TLOAD#, for all supported pressure loads, FORCE1, FORCE2, MOMENT1 and MOMENT2.
  13. This card is represented as a load collector in HyperMesh.