NASTRAN File: Case Control Statements

Description

This section specifies load case definitions and defines data input and output selections. In addition to primary load case data, Straus7 also supports the import and export of secondary load case combination data.

Importing

Straus7 imports linear load case combination data. Other data is ignored. There are four steps involved in reading the case combinations:

  1. For each instance of SUBCASE, the corresponding load set ID is stored. For example,

    SUBCASE 4

    LOAD = 12

    indicates that load set 12 is referenced by subcase 4.

  2. For each instance of SUBCOM, a Straus7 load case combination is created, with the title assigned based on LABEL. The load case combination factors specified by SUBSEQ are used to define the combination factors. For example,

    SUBCOM 2

    LABEL = Wind + Gravity

    SUBSEQ = 0.3,0.2,1.0,0.7,0.2

    indicates that Secondary Load Case 2 has the title "Wind + Gravity", and has the case combination factors 0.3, 0.2, 1.0, 0.7, 0.2. These numbers refer to subcases, not to load cases.

  3. The subsequent sections of the NASTRAN file are imported. A new load case is created each time an attribute is read that uses a load case that does not yet exist.

  4. The load case combination factors are posted for each secondary load case. For a given SUBSEQ entry, the position of the factor indicates which subcase the factor is applied to. For example, suppose the secondary case "Wind + Gravity" has factors of 0.3, 0.2, 1.0, 0.7, 0.2. The coefficient 0.7 is in position four and hence factors the Straus7 load case that references subcase 4.

NASTRAN also uses LOAD entries to specify load case combinations at the load set level. Straus7 uses this information when importing attributes into each primary load case. LOAD entries do not correspond to Straus7 linear load case combinations.

Exporting

Straus7 issues a set of default statements, which may need to be reviewed before the model can be run in NASTRAN. The case control statements exported depend on the number of load and freedom cases in the Straus7 model.

Straus7 exports the linear load case combinations following the primary load and freedom case definitions. For example, suppose Straus7 contains the following load case combinations:

Primary load cases:

"Wind"

"Gravity"

"Earthquake"

Secondary load cases:

"Half wind" = 1.0*Gravity + 0.5*Wind

"Full wind" = 1.0*Gravity + 1.0*Wind

"Full quake" = 1.0*Gravity + 2.0*Earthquake

The additional case control data exported would be:

SUBCASE 1

SUBTITLE = Wind

LOAD = 1

SUBCASE 2

SUBTITLE = Gravity

LOAD = 2

SUBCASE 3

SUBTITLE = Earthquake

LOAD = 3

SUBCOM 1

SUBTITLE = Load Combination 1

LABEL = Half wind

SUBSEQ = 0.5,1.0,0.0

SUBCOM 2

SUBTITLE = Load Combination 2

LABEL = Full wind

SUBSEQ = 1.0,1.0,0.0

SUBCOM 3

SUBTITLE = Load Combination 3

LABEL = Full quake

SUBSEQ = 0.0,1.0,2.0

Straus7 linear load case combinations are only exported as SUBCOM entries.

See Also