7.5          Free-Field Motion Options

 

7.5.1       Write Free-Field Motion Request

 

WRITE_MOTION

 

            WRITE_MOTION           file_name = "<string>"

 

 

 

Note    Variable Name   Default               Description

 

(1)        File_name            [none]                Name of file to contain motion.  Name must be

                                                                     enclosed in quotation marks.

 

 

Notes/

(1)        This option allows the computed motion of all nodes to be written on a file.

 

 

7.5.2       Read Free-Field Motion Request

 

READ_FREE_FIELD_MOTION

 

            READ_FREE_FIELD_MOTION       file_name = "<string>"

 

 

 

Note    Variable Name   Default               Description

 

(1)        File_name            [none]                Name of file which contains motion.  Name must

                                                                     be enclosed in quotation marks.

 

 

Notes/

(1)        This option allows the motion to be read from a file.

 

 

 

7.5.3       Filter Free-Field Motion Request

 

FILTER_FREE_FIELD_MOTION

 

            FILTER_FREE_FIELD_MOTION             start_node_number = start, etc...

 

This allows the motions of nodes in the free-field to be filtered to remove rigid body motions induced by liquefaction in the free-field.  The motions of all nodes: starting node to ending node by node generation increment, relative to the motions of the reference node number, are then filtered.

 

Note    Variable Name                          Type       Default       Description

 

            Start_node_number                 integer         [0]           Starting node number > 0

 

            End_node_number                  integer         [0]           Ending node number  

                                                                                                     start_node_number

 

            Generation_increment             integer         [0]           Node generation increment

                                                                                                     number  0

 

            Reference_node_number        integer         [0]           Reference node number  0

 

            Low_cut_off_frequency            real         [0.05]         Low cut-off frequency

                                                                                                      (in Hertz) (unit: 1/T)

 

            High_cut_off_frequency           real      [1/(2*Dt)]     High cut-off frequency

                                                                                                     (in Hertz) (unit: 1/T)

 

            Transition_band_width              real      [low/2]      Transition band width

                                                                                                     (in Hertz) (unit: 1/T)

 

 

 

 

 

7.5.4       Free-Field Nodes Data

 

FREE_FIELD_NODES

 

 

            FREE_FIELD_NODES          file_name = "<string>", etc.

 

 

This command is used to input free-field nodes data.  The free-field motion may be prescribed by either assigning the motion of mesh nodes to be the same as computed in previous free-field computations (see Section 7.5.2), or by using a consistent interface boundary (see Section 9.2.1 and/or Section 9.15.1).

 

Note    Variable Name                 Type     Default      Description

 

            Type                                   list        [none]       Free_field type

                 prescribed

                 consistent

 

            Free_field_motion             list        [displ]       Motion type

                 displacement

                 velocity

                 acceleration

 

            File_name                        string      [none]       File name (optional).
                                                                                    Name must be enclosed in quotation marks.

 

• Prescribed Case:

            Free_field nodes data must then follow in the form (Section 7.5.4.1):

                 < Node 1, Node 2, ng, (idof(i), i=1, Ndof) >

                 < etc..., terminate with a blank record >.

 

• Consistent Case:

            Free_field nodes data must then follow in the form (Section 7.5.4.2):

                 < Inside_nodes >

                 < Node_number, load_time_function_number, (load_dof(i), i=1, Ndof) >

                 < etc…, terminate with a blank record >

                 < Outside_nodes >

                 < Node_number, load_time_function_number, (load_dof(i), i=1, Ndof >

                 < etc…, terminate with a blank record >.

 

 

 

 

 

7.5.4.1    Prescribed Free-Field Nodes Data

 

Nodes may be assigned to have the same motion as nodes in the free-field (computed previously) for selected degrees of freedom. Such an option is useful for modeling free-field conditions in seismic calculations. Use of this option must be preceded by a READ_MOTION command (see Section 7.5.2).

 

Note    Variable Name                 Type     Default      Description

 

(1)             Node1                        integer       [0]           Node number 1 (node number in the mesh )

 

                 Node2                        integer       [0]           Node number 2 (node number in the

                                                                                          free-field mesh)

 

(2)               NG                          integer       [0]           Generation increment

 

                IDOF(1)                      integer       [0]           Degree of freedom number

 

                IDOF(2)                      integer       [0]           Degree of freedom number

                      .                                                .                              .

                    etc.                                              .                              .

                      .                                                .                              .

           IDOF(NDOF)                 integer       [0]           Degree of freedom number

 

 

Notes/

(1)        Node number NODE1 is assigned to have the the same motion as node number NODE2 in the free-field, for the degrees of freedom listed on that record. Terminate with a blank record.

 

(2)        Free-field condition data can be generated by employing a two record sequence as follows:

 

            Record 1: LODE1, LODE2, LG, IDOF(1),..., IDOF(NDOF)

            Record 2: NODE1, NODE2, NG, IDOF(1),..., IDOF(NDOF)

 

The free-field conditions codes of all nodes:

 

            LODE1 + LG, LODE1 + 2*LG,..., NODE1 - MOD(NODE1 - LODE1, LG)

            LODE2 + LG, LODE2 + 2*LG,..., NODE2 - MOD(NODE2 - LODE2, LG)

 

(i.e., less than NODE1) are set equal to those of node LODE1. If LG is blank or zero, no generation takes place between LODE1 and NODE1.

 

 

 

7.5.4.2    Consistent Free-Field Data

 

            Nodal data are required for both inside and outside nodes.  Following the corresponding keyword:  "Inside_nodes" or "outside_nodes", nodal data follow as:

 

Note    Variable Name              Type       Default      Description

 

           Node_number               integer          [0]        Node number

 

                   ltime                      integer          [0]        Load_time function number

 

              load_dof(i)                    real            [0.0]      Multiplier for degree of freedom i (i=1, Ndof)

 

 

 

References / Bibliography

 

1.            Bielak, J. and Christiano, P., "On the Effective Seismic Input for Non-Linear Soil-Structure Interaction Systems," Earthquake Engineering and Structural Dynamics, Vol. 12 (1984), 107-119.

 

2.            Cremonini, M, Christiano, P. and Bielak, J., “Implementation of Effective Seismic Input for Soil Structure Interaction Systems,” Earthquake Engineering and Structural Dynamics, Vol. 16 (1988), 615-625.