====== D Command ======

D,<n1>,<n2>,[<inc>],[<val>],<labe1>,[<label2>,...<label6>]

where <label i> can be UX, UY, UZ, DISP, ROTX, ROTY, ROTZ, ROT, or ALL

defines the boundary conditions for the nodes between <n1> and <n2> with step <inc>, <val>=0 for free DOF ,<val>=1 for fixed DOF, and <val> = 2 for DOF controlled by another node (rigid body). This instruction is used to generate the kinematic boundary conditions after the nodes have been previously defined. This fact allows a greater flexibility for the node generation procedure. The default values are: 0 for <val> and 1 for <inc>.

**Note:** Rigid body motion has been deprecated in this version of the SASSI User Interface.

**Note:** Concentrated masses ([[com:MT]] and [[com:MR]] Commands), forces ([[com:F]] Command), or moments forces ([[com:MM]] Command) may be applied on the free degrees of freedom. A fixed degree of freedom does not allow the node to translate or rotate in that direction. Any concentrated masses or forces assigned to this degree of freedom are ignored by ACS SASSI [[SASSI:PREP]] and [[SASSI:acs-sassi_user_interface]].

Removing unwanted degrees of freedom has the advantage of reducing the size of the set of equations that must be solved. The following table lists the degrees of freedom that are defined for each element type. ([[com:GROUP]] Command)

^Element ^DOF with defined stiffness/mass ^^^^^^
^Type ^X ^Y ^Z ^XX ^YY ^ZZ ^
^SOLID |•|•|•| | | |
^BEAM  |•|•|•|•|•|•|
^SHELL  |•|•|•|•|•|•|
^PLANE  |•| |•| | | |
^SPRING  |•|•|•|•|•|•|
^GENERAL  |•|•|•|•|•|•|
^LOVEWAVE  |•|•|•|•|•|•|

**Note:** for example, that for solid elements, only the translations are defined at the nodes. If a node is common to two or more element types, then the non-trivial degrees of freedom are found by combination. For example, all six components are possible at a node common to both beam and solid elements; i.e., beam governs. Symmetrical structures (with symmetrical loading only) may also be analyzed by modelling only one half or one quarter of the structure and constraining appropriate degrees of freedom on the planes of symmetry. ([[com:SYMM]] Command)