CE

CE, NEQN, CONST, NODE1, Lab1, C1, NODE2, Lab2, C2, NODE3, Lab3, C3
Defines a constraint equation relating degrees of freedom.

MP ME ST PR PRN <> EM DY PP EME MFS

NEQN

Set equation reference number:

n

 — 

Arbitrary set number.

HIGH

 — 

The highest defined constraint equation number. This option is especially useful when adding nodes to an existing set.

NEXT

 — 

The highest defined constraint equation number plus one. This option automatically numbers coupled sets so that existing sets are not modified.

The default value is HIGH.

CONST

Constant term of equation.

NODE1

Node for first term of equation. If -NODE1, this term is deleted from the equation.

Lab1

Degree of freedom label for first term of equation. Structural labels: UX, UY, or UZ (displacements); ROTX, ROTY, or ROTZ (rotations, in radians). Thermal labels: TEMP, TBOT, TE2, TE3, . . ., TTOP (temperature). Electric labels: VOLT (voltage). Magnetic labels: MAG (scalar magnetic potential); AX, AY, or AZ (vector magnetic potentials). Diffusion label: CONC (concentration).

C1

Coefficient for first node term of equation. If zero, this term is ignored.

NODE2, Lab2, C2

Node, label, and coefficient for second term.

NODE3, Lab3, C3

Node, label, and coefficient for third term.

Notes

Repeat the CE command to add additional terms to the same equation. To change only the constant term, repeat the command with no node terms specified. Only the constant term can be changed during solution, and only with the CECMOD command.

Linear constraint equations may be used to relate the degrees of freedom of selected nodes in a more general manner than described for nodal coupling [CP]. The constraint equation is of the form:

where U(I) is the degree of freedom (displacement, temperature, etc.) of term (I). The following example is a set of two constraint equations, each containing three terms:

0.0 = 3.0* (1 UX) + 3.0* (4 UX) + (-2.0)* (4 ROTY)

2.0 = 6.0* (2 UX) + 10.0* (4 UY) + 1.0* (3 UZ)

The first unique degree of freedom in the equation is eliminated in terms of all other degrees of freedom in the equation. A unique degree of freedom is one which is not specified in any other constraint equation, coupled node set, specified displacement set, or master degree of freedom set. It is recommended that the first term of the equation be the degree of freedom to be eliminated. The first term of the equation cannot contain a master degree of freedom, and no term can contain coupled degrees of freedom. The same degree of freedom may be specified in more than one equation but care must be taken to avoid over-specification (over-constraint).

The degrees of freedom specified in the equation (i.e., UX, UY, ROTZ, etc.) must also be included in the model (as determined from the element types [ET]). Also, each node in the equation must be defined on an element (any element type containing that degree of freedom will do).

For buckling and modal analyses, the constant term of the equation will not be taken into account (that is, CONST is always zero).

Note that under certain circumstances a constraint equation generated by CE may be modified during the solution. See Program Modification of Constraint Equations for more information.

Menu Paths

Main Menu>Preprocessor>Coupling / Ceqn>Constraint Eqn

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