## Question

**The deformations of master and slave nodes of a rigid link are not exactly same. Why?**

## Answer

**The rotations of slave node must be the same as master node. But, the translational displacements of slave node****are not necessarily the same as master node because the rotation of master node will affect****the translational displacements of slave node.**

Rigid Body Connection constrains the relative movements of the maste r node and slave nodes as if they are interconnected

by a three dimensional rigid body. In this case, relative nodal displacements are kept constant,

and the geometric relationships for the displacements are expressed by the following equations :

The subscripts, m and s, in the above equations represent a master node and slave node s respectively. UX, UY and UZ are displacements

in the Global Coordinate System (GCS) X, Y and Z directions respectively, and RX, RY and RZ are rotations about the GCS X, Y and Z-axes respectively.

Xm, Ym and Zm represent the coordinates of the master node, a nd Xs, Ys and Zs represent the coordinates of a slave node.

This feature may be applied t o certain members whose stiffnesses are substantially larger than the remaining structura

l members such that their deformations can be ignored. It can be also used in the case of a stiffened plate to interconnect its plate and stiffener.

Sample calculation of displacements of a slave node calculated from the displacements of

master node for a sample load is given below :

Node | DX (mm) | DY (mm) | DZ (mm) | RX ([rad]) | RY ([rad]) | RZ ([rad]) |
---|---|---|---|---|---|---|

Master | -1.3725 | -0.02404 | -1.4286 | -0.00022 | 0.05501 | -0.00049 |

Slave | X1 | Y1 | Z1 | -0.00022 | 0.05501 | -0.00049 |

ΔX (mm) | ΔY (mm) | ΔZ (mm) |
---|---|---|

-210 | 0 | 550 |

Distance between slave and master nodes:

X1 = -1.3725 + (0.05501) * (550) - (-0.00049) * (0) = 28.885 mm

Y1 = -0.02404+ (-0.00049) * (-210) - (-0.00022) * (550) = 0.20145 mm

Z1 = -1.4286 + (-0.00022) * (0) - (0.05501) * (-210) = 10.124 mm