2.13 Special elements

2.13.1 LumpedMass element

This element, defined by a single node, allows to introduce additional concentrated mass and/or rotational inertias in a node. A different mass and rotary inertia may be assigned to each coordinate direction. At present, individual mass/inertia components can be specified for every degree of freedom of element node. Only displacement and rotational degrees od freedom are considered. The element features are summarized in Table 46.




Lumped mass element

Specific parameters

components #(ra)


components: allows to specify additional concentrated mass components (Force*Time2/Length) and rotary inertias (Force*Length*Time2) about the nodal coordinate axes.

dofs: dofs to which the components apply.


As specified by dofs.







CS properties






Table 46: LumpedMass element summary

2.13.2 Spring element

This element represent longitudial or torsional spring element. It is defined by two nodes, orientation and a spring constant. The spring element has no mass associated, the mass can be added using LumpedMass element. The spring is linear and works the same way in tension or in compression. The element features are summarized in Table 47.




Spring element

Specific parameters

mode #(in) k #(rn) [m #(rn)] orientation #(ra)


mode: defines the type of spring element (see Table 48).

k: determines the spring constant, corresponding units are [Force/Length] for longitudinal spring and [Force*Length/Radian] for torsional spring.

orientation:defines orientation vector of spring element (of size 3) - for longitudinal spring it defines the direction of spring, for torsional spring it defines the axis of rotation.

m: determines optional mass of the element, zero value assumed by default.


the spring element nodes doesn’t need to be coincident, but the spring orientation is always determined by orientation vector.

Table 47: Spring element summary


0 1D spring element along x-axis,
requires D_u DOF in each node, orientation vector is {1,0,0}
1 2D spring element in xy plane,
requires D_u and D_v DOFs in each node
(orientation vector should be in xy plane)
2 2D spring element in xz plane,
requires D_u and D_w DOFs in each node
(orientation vector should be in xz plane)
3 2D torsional spring element in xz plane,
requires R_v DOFs in each node
4 3D spring element in space,
requires D_u, D_v, and D_w DOFs in each node
5 3D torsional spring in space,
requires R_u, R_v, and R_w DOFs in each node

Table 48: Supported spring element modes