Local axes orientation

The purpose of current page is to describe the convention employed in the definition of local axes within Kratos. This is designed in particular for the "structural" case, consisting in Beams, Shells and Solid elements, however the same conventions shall be employed in other fields when applicable

the following variables, of type "array_1d<double,3>" are defined within the kratos core, and shall be used in naming the axis of choice.

• LOCAL_AXIS_1
• LOCAL_AXIS_2
• LOCAL_AXIS_3

BEAM case

for the case of a Beam, the axis LOCAL_AXIS_1 is chosen as tangent to the beam axis, oriented following the beam natural numbering (for a 2 noded beam, from node 0 towards node 1).

LOCAL_AXIS_2 is expected to be orthogonal to the direction identified by LOCAL_AXIS_1. Such axis can either be provided by the user or computed automatically. LOCAL_AXIS_3 is then computed to form an orthonormal basis with the first 2.

file:///home/rrossi/local_axis_convention

CASE 1 - axis is user prescribed

In this case, LOCAL_AXIS_2 is assumed to be approximatevely orthogonal to the beam axis. It will be made orhogonal and normalized as a very first step. It shall be assigned to the element employing the GetValue/SetValue method, so that it is possible to query whether it was prescribed or not by employing the function "Has".

CASE 2 - axis not prescribed

In this case, LOCAL_AXIS_2 is computed automatically using the following formula: