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Showing posts from February, 2018

U* Index for Load Path Analysis

An XANSYS forum poster pointed out an interesting thesis on load path index U*. There was a brute force method of a solution for every single node shown in Figure 8. Alternately, there is a U* Toolkit found in Nastran which appears to really speed the calculations.

The brute force method was used here in this Ansys Classic input file : link

Figure 1: Load Path Index U*

Torsional Spring in ANSYS Workbench

Torsional springs can come in handy when inertia plays a large role in the dynamic response. Fortunately a simple snippet converts a typical linear spring into a torsional spring. Workbench uses COMBIN14 springs by default.

keyopt, _sid, 3, 1   ! rotational DOF about spring axis
r, _sid, 0.01        ! rotational stiffness

Torsional Mode due to Torsional Spring
One could also specify the radial stiffness of the spring above by specifying the direction. Note that KEYOPT(2)=1.
keyopt, _sid, 2, 1! UX direction about global axis
r, _sid, 1e5            ! Translation stiffness

Same goes for off-axis rotational DOF via KEYOPT(2)=4.
keyopt, _sid, 2, 4! ROTX direction about global axis
r, _sid, 1e5            ! Rotation stiffness

The Workbench (v18.2) Archived File: LINK