Flexcom Coordinate Axes |
 
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Flexcom Coordinate Axes |
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There are three coordinate axis systems in Flexcom, termed the global axes, the local undeformed axes, and the convected axes. Of these, the global axes are the same for all elements of the finite element model. The others are individually defined for each element.
The three coordinate axes are illustrated schematically below.
Global, Local Undeformed and Convected Coordinate Systems
The global axes (
) are the axes in which the total system equations of motion are assembled and solved, and in which the structure motions and reactions at restrained nodes are output.
Each element has associated with it a convected (
) coordinate axis system. The convected axes displace and rotate with the element - these are the axes in which the instantaneous equations of motion at a particular solution time are written for the element. The definition of the convected axes, and the transformation of the equations of motion from the convected to the global axes, is one of the cornerstones of the Flexcom kinematics formulation for handling finite three-dimensional rotations. This is described in many publications by <%COMPANYNAME%> personnel (for example, O’Brien et al., 2002 and O’Brien et al., 2003), and the details are not elaborated further here. Copies of the two papers referenced are available on request from <%COMPANYNAME%>.
Each element also has an associated local undeformed (
) axis system. The local undeformed axes define the orientation of each element when that element is undeformed or stress free. Restoring forces are set up in an element when it deforms relative to its local undeformed axes. The discussion of local undeformed axes that follows is in two parts. The next section, entitled Structures without Cables, discusses these axes in the case of structures defined without invoking the cable pre-static step. The presence of cables complicates the discussion of undeformed configurations somewhat, so a discussion of local undeformed axes in the case of structures with cables is postponed until the following section, entitled Structures with Cables.