Unwarp Shell Elements

It allows the user to have control over shell element warping typically coming from the plating of sculptured surfaces. In general, a four sided face maybe somewhat warped but faces with more than four sides need to be planar. In order to get desirable meshes without warnings and errors, a maximum warping factor should be defined within a certain limit. The area warping factor is the height deviation divided by the square root of the area.

Figure 6:24. Example for different area warping factors

For all shells except those in the "membrane stiffness only" group, if the thickness is available, the thickness warping factor is computed as the edge height difference divided by the average element thickness. This could be substantially higher than the area warping factor.

It may be that elements are created with too sharp angles as a result form the unwarping process. The unwarping is done by subdividing the warped element along lines created by connecting boundary points. The requirement to remove warping is stronger than the angle criteria as a warped element cannot be used while an element with a sharp angle is just undesired.