several questions

[yuejun]

Hi I am a newbie of OpenSees and get several questions.
1, quadrilateral patch command.

Code: Select all

patch quad $matTag $numSubdivIJ $numSubdivJK $yi $zi $yj $zj $yk $zk $yl $zl

There is an example in the Command Language Manual of this command.

Code: Select all

patch quad $coreMatTag 8 8...

It says that this defines a core patch with 8 subdivisions. But in the figure following, there are 12 squares. I am confused with this. What does numSubdiv mean?
2,how is the element coordinate system built? x-axis is connecting the two element nodes. z-axis and y-axis are determined by a vector that lies on a plane parallel to the local x-z plan. How can a x-z plane exist while z-axis is not yet determined?
For a two-dimensional problem, three parameters (vecxzX,vecxzY,vecxzZ) are not necessary. So what is the default local coordinate system?
Thanks a lot.

[silvia]

the picture with the 12 patches is not related to the example usage.
the picture tells you what variables values go with it.