some details about the example of cylinder mesh

[Wenhao Xue]

Hello:

I am trying to test a case with cylindrical mesh in 2D. I followed the tutorial listed in 

https://nek5000.github.io/NekDoc/appendix.html#mesh-modification. I suppose I do not have clear understandings of some details.

The input file  is :

x2d.rea

2                      spatial dimension

1                      number of fields

#

#    comments

#

#

#========================================================

#

Y                   cYlinder

3 -24 1             nelr,nel_theta,nelz

.5 .3               x0,y0 - center of cylinder

ccbb                descriptors: c-cyl, o-oct, b-box (1 character + space)

.5 .55 .7 .8        r0 r1 ... r_nelr

0  1  1             theta0/2pi theta1/2pi  ratio

v  ,W  ,E  ,E  ,    bc's (3 characters + comma)

1. Could someone please tell me the meaning of  ''oct'? The ''ccbb'' means the inner domain is cylindrical and the outer domain is a regular box, right?

2.  I have known the bc's settings is (cbx0, cbx1, cby0, cby1, cbz0, cbz1) in a regular box, is the same as in the cylindrical mesh? Which boundary 'E' refers to?

I would highly appreciate any guidances.

Kind regards.

W.H.Xue