The ELM* data categories will now accept a new ASYM data record. This enables users to generate a structure whose elements are totally axi-symmetric by specifying line of nodes to define a 'profile' line.
A 4-fold symmetrical structure is generated in a special order and has the effect of switching on X and Y symmetry i.e. as if the SYMX and SYMY data records have been input in Data Category 2.
At this time only structures whose axi-symmetric axis is co-incident with the Z Fixed Reference Axis may be generated; in other words, generated nodes are rotated about this axis.
Any number of ASYM data records may be used within the normal restrictions of the maximum number of nodes and elements.
The maximum number of nodes in the profile line used in generating an axi-symmetric structure is 100.
The elements generated will not necessarily produce a mesh with no modeling errors. To a large extent this will depend on the exact geometry of the profile line specified by the user. Note that with 64-fold symmetry the aspect ratio of elements next to the axis cannot be reduced to less than about 1 in 10 and for 2-fold, 1 in 5. This however should not produce significant errors.
Aqwa-Line will automatically use a special N-fold symmetrical solution if all elements are generated by ASYM data records or the user inputs elements which obey the rule of axi-symmetrical element order. This special solution can be up to 2 orders of magnitude faster than even the 4-fold symmetrical solution. For a model with a TOTAL (in ALL quadrants) number of M diffracting elements and having X and Y symmetry, a structure will be solved as an N-fold (N=8,16,32,64) axi-symmetric structure automatically if the 1st set of M/N elements, when rotated by n*360/N degrees, produces the nth set of M/N elements within a tolerance of approximately (0.01m/0.03ft).
The input format is as follows:
5 7 16 21
- --- -- ---- - ---- ----- -------------------------
X|XXX|01|ASYM|X|DIFF| 1|(32)(111)(217)XXXXXXXXXXX
- --- -- ---- - ---- ----- -------------------------
| | | | | | |
| | | | | | |
| | | | | | |_(7)Finish user node no.
| | | | | | (MAX # nodes total = 100)
| | | | | |
| | | | | |_(6)Start user node no.
| | | | |
| | | | |_(5)No. of Axi-symmetric rotations 8,16,32,64
| | | |
| | | |_(4)Element Group Number
| | |
| | |
| | |_(3)Diffracting - leave blank for non diffracting.
| |
| |_(2)Mandatory data record keyword.
|
|_(1)Optional User Identifier
(3) The above example generates diffracting elements. Leave this field blank for non-diffracting elements or elements above the water line.
(4) The element group that will be used for all elements generated by this data record. If 0 or blank is input then the group number will start from 1 and for each set of elements generated along the axis the group number will increment by 1. i.e. groups 1-32 will be generated if 32 is the number of axi-symmetric rotations.
(5) No. of Axi-symmetric rotations to produce a full 360 degree description of the structure. This is restricted to 8,16,32 and 64.
(6/7) The start/finish user node numbers of the line of nodes to be rotated. This defines the 'profile' line. For example:
if the start node is 111
the finish node is 217
and 8 nodes (111,211,113,213,115,215,117,217) exist in the coordinate data category
Then the total M, number of elements = (8-1)*32 will be generated. As 4-fold symmetry is mandatory, 56 elements will be produced in 1 quadrant.
In general, if the profile line has NN nodes in the list and N-fold symmetry is specified then M=(NN-1)*N.
The maximum number of nodes in a profile line is 100.
The following are restrictions on the node coordinates defining the profile line. Failure to comply will produce a fatal error:
X coordinate must be positive (in other words,
0.0).Adjacent nodes cannot both have zero X coordinates.
Y coordinates must be zero.
Distance between adjacent nodes must not be too small.
The profile line must not form a closed loop.