Viewgraphs on unstructured surface grid generation are presented. Topics covered include: requirements for curves, surfaces, solids, and text; surface approximation; triangulation; advancing; projection; mapping; and parametric curves

Samareh-Abolhassani, Jamshid

English

NASA Technical Reports Server

N94"22366
UNSTRUCTURED SURFACE
GENERATION
GRID
JAMSHID SAMAREH-ABOLHASSANI
COMPUTER SCIENCES CORPORATION
P'_I4;_O_NI_ PAGE BLANK NO'[ FILMED
223
https://ntrs.nasa.gov/search.jsp?R=19940017893 2020-06-16T18:22:28+00:00Z
o INTRODUCTION
o REQUIREMENTS
o SURFACE APPROXIMATIONS
o METHODS
o GEOLAB EFFORT
JAMSHID SAMAREH-ABOLHASSANI
_t
-7
o Complex Shapes
o Turn-Around Time
o CPU Time
O Applications
o Advancing Front
o Prismatic Elements
o Delaunay (Steiner Triangulation)
JAMSHID SAMAREH-ABOLHASSANI
224
REQUIREMENTS
Curves, Surfaces, Solids, Text
o Curves and Surfaces
o Bicubic Patches
o Conic Sections
o Splines (any order)
o B-Splines
o Parametric Splines
o Points and Tabulated data
o Ruled Surfaces
o Surfaces of Revolution
o Trimmed Surfaces
Non-Uniform
Rational
B-Splines
(NURBS)
JAMSHID 5AMAREH--ABOLHASSANI F
/
REQUIREMENTS
o Spacing
o Stretching
o Over 50 Surfaces
NURBS, Trimmed
o User Input
Turn-Around Time (Day)
o Adaptivity
o Parametric Study
Cont.
JAMSHID SAMAREH-ABOLHASSANI
L
225
REQUIREMENTS Cont.
Few Surfaces _ ofSimple Configurations J L More User's Tim.e ._
I,otso,Sur,aceslFuture[Few,atchesl
Complex Configurations ,) _Less User's Time ._
JAMSHID SAMAREH-ABOLHASSANI
SURFACE APPROXIMATION (I)
CAD DATA
,1
BOUNDARY CURVES
GRID
JAMSHID SAMAR EH-ABOLHASSANI
226
] /
1
SURFACE APPROXIMATION (II)
CAD DATA
POINTS _ ,
GRID
JAMSHID SAMAREH-ABOLHASSANI
EXACT SURFACE REPRESENTATION
-1
Direct Surface Triangulation Type I and ]! +
Projection
LANGLEY HAS TWO PROJECTION
CODES FOR STRUCTURED AND
UNSTRUCTURED GRIDS
AIAA 93-3454 (august 1993)
info: Jamshid@geosunl.larc.nasa.gov
copy: pkerr@geolab2.1arc.nasa.gov
JAMSHID SAMAREH-ABOLHASSANI
L--
m
227
Advancing Front
JAMSHID SAMAREH°ABOLHASSANI
Lr--
F
_J
METHODS
o 2D (Planes, Triangulation is performed in the parameter space)
O 2 1/2 D (Triangulation is performed in the Parameter Space)
O 3D (Triangulation is performed in the Physical and Parameter Spaces)
JAMS_D SAMAREH-ABOLHASSANI F 7
228
_J
Y
Z
2D (PLANES)
h=..=
y
V
o Exact
o No Shearing (Exact shape and size)
o Speed (0)
J AMSI_D SAMAREH- ABOLHASSANI
I
E
I
]
I
I
I
I
I
I
_I
21/2D Advancing Front
Type I
JAMSHID SAMAREH-ABOLHASSA_
229
Shearing(x, y, z) -_ (u, v) 1 XXX
1
1
XXx
BarnhilI-Gregory-Nlelson Patch
_"_L3 X
L2
JAMSHID SAMAREH-ABOLHASSANI
B
I
L
I
I
,LJ_
L4
Bilinear Coon's Patch
L1
L3
Min(ll3 i - o_il)
JAMSHID SAMAREH-ABOLHASSANI
Shearing
XXX
XXx
X
F
230
Cons:
o Shearing
o Speed (1)
o 3/4 Sided-Patches Only
o More Patches Are Needed
PROJECTION
Pros:
o surfaces Are Exact
o Multiple Surfaces
o T-Connections
JAMSHID SAMAREH-ABOLHASSANI m
X-15
231
_-Jm
2½D Advancing Front
I (Parametric Representation)
MAPPING
GRID
R = (X,Y,Z) GENERATION
BACKWARDMAPPING W = (u,v)
r = (x, y, z)
JAMSHID SAMAREH-ABOLHASSAN! F
2½D Advancing Front Cont.
Uniform Parameter Space (UPS)
MAPPING _x = (U,V)
Nonuniform Parameter Space (NPS)
Jamshld Samamh-Abotl_assant
232
J
MAPPING
(PARAMETRIC REPRESENTATION)
R(u) = {x(u), y(u), z(u)}
x= jz' x/
U
Jamshld Samareh-Aboltamsanl
F-
J
Parametric Curves Monotonic in u
R(1)
I .... UNIFORM PARAMETER
=oU
L
u=l
u=0
NONUNIFORM PARAMETER (U)
[] _ _
U--1
Jamshld Sanmrah-Abolhassanl
L
F
233
JAMSHID SAMAREH-ABOLHASSANI
JAMSHID SAIAAR EH-_HASSANI
234
i
J] JAMSHID SAMAREH-ABOLHASSANI F
_1 t __
@
JAMSHID SAMAREH-ABOLHASSAN1 f
235
L__
PARAMETER SPACE
PHYSICAL SPACE PARAMETER SPACE
Transformatio.o.on {a'_, a'2,_,' 131
JAMSHIO SAMAREH-ABOLHASSANI
J
JAMSHIO SAMAREH--ABOLHASSANI
236
/
A
7
Cons
o Metrics Transformations
o Speed (2)
o One Surface Only
B
o Singularity Could Cause Problems
A
Pros
o Exact Surface
o N-Sided Patches
o Trimmed Surfaces
o Fewer Patches
o No Shearing (?) B
FJAMSHID SAMARElt-ABOLHASSANI
J
L-Ji
3D Advancing Front
Curved Surfaces
-]
o Surface Points
o Surface Normals
o Loops in 3D
Tr,mm 
I JAMSHID SAMAREH-ABOLHASSANI
237
]
PROJECTING POINTS ONTO NURBS SURFACES
AIAA-93-3454
,," .............."j° _,°
° ",_.° j
"_X k./_ / -...
,__'% /" :?
"_J'-..--"_. -_" .... X.-.._i
_d --_ %,,," I -" "_','.
% s % .
% • % I "_ I
_' _ I _'. i
% % .j '_
I _ " ",i
I # ",,,
I #
I#
=/
JAMSIIID SAMAREH-ABOLHASSANI -F
Steps:
1.
2.
3.
4.
5.
P.
C
front
P2
Compute a plane normal to (P1, P2, S)
Generate a New Point (P'3) on the Plane (Spacing and Stretching)
Project Point (P'3) onto the Appropriate Surfaces
Compute a Plane Based on (P1, P2, P'3 )
Repeat Steps 2-4 Till Changes in P'3 Are Very Small
JAMSHID SAMAREH-ABOLHASSANI
238
_J
3D Advancing Front
Curved Surfaces
Cons:
o surface Normals Are Required
o Projection Is Required
o Trimmed Surfaces
o Speed (4)
Pros:
o Triangulation Is Performed in the Physical Space
o No Shearing Due Parameter Space
o Metric Transformation Is not Needed
o N-Sided Patches with With Multiple Loops
o Multiple Surfaces
o Fewer Patches
JAMSHID SAMAREH-ABOLHASSANI
_J
User Input Factor(# of Patches)
CPU Time Factor
Surface Types
Surface Accuracy
(_, (_, [3 Transformation
Problems With Shearing
Parametric Study
Number of Surfaces
N-Sided Patches Possible
Problems with Singularity
Surface Normals Required
History
Type I Type I
2D 21/2 D 21/=DP
1 4 4
1 2 3
P NA NURBS
good poor Good
simple simple simple
None Yes Yes
0 0 2
NA Many Many
Yes No No
No No Yes
No No No
4 3 3
Type 2
21/2 D 3D
3 2
4 5
NURBS NURBS
Good Good
Difficult NA
Possible None
3 3
One Many
Yes Yes
Yes Yes
No Yes
1 0
JAMSHIO SAMAREH-ABOLHASSANI
239
CSC/GEOLAB/'rAB EFFORT
O NURBS Based (IGES, NASA IGES)
o NURBS Surfaces
o NURBS Curves
o Trimmed Surfaces
o Points (network)
o Single Interactive Interface
o Surface Grid Generation
Based on 3D Advancing Front
o Projection
JAMSHID SAMARE H-ABOLHASSANI
Lm
STEPS
STEP 1 POINTS/CURVES/PATCHES
o allowing for future additions
o Surface (points)
o create points/curves/patches for vgrid3d (or other systems)
STEP 2 Background Grid
STEP 3 PROJECTION/SMOOTHING/QUALITY CHECK
STEP 4 ADD SURFACE GRID GENERATION
(Direct Surface Triangulation)
o STEP 5 MOTIF / X BASED (other platform)
JAL_HID SAMARE H-ABOLHASSA_ F
I
i
240
_J
II0
INPUT
ASCII
Restart X
HESS X
D3M X
GRIDGEN X
PLOT3D X
LaWGS X
IGES-128 X
INPUT
Binary
???
NA
NA
X
X
NA
NA
OUTPUT OUTPUT
ASCII Binary
X ???
X NA
X NA
X X
X X
X NA
JA_O SAMAREH-ABOD'I_AH
I SURFACES I
o NURBS (NonUniform Rational B-Spline)
o Converts hess, gridgen, plot3d, lawgs to
equivalent NURBS surfaces
o Defined everywhere
o Display Path (write the grid out)
JAMSHIO SAMAREH-ABOLHASSAN_
241
iBeta Release 1.0 (Mid May)
Release 1.1 (End of Summer)
To Obtain a Copy, Contact:
pkerr@geolab2.1arc.nasa.gov
JAMSI_D SAMAREH-ABOLHASSANI F
242
243
244
245
246
247
248
249



Unstructured surface grid generation

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server