3. Boundary & Load Conditions/Analysis/Post-processing
PATRAN
Flow Chart
Import
solids from
CATIA
Modify surfaces
depending on meshing
needs (regular vs.
scattered, Isomesh vs.
Paver) and possible
geometric
discontinuities
1
Extract
surfaces from
solids and
organize
groups
Check
Fail
Mesh entities surface
by surface according
to given mesh
criteria
Extract surfaces in
CATIA, import back
to PATRAN
2 3
Repeat steps
1-4 for all
remaining
entities
Apply cyclic
symmetry
multipoint
constraint on
disc entities
Apply inertial
“pre-torsion”
load via
fictional node
MPC
Apply
pressure
loads on disc
and flange
entities
Apply 2-D
induced
displacements
on disc flanges
Apply thermal
conditions on
disc entities via
interpolation
Apply
aerodynamic
pressure felt
by the blade
Apply blade
temperature
range
Generate
dataset for
SAMCEF
solver
Launch
static
analysis
iterations
Perform
result post-
processing
on PATRAN
5
Legend
Time
Penalty
Moderate
Timing
No Time
Penalty
Verify Model/Project Nodes
Equivalence
nodes
Manually
move
remaining
problematic
nodes
Verify
boundaries
for free
edges/faces
Verify
duplicates,
jacobian ratio &
zero, and
normal vectors
Lower global tolerance
drastically, reorganize
nodes, save a copy of the
database, and project
nodes on original surface
geometry
4
Create
volume
mesh
4. SNECMA Silvercrest
The new generation business jet engine.
Specifications
Type: Turbofan
Length: ~ 1.90 m
Diameter: Fan ~ 1 m
Components
Compressor: Low pressure 1 axial stage
High pressure 4 axial stages + 1 centrifugal stage
Turbine: Low pressure 4 axial stages
High pressure 1 axial stage
Performances
Overall Pressure Ratio: ~ 27
Max. Thrust: 42 – 53 kN
Applications
Cessna Citation Longitude
PATRAN
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6. Silvercrest – low pressure turbine
Stage 2 (axial) – composed of
three entities
Blade
DiscStage 1
flange
Comparison Subject /1.1.1/
PATRAN
Flow Chart
171 mm
7. 1 mm in the blade and 0.5
mm in the radii
Blade tip
Disc
Blade
root Scattered mesh in the disc
(2 mm)
Given Meshing Criteria /1.1.2/ (general criteria)
PATRAN
Flow Chart
8. Given Meshing Criteria /1.1.2/ (radii)
Lower radius
Upper radius
Nodes
measured
0.506 mm
0.539 mm
PATRAN
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9. Given Meshing Criteria /1.1.2/ (disc socket)
Regular mesh in the disc socket (0.5 mm) 0.489 mm
Nodes
measured
PATRAN
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10. Given Meshing Criteria /1.1.2/ (blade root)
Blade root stilt
(0.7 mm)
Regular mesh in the contact zones of
the blade root (0.5 mm)
Nodes
measured
0.498 mm
0.685 mm
PATRAN
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11. Given Meshing Criteria /1.1.2/ (blade tip)
Blade tip (~ 1 mm)
Nodes
measured
1.06 mm
PATRAN
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12. Geometric Discontinuities /1.1.3/ (bottom blade radius)
ISSUE:
This discontinuity caused an
issue early in meshing process
as it rendered a time penalty in
the surface extraction from the
given CATIA model.
SOLUTION:
Run the surface extraction
process for the failed entity
directly CATIA and re-import
surface geometry in PATRAN
PATRAN
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13. Discontinuity
Geometric Discontinuities /1.1.3/ (upper surface [blade])
ISSUE:
This discontinuity located near the
bottom radius of the upper blade
surface caused a time penalty in
the surface treatment. Many other
discontinuities similar to this one
were present throughout the entire
model.
SOLUTION:
Remove unnecessary vertices
which can be problematic.
Otherwise, take the time to create
intermediate points and chain all
edges within each surface to form
curves and create new surfaces
that will be used solely for
meshing. Nodes must be projected
on original geometry.
S 640
PATRAN
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14. Geometric Discontinuities /1.1.3/ (upper surface [blade])
This surface is the bi-parametric
surface created from chaining the
edges of Surface 640. It has been
used to mesh the problematic
upper surface of the blade. Note
that the nodes generated were then
projected onto S 640, the original
surface.
S 688
PATRAN
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15. Element Jacobian Ratio
Irrelevant – Triangular
elements
Element Jacobian Zero
Illustrates element disparities,
must be positive but contained
Element Normals
Illustrates element
normal vector direction,
must be either +1 or -1
throughout entire model
Boundaries via Free Faces
Displays any free faces or
edges depending on
method. For a closed
solid, the entire model
must be yellow to allow
volume meshing from
surface mesh
Meshing Verifications /1.1.4/
PATRAN
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18. Prelude to L/BC /1.2.1/
Before we dive into the details of the various loads and
conditions applied on this 3-D model, we must first note that
many of these conditions come from an existing model.
Indeed, as in most cases similar in nature to this one, the 3-D
model creation was piloted by an existing 2-D model
(120424_MissionVFD_mct12171.db) created by EATT (SES
France). For the purpose of this benchmark, we were
interested solely by the instant t= 368.39 s which represents
the Take-off segment of the mission.
PATRAN
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19. Cyclic Symmetry Multi-point Constraint /1.2.2/
Cyclic symmetry of disc and flange lateral faces via node
automatic liaison (MPC .LIA) with respect to cylindrical
coord. sys.
Master Surfaces:
Region 1
Slave Surfaces:
Region 2
Cylindrical
coord. sys.
Mécanique/Conditions aux
limites/Liaisons automatiques
PATRAN
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20. Cyclic Symmetry Multi-point Constraint /1.2.2/
The cyclic symmetry of the disc and flange lateral faces is
applied in order to maintain continuity within the turbine.
There are 116 turbine blades in the second stage of this low
pressure turbine. Due to a lack of computing power and in
order to simplify the analysis, we break the disc into 116
equivalent sections. As we know, deformation is a function
of the derivative of displacement. In order for the entire
turbine analysis to be coherent, we must maintain
continuity and derivability. If these are ensured, we can
safely and accurately calculate and predict deformations in
the turbine. Hence, all loads applied to a face of the disc
must be equivalent in magnitude and in direction on the
opposite face.
PATRAN
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21. Pre-torsion Inertial Load /1.2.3/ (preparation)
RM2
Alpha en Degre 2.56
Alpah en Rad 0.045
L 16.087837
delta=L Tan(Alpha) 0.719
Alpha
Adjacent blade induced effect.
PATRAN
Flow Chart
25. Disc and
Flange
Pressures Felt by Disc and Flange /1.2.4/
The pressure markers shown on image on the right display the pressure
distribution on the disc and flange. These were collected from a 2-D
model created first, which pilots the creation of our 3-D model. These
pressures are felt at time (t) = 368.39 seconds which represents the Take-
off instant for the mission VFD.
PATRAN
Flow Chart
26. Aerodynamic Pressures Felt by Blade /1.2.5/ (contours)
The pressure contours shown here refer to the PS3D file:
rm2.YKYL.YKYL_RM2_TO18_SC264_MAJ_VENTIL_ITE02
For a complete explanation of the preparation of these contours, please
refer to the following presentation:
« Formation Pression Aérodynamique pour les Aubes »
Note that, as expected, the
aerodynamic pressure peak is
located on the lower blade
surface and represents a value
of approximately 0.4 MPa.
PATRAN
Flow Chart
27. Aerodynamic Pressures Felt by Blade /1.2.5/ (pressure resultant vector)
Lower blade
surface
Upper blade
surface
As expected, the resultant
pressure vector is directed
from the lower blade
surface to the upper blade
surface.
PATRAN
Flow Chart
28. Temperatures Felt by Blade /1.2.6/
The thermal effects present on the blade are presented as a radial distribution and are
applied using a pre-defined Spatial Field. These temperature values are taken from
the Aero_Meca files provide by SNECMA. We then plot the temperature contours on
the blade entity as shown below.
Min = 600 ° C (located in the neck of the blade)
Max = 993 ° C (located in the blade tip)
PATRAN
Flow Chart
29. Thermal Interpolation in Disc and Flange /1.2.7/ (prep)
This task is the most tedious and delicate task in the PATRAN methodology. It
requires precision and patience. It is also dangerous for the database and if an
incorrect interpolation is done, the whole .db file can be affected. Therefore, it is
essential to save a copy before and after any interpolation is rendered in order to
avoid unfortunate data losses. The interpolation file used is the following:
RTBP_SC_V3_C1.MisVFD_02.mailther
It may not be evident on this
snapshot, but the 2-D thermal
meshing geometry doesn’t
exactly correspond to the
geometry of our 3-D model. In
order to account for this we
have had to create correction
vectors with respect to nodes
from both meshed models. The
vectors used are the following
and they are applied to
mechanical model.
X Y Z
Disc (Stage 2) -0.87839 0 0
Flange (Stage 1) 0.72945 0 2.35003
PATRAN
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30. Thermal Interpolation in Disc and Flange /1.2.7/ (prep)
X Y Z
Disc (Stage 2) -0.87839 0 0
Flange (Stage 1) 0.72945 0 2.35003
Apply
correction
vectors here
PATRAN
Flow Chart
31. Thermal Interpolation in Disc and Flange /1.2.7/ (app)
As we can see here the
correction vectors have
allowed us to mitigate the
effects of the geometry
mismatch in the thermal
interpolation of the disc and
flange entities.
PATRAN
Flow Chart
32. Thermal Interpolation in Disc and Flange /1.2.7/ (verif)
We validate our
interpolated model by
verifying the contours
and making sure that
there are no incoherent
temperature peaks and
that the max and min
values are respectively
located in the socket
and in the bottom of
the disc entity.
PATRAN
Flow Chart
33. Node to Surface Contact /1.2.8/ (prep)
The graphics below show the contact zones we are interested in. The red zones
represent the contact surfaces of the blade neck located at the bottom of the blade
root. The blue zones represent the contact surfaces of the disc socket. In the model
we can see that these zones are not directly in contact but we specify a contact
condition because of the centrifugal force generated by the rotation of the turbine
stage. Note that we specify Cont_SRot in the option field which is a small rotation
hypothesis.
PATRAN
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34. Node to Surface Contact /1.2.8/ (app)
The yellow markers shown
in this graphic denotes an
applied NodeSurf.
contact.
PATRAN
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35. .lia Multi-point Constraints /1.2.9/ (disc & blade)
This MPC creates an axial liaison between the blade and the disc to avoid having
the blade move with respect to the disc in the axial direction. This can be caused
by the various loads applied on the model. We simply specify the liaison on the
turbine rotation axis using two nodes from each entity. These nodes must not be
on the a surface.
PATRAN
Flow Chart
36. .lia Multi-point Constraints /1.2.9/ (disc & flange)
This MPC results from an assumption and an approximation. In reality, the flanges of the turbine
are fastened to the adjacent disc entities using screws of some sort. Since the given geometry did
not include this feature, we assumed that this connection would behave the same way as an
automatic liaison of the surfaces. Hence, we approximated the disc and the adjacent flange to be a
single entity with this multi-point constraint. We applied this liaison via the inside nodes of these
surfaces (avoiding the already constrained outside nodes [cyc. sym.])
PATRAN
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37. Tangential Fixation of Disc and Flange /1.2.10/
The tangential fixation of the disc
and flange entities allows us to void
any induced tangential movement
of the model that could result in
incoherent results. This is done via
a simple “0” displacement in the
tangential direction (Y-dir) applied
on two nodes: one from the disc
and one from the flange as seen on
the image to the left.
PATRAN
Flow Chart
38. Pressures Felt by Blade Tip & Root /1.2.11/
Blade Root
Blade Tip
Blade Tip
As we can see the leading edge
has the highest pressure
associated with it in both the
blade root and tip. These
pressures are applied manually
and are interpolated linearly to
show the transition between
points near the leading edge
and near the trailing edge.
Leading Edge
PATRAN
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39. Load Case Specification /1.2.12/
For the purpose of this study, we have decided to use a single load case for all
loads applied to the model. This simplifies the generation of the data set to be
used for analysis. This rendered a small issue as some of the loads applied are
time dependent while others are not. In order to solve this issue we specified our
single load case as a time dependent one. In order to ensure that the right instant
was applied for the time dependent loads (thermal interpolation for disc and
flange) we used Mecanique/Conditions aux limites/Gestion des L/BC
transitoires/Action: Extraire/Objet: Temperatures. We then select the loads that
we are interested in for the time specification and extract the instants directly
from the load specification. This ensures that the data set includes the effects of
this load despite the fact that it is the only time dependent one. The load case we
have used for the final analysis on PATRAN is called IT_3 and represents the
third iteration of generating the data set.
PATRAN
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41. Material Specification in PATRAN /1.3.1/ (explanation)
A task that must be carried out before generating a data set is the
material and material property specification. For the purpose of this
study we have specified the DMD 456 material for the disc & flange
entities and the DS 200 material for the blade entity. The importance of
this material specification lies in the nature of the material. The disc and
flange entities are fabricated from an isotropic alloy whereas the blade is
manufactured from an anisotropic material. Isotropy is an important
material parameter as it governs the material’s dependency on direction.
An isotropic material has properties which independent of direction
whereas an anisotropic material has properties that depend heavily on
direction. For the purpose of this study, the isotropic material was
specified directly in PATRAN; on the other hand the anisotropic material
had to be inputted directly within the data set (.dat).
PATRAN
Flow Chart
42. Material Specification in PATRAN /1.3.1/ (application)
We use field inputs to specify
the Modulus of Elasticity
(Young’s Mod.), Poisson’s
Ratio, Thermal Expansion
Coefficient, and the density of
the material. All these values,
except for the density, are a
function of the temperature of
the material. As
aforementioned, only the DMD
456 material has been specified
in PATRAN since it is isotropic
and fairly easy to deal with.
NB: we also specify two degrees
of material properties. Degree 1
refers to contacts, limits and
boundary condition zones.
Degree 2 (default) refers to all
other zones.
PATRAN
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43. .dat Generation /1.3.2/
We use the Analysis tool
to generate the data set to
be analyzed by SAMCEF.
PATRAN
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45. .dat Modification /1.3.3/
In order to efficiently modify the data set, we must first specify a dummy
material in PATRAN. We entered obsolete values for the material properties in
order to easily find the SAMCEF code lines associated with the dummy material
and replace them with the given properties for the DS 200 material.
PATRAN
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46. READING RESULTS IN PATRAN
The static results generated by the SAMCEF solver have been plotted in PATRAN.
The following slides display the deformation and stress results rendered by our
mechanical model. Note that some zones required more attention than others due
to the fact that we have had to remove boundary condition zones and contact
zones in order to isolate the “true” theoretical deformation and stress
distributions. SAMCEF analysis codes used: 1411 (stress tensor), 163 (nodal
displacements).
PATRAN
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50. Static Results (Axis-dependent Deformation) /1.4.2/
TANGENTIAL DISPLACEMENT
Max Displacement = 3.86 mm
PATRAN
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51. Static Results (Blade Stresses Global) /1.4.3/
BLADE STRESS GLOBAL
Max Stress = 707.5 MPa
PATRAN
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52. Static Results (Blade Stresses Radii) /1.4.4/
BLADE STRESS BOTTOM RADIUS
Max Stress = 557.8 MPa
Located on the upper blade
surface side of the radius
PATRAN
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53. BLADE STRESS TOP RADIUS
Max Stress = 457.1 MPa
Located on the upper blade
surface side of the radius
Static Results (Blade Stresses Radii) /1.4.4/
PATRAN
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54. Static Results (Disc Stresses Global) /1.4.5/
DISC STRESS GLOBAL
Max Stress = 780.5 MPa
PATRAN
Flow Chart
56. Static Results (Disc Stresses Socket) /1.4.7/
Reading results on the
disc socket was a close
to impossible task due
to the MPC specified
between the disc and
blade. Removing the
elements associated
with the MPC rendered
issues and made it hard
for us to read where the
“true” max stress value
was located. We will
attempt to read results
in this region on WB
and compare
methodology and
performance.
PATRAN
Flow Chart
57. Conclusion
To conclude PHASE 1 of this benchmark study, one can clearly see that
PATRAN is NOT a user friendly tool in any way shape or form. It is
complete in the sense that it allows full control of geometry, finite element
work, and loads and boundary conditions. However, it offers little or no
added value in terms of time saving and efficiency. In most cases, users will
be forced to treat surfaces separately in meshing the model. Applying loads
and conditions, albeit a more efficient task in PATRAN, renders certain
issues which we have discussed previously in this presentation. Two major
issues noted with this tool: lack of a “Model Tree” (Creo, CATIA, WB),
dissociation of geometry and finite element model.
As an outlook on PHASE 2 of this study and in order to shed some light on the
possible alternatives to this accepted paradigm, the following slides present
a predicted flow chart for Workbench as well as a demo of PATRAN 2012.
When an accepted paradigm renders issues that affect efficiency, this
establishes a problem. This problem can be solved by addressing every
single issue or the paradigm can be shifted. “Think of a paradigm shift as a
change from one way of thinking to another. It's a revolution, a
transformation, a sort of metamorphosis. It just does not happen, but
rather it is driven by agents of change.”
PATRAN
Flow Chart
59. Workbench
Predicted Flow Chart
Treat surfaces in
CATIA to avoid
discontinuities and
prepare model for
boundary conditions
Regenerate
solids and
import into WB
Simplify the
geometry using
the Virtual
Topology tool
Create named
selections and specify
various mesh criteria
regions and boundary
condition zones
Launch mesh
using criteria
specified in the
named selections
Apply loads and
boundary
conditions via
named selections
Specify solver
and analyze
locally
Generate data set
and analyze via
server
Read results in
WB
60. Boundary & Load Conditions/Analysis/Post-processing
PATRAN
Flow Chart
Import
solids from
CATIA
Modify surfaces
depending on meshing
needs (regular vs.
scattered, Isomesh vs.
Paver) and possible
geometric
discontinuities
1
Extract
surfaces from
solids and
organize
groups
Check
Fail
Mesh entities surface
by surface according
to given mesh
criteria
Extract surfaces in
CATIA, import back
to PATRAN
2 3
Repeat steps
1-4 for all
remaining
entities
Apply cyclic
symmetry
multipoint
constraint on
disc entities
Apply inertial
“pre-torsion”
load via
fictional node
MPC
Apply
pressure
loads on disc
and flange
entities
Apply 2-D
induced
displacements
on disc flanges
Apply thermal
conditions on
disc entities via
interpolation
Apply
aerodynamic
pressure felt
by the blade
Apply blade
temperature
range
Generate
dataset for
SAMCEF
solver
Launch
static and
dynamic
analysis
iterations
Perform
result post-
processing
on PATRAN
5
Legend
Time
Penalty
Moderate
Timing
No Time
Penalty
Verify Model/Project Nodes
Equivalence
nodes
Manually
move
remaining
problematic
nodes
Verify
boundaries
for free
edges/faces
Verify
duplicates,
jacobian ratio &
zero, and
normal vectors
Lower global tolerance
drastically, reorganize
nodes, save a copy of the
database, and project
nodes on original surface
geometry
4
Create
volume
mesh
