How to Export Complex 3D Meshes from Midas GTS NX to ...

Dr. Javier Moreno RoblesCivil Engineer

Geotechnical Laboratory. CEDEX. Spain

Professor U.P.M.

How to Export Complex 3D Meshes from Midas GTS NX to Flac3D

01. Learning Objective

02. Differences between Midas GTS NX (FEM) and Flac3D (FDM)

03. Structure of the import file ( impgrid)

04. Description of the FISH subroutine

05. Application example nº1: Stress-Deformational

06. Application example nº2: Seepage

07. Conclusions

Content

Learning Objective

1-5


Key Points:

- Importing the volumetric meshes generated in midas GTS NX to Flac3D.

- Review of the conceptual differences in FEM and FDM.

- Breakdown of the subroutine of FISH mesh importing.

- Two application examples of the subroutine generated meshes to show compatibility.

- The most notable results obtained in both software will be compared.

This will not be a comparison of which software is better, as both software are prestigious.

Learning Objective:

The goal is to show the 1:1 comparison between the notable results between midas GTS NX and Flac3D on two project applications.


02. Differences between midas GTS NX (FEM) and Flac3D (FDM)





07. Conclusions

Content

Differences between

Midas GTS NX (FEM)

and Flac3D (FDM)

1-8

02. Differences between Midas GTS NX(FEM) and Flac3D(FDM)

Flac3D is a numerical code thatis formulated under the FiniteDifference Model method.

• No need to assemble stiffness matrix tosolve.

• All calculations are dynamic.

• The calculation is Explicit, so need to set asmall time step Δt.

Midas GTS NX is a numericalcode that is formulated underthe finite element method.

• Need to assemble a stiffness matrix.

• Calculation is stopped by singularity in thematrix.

• The calculations can be static or dynamic.

• The dynamic calculation can be carriedout with an explicit and implicit scheme.

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For static analysis, the software over-dampensthe material to avoid parasitic oscillations.

Time does not have a temporal concept, butrather diffuses the energy applied in themodel.

Dynamic analysis are performed in the timedomain.

Computation time in elastic and elastoplasticanalysis are equivalent.

Can run eigenvalue analysis and obtain theproper frequencies / vibration modes.

Dynamic analysis can be made in the time andfrequency domain.

Computational time in elastic analysis issignificantly lower than elasto-plastic analysis.


Flac3D GTS NX

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The input of geometry, materials, analysistypes, etc. is done through a command file.

FISH programming language can be used toperform multiple purpose subroutines.

It is common to make an intensive use of FISHsubroutines in advanced Flac3D models.

The input of geometry, materials, analysistypes, etc. is done entirely through thegraphical interface.


Flac3D GTS NX

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Solids are meshed from 13 primitive geometries.

Solids are meshed from any volumes that are defined by importing: • CAD programs • Elementary geometries• Boolean operations (with entities of the

same or lower order, extrusion, etc.)


Flac3D GTS NX

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The geometric definition andmeshing of the primitive shapesmust comply with specific norms.


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During meshing, a volume is divided into ZONES that have a mesh grid point at each vertex (GP).

NO GP'S EXIST IN THE MIDPOINTS OF THE ELEMENT. (No second order elements)

During meshing, a volume is divided into ELEMENTS that have mesh points (NODES).

Linear elements have NODES in each vertex.

Second order elements have additional NODES in the midpoints.

Flac3D GTS NX

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ZONE

GRIDPOINT

ELEMENT

NODE


Flac3D GTS NX



03. Structure of the Import File ( impgrid)




07. Conclusions

Content

Structure of the Import File

(impgrid)

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03. Structure of the import file (impgrid)

impgrid - Flac3D import command for volumetric geometry meshes.

The application format is:IMpgrid filename <keyword>

with the following characteristics:

filename is the name of the file, whose extension, if not expressly indicated, is *.FLAC3D

<keyword> usegivenids forces Flac3D to use the same GP identifiers (gridpoint)and zone as those indicated in the import file.

The command creates a new GP for each point indicated in the input file.

In this way, an imported mesh can be incorporated into an existing mesh.

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The rules of the file filename are the following:

• It must be an ASCII file (American Standard Code for Information Interchange)

• Lines with comments must have a ‘*’ at the beginning.

• The white lines will be ignored.

• A line that begins with G indicates a GP, and must contain a GP identifier (ID)followed by the x, y, z coordinates.

• A line that begins with Z indicates a Zone, and must contain a zone identifier(ID) followed by the type of zone and the GP’s (in the form of ID).

• The ID’s of the GP’s and the Zones must be positive integers, but don’t have tobe ordered.


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The zone types, with the appropriate GP order, are:

• B8→ Cube zone (8 GP)

• W6→Wedge zone (6 GP)

• P5→ Pyramid zone (5 GP)


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The zone types, with the appropriate GP order, are:

• B7→ Degenerated Cube zone(7 GP)

• T4→ Tetrahedron zone (4 GP)

• The order of GP must be in accordance with that of the figures when defining each zone.

• Otherwise, it will give an import error.


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The rules of the file filename are thefollowing:

• A line that starts with ZGROUPindicates that of a group ofzones.

• The text that follows is thename of the group.

• Then all the zones of said groupwill be included.

Example








07. Conclusions

Content

Description of the FISH

subroutine

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Short 3D Mesh Export

Example

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Generate nodes table into .txt file

1. Mesh > Nodes Table2. Select All > OK3. Copy-Paste All to Excel4. Save as .txt TAB delimited

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Generate Element table into .txt file

1. Mesh > Element Table2. Select All > OK3. Copy-Paste All to Excel4. Replace All of Column C

names with corresponding property number

5. Save as .txt TAB delimited

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Update Fish Import.dat file

• Call new .txt files and save mesh as flac3d file

• Files Called in Red

• Files Created in Green

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Update Fish Import.dat file

• Save new imported mesh

as flac3d file

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Create Fish Calc .dat file

• In this example, no calculation takes place

• Import of mesh happens by calling Import

Fish . DAT File

• Next 2exampleswillhaveFishcommands

forcalculation of given models.

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Open Flac3D, run .dat files





05. Application Example nº1: Stress-Deformational


07. Conclusions

Content

Application Example nº1

Stress-Deformation

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05. Application example nº1 Stress-Deformation Calculation

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MATERIALES INVOLUCRADOS

Concrete Pier

Concrete Footing

Fill

Unit 1b

Unit 2a Unit 2b1 Level 1-2

Unit 2b1 Level 3

Unit 2b1 Level 4

Unit 2b2

Unit 2c


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Stage 1: Initial Stresses


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Stage 2: Excavation


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Stage 3: Filling


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Stage 4: Construction of Footings


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Stage 5: Construction of Bridge Pier


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Stage 6: Application of Asymmetric Loads(The displacements from previous stages were cleared)

Fx = 500 tons (horizontal longitudinal)Fy = 400 tons (horizontal transversal)Fz = 20,000 tons (vertical)

Calculation Time = 12 minute


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MIDAS GTS NX MESH PREPARATION

• MESH SET (Midas GTS NX)→ Groups Flac3D• In each Mesh Set assign a different property→ 1 MS = 1 Prop• Avoid meshes “matching space”→ Fits the way you work with Flac3D


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FLAC3D MODEL


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FLAC3D MODEL

11


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FLAC3D MODEL


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FLAC3D MODEL


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MODEL LIST FLAC3D

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MODEL LIST FLAC3D

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MODEL LIST FLAC3D

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Default Software Value

Calculation Time = 466 minute


MODEL LIST FLAC3D

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Ux


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Ux (1E-5)


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Ux (1E-7)


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Ux (<1E-7)


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Uy


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Uy (1E-5)


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Uy (1E-7)


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Uy (<1E-7)


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Uz


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Uz (1E-5)


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Uz (1E-7)


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05. Application Example nº1: Stress-Deformation

Uz (<1E-7)







07. Conclusions

Content

Application example nº2:

Seepage

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Model 2D

T cálculo = 1 minuto


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Model 2D – 3D


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Model 2D – 3D

Y MIDAS→ Z Flac3D

Z MIDAS→ Y Flac3D


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w

FLAC

KK

=


MODEL LIST FLAC3D

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MODEL LIST FLAC3D

Eq. Dupuit

Calculation Time = 77 minutos


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Pp

06. Application example nº2: Stress-Seepage

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Pp

= 1·(152-102)/(2·100) = 0.625 m3/day/m


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Pp

= 1·(152-102)/(2·100) = 0.625 m3/day/m







07. Conclusions

Content

Conclusions

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07. Conclusions

The session has shown:

1. Flac3D program allows users to import a volumetric mesh according to a certain filestructure.

2. There are important differences between the modeling in midas GTS NX and Flac3D(elements vs zones, model introduction, generation of stages, etc.)

3. Using the FISH subroutine, users can easily import a volumetric mesh from midas GTSNX to Flac3D.

4. The workflow to generate the auxiliary files needed in the import was shown.5. The exported mesh allows calculation in Flac3D both stress-deformation and seepage.6. From the exported mesh, Flac3D must generate a calculation file. Therefore any type

of calculation can be made.7. The results obtained are similar in midas GTS NX and Flac3D.8. The calculation time of MIDAS is significantly lower than Flac.9. Flac3D requires more training and technical skills to complete a similar model than in

MIDAS GTS NX.

How to Export Complex 3D Meshes from Midas GTS NX to ...

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