Modal Analysis using Plate Elements

I am a new user of Salome-Meca.

My goal is to build a model which will consist of a a concrete slab on beams with a concrete pedestal motor base on top of the slab. I then intend to find the natural frequencies, and compare them with model test results.

The beams are planned to be modeled with beam elements. (POU_D_T in all probability)

The concrete slab with shell or plate elements (DKT in all probability)

The concrete pedestal with 3D solid elements.

If there is a tutorial or example file of a similar problem, I would really appreciate it.

Also I have tried modeling the modes of a plate and comparing them with the frequencies from Blevin's textbook. The frequencies from Code-Aster are insensitive to plate thickness. Theoretically they are linearly dependent upon plate thickness, so I am having a problem. If someone can review the .comm file I would appreciate it. I have also attached the .hdf file and a document showing the steps I went through to create the example.

Many thanks in advance.

Thanks Kees it helped alot. Some learning curves to get it to work without using the Python script, The tutorial does not mention that the mesh needs to be converted to quadratic elements.

My first note included some attachments, but they don't seem to show up in the forum. If you send your email address I will gladly send some files.

Here is what I did.

Kees Wouters plateDynamics tutorial

comment out the mesh groups in the geom_mesh python script and it works as well. Using a fresh install of Salome-Meca from CAElinux 2011. ie Code Aster 10.5 is used.

# add groups in the mesh for boundary conditions, loads, etc

# Linex1 = Mshell.Group(Linex1)

# Liney1 = Mshell.Group(Liney1)

# Linex0 = Mshell.Group(Linex0)

# Liney0 = Mshell.Group(Liney0)

# shell = Mshell.Group(shell)

Run from within Salome-Meca using the commands

change task to Aster

Aster → Add Study Case

Name: plateDyn
Command File: from disk Name: ./shelldyn.comm
Mesh: from object browzer Name: Mshell
default the rest

Right Click plateDyn → Run

Right Click PostPro → Activate
Right Click 4.88 Hz → Deformed Shape and scaler map – set scale factor to 1 OK

shape shows fine, but only at nodes rather than at contours.

Note that there is no data on the meshmod data.

The mess file gives a number of alarms such as this just after command 0003

modinit=AFFE_MODELE(MAILLAGE=meshinit,

INFO=1,

AFFE=_F(PHENOMENE='MECANIQUE',

TOUT='OUI',

MODELISATION='3D'),

PARTITION=_F(PARALLELISME='GROUP_ELEM'),

VERI_JACOBIEN='OUI',

);





SUR LES 837 MAILLES DU MAILLAGE meshinit

ON A DEMANDE L'AFFECTATION DE 837

ON A PU EN AFFECTER 837



!

---

!

! <A> <CALCULEL2_63> !

! !

! -> La maille M1 porte un élément fini de bord, mais elle ne borde !

! aucun élément ayant une "rigidité". !

! !

! -> Risque & Conseil : !

! Cela peut entrainer des problèmes de "pivot nul" lors de la résolution. !

! Si la résolution des systèmes linéaires ne pose pas de problèmes, vous !

! pouvez ignorer ce message. !

! Sinon, vérifier la définition du modèle (AFFE_MODELE) en évitant l'utilisation !

! de l'opérande TOUT='OUI'. !

! !

! !

! Ceci est une alarme. Si vous ne comprenez pas le sens de cette !

! alarme, vous pouvez obtenir des résultats inattendus ! !

!

---

!

When I create the geometry by hand as given in the tutorial, and then run the mesh script, Python cannot find (Face1). Not sure why.

Meshing manually works fine. Tutorial does not include the command to covert the linear quadrilateral elements to quadratic elements.

Try meshing in a different simpler manner

New Entity → Sketch 2D
0,0 Apply
1,0 Apply
1,1 Apply
0,1 Apply
Sketch Closure

New Entity → Build → Face
Name: Face1
Objects Wire_1
Apply and Close

New Entity → Group → Create
Shape Type: plane
Name: shell
Main Shape: Face1
Select All
Apply and Close

New Entity → Explode
Main Object: Face1
Sub Shapes Type: Edge
Apply and Close
0.0592192
Rename Edge_1 → Linex0 % right click → rename
Rename Edge_2 → Liney0
Rename Edge_3 → Liney1
Rename Edge_4 → Linex1

Go to Mesh task
Mesh → Create Mesh
Name: Mshell
Object: Face1
Assign a set of hypothesis: 2D Automatic Quadrangulization
Number of segments: 30
Default remainder

Compared with equations in Blevins book “Formulas for Natural Frequency and Mode Shape”. If you give me your email address I will send a MathCad file that shows this.