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#1 Re: Code_Aster usage » Modal Analysis with Fluid - Frequency Output » 2021-11-23 18:56:08

CLF

Hi

Congrats to your success. smile

To help new users and save future work - why not post a small and complete example? Ideally, with a well commented *.comm file and example outputs where possible.

Sincerely
Claes

#2 Re: Code_Aster usage » Attach point mass in a FSI problem » 2021-07-27 14:59:30

CLF

Hi

If you follow my workflow, CA works.

I suggest that you first give it a try.

/C

#3 Re: Code_Aster usage » Attach point mass in a FSI problem » 2021-07-21 19:23:59

CLF

Hi

MODELE=AFFE_MODELE(MAILLAGE=MAILLA2,
                   AFFE=(_F(GROUP_MA='POI1',
                            PHENOMENE='MECANIQUE',
                            MODELISATION='DIS_T',),
                           _F(GROUP_MA=('SURFLIBR',),
                              PHENOMENE='MECANIQUE',
                              MODELISATION='2D_FLUI_PESA',),
                         _F(GROUP_MA=('FLUID1','FLUID2','FACELATE',),
                            PHENOMENE='MECANIQUE',
                            MODELISATION='3D_FLUIDE',),
                         _F(GROUP_MA=('IFLUSTRU',),
                            PHENOMENE='MECANIQUE',
                            MODELISATION='FLUI_STRU',),
                         _F(GROUP_MA=('PLAQUE',),
                            PHENOMENE='MECANIQUE',
                            MODELISATION='3D',),
                         _F(GROUP_MA=('FONDS',),
                            PHENOMENE='MECANIQUE',
                            MODELISATION='DKT',),),);

You need to check documentation, but my guess is

'FLUIDx' : 'IFLUSTRU' : 'FONDS'

'DKT' ('FONDS') is a shell element. Might be 'FLUID1' or 'FLUID2' that is a Face element

The above demonstrate the usefulness of having a strict naming convention in CA.

Have fun
C

#4 Re: Code_Aster usage » Attach point mass in a FSI problem » 2021-07-20 01:03:46

CLF

Hi

I hope I get this right (from memory).

Identical meshes, different nodes for acoustic/structure.

The FLUI_STRU can be a copy of either group, ie I think it can share nodes from either group, but I am not quite sure wrt this.

Suggestion - start with something simple, eg a box of solid 3D acoustic elements. Use one side as Face, copy this face mesh for a FLUI_STRU and for a Shell. You can make the shell simply supported and excite a node on the shell with a force.

Yes, you should find example cases. (I haven't looked them up).

/C

#5 Re: Code_Aster usage » Attach point mass in a FSI problem » 2021-07-18 08:50:20

CLF

Hi

At present, I have no way to run your problem, so I can just look at your model definition.

The topology in CA looks like this.

Acoustic element, eg 3D with 2D Face : connects to : FLUI_STRU : connects to : 2D structural element or a 2D Face of a 3D structural element. Differently stated, CA uses an element matching procedure.

Therefore, there must be a 1:1:1 2DFace:FLUI_STRU:2D structural element/face matching, usually achieved by copying element groups.

To connect a 0D element like a mass or spring, it is connected to a structural element node.

Looking at your AFFE_MODELE, you define a FLUI_STRU group called FSI, a 3D element group called solid, but no 2D Face (e.g. named solid_FSI) of these elements, i.e. you leave CA clueless on which structural Face elements to connect to your FSI group unless you define also 2D faces of your 3D solid.

The 3D_FLUIDE has fluid, walls and bottom groups defined. I assume walls and bottom are 2D Face elements. However, these groups do not seem to be identical with the FSI elements group, as one is used as velocity excitation and the other is fitted with an acoustic impedance boundary condition. It seems that you need to define a 2D Face group of the 3D_FLUIDE elements with elements that are identical to the FSI group (e.g. named fluid_FSI).

The simplest way to define an interface, usually is to copy a structure or acoustic group and define it as the FLUI_STRU elements using CA element copying commands, i.e. it can be done in the *.comm file and does not have to happen in the pre-processor.

So, all in all,
1) if you define 2D face elements of the 3D structure elements that are 'wet'
2) 2D face elements of the 3D_Fluide that meet structure
3) The 2D Face elements are identical to your FLUI_STRU elements
4) You add these definitions to your AFFE_MODELE and Material definitions
, then there is a chance that your script might execute as CA then understands where to connect the structure domain to the acoustic domain.

Last - a piece of advice - it usually pays off to have very clear group names when using CA.

So, application of strict define naming rules for your models make it easier for you to see if a step in the model definition is wrong or forgotten.

Hope this helps
Claes

#6 Re: Code_Aster usage » Attach point mass in a FSI problem » 2021-07-02 15:38:48

CLF

Hi

You should not attach other than matching structure/acoustic elements to a FLUI_STRU interface element.

To clarify, a 2D shell connects to the 2D FLUI_STRU, which in turn connects to the 2D Face of an acoustic 3D element. This is an element matching.

You connect beams and lumped elements to the structure shell nodes.

/Claes

#7 Re: Code_Aster usage » Attach point mass in a FSI problem » 2021-07-01 15:22:17

CLF

Hi

No, FLUI_STRU are Interface elements.

/Claes

#8 Re: Code_Aster usage » Attach point mass in a FSI problem » 2021-06-29 21:54:48

CLF

Hi

No. You cannot.

Structure elements can only connect to other structure elements.

/Claes

#9 Re: Code_Aster usage » Attach point mass in a FSI problem » 2021-06-27 12:40:06

CLF

Hi

Are you dealing with fluid flow - structure interaction or, do you refer to a vibroacoustic analysis?

CA cannot do flow-structure, but is quite capable wrt vibroacoustics.

/C

#10 Re: Code_Aster usage » Rigid boundary in fluids » 2021-05-11 14:23:46

CLF

Hi

If you refer to MODELISATION = '3D_FLUIDE', then it is acoustics, ie to the best of my knowledge with zero net flow and wave propagation only.

/Claes

#11 Re: Code_Aster usage » Rigid boundary in fluids » 2021-05-07 21:48:22

CLF

Hi

I have never addressed this problem.

I assume the fluid elements reside in your CFD code, the structural elements in CA, then I assume you simply would use pressure to load the structure and structural displacement to affect the flow.

To connect the above, you would have to set up the appropriate equation systems and solve the problem.

/C

#12 Re: Code_Aster usage » Rigid boundary in fluids » 2021-05-07 20:55:53

CLF

Hi

I am not sure I 100% understand your question, so...

You just define your acoustic model using 3D acoustic elements and you have hard walls by default at the 'free' faces of the acoustic elements.

If you  want hard walls inside a volume, you need to split the nodes to have 'free' faces inside the volume.

If you want a hard walled box, say at the centre, you simply delete one or more elements to get this empty box space.

/C

#13 Re: Code_Aster usage » Rigid boundary in fluids » 2021-05-07 20:18:14

CLF

Hi

By default, all walls are rigid in the acoustic domain.

If you want to impose a zero acoustic pressure condition, you use the variable PHI.

Sincerely
Claes

#14 Re: Code_Aster usage » Simulating carbon fiber parts » 2021-04-12 18:35:39

CLF

Hi

Please share your progress with the forum.

As stated in my reply, my gut feel is that you need a Python implementation for the composite part and thereafter simply add its output as python variables to a suitable materials and properties card in CA.

Similarly, ply stress and similar would have to be derived as a Python driven post processing step.

Just my 2 cents
Claes

#15 Re: Code_Aster usage » Simulating carbon fiber parts » 2021-04-07 11:32:56

CLF

Hi

Not a topic I am well versed in, but I happened to see this resource a few days ago. Perhaps it is worth a look?

Search for espcomposites and Practical Analysis of Aircraft Composites

Practical Analysis of Aircraft Composites is a comprehensive guide to the analysis of composite aircraft materials, combining theory with proven practical approaches. Invaluable to both practicing professionals and academics, Practical Analysis of Aircraft Composites covers a wide variety of topics including:

Basic mechanics of composite materials
Principles of Classical Laminate Theory
Unnotched strength prediction and notched strength prediction
Analysis methods for mechanically fastened joints
Bonded joint analysis for both metal and composite adherends
Stability solutions for laminated plates and built-up structures
Composite beams and sandwich structures
Unique mechanical properties of composites
Structural requirements and structural substantiation for aircraft composites
Practical aspects for Durability and Damage Tolerance (DaDT)
Standard design practices for laminates, joints, and sandwich structures

The reason being that I would guess that you have to implement composites either using analytic formulas (Python) or by the use of macro-micro analysis, ie make a 3d model of the composite and get the macro properties from this.

CA executes in Python, so a neat Python package might be a good companion. Github has lamipy that may be worth looking at.

Hope this helps

Claes

#16 Re: Code_Aster usage » How to simulate fatigue in composites » 2021-01-18 12:36:33

CLF

Hi

Perhaps DNV OS C501 can provide some insights?

Search for a pdf on Google.

I believe the fatigue concept used is residual strength, ie how much load capacity is left.

/C

#17 Re: Code_Aster usage » Poroelastic material » 2020-11-25 14:23:11

CLF

Hi Danillo

As you know, the impedance boundary condition is correct only for one angle of incidence. It works fine for 1D.

For simple absorbing boundary conditions, you have a rubber band mesh that absorb.

A more rigorous bc is to use the BE code Miss3D. This one, I have not used.

Sincerely
Claes

#18 Re: Code_Aster usage » Poroelastic material » 2020-11-18 16:35:10

CLF

Hi Danillo

I cannot really answer your question as such.

There are soil material models that ought to work also for acoustics, though I have neither looked at, nor really tried them.

That said, CA executes in Python. So, you can mix and match.

This open source module runs in matlab.
github.com/JPPM-KTH/ARAMiS

If the built in material modes do not work, you can (probably, haven't tried this one either) either use these to generate matrix elements or drive Matlab from Python.

Aramis seems to compute absorption data. As it uses a transmission matrix method, I am guessing there might be meatier data that can be extracted from the code.

Hope this helps at least a little.

Sincerely
Claes

#19 Re: Code_Aster usage » Element birth and death in Code aster? » 2020-11-03 14:54:26

CLF

Hi

I don't know if this is applicable for your situation.

An old Nastran trick is to define two elements with 50% of the properties in each. You can then let the element die simply by flipping the sign on the Youngs modulus and the density.

HillaBilly style, but it works.

Hope this helps
Claes

#20 Re: Code_Aster usage » surface integral over boundary » 2020-09-30 12:58:37

CLF

Hi

Would it work to output your integral to a node using an explicit equation? If so, see document R4.44.01.

Sincerely
Claes

#21 Re: Code_Aster usage » Modal Strain Energy » 2020-09-30 12:55:47

CLF

Hi

MSE gives you modal loss factors.

So, yes, you can use modal substructuring and these loss factors for N-bodies.

The advantage in doing so lies in the tacit assumption that modal damping is light and evenly distributed. This may be more motivated in a substructured model.

Sincerely
Claes

#22 Re: Code_Aster usage » Free-field/ Far field/ Viscous boundary/ Absorbing boundary elements » 2020-09-30 12:39:39

CLF

Hi

There is an absorbing 'rubber band mesh' that is simple to use. This mesh, however, is not perfectly absorbing. See
* 3D_FLUI_ABSO - Rubber band mesh with anechoic termination for fluid elements. This element has the dofs PRES and PHI (acoustic displacement). See document R4.02.05.
* 3D_ABSO - Rubber band mesh with anechoic termination for structure (soil) elements. These elements can be used for analysis of soil-structure interaction analysis. This element has the dofs DX, DY, DZ. See document U3.14.09.

A bit more advanced is to use instead a Miss3D Boundary Element model on the boundary. This should be reflection free but come at the cost of increased analysis effort.

I have not used Miss3D, which is part of the SalomeMeca package. You need to search the forum for help on that one.

Hope this helps
Claes

#23 Re: Code_Aster usage » Simulate the transmission loss of a muffler » 2019-07-02 21:29:40

CLF

Hi

Perhaps here is a good place to start?  (cannot post links)
Index» Code_Aster usage» Acoustics - Internal Wall/Hard Boundary

You can use CA to calculate TL but only without Mach compensation.

TL keeps popping up for acoustics. It is good to search the forum on Acoustics. 

/Claes

#24 Re: Code_Aster usage » Acoustics - Internal Wall/Hard Boundary » 2019-06-04 15:30:52

CLF

Hi

Glad it worked out in the end.

A request - for the benefit of other, new users, who also are likely to start with a case similar to yours. Can you please add a 100% working model, analysis files and output data to the forum? I believe this is good practice, i.e. not only to show problem scenarios but also ones that do work as expected.

Last, feel free to drop me a private mail. I may have something for you.

/Claes

#25 Re: Code_Aster usage » Acoustics - Internal Wall/Hard Boundary » 2019-05-29 08:34:35

CLF

Hi

Your set up looks OK to me & still data is wrong.

For what it is worth. Theory is without any damping. Perhaps we should try to bark up this tree?

You input complex data with zero imaginary part. This should produce zero damping. However, in practice, there will always be some damping in there due to rounding.  Also, there is the case where you phase shift excitation 90 degrees.

You solution scheme states an acoustic damping matrix C1. My suggestion - try to eliminate C1 and solve the case again.

It should not matter, but your parameter value PUIS_PULS=1 should not be needed as you state velocity as BC. Also, the 90 degree phase shift on excitation combined with complex data that should be zero may cause unfortunate numerical problems. It may be worth a try to toy a little with these to see if anything happens on the TL.

A comment - TL is one thing. Insertion Loss is the better descriptor of actual performance.

Hope this helps.

Sincerely
Claes