SPH- Smoothed Particle Hydrodynamics

Altair Forum User

Hi everybody

 

i would perform a simulation of a lifeboat ditching, like in the tutorials where is used an ALE approximation, but 

 

using the SPH approximation, smoothed particle hydrodynamics. Does anyone know how build a sph model in hypermesh

 

 and solve it with radioss? Are any kind of tutorial about SPH simulation online? i was not able find it anywhere...

 

Thank you!!!

Altair Forum User

Hi tapy88,

 

Maybe you can refer to example 22.1 Ditching using SPH which can be found in following path           file:///C:/Program%20Files/Altair/12.0/help/hwsolvers/hwsolvers.htm?22_1_ditching_using_sph.htm

 

Regards.

Altair Forum User

Thankyou very much NSKRTLUS

 

i found and launch it!

 

i need to understand the meaning of the single card used, but i can't understand it from the explication given in the user's manual...

 

Have you any advise to give me?

 

Regards 

Altair Forum User

Hi tapy88,

 

I am pleased that it helped you.Actually i didn't work about SPH elements deeply so i don't have much more information.Maybe someone who have knowledge about this topic in the forum, can help you.

Additionally,the page    file:///C:/Program%20Files/Altair/12.0/help/hwsolvers/hwsolvers.htm?smooth_particle_hydrodynamics_sph.htm      may can help you.

 

Regards.

Altair Forum User

Hi everybody 

 

i'm again here; after a long time I figured out how to create a model of an object ditching in water, using SPH method;

 

this is a fluid structure interface model, so water (sph nodes) and something structural, like a tank or a spiceman (surface mesh, shell).

 

I must now deal with different problem; i have to model the impact of two solid objects, both of the modelledwith SPH;

 

I suppose a elato plastic behavior for the materials, with different mechanics characteristics.

 

i would to understand what kind of interface to use.... with two solids modelled with SPH, i have node to node contacts and so 

 

i don't know wath kind of /INTER to use.

 

could some one help me...pleeeeaseeee

Altair Forum User

Hi tapy,

 

You can use type 7 interface for sph/solid interaction.

Altair Forum User

Hi,

 

you can try Type 7 with SPH as slave nodes.

Altair Forum User

thanks NSKRTLUS, Prakash Pagadala, i'll try in this way....

 

I have a question about the flotation;

 

i create a tank full of water (sph) with a sphere positioned centrally completely submerged in the sph.

 

The sphere is shell meshed with a thikness set in a manner to obtain a determinate mass (body rho < water rho).

 

The body should rise to the surface with a water line located approximately at mid-height of the body.

 

I set a TYPE7 interface and a gravity load on the rigid's master node inside the sphere.

 

The sphere doesn't float until the surface, but falls down until the bottom of the container.

 

Someone could try to explain me what could be the causes of this behavior?

 

Shall i need to set also another component inside the sphere, modelling in such way the AIR.

 

many thanks

 

Damir

Altair Forum User

could it be due to the gravity load not applied to the SPH nodes?

 

tanks

Altair Forum User

Hi,

 

Have you applied gravity to sphere alone?

Altair Forum User

Also, you may try changing the Isf in type7 interface card.

Altair Forum User

@Prakash Prakash

thank you for reply...

 

I use Type 7 with Istf 1, SFAC 2000 Pa, Gap min 0.01 (particlesize/2)

 

Two gravity collector applyed respectively on rigid's masternode of submerged body and on sph node set (all sph particle)

 

Do you have any advice on h ( smoothing length) value, in auto generated sph property?

 

thanks

Altair Forum User

Hi,

 

is it possible to share the output files?

 

you can use the dropbox link in my signature to share the files.

Altair Forum User

good morning Prakash

 

i shared .out file...

 

i have a lot of question about SPH modelling and Fluid Structure Interaction, but first of all i need to see and understand the basics and natural behavior

 

of bodies in a fluid.

 

best regards

Altair Forum User

I would like to know the methods, if there are, to calculate the STFAC, FRIC, and GAPmin in INTERFACE TYPE7

 

in relation to the particular problem of coupling and interaction between structures(FEM) and liquids(SPH).

Altair Forum User

Hi,

 

what is the unit system used?

Altair Forum User

Meters Kilograms Seconds

Altair Forum User

Hi,

 

can you reduce the density of the wood and check if that is working for you?

Altair Forum User

Hi Prakash

 

i have tried with 250Kg/m^3 but nothing happens...

 

just for scruple i explain my procedure, maybe i make some mistakes in other steps

 

1) first of all i create a geometry, surface, for the tank...and i mesh it 2d Automesh

   1.1) I create property surface (shell) and material (elastic) matlaw1 for the steel tank

2) For the sph: i create the same geometry of the tank, little less high, and closed, like a cube, but only surface

   2.1) i mesh this component with 1D, introducing the pitch and density value, the sph particle are automtically created as the relative property (sph1)

   2.2) i create the material of water, hydrodynamics, mat law6, giving only rho, nu, C1, Pmin, values, in edit panel

3) then i create the supposing /emoticons/default_angry.png' alt=''>  /emoticons/default_angry.png' alt=''>  /emoticons/default_angry.png' alt=''>  'must be' floating cube or sphere or whatever you need, into the sph component, in the middle of sph particles

   3.1) i create the mesh, properety (surface, shell) and material (wood )of cube

4) I mask all the sph particles around cube, and delete only the sph elements remained into the cube surface

   4.1) i create a rigid into the cube

5) i create all the element set i need

6)i create a gravity curve, and impose gravity in BC's panel, to sph and the master node of rigid associated to the cube, and boundary conditions for the tank

7) i create a type7 interface between tank and sph, and between cube and sph, [maybe here i do my mistakes, i'm not sure of the values to give at STFAC, FRICTION, GAPmin, for GAPmin i use the half of particlesize, a very small Friction value, but i'm not able to understand witch value of stifness factor to use]

with roh body< rho water, why doesn't it come to surface???

Archimedes would be furious!!! /emoticons/default_biggrin.png' alt=':D' srcset='/emoticons/biggrin@2x.png 2x' width='20' height='20'>  /emoticons/default_biggrin.png' alt=':D' srcset='/emoticons/biggrin@2x.png 2x' width='20' height='20'>

 

maybe masking sph around cube and delating the rest inside the cube could be the error, because in the sloshing simulation all works fine;

maybe the software understands it (delating of sph into cube) as if the cube into water doesn't move any quantity of water, so receives no push from the bottom upwards

as the Archimedes principle describes.

 

Hope that with this new elements you can help me

 

thanks for attention

 

Damir

Altair Forum User

Hi,

 

May be you forgot to apply a doping velocity to the block.

Altair Forum User

Hi, 

 

A dropping velocity? i have tryed it, and an other spiceman floats on the free suface of fluid!!!

 

My dilemma is to prove the simple archimedes principle....a initial submerged body must come to surface (rho body< rho h2o)

Altair Forum User

Hi,

 

in order to make to object accelerate to the top, the weight of the object should be less than the buoyant force.

Altair Forum User

Hi Everybody

 

Because of the SPH model of a ditching body i have to set up is very haevy, i need to symmetrize the model respect a plane, so to build only an half of model.

 

About the ditching body i impose the symmetry conditions blocking the traslation normal to the symmetry plane and the rotations round the other two directions.

 

For the SPH, i need to use the /SPHBCS/  card of loadcollectors but is not clear the way to use it: with DIR i impose the normal of the symmetry plane;

 

with FrameId i chose the eventual reference system; Grnod_Id i do not know what it's...for the symmetry plane definition or a reference to build the ghost particles?

 

ILEV=1 for the sph (as online help says)

 

SLIDE or TIELD for symmetry type; I choose SLIDE

 

could anyone help me explaining hoe set a symmeties

 

thank you

Altair Forum User

Good Morning Everybody

 

I solved the problem of Invel or Impvel for sph dropping test; it doesn't work with invel because of some problem exporting the .rad model that

i found opening the .rad file with text editor and comparing the model with other working well.

 

Now i have to solve other problem: i have a solid woody sphere entering in water tank; i model it using P1shell elements giving only thik prop.

I created a Rbody linking all sphere surface nodes with the Rbody masternode; i use the masternode just to apply the gravity load and the initial velocity load.

I do not add any mass in Rbody card, but by mass calc opition the elemnts sphere mass is the same of real drop test.

 

Because of the behaviour of water splash is not the same of my simple experiment, i wonder if this may be due to the fact that i model the sphere by shell elements,

and solid elements. I add that the sphere, in my model, does not go down until tank bottom like in real experience but just until the half height line of tank.

In addition to this i do not model the air sorrounding the water; could it have any influence?

 

Some advice?

 

Best regards and and happy Xmas

 

Damir

Altair Forum User

Hi Damir,

 

can you increase the mass of the sphere and check how it behaves?

Altair Forum User

Hello,

I want to create sph in the half of the box, outside the pipe ( a photo was attached).( I do not want to have sph inside the pipe). I used automesh to mesh them as well.

I selected the box and pipe and then in volume definition I selected pipe as an exclude enclosed. But the sph was not generated and I got an error which says '' No volume selected for meshing''.

would you please help me.

I appreciate your help.

Best,

sara

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Altair Forum User

Hi,

Unfortunately there are some issues related with 'Exclude enclosed' option in HyperMesh and our developers are working on it to get in fixed in the next release.

As for now, you have to create SPH elements throughout the box and manually delete those inside the pipe surface.