fenics team mailing list archive

["Johan Hoffman" <jhoffman@xxxxxxxxxx>]

Angelo,

You can download the movies at:
www.csc.kth.se/~jhoffman/pub/

/Johan

> Johan, it seems that something went wrong with the files you posted
> (their size is zero). Could you post them again? Thanks,
> angelo
>
>
>
> Johan Hoffman wrote:
>> The geometry engine is a missing piece in FEniCS, which we have not got
>> to
>> yet. But of course this should be done. Today we only work with a given
>> mesh, which may have been generated from a complicated CAD geometry in
>> the
>> first place (we have more comlex geometries that cylinders, for example
>> a
>> full model of a car), but today the original geometry description is not
>> used in mesh refinement/movement; if the mesh is refined/moved, no
>> update
>> is made with respect to the original geometry. But as I said, this is
>> what
>> we want. In an old code I added these things manually, but for DOLFIN we
>> want to take a general approach.
>>
>> We have a project running now on fluid-structure interaction (FSI) with
>> ALE where the mesh is moving. I have attached a few movies from
>> preliminary tests on model problems of ALE for the flow part, we are
>> currently working on the full FSI problem.
>>
>> The standard approach to FSI is (as you say) to iterate between a fluid
>> and structure solver in one way or another; for refs. see e.g. the group
>> of Alfio Quarteroni in Lausanne/Milan. In our project we are trying a
>> somewhat different approach, which I will keep you updated on (e.g.
>> through the fenics-list), and the algorithms will be implemented in
>> DOLFIN, in an experimental version rather soon I hope.
>>
>> We also have a project in collision of cars for animation/simulators,
>> where the goal is real time and interactivity. For a flow problem I'd
>> say
>> that the computational cost is today still too significant for
>> interatcivity of a reasonably fine model, but that we should be able to
>> address in the future I think, in particular with a superfast Stillwater
>> machine...
>>
>> /Johan
>>
>>
>>> CAD geometry is specified in terms of primitive shapes and Boolean
>>>
>> operators. A "geometry engine" is the black box that defines some set of
>> primitives and operators to construct arbitrary shapes and the ability
>> to
>>
>>> determine if a point is inside/outside or on the surface. Typically the
>>>
>> geometry engine also provides the ability to extract a surface mesh for
>> display.
>>
>>> I am becoming comfortable with the task of generating a mesh generator
>>>
>> (or
>>
>>> better said: rip one off from CGAL or CAMAL), and I understand the GUI
>>>
>> issues. I don't comprehend the amount of work of the other two you
>> mentioned: the variational formulation and the solver. The solution I
>> was
>>
>>> thinking along is that of a two domain solver where one iteratively
>>>
>> solves
>>
>>> the fluid flow, extracts the boundary conditions, and applies them to
>>>
>> the
>>
>>> structure. I haven't found any material that describes a coupled system
>>>
>> yet.
>>
>>> Are you aware of such a reference?
>>>
>>> Theo
>>>
>>> -----Original Message-----
>>> From: fenics-dev-bounces@xxxxxxxxxx
>>>
>> [mailto:fenics-dev-bounces@xxxxxxxxxx]
>>
>>> On Behalf Of 'Anders Logg'
>>> Sent: Wednesday, December 06, 2006 4:12 PM
>>> To: fenics-dev@xxxxxxxxxx
>>> Subject: Re: [FEniCS-dev] AMR
>>>
>>> On Wed, Dec 06, 2006 at 04:08:15PM -0500, Theodore Omtzigt wrote:
>>>
>>>> Yes, but putting the pieces together to make that happen would be
>>>>
>> non-trivial.
>>
>>>> /Anders
>>>> Is it non-trivial due to the lack of a geometry engine, or the lack of
>>>>
>> moving grid functionality, or something else?
>>
>>>> Theo
>>>>
>>> I don't really know what you mean by "geometry engine", but you will
>>>
>> have to write a substantial amount of code to put everything together:
>> mesh, variational formulation of the fluid-structure interaction
>> problem, solvers etc, not to mention the graphical user interface for
>> interacting with the mesh.
>>
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