[Nek5000-users] Object definition for surface integrals

[nek5000-users at lists.mcs.anl.gov]

Hi Ravi,

Inspection of the source routine navier5.f will reveal most of the answers to
your questions.  That is where drag and torque are calculated.   (I recommend
torque_calc, which gives the drag as well and is somewhat superior to drag_calc.)

hcode = history code --- there are several codes used (the convention
follows the Nekton 2.0 convention established in the 80s). Of relevance to
drag/lift/torque are hcode(10,.), which must be 'I' for Integral
quantity, and 1,2,3, which must be 'F' for force.   Just follow the
convention in the ext_cyl.usr example.

Note that the 2nd argument of hcode indicates how many objects
you have.  An Object is a collection of faces. So, you might have
more than one cylinder on which to compute drag, in which case you
would have more than one object.

Each object comprises "nmember(iobj)" faces.

nhis is the number of history elements you are tracking.
It is normally zero, plus the number of objects.  It is
a measure of the number of lines of information dumped to
the .sch file per timestep.

cbc is the character array holding the boundary condition
specifier - one per face per field (velocity, temperature, etc.)

object is a pointer to the members of an object. A member of
an object is a given face (1-6) of a given element.   The
element id is global -- (i.e., not the local element number
which is specific to a given mpi rank).

Paul

________________________________
From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov]
Sent: Monday, May 26, 2014 4:39 PM
To: nek5000-users at lists.mcs.anl.gov
Subject: [Nek5000-users] Object definition for surface integrals

Dean NEK Users,

I am looking for some sort of help or documentation explaining the object definitions for evaluating surface integrals.

My eventual application will be to evaluate the drag and lift forces for the case of a 2D flow past a cylinder, supported on elastic foundation, i.e., vortex-induced vibration simulations using NEK5000.

So far, the examples available in the repository and the NEK mailing list have enabled me to simulate the motionless cylinder and the case of cylinder moving with a prescribed motion.

However, I have hard time decoding the surface integral evaluation in subroutine "set_obj" available in the "ext_cyl.usr". Overall, I understand that there is a conditional statement to find all the elements (or element edges) with "W" boundary condition and then an object is created for each of those elements. It would be very helpful is someone could point me to a documentation/help, which gives an explanation for the following functions or variables which have been used in the "set_obj" subroutine.

1. variable "hcode"
2. variable "lochis"
3. variable "nhis"
4. function or variable "cbc"
5. variable "nmember"
6. function or variable "object"

Any hints to understand this subroutine "set_obj" of the example model "ext_cyl" would be of great help for me to understand and develop the model for vortex-induced vibration.

In addition, if there is already an example model to perform vortex-induced vibration, please let me know.

Thanks in advance. Any hints and tips are much appreciated.

Regards,
Ravi


--
Ravi Kumar T R

University of Illinois at Urbana-Champaign
ph : +1 217 778 7538<tel:%2B1%20217%20778%207538>
http://lndvl.mechse.illinois.edu/
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/nek5000-users/attachments/20140526/16b28609/attachment.html>