# How to applied a force on the fluid?

Hello,

Can you tell me how to applied a force on the fluid? A forum user told me to use a forcing scheme (like in forcedpoiseille2D) but I don’t know how to do and I don’t find information about this subject in the documentation.

I would like to simulate in 2D the movement of a fluid when a plate move from x to x+dx.

Thank you!

Whether you model a moving obstacle through an appropriate boundary condition or by other means is mainly a question of your point of view. I wouldn’t say that obstacles are necessarily considered a special case of boundary condition in lattice Boltzmann. But there have been a few approaches using moving boundaries in the literature which I am sure will help you with your windmill problem.

It is a recurrent problem that scientific work is inaccessible because articles in scientific journals are proprietary. My suggestion is to contact the authors and ask them for a preprint of their paper.

Hello,

I would like to simulate a vertical windmill (in 2D) using OpenLB. In the documentation, the section dedicated to rigid body mechanics is empty…
In the collision “step” of the LBM, is it possible to take in account an external force applied by a rigid body?

Best Regards,
Rodrigue

Could you give a little bit more information about what you want to do? With a vertical windmill, do you mean something like this:

http://www.popularmechanics.com/technology/industry/1288371.html

And if yes, how do you want to simulate it in 2D?

implement boundary: use bounce-back (see cylinder2d as an example)
act with an external force on the fluid: use forcing scheme (see forcedPoiseuille2d as an example)

Hello,

At the end, I would like to simulate a real windmill in 3D but for the moment I’m trying to work on a simple example.

What I would like to simulate is a system like this one:
http://img204.imageshack.us/img204/8021/verticalwindmillpr7.png

I’ve already studied the examples which comes with openlb but I didn’t find anywhere explanations about “forces” (what you called forcing scheme).

It would be great if I can simulate a thin plate moving in a steady air flow (and view the wind/water moving influenced by the plate).

Nobody?

Hi all:

I am new in OpenLB, anb I am very interested in the simulation of VAWT, Vertical Axis Wind Mills, I am tyring to use it for that.

I have created a circshift circshift3d functions to use MATLAB version of OpenLB in MATLAB 5.

I have coded a set of three MATLAB functions that let you write the data calculated by the MATLAB version of OpenLB in VTK file format to visualize using the freeware software ParaView. Visit my web page: http://www.tinet.org/~sje/mtlb2vtk/mtlb2vtk_en.htm

And now, I working in a MATLAB code that let you use bitmap files to define obstacles, with this you can define an obstacle using Paint, or any Bitmap editor in Black & White, and then use in MATLAB OpenLB. Or you can make de drawing using your CAD application, capture de image, reshape, convert to Black & White and put in to MATLAB OpenLB.

Then I will need to learn how to obtain presure distribution and the force appliaed to the obstacles.

Regards.

I didn’t know that a matlab version of openLB exists! Is it this: http://www.lbmethod.org/numerics:matlab_samples ?

OpenLB is coded in C++ langage.

It’s not a problem for me to create a software which takes an image (.bmp, .jpg, etc.) as an entry parameter…
It’s not very difficult to obtain the pressure distribution and to compute forces applied to obstacles.

What I would like is to be able to applied a force on the fluid… Adam told me to use a forcing scheme but I don’t know how it works an I don’t find information in the documentation about this subject.

You can find the MATLAB and other languages code from http://www.openlb.org/lb.examples.html

Sorry but I don’t know about forcing scheme.

Hi,

There is no such thing as a Matlab version of OpenLB. The Matlab scripts on the LBMethod.org web page serve an educational purpose, as they illustrate important concepts of lattice Boltzmann in a few lines of code. But they implement only specific 2D test cases, as opposed to OpenLB which is a generic framework for doing lattice Boltzmann.

You can implement a body force in OpenLB by replacing BGKdynamics objects by ForcedBGKdynamics objects. On each point of the lattice, it is possible to decide for the value of the forcing term, i.e., the amount of momentum which is added to the fluid per cell and per iteration step. This is useful to implement physical phenomena such as gravity. Have a look at the example forcedPoiseuille2D, and, if there is something you don’t understand there, try to ask more specific questions.

Although I have no strong opinion on this, I don’t think that adding a body force is helpful in modeling the fluid-solid interaction for your windmill problem. A body force term is used to add momentum to all cells, or at least a spatially extended group of cells on your lattice. In your case, momentum is only added along the boundaries of the windmill. Such a thing would usually be implemented as part of the boundary condition.

OpenLB does not offer moving boundaries in its current version, and you’re on your own for implementing this. Try googling for lattice Boltzmann and moving boundaries, as there are many papers on this subject.

Although I have no strong opinion on this, I don’t think that adding a body force is helpful in modeling the fluid-solid interaction for your windmill problem. A body force term is used to add momentum to all cells, or at least a spatially extended group of cells on your lattice.

Like a pump, I suppose?

In your case, momentum is only added along the boundaries of the windmill. Such a thing would usually be implemented as part of the boundary condition.

Ok, I understand. Thank you!

OpenLB does not offer moving boundaries in its current version, and you’re on your own for implementing this. Try googling for lattice Boltzmann and moving boundaries, as there are many papers on this subject.