Double Precision and Prescribed Force

COertel

Hi,

as you said, next release will include double precision. I was a little bit confused so sorry for the question. It sounded so much general... Do you mean it will do calculation in double precision, even on standard-GPU´s? I´m just asking, because I will buy a GPU soon and do not know if I buy a Tesla or Titan. Maybe I misunderstood you and you meant CPU and "double precision GPU". Otherwise single precision.

Second question is on applying forces to a movable boundary. I want to move a plate due to a prescribed force. In CASEFORCE it is shown, that acceleration can be applied to fluid particles. Is it possible to apply it to boundary particles as well?

Thanks in advance!

Best regards

Chris

EDIT: One additional Question: Can the actual timestep be plotted?

Alex

Here some tips to your questions:

1) Next release will include double precision for some variables and computations for both implementations CPU and GPU.

2) If you are goint to impose a prescribed motion, just use a text file where you are reading time vs position. There are some examples of motion reading a file.

3) Sorry next version will include an option to plot DT. Now you will have to code it...

Regards

COertel

Hi Alex, thank you for your quick response.

Do you mean, it doesn´t matter if I have a single precision GPU? I can do double precision anyway? Thats what I meant, because it doensn´t make sense to me. (But this doesn´t mean you did it and I just don´t understand it )

To the second question: The thing is, that I don´t want to apply a prescribed motion. I want to define the force. For example pressing a boundary-plate with 1000N on a fluid.

Is this possible?

Thank you again.
Best regards

Chris

gfourtakas

Hi Chris,

You can apply any force you like (constant or not) by the same way we apply gravity to the particles, but.. you need to go into the code.. (or force for that matter), however we do not provide the functionality through the xml, maybe the acceleration file?

anyway, it is a good exercise for the soul.. have a look at the code, the modification is very simple,

good luck

Alex

Sorry if I was not initiall clear: You need a GPU card supporting double precision to use double precision, of course

COertel

Sorry for the stupid question and thank you all for your help

MikeHersee

A bit late, but just in case still relevant: Tesla cards such as the M2090 are optimised for double-precision and can compete with high-end consumer cards such as the 770 on that score. Tesla M2090's are becoming quite cheap now, although they consume quite a bit of power even when they're not doing much. However, bear in mind that the Tesla cards don't have any graphics output at all and you will need to use either an additional graphics card for actual monitor output or the built-in graphics facility. Bear in mind also that many motherboards will not support both internal and external graphics cards simultaneously at a bios level so you need to specifically check that the motherboard will allow simultaneous use of two graphics devices, I found out. The hard way.

Mike

MikeHersee

Just to point out, you may find you need an upgraded power supply if you install a Tesla device, more so than for a Titan possibly. You pays your money...

Alex

Tesla GTX Titan (Z, Black...) do not need a very power supply since those cards are more effincient and they even dissipate less.

Regards

andi_tri

for next release are we still possible to use GPU with single precision to run simulation?or we need new GPU with double precision to use DualSPHysics 4.0?

Regards

Alex

You only need a GPU that 100% supports double precision if you need simulations to be run in double precision... if not, the old GPUs will be fine