CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums

Blog Entries

Register Blogs Members List Search Today's Posts Mark Forums Read

Old

Dark side of Amdahl's law. Part II

Posted December 4, 2011 at 10:57 by SergeAS
Updated December 4, 2011 at 11:44 by SergeAS
Tags mpi, parallel

Let us consider in more detail how works domain decomposition in the simplest 1D case.
The computational domain is divided into several subdomains along one (usually the longest) dimension. The number of such subdomains usually corresponds to the number cores involved. The main data exchanges take place between neighboring subdomains. The size of transmitted data between adjacent subdomains in the general case depends on many factors (number of equations in the system, the size of the computational...
Attached Thumbnails
Click image for larger version

Name:	HyperFLOW2D-parallel-factor.png
Views:	325
Size:	11.3 KB
ID:	38   Click image for larger version

Name:	HyperFLOW2D-speedup.png
Views:	341
Size:	11.0 KB
ID:	39   Click image for larger version

Name:	HyperFLOW2D-speed.png
Views:	335
Size:	11.1 KB
ID:	40   Click image for larger version

Name:	domain.png
Views:	330
Size:	10.2 KB
ID:	41  
SergeAS's Avatar
Member
Posted in Uncategorized
Views 937 Comments 0 SergeAS is offline Edit Tags
Old

Slip/No-Slip Flow

Posted December 2, 2011 at 23:19 by MatthewSlaby

Hi, I'm Matthew.

You asked what the physical meaning of the slip/no-slip condition means.

You need to look up the term "Knudsen Number".

This is simply a reminder of what CFD is base upon.

This will give insight into your question.

Fluid Dynamics is mostly based on Continuim Mechanics which assumes that the properties of a gas or liquid can be approximated by some very simple rules.

These would be:
...
New Member
Posted in Uncategorized
Views 712 Comments 0 MatthewSlaby is offline Edit Tags
Old

Dark side of Amdahl's law

Posted November 25, 2011 at 16:19 by SergeAS
Updated November 27, 2011 at 06:44 by SergeAS
Tags mpi, parallel

Looking the latest HPCSource I came across very well-known picture, illustrating the Amdahl's law:
S_p = \cfrac{1}{\alpha + \cfrac{1 - \alpha}{p}}


which shows the dependence of the speedup parallel code on number of processor cores for different fraction of time (\alpha \ne 0) spent in the part that was not parallelized. This diagram is interested in me for the...
Attached Thumbnails
Click image for larger version

Name:	HyperFLOW2D-speedup.png
Views:	386
Size:	7.7 KB
ID:	31   Click image for larger version

Name:	HyperFLOW2D-speed.png
Views:	380
Size:	7.2 KB
ID:	32   Click image for larger version

Name:	HyperFLOW2D-parallel-factor.png
Views:	377
Size:	6.5 KB
ID:	33   Click image for larger version

Name:	VonKarmanVorticeStreet2.gif
Views:	385
Size:	87.4 KB
ID:	36  
SergeAS's Avatar
Member
Posted in Uncategorized
Views 1217 Comments 2 SergeAS is offline Edit Tags
Old

Paraview: How to visualize cell data as text written in cells

Posted November 21, 2011 at 11:16 by tomislav_maric

If you are dealing with some delicate computations that require you to investigate the values of fields in some cells (I use this for debugging), there is a way to do this in Paraview:

View->Selection Inspector

Create Selection

Selection Type: Thresholds

Check the box: Invert selection

Scroll down to the Display Style subwindow and select Cell Label

Check the box: Visible

Choose: "p" for pressure...
Senior Member
Posted in Uncategorized
Views 1257 Comments 0 tomislav_maric is offline Edit Tags
Old

How to synchronise a bunch of .vtk files with OpenFOAM runTime

Posted November 21, 2011 at 11:03 by tomislav_maric

If you are visualising a bunch of .vtk files that were generated separately from the standard fields in OpenFOAM, and if you are a lucky person like me at this point (your time steps are constant), there exists a simple way to visualize the files alongside OpenFOAM data:

1) Open the OpenFOAM case as usual.
2) Open the .vtk files. The files have to be named appropriately to be read as time-dependent data: someName-001.vtk, someName-002.vtk, guess what is the next name. ...
Senior Member
Posted in Uncategorized
Views 580 Comments 0 tomislav_maric is offline Edit Tags

All times are GMT -4. The time now is 12:41.