What happens by doing Bandwidth Reduction?

mariachi · January 29, 2010, 12:50

Hey friends,

In fluent, what happens when u do bandwidth reduction by grid>reorder>domain

Why and when do u do it?

Thanks

DoHander · January 30, 2010, 13:52

After you read your mesh in Fluent you can do the bandwidth reduction. Basically Fluent will renumber the nodes of your mesh in order to have a "more diagonal" array. This will allow you to use less memory and also the solution will converge faster.

Do

mariachi · January 31, 2010, 06:25

Hey DoHander,

So basically, it means that one should make it a practice to always do bandwidth reduction after reading any mesh into Fluent...

DoHander · January 31, 2010, 13:54

If you use any of the implicit solvers of Fluent yes, you should always do the bandwidth reduction. For the explicit solver this is useless.

Do

mariachi · February 1, 2010, 12:26

Thanks DoHander

daandb · February 28, 2013, 06:24

I also have a question on this, till what value you need to reorder to achieve the most optimal bandwidth? Seem to me that the lower the bandwidth value the better?

cfd seeker · April 15, 2014, 03:32

Quote:

Originally Posted by daandb

I also have a question on this, till what value you need to reorder to achieve the most optimal bandwidth? Seem to me that the lower the bandwidth value the better?

Yup, lower the bandwidth value the better the solution will get in terms of solution time!! But you cannot control the value to which the bandwidth (of matrix) can be reduced, as it depends on the number of non-zero entries in the matrix(the matrix generated as the fluent solves the N-S equations)

Far · July 19, 2014, 06:59

details can be found here...

http://en.wikipedia.org/wiki/Banded_matrix

This also clearly shows why you cannot have advantage of reordering for explicit solver...

Far · July 19, 2014, 07:05

details can be found here...

http://en.wikipedia.org/wiki/Banded_matrix

This also clearly shows why you cannot have advantage of reordering for explicit solver...

Rasmusiwersen · October 4, 2019, 10:30

Quote:

Originally Posted by Far

details can be found here...

http://en.wikipedia.org/wiki/Banded_matrix

This also clearly shows why you cannot have advantage of reordering for explicit solver...

To me it is not clear why there is no advantage to reorder explicit solvers. Would you care to elaborate?

Thanks

/Rasmus

LuckyTran · October 4, 2019, 16:22

Quote:

Originally Posted by Rasmusiwersen

To me it is not clear why there is no advantage to reorder explicit solvers. Would you care to elaborate?

Thanks

/Rasmus

Implicit solvers solve liner systems: e.g. Ax=b for the unknown x. When A has a lower bandwidth, certain algorithms (i.e. Gaussian elimination) are faster.

Explicit solvers don't solve linear systems, they simply compute Ax=y for a new y. Regardless of the bandwidth of A, it's simple algebra.

Rasmusiwersen · October 7, 2019, 07:59

Quote:

Originally Posted by LuckyTran

Implicit solvers solve liner systems: e.g. Ax=b for the unknown x. When A has a lower bandwidth, certain algorithms (i.e. Gaussian elimination) are faster.

Explicit solvers don't solve linear systems, they simply compute Ax=y for a new y. Regardless of the bandwidth of A, it's simple algebra.

Ah, i see. Thanks for the reply :-)

January 29, 2010, 12:50	What happens by doing Bandwidth Reduction?	#1
mariachi Member Join Date: Jan 2010 Posts: 54 Rep Power: 16	Hey friends, In fluent, what happens when u do bandwidth reduction by grid>reorder>domain Why and when do u do it? Thanks

July 19, 2014, 06:59		#8
Far Senior Member Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,558 Blog Entries: 6 Rep Power: 54	details can be found here... http://en.wikipedia.org/wiki/Banded_matrix This also clearly shows why you cannot have advantage of reordering for explicit solver... jotac likes this.

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January 30, 2010, 13:52		#2
DoHander Senior Member Join Date: Nov 2009 Posts: 411 Rep Power: 19	After you read your mesh in Fluent you can do the bandwidth reduction. Basically Fluent will renumber the nodes of your mesh in order to have a "more diagonal" array. This will allow you to use less memory and also the solution will converge faster. Do

January 31, 2010, 06:25		#3
mariachi Member Join Date: Jan 2010 Posts: 54 Rep Power: 16	Hey DoHander, So basically, it means that one should make it a practice to always do bandwidth reduction after reading any mesh into Fluent...

January 31, 2010, 13:54		#4
DoHander Senior Member Join Date: Nov 2009 Posts: 411 Rep Power: 19	If you use any of the implicit solvers of Fluent yes, you should always do the bandwidth reduction. For the explicit solver this is useless. Do

February 1, 2010, 12:26		#5
mariachi Member Join Date: Jan 2010 Posts: 54 Rep Power: 16	Thanks DoHander

February 28, 2013, 06:24		#6
daandb New Member Daan de Boer Join Date: Jun 2012 Posts: 6 Rep Power: 0	I also have a question on this, till what value you need to reorder to achieve the most optimal bandwidth? Seem to me that the lower the bandwidth value the better?

July 19, 2014, 07:05		#9
Far Senior Member Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,558 Blog Entries: 6 Rep Power: 54	details can be found here... http://en.wikipedia.org/wiki/Banded_matrix This also clearly shows why you cannot have advantage of reordering for explicit solver...