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02-13-2009 08:15 AM

Hello everyone,

looking at the NX.nastran user's guide, chapter 15 "Model verification", page 15-27,

it says message UIM 4158 reports the max ratio from decomposition of matrix KLL.

I have to check my models and my requirement is that the max. ratio for KLL is <

10^7, so I perform a modal analysis but every time the output in .f06 (UIM 4158)

talks about KXX matrix, not KLL, and every time the max ratio is 1*10^15, that would

be unacceptable. I paste here below the output:

*** USER INFORMATION MESSAGE 4158 (DFMSA)

---- STATISTICS FOR SPARSE DECOMPOSITION OF DATA BLOCK KXX FOLLOW

NUMBER OF NEGATIVE TERMS ON FACTOR DIAGONAL = 21

MAXIMUM RATIO OF MATRIX DIAGONAL TO FACTOR DIAGONAL = 1.0E+15 AT ROW NUMBER

25660

User information:

One, two or three of the statistics will be printed as follows:

(1) negative terms on factor diagonal only if they exist; (2) maximum

ratio only if it exceeds a threshold defined by the paramater MAXRATIO

(default 1.0E7); (3) spill rows only if the problem spills.

Depending on the context, these messages may indicate modeling

problems. The threshold may be changed with the parameter MAXRATIO,

however, the user is cautioned against arbitrarily increasing the

MAXRATIO value just to get the model to run. The cause of large

MAXRATIOs should be investigated.

This message is also generated (though the text is slightly different)

when a Sturm check is performed during eigenvalue extraction. For this

case, the message does not generally indicate a modeling problem.

See the NX NASTRAN Installation and Operation Instructions for

a discussion of these statistics. See also the NX NASTRAN Numerical

Methods User's Guide.

*** USER WARNING MESSAGE 4698 (DCMPD)

STATISTICS FOR DECOMPOSITION OF MATRIX (NONE) .

THE FOLLOWING DEGREES OF FREEDOM HAVE FACTOR DIAGONAL RATIOS GREATER THAN

1.00000E+07 OR HAVE NEGATIVE TERMS ON THE FACTOR DIAGONAL.

USER INFORMATION:

THIS MESSAGE MAY BE IGNORED IF NO GRID POINT IDS OR HIGH RATIO MESSAGES APPEAR

IN THE TABLE ON THE NEXT PAGE.

User information:

During decomposition, the degrees of freedom listed have pivot

ratios that are that are greater than maxratio or are negative.

Verify that the degrees of freedom are not part of a mechanism

and that elements do not have excessive stiffness. In superelement

analysis this condition causes run termination. PARAM,BAILOUT may

be used to continue the run. See the NX NASTRAN Numerical Methods

User's Guide.

How can I get the KLL max ratio, to show that I'm compliant to my requirement? (I

tried also with simple models, and it always outputs KXX max ratio 1*10^15)

Thanks for the attention

Marco

6 REPLIES

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02-13-2009 07:05 PM

Zero Hz? If you have 6 and your model is unconstrained, then your model may

be OK, but will obviously not run correctly as a static problem (except

using SUPORTs / Inertia Relief). If your model is supposed to be

constrained, but you still have Zero Hz modes, then you have a modelling

problem. Modal analysis can successfully analyze through all kinds of

modelling "errors" (from a static viewpoint). A simple way to look at it is

that if the model is supposed to be constrained and you have, say, 15 Zero

Hz modes, then you have 15 problems to look for (though there may be triples

or sixes of problems related to each other).

I suggest you read the following article to help you understand the basic

sources of singularities.

http://www.endurasim.com.au/web_images/EnDuraSim-O

"Marco"

news:4995727e$1@bbsnotes.ugs.com...

>

> Hello everyone,

>

> looking at the NX.nastran user's guide, chapter 15 "Model verification",

> page 15-27,

> it says message UIM 4158 reports the max ratio from decomposition of

> matrix KLL.

>

> I have to check my models and my requirement is that the max. ratio for

> KLL is <

> 10^7, so I perform a modal analysis but every time the output in .f06 (UIM

> 4158)

> talks about KXX matrix, not KLL, and every time the max ratio is 1*10^15,

> that would

> be unacceptable. I paste here below the output:

>

> *** USER INFORMATION MESSAGE 4158 (DFMSA)

> ---- STATISTICS FOR SPARSE DECOMPOSITION OF DATA BLOCK KXX FOLLOW

> NUMBER OF NEGATIVE TERMS ON FACTOR DIAGONAL = 21

> MAXIMUM RATIO OF MATRIX DIAGONAL TO FACTOR DIAGONAL = 1.0E+15 AT

> ROW NUMBER

> 25660

> User information:

> One, two or three of the statistics will be printed as follows:

> (1) negative terms on factor diagonal only if they exist; (2) maximum

> ratio only if it exceeds a threshold defined by the paramater MAXRATIO

> (default 1.0E7); (3) spill rows only if the problem spills.

> Depending on the context, these messages may indicate modeling

> problems. The threshold may be changed with the parameter MAXRATIO,

> however, the user is cautioned against arbitrarily increasing the

> MAXRATIO value just to get the model to run. The cause of large

> MAXRATIOs should be investigated.

> This message is also generated (though the text is slightly different)

> when a Sturm check is performed during eigenvalue extraction. For this

> case, the message does not generally indicate a modeling problem.

> See the NX NASTRAN Installation and Operation Instructions for

> a discussion of these statistics. See also the NX NASTRAN Numerical

> Methods User's Guide.

> *** USER WARNING MESSAGE 4698 (DCMPD)

> STATISTICS FOR DECOMPOSITION OF MATRIX (NONE) .

> THE FOLLOWING DEGREES OF FREEDOM HAVE FACTOR DIAGONAL RATIOS GREATER

> THAN

> 1.00000E+07 OR HAVE NEGATIVE TERMS ON THE FACTOR DIAGONAL.

> USER INFORMATION:

> THIS MESSAGE MAY BE IGNORED IF NO GRID POINT IDS OR HIGH RATIO

> MESSAGES APPEAR

> IN THE TABLE ON THE NEXT PAGE.

> User information:

> During decomposition, the degrees of freedom listed have pivot

> ratios that are that are greater than maxratio or are negative.

> Verify that the degrees of freedom are not part of a mechanism

> and that elements do not have excessive stiffness. In superelement

> analysis this condition causes run termination. PARAM,BAILOUT may

> be used to continue the run. See the NX NASTRAN Numerical Methods

> User's Guide.

>

>

> How can I get the KLL max ratio, to show that I'm compliant to my

> requirement? (I

> tried also with simple models, and it always outputs KXX max ratio

> 1*10^15)

>

> Thanks for the attention

>

> Marco

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02-23-2009 11:37 AM

Dear Vernon,

actually my model has no problems both in modal and static analysis, so it isn't

underconstrained and it doesn't stop with fatal errors. I would only like to understand

why this message always says MAXIMUM RATIO OF MATRIX DIAGONAL TO FACTOR DIAGONAL

= 1.0E+15 for KXX in any case. I need a KLL MAX RATIO value to demonstrate the

compliance of my model to a requirement but I cannot find it...

Greetings,

Marco

"Vernon McKenzie"

>Your model has singularities. How many modes do you have which are close

>to

>Zero Hz? If you have 6 and your model is unconstrained, then your model may

>

>be OK, but will obviously not run correctly as a static problem (except

>using SUPORTs / Inertia Relief). If your model is supposed to be

>constrained, but you still have Zero Hz modes, then you have a modelling

>

>problem. Modal analysis can successfully analyze through all kinds of

>modelling "errors" (from a static viewpoint). A simple way to look at it

>is

>that if the model is supposed to be constrained and you have, say, 15 Zero

>

>Hz modes, then you have 15 problems to look for (though there may be triples

>

>or sixes of problems related to each other).

>

>I suggest you read the following article to help you understand the basic

>

>sources of singularities.

>

>http://www.endurasim.com.au/web_images/EnDuraSim-O

>

>

>"Marco"

>news:4995727e$1@bbsnotes.ugs.com...

>>

>> Hello everyone,

>>

>> looking at the NX.nastran user's guide, chapter 15 "Model verification",

>

>> page 15-27,

>> it says message UIM 4158 reports the max ratio from decomposition of

>> matrix KLL.

>>

>> I have to check my models and my requirement is that the max. ratio for

>

>> KLL is <

>> 10^7, so I perform a modal analysis but every time the output in .f06 (UIM

>

>> 4158)

>> talks about KXX matrix, not KLL, and every time the max ratio is 1*10^15,

>

>> that would

>> be unacceptable. I paste here below the output:

>>

>> *** USER INFORMATION MESSAGE 4158 (DFMSA)

>> ---- STATISTICS FOR SPARSE DECOMPOSITION OF DATA BLOCK KXX FOLLOW

>> NUMBER OF NEGATIVE TERMS ON FACTOR DIAGONAL = 21

>> MAXIMUM RATIO OF MATRIX DIAGONAL TO FACTOR DIAGONAL = 1.0E+15 AT

>

>> ROW NUMBER

>> 25660

>> User information:

>> One, two or three of the statistics will be printed as follows:

>> (1) negative terms on factor diagonal only if they exist; (2) maximum

>> ratio only if it exceeds a threshold defined by the paramater MAXRATIO

>> (default 1.0E7); (3) spill rows only if the problem spills.

>> Depending on the context, these messages may indicate modeling

>> problems. The threshold may be changed with the parameter MAXRATIO,

>> however, the user is cautioned against arbitrarily increasing the

>> MAXRATIO value just to get the model to run. The cause of large

>> MAXRATIOs should be investigated.

>> This message is also generated (though the text is slightly different)

>> when a Sturm check is performed during eigenvalue extraction. For this

>> case, the message does not generally indicate a modeling problem.

>> See the NX NASTRAN Installation and Operation Instructions for

>> a discussion of these statistics. See also the NX NASTRAN Numerical

>> Methods User's Guide.

>> *** USER WARNING MESSAGE 4698 (DCMPD)

>> STATISTICS FOR DECOMPOSITION OF MATRIX (NONE) .

>> THE FOLLOWING DEGREES OF FREEDOM HAVE FACTOR DIAGONAL RATIOS GREATER

>

>> THAN

>> 1.00000E+07 OR HAVE NEGATIVE TERMS ON THE FACTOR DIAGONAL.

>> USER INFORMATION:

>> THIS MESSAGE MAY BE IGNORED IF NO GRID POINT IDS OR HIGH RATIO

>> MESSAGES APPEAR

>> IN THE TABLE ON THE NEXT PAGE.

>> User information:

>> During decomposition, the degrees of freedom listed have pivot

>> ratios that are that are greater than maxratio or are negative.

>> Verify that the degrees of freedom are not part of a mechanism

>> and that elements do not have excessive stiffness. In superelement

>> analysis this condition causes run termination. PARAM,BAILOUT may

>> be used to continue the run. See the NX NASTRAN Numerical Methods

>> User's Guide.

>>

>>

>> How can I get the KLL max ratio, to show that I'm compliant to my

>> requirement? (I

>> tried also with simple models, and it always outputs KXX max ratio

>> 1*10^15)

>>

>> Thanks for the attention

>>

>> Marco

>

>

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02-23-2009 02:47 PM

Marco,

the maxratio is the ratio ratio of the matrix diagonal to the factor diagonal. A

high maxratio usually is a signal of modelling problems very stiff zone connected

to very soft, I'm sure this is what Vernon wanted to say.

You find a maximum ratio for data block KXX because you are performing a modal analysis,

if you perform a static analysis (SOL 101) you will find the maximum ratio for data

block KLL.

Anyway for KXX or KLL a ratio of 10^15 cannot be accepted unless you can explain

why is present (a very very soft spring connected to kriptonite or whatever). Usually

a method of debugging is to perform a modal unconstrained analysis and inspect the

first rigid modes which if are higher than 10^-3 show grounding or other constraint

which should not be in the model. So I suggest you perform this analysis and I'm

sure you will find where the problem is.

Hope this helps

regards

Francesco

"Marco"

>

>Dear Vernon,

>

>actually my model has no problems both in modal and static analysis, so it

>isn't

>underconstrained and it doesn't stop with fatal errors. I would only like

>to understand

>why this message always says MAXIMUM RATIO OF MATRIX DIAGONAL TO FACTOR DIAGONAL

>= 1.0E+15 for KXX in any case. I need a KLL MAX RATIO value to demonstrate

>the

>compliance of my model to a requirement but I cannot find it...

>

>Greetings,

>

>Marco

>

>"Vernon McKenzie"

>>Your model has singularities. How many modes do you have which are close

>>to

>>Zero Hz? If you have 6 and your model is unconstrained, then your model

>may

>>

>>be OK, but will obviously not run correctly as a static problem (except

>>using SUPORTs / Inertia Relief). If your model is supposed to be

>>constrained, but you still have Zero Hz modes, then you have a modelling

>>

>>problem. Modal analysis can successfully analyze through all kinds of

>>modelling "errors" (from a static viewpoint). A simple way to look at it

>>is

>>that if the model is supposed to be constrained and you have, say, 15 Zero

>>

>>Hz modes, then you have 15 problems to look for (though there may be triples

>>

>>or sixes of problems related to each other).

>>

>>I suggest you read the following article to help you understand the basic

>>

>>sources of singularities.

>>

>>http://www.endurasim.com.au/web_images/EnDuraSim-O

>>

>>

>>"Marco"

>>news:4995727e$1@bbsnotes.ugs.com...

>>>

>>> Hello everyone,

>>>

>>> looking at the NX.nastran user's guide, chapter 15 "Model verification",

>>

>>> page 15-27,

>>> it says message UIM 4158 reports the max ratio from decomposition of

>>> matrix KLL.

>>>

>>> I have to check my models and my requirement is that the max. ratio for

>>

>>> KLL is <

>>> 10^7, so I perform a modal analysis but every time the output in .f06 (UIM

>>

>>> 4158)

>>> talks about KXX matrix, not KLL, and every time the max ratio is 1*10^15,

>>

>>> that would

>>> be unacceptable. I paste here below the output:

>>>

>>> *** USER INFORMATION MESSAGE 4158 (DFMSA)

>>> ---- STATISTICS FOR SPARSE DECOMPOSITION OF DATA BLOCK KXX FOLLOW

>>> NUMBER OF NEGATIVE TERMS ON FACTOR DIAGONAL = 21

>>> MAXIMUM RATIO OF MATRIX DIAGONAL TO FACTOR DIAGONAL = 1.0E+15 AT

>>

>>> ROW NUMBER

>>> 25660

>>> User information:

>>> One, two or three of the statistics will be printed as follows:

>>> (1) negative terms on factor diagonal only if they exist; (2) maximum

>>> ratio only if it exceeds a threshold defined by the paramater MAXRATIO

>>> (default 1.0E7); (3) spill rows only if the problem spills.

>>> Depending on the context, these messages may indicate modeling

>>> problems. The threshold may be changed with the parameter MAXRATIO,

>>> however, the user is cautioned against arbitrarily increasing the

>>> MAXRATIO value just to get the model to run. The cause of large

>>> MAXRATIOs should be investigated.

>>> This message is also generated (though the text is slightly different)

>>> when a Sturm check is performed during eigenvalue extraction. For this

>>> case, the message does not generally indicate a modeling problem.

>>> See the NX NASTRAN Installation and Operation Instructions for

>>> a discussion of these statistics. See also the NX NASTRAN Numerical

>>> Methods User's Guide.

>>> *** USER WARNING MESSAGE 4698 (DCMPD)

>>> STATISTICS FOR DECOMPOSITION OF MATRIX (NONE) .

>>> THE FOLLOWING DEGREES OF FREEDOM HAVE FACTOR DIAGONAL RATIOS GREATER

>>

>>> THAN

>>> 1.00000E+07 OR HAVE NEGATIVE TERMS ON THE FACTOR DIAGONAL.

>>> USER INFORMATION:

>>> THIS MESSAGE MAY BE IGNORED IF NO GRID POINT IDS OR HIGH RATIO

>>> MESSAGES APPEAR

>>> IN THE TABLE ON THE NEXT PAGE.

>>> User information:

>>> During decomposition, the degrees of freedom listed have pivot

>>> ratios that are that are greater than maxratio or are negative.

>>> Verify that the degrees of freedom are not part of a mechanism

>>> and that elements do not have excessive stiffness. In superelement

>>> analysis this condition causes run termination. PARAM,BAILOUT may

>>> be used to continue the run. See the NX NASTRAN Numerical Methods

>>> User's Guide.

>>>

>>>

>>> How can I get the KLL max ratio, to show that I'm compliant to my

>>> requirement? (I

>>> tried also with simple models, and it always outputs KXX max ratio

>>> 1*10^15)

>>>

>>> Thanks for the attention

>>>

>>> Marco

>>

>>

>

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02-25-2009 10:10 AM

Dear Francesco,

I have already performed a modal analysis with my model, and the first 6 rigid modes

have frequencies in the order of magnitude 10^-4 Hz, but nevertheless I always get

the message with KXX max ratio 10^15, so I don't understand. Could it be because

I use solid elements?

Marco

"francesco pelizza"

>

>Marco,

>the maxratio is the ratio ratio of the matrix diagonal to the factor diagonal.

>A

>high maxratio usually is a signal of modelling problems very stiff zone connected

>to very soft, I'm sure this is what Vernon wanted to say.

>You find a maximum ratio for data block KXX because you are performing a modal

>analysis,

>if you perform a static analysis (SOL 101) you will find the maximum ratio

>for data

>block KLL.

>Anyway for KXX or KLL a ratio of 10^15 cannot be accepted unless you can explain

>why is present (a very very soft spring connected to kriptonite or whatever).

>Usually

>a method of debugging is to perform a modal unconstrained analysis and inspect

>the

>first rigid modes which if are higher than 10^-3 show grounding or other constraint

>which should not be in the model. So I suggest you perform this analysis and

>I'm

>sure you will find where the problem is.

>

>Hope this helps

>regards

>

>Francesco

>

>

>

>

>"Marco"

>>

>>Dear Vernon,

>>

>>actually my model has no problems both in modal and static analysis, so it

>>isn't

>>underconstrained and it doesn't stop with fatal errors. I would only like

>>to understand

>>why this message always says MAXIMUM RATIO OF MATRIX DIAGONAL TO FACTOR DIAGONAL

>>= 1.0E+15 for KXX in any case. I need a KLL MAX RATIO value to demonstrate

>>the

>>compliance of my model to a requirement but I cannot find it...

>>

>>Greetings,

>>

>>Marco

>>

>>"Vernon McKenzie"

>>>Your model has singularities. How many modes do you have which are close

>>>to

>>>Zero Hz? If you have 6 and your model is unconstrained, then your model

>>may

>>>

>>>be OK, but will obviously not run correctly as a static problem (except

>

>>>using SUPORTs / Inertia Relief). If your model is supposed to be

>>>constrained, but you still have Zero Hz modes, then you have a modelling

>>>

>>>problem. Modal analysis can successfully analyze through all kinds of

>>>modelling "errors" (from a static viewpoint). A simple way to look at it

>>>is

>>>that if the model is supposed to be constrained and you have, say, 15 Zero

>>>

>>>Hz modes, then you have 15 problems to look for (though there may be triples

>>>

>>>or sixes of problems related to each other).

>>>

>>>I suggest you read the following article to help you understand the basic

>>>

>>>sources of singularities.

>>>

>>>http://www.endurasim.com.au/web_images/EnDuraSim-O

>>>

>>>

>>>"Marco"

>>>news:4995727e$1@bbsnotes.ugs.com...

>>>>

>>>> Hello everyone,

>>>>

>>>> looking at the NX.nastran user's guide, chapter 15 "Model verification",

>>>

>>>> page 15-27,

>>>> it says message UIM 4158 reports the max ratio from decomposition of

>>>> matrix KLL.

>>>>

>>>> I have to check my models and my requirement is that the max. ratio for

>>>

>>>> KLL is <

>>>> 10^7, so I perform a modal analysis but every time the output in .f06

>(UIM

>>>

>>>> 4158)

>>>> talks about KXX matrix, not KLL, and every time the max ratio is 1*10^15,

>>>

>>>> that would

>>>> be unacceptable. I paste here below the output:

>>>>

>>>> *** USER INFORMATION MESSAGE 4158 (DFMSA)

>>>> ---- STATISTICS FOR SPARSE DECOMPOSITION OF DATA BLOCK KXX FOLLOW

>>>> NUMBER OF NEGATIVE TERMS ON FACTOR DIAGONAL = 21

>>>> MAXIMUM RATIO OF MATRIX DIAGONAL TO FACTOR DIAGONAL = 1.0E+15

>AT

>>>

>>>> ROW NUMBER

>>>> 25660

>>>> User information:

>>>> One, two or three of the statistics will be printed as follows:

>>>> (1) negative terms on factor diagonal only if they exist; (2) maximum

>>>> ratio only if it exceeds a threshold defined by the paramater MAXRATIO

>>>> (default 1.0E7); (3) spill rows only if the problem spills.

>>>> Depending on the context, these messages may indicate modeling

>>>> problems. The threshold may be changed with the parameter MAXRATIO,

>>>> however, the user is cautioned against arbitrarily increasing the

>>>> MAXRATIO value just to get the model to run. The cause of large

>>>> MAXRATIOs should be investigated.

>>>> This message is also generated (though the text is slightly different)

>>>> when a Sturm check is performed during eigenvalue extraction. For

>this

>>>> case, the message does not generally indicate a modeling problem.

>>>> See the NX NASTRAN Installation and Operation Instructions for

>>>> a discussion of these statistics. See also the NX NASTRAN Numerical

>>>> Methods User's Guide.

>>>> *** USER WARNING MESSAGE 4698 (DCMPD)

>>>> STATISTICS FOR DECOMPOSITION OF MATRIX (NONE) .

>>>> THE FOLLOWING DEGREES OF FREEDOM HAVE FACTOR DIAGONAL RATIOS GREATER

>>>

>>>> THAN

>>>> 1.00000E+07 OR HAVE NEGATIVE TERMS ON THE FACTOR DIAGONAL.

>>>> USER INFORMATION:

>>>> THIS MESSAGE MAY BE IGNORED IF NO GRID POINT IDS OR HIGH RATIO

>>>> MESSAGES APPEAR

>>>> IN THE TABLE ON THE NEXT PAGE.

>>>> User information:

>>>> During decomposition, the degrees of freedom listed have pivot

>>>> ratios that are that are greater than maxratio or are negative.

>>>> Verify that the degrees of freedom are not part of a mechanism

>>>> and that elements do not have excessive stiffness. In superelement

>>>> analysis this condition causes run termination. PARAM,BAILOUT may

>>>> be used to continue the run. See the NX NASTRAN Numerical Methods

>>>> User's Guide.

>>>>

>>>>

>>>> How can I get the KLL max ratio, to show that I'm compliant to my

>>>> requirement? (I

>>>> tried also with simple models, and it always outputs KXX max ratio

>>>> 1*10^15)

>>>>

>>>> Thanks for the attention

>>>>

>>>> Marco

>>>

>>>

>>

>

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02-27-2009 05:27 AM

Hi Marco,

there could be hundreds reasons. It is difficult without seeing the model.

It could be wrong material properties (E or G very low or very high), wrong connection

between elements (solid elements connected with only one node to a beam, or with

only two nodes to a shell) or other reasons. If you have the first six modes of

10^-4 and the seventh an acceptable value this is already a good sign. Look for

any WARNING in the f06 if you did not do it already and then if you suspect any

zone of the model being the cause try to export from your pre-processor a group

without that elements and perform the free free check again on the partial model.

If the high maxratio disappear you found where the problem is.

Best regards

Francesco

"Marco"

>

>Dear Francesco,

>

>I have already performed a modal analysis with my model, and the first 6 rigid

>modes

>have frequencies in the order of magnitude 10^-4 Hz, but nevertheless I always

>get

>the message with KXX max ratio 10^15, so I don't understand. Could it be because

>I use solid elements?

>

>Marco

>

>

>"francesco pelizza"

>>

>>Marco,

>>the maxratio is the ratio ratio of the matrix diagonal to the factor diagonal.

>>A

>>high maxratio usually is a signal of modelling problems very stiff zone connected

>>to very soft, I'm sure this is what Vernon wanted to say.

>>You find a maximum ratio for data block KXX because you are performing a

>modal

>>analysis,

>>if you perform a static analysis (SOL 101) you will find the maximum ratio

>>for data

>>block KLL.

>>Anyway for KXX or KLL a ratio of 10^15 cannot be accepted unless you can

>explain

>>why is present (a very very soft spring connected to kriptonite or whatever).

>>Usually

>>a method of debugging is to perform a modal unconstrained analysis and inspect

>>the

>>first rigid modes which if are higher than 10^-3 show grounding or other

>constraint

>>which should not be in the model. So I suggest you perform this analysis

>and

>>I'm

>>sure you will find where the problem is.

>>

>>Hope this helps

>>regards

>>

>>Francesco

>>

>>

>>

>>

>>"Marco"

>>>

>>>Dear Vernon,

>>>

>>>actually my model has no problems both in modal and static analysis, so

>it

>>>isn't

>>>underconstrained and it doesn't stop with fatal errors. I would only like

>>>to understand

>>>why this message always says MAXIMUM RATIO OF MATRIX DIAGONAL TO FACTOR

>DIAGONAL

>>>= 1.0E+15 for KXX in any case. I need a KLL MAX RATIO value to demonstrate

>>>the

>>>compliance of my model to a requirement but I cannot find it...

>>>

>>>Greetings,

>>>

>>>Marco

>>>

>>>"Vernon McKenzie"

>>>>Your model has singularities. How many modes do you have which are close

>>>>to

>>>>Zero Hz? If you have 6 and your model is unconstrained, then your model

>>>may

>>>>

>>>>be OK, but will obviously not run correctly as a static problem (except

>>

>>>>using SUPORTs / Inertia Relief). If your model is supposed to be

>>>>constrained, but you still have Zero Hz modes, then you have a modelling

>>>>

>>>>problem. Modal analysis can successfully analyze through all kinds of

>

>>>>modelling "errors" (from a static viewpoint). A simple way to look at

>it

>>>>is

>>>>that if the model is supposed to be constrained and you have, say, 15 Zero

>>>>

>>>>Hz modes, then you have 15 problems to look for (though there may be triples

>>>>

>>>>or sixes of problems related to each other).

>>>>

>>>>I suggest you read the following article to help you understand the basic

>>>>

>>>>sources of singularities.

>>>>

>>>>http://www.endurasim.com.au/web_images/EnDuraSim-O

>>>>

>>>>

>>>>"Marco"

>>>>news:4995727e$1@bbsnotes.ugs.com...

>>>>>

>>>>> Hello everyone,

>>>>>

>>>>> looking at the NX.nastran user's guide, chapter 15 "Model verification",

>>>>

>>>>> page 15-27,

>>>>> it says message UIM 4158 reports the max ratio from decomposition of

>

>>>>> matrix KLL.

>>>>>

>>>>> I have to check my models and my requirement is that the max. ratio for

>>>>

>>>>> KLL is <

>>>>> 10^7, so I perform a modal analysis but every time the output in .f06

>>(UIM

>>>>

>>>>> 4158)

>>>>> talks about KXX matrix, not KLL, and every time the max ratio is 1*10^15,

>>>>

>>>>> that would

>>>>> be unacceptable. I paste here below the output:

>>>>>

>>>>> *** USER INFORMATION MESSAGE 4158 (DFMSA)

>>>>> ---- STATISTICS FOR SPARSE DECOMPOSITION OF DATA BLOCK KXX FOLLOW

>>>>> NUMBER OF NEGATIVE TERMS ON FACTOR DIAGONAL = 21

>>>>> MAXIMUM RATIO OF MATRIX DIAGONAL TO FACTOR DIAGONAL = 1.0E+15

>>AT

>>>>

>>>>> ROW NUMBER

>>>>> 25660

>>>>> User information:

>>>>> One, two or three of the statistics will be printed as follows:

>>>>> (1) negative terms on factor diagonal only if they exist; (2) maximum

>>>>> ratio only if it exceeds a threshold defined by the paramater MAXRATIO

>>>>> (default 1.0E7); (3) spill rows only if the problem spills.

>>>>> Depending on the context, these messages may indicate modeling

>>>>> problems. The threshold may be changed with the parameter MAXRATIO,

>>>>> however, the user is cautioned against arbitrarily increasing the

>>>>> MAXRATIO value just to get the model to run. The cause of large

>>>>> MAXRATIOs should be investigated.

>>>>> This message is also generated (though the text is slightly different)

>>>>> when a Sturm check is performed during eigenvalue extraction. For

>>this

>>>>> case, the message does not generally indicate a modeling problem.

>>>>> See the NX NASTRAN Installation and Operation Instructions for

>>>>> a discussion of these statistics. See also the NX NASTRAN Numerical

>>>>> Methods User's Guide.

>>>>> *** USER WARNING MESSAGE 4698 (DCMPD)

>>>>> STATISTICS FOR DECOMPOSITION OF MATRIX (NONE) .

>>>>> THE FOLLOWING DEGREES OF FREEDOM HAVE FACTOR DIAGONAL RATIOS GREATER

>>>>

>>>>> THAN

>>>>> 1.00000E+07 OR HAVE NEGATIVE TERMS ON THE FACTOR DIAGONAL.

>>>>> USER INFORMATION:

>>>>> THIS MESSAGE MAY BE IGNORED IF NO GRID POINT IDS OR HIGH RATIO

>>>>> MESSAGES APPEAR

>>>>> IN THE TABLE ON THE NEXT PAGE.

>>>>> User information:

>>>>> During decomposition, the degrees of freedom listed have pivot

>>>>> ratios that are that are greater than maxratio or are negative.

>>>>> Verify that the degrees of freedom are not part of a mechanism

>>>>> and that elements do not have excessive stiffness. In superelement

>>>>> analysis this condition causes run termination. PARAM,BAILOUT may

>>>>> be used to continue the run. See the NX NASTRAN Numerical Methods

>>>>> User's Guide.

>>>>>

>>>>>

>>>>> How can I get the KLL max ratio, to show that I'm compliant to my

>>>>> requirement? (I

>>>>> tried also with simple models, and it always outputs KXX max ratio

>>>>> 1*10^15)

>>>>>

>>>>> Thanks for the attention

>>>>>

>>>>> Marco

>>>>

>>>>

>>>

>>

>

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03-01-2009 12:48 PM

Dear Marco,

In fact, without seeing the model is difficult to give a diagnostic of what is happening:

if you have values of 0 Hertz this means you have rigid body motions in your model

and is not properly constrained, the best way is to animate deformations of those

rigid mode shapes and this will give you a clue to investigate what is wrong in

your model.

Best regards,

Blas.

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