Message id 167(negative rho)

See attached screenshot.

Regards

Rahul R

<?xml version="1.0" encoding="UTF-8"?>

Thanks Sir....

Can we use failure model to avoid this problem??

If possible suggest the failure model for material law 37 BIPHAS.

Please make sure you should not have any free edges in model.If possible share input deck.

Regards

Rahul R

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I see you have duplicate elements at the top of all four bottle.Please delete duplicate elements & run.

Regards

Rahul R

Thanks very much.

Will check and modify it.

Hi Sir,

As per your suggestion deleted the duplicate elements at top and some more duplicates elements at the bottom of bottles.

Then run it,but still there is same error(negative rho).

Herewith shared the output file for clarity.

Please check it and suggest solution.

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Hi,

You could also add /UPWM/SUPG 1.0 in engine file. It is better to compute velocities (momentum) with it.

This error has usually 2 origins :

The mass of element is escaping outside the domain:  check BCS and velocity field on border faces.

The numerical scheme is unstable and during mass echange too much mass was sent to adjacent elem : use full upwind and dt_scale =0.5 to be confident.

Keep me informed if you still have NEGATIVE RHO Error.

Regards

Rahul R

Hi Sir,

As suggested added the /UPWM/SUPG 1.0 in engine file(t1_0001.rad).

But it shows the error as following;

          0 ERROR(S)
          1 WARNING(S)
PLEASE CHECK LISTING FILE FOR FURTHER DETAILS

 ==== End of solver screen output ==== 

MESSAGE ID :           73
 ** ERROR IN ENGINE INPUT DECK CARD : UPWM
     ERROR TERMINATION

 ==== End of solver screen output ==== 

Is it correct way to add /UPWM/SUPG 1.0 in engine file???

Also I couldn't get meaning of 'use full upwind and dt_scale=0.5'.

Request you to clarify those things.

See attached screenshot for /UPWM & the way to define Engine keyword.For me with this keyword model is running through.

Regards

Rahul R

<?xml version="1.0" encoding="UTF-8"?>

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Hi Sir,

I used /UPWM/SUPG card and run it.

Still there is no error,but as analysis running it starts creating the animation files.

It created 11 animation files at the time of regular interval(2 minutes).

But after that not a single animation file is created, so I sent the command to create animation file and 3 more animation files were created by sending the command(ANIM).

Herewith shared the output file, please check it and let me know any suggestions if there.

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Hi,

I run it again but same problem occurred...after 11 animation files it didn't create animation files.

Please suggest the soultion.

Hi Sir,

I tried to solve this problem at my end by changing some parameters like ANIM/DT/0.01 to ANIM/DT/0.05

Also defining the contact between all bottles and run it.

Still there is same problem as it created only some animation files and after that it didn't.

Herewith shared the output file of modified one.

Please check it and suggest the some solution.

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Let me try and get back to you.

Regards

Rahul R

Ok Sir,

Thanks very much.

Hi Sir,

Did you checked it...?

Waiting for your positive reply....

Hi,

What is the unit system you are following and what is the natural time scale of this event?

Regards

Rahul R

Hi Sir,

I used the following unit system;

gram,mm,ms,MPa,N.....

Normally natural scale time for this event is not fixed. It is according to clients requirements (Variable).

We can consider the time to be 2 hours for this event.

Herewith shared the pdf document of vibration test that we conducted practically in a lab for your reference.

According to test we should have to conduct the test along with CFB(corrugated flexible box),but for simplicity now we worked on bottles only.

According to pdf,

I used these input for this analysis;

Consider 3 Hz of frequency – 12.5 mm max amplitude (+ve and -ve)

Meaning for 1 sec – thrice throw of the table for a max of 12.5mm (both +ve and -ve), hence divide 1 sec into 6 division

So for IMPDISP curve will be as

0.166    12.5

0.333   -12.5

0.499    12.5

0.666   -12.5

0.833    12.5

0.999  -12.5

Also suggest that,is it correct way of performing this type of analysis??

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Thanks for sharing this info.What I feel is something is wrong in unit system consistency.Also I learnt that /UPWM/SUPG  is applicable for LAW 51.So in your case its not needed.

Will refer above shared info & update.

Regards

Rahul R

Ok Sir,

Thanks very much.

Hi,

Hopefully shared information is sufficient.
Let me know if require more information regarding the same event.

Once you getting some appropriate solution for same update me.

Thanks,

Sachin

Impose a time step and try running the simulation and please let us know the update

/DT/NODA/CST

0.9   XXXX

XXXX-IMPOSED TIME STEP

Hi 

First removed  /UPWM/SUPG card (used for only Mat Law 51) suggested by Rahul R.

Then suggested, imposed the time step and run the analysis.

After importing time step it didn't show negative rho but shows the following error;

ELAPSED TIME=        344.23 s  REMAINING TIME=       4021.51 s
 NC=     900 T= 8.8826E-02 DT= 9.9618E-05 ERR=  6.5% DM/M= 1.8537E-03
 ELAPSED TIME=        387.10 s  REMAINING TIME=       3970.87 s
 NC=    1000 T= 9.8776E-02 DT= 9.9225E-05 ERR=  6.4% DM/M= 1.8732E-03
 ELAPSED TIME=        430.47 s  REMAINING TIME=       3927.58 s
     ANIMATION FILE: t1A003 WRITTEN
 NC=    1100 T= 1.0873E-01 DT= 9.9688E-05 ERR=  6.6% DM/M= 1.8804E-03
 ELAPSED TIME=        474.28 s  REMAINING TIME=       3887.91 s
MESSAGE ID :          166
 ** STOP : ZERO OR NEGATIVE VOLUME FOR 3D-ELEMENT ID=191484
     ERROR TERMINATION

 ==== End of solver screen output ==== 

 ==== Job completed ==== 

Request to suggest some solution.

it is running fine for me.Please find the attached files.

When the run goes upto 1s,u might have noticed that time step increases at a point which shows some element distortion is happening badly. And that results in the error. Calculate a better run time and impose time step respectively.

<?xml version="1.0" encoding="UTF-8"?>

<?xml version="1.0" encoding="UTF-8"?>

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Hi,

Corrected input data and run the analysis.

Unit system defined :  N, mm, MPA, second, gram

Also defined the contact between the bottles.

According to input frequency 3 Hz,calculated run time as 0.33 second.

Maximum Amplitude 12.5mm (+ve and -ve)

So imposed displacement curve will be as

0                                   0

0.0833                     +12.5

0.1666                          0

0.2499                     -12.5

0.3333                          0

In control cards following cards are defined as;

/RUN/run/0/
0.333000000000000   

/ANIM/DT
0.000000000000000    0.003330000000000   

/TFILE/0         
3.33000000000000E-04
 

According to these, 100 animation files should be created.

But only 14 animations files were created and analysis terminated with Message id... Negative rho error.

Request you to run the analysis for some more time. 

You will get the same error.

Herewith shared the modified deck files.

Please  check it and suggest the solution to avoid this error.

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please provide Gap min for the interface and run the analysis.

Hi, 

As suggested,provided min gap and ran it.

Its running and created the 47 animation files,then it didn't created a single animation file as analysis is running.

In this case till 47 animation files run time decreasing, after run time increasing only without creating any animation file.

Herewith shared the respective output file.

Request you to check this file and suggest the some solution to complete analysis.

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From the .out file we can see that element 257724 is behaving weirdly causing the time step to drop drastically. Check its cause in the deck file.

Hi,

I am unable to find the reason behind weird behavior of particular element.

I deleted the element 257724 and run it again.

Same problem for another element 257720(refer shared image).

Please check it and suggest solution.<?xml version="1.0" encoding="UTF-8"?>

Deleting that particular element to run the simulation is not an advisable step. But you can see that the time step was too low last time. This time it has improved. 

Check which object is responsible for the low  time step (.out file). It can be an element, a node or an interface.

For an element, check the related material.There must not be an error in the units system that this data is given in. check the element size also

For a node, check the characteristics of connected elements. If the node is on the master side or the slave side of an interface, this interface must be verified.

For an interface, the gap of the interface must be verified if some failure happens on the master or the slave side of the interface