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Updated: 17 hours 58 min ago

Hello Everyone,

Mon, 2014-07-21 10:38

In reply to Cohesive Zone Model in ANSYS

Hello Everyone,

I got the following answers from ANSYS support and I thought may be someone want to know:(I am using ANSYS APDL 14.5)

 

1-In Workbench V15, we can do cohesive zone modeling based on interface elements. Also we can do two way Fluid Solid interaction problem in Workbench. Currently you are using FLOTRAN for FSI problem. I am not sure if ANSYS supports this anymore because I could not find anything in the help manual. 

2-Yes, this is correct.

3- 

4-There is no special feature in APDL to mesh elliptical areas. You need to split the areas and use mapped meshing.

5-Yes you need to clear the physics before defining a new physics. Attached is one example I found on the internet. In this I noticed, that the author first defined the Fluid physics, then solid physics and at the end solved the FSI using FSSOLVE command. In FSSOLVE command we specifying the physics fluid and solid. This is how it recognizes all the information. (I could not attach here so I put the link of the website he used):

https://engineering.purdue.edu/~abe601/ansys/Fluid_Solid_Interaction_tutorial_v81.pdf

6-According to the attached paper, while defining FLUID physics we need to make solid elements as null and vice versa.

7-If the area are glued then while meshing interfaces will have shared nodes. CZMESH will only work on the shared nodes. So we need to glue the areas so that sharing nodes could be generated. Merging is an option where we can merge the two coincident nodes, area, element, etc.

P.S. But I do not think that it is completely correct. I guess you can use Merge instead of glue for CZM and it was working for me so I guess there is no need to have shared nodes but it is my idea. You can also look at the last chapter of this thesis I found:

ftp://emci.udg.edu/mme/MecFrac/MecFrac.pdf

8-According to the attached paper, I modified your input file. And now it is running fine. The major change I did is that first defined the FLUID physics and then SOLID physics. I am not sure about the results. Please validate it.

 

Please If you have more information let me know.

Thanks,

 

Education in China and in America. What's new?

Mon, 2014-07-21 08:16

In reply to Education in China and in America

I wrote this post in 2007.   The post comes to the list of Popular Content on iMechanica this morning.  China has changed a lot.  Thinking about my trip to China in May this year and now reading this old post, I feel even more that my own years as a college student was such a distant past.  The government has long stopped assigning jobs to college graduates.  Young people (and their parents) need to consider the job market when they enter the colleges.  This condition must have a profound effect on education and on the choice of college majors.  It will be interesting to compare education in China and in US and Europe again.  What do you think?

iPad Air, Dropbox, PDF Expert 5. An update

Sun, 2014-07-20 08:44

In reply to Reading PDF files using iPad 3

By accident I landed on this old post today.  I am still using these three items

  • iPad Air.  Its storage is larger than the storage of iPad 3.  The resolution of the screen seems to be the same as iPad 3.
  • Dropbox.  I use Dropbox for placing most files in the cloud, so that all devices have the same files.  This function has remained unchanged.  Unfortunately, Dropbox is nearly inaccessible in China.  My Chinese collaborators have stopped using Dropbox.  That means we do not have shared folders now.  We are exploring services other than Dropbox.  Annoying!
  • PDF Expert 5.  I read nearly all PDF files using PDF Expert 5 on iPad.  PDF Expert 5 synchronizes files with Dropbox, in a way I described in the original post.  A small change in Version 5 has made a big difference to me.  There is no stop from one page to another.

I read a lot, mostly papers and textbooks, in PDF format, mostly in bed, when light is not on.  PDF Expert 5 allows me to annotate and search.  I have nearly completely stopped reading papers and books on paper.

Do you have any update on how you read?  Have you discovered any useful software and cloud service?   

Same here. I have learned a

Sat, 2014-07-19 05:32

In reply to elastic follow-up

Same here. I have learned a lot through your blog and I think that discussing published papers is a fantastic idea.

Please continue with it.

Best regards,

Emilio Martínez-Pañeda

linking

Sat, 2014-07-19 04:42

In reply to Run Abaqus from a Java code

Dear mMalekan

May be there are a lot of ways to link two softwares .... but my suggestion is to use an interface files to link your java and abaqus...

this interface files is not a complicated files ... this files is just a text file you use to store the data in it ... both abaqus and java read the interface data from this files ....

for example one file for reading stress, one file for reading strain, one file to tell abaqus to continue or stop  and one file to tell java to continue or stop....

I used this method  for linking matlab and ansys ... this is my own created method, may be there is other better methods...

 

 

Dear user

Sat, 2014-07-19 04:33

In reply to VUMAT of Drucker Prager, help needed please..

Dear user

you had a post before and I answered  your post but you didn't reply that post, Plase let other know you have solved your problem...

Sometimes  "small" deviation in your answere and other Fe codes are quiet normal, I will tell you my experience ...

I wrote a full FE code in Fortran two years ago(Drucker prager model), and I  compared my code by ansys and I found some deviation...
My code was correct but the deviation was because of the number 1 in below. there may be  many  reason for deviation:

1- Ansys is using different shape function for elements(extra shape functions)  ( I used classical shape function)

2- Ansys may use different number of integration point

3- Ansys may use B_bar method for calculation of volumetric constrains...

After I changed the setting of the ansys to have same option as my code, my result became accurate up to four floating point.

In your case may be the same happens in abaqus, may be when you use Vumat the abaqus disables some option for elements...

The first step I suggest is to set initial yield condition vey high in order that plastic flow wont happen... then check your elastic answer with the one in original built-in abaqus... this helps you to make sure the deviation is not because of element options ....

 

 

Thanks

Sat, 2014-07-19 02:49

In reply to Hi Geramian

I found it, Thanks

Hi Geramian

Sat, 2014-07-19 00:21

In reply to keywords error in vumat

I think you should look at the abaqus keywords manual.  Your questions are basic abaqus questions, that can be resolved just by looking at the manuals.

 

brunda

Let us wait

Fri, 2014-07-18 22:21

In reply to Harvard professor John Hutchinson is accused of stealing IP from MIT

I am waiting for John Hutchinson's respopnse. It is impolite to post emails others sent to you, unless you are showing them as evidence of misdemeanor.

Can you, pleas, show full

Fri, 2014-07-18 16:25

In reply to Harvard professor John Hutchinson is accused of stealing IP from MIT

Can you, pleas, show full conversation. 

 

Thanks Bafty

STATEV in UMAT

Fri, 2014-07-18 15:55

In reply to Presumably a needless conversion

Hello,

I want to write umat again, but I have a problam on state variable in umat. How can I give initial value to STATEV? I should write "initial condition, Type= Solution" in keywords?

ABAQUS

Fri, 2014-07-18 06:28

In reply to Problem with posting a comment using Internet Explorer

Hi every one

I want to introduce a porous material to abaqus in order to simulate the heat transfer through that... means showing the heat doesnt transfer through voids...

All I have found is about introducing porous media in abaqus for mechanical analysis.

I want to just model a porous material

 It is aluminum foam

 

Plzzzzzz  help me if you know 

Corotational

Thu, 2014-07-17 10:54

In reply to Dear Mohsen

Dear Aslan,

Thanks for your descriptions.

Mohsen

thanks all Dear friend for

Thu, 2014-07-17 07:52

In reply to corotational concept

thanks all Dear friend for colloboration.

Dear Mohsen

Thu, 2014-07-17 07:22

In reply to Rotation, Stiffness Matrices and Corotarional Rates

Dear Mohsen

His question is not about objective rates jaumman(corotational) or other rates... I had the same mistake first, his question is about the kinematic description of a geometrically nonlinear problem. as you know there are three description for geometrical nonlinearity:

1-UL(update lagrangian)

2-TL(total lagrangian)

3-CR(corotational)

corotational description usually deal with large rotation and small strains ... we don't need just rate formulation to describe material behavior ... energy( hyper-elastic for example) formulation can be used too in corotational description...

you are right the bar element stiffness matrix  is not diagonal, i made mistake ... thank you for correcting me

however I find this useful ...

Corotational total Lagrangian formulation for three-dimensional beamelement

 

KUO M. HSIAO
Read More: http://arc.aiaa.org/doi/abs/10.2514/3.10987?journalCode=aiaaj

 

Rotation, Stiffness Matrices and Corotarional Rates

Thu, 2014-07-17 05:53

In reply to Actualy I'm not an expert in

Dear Aslan,

The stiffness matrix for a bar element is not diagonal in local cooridinate system. More importantly the discussion of rotation from local coordinate system to global coordinate system is completely different from the discussion of corotational rates. A corotational rate for example with respect to spin tensor is written like this:

å = d(a)/dt - wa + aw

which is objective under rigid body rotation.

Mohsen

Thanks Atefe. I got this.

Thu, 2014-07-17 05:25

In reply to props are constants and they

Thanks Atefe. I got this.

Actualy I'm not an expert in

Thu, 2014-07-17 04:50

In reply to thanks for your response.

Actualy I'm not an expert in beam theory but I can give some idea for clarification

In Corotational concept a local frame is attache to element or integration point. The local tangent stiffness matrix in this case is different from the global stiffness matrix. for example for a rotated rod the local  stiffness matrix is a diagonal matrix, since the rod axial force is just dependent on deformation of axial displacement (not tangential or transverse displacement), but the global stiffness matrix has both diagonal and non-diagonal terms, the global stiffness matrix is resulted by rotating the local stiffness matrix.

since in TL formulation you drive all derivatives(gradient operators) base on material refrence coardinates, your coardinates can not be rotated. you should deal with refrence coardinates.

but  if you still want to use a local frame attached to the element, it is ok, you can have discret deformation gradients by the chain rule and  this formula:

[B]=round(.)/round(X)= round(.)/round(zeta)*round(zeta)/round(X)

where zeta is your local coardinate parameter....

thanks for your response.

Thu, 2014-07-17 02:56

In reply to Hi

thanks for your response.

I study geometrically nonlinear euler bernoulli beam. beam remains elastic. I obtain tangent stiffness matrix in TL approach. but there are tangant terms in tangent stiffness matrix. I want to use a local frame attaching to element(similar to corotational concept) and then continue problem.

best regards

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