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Detailed Multi-Domain Tutorial

Hi,

I am following the tutorial attached, but it is incredibly hard to follow and doesn't go into much detail. I was wondering if anyone has a more comprehensive tutorial for the multi domain method? Even the RADIOSS User Guide is vague on this topic. For example, both the User Guide and Tutorial say you need to use a type 4 link to connect the nodes of both domains together, however, I am eventually trying to do this with an SPH sub-domain and 2D shell elements, and need details. There are no details as to how these links are defined, as they are predetermined in the mono-domain beforehand. Furthermore, the files I end up with are fine_mesh_0000.rad and coarse_mesh_0000.rad. This is not the case in the file containing the complete multi-domain, which has two _0001.rad files and one _0000.rad file. Supposedly I am also supposed to making an input.rad, but it isn't clear how I can do this in a general case, and from what I can see in the pre-completed multi-domain analysis, this file should be generated automatically, but the instructions say to write it yourself.

Can anyone please refer me to some very detailed instructions on the multi-domain method?

Thanks in advance.

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Simon Križnik

Hi,

check the following tutorials:

RD-E: 4500 Multi-Domain

RD-E: 2203 Ditching using Multi-Domain for SPH and ALE

This could also be helpful:

https://altairatc.com/europe/presentations/Session10/Session10_Altair_Wronski.pdf

https://altairatc.com/europe/Presentations_2009/Session_02/FORDRESEARCH_EHTC09_MultiDomainRadioss_Bach_Ford.pdf

Crashphys

Hyperman,

Following the instructions, I ended up with a .M00 file after exporting from Hypercrash, and no engine files. Can you help with this? The tutorial files have the starter and engine file for the multi domain, and only the engine file for the sub domain. I am only getting a starter file for both the multi domain and subdomain. I realise this is trivial, but I can't seem to find out how they managed to export the engine file.

Simon Križnik

In Hypermesh there exists an option on export panel to merge starter and engine file. In Hypercrash the Export Selection window 'Add model’s control card not linked to any part' accomplishes the same.

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Crashphys

I unchecked the option on the export panel and still ended up with the attached. I then tried it again with it checked, and got the same.

I do not have the engine file merged in with my starter file as you do.

EDIT - SOLVED: I feel very stupid. So, for those with older versions of RADIOSS, the instructions I have followed work. Those with newer versions (I am using RADIOSS V14.0), all you have to do is follow the instructions on page 726 of the RADIOSS Tutorials and Examples Guide. Refer to the suggested reading from Hyperman. Thank you for the help Hyperman.

EDIT 2 - Since we're on the subject, I noticed that AMS and Multidomain are not compatible. I would like to understand why, so if anyone has any further readings on this topic, I'd appreciate it. I was also wondering how to determine which of the two is more effective. I realise AMS has the drawback of reduced accuracy, while Multidomain has none, and Multidomain only works effectively when there are a large number of elements in one domain vs another, but I was wondering if there was some other theory to compare the two methods.

Thanks for all the help!

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Simon Križnik

I'm glad you figured it out.

I do not know why AMS and Multidomain are incompatible, but you can use conventional mass scaling (DT/NODA/CST). Actually, timestep difference is the critical factor for effectivness of Multidomain technique, because the smallest time step determines the performance of the (sub)model. In general, AMS is effective where timestep is homogenous, while Multidomain is the best choice for models with local mesh refinements.

Crashphys

I see. Thank you for the clarification. I suppose I will have to rely on AMS, as it looks like Multi-Domain won't work for my application.

Just to add some further documentation for future viewers: I actually ended up looking deeper into the theory manual as well, and it seems unfortunately for my application it will not work. Turns out for multi-domain, it's also important you have a very small amount of contact surfaces that are well defined, so it's not great for the application of fluid sloshing in tanks, but works great if you have an example like ditching, where it will be a simple and direct interface between the two domains.

Thank you very much for your help Hyperman.

Maya Geoffroy_22197

Hi !

I am also interested in using the multi-domain method and also only have access to the first document mentioned by Crashphys.

Unfortunately, the links for more detail are no longer available. Could it please be possible to give again the links or other information on how to use the method.

I am working on an old version (2018) of Radioss and I am using an implicit solver. I hope the method is also usable in this case.

Thank you very much in advance

PaulAltair

Hi !

I am also interested in using the multi-domain method and also only have access to the first document mentioned by Crashphys.

Unfortunately, the links for more detail are no longer available. Could it please be possible to give again the links or other information on how to use the method.

I am working on an old version (2018) of Radioss and I am using an implicit solver. I hope the method is also usable in this case.

Thank you very much in advance

Multi-Domain will not work with Implicit, but there would be no point to use it in this case, Multi-Domain is to allow 2 different portions of the model to run with different explicit timesteps, but in Implicit analysis, there is no timestep as such.

What problem are you trying to solve?

Maya Geoffroy_22197

Thank you for your quick answer. I was interested in the multi-domain method to define 2 mesh densities on the same model, like in the tutorial I must have misunderstood something.

The model I am working on fully parametric and the geometry is meshed using an in-house code, not on HyperWorks. I'd like to refine an area without redefining the whole parametric mesh.

If the multi-domain does not work with an implicit solver or if it not adapted to what I wish to do, do you know of any other method ?

Thank you very much for your help !

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PaulAltair

Thank you for your quick answer. I was interested in the multi-domain method to define 2 mesh densities on the same model, like in the tutorial I must have misunderstood something.
The model I am working on fully parametric and the geometry is meshed using an in-house code, not on HyperWorks. I'd like to refine an area without redefining the whole parametric mesh.
If the multi-domain does not work with an implicit solver or if it not adapted to what I wish to do, do you know of any other method ?
Thank you very much for your help !

Unable to find an attachment - read this blog

If you just want to have 2 different mesh densities at a mesh boundary of some sort, you could use a tied interface (/INTER/TYPE2) and define the main and secondary entities by part group so the node and element numbering does not matter

Maya Geoffroy_22197

Thank you very much for your answer. I had visibly misunderstood the example.

I might create a new question on the topic if I have further questions.