Moments of inertia: request for documentation

This is a fork of the post GenCase v 5.0.174 and calculation of moments of inertia at https://forums.dual.sphysics.org/discussion/comment/3727/#Comment_3727 (July 2020). For this part can live independently of the continuation there, I split that to avoid oblivion.

I would politely ask to include the following items in the documentation set of DualSPHysics 5.0.

First, one certain outcome of that discussion is that custom-setting the inertia matrix for floating objects is an important, perhaps necessary, option. Would you please add to the XML documentation of 5.0 (XML_GUIDEv5.0.pdf, section 2.6, p.71) which moments of inertia you model in DualSPHysics? I presume that the moments of inertia you have in mind are those with respect to axes parallel to the DualSPHysics reference system and passing through the centre of mass of the object (https://forums.dual.sphysics.org/discussion/comment/3099/#Comment_3099, June 2019). However, the guide still lacks guidance on this topic.

Second, would you mind it to align the User’s Guide to that description? Not unlike some peer-reviewed publications, the formulation at https://github.com/DualSPHysics/DualSPHysics/wiki/3.-SPH-formulation#384-fluid-driven-objects still speaks about a single, scalar moment of inertia, while in the general 3D case it should be a tensor/matrix.

Finally, I understand that GenCase is a closed-source program and am fine with it. Would you mind it, nonetheless, to mention in the User’s Guide which algorithm you use for computing the six elements of an inertia matrix? I would expect an embarrassingly parallel summation of particle masses time squared distances,, but I understood that there may be other ways; naming those would be appropriate, I believe.

Thanks in advance for this. I trust that the documentation will be clearer for the benefit of any reader interested in modelling floating objects.

Comments

  • Dear @sph_tudelft_nl

    1 - This is an open-source project with connected advantages and disadvantages: this means that the requests on the forum are addressed in our available time.

    2 - We do our best to help users which can formulate very specific requests which are (a) of general interest and (b) written using the least possible number of words (some examples). 

    3 – Requests related to specific possible bug and/or issues should include all input files necessary to reproduce the same results by other users/developers.

    3 - Posts that contains no specific requests, but long critiques to the way the code is organized (how variables are named etc...) requires too much time and efforts, therefore are difficult to address.

    4 - The same apply to suggestions for the wiki: we are aware that the wiki if far from being a comprehensive guide for the software, and it is always in a process of being updated within time constraints

    Regards

    DualSPHysics team

  • edited July 7

    Thanks.

    There is nothing in your message I vehemently disagree with. One of the advantages and disadvantages of forum exposure and of open-source projects is that you get feedback and involvement from a wider range of users.

    I do appreciate the 'infowhelm' for sure; sorry if I didn't have time to write a short letter, so I wrote a long one instead. I leave it to your judgement to decide what is correct/relevant/urgent to a greater audience or in a larger time horizon and, primarily, whether behind users' dismay there is a substantial problem to tackle.

    Also, some analyses --- especially out of baffling situations --- only make sense if backed by an extended explanation. Admittedly, they require time to read, but much more time to document and write; so, difficult to address, yes, and difficult to dig out as well. Moreover, they do not cease to exist if they do not fit a chat format.

    So, I dare say, there is no-one who does not do his/her own best and, perhaps, none who finds this particularly entertaining in and of itself either. Nonetheless, I hope that (critiqued) critiques help enhance the project development in a sound way, perhaps through revision other than addition. So I keep on hoping that changes will follow from these discussions, including the above.

    Obviously, there is a lot to congratulate on DualSPHysics, but this does not need as extensive descriptions.

  • edited July 8

    I studied this before. my testing code is shown below, you can test it


    i remerber, it agrees well with GenCase.

    But, i believe that due to the Cartesian distribution, this function would not work well in some cases.

  • @JOJO thanks for your interest and contribution. Would you mind to share this in the thread on the calculation of moments of inertia as well? That is https://forums.dual.sphysics.org/discussion/1813/gencase-v-5-0-174-and-calculation-of-moments-of-inertia#latest And then we can keep this theread focused on the aspect of documentation. For sure: thank you very much.


  • that is OK. But, maybe it require more test, i just test some geo like wedge, sphere...

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