added mass coefficient

Hello,

Added mass coefficient in buoyancy affects to the total weight of the system.

I have some questions.

1. The total weight in frequency results grid is used for calculate for both static and modal? or only modal analysis

2. If the weight is only for modal analysis, whereas the weight for both analysis are different, right?

and It is necessary to use added mass coefficient from inertia coefficient (in hydrodynamic dialog) -1

I ask this because I used added mass coef = 2.29 and my modal analysis, the total captured go up to 57%, But if I use Cm-1 for Ca the Ca equal to 0.88 and the total captured mass is about 9%.

So, I want to know my Ca = 2.29 can represent the realistic results or more conservative case, please suggest

Parents
  • Greetings, 

    To answer your question:

    Q1. 1. The total weight in frequency results grid is used for calculate for both static and modal? or only modal analysis

    Answer: 

    generate a report with the Frequency and Center of gravity sub reports enabled. 

    As one can see the weights from both reports are identical. However one should understand that the program does not consider the total weight of the system but a portion of the total mass of the system.

    Q2. If the weight is only for modal analysis, whereas the weight for both analysis are different, right? and It is necessary to use added mass coefficient from inertia coefficient (in hydrodynamic dialog) -1

    Answer: 

    From your questions, appears that you are trying to model underwater / offshore piping. Your question is not very clear. I believe that you are confusing settings and their locations (ex. there is no "inertia coefficient" or "added mass coefficient" on the hydrodynamic dialog).

    As mentioned above, the weights shown in both reports are identical, and thus are considered by both Static and Dynamic analysis.

    For detailed understanding about a setting in AutoPIPE, open the dialog, please cursor in that field and press the Keyboard F1 key. This should open help on this particular feature. Pease see AutoPIPE help for details on using "Added mass coeff (Ca)" (be sure to read the notes too) or other settings. In addition, see WIKI here for typical offshore modeling approaches. 

    Regards,
    Mike Dattilio
    Design Analysis Engineering Group
    Senior Analyst Bentley Systems Inc
    =============================================================================

Reply
  • Greetings, 

    To answer your question:

    Q1. 1. The total weight in frequency results grid is used for calculate for both static and modal? or only modal analysis

    Answer: 

    generate a report with the Frequency and Center of gravity sub reports enabled. 

    As one can see the weights from both reports are identical. However one should understand that the program does not consider the total weight of the system but a portion of the total mass of the system.

    Q2. If the weight is only for modal analysis, whereas the weight for both analysis are different, right? and It is necessary to use added mass coefficient from inertia coefficient (in hydrodynamic dialog) -1

    Answer: 

    From your questions, appears that you are trying to model underwater / offshore piping. Your question is not very clear. I believe that you are confusing settings and their locations (ex. there is no "inertia coefficient" or "added mass coefficient" on the hydrodynamic dialog).

    As mentioned above, the weights shown in both reports are identical, and thus are considered by both Static and Dynamic analysis.

    For detailed understanding about a setting in AutoPIPE, open the dialog, please cursor in that field and press the Keyboard F1 key. This should open help on this particular feature. Pease see AutoPIPE help for details on using "Added mass coeff (Ca)" (be sure to read the notes too) or other settings. In addition, see WIKI here for typical offshore modeling approaches. 

    Regards,
    Mike Dattilio
    Design Analysis Engineering Group
    Senior Analyst Bentley Systems Inc
    =============================================================================

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