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-   -   Resistance error with deceleration (https://www.cfd-online.com/Forums/star-ccm/233582-resistance-error-deceleration.html)

ali_ebrahimi February 2, 2021 15:27
Resistance error with deceleration
 
Hi
I work in the field of high speed craft simulation in Star CCM+ software.
I did the mesh validation and time step at speed 4.5 m/s (Fr = 1.45) and the results were good.Then I did the simulation for speed 3 m/s (Fr = 0.94) and the results were good.But the results for the speed of 1.5 had a large error (25%) in the amount of resistance.(There is also no numerical ventilation)
1. Do you have a suggestion?
2.What should change in the simulation settings as the speed value changes?

ali_ebrahimi February 5, 2021 04:54
Quote:
Originally Posted by Bulava (Post 795322)
Change the calculation step proportionally to the speed, change the center of gravity and give complete freedom to the body (6 dof). How can you make a calculation without this !? Not every mesh is good for fluid dynamics. Don't use polyhedra. They are good for visualizing small splashes from the bottom at speed, but give a large error in the drag of the boat. Trimmer only.
High-speed vessels should be examined in free movement without fixation along the (x) axis
Anchoring the vessel is possible only after the final stabilization of the vessel, replacing the movement along the abscissa axis with the current speed at the entrance and continue the study with qualitative data, if necessary. Without philosophy, nothing good will come of it, but only count according to known data and compare it with the practical result. It's so boring and won't do for free ship modeling from scratch.
etc.
I work on a high speed catamaran boat.
Due to the complexity of the body shape, trimmer mesh can not be used.
Tested in a vessel laboratory in two degrees of freedom (heave & pitch)
I want to compare my results with laboratory results.So I can not open all the degrees of freedom

Aeronautics El. K. February 6, 2021 04:50
Quote:
Originally Posted by Bulava (Post 795322)
It's so boring and won't do for free ship modeling from scratch.
etc.
No one asked you to. [emoji13]


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