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DAMIR88

SPH ditching IMPVEL or INVEL?

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Hi everybody


 


I'm working on a simple model, a water entry of a sphere, of which i have a rudimental experiment; a woody sphere 40 mm diameter dropped


from 60 cm above water surface in a glass tank 600x300x330 mm.


 


I model the sphere with shell elements, and a rigidbody linkening all sphere's nodes with the master node in the centre of sphere;


 


my problem is this:


 


If i apply an initial velocity, in the master node of RBody, of 3 m/s that is approx the velocity of sphere just before water entry, the behaviour of sphere is not absolutely the same of my experiment; the sphere just enter for some cm and comes to the water surface, in addition the behaviour of water is far from the experiment.


 


If i apply a Imposed velocity of 3m/s  for 0.015 s to the master node the general behaviour is completly different and is more more near the experiment behaviour;


the sphere goes down in water, not until the bottom like in experiment, but much more respect the initial velocity load model; the water splash is much more realistic and almost equal the experiment (considering that i don't model the air, that is incorporated in a small part into the water during the sphere motion, and no atmospheric pressure is applied)


 


I would know why such difference between initial velocity and imposed velocity?


 


regards to all


 


Damir


 


 


 


 


 


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Hi Damir,



 



If the problem is related to dropping then loading has to be Initial velocity.  Imposed velocity is never a load for drop test.  To get the behaviour right,  have sufficiently number of particles ( large number). 


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