SPH ditching IMPVEL or INVEL?

Altair Forum User
Altair Forum User
Altair Employee
edited October 2020 in Community Q&A

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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Answers

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited December 2014


    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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