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How to tell COMSOL to balance the drag force and gravity?
Posted Apr 5, 2012, 9:28 p.m. EDT Fluid & Heat, Computational Fluid Dynamics (CFD) Version 3.5a, Version 5.2 5 Replies
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Hi all,
I have a question related to how COMSOL calculates the drag force and gravity force in a "parachute" model. Imagine that an object is falling down to the ground at a high velocity because of the gravity. When its parachute is opened, the gravity is still the same, but a drag force which is against gravity is generated. Based on stokes law, the drag force can be calculated as "-6*pi*viscosity_air*radius_object*velocity_object". The higher the velocity of the falling object, the higher the drag force will be. After a short while, the drag force will balance the gravity so that the object is considered to be force equibalance. The object will fall down in a constant velocity, and will be finally landed.
However, this situation is not happening in COMSOL simulation. When COMSOL calculates the drag force from the velocity produced by gravity, the drag force is even higher than gravity, which means that the object is driven by drag force and moving up against the gravity. The reason for that, I think, is COMSOL doesn't know how to simulate the situation when two forces are balanced. What should we do to sovle this problem?
Thank you very much in advance!
Sam
I have a question related to how COMSOL calculates the drag force and gravity force in a "parachute" model. Imagine that an object is falling down to the ground at a high velocity because of the gravity. When its parachute is opened, the gravity is still the same, but a drag force which is against gravity is generated. Based on stokes law, the drag force can be calculated as "-6*pi*viscosity_air*radius_object*velocity_object". The higher the velocity of the falling object, the higher the drag force will be. After a short while, the drag force will balance the gravity so that the object is considered to be force equibalance. The object will fall down in a constant velocity, and will be finally landed.
However, this situation is not happening in COMSOL simulation. When COMSOL calculates the drag force from the velocity produced by gravity, the drag force is even higher than gravity, which means that the object is driven by drag force and moving up against the gravity. The reason for that, I think, is COMSOL doesn't know how to simulate the situation when two forces are balanced. What should we do to sovle this problem?
Thank you very much in advance!
Sam
5 Replies Last Post Aug 3, 2017, 3:17 p.m. EDT