Hello
Is the pseudo code below for developping a new contact law? It is
probably useless since there is one law doing what you need already :
the "CohesiveFrictional" class.
There are probably two mistakes in your code :
1/ For sure : what you define as Fs= - Ks*double_ds is in fact a dFs (an
increment), not the total force.
If you check the current contact laws, you will see something like Fs =
Fs - Ks*double_ds. With your equations, Fs is in fact a viscous force,
proportional to the current relative velocity.
2/ Not sure : the fact that rotational velocity is constantly increasing
may be due to a sign error somewhere (e.g. in the normal orientation),
or perhaps an inapropriate timestep (too large). I don't feel like the
first mistake could produce this result.
Bruno
Nice Man a écrit :
Hi,Dear all.
I would like to use cohesive contact model to simulate a rock, the
small rock particle is modeled by cementing them and the force assumed
by the cementing is cohesive force--which can assume normal and shear
force. but I meet problem in moment calculation and the rotational
speed calculation:
just for 2D case ( 'x' is cross(), Normal_directior_unit is from P1
center to P2 center ):
vector_relative_velocity=(Particle1.v+Particle1.omega x
(Particle1.r*Normal_directior_unit) ) -(Particle2.v+Particle2.omega x
(Particle2.r * -Normal_directior_unit) ) ;
vector_relative_shear_velocity=(vector_relative_velocity *
vector_Shear_Direction) * vector_Shear_Direction;
double_relative_shear_velocity=(vector_relative_velocity *
vector_Shear_Direction)
double_ds=double_relative_shear_velocity*dt;
Fs= - Ks*double_ds;
vector_Fs=Fs* vector_Shear_Direction;
Now moment is :
delta_Moment= (Particle1.r * Normal_directior_unit) x vector_Fs; //(Fn
is not calculated here,and also since Fn pass through the center of
the mass, so it has no effect on the rotation)
Total_moment += delta_Moment;
so
Rotational_velocity += ( Total_moment / Inertia)*dt;
My problem met is , after several iterations,
my rotational velocity reachs 1e4 rad/sec, or even more!!! this is
totally incorrect.
So what is the calculation problem in this cohesive condition? ? or
can I do the moment calculation and rotational speed calculation like
this since there is cementing cohension between particles and the
cohension will strict the free to rotate of the particle now? In the
CohesiveFrictionalContactLaw, I see the moment calculation.
need your help. Thanks in advance.
Kan
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