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May 26, 2013, 14:04 
how to constrain rigid body motion

#1 
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Mohamad Alagheband
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Hi
Does anybody know how I can constrain a rigid body motion I mean for like specific rotational angle ? I can not just stop the solution and rerun for fixed boundaries because my inlet velocity profile is pulsatile. thanks 

May 26, 2013, 21:34 

#2 
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Ma.L
Join Date: May 2013
Location: ShangHai,China
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when you define a rigidbody,you can define the degree of freedom of it，including Movement and Rotation。
good luck。 

May 27, 2013, 05:32 

#3  
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Mohamad Alagheband
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Quote:
thanks for reply I knew what you mentioned but i am trying to constrain rotation angle i mean when RB rotated for certain angles then it should be stopped in that position and solution go on with fixed boundaries and i don't know how much time does it take to rotate and i am going to find out by RB simulation? Tnx 

May 27, 2013, 08:17 

#4 
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Matthias Voß
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Location: Berlin, Germany
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hey
not sure if i got you right, but if you can express your RBmovement via CCL then you can simply add another expression with respect to simulation "runtime counters" like AITERN,CITERN,T,TSTEP or ATSTEP. e.g. Code:
RampLength = 1.0[s] Ramp = (2*(min((t)/RampLength,1))^3+3*(min((t)/RampLength,1))^2) 

May 28, 2013, 09:56 

#6 
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Matthias Voß
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some thoughts:
1# you can apply a symmetry on the middle ?! 2# never done smth. with RBM but maybe you can use this as a starting point Code:
New X = ((xX0)Total Mesh Displacement X)*cos(alpha)+((yY0)Total Mesh Displacement Y)*sin(alpha)+X0 New Y = ((xX0)Total Mesh Displacement X)*sin(alpha)+((yY0)Total Mesh Displacement Y)*cos(alpha)+Y0 New Z = ((zZ0)Total Mesh Displacement Z) + Z0 X0 = 0 [mm] Y0 = 0 [mm] Z0 = 0[mm] 3# your are running transient cases, right? 

May 28, 2013, 10:58 

#7 
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Mohamad Alagheband
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Dear Matthias
I am really appreciate for spending time to answer. As you said I am running a transient simulation with symmetric geometry and my biggest problem is finding rotation angle . I know the range of rotation but i do not know exact value for rotation angle and i am trying to find out by RBM (i mean applying momentum forces to RB) and i think that code must work for known rotation angle 

May 28, 2013, 11:09 

#8 
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Matthias Voß
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u r welcome.
You apply the forces on the RB (input) and you are interested in the transient behavior and end position(output) of the RB in equilibrium state when also applying the given inlet conditions?! So to get the real position is totally a topic for postprocessing. Is that correct? First guess define a Monitor point at a certain node of the RB and grab the coordinates. 

May 28, 2013, 13:18 

#9  
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Mohamad Alagheband
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Quote:
this is my problem the leaflet must stop at 85 degree and simulation go on until the end of the pulse thank you a lot Last edited by MUMMED; May 28, 2013 at 15:26. 

May 28, 2013, 15:12 

#10 
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Edmund Singer P.E.
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If you are using the 6DOF solver, as implemented in CFX, you cant constrain a rigid body to rotate about a hingepoint (not coincedent with the body center).
That said, this is easy enough to do with the CEL equations that newbie has layed out (I didnt check for correctness). You can use CEL to limit alpha to what you want, and you can use equations of motion to put d(alpha)/dt in terms of forces (moments), which you can read off the body. Note (X0,Y0,Z0) will be your hinge point. 

May 28, 2013, 15:37 

#11  
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Mohamad Alagheband
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Quote:
up to now I have been working with 6DOF solver and I do not have much experience to apply momentum with CEL. Do you have any suggestion? thanks 

May 28, 2013, 16:39 

#12 
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Edmund Singer P.E.
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Are you familiar with CEL?
Can you discretize angular motion equations? If the answer to both of those is no, I would start with reading up on the CEL section of CFX help docs. Then read up on angular motion in a dynamics book. A complete discussion is more than I want to put in this forum. Specific questions on either of those topics (other than how do i do the entire thing) I can answer. 

May 29, 2013, 02:49 

#13 
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Mohamad Alagheband
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you are right
I read CEL section and angular momentum before and I should take a look again I would like to thank you again for spending time. Thanks 

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