# Monitoring rotating domain angle per timestep

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 November 1, 2017, 12:38 Monitoring rotating domain angle per timestep #1 New Member   Konstantinos Join Date: Jul 2016 Location: Athens Posts: 7 Rep Power: 5 Hello, I 'm trying to simulate a flow in tube with a butterfly valve. I m using a rotating sub-domain around the butterfly valve instead of rigid body motion. I need to monitor butterfly angle per time step so as to calculate the necessary valve rotating velocity (For instance if theta==90 [degrees], omega=0[rad/s],(...)). However, because i m not using rigid body motion, i can't use the classic expression rbstate(Euler Angle Y)@butterfly. Is there any way to monitor the rotation angle? Thank you in advance.

 November 1, 2017, 17:55 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 15,975 Rep Power: 122 I do not know of any variable like that. Please note that rotational frames of reference assumes constant rotation angular velocity. So if you change the velocity (as you appear to be doing) then there are additional terms related to angular acceleration which are not modelled. This means that angular acceleration effects will not be captured properly. Whether this is important depends on how significant your angular accelerations are. If they are important then you will have to go back to moving mesh or rigid body approaches.

 November 2, 2017, 07:15 #3 New Member   Konstantinos Join Date: Jul 2016 Location: Athens Posts: 7 Rep Power: 5 First of all, thank you for your reply. i use rigid body motion but i cant use rotational angle per step in expression. Specifically my model is the following. A tube with inlet and outlet (open boundaries) and a butterfly valve inside to a subdomain. The fluid pressure is sinusoidal. I aim to set an expression with which my model will be able to understand valve angle and calculate the valve torque in order to be closed or opened depending on pressure value. It is known that by using rigid body, solver monitor show euler angle (X,Y,Z). After a lot of research i ended up to the above expression (rbstate(Euler Angle Y)@butterfly (butterfly=rigidbody)). The problem is that in contrast to automatic solver monitor , this expression monitor seems not to change with the time and is equal to zero. I hope to be analytical. Thank you in advance for your time and your help.

 Tags butterfly valve, monitoring angle, rotating domain, valve