Displacements in a DTRAN Solution

mpvnaresh

Hi all 

 In a Direct Transient solution i have given a acceleration load with certain frequency and amplitude.

When  icheck displacements in the location where acceleration is applied, The Displacement curve is a not oscillationg one.Instead it is keep on going.

Can any one help me in getting the oscillating displacements.

I have tried by changing all options of FORM(1) in Displacement output request.but no use.

Please help me in this .

 

 

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Rahul Rajan_21763

Did you specify damping in your model?

mpvnaresh

Yes Sir ,

I specified

 

mpvnaresh

This is not only the model , for all DTRAN analysis i am facing the same problem.

Rahul Rajan_21763

Could you please share the .fem and .out file of the run of any simplified model with this issue?

 

mpvnaresh

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mpvnaresh

Sir

Kindly let me know if any other  information is needed.

 

mpvnaresh

 sir ..any update ?  

Rahul Rajan_21763

Can you give a try with time Vs disp instead of time Vs accel? 

mpvnaresh

Sir 

 

with displacements as input load it is oscillating .But the question remains same.

If i convert it into displacements obviously it oscilates as we are giving displacement directly.

But my load case is in acceleration i need to apply it in accelerations only.

 

Rahul Rajan_21763

Could you please consider initial velocity for the base setup where you have time Vs accel.Transient initial conditions are defined using a TIC Bulk Data Entry. Initial displacements and initial velocities can be defined. This should help you to avoid drift in the displacement plot and get oscillating plot.

mpvnaresh

Thanks For the response .

I will try this and update you .

mpvnaresh

Sir 

 

I am not able to give Input of Initial conditions . Can you please help in how to do this?

How to create TIC Bulk data entry. And also i have no data for initial displacements and initial velocities then how to get those values. 

Rahul Rajan_21763

I got help from my colleague to calculate the initial velocity based on the given acceleration curve.I remember we provided initial velocity of -624.0 and with that we got proper oscillating plot.Attached is the fem file.

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mpvnaresh

Sir

 

I really Appreciate this.

Thanks a lot for your time.

I think this is solved. 

But when try to integrate the acceleration curve to get celocity i am gettion a Zero velocity. Please help me in the methodology for getting velocity.and also how did you created TIC (V).

When i go go to load type page Velocity type is Blank.

 

Thanks again for the support sir.

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Rahul Rajan_21763

TIC V you can create from constraints panel & set the load type to TIC V.Sorry i cant provide you right now the hand calculation which we did to calculate Intial velocity,  as i am away from office desk.However,I do have the math we performed in HyperGraph to crosscheck.PFA mvw file for same,

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mpvnaresh

Thanks Sir

 

mpvnaresh

Sir

 

I calculated Initial Velocity and applied as TIC(V).

But after the compltio of acceleration cycle displacements are cumulative.

(which mathematically  may true, As Acceleration=0,  Velocity which is integral of Acceleration = constant , Then Displacement is a straight line which is cumulative )

How can we make the  velocity, displacement to be zero after the load (Acceleration)is removed . 

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