Simulation Study to Control First Mode using ANSYS

The closed loop controller is introduced in ANSYS© by means of a macro. The sensor output is taken by taking the difference between the X direction displacement (u1 and u2) of two nodes, in the same plane on either side of the centre line. This is divided by the distance between them to get strain. It is then appropriately amplified by multiplying it with sensor gain ks. The controller is then defined by the error function and the voltage va to be applied is calculated by multiplying the error function with appropriate actuator gain (ka).

The generic macro used to simulate the controller action is given below:

• *set,dt,0.0088
• *set,ts2
• *set,nv,559
• *set,nr1,1117
• *set,nr2,455
• *set,dx,18*(8.33e-3)
• *set,ks,1000
• *set,kv,1000
• *set,kc,1
• *set,va,0
• *do,t,3*dt,ts,dt
• *get,u1,node,nr1,u,x
• *get,u2,node,nr2,u,x
• err=0-ks*(u2-u1)/dx
• va=kc*kv*err
• d,nv,volt,va
• time,t
• solve
• *enddo

Where,

• dt : Time step for Transient Analysis in ANSYS©
• ts : Time for which analysis is carried out
• nv : Node at which voltage is applied
• nr1 : Higher node considered for strain calculation
• nr2 : Lower node considered for strain calculation
• dx : Distance between nodes nr1 and nr2
• ks : Sensor gain
• kv : Actuator gain
• kc : Proportional (controller) gain
• va : Applied voltage
• err : Error function

The value of kc is varied to obtain desired controller effect. But constraint is placed on the maximum value of kc due to voltage. The values of Rayleigh damping are taken as 0.002.

Displacement v/s Time Plot for different kc values

Voltage v/s Time Plot for different kc values

Though in above case, the vibration settling time is decreased. But the rate of decrease is quite low. A steeper decrease of vibration settling time can be obtained by increasing the patch size.