Learning Forum

[ZHSBEI]

Hey hello. I am doing analysis of an actuator in which I am doing individual analysis of a piston. I am trying to apply a pressure of 6.5MPa on the piston head to lift a load of 12000N at the end of piston rod but doing so results in an error specifying not enough constraints.

[Saumadeep Choudhury]

!

This analysis can be undertaken in 2 parts (mentioned below) and then the two separate solutions can be combined using Solution Combination (ansys.com) to get the final combined solution.
Applying pressure at the piston head and constraining the piston end.
Applying force at the piston end and constraining the piston head.

Regards Saumadeep

[dlooman]

If the pressure and force are equal and have the same line of action, weak springs can be requested in Analysis Settings to allow the analysis of an unconstrained model. The small imbalance will be carried by the weak springs.

[peteroznewman]

Do analysis 2) you described using the pressure and a fixed support on the other end. In that solution, you can request a Probe of the Reaction Force for the Fixed Support. If the Reaction Force is very close to 12000 N, then you could proceed as described by and run an analysis using no fixed support, and put the measured reaction force on one end and the pressure on the other.
I don't agree withabout adding two solutions because that would result in double the stress in the shaft.

[ZHSBEI]

Hey dlooman and peteroznewman!
I checked if the reaction force was similar to my intended force of 12kN but it was not. The probe was showing a value of 12.77kN. So I changed my force input to 12.7kN and used weak springs and turned on large deflections but now the solver is showing an error of not being able to converge to a solution as shown below. How to counter this error?


Thanks in advanced
ZHSBEI

[peteroznewman]

Does it solve if you set Large Deflection Off?
Did you set the force to the exact value of the Reaction Force or did you round off the number? Don't round off.
You can also try turning on Inertia Relief under Analysis Settings.

[ZHSBEI]

Hey !
I am extremely sorry for taking this long to reply. I had seen your comment but wasn't logged in my account(was busy with exams). Yes it does solve if Large Deflection is set as OFF. Yes if I recall correctly the reaction force was along the lines of 12763.34N and when I entered the value Ansys itself rounded it of to 12764N.
I don't know what Inertia Relief is ,can you explain it a bit.
Thanks in advanced
ZHSBEI

[peteroznewman]