When simulating the hammer impact force of pile driving using the $2$D axisymmetric feature in COMSOL Multiphysics:

$-$ I have added a point load on axis of $250,000$N

$-$ I have time step parameters of: range $[0,1,1\mathrm{.}002]$ in seconds to achieve a blow rate of $60$ impacts per minute.

$($a$)$ How would I change the step parameter, so the point load acts as an impact force with a blow rate of $60$ per minute.

$-$ When I change the $$sequence$$ range to $[0,1,1\mathrm{.}002]$ for $60$ impacts per minute, I receive the following error that the:

$$Nonlinear solver did not converge.

Time: $0\mathrm{.}0028823893229166569$ s$.$

Maximum number of Newton iterations reached.

Last time step is not converged$$

$($b$)$ How can I Apply the Point Load as a Time$-$Dependent Function:

$$ Under the "Point Load $($on Axis$)1"$ node in the Model Builder tree.

$$ My options to select are: $$Point Selection$,$Override and Contribution$,$Equation$$ and $$Force$$

$$ Under "Force," if I enter the expression if$($time

I receive the error that $$unknown variable time$$