I have a model exchange fmus of a damper . When I simulate it in simpack environment as frequency sweep.  I find the most part of the results are good and some parts have spikes. Which is unrealistic.  I guess the solver is not in sync.  How can sync ?

And what is rootstate_0001? 

Also if i do a simulation with constant low frequency it looks good.  AT high frequency it has spikes. 

But the same fmu as co-simulation is working fine. 

Suggest me some tips to rectify this issue.   Also if i could get some tutorial. 

Thanks in advance