I am working with oscillating boundary conditions in FEFLOW. I use the power function tool to set a specified transient head boundary from a timeseries based on a sine curve. I use a free and moveable or the phreatic surface condition at the watertable. The problem is that when I monitor heads on the head-specified boundary nodes they are not consistent with the input values. E.g. the observed head on the boundary node is lagged and never reaches the full amplitude of the sine curve. The lag problem seems to occur in the first couple of timesteps where the head differs significantly from what is prescribed in the timeseries. The amplitude problem persists throughout the simulated period. I have tried to include a long timeseries including several oscillations and then start the model in the "middle" of the power function timeperiod in order to make sure that any interpolation of the sine curve is correct at each end of the period. I have tried different types of interpolation (Akima, Constant, etc etc). None of these approaches seem to help. Can anyone help me?
Thanks in advance!
Regards,
Søren
