pulsatile flow

I simulated the pulsatile flow with the Lattice Boltzmann Method and wrote LBM and analytic velocity of the pulsatile flow codes with c++ language, but there was very different on the wall vicinity between the simulated velocity and the analytic velocity, seeing Fig.1.

Above figure, solid line was analytic velocity, dot was simulated velocity.
I didn’t know where was a preblom.
I added the body force into the collision term, , A was the amplutide of body force; was the angle frequency. The analytic velocity was fllowing equation:

where was the fluid density, L was the width of the channel, and .
I wish you help me if you should simulate pulsatile flow and clearly show where was the error. If you should not simulate the pulsatile flows, can you inquire about your friends who simulated the pulsatile flows.
Thank you a lot!