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Hello,
I have simulated 2d flow for a selected region.From the result file, I have extracted the time series data of free surface and resultant velocity at node=91302.

I have plotted Resultant vel & Free surface data (shown in the attachment) in a single frame.

I could see that all maximum crests of the velocity curve DOES NOT COINCIDE WITH THE PEAK FLOODS AND PEAK EBBS timings OF FREE SURFACE.

In other way, it is expected that during Lowest low water level condition, the velocity should be very less. Highest high level condition should exhibit low velocity. BUT THE RESULT SEEMS TO BE HAVING PHASE SHIFT.

why such lag happens?

Thanks
Vks

Hi
Could you give more information on your model?

Your result sounds logical for an estuary where there always exists a time lag between peak of free surface and velocity...
To explain a little bit, during the ebb, the flow goes from upstream to downstream and at the lowest water level, the velocity is the residual velocity corresponding to the water discharge. When the flow start, there is a current inversion but this arrive later.
But maybe your case is not in an estuary...

Regards

Hi,

1) The model is not an Estuary
2) The model contains coastal region having one side land boundary & rest of the sides open boundary
3) Tpxo_7.2 was imposed along the open boundary with Thomson boundary condition
4) Simulation was made for 15 days

Thanks

Hello

There is no theoritical evidence that allows to coincide peaks of velocity and water elevation. Shallow Water equations are fully non linear and there is no direct link between du/dt=0 and dz/dt=0 (extrema in time for h and u).

kind regards
Riadh

Hello.
I shall put my query in a very clear way.

I understand the nonlinear parts from momentum equations. However, i am expecting the following things in the result.

LOW LEVEL WATER of free surface should coincide the low velocity part of the curve.
HIGH LEVEL WATER of free surfavce should coincide the other low velocity of the curve.

FLOOD of the free surface should coincide the High velocity peak
EBB of the free surface should coincide the other High velocity peak

From the figure it doesn't seems to have the above-mentioned coincidence. Why such lag happens?

Thanks.