[MITgcm-support] parameters in obcs sponge layer

[Yangxin He]

Hey there,


Here is my toy problem,

I have no slip at the bottom, rigid lid at the top, I am sending internal waves of M2 tidal frequency using obcs_calc.F from the left boundary with max(U)=0.02 m/s, I want to impose a sponge layer using orcs_sponge.F on the right boundary.

1 grid cell in the y-direction, i.e. it is a 2d simulation.

50 points vertically with a uniform gird size of 40m.

2000 points horizontally with a uniform gird size of 500m.

An example of my data.obcs file looks like:

# Open-boundaries

 &OBCS_PARM01

 OB_Ieast=-1,

 OB_Iwest=1,

 useOBCSsponge=.TRUE.,

 &

 &OBCS_PARM03

 spongeThickness=800,

 Urelaxobcsinner=89424.,

 Vrelaxobcsinner=89424.,

 Urelaxobcsbound=4471.,

 Vrelaxobcsbound=4471.,

 &

What I want to achieve is this sponge layer shall work well so that all waves are being absorbed, no reflections back and it should work even after 30 or 40 tidal periods or even longer.

I have tried various values for the five parameters listed in &OBCS_PARM3, following the basic principle,

1) a fairly large U/Vrelaxobcsinner to make sure the forcing is small when the waves hit the sponge.

2) a fairly small U/Vrelaxobcsbound to make sure the forcing is still large enough so the waves can be fully absorbed.

1) the thicker the sponge layer is, the better it shall work.

The problem is none of the parameters I tried worked.


I assume somebody must have done similar work as this one. I would really appreciate some insights as to what values I shall assign those parameters.


Thanks


Yangxin

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