# How to simulate a tide boundary?

Hello, everyone, I am a new TOUGH2 user. I want to creat a model using EOS3 module. The left boundary of the model is a water-land interface. The mean sea level is assumed to be 6m below the ground surface. The sea tides fluctuate within a range of -5m ~ -7m in a sine curve.How can I realize it?

Thank you very much for your help!

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• Hi Yang Xin,

You can implement time-dependent Dirichlet boundary conditions (to represent tidal fluctuations) using the approach described in Section 7.2 of the TOUGH2 User's Guide. Granted, this approach is quite tedious. This is why iTOUGH2 and TOUGH3 provide a feature to simply read in a table of time vs. the value of a primary variable (in your case: pressure). Unfortunately, if you are using TOUGH2, you may be stuck with having to specify large, time-dependent gas injection rates into elements with a very large volume, using block GENER.

Good luck!

Stefan

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• Yang Xin
• Yang_Xin
• 4 mths ago
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Stefan Finsterle

Stefan,

Thank you so much for your kind response.

I am still puzzled about some problems. Due to the tidal fluctuations,some elements sometimes  may be under water, sometimes may expose to the air. Should I set multi-phase time dependent bc for these elements? In addition, time-dependent gas injection can make the pressure rise, but how can I realize the reduction of pressure(when the sea level drop)?

Thanks,

Yang Xin

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• Yang Xin,

Use sources AND sinks to accomplish fluctuations. Yes, you have to be inventive about what fluids are injected and produced. Moreover, pick an appropriate weighting scheme (MOP(11)), relative permeabilities, and generation options (MOP(9)). Also, search the Forum and look at my frequent responses on how to specify atmospheric boundary conditions, and adjust them to your problem.

You may also want to consider specifying your time-dependent Dirichlet boundary conditions at a deeper element that is always saturated to avoid changing phases. Think about the underlying physics, and you will find a corresponding way to implement it in TOUGH2.

Best,

Stefan

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