# Homogeneous Dirichlet

Homogeneous Dirichlet conditions force the wavefield to be zero at the specified boundary.

In the scalar acoustic case, this simply gives

${\\phi = 0,\\quad\\text{on~}\\Gamma,}$

and in elastic media, we obtain

${u = 0,\\quad\\text{on~}\\Gamma.}$

It is possible to fix only certain components of the displacement field ${u}$ in the elastic case.

Practical Advice

For coupled simulations of waves propagating along a fluid-solid interface, the homogeneous Dirichlet condition is the physically correct condition to describe the "free-surface condition" in water.

## Further reading

More information on the practical use of absorbing boundaries can be found on the following pages:

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