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A question regarding the setup of the absorbing layer. #68
Description
Hello, I’m very interested in this project! I have a question regarding the setup of the absorbing layer.
In most examples, including acoustic_2D.py and Overthrust_3D.py, I want to set the top boundary as a free surface while applying absorbing boundaries to the other sides. I understand that absorption in simwave is achieved through damping terms. However, when I try different configurations—such as:
space_model.config_boundary(
damping_length=(100, 5000, 5000, 5000),
boundary_condition=("none", "none", "none", "none"),
damping_polynomial_degree=5,
damping_alpha=0.01
)
—none of them seem to produce the desired absorbing effect. Could you please help me resolve this issue?
Activity
hermes-senger commentedon May 16, 2025
Hi,
The problem is here:
boundary_condition=("none", "none", "none", "none"),
"none" means don´t use boundary conditions.
You may use this instead:
...
boundary_condition=("null_neumann", "null_dirichlet", "null_dirichlet", "null_dirichlet" ),
null_neuman will produce the free surface effect you want.
I strongly suggest reading the simwave paper at https://arxiv.org/abs/2201.05278
specially the 2D and 3D examples.
ruihua-chen commentedon May 16, 2025
Thanks. But, when I set (consistent with the paper):
"""
space_model.config_boundary(
damping_length=(0, 700, 700, 700),
boundary_condition=(
"null_neumann", "null_dirichlet", "null_dirichlet", "null_dirichlet",
),
damping_polynomial_degree=3,
damping_alpha=0.001
)
"""
and run the acoustic_2D.py, It doesn't seem to have produced the expected absorption effect
ruihua-chen commentedon May 16, 2025
In other words, I hope there will be no reflected waves in the lower left and right parts and they can be absorbed.
hermes-senger commentedon May 16, 2025
The quality of absorbing results depends on some parameters:
ruihua-chen commentedon May 17, 2025
To be honest, I have tried to adjust these hyperparameters (e.g., damping_length, damping_polynomial_degree, and damping_alpha ), but the result seems to have remained the same.
hermes-senger commentedon Jul 20, 2025
Hello! We changed the way simwave defines the damping mask and fixed the calculation of the absorbing layer term. The parameters damping_polynomial_degree and damping_alpha have been deprecated. It appears to be fine in our tests now. Could you test please?