Numerical dissipation (non-linear wave fsi)

[ncsalis]

Results are significantly worsened when simulating the case with high particle resolution (dx=0.015 circa 8M particles). This did not happened before merge #274 (prevented free surface rising when simulating with low particle resolution). Maybe it's better to revert this change since also @Shuaihao-Zhang encountered problems after this.

[ncsalis]

Snapshot of the wave-structure impact before #274 and after

[Xiangyu-Hu]

It really increases the numerical dissipation of the simulation. We probably can decrease the numerical dissipation, as a first check. As the present limiting parameter is based on previous formulation.

[ncsalis]

I will check the limiter in the following days. I have found this issue also in the 2d_nlwfsi case, the numerical dissipation is quite high even at low particle resolutions.

[ncsalis]

324 is ineffective, with lower limiter the free surface elevation does not improve. Also the dynamics (wave phase) of the wave is significantly modified and this aspect is unchanged

[ncsalis]

In the previous simulations there was a typo in the wave gauge position (1 meter downstream compared to the exp). The dynamics of the wave is good. I have checked the simulation at different merge (#229, #271 and #274). The numerical dissipation was always present, just hidden by the typo.

[Xiangyu-Hu]

So the new formulation is OK?

[ncsalis]

Yes, the new formulation is ok

[Xiangyu-Hu]

For numerical dissipation, Yaru's work will be much helpful. https://arxiv.org/abs/2304.14865

[Xiangyu-Hu]

I made another small change, but the result is similar.

[ncsalis]

Thank you for the suggestion on Yaru's paper. I also was thinking that first order consistency should improve the result

[ncsalis]

The first order consistency correction works very well. Result is now marginally improved

[ncsalis]

With the KGC seems that there is low dissipation thus with higher wave height that leads to higher amplitude of the fsi. How increase dissipation? I have tried by modifying the alpha parameter in the WKGC formulation but it doesn't produce significant result.

[Xiangyu-Hu]

Dear Nicolo,

The overestimate is most probably due to the lack of turbulent dissipation, which is not included in our model.

I think that we need not to tune the numerical dissipation and such slight overestimate, in my opinion, is acceptable.

Best regards,

Xiangyu

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From: Nicolò Salis @.***> Sent: Tuesday, June 13, 2023 8:48:50 AM To: Xiangyu-Hu/SPHinXsys Cc: Xiangyu Hu; Comment Subject: Re: [Xiangyu-Hu/SPHinXsys] High numerical dissipation (non-linear wave fsi) (Issue #319)

With the KGC seems that there is low dissipation thus with higher wave height that leads to higher amplitude of the fsi. How increase dissipation? I have tried by modifying the alpha parameter in the WKGC formulation but it doesn't produce significant result.

[wave__]https://user-images.githubusercontent.com/56539341/245376066-78b4fe44-d10f-4c20-b0d7-d6efb20d7d31.png

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[ncsalis]

Ok, thank you!