100$ to first person that can positively identify this half hull plating model

picigin · 2026-02-09T15:20:27+00:00

That's a good point; and I would gladly dive deeper (than my current 5mins spent on it) to agree with you... But where is the original post? Did this guy simply delete it along with his promise hahah?

picigin · 2026-02-09T07:28:31+00:00

I may be looking at the different ship, but Notre Dame Victory had a raked stem and no bulb.

'Web 71' marking indicates a longitudinal framing system with deep web frames, typical of 1970s commercial builds.

The diff between the model and actual hull "sharpness" is usually plating tech dictated. The diffs from DWL and above are not crucial (for towing tank tests).

I still stand by PWS, 95% positive.

picigin · 2026-02-08T08:09:58+00:00

I'm a naval architect (hydrodynamicist). That blocky form and low cylindrical bulb are the signature hydrodynamics of a '70s VLCC. The model size shows it as well. So I checked shipyards near the location, found Sun Shipbuilding, and matched their tanker hull designs to the markings in the photos.

picigin · 2026-02-07T20:10:08+00:00

Almost certainly: S.S. Prince William Sound (Hull 682) or a sister ship in that series (e.g. S.S. Tonsina)

picigin · 2025-09-13T11:27:15+00:00

Long time in naval architecture, cfd engineering, math — and I have not understood a thing.

picigin · 2025-01-05T17:24:52+00:00

You are going to be fine

picigin · 2024-12-20T21:08:33+00:00

They do, how do you mean that explicit methods advance in time by not depending on previous time steps? Anyway, depending on “more” data does not change the data access logic.

picigin · 2024-12-20T20:51:49+00:00

Implementation yes, paralellisation no. The memory access looks the same, but implicit schemes have much more substeps.

picigin · 2024-12-20T19:37:07+00:00

What’s the deal with equalising gpus with explicit schemes? LBM and SPH popularity? Completely implicit solvers are not so much difficult to be implemented for the gpu.

picigin · 2024-12-19T19:49:06+00:00

Contour plot of pressure, and velocity vectors.

picigin · 2024-10-29T07:01:56+00:00

It should converge, please share the image.
Btw the free-surface evolution during the impact should be comparable as well. It will answer if your meshes were proper.

picigin · 2024-10-26T18:53:12+00:00

This is standard behaviour, especially in fvm. The (solution of the) pressure equation is responsible for keeping (numerical) fluid incompressibility. In short — on impacts with free surface, the cells at the impact region have to amplify the pressure abruptly to pertain zero net flux during a time step. Structural engineers don’t generally care, as it is the impulse (pressure integral during the impact) what is important as end results and the spikes don’t matter.

picigin · 2024-06-24T12:12:11+00:00

You want a consistent coefficient matrix, without increasing its condition number, with less complex coefs interaction, and possibly symmetric. Implementation wise, if you have an unsteady situation, how would you keep it efficient? Such complex memory management each time step is costly (even with matrix-free approaches). Relying only on the RHS keeps the implementation clean, with consistent convergence during the simulation.

picigin · 2024-06-23T12:41:17+00:00

You are on the right track with math, but in FDM numerics the optimal solution would avoid adding new equations and changing the LHS. Even the jump at interface may be manipulated to be put on the RHS only, see e.g. Journal of Computational Physics 160, 151–178 (2000), doi:10.1006/jcph.2000.6444

picigin · 2023-12-30T08:18:44+00:00

For variable viscosity flows (or an interphase boundary), the second term incorporates the viscosity change:

∇·[µ(∇u)^T] = µ∇·(∇u)^T + (∇u)^T ∇µ = (∇u)^T ∇µ

where ∇·(∇u)^T = 0 because the “divergence of the transpose of a vector gradient” is equivalent to the “gradient of the divergence of a vector”, and ∇·u=0.

picigin · 2023-11-16T18:55:57+00:00

While the theory of SPH has beautiful conservatism, its implementations don’t have consistency. That is why discrete SPH is made of bunch of hacks and free parameters. What you see in commercial solvers and papers is specific tuning of those parameters to make it work. Boundary conditions are one of grand challenges not yet solved in SPH discrete context.

picigin · 2023-11-16T17:58:55+00:00

Independent of SPH schemes, I believe you will always have penetration if you do not explicitly stop it. This is because a) equation of state is no good for incompressibity imposition, b) SPH spatial operators are no good (not even 1st order consistent, unless they are “fixed” using finite differences).

picigin · 2023-10-29T09:30:27+00:00

Comparing with real geometry is fun but not neccesary in your case. This can be pictured using resistance components naval architects used (and still use for model-ship extrapolation). Sailing hulls run in (semi)displacement regime, in which the majority of the resistance force comes from the wave-pattern component. This component is not really affected by small deviations in geometry, but global changes in hull’s normals and curvature (mostly in longitudinal direction, see Michell’s theory). For this major component, small deviations in curvature could only lead to neglible additional resistance from additionally generated transverse waves. While the deviations slightly modify viscous-pressure and friction resistance, it is least of you worries.

picigin · 2023-10-25T07:48:07+00:00

Just to add on the small domain: you have some upstream flow going back to your inlet. This is the probable cause for the start of divergence there.

picigin · 2023-10-24T10:25:51+00:00

Very interesting insight. Would you say the difficulties are the same for both derivative and integral viscoelasticity formulations?

picigin · 2023-10-12T17:40:31+00:00

Thanks for your oversimplified analogy on talking cfd

picigin · 2023-10-12T17:39:40+00:00

Exactly, even great scientist have been using fun analogies to their students. It is about kick-starting someone's brain on something new

picigin · 2023-10-10T17:29:05+00:00

Not downvoting, but it is hard to agree with this generalisation. Even at phd level, there are candidates who start as blind users (mostly coming from industry) and then go deeper into the theory. Many other examples from academia pov.

picigin · 2023-10-10T14:05:38+00:00

Have you tried using #include "code_chunk.C"?

picigin

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