From bffab3eb4256902c5513c94006ed625fb939a347 Mon Sep 17 00:00:00 2001 From: Sven Berger Date: Sun, 23 Feb 2025 14:15:35 +0100 Subject: [PATCH] remove viscosity docs --- docs/src/systems/fluid.md | 44 --------------------------------------- 1 file changed, 44 deletions(-) diff --git a/docs/src/systems/fluid.md b/docs/src/systems/fluid.md index 779af8924..a53010a9e 100644 --- a/docs/src/systems/fluid.md +++ b/docs/src/systems/fluid.md @@ -16,50 +16,6 @@ under a given set of conditions. Implementing viscosity correctly in SPH is essential for producing physically accurate results, and different methods exist to capture both numerical stabilization and true viscous effects. -### Artificial (numerical) viscosity - -Artificial (numerical) viscosity is a technique used to stabilize simulations of inviscid flows by preventing -unphysical artificial overlap or penetration of particles that would not occur in a real fluid. -To achieve this, a dissipative term is added to the momentum equations in a way that it -does not significantly alter the physical behavior of the flow. -This approach is especially useful in simulations such as high-speed flows with strong shocks or astrophysical scenarios, -where other approaches are insufficient to stabilize the simulation. - -### Physical (real) viscosity - -Physical viscosity is essential for accurately modeling the true viscous stresses within a fluid. -It ensures that simulations align with a target Reynolds number or adhere to experimentally measured fluid properties. -This is achieved by incorporating forces that replicate the viscous stress term found in the Navier–Stokes equations. -As a result, the method is particularly effective for simulating low-speed, incompressible, or weakly compressible flows, -where it is crucial to capture the actual behavior of the fluid. - -### Model comparison - -#### ArtificialViscosityMonaghan - -ArtificialViscosityMonaghan is designed primarily for compressible, high-speed flows where shock capturing is critical. -In its implementation, the method includes a dissipation term that increases when particles approach each other. -This increase in dissipation is triggered by the relative motion between particles: as particles come closer and compress the local flow, -the artificial viscosity term becomes stronger to damp out rapid changes and prevent unphysical clustering. -This ensures that while the simulation remains stable in challenging flow regimes with large density or pressure variations, -the physical behavior is not overly altered. - -#### ViscosityMorris - -ViscosityMorris is well-suited for moderate to low Mach number flows where modeling realistic viscous behavior is important. -Unlike artificial viscosity, this approach directly simulates the physical viscous stresses encountered in fluids. -Its implementation approximates the diffusion of momentum in a way that naturally reflects the viscous behavior observed in experiments -or specified by a target Reynolds number. Because it mimics the actual viscous forces without introducing excessive damping, -it works effectively in weakly compressible scenarios, allowing for a more accurate representation of the flow dynamics. - -#### ViscosityAdami - -ViscosityAdami is optimized for incompressible or weakly compressible flows, particularly where an accurate treatment of shear stress is needed. -The method improves the representation of boundary layers by using a refined approach that better resolves shear gradients. -In practice, this means that the method enhances the dissipation in regions with steep velocity differences (such as near solid boundaries) -while keeping compressibility effects minimal. As a result, it delivers accurate laminar flow simulations and a more faithful depiction of the physical shear stress, -which is essential for problems where boundary layer behavior plays a crucial role. - ### API ```@autodocs