Fluids & Structural Mechanics > CM Projects > Free Surface Flows (FSF)
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Images | Animations (Below)
Surface Tracking Methods:
In Surface-Tracking Methods, the kinematic and dynamic free-surface boundary conditions are explicitly enforced. Implementation of tracking methods requires solution of an additional 2D hyperbolic wave equation (KFSBC), and dynamic motion of the grid to adapt to the free-surface wave field.
Surface-Tracking Methods are limited to problems which do not exhibit breaking waves. This is a major limitation of the method, and one of the primary motivations for multiphase treatment (VOF and level-set) of the air-water interface.
Overset methods provide the ability to resolve the free-surface layer with a high-density mesh which is capable of resolving body-generated waves, and for changing depth without re-gridding.
Despite the limitations in resolving breaking waves, the method is capable of resolving very steep waves under certain conditions. An example is the thin-sheet of water, or run-up, at the leading edge of a surface-piercing foil at supercritical Froude numbers.
Surface Capturing Methods:
Surface-Capturing Methods offer the ability to resolve ship/wave-field interactions, violent surface motions, and free-surface turbulence, and provides a more robust mechanism for modeling other processes such as sprays, droplets, bubble, air-entrainment, and vaporization. Surface-capturing methods can be further subdivided into either volume of fluid (VOF) or level-set methods.
VOF methods are also capable of resolving smooth wave fields, such as those generated by ships in calm seas. It is important, however, for the method to maintain a sharp interface. This example illustrates how the compressive scheme of rasInterFoam supports the interface across 1 cell.
Fast Methods:
For a variety of reasons (e.g., domain size, CPU time) approximate methods are sometimes employed. An example is Thin-Ship Theory of Tuck et al. (1971). In thin ship theory, an analytical integral equation can be evaluated for the wave field which is much faster than solving the Navier-Stokes equations.
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Figure 5: This example illustrates how the compressive scheme of rasInterFoam supports the interface across 1 cell. |
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Figure 6: Surface-ship waterjets operate near the free-surface, and are a source of air-entrainment and turbulent mixing. |
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Animation 1: |
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Animation 2: N-fluid VOF: Example is for 4 fluid (air-water-oil-mercury) dam break test case. |
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Animation 3: Large interaction with cube mounted transversely in an open-channel flume. |
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Animation 4: 3D dam break problem. |
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Animation 5: 3D dam break problem. |
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Animation 6: A test case is shown for a rigid cube in sinusoidal waves. |
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Animation 7: A test case is shown for a rigid cube in sinusoidal waves. |
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Animation 11: A test case is shown for a rigid cube in sinusoidal waves. |
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Animation 17: Surface-ship waterjets operate near the free-surface, and are a source of air-entrainment and turbulent mixing. |
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Animation 18: Plunging jet and air entrainment |
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Animation 22: Surface-piercing bodies create breaking waves for certain ranges of Froude numbers. Here, the NACA0024 at Fr = 0.55 creates a prominent plunging breaking wave. |
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Animation 23: Surface-piercing bodies create breaking waves for certain ranges of Froude numbers. Here, the NACA0024 at Fr = 0.55 creates a prominent plunging breaking wave. |
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Animation 24: Surface-piercing bodies create breaking waves for certain ranges of Froude numbers. Here, the NACA0024 at Fr = 0.55 creates a prominent plunging breaking wave. |
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Animation 26: VOF methods also present the capability to specify ambient waves. Here, the inflow boundary condition is specified to model Stokes waves at 3 values for wave steepness. |
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Animation 27: VOF methods also present the capability to specify ambient waves. Here, the inflow boundary condition is specified to model Stokes waves at 3 values for wave steepness. |
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