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Theory Manual
Physics and theory for nanoFluidX.
Solver Features
Learn more about advanced solver features in nanoFluidX.
Free Surface Formulation
Standard SPH interpolation heavily depends on the basic premise that each particle has the so called full support. Full support implies that the owner particles can see particles all around itself within the smoothing length of the particle, which mathematically implies that the sum of the kernel, also known as Shepard coefficient, is equal to one.

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What's New
View new features for nanoFluidX 2024.1.
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Tutorials
Discover nanoFluidX functionality with interactive tutorials.
Pre-processing
Create a nanoFluidX model using SimLab.
Command Reference
nanoFluidX commands and parameters with examples.
Post-processing
Theory Manual
Physics and theory for nanoFluidX.
- Physics
  Learn more about the physics features in nanoFluidX.
- Boundary Conditions
  Learn more about the boundary conditions in nanoFluidX.
- Measurements
  Learn more about the measurements features in nanoFluidX.
- Solver Features
  Learn more about advanced solver features in nanoFluidX.
  - Free Surface Formulation
    Standard SPH interpolation heavily depends on the basic premise that each particle has the so called full support. Full support implies that the owner particles can see particles all around itself within the smoothing length of the particle, which mathematically implies that the sum of the kernel, also known as Shepard coefficient, is equal to one.
  - Keychain Validator
    Keychain validator compares the keychains in the .cfg file with valid nanoFluidX keychains, when activated.
  - Operation Modes
    The operationMode option allows you to change the solver for either minimal run time or maximum accuracy.
  - Particle Interaction Schemes
  - Sub-phasing
    Sub-phasing capability, while essentially optional, represents structural change inside nanoFluidX more than a classic feature.
  - Transport Velocity Formulation
    Some main principles and consequences of the transport velocity.
Validation Manual
Error and Warning Messages
This glossary contains generic messages generated by nanoFluidX, their likely causes, and possible methods to resolve the related issues.
Frequently Asked Questions
This section provides quick responses to typical and frequently asked questions regarding nanoFluidX.
Bibliography
References used throughout the nanoFluidX manual.

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Free Surface Formulation

Standard SPH interpolation heavily depends on the basic premise that each particle has the so called full support. Full support implies that the owner particles can see particles all around itself within the smoothing length of the particle, which mathematically implies that the sum of the kernel, also known as Shepard coefficient, is equal to one.

S = \frac{1}{m_{b}} \sum_{b} (V_{a}^{2} + V_{b}^{2}) W (r_{a} - r_{b}, h)

Accurate reconstruction of the variable field depends on this principle. However, in a situation where you have a single phase flow, the particles on the free surface of the fluid are facing what is referred to as “particle vacuum” (absence of particles). In this situation layers of particles near to the surface begin to lose their full support, as shown in Figure 1.

Figure 1. . Simplified sketch of a particles near a free surface losing their full support and consequent drop in density which leads to unphysical behavior.

Free surface switch (freesurface) enables a numerical treatment that prevents the artificial drop of density near a free surface which is facing the particle vacuum, therefore maintaining the physicality of the solution. Despite being designed for single-phase flows, it is strongly recommended to keep the freesurface switch set to true at all times.