Frame Suite

Description of the sliding frame functionality as a part of the nanoFluidX frame suite feature.

Definitions

Road Top Profile Stencil: A set of Y and Z coordinates which defines the road top section profile.
Road Path Stencil: A set of X and Z coordinates which defines the road path in the direction of the moving vehicle.
Spawning: The act of introducing particle stencils into the domain as the frame is moving along the specified vehicle path.

Note: It is critical that in the case of the Road Path, the X coordinate must be strictly increasing; and in the case of Road Top Profile the Y coordinate must be stricltly increasing. Furthermore, it is important to note that it is assumed that the Z coordinate axis is always pointing upwards.

Description

Sliding frame is a part of the “frame suite” feature targeting water wading applications in nanoFluidX. To facilitate the simulation of experiment-like motion of descending into a water filled channel at a reasonable computational cost, sliding frame follows a phase of interest during simulation by moving the computational domain and spawning fluid and road particles as necessary.

There are two modes in which the sliding frame follows the phase of interest. In line lock mode, the sliding frame translates in the X direction only, and in point lock mode, the sliding frame follows both X and Z translational movement of the phase of interest. While the phase of interest may move arbitrarily, the trajectory of the sliding frame is confined to the XZ plane.

The road definition is split into two parts: the road path, which defines the elevation of the road in the XZ plane, and the road top profile, which defines the top side of the road in the YZ plane. It is recommended that both road top profile and road path point coordinates (which define road path and profile lines) are provided in absolute coordinates. Also, you should align the road top profile with the car at the start of the simulation, meaning the road should be close to or touching the tires.

Road top profile notes:

Is a two column file of the Y Z form.
Consists of a minimum of two Y Z pairs (two points defining one line segment).
Has a strictly increasing Y coordinate. Every value in the first column must be bigger than that of the previous line.

Road path profile notes:

Is a two column file with X coordinate in the first and Z coordinate in the second column.
Consists of a minimum of two X Z pairs (two points defining one line segment).
Has a strictly increasing X coordinate.

The road stencil is created from the initial road top profile by first creating a road top stencil. Road top stencil is a set of particles with unique Y coordinates and a distance equal to the particle spacing dx that approximates the profile and is aligned with the bounding box of the case in Y and Z directions to ensure alignment with the vehicle particles. The road top stencil is then filled to create the road stencil, assuring that there are approximately three particles in wall normal direction to impose the wall boundary condition. This stencil is then copied and translated along the X direction and following the road path coordinates to create the full length channel. Fluid particles are spawned accordingly, in conjunction with the frame_fluid_height command input.

Note: It is critical that in order for Frame Suite to work, the positive Z direction needs to be directed upwards (gravity acting in the negative Z direction). Make sure your geometry is oriented in the correct manner during your pre-processing phase.

Freeze and sponge layers are used to avoid fluid spill through X and Y (and potentially Z) bounding planes in the middle of the channel. The following image shows a schematic of the available configurations of these layers. A freeze layer sets the velocity of all particles within the layer to zero. A sponge layer multiplies a hyperbolic tangent profile with the calculated particle velocity. The two layers aim to satisfy the requirement of quiescent fluid near the frame boundaries.