Test wake cluster

A kinematic cluster of drag spheres that shade each other and cast one lumped wake for the other objects.

Collaboration diagram for Test wake cluster:

A cluster of kinematic spheres moving together at a constant velocity, casting one wake.

A test and demonstration model of a SimObject made of several rigid bodies (environment::wake::IndexedWakeCastingObject, environment::wake::BodyWake; design R4, ENV-0098). NumBodies spheres of one Diameter move at the constant TowVelocity from their initial positions, body i at i × Spacing unless the initial condition <Name>.Position sets them; a zero TowVelocity holds them fixed. Each sphere's drag is environment::sphere_hydro's quadratic law, F = ½ ρ C_d A |u| u on u = u_water − TowVelocity, A = π D²/4; it does not act on the motion.

With CastWake the cluster registers one lumped source under its name in FinalSetup and rebuilds it in PreOdeFcn on the schedule of the Wake* parameters. WakeEvaluation decides what the spheres see of each other: Grid or Direct builds a private field of one elementary source per sphere (M = C_d A, by the sphere's shaded inflow) in one pass in flow order, so a sphere in another's wake is shaded in the same build; None builds no private field, and the spheres do not shade each other. Every other object sees one lumped source, M = F·ê_U / (½ ρ q²) of the summed forces, at the rear face of the spheres' frontal rectangle. A sphere's private source sits at its centre with its wake from half a diameter downstream (WakeXStartFactor 0.5), its rear face. The near wake of a solid sphere 1 to 4 diameters behind it is not validated (doc/user/wakes.md, "Multi-body objects").

Example Configuration (XML)

<Lib LibName="fhsim_environment" SimObject="TestWakeCluster" Name="Cluster"
     NumBodies="3" Spacing="3,0,0" Diameter="1" DragCoefficient="0.5"
     CastWake="true" WakeEvaluation="Direct" WakeUpdate="Freeze" />

Input ports

None.

Output ports

Port	Size	Description
Position	3 NumBodies	Centres [m], NED.
WaterVelocity	3 NumBodies	Water velocity at each centre, the other objects' wakes and the cluster's private field included, with waves [m/s], NED.
Force	3 NumBodies	Drag at WaterVelocity [N], NED.

States

Position (3 NumBodies) [m], NED: the centres, x, y, z of body 0 first.

Configuration Parameters

Name	Width	Description
NumBodies	1	Number of spheres [-], >= 1. (Default: 3)
Spacing	3	Initial offset between consecutive spheres [m], NED; the initial condition <Name>.Position overrides it. (Default: 2, 0, 0)
Diameter	1	Diameter D of every sphere [m], > 0. (Default: 1)
DragCoefficient	1	Drag coefficient C_d on the frontal area [-], >= 0; a test value. (Default: 0.5)
Rho	1	Water density [kg/m^3], > 0. (Default: 1025)
TowVelocity	3	Constant velocity of every sphere [m/s], NED. (Default: 0, 0, 0, fixed)
CastWake	1	Register and build the wakes. (Default: false)
WakeEvaluation	1	Grid or Direct: a private field, the spheres shade each other; None: no private field, no shading inside the cluster. (Default: Grid)
WakeUpdate	1	Off, Freeze or Periodic. (Default: Freeze)
ExternalWakeUpdate	1	Step or Evaluation. (Default: Step)

The other wake parameters are those of every source set: doc/user/wakes.md.

This SimObject is referred to as TestWakeCluster