Sphere of sorts

Collaboration diagram for Sphere of sorts:

Spheres that can be connected to other simObjects.

The sphere's inertia is its mass plus the added mass of a sphere in unbounded fluid, 0.5 Rho V, where V is the volume of the sphere, also near and above the surface. Its buoyancy is that of its spherical cap below the wave surface over its centre (owner ruling R66; the waves are not evaluated where the sphere is deeper than MaxWaveElevation plus its radius), and in waves it takes the Froude-Krylov and added-mass excitation (1 + 0.5) Rho V_wet a_w, a_w the water particle acceleration at its centre (owner ruling R67; DNV-RP-C205 (2021) Table A-2), so a neutrally buoyant sphere follows the water.

With CastWake set the sphere casts a lumped wake for the other objects (environment::wake::BodyWake and environment::sphere_hydro::SphereCaster, ADR 0006, MARE-0127): at each rebuild, in PreOdeFcn, its drag at the current-only free stream U (no waves) gives the momentum deficit M = F·ê_U/(½ρ|U|²), its frontal area is πD²/4 (D = SphereD) and the source sits at the rear face, D/2 downstream of the centre. The sphere reads its own flow without its own field. The lumped wake starts as a step at the rear face (x_start = 0): another SimObject that crosses the rear-face plane sees a jump in its inflow, which can collapse the step size or fail the Newton iteration of an implicit integrator such as BDF (MARE-0152). Without CastWake nothing changes.

The sphere needs an Environment SimObject in the configuration for its current, waves and wakes: without one FinalSetup reports a setup error (as Net/Disk does).

Example configuration excerpt

<Lib
   LibName    = "marine_elements"
   SimObject  = "Net/Sphere"
   Name       = "S"
   Rho        = "1025"
   SphereD    = "0.1"
   SphereMass = "1000"
   D          = "0.01"
/>

Input Ports

Name	Width	Description
Force	3	Force acting on the sphere.

Output Ports

Name	Width	Description
Position	3	Position of the sphere.
Velocity	3	Velocity of the sphere.

Configuration parameters

Name	Width	Description
Rho	1	...
SphereD	1	Diameter of the sphere.
SphereMass	1	Mass of the sphere, without the added mass, which is added.
D	1	Diameter of a cable attached to the sphere.
SphereMesh	1	The visualization mesh (geometry) of the Sphere, specified by its filename (Default: fhSphere.mesh).
SphereMaterial	1	The visualization material of the Sphere, specified by its name (Default: firebrick2).
CastWake	1	Register and build the lumped wake; the other wake parameters (Wake*, ExternalWakeUpdate) are listed in fhsim_environment's doc/user/wake-parameters.md. (Default: false)

Initial conditions

Name	Width	Description
Position	3	Position of the sphere.
Velocity	3	Velocity of the sphere.

Full example file

<Contents>
   <OBJECTS>
      <Lib
         LibName    ="marine_elements" 
         SimObject  ="Net/Sphere"  
         Name       ="S"
         Rho        = "1025"
         SphereD    = "1"
         SphereMass = "536.7"
         D          = "0.01"
      />
      <Lib
        LibName="environment"
        SimObject="Environment"
        Name="Environment"
        Waves.Model="Component"
        Waves.NumWaves="0"
        Bathymetry.Depth="500"
        Current.Model = "Constant"
        Current.Vector = "1,0,0"
        />
      <Lib
         LibName            = "marine_elements"
         SimObject          = "RbCable/6DofCable"
         Name               = "C"
         Length             = "6"
         numElements        = "3"
         Alpha              = "0.5"
         Beta               = "0.5"
         Epsilon            = "1e-6"
         Weight             = "200"
         Radius             = "0.005"
         Damping_Tangential = "0.01"
         Damping_Normal     = "1.2"
      />
   </OBJECTS>
   
   <INTERCONNECTIONS>
      <Connection
         S.Force= "0,0,0"
         C.posA = "0,0,0"
         C.posB = "S.Position"
         C.velA = "0,0,0"
         C.velB = "0,0,0"
      />
   </INTERCONNECTIONS>
   
   <INITIALIZATION>
      <InitialCondition
         S.Position = "0.1,0.1,5.9"
         S.Velocity = "0,0,0"
      />
   </INITIALIZATION>
   
   <SIMULATION>
      <Timing TStart="0" TEnd="30"/>
      <Integrator Method="RK45_i" NumCores="1" LogStates="1" UseRSSNorm="0">
        <StepControl StepMax="0.002" StepMin="0.00000001" AbsTol="1e-3" RelTol="1e-3"/>
      </Integrator>
      <!-- TODO migrate_v3: FileOutput="objects:all" -> configure via <OBSERVERS> section -->
   </SIMULATION>
</Contents>

This SimObject is referred to as Net/Sphere