immersionproperties.md

ImmersionProperties

ImmersionProperties {
  SFString fluidName                          ""              # any string
  SFString referenceArea                      "immersed area" # {"immersed area", "xyz-projected area"}
  SFVec3f  dragForceCoefficients              0 0 0           # any positive vector
  SFVec3f  dragTorqueCoefficients             0 0 0           # any positive vector
  SFFloat  viscousResistanceForceCoefficient  0               # [0, inf)
  SFFloat  viscousResistanceTorqueCoefficient 0               # [0, inf)
}

Description

An ImmersionProperties node is used inside the immersionProperties field of a Solid node to specify its dynamical interactions with one or more Fluid nodes.

ImmersionProperties Fields

• fluidName: name of the fluid with which the dynamical interaction is enabled. The string value must coincide with the name field value of an existing Fluid node.

• referenceArea: this field defines the reference area(s) used to compute the drag force and drag torque of the submerging Fluid.

  If the referenceArea is set to "xyz-projected area", the x-coordinate of the drag force vector with respect to the solid frame is given by:

    drag_force_x = - c_x * fluid_density * rel_linear_velocity_x² * sign(rel_linear_velocity_x) * A_x
  

  where c_x is the x-coordinate of the dragForceCoefficients vector, linear_velocity_x the x-coordinate of the linear velocity of the solid with respect to the fluid expressed within the solid frame and A_x is the projected immersed area onto the plane x = 0. Analogous formulas hold for y and z coordinates. The x-coordinate of the drag torque vector with respect to the the solid frame is given by:

    drag_torque_x = - t_x * fluid_density * rel_angular_velocity_x² * sign(rel_angular_velocity_x) * (A_y + A_z)
  

  where t_x is the x-coordinate of the dragTorqueCoefficients vector, angular_velocity_x the x-coordinate of the angular velocity of the solid expressed within the solid frame. Analogous formulas hold for y and z coordinates.

  If the referenceArea value is "immersed area" then the Solid boundingObject's immersed area is used for drag force and drag torque computations:

    drag_force = - c_x * fluid_density * linear_velocity² * immersed_area,
    drag_torque = - t_x * fluid_density * angular_velocity² * immersed_area
  

  all vectors being expressed in world coordinates. Note that in this case the drag coefficients along the y and z axes are ignored.

• dragForceCoefficients and dragTorqueCoefficients: dimensionless non-negative coefficients used to compute the drag force and the drag torque exerted by the fluid on the solid. See above formulas.

• viscousResistanceForceCoefficient and viscousResistanceTorqueCoefficient: this non-negative coefficients, expressed respectively in Ns/m and Nm/s, are used to compute the viscous resistance force and the viscous resistance torque exerted by the fluid on the solid according the following formulas

    viscous_resistance_force = - immersion_ratio * fluid_viscosity * v_force * rel_linear_velocity
    viscous_resistance_torque = - immersion_ratio * fluid_viscosity * v_torque * angular_velocity
  

  where v_force (resp. v_torque) denotes the viscous resistance force (resp. torque) coefficient and immersion_ratio is obtained by dividing the immersed area by the full area.

  The viscous resistance (or linear drag) is appropriate for objects moving through a fluid at relatively low speed where there is no turbulences. By its linear nature it may offer a better numerical stability than the above quadratic drags when the immersed solids are subject to large external forces or torques.

Note: The "xyz-projected area" computation mode is implemented only for boundingObjects that contain fully or partially immersed Box nodes, fully immersed Cylinder, Capsule and Sphere nodes. The "immersed area" computation mode is implemented for every Geometry node.