1. CONB - Description of ball joint connectors

This component can be used to model balljoint, hinges and universal joints. The component has zero length, and adds 6 degrees of freedom to the system model. The forces due to mass and weight are assumed to act at the nodal point at which the component is specified.

This component can not be used in branch lines in standard systems, or in combination with bar elements. Should also be used with care at supernodes with user defined boundary conditions for rotations in AR system to avoid singularities in the FEM solution procedure.

1.1. Data group identifier

NEW COMPonent CONB

1.2. Component type identifier

CMPTYP-ID

  • CMPTYP-ID: character(8): Component type identifier

1.3. Mass and volume

AM AE

  • AM: real: Mass \(\mathrm {[M]}\)

  • AE: real: Displacement volume \(\mathrm {[L^3]}\)

1.4. Hydrodynamic coefficients

ICOO CDX CDY CDZ AMX AMY AMZ

  • ICOO: character: Coordinate system code

    • ICOO=GLOBAL: Coefficients refer to global coordinate system

    • ICOO=LOCAL: Coefficients refer to local coordinate system of neighbour elements in the actual line

  • CDX: real: Drag force coefficient in X-direction \(\mathrm {[F/(L/T)^2)]}\)

  • CDY: real: Drag force coefficient in Y-direction \(\mathrm {[F/(L/T)^2)]}\)

  • CDZ: real: Drag force coefficient in Z-direction \(\mathrm {[F/(L/T)^2)]}\)

  • AMX: real: Added mass in X-direction \(\mathrm {[M]}\)

  • AMY: real: Added mass in Y-direction \(\mathrm {[M]}\)

  • AMZ: real: Added mass in Z-direction \(\mathrm {[M]}\)

The drag forces acting in the global/local coordinate system are computed as:

  • \(\mathrm {F_x=CDX\times VRELX\times VRELX}\)

  • \(\mathrm {F_y=CDY\times VRELY\times VRELY}\)

  • \(\mathrm {F_z=CDZ\times VRELZ\times VRELZ}\)

where:

  • \(\mathrm {CDX,CDY,CDZ}\): are the input drag force coefficients in global/local x, y and z-directions, respectively

  • \(\mathrm {VRELX,VRELY,VRELZ}\): are relative water velocities in global/local x, y and z-directions respectively

The input quadratic drag force coefficients \(\mathrm {CDX}\), \(\mathrm {CDY}\) and \(\mathrm {CDZ}\) will normally be calculated as:

  • \(\mathrm {CDX=\frac{1}{2}\rho B_xC_{dx}}\)

  • \(\mathrm {CDY=\frac{1}{2}\rho B_yC_{dy}}\)

  • \(\mathrm {CDZ=\frac{1}{2}\rho B_zC_{dz}}\)

where:

  • \(\mathrm {\rho }\): water density

  • \(\mathrm {B_x,B_y,B_z}\): projected area per. unit lengt for flow in global/local y and z-directions, respectively

  • \(\mathrm {C_{dx},C_{dy},C_{dz}}\): nondimensional drag coefficients in global/local x, y and z-directions, respectively

1.5. Degrees of freedom

IRX IRY IRZ

  • IRX: integer, default: 0: Rotation freedom code, x-axis

  • IRY: integer, default: 0: Rotation freedom code, y-axis

  • IRZ: integer, default: 0: Rotation freedom code, z-axis

    • 1 - Fixed (no deformation)

    • 0 - Free (zero moment)

x-, y- and z-axes refer to local coordinate system of the neighbour element in the line where the ball joint is specified.

um ii fig114
Figure 1. Rotation freedom for a ball joint component