Skip to content

Home > Model Components > Arches > Properties

Arch properties

The arch properties tab is provided to enter a number of mechanical and hydrodynamic properties for your arch.

  • Buoyancy forces: defines the global vertical force. It is the net buoyancy of the arch (i.e. buoyancy minus weight in air).

    Note

    By default the buoyancy force applies at the master node of the arch and not at the geometrical center of the arch volume.

  • Horizontal and vertical drag global coefficient: These coefficient define the global drag coefficient in horizontal and vertical directions. These coefficients can be calculated as: \(\frac{1}{2}\rho * C_d * S\)

    with Cd: drag coefficient and S: cross section in vertical or horizontal plane. Standard values of CD for a cylinder with two hemispherical caps are :

    • Horizontally 1.2

    • Vertically 1.4

    Note

    Horizontal and vertical drag global coefficients may vary with the relative velocity based on the Reynold's number.

  • Horizontal and vertical inertia global coefficients: defines the global inertia coefficient in horizontal and vertical directions. These coefficients can be calculated as:

    \[ \rho * C_m * V \]

    with Cm: inertia coefficient and V: displaced volume of the arch. Standard values for a vertical cylinder with two hemispherical caps are :

    • Horizontally 1.7

    • Vertically 1.3

  • Added mass coefficient in 6 degrees of freedom. These values refer to masses and not forces. The values specified here are added to the diagonal terms of the mass matrix. These coefficients can be calculated as:

    \[ M_{air} + \rho(C_m - 1)V \]

    with \(M_{air}\) the mass in air of the arch

    \(C_m\) : inertia coefficient

    V: displaced volume of the arch

  • Lift global coefficient: The lift force equals the lift global coefficient (i.e. the parameter to be set) and the horizontal component of the relative velocity squared (where the relative velocity is the fluid velocity minus the arch velocity). The calculated lift force is always along the global Z axis, upwards. defines the factor to be applied on UH^2 for the calculation of the local lift force, where UH is the relative fluid velocity projected on the horizontal plane. These coefficients can be calculated as:

    \[ \frac{1}{2}\rho * C1 * S \]

    with \(C1\) the lift coefficient and \(S\) the cross section in vertical or horizontal plane.

    Note

    A positive global lift coefficient results in a upwards force defined in the global axis. Note also that this value may be velocity dependant according to the Reynolds number.