Example routine for calculating modified body density of seals

calc_mod_density.py

def calc_mod_density(mass_kg, dens_kgm3, n_blocks, block_type):
    '''Calculate the modified density with attached blocks

    Args
    ----
    mass_kg: float
        mass of the seal (kg)
    dens_kgm3: float
        mass of the seal (kg/m^3)
    block_type: str
        Type of modification block for experiment (`weight` or `float`)
    n_blocks: int
        number of modifying blocks attached

    Returns
    -------
    total_dens: float
        combined density of seal and attached blocks

    Notes
    -----
    All blocks dimensions were manually measured and then drawn in FreeCAD and
    the volumes calculated using the FCInfo macro.

    FLOAT:
      Float blocks were made from ____ foam. They were attached with a neoprene
      pouch but were not compensated by a lead strip. The effect of the pouch
      buoyancy was not measured by considered to be negligible.

      Float block dimensions (with and without sailcloth)
        L:150mm, W:40mm, H:30mm (41, 29)
        shaved 45deg on all edges, 5.5 mm from edge

      Volume float           - 0.000174510114214 m³
      Mass float             - 0.034 kg
      Mass float w/sailcloth - 0.042 kg

    WEIGHT AND NEUTRAL:
      Neutral and weight blocks were made from PE plastic with 2 16mm diameter
      holes drilled length-wise to a depth of 144mm. These holes were
      left empty for neutral blocks. For weight blocks, these holes were filled
      with 140mm long ____ bars.

      The buoyancy of the neoprene pouch with which they were attached was
      compensated by a thin strip of lead that allowed the pouch to be neutral
      at surface. As the neoprene compresses with depth, this strip should overcompensate
      to a small degree.

      PE block dimensions:
        L:150mm, W:41mm, H:30mm
        rounded on one width edge - 15mm from edge length-wise and height-wise
      Hole dimensions (2 holes):
        L:144mm length, D:16mm
      Weight rod dimensions (one rod per hole):
        L:140mm, D:15mm

      Mass block w/holes   - 0.118 kg
      Mass weight bar      - 0.260 kg
      Mass weight block    - 0.118 kg + 2(0.260 kg) = 0.638 kg
      Volume block w/holes - 0.00012016274768 m³
      Volume weight bar    - 0.00000176714586764 m³
      Volume weight+2bars  - 1.202e-4 + 2(1.767e-6) = 1.237e-4

      4 weight tubes = 2 weights
    '''

    # Modifier block attributes
    block_types = ['weight', 'float', 'neutral']
    mod_vol_m3 = {'weight':1.237e-4, 'float':1.745e-4, 'neutral':1.202e-4}
    mod_mass_kg = {'weight': 0.638,  'float': 0.034, 'neutral':0.118}

    # Calculate combined density
    if block_type in block_types:
        seal_vol_m3 = mass_kg / dens_kgm3
        total_mass = (mass_kg + (n_blocks * mod_mass_kg[block_type]))
        total_vol  = (seal_vol_m3 + (n_blocks * mod_vol_m3[block_type]))
        total_dens = total_mass / total_vol

    # Raise error if incorrect `block_type` passed
    else:
        raise KeyError("`block_type` must be 'weight', 'float', or 'neutral'"

    return total_dens