structural.py

class openconcept.energy_storage.hydrogen.structural.VacuumTankWeight(**kwargs)

Bases: Group

Sizes the structure and computes the weight of the tank’s vacuum walls. This includes the weight of MLI.

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Inputs:

  • environment_design_pressure (float) – Maximum environment exterior pressure expected, probably ~1 atmosphere (scalar, Pa)

  • max_expected_operating_pressure (float) – Maximum expected operating pressure of tank (scalar, Pa)

  • vacuum_gap (float) – Thickness of vacuum gap, used to compute radius of outer vacuum wall (scalar, m)

  • radius (float) – Tank inner radius of the cylinder and hemispherical end caps (scalar, m)

  • length (float) – Length of JUST THE CYLIDRICAL part of the tank (scalar, m)

  • N_layers (float) – Number of reflective sheild layers in the MLI, should be at least ~10 for model to retain reasonable accuracy (scalar, dimensionless)

Outputs:

weight (float) – Weight of the tank walls (scalar, kg)

Options:

  • weight_fudge_factor (float) – Multiplier on tank weight to account for supports, valves, etc., by default 1.1

  • stiffening_multiplier (float) – Machining stiffeners into the inner side of the vacuum shell enhances its buckling performance, enabling weight reductions. The value provided in this option is a multiplier on the outer wall thickness. The default value of 0.8 is higher than it would be if it were purely empirically determined from Sullivan et al. 2006 (https://ntrs.nasa.gov/citations/20060021606), but has been made much more conservative to fall more in line with ~60% gravimetric efficiency tanks

  • inner_safety_factor (float) – Safety factor for sizing inner wall, by default 1.5

  • inner_yield_stress (float) – Yield stress of inner wall material (Pa), by default Al 2014-T6 taken from Table IV of Sullivan et al. 2006 (https://ntrs.nasa.gov/citations/20060021606)

  • inner_density (float) – Density of inner wall material (kg/m^3), by default Al 2014-T6 taken from Table IV of Sullivan et al. 2006 (https://ntrs.nasa.gov/citations/20060021606)

  • outer_safety_factor (float) – Safety factor for sizing outer wall, by default 2

  • outer_youngs_modulus (float) – Young’s modulus of outer wall material (Pa), by default LiAl 2090 taken from Table XIII of Sullivan et al. 2006 (https://ntrs.nasa.gov/citations/20060021606)

  • outer_density (float) – Density of outer wall material (kg/m^3), by default LiAl 2090 taken from Table XIII of Sullivan et al. 2006 (https://ntrs.nasa.gov/citations/20060021606)

class openconcept.energy_storage.hydrogen.structural.PressureVesselWallThickness(**kwargs)

Bases: ExplicitComponent

Compute the wall thickness of a metallic pressure vessel to support a specified pressure load. The model assumes an isotropic wall material, hence the metallic constraint. This uses a simple equation to compute the hoop stress (also referred to as Barlow’s formula) to size the wall thickness.

This component assumes that the wall is thin enough relative to the radius such that it is valid to compute the weight as the product of the surface area, wall thickness, and material density.

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Inputs:

  • design_pressure_differential (float) – The maximum pressure differential between the interior and exterior of the pressure vessel that is used to size the wall thickness; should ALWAYS be positive, otherwise wall thickness and weight will be negative (scalar, Pa)

  • radius (float) – Inner radius of the cylinder and hemispherical end caps (scalar, m)

  • length (float) – Length of JUST THE CYLIDRICAL part of the tank (scalar, m)

Outputs:

  • thickness (float) – Pressure vessel wall thickness (scalar, m)

  • weight (float) – Weight of the wall (scalar, kg)

Options:
class openconcept.energy_storage.hydrogen.structural.VacuumWallThickness(**kwargs)

Bases: ExplicitComponent

Compute the wall thickness when the exterior pressure is greater than the interior one. This applies to the outer wall of a vacuum-insulated tank. It does this by computing the necessary wall thickness for a cylindrical shell under uniform compression and sphere under uniform compression and taking the maximum thickness of the two.

The equations are from Table 15.2 of Roark’s Formulas for Stress and Strain, 9th Edition by Budynas and Sadegh.

This component assumes that the wall is thin relative to the radius.

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  ,'                    `.       | radius
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     ` -------------- '
Inputs:

  • design_pressure_differential (float) – The maximum pressure differential between the interior and exterior of the pressure vessel that is used to size the wall thickness; should ALWAYS be positive (scalar, Pa)

  • radius (float) – Inner radius of the cylinder and hemispherical end caps (scalar, m)

  • length (float) – Length of JUST THE CYLIDRICAL part of the tank (scalar, m)

Outputs:

  • thickness (float) – Pressure vessel wall thickness (scalar, m)

  • weight (float) – Weight of the wall (scalar, kg)

Options:

  • safety_factor (float) – Safety factor for sizing wall applied to design pressure, by default 2

  • stiffening_multiplier (float) – Machining stiffeners into the inner side of the vacuum shell enhances its buckling performance, enabling weight reductions. The value provided in this option is a multiplier on the outer wall thickness. The default value of 0.8 is higher than it would be if it were purely empirically determined from Sullivan et al. 2006 (https://ntrs.nasa.gov/citations/20060021606), but has been made much more conservative to fall more in line with ~60% gravimetric efficiency tanks

  • youngs_modulus (float) – Young’s modulus of wall material (Pa), by default LiAl 2090 taken from Table XIII of Sullivan et al. 2006 (https://ntrs.nasa.gov/citations/20060021606)

  • density (float) – Density of wall material (kg/m^3), by default LiAl 2090 taken from Table XIII of Sullivan et al. 2006 (https://ntrs.nasa.gov/citations/20060021606)

class openconcept.energy_storage.hydrogen.structural.MLIWeight(**kwargs)

Bases: ExplicitComponent

Compute the weight of the MLI given the tank geometry and number of MLI layers. Foil and spacer areal density per layer estimated from here: https://frakoterm.com/cryogenics/multi-layer-insulation-mli/

Inputs:

  • radius (float) – Inner radius of the cylinder and hemispherical end caps. This value does not include the insulation (scalar, m).

  • length (float) – Length of JUST THE CYLIDRICAL part of the tank (scalar, m)

  • N_layers (float) – Number of reflective sheild layers in the MLI, should be at least ~10 for model to retain reasonable accuracy (scalar, dimensionless)

Outputs:

weight (float) – Total weight of the MLI insulation (scalar, kg)

Options:

  • foil_layer_areal_weight (float) – Areal weight of a single foil layer, by default 18e-3 (scalar, kg/m^2)

  • spacer_layer_areal_weight (float) – Areal weight of a single spacer layer, by default 12e-3 (scalar, kg/m^2)