DynamicLH2PoolX

DynamicLH2PoolX is a transparent, time-dependent source-term model for a declared liquid-hydrogen (LH₂) inflow that has already reached a horizontal surface. It tracks axisymmetric shallow-layer spreading, local wet-contact evaporation, liquid inventory, and an auditable mass balance. The package also retains the historical quasi-steady LH2PoolX v0.1.2 route for reproducibility of earlier FFI calculations.

DynamicLH2PoolX does not infer how a pressurised jet becomes ground-reaching liquid. That deposition or impact calculation must be supplied by the caller as an explicit DeclaredInflow history.

Verification status

The current release candidate has completed the restricted Stage C component scope. The machine-readable decision is:

PASS_RESTRICTED_STAGE_C_COMPONENT_SCOPE

This means that the declared-ground-inflow, horizontal-surface, smooth-axisymmetric pool source-term route has passed solution checks and the stated component comparisons. It is not a claim that all LH₂ pool formation or spill consequences have been validated.

Quantitative evidence

The HSE radius observations are digitised from a published figure and are labelled figure_digitised in the manifest. The complete trajectory RMSE is 0.438 m; the 1.3–1.4 m expansion/retraction pulse attributed to condensed-air solid deposition is not reproduced by the smooth pool model and is reported as a structural diagnostic, not as a passed trajectory gate.

For JUEL calibration, water Trial 3 and aluminium Trial 5 are used to freeze one surface parameter each before applying the values to Trials 4 and 6. The aluminium multiplier 0.40 remains the predeclared Trial 5 value even though 0.45 gives a slightly lower holdout RMSE; the latter is not selected after seeing the holdout. Because there is only one calibration trial per material, no trial-bootstrap 95% CI is claimed. Digitisation intervals and predeclared parameter sensitivities are reported instead.

See the Stage C completion report for the full scope statement, input basis, source IDs, sensitivity runs, and limitations. The authoritative result is outputs/stage_c/manifest.json.

Scope and limitations

Validated scope:

• declared liquid-to-ground inflow history;
• unconfined, horizontal, axisymmetric shallow-layer spreading;
• water or homogeneous solid surfaces with an explicitly named heat-transfer closure;
• source-term outputs for downstream dispersion calculations.

Outside the validated scope are jet impact, splash and droplet transport, deposition fraction prediction, asymmetric branches, detached liquid pieces, slopes, drains, dikes, barriers, complex terrain, condensed-air solid deposition, and atmospheric dispersion. The water constant-heat-flux closure is limited to the approximately 50–60 s regime supported by the cited JUEL comparison.

The previous FFI source reconstruction continues to use the static LH2PoolX v0.1.2 observed-footprint route. DynamicLH2PoolX results must not be substituted into that calculation without a separate, versioned coupling study.

Installation

From a source checkout

python -m pip install -e .
python -m pip install -r requirements-validation.txt
python -m pytest -q

After the first PyPI release, the package will be installable with:

python -m pip install dynamiclh2poolx

The import name is also dynamiclh2poolx.

Quick start: solid surface

The model requires a time history of liquid that has already reached the ground. Rates are in kg/s, times are in seconds, and all geometry is in metres.

from dynamiclh2poolx import (
    DeclaredInflow,
    DynamicPoolConfig,
    ShallowLayerNumerics,
    SolidSemiInfiniteSurface,
    run_dynamic_pool,
)

surface = SolidSemiInfiniteSurface(
    name="concrete",
    conductivity_W_mK=0.88,
    diffusivity_m2_s=1.5775e-7,
    initial_temperature_K=195.7,
)

numerics = ShallowLayerNumerics(
    domain_radius_m=5.0,
    source_radius_m=0.20,
    radial_step_m=0.01,
    maximum_time_step_s=0.02,
)

inflow = DeclaredInflow(
    times_s=(0.0, 60.0),
    rates_kg_s=(0.10, 0.0),
)

result = run_dynamic_pool(
    DynamicPoolConfig(surface=surface, numerics=numerics),
    inflow,
    output_times_s=(0.0, 10.0, 30.0, 60.0, 90.0),
)

last = result.ledger[-1]
print(f"reported radius: {last.reported_radius_m:.3f} m")
print(f"liquid inventory: {last.liquid_mass_kg:.6g} kg")
print(f"mass residual: {result.mass_balance_residual_kg:.3e} kg")

DeclaredInflow uses a zero-order hold: each rate applies from its timestamp until the next timestamp, and the last rate continues thereafter. The first timestamp must be 0.0, timestamps must be increasing, and rates must be non-negative.

Choosing a surface closure

For a homogeneous solid, use local semi-infinite conduction:

surface = SolidSemiInfiniteSurface(
    name="concrete",
    conductivity_W_mK=0.93,
    diffusivity_m2_s=4.8e-7,
    initial_temperature_K=266.0,
    heat_flux_multiplier=1.0,
)

For the short-duration empirical water route, make the evidence basis explicit:

from dynamiclh2poolx import ConstantHeatFluxWaterSurface

surface = ConstantHeatFluxWaterSurface(
    heat_flux_W_m2=200_000.0,
    calibration_label="Dienhart JUEL-3155 Trial 3 water closure",
)

The default evaporation momentum closure is zero_radial_momentum_vapor, corresponding to zero organised radial velocity of departing vapour in the JUEL-based closure. The alternative liquid_velocity_carryoff is available only for structural sensitivity:

config = DynamicPoolConfig(
    surface=surface,
    numerics=numerics,
    evaporation_momentum_closure="zero_radial_momentum_vapor",
)

If a rough-surface retention layer is physically justified, set surface_retention_depth_m in ShallowLayerNumerics. This is a declared physical input, not a radius-fitting parameter.

Understanding the result

Each DynamicPoolLedger row contains SI-unit fields for inflow, liquid inventory, evaporation, spreading, and provenance. The most important fields are:

• wet_area_m2: computational cells containing liquid above the declared retention layer;
• reported_radius_m and reported_area_m2: observation-operator outputs based on the configured detection depth;
• wet_area_mean_depth_m and wet_area_mean_evaporation_flux_kg_m2_s: averages over the computational wet area, not the reported footprint;
• interval_mean_evaporation_rate_kg_s and last_substep_evaporation_rate_kg_s: explicitly different time averages;
• escaped_domain_mass_kg, cumulative_numerical_mass_adjustment_kg, and unledgered_mass_residual_kg: the mass-accounting audit trail;
• evaporation_momentum_closure, heat_transfer_closure_id, and spreading_closure_id: the selected physics and numerical closures.

DynamicPoolResult.configuration_echo and software_versions record the settings and runtime versions needed to reproduce a run.

Reproducing the validation record

Stage C restricted component validation

The JUEL and HSE PDFs are not redistributed with the package. Supply their local paths explicitly:

.\.venv\Scripts\python.exe scripts/validate_stage_c.py `
  --dienhart-pdf "outputs/sources/dienhart_1995_juel3155.pdf" `
  --rr985-pdf "C:/path/to/rr985.pdf" `
  --rr986-pdf "C:/path/to/rr986.pdf"

This runs the C1 convergence matrix, JUEL calibration/holdout assessment, HSE Test 6 endpoint assessment, and writes hashed manifests under outputs/stage_c/.

Full validation record

If the PRESLHY dataset and Xie PDF are available, run the broader component record:

.\.venv\Scripts\python.exe scripts/validate_all.py `
  --dataset-dir "C:/path/to/PRESLHY/dataset" `
  --xie-pdf "outputs/sources/xie2023.pdf" `
  --dienhart-pdf "outputs/sources/dienhart_1995_juel3155.pdf"

PRESLHY repeated-fill comparisons remain a conditional stress diagnostic because a measured ground-inflow history is unavailable. Validation outputs include comparison tables, figures, source hashes, digitisation records, and software metadata. Source PDFs and other copyrighted raw materials are not redistributed.

Project layout

src/dynamiclh2poolx/       package implementation
tests/                     unit and contract tests
data/                      frozen observations and validation protocols
scripts/                   reproducible validation runners
docs/                      design, audit, and completion reports
outputs/stage_c/           generated validation manifests and figures

License and citation

Code is released under the MIT License. Experimental data and digitised derivative points remain subject to their original source licences. See CITATION.cff and the Stage C completion report for the cited JUEL, HSE, Xie, and supporting sources.