Near-Field Module

Building-wake dispersion for short stacks: a drop-in replacement for WeatherAverager for receptors close to the release. See the near-field example and prototyping/near_field_dispersion.tex for the equations (tagged NF-1 to NF-12 in the code comments).

`ensi_g14_calculator.near_field`

Near-field (building-wake) dispersion for short stacks, see prototyping/near_field_dispersion.tex.

Classes

`Building` `dataclass`

Rectangular building most influencing the flow near the release (SRS-19 Sec. 3.3). Only its dimensions and orientation are used; the wake is assumed to start at the source.

    building = Building(height=20 * u.m, length=60 * u.m, width=25 * u.m, orientation_deg=30.0)
    building.projected_area(30.0)   # wind along the long axis: 20 m x 25 m = 500 m^2

Functions

`crosswind_width(plume_direction_deg)`

Width of the building seen by the wind, W_c(theta).

Parameters:

Name	Type	Description	Default
`plume_direction_deg`		float or array, direction the wind blows towards (deg clockwise from north)	required

Returns:

Type	Description
	crosswind width with units (length)

`projected_area(plume_direction_deg)`

Cross-sectional area A(theta) = H_B * W_c(theta) of the building facing the wind.

Parameters:

Name	Type	Description	Default
`plume_direction_deg`		float or array, direction the wind blows towards (deg clockwise from north)	required

Returns:

Type	Description
	area with units (length^2)

`with_height(height)`

Return a copy with height filled in (used to default H_B to SourceParams.H_G).

`NearFieldConfig` `dataclass`

Building and options of the near-field model, for the scenario runners (picklable, one per chimney).

    near_field = NearFieldConfig(Building(length=60 * u.m, width=25 * u.m), wind_speed_factor=0.7)
    evaluator = ScenarioEvaluator(source, orography, near_field=near_field)
    evaluator.averager.submersion_model = "pki_surrogate"

There is no G-14 submersion (chi_K,S) in the near field: the short-term runner needs the PKI surrogate, the long-term runner the exact PKI (pki_nuclides) for every nuclide of a near-field chimney.

`NearFieldWeatherAverager`

Bases: WeatherAverager

Drop-in replacement for WeatherAverager for receptors close to a short stack in a building wake.

    building = Building(length=60 * u.m, width=25 * u.m, orientation_deg=30.0)  # height: source.H_G
    averager = NearFieldWeatherAverager(orography, source, building)
    chi = averager.average_dispersion_at_points(x, y, z, weather)

Affects the physical dispersion chi_K (inhalation, dry deposition), the exact PKI submersion (which integrates chi_K over the cloud) and the PKI surrogate (submersion_model = "pki_surrogate", through a local power law). The washout uses the same wind speeds (NF-8) and plume height (NF-7), but keeps the G-14 sigma_y0 (no wake spreading). The G-14 submersion polynomial (chi_K,S, >= 200 m, Vogt plume) is still returned by average_dispersion, but the scenario runners refuse to use it for doses with the near-field model.

Functions

`init(orography, source_params, building, *, low_wind_meander=False, gradual_plume_rise=True, wind_speed_factor=1.0, stretched_string=True, recorder=NULL_RECORDER)`

Parameters:

Name	Type	Description	Default
`orography`	`Orography`	Orography instance	required
`source_params`	`SourceParams`	SourceParams of the stack	required
`building`	`Building`	Building most influencing the flow; if its height is None, source_params.H_G is used.	required
`low_wind_meander`	`bool`	add the low-wind meander increments (NF-4, NF-5); lowers concentrations.	`False`
`gradual_plume_rise`	`bool`	evaluate the momentum plume rise at min(x, 200 m) (NF-7).	`True`
`wind_speed_factor`	`float`	f_U > 0 multiplying every wind speed, e.g. < 1 for urban slow-down (NF-8).	`1.0`
`stretched_string`	`bool`	receptors (average_dispersion) see the ground-level component at the slant distance from the stack exit, S = sqrt(x^2 + (z - H_a)^2), instead of at x and at their height above the ground (NF-12). Not used for the PKI cloud.	`True`
`recorder`	`IntermediateRecorder`	IntermediateRecorder for introspection.	`NULL_RECORDER`

Functions

`make_averager(orography, source_params, near_field=None, recorder=NULL_RECORDER)`

WeatherAverager (plain G-14) if near_field is None, else the near-field averager it describes.

Modules

`building`

Classes

`Building` `dataclass`

Rectangular building most influencing the flow near the release (SRS-19 Sec. 3.3). Only its dimensions and orientation are used; the wake is assumed to start at the source.

    building = Building(height=20 * u.m, length=60 * u.m, width=25 * u.m, orientation_deg=30.0)
    building.projected_area(30.0)   # wind along the long axis: 20 m x 25 m = 500 m^2

Functions

crosswind_width(plume_direction_deg)

Width of the building seen by the wind, W_c(theta).

Parameters:

Name	Type	Description	Default
`plume_direction_deg`		float or array, direction the wind blows towards (deg clockwise from north)	required

Returns:

Type	Description
	crosswind width with units (length)

projected_area(plume_direction_deg)

Cross-sectional area A(theta) = H_B * W_c(theta) of the building facing the wind.

Parameters:

Name	Type	Description	Default
`plume_direction_deg`		float or array, direction the wind blows towards (deg clockwise from north)	required

Returns:

Type	Description
	area with units (length^2)

with_height(height)

Return a copy with height filled in (used to default H_B to SourceParams.H_G).

`near_field_averager`

Classes

`NearFieldWeatherAverager`

Bases: WeatherAverager

Drop-in replacement for WeatherAverager for receptors close to a short stack in a building wake.

    building = Building(length=60 * u.m, width=25 * u.m, orientation_deg=30.0)  # height: source.H_G
    averager = NearFieldWeatherAverager(orography, source, building)
    chi = averager.average_dispersion_at_points(x, y, z, weather)

Affects the physical dispersion chi_K (inhalation, dry deposition), the exact PKI submersion (which integrates chi_K over the cloud) and the PKI surrogate (submersion_model = "pki_surrogate", through a local power law). The washout uses the same wind speeds (NF-8) and plume height (NF-7), but keeps the G-14 sigma_y0 (no wake spreading). The G-14 submersion polynomial (chi_K,S, >= 200 m, Vogt plume) is still returned by average_dispersion, but the scenario runners refuse to use it for doses with the near-field model.

Functions

__init__(orography, source_params, building, *, low_wind_meander=False, gradual_plume_rise=True, wind_speed_factor=1.0, stretched_string=True, recorder=NULL_RECORDER)

Parameters:

Name	Type	Description	Default
`orography`	`Orography`	Orography instance	required
`source_params`	`SourceParams`	SourceParams of the stack	required
`building`	`Building`	Building most influencing the flow; if its height is None, source_params.H_G is used.	required
`low_wind_meander`	`bool`	add the low-wind meander increments (NF-4, NF-5); lowers concentrations.	`False`
`gradual_plume_rise`	`bool`	evaluate the momentum plume rise at min(x, 200 m) (NF-7).	`True`
`wind_speed_factor`	`float`	f_U > 0 multiplying every wind speed, e.g. < 1 for urban slow-down (NF-8).	`1.0`
`stretched_string`	`bool`	receptors (average_dispersion) see the ground-level component at the slant distance from the stack exit, S = sqrt(x^2 + (z - H_a)^2), instead of at x and at their height above the ground (NF-12). Not used for the PKI cloud.	`True`
`recorder`	`IntermediateRecorder`	IntermediateRecorder for introspection.	`NULL_RECORDER`

`NearFieldConfig` `dataclass`

Building and options of the near-field model, for the scenario runners (picklable, one per chimney).

    near_field = NearFieldConfig(Building(length=60 * u.m, width=25 * u.m), wind_speed_factor=0.7)
    evaluator = ScenarioEvaluator(source, orography, near_field=near_field)
    evaluator.averager.submersion_model = "pki_surrogate"

There is no G-14 submersion (chi_K,S) in the near field: the short-term runner needs the PKI surrogate, the long-term runner the exact PKI (pki_nuclides) for every nuclide of a near-field chimney.

Functions

`make_averager(orography, source_params, near_field=None, recorder=NULL_RECORDER)`

WeatherAverager (plain G-14) if near_field is None, else the near-field averager it describes.

`wake`

Functions

`wake_sigma_increments(x, U, A)`

Squared increments of sigma_y and sigma_z due to building-wake turbulence (NF-2, NF-3).

Parameters:

Name	Description	Default
`x`	downwind distance from the release, with units (length)	required
`U`	wind speed upwind of the building at building height, with units (length/time)	required
`A`	projected cross-sectional area of the building, with units (length^2)	required

Returns:

Type	Description
	tuple (Delta sigma_y^2, Delta sigma_z^2), with units (length^2)

`low_wind_sigma_increments(x, U)`

Squared increments of sigma_y and sigma_z due to plume meander at low wind speed (NF-4, NF-5). These always lower concentrations; off by default in NearFieldWeatherAverager.

Parameters:

Name	Type	Description	Default
`x`		downwind distance from the release, with units (length)	required
`U`		wind speed, with units (length/time)	required

Returns:

Type	Description
	tuple (Delta sigma_y^2, Delta sigma_z^2), with units (length^2)

`apply_cavity_floor(sigma_y, sigma_z, length_scale, K=1.0 * u.m)`

Enforce Sigma_y * Sigma_z >= length_scale * K (NF-6) by scaling both sigmas by the same factor.

The centreline value of the reflected ground-level plume is 1 / (pi U Sigma_y Sigma_z); SRS-19 eq. 8 bounds the concentration in the cavity zone by 1 / (pi U l_B K). The floor therefore caps the plume at the SRS-19 cavity value and is inactive wherever the Gaussian is already more dilute.

Parameters:

Name	Description	Default
`sigma_y`	horizontal dispersion parameter, with units (length)	required
`sigma_z`	vertical dispersion parameter, with units (length)	required
`length_scale`	l_B = min(building height, crosswind width), with units (length)	required
`K`	SRS-19 constant, 1 m	`1.0 * m`

Returns:

Type	Description
	tuple (sigma_y, sigma_z) after the floor, with units (length)

`wake_sigmas(sigma_y0, sigma_z0, x, U, A, length_scale, *, low_wind_meander=False)`

Dispersion parameters of the ground-level plume in the building wake: (NF-1) then (NF-6).

Parameters:

Name	Description	Default
`sigma_y0`	G-14 (Vogt) ground-level sigma_y at x, with units (length)	required
`sigma_z0`	G-14 (Vogt) ground-level sigma_z at x, with units (length)	required
`x`	downwind distance, with units (length)	required
`U`	wind speed at building height, with units (length/time)	required
`A`	projected building area, with units (length^2)	required
`length_scale`	l_B = min(building height, crosswind width), with units (length)	required
`low_wind_meander`	whether to add the low-wind meander increments (NF-4, NF-5)	`False`

Returns:

Type	Description
	tuple (Sigma_y, Sigma_z), with units (length)

Near-Field Module

ensi_g14_calculator.near_field

Classes

Building dataclass

Functions

crosswind_width(plume_direction_deg)

projected_area(plume_direction_deg)

with_height(height)

NearFieldConfig dataclass

NearFieldWeatherAverager

Functions

__init__(orography, source_params, building, *, low_wind_meander=False, gradual_plume_rise=True, wind_speed_factor=1.0, stretched_string=True, recorder=NULL_RECORDER)

Functions

make_averager(orography, source_params, near_field=None, recorder=NULL_RECORDER)

Modules

building

Classes

Building dataclass

near_field_averager

Classes

NearFieldWeatherAverager

NearFieldConfig dataclass

Functions

make_averager(orography, source_params, near_field=None, recorder=NULL_RECORDER)

wake

Functions

wake_sigma_increments(x, U, A)

low_wind_sigma_increments(x, U)

apply_cavity_floor(sigma_y, sigma_z, length_scale, K=1.0 * u.m)

wake_sigmas(sigma_y0, sigma_z0, x, U, A, length_scale, *, low_wind_meander=False)

`ensi_g14_calculator.near_field`

`Building` `dataclass`

`crosswind_width(plume_direction_deg)`

`projected_area(plume_direction_deg)`

`with_height(height)`

`NearFieldConfig` `dataclass`

`NearFieldWeatherAverager`

`init(orography, source_params, building, *, low_wind_meander=False, gradual_plume_rise=True, wind_speed_factor=1.0, stretched_string=True, recorder=NULL_RECORDER)`

`make_averager(orography, source_params, near_field=None, recorder=NULL_RECORDER)`

`building`

`Building` `dataclass`

`near_field_averager`

`NearFieldWeatherAverager`

`NearFieldConfig` `dataclass`

`make_averager(orography, source_params, near_field=None, recorder=NULL_RECORDER)`

`wake`

`wake_sigma_increments(x, U, A)`

`low_wind_sigma_increments(x, U)`

`apply_cavity_floor(sigma_y, sigma_z, length_scale, K=1.0 * u.m)`

`wake_sigmas(sigma_y0, sigma_z0, x, U, A, length_scale, *, low_wind_meander=False)`