Neqsim Noise Screening

Noise Screening

Use this skill to screen gas-valve and restriction noise at a stated receiver distance from either a representative operating measurement or a conservative energy model. Keep source prediction, receiver/workplace assessment, and acoustic-induced-vibration (AIV) screening as separate decisions.

When to Use

• When a user asks whether a gas valve or restriction is likely to be noisy.
• When current measured noise must be evaluated at a stated operating condition and receiver position.
• When an agent needs a quick action/high noise flag before detailed engineering.
• When examples must run without confidential valve trim or vendor noise data.
• Do not use this skill alone to accept personnel exposure, acoustic fatigue, or AIV.

Inputs

• mass_flow: gas mass flow in kg/s.
• pressure_drop: pressure drop across the restriction in bar.
• inlet_density: inlet gas density in kg/m3.
• sound_speed: speed of sound in m/s (provide this, or temperature and molar mass).
• distance: source-to-receiver distance in m, default 1 m.
• measured_spl_at_distance: optional representative A-weighted measurement in dBA at distance.
• measured_uncertainty_db: optional positive measurement uncertainty in dB.
• specific_heat_ratio: ratio of specific heats k, default 1.3.
• temperature: gas temperature in K (used to estimate sound speed).
• molar_mass: gas molar mass in g/mol (used to estimate sound speed).
• Constructor overrides for action level, high level, model uncertainty, acoustic efficiency, and transmission loss.

Outputs

• vena_contracta_velocity_m_s: estimated velocity at the restriction.
• mach_number: velocity divided by the speed of sound.
• internal_sound_power_level_db: internal sound power level (re 1 pW).
• estimated_spl_1m_dba: screening sound-pressure level at 1 m.
• estimated_spl_at_distance_dba: assessed A-weighted level at the receiver distance.
• assessment_basis: measurement or screening-model.
• noise_warning: ok, action, or high.
• uncertainty_db, standards_basis, and assumptions for review and escalation.

Engineering Method

The Python class ValveNoiseModel uses this decision path:

1. Freeze the operating snapshot, source identity, receiver position, and evidence type.
2. Use measured_spl_at_distance directly when a representative measurement and uncertainty are available.
3. Otherwise estimate vena-contracta velocity with v = sqrt(2 * dP / rho), mechanical stream power with W_m = 0.5 * mdot * v^2, and acoustic power with W_a = min(0.01, eta_f * Mach^3) * W_m.
4. Convert sound power to a 1 m level using a configurable transmission loss, then apply free-field spreading 20 log10(r/1 m) to the receiver.
5. Apply configurable workflow triggers: ok below 85 dBA, action at or above 85 dBA, and high at or above 110 dBA by default.
6. Escalate elevated or uncertain cases to detailed source prediction, a controlled receiver survey, occupational-hygiene review, or separate AIV screening as applicable.

The model is a triage calculation, not a full IEC 60534-8-3 prediction. The default model uncertainty is +/-10 dB. Default thresholds are workflow triggers rather than universal legal exposure limits.

Python Usage Pattern

from noise_screening import ValveNoiseModel

model = ValveNoiseModel()
result = model.evaluate(
    mass_flow=12.0,
    pressure_drop=40.0,
    inlet_density=35.0,
    temperature=310.0,
    molar_mass=19.0,
  distance=3.0,
)

print(result.mach_number)
print(result.estimated_spl_at_distance_dba)
print(result.assessment_basis)
print(result.noise_warning)

For current operating evidence, provide the measured receiver level and its uncertainty:

measured = model.evaluate(
  mass_flow=12.0,
  pressure_drop=40.0,
  inlet_density=35.0,
  sound_speed=410.0,
  distance=3.0,
  measured_spl_at_distance=92.0,
  measured_uncertainty_db=2.0,
)

Related NeqSim Functionality

For detailed valve source prediction, use existing NeqSim classes:

• neqsim.process.equipment.valve.ThrottlingValve — flow-vs-Cv valve and pressure-drop response that defines the noise duty.
• neqsim.process.equipment.valve.ControlValve — control valve with characteristic and controller coupling.
• neqsim.process.mechanicaldesign.valve.ControlValveNoise_IEC_60534_8_3 — aerodynamic source prediction with flow regime, mechanical stream power, pipe-wall transmission loss, and external A-weighted level.

For the detailed class, call setFlowConditions(...), setAcousticProperties(...), setGeometry(...), setValveCoefficients(...), and calcNoise(). Read getSoundPressureLevelDbA(), getOutletMach(), getFlowRegime(), getMechanicalStreamPower(), and getTransmissionLoss(). Obtain density, speed of sound, and isentropic exponent from a flashed NeqSim fluid; treat valve coefficients and geometry as controlled vendor/design inputs.

Validation Checklist

• Mass flow, pressure drop, and density are positive.
• Either a sound speed or temperature and molar mass are supplied.
• Receiver distance, operating timestamp/window, source identity, and evidence basis are recorded.
• Measurement method, instrument, background correction, and uncertainty are recorded when measured data are used.
• The result is treated as screening evidence, not universal exposure or AIV acceptance.
• Detailed source prediction is redirected to NeqSim/vendor tools and qualified review.

Common Mistakes

Limitations

• The model path is not an IEC 60534-8-3 prediction and has no octave-band content.
• Free-field spreading omits reflections, shielding, multiple sources, directivity, atmospheric absorption, and distributed pipe radiation.
• A single dBA value cannot establish daily exposure dose, hearing protection, acoustic fatigue, or AIV acceptability.
• A measurement applies only to its operating state, receiver position, instrument setup, background correction, and uncertainty.
• Design acceptance requires controlled standards editions, verified valve/vendor data, and competent acoustic review.

References

• IEC 60534-8-3, control-valve aerodynamic noise prediction method.
• ISO 3744, sound-power determination from sound-pressure measurements.
• ISO 11201, emission sound-pressure measurement at work stations and specified positions.
• ISO 9613-2, engineering prediction of outdoor sound propagation.
• ISO 15664, noise-control design procedures for open plant.
• ISO 1999, estimation of noise-induced hearing loss.
• NeqSim repository: https://github.com/equinor/neqsim