Acoustic energy is frequently generated within complex, enclosed structures such as underground facilities (UGFs). Thus, there is interested in modeling the sound as it propagates through the facility and exists through various openings.
A complex facility is composed of several components that must be accounted for in any acoustic modeling treatment. The main subsystems are:
• Tunnels (2-port waveguides)
• Chambers (T-junctions, turns, and other discontinuities: (1,2, or 3-port systems)
• Ventilation ducts (1-port terminated waveguides)
The challenge is to segment the modeling approach into regimes based on the acoustic frequencies and facility dimensions. These factors impact which acoustic modes are supported. The regimes can be broken up into: very low frequencies, low frequencies, mid frequencies, and high frequencies.
The Low-frequency Facility Modeler (LFFM) has initially been developed to model the very low frequencies regime (in the infrasound band below 20 Hz). The modeling is successfully accomplished using a combination of:
• Waveguide formulations
• Finite-element-models (FEMs)
• lumped-element characterizations