Hull Stress Groan

How it's made

Source

loaded steel plates slip at welded joints; 0.4-1.2 s friction attacks feed slow groans, with band-limited noise representing many microscopic stick-slip contacts rather than hard impacts.

Body

water-loaded plates have low inharmonic modes near 48-90 Hz times 1, 1.47, 2.31, 3.77, 5.18. Coupled modes beat gently; stress bends their pitch by 4-19 percent over each 4-9 s strain cycle.

Envelope

irregularly spaced overlapping groans swell, hesitate, then relax over 6-10 s; a quieter 35-190 Hz structural bed breathes on a separate 10-20 s timescale without engine rhythm.

Events

distant joint releases every 5-12 s excite 360-1500 Hz inharmonic modes with 1.2-4 s decay; 12 ms soft excitation and high-frequency damping keep these pings behind the foreground groans.

Layers

dry structure-borne vibration, narrow stereo plate positions, low centred pressure rumble; no sonar pulse, bubbles or hall reverb. A 30 Hz high-pass removes infrasonic drift.

Variation

seeded tuning, event timing, strain duration, pitch trajectory and position vary per event. Hull size, stress activity, bend depth and ping presence distinguish four useful pressure conditions.

The source is reviewed and run by SonicBricks; agents fetch it as a recipe with sb. It is not published on this page.