Unusual Mooring Oscillations: Apparent Foucault–Wheatstone Device in the Deep Ocean?
A pressure sensor, located for four months in the middle of a 1275 m-long taut deep-ocean mooring in 2380 m water depth above a seamount with sub-surface top-buoys and seafloor anchor-weight, demonstrates narrow-band spectral peaks of deterministic well-predictable signals with equivalent 0.5 m ampl...
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| Format: | Article |
| Language: | English |
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MDPI AG
2023-05-01
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| Series: | Journal of Marine Science and Engineering |
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| Online Access: | https://www.mdpi.com/2077-1312/11/5/1087 |
| _version_ | 1797599518832721920 |
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| author | Hans van Haren |
| author_facet | Hans van Haren |
| author_sort | Hans van Haren |
| collection | DOAJ |
| description | A pressure sensor, located for four months in the middle of a 1275 m-long taut deep-ocean mooring in 2380 m water depth above a seamount with sub-surface top-buoys and seafloor anchor-weight, demonstrates narrow-band spectral peaks of deterministic well-predictable signals with equivalent 0.5 m amplitudes at uncommon sub-harmonic frequencies f*/4, f*/2, 3f*/4 of the local near-inertial frequency f* = 1.085<i>f</i>, where <i>f</i> denotes the Coriolis parameter. None of these sub-harmonics can be associated with oceanographic motions, which are dominated by super-inertial internal waves that are more broadband and less predictable. No corresponding peaks are found in spectra of other observables like current velocity (differences), temperature, and pressure in the top buoy of the mooring. The mid-cable pressure sensor was mounted on a nearly 1 kN weighing non-swiveled frame. Its data are hypothesized to reflect a resonant mechanical oscillation of the high-tensioned elastic steel mooring cable under repeated short-scale Strouhal cable vibrations induced by vortex-shedding due to water-flow drag and/or possibly by tidal baroclinic motions that are about 50% larger near the sloping seafloor of the seamount than mid-depth thereby modifying the mooring-cable in a helical shape. Cable dynamics and mooring-motion considerations yield inconclusive results to explain the observations. Hypothesizing, the observations suggest, cable dynamically, sub-harmonic drainage of helix-shape source at non-tidal semidiurnal center-frequency (M<sub>2</sub> + S<sub>2</sub>)/2 = 3f*/2, physically, the measurement of Earth rotation thereby mimicking a Foucault–Wheatstone device, and, oceanographically, the relative vortex-rotation <i>ζ</i>/2 = 0.085<i>f</i> being possibly induced by water-flow interacting quasi-permanently with the nearby seamount by a topographic obstruction, so that total local near-inertial frequency f* = <i>f</i> + <i>ζ</i>/2. |
| first_indexed | 2024-03-11T03:35:37Z |
| format | Article |
| id | doaj.art-8c29df62a09d4abe965a6950839b5436 |
| institution | Directory Open Access Journal |
| issn | 2077-1312 |
| language | English |
| last_indexed | 2024-03-11T03:35:37Z |
| publishDate | 2023-05-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Journal of Marine Science and Engineering |
| spelling | doaj.art-8c29df62a09d4abe965a6950839b54362023-11-18T02:01:13ZengMDPI AGJournal of Marine Science and Engineering2077-13122023-05-01115108710.3390/jmse11051087Unusual Mooring Oscillations: Apparent Foucault–Wheatstone Device in the Deep Ocean?Hans van Haren0NIOZ Royal Netherlands Institute for Sea Research, P.O. Box 59, 1790 AB Den Burg, The NetherlandsA pressure sensor, located for four months in the middle of a 1275 m-long taut deep-ocean mooring in 2380 m water depth above a seamount with sub-surface top-buoys and seafloor anchor-weight, demonstrates narrow-band spectral peaks of deterministic well-predictable signals with equivalent 0.5 m amplitudes at uncommon sub-harmonic frequencies f*/4, f*/2, 3f*/4 of the local near-inertial frequency f* = 1.085<i>f</i>, where <i>f</i> denotes the Coriolis parameter. None of these sub-harmonics can be associated with oceanographic motions, which are dominated by super-inertial internal waves that are more broadband and less predictable. No corresponding peaks are found in spectra of other observables like current velocity (differences), temperature, and pressure in the top buoy of the mooring. The mid-cable pressure sensor was mounted on a nearly 1 kN weighing non-swiveled frame. Its data are hypothesized to reflect a resonant mechanical oscillation of the high-tensioned elastic steel mooring cable under repeated short-scale Strouhal cable vibrations induced by vortex-shedding due to water-flow drag and/or possibly by tidal baroclinic motions that are about 50% larger near the sloping seafloor of the seamount than mid-depth thereby modifying the mooring-cable in a helical shape. Cable dynamics and mooring-motion considerations yield inconclusive results to explain the observations. Hypothesizing, the observations suggest, cable dynamically, sub-harmonic drainage of helix-shape source at non-tidal semidiurnal center-frequency (M<sub>2</sub> + S<sub>2</sub>)/2 = 3f*/2, physically, the measurement of Earth rotation thereby mimicking a Foucault–Wheatstone device, and, oceanographically, the relative vortex-rotation <i>ζ</i>/2 = 0.085<i>f</i> being possibly induced by water-flow interacting quasi-permanently with the nearby seamount by a topographic obstruction, so that total local near-inertial frequency f* = <i>f</i> + <i>ζ</i>/2.https://www.mdpi.com/2077-1312/11/5/10871 km-long taut-wire deep-ocean mooringnon-swiveled mid-cable pressure sensordeterministic signals at near-inertial sub-harmonicssharp spectral peaksmooring vibrations due to deep-ocean currentsseamount-related relative vorticity |
| spellingShingle | Hans van Haren Unusual Mooring Oscillations: Apparent Foucault–Wheatstone Device in the Deep Ocean? Journal of Marine Science and Engineering 1 km-long taut-wire deep-ocean mooring non-swiveled mid-cable pressure sensor deterministic signals at near-inertial sub-harmonics sharp spectral peaks mooring vibrations due to deep-ocean currents seamount-related relative vorticity |
| title | Unusual Mooring Oscillations: Apparent Foucault–Wheatstone Device in the Deep Ocean? |
| title_full | Unusual Mooring Oscillations: Apparent Foucault–Wheatstone Device in the Deep Ocean? |
| title_fullStr | Unusual Mooring Oscillations: Apparent Foucault–Wheatstone Device in the Deep Ocean? |
| title_full_unstemmed | Unusual Mooring Oscillations: Apparent Foucault–Wheatstone Device in the Deep Ocean? |
| title_short | Unusual Mooring Oscillations: Apparent Foucault–Wheatstone Device in the Deep Ocean? |
| title_sort | unusual mooring oscillations apparent foucault wheatstone device in the deep ocean |
| topic | 1 km-long taut-wire deep-ocean mooring non-swiveled mid-cable pressure sensor deterministic signals at near-inertial sub-harmonics sharp spectral peaks mooring vibrations due to deep-ocean currents seamount-related relative vorticity |
| url | https://www.mdpi.com/2077-1312/11/5/1087 |
| work_keys_str_mv | AT hansvanharen unusualmooringoscillationsapparentfoucaultwheatstonedeviceinthedeepocean |