3 ms·
>Dr Alastair Lyndon, from Heriot-Watt University, said: “Underwater cables emit an electromagnetic field. When it’s at a strength of 500 microTeslas and above,
by willis936 5y ago
>Dr Alastair Lyndon, from Heriot-Watt University, said: “Underwater cables emit an electromagnetic field. When it’s at a strength of 500 microTeslas and above, which is about five percent of the strength of a fridge door magnet, the crabs seem to be attracted to it and just sit still.
For reference, this is the magnitude of Earth's magnetic field.
What's the strength of magnetic fields around undersea cables?
https://www.mdpi.com/2077-1312/9/7/776/htm#B15-jmse-09-00776 https://www.mdpi.com/2077-1312/9/7/776/htm#B15-jmse-09-00776
From the paper:
>EMF strengths predicted around subsea power cables, as reported in the literature, vary from 140–8000 µT [15,17,18]. A commonly utilised cable operating at 1600 A is expected to produce an EMF of 3200 µT in a perfect wire, at the cable surface [17]. As with all EMF, the values will decrease with distance from the source, resulting in a field strength of 320 µT and 110 µT at 1 m and 4 m respectively [17].
15:
https://dspace.lib.cranfield.ac.uk/bitstream/handle/1826/7785/Final%20report.pdf?sequence=1 https://dspace.lib.cranfield.ac.uk/bitstream/handle/1826/778...
426 pages sheesh. Page 25 (37 in the pdf) discusses the magnetic field strength model. No math but references. I'm getting more nervous because the references are all related to modeling power lines in air.
Table B-1 shows a list of submarine power lines and Table B-2 contains their simulated magnetic field strengths.
Medium does affect magnetic field geometry. It'd be nice if someone took some actual measurements if they're not going to use a decent model.
- idealmedtech 5y agoMy understanding is that, in an ideal case, the medium only affects epsilon and mu, the permittivity and permeability, which are easily found and substituted from lookup tables.
- throwawayninja 5y ago"In theory, practice and theory are the same. In practice, they are not."
- CyberDildonics 5y agoDo you have a reason why lookup tables don't work here or are you regurgitating this quote without evidence that it makes sense in this context?
- deleted 5y ago[deleted]
- willis936 5y agoThe lookup tables were made based off of power lines in air. So much effort has been spent studying the effects but presumably no one has actually checked the magnitude of the magnetic fields around submarine power lines.
- idealmedtech 5y agoI was not referring to the lookup tables in the appendix, rather known lookup tables for relative permittivity and permeability in salt water at 60Hz. If you know those relative parameters you can simply adjust the air-based calculation by multiplying by some function of the ratio of the water parameter to the air parameter (effectively cancelling out). I'm no expert though, only have some high level undergraduate fields and waves course work.
- willis936 5y agoWhich would be fine to do, if it was done. The relatively permeability is implicitly assumed to be 1 in the references that even mention it (17). Maybe that's a reasonable assumption, but is it? It at least warrants discussion in one of these papers.
- jbay808 5y agoHave you ever tried to pick up seawater with an electromagnet?
- 5y ago