Underwater gliders

[Anmdt]

An airborne glider requires sufficient airflow through winds or its motion to float up in the air, yet this is not such for an underwater glider, the buoyancy lifts the vehicle, which naturally floats in and on water. An underwater glider simply uses its buoyancy to adjust its downward or upward motion, using wings to generate backward-forward motion.
Additionally light weight folding propellers can be attached, usually driven by magnetic coupling,to reduce complexity of shafting tube, and frictional losses due to the water-tight bearings.
Removing energy consuming propulsion, and simply adjusting buoyancy through alternative methods, a glider can stay on mission up to months, dodge streams and weather conditions by sinking, can afloat to communicate and to correct its location, usually is driven around the sea by using Inertial GPS and possibly magnetic corrections.
Currently staying on development stage driven by scientific community, gliders are soon expected to be in service of military and national defense.
Since they lack moving parts, gliders are best found to measure acoustics and backscatters, and stores data up to an interval which later is delivered by any preferred communication to powerful servers for analysis. The collective and chaotic distribution of gliders also helps for glitch free measurements.

Underwater glider - Wikipedia

en.wikipedia.org

Underwater Gliders - The U.S. Integrated Ocean Observing System (IOOS)

Gliders are a unique and important observing system used to monitor and view a variety of subsurface missions.

ioos.noaa.gov

Gliders are a unique and important observing system used to serve a variety of subsurface observing missions. Gliders can monitor water currents, temperature, tagged animals and conditions that reveal effects from storms, impacts on fisheries, and the quality of our water. This information creates a more complete picture of what is happening in the ocean, as well as trends scientists might be able to detect. These versatile vehicles collect information from deep water, as well as at the surface, at lower cost and less risk than ever before. As scientists deploy more gliders, they are revolutionizing how we observe our ocean. These robots propel us closer to that revolution.
The IOOS Program Office has taken an active interest in profiling glider observing platforms over the last few years as their role has begun to increase and show extensive value in subsurface water column observing. There is a lot of capacity in the IOOS Regional Associations and there has been interest from the community in looking for opportunities to collaborate and expand the impact and value of profiling gliders. As a result we have developed a glider network white paper, established a glider data assembly center and most recently established an Underwater Glider User Group (UG2). All of these activities are intended to expand the understanding and use of gliders. For more information and latest updates about the UG2, events and more please visit gliders.ioos.us.
Glider Applications Include

• Ecosystem dynamics monitoring
• MBARI dye tracking experiment
• Test performance of acoustic receivers and other sensors
• Fish stock mapping of Red Grouper and others
• Glider speed testing in the Gulf Stream
• Harmful Algal Bloom (HAB) mapping
• Listening to tagged fish, whale acoustics
• Sustained and targeted ocean observations for improving tropical cyclone intensity and hurricane seasonal forecasts
• Upper ocean monitoring of U.S. Caribbean/ Atlantic Economic Exclusion Zone (EEZ)
• Sampling around Station ALOHA and other long term stations
• Hydrographic mapping
• Ocean acidification sampling
• Climate monitoring

An image depicting (source) typical components of an underwater glider, which ballast pump is used to adjust buoyancy by filling with air /oil, sliding mass is used to adjust pitch, thus direction of the motion and rudder to maneuver, the propeller is intended to be used rarely, when needed.

diagram showing typical motion of the glider; advanced controller can be further implemented to operate vehicle at fixed depth using propeller and wings in combination.

Undersea Gliders Help Identify Ocean Sounds | Oregon Coast Daily News

The open ocean might appear to be a vast, mute void, but it is in fact a very noisy place. Below the surface, everything from grunt sculpins and rockfish to orcas and harbor porpoises emit sounds to communicate with one another. On the seafloor, urchins create a raspy din as they graze algae...

oregoncoastdailynews.com

 

[Saithan]

I really hope we have projects like this. I'd love it if we can combine it with smart buoy system and sensor arrays.

 

[Anmdt]

Magnetic coupling is often used on UUV /ROVs to reduce shafting complexity and easily maintain- replace propellers. However these are applicable on materials with proper magnetic permeability, and thin coatings as shown in the diagram below:

Magnetic coupling - Wikipedia

en.wikipedia.org

source of the image along with useful information and drawings of neomidyun magnets based magnetic coupling

 

[Combat-Master]

Magnetic coupling is often used on UUV /ROVs to reduce shafting complexity and easily maintain- replace propellers. However these are applicable on materials with proper magnetic permeability, and thin coatings as shown in the diagram below:

Magnetic coupling - Wikipedia

en.wikipedia.org

View attachment 1802
source of the image along with useful information and drawings of neomidyun magnets based magnetic coupling

Why aren't these types of thrusters used more readily, they seem to take in all the advantages of magnetic coupling..

 

[Anmdt]

Why aren't these types of thrusters used more readily, they seem to take in all the advantages of magnetic coupling..

It takes time to shift from conventional applications on marine industry, related to reliability and stuff since those systems are destined to run smooth in long term.

Rolls royce has industrialized it and i know there is at least one R&D project in turkey for such application.

 

[Anmdt]

I'm aware of that, however the whole notion of tracking something that is only passively receiving (any GNSS receiver) is no-brainer to start with. Unfortunately such notion seem to be very prominent these days due to most people mistook GPS = Google Map service.


If I were the ChiCom I connect them to either Inmarsat or Iridium and subscribing the account from some shell company.


In the most likely case they use the cheap one. But after this they most likely will change.

Is possible for you to share their Sound Profile particularly the China one if you happen to know and allowed to do so? Both in broadband and in narrowband. A simulated view would be fine. I'm curious as how their mechanical transient look like. Thanks Beforehand

Two data i can squeeze out, as these were shared in public presentations if i find more which was published publicly i will share them as well by time:
Acoustic signature up to 1 kHz, recorded by array of hydrophones from 1km median distance. Normalized to 1 meter distance, filtered of background noise. The marine traffic was calm (none at the instant of measurement)<200 Hz the reliability of data is weak for several reasons. Sea state is 2.

Overall noise given in 1/3 octave bands above 1kHz, numbers are rounded (note this was a result of several cycles, above graphic is a single rise -half cycle):

Calculated frequency	OSPL (dB)
1000.0​	105​
2000.0​	96​
4000.0​	96​

In Case of pump off-pitch-roll motor on as taken from report :
Overall noise was was low around at ambient noise while the pump was off, pitch and roll control motors has generated narrow band tonals around 2-3-5kHz (we assumed related with engine order of servo motor).

However, we ,several, times were disturbed by marine traffic which it impossible to detect the glider with acoustic receivers (from 1~2 km) and we used a simple commercial fish sonar to find its location to update in recording units (matters to know distance from each hydrophone to normalize the source strength).

When the pump is on, we could pick a noise at 5km distance ,which i can refer to as "abnormality" standing out from background noise of the calm sea, but should tell again we had network of hydrophones and could retrieve this from phase of the signal, not the strength of the signal so technically if we didn't know it was there it could have been assumed as reflection or anything. The sonar i have mentioned was able to find the thing in 1~2 km with a high reliability and outstanding acoustic reflection profile.
All given ranges are horizontal , the depth of glider was set shallow to test multiple cycles.

Also there is this study, which refrains from sharing data below 4kHZ, the same group has multiple researches. They have also pointed out the multi-tonals for weight shifters. Also to be noted they have used onboard hydrophones which may lack a portion of self noise.

mdpi.com/2076-3417/9/22/4839/html
The pump and roll motor difference can be seen here, the pump motor is dominant in wide frequency range, roll motor has particular frequencies:

But again even with a slightest of marine traffic in circle of 10 km, it would be impossible to detect these using passive receivers, the only logical and affordable option is running commercial fishery or diver detection sonars at where possibly these systems will be passing from.