Diesel Sub Propulsion Question

urmomma158 · 02-08-2007, 22:57 PM

I understand that the motors on diesel sub are AC induction and the generator produces Dc current and the sub needs inverters to convert it from DC to AC power to drive the motor. AC to DC conversion is pretty quiet and all you hear is a buzz noise( think tube lights). And a DC to AC converter is much noisier (things you plug into the cigarrete lighter in your car so you can play videogame s, plug in your radio,hairdryer, etc).

I want to know if a large DC to AC inverter shielded with the amount of sound insulating foam an SSK would use noise level will approach that of a turbine's with the amount of sound insulating foam around it an SSN will use ?

Any ideas?

pdf27 · 02-09-2007, 05:03 AM

Finger-breaking territory methinks!

subba · 02-09-2007, 06:17 AM

While converting AC to DC requires rectifiers which are silent, DC to AC conversions would require a transformer. Which produce a high frequency noise. Shielding the transformer should be good enough. I think high frequency noise emanated in the transformer in a submarine should not travel long distances. OTOH turbines though operating at high speeds will produce low freq noise which will travel much farther distances and much harder to attenuate.

So IMO the DC to AC conversion via a transformer, producing HF noise should be more silent than a turbine ship. I'm just using basic principles here sir, i could be wrong though if i missed out something.

highsea · 02-09-2007, 14:22 PM

Quote:

Originally Posted by subba

...DC to AC conversions would require a transformer.

Transformers are for stepping AC voltage up or down or inducing energy from one circuit to another. Converting DC to AC requires an inverter.

urmomma158 · 02-09-2007, 19:18 PM

Quote:

Originally Posted by subba

While converting AC to DC requires rectifiers which are silent, DC to AC conversions would require a transformer. Which produce a high frequency noise. Shielding the transformer should be good enough. I think high frequency noise emanated in the transformer in a submarine should not travel long distances. OTOH turbines though operating at high speeds will produce low freq noise which will travel much farther distances and much harder to attenuate.

So IMO the DC to AC conversion via a transformer, producing HF noise should be more silent than a turbine ship. I'm just using basic principles here sir, i could be wrong though if i missed out something.

Well the SSN has more space=more foam, and will obviously have a different type of foam for the turbine not to mention other quieting techniques.

One advanatge SSN's have is their pumpjet propulsors which are much quieter than any conventional propellors so in propulsion noise the SSN has the advanatge.
However quieting isn't everything for a sub you still need other things which an SSN clealry has the advanatge in.

pdf27 · 02-09-2007, 21:12 PM

Only some SSNs have pump-jet propulsors, and that isn't limited to SSNs - it's a straight replacement for a prop.

Francois · 02-09-2007, 22:22 PM

False "pdf" (and I don't like you signature, very immature).
Pump-jet needs a lot of energy, that makes it irrelevant for diesel-electrics.

Boycott british food should I say? Poah!

subba · 02-10-2007, 05:47 AM

Quote:

Transformers are for stepping AC voltage up or down or inducing energy from one circuit to another. Converting DC to AC requires an inverter.

Highsea sir, you are correct. But wrt the noise component, i mentioned the transformer as it will be a part of the inverter. Rest of the components of the inverter will produce maybe heat but not noise. Thats why i mentioned the transformer only.

pdf27 · 02-10-2007, 07:45 AM

Quote:

Originally Posted by Francois

False "pdf" (and I don't like you signature, very immature).

So grow a sense of humour then and stop taking yourself so seriously. FFS!

Quote:

Originally Posted by Francois

Pump-jet needs a lot of energy, that makes it irrelevant for diesel-electrics.

Unclear - plenty of references saying so, but in theory efficiency should be higher as there is reduced swirl in the water leaving the prop.
And there are some conventional designs using it - for example the BMT Marine SSGT design - linky: New High Mobility Submarine

Francois · 02-10-2007, 08:30 AM

Your no-respect and arrogance has killed what could have been a debate.
Bye.

urmomma158 · 02-10-2007, 17:27 PM

Quote:

Originally Posted by pdf27

Only some SSNs have pump-jet propulsors, and that isn't limited to SSNs - it's a straight replacement for a prop.

All of the US's top SSN's have it (Seawolf and Virginia)
and Pumpjet propulsors are very heavy, no SSK has one.

ArmchairGeneral · 02-11-2007, 23:51 PM

Quote:

Originally Posted by urmomma158

All of the US's top SSN's have it (Seawolf and Virginia)
and Pumpjet propulsors are very heavy, no SSK has one.

Read pdf's link.

pdf27 · 02-12-2007, 05:58 AM

Quote:

Originally Posted by ArmchairGeneral

Read pdf's link.

It isn't something that has actually been built yet and the power source is gas turbines rather than diesels, but BMT marine are really very good at what they do and wouldn't release a drawing like that if it wasn't possible. The UK CVF carrier design is pretty much all their work.

I suspect what is going on will be that pump jet units are more expensive and suffer greater fouling problems, but give major signature reduction at higher speeds. At low speeds, they probably won't make much or any difference.
SSNs and the SSGT I linked to are designed to transit at high speed, while SSKs very rarely go fast. Hence the lack of diesel-electric subs using them.

ArmchairGeneral · 02-12-2007, 14:48 PM

Makes sense.

IflareR · 03-13-2007, 07:03 AM

why would the current need ac-dc-ac conversion? why not use ac generators and ac motors for propulsion?

02-08-2007, 22:57 PM	#1 (permalink)
urmomma158 the real plastic *Senior Contributor* Join Date: 03-05-06 Location: NJ Turnpike Posts: 937 Country:	Diesel Sub Propulsion Question I understand that the motors on diesel sub are AC induction and the generator produces Dc current and the sub needs inverters to convert it from DC to AC power to drive the motor. AC to DC conversion is pretty quiet and all you hear is a buzz noise( think tube lights). And a DC to AC converter is much noisier (things you plug into the cigarrete lighter in your car so you can play videogame s, plug in your radio,hairdryer, etc). I want to know if a large DC to AC inverter shielded with the amount of sound insulating foam an SSK would use noise level will approach that of a turbine's with the amount of sound insulating foam around it an SSN will use ? Any ideas? __________________

02-09-2007, 05:03 AM	#2 (permalink)
pdf27 Contributor Join Date: 06-05-06 Location: UK Posts: 538 Country:	Finger-breaking territory methinks! __________________ Rule 1: Never trust a Frenchman Rule 2: Treat all members of the press as French

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02-09-2007, 06:17 AM	#3 (permalink)
subba Patron Join Date: 01-10-07 Posts: 282	While converting AC to DC requires rectifiers which are silent, DC to AC conversions would require a transformer. Which produce a high frequency noise. Shielding the transformer should be good enough. I think high frequency noise emanated in the transformer in a submarine should not travel long distances. OTOH turbines though operating at high speeds will produce low freq noise which will travel much farther distances and much harder to attenuate. So IMO the DC to AC conversion via a transformer, producing HF noise should be more silent than a turbine ship. I'm just using basic principles here sir, i could be wrong though if i missed out something.

02-09-2007, 21:12 PM	#6 (permalink)
pdf27 Contributor Join Date: 06-05-06 Location: UK Posts: 538 Country:	Only some SSNs have pump-jet propulsors, and that isn't limited to SSNs - it's a straight replacement for a prop.

02-09-2007, 22:22 PM	#7 (permalink)
Francois *Defense Professional* Join Date: 08-18-05 Posts: 129	False "pdf" (and I don't like you signature, very immature). Pump-jet needs a lot of energy, that makes it irrelevant for diesel-electrics. Boycott british food should I say? Poah!

02-10-2007, 08:30 AM	#10 (permalink)
Francois *Defense Professional* Join Date: 08-18-05 Posts: 129	Your no-respect and arrogance has killed what could have been a debate. Bye.

02-12-2007, 14:48 PM	#14 (permalink)
ArmchairGeneral Devil's Advocate *Senior Contributor* Join Date: 05-03-06 Location: The boonies of NC, USA. Posts: 2,746 Country:	Makes sense.

03-13-2007, 07:03 AM	#15 (permalink)
IflareR New Member Join Date: 12-10-06 Posts: 9	why would the current need ac-dc-ac conversion? why not use ac generators and ac motors for propulsion?

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