Type 076 LHD/LHA discussion

ACuriousPLAFan said:

The exhausts/funnels of Sichuan indicate that the LHD is powered by 2x gas turbine engines and 6x diesel engines as her main engines, in addition to 5x supplementary diesel engines.

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where are the supplementary diesel engines? Also, why is there need for supplementary engines in this case? If one or two engines breakdown, they can still have a short burst at top speed since the IEPS (or IPES they call it here) relies on batteries (if I read the photos correctly) to power the motors.

ACuriousPLAFan said:

Just an oversimplified schematic illustrating the IPES on the 076 LHD. Posted by @应用技术联合体 on Weibo.

View attachment 157177

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basically we have a range extender set up with 076 propulsion. I think they actually use propulsion setup like this with a lot of civilian ships already, but those don't have the same power/speed requirements so I think they just use one main marine engine and maybe a backup.

taxiya said:

[edit]
I've found where "two motor per shaft" is mentioned. It was in the 076 tender. It says "series shaft electrical propulsion". At the time when I see it I thought it can be two electric motors per shaft, but there is a small chance that it is one electric motor on a direct driven shaft (gearbox to GT). The later can not be 100% excluded because there was another paper discussion such configuration for big ships.

View attachment 157194

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why would you do that though? that's would entirely bypass the efficiency you get from centralized power generation that charges the batteries to power each motors.

where are the supplementary diesel engines? Also, why is there need for supplementary engines in this case? If one or two engines breakdown, they can still have a short burst at top speed since the IEPS (or IPES they call it here) relies on batteries (if I read the photos correctly) to power the motors.

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The covered round objects behind the main funnel (GT funnel) in the image are the funnels for the supplementary generators.
Supplementary generators are not backup power; they remain permanently on, as the main engines primarily generates electricity for propulsion. In other words, they are used to maintain onboard power when the main engines is operating at full power for propulsion.

tphuang said:

why would you do that though? that's would entirely bypass the efficiency you get from centralized power generation that charges the batteries to power each motors.

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Electric drive is better for dynamic load when the load distribution among radar, propulsion etc. constantly change in a short period of time. There is penalty of efficiency in electric drive when you convert mechanical energy to electricity (4%) through power grid (?%) then back to mechanic (driving motor 4%). Direct drive's penalty is less than 2% (gear box).

Ships have a total installed power that match the power that ships ever need. Assuming that is 100%, for most of time ships only need X% to run. That percentage depens on type of operation. Y=100-X is the reserved power or boost power that is needed in minority of operation time. Ships that cruise most of time (passenger, cargo ships or LHA/CV) has lower demand of Y, and Y is close to a constant, ships that need extreme acceleration and maneuverability (frigate, destroyer) need big dynamic Y. In any way, if Y is for constant load (propulsion boost), then direct drive is more efficient saving the cost of 2 way conversion. If Y is dynamic (partially for propulsion and radar/weapon, or differenct acceleration) then it is better to use electric drive with energy storage as buffer.

In conclusion, IEPS is preferable but with a set of conditions, power steps of primary mover, operation profile, distribution of various load types.

IEPS uses more strategic materials like copper. It is why it wasn't used in WW2. Today you would use neomydium magnets as well. Huge ones.