PLAN Catapult Development Thread, News, etc.

Discussion in 'Navy' started by antiterror13, Dec 24, 2011.

  1. taxiya
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    taxiya Major
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    Finally the official evidence that USN is pursuing "MVDC" as well after PLAN has leapfrogged.
    A report just published.
    TECHNOLOGY DEVELOPMENT ROADMAP
    THE U.S. NAVY POWER & ENERGY LEAP FORWARD
    NAVAL POWER AND ENERGY SYSTEMS

    Page 28
    Why AC is bad, DC is good.
    Note: there is no long-term in the report

    Page 29
    USN is to develop MVDC from 2019, it does not have it yet. Professor Ma said that China is 10(?) years ahead of any other countries. This is the admission by US.

    Page 30
    The projected circuit breaker is expected latest 2023. The full system is expected to be latest 2037, that is almost 20 years later than PLAN.

    There are other interesting things I have not fully digested such as their primary mover's configuration (seems to be 25M+15M). Overall, very informative.
     
    #361 taxiya, Jul 30, 2019
    Last edited: Jul 30, 2019
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  2. latenlazy
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    latenlazy Colonel

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    Something something how dare America copy China.
     
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  3. taxiya
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    taxiya Major
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    Back to the future. :D
     
  4. taxiya
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    taxiya Major
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    Continue to #361,
    In the report, page 28
    That is essentially referring to the AAG.
    [​IMG]
    AAG absorbs the energy using (7) Water Twister (70%) and (4) Induction Motor (30%). The inertia of other components (cable drum and cable shock absorber) are small and can be neglected in calculation. The percentage is the of the total kinetic energy of the landing aircraft.

    In an AC network, the energy can not be fed back to the grid, therefor the "not exploited". The Induction Motor actually (but) consumes electrical energy from the grid to counter the force from arresting the aircraft. Let's say the consumption is X. This X is approximately less or equal to that 30% because of energy conservation.

    In a DC network, the Induction Motor acts as a generator. It convert the kinetic energy to electricity and fed to the grid, the energy will then be consumed (converted) by any consumers, but primarily by the flywheels in the EM launcher. Depending on how many flywheels are paired, the water-twisters may be eliminated because spinning water turbine is the same as spinning flywheels. This not only simplifies the device reducing the risk of fault and maintenance work, but also reduce total energy consumption of the platform.
     
  5. Max Demian
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    Max Demian Junior Member
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    There is no mention of catapults in the document? This seems mostly about naval IEPS/IPES.

    I would like to understand more why AC is bad? Tesla cars use induction AC motors even though their energy source is DC. From my limited understanding brushless DC motors require powerful permanent magnets, which are not cheap to manufacture, think rare earths (except maybe for China?). They are also quite heavy in comparison.

    Update: I saw you gave one example of energy recovery during aircraft arrest.

    However, how does that connect to MVDC?
     
    #365 Max Demian, Aug 2, 2019
    Last edited: Aug 2, 2019
  6. Max Demian
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    Max Demian Junior Member
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  7. Max Demian
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    Max Demian Junior Member
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    @taxiya
    I don't quite follow your example for the AAG. From what I could find, energy recovery was not a requirement for the system. Whether it is networked to AC or DC for that purpose is irrelevant. If they have need of that, they could hook it up to a battery/capacitor.

    The induction motor is used to accelerate the arrestor shaft in the initial phase and decelerate it in the closing phase, according to the filed patent:
    "To complement the energy-dissipating fluid turbine, an electric motor is coupled to the shaft for creating a decelerating torque on the shaft when the line is pulled by the moving object. For aircraft landing applications, an electric motor control system is provided that is configured to cause the electric motor to produce an accelerating torque on the shaft upon initial engagement of the pendant with the arresting hook to allow for a smooth engagement between the pendant and the arresting hook. After a smooth engagement has been obtained, the electric motor control system causes the electric motor to generate a decelerating torque on the shaft to slow the landing aircraft. "
     
  8. taxiya
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    taxiya Major
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    Page 28
    It does not say A
    To clarify, AC is bad to be the grid, nothing else. But because the grid is connecting everything of different voltage and frequency, it is critical. Therefor, as a whole system, DC grid is better than AC grid.

    Tesla cars use induction AC motor, even in a MVDC network including Professor Ma' envisioned (realized in the sub) DC based the motor is AC motor. AC motor is still better than DC (for the moment) because they can be made power denser.

    The problem of AC grid (DC's advantage) is that:
    1. AC grid MUST maintain a highly accurate and stable frequency, 60Hz in US or 50Hz in China and Europe. All consuming devices and the generator must be syncing to that frequency. Primary movers such as GT must use gearbox to adjust to a fixed RPM (RPM=N*Frequency, N is the number of poles). If the primary movers RPM changes due to load (temperature as in Type45's break down), the control system must immediately adjust the gear. If this is not done in time, the generator and consuming devices will be out of sync. This will generate fluctuating voltage and current which can be strong enough to burn the system. Even circuit breaker won't be able to save, think about the blackout in US recently.
    2. Flywheels are both motor and generator, when it acts as generator, its RPM will drastically drop, that means frequency drop. The launcher is linear motor which also relies on stable frequency. So you can imagine the challenge of regulating the frequency through an AC grid.
    Catapult are the biggest consumer in a IEPS CV. Talking about IEPS have to have catapult in the centre of everything.

    AAG and Catapult are only used by CV, so in other ships, they are irrelevant. On a CV however, considering the motor providing 30% of break in my post, AAG is the second important element in an IEPS.

    AAG energy recovery must be fed to DC grid:
    It was not a requirement not because they don't want to, but because they can't do it without DC grid. One can not just connect the electricity from AAG to anything without regulating its current. AAG generate AC, the voltage and current alternate directions. Battery and Capacitor charging must be DC, either constant current or constant voltage, or some specially designed DC form varying current or voltage, but never alternating direction.

    I must clarify that, I am not saying that PLAN's current arresting gear is recovering the energy as I suggested. What I am trying to say is that it can only be done in a DC grid, and doing so is advantageous.
     
    #368 taxiya, Aug 2, 2019
    Last edited: Aug 2, 2019
  9. Max Demian
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    Max Demian Junior Member
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    OK, I see your point. However, as far as AAG is concerned, the only ship currently employing it is a nuclear powered carrier. Another plausible explanation why energy recovery during arrest was not a requirement on such a platform might've been simply the lack of need for it.
    There could be a stronger case for it on a conventional powered carrier, although it still appears small. According to some 90's era studies, the EMALS can deliver 484MJ of energy in 3s, an amount of energy roughly equivalent to 4 gallons of gasoline. Assuming the same amount can be recovered during arrest, and 160 sorties per day we are looking at about 2000l of fuel, or 1.54 metric tons saved per day. This back of the envelope calculation did not include losses in the launch and arrest energy conversion processes.

    While doing some background study, I ran into this document from 2007: http://www.doerry.org/norbert/papers/090106usna-ngips-final.pdf
    According to this paper, in addition to the reasons Taxiya pointed out, MVDC has the advantage of power density over MVAC or HFAC, which is of high importance to combatants under 10,000 metric tons. The same study is of the opinion that for vessels above 25kt, the higher power density of MVDC does not justify the higher costs and complexity of such a system. For such vessels, MVAC IPS is judged adequate.
     
    #369 Max Demian, Aug 2, 2019
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  10. Max Demian
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    Max Demian Junior Member
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    Another observation, although this is getting off topic, and I am saying this is a non-expert. Steam propulsion has the benefit of a decoupled system, akin to IPS, where generated steam can be distributed to shaft power and electric generators in a fully independent manner. This might reduce some of the loads on the electric IPS, like delegating it to non-propulsion purposes which is how the Ford class is configured, as far as I understood.
     
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