question archive The Russian military Zubr-class air cushioned landing craft (LCAC) is the largest air cushion vehicle (ACV) in service currently
The Russian military Zubr-class air cushioned landing craft (LCAC) is the largest air cushion vehicle (ACV) in service currently
Subject:Mechanical EngineeringPrice: Bought3
The Russian military Zubr-class air cushioned landing craft (LCAC) is the largest air cushion vehicle (ACV) in service currently. Vessel data: length = 57 m, beam = 26 m, flexible skirt height ? 2 m (estimated), displacement = 555 t (fully laden). Showing fully your workings, answer the questions below.
a) Calculate the weight of the LCAC (give your answer in N and kN / MN if appropriate).
b) Treating the LCAC as rectangular in shape, calculate the rigid top deck area beneath which the inflatable skirt operates.
c) Calculate the pressure maintained inside the inflated skirt to ensure vertical force equal and opposite to the weight of the LCAC thus allowing it to sit on the air cushion. Use your answers from parts (a) and (b). to answer and give your answer in N m-2 (and another suitable engineering version of the units e.g. kN m-2 etc.).
d) Pressure is effectively an 'energy per cubic metre' (J m-3) term, so multiplying pressure (in N m-2) by a volume (in m3) gives an energy (in N m or Joules, J - both are energy units). If we assume that the LCAC skirt has vertical sides when inflated, calculate the skirt volume beneath the craft (m3) and use this to estimate the total energy needed to fully inflate the skirt without leaks (owing to the pressure in part (c)) in J, kJ and MJ.
e) Estimate the velocity (in m s-1 and convert to knots as well) of the air being forced into the skirt from the lift fans. Assumptions:
• Bernoulli's Theorem for inviscid, incompressible flow applies and that all the kinetic energy of the air is conserved and transferred to pressure energy inside the skirt as jQuery22407298774706205431_1614528489186??????.
• Air is incompressible and has a density of 1.229 kg m-3 (1this is the sea level standard density value for dry air at 15 ?C).
f) Assuming the skirt of the LCAC takes just 2.2 s to inflate and all the energy in the skirt calculated in part iv. is delivered in that time, calculate the average power required to do that (in MW). Remember: power (W) = energy per unit of time (J s-1)
g) In reality air leaks out beneath the skirt all the time to allow the hovercraft to float on a cushion of air. During the inflation time of 2.2 s, if the power in the skirt is 57 % of the total power from the lift system, calculate the lift system power (in MW) and thus the power lost owing to air leakage (in MW).
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