DieselShip's Online Content Library

Q8. A. Electric motors contain a stationary member as well as a rotating member. For each of the following machines, identify in which part of the motor three field winding and the armature winding are located: three phase induction motor, three phase synchronous motor, d.c. motor. B.  An 18.65 KW,4-pole,50HZ, 3 phase induction motor has friction and windage losses of 2.5 percent of the output. The full load slip is 4% compute for full load (a) the rotor Cu loss (b) the rotor input (c) the shaft torque (d) the gross electromagnetic torque.

Q8. A current has the following steady values in amperes for equal intervals of time and changing instantaneously from one value to next: - 0,10,20,30,20,10,0,0, -10,-20,-30,-20,-10,0 etc. Calculate I. Average value 2. RMS value, 3. Form factor and peak factor.

Q9. A. What are the factors which determine the synchronous speed of a motor? B. The star-connected rotor of an induction motor has a stand-still reactance of 4.5 ohms/phase and a resistance of 0.5 /phase. The motor has an induced emf of 50 V between the slip-rings at stand-still on open circuit when connected to its normal supply voltage. Find the current in each phase and the power factor at start when the slip-ring is short-circuited.

Q9. (a) Explain the concept of dynamical stability.

(b) A ship of 5000 tonne displacement has three rectangular double bottom tanks A: 12m long and 16m wide; Tank B: 14m long and 15m wide; C 14m long and 16m wide.

calculate the free surface effect for any one tank and state in which order the tanks should be filled when making use of them for stability correction.

Q10. A ship of 15000 tonne displacement has an Admiralty Coefficient, based on shaft power, of 420. The mechanical efficiency of the machinery is 83%, shaft losses 6%, propeller efficiency 65% and QPC 0.71. At a particular speed the thrust power is 2550kW.

Calculate:

(i) Indicated power,

(ii) Effective power,

 (iii) Ship speed.

Q10. With reference to the wake of a vessel:

a. Explain Wake fraction and Quasi Propulsive co-efficient(QPC).

b. A ship travelling at 15.5 knots has a propeller of 5.5 m pitch turning at 95 rev/min. The thrust of the propeller is 380 KN and the delivered power 3540 KW. If the real slip is 20% and the thrust deduction factor O.198, calculate the Quasi Propulsive Coefficient (QPC) and the wake fraction.

Q6. A vessel of constant rectangular cross section is 60 m long and 10 m wide, it floats at a level keel draught of 3 m and has a Centre of gravity 2.5 m above the keel. Determine the fore and aft draughts if an empty, full width, fore-end compartment 8 m long is opened to the sea. For simplicity, a permeability of 100 per cent may be assumed. (solve using lost buoyancy method)

Q9. A. Explain the effect on GM during the filing of a double – bottom tank, B. A ship of 8,000 tonnes displacement has KM 7.5m, and KG 7.0m.  A double bottom tank is 12 meters long 15 meters wide and 1 meter deep.  The tank is divided longitudinally at the centre line and both sides are full or small water. Calculate the list if one side is pumped on until it is half empty.

Q8. A. Explain why the amplitude of ship motion should be limited B. A ship of 8100 tonne displacement floats upright in seawater. KG = 7.5m and GM = 0.45m A tank, whose centre of gravity is 0.5m above the keel and 4m from the centreline, contains 100 tonne of water ballast neglecting free face effect, calculate the angle of heel when the ballast is pumped out.

Q8: A box shaped barge of uniform construction is 32 metres long and displaces 352 tonnes when empty, is divided by transverse bulkheads into four equal compartments.  Cargo is loaded into each compartment and level stowed as follows: -

No. 1 hold – 192 tonnes                                               No.2 hold – 124 tonnes

No. 3 hold –272 tonnes                                                No.4 hold – 176 tonnes.

Construct load and shearing force diagram, before calculating the bending moments at the bulkheads and at the position of maximum value; hence draw the bending moment diagram.

Q7. a) Derive the Admiralty Coefficient formula and show how this may be modified to suit a fast ship. (6)

b) A 6m model of a ship has a wetted surface area of 7m2 and when towed in fresh water at

3knots has a total resistance of 35 N. Calculate the effective power of the ship, 120 m long, at its corresponding speed.

n=1.825. f from formula SCF=1.15 (10)

Q10. A. Write shorts notes on various types of DC Motors.

B. A 440V shunt motor takes an armature current of 30A at 700 rev/min. The armature resistance is 0.7ohm. If the flux is suddenly reduced by 20 per cent, to what value will the armature current rise momentarily? Assuming unchanged resisting torque to motion, what will be the new steady values of speed and armature current? Sketch graphs showing armature current and speed as functions of time during the transition from initial to final, steady-state conditions.