2ND EXAM OF MAIN MACHINERY AND AUXILIARY MARINE SYSTEMS

Transcription

1 2ND EXAM OF MAIN MACHINERY AND AUXILIARY MARINE SYSTEMS MASTER DEGREE IN NAVAL ARCHITECTURE AND MARINE ENGINEERING MECHANICAL ENGINEERING DEPARTMENT UNIVERSITY OF LISBON 28th JANUARY 2016 (Duration 3 hr) 1. (2v) You are designing a four-stroke diesel engine to provide a brake power of 300 [kw] naturally aspirated at its maximum rated speed. 1.1 Based on typical values for break mean effective pressure and maximum mean piston speed, estimate the required engine displacement, and the bore and stroke for sensible cylinder geometry and number of engine cylinders; 1.2 What is the maximum rated engine speed [rpm] for your design? 1.3 What would be the break torque [N.m], and the fuel flow rate [g/h] at this maximum speed? You may assume that the maximum mean piston speed is 12 [m/s]; 1.4 State what are the basic choices when selecting a ship s prime mover. Give examples of five typical combined propulsion plant alternatives. There is a current trend to adopt a fully electrical propulsion plant on large cruise vessels. State the reasons for such option. 1.5 State what are the basic choices when selecting a ship s propulsor. Define a theoretical propeller curve, and draw on the same sketch two typical propeller curves corresponding to a displacement vessel and a planing craft. On the same sketch, draw as well a typical performance diagram of a diesel engine having adequate margins to be installed onboard the planing craft, and state what is the aim of this adjustment procedure between the propeller curve and the engine performance diagram. 2. (3v) A ship has a main propulsion system constituted of a diesel engine, a reduction gearbox and a propulsion shaft line, whose engine performance diagram is shown in Annex A. Considering there is a Power Take-Off (PTO) installed at the gearbox to drive an hydraulic circuit, whose speed reduction ratio is 4.1:1 and its power is directly proportional to the shaft speed delivering 110 [kw] at top speed. Determine: 2.1 What would be the maximum brake power available to propel the ship? 2.2 Assuming the propeller has been designed to absorb all the brake power of the main engine when the propeller shaft rotates at a rotational speed of 410 [rpm], what would be the most adequate speed reduction ratio so that all the brake power available could be utilized? 2.3 In case the PTO s clutch was disengaged from the gearbox, state if the ship would be able to sail at a higher speed? Justify your answer. 2.4 What would be the maximum rated power absorbed at the main engine when its crankshaft rotates at a rotational speed of 1500 [rpm]? 3 (2v) Figure 1 shows an articulated rod or link type ram of a steering gear with two double-effect cylinders having each a stroke of 300 [mm] and a tiller to rudder stock distance of 500 [mm], which has been designed to develop a torque of 20 [kn.m]. Determine:

2 3.1 The nominal diameter of the cylinders, assuming a mechanical efficiency of the cylinders of 90% (when design pressure of the hydraulic oil is 120 [bar]). 3.2 The flow rate and power of this rotational vane type pump, assuming that hydraulic pump efficiency is 70%. 3.3 Draw a single-line diagram and explain its working principle of a typical steering gear arrangement of a small boat whose HPU is directly coupled to the main engine (Power Take- Off). Figure 1 Steering gear arrangement. 4. (2.5v) Consider the crane shown in Figure 2, which should be installed onboard a vessel. 4.1 Determine: The power of the winch and its torque which should allow to hoist (move up or down) the cargo hook. You should assume a mechanical transmission efficiency of 96% The winch power reduction if a double hoist block (with two single sheaves, as shown on bottom right corner of Figure 2) was fitted on top of the cargo boom. 4.2 State what would be the other two basic functions required to handle the boom and the cargo of a typical marine crane. Figure 2 Crane arrangement.

3 5. (2.5v) As illustrated in Figure 3, an axial fan is to be selected to cool a machinery room whose dimensions are 12 x 4 x 4 [m]. Half of the volume in the room is expected to be filled with machinery and equipment and the other half to be air space. A 5 [m] diameter hole is available at the upper deck of the machinery room (below the funnel) for the installation of the fan that is to replace the air in the void spaces of the room once every 100 seconds. A few fan-motor combined units are available in the market and their efficiency is estimated to be 30%. Considering air density is 1.2 [kg/m 3 ], determine: 5.1 The electrical power input of the fan-motor unit to be purchased; 5.2 The pressure difference across the fan. Figure 3 Schematic of the axial fan arrangement. 6. (3v) 6.1 Consider a patrol boat having a design displacement = 660 [ t] height GM t = 2.50 [ m] where the fin s lever is r = 4.00 [ m], and a transverse metacentric. Figure 4 shows fins position and orientation angles over the ship s hull, F, the fin lift coefficient at the origin is dc L = , and the maximum angle of attack is α = 25 º. Assuming for a certain dα deg α = 0º design point, that the seaway wave slope is θ = 5º, and the maximum sustained ship s advance speed is U 20 [ kts] w =, determine the planform area of each fin. 6.2 State and justify what would be the most adequate roll stabilisation system to be installed onboard large rectangular pontoon where safety of passengers to be embarked or disembarked from this moored platform is a major concern. Figure 4 Definition of the fins position and orientation angles over the ship s hull.

4 7. (1v) What material is usually utilized to manufacture both inboard and outboard shafting and their shaft sleeves? State what are the two main functions of a thrust block on a shaft line. Explain why some modern thrust blocks are fitted with circular pads. 8. (1v) Provide a distinction between hull equipment and deck machinery and give five examples of each type. 9. (1v) Briefly, but clearly describe the operating principle of rudder roll stabilization system and state which factors do influence the roll damping efficiency that can be achieved by this roll stabilization system. 10. (1v) The rules of the Classification Societies contain tables of required equipment, state which items onboard a typical merchant vessel are identified by, and sized in accordance with an Equipment Number (EN = 2/3 + 2 h 0 B + A/10) included in those tables. Also indicate the meaning of the variables on the right hand side of the EN formulation. Sketch a typical anchorhandling arrangement of a bulk-carrier. 11. (1v) One of the major concerns of pollution from ships is the discharge of oily water from the bilges of machinery spaces. State what are the major reasons why water with high concentration levels of hydrocarbons accumulates in the bilges of the machinery space. Describe the process to prevent discharge of oily water directly to the sea, and, if necessary, you may draw a sketch of the system configuration showing its major components onboard.

5 Annex A