Waterjet propulsion of small-draught inland waterways ships

Transcription

1 Waterjet proplsion of small-draght inland waterways ships Zygfryd Domachowski, Prof. Wiesław Próchnicki, Assoc. Prof., D.Sc. Gdańsk University of Technology ABSTRACT This paper presents some aspects of ship waterjet proplsion. Advantages and limitations of its applicability are discssed. Also, possible se of waterjet propeller to move a small-draght inland waterways ship, is considered. Keywords : ship proplsion, hydromechanics GENERAL CHARACTERISTICS OF SHIP WATERJET PROPULSION Waterjet proplsion of ship is based on application of rd principle of Newton s dynamics : If two bodies mtally interact, their interaction forces are eqal to each other and pointing in opposite directions. In the waterjet proplsion a crcial role is played by a pmp. Located nearby ship s stern, it takes in water throgh a recess in ship s bottom. From otlet of the pmp the water is directed nder high pressre to a nozzle placed in the ship s stern. The force pshing ot the water from the stern is eqal as to its vale to the force moving the ship in the opposite direction. As to rotate the nozzle is possible practically by an arbitrary angle the same ship proplsion force can be obtained at any arbitrary position of the nozzle. The ship proplsion force depends on water flow rate at the nozzle otlet. The pmp is driven throgh the shaft by a diesel engine (in most applications which have been realized so far) or a gas trbine. The waterjet proplsion may even be of a higher energy efficiency as compared with that of the conventional proplsion (screw propeller), however only in the case if the nozzle, pmp and driving engine are properly selected. The steering of waterjet-propelled ship (change of direction of its motion) is effected by an appropriate change of otlet nozzle position. Astern motion is ensred by application of a deflector with the se of which the change of sense of ship proplsion force can be obtained. In general, the waterjet proplsion is considered favorable at the ship speed exceeding knots. However, a correctly designed waterjet proplsion may be competitive against conventional one also at mch smaller speeds. The waterjet proplsion extends its application to the recreation ships and sea-going coastal ships of special se. As compared with conventional one the waterjet proplsion has many advantages which are discssed below. EXAMPLES OF WATERJET PROPULSION APPLICATIONS MADE SO FAR Attempts to apply waterjet proplsion to ships have appeared as early as in the ancient ages. * However the Hamilton s low-power waterjets (9) intended for proplsion of fast river boats can be considered as the first developed constrction. ** Nowadays many firms bild waterjets of a wide range otpt: from a few hndred kw to a few dozen MW. Rolls-Royce company, a leader of modern waterjet constrctions, offers complete proplsion systems for very fast ferry ships, cargo vessels, warships, crise ships and yachts. Up to now abot 00 assemblies of the otpt from.000 kw to kw have been bilt. And, a ship proplsion system of 0 MW otpt is nder development De to the advantages of waterjet proplsion, its application range has become wider and wider. The most important of them are : good manoevrability of ship, environmental safety, comfort for passengers. Ot of the ship waterjet proplsion applications made so far the following are worth mentioning : In the navy it serves for propelling the patrol crafts, torpedo boats, destroyers, frigates and crisers, first of all in USA, bt also in France, Italy, Norway, Astralia, Spain, Thailand, Canada, Japan, Repblic of Soth Africa and Germany In the passenger fleet it serves for propelling small inland waterways ships, fast yachts, recreation ships, inclding fishing ones In the merchant fleet it has so far had rather narrow application, first of all for propelling fast ferries. ADVANTAGES OF WATERJET PROPULSION The waterjet proplsion as far as its application to recreation passenger ships is concerned shows many important advantages. Safety In contrast to the screw propeller drive the waterjet proplsion is not endangered by floating solid fragments, ropes or fishing nets. In particlar, the waterjet proplsion correctly flfils its role in shallow waters (like in the considered case of its application to an inland waterways ship). Also, persons remaining in water : swimmers, water skiers, divers etc are not exposed to hazards from the side of sch device. Any overload of main engine is exclded as its power demand maintains constant regardless of developed ship speed. * Archimedes axial water pmp (7- AChN), Leonardo da Vinci pmp (-9), Toogwood s & Hayese s patent (), Beniamin Franklin s plsators (70-790). ** So-called First Hamiltonians. POLISH MARITIME RESEARCH, Special isse 00/S

2 Manoevrability Even at a low speed of motion the waterjet- propelled ships maintain excellent maneovrability de to possible setting an arbitrary spatial position of the otlet nozzle. Thrst force of an arbitrary vale and arbitrary direction can be applied to ship. It is especially sefl on narrow waterways (like in the considered case). In no circmstances any help from the side of any other floating nit is necessary. Even in rogh weather conditions (strong wind, high waves) ship motion control is possible. Energy efficiency The waterjet proplsion correctly adjsted to the driving engine and ship hll, makes engine work at optimm settings possible, i.e. when the specific fel oil consmption is the lowest. It concerns all its operational phases : moving, starting, stopping and standing-by. Moreover, maintenance cost of sch installation are low; it means that operational costs of sch proplsion system are low. Travelling comfort of passengers As compared with the screw propeller drive the waterjet proplsion ensres lower noise and vibration level on board of ship. In particlar, no cavitation noise from the side of screw propeller is emitted. Screw propellers being of a lower rotational speed than that of rotating elements of waterjet proplsion system, are more bothersome. Pmps are placed in properly inslated casings. Refloating the gronded ship Motion of an inland waterways ship in shallow waters is considered. In the case of gronding the waterjet-propelled ship is able to refloat withot any help bt only by sing its reverse proplsion which can develop a high thrst vale. On standing-by ship or dring manoevres waterjet thrst reaches its maximm vale expressed by the formla : F max = m ( w ) = 0 = m w () m water mass flow rate of waterjet [kg/s] w ot- of- the- nozzle flow velocity ship speed. In the rated working point of waterjet the following relation is satisfied : nom w nom = () ( w ) nom F ( ) w nom hence : max () w 7 F nom ( ) nom It means that on the standing-by ship a proplsion force several times greater than that nominal can be achieved. It is a greatly favorable featre of sch proplsion system as in the case of ship gronding it enables to case an effective motion of ship hll, navailable by means of any other proplsion system. Impact on the environment The waterjet propelled ships generate mch lower waterborne distrbances (noise) as compared with the screw-propelled ones. It is specially important for the water natral environment becase of mch lower hazard to flora and fana. At a properly designed inlet to diffser (based on model test reslts) can be obtained laminar inflow, lack of flow separation and trblence (Fig.). This way only small losses at inlet to diffser are prodced. The following relation is flfilled with a good accracy : w () ship speed w water velocity at inlet to diffser. Frthermore the vertical component velocity of the water flowing into the diffser (Fig. ) : w H = w sinα = tgα () decides on the force imposed on the waterway bed (scoring force); in the case of shallow water it is of a very small vale and amonts to abot 0% of the water inflow velocity w. Therefore it can be stated that erosion impact of waterjet propeller on the bed of shallow water is not greater than that of conventional screw propellers. Fig.. Laminar water flow into diffser. Simplicity of constrction The waterjet propeller is characterized by a high simplicity of constrction. It consists of a flow passage (diffser and confsor), rotary pmp (diagonal, helicoidal or impeller one) and a deflector which makes flow reversing and ship rotating possible. Sch propellers are prodced as complete nits by sch firms as Hamilton Waterjet, Castoldijet, Ka-Me-Wa, Lips, Grapner etc. To drive the waterjet propeller rotary pmp a diesel engine or gas trbine is sed. In Fig. the ship fitted with the waterjet propeller of Ka-Me-Wa, driven by the Rolls-Royce gas trbine, is presented. Owing to the above mentioned advantages the waterjet proplsion constittes an alternative for the screw propeller drive in some, bt not all, applications. It may only spplement bt not POLISH MARITIME RESEARCH, Special isse 00/S 7

3 sbstitte the crew propeller drive. As sally the proper way is to choose one of the two kinds of ship proplsion system by selecting that sitable for a given ship s type and fnction. Fig.. The waterjet propeller driven by the gas trbine LIMITATIONS IN APPLICATION OF WATERJET PROPELLER An important design problem of waterjet propeller is strong dependence of the nozzle otlet area A on the ship speed. N A = () w z ( ) N proplsion power = w velocity index ρ w water density z nmber of otlet nozzles. At given vales of N and the decreasing of the velocity by 0% makes the otlet nozzle area A increasing by 7%; at 0% decrease of the otlet nozzle area increases almost twofold, and the velocity decrease by 0% reslts in the otlet nozzle area A almost three times greater. Taking into consideration the relationship : N = α (7) α coefficient of ship resistance power, one can obtain the following area of a single nozzle : ( ) A = w z The ship resistance power coefficient α is defined as a fnction of the ship mass displacement D w (expressed in tons) and the Admiralty coefficient C 0 : kw D w K M.0 (9) m s C0 knot In Fig. the A - α relationship is presented for the selected vales of the velocity index = 0.; 0.7; 0. and 0.9, and the assmed nmber of otlet nozzles z =. And, as shown in Fig. the smaller ship speed the greater hydralic losses. The coefficient of total hydralic losses has been defined as follows [0] : h N L + N H (0) i = i= m N L power of hydralic losses in flow passage of waterjet propeller () N H power of elevating the water stream which flows ot of the nozzle, p to the level H (H is the height of nozzle axis over the water level). Hence it can be stated that the waterjet propeller is well adjsted to propelling fast ships A [m ] [ kw m /s Fig.. The otlet area of two-nozzle waterjet propeller, A, in fnction of the ship resistance power coefficient α and the velocity index i i = 0. H = 0 0. Fig.. Diagram of total energy losses in flow passage of waterjet propeller. SPECIFIC REQUIREMENTS FOR WATERJET PROPULSION OF SMALL-DRAUGHT INLAND WATERWAYS SHIPS The proplsion system of the two-segment recreation passenger ship intended for inland waterways service, is here considered. Sch application reqires to take into accont a few specific conditions. The following belong to them : 0.7 = w = 0. = [ [m./s] POLISH MARITIME RESEARCH, Special isse 00/S

4 limited width of waterway (limited width of locks) limited depth of waterway (a small draght of ship is demanded) possible events of ship gronding on shallows environmental protection reqirements ensring a necessary travelling comfort for passengers limited ship speed. Possible application of waterjet proplsion shold be analyzed with taking into accont a.o. the above mentioned aspects : As far as the aspect of limited waterway width is concerned, the waterjet proplsion makes it possible to precisely control ship motion at an arbitrary speed. Ship steering at a very low speed ( zero speed ) facilitates berthing the ship as well as keeping it stopped short. The waterjet proplsion ensres also precise steering the ship dring its moving astern. In the waterjet proplsion there are no elements protrding below the hll bottom. This way, ship sailing in very shallow waters is possible. Water-otlet area and ship s bottom srface are matched p. Nozzle s otlet can be located over water level. The more shallow water the lower efficiency of ship screw propeller. It does not concern the waterjet propeller. If waterjet-propelled ship gronds its refloating is facilitated by two circmstances : firstly, sch ships sally have no elements protrding below hll bottom srface, secondly, waterjet proplsion ensres large vale of thrst in moving astern. It is also important that in those conditions to case a failre to waterjet propeller by carried - away sand and gravel is mch less probable as compared with the case of screw propeller. Waterjet- propelled ships are mch less hazardos to the environment than screw-propelled ones. It concerns possible mechanical failres of living organisms (fana and flora), as well as waterborne noise. Passengers onboard waterjet- propelled ship enjoy a higher travelling comfort as compared with that on screw-propelled ship. As thrst force is directly transferred from waterjet propeller to hll, withot help of any shafting and screw propellers the engine and pmp can be seated on an elastic fondation, that redces hll vibrations generated by proplsion system. There are neither hll vibrations de to transmission shafting and screw propellers nor cavitation noise effected from the side of screw propellers. In waterjet proplsion system, engine shaft s rotational speed is mch greater than that in screw propeller drive system. Moreover the whole proplsion system is secred by a tight casing to lower effects of noise emitted to environment. As assessed, the waterjet proplsion system is most efficient at ship s operational speed in the range from 0 to 0 knots. And, at a given ship speed the screw-propeller drive system is a little more efficient than the waterjet proplsion. However the difference is balanced by a little higher ship hll efficiency (de to a lower hll resistance to motion), reslting from lack of screw propellers, shafts, rdders and shaft brackets located otside the hll. As a matter of fact the inflence of the above mentioned elements on hll resistance to motion decreases along with ship speed decreasing. Application of waterjet proplsion to large fast floating nits is wider and wider. And, to decrease ship resistance to motion special hll forms are applied sch as : catamarans, slender hlls (of a large L/B ratio) fitted with side sponsons to improve ship s stability. Worth mentioning, the waterjet proplsion makes it possible to flly make se of driving power at any ship speed vale, a very small too. SPECIFIC FEATURES OF SHIP WATERJET PROPULSION Application of high-speed diesel engine or gas trbine as a waterjet driving motor reqires a transmission gear to be installed between the engine and pmp. Choice of a waterjet propeller depends a.o. on ship s hll form, on one side, and on the other side, in designing the ship hll form the specificity of sch kind of proplsion shold be taken into accont. In selecting the waterjet proplsion an important role is played by the ratio of proplsion power to weight of power plant. A driving engine and propeller itself shold be so selected for a given ship speed as to eliminate phenomenon of cavitation. As ship proplsion thrst force does not affect the driving engine (throgh shafting and transmission gear) the shaftline can be inclined by a small angle to make alignment of shaft and waterjet propeller, easier. The maximm vales of shaft slope angle depend on shaft s rotational speed and are eqal from abot at 000 rpm to abot at 000 rpm. The nderwater exhast gas pipe has not to be located before the water inlet to propeller so as to avoid gas scking -in to the pmp, which cold reslt in lowering the proplsion thrst force. It shold be placed aft the water inlet. The fel oil tank shold be placed in longitdinal position close to ship s centre of gravity so as to avoid ship s trim distrbing as a reslt of fel consmption or refelling operations. The driving engine and electric generator (if a shaft generator is provided for) shold be placed close to ship s centre of gravity. For this reason they shold be installed, if possible, on gides to facilitate ship balance correction after trials. In ship design calclations an additional weight of the water contained in the propeller shold be taken into accont. Application of gas trbine to waterjet proplsion for small- -draght inland waterways ship The otpt power of waterjet propellers is contained in the range of kw. Like in the ship screw- propeller proplsion, also in the waterjet proplsion the application of high-speed diesel engines prevails. Gas trbines are also sed however their share is lower. Gas trbines in a simple arrangement are of a lower thermodynamic efficiency as compared with that of piston engines (in some cases regeneration is applied to improve the efficiency of gas trbines). Whereas it seems that other featres of gas trbine cold prevail in the considered application of waterjet proplsion to the passenger inland waterways ship in qestion. In the above mentioned application the following featres of gas trbine shold be considered favorable : low slphr content in exhast gas (exhast gas cleaning devices - nnecessary) low level of bending and torsional vibrations and noise (passenger cabins can be located close to propeller) low cost of maintenance, overhals and lbricating oil high serviceability (high reliability, and possible fast repair or replacement of engine) small dimensions. The featres predestine gas trbine for propelling the passenger inland waterways ship in qestion. Therefore in the POLISH MARITIME RESEARCH, Special isse 00/S 9

5 preliminary concept of waterjet proplsion system for the ship a gas trbine was chosen to drive the pmp, an element of the waterjet propeller. SUGGESTIONS AS TO POSSIBLE APPLICATION OF WATERJET PROPELLER TO MOVE THE PASSENGER SHIP INTENDED FOR BERLIN KALININGRAD ROUTE a waterjet propeller, selected ot of the nits available on the market (prodced e.g. by Castoldijet or Hamilton Waterjet), shold be adjsted to the assmed nominal velocity =, m/s, by matching - p its nozzle otlet area to the reqired A vale and otpt power if to apply instead of the proposed gas trbine a diesel engine, to obtain total efficiency more than two times greater will be possible. Similarly, if to assme that the centre of otlet nozzle is not placed over water level, i.e. H = 0, the total efficiency will increase by ~% in Fig. and, on the basis of Casteldijet s offer drawings, are presented the gas- trbine-driven proplsion devices arranged in ship s engine room. Fig.. Arrangement of the waterjet propeller in ship engine room side view. FINAL REMARKS Smming p, the following aspects of the ship waterjet proplsion system are worth attention paying : The waterjet proplsion system is of important advantages as compared with the conventional screw - propeller proplsion system : Lack of any movable elements behind the hll Mch lower hll-propeller interaction reslting in the hll efficiency increase by 9% Favorable energy indices at partial load Lower torsional vibrations Easy exection of trns and astern moving Possible elimination of need of blade rdder (which reslts in lowering hll resistance to motion). Losses in flow passage are inversely proportional to and monotonically increasing along with the ship speed increasing (Fig.). The losses depend only slightly on the velocity index. Moreover they depend on smoothness of flow passage, hence its high smoothness shold be ensred. Large dimensions of flow passage constitte an important design problem of waterjet proplsion. The circlar cross- -section area of its otlet, A, is proportional according to some expression as follows : ( A ) α acc. () coefficient of hll resistance to motion the expression proportionally associated with the efficiency : i.e. the greater the assmed efficiency the greater the reqired dimensions of otlet nozzle (and flow passage). Reliable performance of waterjet propeller is ensred by : protection of its pmp and flow passage against hard solid fragments, better control of trning and astern moving, modernization of load - carrying bearing installed inside the pmp, e.g. by applying a bearing fitted with water- -lbricated ceramic sleeves. The small-draght inland waterways ship in qestion has to operate with a low speed. It affects its proplsion efficiency. The ship is slender - hence its flow passage dimensions are restricted, which as a reslt limits waterjet proplsion efficiency. NOMENCLATURE Fig.. Arrangement of the waterjet propeller in ship engine room downward view. A cross-section area of otlet nozzle [m ] F thrst force [N] m rate of water mass flow throgh propeller [kg/s] ship speed [m/s] w, w, w H water velocity of inflow to diffser, otflow from confsor, and vertical component of velocity of water inflow to propeller, respectively [m/s] propeller velocity index [ ] α coefficient of ship hll resistance power [kw/(m/s) ] ρ w water density [kg/m ] ζ i dimensionless coefficient of hydralic losses and those for water stream elevation [ ]. 70 POLISH MARITIME RESEARCH, Special isse 00/S

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