St. Petersburg State Marine Technical University
Department of Power Energy Installations, Systems and Equipment
Course project
Marine hydraulic machines
Completed:
student of group 2331
Mazilevsky I.I.
Checked:
Grishin B.V.
Saint Petersburg
Introduction 3 pages
1 Calculation of a working centrifugal pump with cylindrical blades according to the jet
theories 3 pages
1.1 Initial data 3 pages.
1.2 Determination of impeller parameters 3 pages.
1.3 Calculation of the main dimensions of the impeller inlet 4 pages.
1.4 Calculation of the main dimensions of the impeller outlet 6 pages.
1.5 Calculation and construction of the meridian section of the wheel 8 pages.
1.6 Calculation and construction of a cylindrical impeller blade in plan 9 p.
1.7 Test calculation for cavitation 12 pages.
Introduction
Centrifugal pumps constitute a very broad class of pumps. Pumping liquid or creating pressure is carried out in centrifugal pumps by rotating one or more impellers. The large number of different types of centrifugal pumps manufactured for various purposes can be reduced to a small number of their main types, the difference in the design development of which is dictated mainly by the characteristics of the use of the pumps. As a result of the action of the impeller, the liquid leaves it at a higher pressure and higher speed than at the entrance. The output speed is converted into pressure in the centrifugal pump housing before the fluid exits the pump. The conversion of the velocity pressure into a piezometric pressure is partially carried out in a spiral outlet or guide vane. Despite the fact that the liquid flows from the wheel into the spiral outlet channel with gradually increasing cross-sections, the conversion of the velocity pressure into the piezometric pressure is carried out mainly in the conical pressure pipe. If the fluid from the wheel enters the channels of the guide vane, then most of this transformation occurs in these channels. The guide vane was introduced into the pump design based on the experience of hydraulic turbines, where the presence of a guide vane is mandatory. Early pump designs with a guide vane were called turbopumps.
The most common type of centrifugal pump is a single-stage centrifugal pump with a horizontal shaft and a single-entry impeller.
1 Calculation of a working centrifugal pump with cylindrical blades using jet theory
1.1 Initial data
Feed……………………………………………………….….Q=0.03/0.06 m/sec
Pressure……………………………………………………….…...H=650/1300 J/kg
Pressure in the air extractor…………………………….…...P=1*10 Pa
Suction height………………………..……………….…...h sun = -3 m
Liquid temperature……………………………………………………t=15 o C
Resistance of the receiving pipeline………………...….= 5 J/kg
1.2 Determination of impeller parameters
In a multistage pump, the wheel parameters are determined as follows:
Wheel feed: Q=Q, where Q=0.03m/sec
Wheel pressure: H*i=H, where H=650 J/kg, i=1
All pump wheels are mounted on the same shaft and rotate at the same frequency. The maximum rotation speed is limited by the possibility of cavitation occurring in the pump. The maximum rotation speed is determined as follows:
g=9.81m/s - acceleration due to gravity.
P=1*100000 Pa - inlet pressure.
P=1703 Pa-vaporization pressure at a given temperature.
p = 998.957 kg/m - density of water.
A=1.05….1.3 is the safety factor. Let's take 1.134
h=5 J/kg - hydraulic losses in the receiving water supply.
Let's substitute the values into the equation for and then into H:
1/1.2*((100000-1703)/ 998.957-9.81*(-3)-5)= 108.354 J/kg
H =1/9.81*((10 5 -1703)/ 998.957-1.134*108.354-5)) = -3.000m
Taking the value of the cavitation speed coefficient C = 800, we find the maximum rotation speed:
800*(108.354)/31.15*0.03=4979.707 rpm.
We accept n=2930 rpm
To find we use the formula:
Speed factor for pressure fire pump (50….100)
2930*0,03*20,25/650=79,830
The calculated wheel feed is determined by the equation:
0.03/0.915=0.032 m/sec
Note: Volumetric efficiency value , taking into account fluid leakage through the front wheel seal:
Then volumetric efficiency:
=-(0,03…0,05)= 0,965 -0,05=0,915.
The theoretical wheel pressure is determined by the equation:
The value of hydraulic efficiency can be estimated using A.A. Lomakin’s formula:
Note: The reduced diameter of the wheel entrance is determined by the similarity equation:
3.6…6.5 - selected depending on the cavitation qualities of the wheel; let's choose:
Thus:
650/0.864=752.299J/kg
Mechanical efficiency determined by the equation:
Efficiency factor, which takes into account energy losses due to friction of the outer surface of the wheel on the liquid (disk friction), is determined by the equation:
1/(1+820/)=0,8860;
Efficiency factor, a coefficient that takes into account energy losses due to friction in the bearings and seals of the pump, lies in the range = 0.95…..0.98. Let's choose =0.96
0,96*0,8860=0,8506;
Efficiency pump is determined through its components:
Pump power consumption:
Electric motor: N= 30 kW n=2930 model: A02-72-2M, then
2930*0,03=79,830
1.3 Calculation of the main dimensions of the impeller inlet:
The dimensions of the impeller inlet are calculated based on the condition of ensuring the required cavitation qualities of the wheel and minimal hydraulic losses.
The value of the speed from the flow entry into the wheel is estimated using the formula of S.S. Rudnev:
Note: - is accepted depending on the required cavitation qualities of the wheel and lies in the range of 0.03..0.09, let’s choose 0.040
The shaft is calculated for torsional and bending strength and the rigidity and critical rotation speed are checked. As a first approximation, the diameter of the impeller shaft is calculated based on torsion using the formula:
Torque applied to the shaft;
The amount of torque is determined by the formula:
9.57*N/n=97.9863N*m;
Allowable voltage
=(300-500)*100000 N*m; thus, choose =400*10 5
=(16*97.9863/3.14/400/100000)= 0.02319m
0.031+0.013=0.03619m;
The diameter of the wheel hub is determined structurally by the diameter of the shaft, depending on the method of fastening the wheel to the shaft:
The diameter D o of the entrance to the wheel is found from the continuity equation:
(4*0.0328/(3.14*2.6218)+ 0.05067 2) 1/2 =0.1360m;
The width b 1 of the trailing edge of the impeller blade and its position depend on the cavitation qualities of the wheel and the value of the speed coefficient; b 1 are found from the continuity equation:
The meridian component of absolute speed takes for wheels with average cavitation qualities:
=(0.8…1.0)*=1*=2.622m/s
Wheels with average cavitation qualities (C=800) and low speed
(=40-100), made with cylindrical blades. The diameter of the circle passing through the midpoints of the outlet edges of the blades is equal to:
=(0.9-1.0)*=0.95*0.131=0.1292m;
/2=0.0646m, then:
0.0328/2/0.0646/3.14/2.622=0.0308m.
The trailing edge of the blade is located parallel to the wheel axis or at an angle of 15-30 degrees to the axis. The meridian component of the absolute velocity after the flow enters the inter-blade channel (i.e., taking into account the constraint) is determined by the equation:
1.015*5.234=5.312 m/s, where:
1.05-1.015-input constraint coefficient, choose =1.1;
The peripheral speed at the entrance to the inter-blade channel is determined by the equation:
0.0646*306.67333 =19.811m/s
Angular velocity
3.14*2930/30=306.673rad/s;
The angle of shockless flow entering the blades is found from the equation:
The angle of installation of the blade at the inlet is determined from the formula:
8.282+10=18.282 o;
Note: For wheels with average cavitation properties the following is accepted:
1 - angle of attack; let's choose 10
Usually =18-2;
In a continuous flow around a blade, the flow moves tangentially to the surface of the blade. The relative flow velocity after entering the blade is directed tangentially to the centerline of the blade profile at entry. The relative speed is determined by the equation:
Based on the velocities, velocity triangles are constructed at the entrance to the inter-blade channels of the impeller and the velocities are determined. (Fig. 1)
Figure 1 Velocity triangle at the entrance to the pump impeller
1.4 Calculation of the main dimensions of the impeller outlet:
The outlet dimensions of the impeller, the main ones of which are the outer diameter of the impeller, and the width of the blade at the outlet are determined from the condition of the required pressure at a sufficiently high efficiency.
The outer diameter of the impeller is found by successive approximations. To a first approximation, it is determined by the peripheral speed found from the basic equation of blade machines:
Let's use the experimental speed ratio:
0.5..0.65; Let's take =0.6;
Hence or both:
=(752.299/0.6) 0.5 =35.409m/s;
We determine the outer diameter of the impeller as a first approximation:
From the velocity triangles at the inlet and outlet of the inter-blade channels it follows:
The constraint coefficient at the entrance to the wheel is taken to be 1.0..1.05. To reduce hydraulic losses in the pump, they tend to smoothly sharpen the trailing edge of the blade, i.e. =1.0. To increase the strength of the blade, it can be made of finite thickness, i.e. c - meridian component of absolute speed, selected within the range (0.7...1.15)* for wheels with average cavitation qualities = 1.0;
LEGEND
VL - waterline
CVS - adjustable pitch propeller
VFS - fixed pitch propeller
GVL - load waterline
GNU - gas heating unit
Main switchboard - main distribution board
GTZA - main turbo gear unit
GTU - gas turbine unit
DAU - remote automated control
ICE - internal combustion engine
DG - diesel generator
DP - center plane
DU - diesel unit; remote control
ZX - reverse
KO - boiler department
KPU - command control post
MISH - pitch change mechanism
MO - engine room
MKO - machine and boiler room
OL - main line
OP - main plane
PPU - steam generating unit
PU - control station; thruster
PH - forward movement
SPGG - free-piston gas generator
HPT - high pressure turbine
TVDZH - reverse high-pressure turbine
TVDPH - forward high-pressure turbine
TG - turbogenerator
TZD - reverse turbine
LPT - low pressure turbine
TNDZH - reverse low pressure turbine
TSD - medium pressure turbine
TSDPH - forward moving medium pressure turbine
CPU - central control station
NEU - nuclear power plant
V. m.t. - top dead center
n. m.t. - bottom dead center
B - theoretical width of the vessel
Dy - nominal diameter
F - freeboard height
H - practical side height
L - practical length of the vessel
Lib - maximum length of the vessel
Ru - conditional pressure
T - full draft of the vessel
Tk - draft of the vessel by the stern
Tpr - practical draft of the vessel
00 - plane of the mid-frame
INTRODUCTION
Directives of the XXIV Congress of the CPSU on the five-year plan for 1971-1975. a further increase in maritime transport cargo turnover is envisaged (1.4 times) and the replenishment of the transport fleet with highly economical universal and specialized vessels with comprehensive automation of control of ship mechanisms and systems. At the same time, shipbuilders are faced with a number of tasks to improve the quality of products, reduce their costs, increase labor productivity based on comprehensive mechanization and automation of production, modernize outdated equipment and introduce advanced technological processes. Only competent, highly qualified shipbuilders capable of using the latest achievements of science and technology in the construction of ships can complete the assigned tasks.
All work on the construction of a vessel can be divided into hull-procurement, hull-assembly-welding, plumbing and installation, outfitting and finishing work and mooring, running and acceptance tests of the vessel. With modern methods of building ships, these types of work are closely intertwined. For example, plumbing and installation work begins and is carried out in parallel with hull assembly work until launching, and then continues afloat simultaneously with outfitting and finishing work. An approximate order of installation work during the construction of a serial tanker with a displacement of 16,000 tons is presented in the graph. This order of work can significantly increase the readiness of vessels for launching. The above graph also shows how varied and time-consuming plumbing and installation work is.
Plumbing and installation work includes not only the preparation of foundations for installation, installation of various machines and mechanisms on them with subsequent testing of them in operation, but also various plumbing and mechanical work on the manufacture of individual parts of a ship's machinery installation, shafting, pipelines and devices.
| Name of works | Months | ||||||||||||||
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | |
| Treatment of foundations for the main unit | + | + | |||||||||||||
| Boring of the sternpost, installation of the propeller shaft and preliminary installation of the main unit | + | + | + | ||||||||||||
| Final installation of the main unit and shafting | + | + | |||||||||||||
| Installation of auxiliary mechanisms of machine and boiler rooms | + | + | |||||||||||||
| Installation and installation of mechanisms throughout the vessel | + | + | + | + | + | ||||||||||
| Installation of steering and anchor devices | + | + | |||||||||||||
| Installation of cargo mechanisms and devices | + | + | |||||||||||||
| Manufacturing of pipes in the workshop according to drawings and technological sketches | + | + | + | + | + | + | |||||||||
| Installation of pipelines in the stern of the vessel | + | + | + | + | |||||||||||
| Installation of pipelines in the bow of the vessel | + | + | + | + | |||||||||||
| Hydraulic testing of pipelines and systems | + | + | |||||||||||||
| Preparation for mooring tests | + | + | |||||||||||||
| Mooring tests | + | ||||||||||||||
| Sea trials and control output | + | + | |||||||||||||
The ship's fitter must have a good knowledge of the ship, the location of its premises, holds, compartments, main and auxiliary mechanisms, and be able to read installation drawings and diagrams; know the design and purpose of the machines and mechanisms he installs, have an idea of their relationship with other mechanisms, devices and pipelines. When performing installation work, he must strictly observe the necessary tolerances and clearances in the mating parts of units and mechanisms. Must be able to maintain auxiliary mechanisms and adjust them in different modes of work performed during the mooring, running and commissioning tests of ships. Due to the saturation of modern ships with various electronic and automatic devices, he must know the purpose of these devices, their principle of operation. Finally, the ship's fitter must have a thorough knowledge of advanced fitting and installation technology and skillfully apply it in order to perform high-quality work within the time frames stipulated by the ship's construction and installation schedules.
Maybe, first ship engine appeared like this. Our distant ancestor, sitting on a log that had fallen into a water stream, decided to cross to the other side of the river. Scooping water with his palms, like oars, he combined both the first mover - into one “human” force - and the first mover, which were his hands. But gradually people, having studied the laws of nature, put them to their service. Wind, water and, finally, steam partially replaced muscle strength. The oars were replaced by a sail, and the sails began to be replaced by a machine.
The idea to create steam engine originated more than 2000 years ago. The Greek scientist Heron, who lived in Alexandria, designed the original steam engine. Much later, the English mechanic James Watt created a steam engine, which was destined to become the first ship power plant.
August 11, 1807 is considered to be the birthday of the steam ship. On this day, a test of a steamship built by the talented American engineer Robert Fulton took place. Steamboat« Claremont» launched regular service on the Hudson River between New York and Albany. In 1838 the British steamship« Great Eastern"Crossed the Atlantic without raising sails, although it was rigged. The growth of industry required ships and vessels, which could, regardless of the will of the elements, make regular flights across the Atlantic and Pacific oceans. In the 19th century, the size of steam ships increased sharply, and with them the power of steam engines. By the 90s, their power was increased to 9,000 horsepower.
Gradually, steam engines became more powerful and reliable. The first ship power plants consisted of a piston steam engine and large, low-power boilers heated by coal.
One hundred years later coefficient of performance (efficiency) steam power plant was already 30 percent, and developed power up to 14,720 kW, and the number of service personnel was reduced to 15 people. But the low productivity of steam boilers required an increase in their number.
At the turn of two centuries, steam engines were mainly equipped passenger ships And cargo and passenger ships, there were only pure cargo ships sailboats. This was due to imperfection and low efficiency steam power plant that time.
The use of water-tube boilers, which appeared in the 1880s and now operate on liquid fuel, improved the efficiency of steam power plants. But their efficiency reached only 15 percent, which explains the cessation of the construction of steamships. But nowadays you can still find ships driven by piston steam engines. river steamer« American Queen».
piston steam engine
On ships power plants With steam engines, water vapor is used as the working fluid. Since fresh water can only be carried in limited quantities on ships, in this case a closed water and steam circulation system is used. Of course, during the operation of the power plant, certain losses of steam or water occur, but they are insignificant and are compensated by water from the tank or evaporators.
Working steam is supplied to the steam cylinder through steam pistons. It expands, puts pressure on the piston and causes it to slide down. When the piston reaches its lowest point, the steam distribution spool changes its position. Fresh steam is supplied under the piston, while the steam that previously filled the cylinder is displaced.
The piston now moves in the opposite direction. Thus, the piston makes up and down movements during operation, which, with the help of a crank mechanism consisting of a rod, a slider and a connecting rod connected to the crankshaft, are converted into rotational movements of the crankshaft. The inlet and outlet of fresh and exhaust steam is controlled by a valve. The valve is driven from the crankshaft by means of two eccentrics, which are connected to the spool rod through rods and a connecting rod.
Moving the connecting rod using the transfer lever causes a change in the amount of steam that fills the cylinder during one lift of the piston, and therefore the power and rotation speed of the machine change. When the connecting rod is in the middle position, steam no longer enters the cylinder, and the steam engine stops moving. By further moving the connecting rod using the shift lever, the machine is again set in motion, this time in the opposite direction. This causes the reverse movement of the ship mover.
The first ship propulsion systems used piston steam engines, in which expansion from inlet to outlet pressure to condenser pressure occurred in a single cylinder. The operating principle of a piston steam engine is shown in Figure 2. Over time, multi-stage expansion machines began to be used. The operating principle of the three-stage expansion machine is shown schematically in Figure 3.
piston steam engine
triple expansion piston steam engine
Maybe, first ship engine appeared like this. Our distant ancestor, sitting on a log that had fallen into a water stream, decided to cross to the other side of the river. Scooping water with his palms, like oars, he combined both the first mover - into one “human” force - and the first mover, which were his hands. But gradually people, having studied the laws of nature, put them to their service. Wind, water and, finally, steam partially replaced muscle strength. The oars were replaced by a sail, and the sails began to be replaced by a machine.
The idea to create steam engine originated more than 2000 years ago. The Greek scientist Heron, who lived in Alexandria, designed the original steam engine. Much later, the English mechanic James Watt created a steam engine, which was destined to become the first ship power plant.
August 11, 1807 is considered to be the birthday of the steam ship. On this day, a test of a steamship built by the talented American engineer Robert Fulton took place. Steamboat« Claremont» launched regular service on the Hudson River between New York and Albany. In 1838 the British steamship"" crossed the Atlantic without raising sails, although it was rigged. The growth of industry demanded that, regardless of the will of the elements, they could make regular flights across the Atlantic and Pacific oceans. In the 19th century, the size of steam ships increased sharply, and with them the power of steam engines. By the 90s, their power was increased to 9,000 horsepower.
Gradually, steam engines became more powerful and reliable. The first ship power plants consisted of a piston steam engine and large, low-power boilers heated by coal.
One hundred years later coefficient of performance (efficiency) steam power plant was already 30 percent, and developed power up to 14,720 kW, and the number of service personnel was reduced to 15 people. But the low productivity of steam boilers required an increase in their number.
At the turn of two centuries, steam engines were mainly equipped passenger ships And cargo and passenger ships, there were only pure cargo ships. This was due to imperfection and low efficiency steam power plant that time.
The use of water-tube boilers, which appeared in the 1880s and now operate on liquid fuel, improved the efficiency of steam power plants. But their efficiency reached only 15 percent, which explains the cessation of the construction of steamships. But nowadays you can still find ships driven by piston steam engines. river steamer« ».
piston steam engine
On ships power plants With steam engines, water vapor is used as the working fluid. Since fresh water can only be carried in limited quantities on ships, in this case a closed water and steam circulation system is used. Of course, during the operation of the power plant, certain losses of steam or water occur, but they are insignificant and are compensated by water from the tank or evaporators. A simplified diagram of such circulation is given in Figure 1.
principle of operation of a steam installation
Working steam is supplied to the steam cylinder through steam pistons. It expands, puts pressure on the piston and causes it to slide down. When the piston reaches its lowest point, the steam distribution spool changes its position. Fresh steam is supplied under the piston, while the steam that previously filled the cylinder is displaced.
The piston now moves in the opposite direction. Thus, the piston makes up and down movements during operation, which, with the help of a crank mechanism consisting of a rod, a slider and a connecting rod connected to the crankshaft, are converted into rotational movements of the crankshaft. The inlet and outlet of fresh and exhaust steam is controlled by a valve. The valve is driven from the crankshaft by means of two eccentrics, which are connected to the spool rod through rods and a connecting rod.
Moving the connecting rod using the transfer lever causes a change in the amount of steam that fills the cylinder during one lift of the piston, and therefore the power and rotation speed of the machine change. When the connecting rod is in the middle position, steam no longer enters the cylinder, and the steam engine stops moving. By further moving the connecting rod using the shift lever, the machine is again set in motion, this time in the opposite direction. This causes the reverse movement of the ship.
The first ship propulsion systems used piston steam engines, in which expansion from inlet to outlet pressure to condenser pressure occurred in a single cylinder. The operating principle of a piston steam engine is shown in Figure 2. Over time, multi-stage expansion machines began to be used. The operating principle of the three-stage expansion machine is shown schematically in Figure 3.
piston steam engine
triple expansion piston steam engine
In 1838, residents of St. Petersburg could watch a small boat moving along the Neva without sails, oars or pipes. This was the world's first electric ship, built by academician B. S. Jacobi. The ship's motors consumed energy from batteries. The scientist’s invention was almost a century ahead of world shipbuilding science. But practical application on courts This engine was used only on submarines for submerged movement. To the disadvantages electric ships relate relative difficulty power plant.
ship "Turbinia"
The use of a turbine as a main engine has found its way into ship entitled " Turbinia» with a displacement of 45 tons, which was launched in England by designer Charles Parsons.
Multistage steam turbine plant consisted of steam boilers and three turbines directly connected to the propeller shaft. Each propeller shaft had three propellers (tandem system). The total power of the turbines was 2000 hp. With. at 200 rpm. In 1896, during sea trials vessel« Turbinia"developed a speed of 34.5 knots.
Military sailors appreciated the emergence of a new power plant. The turbine began to be installed on and, and over time it became main engine almost all passenger ships.
In the middle of the 20th century, competition began between steam turbine and diesel engines. power plants for their use on large vessels for transporting bulk cargo, including tankers. Initially, steam turbine power plants predominated on ships with a deadweight of up to 40,000 tons, but the rapid development of internal combustion engines has led to the fact that some ships and vessels with a deadweight of more than 100,000 tons are now equipped with diesel power plants. Steam turbine installations have been preserved even on large warships, as well as on high-speed and large container ships, when the power of the main engine is 40,000 hp. With. and more.
steam turbine with a capacity of 20,000 hp. With.
Steam turbine refers to power plants in which the thermal energy of the supplied steam is initially converted into kinetic energy, and only after that is used for work.
Steam turbines are hydraulic heat engines that, unlike piston steam engines and piston internal combustion engines, do not need to convert the reciprocating motion of the piston into the rotational motion of a propeller. Due to this, the design is simplified and many technical problems are solved. In addition, steam turbines, even with very high power, are relatively small in size, since the rotor speed is quite high and, depending on the type and purpose of the turbine, ranges from 3000 to 8000 rpm.
The use of kinetic energy to perform mechanical work occurs as follows. The steam escaping from the expansion devices hits the concave profiles of the blades, deviates from them, changes its direction and thereby exerts a tangential force on the rotor. As a result, a torque is created that causes the turbine rotor to rotate.
Modern ship steam turbines power plant usually consist of two buildings. One housing contains a high-pressure turbine rotor, and the other contains a low-pressure turbine rotor. Each turbine consists of several stages, which, depending on the type of turbine, are designated as pressure stages or speed stages. The working steam sequentially passes through the fixed rims of the expansion devices and the rims of the working blades. Since the volume of steam constantly increases during the expansion process, the rotor blades must be longer as the pressure drops.
In the housing of the low-pressure turbine there are special rims of the working blades of the reverse turbine. Turbines main power plant on ships whose propellers have variable pitch, they do not need reverse turbines. Along with the main turbines power plant auxiliary turbines are installed in the engine rooms of ships, which are used to drive generators, pumps, fans, etc. Operating principle of the stage steam turbine shown on Figure 4.
ship steam turbine
In the commercial fleet steam turbine received recognition only after its application on, " Mauritania" And " » built in 1907. These ships easily reached a speed of 26 knots. Atlantic Blue Ribbon - " Mauritania"retained it for 20 years.
Power plant, consisting of a steam boiler, turbine, generator and electric motor, were equipped with turbo-electric ships. They are widely used in the USA. Over time, heavy electric generators and electric motors were gradually replaced by gearboxes.
The construction aroused considerable interest turboelectric ship« Canberra" Weight indicators did not stop the designers. It has been calculated that with powers ranging from 75,000 to 100,000 hp. With. energy losses when using alternating current are comparable to losses in the gearbox and hydraulic transmission, and the elimination of reverse stages even increased the economic performance of the power plant. Usually, turboelectric ships Only large ships are considered, most often passenger ships.
At lower powers, it is more advisable to use gearboxes, the losses in which are only 1.5 - 4 percent.
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The content of the article
SHIP POWER PLANTS AND PROPULSIONS, devices for ensuring the movement of ships, boats and other vessels. Propulsors include a propeller and a paddle wheel. As a rule, steam engines and turbines, gas turbines and internal combustion engines, mainly diesel, are used as ship power plants. Large and powerful specialized vessels such as icebreakers and submarines often use nuclear power plants.
Apparently, Leonardo da Vinci (1452–1519) was the first to propose using steam energy to propel ships. In 1705, T. Newcomen (England) patented the first fairly efficient steam engine, but his attempts to use the reciprocating motion of a piston to rotate a paddle wheel were unsuccessful.
Steam is a traditional source of energy for ship propulsion. Steam is produced by burning fuel in water tube boilers. Double-drum water-tube boilers are used most often. These boilers have fireboxes with water-cooled walls, superheaters, economizers, and sometimes air preheaters. Their efficiency reaches 88%.
Diesels first appeared as marine engines in 1903. Fuel consumption in marine diesel engines is 0.25–0.3 kg/kWh, and steam engines consume 0.3–0.5 kg/kWh depending on the design of the engine, drive and other design features. Diesels, especially in combination with an electric drive, are very convenient for use on ferries and tugs, as they provide high maneuverability.
The days of piston engines, which once served a wide variety of purposes, are over. In terms of efficiency, they are significantly inferior to both steam turbines and diesel engines. On those ships that still have steam engines, these are compound machines: steam expands sequentially in three or even four cylinders. The pistons of all cylinders operate on the same shaft.
Marine steam turbines usually consist of two cascades: high and low pressure, each of which rotates the propeller shaft through a reduction gearbox. Naval vessels often additionally install small turbines for cruising mode, which are used to increase efficiency, and at maximum speeds powerful turbines are turned on. The high pressure cascade rotates at 5000 rpm.
On modern steam ships, feed water from condensers is supplied to the heaters through several heating stages. Heating is produced by the heat of the turbine working fluid and exhaust flue gases flowing around the economizer.
Almost all auxiliary equipment is electrically driven. Electric generators driven by steam turbines usually produce direct current with a voltage of 250 V. Alternating current is also used.
If power is transferred from the turbine to the propeller through a gearbox, then an additional small turbine is used to ensure reverse rotation (reverse rotation of the propeller). The power on the shaft during reverse rotation is 20–40% of the main power.
Electric drive from turbine to propeller was very popular in the 1930s. In this case, the turbine rotates a high-speed generator, and the generated electricity is transmitted to low-speed electric motors that rotate the propeller shaft. The efficiency of the gear transmission (gearbox) is approximately 97.5%, the efficiency of the electric drive is about 90%. In the case of an electric drive, reverse rotation is achieved simply by switching the polarity.
Gas turbines appeared on ships much later than in aviation, since the weight gain in shipbuilding is not so important, and this gain did not outweigh the high cost and complexity of installation and operation of the first gas turbines.
Gas turbines are used on ships not only as main engines; They are used as drives for fire pumps and auxiliary electric generators, where their low weight, compactness and quick start-up are beneficial. In the navy, gas turbines are widely used on small high-speed vessels: landing craft, minesweepers, hydrofoils; on larger ships they are used to obtain maximum power.
Modern gas turbines have an acceptable level of reliability, operating and production costs. Given their light weight, compactness and quick start-up, they are in many cases competitive with diesel engines and steam turbines.
For the first time, diesel as a marine engine was installed on the Vandal in St. Petersburg (1903). This happened just 6 years after Diesel invented his engine. The Vandal, which sailed along the Volga, had two propellers; each propeller was mounted on the same shaft with a 75 kW electric motor. Electricity was generated by two diesel generators. Three-cylinder diesel engines with a power of 90 kW each had a constant rotation speed (240 rpm). The power from them could not be transmitted directly to the propeller shaft, since there was no reverse.
Trial operation of the Vandal refuted the general opinion that diesel engines cannot be used on ships due to the danger of vibrations and high pressures. Moreover, fuel consumption was only 20% of the fuel consumption on ships of the same displacement.
In the ten years since the first diesel engine was installed on a river boat, these engines have undergone significant improvements. Their power increased due to an increase in the number of revolutions, an increase in the cylinder diameter, a lengthening of the piston stroke, as well as the development of two-stroke engines.
The speed of existing diesel engines ranges from 100 to 2000 rpm; High-speed diesel engines are used on small high-speed boats and in auxiliary diesel generator systems. Their power varies over an equally wide range (10–20,000 kW). In recent years, supercharged diesel engines have appeared, which increases their power by about 20%.
Diesels have an advantage over steam engines on small boats due to their compactness; in addition, they are lighter with the same power. Diesels consume less fuel per unit of power; True, diesel fuel is more expensive than heating oil. Diesel fuel consumption can be reduced by afterburning exhaust gases. The type of vessel also influences the choice of power plant. Diesel engines start much faster: they do not need to be preheated. This is a very important advantage for harbor ships and auxiliary or standby power units. However, steam turbine plants also have advantages, which are more reliable in operation, capable of operating for a long time without routine maintenance, and have a lower level of vibration due to the absence of reciprocating motion.
Marine diesel engines differ from other diesel engines only in auxiliary elements. They directly or through a gearbox rotate the propeller shaft and must provide reverse rotation. In four-stroke engines, this is done by an additional reverse clutch, which engages when reverse rotation is necessary. In two-stroke engines, reverse rotation is simpler because the valve sequence is determined by the position of the piston in the corresponding cylinder. In small engines, reverse rotation is achieved using a clutch and gear train. Some patrol ships and amphibians less than 60 m in length have reversible propellers ( see below). To ensure that the engine speed does not exceed the safe limit, all engines are equipped with speed limiters.
The term “ships with electric propulsion” refers to ships in which one of the elements of the system for converting fuel energy into mechanical energy of rotation of the propeller shaft is an electric machine. One or more electric motors are connected to the propeller shaft directly or through a gearbox. The electric motors are powered by electric generators driven by a steam or gas turbine or a diesel engine. On submarines, when submerged, the electric motors are powered by batteries, and when on the surface, by diesel generators. DC electric machines are usually installed on small and highly maneuverable vessels. AC machines are used on ocean liners.
In Fig. Figure 1 shows a diagram of a turboelectric drive with a boiler installation for generating steam. The steam turns a turbine, which in turn turns an electric generator. The generated electricity is supplied to electric motors that are connected to the propeller shaft. Typically, each turbogenerator is powered by one electric motor, which rotates its propeller. However, this scheme makes it easy to connect several electric motors, and therefore several propellers, to one turbogenerator.
Marine AC turbine generators can produce current with a frequency ranging from 25–100% of the maximum, but not more than 100 Hz. Alternating current generators produce current with voltages up to 6000 V, direct current – up to ~900 V.
A diesel-electric drive is essentially no different from a turbo-electric drive, except that the boiler plant and steam turbine are replaced by a diesel engine.
On small ships, there is usually one diesel generator and one electric motor per propeller, but if necessary, you can turn off one diesel generator to save money or turn on an additional one to increase power and speed.
Efficiency. DC electric motors produce more torque at low speeds than turbines and diesel engines with mechanical transmission. In addition, both direct and alternating current motors have the same torque during both forward and reverse rotation.
The overall efficiency of a turboelectric drive (the ratio of power on the propeller shaft to the fuel energy released per unit time) is lower than the efficiency of a turbine drive, although the turbine is connected to the propeller shaft through two reduction gearboxes. A turboelectric drive is heavier and more expensive than a mechanical turbine drive. The overall efficiency of a diesel-electric drive is approximately the same as that of a mechanical turbine drive. Each type of drive has its own advantages and disadvantages. Therefore, the choice of the type of propulsion system is determined by the type of vessel and its operating conditions.
In this case, power is transferred from the engine to the propeller by an electromagnetic field. In principle, such a drive is similar to a conventional asynchronous electric motor, except that both the stator and the armature of the electric motor in an electromagnetic drive are made rotating; one of them is connected to the engine shaft, and the other is connected to the propeller shaft. The element associated with the motor is the field winding, which is powered by an external DC source and creates an electromagnetic field. The element connected to the propeller shaft is a short-circuited winding without external power. Both elements are separated by an air gap. The rotating magnetic field excites a current in the winding of the second element, which causes this element to rotate, but always slower (with slip) than the first element. The resulting torque is proportional to the difference in the rotational speeds of these elements. Turning off the excitation current in the primary winding “disconnects” these elements. The rotation frequency of the second element can be adjusted by changing the excitation current. With one diesel engine on a ship, the use of an electromagnetic drive reduces vibrations due to the absence of a mechanical connection between the engine and the propeller shaft; with several diesel engines, such a drive increases the maneuverability of the vessel by switching the propellers, since the direction of their rotation is easy to change.
On ships with nuclear power plants, the main source of energy is a nuclear reactor. The heat released during the fission of nuclear fuel serves to generate steam, which then enters the steam turbine. WITH m. NUCLEAR POWER.
The reactor plant, like a conventional steam boiler, contains pumps, heat exchangers and other auxiliary equipment. A special feature of a nuclear reactor is its radioactive radiation, which requires special protection for operating personnel.
Massive biological protection has to be installed around the reactor. Common radiation shielding materials are concrete, lead, water, plastics and steel.
There is a problem of storing liquid and gaseous radioactive waste. Liquid waste is stored in special containers, and gaseous waste is absorbed by activated charcoal. The waste is then transported ashore to recycling facilities.
The main elements of a nuclear reactor are rods with fissile material (fuel rods), control rods, coolant (coolant), moderator and reflector. These elements are enclosed in a sealed housing and arranged to ensure a controlled nuclear reaction and removal of the generated heat.
The fuel can be uranium-235, plutonium, or a mixture of both; these elements can be chemically bonded with other elements and be in the liquid or solid phase. Heavy or light water, liquid metals, organic compounds or gases are used to cool the reactor. The coolant can be used to transfer heat to another working fluid and produce steam, or it can be used directly to rotate the turbine. The moderator serves to reduce the speed of the neutrons produced to a value that is most effective for the fission reaction. The reflector returns neutrons to the core. The moderator and reflector are usually heavy and light water, liquid metals, graphite and beryllium.
All naval vessels, the first nuclear-powered icebreaker "Lenin", the first cargo-passenger ship "Savannah" have power plants made according to a dual-circuit design. In the primary circuit of such a reactor, water is under pressure up to 13 MPa and therefore does not boil at a temperature of 270 ° C, usual for the reactor cooling path. Water heated in the primary circuit serves as a coolant for producing steam in the secondary circuit.
Liquid metals can also be used in the primary circuit. This scheme was used on the US Navy submarine Sea Wolf, where the coolant is a mixture of liquid sodium and liquid potassium. The pressure in the system of such a scheme is relatively low. The same advantage can be realized by using paraffin-like organic substances - biphenyls and triphenyls - as a coolant. In the first case, the disadvantage is the problem of corrosion, and in the second, the formation of resinous deposits.
There are single-circuit schemes in which the working fluid, heated in the reactor, circulates between it and the main engine. Gas-cooled reactors operate using a single-circuit design. The working fluid is a gas, for example helium, which is heated in a reactor and then rotates a gas turbine.
Its main function is to protect the crew and equipment from radiation emitted by the reactor and other elements that come into contact with radioactive substances. This radiation is divided into two categories: neutrons, released during nuclear fission, and gamma radiation, produced in the core and in activated materials.
In general, ships have two containment shells. The first is located directly around the reactor vessel. Secondary (biological) protection covers steam generating equipment, cleaning systems and waste containers. The primary shield absorbs most of the reactor's neutrons and gamma radiation. This reduces the radioactivity of reactor auxiliary equipment.
Primary protection can be a double-shell sealed tank with a space between the shells filled with water and an outer lead shield 2 to 10 cm thick. Water absorbs most of the neutrons, and gamma radiation is partially absorbed by the walls of the housing, water and lead.
The main function of the secondary protection is to reduce the radiation of the radioactive nitrogen isotope 16 N, which is formed in the coolant passing through the reactor. For secondary protection, water containers, concrete, lead and polyethylene are used.
For warships, the cost of construction and operating costs are less important than the advantages of an almost unlimited cruising range, greater power and speed of ships, compact installation and reduction of maintenance personnel. These advantages of nuclear power plants have led to their widespread use on submarines. The use of atomic energy on icebreakers is also justified.
There are four main types of ship propulsion: water-jet propulsion, paddle wheels, propellers (including those with a guide nozzle) and wing propulsion.
A water jet is essentially just a piston or centrifugal pump that draws water through an opening in the bow or bottom of the ship and expels it through nozzles at the stern. The created thrust (thrust force) is determined by the difference in the amounts of movement of the water jet at the exit and entrance to the propeller. The water-jet propulsion system was first proposed and patented by Toogood and Hayes in England in 1661. Later, various versions of such an engine were proposed by many, but all designs were unsuccessful due to low efficiency. Water-jet propulsion is used in some cases where the low efficiency is compensated by advantages in other respects, for example for navigation in shallow or clogged rivers.
In the simplest case, a rowing wheel is a wide wheel with blades installed around its periphery. In more advanced designs, the blades can be rotated relative to the wheel so that they create the required propulsive force with minimal losses. The axis of rotation of the wheel is located above the water level, and only a small part of it is submerged, so at any given moment only a few blades create a thrust. The efficiency of a paddle wheel, generally speaking, increases with increasing diameter; Diameter values of 6 m or more are not uncommon. The rotation speed of the large wheel is low. The low speed corresponded to the capabilities of the first steam engines; However, over time, cars improved, their speeds increased, and low wheel speeds became a serious obstacle. As a result, paddle wheels gave way to propellers.
Even the ancient Egyptians used a screw to supply water from the Nile. There is evidence that in medieval China, a manually driven propeller was used to propel ships. In Europe, the propeller was first proposed as a ship propulsion system by R. Hooke (1680).
A modern propeller typically has several roughly elliptical blades spaced evenly on a central hub. The surface of the blade facing forward, towards the bow of the vessel, is called suction, while the surface facing backward is called discharge. The suction surface of the blade is convex, the discharge surface is usually almost flat. In Fig. Figure 2 schematically shows a typical propeller blade. The axial movement of the helical surface per revolution is called the pitch p; product of step and number of revolutions per second pn– axial speed of a zero-thickness propeller blade in a non-deformable medium. Difference ( pn- v 0), where v 0 – true axial speed of the screw, characterizes the measure of deformability of the medium, called slip. Attitude ( pn - v 0)/pn– relative slip. This ratio is one of the main parameters of the propeller.
The most important parameter determining the performance characteristics of a propeller is the ratio of the propeller pitch to its diameter. Next in importance are the number of blades, their width, thickness and shape, profile shape and disk ratio (the ratio of the total area of the blades to the area of the circle surrounding them) and the ratio of the hub diameter to the propeller diameter. The ranges of variation of these parameters that provide good performance characteristics have been experimentally determined: pitch ratio (ratio of propeller pitch to its diameter) 0.6–1.5, ratio of maximum blade width to propeller diameter 0.20–0.50, ratio of maximum blade thickness near bushings to diameter 0.04–0.05, ratio of bushing diameter to screw diameter 0.18–0.22. The blade shape is usually ovoid, and the profile shape is smoothly streamlined, very similar to the profile of an airplane wing. The sizes of modern propellers vary from 20 cm to 6 m or more. The power developed by the propeller can be a fraction of a kilowatt, or it can exceed 40,000 kW; accordingly, the rotation speed ranges from 2000 rpm for small screws to 60 for large ones. The efficiency of good propellers is 0.60–0.75 depending on the pitch ratio, number of blades and other parameters.
Ships are equipped with one, two or four propellers, depending on the size of the vessel and the required power. A single propeller provides higher efficiency because there is no interference and part of the energy expended in propelling the vessel is recovered by the propeller. This recovery is higher if the propeller is installed in the middle of the wake just behind the sternpost. Some increase in propulsive force can be achieved using a split rudder, for which the upper and lower parts of the rudder are slightly deflected in opposite directions (corresponding to the rotation of the propeller) in order to use the transverse component of the jet velocity after the propeller to create an additional component of force in the direction of movement of the vessel. The use of several propellers increases the maneuverability of the vessel and the ability to turn without using rudders, when the propellers create emphasis in different directions. As a rule, reversing the thrust (changing the direction of action of the propulsive force to the opposite) is achieved by reversing the rotation of the propeller engines, but there are also special reversible screws that allow you to reverse the thrust without changing the direction of rotation of the shafts; this is achieved by rotating the blades relative to the hub using a mechanism located in the hub and driven through a hollow shaft. Propellers are made of bronze, cast from steel or cast iron. Manganese alloy bronze is the preferred alloy for salt water applications as it is highly grindable and has good resistance to cavitation and salt water attack. High-speed supercavitating propellers, in which the entire suction surface is occupied by a cavitation zone, have been designed and created. At low speeds, such propellers have a slightly lower efficiency, but they are much more efficient than conventional ones at high speeds.
A screw with a nozzle - a regular screw installed in a short nozzle - was invented by the German engineer L. Kort. The nozzle is rigidly connected to the hull of the vessel or is made with it as one piece.
A number of attempts have been made to install a screw in a pipe to improve its performance. In 1925, Cort summarized the results of these studies and significantly improved the design: he turned the pipe into a short nozzle, the diameter of which at the inlet was larger, and the shape corresponded to the airfoil. Cort found that this design provides significantly more thrust for a given power compared to conventional propellers, since the jet accelerated by the propeller is narrowed to a lesser extent in the presence of a nozzle (Fig. 3). At the same flow rates, the speed behind the screw with a nozzle ( v 0 + u u). In this regard, propellers with a nozzle are more often installed on tugs, trawlers and similar vessels that tow heavy loads at low speed. For such vessels, the gain per unit of power created by a propeller with a nozzle can reach 30–40%. On high-speed vessels, a propeller with a nozzle has no advantage, since the small gain in efficiency is lost due to an increase in drag on the nozzle.
Such a propulsion device is a disk on which 6–8 spade-shaped blades are located along the periphery perpendicular to the plane of the disk. The disk is installed flush with the bottom of the ship, and only the propeller blades are lowered into the flow. The disk with blades rotates about its axis, and, in addition, the blades perform a rotational or oscillatory motion relative to their longitudinal axis. As a result of the rotational and oscillatory movements of the blades, the water is accelerated in the required direction, and a stop is created for the movement of the vessel. This type of propulsion has an advantage over the propeller and paddle wheel, since it can create thrust in any desired direction: forward, backward and even sideways without changing the direction of rotation of the engine. Therefore, to control ships with paddle propulsion, no rudders or other mechanisms are required. Although vane propellers cannot replace propellers in terms of versatility, they are quite effective in some special applications.
Literature:
Akimov R.N. and etc. Ship Engineer's Handbook. M., 1973–1974
Samsonov V.I. and etc. Marine internal combustion engines. M., 1981
Ovsyannikov M.K., Petukhov V.A. Marine diesel plants(sp.). L., 1986
Artyushkov L.S. and etc. Ship propulsors. L., 1988
Batyrev A.N. and etc. Shipborne nuclear installations of foreign countries. St. Petersburg, 1994
