Методические указания для студентов 2 курса судомеханического факультета заочного отделения (стр. 5 из 10)
РЕФЕРИРОВАНИЕ - выделение наиболее существенной информации и представление её в виде краткого связного текста с критической оценкой прочитанного. Реферат во многих случаях может заменить сам первоисточник.
Основными требованиями, предъявляемыми к реферату, являются:
1. объективность;
2. полнота изложения;
3. единство формы;
4. объём (2000 печатных знаков независимо от объёма работы). Целесообразно обучать реферированию на материале переведённых
статей. Реферат не является сокращённым переводом текста. Позже, с приобретением известных навыков, можно предлагать и непереведенные статьи. Тексты для реферирования должны быть конкретные, интересные по содержанию, с элементами новизны. На начальном этапе рекомендуется делать реферат на русском языке. Рекомендуются следующие виды упражнений при переходе к процессу реферирования:
1. постановка поисковых задач;
2. деление текста на смысловые отрезки;
3. озаглавливание каждого отрывка;
4. устный перевод отдельных абзацев;
5. составление перечня проблем, затронутых в тексте;
6. сокращение сложных предложений;
7. сокращение (выброс) информации, не относящейся к теме;
8. прочитать текст и найти ответы на вопросы;
9. выделить главную идею, суть;
10. рассказать на русском языке, о чем идет речь;
11. выделить новизну, ценность, полезность информации.
Всякий реферат имеет единую структуру. Синтаксис реферата однообразен. В тексте преобладают простые предложения (неопределённо-личные, безличные). Для связанности изложения используются специфичные выражения, типа: «установили, отмечено, рассматриваются, указывается, вызывает интерес», а также специальные языковые клише: «статья посвящена, автор считает, целью статьи является, первая глава описывает» и т.д. Этапы написания реферата:
1. Прежде чем начать реферировать, необходимо прочесть весь материал, досконально понять все нюансы его содержания.
2. Референт приступает к составлению подробного плана всего первоисточника. Весь материал разбивается на разделы, подразделы и пункты.(Часто сам источник имеет такую разбивку). Жела-
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тельно все пункты такого плана формулировать назывными предложениями, оставляя после каждого пункта свободное место для последующего формулирования главной мысли этого раздела.
3. После составления плана первоисточника референт выделяет главную мысль каждого раздела и важнейшие доказательства, подкрепляющие эту мысль. Они записываются одним-двумя краткими предложениями. Необходимо полностью отвлечься от языка оригинала, выделить главную мысль и суметь кратко сформулировать её.
4. Завершив обработку всех пунктов плана, необходимо сформулировать главную мысль всего первоисточника, если это не сделано самим автором.
5. Составить текст реферата, начав с его формальной части, т.е. с предметной рубрики, темы и выходных данных, после чего записать формулировку главной мысли всего первоисточника и последовательно все формулировки по каждому из пунктов плана.
6. Завершить реферат кратким комментарием по такой схеме: а) актуальность всего материала; б) на кого материал рассчитан.
7. Составив полный текст реферата, его следует весь прочитать и, если необходимо, стилистически отшлифовать, стремясь увязать отдельные пункты реферата в единый связный текст.
Text 1. Building ships
The building of a ship follows a well-ordered sequence of events. After the vessel has been ordered, the plans are completed in the drawing office. Next, the final plans must be approved by a classification society. While the ship is being built, constant checks are made to make sure she is being built to the standards of the society. Classification will show that the ship is seaworthy and able to carry the cargo she has been designed to carry.
Nowadays a shipyard is organized so that each stage in the building of a ship is done in a continuous chain of shops. Each shop is linked by conveyor rollers and moving cranes on rails. First of all, steel plates and bars are taken from the stockyard to the preparation shop. Here they are cleaned by grit blasting. Then, they are coated with a primer paint to prevent corrosion. Later, they are cut and shaped automatically by machines. Cutting is done by gas torches and shaping by giant presses. After that, the pieces are welded together in prefabrication sheds to form sections. The prefabricated sections are then transferred to the building berth. Eventually they are lifted into position by giant cranes.
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When a ship is ready, she is launched. Some ships are built on a slipway and slide into the water. Others are built in a dry dock. The dock is then flooded with water and the ship is floated out. After being launched, she is towed to the fitting-out basin by tugs and completed.
A completed ship goes for sea trials before she is handed over to her new owners. During these the ship and her equipment are thoroughly tested.
Text 2. Different types of marine engine
There are four main types of marine engine: the diesel engine, the steam turbine, the gas turbine, and the marine nuclear plant. Each type of engine has its
own particular application.
The diesel engine is a form of internal combustion engine. Its power is expressed as break horse power (bhp). This is the power put out by the engine. Effective horsepower is the power developed by the piston in the cylinder, but some of this is lost by friction within the engine. The power is now expressed in kilowatts. Large diesel engines, which have cylinder nearly 900 mm in diameter, turn at the relatively slow speed of about 145 rpm and less. They are known as slow-speed diesel engines. They can be connected directly to the propeller without gearing. Although higher power could be produced by higher revolutions, this would reduce the efficiency of the propeller, because the propeller is more efficient the larger it is and the slower it turns. More and more of the larger merchant vessels are being powered by medium-speed diesel engines. These operate between 150 and 450 rpm, therefore they are connected to the propeller by gearing. They are cheaper than slow-speed diesel engines, and their smaller size and weight can
result in a smaller cheaper ship.
In steam turbines high pressure steam is directed into a series of blades or vanes attached to a shaft, causing its to rotate. This rotary motion is transferred to the propeller shaft by gears. Steam is produced by boiling water in a boiler, which is fired by oil. Recent developments in steam turbines which have reduced fuel
consumption and raised power output have made them more attractive as an
alternative to diesel power in ships.
Gas turbines differ from steam turbines if that gas rather than steam is used
to turn a shaft. These have also become more suitable for use in ships. A gas
turbine engine is very light and easily removed for maintenance. It is also suitable
for complete automation.
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Nuclear power in ship has mainly been confined to icebreakers. A nuclear-powered ship differs from a conventional turbine ship in that it uses the energy released by the decay ( распад) of radioactive fuel to generate steam. The steam is used to turn a shaft via a turbine in the conventional way.
Text 3. From the Steam Engine to the DieselDevelopment of the internal combustion engine of which the Diesel constitutes a particular type began in the second half of the 19th century.
The first Diesel engine was built in Germany in 1897 under the direction of Rodolphe Diesel himself. But it was only after the First World war that this engine truly left the experimental.stage thanks to the availability of a mechanical fuel injection system.
The first Diesel locomotive appeared in the USA in 1925. Then beginning in the 1930, railcars engines were put into service in Europe. In the USA Diesels began to be put into general use in the form of medium- power locomotives in 1942 during the Second World War. Their use expanded rapidly in the following years.
From 1950, introduction of powerful Diesel engines made it possible for Diesel locomotives to equal the performance of the electrically powered engines. First the French Railways were equipped with a high number of Diesel engines, but then the density of the rail network and of rail traffic made electrification the preferable choice and it was only for marine industrial and trucking application that Diesels enjoyed extensive development.
Text 4. The Transformation of Potential Energy into Mechanical Energy
The principle of all engines consists in transforming the potential energy of a fuel into mechanical energy, first it is necessary to produce heat, which is then transformed into work.
In almost all current applications, the production of heat is obtained by means of the chemical reaction of oxidation occurring between a hydrocarbon (or other fuel) and an oxidizer which supplies oxygen. The oxidizer is most often air which contains one-fifth oxygen by volume. The products of combustion are: Carbon dioxide
Water, if the fuel burnt contains hydrogen A great deal of heat, which raises the temperature of the gases produced, causing them to expand. The reaction always occurs between gases. If the fuel is not in gaseous form, it is necessary to make it gaseous. If after combustion of all the fuel there is oxygen left over, there is, as one says, an excess of air, meaning the fuel was poor in fuel. If on the other hand, there is unburnt fuel remaining and no oxygen, the mixture is said to be too rich.
The expansion of the gases heated by combustion produces "work" or mechanical energy.
Text 5. Four strokes of diesel engines
The first stroke is suction. The piston is moving downwards an the air inlet valve has been opened by the engine while the others remain closed. Air from the engine room is being drawn into the cylinder, and when the piston reaches the bottom of the stroke, the cylinder will be full of fresh air and the inlet valve will
close.
The second stroke is compression. The piston is now being driven upwards, all valves are shut and the air charge is compressed to a pressure of about 500 lbs. per square inch, at which pressure its temperature is 1200 deg. F. The third stroke is firing. Just before the beginning of the stroke the fuel valve is opened and oil is sprayed into the cylinder in the form of a fine mist. The hot air causes it to burn and this air is further heated by the combustion of the fuel. The fuel valve remains open only for a short period at the beginning of this stroke. The gas expands and the piston is driven downwards and so supplies power to the shafting through the connecting rod and crank.
The fourth stroke is exhaust. The piston is again travelling upwards and the exhaust valve has been opened, the waste or burnt gases are driven out to the silencer through the exhaust valve. The next stroke recommences the cycle of operations, with the admission of a fresh air charge.
Text 6. Two stroke engines
Two-stroke engines are also used for propulsion of ships. These, if single-acting, provide one power-stroke per revolution, while a double-acting 2-stroke engine develops power one every stroke.
A two-stroke engine develops almost twice as much power as a four-stroke engine with the same size and number of cylinders. Since the four operations, i.e. suction, compression, firing and exhaust have to be completed during two strokes of the piston, more than one operation must be performed per stroke. This complicates the engine. The piston is made to control the admission of air and release of the exhaust gases by opening and closing ports or passages in the cylinder walls through which the air and gases pass. The fresh air-charge is pumped into the cylinder at low pressure by means of a scavenging pump which may be driven either by the engine itself or by a separate auxiliary engine or electric motor. This air not only provides the air charge necessary for the proper combustion of the fuel but assists in clearing the burnt gases rapidly out of the cylinder.