VIII. Retell the text “Modern shipbuilding.” unit 2. Ship model basin

I. The words and word combinations to be remembered:

basin – бассейн

a towing tank – буксировочный (опытовый) бассейн

a towing carriage – буксировочная каретка

to be equipped with – оборудоваться чем - либо

propeller thrust – тяга винта

torque – вращающий момент

planar motion mechanism – механизм плоского движения

maneuver – маневр, манипуляция

oblique inflow – наклонный приток

a wave packet – волновой пакет

seakeeping test – мореходный тест

stroboscope – стробоскоп

velocity – скорость, быстрота

to visualize cavitation – видеть кавитацию

II. Read and translate the following text:

Fig.2. US Experimental Model Basin, circa 1900

A ship model basin may be defined as a physical basin or tank used to carry out hydrodynamic tests with ship models, for the purpose of designing a new (full sized) ship, or refining the design of a ship to improve the ship's performance at sea.

The hydrodynamic test facilities present at a model basin site include:

• A towing tank: This is a basin, several meters wide and hundreds of meters long, equipped with a towing carriage that runs on two rails on either side. The towing carriage can either tow the model or follow the self-propelled model, and is equipped with computers and devices to register or control, respectively, variables such as speed, propeller thrust and torque, rudder angle etc. The towing tank serves for resistance and propulsion tests with towed and self-propelled ship models to determine how much power the engine will have to provide to achieve the speed laid down in the contract between shipyard and ship owner. The towing tank also serves to determine the maneuvering behavior in model scale. For this, the self-propelled model is exposed to a series of zigzag maneuvers at different rudder angle amplitudes. Additionally, a towing tank can be equipped with a PMM (planar motion mechanism) or a CPMC (computerized planar motion carriage) to measure the hydrodynamic forces and moments on ships or submerged objects under the influence of oblique inflow and enforced motions. The towing tank can also be equipped with a wave generator to carry out seakeeping tests, either by simulating natural (irregular) waves or by exposing the model to a wave packet that yields a set of statistics known as response amplitude operators, that determine the ship's likely real-life sea-going behavior when operating in seas with varying wave amplitudes and frequencies (these parameters being known as sea states).

• A cavitation tunnel to investigate propellers. This is a vertical water circuit with large diameter pipes. At the top, it carries the measuring facilities. A parallel inflow is established. With or without a ship model, the propeller, attached to a dynamometer, is brought into the inflow, and its thrust and torque is measured at different ratios of propeller speed (number of revolutions) to inflow velocity. A stroboscope synchronized with the propeller speed serves to visualize cavitation as if the cavitation bubble would not move. By this, one can observe if the propeller would be damaged by cavitation. To ensure similarity to the full-scale propeller, the pressure is lowered, and the gas content of the water is controlled.

• Workshops: Ship model basins manufacture their ship models from wood or paraffin with a computerized milling machine. Some of them also manufacture their model propellers. Equipping the ship models with all drives and gauges and manufacturing equipment for non-standard model tests are the main tasks of the workshops.