UNIT 2. SHIP MODEL BASIN

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.

III. Answer the following questions:

1. What is a ship model basin?

2. The towing carriage is equipped with computers and devices to register variables such as speed propeller thrust, isn’t it?

3. What is a towing tank?

4. What does a towing tank serve for?

5. What can a towing tank be equipped with?

6. What is a PMM?

7. What is a CPMC used for?

8. Is a cavitation tunnel a vertical water circuit with large diameter pipes?

9. What is the function of a stroboscope?

10. The propeller is attached to a dynamometer, isn’t it?

IV. Insert the missing word using the text:

1. A towing tank is a …, several meters wide and … of meters long.

2. The towing tank serves for … and … tests to determine how much power the engine will have to provide to achieve the speed laid down in the contract between … and ship owner.

3. A towing tank can be equipped with … … … to measure the hydrodynamic forces under the influence of … inflow and enforced motions.

4. At the top, a cavitation tunnel carries the … …

5. A … synchronized with the propeller speed serves to … cavitation as if the cavitation bubble would not move.

6. Ship model basins manufacture their ship models from … or paraffin with a computerized … …

V. Ask as many questions as possible to the following questions:

1. Resistance and required engine power as well as maneuvering behavior are determined depending on the ice thickness.

2. Ship model basins manufacture their ship models from wood or paraffin with a computerized milling machine.

3. A ship model basin is also an engineering firm that provides hydrodynamic model tests and numerical calculations to support the design and development of ships and offshore structures.

4. Modern seakeeping test facilities can determine RAO statistics with the aid of appropriate computer hardware and software in a single test.

5. A maneuvering and seakeeping basin is a test facility that is wide enough to investigate arbitrary angles between waves and the ship model.

6. The ship model basins worldwide are organized in the International Towing Tank Conference to standardize their model test procedures.

VI. Translate the text: “Ship grounding”

Ship grounding is a type of marine accident that involves the impact of a ship on the seabed, resulting in damage of the submerged part of her hull and in particularly the bottom structure, potentially leading to water ingress and compromise of the ship's structural integrity and stability. Grounding induces extreme loads onto marine structures and is a marine accident of profound importance due to its impact:

· The environmental impact, especially in the case where large tanker ships are involved.

· The loss of human life.

· Financial consequences to local communities close to the accident.

· The financial consequences to ship-owners, due to ship loss or penalties.

The grounding, depending on the maneuvers of the master before the impact, may result in the ship being stranded. Depending on the nature of the relief of the seabed at the location, i.e. being muddy or rocky, different measures have to be taken to release the ship and carry it to a safe harbor.

VII. Retell the text “Ship model basin.”