V. Comment on the use of infinitive in the text.

VI. Translate the text “Methods for calculating.”

When calculating the response of ships in regular waves it is often possible to neglect the effects of viscosity in certain modes of motion. Fairly accurate results can then be found by using potential theory. The calculations are often divided into two sub-problems:

1. Finding the forces on the ship when it is restrained from motion and subjected to regular waves. The forces acting on the body are:

   • The Froude-Krylov force, which is the pressure in the undisturbed waves integrated over the wetted surface of the ship.

   • The Diffraction forces, which are pressures that occur due to the disturbances in the water because of the ship being present.

2. Finding the forces on the ship when it is forced to oscillate in still water conditions. The forces are divided into:

• Added mass forces due to having to accelerate the water along with the ship.

• Damping forces due to the oscillations creating outgoing waves which carry energy away from the ship.

• Restoring forces due to bringing the buoyancy/weight equilibrium out of balance.

On a computer the above algorithm was first introduced by using strip theory. Today strip theory is still used if the need for fast calculations outweigh the need for precise results and the ship designer knows the limitations of strip theory. The more advanced programs that are used today may not use the exact algorithm outlined above and may also include the effects of viscosity.

VII. Use the following words and word combinations in the sentences of your own:

Design of floating structures, to determine the behavior of a ship, the models of proposed ships, to test in a model basin, to transfer functions, to improve stability, to improve fuel consumption, a wide variety of flow conditions, to dimension the ship or structure, to affect the nature of the “ideal” RAO.

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

1. A response amplitude operator is an engineering statistic or set of such statistics, that are used to determine the likely behavior of a ship when operating at sea.

2. Response amplitude operators are usually obtained from models of proposed ship designs tested in a model basin.

3. RAOs are usually calculated for all ship motions and for all wave headings.

4. RAOs are effectively transfer functions used to determine the effect that a sea state will have upon the motion of a ship through the water.

5. Generation of extensive RAOs at the design phase allows shipbuilders to determine the modifications to a design that may be required for safety reasons.

6. The RAOs and hydrodynamic database provide certain assurances about the behavior of a proposed ship design.

IX. Retell the text “Response amplitude operator.” unit 7. Ship stability