The Impact Loads of Ships Colliding With Fixed Structures

When a ship moves forward in water and is decelerated by some obstacle or structure. it is not only the mass of the ship that is decelerated but also a certain amount of water moving along the ship. It is this so-called hydrodynamic added mass which is the crucial factor in the design calculations. The magnitude of this added mass is influenced by: dimensions and shape of the underwater hull. underkeel clearance. spring characteristics of the obstacle and collision mode.

• In order to identify more precisely the influence of all the different contributing parameters. a very extensive model test program has been performed at the Netherlands Ship Model Basin. The program was initiated for two reasons:
• For the design of fender structures and associated jetties. the need for experimental back-up data was felt.

For the validation of computational programs developed at NSMB a good deal of experimental results was needed.
Therefore. a series of some 750 test runs has been performed. During which the sensitivity of the hydrodynamic mass for fender stiffness. collision mode and collision speed was tested.
One of the outcomes of the test series was that the accepted and frequently used hydrodynamic added mass values appear to be too low. a finding which is of direct consequence to the designers.

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