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Should the Morison equation or diffraction analysis be adopted in determining wave force on piles?

The choice between the Morison’s equation and diffraction analysis in determining the wave forces on piles depends on the ratio between the diameters of piles to wavelength. If the ratio between the diameter of piles to wavelength is less than 0.2, the Morison equation is usually recommended.

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Hudson’s formula and Van der Meer formula are commonly used in the design of armour. Which one is a better choice?

Hudson’s formula is commonly adopted in preliminary design to obtain rough initial estimate of rock size. The formula is derived from the results of regular wave tests. However, this formula does not take into account the following elements which Van der Meer formula does: wave period, damage level, permeability of structure and storm duration. Moreover, Hudson’s formula deals with the use of regular waves only.

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What are the factors determining the stability of a single armour unit?

There are mainly three main factors which govern the stability of a armour unit, namely, gravity, intertangling and squeezing. Obviously, it is beyond doubt that the ability of the armour unit to stay in place should be closely related to gravity force.

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Should small vessels be considered in the design of fenders?

Smallest vessel should also be taken into consideration when designing fender system. In vertical orientation of fender system, the types and sizes of all vessels should be considered taking into account the tidal effect at that region. To conduct proper design of fender system, engineers must consider the height and draft of both the smallest and largest vessels to determine the point of contact on the fender. It is not uncommon that design of fender system considers only the largest vessels berthing in the pier which should be avoided as it might not function for smaller vessels berthing in dock.

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Should stiff or soft fenders be designed for berthing in piers?

The elasticity of fenders is related to the ability to release the stored energy during berthing of vessels. However, it has no effect on the reaction force and the deflection of fender system. The amount of energy that a fender can absorb is dependent on the reaction-deflection curve and is represented by the area under the curve. The higher is the reaction force, the higher amount of energy would be absorbed by the fender provided that the resistance of ships’ hull is sufficient to withstand the force without permanent deformations.

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