Mooring Design Analysis

Mooring design and analysis

R. Sharma, Ph.D. Department of Ocean Engineering

IIT Madras, Chennai (TN) – 600 036, India.

Types of moorings : a) Fixed Moorings - Fixed moorings are defined as systems that include tension and compression members. Typical fixed mooring systems include moorings at piers and wharves. b) Fleet Moorings - Fleet moorings are defined as systems that include primarily tension members. Mooring loads are transferred into the earth via anchors. Examples of fleet moorings include fleet mooring buoys and ship’s anchor systems. The more common types of moorings are discussed in this lecture. PURPOSE OF MOORING: The purpose of a mooring is to safely hold a ship in a certain position to accomplish a specific mission. A key need is to safely hold the vessel to protect the ship, life, the

public interest, and to preserve the capabilities of the vessel and surrounding facilities. Ship moorings are provided for: a) Loading/Unloading - Loading and unloading items such as stores, cargo, fuel, personnel, ammunition, etc. b) Ship Storage - Storing the ship in a mooring reduces fuel consumption and personnel costs. Ships in an inactive or reserve status are stored at moorings. c) Maintenance/Repairs - Making a variety of repairs or conducting maintenance on the ship is often performed with a ship moored. d) Mission - Moorings are used to support special mission requirements, such as surveillance, tracking, training, etc. Most DOD moorings are provided in harbors to reduce exposure to waves, reduce ship motions, and reduce dynamic mooring loads. Mooring

in harbors also allows improved access to various services and other forms of transportation.

Governing equations for marine riser



Dynamic Boundary Condition. Consider a wave propagating over a body of water, and assume ideal fluid and irrotational flow. Water for flow speeds much smaller than the sound speed in water can be considered as an incompressible fluid. Under the assumptions above, the velocity field for the flow can be written as the gradient of a potential function . At solid boundaries, like the bottom, the dynamic boundary condition prescribes the flow velocity normal to the body surface, which is

since the bottom is at rest.

Kinematic Boundary Condition - specify the flow velocity at the boundaries. The surface of the body does not allow flow through it. This implies that the difference of the fluid velocity and body surface velocity in the direction normal to the body surface should be zero. This statement is expressed by the equation

and in terms of the potential function we have

The other boundary lies at the infinite (unbounded fluid domain). Far from the body, the fluid is not affected by the body movement, so the velocity field at the infinite should be zero. This is expressed by the equation

and in terms of the potential function we have

Behavior of offshore structures



Mooring Design Analysis

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