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Assessment of dynamic line and fender loads for moored tankers

TERMSIM

TERMSIM is a time domain simulation program to analyse the dynamic behaviour of a moored export tanker subject to wind, waves and current. The mooring system can be a Single Point Mooring (SPM), a Multi Buoy Mooring (MBM) or a Jetty terminal. The program predicts the mooring loads and tanker motions when the system is exposed to operational environmental conditions.

Tanker

The tanker is a crude carrier of regular dimensions. The new OCIMF tanker database containing hydrodynamic data for several tankers is included in the program. Based on the main particulars of the tanker a selection from the OCIMF database is made. Through an expert mode a user defined tanker can be used for the simulations.

Environment

The environmental conditions concern steady current, steady or irregular wind field, swell and long crested irregular waves coming from arbitrary directions. Several spectral formulations for the wind, wave and swell are available. The water depth can be arbitrary.

Mooring systems

Three types of terminals are considered: SPM

The SPM terminal consists of a conventional CALM buoy which is moored to the seabed by means of anchor chains. The tanker is moored to the buoy by means of a bow hawser. The bow hawser can be selected from a database containing characteristics of synthetic material e.g. nylon, polyester, polypropylene and Dyneema.

MBM In a multi buoy terminal the tanker is moored by mooring legs consisting of anchor chains, chain-buoy-steel wire or chain-buoy-synthetic rope.

Jetty For the jetty terminal the tanker can be moored by means of mooring legs and fenders. A mooring leg can consist of a number of parallel running, but equal lines, and can be made of steel wire, synthetic rope or a combination of steel wire with a nylon tail. A selection can be made from six types of fenders.

Input

The input of data is user-friendly. The program makes use of a user interface with a graphical input check.

Databases

Several databases are delivered with the program. Mooring elements

The mooring element database contains particulars of common offshore chains, steel wires, synthetic ropes and fenders.

OCIMF wind and current data This database contains non-dimensional wind and current force/moment coefficients for use in the calculation of wind and current loads on a tanker.

OCIMF diffraction data The new OCIMF diffraction database containing the results of diffraction analyses for several tanker configurations.

Hydrodynamic reaction coefficients This database contains non-dimensional coefficients for use in the formulations of hydro-dynamic reaction forces.

Simulation control

The following situations can be simulated: Intact condition. Damaged condition.

Output

The output of each simulation consists of a binary database containing all samples of the calculated signals. The signals include the tanker motions, mooring loads in all mooring legs and other interesting quantities for the analysis of the mooring system behaviour. The system layout is represented graphically in a schematic format to detect input errors in an early stage. A comprehensive data processing package is delivered with the program to view, plot and print the output results.

Validation

Model tests were carried out in MARIN’s Wave and Current basin. Each terminal type was modelled to moor a tanker. The three systems were exposed to wind, current, swell and waves. In order to validate the computer program the three different systems were also simulated with TERMSIM. A good correlation with the model tests was found.

Note

A special version of TERMSIM is available which computes only mean values of vessel position and line and fender forces. Mooring legs can be composed of lines with buoys and clumps. This version is also suitable for LNG carriers and barges.

For more information please contact the Maritime Simulation & Software Group; T +31 317 493 237 E msg@marin.nl