27.10.2005 Final team meeting!,
Only fine-tuning of the program and releasing the user-manual need to be done, tomorrow the presentation session starts... read more
18.10.2005 Fitfth team meeting,
After some useful comments, the program has to be adjusted once more read more
11.10.2005 Fourth team meeting, The program is nearly running, only few bugs to be fixed read more
During offshore vessel or platform installations it is necessary to accurately calculate the necessary length of the mooring lines.
The length of the mooring lines determines, in a given environmental condition, the tension and thus influences the position of the vessel or platform. It is therefore necessary to calculate the mooring line length carefully in order to position the vessel accurately.
In most conditions also the weight of the mooring lines actively contributes to the ultimate holding capacity of the mooring system. Enough length of the mooring lines has to be present to be able to carry these loads.
The Computational Catenary Calculation Program, or CCCP, developed by CES easily makes it possible to calculate the necessary mooring line length for a given operational condition.
Also the program is able to calculate the extra holding capacity of an existing mooring line. During the lifetime of existing mooring lines some parameters may change, like increasing rope density, caused by fouling or decreasing anchor chain density, caused by corrosion. Also it is possible to measure the down-winded rope length and calculate the necessary tension on the deck-winches.
This makes the program a necessary software application on board offshore moored structures.
The program can be best outlined using the following diagrams. For determining the tension in the anchor line, the program uses the calculation model as shown below, only the most important input parameters are shown:
Both the depth and the mooring line length as well as the anchor line type (with corresponding density per unit length) are known. The tension in the mooring line is initially assumed very small. This will result in a calculated termination depth error. Now, the anchor line tension is iterated until the termination depth corresponds to the defined depth. The corresponding tension is displayed in the output.
In order to determine the used mooring line length, the program uses the calculation mode as shown below:
The shape of the catenary is determined by looking at the forces acting in the anchor line. It is assumed the anchor line has no stiffness and thus the form of the anchor line at location (x,y) is equal to the direction of the resulting force.
The program calcluates the coordinates of the anchor line by looking at the horizontal and vertical forces acting in the anchor line. Because in the first run the tension is very small, the steepness of the catenary will be great and the termination depth accordingly.
By increasing the tension with a large fraction of the anchor line weight of the absolute depth error with each iteration, the anchor line will slowly decrease in steepness and the termination depth will approach the defined depth. The resulting line length is displayed in the output field of the program.
The menu shown below gives an impression of the CCCP's input menu for calculations on the tension in the mooring lines.
It is possible to obtain the program, by clicking the download link below