Study on the Design of Single Point Buoy Mooring
|Month/Year||March 1996 PARI Technical Note 0829|
|Department/Divison||Hydraulic Engineering Division Wave Laboratory|
|Executive Summary|| A buoy is utilized in offshore area to moor a large vessel for efficient cargo handing. Most buoy births are equipped with oil transfer facilities for tankers. In this thesis, this kind of buoy is called Single Buoy Mooring(SBM).
There is no standardized and specific design method of SBM neither in Japan nor in foreign countries. The development of simulation programs is necessary for the design of buoy, because the computer simulations are indispensable as design tools for floating structures. In the design of buoy, storm loads and operating mooring laads are considered separately. Therefore, the designs in storm and operating conditions should be wellbalanced.
In this thesis, numerical simulation programs in wind and waves are developed for SBM design, and the design procedures are also studied. The study has yielded the following conclusions.
(1)Buoy movements and mooring forces in storm conditions
Hydrodynamic forces on vertical cylinder buoy were calculated by the dividing region method. The comparison between calculated and model test results of the wave forces on a fixed buoy and the movements of freely floating buoy showed a good agreement.
Two types of chain-moored buoy were studied; catenary anchor leg mooring (CALM) and single anchor leg mooring (SALM). It was found that the mooring forces of CALM buoy in large waves can not be calculated accurately by the static catenary theory.
The calculated movements of articulated column buoy agreed very well with the results of hydraulic experiments and field observations.
(2)Operating loads by ship motion in wind and waves
A ship moored to SBM moves widely with a long period even in steady wind. The hawser load is increased by the short period ship motion in waves. A numerical model is developed for estimating the ship motion and mooring forces in wind and waves. When the angle between wind and wave directions is less than 60 degrees, the error of calculation compared with laboratory data is at most about 20%.
(3)Design method of SBM
A design method is introduced to select storm and operating design conditions. It is based on a fundamental concept that the encounter probabilities to the design winds and waves in both conditions during the lifetime shouid be of the same value for the well-balanced design.