Catenary Theory Research Articles

Study on Initial Design Method of Underwater Line Structures (2nd Report)

In the previous report, we derived extensible catenary equations and discussed the fundamental characteristics of catenary. We also descrived the ways to solve the equations under various boundary conditions.In this paper, we introduce a program package based on the extensible catenary theory. Next, a simplified dynamic analysis method is shown. The accuracy of calculation by the program package is verified by comparing with the results of tank tests or calculations with other programs. Finally, initial design method of underwater line structures using the program package is shown and typical line structures such as mooring lines, towing lines and flexible marine risers are designed easily applying this method.

Application of extensible catenary theory to determine the displacement of a moored ship

A mathematical model of a ship moored by several cables is developed taking into account the extension of the cables. The equations for a single cable are rigorously developed and then solved numerically for a complete multipoint mooring system. Results are presented to show the relationship between the lateral displacement of the ship, the corresponding restoring force and the length of each cable remaining on the sea bed for a representative system.

Study on Deployment Method of Mooring Chains of Semi-submersible Offshore Units

In the mooring operation of a semisubmersible offshore units, mooring anchors and chains are deployed from units by anchor handling boats. In this case, there are two types of deployment method. In one method, all chains are at first dropped onto seabed, then deployed. In the other method, both dropping and deploying operations are performed simultaneously. To make it clear which deployment method is more efficient, it becomes necessary to investigate behaviours of chains and pull-loads of boats under deployment. In this paper a series of analyses on deployment operations are carried out using a newly developed simulation model where equilibrium states of chains are evaluated based on catenary theory and dropping motions of chains can be considered. According to the results optimum deployment method and control pattern for dropping chains are discussed.

カテナリー理論の応用限界

カテナリー理論の応用限界

Study on the Motions of a Moored Vessel among the Irregular Waves

In this paper, the motions of a large vessel which is moored by the chains among the irregular sea of finite depth are studied.It is the main aim to investigate the phenomenon of slow-drift oscillation of the moorilvsystem.Theoretical and experimental results show the followings :(1) If the damping coefficient of the swaying motion near the natural frequency of the system could be corrected from freely damped oscillation test, the slow-drift oscillation may be estimated by using the already existing method to calculate the spectrum of slowly varying drift force.(2) The tensions of mooring lines are affected definitly by the slow-drift oscillation. Even in such a case, it is permissible in the design sense of the mooring syslem to calculate the maximum tension of the mooring lines from the maximum displacement of swaying using what is called “catenary theory”.(3) Finally, a design method of the mooring system is shown by way of example.

Study on the Motion of a Moored Body and the Tension of Mooring Lines

In these years off-shore structures are built with various purposes. It is important problem to study about their mooring system. And this study is also important for ships. In this paper it is aimed to study the tension of mooring lines.Mooring tension was formerly calculated by what is called “catenary theory”, but it is calculated here by “corrected theory”, which includes the effect of elasticity of the mooring line. Using this theory, the tension is calculated not only in ordinary state but in severe surroundings of wave, wind and current. And in this paper, there are mentioned some practical applications and results of experiments as follows ;I. Calculating formulas are composed for various situations. The result shows good agreement with experimental one. Calculating formulas are also made in case that a sinker or a buoy is installed in the middle of the mooring line.II. The tension calculated by these formulas is applied to analysis of the motion of a moored body. A simple one of two dimensional model is used, that is semi-submerged circular cylinder. The motion of the moored body and the tension of mooring lines are calculated by numerical integral methods. Experiment is carried out under same conditions. Comparison of these results is fairly satisfactory.III. The dynamical effect and the similarity law of the mooring line are considered and a few conclusions are shown.