Mooring and Positioning of Vehicles in a Seaway 



insight and extends the utility of basic "tools" used in hydrodynamic 

 and dynamic investigations. 



When considering the problem of maintaining a ship on station 

 for a long time period, various concepts for achieving a minimum 

 deviation from a derired operating point are possible, with the two 

 main methods being that of fixed mooring or by use of a dynamic 

 positioning system. In certain situations where mobility is required, 

 as well as due to the high capital cost of a mooring system for very 

 deep water operations, the associated high cost of emplacement and 

 the dangers of damage due to large storm conditions, a mooring 

 system does not appear to be attractive. Dynamic positioning is a 

 more recent development, which has only received limited applica- 

 bility to date. 



In order to provide the information ncessary to determine 

 the possibility of an application of dynamic positioning, it is neces- 

 sary to carry out particular analyses to determine the environmental 

 conditions appropriate to possible operating areas; the resulting 

 forces and moments acting on the ship; the arrangement and type of 

 control effectors; the possible signal systems that provide the error 

 and command signals for actuation of controls; possible control 

 system concept designs; etc. 



The important quantities that must be determined for proper 

 design of the positioning system are the disturbing forces that act 

 on the ship. The major forces and moments that affect the ship 

 stationkeeping ability in this case are the more-or-less steady type 

 of "drifting" forces imposed by the environment, and these quantities 

 are amenable to computation by means of hydrodynamic analyses 

 using available theory. 



In all of the foregoing situations the importance of hydrodynamic 

 force evaluation and its applicability to obtain desired engineering 

 performance data is paramount. Many publications are available in 

 the literature on ship motion theoretical studies that can be applied 

 to the above problem areas , with reasonable expectation of validity 

 for the results. The central theme of this Symposium, "Hydrody- 

 namics in the Ocean Environment," is certainly appropriate to the 

 present International Decade of Ocean Exploration which will em- 

 phasize the technology that will yield benefits to Mankind, The 

 application of the basic developments in hydrody nannies of ship motion 

 to the applied engineering problems associate with maintaining 

 vessel operations at fixed positions in the ocean, which will be 

 required as part of this extensive international effort, is a vital 

 element in achieving improved system performance. It is also a 

 good illustration of the direct application of many years of basic 

 research toward the solution of problems that are anticipated as 

 further and deeper ventures into the sea are made. The present 

 paper is aimed at providing a limited description of the use of 

 hydrodynamic analysis when applied to some of these problenn areas. 



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