Research On Ship Effective Wake Fraction

Effective wake fraction is an important index to propulsion system.Traditional predicting methods are not able to reflect inherent law of wake flow and meet the changing patterns of modern ship.Therefore,a research on wake flow and developing a new high-precision method is extremely necessary.The paper studied on the three kind of main ship forms which were classified into single screw and twin-screw ship.The study on every type of ship had the support of tank test and CFD,the date was reliable.The paper studied on single screw ship at first.Analysis is the basis of study,model self-propulsion test is the most common and effective way to acquire effective wake fraction.Therefore,the paper analyzed effective wake fraction at first and elaborated the impacting mechanism of some parameters then,lastly it studied the influence rule of these parameters by model self-propulsion test.The result was obvious and different for each type of ship.CFD is a conveniently and effectively auxiliary way for study.The paper selected a bulk carrier and container with modeling,meshing and solving to explore the influence rule of parameters.Meanwhile,it analyzed other characteristics by taking advantage of CFD technology like uniformity.The CFD result presented same conclusion like self-propulsion test and demonstrated the right of influence rule indirectly.Tangential effective wake is the characteristic of win-screw ship.Firstly,the paper illustrated its property and importance in design based on tangential effective wake analysis.Secondly,it studied the problem of tangential effective wake in scale effect by self-propulsion test and CFD.Thirdly,the paper measured one twin-screw ship's tangential effective wake fraction with 3 different methods.The result showed there was difference between 3 methods and PIV technology is more accurate than others.The paper proposed a new way to predict effective wake fraction based on the above findings and empirical formula.Meanwhile,it was programmed using FORTRAN for convenience.The program can predict not only effective wake fraction,but also thrust,torque,delivered power and so on.Comparing with self-propulsion test result it was founded that new method had certain practical value with acceptable error.