Non-stationary Analysis Of Main Engine Output Power Fluctuation Based On Discrete Wavelet Transform

To reduce the GHG(Greenhouse Gas)emissions from shipping,the Energy Efficiency Design Index(EEDI)and the Ship Energy Efficiency Management Plan(SEEMP)were made mandatory at MEPC 62(July 2011).Among the shipping companies and the ship operators,the Energy Efficiency Operational Indicator(EEOI)was defined as a tool of SEEMP and “slow steaming”,“weather routing” and “just in time arrival” are considered as the most effective SEEMP related measures.From the viewpoint of actual powering in a seaway,however,it should be noted that the mechanism of the added resistance,the loss in propulsive efficiency and the drop of fuel efficiency have not been sufficiently analyzed yet.Multi-Resolution Analysis(MRA)based on the discrete wavelet transform(DWT)is applied to non-stationary main engine power response of a ship.The data was obtained by on-board measurements that were carried out under relatively severe sea conditions.In the full scale measurements,the ship travelled on several courses to investigate the change of the main engine response relative to the encounter wave angle.The power spectra of ship motions and main engine power are achieved and analyzed using Fourier analysis.In the thesis,characteristics of MRA are investigated by comparing to the results of Fourier analysis.Using MRA of DWT,the main engine response could be separated into several details and a smooth.A detail and a smooth were influenced by the ship motions and course alterations respectively.MRA is recognized as a kind of band pass filtering.MRA base on FFT and inverse FFT can be achieved.Through comparative analysis,MRA of DWT cannot be recognized as a band pass filtering in the strict sense and its physical meaning should be clarified for more valid usability.During the full-scale experiment,fuel consumption was measured by reading the fuel flow meter and the fuel temperature at the beginning and the end of each run,and the relationship between the main engine power and fuel consumption can be expressed as a linear function.It is shown that MRA is very useful to estimate changes of the main engine response and can be applied to estimate the fuel efficiency.Fuel consumption can be estimated by the smooth of the main engine power without direct measurements.And an ecofriendly navigation support system also can be realized without direct measurement of the main engine power and fuel consumption.The main engine power can be estimated by a combination of the smooths of the ship motions,but the change of fuel consumption in waves can be roughly estimated by DWT smooths of ship motions.Furthermore,relative power contribution analyzes of Multivariate Auto-regressive(MAR)model are introduced.Based on the MRA analysis,it has been shown that the fluctuation of the main engine power consists mainly of the smooth ‘SJ' and the third detail ‘D3'.And we estimate the relative power of the ‘D3' spectra by the MAR modelling.Time series of the main engine power and the six ship motions are used to formulate the MAR model to investigate ship motions influencing the main engine power fluctuation.It is shown that the combination of MRA and MAR modelling are very useful to estimate changes of the main engine response and the combination can be applied to estimate the fuel efficiency.