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1
Content available Impact of propeller emergence on hull, propeller, engine, and fuel consumption performance in regular head waves
Ghaemi Mohammad Hossein, Zeraatgar Hamid
Polish Maritime Research
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2022
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nr 4
56--76
EN
In this study, the impact of propeller emergence on the performance of a ship (speed), propeller (thrust, torque, and RPM), a diesel engine (torque and RPM) and fuel consumption are analysed under severe sea conditions. The goal is to describe the variation in the system variables and fuel consumption rather than analysing the motion of the ship or the phenomenon of propeller ventilation in itself. A mathematical model of the hull, propeller, and engine interactions is developed in which the propeller emergence is included. The system parameters are set using model experiments, empirical formulae, and available data for the engine. The dynamic response of the system is examined in regular head waves under submerged and emerged conditions of the propeller. The pulsatility and the extent of variation of 20 selected variables for the coupled system of hull, propeller, and engine are elaborated using quantitative and qualitative terms and absolute and relative scales. The simulation begins with a ship moving on a straight path, in calm water, with a constant speed for the ship, propeller and engine under steady conditions. The ship then encounters regular head waves with a known time series of the total resistance of the ship in waves. Large motions of the ship create propeller emergence, which in turn reduces the propeller thrust and torque. This study shows that for a specific ship, the mean ship speed, shaft angular velocity, and engine power were slightly reduced in submerged conditions with respect to calm water. We compared the mean values of the variables to those in the emerged condition, and found that the shaft angular velocity was almost the same, the ship speed was considerably reduced, and the engine power significantly dropped with respect to calm water. The ratios of the amplitude of fluctuation to the mean (Amp/Mean) for the ship speed and angular velocity of the shaft under both conditions were considerable, while the Amp/Mean for the power delivered by the engine was extremely high. The outcomes of the study show the degree of influence of propeller emergence on these variables. We identify the extent of each change and categorise the variables into three main groups based on the results.
2
Content available Energy retrieval from sea waves
Szelangiewicz T., Żelazny K.
Zeszyty Naukowe Akademii Morskiej w Szczecinie
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2015
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nr 41 (113)
30--34
EN
Seas and oceans occupy approx. 71% of the Earth. On their surface wave action of stronger or weaker magnitude can be observed throughout a major part of the year. Wind-generated wave action contains energy, which can be retrieved and used for electrical current production. The paper shows what energy is contained in wind-generated waves on various ocean areas, presents dynamics of water movement in a wave as well as several examples of calculation results of the velocity of water particles and hydrodynamic pressures occurring in a wave.
3
Content available An overview of methods for wave energy conversion
Chybowski L., Kuźniewski B.
Zeszyty Naukowe Akademii Morskiej w Szczecinie
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2015
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nr 41 (113)
17--23
EN
Legal and economic aspects connected with generating electricity from waves are discussed and a classification of wave energy converters is shown. The study discusses selected technical solutions generating electricity from sea and ocean waves. Research directions of the Maritime University of Szczecin, Poland, are presented in terms of energy conversion from wave energy into electricity and using sea wave energy for coast protection against waves. The potential of waves as a renewable energy source (in Europe and outside) is evaluated and problems connected with implementing wave energy conversion systems are outlined.
4
Content available Sea waves models used in maritime simulators
Zwolan P., Czaplewski K.
Zeszyty Naukowe / Akademia Morska w Szczecinie
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2012
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nr 32 (104) z. 2
186-190
EN
The modern simulation software includes an impact of forces acting on the ship hull. One of the most significant forces is sea waves acting. The mathematical model allows simulation of ship motions in irregular sea wave area, both – at deep and shallow waters. The wave surface model enables simulation of the wave elevation in compliance with wave spectrum occurring in various conditions. The paper presents general description of the sea wave model used in maritime simulators. An example of such simulators is used at the laboratory of the Naval University of Gdynia, where it is operated basing on NT-Pro 5000 software by Transas Marine. The latest version of simulation software gives a possibility to select the wave spectrum. Selection of the waving type, depending on sea area location, makes the ship movement more reliable. This is an important element in testing the ships behavior process.
5
Content available State equations in the mathematical model of dynamic behaviour of multihull floating unit
Królicka A.
Polish Maritime Research
|
2010
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nr 1
33-38
EN
This paper concerns dynamic behaviour of multihull floating unit of catamaran type exposed to excitations due to irregular sea waves. Dynamic analysis of multihull floating unit necessitates, in its initial stage, to determine physical model of the unit and next to assume an identified mathematical model. Correctly elaborated physical models should contain information on the basis of which a mathematical model could be built. Mathematical models describe mutual relations between crucial quantities which characterize a given system in time domain. The dynamic analysis of multihull unit was performed under assumption that the unit’s model has been linear and exposed to action of irregular sea waves. Mathematical model of such dynamic system is represented by state equations. The formulated equations take into account encounter of head wave which generates symmetrical motions of the unit, i.e. surge, heave and pitch. For solving the equations the following three wave spectra were taken into consideration: - ISSC (International Ship Structures Congress) spectrum - Pierson-Moskowitz spectrum - Paszkiewicz spectrum.
6
Content available remote Stochastic approach to movements of a multihull on waves
Królicka A.
Vibrations in Physical Systems
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2008
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Vol. 23
217--222
EN
Due to difficulties in determining precise initial conditions for the motion of sea waves and the nature of wind undulation, the dynamics of sea waves can be only modelled within the framework of a stochastic theory. The article presents a method for determining differential equations of motion for multihulls, such as catamaran or trimaran. The catamaran sails at constant translatory velocity and at an arbitrary angle to the undulation direction. The set of differential equations of motion presented in the article models anti-symmetric (lateral) movements of the catamaran. For those movements, stochastic differential equations ( Itô equations) are constructed in the form of the equation set (8). Using the state vector X and the excitation vector Y , the Itô equations take the form (9) and (10).
7
Content available Application of neural networks to the prediction of significant wave height at selected locations on the Baltic Sea
Paplińska-Swerpel B.
Archives of Hydro-Engineering and Environmental Mechanics
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2006
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Vol. 53, nr 3
183-201
EN
This paper describes the application of methodology based on the artificial neural network technique to make short-term wave forecasts. The neural network model is used to predict significant wave height at a selected location on the Baltic Sea based on wave and/or wind data at ten points scattered on the sea. High quality hindcast data were used in the process of developing the forecast methodology. The data originated from the WAM4 wave model. The results show that the neural network technique allowed significant wave height to be predicted accurately. The agreement obtained by a comparison with a testing data set was sufficiently good to confirm the effectiveness of this approach.
8
Content available Specific features of sea waves in the Pomeranian Bay
Paplińska B.
Archives of Hydro-Engineering and Environmental Mechanics
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2001
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Vol. 48, nr 2
55-72
EN
The paper concerns investigations of regional variability of the wave climate in the Pomeranian Bay. Analysis is based on the wave measurements taken during a period of four months and numerical wave model WAM4 results. The calculations covered period of 3 months in 1997 (Oct., Nov., Dec.) and two years: 1998,1999. Analysis of wave modelling results shows that wave fields are not homogeneous in the whole area. The gradual increase (up to 50%) of yearly mean values of selected wave parameters can be observed going from the south-westerly of the Bay to north-easterly direction. Directional distribution of significant wave height is determined by wind climate and shape of the basin and prevails in easterly, south-easterly, south-westerly directions.
9
Content available remote Wave analysis at Lubiatowo and in the Pomeranian Bay based on measurements from 1997/1998 - comparison with modelled data (WAM4 model)
Papińska B.
Oceanologia
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1999
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No. 41 (2)
241-254
EN
The third generation WAM4 wave model was applied to the Baltic Sea. The computed significant wave height was compared with wave measurements for the periods October-November 1997 and February-May 1998. The calculations were conducted with wind fields obtained from the numerical weather prediction system at present in use as a quasi-operational system at ICM. Statistical analysis indicates good agreement between the modelled and measured significant wave height. Finally, a visualisation of wave fields is presented in the form in which it could be published in a daily meteorological forecast.
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