Wyniki wyszukiwania - BazTech

1

Investigating fuel injection strategies to enhance ship energy efficiency in wave conditions

Ghaemi Hossein, Zeraatgar Hamid, Barjasteh Mojtaba

Polish Maritime Research

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2024

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nr 1

85--93

EN

The prediction of fuel consumption and resulting transportation costs is a crucial stage in ship design, particularly for conditions involving motion in waves. This study investigates the real-time fuel consumption of a container ship when sailing in waves. The overall ship performance is evaluated using a novel non-linear coupled hull-engine-propeller interaction model. A series of towing tank experiments for hull resistance in waves and propeller performance are conducted. The ship engine is mathematically modelled by a quasi-steady-state model equipped with a linear Proportional-Integrator (PI) governor. Various scenarios of shipping transportation are studied, and the resulting instantaneous fuel consumptions and their correlation to other dynamic particulars are demonstrated. Additionally, daily fuel consumption and fuel cost per voyage distance are presented. It is also shown that the controller can effectively adjust the fuel rate, resulting in minimum fuel consumption. The study concludes that there is no correlation between fuel consumption and the frequency of fuel rates. The present framework and mathematical model can also be employed for ship design and existing ships to predict the total required energy per voyage.

2

Effects of propeller fouling on the hydrodynamic performance of a marine propeller

Zinati Ali, Ketabdari Mohammad Javad, Zeraatgar Hamid

Polish Maritime Research

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2023

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nr 4

61--73

EN

Propeller performance is typically considered under clean conditions, despite the fact that fouling is an inevitable phenomenon for propellers. The main objective of this study is to investigate the effects of roughness due to fouling on the performance of a propeller using a CFD simulation in conjunction with the roughness function model. A simulation of a clean propeller is verified for a five-blade propeller model using existing experimental results. A roughness function model is then suggested based on existing measured roughness data. The simulations are extended for the same propeller under varying severities of roughness. Initially, it is concluded that KT and ηo gradually decrease with increasing fouling roughness, while KQ increases, compared to smooth propeller. For instance, at J=1.2 for medium calcareous fouling, KT is reduced by about 26%, KQ increases by about 7.0%, and ηo decreases by 30.9%. In addition, for the rough propeller, the extra power required is defined as the specific sea margin (SSM) to compensate for the power loss. A slight roughness causes a large decrease in ηo. A propeller painted with foul-release paint and an unpainted propeller are found to require 2.7% SSM and 57.8% SSM over four years of service, respectively. Finally, the use of foul-release paints for propeller painting is strongly advised.

3

Simulation of turning manoeuvre of planing craft taking into account the running attitude change in a simplified manner

Sadati Kazem, Zeraatgar Hamid, Moghaddas Aliasghar

Polish Maritime Research

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2022

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nr 4

12--25

EN

The modelling and simulation of planing craft manoeuvres requires coupled six degrees of freedom (6 DOF) motion equations. A coupled 6 DOF motion equation needs hundreds of manoeuvring hydrodynamic coefficients (MHCs) that are mostly determined using the planar motion mechanism (PMM) test. The number of test runs is too high, unless a kind of simplification is imposed to the motion equations. This study modifies 6 DOF motion equations to 4+2 DOF motion equations in which heave and pitch equations are replaced by dynamic draught and trim (so-called running attitude), respectively. The method is applicable for a manoeuvre that commences in the planing regime and ends in the same regime. On that basis, the PMM test is conducted and the model is restrained in the vertical plane at a certain running attitude, determined by a resistance test. The 4+2 DOF method, together with MHCs from the PMM test, are employed for the simulation of turning manoeuvres of a 25° prismatic planing hull. The results of the simulation indicate that the 4+2 DOF method reasonably predicts the path of the craft during the turning manoeuvre and cuts the number of PMM tests required at the same time. The PMM test results show that MHCs are highly related to forward speed and wetted surfaces. The turning manoeuvre simulation shows that the non-linear terms of MHCs cannot be ignored. The STD/L (Steady Turning Diameter divided by Length of the craft) for a planing craft is very large, compared to ships.

4

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.

5

A combined method to predict impact pressure on planing craft

Tahmasvand Hossein, Zeraatgar Hamid

Polish Maritime Research

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2021

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nr 1

4--15

EN

Prediction of the pressure distribution on a planing craft in waves deeply affects its structural design and safe operation. In this paper, the possibility of pressure prediction for the planing craft in waves is studied. A combined method is formulated by which craft motions in waves are computed using a 2.5D method, and the impact pressure is anticipated by the equivalent wedge method. Experiments are conducted to record the vertical acceleration and pressure time trends on a model. Comparing the results of the combined method with the experiments indicates that this approach successfully predicts the heave and pitch motions and the time evolution of the acceleration and pressure. The method presents good estimations for the peaks of the acceleration and pressure. Using the combined method, a parametric study on maximum peak acceleration and pressure is also conducted for various forward velocities and wave heights. It has been shown that the combined method is a fast and reliable tool for maximum peak pressure prediction. The method may be employed for structural design and optimization.

6

Propeller hydrodynamic characteristics in oblique flow by unsteady ranse solver

Nouroozi Hossein, Zeraatgar Hamid

Polish Maritime Research

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2020

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nr 1

6--17

EN

Propellers may encounter oblique flow during operation in off-design conditions. Study of this issue is important from the design and ship performance points of view. On the other hand, a propeller operating in oblique flow may sometimes result in a better propulsion efficiency. The main goal of the present study is to provide an insight on the propeller characteristics in the oblique flow condition. In this research, the performance of the DTMB 4419 propeller is studied by the numerical method based on solving Reynolds Averaged Navier‒Stokes (RANS) equations in several inflow angles. The sliding mesh approach is used to model the rotary motion of the propeller. Initially, the numerical method is verified by grid and time step dependency analysis at various inflow angles. Additionally, computed results at zero inflow angle are compared with the available experimental data and good agreement is achieved. Finally, the forces and moments acting on the propeller are obtained for 0° to 30° inflow angles. It is concluded that the inflow angle up to 10° has no significant influence on the thrust and torque coefficients as well as the propeller efficiency. However, at high angles up to 30°, the thrust and torque coefficients increase as the inflow angle increases, which may result in a significant improvement of propeller efficiency.

7

The analysis of overall ship fuel consumption in acceleration manoeuvre using hull-propeller-engine interaction principles and governor features

Zeraatgar Hamid, Ghaemi M. Hossein

Polish Maritime Research

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2019

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nr 1

162--163

EN

The problem of reduction of greenhouse gas emissions in shipping is currently addressed by many research works and related industries. There are many existing and visionary technologies and ideas, which are conceptually defined or practically realised. This goal can be achieved in different ways, and reducing fuel consumption is one of the major methods. In these circumstances, the aim of this study is to analyse the possibility of fuel consumption reduction by using an alternative control strategy for low-speed marine diesel engines which would take into account the interactions between hull, propeller and main engine. For this purpose, a mathematical model including ship hull and propulsion system is developed. A case study is conducted for a ship for which the results of both the ship hull and screw propeller model tests are available. A low-speed two-stroke diesel engine is then selected for the considered ship. Two different governors are included in the model and their parameters are changed to investigate the dynamic behaviour of the system when simulating the forward acceleration mode in calm sea conditions. The research is mainly focused on variations of fuel consumption by the ship passing a certain distance to reach the nominal constant speed. It is concluded that, for a given travel distance, it is possible to save considerable amount of fuel at the expense of slight increase of journey time.