1,721,152 research outputs found
A numerical investigation of the squat and resistance of ships advancing through a canal using CFD
No full textAs a ship approaches shallow water, a number of changes arise owing to the hydrodynamic interaction between the bottom of the ship’s hull and the seafloor. The flow velocity between the bottom of the hull and the seafloor increases, which leads to an increase in sinkage, trim and resistance. As the ship travels forward, squat of the ship may occur, stemming from this increase in sinkage and trim. Knowledge of a ship’s squat is necessary when navigating vessels through shallow water regions, such as rivers, channels and harbours. Accurate prediction of a ship’s squat is therefore essential, to minimize the risk of grounding for ships. Similarly, predicting a ship’s resistance in shallow water is equally important, to be able to calculate its power requirements. The key objective of this study was to perform fully nonlinear unsteady RANS simulations to predict the squat and resistance of a model-scale Duisburg Test Case container ship advancing in a canal. The analyses were carried out in different ship drafts at various speeds, utilizing a commercial CFD software package. The squat results obtained by CFD were then compared with available experimental data
Full-scale unsteady RANS simulations of vertical ship motions in shallow water
No full textThe seakeeping behaviour of a vessel in shallow water differs significantly from its behaviour in deep water. In shallow water, a vessel’s motion responses to incident waves will be affected by hydrodynamic effects caused by the presence of a finite depth. Given that a vessel will sail in shallow water at various times during its service life, such as when entering harbours, it is important to have an understanding of the influence of shallow water on ship motions. In this study, using a commercial unsteady Reynolds-Averaged Navier-Stokes solver, a numerical study of ship motions in shallow water was carried out. Firstly, the characteristics of shallow water waves were investigated by conducting a series of simulations. Then, a full-scale large tanker model was used as a case study to predict its heave and pitch responses to head waves at various water depths, covering a range of wave frequencies at zero speed. The motion results obtained were validated against related experimental studies available in the literature, and were also compared to those from 3-D potential theory. The results were found to be in good agreement with the experimental data. Finally, it was shown that vertical motions were significantly affected by shallow water
Operability assessment of high speed passenger ships based on human comfort criteria
No full textThe growing popularity of passenger cruise lines means continual challenges are faced concerning both a vessel׳s design and its operational ability. Vessel dimensions, service speeds and performance rates are rapidly increasing to keep pace with this expanding interest. It is essential that vessels demonstrate high performances, even in adverse sea and weather conditions, and ensure the comfort of passengers and the safety of cargo. A vessel׳s operability can be defined as the percentage of time in which the vessel is capable of performing her tasks securely. In order to calculate a vessel׳s operability index, many key parameters are required. These include the dynamic responses of the ship to regular waves, the wave climate of the sea around the ship׳s route, and the assigned missions of the vessel. This paper presents a procedure to calculate the operability index of a ship using seakeeping analyses. A discussion of the sensitivity of the results relative to three different employed seakeeping methods is then given. The effect of seasonality on a ship׳s estimated operability is also investigated using wave scatter diagrams. Finally, a high speed catamaran ferry is explored as a case study and its operability is assessed with regards to human comfort criteria
Development of a CFD methodology for the numerical simulation of irregular sea-states
Full text linkThis paper aims to investigate and propose a clear methodology for simulating and maintaining irregular sea simulations within Computational Fluid Dynamics (CFD) for all aspects of the marine industry. As the industry becomes ever more conscious of its overall global emissions, there is an increased interest in beginning to model ever more complex and realistic marine environments. The first step in the beginning to model real-ocean and coastal conditions in CFD is to model irregular seas rather than regular waves. Once this has been achieved further conditions defining realistic oceans can be added, such as varying wind speeds, to these CFD simulations. To achieve the first step in moving towards realistic ocean simulations, this paper proposes a methodology for meshing and time step calculations for completely unknown irregular seas, along with the best practices for such simulations. The methodology is based upon a preliminary statistical analysis of irregular seas, aiming to break down the irregular sea into key points that will define both the meshing and time step methodologies. Further to this, example simulations solely focusing on the generated free-surfaces are presented, along with a discussion on the methodology’s accuracy and limitations within CFD. These simulations also provide practical data on the modelling and simulating of irregular seas
Hydrodynamics of heaving twin cylinders in a free surface using an unsteady-RANS method
No full textThis paper discusses hydrodynamics of heaving twin cylinders in a free surface using an unsteady-RANS method. It was presented at the International Conference on Maritime Technology, Glasgow UK 7th – 9th July 2014
Compass Project: new findings regarding effects of ship motions on human comfort and the way forward
No full textEstimation of the dominant process parameters on coating thickness in a continuous galvanizing line with computational fluid dynamics and machine learning approaches
No full textIn this study, the dominant process parameters in the air-jet continuous galvanizing line on coating thickness were estimated by computational fluid dynamics and machine learning approaches. First, 128 different cases consisting of different levels of process parameters were created with the Taguchi method. Then, numerical analyses were performed for each case, calculating the maximum pressure gradient and maximum shear stress values on the strip, which were then used in the analytical model developed based on one-dimensional lubrication theory to obtain coating thickness values. Lastly, artificial intelligence techniques based on different machine learning algorithms such as K-Nearest Neighbors, linear regression, random forest and Adaboost, the relative effects of the process parameters influencing the coating thickness were compared through the feature importance values. It was observed that the dominant process parameters differ in low and high jet pressure cases. Accordingly, in the case of low jet pressure, air jet pressure, nozzle slot opening and velocity of the steel strip stand out as the dominant parameters, while in the case of high jet pressure, the most effective parameters influencing the coating thickness are air jet pressure and nozzle slot opening. In addition to this, the effect of the distance between the nozzle and the zinc pot influencing the coating thickness can also be neglected in both low and high pressure cases. Moreover, it was also noticed that the effects of nozzle angle and the distance between the nozzle and the steel strip influencing the coating thickness increase with increasing jet pressure
Unsteady RANSE and detached-eddy simulations of cavitating flow
No full textThe Twisted Delft Hydrofoil and the Potsdam Propeller Test Case (PPTC) were used to analyse and compare the capabilities of Reynolds-Averaged Navier Stokes Equations simulations (RANSE simulations) and detached-eddy simulations (DES) to predict three-dimensional cavitating flow. Although the RANSE simulations were able to predict the lift and drag forces in reasonable agreement with the experiments, it has been shown that the accurate numerical simulation of cavitational flow requires the use of an advanced model such as the SST k-omega detached-eddy model
Assessing the impact of a slow steaming approach on reducing the fuel consumption of a containership advancing in head seas
No full textIt is very important to be able to evaluate a ship’s response to waves, because any added resistance or loss of speed may cause delays or course alterations, leading to financial losses. The slow steaming approach is increasing in popularity for commercial vessels, as it provides a method of reducing fuel use, and therefore operating costs, in the current economic climate. Potential flow theory based linear strip theory is still a widely used method among naval architects, due to its fast solutions with sufficient engineering accuracy. The key objective of this study is to predict the ship motions and added resistance of the S-175 containership, and to estimate the increase in effective power and fuel consumption due to its operation in regular and irregular head seas. The analyses were performed at design and slow steaming speeds, for a range of wave conditions in regular seas, and for three different sea states in irregular seas. The results obtained at a ship speed corresponding to Froude number 0.25 were compared to available experimental data and were found to be in good agreement with the experiments. The numerical analyses were carried out using VERES, which is based on potential flow theory
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