Journal of Naval Architecture and Marine Engineering

Numerical investigation of hydrodynamic performance of conventional and ducted propellers

Md Shahjada Tarafder, Md Imdadul Haque, Md Asaduzzaman, Md Zahidul Islam Laku — Sun, 31 Dec 2023 00:00:00 +0000

An efficient and optimized propeller can reduce ship operating costs substantially. The recent development of Computational Fluid Dynamics (CFD) has a significant impact on the initial stage of propeller design. Being motivated by the success of a CFD approach known as Reynolds Averaged Navier-Stokes Equation (RANSE) in solving many hydrodynamic problems, this paper explores the use of RANSE solver to estimate propeller open water characteristics. Multiple RANSE solvers can be used for CFD simulation. Among these k-ϵ turbulence model is used for its better performance on propeller analysis. Numerical results are compared with the results obtained from well-established polynomial regression formulae of Wageningen-B series propeller. A comparison shows an error of less than 5% for most of the cases. The same propeller is numerically analyzed again after fitting a 19A duct on it. To achieve optimal performance space between the duct and propeller blade tip is kept as small as possible. Grid independence test is done in both cases for a more accurate estimation within a particular time frame. Mesh sensitivity analysis is carried out in this paper based on thrust and torque coefficients. This paper shows that the maximum computed efficiencies for both the conventional and ducted propeller systems are found to be 60% but at different speeds. The ducted propeller system gives better performance up to advance coefficient J=0.48.

Journal of Naval Architecture and Marine Engineering, 20(3), 1–10

Artificial intelligence for ship design process improvement: a conceptual paper

A Maimun, S C Loon, J Khairuddin — Sun, 31 Dec 2023 00:00:00 +0000

This paper explores the artificial intelligence (AI) concept for complex engineering design processes in the shipping industry. It is driven by the computer technologies advancement for fast and concurrent tasks processing, machine learnability, and data-centric approach. While AI has been adopted in many industries, it is still lacking the structured approaches for practical implementation. This is especially on the generality of the methodologies and explaining AI to the non-technical members and their preparedness. Therefore, this work proposed a conceptual framework to systematically extract, represent and visualize the ship design knowledge, to develop and deploy the machine learning (ML) models, and to demonstrate the AI-based ship design processes. Comparisons to the generic ship design model were made and discussed to highlight the improvements observed. It is found that while the conventional algorithmic approach procedures were faster in terms of execution time, the stepwise empirical models were often limited by the dataset and the design assumptions with restricted estimation capabilities for solving the nonlinear ship design problems. The findings presented the impact in improving the existing processes and effectively reducing its cycle. Additionally, the approach emphasised on the validated ship design data thus its generalization for fast and wide adoptions at scales.

Journal of Naval Architecture and Marine Engineering, 20(3), 1–7.

A numerical investigation on hydrodynamic interaction coefficients for two freely floating barges of tandem configuration in waves

Mir Tareque Ali, G Sobahani — Sun, 31 Dec 2023 00:00:00 +0000

While installing offshore structures two or more structures are observed floating close to each other in waves. Consequently, the adjacent floating structures influence the fluid loading on each body. Due to radiated waves produced by the motion of adjoining floating structures and the wave reflection or, sheltering effect because of the presence of these nearby structures, the wave loading for the multi-body case will be quite different from that of a single-body case. Accurate computation of hydrodynamic interaction coefficients and hydrodynamic coefficients are vital for a multiple floating body case since the motion response prediction uses these parameters in solving the 6xN simultaneous equations (where N is the number of closely floating structures). The hydrodynamic interaction coefficients are investigated in this paper for two three-dimensional (3-D) structures floating closely in water. A commercial hydrodynamic software named Hydrostar (introduced by Bureau Veritas) which is based on linear three-dimensional potential theory is adopted for numerical simulations of the present problem. To validate the numerical results for hydrodynamic interaction coefficients, the present computation results are compared with the published results for a rectangular box and a vertical circular cylinder model floating closely in regular waves, and a satisfactory agreement is observed. Finally, numerical simulations are performed for two identical rectangular barges floating close to each other in the tandem arrangement in regular waves. During the computations, the gap between the floating barges is varied and the occurrence of hydrodynamic resonances in the gap is also examined. Lastly, considering the analysis for the multi-body case, a few conclusions are made.

Numerical analysis of flow over bluff bodies with different shapes

A M Abir , P R Chowdhury, G K Saha — Sun, 31 Dec 2023 00:00:00 +0000

In this study, Ansys Fluent solver with SIMPLE algorithm and K-Epsilon turbulence model is used to determine the drag forces on bluff bodies with different shapes and arrangements at different Reynolds numbers. In the process, the cross-sectional areas of all the bodies are kept approximately the same to keep the amount of material same for all the cases. First, simulations of the 2D unsteady viscous flow around cylinders of circular and elliptical shapes with the same cross-sectional area are performed at Reynolds number 1000. In the case of elliptical cylinder, two different orientations are used, namely: major axis along the flow (horizontal orientation) and major axis perpendicular to the flow (vertical orientation) for aspect ratio of 0.8. The horizontally oriented elliptical cylinder shows the least drag compared to the circular and vertically oriented elliptical cylinders. The vertically oriented elliptical cylinder shows the maximum drag because of the large projected area and early flow separation from the cylinder. Later, the drag coefficients of two circular cylinders of the same diameter in tandem arrangement are investigated at inlet speeds of 2.5, 5, 7.5, and 10.5 knots considering L/D ratios of 2.0, 2.5, and 3.0, where L is the center-to-center distance and D is the diameter of the cylinders. For the upstream(first) cylinder, the flow separation from the cylinder is delayed as the speed increases, and the wake becomes narrower. Consequently, the drag coefficient for the first cylinder decreases with increase in speed. As the speed increases, the disturbance on the downstream(second) cylinder increases with respect to the first cylinder, and hence the drag coefficient increases.

Journal of Naval Architecture and Marine Engineering, 20(3), 1–10

Finite element approach to analyze structural discontinuities associated with ship hull

Kazi Naimul Hoque, Md Shahidul Islam — Sun, 31 Dec 2023 00:00:00 +0000

The finite element method (FEM) is widely recognized as a powerful numerical analysis technique for approximating solutions in structural mechanics. Addressing the configuration of plate-type structures, particularly those with discontinuities, is crucial not only in ship and aircraft construction but also in various other fields. Structural discontinuities occur when there are sudden changes in the cross-section of structural members due to material imperfections or high-stress areas. This paper focuses on the fundamental principles of FEM for solving two-dimensional plane stress problems and analyzing stresses such as normal stress, shear stress, and von-mises stress at the four integration points (gauss points) in different sections of ship structures, particularly in vulnerable regions. To address structural discontinuity problems in various ship structures, a finite element program utilizing object-oriented techniques was developed, employing four-node quadrilateral elements. The analysis results of gauss point stresses obtained from the developed program were validated against a commercial finite element analysis software to ensure accuracy and reliability. Additionally, a mesh viewing program has been developed in the Python programming language to enable the visualization and analysis of the generated mesh using the developed object-oriented finite element program.

J. Nav. Arch. Mar. Engg., Vol 20(2), December, 2023; p 1-14

Energy-efficient inland cargo ship design based on fuel consumption and CO2 emission control using CFD

S M Rashidul Hasan, Md Mashud Karim — Sun, 31 Dec 2023 00:00:00 +0000

Inland ships usually face some additional restrictions in comparison to the sea-going ship. Apart from the regulations imposed by each country, the effect of restricted waterways governs the major ship design constraints. For this reason, designing energy-efficient inland ships incorporating shallow water effects is very challenging. There is little research done to overcome these challenges; most of them lack the comparison of improved design with the existing one. This paper has analysed1634 general cargo ships from existing Bangladeshi inland cargo ships' data and considered 281 ships only for performance evaluation after data verification. The selected cargo ships were further assessed by using revised Energy Efficiency Design Index (EEDI) parameters applicable for inland ships of Bangladesh. Fuel efficient and less CO₂ emitter efficient cargo ships were identified. After considering the effect of shallow water, a set of ship design suggestions is proposed. These suggestions were validated by redesigning an existing cargo ship based on the suggestions and comparing their resistance with the parent hulls. Computational Fluid Dynamics (CFD) is used to calculate the ship resistances and it is found that 13%reduction in total resistance can be achieved simply by choosing improved principal particulars based on the proposed design suggestions.

J. Nav. Arch. Mar. Engg., Vol 20(2), December, 2023; p 1-10

Numerical prediction of free surface water wave for the flow around cambered hydrofoil

Sajid Hossain, Tawhidur Rahman, Md Mashud Karim — Sun, 31 Dec 2023 00:00:00 +0000

In this study, the implicit Finite Volume Method (FVM) based on Reynolds-Averaged Navier-Stokes (RANS) equations are used to simulate the flow past a hydrofoil that is submerged in the vicinity of the free surface of water. To simulate the turbulent flow around the hydrofoil surface, realizable k-ε turbulence model is used. The Volume of Fluid (VOF) method is incorporated into the numerical simulation to capture the interface between water and air. The free surface wave generated by the stream around NACA 0012 hydrofoil is computed and compared with experimental results to validate the numerical simulation. Grid independency is checked by using three different grid sizes and the validation is done by comparing the experimental results of ratio of submergence level h/c=0.95. Finally, the cambered hydrofoil NACA 2412 is analyzed to predict the free surface water waves for seven submergence ratios, ranging from submergence level h/c= 0.95 to 5.5. The pressure coefficient, velocity contour, static pressure contour, and force coefficients are shown graphically and in tabular form for Froude number 0.57. The restricted and shallow water effects are also studied in this research. This study reveals that implicit finite volume method can predict the wave of free surface due to flow past cambered hydrofoil satisfactorily.

J. Nav. Arch. Mar. Engg., Vol 20(2), December, 2023; p 1-10

A study on the financial feasibility of compliant ship recycling yards in Bangladesh

Sun, 31 Dec 2023 00:00:00 +0000

Ship recycling is one of the most promising industries for Bangladesh. A significant amount of local steel demand is fulfilled by scrap metals from ship recycling yards. Bangladesh has been maintaining a competitive position in the ship recycling sector along with China, India, and Pakistan. But, in the absence of substantial workplace safety and infrastructure development and for not following international regulations, Bangladesh may lose its market share to other countries in this sector. This paper presents a financial analysis to establish compliant ship recycling facilities that will fulfill the Hong Kong Convention (HKC) requirements. This analysis has considered all the facilities of a compliant ship-recycling yard, including impermeable floors, mechanized systems, oily water separators, firefighting systems, and other special features. The worthiness, scalability, and sustainability of investing in the development of compliant ship recycling facilities have been assessed from Bangladesh’s perspective and the benefits over the conventional ones have been discussed. Also, the challenges for ship recyclers and their prevalent perspective toward establishing compliant ship recycling facilities have been depicted. Lastly, recommendations have been suggested to assist the ship recyclers in Bangladesh by encouraging them to invest and enable HKC-compliant ship recycling to harness long-term economic rewards.

J. Nav. Arch. Mar. Engg., Vol 20(2), December, 2023; p 1-8

A step towards IMO greenhouse gas reduction goal: effectiveness of machine learning based CO2 emission prediction model

Ishrar Israil Monisha, Nafisa Mehtaj, Zobair Ibn Awal — Sun, 31 Dec 2023 00:00:00 +0000

Ships are the world’s most economical means of freight transportation, and they are expanding quickly day by day. The increase in ship transportation activities has resulted in a significant concern about CO₂ emissions. International Maritime Organization has agreed to set a goal of reducing the maritime sector’s total gas emissions by at least 50% by 2050. In this regard, a CO₂ emission prediction model followed by an emission inventory can play a vital role in decision-making to optimize the ship’s speed, draft, trim, and other influencing parameters under the Ship Energy Efficiency Management Plan to decrease carbon emissions during operation. Machine learning, a branch of the data science approach, can be utilized to create effective emission-prediction models. In this research, two machine-learning models have been developed using actual voyage data collected from the noon reports of ships in Bangladesh. The models have been trained with the ship’s speed, engine rpm, wind force, and sea condition during voyages. The models’ performances have been assessed employing the Coefficient of Determination (R²) and Root Mean Square Error (RMSE). The prediction accuracies for the K Nearest Neighbor Regression model and the Light Gradient Boosted Machine Regression model are 84% and 81%, with RMSE of 5.12 and 5.53, respectively.

J. nav. arch. mar. engg., 20(3), pp.1-8