Influence of the transom immersion to ship resistance components at low and medium speeds

The transom stern offered some advantages over the traditional rounded cruiser stern reducing the resistance of a ship. This can only be achieved if the transom stern is carefully designed with suitable transom immersion ratio. In this study, the influence of different transom area immersion ratios on the resistance components was investigated for a semi-displacement hull and a full displacement hull. The base hull was based on NPL hull form and KCS hull form for a semi-displacement and full-displacement hull respectively. The transom immersion ratios for the NPL hull were varied at a ratio of 0.5, 0.7, 0.8 and 1.0. The resistance of each of the NPL hull form was simulated at Froude number 0.3 up to 0.6. The transom immersion ratios for the KCS hull were varied at a ratio of 0.05, 0.1, 0.15 and 0.3. The resistance of each of the KCS hull form was simulated at Froude number 0.195, 0.23, 0.26 and 0.28. The transoms of both hulls were modified or varied systematically to study the influence of the transom shape or immersion on the total and wave resistance components. The investigation was carried out using a CFD software named SHIPFLOW 6.3 based on RANSE solver. These results on the NPL hull shows that the larger the transom immersion, the higher the resistance will be for a semi-displacement vessel. The increased resistance is contributed by additional frictional and wave resistance components. The results for the KCS hull seems to contradict with the results obtained from the NPL hull. The larger and deeper transom for the case of KCS hull form sometimes can be beneficial at higher Froude number.

Gravitation modulation impact on MHD free convection flow of micropolar fluid

In this paper, a theoretical study is carried out on unsteady three dimensional, laminar, free convective flow of micropolar fluid with Hall effect, Joule heating and heat sink under gravitation modulation. A uniform transverse magnetic field is applied normal to the plate along the fluid region. The magnetic Reynolds number is considered to be small due to incomparability of applied and induced magnetic field, as such the influence of induced magnetic field can be neglected. The multi parameter perturbation technique is used to solve the governed dimensionless equations. The fluid velocity profile, temperature profile and the concentration profiles are discussed with the aid of graphs and tables. The coefficient of skin friction and couple stresses are numerically computed in addition to Nusselt number and Sherwood number. The result reveals that the linear velocity increases due to escalation in gravitation modulation parameter values but for intensification in values of gravitation modulation parameter, a reverse effect is observed for the rotational velocity. A comparative analysis shows that the skin friction coefficient is less in micropolar fluid than the corresponding Newtonian fluids.

Waste management of a maritime port-the case of Mongla port authority

During voyage of a ship from one port to another, different types of wastes generated due to operation of the ship and livelihood of the crews, which fall under the scope of international convention for the prevention of pollution from ships, MARPOL 73/78. It is seen that almost 1000 nos. of ships are calling in to Mongla port every year which is gradually increasing day by day. However, there is no waste management system in the port now. IMO has recognized that provisions of proper wastes collection vessel as well as oil spill management vessel and reception facilities are crucial for effective MARPOL implementation in the maritime port. In view of the same, the feasibility of establishment of a standard and modern waste management system for Mongla port has been studied. First of all, amount of different types of wastes sourced from the shipping operation at the port of Mongla has been estimated following standard procedure and to facilitate the necessary services to incoming ships, a proposal has been made to procure a waste collection vessel, oil spill collection vessels and port reception and treatment facilities by Mongla Port Authority along with other necessary vessels and equipment. The procurement, operation and maintenance costs as well as revenue to be collected from the incoming ships for wastes quantities, alternative uses of the vessels and facilities and earnings from selling the product of the treatment have been examined. It is found from the study that the investment is technically, financially and economically viable.

Investigation of variable viscosity and thermal conductivity on MHD mass transfer flow problem over a moving non-isothermal vertical plate

In this paper we investigate numerically the influence of variable viscosity and thermal conductivity on MHD convective flow of heat and mass transfer problem over a moving non-isothermal vertical plate. The viscosity of the fluid and thermal conductivity are presumed to be the inverse linear functions of temperature. With the help of similarity substitution, the flow governing equations and boundary conditions are transformed into non-dimensional ordinary differential equations. The boundary value problem so obtained is then solved using MATLAB bvp4c solver. The effects of various parameters viz. magnetic parameter, viscosity parameter, thermal conductivity parameter, stratification parameter and Schmidt number on velocity, temperature and concentration are obtained numerically and presented trough graphs. Also the coefficient of skin-friction, Nusselt number and Sherwood number are computed and displayed in tabular form. The effects of the viscosity parameter and thermal conductivity parameter in particular are prominent. This study has applications in a number of technological processes such as metal and polymer extrusion.

Thermal radiation and Joule heating effects on a magnetohydrodynamic Casson nanofluid flow in the presence of chemical reaction through a non-linear inclined porous stretching sheet

The present study explores the thermal and Joule heating effect of Casson nanofluid flow with chemical reaction over an inclined porous stretching surface. The results of heat source/sink, viscous dissipation, and suction are regarded. The new physical governing equations of partial differential flow equations are converted into nonlinear ordinary differential equations and are numerically resolved employing the implicit finite difference technique. The influence on velocity, temperature, and concentration fields of many flow variables are addressed. The numerical and graphical findings are defined for the numerous related attentiveness flow parameters. The empirical data reported are compared with the published outcomes.

Natural convection of fluid with variable viscosity and viscous dissipation from a heated vertical wavy surface in presence of magnetic field

ABSTRACT The present numerical work describes the effect of the temperature dependent variable viscosity and viscous dissipation on natural convection heat transfer boundary layer flow of a viscous incompressible electrically conducting fluid along a vertical wavy surface in presence of a transverse magnetic field. The wavy surface is maintained at uniform wall temperature that is higher than that of the ambient. A simple coordinate transformation is employed to transform the wavy surface into a flat plate. A marching finite difference scheme is used for present analysis. The numerical results, including the developments of the skin friction coefficients, the local Nusselt number, the streamlines as well as the isotherms are presented and discussed in detail. The results of this investigation illustrated that the skin friction coefficient increase with an increase of the variable viscosity and viscous dissipation parameter, while the local Nusselt number at the heated surface decrease with increasing values of variable viscosity, intensity of magnetic field and viscous dissipation parameter.

Effect of geometrical features on the contra-rotating propeller hydrodynamic performances

New contra-rotating four-bladed DTMB propeller configurations operating in open water are numerically studied to determine their hydrodynamic performances. The unsteady turbulent flow around propellers is modelled by RANS equations with Kω SST model then solved by a CFD code. The computational domain is divided in two blocks linked with a rotating interface. The obtained results show that thrust and efficiency of the contra-rotating (CRP) increase compared to the single propeller, leading to a significant reduction of the propeller diameter. The variation in axial spacing and angular displacement seems to have little effect on the CRP efficiency. The results also show that the thrust can be further improved by adopting a moderate negative twist angle of the rear propeller. Keywords: CRP contra-rotating propeller, axial spacing, angular spacing, twist angle, CFD.

CFD analysis of unsteady propeller performance operating at different inclined shaft angles for long-tail boat in Thailand

Inclined shaft propeller arrangements are demonstrated in the high-speed boat. The flow field around the propeller blades with inclined shaft propeller is unsteady due to the cross-flow component from the influx of the shaft direction which complicated more than the straight shaft propeller condition (without inclined shaft propeller). Therefore, realistic flow around inclined shaft propeller is important to the actual efficiency of propeller. In addition, propeller characteristics such as the pitch, skew and rake are influences to propeller performance, maybe not done in design condition which is different from the straight shaft propeller. This paper offers the investigation of unsteady propeller performance with operating the different inclined shaft angle conditions for Long-Tail Boat (LTB) using a Reynolds Averaged Navier-Stokes (RANS) solver. The unsteady calculations are conducted by inclined flow conditions. The computational results of propeller performance and pressure distribution on the suction and pressure sides at the blades of time-accuracy have been compared to each other including the wake effect behind the propeller. The results can be applied to adjust the inclined shaft angle of the boat.

Enhancement of natural convection heat transfer in concentric annular space using inclined elliptical cylinder

The governing equations of continuity, momentum and energy are numerically solved to study the laminar natural convection heat transfer of Newtonian fluid confined within two concentric cylinders. The inner cylinder is elliptical cross-section with different aspect ratio E = 0.1 to 0.5 and it is considered to be hot, whereas the outer cylinder is circular and it is supposed to be cold. The annular spacing between the cylinders is defined based on radii ratio (RR = 2.5). Also, the inner cylinder is inclined with an inclination angle (θ = 0 to 90). The main purpose of this study is to determine the effects of inclination angle (θ = 0° to 90°), aspect ratio of inner cylinder (E = 0.1 to 0.5), Prandtl number (Pr = 0.71 and 7.01) and Rayleigh number (Ra = 103 to 105) on fluid flow and heat transfer rate. The flow patterns and temperature distributions are potted in terms of streamlines and isotherms respectively. The obtained results showed that increase in inclination angle enhances the heat transfer rate of inner cylinder for all values of aspect ratio. Also, for the inclination angle (θ = 90°), the decrease in aspect ratio (E) improves the heat transfer rate of inner cylinder.

Peristaltic pumping of Ellis fluid through a flexible tube with complete slip effects

The paper investigates the role of complete velocity slip on the axisymmetric peristaltic transport of Ellis fluid through a uniform flexible tube considering the long wavelength and tiny Reynolds number assumptions. The equations governing the axisymmetric flow are solved and provided the analytical expressions for axial velocity, stream function, pressure difference for shear thickening and shear thinning fluids and the effect of emerging parameters on the pressure rise with time averaged flux and stream line patterns have been discussed graphically. The trapping phenomenon results showed that the size of trapping bolus enhances with increasing values of first and second slip parameters.