Showing papers in "Journal of Naval Architecture and Marine Engineering in 2011"

Effects of heat transfer and viscous dissipation on mhd free convection flow past an exponentially accelerated vertical plate with variable temperature

Abstract: The unsteady free convection flow of an incompressible viscous fluid past an exponentially accelerated vertical plate is analyzed by taking into an account the heat due to viscous dissipation under the influence of a uniform transverse magnetic field. The problem is governed by coupled non-linear partial differential equations. Dimensionless equations of the problem have been solved numerically by the implicit finite difference method of Crank – Nicolson’s type. The effect of magnetic parameter M, Grashof number Gr, Eckert number E, time and an acceleration parameter a on velocity and temperature fields are investigated through graphs. Skin friction coefficient is derived, discussed numerically and presented through a table. DOI: 10.3329/jname.v7i2.4370

Induced magnetic field with radiating fluid over a porous vertical plate: analytical study

Abstract: The objective of this investigation is to study the influence of thermal radiation and magnetic Prandtl number on the steady MHD heat and mass transfer by mixed convection flow of a viscous, incompressible, electrically-conducting, Newtonian fluid which is an optically thin gray gas over a vertical porous plate taking into account the induced magnetic field. The similarity solutions of the transformed dimensionless governing equations are obtained by series solution. It is found that, velocity is reduced considerably with a rise in conduction-radiation parameter ( R ) or Hartmann number ( M ) whereas the skin friction is found to be markedly boosted with an increase in M or Magnetic Prandtl number ( Pm ) . An increase in magnetic body parameter ( M ) or Magnetic Prandtl number ( Pm ) is found to escalate induced magnetic field whereas an increase in R is shown to exert the opposite effect. Applications of the study include laminar magneto-aerodynamics, materials processing and MHD propulsion thermo-fluid dynamics. DOI: 10.3329/jname.v7i2.5662

Application of non-linear k-e turbulence model in flow simulation over underwater axisymmetric hull at higher angle of attack

Abstract: This paper addresses the Computational Fluid Dynamics Approach (CFD) to simulate the flow over underwater axisymmetric bodies at higher angle of attacks. Three Dimensional (3D) flow simulation is carried out over MAYA Autonomous Underwater Vehicle (AUV) at a Reynolds number (Re) of 2.09×10 6 . These 3D flows are complex due to cross flow interaction with hull which produces nonlinearity in the flow. Cross flow interaction between pressure side and suction side is studied in the presence of angle of attack. For the present study standard k-e model, non-linear k-e model models of turbulence are used for solving the Reynolds Averaged Navier-Stokes Equation (RANS). The non-linear k-e turbulence model is validated against DARPA Suboff axisymmetric hull and its applicability for flow simulation over underwater axisymmetric hull is examined. The non-linear k-e model performs well in 3D complex turbulent flows with flow separation and flow reattachment. The effect of angle of attack over flow structure, force coefficients and wall related flow variables are discussed in detail. Keywords: Computational Fluid Dynamics (CFD); Autonomous Underwater Vehicle (AUV); Reynolds averaged Navier-Stokes Equation (RANS); non-linear k-e turbulence model doi: http://dx.doi.org/10.3329/jname.v8i2.6984 Journal of Naval Architecture and Marine Engineering 8(2011) 149-163

Effects of viscous dissipation on MHD flow with heat and mass transfer over a stretching surface with heat source, thermal stratification and chemical reaction

Abstract: This paper deals with the study of nonlinear MHD flow, with heat and mass transfer characteristics of an incompressible, viscous, electrically conducting and Boussinesq fluid on a vertical stretching surface with thermal stratification and chemical reaction by taking in to account the viscous dissipation effects. Adopting the similarity transformation, governing nonlinear partial differential equations of the problem are transformed to nonlinear ordinary differential equations. The Quasi-linearization technique is used for the non-linear momentum equation and then the numerical solution of the problem is derived using implicit finite difference technique, for different values of the dimensionless parameters. The numerical values obtained for velocity profiles, temperature profiles and concentration profiles are represent graphically in figures. The results obtained show that the flow field is influenced appreciably by the presence of viscous dissipation, thermal stratification, chemical reaction and magnetic field. DOI: 10.3329/jname.v7i1.3254

Effective simple methods for numerical modelling of marine engines in ship propulsion control systems design

Abstract: In the last year, the Department of Naval Architecture and Marine Engineering of Genoa University (now Department of Naval Architecture, Marine Technology and Electrical Engineering) collaborated to the design of the propulsion automation of two different naval vessels; within these projects the authors developed different ship propulsion simulators used to design and test the propulsion control schemes. In these time-domain simulators, each propulsion component is represented by a specific mathematical model, mainly based on algebraic and differential equations. One of the key aspects of the propulsion simulation is the engine dynamics. This problem in principle can be dealt with models based on thermodynamic principles, which are able to represent in detail the behaviour of many variables of interest (engine power and speed, air and gas pressures, temperatures, stresses, etc.). However, thermodynamic models are often characterized by a long computation-time and moreover their development usually requires the knowledge of specific engine information not always available. It is generally preferable to adopt simpler simulation models, for the development of which, very few kinds of information are necessary. In fact, for the rapid prototyping of control schemes, it is generally more important to model the whole plant (in a relatively coarse way) rather than the detailed model of some components. This paper deals with simple mathematical methods, able to represent the engine power or torque only, but they can be suitably applied to many types of marine engines in a straightforward way. The proposed simulation approaches derived from the authors’ experience, gained during their activity in the marine simulation field, and they are particularly suitable for a fast prototyping of the marine propulsion control systems. The validation process of these particular models, regarding a Diesel engine, a marine gas turbine and an electric motor, is illustrated based on the sea trials data and engine manufacturers’ data. Keywords: Dynamic simulation; marine engines performance; gas turbine; propulsion control. doi: http://dx.doi.org/10.3329/jname.v8i2.7366 Journal of Naval Architecture and Marine Engineering 8(2011) 129-147

Mixed magnetoconvection in a lid-driven cavity with a sinusoidal wavy wall and a central heat conducting body

Abstract: A numerical study has been performed to explore the mixed magnetoconvective flow and heat transfer characteristics of fluid contained in a lid-driven cavity having a sinusoidal wavy vertical surface. A heat conducting square body is located at the centre of cavity. The cavity horizontal walls are perfectly insulated while the corrugated right vertical surface is maintained at a uniform temperature higher than the left lid. The flow is assumed to be two-dimensional and Joule heating effect is considered. Calculations are carried out through solving governing equations for different parameters by using Galarkin’s weighted residual finite element method. The flow pattern and the heat transfer characteristics inside the cavity are presented in the form of streamlines, isotherms, average temperature of the fluid and temperature of solid body centre for various values of Prandtl number Pr , Richardson number Ri and magnetic parameter Ha . The heat transfer rate is detected maximum for the highest Pr and absence of magnetic field. DOI: http://dx.doi.org/10.3329/jname.v8i1.6793

Mechanical properties and corrosion resistance of normal strength and high strength steels in chloride solution

Abstract: The corrosion resistance (weight loss) and mechanical properties (i.e. yield strength, ultimate strength and elongation) for three carbon steels, normal strength and high strength steels using tension test are investigated. The specimens are kept in chloride solution (20% NaCl) up to 240 hours. At every 48 hours, thickness and weight loss is measured and tension test is carried out. It was found that the susceptibility of the steels to corrosion based on their weight loss were identical prior to 144 hours, after that is accelerated for high strength steel. In addition, it was found that manganese (Mn) has reduced corrosion rate at early stage of corrosion. The change in mechanical properties by corrosion for all steels are the same, and ultimate strength is reduced, which for limit state design of aged structure should be taken into account. DOI: 10.3329/jname.v7i2.5309

Unsteady double-diffusive natural convective mhd flow along a vertical cylinder in the presence of chemical reaction, thermal radiation and soret and dufour effects

Abstract: This work is focused on the numerical solution of unsteady double-diffusive free convective flow along a vertical isothermal cylinder in the presence of a transverse magnetic field, first-order homogeneous chemical reaction, thermal radiation and Soret and Dufour effects. The Rosseland approximation is used to describe the radiative heat flux in the energy equation. The governing equations are formulated and a numerical solution is obtained by using an explicit finite-difference scheme. The solutions at each time step have been found to reach the steady state solution properly. Representative results for the fluid velocity, temperature and solute concentration profiles as well as the local heat and mass transfer rates for various values of the physical parameters are displayed in both graphical and tabular forms. DOI: http://dx.doi.org/10.3329/jname.v8i1.7250

Critical behaviour of the MHD flow in convergent-divergent channels

Abstract: Normal 0 MicrosoftInternetExplorer4 The effect of external Magnetohydrodynamic (MHD) field on the steady two-dimensional nonlinear flow through Convergent-Divergent Channels of a viscous incompressible electrically conducting fluid is investigated. We compute the critical behaviour of the solution govern by the equation. Our approach uses the power series in order to observe the instability of the problem. The series is then summed by using various generalizations of the approximants. We find the critical values of various parameters and type of the principal singularity for different choice of MHD effect. DOI: 10.3329/jname.v7i2.5635

Heat transfer in a nanofluid flow past a permeable continuous moving surface

Abstract: A boundary layer analysis is presented for the warm, laminar nanoliquid flow to a melting surface moving parallel to a uniform free stream. The resulting system of non-linear ordinary differential equations is solved numerically using Runge-Kutta method with shooting techniques. Numerical results are obtained for the velocity, temperature and concentration distributions, as well as the friction factor, local Nusselt number and local Sherwood number for several values of the parameters, namely the velocity ratio parameter, melting parameter and nanofluid parameters. The obtained results are presented graphically and in tabular form and the physical aspects of the problem are discussed. Keywords: Suction/injection; moving surface; nanofluid; boundary layer; shooting technique. doi: http://dx.doi.org/10.3329/jname.v8i2.6830 Journal of Naval Architecture and Marine Engineering 8(2011) 83-92

Natural Convection Flow in a Square Cavity with Internal Heat generation and a Flush Mounted Heater on a Side Wall

Abstract: In this study natural convection flow in a square cavity with heat generating fluid and a finite size heater on the vertical wall have been investigated numerically . To change the heat transfer in the cavity, a heater is placed at different locations on the right vertical wall of the cavity, while the left wall is considered to be cold. In addition, the top and bottom horizontal walls are considered to be adiabatic and the cavity is assumed to be filled with a Bousinessq fluid having a Prandtl number of 0.72. The governing mass, momentum and energy equations along with boundary conditions are expressed in a normalized primitive variables formulation. Finite Element Method is used in solution of the normalized governing equations. The parameters leading the problem are the Rayleigh number, location of the heater, length of the heater and heat generation. To observe the effects of the mentioned parameters on natural convection in the cavity, we considered various values of heater locations, heater length and heat generation parameter for different values of Ra varying in the range 10 2 to 10 5 . Results are presented in terms of streamlines, isotherms, average Nusselt number at the hot wall and average fluid temperature in the cavity for the mentioned parameters. The results showed that the flow and thermal fields through streamlines and isotherms as well as the rate of heat transfer from the heated wall in terms of Nusselt number are strongly dependent on the length and locations of the heater as well as heat generating parameter. DOI: 10.3329/jname.v7i2.3292

Radiation and mass transfer effects on mhd free convection flow past a moving vertical cylinder in a porous medium

Abstract: The interaction of free convection with thermal radiation of a viscous incompressible unsteady MHD flow past a moving vertical cylinder with heat and mass transfer in a porous medium is analyzed. The fluid is a gray, absorbing-emitting but non-scattering medium and the Rosseland approximation is used to describe the radiative heat flux in the energy equation. The governing equations are solved by using an implicit finite-difference scheme of Crank-Nicolson type. The effects of various physical parameters such as thermal Grashof number, mass Grashof number, magnetic parameter, radiation parameter and Schmidt number on the velocity, temperature, concentration, local as well as average skin-friction, Nusselt number and Sherwood number for various parameters are computed and represented graphically. It is found that at small values of radiation parameter , the velocity and temperature of the fluid increases sharply near the cylinder as the time increases. Also, an increase in the magnetic field leads to a decrease in the velocity and a rise in the temperature.As the permeability parameter increases,it is seen that the flow accelerates. This model finds applications in geophysics and engineering. DOI: 10.3329/jname.v7i1.2901

Finite element analysis of free convection flow with MHD micropolar and viscous fluids in a vertical channel with dissipative effects

Abstract: Normal 0 false false false MicrosoftInternetExplorer4 In the present study, the vertical channel is divided in to two regions one region is filled with Micropolar fluid and the other region is filled with viscous fluid. The channel is subjected to the transverse magnetic field. The coupled governing equations are solved subjected to the boundary conditions proposed by the previous authors using F.E.M. The results are compared with Kumar et al (2010). It is found that the increase in the magnetic field reduces the micro rotation (N) and velocity and enhances the temperature. Increase in the Eckert (Ec) number, decreases the velocity, temperature and micro rotation. The Nusselt number and shear stress values are also analyzed. DOI: http://dx.doi.org/10.3329/jname.v8i1.5808

Viscous dissipation and joule heating effects on steady mhd combined heat and mass transfer flow through a porous medium in a rotating system

Abstract: Normal 0 MicrosoftInternetExplorer4 Viscous dissipation and Joule heating effects on steady MHD combined heat and mass transfer flow through a porous medium along a semi-infinite vertical porous plate in a rotating system has been studied numerically. The boundary layer equations have been transformed into dimensionless coupled nonlinear ordinary differential equations by appropriate transformations. The similarity solutions of the transformed dimensionless equations for the flow field and heat and mass transfer characteristics are obtained by shooting iteration technique. Numerical results are presented in the form of primary and secondary velocities, temperature and concentration distributions within the boundary layer for different parameters entering into the analysis. Finally, the effects of the pertinent parameters on the Skin-friction coefficients, Nusselt number and Sherwood number are also examined. Keywords: MHD; Joule heating; porous medium; rotating system simulation. doi: http://dx.doi.org/10.3329/jname.v8i2.5055 Journal of Naval Architecture and Marine Engineering 8(2011) 105-120

Soret and Dufour effects on an unsteady MHD free convection flow past a semi-infinite permeable vertical moving plate in a porous medium with chemical reaction

Abstract: In the present study, an unsteady two-dimensional MHD free convection flow chemical reacting fluid past a semi-infinite permeable vertical moving plate in a porous medium with Soret and Dufour effects is analyzed. The dimensionless governing equations are solved numerically by a finite element method. Computations are performed for a wide range of the governing flow parameters, viz., the thermal Grashof number, solutal Grashof number, Magnetic field parameter, Permeability parameter, Prandtl number, Heat absorption parameter, Dufour number, Schmidt number, Chemical reaction parameter and Soret number. The effects of these flow parameters on the velocity, temperature and concentration are shown graphically. Finally, the effects of various parameters on the skin-friction coefficient, Nusselt number and Sherwood number are shown in Tables. DOI: http://dx.doi.org/10.3329/jname.v8i1.6054

Stable solution zone for fluid flow through curved pipe with circular cross-section

Abstract: Numerical study is performed to examine numerically the stable solution for the incompressible viscous steady flow through a curved pipe with circular cross-section. Also the combined effects of high Dean Number Dn and curvature δ on the flow are investigated. Spectral method is applied as a main tool for the numerical technique; where, Fourier series, Chebyshev polynomials, Collocation methods, and Iteration method are used as secondary tools. The flow patterns have been shown graphically for large Dean Numbers and a wide range of curvature, 0.01≤δ≤0.9.Two vortex solutions have been found for secondary flow. Axial velocity has been found to increase with the increase of Dean number and decrease with the increase of curvature. For high Dean number and low curvature almost all the fluid particles leave the inner half of the cross-section. The stable solution zone increases with the increase of curvature up to a certain limit, then decrease. DOI: 10.3329/jname.v7i1.3630

Finite element analysis of Soret and Dufour effects on unsteady MHD free convection flow past an impulsively started vertical porous plate with viscous dissipation

Abstract: The free convection flow of an unsteady magnetohydrodynamic and viscous dissipating fluid past an impulsively started vertical plate with soret and dufour effects has been analyzed. With appropriate transformations the boundary layer equations are transformed into nonlinear ordinary differential equations. The local unsteady similarity solutions of the transformed dimensionless equations for the flow. These equations are solved numerically by a finite element method. Favorable comparisons with previously published work are obtained. The effects of the various parameters on the velocity, temperature and concentration profiles as well as the skin-friction coefficient, Nusselt number and Sherwood number are presented graphically and in tabulated form. DOI: http://dx.doi.org/10.3329/jname.v8i1.3507

Influence of centered conducting obstacle on MHD combined convection in a wavy chamber

Abstract: The development of centered heat conducting obstacle effect on combined magnetoconvective flow in a lid driven chamber has been numerically studied. The enclosure considered has rectangular horizontal lower surfaces and vertical side surfaces. The lower and upper surfaces are insulated. The left wall is mechanically lid driven having uniform temperature Ti and velocity v0 while other vertical side is wavy and maintains higher temperature Th than the lid. The governing two-dimensional flow equations have been solved by using Galerkin weighted residual finite element technique. The investigations are conducted for different values of Richardson number (Ri) and physical parameter i.e. diameter (D) of square solid body. Various characteristics such as streamlines, isotherms and heat transfer rate in terms of the mean Nusselt number (Nu), the average temperature (?av) of the fluid and temperature of obstacle center (?c) are presented. The results indicate that the mentioned parameters strongly affect the flow phenomenon and temperature field inside the chamber. Conducting largest obstacle is preferable for effective heat transfer mechanism in presence of magnetic field. Keywords: Combined convection, MHD, wavy chamber, heat conducting obstacle, finite element simulation. doi: http://dx.doi.org/10.3329/jname.v8i2.7392 Journal of Naval Architecture and Marine Engineering 8(2011) 93-104

Numerical study of unsteady flow around a cavitating hydrofoil

Abstract: This paper presents a numerical study of the non-cavitating and cavitating flow around CAV 2003 hydrofoil. The phenomenon of cavitation is modeled through a mixture model. For the numerical solution of cavitating flow a bubble dynamics cavitation model is used to describe the generation and evaporation of vapor phase. The non-cavitating study focuses on the influence of the turbulence model and different mesh sizes used in the computation. Three turbulence models such as Spalart-Allmaras, Shear Stress Turbulence (SST) k-? model, RNG k-? with enhanced wall treatment are used to capture turbulent boundary layer along the hydrofoil surface. The results predicted by these models are compared with each other. The cavitating study first presented an unsteady behavior of the partial cavity attached to the foil. Then, an analysis of a supercavitating condition is performed. The predicted results show good agreement with results published by other researchers.DOI: 10.3329/jname.v7i2.5270

Effects of variable thermal conductivity on the coupling of conduction and joule heating with mhd free convection flow along a vertical flat plate

Abstract: The effects of variable thermal conductivity on the coupling of conduction and Joule heating with MHD free convection flow along a vertical flat plate have been described by this present work. With a goal to attain similarity solutions of the problem posed, the developed equations are made dimensionless by using suitable transformations. The non-dimensional equations are then transformed into non-linear equations by introducing a non- similarity transformation. The resulting non-similar equations together with their corresponding boundary conditions based on conduction and convection are solved numerically by using the implicit finite difference method along with Keller-box scheme. Numerical results for the details of the velocity profile, temperature profile, skin friction coefficient and the surface temperature profile are shown both on graphs and tabular form for different values of the set of parameters entering into the problem. DOI: 10.3329/jname.v7i1.4322

Comparative study between flows around sphere and pod using finite volume method

Abstract: Two-dimensional Finite Volume Method (FVM) based on Reynolds-averaged Navier-Stokes (RANS) equations is applied to solve the turbulent viscous flow around sphere and pod. Unstructured grid with boundary layer treatment is constructed around sphere whereas structured grid is generated around pod. Spalart-Allmaras (S-A) and Shear Stress Transport (SST) k-ω turbulence models are used for sphere but SST k-ω turbulence model is used only for pod to solve turbulent viscous flows at Reynold’s number of 5×10 6 and 3×10 6 respectively. The numerical results in terms of the skin friction coefficient, pressure coefficient and drag coefficient are shown either graphically or in the tabular form. Velocity vectors as well as contour of pressure and velocity distribution are also displayed. Finally, the comparative study between flows around sphere and pod is done. DOI: http://dx.doi.org/10.3329/jname.v8i1.7388

Evaluation of the performance of contemporary shipbuilding industries in Bangladesh

Abstract: In this paper, an effort has been made to evaluate the present shipbuilding industries in Bangladesh. To do this, at first an overall picture of this industries have been depicted by identifying the actual shipbuilding practice in both public and private sector. Relevant data have been explored through extensive review of literature, field visits, interacting with shipyard and Ship owners, shipyard managers, Government regulatory and monitoring bodies using structured, unstructured and open ended questionnaires. Existing and upcoming yards have been identified and yards have been categorized by describing the shipyard in terms of modern shipbuilding requirements. The labor cost, labor hour, relative labor rate, productivity etc. have been quantified and compared with other nations. An investigation of cost breakdown of a sample exportable quality ship has been assessed to find out percentage of local components of total cost structure. The potentiality, capability and problems of the shipbuilding sector of Bangladesh have been identified & some recommendations have been made in line with this study. DOI: 10.3329/jname.v7i2.5407

A flexible system for initial ship design parameters estimation using a system of neural networks

Abstract: To initialize ship design process, it is very important to be able to develop an initial estimate of ship parameters to satisfy designer required specifications. For new emerging designs, this estimate has to be made based on a limited available set of examples. Moreover, a practical estimate prediction strategy should be flexible enough having no distinction between input (specified constraints) and outputs (parameters required to be estimated), since these vary from one design case to another. Conventional regression-based techniques, which are usually employed to provide the required estimates, suffer from low accuracy in case of a small number of available examples. In addition to that, they fail to capture the interrelation between different design parameters. To overcome these limitations and others, the present paper proposes a new approach based on a system of artificial neural-networks (ANNs). The new approach not only overcomes regression limitations but is also capable of providing a reliable estimate of initial design offset table based on different ANN outputs. The paper uses a case study for demonstrating the merits of the proposed approach. Keywords: Ship design; regression; ship series; Artificial Neural Networks (ANNs); Multilayer Perceptrons (MLPs); Normalized Gaussian Modified Lagrangian (NGML) doi: http://dx.doi.org/10.3329/jname.v8i2.6945 Journal of Naval Architecture and Marine Engineering 8(2011) 71-82

Improving the quality of hexahedral mesh generated by automatic mesh generators

Abstract: Automatic hexahedral mesh generation is a very deserving solution for better performance of finite element analysis of complex large structures. At present plastering, whisker weaving and whisker weaving based plastering algorithm are available to perform such tasks. As these hexahedral mesh generation processes are fully automatic, it is possible to form some elements, which don’t have high enough qualities for finite element analysis. For this reason, a reliable post-processing method is presented in this paper which can modify the shapes of the already generated hexahedrons. Four different structural models are tested and the results show that the proposed method can effectively modify the quality of the inverted hexahedrons and eliminate the invalid ones. Keywords: Doublet; triplet; quadruplet; Whisker weaving based plastering algorithm; hexahedral mesh DOI: http://dx.doi.org/10.3329/jname.v8i2.5646 Journal of Naval Architecture and Marine Engineering 8(2011) 121-128