Abstract: This paper describes a contra-rotating propeller (CRP) system to calculate the hydrodyn... more Abstract: This paper describes a contra-rotating propeller (CRP) system to calculate the hydrodynamic characteristics and then design the optimum operational condition to be installed on two different large bulk carriers and VLCC. The method is based on boundary element method (BEM) to obtain the hydrodynamic performance of any complicated configuration such as CRP system, and then the optimum propeller data is obtained by the systematic method at the design condition. The researchers prepared a software package code, namely SPD, which has model mesh generation, solver and numerical output results. The comparison of the propulsive performance was made between the propeller alone and CRP arrangement. Major finding include optimal agreement between predictions using the numerical code and
In this paper, water entry of wedges with deadrise angles ranging from 10 to 80 degrees at two di... more In this paper, water entry of wedges with deadrise angles ranging from 10 to 80 degrees at two different velocities is simulated. Impact forces, spray parameters, cavity formation above the chine, and secondary impact forces due to the cavity formation are investigated with particular focus on the extreme angles. To this end, a two dimensional two-phase FiniteElement based Finite-Volume (FEM-FVM) code is developed and validated against experimental data with good compliance. Free surface modeling in this software is accomplished by applying Volume of Fluid (VOF) method. In addition to the extraction of impact forces, secondary impact forces, spray characteristics, and cavity formation, it is demonstrated that there is a combined critical length and entry velocity where the spray formation stops and the spray vanishes. It is also shown that the cavity and secondary impact do not occur under these circumstances. Moreover, it is concluded that for these particular cases, there is a max...
This paper presents numerical calculations for podded propulsion system using vortex theory and p... more This paper presents numerical calculations for podded propulsion system using vortex theory and potential panel method. The method discretizes the surface boundary of the body (propeller +pod+strut) and obtained the vortex and propeller surface and potential on strut and pod. A model propeller and strut are considered for these calculations and the results of pressure distribution, flow field around the propeller and hydrodynamic characteristics of the propeller are given. The calculated hydrodynamic characteristics of the propeller are compared with the experimental data and it is shown in good agreement with them.
Viscous and incompressible flow is simulated over an equilateral triangular obstacle placed in a ... more Viscous and incompressible flow is simulated over an equilateral triangular obstacle placed in a horizontal channel. Different from the previous studies, the governing Navier-Stokes equations along with appropriate boundary conditions are solved by a particular finite volume generated code. A fixed blockage ratio (β=0.05) is considered. Different ranges of Reynolds numbers in laminar regime under critical value of the Reynolds number (Re ≤ 38.03) are investigated. Range of this study is from 1.4 to 38.03. The flow characteristics are analyzed in the forms of streamlines and pressure fields at various Reynolds numbers. Diagram of drag coefficient versus Reynolds numbers is presented and discussed. Results are compared with the available data in the literature that display good agreements.
Abstract: This paper describes a contra-rotating propeller (CRP) system to calculate the hydrodyn... more Abstract: This paper describes a contra-rotating propeller (CRP) system to calculate the hydrodynamic characteristics and then design the optimum operational condition to be installed on two different large bulk carriers and VLCC. The method is based on boundary element method (BEM) ...
Volume 4: Ocean Engineering; Ocean Renewable Energy; Ocean Space Utilization, Parts A and B, 2009
Market demands for high-speed marine vehicles (HSMVs) are high in both commercial and naval branc... more Market demands for high-speed marine vehicles (HSMVs) are high in both commercial and naval branches. It is the naval architects’ task to design the hull and propulsion system to diminish drag, improve the propulsive efficiency, higher safety and better maneuverability. Surface Piercing Propellers (SPPs) may provide those possessions for the vehicles. Unlike immersed propellers, behavior of the SPPs is susceptible to immersed depth, Weber number and shaft inclination angle. This paper uses a specially practical and numerical method to predict the hydrodynamic characteristics of the SPPs. Critical advance ratio is obtained by practical formula, using Weber number and pitch ratio in the transition mode. Numerical method employs the potential based boundary element method (BEM) on the engaged surfaces. Two models of three and six bladed of the SPPs (SPP-1 and SPP-2) are selected and some results are shown.
In this study, the unsteady flow of three dimensional rectangular ducts is investigated using the... more In this study, the unsteady flow of three dimensional rectangular ducts is investigated using the energy gradient method. The instability maximum ratio of the energy gradient in the two orthogonal directions is predicted for different aspect ratios. For specific Reynolds numbers, the ratio of the energy gradient in the two orthogonal directions is obtained for different aspect ratios and validated with the previous available data. The comparison of the present results shows excellent agreement with the previous available data. From the results of present work we conclude that as the aspect ratio increases the time required for the flow to reach the steady state is lesser, in other words the larger the aspect ratios are the sooner the steady state flow conditions are achieved. Resultsof this paper show that the maximum ratio of the energy gradient in the two orthogonal directions, Kmax, for three dimensional rectangular duct flows is in the range of 402-403.Also, the variations of K/Re versus y/b at differ...
Viscous and incompressible flow is simulated over an equilateral triangular obstacle placed in a ... more Viscous and incompressible flow is simulated over an equilateral triangular obstacle placed in a horizontal channel. Different from the previous studies, the governing Navier-Stokes equations along with appropriate boundary conditions are solved by a particular finite volume generated code. A fixed blockage ratio (β=0.05) is considered. Different ranges of Reynolds numbers in laminar regime under critical value of the Reynolds number (Re ≤ 38.03) are investigated. Range of this study is from 1.4 to 38.03. The flow characteristics are analyzed in the forms of streamlines and pressure fields at various Reynolds numbers. Diagram of drag coefficient versus Reynolds numbers is presented and discussed. Results are compared with the available data in the literature that display good agreements.
Volume 4: Ocean Engineering; Ocean Renewable Energy; Ocean Space Utilization, Parts A and B, 2009
ABSTRACT Market demands for high-speed marine vehicles (HSMVs) are high in both commercial and na... more ABSTRACT Market demands for high-speed marine vehicles (HSMVs) are high in both commercial and naval branches. It is the naval architects’ task to design the hull and propulsion system to diminish drag, improve the propulsive efficiency, higher safety and better maneuverability. Surface Piercing Propellers (SPPs) may provide those possessions for the vehicles. Unlike immersed propellers, behavior of the SPPs is susceptible to immersed depth, Weber number and shaft inclination angle. This paper uses a specially practical and numerical method to predict the hydrodynamic characteristics of the SPPs. Critical advance ratio is obtained by practical formula, using Weber number and pitch ratio in the transition mode. Numerical method employs the potential based boundary element method (BEM) on the engaged surfaces. Two models of three and six bladed of the SPPs (SPP-1 and SPP-2) are selected and some results are shown.
Abstract: This paper describes a contra-rotating propeller (CRP) system to calculate the hydrodyn... more Abstract: This paper describes a contra-rotating propeller (CRP) system to calculate the hydrodynamic characteristics and then design the optimum operational condition to be installed on two different large bulk carriers and VLCC. The method is based on boundary element method (BEM) to obtain the hydrodynamic performance of any complicated configuration such as CRP system, and then the optimum propeller data is obtained by the systematic method at the design condition. The researchers prepared a software package code, namely SPD, which has model mesh generation, solver and numerical output results. The comparison of the propulsive performance was made between the propeller alone and CRP arrangement. Major finding include optimal agreement between predictions using the numerical code and
In this paper, water entry of wedges with deadrise angles ranging from 10 to 80 degrees at two di... more In this paper, water entry of wedges with deadrise angles ranging from 10 to 80 degrees at two different velocities is simulated. Impact forces, spray parameters, cavity formation above the chine, and secondary impact forces due to the cavity formation are investigated with particular focus on the extreme angles. To this end, a two dimensional two-phase FiniteElement based Finite-Volume (FEM-FVM) code is developed and validated against experimental data with good compliance. Free surface modeling in this software is accomplished by applying Volume of Fluid (VOF) method. In addition to the extraction of impact forces, secondary impact forces, spray characteristics, and cavity formation, it is demonstrated that there is a combined critical length and entry velocity where the spray formation stops and the spray vanishes. It is also shown that the cavity and secondary impact do not occur under these circumstances. Moreover, it is concluded that for these particular cases, there is a max...
This paper presents numerical calculations for podded propulsion system using vortex theory and p... more This paper presents numerical calculations for podded propulsion system using vortex theory and potential panel method. The method discretizes the surface boundary of the body (propeller +pod+strut) and obtained the vortex and propeller surface and potential on strut and pod. A model propeller and strut are considered for these calculations and the results of pressure distribution, flow field around the propeller and hydrodynamic characteristics of the propeller are given. The calculated hydrodynamic characteristics of the propeller are compared with the experimental data and it is shown in good agreement with them.
Viscous and incompressible flow is simulated over an equilateral triangular obstacle placed in a ... more Viscous and incompressible flow is simulated over an equilateral triangular obstacle placed in a horizontal channel. Different from the previous studies, the governing Navier-Stokes equations along with appropriate boundary conditions are solved by a particular finite volume generated code. A fixed blockage ratio (β=0.05) is considered. Different ranges of Reynolds numbers in laminar regime under critical value of the Reynolds number (Re ≤ 38.03) are investigated. Range of this study is from 1.4 to 38.03. The flow characteristics are analyzed in the forms of streamlines and pressure fields at various Reynolds numbers. Diagram of drag coefficient versus Reynolds numbers is presented and discussed. Results are compared with the available data in the literature that display good agreements.
Abstract: This paper describes a contra-rotating propeller (CRP) system to calculate the hydrodyn... more Abstract: This paper describes a contra-rotating propeller (CRP) system to calculate the hydrodynamic characteristics and then design the optimum operational condition to be installed on two different large bulk carriers and VLCC. The method is based on boundary element method (BEM) ...
Volume 4: Ocean Engineering; Ocean Renewable Energy; Ocean Space Utilization, Parts A and B, 2009
Market demands for high-speed marine vehicles (HSMVs) are high in both commercial and naval branc... more Market demands for high-speed marine vehicles (HSMVs) are high in both commercial and naval branches. It is the naval architects’ task to design the hull and propulsion system to diminish drag, improve the propulsive efficiency, higher safety and better maneuverability. Surface Piercing Propellers (SPPs) may provide those possessions for the vehicles. Unlike immersed propellers, behavior of the SPPs is susceptible to immersed depth, Weber number and shaft inclination angle. This paper uses a specially practical and numerical method to predict the hydrodynamic characteristics of the SPPs. Critical advance ratio is obtained by practical formula, using Weber number and pitch ratio in the transition mode. Numerical method employs the potential based boundary element method (BEM) on the engaged surfaces. Two models of three and six bladed of the SPPs (SPP-1 and SPP-2) are selected and some results are shown.
In this study, the unsteady flow of three dimensional rectangular ducts is investigated using the... more In this study, the unsteady flow of three dimensional rectangular ducts is investigated using the energy gradient method. The instability maximum ratio of the energy gradient in the two orthogonal directions is predicted for different aspect ratios. For specific Reynolds numbers, the ratio of the energy gradient in the two orthogonal directions is obtained for different aspect ratios and validated with the previous available data. The comparison of the present results shows excellent agreement with the previous available data. From the results of present work we conclude that as the aspect ratio increases the time required for the flow to reach the steady state is lesser, in other words the larger the aspect ratios are the sooner the steady state flow conditions are achieved. Resultsof this paper show that the maximum ratio of the energy gradient in the two orthogonal directions, Kmax, for three dimensional rectangular duct flows is in the range of 402-403.Also, the variations of K/Re versus y/b at differ...
Viscous and incompressible flow is simulated over an equilateral triangular obstacle placed in a ... more Viscous and incompressible flow is simulated over an equilateral triangular obstacle placed in a horizontal channel. Different from the previous studies, the governing Navier-Stokes equations along with appropriate boundary conditions are solved by a particular finite volume generated code. A fixed blockage ratio (β=0.05) is considered. Different ranges of Reynolds numbers in laminar regime under critical value of the Reynolds number (Re ≤ 38.03) are investigated. Range of this study is from 1.4 to 38.03. The flow characteristics are analyzed in the forms of streamlines and pressure fields at various Reynolds numbers. Diagram of drag coefficient versus Reynolds numbers is presented and discussed. Results are compared with the available data in the literature that display good agreements.
Volume 4: Ocean Engineering; Ocean Renewable Energy; Ocean Space Utilization, Parts A and B, 2009
ABSTRACT Market demands for high-speed marine vehicles (HSMVs) are high in both commercial and na... more ABSTRACT Market demands for high-speed marine vehicles (HSMVs) are high in both commercial and naval branches. It is the naval architects’ task to design the hull and propulsion system to diminish drag, improve the propulsive efficiency, higher safety and better maneuverability. Surface Piercing Propellers (SPPs) may provide those possessions for the vehicles. Unlike immersed propellers, behavior of the SPPs is susceptible to immersed depth, Weber number and shaft inclination angle. This paper uses a specially practical and numerical method to predict the hydrodynamic characteristics of the SPPs. Critical advance ratio is obtained by practical formula, using Weber number and pitch ratio in the transition mode. Numerical method employs the potential based boundary element method (BEM) on the engaged surfaces. Two models of three and six bladed of the SPPs (SPP-1 and SPP-2) are selected and some results are shown.
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