Proceedings of the International Offshore and Polar Engineering Conference, 2009
This paper describes the full scale experiment using air lubrication method to reduce the frictio... more This paper describes the full scale experiment using air lubrication method to reduce the frictional resistance. The full scale experiment with the cement carrier Pacific Seagull was conducted from January to March, 2008. Torque and thrust are decreased due to the effect of bubbles. If we assume the value of thrust deduction is constant with and without bubbles, the effect of bubbles in reducing frictional resistance or ship resistance is clearly proved by the experimental results. The maximum total resistance reduction in case of ballast condition and full load condition are about 11% and 6% respectively. The mean propeller inflow velocity was increased for with air lubrication from no air condition due to the viscous resistance reduction. This phenomenon was considered using very simple boundary layer method.
Precise information of viscous flow field around propeller is required to design energy saving de... more Precise information of viscous flow field around propeller is required to design energy saving devices equipped near ship stern. This work presents the detailed flow field measurement data around rotating propeller. The measurements were done using LaVision stereo Particle Image Velocimetry (PIV) system. The model ship used in the work is Japan Bulk Carrier (JBC) with/without round shaped small duct equipped at the upstream position of propeller as an energy saving device (ESD). In this paper, measured mean flow field upstream/downstream of rotating propeller with/without duct are presented and the turbulent kinetic energy at one station is also discussed. These data set would be useful to consider the availability of the basic idea of the device and to validate the theoretical prediction of the performance development including advanced CFD (Computational Fluid Dynamics) computation results in respect of accuracy. Overall, this study will be helpful to design duct-type ESD.
The effect of free surface on the flow around a rotating propeller and the open water characteris... more The effect of free surface on the flow around a rotating propeller and the open water characteristics are studied by varying the propeller immersion depth to investigate the applicability of the new body-force method. A simplified quasi-steady blade element theory (BET) with the infinite-bladed propeller model is coupled with the Reynolds averaged Navier-Stokes (RANS) code CFDSHIP-IOWA to calculate the flow around the propeller near the free surface. Propeller open-water characteristics are simulated in still water for different immersion depths for the Methodical-AU type fixed-pitch propeller. The results show that the wake structure is heavily affected by the free surface. The propeller open characteristics are compared with experiment.
Flow around a fish is investigated by solving Navier-Stokes equations and the continuity equation... more Flow around a fish is investigated by solving Navier-Stokes equations and the continuity equation numerically. The two dimensional wing which moves like a fish is considered as the simplest model. The motion has a transverse wave progressing along the body from head to tail and the amplitude of the wave increases from zero at the head to a maximum at the tail. The laminar flow field is solved for simplicity. The equation is discretized by first-order backward difference for time and the 5-point finite analytic of Chen and Patel for space. The pressure velocity coupling is accomplished by the SIMPLER algorithm. The moving body fitted grid system is used for the moving body and the grid is generated at each time step. The computational results show a very complicated vortical wake and flow field around the wing. The axial and lateral forces are also presented and discussed. The results for some other pattern movement show the essential feature of the fish like motion.
Further validation of a viscous-flow method for predicting propeller-hull interaction is provided... more Further validation of a viscous-flow method for predicting propeller-hull interaction is provided through detailed comparisons with recent experimental data for the practical configuration of the Iowa axisymmetric body. Modifications are made to the k-ε turbulence model and wall functions for axisymmetric bodies. Close agreement is demonstrated between the calculations and the data, which supports the conclusion that the present procedures can accurately simulate the steady part of the combined propeller-hull flow field. However, the present extensive comparisons also point out the critical role of turbulence modeling and detailed numerical treatments. Also, comparisons are made with Huang's inviscid-flow method. Although both methods show similar trends, there are some important differences; for example, Huang's method predicts reduced propeller loading and larger axial velocities in the propeller plane near the body surface and propeller tip. Near the propeller tip, the present method exhibits a velocity defect region, which is absent in Huang's method. In consideration of the greater rigor of the present method, such differences imply that viscous effects play an important role in propeller-hull interaction even for the relatively simple case of an axisymmetric body and should be accounted for in the design procedures of wake-adapated propellers. However, part of the differences may be due to some of the present detailed numerical treatments, which indicate the need for continued refinement of comprehensive methods, such as the present one, and more detailed experimental information for validation purposes.
Numerical computation of two-dimensional incompressible flow was conducted around a finite flat p... more Numerical computation of two-dimensional incompressible flow was conducted around a finite flat plate. A full implicit scheme was used to solve the Navier-Stokes equations and a continuity equation. The three basic equations were descritized by finite difference method and the predictor-corrector method. The subsequent algebraic matrix was solved directly at the same time. The examples of the results were presented for the steady and unsteady cases at a Reynolds number 105. The latter case is the flow field around a flat plate in surging motion around a mean advance speed. The steady state solution was compared with the Blasius solution and the numerical solution of the triple-deck theory. The close agreements were obtained. With regard to the unsteady case, the solution is compared with Lin's analysis which assume the small amplitude and the high frequency of the unsteady motion. For the case in which Lin's assumption is valid, the numerical solution was in close agreement with the analysis. From these solutions, the present scheme has the ability to resolve the trailing edge interaction and the unsteady effect. For the unsteady flow, the solutions were also obtained for the large amplitude case and the medium frequency case. In the former, the small nonlinear effect to the averaged velocity was observed, where in the latter the large difference was observed for the fluctuation part.
An integral method of predicting the three-dimensional boundary layer using higher order terms is... more An integral method of predicting the three-dimensional boundary layer using higher order terms is presented. Numerical calculations assuming a small cross flow are performed for two simple models; there is reasonable agreement with experimental results.
In the ship design process, ship motion and propulsion performance in sea waves became very impor... more In the ship design process, ship motion and propulsion performance in sea waves became very important issues. Especially, prediction of ship propulsion performance during real operation is an important challenge to ship owners for economic operation in terms of fuel consumption and route-time evaluation. Therefore, it should be considered in the early design stages of the ship. It is thought that the averaged value and fluctuation of effective inflow velocity to the propeller have a great effect on the propulsion performance in waves. However, even for the nominal velocity distribution, very few results have been presented due to some technical difficulties in experiments. In this study, flow measurements near the propeller plane using a stereo PIV system were performed. Phase-averaged flow fields on the propeller plane of a KVLCC2 model ship in waves were measured in the towing tank by using the stereo PIV system and a phase synchronizer with heave motion. The experiment was carried out at fully loaded condition with making surge, heave and pitch motions free at a forward speed corresponding to Fr=0.142 (Re=2.55×106) in various head waves and calm water condition. The phase averaged nominal velocity fields obtained from the measurements are discussed with respect to effects of wave orbital velocity and ship motion. The low velocity region is affected by pressure gradient and ship motion.
Results are presented from a towing-tank experiment of propeller-huil interaction conducted in or... more Results are presented from a towing-tank experiment of propeller-huil interaction conducted in order to provide detailed documentation of the complete flow field appropriate both for explicating the f l.ow physics and validating computational methods. Mean-veloci ty and pressure field measurements were made for the wi th-and without-propeller conditions for the Series 60 CB .6 hul l, form at numerous stations both upstream and downstream of the propeller and in the near wake region. Surface-pressure distributions and wave profiles were measured for both conditions. Resistance and self-propulsion tests were also conducted. The experimental equipment and procedures are described, and the results are discussed to ated Research Initiative (Special Focus
The Journal of Japan Institute of Navigation, 1999
The ship speed near the berth is very low and the fluid flow around a ship hull is un − steady ． ... more The ship speed near the berth is very low and the fluid flow around a ship hull is un − steady ． So， the transient fiuid mQtion should be considered to estimate the drag force acting on the ship hu1L Especially ， the lateral motion in a berthing maneuver of a VLCC starts frQm the rest and ends within one ship length． In that problem ， the force is usually estimated using steady state drag fQrce coefficient Qbtained by towing tank experiment
Over the years, shipping has been played on one of the most used transportation methods and marin... more Over the years, shipping has been played on one of the most used transportation methods and marine trading is increasing more and more these days. As a result, the shipbuilders are trying to design and construct an efficient and enormous ship to be economical. On the other hand, the environmental awareness to eliminate greenhouse gas emission is rising due to the effect of global warming. Such factors make the various types of energy-saving devices (ESDs) to be developed reliably without affecting other functions. This paper characterizes the performance of the rudder bulb-fins system (RBF) fixed behind the propeller in wave. In this study, the analysis of dynamics forces and velocity fields around the stern which are crucial in evaluating the performance of ESDs were implemented using CFDShip-Iowa V4.5. The effect of the ESD on ship's motion was analyzed by performing motions analysis in various regular head waves. The computational results were validated with the experiments conducted in the towing tank of Osaka University. The calculations were done for three cases of rudder conditions: the ship without a rudder, the ship with conventional rudder, and the ship with RBF. The predicted results and measured data reveal that the currently designed RBF can diminish the hub vortex strength and improve the hull efficiency due to the increase of thrust and wake gain without any adverse conditions. It can be confirmed that the computational simulations predicted and followed the trend of experimentally measured data well.
The KVLCC2 tanker in fully-loaded condition free to heave and pitch at Froude number 0.142 in thr... more The KVLCC2 tanker in fully-loaded condition free to heave and pitch at Froude number 0.142 in three head wave-ship length ratios (0.6, 1.1 and 1.6) is simulated by CFDSHIP-IOWA V4.5. The detailed phenomena of nominal wake behaving in waves are studied by analyzing the velocity and vorticity distribution, and vector field on the propeller plane. The periodic change with phase lag for the volume average axial velocity and circulation are observed. The axial velocity distribution is also decomposed by Fourier analysis. Two vortex systems appear: bilge vortex shedding from the hull body and secondary vortex shedding around the shaft. Based on the results, the propulsion design with higher efficiency, more proper engine margin and lower gas emission are expected.
Proceedings of the International Offshore and Polar Engineering Conference, 2009
This paper describes the full scale experiment using air lubrication method to reduce the frictio... more This paper describes the full scale experiment using air lubrication method to reduce the frictional resistance. The full scale experiment with the cement carrier Pacific Seagull was conducted from January to March, 2008. Torque and thrust are decreased due to the effect of bubbles. If we assume the value of thrust deduction is constant with and without bubbles, the effect of bubbles in reducing frictional resistance or ship resistance is clearly proved by the experimental results. The maximum total resistance reduction in case of ballast condition and full load condition are about 11% and 6% respectively. The mean propeller inflow velocity was increased for with air lubrication from no air condition due to the viscous resistance reduction. This phenomenon was considered using very simple boundary layer method.
Precise information of viscous flow field around propeller is required to design energy saving de... more Precise information of viscous flow field around propeller is required to design energy saving devices equipped near ship stern. This work presents the detailed flow field measurement data around rotating propeller. The measurements were done using LaVision stereo Particle Image Velocimetry (PIV) system. The model ship used in the work is Japan Bulk Carrier (JBC) with/without round shaped small duct equipped at the upstream position of propeller as an energy saving device (ESD). In this paper, measured mean flow field upstream/downstream of rotating propeller with/without duct are presented and the turbulent kinetic energy at one station is also discussed. These data set would be useful to consider the availability of the basic idea of the device and to validate the theoretical prediction of the performance development including advanced CFD (Computational Fluid Dynamics) computation results in respect of accuracy. Overall, this study will be helpful to design duct-type ESD.
The effect of free surface on the flow around a rotating propeller and the open water characteris... more The effect of free surface on the flow around a rotating propeller and the open water characteristics are studied by varying the propeller immersion depth to investigate the applicability of the new body-force method. A simplified quasi-steady blade element theory (BET) with the infinite-bladed propeller model is coupled with the Reynolds averaged Navier-Stokes (RANS) code CFDSHIP-IOWA to calculate the flow around the propeller near the free surface. Propeller open-water characteristics are simulated in still water for different immersion depths for the Methodical-AU type fixed-pitch propeller. The results show that the wake structure is heavily affected by the free surface. The propeller open characteristics are compared with experiment.
Flow around a fish is investigated by solving Navier-Stokes equations and the continuity equation... more Flow around a fish is investigated by solving Navier-Stokes equations and the continuity equation numerically. The two dimensional wing which moves like a fish is considered as the simplest model. The motion has a transverse wave progressing along the body from head to tail and the amplitude of the wave increases from zero at the head to a maximum at the tail. The laminar flow field is solved for simplicity. The equation is discretized by first-order backward difference for time and the 5-point finite analytic of Chen and Patel for space. The pressure velocity coupling is accomplished by the SIMPLER algorithm. The moving body fitted grid system is used for the moving body and the grid is generated at each time step. The computational results show a very complicated vortical wake and flow field around the wing. The axial and lateral forces are also presented and discussed. The results for some other pattern movement show the essential feature of the fish like motion.
Further validation of a viscous-flow method for predicting propeller-hull interaction is provided... more Further validation of a viscous-flow method for predicting propeller-hull interaction is provided through detailed comparisons with recent experimental data for the practical configuration of the Iowa axisymmetric body. Modifications are made to the k-ε turbulence model and wall functions for axisymmetric bodies. Close agreement is demonstrated between the calculations and the data, which supports the conclusion that the present procedures can accurately simulate the steady part of the combined propeller-hull flow field. However, the present extensive comparisons also point out the critical role of turbulence modeling and detailed numerical treatments. Also, comparisons are made with Huang's inviscid-flow method. Although both methods show similar trends, there are some important differences; for example, Huang's method predicts reduced propeller loading and larger axial velocities in the propeller plane near the body surface and propeller tip. Near the propeller tip, the present method exhibits a velocity defect region, which is absent in Huang's method. In consideration of the greater rigor of the present method, such differences imply that viscous effects play an important role in propeller-hull interaction even for the relatively simple case of an axisymmetric body and should be accounted for in the design procedures of wake-adapated propellers. However, part of the differences may be due to some of the present detailed numerical treatments, which indicate the need for continued refinement of comprehensive methods, such as the present one, and more detailed experimental information for validation purposes.
Numerical computation of two-dimensional incompressible flow was conducted around a finite flat p... more Numerical computation of two-dimensional incompressible flow was conducted around a finite flat plate. A full implicit scheme was used to solve the Navier-Stokes equations and a continuity equation. The three basic equations were descritized by finite difference method and the predictor-corrector method. The subsequent algebraic matrix was solved directly at the same time. The examples of the results were presented for the steady and unsteady cases at a Reynolds number 105. The latter case is the flow field around a flat plate in surging motion around a mean advance speed. The steady state solution was compared with the Blasius solution and the numerical solution of the triple-deck theory. The close agreements were obtained. With regard to the unsteady case, the solution is compared with Lin's analysis which assume the small amplitude and the high frequency of the unsteady motion. For the case in which Lin's assumption is valid, the numerical solution was in close agreement with the analysis. From these solutions, the present scheme has the ability to resolve the trailing edge interaction and the unsteady effect. For the unsteady flow, the solutions were also obtained for the large amplitude case and the medium frequency case. In the former, the small nonlinear effect to the averaged velocity was observed, where in the latter the large difference was observed for the fluctuation part.
An integral method of predicting the three-dimensional boundary layer using higher order terms is... more An integral method of predicting the three-dimensional boundary layer using higher order terms is presented. Numerical calculations assuming a small cross flow are performed for two simple models; there is reasonable agreement with experimental results.
In the ship design process, ship motion and propulsion performance in sea waves became very impor... more In the ship design process, ship motion and propulsion performance in sea waves became very important issues. Especially, prediction of ship propulsion performance during real operation is an important challenge to ship owners for economic operation in terms of fuel consumption and route-time evaluation. Therefore, it should be considered in the early design stages of the ship. It is thought that the averaged value and fluctuation of effective inflow velocity to the propeller have a great effect on the propulsion performance in waves. However, even for the nominal velocity distribution, very few results have been presented due to some technical difficulties in experiments. In this study, flow measurements near the propeller plane using a stereo PIV system were performed. Phase-averaged flow fields on the propeller plane of a KVLCC2 model ship in waves were measured in the towing tank by using the stereo PIV system and a phase synchronizer with heave motion. The experiment was carried out at fully loaded condition with making surge, heave and pitch motions free at a forward speed corresponding to Fr=0.142 (Re=2.55×106) in various head waves and calm water condition. The phase averaged nominal velocity fields obtained from the measurements are discussed with respect to effects of wave orbital velocity and ship motion. The low velocity region is affected by pressure gradient and ship motion.
Results are presented from a towing-tank experiment of propeller-huil interaction conducted in or... more Results are presented from a towing-tank experiment of propeller-huil interaction conducted in order to provide detailed documentation of the complete flow field appropriate both for explicating the f l.ow physics and validating computational methods. Mean-veloci ty and pressure field measurements were made for the wi th-and without-propeller conditions for the Series 60 CB .6 hul l, form at numerous stations both upstream and downstream of the propeller and in the near wake region. Surface-pressure distributions and wave profiles were measured for both conditions. Resistance and self-propulsion tests were also conducted. The experimental equipment and procedures are described, and the results are discussed to ated Research Initiative (Special Focus
The Journal of Japan Institute of Navigation, 1999
The ship speed near the berth is very low and the fluid flow around a ship hull is un − steady ． ... more The ship speed near the berth is very low and the fluid flow around a ship hull is un − steady ． So， the transient fiuid mQtion should be considered to estimate the drag force acting on the ship hu1L Especially ， the lateral motion in a berthing maneuver of a VLCC starts frQm the rest and ends within one ship length． In that problem ， the force is usually estimated using steady state drag fQrce coefficient Qbtained by towing tank experiment
Over the years, shipping has been played on one of the most used transportation methods and marin... more Over the years, shipping has been played on one of the most used transportation methods and marine trading is increasing more and more these days. As a result, the shipbuilders are trying to design and construct an efficient and enormous ship to be economical. On the other hand, the environmental awareness to eliminate greenhouse gas emission is rising due to the effect of global warming. Such factors make the various types of energy-saving devices (ESDs) to be developed reliably without affecting other functions. This paper characterizes the performance of the rudder bulb-fins system (RBF) fixed behind the propeller in wave. In this study, the analysis of dynamics forces and velocity fields around the stern which are crucial in evaluating the performance of ESDs were implemented using CFDShip-Iowa V4.5. The effect of the ESD on ship's motion was analyzed by performing motions analysis in various regular head waves. The computational results were validated with the experiments conducted in the towing tank of Osaka University. The calculations were done for three cases of rudder conditions: the ship without a rudder, the ship with conventional rudder, and the ship with RBF. The predicted results and measured data reveal that the currently designed RBF can diminish the hub vortex strength and improve the hull efficiency due to the increase of thrust and wake gain without any adverse conditions. It can be confirmed that the computational simulations predicted and followed the trend of experimentally measured data well.
The KVLCC2 tanker in fully-loaded condition free to heave and pitch at Froude number 0.142 in thr... more The KVLCC2 tanker in fully-loaded condition free to heave and pitch at Froude number 0.142 in three head wave-ship length ratios (0.6, 1.1 and 1.6) is simulated by CFDSHIP-IOWA V4.5. The detailed phenomena of nominal wake behaving in waves are studied by analyzing the velocity and vorticity distribution, and vector field on the propeller plane. The periodic change with phase lag for the volume average axial velocity and circulation are observed. The axial velocity distribution is also decomposed by Fourier analysis. Two vortex systems appear: bilge vortex shedding from the hull body and secondary vortex shedding around the shaft. Based on the results, the propulsion design with higher efficiency, more proper engine margin and lower gas emission are expected.
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Papers by Yasuyuki Toda