Numerical Analysis of Propeller During Heave Motion Near a Free Surface

2017 ◽  
Vol 51 (1) ◽  
pp. 40-51 ◽  
Author(s):  
Wang Lian-zhou ◽  
Guo Chun-yu ◽  
Wan Lei ◽  
Su Yu-min
Keyword(s):  
Free Surface ◽  
Coupling Effect ◽  
Hydrodynamic Performance ◽  
Navier Stokes ◽  
Grid Technology ◽  
Thrust Coefficient ◽  
Motion State ◽  
Sinusoidal Motion ◽  
Torque Coefficient ◽  
Heave Motion

AbstractThe interaction between the free surface and the propeller during heave motion near the free surface was analyzed numerically using the Reynolds-Averaged Navier-Stokes (RANS) method. The coupling effect between the rotation and heave motions of the propeller was modeled using a motion equation developed in this study; the heave motion was simplified as a periodic motion based on the sinusoidal motion law; and the transfer of numerical values for unsteady flow fields was implemented using overset grid technology. A comparative analysis of the unsteady thrust coefficient and torque coefficient under different advance coefficient conditions was conducted, and the air ingestion phenomenon of the propeller was analyzed. The research highlighted the interaction between the coupled heave and rotation motions of the propeller and the free surface. The results showed that, when the advance coefficient was low, the hydrodynamic performance of the propeller during heave motion near a free surface was strongly influenced by the free surface and that a remarkable interaction existed between the propeller and the free surface. As the advance coefficient increased, the interaction between the propeller and the free surface weakened. The air ingestion that the propeller exerts upon the free surface during heave motion is a complex coupled superposition process. This phenomenon is correlated to the motion state and working time of the propeller, as well as the distance between the propeller and the free surface.

Numerical Analysis of a Floating Body With Two-Dimensional Moonpool Including Piston Mode

2010 ◽  
Author(s):  
Jaekyung Heo ◽  
Jong-Chun Park ◽  
Moo-Hyun Kim ◽  
Weon-Cheol Koo
Keyword(s):  
Free Surface ◽  
Viscous Flow ◽  
Experimental Results ◽  
Floating Body ◽  
Navier Stokes ◽  
Linear Potential ◽  
Navier Stokes Equation ◽  
Nonlinear Potential ◽  
Heave Motion ◽  
Piston Mode

In this paper, the potential and viscous flows are simulated numerically around a 2-D floating body with a moonpool (or a small gap) with particular emphasis on the piston mode. The floating body with moonpool is forced to heave in time domain. Linear potential code is known to give overestimated free-surface heights inside the moonpool. Therefore, a free-surface lid in the gap or similar treatments are widely employed to suppress the exaggerated phenomenon by potential theory. On the other hand, Navier-Stokes equation solvers based on a FVM can be used to take account of viscosity. Wave height and phase shift inside and outside the moon-pool are computed and compared with experimental results by Faltinsen et al. (2007) over various heaving frequencies. Pressure and vorticity fields are investigated to better understand the mechanism of the sway force induced by the heave motion. Furthermore, a nonlinear potential code is utilized to compare with the viscous flow. The viscosity effects are investigated in more detail by solving Euler equations. It is found that the viscous flow simulations agree very well with the experimental results without any numerical treatment.

On the Hydrodynamic Interaction Between Ship and Free-Surface Motions on Vessels With Moonpools

2019 ◽  
Author(s):  
Senthuran Ravinthrakumar ◽  
Trygve Kristiansen ◽  
Babak Ommani
Keyword(s):  
Free Surface ◽  
Flow Separation ◽  
Coupling Effect ◽  
Three Dimensional ◽  
Dimensional Case ◽  
Navier Stokes ◽  
Linear Potential ◽  
Two Dimensional ◽  
Sloshing Mode ◽  
Vessel Motion

Abstract Coupling between moonpool resonance and vessel motion is investigated in two-dimensional and quasi three-dimensional settings, where the models are studied in forced heave and in freely floating conditions. The two-dimensional setups are with a recess, while the quasi three-dimensional setups are without recess. One configuration with recess is presented for the two-dimensional case, while three different moonpool sizes (without recess) are tested for the quasi three-dimensional setup. A large number of forcing periods, and three wave steepnesses are tested. Boundary Element Method (BEM) and Viscous BEM (VBEM) time-domain codes based on linear potential flow theory, and a Navier–Stokes solver with linear free-surface and body-boundary conditions, are implemented to investigate resonant motion of the free-surface and the model. Damping due to flow separation from the sharp corners of the moonpool inlets is shown to matter for both vessel motions and moonpool response around the piston mode. In general, the CFD simulations compare well with the experimental results. BEM over-predicts the response significantly at resonance. VBEM provides improved results compared to the BEM, but still over-predicts the response. In the two-dimensional study there are significant coupling effects between heave, pitch and moonpool responses. In the quasi three-dimensional tests, the coupling effect is reduced significantly as the moonpool dimensions relative to the displaced volume of the ship is reduced. The first sloshing mode is investigated in the two-dimensional case. The studies show that damping due to flow separation is dominant. The vessel motions are unaffected by the moonpool response around the first sloshing mode.

Experimental Study and Hydrodynamic Performance Analysis of a Bio-Tail Fin Propellant System

2009 ◽  
Vol 419-420 ◽  
pp. 77-80 ◽  
Author(s):  
Yu Min Su ◽  
Shi Qi Zhao ◽  
Liang Yang
Keyword(s):  
Experimental Data ◽  
Lateral Force ◽  
Hydrodynamic Performance ◽  
Force Coefficient ◽  
Thrust Coefficient ◽  
Propulsion Efficiency ◽  
Design Concepts ◽  
Torque Coefficient ◽  
Precise Experimental Data ◽  
Selection Of

In order to research the bionic mechanics in unsteady flow and the hydrodynamic performance of the oscillating tail fin, in this paper, an experimental device imitating bionic tail fin were built, the design concepts and the rolling systems of the mechanical tail fins were demonstrated, including the procedures and correlated works on the selection of the servo motors, online control and signal data collecting and processing. The movements of the mechanical tail fin could be optimized by the comparisons of the propulsion efficiency, thrust coefficient, lateral force coefficient and torque coefficient at different conditions. Meanwhile, error analysis is carried out to correct the movement curves and obtain more precise experimental data and results.

Numerical analysis on effects of blade number on hydrodynamic performance of low-pitch marine cycloidal propeller

2019 ◽  
Vol 234 (2) ◽  
pp. 490-501
Author(s):  
Mohammad Bakhtiari ◽  
Hassan Ghassemi
Keyword(s):  
Numerical Method ◽  
Stokes Equations ◽  
Thrust Force ◽  
Circular Disk ◽  
Hydrodynamic Performance ◽  
Navier Stokes ◽  
Thrust Coefficient ◽  
Navier Stokes Equations ◽  
Blade Number ◽  
Marine Propulsion

Marine cycloidal propeller, as a special type of marine propulsion system, is used for ships that require high maneuverability, such as tugs and ferries. In a marine cycloidal propeller, the thrust force is generated by rotation of a circular disk with a number of lifting blades fitted on the periphery of the disk, so that the propeller axis of rotation is perpendicular to the direction of thrust force. Each blade pitches about its own axis, and the thrust magnitude and direction can be adjusted by controlling the pitching angle of the blades. Therefore, the propulsion and maneuvering units are combined together and no separate rudder is needed to maneuver the ship. Two configurations of marine cycloidal propeller have been studied and developed based on propeller pitch: low-pitch propeller (designed for advance coefficient less than one, means λ < 1) and high-pitch propeller (designed for λ > 1). Low-pitch marine cycloidal propellers are used in applications with low-speed maneuvering requirements, such as tugboats and minesweepers. In this study, the effects of blade number on hydrodynamic performance of low-pitch marine cycloidal propeller with pure cycloidal motion of the blades are investigated. The turbulent flow around marine cycloidal propeller is solved using a 2.5D numerical method based on unsteady Reynolds-averaged Navier–Stokes equations with shear-stress transport k–ω turbulent model. The presented numerical method was validated against experimental data and showed good agreement. The results showed that the thrust coefficient of marine cycloidal propeller generally decreases by increasing the blade number, whereas the torque coefficient increases. Consequently, the hydrodynamic efficiency of marine cycloidal propeller drops as the blade number increases.

Multi-objective optimization of trimaran sidehull arrangement via surrogate-based approach for reducing resistance and improving the seakeeping performance

2020 ◽  
pp. 147509022098027
Author(s):  
Amin Nazemian ◽  
Parviz Ghadimi
Keyword(s):  
Drag Reduction ◽  
Hydrodynamic Performance ◽  
Navier Stokes ◽  
Computational Time ◽  
Vertical Position ◽  
Vertical Acceleration ◽  
Seakeeping Performance ◽  
Hull Design ◽  
Hull Forms ◽  
Heave Motion

Trimaran hull forms have been very attractive in the past decade. Hydrodynamic performance of trimaran ships is influenced by sidehull arrangement. The present study was intended to construct a surrogate model for better understanding of the hydrodynamic performance of a trimaran ship. Accordingly, seakeeping and resistance of an inverted-bow trimaran were considered as objectives of a simulation-based design (SBD) optimization framework. Different longitudinal, transversal, and vertical position of trimaran’s sidehull were investigated based on an advanced free-surface steady Reynolds-averaged Navier–Stokes (URANS) solver within StarCCM+ for resistance calculation and 3D panel method in Ansys-AQWA for seakeeping analyses. Quality and applicability of metamodeling optimization and its computational time were examined for future trimaran hull design projects. Total resistance for drag reduction, pitch and heave motion, and vertical acceleration at fore perpendicular for seakeeping performance were objectives of the study. The optimization results indicated a 6.9% drag reduction and 4.7% improvement in seakeeping performance, which yield lower longitudinal and large transversal distances of the sidehull. Furthermore, the conducted investigations demonstrated the effectiveness and capability of the proposed optimization platform for other marine industrial projects.

A Robust and Simple Low-Mach Number Solver for Flapping-Wing Simulations

2011 ◽  
Author(s):  
Jeu-Jiun Hu ◽  
Yang-Yao Niu
Keyword(s):  
Aerodynamic Force ◽  
Lift Coefficient ◽  
Unsteady Aerodynamics ◽  
Numerical Results ◽  
Navier Stokes ◽  
Finite Volume Scheme ◽  
Neutral Position ◽  
Thrust Coefficient ◽  
Time Stepping ◽  
Heave Motion

In the current study, a very simple preconditioned Navier-Stokes solver based on Roe type numerical fluxes is developed to investigate the unsteady aerodynamics around the flapping wings. A modified Osher-Chakravarthy (MOC) upwind finite-volume scheme is used for space discrete. To evaluate unsteady accuracy, a dual-time stepping strategy including the second-order Euler implicit method and diagonal dominant alternating direction implicit scheme (DDADI) are selected for the physical time and pseudo time stepping implements. In the test cases, two-dimensional airfoil in pure plunging and pitching motion are computed for validation of purpose scheme, respectively. The present numerical results are in good agreement with other’s numerical results. Then, the simulation is carried out on a NACA0012 wing oscillating in heave motion. As a result, the frequency of thrust coefficient is twice the plunging frequency since the maximum thrust is occurred as the airfoil passes the neutral position twice in one period and the frequency of the lift coefficient is the same. By testing the aerodynamic force varying with the reduce frequency of pure heave motion airfoil, the results indicate that the mean thrust output increasing and propulsion efficiency decreasing while reduce frequency is increasing.

scholarly journals A Theoretical Study on the Hydrodynamics of a Zero-Pressurized Air-Cushion-Assisted Barge Platform

2020 ◽  
Vol 8 (9) ◽  
pp. 664
Author(s):  
Fengmei Jing ◽  
Li Xu ◽  
Zhiqun Guo ◽  
Hengxu Liu
Keyword(s):  
Coupling Effect ◽  
Low Cost ◽  
Engineering Application ◽  
Theoretical Method ◽  
Hydrodynamic Performance ◽  
Irregular Waves ◽  
Floating Body ◽  
Motion Response ◽  
Air Cushion ◽  
Heave Motion

Thebarge platform has the advantages of low cost, simple structure, and reliable hydrodynamic performance. In order to further improve the hydrodynamics of the barge platform and to reduce its motion response in waves, a zero-pressurized air cushion is incorporated into the platform in this paper. The pressure of the zero-pressurized air cushion is equal to atmospheric pressure and thus does not provide buoyancy to the platform. As compared to the conventional pressurized air cushion, the zero-pressurized one has advantages of less air leakage risk. However, due to the coupling effect on the interface between water and air cushion, the influence of the gas inside the air cushion on the performance of the floating body has become a difficult problem. Based on the boundary element method, the motion response of the zero-pressurized air-cushion-assisted barge platform under regular and irregular waves is calculated and analyzed in the paper. Compared with the barge platform without air cushion, numerical results from the theoretical method show that in regular waves, the air cushion could significantly reduce the amplitude of heave and pitch (roll) response of the round barge platform in the vicinity of resonance. In irregular waves, the air cushion also observably reduces the pitch (roll) motion, though amplifies the heave motion due to the transfer of heave resonance frequency. Thetheoretical study demonstrates that the zero-pressurized air cushion can reduce the seakeeping motion of barge platforms in high sea states, but might also bring negative effects to heave motion in low sea states. One should carefully design the air cushion for barge platforms according to the operating sea states to achieve satisfactory hydrodynamic performance in engineering application.

scholarly journals Inhibition and Hydrodynamic Analysis of Twin Side-Hulls on the Porpoising Instability of Planing Boats

2021 ◽  
Vol 9 (1) ◽  
pp. 50
Author(s):  
Jiandong Wang ◽  
Jiayuan Zhuang ◽  
Yumin Su ◽  
Xiaosheng Bi
Keyword(s):  
Sampling Method ◽  
Hydrodynamic Performance ◽  
Navier Stokes ◽  
Inhibition Mechanism ◽  
Grid Technology ◽  
Vertical Side ◽  
Hydrodynamic Analysis ◽  
Planing Craft ◽  
Factor Design ◽  
Monomer Form

A comparative analysis of the hydrodynamic performance of a planing craft in the monomer-form state (MFS) and trimaran-form state (TFS) was performed, and the inhibition mechanism of twin side-hulls on porpoising instability was evaluated based on the numerical method. A series of drag tests were conducted on the monomer-form models with different longitudinal locations of the center of gravity (Lcg); the occurrence of porpoising and the influence of Lcg on porpoising by the model was discussed. Then, based on the Reynolds-averaged Navier–Stokes (RANS) solver and overset grid technology, numerical simulations of the model were performed, and using test data, the results were verified by incorporating the whisker spray equation of Savitsky. To determine how the porpoising is inhibited in the TFS, simulations for the craft in the MFS and TFS when porpoising were performed and the influence of side-hulls on sailing attitudes and hydrodynamic performance at different speeds were analyzed. Using the full factor design spatial sampling method, the influence of longitudinal and vertical side-hull placements on porpoising inhibition were deliberated, and the optimal side-hull location range is reported and verified on the scale of a real ship. The results indicate that the longitudinal side-hull location should be set in the ratio (a/Lm) range from 0.1 to 0.3, and vertically, the draft ratio (Dd/Tm) should be less than 0.442. Following these recommendations, porpoising instability can be inhibited, and lesser resistance can be achieved.

scholarly journals Analysis of Hydrodynamic Performance of L-Type Podded Propulsion with Oblique Flow Angle

2019 ◽  
Vol 7 (2) ◽  
pp. 51 ◽  
Author(s):  
Wei Wang ◽  
Dagang Zhao ◽  
Chunyu Guo ◽  
Yongjie Pang
Keyword(s):  
Hydrodynamic Performance ◽  
Navier Stokes ◽  
Thrust Coefficient ◽  
Flow Angle ◽  
Oblique Flow ◽  
Vertical Distributions ◽  
Experimental Values ◽  
Horizontal And Vertical Distributions ◽  
The Impact ◽  
Good Agreement

In this study, the Reynolds-averaged Navier–Stokes (RANS) method and a model experimental test in a towing tank are used to investigate the unsteady hydrodynamic performance of L-type podded propulsion under different oblique flow angles and advance coefficients. The results show that the load of the operative propeller increases with oblique flow angle and the bracket adds resistance to the pod due to the impact of water flow, leading to a reduced propeller thrust coefficient with increased oblique flow angle. Under a high advance coefficient, the speed of increase of the pressure effect is higher than that of the viscosity effect, and the propeller efficiency increases with the oblique flow angle. The nonuniformity of the inflow results in varying degrees of asymmetry in the horizontal and vertical distributions of the propeller blade pressure. Under high oblique flow angle, relatively strong interference effects are seen between venting vortexes and the cabin after blades, leading to a disorderly venting vortex system after the blade. The numerical simulation results are in good agreement with the experimental values. The study findings provide a foundation for further research on L-type podded propulsors.

scholarly journals Effect of Active and Passive Curvature on the Hydrodynamic Performance of Flapping Fins

2020 ◽  
Author(s):  
David Fernández-Gutiérrez ◽  
Wim M. van Rees
Keyword(s):  
Torsional Stiffness ◽  
Hydrodynamic Performance ◽  
Navier Stokes ◽  
Thrust Coefficient ◽  
Active Deformation ◽  
Hydrodynamic Loading ◽  
Passive Deformation ◽  
Curvature Distribution ◽  
The Impact ◽  
Fin Shape

Abstract Ray-finned fish swim by flapping their fins, which are composed of bony rays connected by an inextensible membrane. Throughout the flapping cycle, the fins typically undergo both ‘passive’ deformation due to hydrodynamic loading, and ‘active’ deformation arising from internal musculature deforming the fin against the flow. To systematically analyze the impact of fin shape on hydrodynamic performance, a parametric definition of the fin geometry and its modes of deformation is required, consistent with the fin’s material and mechanical properties. In this paper we present a model and algorithm to determine the fin shape corresponding to an arbitrary out-of-plane curvature distribution for each ray. The shape is computed by iteratively enforcing constraints corresponding to membrane inextensibility, and negligible torsional stiffness of the rays. Based on this model, we present a low-order parametrization of fin shapes that capture the predominant deformation modes due to combined hydrodynamic loading and intrinsic actuation, as compared to experimental observations. To demonstrate the model’s ability to provide insight into the effect of curvature on hydrodynamic fin performance, we integrate our algorithm into a 3D Navier-Stokes solver Using this framework, we present initial results on the cycle-averaged thrust coefficient of a passively and actively deforming generalized trapezoidal caudal fin model at Reynolds number 1500 and Strouhal number 0.3. The results demonstrate that our model, algorithm, and integration with the flow solver form a useful framework to understand the effect of 3D curvature on hydrodynamic performance of flapping fins.

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