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A. G. Molland - One of the best experts on this subject based on the ideXlab platform.
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Energy efficiency of ship propulsive systems: rudder-propeller interaction
Ship Propulsion Systems Conference, 2010Co-Authors: Stephen R. Turnock, A. G. MollandAbstract:The rudder of a ship is used to maintain its direction and for changing course. As such the goal of rudder design is to maximise Sideforce for control of course while minimising resistive drag. Ship rudders are typically mounted downstream of the propeller to take advantage of the higher speed flow in the propeller race. This flow also has a swirl component that results in a complex flow regime arriving at the rudder. Likewise, the presence of the rudder has an influence on the flow speed and direction passing through the propeller. It is therefore recommended that design of the propulsive system incorporates the rudder design. This will ensure that appropriate decisions are made that maximise the net propulsive thrust for a given engine power. We examine in this paper how the design of the combined propeller-rudder system can be best achieved for a goal of maximising propulsive efficiency without sacrificing the ability to manoeuvre. The design of the rudder requires careful thought as to its longitudinal, lateral and vertical position. The swirl component of propeller race results in a force distribution over the rudder that can give a net propulsive thrust by extracting energy from the flow rotation. Such effects can be used to compensate for the resistive drag of the form and surface area of the rudder itself. Design of rudders are often based on evolutionary principles that will not capture the subtleties necessary to enhance propulsive efficiency. We discuss a hierarchy of computational analysis tools that includes unsteady solution of the Navier Stokes equations, their coupling with propeller blade element momentum analysis and use of surface panel and lifting line theories to understand rudder forces. Such techniques are suitable for design optimization. Conventionally it is the rudder structural strength and associated cost of construction that limits the types of rudders that can be designed. Recent work on a variety of twisted rudders has shown that there can be significant performance gains. For more radical shapes the use of suitable composite construction will give cost-effective performance while also reducing rudder mass as well. We show through three case studies related to: (1) twisted rudders, (2) cathodic protection and (3) the influence of the rudder on kite assisted ship propulsion; that to achieve improved propulsive performance all that is required is greater care and attention to the rudder design process. Such design detail will more than cover its cost in fuel savings and the resultant reduced engine emissions
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Experimental measurement of Sideforce and induced drag on catamaran demihulls
International shipbuilding progress, 1998Co-Authors: P.r. Couser, J.f. Wellicome, A. G. MollandAbstract:A catamaran comprises two demihulls and although the flow about the catamaran centre line is symmetric the flow about the centre lines of the individual demihulls is not. The asymmetric nature of the fluid crossflow around the demihulls causes Sideforce and hence induced drag to be experienced on the demihulls. The Sideforces generated by each demihull act in opposition and cancel whereas the induced drags of both demihulls act together to resist the forward motion of the vessel. Experimental procedures used to estimate the Sideforce and induced drag are presented together with results for one hullform at two demihull separations (S/L = 0.225 and S/L = 0.329) and at several Froude Numbers. It is shown that the induced drag generated by the demihulls is negligible despite the generation of significant Sideforce. The Sideforce produced was found to reduce rapidly with increasing demihull separation.
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Wind tunnel investigation of a pair of ellipsoids in close proximity
1997Co-Authors: A. G. Molland, I.k.a.p. UtamaAbstract:The results of wind tunnel experiments on a pair of ellipsoids in close proximity are presented. The experiments represented a reflex model of a multihull ship and investigated the components of viscous drag and viscous interaction effects between the hulls. The tests were carried out with and without turbulence transition strip at separation to length (S/L) raios of 0.27, 0.37, 0.47 and 0.57 and at Reynolds Number values up to 3.2 x 10 to the power of 6. Tests were included with a single-hull configuration with which the resistance characteristics of the twin-hull configuration could be compared. Results are presented for each S/L configuration as drag and Sideforce coefficients at zero incidence. Surface pressure distributions over the hull were also obtained in order to provide a detailed knowledge of the distribution of forces over the hulls. The overall drag coefficients and pressure distributions were comparable with previously published data for single bodies of revolution in isolation. The results with two bodies demonstrated the existence of a viscous drag interaction between the bodies, and that this interaction is maintained at an approximately constant level up to about S/L = 0.5.
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Wind tunnel investigation of the influence of propeller loading on ship rudder performance
1993Co-Authors: A. G. Molland, Stephen R. TurnockAbstract:A detailed investigation has been carried out into the interaction between a ship rudder and propeller combination. The tests used the 11' x 8' low speed wind tunnel at the University of Southampton. This report presents results for a series of three all-movable rudders with the same mean chord of 667mm and NACA0020 sections, but with varying aspect ratio and taper ratio. A four-bladed, 800mm diameter, adjustable pitch propeller was used. This propeller is a modified version of the Wageningen B4.40 series. Open-water results for the modified design were validated against published data. The test consisted of a series of parametric studies into the effect of the longitudinal distance between the propeller and rudder, propeller thrust loading, rudder aspect ratio, and rudder taper ratio. A five-component strain-gauge dynamometer was used to measure lift, drag and three moments on the rudder and a rotating strain gauge dynamometer the developed thrust and torque of the propeller. In addition, both spanwise and chordwise pressure distributions were measured on the rudder surface. Propeller revolutions were varied between 0 and 3,000 rpm and tunnel wind speeds up to 20m/s were used. Results are presented in the form of non-dimensional coefficients of lift (C subscript L), drag (C subscript D), spanwise (CP subscript S) and chordwise (CP subscript C) position of the centre of pressure variation with incidence for the rudder. The influence of rudder on propeller performance is given in terms of non-dimensional thrust (K subscript T) and torque (K subscript Q) coefficient variation with advance ratio (J). The surface pressure measurements on the rudder are presented as both a spanwise distribution of the local lift coefficient (C subscript L) and as a surface pressure distribution. Principal findings of the work were that: increasing propeller thrust loading increased rudder Sideforce while delaying stall. For constant rpm the presence of the rudder alters the propellers developed thrust and torque characteristic. Changes in the longitudinal separation of the rudder and propeller had only a minimal effect on the Sideforce characteristics of the rudder. The information presented should be of considerable use in numerically modelling the flow interaction and in the development of more advanced ship manoeuvring simulations.
N.j. Van Der Kolk - One of the best experts on this subject based on the ideXlab platform.
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Part 2: Simulation methodology and numerical uncertainty for RANS-CFD for the hydrodynamics of wind-assisted ships operating at leeway angles
Ocean Engineering, 2020Co-Authors: N.j. Van Der Kolk, I. Akkerman, J.a. Keuning, Rene HuijsmansAbstract:Abstract A Reynolds-averaged Navier Stokes computational fluid dynamics (RANS-CFD) package will be one of the primary tools used during the development of a performance prediction program for wind-assisted commercial ships. This paper describes the simulation verification exercise, performed in support of the experimental validation presented in Part 1 of this two-part series describing the RANS-CFD method employed in this research. The predominance of large-scale separated flow structures in the wake of the sailing ship, an artefact of Sideforce production necessary for sailing, points to a careful verification exercise and estimate for the numerical uncertainty to support the systematic investigation of wind-assisted ship hydromechanics and meshing guidelines within the available computer resources. Methods for CFD uncertainty quantification are defined and implemented for verification cases at leeway angles equal to 0ᵒ, 6ᵒ, and 9ᵒ. Analysis for four sets of grids with different meshing strategies and for varying time steps results in a grid definition and time step for simulation validation. Numerical uncertainty as adopted in Part 1 for validation is defined. Finally, the meshing strategy for full-scale simulation is described, as used for the production runs of the Delft Wind Assist Series.
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Hydrodynamics of wind-assisted ship propulsion validation of RANS-CFD methodology
2017Co-Authors: N.j. Van Der Kolk, J.a. Keuning, Rene HuijsmansAbstract:A Reynolds-Averaged Navier Stokes computational fluid dynamics (RANS-CFD) package will be one of the primary tools used during the development of a performance prediction program for Wind-Assisted commercial ships. The modelling challenge presented by large separated flow structures in the wake of the sailing ship points to a conscientious validation study. A validation data set, consisting of hydrodynamic forces acting on the ship sailing with a leeway angle, was collected at the Delft University of Technology towing tank facility, for bare-hull and appended cases. Four hull geometries were selected to represent of the Delft Wind-Assist Systematic Series. Appended cases were designed to represent a broad range of appendage topologies: Rudder, Bilge-keels, Skeg, and Barkeel. The direct validation exercise for the bare-hull case was successful, with the validation level for the Sideforce equal to 9.5% (fine mesh: 9M cells). An extended validation statement is made for simulations for the entire series. This exercise was successful for leeway angles equal to 훽훽=[3표표,6표표]. The validation level (base mesh, 3M cells) for each force component is:푢푢푋푋′=12%, 푢푢푌푌′=17%, 푢푢푁푁′=10%. The validation for appended geometries was not regarded as successful, with the exception of the Rudder case. The numerical uncertainty is the dominant contribution for the validation level, motivating a proportionate refinement of the grid. Here, it is sufficient to achieve parity with other contributions to the uncertainty within the larger context of the project.
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Hydromechanics of wind-assisted ship propulsion : Modeling of hydrodynamic Sideforce
2016Co-Authors: N.j. Van Der KolkAbstract:This paper deals with the hydrodynamic Sideforce production of a wind-assisted ship. The subject is introduced, both in physical terms, and with an overview of current and recent work. The importance of the hydrodynamic Sideforce is established, before classical models are reviewed. Finally, the complications arising from diverse appendage topologies are discussed, and a theory for zero-aspect ratio lifting surfaces is discussed. The paper concludes with a short summary of ongoing work.
Sonya T Smith - One of the best experts on this subject based on the ideXlab platform.
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Modeling of Wake-vortex Aircraft Encounters
2013Co-Authors: Sonya T SmithAbstract:There are more people passing through the world's airports today than at any other time in history. With this increase in civil transport, airports are becoming capacity limited. In order to increase capacity and thus meet the demands of the flying public, the number of runways and number of flights per runway must be increased. In response to the demand, the National Aeronautics and Space Administration (NASA), in conjunction with the Federal Aviation Administration (FAA), airport operators, and the airline industry are taking steps to increase airport capacity without jeopardizing safety. Increasing the production per runway increases the likelihood that an aircraft will encounter the trailing wake-vortex of another aircraft. The hazard of a wake-vortex encounter is that heavy load aircraft can produce high intensity wake turbulence, through the development of its wing-tip vortices. A smaller aircraft following in the wake of the heavy load aircraft will experience redistribution of its aerodynamic load. This creates a safety hazard for the smaller aircraft. Understanding this load redistribution is of great importance, particularly during landing and take-off. In this research wake-vortex effects on an encountering 10% scale model of the B737-100 aircraft are modeled using both strip theory and vortex-lattice modeling methods. The models are then compared to wind tunnel data that was taken in the 30ft x 60ft wind tunnel at NASA Langley Research Center (LaRC). Comparisons are made to determine if the models will have acceptable accuracy when parts of the geometry are removed, such as the horizontal stabilizer and the vertical tail. A sensitivity analysis was also performed to observe how accurately the models could match the experimental data if there was a 10% error in the circulation strength. It was determined that both models show accurate results when the wing, horizontal stabilizer, and vertical tail were a part of the geometry. When the horizontal stabilizer and vertical tail were removed there were difficulties modeling the Sideforce coefficient and pitching moment. With the removal of only the vertical tail unacceptable errors occurred when modeling the Sideforce coefficient and yawing moment. Lift could not be modeled with either the full geometry or the reduced geometry attempts.
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Model Validation of Wake-Vortex / Aircraft Encounters
Atmospheric Flight Mechanics Conference, 2000Co-Authors: Kimberly R Pete, Sonya T Smith, Dan D VicroyAbstract:Wake-vortex effects on an 10% scale model of the B737-100 aircraft are calculated using both strip theory and vortex-lattice methods. The results are then compared to data taken in the 30ft x 60ft wind tunnel at NASA Langley Research Center (LaRC). The accuracy of the models for a reduced geometry, such with the horizontal stabilizer and the vertical tail removed, is also investigated. Using a 10% error in the circulation strength and comparing the model's results with the experiment illustrates the sensitivity of the models to the vortex circulation strength. It was determined that both strip theory and the vortex lattice method give accurate results when all the geometrical information is used. When the horizontal stabilizer and vertical tail were removed there were difficulties modeling the Sideforce coefficient and pitching moment. With the removal of only the vertical tail unacceptable errors occurred when modeling the Sideforce coefficient and yawing moment. Lift could not be accurately modeled with either the full geometry or the reduced geometry.
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Model Validation of Wake-Vortex/Aircraft Encounters
2000Co-Authors: Kimberly R Pete, Sonya T Smith, Dan D VicroyAbstract:Wake-vortex effects on an 10% scale model of the B737-100 aircraft are calculated using both strip theory and vortex-lattice methods. The results are then compared to data taken in the 30' x 60' wind tunnel at NASA Langley Research Center (LaRC). The accuracy of the models for a reduced geometry, such with the horizontal stabilizer and the vertical tail removed, is also investigated. Using a 10% error in the circulation strength and comparing the model's results with the experiment illustrates the sensitivity of the models to the vortex circulation strength. It was determined that both strip theory and the vortex lattice method give accurate results when all the geometrical information is used. When the horizontal stabilizer and vertical tail were removed there were difficulties modeling the Sideforce coefficient and pitching moment. With the removal of only the vertical tail unacceptable errors occurred when modeling the Sideforce coefficient and yawing moment. Lift could not be accurately modeled with either the full geometry or the reduced geometry.
Huijsmans R.h.m. - One of the best experts on this subject based on the ideXlab platform.
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Dataset: Bilge Keels for Course Stability and Sailing Efficiency of Wind-Assisted Ships
4TU.Centre for Research Data, 2019Co-Authors: Van Der Kolk N. J., Keuning J.a., Huijsmans R.h.m.Abstract:Experimental results for the sailing performance of ships fitted with bilge keel appendages are presented. Sailing performance is synonymous with manoeuvring forces for the steady drift condition, i.e. increase in resistance, lateral force production, and yaw moment for leeway (drift) angle. Systematic variations in appendage height, length, and position are tested, including several special cases. The appendage typology is shown to mitigate the strong ‘destabilizing’ yaw moment that is characteristic for wind assisted commercial vessels and to promote the non-linear Sideforce component. The entire data set, including all derived quantities and details for the uncertainty assessment, is made available to support ongoing research and eventual commercial uptake for wind-assist ship propulsion
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Hydrodynamics of wind-assisted ship propulsion validation of RANS-CFD methodology
Sailing Yard Research Foundation (SYRF), 2017Co-Authors: Van Der Kolk N.j., Keuning J.a., Huijsmans R.h.m.Abstract:A Reynolds-Averaged Navier Stokes computational fluid dynamics (RANS-CFD) package will be one of the primary tools used during the development of a performance prediction program for Wind-Assisted commercial ships. The modelling challenge presented by large separated flow structures in the wake of the sailing ship points to a conscientious validation study. A validation data set, consisting of hydrodynamic forces acting on the ship sailing with a leeway angle, was collected at the Delft University of Technology towing tank facility, for bare-hull and appended cases. Four hull geometries were selected to represent of the Delft Wind-Assist Systematic Series. Appended cases were designed to represent a broad range of appendage topologies: Rudder, Bilge-keels, Skeg, and Barkeel. The direct validation exercise for the bare-hull case was successful, with the validation level for the Sideforce equal to 9.5% (fine mesh: 9M cells). An extended validation statement is made for simulations for the entire series. This exercise was successful for leeway angles equal to 훽훽=[3표표,6표표]. The validation level (base mesh, 3M cells) for each force component is:푢푢푋푋′=12%, 푢푢푌푌′=17%, 푢푢푁푁′=10%. The validation for appended geometries was not regarded as successful, with the exception of the Rudder case. The numerical uncertainty is the dominant contribution for the validation level, motivating a proportionate refinement of the grid. Here, it is sufficient to achieve parity with other contributions to the uncertainty within the larger context of the project.Ship Hydromechanics and Structure
Dan D Vicroy - One of the best experts on this subject based on the ideXlab platform.
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Model Validation of Wake-Vortex / Aircraft Encounters
Atmospheric Flight Mechanics Conference, 2000Co-Authors: Kimberly R Pete, Sonya T Smith, Dan D VicroyAbstract:Wake-vortex effects on an 10% scale model of the B737-100 aircraft are calculated using both strip theory and vortex-lattice methods. The results are then compared to data taken in the 30ft x 60ft wind tunnel at NASA Langley Research Center (LaRC). The accuracy of the models for a reduced geometry, such with the horizontal stabilizer and the vertical tail removed, is also investigated. Using a 10% error in the circulation strength and comparing the model's results with the experiment illustrates the sensitivity of the models to the vortex circulation strength. It was determined that both strip theory and the vortex lattice method give accurate results when all the geometrical information is used. When the horizontal stabilizer and vertical tail were removed there were difficulties modeling the Sideforce coefficient and pitching moment. With the removal of only the vertical tail unacceptable errors occurred when modeling the Sideforce coefficient and yawing moment. Lift could not be accurately modeled with either the full geometry or the reduced geometry.
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Model Validation of Wake-Vortex/Aircraft Encounters
2000Co-Authors: Kimberly R Pete, Sonya T Smith, Dan D VicroyAbstract:Wake-vortex effects on an 10% scale model of the B737-100 aircraft are calculated using both strip theory and vortex-lattice methods. The results are then compared to data taken in the 30' x 60' wind tunnel at NASA Langley Research Center (LaRC). The accuracy of the models for a reduced geometry, such with the horizontal stabilizer and the vertical tail removed, is also investigated. Using a 10% error in the circulation strength and comparing the model's results with the experiment illustrates the sensitivity of the models to the vortex circulation strength. It was determined that both strip theory and the vortex lattice method give accurate results when all the geometrical information is used. When the horizontal stabilizer and vertical tail were removed there were difficulties modeling the Sideforce coefficient and pitching moment. With the removal of only the vertical tail unacceptable errors occurred when modeling the Sideforce coefficient and yawing moment. Lift could not be accurately modeled with either the full geometry or the reduced geometry.