scholarly journals Hydrodynamic Testing of a High Performance Skiff at Model and Full Scale

2019 ◽  
Vol 4 (01) ◽  
pp. 17-44
Author(s):  
A. H. Day ◽  
P. Cameron ◽  
S. Dai
Keyword(s):  
High Performance ◽  
Open Water ◽  
Full Scale ◽  
Hydrodynamic Performance ◽  
Regression Equations ◽  
Water Testing ◽  
Model Scale ◽  
Speed Range ◽  
The Impact ◽  
Good Agreement

Abstract: This study examines the hydrodynamic performance of a high performance skiff hull using three different physical testing techniques which may be used in early stage design for assessment of the upright resistance of sailing vessels. The hull chosen as a benchmark form is a high-speed hard-chine sailing dinghy, typical of modern trends in skiff design, and is broadly similar to some high performance yacht hulls. The 4.55 m hull was tested at full scale in a moderate size towing tank, at 1:2.5 scale in the same tank, and at full-scale by towing on open water. The work presented here builds on the study of Day & Cameron (2017), with the model tests repeated and re-analyzed in the present study and additional results presented. The challenges of full-scale open-water testing are discussed and several potential improvements in practice are identified for future work. Results show that the open water testing broadly matches well with model-scale tank testing, with the mean discrepancy in the measured resistance between the two around 4% over the speed range tested after correction for the presence of the rudder. Agreement is initially less good for the full-scale hull in the tank for higher speeds, both for resistance and trim. ITTC guidelines suggest that blockage may be an issue for the full-scale boat in this size of tank; comparison of the results suggests that blockage, and/or finite depth effects for the full-scale hull in the tank present a substantial problem at the higher speeds. A correction approach for the wave resistance of the full scale results using a calculation based on a linear thin ship theory is effective in this case, and results show that the full scale and model scale tests agree satisfactorily for the majority of the speed range after this correction. In addition to upright resistance in calm water, results are presented for the impact of small waves, the addition of the rudder, and variations in displacement and trim on resistance for a skiff hull. Finally, the results are compared with predictions from the well-known Delft series regression equations, Savitsky's methods, and a thin ship calculation. The thin ship approach gives good agreement for the case in which the hull is trimmed bow-down and the transom is not immersed, while the Savitsky pre-planing approach gives good agreement for the level trim case. The Delft series and Savitsky planing hull approaches do not give good agreement with physical measurements.

scholarly journals Model-Scale/Full-Scale Correlation in Open Water and Ice for Canadian Coast Guard “R-Class” Icebreakers

2001 ◽  
Vol 45 (04) ◽  
pp. 249-261
Author(s):  
Don Spencer ◽  
Stephen J. Jones
Keyword(s):  
Friction Coefficient ◽  
Structural Damage ◽  
National Research Council ◽  
Open Water ◽  
Model Tests ◽  
Full Scale ◽  
Coast Guard ◽  
Model Scale ◽  
Ice Friction ◽  
Good Agreement

CCGS Pierre Radisson, one of the R-Class icebreakers Model-scale data from the National Research Council of Canada, Institute for Marine Dynamics' water and ice towing tanks for the Canadian Coast Guard's R-Class icebreaker are compared with previous model tests and, more importantly, with three sets of full-scale ice trials data collected in 1978, 1979 and 1991. In open water, good agreement between model-and full-scale was found for bollard tests, and for self-propulsion tests provided a roughness allowance of 0.0008 was used. In ice, good correlation was found with the 1978 tests when the ship was new and there was little snow cover, using a model hull/ice friction coefficient of 0.05. Good agreement with the later tests, 1979 and 1991, was also obtained with somewhat higher model/ice friction coefficients of 0.055 and 0.065. This is attributed to a deteriorating, and hence rougher, full-scale ship hull surface. The model tests showed that a change in friction coefficient from 0.03 to 0.09 causes a doubling of the delivered power. For the full-scale ship, it is suggested that relatively inexpensive localized hull maintenance in the shoulder area, where ice jamming occurs and hence hull/ice friction is important, could improve performance and reduce the chance of structural damage.

scholarly journals CFD analysis of hover performance of rotors at full- and model-scale conditions

2016 ◽  
Vol 120 (1231) ◽  
pp. 1386-1424 ◽  
Author(s):  
G.N. Barakos ◽  
A. Jimenez Garcia
Keyword(s):  
Full Scale ◽  
Rotor Blades ◽  
Loosely Coupled ◽  
Model Scale ◽  
Acoustic Study ◽  
Hover Performance ◽  
Computational Structural Dynamics ◽  
Computational Fluid Dynamics Cfd ◽  
Cfd Method ◽  
Good Agreement

ABSTRACTAnalysis of the performance of a 1/4.71 model-scale and full-scale Sikorsky S-76 main rotor in hover is presented using the multi-block computational fluid dynamics (CFD) solver of Glasgow University. For the model-scale blade, three different tip shapes were compared for a range of collective pitch and tip Mach numbers. It was found that the anhedral tip provided the highest Figure of Merit. Rigid and elastic full-scale S-76 rotor blades were investigated using a loosely coupled CFD/Computational Structural Dynamics (CSD) method. Results showed that aeroelastic effects were more significant for high thrust cases. Finally, an acoustic study was performed in the tip-path-plane of both rotors, showing good agreement in the thickness and loading noise with the theory. For the anhedral tip of the model-scale blade, a reduction of 5% of the noise level was predicted. The overall good agreement with the theory and experimental data demonstrated the capability of the present CFD method to predict rotor flows accurately.

A study on the influence of hull wake on model scale cavitation and noise tests for a fast twin screw vessel with inclined shaft

2017 ◽  
Vol 232 (3) ◽  
pp. 307-330
Author(s):  
Giorgio Tani ◽  
Michele Viviani ◽  
Diego Villa ◽  
Marco Ferrando
Keyword(s):  
Scale Effects ◽  
Full Scale ◽  
Ship Wake ◽  
Radiated Noise ◽  
Wake Field ◽  
Model Scale ◽  
Propeller Noise ◽  
Twin Screw ◽  
Long Time ◽  
The Impact

The study of ship underwater radiated noise is nowadays a topic of great and largely recognized importance. This is due to the fact that in the last decades, the problem of the impact of anthropogenic noise on marine life has been addressed with higher emphasis, giving rise to different efforts aimed to the analysis of its effects on different organisms and, in parallel, to means for the reduction of shipping noise. In this context, attention is focused on the propeller noise, which, in cavitating conditions, may represent the most important noise source of the ship. The propeller noise has been studied for long time with different approaches. One of the most effective approaches is represented by model scale testing in cavitation tunnels or similar facilities. Despite having been adopted for several years, radiated noise experiments in model scale are usually affected by significant scale effects and technical issues. One of these aspects is represented by the correct modelling of the propeller inflow; different techniques are adopted, depending on the facility, in order to reproduce a certain target wake. One of the main problems is to define this target wake, which should in principle coincide with the ship wake; as it is well known, it is usually derived from model scale towing tank measurements, with the necessity for the prediction of the full-scale wake field. Starting from the outcomes of a previous work on the influence of different approaches for the prediction of the full-scale wake field for a single screw ship, in this work, attention is focused on the case of a fast twin screw vessel, analysing the different issues which may be connected to this hull form.

A Simple Dynamic Model For Simulating Draft-Gear Behavior In Rail-Car Impacts

1978 ◽  
Vol 100 (4) ◽  
pp. 492-496 ◽  
Author(s):  
T.-K. Hsu ◽  
D. A. Peters
Keyword(s):  
Dynamic Model ◽  
Static Friction ◽  
Full Scale ◽  
Stick Slip ◽  
Drop Hammer ◽  
Draft Gear ◽  
The Individual ◽  
The Impact ◽  
Good Agreement

A new, simple dynamic model is developed for use in simulating draft-gear behavior in rail-car impacts. The model is based on an analysis of the individual components inside several types of draft gears. The transition from kinetic to static friction during the impact is included. Comparisons with drop-hammer tests and full-scale impacts show good agreement with the experimental forces and deflections. In particular two very important phenomena are correctly simulated: 1) the rise in force just before maximum travel, and 2) the stick-slip-grab phenomenon during impact.

Four Quadrants Numerical Prediction for Hydrodynamic Performance of Open-Water Propeller

2010 ◽  
Vol 143-144 ◽  
pp. 1143-1147
Author(s):  
Bing Xiao ◽  
Xiao Wang ◽  
Ai Guo Shi ◽  
Ming Wu
Keyword(s):  
Three Dimensional ◽  
Open Water ◽  
Mathematic Model ◽  
Hydrodynamic Performance ◽  
Computational Domain ◽  
Basic Parameters ◽  
Tank Test ◽  
Open Water Performance ◽  
Thrust And Torque ◽  
Good Agreement

In order to obtain the four quadrants hydrodynamic performance of open water propeller by means of CFD, a mathematic model of three dimensional coordinates points was established and programmed using Matlab based on the basic parameters of propeller. A smooth model propeller was made by importing these points into front end software. Then taking AU model for example, numerical simulations of propeller turning ahead while going ahead, turning ahead while going astern, turning astern while going ahead and turning astern while going astern were carried out. At the same time, the thrust and torque coefficients were presented. The simulation results showed good agreement with the results of tank test. The influence of mesh generation and computational domain on open-water performance were also discussed.

Determining Side-by-Side Current Loads Using CFD and Model Tests

2016 ◽  
Author(s):  
Arjen Koop
Keyword(s):  
Reynolds Number ◽  
Model Test ◽  
Full Scale ◽  
Test Results ◽  
Model Scale ◽  
Moment Coefficient ◽  
The Difference ◽  
The Moment ◽  
Good Agreement ◽  
Shielding Effects

When two vessels are positioned close to each other in a current, significant shielding or interaction effects can be observed. In this paper the current loads are determined for a LNG carrier alone, a Shuttle tanker alone and both vessels in side-by-side configuration. The current loads are determined by means of tow tests in a water basin at scale 1:60 and by CFD calculations at model-scale and full-scale Reynolds number. The objective of the measurements was to obtain reference data including shielding effects. CFD calculations at model-scale Reynolds number are carried out and compared with the model test results to determine the capability of CFD to predict the side-by-side current load coefficients. Furthermore, CFD calculations at full-scale Reynolds number are performed to determine the scale effects on current loads. We estimate that the experimental uncertainty ranges between 3% and 5% for the force coefficients CY and CMZ and between 3% and 10% for CX. Based on a grid sensitivity study the numerical sensitivity is estimated to be below 5%. Considering the uncertainties mentioned above, we assume that a good agreement between experiments and CFD calculations is obtained when the difference is within 10%. The best agreement between the model test results and the CFD results for model-scale Reynolds number is obtained for the CY coefficient with differences around 5%. For the CX coefficient the difference can be larger as this coefficient is mainly dominated by the friction component. In the model tests this force is small and therefore difficult to measure. In the CFD calculations the turbulence model used may not be suitable to capture transition from laminar to turbulent flow. A good agreement (around 5% difference) is obtained for the moment coefficient for headings without shielding effects. With shielding effects larger differences can be obtained as for these headings a slight deviation in the wake behind the upstream vessel may result in a large difference for the moment coefficient. Comparing the CFD results at full-scale Reynolds number with the CFD results at model-scale Reynolds number significant differences are found for friction dominated forces. For the CX coefficient a reduction up to 50% can be observed at full-scale Reynolds number. The differences for pressure dominated forces are smaller. For the CY coefficient 5–10% lower values are obtained at full-scale Reynolds number. The moment coefficient CMZ is also dominated by the pressure force, but up to 30% lower values are found at full-scale Reynolds number. The shielding effects appear to be slightly smaller at full-scale Reynolds number as the wake from the upstream vessel is slightly smaller in size resulting in larger forces on the downstream vessel.

scholarly journals An experimental study of interceptor’s effectiveness on hydrodynamic performance of high-speed planing crafts

2013 ◽  
Vol 20 (2) ◽  
pp. 21-29 ◽  
Author(s):  
Mohammad Hosein Karimi ◽  
Mohammad Saeed Seif ◽  
Madjid Abbaspoor
Keyword(s):  
Drag Reduction ◽  
High Speed ◽  
Hydrodynamic Performance ◽  
Control Mechanisms ◽  
Towing Tank ◽  
University Of Technology ◽  
Speed Range ◽  
Calm Water ◽  
Wide Speed Range ◽  
The Impact

Abstract Trim control mechanisms such as interceptors and trim flaps have been widely used in recent years in highspeed crafts for ride and trim control. In spite of their extensive application, a few studies investigating the impact of interceptors on planing craft performance, have been published. In the present study, the impact of interceptors on planing crafts hydrodynamic quality is investigated through application of an experimental method. Two scaled-down models of high-speed planing mono-hull and catamaran are tested with and without interceptors in calm water at different heights of the interceptors to investigate the effect of interceptors on drag reduction of the models. The first one is a scaled-down model of 11 m planing mono-hull boat and the test was conducted at the towing tank of Sharif University of Technology, Iran. The second one is a scaled-down model of 18 m planing catamaran boat and the test was conducted at the towing tank of Krylov Shipbuilding Research Institute (KSRI), Russia. The experimental results show a remarkable drag reduction of up to 15% for mono-hull model and up to 12% for catamaran model over the wide speed range of the models.

Effects of Aspect Ratio on the Hydrodynamic Performance of Circular Cambered Otter Board

2018 ◽  
Author(s):  
Liuyi Huang ◽  
Yuyan Li ◽  
Jiqiang Xu ◽  
Qingchang Xu ◽  
Fenfang Zhao ◽  
...  
Keyword(s):  
Lift Coefficient ◽  
Flow Distribution ◽  
Full Scale ◽  
Hydrodynamic Performance ◽  
High Lift ◽  
Aspect Ratios ◽  
Simulation Results ◽  
Drag Ratio ◽  
Lift To Drag Ratio ◽  
Good Agreement

An otter board is an important device that provides a desired horizontal opening of a trawl net. A high lift coefficient or lift-to-drag ratio is required for an otter board to maintain fishing efficiency. In the present work, the hydrodynamic performance of a circular cambered otter board was studied by numerical simulation, including the effects of aspect ratios (AR), and flow distribution around the otter board. Model tests were conducted in the flume tank as well as a comparison to the numerical results. It showed that simulation results exhibited very good agreement with experiment results. Results demonstrated that the model otter board had a critical angle of attack (AOA) of 50° (when the stall appeared). The maximum lift coefficient and lift-to-drag ratio of the model otter board were 2.421 and 3.719, respectively. However, the maximum values of the full-scale otter board increased first and then decreased with an increasing AR. And the full-scale otter board had a better performance when AR = 2.489, it can enhance the lift coefficient by 17.4% compared with the initial otter board (AR = 1.25). In addition, the flow distribution around the otter board showed that the flow was smooth at small AOAs, when it attacked at large AOA (exceeded 55°), flow separation and eddies were appeared at the lee-side of the otter board.

scholarly journals Numerical Analysis of Full-Scale Ship Self-Propulsion Performance with Direct Comparison to Statistical Sea Trail Results

2020 ◽  
Vol 8 (1) ◽  
pp. 24 ◽  
Author(s):  
Wenyu Sun ◽  
Qiong Hu ◽  
Shiliang Hu ◽  
Jia Su ◽  
Jie Xu ◽  
...  
Keyword(s):  
Free Surface ◽  
Numerical Simulations ◽  
Scale Effect ◽  
Full Scale ◽  
Hydrodynamic Performance ◽  
Local Flow ◽  
Model Scale ◽  
Propulsion Performance ◽  
The Difference ◽  
Thrust And Torque

Accurate prediction of the self-propulsion performance is one of the most important factors for the energy-efficient design of a ship. In general, the hydrodynamic performance of a full-scale ship could be achieved by model-scale simulation or towing tank tests with extrapolations. With the development of CFD methods and computing power, directly predict ship performance with full-scale CFD is an important approach. In this article, a numerical study on the full-scale self-propulsion performance with propeller operating behind ship at model- and full-scale is presented. The study includes numerical simulations using the RANS method with a double-model and VOF (Volume-of-Fluid) model respectively and scale effect analysis based on overall performance, local flow fields and detailed vortex identification. The verification study on grid convergence is also performed for full-scale simulation with global and local mesh refinements. A series of sea trail tests were performed to collect reliable data for the validation of CFD predictions. The analysis of scale effect on hull-propeller interaction shows that the difference of hull boundary layer and flow separation is the main source of scale effect on ship wake. The results of the fluctuations of propeller thrust and torque along with circulation distribution and local flow field show that the propeller’s loading is significantly higher for model-scale ship. It is suggested that the difference of vortex evolution and interaction is more pronounced and has larger effects on the ship’s powering performance at model-scale than full-scale according to the simulation results. From the study on self-propulsion prediction, it could be concluded that the simplification on free surface treatment does not only affect the wave-making resistance for bare hull but also the propeller performance and propeller induced ship resistance which can be produced up to 5% uncertainty to the power prediction. Roughness is another important factor in full-scale simulation because it has up to an approximately 7% effect on the delivery power. As a result of the validation study, the numerical simulations of full-scale ship self-propulsion shows good agreement with the sea trail data especially for cases that have considered both roughness and free surface effects. This result will largely enhance our confidence to apply full-scale simulation in the prediction of ship’s self-propulsion performance in the future ship designs.

scholarly journals Hydrodynamic Performance Evaluation of an Ice Class Podded Propeller Under Ice Interaction

2008 ◽  
Author(s):  
Pengfei Liu ◽  
Ayhan Akinturk ◽  
Moqin He ◽  
Mohammed Fakhrul Islam ◽  
Brian Veitch
Keyword(s):  
Leading Edge ◽  
Open Water ◽  
Hydrodynamic Performance ◽  
Test Program ◽  
Large Size ◽  
Water Conditions ◽  
Tank Test ◽  
Propeller Blades ◽  
The Impact ◽  
Method Model

Fluid-structure interaction between an ice sheet on the water surface and a podded R-Class propeller was examined and analyzed in terms of numerical simulation using a newly enhanced unsteady time-domain, multiple body panel method model. The numerical model was validated and verified and also checked against various previous in-house experimental measurements. The simulation was performed in a real unsteady case, that is, the ice piece stands still and the podded propeller moves and approaches the ice piece until collision occurs. Experimental data were taken from a previous cavitation tunnel test program for a bare R-Class ice breaker propeller under open water conditions, for the R-Class propeller approaching a blade-leading-edge contoured large size ice block under the proximity condition, and from an ice tank test program for a tractor type podded/strutted R-Class propeller under open water conditions. Comparison between experimental and numerical results was made. A general agreement was obtained. The magnitude of force fluctuations during the interaction increased significantly at the instant immediately before the impact between the propeller blades and the ice piece.

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