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

2019 ◽  
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 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 test 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 RANS method with double-model and VOF model respectively and scale effect analysis based on overall performance, local flow fields and detailed vortex identification. Verification study on grid convergence is also performed for full-scale simulation with global and local mesh refinements. And 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 on hull boundary layer and flow separation is the main source of scale effect on ship wake. And the results of the fluctuations of propeller thrust and torque along with circulation distribution and local flow field show that propeller’s loading is significantly higher for model-scale ship. It is suggested that the difference on vortex evolution and interaction is more pronounced and have larger effects on 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 produced up to 5% uncertainty to the power prediction. Roughness is another important factor in full-scale simulation because it has up to approximately 7% effect on the delivery power. As a result of 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 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.

Benchmark Case Study of Scale Effect in Self-Propelled Container Ship Squat

2020 ◽  
Author(s):  
Zhen Kok ◽  
Jonathan Duffy ◽  
Shuhong Chai ◽  
Yuting Jin
Keyword(s):  
Scale Effect ◽  
Body Force ◽  
Full Scale ◽  
The Body ◽  
Water Model ◽  
Container Ship ◽  
Confined Water ◽  
Cfd Model ◽  
Empirical Prediction ◽  
Model Scale

Abstract A URANS CFD-based study has been undertaken to investigate scale effect in container ship squat. Initially, CFD studies were carried out for the model scale benchmarking squat cases of a self-propelled DTC container ship. In this study, a quasi-static modelling approach was adopted where the hull was fixed from sinking and trimming which is computationally more efficient than dynamic mesh methods that models actual motion directly. Instead, the quasi-static approach allows estimation of the squat base on the recorded hydrodynamic forces and moments. Propulsion of the vessel was modelled by the body-force actuator disc method. Upon successful verification and validation of the model scale self-propelled CFD model against benchmark data, full scale investigations were then undertaken. Validation of the full scale set-up was demonstrated by computing the full scale bare hull resistance in deep, laterally unrestricted water and comparing against the extrapolated resistance of model scale benchmark resistance data. Upon validating the setup, it was used to predict full scale ship squat in confined waters. The credibility of the full scale confined water model was checked by comparing vessel resistance in confined water against the Landweber empirical prediction. To quantify scale effect in ship squat predicitons, the benchmarking squat cases were computed by adopting the validated full scale CFD model with body-force propulsion. Comparison between the full scale CFD, model scale CFD and model scale benchmark EFD squat results demonstrates that scale effect is negligible.

scholarly journals Cavitation on Model- and Full-Scale Marine Propellers: Steady And Transient Viscous Flow Simulations At Different Reynolds Numbers

2020 ◽  
Vol 8 (2) ◽  
pp. 141 ◽  
Author(s):  
Ville Viitanen ◽  
Timo Siikonen ◽  
Antonio Sánchez-Caja
Keyword(s):  
Reynolds Number ◽  
Numerical Simulations ◽  
Full Scale ◽  
Tip Vortex ◽  
Wake Flow ◽  
Time Step ◽  
Two Phase ◽  
Marine Propellers ◽  
Model Scale ◽  
Propeller Performance

In this paper, we conducted numerical simulations to investigate single and two-phase flows around marine propellers in open-water conditions at different Reynolds number regimes. The simulations were carried out using a homogeneous compressible two-phase flow model with RANS and hybrid RANS/LES turbulence modeling approaches. Transition was accounted for in the model-scale simulations by employing an LCTM transition model. In model scale, also an anisotropic RANS model was utilized. We investigated two types of marine propellers: a conventional and a tip-loaded one. We compared the results of the simulations to experimental results in terms of global propeller performance and cavitation observations. The propeller cavitation, near-blade flow phenomena, and propeller wake flow characteristics were investigated in model- and full-scale conditions. A grid and time step sensitivity studies were carried out with respect to the propeller performance and cavitation characteristics. The model-scale propeller performance and the cavitation patterns were captured well with the numerical simulations, with little difference between the utilized turbulence models. The global propeller performance and the cavitation patterns were similar between the model- and full-scale simulations. A tendency of increased cavitation extent was observed as the Reynolds number increases. At the same time, greater dissipation of the cavitating tip vortex was noted in the full-scale conditions.

scholarly journals THE RESISTANCE ASPECT OF FISHING BOAT SKIPJACK POLE AND LINE

2021 ◽  
Vol 4 ◽  
pp. 1-7
Author(s):  
Wolter R Hetharia ◽  
Eliza R De Fretes ◽  
Reico H Siahainenia
Keyword(s):  
Model Test ◽  
Ship Design ◽  
Full Scale ◽  
Suitable Method ◽  
Design Phase ◽  
Towing Tank ◽  
Model Scale ◽  
Fishing Boat ◽  
Fishing Vessels ◽  
The Difference

The operation of fishing vessels skipjack pole and line contributes in catching tuna and skipjack fishes particularly in Indonesian waters. A previous study conducted by the authors found that there was no suitable method provided for the resistance computation atearly ship design phase. Besides, there was aninitial trim existed on the vessel during the operation which contributes for the resistance. The purpose of the study is to find the difference of resistance between the model test and the existing methods. The study was executed also to find the effect of initial trim of the vessel. The study began with collecting the database of a parent ship then to develop and transform into a model-scale for testing purpose in the towing tank. The results of model test were converted to the full-scale vessel. The resistance of full-scale vessel was computed based on the Holtrop and Guldhammer methods. The result of full-of resistance obtained from the model test and the methods were collected, evaluated and compared. The results showed the difference of the resistance for all methods. The result of model test is greater 21 % than that of Holtrop method at the service speed of 10 knots. Meanwhile, the result of model test is lower 14 % than that of Gulhammer method at the same speed. In addition, at the speed of 10 knots the initial trim of 0.5O increase 5 % ofthe resistance, the initial trim of 1O increase 10 % of resistance and the initial trim of 2O increase 16 % of resistance compared to the vesselwithout initial trim. In conclusion, the existing resistance methods are not suitable to be applied for skipjack pole and line fishing vessels. In addition, the initial trim contributes to increase the resistance and should be avoided during the vessel operation.

Five Years of Numerical Naval Ship Hydrodynamics at DTNSRDC

1981 ◽  
Vol 25 (04) ◽  
pp. 219-235
Author(s):  
Nils Salvesen
Keyword(s):  
Free Surface ◽  
Numerical Methods ◽  
Initial Period ◽  
Three Dimensional ◽  
Hydrodynamic Performance ◽  
Ship Motions ◽  
Surface Boundary ◽  
Local Flow ◽  
Ship Hydrodynamics ◽  
Naval Ship

In 1974 the Numerical Naval Ship Hydrodynamics Program was established at the David W. Taylor Naval Ship Research and Development Center. The objective of the program is to develop new numerical methods which can be used to evaluate those hydrodynamic performance characteristics which cannot be satisfactorily predicted by traditional methods. In this paper, the accomplishments during the first five-year period (1974–1979) are discussed. During this initial period, the effort was devoted entirely to naval ship free-surface problems. Several successful methods have been developed for solving fully three-dimensional ship-motions, ship-wave-resistance and local-flow problems using linearized free-surface boundary conditions. Numerical methods have also been developed for unsteady and steady two-dimensional problems where the exact free-surface conditions are satisfied. These new numerical methods are more accurate than the conventional computational methods and they can be used to analyze several naval free-surface problems which previously could only be investigated experimentally. It is concluded that the Numerical Naval Ship Hydrodynamics Program should include consideration of all areas in naval ship hydrodynamics where it is believed that the application of advanced numerical techniques and computers can result in better solution techniques.

Scale and Roughness Effects in Ship Performance from the Designer’s Viewpoint

1995 ◽  
Vol 32 (02) ◽  
pp. 126-131
Author(s):  
Victor Mishkevich
Keyword(s):  
Boundary Layer ◽  
Scale Effect ◽  
Large Scale ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
Full Scale ◽  
Viscous Effects ◽  
Lifting Force ◽  
Lift Forces ◽  
The Difference

Evaluation of the scale effect in the absence of flow separation is usually based on two independent calculation procedures for the drag and lifting forces. Prediction of the full-scale drag forces is based on modeling of the viscous part of the resistance in accordance with the difference in Reynolds numbers. As a rule, a lifting force coefficient for full-scale bodies is treated as a lift coefficient for a model having the same Froude number. The proposed method is based on the idea that an initiation of the lifting force is associated with the viscous effects in the boundary layer. According to this approach, an estimation of the scale effect is based on a calculation of potential, boundary layer and wake flows with viscous/nonviscous interaction for given Froude and Reynolds numbers. The roughness of a surface is taken into account due to the use of special velocity profile parameters. These parameters depend on type and height roughness (casting, milling grooves, polishing, paint, fouling, acid deposit, etc.). As a result, the effects of viscosity (Reynolds number) and surface roughness are determined as the difference between the drag and lift forces calculated for the model and full-scale conditions. The magnitude of the scale effect may reach 50% to 70% for the drag and 10% to 20% for the lift forces. The unusually large scale effect for the lift may play a significant role in engineering applications. Results of the systematic calculations and experimental evaluations are reported for a broad range of ship types and propellers.

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.

Analysis of U-Type Anti-Roll Tank Using URANS: Sensitivity and Validation

2014 ◽  
Author(s):  
Maarten Kerkvliet ◽  
Guilherme Vaz ◽  
Nicolas Carette ◽  
Michiel Gunsing
Keyword(s):  
Free Surface ◽  
Full Scale ◽  
Grid Resolution ◽  
Experimental Results ◽  
Green Water ◽  
Roll Motion ◽  
Time Step ◽  
Roll Damping ◽  
Maximum Acceleration ◽  
Model Scale

The roll motion of ships operating in a seaway is often limiting operations. These limits could be due to, e.g. maximum acceleration, green water, capsize risk or just comfort. Therefore additional roll damping is desired to prevent uncontrolled roll motion. Different means are available to decrease the roll motion of a ship, amongst other these include bilge keels, active fin stabilizers (either for forward or zero speed) and U-shape or free surface anti-roll tanks (ART). The amplitude and phase of the roll opposing moment resulting from the water that moves inside the ART are a function of the geometry of the tank and especially its internal damping. Due to the complex and non-linear nature of this flow, the use of Computational Fluid Dynamics (CFD) was chosen to analyse the details of the flow inside the tank and its anti-roll performance. The present paper focuses on the sensitivity and validation of the anti-roll performances of passive U-type ART using CFD. For this, the incompressible Unsteady Reynolds Averaged Navier-Stokes (URANS) code ReFRESCO was used. The sensitivity on the results for the U-tank is analysed by varying the grid resolution and the numerical time step. The two-dimensional (2D) full-scale and Froude based model-scale ReFRESCO results are compared to 2D and 3D full-scale CFD results of Delaunay (2012) [1] and Thanyamanta and Molyneux (2012) [2] and validated with model-scale experimental results of Field and Martin (1975) [3] and MARIN experimental results by Gunsing et al. (2014) [4]. This paper shows the influence of the convective scheme for capturing the free-surface interface and provides recommendations for a time step and grid resolution to effectively calculate the roll damping of an ART.

Hydrodynamic Performance and Cavitation of an Open Propeller in a Simulated Ice-Blocked Flow

1994 ◽  
Vol 116 (3) ◽  
pp. 185-189 ◽  
Author(s):  
D. Walker ◽  
N. Bose ◽  
H. Yamaguchi
Keyword(s):  
Uniform Flow ◽  
Full Scale ◽  
Hydrodynamic Performance ◽  
Mean Values ◽  
Cavitation Tunnel ◽  
Propeller Performance ◽  
Thrust And Torque

Experiments were done on a 200-mm-dia open propeller behind a simulated ice blockage in a cavitation tunnel. The propeller performance in uniform flow and blocked flow is contrasted over a range of advance coefficients and at different cavitation numbers. Mean thrust and torque coefficients are presented. The types of cavitation, and its intermittent nature over a cycle of operation, are reported. The experiments indicate the likelihood of cavitation at full scale for blocked conditions and illustrate the effects of cavitation on mean values of thrust and torque.

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.

Sign in / Sign up

Export Citation Format

Share Document