Resistance Prediction on Submerged Axisymmetric Bodies Fitted with Turbulent Spot Inducers

2015 ◽  
Vol 59 (02) ◽  
pp. 85-98
Author(s):  
Young T. Shen ◽  
Michael J. Hughes ◽  
Joseph J. Gorski
Keyword(s):  
Drag Coefficient ◽  
Form Factors ◽  
Model Tests ◽  
Full Scale ◽  
Turbulent Spot ◽  
Friction Drag ◽  
Noticeable Effect ◽  
New Device ◽  
Model Scale ◽  
Marine Industry

A method to predict bare hull ship resistance is presented in this article. Hull resistance is assumed to consist of friction drag and residual drag. The friction drag coefficient is represented by an equivalent flat plate coefficient multiplied by a form factor to incorporate effects of body geometry and boundary layer (BL) characteristics on drag. Theories of form factors including the effect of BL transition locations have been successfully derived. Form factors are shown to have a noticeable effect on body drag at high Reynolds numbers (Re) and a significant effect at model Re. Residual drag coefficient is obtained from model tests with application of scaling formulae to relate model scale residual drag coefficient to full scale drag coefficient. To address the issue of laminar flow on models in residual drag measurements, a new device termed a "turbulent spot inducer" is introduced in model tests. Finally, a new scaling formula to relate model scale residual drag coefficient to full scale residual drag coefficient with the flow on body surface partly laminar and partly turbulent is derived. It is shown that a traditional 1þK scaling method used in the marine industry is a special case of the newly derived residual drag scaling formula.

scholarly journals Model-Scale/Full-Scale Correlation of NRC-OCRE’s Model Resistance, Propulsion and Maneuvering Test Results

2015 ◽  
Author(s):  
Michael Lau
Keyword(s):  
Test Data ◽  
Model Test ◽  
Model Tests ◽  
Full Scale ◽  
Test Results ◽  
Sea Trial ◽  
Model Scale ◽  
Performance Predictions ◽  
Ice Strength ◽  
Scale Data

There are a variety of model ices and test techniques adopted by model test facilities. Most often, the clients would ask: “How well can you predict the full scale performance from your model test results?” Model-scale/full-scale correlation becomes an important litmus test to validate a model test technique and its results. This paper summarizes the model-scale/full-scale correlation performed on model test data generated at the National Research Council - Ocean, Coastal, and River Engineering’s (NRC-OCRE) test facility in St. John’s. This correlation includes ship performance predictions, i.e., resistance, propulsion and maneuvering. Selected works from NRC-OCRE on the USCGC icebreaker Healy, the CCGS icebreaker Terry-Fox, the CCGS R-Class icebreakers Pierre Radisson and Sir John Franklin and the CCGS icebreaker Louis S. St. Laurent were reviewed and summarized. The model tests were conducted at NRC-OCRE’s ice tank with the correct density (CD) EGADS model ice. This correlation is based on the concept that a “correlation friction coefficient” (CFC) can be used to predict full-scale ship icebreaking resistance from model test data. The CFCs have been compared for correlation studies using good-quality full-scale information for the five icebreaker models in the NRC-OCRE’s model test database. The review has shown a good agreement between NRCOCRE’s model test predictions and full-scale measurements. The resistance and power correlation were performed for five sets of full-scale data. Although there is substantial uncertainty on ice thickness and ice strength within the full scale data sets that contributes to data scattering, the data suggest a conservative estimate can be obtained to address reasonably this uncertainty by increasing the model prediction by 15% that envelopes most data points. Limited correlation for maneuvering in ice was performed for the USCGC icebreaker Healy. Selected test conditions from the sea trials were duplicated for the maneuvering tests and turning diameters were measured from the arcs of partial circles made in the ice tank. Performance predictions were then compared to the full-scale data previously collected. Despite some discrepancy in ice strength and power level between the model tests and sea trial, the model data agree well with the sea trial data except for three outliers. Otherwise, the maneuvering data show a good correlation between the model test and sea trial results.

Development of a Scaled-Down Floating Wind Turbine for Offshore Basin Testing

2014 ◽  
Author(s):  
Erik-Jan de Ridder ◽  
William Otto ◽  
Gert-Jan Zondervan ◽  
Fons Huijs ◽  
Guilherme Vaz
Keyword(s):  
Wind Turbine ◽  
Wind Velocity ◽  
Scaling Laws ◽  
Scale Effects ◽  
Model Testing ◽  
Model Tests ◽  
Full Scale ◽  
Pitch Control ◽  
Model Scale ◽  
Floating Wind Turbine

In the last years MARIN has been involved in an increasing number of projects for the offshore wind industry. New techniques in model testing and numerical simulations have been developed in this field. In this paper the development of a scaled-down wind turbine operating on a floating offshore platform, similar to the well-known 5MW NREL wind turbine is discussed. To simulate the response of a floating wind turbine correctly it is important that the environmental loads due to wind, waves and current are in line with full scale. For dynamic similarity on model scale, Froude scaling laws are used successfully in the Offshore industry for the underwater loads. To be consistent with the underwater loads, the winds loads have to be scaled according to Froude as well. Previous model tests described by Robertson et al [1] showed that a geometrically-scaled turbine generated a lower thrust and power coefficient with a Froude-scaled wind velocity due to the strong Reynolds scale effects on the flow. To improve future model testing, a new scaling method for the wind turbine blades was developed originally by University of Maine, and here improved and applied. In this methodology, the objective is to obtain power and thrust coefficients which are similar to the full-scale turbine in Froude-scaled wind. This is obtained by changing the geometry of the blades in order to provide thrust equality between model and full scale, and can therefore be considered as a “performance scaling”. This method was then used to design and construct a new MARIN Stock Wind Turbine (MSWT) based on the NREL 5MW wind turbine blade, including an active blade pitch control to simulate different blade pitch control systems. MARIN’s high-quality wind setup in combination with the new model scale stock wind turbine was used for testing the GustoMSC Tri-Floater semi-submersible as presented in Figure 1, including an ECN active blade pitch control algorithm. From the model tests it was concluded that the measured thrust versus wind velocity characteristics of the new MSWT were in line with the full scale prediction and with CFD (Computational Fluid Dynamics) results.

Effects of Appendages and Small Currents on the Hydrodynamic Heave Damping of TLP Columns

1998 ◽  
Vol 120 (1) ◽  
pp. 37-42 ◽  
Author(s):  
K. P. Thiagarajan ◽  
A. W. Troesch
Keyword(s):  
Drag Coefficient ◽  
Current Velocity ◽  
Scaling Laws ◽  
Damping Ratio ◽  
Current Model ◽  
Model Tests ◽  
Full Scale ◽  
Form Drag ◽  
Small Current ◽  
Uniform Current

A previous paper by the authors reported on the estimation of resonant heave (springing) damping of tension leg platforms (TLPs) and a method of scaling for full-scale prototypes. The present paper is a sequel to this work, and examines the effect of adding an appendage in the form of a disk to TLP columns, and the influence of a small uniform current. Model tests conducted on a cylinder + disk in heave show that the heave damping induced by the disk is linear with the amplitude of oscillation. The disk is found to increase the form drag coefficient twofold, in accordance with published results based on isolated edge theory. The effects of a small uniform current were also examined during the model tests. Results show an increase in heave damping ratio that is linear with the current velocity. In the presence of a disk, the damping induced by the current is doubled as well. Scaling laws are proposed in this paper that enable extrapolation of heave damping due to appendages and small currents to full scale. An example calculation shows that for a full-scale TLP column, the heave damping is increased by about 300 percent due to addition of the disk, and by 87 percent due to a small current. The combination of the disk and the current increases the heave damping of the column by a factor of six.

Benchmark Study on Thruster-Hull Interaction in Current on a Semi-Submersible Crane Vessel

2012 ◽  
Author(s):  
Harald Ottens ◽  
Radboud van Dijk
Keyword(s):  
Test Data ◽  
Model Test ◽  
Numerical Study ◽  
Numerical Data ◽  
Model Tests ◽  
Full Scale ◽  
Model Scale ◽  
Thrust Efficiency ◽  
Force Components ◽  
The Individual

The ability of a DP-vessel to keep its position depends highly on the performance of the DP system. The thrust efficiency of the DP-system depends on the efficiency of the individual thrusters, but also on the interaction of the thruster wake and the hull of the vessel. This thruster-hull interaction becomes even more important when the vessel is a semi-submersible vessel; the thruster wake of the thruster on the upstream pontoon might impinge on the downstream pontoon resulting in high losses in efficiency and reduced DP-capability. Heerema Marine Contractors has two DP-semi-submersible crane vessels; the Thialf and Balder. An assessment of the thrust efficiency of the DP thrusters of these vessels has been made by comparing CFD computations with dedicated model tests. In previous benchmark studies CFD is used to assess the current loads as well as thruster-hull interaction without current on a semi-submersible vessel. The logical next step is to perform a numerical study on a thruster-hull interaction with current. Similar as the previous benchmark studies the numerical data are validated with a series of dedicated model tests. The model test data include the global forces, the forces on each individual pontoon and the forces of each individual thruster, including the nozzle thrust and propeller thrust. The comparison between the CFD and model test data shows that CFD is able to predict the relevant force components within a sufficient accuracy for engineering purposes. At present not much is known about the extrapolation of model scale DP-thrust efficiency to full scale DP-thrust efficiency, neither for model test results, nor for CFD results. Scaling CFD from model scale to full scale is not trivial; it involves a significant change in Reynolds number, a different description of boundary layer and poses challenges to meshing and grid. Therefore, validation is required. A first validation study is performed based on data acquired during a transit of SSCV Thialf in Q4 2011. In preparation, CFD simulations are performed for different thrust combinations. These results are compared to full scale observations and, where possible, improvements to the numerical modeling are assessed. The paper addresses lessons learnt to improve the CFD computations as well as practical aspects and limitations of thrust efficiency modeling, including all interaction effects, using CFD from an engineering perspective.

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 A study on the effect of flat plate friction resistance on speed performance prediction of full scale

2015 ◽  
Vol 7 (1) ◽  
Author(s):  
Dong-Woo Park
Keyword(s):  
Form Factor ◽  
Flat Plate ◽  
Great Influence ◽  
Form Factors ◽  
Model Tests ◽  
Full Scale ◽  
Friction Resistance ◽  
Test Operation ◽  
Speed Performance ◽  
Resistance Curves

ABSTRACTFlat plate friction lines hare been used in the process to estimate speed performance of full-scale ships in model tests. The results of the previous studies showed considerable differences in determining form factors depending on changes in plate friction lines and Reynolds numbers. These differences had a great influence on estimation of speed performance of full-scale ships. This study- was conducted in two parts. In the first part, the scale effect of the form factor depending on change in the Reynolds number was studied based on CFD, in connection with three kinds of friction resistance curves: the ITTC-1957, the curve proposed by Grigson (1993; 1996), and the curve developed by Katsui et al (2005). In the second part, change in the form factor by three kinds offriction resistance curves was investigated based on model tests, and then the brake power and the revolution that were finally determined by expansion processes of full-scale ships. When three kinds of friction resistance curves were applied to each kind of ships, these were investigated: differences between resistance and self-propulsion components induced in the expansion processes of full-scale ships, correlation of effects between these components, and tendency of each kind of ships. Finally, what friction resistance curve was well consistent with results of test operation was examined per each kind of ships.

Guidelines for CFD Simulations of Spar VIM

2013 ◽  
Author(s):  
Charles Lefevre ◽  
Yiannis Constantinides ◽  
Jang Whan Kim ◽  
Mike Henneke ◽  
Robert Gordon ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Test Data ◽  
Model Test ◽  
Model Tests ◽  
Full Scale ◽  
Mooring System ◽  
Time Step ◽  
Cfd Simulations ◽  
Scaled Model ◽  
Sway Motion

Vortex-Induced Motion (VIM), which occurs as a consequence of exposure to strong current such as Loop Current eddies in the Gulf of Mexico, is one of the critical factors in the design of the mooring and riser systems for deepwater offshore structures such as Spars and multi-column Deep Draft Floaters (DDFs). The VIM response can have a significant impact on the fatigue life of mooring and riser components. In particular, Steel Catenary Risers (SCRs) suspended from the floater can be sensitive to VIM-induced fatigue at their mudline touchdown points. Industry currently relies on scaled model testing to determine VIM for design. However, scaled model tests are limited in their ability to represent VIM for the full scale structure since they are generally not able to represent the full scale Reynolds number and also cannot fully represent waves effects, nonlinear mooring system behavior or sheared and unsteady currents. The use of Computational Fluid Dynamics (CFD) to simulate VIM can more realistically represent the full scale Reynolds number, waves effects, mooring system, and ocean currents than scaled physical model tests. This paper describes a set of VIM CFD simulations for a Spar hard tank with appurtenances and their comparison against a high quality scaled model test. The test data showed considerable sensitivity to heading angle relative to the incident flow as well as to reduced velocity. The simulated VIM-induced sway motion was compared against the model test data for different reduced velocities (Vm) and Spar headings. Agreement between CFD and model test VIM-induced sway motion was within 9% over the full range of Vm and headings. Use of the Improved Delayed Detached Eddy Simulation (IDDES, Shur et al 2008) turbulence model gives the best agreement with the model test measurements. Guidelines are provided for meshing and time step/solver setting selection.

Launching of Ships and Floating Structures from Horizontal Berth by Tipping Table

1998 ◽  
Vol 14 (04) ◽  
pp. 265-276
Author(s):  
Ivo Senjanovic
Keyword(s):  
Structural Dynamics ◽  
Review Paper ◽  
Offshore Structures ◽  
Model Tests ◽  
Full Scale ◽  
Strength Analysis ◽  
Test Results ◽  
Floating Structures ◽  
Measurement Results

This review paper covers extensive investigations which were undertaken in order to verify the idea of launching of ships and other floating structures from a horizontal berth by a set of turning pads. This includes structural dynamics during launching, model tests and strength analysis of the structure and the launching system. The most important results, which were used for the design of the launching system, are presented. The preparation of a barge for side launching is described, and the full-scale measurement results are compared with the test results. The advantages of building ships and offshore structures on a horizontal berth are pointed out in the conclusion.

Model tests and full-scale sea trials for drag force and deformation of a marine aquaculture net cage

2021 ◽  
Vol 240 ◽  
pp. 109941
Author(s):  
Shuchuang Dong ◽  
Sang-gyu Park ◽  
Daisuke Kitazawa ◽  
Jinxin Zhou ◽  
Takero Yoshida ◽  
...  
Keyword(s):  
Drag Force ◽  
Model Tests ◽  
Full Scale ◽  
Marine Aquaculture ◽  
Net Cage

A New Method of Modeling Underexpanded Exhaust Plumes for Wind Tunnel Aerodynamic Testing

1989 ◽  
Vol 111 (4) ◽  
pp. 748-754
Author(s):  
V. Salemann ◽  
J. M. Williams
Keyword(s):  
Wind Tunnel ◽  
Free Stream ◽  
Dynamic Pressure ◽  
Pressure Ratio ◽  
Area Ratio ◽  
Full Scale ◽  
New Method ◽  
Thrust Coefficient ◽  
Model Scale ◽  
Exhaust Plumes

A new method for modeling hot underexpanded exhaust plumes with cold model scale plumes in aerodynamic wind tunnel testing has been developed. The method is applicable to aeropropulsion testing where significant interaction between the exhaust and the free stream and aftbody may be present. The technique scales the model and nozzle external geometry, including the nozzle exit area, matches the model jet to free-stream dynamic pressure ratio to full-scale jet to free-stream dynamic pressure ratio, and matches the model thrust coefficient to full-scale thrust coefficient. The technique does not require scaling of the internal nozzle geometry. A generalized method of characteristic computer code was used to predict the plume shapes of a hot (γ = 1.2) half-scale nozzle of area ratio 3.2 and of a cold (γ = 1.4) model scale nozzle of area ratio 1.3, whose pressure ratio and area ratio were selected to satisfy the above criteria and other testing requirements. The plume shapes showed good agreement. Code validity was checked by comparing code results for cold air exhausting into a quiescent atmosphere to pilot surveys and shadowgraphs of model nozzle plumes taken in a static facility.

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