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.

Correlation Allowances in Model Tests Results: A Delicate Balance Between Performance, Accuracy and Commercial Interests?

2016 ◽  
Author(s):  
Gerco Hagesteijn ◽  
Patrick Hooijmans ◽  
Karola van der Meij
Keyword(s):  
Model Test ◽  
Performance Prediction ◽  
Model Tests ◽  
Full Scale ◽  
Test Results ◽  
Power Performance ◽  
Low Light ◽  
Sea Trial ◽  
Performance Accuracy ◽  
Full Scale Tests

Model tests at ballast and design draught are used to convert the sea trial results from the ballast trial draught to the contractual design draught. Correlation allowances in model test results and their effect on the trial performance prediction are of major importance. Nowadays it is not only typical to verify the contract speed but also the EEDI certification requires a verification of the speed power performance of the vessel. The use of a to favorable CA-value may lead to attractive performance figures, but also leads to higher fuel consumption figures than expected. Furthermore the design point of the propeller is affected, which leads to a too low light running margin and in some cases to erosive cavitation. During a study, large spreading in the values of the correlation allowances for design draughts have been found for merchant vessels tested at different model test institutes, but at ballast trial draught the spreading is much less. Can it happen that some institutes select favorable correlations allowances on the basis of inaccurate trial data of shipyards? Or should we accept a large spreading in correlation allowances and have these indeed been confirmed by sea trials at design draught? This paper will present a discussion using the experience of a large full scale trial database as well as the accuracy of model and full scale tests.

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.

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.

Infrared Signature Suppression for Marine Gas Turbines: Comparison of Sea Trial and Model Test Results for the DRES Ball IRSS System

1994 ◽  
Vol 116 (1) ◽  
pp. 75-81 ◽  
Author(s):  
A. M. Birk ◽  
D. VanDam
Keyword(s):  
Model Test ◽  
Gas Turbines ◽  
Flow Model ◽  
Full Scale ◽  
Scale Model ◽  
Test Results ◽  
Sea Trial ◽  
Infrared Signature ◽  
Plume Temperature ◽  
Better Than

Sea Trials have recently been underway for Canada’s new City Class Patrol Frigate (CPF). These trials provided the first opportunity to measure the performance of the new DRES Ball Infrared Signature Suppression (IRSS) system installed on a ship. Prior to these trials 1/4-scale hot flow model test and computer simulation performance results were available. The CPF DRES Ball IRSS systems are installed on the exhaust uptakes of the GE LM2500 main gas turbines. The DRES Ball provides both metal surface cooling for all view angles and plume cooling. The DRES Ball significantly reduces the IR signature of the LM2500 exhaust. This paper presents a comparison between the 1/4-scale hot flow model test results with the full-scale sea trial results. Performance variables included in the comparison are: metal surface temperatures, back pressure, plume temperature distribution, and surface static pressures. Because of the confidential nature of the DRES Ball system performance, all classified data have been nondimensionalized so that only relative comparisons can be made between the full-scale and 1/4-scale data. The results show that the full-scale system performs better than the 1/4-scale model because of Reynolds number effects. The plume temperature, surface temperatures, and back pressure were all lower (better) than in the 1/4-scale model tests. One of the original concerns with the installation was that relative wind would degrade the performance of the DRES Ball onboard a ship. The wind effect was found to be benign during the trials.

Full Scale CFD Validation on Thruster-Hull Interaction on a Semi-Submersible Crane Vessel in Transit Condition

2013 ◽  
Author(s):  
Harald Ottens ◽  
Norbert Bulten ◽  
Radboud van Dijk
Keyword(s):  
Test Data ◽  
Model Test ◽  
Life Time ◽  
Full Scale ◽  
Cfd Simulations ◽  
Cfd Validation ◽  
Lessons Learnt ◽  
Thrust Efficiency ◽  
In Transit ◽  
Scale Data

Heerema Marine Contractors operates three semi-submersible crane vessels; the Thialf, Balder and Hermod. The first two vessels are equipped with a DP system. The ability of each crane vessel to keep its position depends highly on the performance of the DP system of that crane vessel. The thrust efficiency of the DP system depends on the efficiency of the individual thruster, but also on the interaction of the thruster wake and the hull of the vessel. Thruster-hull interaction is important during operations, but also during transits from one location to another. During the transits of the Balder and Thialf, the DP thrusters are used as propulsion. Understanding the thruster-hull interaction effects in this transit condition can result in an optimum thrust setting. In previous validation studies CFD was used to assess the current loads and the thruster-hull interaction on a semi-submersible vessel. In these studies the CFD results were validated with a series of dedicated model tests. 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. However, Heerema Marine Contractors is mainly interested in full scale data. Unfortunately, not much full scale data is available to validate the extrapolation of model test and CFD results to full scale thruster efficiency. Therefore a first validation study is performed based on acquired full scale data during a transit of the Thialf in Q4 2011. Comparing the full scale test data with the CFD results shows that the CFD can be used to predict which settings is the most efficient. Optimization of thruster settings on semi-submersible vessels is not trivial due to number and location of the azimuth thrusters. Using CFD simulations the power settings and azimuth angles of the thrusters were changed to obtain the optimal thrust setting during transit. In Q2 2012 the Thialf made her first transit after a dry-dock period in which the hull was cleaned and painted. Repeating similar tests conditions as in Q4 2011 demonstrates the effect of a clean hull. Additional tests demonstrated the effect of a more efficient thrust setting originated by the CFD results. The implications of the optimized azimuth setting in transit on the life time of the thruster is verified using CFD and FEM. The paper addresses lessons learnt to improve the CFD simulations as well as practical aspects and limitations of thrust efficiency modeling using CFD. It demonstrates that CFD can be used to understand the associated flow physics and that CFD can be used to predict improvements in thrust efficiencies. In addition, some lessons learnt on full scale monitoring will be addressed.

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.

Infra-Red Signature Suppression for Marine Gas Turbines: Comparison of Sea Trial and Model Test Results for the DRES Ball IRSS System

1992 ◽  
Author(s):  
A. M. Birk ◽  
D. Vandam
Keyword(s):  
Model Test ◽  
Gas Turbines ◽  
Flow Model ◽  
Full Scale ◽  
Scale Model ◽  
Test Results ◽  
Sea Trial ◽  
Infra Red ◽  
Plume Temperature ◽  
Better Than

Sea Trials have recently been underway for Canada’s new City Class Patrol Frigate (CPF). These trials provided the first opportunity to measure the performance of the new DRES Ball Infra-red Signature Suppression (IRSS) system installed on a ship. Prior to these trials 1/4 scale hot flow model test and computer simulation performance results were available. The CPF DRES Ball IRSS systems are installed on the exhaust uptakes of the GE LM2500 main gas turbines. The DRES Ball provides both metal surface cooling for all view angles and plume cooling. The DRES Ball significantly reduces the IR signature of the LM2500 exhaust. This paper presents a comparison between the 1/4 scale hot flow model test results with the full scale sea trial results. Performance variables included in the comparison are; metal surface temperatures, back pressure, plume temperature distribution, and surface static pressures. Because of the confidential nature of the DRES Ball system performance, all classified data has been nondimensionalized so that only relative comparisons can be made between the full scale and 1/4 scale data. The results show that the full scale system performs better than the 1/4 scale model because of Reynolds number effects. The plume temperature, surface temperatures and back pressure were all lower (better) than in the 1/4 scale model tests. One of the original concerns with the installation was that relative wind would degrade the performance of the DRES Ball onboard a ship. The wind effect was found to be benign during the trials.

Component Approach for Confident Predications of Deepwater CALM Buoy Coupled Motions: Part 2 — Analytical Implementation

2005 ◽  
Author(s):  
M. J. Santala ◽  
Z. J. Huang ◽  
H. Wang ◽  
T. W. Yung ◽  
W. Kan ◽  
...  
Keyword(s):  
Test Data ◽  
Model Test ◽  
System Analysis ◽  
Line Tension ◽  
Analytical Tool ◽  
Full Scale ◽  
Hydrodynamic Coefficients ◽  
Model Scale ◽  
Oscillation Test ◽  
Component Approach

This paper describes an analytical implementation of the component approach for motion predictions of a deepwater CALM buoy as described in the companion paper “Component Approach for Confident Predictions of Deepwater CALM Buoy Coupled Motions — Part 1: Philosophy”. The implementation of the approach starts with a “model-of-the-model” validation of the analytical tool. Emphasis is given to making an accurate analytical characterization of the model as tested. To capture the strong coupling between the buoy motions and line dynamics the analyses described herein were carried out in the time-domain. This allows a rigorous treatment of the hydrodynamic forces on the buoy as well as the non-linear mooring loads when analyzing the buoy responses in waves. Since the validation analysis is a model-of-the-model practice at model scale, the proper application of the validated tool to the full-scale system is discussed. This involves modeling of the exact full-scale system and the proper selection of the hydrodynamic coefficients for the buoy and lines. In this paper we will present the numerical modeling procedures and the results from validation work to confirm that the analytical tool is validated correctly. Detailed results from validation analysis versus model test data will be shown for system components including buoy hydrodynamics from the forced oscillation test, line tension from line oscillation test, and the motions and tensions of integrated buoy/mooring/riser system. We point out that the hydrodynamic coefficients at model scale can not be directly applied to the full-scale system analysis even though they are from model test measurements. We will present the difference between the results of the model-scale system using model scale hydrodynamic coefficients and those based on a proper range of the coefficients at full-scale. This will highlight the need to design component tests to determine appropriate full scale coefficients in order to improve the accuracy of full-scale design predictions. These results will show the advantages of adopting a component approach over the common industry practices in the areas of correct use of model test data, validation analysis and the analysis of the coupled CALM buoy system responses in waves.

scholarly journals Study on the Correction Method of Ice Strength and Thickness Applied to the Sea Trial Condition Based on the Ice Model Test Results

2011 ◽  
Vol 48 (5) ◽  
pp. 457-464 ◽  
Author(s):  
Seung-Ki Lee ◽  
Moon-Chan Kim ◽  
Won-Jun Lee ◽  
Hyun-Soo Kim ◽  
Chun-Ju Lee
Keyword(s):  
Model Test ◽  
Correction Method ◽  
Test Results ◽  
Sea Trial ◽  
Ice Strength ◽  
Ice Model Test ◽  
Ice Model

Paper 11. Yaw Motion Stability; Twin-Screw, Twin-Rudder Ships—Some Model and Ship Results

1972 ◽  
Vol 14 (7) ◽  
pp. 75-79
Author(s):  
G. D. Thurman
Keyword(s):  
Model Test ◽  
Model Tests ◽  
Full Scale ◽  
Test Results ◽  
Motion Stability ◽  
Ship Model ◽  
Pull Out ◽  
Twin Screw ◽  
Model Correlation ◽  
Stability Results

This paper describes the pull-out manoeuvre as an indication of yaw motion stability. Results of model tests at the Admiralty Experiment Works and full-scale trials data are presented as a demonstration of ship/model correlation; additional model test results are given to illustrate use of the manoeuvre for detecting changes in stability due to alterations in ship configuration.

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