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

2011 ◽  
Author(s):  
Harald Ottens ◽  
Radboud van Dijk ◽  
Geert Meskers
Keyword(s):  
Test Data ◽  
Model Test ◽  
Numerical Study ◽  
Open Water ◽  
Model Tests ◽  
Complex Flow ◽  
Calculation Results ◽  
Thrust Efficiency ◽  
Force Components ◽  
The Individual

During offshore heavy lift or pipelay operations the station keeping capabilities of a DP-vessel have an important influence on operability limits of these operations. Heerema Marine Contractors has two DP3-class semi-submersible crane vessels for these operations; 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. A numerical study using CFD is performed to assess thruster-hull interaction on a semi-submersible vessel. The CFD results are validated with a series of model tests, including an open water thruster, single thruster-hull interaction without current and full thruster-hull interaction with all thrusters active without current. The CFD calculation results show good agreement with the model test data. The forces on the semi-submersible as well as on the individual floaters with active thrusters using CFD are within 10% of the model test data. The largest discrepancies are in the bow quartering conditions when the thruster-hull interaction show the most complex flow pattern due to the location and shape of the stern keel. The comparison between the CFD and model test data demonstrates that CFD is able to predict the relevant force components well within a sufficient accuracy for engineering purposes. The paper also addresses lessons learnt to improve the CFD computations as well as practical aspects and limitations of thrust efficiency modeling using CFD from an engineering perspective.

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.

Double Acting Tanker: Experiences from Model Tests and Sea Trials

2005 ◽  
Vol 219 (3) ◽  
pp. 109-119 ◽  
Author(s):  
P Trägärdh ◽  
P Lindell ◽  
N Sasaki
Keyword(s):  
Model Test ◽  
Oil And Gas ◽  
Single Point ◽  
Open Water ◽  
Model Tests ◽  
Water Model ◽  
Research Centre ◽  
Sea Trial ◽  
Cavitation Performance ◽  
Ice Conditions

The acronym DAT stands for double acting tanker, a concept where the ship is designed to run astern in heavy ice conditions while remaining hydrodynamically efficient for ahead propulsion in open water conditions. Two large aframax DATs - 106.000 dwt (deadweight tons) each - have been delivered by Sumitomo Heavy Industries to Fortum Oil and Gas OY. They are the first crude carriers built according to the DAT principle and also the first using pod propulsion from the beginning (Fig. 1). They will also be the world's largest crude carriers with ice class 1A super and are primarily intended for year-round transportation of North Sea crude to Fortum's refineries in the Gulf of Finland. The ships were appointed ‘ship of the year’ in Japan in 2003. SSPA was contracted by Sumitomo Heavy Industries to perform model tests. A comprehensive open water model test programme was used to investigate aspects of resistance and propulsion, manoeuvring, and cavitation performance. As the ship is designed to operate both in ahead and astern conditions for prolonged periods of time, most tests were performed both ahead and astern. Also, a simulation study of dynamic positioning at buoy or floating production, storage offshore (FPSO) loading was made by SSPA. Comprehensive tests of the ship's performance in ice were performed in the ice tank at MARC (Masa-Yards Artic Research Centre). The eight-month model testing and development campaign resulted in a ship with excellent propulsion and manoeuvring performance, especially with regard to the high ice class. Sea trials carried out with ship in August 2002 confirmed the results of the model test. Interesting experiences of the model test campaign and comparison between model test and sea trial results are presented, as well as some examples of single-point mooring simulations.

Numerical Investigation for Vortex-Induced Vibrations of Steel-Lazy-Wave-Risers: Part I — CFD Validation Against Forced Oscillation Model Test

2019 ◽  
Author(s):  
Hyunchul Jang ◽  
Jang Whan Kim
Keyword(s):  
Test Data ◽  
Model Test ◽  
Cfd Simulation ◽  
Assessment Tool ◽  
Forced Oscillation ◽  
Model Tests ◽  
Hydrodynamic Coefficients ◽  
Cfd Validation ◽  
Oscillation Model ◽  
Water Developments

Abstract Vortex-Induced Vibration (VIV) is one of the main sources of fatigue damage for long slender risers. Typical VIV assessment of risers is conducted using semi-empirical software tools with the sectional hydrodynamic coefficients derived from forced-oscillation model tests on short rigid riser sections. The Steel Lazy Wave Riser (SLWR) with buoyancy sections is an attractive concept for improving fatigue performance in deep water developments, but there is limited model test data available for the hydrodynamic coefficients on SLWR’s. CFD simulation is an alternative VIV assessment tool, once it is validated for an existing model test. It can provide accurate estimates of VIV response and help to design configurations of SLWR’s without additional model tests. The present CFD simulations are performed to validate hydrodynamic coefficients of a SLWR section. The predicted drag and excitation (lift) coefficients on both bare riser and buoyancy sections are compared to the test data with respect to oscillation frequency and amplitude.

Performance Simulation of a Dual-Direction Ship in Level Ice

2014 ◽  
Vol 58 (03) ◽  
pp. 168-181
Author(s):  
Xiang Tang ◽  
Kaj Riska ◽  
Torgeir Moan
Keyword(s):  
Test Data ◽  
Model Test ◽  
Performance Prediction ◽  
Numerical Procedure ◽  
Model Tests ◽  
Prediction Tool ◽  
Continuous Mode ◽  
Performance Simulation ◽  
Level Ice ◽  
A Performance

The ice performance of a dual-direction ship is investigated through a numerical procedure developed to simulate the continuous-mode icebreaking in level ice. The effect of the propeller-hull-ice interaction for running astern is accounted for by applying the knowledge obtained from model tests to the numerical procedure. The numerical procedure is in turn used as a performance prediction tool to supplement the model test data to investigate the thrust deduction in ice.

Benchmark Study Between CFD and Model Tests on a Semi-Submersible Crane Vessel

2009 ◽  
Author(s):  
Harald Ottens ◽  
Radboud van Dijk ◽  
Geert Meskers
Keyword(s):  
Test Data ◽  
Model Test ◽  
Offshore Structures ◽  
Model Tests ◽  
Lessons Learned ◽  
Data Sets ◽  
General Acceptance ◽  
Heavy Lift ◽  
Semi Empirical ◽  
Proven Method

Accurate assessment of current loads on offshore vessels is required to determine operability of heavy lift and pipe lay operations. Whereas in the past only semi-empirical methods or model tests were suitable to obtain these data, CFD has recently become available as engineering tool to assess current loads on offshore structures. CFD has the potential to assess current loads more flexible in a numerical manner. Although the application of CFD has proven its value in assessment of ships resistance and VIV calculations, CFD is still not yet a fully proven method to calculate the current loads on offshore structures. Therefore validation of the results is further required to reach general acceptance of this method for offshore applications. HMC took the initiative to compare and validate CFD results with its model test data of current loads on one of its semi-submersible crane vessels. In this paper a comparison of CFD results with model test data of the current loads of a semi-submersible crane vessel is presented. The CFD calculations are performed as blind computations, so the model tests results were unknown. Afterwards the CFD results are compared with the results of the model tests. Based on both data sets lessons learned are addressed to improve the CFD computations as well as practical aspects and limitations of current load model testing. Furthermore, the possibilities to use CFD to scale the results of the model tests to full scale are explored. Based on this comparison CFD appears to be a complementary, flexible and reliable tool in assessing the current loads on mission critical vessel operations.

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.

scholarly journals Validation of Numerical Wave Tank Simulations Using REEF3D With JONSWAP Spectra in Intermediate Water Depth

2020 ◽  
Author(s):  
Csaba Pakozdi ◽  
Sebastien Fouques ◽  
Maxime Thys ◽  
Arun Kamath ◽  
Weizhi Wang ◽  
...  
Keyword(s):  
Test Data ◽  
Model Test ◽  
Water Depth ◽  
Model Tests ◽  
Irregular Waves ◽  
Wave Crest ◽  
Intermediate Water ◽  
Numerical Wave Tank ◽  
Wave Tank ◽  
Numerical Wave

Abstract As offshore wind turbines increase in size and output, the support structures are also growing. More sophisticated assessment of the hydrodynamic loads is needed, particularly for the ultimate limit state design. For higher-order phenomena related to rare steep wave events such as ringing, a better understanding of the stochastic loads is needed. As an innovative step forward to reduce the cost of extensive model tests with irregular waves, a larger number of investigations can be carried out using high-performance high-fidelity numerical simulations after an initial stochastic validation with model test data. In this paper, the open-source hydrodynamic model REEF3D::FNPF (Fully Nonlinear Potential Flow) is used to carry out three-hour long simulations with the JONSWAP spectrum in intermediate water depth conditions. Statistical properties of the free surface elevation in the numerical wave tank are validated using the available data from model tests carried out at SINTEF Ocean/NTNU. The spectral shape, significant wave height, peak period, skewness, kurtosis, and wave crest height statistics are compared. The results are analyzed and it is found that the numerical model provides reasonably good agreement with the model test data.

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.

RANS Based Calm Water Resistance Prediction for Tumblehome Hull With Different Bow Appendages

2019 ◽  
Author(s):  
Shuzheng Sun ◽  
Xin Zhao
Keyword(s):  
Flow Field ◽  
Test Data ◽  
Model Test ◽  
Water Resistance ◽  
Grid Size ◽  
Time Step ◽  
Submerged Body ◽  
Calm Water ◽  
Calculation Results ◽  
Resistance Prediction

Abstract The calm water resistance of the models a bare tumblehome hull and with 3 different bow appendages (triangle fins, rectangular foil, and semi-submerged body) are predicted based on RANS and k-ε turbulence model using STAR CCM+ software. VOF method is used for the 2-phases simulation. The resistance calculation results of the bare hull are validated against model test data. The verification and convergence studies are carried out on the grid size and time step. The validation studies show that the relative changes of the resistance calculation results compared with the model test data for Fr = 0.294 are 5–6%. The results of resistance prediction for the hulls with 3 bow appendages show that the bow fin configuration shows the best performance at Fr = 0.220, and the semi-submerged body configuration shows the best performance at Fr = 0.367. The details of flow field of different hulls will be analysed in this paper.

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