1.  Koop, Arjen: SHALLOW WATER CURRENT LOADS ON A LNG CARRIER USING CFD. Proceedings of the ASME 2015 34st International Conference on Ocean, Offshore and Arctic Engineering, May 31stJune 5th, St. John’s, Canada, 2015. (Type: Conference  Abstract  Links  BibTeX) @conference{2015OMAE41275_Koop_LNGC_Shallow+Blockage, title = {SHALLOW WATER CURRENT LOADS ON A LNG CARRIER USING CFD}, author = {Arjen Koop}, url = {http://www.refresco.org/?p=1443}, year = {2015}, date = {20150604}, booktitle = {Proceedings of the ASME 2015 34st International Conference on Ocean, Offshore and Arctic Engineering, May 31stJune 5th, St. John’s, Canada}, abstract = {To determine shallow water effects on current loads for an LNG Carrier, CFD calculations with MARIN’s CFD code ReFRESCO have been carried out. The CFD results are compared to model tests carried out in MARIN’s Shallow Water Basin for the HAWAI JIP. The loads have been determined for three different water depth to draft ratio’s, from relatively deep water to shallow water. For all water depths the difference in CY coefficient between the CFD results and experiments is 510%. Furthermore, the blockage effects from basin side walls are investigated. For shallow water it was found that the blockage effects are significant, i.e. 3050%, and that they vary for different current headings. For deeper water the blockage effects are smaller than 5%. The influence of “towing” versus a “current” flow situation is also studied. In the experiments the model is towed through the basin leading to a relative velocity between the model and the basin floor. It is found that for shallow water the results for the “tow” situation are 10% lower than for the “current” situation. Lastly, preliminary results for full scale are presented. At full scale the current coefficients are found to be lower than at model scale. However, more investigations should be carried out at full scale to be able to draw definite conclusions. From the results presented in this paper it is concluded that shallow water effects on current loads can be accurately obtained with CFD. Furthermore, blockage effects and the influence of “towing” versus a “current” situation have been quantified and a first study into scale effects has been presented.}, keywords = {}, pubstate = {published}, tppubtype = {conference} } To determine shallow water effects on current loads for an LNG Carrier, CFD calculations with MARIN’s CFD code ReFRESCO have been carried out. The CFD results are compared to model tests carried out in MARIN’s Shallow Water Basin for the HAWAI JIP. The loads have been determined for three different water depth to draft ratio’s, from relatively deep water to shallow water. For all water depths the difference in CY coefficient between the CFD results and experiments is 510%. Furthermore, the blockage effects from basin side walls are investigated. For shallow water it was found that the blockage effects are significant, i.e. 3050%, and that they vary for different current headings. For deeper water the blockage effects are smaller than 5%. The influence of “towing” versus a “current” flow situation is also studied. In the experiments the model is towed through the basin leading to a relative velocity between the model and the basin floor. It is found that for shallow water the results for the “tow” situation are 10% lower than for the “current” situation. Lastly, preliminary results for full scale are presented. At full scale the current coefficients are found to be lower than at model scale. However, more investigations should be carried out at full scale to be able to draw definite conclusions. From the results presented in this paper it is concluded that shallow water effects on current loads can be accurately obtained with CFD. Furthermore, blockage effects and the influence of “towing” versus a “current” situation have been quantified and a first study into scale effects has been presented. 
2.  Koop, Arjen; Klaij, Christiaan; Vaz, Guilherme: VISCOUSFLOW CALCULATIONS FOR MODEL AND FULLSCALE CURRENT LOADS ON TYPICAL OFFSHORE STRUCTURES. MARINE2011 Lisbon, Portugal, 2013. (Type: Conference  Abstract  Links  BibTeX) @conference{2011MARINE2011_KoopKlayVaz_CurrentCoefs_MS&FS, title = {VISCOUSFLOW CALCULATIONS FOR MODEL AND FULLSCALE CURRENT LOADS ON TYPICAL OFFSHORE STRUCTURES}, author = {Arjen Koop and Christiaan Klaij and Guilherme Vaz}, url = {http://www.refresco.org/download/2011marine2011_koopklayvaz_currentcoefs_msfs/}, year = {2013}, date = {20130928}, address = {Lisbon, Portugal}, organization = {MARINE2011}, abstract = {In this paper, CFD calculations for current loads on an LNG carrier and a semisubmersible are presented, both for model and fullscale situations, for current angles ranging from 180 to 0 degrees. MARIN's inhouse URANS code ReFRESCO is used. Numerical studies are carried out concerning itera tive convergence and grid refinement. In total, more than 100 calculations have been performed. Detailed verification analysis is carried out using modern techniques, and numerical uncertainties are calculated. Afterwards, quantitative validation for modelscale Reynolds number is done taking into account numerical and experimental uncertainties. Scale effects on the current coefficients are investigated, having in mind the estimated numerical uncertainties, and unsteady effects are briefly studied. Good iterative convergence is obtained in most calculations, i.e. a decrease in residuals of more than 5 orders is achieved. The sensitivity to grid resolution has been investigated for both model and full scale using five consecutively refined grids and for 3 current headings. The differences in the solution between two consecutive refinements converge for all cases. The numerical uncertainties are larger for angles with small values of the loads. Comparison with experiments shows that ReFRESCO provides good quantitative prediction of the current loads at model scale: for angles with larger forces the CFD results are validated with 15% of uncertainty. To determine scale effects the numerical uncertainties must be considered in order to prevent wrong conclusions drawn on basis of numerical differences rather than on physical differences. For the fullscale results larger numerical uncertainties are found than for model scale and for absolute values for scale effects this uncertainty should be improved. For the LNG carrier significant scale effects, i.e. more than 40%, have been obtained for current angles where the friction component is dominant. For these cases the numerical uncertainty is relatively low. For the other current angles differences of 830% between model and full scale can be observed, but here larger numerical uncertainties are found. For the semisubmersible the numerical uncertainties for the fullscale results are larger than for the LNG carrier. For the semisubmersible the pressure component of the force is highly dominant, i.e. larger than 90% of the total force. On average the fullscale current coefficients are 20% lower than at model scale, but larger differences for a number of angles can be observed.}, keywords = {}, pubstate = {published}, tppubtype = {conference} } In this paper, CFD calculations for current loads on an LNG carrier and a semisubmersible are presented, both for model and fullscale situations, for current angles ranging from 180 to 0 degrees. MARIN's inhouse URANS code ReFRESCO is used. Numerical studies are carried out concerning itera tive convergence and grid refinement. In total, more than 100 calculations have been performed. Detailed verification analysis is carried out using modern techniques, and numerical uncertainties are calculated. Afterwards, quantitative validation for modelscale Reynolds number is done taking into account numerical and experimental uncertainties. Scale effects on the current coefficients are investigated, having in mind the estimated numerical uncertainties, and unsteady effects are briefly studied. Good iterative convergence is obtained in most calculations, i.e. a decrease in residuals of more than 5 orders is achieved. The sensitivity to grid resolution has been investigated for both model and full scale using five consecutively refined grids and for 3 current headings. The differences in the solution between two consecutive refinements converge for all cases. The numerical uncertainties are larger for angles with small values of the loads. Comparison with experiments shows that ReFRESCO provides good quantitative prediction of the current loads at model scale: for angles with larger forces the CFD results are validated with 15% of uncertainty. To determine scale effects the numerical uncertainties must be considered in order to prevent wrong conclusions drawn on basis of numerical differences rather than on physical differences. For the fullscale results larger numerical uncertainties are found than for model scale and for absolute values for scale effects this uncertainty should be improved. For the LNG carrier significant scale effects, i.e. more than 40%, have been obtained for current angles where the friction component is dominant. For these cases the numerical uncertainty is relatively low. For the other current angles differences of 830% between model and full scale can be observed, but here larger numerical uncertainties are found. For the semisubmersible the numerical uncertainties for the fullscale results are larger than for the LNG carrier. For the semisubmersible the pressure component of the force is highly dominant, i.e. larger than 90% of the total force. On average the fullscale current coefficients are 20% lower than at model scale, but larger differences for a number of angles can be observed. 
3.  Koop, Arjen; Klaij, Christiaan; Vaz, Guilherme: ViscousFlow Calculations for Model and FullScale Current Loads on Typical Offshore Structures. In: Computational Methods in Applied Sciences, 29 (Part1), pp. 329, 2013. (Type: Journal Article  Abstract  Links  BibTeX) @article{2013CMAS_Koop_et_al_CurrentLoads, title = {ViscousFlow Calculations for Model and FullScale Current Loads on Typical Offshore Structures}, author = {Arjen Koop and Christiaan Klaij and Guilherme Vaz}, url = { http://www.refresco.org/?wpdmpro=2011_marine2011springer_koopklaijvazpdf}, doi = {DOI: 10.1007/9789400761438_1}, year = {2013}, date = {20130201}, journal = {Computational Methods in Applied Sciences}, volume = {29}, number = {Part1}, pages = {329}, abstract = {In this paper, CFD calculations for current loads on an LNG carrier and a semisubmersible are presented, both for model and fullscale situations, for current angles ranging from 180 to 0 degrees. MARIN’s inhouse URANS code ReFRESCO is used. Numerical studies are carried out concerning iterative convergence and grid refinement. In total,more than 100 calculations have been performed. Detailed verification analysis is carried out using modern techniques, and numerical uncertainties are calculated. Afterwards, quantitative validation for modelscale Reynolds number is done taking into account numerical and experimental uncertainties. Scale effects on the current coefficients are investigated, having in mind the estimated numerical uncertainties, and unsteady effects are briefly studied. Good iterative convergence is obtained in most calculations, i.e. a decrease in residuals of more than 5 orders is achieved. The sensitivity to grid resolution has been investigated for both model and full scale using five consecutively refined grids and for 3 current headings. The differences in the solution between two consecutive refinements converge for all cases. The numerical uncertainties are larger for angles with small values of the loads. Comparison with experiments shows that ReFRESCO provides good quantitative prediction of the current loads at model scale: for angles with larger forces the CFD results are validated with 15 % of uncertainty. To determine scale effects the numerical uncertainties must be considered in order to prevent wrong conclusions drawn on basis of numerical differences rather than on physical differences. For the fullscale results larger numerical uncertainties are found than for model scale and for absolute values for scale effects this uncertainty should be improved. For the LNG carrier significant scale effects, i.e. more than 40 %, have been obtained for current angles where the friction component is dominant. For these cases the numerical uncertainty is relatively low. For the other current angles differences of 8–30 % between model and full scale can be observed, but here larger numerical uncertainties are found. For the semisubmersible the numerical uncertainties for the fullscale results are larger than for the LNG carrier. For the semisubmersible the pressure component of the force is highly dominant, i.e. larger than 90 % of the total force. On average the fullscale current coefficients are 20 % lower than at model scale, but larger differences for a number of angles can be observed.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this paper, CFD calculations for current loads on an LNG carrier and a semisubmersible are presented, both for model and fullscale situations, for current angles ranging from 180 to 0 degrees. MARIN’s inhouse URANS code ReFRESCO is used. Numerical studies are carried out concerning iterative convergence and grid refinement. In total,more than 100 calculations have been performed. Detailed verification analysis is carried out using modern techniques, and numerical uncertainties are calculated. Afterwards, quantitative validation for modelscale Reynolds number is done taking into account numerical and experimental uncertainties. Scale effects on the current coefficients are investigated, having in mind the estimated numerical uncertainties, and unsteady effects are briefly studied. Good iterative convergence is obtained in most calculations, i.e. a decrease in residuals of more than 5 orders is achieved. The sensitivity to grid resolution has been investigated for both model and full scale using five consecutively refined grids and for 3 current headings. The differences in the solution between two consecutive refinements converge for all cases. The numerical uncertainties are larger for angles with small values of the loads. Comparison with experiments shows that ReFRESCO provides good quantitative prediction of the current loads at model scale: for angles with larger forces the CFD results are validated with 15 % of uncertainty. To determine scale effects the numerical uncertainties must be considered in order to prevent wrong conclusions drawn on basis of numerical differences rather than on physical differences. For the fullscale results larger numerical uncertainties are found than for model scale and for absolute values for scale effects this uncertainty should be improved. For the LNG carrier significant scale effects, i.e. more than 40 %, have been obtained for current angles where the friction component is dominant. For these cases the numerical uncertainty is relatively low. For the other current angles differences of 8–30 % between model and full scale can be observed, but here larger numerical uncertainties are found. For the semisubmersible the numerical uncertainties for the fullscale results are larger than for the LNG carrier. For the semisubmersible the pressure component of the force is highly dominant, i.e. larger than 90 % of the total force. On average the fullscale current coefficients are 20 % lower than at model scale, but larger differences for a number of angles can be observed. 
4.  Koop, Arjen; Klaij, Christiaan; Vaz, Guilherme: ViscousFlow Calculations for Model and FullScale Current Loads on Typical Offshore Structures. IV International Conference on Computational Methods in Marine Engineering (ECCOMAS MARINE), Lisbon, Portugal, 2011. (Type: Conference  Abstract  Links  BibTeX) @conference{Koop2011b, title = {ViscousFlow Calculations for Model and FullScale Current Loads on Typical Offshore Structures}, author = {Arjen Koop and Christiaan Klaij and Guilherme Vaz}, editor = {Arjen Koop and Christiaan Klaij and Guilherme Vaz}, url = {http://www.refresco.org/download/2011marine2011_koopklayvaz_currentcoefs_msfspdf/}, doi = {10.1007/9789400761438_1}, year = {2011}, date = {20110928}, booktitle = {IV International Conference on Computational Methods in Marine Engineering (ECCOMAS MARINE), Lisbon, Portugal}, abstract = {In this paper, CFD calculations for current loads on an LNG carrier and a semisubmersible are presented, both for model and fullscale situations, for current angles ranging from 180 to 0 degrees. MARIN’s inhouse URANS code ReFRESCO is used. Numerical studies are carried out concerning iterative convergence and grid refinement. In total,more than 100 calculations have been performed. Detailed verification analysis is carried out using modern techniques, and numerical uncertainties are calculated. Afterwards, quantitative validation for modelscale Reynolds number is done taking into account numerical and experimental uncertainties. Scale effects on the current coefficients are investigated, having in mind the estimated numerical uncertainties, and unsteady effects are briefly studied. Good iterative convergence is obtained in most calculations, i.e. a decrease in residuals of more than 5 orders is achieved. The sensitivity to grid resolution has been investigated for both model and full scale using five consecutively refined grids and for 3 current headings. The differences in the solution between two consecutive refinements converge for all cases. The numerical uncertainties are larger for angles with small values of the loads. Comparison with experiments shows that ReFRESCO provides good quantitative prediction of the current loads at model scale: for angles with larger forces the CFD results are validated with 15 % of uncertainty. To determine scale effects the numerical uncertainties must be considered in order to prevent wrong conclusions drawn on basis of numerical differences rather than on physical differences. For the fullscale results larger numerical uncertainties are found than for model scale and for absolute values for scale effects this uncertainty should be improved. For the LNG carrier significant scale effects, i.e. more than 40 %, have been obtained for current angles where the friction component is dominant. For these cases the numerical uncertainty is relatively low. For the other current angles differences of 8–30 % between model and full scale can be observed, but here larger numerical uncertainties are found. For the semisubmersible the numerical uncertainties for the fullscale results are larger than for the LNG carrier. For the semisubmersible the pressure component of the force is highly dominant, i.e. larger than 90 % of the total force. On average the fullscale current coefficients are 20 % lower than at model scale, but larger differences for a number of angles can be observed.}, keywords = {}, pubstate = {published}, tppubtype = {conference} } In this paper, CFD calculations for current loads on an LNG carrier and a semisubmersible are presented, both for model and fullscale situations, for current angles ranging from 180 to 0 degrees. MARIN’s inhouse URANS code ReFRESCO is used. Numerical studies are carried out concerning iterative convergence and grid refinement. In total,more than 100 calculations have been performed. Detailed verification analysis is carried out using modern techniques, and numerical uncertainties are calculated. Afterwards, quantitative validation for modelscale Reynolds number is done taking into account numerical and experimental uncertainties. Scale effects on the current coefficients are investigated, having in mind the estimated numerical uncertainties, and unsteady effects are briefly studied. Good iterative convergence is obtained in most calculations, i.e. a decrease in residuals of more than 5 orders is achieved. The sensitivity to grid resolution has been investigated for both model and full scale using five consecutively refined grids and for 3 current headings. The differences in the solution between two consecutive refinements converge for all cases. The numerical uncertainties are larger for angles with small values of the loads. Comparison with experiments shows that ReFRESCO provides good quantitative prediction of the current loads at model scale: for angles with larger forces the CFD results are validated with 15 % of uncertainty. To determine scale effects the numerical uncertainties must be considered in order to prevent wrong conclusions drawn on basis of numerical differences rather than on physical differences. For the fullscale results larger numerical uncertainties are found than for model scale and for absolute values for scale effects this uncertainty should be improved. For the LNG carrier significant scale effects, i.e. more than 40 %, have been obtained for current angles where the friction component is dominant. For these cases the numerical uncertainty is relatively low. For the other current angles differences of 8–30 % between model and full scale can be observed, but here larger numerical uncertainties are found. For the semisubmersible the numerical uncertainties for the fullscale results are larger than for the LNG carrier. For the semisubmersible the pressure component of the force is highly dominant, i.e. larger than 90 % of the total force. On average the fullscale current coefficients are 20 % lower than at model scale, but larger differences for a number of angles can be observed. 
5.  Koop, Arjen; Bereznitski, Alexei: ModelScale And FullScale CFD Calculations For Current Loads On SemiSubmersible. 30th International Conference on Ocean, Offshore and Arctic Engineering (OMAE), Rotterdam, The Netherlands, 2011. (Type: Conference  Abstract  Links  BibTeX) @conference{Koop2011b, title = {ModelScale And FullScale CFD Calculations For Current Loads On SemiSubmersible}, author = {Arjen Koop and Alexei Bereznitski}, editor = {Arjen Koop and Alexei Bereznitski}, url = {http://www.refresco.org/download/2011omae49204akabhuijsmanssemipdf/}, year = {2011}, date = {20110619}, booktitle = {30th International Conference on Ocean, Offshore and Arctic Engineering (OMAE), Rotterdam, The Netherlands}, abstract = {In this paper results of CFD calculations with the MARIN inhouse code ReFRESCO are presented for the JBF14000 SemiSubmersible designed by Huisman Equipment BV. The objective of the CFD calculations is to investigate the applicability, the costs and the accuracy of CFD to obtain the current coefficients of a semisubmersible for all headings. Furthermore, full scale CFD calculations are carried out to investigate possible scale effects on the current coefficients. An extensive verification study has been carried for the modelscale current loads on a semisubmersible using 10 different grids of different grid type for 3 different headings, i.e. 180, 150 and 90 degrees. These headings represent the main different flow regions around the semisubmersible. The CFD results are compared with the results from wind tunnel experiments and tests in the Offshore Basin for a range of current headings. The results for the force coefficients are not very dependent on grid resolution and grid type. The largest differences found are less than 10% and these are obtained for CX results for 180 degrees. For the results obtained on the same grid type the results change less than 4% when the grid is refined. These verification results give good confidence in the CFD results. For the angles with larger forces, i.e. the range [180:130] for CX and the range [150:90] for CY the CFD results are within 12% or better from the experiments. Fullscale force coefficients are calculated using 5 subsequently refined grids for three different headings, i.e. 180, 150 and 90 degrees. Scale effects should only be determined when the effect of grid refining is investigated. The trend of the force coefficients when refining the grid, can be different for modelscale and fullscale. The use of coarse grids can lead to misleading conclusions. On average the fullscale values are approximately 1520% lower than for modelscale. However, larger differences for a number of angles do exist.}, keywords = {}, pubstate = {published}, tppubtype = {conference} } In this paper results of CFD calculations with the MARIN inhouse code ReFRESCO are presented for the JBF14000 SemiSubmersible designed by Huisman Equipment BV. The objective of the CFD calculations is to investigate the applicability, the costs and the accuracy of CFD to obtain the current coefficients of a semisubmersible for all headings. Furthermore, full scale CFD calculations are carried out to investigate possible scale effects on the current coefficients. An extensive verification study has been carried for the modelscale current loads on a semisubmersible using 10 different grids of different grid type for 3 different headings, i.e. 180, 150 and 90 degrees. These headings represent the main different flow regions around the semisubmersible. The CFD results are compared with the results from wind tunnel experiments and tests in the Offshore Basin for a range of current headings. The results for the force coefficients are not very dependent on grid resolution and grid type. The largest differences found are less than 10% and these are obtained for CX results for 180 degrees. For the results obtained on the same grid type the results change less than 4% when the grid is refined. These verification results give good confidence in the CFD results. For the angles with larger forces, i.e. the range [180:130] for CX and the range [150:90] for CY the CFD results are within 12% or better from the experiments. Fullscale force coefficients are calculated using 5 subsequently refined grids for three different headings, i.e. 180, 150 and 90 degrees. Scale effects should only be determined when the effect of grid refining is investigated. The trend of the force coefficients when refining the grid, can be different for modelscale and fullscale. The use of coarse grids can lead to misleading conclusions. On average the fullscale values are approximately 1520% lower than for modelscale. However, larger differences for a number of angles do exist. 
6.  Fathi, Fahd; Klaij, Christiaan; Koop, Arjen: Predicting Loads on an LNG Carrier with CFD. Proceedings of the 29th International Conference on Ocean, Offshore and Arctic Engineering, OMAE 2010, June 611, 2010, Shanghai, China, 2010. (Type: Conference  Abstract  Links  BibTeX) @conference{Fathi2010, title = {Predicting Loads on an LNG Carrier with CFD}, author = {Fahd Fathi and Christiaan Klaij and Arjen Koop}, editor = {Fahd Fathi and Christiaan Klaij and Arjen Koop}, url = {http://www.refresco.org/download/2010omae20122fathiklaijkooppdfs/}, year = {2010}, date = {20100610}, booktitle = {Proceedings of the 29th International Conference on Ocean, Offshore and Arctic Engineering, OMAE 2010, June 611, 2010, Shanghai, China}, abstract = {The Current Affairs Joint Industry Project was initiated to develop the understanding and tools for the assessment of current loads on offshore structures. CFD is one of these tools requiring a good understanding of the underlying physical and mathematical models. In order to assess its suitability for the prediction of current loads on monohulls, the flow around a LNG carrier for which model scale data is available was considered. The LNG carrier, including bilgekeels and rudder, was towed at scale 1/50 in Marin's shallow water basin during the HAWAI JIP, for flow angles between 0 and 180 degrees. The measurements were shared with the Current Affairs JIP, for which the participants were invited to perform CFD computations reproducing the model test results. A number of these simulations are presented in this paper. The analysis of the results includes discussion on the grid generation as well as the numerical and physical parameters of the simulation. The comparison between experiments and computations shows that CFD can provide good qualitative predictions for the variation of force coefficients with inflow angle. The origin of the result variability between the participants is discussed and attention is drawn to the different factors influencing the quality of the simulation.}, keywords = {}, pubstate = {published}, tppubtype = {conference} } The Current Affairs Joint Industry Project was initiated to develop the understanding and tools for the assessment of current loads on offshore structures. CFD is one of these tools requiring a good understanding of the underlying physical and mathematical models. In order to assess its suitability for the prediction of current loads on monohulls, the flow around a LNG carrier for which model scale data is available was considered. The LNG carrier, including bilgekeels and rudder, was towed at scale 1/50 in Marin's shallow water basin during the HAWAI JIP, for flow angles between 0 and 180 degrees. The measurements were shared with the Current Affairs JIP, for which the participants were invited to perform CFD computations reproducing the model test results. A number of these simulations are presented in this paper. The analysis of the results includes discussion on the grid generation as well as the numerical and physical parameters of the simulation. The comparison between experiments and computations shows that CFD can provide good qualitative predictions for the variation of force coefficients with inflow angle. The origin of the result variability between the participants is discussed and attention is drawn to the different factors influencing the quality of the simulation. 
7.  Vaz, Guilherme; Waals, Olaf; Ottens, Harald; Fathi, Fahd; Souëf, Tim Le; Kiu, Kwong: Current Affairs: Model Tests, SemiEmpirical Predictions and CFD Computations for Current Coefficients of SemiSubmersibles. Proceedings of ASME 28th International Conference on Ocean, Offshore and Arctic Engineering OMAE2009 May 31June 5, 2009, Honolulu, Hawaii, 2009. (Type: Conference  Abstract  Links  BibTeX) @conference{2009OMAE80216_VazWaalsOttensFathiSouefKiu, title = {Current Affairs: Model Tests, SemiEmpirical Predictions and CFD Computations for Current Coefficients of SemiSubmersibles}, author = {Guilherme Vaz and Olaf Waals and Harald Ottens and Fahd Fathi and Tim Le Souëf and Kwong Kiu}, url = {http://www.refresco.org/download/2009omae80216_vazwaalsottensfathisouefkiupdf http://www.asmeconferences.org/}, year = {2009}, date = {20090531}, booktitle = {Proceedings of ASME 28th International Conference on Ocean, Offshore and Arctic Engineering OMAE2009 May 31June 5, 2009, Honolulu, Hawaii}, abstract = {Current loads on stationary vessels have been investigated as part of the Current Affairs Joint Industry project (JIP). Modeltests, semiempirical models and CFD methods were used to predict these loads. This paper examines one configuration out of the eight tested in the JIP; an idealized semisubmersible consisting of two square roundedcorner columns connected with a pontoon. The model experiments, empirical model predictions and CFD results are presented and discussed. ‘Blind’ and ‘Improved’ CFD computations (with and without knowledge of the experimental results) have been carried out by the JIP participants. Comparisons between these results are made, deviations from the experimental data are quantified and conclusions are drawn. Two key issues for modeling accuracy are identified and discussed; the location of the transition to turbulent flow and the control of the numerical errors.}, keywords = {}, pubstate = {published}, tppubtype = {conference} } Current loads on stationary vessels have been investigated as part of the Current Affairs Joint Industry project (JIP). Modeltests, semiempirical models and CFD methods were used to predict these loads. This paper examines one configuration out of the eight tested in the JIP; an idealized semisubmersible consisting of two square roundedcorner columns connected with a pontoon. The model experiments, empirical model predictions and CFD results are presented and discussed. ‘Blind’ and ‘Improved’ CFD computations (with and without knowledge of the experimental results) have been carried out by the JIP participants. Comparisons between these results are made, deviations from the experimental data are quantified and conclusions are drawn. Two key issues for modeling accuracy are identified and discussed; the location of the transition to turbulent flow and the control of the numerical errors. 
8.  Toxopeus, Serge; Vaz, Guilherme: Calculation Of Current Or Manoeuvring Forces Using A ViscousFlow Solver. Proceedings of ASME 28th International Conference on Ocean, Offshore and Arctic Engineering OMAE2009 May 31June 5, 2009, Honolulu, Hawaii, 2009. (Type: Conference  Abstract  Links  BibTeX) @conference{2009OMAE79782ToxopeusVaz, title = {Calculation Of Current Or Manoeuvring Forces Using A ViscousFlow Solver}, author = {Serge Toxopeus and Guilherme Vaz}, url = {http://www.refresco.org/download/2009omae79782toxopeusvazpdf http://www.asmeconferences.org/}, year = {2009}, date = {20090531}, booktitle = {Proceedings of ASME 28th International Conference on Ocean, Offshore and Arctic Engineering OMAE2009 May 31June 5, 2009, Honolulu, Hawaii}, journal = {Proceedings of ASME 28th International Conference on Ocean, Offshore and Arctic Engineering OMAE2009 May 31June 5, 2009, Honolulu, Hawaii}, abstract = {To investigate the capabilities of using a viscousflow solver to calculate current or manoeuvring forces on ship hulls, calculations have been conducted for a test hull under several oblique inflow conditions. All calculations were performed with a single grid topology to reduce the amount of grid generation time. Verification and validation of the predicted loads and flow around the hull has been performed through grid refinement studies and comparison with experiments and results from previous calculations. Furthermore, the influence of unsteady behaviour on the results for large inflow angles is shown. Conclusions are drawn regarding the accuracy of the results and recommendations for improvements and further work are given.}, keywords = {}, pubstate = {published}, tppubtype = {conference} } To investigate the capabilities of using a viscousflow solver to calculate current or manoeuvring forces on ship hulls, calculations have been conducted for a test hull under several oblique inflow conditions. All calculations were performed with a single grid topology to reduce the amount of grid generation time. Verification and validation of the predicted loads and flow around the hull has been performed through grid refinement studies and comparison with experiments and results from previous calculations. Furthermore, the influence of unsteady behaviour on the results for large inflow angles is shown. Conclusions are drawn regarding the accuracy of the results and recommendations for improvements and further work are given. 
2015 

Koop, Arjen SHALLOW WATER CURRENT LOADS ON A LNG CARRIER USING CFD Conference Proceedings of the ASME 2015 34st International Conference on Ocean, Offshore and Arctic Engineering, May 31stJune 5th, St. John’s, Canada, 2015. Abstract  Links  BibTeX  Tags: Blockage Effects, Current Loads, Interfaces, RANS, ScaleEffects, SST, Validation @conference{2015OMAE41275_Koop_LNGC_Shallow+Blockage, title = {SHALLOW WATER CURRENT LOADS ON A LNG CARRIER USING CFD}, author = {Arjen Koop}, url = {http://www.refresco.org/?p=1443}, year = {2015}, date = {20150604}, booktitle = {Proceedings of the ASME 2015 34st International Conference on Ocean, Offshore and Arctic Engineering, May 31stJune 5th, St. John’s, Canada}, abstract = {To determine shallow water effects on current loads for an LNG Carrier, CFD calculations with MARIN’s CFD code ReFRESCO have been carried out. The CFD results are compared to model tests carried out in MARIN’s Shallow Water Basin for the HAWAI JIP. The loads have been determined for three different water depth to draft ratio’s, from relatively deep water to shallow water. For all water depths the difference in CY coefficient between the CFD results and experiments is 510%. Furthermore, the blockage effects from basin side walls are investigated. For shallow water it was found that the blockage effects are significant, i.e. 3050%, and that they vary for different current headings. For deeper water the blockage effects are smaller than 5%. The influence of “towing” versus a “current” flow situation is also studied. In the experiments the model is towed through the basin leading to a relative velocity between the model and the basin floor. It is found that for shallow water the results for the “tow” situation are 10% lower than for the “current” situation. Lastly, preliminary results for full scale are presented. At full scale the current coefficients are found to be lower than at model scale. However, more investigations should be carried out at full scale to be able to draw definite conclusions. From the results presented in this paper it is concluded that shallow water effects on current loads can be accurately obtained with CFD. Furthermore, blockage effects and the influence of “towing” versus a “current” situation have been quantified and a first study into scale effects has been presented.}, keywords = {Blockage Effects, Current Loads, Interfaces, RANS, ScaleEffects, SST, Validation}, pubstate = {published}, tppubtype = {conference} } To determine shallow water effects on current loads for an LNG Carrier, CFD calculations with MARIN’s CFD code ReFRESCO have been carried out. The CFD results are compared to model tests carried out in MARIN’s Shallow Water Basin for the HAWAI JIP. The loads have been determined for three different water depth to draft ratio’s, from relatively deep water to shallow water. For all water depths the difference in CY coefficient between the CFD results and experiments is 510%. Furthermore, the blockage effects from basin side walls are investigated. For shallow water it was found that the blockage effects are significant, i.e. 3050%, and that they vary for different current headings. For deeper water the blockage effects are smaller than 5%. The influence of “towing” versus a “current” flow situation is also studied. In the experiments the model is towed through the basin leading to a relative velocity between the model and the basin floor. It is found that for shallow water the results for the “tow” situation are 10% lower than for the “current” situation. Lastly, preliminary results for full scale are presented. At full scale the current coefficients are found to be lower than at model scale. However, more investigations should be carried out at full scale to be able to draw definite conclusions. From the results presented in this paper it is concluded that shallow water effects on current loads can be accurately obtained with CFD. Furthermore, blockage effects and the influence of “towing” versus a “current” situation have been quantified and a first study into scale effects has been presented.  
2013 

Koop, Arjen; Klaij, Christiaan; Vaz, Guilherme VISCOUSFLOW CALCULATIONS FOR MODEL AND FULLSCALE CURRENT LOADS ON TYPICAL OFFSHORE STRUCTURES Conference MARINE2011 Lisbon, Portugal, 2013. Abstract  Links  BibTeX  Tags: CFD, Current Loads, LNG Carrier, RANS, Scale Eects, Semi submersible, Validation, Verication @conference{2011MARINE2011_KoopKlayVaz_CurrentCoefs_MS&FS, title = {VISCOUSFLOW CALCULATIONS FOR MODEL AND FULLSCALE CURRENT LOADS ON TYPICAL OFFSHORE STRUCTURES}, author = {Arjen Koop and Christiaan Klaij and Guilherme Vaz}, url = {http://www.refresco.org/download/2011marine2011_koopklayvaz_currentcoefs_msfs/}, year = {2013}, date = {20130928}, address = {Lisbon, Portugal}, organization = {MARINE2011}, abstract = {In this paper, CFD calculations for current loads on an LNG carrier and a semisubmersible are presented, both for model and fullscale situations, for current angles ranging from 180 to 0 degrees. MARIN's inhouse URANS code ReFRESCO is used. Numerical studies are carried out concerning itera tive convergence and grid refinement. In total, more than 100 calculations have been performed. Detailed verification analysis is carried out using modern techniques, and numerical uncertainties are calculated. Afterwards, quantitative validation for modelscale Reynolds number is done taking into account numerical and experimental uncertainties. Scale effects on the current coefficients are investigated, having in mind the estimated numerical uncertainties, and unsteady effects are briefly studied. Good iterative convergence is obtained in most calculations, i.e. a decrease in residuals of more than 5 orders is achieved. The sensitivity to grid resolution has been investigated for both model and full scale using five consecutively refined grids and for 3 current headings. The differences in the solution between two consecutive refinements converge for all cases. The numerical uncertainties are larger for angles with small values of the loads. Comparison with experiments shows that ReFRESCO provides good quantitative prediction of the current loads at model scale: for angles with larger forces the CFD results are validated with 15% of uncertainty. To determine scale effects the numerical uncertainties must be considered in order to prevent wrong conclusions drawn on basis of numerical differences rather than on physical differences. For the fullscale results larger numerical uncertainties are found than for model scale and for absolute values for scale effects this uncertainty should be improved. For the LNG carrier significant scale effects, i.e. more than 40%, have been obtained for current angles where the friction component is dominant. For these cases the numerical uncertainty is relatively low. For the other current angles differences of 830% between model and full scale can be observed, but here larger numerical uncertainties are found. For the semisubmersible the numerical uncertainties for the fullscale results are larger than for the LNG carrier. For the semisubmersible the pressure component of the force is highly dominant, i.e. larger than 90% of the total force. On average the fullscale current coefficients are 20% lower than at model scale, but larger differences for a number of angles can be observed.}, keywords = {CFD, Current Loads, LNG Carrier, RANS, Scale Eects, Semi submersible, Validation, Verication}, pubstate = {published}, tppubtype = {conference} } In this paper, CFD calculations for current loads on an LNG carrier and a semisubmersible are presented, both for model and fullscale situations, for current angles ranging from 180 to 0 degrees. MARIN's inhouse URANS code ReFRESCO is used. Numerical studies are carried out concerning itera tive convergence and grid refinement. In total, more than 100 calculations have been performed. Detailed verification analysis is carried out using modern techniques, and numerical uncertainties are calculated. Afterwards, quantitative validation for modelscale Reynolds number is done taking into account numerical and experimental uncertainties. Scale effects on the current coefficients are investigated, having in mind the estimated numerical uncertainties, and unsteady effects are briefly studied. Good iterative convergence is obtained in most calculations, i.e. a decrease in residuals of more than 5 orders is achieved. The sensitivity to grid resolution has been investigated for both model and full scale using five consecutively refined grids and for 3 current headings. The differences in the solution between two consecutive refinements converge for all cases. The numerical uncertainties are larger for angles with small values of the loads. Comparison with experiments shows that ReFRESCO provides good quantitative prediction of the current loads at model scale: for angles with larger forces the CFD results are validated with 15% of uncertainty. To determine scale effects the numerical uncertainties must be considered in order to prevent wrong conclusions drawn on basis of numerical differences rather than on physical differences. For the fullscale results larger numerical uncertainties are found than for model scale and for absolute values for scale effects this uncertainty should be improved. For the LNG carrier significant scale effects, i.e. more than 40%, have been obtained for current angles where the friction component is dominant. For these cases the numerical uncertainty is relatively low. For the other current angles differences of 830% between model and full scale can be observed, but here larger numerical uncertainties are found. For the semisubmersible the numerical uncertainties for the fullscale results are larger than for the LNG carrier. For the semisubmersible the pressure component of the force is highly dominant, i.e. larger than 90% of the total force. On average the fullscale current coefficients are 20% lower than at model scale, but larger differences for a number of angles can be observed.  
Koop, Arjen; Klaij, Christiaan; Vaz, Guilherme ViscousFlow Calculations for Model and FullScale Current Loads on Typical Offshore Structures Journal Article Computational Methods in Applied Sciences, 29 (Part1), pp. 329, 2013. Abstract  Links  BibTeX  Tags: Current Loads, Drag, Lift, LNG Carrier, RANS, Resistance, ScaleEffects, Semisubmersibles, Ships, SST, Validation, Verification @article{2013CMAS_Koop_et_al_CurrentLoads, title = {ViscousFlow Calculations for Model and FullScale Current Loads on Typical Offshore Structures}, author = {Arjen Koop and Christiaan Klaij and Guilherme Vaz}, url = { http://www.refresco.org/?wpdmpro=2011_marine2011springer_koopklaijvazpdf}, doi = {DOI: 10.1007/9789400761438_1}, year = {2013}, date = {20130201}, journal = {Computational Methods in Applied Sciences}, volume = {29}, number = {Part1}, pages = {329}, abstract = {In this paper, CFD calculations for current loads on an LNG carrier and a semisubmersible are presented, both for model and fullscale situations, for current angles ranging from 180 to 0 degrees. MARIN’s inhouse URANS code ReFRESCO is used. Numerical studies are carried out concerning iterative convergence and grid refinement. In total,more than 100 calculations have been performed. Detailed verification analysis is carried out using modern techniques, and numerical uncertainties are calculated. Afterwards, quantitative validation for modelscale Reynolds number is done taking into account numerical and experimental uncertainties. Scale effects on the current coefficients are investigated, having in mind the estimated numerical uncertainties, and unsteady effects are briefly studied. Good iterative convergence is obtained in most calculations, i.e. a decrease in residuals of more than 5 orders is achieved. The sensitivity to grid resolution has been investigated for both model and full scale using five consecutively refined grids and for 3 current headings. The differences in the solution between two consecutive refinements converge for all cases. The numerical uncertainties are larger for angles with small values of the loads. Comparison with experiments shows that ReFRESCO provides good quantitative prediction of the current loads at model scale: for angles with larger forces the CFD results are validated with 15 % of uncertainty. To determine scale effects the numerical uncertainties must be considered in order to prevent wrong conclusions drawn on basis of numerical differences rather than on physical differences. For the fullscale results larger numerical uncertainties are found than for model scale and for absolute values for scale effects this uncertainty should be improved. For the LNG carrier significant scale effects, i.e. more than 40 %, have been obtained for current angles where the friction component is dominant. For these cases the numerical uncertainty is relatively low. For the other current angles differences of 8–30 % between model and full scale can be observed, but here larger numerical uncertainties are found. For the semisubmersible the numerical uncertainties for the fullscale results are larger than for the LNG carrier. For the semisubmersible the pressure component of the force is highly dominant, i.e. larger than 90 % of the total force. On average the fullscale current coefficients are 20 % lower than at model scale, but larger differences for a number of angles can be observed.}, keywords = {Current Loads, Drag, Lift, LNG Carrier, RANS, Resistance, ScaleEffects, Semisubmersibles, Ships, SST, Validation, Verification}, pubstate = {published}, tppubtype = {article} } In this paper, CFD calculations for current loads on an LNG carrier and a semisubmersible are presented, both for model and fullscale situations, for current angles ranging from 180 to 0 degrees. MARIN’s inhouse URANS code ReFRESCO is used. Numerical studies are carried out concerning iterative convergence and grid refinement. In total,more than 100 calculations have been performed. Detailed verification analysis is carried out using modern techniques, and numerical uncertainties are calculated. Afterwards, quantitative validation for modelscale Reynolds number is done taking into account numerical and experimental uncertainties. Scale effects on the current coefficients are investigated, having in mind the estimated numerical uncertainties, and unsteady effects are briefly studied. Good iterative convergence is obtained in most calculations, i.e. a decrease in residuals of more than 5 orders is achieved. The sensitivity to grid resolution has been investigated for both model and full scale using five consecutively refined grids and for 3 current headings. The differences in the solution between two consecutive refinements converge for all cases. The numerical uncertainties are larger for angles with small values of the loads. Comparison with experiments shows that ReFRESCO provides good quantitative prediction of the current loads at model scale: for angles with larger forces the CFD results are validated with 15 % of uncertainty. To determine scale effects the numerical uncertainties must be considered in order to prevent wrong conclusions drawn on basis of numerical differences rather than on physical differences. For the fullscale results larger numerical uncertainties are found than for model scale and for absolute values for scale effects this uncertainty should be improved. For the LNG carrier significant scale effects, i.e. more than 40 %, have been obtained for current angles where the friction component is dominant. For these cases the numerical uncertainty is relatively low. For the other current angles differences of 8–30 % between model and full scale can be observed, but here larger numerical uncertainties are found. For the semisubmersible the numerical uncertainties for the fullscale results are larger than for the LNG carrier. For the semisubmersible the pressure component of the force is highly dominant, i.e. larger than 90 % of the total force. On average the fullscale current coefficients are 20 % lower than at model scale, but larger differences for a number of angles can be observed.  
2011 

Koop, Arjen; Klaij, Christiaan; Vaz, Guilherme ViscousFlow Calculations for Model and FullScale Current Loads on Typical Offshore Structures Conference IV International Conference on Computational Methods in Marine Engineering (ECCOMAS MARINE), Lisbon, Portugal, 2011. Abstract  Links  BibTeX  Tags: Current Loads, offshore, RANS @conference{Koop2011b, title = {ViscousFlow Calculations for Model and FullScale Current Loads on Typical Offshore Structures}, author = {Arjen Koop and Christiaan Klaij and Guilherme Vaz}, editor = {Arjen Koop and Christiaan Klaij and Guilherme Vaz}, url = {http://www.refresco.org/download/2011marine2011_koopklayvaz_currentcoefs_msfspdf/}, doi = {10.1007/9789400761438_1}, year = {2011}, date = {20110928}, booktitle = {IV International Conference on Computational Methods in Marine Engineering (ECCOMAS MARINE), Lisbon, Portugal}, abstract = {In this paper, CFD calculations for current loads on an LNG carrier and a semisubmersible are presented, both for model and fullscale situations, for current angles ranging from 180 to 0 degrees. MARIN’s inhouse URANS code ReFRESCO is used. Numerical studies are carried out concerning iterative convergence and grid refinement. In total,more than 100 calculations have been performed. Detailed verification analysis is carried out using modern techniques, and numerical uncertainties are calculated. Afterwards, quantitative validation for modelscale Reynolds number is done taking into account numerical and experimental uncertainties. Scale effects on the current coefficients are investigated, having in mind the estimated numerical uncertainties, and unsteady effects are briefly studied. Good iterative convergence is obtained in most calculations, i.e. a decrease in residuals of more than 5 orders is achieved. The sensitivity to grid resolution has been investigated for both model and full scale using five consecutively refined grids and for 3 current headings. The differences in the solution between two consecutive refinements converge for all cases. The numerical uncertainties are larger for angles with small values of the loads. Comparison with experiments shows that ReFRESCO provides good quantitative prediction of the current loads at model scale: for angles with larger forces the CFD results are validated with 15 % of uncertainty. To determine scale effects the numerical uncertainties must be considered in order to prevent wrong conclusions drawn on basis of numerical differences rather than on physical differences. For the fullscale results larger numerical uncertainties are found than for model scale and for absolute values for scale effects this uncertainty should be improved. For the LNG carrier significant scale effects, i.e. more than 40 %, have been obtained for current angles where the friction component is dominant. For these cases the numerical uncertainty is relatively low. For the other current angles differences of 8–30 % between model and full scale can be observed, but here larger numerical uncertainties are found. For the semisubmersible the numerical uncertainties for the fullscale results are larger than for the LNG carrier. For the semisubmersible the pressure component of the force is highly dominant, i.e. larger than 90 % of the total force. On average the fullscale current coefficients are 20 % lower than at model scale, but larger differences for a number of angles can be observed.}, keywords = {Current Loads, offshore, RANS}, pubstate = {published}, tppubtype = {conference} } In this paper, CFD calculations for current loads on an LNG carrier and a semisubmersible are presented, both for model and fullscale situations, for current angles ranging from 180 to 0 degrees. MARIN’s inhouse URANS code ReFRESCO is used. Numerical studies are carried out concerning iterative convergence and grid refinement. In total,more than 100 calculations have been performed. Detailed verification analysis is carried out using modern techniques, and numerical uncertainties are calculated. Afterwards, quantitative validation for modelscale Reynolds number is done taking into account numerical and experimental uncertainties. Scale effects on the current coefficients are investigated, having in mind the estimated numerical uncertainties, and unsteady effects are briefly studied. Good iterative convergence is obtained in most calculations, i.e. a decrease in residuals of more than 5 orders is achieved. The sensitivity to grid resolution has been investigated for both model and full scale using five consecutively refined grids and for 3 current headings. The differences in the solution between two consecutive refinements converge for all cases. The numerical uncertainties are larger for angles with small values of the loads. Comparison with experiments shows that ReFRESCO provides good quantitative prediction of the current loads at model scale: for angles with larger forces the CFD results are validated with 15 % of uncertainty. To determine scale effects the numerical uncertainties must be considered in order to prevent wrong conclusions drawn on basis of numerical differences rather than on physical differences. For the fullscale results larger numerical uncertainties are found than for model scale and for absolute values for scale effects this uncertainty should be improved. For the LNG carrier significant scale effects, i.e. more than 40 %, have been obtained for current angles where the friction component is dominant. For these cases the numerical uncertainty is relatively low. For the other current angles differences of 8–30 % between model and full scale can be observed, but here larger numerical uncertainties are found. For the semisubmersible the numerical uncertainties for the fullscale results are larger than for the LNG carrier. For the semisubmersible the pressure component of the force is highly dominant, i.e. larger than 90 % of the total force. On average the fullscale current coefficients are 20 % lower than at model scale, but larger differences for a number of angles can be observed.  
Koop, Arjen; Bereznitski, Alexei ModelScale And FullScale CFD Calculations For Current Loads On SemiSubmersible Conference 30th International Conference on Ocean, Offshore and Arctic Engineering (OMAE), Rotterdam, The Netherlands, 2011. Abstract  Links  BibTeX  Tags: Current Loads, offshore, RANS @conference{Koop2011b, title = {ModelScale And FullScale CFD Calculations For Current Loads On SemiSubmersible}, author = {Arjen Koop and Alexei Bereznitski}, editor = {Arjen Koop and Alexei Bereznitski}, url = {http://www.refresco.org/download/2011omae49204akabhuijsmanssemipdf/}, year = {2011}, date = {20110619}, booktitle = {30th International Conference on Ocean, Offshore and Arctic Engineering (OMAE), Rotterdam, The Netherlands}, abstract = {In this paper results of CFD calculations with the MARIN inhouse code ReFRESCO are presented for the JBF14000 SemiSubmersible designed by Huisman Equipment BV. The objective of the CFD calculations is to investigate the applicability, the costs and the accuracy of CFD to obtain the current coefficients of a semisubmersible for all headings. Furthermore, full scale CFD calculations are carried out to investigate possible scale effects on the current coefficients. An extensive verification study has been carried for the modelscale current loads on a semisubmersible using 10 different grids of different grid type for 3 different headings, i.e. 180, 150 and 90 degrees. These headings represent the main different flow regions around the semisubmersible. The CFD results are compared with the results from wind tunnel experiments and tests in the Offshore Basin for a range of current headings. The results for the force coefficients are not very dependent on grid resolution and grid type. The largest differences found are less than 10% and these are obtained for CX results for 180 degrees. For the results obtained on the same grid type the results change less than 4% when the grid is refined. These verification results give good confidence in the CFD results. For the angles with larger forces, i.e. the range [180:130] for CX and the range [150:90] for CY the CFD results are within 12% or better from the experiments. Fullscale force coefficients are calculated using 5 subsequently refined grids for three different headings, i.e. 180, 150 and 90 degrees. Scale effects should only be determined when the effect of grid refining is investigated. The trend of the force coefficients when refining the grid, can be different for modelscale and fullscale. The use of coarse grids can lead to misleading conclusions. On average the fullscale values are approximately 1520% lower than for modelscale. However, larger differences for a number of angles do exist.}, keywords = {Current Loads, offshore, RANS}, pubstate = {published}, tppubtype = {conference} } In this paper results of CFD calculations with the MARIN inhouse code ReFRESCO are presented for the JBF14000 SemiSubmersible designed by Huisman Equipment BV. The objective of the CFD calculations is to investigate the applicability, the costs and the accuracy of CFD to obtain the current coefficients of a semisubmersible for all headings. Furthermore, full scale CFD calculations are carried out to investigate possible scale effects on the current coefficients. An extensive verification study has been carried for the modelscale current loads on a semisubmersible using 10 different grids of different grid type for 3 different headings, i.e. 180, 150 and 90 degrees. These headings represent the main different flow regions around the semisubmersible. The CFD results are compared with the results from wind tunnel experiments and tests in the Offshore Basin for a range of current headings. The results for the force coefficients are not very dependent on grid resolution and grid type. The largest differences found are less than 10% and these are obtained for CX results for 180 degrees. For the results obtained on the same grid type the results change less than 4% when the grid is refined. These verification results give good confidence in the CFD results. For the angles with larger forces, i.e. the range [180:130] for CX and the range [150:90] for CY the CFD results are within 12% or better from the experiments. Fullscale force coefficients are calculated using 5 subsequently refined grids for three different headings, i.e. 180, 150 and 90 degrees. Scale effects should only be determined when the effect of grid refining is investigated. The trend of the force coefficients when refining the grid, can be different for modelscale and fullscale. The use of coarse grids can lead to misleading conclusions. On average the fullscale values are approximately 1520% lower than for modelscale. However, larger differences for a number of angles do exist.  
2010 

Fathi, Fahd; Klaij, Christiaan; Koop, Arjen Predicting Loads on an LNG Carrier with CFD Conference Proceedings of the 29th International Conference on Ocean, Offshore and Arctic Engineering, OMAE 2010, June 611, 2010, Shanghai, China, 2010. Abstract  Links  BibTeX  Tags: Current Loads, offshore, RANS @conference{Fathi2010, title = {Predicting Loads on an LNG Carrier with CFD}, author = {Fahd Fathi and Christiaan Klaij and Arjen Koop}, editor = {Fahd Fathi and Christiaan Klaij and Arjen Koop}, url = {http://www.refresco.org/download/2010omae20122fathiklaijkooppdfs/}, year = {2010}, date = {20100610}, booktitle = {Proceedings of the 29th International Conference on Ocean, Offshore and Arctic Engineering, OMAE 2010, June 611, 2010, Shanghai, China}, abstract = {The Current Affairs Joint Industry Project was initiated to develop the understanding and tools for the assessment of current loads on offshore structures. CFD is one of these tools requiring a good understanding of the underlying physical and mathematical models. In order to assess its suitability for the prediction of current loads on monohulls, the flow around a LNG carrier for which model scale data is available was considered. The LNG carrier, including bilgekeels and rudder, was towed at scale 1/50 in Marin's shallow water basin during the HAWAI JIP, for flow angles between 0 and 180 degrees. The measurements were shared with the Current Affairs JIP, for which the participants were invited to perform CFD computations reproducing the model test results. A number of these simulations are presented in this paper. The analysis of the results includes discussion on the grid generation as well as the numerical and physical parameters of the simulation. The comparison between experiments and computations shows that CFD can provide good qualitative predictions for the variation of force coefficients with inflow angle. The origin of the result variability between the participants is discussed and attention is drawn to the different factors influencing the quality of the simulation.}, keywords = {Current Loads, offshore, RANS}, pubstate = {published}, tppubtype = {conference} } The Current Affairs Joint Industry Project was initiated to develop the understanding and tools for the assessment of current loads on offshore structures. CFD is one of these tools requiring a good understanding of the underlying physical and mathematical models. In order to assess its suitability for the prediction of current loads on monohulls, the flow around a LNG carrier for which model scale data is available was considered. The LNG carrier, including bilgekeels and rudder, was towed at scale 1/50 in Marin's shallow water basin during the HAWAI JIP, for flow angles between 0 and 180 degrees. The measurements were shared with the Current Affairs JIP, for which the participants were invited to perform CFD computations reproducing the model test results. A number of these simulations are presented in this paper. The analysis of the results includes discussion on the grid generation as well as the numerical and physical parameters of the simulation. The comparison between experiments and computations shows that CFD can provide good qualitative predictions for the variation of force coefficients with inflow angle. The origin of the result variability between the participants is discussed and attention is drawn to the different factors influencing the quality of the simulation.  
2009 

Vaz, Guilherme; Waals, Olaf; Ottens, Harald; Fathi, Fahd; Souëf, Tim Le; Kiu, Kwong Proceedings of ASME 28th International Conference on Ocean, Offshore and Arctic Engineering OMAE2009 May 31June 5, 2009, Honolulu, Hawaii, 2009. Abstract  Links  BibTeX  Tags: Current Loads, offshore, URANS, Validation, Verification @conference{2009OMAE80216_VazWaalsOttensFathiSouefKiu, title = {Current Affairs: Model Tests, SemiEmpirical Predictions and CFD Computations for Current Coefficients of SemiSubmersibles}, author = {Guilherme Vaz and Olaf Waals and Harald Ottens and Fahd Fathi and Tim Le Souëf and Kwong Kiu}, url = {http://www.refresco.org/download/2009omae80216_vazwaalsottensfathisouefkiupdf http://www.asmeconferences.org/}, year = {2009}, date = {20090531}, booktitle = {Proceedings of ASME 28th International Conference on Ocean, Offshore and Arctic Engineering OMAE2009 May 31June 5, 2009, Honolulu, Hawaii}, abstract = {Current loads on stationary vessels have been investigated as part of the Current Affairs Joint Industry project (JIP). Modeltests, semiempirical models and CFD methods were used to predict these loads. This paper examines one configuration out of the eight tested in the JIP; an idealized semisubmersible consisting of two square roundedcorner columns connected with a pontoon. The model experiments, empirical model predictions and CFD results are presented and discussed. ‘Blind’ and ‘Improved’ CFD computations (with and without knowledge of the experimental results) have been carried out by the JIP participants. Comparisons between these results are made, deviations from the experimental data are quantified and conclusions are drawn. Two key issues for modeling accuracy are identified and discussed; the location of the transition to turbulent flow and the control of the numerical errors.}, keywords = {Current Loads, offshore, URANS, Validation, Verification}, pubstate = {published}, tppubtype = {conference} } Current loads on stationary vessels have been investigated as part of the Current Affairs Joint Industry project (JIP). Modeltests, semiempirical models and CFD methods were used to predict these loads. This paper examines one configuration out of the eight tested in the JIP; an idealized semisubmersible consisting of two square roundedcorner columns connected with a pontoon. The model experiments, empirical model predictions and CFD results are presented and discussed. ‘Blind’ and ‘Improved’ CFD computations (with and without knowledge of the experimental results) have been carried out by the JIP participants. Comparisons between these results are made, deviations from the experimental data are quantified and conclusions are drawn. Two key issues for modeling accuracy are identified and discussed; the location of the transition to turbulent flow and the control of the numerical errors.  
Toxopeus, Serge; Vaz, Guilherme Calculation Of Current Or Manoeuvring Forces Using A ViscousFlow Solver Conference Proceedings of ASME 28th International Conference on Ocean, Offshore and Arctic Engineering OMAE2009 May 31June 5, 2009, Honolulu, Hawaii, 2009. Abstract  Links  BibTeX  Tags: Current Loads, Manoeuvring, URANS, Validation, Verification @conference{2009OMAE79782ToxopeusVaz, title = {Calculation Of Current Or Manoeuvring Forces Using A ViscousFlow Solver}, author = {Serge Toxopeus and Guilherme Vaz}, url = {http://www.refresco.org/download/2009omae79782toxopeusvazpdf http://www.asmeconferences.org/}, year = {2009}, date = {20090531}, booktitle = {Proceedings of ASME 28th International Conference on Ocean, Offshore and Arctic Engineering OMAE2009 May 31June 5, 2009, Honolulu, Hawaii}, journal = {Proceedings of ASME 28th International Conference on Ocean, Offshore and Arctic Engineering OMAE2009 May 31June 5, 2009, Honolulu, Hawaii}, abstract = {To investigate the capabilities of using a viscousflow solver to calculate current or manoeuvring forces on ship hulls, calculations have been conducted for a test hull under several oblique inflow conditions. All calculations were performed with a single grid topology to reduce the amount of grid generation time. Verification and validation of the predicted loads and flow around the hull has been performed through grid refinement studies and comparison with experiments and results from previous calculations. Furthermore, the influence of unsteady behaviour on the results for large inflow angles is shown. Conclusions are drawn regarding the accuracy of the results and recommendations for improvements and further work are given.}, keywords = {Current Loads, Manoeuvring, URANS, Validation, Verification}, pubstate = {published}, tppubtype = {conference} } To investigate the capabilities of using a viscousflow solver to calculate current or manoeuvring forces on ship hulls, calculations have been conducted for a test hull under several oblique inflow conditions. All calculations were performed with a single grid topology to reduce the amount of grid generation time. Verification and validation of the predicted loads and flow around the hull has been performed through grid refinement studies and comparison with experiments and results from previous calculations. Furthermore, the influence of unsteady behaviour on the results for large inflow angles is shown. Conclusions are drawn regarding the accuracy of the results and recommendations for improvements and further work are given. 