simman 2014 - vliz · 3.0 13/08/2015 final version van hoydonck, w. abstract this report contains...

WL Rapporten00_066

SHALLOW-WATER CFD COMPUTATIONS

SIMMAN 2014

Vlaamse overheid

SIMMAN 2014

Shallow-water CFD Computations

Van Hoydonck, W.; Delefortrie, G.; Eloot, K.; Peeters, P.; Mostaert, F.

August 2015

WL2015R00_066_3

fhr.cls2015/08/18 – version 0.14

This publication must be cited as follows:

Van Hoydonck, W.; Delefortrie, G.; Eloot, K.; Peeters, P.; Mostaert, F. (2015). SIMMAN 2014: Shallow-waterCFD Computations. Version 3.0. WL Rapporten, 00_066. Flanders Hydraulics Research: Antwerp, Belgium.

Waterbouwkundig Laboratorium

Flanders Hydraulics Research

Berchemlei 115B-2140 AntwerpTel.+32 (0)3 224 60 35Fax +32 (0)3 224 60 36E-mail: [email protected]

Nothing from this publication may be duplicated and/or published by means of print, photocopy, microfilm orotherwise, without the written consent of the publisher.


F-WL-PP10-1 Versie 04 GELDIG VANAF: 12/11/2012

Document identification

Title: SIMMAN 2014: Shallow-water CFD Computations

Customer: Waterbouwkundig Laboratorium Ref.: WL2015R00_066_3

Keywords (3-5): CFD, shallow water, SIMMAN 2014

Text (p.): 31 Appendices (p.): 5

Confidentiality: ☐ Yes Exceptions: ☐ Customer

☐ Internal

☐ Flemish government

Released as from: August 2015

☒ No ☐ Available online

Approval

Author Van Hoydonck, W

Reviser Delefortrie, G.

Eloot, K.

Project Leader Delefortrie, G.

Research & Consulting Manager Peeters, P.

Head of Division Mostaert, F.

Revisions

Nr. Date Definition Author(s)

1.0 01/07/2015 Concept version Van Hoydonck, W.

2.0 06/08/2015 Substantive revision Delefortrie, G.; Eloot, K.

3.0 13/08/2015 Final version Van Hoydonck, W.

Abstract

This report contains an overview of the computational work done for the 2014 SIMMAN workshop. It is based on a paper submitted for the workshop proceedings and a poster that was presented at the workshop. Three test cases (1b-1, 1b-3 and 1c-1) were selected for CFD computations. Of these, the latter two have a drift angle of 4 degrees, for case 1b-1, the ship sails straight ahead. A grid convergence study was executed for case 1c-1. All computations were carried out blind (so without knowing the experimental values). In addition to the contents of the paper, this report contains an analysis of the experimental data used as a reference, a comparison of the CFD result with the EFD results, and some flow visualisations that were not included in the paper due to page limitations. Apart from the lateral force for case 1b-1 (without drift), results are in very good agreement with the experimental data.

SIMMAN 2014: Shallow-water CFD Computations

Contents

1 Introduction .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2 Analysis of experimental data .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.1 Rail alignment corrections .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.2 Averages and standard deviations for case 1b-3 .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42.3 Averages and standard deviations for case 1b-1 .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.4 Averages and standard deviations for case 1c-1 .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62.5 Time history analysis .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

3 Computational Setup .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103.1 Test conditions .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103.2 KVLCC2 CAD Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113.3 Domain Size and Ship Position .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113.4 Topology and General Refinement Settings .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123.5 Solution Method and Flow Settings .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4 Grid convergence study for case 1c-1 .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144.1 Base meshes .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144.2 Generation of derived meshes .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144.3 Results .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

5 Cases 1b-1 and 1b-3 .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185.1 Setup .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185.2 Results .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

6 Comparison of CFD and EFD results.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

7 Flow visualisations .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247.1 Water surface.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247.2 Hydrodynamic pressure on the hull and tank.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

8 Conclusions .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

References .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

A Additional time analysis plots of the EFD data .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

B Additional views of the grid using cutplanes .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Final versionfhr.cls2015/08/18 – version 0.14

WL2015R00_066_3 iv


List of Figures

Figure 1 Fore and aft rail alignment corrections for T0Z02A03 and T0Z03A03 tests. T0Z03A03shows suspicious oscillations during the first 30 meter and the last 10 meter of the test.. . . 4

Figure 2 Thrust versus torque for test cases T0Z02A03_C4700x. The numbers next to the blackpoints denote the last number of the test identification (see Table 1). . . . . . . . . . . . . . . . . . . . . . . . . . 5

Figure 3 Thrust versus X-force for test cases T0Z02A03_C4700x. The numbers next to the blackpoints denote the last number of the test identification (see Table 1). . . . . . . . . . . . . . . . . . . . . . . . . . 5

Figure 4 Measured sinkages for test T0Z03A03_C47000 showing multiple time intervals with con-stant measured value.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Figure 5 Convergence of total X-force for test T0Z02A03_C40000. .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Figure 6 Convergence of propeller torque for test T0Z02A03_C40000. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Figure 7 Convergence of total Y-force for test T0Z02A03_C40000. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Figure 8 Convergence of midship sinkage for test T0Z02A03_C40000. .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Figure 9 Bottom, front, back and isometric view of the Parasolid CAD model of the KVLCC2 asused for the CFD computations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Figure 10 Top view of domain box with dimensions and global axis system orientation. . . . . . . . . . . . . . . . . 12Figure 11 Overview of refinement boxes and refinement surfaces with absolute target cell sizes. . . . . 13

Figure 12 View of the grid near the stern in the symmetry plane of the ship for the six different cases. 15Figure 13 Iterative convergence and final values for , and for 1c-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16Figure 14 Iterative convergence and final values for sinkage, pitch and for case 1c-1. . . . . . . . . . . . . 17

Figure 15 Graphical representation of the actuator disk properties listed in Table 11. .. . . . . . . . . . . . . . . . . . 19Figure 16 Iterative convergence for , , , sinkage and pitch for case 1b-1. . . . . . . . . . . . . . . . . . . . . . . . 20Figure 17 Iterative convergence for , , , sinkage and pitch for case 1b-3. . . . . . . . . . . . . . . . . . . . . . . . 21

Figure 18 Comparison of longitudinal forces. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22Figure 19 Comparison of lateral forces.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22Figure 20 Comparison of roll moments.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Figure 21 Comparison of yawing moments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Figure 22 Visualisation of the water surface coloured with the elevation for case 1c-1 (drift angle 4degrees).. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Figure 23 Visualisation of the water surface coloured with the elevation for case 1b-1 (straight ahead). 25Figure 24 Visualisation of the water surface coloured with the elevation for case 1b-3 with propulsion

(drift angle 4 ).. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Figure 25 Visualisation of the pressure coefficient on the submerged part of the ship and tank

walls for 1c-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Figure 26 Visualisation of the pressure coefficient on the submerged part of the ship and tank

walls for 1b-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28Figure 27 Visualisation of the pressure coefficient on the submerged part of the ship and tank

walls for 1b-3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Figure 28 Convergence of aft lateral force measurement for test T0Z02A03_C40000. .. . . . . . . . . . . . . . . . 32Figure 29 Convergence of fore lateral force measurement for test T0Z02A03_C40000... . . . . . . . . . . . . . . 32

Figure 30 View of the grid at the aft perpendicular (AP) of the ship. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33Figure 31 View of the grid at the mid section of the ship. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34Figure 32 View of the grid at the fore perpendicular (FP) of the ship. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35Figure 33 View of the grid near the bow in the symmetry plane of the ship. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36Figure 34 Overview of the grid in the symmetry plane of the ship. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36


WL2015R00_066_3 v


List of Tables

Table 1 Overview of the EFD tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Table 2 Averages, standard deviations and relative standard deviations for case 1b-3 rounded to

four significant digits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Table 3 Averages and standard deviations for case 1b-1 rounded to four significant digits. . . . . . . . . . . . 6Table 4 Averages and standard deviations for case 1c-1 rounded to four significant digits. . . . . . . . . . . . 6

Table 5 Reference conditions .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Table 6 Settings for refinement surfaces and refinement boxes with absolute target cell sizes as

shown in Fig. 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Table 7 Number of cells for the coarse, medium and fine initial Cartesian mesh for the case basedon /7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Table 8 Number of cells for the coarse, medium and fine initial Cartesian mesh for the case basedon /5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Table 9 Total cell count for the coarse, medium and fine meshes for case 1c-1 based on /7 and/5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Table 10 Thrust and torque values used as input for two of the CFD computations. . . . . . . . . . . . . . . . . . . . . . 18Table 11 Geometry properties of the actuator disk .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Table 12 Overview of results .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30


WL2015R00_066_3 vi


1 Introduction

Nautical research at Flanders Hydraulics Research (FHR) (Waterbouwkundig Laboratorium – Flanders Hy-draulics Research n.d.) focuses on ships manoeuvring in shallow and confined water. For this research atowing tank for manoeuvres in shallow water (cooperation FHR - Ghent University (Knowledge Centre Ma-noeuvring in Shallow and Confined Water n.d.)) is available where experimental research is conducted. Thetest results are used to generate mathematical manoeuvring models for fast-time and real-time simulations inshallow and confined water. Amongst others, these mathematical models are used in the ship simulators ofFHR where maritime pilots of the ports of Antwerp, Zeebrugge and Ghent receive training. Traditionally, exper-imental research has been the sole source of input for the mathematical manoeuvring models. In recent years,Computational Fluid Dynamics (CFD) has seen significant improvements in the computational algorithms re-lated to two-phase flows and in the mean time, the cost of the computational facilities to run the software inan efficient manner has decreased significantly. For these reasons, FHR has started to use CFD as an alter-native means to generate input for the mathematical manoeuvring models used in its real-time simulations. Avariety of shallow water test cases for the SIMMAN 2014 workshop were conducted at FHR (Delefortrie et al.,2011) with models of the KCS and KVLCC2 and for some of these, CFD computations are performed for theSIMMAN 2014 workshop. For the shallow water cases 1b-1, 1b-3 and 1c-1, computations are executed usingthe CFD package FINE/Marine.

This report is based on the paper that was written for the workshop (Van Hoydonck and Eloot, 2014). The CFDcomputations reported there were carried out blind, meaning that the experimental data could not be used tocompare results before the start of the workshop. The final workshop proceedings have not been publishedso the decision was made to include a comparison with experimental values in this report.

This report starts with an analysis of the experimental data in Chapter 2. Afterwards, in Chapter 3 the setupof the computations is discussed. This is followed in Chapter 4 by a grid convergence study for case 1c-1.The resulting grid settings are used for cases 1b-1 and 1b-3 as discussed in Chapter 5. A comparison ofthe numerical results with the experimental data is presented in Chapter 6 and the flow visualisations of thesolutions are shown in Chapter 7. Due to page limitations, these visualisations were not included in the paperfor the workshop. The report ends with conclusions.


WL2015R00_066_3 1


2 Analysis of experimental data

Since the SIMMAN workshop proceedings with the EFD-CFD comparisons haven’t been released, a compar-ison is added here. In this chapter, the EFD data is analysed.

Table 1 shows an overview of the experimental data (extracted from the DOC files) that is used as a reference.For one of the computational cases, the towing tank experiment was repeated 10 times, which means thatapart from average values, standard deviations can be computed as well. The standard deviations for thiscase will be used for the other two test cases as well. Inspection of Table 1 shows that the draft of the KVLCC2in the experiments (0.2759 m) is different from the draft that was requested in the CFD instructions (0.2776 m).As a result, the experiments were executed with a UKC value of 20.6% instead of 20.0% (that is, if the datastored in the DOC files is correct). The draft of the KVLCC2 reported in Delefortrie et al. (2011) and Delefortrieet al. (2014) differs from the values shown in the DOC files.

Averages for the captive stationary tests are computed from the data in the 30% and 95% time interval of thetest.

The following quantities are used in the comparison with CFD results and will be analysed here:

• Sinkage mid,

• Pitch,

• X-force,

• Y-force,

• X-moment,

• Z-moment,

• Propeller thrust,

• Propeller torque.

Of these, the X-moment is the only value that is directly recorded during the towing tank tests. The yawingmoment is computed from the lateral force measurements, the forces are summed from the fore and aftmeasurements and the sinkage at the midship location is a linear interpolation using the fore and aft sinkagemeasurements (after correction with the rail alignment data, see § 2.1). The pitch angle is also computed fromthe fore and aft sinkages.

2.1 Rail alignment corrections

The file with rail alignment correction data for CFD tests 1b-1 and 1b-3 is T0Z02A03_IJKR00.IJK. For test1c-1, the file with rail alignment correction data is T0Z03A03_IJKR00.IJK. The data recorded in these filesis shown Fig. 1. The overall shape of the rail alignment corrections are similar for both IJK files, however,T0Z03A03_IJKR00.IJK contains suspicious oscillations for the first 25 meter and the last 10 meter of themeasurement. It is very likely that these oscillations will be visible in a plot of the time series of the midshipsinkage of T0Z03A03_C47000. The original IJKR-test on which the data in T0Z03A03_IJKR00.IJK is basedalso contains these oscillations.


WL2015R00_066_3 2


Table1–OverviewoftheEFD

tests.

CFD

case

docfile

date

waterdepth

draft

ukc

heading

drift

lat.position

req.

prop.rate

Fr(v)

Fr(d)

velocity

samplingrate

/1c-1

T0Z0

3A03_C

47000.DOC

06/12/2010

0.3328

0.2759

20.6

4.0

4.0

-0.0001

0.0

0.064

0.23

0.416

40.0

1b-1

T0Z0

2A03_C

40000.DOC

12/11/2010

0.3328

0.2759

20.6

0.0

0.0

-400.104

0.064

0.23

0.416

40.0

1b-3

T0Z0

2A03_C

47000.DOC

10/11/2010

0.3328

0.2759

20.6

4.0

4.0

-0.0001

400.104

0.064

0.23

0.416

40.0

1b-3

T0Z0

2A03_C

47001.DOC

11/11/2010

0.3328

0.2759

20.6

4.0

4.0

0.0

400.104

0.064

0.23

0.416

40.0

1b-3

T0Z0

2A03_C

47002.DOC

11/11/2010

0.3328

0.2759

20.6

4.0

4.0

0.0

400.104

0.064

0.23

0.416

40.0

1b-3

T0Z0

2A03_C

47003.DOC

12/11/2010

0.3328

0.2759

20.6

4.0

4.0

-0.0001

400.104

0.064

0.23

0.416

40.0

1b-3

T0Z0

2A03_C

47004.DOC

12/11/2010

0.3328

0.2759

20.6

4.0

4.0

0.0

400.104

0.064

0.23

0.416

40.0

1b-3

T0Z0

2A03_C

47005.DOC

12/11/2010

0.3328

0.2759

20.6

4.0

4.0

0.0

400.104

0.064

0.23

0.416

40.0

1b-3

T0Z0

2A03_C

47006.DOC

13/11/2010

0.3328

0.2759

20.6

4.0

4.0

-0.0001

400.104

0.064

0.23

0.416

40.0

1b-3

T0Z0

2A03_C

47007.DOC

14/11/2010

0.3328

0.2759

20.6

4.0

4.0

0.0

400.104

0.064

0.23

0.416

40.0

1b-3

T0Z0

2A03_C

47008.DOC

14/11/2010

0.3328

0.2759

20.6

4.0

4.0

0.0

400.104

0.064

0.23

0.416

40.0

1b-3

T0Z0

2A03_C

47009.DOC

14/11/2010

0.3328

0.2759

20.6

4.0

4.0

0.0

400.104

0.064

0.23

0.416

40.0


WL2015R00_066_3 3


Figure 1 – Fore and aft rail alignment corrections for T0Z02A03 and T0Z03A03 tests. T0Z03A03 shows suspiciousoscillations during the first 30 meter and the last 10 meter of the test.

2.2 Averages and standard deviations for case 1b-3

Between 10 and 14 November 2010, ten tests were executed for the condition of case 1b-3 (see Table 1). Bycomputing averages for the aforementioned quantities for each of these tests, the spread in the values can becomputed. This way, an uncertainty band can be determined for the reference values.

In Fig. 2, the thurst and torque values for the 10 tests are shown. The average value and its standard deviationare shown in red. Figure 3 shows the values of as a function of thurst for the same 10 test cases. Theaverages, standard deviations and relative standard deviations are shown in Table 2. Since these valueswere computed using a set of Python scripts that utilize the original DOC files as input, it is possible that slightdifferences are present when the values are compared to average values computed using the derived KRTfiles using ZeeMan.

Table 2 – Averages, standard deviations and relative standard deviations for case 1b-3 rounded to four significant digits.

Quantity unit average std. rel. std. (%)

N -1.400 0.07797 5.569N 13.98 0.08694 0.6218Nm -0.6224 0.02452 3.939Nm 14.92 0.05939 0.3980

Sinkage mm 3.899 0.01905 0.4885Pitch deg -0.04324 0.0003857 0.8920

N 2.616 0.1719 6.572Nmm 47.61 2.253 4.731


WL2015R00_066_3 4


Figure 2 – Thrust versus torque for test cases T0Z02A03_C4700x. The numbers next to the black points denote the lastnumber of the test identification (see Table 1).

Figure 3 – Thrust versus X-force for test cases T0Z02A03_C4700x. The numbers next to the black points denote the lastnumber of the test identification (see Table 1).

2.3 Averages and standard deviations for case 1b-1

For case 1b-1, only one test was executed in the towing tank at FHR (T0Z02A03_C40000.DOC). Hence,the reference values are computed from this one test. Standard deviations are estimated using the relativestandard deviations computed for case 1b-3. The resulting are presented in Table 3.


WL2015R00_066_3 5


Table 3 – Averages and standard deviations for case 1b-1 rounded to four significant digits.

Quantity unit average std.

N -0.6588 0.03669N 1.127 0.007006Nm 0.01025 0.0004035Nm 0.9256 0.003684

Sinkage mm 3.45 0.01685Pitch deg -0.03877 0.0003458

N 3.198 0.2101Nmm 54.86 2.596

2.4 Averages and standard deviations for case 1c-1

Similar to case 1b-1, only one test was executed in the towing tank at FHR for case 1c-1 (T0Z03A03_C47000.DOC).Hence, the reference values are computed from this one test. Standard deviations are estimated using therelative standard deviations computed for case 1b-3. The resulting values are presented in Table 4. This casewas executed using a bare hull, hence thrust and torque values are not included.

Table 4 – Averages and standard deviations for case 1c-1 rounded to four significant digits.

Quantity unit average std.

N -3.693 0.2056N 12.55 0.07802Nm -0.4456 0.01755Nm 16.33 0.06497

Sinkage mm 3.654 0.01785Pitch deg -0.04983 0.0004445

2.5 Time history analysis

In this section, some time history plots of the experimental quantities of interest will be shown1. For eachquantity shown, the normalized cumulative moving average (nCMA) and the normalized cumulative standarddeviation (nCSTD) are computed for the part of the test that is used to compute average values. The derivativesof these two quantities can be used to judge the convergence of the time history of the quantity: if the derivativeof nCMA decreases as time progresses, the cumulative moving average converges towards a fixed value. Thesame holds true for the standard deviation: if its derivative decreases as time progresses, the magnitude ofthe fluctuations converges as well. In addition, the frequency content of the data is shown using an FFT plot.This data can be used to find trends in the data: if the lowest frequencies have the highest value, the quantityis not stationary in time but contains a trend.

It should be noted that while processing the DOC files, it was noticed that the measured values for the foresinkage measurement remain exactly the same for longer time periods (in some cases 10 seconds or more).This is only observed for the fore sinkage, not the aft sinkage. In a single measurement, it can occur multipletimes, and the measured value is exactly the same. It appears as if the measurement device is stuck duringthese time intervals. The top graph in Fig. 4 shows multiple intervals like these, the longest one takes approx-imately 10 seconds and starts at = 112 . There is another one that starts at = 173 , right before the start of

1Eight plots (one for each quantity) are created for each of the data sets, which amounts to 96 plots. At two plots per page, this wouldadd 48 pages to the report. The plots are available upon request.


WL2015R00_066_3 6


the deceleration phase of the test. After correcting the measured sinkages with the rail alignment corrections,these intervals with constant measured values disappear.

Figure 4 – Measured sinkages for test T0Z03A03_C47000 showing multiple time intervals with constant measured value.

Figure 5 shows the convergence characteristics of the total measured X-force (the sum of the forward and aftmeasurements) for test T0Z02A03_C40000. During the last twenty seconds of the measurement interval, thenCMA value remains within 2% of the final value. The fluctuations around the average remain within 2% ofthe final value for the last 40 seconds. The dominant frequency for this time signal is 2.4 Hz.

For the same test, Fig. 6 shows the convergence of the propeller torque and in Fig. 7 the convergence analysisof total lateral force is shown. According to the DOC file for this case (see Table 1), the requested propellerrate was about 400 rpm or 6.66 Hz. This value is the dominant frequency in the lower plot of Fig. 6. Thetwo-per-rev frequency (at 13.3 Hz) is also clearly visible. The three-per-rev frequency is just visible at 20 Hz,the Nyquist frequency of the recording (the sampling rate for the experiments equals 40 Hz). Convergencefor the torque is very good, both the average value and the fluctuations.

The CMA convergence of the lateral force (Fig. 7) is not as good as the convergence for the longitudinalforce. The time history plot shows signficant fluctuations in the amplitude, which is reflected in the plot of thenormalised cumulative standard deviation. Also, the average value converges only very slowly towards itsfinal value, with deviations up to 20% from the final value during the last minute of the measurement interval.The frequency plot shows that the dominant frequency is located at 19.6 Hz (this may not be clear from thefigure itself but a close inspection of the interactive figure shows that the peak at 19.6 Hz is indeed the highestone). A broad peak centered at f = 3.2 Hz is only slightly lower in magnitude. The signals with the lowestfrequencies also have a significant power. Inspection of the time series of the fore and aft components fromwhich the lateral force is computed, shows that the average of the fore measurement is close to the averageof the total lateral force. The average of the aft measurement is close to zero. The plots for the fore and aftmeasurements are displayed in Appendix A.

The sinkage at the midship location is computed from the fore and aft sinkage measurements and shown inFig. 8. Low-frequency oscillations dominate the time signal. Convergence towards the final mean value isreasonable: the nCMA of the sinkage remains within 2% of the final value for the last minute of the measure-ment interval. Although the convergence of the nCMA appear erratic, the derivatives are smaller than 10 4 forthe last 110 seconds of the measurement interval, which is significantly better than the convergence of e.g.the X-force (Fig. 5).


WL2015R00_066_3 7


Figure 5 – Convergence of total X-force for test T0Z02A03_C40000.

Figure 6 – Convergence of propeller torque for test T0Z02A03_C40000.


WL2015R00_066_3 8


Figure 7 – Convergence of total Y-force for test T0Z02A03_C40000.

Figure 8 – Convergence of midship sinkage for test T0Z02A03_C40000.


WL2015R00_066_3 9


3 Computational Setup

3.1 Test conditions

This section contains the relevant data related to the CFD computations documented in this report that wasprovided by the organizing committee of SIMMAN 2014. Cases 1b-1 and 1b-3 are characterized by:

• captive simulation in shallow still water condition;

• Pitch and heave free; otherwise restrained;

• Speed ratio / 0 = 1.0 with an approach speed 0 = 7 at full scale;• model length = 4.2667 ;• water depth: / = 1.2;• width of basin: 7.0 m;

• Tests performed at model self-propulsion point;

• Appendages: Propeller and rudder;

• Available EFD data:

– Static tests – Forces/Moments including rudder forces;

– Dynamic tests – Time histories of Forces/Moments including rudder forces;

For case 1c-1, the characteristics are:

• Bare hull captive simulation in shallow still water condition;

• Pitch and heave free; otherwise restrained;

• Speed ratio / 0 = 1.0 with an approach speed 0 = 7 ;• model length = 4.2667 ;• water depth: / = 1.2;• width of basin: 7.0 m;

• Appendages: none

• Available EFD data:

– Static tests – Forces/Moments;

A summary of the test conditions is listed in Table 5.

Table 5 – Reference conditions

TestNo - - m/s rps deg

1b-1 0.063 2 106 0.416 6.67 0 01b-3 0.063 2 106 0.416 6.67 4.0 0.0701c-1 0.063 2 106 0.416 - 4.0 0.070


WL2015R00_066_3 10


3.2 KVLCC2 CAD Model

A cleaned version of the IGES file that can be found on the SIMMAN website is available at FHR. It can befound in the /cfd/cfd/cad_models/ships/T0Z/parasolid/ folder on the cluster. The cleaned Parasolidfile (VLCCmodelscale_cf.x_t) is used by a set of domain creation scripts that automate the majority of tasksneeded for creating a setup of a CFD computation using FINE/Marine. The CAD model of the hull is shown inFig. 9. For the appended cases, a simplified rudder model is attached to the hull. For the bare hull case, thesmall part of the rudder attached to the hull is included as well.

Figure 9 – Bottom, front, back and isometric view of the Parasolid CAD model of the KVLCC2 as used for the CFDcomputations.

3.3 Domain Size and Ship Position

The three cases follow the same general setup. The computational domain is as wide as the towing tankwhere the experiments were executed (7 m). It extends 1.5 ahead of the ship bow and 2.5 aft of theship stern (see Fig. 10). The ship draft in the experiments is 0.2773 m (MOERI KVLCC2 Tanker – Geometryand conditions n.d.), which means that the water depth for a depth to draft ratio / = 1.2 is 0.3328 m.Above the water level, the domain extends 0.5 upward. In absolute dimensions, the length, width andheight of the domain box are 21.96 m, 7 m, and 2.46615 m, respectively. To prevent the cells below the hullfrom compressing too much in the final position, the ship is meshed three millimeters below the hydrostaticequilibrium.

In longitudinal direction, the aft perpendicular is located at the origin of the global axis system (as shown inFig. 10). For cases 1c-1 and 1b-3, the ship is rotated around its midship location, which is located at /2 onthe x-axis of the global axis system.

The initial location of the centre of gravity in the global axis system is 2.2825, 0, 0.3298, which is 3 mm belowthe water level. Using domhydro, a mass of 740.7429 kg was computed based on the given draft.


WL2015R00_066_3 11


1.5 Lpp2.5 Lpp7 m

21.96 m

2.46615 m

x

y

x

z

Figure 10 – Top view of domain box with dimensions and global axis system orientation.

3.4 Topology and General Refinement Settings

The hull of the KVLCC2 is simplified to the point where it consists of the deck surface, transom surface, twohull halves and the propeller shaft surface. For the appended cases (1b-1 and 1b-3), the rudder has a blunttrailing edge that is approximately 0.5 mm wide.

The global refinement diffusion factor is increased to five (from the default of two) to improve the prediction ofdrag.

All rudder surfaces have a refinement of 8, as does the propeller shaft surface. The transom and hull halvesget six refinements and the deck four. A refinement surface that covers the complete domain is used to capturethe complete water surface (Fig. 11a); a smaller surface located close to the ship increases the resolution ofthe water surface near the ship (Fig. 11b). The relevant refinement settings for these surfaces are displayedin Table 6. For the cases with propulsion, a refinement surface is added at the propeller location to increasethe cell count in this region.

Two refinement boxes are used to control the cell sizes of the water volume. The first one starts at the domaininlet and ends halfway between the ship transom and the domain outlet (Fig. 11c). The last one encloses therest of the water volume (Fig. 11d). Both of these boxes are volumic.

Three non-volumic refinement boxes are used to refine cells close to the ship hull. One of them covers thelast quarter of the hull, the second one covers the front eighth part of the hull. The last one covers the lowerpart of the hull and the tank bottom, and is as wide as the hull. Seven refinement levels are used for theseboxes, one more than the refinement level for the two hull halves.

By default, the target cell sizes as listed in Table 6 are used for the water surface refinement planes and thewater volume refinement boxes with absolute target cell sizes.

Table 6 – Settings for refinement surfaces and refinement boxes with absolute target cell sizes as shown in Fig. 11.

refinement surface/box

large refinement surface (Fig. 11a) /8 /8 /500small refinement surface (Fig. 11b) /16 /16 /1000front refinement box (Fig. 11c) /12.5 /50 /100aft refinement box (Fig. 11d) 3 /25 3 /100 3 /200

The final cell size for refinement surfaces depends on the initial cells size, which is used as a parameter in thegrid independence study as explained in the next section.


WL2015R00_066_3 12


(a) Large water surface refinement plane. (b) Small water surface refinement plane.

(c) Front water volume refinement box. (d) Aft water volume refinement box.

Figure 11 – Overview of refinement boxes and refinement surfaces with absolute target cell sizes.

High quality viscous layers are inserted on the hull and tank bottom to account for viscous effects. On the hull(and the rudder for 1b-1 and 1b-3), the target + value is smaller than 1, i.e., no wall functions are employed.For the tank bottom, wall functions are employed to model the velocity profile in the viscous layer.

3.5 Solution Method and Flow Settings

The density and dynamic viscosity of water (999.147 / 3 and 0.00114696 ) are based on standardsweet water (Anon., 2011) with a temperature of 14.7 degrees Celsius.

In all cases, the ship starts from rest, and is accelerated to the final velocity using a velocity profile based ona cosine function. At the start of a simulation, the ship degrees of freedom (sinkage and trim) are released aswell. The consequence of meshing the ship below the hydrostatic position at rest is that the initial motion ofthe ship will be upward, stretching the mesh below the ship.

The reference length is 4.2667 m, the length between perpendiculars of the ship model, and the referencevelocity is 0.416 m/s. For the computations reported here, the Reynolds number is about 1.5 106, whichcorresponds to fully turbulent flow. Results are computed by solving the incompressible, two-phase Reynolds-Averaged Navier-Stokes (RANS) equations, which means that the complete spectrum of turbulence (from thelargest scales down to the Kolmogorov scales) is modelled. The interface between the air and water phaseis tracked with a Volume-of-Fluid (VOF) method. The turbulence closure model used is the Explicit AlgebraicStress Model (EASM) (Anon., 2014). The boundary condition applied on the tank lateral sides and the shipdeck is a slip condition, while on all other ship surfaces, a no-slip condition is applied. For the upper surfaceof the domain, the pressure is prescribed (updated hydrostatic pressure). The boundary condition for the inletand outlet surfaces is zero far field velocity. Turbulence initialization levels are left at their default values.


WL2015R00_066_3 13


4 Grid convergence study for case 1c-1

4.1 Base meshes

By default, HEXPRESS uses cell sizes that are approximately cubic with a total that is as close to 1000 as pos-sible. Here, the initial cell size is coupled to the size of the ship in terms of its length between perpendiculars,

.

The domain box is divided along the three axes such that the resulting cells are approximately cubic and havelinear dimensions that are as close to /7 as possible1. In addition, a base mesh is created with cubic cellsthat have linear dimensions close to /5. Using these two base meshes, six derived meshes are createdthat are used for the grid convergence study.

4.2 Generation of derived meshes

For the first case (based on /7), this gives 36, 11 and 4 cells in the x, y and z-direction, respectively, for atotal of 1584 cells. After an initial mesh is generated, the complete project is duplicated and all absolute cellsize settings are reduced by a factor 1.4 to get a finer mesh. For the third mesh the initial cell size settings areincreased by a factor 1.4 from their initial values to get a coarse mesh. The number of cells for the coarse,medium and fine initial Cartesian meshes are listed in Table 7 for the case based on /7 and in Table 8 forthe case based on /5. By accident, the number cells for the fine mesh based on /5 is the same as themedium mesh for /7, in addition, both coarse meshes have the same number of cells.

Table 7 – Number of cells for the coarse, medium and fine initial Cartesian mesh for the case based on /7.x y z total

coarse 18 6 2 216medium 36 11 4 1584fine 50 15 6 4500

Table 8 – Number of cells for the coarse, medium and fine initial Cartesian mesh for the case based on /5.x y z total

coarse 18 6 2 216medium 26 8 3 624fine 36 11 4 1584

The target + values for the viscous layers on the ship and tank bottom were changed in a manner similar tothe changes in absolute target cell sizes.

For all cases, the grid near the stern in the lateral symmetry plane of the ship is shown in Fig. 12. Other viewsare shown in Appendix B.

1With this setting, six levels of refinement give target cell sizes slightly smaller than 0.01 m. Ten levels of refinement give target cellsizes smaller than 0.0006 m


WL2015R00_066_3 14


Table 9 – Total cell count for the coarse, medium and fine meshes for case 1c-1 based on /7 and /5./7 /5

coarse 2 673 963 2 673 963medium 6 567 806 4 509 538fine 11 221 780 7 667 172

(a) /5, coarse (b) /7, coarse

(c) /5, medium (d) /7, medium

(e) /5, fine (f) /7, fineFigure 12 – View of the grid near the stern in the symmetry plane of the ship for the six different cases.

4.3 Results

For each of the six cases as discussed in the previous section, a steady simulation (10000 iterations, timestep = 0.05 ) is performed where the trim and sinkage of the ship are the only degrees of freedom. InFig. 13, convergence of , and versus time are shown, as are values averaged over the last 500iterations. Close inspection of the convergence histories (Figs. 13a, 13c and 13e) shows that for the coarsemeshes, initially, results are converging, but approximately halfway, the trends become unstable. This mayindicate that the mesh is too coarse for the problem at hand. Differences between results on the medium andfine meshes are smaller than differences between results on the coarse and medium meshes, which indicatesthat as the cell sizes are reduced, the solution converges to a single value.


WL2015R00_066_3 15


(a) vs time. (b) vs # cells.

(c) vs time. (d) vs # cells.

(e) vs time. (f) vs # cells.

Figure 13 – Iterative convergence and final values for , and for 1c-1.

No uncertainty analysis has been performed as iterative convergence is not satisfactory for results computedwith the coarse meshes. Similar conclusions can be drawn after inspection of Fig. 14.

For all quantities, the differences between the medium and fine meshes are sufficiently small to assume thatcomputations based on the medium grid give adequate results. For the rest of the computations, the settingsbased on /7 will be used.


WL2015R00_066_3 16


(a) Sinkage vs time. (b) Sinkage vs # cells.

(c) Pitch vs time. (d) Pitch vs # cells.

(e) vs time. (f) vs # cells.

Figure 14 – Iterative convergence and final values for sinkage, pitch and for case 1c-1.


WL2015R00_066_3 17


5 Cases 1b-1 and 1b-3

5.1 Setup

Based on the grid study for case 1c-1, it was decided to generate meshes for cases 1b-1 and 1b-3 startingfrom the settings as used for the medium mesh of 1c-1. Some modifications are necessary, as cases 1b-1and 1b-3 include propulsion. A refinement surface is added at the location of the propeller to increase the cellcount in this area. The selected target cells size for this refinement surface is 0.005 m in the three dimensions.Furthermore, the target cell sizes for the refinement surface shown in Fig. 11b were reduced to 0.1, 0.1 and0.003 m. The consequence of these changes is that the cell count for 1b-1 and 1b-3 increases to 15.4 and16.4 million cells, respectively.

The thrust and torque values are required as input for propulsion modeling using an actuator disk. The valuesmeasured during the experiments are used for this (Delefortrie et al., 2014), they are shown in Table 10.

Table 10 – Thrust and torque values used as input for two of the CFD computations.

case thrust, torque,

1b-1 3.198 54.8581b-3 2.616 47.61

Past experience with the use of FINE/Marine has shown that in order to run a simulation with an actuator disk,first a simulation should be run without propulsion (but with free trim and sinkage) so that the initial transientssubside. In a second computation that starts from the end result of the first computation, the actuator diskmodel is activated.

The geometric properties of the actuator disk (inner and outer radius, thickness and origin) are listed in Table 11.For case 1b-3, the location is modified to account for the drift angle, in a similar way that the ship orientationitself is modified.

Table 11 – Geometry properties of the actuator disk

property value unit

inner radius 0.0107 mouter radius 0.75 mthickness 0.02 mcenter x-coordinate 0.0869 mcenter y-coordinate 0.0 mcenter z-coordinate 0.1298 m

5.2 Results

Iterative convergence plots are shown in Fig. 16 for 1b-1 and in Fig. 17 for case 1b-3. In all these figures,the first 500 seconds show results without propulsion, and the last 500 seconds show results with propulsionactivated. In the cases with propulsion, as shown in Figs. 16a and 17a is the sum of the pressure andviscous force acting on the ship in the longitudinal direction, so this does not include the contribution dueto the propeller. The resultant force (that would be measured in the experimental results), can be found byadding the thrust (shown in Table 10) to . In both cases, iterative convergence for all quantities is sufficientto consider the results converged. It should be noted that despite the large number of cells for these cases,


WL2015R00_066_3 18


Figure 15 – Graphical representation of the actuator disk properties listed in Table 11.

the use of an actuator disk to model propulsion may have a negative impact on the accuracy of the resultswhen compared to cases without propulsion for a similar number of cells. It is the simplest (and least accuratemethod) to take propulsion into account in CFD computations.


WL2015R00_066_3 19


0 200 400 600 800 1000Time, s

�5

�4

�3

�2

�1

0

Fx, N

(a) vs time.

0 200 400 600 800 1000Time, s

�0.4�0.2

0.00.20.40.60.81.01.21.4

Fy, N

(b) vs time.

0 200 400 600 800 1000Time, s

�0.5

0.0

0.5

1.0

1.5

Mz,

N

(c) vs time.

0 200 400 600 800 1000Time, s

0.0000

0.0005

0.0010

0.0015

0.0020

0.0025

0.0030

0.0035

0.0040

Sink

age,

mm

(d) Sinkage vs time.

0 200 400 600 800 1000Time, s

�0.10

�0.08

�0.06

�0.04

�0.02

0.00

0.02

0.04

Pitc

h, d

eg

(e) Pitch vs time.

Figure 16 – Iterative convergence for , , , sinkage and pitch for case 1b-1.


WL2015R00_066_3 20


0 100 200 300 400 500 600Time, s

�5

�4

�3

�2

�1

0

Fx, N

(a) vs time.

0 100 200 300 400 500 600Time, s

�14

�12

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�6

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(b) vs time.

0 100 200 300 400 500 600Time, s

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(c) vs time.

0 100 200 300 400 500 600Time, s

0.00000.00050.00100.00150.00200.00250.00300.00350.00400.0045

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age,

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(d) Sinkage vs time.

0 100 200 300 400 500 600Time, s

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(e) Pitch vs time.

Figure 17 – Iterative convergence for , , , sinkage and pitch for case 1b-3.


WL2015R00_066_3 21


6 Comparison of CFD and EFD results

Results of CFD computations discussed in Chapters 4 and 5 are compared with the experimental values aspresented in Chapter 2. For each quantity that is compared, first absolute values are shown and then relativeerrors. These relative errors are computed from the absolute values as follows

(% ) = (1)where is the CFD result and is the experimental reference value.

For the absolute plots, the standard deviations are shown using vertical bars. For the longitudinal force com-ponent, the resultant X-force on the hull (sum of pressure and viscous forces) is compared with the resultantforce minus the measured thrust (see Fig. 18). The standard deviations shown in Fig. 18a consist of the stan-dard deviations of the resultant longitudinal force for case 1c-1 (see Table 4), and for cases 1b-1 and 1b-3, thestandard deviations shown are the sum of the standard deviations for the longitudinal force and the standarddeviations of the measured thrust (see Tables 2 and 3).

(a) Absolute values. (b) Relative errors.

Figure 18 – Comparison of longitudinal forces.

In all three cases, the CFD predictions of the longitudinal force on the hull are very close to the experimentalvalues. For two cases (1c-1 and 1b-3), the error is smaller than or equal to the standard deviation associatedwith the measurement. For case 1b-1, the error is about 0.5 N larger than the standard deviation of theexperiment. Figure 18b shows that on a relative scale, the errors vary between -6% and +7%, which is verygood. The best value is achieved for case 1b-3, with an error smaller than 4%.

The lateral force comparison is presented in Fig. 19. The magnitude of the standard deviations of the exper-imental values are so small that the error bars are not discernible. The result for case 1b-1 is noteworthy asthe magnitude is almost right, but the CFD prediction has the wrong sign. As a result, the relative error forthis case is close to 200%. The ship sails straight ahead in this case (no drift angle), so the asymmetry inthe lateral force can only be caused by the interaction between the propeller and the rudder. The actuatordisk model in FINE/Marine uses both a thrust force, and a torque as input. It is possible that this model istoo simplistic for the case at hand and one should use more advanced methods, such as a potential panelmethod where the actual geometry of the propeller is modelled. For cases 1c-1 and 1b-3, the lateral forcesare predicted with errors smaller than -2% and -4%, respectively.


Figure 19 – Comparison of lateral forces.


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The small reference values for the roll moments mean that the errors for these cases are larger (Fig. 20). Thebest result is achieved for case 1b-3 with an error of 9%. The relative errors shown in Fig. 20b are misleading:on an absolute scale, the prediction for case 1b-1 is the best, with a difference of approximately 0.02 Nm; therelative error is more than 200% for this case.

The comparison of the yawing moment is shown in Fig. 21. On an absolute scale, the results are again verygood. The yawing moment for 1c-1 is predicted with an error smaller than 2%. For case 1b-3, the error is 6%and for 1b-1, it is approximately 20%. On an absolute scale, the error for the latter case is 0.2 Nm, while for1c-1, it is 0.26 Nm and for 1b-3 it is slighly less than 1 Nm.


Figure 20 – Comparison of roll moments.


Figure 21 – Comparison of yawing moments.


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7 Flow visualisations

7.1 Water surface

The water surface elevation around the KVLCC2 hull for the three cases is shown in Figs. 22, 23 and 24. Forthe latter two, the water surface elevation is shown for both the computation without propulsion and for therestart computation with propulsion.

The mesh for case 1c-1 uses a refinement surface for the water surface with coarser cells. Hence, less detailis visible in the wave pattern produced by the vessel (Fig. 22). By using automatic grid refinement (AGR), itis possible to improve the water surface without adding cells in places where they are not needed. The AGRfunctionality in the ISIS CFD solver has not been used up to this point.

Figure 22 – Visualisation of the water surface coloured with the elevation for case 1c-1 (drift angle 4 degrees).

7.2 Hydrodynamic pressure on the hull and tank

For the three cases, the pressure coefficient is shown where the mass fraction is larger than or equal to0.5 (water). The pressure coefficient is defined as

= 12 2 (2)where is the hydrodynamic pressure, is the water density and is the reference velocity. In stagnationpoints, the value of equals one.

There are significant differences between the pressure distributions for the two cases with non-zero drift angle(Fig. 25 and 27). For the latter case, signficant fluctuations can be observed on the leeward side of the hull,aft of the midship location near the water surface. Due to the differences in grid resolution between 1c-1and 1b-3 it is unclear what the cause is of these differences (either the grid resolution or the influence of thepropeller).


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(a) Without propulsion.

(b) With propulsion.

Figure 23 – Visualisation of the water surface coloured with the elevation for case 1b-1 (straight ahead).


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(a) Without propulsion.

(b) With propulsion.

Figure 24 – Visualisation of the water surface coloured with the elevation for case 1b-3 with propulsion (drift angle 4 ).


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(a) Overview.

(b) Close-up.

Figure 25 – Visualisation of the pressure coefficient on the submerged part of the ship and tank walls for 1c-1.


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(a) Overview.

(b) Close-up.

Figure 26 – Visualisation of the pressure coefficient on the submerged part of the ship and tank walls for 1b-1.


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(a) Overview.

(b) Close-up.

Figure 27 – Visualisation of the pressure coefficient on the submerged part of the ship and tank walls for 1b-3.


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8 Conclusions

This report documents the CFD computations that were executed for the SIMMAN 2014 workshop in Denmark.FHR executed tests with the KVLCC2 and KCS ship models in the towing tank for shallow and confined waterfor this workshop. A subset of these tests were used as reference for blind CFD computations. For three ofthese tests (1c-1, 1b-1 and 1b-3) CFD computations were carried out using the FINE/Marine CFD software.This report is based on a paper that will be included in the workshop proceedings and a poster that waspresented at the poster session of the workshop. The final workshop proceedings haven’t been released,which means that it is unknown how close the CFD computations are to the EFD data. For this reason, thecurrent report contains an analysis of the experimental data, a comparison of the CFD results with the EFDresults and some flow visualisations.

The EFD analysis showed that there may be issues with the rail alignment data for case 1c-1. Compared tothe rail alignment data for the other two cases, the rail alignment data for 1c-1 contains suspicious oscillationsduring the first 25 meter of the tests and the last 10 meter of the test. It was also noticed that the raw data ofthe front sinkage shows suspiciously constant values for longer time periods, something that is not observedfor the aft sinkage measurements. For one case (1b-3), the experiment was repeated 10 times. Apart fromaverage values, standard deviations were computed for this case as well. It was found that relative standarddeviations are largest for the longitudinal force, the thrust, torque and roll moment, at 5.6%, 6.5%, 4.7% and4.0%, respectively. For the other quantities of interest, the relative standard deviations are all smaller than1%. These relative standard deviations were used to estimate standard deviations for the other two testcases.

For case 1c-1, a grid convergence study was performed to investigate the influence of the initial cell size onthe final result. It was decided to use an initial grid with cells that have a linear dimension close to /7. Forcase 1c-1, the grid contains 11.2 million cells. The grids of 1b-1 and 1b-3 contain 15.4 and 16.4 million cells,due to using smaller target cells sizes for the water surface refinement. The smaller cell size near the watersurface results in more detailed wave patterns.

The comparison of the EFD and CFD results shows that (apart from the lateral force for case 1b-1) the resultsare in very good agreement with the experimental values (these are shown again in Table 12). The errors for

are smaller than 8%. The best result is achieved for 1b-3, with an error less than 4% for . Case 1b-1 isthe only one without drift. For this case, the reference values of , and are rather smaller than for theother two cases which results in large relative errors (up to 200%). Although both thrust and torque are usedas input for the actuator disk model, it is possible that this model is too simple for this specific case.

Table 12 – Overview of results

caseEFD, N CFD, N E(%D) EFD, N CFD, N E(%D)

1c-1 -3.693 -3.481 -5.731 12.55 12.35 -1.5721b-1 -0.6588 -4.152 7.66 1.127 -1.245 -210.51b-3 -1.4 -4.174 3.918 13.98 13.4 -4.197

caseEFD, Nm CFD, Nm E(%D) EFD, Nm CFD, Nm E(%D)

1c-1 -0.4456 -0.6508 46.06 16.33 16.59 1.5951b-1 0.01025 0.03259 218.1 0.9256 1.117 20.621b-3 -0.6224 -0.6773 8.822 14.92 15.85 6.196


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References

Anon. (2011). FreshWater and Seawater Properties. http://ittc.sname.org/CD2011/pdfProcedures2011/7.5-02-01-03.pdf

— (2014). Theoretical Manual ISIS-CFD v3.1

Delefortrie, G.; Eloot, K.; Mostaert, F. (2011). SIMMAN 2012: Execution of model tests with KCS andKVLCC2.WL Rapporten, 846_01. Version 2.0. Antwerp, Belgium

Delefortrie, G.; Eloot, K.; Peeters, P.; Mostaert, F. (2014). SIMMAN 2014: Revised Shallow Water ModelTests with KCS and KVLCC2.WL Rapporten, 00_066. Version 3.0. Antwerp, Belgium

Knowledge Centre Manoeuvring in Shallow and Confined Water. http://www.shallowwater.be/

MOERI KVLCC2 Tanker – Geometry and conditions. http://www.simman2014.dk/cms/site.aspx?p=13327

Van Hoydonck, W.; Eloot, K. (2014). Shallow Water CFD Computations for SIMMAN 2014. In: SIMMAN2014 Workshop on Verification and Validation of Ship Manoeuvring Simulation Models. Preprints of WorkshopProceedings. Ed. by J. F. Otzen; C. D. Simonsen

Waterbouwkundig Laboratorium – Flanders Hydraulics Research. http://www.watlab.be


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http://ittc.sname.org/CD 2011/pdf Procedures 2011/7.5-02-01-03.pdfhttp://ittc.sname.org/CD 2011/pdf Procedures 2011/7.5-02-01-03.pdfhttp://www.shallowwater.be/http://www.simman2014.dk/cms/site.aspx?p=13327http://www.simman2014.dk/cms/site.aspx?p=13327http://www.watlab.be


A Additional time analysis plots of the EFD data

Figures 28 and 29 show the aft and fore lateral force measurements that are used to compute the lateral force(Fig. 7) for test case T0Z02A03_C40000. Themean of the aft measurement equals 0.09722 N, the mean of thefore measurement is 1.030 N. The standard deviations are 0.6152 and 1.005, respectively: the measurementwith the smallest mean value has the largest standard deviation, and vice versa. From the time histories ofthe normalized CMA, it is apparent that during the whole test, the CMA oscillates around its final value for thefore measurement, whereas for the aft measurement, the CMA value oscillates around 2, and only starts todecrease towards 1 around t = 155 s. The FFT plots of both measurements are very similar.

Figure 28 – Convergence of aft lateral force measurement for test T0Z02A03_C40000.

Figure 29 – Convergence of fore lateral force measurement for test T0Z02A03_C40000.


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B Additional views of the grid using cutplanes



(e) /5, fine (f) /7, fineFigure 30 – View of the grid at the aft perpendicular (AP) of the ship.


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(e) /5, fine (f) /7, fineFigure 31 – View of the grid at the mid section of the ship.


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(e) /5, fine (f) /7, fineFigure 32 – View of the grid at the fore perpendicular (FP) of the ship.


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(e) /5, fine (f) /7, fineFigure 33 – View of the grid near the bow in the symmetry plane of the ship.



(e) /5, fine (f) /7, fineFigure 34 – Overview of the grid in the symmetry plane of the ship.


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Waterbouwkundig Laboratorium

Flanders Hydraulics Research

Berchemlei 115B-2140 AntwerpTel.+32 (0)3 224 60 35Fax +32 (0)3 224 60 36E-mail: [email protected]


1 Introduction2 Analysis of experimental data2.1 Rail alignment corrections2.2 Averages and standard deviations for case 1b-32.3 Averages and standard deviations for case 1b-12.4 Averages and standard deviations for case 1c-12.5 Time history analysis

3 Computational Setup3.1 Test conditions3.2 KVLCC2 CAD Model3.3 Domain Size and Ship Position3.4 Topology and General Refinement Settings3.5 Solution Method and Flow Settings

4 Grid convergence study for case 1c-14.1 Base meshes4.2 Generation of derived meshes4.3 Results

5 Cases 1b-1 and 1b-35.1 Setup5.2 Results

6 Comparison of CFD and EFD results7 Flow visualisations7.1 Water surface7.2 Hydrodynamic pressure on the hull and tank

8 ConclusionsReferencesA Additional time analysis plots of the EFD dataB Additional views of the grid using cutplanes

simman 2014 - vliz · 3.0 13/08/2015 final version van hoydonck, w. abstract this report contains...

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