Revised simulation model for a Very Large Crude Carrier (VLCC)
In this thesis a simulation model for a Very Large Crude Carrier is revised. MARINTEKs software ShipX is used to develop, improve, test and validate a model for the case vessel KVLCC2. The Manoeuvring Plug-In (SIMAN, 3-DOF) and the Vessel Simulator Plug-In (VeSim, 6-DOF) are utilized for this purpose. The underlying field of study has been ship manoeuvrability.
KVLCC2s hull lines, propeller and rudder data are available at SIMMAN 2014 websites . Captive and free model tests conducted in connection to the workshop on verification and validation of ship manoeuvring simulation methods SIMMAN 2008 are available. The methodology for improving the simulation model is to use the model to simulate the IMO standard manoeuvres. Turning circles, zig-zag and stopping tests in deep water is simulated. Turning circles(35), zig-zag(10/2.5, 20/5) and spiral tests are simulated in shallow water. The simulation results are compared to results from SIMMAN in 2008. The 26th ITTC has suggested benchmark data from average values of the free sailing model tests from the workshop that are used for model validation. The simulation results are also evaluated and compared to the results from MARINTEKs contribution in SIMMAN 2008 using SIMAN. A sensitivity analysis is performed to find which parameters are of high importance in the model. The parameters of high importance are investigated further. The linear velocity coefficients are compared with empirical methods and PMM tests. Shallow water effects and low speed manoeuvring are assessed. The shallow water simulations at low speed are compared with the shallow water effect trends from full-scale trials with Esso Osaka. Validation and verification of simulation models
are assessed and understood.
The simulation model does fulfil all the IMO criteria of turning, initial turning/course-changing, yaw-checking abilities in both VeSim and SIMAN. The model in VeSim fulfil the IMO criteria of stopping ability, while the model in SIMAN does not. The differences in the results of VeSim and SIMAN and small. The simulation results do not correspond well with the benchmark data based on free model tests from SIMMAN 2008, and the model can not be validated. MARINTEKs contribution using SIMAN in 2008 was more consistent with the benchmark data, and indicates that the changes made in the plug-in does not give better results for KVLCC2. Changes has been observed in the calculation of the hydrodynamic coefficients and resistance polynomial. Especially the calculation methods of Yr and Nr have been altered. When using
the same input parameters as well as the same hydrodynamic coefficients and resistance polynomial as in 2008 the manoeuvring simulations deviates substantially. These deviations must be because of changes in either non-linear cross-flow drag, rudder module or the propeller module(or all). These subroutines are hard to assess because of lack of updated documentation. The linear damping coefficients proved to be of high importance in the sensitivity analysis, especially Nv and Nr. Wake fraction and thrust deduction are also of some importance. ShipX tends to overestimate Nv and underestimate Nr and can not be validated against results from PMM tests. An input value of 0.150 [-] for the wake fraction of the hull has been observed to be too low compared to literature and other wake fractions used in SIMMAN 2008. The same shallow water trends for KVLCC2 are observed as for Esso Osaka for the turning circle test. The same trends are not found for checking and counter turning ability for KVLCC2. From the 23rd ITTC committees review of shallow water ratios as well as using methods of Clarke, Ankudinov and Kijima it seems like SIMANs shallow water formulae underestimates the linear
velocity coefficient ratios.
There has been made several changes in the different subroutines and modules of the plugin during the last six years. These changes are easily noticed by looking at results when using exactly the same inputs and coefficients. It is impossible to assess and suggest improvements to the cross-flow drag, rudder module and propeller module when the documentation is not updated. Nv is overestimated and Nr is underestimated compared to empirical methods and PMM tests. Due to the high importance of these a review of the current calculation methods of these should be looked into. SIMAN and VeSim is tuned for offshore vessels, which could have an impact of the results since KVLCC2 is a VLCC. An assessment of SIMANs shallow water formulae is hard to do as well due to lack of documentation, but this should be looked into after SIMMAN 2014.
Place, publisher, year, edition, pages
Institutt for marin teknikk , 2014. , 124 p.
IdentifiersURN: urn:nbn:no:ntnu:diva-25805Local ID: ntnudaim:11166OAI: oai:DiVA.org:ntnu-25805DiVA: diva2:740989
Berg, Tor Einar, Professor II