The course TMR 4220 – Naval hydrodynamics lectured at NTNU gives an introduction to the standard simulation tests and requirements. The lecture notes to this course, along with the International Maritime Organization’s (IMO) resolutions and explanatory notes.
The thesis includes explanatory chapters and sections explaining the different methods of retrieving the input parameters to the simulation model and how they are applied. References are given throughout the thesis showing where the information has been found and gives the reader the opportunity to further investigate what has been presented in the thesis.
This thesis has its origin in the project thesis written autumn 2013. A validation of the simulation tool SIMAN was presented as a comparison of simulated manoeuvres, IMO requirements and preliminary full-scale trials. The initial results were not as satisfactory as hoped and resulted in a conclusion that SIMAN was not a suited simulation tool for MF Landegode at the present time.
The main objectives of this thesis are to:
- Give a brief introduction on how to validate a simulation model;
- Give a brief introduction on the International Maritime Organization and its purpose;
- Give an introduction to the IMO standard manoeuvring tests and criteria;
- Give an introduction to additional low speed manoeuvring tests;
- Give an introduction to the simulation model Vessel Simulator (VeSim) and the structure of the model;
- Give an explanatory note on the mathematical model used in the simulation model;
- Gather and process full-scale trial measurements, and present the trial conditions and results in a lucid manner;
- Simulate the IMO standard manoeuvres, in addition to low speed manoeuvres and compare the results with full-scale results;
- Discuss the validity of the simulation model based upon the presented results and comparisons;
- Give a conclusion on whether or not this is a suitable simulation model for the case vessel;
- Suggest further work.
The full-scale results presented are affected by weather conditions. These are not easy to account for in post-processing of the data and will have an effect on the similarity of the simulations. Some of the manoeuvres have been treated to account for weather conditions, which will be described. The simulation tool used was preliminary unknown to the student, and getting to know the program is therefore a part of the study. Due to time restraints, a brief study of all the manoeuvres will be addressed instead of a higher detailed study of a specific manoeuvre or aspect of the simulation model. Regarding the ship’s hull lines and properties supplied by MARINTEK, they are confidential and will not be reproduced in the thesis.
One of the bullet points in the scope of the thesis suggests comparing the simulation results with results from the training simulator at Bodin. The hydrodynamic coefficients that were intended for analysis from the PMM tests conducted at MARINTEK and used in the training simulator, were not obtainable within the time of completing the study. The secondary objective is hence not evaluated in the thesis.
To understand the purpose and process of validating and verifying a simulation model, a literature study has been conducted. This includes reading different papers published by amongst others, the ITTC, OMAE and SIMMAN initiative, and studying the different parameters that are of interest in the specific manoeuvres. To evaluate these manoeuvres, different organizations as the IMO and ISO are studied. Here, the manoeuvres are explained in detail, along with limitations to the standard tests. The mathematical formulations behind manoeuvring theory is studied with the simulation model used as a basis. The simulation model Vessel Simulator is used, which is developed by MARINTEK. The manual of the plug-in has been studied to get an overview of the model. Input parameters, restrictions and assumptions have been addressed to understand how the program calculate and estimate the motions of the vessel.
The result of the simulations is compared with the IMO requirements and post-processed full-scale trials, conducted in August 2013, to evaluate the similarity and give an assessment on the validity of the simulation model. A discussion of any influencing sources and errors in the calculation is given on the basis of the results, also to address the validity of the model.
As a concluding remark, further work is suggested on the basis of information extracted from the findings, and which areas of the process that needs to be studied in more detail to give a more tangible decision on the validity of this model.
Verification and validation of simulation models
Development of ship manoeuvring simulators have been of great concern in recent time when international manoeuvring standards have been developed. Ship manoeuvring simulation models can be separated by models for prediction of manoeuvrability and models for use in simulators. High-quality simulation models are often used for the study of advanced marine operations and investigations of maritime accidents, as for instance collisions and groundings. To ensure the validity of the models, careful consideration and verification of the simulation models must be conducted and gathered.
Maritime simulation models will require a larger degree of validation than of the prediction in ship manoeuvrability, because of the large amount of different parameters involved, such as wind, current, waves and operating conditions of the vessel. This thesis will focus on the manoeuvrability of a ship and the validation of the model will therefore be less detailed than for maritime simulation models. The main details of the validation procedure of a manoeuvrability model will be discussed in the following.
The main content of a manoeuvring model and intention of a well validated model will contain the following aspects and procedures:
- Ship particulars;
- Prediction of hydrodynamic forces;
- Modelling of forces in a structured mathematical model;
- Integration method;
- Simulation software;
- Simulated manoeuvres.
The process of the simulation and the documentation should be given such that it clearly shows the validity of the model and the simulated manoeuvres. That be the standard manoeuvres defined by the IMO, along with the low speed manoeuvres and the accuracy of the model.
When a manoeuvre has been simulated and the results have been presented, the normal procedure for validation is by comparing the results with known benchmarking data. The documentation of the validation should be available in the form of a report or published paper. Benchmarking data are used for comparing of the various methods for predicting ship manoeuvrability. There are little full-scale benchmark data available on the open market. The Esso Osaka is a much used ship for comparison of manoeuvring data. However, due to its outdated hull design and lack of a bulb, the Esso Osaka is a poor comparison ship with regard to new ships with more modern design.
Captive model tests, as well as free running model tests are frequently used as substitutes for full-scale trials and are thought to be as precise as the full-scale trials. Although scale effects are not well documented, the control of environment and test parameters can be fairly controlled.
The SIMMAN initiative
The SIMMAN 2008 initiative is a workshop where new benchmarking models, data as well as proceedings have been documented. The main purpose of the workshop was to obtain, as mentioned, new benchmarking data for newer vessels and document the different simulation models different capabilities including systems and CFD based methods, through comparison of the different ship hulls. The ships used in the SIMMAN 2008 workshop included a tanker (KVLCC1 and KVLCC2), a container ship (KCS) and a surface combatant hull (5415). The different simulation models were compared with PMM and rotating arm tests. None of these ships exist in full-scale, but only as scaled models. They are provided with geometrical data for hull, propeller, rudder and appendages for the public to view.
Further work on establishing more benchmarking data is planned. A new session of a SIMMAN workshop is being planned, and institutes like NTNU are constantly developing their simulation tools with comparison of new vessels, like the MF Landegode. The vessel is depicted in Picture 1.