Scenario based optimization of a container vessel with respect to its projected operating conditions

International Journal of Naval Architecture and Ocean Engineering.
2014.
Jun,
6(2):
496-506

This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

- Published : June 30, 2014

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Ship design
;
Hull form optimization
;
Scenario
;
Operating conditions
;
Life-cycle analysis
;
Potential flow calculation

INTRODUCTION

At least since the economical crisis the traditional way of designing ships is considered to be outdated. Operating ships at off-design conditions may appear as a good solution in times of a crisis and apparently leads to lower fuel consumption but there is a potential to save even more energy if the vessels would have been designed with respect to more operational conditions. But even without the crisis the process of designing a ship onto one operating condition had to be reconsidered, for the fact that both calculations or prognosis as done by
Røe (2010)
and analyses of operating profiles of real ships have shown that merchant vessels only operate at their respective design condition (e.g. at 85% Maximum Continuous Rating (MCR)) for a small amount of time.
Despite this fact, the knowledge of a vessels future operational profile is of great interest when it comes to environmental issues as a suboptimal ship design has a higher emission rate than an optimal one.
These problems necessitate a new approach which is capable to deal with future needs and uncertainties and which considers the vessels life-long operating situation. Keeping that in mind, scenario methods seem to be a suitable solution. By linking economical trend analysis with detailed operation profiles the usage of these methods offers the possibility to design ships which are not optimized to one or two particular operational conditions but will be significantly more efficient related to their overall operating time.
LITERATURE REVIEW

The idea of using a complete operational profile as the basis for the development or optimization of a hull form instead of a single or only a few design points has been adapted within a few projects before. Two of them are in short presented in the following.
As an example,
Temple and Collette (2012)
have been using probability density functions in order to display the speed range of two vessels (DTMB-5145 naval combatant and KCS container ship) for a following multi-objective optimization of their hull forms. The optimization is done using a Multi-Objective Genetic Algorithm (MOGA) with the lifetime resistance being calculated from the integral over the speed dependant total resistance (estimated using the thin ship theory) multiplied by the Probability Density Function (PDF). The respective PDFs have been generated by applying a bimodal distribution with the two modes representing the vessel’s endurance and mission speed in case of the DTMB-5145 and an unimodal distribution with the mode at the vessels design speed for the KCS. As far as the author is aware, those distribution functions are not based on statistics of existing vessels but on the author’s consideration.
Statistically based probability distribution functions have been used by
Eljardt (2010)
in order to assess different vessel types, shipping routes or the commodity flow. Despite the speed distribution, he also considers environmental data such as seastate and wind conditions and other vessel specific data, e.g. the trim. Thereby, the respective distribution functions are taken from statistical analysis and / or prognosis. Within this work the distribution functions are used for sampling a sufficient number of ship operation conditions using the Monte Carlo Method in order to serve for example as the target function for an optimization of a ship’s hull form and propulsion system. Although considering a wide range of parameters, this approach differs to the scenario based approach presented in this paper as it does not completely consider the coupled or correlated appearance of different parameters, which can lead to incorrect results in the target function (see next section for details).
GENERAL APPROACH

The basic idea of the scenario based approach is to predict the most probable operating conditions the designated vessel will stay in during its operating time in order to find the most suitable design variant.
Fig. 1
shows the flow chart of the complete optimization process as presented in
Wagner and Bronsart (2011)
.
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BASIC DATA

To have a realistic basis to start with, the log-data of an existing comparable 3600
- • Loop 1: -0.5% per year (decrease).
- • Loop 2: 0% per year (stagnation).
- • Loop 3: 0.5% per year (increase).

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Operational profile.

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MODEL

The parametric Model of the KCS is build based on the IGS-file offered by the SIMMAN 2008 workshop. Whilst the midship and the stern section have not been touched the stem has been parametrically remodeled. To do this, in compliance with
Kracht (1978)
the following four parameters have been introduced:
- • ΔLB: change of length of bulbous bow.
- • ΔZB: change of height of bulbous bow.
- • PBy, PBz: change of breadth of bulbous bow.

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Parameter boundaries.

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OPTIMIZATION

The optimization of the KCS’ stem section has been done with respect to the vessels weighted effective Power P
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RESULTS

The optimization leads to a design variant with the parameters given in
Table 3
.
Those values acknowledge the trends gained from the
Optimal design parameters.

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Detailed optimization results and comparison to initial hull form.

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CONCLUSIONS AND OUTLOOK

The presented method for the scenario based optimization of parametrically modeled hull forms has shown to be reliable and to achieve reductions in the needed effective power. In order to validate the method more and especially more comprehensive optimizations have to be done as the achieved results seem to be dependent on many factors.
At first, the data taken as basic input to the scenario development is of great importance. It should be taken care of, that the data cover a sufficiently long period of time and can be considered to be complete. Furthermore they should belong to a comparative vessel operating on a comparable or the same route.
The second point aims at the uncertainties. As shown in
Fig. 9
the consideration of higher uncertainties results in flattened operational profiles, which leads to the need of considering more than four operation conditions within the objective function. In the course of this it should be analyzed, whether the consideration of a higher coverage of the selected operating conditions leads to better results.
Despite those factors there are some other possibilities for increasing the approaches accuracy. One exists in reducing the bins, allowing it to optimize onto more specific operating conditions. On the other hand and in accordance to the increase of uncertainties reduced bins would raise the need for considering a higher number of operating conditions in order to achieve a certain coverage. It has to be noted, that not only the size but also the bins’ position has a notable influence on the objective function.
Other possible improvements can be done by using RANSE instead of potential flow code or a more sophisticated model with more parameters that make it possible to control the complete hull form instead of only the bulbous bow.
The next steps in developing the scenario based optimization approach primarily focus on the implementation of more features into the scenario development. As an example future versions should be able to predict and consider weather conditions and should come with an enhanced objective function. The latter will be capable of executing life-cycle analyses taking into account economic parameters like for example constantly developing fuel oil prices.
Eljardt G.
2010
Entwicklung einer statistikbasierten Simulationsmethodik für Schiffsentwürfe unter realistischen betriebsbedingungen
Technische Universität Hamburg-Harburg
Hamburg

Ernst G.
,
Hollenbach U.
2011
Design-optimierung von containerschiffen
Schiff & Hafen
(Nr. 9)
50 -
52

Kracht A.
1978
Design of bulbous bows
The Society of Naval Architects and Marine Engineers (SNAME) Transactions
86
197 -
217

Marzi J.
,
Hafermann D.
,
Ernst G.
2010
The ν-SHALLO user guide, HSVA –
Hamburgische Schiffbau Versuchsanstalt GmbH
Hamburg

Temple D.
,
Collette M.
2012
Multi-objective hull form optimization to compare build cost and lifetime fuel consumption
International Marine Design Conference, IMDC
II
391 -
403

Røe M.A.
2010
Quantum - A container ship concept for the future. DNV Container Ship Update, No. 1 2010
DNV
Oslo

Wagner J.
,
Bronsart R.
2011
A contribution to scenario based ship design
International Conference on ComputerApplication in Shipbuilding. ICCAS
I
47 -
52

Citing 'Scenario based optimization of a container vessel with respect to its projected operating conditions
'

@article{ E1JSE6_2014_v6n2_496}
,title={Scenario based optimization of a container vessel with respect to its projected operating conditions}
,volume={2}
, url={http://dx.doi.org/10.2478/IJNAOE-2013-0195}, DOI={10.2478/IJNAOE-2013-0195}
, number= {2}
, journal={International Journal of Naval Architecture and Ocean Engineering}
, publisher={The Society of Naval Architects of Korea}
, author={Wagner, Jonas
and
Binkowski, Eva
and
Bronsart, Robert}
, year={2014}
, month={Jun}