Lifecycle Model for LNG fueled Ships Operating in the Arctic via Epoch-Era Analysis
by Henrique M. Gaspar - Associate Professor Aalesund University College / Ulstein International SA
(hega @ hials.no), v0.1, Jan 2013.
Part of "Challenges for Using LNG fueled Ships for Arctic Routes", Gaspar, H.M., Ehlers, S., Æsøy, V., Erceg, S., Balland, O. and Hildre, H.P., in OMAE 2014, San Francisco, CA, USA.
Uncertainties related to LNG fueled ships operating in the Arctic
Epoch-Era Analysis for LNG-Arctic case
1 - Epoch Variables
In the EEA methodology future scenarios are represented by the discretization of the contextual factors into epoch variables , within a range that takes into account the uncertainties and expectations. An epoch is defined by one of the possible combinations of the parameters, while the sum of all epochs defines an epoch space .
Table 1 describes a simple example for defining epochs variables for the LNG-ARCTIC case. Contextual factors are divided into: environmental conditions (ice conditions), regulations (HFO ban and ECA), season opening for the route (months) and level of risk.
Table 1 - Epoch Variables
|Season Open||Months Open||months||0-6||7|
|Environmental||Ice Conditions||Ice Class||none - 1C||4|
|Epoch space (total):||336 epochs|
Each epoch variable represents a possible cetgory change in a contextual factor, and is used as instrument to the mapping between context parameters and vessel performance.
2 - Design Variables
The next step consists of the decomposition of the structural aspects of an LNG fueled vessel,via a discretization in terms of design variables, within a range maximum-minimum. A design is defined by one of the possible combinations of the variables, while the sum of all designs defines an design space.
Table 2 - Design Variables
|Propulsion||Type||Machinery Type||LNG - Conventional||2|
|Design space (total):||8 designs|
Each design variable represents a possible categorial change in the ship, and is used as instrument to the mapping between context parameters and vessel performance.
3 - Vessel Performance (Design Attributes)
Design Attrobutes are used as one of the criteria to evaluate the performance of a design under an epoch/era. A set of concepts and assumptions is then defined, for the mapping between the design variables and design behavior. This process includes the knowledge intrinsic to the design process. In this example, only for illustrative purposes, our KPIs will be connectd to the machinery and output of it. Only diesel mechanic and gas mechanic solutions for machinery are compared, as well as four ice classes. A list of the required KPIs is found in Table 3.
Table 3 - Design Attributes
Air emissions are connected to fuel type, route and speed. CAPEX is connected to the cost of installation, while OPEX is connected to the performance of the ship within a route and its conditions. A lower value is considered better utility. The final data is normalized, using design number five as reference.
- Each epoch lasts 6 months.
- CAPEX is connected to the type of machinery and ice class of the design.
- OPEX and CAPEX values are normalized to design number five (ID=5 - non ice-class, conventional diesel mechanic machinery).
- Ice Class is mandatory, and epochs with a higher ice-class requirement than the vessel will not be considered for that design.
- Roughly, the price per quivalent barrel of LNG is the same as HFO.
- Risk is connected to the level of uncertainty for the northsea route. A higher risk means a higher OPEX.
- OPEX is connected to the route. HFO ban and ECA requirements raise OPEX for conventional machinery, since it requires a cleaner fuel.
- Emissions are calculated based on the amount of fuel used during the 6 months period.
4 - Epoch Space
Epoch space contains all the possible epochs that can be created based on the decomposition of the uncertainties. The following tree diagram presents the epoch space based on Table 1, with all 336 epochs.
Epochs are organized by the order that they are presented in Table 1. Click to expand or collapse a subset of epochs.
5 - Design Space
Design space contains all the possible designs that can be created based on the decomposition of the design variables. The following tree diagram presents the design space based on Table 2, with all 8 designs. At this stage, we are able to calculate the CAPEX of each design.
Designs are organized by the order that they are presented in Table 2. The size of the olive circles at the right is proportional to the CAPEX. Click to expand or collapse a subset of designs.
6 - Tradespace Evaluation
This step of the process evaluates the design space is evaluated within the performance attributes. It means evaluating the whole tradespace (the span of enumerated design variables) for each of the epochs (fixed set of epoch variables). This evaluation is made via modeling and simulation, and as output we obtain the attributes, utilities and cost of each design for each epoch.
The following tree diagram illustrates the idea that each epoch will be analysed for all design space.
7 - Epoch Analysis
This process deals with the extensive amount of data obtained from the tradespace evaluation. The objective is to obtain insight from these data, via an analysis of the good design solutions among the epochs.
For the sake of illustration, let's compare all design performances between Epoch and Epoch .
8 - Era Construction
An era represents a full potential lifespan of the system, and it is defined as a time-ordered sequence of contexts. The era space is created by combining elements of the epoch space in order to construct long-term scenarios. The epoch sequencing must obey consistency rules in the epoch variables, such as continuity constraints and consistency in the progression of epoch variables.
The possible era space is normally very large, and with a high computational cost for it to be calculated in its entirety. This space can be based on probabilistic distribution and/or stakeholder’s preferences (a more risky or conservative approach, for instance).
For the sake of illustration, let's create an eras via storytelling approach. Era 1 encloses winter period for 10 years. Ever season is composed by 6 months, where in the first six years the NSR is open for 3 months. For the last four years, the NSR is open for 4 months. In the regulatory field, no regulations for the first 3 years, and HFO is banned after it. ECA regulations are valid from the 7th year. Ice Class 1A is required, and the leve risk is normal. Table 4 summarizes the era construction process.
Table 4 - Era Construction
|Open 3 Months, yes Ice Class, no HFO/ECA, normal risk||161||3|
|Open 3 Months, yes Ice Class, yes HFO, no ECA, normal risk||164||3|
|Open 4 Months, yes Ice Class, yes HFO/ECA, normal risk||215||4|
Other methods to construct eras can be based on probailistic distribution of the uncertainties, tunned by stakeholder's stylistic preferences.
The diagram below illustrates Era 1.
9 - Era Analysis
The last process of the RSC method deals with the analysis of the design set among selected eras. It includes the comparison of solutions, trade-offs and possible strategies to transform one design into a more value robust one. The output for each lifecycle analysis is similar to the epoch analysis: opex and air emissions.
The following bar chart compare designs for Era 1.
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- Gaspar, H.M. et al. Handling Temporal Complexity in the Design of Non-Transport Ships Using Epoch-Era Analysis. Transactions RINA, Vol 154, Part A3, International Journal Maritime Engineering, Jul-Sep 2012
- Gaspar, H.M. et al., Addressing Complexity Aspects in Conceptual Ship Design - A Systems Engineering Approach. Transactions of SNAME, Vol. 120, 2013
- Erikstad, S. O., Ehlers, S.,Decision Support Framework for Exploiting Northern Sea Route Transport Opportunities. Ship Technology Research. 2012; volume 59 (2). S. 34-43.