1 System Selection and Motivation

In today’s world, fulfilling the demand for energy and resources plays a major role in enabling our standard of living. The generation of power and heat for industrial and civil uses is still dominated by oil and gas products whereby the transportation of the commodities is a crucial part of the value chain. In terms of economy and safety, pipelines have proven their worth for long-distance transport, such that an extensive network of pipelines distributes fluids all over the world (Mohitpour et al., 2007, p. 1). In recent times following the 2022 Russian invasion of Ukraine, the supply of natural gas to Europe gained public attention caused by shortcuts of Russian deliveries. Together with this, the substantial importance of the pipeline infrastructure became visible, also due to the demand for alternative procurement possibilities in the form of liquefied petroleum gas (LNG) and the necessary construction of new terminals and pipelines (DW, 2022; Reuters, 2022). With a view to the transition to renewable energies, the call for energy storage regarding the volatile nature of those sources and production of sustainable fuels grew louder and led to the approach of using hydrogen as an energy carrier. Therefore, the distribution and storage may use existing infrastructure but most certainly requires the construction of new pipeline networks (EHB, 2022). The engineering challenge of designing and constructing such infrastructure lies not only in the technicalities that make the operation of pipeline networks possible, but especially in the routing and laying of the pipeline through 10s to 1000s kilometers of various terrain and locating of the necessary facilities along the route. The industry distinguishes three segments within the value chain where pipelines are used: In the upstream segment pipelines are gathering fluids from various supply points to e.g., storage, refineries, or other treating facilities (gathering pipelines), in the midstream segment the fluids are transported over long distances to delivery points (transmission pipelines), from where a network of distribution pipelines within the downstream segment enables the transport to end users or further processing facilities (see Fig. 1). (Adam & Davis, 2009, p. 35)

Fig. 1: Typology of pipelines on the example of natural gas (Ram B. Gupta et al., 2016, p. 304)

The mainlines that cover long transport routes emerge as a common feature of the various layouts of pipeline networks and represent the most important part of the overall system. Thus, the subsystem of transmission pipelines will be the selected system as part of this project assignment. The focus is placed on the challenges of routing and designing the mainline of long-distance transmission pipelines with the affiliated facilities, depending on the transported fluid, but also its interaction with the immediate environment.

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Chapter 2 Ontological Model

2 Ontological Model

Ontological models serve as a tool to aggregate, analyze, and share knowledge in a specific domain. Although the range of possible use cases is rather wide, in the field of civil engineering it will most of the time describe an engineering system regarding a specific challenge or project. Prior to the design of the ontology, one must specify the boundaries and degree of abstraction regarding the system. Since the scope of application implies the needed level of detail and range of elements which will be considered as part of the ontology, the purpose of the ontology must be defined. Literature research will then help to examine the system and its properties, to develop a terminology and understanding of the components and reveal their relations and the interfaces to the environment. With the help of design guidelines for creating ontologies inside the open-source editor protégé (Noy & McGuinness, n.d.) in combination with basic principles of logical axioms in systems modelling, an OWL (web ontology language) ontology will be the result of this chapter.

2.1 Purpose of the Ontology

In general, the design of transmission pipelines can be divided in two levels: The challenge of finding a viable route in the first place and the design and dimensioning of the mechanical installations to enable the operation as the second one. Caused by the fact of bridging long distances for the transportation of different commodities from a supply point to a demand point, the task to find a cost-effective route through the prevailing terrain is the main objective of long-distance transmission pipeline design (see Fig. 2). Historically the job was handed to surveyors similar to the construction of railway routes. In present days, experts in the field of geomatics are conducting the necessary examinations of topology and further environmental aspects. With the help of geospatial data and geographic information systems (GIS) optimal routes are chosen and further steps in designing and optimizing the facilities of the pipeline can be executed (Adam & Davis, 2009, p. 2). To verify the feasibility of a possible pipeline and assess its economical effectiveness, it is important to not only consider as many influences and constraints in the earliest phases of the planning process but also to use tools to optimize possible routes in relation to the cost drivers in construction and operation of the pipeline. Hence, the analysis of external factors which influence the route of a pipeline must be examined as well. Through the parametrization of such models, optimization algorithms will help to search for routes as a basis for the further process of detailed design outside the scope of this ontology.

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Chapter 2 Ontological Model

To sharpen the picture of the requirements regarding the ontology, the following facts are stated and serve as goals for the design process and application of this ontology:

1. Purpose: This ontology will assist the routing and design of the mainline of long- distance transmission pipelines in early design phases.
2. Scope: All relevant parameters and components of the pipeline regarding its route, in addition to its interaction with the environment along the preliminary route options.
3. Intended end-users: Engineers and planners who are part of the early phases. The end-users can originate from different project parties, e.g., contractors, clients orauthorities.
4. Intended use: A knowledge representation of the required aspects in early phaseplanning of a transmission pipeline, used for parametric modelling with the objective of route optimization and evaluating the feasibility of a pipeline project.

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Chapter 2 Ontological Model

2.2 Description of Transmission Pipeline Systems

To meet the purpose of the ontology, the optimal level of abstraction for describing the system must be chosen. Based on the literature research, the most important elements in terms of route planning could be identified as the pipeline, its method of laying, the environment, and the required facilities. The relation of these elements and specific sub- elements are illustrated in Fig. 3 and outlined below.

Fig. 3: The main elements of pipeline routing and exemplary sub-elements

Regarding the pipeline itself, the fluid is the core requirement for the design. The types of fluids are covering liquids such as crude oil, petroleum products, LNG, liquified petroleum gas (LPG) or plain water, in addition to gases such as natural gas, hydrogen, carbon dioxide, and lastly slurries, where water is mixed with coal, copper or magnetite concentrates in most cases. When it comes to the routing, the parameters of the pipe (such as diameter, material, wall thickness) and its components (such as valves and supports) are secondary and rather a part of the detailed design. (Mohitpour et al., 2007; Mokhatab et al., 2014)

The fluids implication onto the layout of the pipeline are primarily expressed in the choice of the facilities. Facilities along the route enable the operation and monitoring of the pipeline. In case of liquids and slurries, pumps are distributed along the line to manage the flow, while gases need compressor stations to keep the pressure in the required range, as seen in Fig. 4. The pump or compressor positions must be planned early on to ensure cost effectiveness, accessibility during construction and optimal operation. (Mohitpour et al., 2007, pp. 129, 227)

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Chapter 2 Ontological Model

Pipelines can be laid above ground, whereby footings, piles or slabs serve as a support structure. In case of below ground laying, trenches must be dug, and the pipe will be lowered down with cranes after welding (see Fig. 5). The method of laying is an important part for early cost estimates and highly dependent on the environment.

The local environment affects the previously described elements design-wise and therefore regarding their costs. In the first place the environment affects the pipeline due to the terrain. The slope, whether its longitudinal or orthogonal to the pipe, impacts the construction and leads to significant higher costs compared to flat terrain. The effect on the fluids must also be held in account with additional pumps or compressors at the given sections. Therefore, the route should avoid unnecessary inclines but also remain on the shortest possible track. The land use may also affect the position of facilities in such way, that e.g., blowdown valves shouldn’t be located in protected areas and urban areas should be avoided at all to minimize consequences of damage. Depending on the type of soil, the appropriate method of laying must be chosen. In case of arctic or rock soil, above ground laying is preferred, while clay or sand soil allows for below ground laying. The laying of pipelines in case of a road, river, railway, or other type of crossing, must be adjusted to the installation of a bridge, culvert, or trenchless section. Hence, the number of crossings should be minimized in order to avoid the significant higher construction efforts needed within those methods and to reduce the related costs. The following figures are showing exemplary schematics of transmission pipelines. (Mohitpour et al., 2007; Singh, 2013)

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Ontological Model

The subclasses derive from the aspects which are described earlier. They’ll serve as the base components for creating the variables and constraints of a parametric model (see Fig. 10). The next steps included the creation and assigning of object properties and property restrictions. Design options are held ready as individuals inside the route sub classes, where one route concept for a given fluid, and fixed start and end points can be equipped with different options according to the analyzed routings (see Fig. 11). The options are populated with individual characteristics based on the data property assertions. Therefor the coordinates of the start and end points must be stated, as well as the distance of all options, their cumulated elevation, and other route-specific data for comparison with alternative routes. Hand in hand with the creation of classes, properties, and individuals, axioms which describe the relations between the elements are implemented, of which a few examples are listed in Tab. 1 (Krötzsch et al., 2013).

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Atomic concept Individual name

Atomic role Inverse role

Intersection

Union

Top concept Bottom concept

Existential restriction At-least restriction Nominal

Semantic DL

AI aI

RI {⟨x,y⟩∣⟨y,x⟩∈RI}

CI∩DI

CI∪DI

ΔI

∅

{x| some RI-successor ofxisinCI}

{x| at least n RI- successor of x is in CI}

{aI}

Protégé implementation

PipelineRoute Route01Option01

hasFacility isFacilityOf

Route01Option01 hasRiverCrossing River01 and Route01Option02 hasRiverCrossing River01

CompressorFacility and PumpFacility are PipelineFacility

hasFacility Domains: PipelineRoute hasFacility Ranges: PipelineFacility

hasFacility some PumpFacility hasFacility min 1 PipelineFacility

hasRiverCrossing value River01 [hasName “Spree”^^xsd:string]