A major challenge in next-generation industrial applications is to improve numerical analysis by quantifying uncertainties in predictions. In this work we present a formulation of a fully nonlinear and dispersive potential flow water wave model with random inputs for the probabilistic description of the evolution of waves. The model is analyzed using random sampling techniques and nonintrusive methods based on generalized polynomial chaos (PC). These methods allow us to accurately and efficiently estimate the probability distribution of the solution and require only the computation of the solution at different points in the parameter space, allowing for the reuse of existing simulation software. The choice of the applied methods is driven by the number of uncertain input parameters and by the fact that finding the solution of the considered model is computationally intensive. We revisit experimental benchmarks often used for validation of deterministic water wave models. Based on numerical experiments and assumed uncertainties in boundary data, our analysis reveals that some of the known discrepancies from deterministic simulation in comparison with experimental measurements could be partially explained by the variability in the model input. Finally, we present a synthetic experiment studying the variance-based sensitivity of the wave load on an offshore structure to a number of input uncertainties. In the numerical examples presented the PC methods exhibit fast convergence, suggesting that the problem is amenable to analysis using such methods.
We present an arbitrary-order spectral element method for general-purpose simulation of non-overturning water waves, described by fully nonlinear potential theory. The method can be viewed as a high-order extension of the classical finite element method proposed by Cai et al. (1998)[5], although the numerical implementation differs greatly. Features of the proposed spectral element method include: nodal Lagrange basis functions, a general quadrature-free approach and gradient recovery using global L2projections. The quartic nonlinear terms present in the Zakharov form of the free surface conditions can cause severe aliasing problems and consequently numerical instability for marginally resolved or very steep waves. We show how the scheme can be stabilised through a combination of over-integration of the Galerkin projections and a mild spectral filtering on a per element basis. This effectively removes any aliasing driven instabilities while retaining the high-order accuracy of the numerical scheme. The additional computational cost of the over-integration is found insignificant compared to the cost of solving the Laplace problem. The model is applied to several benchmark cases in two dimensions. The results confirm the high order accuracy of the model (exponential convergence), and demonstrate the potential for accuracy and speedup. The results of numerical experiments are in excellent agreement with both analytical and experimental results for strongly nonlinear and irregular dispersive wave propagation. The benefit of using a high-order – possibly adapted – spatial discretisation for accurate water wave propagation over long times and distances is particularly attractive for marine hydrodynamics applications.
When an offshore wind power plant is connected to the grid, there is a risk of amplification of certain harmonics and appearance resonances at the point of connection due to the interaction between the grid network and the wind power plant network. Hence, the plant developer is obliged to maintain the harmonic distortion at the point of common coupling within the planning level limits using harmonic compensation, which is usually done by passive filters. In this paper a novel active harmonic compensation technique using voltage feedback from a non-local bus has been proposed and analyzed. Its effectiveness has been demonstrated through real time simulations on a test system model.
Denne afhandling omhandler steds- og mobilitetsudfordringer samt byudviklingspotentialer
for det, der i afhandlingen betegnes ’transit- og levebyer’. Provins- og havnebyen Hirtshals,
beliggende på Danmarks nordlige vestkyst, fungerer i afhandlingen som gennemgående case,
der overordnet illustrerer, hvordan et sted kan være i vækst og tilbagegang på samme tid.
Afhandlingens problemfelt indskriver sig i en samfundsmæssig kontekst af øget mobilitet samt
centralisering og yderområder, og påpeger provinsbyens rolle som et lokalt knudepunkt samt
havnebyens rolle som et nationalt knudepunkt. Således er casen også et eksempel på et stærkt
mobilitetspåvirket sted i det, jeg benævner ’Gennemfartsdanmark’, hvor mange mennesker
rejser igennem, men kun få gør ophold. Afhandlingen sætter spørgsmålstegn ved, om et sådan
sted overhovedet opfattes som en by med et godt og attraktivt byliv, eller kun som et transit-hub.
Havnen i Hirtshals er et logistisk knudepunkt for både mennesker og gods, med gode
forbindelser til bl.a. Norge, Island, Færøerne og Storbritannien, og med direkte adgang til den
europæiske motorvejskorridor. Der investeres i Hirtshals i store infrastrukturprojekter for at
understøtte havnens aktiviteter og virke, som genererer arbejdspladser og et stigende antal
gennemrejsende erhvervschauffører og turister. Samtidig falder befolkningstallet hastigt: fra mere
end 7.000 indbyggere til mindre end 6.000 indbyggere de sidste 15 år. Afhandlingen adresserer
og udfordrer på den baggrund den i udgangspunktet ofte fremførte samfundsmæssige diskurs,
at øget mobilitet skaber vækst og fremgang for byer per se!
Ph.d.-projektet er opbygget omkring et overvejende kvalitativt forskningsdesign, og søger
derved at komme frem til en dybere forståelse af, hvad der ligger bag det statistiske materiale
om befolknings- og erhvervsudvikling i Hirtshals. Videnskabsteoretisk bygger afhandlingen
på en pragmatisk forståelsesramme, der tilskynder at lade empirien være omdrejningspunkt
for forskning, mens teorier og metoder anses som praktiske værktøjer i vidensproduktionen.
Forskningsprojektet undersøger empirisk forholdet mellem vækst i infrastrukturprojekter,
erhverv, gods og rejsende og tilbagegang i befolkningstal, offentlige funktioner og det byggede
miljø. Dette belyses gennem casestudiet, der er baseret på en række forskellige praktiske metoder,
herunder dokumentanalyser, interviews, spørgeskemaundersøgelser, registerdata og fysiskrumlige stedsanalyser. Blandingen af metoder muliggør at studere casen fra mange vinkler, og
belyse Hirtshals’ fortid og nutid samt fremtidsperspektiver.
Afhandlingen skaber en forståelse omkring casens stedslige og mobilitetsrelaterede
udfordringer, kvaliteter og potentialer, for derved at kvalificere en række byudviklingsperspektiver.
Teoretisk er forskningsprojektet funderet i begreberne sted og mobilitet, og udvikler derudfra
en terminologi omkring ‘transitbyer’ og ‘levebyer’. Den klassiske stedsteori og konventionelle
transportforskning udfordres gennem en relationel og mobilitetsorienteret stedsforståelse, der
bruges til at analysere casen. En relationel og mobilitetsorienteret stedsforståelse betyder, at sted
konkret må opfattes og defineres som en relation mellem fysik og geografi, mobilitet og sociale
sammenhænge, historie og betydning.
På baggrund af afhandlingen kan det konkluderes, at Hirtshals hverken kan forstås isoleret
som transitby eller isoleret som leveby, men at Hirtshals netop består, fungerer og eksisterer i
kraft af begge dele. Derfor peger afhandlingen på, at det er vigtigt i forhold til byplanlægning i
Hirtshals og andre stærkt mobilitetspåvirkede byer og steder, at tænke kvaliteterne ved transitby
og leveby sammen. På baggrund af casestudiet udvikles en relationel og mobilitetsorienteret
stedsstrategi med generelle anbefalinger for Hirtshals og andre transit- og levebyer.
Det er ønsket med denne afhandling at kondensere en række læringspunkter fra
Hirtshals, der kan være medvirkende til at gøre en forskel i praksis. Casestudiets resultater er i
udgangspunktet kontekstafhængige, men rummer samtidig almengyldige kvaliteter. Studiet af
Hirtshals kan således generere værdifuld viden til planlægningen i byer, der som Hirtshals er
stærkt mobilitetspåvirkede, og hvor der kan stilles spørgsmålstegn ved, om den pågældende by
overvejende er en transit- eller leveby?
Green House Gas (GHG) emissions are not the only emissions of concern to the international transport community. SOx emissions are non-GHG emissions that are caused by the presence of sulphur in the fuel. As the maximum percentage of sulphur in automotive and aviation fuels is strictly regulated in most countries around the world, much of the attention in recent years has focused on maritime transport. The attention mainly stems from the fact that in marine fuels the percentage of sulphur can be very high: it can be as high as 4.5 % in Heavy Fuel Oil (HFO), which is the fuel typically used in all deep-sea trades. Even though the amounts of SOx produced by ships are substantially lower than CO2, SOx emissions are highly undesirable as they cause acid rain and undesirable health effects in humans and animals. To mitigate these adverse environmental effects, the international shipping community has taken substantial policy measures. With the introduction of new limits for the content of sulphur in marine fuels in Northern European and North American sea areas, short-sea companies operating in these areas will face substantial additional cost. As of 1/1/2015, international regulations stipulate, among other things, a 0.1 % limit in the sulphur content of marine fuels, or equivalent measures limiting the percent of SOx emissions to the same amount. As low-sulphur fuel is substantially more expensive than HFO, there is little or no room within these companies current margins to absorb such additional cost, and thus significant price increases must be expected. Unlike its deep-sea counterpart, in short-sea shipping such a freight rate increase may induce shippers to use land-based alternatives (mainly road). A reverse shift of cargo would go against the EU policy to shift traffic from land to sea to reduce congestion, and might ultimately (under certain circumstances) increase the overall level of CO2 emissions along the entire supply chain. The purpose of this chapter is to investigate the potential effect of sulphur regulations on the share of cargo transported by the waterborne mode vis-à-vis land-based alternative
This article aims to present the most relevant practices of offshore oil contracting at an international level, in order to better understand the legal dynamics of the sector. The problem investigated deals with the terms of the legal relationship between the State and national and foreign public companies, as well as the relationship between States, with a view to the exploitation of shared offshore oil resources. This problem is current, taking into account both the fact that oil is a scarce resource, as well as the fact that its offshore exploration is particularly complex and risky. This article presents, in a non-exhaustive way, some examples of practices that illustrate contractual trends that have already crystallized. The approach to its content is made from an international law perspective, focused on the transnational challenges posed to States and operators. It is concluded that the sector is characterized by a huge variety of practices, which reveals an ability of operators to adapt to the characteristics of the concrete challenges of an offshore exploration project. It also shows the political and economic particularities of the States involved in the process.
Supply chain researchers are confronted with a dizzying array of research questions, many of which are not mutually independent. This research was motivated by the need to map the landscape of research themes, identify potential overlapping areas and interactions, and provide guidelines on areas of focus for researchers to pursue. We conducted a three-phase research study, beginning with an open-ended collection of opinions on research themes collected from 102 supply chain management (SCM) researchers, followed by an evaluation of a consolidated list of themes by 141 SCM researchers. These results were then reviewed by 10 SCM scholars. Potential interactions and areas of overlap were identified, classified, and integrated into a compelling set of ideas for future research in the field of SCM. We believe these ideas provide a forward-looking view on those themes that will become important, as well as those that researchers believe should be focused on. While areas of research deemed to become most important include big data and analytics, the most under-researched areas include efforts that target the “people dimension” of SCM, ethical issues and internal integration. The themes are discussed in the context of current developments that the authors believe will provide a valuable foundation for future research.
Piracy has unfortunately become a health and safety risk for seafarers in the maritime industry today. However, little do we know about the impact of a pirate hijacking situation and how seafarers cope. Focusing on negotiation communication, the analysis debouches in a discussion of the dynamics of coping strategies, by investigating 173 authentic audio recordings of communication sequences recorded during a pirate hijacking situation that were donated voluntarily by a shipping company. The Captain assessed and reflected on the course of events in the situation, to which the negotiator responded appropriately, with acknowledging brief responses or psychological aid. This is similar to other highly dynamic decision-making settings, where decision-makers tend to continuously reflect and revise their view of the situation (Eraut 2000). The data is also consistent with the “reflection-in-action” concept by Schön (1983) used by van den Heuvel et al. (Cogn Technol Work 16: 25–45, 2014) in their investigation of communication of police officers in hostage situations. However, the coping dynamics changed when the negotiator’s responses became too minimal. This shows how the context and the individual’s cognitive appraisal of the encounter co-shapes the coping dynamics in the situation. It is urged that pre-piracy care and seafarer training involves practical examples and information about roles and coping dynamics in negotiation communication as part of an orchestrated approach to the scourge of piracy.
The shipping industry faces huge challenges with regard to improving its environmental performance. The current regulatory approach has not been successful. Public and private actors increasingly rely on partnerships. The literature on partnerships for sustainability has contributed to a better conceptualisation of the subject. However, less is known about the processes and the outcomes of the partnerships as well as interactions between partnerships. This paper aims to improve the understanding of how partnerships contribute to developing cleaner technologies in the Danish shipping industry. Two partnerships have been analysed: Partnership for Cleaner Shipping and the Green Ship of the Future. Participation, scope and division of roles among partners have influenced both partnerships. Furthermore, both partnerships have developed organisational forms that proved to overcome the tensions in traditional partnerships, between open and information-based networking on the one side and closed and development-oriented collaboration on the other side.
In a number of experiments and field tests of point absorbers, snap loads have been identified to cause damage on the mooring cables. Snap loads are basically propagating shock waves, which require special care in the numerical modeling of the mooring cable dynamics. In this paper we present a mooring cable model based on a conservative formulation, discretized using the Runge-Kutta discontinuous Galerkin method. The numerical model is thus well suited for correctly capturing snap loads. The numerical model is verified and validated using analytic and experimental data and the computed results are satisfactory.