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Numerical Simulation of Combustion under Marine Engine Like Conditions

Arash Nemati

This thesis presents the numerical study of combustion under marine engine like condi- tions. The thesis is divided into two main parts. In the first part, combustion is studied in a large two-stroke marine engine with conventional diesel fuel. In the second part, two different dual-fuel combustion modes of diesel-methane i.e. non-premixed combus- tion and premixed combustion are studied. All numerical models are validated with the experimental data.
First, in a simplified geometry of the marine engine, conjugate heat transfer (CHT) calculations are applied to simultaneously solve the in-cylinder gas phase dynamics and the temperature field within the liner of the engine. The effects of different initial tem- peratures across the liner and the effects of the amount of water vapor in the air on the sulfuric acid formation and condensation in a large two-stroke marine engine are studied. An initial temperature is calculated based on heat transfer modeling and it is observed that the sulfuric acid vapor formation is more sensitive to the variation of the water vapor amount than the sulfuric acid condensation. In the next step, the effects of the turbulence modelling on the simulation of the full cycle of the engine including scavenging process, combustion, and emission formation is studied in a real geometry of a large two-stroke marine research engine. The Unsteady Reynolds Averaged Navier- Stokes (URANS) and Large Eddy Simulation (LES) turbulence models are utilized for modeling of in-cylinder turbulent flow. The accuracy of the tangential velocity and swirl flow in the top of the cylinder where the fuel is injected is crucial to predict the air-fuel mixing correctly. It is found that URANS predicts a solid body rotation for the tangential velocity in this region. However, LES predicts a tangential velocity that is uniformly distributed in the radial direction that is consistent with experimental results. Furthermore, during the scavenging process, LES is able to predict the Burgers vortex upstream of the cylinder near the scavenging ports. Also, LES predicts a higher angu- lar momentum inside the cylinder in comparison with URANS. During the combustion process, the LES model shows a moderately better performance in capturing the experi- mental pressure and heat release rate profiles than URANS. However, the predicted gas temperature at the liner wall is approximately 45 % higher for URANS than LES during the expansion stroke, which is attributed to a higher predicted turbulent viscosity in the URANS case. A higher temperature of gas beside the liner wall may decrease the sulfuric acid formation and increase the heat transfer. The higher predicted swirl by LES than that in URANS leads to an earlier and stronger interaction between the flame and the spray, decreasing the oxidation of the emissions. The second cycle LES simula- tion shows that the solutions after the scavenging process are in-sensitive to the initial conditions and the main governing parameters are boundary conditions and injection characteristics.
Next, two different dual-fuel combustion modes of non-premixed combustion and premixed combustion are studied. The non-premixed combustion is simulated and val- idated with the experimental data of a large two-stroke marine research engine under low and high engine loads. Based on the results, further methane jets penetration in the low load case leads to better air-fuel mixing and a higher combustion intensity than that in the high load. Effects of the pilot diesel fuel injection timing on combustion and emission formation and the governing mechanisms are also investigated in detail. Results indicate that the intense combustion of the accumulated methane expands the methane flame towards the piston when the pilot injection timing is retarded. The NO formation is lower in the high load case due to the lower combustion intensity. Also, retarding the pilot injection timing decreases the NO formation. Furthermore, the effect of the direction of pilot diesel injection is investigated which shows a significant effect on the methane start of combustion and intensity as well as flame propagation direction which leads to different heat transfer trends from the combustion chamber walls.
Premixed combustion is analysed in a constant volume combustion chamber (CVCC) and validated with experimental data. Results show that by simulation of methane-air mixing, the numerical model is able to capture the ignition delay time (IDT) within a maximum relative difference of 7 % to the measurements. A higher relative difference of 38% is obtained when methane gas injection is omitted and the methane-air and temperature are assumed homogeneous. Therefore, it is concluded that the simulation of methane-air mixing process is crucial in this type of combustion due to the presence of inhomogeneities in both methane fuel and temperature distribution after mixing. Creating the idealized inhomogeneities for separately investigation of methane and tem- perature inhomogeneities shows that the inhomogeneity in the temperature has a more profound influence on the IDT than the inhomogeneity in the methane distribution. Furthermore, the effects of the number of pilot fuel nozzle holes on the auto-ignition are studied. The auto-ignition process in two cases with 4 nozzle holes is investigated and compared with the base case with 8 nozzle holes. Considering the same amount of pilot fuel, the injection rate is assumed to be double in one of the cases, while in the other case, the injection duration is doubled. Results show that a reduction of the nozzle hole numbers can improve the pilot diesel ignition in the case with 4 nozzle holes and double injection duration compared to the base case with 8 nozzle holes. However, combustion in the case with 4 nozzle holes and a double injection rate is incomplete due to flame impingement on the walls.

Technical University of Denmark / 2022
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A High-order Finite Difference Method on Overlapping Grids for Predicting the Hydroelastic Response of Ships

Baoshun Zhou

This PhD thesis presents a numerical solution of the hydroelastic problems encountered especially by large flexible ships sailing in waves. The solution is implemented by extending an existing seakeeping tool (OceanWave3D-seakeeping) to allow for the efficient and accurate evaluation of the hydroelastic response of ships. OceanWave3D-seakeeping has been developed by the Maritime Group at DTU-Construct based on solving the linearized potential flow theory using high-order finite differences on overlapping curvilinear boundary-fitted grids. Modal superposition is employed to couple the hydrodynamic and structural analysis of ships at both zero and non-zero forward speed. The ship girder is approximated by an Euler-Bernoulli or a Timoshenko beam, and the vertical bending deformation is mainly considered in this work. The shear effects on the hydroelastic response are also investigated in the Timoshenko beam approximation. The solution has been validated against experimental measurements and reference numerical solutions for several test cases. The correct computation of the hydrostatic stiffness, structural stiffness and hydrodynamic forces is the key to the
accurate prediction of the hydroelastic response, and these three terms are discussed deeply in this thesis.

With respect to the hydrostatic stiffness model, some controversy has long existed in the literature about its correct form for elastic motion modes, with Newman [1] and Malenica [2] arriving at different forms which are respectively defined in earthand body-fixed reference systems. In this thesis a complete derivation of both forms including the buoyancy and gravitational terms is provided, and the equivalence of the two models associated with elastic motions is confirmed.

A finite element method (FEM) is a common way to compute the structural stiffness of ship hulls. However, for large modern ships, a FEM calculation based on a full structure is inevitably time-consuming since distinguished differences between the longitudinal and the cross-sectional scales of ship hulls usually exist, and the sectional configurations are generally complex, bringing difficulties to numerical modeling. Considering that the structure of modern ships (for example container ships), is usually nearly periodic in the longitudinal direction, in this thesis the ship hull is approximated as a periodic beam and a new implementation of asymptotic homogenization (NIAH) is introduced to efficiently calculate the structural stiffness. This can greatly improve the computational efficiency compared with a full FEM model. Several test cases with both solid and thin-walled sections are given to validate the proposed technique. A range of representative mid-ship sections for a container ship are also considered to investigate the influence of stiffeners on the hydroelastic response.

In the hydrodynamic part, zero-speed and forward-speed radiation and diffraction problems including the well-known m−terms in the body boundary conditions, have both been solved. For generalized modes, the boundary conditions using the corresponding generalized m−terms are applied in the calculation. Neumann-Kelvin (NK) and double-body (DB) linearization models are applied as the steady base flow, and their performance is investigated by comparison with experimental measurements. In head seas, the influence of increasing forward speed on the resonant response of the flexible modes is also studied.

Through the integration of hydroelastic analysis using potential flow theory, and advanced numerical techniques, this thesis contributes to a deeper understanding of the complex interaction between flexible ship hulls and ocean waves, offering valuable insights for the maritime industry.

Technical University of Denmark / 2024
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Pragmatic Spaces and the Maritime Security Agenda

Bueger, Christian

The oceans are increasingly understood as a security space. Does the new maritime security agenda lead to new spatial configurations? This chapter introduces the concept of ‘pragmatic spaces’ to explore spatial configurations produced in responses to maritime security. Four exemplary spaces are discussed: how counter-piracy led to the development of high risk areas, how maritime security capacity building produced new regions constructed through codes of conduct, how the identification of smuggling routes established new forms of international partnerships, and how maritime domain awareness systems advance new transnational spaces of surveillance. These new spatial configurations were introduced to manage maritime security issues and enable transnational forms of governance.

Book chapter in in J Anderson, A Davies, K Peters & P Steinberg (eds), The Handbook of Ocean Space. Routledge. / 2021
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Maritime insecurities

Bueger, Christian; Larsen, Jessica

This chapter provides first a discussion of how maritime security has been conceptualized and theorized and how the field has evolved. It discusses the more particular debates on dedicated maritime security issues: piracy, terrorism, smuggling, environmental crimes and the protection of critical maritime infrastructure. Although the oceans have featured occasionally in the literature on security, peace and development, it is fair to say that for decades scholars were suffering from what some have referred to as collective ‘seablindness’. A range of maritime insecurities have been extensively analysed. These include piracy; terrorism; various forms of smuggling; environmental crimes, hereunder illegal fishing; as well as a nascent literature on maritime critical infrastructures. With ongoing crises in different parts of the world’s oceans, maritime insecurity will continue to be recognized as one of the core dimensions of violence and insecurity. Maritime security also needs to be seen in the context of other international policy areas.

Book chapter in in B Osler Hampson, A Õzerdem & J Kent (eds), Routledge handbook of Peace, Security and Development / 2020
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Is There a Case for State Ownership in Ports and Shipping?

De Langen, Peter; Sornn-Friese, Henrik

This chapter assesses the role of state-owned enterprises (SOEs) in ports and shipping. Insights from regulatory economics are used to identify industry characteristics under which the SOE model is expected to be effective. With the use of these insights, characteristics of ports, terminals and shipping services that may lead to the establishment of SOEs are identified. The empirical overview of SOEs in shipping and ports shows a rather large use of SOEs, especially in container terminal operations and port development. The use of SOEs particularly in port development can be well understood with insights from regulatory economics. The majority of SOEs in ports, terminals and shipping are active internationally. This raises important additional research questions, most importantly regarding the strategic rationale of SOE internationalization and the role of geopolitical considerations in international activities.

Book chapter in G. Wilmsmeier, & J. Monios (Eds.), Geographies of Maritime Transport: Transport, Mobilities and Spatial Change / 2020
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Ports and the Circular Economy

De Langen, Peter; Sornn-Friese, Henrik

The ongoing shift toward a circular economy, in which end-of-life (EOL) products are reused, remanufactured, or recycled, has major implications for seaports, especially seaports in metropolitan areas, as in such areas, huge amounts of EOL products are available. Ports are therefore relevant locations for circular economy activities. This chapter identifies the main commodities in volume terms and the set of associated activities and assesses resulting opportunities and threats for ports. Case studies of Dutch ports are used to illustrate this analysis.

Book chapter in R. Bergqvist, & J. Monios (Eds.), Green Ports: Inland and Seaside Sustainable Transportation Strategies / 2019
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Autonomous Ships from the Perspective of Operation and Maintenance

Eriksen, Stig

This PhD theis focuses on identifying the opportunities and challenges that on-board maintenance and practical operation of vessels poses in the development of autonomous ships. Inspired by the rapid development of autonomous vehicles considerable effort and interest is now invested in the development of autonomous ships. So far however, most of the research has focused on the legal aspect of unmanned vessels and on developing a system enabling a vessel to operate within the maritime collision regulation without human interaction. Specifically, the theisi looks into three research questions: (1) How is autonomous technology going to affect the workload required for operating and maintaining modern cargo vessels? (2) How is autonomous technology going to affect the operational patterns of the vessels? And (3) How is autonomous technology going to affect the reliability and utilization rate of the vessels?

The study is planned in cooperation between Svendborg International Maritime Academy (SIMAC) and University of Southern Denmark.

Syddansk Universitet, Teknisk fakultet / 2021
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Capitalism and the Sea: The Maritime Factor in the Making of the Modern World

Federico Jensen

What is the role of the sea in globalized capitalism? In their new book Capitalism and the Sea: The Maritime Factor in the Making of the Modern World, Liam Campling and Alejandro Colás explore this question through a historical and geographical lens. In this book, the authors track the larger history of maritime commerce and pursue new understandings of the role of the sea in the global economy. In doing so, they illuminate the understudied maritime spaces, systems, and flows that underpin the global economy and create the foundations of global material circulation.

The AAG Review of Books / 2022
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Trade makes states

Finn Stepputat

Once known as an example of state collapse, Somali territories today see a number of competing public administrations, which, as this book argues, depend on a dynamic trade sector for revenues. Riffing on Tilly’s idea that ‘war makes states,’ the authors argue instead that ‘trade makes states,’ that the facilitation and capture of commodity flows have been instrumental in making and unmaking state-projects across the Somali territories. The volume draws on multi-sited research of everyday economic life along trade corridors in Somali East Africa, including parts of Kenya and Ethiopia. It examines how government officials, informal traders, militias, local businessmen, international investors, and donors feed into systems of regulatory control in ports, at marketplaces, and along transport corridors. Contributions to the volume draw attention to the ingenuities of transnational Somali trade and the ‘politics of circulation,’ providing important insights into contemporary state formation on the margins of global supply chain capitalism.

DIIS / 2023
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Forecasting for the weather driven energy system – A new task under IEA wind

G. Giebel*, C. Draxl, H. Frank, J. Zack, C. Möhrlen, G. Kariniotakis, J. Browell, R. Bessa, D. Lenaghan

The energy system needs a range of forecast types for its operation in addition to the narrow wind power forecast that has been the focus of considerable recent attention. Therefore, the group behind the former IEA Wind Task 36 Forecasting for Wind Energy has initiated a new IEA Wind Task with a much broader perspective, which includes prospective interaction with other IEA Technology Collaboration Programmes such as the ones for PV, hydropower, system integration, hydrogen etc. In the new IEA Wind Task 51 (entitled "Foreacsting for the Weather Drive Energy System") the existing Work Packages (WPs) are complemented by work streams in a matrix structure. The Task is divided in three WPs according to the stakeholders: WP1 is mainly aimed at meteorologists, providing the weather forecast basis for the power forecasts. In WP2, the forecast service vendors are the main stakeholders, while the end users populate WP3. The new Task 51 started in January 2022. Planned activities include 4 workshops. The first will focus on the state of the art in forecasting for the energy system plus related research issues and be held during September 2022 in Dublin. The other three workshops will be held later during the 4-year Task period and address (1) seasonal forecasting with emphasis on Dunkelflaute, storage and hydro, (2) minute-scale forecasting, and (3) extreme power system events. The issues and conclusions of each of the workshops will be documented by a published paper. Additionally, the Recommended Practice on Forecast Solution Selection will be updated to reflect the broader perspective.

Institution of Engineering and Technology / 2023
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