Keyword: ships


An efficient method for estimating the structural stiffness of flexible floating structures

Baoshun Zhou, Zhixun Yang, Mostafa Amini-Afshar, Yanlin Shao, Harry B. Bingham

In the hydroelastic analysis of large floating structures, the structural and hydrodynamic analyses are coupled, and the structural stiffness plays an important role in the accurate prediction of the response. However, there is usually a large difference between the longitudinal and the cross-sectional scales of modern ships, and the sectional configurations are generally complex, making it difficult to obtain the exact structural stiffness. Using a full finite element model to calculate the structural stiffness is inevitably time-consuming. Since modern ship structures are usually nearly periodic in the longitudinal direction, we treat the hull as a periodic Euler–Bernoulli beam and use a novel implementation of asymptotic homogenization (NIAH) to calculate the effective stiffness. This can greatly improve the computational efficiency compared with a full finite element model. Based on a combination of finite element and finite difference methods, we develop an efficient analysis technique to solve the hydroelastic problem for nearly-periodic floating structures. The finite element method is used to efficiently calculate the structural stiffness, and the finite difference method is used to solve the hydrodynamic problem. This proposed technique is validated through several test cases with both solid and thin-walled sections. A range of representative mid-ship sections for a container ship are then considered to investigate the influence of both transverse and longitudinal stiffeners on the structural deformations. A simple method for including non-periodic end effects is also suggested.

Marine Structures / 2024
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Digital Ship Operations – Engine & Equipment Performance

Avendaño-Valencia, Luis David (Projektdeltager)Asimakopoulos, Ioannis (Projektdeltager)Rytter, Niels Gorm (Projektdeltager)

Ship engines are subject to a very demanding work environment, where maximum availability is a must. In this project we look at different operational variables of a marine engine from large cargo ships, with the aim of detecting and trending damage onset on different engine sub-components. This information can be used by owners to expedite O&M interventions and maximize ship availability.

Aalborg Universitet / 2023
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Hydroelastic solutions using a high-order finite difference method based on the mode functions of a Timoshenko beam

Zhou, Baoshun; Amini Afshar, Mostafa; Bingham, Harry B.; Shao, Yanlin

This work is part of the ongoing implementation of hydroelastic solution for ships inside the OceanWave3D-seakeeping code. This solver has been developed by the Maritime Group at DTU- Department of Civil and Mechanical Engineering based on linearized potential flow theory. The numerical implementation has been conducted on overlapping grids using a high-order finite difference method. A Fast Fourier Transform (FFT) has been employed to transform the time-domain hydrodynamic solutions to frequency-domain solutions. A pseudo-impulse tailored to the desired frequency range is used as the forcing for the time-domain solution. In previous work, a preliminary implementation of hydroelastic solutions was implemented in OceanWave3D-seakeeping with an Euler-Bernoulli beam model to represent the eigenmodes of the flexible ship hull. However, shear effects are ignored by this beam theory, even though the shear effect is very important to acurately predict the structural deformation especially for a thick beam model. In this work, ship hulls have been treated using the Timoshenko beam model includ- ing shear effects. The influence of shear effects are also discussed through a couple of numerical test cases. Good agreement with reference solutions illustrates the effectiveness of the numerical implementation. The current work focuses on zero speed, and work is also in progress to validate the implementation at forward speeds

Abstract from 23rd Nordic Maritime Universities Workshop, Göteborg, Sweden / 2023
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Estimating waves via measured ship responses

Ulrik D Nielsen*, Harry B Bingham, Astrid H Brodtkorb, Toshio Iseki, Jørgen J. Jensen, Malte Mittendorf, Raphaël E. G. Mounet, Yanlin Shao, Gaute Storhaug, Asgeir J Sørensen, Tomoki Takami

Optimisation of energy efficiency and operational performance as well as assessment of safety levels and emissions of marine operations require detailed information about the acting wave system. It is possible-with an analogy to classical wave buoys-to estimate the directional wave spectrum by processing sensor measurements of wave-induced responses (e.g., motions and structural responses) from a ship. Compared to other sources of wave data (e.g., buoys, satellites, third-generation wave models), estimation concepts using the ship itself as a buoy provide the wave spectrum at the exact spatio-temporal point, potentially increasing accuracy and with minimal associated cost. This paper gives an overview of the technology, discusses associated uncertainties, and highlights new developments made for estimating waves via measured ship responses.

Scientific Reports / 2023
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Hydroelastic Solutions using a High-order Finite Difference Method on Overlapping Grids

Zhou, Baoshun; Amini-Afshar, Mostafa ; Bingham, Harry B.; Shao, Yanlin

This work is part of the ongoing implementation of generalized modes for ship hydroe- lasticity inside the OceanWave3D-seakeeping solver. The solver has been developed by the Mar- itime Group at DTU- Civil & Mechanical Engineering based on solving the linearized potential flow problem using a high-order finite difference method on overlapping grids. The focus of this paper is a comparison between the hydroelastic solutions obtained using two different implementations of the hydrostatic restoring force coefficients. The first hydrostatic model is according to Newman, and the second model is based on Malenica and Bigot. These two hydrostatic models agree for the rigid modes, but are slightly different for the flexible modes. The results are validated using both numerical and experimental solutions for two different ship geometries at zero forward speed.

9th International Conference Hydroelasticity in Marine Technology, Rome, Italy / 2022
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Projections of shipping emissions and the related impact on air pollution and human health in the Nordic region

Camilla Geels, Morten Winther, Camilla Andersson, Jukka-Pekka Jalkanen, Jørgen Brandt, Lise M. Frohn, Ulas Im, Wing Leung, and Jesper H. Christensen

International initiatives have successfully brought down the emissions, and hence also the related negative impacts on environment and human health, from shipping in Emission Control Areas (ECAs). However, the question remains as to whether increased shipping in the future will counteract these emission reductions. The overall goal of this study is to provide an up-to-date view on future ship emissions and provide a holistic view on atmospheric pollutants and their contribution to air quality in the Nordic (and Arctic) area. The first step has been to set up new and detailed scenarios for the potential developments in global shipping emissions, including different regulations and new routes in the Arctic. The scenarios include a Baseline scenario and two additional SOx Emission Control Areas (SE-CAs) and heavy fuel oil (HFO) ban scenarios. All three scenarios are calculated in two variants involving Business-AsUsual (BAU) and High-Growth (HiG) traffic scenarios. Additionally a Polar route scenario is included with new ship traffic routes in the future Arctic with less sea ice. This has been combined with existing Current Legislation scenarios for the land-based emissions (ECLIPSE V5a) and used as input for two Nordic chemistry transport models (DEHM and MATCH). Thereby, the current (2015) and future (2030, 2050) air pollution levels and the contribution from shipping have been simulated for the Nordic and Arctic areas. Population exposure and the number of premature deaths attributable to air pollution in the Nordic area have thereafter been assessed by using the health assessment model EVA (Economic Valuation of Air pollution). It is estimated that within the Nordic region approximately 9900 persons died prematurely due to air pollution in 2015 (corresponding to approximately 37 premature deaths for every 100 000 inhabitants). When including the projected development in both shipping and land-based emissions, this number is estimated to decrease to approximately 7900 in 2050. Shipping alone is associated with about 850 premature deaths during presentday conditions (as a mean over the two models), decreasing to approximately 600 cases in the 2050 BAU scenario. Introducing a HFO ban has the potential to lower the number of cases associated with emissions from shipping to approximately 550 in 2050, while the SECA scenario has a smaller impact. The "worst-case" scenario of no additional regulation of shipping emissions combined with a high growth in the shipping traffic will, on the other hand, lead to a small increase in the relative impact of shipping, and the number of premature deaths related to shipping is in that scenario projected to be around 900 in 2050. This scenario also leads to increased deposition of nitrogen and black carbon in the Arctic, with potential impacts on environment and climate.

Atmospheric Chemistry and Physics / 2021
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A practical AIS-based route library for voyage planning at the pre-fixture stage

Jie Cai*, Gang Chen, Marie Lützen, Niels Gorm Maly Rytter

In tramp shipping, a preliminary route is required for voyage planning at the pre-fixture stage (before a chartering contract is agreed). Such routes are conventionally designated by using pilot charts or software considering long-term statistical weather. However, it has been experienced by tramp operators that such route solutions often poorly estimated sailing distances for long journeys and thereby cause inappropriate cost estimation and bad voyage plan. To fill this gap, a data-driven methodology is proposed in this paper to establish a practical route library with the consideration of ship sizes, load conditions and seasonality. In this method, it first requires a dividing of ship trajectories into local sea passage and open sea passage. The voyage trajectories made of AIS points are then simplified to pattern nodes based on a speed-weighted geolocation method. Afterwards, the KMeans algorithm is deployed to properly classify these pattern nodes, identifying the most representative nodes (routes) in open sea passages. Simultaneously, the connection points are identified by DBSCAN algorithm, representing local sea passages. Combining the representative routes in open sea passages and the connection points in local sea passages, the most navigated routes between two ports are obtained. Finally, case studies are conducted for the Pacific Ocean and the Atlantic Ocean respectively using global AIS data from tanker vessels to demonstrate the feasibility and effectiveness of this methodology. The proposed route library is capable of providing reliable route references to support the decision-making at the pre-fixture stage.

Ocean Engineering / 2021
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Maritime industry processes in the Baltic Sea Region: Synthesis of eco-inefficiencies and the potential of digital technologies for solving them

Elisa Aro, Niels Gorm Maly Rytter, Teemu Itälinna

ECOPRODIGI (2017-2020) is an Interreg Baltic Sea Region flagship project, which links research organisations, enterprises, associations and business support organisations. Altogether, 21 partners jointly investigate the most critical eco-inefficiencies in maritime processes in the Baltic Sea Region as well as develop and pilot digital solutions for improving the eco-efficiency by focusing on three specific cases: 1) digital performance monitoring of vessels, 2) cargo stowage optimisation at ports and 3) process optimisation at shipyards. Furthermore, looking towards the future, the project partners, on one hand, create a digitalisation roadmap and training modules for future decision makers in the maritime industry but also reach out to policymakers to engage them in discussion regarding how they can support the digital change. This report provides an overview of the project and main findings achieved to date, describes the main eco-inefficiencies identified and presents the potential of digital technologies and new concepts for improving them. Also, as the current digital transformation relates to the way how changes are managed in organisations, this report presents the main challenges and requirements identified in the process of moving towards more digitalised business operations. Finally, the last section looks at the maritime sector from a broader perspective and provides some ideas about the most likely future developments. The main findings of the project so far indicate that major improvements in eco-efficiency can be carried out in the maritime industry. They can be summarised as follows: 1) In the first case, ‘digital performance monitoring’, the project partners estimate, for instance, that fuel consumption and emissions can potentially be reduced by 2-20% based on data and analysis from distinct ship segments, routes and their baseline situations. The reductions are possible to achieve by taking such actions as capitalising on the latest digital technologies, utilising and analysing real-time operational data and vessel performance, anticipating operating conditions and maintenance of the ship and its components, changing working methods and improving practices as well as placing a focus on the training of personnel. 2) In the second case, ‘cargo stowage optimisation’ the project partners identified a set of eco-efficiency bottlenecks in the cargo stowage processes at ports that can be subject to improvement. The use of advanced digital technologies can contribute to more efficient utilisation of vessels and terminal operations. The port stays can be reduced, and, thereby, vessels can sail more slowly and reduce fuel consumption and emissions. Moreover, when stability calculations improve due to further digitalisation of cargo unit data, the ship can be loaded more optimally and the amount of ballast water can potentially be decreased without compromising safety, which again reduces fuel consumption on the sea leg. It is estimated that fuel consumption and emissions can potentially be reduced by 2-10% per route and ship and that additional benefits can be gained on the landside due to future digital decision support tools applied for the end-to-end stowage process. In addition, improved cargo unit pick up time estimates can be provided to customers waiting for the cargo to be handled at port, whereby the service improves. 3) In the third case, ‘process optimisation at shipyards’, improved situational awareness and process management, including the use of new technologies, such as 3D and solutions for managing the complex supply chain, have potential for improving the shipyard processes aimed at increased eco-efficiency. For example, in block building phase 3D technology reduces lead-time and potentially saves hundreds of man-hours in rework due to the fact that more efficient processes and proactive actions are enabled.

ECOPRODIGI Project / 2020
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Ship Propulsion Hydrodynamics in Waves

Simone Saettone

The shipping industry is paramount for global economic growth by enabling the trading of enormous volumes of goods across the world. However, maritime transport is a huge and growing source of greenhouse gas emissions. Consequently, the shipping industry is required to speed up its environmental transition towards a zero-carbon emissions fleet. Alternative marine fuels, in combination with ship optimization in realistic operating conditions, could be a solution to reduce the marine ship emissions drastically.

The emissions of harmful gases and particulates from the engine increase when the ship operates in waves. This phenomenon is particularity problematic for lean-burn natural gas engines because of the increased amount of unburnt methane emitted. The solution to this problem requires studying the interaction between the ship hydrodynamics and the engine dynamics. For this purpose, a coupled engine-shaft-propeller model capable of predicting its performance in waves needs to be developed. At the same time, evaluating the ship propulsion system performance in realistic operating conditions is essential to estimate the installed power of the main engine and to optimize the ship voyage.

The purpose of the present work is to investigate the interaction between propeller loads and engine response of a ship sailing in realistic operating conditions. First, an investigation was carried out to determine the propeller model necessary to estimate the propulsive forces in waves. Second, a coupled propeller-engine model was built to evaluate how the environmental effects influence the ship propulsion system performance in terms of propulsive forces and unburnt methane released in theatmosphere. Third, the effect of waves on the propulsive coefficients was studied by conducting numerical simulations and model experiments.
The traditional method applied to compute the propeller performance in waves, knownas the quasi-steady approach, was adequate to estimate the propulsive forces in realistic operating conditions. The simulations performed with the coupled engine-propeller model proved that neglecting time-varying wake field, ship motions,and propeller close-to-or-breaking water effects would lead to a poor prediction of the propulsive forces in waves. The coupled engine-propeller model allowed determining that the amount of unburnt methane released in the atmosphere considerably increases when the ship operates in waves. The investigation conducted on the propulsive coefficients showed that the effective wake fraction depends on both the propeller loading and the motions of the ship. An inverse non-linear correlation between the thrust deduction fraction and the propeller loading was observed. A small influence of the ship motions on the thrust deduction fraction was noticed. The propulsive efficiency was mainly affected by the variation of the open-water efficiency caused by the propeller loading. Therefore, using the propeller open-water curves or performing overload self-propulsion model-scale experiments in calm water would provide a sufficiently accurate estimation of the time-averaged propulsive efficiency in waves for the considered case studies.
The results of the PhD project are useful to investigate the performance of marine propulsion systems in realistic operating conditions. The techniques and tools employed in the current study can be directly applied in the ship propulsion optimization process to include the effect of waves. The work conducted in this research also constitutes a step towards the implementation of the liquefied-natural gas as a marine fuel.

Technical University of Denmark / 2020
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Emissioner fra skibe i Københavns Havn i en 5-årig periode fra 2015 til 2019

Morten Winther

Denne artikel beretter om CO2, NOx og PM2,5 emissioner fra skibe i Københavns Havn for perioden 2015-2019 beregnet i projektet ” ” Kortlægning af udviklingen i luftforurening fra krydstogsskibe og andre skibe i danske havne” udført af DCE - Nationalt Center for Miljø og Energi under Aarhus Universitet, for Miljø- og Fødevareministeriet (MFVM). De største kilder i havnen i alle år er krydstogtskibe, fulgt af tankskibes oliepumpning (losning af olieprodukter), passagerskibe, tankskibe, containerskibe og general cargo. Mindre bidrag beregnes for ro-ro cargo og slæbebåde samt uddybningsfartøjer, bulkskibe, forskningsskibe, offshorefartøjer og flydekraner. Pr. skibstype i 2019 beregnes følgende resultater for energiforbrug, CO2, NOx og PM2.5 (procentandele i parentes) for krydstogtskibe (56 %, 57 %, 50 %, 71 %), tankskibes oliepumpning (14 %, 13 %, 18 %, 8 %), passagerskibe (9 %, 9 %, 7 %, 9 %), tankskibe (6 %, 6 %, 8 %, 4 %), containerskibe (5 %, 5 %, 6 %, 3 %), general cargo (5 %, 5 %, 5 %, 2 %), slæbebåde (2 %, 2 %, 1 %, 1 %), ro-ro cargo (1 %, 1 %, 1 %, 0 %) og øvrige skibe (2 %, 2 %, 3 %, 1 %). Øvrige skibe omfatter uddybningsfartøjer, bulkskibe, forskningsskibe, offshorefartøjer og flydekraner.Udviklingen i CO2 emissionerne følger udviklingen i energiforbruget. De totale CO2 emissioner ændrer sig kun lidt i perioden fra 2015 til 2019, men varierer en del fra år til år for de forskellige skibstyper. Fra 2015 til 2019 stiger de samlede CO2 NOx og PM2.5 emissioner med hhv. 7 %, 5 % og 31 %. De totale emissionsstigninger skyldes især 24 % flere anløb med gradvist større krydstogtskibe i perioden, der i højere grad benytter tung olie og scrubberteknologi. Scrubberen, hvis funktion er at rense røggassen for svovl, er mindre effektiv til at begrænse udledningen af PM2.5. For krydstogtskibe beregnes CO2[NOx, PM2.5] e missionsstigninger på 34 %[26 %, 62 %]. For alle andre skibe og olie pumpning falder CO2[NOx, PM2.5] emissionerne med hhv. 13 %[8 %, 8 %]og 17 %[15 %, 16 %].

Selected Proceedings from the Annual Transport Conference at Aalborg University / Udvalgte artikler fra Trafikdage på Aalborg Universitet / 2020
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