| 1. |
- Lindgren, Georg, et al.
(författare)
-
Wave characteristics distributions for Gaussian waves - wave-length, amplitude and steepness
- 1982
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Ingår i: Ocean Engineering. - : Elsevier BV. - 1873-5258 .- 0029-8018. ; 9:5, s. 411-432
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Tidskriftsartikel (refereegranskat)abstract
- In as tationary stochastic process the wave-length and amplitude are defined as the difference in time and height between a crest and the following trough. The distributions of these quantities are of great practical importance, but no closed form expressions are known at present. In previous papers we have presented an approximation which gives correct upper and lower bounds, regardless of the covariance structure under Gaussian assumptions. In this paper the suggested approximations are compared to two simpler approximations, one due to Cavanié et al. (1976) based on a cosine process and a new one, derived by replacing the model process by its regression curve.
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| 2. |
- Jönsson, Anette, et al.
(författare)
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Variations in the Baltic Sea wave fields
- 2003
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Ingår i: Ocean Engineering. - 0029-8018. ; 30:1, s. 107-126
-
Tidskriftsartikel (refereegranskat)abstract
- The surface waves in the Baltic Sea are hindcast with the spectral wave model HYPAS during a 12-month period. The model results show a strong temporal and spatial variation in the wave field due to the physical dimensions of the different basins and the predominant wind field. The highest waves in the area are found in the outer part of Skagerrak, as well as in the central and southern parts of the Baltic Proper. To get significant waves above 6 m high, strong winds (15–20 m/s) must have been blowing for 6 to 24 h from a favourable direction over a deep area.
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| 3. |
- Alexandersson, Martin, 1983, et al.
(författare)
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System identification of a physics-informed ship model for better predictions in wind conditions
- 2024
-
Ingår i: Ocean Engineering. - 0029-8018. ; 310:1
-
Tidskriftsartikel (refereegranskat)abstract
- System identification offers ways to obtain proper models describing a ship’s dynamics in real operational conditions but poses significant challenges, such as the multicollinearity and generality of the identified model. This paper proposes a new physics-informed ship manoeuvring model, where a deterministic semi-empirical rudder model has been added, to guide the identification towards a physically correct hydrodynamic model. This is an essential building block to distinguish the hydrodynamic modelling uncertainties from wind, waves, and currents – in real sea conditions – which is particularly important for ships with wind-assisted propulsion. In the physics-informed manoeuvring modelling framework, a systematical procedure is developed to establish various force/motion components within the manoeuvring system by inverse dynamics regression. The novel test case wind-powered pure car carrier (wPCC) assesses the physical correctness. First, a reference model, assumed to resemble the physically correct kinetics, is established via parameter identification on virtual captive tests. Then, the model tests are used to build both the physics-informed model and a physics-uninformed mathematical model for comparison. All models predicted the zigzag tests with satisfactory agreement. Thus, they can indeed be considered as being mathematically correct. However, introducing a semi-empirical rudder model seems to have guided the identification towards a more physically correct calm water hydrodynamic model, having lower multicollinearity and better generalization.
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| 4. |
- Alexandersson, Martin, et al.
(författare)
-
System identification of Vessel Manoeuvring Models
- 2022
-
Ingår i: Ocean Engineering. - : Elsevier Ltd. - 0029-8018 .- 1873-5258. ; 266
-
Tidskriftsartikel (refereegranskat)abstract
- Identifying the ship's maneuvering dynamics can build models for ship maneuverability predictions with a wide range of useful applications. A majority of the publications in this field are based on simulated data. In this paper model test data is used. The identification process can be decomposed into finding a suitable manoeuvring model for the hydrodynamic forces and to correctly handle errors from the measurement noise. A parameter estimation is proposed to identify the hydrodynamic derivatives. The most suitable manoeuvring model is found using the parameter estimation with cross-validation on a set of competing manoeuvring models. The parameter estimation uses inverse dynamics regression and Extended Kalman filter (EKF) with a Rauch Tung Striebel (RTS) smoother. Two case study vessels, wPCC and KVLCC2, with very different maneuverability characteristics are used to demonstrate and validate the proposed method. Turning circle predictions with the robust manoeuvring models, trained on zigzag model tests, show good agreement with the corresponding model test results for both ships. © 2022 The Author(s)
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| 5. |
- Alves Lopes, Rui Miguel, 1992, et al.
(författare)
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A numerical study on the influence of crossflow transition on a marine propeller in open water
- 2024
-
Ingår i: Ocean Engineering. - 0029-8018. ; 310
-
Tidskriftsartikel (refereegranskat)abstract
- This work studies the influence of crossflow transition modelling on the performance and flow field of a controllable pitch propeller. The simulations are performed for two different crossflow terms, and baseline simulations without crossflow transition are performed as well. The results show that in the absence of a crossflow term, the flow over the propeller blades is almost fully laminar. When a crossflow term is included, a significant part of the flow becomes turbulent, thus causing a decrease in the thrust and torque coefficients. The change in the propeller performance is also due to the absence of laminar flow separation near the trailing edge, which is prevented when transition occurs upstream of that location due to crossflow. The comparison between the two crossflow terms shows that one always leads to a larger extent of turbulent flow and earlier transition than the other, although this not always translates in lower thrust and torque, depending on the considered advance coefficient. This illustrates the delicate balance in the effects taking place on the pressure and suction side of the propeller blades, and the importance of correctly including crossflow effects in simulations of model-scale propellers.
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| 6. |
- Anand, R. S., et al.
(författare)
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A comprehensive review on Crossflow turbine for hydropower applications
- 2021
-
Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018 .- 1873-5258. ; 240
-
Forskningsöversikt (refereegranskat)abstract
- A Crossflow turbine is a device used to generate power from hydro, which is a renewable source of energy. The salient feature of this turbine is its simplicity in construction. In the past few decades, variables such as flow diverter, air holes, bidirectional flow were introduced in the turbine design to improve its efficiency. This paper presents a comprehensive review of the performance of the cross flow turbine. The review of literature is classified into experimental and numerical studies. The present study highlights the optimum range of geometrical variables required for the efficient design of a cross flow turbine. The study also emphasizes the importance of employing the cross flow turbine in remote places where run-of-river hydro power plants are feasible, as it provides a low-cost energy solution. The outcome of the present study will help the researchers to identify the research gap based on the present status of work done and to improve the performance of the cross flow turbine further in the future.
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| 7. |
- Andersson, C., et al.
(författare)
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Fully electric ship propulsion reduces airborne noise but not underwater noise
- 2024
-
Ingår i: Ocean Engineering. - Göteborg : Elsevier. - 0029-8018 .- 1873-5258. ; 302
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Tidskriftsartikel (refereegranskat)abstract
- Electrification of ships offers zero-emission travel and is spreading rapidly, but the relation between electric ship propulsion and noise pollution is not generally understood. Here, three different types of diesel-electric hybrid ferries have been measured in two operating modes: running in hybrid mode with the diesel engine powering an electric generator; and running in fully electric battery powered mode. Measurements were performed to simultaneously quantify airborne and underwater radiated noise. Findings are that on-board diesel engines for electricity generation do not contribute a large extent of the underwater radiated noise, whilst a major source of airborne low-frequency radiation.
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| 8. |
- Andersson, Jennie, 1986, et al.
(författare)
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Energy balance analysis of a propeller in open water
- 2018
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Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 158, s. 162-170
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Tidskriftsartikel (refereegranskat)abstract
- This paper proposes a methodology based on control volume analysis of energy, applied on Computational Fluid Dynamics (CFD) results, for analyzing ship propulsion interaction effects as a complement to the well-established terminology, including thrust deduction, wake fraction and propulsive efficiency. The method, titled Energy Balance Analysis, is demonstrated on a propeller operating in open water. Through consideration of a complete energy balance, including kinetic energy flux, turbulent kinetic energy flux, internal energy flux (originating from dissipation) and pressure work, all possible hydrodynamic losses are included in the analysis, implying that it should be possible to avoid sub-optimized solutions. The results for different control volumes and grid refinements are compared. The deviation of the power obtained from the proposed energy balance analysis relative to the power based on integrated forces on the propeller is less than 1%. The method is considered promising for analyzing and understanding propulsor hull interaction for conventional, as well as novel propulsion configurations. The energy balance analysis is conducted as a post-processing step and could be used in automated optimization procedures.
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| 9. |
- Andersson, Jennie, 1986, et al.
(författare)
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Energy balance analysis of model-scale vessel with open and ducted propeller configuration
- 2018
-
Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 167, s. 369-379
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Tidskriftsartikel (refereegranskat)abstract
- This paper focuses on performance analysis of a model scale vessel equipped with an open versus a ducted propeller in self-propulsion using a control volume analysis of energy, applied on Computational Fluid Dynamics (CFD) results. An energy balance analysis decompose the delivered power for each system into internal and turbulent kinetic energy fluxes, i.e. viscous losses, transverse kinetic energy losses, and pressure work and axial kinetic energy fluxes. Such a decomposition can facilitate understanding of system performance and pinpoint enhancement possibilities. For this specific case it is shown that the much higher required power for the ducted propeller configuration to the largest extent is due to higher viscous losses, caused by mainly propeller duct and different rudder configuration. The energy balance analysis is a post-processing tool with the only additional requirement of solving the energy equation, which can be employed with any CFD-code based on commonly available variables.
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| 10. |
- Andersson, Jennie, 1986, et al.
(författare)
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Propeller-hull interaction beyond the propulsive factors-A case study on the performance of different propeller designs
- 2022
-
Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 256
-
Tidskriftsartikel (refereegranskat)abstract
- The propulsive factors are critical for scaling of model-test data, and hence important for the final power prediction. When comparing different propulsion systems based on model-scale tests, differences in propulsive factors, and hence the propeller-hull interaction, are often not well understood. In this study the propeller-hull interaction is instead described and compared using CFD for three different propulsion systems, a tip-unloaded ice-classed propeller, an ice-classed propeller with conventional radial load distribution and a non ice-classed propeller with conventional radial load distribution. To post-process the results KT/KQ is evaluated for one blade around a revolution and complemented with radial distributions of the same measure. Both tip-unloaded blades and sharp leading edges suffer in-behind due to poor performance at low load. Open water performance dependency on Reynolds number reveals that ice-classed propellers are more negatively influenced by the low Reynolds numbers of self-propulsion tests. Further, it is noted that a more even radial load distribution favours a low thrust deduction factor. Since the propulsive factors to a large extent are influenced by scale-effects and also due to that their association to the observed hydrodynamics makes the commonly applied scaling procedure of them questionable, they are not considered representative for ship-scale power prediction.
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| 11. |
- Asnaghi, Abolfazl, 1984, et al.
(författare)
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Analysis of tip vortex inception prediction methods
- 2018
-
Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 167, s. 187-203
-
Tidskriftsartikel (refereegranskat)abstract
- The current study investigates different cavitation inception prediction methods to characterize tip vortex flows around an elliptical foil, and a high skewed low-noise propeller. Adapted inception models cover different levels of complexity including wetted flow, Eulerian cavitation simulations, and Rayleigh-Plesset bubble dynamics models. The tip vortex flows are simulated by Implicit Large Eddy Simulation on appropriate grid resolutions for tip vortex propagation, at least 32 cells per vortex diameter according to previous studies guidelines. The results indicate that the cavitation inception predictions by the minimum pressure criterion of the wetted flow analysis are similar to weak water inception measurements. In the wetted flow analysis, the proposed energy criterion is noted to provide reasonably accurate inception predictions, similar to the predictions by Eulerian cavitation simulations with much lower computational costs. Comparison between high speed videos and numerical results of the propeller shows the capability of the numerical methodology in predicting tip vortex structures in different conditions. The interaction between vortices and their impact on the pressure field and the cavitation inception are also highlighted. The strong dependency of the inception on the initial nuclei sizes are demonstrated, and it is shown that for weaker tip vortices this dependency becomes more significant.
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| 12. |
- Asnaghi, Abolfazl, 1984, et al.
(författare)
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Large Eddy Simulations of cavitating tip vortex flows
- 2020
-
Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 195
-
Tidskriftsartikel (refereegranskat)abstract
- In the current study, tip vortex flows are numerically studied by employing Large Eddy Simulation. Wet flow, cavitation inception, and cavitating tip vortex simulations are carried out on an elliptical foil. The mesh resolution requirements for tip vortex prediction are evaluated by employing different mesh resolutions. Two different LES models, Implicit LES and Localized Dynamic Kinematic Model, are utilized to model the sub-grid scale viscosity, and its impacts on the tip vortex prediction. For the wet flow, vortex properties are computed for each resolution and compared with experimental data. Comparisons show that at least 16 cells per vortex radius is required to predict the tip vortex in the near field region. Employed numerical approach is fully capable of capturing the accelerated axial velocity at the vortex core, and shows good agreement with the experimental observations. The analysis of bubble dynamics shows that tip vortex inception strongly depends on the initial bubble radius, especially where the radius is smaller than 50 μm. The predicted azimuthal velocity, the diameter of the cavitating tip vortex, and the velocity flow fields are compared with experimental measurements. The comparisons show that the current numerical approach can provide accurate prediction of tip vortex flows also in cavitating conditions.
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| 13. |
- Bačkalov, I., et al.
(författare)
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Improvement of ship stability and safety in intact condition through operational measures : Challenges and opportunities
- 2016
-
Ingår i: Ocean Engineering. - : Elsevier. - 0029-8018 .- 1873-5258. ; 120, s. 353-361
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Tidskriftsartikel (refereegranskat)abstract
- Attaining a sufficient level of safety from the point of view of stability is typically considered to be a matter of design. However, it is impossible to ensure safety only by design measures, and operational measures can then represent a complementary tool for efficiently and cost-effectively increasing the overall safety of the vessel. Time could therefore be coming for systematically considering operational measures as a recognised and regulated integral part of a holistic approach to ship safety from the point of view of stability. This paper therefore aims at capturing recent trends of research targeting operational safety measures, with specific attention to the intact ship condition. Open challenges and opportunities for research are identified, potential benefits and shortcomings of different options are discussed, and needs and possibilities for further developments in this area are explored. As an overall goal, this paper aims at providing food for thoughts as well as a ground for further proceeding towards the target of implementing a virtuous integrated approach to intact ship safety, from the point of view of stability, which gives due credit to effective and robust operational risk control options.
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| 14. |
- Bačkalov, I., et al.
(författare)
-
Ship stability, dynamics and safety : Status and perspectives from a review of recent STAB conferences and ISSW events
- 2016
-
Ingår i: Ocean Engineering. - : Elsevier. - 0029-8018 .- 1873-5258. ; 116, s. 312-349
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Forskningsöversikt (refereegranskat)abstract
- In Naval Architecture, the concept of "stability" has a very wide meaning, embracing ship stability fundamentals with ship dynamics and ultimately ship safety. As such, the subject is of paramount importance for its wide implications on design and operation of ships and floating units. Research in this field has, therefore, an important impact on the fleet safety, and the International Conferences on Stability of Ships and Ocean Vehicles (STAB Conferences) and the International Ship Stability Workshops (ISSW) are certainly the venues where expertise and contemporary developments in this specific field tend to be collected and thoroughly debated. With the aim of analysing the current status and possible future perspectives of research in the field of ship stability, dynamics and safety, this paper provides an extensive review of the findings presented at STAB Conferences and ISSW events in the period 2009-2014. The reviewed material is organised according to a set of identified macro-topics of research. On the basis of the reviewed material, consolidated research topics as well as emerging subjects are laid out, and ideas for possible future research are also brought forward. Discussion is also provided regarding the link between research and educational aspects.
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| 15. |
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| 16. |
- Baldi, Francesco, 1986, et al.
(författare)
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Comparison of different procedures for the optimisation of a combined Diesel engine and organic Rankine cycle system based on ship operational profile
- 2015
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Ingår i: Applied Energy. - : Elsevier BV. - 1872-9118 .- 0306-2619. ; 110:Part B, s. 85-93
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Tidskriftsartikel (refereegranskat)abstract
- At a time of strong challenges for shipping in relation to economic and environmental performance, the potential of waste heat recovery has been identified as among the most important technologies to lower fuel consumption. This paper presents the comparison of four different procedures for the optimisation of a combined Diesel and organic Rankine cycle system with increasing attention to the ship operational profile and to the inclusion of engine control variables in the optimisation procedure. Measured data from two years of operations of a chemical tanker are used to test the application of the different procedures. The results indicate that for the investigated case study the application of an optimisation procedure which takes the operational profile into account can increase the savings of the installation of an organic Rankine cycle from 7.3% to 11.4% of the original yearly fuel consumption. The results of this study further show that (i) simulating the part-load behavior of the ORC is important to ensure its correct operations at low engine load and (ii) allowing the engine control strategy to be part of the optimisation procedure leads to significantly larger fuel savings than the optimisation of the waste recovery system alone.
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| 17. |
- Baxevani, Anastassia, et al.
(författare)
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Maxima for Gaussian seas
- 2006
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Ingår i: Ocean Engineering. - : Elsevier BV. - 1873-5258 .- 0029-8018. ; 33:7, s. 895-911
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Tidskriftsartikel (refereegranskat)abstract
- The probability distribution of the height of global maximum for a Gaussian random field evolving in time is studied. In particular, the effect of spreading is studied and the role of the wave kinematics is discussed. It is observed that taking into account time dynamics of spatial characteristics results in distributions different from those obtained for the static case. The results are illustrated by computing the derived distribution for different Gaussian seas for three distinct sampling schemes. The resulting distributions are also used to compute return periods for rogue waves. (c) 2005 Elsevier Ltd. All rights reserved.
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| 18. |
- Begovic, Ermina, et al.
(författare)
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Experimental modelling of local structure responses for high-speed planing craft in waves
- 2020
-
Ingår i: Ocean Engineering. - : Elsevier Ltd. - 0029-8018 .- 1873-5258. ; 216
-
Tidskriftsartikel (refereegranskat)abstract
- The modelling of planing craft dynamics in waves and related fluid-structure interaction is a hard challenge due to the highly nonlinear, transient and stochastic nature of the whole process. This paper explores the prospectives of detailed experimental modelling of the local structure responses for high-speed planing craft in waves. A novel experimental setup is presented where a well-defined model structure is integrated into the hull bottom of a typical planing craft model. The model is instrumented for measuring strains in the model structure, related slamming pressures, craft rigid body motions and accelerations. The experimental setup is thoroughly described and motivated and crucial aspects of the setup are verified through testing in idealized static loading conditions and by modal analysis. The capabilities of the experimental setup are demonstrated through systematic experiments in regular waves. The most indicative results are presented and discussed in relation to corresponding results from time-domain simulations The presented experimental modelling approach is concluded to enable uniquely detailed studies of the complete slamming related fluid-structure interaction process and provides a good tool for further research and development towards establishment of first principles-based methods for hydrodynamic and structure design of high-speed planing craft.
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| 19. |
- Bilandi, R. N., et al.
(författare)
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Hydrodynamic study of heeled double-stepped planing hulls using CFD and 2D+T method
- 2020
-
Ingår i: Ocean Engineering. - : Elsevier Ltd. - 0029-8018 .- 1873-5258. ; 196
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Tidskriftsartikel (refereegranskat)abstract
- In the current paper, we have developed a method, based on 2D+T theory, to model the performance of doubled-stepped planing hulls in asymmetric conditions. We have performed Computational Fluid Dynamics (CFD) simulations to evaluate the difference between the results of the 2D+T method and CFD. We have validated 2D+T and CFD simulations. The quantitative comparison between the results of both methods shows they predict almost similar heeling moment, resistance and trim angle for a doubled-stepped planing hull. Results of non-stepped and doubled-stepped planing hulls are compared against each other, demonstrating that an increase in heel angle has less influence on the performance of the doubled-stepped planing hull. The heeling moment of a double-stepped planing hull is found to be smaller than a heeling moment of a non-stepped planing hull at early planing speeds, but, by the increase in speed, heeling moment of doubled-stepped planing hulls becomes slightly larger.
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| 20. |
- Bitner-Gregersen, E. M., et al.
(författare)
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Recent developments of ocean environmental description with focus on uncertainties
- 2014
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Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 86, s. 26-46
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Tidskriftsartikel (refereegranskat)abstract
- A review of the recent progress made regarding ocean environmental data and models with uncertainties in focus is given in the perspective of marine structures' design and operations. Uncertainties of wind, waves, current, sea water level and ice data and models are discussed and recent achievements leading to improvement of their accuracy are addressed. The study includes mathematical, probabilistic, empirical and statistical models. Particular attention is given to rogue waves. Challenges related to wind data and models due to the increase of offshore wind energy installations are presented focusing on wind forecast, information about the wind profile and extreme wind events. Attention is also given to ice which is of particular importance due to the projected climate changes opening new opportunities in the Arctic regions for the marine industry. Impacts of improved accuracy of environmental description on design and operations of ships and offshore structures are highlighted.
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| 21. |
- Bitner-Gregersen, E. M., et al.
(författare)
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Sea state conditions for marine structures' analysis and model tests
- 2016
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Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 119, s. 309-322
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Tidskriftsartikel (refereegranskat)abstract
- The study reviews, based on the state-of-the-art findings, some uncertainties associated with wave data and models currently used in design and operation procedures of ship and offshore structures. Although the same basic principles prevail for hydrodynamic loads on ships and offshore structures, actual problems and methods for assessing these loads in the design and operation stage are not the same. Different wave data and models are used for specifying design and operational criteria for these two types of platforms and different uncertainties are related to them. Wave data and models used to define sea state characteristics are discussed and particular attention is given to the associated sources of uncertainties. Some weaknesses of wave input used in design and operational procedures for marine structures are pointed out. Focus is also given on uncertainties related to model tests as tank testing is an important supporting tool for design and operation. Impact of some selected uncertainties on wave description and wave loads is demonstrated by examples. (c) 2016 Elsevier Ltd. All rights reserved.
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| 22. |
- Castaldi, Luca, et al.
(författare)
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The effect of spray deflection on the performance of high speed craft in calm water
- 2021
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Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018 .- 1873-5258. ; 229
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Tidskriftsartikel (refereegranskat)abstract
- Hydrodynamic analysis of high speed craft is a complex problem. Naval architects have been improving the efficiency of high speed hulls by introducing hard chines, warping, adding spray rails and steps, or forcing air ventilation. Spray deflectors is a novel spray redirection technology inspired by spray rails. It has shown potential for further improving the performance of high speed craft. Spray deflectors run parallel to the stagnation line from the keel to the chine through the spray area. Previous numerical and experimental studies focusing on spray deflectors have been unable to draw definite conclusions regarding the efficiency and optimal design of the deflectors. This paper aims to experimentally investigate, through towing tank testing, the effect on the total resistance using spray deflectors to redirect the spray. Three spray deflectors were designed for different design speeds, tested, and compared in terms of the resulting bare hull for resistance, trim, and heave response. The new deflector designs did not affect the running position of the hull, allowing for an unequivocal resistance comparison. Deflectors reduced resistance by up to 5% with the highest reduction achieved when the stagnation line crossed the deflector at about a quarter beam from the chine.
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| 23. |
- Cerik, Burak Can, et al.
(författare)
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Revisiting MARSTRUCT benchmark study on side-shell collision with a combined localized necking and stress-state dependent ductile fracture model
- 2019
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Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 187:1, s. 1-16
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Tidskriftsartikel (refereegranskat)abstract
- The MARSTRUCT benchmark study on a small-scale double hull structure penetrated by a hemispherical punch was revisited by employing a combined localized necking and stress-state dependent ductile fracture model. By using the limited information provided to the participants of the benchmark study, the plasticity and fracture model parameters were identified. To model the material behavior beyond moderate plasticity, a combination of the Swift and Voce strain hardening laws was used. The damage indicator framework using the Hosford–Coulomb fracture model, combined with the Domain of Shell-to-Solid-Equivalence (DSSE) concept, was adopted to predict the initiation and propagation of ductile fracture. Using the adopted approach, the predicted instant and force levels corresponding to the fracture initiation in the upper and lower plates were found to be in good agreement with the test results. The deformation of the structural elements was also accurately captured. The benefits of adopting the damage indicator framework and distinguishing different failure modes were investigated.
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| 24. |
- Chatzigiannakou, Maria Angeliki, et al.
(författare)
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Numerical analysis of an Uppsala University WEC deployment by a barge for different sea states
- 2020
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Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018 .- 1873-5258. ; 205
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Tidskriftsartikel (refereegranskat)abstract
- Wave energy converters (WECs) have been deployed onshore, nearshore, and offshore to convert ocean wave movement into electricity. The exploitation of renewable energy sources has restrictions; in the case of wave energy, high installation, maintenance, and decommissioning costs have limited their commercial use. Moreover, these offshore operations can be compromised by safety issues. This paper draws attention to offshore operation safety of a WEC developed by Uppsala University. Specifically, this paper investigates what sea states are suitable for the safe deployment of a WEC from a barge. This study follows recommendations in DNV-RP-H103 for analysis of offshore operations, namely lifting through the wave zone. ANSYS Aqwa is used to find hydrodynamic forces acting on a typical barge, using frequency domain analysis. Based on these hydrodynamic simulation results and methodology given in DNV-RP-H103, tables are created to show the sea states that would allow for the safe installation of a WEC using a typical barge. Considered sea states have significant wave heights varying between 0 m and 3 m and the wave zero crossing periods varying between 3 s and 13 s. The WEC submersions are considered between 0 m and 7 m, i.e. when the WEC is in the air until it is fully submerged. © 2020 Elsevier Ltd
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| 25. |
- Chen, Wenchuang, et al.
(författare)
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Experiments and CFD modeling of a dual-raft wave energy dissipator
- 2021
-
Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018 .- 1873-5258. ; 237
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Tidskriftsartikel (refereegranskat)abstract
- A wave energy dissipator (WED) is proposed in this paper, composed of two asymmetric hinged floaters and two hydraulic cylinders, with the purpose to resist wave-induced relative rotation around the hinge. Experimental studies are performed to explore its performance under a wide range of regular waves. Based on Reynolds-averaged Navier-Stokes equations, a 3D numerical model is set up, considering the non-linear interaction of wave and WED. The agreement between the experimental and numerical results is good. With the validated numerical model, the influence of the WED geometrical factors on energy conversion and wave transmission is examined. For a given raft length, the difference in energy conversion between the two multiplicative inverse fore-and-aft raft lengths is significant, which is dependent on the wave frequency. However, as for the wave transmission, the difference in between is insignificantly small, almost independent of the wave frequency. The findings demonstrate that, for energy conversion, its maximum value per unit length corresponds to a large fore-and-aft length ratio but a small total raft length. The combination of experiments and simulations provides reference for both understanding of hydrodynamic behaviours and design including parameter selection of the dissipator.
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| 26. |
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| 27. |
- Chuang, Zhenju, et al.
(författare)
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Numerical analysis of blade icing influence on the dynamic response of an integrated offshore wind turbine
- 2022
-
Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 257
-
Tidskriftsartikel (refereegranskat)abstract
- When a wind turbine is working in a cold and humid environment, icing may occur which lead to its performance reduction or even blades fracture. In this paper, a CFD-WTIA (Wind Turbine Integrated Analysis) coupled method is established to analyze the blade icing process and its influence on the overall dynamic performance of an integrated jacket-support offshore wind turbine. Firstly, motions of the blades are calculated by the WTIA method and used as input into CFD. Then, dispersed multi-phase model and melting-solidification model are used to simulate the icing growth phenomenon of three-dimensional blades. The k-ε turbulence model is used to calculate the aerodynamic performance before and after icing. Finally, the aerodynamic results after blade icing are returned to WTIA for integrated dynamic response acquisition. At the same time, the dynamic response of the wind turbine under the combined influence of ice and sea ice is analyzed. Results show that the blade ice-accretion increases linearly along the blade span-wise direction and is mainly concentrated on the leading edge of the blade. Lift and drag coefficients are seen deceased and increased respectively after icing. Power production, generator torque, rotor speed, as well as blade vibration are quantitatively studied. The methodology and findings of this paper can provide a good reference for the safety performance evaluation of an icing offshore wind turbine.
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| 28. |
- Coraddu, A., et al.
(författare)
-
Vessels fuel consumption forecast and trim optimisation: A data analytics perspective
- 2017
-
Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 130, s. 351-370
-
Forskningsöversikt (refereegranskat)abstract
- In this paper the authors investigate the problems of predicting the fuel consumption and of providing the best value for the trim of a vessel in real operations based on data measured by the onboard automation systems. Three different approaches for the prediction of the fuel consumption are compared: White, Black and Gray Box Models. White Box Models (WBM) are based on the knowledge of the physical underling processes. Black Box Models (BBMs) build upon statistical inference procedures based on the historical data collection. Finally, the authors propose two different Gray Box Model (GBM) which are able to exploit both mechanistic knowledge of the underlying physical principles and available measurements. Based on these predictive models of the fuel consumption a new strategy for the optimisation of the trim of a vessel is proposed. Results on real world operational data show that the BBM is able to remarkably improve a state-of-the-art WBM, while the GBM is able to encapsulate the a-priory knowledge of the WBM into the BBM so to achieve the same performance of the latter but requiring less historical data. Moreover, results show that the GBM can be used as an effective tool for optimising the trim of a vessel in real operational conditions.
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| 29. |
- Coslovich, Francesco, 1990, et al.
(författare)
-
Added resistance, heave and pitch for the KVLCC2 tanker using a fully nonlinear unsteady potential flow boundary element method
- 2021
-
Ingår i: Ocean Engineering. - : Elsevier Ltd. - 0029-8018 .- 1873-5258. ; 229
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, a fully nonlinear unsteady potential flow method is used to predict added resistance, heave and pitch for the KVLCC2 hull in regular head waves at design speed. The method presents a nonlinear decomposition of the velocity potential and the wave field and an adaptive grid refinement. A formulation for the acceleration potential is used to obtain the pressure. To improve computational efficiency, a Barnes-Hut algorithm is introduced. A grid dependency study and a study on the impact of different time steps on the solution are performed. Numerical results have been compared with experimental data for the design speed. A general good agreement is found for added resistance, especially for longer waves. Heave and pitch are properly computed for all wave lengths in the range λ/Lpp=0.4 to 1.4. © 2021 The Author(s)
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| 30. |
- Depalo, Francesco, et al.
(författare)
-
Effects of dynamic axial stiffness of elastic moorings for a wave energy converter
- 2022
-
Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 251
-
Tidskriftsartikel (refereegranskat)abstract
- This work studies the effects of the dynamic axial stiffness of elastic moorings on the dynamic behaviour of a point absorber wave energy converter. Following two mooring analysis procedures, coupled dynamic analysis of a taut-moored WEC with three legs is performed using the FEM program DeepC in three irregular wave conditions. Two synthetic fibre rope materials are investigated, i.e. a normally stiff polyester and a wire-lay 3-strand nylon rope. The results of WEC motions and mooring tensions obtained from a quasi-static stiffness model and the dynamic stiffness model are compared and discussed. The former analysis applies the non-linear stiffness working curves of the ropes in the simulations, while the latter utilizes the dynamic stiffness expression with an iterative process following a practical mooring analysis procedure. For the nylon rope, the influence of the load amplitude on the dynamic stiffness and the WEC response is presented and analysed. It was found that the quasi-static stiffness model tends to underestimate the maximum mooring tensions, leading to 30%–40% lower results compared to the one accounting for the dynamic stiffness effects. For the studied WEC system, the nylon rope shows advantages over polyester, because of the lower mooring tensions and higher WEC motions.
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| 31. |
- Deutsch, Clemens, et al.
(författare)
-
Glider performance analysis and intermediate-fidelity modelling of underwater vehicles
- 2020
-
Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018 .- 1873-5258. ; 210
-
Tidskriftsartikel (refereegranskat)abstract
- This paper analyses the transit performance of state-of-the-art underwater vehicles and presents an intermediate-fidelity steady-state flight mechanics model for qualitative performance assessment of underwater vehicles. Focusing on the comparison of underwater gliders and propeller-driven AUVs, a simple glide metric is presented and the transit performance of the legacy underwater gliders Slocum, Spray and Seaglider as well as propeller-modified versions thereof is evaluated. The evaluation is based on various data sets from wind tunnel tests and Computational Fluid Dynamics (CFD) studies, and shows that for the respective hull shapes gliding locomotion proves more efficient in ideal conditions. However, biofouling conditions inflict a double penalty on glider performance, rendering gliders inferior to propeller-driven vehicles. The Slocum data set is used to validate a steady-state flight mechanics model for qualitative performance prediction. It is shown that even simplistic models based on semi-empirical and analytical expressions can be successfully used for design optimization through parametrization. Being computationally efficient, the model can be a useful tool for design engineers in early design phases. The model is used to evaluate the effects of wing span on gliding efficiency, indicating that the current design of the Slocum glider is near-optimal.
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| 32. |
- Eslamdoost, Arash, 1982, et al.
(författare)
-
A device for reducing the resistance of transom stern hulls
- 2021
-
Ingår i: Ocean Engineering. - : Elsevier Ltd. - 0029-8018 .- 1873-5258. ; 235
-
Tidskriftsartikel (refereegranskat)abstract
- A novel idea to reduce the resistance of a transom stern hull in displacement and semi-planing modes is investigated. By placing a spoon-shaped device in the recirculating zone behind the transom, the momentum of the forward-moving water will be absorbed, and a pushing force generated on the device. Numerical and experimental techniques are applied on a transom stern hull to optimize the shape and position of the device and to explore in detail the physics behind the gain. For the towed hull at a Froude number of 0.4, the maximum measured resistance reduction is 11%, while the computed maximum reduction is 17%. In self-propulsion with one propeller, the measured power reduction is 15%. The power cannot be computed with the applied propeller model, which is an axial body-force distribution in the propeller disk, but the reduction in thrust using the device is 11%. More significant gains are possible at smaller Froude numbers, while the effect is reduced at higher Froude numbers. Larger gains are achieved by splitting the thrust on two propellers. © 2021 The Authors
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| 33. |
- Eslamdoost, Arash, 1982, et al.
(författare)
-
A pressure jump method for modeling waterjet/hull interaction
- 2014
-
Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 88, s. 120-130
-
Tidskriftsartikel (refereegranskat)abstract
- A fast and robust method for the simulation of waterjet hull interaction is presented. Balancing the thrust force of the waterjet unit with the hull resistance, a method is developed for the prediction of the flow rate through the unit. The method is called the Pressure Jump Method and may be used in combination with both potential flow/boundary layer methods and more advanced viscous flow methods, for instance of the RANS type. In the present work the potential flow/boundary layer approach has been used. Validation of the method is accomplished through comparison of predicted results with measured data. The inlet velocity ratio, nozzle velocity ratio, gross thrust and thrust deduction are all within the experimental scatter. For the case studied the force and moment created by the waterjet unit cause the hull to sink deeper and attain a bow down trim compared to the bare hull case. The thrust deduction fraction is positive both in the computations and the measurements.
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| 34. |
- Eslamdoost, Arash, 1982, et al.
(författare)
-
Analysis of the thrust deduction in waterjet propulsion – The Froude number dependence
- 2018
-
Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 152, s. 100-112
-
Tidskriftsartikel (refereegranskat)abstract
- The definition of thrust deduction in waterjet propulsion is different from that of a propeller driven hull and cannot be interpreted in the same way. A particularly interesting feature of the waterjet thrust deduction is the large variation with Froude number. This is well known from experience, but has never been fully explained. The objective of this paper is to use CFD to address the reasons for these large variations. To this end, the thrust deduction fraction is split into resistance increment fraction and jet thrust deduction fraction. The former is due to the self-propelled hull resistance change in comparison with the bare hull resistance and the latter is due to the difference between gross and net thrust. This split reveals that the main reason for the thrust deduction variation is the hull resistance change. Analysis of the resistance increment in different speed ranges is performed by studying the hydrostatic and hydrodynamic pressure changes on the hull as well as the friction change due to the waterjet system. Despite the negative thrust deduction fraction in the intermediate speed range there is no indication of a resistance reduction compared to that of the bare hull at these speeds.
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| 35. |
- Eslamdoost, Arash, 1982, et al.
(författare)
-
On transom clearance
- 2015
-
Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 99, s. 55-62
-
Tidskriftsartikel (refereegranskat)abstract
- This paper deals with transom stern flow phenomena around the Froude number where the transom clears the water. Experimental and numerical results for a high-speed hull exhibit a pronounced peak in the resistance coefficient at the clearance speed. This is associated with a maximum in the non- dimensional transom submergence, a minimum in the pressure coefficient at the transom edge and a maximum in the curvature of the flow leaving the edge. Just before clearance, the sum of the hydrodynamic and hydrostatic pressures on the transom yields a force pointing forwards, thereby reducing resistance. This pushing force diminishes abruptly as the transom becomes dry. The total pressure resistance of the rest of the hull increases rapidly just before clearance, mostly due to the increase in hydrostatic pressure resistance, caused by the sudden increase in aft draft. It is the rapid loss of the transom pushing force, together with the rapid increase in pressure resistance of the rest of the hull just before clearance that creates the peak in the total resistance coefficient.
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| 36. |
- Feng, Na, et al.
(författare)
-
Predictive compensator based event-triggered model predictive control with nonlinear disturbance observer for unmanned surface vehicle under cyber-attacks
- 2022
-
Ingår i: Ocean Engineering. - : Elsevier. - 0029-8018 .- 1873-5258. ; 259
-
Tidskriftsartikel (refereegranskat)abstract
- The trajectory tracking problem of unmanned surface vehicles (USVs) with external disturbances and input constraints, under denial of service (DoS) is addressed in this paper. We propose a predictive compensator based event-triggered model predictive control with nonlinear disturbance observer (PC-ETMPC with NDO) strategy. A model predictive controller (MPC) based on a nominal USV model is combined with a nonlinear disturbance observer (NDO) to estimate and compensate external disturbances. A predictive compensator (PC) is used to compensate network attack signals, which reduces the adverse impact of cyber-attack on the system, and an event-triggered mechanism is used to save computational resources of the calculation of the MPC. The proposed strategy is feasible for implementation, and its stability is proved to ensure the stable operation of the system. Numerical simulations and comparison are performed to demonstrate the effectiveness and superiority of the proposed control strategy.
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| 37. |
- Gaiotti, Marco, et al.
(författare)
-
A numerical sensitivity analysis on the cohesive parameters of a carbon-steel single lap joint
- 2020
-
Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 198
-
Tidskriftsartikel (refereegranskat)abstract
- One of the key issues concerning the use of composite materials in the construction of steel ships, or vice versa, the use of steel in the construction of composite ships, is related to the ways of joining composite parts to the adjacent steel structure. Carbon-steel joints are of increasing interest for the maritime industry, but knowledge is scarce. Applications of adhesive joints as an alternative method to welding or riveting has numerous advantages. Still, gathering more information about the behaviour of such joints through numerical sensitivity analysis and simulation are necessary to speed up applications on ships and marine structures. The present investigation aims at assessing the sensitivity of the parameters that define the traction separation law on the numerical simulation of the de-bonding of a steel to composite single lap joint, following a previous experimental campaign. The test is intended to induce a mode II separation, although the slight bending moment caused by the misalignment of the two ends leads to mixed mode effects, as well. Two finite element software were compared, ADINA and LS-DYNA. The influence of peak traction, penalty stiffness and energy release rate were investigated, along with the effect of a mixed mode opening behaviour.
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| 38. |
- Gao, Yan, 1970, et al.
(författare)
-
An elastic–plastic ice material model for ship-iceberg collision simulations
- 2015
-
Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 102:1, s. 27-39
-
Tidskriftsartikel (refereegranskat)abstract
- Ship-iceberg collisions are currently a hot topic of research. The modeling of iceberg material is crucial for ice mechanics, and the main objective of the present work is to propose an isotropic elastic-perfectly plastic material model to simulate the mechanical behavior of ice in a ship-iceberg collision scenario for Accidental Limit State conditions. The “Tsai-Wu” yield surface model and a new empirical failure criterion were used to describe the plastic flow of iceberg material, while a cutting-plane algorithm was adopted to address the plastic stress-strain relationship. The proposed iceberg material model was incorporated into the LS-DYNA finite element code using a user-defined subroutine. Calibration of the proposed material model was conducted through a comparison with an abnormal level ice event pressure-area curve. The calculated pressure-area curve was comparable to that recommended by the International Organization for Standardization (ISO) rule. A sensitivity analysis was then conducted, and the proposed ice model was found to be more sensitive to the mesh size than to other parameters. Numerical simulations of iceberg-tanker side and iceberg-ship bow collisions were also analyzed. Moreover, the impact force and energy dissipation were examined. The results from these simulations showed that the proposed isotropic elastic-perfectly plastic iceberg material model can be employed to simulate iceberg behavior in ship-iceberg collisions under Accidental Limit State conditions.
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| 39. |
- Ge, Muye, 1991, et al.
(författare)
-
Investigation on RANS prediction of propeller induced pressure pulses and sheet-tip cavitation interactions in behind hull condition
- 2020
-
Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 209
-
Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the numerical prediction of cavitation and hull pressure pulses induced by a marine propeller operating in behind-hull conditions of a container vessel in model scale. Simulations are performed using commercial package Star-CCM+ and opensource package OpenFOAM using RANS approach and predictions are compared with experimental measurements. A mesh dependency study with respect to wake prediction is also presented. Operating conditions scaled to two different Reynolds numbers with the same propulsion characteristics and cavitation number are considered to study scaling effect. Simulations using tip refined mesh are performed and compared with using base mesh to study the tip vortex generation, tip vortex cavitation, its interaction with sheet cavity and induced pressure pulses. The influence of time step length is also investigated. Star-CCM+ and OpenFOAM predict consistent results. The predicted cavitation patterns agree well compared to experimental measurements as well as pressure pulse levels up to 3~4 times blade passing frequency (BPF) especially for the predictions with tip refined mesh. The sheet cavitation is the major contribution to 1st and 2nd order BPF pressure pulses and its closure has significant contributions to higher-order pressure pulses. Deduced pressure pulses by tip vortex cavitation (TVC) are significant ranging from 3rd order to 10th order of BPFs. The TVC induced pressure pulses are related to its violent bursting behavior which is influenced by the closure of the sheet cavity. © 2020 Elsevier Ltd
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| 40. |
- Ge, Muye, 1991, et al.
(författare)
-
Investigations on prediction of ship noise using the FWH acoustic analogy with incompressible flow input
- 2022
-
Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 257
-
Tidskriftsartikel (refereegranskat)abstract
- Ship noise predictions using FWH acoustic analogy with incompressible flow solution inputs are investigated for a model scale container vessel with a cavitating propeller. Numerical predictions of cavitation and hull pressure pulse predictions are validated first, comparing simulations performed for the tunnel test section and experimental measurements inside a large-size cavitation tunnel. The predictions agree well including the sheet cavitation development, tip vortex cavitation (TVC) bursting, convex shaped sheet cavitation closure line and the traveling re-entrant jet underneath the sheet cavity triggers the TVC bursting behavior. Noise predictions are performed within a large open simulation domain instead of the cavitation tunnel test section. With incompressible solutions, noise levels are predicted based on two different placements of Permeable/Porous Data Surfaces (PDS) where one encloses the cavitating propeller, rudder and downstream wake (PDS−L1) and one encloses the whole ship as a rectangular box (PDS−L2). The FWH noise predictions with impermeable surfaces (S−FWH) are also studied. Differences between predictions using PDS−L1, PDS−L2, and S−FWH are discussed. To compare calculated noise source level (Ls) at different noise receivers at varying distances, normalization assuming spherical spreading acoustic wave is used. In certain combinations of receiver point and method of acoustic computation, the predicted Ls agreed well comparing to experimental measurements, including the prediction with PDS−L2 and receiver close to the PDS and direct probed incompressible hydrodynamic pressure at similar receiver locations. However, with increasing distance to the receiver, the predicted Ls increases for higher frequencies and levels out at unrealistically high levels. To study this phenomenon, a free-field monopole representing the cavity structure dynamics is tested with different combination of PDS and receiver placements, using both incompressible and compressible input. This analysis gives a clear indication that the origin of this erroneous effect is the combination of the FWH acoustic analogy with an incompressible solver.
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| 41. |
- Giassi, Marianna, et al.
(författare)
-
Layout design of wave energy parks by a genetic algorithm
- 2018
-
Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018 .- 1873-5258. ; 154, s. 252-261
-
Tidskriftsartikel (refereegranskat)abstract
- If wave energy systems are to become a viable option competitive with more mature renewable energy sources, the systems must be optimized with respect to maximal electricity production and minimized costs. The number of parameters involved in large-scale wave energy systems is typically too large for traditional optimization methods to be feasible, and the solution space may contain many local minima. Here, an optimization tool for application in wave energy design based on a genetic algorithm is presented. The internal parameters of single point-absorbing wave energy converters (buoy radius, draft and generator damping) are optimized and the results validated against parameters sweep optimization. Further, since the individual devices in a park affect each other by scattered and radiated waves propagating in all directions, the tool is used to find the optimal spatial layout of parks. Arrays with different number of devices are studied and similar optimal layouts appear in all cases, which allows extrapolation of the results to even larger parks. The results show that the tool is effective in finding layouts that avoid destructive interactions and get a q-factor slightly above 1.
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| 42. |
- Gracia, Luis De, et al.
(författare)
-
Comparison of two statistical wave models for fatigue and fracture analysis of ship structures
- 2019
-
Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; Vol.187
-
Tidskriftsartikel (refereegranskat)abstract
- Ocean crossing ship structures are continuously suffering from wave loads when sailing at sea. The wave loads cause large variation of structural stresses, leading to fatigue accumulation in ship structures. For the fatigue life prediction of ship structures, it is important to obtain both the long-term distribution and the time history of wave-induced loads. An essential step is to get reliable wave statistics and accurate description of the stochastic nature of sea state along a ship’s sailing routes during her service time. Generally, the wave statistics are pro- vided by the classification societies as a joint probability of significant wave height and mean wave period, also known as wave scatter diagram. In addition, different statistical wave models have been developed to describe wave environments along arbitrary shipping routes based on different data sources, e.g., hindcast data, satellite measurements, buoys, etc. In this paper, two statistical wave models based on hindcast data and satellite wave measurements are briefly introduced and compared with the wave measurements carried out by onboard radar. Both of the wave models are then used to generate the wave environments along given shipping routes. The effectiveness of the wave models is demonstrated by comparing the stochastic nature and the statistical char- acteristics of simulated sea state histories with those of the source oceanographic data. Finally, an application of the wave model to the fatigue assessment is presented.
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| 43. |
- Gu, Yingjie, et al.
(författare)
-
Numerical simulation of ship maneuverability in level ice considering ice crushing failure
- 2022
-
Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018 .- 1873-5258. ; 251
-
Tidskriftsartikel (refereegranskat)abstract
- For polar ship operating in ice-covered areas, numerical prediction and relevant research on maneuverability are particularly important. In this paper, a numerical method considering circumferential crack fracture of level ice based on former research is applied to calculate ice load and predict motion of ship turning in level ice. The difference between bending failure and crushing failure are also taken into consideration during the turning simulation, meanwhile crushing failure pattern is validated with measured data. The turning performance of icebreaker AHTS/IB Tor Viking Ⅱ based on present method is analyzed and compared with full scale measurement. The simulated icebreaking capability of the ship is also validated with sea trials and previous work. The results show that good agreement is achieved and the accuracy of the numerical prediction is improved by including crushing failure into previous research.
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| 44. |
- Gunbeyaz, Sefer Anil, et al.
(författare)
-
Workers' exposure to dust and potentially toxic elements during steel cutting in two ship dismantling cases
- 2023
-
Ingår i: Ocean Engineering. - : Elsevier Ltd. - 0029-8018 .- 1873-5258. ; 270
-
Tidskriftsartikel (refereegranskat)abstract
- Ship dismantling is the recommended recycling solution for the end of a ship's life, but the process is not free of occupational risk. Despite proper regulations, there are underlying chemical and physical hazards, mainly due to the cutting of steel parts, which is the core of the recycling process. The overall aim of this research study is to determine, in two case study examples, the ship recycling workers' potential occupational exposure by inhalation of chemical agents generated by the torch cutting process of coated and de-coated steel. This was carried out specifically through (i) monitoring and measuring ship recycling workers' local environment for the inhalable (total dust) and respirable (fine dust) fractions during their working operations, (ii) analysing the heavy metal content of the dust and (iii) calculating and comparing this against occupational exposure limits, (iv) comparing de-coating operations with cutting of coated and de-coated steel. Results of this study show that without further mitigation workers involved in torch cutting processes are at high risk of exposure to heavy metals by inhalation as these are exceeding the norms defined by regulatory bodies. © 2023 The Authors
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| 45. |
- Gypa, Ioli, 1991, et al.
(författare)
-
Controllable-pitch propeller design process for a wind-powered car-carrier optimising for total energy consumption
- 2023
-
Ingår i: Ocean Engineering. - : Elsevier Ltd. - 0029-8018 .- 1873-5258. ; 269
-
Tidskriftsartikel (refereegranskat)abstract
- Wind-powered ship propulsion (WPSP) is the concept where the wind is the main source of thrust, while the traditional propulsion system operates when needed. This type of propulsion can lead to considerably reduced emissions, something that the shipping community is striving for. A well-known example of WPSP is the Oceanbird with the goal to cut emissions of up to 90%. In this study, the propeller design process for a wind-powered car-carrier (wPCC) such as the Oceanbird is investigated, what the various challenges of WPSP are and therefore how an automated optimisation procedure should be approached. A controllable-pitch propeller was selected as suitable propeller type for the operation of the wPCC, and various functions such as windmilling, feathering and harvesting have been explored. Regarding the optimisation procedure, an essential input is the definition of the operational profile, in order to determine the most important conditions for the route. The main objective of the optimisation is the minimisation of the total energy consumption (TEC), calculated based on a selection of conditions using the potential flow solver MPUF-3A. Cavitation has been evaluated by the blade designer, through an interactive optimisation method. The results showed that designing and optimising for the most highly loaded condition led to solutions with the lowest TEC. © 2022 The Author(s)
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| 46. |
- Göteman, Malin, 1980-, et al.
(författare)
-
Resilience of wave energy farms using metocean dependent failure rates and repair operations
- 2023
-
Ingår i: Ocean Engineering. - : Elsevier. - 0029-8018 .- 1873-5258. ; 280
-
Tidskriftsartikel (refereegranskat)abstract
- Emerging offshore renewable energy technologies are expected to become an important part of the futureenergy system, and reliability for these new technologies in different metocean scenarios must be guaranteed.This poses a challenge in extreme weather scenarios like storms, in particular for less mature technologiessuch as wave energy. Not only the offshore survivability must be controlled; the restoration after disruptiveevents and failures should be addressed and optimized. Offshore operations are costly and cannot be carriedout if the weather is too harsh, and the resulting downtime after failures may be financially devastating forprojects. In this paper, the resilience of large wave energy systems is studied with respect to wave conditions,metocean dependent failure rates, and weather windows available for offshore repair operations. A metocean-and time-dependent failure rate is derived based on a Weibull distribution, which is a novelty of the paper.The performance of the farm is assessed using the varying failure rates and metocean data at different offshoresites. Critical metocean thresholds for different offshore vessels are considered, and the resilience is quantifiedusing relevant measures such as unavailability and expected energy not supplied. The resilience analysis iscoupled to an economic assessment of the wave farm and different repair strategies. Our results show thatthe commonly used assumption of constant failure rates is seen to overestimate the annual energy productionthan when a more realistic varying failure rate is used. Two offshore sites are compared, and the availabilityis found to be higher at the calmer site. Most of the evaluated repair strategies cannot be considered to beeconomically justified, when compared to the cost of the energy not supplied.
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| 47. |
- He, Yapeng, et al.
(författare)
-
Two-phase energy efficiency optimisation for ships using parallel hybrid electric propulsion system
- 2021
-
Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 238
-
Tidskriftsartikel (refereegranskat)abstract
- Developing a green, intelligent, and efficient power system is an important way for the shipping industry to respond to increasingly stringent emission regulations, and to achieve improvements in energy conservation and efficiency. In this study, a two-phase energy efficiency optimisation method is proposed for reducing energy consumption. The method comprises a combination of speed optimisation and energy management. On the demand side, the minimum accumulated power consumption required by the propeller is set as the objective function for the speed optimisation model, whereas on the supply side, the lowest cost of energy consumed by the hybrid power system is set as the objective function for the energy management model. An inland parallel hybrid electric powered bulk carrier is selected for a case study of the two-phase energy efficiency optimisation method. The optimisation results are compared with the energy consumption data of a bulk carrier under normal working conditions. The results show that the proposed method can reduce the energy consumption by 2.60% and 9.86% in the westbound and eastbound voyages, respectively. Accordingly, this study can provide methodological support for inland hybrid-powered ships aiming to achieve intelligent energy efficiency management.
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| 48. |
- Hogström, Per, 1979, et al.
(författare)
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Assessment of the crashworthiness of a selection of innovative ship structures
- 2013
-
Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 59:1, s. 58-72
-
Tidskriftsartikel (refereegranskat)abstract
- The purpose of the current study is to assess a selection new innovative crashworthy side-shell structures, with respect to their contribution to the crashworthiness of ships, and compare them to a conventional reference structure. Explicit finite element (FE) simulations are used to assess the performance of each structure on a small-scale experimental structure as well as in simulations of large-scale ship collisions. The structures compared are divided into two concepts: the maximization of striking bow-struck ship contact area by allowing for a large intrusion depth of the bow before the watertight integrity is breached (ductile design), and the maximization of energy absorption of the structure and low intrusion depth of the striking bow (strength design). The assessment is made by comparing the intrusion depth before rupture of the inner side-shell of a double-hull structure occurs, energy absorption during the indentation, the final damage opening area as well as the weight and manufacturing costs of each structure. It was found that the strength design concept – the X-core structure – was in favour of the ductile design concept – the corrugated inner side-shell structure. The results provide basis for discussing the potential and challenges related to the implementation of each structure.
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| 49. |
- Hosseini, Azim, et al.
(författare)
-
Drift test analysis of a conventional planing hull utilising CFD and 2D+t models
- 2024
-
Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018 .- 1873-5258. ; 308
-
Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the maneuvering characteristics of a planing hull free to move in heave and pitch directions undergoing a steady drift test. Results assess and compare predictions from Computational Fluid Dynamics (CFD) Detached Eddy Simulation (DES) and a 2D + t strip theory models against available experimental data from Katayama et al. (2005). At high yaw angles and high Froude numbers of predictions from both models marginally deviate from the experimental longitudinal force measurements. Whereas strip theory confronts difficulties in predicting dynamic trim angle and CG rise-up when either Froude number or yaw angle increases and hence nonlinear hydrodynamics prevail, CFD generally agrees well with experimental data. The CFD model is seen to result in numerical ventilation in zero-drift cases, leading to lower pressure and a localized reduction in the skin friction coefficient. These phenomena are hypothesized to contribute to the under-prediction of trim angle and longitudinal force in zero-drift scenarios. Strip theory provides less reliable results in terms of predicting the sway forces at larger yaw angles, the yaw moment at low Froude numbers and sway forces and associated maximum pressures near the stagnation line. This model cannot capture the asymmetric pressure distribution that emerges on the bottom of the hull at large speed and yaw angles, which is likely to be one of the reasons for errors in predicting the side force. Detached Eddy Simulations demonstrate the strong asymmetric vorticity field formation on the exposed side of the hull at nonzero drift angle. This means that added masses used in the 2D + t model can cause large errors in equilibrium predictions.
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| 50. |
- Huang, Luofeng, et al.
(författare)
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An investigation on the speed dependence of ice resistance using an advanced CFD+DEM approach based on pre-sawn ice tests
- 2022
-
Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 264
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Tidskriftsartikel (refereegranskat)abstract
- Over the past decades, the underlying mechanism of level ice resistance changing with ship speed has not been fully understood, particularly the resistance component due to ship interactions with broken ice pieces. Pre-sawn ice test can negate icebreaking component from the whole resistance of a ship in level ice, providing an effective approach to decompose ship-ice interactions and investigate the speed-dependent resistance from broken ice pieces. This work has built a computational model that can realistically simulate a ship advancing in a pre-sawn ice channel. The model applies Computational Fluid Dynamics (CFD) to solve the flow around an advancing ship, which is coupled with an enhanced Discrete Element Method (DEM) to model pre-sawn ice pieces. Model-scale experiments have also been conducted at the Aalto Ice Tank to validate the simulations, which shows the computational model can provide a reasonable estimation of the pre-sawn ice's resistance and movement around the ship. Upon validation, the dependence of ice resistance on ship speed was analysed. The simulations enable underwater monitoring of the ice motions, indicating that the speed dependence results from the mass of ice submerged underneath the ship and the displacement of broken ice induced by the ship. The identified relationships are more complex than the widely-used assumption that ice resistance linearly changes with ship speed in all cases, which provides a deeper understanding of ice resistance. As such, the findings from this study can potentially facilitate improvements in relevant empirical equations, useful for ship design, operational strategies and maritime management in polar regions.
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