| 1. |
- Lindgren, Georg, et al.
(författare)
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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
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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, et al.
(författare)
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System identification of Vessel Manoeuvring Models
- 2022
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Ingår i: Ocean Engineering. - : Elsevier Ltd. - 0029-8018 .- 1873-5258. ; 266
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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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| 4. |
- Anand, R. S., et al.
(författare)
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A comprehensive review on Crossflow turbine for hydropower applications
- 2021
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Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018 .- 1873-5258. ; 240
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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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| 5. |
- Andersson, C., et al.
(författare)
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Fully electric ship propulsion reduces airborne noise but not underwater noise
- 2024
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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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| 6. |
- 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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| 7. |
- Andersson, Jennie, 1986, et al.
(författare)
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Energy balance analysis of model-scale vessel with open and ducted propeller configuration
- 2018
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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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| 8. |
- 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
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Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 256
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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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| 9. |
- Asnaghi, Abolfazl, 1984, et al.
(författare)
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Analysis of tip vortex inception prediction methods
- 2018
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Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 167, s. 187-203
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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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| 10. |
- Asnaghi, Abolfazl, 1984, et al.
(författare)
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Large Eddy Simulations of cavitating tip vortex flows
- 2020
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Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 195
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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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