| 1. |
- Alexandersson, Martin, et al.
(författare)
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A comparison of ship manoeuvrability models to approximate ship navigation trajectories
- 2023
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Ingår i: Ships and Offshore Structures. - : Taylor and Francis Ltd.. - 1744-5302 .- 1754-212X. ; 18:4, s. 550-557
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Tidskriftsartikel (refereegranskat)abstract
- It is essential to describe a ship’s manoeuvrability for various applications, e.g. optimal control of unmanned surface vehicles (USVs). In this study, the capability of two recognised manoeuvrability models to predict ships’ trajectories is investigated based on both simulation and open-water experiment test data. The parameters of these models are estimated by a statistical learning method. The goodness of the two estimated models for describing a merchant ship’s manoeuvrability is first studied using her manoeuvring simulation data. Then, experimental manoeuvring tests to use a USV in open water with wind and drifting effects are used to check the conventional model identification procedures. Finally, some modifications and adjustments are proposed to improve the conventional procedures. It shows that the proposed procedures can accurately derive the ship’s manoeuvrability based on experimental data. © 2022 The Author(s).
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| 2. |
- Alexandersson, Martin, et al.
(författare)
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Analysis of roll damping model scale data
- 2021
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Ingår i: Ships and Offshore Structures. - : Taylor and Francis Ltd.. - 1744-5302 .- 1754-212X. ; 16:S1, s. 85-92
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Tidskriftsartikel (refereegranskat)abstract
- Having an accurate prediction of ship roll damping is crucial when analysing roll motions. In this paper, the simplified Ikeda method (SI-method) is compared with the original Ikeda method. The methods are compared using results from a database of roll decay tests carried out on modern merchant ships and a smaller set of predictions in which the original Ikeda method was used. It was found that most of the ships in the database had dimensions outside the limits of the SI-method. Thus, the SI-method showed poor agreement with model tests outside its limits but acceptable agreement for ships within limits. It was found that the deviations were caused by extrapolation errors of the wave-damping in the SI-method. Two ways to improve the accuracy of the SI-method were proposed based on regression, which gave about the same accuracy as the original Ikeda method. © 2021 The Author(s).
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| 3. |
- Alexandersson, Martin, et al.
(författare)
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Prediction of roll motion using fully nonlinear potential flow and ikeda’s method
- 2021
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Ingår i: Proceedings of the International Offshore and Polar Engineering Conference. - : International Society of Offshore and Polar Engineers. - 1098-6189 .- 1555-1792. - 9781880653821 ; , s. 1670-1679
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Konferensbidrag (refereegranskat)abstract
- Getting the best possible accuracy with the lowest possible computational cost is an important factor in the early design stage of ships. Potential flow-based analysis presents such a solution for seakeeping analyses. The accuracy of roll motion in potential flow is however not so good, due to the large influence from vicsous roll damping, which is missing in these calculations. This paper proposes a hybrid method, as a solution to this problem, where the viscous roll damping from Ikeda’s semi-empirical method is injected into an existing 3D unsteady fully nonlinear potential flow (FNPF) method. The hybrid method is investigated using roll decay tests with the KVLCC2 test case. This investigation shows that the accuracy of simulated roll motions is significantly improved and also shows good agreement with the corresponding roll decay model tests.
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| 4. |
- 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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| 5. |
- Andersson, Peter, 1986, et al.
(författare)
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Development and analysis of composite car deck structures
- 2012
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Ingår i: Proceedings of The 2nd International Conference on Light Weight Marine Structures (LIWEM 2012). ; , s. 1-11
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Konferensbidrag (refereegranskat)abstract
- This study discusses the subjects of the joining of and lashing in a composite car deck structure. Systems engineering methods were used to develop concepts for the joining of and lashing in a predetermined composite car deck section. Conceptual designs were evaluated by means of finite element analyses with respect to stakeholder-defined criteria, such as strength and the maximum allowed deflection during loading. The evaluation and analyses resulted in a composite car deck design composed of a glass fibre-reinforced plastic sandwich with balsa core material. The core has chamfered edges for easy assembly and disassembly by screws through single laminate edges. For the lashing of cars, metal inserts in prefabricated holes were proposed.
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| 6. |
- Cai, Fanfan, et al.
(författare)
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Characteristics and mechanisms of low-alloy high-strength steel corrosion behavior under barnacle adhesion based on a comparison experiment
- 2023
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Ingår i: Corrosion Science. - : Elsevier BV. - 0010-938X. ; 217
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Tidskriftsartikel (refereegranskat)abstract
- A comparative experiment was set up in a field site and laboratory to study the effect of barnacles (model organisms of macrofouling) on the corrosion behavior of a low-alloy high-strength steel. The results indicated that barnacle adhesion can slow the corrosion rate of steel in an immersion environment by hindering the diffusion of corrosive ions. It was found that barnacle adhesion had a significant promotion effect on localized corrosion. Due to steel’s high corrosion rate, the corrosion-impeding effect was improved, and the promotioneffect on localized corrosion was weakened. The study proposed a corrosion mechanism model influenced by barnacles.
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| 7. |
- 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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| 8. |
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| 9. |
- Daiyong, Zhang, 1991, et al.
(författare)
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A comparison of ship maneuverability models to approximate ship navigation trajectories
- 2021
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Ingår i: Proceedings of The 6th International Conference on Ships and Offshore Structures (ICSOS 2021). ; , s. 1-9
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Konferensbidrag (refereegranskat)abstract
- For optimal control of unmanned surface vehicles (USVs), it is essential to understand the maneuverability of the USVs. In this study, two well-recognized maneuverability models are compared for their capability to predict the trajectories of a simulation and an experiment ship models. The parameters of these maneuverability models are estimated by a statistical learning method. The goodness of the two models for describing a simulated merchant ship’s maneuverability is firstly studied using her simulated trajectories. Finally, the capability of those modelling methods is further investigated using experimental tests of a ship model at an open lake. The experimental tests can model a bit “real” sailing conditions to a USV with wind and drift effects. Finally, some modification and improvement techniques are suggested to accurately derive her maneuverability model based on experimental data.
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| 10. |
- Depalo, Francesco, et al.
(författare)
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Effects of dynamic axial stiffness of elastic moorings for a wave energy converter
- 2022
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Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 251
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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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