| 1. |
- Li, Zhiyuan, 1974, et al.
(författare)
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Time-domain fatigue assessment of ship side-shell structures
- 2013
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Ingår i: International Journal of Fatigue. - : Elsevier BV. - 0142-1123. ; 55:1, s. 276-290
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Tidskriftsartikel (refereegranskat)abstract
- Loads acting on ship side-shell structures are complex and vary randomly over time. The current study proposes a direct calculation procedure for the fatigue assessment of ship side-shell structures. The calculation procedure is characterised by nonlinear time-domain hydrodynamic simulations followed by finite element (FE) analyses. Sensitivity and feasibility analyses of the proposed time-domain procedure were carried out, and the calculated fatigue damages were compared with full-scale measurements made on a container vessel. Fatigue life analyses were carried out by both the spectral method and the time-domain approach. In addition, two approaches for local stress analysis are presented and discussed: an engineering-based definition of the stress concentration factor (SCF) and a proposed local stress factor (LSF) that utilises stress ranges extracted from the stress history. The results from the fatigue analysis using the LSF indicated a shorter fatigue life than the results obtained using the SCF. This difference is observed because the LSF accounts for the effects of wave-induced loads under ship operation conditions in a more realistic manner.
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| 2. |
- Ringsberg, Jonas, 1971, et al.
(författare)
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Fatigue crack growth in welded rails
- 2005
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Ingår i: Proceedings of The 11th International Conference on Fracture (ICF11). ; , s. 1-6
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Konferensbidrag (refereegranskat)
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| 3. |
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| 4. |
- Ringsberg, Jonas, 1971, et al.
(författare)
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Mooring forces in a floating point-absorbing WEC system–a comparison between full-scale measurements and numerical simulations
- 2021
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Ingår i: Ships and Offshore Structures. - : Taylor and Francis Ltd.. - 1744-5302 .- 1754-212X. ; 15:S1, s. S70-S81
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Tidskriftsartikel (refereegranskat)abstract
- The study presents an investigation of Waves4Power’s WaveEL 3.0 wave energy converter (WEC). It was used as a reference for full-scale measurements of the mooring forces and buoy motions in a measurement campaign 2017 at an installation location off the coast of Runde in Norway. A numerical simulation model of the installation was developed in the DNV GL software SESAM. Unfortunately, the sea state conditions were not measured during the measurement campaign. Hence, a methodology was developed that used the recorded motion data to compute the sea state conditions at the test site. The simulated WEC motions based on the computed sea states agreed very well with the measured WEC motions. The measured and simulated mooring forces were compared under various environmental conditions. 3-hour sea state realizations are typically preferred in numerical simulations. However, influences from the tide at the test site showed that sea states were normally stationary for only 1–2 h. The measured and simulated average mooring forces agreed very well during 1-hour periods, whereas the simulations overestimated the mooring forces in 3-hour periods because of the tide. © 2020 The Author(s).
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| 5. |
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| 6. |
- 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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| 7. |
- 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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| 8. |
- 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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| 9. |
- 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
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Ingår i: Ocean Engineering. - 0029-8018. ; 310:1
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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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| 10. |
- 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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| 11. |
- 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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| 12. |
- 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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| 13. |
- 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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| 14. |
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| 15. |
- 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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| 16. |
- 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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| 17. |
- Ekberg, Anders, 1967, et al.
(författare)
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Guest editorial
- 2005
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Ingår i: Wear. ; 258:7-8, s. 953-954
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Tidskriftsartikel (refereegranskat)
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| 18. |
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| 19. |
- Evegren, Franz, et al.
(författare)
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Structural fire integrity testing of lightweight multiple core sandwich structures
- 2017
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Ingår i: Progress in the Analysis and Design of Marine Structures - The 6th International Conference on Marine Structures (MARSTRUCT 2017). - : CRC Press. ; , s. 869-876
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Konferensbidrag (refereegranskat)abstract
- Lightweight structures become increasingly important to reduce environmental impact and to improve payload/deadweight ratio of ships. Significant weight savings can be accomplished by replacing steel with fibre reinforced polymer (FRP) sandwich panels. An assessment is then necessary to ensure that equivalent fire safety is provided, since these structures are combustible. To support such assessments, this paper presents results from vertically loaded fire resistance tests of two structures: (1) a “conventional” FRP sandwich bulkhead with thermal insulation (providing load carrying fire resistance for 60 minutes) and (2) a multiple core FRP sandwich bulkhead without insulation. Both bulkheads were constructed for and tested with the same design load. The multiple core sandwich bulkhead demonstrated structural fire integrity performance well beyond 60 minutes whilst having a significantly lower structural weight and thickness. The new type of multiple core sandwich structure thus provides great potential, both from a weight-savings and a fire safety perspective.
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| 20. |
- Gao, Yan, 1970, et al.
(författare)
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An elastic–plastic ice material model for ship-iceberg collision simulations
- 2015
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Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 102:1, s. 27-39
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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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| 21. |
- Heggelund, Svein Erling, 1970, et al.
(författare)
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Quasi-static assessment of response to slamming impact on free fall lifeboats
- 2015
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Ingår i: Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE. ; 3, s. 1-10
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Konferensbidrag (refereegranskat)abstract
- Design against impact loads (slamming) can be challenging and time consuming and can involve complex calculations. Application of simplified, quasi-static calculation approaches will make the design process much easier. In this paper, such simplified methods are discussed using free fall lifeboats as a case. Results from non-linear FE-analysis show that the response is non-linear due to large deformations. The impact pressure is then mainly carried by membrane stress and the dynamic response is small. A non-linear beam theory approach for hand calculation is established. As the non-linear calculation model is the most realistic, it is recommended that this is used in an initial design assessment. Although the results are on the conservative side, simple hand calculations including non-linear geometry can be used to predict the maximum strain. Linear methods are also investigated. However, these methods should be used with more rigid structures such as stiffened steel and aluminium panels.
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| 22. |
- Heiskari, Janne, et al.
(författare)
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Influence of the design constraints on the thickness optimization of glass panes to achieve lightweight insulating glass units in cruise ships
- 2023
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Ingår i: Marine Structures. - : Elsevier BV. - 0951-8339. ; 89
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Tidskriftsartikel (refereegranskat)abstract
- The increasing complexity and size in cruise ships demands for lightweight structures and practical but accurate design methods. Conventionally, the focus has been on the steel parts of the ship, as they make most of its weight. However, the proportions of other materials are increasing. Therefore, this study attempts to provide better understanding how one could reach the lightweight designs of insulating glass units (IGUs) in ships. These are windows where at least two glass panes are separated by a hermetically sealed cavity. They are thin-walled structures that benefit not only from the geometrically nonlinear behavior, but also from the load sharing. Considering these effects, their behavior is studied using the nonlinear Finite Element Method and Particle Swarm Optimization. Different design criteria are imposed on the thickness determination of the glass panes with different shapes. Rectangular, triangular, and circular shapes are considered. The results show that the triangular shapes have the least weight for a given area when the deflection criterion is the dominating one. When maximum principal stress is the thickness defining criterion, the shapes perform almost equally well. The ratio between the pane thicknesses had the most influence on the behavior of the IGU. As it increases, i.e., one pane is significantly thicker than the other, the load sharing percentage drops, but it provides the most lightweight solution. Closer it is to 1, more equally the structural stresses are divided between the panes, i.e., redundancy is achieved. Finally, it is possible to establish a simple but effective method for the thickness determination of these IGUs using the results of this study. However, more work is required, including numerical analysis and experimental testing.
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| 23. |
- Heiskari, Janne, et al.
(författare)
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On the thickness determination of rectangular glass panes in insulating glass units considering the load sharing and geometrically nonlinear bending
- 2022
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Ingår i: Thin-Walled Structures. - : Elsevier BV. - 0263-8231. ; 171
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Tidskriftsartikel (refereegranskat)abstract
- The number and size of windows has increased in large cruise ships, especially on the top decks. They have therefore become a weight and stability-critical component of the structure. Their thickness is determined according to the classification rules which are generalized for all type of passenger ships. That is, the provided formulae are based on linear-elastic, small deformation, plate theory and therefore more suitable for smaller windows in non-weight critical applications. However, majority of the windows are large insulating glass units (IGUs) that exhibit two e ects that the rules do not currently consider: development of membrane stresses in the glass panes at large deflections due to the von Karman strains (geometric nonlinearity) and interaction of the glass panes due to the internal cavity pressure between them (load sharing). Both increase the load bearing capacity of the IGUs. Therefore, extension to the thickness determination is needed for achieving the lightweight design. This paper uses nonlinear Finite Element Method to study the IGUs static response under uniformly distributed load considering the e ects. The response consists of principal stress and deflection of the panes, and the cavity pressure. Validation is carried out by experimental results from scientific literature. Case study on typical panes from cruise ships indicate that considering the two beneficial effects, the thickness of the glass panes in the IGUs may potentially be reduced between 26-54 % with respect to the classification rule-based design. That is, by using the same allowable principal stress criterion between the linear and nonlinear predictions.
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| 24. |
- Heiskari, Janne, et al.
(författare)
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Thickness optimization of insulating glass unit in cruise ships
- 2022
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Ingår i: Proceedings of 15th International Symposium on Practical Design of Ships and Other Floating Structures (PRADS 2022). - 9789537738884 ; , s. 1-15
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Konferensbidrag (refereegranskat)abstract
- Modern cruise ships employ more and more windows and glass structures, especially on the top decks. However, lightweight solutions are desirable as the cruise ships are weight and stability sensitive vessels. The design of the windows according to the classification rules is common for all type of passenger vessels and is based on linear plate theory for monolithic glass panes. However, the windows separating the indoor and the outdoor spaces are insulating glass unit-type (IGU) windows that consist of at least two glass panes separated by a hermetically sealed cavity. These IGUs exhibit two effects that the rules do not currently consider: 1) geometric nonlinearity of the glass panes and 2) load sharing between them. The authors recently included these effects in a nonlinear Finite Element analysis and showed their beneficial influence on the generated stress state of a rectangular IGU under static uniform pressure. There, only maximum principal stress design constraint was considered. However, there are other design constraints (e.g., deflection limit) that arise for fulfilling the IGUs intended function. Therefore, the nonlinear FE model and the design constraints are implemented in a Particle Swarm Optimization (PSO) routine to calculate the optimized thicknesses of the glass panes for different sized IGUs. Thus, this study aims to present how the different designs constraints affect the IGUs response and what are their implications on the reflected classification rules. The results indicate that the thickness determination is sensitive to the chosen constraints. Choosing the constraints is not a trivial task and requires further experimental work.
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| 25. |
- Hess, Paul, et al.
(författare)
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ISSC Technical Committee III.1 - Ultimate Strength
- 2022
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Ingår i: Proceedings of The 21st International Ship and Offshore Structures Congress (ISSC 2022). ; 1, s. 395-499
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Konferensbidrag (refereegranskat)abstract
- Concern for the collapse behaviour of ships and offshore structures and their structural components under ultimate conditions. Uncertainties in strength assessment shall be highlighted. Attention shall be given to the influence of response to load combinations including accidents; fabrication imperfections; life-cycle effects; and user approach. Consideration shall be given to the practical application of methods.
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