| 1. |
- Bengtsson, Anders, et al.
(author)
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Uncertainty of estimated rainflow damage for random loads
- 2009
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In: Marine Structures. - : Elsevier BV. - 0951-8339 .- 1873-4170. ; 22:2, s. 261-274
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Journal article (peer-reviewed)abstract
- One way to assess the uncertainty in fatigue damage analysis is to use a so-called safety index. In the computation of such an index the coefficient of variation for the accumulated damage is needed. Employing the rainflow cycle count method for fatigue damage leads to, in most cases, complicated calculations. Here we present a new and simplified method to estimate the coefficient of variation for the accumulated damage when only one sample path of the load is available. Non-stationary, slowly changing, Gaussian loads are given special attention. The approach is illustrated by means of stationary Gaussian loads with nine different spectra, a measured non-Gaussian load, a skewed load and the wave load accumulated during one year in a "seasonally changing environment"
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| 2. |
- Fitzgerald, John, 1979, et al.
(author)
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Including moorings in the assessment of a generic offshore wave energy converter: A frequency domain approach
- 2008
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In: Marine Structures. - : Elsevier BV. - 0951-8339. ; 21:1, s. 23-46
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Journal article (peer-reviewed)abstract
- A method to include the influence of mooring cables in the frequency domain analysis of wave energy converters is presented. In brief the method consists of:(i) A non-linear time domain solution of the mooring line in isolation and at an appropriate equilibrium condition. This is done by enforcing a sinusoidal displacement at the mooring attachment point in each translational degree of freedom. This is repeated at a number of frequencies.(ii) The amplitude and phase of the resulting force is recorded, allowing the equivalent linear resistive and reactive contribution of the mooring line to be estimated separately. Using results at a number of frequencies, frequency dependent impedance properties of the mooring cable can be estimated.(iii) Considering the attachment point and orientation of the mooring cables in a suitable equilibrium condition of the device, the contribution of each mooring cable is resolved to the global co-ordinates of the device and added to the frequency domain equation of motion.The method here is applied to a generic wave energy device based on a truncated vertical cylinder of 100 tonne displacement. The results for the unmoored device are compared to the same device with moorings of varying configuration. The results indicate that moorings may have a significant impact on the performance of devices of this scale, both beneficial and detrimental. The introduction of mooring terms can upset device symmetry and introduce significant cross coupling in the overall mechanical impedance of the device. Arrangements where this can benefit as well as detriment performance are studied.
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| 3. |
- Fitzgerald, John, 1979, et al.
(author)
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Rigid moorings in shallow water: A wave power application. Part I: Experimental verification of methods
- 2009
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In: Marine Structures. - : Elsevier BV. - 0951-8339. ; 22:4, s. 809-835
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Journal article (peer-reviewed)abstract
- Experimental work carried out at 1:60 scale in a wave flume assessed the pitch motion and anchor loading of 3 articulated tower installations in 50 m water depth while being exposed to north Atlantic storms with Hs of 15.2 m and Tp of 18.4 s. The three installations differ only in that their mass and buoyancy characteristics provide a natural period in pitch at equilibrium of 13 s, 20 s and 34 s respectively. It is verified that the dominant behaviour can be simulated by a relatively simple mathematical model, allowing the critical parameters of peak anchor loads and pitch angles to be calculated and extrapolated to full scale. It is demonstrated from the experimental and simulation results that the mass characteristics of a non surface piercing tower can be used to offset some of the challenges of moving to shallow water. If done correctly, it is possible to keep horizontal anchor loads under control and reduce vortex-induced transverse loading at the expense of increased pitch motions. Overall, the use of articulated tower installations in water depths of 50 m would appear to be technically feasible, even in exposed areas. The limitations on the size of such structures and the consequences of the resulting pitch accelerations and induced anchor loads are the subject of further study. It is proposed that the model verified herein can be used to further assess their potential at delivering viable wave power position mooring systems.
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| 4. |
- Heiskari, Janne, et al.
(author)
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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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In: Marine Structures. - : Elsevier BV. - 0951-8339. ; 89
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Journal article (peer-reviewed)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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| 5. |
- Hogström, Per, 1979, et al.
(author)
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An extensive study of a ship's survivability after collision – A parameter study of material characteristics, non-linear FEA and damage stability analyses
- 2012
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In: Marine Structures. - : Elsevier BV. - 0951-8339. ; 27:1, s. 1-28
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Journal article (peer-reviewed)abstract
- Throughout the world, ships are continuously being declared as total losses and a significant part of these accidents are collisions between ships. The International Maritime Organization strives towards a more risk-based view on addressing the damage stability of ships. The current study addresses the survivability following a ship collision by the use of a sequential (de-coupled) computational methodology. The methodology is comprised of structural analysis of a collision scenario followed by dynamic damage stability simulations of the struck ship in order to establish the time to capsize of the struck ship. The emphasis of the current investigation is on the structural computations of the collision event; explicit finite element analyses are presented for a case study of a collision scenario. In particular, uncertainties of input parameters in the finite element simulations and their impact on the shape and size of the damage opening area, and time to capsize of the struck ship, are addressed. Material modelling aspects are studied; scatter in material properties within a material class as well as damage modelling. In addition, the effects of using a deformable or rigid striking bow section, the friction coefficient, the collision angle and the speed of the striking ship are studied. On the basis of the results presented, assumptions commonly used in these kinds of analysis are discussed. Recommendations for a sufficient level of simplifications for arriving at reliable results in numerical simulation of ship collisions are made.
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| 6. |
- Huang, Luofeng, 1993, et al.
(author)
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Ship resistance when operating in floating ice floes: derivation, validation, and application of an empirical equation
- 2021
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In: Marine Structures. - : Elsevier BV. - 0951-8339. ; 79:1, s. 1-20
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Journal article (peer-reviewed)abstract
- With the effects of global warming, the Arctic is presenting a new environment where numerous ice floes are floating on the open sea surface. Whilst this has improved Arctic shipping navigability in an unprecedented way, the interaction of such floes with ships is yet to be understood to aid the designing of ships and route planning for this region. To further explore this topic, the present work develops a procedure to derive an empirical equation that can predict the effects of such floes on ship resistance. Based on a validated computational approach, extensive data are extracted from simulations of three different ships with varying operational and environmental conditions. The ice-floe resistance is shown to strongly correlate with ship beam, ship buttock angle, ship waterline angle, ship speed, ice concentration, ice thickness and floe diameter, and the regression powers of each of the parameters on resistance are ascertained. This leads to a generic empirical equation that can swiftly predict ice-floe resistance for a given ship in a given condition. Subsequently, demonstrations are given on the incorporation of the derived equation into a set of real-time Arctic ship performance model and voyage planning tool, which can predict a ship’s fuel consumption in ice-infested seas and dynamically suggest a route with the least safety concern and fuel consumption. Moreover, the equation is validated by providing ice resistance prediction for experimental and full-scale conditions from multiple sources, showing high accuracy. In conclusion, the empirical equation is shown to give valid and rapid estimates for ice-floe resistance, providing valuable insights into ship designs for the region, as well as facilitating practical applications for polar navigation.
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| 7. |
- Jia, Junbo, 1979, et al.
(author)
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Structural behaviour of a high tensile steel deck using trapezoidal stiffeners and dynamics of vehicle–deck interactions
- 2005
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In: Marine Structures. - : Elsevier BV. - 0951-8339. ; 18:1, s. 1-24
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Journal article (peer-reviewed)abstract
- As an early part of a large design and fabrication-oriented project FasdHTS funded by the GROWTH programme of the European Commission, an exotic concept ship was designed in very high tensile steel (EHS690) with the purpose of finding out consequences for design and production. The project has already produced a considerable bank of knowledge for design and shipyard production in this material.This paper presents analysis and discussions on static and dynamic behaviour of a high tensile steel deck designed with trapezoidal stiffeners. First, a finite element model of the deck structure is created. The influence of support condition for the longitudinal girders, and the contact area between the vehicle tyre and panel were analysed. The results from modal analysis of the structure under different load conditions are presented. The different load conditions comprise the unloaded and loaded deck, and the load type, i.e. cargo loads or vehicle loads (car loads or truck loads). From the frequency response analysis under harmonic excitation, it shows how the locations and numbers of cars parked on the deck influence the dynamic response of the structure. Furthermore, by studying the cardeck interaction, it is found that the effects of normal cargo loads are quite different from the vehicle loads due to the spring/damping effects of the vehicles. It is suggested that the carloads have a similar mechanism to that of tuned mass dampers. Finally, two transient analyses of the structure due to excitations transferred from deck supports and lorry braking-induced loading are performed. It is suggested that the deck structure and vehicle design could have more interactions with each other.
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| 8. |
- Jia, Zhibin, 1974, et al.
(author)
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A return period based plastic design approach for ice loaded side-shell/bow structures
- 2009
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In: Marine Structures. - 0951-8339. ; 22:3, s. 438-456
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Journal article (peer-reviewed)abstract
- Based on the design ice load that corresponds to a certain return period, a practical approach for designing the frames behind the side-shell or the bow of a ship subject to ice loading is proposed. Four typical types of section profiles have been selected for modelling and numerical analysis. Nonlinear finite element analyses that involve both the geometric and material nonlinearity were performed. From the analyses, the relationships between the loads and the beam’s cross-section properties were obtained for different permanent set requirements. These relationships were then used for finding the section modulus from which the cross-section of the beam can be decided. Finally, a design example is presented for illustration.
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| 9. |
- Kolsters, Hans, et al.
(author)
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Optimisation of laser-welded sandwich panels with multiple design constraints
- 2009
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In: Marine Structures. - : Elsevier BV. - 0951-8339 .- 1873-4170. ; 22:2, s. 154-171
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Journal article (peer-reviewed)abstract
- This paper investigates the possibilities for structural optimisation of laser-welded sandwich panels with an adhesively bonded core and uni-directional vertical webs. Closed form expressions for the equivalent stiffness and elastic buckling strength of laser-welded sandwich panels are discussed and numerically evaluated to demonstrate the effect of parameter variations on stress and deflection. Due to the number of design variables and constraints a structural optimisation method based on the method of moving asymptotes (MMA) is implemented and used to minimise the structural weight per square meter of panel for a typical accommodation deck configuration. It is concluded that, within the span of production parameters and rule requirements, substantial improvements can be made with or without an adhesively bonded core. Without core material and without any changes to the surrounding structure the structural weight for standard production panels can be reduced considerably, by reducing the face plate thickness and by using thinner and fewer webs. Additional weight can be saved by removing all but a few webs and injecting low-cost polyurethane foam into the cavities, giving added thermal-acoustic insulation, or by incorporating a more structural core with greater thickness and higher density, by which the free span of the sandwich panel can be increased.
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| 10. |
- Kuznecovs, Artjoms, 1990, et al.
(author)
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Methodology for the simulation of a ship’s damage stability and ultimate strength conditions following a collision
- 2021
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In: Marine Structures. - : Elsevier BV. - 0951-8339. ; 79:1, s. 1-19
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Journal article (peer-reviewed)abstract
- This paper presents a methodology called SHARC developed for the simulation and analysis of a ship’s damage stability and ULS conditions following a collision. SHARC combines three types of methods: advanced nonlinear finite element simulations that simulate the collision scenario, a dynamic damage stability simulation tool called SIMCAP, and a modified Smith method for the ULS analysis of a collision-damaged ship structure. The novelty of the presented methodology is that it can be used for real-time simulations to study the ingress of water through the damage opening of a struck vessel and how it affects the ship’s stability, structural integrity (ULS) and survival capability against, e.g., capsizing. The results for an intact and a damaged oil tanker under noncorroded and corroded structural conditions and various sea states are presented to demonstrate the features of SHARC.
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