| 1. |
- Bengtsson, Anders, et al.
(författare)
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Uncertainty of estimated rainflow damage for random loads
- 2009
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Ingår i: Marine Structures. - : Elsevier BV. - 0951-8339 .- 1873-4170. ; 22:2, s. 261-274
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Tidskriftsartikel (refereegranskat)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. |
- Kolsters, Hans, et al.
(författare)
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Optimisation of laser-welded sandwich panels with multiple design constraints
- 2009
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Ingår i: Marine Structures. - : Elsevier BV. - 0951-8339 .- 1873-4170. ; 22:2, s. 154-171
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Tidskriftsartikel (refereegranskat)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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| 3. |
- Liwång, Hans
(författare)
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Survivability of an Ocean Patrol Vessels - Analysis approach and uncertainty treatment
- 2015
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Ingår i: Marine Structures. - : Elsevier BV. - 0951-8339 .- 1873-4170. ; 43, s. 1-21
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Tidskriftsartikel (refereegranskat)abstract
- Military ocean patrol vessels (OPVs) are today an increasingly common type of naval ship. To facilitate the wide range of tasks with small crews, OPVs represent several ship design compromises between, for example, survivability, redundancy and technical endurance, and some of these compromises are new to military ships.The aim of this study is to examine how the design risk control options in relation to survivability, redundancy and technical endurance can be linked to the operational risk in a patrol and surveillance scenario. The ship operation for a generic OPV, including the actions of the threat, is modelled with a Bayesian network describing the scenario and the dependency among different influences.The scenario is described with expert data collected from subject matter experts. The approach includes an analysis of uncertainty using Monte Carlo analysis and numerical derivative analysis.The results show that it is possible to link the performance of specific ship design features to the operational risk. Being able to propagate the epistemic uncertainties through the model is important to understand how the uncertainty in the input affects the output and the output uncertainty for the studied case is small relative to the input uncertainty. The study shows that linking different ship design features for aspects such as survivability, redundancy and technical endurance to the operational risk gives important information for the ship design decision-making process.
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| 4. |
- Stenius, Ivan, et al.
(författare)
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On Structural Design of Energy Efficient Small High-Speed Craft
- 2011
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Ingår i: Marine Structures. - : Elsevier BV. - 0951-8339 .- 1873-4170. ; 24:1, s. 43-59
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents an integrated design procedure for determination of structural arrangement and scantlings for the complete structure of small high-speed craft. The purpose of the procedure is to serve as a tool in the preliminary design stage where it enables generation of weight minimized designs with very limited effort. The design procedure is applied in a material concept study for a high-speed patrol craft. The various concepts include single skin and sandwich composites, aluminum and steel. It is demonstrated that the mass of the aluminum hull structure can be reduced from the original 11.7 tonnes to 9.6 tonnes through application of the presented design procedure. The most weight efficient material concept is a carbon-fiber foam-cored sandwich with a structural mass of 4.8 tonnes, which is about 50% less than the refined aluminum version. Through simple hydromechanic analysis, potential for fuel and CO2 emission reductions of 8% for the refined aluminum version and 27% for the carbon-fiber sandwich version in relation to the original craft are indicated.
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| 5. |
- Sun, Qianyang, et al.
(författare)
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A machine learning-based method for prediction of ship performance in ice : Part I. ice resistance
- 2022
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Ingår i: Marine Structures. - : Elsevier BV. - 0951-8339 .- 1873-4170. ; 83, s. 103181-103181
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Tidskriftsartikel (refereegranskat)abstract
- This article focuses on design of an Artificial Neural Network (ANN) model to estimate ship resistance in ice-covered water by using suitable ship and ice parameters. In order to develop a reliable model, as much ice resistance test data as from the ship sea trials and model test measurements are collected to train the neural network. Different features (ship design parameters and ice mechanic properties) are explored to find a suitable combination of input features. Several algorithms are tested and compared to select a good model for resistance prediction. It turns out that seven features and the Radial Basis Function - Particle Swarm Optimization algorithm (RBF-PSO) can provide a reasonable generalization model. This study shows that the ice resistance predicted by the ANN correlates well with the measured data. The model developed herein can be used as an ice resistance prediction tool with high accuracy compared to the conventional semi-empirical formulae used in polar ship design.
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| 6. |
- Wall, Henrik, et al.
(författare)
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Corrosion rate measurements in steel sheet pile walls in a marine environment
- 2013
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Ingår i: Marine Structures. - : Elsevier BV. - 1873-4170 .- 0951-8339. ; 33, s. 21-32
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Tidskriftsartikel (refereegranskat)abstract
- Corrosion of steel structures in the marine environment is a major problem. The deterioration of this kind of structures is costly and difficult to predict both when designing new structures and when estimating the remaining service life time for existing structures. The aim of this investigation was to find indicative values for the corrosion rate of steel sheet piles on the Swedish west coast. Such corrosion rates (mm/year) can be used both when designing new structures by oversizing the steel thickness and when estimating the bearing capacity of existing sheet pile structures. Earlier investigations on the corrosion rates along the Swedish east coast – with salinity from about 0.2% - 0.8% – are still used today as guidelines for the corrosion rate of all steel structures in the Swedish maritime environment even though the salinity on the west coast can be as high as 3.0%. Steel sheet pile wharfs located in the port of Halmstad on the Swedish west coast were inspected by ultrasonic measurements. Three wharf structures with a total length of about 700 m were inspected. None of the inspected wharfs had or have had cathodic protection. The thickness measurements of the steel sheet pile structures were performed by divers. The age of the three inspected sheet pile structures ranged from 36 to 51 years. The dimensions of the original sheet pile sections are known. One of the quay structures is located along a river. The salinity at all wharfs varied from low values at the surface to approx. 2% at the bottom (also in the river outflow). The measured average corrosion rates were in the same order as the design values in the European code. However, the results indicate increased corrosion rates about one meter below the mean water surface and at the level of the propellers from the ships berthing the most frequented of the inspected wharfs, 3 to 6 meters below water surface. The tolerances of steel sheet thicknesses – usually in the order of ±6% – are often neglected when investigating the remaining thickness in steel sheet piles. A simple calculation model shows that the sheet pile must be almost 50 years of age before an accurate estimation on the corrosion rate can be made, considering the tolerances, if the true original sheet pile thickness is not known.
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| 7. |
- Fitzgerald, John, 1979, et al.
(författare)
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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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Ingår i: Marine Structures. - : Elsevier BV. - 0951-8339. ; 21:1, s. 23-46
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Tidskriftsartikel (refereegranskat)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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| 8. |
- Fitzgerald, John, 1979, et al.
(författare)
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Rigid moorings in shallow water: A wave power application. Part I: Experimental verification of methods
- 2009
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Ingår i: Marine Structures. - : Elsevier BV. - 0951-8339. ; 22:4, s. 809-835
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Tidskriftsartikel (refereegranskat)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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| 9. |
- 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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| 10. |
- Hogström, Per, 1979, et al.
(författare)
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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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Ingår i: Marine Structures. - : Elsevier BV. - 0951-8339. ; 27:1, s. 1-28
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Tidskriftsartikel (refereegranskat)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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