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The engineering modelling of ship hull girder strength consists of global and local levels. The Smith-type progressive collapse analysis is a typical example of this, in which the global model requires input from the local model to describe the underlying local structural behaviour, i.e., load-shortening curve (LSC). However, the modelling is prone to uncertainty due to the statistical variability of the basic variables (aleatoric uncertainty) and the inadequacy of engineering models in both global and local levels (epistemic uncertainty). The former can be well tackled by a probabilistic sampling, whereas dealing with the latter for ship hull girder strength lacks an established approach. There can be different sources of epistemic uncertainty. In the modelling of ship hull girder strength, this may be partially manifested as that caused by different choices of local engineering models for predicting the LSC. In light of this, a novel probabilistic method is applied in this research to quantify the uncertainty related to the local models, i.e., the combined computational uncertainty of ultimate compressive strength and post-collapse strength of structural elements. The adopted approach is a hybrid method incorporating the Smith-type progressive collapse method with Monte-Carlo Simulation and an adaptable LSC algorithm. Case studies are performed for the first time on four merchant ships under both uni-axial and bi-axial bending load cases. It is shown that the ultimate strength in sagging is subjected to the most significant computational uncertainty as compared with those in hogging and horizontal bending. In a bi-axial load case, the computational uncertainty estimated for vertical bending will be counteracted as the horizontal bending increases. Nevertheless, this change is not directly proportional to the bi-axial load component ratio and appreciably varies between different ship types. The insights and data provided by this study may eventually resolve the epistemic uncertainty in ship hull girder strength estimation so that improving the ultimate limit state-based reliability analysis. [ABSTRACT FROM AUTHOR]

There is an environmentally and economically motivated need to reduce the fuel consumption and air emissions of ships. To achieve a reduction in energy consumption, the energy flow in the entire energy system of a ship must be analysed in both the component, or subsystem, level as well as in a holistic way to capture the interactions between the components. Of the currently available energy consumption monitoring and prediction methods or models, no single model or method can be used to assess the energy efficiency of an arbitrary vessel in both the early design phase and during operation. This study presents a new generic ship energy systems model that can be used for this purpose. This new model has two parts: one for the assessment of a ship’s energy consumption based on an ordinary static power prediction and one for advanced operational analysis, considering hydrodynamic and machinery systems effects. A Panamax tanker vessel was used as the case study vessel to prove the versatility of the model for five example simulations for the design and operation of ships. The examples include variations of the main dimensions, propeller design, engine layout and the operational profile on a North Atlantic route. From the results, different areas with a potential for energy savings were identified. [ABSTRACT FROM AUTHOR]

In this paper, a simple fatigue estimation model using only encountered significant wave height, is used for predicting fatigue accumulation of a vessel during a voyage. The formulation of the model is developed based on the narrow-band approximation. It is assumed that the significant response range, hs, has a linear relationship with encountered significant wave height, Hs. The mean stress up-crossing frequency, fz, is represented by the corresponding encountered wave frequency and it is expressed as a function ofHs. The capacity and accuracy of the model is illustrated by application to one container vessel's fatigue damage accumulation in an amidships detail, operating in the North Atlantic during 2008. For this vessel, all the necessary data needed in the fatigue model, and for verification of it, was obtained by measurements. The results from the proposed fatigue model are compared with the well-known and accurate rainflow analysis. Influence of nonlinearities, e.g. whipping, on fatigue damage predictions and extreme responses is also discussed. [ABSTRACT FROM AUTHOR]

A finite element (FE) tool was developed for the analysis of rolling contact fatigue crack initiation in railheads. An elastic-plastic non-linear kinematic hardening material model is included in the tool, which can model decaying ratcheting rate. The FE tool was applied to rails used in commuter train traffic at a Swedish test site. Two rolling contact conditions were compared, with respect to fatigue crack initiation, by modelling the contact loads differently. The two conditions were newly manufactured rails (Hertzian distribution) and rails that have been in service for 16 months (non-Hertzian distribution). A strategy proposed for fatigue analysis comprises a critical plane approach used together with a multiaxial fatigue model; a damage accumulation rule is also proposed that takes into account low-cycle fatigue and ratcheting damage mechanisms. Together with a two-dimensional FE analysis of a twin disc test, the fatigue evaluation strategy was validated by a set of twin disc data with good agreement. A fatigue analysis of the results from the FE tool show good agreement with observations and measurements made at the Swedish test site with respect to position for fatigue crack initiation, angle of the crack plane and the calculated number of wheel passages to initiation of head checks. Agreement was particularly good for the Hertzian distribution. [ABSTRACT FROM AUTHOR]

Two-dimensional elastic-plastic finite element (FE) simulations of a rolling contact problem are presented. The objective was to evaluate three elastic-plastic material models, all of them able to simulate decay in ratchetting rate, by studying the cyclic ratchetting material response and failure of a pearlitic rail steel. The FE simulation, which were performed for different magnitudes of contact pressure and traction forces showed a large accumulation of shear deformation of the surface at the rolling contact. The critical plane (crack plane) for crack initiation on the crack planes was calculated using this model, as well as an empirical model for failure by ratchetting, for comparison. The results from the evaluation of the three material models show that the material model which could best mimic the stress-strain cycles and ratchetting rate, from cyclic uniaxial experiments, was also able to resolve the stress and strain field correctly in the FE simulations and to give reliable results. Low-cycle fatigue governed fatigue crack initiations, and the angles calculated for the crack plane showed good agreement with observations from experiments. [ABSTRACT FROM AUTHOR]