Since the 19th century hopper dredgers have been used for civil operations such as land reclamation and water way maintenance. In the past 25 years a trend of scale enlargement of hopper dredgers driven by economic and productivity reasons is seen. Scaling of the designs has effect on strength and fatigue assessment as well on settling of particles which affect the rate op production. This thesis is focussed on the fatigue assessment of the hopper dredger. Cracked damages in coaming and bottom door areas have been found in relatively large hopper dredgers that are classed by Bureau Veritas. According to Bureau Veritas rules for steel ships fatigue assessment is required if the ship has length greater than 170 m but damages have also been observed in hopper dredgers with a smaller length. This indicates that the hopper dredger design demands for a specific fatigue assessment procedure. The hopper dredger has a unique characteristic load profile consisting of loading and unloading cargo several times a day in combination with small wave heights due to reduced freeboard regulations. Special interest is given on the effect of the loading and unloading cycle in the corners of the bottom discharge openings. It is suspected that the effect of this characteristic cycle may be underestimated and requires an alternative assessment procedure. The main question is what the contribution of this cycle is and how it should be assessed. The relatively low frequency of the cycle raises the suspicion of low-cycle fatigue and this phenomenon is therefore investigated. It is concluded that the loading and unloading cycle has a major contribution to the fatigue damage in the bottom opening corners. In fact 97% of the fatigue damage is induced by the dredging cycle and therefore this cycle could be seen as the sole cause for fatigue cracks in the bottom opening corner structural details. The high stress ranges confirm the suspicion of a low-cycle fatigue phenomenon and therefore further research is done on how to approach this type of fatigue. A method is proposed to take into account bi-axial cyclic plasticity and material hardening based on the use of a maximum principal hot spot stress range. Linear-elastic stresses are corrected to pseudo elastic stresses and effects of SN-curve selection, material selection, bi-axiallity and residual stress are analysed. Based on the found pseudo hot spot stress ranges it is concluded that the linear-elastic stresses in the analysed hopper are not high enough to demand for such a low-cycle fatigue assessment approach. The bi-axial ratio between the two multi-axial plane stress components has no effect on this conclusion.

This thesis research is conducted on behalf of the Delft University of Technology and Bureau Veritas Rotterdam BV, and the goal is to improve ship evacuation by analyzing this aspect early on in the design process. First, this summary will provide a background on the difficulties involved with the ship evacuation process . Next, an explanation is given why this thesis proposes a different model. And lastly, how this model is validated is elaborated upon. A ship evacuation is a highly complex process and it is one of the most important aspects concerning the safety of crew and passengers on-board. This process is affected by various factors, largely by the general arrangement. The layout of a ship varies throughout the design period but the most design freedom occurs during the early stage. An estimated 90% of the decisions which have major impact on final design have been made in this stage. As a result, this stage holds the most potential to improve the ship evacuation performance. This stage is characterized by a lack of detailed layout information available, which results in reduced accuracy in evacuation prediction. As of 1st of July 2020 all passenger ships with more than 36 passengers have to perform an evacuation analysis based on guidelines created by the International Maritime Organization (IMO). The guidelines describe two methods, a simplified method for the early design stage, and an advanced method for the detailed or final design stage. The simplified method translates the ship design to a hydraulic network which in turn results in various method limitations. The goal of an evacuation analysis is, among other things, to provide the designer with information about possible congestion points, identify areas of counter- and cross flows, prove that the escape arrangements are sufficiently flexible, and prove that the evacuation time does not exceed a threshold. Evacuation models capable of performing an evacuation analysis tend to have four general components that define the various aspects influencing the process. The four components are configuration, environmental, procedural, and behavior component. Including evacuee behavior in an evacuation model tends to be difficult due to the complexity and lack of research available. Evacuation models can be categorized using various descriptors however resolution tends to dominate. High resolution models are called macroscopic models whereas low resolution models are called microscopic models. Microscopic models simulate each individual evacuee as an agent with certain attributes, such as walking speed and destination. Most early stage evacuation analysis are macroscopic models and simulate the population as a whole. A different macroscopic approach is proposed by Kana and Singer, which uses probability theory to incorporate the stochastic nature of an evacuation process. This method consists of a Markov-Decision-Process (MDP) to calculate the most probable evacuation routes. Policies are determined for each small geometric area, called a state, in the layout. These policies affect evacuation routes. The evacuation process can then be simulated by using the MDP policies and an initial population distribution. The initial population distributions are defined by the Fire Safety Systems Code. Design variations can be compared based on the calculated optimal routes, the time it takes for the process to converge, and how the population is distributed among the exits. A lack of literature is noticed that investigates the relationship between early stage ship design and the ship evacuation performance. Two different studies were found which can be used to validate the MDP methodology. The first validation study determines which exit configuration is most optimal from an egress perspective. Kurdi et al. defined four different layouts for two population sizes. Having exits on all sides was determined to be the most efficient layout. The MDP model consisted of the same setup as the validation study. The MDP method is able to identify the same exit configuration as most efficient based on the population distributed among the exits and simulation convergence times. The second validation study evaluates two different frigate layouts with varying passageway configuration. One layout has a single passageway throughout the ship. The other layout has a parallel passageway configuration. Casarosa applied a microscopic model to calculate a range of performance metrics for 7 different scenarios. All evacuees were modeled as singular agents with different behavior and objectives. 3 out of 7 scenarios were emergency scenarios, where only 1 scenario corresponds with the MDP assumptions. Discrepancy between models is considered as a result of limited, and confidential, layout information used by Casarosa. The MDP method was able to differentiate between the two layout configurations and can identify critical areas in the layout. However, due to the assumptions, it cannot be determined to what extend the method inputs were similar. Nevertheless, both validation studies showed the potential of using a Markov-Decision-Process based method to evaluate early stage ship designs on evacuation performance.