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ISBN 978-91-88001-33-7

There is an increased tendency towards the use of novel lightweight materials, particularly fibre-reinforced plastic composites, in shipbuilding. Composites offer the advantage of reduced structural weight and increased moulding freedom unattainable for traditional materials such as steel. The use of composites for building ships, however, is limited by the current regulations due to their challenging fire behaviour. Recent development of numerical simulation techniques has enabled the study of the thermo-mechanical behaviour of fire-exposed polymer composites, including scenarios relevant for the maritime industries. Even though advanced numerical methods are already used in the design and approval process, there is much potential for their wider application. For instance for design optimisation with reduced need for experiments and testing, thus providing a basis for a more computerised design process including the analysis of fire resistance. During the EU FP7 project Fire-Resist (2011-2015), a multi-field simulation concept was developed based on the interoperability of computational fluid dynamics fire simulation and finite element analysis. This simulation concept enables the comparative analysis of thermal and mechanical behaviour of fire-exposed structures, for instance in the context of the SOLAS Alternative Design process, with respect to load-bearing capacity during and after a fire. The capabilities of the simulation concept are demonstrated by a thermo-mechanical analysis of a typical ship structural element, focusing on a comparative analysis between a SOLAS compliant steel structure and a novel design employing FRP composite material.

Navies have been facing budget reductions over the past decade. Since crew size is a major cost driver, this has led to efforts to reduce manning on board naval ships. Traditionally, damage control and firefighting were manpower intensive operations. To enable crewing level reductions without compromising the ability to deal with damage and firefighting requires both the introduction of new technologies and changes in how damage control and firefighting are carried out. Newly built warships are being fitted with more fixed firefighting systems, in particular water mist systems. The design of these systems is based on requirements and applications in civilian (commercial shipping) environments where the possibility of damage to piping infrastructure or pumps arising from battle damage was not taken into account. This paper describes the results of an experimental program that investigated the influence of fragment holes in water mist system piping on the system’s firefighting efficiency. A test chamber of 7.5 × 7.5 x 2.4 m³ was equipped with a four-nozzle high pressure water mist system. Systematically, the water flow to 1, 2 and 4 of the water mist nozzles was altered by damage to the water feed line piping. The systems performance against a 1.3 MW diesel pool fire was evaluated by evaluating compartment gas temperatures and time to extinguishment. Pressure drops in the system and water loss through the fragment holes were measured. The research has both provided insight into the physical phenomena behind water mist fire extinguishment and the residual fire suppression capacity of damaged water mist systems. The paper also highlights practical suggestions for design of water mist systems when considering battle damage. Over all, the capability of the water mist system evaluated showed good resilience against pressure drops and water loss through moderately sized fragment holes. This research was carried out as part of a collaborative research project involving the Canadian Department of National Defence and the Swedish and Netherlands’ Ministries of Defence.

One major concern when it comes to storage of wood pellets is the risk for self-heating. The propensity for self-heating varies between different types of pellets. It also depends on how the pellets have been handled and on the storage conditions, e.g. the temperature and humidity. Within the framework of the research project “Large scale Utilization of Biopellets for Energy Applications –LUBA” different laboratory-scale methods have been used to study different thermal properties and the propensity for self-heating for different types of pellets. The different methods used include micro calorimetry also called isothermal calorimetry, basket-heating tests and transient plane source (TPS). In total 21 different pellets samples were tested in the micro calorimeter, three in the basket-heating test and three in the TPS. The samples showed significant differences in propensity for self-heating. Differences could be seen both between different types of pellets and depending on the age of the pellets. Comparing the reactivity rates from the basket-heating tests and those from the isothermal calorimetry tests with the same type of pellets, both methods gave the same ranking of reactivity. It was shown that the TPS-method is applicable for the determination of thermal properties both for measurements on single pellets and for measurement on bulk pellet material.

In dieser Arbeit wurden ferromagnetische Kreisscheiben aus Permalloy mit Hilfe der Mikro-Hall-Magnetometrie und mit mikromagnetischen Simulationen untersucht. Aus GaAs/AlGaAs-Heterostrukturen gefertigte Mikro-Hall-Sonden gestatten die Messung von Streufeld-Hysteresekurven individueller Partikel mit Ausdehnungen weit unter einem Mikrometer. Die Entstehung einer magnetischen Wirbelstruktur (Vortex) in Permalloy-Kreisscheiben (Dicke t zwischen 20 und 60 nm und Durchmesser D von 300 bis 800 nm) wird durch die Bildung von Buckling-Zuständen eingeleitet. Je nach Magnetisierungsstruktur unterscheidet man zwischen c- und s-Zuständen sowie Buckling-Mustern höherer Ordnung. In größeren Kreisscheiben (t > 40 nm und D > 500 nm) kann vor der Vortex-Entstehung eine metastabile Doppelvortex-Konfiguration auftreten. Da sich die diversen Buckling-Zustände energetisch nur unwesentlich voneinander unterscheiden, wird die Magnetisierung im Feldbereich der Vortex-Nukleation durch Defekte und die magnetische Vorgeschichte maßgeblich beeinflusst. Während die Vortex-Nukleation also einen gleichermaßen komplexen wie schwer kontrollierbaren Vorgang darstellt, bieten künstliche Punktdefekte in den Nanoscheiben die Möglichkeit, auf das magnetische Verhalten im Vortex-Zustand gezielt Einfluss zu nehmen. Das Zentrum der Vortex-Struktur kann mit Hilfe eines Punktdefekts (magnetischer Antidot) eingefangen und festgehalten werden, was im entsprechenden Feldbereich zu verringerter magnetischer Suszeptibilität führt. In der zugehörigen Hysteresekurve hat dies das Auftreten eines Plateaus zur Folge. Permalloy-Scheiben (t = 30 nm und D = 500 nm) mit zwei Antidots zeigen bistabiles magnetisches Verhalten: Der Übergang zwischen zwei reversibel durchlaufenen Plateaus erfolgt durch einen irreversiblen Sprung, sobald eine charakteristische Feldstärke (Schaltfeldstärke) überschritten wird. Während die beiden Plateaus den Zuständen des am rechten oder linken Antidot gepinnten Vortex zugeordnet werden, entspricht der irreversible Sprung dem vom externen Magnetfeld erzwungenen Wechsel des Vortex-Kerns zwischen den Antidots. In Einklang mit dieser Erklärung weisen größere Permalloy-Scheiben (t = 30 nm und D = 800 nm) mit drei bzw. vier Antidots entsprechend viele Plateaus auf. Das Auftreten mehrerer stabiler remanenter Zustände, kurze Schaltzeiten unter 1 ns und die Beeinflussbarkeit der Schaltfeldstärke durch geometrische Faktoren und Biasfelder lässt Nanoscheiben mit Antidots für Speicheranwendungen als prädestiniert erscheinen. Die Integration solcher Strukturen in MRAM-Speicher und kombinierte Speicher-Logik-Elemente wird ausführlich diskutiert., Disk-shaped ferromagnetic particles of Permalloy are investigated using micro-Hall magnetometry and micromagnetic simulations. Micro-Hall sensors fabricated from GaAs/AlGaAs heterostructure material can be employed to measure stray-field hysteresis loops of individual submicron-sized particles. Nucleation of magnetic vortex structures in Permalloy-nanodisks (thickness t between 20 and 60 nm and diameter D in the range of 300 to 800 nm) is initiated by buckling states. Depending on their particular magnetization configurations, the buckling states can be divided into c- and s-states or buckling patterns of higher order. In larger disks (t > 40 nm und D > 500 nm) an intermediately stable double vortex configuration can be established, before the single vortex structure is built. As the various buckling states have almost the same energy, the process of vortex nucleation is strongly affected by defects and magnetic history. On the one hand, vortex nucleation has shown to be a complex process, which is hard to control. On the other hand, however, as soon as the vortex state has entered the disk, magnetic behaviour can be controlled by using artificial point defects. The centre of the vortex structure can be pinned to a point defect (magnetic antidot), leading to reduced magnetic susceptibility. Therefore, corresponding hysteresis loops exhibit a plateau of distinctly diminished slope. Measurements on Permalloy-disks (t = 30 nm und D = 500 nm) containing two antidots reveal bistable magnetic behaviour: Minor hysteresis loops consist of two plateaus, which show reversible magnetic behaviour. However, an irreversible jump from one plateau to the other one occurs as soon as a characteristic strength of the applied field (switching field) is exceeded. While the plateaus are ascribed to the pinned vortex states (the vortex core can be captured either by the right or the left antidot), the irreversible jump results from the transition of the vortex core from one pinning site to the other one. This also explains why three and four plateaus are observed in larger Permalloy-disks (t = 30 nm und D = 800 nm) containing three and four antidots, respectively. Due to the existence of several stable remanent states and short switching times below 1 ns, nanodisks containing antidots appear to be predestined for memory applications. This is supported by the fact that the switching field can be varied by sample geometry or by applying additional bias fields. The integration of nanodisks with antidots in MRAM elements and in devices featuring both memory and logic applications are discussed in detail.