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This study summarizes four representative failure criteria which could be applied in ship impact analysis. Robustness of these criteria are examined by simulating penetration tests of stiffened panels as well as the double hull structure. The results show that all the investigated failure criteria produce a wide scatter in ductile fracture prediction when varying mesh sizes are applied, and the predictive capacities of these criteria are variant in different validation cases. Based on it, discussions are carried out with emphasis given on the fracture mechanisms of different structural components as well as the crack propagation prediction.

Several alternative engineering models are available for the use in analysis of offshore wind turbines. However, it is not always clear which of the models will yield the most accurate or sufficiently conservative results. This paper investigates the effect of using two alternative soil-structure interaction models and two wind coherence models. The focus is on assessing how these modelling choices influence the predicted long-term fatigue damage in the support structure. The two soil models are a macro-element model and a p-y-curve model with Rayleigh damping. This gives differences in both the damping and stiffness properties of the turbine model. The differences between the two soil models tend to decrease as the turbine size increases. The wind coherence models considered are the Kaimal spectrum with exponential coherence and the Mann uniform shear turbulence model. The Kaimal model predicts the highest response at low frequencies, while the Mann model gives the highest response predictions at higher frequencies. Which turbulence model predicts the highest long-term fatigue damage is then determined by the natural frequencies, rotor and blade passing frequencies of the different turbines.

In this paper, a verification is presented of a simplified analytical method for the predictions from numerical simulations of structural performance during ship groundings over seabed obstacles with large contact surfaces and trapezoidal cross-section. This simplified analytical method was developed by Lin Hong and Jorgen Amdahl and calculates grounding characteristics, such as resistance and distortion energy, for double-bottomed ships in shoal grounding accidents. Two finite-element models are presented. One was built for a hold, and the other was built for a hold and a ship hull girder and also considers sectional properties, ship mass, added mass and the hydrodynamic restoring force. The verification was completed by comparing horizontal and vertical resistances and the distortion energy between seven numerical-simulation cases and a set of corresponding cases computed by a simplified analytical method. The results show that the resistances obtained by the simplified analytical method are close to the mean values of the resistance curves obtained by numerical simulations. The comparisons prove that the energy dissipation-prediction capability of the simplified analytical method is valuable. Thus, the simplified analytical method is feasible for assessing ship groundings over seabed obstacles with large contact surfaces and trapezoidal cross-section. Furthermore, studies of the influence of ship motion during groundings ascertained that ship motion affects structural performance characteristics. Resistances are lessened at the end of the grounding due to the reduction of indentations caused by heave and pitch motions of the ship hull girder. Finally, a new method for predicting the structural performance of the time-consuming complete-ship model by applying a combination of normal numerical simulations and ship-motion calculations is proposed and proven.

With the increase of the maritime production and transportation in the arctic area, more offshore structures and ships are designed and built for operation in the ice infested water. The potential impact with the ice features is focused to maintain the structural integrity for design purpose. In this thesis, the interaction between the iceberg and the structure during the impact are analyzed to increase the understanding of the ice load on the structure and the response. The thesis mainly includes the literature review of related topics, the analysis of the design ice load in the rules, the modification of a numerical ice material model and the simulation of the slide impact between the iceberg and ship structure. Through the review of the existed ice class rules and ice mechanics theories, the knowledge of the design ice load determination and ice material properties during the impact is developed to generate theoretical basis for analysis and discussion. A new design ice load model is derived based on the first principles of the ice mechanic. With the same impact scenario and the hull geometry, the new design ice load from the ice mechanics model is lower than the rules. Form the point view of the ice, such large loads on the structure as the rules suggest are too conservative, especially for the high polar classes such PC1 and PC2. The ship speed is considered continuously through the strain rate effect in the new model, while a discrete consideration of polar class dependent speed is taken in the rules due to lack of operating experience. The increasing trend of the design ice load with the ship displacement in the rules is not obvious in the ice mechanics model, which is believed also out of conservative consideration. Some topics are summarized into a prepared paper. To apply the integrated analysis with both explicitly modelled objects, a consistent constitutive material model for the iceberg ice is modified based on a developed model. A damage stage is introduced to improve the erosion procedure of failing elements. The stress degradation is implemented by damage variables, a damage evolution law and a final failure criterion, which are developed based on the continuum material mechanics. With the damage stage, more plastic deformation is allowed before erosion for the ice material, so the non-contact space between the iceberg and the structure is eliminated. The oscillation of the force during the application of the original material model can be reduced effectively. The improper behavior of the original model during the unloading is improved by adjusting Bulk Viscosity in the ABAQUS. The uniaxial loading, uniaxial loading-unloading and rigid wall crushing simulations are applied to verify the behavior of the modified material model. Acceptable results are generated and mesh-insensitivity is proved in the verification simulations. Through the calibration, the parameters in the material model are adjusted to generate the same crushing force curve as the PC1 in the rules. With the modified material model, the nonlinear simulations of the impact between the iceberg and a ship side structure are applied in the ABAQUS. Both the predefined path impact and the more realistic impact with the rigid body motion are simulated. Critical impact cases are applied in the simulations, resulting in substantial energy dissipation. The influence to the interaction process from the impact parameters are obvious and revealed simply through the parametric study. Based on an analytical impact model, the equivalent friction factor could be used to estimate the the tangential contact force from the normal contact force during the slide impact. From the simulation results, a value between 0.5 to 1 is suggested for the slide impact between the iceberg and stiffened panel used in the marine structure widely. The factor is found rather sensitive to the material properties, involved hydro-forces and impact parameters. For simplicity, it could be determined based on the lateral penetration because the factor partly depends on the deformation and damage. The more deformation or damage is generated in the structure and the iceberg, the larger is the equivalent friction factor. Thus, the influence of the other conditions could be reflected by a larger or smaller penetration distance in general. Due to the time and personal capacity limit, there are still defects in the thesis. It is found that the derived new design ice load model is sensitive to the impact geometry, which is not discussed in detail. Several theoretical assumptions are made in the development of the damage stage for the ice material model, which will be improved if an analytical material model for the damage ice could be referred. Thus, the recommendations for the further work are addressed.

Slamming impact is a hazardous phenomenon to ships and offshore structures, which is characterised by a highly nonlinear coupling interaction between the structure and the fluid. To evaluate it correctly and accurately is a fundamental task for marine engineers. There are several methods to simulate this phenomenon. One is the model test by experiments. But the disadvantage of the experiment is expensive and time-consuming, which makes the model test more challenging to handle in daily time. Other methods alternatively, like simplified calculation and numerical calculation in commercial codes also have their advantages and disadvantages. However, compared to the experiments, these methods could be convenient to access for the engineer. As the development of commercial software these years, some representative software, e.g. LS-Dyna, ADyna could already give more accurate results than before. The solver could use less time to solve the problems with complex geometry. In this report, the slamming impact has been modelled as drop tests of a stiffened plate with a constant velocity. The drop tests were simulated in the finite element software LS-Dyna, where the fluid-structure interaction was modelled by ALE formulation. The primary purpose of this thesis is to explore the slamming phenomenon in numerical way, experience the procedure to proofread the structure and calculate the response under the slamming loads and find a more convenient method to approximate the impact response. In this thesis, the steel column model is established first. For the FEM model in LS-Dyna, static analysis is conducted following. The boundary effects on the resistance curve of the steel column would be analysed. It is proved that the rear end boundary condition does not affect the resistance curve of the steel column. Different resistance curves are plotted in models with different plate thickness. SDOF parameters could be found from these plots. In ALE drop test, the detailed process of slamming events have been analysed. The displacement curve shows excellent consistency with the analytical model. From the section plots in the Appendix, the stiffeners deform first and the bulkhead following, the side plate girders give the plate and stiffeners robust support and almost unreformed during the whole impact process. Three groups of parametric study have been made to evaluate the effect of material properties, velocities, and plate thickness on the response of the structures. SDOF method has also been established by using the parameters from static analysis. Comparison between the SDOF method and ALE methods shows a feasible approximation by using the SDOF method to predict ALE results. Finally, dynamic tests are made trying to find the possibility to use the elastic material result to predict the response of elasto-plastic material. Even though the effect is not impressive, it provides a new way of thinking.

Flytende offshore vindmøller er, i likhet med andre offshore strukturer, utsatt for skipskollisjoner. Fremtidige vindparker kan bli plassert i nærhet av skipstrafikk, og tøffere værforhold sørger også for større forsyningsskip. Ved en kollisjon kan konsekvensene variere. Alt fra mindre reperasjoner til skade av personell er mulig. I denne oppgaven er målet å studere OO-Star Wind Floater når den er utsatt for skipsstøt. Elementanalyse har blitt utført i LS-DYNA og USFOS. OO-Star Wind Floater er laget i betong, og ved en kollisjon så antas små deformasjoner av søylene. Det vil si at mesteparten av deformasjon skjer i skipet. I denne oppgaven har både skipskollisjon med baug og side blitt analysert. Kraft-deformasjons kurver har blitt beregnet ved å bruke LS-DYNA. Forsterket betong er utsatt for svikt ved store lokale krefter, og dette har blitt analysert. En parameterstudie med ulike tykkelser har vist at slik type svikt er mulig dersom tykkelsen på betongen er mindre enn 0.4 m. Global respons har blitt analysert i USFOS, og både parkert og operativ turbin har blitt undersøkt. Skipskollisjonen er modellert ved å bruke ulineære fjærer som inneholder kraft-deformasjonskurvene fra LS-DYNA. Relevante standarder for flytende vind turbin strukturer har blitt brukt til å bestemme kollisjonsenergiene for de to ulike scenarioene. Elektrisk utstyr er utsatt dersom akselerasjonene av toppen blir for store, og tidligere studier har forespeilet at akselerasjonen ikke bør overskride 2-3 m/s. Dette kravet er derimot svært utsatt for å bli overskridet ved en skipskollisjon. Lokal knekking av turbin tårnet er en risiko ved en skipskollisjon. De mest kritiske tilfellene er når støtet skjer normalt på rotor planet. Knekking er utløst ved en sideveis hastighet på 5 m/s, og dette scenario fører til at tårnet knekker i retning av skipet. Dette er antatt å være et svært kritisk resultat. For å forhindre kollisjon mellom bladene og tårnet er det som regel stor klaring til tårn. De verste kollisjonsscenarioene fører derimot til en risiko for at dette kan skje. På den andre siden er klaringen som er modellert i USFOS betraktelig lavere en for den faktiske turbinen, så det kan godt hende at den faktiske strukturen er trygg. Helt til slutt er også scenario hvor skipet og flyteren blir låst til hverandre etter kollisjon analysert. Dette gir store krefter i forankringslinene, men systemet klarer å motstå dette. Generelt sett er skipskollisjon kritisk for den flytende strukturen. Det er derfor anbefalt å utføre kollisjonsanalyser i tidlig design fase, da dette kan påvirke designet. Floating offshore wind turbines are, like all other offshore structures, exposed to the risk of ship collisions. Future wind farms may be located closer to traffic cargo and passenger lanes, and moving them farther offshore introduces more hostile environments and larger service vessels. The consequences of a ship-FOWT collision can range from minor to major, i.e., from repair cost to injuries or fatalities. This Master's Thesis objective is to study the global and local behavior of the floating offshore wind turbine OO-Star Wind Floater when subjected to ship collision. Finite element analyses have been conducted using LS-DYNA and USFOS. OO-Star Wind floater is built in post-tensioned concrete, and impacts are considered to follow the strength design principle. In general, this means that the concrete columns are considered as rigid. Two impact-scenarios have been studied: broadside impact and bulbous bow impact by the UT745 Platform Supply Vessel. The force-displacement curves for this ship have been established in LS-DYNA. Additionally, reinforced concrete structures are exposed to punching shear failure due to large localized forces, and a parameter study on different thicknesses have been performed. This study display that for a column thickness of 0.4 m, punching shear can occur. This will lead to flooding of watertight compartments, and endanger the structural integrity of the floating offshore wind turbine. Global response analyses in USFOS have been performed for both parked and operating turbine. The ship impact is modeled by nonlinear springs containing the force-displacement relationship established in LS-DYNA. The collision energies are based on code formulations, i.e., the impact velocity is 2 m/s for side-impact and 3 m/s for bow impact. Previous studies have proposed to limit the acceleration of the nacelle to 2-3 m/s, and collision analyses performed in this thesis violates this criterion. The electrical equipment is endangered, which may lead to extensive economic consequences. The turbine tower is an unstiffened cylindrical shell, and local buckling is a risk during a ship impact. In operational condition, impacts normal to the rotor plane are most critical, and buckling is triggered by increasing the speed for sideways impact to 5 m/s. The buckling mode causes the tower to fall in the direction of the ship, posing a real threat to health and safety. The risk of the blades hitting the tower has also been investigated. For the worst scenarios, this event is plausible. However, the modeled tower clearance in USFOS is lower than originally for the 10MW reference wind turbine, so the risk is lower for the real structure. Finally, analyses where the ship and FOWT are locked together after impact has also been investigated. The catenary mooring system is capable of withstanding the forces from this impact scenario. Generally, accidental loads from ship collisions are critical for the floating offshore wind turbine. Impact analyses in the preliminary design phase are recommended.

Offshore vindindustri har opplevd en hurtig utvikling de siste årene. På bare to tiår har turbinene vokst fra å være relativt små til å bli enorme strukturer på flere hundre meter som genererer strøm til tusenvis av mennesker. Den innledende delen av denne rapporten beskriver utviklingen av havvind-turbiner som har blitt gjort de siste årene. Økningen i størrelse, vanndybde og avstand til land brukes til å presentere de potensielle utfordringene dette kan medføre. I dette tilfellet er utfordringen skipskollisjoner med fartøyer som opererer i nærliggende områder. Skipskollisjoner med vindturbiner er av interesse fordi det kan forårsake økonomisk tap, materielle skader og i verste fall skader på mennesker. Hoveddelen av denne avhandlingen tar for seg endelig elementmodellering og analyser av en offshore vindturbin utsatt for skipskollisjoner, i tillegg til en jordskjelvhendelse. Vindturbinen blir analysert i både parkert og operasjonell tilstand. Hovedmålet er å undersøke vindmøllens forskjellige responser, og finne ut om noen av de er kritiske når det gjelder strukturens integritet. Modelleringen og analysene har blitt utført ved hjelp av dataprogrammene USFOS og LS-DYNA. Skipet som brukes til kollisjonene er et standard forsyningsfartøy på 7500 tonn. To kollisjonshastigheter på 3m/s og 5m/s har blitt undersøkt. Dette tilsvarer en initiell kinetisk energi på 37MJ og 103MJ for sammenstøtet. Skipet er modellert for å kollidere i massesenteret til overgangsstykket mellom monopælen og tårnet til vindturbinen. Dette er en konservativt tilnærmelse. Resultatene viser at vindturbinen generelt har høy motstand mot global kollaps for alle de studerte scenariene. De mest kritiske resultatene når det kommer til svikt av turbinen er spenningene som oppstår i nedre og midtre del av tårnet, og akselerasjonen av nacellen på toppen av tårnet. Monopælen og overgangsstykket mellom denne og tårnet ble mindre påvirket av lastene. Utnyttelsen av jordkapasiteten ble funnet til å være høy for de øverste lagene, men betydelig mindre i de dypere lagene. Effekten av den operasjonelle tilstanden viste seg å ha positiv effekt på jordutnyttelsen og en negative effekt på momentkraften i bunnen av tårnet. For de mest kritiske tilfellene ble det oppservert noe lokal buling i bunnen og den midtre delen av tårnet for henholdsvis den største kollisjonen og jordskjelvet. Selv om dette oppsto, førte det ikke til at strukturen kollapset. For å undersøke kollapsmekanismen til vindturbinen ble knekkingen utløst enten ved reduksjon av veggtykkelse eller økning av påført last. Alle kollapsmekanismene som oppsto var ønskelig, siden de førte til at vindturbinen falt i motsatt retning av det kolliderende skipet. The offshore wind industry has shown rapid development in recent years. In only two decades, the turbines have grown from being relatively small to becoming huge structures of several hundred meters, generating power for thousands of people. The first part of this report describes the development of the offshore wind turbines in recent years. The increase in size, water depth and distance to shore is used to present the potential challenges it may cause concerning ship impacts from vessels operating in the same area. Ship impact events are of interest as it causes economic loss, property damage, and at worst human injuries. The major part of this thesis considers finite element modeling and analyses of a monopile supported offshore wind turbine, subjected to ship impacts and an earthquake event. Both parked and operating conditions of the turbine are considered. The main goal is to investigate the different responses of the wind turbine, and to find out if any of the responses are critical concerning the structural integrity. The modeling and analyses are performed using the computer programs USFOS and LS-DYNA. The ship used for the collision is a standard supply vessel of 7500 tons displacement, with a bulbous bow. Two impact velocities of 3m/s and 5m/s are investigated, corresponding to an initial kinetic energy of 37MJ and 103MJ. The ship is modeled to collide head-on in the center of mass of the transition piece of the wind turbine, which is a conservative approach. The results showed that the offshore wind turbine, in general, has a high resistance against global collapse for all the studied scenarios. The most critical results concerning the failure of the turbine were found to be the forces in the bottom and mid part of the tower and the accelerations of the nacelle. The monopile and transition piece were less affected. The soil utilization was found to be high in the upper layers, but considerably lower in the deeper layers. The operating condition proved to have a positive effect on the soil utilization and a negative effect on the moment force in the bottom part of the tower. For the most critical scenarios, the tower experienced some local buckling in the bottom and middle part for the collision and earthquake, respectively. However, this did not cause a collapse of the structure. In order to investigate the collapse mechanisms, buckling in these sections were triggered by either reducing the thickness or increasing the loads. All collapse mechanisms were found to be desirable, as they resulted in the wind turbine falling away from the vessel.

Etterspørselen etter store LNG-skip har økt. Den enkleste måten å øke kapasiteten til Moss LNG-skip er å øke diameteren til de sfæriske tankene, og dermed også skipets bredde. På grunn av begrensningene på skipets dimensjoner i Panamakanalen, er ikke dette en ideell løsning. Dermed er det ønskelig å endre tankens form fra den sfæriske for å forbedre utnyttelsen av skipets deplasement. Denne oppgaven fokuserer på mulighetene for å "strekke" tankene i langskips retning, ved å introdusere en sylinderformet del, mellom to halvkuler. FEM-analysene har vært begrenset til knekkingsanalyser av slike tanker, og sammenligning med gjeldende regelverk for slike tanker er gjort. Flere av analysene er gjort med kun ytre trykk som last. Dette er en enkel måte å vurdere hvordan styrken til tankene varierer ved ulike konfigurasjoner, som for eksempel sylinderdelens lengde. Å bruke kun ytre trykk som last er en enkel måte å finne kritisk spenning for tankene. I tillegg har sloshing-laster blitt analysert. Denne lasten er sett på som mer kritisk for tankene. Både en sfærisk tank og en langskips strekt tank med en sylindrisk del har blitt studert, og resultatene har blitt sammenlignet. Resultatene antyder at DNV GLs bruk av likningen for elastisk knekkspenning for sylindre passer dårlig for sylindre med et så lavt lengde/radius forhold som slike sylindre vil ha. En modifikasjon til denne metoden, basert på resultatene fra analysene er foreslått i denne oppgaven. Analysene med sloshing-laster indikerer at de strekte tankene er betydelig svakere enn de originale sfæriske tankene i forhold til knekking. Å øke tykkelsen på de strekte tankene i spesielt kritiske områder virker som en mulig og enkel løsning for å øke styrken. Dette vil dessverre også medføre økt vekt og byggekostnad. Basert på resultatene i denne oppgaven er det ingenting som tilsier at den reduserte knekkstyrken vil gjøre langskips strekte LNG-tanker til en umulig løsning. Det er vurdert som sannsynlig at andre strukturelle aspekter enn knekking av tanken vil være mer kritisk for en slik konfigurasjon. Sammenligning av maksimalt tillatte spenningsverdier fra DNV GL og de kritiske knekkspenningene fra analysene indikerer at de foreslåtte maksverdiene fra DNV GL er konservative. Resultatene tilsier at maksimalt tillatte spenningsverdier fra DNV GL gir en sikkerhetsfaktor på omtrent to. Det er mulig at det å tillate høyere spenninger i tankene vil føre til mer lønnsomme LNG-skip uten at det går utover sikkerheten. Denne observasjonen er utelukkende basert på resultatene fra denne oppgaven, og videre analyse og verifikasjon vil være nødvendig før noen endringer kan gjøres i forhold til nåværende regelverk. The demand for large LNG-Carriers has increased. The easiest way to increase the capacity of the LNG-Carriers of the Moss-design with spherical tanks, is to increase the tank diameter, and consequently the ship beam. Due to the limitations of the Panama Canal concerning ship dimensions, the remaining way to increase the capacity of the vessels is to modify the shape of the tanks to improve the utilization of the ship displacement. This thesis has focused on the possibilities of a longitudinally elongated tank, which includes a cylindrical part between the two spherical end-caps. The FEM-analysis has been limited to buckling analyses of such tanks, and comparison with the current rules and regulations of non-spherical LNG-tanks have been done. Several analyses with only external pressure as load have been done to study the buckling strength of longitudinally stretched tanks, focusing on critical stresses and comparison with current rules and regulations. Additionally, the load assumed to be the most critical to buckling of the tanks, which is the sloshing load has been analysed. Both a spherical and a longitudinally stretched tank with a cylindrical part was analysed, and the results were compared. Based on the results obtained in this project, DNV GLs use of the equation for elastic buckling stress for short cylinders seems unsuitable. A modification to the current Class Guidelines has been suggested in this thesis. The sloshing analyses indicate that the buckling strength of a longitudinally stretched tank is significantly lower than the strength of the original spherical tank. However, the buckling strength can be increased by increasing the thickness in critical parts of the LNG-tank, although this will have some negative consequences in terms of weight and cost. Based on the results obtained in this thesis there is no indication that the reduction in buckling strength will make the longitudinally stretched tanks unfeasible, and it is deemed likely that other structural aspects will be more severe. Comparison of maximum allowable stresses by DNV GL and the critical buckling stresses obtained in the FEA indicates that the maximum allowable stresses proposed by DNV GL are quite conservative, where the FEA-results indicate that the maximum allowable stresses by DNV GL have a safety factor of around 2. Hence, it is possible that allowing larger design stresses in the tanks may lead to more cost-efficient LNG-Carriers without introducing safety issues. This observation is based exclusively on the results obtained in this thesis and would need to be verified before introducing any changes to the current rules and regulations.