An explosion on a typical offshore installation is a critical, however rare accidental event which may result in damage and loss of property, and in the worse case loss of lives. Top-side sections on an offshore installation which are exposed to an explosion blast should be designed to withstand such an event in a way that further escalation of the damage on personnel or property is avoided. There is however limited information on the modeling and analysis procedures for dealing with such events, and most classification rules on this subject give limited information and guidelines on the practical implementation of such effects for general analysis purposes. This thesis has been an investigation on these matters.The basis of this Master thesis has been on a pipe rack structure from one of Aker Solutions' top-side projects. It has been assumed that this structure is exposed to an accidental hydrocarbon explosion, and the resulting structural response has been investigated. A parameter study has been performed by varying blast load levels and durations. The effects due to the weight of the piping on the structure have also been studied. The main task of this thesis has been to compare simplified, static analysis models against dynamic analysis models as to calculate dynamic amplification factors (DAF), the purpose of this is to better understand the dynamic behavior of the structure due to the blast loading. The intention is that the dynamic amplification factors are to be used further by the engineers at Aker Solutions for dimensioning and designing of similar structures.Results showed that the blast loads as used in the analyses did not cause any structural responses within the material's plastic range. Further on, it was found that the magnitude of dynamic amplification is depending on both the blast duration emph{and} the weight of the pipes on the pipe rack. Typical results indicated that this dynamic amplification was reduced with increased blast duration.

Due to a rising interest in oil exploration in Arctic areas several new platform designs have been introduced to combat the problems with level ice loads. This has led to research into ice strengthening and how this affects the open water behaviour. One of the new designs, called the Total Buoy, has a slanted hull in the waterline intended to deflect level ice down and around the structure, but this hull design introduces a geometrical non-linearity. This non-linearity causes problems in the design of these types of structures, because most hydrodynamic program cannot handle the rapid change of geometry in the waterline. This has inspired several attempts to write a simple numerical model to handle the calculation, and avoid costly model tests in the pre-design.A large part of this thesis presents the theory and methods used in the development of this new numerical model. This is meant to document the thought process in a way which can allow others to continue the development. The numerical model was developed to calculate motion results from regular waves in the three symmetric motions; Surge, Heave and Pitch. In addition to this a very simple ice calculation was included as a starting point for further development.As part of this work on a new numerical model a parallel study of an alternative commercial program was done. This is to test the usability of an (expensive) commercial program in relation to this non-linear problem. The DNV program Wasim was selected for this purpose, and the modelling has also been documented and the input files are included in the electronic appendix.After documenting the basis of the numerical model and Wasim model it was necessary to do a comprehensive comparison study of the models. To help with the comparison Force Technology allowed the use of model tests results which were performed on the Total Buoy concept in 2006. The comparisons showed that while the numerical model was showing some large responses around the heave natural period in both heave and pitch the results were in general close to the model tests. The Wasim model did not show the same correlation in surge and pitch, but the heave results were shown to be close, but the use of the Wasim program is believed to be unwise on this type of problem.Finally, an assessment of the Total Buoy's open water and level ice behaviour was done. This assessment showed that the Total buoy would most likely have problems with large pitch motions. This was shown to be true in both the Norwegian Sea and the Eastern Barents Sea, the Norwegian Sea was found to be a unlikely deployment area due to the lack of level ice. The pitch motion was so large that it would make year round human habitation impossible, and it was advised that the buoy should not be used for this purpose, and only in the eastern Barents Sea. Finally, it was found that the ice theory which was applied for the ice calculation could not give a true assessment of the level ice capabilities of the buoy, and the lack of other alternative solutions made the assessment impossible.

During this Master Thesis, leg-segments of jacket platforms subjected to supply vessel impacts have been considered. Finite element analyses (FEA) have been conducted using the explicit solver LS DYNA. The FEA results have been discussed and compared against simplified calculation methods and basic theory. In order to investigate the effect of the surrounding structure, two sets of boundary conditions have been considered for the columns:-Perfectly clamed boundary conditions-Axial flexible boundary conditions. The results have shown that the effect of the surrounding structure should be included. The effect is most important of the strength of the column is small relative to the striking ship. Parameter studies of the column-design with respect to column diameter and thickness have been performed. Three column diameters have been considered, namely 1.0 m, 1.5 m and 2.0 m. The thickness has been varied from 30 mm – 70 mm. Force-deformation relationships for the different columns have been compared and discussed. Based on the available amount of impact-energy, the different column-designs have been categorised as strength-designed, ductile-designed or shared-energy designed. The parameter study shows that if strength-design is aimed for, a column thickness of 70 mm in the case where the diameter = 1.5 m is required. If the column diameter is 2.0 m, strength design is achieved with a column thickness of 60 mm. Strength design was not achieved for the column with diameter = 1.0 m. However, based on the results, strength design of the 1.0 m column would probably require a thickness above 70 mm. The resistance against local indentation for the different columns have been considered and compared against resistance curves recommended by NORSOK N-004. The NORSOK-curves give a reasonable estimation of the strength for the weakest columns but becomes quite conservative compared to the strongest columns. An empirical design curve which takes the gradual increasing contact area into account was suggested based on the results. The resistance against global deformations have been compared against a simplified collapse mechanism. The results show that the accuracy of the simplified model is very dependent on the load definition and whether or not effects of reduced capacity due to local indentations are included. Two impact-scenarios have been considered: beam impacts and stern impacts. The beam impacts scenario proved to be the critical case in most cases. Finally, the effect of ring stiffeners applied in the collision-zone of the platform leg has been considered. 4 different designs have been evaluated. However, it was found that the effect on the column strength is larger if the column thickness is increased.

The oil price continues to increase while oil companies search for oil in new areas. There is assumed that 25% of the world’s hydrocarbons are located in the arctic area. Operating in these areas will be a huge challenge due to extreme low temperatures and ice condition Today one can predict with good accuracy how a ship will manage in different ice condition. Research on ship operating in ice the last decades has resulted in many different formulas for predicting ice resistance on a ship hull. Analytical and numerical methods are developed to estimate the resistance working on the ship hull under different ice conditions. Model test will still be the most accurate prediction, but the other methods may give you some guidelines on what to expect. This thesis contain a theoretically study of ice physics and mechanics. The formation and development of sea ice has been reviewed. The Ice Load Monitoring system tested on the Norwegian coast guard vessel KV Svalbard is described. Three different analytical ice resistance calculation methods are described. The three methods are Lindqvist (1989), Keinonen et al. (1996) and Riska et al. (1997). Data obtained from the Ice Load Monitoring system are used to estimate the full scale ice resistance on KV Svalbard. The three analytical methods are calculated with KV Svalbard as a reference ship to be able to compare with the full scale measurements. MATLAB is used for the calculations.