Filters

Settings

Now showing1 - 10 of 16
  • Some of the metrics are blocked by your 
    consent settings
    Item type:Project, Access status: without files ,
      60
  • Some of the metrics are blocked by your 
    consent settings
    Item type:Project, Access status: without files ,
      91
  • Some of the metrics are blocked by your 
    consent settings
    Item type:Project, Access status: without files ,
    Development of a multi scale ice material model for the simulation of brittle ice structure interaction
    Ice covered sea areas have become attractive for various stakeholders. This includes e.g. oil and gas, navy and fishing. At the same time it is known that sea ice can cause significant damage. Hence the need for reliable ice load design methods for ships and offshore structures operating in these areas has increased. At present, this is mostly done with empirical methods or model scale ice tests. Both methods come with drawbacks. Empirical methods fail to predict ice-induced loading with sufficient accuracy and only give global ice loads. Mode scale ice tests are linked to controversial topics such as scaling laws or ways of making artificially weakened ice.In this regard, numerical simulations of ice interaction are a desirable tool. Simulations include additional aspects in the design process such as local loads or deformable structures which are not covered by current methods. However, the accuracy of simulations is limited by available ice material models, which only partially capture complex ice behavior. This research aims to identify dominant features of brittle ice structure interaction (ISI) with regard to ice loads. A multi-scale ice material model is to be developed which reflects these dominant features. The key concepts are the use of sub models, where every sub model reflects another aspect of ISI, and scalability, i.e. applicability of the material model to different scales. Three sub models will be used, one will reflect the bulk behavior of ice, e.g. elasticity, a fracture model will reflect multiple macro fractures and finally a stochastic model for the variation of material properties. Further, each sub model will be verified with a broad range of experiments on different scales. Ultimately, the complete material model will be verified against a large scale laboratory experiment. A series of well documented benchmark experiments will be established for comparison and verification of ice material models from other researchers. Additionally, an existing large data experimental data base will be used and extended within this project. Both the benchmarks and the data base will be made available to the public.Presuming success, a future transfer to full scale applications with saline ice is within reach.
      265
  • Some of the metrics are blocked by your 
    consent settings
    Item type:Project, Access status: without files ,
      146
  • Some of the metrics are blocked by your 
    consent settings
    Item type:Project, Access status: without files ,
    Optimisation of large complex structures in an early design stage considering accidental loads
    ‘Designers create and Engineers analyse’ (Erichsen (1989)). This separation is still valid for most of today’s design and analysis tasks carried out for ship and offshore structures as the structural design, i.e. dimensioning of the structural components and their analysis, is today mostly conducted independently from other disciplines on the basis of an agreed conceptual design. Thus, necessary analyses are performed after the global design parameters are defined and analysis models are derived from this conceptual design. This approach is known as ‘engineering analysis’. In engineering analysis the basic components of a conceptual design analysed individually may be altered, but the influence of these alterations on other aspects is in most cases not assessed, because such analyses are complex and costly. This hinders the identification of true optima, because modifications are always based on the preceding, but not necessarily best, alternative. A better alternative is to identify the optimal design based on safety and operational objectives, whereby the final design depends on the requirements of each discipline leading to a new and currently unknown design. This holistic approach called ‘engineering design’ requires efficient analysis techniques in all involved disciplines for the fast and repetitive assessment of changes and to identify further optimisation potential. However, OPTICS cannot cover all disciplines and concentrates on the development of an efficient analysis method for the structural design. This is a considerable contribution on the path to engineering design. In addition OPTICS takes into account accidental loads. If a marine structure is subjected to service and/or accidental loads that are higher than the loads the structure was designed for, it may fail and the consequences can be severe. Failure reaches from small fractures within and/or on the outer hull of the structure up to breaking the entire structure into parts. Consequently, we must prevent such failure by design and thus account for possible accidental loads and responses already during the conceptual design stage with direct load and response calculations. Therefore, this project seeks to develop an efficient modelling and analysis approach suitable for the optimisation of large complex structures (OPTICS) in an early design stage considering also accidental loads.
      690
  • Some of the metrics are blocked by your 
    consent settings
    Item type:Project, Access status: without files ,
      101
  • Some of the metrics are blocked by your 
    consent settings
    Item type:Project, Access status: without files ,
      147
  • Some of the metrics are blocked by your 
    consent settings
    Item type:Project, Access status: without files ,
      93
  • Some of the metrics are blocked by your 
    consent settings
    Item type:Project, Access status: without files ,
      67
  • Some of the metrics are blocked by your 
    consent settings
    Item type:Project, Access status: without files ,
    Approach to consider welding residual stresses in fatigue design using direct numerical simulations
    The overall objective of this project is to develop an approach to include the influence of welding residual stresses in fatigue assessments through direct simulations. First, welding residual stresses in small-scale specimens and in large structures will be determined and compared. Residual stresses in small specimens used for experimental investigations are often relatively low due to the lack of structural constraints. The investigations will show in what range residual stresses are present in small-scale specimens used for fatigue tests and how they will differ in larger components. Using numerical welding simulations, a wide range of plate thicknesses and specimen dimensions will be assessed in order to identify the influence of geometrical parameters on residual stresses. The simulation results for the models of different dimensions, will allow a comparison between residual stresses in small-scale specimens and large structures. Since residual stresses may be redistributed or relaxed by superimposed external loads, for fatigue assessments the stabilized residual stresses after loading are relevant. Using numerical simulations, this redistribution is calculated for different load levels between compression and tension, i.e. different load ratios. As a result, the effective residual stresses affecting fatigue will be determined for different combinations of residual stress levels and load cases and compared for small and large-scale components. In fatigue tests it will then be investigated how residual stresses affect fatigue behaviour. Since residual stresses are generally not uniform over the plate thickness, the influence on crack initiation and propagation will be distinguished. Furthermore, two different weld geometries with different residual stress distributions and stress concentration factors will be compared: cruciform joints, transversal to the loading direction, and stiffeners longitudinal to the loading direction. Subsequently the residual stress influence will be compared to that of mean stresses. Overall, the test results will give information on the influence residual stresses have on different weld geometries compared to mean stresses. Finally, the results of the simulations and experiments will be evaluated to develop an approach to consider residual stresses in fatigue assessments using direct numerical simulations. For this purpose, it has to be determined which level of accuracy is needed in the simulations and how to read out residual stresses in order to obtain conservative outcomes. The effective stress ratio is determined by simulating the residual stress redistribution under loading. It is then used to calculate a stress ratio correction. Thus, it will be verified if such procedure based on a residual stress value on the plate surface is applicable or if further corrections are needed. The results of this project will further improve efficiency and safety in future design procedures.
      287