phase 4 report - DNV

RN02: DESIGN OF FLOATING STRUCTURES IN ICE // PART 4 ANNEX ABarents 2020Table A.16-3 - Ice processes and variables that it is important to modelPrevious investigations of ice ride-up and ridge building are examples where this approach has been used.Initially, simple model tests were done to investigate ice ride-up and ridge building processes. These basic data arepart of the information set that is used to address more complex issues such as––designing islands and structures to avoid ice ride-up problems;––quantifying pack ice driving actions and developing satellite structures designedto form protective rubble around drilling structures in the Beaufort Sea.Scaling uncertainties and modelling artefacts are another important issue that should be considered in planningan ice model test programme. These can arise from imperfections in the ice modelling material being used. Somemodel ices are better able to simulate some types of ice interactions than others.A.16.5.2 ScalingThe objective of model experiments is to create dynamic similarity between the model and the prototype. If thisis achieved, then forces and responses on the model and the full scale are in the correct ratio. This is difficult toachieve for all forces, and so ice modeling has focused on scaling the forces and motions most significant to theproblem.When model testing is used for ice-structure interactions, appropriate scaling relationships should be selectedto represent the mechanisms or processes that dominate the ice actions or action effect to ice actions. In thephysical modelling of ice and structure interactions, Froude similarity (the ratio of inertial to gravitationalaction) and Cauchy similarity (the ratio of inertial to elastic forces) are maintained between the prototype andthe model [A.16-68] . Considerable effort has been expended on the development of model ice with mechanicalproperties scaled to prototype ice and with analogous failure behaviour. There can also be rigorous modellingof the structure shape, stiffness, and surface characteristics. As long as the failure modes expected in theprototype are correctly simulated, model tests can provide an important input into the design process. Modelice can provide optimum simulation of ice interactions only over a certain range of scale factors, generallywithin about 10 to 50. Tests done at scale factors that are too high are likely to produce results that aresubject to modelling distortions.Report no 2012-0690 93