Today's best engineering practice for the design of a stationary floating structure in ice infested water is articulated around physical testing in an ice basin and numerical modelling of the structure response to the relevant ice interactions.Ice basin testing is the best way to simulate the complex scenario of a moored floating structure interacting with drifting intact level ice and ridges. It is also per today the main source of experience for the design of such structures as full scale experience is sparse. However, ice basin testing suffers from deviations due to scaling effects or mismatch between one or several of the achieved and targeted properties (of the modelled ice and structure).As a consequence, the outcome of ice basin tests needs to be assessed and correction of measurements are required. An efficient way is to use an engineering numerical model to simulate the achieved ice-structure interaction in the ice basin, qualify the numerical model by comparing simulation results and measurements, and then simulate the targeted interactions with the numerical model. Such a numerical model may further be used to simulate the full range target design conditions for the ice structure interaction.The RITAS ice basin campaign tested a structure element designed to gain insight in the level ice bending and accumulation process around a traditional moored floating arctic structure design. These measurements are well suited to assess the validity of a numerical model designed to replicate this type of interaction. The SimShipIce numerical model is an engineering tool which focuses on replicating the steering processes during the interaction between a moored structure and drifting intact level ice and ridges. Such a model needs to be calibrated against ice basin test outcome.In order to gain confidence in the general applicability of the model for a traditional moored structure design for ice infested waters, the RITAS tests are simulated with the numerical model. It is shown that the simplified model of the interaction and subsurface transport implemented in SimShipIce captures: The variation in the ice load level with varying ice drift incidence,  The variation in the ice transport with varying ice drift incidence. In addition, some small local deviations are observed, indicating potential areas for improvement of the model. Background Design of moored structures for ice infested watersMoored floating structures are considered to be an attractive concept for the exploitation of offshore hydrocarbon fields in sea ice infested and deeper waters. There is little experience with previous design and operation of such moored structures. Per today, the screening, feasibility or detailed design phases of such concept rely greatly on ice basin tests. This is inline with ISO 19906 (2010).Ice basin testing provides the best way to physically model the complex interaction between a moored floating structure and drifting sea ice. However, ice basin tests have some limitations. Apart from the cost and time expenses, model...

This paper presents a performance evaluation method of a floating, geo-stationary structure in sea ice. Using a turret-moored drillship as an example, the paper explains an approach to efficiently combine model-scale experiments and numerical simulations to analyze ice-structure interactions. A novel numerical simulation tool - Statoil's SIBIS model - is used to investigate the performance of the drillship concept in various design ice conditions. The presented method allows cost-efficient performance evaluations of ice-capable platforms throughout the early-phase design process, and leads to increased safety and commerciality of exploration operations in the Arctic.

The use of moored structures in ice infested waters is of relevance for the exploration or the exploitation of hydrocarbon fields in arctic waters. The assessment of the impact of ice actions in the design process is challenging as the ice actions and the structural response will differ for a moored structure. Further, design criteria may be given by severe and complex scenarios resulting from the interaction with intact level ice and ice ridges in variable ice drift.Ice model testing is an important part in the design process of a moored structure designed to operate in ice infested waters. The ice basin tests allow the measurement of the structure response to complex ice interactions. However, the conditions achieved in the ice tank can deviate from the target full scale scenario. Some structural parameters may not be replicated fully (for instance mooring forces on the structure), and the achieved ice conditions at the instant of the testing may deviate partially from the target ones (it is challenging to scale several ice parameters at the same time resulting in distorted ice properties).A numerical model was developed to simulate the response in real time of moored structures to drifting level and ridged ice. The engine simulates ice actions of the structure including sub-surface ice transport of broken ice around and under the structure. The response of the structure is computed accounting for non-linear effects in the time domain.The most promising use of these modeling capabilities is the possibility to correct and update ice basin measurements for the deviations between the achieved and target interaction scenarios: The tests performed in the ice basin are simulated numerically. A numerical model of the test setup needs to be built (of the structure, the mooring and the achieved ice conditions). By comparing the simulated and measured response, the numerical model can be calibrated and validated.  Numerical simulation of the target scenarios: A numerical model of the target design setup is built, and the response of the structure to full-scale target ice interactions is then estimated. The numerical simulation of the target scenarios represents then the corrected ice basin measurements accounting for all deviations. The simulated response will be used further in the design process, with a confidence based on the quality of the calibration exercise.Examples from two ice basin campaigns are presented where numerical simulations are compared with ice basin measurements, and where full-scale responses to target scenarios are then simulated numerically: Turret moored Offloading IceBreaker (OIB) vaning in level ice (Breivik et al., 2007),  Turret moored Arctic Shuttle Barge (ASB) interacting with drifting ice ridges (Jensen et al., 2000a,b). BackgroundMoored structures are a promising alternative for the development of fields in areas which present sea ice intrusions. Ice actions and the corresponding structural response have to be assessed in the design process. Both extreme and operational aspects are of...