Search

Floating glacial ice features of various sizes pose great threats to the structural integrity of offshore structures in arctic regions. Potential collisions with large icebergs should generally be avoided through proper ice management, but smaller glacial ice features such as bergy bits or growlers (with a characteristic water line < 15 m) may be overlooked by radar in high sea states, and are likely to hit the platform accidentally. This paper evaluates the load carrying capacity of a semi-submersible platform to accidental ice impacts. The shared energy approach is adopted as done in ship collision analysis, assuming collision scenarios with rigid platform-deformable ice on the one hand, and rigid ice-deformable structures on the other hand. Both ice and the platform should deform and dissipate energy under the same force level. For structural analysis, non-linear finite element code LS-DYNA is used. An alternative approach is the simplified analytical method, which allows for fast and reasonable prediction of structural damage. Simplified expressions for stiffened panels under ice pressure patch loading are introduced. The resulting resistance curves compare reasonably with LS-DYNA simulations.

For the northernmost ocean regions, where the ice is occasionally present, one must design a robust structure that can withstand rare ice events (i.e., a glacial ice impact). Despite existing engineering practice is well developed, many challenges remain. One of them is an understanding of local ice actions and action effects. The engineering community has adopted the limit-state design methodology for offshore structures, however, adequate guidance on how to design a structure against an accidental limit state (ALS) due to ice actions is lacking. The majority of existing experimental and full-scale ice data come from the structures that are virtually rigid and thus may not be representative for the scenarios where the structure deforms. Floating-ice impacts in which the structure sustains damage are in the shared-energy regime – both the ice and the structure dissipate energy through inelastic deformation. When analysts consider the shared-energy approach for assessment of the structure’s capability to withstand glacial ice impacts, they should be aware of the variations in input data and of how they might affect their analysis. This study is a follow up of the response assessment of a hull structure under glacial ice impact loads. The paper examines the required information for application of the shared energy method, the variances in that information, and how these variances affect the assessment of structural performance. Results of analysis indicate that using the rule-based ice load models may be insufficient for damage assessment under the ALS caused by ice. It requires a case-tailored view on the energy absorption capacity of ice and ALS criteria. Published by Port and Ocean Engineering under Arctic Conditions. http://www.poac.com/PastConferences.html

A modified Morison model is presented for calculation of hydrodynamic forces on aquaculture net cages. The model is based on a simple method for conversion of ”screen model force coefficients” to approximate equivalent directional dependent Morison coefficients. The motivation for this is that experimentally obtained force coefficients for net panels are generally presented as screen model force coefficients, while commercial analysis software are often restricted to a Morison model. Based on the screen model force coefficients defined by Løland’s formulas, the method is implemented in the nonlinear finite element program USFOS. Analyses with the modified Morison model are performed, investigating the viscous forces on a net panel for different inflow angles. The numerical results are benchmarked against Løland’s original screen model, showing good agreement for all inflow angles. Comparison with the classical Morison model is made to illustrate the advantage of the proposed method. The model is also applied for calculation of hydrodynamic forces on the net of a real aquaculture structure exposed to a steady current. Again, the results are compared to Løland’s original screen model, showing an almost exact reproduction of the global drag force.

The cost-effectiveness of first-line treatment with lapatinib plus letrozole for postmenopausal women with hormone receptor&ndash, positive (hr+), human epidermal growth factor receptor 2&ndash, positive (her2+) metastatic breast cancer (mbc) has not been assessed from the Canadian health care system and societal perspectives. A partitioned survival analysis model with 3 health states (alive, pre-progression, alive, post-progression, dead) was developed to estimate direct and indirect costs and quality-adjusted life years (qalys) with lapatinib&ndash, letrozole, letrozole, anastrozole, or trastuzumab&ndash, anastrozole as first-line treatment. Clinical inputs for lapatinib&ndash, letrozole and letrozole were taken from the EGF30008 trial (NCT00073528). Clinical inputs for anastrozole and trastuzumab&ndash, anastrozole were taken from a network meta-analysis of published studies. Drug costs were obtained from the manufacturer&rsquo, s price list, the Quebec list of medications, and imsBrogan. Other costs were taken from the Ontario Health Insurance Plan&rsquo, s Schedule of Benefits and Fees and published studies. A 10-year time horizon was used. Costs and qalys were discounted at 5% annually. Deterministic and probabilistic sensitivity analyses were performed to assess the effects of changes in model parameters. Quality-adjusted life years gained with lapatinib&ndash, letrozole were 0.236 compared with trastuzumab&ndash, anastrozole, 0.440 compared with letrozole, and 0.568 compared with anastrozole. Assuming a health care system perspective, incremental costs were $5,805, $67,029, and $67,472 respectively. Given a cost per qaly threshold of $100,000, the probability that lapatinib&ndash, letrozole is preferred was 21% compared with letrozole, 36% compared with anastrozole, and 68% compared with trastuzumab&ndash, anastrozole. Results from the societal perspective were similar. In postmenopausal women with hr+/her2+ mbc receiving first-line treatment, lapatinib&ndash, letrozole may not be cost-effective compared with letrozole or anastrozole, but may be cost-effective compared with trastuzumab&ndash, anastrozole.

A Timoshenko beam finite element model is formulated based on the Lagrange and Hermitian interpolations, in which the transverse shear deformation is explicitly evaluated. To account for the local inelastic buckling, the finite element formulation is coupled with a Smith-type progressive collapse method where the nonlinear responses of local structural members can be assessed. The effect of shear lag is accounted by an effective breadth theory. This coupled model enables an efficient prediction of the flexural behaviour of a thin-walled box girder under lateral loading. To demonstrate its capability, a case study is completed on a single-skin box girder under four-point bending. Equivalent finite shell element analysis is carried out for validation. The proposed method shows a close correlation with the shell element model in both strength and stiffness predictions. It is found that the effect of shear lag is significant in this case study, which substantially reduces the stiffness of the box girder.