access: v.10, no.02, Summer 1996

published or submitted for publicatio

Comparison of spar and semi-submersible floating wind turbine concepts with respect to seasickness of the maintenance personnel

Floating offshore wind turbines (FOWTs) are remotely located structures that are operating without humans on board. The technicians are expected to be on board from time to time throughout the life cycle of FOWTs for maintenance activities such as regular inspections, fault-findings, component changing etc. Due to their remote location, FOWTs are usually subjected to harsh environmental conditions that may cause large motions on the platform. Such motions may obstruct access to the platform and the maintenance work that is going to be conducted on the platform by the technicians. To address the problem and define the objectives, a literature study is conducted on the maintenance process of the FOWTs, the effects of platform motions on the humans located on the structure. The standards and regulations regarding the seakeeping performance of the vessels for human effectiveness and health are demonstrated. Then the motions of the floaters, modelling of the offshore sea conditions and the working principle of the software used are covered with a compact theory. A methodology is developed for the frequency domain to simulate the motions of the floaters in offshore conditions and model the motion exposure of the personnel on the structure. The developed methodology is utilised for three chosen study case floaters. OC3-Hywind, CSC-Semisubmersible and WindFloat are selected for comparative simulation studies where the workability of the technicians on each floater is investigated under different loading conditions. The load cases are modelled with both the JONSWAP and the Torsethaugen wave spectra based on hindcast data from two locations that are relevant for FOWT deployment. The conducted research is presented as a journal paper within this thesis. Additional results which were not included in the paper such as the investigation of the developed methodology and the expected extreme accelerations on the floaters are presented within the thesis. Instantaneous accelerations expected on each floater are graded regarding criteria for the human comfort reactions to vibration environments. Conclusions are made based on the findings from the comparative studies. The thesis is finalised with recommendations for further work

Flow around two elastically-mounted cylinders with different diameters in tandem and staggered configurations in the subcritical Reynolds number regime

Flow around two cylinders with different diameters undergoing Flow-Induced Vibrations (FIV) in the subcritical flow regime is investigated using two-dimensional Unsteady Reynolds Averaged Navier-Stokes (URANS) approach. Physical parameters of the system are chosen to represent the free spanning pipelines laid in proximity. The two cylinders are initially placed at various tandem and staggered positions with one in the wake of the other, and subject to steady current flows. The two cylinders are free to respond in both in-line and transverse directions. The investigated Reynolds numbers (Re) are Re1 = 1.4 × 105 based on the diameter of the larger cylinder and Re2 = 1.15 × 105 based on the diameter of the smaller cylinder. A parametric study investigating the effects of relative spacing of the cylinders on the vibration response of the system is performed. First and second order statistics of the flow, frequency domain analysis and flow field visualizations are used to characterize the dynamic behavior of the system. It is found that the motion trajectories of the downstream cylinder show a qualitative difference depending upon whether it is in tandem with the upstream cylinder or in the wake with a transverse offset. A large amplification of the in-line response is observed in the positions with a transverse offset. The vibration response of the upstream cylinder is affected by the presence of the downstream cylinder only when the horizontal center-to-center distance is small (L/D1 = 2.06 where D1 is the diameter of the larger cylinder) and is largely unaffected when the horizontal distance is increased to L/D1 = 3.22.publishedVersio

On the future navigability of Arctic sea routes: high-resolution projections of the Arctic Ocean and sea ice

The rapid Arctic summer sea ice reduction in the last decade has lead to debates in the maritime industries on the possibility of an increase in cargo transportation in the region. Average sailing times on the North Sea Route along the Siberian Coast have fallen from 20 days in the 1990s to 11 days in 2012–2013, attributed to easing sea ice conditions along the Siberian coast. However, the economic risk of exploiting the Arctic shipping routes is substantial. Here a detailed high-resolution projection of ocean and sea ice to the end of the 21st century forced with the RCP8.5 IPCC emission scenario is used to examine navigability of the Arctic sea routes. In summer, opening of large areas of the Arctic Ocean previously covered by pack ice to the wind and surface waves leads to Arctic pack ice cover evolving into the Marginal Ice Zone. The emerging state of the Arctic Ocean features more fragmented thinner sea ice, stronger winds, ocean currents and waves. By the mid 21st century, summer season sailing times along the route via the North Pole are estimated to be 13–17 days, which could make this route as fast as the North Sea Route

Columbia Poetry Review

Literary journal produced annually. Student editors: Hanna Andrews, Amanda M. Johnson, Becca Klaver, BJ Soloy, Jennifer Watman. Assistant editors: Margaret Brady, C.H. Eding, Monica Gerstemeier. Editorial Board: N\u27Kyenge Brown, Piper Daniels, Joe Eldridge, Ted Jackle, Shanley Erin Kane, Daniela Olszewska, Kristen Orser, Jessica Rose, Jennifer Steele, Nicole Wilson. Cover: Julie Heffernan.https://digitalcommons.colum.edu/cpr/1019/thumbnail.jp