1,869 research outputs found
Variable sequence of events during the past seven terminations in two deep-sea cores from the Southern Ocean
The relationships among internally consistent records of summer sea-surface temperature (SSST), winter sea
ice (WSI), and diatomaceous stable isotopes were studied across seven terminations over the last 660 ka in
sedimentary cores from ODP sites 1093 and 1094. The sequence of events at both sites indicates that SSST
and WSI changes led the carbon and nitrogen isotopic changes in three Terminations (TI, TII and TVI) and followed
them in the other four Terminations (TIII, TIV, TV and TVII). In both TIII and TIV, the leads and lags between
the proxies were related to weak glacial mode, while in TV and TVII they were due to the influence of
the mid-Pleistocene transition. We show that the sequence of events is not unique and does not follow the
same pattern across terminations, implying that the processes that initiated climate change in the Southern
Ocean has varied through time
NOUS: Construction and Querying of Dynamic Knowledge Graphs
The ability to construct domain specific knowledge graphs (KG) and perform
question-answering or hypothesis generation is a transformative capability.
Despite their value, automated construction of knowledge graphs remains an
expensive technical challenge that is beyond the reach for most enterprises and
academic institutions. We propose an end-to-end framework for developing custom
knowledge graph driven analytics for arbitrary application domains. The
uniqueness of our system lies A) in its combination of curated KGs along with
knowledge extracted from unstructured text, B) support for advanced trending
and explanatory questions on a dynamic KG, and C) the ability to answer queries
where the answer is embedded across multiple data sources.Comment: Codebase: https://github.com/streaming-graphs/NOU
Trailed vorticity modeling for aeroelastic wind turbine simulations in stand still
Current fast
aeroelastic wind turbine codes suitable for certification lack an induction\ud
model for standstill conditions. A trailed vorticity model previously used as
an addition to a blade element momentum theory based aerodynamic model in
normal operation has been extended to allow computing the induced velocities
in standstill. The model is validated against analytical results for an
elliptical wing in constant inflow and against standstill measurements from
the NREL/NASA Phase VI unsteady experiment. The extended model obtains good
results in the case of the elliptical wing but underpredicts the steady
loading for the Phase VI blade in attached flow. The prediction of the
dynamic force coefficient loops from the Phase VI experiment is improved by
the trailed vorticity modeling in both attached flow and stall in most cases.
The exception is the tangential force coefficient in stall, where the codes
and measurements deviate and no clear improvement is visible. This article
also contains aeroelastic simulations of the DTU
10 MW reference turbine in standstill at turbulent inflow with a fixed and
idling rotor. The influence of the trailed vorticity modeling on the extreme
flapwise blade root bending moment is found to be small
Fundamental aeroelastic properties of a bend–twist coupled blade section
AbstractThe effects of bend–twist coupling on the aeroelastic modal properties and stability limits of a two-dimensional blade section in attached flow are investigated. Bend–twist coupling is introduced in the stiffness matrix of the structural blade section model. The structural model is coupled with an unsteady aerodynamic model in a linearised state–space formulation. A numerical study is performed using structural and aerodynamic parameters representative for wind turbine blades. It is shown that damping of the edgewise mode is primarily influenced by the work of the lift which is close to antiphase, making the stability of the mode sensitive to changes in the stiffness matrix. The aerodynamic forces increase the stiffness of the flapwise mode for flap–twist coupling to feather for downwind deflections. The stiffness reduces and damping increases for flap–twist to stall. Edge–twist coupling is prone to an edgetwist flutter instability at much lower inflow speeds than the uncoupled blade section. Flap–twist coupling results in a moderate reduction of the flutter speed for twist to feather and divergence for twist to stall
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