302 research outputs found
Optimization-based calibration of hydrodynamic drag coefficients for a semisubmersible platform using experimental data of an irregular sea state
For the simulation of the coupled dynamic response of floating offshore wind turbines, it is crucial to calibrate the hydrodynamic damping with experimental data. The aim of this work is to find a set of hydrodynamic drag coefficients for the semisubmersible platform of the Offshore Code Comparison Collaboration, Continuation, with Correlation and unCertainity (OC6) project which provides suitable results for an irregular sea state. Due to the complex interaction of several degrees of freedom (DOF), it is common to calibrate drag coefficients with the time series of decay tests. However, applying these drag coefficients for the simulation of an irregular sea state results in misprediction of the motions. By using numerical optimization, it is possible to calibrate multiple drag coefficients simultaneously and effectively, while also considering several DOF. This work considers time series of structural displacements from wave tank tests of the OC6 project and from simulations of the same load cases in OpenFAST. Results are transferred into the frequency domain and the deviation between power spectral densities of surge, pitch and heave from experiment and numerical simulation is used as an objective function to obtain the best fitting drag coefficients. This novel numerical optimization approach enables finding one set of drag coefficients for different load cases, which is a major improvement compared to decay-test-tuned drag coefficients. © Published under licence by IOP Publishing Ltd
Double proximity effect in hybrid planar Superconductor-(Normal metal/Ferromagnet)-Superconductor structures
We have investigated the differential resistance of hybrid planar
Al-(Cu/Fe)-Al submicron bridges at low temperatures and in weak magnetic
fields. The structure consists of Cu/Fe-bilayer forming a bridge between two
superconducting Al-electrodes. In superconducting state of Al-electrodes, we
have observed a double-peak peculiarity in differential resistance of the
S-(N/F)-S structures at a bias voltage corresponding to the minigap. We claim
that this effect (the doubling of the minigap) is due to an electron spin
polarization in the normal metal which is induced by the ferromagnet. We have
demonstrated that the double-peak peculiarity is converted to a single peak at
a coercive applied field corresponding to zero magnetization of the Fe-layer
Adaptation to the Edge of Chaos in the Self-Adjusting Logistic Map
Self-adjusting, or adaptive systems have gathered much recent interest. We
present a model for self-adjusting systems which treats the control parameters
of the system as slowly varying, rather than constant. The dynamics of these
parameters is governed by a low-pass filtered feedback from the dynamical
variables of the system. We apply this model to the logistic map and examine
the behavior of the control parameter. We find that the parameter leaves the
chaotic regime. We observe a high probability of finding the parameter at the
boundary between periodicity and chaos. We therefore find that this system
exhibits adaptation to the edge of chaos.Comment: 3 figure
Establishing a pre-clinical growing animal model to test a tissue engineered valved pulmonary conduit
Background: Many valvular pathologies of the heart may be only sufficiently treated by replacement of the valve if a reconstruction is not feasible. However, structural deterioration, thrombosis with thromboembolic events and infective endocarditis are commonly encountered complications over time and often demand a re-operation. In congenital heart disease the lack of small diameter valves with the potential to grow poses additional challenges and limits treatment options to homo- or xenograft implants.
Methods: In this study, a chronic sheep model (24 months follow-up), a self-constructed valved conduit was created out of a tissue engineered (TE) patch (CorMatrix® Cardiovascular, Inc, USA) and implanted in orthotopic right ventricular (RV)-pulmonary artery (PA) position. Thereafter, the sheep were regularly monitored by clinical, laboratory and echocardiographic examinations to evaluate cardiac function and the implanted RV-PA-conduit.
Discussion: Here, we summarize the study protocol and our experiences during the perioperative phase and the follow up period and explain how we constructed a valved conduit out of a commercially available TE patch.
Trial registration: License number: ZH 284/14
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