Performance of an ideal turbine in an inviscid shear flow

Although wind and tidal turbines operate in turbulent shear flow, most theoretical results concerning turbine performance, such as the well-known Betz limit, assume the upstream velocity profile is uniform. To improve on these existing results we extend the classical actuator disc model in this paper to investigate the performance of an ideal turbine in steady, inviscid shear flow. The model is developed on the assumption that there is negligible lateral interaction in the flow passing through the disc and that the actuator applies a uniform resistance across its area. With these assumptions, solution of the model leads to two key results. First, for laterally unbounded shear flow, it is shown that the normalised power extracted is the same as that for an ideal turbine in uniform flow, if the average of the cube of the upstream velocity of the fluid passing through the turbine is used in the normalisation. Second, for a laterally bounded shear flow, it is shown that the same normalisation can be applied, but allowance must also be made for the fact that non-uniform flow bypassing the turbine alters the background pressure gradient and, in turn, the turbines ‘effective blockage’ (so that it may be greater or less than the geometric blockage, defined as the ratio of turbine disc area to cross-sectional area of the flow). Predictions based on the extended model agree well with numerical simulations approximating the incompressible Euler equations. The model may be used to improve interpretation of model-scale results for wind and tidal turbines in tunnels/flumes, to investigate the variation in force across a turbine and to update existing theoretical models of arrays of tidal turbines

Nondestructive Integrated CT-XRD Method for Research on Hydrated Cement System

A nondestructive integrated CT-XRD method has been developed and used to study hydrated cement system. In this research, a beam line (BL) at the third-generation synchrotron radiation facility, SPring-8, in Japan, was used. First, X-ray computed tomography (CT) was employed to obtain three-dimensional (3D) images and select a region of interest (ROI) in a given plane section of the hardened cement paste. Then, X-ray diffraction analysis (XRD) was conducted on the specified region. These operations were implemented in situ without the removal of specimen from the stage inside the BL. The hardened cement paste was precracked and then leached by continuous water flow through the specimen, and the integrated CT-XRD method was conducted before and after the leaching test. In this way, the change in the hydrated cement system was characterized over time using the same specimen. CT observation provides the location of cracks and air voids as well as high and low density substances present in the hydrated cement system. ROI is arbitrarily determined at a set of coordinates at which one likes to evaluate the change in the cement system using XRD. This newly developed technique enables the evaluation of the presence of calcium hydroxide (portlandite) over time and space

Magnetic-Field Dependences of Thermodynamic Quantities in the Vortex State of Type-II Superconductors

We develop an alternative method to solve the Eilenberger equations numerically for the vortex-lattice states of type-II superconductors. Using it, we clarify the magnetic-field and impurity-concentration dependences of the magnetization, the entropy, the Pauli paramagnetism, and the mixing of higher Landau levels in the pair potential for two-dimensional $s$- and $d_{x^2-y^2}$-wave superconductors with the cylindrical Fermi surface.Comment: 8 pages, 6 figure

Marine Impacts and Environmental Consequences—Drilling of the Mjølnir Structure, the Barents Sea

In September 2007, thirty-three scientists attended an international workshop in Longyearbyen (Svalbard, Norway) to discuss impacts of extraterrestrial bodies into marine environment and to prepare for the drilling of the 142-Ma-old Mjølnir impact structure in the Barents Sea (Fig. 1; Gudlaugsson, 1993; Dypvik et al., 1996, Tsikalas et al., 1998). A field trip visited the ejecta layer in the Janusfjellet Mountain in Isfjorden, just outside Longyearbyen (Fig. 2). The workshop focused on two topics: 1) mechanisms of marine impact cratering including ejecta formation and distribution, geothermal reactions, and the formation of tsunami, and 2) environmental effects of marine impacts. Both topics are highly relevant to the Mjølnir event and the geological evolution of the Arctic, as well as to the biological changes at the Jurassic-Cretaceous boundary. Against thisbackground were a) concrete drilling targets formulated, b) plans outlined for compiling data from existing geological and geophysical surveys as the basis for Integrated Ocean Drilling Program (IODP) and International Continental Scientific Drilling Program (ICDP) drilling proposals, and c) a steering group and science teams established for compiling old and new material as a foundation for the developmentof drilling proposal

Electronic inhomogeneity in EuO: Possibility of magnetic polaron states

We have observed the spatial inhomogeneity of the electronic structure of a single-crystalline electron-doped EuO thin film with ferromagnetic ordering by employing infrared magneto-optical imaging with synchrotron radiation. The uniform paramagnetic electronic structure changes to a uniform ferromagnetic structure via an inhomogeneous state with decreasing temperature and increasing magnetic field slightly above the ordering temperature. One possibility of the origin of the inhomogeneity is the appearance of magnetic polaron states.Comment: 4 pages, 3 figure

Playing for Data: Ground Truth from Computer Games

Recent progress in computer vision has been driven by high-capacity models trained on large datasets. Unfortunately, creating large datasets with pixel-level labels has been extremely costly due to the amount of human effort required. In this paper, we present an approach to rapidly creating pixel-accurate semantic label maps for images extracted from modern computer games. Although the source code and the internal operation of commercial games are inaccessible, we show that associations between image patches can be reconstructed from the communication between the game and the graphics hardware. This enables rapid propagation of semantic labels within and across images synthesized by the game, with no access to the source code or the content. We validate the presented approach by producing dense pixel-level semantic annotations for 25 thousand images synthesized by a photorealistic open-world computer game. Experiments on semantic segmentation datasets show that using the acquired data to supplement real-world images significantly increases accuracy and that the acquired data enables reducing the amount of hand-labeled real-world data: models trained with game data and just 1/3 of the CamVid training set outperform models trained on the complete CamVid training set.Comment: Accepted to the 14th European Conference on Computer Vision (ECCV 2016