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991.
The interaction of a vortical unsteady flow with structures is often encountered in engineering applications. Such flow structure
interactions (FSI) can be responsible for generating significant loads and can have many detrimental structural and acoustic
side effects, such as structural fatigue, radiated noise and even catastrophic results. Amongst the different types of FSI,
the parallel blade–vortex interaction (BVI) is the most common, often encountered in helicopters and propulsors. In this work,
we report on the implementation of leading edge blowing (LEB) active flow control for successfully minimizing the parallel
BVI. Our results show reduction of the airfoil vibrations up to 38% based on the root-mean-square of the vibration velocity
amplitude. This technique is based on displacing an incident vortex using a jet issued from the leading edge of a sharp airfoil
effectively increasing the stand-off distance of the vortex from the body. The effectiveness of the method was experimentally
analyzed using time-resolved digital particle image velocimetry (TRDPIV) recorded at an 800 Hz rate, which is sufficient to
resolve the spatio-temporal dynamics of the flow field and it was combined with simultaneous accelerometer measurements of
the airfoil, which was free to oscillate in a direction perpendicular to the freestream. Analysis of the flow field spectra
and a Proper Orthogonal Decomposition (POD) of the TRDPIV data of the temporally resolved planar flow fields indicate that
the LEB effectively modified the flow field surrounding the airfoil and increased the convecting vortices stand-off distance
for over half of the airfoil chord length. It is shown that LEB also causes a redistribution of the flow field spectral energy
over a larger range of frequencies. 相似文献
992.
Peter Harris Mustafa Arafa Grzegorz Litak Chris R. Bowen Joanna Iwaniec 《The European Physical Journal B - Condensed Matter and Complex Systems》2017,90(1):20
In this paper we examine in detail the multiple responses of a novel vibrational energy harvester composed of a vertical bistable beam whose complex non-linear behavior is tuned via magnetic interaction. The beam was excited horizontally by a harmonic inertial force while mechanical vibrational energy is converted to electrical power through a piezoelectric element. The bistable laminate beam coupled to the piezoelectric transducer showed a variety of complex responses in terms of the beam displacement and harvested power output. The range of vibration patterns in this non-linear system included single-well oscillations and snap-through vibrations of periodic and chaotic character. Harvested power was found to be strongly dependent on the vibration pattern with nonlinearities providing a broadband response for energy harvesting. Wavelet analysis of measured voltage, displacement and velocity time histories indicated the presence of a variety of nonlinear periodic and also chaotic phenomena. To measure the complexity of response time series we applied phase portraits and determine stroboscopic points and multiscale entropy. It is demonstrated that by changing parameters such as the magnetic interaction, the characteristics of the bistable laminate harvester, such as the natural frequency, bandwidth, vibration response and peak power can be readily tailored for harvesting applications. 相似文献
993.
Michael W. Swift Chris G. Van de Walle 《The European Physical Journal B - Condensed Matter and Complex Systems》2017,90(8):151
Many complex oxides (including titanates, nickelates and cuprates) show a regime in which resistivity follows a power law in temperature (ρ ∝ T 2). By analogy to a similar phenomenon observed in some metals at low temperature, this has often been attributed to electron-electron (Baber) scattering. We show that Baber scattering results in a T 2 power law only under several crucial assumptions which may not hold for complex oxides. We illustrate this with sodium metal (ρ el?el ∝ T 2) and strontium titanate (ρ el?el \(\hbox{$\not\propto$}\) T 2). We conclude that an observation of ρ ∝T 2 is not always sufficient evidence for electron-electron scattering. 相似文献
994.
Bayesian approach to network modularity 总被引:2,自引:0,他引:2
We present an efficient, principled, and interpretable technique for inferring module assignments and for identifying the optimal number of modules in a given network. We show how several existing methods for finding modules can be described as variant, special, or limiting cases of our work, and how the method overcomes the resolution limit problem, accurately recovering the true number of modules. Our approach is based on Bayesian methods for model selection which have been used with success for almost a century, implemented using a variational technique developed only in the past decade. We apply the technique to synthetic and real networks and outline how the method naturally allows selection among competing models. 相似文献
995.
To date, there has been no general way of determining if the Copernican principle--that we live at a typical position in the Universe--is in fact a valid assumption, significantly weakening the foundations of cosmology as a scientific endeavor. Here we present an observational test for the Copernican assumption which can be automatically implemented while we search for dark energy in the coming decade. Our test is entirely independent of any model for dark energy or theory of gravity and thereby represents a model-independent test of the Copernican principle. 相似文献
996.
Dan J. Wilson Björn Winkler Alexandra Friedrich Chris J. Pickard 《Journal of Physics and Chemistry of Solids》2008,69(7):1861-1868
We present a density functional theory study of a variety of nitridosilicate and oxonitridoaluminosilicate systems. For the nitridosilicates, we have shown that the DFT-calculated equilibrium structures of BaYb-Si4N7, SrYb-Si4N7 and EuYb-Si4N7 are in good agreement with experiment. We then used the virtual crystal approximation (VCA) to study the effects of oxygen-doping on the nitrogen sites. We then added Si/Al disorder into our system, in order to model the properties of BaYb-SiAlON for pressures up to 50 GPa, in order to investigate recent experimental findings. We have found that this system is stable over the whole pressure range, and that the compression mechanism is pure bond length shortening. 相似文献
997.
A two-stage process with temperature-shift has been developed to enhance the anthocyanin yield in suspension cultures of strawberry cells. The effect of the temperature-shift interval and the shift-time point was investigated for the optimization of this strategy. In this process, strawberry cells were grown at 30℃ (the optimum temperature for cell growth) for a certain period as the first stage, with the temperature shifted to a lower temperature for the second stage. In response to the temperature shift-down, anthoeyanin synthesis was stimulated and a higher content could be achieved than that at both boundary temperatures but cell growth was suppressed. When the lower boundary temperature was deereased, cell growth was lowered and a delayed, sustained maximum anthocyanin content was achieved. Anthocyanin synthesis was strongly influeneed by the shift-time point but cell growth was not. Consequently, the maximum anthocyanin content of 2.7 mg(?)g-fresh cell~(-1) was obtained on day 9 by a temperature- 相似文献
998.
999.
Chris Pollett 《Mathematical Logic Quarterly》2000,46(2):249-256
The purpose of this paper is to explore the relationship between IΔ0 + exp and its weaker subtheories. We give a method of translating certain classes of IΔ0 + exp proofs into weaker systems of arithmetic such as Buss' systems S2. We show if IEi (exp) ⊢ A with a proof P of expind‐rank(P) ≤ n + 1where all (∀ ≤: right) or (∃ ≤: left) have bounding terms not containing function symbols, then Si 2 ⊇ IEi,2 ⊢ An. Here A is not necessarily a bounded formula. For IOpen(exp) we prove a similar result. Using our translations we show IOpen(exp) ⊊ IΔ0(exp). Here IΔ0(exp) is a conservative extension of IΔ0 + exp obtained by adding to IΔ0 a symbol for 2 x to the language as well as defining axioms for it. 相似文献
1000.