风力机叶尖涡尾迹结构PIV测量研究

空气动力研究与发展中心低速空气动力研究所依托工程型大风洞（实验段直径3.2 m）,采用高分辨率CCD相机（4 008像素×2 672像素）,针对旋转状态下的风力机叶片尾流开展大视场（单个观测区域达到570 mm×380 mm）PIV(particle image velocimetry)测量,以NREL UAE Phase Ⅵ风力机叶片1/8缩比模型为实验对象,获取了叶尖涡产生、发展的流动数据,为研究风力机叶尖涡结构和流动机理研究提供重要的基础数据．观测结果表明,叶尖涡从后缘脱落后首先有一个短时间的向内运动,然后随着尾流的膨胀向外运动,其涡强度则先是短时间内降低,然后随着涡的卷起而增强,从而形成一个强大的叶尖涡．在实验观察范围内叶尖涡在来流方向的迁移规律近似线性．     

Input‐to‐Output Linearization of Explicit Control Systems with Constrained Measurements

Many design methods for non‐linear control problems require the measurement of the whole state of the plant. This contribution deals with a refinement of the well established exact input‐to‐output linearization such that the control laws depend only on a predefined set of measurements. More precisely, we derive the determining equations for all static control laws, such that the input‐to‐output map from the new input to the new output is linear and such that the constraints concerning the measurements are met.     

Spatial Velocity and Temperature Measurements in Non‐Isothermal Liquid Flows

A surface tension driven flow in the liquid vicinity of an air bubble on a heated wall is studied experimentally. The liquid flow caused by the temperature gradient along the surface of the bubble is termed thermocapillary convection. The surface tension force and the buoyancy force oppose one another. The measurement technique is the 3D particle tracking velocity and thermometry, 3D PTV/T, using thermochromic liquid crystals and digital image processing. The paper describes the method in some detail and presents quantitative results for different Marangoni numbers. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Determination of the Density Distribution of a Gas Flowing in a Pipe from Mean Density Measurements

Information about the density distribution of a gas flowingin a pipe is obtained by measuring the mean densities alongstraight lines across the pipe. The density distribution isrepresented by a Fourier series with variable coefficients whichsatisfy a Volterra type integral equation of the first kind.This equation is solved and a numerical technique for calculatingthe solution is given.     

Simulation of High‐Frequency Atmospheric Gas Discharges

The generation of atmospheric gas discharges is an important concern in many industrial applications. We are investigating here a special type of high‐frequency atmospheric gas discharge. The results of modelling the breakdown mechanism and of the development phase of the discharge will be presented. Furthermore we will show first numerical results. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Incomplete Self‐Similar Blow‐Up in a Semilinear Fourth‐Order Reaction‐Diffusion Equation

Blow‐up behavior for the fourth‐order semilinear reaction‐diffusion equation (1) is studied. For the classic semilinear heat equation from combustion theory (2) various blow‐up patterns were investigated since 1970s, while the case of higher‐order diffusion was studied much less. Blow‐up self‐similar solutions of (1) of the form are constructed. These are shown to admit global similarity extensions for t > T : The continuity at t = T is preserved in the sense that This is in a striking difference with blow‐up for (2) , which is known to be always complete in the sense that the minimal (proper) extension beyond blow‐up is u(x, t) ≡+∞ for t > T . Difficult fourth‐order dynamical systems for extension pairs {f(y), F(y)} are studied by a combination of various analytic, formal, and numerical methods. Other nonsimilarity patterns for (1) with nongeneric complete blow‐up are also discussed.     

Eigenvalue problems for a non‐self‐adjoint Bessel‐type operators in limit‐point case

It is shown in the Weyl limit‐point case that system of root functions of the non‐self‐adjoint Bessel operator and its perturbation Sturm–Liouville operator form a complete system in the Hilbert space. Furthermore, asymptotic behavior of the eigenvalues of the non‐self‐adjoint Bessel operators is investigated, and it is proved that system of root functions form a Bari basis in the same Hilbert space. Copyright © 2013 John Wiley & Sons, Ltd.     

Global Ill‐Posedness of the Isentropic System of Gas Dynamics

We consider the isentropic compressible Euler system in 2 space dimensions with pressure law p (ρ) = ρ² and we show the existence of classical Riemann data, i.e. pure jump discontinuities across a line, for which there are infinitely many admissible bounded weak solutions (bounded away from the void). We also show that some of these Riemann data are generated by a 1‐dimensional compression wave: our theorem leads therefore to Lipschitz initial data for which there are infinitely many global bounded admissible weak solutions. © 2015 Wiley Periodicals, Inc.     

Channel coordination in a consignment contract

With the emergence of virtual market places, consignment selling has been thriving at an unprecedented pace. It has been shown in the literature that inefficiency exists in a decentralized consignment channel with a single revenue share agreement. In our study, we analyze contracts observed in practice that contain bonus or side payment terms, and examine whether they can promote better coordination between the supplier and the retailer. We found that no multi-tier Bonus system can fully coordinate the consignment channel. However, fine adjustments of bonus parameters can bring the channel close to full coordination. Additionally, we found revenue sharing with side payment contracts not only fully coordinate the channel, but they can also be customized to meet the needs of small, medium and large suppliers for extra retailer services such as warehousing and transportation. Managerial insights on how to design the contracts from the supplier, retailer and channel perspectives are discussed in the paper.     

Cooperative Advertising in a Marketing Channel

This paper examines dynamic advertising and promotion strategies in a marketing channel where the retailer promotes the manufacturer product and the manufacturer spends on advertising to build a stock of goodwill. We assume that sales depend on goodwill and promotion activities and that there are decreasing marginal returns to goodwill. Two scenarios are studied. First, the manufacturer and retailer determine noncooperatively their respective strategies. Second, the game is played à la Stackelberg with the manufacturer as the leader who supports partially the cost of the promotion activities of the retailer. In both cases, stationary Markovian strategies are characterized. These scenarios are examined also in the absence of decreasing marginal effect of goodwill on sales. The results show that, whether or not the goodwill stock has a decreasing marginal effect on sales, the cooperative advertising program is a coordinating mechanism in the marketing channel, i.e., both players receive higher payoffs.     

Pricing VIX options in a stochastic vol‐of‐vol model

This paper proposes and makes a study of a new model for volatility index option pricing. Factors such as mean‐reversion, jumps, and stochastic volatility are taken into consideration. In particular, the positive volatility skew is addressed by the jump and the stochastic volatility of volatility. Daily calibration is used to check whether the model fits market prices and generates positive volatility skews. Overall, the results show that the mean‐reverting logarithmic jump and stochastic volatility model (called MRLRJSV in the paper) serves as the best model in all the required aspects. Copyright © 2015 John Wiley & Sons, Ltd.     

On Saint‐Venant's principle in a poroelastic arch‐like region

In this paper we consider the state of plane strain in an elastic material with voids occupying a curvilinear strip as an arch‐like region described by R: a<r<b, 0<θ<ω, where r and θ are polar coordinates and a, b, and ω (<2π) are prescribed positive constants. Such a curvilinear strip is maintained in equilibrium under self‐equilibrated traction and equilibrated force applied on one of the edges, whereas the other three edges are traction free and subjected to zero volumetric fraction or zero equilibrated force. In fact, we study the case when one right or curved edge is loaded. Our aim is to derive some explicit spatial estimates describing how some appropriate measures of a specific Airy stress function and volume fraction evolve with respect to the distance to the loaded edge. The results of the present paper prove how the spatial decay rate varies with the constitutive profile. For the problem corresponding to a loaded right edge, we are able to establish an exponential decay estimate with respect to the angle θ. Whereas for the problem corresponding to a loaded curved edge, we establish an algebraical spatial decay with respect to the polar distance r, provided the angle ω is lower than the critical value $\pi\sqrt{2}$. The intended applications of these results concern various branches of medicine as for example the bone implants. Copyright © 2010 John Wiley & Sons, Ltd.     

Components for a planar three–component velocimeter using Doppler global velocimetry (DGV) and PIV

Doppler global velocimetry (DGV) is a planar velocity measurement technique which is based on the determination of the Doppler shift of laser light scattered off particles by using a molecular filter. Currently a pulsed Doppler global velocimeter is being constructed at the Institute of Fluid Dynamics. The out–of–plane component of each velocity vector in the laser‐illuminated plane is obtained by that configuration. The experimental setup is extended so as to measure the in–plane component of those velocity vectors by using particle image velocimetry (PIV). Thus, a measurement system is being developed which is capable of obtaining three components of the velocity vectors located in a plane by using one single camera system. Due to the elaborate setup which includes a pulsed laser system, a filter cell and a camera system, the overall system quality is strongly connected to the technical performance of each single component. Therefore the technical specifications of all velocimeter components have been evaluated experimentally. Evaluation data are presented in this report.     

Non‐relativistic continuous states in arbitrary dimension for a ring‐shaped pseudo‐Coulomb and energy‐dependent potentials

In this research, the non‐relativistic particle scattering has been investigated for an alternative pseudo‐Coulomb potential plus ring‐shaped and an energy‐dependent potentials in D‐dimensional space. The normalized wave functions of continuous states on the k/2π scale are expressed in terms of the hyper‐geometric series, and formula of phase shifts is presented. Analytical properties of the scattering amplitude and thermodynamics properties are discussed. Some of the numerical results of energy levels have been calculated too. Copyright © 2015 John Wiley & Sons, Ltd.     

Decay in time for a one‐dimensional two‐component plasma

The motion of a collisionless plasma is described by the Vlasov–Poisson (VP) system, or in the presence of large velocities, the relativistic VP system. Both systems are considered in one space and one momentum dimension, with two species of oppositely charged particles. A new identity is derived for both systems and is used to study the behavior of solutions for large times. Copyright © 2008 John Wiley & Sons, Ltd.     

Local well‐posedness and blow‐up criterion for a compressible Navier‐Stokes‐Fourier‐P1 approximate model arising in radiation hydrodynamics

We establish a local well‐posedness and a blow‐up criterion of strong solutions for the compressible Navier‐Stokes‐Fourier‐P1 approximate model arising in radiation hydrodynamics. For the local well‐posedness result, we do not need the assumption on the positivity of the initial density and it may vanish in an open subset of the domain.     

Optimal combinational quota‐share and excess‐of‐loss reinsurance policies in a dynamic setting

In this paper, we describe a large insurance company's surplus by a Brownian motion with positive drift, which is the approximation of a classical risk process. The problem of minimizing the probability of ruin by controlling the combinational quota‐share and excess‐of‐loss reinsurance strategy is considered. We show that the optimal combinational reinsurance strategy must be the pure excess‐of‐loss reinsurance strategy. Moreover, we give an explicit solution for the optimal reinsurance strategy. Copyright © 2006 John Wiley & Sons, Ltd.     

Supercritical Neimark‐Sacker bifurcation of a discrete‐time Nicholson‐Bailey model

We study the local dynamics and supercritical Neimark‐Sacker bifurcation of a discrete‐time Nicholson‐Bailey host‐parasitoid model in the interior of . It is proved that if α>1, then the model has a unique positive equilibrium point , which is locally asymptotically focus, unstable focus and nonhyperbolic under certain parametric condition. Furthermore, it is proved that the model undergoes a supercritical Neimark‐Sacker bifurcation in a small neighborhood of the unique positive equilibrium point , and meanwhile, the stable closed curve appears. From the viewpoint of biology, the stable closed curve corresponds to the period or quasiperiodic oscillations between host and parasitoid populations. Some numerical simulations are presented to verify theoretical results.     

Flexural‐Gravity Wave Scattering by a Circular‐Arc‐Shaped Porous Plate

The interaction of flexural‐gravity waves with a thin circular‐arc‐shaped permeable plate submerged beneath the ice‐covered surface of water with uniform finite depth is considered under the assumption of linear theory. The problem is reduced to a second kind hypersingular integral equation for the potential difference across the plate which is solved approximately by an expansion–collocation method. Utilizing the solution, the reflection and the transmission coefficients and the hydrodynamic forces are evaluated numerically. The focus of the paper is to illustrate the effect of a porous curved plate submerged in finite depth water with an ice‐cover on the normally incident waves. Numerical results for a circular‐arc‐shaped plate for different configurations are derived and represented graphically. Also, by choosing an appropriate set of parameters, the known results for a circular‐arc‐shaped rigid plate submerged in deep water and a semicircular porous plate submerged in finite depth water with a free surface are recovered as special cases.