Shock wave kinetics of Fe + NO based on Fe, O, and N atom measurements

The reaction of Fe atoms with NO was studied behind incident shock waves in the temperature range of 780–1,020 K at pressures between 0.3 and 1.2 bar. Atomic-resonance-absorption spectroscopy (ARAS) was applied for the time-resolved measurement of Fe , N, and O atoms in gas mixtures containing Fe(CO)₅ and NO, highly diluted in argon. The experiments showed a Fe-atom consumption without an associated O- or N-atom formation which can be explained by a recombination of Fe and NO:

The effective medium and the average field approximations vis-à-vis the Hashin-Shtrikman bounds. I. The self-consistent scheme in matrix-based composites

The effective medium approximation (EMA) and the average field approximation (AFA) are two classical micromechanics models for the determination of effective properties of heterogeneous media. They are also known in the literature as ‘self-consistent’ approximations. In the AFA, the basic idea is to estimate the actual average field existing in a phase through a configuration in which a typical particle of that phase is embedded in the homogenized medium. In the EMA, on the other hand, one or more representative microstructural elements of the composite is embedded in the homogenized effective medium subjected to a uniform field, and the demand is made that the dominant part of the far-field disturbance vanishes. Both parts of this study are concerned with two-phase, matrix-based, effectively isotropic composites with an inclusion phase consisting of randomly oriented particles of arbitrary shape in general, and ellipsoidal shape in particular. The constituent phases are assumed to be isotropic. It is shown that in those systems the AFA and EMA give different predictions, with the distinction between them becoming especially striking regarding their standing vis-à-vis the Hashin-Shtrikman (HS-bounds). While due to its realizability property the EMA will always obey the bounds, we show that there are circumstances in which the AFA may violate the bounds. In the AFA for two-phase matrix-based composites, the embedded inclusion is a particle of the inclusion phase. If the particle is directly embedded in the effective medium, the method is called here the self-consistent scheme-average field approximation (SCS-AFA), and will obey the HS-bounds for an inclusion shape that is simply connected. If the embedded entity is a matrix-coated particle, then the method is called the generalized self-consistent scheme-average field approximation (GSCS-AFA), and may violate the HS-bounds. On the other hand, in the EMA for matrix-based composites with well-separated inclusions, we indicate that in view of its premises the embedding with a matrix-coated particle generally becomes the appropriate one, and the method is thus called the generalized self-consistent scheme-effective medium approximation (GSCS-EMA). Part I of this study is concerned with SCS-AFA in dielectrics and elasticity, and Part II with the GSCS-AFA and GSCS-EMA in dielectrics.     

The effective medium and the average field approximations vis-à-vis the Hashin-Shtrikman bounds. II. The generalized self-consistent scheme in matrix-based composites

The present Part II of this two-part study is concerned with the average field approximation (AFA), and the effective medium approximation (EMA) in two-phase matrix-based dielectric composites through the use of an auxiliary configuration in which a particle of the inclusion phase is first surrounded by some matrix material, and then embedded in the effective medium. Those models will be referred as the generalized self-consistent scheme-average field approximation (GSCS-AFA), and the generalized self-consistent scheme-effective medium approximation (GSCS-EMA). We show that there are four types of the GSCS-AFA and a single type of the GSCS-EMA. In this paper the application of those models to dielectric composites with isotropic constituents and an inclusion phase that consists of randomly oriented ellipsoidal particles will be studied. The analytical solution of the auxiliary problem, which consists of an ellipsoidal particle confocally surrounded by a matrix shell and embedded in the effective medium, is achieved by means of ellipsoidal harmonics. Our results show that the effective property predictions of the GSCS-EMA and GSCS-AFA for the considered systems differ from each other, and more importantly, out of the four GSCS-AFA models, three of them violate the Hashin-Shtrikman bounds. The predictions of the GSCS-EMA obey the bounds. It is then shown that the version of the GSCS-AFA which obeys the Hashin-Shtrikman bounds for an inclusion phase with randomly oriented ellipsoids will violate them in the case of a particle shape which is not simply connected. Moreover, it turns out that the SCS-AFA studied in Part I also violates the Hashin-Shtrikman bounds in that case; the EMA, as expected, owing to its realizability property, continues to obey the bounds. Among the AFA and EMA in matrix-based composites, the GSCS-EMA therefore stands out as the method to be recommended.     

Investigation of horizontal-axis wind turbine (HAWT) blade threedimensional rotational effect based on field experiments

Field experiments are performed on a two-bladed 33 kW horizontal-axis wind turbine (HAWT). The pressures are measured with 191 pressure sensors positioned around the surfaces of seven spanwise section airfoils on one of the two blades. Three-dimensional (3D) and two-dimensional (2D) numerical simulations are performed, respectively, on the rotor and the seven airfoils of the blade. The results are compared with the experimental results of the pressure distribution on the seven airfoils and the lift coefficients. The 3D rotational effect on the blade aerodynamic characteristics is then studied with a numerical approach. Finally, some conclusions are drawn as follows. From the tip to the root of the blade, the experimental differential pressure of the blade section airfoil increases at first and then decreases gradually. The calculated 3D result of the pressure distribution on the blade surface is closer to that of the experiment than the 2D result. The 3D rotational effect has a significant impact on the blade surface flow and the aerodynamic load, leading to an increase of the differential pressure on the airfoils and their lift coefficient than that with the 2D one because of the stall delay. The influence of the 3D rotational effect on the wind turbine blade especially takes place on the sections with flow separation.     

基于精化锯齿理论的功能梯度夹心微板静弯曲模型

基于精化锯齿理论和新修正偶应力理论,建立了能够准确预测功能梯度夹心微板挠度、位移和应力的静弯曲模型。为了描述微板不同方向上的尺度效应,将两个正交材料尺度参数引入本文模型。以受双向正弦载荷作用的简支板为例,探究了夹心微板弯曲行为中尺度效应对结构刚度的影响。算例结果表明,当微板几何参数与材料尺度参数接近时,基于本文模型所测微板的最大弯曲挠度、局部位移和应力均小于传统精化锯齿理论给出的结果,捕捉到了尺度效应;尺度效应随着微板几何尺寸的增大而逐渐减弱,当微板几何尺寸远大于材料尺度参数时,尺度效应消失。此外,板的跨厚比和功能梯度变化指数也会对尺度效应产生一定影响。     

Hysteretic behavior of rectangular tube (box) sections based on Preisach model

In the present paper, the Preisach model of hysteresis is applied to model cyclic behavior of elasto-plastic material. Rate of loading and viscous effects will not be considered. The problem of axial loading of rectangular cross-section and cyclic bending of rectangular tube (box) will be studied in details. Hysteretic stress–strain loop for prescribed history of stress change is plotted for material modeled by series connection of three unite element. Also moment–curvature hysteretic loop is obtained for a prescribed curvature change of rectangular tube (box). All obtained results clearly show advantages of the Preisach model for describing cyclic behavior of elasto-plastic material.     

第二届亚洲功能材料与结构力学大会简介

第二届亚洲功能材料与结构力学大会于2010年10月22～25日在南京航空航天大学成功举行.本届大会由中国力学学会和江苏省力学学会主办、南京航空航天大学承办.会议延续在日本Matsue召开首届大会的目的:旨为亚洲及其周边地区从事功能材料与结构力学的科研工作者提供一个交流的平台,共同促进该领域在理论与应用方面的发展.     

Transmural pressure effects on the stability of clamped cylindrical shells subjected to internal fluid flow: Theory and experiments

An experimental and theoretical parametric study is undertaken to investigate the effect of transmural pressure on the non-linear dynamics and stability of circular cylindrical shells with clamped ends subjected to internal fluid flow. The theoretical structural model is based on the Donnell non-linear shallow shell theory, and potential flow theory is employed to describe the fluid-structure interaction. It is found that, for low transmural pressures in the range investigated, the shell loses stability by static subcritical divergence, while for higher transmural pressures the loss of stability is supercritical. In addition, there are ranges of flow velocity in which the shell exhibits quasi-periodic or even chaotic behaviour.     

Viscoplastic behaviour of a medium density polyethylene (MDPE): Constitutive equations based on double nonlinear deformation model

The viscoplastic behaviour of a medium density ethylene–butene copolymer (MDPE) is investigated by using samples cut out from thick-walled MDPE pipe. Extensive experimental work has been performed to characterise the nonlinear time-dependent response of such semi-crystalline thermoplastic material. Tests were carried out at 60 °C, on smooth tensile, full axisymmetrically notched creep tensile (FNCT) and double edge notched tensile (DENT) specimens.     

A simple model to describe the kinetics of the coagulation of casein (milk) and fibrin (blood)

Summary It is shown that, on the assumption that the accelerating (growth) and decelerating (decay) phases of coagulation are most simply described by exponential equations, whereas the direct combination of these equations leads to a power equation, the introduction of a power which falls linearly with time, leads to the coagulation equation which has already been found to hold extremely well for both blood and milk. The three equations, in differentiated form, form part of a series in which the negative power of time increases by unity for each successive term. But it is stressed that this treatment postulates the simplest possible conditions and that, like all basic equations, the coagulation equation will doubtless require modification for some systems.

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Zusammenfassung Es wird gezeigt, daß unter der Annahme, daß die Beschleunigungs-(Wachstums-) und Verzögerungs-(Zerfalls-)Phasen der Koagulation sich sehr leicht durch Exponentialgleichungen beschreiben lassen, wobei die direkte Kombination dieser Gleichungen zu einer Kraftbeziehung führen, die Einführung einer linear mit der Zeit abnehmenden Kraft zu einer Koagulationsgleichung führt, von der bereits jetzt bekannt ist, daß sie sehr gut sowohl auf Blut als auch auf Milch anwendbar ist. Die 3 Gleichungen stellen in der differenzierten Form den Teil einer Reihe dar, bei der die negative Potenz der Zeit für jeden folgenden Term um eine Größenordnung ansteigt. Es wird betont, daß dieser Weg die einfachst möglichen Bedingungen erfordert und daß die Koagulationsgleichung, ähnlich wie alle Grundgleichungen, zweifellos eine Modifikation für einige Systeme erfordert.

     

Theory and model implementation for analyzing line structures subject to dynamic motions of large deformation and elongation using the absolute nodal coordinate formulation (ANCF) approach

This paper presents the theory development and numerical implementation of a new gradient-deficient-based ANCF (Absolute Nodal Coordinate Formulation) model applied to perform the nonlinear dynamic analysis of elastic line structures subject to large stretching and deformation. The derivations of model equations, introduced numerical approaches, and result validations are the focuses of this study. Different from the traditional rod theory for small stretching consideration, the present model implements the line structures’ large elongation concepts into both the control mechanisms of constitutive formulations and equations of motion. The effect of external hydrodynamic forces on structures is also included in the model formulations. Based on the conservation of energy, the line model developed in this study covers the variation in strain and takes a full account of the bending effect with large stretching. A finite-element-based implicit scheme according to a modified Newmark-beta method is employed to solve the assembled system equations with unknown variables of nodal position vectors, their tangential derivatives, and strains. Selected cases with dynamic motions, such as nonlinear oscillation of a compound pendulum, free falling of a horizontal elastic beam in air with two different settings of gravity, free falling of a submerged horizontal tether with and without an attached concentrated mass, and a submerged vertical tether with a prescribed translational motion, are simulated to verify the developed model by comparing the results with analytical solutions and published experimental data and numerical results. It is found the present ANCF model, as noticed with good matched results with analytical solutions, measurements and other published solutions, is demonstrated to be able to provide converged and reasonably accurate predictions on the responses of line structures subject to large dynamic motions.

     

Mechanical and structural investigation of isotropic and anisotropic thermoplastic magnetorheological elastomer composites based on poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS)

Novel smart thermoplastic magnetorheological elastomer composites containing micron-sized magnetic carbonyl iron (CI) particles were prepared with a poly(styrene-ethylene-butylene-styrene) (SEBS) triblock copolymer utilized as the thermoplastic matrix rubber, and the structures and properties of the CI-SEBS composites were examined. The CI particles were uniformly dispersed in the composites prepared in the absence of the magnetic field at high temperatures T (>T $_{\rm g}^{\rm S})$ , and this isotropic composite exhibited a larger storage modulus G^?? compared to the SEBS matrix at room temperature (<?<T $_{\rm g}^{\rm S})$ where the EB phase therein was rubbery while the PS phase was in the glassy state. In contrast, the SEBS composite prepared under the magnetic field (with the intensity ???< 2.5?T) at high T (>T $_{\rm g}^{\rm S})$ contained a chain structure of CI particles. This chain structure became longer and better aligned on an increase of ?? up to a saturation of the particle magnetization and on an increase of the time interval of applying the field (that allowed the particles to move and equilibrate their aligned structure). The modulus G^?? of this ??pre-structured?? composite measured for both cases of ?? = 0 and ???> 0 in the direction perpendicular to the chain structure at room temperature was enhanced compared to G^?? of the isotropic composites. This difference of the filler effect (for ???=?0) and the magnetorheological effect (for ???> 0) between the pre-structured and isotropic composites was enhanced when the chain structure of the CI particles in the pre-structured composites became longer and better aligned. A mechanism(s) of this enhancement was discussed in relation to the morphologies (particle distribution) in the composites with the aid of a filler model and a molecular expression of the stress due to magnetically interacting particles.     

A shock tube study on the thermal decomposition of CS2 based on S(3P) and S(1D) concentration measurements

The thermal decomposition of CS₂ highly diluted in Ar was studied behind reflected shock waves by monitoring time-dependent absorption profiles of S(³P) and S(¹D) using atomic resonance absorption spectroscopy (ARAS). The rate coefficient of the reaction:

CONSOLIDATION HEORY OF UNSATURATED SOIL BASED ON THE THEORY OF MIXTURE(Ⅰ)

Unsaturated soil is a three-phase media and is composed of soil grain, water and gas. In this paper, the consolidation problem of unsaturated soil is investigated based on the theory of mixture. A theoretical formula of effective stress on anisotropic porous media and unsaturated soil is derived. The principle of effective stress and the principle of Curie symmetry are taken as two fundamental constitutive principles of unsaturated soil. A mathematical model of consolidation of unsaturated soil is proposed, which consists of 25 partial differenfial equations with 25 unknowns. With the help of increament linearizing method, the model is reduced to 5 governing equations with 5 unknowns, i.e., the three displacement components of solid phase, the pore water pressure and the pore gas pressure. 7 material parameters are involved in the model and all of them can he measured using soil tests. It is convenient to use the model to engineering practice. The well known Biot’s theory is a special case of the model.