On the interaction between two fixed spherical particles

The variation of the drag (C_D) and lift coefficients (C_L) of two fixed solid spherical particles placed at different positions relative each other is studied. Simulations are carried out for particle Reynolds numbers of 50, 100 and 200 and the particle position is defined by the angle between the line connecting the centers of the particles and the free-stream direction (α) and the separation distance (d₀) between the particles. The flow around the particles is simulated using two different methods; the Lattice Boltzmann Method (LBM), using two different computational codes, and a conventional finite difference approach, where the Volume of Solid Method (VOS) is used to represent the particles. Comparisons with available numerical and experimental data show that both methods can be used to accurately resolve the flow field around particles and calculate the forces the particles are subjected to. Independent of the Reynolds number, the largest change in drag, as compared to the single particle case, occurs for particles placed in tandem formation. Compared to a single particle, the drag reduction for the secondary particle in tandem arrangement is as high as 60%, 70% and 80% for Re = 50, 100 and 200, respectively. The development of the recirculation zone is found to have a significant influence on the drag force. Depending on the flow situation in-between the particles for various particle arrangements, attraction and repulsion forces are detected due to low and high pressure regions, respectively. The results show that the inter-particle forces are not negligible even under very dilute conditions.     

On the interaction between two inclined cracks under biaxial load

Summary An analysis of the in-plane biaxial loading of an infinite homogeneous and isotropic elastic plate with two inclined collinear cracks of equal length is performed. The boundary value problem is solved by using the complex potentials method. The influence of the lateral load on the local stress distributions as well as on the crack tips behaviour is analyzed and the features of the interaction are described.

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Sommario Viene studiato il problema piano di due fessure inclinate ed allineate, di uguale lunghezza, in una lastra piana infinita di materiale elastico omogeneo ed isotropo, in regime di carico biassiale. Il problema dei valori al contorno viene risolto mediante la tecnica di potenziali complessi. Vengono analizzati gli effetti del carico laterale sia sui campi locali degli sforzi che sul comportamento delle estremitá delle fessure e descritte le modalità di interazione.

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Financial support of the National Research Council (C.N.R.) through research contribution N. 80.02203.07.     

On the interaction between two consecutive elongated bubbles in a vertical pipe

The motion of elongated air bubbles in a vertical pipe filled with water is studied quantitatively using video imaging of the flow and subsequent digital image processing of the recorded sequence of images. Experiments are carried out to determine the influence of the separation distance between two consecutive bubbles (liquid slug length) upon the behavior of the trailing bubble in vertical slug flow. The details of the trailing bubble acceleration and merging process are observed and the instantaneous parameters of the trailing bubble, such as its shape, velocity, acceleration, etc., are measured as a function of the separation distance. The leading bubble is found to be unaffected by the trailing elongated bubble.     

Fluid-dynamic interaction between two spheres

Experiment of fluid-dynamic interaction between two spheres was conducted to obtain basic information concerning the two-phase flow, especially in dense phase. Two or three spheres were set up in a water tunnel in the longitudinal or transverse direction with Reynolds numbers less than 10³. The flow behind the sphere was visualized by the use of condense milk and change in vortex structure due to the interaction was observed in detail. Additionally, drag force on the sphere was measured by a pendulum method which was developed to detect small drag, and the range of distance in which the drag is affected by the interaction was shown.     

A study of the interaction between two triple points

In the Mach reflection of plane shock on a concave double wedge, after two triple points collide with each other, the wave pattern is usually complicated. In this paper, firstly, a shock dynamic approach is used for studying this problem. In this approach, the method of shock-shock polar is used for better understanding the pattern of disturbance propagation. A downward-traveling shock-shock disturbance on the Mach stem is predicted theoretically. Secondly, based on the idea of shock dynamic approach, a gas dynamic model is built for studying the same problem. A similar result is obtained and the formation of the downward-traveling triple point is analyzed. This downward-traveling disturbance propagates and reflects between the upward-traveling shock-shock locus and the wall surface, causing the Mach number of Mach stem to increase and making the wave configuration approach to the one in the Mach reflection on a single wedge.Received: 19 April 2004, Accepted: 2 December 2004, Published online: 16 March 2005[/PUBLISHED]Correspondence to: P. Xie, Z.Y. Han     

Hierarchical structural optimization of laminated plates using polar representation

A novel methodology for the design of optimal uncoupled laminated plates under membrane only or bending only loading is introduced. This approach is supported by the polar representation of anisotropy. First, topology optimization, aimed at maximizing global stiffness of the structure, allows to find an optimal distribution of polar components. Then, based on the latter structural results, a matching feasible lamination sequence is determined.     

On the elastic strain energy representation of a dislocated body and dislocation equilibrium conditions

Various equilibrium dislocation distributions in finite and infinite media were recently analyzed [5], both from theoretical and computational standpoints. In this paper we shed further light on this issue, by elaborating on a variational procedure that gives the required equilibrium conditions: the glide forces on each dislocation represent a set of self-equilibrating forces. The derivation is carried out in a general 3-dimensional setting, with adequate specifications for edge dislocations in plain-strain case.     

2次爆炸事件的相关性与能量比研究

主要对全球地震台网(GSN)牡丹江(MDJ)地震台记录的2006年10月9日与2009年5月25日爆 炸事件进行分析对比研究。应用2次事件的P震相最大振幅比值和功率谱比值估计了2次事件的能量比。 应用互相关值和相干函数方法计算了2次事件在时域与频域的相关性。最后得出,2009年的爆炸事件与 2006年爆炸事件相比,3个方向的P震相最大单振幅比值平均为3.97,功率谱比值平均为4.5,由此估计 2009年爆炸事件是2006年爆炸事件能量的4~5倍。MDJ台3个方向(Z、N、E)记录的2次事件在1~4Hz 频段的互相关值平均为0.88,相干函数平均为0.8左右。     

Dependence of slip coefficients on the nature of the interaction between gas molecules and a wall

A method of solution of the boundary-value problems of kinetic gas theory is developed, making it possible to use the boundary conditions in the most general form. The generalized Maxwell boundary condition that takes into account the dependence of the accommodation coefficient on the angle of incidence of gas molecules is considered as an example.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 149–152, September–October, 1986.     

Experiments characterizing the interaction between two sprays of electrically charged liquid droplets

Experiments were conducted to characterize the interaction between two sprays of electrically charged ethanol droplets. The micrometer-size droplet sprays were generated electrohydrodynamically by applying a high positive voltage to two adjacent parallel needles that were located above a distant, electrically grounded funnel. The resultant droplet axial and lateral velocity components and diameter were measured as a function of needle spacing and applied voltage using a Phase Doppler Particle Analyzer. Data were acquired at two axial positions below the needles' tips, for two needle spacings, four applied voltages and at a single flow rate.The results revealed that an increase in applied voltage yielded an increase in the spray charge density. This produced an increase in both the axial and lateral droplet velocity components and a decrease in the droplet Sauter mean diameter and in its variation across the spray. An increase in needle spacing yielded a decrease in the axial velocity component. The lateral velocity component and the Sauter mean diameter, however, were not noticeably affected by this increase. Photographic data established a relationship between the lateral half-width of the spray and axial distance. This was used to identify a nondimensional similarity between the axial mean velocity component and lateral position. The results collectively support that appropriate variations in the applied voltage and needle spacing can yield more spatially uniform mean velocity component and Sauter mean diameter profiles. These variations bring about increased mixing between the two needles' sprays and, thus, an enhanced development of the combined droplet spray.     

Hydrodynamic interaction between two vertical cylinders in water waves

I.IntroductionWiththeconstructionoflargeoffshorestructures-wavediffractionandradiationproblemscausedbyseveralbodiesbecomeincreasinglyimportant.LargeoffShoreplatforms,wave-powerextractiondevices,Iargestoragefacilitiesandoffshorefloatingairportsl']havebeenp…     

关于应变强度表示的讨论

全量理论中,应变强度的表示不会产生可加性的矛盾．     

On the relationship between impact energy and delamination area

Thin glass/epoxy plates fabricated from 3M prepreg tape were subjected to low-velocity impact. Delamination in the impacted composite plates was measured by edge replication and was identified as the major damage mode. The effects of fiber orientation, thickness, and lamination on the delamination resistance were investigated. Experimental results verified three previous findings: (1) a linear relationship holds between delamination area and impact energy, (2) the mismatch of bending stiffness between adjacent laminae can be correlated with the delamination area on the interface, and (3) the behavior of a thin composite plate under low-velocity impact is very similar to that caused by global bending. In addition, based on the calculation of impact energy per unit delamination area, the dynamic fracture energy and the energy of dissipation in the thin glass/epoxy plates can be examined.     

On the flow between two counter-rotating infinite plane disks

This paper studies the boundary-value problem arising from the behaviour of a fluid occupying the region -1≦x≦1 between two rotating disks, rotating about a common axis perpendicular to their planes when the disks are rotating with the same speed Ω₀ but in the opposite sense. The equations which describe the axially symmetric similarity solutions of this problem are $$\varepsilon H^{iv} + HH''' + GG' = 0$$ $$\varepsilon G'' + HG' - H'G = 0$$ with the boundary conditions $$H( \pm 1) = H'( \pm 1) = 0$$ $$G( - 1) = - 1,{\text{ }}G(1) = 1$$ where ?=v/2Ω₀ and v is the kinematic viscosity. The existence of an odd solution is established. This particular solution satisfies many special conditions, for example, G′ (x, ?)>0. Moreover, precise estimates are obtained on the size and behaviour of the solution as ? ↓ 0.     

On the interaction between the input signal and the singularity expansion method

For transient excitation, it is well known that the Singularity Expansion Method (SEM) is a late time technique that is not in general suitable for early time. Lossy dielectric slab studies, with bounded integrable finite-duration input signal, have shown that the SEM representation for early time requires an additional branch cut contribution and a modification of the SEM series for completeness. Other researchers indicated that the SEM representation is not complete for most cases of practical interest and that it may not converge for early time. In this paper, we present an approach, using the input signal, to obtain a convergent SEM series that is valid for early as well as for late time. In this approach the branch cut contribution is not needed and instead we have pole contributions form the input signal and a modified SEM series. In addition, two forms of SEM representations will be presented, the traditional form and the time varying coupling coefficient form. Furthermore, the interaction and the effect of the input signal choice on the SEM representation will be clarified. This will be done for a dielectric slab backed by a perfect conductor.