Stretches of Fluid Materials for Stokes Flow in Circular Cavity

Stretching for fluid materials slowly flowing within a circular cavity is investigated in the present study. Two belts, which are performed in periodic rotations on the boundary, are used to drive the flow motions. It is shown that the stretching values of fluid filaments are very sensitive to the boundary conditions for which different periods and different angle-phase-shifts are used. Flows generated by the rotations with longer periods and∕or flows generated by the two belts rotating out-phase will create greater stretchings, and possibly better stirrings. Furthermore, under these situations the stretching values associated to fluid filaments are much uniformly distributed.     

Optimization of Rotating Blades with Dynamic‐Behavior Constraints

The optimal design of rotating pretwisted blades subject to dynamic behavior constraints is studied. The restrictions on multiple blade natural frequencies and on maximum blade dynamic deflections are considered the dynamic behavior constraints. The aerodynamic forces acting on the rotating blades are simulated as harmonic excitations. Optimization techniques of the optimality‐criterion method and the method of modified feasible directions have been successfully developed and applied to minimize the weight of rotating pretwisted blades. Based on these techniques, the numerical results show that the effect of setting angle on the optimal design weight for the first frequency‐constraint case is more significant than that for the second frequency‐constraint case. It is also shown that the changes of pretwist angle will considerably affect the optimal design weight for the second frequency‐constraint case. However the effect is not significant for the fundamental frequency‐constraint case. The results also indicate that the increase of rotating speed will decrease the optimal design weight.     

Vibration of Axially Loaded Rotating Cross-Ply Laminated Cylindrical Shells via Ritz Method

This paper presents the free vibration analysis of axially loaded rotating cross-ply laminated cylindrical shells with the consideration of the effects of centrifugal and Coriolis forces as well as the initial hoop tension due to the rotation. The Ritz method is employed for the solution of this problem. Adopting the trigonometric series as the admissible displacement functions, a set of frequency characteristics equations is derived. The frequency characteristic analysis for shells of simply supported boundary conditions is examined and the frequency characteristics of various lamination schemes are investigated. The results from the present analysis are compared with the available solutions to validate its accuracy.     

Method of Fundamental Solutions for Three-Dimensional Stokes Flow in Exterior Field

The main purpose of the present paper is to provide practical and numerical implementations of the method of fundamental solutions for three-dimensional exterior Stokes problems with quiet far-field condition and discuss the issues therein. The solutions of the steady Stokes problems are obtained by utilizing the boundary collocation method as well as the expansion of Stokeslets, which are the fundamental solutions of the steady Stokes equations. To validate the proposed model, numerical results of a lid-driven cavity flow, uniform flow passing a sphere, and a rotating dumbbell-shaped body show good agreement with the numerical and analytical solutions available in the literature. Also, a hypothetical problem with both vorticity and velocity boundary conditions is solved and compared with the analytical solution. The proposed model is then properly exploited to obtain the flow results of uniform flow passing a pair of vertical spheres in tandem and uniform flow passing a pair of horizontal spheres in tandem. Furthermore, the accuracy of the present numerical scheme is addressed and the detail flow characteristics, such as pressure distribution, streamline contour, velocity field, and vorticity fields are sketched.     

Recurrent Single Delaminated Beam Model for Vibration Analysis of Multidelaminated Beams

Free vibration analysis of a through-width multidelaminated beam is performed in the present study. Multiple delaminations are assumed to spread from the top through the thickness direction of the beam. The natural frequencies of the multidelaminated beams are obtained from a recurrent single delaminated beam (RSDB) model, which is the subsingle delaminated beam from the top surface of a global beam. Each frequency equation for the RSDB with unknown boundary conditions is obtained through continuity conditions. Then this result is updated to the next one. With these sequential operations, the final frequency equation of the multidelaminated beams is obtained for both end boundary conditions of the global beam. The numerical results for the beams are compared with those of finite element analysis to give the reliance on the proposed model and to investigate the effects of the shape, number, and size of multidelaminations on the natural frequency. It was shown that the variations in the natural frequency for the multidelaminated beams were significantly affected by the delamination length.     

The role of hydrodynamic interaction in the locomotion of microorganisms

A general Boundary Element Method is presented and benchmarked with existing Slender Body Theory results and reflection solutions for the motion of spheres and slender bodies near plane boundaries. This method is used to model the swimming of a microorganism with a spherical cell body, propelled by a single rotating flagellum. The swimming of such an organism near a plane boundary, midway between two plane boundaries or in the vicinity of another similar organism, is investigated. It is found that only a small increase (less than 10%) results in the mean swimming speed of an organism swimming near and parallel to another identical organism. Similarly, only a minor propulsive advantage (again, less than 10% increase in mean swimming speed) is predicted when an organism swims very close and parallel to plane boundaries (such as a microscopic plate and (or) a coverslip, for example). This is explained in terms of the flagellar propulsive advantage derived from an increase in the ratio of the normal to tangential resistance coefficients of a slender body being offset by the apparently equally significant increase in the cell body drag. For an organism swimming normal to and toward a plane boundary, however, it is predicted that (assuming it is rotating its flagellum, relative to its cell body, with a constant angular frequency) the resulting swimming speed decreases asymptotically as the organism approaches the boundary.     

Grain boundary precipitation in aluminum alloys: Effect of boundary structure

A transmission electron microscope study of grain boundary precipitation in Al-Zn and Al-Zn-Mg alloys has been conducted with emphasis on the influence of localized boundary structure. Intrinsic grain boundary defects are found to have a significant effect on the precipitation sequence in that they assist the emerging precipitates in establishing a low energy habit plane relationship with at least one bordering grain. Under more extreme conditions of unavailable habits or unfavorable intrinsic structures, extrinsic defects dominate the precipitation reaction.     

Free-Vibration Analysis and Material Constants Identification of Laminated Composite Sandwich Plates

Free vibration of symmetrically laminated composite sandwich plates with elastic edge restraints is studied via the Rayleigh–Ritz approach. The proposed Rayleigh–Ritz method is constructed on the basis of the layer-wise linear displacement theory. The accuracy of the method in predicting natural frequencies of composite sandwich plates with different boundary conditions is verified by the results reported in the literature or the experimental data obtained in this study. The proposed method is then applied to the material constant identification of free composite sandwich plates using the first six theoretical natural frequencies of the plates. In the identification process, trial material constants are used in the present method to predict the theoretical natural frequencies, a frequency discrepancy function is established to measure the sum of the squared differences between the experimental and theoretical natural frequencies, and a stochastic global minimization algorithm is used to search for the best estimates of the material constants by making the frequency discrepancy function a global minimum. Applications of the material constant identification technique are demonstrated by means of several examples.     

Solute segregation and brittle fracture in an alloy steel

Using an Sb doped Ni-Cr steel as a model material, the mechanism of intergranular brittle fracture was studied by means of tests on smooth, notched, and precracked specimens, in conjunction with statistically analyzed, selected area Auger electron spectroscopy.The critical local stress for fracture of a grain boundary was determined as a function of the Sb concentration on that boundary. The Sb effect can be understood in terms of its influence on cohesive energy, which controls the plastic work associated with brittle fracture. The results indicate that the optimum method for assessing embrittlement behavior of such a steel with minimum ambiguity is to use a notched specimen at a fixed test temperature in the appropriate temperature range for that material. The conditions which govern brittle crack nucleation in steel and the factors which influence the plastic work are discussed.     

For a psycholinguistic model of handwriting production: Testing the syllable-bigram controversy.

This study examined the theoretical controversy on the impact of syllables and bigrams in handwriting production. French children and adults wrote words on a digitizer so that we could collect data on the local, online processing of handwriting production. The words differed in the position of the lowest frequency bigram. In one condition, it coincided with the word's syllable boundary. In the other condition, it was located before the syllable boundary. The results yielded higher movement durations at the position where the low-frequency bigram coincided with the syllable boundary compared to where the low-frequency bigram appeared before the syllable boundary. Syllable-oriented strategies failed with the presence of a very low-frequency bigram within the initial syllable. Further analysis showed that children in grades 3 and 4 privileged syllable-oriented programming strategies. The production times of children in grade 4 were also affected by syllable frequency and, to a lesser extent, bigram frequency. The adults writing durations were modulated by bigram frequency. Therefore, both bigrams and syllables regulate handwriting production although the influence of bigrams was stronger in adults than children. In the light of these results, we propose a psycholinguistic model of handwriting production. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Torsional vibration measurement of the viscosity of a metallic melt

The liquid Co₉₁B₉ alloy is used as an example to study the influence of boundary conditions at the upper melt boundary on the results of viscosity measurements using torsional vibrations. Specific features related to film effects and wetting phenomena are shown to appear in the temperature dependence of logarithmic decrement. To exclude the influence of these effects and phenomena, viscosity measurements should be performed under the experimental conditions where the melt to be studied is in closed volume and the internal crucible walls are fully wetted. The temperature dependence of the kinematic viscosity of the Co₉₁B₉ melt that is obtained under such experimental conditions has a monotonic character.     

Boundary Condition Effects in Buckling of “Soft” Core Sandwich Panels

The effects of boundary conditions on the critical load level and the corresponding deflection mode shape of sandwich panels with a “soft” core due to in-plane loads are presented. The study is conducted using a closed-form high-order linearized buckling analysis that includes the influence of the transverse flexibility of the core as well as of the localized effects on the overall sandwich panel behavior, and allows the use of different boundary conditions for the upper and lower skin at the same section. The panel construction is general and consists of two skins (not necessarily identical), metallic or composite-laminated symmetric, and a soft core made of foam or a low-strength honeycomb. The closed-form high-order analysis yields the general buckling behavior of the structure, which means that the solutions obtained allow for interaction between the skins and the core. The solutions are general and are not based on separation of the buckling response on several types of uncoupled buckling modes, such as overall buckling, skins wrinkling, etc., as commonly used in the literature. The numerical scheme consists of finite differences to approximate the governing equations of the closed-form high-order formulation and to transform the set of linearized governing differential equations into an eigenvalue problem that is solved using the deflated iterative Arnoldi procedure. The influence of a general type of boundary conditions, including different conditions throughout the height of the same section and nonidentical conditions at the upper and lower skin, as well as of the core properties, on the buckling behavior of the sandwich panels is considered. The discrepancy between the Timoshenko-Reissner model and the present formulation is discussed. In particular, a partial fixity phenomenon due to the existence of the pinned boundary conditions, i.e., simply supported conditions, at the upper and lower skins at the edge is demonstrated. It is shown that the core properties affect the buckling loads and the corresponding modes of the panel in such a way that the structures with identical boundary conditions but with different cores may undergo different types of buckling such as overall and local as well as interactive loss of stability. The effect of an edge concentrated moment, induced by a couple and exerted on the skins only is also studied.     

Nonlinear Static Response and Free Vibration Analysis of Doubly Curved Cross-Ply Panels

In this paper, the nonlinear static and free vibration analyses of doubly curved cross-ply laminated panels subjected to thermomechanical loading are examined. The shell theory adopted in the present case is an extension of Reissner’s shallow shell simplifications that accounts for parabolic distribution of the transverse shear strains through thickness of the shell and tangential stress-free boundary conditions. A multiterm Galerkin’s method is adopted to solve the governing nonlinear partial differential equations. The static equilibrium paths are traced using the Newton-Raphson method in conjunction with the Riks approach to overcome the limit points. The free vibration frequencies about a static equilibrium state of a deformed panel are reported by solving the linear eigenvalue problem. Analytical results are presented for symmetric [0/90/0] and antisymmetric [0/90] cross-ply laminated doubly curved panels that illustrate the influence of geometric properties, in-plane edge boundary conditions, lateral distributed load and temperature field on the nonlinear behavior and natural frequencies.     

Feasibility Study of Hydrogen Generator with Molten Slag Granulation

A huge amount of hot molten oxides, such as steelmaking slag and molten municipal waste, is discharged at present without heat recovery, in spite of its very high potential. For example, hot molten slag as a by‐product in the Japanese steelmaking industry, over 1723 K in temperature, reaches as much as 30 million tonnes annually. To recover heat of the viscous slag chemically, the strongly endothermic reaction CH₄+H₂O →3H₂+CO was selected and then the property of dry granulation of the molten slag by Rotary Cup Atomizer (RCA) for expanding surface area of the slag was experimentally studied. The purpose of this paper was, therefore, to study slag granulation under various conditions for promoting heat exchange between slag and gas, in which the influence of the rotating speed and the shape of the cup on the slag drop size was mainly examined. The collected slag drops were correlated with operating conditions such as rotating speed, cup shape, etc. Most significantly, the molten slag was successfully granulated under the dry conditions without water impingement. The rotating speed of the cup influenced the diameter and shape of the slag drops very strongly. The higher rotating speed made the slag drops smaller, more spherical and uniform. Drops with 5 to 6 mm of average dimension were obtained at a rotating speed of 15 rps (900 rpm), and drops with about 1 mm at 50 rps (3000 rpm). In the former case, the shape of the obtained drops changed from spherical to ribbon‐like. These results will be useful to establish new heat recovery processes with hydrogen generation from molten slag with many benefits. Energy analysis and cost evaluation were also conducted, to study the benefit of the proposed process.     

Condition Assessment of Shear Connectors in Slab-Girder Bridges via Vibration Measurements

The paper presents a field study on condition assessment of the shear connectors in a full slab-girder bridge via vibration measurements. First, a model updating technique is employed to assess the condition of the whole structure, including boundary conditions, bearings, girders, slab, and shear connectors, from the accelerations on the slab measured in vibration testing. Then, a new damage index based on the difference of frequency response functions on the slab and the corresponding points on the girder is developed to evaluate the condition of shear connectors. The advantage of the new method lies in the fact that it does not need any reference data (undamaged data) for the structure. Compared with the results obtained using the model updating technique, the method is more reliable and accurate in assessing the condition of the shear connectors between the slab and girders. The effects of measurement noise on the damage identification results and the damage quantification are also studied through numerical simulation.     

A simple method for the calibration and equalization of whole-body startle measurements in the rat

A dynamic calibration method for startle amplitude measurement systems for rats is described that is based on rotating weights. The calibration is dependent exclusively on: the mass of the weights, the eccentricity of the weights with respect to the rotation axis, and the rotation velocity in revolutions per second, all of which are easily and accurately measurable parameters. Because of the variability of the frequency spectrum of whole-body startle reactions, it is important to measure the frequency transfer function of startle measuring devices and if necessary to correct the transfer function in the preamplifier so that a flat transfer function in the relevant frequency range results.     

COREX熔化气化炉风口回旋区的分形研究

以COREX熔化气化炉物理模型为基础,对高速摄影仪记录的回旋区颗粒运动情况进行分析得到模型观察面上回旋区的颗粒速度场,运用分形方法对回旋区内不规则边界的表面积进行研究。结果表明：不同条件下,回旋区内表面边界的分维数变化不大;回旋区内表面积随着风量的增大而增大,当吹气量由106 m3/h变为122 m3/h时,回旋区表面...     

基于自适应数字滤波的旋转机械动平衡边缘计算

为了提高机械设备不平衡故障的判断准确率,针对目前振动信号检测分析计算均在服务器云平台进行的现状,设计一种在边缘计算端实现的方式.通过自适应数字滤波方法分析出旋转机械不平衡故障,利用中心频率自适应带通数字滤波器实现噪声去除,并且将算法固化到嵌入式单片机上.通过中心频率带通滤波器,利用数字化滤波器传递函数,对采集的信号数据...     

Numerical and Physical Modeling of Steel Flow in a Two-Strand Tundish for Different Casting Conditions

This article presents computational and water model studies of the three-dimensional turbulent fluid flow in a two-strand tundish for steady-state and transient casting conditions. First, it presents the flow field measurements obtained at a 1:3-scale water model of the tundish with the particle-image velocimetry (PIV) method during steady-state casting. The PIV measurements were performed using the Reynolds-similarity criterion. Thereafter, numerical simulation is carried out with the computational fluid dynamic software, FLUENT, using the realizable k-ε turbulence model. The numerical model is validated using the measurement results obtained with the water model. The results of the numerical calculations are in good agreement with the PIV measurements. On this basis, the validated numerical model is adapted to simulate the 1:1-scale steel flow with boundary conditions that are derived from the real casting process. The nonisothermal, unsteady numerical calculations concerning the cooling process of steel melt inside the tundish are done for a 1:1-scale industrial facility—a 69-t two-strand tundish with a 380-t ladle. The influence of transient boundary conditions at the outlet of the tundish (one blocked strand) on the flow structure and mixing process of fluid during the casting process are investigated. The evaluation of the flow structure is performed using a zonal method, which relates the fluid flow with the mixing processes.