Measurement of developing turbulent flow in a U-bend of circular cross-section

Hot-wire measurements of the full mapping of the velocity and Reynolds stress components are reported for developing turbulent flow in a strongly curved 180 deg pipe and its tangents. A slanted wire is rotated into 6 orientations and the voltage outputs from wires are combined to obtain the mean velocity and Reynolds stress components. The strength of secondary flow reaches up to the 28% of bulk mean velocity. The strong counter-rotating vortex pair induced by the transverse pressure gradient and centrifugal force imbalance grows up to Θ = 67.5° into the bend. But the vortex pair breaks down into two cell pattern after Θ=90° Core vortex formation and reversal of secondary flow direction along the bend symmetry plane is cleanly found in the secondary vector plot. At Θ=67.5° and Θ = 90° into bend a large “trough” develops in the longitudinal velocity toward the inside of the bend due to the breakdown of secondary flow. In the bend, the mean longitudinal velocity component changes little after Θ=90°, but secondary flow never achieves fully-developed state. Similar behaviors are observed in the radial and circumferential stresses.     

Automation and parameters optimization in production line: a case of study

A metal-forming production line was automated and the critical parameters of the process of feeding to the press were determined using experiments designed to optimize production with a minimum number of tests. In order to carry out a factorial design of experiments, we registered the level of lubricant, the speed of the feeder, the advance of raw material, and the pressure of the lubrication to be taken as experimental factors. The results of the experiment design showed that the advance of raw material and the interactions between the level of lubricant and the pressure of the lubricant and between the feeder speed, the level of lubricant, and the pressure of the lubricant are the main parameters for feeding to the press for production optimization. Several tests were carried out and the production in the automated and optimized process increased more than 400 % with respect to the artisan process. This paper demonstrates that optimization of the feed to the press in a production line is very important for high operational efficiency and for maintaining a factory competitive and sustainable.     

Analysis of rotation in the lubrication of a porous slider bearing: Small rotation

A mathematical model is developed to investigate the behaviour of a plane-inclined porous slider bearing under the effect of a uniform small rotation. The Beavers-Joseph slip condition was used for the slip velocity at the porous boundary. The expressions for dimensionless pressure distribution, load-carrying capacity and coefficient of friction are obtained. It is concluded that the load-carrying capacity and coefficient of friction depend on the direction and magnitude of rotation. For a negative rotation the load-carrying capacity increases and the coefficient of friction decreases. The load-carrying capacity also decreases with increase in the slip velocity parameter.     

Simultaneous optimization of multiple performance characteristics of carbonitrided pellets: a case study

The performance of a product is generally characterized by more than one response variable. Hence, the management often faces the problem of simultaneous optimization of many response variables. In recent years, a lot of literature has been published on various methodologies for tackling the multi-response optimization problems. Among them, the approach based on Taguchi’s quality loss function is very popular. This paper discusses a case study on multiple response optimization in carbonitriding process. The surface hardness, case depth, and dimensional variation of carbonitrided pellets were simultaneously optimized using quality loss function methodology. The optimum obtained through loss function approach was found to be superior to the ones obtained through optimizing the response variables separately. The result obtained through the implementation of the solution is also presented in the study.     

Note: Production of sharp gold tips with high surface quality

We present a simple method to produce sharp gold tips with excellent surface quality based on electrochemical etching with potassium chloride. Radii of curvature lie in the range of 20-40 nm and the surface roughness is measured to less than 0.8?nm. The tips are well suited for field emission, field ion microscopy, and likely for tip-enhanced Raman scattering as well as tip-enhanced near-field imaging.     

封闭体内电机转速测量仪的研制

以小型往复式制冷压缩机为典型研究对象，通过对其封闭壳体的振动分析，指出了壳体振动的基频即为电机的转速。提出了一种基于微机技术的通过测量振动基频来间接测量封闭体内电机转速的方法以及装置构成。     

The dynamics of a complex machine assembly: Vibration-induced drag on the rotation

An engineering system of complex real machine assembly is considered that, in contrast to a conventional assembly, has additional degrees of freedom. These degrees of freedom are considered to be latent, i.e., those that modify the dynamics of the basic degree of freedom on average. According to this approach, the authors obtained an averaged equation that has the form of a classical equation of a simple real assembly, but contains an additional moment of load that considers resonance phenomena. The derivation of the equation is exemplified by a vehicle that moves along an uneven road.     

Deformation behaviour of soft-brittle polycrystalline materials determined by nanoscratching with a sharp indenter

Polycrystalline zinc selenide (p-ZnSe) is a typical soft brittle material with important optical applications. In this work, single and repeated nanoscratching tests were performed using a Berkovich indenter along the face-forward (FF) and edge-forward (EF) directions. The morphological features of the scratched grooves and the subsurface microstructural changes in the material were characterised by scanning electron microscopy, Raman spectroscopy, and electron backscatter diffraction (EBSD). Material removal in the ductile mode was obtained in the EF scratching direction; this was accompanied by the slip lines, and the radial cracks generated along grain boundaries. In contrast, brittle fractures occurred in the FF scratching direction, resulting in radial and lateral cracks which are responsible for generating the peeling of the material. The EBSD results demonstrated that the {111} planes are the primary slip plane and secondary cleavage plane, whereas the {110} planes are the primary cleavage plane and secondary slip planes. Tensile residual stress was detected in the subsurface region of the grooves scratched along the FF direction, whereas compressive residual stress was detected in the EF scratching direction. Fishbone-like patterns were observed in the scratched grooves under all conditions, while no phase transformation was detected. This study provides insights into the fundamental material removal mechanisms of soft brittle crystals in various abrasive machining processes, such as grinding, lapping, and polishing.     

Note: A time-resolved Kerr rotation system with a rotatable in-plane magnetic field

A time-resolved Kerr rotation system with a rotatable in-plane magnetic field has been constructed to study anisotropic spin relaxation of electrons in semiconductors. A permanent magnet magic ring is placed on top of a motor-driven rotation stage (RS) to create the rotatable in-plane magnetic field. The RS is placed on a second translation stage to vary the local magnetic field around a sample. The in-plane magnetic field in such a system varies from 0.05 to 0.95 T, with full-round 360° rotatablity, thus offering a convenient and low-cost way to study the anisotropy of spin dynamics in semiconductors. Its performance was demonstrated via measurement of the anisotropy of the spin dephasing time (SDT) of electrons in a two-dimensional electron system embedded in a GaAs/Al(0.35)Ga(0.65)As heterostructure. The SDT with B∥[110] was observed to be 10% larger than that with B∥[110], consistent with the results of others, which was measured via rotating sample.     

The effect of rotation in lubrication problems

A mathematical analysis of the effect of rotation in lubrication problems is presented. The generalized Reynolds equation is derived for the case of a small rotation number M. An exact solution is obtained for the short bearing problem. It is shown that the load capacity of the bearing is dependent on the bearing diameter (this is not so when rotation is absent) that it increases with increasing values of ¦M¦ when M is negative and that it decreases with increasing values of M when M is positive.     

Steady rotation of a sphere in a paramagnetic fluid

The steady rotation of a non-conducting sphere in an unbounded electrically non-conducting incompressible paramagnetic fluid was investigated. An external magnetic field acted parallel to the axis of rotation. The non-dimensional partial differential equations governing the magnetic field, magnetization and velocity were solved numerically. The magnetic field is comparatively weak in the radial direction and strong in the transverse direction over regions nearer the sphere. At points equidistant from the sphere the radial component of the magnetic field is maximum at an angle 14° from the axis. At points equidistant from the centre of the sphere the transverse component of the magnetic field is maximum at points near the equator and minimum at points near the axis. The magnetization increases with the applied magnetic field. At points near the equator and the axis the dipoles are oriented almost parallel to the applied magnetic field. In the remaining region they make an angle with the direction of the applied field which decreases with increasing applied magnetic field until at saturation magnetization they are oriented in the direction of the applied field. At points very near to the sphere the velocity is not affected by the magnetic field. Away from the sphere magnetization retards the flow.     

Reflections of ions in electrostatic analyzers: a case study with New Horizons/Solar Wind Around Pluto

Electrostatic analyzers (ESAs), in various forms, are used to measure plasma in a range of applications. In this article, we describe how ions reflect from the interior surfaces of an ESA, the detection of which constitutes a fundamentally nonideal response of ESAs. We demonstrate this effect by comparing laboratory data from a real ESA-based space instrument, the Solar Wind Around Pluto (SWAP) instrument, aboard the NASA New Horizons spacecraft, to results from a model based on quantum mechanical simulations of particles reflected from the instrument's surfaces combined with simulations of particle trajectories through the instrument's applied electrostatic fields. Thus, we show, for the first time, how reflected ions in ESAs lead to nonideal effects that have important implications for understanding the data returned by these instruments, as well as for designing new low-background ESA-based instruments. Specifically, we show that the response of SWAP widens considerably below a level of 10(-3) of the peak response. Thus, a direct measurement of a plasma distribution with SWAP will have an energy-dependent background on the order of ≤10(-3) of the peak of the signal due to that distribution. We predict that this order of magnitude estimate for the background applies to a large number of ESA-based instruments because ESAs operate using a common principle. However, the exact shape of the energy-dependent response will be different for different instruments. The principle of operation is that ions outside the ideal range of energy-per-charge are deflected into the walls of the ESA. Therefore, we propose that a new design paradigm is necessary to mitigate the effect of ion reflections and thus accurately and directly measure the energy spectrum of a plasma using ESAs. In this article, we build a framework for minimizing the effect of ion reflections in the design of new ESAs. Through the use of existing computer simulation software, a design team can use our method to quantify the amount of reflections in their instrument and iteratively change design parameters before fabrication, conserving resources. A possible direction for the new design paradigm is having nonsolid walls of the ESA, already used in some applications.     

支撑面转动时弹簧的刚度特性分析

目前,对弹簧特性的研究大都集中在上下支撑保持平行情况下,水平刚度和垂直刚度比值与弹簧高度和中径比值之间的关系等方面,而在弹簧上支撑可以转动的情况下,对弹簧的刚度特性研究比较少.将对弹簧上支撑在自由转动情况下,对弹簧水平刚度和垂直刚度比值与弹簧高径比之间的关系进行讨论,得到该条件下水平刚度和垂直刚度比值与弹簧高径比之间的确切关系,并通过实验对其进行验证.     

Numerical analysis of turbulent flow and heat transfer in a square sectioned U-bend duct by elliptic-blending second moment closure

A second moment turbulence closure using the elliptic-blending equation is introduced to analyze the turbulence and heat transfer in a square sectioned U-bend duct flow. The turbulent heat flux model based on the elliptic concept satisfies the near-wall balance between viscous diffusion, viscous dissipation and temperature-pressure gradient correlation, and also has the characteristics of approaching its respective conventional high Reynolds number model far away from the wall. Also, the traditional GGDH heat flux model is compared with the present elliptic concept-based heat flux model. The turbulent heat flux models are closely linked to the ellipticblending second moment closure which is used for the prediction of Reynolds stresses. The predicted results show their reasonable agreement with experimental data for a square sectioned U-bend duct flow field adopted in the present study.     

The berth scheduling problem with customer differentiation: a new methodological approach based on hierarchical optimization

The berth scheduling problem deals with the assignment of vessels to berth space in a container terminal. Defining berth schedules in container terminal operations translates in meeting different objectives that are often non-commensurable and gaining an improvement on one objective often causes degrading performance on the others. In this paper the discrete space and dynamic arrival berth scheduling problem is studied and formulated for the first time via a hierarchical optimization framework, using two levels of hierarchy that differentiate between two conflicting objectives terminal operators face when defining vessel to berth assignments. For the resolution of this problem an interactive algorithm is developed based on the k-th best algorithm for the case where multi-objective functions are considered in the upper level. Computational examples showed that the proposed algorithm gives optimal or near optimal solutions that are comparable to the ones obtained by its single level formulation counterpart.     

Preform design of hybrid-forming process to make sheet metal IT products with a sharp edge

Existing forging processes have limitations in forming products with sharp edges. Therefore, a new hybrid-forming process that combines drawing and forging processes was designed to form a sharp-edged product. First, a corner radius of a preform design was arranged to be smaller than the minimum bent area corner radius formed in general drawing processes. Then, the shape of the preform was planned to have the exact shape of the final product. Given that forming loads are a limiting condition in forging processes, they were set as an evaluation criterion to determine design requirements for final product shapes and the shapes of preforms. The reliability of finite element analysis results was verified by comparing analysis and experiment results, and a multistage preforming process was implemented to satisfy the determined evaluation criterion. This study demonstrates that IT products with sharp edges can be formed.     

Wear behaviour of dental enamel at the nanoscale with a sharp and blunt indenter tip

Two different diamond nanoindenter tips, a rounded conical (～1200 nm radius) and a sharp cube corner (20–50 nm radius) were used to abrade bovine enamel. Square abraded areas (2 μm × 2 μm, 5 μm × 5 μm, 10 μm × 10 μm) were generated with loads that varied from 50 μN to 500 μN depending on the indenter tip. In addition normal and lateral forces were simultaneously measured along 10 μm single scratched lines with the sharp cube corner tip. SEM (scanning electron microscopy) and TEM (transmission electron microscopy) were also used to characterise the worn areas and debris. Two different wear mechanisms were observed depending on the geometry of the tip. The rounded tip generates a predominantly elastic contact that mainly compresses and plastically deforms the superficial material and generates severe shear deformation within the sub-surface material which, under certain conditions, fractures and removes material from the sample. The sharp tip cuts into and ploughs the enamel creating a wedge or ridge of material ahead of itself which eventually detaches. This sequence is repeated continuously for every passage of the sharp indenter tip. The different mechanisms are discussed in terms of abrading tip contact angle and enamel microstructure.     

Application of PCA-based hybrid Taguchi method for correlated multicriteria optimization of submerged arc weld: a case study

Fluid dispensing is a method by which fluid materials, such as epoxy, adhesive, and encapsulant, are delivered in a controlled manner in electronics packaging. This paper presents a brief review of past and recent developments in the modeling and control of the time-pressure fluid dispensing process. In particular, the characterization of the fluid flow behavior is addressed by reviewing several promising models from both time-independent and time-dependent perspectives. In the modeling of the time-pressure fluid dispensing process, various approaches for representing the flow rate of fluid dispensed and the profile of fluid formed on target are examined; and the issues involved are identified. In the control of time-pressure dispensing process, a brief review of various control methods is presented along with their limitations. The challenges associated with this control problem are also discussed. This paper is concluded with the recommendations of research in the future.     

Mode-locking optimization with a real-time feedback system in a Nd:yttrium lithium fluoride laser cavity

We present a control system, which allows an automatic optimization of the pulse train stability in a mode-locked laser cavity. In order to obtain real-time corrections, we chose a closed loop approach. The control variable is the cavity length, mechanically adjusted by gear system acting on the rear cavity mirror, and the controlled variable is the envelope modulation of the mode-locked pulse train. Such automatic control system maintains the amplitude of the mode-locking pulse train stable within a few percent rms during the working time of the laser. Full implementation of the system on an Nd:yttrium lithium fluoride actively mode-locked laser is presented.     

Measurement of developing turbulent flows in a 90-degree square bend with spanwise rotation

Mean flow and turbulence properties of developing turbulent flows in a 90 degree square bend with span-wise rotation are measured by a hot-wire anemometer. A slanted wire is rotated into 6 orientations and the voltage outputs from them are combined to obtain the mean velocity and the Reynolds stress components. Combined effects of the centrifugal and Coriolis forces due to the curvature and the rotation of the bend on the mean motion and turbulence structures are investigated experimentally. Results show that the two body forces can either enhance or counteract each other depending on the flow direction in the bend.