Search

Copyright of Machine Tool & Hydraulics is the property of Guangzhou Mechanical Engineering Research Institute (GMERI) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

As an independent sand control unit or a common protective shell of a high-quality screen, the punching screen is the outermost sand retaining unit of the sand control pipe which is used in geothermal well or oil and gas well. However, most screens only consider the influence of the internal sand retaining medium parameters in the sand control performance design while ignoring the influence of the plugging of the punching screen on the overall sand retaining performance of the screen. To explore the clogging mechanism of the punching screen, this paper established the clogging mechanism calculation model of a single punching screen sand control unit by using the computational fluid mechanics-discrete element method (CFD-DEM) combined method. According to the combined motion of particles and fluids, the influence of the internal flow state on particle motion and accumulation was analyzed. The results showed that (1) the clogging process of the punching sand control unit is divided into three stages: initial clogging, aggravation of clogging and stability of clogging. In the initial stage of blockage, coarse particles form a loose bridge structure, and blockage often occurs preferentially at the streamline gathering place below chamfering inside the sand control unit. In the stage of blockage intensification, the particle mass develops into a relatively complete sand bridge, which develops from both ends of the opening to the center of the opening. In the stable plugging stage, the sand deposits show a "fan shape" and form a "Vshaped" gully inside the punching slot element. (2) Under a certain reservoir particle-size distribution, The slit length and opening height have a large influence on the permeability and blockage rate, while the slit width size has little influence on the permeability and blockage rate. The microscopic clogging mechanism and its law of the punching screen prevention unit are proposed in this study, which has some field guidance significance for the design of punching screen and sand prevention selection. [ABSTRACT FROM AUTHOR]

Photoelectric smoke detectors, commonly used in aircraft cargo compartments, have high false alarm rates, which may result in huge economic losses and threaten flight safety. Dust aerosols are conventionally considered the main reason for this. Distinguishing dust aerosols from fire smoke by considering the difference between their scattering characteristics using a relatively simple combination of optical elements is crucial for reducing the false alarm rate. According to the relevant provisions for fire smoke and dust specified in the aerospace standard (AS 8036A) of the Society of Automotive Engineers (SAE) and considering the common cargo types, we studied the scattering characteristics of three types of aerosols, including six non-flaming fire smokes, four flaming fire smokes, and two dust aerosols, through numerical calculation and experimental methods. The results showed that these aerosols have different light scattering characteristics for forward and backward scattering due to particle size, morphology, etc. Considering these differences, we distinguished fire smoke from dust aerosols and reduced the false alarm rate in photoelectric smoke detectors in aircraft cargo compartments using an optimised optical structure design with dual wavelengths of 405 and 850 nm and dual scattering angles of 45° and 135°. [ABSTRACT FROM AUTHOR]

Nickel-based superalloy (GH4169) has been widely used to manufacture critical parts in the aerospace field due to its excellent properties, such as high thermal strength, excellent thermal stability, and fatigue resistance. However, it is a difficult-to-machine material because of its inherent properties. Large cutting forces, high cutting temperatures, severe tool wear, and other problems are common in the cutting process. In this study, to improve the cutting performance of GH4169, micro - textured tools were used to cut GH4169 in spray cooling. The micro-texture morphology, size parameters, and cutting parameters of the tools were studied. Five micro-textured tools with different morphology were designed. The finite element simulation models of micro-textured tools turning GH4169 were established by DEFORM, and cutting simulation analysis of the five micro-textured tools was carried out. The shape of the micro-textured tool with the most minor cutting force was selected. Furthermore, based on the optimized shape, the micro-textured tools with different size parameters of the shape were designed and simulated. The range analysis and genetic optimization algorithm were used to analyze the simulation results, and the optimal micro-texture size parameters with the minimum cutting force were obtained. Then, based on the optimized size parameters, different cutting parameters of the micro-textured tool cutting GH4169 were designed and simulated, and the range algorithm was used to optimize the cutting parameters. Finally, the micro-textured tools for cutting experiments were manufactured and the simulations were verified. It provides a guiding basis for the high-efficiency machining of GH4169 and the design and application of microtextured tools. [ABSTRACT FROM AUTHOR]

We report on the results of numerical simulation based on the Mie theory of the super-resonance effect (the higher-order Fano resonance) for a mesoscale dielectric sphere located in air, since the vacuum environment is an idealization that is almost never encountered in nature. It is first shown using the example of a particle with a refractive index of 1.5 and size parameters of q ∼ 26 and q ∼ 38 that a change in the refractive index of the environment by 2 × 10−4 leads to drop in field intensity in the region of the shadow pole of a sphere by an order of magnitude and a shift in resonance size parameter q to the short-wavelength region. In this case, the relative intensities of the resonance peaks for both the magnetic and electric field in the vicinity of the sphere poles in the optical range can attain these values (106‒107) for a particle in vacuum with an appropriate correction of the resonance size parameter. [ABSTRACT FROM AUTHOR]

Copyright of Architectural Journal / Jian Zhu Xue Bao is the property of Architectural Journal Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Recent studies suggest that resonant absorption of sunlight by cloud droplets may constitute a significant and unaccounted-for solar energy sink in the atmosphere. We spectrally resolve, for the first time, all solar absorption, including sharp resonances, in typical liquid water clouds. Resolving all sharp resonances requires a resolution in size parameter χ=2π r/λ (r—droplet radius, λ—incident wavelength) of about 10-7. The canonical integration resolution Δχ≈10-1 produces absorption biases up to 70% over 10 nm spectral bands. Hence, neglecting Mie resonances may cause substantial biases in radiance-based retrievals from sensor channels where atmospheric absorption is particle dominated.The canonical resolution produces broadband solar mean and RMS absorption coefficient biases of about 0.02% and 4%, respectively. Self-cancellation of the pseudo-randomly distributed biases explains why the mean bias is much smaller than the RMS bias. Exceeding 1% RMS accuracy in solar absorption requiresΔχ

Organic Rankine Cycle (ORC) systems represent an efficient technology for power generation from low-to-medium temperature heat sources. Most of the efforts in the recent literature are addressed to the improvement of turbine design and efficiency by taking advantage of the low enthalpy drops while dealing with the large volume flow ratios across the expansion process and low speed of sound typical of high molecular weight fluids. These peculiar conditions make the choice and the design of an ORC turbine a challenging task, exacerbated by the only few experimental data available in the open literature. The aim of this paper is to obtain the optimum design and corresponding maximum efficiency of single stage radial inflow turbines for different cycle design specifications (i.e., mass flow rate and enthalpy drop) using the real gas properties of refrigerant R245fa. This aim is pursued by means of a mean-line model developed in Matlab ® which includes the design and performance analysis procedure suggested by Aungier (2005). Results indicate how different design choices in terms of specific speed and velocity ratio, and different working conditions in terms of expansion ratio and turbine size may affect the efficiency of single stage radial inflow turbines in ORC systems. [ABSTRACT FROM AUTHOR]

The variety of decision variables involved in the design of Organic Rankine Cycles (ORCs) and equipment still open opportunities to enhance efficiency and performance in the recovery of low grade and waste heat in spite of the high number of studies already available in the literature and the rapidly growing number of existing applications. Most of the literature focuses on cycle configuration, design parameters and working fluid that maximize different performance metrics, but often ignores the expander design features that are necessary to obtain them, by fixing in advance the expander efficiency. This approach is questionable for ORC systems where the high volumetric expansion ratios, variable sizes and working fluids may markedly affect expander efficiency. This study provides a design criterion of axial flow turbines which gives a reliable estimate of their efficiency for a wide range of operating duty specifications and working fluids. For fixed values of size parameter and volumetric expansion ratio the optimum values of duty parameters (flow and loading coefficients, degrees of reaction) and the associated turbine efficiency are obtained by a mean line design procedure including real gas properties and the recent loss correlations proposed by Aungier. For each working fluid, all the efficiency values obtained by this procedure for a wide set of size parameter and volumetric expansion ratio are included in a map, which updates a similar map obtained for high molecular weight ideal gases by Macchi and Perdichizzi in the eighties. A wide spectrum of working fluids and operating conditions is considered here to explore the effect of fluid characteristics on the shape of the efficiency maps. Results show that the influence of the working fluid on the efficiency maps may be not negligible, and can be taken into account by including the working fluid critical temperature in addition to the size parameter and volumetric expansion ratio. Accordingly, a generalized efficiency map is obtained which is valid for any fluid, and can be easily integrated into a comprehensive thermodynamic cycle analysis and optimization to account for the real turbine performance. [ABSTRACT FROM AUTHOR]

In this paper, vibrations of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) nanoplates are investigated. In doing so, the third order shear deformation theory is used and the size parameter is taken into consideration by using Mindlin’s strain gradient theory. Equations of FG-CNTRC nanoplates motion with partial differentials are derived from Hamilton’s principle. Mechanical properties of the FG-CNTRC nanoplates are determined using the rule of mixture. Here, the FG-CNTRC nanoplate is modeled as simply supported and the Navier solution is used to solve the vibration problem. The results of the new model are compared with those of the classical model, which leads to the conclusion that the classical model is a special case of the Mindlin’s strain gradient theory. More results show that the rigidity of the FG-CNTRC nanoplates in the Mindlin’s strain gradient theory is more than that in the classical theory, which leads to an increase in natural frequencies. Moreover, in the present study, the effect of the manner of distribution of Carbon nanotubes (CNTs) in the nanoplate and the effect of the volume fraction of the CNTs on the vibration of the FG-CNTRC nanoplates is investigated. [ABSTRACT FROM AUTHOR]

The size parameters of 6061 aluminum alloy rib-web forging were optimized by using hot-processing map and finite element method (FEM) based on high-temperature compression data. The results show that the stress level of the alloy can be represented by a Zener-Holloman parameter in a hyperbolic sine-type equation with the hot deformation activation energy of 343.7 kJ/mol. Dynamic recovery and dynamic recrystallization concurrently preceded during high-temperature deformation of the alloy. Optimal hot-processing parameters for the alloy corresponding to the peak value of 0.42 are 753 K and 0.001 s. The instability domain occurs at deformation temperature lower than 653 K. FEM is an available method to validate hot-processing map in actual manufacture by analyzing the effect of corner radius, rib width, and web thickness on workability of rib-web forging of the alloy. Size parameters of die forgings can be optimized conveniently by combining hot-processing map and FEM. [ABSTRACT FROM AUTHOR]

Morphological spatial pattern analysis (MSPA) employs concepts of mathematical morphology to segment input binary objects into a series of categories revealing information about size, shape and connectivity. It emphasises on connectivity between the objects' parts as measured via various values of size parameters. MSPA has been has become a popular tool for landscape modelling, but has yet to receive significant attention in other areas of applications. In this paper, MSPA is employed to segment mountains extracted from digital elevation models (DEMs) into seven mutually exclusive categories; core, islet, bridge, loop, edge, perforation and branch. The effect of various values of s on the classification of these categories is studied. It is observed that smaller values of s provide more differentiation among the categories, and hence, better information about the classification of the extracted mountains. However, as pattern measurements are scale-dependent, and since s is a part of the definition of scale of observation, it is advisable that various values of s are employed to determine the appropriate levels of classification for various applications. [ABSTRACT FROM AUTHOR]

The study deals with photophoresis of a spherical micro-particle suspended in absorbing gaseous media. Photophoretic motion of the particle stems from the asymmetric distribution of absorbed energy within the particle. By evaluating the so-called heat source function at various conditions, the study focuses on the effects of governing parameters on the energy distribution within the particle and their potential influences to the photophoresis. The results reveal that the increase in either particle size or absorptivity enhances the energy intensity on the illuminated (leading) side and tends to generate positive photophoresis. For a particle of low absorptivity, the energy distribution is dominated by particle refraction. Enhancing particle refractivity, the energy tends to be focused onto a certain spot area on the shaded (trailing) side and leads to a tendency of negative photophoresis. Increasing medium absorptivity significantly degrades the level of energy absorbed by the particle and in turn weakens the driving force of the particle photophoresis. [ABSTRACT FROM AUTHOR]

Abstract: Rayleigh optical depth is an integral part of many radiative transfer problems. This paper discusses different elements and approaches of its determination. Then, it presents a method, which ensures more realistic estimate of Rayleigh optical depth by using refractive index and depolarization factor (including rotational Raman lines) adjusted according to the state and composition of the atmosphere. It is based on the published experimental and theoretical results. The Rayleigh optical depth calculations are compared with the Elterman’s model calculations for trend analysis purpose. Rayleigh optical depths are found to be around 3.4% lower than previous researchers, as they ignored the constraints of conservation of angular momentum in the rotational/vibrational transitions of the molecules during scattering. [Copyright &y& Elsevier]

Abstract: The morphology of WO3 aggregates formed by irregular nanoparticles (D∼40nm) and nanowires of different aspect ratios (2, 4, 6, and 10μm nominal lengths) dispersed in commonly used polar solvents without dispersant agents is investigated using a small-angle light scattering technique and by means of fractal theory. Nanoparticles form compact spherical aggregates (D f∼2.6), whereas 2μm nanowires with low aspect ratio (L/D∼10) follow a slow cluster–cluster aggregation mechanism with no discernable change in fractal dimension (D f=2.1) monitored in an extended period of 6 months, despite a notable growth in size (R g =2.3–3.1μm). For higher aspect ratio nanowires, scattered intensity profiles, which migrate towards the Porod regime, qualitatively obey the Lorenz–Mie theory predictions. The 10μm nanowires with very high aspect ratio (L/D∼250) are observed to form stable dispersions in a time span of 6 days. Analytical methods based on spherical primary particle formulations predict D f=1.9, 1.7, and 1.4 for 4, 6, and 10μm nanowires, respectively. [Copyright &y& Elsevier]

Laser diffraction is now widely used for particle size distribution analysis of sediments and soils. The technique can be very precise, and offers advantages of speed and cost over many other methods when used to analyse mixtures of sand, silt and clay. This study presents the results of an experimental investigation that examined the sensitivity of the Beckman-Coulter LS230 instrument to mixtures of different grain populations and differences in particle shape. The instrument was found to have high sensitivity to coarse particles in a finer matrix (detection threshold 1–2%), but much lower sensitivity to finer particles in a coarser mixture (detection threshold 12–17%). Experiments using near-spherical ballotini showed that laser analysis provides very similar values to dry sieving for the mean, median and mode, but for a range of natural sand samples values for the mean, median and mode were offset by 8–21%, with an average of ca 15%, compared with sieving. Analysis using a Beckman-Coulter RapidVUE instrument, which provides both size and shape information, provided support for the hypothesis that the differences between laser analysis and sieving are partly attributable to the effects of particle shape. However, an additional factor is the way in which the laser software interprets the optical diffraction data. The software predicts a high degree of log-normality in the size distribution, such that highly skewed, truncated or bimodal samples are poorly represented. Experiments using sieved fractions of ballotini indicated that, even with near-perfectly spherical particles, the particle size distribution predicted by the laser software includes a relatively large percentage of particles outside the sieve class limits. [ABSTRACT FROM AUTHOR]

Abstract: We consider percolation thresholds which arise in the homogenization of composite mediums based on three different types of component particles. An extension of the standard Bruggeman homogenization formalism is implemented in order to take account of the sizes, shapes, and orientations of the component particles. The relationships between the geometric attributes of the component particles and the constitutive parameters of the homogenized composite mediums are investigated. In particular, percolation thresholds arising in the homogenization of conducting component particles oriented in two directions and nonconducting component particles are explored via representative numerical examples. Anisotropies in these percolation thresholds are highlighted. [Copyright &y& Elsevier]

Abstract: A comparison of the rain rate estimated with the assumptions of Rayleigh and Mie scattering is made. We analyzed the different relationships between the radar reflective factor and rain rate (so-called Z–R relationship) with both scattering models for different DSDs (droplet size distributions) and rainfall types as the wavelength is 2.2cm which is in accord with the band of TRMM/PR. Meanwhile we introduced a discrete ordinates method to retrieve the Z–R relationship for Mie scattering assumption. It is found that the retrieval result can be represented as the sum of some simple Z–R relationships. By the analysis of the Z–R relationships estimated from Rayleigh and Mie scattering assumptions in the rain types, we found that the difference of Z–R relationships between Rayleigh and Mie scattering in the thunderstorm that represents the larger raindrop size is larger than that in the drizzle that represent the smaller raindrop size. [Copyright &y& Elsevier]