The analytical efficiency expression of a compound epicyclic gear train with split power is derived via the approach based on virtual power. New concepts, the split-power ratio and the virtual split-power ratio, are introduced to handle the compound gear train. The efficiency formula is verified by a particular condition. The phenomenon of self-lock is disclosed in this compound gear train. It is observed that the power loss on one planet is dominant. This dominant power loss is caused by the immense virtual power passing through one gear mesh. Based on the analytical results, suggestions on design are given to avoid self-lock and increase the total efficiency.
DOI : 10.1016/j.mechmachtheory.2012.09.004 Anahtar Kelimeler :
Epicyclic gear train, Power flow, Efficiency, Split power
Cilt: 59 Sayı: 0 Sayfa: 96-106 ISSN: 0094-114X
The mobility or degrees of freedom is a fundamental issue in mechanisms and robotics. In this work, we distinguish the global mobility and local mobilities with different orders, and derive the corresponding conditions systematically. The relations between the global mobility and the local mobilities are disclosed. We show that the rank-deficiency of Jacobian matrix is equivalent to the first-order local mobility, and the global mobility is equivalent to the infinite-order local mobility. The second-order local mobility can be considered as a point freely moving a submanifold, which shares the same curvature with all hypersurfaces defined by constraints. We further discover a novel four-bar linkage with the second-order local mobility, which validates the theoretical mobility analysis.
DOI : 10.1016/j.mechmachtheory.2011.04.007 Anahtar Kelimeler :
Mechanism, Local mobility, Global mobility
Cilt: 46 Sayı: 9 Sayfa: 1251-1264 ISSN: 0094-114X
Special finite elements are developed for efficient evaluation of stress concentration around a hole in complex structures. The complex variable formulation is used to derive a special set of stress functions which embody the stress concentration effects of a hole. The stress functions in combination with an independent displacement field assumed along the element boundary are used to construct the special elements with the hybrid displacement finite element method. Several numerical examples are presented to show that the used of special finite elements to model critical regions around a hole, together with conventional finite elements to model other regions away from the hole, is not only very convenient but also highly accurate.
In the microdialysis zero-net-flux (ZNF) method the extraction efficiency is conventionally obtained by linear regression. The linear analysis may become invalid for certain analytes that have nonlinear uptake/release processes in the tissue. To examine this hypothesis, a nonlinear model was used to numerically investigate the nonlinearity of the ZNF plot caused by nonlinear uptake and release processes. Three findings from this analysis are: (i) the ZNF method is markedly insensitive to the nonlinear active processes; (ii) a slow infusion rate or a long probe membrane can suppress the nonlinearity; (iii) the release under autoreceptor control does not affect the slope and linearity of the concentration difference plot. It is concluded that in the nM infusion range, the ZNF method is unable to distinguish whether or not the tissue clearance process is nonlinear. During electrical stimulation, neurotransmitter overflow may cause the microdialysis ZNF method to exhibit nonlinearity.
We present a model that simulates the conventional tube-furnace experiment used for ignition studies. The Distributed Activation Energy Model of Ignition accounts for particle-to-particle variations in reactivity by having a single preexponential factor and a Gaussian distribution of activation energies among the particles. The results show that the model captures the key experimental observations, namely, the linear increase in ignition frequency with increasing gas temperature and the variation of the slope of the ignition frequency with oxygen concentration. The article also shows that adjustments to the model parameters permit a good fit with experimental data.
In this paper, a design methodology for synthesizing efficient parallel algorithms and VLSI architectures is presented. A design process starts with a problem definition specified in the parallel programming language Crystal and is followed by a series of program transformations in Crystal, each aiming at optimizing the target design for a specific purpose. To illustrate the design methodology, a set of design methods for deriving systolic algorithms and architectures is given and the use of these methods in the design of a dynamic programming solver is described. The design methodology, together with this particular set of design methods, can be viewed as a general theory of systolic designs (or multidimensional pipelines). The fact that Crystal is a general purpose language for parallel programming allows new design methods and synthesis techniques, properties and theorems about problems in specific application domains, and new insights into any given problem to be integrated readily within the existing design framework.
Convective boiling beyond critical-heat-flux (CHF) is encountered in a number of applications including steam generators, nuclear reactors, cryogenic systems, and metallurgical processing. At high void fractions (moderate to high vapor qualities) post-CHF heat transfer occurs with dispersed flow where the liquid phase is distributed as droplets entrained in the continuous vapor phase. It appears today that there is strong theoretical and experimental cause to believe that thermodynamic nonequilibrium is highly likely in dispersed flow, convective post-CHF boiling heat transfer. The experimental data base on the degree of nonequilibrium is very sparse and needs to be greatly expanded as the technical community seek to quantify this important phenomenon.
In seeking understanding of fast fluidization, researchers have encountered a number of important and intriguing phenomenological issues. The answers to these issues influence the nature of our predictive models and strongly effect our ability to engineer fast fluidized beds. The research community has responded with a number of inventive experimental techniques, which are tailored to address specific phenomena. four of these issues, and the corresponding experimental investigations, are reviewed and summarized in this paper.
The problem of radiant cooling of a fluid in laminar flow through a tube was described by a nonlinear integral equation, and an approximate solution obtained in terms of the Liouville-Neumann series. Results were also obtained by an exact iterative numerical solution. Local Nusselt numbers are presented as a function of dimensionless distance, x = Z/RePrR, and a dimensionless parameter, α = ϵσT30/k. An empirical equation, Nu(α, x) = (0·928 − 0·023 Inα)Nuq(x) where Nuq = Nusselt number for the constant heat flux case, was found to give results accurate to within ± 2 per cent for the ranges of variables of interest.