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991.
Compared to other fields of engineering, in mechanical engineering, the Discrete Element Method (DEM) is not yet a well known
method. Nevertheless, there is a variety of simulation problems where the method has obvious advantages due to its meshless
nature. For problems where several free bodies can collide and break after having been largely deformed, the DEM is the method
of choice. Neighborhood search and collision detection between bodies as well as the separation of large solids into smaller
particles are naturally incorporated in the method. The main DEM algorithm consists of a relatively simple loop that basically
contains the three substeps contact detection, force computation and integration. However, there exists a large variety of
different algorithms to choose the substeps to compose the optimal method for a given problem. In this contribution, we describe
the dynamics of particle systems together with appropriate numerical integration schemes and give an overview over different
types of particle interactions that can be composed to adapt the method to fit to a given simulation problem. Surface triangulations
are used to model complicated, non-convex bodies in contact with particle systems. The capabilities of the method are finally
demonstrated by means of application examples.
Commemorative Contribution. 相似文献
992.
Modeling mechatronic multibody systems requires the same type of methodology as for designing and prototyping mechatronic
devices: a unified and integrated engineering approach. Various formulations are currently proposed to deal with multiphysics
modeling, e.g., graph theories, equational approaches, co-simulation techniques. Recent works have pointed out their relative
advantages and drawbacks, depending on the application to deal with: model size, model complexity, degree of coupling, frequency
range, etc. This paper is the result of a close collaboration between three laboratories, and aims at showing that for “non-academic”
mechatronic applications (i.e., issuing from real industrial issues), multibody dynamics formulations can be generalized to
mechatronic systems, for the model generation as well as for the numerical analysis phases. Model portability being also an
important aspect of the work, they must be easily interfaced with control design and optimization programs. A global “demonstrator”,
based on an industrial case, is discussed: multiphysics modeling and mathematical optimization are carried out to illustrate
the consistency and the efficiency of the proposed approaches. 相似文献
993.
994.
Hitsman Brian; Borrelli Belinda; McChargue Dennis E.; Spring Bonnie; Niaura Raymond 《Canadian Metallurgical Quarterly》2003,71(4):657
The authors conducted a meta-analysis of published studies to (a) evaluate the premise that a history of major depression is associated with failure to quit smoking and (b) identify factors that moderate the relationship between history of depression and cessation outcome. Fifteen studies met the selection requirements and were coded for various study methodology and treatment characteristics. DSTAT was used to calculate individual study effect sizes, determine the mean effect size across studies. and test for moderator effects. No differences in either short-term (≤ 3 months) or long-term abstinence rates (≥ 6 months) were observed between smokers positive versus negative for history of depression. Lifetime history of major depression does not appear to be an independent risk factor for cessation failure in smoking cessation treatment. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
995.
996.
997.
E. M. Gavrishchuk E. Yu. Vilkova O. V. Timofeev U. P. Borovskikh E. L. Tikhonova 《Inorganic Materials》2007,43(6):579-583
Chemical interaction between polished surfaces of polycrystalline zinc selenide and inorganic acid solutions of various concentrations has been studied. 相似文献
998.
V. V. Ustinov A. B. Rinkevich L. N. Romashev E. A. Kuznetsov 《Technical Physics Letters》2007,33(9):771-774
The reflection of electromagnetic waves in the millimeter wave band from Fe/Cr nanostructures has been studied. It is established that the giant magnetoresistance (GMR) in the nanostructure leads to an increase in the reflection and a decrease in the transmission of microwaves, while the magnetic resonance leads to a decrease in both the reflection and transmission coefficients. 相似文献
999.
I. V. Oryshich N. E. Poryadchenko N. P. Brodnikovskii 《Powder Metallurgy and Metal Ceramics》2004,43(9-10):497-503
We have studied the oxidation resistance of chromium intermetallics: TiCr2, HfCr2, and ZrCr2, in the temperature interval 873–1473 K with isothermal holding of the specimens for up to 20 h. We have shown that the intermetallics TiCr2 and HfCr2 are oxidized 2–3 times more slowly than pure titanium and hafnium, but more than 1–2 orders of magnitude faster than chromium at T≤1273 K and 4–6 times faster at 1473 K. In this temperature interval, the intermetallic ZrCr2 is rapidly oxidized at an increasing rate as the heating temperature rises. The scaling resistance of intermetallics of Group IV d metals with chromium is determined by formation of scales in which the major role is played by the oxides TiO2, HfO2, and ZrO2, with weak protective properties. 相似文献
1000.
A construction of a globally asymptotically stable time-invariant system which can be destabilized by some integrable perturbation is given. Besides its intrinsic interest, this serves to provide counterexamples to an open question regarding Lyapunov functions. 相似文献