检索结果-南通市图书馆

Non-linear Constitutive Model for the Oligocarbonate Polyurethane Material

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Polymer Science 2014年第12期32卷 1666-1677页

作者： marek Pawlikowski Warsaw University of Technology Institute of Mechanics and Printing

The polyurethane, which was the subject of the constitutive research presented in the paper, was based on oligocarbonate diols Desmophen C2100 produced by Bayer？. The constitutive modelling was performed with a view to applying the material as the inlay of intervertebral disc prostheses. The polyurethane was assumed to be non-linearly viscohyperelastic, isotropic and incompressible. The constitutive equation was derived from the postulated strain energy function. The elastic and rheological constants were identified on the basis of experimental tests, i.e. relaxation tests and monotonic uniaxial tests at two different strain rates, i.e. λ= 0.1 min-1 and λ= 1.0 min-1. The stiffness tensor was derived and introduced to Abaqus？finite element（FE） software in order to numerically validate the constitutive model. The results of the constants identification and numerical implementation show that the derived constitutive equation is fully adequate to model stress-strain behavior of the polyurethane material.

关键词： Constitutive model Viscoelastic material Stress relaxation Finite elements.

Statistical variation of characteristics of random packed beds of Raschig rings:The influence of the sample size

在线全文

学校读者我要写书评

暂无评论

Particuology 2021年第3期19卷 50-61页

作者： PawełNiegodajew Maciej marek Czestochowa University of Technology Department of Thermal Machineryal.Armii Krajowej 2142-200 CzestochowaPoland

Many studies on random packed beds have been dedicated to local porosity(void fraction)or orientation distribution of ***,despite the random nature of the considered packings,very little attention has been devoted to examination whether the number of particles used in experiments/simulations is sufficiently large to get reproducible *** reproducibility of the key packing parameters depends on the size of the population of particles(sample size)and ordering effects induced by the confining *** work investigates quantitatively the influence of the sample size on the statistical variation of the packed bed *** beds of Raschig rings were generated with a sequential algorithm and three column diameters were *** has been found that in the case of the orientation distribution the results depend strongly on the sample size,especially for slender columns,while the porosity profiles are well-reproducible characteristics even for relatively small packings of *** complementary results for full cylinders are also included.

关键词： Random packing Raschig rings Full cylinders Particle orientation Porosity Reproducibility

Shape Optimization of the Turbomachine Channel by a Gradient Method - Accuracy Improvement

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Thermal Science 2003年第3期12卷 239-244页

作者： marek Rabiega Institute of Turbomachinery Technical University of Lodz219/223 Wolczanska St93-005 LodzPoland

An algorithm of the gradient method of the channel shape optimization has been built on the basis of 3D equations of mass, momentum and energy conservation in the fluid flow. The gradient of the functional that is posed for minimization has been calculated by two methods, via sensitivities and - for comparison - by the finite difference approximation. The equations for sensitivities have been generated through a differentiate-then-discretize approach. The exemplary optimization of the blade shape of the centrifugal compressor wheel has been carried out for the inviscid gas flow governed by Euler equations with a non-uniform mass flow distribution as the inlet boundary condition. Mixing losses have been minimized downstream the outlet of the centrifugal wheel in this exemplary optimization. The results of the optimization problem accomplished by the two above-mentioned methods have been presented. In the case sparse grids have been used, the method with the gradient approximated by finite differences has been found to be more consistent. The discretization accuracy has turned out to be crucial for the consistency of the gradient method via sensitivities.

关键词： numerical fluid dynamics shape optimization turbomachine channels

Temporal inequalities for sequential multi-time actions in quantum information processing

在线全文

学校读者我要写书评

暂无评论

Frontiers of physics 2014年第5期9卷 629-633页

作者： marek Zukowski Institute for Theoretical Physics and Astrophysics Uniwersytet Gdanski PL-80-952 Gdadsk Poland Hefei National Laboratory of Physical Sciences at the Mieroscale University of Science and Technology of China Hefei 230026 China

A new kind of temporal inequalities are discussed, which apply to algorithmic processes, involving a finite memory processing unit. They are an alternative to the Leggett-Grag ones, as well as to the modified ones by Brukner et al. If one considers comparison of quantum anti classical processes involving systems of finite memory （of the same capacity in both cases）, the inequalities give a clear message why we can expect quantum speed-up. In a classical process one always has clearly defined values of possible measurements, or in terms of the information processing language, if we have a sequential computations of some function depending on data arriving at each step on an algorithm, the function always has a clearly defined value. In the quantum case only the final value, after the end of the algorithm, is defined. All intermediate values, in agreement with Bohr＇s complementarity, cannot be ascribed a definite value.

关键词： temporal inequalities quantum information

Representative elementary volume analysis of polydisperse granular packings using discrete element method

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Particuology 2016年第4期14卷 88-94页

作者： Joanna Wiacek marek Molenda Institute of Agrophysics Polish Academy of Sciences Doswiadczalna 4 20-290 l.ublin Poland

The representative elementary volume （REV） for three-dimensional polydisperse granular packings was determined using discrete element method simulations. Granular mixtures of various sizes and particle size distributions were poured into a cuboid chamber and subjected to uniaxial compression, Findings showed that the minimum REV for porosity was larger compared with the REV for parameters such as coordination number, effective elastic modulus, and pressure ratio. The minimum REV for porosity and other parameters was found to equal 15,10, and 5 times the average grain diameter, respectively. A study of the influence of sample size on energy dissipation in random packing of spheres has also confirmed that the REV size is about 15 times the average grain diameter. The heterogeneity of systems was found to have no effect on the REV for the parameters of interest for the narrow range of coefficient of uniformity analyzed in this paper. As the REV approach is commonly applied in both experimental and numerical studies, determining minimum REV size for polydisperse granular packings remains a crucial issue.

关键词： Representative elementary volume Polydisperse packing Discrete element method Sample size effect

Effect of particle polydispersity on micromechanical properties and energy dissipation in granular mixtures

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Particuology 2014年第5期12卷 91-99页

作者： Joanna Wiacek marek Molenda Institute of Agrophysics Polish Academy of SciencesDoswiadczalna 420-290 Lublin 27Poland

A series of numerical tests was conducted to study the micromechanical properties and energy dissipation in polydisperse assemblies of spherical particles subjected to uniaxial compression. In general, distributed particle size assemblies with standard deviations ranging from 0% to 80% of the particle mean diameter were examined. The microscale analyses included the trace of the fabric tensor, magnitude and orien- tation of the contact forces, trace of stress, number of contacts and degree of mobilization of friction in contacts between particles. In polydisperse samples, the average coordination numbers were lower than in monodisperse assemblies, and the mobilization of friction was higher than in monodisperse assemblies due to the non-uniform spatial rearrangement of spheres in the samples and the smaller displacements of the particles. The effect of particle size heterogeneity on both the energy density and energy dissipation in systems was also investigated.

关键词： Polydisperse packing Discrete element method Micromechanics Energy dissipation

Numerical assessment of the influence of former mining activities and plasticity of rock mass on deformations of terrain surface

在线全文

学校读者我要写书评

暂无评论

International Journal of Mining Science and Technology 2021年第2期31卷 209-214页

作者： PawełSikora marek Wesołowski Department of Mining Faculty of MiningSafety Engineering and Industrial AutomationSilesian University of Technology44-100 GliwicePoland

This paper presents the results of numerical simulations carried out to confirm the influence of former mining activities on deformation of the mining *** assessment of deformation changes was carried out with the use of FLAC3 D program based on the finite difference *** calculations were carried out for the example of actual mining operations in seams 703/1-2 and 707/2 of‘‘Marcel"Coal *** into account the influence of the model’s plastic features and the so-called activation of a higher occurring seam in conducted simulations enabled obtaining a very good description of the measured *** on the results one may state that numerical model can be used to assess the influence of former mining activities and the direction of conducted exploitation on deformations of the mining *** factors are not recognized by geometric-integral theories commonly used for predicting the influence of mining operations on the *** results presented in this paper confirm that the applied method of simulating the phenomenon of reactivation of post-mining goafs is correct.

关键词： Rock mass Numerical modeling Post-mining Goafs Land surface deformations

Random failure mechanism method for assessment of working platform bearing capacity with a linear trend in undrained shear strength

在线全文

学校读者我要写书评

暂无评论

Journal of Rock Mechanics and Geotechnical Engineering 2021年第6期13卷 1513-1530页

作者： Marcin Chwaa marek Kawa Department of Civil Engineering Wroclaw University of Science and TechnologyWybrzeze Wyspianskiego 27Wrocław50-370Poland

A bearing capacity evaluation for the surface strip foundation on a working platform modelled on a twolayered substrate is considered in the *** upper layer is assumed as man-made and wellcontrolled and thus *** lower layer modelling natural cohesive soil is subjected to spatial variability of undrained shear *** random failure mechanism method(RFMM)is used to evaluate the bearing *** approach employs a kinematic assessment of the critical load and incorporates the averaging of three-dimensional(3 D)random field along dissipation surfaces that result from the failure mechanism geometry.A novel version of the approach considering an additional linear trend of undrained shear strength in the spatially variable layer is *** high efficiency of the RFMM algorithm is *** influences of foundation length,trend slope in the spatially variable layer,fluctuation scales,and thickness of the homogenous sand layer on the resulting bearing capacity evaluations are ***,for selected cases,verification of the RFMM based assessment obtained using random finite difference method(RFDM)based on 3 D analysis is *** types of analyses are performed using RFDM based on associated and non-associated flow *** associated flow rule which corresponds to RFMM,the RFMM is conservative and efficient and thus it seems ***,if RFDM employs non-associated flow rule(much lower dilation angle for sand layer),the efficient RFMM is no longer *** this situation,a combined approach that improves the efficiency of the numerical method is suggested.

关键词： Two-layered soil Random bearing capacity Fluctuation scale Kinematical approach Upper bound Random finite difference method(RFDM) Working platform

Demise of the Jablonna Reef(Zechstein Limestone)and the onset of gypsum deposition(Wuchiapingian,west Poland):carbonate-to-evaporite transition in a saline giant

在线全文

学校读者我要写书评

暂无评论

Journal of Palaeogeography 2020年第3期9卷 363-377页

作者： Tadeusz marek Peryt marek Jasionowski Pawet Raczyiiski Krzysztof Chtdek Polish Geological Institute-National Research Institute Rakowiecka 400-975 WarszawaPoland lnstitute of Geological Sciences University of WrodawPI.Maksa Borna 950-205 WroclawPoland Polish Oil and Gas Company Naftowa 365-705 Zielona G6raPoland.

Microbial deposits commonly occur at the transition between carbonate and sulphate facies,and they also abound in the uppermost part of the middle Wuchiapingian Zechstein Limestone in west *** deposits occur as isolated reefs of the basinal zone and in the condensed sequences in most parts of the study *** deposits of the latter category reflect evaporative drawdown,and the abrupt boundary between the carbonate and sulphate deposits in the basin suggests the nature of evaporites that start to precipitate as soon as they reach the saturation level.A few-metre-thick unit of mostly brecciated microbial deposits at the top,reefal portion of the Zechstein Limestone records extreme palaeoenvironmental events that occurred at the transition from carbonate to sulphate *** events are related first to subaerial exposure of the reef,which lasted several 10~5 years and then to the Lower Anhydrite transgression.

关键词： Carbonate-sulphate transition Late Permian Reefs Microbial deposits Salt giants Central Europe