Improved contact algorithm for the material point method and application to stress propagation in granular material

Journal ArticleContact between deformable bodies is a difficult problem in the analysis of engineering systems. A new approach to contact has been implemented using the Material Point Method for solid mechanics, Bardenhagen, Brackbill, and Sulsky (2000a). Here two improvements to the algorithm are described. The first is to include the normal traction in the contact logic to more appropriately determine the free separation criterion. The second is to provide numerical stability by scaling the contact impulse when computational grid information is suspect, a condition which can be expected to occur occasionally as material bodies move through the computational grid. The modifications described preserve important properties of the original algorithm, namely conservation of momentum, and the use of global quantities which obviate the need for neighbor searches and result in the computational cost scaling linearly with the number of contacting bodies. The algorithm is demonstrated on several examples. Deformable body solutions compare favorably with several problems which, for rigid bodies, have analytical solutions. A much more demanding simulation of stress propagation through idealized granular material, for which high fidelity data has been obtained, is examined in detail. Excellent qualitative agreement is found for a variety of contact conditions. Important material parameters needed for more quantitative comparisons are identified

Kohlenstoff Xerogele als Kathodenmaterial für die aprotische Lithium/Sauerstoff Batterie : Einfluss der Porenstruktur auf die physikalischen und elektrochemischen Eigenschaften

In this work the influence of the pore structure of the GDE on the discharge reaction od the aprotic Lithium-oxygen battery has been investigated. Therefore, carbon xerogels with different pore sizes were synthesized and analyzed by nitrogen adsorption. The samples with the highest and lowest mesopore size have been chosen to investigate the wetting behavior of solvents on the pore walls. Nuclear magnetic resonance (NMR) measurements were conducted to resolve the liquid phase inside of the porous structure. To use the carbon xerogels as active material in the GDE they were directly synthesized in a carbon fiber paper. The resulting ready-to-use and binder-free cathodes were discharged in the lithium/oxygen system and the deposition of discharge products was investigated. Electrochemical impedance measurements were conducted to observe the changes at the cathode during discharge revealing that the charge transfer between the carbon surface and the oxygen stays nearly constant. On the other hand it was also found that the pore clogging with discharge product and consequently the hindered oxygen diffusion are the limiting processes in this type of GDE

Rule knowledge aids performance on spatial and object alternation tasks by alcoholic patients with and without Korsakoff’s amnesia

Delayed alternation (DA) and object alternation (OA) tasks traditionally have been used to measure defective response inhibition associated with dysfunction of frontal brain systems. However, these tasks are also sensitive to nonfrontal lesions, and cognitive processes such as the induction of rule-learning strategies also are needed in order to perform well on these tasks. Performance on DA and OA tasks was explored in 10 patients with alcohol-induced persisting amnestic disorder (Korsakoff’s syndrome), 11 abstinent long-term alcoholics, and 13 healthy non-alcoholic controls under each of two rule provision conditions: Alternation Rule and Correction Rule. Results confirmed that rule knowledge is a crucial cognitive component for solving problems such as DA and OA, and therefore, that errors on these tasks are not due to defective response inhibition alone. Further, rule-induction strategies were helpful to Korsakoff patients, despite their poorer performance on the tasks. These results stress the role of multiple cognitive abilities in successful performance on rule induction tasks. Evidence that these cognitive abilities are served by diffusely distributed neural networks should be considered when interpreting behavioral impairments on these tasks

ADVANCED MORPHOLOGICAL APPROACH IN AEROSPACE DESIGN DURING CONCEPTUAL STAGE

This paper presents an advanced morphological approach supporting designers and developers in their search for as well as synthesis and analysis of new engineering solutions during the conceptual design stage. The proposed method is based on the cluster analysis and the set theory, the set of rules and engineering implementations maximizing the gain of the products potential. The number of possible combinations using the standard morphological technology is extremely large. We present a mathematical framework that handles this problem. The method was evaluated with case studies of new engineering solutions in aerospace, ecology and adaptive soundproofing system. The case studies verified the significant potential of the proposed approach in comparison with the methods presently in use

Derivation of higher order gradient continuum theories in 2,3-d non-linear elasticity from periodic lattice models

localization of deformation (in the form of shear bands) at sufficiently high levels of strain, are frequently modeled by gradient type non-local constitutive laws, i.e. continuum theories that include higher order deformation gradients. These models incorporate a length scale for the localized deformation zone and are either postulated or justified from micromechanical considerations. Of interest here is the consistent derivation of such models from a given microstructure and the subsequent investigation of their localization and stability behavior under finite strains.In the interest of simplicity, the microscopic model is a discrete, periodic, non-linear elastic lattice structure in two or three dimensions. The corresponding macroscopic model is a continuum constitutive law involving displacement gradients of all orders. Attention is focused on the simplest such model, namely the one whose energy density includes gradients of the displacements only up to the second order. The relation between the ellipticity of the resulting first (local) and second (non-local) order gradient models at finite strains, the stability of uniform strain solutions and the possibility of localized deformation zones is discussed. The investigations of the resulting continuum are done for two different microstructures, the second one of which approximates the behavior of perfect monatomic crystals in plane strain. Localized strain solutions based on the continuum approximation are possible with the first microstructurc but not with the second. Implications for the stability of three-dimensional crystals using realistic interaction potentials are also discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31886/1/0000838.pd

Valuing Place through Resources: Incorporating Multi-dimensional Values in Decision Processes

Including values for non-market natural and cultural resources in decision processes present challenges to resource managers. This dissertation uses a place-based resource-driven approach to assess the values associated with non-market resources in a national park. Existing valuation methods produce reliable measures for market resources, but are criticized for their inability to express values beyond uni-dimensional monetary values. Expressed values of park visitors for the natural and cultural resources within a national park are analyzed in order to quantitatively depict multiple dimensions of value for each resource relative to all others. Resulting abstract value-spaces are used to depict stakeholder group values and illustrate shared and unique values that can aid in decision processes. Value spaces are also used to examine the effects of resource losses on expressed values. These are observed through potential impact scenarios and can inform long-range planning and adaptation efforts. This research finds that a two-dimensional value space, representing aesthetic and functional qualities of resources can be formed to depict the values for included resources relative to one another. A core set of resources commonly valued by all major stakeholder groups is easily identifiable. Direct comparisons of value spaces for groups provides clear distinctions between group values for specific resources. Finally, subjecting value spaces to resource loss scenarios, indicates consistent changes in values while patterns of resource values remain stable, which can be used in participation and in conflict resolution efforts. These findings provide previously unobservable insight regarding the similarities and differences of group values and value stability as resource managers seek public input, resolve conflicts and craft long-range resource plans. This methodology establishes a basic framework for assessing relative resource values, non-monetarily, and along multiple dimensions. Value spaces can be used to proactively inform planning and decision processes from initial problem identification, establishment of alternative solutions and through assessments of implementation

Particle In Cell Simulation of Combustion Synthesis of TiC Nanoparticles

A coupled continuum-discrete numerical model is presented to study the synthesis of TiC nanosized aggregates during a self-propagating combustion synthesis (SHS) process. The overall model describes the transient of the basic mechanisms governing the SHS process in a two-dimensional micrometer size geometry system. At each time step, the continuum (micrometer scale) model computes the current temperature field according to the prescribed boundary conditions. The overall system domain is discretized with a desired number of uniform computational cells. Each cell contains a convenient number of computation particles which represent the actual particles mixture. The particle-in-cell (discrete) model maps the temperature field from the (continuum) cells to the respective internal particles. Depending on the temperature reached by the cell, the titanium particles may undergo a solid-liquid transformation. If the distance between the carbon particle and the liquid titanium particles is within a certain tolerance they will react and a TiC particle will be formed in the cell. Accordingly, the molecular dynamic method will update the location of all particles in the cell and the amount of transformation heat accounted by the cell will be entered into the source term of the (continuum) heat conduction equation. The new temperature distribution will progress depending on the cells which will time-by-time undergo the chemical reaction. As a demonstration of the effectiveness of the overall model some paradigmatic examples are shown.Comment: submitted to Computer Physics Communication

Multi-parameter generalization of nonextensive statistical mechanics

We show that the stochastic interpretation of Tsallis' thermostatistics given recently by Beck [Phys. Rev. Lett {\bf 87}, 180601 (2001)] leads naturally to a multi-parameter generalization. The resulting class of distributions is able to fit experimental results which cannot be reproduced within the Boltzmann's or Tsallis' formalism.Comment: ReVTex 4.0, 4 eps figure