11,379 research outputs found
Particles with selective wetting affect spinodal decomposition microstructures
We have used mesoscale simulations to study the effect of immobile particles
on microstructure formation during spinodal decomposition in ternary mixtures
such as polymer blends. Specifically, we have explored a regime of
interparticle spacings (which are a few times the characteristic spinodal
length scale) in which we might expect interesting new effects arising from
interactions among wetting, spinodal decomposition and coarsening. In this
paper, we report three new effects for systems in which the particle phase has
a strong preference for being wetted by one of the components (say, A). In the
presence of particles, microstructures are not bicontinuous in a symmetric
mixture. An asymmetric mixture, on the other hand, first forms a
non-bicontinuous microstructure which then evolves into a bicontinuous one at
intermediate times. Moreover, while wetting of the particle phase by the
preferred component (A) creates alternating A-rich and B-rich layers around the
particles, curvature-driven coarsening leads to shrinking and disappearance of
the first A-rich layer, leaving a layer of the non-preferred component in
contact with the particle. At late simulation times, domains of the matrix
components coarsen following the Lifshitz-Slyozov-Wagner law, .Comment: Accepted for publication in PCCP on 24th May 201
Sharp interface limit of an energy modelling nanoparticle-polymer blends
We identify the -limit of a nanoparticle-polymer model as the number
of particles goes to infinity and as the size of the particles and the phase
transition thickness of the polymer phases approach zero. The limiting energy
consists of two terms: the perimeter of the interface separating the phases and
a penalization term related to the density distribution of the infinitely many
small nanoparticles. We prove that local minimizers of the limiting energy
admit regular phase boundaries and derive necessary conditions of local
minimality via the first variation. Finally we discuss possible critical and
minimizing patterns in two dimensions and how these patterns vary from global
minimizers of the purely local isoperimetric problem.Comment: Minor changes. Rephrased introduction. This version is to appear in
Interfaces and Free Boundarie
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Reverse Engineering Trimmed NURB Surfaces From Laser Scanned Data
A common reverse engineering problem is to convert several hundred thousand points
collected from the surface of an object via a digitizing process, into a coherent geometric
model that is easily transferred to a CAD software such as a solid modeler for either design
improvement or manufacturing and analysis. These data are very dense and make data-set
manipulation difficult and tedious. Many commercial solutions exist but involve time
consuming interaction to go from points to surface meshes such as BSplines or NURBS (Non
Uniform Rational BSplines). Our approach differs from current industry practice in that we
produce a mesh with little or no interaction from the user. The user can produce degree 2 and
higher BSpline surfaces and can choose the degree and number ofsegments as parameters to
the system. The BSpline surface is both compact and curvature continuous. The former
property reduces the large storage overhead, and the later implies a smooth can be created
from noisy data. In addition, the nature ofthe BSpline allows one to easily and smoothly alter
the surface, making re-engineering extremely feasible. The BSpline surface is created using
the principle ofhigher orders least squares with smoothing functions at the edges. Both linear
and cylindrical data sets are handled using an automated parameterization method. Also,
because ofthe BSpline's continuous nature, a multiresolutional-triangulated mesh can quickly
be produced. This last fact means that an STL file is simple to generate. STL files can also be
easily used as input to the system.Mechanical Engineerin
Reverse Engineering Trimmed NURB Surfaces From Laser Scanned Data
A common reverse engineering problem is to convert several hundred thousand points
collected from the surface of an object via a digitizing process, into a coherent geometric
model that is easily transferred to a CAD software such as a solid modeler for either design
improvement or manufacturing and analysis. These data are very dense and make data-set
manipulation difficult and tedious. Many commercial solutions exist but involve time
consuming interaction to go from points to surface meshes such as BSplines or NURBS (Non
Uniform Rational BSplines). Our approach differs from current industry practice in that we
produce a mesh with little or no interaction from the user. The user can produce degree 2 and
higher BSpline surfaces and can choose the degree and number ofsegments as parameters to
the system. The BSpline surface is both compact and curvature continuous. The former
property reduces the large storage overhead, and the later implies a smooth can be created
from noisy data. In addition, the nature ofthe BSpline allows one to easily and smoothly alter
the surface, making re-engineering extremely feasible. The BSpline surface is created using
the principle ofhigher orders least squares with smoothing functions at the edges. Both linear
and cylindrical data sets are handled using an automated parameterization method. Also,
because ofthe BSpline's continuous nature, a multiresolutional-triangulated mesh can quickly
be produced. This last fact means that an STL file is simple to generate. STL files can also be
easily used as input to the system.Mechanical Engineerin
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Smooth parametric surfaces and n-sided patches
The theory of 'geometric continuity' within the subject of CAGD is reviewed. In particular, we are concerned with how parametric surface patches for CAGD can be pieced together to form a smooth Ck surface. The theory is applied to the problem of filling an n-sided hole occurring within a smooth rectangular patch complex. A number of solutions to this problem are surveyed
Geometry Modeling for Unstructured Mesh Adaptation
The quantification and control of discretization error is critical to obtaining reliable simulation results. Adaptive mesh techniques have the potential to automate discretization error control, but have made limited impact on production analysis workflow. Recent progress has matured a number of independent implementations of flow solvers, error estimation methods, and anisotropic mesh adaptation mechanics. However, the poor integration of initial mesh generation and adaptive mesh mechanics to typical sources of geometry has hindered adoption of adaptive mesh techniques, where these geometries are often created in Mechanical Computer- Aided Design (MCAD) systems. The difficulty of this coupling is compounded by two factors: the inherent complexity of the model (e.g., large range of scales, bodies in proximity, details not required for analysis) and unintended geometry construction artifacts (e.g., translation, uneven parameterization, degeneracy, self-intersection, sliver faces, gaps, large tolerances be- tween topological elements, local high curvature to enforce continuity). Manual preparation of geometry is commonly employed to enable fixed-grid and adaptive-grid workflows by reducing the severity and negative impacts of these construction artifacts, but manual process interaction inhibits workflow automation. Techniques to permit the use of complex geometry models and reduce the impact of geometry construction artifacts on unstructured grid workflows are models from the AIAA Sonic Boom and High Lift Prediction are shown to demonstrate the utility of the current approach
Optimized normal and distance matching for heterogeneous object modeling
This paper presents a new optimization methodology of material blending for heterogeneous object modeling by matching the material governing features for designing a heterogeneous object. The proposed method establishes point-to-point correspondence represented by a set of connecting lines between two material directrices. To blend the material features between the directrices, a heuristic optimization method developed with the objective is to maximize the sum of the inner products of the unit normals at the end points of the connecting lines and minimize the sum of the lengths of connecting lines. The geometric features with material information are matched to generate non-self-intersecting and non-twisted connecting surfaces. By subdividing the connecting lines into equal number of segments, a series of intermediate piecewise curves are generated to represent the material metamorphosis between the governing material features. Alternatively, a dynamic programming approach developed in our earlier work is presented for comparison purposes. Result and computational efficiency of the proposed heuristic method is also compared with earlier techniques in the literature. Computer interface implementation and illustrative examples are also presented in this paper
Bicontinuous minimal surface nanostructures for polymer blend solar cells
This paper presents the first examination of the potential for bicontinuous structures such as the gyroid structure to produce high efficiency solar cells based on conjugated polymers. The solar cell characteristics are predicted by a simulation model that shows how the morphology influences device performance through integration of all the processes occurring in organic photocells in a specified morphology. In bicontinuous phases, the surface de. ning the interface between the electron and hole transporting phases divides the volume into two disjoint subvolumes. Exciton loss is reduced because the interface at which charge separation occurs permeates the device so excitons have only a short distance to reach the interface. As each of the component phases is connected, charges will be able to reach the electrodes more easily. In simulations of the current-voltage characteristics of organic cells with gyroid, disordered blend and vertical rod (rods normal to the electrodes) morphologies, we find that gyroids have a lower than anticipated performance advantage over disordered blends, and that vertical rods are superior. These results are explored thoroughly, with geminate recombination, i.e. recombination of charges originating from the same exciton, identified as the primary source of loss. Thus, if an appropriate materials choice could reduce geminate recombination, gyroids show great promise for future research and applications
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