2,302 research outputs found
Convergence study and optimal weight functions of an explicit particle method for the incompressible Navier--Stokes equations
To increase the reliability of simulations by particle methods for
incompressible viscous flow problems, convergence studies and improvements of
accuracy are considered for a fully explicit particle method for incompressible
Navier--Stokes equations. The explicit particle method is based on a penalty
problem, which converges theoretically to the incompressible Navier--Stokes
equations, and is discretized in space by generalized approximate operators
defined as a wider class of approximate operators than those of the smoothed
particle hydrodynamics (SPH) and moving particle semi-implicit (MPS) methods.
By considering an analytical derivation of the explicit particle method and
truncation error estimates of the generalized approximate operators, sufficient
conditions of convergence are conjectured.Under these conditions, the
convergence of the explicit particle method is confirmed by numerically
comparing errors between exact and approximate solutions. Moreover, by focusing
on the truncation errors of the generalized approximate operators, an optimal
weight function is derived by reducing the truncation errors over general
particle distributions. The effectiveness of the generalized approximate
operators with the optimal weight functions is confirmed using numerical
results of truncation errors and driven cavity flow. As an application for flow
problems with free surface effects, the explicit particle method is applied to
a dam break flow.Comment: 27 pages, 13 figure
Interspecific differences in the larval performance of Pieris butterflies (Lepidoptera: Pieridae) are associated with differences in the glucosinolate profiles of host plants
The tremendous diversity of plants and herbivores has arisen from a coevolutionary relationship characterized by plant defense and herbivore counter adaptation. Pierid butterfly species feed on Brassicales plants that produce glucosinolates as a chemical deterrent against herbivory. In turn, the larvae of pierids have nitrile specifier proteins (NSPs) that are expressed in their gut and disarm glucosinolates. Pierid butterflies are known to have diversified in response to glucosinolate diversification in Brassicales. Therefore, each pierid species is expected to have a spectrum of host plants characterized by specific glucosinolate profiles. In this study, we tested whether the larval performance of different Pieris species, a genus in Pieridae (Lepidoptera: Pieridae), was associated with plant defense traits of putative host plants. We conducted feeding assays using larvae of three Pieris species and 10 species of the Brassicaceae family possessing different leaf physical traits and glucosinolate profile measurements. The larvae of Pieris rapae responded differently in the feeding assays compared with the other two Pieris species. This difference was associated with differences in glucosinolate profiles but not with variations in physical traits of the host plants. This result suggests that individual Pieris species are adapted to a subset of glucosinolate profiles within the Brassicaceae. Our results support the idea that the host ranges of Pieris species depend on larval responses to glucosinolate diversification in the host species, supporting the hypothesis of coevolution between butterflies and host plants mediated by the chemical arms race
Large-scale simulations of viscoelastic deformable multi-body systems using quadruple discrete element method on supercomputers
Contact problems among viscoelastic materials in the multibody system is one of
the challenging topics in science and many engineering applications. We have developed an effective
simulation method of combining QDEM (Quadruple Discrete Element Method) for the deformation
analysis of structures with the DEM for the collisions among structures. However, it is
still difficult to reproduce surface topography of structures because particles only set on four
nodes of tetrahedrons in our current method. In this paper, QDEMSM (QDEM with Surface
Modeling) is newly developed. Point-polygon collisions and line-line collisions are effectively
coupled with QDEM. Our improved method was validated by several simulation results; domino
simulations using the 40 pieces of shogi (= Japanese chess) were successfully carried out. It
was also found the friction forces acted on the surface critically effected on the
propagation speeds of contact forces. In parallel computing, by applying the space-filling
curve to decomposition of the computational domain, we make it possible to contain the same
number of nodes in each decomposed domain. Our parallel
simulation code achieves a good weak scalability on the TSUBAME2.5 supercomputer
Simulation Optimization Using Swarm Intelligence as Tool for Cooperation Strategy Design in 3D Predator-Prey Game
Rotational placement of irregular polygons over containers with fixed dimensions using simulated annealing and no-fit polygons
This work deals with the problem of minimizing the waste of space that occurs on a rotational placement of a set of irregular bi-dimensional small items inside a bi-dimensional large object. This problem is approached with an heuristic based on simulated annealing. Traditional " external penalization" techniques are avoided through the application of the no-fit polygon, that determinates the collision-free region for each small item before its placement. The simulated annealing controls: the rotation applied and the placement of the small item. For each non-placed small item, a limited depth binary search is performed to find a scale factor that when applied to the small item, would allow it to be fitted in the large object. Three possibilities to define the sequence on which the small items are placed are studied: larger-first, random permutation and weight sorted. The proposed algorithm is suited for non-convex small items and large objects
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