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Flow Algorithm (flow + algorithm)

Distribution by Scientific Domains

Mathematics and Statistics	50%

Selected Abstracts

Simulating three-dimensional aeronautical flows on mixed block-structured/semi-structured/unstructured meshes

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 3 2002
J. A. Shaw
Abstract The design requirements of a computational fluid dynamics (CFD) method for modelling high Reynolds number flows over complete aircraft are reviewed. It is found that the specifications are unlikely to be met by an approach based on the sole use of either structured or unstructured grids. Instead, it is proposed that a hybrid combination of these grids is appropriate. Techniques for developing such meshes are given and the process of establishing the data structure defining the meshes described. Details of a flow algorithm which operates on a hybrid mesh are presented. A description is given of the suitability and generation of hybrid grids for a number of examples, and results from flow simulations shown. Finally, issues still to be addressed in the practical use of these meshes are discussed. Copyright © 2002 John Wiley & Sons, Ltd. [source]

A general strategic capacity planning model under demand uncertainty

NAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 2 2006
Woonghee Tim Huh
Abstract Capacity planning decisions affect a significant portion of future revenue. In equipment intensive industries, these decisions usually need to be made in the presence of both highly volatile demand and long capacity installation lead times. For a multiple product case, we present a continuous-time capacity planning model that addresses problems of realistic size and complexity found in current practice. Each product requires specific operations that can be performed by one or more tool groups. We consider a number of capacity allocation policies. We allow tool retirements in addition to purchases because the stochastic demand forecast for each product can be decreasing. We present a cluster-based heuristic algorithm that can incorporate both variance reduction techniques from the simulation literature and the principles of a generalized maximum flow algorithm from the network optimization literature. © 2005 Wiley Periodicals, Inc. Naval Research Logistics, 2006 [source]

A network flow algorithm to minimize beam-on time for unconstrained multileaf collimator problems in cancer radiation therapy

NETWORKS: AN INTERNATIONAL JOURNAL, Issue 1 2005
Ravindra K. Ahuja
Abstract In this article, we study the modulation of intensity matrices arising in cancer radiation therapy using multileaf collimators. This problem can be formulated by decomposing a given m × n integer matrix into a positive linear combination of (0, 1) matrices with the strict consecutive 1's property in rows. We consider a special case in which no technical constraints have to be taken into account. In this situation, the rows of the intensity matrix are independent of each other and the problem is equivalent to decomposing m intensity rows,independent of each other,into positive linear combinations of (0, 1) rows with the consecutive 1's property. We demonstrate that this problem can be transformed into a minimum cost flow problem in a directed network that has the following special structures: (1) the network is acyclic; (2) it is a complete graph (that is, there is an arc (i, j) whenever i < j); (3) each arc cost is 1; and (4) each arc is uncapacitated (that is, it has infinite capacity). We show that using this special structure, the minimum cost flow problem can be solved in O(n) time. Because we need to solve m such problems, the total running time of our algorithm is O(nm), which is an optimal algorithm to decompose a given m × n integer matrix into a positive linear combination of (0, 1) matrices. © 2004 Wiley Periodicals, Inc. NETWORKS, Vol. 45(1), 36,41 2005 [source]

Compensating for die swell in the design of profile dies

POLYMER ENGINEERING & SCIENCE, Issue 10 2003
W. A. Gifford
Because of the effects of die swell, the final shape of an extrudate is often substantially different from that of the exit opening of the die. As a result, the design of profile dies producing complex shapes often involves more than just "balancing" the die but also compensating for the effects of die swell. Typically, a successful design of such dies is achieved only through much "cut and try," However, with the use of a fully three-dimensional finite element flow algorithm along with quick mesh generating capabilities, the usual cut and try involved in the design of many profile dies can be greatly reduced, if not eliminated. This paper demonstrates how the effects of die swell can be compensated for in the design of profile dies. For profiles with one plane of symmetry, this includes compensating for the sideways translation of the extrudate as well as the change in shape that the extrudate experiences. Completely asymmetric profiles undergo a "twisting" downstream of the die. This twisting, which appears not to have been reported in the literature (at least for isothermal extrusion), is also accounted for here, along with the change in shape that the extrudate undergoes. The translation or twisting of profiles downstream of a die is often attributed to non-Newtonian or non-isothermal effects. Only isothermal Newtonian examples are considered here. These results clearly show that asymmetry of the profile will result in a translation and twisting of the extrudate even in the isothermal Newtonian case. [source]