Seminars & Colloquia
UNC Chapel Hill
"Changing the problem: Robust geometric computations for neutron tracking"
Monday October 01, 2018 10:30 AM
Location: 3211, EB2 NCSU Centennial Campus
(Visitor parking instructions)
This talk is part of the Theory Seminar Series
In this talk we consider neutron tracking, in a form suggested by David Greisheimer of Bettis labs: Given a CAD model of nuclear reactor in a hierarchical Constructive Solid Geometry (CSG) representation, with unions and intersections of geometric primitives bounded by quadratic surfaces specified by floating point coefficients, track the materials pierced by a point moving in a straight line. A straightforward attempt to follow the point through surfaces can have surprising results – they have seen neutrons get stuck in a model (which makes a physicist rather nervous, since the code violates basic conservation laws.)
Analysis of the degrees of the geometric operations used reveals why, and suggests changing the problem to tracking line segments, where we apply geometric rounding to the segment endpoints. By doing so, we can continue to use fast floating-point arithmetic, but give guarantees on both geometric and topological properties (e.g., every neutron entering a bounded region must also exit). This is work with David Millman and Michael Deakin.
Host: Blair Sullivan, CSC