Publications

Abstract not provided.

A methodology was developed for computing the probability that the sensor dart for the 'Near Real-Time Site Characterization for Assured HDBT Defeat' Grand-Challenge LDRD project will survive deployment over a forested region. The probability can be decomposed into three approximately independent probabilities that account for forest coverage, branch density and the physics of an impact between the dart and a tree branch. The probability that a dart survives an impact with a tree branch was determined from the deflection induced by the impact. If a dart that was deflected so that it impacted the ground at an angle of attack exceeding a user-specified, threshold value, the dart was assumed to not survive the impact with the branch; otherwise it was assumed to have survived. A computer code was developed for calculating dart angle of attack at impact with the ground and a Monte Carlo scheme was used to calculate the probability distribution of a sensor dart surviving an impact with a branch as a function of branch radius, length, and height from the ground. Both an early prototype design and the current dart design were used in these studies. As a general rule of thumb, it we observed that for reasonably generic trees and for a threshold angle of attack of 5{sup o} (which is conservative for dart survival), the probability of reaching the ground with an angle of attack less than the threshold is on the order of 30% for the prototype dart design and 60% for the current dart design, though these numbers should be treated with some caution.

Multifidelity modeling, in which one component of a system is modeled at a significantly different level of fidelity than another, has several potential advantages. For example, a higher-fidelity component model can be evaluated in the context of a lower-fidelity full system model that provides more realistic boundary conditions and yet can be executed quickly enough for rapid design changes or design optimization. Developing such multifidelity models presents challenges in several areas, including coupling models with differing spatial dimensionalities. In this report we describe a multifidelity algorithm for thermal radiation problems in which a three-dimensional, finite-element model of a system component is embedded in a system of zero-dimensional (lumped-parameter) components. We tested the algorithm on a prototype system with three problems: heating to a constant temperature, cooling to a constant temperature, and a simulated fire environment. The prototype system consisted of an aeroshell enclosing three components, one of which was represented by a three-dimensional finite-element model. We tested two versions of the algorithm; one used the surface-average temperature of the three dimensional component to couple it to the system model, and the other used the volume-average temperature. Using the surface-average temperature provided somewhat better temperature predictions than using the volume-average temperature. Our results illustrate the difficulty in specifying consistency for multifidelity models. In particular, we show that two models may be consistent for one application but not for another. While the temperatures predicted by the multifidelity model were not as accurate as those predicted by a full three-dimensional model, our results show that a multifidelity system model can potentially execute much faster than a full three-dimensional finite-element model for thermal radiation problems with sufficient accuracy for some applications, while still predicting internal temperatures for the higher fidelity component. These results indicate that optimization studies with mixed-fidelity models are feasible when they may not be feasible with three-dimensional system models, if the concomitant loss in accuracy is within acceptable bounds.

This report describes research and development of methods to couple vastly different subsystems and physical models and to encapsulate these methods in a Java{trademark}-based framework. The work described here focused on developing a capability to enable design engineers and safety analysts to perform multifidelity, multiphysics analyses more simply. In particular this report describes a multifidelity algorithm for thermal radiative heat transfer and illustrates its performance. Additionally, it describes a module-based computer software architecture that facilitates multifidelity, multiphysics simulations. The architecture is currently being used to develop an environment for modeling the effects of radiation on electronic circuits in support of the FY 2003 Hostile Environments Milestone for the Accelerated Strategic Computing Initiative.

The Entero Software Project emphasizes flexibility, integration and scalability in modeling complex engineering systems. The GUIGenerator project supports the Entero environment by providing a user-friendly graphical representation of systems, mutable at runtime. The first phase requires formal language specification describing the syntax and semantics of extensible Markup Language (XML) elements to he utilized, depicted through an XML schema. Given a system, front end user interaction with stored system data occurs through Java Graphical User Interfaces (GUIs), where often only subsets of system data require user input. The second phase demands interpreting well-formed XML documents into predefined graphical components, including the addition of fixed components not represented in systems such as buttons. The conversion process utilizes the critical features of JDOM, a Java based XML parser, and Core Java Reflection, an advanced Java feature that generates objects at runtime using XML input data. Finally, a searching mechanism provides the capability of referencing specific system components through a combination of established search engine techniques and regular expressions, useful for altering visual properties of output. The GUIGenerator will be used to create user interfaces for the Entero environment's code coupling in support of the ASCI Hostile Environments Level 2 milestones in 2003.