Professor

Department of Mechanical and Aerospace Engineering

University of Colorado at Colorado Springs

Contact Information:

physical address:

A438 Osborne Center for Science and Engineering (OCSE)

University of Colorado at Colorado Springs

Colorado Springs, CO 80918

mailing address:

University of Coloroado at Colorado Springs

Mechanical and Aerospace Engineering Dept.

1420 Austin Bluffs Parkway

Colorado Springs, CO 80918

E-mail: jstevens@uccs.edu

Current Research Topics(I invite inquiries from potential graduate students interested in these or other thermal science research areas.)

All common engineering approaches to the propagation of uncertainty are based on a first-order Taylor series (linear) expansion of the analysis equation. This presumes linear behavior for small perturbations in the measured variables. For larger perturbations (non-linear behavior), statistical approaches must be used which are often inconvenient or intractable for engineering applications. A direct approach to estimating non-linear uncertainty propagation is being developed which relies solely on evaluation of the analysis equation and the error function (erf) and requires fewer (by several orders of magnitude) analysis equation evaluations than Monte Carlo methods.

Liquid piston engines use the dynamics of an oscillating column of liquid to achieve the proper engine phasing to extract power from any convenient external heat source. They operate on a Stirling-like cycle, but without the need of sliding seals or close manufacturing tolerances. Advantages include very low capital construction costs, geometric flexibility, and the ability to use low cost heat sources including industrial waste heat and solar heat. The thermodynamic cycle of these machines, while robust, is poorly understood since it involves some similarities to a traditional Stirling cycle, yet incorporates phase change and other differences. Research is in progress to provide a better understanding of this thermodynamic cycle in order to improve the engineering design and application of this class of engines.