Control of Nonlinear Dynamic Systems
D. A. Tortorelli*
National Science Foundation, DDM 93-58132 NYI

Sensitivity analysis and optimization techniques are used to design control systems for nonlinear plants. These plants usually preclude classical/modern control strategies because of their complex nonlinear behavior. A rigorous dynamic model of the system under consideration is derived, and an open loop control law is determined minimizing the desired cost function through sensitivity analysis and optimization techniques. Unfortunately, open loop schemes never completely solve automatic control problems as they lack desirable features of feedback control such as disturbance rejection and lowered sensitivity to parameter variation. Hence, we seek to combine open- and closed-loop strategies in the overall control scheme.

Design of Fiber Brushes for Homopolar Machines
J. S. Walker,* M. N. Alexakis
Naval Surface Warfare Center, N65540-99-M-0121

In fiber brushes for homopolar motors and generators, electric current flows through thin copper fibers whose tips slide over the surface of a rotating copper drum. Large electromagnetic forces on the fibers can dramatically increase or decrease the contact force between the tip of each fiber and the rotating drum. This contact force must be greater than a minimum value to maintain electrical contact and must be less than a maximum value to minimize wear. Models with large-deflection beam theory are being developed to achieve an optimal design.

Evaluating Operator Visibility of Earth-moving Equipment
C. S. Larson,* R. Ingram,* B. Keenan
Caterpillar, Inc.

The objective of this study is to evaluate operator visibility of earth-moving equipment using Caterpillar's virtual prototyping system. This system uses real-time interactive graphics by means of the National Center for Supercomputing Applications CAVE?. Equipment part designs are converted from CAD files and placed directly into the virtual environment, giving an accurate representation of the vehicle, which is controlled using a dynamics simulation package. Then, within the environment, qualitative and quantitative studies on operator visibility can be performed. By using this system first, operator visibility can be evaluated much more quickly and inexpensively than by making a physical prototype.

Friction and Wear Measurements of Cast Iron Compressor Surfaces
A. A. Polycarpou*
Copeland Corporation

The main objective of this study is to experimentally investigate the friction and wear for scroll compressor cast iron surfaces with different lubricants in a controlled environment that accurately simulates application conditions. The contact geometry is that of pin on disk, i.e., extended contact geometry. A high-pressure tribometer will be used for the tests, which provides independent control of normal load, speed, temperature, pressure, and oil/refrigerant mixture supply rate at the interface.

Friction/Vibration Interaction for Contact Recording at the Head/Disk Interface
A. A. Polycarpou*
University of Illinois

Future trends in magnetic storage emphasize the need for reduced head/disk spacing, which is coupled directly to the achievement of higher recording densities in hard disk drive systems. It is projected that in the very near future the spacing has to be reduced to few nm, which makes contact unavoidable. Two major issues with such low normal load and super smooth contacting interfaces are reliability (low friction and wear) and small vibrations. In this research we will investigate experimentally and analytically the friction/vibration interaction of typical contacting head/disk interfaces. Surface roughness, elastic/plastic deformations, contact stiffness, and thermal effects will be included.

Optimal Path Planning for an Earth-moving Vehicle
C. S. Larson,* R. Ingram,* M. Vande Wiele
Caterpillar, Inc.

The objective of this project is to develop a system to calculate the optimal path from given starting and ending points for an earth-moving vehicle to follow during a typical work cycle. Constraints considered in calculating the optimal path are the vehicle geometry, vehicle performance limits, work area configuration, and vehicle jerk and acceleration limits. The applications of this research will include use as a design tool to assist engineers in determining vehicle specifications.

Smart Mesoflaps for Aeroelastic Transpiration to Control Shock/Boundary-Layer Interactions
D. A. Tortorelli,* J. Y. Kim
Defense Advanced Research Projects Agency

The capability and performance of Smart Mesoflaps for Aeroelastic Transpiration (SMAT) is investigated, which will provide mass and momentum transfer to control Shock/Boundary-Layer Interactions (SBLIs). Numerical and experimental investigations will be closely integrated in relevant SBLI flowfields. Numerical studies will employ an aeroelastic, finite element code to investigate the fluid physics between the supersonic turbulent boundary layer, the subsonic cavity flow, and the deforming mesoflaps. This will be coupled to advanced shape- and topology-optimization techniques so that the numerical representation of the nonlinear adaptive controllers such that mesoflap design can be designed for a given flowfield.

Synthesis and Optimization of Planar Mechanisms
D. A. Tortorelli,* S. Chen
Caterpillar, Inc.

A computer-aided design methodology is developed to automate the design of mechanisms. The approach uses efficiently computed design sensitivities of the generalized coordinates and reaction forces with respect to local joint positions. Sensitivities are combined with numerical optimization to optimally locate joint coordinates to minimize a cost function while satisfying constraints. These sensitivities are efficiently computed because they utilize the decomposed Jacobian from the kinematic analysis. Mathematica' is used to expedite the analytical derivations. The analytical sensitivities are verified with finite-difference sensitivities. Mechanisms with known analytical solutions are optimized for verification purposes. Finally, the design of a wheel loader bucket mechanism is studied.

Topology Optimization of Geometrically Nonlinear Structures and Compliant Mechanisms
D. A. Tortorelli,* T. E. Bruns
National Science Foundation, DMM 93-58132 NYI

Toplogy optimization of structures has become an area of rapidly increasing interest to researchers during the past decade. Most structural topology optimization problems assume a linear elastic response. This assumption is not valid for systems undergoing large deformation. The structural analysis here accommodates geometric and material nonlinearities and its impact on the topology optimization is investigated. A well-posed, regularized topology optimization problem is developed by introducing a Gaussian-weighted density measure. Topology results based on the linear and nonlinear elastic formulations are compared. The formulation of the structural design problem is then extended to design compliant mechanisms undergoing large displacements.