|
| Contract Research and Consulting Engineering Services |
Since 1957, STI has been providing engineering consulting services and performing contract research in the general area of physical system dynamics and control - both automatic control and manual control. We specialize in vehicle dynamics and control. STI's initial focus was aircraft dynamics and flight control, but over nearly 50 years STI's activities have been expanded to a wide range of vehicles including aerospace craft, ground and marine vehicles. We have stretched the rubric of "vehicles" to include such dynamic systems as astronomical telescopes and oilfield drilling rigs. Areas of Expertise System Modeling Much of STI's work begins with the formulation of appropriate equations of motion for the vehicle or other physical system of interest. These are evolved from core knowledge of rigid body dynamics which is artfully specialized to the system and problem at hand. In STI's practice we typically approach problems using a range of model complexity from low order transfer functions to high-level simulations with many degrees of freedom. Our long experience in vehicle dynamics has shown us that simple models can often expose the fundamental characteristics, which can be easily be lost in high-level simulations. Thus we routinely develop complex high-level simulations as required but use these synergistically with lower order approximations to maximize physical insight into the problem at hand. Much of the difficulty of formulating specific models of vehicles or other physical systems is characterizing the elements that produce forces acting on the vehicle. For ground vehicles as well as aerospace craft these include complex aerodynamic forces which are often not well-defined in the early stages of design. When necessary, STI can estimate these from wind tunnel data or semi-empirical estimation procedures. For ground vehicles characterizing tire forces is an essential and complex problem. At STI this often involves specialized tire tests to generate empirical data that is fitted to the STI tire model. System Identification As an alternative or complement to direct measurement or analytical estimation of vehicle dynamic parameters, STI routinely uses parametric system identification. This is often done in the frequency domain. STI has developed techniques for identifying vehicle parameters using "frequency sweeps" (chirps) that are quite efficient for flight or road tests. Recent developments of wavelet methods by STI extend these identification methods to even simpler transient inputs. Such spectral methods allow test pilots or drivers to easily and quickly generate test inputs that produce accurate identification results. These methods can address both the rigid body and flexible characteristics of vehicle or mechanical systems. They can also be used to characterize components such as servoactuators. Dynamics, Performance and Environmental Factors Once the equations of motion have been specialized to a particular vehicle, trim and stability assessments can be made using a variety of methods. These encompass the concepts of classical aircraft stability and control with extensions to other vehicles. Steady state solutions of the equations of motion can provide the basis for performance calculations such as range and endurance. STI studies environmental factors that produce disturbances, typically vehicle motion. These include wind shears and turbulence affecting aircraft, ocean wave spectra that influence ship motion and its prediction and highway and off-road terrain characteristics that influence ground vehicle motion and stability. STI's research interest in these areas includes not only description of the environmental characteristics, but also the mechanics of their interaction with the vehicle. The latter includes, for example, formulation of specialized tire models that relate not only to particular terrain types, but also to specific types of dynamic analysis such as vehicle durability assessment. Control System Design and Analysis Much of STI's work is focused on the control of vehicles and other physical systems using a wide range of classical and modern methods. STI often employs classical control to obtain particular physical insight into problems. This is used to provide balance to computationally intensive modern optimal control schemes. Much of STI's work has been focused on flight control of aircraft and other aerospace vehicles. This encompasses inner loop stability and control augmentation systems through outer loop guidance and navigation. Linear feedback control analysis and synthesis is routinely done with STI's Program CC control system analysis software using classical or optimal methods. Development of such automatic control systems includes consideration of sensors and actuators as well as control laws. Manual Control Theory and Human Operator Characterization In addition to our capability in automatic control synthesis, analysis and validation, STI has long done research and consulting in manual control theory and related areas such as mathematical modeling of human operators. Early in its history STI pioneered the formulation of mathematical models of human operators based on the principles of classical control theory. STI routinely applies a variety of human operator models of various levels complexity based on describing functions, optimal control theory and neural networks. The simple, but fundamental, "crossover model" has exceptional ability to provide unique insight into the problems of human operators controlling vehicles or other physical systems. Handling Qualities STI's expertise in manual control theory and human factors has long supported our work in vehicle handling qualities, which represents a unique interface between the engineering and behavioral sciences. STI has been involved with development of recent military flying qualities specifications for fixed wing aircraft, V/STOL and rotorcraft. Our work in the development of handling qualities metrics and specifications has led to extensive use of major research simulator facilities and development of specialized simulators at STI. This capability includes the formulation of real time simulator models appropriate for handling qualities research as well as experimental design, execution of simulator studies, and data analysis. Human Factors and Human Performance STI's work in manual control theory and handling qualities is supported by a long history of work in human factors relevant to manual control and decision making. This connects to STI's work in the areas of workload, divided attention and fitness for duty and general studies into factors that degrade human performance including drugs, alcohol and fatigue. STI also does research in specialized areas of training and in particular in the use of simulators for training and human performance assessment. STI has recently focused on the use of our STISIM driving simulator as a tool for clinical and pharmacological research.
Contact Us For more information about STI's Contract Research and Engineering Consulting services, please call Tom Myers at 310/679-2281, ext. 47.
|