Hayrani Oz

The Ohio State University | OSU · Department of Mechanical and Aerospace Engineering

Cerium oxide (CeO2) was prepared using a controlled-precipitation method under microgravity at the International Space Station (ISS). For comparison, ceria was also synthesized under normal-gravity conditions (referred as control). The Brunauer-Emmett-Teller (BET) surface area, pore volume and pore size analysis results indicated that the ceria par...

A vector-space implementation of the equation that has been known as Hamilton's Law of Varying Action is used with a non-virtual perspective to generate direct solutions to nonlinear initial value response problems in the time domain. This novel vector-space perspective unleashes the power of linear algebra to provide new capabilities with Hamilton...

This chapter focuses on a novel theoretical foundation Evolutionary Energy Method (EEM) with its root in the natural law of energy conservation, precisely the first Law of Thermodynamics. The Law of Evolutionary Energy (LEE) is the encompassing foundational evolutionary equation, where the evolutionary operator D{stroke} is a directional change ope...

The "direct control method" is a novel concept that is an attractive alternative and competitor to the differential-equation-based methods. The direct method is equally well applicable to nonlinear, linear, time-varying, and time-invariant systems. For all such systems, the method yields explicit closed-form control laws based on minimization of a...

A technique for deforming a flexible wing to achieve a specified roll rate within a specified time at different Mach Numbers is examined. Rather than using an aileron system for roll, antisymmetric elastic twist and camber is determined to achieve the required rolling moment for a specified roll rate. The elastic twist and camber is achieved by pro...

A vector space approach for generating the response of linear multi-degree-of-freedom time-invariant and time-varying dynamic systems using Hamilton's law of varying action (HLVA) is presented. The boundary (initial) condition constraints on the temporal-basis-function expansions of the time-dependent variables has been removed, while preserving HL...

The focus is on obtaining and identifying optimal distributed- parameter-control equivalent actuation profiles for desired roll maneuvers by a modal synthesis approach. The solution for distributed-parameter-control of an aeroelastic system is developed by synthesis of modal-state-space controllers designed via the globally power optimal Independen...

This report describes the work done by the author to study the feasibility of shaping lifting surfaces via distributed smart actuation systems to achieve high performance flight configurations. In this report, the focus is on first obtaining and identifying optimal distributed-parameter-control equivalent actuation profiles for desired flight maneu...

The study of dynamic systems without resorting to or any knowledge of differential equations is known as the “direct method”. In this method, algebraic equations of motion characterize the system dynamics. The algebraic optimal control laws can be derived in an explicit form for general nonlinear time-varying and time-invariant systems by minimizin...

The study of dynamic systems without resorting to or any knowledge of differential equations is known as the direct method. In this method, algebraic equations of motion characterize the system dynamics. The algebraic optimal control laws can be derived in an explicit form for general nonlinear time-varying and time-invariant systems by minimizing...

Thanks to the recent advances in control of structures by distributed piezoelectric elements, the concept of independent control and sensing of the structural modes has reemerged in the published literature. In particular, to this end, piezoelectric orthogonal actuators and sensors have been introduced. On the other hand, Independent Modal-Space Co...

The study of dynamic systems without resorting to or any knowledge of differential equations is known as the “direct method”. In this method, algebraic equations of motion characterize the system dynamics. The algebraic optimal control laws can be derived in an explicit form for general nonlinear time-varying and time-invariant systems by minimizin...

The study of dynamic systems without resorting to or any knowledge of differential equations is known as the “direct method”. In this method, algebraic equations of motion characterize the system dynamics. The algebraic optimal control laws can be derived in an explicit form for general nonlinear time-varying and time-invariant systems by minimizin...

An efficiency eigenvalue problem is defined associated with the structure-control system efficiency previously defined by the author. The eigenvalue problem leads to the definition of controller efficiency modes alongside the familiar structural modes. The control-structure interaction is characterized through a spectral decomposition of unique con...

A completely algebraic direct optimal tracking methodology is developed and illustrated for the control of nonlinear, time-varying, spatially discrete mechanical systems. System dynamics is obtained from the work-energy equation given by Hamilton's Law, using an assumed time-modes approach. Expansion coefficients of admissible time-modes for the de...

Direct optimal contol policies are developed for tracking control of spatially discrete linear systems. An assumed time-modes method in which the dependent variables of the dynamics problem are expanded in, terms of admissible basis functions in time is extended to include a similar representation of the control inputs. This approach together with...

The efficiency of a structure-control system is a nondimensional parameter which indicates the fraction of the total control power expended usefully in controlling a finite-dimensional system. The balance of control power is wasted on the truncated dynamics serving no useful purpose towards the control objectives. Recently, it has been demonstrated...

An integrated design approach for aeroelastic control of laminated composite lifting surfaces is formulated and demonstrated. The design is posed as an optimization problem to determine the optimum ply orientation angles and the control law which maximizes the aeroelastic instability speed of an actively controlled laminated composite lifting surfa...

Phase 3 of Project WISH saw the evolution of the Emerald City (E-City) from a collection of specialized independent analyses and ideas to a working structural design integrated with major support systems and analyses. Emphasis was placed on comparing and contrasting the closed and open cycle gas core nuclear rocket engines to further determine the...

Thesis (Ph. D.)--Ohio State University, 1988. Includes bibliographical references. Advisor: Hayrani, Öz, Dept. of Aeronautical and Astronautical Engineering.

Based on direct application of Hamilton's Law of Varying Action in conjunction with an assumed-time-modes approach for both the generalized coordinates and input functions, a direct optimal control methodology is developed for the control of nonlinear, time varying, spatially discrete mechanical systems. Expansion coefficients of admissible time mo...

The report develops concepts of efficiency for the control of structural dynamic systems. The efficiencies defined are unique nondimensional measures of structure control system performance forming a common basis of evaluation of such systems. Developments are presented both for distributed parameter systems and spatially discrete, typically finite...

The preliminary design of a permanently manned autonomous space oasis (PEMASO), including its pertinent subsystems, was performed during the 1990 Winter and Spring quarters. The purpose for the space oasis was defined and the preliminary design work was started with emphasis placed on the study of orbital mechanics, power systems and propulsion sys...

The concept of efficiency is introduced as a nondimensional measure of structure-control system evaluation. This concept has the potential to characterize quantitatively and qualitatively the control designer's ability in dealing with some of the problem areas in structural control. The efficiency of the system is defined as the ratio of two contro...

Without consideration of force equilibrium and differential equations of motion, a general derivation of algebraic equations for dynamic systems is presented. This is achieved by an assumed time-modes approach in conjunction with direct application of Hamiltons Law of Varying Action. By assumed time-modes, it is implied that the dependent variables...

The structure-control system optimization problem is formulated with constraints on the closed-loop eigenvalues and the efficiency of the reduced order system. The feasibility of the approach is illustrated by designing the ACOSS-FOUR structure with a reduced order system and improving the efficiency characteristics of the structures-control system...

Variable Structure Control Systems (VSCS) represent a real-time implementable approach to control in contrast to algorithmic approaches, and therefore eliminate the computational burden. However, a practical problem in the implementation of VSCS theory is the possibility of chatter about hypersurfaces known as sliding regimes. Chatter is a high-fre...

Variable structure control system (VSCS) are a class of nonlinear systems which change the structure of the controls when a set of prescribed hypersurfaces are reached in the phase space. The VSCS theory has desirable insensitivity properties under parameter uncertainties, nonlinear effects, and external disturbances. The theory represents a real-t...

A structure/control system optimization problem has been formulated with constraints on the closed-loop eigenvalue distribution, structural frequencies, and the minimum Frobenius norm of the required control gains. Suggested is simultaneous optimization where, at each iteration, the control objective function is minimized first with the closed-loop...

Common control approaches for flexible systems are evaluated in regards to their compatibility with the fundamentals of mechanics of structural systems. It is shown that depending on the formulation, control problems may be ill-posed leading to incompatibilities with the basic laws of mechanics. In an effort to eliminate the incompatibilities const...

This paper presents a method for discrete-time control and estimation applicable to flexible structures in the presence of actuators and sensors noise. The approach consists of complete decoupling of the modal plant and estimator dynamics based on the independent modal-space control (IMSC) technique and modal spatial filtering of the system output....

One problem peculiar to spacecraft in free space is that of ignorable coordinates, which are present when the spacecraft has no natural ability of preventing rigid-body motions. Ignorable coordinates can be eliminated from the problem formulation by introducing a reduced state vector. However, this results in having the ignorable coordinates uncont...

Digital control of a continuoiis-time system implies discretization in time of the system. The discretization is likely to bring about changes in the dynamic characteristics of the continuous-time system. Two approaches to the design of a digital control system can be considered: 1) discretization of a previously designed continuoustime control sys...

A scheme for the control and maneuvering of a large flexible spacecraft by means of two flexible AMCD's using noncontacting magnetic suspension is presented. The system consists of a flexible vehicle, two flexible rings and a magnetic suspension and driving assembly. The necessary skewing of the rings for maneuvering of the vehicle is accomplished...

This paper presents a control scheme for distributed gyroscopic systems based on modal synthesis. It includes specifications of actual control forces and torques and sensors positions. The control parameters for each controlled mode are chosen independently of those for any other mode, thus resulting in a diagonal gain matrix for the controlled mod...

The derivation of the force-free equations of motion of a spinning flexible ring via Lagrange's equations is presented. Closed-form expressions for the natural frequencies are obtained for the most general motion of the ring. Numerical results for rings of different radii and spin rates are presented.

Control of a spinning flexible spacecraft by modal synthesis is presented, taking into account the distributed nature of the system. Control laws based on the discretized system equations are related to the actuators, where the latter are distributed throughout the spacecraft. In addition, the relations between the generalized velocities and the ab...

This paper advances a unified theory for the modal-space control method developed by these authors for the control of large flexible structures and places the theory on a more rigorous foundation. The unified approach permits the simultaneous treatment of a broad spectrum of interrelated problems. In particular, the theory is valid for both nongyro...

Large flexible spacecraft represent highly complex distributed-parameter systems. In theory, a distributed-parameter system possesses an infinite number of degrees of freedom. For practical reasons, however, it must be discretized, which implies truncation. From a structural dynamics point of view, a mathematical model can be made more accurate by...

A procedure is presented for the active control of a spinning flexible spacecraft. Such a system exhibits gyroscopic effects. The design of the controller is based on modal decomposition of the gyroscopic system. This modal decoupling procedure leads to a control mechanism implemented in modular form, which represents a distinct computational advan...

Thesis--Virginia Polytechnic Institute and State University. Vita. Abstract. Includes bibliographical references (leaves 177-180).

Thesis (M.S.)--Ohio State University, 1988. Includes bibliographical references (leaf 70). Advisor: Hayrani Öz, Dept. of Aeronautical and Astronautical Engineering.