VTechWorks Repository :: Browsing by Author "Nayfeh, Ali H."

Browsing by Author "Nayfeh, Ali H."

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Acoustic Receptivity of a Boundary-Layer to Tollmien-Schlichting Waves Resulting From a Finite-Height Hump At Finite Reynolds-Numbers
Nayfeh, Ali H.; Ashour, O. N. (AIP Publishing, 1994-11-01)
The acoustic receptivity of a boundary layer to Tollmien-Schlichting (T-S) waves resulting from a finite-height hump at finite Reynolds numbers is investigated. The steady flow is calculated using an interacting boundary-layer (IBL) scheme that accounts for viscous/inviscid interactions. The unsteady flow is written as the sum of a Stokes wave and a traveling wave generated due to the interaction of the Stokes flow with the steady disturbance resulting from the hump. The traveling wave is governed by a set of nonhomogeneous equations, which is a generalization of the Orr-Sommerfeld equation. The solution of these nonhomogeneous equations is projected onto the quasiparallel eigenmode using the quasiparallel adjoint. This leads to a nonhomogeneous equation with variable coefficients governing the amplitude and phase of the T-S wave. Results are presented for the amplitude variation and the receptivity at finite Reynolds numbers. The results are in good agreement with the experimental results of Saric, Hoos, and Radeztsky [Boundary Layer Stability and Transition to Turbulence (ASME, New York, 1991), FED No. 114, pp. 17-22] for all tested hump heights at the two-tested sound pressure levels. Application of this paper's theory to small humps yields results that agree with those of Choudhari and Streett [Phys. Fluids A 4, 2495 (1992)]; and Crouch [Phys. Fluids A 4, 1408 (1992)]. Application of suction is shown to reduce the receptivity resulting from the hump.
Acoustic waves in ducts with sinusoidally perturbed walls and mean flow
Nayfeh, Ali H. (Acoustical Society of America, 1975)
An analysis is presented of the propagation of acoustic waves in a hard-walled duct with sinusoidally perturbed walls and carrying mean flow. The results show that resonance occurs whenever the wavenumber of the wall undulations is approximately equal to the difference between the wavenumber of any two propagating modes. It is shown that neither of the resonating modes could exist in the duct without strongly exciting the other resonating mode.
Adaptation of Nontraditional Control Techniques to Nonlinear Micro and Macro Mechanical Systems
Daqaq, Mohammed F. (Virginia Tech, 2006-07-28)
We investigate the implementation of nontraditional open-loop and closed-loop control techniques to systems at the micro and macro scales. At the macro level, we consider a quay-side container crane. It is known that the United States relies on ocean transportation for 95% of cargo tonnage that moves in and out of the country. Each year over six million loaded marine containers enter U.S. ports. Current growth predictions indicate that container cargo will quadruple in the next twenty years. To cope with this rapid growth, we develop a novel open-loop input-shaping control technique to mitigate payload oscillations on quay-side container cranes. The proposed approach is suitable for automated crane operations, does not require any alterations to the existing crane structure, uses the maximum crane capabilities, and is based on an accurate two-dimensional four-bar-mechanism model of a container crane. The shaped commands are based on a nonlinear approximation of the two-dimensional model frequency and, unlike traditional input-shaping techniques, our approach can account for large hoisting operations. For operator-in-the-loop crane operations, we develop a closed-loop nonlinear delayed-position feedback controller. Key features of this controller are that it: does not require major modifications to the existing crane structure, accounts for motion inversion delays, rejects external disturbances, and is superimposed on the crane operator commands. To validate the controllers, we construct a 1:10 scale model of a 65-ton quay-side container crane. The facility consists of a 7-meter track, 3.5-meter hoisting cables, a trolley, a traverse motor, two hoisting motors, and a 50-pound payload. Using this setup, we demonstrated the effectiveness of the controllers in mitigating payload oscillations in both of the open-loop and closed-loop modes of operation. At the micro level, we consider a micro optical device known as the torsional micromirror. This device has a tremendous number of industrial and consumer market applications including optical switching, light scanning, digital displays, etc. To analyze this device, we develop a comprehensive model of an electrically actuated torsional mirror. Using a Galerkin expansion, we develop a reduced-order model of the mirror and verify it against experimental data. We investigate the accuracy of representing the mirror using a two-degrees-of-freedom lumped-mass model. We conclude that, under normal operating conditions, the statics and dynamics of the mirror can be accurately represented by the simplified lumped-mass system. We utilize the lumped-mass model to study and analyze the nonlinear dynamics of torsional micromirrors subjected to combined DC and resonant AC excitations. The analysis is aimed at enhancing the performance of micromirrors used for scanning applications by providing better insight into the effects of system parameters on the microscanner's optimal design and performance. Examining the characteristics of the mirror response, we found that, for a certain DC voltage range, a two-to-one internal resonance might be activated between the first two modes. Due to this internal resonance, the mirror exhibits complex dynamic behavior. This behavior results in undesirable vibrations that can be detrimental to the scanner performance. Torsional micromirrors are currently being implemented to provide all-optical switching in fiber optic networks. Traditional switching techniques are based on converting the optical signal into electrical signal and back into optical signal before it can be switched into another fiber. This reduces the rate of data transfer substantially. To realize fast all-optical switching, we enhance the transient dynamic characteristics and performance of torsional micromirrors by developing a novel technique for preshaping the voltage commands applied to activate the mirror. This new approach is the first to effectively account for inherent nonlinearities, damping effects, and the energy of the significant higher modes. Using this technique, we are able to realize very fast switching operations with minimal settling time and almost zero overshoot.
Adiabatic Following in Two-Photon Transition
Nayfeh, Munir H.; Nayfeh, Ali H. (American Physical Society, 1977-03-01)
The coherent interaction of two smoothly varying, near-resonant, two-photon pulses with a three-level system can be described by "two-photon damped Bloch equations" which are analogous to those for a one-photon transition in a two-level system except for the presence of a two-photon coupling and a frequency shift. These equations are solved for the cases γ1, γ2≪Ω, γ1=γ2, and γ2k2ε4Ω2, γ1≪Ω, where γ1 and γ2 are the atomic energy and phase relaxation widths, respectively, and Ω is the Rabi frequency. The leading contribution to the refractive index is intensity dependent, caused by the level shifts inherent in multiphoton processes; it includes a relaxation dependent part which is important at times shorter than γ−11. The second-order contributions depend on the square of the intensity and the time-integrated square of the intensity. The latter contribution, which is relaxation dependent, causes line asymmetry at the long-wavelength wing; it consists of a term proportional to γ2−γ1 and only important at early times and a term proportional to 2γ2−γ1.
Algebraically growing waves in ducts with sheared mean flow
Nayfeh, Ali H.; Telionis, Demetri P. (Acoustical Society of America, 1974)
Standing or traveling waves which vary algebraically with the axial distance in uniform ducts with sheared mean velocity profiles are investigated. The results show that such waves are not possible for ducts with uniform cross sections and fully developed mean flows.
Analysis and Modeling of World Wide Web Traffic
Abdulla, Ghaleb (Virginia Tech, 1998-04-27)
This dissertation deals with monitoring, collecting, analyzing, and modeling of World Wide Web (WWW) traffic and client interactions. The rapid growth of WWW usage has not been accompanied by an overall understanding of models of information resources and their deployment strategies. Consequently, the current Web architecture often faces performance and reliability problems. Scalability, latency, bandwidth, and disconnected operations are some of the important issues that should be considered when attempting to adjust for the growth in Web usage. The WWW Consortium launched an effort to design a new protocol that will be able to support future demands. Before doing that, however, we need to characterize current users' interactions with the WWW and understand how it is being used. We focus on proxies since they provide a good medium or caching, filtering information, payment methods, and copyright management. We collected proxy data from our environment over a period of more than two years. We also collected data from other sources such as schools, information service providers, and commercial aites. Sampling times range from days to years. We analyzed the collected data looking for important characteristics that can help in designing a better HTTP protocol. We developed a modeling approach that considers Web traffic characteristics such as self-similarity and long-range dependency. We developed an algorithm to characterize users' sessions. Finally we developed a high-level Web traffic model suitable for sensitivity analysis. As a result of this work we develop statistical models of parameters such as arrival times, file sizes, file types, and locality of reference. We describe an approach to model long-range and dependent Web traffic and we characterize activities of users accessing a digital library courseware server or Web search tools. Temporal and spatial locality of reference within examined user communities is high, so caching can be an effective tool to help reduce network traffic and to help solve the scalability problem. We recommend utilizing our findings to promote a smart distribution or push model to cache documents when there is likelihood of repeat accesses.
Analytical and Computational Tools for the Study of Grazing Bifurcations of Periodic Orbits and Invariant Tori
Thota, Phanikrishna (Virginia Tech, 2007-02-02)
The objective of this dissertation is to develop theoretical and computational tools for the study of qualitative changes in the dynamics of systems with discontinuities, also known as nonsmooth or hybrid dynamical systems, under parameter variations. Accordingly, this dissertation is divided into two parts. The analytical section of this dissertation discusses mathematical tools for the analysis of hybrid dynamical systems and their application to a series of model examples. Specifically, qualitative changes in the system dynamics from a nonimpacting to an impacting motion, referred to as grazing bifurcations, are studied in oscillators where the discontinuities are caused by impacts. Here, the study emphasizes the formulation of conditions for the persistence of a steady state motion in the immediate vicinity of periodic and quasiperiodic grazing trajectories in an impacting mechanical system. A local analysis based on the discontinuity-mapping approach is employed to derive a normal-form description of the dynamics near a grazing trajectory. Also, the results obtained using the discontinuity-mapping approach and direct numerical integration are found to be in good agreement. It is found that the instabilities caused by the presence of the square-root singularity in the normal-form description affect the grazing bifurcation scenario differently depending on the relative dimensionality of the state space and the steady state motion at the grazing contact. The computational section presents the structure and applications of a software program, TC-HAT, developed to study the bifurcation analysis of hybrid dynamical systems. Here, we present a general boundary value problem (BVP) approach to locate periodic trajectories corresponding to a hybrid dynamical system under parameter variations. A methodology to compute the eigenvalues of periodic trajectories when using the BVP formulation is illustrated using a model example. Finally, bifurcation analysis of four model hybrid dynamical systems is performed using TC-HAT.
Anti-Swing Control of Gantry and Tower Cranes Using Fuzzy and Time-Delayed Feedback with Friction Compensation
Omar, Hanafy M.; Nayfeh, Ali H. (Hindawi, 2005-01-01)
We designed a feedback controller to automate crane operations by controlling the load position and its swing. First, a PD tracking controller is designed to follow a prescribed trajectory. Then, another controller is added to the control loop to damp the load swing. The anti-swing controller is designed based on two techniques: a time-delayed feedback of the load swing angle and an anti-swing fuzzy logic controller (FLC). The rules of the FLC are generated by mapping the performance of the time-delayed feedback controller. The same mapping method used for generating the rules can be applied to mimic the performance of an expert operator. The control algorithms were designed for gantry cranes and then extended to tower cranes by considering the coupling between the translational and rotational motions. Experimental results show that the controller is effective in reducing load oscillations and transferring the load in a reasonable time. To experimentally validate the theory, we had to compensate for friction. To this end, we estimated the friction and then applied a control action to cancel it. The friction force was estimated by assuming a mathematical model and then estimating the model coefficients using an off-line identification technique, the method of least squares (LS).
Application of Bifurcation Theory to Subsynchronous Resonance in Power Systems
Harb, Ahmad M. (Virginia Tech, 1996-12-16)
A bifurcation analysis is used to investigate the complex dynamics of two heavily loaded single-machine-infinite-busbar power systems modeling the characteristics of the BOARDMAN generator with respect to the rest of the North-Western American Power System and the CHOLLA# generator with respect to the SOWARO station. In the BOARDMAN system, we show that there are three Hopf bifurcations at practical compensation values, while in the CHOLLA#4 system, we show that there is only one Hopf bifurcation. The results show that as the compensation level increases, the operating condition loses stability with a complex conjugate pair of eigenvalues of the Jacobian matrix crossing transversely from the left- to the right-half of the complex plane, signifying a Hopf bifurcation. As a result, the power system oscillates subsynchronously with a small limit-cycle attractor. As the compensation level increases, the limit cycle grows and then loses stability via a secondary Hopf bifurcation, resulting in the creation of a two-period quasiperiodic subsynchronous oscillation, a two-torus attractor. On further increases of the compensation level, the quasiperiodic attractor collides with its basin boundary, resulting in the destruction of the attractor and its basin boundary in a bluesky catastrophe. Consequently, there are no bounded motions. When a damper winding is placed either along the q-axis, or d-axis, or both axes of the BOARDMAN system and the machine saturation is considered in the CHOLLA#4 system, the study shows that, there is only one Hopf bifurcation and it occurs at a much lower level of compensation, indicating that the damper windings and the machine saturation destabilize the system by inducing subsynchronous resonance. Finally, we investigate the effect of linear and nonlinear controllers on mitigating subsynchronous resonance in the CHOLLA#4 system . The study shows that the linear controller increases the compensation level at which subsynchronous resonance occurs and the nonlinear controller does not affect the location and type of the Hopf bifurcation, but it reduces the amplitude of the limit cycle born as a result of the Hopf bifurcation.
Asymptotic Solutions Of Second-Order Linear Equations with 3 Transition Points
Nayfeh, Ali H. (AIP Publishing, 1974-12-01)
A uniformly valid asymptotic expansion is obtained for the regular solution of a class of second_order linear differential equations with three transition points_a turning point and two regular singular points. The solution is found by matching three different solutions obtained using the Langer Transformation. The matching yields the eigenvalues and the eigenfunctions.
Axisymmetric Natural Frequencies of Statically Loaded Annular Plates
Abdel-Rahman, Eihab M.; Faris, Waleed F.; Nayfeh, Ali H. (Hindawi, 2003-01-01)
We present a numerical procedure to solve the axisymmetric vibration problem of statically loaded annular plates. We use the von Kármán nonlinear plate model to account for large deformations and study the effect of static deflections on the natural frequencies and mode shapes for six combinations of boundary conditions. The shooting method is used to solve the resulting eigenvalue problem. Our results show that static deformations have a significant effect on the natural frequencies and small effect on the mode shapes of the plate. Further, the results show that the presence of in-plane stresses has a significant effect on the natural frequencies.
Cargo Pendulation Reduction on Ship-Mounted Cranes
Henry, Ryan J. (Virginia Tech, 1997-05-08)
It is sometimes necessary to transfer cargo from a large ship to a smaller ship at sea. Specially designed craneships are used for this task, however the wave-induced motions of the ship can cause large pendulations of cargo being hoisted by a ship-mounted crane. This makes cargo transfer in rough seas extremely dangerous and therefore transfer operations normally cease when sea state 3 is reached. If the cargo pendulations could be reduced in higher sea states, transfer operations would be possible. By controlling the boom luff angle, one can reduce the cargo pendulations in the plane of the boom significantly. A two-dimensional pendulum with a rigid massless cable and massive point load is used to model the system. A control law using time-delayed position feedback is developed and the system is simulated on a computer using the full nonlinear equations of motion. A three-degree-of-freedom ship-motion simulation platform, capable of simulating heave, pitch, and roll motions, was built. The computer simulation results were experimentally verified by mounting a 1/24th scale model of a T-ACS crane on the ship-motion simulation platform.
Characterization, Modeling, and Control of Ionic Polymer Transducers
Newbury, Kenneth Matthew (Virginia Tech, 2002-09-06)
Ionic polymers are a recently discovered class of active materials that exhibit bidirectional electromechanical coupling. They are `soft' transducers that perform best when the mechanical deformation involves bending of the transducer. Ionic polymers are low voltage actuators -- they only require inputs on the order of 1V and cannot tolerate voltages above approximately 10V. The mechanisms responsible for the electromechanical coupling are not yet fully understood, and reports of the capabilities and limitations of ionic polymer transducers vary widely. In addition, suitable engineering models have not been developed. This document presents a dynamic model for ionic polymer transducers that is based on a pair of symmetric, linearly coupled equations with frequency dependent coefficients. The model is presented in the form of an equivalent circuit, employing an ideal transformer with a frequency dependent turns ratio to represent the electromechanical coupling. The circuit elements have clear physical interpretations, and expressions relating them to transducer dimensions and material properties are derived herein. The material parameters required for the model: modulus, density, electrical properties, and electromechanical coupling term are determined experimentally. The model is then validated by comparing simulated and experimental responses, and the agreement is good. Further validation is presented in the form of extensive experiments that confirm the predicted changes in transducer performance as transducer dimensions are varied. In addition, reciprocity between mechanical and electrical domains is demonstrated. This reciprocity is predicted by the model, and is a direct result of the symmetry in the equations on which the model is based. The capabilities of ionic polymer sensors and actuators, when used in the cantilevered bender configuration, are discussed and compared to piezoceramic and piezo polymer cantilevered benders. The energy density of all three actuators are within an order of magnitude of one another, with peak values of approximately 10J/m^3 and 4mJ/kg for ionic polymer actuators actuated with a 1.2V signal. Ionic polymer sensors compare favorably to piezoelectric sensors. Their charge sensitivity is approximately 320E-6C/m for a 0.2 x 5 x 17mm cantilevered bender, two orders of magnitude greater than a piezo polymer sensor with identical dimensions. This work is concluded with a demonstration of feedback control of a device powered by ionic polymer actuators. An ionic polymer sensor was used to provide the displacement feedback signal. This experiment is the first demonstration of feedback control using an ionic polymer sensor. Compensator design was performed using the model developed in the first chapter of this document, and experiments confirmed that implementation of the control scheme improved, in a narrow frequency range, the system's ability to track sinusoidal inputs.
Combat System Modeling:Modeling Large-Scale Software and Hardware Application Using UML
AL-Aqrabawi, Mohammad Saleh (Virginia Tech, 2001-05-09)
Maintaining large-scale legacy applications has been a major challenge for software producers. As the application evolves and gets more complicated, it becomes harder to understand, debug, or modify the code. Moreover, as new members are joining the development team, and others are leaving, the need for a well-documented code arises. Good documentation necessitates the visualization of the code in an easy to understand manner. The Unified Modeling Language (UML), an Object Management Group's (OMG) standard, is a graphical modeling language used for specifying, visualizing, constructing, and documenting software intensive artifacts. UML, which has been accepted as an industry standard in November 1997, has aided the design and maintenance of object-oriented legacy applications. While the software developers were building UML models for their existing applications as part of a reverse-engineering process, development of next generation software applications started from the models (forward-engineering process). In the forward engineering process, the system's code is specified and constructed from the UML models, which evolve as the system evolves in order to maintain consistent documentation and visualization of the system. Moreover, UML has the power of hiding unnecessary details of the system by the ability to model its different views. This enables visualizing the system at different levels of hierarchy. This thesis documents how to use UML to model a software-intensive simulation for the combat systems of a fully automated naval "digital ship". This process started with building the use case diagrams based on the system requirements given by the domain experts. Then activity diagrams were used to describe the exact performance of the use cases. The logical view of the system was built using class, interaction, and activity diagrams. Then, the physical view of the system was built using component diagrams. Finally, an example of the code generation process from the UML models was carried out for one of the system components. These models are to be maintained as the application evolves. Using UML has aided in building a well-structured object-oriented application, validating the use cases of the application with the domain experts, visualizing and validating the structure of the source code before writing it, communicating between different members of the development team, and providing an easily understandable documentation of the system.
Compressible Boundary Layers Over Wavy Walls
Lekoudis, S. G.; Nayfeh, Ali H.; Saric, W. S. (AIP Publishing, 1976)
An analysis is presented of compressible viscous flows past wavy walls without restricting the mean flow to be linear in the disturbance layer. Linearization of the compressible disturbance equations results in a system of six first_order differential equations for the perturbation quantities. The method of orthonormalization is used to control the error growth in the numerical solution of these equations. The present results agree more closely with experimental data than the results obtained by using Lighthill's theory, which restricts the mean flow to be linear in the disturbance layer.
Control of Gantry and Tower Cranes
Omar, Hanafy M. (Virginia Tech, 2003-01-24)
The main objective of this work is to design robust, fast, and practical controllers for gantry and tower cranes. The controllers are designed to transfer the load from point to point as fast as possible and, at the same time, the load swing is kept small during the transfer process and completely vanishes at the load destination. Moreover, variations of the system parameters, such as the cable length and the load weight, are also included. Practical considerations, such as the control action power, and the maximum acceleration and velocity, are taken into account. In addition, friction effects are included in the design using a friction-compensation technique. The designed controllers are based on two approaches. In the first approach, a gain-scheduling feedback controller is designed to move the load from point to point within one oscillation cycle without inducing large swings. The settling time of the system is taken to be equal to the period of oscillation of the load. This criterion enables calculation of the controller feedback gains for varying load weight and cable length. The position references for this controller are step functions. Moreover, the position and swing controllers are treated in a unified way. In the second approach, the transfer process and the swing control are separated in the controller design. This approach requires designing two controllers independently: an anti-swing controller and a tracking controller. The objective of the anti-swing controller is to reduce the load swing. The tracking controller is responsible for making the trolley follow a reference position trajectory. We use a PD-controller for tracking, while the anti-swing controller is designed using three different methods: (a) a classical PD controller, (b) two controllers based on a delayed-feedback technique, and (c) a fuzzy logic controller that maps the delayed-feedback controller performance. To validate the designed controllers, an experimental setup was built. Although the designed controllers work perfectly in the computer simulations, the experimental results are unacceptable due to the high friction in the system. This friction deteriorates the system response by introducing time delay, high steady-state error in the trolley and tower positions, and high residual load swings. To overcome friction in the tower-crane model, we estimate the friction, then we apply an opposite control action to cancel it. To estimate the friction force, we assume a mathematical model and estimate the model coefficients using an off-line identification technique using the method of least squares. With friction compensation, the experimental results are in good agreement with the computer simulations. The gain-scheduling controllers transfer the load smoothly without inducing an overshoot in the trolley position. Moreover, the load can be transferred in a time near to the optimal time with small swing angles during the transfer process. With full-state feedback, the crane can reach any position in the working environment without exceeding the system power capability by controlling the forward gain in the feedback loop. For large distances, we have to decrease this gain, which in turn slows the transfer process. Therefore, this approach is more suitable for short distances. The tracking-anti-swing control approach is usually associated with overshoots in the translational and rotational motions. These overshoots increase with an increase in the maximum acceleration of the trajectories . The transfer time is longer than that obtained with the first approach. However, the crane can follow any trajectory, which makes the controller cope with obstacles in the working environment. Also, we do not need to recalculate the feedback gains for each transfer distance as in the gain-scheduling feedback controller.
Control of Limit Cycle Oscillations of a Two-Dimensional Aeroelastic System
Ghommem, Mehdi; Nayfeh, Ali H.; Hajj, Muhammad R. (Hindawi Publishing Corporation, 2010)
Linear and nonlinear static feedback controls are implemented on a nonlinear aeroelastic system that consists of a rigid airfoil supported by nonlinear springs in the pitch and plunge directions and subjected to nonlinear aerodynamic loads. The normal form is used to investigate the Hopf bifurcation that occurs as the freestream velocity is increased and to analytically predict the amplitude and frequency of the ensuing limit cycle oscillations (LCO). It is shown that linear control can be used to delay the flutter onset and reduce the LCO amplitude. Yet, its required gains remain a function of the speed. On the other hand, nonlinear control can be efficiently implemented to convert any subcritical Hopf bifurcation into a supercritical one and to significantly reduce the LCO amplitude.
Control of Rotary Cranes Using Fuzzy Logic
Al-mousa, Amjed A.; Nayfeh, Ali H.; Kachroo, Pushkin (Hindawi, 2003-01-01)
Rotary cranes (tower cranes) are common industrial structures that are used in building construction, factories, and harbors. These cranes are usually operated manually. With the size of these cranes becoming larger and the motion expected to be faster, the process of controlling them has become difficult without using automatic control methods. In general, the movement of cranes has no prescribed path. Cranes have to be run under different operating conditions, which makes closed-loop control attractive.In this work a fuzzy logic controller is introduced with the idea of “split-horizon”; that is, fuzzy inference engines (FIE) are used for tracking the position and others are used for damping the load oscillations. The controller consists of two independent sub-controllers: radial and rotational. Each of these controllers has two fuzzy inference engines (FIE). Computer simulations are used to verify the performance of the controller. Three simulation cases are presented. In the first case, the crane is operated in the gantry (radial) mode in which the trolley moves along the jib while the jib is fixed. In the second case (rotary mode), the trolley moves along the jib and the jib rotates. In the third case, the trolley and jib are fixed while the load is given an initial disturbance. The results from the simulations show that the fuzzy controller is capable of keeping the load-oscillation angles small throughout the maneuvers while completing the maneuvers in relatively reasonable times.
Control of Rotary Cranes Using Fuzzy Logic and Time-Delayed Position Feedback Control
Al-Mousa, Amjed A. (Virginia Tech, 2000-11-27)
Rotary Cranes (Tower Cranes) are common industrial structures that are used in building construction, factories, and harbors. These cranes are usually operated manually. With the size of these cranes becoming larger and the motion expected to be faster, the process of controlling them became dicult without using automatic control methods. In general, the movement of cranes has no prescribed path. Cranes have to be run under dierent operating conditions, which makes closed-loop control preferable. In this work, two types of controllers are studied: fuzzy logic and time-delayed position feedback controllers. The fuzzy logic controller is introduced first with the idea of split-horizon; that is, to use some fuzzy engines for tracking position and others for damping load oscillations. Then the time-delayed position feedback method is applied. Finally, an attempt to combine these two controllers into a hybrid controller is introduced. Computer simulations are used to verify the performance of these controllers. An experimental setup was built on which the time-delayed position feedback controller was tested. The results showed good performance.
A Control System for the Reduction of Cargo Pendulation of Ship-Mounted Cranes
Masoud, Ziyad Nayif (Virginia Tech, 2000-12-04)
Ship-mounted cranes are used to transfer cargo from large container ships to smaller lighters when deep-water ports are not available. The wave-induced motion of the crane ship produces large pendulations of hoisted cargo and causes operations to be suspended. In this work, we show that in boom type ship-mounted cranes, it is possible to reduce these pendulations significantly by controlling the slew and luff angles of the boom. Such a control can be achieved with the heavy equipment that is already part of the crane so that retrofitting existing cranes would require a small effort. Moreover, the control is superimposed on the commands of the operator transparently. The successful control strategy is based on delayed-position feedback of the cargo motion in-plane and out-of-plane of the boom and crane tower. Its effectiveness is demonstrated with a fully nonlinear three-dimensional computer simulation and with an experiment on a 1/24 scale model of a T-ACS (The Auxiliary Crane Ship) crane mounted on a platform moving with three degrees of freedom to simulate the ship roll, pitch, and heave motions of the crane ship. The results demonstrate that the pendulations can be significantly reduced, and therefore the range of sea conditions in which cargo-transfer operations could take place can be greatly expanded. Furthermore, the control strategy is applied experimentally to a scaled model of a tower crane. The effectiveness of the controller is demonstrated for both rotary and gantry modes of operation of the crane. This work was supported by the Office of Naval Research under Contract #N00014-96-1-1123.

Browsing by Author "Nayfeh, Ali H."

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