bluuebunny/crossref_metadata_2025 huggingface dataset:
A Model-Based Formulation of Robust Design
Authors: Al-Widyan Khalid , Angeles Jorge
Published: May 2005

Laid down in this paper are the foundations on which the design of engineering systems, in the presence of an uncontrollable changing environment, can be based. The changes in environment conditions are accounted for by means of robustness. To this end, a theoretical framework as well as a general methodology for model-based robust design are proposed. Within this framework, all quantities involved in a design task are classified into three sets: the design variables (DV), grouped in vector x, which are to be assigned values as an outcome of the design task; the design-environment parameters (DEP), grouped in vector p, over which the designer has no control; and the performance functions (PF), grouped in vector f, representing the functional relations among performance, DV, and DEP. A distinction is made between global robust design and local robust design, this paper focusing on the latter. The robust design problem is formulated as the minimization of a norm of the covariance matrix of the variations in PF upon variations in the DEP, aka noise in the literature on robust design. Moreover, one pertinent concept is introduced: design isotropy. We show that isotropic designs lead to robustness, even in the absence of knowledge of the statistical properties of the variations of the DEP. To demonstrate our approach, a few examples are included.
A Methodology for Model Selection in Engineering Design
Authors: Radhakrishnan Rajesh , McAdams Daniel A.
Published: May 2005

Engineering design consists of a series of stages during which a number of decisions need to be made by the designer. Since the information available to the designer is limited during initial design stages, to make these decisions and be able to proceed further in the design process, the designer needs to depict the nature, visualize the form, and predict the behavior of the product through the use of aids called models. These models guide these decisions, therefore, the designer needs to ensure the downstream validity of these decisions by constructing models with sufficient accuracy and resolution. Because higher quality and accuracy of information is most often accompanied by a higher cost for a model, determining a satisfactory level of goodness for a model is a fundamental and pervasive question in engineering. Hence, a key aspect of design model construction is deciding whether a model is appropriate for a particular design specification or evaluation, considering accuracy and cost factors. This paper presents an approach for design model construction using utility theory. Since model selection is a design decision, uncertainties in parameters and models are considered by evaluating the confidence in the selection of any model. A method for proceeding in the reverse manner to determine the required goodness of a model is also discussed. We present this research through application to a race car sway bar.
Vortex Breakdown in a Differentially Rotating Cylindrical Container
Authors: Koide Teruaki , Koyama Hide S.
Published: May 2005

Numerical studies are reported on the vortex breakdown in a differentially-rotating cylindrical container in which the top endwall rotates at a high angular velocity Ωt and the cylinder and bottom endwall rotate at a low angular velocity Ωsb. Critical boundaries and the location and size of the vortex breakdown bubble are quite different from the case when the top endwall rotates and the cylinder and the bottom endwall are stationary. As |Ωsb/Ωt| is increased, the breakdown bubble moves toward downstream for Ωsb/Ωt<0, whereas the bubble moves toward upstream for Ωsb/Ωt>0. The Brown and Lopez criterion is extended to a differentially-rotating container.
Weights, Norms, and Notation in Analytical Target Cascading
Authors: Michalek Jeremy J. , Papalambros Panos Y.
Published: May 2005

This technical note provides clarification, modification, and generalization of the notation used to describe analytical target cascading, a model-based hierarchical optimization methodology for systems design.
The Modeling of Engineering Systems for Their Computer-Based Embodiment With Standard Components
Authors: Hicks B. J. , Culley S. J. , Mullineux G.
Published: May 2005

Engineering products and systems consist of varying numbers of components, connecting elements, and structures. The effective design and selection of these is essential for the commercial success of a product. The designer or design team must consider not only physical attributes and performance capabilities but also economic considerations. Their ability to consider these various factors and explore an optimum solution is severely frustrated by the analytically intensive and time-consuming aspects of embodying a system. This embodiment process can become complex where a large number of what can be termed standard components are included. Thus the creation of supportive methods or tools to expedite the embodiment process with these standard components is particularly important. This paper presents a number of techniques that have been generated to enable the consideration of proprietary models of standard components within an overall systems modeling approach. This modeling approach aims to support the designer during the transformation of an idea into a product or system. In particular, this paper deals with the issues concerning the representation of a system as a whole while providing for the specification and/or selection of individual components from a variety of electronic representations. The method for representing a mechanical system is summarized and the general issues of interfacing proprietary electronic representations with a systems modeling tool are discussed. An approach is developed and the process of constructing a system model, selecting electronic representations, and system resolution are described. An industrial case study is used to demonstrate the ability of the approach to embody a system in an integrated and holistic manner. This enables the development of a more refined design solution and consequently more fully informed decisions, based on actual data, to be taken earlier in the design process.
The Function-Failure Design Method
Authors: Stone Robert B. , Tumer Irem Y. , Van Wie Michael
Published: May 2005

To succeed in the product development market today, firms must quickly and accurately satisfy customer needs while designing products that adequately accomplish their desired functions with a minimum number of failures. When failure analysis and prevention are coupled with a product’s design from its conception, potentially shorter design times and fewer redesigns are necessary to arrive at a final product design. In this article, we explore the utility of a novel design methodology that allows failure modes and effects analysis (FMEA)-style failure analysis to be conducted during conceptual design. The function-failure design method (FFDM) guides designers towards improved designs by predicting likely failure modes based on intended product functionality.
Generalized Random Tunneling Algorithm for Continuous Design
Variables
Authors: Kitayama Satoshi , Yamazaki Koetsu
Published: May 2005

This paper presents a global optimization method for continuous design variables. We call this method a generalized random tunneling algorithm (GRTA) because this method can treat the behavior constraints as well as the side constraints without using penalty parameters for the behavior constraints. The GRTA consists of three phases, that is, the minimization phase, the tunneling phase, and the constraint phase. In the minimization phase, local search technique, which is based on the gradient of the objective and constraint functions, is used. The objective of the tunneling phase is to find a point that improves the objective function obtained in the minimization phase. In the constraint phase, the feasibility of the point obtained in the tunneling phase is checked. By iterating these three phases, global or quasi-optimum may be obtained. Through mathematical and structural optimization problems, the validity and efficiency of the GRTA are examined.
Dynamics of a Multibody Mechanical System With Lubricated Long Journal Bearings
Authors: Alshaer B. J. , Nagarajan H. , Beheshti H. K. , Lankarani H. M. , Shivaswamy S.
Published: May 2005

Clearances exist in different kinds of joints in multibody mechanical systems, which could drastically affect the dynamic behavior of the system. If the joint is dry with no lubricant, impact occurs, resulting in wear and tear of the joint. In practical engineering design of machines, joints are usually designed to operate with some lubricant. Lubricated journal bearings are designed so that even when the maximum load is applied, the joint surfaces do not come into contact with each other. In this paper, a general methodology for modeling lubricated long journal bearings in multibody mechanical systems is presented. This modeling utilizes a method of solving for the forces produced by the lubricant in a dynamically loaded long journal bearing. A perfect revolute joint in a multibody mechanical system imposes kinematic constraints, while a lubricated journal bearing joint imposes force constraints. As an application, the dynamic response of a slider-crank mechanism including a lubricated journal bearing joint between the connecting rod and the slider is considered and analyzed. The dynamic response is obtained by numerically solving the constraint equations and the forces produced by the lubricant simultaneously with the differential equations of motion and a set of initial conditions numerically. The results are compared with the previous studies performed on the same mechanism as well a dry clearance joint. It is shown that in a multibody mechanical system, the journal bearing lubricant introduces damping and stiffness to the system. The earlier studies predict that the order of magnitude of the reaction moment is twice that of a perfect revolute joint. The proposed model predicts that the reaction moment is within the same order of magnitude of the perfect joint simulation case.
Application of a System Level Model to Study the Planetary Load Sharing Behavior
Authors: Singh Avinash
Published: May 2005

In planetary transmissions, the input torque is split between a number of parallel sun-pinion-ring gear paths. Under ideal conditions, each parallel path carries the same amount of torque. However, manufacturing errors in the pinion pin-hole location cause unequal load sharing between the parallel paths. The nature of this load sharing behavior depends upon the number of pinions in the planetary system. This load sharing behavior is studied for 4, 5, and 6-pinion variants of a planetary transmission. Critical manufacturing tolerances are identified and loss function curves are generated. The effects of sun gear support stiffness and pinion needle bearing stiffness on the load sharing results are also studied. It is shown that as the number of pinions in a planetary transmission increases, the pin-hole position error tolerance has to be tightened in order to reap the full benefits of load sharing between the pinions. Gear system analysis modules (GSAM) is an analytical tool that can model entire gear systems and will be used in this paper to quantify the load sharing between pinions. The numerical techniques implemented in GSAM will be briefly reviewed.
Force Balancing of Robotic Mechanisms Based on Adjustment of Kinematic Parameters
Authors: Ouyang P. R. , Zhang W. J.
Published: May 2005

Force balancing is a very important issue in mechanism design and has only recently been introduced to the design of robotic mechanisms. In this paper, a force balancing method called adjusting kinematic parameters (AKP) for robotic mechanisms or real-time controllable (RTC) mechanisms is proposed, as opposed to force balancing methods, e.g., the counterweights (CW) method. Both the working principle of the AKP method and the design equation with which to construct a force balanced mechanism are described in detail. A particular implementation of the AKP method for the RTC mechanisms where two pivots on a link are adjustable is presented. A comparison of the two methods, namely the AKP method and the CW method, is made for two RTC mechanisms with different mass distribution. The joint forces and torques are calculated for the trajectory tracking of the RTC mechanisms. The result shows that the AKP method is consistently better than the CW method in terms of the reduction of the joint forces and the torques in the servomotors, and the smoothing of the fluctuation of the joint force.
Twisting Wire Actuator
Authors: Shoham Moshe
Published: May 2005

A type of actuation used in ancient times, based on twisting wires, is reinvented in this paper. Twisting wires actuation was used long ago to pull heavy objects, but, to the best of the author’s knowledge, this investigation represents the first demonstration of its ability to achieve submicron motion resolution. Twisting wires actuation achieves this high resolution without the use of gears, sliders, high-precision lead screws, etc., thus simplifying the actuation system and eliminating sources of friction. The investigation further proves that the use of two opposing wires drastically reduces the nonlinearity effect inherent in this type of actuation, thus in effect turning the system into a linear one. Several experiments verify the theoretical results.
A Method for Adjustable Planar and Spherical Four-Bar Linkage Synthesis
Authors: Hong Boyang , Erdman Arthur G.
Published: May 2005

This paper describes a new method to synthesize adjustable four-bar linkages, both in planar and spherical form. This method uses fixed ground pivots and an adjustable length for input and output links. A new application of Burmester curves for adjustable linkages is introduced, and a numerical example is discussed. This paper also compares a conventional synthesis method (nonadjustable linkage) to the new method. Nonadjustable four-bar linkages provide limited solutions for five-position synthesis. Adjustable linkages generate one infinity of solution choices. This paper also shows that the nonadjustable solutions are special cases of adjustable solutions. This new method can be extended to six position synthesis, with adjustable ground pivots locations.
Discussions on Behavior of Bolted Joints in Tension
Authors: Zhang Ouqi
Published: May 2005

It is known that the behavior of real axisymmetric bolted joints in tension is much more complicated than that the conventional theory describes. Phenomenon conflicting with the theory prediction was observed in experimental and finite element analysis [Kwiatkowski, J. K., Winnicki, L. A., and Krzyspiak, A., 1986, “Stress Analysis of Bolted Tensile End Plate Connections,” Rozprawy Inzynierskie Eng. Trans., 34, pp. 113–137; Webjörn, J., 1988, “Die Moderne Schraubenverbindung,” VDI-Z, 130, pp. 76–78; Grosse, I. R., and Mitchell, L. D., 1990, “Nonlinear Axial Stiffness Characteristics of Bolted Joints,” ASME J. Mech. Des., 122, pp. 442–449; Gerbert, G., Bastedt, H., 1993, “Centrically Loaded Bolt Joints,” ASME J. Mech. Des., 115, pp. 701–705]. Recently, a new analytical model of bolted joints was presented [Zhang, O., and Poirier, J. A., 2004, “New Analytical Model for Axisymmetric Bolted Joints,” ASME J. Mech. Des., 126, pp. 721–728], based on which some discussions are further made in this note.
Control Oriented Modeling of a Diesel Active Lean NOx Catalyst Aftertreatment System
Authors: Aswani D. J. , van Nieuwstadt M. J. , Cook J. A. , Grizzle J. W.
Published: May 2005

The 2004 Federal Tier II and California LEV I emission standards for diesel light trucks mandate tailpipe NOx levels of 0.6g∕mi. Active lean NOx catalysts (ALNC or LNC) have been proposed as a means to achieve this standard. These catalysts require the delivery of supplemental hydrocarbons in order to reduce NOx in the lean environment typical of diesel exhaust. In the system studied here, these additional hydrocarbons are injected into the exhaust system downstream of the turbocharger. A control-oriented, gray-box mathematical model is developed for diesel active lean NOx catalysts. The model represents the phenomena relevant to NOx reduction and HC consumption, namely, the catalyst chemical reactions, HC storage in the ALNC, and heat transfer behavior on the basis of an individual exhaust element. As an illustration of how the model may be used, dynamic programing is applied to determine the optimal trade-off of NOx conversion efficiency versus quantity of injected hydrocarbons.
Dynamic Friction Model-Based Tire-Road Friction Estimation and Emergency Braking Control
Authors: Alvarez Luis , Yi Jingang , Horowitz Roberto , Olmos Luis
Published: May 2005

An adaptive control scheme for emergency braking of vehicles is designed based on a LuGre dynamic model for the tire-road friction. The wheel angular speed and longitudinal vehicle acceleration information are used to design a fast convergence observer to estimate the vehicle velocity and the internal state of the friction model. The unknown parameters of the dynamic friction model are estimated through a parameter adaptation law. A Lyapunov-based state estimator and a stabilizing braking controller are designed to achieve near to maximum braking capability of the vehicle. Underestimation of the maximum friction coefficient, a very desirable feature from the perspective of safety, is guaranteed by a proper choice of adaptation gains and initial values of the estimated friction parameters.
Energy Regenerative Actuator for Motion Control With Application to Fluid Power Systems
Authors: Margolis Donald
Published: May 2005

Motion control is principally involved with moving a load along some prescribed trajectory. Flight simulators and numerically controlled machine tools are examples where motion control is required. Actuators for motion control are typically electrohydraulic, electropneumatic, or electromechanical. An electric signal from a controller modulates high-power elements that control motion of a load in some prescribed manner. Since loads are continuously being accelerated and decelerated, actuators absorb energy as frequently as they output energy, but power is required from the supply regardless of the direction of power flow in the actuator. The absorbed power is simply dissipated in the actuator or power supply. An actuator concept is developed here in which energy storage elements become part of the actuator, and absorbed power is recovered while still performing a high level of motion control. The concept is developed for a fluid power application, but is not restricted to fluid-type devices. Practical realizations of this concept will allow downsizing of power supplies as well as reduced power consumption for any particular application.
Effects of Flexibility on the Stability of Flying Aircraft
Authors: Tuzcu Ilhan , Meirovitch Leonard
Published: May 2005

Traditionally, flying aircraft have been treated within the confines of flight dynamics, which is concerned, for the most part, with rigid aircraft. On the other hand, flexible aircraft fall in the domain of aeroelasticity. In reality all aircraft possess some measure of flexibility and carry out rigid body maneuvers, so that the question arises as to whether rigid body motions and flexibility in combination can affect adversely the stability of flying aircraft. This paper addresses this question by solving the eigenvalue problem for the following three cases: (i) the flight dynamics of a flexible aircraft regarded as rigid and whose perturbations about the flight path are controlled by feedback control, (ii) the aeroelasticity of a corresponding flexible aircraft prevented from undergoing rigid body translations and rotations, and (iii) the control of the actual flexible aircraft using the control gains derived in the first case by regarding the aircraft as rigid. This investigation demonstrates that it is not always safe to treat separately rigid body and flexibility effects in a flying flexible aircraft.
A Comparison of Process Variation Estimators for In-Process Dimensional Measurements and Control
Authors: Ding Yu , Zhou Shiyu , Chen Yong
Published: May 2005

Dimensional variation reduction is critical to assure high product quality in discrete-part manufacturing. Recent innovations in sensor technology enable in-process implementation of laser-optical coordinate sensors and continuous monitoring of product dimensional quality. The abundance of measurement data provides an opportunity to develop next generation process control technologies that not only detect process change, but also provide guidelines respective of root cause identification. Given continuous product dimensional measurements, a critical step leading to root cause identification is the variance estimation of process variation sources. A few on-line variance estimators are available. The focus of this paper is to study the interrelationships and properties of the available variance estimators and compare their performance. An operating characteristics curve is developed as a convenient tool to guide the appropriate use of on-line variance estimators under specific circumstances. The method is illustrated using examples of dimensional control for a panel assembly process.
Galerkin Projections for Delay Differential Equations
Authors: Wahi Pankaj , Chatterjee Anindya
Published: May 2005

We present a Galerkin projection technique by which finite-dimensional ordinary differential equation (ODE) approximations for delay differential equations (DDEs) can be obtained in a straightforward fashion. The technique requires neither the system to be near a bifurcation point, nor the delayed terms to have any specific restrictive form, or even the delay, nonlinearities, and/or forcing to be small. We show through several numerical examples that the systems of ODEs obtained using this procedure can accurately capture the dynamics of the DDEs under study, and that the accuracy of solutions increases with increasing numbers of shape functions used in the Galerkin projection. Examples studied here include a linear constant coefficient DDE as well as forced nonlinear DDEs with one or more delays and possibly nonlinear delayed terms. Parameter studies, with associated bifurcation diagrams, show that the qualitative dynamics of the DDEs can be captured satisfactorily with a modest number of shape functions in the Galerkin projection.
On Stability in Nonsequential MIMO QFT Designs
Authors: Kerr Murray L. , Jayasuriya Suhada , Asokanthan Samuel F.
Published: May 2005

This paper reexamines the stability of uncertain closed-loop systems resulting from the nonsequential (NS) MIMO QFT design methodology. By combining the effect of satisfying both the robust stability and robust performance specifications in a NS MIMO QFT design, a proof for the stability of the uncertain closed-loop system is derived. The stability theorem proves that, subject to the satisfaction of a critical necessary and sufficient condition, the original NS MIMO QFT design methodology will provide a robustly stable closed-loop system. This necessary and sufficient condition provides a useful existence test for a successful NS MIMO QFT design. The results expose the salient features of the NS MIMO QFT design methodology. Two 2×2 MIMO design examples are presented to illustrate the key features of the stability theorem.
Improved Algorithm for Set Inversion With Application to a Jet Engine Control System
Authors: Nataraj P. S. V. , Prakash A. K. , Srivastava S.
Published: May 2005

We present an algorithm to characterize the set S={x∊Rl:f(x)>0}=f−1(]0,∞[m) in the framework of set inversion using interval analysis. The proposed algorithm improves on the algorithm of Jaulin et al. (Jaulin, L., Kieffer, M., Didrit, O., and Walter, E., 2001, Applied Interval Analysis, Springer, London). The improvements exploit the powerful tool of monotonicity. We test and compare the performance of the proposed algorithm with that of Jaulin et al. in characterizing the domain of robust stability for the speed control loop of a jet engine. The results of testing show that the proposed algorithm encloses S more accurately, meaning that it gives a larger region of compensator parameter values for which the system stability is guaranteed and a smaller region of the same for which the system stability is indeterminate.
Understanding Snakelike Locomotion Through a Novel Push-Point Approach
Authors: Bayraktaroglu Zeki Y. , Blazevic Pierre
Published: May 2005

Limbless locomotion reveals increasing interest among locomotion methods inspiring mobile robots. This paper deals with the lateral undulation, one type of terrestrial snakelike locomotion. It represents the first part of a research project based on a biologically inspired approach. The purpose, in this first place, is to cover the physical principles involved in lateral undulation. Following an overview of the lateral undulation as it occurs in nature, the authors consider a generic planar mechanism and a related environment that suit to satisfy the fundamental mechanical phenomenon observed in the locomotion of terrestrial snakes. Application of a relatively simple control law is tested through dynamic simulations. In the second place, the results of this introductory study are going to be used in the research of an appropriate technological solution for an artificial snake exerting lateral undulation. The approach presented differs from other works on the subject in the sense that it does not require any wheeled structure.
Control-Relevant Discretization of Nonlinear Systems With Time-Delay Using Taylor-Lie Series
Authors: Kazantzis Nikolaos , Chong K. T. , Park J. H. , Parlos Alexander G.
Published: May 2005

A new time-discretization method for the development of a sampled-data representation of a nonlinear continuous-time input-driven system with time delay is proposed. It is based on the Taylor-Lie series expansion method and zero-order hold assumption. The mathematical structure of the new discretization scheme is explored and characterized as useful for establishing concrete connections between numerical and system-theoretic properties. In particular, the effect of the time-discretization method on key properties of nonlinear control systems, such as equilibrium properties and asymptotic stability, is examined. The resulting time-discretization provides a finite-dimensional representation for nonlinear control systems with time-delay enabling the application of existing controller design techniques. The performance of the proposed discretization procedure is evaluated using the case study of a two-degree-of-freedom mechanical system that exhibits nonlinear behavior. Various sampling rates and time-delay values are considered.
Computation of High-Gain Observers for Nonlinear Systems Using Automatic Differentiation
Authors: Röbenack Klaus
Published: May 2005

The design of high-gain observers using the observability canonical form is reviewed. Up to the present, gradients of Lie derivatives required by the design algorithms have been computed symbolically. A symbolic computation of the observer gain yields quite often extremely large expressions, even for systems of moderate dimension and complexity. We show how automatic differentiation may be used to compute the observer gain.
A Polytopic System Approach for the Hybrid Control of a Diesel Engine Using VGT/EGR
Authors: Bengea Sorin , DeCarlo Ray , Corless Martin , Rizzoni Giorgio
Published: May 2005

This paper develops a hybrid/gain scheduled controller for moving the state of a diesel engine through a driving profile represented as a sequence of operating points in the seven-dimensional state space of a mean value breathing nonlinear engine state model. The calculations for the control design are based on a third-order (reduced) model of the diesel engine, on whose state space the operating points are projected. About each operating point, we generate a third-order nonlinear error model in polytopic form. Using the polytopic error model at each operating point, a control design is set forth as a system of LMIs. The solution of each system of LMIs produces a norm bounded controller guaranteeing that xi−1d→xid where xid is the ith desired operating point in the three-dimensional state space. The control performance is then evaluated on the seventh order model.
Total Least-Squares Methods for Active View Registration of Three-Dimensional Line Laser Scanning Data
Authors: Xi F. , Nancoo D. , Knopf G.
Published: May 2005

In this paper a method is proposed to register three-dimensional line laser scanning data acquired in two different viewpoints. The proposed method is based on three-point position measurement by scanning three reference balls to determine the transformation between two views. Since there are errors in laser scanning data and sphere fitting, the two sets of three-point position measurement data at two different views are both subject to errors. For this reason, total least-squares methods are applied to determine the transformation, because they take into consideration the errors both at inputs and outputs. Simulations and experiment are carried to compare three methods, namely, ordinary least-squares method, unconstrained total least-squares method, and constrained total least-squares method. It is found that the last method gives the most accurate results.
A Convex Approach Solving Simultaneous Mechanical Structure and Control System Design Problems With Multiple Closed-loop Performance Specifications
Authors: Fu Ke , Mills James K.
Published: May 2005

In this paper, a new integrated design method, referred to as the extended multiple simultaneous specification (EMSS) method, is proposed to solve simultaneous mechanical structure and control system design problems in which a set of n multiple closed-loop performance specifications must be simultaneously satisfied. To utilize this approach, all closed-loop performance specifications considered must have the property that they are convex with respect to the closed-loop system transfer matrix. With the proposed approach, a simply implemented two-stage design approach is used to determine a set of open-loop mechanical system design parameters and a closed-loop controller which simultaneously satisfies a set of n closed-loop performance specifications. In the first stage, for each closed-loop performance specification, one “sample system,” i.e., the closed-loop system with one set of mechanical design parameters with a closed-loop controller chosen from the set of all linear controllers, is determined by trial and error, such that the specification is satisfied. In the second stage, the transfer matrix of the final system, which satisfies all n performance specifications, is determined through the convex combination of the transfer matrices of n sample systems. A linear programming problem is solved to give the combination vector for this convex combination. With the closed-loop transfer matrix given, the mechanical design parameters, the closed-loop controller structure and its gains, are solved algebraically. In this paper, we establish conditions for the existence of a solution to this integrated design problem as well as prove that the EMSS approach retains the stability properties of the sample systems. Experimental results of the EMSS method, carried out on a linear positioning system are given, verifying the effectiveness of the proposed method. We note that the proposed EMSS method works well when the number of design parameters to be determined is small. Further, the proposed EMSS method also has some utility as a controller design method, to determine a closed-loop controller that satisfies a set of n multiple closed-loop performance specifications, given a fixed mechanical system structure.
The Cluster Treatment of Characteristic Roots and the Neutral Type Time-Delayed Systems
Authors: Olgac Nejat , Sipahi Rifat
Published: May 2005

A new methodology is presented for assessing the stability posture of a general class of linear time-invariant—neutral time-delayed systems (LTI-NTDS). It is based on a “Cluster Treatment of Characteristic Roots CTCR” paradigm, which yields a procedure called the Direct Method (DM). The technique offers a number of unique features: It returns exact bounds of time delay for stability, as well as the number of unstable characteristic roots of the system in an explicit and nonsequentially evaluated function of time delay. As a direct consequence of the latter feature, the new methodology creates entirely, all existing stability intervals of delay, τ. It is shown that the Direct Method inherently enforces an intriguing necessary condition for τ-stabilizability, which is the main contribution of this paper. This, so-called, “small delay” effect, was recognized earlier for NTDS, only through some cumbersome mathematics. Furthermore, the Direct Method is also unique in handling systems with unstable starting posture for τ=0, which may be τ-stabilized for higher values of delay. Example cases are provided.
Structural Analysis and Optimization of Nonlinear Control Systems Using Singular Value Decomposition
Authors: Gwak Kwan-Woong , Masada Glenn Y.
Published: May 2005

Structural information of a system/controller allows a designer to diagnose performance characteristics in advance and to make better choices of solution methods. Singular value decomposition (SVD) is a powerful structural analysis tool for linear systems, but it has not been applied to nonlinear systems. In this paper, SVD is used to structurally analyze and to optimally design nonlinear control systems using the linear algebraic equivalence of the nonlinear controller. Specifically, SVD is used to identify control input/output mode shapes, and the control input/output distribution patterns are analyzed using the mode shapes. Optimizing control effort and performance is achieved by truncating some mode shapes in the linear mode shape combinations. The proposed method is applied to the temperature control of a thermal system, and design guidelines are provided to overcome input-constraint-violating solutions.
Dynamic Emulation Using an Indirect Control Input
Authors: Zhang Rong , Alleyne Andrew G.
Published: May 2005

This paper presents a generalized framework to analyze and design controllers for a class of dynamic emulation systems. This class of systems features some structurally distinctive control frameworks which inherently limit the available bandwidth for dynamic emulation. The primary focus is on control structures that we define as indirect. This means the signal from the controller does not affect the physical plant directly; it interacts in combination with other exogenous signals to affect a behavior on the physical system interacting with the emulated load. It is shown that the achievable closed-loop performance is limited in a unique way: the high-frequency response of the controlled closed-loop system converges to the dynamics of the open-loop physical plant that is interacting with the emulated load. This paper illustrates the three controller configurations of the indirect emulation and gives guidelines on how to improve the performance within the identified structural limitations. The three configurations are: a feedback design measuring plant output only, a feedforward design measuring an exogenous signal, and a two degree-of-freedom design combining feedback and feedforward measurements. A detailed analysis in the frequency domain is used to support the experimental results illustrated on a Hardware-in-the-Loop (HIL) system. The demonstration case is a high-bandwidth transient dynamometer to emulate rapidly varying loads associated with an earthmoving vehicle powertrain.
Experimental and Numerical Investigation of the Flow Field in the Tip Region of an Axial Ventilation Fan
Authors: Zhu Xiaocheng , Lin Wanlai , Du Zhaohui
Published: May 2005

The tip leakage flow in an axial ventilation fan with various tip clearances is investigated by experimental measurement and numerical simulation. For a low-rotating-speed ventilation fan with a large tip clearance, both experimental measurement and numerical simulation indicate that the leakage flow originating from the tip clearance along the chord rolls up into a three-dimensional spiral structure to form a leakage flow vortex. The mixing interaction between the tip leakage flow and the main flow produces a low axial velocity region in the tip region, which leads to blockage of the main flow. As the tip clearance increases, the tip leakage flow and the reverse flow become stronger and fully developed. In addition, the position of the first appearance of the tip leakage vortex moves further downstream in a direction parallel to the mid chord line.
Numerical Simulation and Experimental Measurement of Pressure Pulses Produced by a Pulp Screen Foil Rotor
Authors: Feng Mei , Gonzalez Jaime , Olson James A. , Ollivier-Gooch Carl , Gooding Robert W.
Published: May 2005

Pressure screening is an efficient means of removing various contaminants that degrade the appearance and strength of paper. A critical component of a screen is the rotor, which induces a tangential velocity to the suspension and produces pressure pulses to keep the screen apertures clear. To understand the effect of key design and operating variables for a NACA foil rotor, a computational fluid dynamic (CFD) simulation was developed using FLUENT, and the results were compared to experimental measurements. Comparing the pressure pulses obtained through CFD to experimental measurements over a wide range of foil tip speeds, clearances, angles of attack, and foil cambers, general trends of the pressure pulses were similar, but the overall computed values were 40% smaller than the measured values. The pressure pulse peak was found to increase linearly with the square of tip speed for all the angles of attack studied. The maximum magnitudes of negative pressure pulse occurred for the NACA 0012 and 4312 foils at a 5deg angle of attack and for the NACA 8312 foil at 0deg. The stall angle of attack was found to be ∼5deg for NACA 8312, ∼10deg for NACA 4312, and ∼15deg for NACA 0012. The positive pressure peak near the leading edge of the foil was eliminated for foils operating at a positive angle of attack. The magnitude of the negative pressure coefficient peak increased as clearance decreased. Increased camber increases both the magnitude and width of the negative pressure pulse.
Cavitation Properties of Oils Under Dynamic Stressing by Tension
Authors: Williams P. R. , Williams R. L.
Published: May 2005

We report measurements of the effective tensile strength Fc of commercial “multigrade” oils (in the SAE viscosity grades 5W-30 and 10W-40) over a range of temperatures T, which are representative of those encountered under their normal operating conditions (in the range 20°C⩽T⩽140°C). Also reported are the values of Fc that are obtained for Newtonian silicone oils over a range of shear viscosities. In the experiments reported herein, samples of liquid are subjected to dynamic stressing by a pressure-tension cycle, this being a feature of the conditions experienced by a lubricant within a dynamically loaded journal bearing and the method used to estimate Fc avoids reliance on direct measurements of substantial dynamic tensions using conventional pressure transducers.
Vortex-Induced Vibration Characteristics of an Elastic Square Cylinder on Fixed Supports
Authors: Wang Z. J. , Zhou Y.
Published: May 2005

The vortex-induced structural vibration of an elastic square cylinder, on fixed supports at both ends, in a uniform cross flow was measured using fiber-optic Bragg grating sensors. The measurements are compared to those obtained for an elastic circular cylinder of the same hydraulic diameter in an effort to understand the effect of the nature (fixed or oscillating) of the flow separation point on the vortex-induced vibration. It is found that a violent vibration occurs at the third-mode resonance when the vortex-shedding frequency coincides with the third-mode natural frequency of the fluid-structure system, irrespective of the cross-sectional geometry of the cylinder. This is in distinct contrast to previous reports of flexibly supported rigid cylinders, where the first-mode vibration dominates, thus giving little information on the vibration of other modes. The resonance behavior is neither affected by the incidence angle (α) of the free stream, nor by the nature of the flow separation point. However, the vibration amplitude of the square cylinder is about twice that of the circular cylinder even though the flexural rigidity of the former is larger. This is ascribed to a difference in the nature of the flow separation point between the two types of structures. The characteristics of the effective modal damping ratios, defined as the sum of structural and fluid damping ratios, and the system natural frequencies are also investigated. The damping ratios and the system natural frequencies vary little with the reduced velocity at α=0deg, but appreciable at α⩾15deg; they further experience a sharp variation, dictated by the vortex-shedding frequency, near resonance.
Experimental Analysis on Tip Leakage and Wake Flow in an Axial Flow Fan According to Flow Rates
Authors: Jang C.-M. , Sato D. , Fukano T.
Published: May 2005

The flow characteristics in the blade passage and in the wake region of a low-speed axial flow fan have been investigated by experimental analysis using a rotating hot-wire sensor and a five-hole probe for design and off-design operating conditions. The results show that the tip leakage vortex is moved upstream when the flow rate is decreased, thus disturbing the formation of wake flow near the rotor tip. That is, the tip leakage vortex interfaces with the blade suction surface and results in high velocity fluctuation near the blade suction surface. From axial velocity distributions downstream of the fan rotor, large axial velocity decay near the rotor tip is observed at near-stall condition, which results in a large blockage compared to that at the design condition. Finally, the wake flow downstream of the rotor blade is clearly measured at the design and off-design conditions. However, the trough of the high velocity fluctuation due to Karmann vortex street in the wake flow is observed at a higher flow condition than the design flow rate.
Wind-Driven Rivulet Breakoff and Droplet Flows in Microgravity and Terrestrial-Gravity Conditions
Authors: McAlister G. , Ettema R. , Marshall J. S.
Published: May 2005

A study is reported of the wind-driven breakoff of rivulets and subsequent droplet flows on a horizontal plate subject to different normal gravitational states, ranging from zero- to terrestrial-gravity conditions (1 g), and including some data for partial gravity conditions (between 0.1 g and 0.38 g). The study entailed experiments conducted in the authors’ laboratory at the University of Iowa and onboard the NASA KC-135, parabolic-flight aircraft. The wind-driven rivulets exhibited a breakoff phenomenon over a broad range of flow rates, in which a “head” at the tip of the rivulet broke off periodically to form a droplet that advected down the plate. The rivulet breakoff phenomena was sensitive to the normal gravitational force acting on the plate. For instance, the frequency of rivulet breakoff was nearly an order-of-magnitude greater for the 0 g condition than for the same flow in the 1 g condition. The droplet shape and behavior were observed to be quite different between the two cases. It was furthermore found in all cases examined that wind-driven rivulet and droplet flows are markedly different from gravitationally driven flows. These differences arise primarily from the role of form drag on the droplets and on the raised ridge of the rivulet and pool flows near the moving contact line.
Modeling of Wall Pressure Fluctuations Based on Time Mean Flow Field
Authors: Lee Yu-Tai , Blake William K. , Farabee Theodore M.
Published: May 2005

Time-mean flow fields and turbulent flow characteristics obtained from solving the Reynolds averaged Navier-Stokes equations with a k‐ε turbulence model are used to predict the frequency spectrum of wall pressure fluctuations. The vertical turbulent velocity is represented by the turbulent kinetic energy contained in the local flow. An anisotropic distribution of the turbulent kinetic energy is implemented based on an equilibrium turbulent shear flow, which assumes flow with a zero streamwise pressure gradient. The spectral correlation model for predicting the wall pressure fluctuation is obtained through a Green’s function formulation and modeling of the streamwise and spanwise wave number spectra. Predictions for equilibrium flow agree well with measurements and demonstrate that when outer-flow and inner-flow activity contribute significantly, an overlap region exists in which the pressure spectrum scales as the inverse of frequency. Predictions of the surface pressure spectrum for flow over a backward-facing step are used to validate the current approach for a nonequilibrium flow.
A New Class of Synthetic Jet Actuators—Part II: Application to Flow Separation Control
Authors: Gilarranz J. L. , Traub L. W. , Rediniotis O. K.
Published: May 2005

In this work we present the application of the new synthetic jet actuator (SJA) to flow separation control over a NACA 0015 wing. The actuator is compact enough to fit in the interior of the wing that has a chord of 0.375 m. The wing was tested in the Texas A&M University Aerospace Engineering 3 ft×4 ft wind tunnel. An experimental investigation into the effects of the synthetic jet actuator on the performance of the wing is described. Emphasis is placed on the capabilities of the actuator to control the separation of the flow over the wing at high angles of attack. The results include force balance measurements, on surface and off surface flow visualization, surface pressure measurements, and wake surveys. All of the reported tests were performed at a free-stream velocity of 35 m/s, corresponding to a Reynolds number of 8.96×105. The angle of attack was varied from −2.0 deg to 29.0 deg. For the results presented, at angles of attack lower than 10 deg, the actuator has minimal effects. At higher angles of attack, the SJA delays the onset of stall. The use of the actuator causes an 80% increase in the maximum lift coefficient, while the angle at which stall occurs is increased from 12 to 18 deg. The drag on the wing is decreased as a consequence of SJA actuation. For angles of attack larger than 18 deg, where the wing experiences massive separation, the SJA still provides a moderate amount of lift augmentation compared to the unforced case. At angles of attack larger than 25°, a larger frequency of actuation is required to produce significant effects.
Experimental Investigation of the Turbulent Boundary Layer of Surfaces Coated With Marine Antifoulings
Authors: Candries M. , Atlar M.
Published: May 2005

Turbulent boundary-layer measurements have been carried out on flat surfaces coated with two different new generation marine antifoulings. The coatings were applied on 1-m-long test sections that were fitted in a 2.1-m-long flat plate setup. The measurements were carried out in two different recirculating water tunnels by means of two-component laser Doppler velocimetry and were compared with measurements of a smooth steel reference surface and a surface covered with sand grit. Both coatings exhibited an increase in frictional resistance compared to the reference surface, but the increase was significantly smaller for the Foul(ing) Release coatings than for the Tin-free SPC coating. The coatings did not significantly affect the boundary-layer thickness. When expressed in inner variables, the coatings did not have an effect on the turbulence intensity profiles, but when expressed in outer variables, the coatings affected the near-wall turbulence intensities.