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Recognized internationally for his innovative algorithms and software, Tim Davis's research has been applied in a vast range of real-world technological and social applications, from MATLAB to Google Street View, [...]

A novel grid-stitching algorithm has been developed for generating Cartesian-like grids for viscous flow calculations. A grid is generated by recursive division of Cartesian cells. Unlike the conventional Cartesian-mesh calculations that involve unit aspect ratio cells, stretching is used to get the high aspect ratio cells and smooth grid near the body. The grid data are collected in an unstructured format. This novel approach, along with an unstructured mesh-based flow solver (HIFUN-2D, developed in-house), has been successfully used for numerical simulations. This grid is successfully used for Euler and laminar flow computations. Partial success has been achieved for turbulent flow simulations. DOI: 10.2514/1.27854

An [H.sub.[infinity]] direct output feedback control algorithm through minimizing the entropy, a performance index measuring the tradeoff between [H.sub.[infinity]] optimality and [H.sub.2] optimality, is developed in this paper to reduce the earthquake response of structures. To achieve optimal control performance and assure control system stability, the strategy to select both control parameters [gamma] and [alpha] is extensively investigated considering the control force execution time delay. It is found that a lower bound of [gamma] and an upper bound of [alpha] exist. The selection beyond these values will cause the control system instability. For a damped structure, analytical expressions of direct output feedback gains, controlled frequencies and damping ratios are derived. It can be proved that the conventional LQR control is a special case of the developed [H.sub.[infinity]] control. In real active control, control force execution time delay cannot be avoided. This paper gives explicit formulas of maximum allowable delay time and critical control parameters for the design of a stable control system. Some solutions are also proposed to lengthen maximum allowable delay times. DOI: 10.1061/(ASCE)0733-9399(2006)132:10(1096) CE Database subject headings: Entropy; Delay time; Earthquake engineering; Control systems.

The nonlinear response of multi-layered composite cylindrical shell panels subjected to thermomechanical loads are studied in this article. The structural model is based on the first order shear deformation theory incorporating geometric nonlinearities. The nonlinear equilibrium paths are traced using the arc-length control algorithm within the framework of finite element method. Hashin's failure criterion has been adopted to predict the first-ply failure of cylindrical laminates. Both temperature independent and temperature dependent elastic properties are considered in the analysis. Specific numerical results are reported to show the effect of radius-to-span ratio, thickness-to-span ratio, laminate stacking sequence, and boundary condition on stability characteristics of laminated cylindrical shell panels subjected to combined thermal and mechanical transverse loads. DOI: 10.1061/(ASCE)0733-9399(2006)132:10(1088) CE Database subject headings: Nonlinear response; Laminates; Cylindrical shells; Panels.

Active control was simulated numerically for the subsonic flow through a highly loaded low-pressure turbine. The configuration approximated cascade experiments that were conducted to investigate a reduction in turbine stage blade count, which can decrease both weight and mechanical complexity. At a nominal Reynolds number of 25,000 based upon axial chord and inlet conditions, massive separation occurred on the suction surface of each blade due to uncovered turning. Vortex generating jets were then used to help mitigate separation, thereby reducing wake losses. Computations were performed using both steady blowing and pulsed mass injection m study the effects of active flow control on the transitional flow occurring in the aft-blade and near-wake regions. The numerical method utilized a centered compact finite-difference scheme to represent spatial derivatives, that was used in conjunction with a low-pass Pade-type nondispersive filter operator to maintain stability. An implicit approximately factored time-marching algorithm was employed, and Newton-like subiterations were applied to achieve second-order temporal accuracy. Calculations were carried out on a massively parallel computing platform, using domain decomposition to distribute subzones on individual processors. A high-order overset grid approach preserved spatial accuracy in locally refined embedded regions. Features of the flowfields are described, and simulations are compared with each other; with available experimental data, and with a previously obtained baseline case for the noncontrolled flow. It was found that active flow control was able in maintain attached flow over an additional distance of 19-21% of the blade chord, relative to the baseline case, which resulted in a reduction of the wake total pressure loss coefficient of 53-56%. [DOI: 10.1115/1.2238877] Keywords: active flow control, low-pressure turbine, high-order numerical method

This paper discusses the modeling and simulation of a parallel-plate Electrowetting On Dielectric (EWOD) device that moves fluid droplets through surface tension effects. We nmdel the fluid dynamics by using Hele-Shaw type equations with a fncus on including the relevant boundary phenomena. Specifically, we show that contact angle saturation and hysteresis are needed to predict the correct shape and time scale of droplet motion. We demonstrate this by comparing our simulation to experimental data for a splitting droplet. Without these boundary effects, the simulation shows the droplet splitting into three pieces instead of two and the motion is over 15 times faster than the experiment. We then show how including the saturation characteristics of the device, and a simple model of contact angle hysteresis, allows the simulation to better predict the splitting experiment. The match is not perfect and suffers mainly because contact line pinning is not included. This is followed by a comparison between our simulation, whose parameters are now frozen, and a new experiment involving bulk droplet motion. Our numerical implementation uses the level set method, is fast, and is being used to design algorithms for the precise control of microdroplet motion, mixing, and splitting. [1439] Index Terms--Control, electrowetting, level set method, microfluidics, modeling, two-phase flow.

In this paper, we show how to combine microfluidics and feedback control to independently steer multiple particles with micrometer accuracy in two spatial dimensions. The particles are steered by creating a fluid flow that carries all the particles from where they are to where they should be at each time step. Our control loop comprises sensing, computation, and actuation to steer particles along user-input trajectories. Particle locations are identified in real-time by an optical system and transferred to a control algorithm that then determines the electrode voltages necessary to create a flow field to carry all the particles to their next desired locations. The process repeats at the next time instant. Our method achieves inexpensive steering of particles by using conventional electroosmotic actuation in microfluidic channels. This type of particle steering does not require optical traps and can noninvasively steer neutral or charged particles and objects that cannot be captured by laser tweezers. (Laser tweezers cannot steer reflective particles, or particles where the index of refraction is lower than (or for more sophisticated optical vortex holographic tweezers does not differ substantially from) that of the surrounding medium.) We show proof-of-concept PDMS devices, having four and eight electrodes, with control algorithms that can steer one and three particles, respectively. In particular, we demonstrate experimentally that it is possible to use electroosmotic flow to accurately steer and trap multiple particles at once. [1541] Index Terms--Electroosmotic actuation, electrophnretic, feedback control, microfluidics, particles, steering, trapping.

A procedure that can be used to inspect planar cam contours and to evaluate their follower displacement, velocity, and acceleration curves with a higher degree of accuracy, without the aid of approximating follower displacements in traditional methods, is constructed. Based on the geometric relationships at the contact point between a planar cam profile and its follower, analytical descriptions that can be utilized to determine the follower displacement curve and its derivatives are first identified. To verify the feasibility and accuracy of the proposed procedure, analytical results generated from a theoretical design are compared to those obtained by the application of the procedure. To demonstrate the effectiveness and usefulness of the developed procedure, a measuring test bed has been constructed for a practical application example. Furthermore, the results obtained by using the developed procedure with the built measuring test bed are also compared to those obtained by using a coordinate measuring machine with the proposed algorithms. [DOI: 10.1115/1.2163361]

This study presents an optimized matching algorithm for a dual-orthogonal fluoroscopic image system used to determine six degrees-of-freedom total knee arthroplasty (TKA) kinematics in-vivo. The algorithm was evaluated using controlled conditions and standard geometries. Results of the validation demonstrate the algorithm's robustness and capability of realizing a pose from a variety of initial poses. Under idealized conditions, poses of a TKA system were recreated to within 0.02 [+ or -] 0.01 mm and 0.02 [+ or -] 0.03 deg for the femoral component and 0.07 [+ or -] 0.09 mm and 0.16 [+ or -] 0.18 deg for the tibial component. By employing a standardized geometry with spheres, the translational accuracy and repeatability under actual conditions was found to be 0.01 [+ or -] 0.06 mm. Application of the optimized matching algorithm to a TKA patient showed that the pose of in-vivo TKA components can be repeatedly located, with standard deviations less than [+ or -] 0.12 mm and [+ or -] 0.12 deg for the femoral component and [+ or -] 0.29 mm and [+ or -] 0.25 deg for the tibial component. This methodology presents a useful tool that can be readily applied to the investigation of in-vivo motion of TKA kinematics. [DOI: 10.1115/1.2205865]

This paper attempts to use evolutionary algorithms to solve the problem of minimizing construction project duration in deterministic conditions, with in-time changeable and limited accessibility of renewable resources (workforce, machines, and equipment). Particular construction processes (with various levels of complexity) must be conducted in the established technological order and can be executed with different technological and organizational variants (different contractors, technologies, and ways of using resources). Such a description of realization conditions allows the method to also be applied to solving more complex problems that occur in construction practice (e.g., scheduling resources for a whole company, not only for a single project). The method's versatility distinguishes it from other approaches presented in numerous publications. To assess the solutions generated by the evolutionary algorithm, the writers worked a heuristic algorithm (for the allocation of resources and the calculation of the shortest project duration). The results obtained by means of this methodology seem to be similar to outcomes of other comparable methodologies. The proposed methodology (the model and the computer system) may be of great significance to the construction industry. The paper contains some examples of the practical use of the evolutionary algorithm for project planning with time constraints. DOI: 10.1061/(ASCE)0733-9364(2006)132:8(861) CE Database subject headings: Scheduling; Project management; Algorithms; Construction management.

Early in the engineering design cycle, it is difficult to quantify product reliability or compliance to performance targets due to insufficient data or information to model uncertainties. Probability theory cannot be, therefore, used. Design decisions are usually based on fuzzy information that is vague, imprecise qualitative, linguistic or incomplete. Recently, evidence theory has been proposed to handle uncertainty with limited information as an alternative to probability theory. In this paper, a computationally efficient design optimization method is proposed based on evidence theory, which can handle a mixture of epistemic and random uncertainties. It quickly identifies the vicinity of the optimal point and the active constraints by moving a hyperellipse in the original design space, using a reliability-based design optimization (RBDO) algorithm. Subsequently, a derivative-free optimizer calculates the evidence-based optimum, starting from the close-by RBDO optimum, considering only the identified active constraints. The computational cost is kept low by first moving to the vicinity of the optimum quickly and subsequently using local surrogate models of the active constraints only. Two examples demonstrate the proposed evidence-based design optimization method. [DOI: 10.1115/1.2204970]

Probabilistic design optimization addresses the presence of uncertainty in design problems. Extensive studies on reliability-based design optimization, i.e., problems with random variables and probabilistic constraints, have focused on improving computational efficiency of estimating values for the probabilistic functions. In the presence of many probabilistic inequality constraints, computational costs can be reduced if probabilistic values are computed only for constraints that are known to be active or likely active. This article presents an extension of monotonicity analysis concepts from deterministic problems to probabilistic ones, based on the fact that several probability metrics are monotonic transformations. These concepts can be used to construct active set strategies that reduce the computational cost associated with handling inequality constraints, similarly to the deterministic case. Such a strategy is presented as part of a sequential linear programming algorithm along with numerical examples. [DOI: 10.1115/1.2202887] Keywords: monotonicity, active set strategy, RBDO, probabilistic design, optimization under uncertainty

In this paper, a safety envelope concept for load tolerance is introduced. This shows the capacity of the current design as a future reference for design upgrade, maintenance, and control. The safety envelope is applied to estimate the load tolerance of a structural part with respect to the fatigue reliability. First, the dynamic load history is decomposed into the average value and amplitude, which are modeled as random variables. Second, through fatigue analysis and uncertainty propagation, the reliability is calculated. Last, based on the implicit function evaluation for the reliability, the boundary of the safety envelope is calculated numerically. The effect of different distribution types of random variables is then investigated to identify the conservative envelope. In order to improve the efficiency of searching the boundary, probabilistic sensitivity information is utilized. When the relationship between the safety of the system and the load tolerance is linear or mildly nonlinear, the linear estimation of the safety envelope turns out to be accurate and efficient. During the application of the algorithm, a stochastic response surface of logarithmic fatigue life with respect to the load capacity coefficient is constructed, and the Monte Carlo simulation is utilized to calculate the reliability and its sensitivities. [DOI: 10.1115/1.2204971]

This paper is concerned with robust aerodynamic design of compressor blades against erosion. The proposed approach combines a multiobjective genetic algorithm with geometry modeling methods, high-fidelity computational fluid dynamics, and surrogate models to arrive at robust designs on a limited computational budget. The multiobjective formulation used here allows explicit trade-off between the mean and variance of the performance to be carried out. Detailed numerical studies are presented for robust geometric design of a typical compressor fan blade section to illustrate the proposed methodology. The performance of a selected robust optimal solution on the Pareto front is compared to a deterministic optimal solution to demonstrate that significant improvements in the mean shift and variance can be achieved. [DOI: 10.1115/1.2202886] Keywords: robust design, multiobjective optimization, surrogate modeling, compressor blades, erosion

This paper describes a relaxation-based method for simulating 2D and 3D compound kinematic mechanisms. The relaxational process iteratively propagates node motions and degrees of freedom throughout a given kinematic mechanism. While relaxation methods were classically used to solve static problems, we show that the propagation of displacements during the calculation process itself reveals the kinematics of the structure. The method is slower than approaches based on solving simultaneous differential equations of motion, but provides several advantages: It achieves a higher level of accuracy, is more robust in handling transient singularities and degeneracies of the mechanism, and can handle more complex compound mechanisms with many links in multiple entangled kinematic chains. It also allows straightforward introduction of linkages with nonlinear behaviors such as wrapping strings, hydraulics, actuators, contacts, and other arbitrary responses. The basic simulation algorithm is presented, and a number of applications are provided including robotics, design, and biomechanics. [DOI: 10.1115/1.2198255] Keywords: kinematics simulation, relaxation, robotics, biomechanics

Trends towards distributed power generation and the deregulation of energy markets are increasing the requirement for software tools that optimize power generation plant design and operation. In this context, this paper describes the GTPOM (thermo-economic optimization of whole gas turbine plant) European project, funded in part through the European Commission's 5th Framework Programme, focusing on the development and demonstration of an original software tool for the thermo-economic analysis and optimization of conventional and advanced energy systems based on gas turbine plant. PSEconomy, the software tool developed during the GTPOM project, provides a thermo-economic optimization capability for advanced and more-conventional energy systems, enabling the complex trade-offs between system performance and installed costs to be determined for different operational duties and market scenarios. Furthermore, the code is capable of determining the potential benefits of innovative cycles or layout modifications to existing plants compared with current plant configurations. The economic assessment is performed through a complete through-life cycle cost analysis, which includes the total capital cost of the plant, the cost of fuel, O&M costs and the expected revenues from the sale of power and heat. The optimization process, carried out with a GA-based algorithm, is able to pursue different objective functions as specified by the User. These include system efficiency, through-life cost of electricity and through-life internal rate of return. Three case studies demonstrating the capabilities of the new tool are presented in this paper, covering a conventional combined cycle system, a biomass plant and a C[O.sub.2] sequestration gas turbine cycle. The software code is now commercially available and is expected to provide significant advantages in the near and long-term development of energy cycles. [DOI: 10.1115/1.1850511]

A way to gain insight into the flow field conditions in turbomachinery is by carrying out a series of point measurements in a cross section of the flow, for example, with a miniature multihole pressure probe. A problem commonly encountered in situations like these is the selection of a suitable measurement grid layout and density for obtaining all essential information in a cost-effective and timely manner. In order to achieve the latter, a novel adaptive multidimensional data sampling technique has been developed at Cranfield University. This paper describes the underlying principles of this technique, the algorithms utilized, and the results obtained during its successful application to data sets of two different flow fields in a high-speed research compressor. [DOI: 10.1115/1.2135822]

In the paper, self-adapting models capable of reproducing time-dependent data with high computational speed are investigated. The considered models are recurrent feed-forward neural networks (RNNs) with one feedback loop in a recursive computational structure, trained by using a back-propagation learning algorithm. The data used for both training and testing the RNNs have been generated by means of a nonlinear physics-based model for compressor dynamic simulation, which was calibrated on a multistage axial-centrifugal small size compressor. The first step of the analysis is the selection of the compressor maneuver to be used for optimizing RNN training. The subsequent step consists in evaluating the most appropriate RNN structure (optimal number of neurons in the hidden layer and number of outputs) and RNN proper delay time. Then, the robustness of the model response towards measurement uncertainty is ascertained, by comparing the performance of RNNs trained on data uncorrupted or corrupted with measurement errors with respect to the simulation of data corrupted with measurement errors. Finally, the best RNN model is tested on .field data taken on the axial-centrifugal compressor on which the physics-based model was calibrated, by comparing physics-based model and RNN predictions against measured data. The comparison between RNN predictions and measured data shows that the agreement can be considered acceptable for inlet pressure, outlet pressure and outlet temperature, while errors are significant for inlet mass flow rate.

This technical note presents a method of checking the number of complex eigenvalues in some interested regions or the multiplicity of some complex eigenvalues for nonproportionally damped system. A Schur-Cohn matrix is constructed from the coefficients of the characteristic polynomial for the damped system, and [LDL.sup.T] factorized using some standard numerical algorithms. By observing signs of the diagonal elements of the above diagonal matrix D, we can determine the number of complex eigenvalues in some interested regions or the multiplicity of some complex eigenvalues, which is very similar to the well-known Sturm sequence property for undamped systems. To verify the applicability of the proposed method, two numerical examples are considered. CE Database subject headings: Damping; Eigenvalues; Dynamic response.

A genetic algorithm is presented that can simultaneously optimize size, shape, and topology of skeletal structures, including both trusses and frames. The algorithm is unique because it finds multiple optimum and near-optimum topologies in a single run. The algorithm was executed on a bridge example where it found both traditionally recognized bridge topologies as well as less familiar topologies. It was also executed on two standard test problems as well as on a plane frame example. This algorithm presents the designer with more choices and more information than algorithms that converge to a single optimum design. CE Database subject headings: Topology; Trusses; Configuration; Shape; Size; Algorithms; Optimization.

A sampled data control algorithm taking into account external excitations was developed for structural engineering applications. The structure was modeled as a continuous system controlled by a digital control system. In addition to the feedback gain obtained using a conventional control design method, a linear feedforward gain was proposed to improve control efficiency. In order to ensure a satisfactory control performance, an adaptive scheme was developed to adjust this feedforward gain in real time according to the measurement history. The conventional sampled data linear quadratic regulator design was used as a baseline to evaluate the effectiveness of the proposed control algorithm. Some practical issues such as the effects of sampling frequency, time delay and actuator dynamics were addressed. This method was validated on the examples of two multistory shear beam lumped mass models. The numerical examples show that combining both the feedforward and feedback terms can improve the control efficiency significantly as compared to the case with feedback control only. It is also shown that the improvement on the control efficiency obtained with the proposed method is still noticeable when time delay is considered and compensated properly. CE Database subject headings: Data analysis; Excitation; Control systems; Structural control.

The Saint Venant equations are often combined into a single equation for ease of solution. As a result however, this single equation gives rise to several redundant nonlinear terms that may impose significant limitations on model analyses. In order to avoid this, our paper employs a new procedure that separates, in the Laplace frequency domain, the governing equation of water depth from that of flow velocity and thus enables us to consider two independent equations rather than two coupled ones. The so-obtained analytical solutions are valid for prismatic channels of any shape. Solution validity is assured by repeated comparison with the corresponding numerical solutions based on Crump's algorithm, which accelerates solution convergence. Utilizing this new procedure, this paper will construct a basic wave spectrum for classifying subcritical flow waves in a prismatic channel. The spectrum is basically a contour plot of the normalized specific energy loss for a small water wave moving in the channel for a finite distance of approximately 100 m. The distance is chosen so that four distinct regions with different contour patterns that represent kinematic, diffusion, gravity, and dynamic waves in a river are shown in the spectrum. By incorporating the spectrum with Ferrick's criteria and Manning's formula, a single contour line is also generated, which serves as the boundary of the tour regions. Example computations show that the spectrum predicts a similar trend of wave attenuation for waves propagating in a trapezoidal channel. When the rising speed of a wave is of concern, the full Saint Venant equations are solved numerically to reconstruct a similar spectrum good for supercritical flow as well. DOI: 10.106I/(ASCE)0733-9429(2006)132:7(666) CE Database subject headings: Spectra; Open channel flow; Wave propagation.

The accurate simulation of pressure transients in pipelines and pipe networks is becoming increasingly important in water engineering. Applications such as inverse transient analysis for condition assessment, leak detection, and pipe roughness calibration require accurate modeling of transients for longer simulation periods that, in many situations, requires improved modeling of unsteady frictional behavior. In addition, the numerical algorithm used for unsteady friction should be highly efficient, as inverse analysis requires the transient model to be run many times. A popular model of unsteady friction that is applicable to a short-duration transient event type is the weighting function-based type, as first derived by Zielke in 1968. Approximation of the weighting function with a sum of exponential terms allows for a considerable increase in computation speed using recursive algorithms. A neglected topic in the application of such models is evaluation of numerical error. This paper presents a discussion and quantification of the numerical errors that occur when using weighting function-based models for the simulation of unsteady friction in pipe transients. Comparisons of numerical error arising from approximations are made in the Fourier domain where exact solutions can be determined. Additionally, the relative importance of error in unsteady friction modeling and unsteady friction itself in the context of general simulation is discussed. DOI: 10.1061/(ASCE)0733-9429(2006)132:7(709) CE Database subject headings: Frictions; Pipes; Transients; Unsteady flow; Numerical analysis; Errors.

An existing automatic loop shaping algorithm for designing SISO controllers is extended to automatic loop shaping of MIMO controllers that is based on the sequential QFT method. The algorithm is efficient and fast and can search for controllers satisfying many types of restrictions, including constraints on each one of the controller's elements such as hard restrictions on the high-frequency amplitude or damping factor of notch filters. Moreover, the algorithm can be applied to unstructured uncertain plants, be they stable, unstable, or nonminimum phase, including pure delay. [DOI: 10.1115/1.2199856]

A numerical method based on the Rayleigh-Ritz method has been presented for the forced vibration of open cylindrical shells. The equations are derived from the three-dimensional strain-displacement relations in the cylindrical coordinate system. The middle surface of the shell represents the geometry, which is defined by an angle that subtends the curved edges, the length, and the thickness. The displacement fields are generated with a predefined set of grid points on the middle surface using considerably high-order polynomials. Each grid point has five degrees of freedom, viz., three translational components along the cylindrical coordinates and two rotational components of the normal to the middle surface. Then the strain and kinetic energy expressions are obtained in terms of these displacement fields. The differential equation governing the vibration characteristics of the shell is expressed in terms of the mass, stiffness, and the load consistent with the prescribed displacement fields. The transient response of the shell with and without damping is sought by transforming the equation of motion to the state-space model and then the state-space differential equations are solved using the Runge-Kutta algorithm. [DOI: 10.1115/1.2172264] Keywords: vibration, open cylindrical sheil cylindrical panel Rayleigh-Ritz, p-type, state space, Runge-Kutta

The map projection problem involves transforming the graticule of meridians and parallels of a sphere onto a plane using a specified mathematical method according to certain conditions. Map projection transformations are a research field dealing with the method of transforming one kind of map projection coordinates to another. The conversion from geographical to plane coordinates is the normal practice in cartography, which is called forward transformation. The inverse transformation, which yields geographical coordinates from map coordinates, is a more recent development due to the need for transformation between different map projections, especially in Geographic Information Systems (GIS). The direct inverse equations for most of the map projections are already in existence, but for the projections, which have complex functions for forward transformation, defining the inverse projection is not easy. This paper describes an iteration algorithm to derive the inverse equations of the Winkel tripel projection using the Newton--Raphson iteration method. DOI: 10.1061/(ASCE)0733-9453(2005)131:4(125) CE Database subject headings: Computer programming; Mapping; Cartography: Surveys; Geographic information systems.

A probabilistic analysis is presented for studying the variation effects on the main bearing performance of an 1.C. engine system, under structural dynamic conditions. For computational efficiency, the probabilistic analysis is based on surrogate models (metamodels), which are developed using the kriging method. An optimum symmetric Latin hypercube algorithm is used for efficient 'space-filling' sampling of the design space. The metamodels provide an efficient and accurate substitute to the actual engine bearing simulation models. The bearing performance is based on a comprehensive engine system dynamic analysis which couples the flexible crankshaft and block dynamics with a detailed main bearing elastohydrodynamic analysis. The clearance of all main bearings and the oil viscosity comprise the random variables in the probabilistic analysis. The maximum oil pressure and the percentage of time within each cycle that a bearing operates with oil film thickness below a threshold value of 0.27 [micro]m at each main bearing constitute the system performance measures. Probabilistic analyses are first performed to calculate the mean, standard deviation and probability density function of the bearing performance measures. Subsequently, a probabilistic sensitivity analysis is described for identifying the important random variables. Finally, a reliability-based design optimization study is conducted for optimizing the main bearing performance under uncertainty. Results from a V6 engine are presented. [DOI: 10.1115/1.2000268]

The no-slip boundary condition is part of the foundation of the traditional lubrication theory. It states that fluid adjacent to a solid boundary has zero velocity relative to the solid surface. For most practical applications, the no-slip boundary condition is a good model for predicting fluid behavior. However, recent experimental research has found that for certain engineered surfaces the no-slip boundary condition is not valid. Measured velocity profiles show that slip occurs at the interface. In the present study, the effect of an engineered slip/no-slip surface on journal bearing performance is examined. A heterogeneous pattern, in which slip occurs in certain regions and is absent in others, is applied to the bearing surface. Fluid slip is assumed to occur according to the Navier relation. Analysis is performed numerically using a mass conserving algorithm for the solution of the Reynolds equation. Load carrying capacity, side leakage rate, and friction force are evaluated. In addition, results are presented in the form of Raimondi and Boyd graphs. It is found that the judicious application of slip to a journal bearing's surface can lead to improved bearing performance. [DOI: 10.1115/1.2033897]

In this paper, we will present a nonlinear-model-based adaptive semiactive control algorithm developed for magnetorheological (MR) suspension systems exposed to broadband nonstationary random vibration sources that are assumed to be unknown or not measurable. If there exist unknown and/or varying parameters of the dynamic system such as mass and stiffness, then the adaptive algorithm can include on-line system identification such as a recursive least-squares method. Based on a nonparametric MR damper model, the adaptive system stability is proved by converting the hysteresis inherent with MR dampers to a memoryless nonlinearity with sector conditions. The convergence of the adaptive system, however, is investigated through a linearization approach including further numerical illustration of specific cases. Finally the simulation results for a magnetorheological seat suspension system with the suggested adaptive control are presented. The results are compared with low-damping and high-damping cases, and such comparison further shows the effectiveness of the proposed nonlinear model-based adaptive control algorithm for damping tuning. [DOI: 10.1115/1.2013295]

One challenge in the application of control systems to civil engineering structures is appropriate integration of a control system into a structure to achieve effective performance. Placement of control devices is strongly linked to the performance of a control system, and the most appropriate device placement scheme is strongly dependent on the performance objectives of the control system. Additionally, for the most effective control system, the placement scheme should be integrated with the design of the controller rather than sequential. This paper proposes an integrated technique to place devices and design controllers based on the use of genetic algorithms. The approach is flexible, allowing the designer to base the placement scheme on performance goals and/or system requirements. Active control devices are used and an [H.sub.2]/LQG controller based on acceleration feedback is selected for this study based on previous successes with this approach in civil engineering systems. To illustrate the proposed methodology, two numerical examples are considered. The first example considers a 40-story shear building, and the second is a full-scale, irregular, nine-story building. Control is achieved through the placement of one or more active control devices placed on various floors in an active bracing configuration. The improvements in the effectiveness of the proposed methodology as compared to previously developed techniques are demonstrated through comparative studies. DOI: 10.1061/(ASCE)0733-9445(2005)131:10(1489) CE Database subject headings: Active control: Algorithms; Protective structures; Structural design; Control systems.

A genetic algorithm (GA), a well-known numerical method, is widely applied in different areas of optimal studies. It is found that if the solution-search space is wide or if the selected fitness function is highly nonlinear, the GA's solutions can strongly depend on the set parameters, which include population size, crossover rate, mutation rate, and the remaining size of the parent in the GA. This paper combines the Taguchi experimental method, which serves as a rough search tool, with the GA, which serves as a fine search tool, to find the best combination of the GA parameters for different flight-control problems. The purpose of such a combination is to make control more robust and closer to the optimal solution. To demonstrate this new idea, the writers consider its application to different flight-control problems for the F-16 fighter by using autostabilization, linear quadratic regulator (LQR) and [H.sub.[infinity]] design. The simulation results not only achieve the expected optimal design for flight-control problems but also justify the reliability and feasibility of the combination of the GA and the Taguchi method. DOI: 10.1061/(ASCE)0893-1321(2005)18:4(232) CE Database subject headings: Algorithms; Aerospace engineering; Aircraft; Control; Design.

Focusing errors in optical disk drives comprise significant periodic components and an eventful dc content. The dc component is not explicitly taken into account in many periodic compensation methods. This paper investigates the design of adaptive feedforward cancellation (AFC) and frequency adaptive control technique (FACT) algorithms for periodic components as well as dc disturbance compensation. Both algorithms are applied as a plug-in module to an optical disk drive for demonstrating their facility in the reduction of focusing errors. By making good use of frequency sampling filter (FSF), the real-time harmonic identification can be fulfilled in FACT method for various playing speeds. Analysis and experimental results show that FACT has better properties than AFC in terms of dc cancellation and harmonic independence. It is also shown that AFC fails when both the dc content and harmonics are compensated simultaneously: [DOI: 10.1115/1.1988339]

This paper presents a robust noniterative algorithm for the design of controllers of a given structure satisfying frequency-dependent sensitivity specifications. The method is well suited for automatic loop shaping, particularly in the context of Quantitative Feedback Theory (QFT), and offers several advantages, including (i) it can be applied to unstructured uncertain plants, be they stable, unstable or nonminimum phase, (ii) it can be used to design a satisfactory controller of a given structure for plants which are typically difficult to control, such as highly underdamped plants, and (iii) it is suited for design problems incorporating hard restrictions such as bounds on the high-frequency gain or damping of a notch filter. It is assumed that the designer has some idea of the controller structure appropriate for the loop shaping problem. [DOI: 10.1115/1.1985441] Keywords: Automatic Loop Shaping, Robust Control, QFT, Linear Feedback Systems

Scaling laws provide a simple yet meaningful representation of the dominant factors of complex engineering systems, and thus are well suited to guide engineering design. Current methods to obtain useful models of complex engineering systems are typically ad hoc, tedious, and time consuming. Here, we present an algorithm that obtains a scaling law in the form of a power law from experimental data (including simulated experiments). The proposed algorithm integrates dimensional analysis into the backward elimination procedure of multivariate linear regressions. In addition to the scaling laws, the algorithm returns a set of dimensionless groups ranked by relevance. We apply the algorithm to three examples, in each obtaining the scaling law that describes the system with minimal user input. [DOI: 10.1115/1.1943434]

Adaptive design refers to experimental design where the next sample point is determined by information from previous experiments. This article presents a constrained optimization algorithm known as superEGO (a variant of the EGO algorithm of Schonlau, Welch, and Jones) that can create adaptive designs using kriging approximations. Our primary goal is to illustrate that superEGO is well-suited to generating adaptive designs which have many advantages over competing methods. The approach is demonstrated on a novel human-reach experiment where the selection of sampling points adapts to the individual test subject. Results indicate that superEGO is effective at satisfying the experimental objectives. [DOI: 10.1115/1.1906247]

A tabu-gradient search is herein presented for optimum synthesis of planar mechanisms. The solution generated by a recency-based, short term memory tabu search is used to start a gradient search to drive the solution ever closer to the global minimum. A brief overview of the tabu-search method is first presented. A tabu-gradient algorithm is then used to synthesize four-bar mechanisms for path generation tasks by way of three examples, including two benchmark examples used before to test other deterministic and intelligent optimization schemes. Compared with the corresponding results generated by other schemes, the tabu-gradient search rendered the most optimal solutions of all. [DOI: 10.1115/1.1904640]

This paper presents a novel method for the automated type synthesis of planar mechanisms and multibody systems. The method explicitly includes topology as a design variable in an optimization framework based on a genetic algorithm (GA). Each binary string genome of the GA represents the concatenation of the upper-right triangular portion of the link adjacency matrix of a mechanism. Different topologies can be explored by the GA by applying genetic operators to the genomes. The evolutionary process is not dependent on the results obtained from enumeration. Two examples of topology-based optimization show the applicability of this method to mechanism type synthesis problems. This method is distinct from others in the literature in that it represents the first fully automated algorithm for solving a general type synthesis problem with the help of a numeric optimizer. [DOI: 10.1115/1.1904049]

It is known in literature that a wheeled mobile robot (WMR), with fixed length axle, will undergo slip when it negotiates an uneven terrain. However, motion without slip is desired in WMR's, since slip at the wheel-ground contact may result in significant wastage of energy and may lead to a larger burden on sensor based navigation algorithms. To avoid slip, the use of a variable length axle (VLA) has been proposed in the literature and the kinematics of the vehicle has been solved depicting no-slip motion. However, the dynamic issues have not been addressed adequately and it is not clear if the VLA concept will work when gravity and inertial loads are taken into account. To achieve slip-free motion on uneven terrain, we have proposed a three-wheeled WMR architecture with torus shaped wheels, and the two rear wheels having lateral tilt capability. The direct and inverse kinematics problem of this WMR has been solved earlier and it was shown by simulation that such a WMR can travel on uneven terrain without slip. In this paper, we derive a set of 27 ordinary differential equations (ODES) which form the dynamic model of the three-wheeled WMR. The dynamic equations of motion have been derived symbolically using a Lagrangian approach and computer algebra. The holonomic and nonholonomic constraints of constant length and no-slip, respectively, are taken into account in the model. Simulation results clearly show that the three-wheeled WMR can achieve no-slip motion even when dynamic effects are taken into consideration. [DOI: 10.1115/1.1867503]

This study deals with a method to identify structural damage using the combined finite element method and the advanced uniform microgenetic algorithm. The novelty of this study is the use of dynamic loading and its response due to the anomalies in a structure under testing. The technique described in this paper may allow us not only to detect the damaged elements but also to find their numbers, locations, and the extent of damage. To demonstrate the feasibility of the method, the algorithm is applied to a cantilever beam and plate structures with defects. In addition, a laminated composite plate is tested numerically using the first shear deformation theory, and the effect of noise is simulated to study the influence of measurement errors and uncertainty of the method. The results demonstrate the excellencies of the method from the standpoints of computation efficiency as well as its ability to avoid premature convergence. CE Database subject headings: Damage assessment: Dynamic response: Finite element method; Algorithms.

Different methods are proposed in literature using experimental modal information to detect possible damage. In this paper a finite-element (FE) model updating technique is applied. The unknown properties of a FE model are adapted, such that the differences between experimental modal data (modal curvature in combination with eigenfrequencies and mode shapes) and the corresponding analytical predictions are minimized. An iterative sensitivity based algorithm is used for solving this optimization problem. The method is applied to the damage assessment of a gradually damaged prestressed concrete beam. It is assumed, that damage can be characterized by reducing the bending stiffness. The main focus of this paper is to analyze the influence of using modal curvatures. In contrast to eigenfrequencies and mode shapes, modal curvatures are very sensitive to local changes of the bending stiffness nearby the sensor location, but insensitive to local changes far from the measurement location. CE Database subject headings: Damage; Concrete, prestressed; Modal analysis; Curvature; Bending; Finite element method; Optimization; Identification.

In urban areas, when heavy rains occur, the discharge capacity of sewers is usually unable to transport the effective rainfall reaching the streets. When the runoff flow rate exceeds the capacity of the storm sewer system, the excess flow' is conveyed through the street network as overland flow. A dual model is proposed for modeling the system as a double network, formed by an upper network of open channels (street gutters) and a lower network of closed conduits (sewer pipes). What is new in this model is its capacity to take into account the hydrodynamic relationship between the flows in the upper and lower networks. The model is applied to computing the response of a real monitored basin; the historical flow rates measured during a first rainfall event are used to calibrate the model, which is then validated using the simulation of two other measured events. CE Database subject headings: Urban runoff; Surface runoff; Outfall sewers; Hydraulic models; Surcharge; Algorithms.

Large admissible perturbations (LEAP) is a general methodology, which solves redesign problems of complex structures with, among others, forced response amplitude constraints. In previous work, two LEAP algorithms, namely the incremental method (IM) and the direct method (DM), were developed. A powerful feature of LEAP is the general perturbation equations derived in terms of normal modes, the selection of which is a determinant factor for a successful redesign. The normal modes of a structure may be categorized as stretching, bending, torsional, and mixed modes and grouped into cognate spaces. In the context of redesign by LEAP, the physical interpretation of a mode-to-response cognate space lies in the fact that a mode from one space barely affects change in a mode from another space. Perturbation equations require computation of many perturbation terms corresponding to individual modes. Identifying modes with negligible contribution to the change in forced response amplitude eliminates a priori computation of numerous perturbation terms. Two methods of determining mode-to-response cognate spaces, one for IM and one for DM, are presented and compared. Trade-off between computational time and accuracy is assessed in order to provide practical guidelines to the designer. The developed LEAP redesign algorithms are applied to the redesign of a simple cantilever beam and a complex offshore tower. [DOI: 10.1115/1.1979512]

Particleboard panels are widely utilized as a raw material in the wood processing industry. It ends up as furniture, cabinets, and other industrial products. One of the problems particleboard mills face concerns the surface quality of their boards. As the demands of customers become more precise, very thin overlays are becoming more popular. Thus the problem of surface quality control and classification is clearly identified. In this paper, a particleboard surface-roughness classification system is modeled, simulated, and implemented. The particleboard model is based on the characterization of surface anomalies (pinholes, sander streaks, and grooves). Furthermore, an optical stylus surface-roughness measurement system is also modeled in order to determine whether it can be used to characterize a particleboard 'on-ine.' A classification algorithm is proposed to serve as an aid to the quality control operator. Simulation results are presented illustrating the change of surface roughness with increasing amounts of surface anomalies. A classification algorithm is used to sort the simulated panels into different classes. A trial bench test using 225 panels is made to determine the applicability of this system to the industrial context. [DOI: 10.1115/1.1954795] Keywords: Particleboard, Surface Anomalies, Roughness Measurement, Modeling, Simulation, Classification, Quality Control, Wood Board Sanding

This work combines experimental studies with finite element simulations to develop a reliable numerical model for the simulation of shearing process in aluminum alloys. The critical concern with respect to product quality in this important process is burr formation. Numerical simulations are aimed at understanding the role of process variables on burr formation and for recommending process design parameters. The commercial code ABAQUS-Explicit with the arbitrary Lagrangian-Eulerian kinematic description is used in this study for numerical simulations. An elastic-plastic constitutive model with experimentally validated damage models are incorporated through the user subroutine VUMAT in ABAQUS, for modeling deformation and ductile fracture in the material. Macroscopic experiments with microscopic observations are conducted to characterize the material and to calibrate the constitutive and damage models. Parametric study is done to probe the effect of process parameters and finally, a genetic algorithm (GA) based design method is used to determine process parameters for minimum burr formation. [DOI: 10.1115/1.1951787]

In this paper, a macromodeling methodology for lateral air damping effect is presented. This methodology employs a simplified governing equation, the Quasi-3D (Q3D) Stokes equation, and an Arnoldi-based model-order-reduction algorithm. A finite-difference (FDM) solver based on the Q3D-Stokes equation is implemented, and then the Arnoldi-based algorithm is used to create macromodels from the system matrices generated by the solver. This methodology can also be realized by using commercial MEMS packages for solid-model generation, and by using commercial finite-element (FEM) thermal packages for system-matrix generation. The generated macromodels are compatible with system-level modeling simulators, such as SPICE, Saber, of Simulink for fast transient and frequency analyses. It is demonstrated that the macromodels are at least 600 times more efficient than the FDM Q3D Stokes solver, while are still capable of capturing the three-dimensional (3-D) effect that usually requires very expensive 3-D FEM Stokes-flow calculations. Experimental results of comb-drive devices show that the error of the macromodel is less than 10%, which is a significant improvement when compared with the results by widely used 1-D analytical approaches. Finally, the guidelines of using this macromodeling methodology for typical MEMS devices are also provided. [1262] Index Terms--Arnoldi algorithm, lateral air damping, macro-model, stokes equation, system-level analysis.

Modern road profilers deliver long sequences of measurements on road characteristics including a road's longitudinal and transversal unevenness. These measurements represent adjacent parts of the physical road, and interest focuses more on the overall pattern of these measurements than on each single value. In order to systematically assess the information contained in these measurement series, one typically wishes to partition a given series into segments, where each segment contains measurements which are 'similar' to each other but 'dissimilar' to the elements in the neighboring segments. An algorithm is suggested that combines a recently developed Bayesian identification of transitions between two homogeneous road sections with a heuristic approach that uses this technique iteratively to find multiple homogeneous sections in arbitrary long measurement series. The approach is demonstrated with narrowly spaced measurement series of the international roughness index as well as rutting. DOI: 10.1061/(ASCE)0733-947X(2005)131:8(591) CE Database subject headings: Highway maintenance; Pavement management; Pavement condition; Road surface; Segmented elements; Homogeneity; Bayesian analysis; Statistical analysis.

In this paper, global positioning system (GPS) data collected by seven permanent GPS stations of Southern California Integrated GPS Network during the launch of the long-range Minuteman II missile from Vandenberg Air Force Base on July 8, 2000 is processed. By manipulating and passing the total electron content through a high-pass filter, the energy released by the missile launch was detected. After that, the basic concept of positioning used in GPS is applied to the problem to pinpoint the position of the missile launch pad. This is done by the implementation of the concept of subionospheric points that serve analogously to GPS satellites. The simulation of the analysis with prior data proves that the launch pad can indeed be positioned with this algorithm. However, real-life analysis without prior data highlights the existence of three problems that need to be overcome to pinpoint that pad. DOI: 10.1061/(ASCE)0733-9453(2005)131:3(78) CE Database subject headings: Geographic information systems; Data collection; California; Positioning.

This paper describes an automatic approach in architectural photogrammetry for the documentation and analysis of historic facades. Multispectral close-range images were taken and evaluated for identification of masonry wall materials. Digital image processing and close-range photogrammetric techniques were used to identify, nondestructively recognize, and map the materials and damages of a historic facade. Two supervised classification algorithms were analyzed: Maximum likelihood and minimum distance. Although the maximum likelihood was somewhat slower, it provides much higher classification accuracy than the minimum distance classifier. Additional to the statistical data, thematic images were obtained semiautomatically for visualization, management, and decision-making purposes. DOI: 10.1061/(ASCE)0733-9453(2005)131:3(73) CE Database subject headings: Photogrammetry; Imaging techniques; Digital techniques; Classification; Architecture; Plotting.

Dynamic programming algorithms guarantee to find the optimal alignment between two sequences. For more than a few sequences, exact algorithms become computationally impractical, and progressive algorithms iterating pairwise alignments are widely used. These heuristic methods have a serious drawback because pairwise algorithms do not differentiate insertions from deletions and end up penalizing single insertion events multiple times. Such an unrealistically high penalty for insertions typically results in overmatching of sequences and an underestimation of the number of insertion events. We describe a modification of the traditional alignment algorithm that can distinguish insertion from deletion and avoid repeated penalization of insertions and illustrate this method with a pair hidden Markov model that uses an evolutionary scoring function. In comparison with a traditional progressive alignment method, our algorithm infers a greater number of insertion events and creates gaps that are phylogenetically consistent but spatially less concentrated. Our results suggest that some insertion/deletion 'hot spots' may actually be artifacts of traditional alignment algorithms. insertion/deletion | progressive algorithm | sequence alignment