Design Parameters (design + parameter)

Distribution by Scientific Domains
Distribution within Engineering

Kinds of Design Parameters

  • optimal design parameter

  • Selected Abstracts

    Improved design method for optimum gain pyramidal horns

    Kerim Gney
    Abstract A technique, simple and easy to use, is presented to design the optimum gain pyramidal horn. The optimum gain pyramidal horn design equation available in the literature is improved. Design parameters are computed from the simple and explicit analytical formulas. The pyramidal horn gain is determined with no path length error approximation. Several design examples are given to show the performance of the improved design technique. 2001 John Wiley & Sons, Inc. Int J RF and Microwave CAE 11: 188,193, 2001. [source]

    Microstrip stepped-impedance hairpin resonator low-pass filter with defected ground structure

    Ju-Hyun Cho
    Abstract In this paper, a new microstrip stepped-impedance hairpin resonator (SIR) low-pass filter (LPF) using a defected ground structure (DGS) is proposed. The proposed SIR hairpin low-pass filter using DGS provides a very sharp cutoff frequency response with low insertion loss. Furthermore, the SIR hairpin low-pass filter can provide attenuation poles for the wide-stopband characteristic due to the resonance characteristic of the DGS. Design parameters for the SIR low-pass filter are derived based on stepped-impedance theory and the equivalent-circuit model for the DGS. The experimental results show excellent agreement with the theoretical simulation results. 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 405,408, 2006; Published online in Wiley InterScience ( DOI 10.1002/mop.21364 [source]

    The concept of work compatibility: An integrated design criterion for improving workplace human performance in manufacturing systems

    S. Abdallah
    In this paper, we present the concept of work compatibility as an integrated work design criterion that simultaneously improves human health and safety, productivity, and work quality in manufacturing systems. In this respect, we have modeled work compatibility as a work design parameter that mathematically integrates the energizing (i.e., system resources) and the demand (i.e., system requirements) forces in the work system. A mathematical equation has been derived for the work compatibility matrix. Furthermore, an operating zone has been developed in which there is a region of optimality for the employee to function on practical grounds with a good degree of efficiency and sustainability. An application example is provided to demonstrate the potential of work compatibility to improve productivity and quality along with improvement in worker safety and health. 2004 Wiley Periodicals, Inc. Hum Factors Man 14: 379,402, 2004. [source]

    A stabilized pseudo-shell approach for surface parametrization in CFD design problems

    O. Soto
    Abstract A surface representation for computational fluid dynamics (CFD) shape design problems is presented. The surface representation is based on the solution of a simplified pseudo-shell problem on the surface to be optimized. A stabilized finite element formulation is used to perform this step. The methodology has the advantage of being completely independent of the CAD representation. Moreover, the user does not have to predefine any set of shape functions to parameterize the surface. The scheme uses a reasonable discretization of the surface to automatically build the shape deformation modes, by using the pseudo-shell approach and the design parameter positions. Almost every point of the surface grid can be chosen as design parameter, which leads to a very rich design space. Most of the design variables are chosen in an automatic way, which makes the scheme easy to use. Furthermore, the surface grid is not distorted through the design cycles which avoids remeshing procedures. An example is presented to demonstrate the proposed methodology. Copyright 2002 John Wiley & Sons, Ltd. [source]

    Design of a near-optimal adaptive filter in digital signal processor for active noise control

    S. M. Yang
    Abstract Adaptive filter has been applied in adaptive feedback and feedforward control systems, where the filter dimension is often determined by trial-and-error. The controller design based on a near-optimal adaptive filter in digital signal processor (DSP) is developed in this paper for real-time applications. The design integrates the adaptive filter and the experimental design such that their advantages in stability and robustness can be combined. The near-optimal set of controller parameters, including the sampling rate, the dimension of system identification model, the dimension (order) of adaptive controller in the form of an FIR filter, and the convergence rate of adaptation is shown to achieve the best possible system performance. In addition, the sensitivity of each design parameter can be determined by analysis of means and analysis of variance. Effectiveness of the adaptive controller on a DSP is validated by an active noise control experiment. Copyright 2007 John Wiley & Sons, Ltd. [source]

    Low power switched-current circuits with low sensitivity to the rise/fall time of the clock

    Radek Rudnicki
    Abstract The switched-current (SI) technique permits realizing analog discrete-time circuits in standard digital CMOS technology. A very important property of the analog part of a system on a chip is the possibility it offers for realizing some functions of a digital circuit, but with reduced power consumption. In this paper, a low power SI integrator is presented. It is shown that an integrator consuming a fraction of a milliwatt can be designed in 0.35m CMOS technology with the use of narrow transistor channels, and with the channel length as a design parameter. The impact of the rise/fall time of the clock signal on the integrator operation is observed. It is shown that this effect can be reduced when the proper switch dimensions are taken for the integrator. Analysis and measurements of the integrator noise are presented. The integrator was built with equal size transistors, yielding less sensitivity to variations in production parameters. An experimental chip in 0.35m CMOS technology was fabricated, and measurements are compared with results obtained during analysis and simulations. In order to verify the properties of the designed integrator experimentally, a first-order filter is built with the use of elementary cells on the chip. Copyright 2008 John Wiley & Sons, Ltd. [source]

    Efficient power analysis for an irreversible Carnot heat engine

    Tamer Yilmaz
    Abstract In this paper, the finite-time thermodynamic optimization is carried out based on the efficient power criterion for an irreversible Carnot heat engine. The obtained results are compared with those obtained by using the maximum power (MP) and maximum power density (MPD) criteria. The optimal design parameters have been derived analytically, and the effect of the irreversibilities on the general and optimal performances is investigated. Maximizing the efficient power gives a compromise between power and efficiency. The results showed that the design parameter at the maximum efficient power (MEP) condition leads to more efficient engines than at the MP conditions and that the MEP criterion may have a significant power advantage with respect to the MPD criterion. Copyright 2007 John Wiley & Sons, Ltd. [source]

    Optimal hold functions for MDCS sampled-data problems

    Leonid Mirkin
    Abstract In this paper the H2 and H, sampled-data problems with mixed discrete/continuous specifications (MDCS) are considered. The hold function is not fixed a priory but rather is the design parameter. The (sub)optimal controller obtained is of the form of a serial interconnection of a (sub)optimal digital controller and a (sub)optimal hold function. It is demonstrated that the incorporation of the hold function into the sampled-data design with MDCS extends considerably the possibility to reach a required trade-off between discrete and continuous specifications in comparison with designs with a fixed hold function. Copyright 2003 John Wiley & Sons, Ltd. [source]

    Analysis and optimization of low-pressure drop static mixers

    AICHE JOURNAL, Issue 9 2009
    Mrityunjay K. Singh
    Abstract Various designs of the so called Low-Pressure Drop (LPD) static mixer are analyzed for their mixing performance using the mapping method. The two types of LPD designs, the RR and RL type, show essentially different mixing patterns. The RL design provides globally chaotic mixing, whereas the RR design always yields unmixed regions separated by KAM boundaries from mixed regions. The crossing angle between the elliptical plates of the LPD is the key design parameter to decide the performance of various designs. Four different crossing angles from 90 to 160 are used for both the RR and RL designs. Mixing performance is computed as a function of the energy to mix, reflected in overall pressure drop for all designs. Optimization using the flux-weighted intensity of segregation versus pressure drop proves the existence of the best mixer with an optimized crossing angle. The optimized angle proves to be indeed the LLPD design used in practice: the RL-120 with , = 120, although RL-140 , = 140 performs as good. Shear thinning shows minor effects on the mixing profiles, and the main optimization conclusions remain unaltered. 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]

    Behavior of fully filled regions in a non-intermeshing twin-screw extruder

    Rajath Mudalamane
    Twin-screw extruders are operated with sequential filled and partially filled regions in order to perform the required unit processes. Channel fill length, defined as the length of fully filled regions in an extrusion screw, is gaining importance as a design parameter because of its implications on residence time distribution, distributive and dispersive mixing, and also process stability. A detailed study,experimental and theoretical,of the behavior of fill lengths in response to operating conditions (throughput, screw speed) and screw geometry is presented in this paper. Mean residence times were also measured for each geometry and operating condition. The apparatus consisted of a non-intermeshing counter-rotating twin-screw extruder (NITSE) with a transparent (acrylic) barrel, fed with corn syrup (Newtonian at room temperature). Fill length exhibits a nonlinear relationship with specific throughput (Q/N), with the slope increasing monotonously as the throughput Q increases at a given screw speed N. The mean residence time exhibits a strong linear relationship with inverse specific throughput and inverse fill length. A theoretical model was developed to predict the filled length based on pressure-throughput relationships taken from literature for this system, and the predictions were found to agree very well with experimental observations. [source]

    Usability in space science instrumentation

    ASTRONOMY & GEOPHYSICS, Issue 6 2009
    Article first published online: 23 NOV 200
    The scientists who will eventually use data from a space instrument may not be the most important people to consider during the development programme, argues Alec McCalden. Better results could come from treating instrument usability as a design parameter from the start. [source]

    Oxygen transport and consumption by suspended cells in microgravity: A multiphase analysis

    Ohwon Kwon
    Abstract A rotating bioreactor for the cell/tissue culture should be operated to obtain sufficient nutrient transfer and avoid damage to the culture materials. Thus, the objective of the present study is to determine the appropriate suspension conditions for the bead/cell distribution and evaluate oxygen transport in the rotating wall vessel (RWV) bioreactor. A numerical analysis of the RWV bioreactor is conducted by incorporating the Eulerian,Eulerian multiphase and oxygen transport equations. The bead size and rotating speed are the control variables in the calculations. The present results show that the rotating speed for appropriate suspensions needs to be increased as the size of the bead/cell increases: 10 rpm for 200 m; 12 rpm for 300 m; 14 rpm for 400 m; 18 rpm for 600 m. As the rotating speed and the bead size increase from 10 rpm/200 m to 18 rpm/600 m, the mean oxygen concentration in the 80% midzone of the vessel is increased by ,85% after 1-h rotation due to the high convective flow for 18 rpm/600 m case as compared to 10 rpm/200 m case. The present results may serve as criteria to set the operating parameters for a RWV bioreactor, such as the size of beads and the rotating speed, according to the growth of cell aggregates. In addition, it might provide a design parameter for an advanced suspension bioreactor for 3-D engineered cell and tissue cultures. Biotechnol. Bioeng. 2008;99: 99,107. 2007 Wiley Periodicals, Inc. [source]

    Topology Design of Truss Structures in a Multicriteria Environment

    Won-Sun Ruy
    As an analogy of the general design process, this article presents a novel design approach that could generate structural design alternatives having different topologies and then select the optimal structures from them together with simultaneously determining the optimal design variables related to geometry and member size subjected to a multiple objective design environment. For this purpose, a specialized genetic algorithm, called StrGA_DeAl+MOGA, that can handle the design alternatives and multicriteria problems very effectively is developed for the optimal structural design. To validate the developed method, plain-truss design problems are considered as illustrative examples. To begin with, the promising topologies are generated under the name of "design alternatives" with consideration of the given multiobjective environment. Based on the selected topology of truss structures, the sizing or geometric optimization process starts to determine the optimal design parameters. Three-bar and ten-bar truss problems are treated in the article to test the concept and methodology. [source]

    Self-centering structural systems with combination of hysteretic and viscous energy dissipations

    Weng Yuen Kam
    Abstract This paper presents an innovative set of high-seismic-resistant structural systems termed Advanced Flag-Shaped (AFS) systems, where self-centering elements are used with combinations of various alternative energy dissipation elements (hysteretic, viscous or visco-elasto-plastic) in series and/or in parallel. AFS systems is developed using the rationale of combining velocity-dependent with displacement-dependent energy dissipation for self-centering systems, particularly to counteract near-fault earthquakes. Non-linear time-history analyses (NLTHA) on a set of four single-degree-of-freedom (SDOF) systems under a suite of 20 far-field and 20 near-fault ground motions are used to compare the seismic performance of AFS systems with the conventional systems. It is shown that AFS systems with a combination in parallel of hysteretic and viscous energy dissipations achieved greater performance in terms of the three performance indices. Furthermore, the use of friction slip in series of viscous energy dissipation is shown to limit the peak response acceleration and induced base-shear. An extensive parametric analysis is carried out to investigate the influence of two design parameters, ,1 and ,2 on the response of SDOF AFS systems with initial periods ranging from 0.2 to 3.0,s and with various strength levels when subjected to far-field and near-fault earthquakes. For the design of self-centering systems with combined hysteretic and viscous energy dissipation (AFS) systems, ,1 is recommended to be in the range of 0.8,1.6 while ,2 to be between 0.25 and 0.75 to ensure sufficient self-centering and energy dissipation capacities, respectively. Copyright 2010 John Wiley & Sons, Ltd. [source]

    Effect of cumulative seismic damage and corrosion on the life-cycle cost of reinforced concrete bridges

    R. Kumar
    Abstract Bridge design should take into account not only safety and functionality, but also the cost effectiveness of investments throughout a bridge life-cycle. This paper presents a probabilistic approach to compute the life-cycle cost (LCC) of corroding reinforced concrete (RC) bridges in earthquake-prone regions. The approach is developed by combining cumulative seismic damage and damage associated with corrosion due to environmental conditions. Cumulative seismic damage is obtained from a low-cycle fatigue analysis. Chloride-induced corrosion of steel reinforcement is computed based on Fick's second law of diffusion. The proposed methodology accounts for the uncertainties in the ground motion parameters, the distance from the source, the seismic demand on the bridge, and the corrosion initiation time. The statistics of the accumulated damage and the cost of repairs throughout the bridge life-cycle are obtained by Monte-Carlo simulation. As an illustration of the proposed approach, the effects of design parameters on the LCC of an example RC bridge are studied. The results are valuable in better estimating the condition of existing bridges and, therefore, can help to schedule inspection and maintenance programs. In addition, by taking into consideration the two deterioration processes over a bridge life-cycle, it is possible to estimate the optimal design parameters by minimizing, for example, the expected cost throughout the life of the structure. A comparison between the effects of the two deterioration processes shows that, in seismic regions, the cumulative seismic damage affects the reliability of bridges over time more than the corrosion even for corrosive environments. Copyright 2008 John Wiley & Sons, Ltd. [source]

    Earthquake-resistant structural design through energy demand and capacity

    Adang Surahman
    Abstract An energy-based earthquake-resistant structural design method is proposed. The proposed method uses specific input energy spectra, modal or time-history analyses, and energy distribution among structural members. For a given member strength and stiffness, a relationship between the energy attributable to damage absorbed by a member and its cumulative ductility demand can be determined. Member strength, stiffness and energy capacity are design parameters which are simultaneously used in the design. The method can avoid soft-storey design. The damage is measured based on a cumulative basis considering earthquake magnitude, frequency, and duration. Tests have been carried out to determine energy absorbing capacities of various structural components. More efforts are needed to make the energy-based earthquake-resistant structural design practical, but ssimple formulations for this method are possible. Copyright 2007 John Wiley & Sons, Ltd. [source]

    Tuned mass dampers for response control of torsional buildings

    Mahendra P. Singh
    Abstract This paper presents an approach for optimum design of tuned mass dampers for response control of torsional building systems subjected to bi-directional seismic inputs. Four dampers with fourteen distinct design parameters, installed in pairs along two orthogonal directions, are optimally designed. A genetic algorithm is used to search for the optimum parameter values for the four dampers. This approach is quite versatile as it can be used with different design criteria and definitions of seismic inputs. It usually provides a globally optimum solution. Several optimal design criteria, expressed in terms of performance functions that depend on the structural response, are used. Several sets of numerical results for a torsional system excited by random and response spectrum models of seismic inputs are presented to show the effectiveness of the optimum designs in reducing the system response. Copyright 2002 John Wiley & Sons, Ltd. [source]

    Characterization of voltage degradation in dynamic field gradient focusing

    ELECTROPHORESIS, Issue 5 2008
    Jeffrey M. Burke
    Abstract Dynamic field gradient focusing (DFGF) is an equilibrium gradient method that utilizes an electric field gradient to simultaneously separate and concentrate charged analytes based on their individual electrophoretic mobilities. This work describes the use of a 2-D nonlinear, numerical simulation to examine the impact of voltage loss from the electrodes to the separation channel, termed voltage degradation, and distortions in the electric field on the performance of DFGF. One of the design parameters that has a large impact on the degree of voltage degradation is the placement of the electrodes in relation to the separation channel. The simulation shows that a distance of about 3,mm from the electrodes to the separation channel gives the electric field profile with least amount of voltage degradation. The simulation was also used to describe the elution of focused protein peaks. The simulation shows that elution under constant electric field gradient gives better performance than elution through shallowing of the electric field. Qualitative agreement between the numerical simulation and experimental results is shown. The simulation also illustrates that the presence of a defocusing region at the cathodic end of the separation channel causes peak dispersion during elution. The numerical model is then used to design a system that does not suffer from a defocusing region. Peaks eluted under this design experienced no band broadening in our simulations. Preliminary experimental results using the redesigned chamber are shown. [source]

    Baghouse system design based on economic optimization

    Antonio C. Caputo
    In this paper a method is described for using economic optimization in the design of baghouse systems. That is, for a given emission control problem, the total filtration surface area, the overall pressure drop, fabric material effects, and the cleaning cycle frequency, may all be evaluated simultaneously. In fact, as baghouse design parameters affect capital and operating expenses in interrelated and counteracting manners, a minimum total cost may be searched defining the best arrangement of dust collection devices. With this in mind, detailed cost functions have been developed with the aim of providing an overall economic model. As a result, a discounted total annual cost has been obtained that may be minimized by allowing for optimal baghouse characterization. Finally, in order to highlight the capabilities of the proposed methodology, some optimized solutions are also presented, which consider the economic impact of both bag materials and dust properties. [source]

    Optimal design of an induction motor for an electric vehicle

    Jawad Faiz
    Abstract In this paper a squirrel-cage three-phase induction motor, selected as the driving power of an electric vehicle (EV), is designed optimally using a modified-Hooke,Jeeves optimization technique. The optimal designs are analyzed and compared with varying pole number, rated base speed and slot shapes. This optimization technique has the same advantages such as simple programming, non-gradient, short convergence time and independent variation of each parameter. Variation of design parameters of optimally designed motors versus rated base speed for 2- and 4-pole motors are presented and discussed. The results show that a 2-pole motor with parallel-sided stator and rotor slots and rated speed 1800,rpm has the best performance. Copyright 2005 John Wiley & Sons, Ltd. [source]

    Fixed relaying with adaptive antenna arrays for the downlink of multihop cellular networks

    Zaher Dawy
    Multihop cellular networks are expected to play an important role in the evolution towards 4G. In this work, we propose the use of advanced antenna techniques (adaptive antenna arrays and directional antennas) at fixed relay stations in order to enhance the downlink performance of multihop cellular networks. The performance gains of various adaptive antenna configurations are analytically studied by introducing a new system-level parameter called the interference reduction factor. Moreover, Monte-Carlo simulation results as a function of various design parameters are presented and analysed in order to further highlight the gains of advanced antenna techniques. Based on the presented analysis, we propose the use of a hybrid antenna configuration at relay stations in order to obtain high gains with limited increase in complexity and cost. Copyright 2010 John Wiley & Sons, Ltd. [source]

    Development of an Expert System Shell Based on Genetic Algorithms for the Selection of the Energy Best Available Technologies and their Optimal Operating Conditions for the Process Industry

    EXPERT SYSTEMS, Issue 3 2001
    D.A. Manolas
    The development of genetic algorithms started almost three decades ago in an attempt to imitate the mechanics of natural systems. Since their inception, they have been applied successfully as optimization methods, and as expert systems, in many diverse applications. In this paper, a genetic-algorithm-based expert system shell is presented that, when combined with a proper database comprising the available energy-saving technologies for the process industry, is able to perform the following tasks: (a) identify the best available technologies (BATs) among the available ones for a given process industry, and (b) calculate their optimal design parameters in such a way that they comply with the energy requirements of the process. By the term BAT is meant the available energy-saving technology, among the existing ones in the market, that is the best for the case. [source]

    Designer Biomaterials for Nanomedicine

    Nishit Doshi
    Abstract Nanotechnology has had tremendous impact on medical science and has resulted in phenomenal progress in the field of drug delivery and diagnostics. A wide spectrum of novel nanomaterials including polymeric particles, liposomes, quantum dots, and iron oxide particles have been developed for applications in therapeutic delivery and diagnostics. This has resulted in control over the rate and period of delivery and targeting of drugs to specific organs in the human body. This feature article focuses on the delivery of drugs using polymeric particles. The size, choice of polymer, surface chemistry, shape, and mechanical properties of the particles are parameters that critically affect particle function. Numerous biomaterials and fabrication techniques have been developed in the last decade that focus on novel design parameters, such as shape and mechanical properties and the interplay of these parameters with the size and surface chemistry of particles. Recent advances with particular focus on the importance of particle shape are highlighted, and the challenges that are yet to be fulfilled are underscored. [source]

    Conjugated Polymers Combined with a Molecular Beacon for Label-Free and Self-Signal-Amplifying DNA Microarrays

    Kangwon Lee
    Abstract A conjugated polymer (CP) and molecular-beacon-based solid-state DNA sensing system is developed to achieve sensitive, label-free detection. A novel conjugated poly(oxadiazole) derivative exhibiting amine and thiol functional groups (POX-SH) is developed for unique chemical and photochemical stability and convenient solid-state on-chip DNA synthesis. POX-SH is soluble in most nonpolar organic solvents and exhibits intense blue fluorescence. POX-SH is covalently immobilized onto a maleimido-functionalized glass slide by means of its thiol group. Molecular beacons having a fluorescent dye or quencher molecule as the fluorescence resonance energy transfer (FRET) acceptor are synthesized on the immobilized POX-SH layer through direct on-chip oligonucleotide synthesis using the amine side chain of POX-SH. Selective hybridization of the molecular beacon probes with the target DNA sequence opens up the molecular beacon probes and affects the FRET between POX-SH and the dye or quencher, producing a sensitive and label-free fluorescence sensory signal. Various molecular design parameters, such as the size of the stem and loop of the molecular beacon, the choice of dye, and the number of quencher molecules are systematically controlled, and their effects on the sensitivity and selectivity are investigated. [source]

    Cost optimization of composite floors using neural dynamics model

    Hojjat Adeli
    Abstract The design of composite beams is complicated and highly iterative. Depending on the design parameters a beam can be fully composite or partially composite. In the case of design on the basis of the American Institute of Steel Construction (AISC) Load and Resistance Factor Design (LRFD) one has to consider the plastic deformations. As pointed out by Lorenz, the real advantage of the LRFD code can be realized in the minimum cost design. In this article, we present a general formulation for the cost optimization of composite beams based on the AISC LRFD specifications by including the costs of (a) concrete, (b) steel beam, and (c) shear studs. The problem is formulated as a mixed integer-discrete non-linear programming problem and solved by the recently patented neural dynamics model of Adeli and Park (U.S. patent 5,815,394 issued on September 29, 1998). It is shown that use of the cost optimization algorithm presented in this article results in substantial cost savings. Copyright 2001 John Wiley & Sons, Ltd. [source]

    Shape optimization of piezoelectric devices using an enriched meshfree method

    C. W. Liu
    Abstract We present an enriched reproducing kernel particle method for shape sensitivity analysis and shape optimization of two-dimensional electromechanical domains. This meshfree method incorporates enrichment functions for better representation of discontinuous electromechanical fields across internal boundaries. We use cubic splines for delineating the geometry of internal/external domain boundaries; and the nodal coordinates and slopes of these splines at their control points become the design parameters. This approach enables smooth manipulations of bi-material interfaces and external boundaries during the optimization process. It also enables the calculation of displacement and electric-potential field sensitivities with respect to the design parameters through direct differentiation, for which we adopt the classical material derivative approach. We verify this implementation of sensitivity calculations against an exact solution to a variant of Lam's problem, and also, finite-difference approximations. We follow a sequential quadratic programming approach to minimize the cost function; and demonstrate the utility of the overall technique through a model problem that involves the shape optimization of a piezoelectric fan. Copyright 2008 John Wiley & Sons, Ltd. [source]

    Meshless approach to shape optimization of linear thermoelastic solids

    Florin Bobaru
    Abstract This paper presents a formulation for shape optimization in thermoelasticity using a meshless method, namely the element-free Galerkin method. Two examples are treated in detail and comparisons with previously published finite element analysis results demonstrate the excellent opportunities the EFG offers for solving these types of problems. Smoother stresses, no remeshing, and better accuracy than finite element solutions, permit answers to shape optimization problems in thermoelasticity that are practically unattainable with the classical FEM without remeshing. For the thermal fin example, the EFG finds finger shapes that are missed by the FEM analysis, and the objective value is greatly improved compared to the FEM solution. A study of the influence of the number of design parameters is performed and it is observed that the EFG can give better results with a smaller number of design parameters than is possible with traditional methods. Copyright 2001 John Wiley & Sons, Ltd. [source]

    Optimal airfoil shapes for low Reynolds number flows

    D. N. Srinath
    Abstract Flow over NACA 0012 airfoil is studied at , = 4, and 12, for Re,500. It is seen that the flow is very sensitive to Re. A continuous adjoint based method is formulated and implemented for the design of airfoils at low Reynolds numbers. The airfoil shape is parametrized with a non-uniform rational B-splines (NURBS). Optimization studies are carried out using different objective functions namely: (1) minimize drag, (2) maximize lift, (3) maximize lift to drag ratio, (4) minimize drag and maximize lift and (5) minimize drag at constant lift. The effect of Reynolds number and definition of the objective function on the optimization process is investigated. Very interesting shapes are discovered at low Re. It is found that, for the range of Re studied, none of the objective functions considered show a clear preference with respect to the maximum lift that can be achieved. The five objective functions result in fairly diverse geometries. With the addition of an inverse constraint on the volume of the airfoil the range of optimal shapes, produced by different objective functions, is smaller. The non-monotonic behavior of the objective functions with respect to the design variables is demonstrated. The effect of the number of design parameters on the optimal shapes is studied. As expected, richer design space leads to geometries with better aerodynamic properties. This study demonstrates the need to consider several objective functions to achieve an optimal design when an algorithm that seeks local optima is used. Copyright 2008 John Wiley & Sons, Ltd. [source]

    Robust adaptive output-feedback control for a class of nonlinear systems with time-varying actuator faults

    Zhengqiang Zhang
    Abstract A robust adaptive output-feedback control scheme is proposed for a class of nonlinear systems with unknown time-varying actuator faults. Additional unmodelled terms in the actuator fault model are considered. A new linearly parameterized model is proposed. The boundedness of all the closed-loop signals is established. The desired control performance of the closed-loop system is guaranteed by appropriately choosing the design parameters. The properties of the proposed control algorithm are demonstrated by two simulation examples. Copyright 2010 John Wiley & Sons, Ltd. [source]

    Neural network-based adaptive attitude tracking control for flexible spacecraft with unknown high-frequency gain

    Qinglei Hu
    Abstract Adaptive control design using neural networks (a) is investigated for attitude tracking and vibration stabilization of a flexible spacecraft, which is operated at highly nonlinear dynamic regimes. The spacecraft considered consists of a rigid body and two flexible appendages, and it is assumed that the system parameters are unknown and the truncated model of the spacecraft has finite but arbitrary dimension as well, for the purpose of design. Based on this nonlinear model, the derivation of an adaptive control law using neural networks (NNs) is treated, when the dynamics of unstructured and state-dependent nonlinear function are completely unknown. A radial basis function network that is used here for synthesizing the controller and adaptive mechanisms is derived for adjusting the parameters of the network and estimating the unknown parameters. In this derivation, the Nussbaum gain technique is also employed to relax the sign assumption for the high-frequency gain for the neural adaptive control. Moreover, systematic design procedure is developed for the synthesis of adaptive NN tracking control with L2 -gain performance. The resulting closed-loop system is proven to be globally stable by Lyapunov's theory and the effect of the external disturbances and elastic vibrations on the tracking error can be attenuated to the prescribed level by appropriately choosing the design parameters. Numerical simulations are performed to show that attitude tracking control and vibration suppression are accomplished in spite of the presence of disturbance torque/parameter uncertainty. Copyright 2009 John Wiley & Sons, Ltd. [source]