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Optimization Procedure (optimization + procedure)
Selected AbstractsOptimal design of added viscoelastic dampers and supporting bracesEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 4 2004Ji-Hun Park Abstract This paper presents a simultaneous optimization procedure for both viscoelastic dampers (VEDs) and supporting braces installed in a structure. The effect of supporting braces on the control efficiency of VEDs is also investigated. To apply a general gradient-based optimization algorithm, closed-form expressions for the gradients of objective function and constraints are derived. Also, the constraint on the dynamic behavior of a structure is embedded in the gradient computation procedure to reduce the number of variables in the optimization. From numerical analysis of an example structure, it was found that when sufficient stiffness cannot be provided for the supporting braces, the flexibility of the brace should be taken into account in the design of the VED to achieve the desired performance of the structure. It was also observed that, as a result of the proposed optimization process, the size of the supporting brace could be reduced while the additional VED size (to compensate for the loss of the control effect) was insignificant. Copyright © 2003 John Wiley & Sons, Ltd. [source] Optimal seismic design of steel frame buildings based on life cycle cost considerationsEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 9 2003Min Liu Abstract A multi-objective optimization procedure is presented for designing steel moment resisting frame buildings within a performance-based seismic design framework. Life cycle costs are considered by treating the initial material costs and lifetime seismic damage costs as two separate objectives. Practical design/construction complexity, important but difficult to be included in initial cost analysis, is taken into due account by a proposed diversity index as another objective. Structural members are selected from a database of commercially available wide flange steel sections. Current seismic design criteria (AISC-LRFD seismic provisions and 1997 NEHRP provisions) are used to check the validity of any design alternative. Seismic performance, in terms of the maximum inter-storey drift ratio, of a code-verified design is evaluated using an equivalent single-degree-of-freedom system obtained through a static pushover analysis of the original multi-degree-of-freedom frame building. A simple genetic algorithm code is used to find a Pareto optimal design set. A numerical example of designing a five-storey perimeter steel frame building is provided using the proposed procedure. It is found that a wide range of valid design alternatives exists, from which a decision maker selects the one that balances different objectives in the most preferred way. Copyright © 2003 John Wiley & Sons, Ltd. [source] Inverse estimation of material properties for sheet metalsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 2 2004K. M. Zhao The main objective of this paper is to estimate the material properties for sheet metals subjected to loading and reverse loading by using an inverse method. Cyclic three-point bending tests are conducted. Bending moments are computed from the measured data, namely, punch stroke, punch load, bending strain and bending angle. Bending moments are also calculated based on the selected constitutive model. Normal anisotropy and non-linear isotropic/kinematic hardening are considered. Material parameters are estimated by minimizing the difference between these two bending moments. Modified Levenberg,Marquardt method is used in the optimization procedure. Stress,strain curves are generated with the material parameters found in this way. Copyright © 2004 John Wiley & Sons, Ltd. [source] A mixed FEM approach to stress-constrained topology optimizationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2008M. Bruggi Abstract We present an alternative topology optimization formulation capable of handling the presence of stress constraints in a straightforward fashion. The main idea is to adopt a mixed finite-element discretization scheme wherein not only displacements (as usual) but also stresses are the variables entering the formulation. By doing so, any stress constraint may be handled within the optimization procedure without resorting to post-processing operation typical of displacement-based techniques that may also cause a loss in accuracy in stress computation if no smoothing of the stress is performed. Two dual variational principles of Hellinger,Reissner type are presented in continuous and discrete form that, which included in a rather general topology optimization problem in the presence of stress constraints that is solved by the method of moving asymptotes (Int. J. Numer. Meth. Engng. 1984; 24(3):359,373). Extensive numerical simulations are performed and ongoing extensions outlined, including the optimization of elastoplastic and incompressible media. Copyright © 2007 John Wiley & Sons, Ltd. [source] Optimal flow control for Navier,Stokes equations: drag minimizationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 4 2007L. Dedè Abstract Optimal control and shape optimization techniques have an increasing role in Fluid Dynamics problems governed by partial differential equations (PDEs). In this paper, we consider the problem of drag minimization for a body in relative motion in a fluid by controlling the velocity through the body boundary. With this aim, we handle with an optimal control approach applied to the steady incompressible Navier,Stokes equations. We use the Lagrangian functional approach and we consider the Lagrangian multiplier method for the treatment of the Dirichlet boundary conditions, which include the control function itself. Moreover, we express the drag coefficient, which is the functional to be minimized, through the variational form of the Navier,Stokes equations. In this way, we can derive, in a straightforward manner, the adjoint and sensitivity equations associated with the optimal control problem, even in the presence of Dirichlet control functions. The problem is solved numerically by an iterative optimization procedure applied to state and adjoint PDEs which we approximate by the finite element method. Copyright © 2007 John Wiley & Sons, Ltd. [source] A general framework for evaluating nonlinearity, noise and dynamic range in continuous-time OTA-C filters for computer-aided design and optimizationINTERNATIONAL JOURNAL OF CIRCUIT THEORY AND APPLICATIONS, Issue 4 2007S. Koziel Abstract Efficient procedures for evaluating nonlinear distortion and noise valid for any OTA-C filter of arbitrary order are developed based on matrix description of a general OTA-C filter model. Since those procedures use OTA macromodels, they allow us to obtain the results significantly faster than transistor-level simulation. On the other hand, the general OTA-C filter model allows us to apply matrix transforms that manipulate (rescale) filter element values and/or change topology without changing its transfer function. Due to this, the proposed procedures can be used in direct optimization of OTA-C filters with respect to important characteristics such as noise performance, THD, IM3, DR or SNR. As an example, a simple optimization procedure using equivalence transformations is discussed. An application example of the proposed approach to optimal block sequencing and gain distribution of 8th order cascade Butterworth filter is given. Accuracy of the theoretical tools has been verified by comparing to transistor-level simulation results and to experimental results. Copyright © 2006 John Wiley & Sons, Ltd. [source] Energy, exergy and exergoeconomic analysis of a steam power plant: A case studyINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 5 2009Mohammad Ameri Abstract The objective of this paper is to perform the energy, exergy and exergoeconomic analysis for the Hamedan steam power plant. In the first part of the paper, the exergy destruction and exergy loss of each component of this power plant is estimated. Moreover, the effects of the load variations and ambient temperature are calculated in order to obtain a good insight into this analysis. The exergy efficiencies of the boiler, turbine, pump, heaters and the condenser are estimated at different ambient temperatures. The results show that energy losses have mainly occurred in the condenser where 306.9,MW is lost to the environment while only 67.63,MW has been lost from the boiler. Nevertheless, the irreversibility rate of the boiler is higher than the irreversibility rates of the other components. It is due to the fact that the combustion reaction and its high temperature are the most significant sources of exergy destruction in the boiler system, which can be reduced by preheating the combustion air and reducing the air,fuel ratio. When the ambient temperature is increased from 5 to 24°C, the irreversibility rate of the boiler, turbine, feed water heaters, pumps and the total irreversibility rate of the plant are increased. In addition, as the load varies from 125 to 250,MW (i.e. full load) the exergy efficiency of the boiler and turbine, condenser and heaters are increased due to the fact that the power plant is designed for the full load. In the second part of the paper, the exergoeconomic analysis is done for each component of the power plant in order to calculate the cost of exergy destruction. The results show that the boiler has the highest cost of exergy destruction. In addition, an optimization procedure is developed for that power plant. The results show that by considering the decision variables, the cost of exergy destruction and purchase can be decreased by almost 17.11%. Copyright © 2008 John Wiley & Sons, Ltd. [source] Modeling and optimization of a novel pressurized CHP system with water extraction and refrigerationINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 8 2008J. R. Khan Abstract A novel cooling, heat, and power (CHP) system has been proposed that features a semi-closed Brayton cycle with pressurized recuperation, integrated with a vapor absorption refrigeration system (VARS). The semi-closed Brayton cycle is called the high-pressure regenerative turbine engine (HPRTE). The VARS interacts with the HPRTE power cycle through heat exchange in the generator and the evaporator. Waste heat from the recirculated combustion gas of the HPRTE is used to power the absorption refrigeration unit, which cools the high-pressure compressor inlet of the HPRTE to below ambient conditions and also produces excess refrigeration in an amount that depends on ambient conditions. Water produced as a product of combustion is intentionally condensed in the evaporator of the VARS, which is designed to provide sufficient cooling for the inlet air to the high-pressure compressor, water extraction, and for an external cooling load. The computer model of the combined HPRTE/VARS cycle predicts that with steam blade cooling and a medium-sized engine, the cycle will have a thermal efficiency of 49% for a turbine inlet temperature of 1400°C. This thermal efficiency, is in addition to the large external cooling load, generated in the combined cycle, which is 13% of the net work output. In addition, it also produces up to 1.4 kg of water for each kg of fuel consumed, depending upon the fuel type. When the combined HPRTE/VARS cycle is optimized for maximum thermal efficiency, the optimum occurs for a broad range of operating conditions. Details of the multivariate optimization procedure and results are presented in this paper. Copyright © 2008 John Wiley & Sons, Ltd. [source] Optimization of a finned heat sink array based on thermoeconomic analysisINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 5 2007S. Z. Shuja Abstract The design and specification of heat sinks for electronic systems is not easily accomplished through the use of standard thermal design and analysis tools since geometric and boundary conditions are not typically known in advance. A second-law based thermoeconomic optimization procedure is presented for a finned heat sink array. This involves including costs associated with material, and irreversible losses due to heat transfer and pressure drop. The influence of important physical, geometrical and unit cost parameters on the overall finned array are optimized for some typical operating conditions that are representative of electronic cooling applications. The optimized cost results are presented in terms of ReD, ReL, ,P / ,H, and q for a finned system in a graphical form. In addition the methodology of obtaining optimum parameters for a finned heat sink system which will result in minimum operating cost is demonstrated. Copyright © 2006 John Wiley & Sons, Ltd. [source] Video tracking system optimization using evolution strategiesINTERNATIONAL JOURNAL OF IMAGING SYSTEMS AND TECHNOLOGY, Issue 2 2007Jesús García Abstract A video-based tracking system for airport surveillance, composed by modules performing vision tasks at different levels, is adapted for operational conditions by means of Evolution Strategies (ES). An optimization procedure has been carried out considering different scenes composed of representative trajectories, supported by a global evaluation metric proposed to quantify the system performance. The generalization problem (the search of appropriate solutions for general situations, avoiding over-adaptation to particular conditions) is approached considering evaluation of ES-individuals over combinations of trajectories to build the fitness function. In this way, the optimization procedure covers sets of trajectories representing different types of problems. Besides, alternative operators for aggregating partial evaluations have been analysed. Results show how the optimization strategy provides a sensitive tuning of performance related to input parameters at different levels, and how the combination of different situations improves the generalization capability of the trained system. The global performance final system after optimization is also compared with representative algorithms in the state of the art of visual tracking. © 2007 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 17, 75,90, 2007 [source] Model-based shape from shading for microelectronics applicationsINTERNATIONAL JOURNAL OF IMAGING SYSTEMS AND TECHNOLOGY, Issue 2 2006A. Nissenboim Abstract Model-based shape from shading (SFS) is a promising paradigm introduced by Atick et al. [Neural Comput 8 (1996), 1321,1340] in 1996 for solving inverse problems when we happen to have a lot of prior information on the depth profiles to be recovered. In the present work we adopt this approach to address the problem of recovering wafer profiles from images taken using a scanning electron microscope (SEM). This problem arises naturally in the microelectronics inspection industry. A low-dimensional model, based on our prior knowledge on the types of depth profiles of wafer surfaces, has been developed, and based on it the SFS problem becomes an optimal parameter estimation. Wavelet techniques were then employed to calculate a good initial guess to be used in a minimization process that yields the desired profile parametrization. A Levenberg,Marguardt (LM) optimization procedure has been adopted to address ill-posedness of the SFS problem and to ensure stable numerical convergence. The proposed algorithm has been tested on synthetic images, using both Lambertian and SEM imaging models. © 2006 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 16, 65,76, 2006 [source] Sample movement optimization for uniform heating in microwave heating ovensINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 2 2007J. L. Pedreño-Molina Abstract A technique for improving the uniformity of heating patterns of dielectric samples in a multimode cavity is presented based on a strategic movement of the sample inside the microwave applicator. Different optimization algorithms are compared to determine the best microwave irradiation period for each sample position. A new optimization procedure that minimizes electric field variance is also presented and assessed. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007. [source] Pseudo alternating least squares algorithm for trilinear decompositionJOURNAL OF CHEMOMETRICS, Issue 3 2001Zeng-Ping Chen Abstract In chemistry, PARAFAC is one of the most widely used algorithms for trilinear decomposition. However, the problem of PARAFAC requiring an accurate estimation of the number of factors in the system under study limits its applications to some extent. This troublesome problem has been tackled by the pseudo alternating least squares (PALS) algorithm designed in this paper. PALS is a unique algorithm which tries to alternately optimize three different objective functions to obtain the solutions for the trilinear decomposition model. It has the outstanding feature of being resistant to the influence of N (the number of factors chosen in calculation), which has been proved mathematically under some mild conditions. Although the optimization procedure of PALS is different from that of PARAFAC, an alternating least squares scheme, and hinders a straightforward analysis of its convergence properties, studies on simulated as well as real data arrays reveal that PALS can often converge to satisfactory results within a reasonable computation time, even if excess factors are used in calculation. Copyright © 2001 John Wiley & Sons, Ltd. [source] Orbital-orthogonality constraints and basis-set optimizationJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 6 2006Fabio E. Penotti Abstract A new procedure is presented for introducing arbitrary orbital-orthogonality constraints in the variational optimization of otherwise nonorthogonal multiconfiguration electronic wave functions. It is based on suitable analytical changes to the expressions for the first and second derivatives of the electronic energy with respect to the independent variational parameters, and can be applied in the presence of symmetry constraints. It is tested using a second-derivative optimization procedure, the Optimized Basis Set,Generalized Multiconfiguration Spin-Coupled (OBS-GMCSC) approach, that can treat basis-function exponential parameters as variational parameters, to be optimized simultaneously with configuration, spin-coupling, and orbital coefficients. This enables rigorous optimization of basis-set exponential parameters even for fully orthogonal multiconfiguration wave functions. Test calculations are carried out, with optimized even-tempered basis sets, on Li2 and on the CH radical. For the latter, special attention is paid to the electronic spin density at the nuclei. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 762,772, 2006 [source] Folding funnels: The key to robust protein structure predictionJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 1 2002Corey Hardin Abstract Natural proteins fold because their free energy landscapes are funneled to their native states. The degree to which a model energy function for protein structure prediction can avoid the multiple minima problem and reliably yield at least low-resolution predictions is also dependent on the topography of the energy landscape. We show that the degree of funneling can be quantitatively expressed in terms of a few averaged properties of the landscape. This allows us to optimize simplified energy functions for protein structure prediction even in the absence of homology information. Here we outline the optimization procedure in the context of associative memory energy functions originally introduced for tertiary structure recognition and demonstrate that even partially funneled landscapes lead to qualitatively correct, low-resolution predictions. © 2002 Wiley Periodicals, Inc. J Comput Chem 23: 138,146, 2002 [source] A new Bayesian formulation for Holt's exponential smoothingJOURNAL OF FORECASTING, Issue 3 2009Robert R. Andrawis Abstract In this paper we propose a Bayesian forecasting approach for Holt's additive exponential smoothing method. Starting from the state space formulation, a formula for the forecast is derived and reduced to a two-dimensional integration that can be computed numerically in a straightforward way. In contrast to much of the work for exponential smoothing, this method produces the forecast density and, in addition, it considers the initial level and initial trend as part of the parameters to be evaluated. Another contribution of this paper is that we have derived a way to reduce the computation of the maximum likelihood parameter estimation procedure to that of evaluating a two-dimensional grid, rather than applying a five-variable optimization procedure. Simulation experiments confirm that both proposed methods give favorable performance compared to other approaches. Copyright © 2008 John Wiley & Sons, Ltd. [source] Application of solid-phase concentration-dependent HSDM to the acid dye adsorption systemAICHE JOURNAL, Issue 1 2005Vinci K. C. Lee Abstract The fixed-bed adsorption of acid dyes onto granular activated carbon (Chemviron Filtrasorb 400) has been studied using a homogeneous surface diffusion model (HSDM). The model incorporates the external boundary layer mass transport and homogeneous diffusion inside the particle. A new orthogonal collocation method has been developed and used to solve the diffusion equations. This orthogonal collocation gives a faster solution method compared with the numerical Crank,Nicolson method. The surface diffusivity has been determined by an optimization procedure with minimization of sum of the error squared. The equilibrium relationship between the liquid-phase concentration and the solid-phase concentration has been described by the Redlich,Peterson isotherm. A solid-phase concentration-dependent surface diffusivity was introduced. The Darken model with the Redlich,Peterson isotherm was found to be a suitable correlation model for the adsorption of the acid dyes on carbon. The magnitude of the averaged Ds0 of each dye is in the order of AR114 > AB80 > AY117, which implies that, under the same solid-phase concentration gradient, the rate of mass transport diffusion is higher in AR114 than that in AB80 and AY117. This phenomenon may be explained by the different mobilities of the dye molecules present in the solution by the different arrangements of two sulfonic acid groups in the dye structures. © 2004 American Institute of Chemical Engineers AIChE J, 51: 323-332, 2005 [source] Quantitative structure/property relationship analysis of Caco-2 permeability using a genetic algorithm-based partial least squares methodJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 10 2002Fumiyoshi Yamashita Abstract Caco-2 cell monolayers are widely used systems for predicting human intestinal absorption. This study was carried out to develop a quantitative structure,property relationship (QSPR) model of Caco-2 permeability using a novel genetic algorithm-based partial least squares (GA-PLS) method. The Caco-2 permeability data for 73 compounds were taken from the literature. Molconn-Z descriptors of these compounds were calculated as molecular descriptors, and the optimal subset of the descriptors was explored by GA-PLS analysis. A fitness function considering both goodness-of-fit to the training data and predictability of the testing data was adopted throughout the genetic algorithm-driven optimization procedure. The final PLS model consisting of 24 descriptors gave a correlation coefficient (r) of 0.886 for the entire dataset and a predictive correlation coefficient (rpred) of 0.825 that was evaluated by a leave-some-out cross-validation procedure. Thus, the GA-PLS analysis proved to be a reasonable QSPR modeling approach for predicting Caco-2 permeability. © 2002 Wiley-Liss Inc. and the American Pharmaceutical Association J Pharm Sci 91:2230,2239, 2002 [source] Cycle-based algorithms for multicommodity network flow problems with separable piecewise convex costsNETWORKS: AN INTERNATIONAL JOURNAL, Issue 2 2008Mauricio C. de Souza Abstract We present cycle-based algorithmic approaches to find local minima of a nonconvex and nonsmooth model for capacity expansion of a network supporting multicommodity flows. By exploiting complete optimality conditions for local minima, we give the convergence analysis of the negative-cost cycle canceling method. The cycle canceling method is embedded in a tabu search strategy to explore the solution space beyond the first local optimum. Reaching a local optimum, the idea is to accept a cost-increasing solution by pushing flow around a positive-cost cycle, and then to make use of the cycle cancelling method incorporating tabu search memory structures to find high quality local optima. Computational experiments on instances of the literature show that the tabu search algorithm can significantly improve feasible solutions obtained by the local optimization procedure, and it outperforms the capacity and flow assignment heuristic in terms of solution quality. © 2007 Wiley Periodicals, Inc. NETWORKS, 2008 [source] A convex optimization procedure to compute ,2 and ,, norms for uncertain linear systems in polytopic domainsOPTIMAL CONTROL APPLICATIONS AND METHODS, Issue 4 2008Ricardo C. L. F. Oliveira Abstract In this paper, a convergent numerical procedure to compute ,2 and ,, norms of uncertain time-invariant linear systems in polytopic domains is proposed. The norms are characterized by means of homogeneous polynomially parameter-dependent Lyapunov functions of arbitrary degree g solving parameter-dependent linear matrix inequalities. Using an extension of Pólya's Theorem to the case of matrix-valued polynomials, a sequence of linear matrix inequalities is constructed in terms of an integer d providing a Lyapunov solution for a given degree g and guaranteed ,2 and ,, costs whenever such a solution exists. As the degree of the homogeneous polynomial matrices increases, the guaranteed costs tend to the worst-case norm evaluations in the polytope. Both continuous- and discrete-time uncertain systems are investigated, as illustrated by numerical examples that include comparisons with other techniques from the literature. Copyright © 2007 John Wiley & Sons, Ltd. [source] Optimal auditing in the banking industryOPTIMAL CONTROL APPLICATIONS AND METHODS, Issue 2 2008T. Bosch Abstract As a result of the new regulatory prescripts for banks, known as the Basel II Capital Accord, there has been a heightened interest in the auditing process. Our paper considers this issue with a particular emphasis on the auditing of reserves, assets and capital in both a random and non-random framework. The analysis relies on the stochastic dynamic modeling of banking items such as loans, reserves, Treasuries, outstanding debts, bank capital and government subsidies. In this regard, one of the main novelties of our contribution is the establishment of optimal bank reserves and a rate of depository consumption that is of importance during an (random) audit of the reserve requirements. Here the specific choice of a power utility function is made in order to obtain an analytic solution in a Lévy process setting. Furthermore, we provide explicit formulas for the shareholder default and regulator closure rules, for the case of a Poisson-distributed random audit. A property of these rules is that they define the standard for minimum capital adequacy in an implicit way. In addition, we solve an optimal auditing time problem for the Basel II capital adequacy requirement by making use of Lévy process-based models. This result provides information about the optimal timing of an internal audit when the ambient value of the capital adequacy ratio is taken into account and the bank is able to choose the time at which the audit takes place. Finally, we discuss some of the economic issues arising from the analysis of the stochastic dynamic models of banking items and the optimization procedure related to the auditing process. Copyright © 2007 John Wiley & Sons, Ltd. [source] An optimization procedure for the pultrusion process based on a finite element formulationPOLYMER COMPOSITES, Issue 3 2002R. M. L. Coelho Composite materials are manufactured by different processes. In all, the process variables have to be analyzed in order to obtain a part with uniform mechanical properties. In the pultrusion process, two variables are the most important: the pulling speed of resin-impregnated fibers and the temperature profile (boundary condition) imposed on the mold wall. Mathematical modeling of this process results in partial differential equations that are solved here by a detailed procedure based on the Galerkin weighted residual finite element method. The combination of the Picard and Newton-Raphson methods with an analytical Jacobian calculation proves to be robust, and a mesh adaptation procedure is presented in order to avoid integration errors during the process optimization. The two earlier-mentioned variables are optimized by the Simulated Annealing method with some constraints, such as a minimum degree of cure at the end of the process, and the resin degradation (the part temperature cannot be higher than the resin degradation temperature at any time during the whole process). Herein, the proposed objective function is an economic criterion instead of the pulling speed of resin-impregnated fibers, used in the majority of papers. [source] Multiobjective optimization of polymerization reaction of vinyl acetate by genetic algorithm technique with a new replacement criterionPOLYMER ENGINEERING & SCIENCE, Issue 5 2008Maryam Sadi A multiobjective optimization procedure based on genetic algorithm has been developed to determine optimum operational conditions of polymerization reaction. In this article by using a new selection criterion to choose the next generation members with better quality, optimization efficiency is improved and the number of generations to obtain Pareto optimal set reduced. In this proposed method a novel replacement criterion based on ranking level information and proximity of solutions to the Pareto optimal front is used to choose the next generation members. The polymerization of vinyl acetate has been chosen as an example. Two objective functions, which used in this study, are maximization of the weight average molecular weight up to the desired value and minimization of the residual initiator concentration. A Pareto optimal set of objective functions has been obtained by application of a Pareto set filter operator. Furthermore, the influence of genetic algorithm parameters on the efficiency and convergence of genetic algorithm is studied by changing cross over and mutation probabilities. Because of the flexibility and generality of genetic algorithm, this optimization method is a useful technique with lots of potentials in determination of optimum value of operation parameters. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers [source] Process optimization of injection molding using an adaptive surrogate model with Gaussian process approachPOLYMER ENGINEERING & SCIENCE, Issue 5 2007Jian Zhou This article presents an integrated, simulation-based optimization procedure that can determine the optimal process conditions for injection molding without user intervention. The idea is to use a nonlinear statistical regression technique and design of computer experiments to establish an adaptive surrogate model with short turn-around time and adequate accuracy for substituting time-consuming computer simulations during system-level optimization. A special surrogate model based on the Gaussian process (GP) approach, which has not been employed previously for injection molding optimization, is introduced. GP is capable of giving both a prediction and an estimate of the confidence (variance) for the prediction simultaneously, thus providing direction as to where additional training samples could be added to improve the surrogate model. While the surrogate model is being established, a hybrid genetic algorithm is employed to evaluate the model to search for the global optimal solutions in a concurrent fashion. The examples presented in this article show that the proposed adaptive optimization procedure helps engineers determine the optimal process conditions more efficiently and effectively. POLYM. ENG. SCI., 47:684,694, 2007. © 2007 Society of Plastics Engineers. [source] Effective Dynamic Material Properties of Foam-like MicrostructuresPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2005S. Alvermann The effective material parameters of a microstructured material can be found using homogenization procedures based on calculations of a Representative Volume Element (RVE) of the material. In our approach the RVE is calculated in frequency domain and inertia is taken into account, leading to a frequency dependent behavior of the RVE. With the frequency response of the RVE, effective dynamic properties of the material are calculated using an optimization procedure. Due to the frequency dependent material behavior on the microscale a viscoelastic constitutive equation is applied on the macroscale. An example calculation is presented for an auxetic 2-D foam-like microstructure which is modelled as a plane frame structure. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Social Optimal Location of Facilities with Fixed Servers, Stochastic Demand, and CongestionPRODUCTION AND OPERATIONS MANAGEMENT, Issue 6 2009Ignacio Castillo We consider two capacity choice scenarios for the optimal location of facilities with fixed servers, stochastic demand, and congestion. Motivating applications include virtual call centers, consisting of geographically dispersed centers, walk-in health clinics, motor vehicle inspection stations, automobile emissions testing stations, and internal service systems. The choice of locations for such facilities influences both the travel cost and waiting times of users. In contrast to most previous research, we explicitly embed both customer travel/connection and delay costs in the objective function and solve the location,allocation problem and choose facility capacities simultaneously. The choice of capacity for a facility that is viewed as a queueing system with Poisson arrivals and exponential service times could mean choosing a service rate for the servers (Scenario 1) or choosing the number of servers (Scenario 2). We express the optimal service rate in closed form in Scenario 1 and the (asymptotically) optimal number of servers in closed form in Scenario 2. This allows us to eliminate both the number of servers and the service rates from the optimization problems, leading to tractable mixed-integer nonlinear programs. Our computational results show that both problems can be solved efficiently using a Lagrangian relaxation optimization procedure. [source] Optimization of a model IV fluidized catalytic cracking unitTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2001Rein Luus Abstract Maximization of a profit function related to a fluidized catalytic cracking unit model was carried out by Luus-jaakola optimization procedure. A 7-dimensional search is carried out on a FCC unit described by 113 nonlinear algebraic equations and 9 differential equations. Despite the low sensitivity and the existence of several local optima, the global optimum was obtained with reasonable amount of computational effort. At the optimum, the profit function is 1% higher than when the air blowers are constrained to operate at their maximum capacity. On a réalisé par la méthode d'optimisation de Luus-jaakola la maximisation d'une fonction de profit relativement à un modèle d'unité de craquage catarytique fluidisé (FCC). Une recherche en sept dimensions est menée sur une unité FCC décrite par 113 équations algébriques non linéaires et 9 équations différentielles. Malgré la faible sensibilité et l'existence de plusieurs optimums locaux, l'optimum global a été atteint avec des efforts raisonnables en termes de calcul. À l'optimum, la fonction de profit est de 1% supérieure à celle obtenue lorsqu'on force les ventilateurs soufflants à fonctionner à leur capacité maximum. [source] Robust Isolation Of Sensor FailuresASIAN JOURNAL OF CONTROL, Issue 1 2003R. Xu ABSTRACT Sensor self-validity check is a critical step in system control and fault diagnostics. In this paper, a robust approach to isolate sensor failures is proposed. First, a residual model for a given system is built off-line and directly based on input-output measurement data. The residual model outputs are called "primary residuals" and are zero when there is no fault. Most conventional approaches to residual model generation are indirect, as they first require the determination of state-space or other models using standard system identification algorithms. Second, a new max-min design of structured residuals, which can maximize the sensitivity of structured residuals with respect to sensor failures, is proposed. Based on the structured residuals, one can then isolate the sensor failures. This design can also be done in an off-line manner. It is an optimization procedure that avoids local optimal solutions. Simulation and experimental results demonstrated the effectiveness of the proposed method. [source] Polynomial Spline Estimation and Inference of Proportional Hazards Regression Models with Flexible Relative Risk FormBIOMETRICS, Issue 3 2006Jianhua Z. Huang Summary The Cox proportional hazards model usually assumes an exponential form for the dependence of the hazard function on covariate variables. However, in practice this assumption may be violated and other relative risk forms may be more appropriate. In this article, we consider the proportional hazards model with an unknown relative risk form. Issues in model interpretation are addressed. We propose a method to estimate the relative risk form and the regression parameters simultaneously by first approximating the logarithm of the relative risk form by a spline, and then employing the maximum partial likelihood estimation. An iterative alternating optimization procedure is developed for efficient implementation. Statistical inference of the regression coefficients and of the relative risk form based on parametric asymptotic theory is discussed. The proposed methods are illustrated using simulation and an application to the Veteran's Administration lung cancer data. [source] Rapid Matrix-Assisted Refolding of Histidine-Tagged ProteinsCHEMBIOCHEM, Issue 5 2009Tetyana Dashivets Abstract Matrix refolded: The formation of inclusion bodies, which are amorphous aggregates of misfolded insoluble protein, during recombinant protein expression, is one of the biggest bottlenecks in protein science. We report a stepwise, rational optimization procedure for refolding of insoluble proteins (see scheme). In comparison to refolding in-solution, this parallelized, matrix-assisted approach allows the refolding of various proteins in a fast and efficient manner. The formation of inclusion bodies (IBs),amorphous aggregates of misfolded insoluble protein,during recombinant protein expression, is still one of the biggest bottlenecks in protein science. We have developed and analyzed a rapid parallel approach for matrix-assisted refolding of recombinant His6 -tagged proteins. Efficiencies of matrix-assisted refolding were screened in a 96-well format. The developed methodology allowed the efficient refolding of five different test proteins, including monomeric and oligomeric proteins. Compared to refolding in-solution, the matrix-assisted refolding strategy proved equal or better for all five proteins tested. Interestingly, specifically oligomeric proteins displayed significantly higher levels of refolding compared to refolding in-solution. Mechanistically, matrix-assisted folding seems to differ from folding in-solution, as the reaction proceeds more rapidly and shows a remarkably different concentration dependence,it allows refolding at up to 1000-fold higher protein concentration than folding in-solution. [source] | ||||||||||||||||||||||