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Design Optimization (design + optimization)
Terms modified by Design Optimization Selected AbstractsDesign Optimization of Blood Shearing Instrument by Computational Fluid DynamicsARTIFICIAL ORGANS, Issue 6 2005Jingchun Wu Abstract:, Rational design of blood-wetted devices requires a careful consideration of shear-induced trauma and activation of blood elements. Critical levels of shear exposure may be established in vitro through the use of devices specifically designed to prescribe both the magnitude and duration of shear exposure. However, it is exceptionally difficult to create a homogeneous shear-exposure history by conventional means. This study was undertaken to develop a Blood Shearing Instrument (BSI) with an optimized flow path which localized shear exposure within a rotating outer ring and a stationary conical spindle. By adjustment of the rotational speed and the gap dimension, the BSI is designed to generate shear stress magnitudes up to 1500 Pa for exposure time between 0.0015 and 0.20 s with a pressure drop of 100 mm Hg. Computational fluid dynamics (CFD) revealed that a flow path designed by first-order analysis and intuition exhibited unfavorable pressure gradient, vortices, and undesirable regions of reverse flow. An optimized design was evolved utilizing a parameterized geometric model and automatic mesh generation to eliminate vortices and reversal flow and to avoid unfavorable pressure gradients. Analysis of the flow and shear fields for the extreme limits of the shear gap demonstrated an improvement in homogeneity due to shape optimization and the limitations of an annular shear device for achieving completely uniform shear exposure. [source] 96-Channel receive-only head coil for 3 Tesla: Design optimization and evaluationMAGNETIC RESONANCE IN MEDICINE, Issue 3 2009Graham C. Wiggins Abstract The benefits and challenges of highly parallel array coils for head imaging were investigated through the development of a 3T receive-only phased-array head coil with 96 receive elements constructed on a close-fitting helmet-shaped former. We evaluated several designs for the coil elements and matching circuitry, with particular attention to sources of signal-to-noise ratio (SNR) loss, including various sources of coil loading and coupling between the array elements. The SNR and noise amplification (g -factor) in accelerated imaging were quantitatively evaluated in phantom and human imaging and compared to a 32-channel array built on an identical helmet-shaped former and to a larger commercial 12-channel head coil. The 96-channel coil provided substantial SNR gains in the distal cortex compared to the 12- and 32-channel coils. The central SNR for the 96-channel coil was similar to the 32-channel coil for optimum SNR combination and 20% lower for root-sum-of-squares combination. There was a significant reduction in the maximum g -factor for 96 channels compared to 32; for example, the 96-channel maximum g -factor was 65% of the 32-channel value for acceleration rate 4. The performance of the array is demonstrated in highly accelerated brain images. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc. [source] Design optimization for higher stabilized efficiency and reduced light-induced degradation in boron-doped Czochralski silicon solar cellsPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 3 2002B. Damiani Traditional boron-doped Czochralski-grown Si solar cells are known to suffer from light-induced degradation (LID). By replacing B with Ga as the dopant in the Cz melt or by reducing the oxygen content by implementing the magnetic-Cz (MCz) growth technique, not only can LID be eliminated, but also higher efficiency manufacturable screen-printed cells can be achieved. The use of thinner wafers for cell fabrication can significantly reduce the impact of LID on conventional boron-doped Cz cells. Knowledge of the degraded cell parameters can be used to determine the optimal thickness for the highest stabilized efficiency. A methodology is developed to maximize the stabilized efficiency after LID by using thinner wafers. A combination of device modeling and experimental data is used to demonstrate that, for traditional B-doped Cz Si, which degraded from 75 to 20,,s, the optimum cell thickness is in the range of 150,190,,m for a back-surface recombination velocity of ,104 cm/s. This cell design reduces the material cost and the absolute efficiency degradation from 0.75% (375,,m device) to 0.24% (157,,m device) and gives the highest stabilized Cz cell efficiency. Copyright © 2002 John Wiley & Sons, Ltd. [source] Elastic and inelastic drift performance optimization for reinforced concrete buildings under earthquake loadsEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 8 2004Chun-Man Chan Abstract This paper presents an effective optimization technique for the elastic and inelastic drift performance design of reinforced concrete buildings under response spectrum loading and pushover loading. Attempts have been made to develop an automatic optimal elastic and inelastic drift design of concrete framework structures. The entire optimization procedure can be divided into elastic design optimization and inelastic design optimization. Using the principle of virtual work, the elastic drift response generated by the response spectrum loading and the inelastic drift response produced by the non-linear pushover loading can be explicitly expressed in terms of element sizing design variables. The optimization methodology for the solution of the explicit design problem of buildings is fundamentally based on the Optimality Criteria approach. One ten-story, two-bay building frame example is presented to illustrate the effectiveness and practicality of the proposed optimal design method. While rapid convergence in a few design cycles is found in the elastic optimization process, relatively slow but steady and smooth convergence of the optimal performance-based design is found in the inelastic optimization process. Copyright © 2004 John Wiley & Sons, Ltd. [source] Approximation methods for reliability-based design optimization problemsGAMM - MITTEILUNGEN, Issue 2 2007Irfan Kaymaz Abstract Deterministic optimum designs are obtained without considering of uncertainties related to the problem parameters such as material parameters (yield stress, allowable stresses, moment capacities, etc.), external loadings, manufacturing errors, tolerances, cost functions, which could lead to unreliable designs, therefore several methods have been developed to treat uncertainties in engineering analysis and, more recently, to carry out design optimization with the additional requirement of reliability, which referred to as reliability-based design optimization. In this paper, two most common approaches for reliability-based design optimization are reviewed, one of which is reliability-index based approach and the other performancemeasure approach. Although both approaches can be used to evaluate the probabilistic constraint, their use can be prohibitive when the associated function evaluation required by the probabilistic constraint is expensive, especially for real engineering problems. Therefore, an adaptive response surface method is proposed by which the probabilistic constraint is replaced with a simple polynomial function, thus the computational time can be reduced significantly as presented in the example given in this paper. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Sensitivity analyses of FORM-based and DRM-based performance measure approach (PMA) for reliability-based design optimization (RBDO)INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 1 2010Ikjin Lee Abstract In gradient-based design optimization, the sensitivities of the constraint with respect to the design variables are required. In reliability-based design optimization (RBDO), the probabilistic constraint is evaluated at the most probable point (MPP), and thus the sensitivities of the probabilistic constraints at MPP are required. This paper presents the rigorous analytic derivation of the sensitivities of the probabilistic constraint at MPP for both first-order reliability method (FORM)-based performance measure approach (PMA) and dimension reduction method (DRM)-based PMA. Numerical examples are used to demonstrate that the analytic sensitivities agree very well with the sensitivities obtained from the finite difference method (FDM). However, as the sensitivity calculation at the true DRM-based MPP requires the second-order derivatives and additional MPP search, the sensitivity derivation at the approximated DRM-based MPP, which does not require the second-order derivatives and additional MPP search to find the DRM-based MPP, is proposed in this paper. A convergence study illustrates that the sensitivity at the approximated DRM-based MPP converges to the sensitivity at the true DRM-based MPP as the design approaches the optimum design. Hence, the sensitivity at the approximated DRM-based MPP is proposed to be used for the DRM-based RBDO to enhance the efficiency of the optimization. Copyright © 2009 John Wiley & Sons, Ltd. [source] Reliability-based design optimization with equality constraintsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 11 2007Xiaoping Du Abstract Equality constraints have been well studied and widely used in deterministic optimization, but they have rarely been addressed in reliability-based design optimization (RBDO). The inclusion of an equality constraint in RBDO results in dependency among random variables. Theoretically, one random variable can be substituted in terms of remaining random variables given an equality constraint; and the equality constraint can then be eliminated. However, in practice, eliminating an equality constraint may be difficult or impossible because of complexities such as coupling, recursion, high dimensionality, non-linearity, implicit formats, and high computational costs. The objective of this work is to develop a methodology to model equality constraints and a numerical procedure to solve a RBDO problem with equality constraints. Equality constraints are classified into demand-based type and physics-based type. A sequential optimization and reliability analysis strategy is used to solve RBDO with physics-based equality constraints. The first-order reliability method is employed for reliability analysis. The proposed method is illustrated by a mathematical example and a two-member frame design problem. Copyright © 2007 John Wiley & Sons, Ltd. [source] A robust design method using variable transformation and Gauss,Hermite integrationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2006Beiqing Huang Abstract Robust design seeks an optimal solution where the design objective is insensitive to the variations of input variables while the design feasibility under the variations is maintained. Accurate robustness assessment for both design objective and feasibility usually requires an intensive computational effort. In this paper, an accurate robustness assessment method with a moderate computational effort is proposed. The numerical Gauss,Hermite integration technique is employed to calculate the mean and standard deviation of the objective and constraint functions. To effectively use the Gauss,Hermite integration technique, a transformation from a general random variable into a normal variable is performed. The Gauss,Hermite integration and the transformation result in concise formulas and produce an accurate approximation to the mean and standard deviation. This approach is then incorporated into the framework of robust design optimization. The design of a two-bar truss and an automobile torque arm is used to demonstrate the effectiveness of the proposed method. The results are compared with the commonly used Taylor expansion method and Monte Carlo simulation in terms of accuracy and efficiency. Copyright © 2005 John Wiley & Sons, Ltd. [source] Improved genetic algorithm for design optimization of truss structures with sizing, shape and topology variablesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 13 2005Wenyan Tang Abstract This paper presents an improved genetic algorithm (GA) to minimize weight of truss with sizing, shape and topology variables. Because of the nature of discrete and continuous variables, mixed coding schemes are proposed, including binary and float coding, integer and float coding. Surrogate function is applied to unify the constraints into single one; moreover surrogate reproduction is developed to select good individuals to mating pool on the basis of constraint and fitness values, which completely considers the character of constrained optimization. This paper proposes a new strategy of creating next population by competing between parent and offspring population based on constraint and fitness values; so that lifetime of excellent gene is prolonged. Because the initial population is created randomly and three operators of GA are also indeterminable, it is necessary to check whether the structural topology is desirable. An improved restart operator is proposed to introduce new gene and explore new space, so that the reliability of GA is enhanced. Selected examples are solved; the improved numerical results demonstrate that the enhanced GA scheme is feasible and effective. Copyright © 2005 John Wiley & Sons, Ltd. [source] A multicriteria evolutionary algorithm for mechanical design optimization with expert rulesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 4 2005R. Filomeno Coelho Abstract This paper addresses the problem of optimizing mechanical components during the first stage of the design process. While a previous study focused on parameterized designs with fixed configurations,which led to the development of the PAMUC (Preferences Applied to Multiobjectivity and Constraints) method, to tackle constraints and preferences in evolutionary algorithms (EAs),, the models to be considered in this work are enriched by the presence of topological variables. In this context, in order to create optimal but also realistic designs, i.e. fulfilling not only technical requirements but also technological constraints (more naturally expressed in terms of rules), a novel approach is proposed: PAMUC II. It consists in integrating an inference engine within the EA to repair the individuals violating the user-defined rules. PAMUC II is tested on mechanical benchmarks, and provides very satisfactory results in comparison with a weighted sum method with penalization to deal with the constraints. Copyright © 2004 John Wiley & Sons, Ltd. [source] Analytical stiffness matrices with Green,Lagrange strain measureINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 3 2005Pauli Pedersen Abstract Separating the dependence on material and stress/strain state from the dependence on initial geometry, we obtain analytical secant and tangent stiffness matrices. For the case of a linear displacement triangle with uniform thickness and uniform constitutive behaviour closed-form results are listed, directly suited for coding in a finite element program. The nodal positions of an element and the displacement assumption give three basic matrices of order three. These matrices do not depend on material and stress/strain state, and thus are unchanged during the necessary iterations for obtaining a solution based on Green,Lagrange strain measure. The approach is especially useful in design optimization, because analytical sensitivity analysis then can be performed. The case of a three node triangular ring element for axisymmetric analysis involves small modifications and extension to four node tetrahedron elements should be straight forward. Copyright © 2004 John Wiley & Sons, Ltd. [source] A continuum sensitivity method for finite thermo-inelastic deformations with applications to the design of hot forming processesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2002Shankar Ganapathysubramanian Abstract A computational framework is presented to evaluate the shape as well as non-shape (parameter) sensitivity of finite thermo-inelastic deformations using the continuum sensitivity method (CSM). Weak sensitivity equations are developed for the large thermo-mechanical deformation of hyperelastic thermo-viscoplastic materials that are consistent with the kinematic, constitutive, contact and thermal analyses used in the solution of the direct deformation problem. The sensitivities are defined in a rigorous sense and the sensitivity analysis is performed in an infinite-dimensional continuum framework. The effects of perturbation in the preform, die surface, or other process parameters are carefully considered in the CSM development for the computation of the die temperature sensitivity fields. The direct deformation and sensitivity deformation problems are solved using the finite element method. The results of the continuum sensitivity analysis are validated extensively by a comparison with those obtained by finite difference approximations (i.e. using the solution of a deformation problem with perturbed design variables). The effectiveness of the method is demonstrated with a number of applications in the design optimization of metal forming processes. Copyright © 2002 John Wiley & Sons, Ltd. [source] Die shape design optimization of sheet metal stamping process using meshfree methodINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2001Nam Ho Kim Abstract A die shape design sensitivity analysis (DSA) and optimization for a sheet metal stamping process is proposed based on a Lagrangian formulation. A hyperelasticity-based elastoplastic material model is used for the constitutive relation that includes a large deformation effect. The contact condition between a workpiece and a rigid die is imposed through the penalty method with a modified Coulomb friction model. The domain of the workpiece is discretized by a meshfree method. A continuum-based DSA with respect to the rigid die shape parameter is formulated using a design velocity concept. The die shape perturbation has an effect on structural performance through the contact variational form. The effect of the deformation-dependent pressure load to the design sensitivity is discussed. It is shown that the design sensitivity equation uses the same tangent stiffness matrix as the response analysis. The linear design sensitivity equation is solved at each converged load step without the need of iteration, which is quite efficient in computation. The accuracy of sensitivity information is compared to that of the finite difference method with an excellent agreement. A die shape design optimization problem is solved to obtain the desired shape of the workpiece to minimize spring-back effect and to show the feasibility of the proposed method. Copyright © 2001 John Wiley & Sons, Ltd. [source] Multi-objective turbomachinery optimization using a gradient-enhanced multi-layer perceptronINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 6 2009M. C. Duta Abstract Response surface models (RSMs) have found widespread use to reduce the overall computational cost of turbomachinery blading design optimization. Recent developments have seen the successful use of gradient information alongside sampled response values in building accurate response surfaces. This paper describes the use of gradients to enhance the performance of the RSM provided by a multi-layer perceptron. Gradient information is included in the perceptron by modifying the error function such that the perceptron is trained to fit the gradients as well as the response values. As a consequence, the back-propagation scheme that assists the training is also changed. The paper formulates the gradient-enhanced multi-layer perceptron using algebraic notation, with an emphasis on the ease of use and efficiency of computer code implementation. To illustrate the benefit of using gradient information, the enhanced neural network model is used in a multi-objective transonic fan blade optimization exercise of engineering relevance. Copyright © 2008 John Wiley & Sons, Ltd. [source] Heat exchanger: from micro- to multi-scale design optimizationINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 13 2007Lingai Luo Abstract This paper presents a consideration of micro-heat exchangers design optimization for the aim of process intensification. Two examples are discussed to illustrate different ways of heat transfer intensification in micro-heat exchangers. To solve the key issue of the link between the micro-scale and the macro-scale, a multi-scale design optimization method using fractal and constructal approaches is introduced. The concept of a novel constructal heat exchanger is also proposed. Copyright © 2007 John Wiley & Sons, Ltd. [source] The state of the art of microwave CAD: EM-based optimization and modelingINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 5 2010Qingsha S. Cheng Abstract We briefly review the current state of the art of microwave CAD technologies. We look into the history of design optimization and CAD-oriented modeling of microwave circuits as well as electromagnetics-based optimization techniques. We emphasize certain direct approaches that utilize efficient sensitivity evaluations as well as surrogate-based optimization approaches that greatly enhance electromagnetics-based optimization performance. On the one hand, we review recent adjoint methodologies, on the other we focus on space mapping implementations, including the original, aggressive, implicit, output, tuning, and related developments. We illustrate our presentation with suitable examples and applications. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010. [source] OPTIMIZATION CRITERIA FOR BATCH RETORT BATTERY DESIGN AND OPERATION IN FOOD CANNING-PLANTSJOURNAL OF FOOD PROCESS ENGINEERING, Issue 6 2003R. SIMPSON ABSTRACT Optimization of thermal processing in the commercial sterilization of canned foods is of great interest because the canning industry plays an important role within the economy of the food processing sector. Many food canning plants operate in a batch mode with a battery of individual batch retorts. The aim of this study was to propose and analyze several criteria and methodologies for optimum design and operation of such retort systems. Two criteria were proposed in the case of choosing the optimum number of retorts to be installed when designing a new batch-operated canning line. The third criterion dealt with seeking optimum process conditions for maximizing output from a fixed number of retorts when processing small batches of different products and container sizes. In the case of new plant design optimization, one objective was to determine the optimum number of retorts that would minimize on-going processing costs related to labor and energy. Retort scheduling (programming) was studied from which a simple mathematical expression was derived for this purpose. A second objective was to determine the optimum number of retorts that would maximize the net present value of initial investment. Approaches based upon engineering economics were studied from which to develop a mathematical procedure for this purpose. In the case of maximizing output from a fixed number of retorts for different products and container sizes, isolethal processes were identified for various product/containers from which a common set of process conditions could be chosen for simultaneous processing of different product lots in the same retort. [source] Strength Properties of Poled Lead Zirconate Titanate Subjected to Biaxial Flexural Loading in High Electric FieldJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2010Hong Wang The mechanical strength of poled lead zirconate titanate (PZT) has been studied using ball-on-ring (BoR) biaxial flexure tests with a high electric field applied concurrently. Both the as-received and the aged PZT specimens were tested. The Weibull plot and a 95% confidence ratio ring were used to characterize the responses of mechanical strength under various electric loading conditions. A fractographical study has been conducted at the same time, and the fracture origins or strength-limiting flaws of tested PZT specimens have been identified and characterized accordingly. The fracture toughness was further estimated to correlate with the obtained fracture stresses and flaws. It has been observed that electric field affects the mechanical strength of poled PZT, and the degree of the effect depends on the sign and magnitude of the applied electric field. Within the examined electric field range of ,3 to +3 times the coercive field, an increasing electric field resulted in a rapid strength decrease and a sharp increase with the turning point around the negative coercive field. Surface-located volume-distributed flaws were identified to be strength limiting for this PZT material. Variations of the mechanical strength with the electric field were believed to be related to the domain switching and amount of switchable domains. An aging effect on the mechanical strength of poled PZT could be significant, especially in the OC condition. These results and observations have the potential to serve probabilistic reliability analysis and design optimization of multilayer PZT piezo actuators. [source] Bicriteria product design optimization: An efficient solution procedure using AND/OR treesNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 6 2002S. Raghavan Competitive imperatives are causing manufacturing firms to consider multiple criteria when designing products. However, current methods to deal with multiple criteria in product design are ad hoc in nature. In this paper we present a systematic procedure to efficiently solve bicriteria product design optimization problems. We first present a modeling framework, the AND/OR tree, which permits a simplified representation of product design optimization problems. We then show how product design optimization problems on AND/OR trees can be framed as network design problems on a special graph,a directed series-parallel graph. We develop an enumerative solution algorithm for the bicriteria problem that requires as a subroutine the solution of the parametric shortest path problem. Although this parametric problem is hard on general graphs, we show that it is polynomially solvable on the series-parallel graph. As a result we develop an efficient solution algorithm for the product design optimization problem that does not require the use of complex and expensive linear/integer programming solvers. As a byproduct of the solution algorithm, sensitivity analysis for product design optimization is also efficiently performed under this framework. © 2002 Wiley Periodicals, Inc. Naval Research Logistics 49: 574,592, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/nav.10031 [source] Design of cellular porous biomaterials for wall shear stress criterionBIOTECHNOLOGY & BIOENGINEERING, Issue 4 2010Yuhang Chen Abstract The microfluidic environment provided by implanted prostheses has a decisive influence on the viability, proliferation and differentiation of cells. In bone tissue engineering, for instance, experiments have confirmed that a certain level of wall shear stress (WSS) is more advantageous to osteoblastic differentiation. This paper proposes a level-set-based topology optimization method to regulate fluidic WSS distribution for design of cellular biomaterials. The topological boundary of fluid phase is represented by a level-set model embedded in a higher-dimensional scalar function. WSS is determined by the computational fluid dynamics analysis in the scale of cellular base cells. To achieve a uniform WSS distribution at the solid,fluid interface, the difference between local and target WSS is taken as the design criterion, which determines the speed of the boundary evolution in the level-set model. The examples demonstrate the effectiveness of the presented method and exhibit a considerable potential in the design optimization and fabrication of new prosthetic cellular materials for bioengineering applications. Biotechnol. Bioeng. 2010;107:737,746. © 2010 Wiley Periodicals, Inc. [source] | |||||||||||||||||||