This paper demonstrates through examples that erroneous material constants for complex visco-plastic material models can be obtained from simultaneous parameter estimation by nonlinear optimization methods unless the ...
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This paper demonstrates through examples that erroneous material constants for complex visco-plastic material models can be obtained from simultaneous parameter estimation by nonlinear optimization methods unless the laboratory load paths used in the fitting process give significant model response sensitivities to changes in all of the material parameters. A general procedure is proposed in which a nonlinear optimization algorithm is coupled with analytically/numerically derived response sensitivities to evaluate an unambiguous set of material parameters. Response sensitivities enter into the parameter estimation procedure in two ways. Relative response sensitivities are first used to identify an efficient test matrix that when simulated with the model, give model responses that are sensitive to changes in each of the material parameters. Then the corresponding nonzero response sensitivities are used to construct the gradient and Hessian matrices in a gradient-driven optimization algorithm to evaluate the material parameters. A model for braze alloys is used to demonstrate that erroneous parameter values may result if not all of the relative response sensitivities are ''nonzero'' and district.
The survey describes specific features of digital signal processors (DSPs) and the related optimization techniques that can be implemented in C compilers. optimization algorithms and the mutual influence of different ...
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The survey describes specific features of digital signal processors (DSPs) and the related optimization techniques that can be implemented in C compilers. optimization algorithms and the mutual influence of different optimizations are considered.
This paper presents a new hybrid technique for mechanical characterization of hyperelastic materials. The research is motivated by the fact that standard identification procedures based on the fitting of strain-stress...
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This paper presents a new hybrid technique for mechanical characterization of hyperelastic materials. The research is motivated by the fact that standard identification procedures based on the fitting of strain-stress curves determined experimentally from planar biaxial tests may be inaccurate for non-uniform states of deformation. Therefore, we propose an alternative approach where the difference ohm between the displacement field measured with Projection Moire and its counterpart predicted by FEM is minimized using non-linear optimization algorithms that finally find unknown material properties. In order to check the feasibility of the new procedure, we considered a thin latex membrane modelling it as a two-parameter Mooney-Rivlin (MR) hypcrelastic material. The ohm function is minimized either using optimization routines available in a commercial finite element package and by implementing a global optimizer able to deal with non-linearity and non-convexity included in the identification process. In order to check accuracy of optimization results, target values of MR constants for the latex specimen tested have previously been determined by fitting experimental stress-strain data gathered from a standard planar biaxial tension test. Results indicate that the present hybrid identification procedure can determine accurately properties of the hyperelastic material under investigation. In fact, the average residual error on displacements was less than 1% while the difference between the MR constants found with optimization and their target values was less than 3.5%. (c) 2005 Elsevier Ltd. All rights reserved.
We describe the use of a stochastic algorithm, called ALOPEX, which could be implemented in VLSI for optimizing the buffer allocation process in ATM switching networks. We present the results of computer simulations f...
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We describe the use of a stochastic algorithm, called ALOPEX, which could be implemented in VLSI for optimizing the buffer allocation process in ATM switching networks. We present the results of computer simulations for buffer allocation in ATM switching networks using the ALOPEX algorithm. The algorithm uses a scalar cost function which is a measure of global performance. The ALOPEX works by broadcasting the global cost function to all neural processors in the neural network. Since each neural processor solely depends on the global cost function no interaction is needed between the neural processors and the algorithm is more amenable to massively parallel implementation. The application of the ALOPEX algorithm for the buffer allocation optimization in ATM networks assumes limited buffer capacity. The proposed ALOPEX-based approach takes advantage of the favorable control characteristics of the algorithm such as high adaptability and high speed collective computing power for effective buffer utilization. The proposed model uses complete sharing buffer allocation strategy and enhances its performance for high traffic loads by regulating the buffer allocation process dynamically. (C) 1999 Published by Elsevier Science B.V. All rights reserved.
In this paper, we analyse various minimization algorithms applied to the problem of determining elasto-plastic material parameters using an inverse analysis and digital image correlation (DIC) system. As the DIC syste...
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In this paper, we analyse various minimization algorithms applied to the problem of determining elasto-plastic material parameters using an inverse analysis and digital image correlation (DIC) system. As the DIC system, ARAMIS is used, while for the finite element solution of boundary value problems, Abaqus software is applied. Different minimization algorithms, implemented in the SciPy Python library, were initially juxtaposed, compared and evaluated based on benchmark functions. Next the proper evaluation of the algorithms was performed to determine the material parameters for isotropic metal plasticity with the Huber-Mises yield criterion and isotropic or combined kinematic-isotropic plastic hardening models. For all researchers utilizing back calculation methods based on a DIC measuring system, such analysis results may be interesting. It was concluded that among the local minimization methods, derivative free optimization algorithms, especially the Powell algorithm, perform the most efficiently.
In order to enhance spectrum competence for successful data rates, future generation vehicle networks will be able to provide the method for effective data dissemination via diverse radio technologies. Higher mobility...
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In order to enhance spectrum competence for successful data rates, future generation vehicle networks will be able to provide the method for effective data dissemination via diverse radio technologies. Higher mobility networks cause unnecessary handoffs since a vehicle regularly moves between various diverse networks. In this case, a subpar handoff algorithm exacerbates this issue by causing significant packet loss during frequent and erratic handoffs, commonly referred to as ping-pong handoffs. The proposed model Hybrid Cat Swarm optimization-TOPSIS Algorithm (HCSTA) is used to execute the vertical handoffs in urban VANET. Both mobility and network simulator are employed to demonstrate the effectiveness of the proposed techniques. The effectiveness of this work is demonstrated through the combined utilization of mobility and network simulators. Handoff occurrences are affected by the direction of moving vehicles and usage technology. In the Same direction, 150 vehicles experienced 6 handoffs due to longer dwell times, while those in the opposite direction encountered 11 handoffs. In the utility comparison, UMTS (Universal Mobile Telecommunications System) to Wi-Fi transitions face low handoffs compared to DSRC (Dedicated Short Range Communication) to WiMAX (Worldwide Interoperability for Microwave Access), in opposite directions. Utility rates of technologies like Wi-Fi (Wirelesss Fidelity), WiMAX, UMTS, and DSRC vary with speed as high, moderate and low, with WiMAX providing the most consistent performance. The packet delivery rate (0.78) decreases with higher vehicle densities 150 and speeds 85 Kmph due to increased network load and high bandwidth utilization compared to low speed scenarios. The overall network throughput increases from 38.9 to 39.9 Kbps with moderate vehicle densities, with a level noted at 85 and 115 vehicles for the 50-60 km/h speed category, indicating optimal load and moderate bandwidth efficiency.
Over the last three decades, storm-water quality modeling has been used increasingly commonly to describe the general system behavior and assess the pollution loads transferred in and spilled out of combined sewer sys...
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Over the last three decades, storm-water quality modeling has been used increasingly commonly to describe the general system behavior and assess the pollution loads transferred in and spilled out of combined sewer systems. The calibration of quality models is, in most cases, based on conventionally obtained calibration data, e.g., by automated sampling. Long-term high-resolution online measurement data are available for the Graz West catchment (Graz, Austria), allowing an assessment of the full dynamics of discharge and pollution concentrations. This paper focuses on the application and comparison of single-event and two different multievent optimization schemes for sewer-water quality model calibration. While both single- and multievent optimization lead to satisfying results for the calibration events in discharge calibration, it is shown that validation events are better reproduced by using multievent calibration. Single- and multievent autocalibration of pollution concentration is based on the best dataset obtained from the discharge calibration. As for discharge, the pollutographs are reproduced satisfactorily, and multievent calibration is more stable. In all cases, the two multievent approaches performed equally well. DOI: 10.1061/(ASCE)EE.1943-7870.0000356. (C) 2011 American Society of Civil Engineers.
A general class of derivative-free optimization procedures is presented including the corresponding convergence theory. This theory turns out to be very constructive, in the sense that the convergence conditions not o...
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A general class of derivative-free optimization procedures is presented including the corresponding convergence theory. This theory turns out to be very constructive, in the sense that the convergence conditions not only can be verified easily for many existing algorithms, but also allow one to construct new procedures. It is shown that popular methods such as branch-and-bound concepts, Pintér's general class of procedures, the algorithms of Pijavskii, Shubert, and Mladineo, and the approach of Zheng and Galperin can not only be subsumed under this class of methods, but also partly be improved by regarding them within the framework presented.
The detection of significant local reflectional symmetry in grey level images is considered. Prior segmentation is not assumed, and it is intended that the results could be used for guiding visual attention and for pr...
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The detection of significant local reflectional symmetry in grey level images is considered. Prior segmentation is not assumed, and it is intended that the results could be used for guiding visual attention and for providing side information to segmentation algorithms. A local measure of reflectional symmetry that transforms the symmetry detection problem to a global optimization problem is defined. Reflectional symmetry detection becomes equivalent to finding the global maximum of a complicated multimodal function parameterized by the location of the center of the supporting region, its size, and the orientation of the symmetry axis. Unlike previous approaches, time consuming exhaustive search is avoided. A global optimization algorithm for solving the problem is presented. It is related to genetic algorithms and to adaptive random search techniques. The efficiency of the suggested algorithm is experimentally demonstrated. Just one thousand evaluations of the local symmetry measure are typically needed in order to locate the dominant symmetry in natural test images.
This paper presents the use of numerical simulations coupled with optimization techniques in oil reservoir modeling and production optimization. We describe three main components of an autonomic oil production managem...
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This paper presents the use of numerical simulations coupled with optimization techniques in oil reservoir modeling and production optimization. We describe three main components of an autonomic oil production management framework. The framework implements a dynamic, data-driven approach and enables Grid-based large scale optimization formulations in reservoir modeling. (C) 2004 Elsevier B.V. All rights reserved.
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