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Fast analysis of electromagnetic scattering from body of revolution using high-order basis functions

IET MICROWAVES ANTENNAS & PROPAGATION 2012年第14期6卷 1542-1547页

作者： Ding, D. Z. Li, Z. J. Chen, R. S. Nanjing Univ Sci & Technol Dept Commun Engn Nanjing 210094 Jiangsu Peoples R China

Electromagnetic scattering by conducting body of revolution (BOR) is formulated in terms of the electric field integral equation combined with high-order basis function based on curved-wire segment. Owing to the rotational symmetry property of BOR, the currents are represented using high-order basis functions along the generating arc and Fourier series expansion for the periodic azimuthal variation. The method of moment for BOR (BORMoM) is applied to the linear system solved by the direct solver. The parallelisation is carried out in the high-order BORMoM to further reduce the computation time. Numerical results are presented to demonstrate the accuracy and efficiency of the proposed method.

关键词： rotational symmetry property parallelisation high-order basis functions method of moment for BOR curved-wire segment Numerical approximation and analysis arc expansion direct solver linear system Electromagnetic waves: theory periodic azimuthal variation Integral equations (numerical analysis) Fourier series computation time fast analysis electromagnetic scattering BORMoM method of moments electromagnetic wave scattering Electromagnetic wave propagation computational complexity body of revolution electric field integral equations Fourier series expansion electric field integral equation

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An optimal multiple-model strategy to design a controller for nonlinear processes: A boiler-turbine unit

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COMPUTERS & CHEMICAL ENGINEERING 2012年 46卷 48-58页

作者： Jalali, Ali Akbar Golmohammad, Hassan IUST Dept Elect Engn Tehran Iran

The paper documents an optimal multiple-model strategy to design a controller for the boiler-turbine unit. There are two important problems associated with multiple-model controllers: number of models and their locations in an operating space. A method based on Vinnicombe distance is used to find minimum number of local models. First the stability of the control scheme is verified in theory. Using the closed-loop stability condition the minimum number of models is found and the models are located in a space of an unknown parameter. The performance of the proposed controller is evaluated in simulation and compared with a PI controller designed using H-infinity approach and an MPC-based controller in the literature. The designed controller based on the linear local models can ensure satisfactory performance. The novel idea of this paper is the optimal strategy finding minimum number of local models in order to reduce the computational cost and processing time. (C) 2012 Elsevier Ltd. All rights reserved.

关键词： Stable Multiple-model controller Boiler-turbine Number of models Vinnicombe metric computation time

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Evaluation of temperature field and heat flux by inverse analysis during steel strip rolling

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INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER 2012年第4期55卷 629-641页

作者： Weisz-Patrault, Daniel Ehrlacher, Alain Legrand, Nicolas Ecole Ponts ParisTech UR Navier F-77455 Marne La Vallee France Maiziere Proc Vole Romaine ArcelorMittal Global Res & Dev F-57283 Moizieres Les Metz France

Knowledge of the temperature field in the roll is a critical factor of modern, high-speed rolling mills. In this paper, an inverse analytical method is developed to determine the temperature field and especially the temperature (and heat flux) at the surface of the roll by measuring the temperature with a thermocouple (fully embedded) at only one point inside the roll. Iterative methods are not studied because short computation times are desired. Some assumptions are done to resolve analytically the unsteady heat equation, taking into account the restrictions of the measurement system (e.g., measurement according to successive times). The solution is validated by comparing the outputs of the method and prescribed analytical temperature fields. Good agreement is obtained. Noise sensitivity is estimated by adding artificial random numbers to the inputs. Good accuracy is observed. A 10% error of the temperature sensor depth is also considered and does not compromise the method. On the other hand, the computation time (around 0.05 s by cycle) is studied to rapidly optimise the industrial parameters during the rolling process. (C) 2011 Elsevier Ltd. All rights reserved.

关键词： Steel rolling Thermal sensor Free from damage computation time Inverse analysis

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Variable ordering for shared binary decision diagrams targeting node count and path length optimisation using particle swarm technique

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IET COMPUTERS AND DIGITAL TECHNIQUES 2012年第6期6卷 353-361页

作者： Mitra, A. Chattopadhyay, S. IIT Kharagpur Dept Elect & Elect Commun Engn Kharagpur W Bengal India

This study presents a particle swarm optimisation (PSO)-based approach to optimise node count and path length of the binary decision diagram (BDD) representation of Boolean function. The optimisation is achieved by identifying a good ordering of the input variables of the function. This affects the structure of the resulting BDD. Both node count and longest path length of the shared BDDs using the identified input ordering are found to be much superior to the existing results. The improvements are more prominent for larger benchmarks. The PSO parameters have been tuned suitably to explore a large search space within a reasonable computation time.

关键词： Optimisation Optimisation techniques particle swarm optimisation search problems path length optimisation binary decision diagrams variable ordering computation time Combinatorial mathematics shared binary decision diagrams BDD input ordering Boolean function Algebra, set theory, and graph theory node count optimisation directed graphs particle swarm technique PSO search space directed acyclic graph

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Comparison of the performance of different tools for fast simulation of ultrasound data

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ULTRASONICS 2012年第5期52卷 573-577页

作者： Gao, Hang Hergum, Torbjorn Torp, Hans D'hooge, Jan Katholieke Univ Leuven Dept Cardiovasc Dis Lab Cardiovasc Imaging & Dynam Louvain Belgium Norwegian Univ Sci & Technol Dept Circulat & Med Imaging N-7034 Trondheim Norway

Simulation of ultrasound data is often performed for developing new ultrasound data processing techniques. The spatial impulse response method (as implemented in FieldII) has typically been used as the gold standard due to its excellent accuracy in the linear domain. When scatterer numbers become significant and when 3D volumetric data sets need to be computed, calculation time can become an issue however. In order to solve this problem, two alternative methods have recently been proposed both of which are based on the principle of convolving a set of point scatterers with a point spread function. "FUSK" operates in the frequency domain while "COLE" runs in the spatio-temporal domain. The aim of this study was to directly contrast both methodologies in terms of accuracy and processing speed using FieldII as a reference. (C) 2012 Elsevier B. V. All rights reserved.

关键词： Fast simulation Ultrasound data Accuracy computation time

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A new sensor for the evaluation of contact stress by inverse analysis during steel strip rolling

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JOURNAL OF MATERIALS PROCESSING TECHNOLOGY 2011年第9期211卷 1500-1509页

作者： Weisz-Patrault, Daniel Ehrlacher, Alain Legrand, Nicolas Ecole Ponts ParisTech UR Navier F-77455 Marne La Vallee France ArcelorMittal Dofasco Res & Dev Hamilton ON L8N 3J5 Canada

Knowledge of the contact stress between roll and strip becomes a critical factor in modern, high-speed rolling mills. In this paper, an inverse analytical method is developed to determine the contact stress in the roll gap by measuring the stress tensor with fibre optics at only one point inside the roll. Unlike many inverse methods, no matrix inversion is needed because the very small contact length would lead to ill-conditioned matrices. Iterative methods are also not studied because short computation times are desired. This approach uses the theory of elasticity on the assumption that the problem is isothermal and planar and relies on the expansion of holomorphic functions into a power series. On the other hand, the computation time is studied to rapidly optimise the industrial parameters during the rolling process. Hot, cold and temper-rolling simulations are given to demonstrate the accuracy of the method and the feasibility of this new kind of sensor, taking into account the restrictions (e.g., frequency of acquisition) of the local measurement system. (C) 2011 Elsevier B.V. All rights reserved.

关键词： Steel rolling Friction sensor Free from damage computation time Inverse analysis

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Assessing the convergence of LHS Monte Carlo simulations of wastewater treatment models

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WATER SCIENCE AND TECHNOLOGY 2011年第10期63卷 2219-2224页

作者： Benedetti, Lorenzo Claeys, Filip Nopens, Ingmar Vanrolleghem, Peter A. Univ Ghent BIOMATH B-9000 Ghent Belgium MOSTforWATER NV B-8500 Kortrijk Belgium Univ Laval ModelEAU Dept Genie Civil & Genie Eaux Quebec City PQ G1V 0A6 Canada

Monte Carlo (MC) simulation appears to be the only currently adopted tool to estimate global sensitivities and uncertainties in wastewater treatment modelling. Such models are highly complex, dynamic and non-linear, requiring long computation times, especially in the scope of MC simulation, due to the large number of simulations usually required. However, no stopping rule to decide on the number of simulations required to achieve a given confidence in the MC simulation results has been adopted so far in the field. In this work, a pragmatic method is proposed to minimize the computation time by using a combination of several criteria. It makes no use of prior knowledge about the model, is very simple, intuitive and can be automated: all convenient features in engineering applications. A case study is used to show an application of the method, and the results indicate that the required number of simulations strongly depends on the model output(s) selected, and on the type and desired accuracy of the analysis conducted. Hence, no prior indication is available regarding the necessary number of MC simulations, but the proposed method is capable of dealing with these variations and stopping the calculations after convergence is reached.

关键词： computation time global methods sensitivity and uncertainty analysis

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Even/uneven complex FDM mesh technology and its application on mould filling simulation

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INTERNATIONAL JOURNAL OF CAST METALS RESEARCH 2011年第3-4期24卷 203-206页

作者： Liao, D. -M. Zhou, J. -X. Chen, L. -L. Liu, R. -X. Huazhong Univ Sci & Technol State Key Lab Mat Proc & Die & Mould Technol Wuhan 430074 Peoples R China

Numerical simulation of the mould filling process is a very important aspect of casting computer aided engineering technology. However, it is time consuming;it may take a day, or even several days. This study tries to reduce the computational time of mould filling simulation by the even/uneven complex finite difference method (FDM) mesh technology. First, this paper introduces a mathematical model of the mould filling process. Then, the even FDM mesh technology, the uneven FDM mesh technology and the even/uneven complex FDM mesh technology are introduced;this paper also gives the even FDM mesh model and uneven FDM mesh model of a benchmark casting, and comprises the simulation results and computational time of the mould filling simulation by different mesh technologies. Finally, this paper gives an application on a die casting's mould filling simulation using the even/uneven complex FDM mesh technology. The results show that the even/uneven complex FDM mesh technology has the advantages of both even and uneven FDM mesh technologies and thus can reduce the computation time of mould filling simulation efficiently.

关键词： Even/uneven complex FDM mesh technology Mould filling Casting Numerical simulation SOLA-VOF computation time

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The In-Crowd Algorithm for Fast Basis Pursuit Denoising

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IEEE TRANSACTIONS ON SIGNAL PROCESSING 2011年第10期59卷 4595-4605页

作者： Gill, Patrick R. Wang, Albert Molnar, Alyosha Cornell Univ Sch Elect & Comp Engn Ithaca NY 14853 USA

We introduce a fast method, the "in-crowd" algorithm, for finding the exact solution to basis pursuit denoising problems. The in-crowd algorithm discovers a sequence of subspaces guaranteed to arrive at the support set of the final solution of l(1)-regularized least squares problems. We provide theorems showing that the in-crowd algorithm always converges to the correct global solution to basis pursuit denoising problems. We show empirically that the in-crowd algorithm is faster than the best alternative solvers (homotopy, fixed point continuation and spectral projected gradient for l(1) minimization) on certain well-and ill-conditioned sparse problems with more than 1000 unknowns. We compare the in-crowd algorithm's performance in high-and low-noise regimes, demonstrate its performance on more dense problems, and derive expressions giving its computational complexity.

关键词： Algorithms computation time optimization methods tomography

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Efficient Network Reconfiguration Using Minimum Cost Maximum Flow-Based Branch Exchanges and Random Walks-Based Loss Estimations

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IEEE TRANSACTIONS ON POWER SYSTEMS 2011年第1期26卷 30-37页

作者： Ababei, Cristinel Kavasseri, Rajesh N Dakota State Univ Dept Elect & Comp Engn Fargo ND 58108 USA

The efficiency of network reconfiguration depends on both the efficiency of the loss estimation technique and the efficiency of the reconfiguration approach itself. We propose two novel algorithmic techniques for speeding-up the computational runtime of both problems. First, we propose an efficient heuristic algorithm to solve the distribution network reconfiguration problem for loss reduction. We formulate the problem of finding incremental branch exchanges as a minimum cost maximum flow problem. This approach finds the best set of concurrent branch exchanges yielding larger loss reduction with fewer iterations, hence significantly reducing the computational runtime. Second, we propose an efficient random walks-based technique for the loss estimation in radial distribution systems. The novelty of this approach lies in its property of localizing the computation. Therefore, bus voltage magnitude updates can be calculated in much shorter computational runtimes in scenarios where the distribution system undergoes isolated topological changes, such as in the case of network reconfiguration. Experiments on distribution systems with sizes of up to 10 476 buses demonstrate that the proposed techniques can achieve computational runtimes shorter with up to 7.78 times and with similar or better loss reduction compared to the Baran's reconfiguration technique [1].

关键词： computation time losses networks power distribution control

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