Fast resolution of incremental forming processes by the Multi-Mesh method. Application to cogging

A Multi-Mesh Multi-Physics (MMMP) method is developed to reduce the very long computational time required for simulating incremental forming processes such as cogging or ring rolling. It consists in using several finite element meshes on the same domain to solve the different physics of the problem. A reference mesh is used to accurately store the results and history variables, while the different computational meshes are optimized to solve each physic of the problem. The MMMP algorithm consists in two main key-steps: the generation of the different unstructured meshes and the data transfer between the meshes. The accuracy of the method is supported by using meshes that are embedded by nodes. The method is applied to the simulation of the cogging metal forming process for which it shows as accurate and more than ten times faster than the standard method with a single mesh.     

Reliable phase unwrapping algorithm based on rotational and direct compensators

Phase unwrapping still plays an important role in many data-processing chains based on phase information. Here, we introduce a new phase unwrapping approach for noisy wrapped phase maps of continuous objects to improve the accuracy and computational time requirements of phase unwrapping using a rotational compensator (RC) method. The proposed algorithm is based on compensating the singularity of discontinuity sources. It uses direct compensation for adjoining singular point (SP) pairs and uses RC for other SP pairs. The performance of the proposed method is tested through both simulated and real wrapped phase data. The proposed algorithm is faster than the original algorithm with the RC and has proved efficiency compared to other phase unwrapping methods.     

A heuristic algorithm for master production scheduling problem with controllable processing times and scenario-based demands

Master production scheduling (MPS) is widely used by manufacturing industries in order to handle the production scheduling decisions in the production planning hierarchy. The classical approach to MPS assumes infinite capacity, fixed (i.e. non-controllable) processing times and a single pre-determined scenario for the demand forecasts. However, the deterministic optimisation approaches are sometimes not suitable for addressing the real-world problems with high uncertainty and flexibility. Accordingly, in this paper, we propose a new practical model for designing an optimal MPS for the environments in which processing times may be controllable by allocating resources such as facilities, energy or manpower. Due to the NP-hardness of our model, an efficient heuristic algorithm using local search technique and theory of constraints is developed and analysed. The computational results especially for large-sized test problems show that the average optimality gap of proposed algorithm is four times lower than that of exact solution using GAMS while it consumes also significantly smaller run times. Also, the analysis of computational results confirms that considering the controllable processing times may improve the solution space and help to more efficiently utilise the available resources. According to the model structure and performance of the algorithm, it may be proposed for solving large and complex real-world problems particularly the machining and steel industries.     

Unified inversion scheme that uses light scattering for morphological parameters and optical properties of aggregated aerosols

A robust scheme for characterizing chainlike aggregated aerosols by use of nonintrusive light-scattering measurements is presented. This scheme entails the selection of suitable scattering quantities and their optimal measurement angles; the development of an inversion algorithm to yield the complex refractive index of agglomerates m = n + ik, the primary particle diameter d(p), the number of primary particles per agglomerate N(p), the number density of agglomerates n(A), and the volume fraction of agglomerates f(v); and evaluation of the uncertainties of the inferred parameters that correspond to measuring uncertainties. The data-inversion algorithm is based on the exact formulation of light scattering for agglomerates that consist of primary particles in the Rayleigh limit and therefore has solid theoretical foundations. In addition, this approach yields all the desired parameters of the aggregated aerosols by using in situ light-scattering measurements with a minimum of possible uncertainties. Furthermore, the methodology developed here can be extended to aerosols with other types of morphology and optical property.     

Controlled Release Salbutamol Sulphate Molded Tablets Using Eudragit Retard

Permeable acrylic resins were used as efficient retarding materials to prepare controlled release salbutamol sulphate molded tablets. The formulation is simple, efficient, economic and is easily shaped into molded tablets. The effects of two types of acrylic resins, namely: Eudragit RL100 ad Eudragit RS100 in concentrations 1, 2 and 5% w/w on the physical characteristics as well as on the in vitro release patterns of salbutamol sulphate from molded tablets prepared with either polyethylene glycol (PEG) 4000 or 6000 were studied. It was revealed that, as the molecular weight of the PEG increased, the hardness of the tablets increased. Considerable retardation in the drug release was observed by using Eudragit RS100 as compared to Eudragit RL100. The formulation prepared with PEG 6000 and 5% Eudragit RS100 produced much more release time prolongation than the other tested formulations. On the other hand, tablets prepared by the direct compression technique produced a faster release of salbutamol sulphate than those prepared by molding.     

Controlled Release Salbutamol Sulphate Molded Tablets Using Eudragit Retard

Abstract

Permeable acrylic resins were used as efficient retarding materials to prepare controlled release salbutamol sulphate molded tablets. The formulation is simple, efficient, economic and is easily shaped into molded tablets. The effects of two types of acrylic resins, namely: Eudragit RL100 ad Eudragit RS100 in concentrations 1, 2 and 5% w/w on the physical characteristics as well as on the in vitro release patterns of salbutamol sulphate from molded tablets prepared with either polyethylene glycol (PEG) 4000 or 6000 were studied. It was revealed that, as the molecular weight of the PEG increased, the hardness of the tablets increased. Considerable retardation in the drug release was observed by using Eudragit RS100 as compared to Eudragit RL100. The formulation prepared with PEG 6000 and 5% Eudragit RS100 produced much more release time prolongation than the other tested formulations. On the other hand, tablets prepared by the direct compression technique produced a faster release of salbutamol sulphate than those prepared by molding.     

Harmony search optimization algorithm for a novel transportation problem in a consolidation network

This article presents a new harmony search optimization algorithm to solve a novel integer programming model developed for a consolidation network. In this network, a set of vehicles is used to transport goods from suppliers to their corresponding customers via two transportation systems: direct shipment and milk run logistics. The objective of this problem is to minimize the total shipping cost in the network, so it tries to reduce the number of required vehicles using an efficient vehicle routing strategy in the solution approach. Solving several numerical examples confirms that the proposed solution approach based on the harmony search algorithm performs much better than CPLEX in reducing both the shipping cost in the network and computational time requirement, especially for realistic size problem instances.     

Verification and comparison of a fast fourier transform-based full diffraction method for tilted and offset planes

The recent introduction of a fast Fourier transform- (FFT-) based method for calculating the Rayleigh-Sommerfeld full diffraction integral for tilted and offset planes permits high-speed evaluation of integrated optical systems. An important part of introducing a new calculational tool is its validation and an assessment of its limitations. The validity of the new FFT-based method was determined by comparison of that method with direct integration (DI) of the Rayleigh-Sommerfeld integral, a well-established method. Points of comparison were accuracy, computational speed, memory requirements of the host computer, and applicability to various optical modeling situations. The new FFT-based method is 228 times faster, yet requires 14 times more memory, than the DI method for a 500 mum by 500 mum real computational window.     

Discrete dipole moment method for calculation of the T matrix for nonspherical particles

A computational method, based on a moment solution to the discrete dipole approximation (DDA) interaction equations, is proposed for calculation of the T matrix of arbitrary-shaped particles. It is shown that the method will automatically provide the conservation-of-energy and origin-invariance properties required of the T matrix. Furthermore, the method is significantly faster than a T-matrix calculation by direct inversion of the DDA equations. Because the method retains the dipole lattice representation of the particle, it can be applied with relative ease to particles with irregular shapes-although in the same respect it will not automatically simplify for axisymmetric particles. Calculations of scattering matrix distributions, in fixed and random orientations, are made for tetrahedron, cylindrical, and prolate spheroid particle shapes and compared with DDA and extended boundary condition method results.     

Analytical model to estimate performances of autonomous vehicle storage and retrieval systems for product totes

In today's competitive scenario of increasingly faster deliveries and smaller order sizes, material-handling providers are progressively developing new solutions. A recent, automated material-handling technology for unit load storage and retrieval consists of an autonomous vehicle storage and retrieval system (AVS/RS). The present paper presents an analytical model to estimate the performances (the transaction cycle time and waiting times) of AVS/RS for product tote movement. The model is based on an open queuing network approach. The model effectiveness in performance estimation is validated through simulation.     

A fast algorithm for polynomial evaluation in Reed-Solomon codec

An efficient lookup table algorithm for computing the values of message polynomials during high throughput encoding of Reed–Solomon (RS) codes is presented in this paper. The algorithm can be applied to RS codes encoders, which are based on Vandermonde matrix and the polynomial computations. The lookup table derived from the algorithm can then be applied not only to an encoder of RS codes but also to syndromes evaluation in the decoding of RS codes. By comparison with Horner’s rule, one of the advantages of utilizing this algorithm is that the table lookup operations for computing the values of the message polynomial are reduced by a factor of three. It would reduce the encoding time by fifty-percent using the linear feedback shift register to encode the (204, 188, t = 8) RS code. The algorithm can also be used to evaluate the syndromes needed in part of the RS decoder, and thus the speed is much faster than Horner’s rule. Ultimately, the proposed encoding and syndrome evaluation algorithm for RS codes can be made regular, simple and suitable for software implementations.     

Reciprocity theorem for the calculation of average scattering properties of agglomerated particles

The reciprocity theorem in light scattering is a general theorem that is verified theoretically and experimentally. However, violation of the reciprocity theorem has been encountered in previous investigations for simulation of light scattering from agglomerates. We demonstrate that the violations of the reciprocity theorem are due to inappropriate orientation averaging or the incorrect formulation of light-scattering quantities. In situ optical diagnostics of aggregated aerosols requires the calculation of the orientation averages of scattering quantities. Thus it is imperative to establish a criterion that can be used to determine a sufficient number of orientations for the reliable calculation of averages for the scattering quantities. It is demonstrated that the reciprocity theorem may serve as such a criterion for typical sizes of agglomerates such as flame soot with fractal dimensions D(f) = 1.8, primary particle size parameter x 相似文献   

Effect of orienting fields on agglomeration in dilute dispersions of magnetic fine particles

Static light scattering was used to investigate dilute dispersions of fine gamma -Fe/sub 2/O/sub 3/ magnetic particles. The particles were acicular and on average 0.39 mu m long and 0.056 mu m in diameter. They were dispersed in organic solvents at concentrations of approximately 10/sup -4/ vol%, corresponding to an average interparticle separation of 9 mu m. Computer programs using a coupled dipole algorithm to predict the scattering from the particles were written. Experimental results do not agree with computer calculations of the light scattering from single particles, but are consistent with scattering from thick ropelike agglomerates of particles. The size of these agglomerates was estimated after 10 s to be less than 100 particles, while the thickness of the ropes is at least 5 particles.<>     

Fast wavelet-based multiresolution image registration on a multiprocessing digital signal processor

Image registration is a fundamental task in image processing. It is used in matching two or more images taken at different times, from different imaging modalities, or from different viewpoints. One of the obstacles in achieving practical acceptance of image registration techniques is their computational complexity, which results in a long response time. In this article we present a fast multiresolution image registration algorithm using wavelet transform for the translational and rotational alignment of two-dimensional images. In particular, a novel approach to determine the algorithm parameters to balance the registration accuracy and computational requirement is also described. We implemented this algorithm on a PC-based multimedia and imaging system using a multiprocessing digital signal processor. The algorithm is capable of achieving a subpixel registration accuracy reliably under various noise levels. The multiresolution algorithm implemented on this desktop system was able to register two 256 × 256 images in 466 ms, which is 40 times faster than the uniresolution exhaustive search approach. © 1998 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 9, 29–37, 1998     

On the implementation of an analog ATPG: the nonlinear case

In order to reduce the complexity of the fault diagnosis equations and still retain computational simplicity, a self-testing algorithm has been proposed and implemented on a VMS VAX 11/780 for linear circuits. A prototype implementation of such an algorithm for nonlinear circuits and systems is presented. The proposed analog automatic test program generator (AATPG) for nonlinear circuits and systems is divided into offline and online processes. Unlike the simulation of the pseudocircuits in the linear case, which can be achieved by a matrix/vector multiplication, the circuit simulator SPICE is used to simulate the nonlinear pseudocircuits. The automatic SPICE code generator required for this simulation is presented. The proposed AATPG for nonlinear circuits has been implemented on a VMS VAX 11/780. The actual test can be run in either a fully automatic mode or interactively     

基于混合算法的单堆垛机多巷道拣选作业调度研究

针对单堆垛机在多巷道自动化仓库中的拣选路径规划问题,建立了求解含周转箱约束的堆垛机拣选作业最短路径数学模型,提出用遗传模拟退火混合算法进行求解。通过Matlab分别对不同算法进行实例仿真,结果表明：该混合算法克服了遗传算法早熟,以及模拟退火算法收敛性慢的缺点,求出的解更优,收敛速度更快,稳定性更好。该混合算法具有可行性和高效性。     

Parallel asynchronous particle swarm optimization

The high computational cost of complex engineering optimization problems has motivated the development of parallel optimization algorithms. A recent example is the parallel particle swarm optimization (PSO) algorithm, which is valuable due to its global search capabilities. Unfortunately, because existing parallel implementations are synchronous (PSPSO), they do not make efficient use of computational resources when a load imbalance exists. In this study, we introduce a parallel asynchronous PSO (PAPSO) algorithm to enhance computational efficiency. The performance of the PAPSO algorithm was compared to that of a PSPSO algorithm in homogeneous and heterogeneous computing environments for small- to medium-scale analytical test problems and a medium-scale biomechanical test problem. For all problems, the robustness and convergence rate of PAPSO were comparable to those of PSPSO. However, the parallel performance of PAPSO was significantly better than that of PSPSO for heterogeneous computing environments or heterogeneous computational tasks. For example, PAPSO was 3.5 times faster than was PSPSO for the biomechanical test problem executed on a heterogeneous cluster with 20 processors. Overall, PAPSO exhibits excellent parallel performance when a large number of processors (more than about 15) is utilized and either (1) heterogeneity exists in the computational task or environment, or (2) the computation-to-communication time ratio is relatively small.     

基于lp范数的ECT图像重建算法研究

针对在ECT图像重建过程中,基于lp-范数的非凸压缩感知算法常存在计算量较大以及现有的近端映射算法受一些特定的p值限制而导致成像分辨率较低的问题,利用改进的插值函数替换lp-范数xpp,通过调整参数使得改进的函数无限逼近lp-范数xpp,同时引入阈值表示理论,并在此基础上提出新的自适应阈值迭代算法对新模型进行求解。实验结果表明,改进后的自适应lp-范数重构算法相对于Landwebr算法、迭代重加权最小二乘法具有更强的适应性,更高的图像分辨率,更快的成像速度。     

Diffracted-ray approach to the fast evaluation of diffractive lenses

We employ a combination of asymptotic methods to speed up the computation of fields in the focal region of a diffractive lens (DL). The DL is treated locally as a linear grating with a slowly varying period and groove orientation. We employ rigorous electromagnetic diffraction theory locally to obtain the field just behind the DL. A simple diffracted-ray formula is derived for the field in the focal region of the DL at observation points that are not in the immediate vicinity of the optical axis. A careful study of the range of validity of this formula is made. For observation points that are not in the immediate vicinity of the optical axis the new algorithm is 3 x 10(5) times faster than the application of numerical integration to the double integrals involved and approximately 1000-1200 times faster than a recently published algorithm based on using asymptotic theory to replace the double integral with a single integral.     

An ant colony optimisation algorithm for balancing two-sided U-type assembly lines with sequence-dependent set-up times

Some practical arrangements in assembly lines necessitate set-up times between consecutive tasks. To create more realistic models of operations, set-up times must be considered. In this study, a sequence-dependent set-up times approach for two-sided u-type assembly line (TUAL) structures is proposed for the first time. Previous studies on TUAL have not included set-up times in their analyses. Furthermore, an algorithm based on the Ant Colony Optimization (ACO) algorithm, which is using a heuristic priority rule based procedure has been proposed in order to solve this new approach. In this paper, we look at the sequence-dependent set-up times between consecutive tasks and consecutive cycles, called the “forward set-up time” and the “backward set-up time”, respectively. Additionally, we examine the “crossover set-up time”, which arises from a new sequence of tasks in a crossover station. In order to model more realistic assembly line configurations, it is necessary to include sequence-dependent set-up times when computing all of the operational times such as task starting times and finishing times as well as the total workstation time. In this study, the proposed approach aims to minimize the number of mated-stations as the primary objective and to minimize the number of total workstations as a secondary objective. In order to evaluate the efficiency of the proposed algorithm, a computational study is performed. As can be seen from the experimental results the proposed approach finds promising results for all literature-test problems.