A synchronized strategy to minimize vehicle dispatching time: a real example of steel industry

Time compression in supply chains is a crucial aspect involved in the integration of warehousing and transport operations in the manufacturing industries. Supply chain flows could be interrupted due to many sources of delays that lead to additional time in dispatching process and reduction in customer service level. The problem considered in this paper consists of long waiting times of loading vehicles inside the plant. This work presents a simulation-based study to minimize vehicle dispatching time in a steel wire plant. Value stream map is developed to present a system perspective of processes involved in the overall supply chain. Process activity mapping is completed to provide a step by step analysis of activities involved in the vehicle dispatch process. A simulation model is developed for the system and a new model is proposed to improve the delivery performance by minimizing vehicles’ waiting time.     

Order batching to minimize total travel time in a parallel-aisle warehouse

Although the picking of items may make up as much as 60% of all labor activities in a warehouse and may account for as much as 65% of all operating expenses, many order picking problems are still not well understood. Indeed, usually simple rules of thumb or straightforward constructive heuristics are used in practice, even in state-of-the-art warehouse management systems, however, it might well be that more attractive algorithmic alternatives could be developed. We address one such a fundamental materials handling problem: the batching of orders in a parallel-aisle warehouse so as to minimize the total traveling time needed to pick all items. Many heuristics have been proposed for this problem, however, a fundamental analysis of the problem is still lacking. In this paper, we first address the computational complexity of the problem. We prove that this problem is NP-hard in the strong sense but that it is solvable in polynomial time if no batch contains more than two orders. This result is not really surprising but it justifies the development of approximation and/or enumerative optimization algorithms for the general case. Our primary goal is to develop a branch-and-price optimization algorithm for the problem. To this end, we model the problem as a generalized set partitioning problem and present a column generation algorithm to solve its linear programming relaxation. Furthermore, we develop a new approximation algorithm for the problem. Finally, we test the performance of the branch-and-price algorithm and the approximation algorithm on a comprehensive set of instances. The computational experiments show the compelling performance of both algorithms.     

Using polymers to minimize corrosion of steel in concrete

Efforts to restrict chloride transport can lead to changes in the corrosion rate of steel in cement-based materials, such as concrete. Two potential methods have been examined for several years. They include: the addition of polymer fibers to the concrete at the time of mixing; and the encapsulation of previously contaminated concrete using polymer resin or polymer composites. It has been reported that the first method could minimize initial chloride intrusion and that the latter method could prevent additional chloride intrusion if concrete is already salt-contaminated. The effectiveness of these methods in minimizing corrosion was evaluated based on changes in corrosion rates determined using polarization resistance measurements. The results, which have been observed over a period of several years, will be reported. Limitations of polarization resistance measurements to evaluate the effectiveness of these methods as means of minimizing corrosion will also be discussed.     

Assigning jobs to time frames on a single machine to minimize total tardiness

This paper deals with a sequencing problem arising in the management of paced-flowlines, that is production lines where jobs are released at constant time intervals. The problem is to sequence jobs to minimis total tardiness. The problem can be formulated as an assignment problem with a number of knapsack constraints. We prove the strong NP-hardness of the problem and give a number of lower bounds which are used in a branch-and-bound algorithm. Computational results in realistic settings confirm the effectiveness of the procedure developed. The results are particularly interesting with reference to mixed-model assembly lines in which several jobs of few different types are produced periodically.     

Using tool life models to minimize processing time on a flexible machine

Economic tool life models are presented for machines with finite capacity tool magazines and variable processing speed capability. Single and multiple part models for minimizing the total throughput time are formulated as nonlinear, integer programs (NLIP). An algorithm is presented for the NLP relaxation and a marginal analysis approach for solving the NLIP is detailed, giving an optimal tool loading policy as well as the processing speeds for each of the part types so as to minimize the makespan. A numerical example illustrates the procedures.     

A dispatching rule and a random iterated greedy metaheuristic for identical parallel machine scheduling to minimize total tardiness

This paper addresses a real-life production scheduling problem with identical parallel machines, originating from a plant producing Acrylonitrile-Butadiene-Styrene (ABS) plate products. In the considered practical scheduling problem, ABS plate has some specific specifications and each specification has several different levels. Because there is at least one different level of specification between two ABS plate products, it is necessary to make a set-up adjustment on each machine whenever a switch occurs from processing one ABS plate product to another product. As tardiness leads to extra penalty costs and opportunity losses, the objective of minimising total tardiness has become one of the most important tasks for the schedule manager in the plant. The problem can be classified as an identical parallel machine scheduling problem to minimise the total tardiness. A dispatching rule is proposed for this problem and evaluated by comparing it with the current scheduling method and several existing approaches. Moreover, an iterated greedy-based metaheuristic is developed to further improve the initial solution. The experimental results show that the proposed metaheuristic can perform better than an existing tabu search algorithm, and obtain the optimal solution for small-sized problems and significantly improve the initial solutions for large-sized problems.     

基于PLC的实时监控系统在辐射产业的应用

针对辐射产业中广泛应用的EPS加速器束下工艺落后的现状 ,提出采用PLC和工业PC两级控制方式 ,实现对EPS加速器束下工艺的自动控制。实践证明 ,该系统有效地提高了产品辐照质量 ,并且性能可靠 ,调试方便 ,维护简单 ,可移植性好。     

Vibrations of a vehicle excited by real road profiles

Based on experimental data obtained from the Lublin III delivery car, we have performed a vibration analysis of the vehicle suspension system. Vertical accelerations on the left and right sides of the suspension system were measured. Experiments were carried out on three types of road surfaces: (a) asphalt, (b) sett, and (c) railway cross. The acceleration signals were examined using Fourier transform, multiscale entropy analysis and continuous wavelet transform. These methods reveal the characteristics of the vibration patterns produced by the various road surface profiles. Our results can be used to assess the efficacy of a vehicle suspension system under different road conditions.     

Dynamic relative positioning of AGVs in a loop layout to minimize mean system response time

One of the control decisions in the operation of an automated guided vehicle (AGV) system is to determine the home locations of idle vehicles. In this paper, the problems of selecting home location of a vehicle when idle in a single loop AGV network is presented. As the number of unit loads to be picked up at each workstation dynamically changes over time, the optimum home location of vehicles may also change. Based on the objective of minimizing the expected response time of a vehicle, models are constructed. Example problems are given to illustrate the use of the solution algorithms. The results of the system response times obtained using the dynamic dwell point models are compared with those of other dwell point rules.     

Solving vehicle assignment problems by process-network synthesis to minimize cost and environmental impact of transportation

A method and software are proposed for optimal assignment of vehicles to transportation tasks in terms of total cost and emission. The assignment problem is transformed into a process-network synthesis problem that can be algorithmically handled by the P-graph framework. In the proposed method, each task is given by a set of attributes to be taken account in the assignment; this is also the case for each vehicle. The overall mileage is calculated as the sum of the lengths of all the routes to be travelled during, before, after, and between the tasks (Desaulniers et al. 1998; Baita et al. 2000). Cost and emission are assigned to the mileages of each vehicle type. In addition to the globally optimal solution of the assignment problem, the P-graph framework provides the n-best suboptimal solutions that can be ranked according to multiple criteria. The viability of the proposed method is illustrated by an example.     

Optimal dwell point location of automated guided vehicles to minimize mean response time in a loop layout

An important control issue in operating an automated guided vehicle system is where to locate idle vehicles. Dwell points for idle vehicles affect the performance of manufacturing systems. A polynomial time algorithm has been developed to determine dwell points for idle automated guided vehicles that minimize the mean response time. Both uni- and bidirectional loop layouts are considered. The proposed algorithm, based on a dynamic programming model, partitions the set of pick-up stations into subsets so that a single vehicle serves all stations in a subset. The dynamic programming algorithm has been streamlined by applying certain optimality properties. Computational results show that the proposed algorithm can solve large-scale problems in a reasonable time. A simulation experiment has also been conducted to compare several idle vehicle positioning rules, and the results show that best performance is obtained by positioning idle vehicles in dwell points that minimize the mean response time.     

Studying early time HWCVD growth of a-Si:H by real time spectroscopic ellipsometry

We have applied real time spectroscopic ellipsometry and secondary ion mass spectrometry to study the growth of amorphous silicon by hot-wire chemical vapor deposition. Differences in temperature and hydrogen content affect the optical properties of the film. These effects provide valuable insight into the growth process. We have compared a-Si:H films grown at two different temperatures to better understand these effects. Our studies reveal the presence of a distinct 100–200-thick layer at the top of the growing film. The properties of this layer are primarily determined by the ambient conditions in the growth chamber and appear relatively independent of substrate temperature. In contrast, the properties of the bulk of the film are strongly influenced by substrate temperature. These results imply that differences in film properties associated with substrate temperature are the result of subsurface reconstruction and diffusion processes.     

Optimisation of a vehicle energy absorbing steel component with experimental validation

The paper deals with the optimisation of a tapered tubular steel component to be used as an energy-absorbing device in the front structure of a vehicle body. Aim of the optimisation problem is the minimisation of a load uniformity parameter evaluated as the ratio between the maximum and the average crushing loads. The optimisation problem takes into account two design variables describing a tapered geometrical configuration, the diameter of the component at one of its bounds and the tapering length. Two improved geometrical configurations have been found and have been experimentally tested to verify the numerical results with impact velocities up to 10 m/s.     

A colorimetric gold nanoparticle sensor to interrogate biomolecular interactions in real time on a surface

This paper presents a new label-free optical method to study biomolecular interactions in real time at the surface of an optically transparent substrate. The method relies on the change in the absorbance spectrum of a self-assembled monolayer of colloidal gold on glass, as a function of biomolecular binding to the surface of the immobilized colloids. Using this approach, we demonstrate proof of principle of a label-free optical biosensor to quantify biomolecular interactions in real time on a surface in a commercially available UV-visible spectrophotometer and of a colorimetric end-point assay using an optical scanner. The spectrophotometric sensor shows concentration-dependent binding and a detection limit of 16 nM for streptavidin. The sensor is easy to fabricate, is reproducible in its performance, has minimal technological requirements, namely, the availability of an UV-visible spectrophotometer or an optical scanner, and will enable high-throughput screening of biomolecular interactions in real time in an array-based format.     

钢铁等行业发展形势及气体分离设备行业的机遇

论述了钢铁等行业的发展形势,各行业迅猛的发展势头给气体分离设备行业的发展提供了机遇:服务好各行业的快速发展,看好能源领域,追踪朝阳行业,做大做强,拓展国内和国际两大市场。     

Erosion-corrosion of a stainless steel distillation column in food industry

Unusual extended corrosion phenomena were detected in a distillation column made in AISI type 316 stainless steel (UNS S31600) of a plant for natural pectins extraction from citrus. The column was the first of a series of two distillation columns representing the unit core. Corrosion problems were observed only in that column and mainly along the surface of the trays located in the lower section of the column. The phenomenon was observed subsequently to a modification of the original plant layout that caused an increase of the operating temperatures and turbulence of the process stream inside the column.     

The use of synchrotron X-rays to observe copper corrosion in real time

We have developed and tested two complementary methods for making time-lapse synchrotron X-ray diffraction (XRD) measurements of the growth of synthetic corrosion layers using a protocol for producing copper(I) chloride (nantokite), on copper as a test. In the first method, a copper coupon was spin-coated with saturated copper(II) chloride solution in air while the surface was characterized in real time using XRD with a fast one-dimensional (1-D) detector. In the second, a droplet of the same reagent was suspended from an X-ray-transparent window in a hermetically sealed cell and the coupon was brought into contact with this while XRD diffractograms were acquired with a charge-coupled device (CCD) camera. The protocol is completed by a deionized water rinse, which was also studied. The XRD shows nantokite precipitation in solution as well as growth on the surface, but the end products were variable proportions of nantokite, cuprite (Cu(2)O), and paratacamite (Cu(2)(OH)(3)Cl). The latter two were observed forming in a reaction between the nantokite and the rinsing water. Comparisons between samples analyzed in the synchrotron and at lower power densities show that the effects of any radiolysis or slight heating of the sample are insignificant in this case. It would be simple to extend these methods to other corrosion or surface reaction systems.     

Use of Centroidal Voronoi Diagram to find optimal gate locations to minimize mold filling time in resin transfer molding

In Resin Transfer Molding (RTM) processes, liquid resin is injected into a dry reinforcement structure to create a composite part within given time limits. To reduce the fill time, resin may be injected into the mold through multiple gates. The minimum number of gates and their locations needs to be determined. To reduce the number of scenarios to be simulated, an iterative method is implemented for multiple-gate injection optimization. The inlet nodes on the mesh surface are used to generate a Voronoi Diagram of the mold geometry. Then the optimal Centroidal Voronoi Diagram (CVD) of the mold surface is searched iteratively. It is shown that the generation points associated with the optimal CVD correspond with the gate locations that yield the shortest fill time. The results are compared with exhaustive search and genetic algorithms results to illustrate the efficiency and accuracy of CVD method.     

汽车转向试验台加载系统惯性力补偿策略研究

针对汽车转向试验台加载系统的惯性力进行了补偿方法研究,通过机理建模原理建立了汽车转向试验台数学模型并得到简化方框图,求出方框图中相应的传递函数,分析试验台中转向器驱动系统和加载系统存在的耦合,并根据前馈补偿解耦原理设计了前馈补偿解耦控制器,以消除加载系统惯性力,最后将加载系统补偿前后的模型进行了Simulink仿真。解耦仿真结果表明,加入前馈补偿解耦器后,加载系统在不同频率下具有较高的跟踪精度,惯性力有效地得到补偿。     

Electrocoagulation of a real reactive dyebath effluent using aluminum and stainless steel electrodes

Treatment of real reactive dyebath effluent comprising of an exhausted reactive dyebath and its sequential rinses with electrocoagulation (EC) using aluminum (Al) and stainless steel (SS) electrodes was investigated. The experimental study focused on the effect of applied current density (22-87 mA/cm(2); at an initial, optimum pH of 5.5) on decolorization and COD removal rates using Al and SS as electrode materials. Results have indicated that the treatment efficiency was enhanced appreciably by increasing the applied current density when Al electrodes were used for EC, whereas no clear correlation existed between current density and removal rates for EC with SS electrodes the treatment efficiency could only be improved when the applied current density was in the range of 33-65 mA/cm(2). It was established that EC with SS electrodes was superior in terms of decolorization kinetics (99-100% color removal after 10-15 min EC at all studied current densities), whereas EC with Al electrodes was more beneficial for COD removal in terms of electrical energy consumption (5 kWh/m(3) wastewater for EC with Al electrodes instead of 9 kWh/m(3) wastewater for EC with SS electrodes).