Material flow analysis and volume distance sampling in heuristic line layout procedures

An empirical investigation is focused on the relationship between material flow patterns in a manufacturing system and the distribution of the volume distance values associated with all possible solutions to a line layout problem. Volume distance distribution for line layout problems are shown to follow roughly normal distribution for some common material flow patterns. Based on this result, sampling procedures are described for estimating the parameters of volume distance distributions and proposed as a basis for formulating satisficing criteria for use with heuristic line layout procedures. Subsequent empirical studies suggest relatively low levels of error are observed in the estimation of volume distance parameters for most material flow patterns. These results suggest that volume distance sampling and material flow analysis procedures may have practical value in the development of cost effective stopping criteria for heuristic line layout methods.     

MULTI-HOPE: A tool for multiple floor layout problems

The objective of most facility layout problems is to minimize material handling cost, which is directly proportional to both the distance between the machines and the mix, as well as the volume of products handled. The mix and volume of products are dependent on the demand patterns, and the distance is dependent on the layout plan used for the facility. Because it is relatively difficult to change the demand patterns, and hence the mix and volume of products, the primary focus of most designers has been to deal with the distance attribute of the material handling costs. The limitations of available horizontal space create a need to explore vertical expansion of facilities. This brings up new aspects of vertical material handling and flow that need to be considered in the facility design problem. In this paper, we present a genetic algorithm-based heuristic for generating block layouts for multiple-floor layout problems. This approach produces better solutions than existing simulated annealing-based heuristics for all but one of five multiplefloor test problems available in the literature.     

Analytical models for pick distances in fishbone warehouse based on exact distance contour

The pick distance models for a unit load warehouse employing fishbone layout conventionally use semicircular approximation for distance contour which can result in significant error. This paper develops discrete and continuous pick distance models for fishbone layout under random, full turnover, and class-based storage policies based on exact polygonal distance contour. Class-based storage policy with three classes was found to give pick distance comparable to full turnover policy over a range of demand skews and warehouse shapes studied. The discrete and continuous models are compared considering finite storage space, aisle width and discontinues in the ABC curve for a real life data. The sensitivity of warehouse performance over a range of warehouse parameters is studied. We also outline a methodology for class-based storage design where class partitions can be derived for a warehouse of any dimension from the results of a unit area warehouse.     

Re-examination of peak stress and scaled distance due to ground shock

Ground motions associated with the passage of blast transients are important in two respects. Firstly, they develop as a result of the dynamic pressure pulse and are integrally related to the strains suffered by the soils. Secondly, ground motions subject nearby structures, buried or aboveground, to possible damaging vibrations. An accurate assessment of ground shock parameters, especially peak stresses, is thus essential for a reliable design against blast loading. Reliable ground shock parameters can be obtained from full-scale tests or small-scale tests complemented by numerical analyses. The US Army Corps of Engineers TM5-855-1 manual is widely used for estimates of ground shock parameters. This paper examines the TM5-855-1 estimation of the peak stresses in the light of small-scale field explosion tests in Singapore residual soils. The TM5-855-1 equations for ground shock predictions are not dimensionally consistent and become cumbersome when the need for units conversion arises. To overcome this problem, dimensionless parameters are proposed. A better understanding of the peak pressure–scaled distance plot in TM5-855-1 is provided using the dimensionless parameters.     

Incorporating heterogeneous distance metrics within block layout design

This paper focuses on optimal design of block layouts when using more than one distance metric within a single facility. Previous work in block layout has assumed a single distance metric, usually the shortest rectilinear distance between department centroids, during the design step. However, most facilities have more than one method of material handling and alternative material handling systems can imply alternative distance metrics and cost structures. Specifically, up to three distance metrics within a single facility are considered--the shortest rectilinear distance between centroids (appropriate for automated guided vehicles and forklift trucks), the Tchebychev (maximum) distance (appropriate for overhead cranes) and the shortest Euclidean distance between centroids (appropriate for conveyor lines). Optimal block layouts using each of these distance metrics individually and then collectively are compared and contrasted. This approach can also be used to compare layouts when the choice of material handling system is not clear. It is argued that incorporating the distance metric that best reflects the planned material handling device is more realistic than previous formulations, avoids block layouts that are sub-optimal for the material handling systems installed, and is quite workable within a heuristic optimization framework.     

Rectangular Layout Problems with Worst-Case Distance Measures

This paper considers two related problems involving the design of rectangular layouts of m activities. In each of the problems, costs are incurred which are nondecreasing in distance between activities. The distance between two activities is either the worst-case rectilinear distance, or the worst-case Tchebyshev distance. Minisum and minimax layout problems are then considered and solution techniques are provided. The solution techniques demonstrate that both the area (e.g., number of square feet) taken up by the facilities, as well as the relative use of the facilities, must be considered in order to solve the layout problems of interest.     

An improved facility layout construction method

This study presents a new distance-based facility layout construction technique. Given a two-dimensional (i.e. single-floor) facility layout construction problem in which the order of placement of individual departments is known (a challenging problem in itself), the technique presented herein proposes the use of sub-departments and expected distance functions instead of centroid-to-centroid distances for the placement of departments. In this paper an expected distance function is defined as the probabilistic expectation of the particular distance metric of interest (rectilinear, Euclidean, etc.) in which the parameters involved are defined by random vectors in 2-dimensional Euclidean space. This study presents an enhanced facility layout construction technique that incorporates several enhancements over the well-known systematic layout procedure (SLP). The goal herein is to minimise the error induced by the use of the centroid-to-centroid distances between the departments inherent to the SLP.     

Minimum distance of some evaluation codes

Evaluation codes have been studied since some years ago. At the very beginning they were called projective Reed-Muller type codes and their main parameters (length, dimension and minimum distance) were computed in several particular cases. In fact, the length and dimension of the evaluation codes arising from a complete intersection are known. In this paper we will calculate the minimum distance of some evaluation codes associated to a subset of the projective space that is a complete intersection. These codes are a generalization of the evaluation codes associated to a projective torus which are called generalized projective Reed-Solomon codes.     

Integrated facilities design using a contour distance metric

The unequal area facility design problem has been studied in the literature generally by considering block layout separate from detailed design. This paper shows a tractable method for concurrently optimizing department shape and location within the facility, and selection of the appropriate number of Input/Output (I/O) stations per department and then optimally locating them. The distance metric used is the contour distance that measures transport between I/O stations along the perimeters of departmental boundaries. This distance metric better reflects allowable material flow for many industrial applications and it directly implies the optimal aisle structure for the facility.     

A methodology for solving the unequal area facility layout problem using distance and shape-based measures

This paper presents a methodology for solving the unequal area facility layout problem commonly encountered in industry practice. A mixed-binary nonlinear-programming model is formulated to capture the operational issues encountered on the shop floor. In particular, in addition to the distance measure that is typically used to quantify the material handling costs, the impact of geometry or the shape of the departments is quantified in the formulation of the model. A higher-level heuristic solution algorithm, based on a concept known as ‘tabu search’, is proposed to efficiently solve industry-relevant problems. The methodology not only considers the impact of both distance and shape-based measures simultaneously in the proposed initial solution finding mechanism, but also in the evaluation of the objective function during the entire search procedure, in the hope that it will lead to identifying a better final solution. Taking into consideration fixed and variable tabu list sizes, along with long-term memory with maximum and minimum frequencies, has led to developing six different heuristics for the solution algorithm. A single factor experiment based on randomized block design has been used to compare the performances of the six different heuristics on three different problem structures—small, medium, and large—using the total cost as the criterion. Based on this experiment, the characterizations of search procedures have been recommended to facilitate identifying the best solution for each problem structure. The proposed method is also compared with those in the published literature by solving fairly well known unequal area facility layout problems. When an improvement is observed, the comparison has led to identifying a percentage improvement in total cost of approximately 2.8% to 11.8%, thus demonstrating the effectiveness of the model and the algorithm.     

Multi-item distribution network design problems under volume discount on transportation cost

This study considers the distribution network design problems of multi-echelon, multi-item supply chains under volume (weight) discounts on transportation costs. Minimising the total network cost requires determining the following: (1) the service area of distribution centres (DCs); (2) the assignment of retail stores to DCs; and (3) the inventory volume at DCs. This study compares various replenishment policies and discusses the effects of such policies on distribution network design. In general, the results show that single-cluster replenishment is superior to joint cluster replenishment. However, joint cluster replenishment may be superior to single-cluster replenishment under volume (weight) discounts on transportation costs. The results additionally show that single-item replenishment is inferior to multi-item replenishment under volume (weight) discounts on transportation costs. All the problems are formulated as piecewise non-linear programming models with multiple variables. Algorithms are proposed for solving these piecewise non-linear programming problems. Several numerical studies demonstrate the solution procedures and the effects of changing parameters on decision-making.     

Layout design in fractal organizations

Today's complex, unpredictable and unstable marketplace requires flexible manufacturing systems capable of cost-effective high variety–low volume production in frequently changing product demand and mix. In fractal organizations, system flexibility and responsiveness are achieved by allocating all manufacturing resources into multifunctional cells that are capable of processing a wide variety of products. In this paper, various fractal cell configuration methods for different system design objectives and constraints are proposed. These parameters determine the level of interaction between the cells, the distribution of different product types among the cells and the similarity of cell capabilities. A tabu-search-based method is proposed to optimize the product distribution to the cells and the arrangement of machines and cells on the shop floor. This optimization is performed for different fractal cell configuration methods and cell quantities. The quality of the resulting shop floor layouts is measured in terms of resource requirements and material movements. The results indicate that in fractal layouts, a trade-off is required between machine quantities and material travelling distance. It was generally possible to reduce travelling distances by increasing the degree of optimization on machine layout and product distribution for a specific product demand and mix.     

Inference for two-parameter Rayleigh competing risks data under generalized progressive hybrid censoring

In this paper, a competing risks model based on the generalized progressive hybrid censored two-parameter Rayleigh distributions is studied under the assumption that the lifetime distributions of failure causes are identically distributed with same location and different scale parameters. We obtain maximum likelihood estimates of unknown parameters with associated existence uniqueness. The approximate confidence intervals are constructed using the asymptotic distribution of maximum likelihood estimates via the observed information matrix. Further, Bayes point estimates and the highest probability density credible intervals of unknown parameters are presented, and the Gibbs sampling technique is used to approximate corresponding estimates. A Monte Carlo simulation study is conducted to compare the accuracy of proposed estimates. Finally, a real-life example is presented for illustration purpose.     

Order picking system design: the storage assignment and travel distance estimation (SA&TDE) joint method

Of all the warehouse activities, order picking is one of the most time-consuming and expensive. In order to improve the task, several researches have pointed out the need to consider jointly the layout of the warehouse, the storage assignment strategy and the routing policy to reduce travelled distances and picking time. This paper presents the storage assignment and travel distance estimation (SA&TDE) joint method, a new approach useful to design and evaluate a manual picker-to-parts picking system, focusing on goods allocation and distances estimation. Starting from a set of picking orders received in a certain time range, this approach allows to evaluate the combinations of product codes assigned to storage locations, aisles, sections or warehouse areas and to assess the most relevant ones, for the best location and warehouse layout, with the aim of ensuring optimal picking routes, through the application of the multinomial probability distribution. A case study is developed as well, in order to clarify the concept that underlies the SA&TDE joint method, and to show the validity and the flexibility of the approach, through the calculation of the saving at different levels of detail.     

Four‐parameter beta distribution estimation and skewness test

Sequential tolerance control (STC) is a tolerance control methodology used in discrete parts manufacturing. Recently, an adaptive sphere‐fitting method for STC (ASF–STC) was developed to account for potential skewness in manufacturing operations' distributions, a factor not considered in conventional STC. ASF–STC offers significant improvements over conventional STC when such skewness exists. The direction of skewness of an operations' distribution is a necessary input to ASF–STC. Thus, a novel approach to determining the skewness of a distribution for small sample sizes is presented here. ASF–STC has an additional requirement of distribution information for each operation. The beta distribution is an ideal candidate here, as it is very flexible in shape. The literature on four‐parameter beta estimation is very limited, and their performance for small sample sizes is poor. STC was designed for low‐volume production, thus the estimation for small sample sizes is necessary here. This study presents a heuristic, based on the method of moments estimates for a beta distribution, that estimates the four parameters for a beta distribution with small sample size. Several computational results are provided to compare this heuristic to the best‐known procedure, with the heuristic found to perform better for the test problems considered. Copyright © 2002 John Wiley & Sons, Ltd.     

On the distance between the roots of a polynomial

We prove a lower bound for the distance between two roots of a polynomial with complex coefficients. Such estimates are used to separate the roots of a polynomial.     

ELEMENTS OF WAREHOUSE LAYOUT

The work summarised in this paper has been directed to examine the basic requirements of warehouse layouts. Two simple types of layout have been examined and equations derived for the dimensioning of these, given such information as total volume of stock and number of stock lines. A sketch of the layouts is given.

Ten factors have been considered in arriving at the theoretical layouts and it is shown that different types of layout are affected by different factors, some layouts being independent of factors to which others are sensitive.

Dimensions of a layout can be calculated to minimise handling distance, handling time or space utilisation. Where cost functions are available for these parameters, total cost can also be minimised. The formulae lend themselves readily to computer manipulation, enabling an optimum layout to be determined given only the number of stock lines and volumes stored.     

Lightning striking distance of complex structures

Traditionally, the location of lightning strike points has been determined by using the rolling sphere method, but recently the collection volume method (CVM) has also been proposed for the placement of air terminals on complex structures. Both these methods are empirical in nature and a more advanced model based on physics of discharges is needed to improve the state of affairs. This model is used to evaluate the striking distance from corners and air terminals on actual buildings and the results are qualitatively compared with the predictions of the rolling sphere method and the CVM. The results show that the striking distance not only depends upon the prospective return stroke current and the geometry of the building, but also on the lateral position of the downward leader with respect to the strike point. A further analysis is performed to qualitatively compare the lightning attraction zones obtained with the CVM and the leader inception zones obtained for a building with and without air terminals. The obtained results suggest that the collection volume concept overestimates the protection areas of air terminals placed on complex structures, bringing serious doubts on the validity of this method.     

Analysis of healthy and tumour DNA methylation distributions in kidney‐renal‐clear‐cell‐carcinoma using Kullback–Leibler and Jensen–Shannon distance measures

DNA methylation is an epigenetic phenomenon in which methyl groups get bonded to the cytosines of the DNA molecule altering the expression of the associated genes. Cancer is linked with hypo or hyper‐methylation of specific genes as well as global changes in DNA methylation. In this study, the authors study the probability density function distribution of DNA methylation in various significant genes and across the genome in healthy and tumour samples. They propose a unique ‘average healthy methylation distribution’ based on the methylation values of several healthy samples. They then obtain the Kullback–Leibler and Jensen–Shannon distances between methylation distributions of the healthy and tumour samples and the average healthy methylation distribution. The distance measures of the healthy and tumour samples from the average healthy methylation distribution are compared and the differences in the distances are analysed as possible parameters for cancer. A classifier trained on these values was found to provide high values of sensitivity and specificity. They consider this to be a computationally efficient approach to predict tumour samples based on DNA methylation data. This technique can also be improvised to consider other differentially methylated genes significant in cancer or other epigenetic diseases.Inspec keywords: cancer, tumours, DNA, genetics, molecular biophysicsOther keywords: tumour DNA methylation distributions, kidney‐renal‐clear‐cell‐carcinoma, Kullback–Leibler distance measure, Jensen–Shannon distance measure, epigenetic phenomenon, methyl groups, cytosines, hyper‐methylation, probability density function distribution, average healthy methylation distribution     

RMS中工件路径网络生成方法

利用图论建立RMS中工件路径网络生成模型。给出设备物理布局生成的3种算法：设备物理规划布局算法、基于二次布置问题(QAP)模型的VMC设备物理布局算法以及已有设备物理布局算法。给出AGV路径网络生成算法、AGV路径网络生成改进算法、可替代路径网络生成算法,包括节点间最短路径寻找子算法、路径网络预处理子算法。算法的输入为表示重构对象节点间距离信息的距离矩阵文件和表示某生产周期多工艺路线的流量文件,输出为优化的路径网络。用Visual C 实现了以上算法,实例测试验证了算法的正确性。