首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 46 毫秒
1.
Lumpy demand is a phenomenon encountered in manufacturing or retailing when the items are slow-moving or too expensive, for example fighter plane engines. So far, the seminal procedure of Croston's (1972 Croston, JD. 1972. Stock levels for slow-moving items. Op. Res. Q., 25(1): 123130. [Taylor &; Francis Online] [Google Scholar]), with or without modifications, has been the preference for forecasting lumpy demand. Nevertheless, Croston (1974 Croston, JD. 1974. Forecasting and stock control for intermittent demand. Op. Res. Q., 23(3): 289303. [Taylor &; Francis Online] [Google Scholar]) and others, such as Venkitachalam et al . (2002 Venkitachalam, GHK, Pratt, DB, Young, CF, Morris, S and Goldstein, ML. 2002. Forecasting and inventory planning for parts with intermittent demand–a case study [http://anaconda.ecen.okstate.edu/publications/ERC2003-ADF-Final.doc] [Google Scholar]), have suggested the use of zero forecasts when the demand contains many zeros. In this paper, we put to the test this idea by doing a full factorial study comparing five forecasting methods, including all-zero, under several levels of demand lumpiness, demand variation and ordering, holding and shortage cost. We evaluate the forecasting methods by three measures of forecast error and two measures of inventory cost. We find that all-zero forecasts yield the lowest cost when lumpiness is high; is it also best for mid-lumpiness, if the shortage cost is much higher than the holding cost. We also find that the lowest forecasting error does not necessarily lead to the lowest system cost. And contrary to the assertions in Chen et al . (2000b Chen, F, Ryan, JK and Simchi-Levi, D. 2000b. The impact of exponential smoothing forecasts on the bullwhip effect. Naval Research Logistics, 42: 269286.  [Google Scholar]) and Dejonckheere et al . (2003 Dejonckheere, J, Disney, SM, Lambrecht, MR and Towill, DR. 2003. Measuring the Bullwhip Effect: a Control Theoretic Approach to Analyse Forecasting Induced Bullwhip in Order-Up-To Policies. Eur. J. Op. Res., 147(3): 567590. [Crossref], [Web of Science ®] [Google Scholar], 2004 Dejonckheere, J, Disney, SM, Lambrecht, MR and Towill, DR. 2004. The impact of information enrichment on the bullwhip effect in supply chains: a control theoretic approach. Eur. J. Op. Res., 153(3): 727750. [Crossref], [Web of Science ®] [Google Scholar]), our factorial experiment reinforces the intuition that simple exponential smoothing is superior to an equivalent moving average.  相似文献   

2.
In this paper, the problem of minimising maximum completion time on a single batch processing machine is studied. A batch processing is performed on a machine which can simultaneously process several jobs as a batch. The processing time of a batch is determined by the longest processing time of jobs in the batch. The batch processing machine problem is encountered in many manufacturing systems such as burn-in operations in the semiconductor industry and heat treatment operations in the metalworking industries. Heuristics are developed by iterative decomposition of a mixed integer programming model, modified from the successive knapsack problem by Ghazvini and Dupont (1998 Ghazvini, F.J. and Dupont, L. 1998. Minimising mean flow times criteria on a single batch processing machine with non-identical jobs sizes. International Journal of Production Economics, 55: 273280. [Crossref], [Web of Science ®] [Google Scholar], Minimising mean flow times criteria on a single batch processing machine with non-identical jobs sizes. International Journal of Production Economics 55: 273–280) and the waste of batch clustering algorithm by Chen, Du, and Huang (2011 Chen, H., Du, B. and Huang, G.Q. 2011. Scheduling a batch processing machine with non-identical job sizes: a clustering perspective. International Journal of Production Research, 49(19): 57555778. [Taylor &; Francis Online], [Web of Science ®] [Google Scholar], Scheduling a batch processing machine with non-identical job sizes: a clustering perspective. International Journal of Production Research 49 (19): 5755–5778). Experimental results show that the suggested heuristics produce high-quality solutions comparable to those of previous heuristics in a reasonable computation time.  相似文献   

3.
This paper presents a corrected formulation to the mixed integer programming model of the double-row layout problem (DRLP), first proposed by Chung and Tanchoco (2010 Chung, J and Tanchoco, J. 2010. The double row layout problem. International Journal of Production Research, 48(3): 709727. [Taylor &; Francis Online], [Web of Science ®] [Google Scholar], The double row layout problem. International Journal of Production Research, 48 (3), 709–727). In the DRLP, machines are placed along two rows of a corridor, where the objective is to minimise the total cost of material handling for products that move between these machines. We highlight the errors in the original formulation, propose corrections to the formulation, and provide an analytical validation of the corrections.  相似文献   

4.
Employing data from a sample of 1,161 small firms, the paper draws broad comparisons between patterns of innovation expenditure and output, innovation networking, knowledge intensity and competition within Knowledge‐Intensive Business Services (KIBS; N = 563) and manufacturing firms (N = 598). In so doing, KIBS are further disaggregated along lines proposed by Miles et al. (1995 Miles, I., Kastrinos, N., Flanagan, K., Bilderbeek, R., den Hertog, P., Huitink, W. and Bouman, M. 1995. Knowledge Intensive Business Services: Their Role as Users, Carriers and Sources of Innovation EIMS Publication No. 15, Innovation Programme, DGXIII, Luxembourg [Google Scholar]). That is, as technology‐based KIBS (t‐KIBS; N = 264) and professional KIBS (p‐KIBS; N = 299). However, detailing such broad patterns is preliminary. The principal interest of the paper is in identifying the factors associated with higher levels of innovativeness, within each sector, and the extent to which such “success” factors vary across sectors. The results of the analysis appear to offer support for some widely held beliefs about the relative roles of “softer” and “harder” sources of knowledge and technology within services and manufacturing (Tether, 2004 Tether, B. 2004. Do Services Innovate (Differently)?, Manchester: University of Manchester. CRIC Discussion Paper 66 [Google Scholar]). However, some important qualifications are also apparent.  相似文献   

5.
6.
Pharmaceutical preparations are the final product of a technological process that gives the drugs the characteristics appropriate for easy administration, proper dosage, and enhancement of the therapeutic efficacy. The design of pharmaceutical preparations in nanoparticulate form has emerged as a new strategy for drug delivery (Pasquali, Bettini, and Giordano, 2006 Pasquali , I. , R. Bettini , and F. Giordano . 2006 . Solid-state chemistry and particle engineering with supercritical fluids in pharmaceutics . Eur. J. Pharm. Sci. 27 : 299310 .[Crossref], [PubMed], [Web of Science ®] [Google Scholar]). Particle size (PS) and particle size distribution (PSD) are critical parameters that determine the rate of dissolution of the drug in the biological fluids and, hence, have a significant effect on the bioavailability of those drugs that have poor solubility in water, for which the dissolution is the rate-limiting step in the absorption process (Perrut, Jung, and Leboeuf, 2005 Perrut , M. , J. Jung , and F. Leboeuf . 2005 . Enhancement of dissolution rate of poorly-soluble active ingredients by supercritical fluid processes: Part I: Micronization of neat particles . Int. J. Pharm. 288 : 310 .[Crossref], [PubMed], [Web of Science ®] [Google Scholar]; Van Nijlen et al., 2003 Van Nijlen , T., G. Van Den Mooter , R. Kinget , P. Augustijns , N. Blaton , and K. Brennan . 2003 . Improvement of the dissolution rate of artemisinin by means of supercritical fluid technology and solid dispersions . Int. J. Pharm. 254 : 173181 .[Crossref], [PubMed], [Web of Science ®] [Google Scholar]). Supercritical antisolvent (SAS) processes have been widely used to precipitate active pharmaceutical ingredients (APIs) (Chattopadhyay and Gupta, 2001 Chattopadhyay , P. , and R. B. Gupta . 2001 . Production of antibiotic nanoparticles using supercritical CO2 as antisolvent with enhanced mass transfer . Ind. Eng. Chem. Res. 40 : 35303539 .[Crossref], [Web of Science ®] [Google Scholar]; Rehman et al., 2001 Rehman , M. , B. Y. Shekunov , P. York , and P. Colthorpe . 2001 . Solubility and precipitation of nicotinic acid in supercritical carbon dioxide . J. Pharm. Sci. 90 : 15701582 .[Crossref], [PubMed], [Web of Science ®] [Google Scholar]) with a high level of purity, suitable dimensional characteristics, narrow PSD, and spherical morphologies. The SAS process is based on the particular properties of the supercritical fluids (SCFs). These fluids have diffusivities two orders of magnitude larger than those of liquids, resulting in a faster mass transfer rate SCF properties (solvent power and selectivity) can be also adjusted continuously by altering the experimental conditions (temperature and pressure). As a consequence, SCFs can be removed from the process by a simple change from the supercritical to room conditions, which avoids difficult post-treatments of waste liquid streams. Carbon dioxide (CO2) at supercritical conditions, among all possible SCFs, is largely used because of its relatively low critical temperature (31.1°C) and pressure (73.8 bar), low toxicity, and low cost. In this article, we show some results about processed antibiotics (ampicillin and amoxicillin), two of the world's most widely prescribed antibiotics, when they are dissolved in 1-methyl-2-pyrrolidone (NMP) and carbon dioxide is used as antisolvent.  相似文献   

7.
Two constitutive models representative of two well-known modeling techniques for superelastic shape-memory wires are reviewed. The first model has been proposed by Kim and Aberayatne in the framework of finite thermo-elasticity with non-convex energy [1 S.-J. Kim and R. Abeyaratne, On the effect of the heat generated during a stress-induced thermoelastic phase transformation, Continuum Mech. Thermodyn., vol. 7, pp. 311332, 1995.[Crossref], [Web of Science ®] [Google Scholar]]. In the present article this model has been modified in order to take into account the difference between elastic moduli of austenite and martensite and to introduce the isothermal approximation proposed in [1 S.-J. Kim and R. Abeyaratne, On the effect of the heat generated during a stress-induced thermoelastic phase transformation, Continuum Mech. Thermodyn., vol. 7, pp. 311332, 1995.[Crossref], [Web of Science ®] [Google Scholar]]. The second model has been developed by Auricchio et al. within the theory of irreversible thermodynamics with internal variables [2 F. Auricchio, D. Fugazza, and R. DesRoches, Rate-dependent thermo-mechanical modelling of superelastic shape-memory alloys for seismic applications, J. Intell. Mater. Syst. Struct., vol. 19, pp. 4761, 2008.[Crossref], [Web of Science ®] [Google Scholar]]. Both models are temperature and strain rate dependent and they take into account thermal effects. The focus in this article is on investigating how the two models compare with experimental data obtained from testing superelastic NiTi wires used in the design of a prototypal anti-seismic device [3 M. Indirli and M.G. Castellano, Shape memory alloy devices for the structural improvement of masonry heritage structures, Int. J. Archit. Heritage, vol. 2, no. 2, pp. 93119, 2008.[Taylor &; Francis Online], [Web of Science ®] [Google Scholar], 4 A. Chiozzi, M. Merlin, R. Rizzoni, and A. Tralli, Experimental comparison for two one-dimensional constitutive models for shape memory alloy wires used in anti-seismic applications. In: European Congress on Computational Methods in Applied Sciences and Engineering (ECCOMAS 2012), e-Book Full Papers, pp. 46724682, 2012. [Google Scholar]]. After model calibration and numerical implementation, numerical simulations based on the two models are compared with data obtained from uniaxial tensile tests performed at two different temperatures and various strain rates.  相似文献   

8.
In this contribution, we present a novel polygonal finite element method applied to hyperelastic analysis. For generating polygonal meshes in a bounded period of time, we use the adaptive Delaunay tessellation (ADT) proposed by Constantinu et al. [1 A. Constantinu, P. Steinmann, T. Bobach, G. Farin, and G. Umlauf, The adaptive Delaunay tessellation: A neighborhood covering meshing technique., Comput. Mech., vol. 42, no. 5, pp. 655669, 2008.[Crossref], [Web of Science ®] [Google Scholar]]. ADT is an unstructured hybrid tessellation of a scattered point set that minimally covers the proximal space around each point. In this work, we have extended the ADT to nonconvex domains using concepts from constrained Delaunay triangulation (CDT). The proposed method is thus based on a constrained adaptive Delaunay tessellation (CADT) for the discretization of domains into polygonal regions. We involve the metric coordinate (Malsch) method for obtaining the interpolation over convex and nonconvex domains. For the numerical integration of the Galerkin weak form, we resort to classical Gaussian quadrature based on triangles. Numerical examples of two-dimensional hyperelasticity are considered to demonstrate the advantages of the polygonal finite element method.  相似文献   

9.
The Kaushal and Tomita's (2002a Kaushal , D. R. , and Y. Tomita . 2002a . An improved method for predicting pressure drop along slurry pipeline . Particulate Science and Technology 20 : 120 .[Taylor & Francis Online] [Google Scholar]) model, which has already been found satisfactory for broadly graded multisized particulate zinc tailings slurry with moderate concentration up to 26%, flow velocity up to 3.5 m/s in 105 mm diameter pipe, mean diameter 140 μm, and geometric standard deviation of particles of 4.0, is tested for concentration distribution data collected by Kaushal et al. (2005 Kaushal , D. R. , K. Sato , T. Toyota , K. Funatsu , and Y. Tomita . 2005 . Effect of particle size distribution on pressure drop and concentration profile in pipeline flow of highly concentrated slurry . International Journal of Multiphase Flow. 31 : 809823 .[Crossref], [Web of Science ®] [Google Scholar]) on two sizes of glass beads, of which mean diameter and geometric standard deviation are 440 μm and 1.2, and 125 μm and 1.15, respectively, with concentration up to 50% and flow velocity up to 5 m/s in 54.9 mm diameter pipe. Kaushal and Tomita's (2002a) model gives more asymmetric concentration distributions. A modified model is proposed by alleviating some of the restrictive assumptions used in the existing model. Comparison of experimental data by Kaushal et al. (2005 Kaushal , D. R. , K. Sato , T. Toyota , K. Funatsu , and Y. Tomita . 2005 . Effect of particle size distribution on pressure drop and concentration profile in pipeline flow of highly concentrated slurry . International Journal of Multiphase Flow. 31 : 809823 .[Crossref], [Web of Science ®] [Google Scholar]), Gillies and Shook (1994 Gillies , R. G. , and C. A. Shook . 1994 . Concentration distributions of sand slurries in horizontal pipe flow . Particulate Science Technology 12 : 4569 .[Taylor & Francis Online], [Web of Science ®] [Google Scholar]), and Matousek (2009 Matousek , V. 2009 . Concentration profiles and solids transport above stationary deposit in enclosed conduit . Journal of Hydraulic Engineering 135 : 11011106 .[Crossref], [Web of Science ®] [Google Scholar]) with the proposed model is satisfactory.  相似文献   

10.
Two- and three-dimensional simulations (created using volume of fluid-fluent) concerning the rise and interactions of two/multiple thermocapillary bubbles arranged horizontally and perpendicular to a hot surface are investigated and presented in this paper. The results indicate that thermocapillary bubble agglomeration can occur in zero gravity. Furthermore, the temperature gradient and bubble diameter were found to have a major impact on the collision between bubbles. The results of Nas and Tryggvason (1993 Nas, S., and G. Tryggvason. 1993. Computational investigation of the thermal migration of bubbles and drops. 175 Fluid Mechanics Phenomena In Microgravity 7183. [Google Scholar]) in their three-dimensional numerical study reported that no such collisions could occur in zero gravity and that bubbles repel each other due to the cold liquid carried between particles during migration. Their results contrast with both the present results and those recorded onboard the Chinese 22nd recoverable satellite experiment by Kang et al. (2008 Kang, Q., H. L. Cui, L. Hu, and L. Duan. 2008. On-board experimental study of bubble thermocapillary migration in a recoverable satellite. Microgravity Science And Technology 20:6771.[Crossref], [Web of Science ®] [Google Scholar]), who observed a total of 19 coalescences between the air bubbles injected in the direction of the temperature gradient of the stagnant heated liquid.  相似文献   

11.
A strategy is presented to obtain production sequences resulting in minimal tooling replacements. An objective function is employed to distribute the tool wear as evenly as possible throughout the sequence. This objective function is an extension of Miltenburg's earlier work (1989 Miltenburg, J. 1989. Level schedules for mixed-model assembly lines in just-in-time production systems. Manage. Sci., 35: 192207. [Crossref], [Web of Science ®] [Google Scholar]) concerned with obtaining production sequences while evenly distributing the satisfaction of demand. Smaller problems are solved to optimality, while larger problems are solved as close as possible to optimality. The production sequences are simulated to estimate required tooling replacements. The methodology presented here consistently results in fewer tooling replacements when compared with earlier published work (McMullen et al. 2002 McMullen, PR, Clark, M, Bell, J and Albritton, D. 2002. A correlation and heuristic approach to production sequences with uniformity of tool wear. Comp.?&;?Op. Res., 30: 435454.  [Google Scholar], McMullen 2003 McMullen, PR. 2003. Sequencing for minimal tooling replacements via a variety of objective functions. Int. J. Prod. Res., 41: 21832199. [Taylor &; Francis Online], [Web of Science ®] [Google Scholar]).  相似文献   

12.
Following on from the work of Anabtawi et al. (2003) Anabtawi, M. Z., Hilal, N. and Al Muftah, A. E. 2003. Volumetric mass transfer coefficient in non-Newtonian fluids in spouted-fluid beds: Part I. Chem. Eng. Technol., 26: 759764.  [Google Scholar], this study examined how the volumetric liquid-phase mass transfer coefficient, k L a, of oxygen in air in three-phase spout-fluid beds was affected by varying the system parameters of bed height, bed diameter, gas velocity, and liquid velocity. The liquid used was 0.1% CMC solution, displaying a pseudo-plastic rheology, with 1.75 mm glass spheres as packing. The values of the Sherwood number were lower than in previous studies (Anabtawi et al., 2003 Anabtawi, M. Z., Hilal, N. and Al Muftah, A. E. 2003. Volumetric mass transfer coefficient in non-Newtonian fluids in spouted-fluid beds: Part I. Chem. Eng. Technol., 26: 759764.  [Google Scholar]), in the range 9,000–186,000. Gas velocity had a similar effect on k L a as in a bubble column, with results also giving good agreement with previous work on two-phase and three-phase spouted bed systems. The correlation obtained for the effect of liquid velocity on k L a compared well with that of Schumpe et al. (1989) Schumpe, A., Deckwer, W. and Nigam, K. D. P. 1989. Gas-liquid mass transfer in three- phase fluidized beds with viscous pseudoplastic liquids. Can. J. Chem. Eng., 67: 873877. [Crossref] [Google Scholar]. An increase in the height of packing increased k L a to the power of 0.319, with an increase in column diameter also causing an increase in k L a, which is in agreement with the results of Akita and Yoshida (1973) Akita, K. and Yoshida, F. 1973. Gas hold-up and volumetric mass transfer coefficient in bubble columns. Ind. Eng. Chem. Process Des. Dev., 12: 7680. [Crossref] [Google Scholar].  相似文献   

13.
Bench scale tests were carried out to investigate the rheological properties of multi-sized particulate Bingham slurries at high solid concentrations ranging from 50% to 70% by weight. In addition, rheological data from Biswas et al. (2000 Biswas, A., B. K. Gandhi, S. N. Singh, and V. Seshari. 2000. Characteristics of coal ash and their role in hydraulic design of ash disposal pipelines. Indian Journal of Engineering and Materials Sciences 7:17.[Web of Science ®] [Google Scholar]) and Chandel et al. (2009, 2010) have also been considered. Based on these extensive amount of rheological data, an empirical model is proposed for viscosity as a function of solid volume fraction (?), maximum solid volume fraction (?m), median particle diameter (d50), and coefficient of uniformity (Cu) using optimization and nonlinear least-square curve-fitting technique. The proposed model shows good agreement with the experimental data considered in the present study and is found to be much better than the previously developed models in predicting the viscosity of multi-sized particulate Bingham slurries at high solid concentrations.  相似文献   

14.
Ehsan Valian  Elham Valian 《工程优选》2013,45(11):1273-1286
A new metaheuristic optimization algorithm, called cuckoo search (CS), was recently developed by Yang and Deb (2009 Yang, X.S. and Deb, S., 2009. Cuckoo search via Lévy flights. In: Proceedings of world congress on nature &; biologically inspired computing (NaBIC 2009), 9–11 December 2009, Coimbatore, India. Piscataway, NJ: IEEE Press, 210214.[Crossref] [Google Scholar], 2010 Yang, X.S. and Deb, S., 2010. Engineering optimisation by cuckoo search. International Journal of Mathematical Modelling and Numerical Optimisation, 1, 330343. doi: 10.1504/IJMMNO.2010.035430[Crossref] [Google Scholar]). This article uses CS and Lévy flights to solve the reliability redundancy allocation problem. The redundancy allocation problem involves setting reliability objectives for components or subsystems in order to meet the resource consumption constraint, e.g. the total cost. The difficulties facing the redundancy allocation problem are to maintain feasibility with respect to three nonlinear constraints, namely, cost, weight and volume-related constraints. The redundancy allocation problems have been studied in the literature for decades, usually using mathematical programming or metaheuristic optimization algorithms. The performance of the algorithm is tested on five well-known reliability redundancy allocation problems and is compared with several well-known methods. Simulation results demonstrate that the optimal solutions obtained by CS are better than the best solutions obtained by other methods.  相似文献   

15.
Ice is being used in certain deep mines to transport refrigeration to underground areas. Research has been carried out previously into the pipeline conveying characteristics of ice with air, but there remains a lack of knowledge about some aspects of this complex flow. Previous articles (Sheer, 1995 Sheer , T. J. 1995 . Pneumatic conveying of ice particles through mine-shaft pipelines . Powder Technol. 85 : 203219 . [Google Scholar]; Sheer et al., 2001 Sheer , T. J. , R. Ramsden , & M. Butterworth . 2001. The design of pipelines for transporting ice into deep mines. In Handbook of Conveying and Handling of Particulate Solids , eds. A. Levy and H. Kalman . New York : Elsevier Science. pp. 425433. [Google Scholar]) have described experimental results on the pneumatic conveying of ice in particulate form (“hard” ice) through successive long horizontal and vertical sections of pipelines into mines. More recent research has been carried out to determine the conveying characteristics of “slush” ice that resembles wet snow, with an ice mass fraction range of 65–75%. Laboratory pneumatic conveying tests with slush ice were conducted through three horizontal plastic pipelines with inner diameters of 43, 54, and 69 mm, each pipeline being approximately 50 m long and including various bends. The tests yielded numerical and photographic data that were used to investigate the conveying characteristics of slush ice (including flow regime transition to plug flow and pressure gradients) and to compare them with the previous results for particulate ice. It was found that the conveying characteristics of the slush depend strongly on the water content. Correlations are proposed for multiphase friction factors.  相似文献   

16.
In this paper, the exponential stability of travelling waves solutions for nonlinear cellular neural networks with distribute delays in the lattice is studied. The weighted energy method and comparison principle are employed to derive the sufficient conditions under which the networks proposed are exponentially stable. Following the study [13 X. Liu, P. Weng, and Z. Xu, Existence of traveling wave solutions in nonlinear delayed cellular neural networks, Nonlinear Anal. Real World Appl. 10(1) (2009), pp. 277286.[Crossref], [Web of Science ®] [Google Scholar]] on the existence of the travelling wave solutions in nonlinear delayed cellular neural networks, this paper is focused on the exponential stability of these travelling wave solutions.  相似文献   

17.
For single end-product master production scheduling with time-varying demand uncertainty and supply capacity, we study approaches to set replenishment quantities over the planning horizon. We present a stochastic programming model along with a simulation-based optimisation and two traditional approaches for setting order quantities. We compare these approaches to two new methods: gamma approximation and safety stock search. Computational experiments show that the gamma approximation and safety stock search perform well in terms of holding and shortage costs, with expected total cost on average, respectively, within 0.06% and 0.66% of the optimal from the stochastic program. On average, the two traditional approaches incur 12% and 45% higher cost than optimal. We provide managerial insights on the effects of parameters such as demand coefficient of variation (cv), utilisation, and target service level on the optimal total cost, the corresponding fill rate, and the relative performance of the approaches. We find that, for finite-normal demand, on average, the impact of target service level on cost is larger than that of demand cv, whose impact is larger than utilisation, except at high utilisation. We illustrate that, when demand is not normal, the gamma approximation significantly outperforms the existing normal approximation from Bollapragada and Rao (2006 Bollapragada, R and Rao, US. 2006. Replenishment planning in discrete-time, capacitated, non-stationary, stochastic inventory systems. IIE Transactions, 38(7): 583595.  [Google Scholar]).  相似文献   

18.
《国际生产研究杂志》2012,50(13):3630-3642
In this paper, an approach is developed to solve the joint production planning and maintenance problem. Moreover, some propositions and mathematical properties were suggested and applied in the proposed heuristic to solve this integrated problem. It is based on Lagrangian relaxation (Fisher, M.L., 1981 Fisher, M.L. 1981. Lagrangian relaxation method for solving integer programming problem. Management Science, 27(1): 118. [Crossref], [Web of Science ®] [Google Scholar]. Lagrangian relaxation method for solving integer programming problem. Management Science, 27 (1), 1–18) of the capacity constraints and sub-gradient optimisation. At every step of the sub-gradient method, a smoothing procedure is applied to the solution of the Lagrangian problem to ensure the feasibility of solution and to improve it. Computational experiments are carried out to show the results obtained by our approaches and are compared to those of a commercial solver.  相似文献   

19.
Many rapid prototyping systems which produce prototypes by layer-by-layer material deposition are now commercially available. The layer-by-layer deposition process leads to a stepped surface known as staircase. Staircase formation is a geometric constraint of the layered manufacturing, which can not be eliminated. The presence of staircase on the surface of a prototype detracts from the surface finish and hence restricts functionality of prototypes. It is realized that there is a need to make modifications in RP (rapid prototyping) systems so that prototypes with better surface finish can be produced without incurring high production costs. A virtual hybrid fused deposition modelling system (hybrid-FDM) is proposed in the present work that uses both layer-by-layer deposition and machining. In this system, CAD model is sliced adaptively using limited centre line average (Ra) value as a criterion (Pandey et al. 2003a Pandey, P.M., Reddy, N.V. and Dhande, S.G. 2003a. A real time adaptive slicing for fused deposition modelling. Int. J. Machine Tools and Manufacture, 43: 6171.  [Google Scholar]). Hot cutter machining/ploughing (HCM) (Pandey et al. 2003b Pandey, P.M., Reddy, N.V. and Dhande, S.G. 2003b. Improvement of surface finish by staircase machining in fused deposition modelling. Journal of Material Processing Technology, 132: 323331. [Crossref], [Web of Science ®] [Google Scholar]) is recommended to machine the build edges (staircase) of ABS material. Numerically controlled x?y traversing mechanism is proposed as an attachment to move hot cutters along the periphery of slices to machine build edges. In this paper, geometrical designs of cutters are proposed. A process planning system to decide the number of layers to be deposited and then machined in order to access intricate features of a part is implemented. The developed system simulates surface roughness, before and after hot cutter machining. An experimental study is carried out by machining the build edges of an axisymmetric FDM part on lathe machine to form a basis for a hybrid-FDM system.  相似文献   

20.
The problem of designing a water quality monitoring network for river systems is to find the optimal location of a finite number of monitoring devices that minimizes the expected detection time of a contaminant spill event while guaranteeing good detection reliability. When uncertainties in spill and rain events are considered, both the expected detection time and detection reliability need to be estimated by stochastic simulation. This problem is formulated as a stochastic discrete optimization via simulation (OvS) problem on the expected detection time with a stochastic constraint on detection reliability; and it is solved with an OvS algorithm combined with a recently proposed method called penalty function with memory (PFM). The performance of the algorithm is tested on the Altamaha River and compared with that of a genetic algorithm due to Telci, Nam, Guan and Aral (2009) Telci, I. T., K. Nam, J. Guan, and M.M. Aral, 2009. “Optimal Water Quality Monitoring Network Design for River Systems.” Journal of Environmental Management, 90 (3–4): 29872998. doi: 10.1016/j.jenvman.2009.04.011[Crossref], [PubMed], [Web of Science ®] [Google Scholar].  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号