scholarly journals Analysis of make-to-stock queues with general processing times and start-up and lost sales costs

2021 ◽  
Vol 12 (1) ◽  
pp. 8-19
Author(s):  
Sinem Özkan ◽  
Önder Bulut
Keyword(s):  
Numerical Study ◽  
Production Costs ◽  
Lost Sales ◽  
Critical Number ◽  
Line Production ◽  
Processing Times ◽  
Long Run ◽  
Average System ◽  
General Production ◽  
Make To Stock

We consider a make-to-stock environment with a single production unit that corresponds to a single machine or a line. Production and hence inventory are controlled by the two-critical-number policy. Production times are independent and identically distributed general random variables and demands are generated according to a stationary Poisson process. We model this production-inventory system as an M/G/1 make-to-stock queue. The main contribution of the study is to extend the control of make-to-stock literature by considering general production times, lost sales and fixed production costs at the same time. We characterize the long-run behaviour of the system and also propose a simple but very effective approximation to calculate the control parameters of the two-critical-number policy. An extensive numerical study exhibits the effects of the production time distribution and the system parameters on the policy control levels and average system cost.

OPTIMAL PRICING AND PRODUCTION POLICIES OF A MAKE-TO-STOCK SYSTEM WITH FLUCTUATING DEMAND

2009 ◽  
Vol 23 (2) ◽  
pp. 205-230 ◽  
Author(s):  
Jean-Philippe Gayon ◽  
Işılay Talay-Değirmenci ◽  
Fikri Karaesmen ◽  
E. Lerzan Örmeci
Keyword(s):  
Dynamic Pricing ◽  
Numerical Study ◽  
Optimal Pricing ◽  
Pricing Strategies ◽  
Pricing Policy ◽  
Stock Level ◽  
Production Inventory ◽  
Static Pricing ◽  
Make To Stock ◽  
Production Inventory System

We study the effects of different pricing strategies available to a production–inventory system with capacitated supply, which operates in a fluctuating demand environment. The demand depends on the environment and on the offered price. For such systems, three plausible pricing strategies are investigated: static pricing, for which only one price is used at all times, environment-dependent pricing, for which price changes with the environment, and dynamic pricing, for which price depends on both the current environment and the stock level. The objective is to find an optimal replenishment and pricing policy under each of these strategies. This article presents some structural properties of optimal replenishment policies and a numerical study that compares the performances of these three pricing strategies.

SINGLE-MACHINE MULTIPLE-RECIPE PREDICTIVE MAINTENANCE

2013 ◽  
Vol 27 (2) ◽  
pp. 209-235 ◽  
Author(s):  
Yiwei Cai ◽  
John J. Hasenbein ◽  
Erhan Kutanoglu ◽  
Melody Liao
Keyword(s):  
Optimal Policy ◽  
Predictive Maintenance ◽  
Production Costs ◽  
Threshold Policy ◽  
Discrete Time Markov Chain ◽  
System A ◽  
Long Run ◽  
Monotonicity Result ◽  
Maintenance Policies ◽  
Discounted Costs

This paper studies a multiple-recipe predictive maintenance problem with M/G/1 queueing effects. The server degrades according to a discrete-time Markov chain and we assume that the controller knows both the machine status and the current number of jobs in the system. The controller's objective is to minimize total discounted costs or long-run average costs which include preventative and corrective maintenance costs, holdings costs, and possibly production costs. An optimal policy determines both when to perform maintenance and which type of job to process. Since the policy takes into account the machine's degradation status, such control decisions are known as predictive maintenance policies. In the single-recipe case, we prove that the optimal policy is monotone in the machine status, but not in the number of jobs in the system. A similar monotonicity result holds in the two-recipe case. Finally, we provide computational results indicating that significant savings can be realized when implementing a predictive maintenance policies instead of a traditional job-based threshold policy for preventive maintenances.

scholarly journals Doubled haploid technology for line development in maize: technical advances and prospects

2019 ◽  
Vol 132 (12) ◽  
pp. 3227-3243 ◽  
Author(s):  
Vijay Chaikam ◽  
Willem Molenaar ◽  
Albrecht E. Melchinger ◽  
Prasanna M. Boddupalli
Keyword(s):  
Doubled Haploid ◽  
Chromosome Doubling ◽  
Production Costs ◽  
Great Promise ◽  
Success Rates ◽  
Haploid Induction ◽  
Maize Breeding ◽  
Breeding Programs ◽  
Line Production

Key Message Increased efficiencies achieved in different steps of DH line production offer greater benefits to maize breeding programs. Abstract Doubled haploid (DH) technology has become an integral part of many commercial maize breeding programs as DH lines offer several economic, logistic and genetic benefits over conventional inbred lines. Further, new advances in DH technology continue to improve the efficiency of DH line development and fuel its increased adoption in breeding programs worldwide. The established method for maize DH production covered in this review involves in vivo induction of maternal haploids by a male haploid inducer genotype, identification of haploids from diploids at the seed or seedling stage, chromosome doubling of haploid (D0) seedlings and finally, selfing of fertile D0 plants. Development of haploid inducers with high haploid induction rates and adaptation to different target environments have facilitated increased adoption of DH technology in the tropics. New marker systems for haploid identification, such as the red root marker and high oil marker, are being increasingly integrated into new haploid inducers and have the potential to make DH technology accessible in germplasm such as some Flint, landrace, or tropical material, where the standard R1-nj marker is inhibited. Automation holds great promise to further reduce the cost and time in haploid identification. Increasing success rates in chromosome doubling protocols and/or reducing environmental and human toxicity of chromosome doubling protocols, including research on genetic improvement in spontaneous chromosome doubling, have the potential to greatly reduce the production costs per DH line.

A Numerical Study of Solder Paste Rolling Process for PCB Printing

2018 ◽  
Author(s):  
Ricardo F. Oliveira ◽  
Nelson Rodrigues ◽  
José Carlos Teixeira ◽  
Duarte Santos ◽  
Delfim Soares ◽  
...  
Keyword(s):  
Numerical Study ◽  
Flow Simulation ◽  
Rolling Process ◽  
Production Costs ◽  
Process Efficiency ◽  
Solder Paste ◽  
Filling Process ◽  
Newtonian Viscosity ◽  
Air Interface ◽  
Increasing Demand

The increasing demand for electronic devices associated with the increasing competitiveness between enterprises, pushes towards process automation to decrease production costs. The reflow soldering has proven to be effective in this regard. This is composed by a series of steps or processes, such as: (a) stencil printing, (b) component placement and (c) reflow oven soldering. Each process has its specific traits that contribute to the overall process efficiency. The present study is directed towards process (a), which includes the rolling of the solder paste over the stencil surface, followed by the subsequent filling of the stencil apertures. Several parameters influence the solder paste behaviour and thus the effectiveness of the rolling process. This work focuses on the solder paste non-Newtonian viscosity properties, with the solder paste presenting a thixotropic behaviour, necessary for the filling of the stencil apertures. Although the increase in the squeegee velocity causes extra shear in the solder paste and consequently lower viscosity, the excess of velocity may cause defects in the aperture filling process. In addition, during the rolling process, air may become entrapped in the solder paste. The complexity of this process is addressed by numerical simulation, in particular, using the work-package ANSYS to study the solder paste progress, during the rolling process, as well as the parameters influencing it. The fluid flow simulation is solved using the solver FLUENT®, a simplified 2D domain with real case dimensions, a transient prediction of the viscosity, which is a function of the solder paste solicitation, and finally by using the Volume of Fluid (VOF) method to track the solder-air interface boundary. Dynamic meshing methods are also employed to replicate the movement of the squeegee wall, in its task to push the solder paste tumble over the stencil. This study enlightens the role played by the printing velocity in the stencil aperture filling, a logarithm correlation can be found between them. It was found that lower print velocities provide better results than higher speeds. It was observed that the back tip of the squeegee blade causes a partial removal of the solder paste from the aperture, which is higher for faster print processes. An analysis of the filling process over time concluded that, independently of the printing velocity, 90% of the filling occurs in the first quarter of the process.

Technical and Economic Evaluation of Three Types of Tomato Nutrient Solutions under Semi-Controlled Conditions

2016 ◽  
Vol 8 (8) ◽  
pp. 68 ◽  
Author(s):  
Lady Arbelaez ◽  
John Rivera ◽  
Alejandro Hurtado-Salazar ◽  
Nelson Ceballos-Aguirre
Keyword(s):  
Net Present Value ◽  
Root Zone ◽  
Irrigation System ◽  
Cost Benefit ◽  
Production Costs ◽  
Selling Price ◽  
Controlled Conditions ◽  
Cost Benefit Ratio ◽  
General Production ◽  
Nutrient Solutions

<p>This study was conducted to evaluate the effect of three types of nutrient solutions on the development, performance, quality and cost of chonto tomato (<em>Solanum lycopersicum</em> L.) under semi-controlled conditions. The assessment was conducted in the farm Tesorito, Manizales, Colombia. An experimental design was established in randomized complete blocks (RCB), with 3 treatments, 4 replicates per treatment and 10 effective plants per replicate. The variables were: height of the first cluster, production per plant, yield t ha-1 and qualities of the fruit. The economic variables were production costs, cost-benefit ratio (C/BR), rate of return (IRR) and net present value (NPV). In general, production per plant was greater than 4.7 kg plant<sup>-1</sup> and the average yield was 92 t ha<sup>-1</sup>. The use of conventional fertilization (tt2) generated increased production of premium quality fruit with a value of 37.11 t ha<sup>-1</sup>, demonstrating that conventional soil fertilization implemented in this culture under semi-controlled conditions in the company of drip irrigation system in the root zone improve outcomes of productive variables, increasing profitability and competitiveness with a net profit of USD$ $ 25203.68 ha<sup>-1</sup>, with average selling price of USD$ 0.45 per kilogram and a unit production margin of USD$ 0.21 per kilogram, making this technology attractive and economically viable.</p>

scholarly journals Integrating Queueing Theory and Scheduling for Dynamic Scheduling Problems

2014 ◽  
Vol 50 ◽  
pp. 535-572 ◽  
Author(s):  
D. Terekhov ◽  
T. T. Tran ◽  
D. G. Down ◽  
J.C. Beck
Keyword(s):  
Queueing Theory ◽  
Dynamic Scheduling ◽  
Queueing Network ◽  
Scheduling Problems ◽  
Short Term ◽  
Arrival Times ◽  
Processing Times ◽  
Long Run ◽  
Resource Requirements ◽  
First Time

Dynamic scheduling problems consist of both challenging combinatorics, as found in classical scheduling problems, and stochastics due to uncertainty about the arrival times, resource requirements, and processing times of jobs. To address these two challenges, we investigate the integration of queueing theory and scheduling. The former reasons about long-run stochastic system characteristics, whereas the latter typically deals with short-term combinatorics. We investigate two simple problems to isolate the core differences and potential synergies between the two approaches: a two-machine dynamic flowshop and a flexible queueing network. We show for the first time that stability, a fundamental characteristic in queueing theory, can be applied to approaches that periodically solve combinatorial scheduling problems. We empirically demonstrate that for a dynamic flowshop, the use of combinatorial reasoning has little impact on schedule quality beyond queueing approaches. In contrast, for the more complicated flexible queueing network, a novel algorithm that combines long-term guidance from queueing theory with short-term combinatorial decision making outperforms all other tested approaches. To our knowledge, this is the first time that such a hybrid of queueing theory and scheduling techniques has been proposed and evaluated.

scholarly journals Numerical study of the square cup stamping process: a stochastic analysis

2021 ◽  
Author(s):  
André Filipe Gomes Pereira ◽  
Miguel Fernandes Ruivo ◽  
Marta Cristina Oliveira ◽  
José Valdemar Fernandes ◽  
Pedro André Prates
Keyword(s):  
Numerical Study ◽  
Equivalent Plastic Strain ◽  
Production Costs ◽  
Element Analysis ◽  
Widespread Application ◽  
Punch Force ◽  
Quasi Monte Carlo ◽  
Hardening Law ◽  
Input Parameters ◽  
Anisotropy Coefficients

The industrial demand for products with better quality and lower production costs have encouraged the widespread application of the finite element analysis (FEA) in the development and optimization of sheet metal forming processes. To ensure that the FEA solutions are reliable and robust it is important to take into account the uncertainties that inevitably arise in a real industrial environment. In this context, a numerical study on the influence of the material and process uncertainty in the stamping results of a square cup is presented. In this analysis, it is assumed uncertainty in the elasticity properties, hardening law parameters, anisotropy coefficients, blank thickness, friction coefficient and in the blank holder force. The effect of the uncertainty in these input parameters is evaluated in the punch force, equivalent plastic strain, thickness and cup geometry. Firstly, quasi-Monte Carlo method was used to evaluate the variability in the simulation outputs, considering the uncertainty of the input parameters. This analysis shows that the geometry is the output most sensitive to the uncertainty of the input parameters. Afterwards, a variance-based sensitivity analysis was carried out to identify the input parameters that most influence the output variability. It was concluded that the hardening law parameters and the anisotropy coefficients have the most influence in the stamping results variability of a square cup.

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