A two-product inventory system with product interaction

In this paper, we study a two-component continuous review inventory system. We assume that demand occurs according to a Poisson process and that a demand can be satisfied only if both the components are available in the inventory. Back-orders are not permitted. We assume that the lead-time distribution of one product is arbitrary and the other is exponential. Identifying the underlying process as a semi-regeneration process we find the stationary distribution of the inventory level, the performance measures such as mean stationary rate of number of lost demands, the demands and the reorders made. A numerical example illustrates the results.Die artikel ondersoek 'n tweekomponent- deurlopende oorsigvoorraadstelsel. Daar word aanvaar dat aanvraag 'n Poissonproses is en dat aanvraag slegs bevredig kan word indien beide die komponente in die voorraad beskikbaar is. Agterstallige bestellings word nie toegelaat nie. Daar word aanvaar dat die lewertydverdeling van die een produk arbitrêr en die ander eksponensieël is. Indien die onderliggende proses as 'n semigenerasieproses geïdentifiseer word, kan die stasionêre verspreiding van die voorraadvlak bepaal word. Maatstawwe van vertoning soos mediaan- stasionêre koers van die hoeveelheid verlore aanvraag, die aanvraag en herbestellings wat gedoen is word bepaal. 'n Numeriese voorbeeld illustreer die resultate.http://sajie.journals.ac.z

Electricity load forecasting with artificial neural networks

Artificial neural networks are powerful tools for time series forecasting. The problem addressed in this article is to do multi-step prediction of a stationary time series, and to find the associated prediction limits. Artificial neural network models for time series are non-linear. However, results that are applicable to linear models are sometimes mistakenly applied to non-linear models. One example where this is observed is in multi-step forecasting. A bootstrap method is proposed to calculate one- and multi-step predictions and prediction limits. The results are applied to an electricity load time series as well as to a pure autoregressive time series.Kunsmatige neurale netwerke is kragtige instrumente vir tydreeksvoorspelling. In hierdie artikel word multistap-vooruitberaming van ‘n stasionêre tydreeks en die gepaardgaande vertroueinterval behandel. Resultate wat slegs geldig is vir lineêre modelle word soms verkeerdelik op neurale netwerkmodelle toegepas. ‘n Voorbeeld hiervan kom in multistap-voorspelling voor. ‘n Skoenlusmetode, word voorgestel waarvolgens eenstap- en multistap- voorspellings en vertroueintervalle bereken kan word. Die resultate word op ‘n elektrisiteitslastydreeks en op ‘n suiwer outoregressiewe tydreeks toegepas.http://sajie.journals.ac.z

Minimising electricity costs by developing an effective combination of alternative energy sources

This study evaluates the high electricity costs faced at a carpet manufacturing company. Research was conducted by focusing on the supply and availability of electricity in South Africa and alternative energy sources. Modelling methods were investigated to determine an appropriate approach to solving the high-cost problem at the company to ensure that the model could be reused for similar scenarios. The findings provide an electricity minimisation solution that requires the installation of a solar system. Using generated solar energy, and consuming generator power to maintain optimal monthly municipal thresholds, electricity costs would be reduced by over R100 000 monthly.Hierdie studie evalueer die hoë kostes van elektrisiteit by ʼn matvervaardigingsmaatskappy. Navorsing het gefokus op die verskaffing en beskikbaarheid van elektrisiteit in Suid-Afrika en alternatiewe energiebronne. Modelleringsmetodes is ondersoek om ʼn gepaste benadering te identifiseer om die hoë-koste probleem by die maatskappy op te los. Die bevindinge verskaf ʼn elektrisiteit minimering oplossing wat die installasie van ʼn sonpaneel stelsel vereis. Deur sonenergie op te wek, en deur dieselgenerator krag te gebruik om die optimale maandelikse munisipale drempels te handhaaf, kan maandelikse energiekostebesparings van meer as R100 000 gerealiseer word.http://sajie.journals.ac.za/pubam2021Industrial and Systems Engineerin

A supply chain management model to optimise the sorting capability of a ‘third party logistics’ distribution centre

In this paper, the process flow within a high-end 3PL distribution centre is studied in order to determine the optimal split between the parcel size categories moved within the system. The article considers the application of an optimisation (MIQP) model with a corresponding discrete event simulation model to validate the authenticity of the solution. The study assumes that the current process flow and layout of the centre remains fixed; the entering and exiting routes to and from the centre and the centre itself are located optimally within the network and the models have base times of one and seven days respectively. Performance measures have been analysed through utilization states of equipment and labour, queue contents versus time and average throughput times of each of the parcel categories. The findings in this paper can create a positive trigger for improvement within the distribution centre as equipment and labour can be downsized to decrease costs and improve safety and benefit the company through the alignment of a network of distribution centres that each applies modified relevant versions of the modelling logic conveyed in this paper.V.S.S. Yadavalli is thankful to NRF for their financial support.http://www.journals.co.za/content/journal/busmanam2017Industrial and Systems Engineerin

A finite source perishable inventory system with second optional service and server interruptions

In this article, a service facility inventory system with server interruptions and a nite number of sources are considered. The inventory is replenished according to (s; S) ordering policy. Using the matrix methods, the stationary distribution of the stock level, server status and waiting area level is obtained in the steady state case. The Laplace-Stieltjes transform of the waiting time of the tagged customer is derived. Many impartment system performance measures are derived and the total expected cost rate is computed under a suitable cost structure. The results are illustrated numerically.The second author research was supported by DST PURSE Phase II for newly recruited faculty of University of Madras (no. DST-PURSE PHASE II/ 2014/ 686).http://orion.journals.ac.zaam2016Industrial and Systems Engineerin

Increasing warehouse throughput through the development of a dynamic class-based storage assignment algorithm

This study investigates the problems faced by an agricultural wholesaler arising from an inefficient random storage assignment policy. Research was conducted on warehouse operations and storage policies. The ABC classification technique was used to create a class-based storage assignment policy. This policy was then input into an algorithm that packs products according to how frequently they are ordered. The aim of the algorithm is to store fast-moving products closest to the shipping area. If this is done, the order picking times would decrease by an average of 3 hours 20 mins per day. This would increase the warehouse’s throughput and profitability.Hierdie studie ondersoek die probleme ervaar deur ’n landbou groothandelaar as gevolg van ’n ondoeltreffende toevaksgebaseerde stoorbeleid. Navorsing is gedoen oor pakhuisbedrywighede en stoorbeleide. Die ABC-klassifikasie tegniek is gebruik om ’n klasgebaseerde stoorbeleid op te stel. Hierdie beleid is toe ingevoer in ’n algoritme wat produkte verpak volgens hoe gereeld die produkte bestel word. Die doel van die algoritme is om produkte wat vinnig beweeg naaste aan die versendingsarea te stoor. As dit gedoen word, sal die bestellingopteltye verminder met ’n gemiddelde tyd van 3 ure en 20 minute per dag. Dit sal die deurset en winsgewendheid van die pakhuis verhoog.http://sajie.journals.ac.zaam2023Industrial and Systems Engineerin

A lot-sizing model for a multi-state system with deteriorating items, variable production rate, and imperfect quality

Conventional production systems assume that during the manufacturing processes, machines operate without breakdown over an infinite planning horizon and manufacture only products of good quality. Imperfect production processes as a result of machine degradation are common in manufacturing. This paper deals with a problem that concerns the modelling and evaluation of the performance of a multi-state production system that is subject to degradation and its effect on lot sizing. Here, we consider that the cycle starts with a particular production rate until a point when the inventory reaches a certain level after which the failure mode is activated due to the deterioration of certain components, leading to a reduction in the production rate in order to ensure the continuity of supply until the maximum inventory level is reached. Production then stops to restore the machine and the cycle starts again. We have assumed that the rate at which inventory deteriorates is exponential and that demand is constant. A numerical example is used to illustrate the model application, followed by sensitivity analysis. This paper contributes to lot sizing in the area of machine reliability by considering a production system in a degraded state with a non-increasing production rate for deteriorating items with imperfect quality and partial backlogging.http://www.ijmems.inhj2023Industrial and Systems Engineerin

Assessment of the quality of service provided by a national regulatory institution

Government institutions need to assess how well they meet the needs of their customers, and what their customers think about the quality of the services they provide. This is aligned with the ‘Batho Pele’ principle of the South African government. The SERVQUAL scale, augmented with a qualitative survey, was used to determine how the National Home Builders Registration Council (NHBRC) is perceived by its clients, which key factors drive such perceptions, and whether the perceptions are consistent across the different client groups of this regulatory institution. The complementary role of qualitative data in illuminating issues driving quantitative results is highlighted. Service quality scores are computed for the NHBRC. The convergence of opinions of different customer groups was studied using correlation analysis. The significance of service quality perception gaps was tested using the multivariate analysis of variance, and the reliability of the SERVQUAL scale was examined using exploratory factor analysis. It was observed that by improving the feedback mechanism of the NHBRC, their clients’ customer service quality perceptions could be enhanced.Staatsinstansies moet vasstel hoe goed daar voldoen word aan die verwagtinge van hulle kliënte en wat die opinie van hulle kliënte is aangaande die kwaliteit van die diens wat gelewer word. Dit is belyn met die ‘Batho Pele’-beginsel van die Suid-Afrikaanse regering. Die SERVQUAL-skaal , aangevul met ’n kwalitatiewe opname, is gebruik om te bepaal hoe die NHBRC waargeneem word deur sy kliënte, watter faktore hierdie persepsies skep en of die perspesies konsekwent voorkom in die verskillende kliënte-groepe van hierdie regula-toriese instansie. Die komplimentêre rol wat kwalitatiewe data speel om lig te werp op die kwantitatiewe resultate word uitgewys. Verskeie statistiese metodes is aangewend om onder meer die konvergensie van opinie, die betekenisvolheid van diensgapings en die betroubaarheid van die SERVQUAL-skaal te ondersoek. Daar is gevind dat verbeterde terugvoermeganismes binne die NHBRC die persepsie aangaande kwaliteit by hulle kliënte sal verbeter.NRF and RDPhttp://sajie.journals.ac.zaam201

On Gaver's parallel system

Gaver’s parallel system (and its variants) has received considerable attention in the literature. The Laplace-transform (LT) of the survival function, corresponding to the underlying systems, has been derived by various (alternative) methods. Unfortunately, little-to-no attention has been paid to invert the corresponding transform. First, we present a general reliability analysis of Gaver’s basic parallel system (valid for an arbitrary repair time distribution). Then, we formulate some general hints to obtain the numerical inverse. Finally, we propose a tangible methodology to derive the exact inverse in some particular but important cases of non-rotational transforms.Gaver se parallelsisteem (en variante daarvan) is reeds dikwels behandel in die literatuur. Die Laplacetransformasie van die oorlewingsfunksie van die onderliggende sisteme is reeds afgelei op verskillende uiteenlopende wyses. Ongelukkigerwys is min aandag gegee aan die ooreenstemmende inverse transformasie. Ten aanvang word 'n algemene betroubaarheidsontleding van Gaver se basiese parallelsisteem voorgehou (geldig vir 'n arbitrêre hersteltyd-verdeling). Dit word gevolg deur wenke vir bepaling van die numeriese inverse. Ten slotte word 'n tasbare metodologie vir die afleiding van die presiese inverse vir sekere belangrike nie-rotasionele transformasies voorgestel.http://sajie.journals.ac.z

Low-cost energy meter calibration method for measurement and verification

Energy meters need to be calibrated for use in Measurement and Verification (M&V) projects. However, calibration can be prohibitively expensive and a ect project feasibility negatively. This study presents a novel low-cost in-situ meter data calibration technique using a relatively low accuracy commercial energy meter as a calibrator. Calibration is achieved by combining two machine learning tools: the SIMulation EXtrapolation (SIMEX) Measurement Error Model and Bayesian regression. The model is trained or calibrated on half-hourly building energy data for 24 hours. Measurements are then compared to the true values over the following months to verify the method. Results show that the hybrid method significantly improves parameter estimates and goodness of fit when compared to Ordinary Least Squares regression or standard SIMEX. This study also addresses the e ect of mismeasurement in energy monitoring, and implements a powerful technique for mitigating the bias that arises because of it. Meters calibrated by the technique presented have adequate accuracy for most M&V applications, at a significantly lower cost.The National Research Foundation (NRF) and the National Hub for the Postgraduate Programme in Energy Efficiency and Demand Side Management.http://www.elsevier.com/locate/apenergy2018-02-28hb2017Electrical, Electronic and Computer EngineeringIndustrial and Systems Engineerin