22 research outputs found
Three-echelon circular economic production–inventory model for deteriorating items with imperfect quality and carbon emissions considerations under various emissions policies
No full textThe original publication is available at: https://www.sciencedirect.com/Traditional production systems have a sole focus of maximising economic outcomes but due to the world’s ever-growing awareness about environmental issues, circular production systems, with a dual focus of maximising economic output and minimising environmental impact, have become prevalent in recent years. These types of production systems incorporate circular economy initiatives in their operational processes with the aim of reducing their carbon footprints. However, this is a voluntary measure to reduce carbon footprints and for this reason, various governments have introduced regulatory measures to involuntarily reduce carbon footprints of production systems. These regulatory measures include carbon tax, cap, cap-and-trade and cap-and-offset policies that are designed to reduce carbon emissions from production processes. With this in mind, this paper proposes an integrated sustainable production–inventory model for a three-echelon supply chain for imperfect quality deteriorating items with a circular economy indicator under various carbon emissions regulations. Using four different combinations of functions for both the demand rate and unit gross profit and four different carbon emissions regulations, 16 variants of the model are solved and analysed using heuristic algorithms. The model variants are not only aimed at optimising inventory replenishment decisions but also the circularity economy indicator of the deteriorating inventory. Of the 16 variants, the highest profit is achieved for the logistic demand and linear profit functions combination under cap-and-offset, despite a circularity indicator of 81.75%. The results also show that carbon emissions policies are effective at reducing the supply chain’s carbon footprint, albeit with a slight impact on the profit.https://www.sciencedirect.com/science/article/pii/S0957417424010285?via%3DihubPublisher’s versio
Sustainable inventory models under carbon emissions regulations: Taxonomy and literature review
No full textThe original publication is available at https://www.sciencedirect.com/Atmospheric levels of carbon emissions have been increasing rapidly due to factors such as industrialisation. In response to this, various governments around the world have introduced carbon emissions regulations to curb the negative effects of emissions. Such regulations include carbon tax, cap, cap-and-trade, and cap-and-offset, among others. Given that supply chains are a major source of emissions, research in the broader subject of green supply chain management has experienced rapid growth in recent years. The prevalence of emissions regulations around the world has forced researchers in the area of inventory management to incorporate various emissions regulations into inventory models. Consequently, the sub-area of sustainable inventory models under emissions regulations has emerged as a very active research field within a short space of time. This paper aims to review the current literature on sustainable inventory models under carbon emissions regulations over the period 2013–2023. In addition, the paper also develops a novel taxonomy for classifying the literature, utilising factors such as types of emissions regulations, input data, types of items, shortages, delayed payments, nature of the demand, and objective function, among others. An analysis of the reviewed literature indicates that sustainable inventory models under emissions regulations is a rapidly growing area of research, driven mostly by the increased legislation around emissions. In terms of future research agenda, accounting for uncertainties, bridging the gap between theory and practice via real-life case studies, and applying soft computing methods represent some of the most promising areas for further development.https://www.sciencedirect.com/science/article/pii/S030505482400337
The impact of preservation technology investments on lot-sizing and shipment strategies in a three-echelon food supply chain involving growing and deteriorating items
No full textFood production systems are complex industrial operations that often involve multiple parties. This study
proposes inventory management strategies for a multi-echelon perishable food supply chain with growing
and deteriorating items. The upstream end of the proposed food supply chain is the farming echelon where
newborn growing items are reared to maturity. Following this, the items are sent to the processing echelon for
processing, a term that collectively describes activities such as slaughtering, cutting and packaging. The aim
of the processing echelon is to transform live growing items into processed food products that are suitable for
human consumption. The downstream end of the supply chain is the retail echelon where consumer demand
for processed food products is met. Once the items are processed, they are subject to deterioration at both
the processing and retail echelons. In light of this, an integrated inventory model aimed at optimising the
performance of the entire food supply chain is formulated. The impact of investing in preservation technologies
is also investigated due to the perishable nature of food products. To do this, a secondary model that
incorporates an investment in preservation technologies is formulated. The model, representing a simplified
industrial food production system, is aimed at jointly optimising the lot-size, number of shipments, growing
cycle duration, processing cycle duration and the preservation technology investment amount. The results
from the numerical example demonstrate that the preservation technology investment is worthwhile because
it results in reduced inventory management costs across the supply chain.http://www.elsevier.com/locate/orpam2023Industrial and Systems Engineerin
The impact of preservation technology investments on lot-sizing and shipment strategies in a three-echelon food supply chain involving growing and deteriorating items
No full textFood production systems are complex industrial operations that often involve multiple parties. This study proposes inventory management strategies for a multi-echelon perishable food supply chain with growing and deteriorating items. The upstream end of the proposed food supply chain is the farming echelon where newborn growing items are reared to maturity. Following this, the items are sent to the processing echelon for processing, a term that collectively describes activities such as slaughtering, cutting and packaging. The aim of the processing echelon is to transform live growing items into processed food products that are suitable for human consumption. The downstream end of the supply chain is the retail echelon where consumer demand for processed food products is met. Once the items are processed, they are subject to deterioration at both the processing and retail echelons. In light of this, an integrated inventory model aimed at optimising the performance of the entire food supply chain is formulated. The impact of investing in preservation technologies is also investigated due to the perishable nature of food products. To do this, a secondary model that incorporates an investment in preservation technologies is formulated. The model, representing a simplified industrial food production system, is aimed at jointly optimising the lot-size, number of shipments, growing cycle duration, processing cycle duration and the preservation technology investment amount. The results from the numerical example demonstrate that the preservation technology investment is worthwhile because it results in reduced inventory management costs across the supply chain
Inventory management for growing items in multi-echelon supply chains
No full textThesis (PhD)--University of Pretoria, 2020.Growing items have, in recent years, emerged as a distinct class of items within inventory modelling, similar to perishable or repairable items, for example. This class of items includes livestock, crops and fish, to name a few. The importance of inventory models developed specifically for growing items is due to the utility of these items to humanity and the financial implication that a poor inventory management system can have on a business. Most growing items are consumed as food products, albeit in a form that is suitable for human consumption. From a financial standpoint, inventory often accounts for the biggest portion of the current assets of a business' balance sheet and therefore, a poorly managed inventory system has the potential to financially cripple a business.
The objective of this research is to develop models for managing growing inventory items in multi-echelon supply chain settings. Food production operations are complex industrial systems that often involve multiple entities and processes. Food production systems often start with farming operations at the upstream end of the supply chain, where the live growing items are reared, and end with retail operations at the downstream end of the supply chain, where consumable food products are sold to end-users. The farming and retail ends of the supply chain are often connected by various forms of value-adding operations such as, in the case of livestock, de-feathering, stunning, slaughtering, processing and packaging. These value-adding activities transform the live items into a form that is safe for sale and consumption. Hence, a multi-echelon supply chain structure best represents these operations. This is a departure from most current literature whereby the models not only ignore the value-adding operations but also the multi-echelon nature of food production systems. By accounting for these shortcomings in the current literature, the models presented in this thesis are more realistic and are thus, useful for operations and supply chain management practitioners who can use them when making ordering and shipment decisions in multi-echelon supply chains that involve growing items.
Furthermore, issues such as item mortality, quality control, pricing decisions, quantities of stock on shelves and expiration dates are also taken into account. These issues are important in food production systems and this further enhances the practical use of the models. The importance of these issues, along with that of collaboration between all supply chain members, is quantified through numerical experimentation. In certain instances, the profit generated across the supply chain can increase by as much as 15% if all members collaborate and integrate their ordering and shipment decisions. Prolonging the shelf life (expiration date) of food products by 40% can increase supply chain profits by as much as 21%. Furthermore, supply chain profits can be increased by as much as 10% and 21%, respectively, if survival rates of live inventory items and acceptable quality levels of the processed inventory are kept at 100%. While 100% survival rates and 100% acceptable quality levels might not be possible in reality, operations and supply chain management practitioners should strive to keep them as high as possible. Practitioners should also invest in preservation technologies that have the potential to improve the freshness of products. All these measures, along with increased collaboration between supply chain members, can be used by supply chain practitioners to increase profits across food production systems.Industrial and Systems EngineeringPhDUnrestricte
Selected deterministic models for lot sizing of growing items inventory
No full textDissertation (MEng)--University of Pretoria, 2018.One of the more recent advances in inventory management is the modelling of inventory
systems consisting of items which are capable of growing during the course of the replen-
ishment cycle. These items, such as livestock, are a vital part of life because most of
them serve as saleable food items downstream in supply chains.
In the context of this study, growth is de ned as achieving an increase in weight.
This increase in weight is what di erentiates growing items from conventional items. A
typical inventory system for growing items has two distinct periods, namely growing and
consumption periods. The growth period starts when a shipment of live newborn arrives.
The live items are fed so that they can grow. All the items in each lot are assumed
to grow at the same rate. Once the weight of the items reaches a speci c target, they
are slaughtered. This marks the end of the growth period and thus the start of the
consumption period. The slaughtered items are kept in stock and consumed continuously
at a given demand rate. At the instant that the consumption period ends, items in the
next cycle would have completed their growth period and they will be ready for slaughter
and consumption. A feeding cost is incurred for feeding the live items during the growth
period whereas holding costs are incurred for keeping the slaughtered items in stock
during the consumption period.
This study is aimed at developing lot sizing models for growing items under three
di erent conditions which might occur in food supply chains. These selected conditions
are used to develop three Economic Order Quantity (EOQ) models for growing items. In
addition to item growth, these three models assume, respectively, that a certain fraction
of the items is of imperfect quality due to errors in one of the processing stages; the
available growing and storage facilities have limited capacities; and the vendor of the
items o ers incremental quantity discounts. These models are aimed at answering two of
the most important questions facing inventory managers, namely \how much to order?"
and \when to place order?". A third question, which is speci c to growing items, arises,
namely \when should the items be slaughtered?".
In the imperfect quality model, it is assumed that the poor quality items are also
sold, but at a discounted price. Furthermore, there is a screening process, conducted
on all the items before they are sold, to separate the poor quality items from those of
good quality. For the limited capacity model, it is assumed that if the order quantity
exceeds the available capacity, additional growing and storage capacities are rented from
an external service provider, but this comes at a cost as the rented warehouse has higher holding costs. The nal model assumes that the supplier of the newborn items o ers the
purchasing company incremental quantity discounts.
For all three model presented in this study, the proposed inventory systems are given
vivid descriptions which are used to formulate corresponding mathematical models. So-
lution procedures for solving the proposed mathematical models are also presented. Nu-
merical examples are provided to demonstrate the solution procedures and to conduct
sensitivity analyses on the major input parameters.
The presence of poor quality items means that more items need to be ordered in or-
der to meet a speci c demand for good quality items. The e ect worsens as the fraction
of imperfect quality items increases. Having capacity constraints on the growing and
storage facilities increases total costs mainly because of the higher holding costs in the
rented facility. As the capacity increases, the total costs decrease, but increasing capacity
is capital intensive and poses nancial risks if market conditions change for the worst.
Quantity discounts were shown to reduce the purchasing cost of the newborn items, how-
ever ordering very large quantities has downsides as well. The biggest downsides are the
risk of running out of storage capacity, the increased holding costs and item deterioration
since larger order quantities result in increased cycle times. Through sensitivity analyses
conducted for all three models, the target slaughter weight was shown to have the greatest
e ect on the EOQ than any other input parameter.
The inventory models presented in this study can be used by procurement and in-
ventory managers, working in industries which stock growing items, as a guideline when
making purchasing decisions. This can result in sizable reductions in inventory-related
costs. Seeing that growing items are an integral part of food supply chains, the result-
ing cost savings can be used to cushion consumers against rising food prices or from a
nancial stand point, the savings can be used to boost pro t margins.Industrial and Systems EngineeringMEngUnrestricte
A sustainable inventory model for a two-echelon cold chain with green technology investments and stock-dependent demand under carbon emissions tax regulation
No full textCold chains are specialised supply chains that make use of refrigerated storage facilities and distribution nodes. Products that have to be stored and distributed via cold chains are temperature-sensitive items such as perishable food or vaccines. If these products are not maintained at the correct temperatures, their safety and quality may be comprised with dire consequences for end-users. Operating refrigerated storage units consumes a lot of energy and the majority of transportation trucks used for distribution are powered by fossil fuels and therefore, cold chains are a major source of carbon emissions. With this in mind, this paper proposes a sustainable inventory model for a two-echelon cold chain with stock-dependent demand and green technology investments under a carbon emissions tax regulation. The carbon tax is imposed by policy makers to encourage the cold chain to reduce its emissions whereas, the green technology investment is a voluntary measure taken by the cold chain to reduce its carbon emissions. Based on the results, a carbon tax regulation is about 3% more effective than a green technology investment in terms of profit maximisation potential. Moreover, when it comes to investing in green technologies, there is an optimal investment amount above which increasing the investment results in decreased profits and increased emissions. Other avenues that the cold chain can explore in effort to improve profitability include increasing the potential market size, displaying higher volumes of stocks, using larger capacity transportation trucks and filling the trucks to capacity
Sustainable inventory, pricing, and marketing strategies for imperfect quality perishable items with inspection errors and advertisement-, expiration date- and price-dependent demand under carbon emissions policies
No full textThe demand for perishable products is affected by freshness levels, advertising efforts and selling prices, among other factors. By virtue of being consumed mostly by humans, quality control is also an important factor in perishable production systems. Moreover, inventory management related operations in such production systems release sizeable quantities of carbon emissions that are often regulated by carbon policies. To study the interactions of all these attributes in the context of a perishable inventory system, this paper proposes four sustainable inventory models for a perishable product with imperfect quality, inspection errors and whose demand depends on the advertising frequency, expiration date and selling price. The emissions released are assumed to be governed by carbon tax and carbon cap policies. Two of the models are developed under the assumption that the quality inspection process is 100% effective while the other two models consider the possibility of committing inspection errors, and additionally, for each pair of models, one is developed under a carbon tax policy and the other under a carbon cap policy. All the models are aimed at jointly optimising the perishable product’s lot-size, advertising frequency and selling price. The numerical results show that the presence of inspection errors leads to 28% and 23% lower profits under carbon tax and cap policies, respectively. Moreover, profit can be maximised by either stocking perishable products with longer shelf lives or targeting customers that engage with advertising mediums and those that are not price-conscious, while emissions can be minimised via the enforcement of carbon policies
Economic order quantity model for growing items with incremental quantity discounts
No full textCertain inventory items are living organisms, for example livestock, and are therefore capable of growing during the replenishment cycle. These items often serve as various saleable food items downstream in supply chains. The purpose of this paper is to
develop a lot sizing model for growing items if the supplier of the items ofers incremental quantity discounts. A mathematical
model is derived to determine the optimal inventory policy which minimises the total inventory cost in both the owned and
rented facilities. A solution procedure for solving the model is developed and illustrated through a numerical example. Sensitivity
analysis is performed to demonstrate the response of the order quantity and total costs to some key input parameters. Incremental quantity discounts result in reduced purchasing costs; however, ordering very large quantities has downsides as well. The
biggest downsides include the increased holding costs, the risks of running out of storage capacity and item deterioration since
the cycle time increases if larger quantities are purchased. Owing to the importance of growing items in the food supply chains,
the model presented in this article can be used by procurement and inventory mangers when making purchasing decisions.https://link.springer.com/journal/40092/volumes-and-issuespm2020Industrial and Systems Engineerin
Optimal inventory replenishment and shipment policies in a three-echelon supply chain for growing items with expiration dates
No full textThe primary source of a vast majority of consumable food products is growing items such as crops or livestock. Most of these food products have specified maximum shelf lives or expiration dates. This implies that the products are no longer suitable for human consumption beyond their expiration dates. In addition, consumers rarely eat these products in their original form, this means that there are usually some forms of value-adding activities performed on the growing items in order to transform them into a consumable form, for instance, processing and packaging. Consequently, this study develops a model for managing inventory in a three-echelon supply chain for growing items with distinct farming, processing and retail operations. At the farming echelon, the growing items are reared but there is the possibility that some of them might die. The surviving items are then transferred to the processing echelon for slaughtering, processing and packaging. The processed inventory is then transferred to the retail echelon where consumer demand for consumable (i.e. processed and packaged) inventory is met under the assumption that the inventory has a specified expiration date. The proposed supply chain system is modelled as a cost minimisation problem. The benefits of integrating inventory replenishment decisions among all supply chain members are quantified through a numerical example.https://www.springer.com/journal/125972023-03-16hj2022Industrial and Systems Engineerin
