Stability Analysis and Stabilization Strategies for Linear Supply Chains

Due to delays in the adaptation of production or delivery rates, supply chains can be dynamically unstable with respect to perturbations in the consumption rate, which is known as "bull-whip effect". Here, we study several conceivable production strategies to stabilize supply chains, which is expressed by different specifications of the management function controlling the production speed in dependence of the stock levels. In particular, we will investigate, whether the reaction to stock levels of other producers or suppliers has a stabilizing effect. We will also demonstrate that the anticipation of future stock levels can stabilize the supply system, given the forecast horizon is long enough. To show this, we derive linear stability conditions and carry out simulations for different control strategies. The results indicate that the linear stability analysis is a helpful tool for the judgement of the stabilization effect, although unexpected deviations can occur in the non-linear regime. There are also signs of phase transitions and chaotic behavior, but this remains to be investigated more thoroughly in the future.Comment: For related work see http://www.helbing.or

Dampening variability by using smoothing replenishment rules.

A major cause of supply chain deficiencies is the bullwhip effect which can be substantial even over a single echelon. This effect refers to the tendency of the variance of the replenishment orders to increase as it moves up a supply chain. Supply chain managers experience this variance amplification in both inventory levels and replenishment orders. As a result, companies face shortages or bloated inventories, run-away transportation and warehousing costs and major production adjustment costs. In this article we analyse a major cause of the bullwhip effect and suggest a remedy. We focus on a smoothing replenishment rule that is able to reduce the bullwhip effect across a single echelon. In general, dampening variability in orders may have a negative impact on customer service due to inventory variance increases. We therefore quantify the variance of the net stock and compute the required safety stock as a function of the smoothing required. Our analysis shows that bullwhip can be satisfactorily managed without unduly increasing stock levels to maintain target fill rates.Bullwhip effect; Companies; Cost; Costs; Impact; Inventory; Managers; Order; Replenishment rule; Rules; Safety stock; Supply chain; Supply chain management; Variability; Variance; Variance reduction;

Effects of a Trust Mechanism on Complex Adaptive Supply Networks: An Agent-Based Social Simulation Study

This paper models a supply network as a complex adaptive system (CAS), in which firms or agents interact with one another and adapt themselves. And it applies agent-based social simulation (ABSS), a research method of simulating social systems under the CAS paradigm, to observe emergent outcomes. The main purposes of this paper are to consider a social factor, trust, in modeling the agents\' behavioral decision-makings and, through the simulation studies, to examine the intermediate self-organizing processes and the resulting macro-level system behaviors. The simulations results reveal symmetrical trust levels between two trading agents, based on which the degree of trust relationship in each pair of trading agents as well as the resulting collaboration patterns in the entire supply network emerge. Also, it is shown that agents\' decision-making behavior based on the trust relationship can contribute to the reduction in the variability of inventory levels. This result can be explained by the fact that mutual trust relationship based on the past experiences of trading diminishes an agent\'s uncertainties about the trustworthiness of its trading partners and thereby tends to stabilize its inventory levels.Complex Adaptive System, Agent-Based Social Simulation, Supply Network, Trust

The effects of the lack of coordination within the supply chain

The present article refers to the bullwhip effect that negatively influences the supply chain performance. This effect is experienced by various industries, from fast moving consumer goods to IT products. The consequences for the supply chain members are the following: increased costs, lower profitability, longer lead times and lower product availability. The main factors that generate this effect are the types of incentives provided by suppliers to the downstream customers, the information distortion, the order placing practices, the pricing policies encouraging the forward buying and the specific behavior of the supply chain members focused on local optimization. The only way in which supply chain members may eradicate the bullwhip effect is to enhance coordination among the subsequent stages. Some of the strategies to be considered are the alignment of goals and objectives, data sharing among members, single stage control of replenishment, strategies for the improvement of the operational performance, stabilizing orders with appropriate pricing strategies and building strategic partnerships and trust. The incidence and amplitude of the bullwhip effect may be reduced by strategies and decisions that are harmonized along the stages of the supply chain. The key words in the endeavor to diminish the bullwhip effect are cooperation, coordination, communication and trust.bullwhip effect, logistics, supply chain, coordination, information distortion

System Dynamics Simulation to Test Operational Policies in the Milk-Cheese Supply Chain Case study: Piar Municipality, Bolivar State, Venezuela.

With the purpose of detecting the impact that variations of demand cause in the milk-cheese supply chain, and determining how the operational policies of capacity, inventories or labor force can mitigate this impact, a system dynamics simulation model has been designed based on a survey conducted on a sample of cheese manufacturers and their links with milk farms, transportation companies and cheese distributors. This supply chain will be consolidated when a milk center that will collect the raw milk is completed. From this center, and after adequate treatment, milk will be distributed to the different cheese manufacturers in the supply chain. Managing adequately the milk-cheese supply chain represents an important challenge due to the short life of these products. Although this study was done in a region in Latin America, its results can be applicable to food supply chains by introducing some modifications. The milk-cheese supply chain in this case study contemplates three milk producers, one milk center, five cheese producers and several distributing agents. These companies operate individually under normal conditions, but they have understood that their integration in a supply chain improves the competitiveness of all its members. That is to say, the sum is greater than the parts. For its initial design a simulation software model is used in which the resources of the supply chain are optimized. Later the product of this optimization facilitates some initial values to be used in the system dynamics model in which causeeffect or influence relationships have been previously established considering the most representative variables. Finally, changes in operational policies that can reduce the level of pending orders in the supply chain are tested using other simulation software. The main contribution of this research is that it can serve as support or contribute to reduce the uncertainty in the decision making process of the supply chain management due to the speed with which individual or combined policies can be analyzed. In response to a variation of demand the most adequate policy may be selected and that can be done before the policy is implemented

Smooth is smart: bullwhip, inventory, fill-rates and the golden ratio.

Inventory;

The strategic integration of agile and lean supply

Lean supply is closely associated with enabling flow and the elimination of wasteful variation within the supply chain. However, lean operations depend on level scheduling and the growing need to accommodate variety and demand uncertainty has resulted in the emergence of the concept of agility. This paper explores the role of inventory and capacity in accommodating such variation and identifies how TRIZ separation principles and TOC tools may be combined in the integrated development of responsive and efficient supply chains. A detailed apparel industry case study is used to illustrate the application of these concepts and tools

Integrating supply chains: An investigation of collaborative knowledge transfers

This paper aims to empirically investigate the impact upon performance of explicit knowledge transfer in the integrated supply chain between a manufacturer and its external suppliers and customers. Literature derived hypotheses were evaluated using International Manufacturing Strategy Survey data from 338 companies. Valid and reliable scales were created via confirmatory factor analysis, and effects upon inventory performance tested via regression techniques. Whilst knowledge transfers from upstream and downstream directions were positively related to a manufacturer's performance, knowledge derived from customers was more powerful. Furthermore, integrated knowledge transfer- the combination of knowledge emanating from both suppliers and customers- had the strongest link to performance. The implications for practioners are that integrating knowledge across supply chains could be more far reaching than the exchange of assets, data and information usually considered in supply chain literature. Furthermore the current generalized approach to managing external knowledge is inadequate. This study expands upon existing literature by including directional implications as to which knowledge inflows are most valuable. For academics, this paper supports and extends existing literature by considering the supplier-manufacturer-customer triad in unison. The focus goes beyond asset, data and information exchange towards the leveraging of external knowledge. Relevant perspectives and dimensions were adopted from the knowledge management stream in order to add conceptual depth. Several areas of knowledge-based supply chain research have been identified as potential opportunities for further investigation.Supply Chain; Knowledge Management; Empirical Research: