Wentian Cui

Overlapping and communication policies in product development

Shorter product life cycles in many industries impel firms to accelerate the product development process. Overlapping development stages, combined with frequent information exchange, is commonly regarded as a core technique for faster product development. However, overlapping and communication require additional resources and can be costly. We investigate the time-cost tradeoffs involved in concurrent product development to determine the optimal overlapping and communication strategies. The methodology was applied to a refrigerator development process in order to illustrate its utility.

Robust makespan minimisation in identical parallel machine scheduling problem with interval data

Parallel machine scheduling problems are commonly encountered in a wide variety of manufacturing environments and have been extensively studied. This paper addresses a makespan minimisation scheduling problem on identical parallel machines, in which the specific processing time of each job is uncertain, and its probability distribution is unknown because of limited information. In this case, the deterministic or stochastic scheduling model may be unsuitable. We propose a robust (min–max regret) scheduling model for identifying a robust schedule with minimal maximal deviation from the corresponding optimal schedule across all possible job-processing times (called scenarios). These scenarios are specified as closed intervals. To solve the robust scheduling problem, which is NP-hard, we first prove that a regret-maximising scenario for any schedule belongs to a finite set of extreme point scenarios. We then derive two exact algorithms to optimise this problem using a general iterative relaxation procedure. Moreover, a good initial solution (optimal schedule under a mid-point scenario) for the aforementioned algorithms is discussed. Several heuristics are developed to solve large-scale problems. Finally, computational experiments are conducted to evaluate the performance of the proposed methods.

Cost range and the stable network structures

Abstract The work of this paper concerns with the stable structures in different cost range identified by Doreian in his paper [Doreian, P., 2006. Actor network utilities and network evolution. Social Networks 28, 137–164]. We point out some problems with his Theorem 4 and present our corrections to that theorem.

A fuzzy approach for sequencing interrelated activities in a DSM

Production and manufacturing systems often involve a myriad of interrelated activities. How these activities are organised and scheduled has a significant effect on the success of a system. Recently, the Design Structure Matrix (DSM) has been regarded as an effective tool for modelling and scheduling interrelated activities. Based on fuzzy set theory, this study explicitly addresses the uncertain activity dependencies in our formulation and develops a mathematical model for sequencing interrelated activities in a DSM. Because of the complexity of the model, a new approach, which embeds an exact algorithm within a framework of a local search heuristic, is presented for solving large problem instances. Testing results demonstrate that relatively good solutions can be easily obtained by our approach, thereby providing managers with an effective tool for scheduling a large number of interrelated activities with uncertain dependencies.

An effective approach for scheduling coupled activities in development projects

One of the greatest challenges in managing product development projects is identifying an appropriate sequence of many coupled activities. The current study presents an effective approach for determining the activity sequence with minimum total feedback time in a design structure matrix (DSM). First, a new formulation of the optimization problem is proposed, which allows us to obtain optimal solutions in a reasonable amount of time for problems up to 40 coupled activities. Second, two simple rules are proposed, which can be conveniently used by management to reduce the total feedback time. We also prove that if the sequence of activities in a subproblem is altered, then the change of total feedback time in the overall problem equals to the change in the subproblem. Because the optimization problem is NP-complete, we further develop a heuristic approach that is able to provide good solutions for large instances. To illustrate its application, we apply the presented approach to the design of balancing machines in an international firm. Finally, we perform a large number of random experiments to demonstrate that the presented approach outperforms existing state-of-art heuristics.

Hedge against total flow time uncertainty of the uniform parallel machine scheduling problem with interval data

We consider a total flow time minimisation problem of uniform parallel machine scheduling when job processing times are only known to be bounded within certain given intervals. A minmax regret model is proposed to identify a robust schedule that minimises the maximum deviation from the optimal total flow time over all possible realisations of the job processing times. To solve this problem, we first prove that the maximal regret for any schedule can be obtained in polynomial time. Then, we derive a mixed-integer linear programming (MILP) formulation of our problem by exploiting its structural properties. To reduce the computational time, we further transform our problem into a robust single-machine scheduling problem and derive another MILP formulation with fewer variables and constraints. Moreover, we prove that the optimal schedule under the midpoint scenario is a 2-approximation for our minmax regret problem. Finally, computational experiments are conducted to evaluate the performance of the proposed methods.

Managing the Concurrent Execution of Dependent Product Development Stages

Concurrent product development, the practice of executing dependent product development stages simultaneously, has become the common mode of new product development because of the increasing importance of time-to-market. However, such simultaneous execution of dependent stages may substantially increase the total amount of rework. This research addresses the trade-offs involved in concurrent process, presents analytical models to determine the optimal priority ordering of initial development and rework, and the optimal overlapping duration. We first show that initial development is prior to rework when learning effect is taken into account. Then, based on the general assumption of nonnegative upstream evolution and the clear definition of maximum concurrency, we prove that the total development cost (including rework cost and opportunity cost of time) is convex with respect to the overlapping duration, and so the optimal overlapping duration can be identified by a simple binary search. After that we investigate the Pareto-optimal overlapping strategies for the cases where budget is given or the time to market is predetermined. Finally, the methodology is illustrated with a case study at a handset design company.

A note on the paper ‘cost range and the stable network structures’

Abstract The analysis in the paper ‘cost range and the stable network structures’ missed a stable structure —— a line. We explain its reason and reinforce the initial conclusion.

Prisoner's dilemma game on adaptive networks under limited foresight

We study the emergence of cooperation in an environment where players in prisoners dilemma game PDG not only update their strategies but also change their interaction relations. Different from previous studies in which players update their strategies according to the imitation rule, in this article, the strategies are updated with limited foresight. We find that two absorbing states-full cooperation and full defection-can be reached, assuming that players can delete interaction relations unilaterally, but new relations can only be created with the mutual consent of both partners. Simulation experiments show that high levels of cooperation in large populations can be achieved when the temptation to defect in PDG is low. Moreover, we explore the factors which influence the level of cooperation. These results provide new insights into the cooperation in social dilemma and into corresponding control strategies.

Exploring express delivery networks in China based on complex network theory

Based on the complex network theory, we explore an express delivery system in China, which consists of two delivery networks, namely, the air delivery network ADN and the ground delivery network GDN. Systematic structural analysis indicates that both delivery networks exhibit small-world phenomenon, disassortative mixing behavior, and rich-club phenomenon. However, there are significant differences between ADN and GDN in terms of degree distribution property and community structure. On the basis of the Barabasi-Albert model, we have proposed a network model incorporating the structural features of the two delivery networks to reveal their evolutionary mechanisms. Lastly, the parcel strength and the distance strength are analyzed, which, respectively, reflect the number of parcels and the long-haul delivery distance handled by a node city. The strengths are highly heterogeneous in both delivery networks and have intense correlations with topological structures. These works are beneficial for express enterprises to construct or extend their express delivery networks, and provide some useful insights on improving parcel delivery service.