Wen-Kai Hsu

A single-period inventory model with fuzzy demand

Abstract The single-period inventory models have wide applications in the real world in assisting the decision maker to determine the optimal quantity to order. Due to lack of historical data, the demand has to be subjectively determined in many cases. In this paper, a single-period inventory model for cases of fuzzy demand is constructed. The costs considered include the procurement cost, shortage cost, and holding cost. For different fuzzy total cost resulted from different order quantity, a method for ranking fuzzy numbers is adopted to find the optimal order quantity in terms of the cost. When the profit gained from selling one item is less (greater) than the loss incurred due to one unsold item, the optimal order quantity lies in the range defined for the left-shape (right-shape) function of the fuzzy demand. If the unit profit is equal to the unit loss, then all quantities with a membership grade 1 are optimal to be ordered. The methodology of this paper can be applied to construct other inventory models with fuzzy demand.

Lot size-reorder point inventory model with fuzzy demands

Abstract This paper discusses the lot size-reorder point inventory problem with fuzzy demands. Different from the existing studies, the shortages are backordered with shortage cost incurred. The α cut of the fuzzy demand is used to construct the fuzzy total inventory cost for each inventory policy ( Q , r ), where Q is the quantity to be ordered and r is the reorder point. Yagers ranking method for fuzzy numbers is utilized to find the best inventory policy in terms of the fuzzy total cost. Five pairs of simultaneous nonlinear equations for the optimal Q ∗ and r ∗ are derived for r in five different ranges of the fuzzy demand. When the demand is a trapezoidal fuzzy number, each pair of the simultaneous equations reduces to a set of closed-form equations. They are proved to be able to produce the optimal solution. Apparently, the methodology developed in this paper can be applied to other types of inventory problems to find the best inventory policy.

Improving the service operations of container terminals

Purposes – In the relevant literature about container terminals (CTs), most studies focused on the internal operational management of CT operators. In practice, for improving the performance of CT operators, the external customers’ requirements should also be considered. The purpose of this paper is to discuss the improvement of service operations of CTs from users’ requirement perspectives.Design/methodology/approach – In this paper, the customer requirements for container terminal are first examined. Based on the customer requirements, a quality function deployment (QFD) model is then constructed to translate the customer requirements into service operations of the container terminals, by which CT operators may make policies to improve their service operations. As an empirical study, the container terminal of Yang‐Ming Shipping Line (YML CT) at Kaohsiung Port and its users were investigated to validate the model.Findings – The result proposes 19 customer requirement attributes from users’ perspectives a...

Evaluating the service requirements of dedicated container terminals: a revised IPA model with fuzzy AHP

The purpose of this article is to evaluate the service requirements of dedicated container terminals (DCTs). In this article, the service attributes (SAs) of DCTs were first discussed. A fuzzy analytic hierarchy process model was then constructed to measure the users’ perceived importance and dissatisfaction for each of the SAs. Based on these two measurements, a revised importance-performance analysis model was proposed to identify the SAs that should be improved. To validate the model, the dedicated container terminal of Evergreen Marine Corp. (EMC DCT) at Kaohsiung Port and its users were empirically investigated. With respect to the empirical results, managerial implications of the findings in improving service quality for the EMC DCT are discussed.

An EOQ model with imperfective quality items under an announced price increase

The economic ordering quantity (EOQ) model has been widely applied to inventory management. However, some assumptions in the model are unrealistic in practice. One of the assumptions is that all produced units are of good quality. This article deals with an EOQ model for products with imperfect quality under an announced price increase, where the defectives are screened out by a 100% inspection process, and which can be sold as a single batch at the end of the inspection process. The optimal ordering policies associated with three kinds of effective times of the price increase are obtained. A numerical example is then provided to illustrate the proposed model. Besides, based on the numerical example, the effects of some important parameters on the optimal order quantity and the corresponding saving in cost are also investigated.

EOQ model where a portion of the defectives can be used as perfect quality

The main purpose of this article is to investigate an economic order quantity model for products with imperfect quality, where the defective items are screened out by a 100% inspection process and then can be sold in a single batch by the end of the inspection process. However, differing from the previous studies on the topic, we assume, in this article, that a portion of the defectives (called the acceptable defective part) can be utilised as perfect quality and that the utilisation of the acceptable defective part will reduce the consumption of the remaining perfect quality items after the defectives are sold. In practice, there are a number of goods (e.g. clothes, sporting shoes, purses, porcelain dishes, fruits, vegetables, etc.) with such characteristic. First, we construct the model in terms of annual profit and find the optimal order quantity with a constant defective percentage. Next, we determine the optimal order quantity for the case that the defective percentage follows a uniform distribution by maximising the expected annual profit. For both cases, two properties of the optimal order quantity and the corresponding annual profit are also given. Finally, two numerical examples are provided to illustrate the proposed models.

The integrated policy with immediate return for defective items

The economic production quantity (EPQ) and the economic order quantity (EOQ) models have been widely used in inventory management for vendors and retailers, respectively. However, an optimal solution for the EPQ or the EOQ model is only based on either vendors’ or buyers’ viewpoint. That is, such an optimal solution is usually beneficial to one of the vendors and buyers, but detrimental to the others. Hence, to establish a long-term cooperative relationship between the vendor and buyer, an integrated inventory model is needed. The purpose of this paper is to investigate a single-vendor single-retailer production-inventory model for products with imperfect quality. It is assumed that a 100% inspection process is conducted to screen out the defectives contained in the received lot and the defectives screened out during the 100% inspection process will be returned to the vendor immediately. By maximizing the expected annual integrated total profit, the optimal number of shipments in a cycle and the optimal size of each shipment are determined. A numerical example is provided to illustrate the proposed model and demonstrate the superiority of the proposed model to a general single supplier-single buyer system not considering lot-splitting shipments.

An EOQ model with immediate return for imperfect items under an announced price increase

The main purpose of this article is to investigate an economic ordering quantity model with imperfect quality under an announced price increase. It is assumed that a 100% inspection process is conducted to screen out the defectives contained in the received lot, and the defectives thus screened out will be returned to the vendor immediately. In practice, the mechanism of returning defectives to the vendor immediately may result from the increasingly exerted power of retailers, the need of satisfying strict quality requirement of customers, or the limitation of the storage space of retailers. Besides, the mechanism of immediate return usually indicates a promise of the vendor to his/her customers and is used to highlight the vendors confidence in his/her products. The optimal ordering policies associated with three kinds of effective times of the price increase are obtained. A numerical example is then provided to illustrate the proposed model. The results indicate that the optimal special ordering quantity and the corresponding saving cost for an increase in price are both increasing with the increment of the price. For any price increase, both of the optimal special ordering quantity and the corresponding saving cost are negatively related to the remnant stock level at the time that the price increase is effective.

An assessment of service quality for international distribution centers in Taiwan – a QFD approach with fuzzy AHP

ABSTRACT The purpose of this article is to examine the service quality of international distribution centers (IDCs). In this article, a quality function deployment with fuzzy analytic hierarchy process model was proposed to translate the service requirement attributes (SRAs) of the IDC users into the service operations attributes (SOAs) of IDC operators. Further, the IDCs in Taiwan were empirically investigated to validate the proposed model. The results create 18 SRAs and 17 SOAs for IDCs, in which the top five SRAs the IDC users perceive as important are: handlings of damaged cargos, correctness of shipping orders, punctuality, storage spaces, and frequency and routes of transportation. Further, with respect to those SRAs, the top five SOAs in terms of priority for IDC operators are: consolidation & deconsolidation, cargo stowage & discharge, delivery scheduling, logistic processing, and business inquiry. Finally, the theoretical and managerial implications of the findings are discussed.

The Acceptance of Workplace Users for a New IT with Mandatory Use

The paper discusses the acceptance of workplace users for a new information technology (IT) with mandatory use. The learning intention of users is employed to define the acceptance. Through three intermediate variables, workload pressure, perceived ease of use, and perceived usefulness, four exogenous variables including computer knowledge of users, technology support, subjective norms, and training were investigated to analyse the determinants that affect the learning intention. For the above analysis, a causal model with an IT of Enterprise Resources Planning (ERP) systems was constructed. As an empirical study, 112 workplace users were sampled to validate the model. The results indicated that, except training factor, all of the exogenous variables have significant direct or indirect effects on user learning intention respectively. The training factor, even though does not affect the user learning intention, has significant relations with technology support and subjective norms. The results provide both theoretical and practical implications for organizations in implementing new IT with mandatory use, especially the IT of ERP systems.