二次軸輻路網指派求解法之比較研究

Abstract

摘要 1970年代貨櫃化運輸的興起，使得定期航運市場的營運型態轉變為以貨櫃船為主之運送。由於海運市場中，貨物流量的不平均與不確定性，使得此產業所要面臨的環境更為棘手。另外，就海運營運成本而言，港埠成本佔有極高的比重，為降低每單位運送成本，利用大型船舶經營軸心港構成之主航線，輔以小型接駁船經營支線港的經營策略，亦即以海運軸輻路網為定線基礎，發展船隊航線指派策略，其為現階段航線規劃之主流，而目的在於追求利潤最大，並可降低營運成本、擴大服務路網涵蓋率、及提高服務水準，進而增強整體的競爭力。 本研究以最大化利潤為目標，考慮市場運費、貨物流量、裝卸費成本及港埠費用，使用二次指派(Quadratic Assignment)的整數規劃方法，建立軸心港最大利潤的模式與支線港最大利潤的模式，利用窮舉法，求解軸心港及支線港的選擇及配置。而後再比較窮舉法與O’Kelly(1987)的啟發式解法，以獲得最大利潤之支線港指派方式。支線指派均允許支線港與軸心港可不直接相連，子船使用迴圈式航行於軸心港與支線港之間。 研究範圍以遠東-北美西岸為實例，選擇12個港口作為候選港口，並運用上述方法求解航商以追求最大利潤為目標，獲得航線指派之方式。模式經求解得知軸心港與支線港的總利潤相對於軸心港個數為一凸向上的函數(Concave function)；其意義顯示軸心港個數必須適度的選擇才能令航商獲取最大的利潤；軸心港個數由兩個開始增加時，總利潤會隨著增加，但增加到數個後，如繼續增加，反而會使利潤開始遞減，凸向上曲線的最高點所對應的軸心港個數就是海運軸輻路網中最佳的軸心港數。研究結果顯示本模式對於航商在決定軸心港個數與位置時都能有具體的幫助。

Abstract During 1970, the transportation of containers has raised. It made the operation pattern of regular shipping market turned to give priority to container ships. In see transportation, due to the uncertainty and unbalance of cargo flow, the environment that sea transportation has to face is getting more and more troublesome. Additional, to the operation costs of sea transportation, the costs of harbors took extremely high proportion. In order to lower the shipping cost per unit, we adopt the operation policy. We use big ships in the hubs to establish the main courses, and use smaller ships in the spokes. In brief, we use the hub-and-spoke as the base of shipping routes, and then we develop the assigned strategy of the fleets. It is the main stream of deciding nowadays fleet courses, in order to maximize the profits. Besides, it can also lower the costs, enlarge the coverage of service network, improve the service level and to increase the competition advantages of fleets. The purpose of this paper is to maximize the profits, considering the freight of market, the cargo flow, the loading fee and the harbors charges, and use the Quadratic assignment to establish the maximum profit model of hub harbors and the maximum profit model of spoke harbors. Then use total enumeration to solve the optimal solutions of the choices of the hub-and-spoke harbors. Then we compare total enumeration to O’ Kelly’s heuristic method, to obtain the mode of assigned of spoke harbors which can apply the maximum profits. The number of feeders on branch network, given the loop type to match with the traffic flow. We took Far East – North America coast as the research range, then choose 12 harbors as the candidate harbors, and use the algorithm mentioned above to sole, in order to maximize the profit. Then we can obtain the mode of the assigned about shipping routes. After solving the models, we can get one concave function of the total profits of hub-and-spoke harbors in opposition to the numbers of hub harbors. It means that the shippers must choose their hub harbors carefully then could get the maximum profits. The hub harbors start increasing to two hubs, the total profits also start to increase. Nevertheless, if they start increasing a few hubs, if keep increasing, the total profits will decrease. The top point of the concave function represents the numbers of the hubs as the optimal numbers the shippers should choose. The result of this paper can help the shippers to decide the numbers and locations of hubs.