ScholarBank@NUShttps://scholarbank.nus.edu.sgThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Tue, 30 Nov 2021 16:32:02 GMT2021-11-30T16:32:02Z50611- A simulation study on the uses of shuttle carriers in the container yardhttps://scholarbank.nus.edu.sg/handle/10635/72257Title: A simulation study on the uses of shuttle carriers in the container yard
Authors: Lee, L.H.; Chew, E.P.; Tan, K.C.; Huang, H.C.; Lin, W.; Han, Y.; Chan, T.H.
Abstract: In this paper, we investigate how two main factors affect the efficiency of the port operation. The two main factors are type of transport vehicles and layout of the storage yard. Two different types of transport vehicles (i.e., prime mover and shuttle carrier) and two different types of layouts (i.e., with or without chassis lane beside the container blocks) are modeled in this study, A total of four simulation models are created to conduct this study. To evaluate the performance, the gross crane rate is used as the main performance measure, which is defined as the number of containers moved per quay crane per working hour. In this paper, it has been shown that the incorporation of the chassis lane improves the gross crane rate for both prime movers and shuttle carriers. The improvement is more substantial when the port utilizes shuttle carriers. © 2007 IEEE.
Mon, 01 Jan 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/722572007-01-01T00:00:00Z
- ON MINIMIZING FLOW TIME ON PROCESSORS WITH VARIABLE UNIT PROCESSING TIME.https://scholarbank.nus.edu.sg/handle/10635/19364Title: ON MINIMIZING FLOW TIME ON PROCESSORS WITH VARIABLE UNIT PROCESSING TIME.
Authors: Huang, H.C.
Wed, 01 Jan 1986 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/193641986-01-01T00:00:00Z
- Analysing a mental health survey by chi-squared automatic interaction detection.https://scholarbank.nus.edu.sg/handle/10635/19356Title: Analysing a mental health survey by chi-squared automatic interaction detection.
Authors: Huang, H.C.; Lin, T.K.; Ngui, P.W.
Fri, 01 Jan 1993 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/193561993-01-01T00:00:00Z
- Discrete event simulation model for airline operations: SIMAIRhttps://scholarbank.nus.edu.sg/handle/10635/72317Title: Discrete event simulation model for airline operations: SIMAIR
Authors: Lee, L.H.; Huang, H.C.; Lee, C.; Chew, E.P.; Jaruphongsa, W.; Yong, Y.Y.; Liang, Z.; Leong, C.H.; Tan, Y.P.; Namburi, K.; Johnson, E.; Banks, J.
Abstract: SIMAIR is a C++ based research tool meant for the simulation of airline operations. It provides a means for devising and evaluating various airline recovery mechanisms to handle disruptions, and can also be used as a tool to evaluate the performance of a given schedule of operations. The performance of a given recovery mechanism can be quantified for research and evaluation purposes.
Wed, 01 Jan 2003 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/723172003-01-01T00:00:00Z
- EXPECTED PERFORMANCE OF SOME LOT-SIZING HEURISTICS IN A ROLLING-SCHEDULE ENVIRONMENT.https://scholarbank.nus.edu.sg/handle/10635/19348Title: EXPECTED PERFORMANCE OF SOME LOT-SIZING HEURISTICS IN A ROLLING-SCHEDULE ENVIRONMENT.
Authors: Huang, Huei Chuen; Ong, Hoon Liong
Sun, 01 Jan 1984 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/193481984-01-01T00:00:00Z
- Asymptotic expected performance of some TSP heuristics: An empirical evaluationhttps://scholarbank.nus.edu.sg/handle/10635/19341Title: Asymptotic expected performance of some TSP heuristics: An empirical evaluation
Authors: Ong, H.L.; Huang, H.C.
Sun, 01 Jan 1989 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/193411989-01-01T00:00:00Z
- Simultaneous fleet assignment and cargo routing using benders decompositionhttps://scholarbank.nus.edu.sg/handle/10635/68049Title: Simultaneous fleet assignment and cargo routing using benders decomposition
Authors: Li, D.; Huang, H.-C.; Chew, E.-P.; Morton, A.D.
Abstract: In this paper, we incorporate the cargo routing problem into fleet assignment to model the fleet assignment more accurately. An integrated model and a Benders decomposition-based approach are developed to simultaneously obtain the optimal assignment of fleet to legs and the routing of forecasted cargo demand over the network. Computational experiments show that this integrated approach converges very fast for all different test scenarios. © 2007 Springer-Verlag Berlin Heidelberg.
Mon, 01 Jan 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/680492007-01-01T00:00:00Z
- The workload balancing problem at air cargo terminalshttps://scholarbank.nus.edu.sg/handle/10635/68064Title: The workload balancing problem at air cargo terminals
Authors: Huang, H.C.; Lee, C.; Xu, Z.
Abstract: We consider a large air cargo handling facility composed of two identical cargo terminals. In order to improve the operational efficiency, the workload must be balanced between the terminals. Thus, we must assign each airline served by the facility to one of the terminals such that (ideally): (1) each terminal has the same total workload, and (2) the workload at each terminal is distributed evenly along the timeline. Complicating the problem is that cargo loads are difficult to predict (stochastic). We develop a stochastic mixed integer linear program model in which a weighted sum of the balance measures is minimized. We employ sample average approximation for the stochastic program and develop an accelerated Benders decomposition algorithm to reduce the computational time. The proposed model can also be applied to partially reassign the airlines for the operational schedule changes. The computational results show that a small number of reassignments are often sufficient to rebalance the workload. The simulation results based on data from a large international airport show that the proposed algorithms efficiently balance the workload and the cargo service time is consistently reduced. © 2007 Springer-Verlag Berlin Heidelberg.
Mon, 01 Jan 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/680642007-01-01T00:00:00Z
- Reservation storage policy for AS/RS at air cargo terminalshttps://scholarbank.nus.edu.sg/handle/10635/72396Title: Reservation storage policy for AS/RS at air cargo terminals
Authors: Lee, C.; Liu, B.; Huang, H.C.; Xu, Z.; Goldsman, P.
Abstract: At air cargo terminals, the operations of an automatic storage and retrieval system (AS/RS) have certain special characteristics that both cargo arrival rates and storage duration are stochastic, and the probability distributions can only come from the empirical data. According to such particularities, this paper proposes a class-based reservation storage policy for AS/RS at air cargo terminals and an analytical model is developed. Two classes are investigated and a certain storage spaces are reserved for one priority class in such a way that the one-way travel time of S/R machine is minimized. The optimal reservation space is obtained by numerical searching. A simulation model is developed and the simulation results validate the optimal solution from the analytical model.
Sat, 01 Jan 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/723962005-01-01T00:00:00Z
- Modeling the vehicle routine problem for a soft drink distribution companyhttps://scholarbank.nus.edu.sg/handle/10635/87077Title: Modeling the vehicle routine problem for a soft drink distribution company
Authors: Cheong, Y.M.; Ong, H.L.; Huang, H.C.
Abstract: In this paper, we present a modeling study of vehicle routing problem (VRP) for a soft drink distribution company and propose a method to solve it. The distribution problem is concerned with assigning a fixed fleet of heterogeneous vehicles to serve the customers at various districts. The proposed methodology consists of two phases. Phase I is used to assign a fixed fleet of vehicles to districts on a long-term basis. In Phase II, three methods are proposed to reroute the assigned vehicles to solve the daily VRP. Customer demand data over a 23-day period are used to evaluate the performance of the proposed methods. The results show that the proposed methods give a better solution to the current distribution problem.
Wed, 01 May 2002 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/870772002-05-01T00:00:00Z
- Reservation storage policy for AS/RS at air cargo terminalshttps://scholarbank.nus.edu.sg/handle/10635/87395Title: Reservation storage policy for AS/RS at air cargo terminals
Authors: Lee, C.; Liu, B.; Huang, H.C.; Xu, Z.; Goldsman, P.
Abstract: At air cargo terminals, the operations of an automatic storage and retrieval system (AS/RS) have certain special characteristics that both cargo arrival rates and storage duration are stochastic, and the probability distributions can only come from the empirical data. According to such particularities, this paper proposes a class-based reservation storage policy for AS/RS at air cargo terminals and an analytical model is developed. Two classes are investigated and a certain storage spaces are reserved for one priority class in such a way that the one-way travel time of S/R machine is minimized. The optimal reservation space is obtained by numerical searching. A simulation model is developed and the simulation results validate the optimal solution from the analytical model.
Sat, 01 Jan 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/873952005-01-01T00:00:00Z
- Performance measures for returnable inventory: A case studyhttps://scholarbank.nus.edu.sg/handle/10635/87167Title: Performance measures for returnable inventory: A case study
Authors: Chew, E.P.; Huang, H.C.; Horiana
Abstract: This paper is concerned with developing relevant performance measures for an industrial gas manufacturer to monitor and control the deployment of the firm's cylinders, which represent a significant portion of the firm's investment. In particular, four interrelated performance measures that are relevant to returnable inventory are proposed and derived. They address questions such as how frequently the cylinders are being used, how long they are used each time, whether they are effectively utilized, and how much of safety stock to keep. The application and usefulness of the proposed measures are illustrated on one of the gas products of a major industrial gas manufacturer. These measures enable planners to predict the proper level of cylinders required in the future as well as taking corrective measures whenever appropriate.
Mon, 01 Jul 2002 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/871672002-07-01T00:00:00Z
- On-line Scheduling for jobs with arbitrary release timeshttps://scholarbank.nus.edu.sg/handle/10635/87129Title: On-line Scheduling for jobs with arbitrary release times
Authors: Li, R.; Huang, H.-C.
Abstract: This paper considers the problem of on-line scheduling a list of independent jobs in which each job has an arbitrary release time on m parallel identical machines. A tight bound is given for List Scheduling(LS) algorithm and a better algorithm is given for m ≥ 2.
Thu, 01 Jan 2004 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/871292004-01-01T00:00:00Z
- Analytical representation of probabilities under the IAC conditionhttps://scholarbank.nus.edu.sg/handle/10635/63026Title: Analytical representation of probabilities under the IAC condition
Authors: Huang, H.C.; Chua, V.C.H.
Abstract: This paper extends the work of Gehrlein and Fishburn (1976) and Gehrlein (1982) by providing a general theorem relating to the analytical representation of the probability of an event in a given space of profiles. It applies to any event characterized by a set of linear inequalities regardless of whether the coefficients defining the inequalities are integer or fractional coefficients. An algorithm for the probability calculation is also suggested. This suggested methodology is used to provide a complete characterization of the vulnerability properties of the four scoring rules studied in Lepelley and Mbih (1994) to manipulation by coalitions in a 3-alternative n-agent society. © Springer-Verlag 2000.
Sat, 01 Jan 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/630262000-01-01T00:00:00Z
- A successive convex approximation method for multistage workforce capacity planning problem with turnoverhttps://scholarbank.nus.edu.sg/handle/10635/62973Title: A successive convex approximation method for multistage workforce capacity planning problem with turnover
Authors: Song, H.; Huang, H.-C.
Abstract: Workforce capacity planning in human resource management is a critical and essential component of the services supply chain management. In this paper, we consider the planning problem of transferring, hiring, or firing employees among different departments or branches of an organization under an environment of uncertain workforce demands and turnover, with the objective of minimizing the expected cost over a finite planning horizon. We model the problem as a multistage stochastic program and propose a successive convex approximation method which solves the problem in stages and iteratively. An advantage of the method is that it can handle problems of large size where normally solving the problems by equivalent deterministic linear programs is considered to be computationally infeasible. Numerical experiments indicate that solutions obtained by the proposed method have expected costs near optimal. © 2007 Elsevier B.V. All rights reserved.
Tue, 01 Jul 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/629732008-07-01T00:00:00Z
- Short-term booking of air cargo spacehttps://scholarbank.nus.edu.sg/handle/10635/63311Title: Short-term booking of air cargo space
Authors: Chew, E.-P.; Huang, H.-C.; Johnson, E.L.; Nemhauser, G.L.; Sokol, J.S.; Leong, C.-H.
Abstract: This paper proposes a stochastic dynamic programming model for a short-term capacity planning model for air cargo space. Long-term cargo space is usually acquired by freight forwarders or shippers many months ahead on a contract basis, and usually the forecasted demand is unreliable. A re-planning of cargo space is needed when the date draws nearer to the flight departure time. Hence, for a given amount of long-term contract space, the decision for each stage is the quantity of additional space required for the next stage and the decision planning model evaluates the optimal cost policy based on the economic trade-off between the cost of backlogged shipment and the cost of acquiring additional cargo space. Under certain conditions, we show that the return function is convex with respect to the additional space acquired for a given state and the optimal expected cost for the remaining stages is an increasing convex function with respect to the state variables. These two properties can be carried backward recursively and therefore the optimal cost policy can be determined efficiently. © 2005 Elsevier B.V. All rights reserved.
Wed, 01 Nov 2006 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/633112006-11-01T00:00:00Z
- SimMan-A simulation model for workforce capacity planninghttps://scholarbank.nus.edu.sg/handle/10635/63312Title: SimMan-A simulation model for workforce capacity planning
Authors: Huang, H.-C.; Lee, L.-H.; Song, H.; Thomas Eck, B.
Abstract: Motivated by the difficulty in predicting the actual performance of workforce capacity planning solutions obtained from mathematical models, we develop a simulator, SimMan, to serve as a test bed for evaluating the effectiveness and robustness of different planning options and assignment rules. To facilitate the ease of use, the simulator is developed in C++ language with a modular structure so that different users or planners can customize the modules according to their specifications. We further develop a mathematical model for the workforce capacity planning problem, where the uncertainty of the demand is handled by the safety stock concepts. We also suggest a number of practical planning alternatives and assignment rules based on information from IBM. These rules are implemented as modules in SimMan and tested numerically to provide managerial insights. © 2008 Elsevier Ltd. All rights reserved.
Sat, 01 Aug 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/633122009-08-01T00:00:00Z
- On-line Scheduling for jobs with arbitrary release timeshttps://scholarbank.nus.edu.sg/handle/10635/63227Title: On-line Scheduling for jobs with arbitrary release times
Authors: Li, R.; Huang, H.-C.
Abstract: This paper considers the problem of on-line scheduling a list of independent jobs in which each job has an arbitrary release time on m parallel identical machines. A tight bound is given for List Scheduling(LS) algorithm and a better algorithm is given for m ≥ 2.
Thu, 01 Jan 2004 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/632272004-01-01T00:00:00Z
- Modeling the vehicle routine problem for a soft drink distribution companyhttps://scholarbank.nus.edu.sg/handle/10635/63186Title: Modeling the vehicle routine problem for a soft drink distribution company
Authors: Cheong, Y.M.; Ong, H.L.; Huang, H.C.
Abstract: In this paper, we present a modeling study of vehicle routing problem (VRP) for a soft drink distribution company and propose a method to solve it. The distribution problem is concerned with assigning a fixed fleet of heterogeneous vehicles to serve the customers at various districts. The proposed methodology consists of two phases. Phase I is used to assign a fixed fleet of vehicles to districts on a long-term basis. In Phase II, three methods are proposed to reroute the assigned vehicles to solve the daily VRP. Customer demand data over a 23-day period are used to evaluate the performance of the proposed methods. The results show that the proposed methods give a better solution to the current distribution problem.
Wed, 01 May 2002 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/631862002-05-01T00:00:00Z
- Genetic algorithms for the multiple-machine economic lot scheduling problemhttps://scholarbank.nus.edu.sg/handle/10635/63144Title: Genetic algorithms for the multiple-machine economic lot scheduling problem
Authors: Sun, H.; Huang, H.-C.; Jaruphongsa, W.
Abstract: This paper focuses on an extension of the Economic Lot Scheduling Problem, which schedules productions of products on multiple identical machines. The objective is to minimize the total average production and inventory costs per unit time for all products. We develop a genetic algorithm under the Common Cycle policy and compare it with an existing heuristic under the same policy. Computational results show that our genetic algorithm outperforms the existing heuristic and its running time does not increase much even for high utilization problems, while the latter requires substantial time to solve most of the high utilization problems. In addition, a genetic algorithm under the Extended Basic Period and Power-of-Two policy is proposed. This new heuristic performs much better, especially when the number of machines is small and the machine utilization is not very high. © 2008 Springer-Verlag London Limited.
Sat, 01 Aug 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/631442009-08-01T00:00:00Z
- A comparative study of metaheuristics for vehicle routing problem with stochastic demandshttps://scholarbank.nus.edu.sg/handle/10635/53975Title: A comparative study of metaheuristics for vehicle routing problem with stochastic demands
Authors: Teng, S.; Ong, H.L.; Huang, H.C.
Abstract: The vehicle routing problem with stochastic demands (VRPSD) is usually modeled as a stochastic program with recourse (SPR). In this paper, we present three metaheuristics, simulated annealing (SA), threshold accepting (TA) and tabu search (TS) for this problem. Based on the same neighborhood structure, a comparative study is carried out to compare the performance of these three metaheuristics. Computational results show that the solution quality of the TS outperforms the other heuristics for all the problems tested. With respect to computational time, metaheuristics are much more time consuming as compared to other local search heuristics. However, when comparing TS with SA, it takes less computational time. Though TA is the least time consuming one, its solution quality is not as good.
Thu, 01 May 2003 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/539752003-05-01T00:00:00Z
- Two bi-directional heuristics for the assembly line type II problemhttps://scholarbank.nus.edu.sg/handle/10635/50748Title: Two bi-directional heuristics for the assembly line type II problem
Authors: Liu, S.B.; Ong, H.L.; Huang, H.C.
Abstract: In this paper, we proposed two heuristic algorithms for solving the assembly line balancing type II problem. The proposed algorithms first generate an initial solution by a bi-directional assignment procedure, then the obtained initial solution is further improved by swapping tasks among workstations. In order to test the performance of the two algorithms, a comparison is carried out on a set of 302 instances found in the literature and a set of 1440 randomly generated instances. The computational results show that the proposed heuristic algorithms for solving the assembly line balancing Type II problem are efficient in minimizing both the cycle time and the mean absolute deviation.
Wed, 01 Jan 2003 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/507482003-01-01T00:00:00Z
- Flight assignment plan for an air cargo inbound terminalhttps://scholarbank.nus.edu.sg/handle/10635/87324Title: Flight assignment plan for an air cargo inbound terminal
Authors: Lee, L.H.; Huang, H.C.; Huang, P.
Abstract: The paper studies the modeling and optimization for the flight assignment plan for an air cargo inbound terminal. A multi-objective Mixed Integer Programming (MIP) model is formulated to determine this plan. A set of non-dominated solutions are obtained by solving this multi-objective model and they are further analyzed by a simulation model to identify the best one. ©2010 IEEE.
Fri, 01 Jan 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/873242010-01-01T00:00:00Z
- Human resource planning with worker attendance uncertaintyhttps://scholarbank.nus.edu.sg/handle/10635/87329Title: Human resource planning with worker attendance uncertainty
Authors: Ng, T.S.; Huang, H.C.; Ng, J.Y.
Abstract: We consider a human resource supply planning problem given a set of job demands. The staffing levels of different workforce types to fulfill the jobs need to be determined, a priori to full knowledge of the attendance rates of the workers. The objective is to find the optimal staffing levels that minimize the hiring costs while maintaining a high certainty of fulfilling all the jobs. We propose six different approaches for generating solutions to the problem. Computational experiments are conducted to evaluate the performance of the approaches. Our experimental results show that two approaches: one based on stochastic programming and the other based on robust optimization using an ellipsoid uncertainty set, outperforms the other approaches consistently in various performance measures. © 2008 IEEE.
Tue, 01 Jan 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/873292008-01-01T00:00:00Z
- The Shapley-Shubik index, the donation paradox and ternary gameshttps://scholarbank.nus.edu.sg/handle/10635/87282Title: The Shapley-Shubik index, the donation paradox and ternary games
Authors: Chua, V.C.H.; Huang, H.C.
Abstract: In this paper, we show that although the Shapley-Shubik index is immune to the donation paradox in weighted binary games, extension of the index to ternary games along the direction suggested in Felsenthal and Machover (1996, 1997) will cause it to be vulnerable to the paradox and this is the case as long as the number of players in the game exceeds three. This undermines the attractiveness of the Shapley-Shubik index as a measure of a priori voting power.
Sun, 01 Jun 2003 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/872822003-06-01T00:00:00Z
- The economic lot scheduling problem under extended basic period and power-of-two policyhttps://scholarbank.nus.edu.sg/handle/10635/87265Title: The economic lot scheduling problem under extended basic period and power-of-two policy
Authors: Sun, H.; Huang, H.-C.; Jaruphongsa, W.
Abstract: The economic lot scheduling problem schedules the production of several different products on a single machine over an infinite planning horizon. In this paper, a nonlinear integer programming model is used to determine the optimal solution under the extended basic period and power-of-two policy. A small-step search algorithm is presented to find a solution which approaches optimal when the step size approaches zero, where a divide-and-conquer procedure is introduced to speed up the search. Further a faster heuristic algorithm is proposed which finds the same solutions in almost all the randomly generated sample cases. © 2009 Springer-Verlag.
Fri, 01 Jan 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/872652010-01-01T00:00:00Z
- Properties and linkages of some index decomposition analysis methodshttps://scholarbank.nus.edu.sg/handle/10635/87184Title: Properties and linkages of some index decomposition analysis methods
Authors: Ang, B.W.; Huang, H.C.; Mu, A.R.
Abstract: We study the properties and linkages of some popular index decomposition analysis (IDA) methods in energy and carbon emission analyses. Specifically, we introduce a simple relationship between the arithmetic mean Divisia index (AMDI) method and the logarithmic mean Divisia index method I (LMDI I), and show that such a relationship can be extended to cover most IDA methods linked to the Divisia index. We also formalize the relationship between the Laspeyres index method and the Shapley value in the IDA context. Similarly, such a relationship can be extended to cover other IDA methods linked to the Laspeyres index through defining the characteristic function in the Shapley value. It is found that these properties and linkages apply to decomposition of changes conducted additively. Similar properties and linkages cannot be established in the multiplicative case. The implications of the findings on IDA studies are discussed. © 2009 Elsevier Ltd. All rights reserved.
Sun, 01 Nov 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/871842009-11-01T00:00:00Z
- Heuristic algorithms for general k-level facility location problemshttps://scholarbank.nus.edu.sg/handle/10635/87030Title: Heuristic algorithms for general k-level facility location problems
Authors: Li, R.; Huang, H.-C.; Huang, J.
Abstract: In a general k-level uncapacitated facility location problem (k-GLUFLP), we are given a set of demand points, denoted by D, where clients are located. Facilities have to be located at a given set of potential sites, which is denoted by F in order to serve the clients. Each client needs to be served by a chain of k different facilities. The problem is to determine some sites of F to be set up and to find an assignment of each client to a chain of k facilities so that the sum of the setup costs and the shipping costs is minimized. In this paper, for a fixed k, an approximation algorithm within a factor of 3 of the optimum cost is presented for k-GLUFLP under the assumption that the shipping costs satisfy the properties of metric space. In addition, when no fixed cost is charged for setting up the facilities and k2, we show that the problem is strong NP-complete and the constant approximation factor is further sharpen to be 3/2 by a simple algorithm. Furthermore, it is shown that this ratio analysis is tight. © 2013 Operational Research Society Ltd. All rights reserved.
Tue, 01 Jan 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/870302013-01-01T00:00:00Z
- Improved algorithm for a generalized on-line scheduling problem on identical machineshttps://scholarbank.nus.edu.sg/handle/10635/87035Title: Improved algorithm for a generalized on-line scheduling problem on identical machines
Authors: Li, R.; Huang, H.-C.
Abstract: This paper considers the problem of on-line scheduling a list of independent jobs in which each job has an arbitrary release time on m parallel identical machines. In this problem, jobs arrive in form of order before its release time and decisions have to be made whenever an order is placed and the orders arrive according to any sequence. A heuristic algorithm, NMLS, better than MLS is given for any m ≥ 2. The competitive ratio is improved from 2.93920 to 2.78436. © 2005 Elsevier B.V. All rights reserved.
Mon, 01 Jan 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/870352007-01-01T00:00:00Z
- On a new rotation tour network model for aircraft maintenance routing problemhttps://scholarbank.nus.edu.sg/handle/10635/87107Title: On a new rotation tour network model for aircraft maintenance routing problem
Authors: Liang, Z.; Chaovalitwongse, W.A.; Huang, H.C.; Johnson, E.L.
Abstract: The airline industry currently has a $40-billion plus market and is expected to grow rapidly with the population growth and growth in the overall economy. Everyday, thousands of aircrafts undergo maintenance, repair, and overhaul. The aircraft maintenance problem is one of the important logistic problems in the airline industry. It is aimed at scheduling the aircrafts' routing so that enough maintenance opportunities are provided to every aircraft in the fleet. In this paper, we present a new compact network representation of the aircraft maintenance routing problem (AMR) and propose a new mixed-integer linear programming formulation to solve the problem. The quality of this model was assessed on four real test instances from a major U.S. carrier, and compared with the flight string model proposed in the literature. The computational results show that the proposed model is able to obtain the optimal solutions to all test instances in reasonable time. This study suggests that this model can be applied to integrated problems of the AMR and other planning problems such as the fleet assignment problem and crew pairing problem.
Tue, 01 Feb 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/871072011-02-01T00:00:00Z
- List scheduling for jobs with arbitrary release times and similar lengthshttps://scholarbank.nus.edu.sg/handle/10635/87061Title: List scheduling for jobs with arbitrary release times and similar lengths
Authors: Li, R.; Huang, H.-C.
Abstract: This paper considers the problem of on-line scheduling a list of independent jobs in which each job has an arbitrary release time and length in [1,r] with r1 on m parallel identical machines. For the list scheduling algorithm, we give an upper bound of the competitive ratio for any m1 and show that the upper bound is tight when m=1. When m=2, we present a tight bound for r4. For r
Sat, 01 Dec 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/870612007-12-01T00:00:00Z
- The workload balancing problem at air cargo terminalshttps://scholarbank.nus.edu.sg/handle/10635/63379Title: The workload balancing problem at air cargo terminals
Authors: Huang, H.C.; Lee, C.; Xu, Z.
Abstract: We consider a large air cargo handling facility composed of two identical cargo terminals. In order to improve the operational efficiency, the workload must be balanced between the terminals. Thus, we must assign each airline served by the facility to one of the terminals such that (ideally): (1) each terminal has the same total workload, and (2) the workload at each terminal is distributed evenly along the timeline. Complicating the problem is that cargo loads are difficult to predict (stochastic). We develop a stochastic mixed integer linear program model in which a weighted sum of the balance measures is minimized. We employ sample average approximation for the stochastic program and develop an accelerated Benders decomposition algorithm to reduce the computational time. The proposed model can also be applied to partially reassign the airlines for the operational schedule changes. The computational results show that a small number of reassignments are often sufficient to rebalance the workload. The simulation results based on data from a large international airport show that the proposed algorithms efficiently balance the workload and the cargo service time is consistently reduced.
Sun, 01 Oct 2006 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/633792006-10-01T00:00:00Z
- Performance measures for returnable inventory: A case studyhttps://scholarbank.nus.edu.sg/handle/10635/63255Title: Performance measures for returnable inventory: A case study
Authors: Chew, E.P.; Huang, H.C.; Horiana
Abstract: This paper is concerned with developing relevant performance measures for an industrial gas manufacturer to monitor and control the deployment of the firm's cylinders, which represent a significant portion of the firm's investment. In particular, four interrelated performance measures that are relevant to returnable inventory are proposed and derived. They address questions such as how frequently the cylinders are being used, how long they are used each time, whether they are effectively utilized, and how much of safety stock to keep. The application and usefulness of the proposed measures are illustrated on one of the gas products of a major industrial gas manufacturer. These measures enable planners to predict the proper level of cylinders required in the future as well as taking corrective measures whenever appropriate.
Mon, 01 Jul 2002 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/632552002-07-01T00:00:00Z
- Modified base-stock policies for semiconductor production system with dependent yield rateshttps://scholarbank.nus.edu.sg/handle/10635/87081Title: Modified base-stock policies for semiconductor production system with dependent yield rates
Authors: Huang, H.-C.; Song, H.
Abstract: We consider a two-stage production system faced by semiconductor manufacturing which produces a hierarchy of multiple grades of outputs. In the first stage, a single type of input (wafer) is used to produce multiple types of semi-finished parts with dependent yield rates, and in the second stage, each type of semi-finished parts can be transformed into a corresponding type of final products, or downgraded to a type of lower grade final products. Random customer demands are faced on the final products, and demands of different types of final products are not allowed to be substituted. The advantage of this production system is that it can prevent unhealthy ordering from customers who intentionally send out false demand signals for high grade products and revise the orders to lower grade products when the delivery time is close, which was observed in semiconductor manufacturing. The objective of the study is to plan the quantity of the input at the first stage and the respective downgrade quantities at the second stage so as to meet the required service level at the minimum cost. With some common assumptions, we propose a modified base-stock policy for this two-stage production system and show that the occurrence of nil excess inventory above the base-stock level follows a renewal process. We further extend the modified base-stock policy to a better policy that invokes risk pooling over multiple grade products. The performance of these two polices are evaluated via simulation to provide managerial insights. © 2010 Elsevier B.V. All rights reserved.
Tue, 16 Nov 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/870812010-11-16T00:00:00Z
- Dynamic stochastic programming for asset allocation problemhttps://scholarbank.nus.edu.sg/handle/10635/72320Title: Dynamic stochastic programming for asset allocation problem
Authors: Song, H.; Huang, H.-C.
Abstract: Asset allocation is an important decision problem in financial planning. In this paper, we study the multistage dynamic asset allocation problem which an investor is allowed to reallocate its wealth among a set of assets over finite discrete decision points, in which the stochastic return rates of the assets follow a Markov chain with nonstationary transition probabilities. The objective is to maximize the utility of the wealth at the end of the planning horizon where the utility of the wealth follows a general piecewise linear and concave function. Transaction costs are considered. We formulate the problem with a dynamic stochastic programming model and develop a method that decomposes the problem into stage-based subproblems to solve it. The main advantage of this method is that it provides a computationally tractable tool to deal with the dynamic asset allocation problem of long planning horizon. © 2007 IEEE.
Mon, 01 Jan 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/723202007-01-01T00:00:00Z
- Genetic algorithms for the multiple-machine economic lot scheduling problemhttps://scholarbank.nus.edu.sg/handle/10635/87024Title: Genetic algorithms for the multiple-machine economic lot scheduling problem
Authors: Sun, H.; Huang, H.-C.; Jaruphongsa, W.
Abstract: This paper focuses on an extension of the Economic Lot Scheduling Problem, which schedules productions of products on multiple identical machines. The objective is to minimize the total average production and inventory costs per unit time for all products. We develop a genetic algorithm under the Common Cycle policy and compare it with an existing heuristic under the same policy. Computational results show that our genetic algorithm outperforms the existing heuristic and its running time does not increase much even for high utilization problems, while the latter requires substantial time to solve most of the high utilization problems. In addition, a genetic algorithm under the Extended Basic Period and Power-of-Two policy is proposed. This new heuristic performs much better, especially when the number of machines is small and the machine utilization is not very high. © 2008 Springer-Verlag London Limited.
Sat, 01 Aug 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/870242009-08-01T00:00:00Z
- A dynamic stochastic network model for asset allocation problemhttps://scholarbank.nus.edu.sg/handle/10635/72235Title: A dynamic stochastic network model for asset allocation problem
Authors: Song, H.; Huang, H.-C.; Shi, N.; K. K. Lai
Abstract: Asset allocation is an important decision problem in financial planning. In this paper, we study the multistage dynamic asset allocation problem in which an investor is allowed to reallocate its wealth among a set of assets over finite discrete decision points and the stochastic return rates of the assets follow aMarkov chain with nonstationary transition probabilities. The objective is to maximize the utility of the wealth at the end of the planning horizon where the utility of the wealth follows a general piecewise linear and concave function. Transaction costs are considered. We formulate the problem with a dynamic stochastic network model which has potential to introduce a computationally tractable tool to deal with the dynamic asset allocation problem of large number of assets and long planning horizon. © 2009 IEEE.
Thu, 01 Jan 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/722352009-01-01T00:00:00Z
- Two bi-directional heuristics for the assembly line type II problemhttps://scholarbank.nus.edu.sg/handle/10635/87297Title: Two bi-directional heuristics for the assembly line type II problem
Authors: Liu, S.B.; Ong, H.L.; Huang, H.C.
Abstract: In this paper, we proposed two heuristic algorithms for solving the assembly line balancing type II problem. The proposed algorithms first generate an initial solution by a bi-directional assignment procedure, then the obtained initial solution is further improved by swapping tasks among workstations. In order to test the performance of the two algorithms, a comparison is carried out on a set of 302 instances found in the literature and a set of 1440 randomly generated instances. The computational results show that the proposed heuristic algorithms for solving the assembly line balancing Type II problem are efficient in minimizing both the cycle time and the mean absolute deviation.
Wed, 01 Jan 2003 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/872972003-01-01T00:00:00Z
- Finding the exact volume of a polyhedronhttps://scholarbank.nus.edu.sg/handle/10635/87014Title: Finding the exact volume of a polyhedron
Authors: Ong, H.L.; Huang, H.C.; Huin, W.M.
Abstract: This paper addresses the design and development of a computer program for finding the exact volume of a multi-dimensional polyhedron that is enclosed by a set of linear inequalities. The program is designed to calculate the volume of a polyhedron of any dimensions defined by a set of linear inequalities. The speed of the program depends on the number of inequalities and the number of variables. The program has been tested against several two- and three-dimensional polygons in which the volume can be calculated by formulae. The results of the tests show that the accuracy of the program is at least up to 10-6 and it can calculate the volume of a three-dimensional polygon defined by a few hundred inequalities in just a few minutes. However, as the number of variables increases, the computation time increases exponentially. The program can be used in some science and engineering application such as finding the probability of an event, the volume of a crystal in a wafer fabrication industry, and other applications in the manufacturing industry. © 2003 Elsevier Science Ltd. All rights reserved.
Sun, 01 Jun 2003 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/870142003-06-01T00:00:00Z
- Improved algorithm for a generalized on-line scheduling problem on identical machineshttps://scholarbank.nus.edu.sg/handle/10635/63152Title: Improved algorithm for a generalized on-line scheduling problem on identical machines
Authors: Li, R.; Huang, H.-C.
Abstract: This paper considers the problem of on-line scheduling a list of independent jobs in which each job has an arbitrary release time on m parallel identical machines. In this problem, jobs arrive in form of order before its release time and decisions have to be made whenever an order is placed and the orders arrive according to any sequence. A heuristic algorithm, NMLS, better than MLS is given for any m ≥ 2. The competitive ratio is improved from 2.93920 to 2.78436. © 2005 Elsevier B.V. All rights reserved.
Mon, 01 Jan 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/631522007-01-01T00:00:00Z
- Properties and linkages of some index decomposition analysis methodshttps://scholarbank.nus.edu.sg/handle/10635/63271Title: Properties and linkages of some index decomposition analysis methods
Authors: Ang, B.W.; Huang, H.C.; Mu, A.R.
Abstract: We study the properties and linkages of some popular index decomposition analysis (IDA) methods in energy and carbon emission analyses. Specifically, we introduce a simple relationship between the arithmetic mean Divisia index (AMDI) method and the logarithmic mean Divisia index method I (LMDI I), and show that such a relationship can be extended to cover most IDA methods linked to the Divisia index. We also formalize the relationship between the Laspeyres index method and the Shapley value in the IDA context. Similarly, such a relationship can be extended to cover other IDA methods linked to the Laspeyres index through defining the characteristic function in the Shapley value. It is found that these properties and linkages apply to decomposition of changes conducted additively. Similar properties and linkages cannot be established in the multiplicative case. The implications of the findings on IDA studies are discussed. © 2009 Elsevier Ltd. All rights reserved.
Sun, 01 Nov 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/632712009-11-01T00:00:00Z
- Flight assignment plan for an air cargo inbound terminalhttps://scholarbank.nus.edu.sg/handle/10635/72331Title: Flight assignment plan for an air cargo inbound terminal
Authors: Lee, L.H.; Huang, H.C.; Huang, P.
Abstract: The paper studies the modeling and optimization for the flight assignment plan for an air cargo inbound terminal. A multi-objective Mixed Integer Programming (MIP) model is formulated to determine this plan. A set of non-dominated solutions are obtained by solving this multi-objective model and they are further analyzed by a simulation model to identify the best one. ©2010 IEEE.
Fri, 01 Jan 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/723312010-01-01T00:00:00Z
- SimMan-A simulation model for workforce capacity planninghttps://scholarbank.nus.edu.sg/handle/10635/87230Title: SimMan-A simulation model for workforce capacity planning
Authors: Huang, H.-C.; Lee, L.-H.; Song, H.; Thomas Eck, B.
Abstract: Motivated by the difficulty in predicting the actual performance of workforce capacity planning solutions obtained from mathematical models, we develop a simulator, SimMan, to serve as a test bed for evaluating the effectiveness and robustness of different planning options and assignment rules. To facilitate the ease of use, the simulator is developed in C++ language with a modular structure so that different users or planners can customize the modules according to their specifications. We further develop a mathematical model for the workforce capacity planning problem, where the uncertainty of the demand is handled by the safety stock concepts. We also suggest a number of practical planning alternatives and assignment rules based on information from IBM. These rules are implemented as modules in SimMan and tested numerically to provide managerial insights. © 2008 Elsevier Ltd. All rights reserved.
Sat, 01 Aug 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/872302009-08-01T00:00:00Z
- A genetic algorithm for the economic lot scheduling problem under the extended basic period and power-of-two policyhttps://scholarbank.nus.edu.sg/handle/10635/54213Title: A genetic algorithm for the economic lot scheduling problem under the extended basic period and power-of-two policy
Authors: Sun, H.; Huang, H.-C.; Jaruphongsa, W.
Abstract: The economic lot scheduling problem is a well-studied problem, which remains difficult to be solved optimally in its original form. The extended basic period and power-of-two policy restricts the solution choice but provides a good solution to the problem. However, this restricted problem is still NP-hard due to its combinatorial nature. In this paper, a genetic algorithm is investigated for solving the problem. The genetic algorithm uses an integer encoding scheme which encodes the basic period only implicitly. This lean representation cuts down the search space by one dimension which speeds up the search. In the evolution, both feasible and infeasible solutions are kept in the population, which works very well for high utilization problems. The experimental study shows that the designed algorithm is fast and efficient. It finds optimal solutions under the extended basic period and power-of-two policy for almost all the tested sample problems. © 2009 CIRP.
Thu, 01 Jan 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/542132009-01-01T00:00:00Z
- A k-product uncapacitated facility location problemhttps://scholarbank.nus.edu.sg/handle/10635/54293Title: A k-product uncapacitated facility location problem
Authors: Huang, H.-C.; Li, R.
Abstract: A k-product uncapacitated facility location problem can be described as follows. There is a set of demand points where clients are located and a set of potential sites where facilities of unlimited capacities can be set up. There are k different kinds of products. Each client needs to be supplied with k kinds of products by a set of k different facilities and each facility can be set up to supply only a distinct product with a non-negative fixed cost determined by the product it intends to supply. There is a non-negative cost of shipping goods between each pair of locations. These costs are assumed to be symmetric and satisfy the triangle inequality. The problem is to select a set of facilities to be set up and their designated products and to find an assignment for each client to a set of k facilities so that the sum of the setup costs and the shipping costs is minimized. In this paper, an approximation algorithm within a factor of 2 k + 1 of the optimum cost is presented. Assuming that fixed setup costs are zero, we give a 2 k - 1 approximation algorithm for the problem. In addition we show that for the case k = 2, the problem is NP-complete when the cost structure is general and there is a 2-approximation algorithm when the costs are symmetric and satisfy the triangle inequality. The algorithm is shown to produce an optimal solution if the 2-product uncapacitated facility location problem with no fixed costs happens to fall on a tree graph. © 2007 Elsevier B.V. All rights reserved.
Sat, 01 Mar 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/542932008-03-01T00:00:00Z
- The economic lot scheduling problem under extended basic period and power-of-two policyhttps://scholarbank.nus.edu.sg/handle/10635/63358Title: The economic lot scheduling problem under extended basic period and power-of-two policy
Authors: Sun, H.; Huang, H.-C.; Jaruphongsa, W.
Abstract: The economic lot scheduling problem schedules the production of several different products on a single machine over an infinite planning horizon. In this paper, a nonlinear integer programming model is used to determine the optimal solution under the extended basic period and power-of-two policy. A small-step search algorithm is presented to find a solution which approaches optimal when the step size approaches zero, where a divide-and-conquer procedure is introduced to speed up the search. Further a faster heuristic algorithm is proposed which finds the same solutions in almost all the randomly generated sample cases. © 2009 Springer-Verlag.
Fri, 01 Jan 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/633582010-01-01T00:00:00Z
- Human resource planning with worker attendance uncertaintyhttps://scholarbank.nus.edu.sg/handle/10635/72336Title: Human resource planning with worker attendance uncertainty
Authors: Ng, T.S.; Huang, H.C.; Ng, J.Y.
Abstract: We consider a human resource supply planning problem given a set of job demands. The staffing levels of different workforce types to fulfill the jobs need to be determined, a priori to full knowledge of the attendance rates of the workers. The objective is to find the optimal staffing levels that minimize the hiring costs while maintaining a high certainty of fulfilling all the jobs. We propose six different approaches for generating solutions to the problem. Computational experiments are conducted to evaluate the performance of the approaches. Our experimental results show that two approaches: one based on stochastic programming and the other based on robust optimization using an ellipsoid uncertainty set, outperforms the other approaches consistently in various performance measures. © 2008 IEEE.
Tue, 01 Jan 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/723362008-01-01T00:00:00Z
- A bidirectional heuristic for stochastic assembly line balancing type II problemhttps://scholarbank.nus.edu.sg/handle/10635/50757Title: A bidirectional heuristic for stochastic assembly line balancing type II problem
Authors: Liu, S.B.; Ong, H.L.; Huang, H.C.
Abstract: In this paper, a heuristic algorithm is proposed to solve the single-model stochastic assembly line balancing Type II problem. For a given number of workstations and a pre-specified assembly line reliability, which is the probability of the work-load not exceeding the cycle time for the whole assembly line, the proposed algorithm tries to obtain a solution with the smallest cycle time. In the first stage, the tasks are assigned to workstations from the forward and backward directions alternatively. In the second stage, the workload is smoothed by swapping tasks among workstations. At last, the upper bound of the cycle time obtained in the second stage is reduced step by step until the smallest cycle time satisfies the pre-specified assembly line reliability. The performance of the proposed algorithm is compared with a modified version of Moodie and Young's algorithm by applying them to some literature problems. The computational results show that the proposed algorithm is efficient in minimizing the cycle time for the single-model stochastic assembly line balancing problem.
Sat, 01 Jan 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/507572005-01-01T00:00:00Z
- Heuristic algorithms for general k-level facility location problemshttps://scholarbank.nus.edu.sg/handle/10635/63149Title: Heuristic algorithms for general k-level facility location problems
Authors: Li, R.; Huang, H.-C.; Huang, J.
Abstract: In a general k-level uncapacitated facility location problem (k-GLUFLP), we are given a set of demand points, denoted by D, where clients are located. Facilities have to be located at a given set of potential sites, which is denoted by F in order to serve the clients. Each client needs to be served by a chain of k different facilities. The problem is to determine some sites of F to be set up and to find an assignment of each client to a chain of k facilities so that the sum of the setup costs and the shipping costs is minimized. In this paper, for a fixed k, an approximation algorithm within a factor of 3 of the optimum cost is presented for k-GLUFLP under the assumption that the shipping costs satisfy the properties of metric space. In addition, when no fixed cost is charged for setting up the facilities and k2, we show that the problem is strong NP-complete and the constant approximation factor is further sharpen to be 3/2 by a simple algorithm. Furthermore, it is shown that this ratio analysis is tight. © 2013 Operational Research Society Ltd. All rights reserved.
Tue, 01 Jan 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/631492013-01-01T00:00:00Z
- A Markov model for single-leg air cargo revenue management under a bid-price policyhttps://scholarbank.nus.edu.sg/handle/10635/54330Title: A Markov model for single-leg air cargo revenue management under a bid-price policy
Authors: Han, D.L.; Tang, L.C.; Huang, H.C.
Abstract: In this paper, we consider the capacity allocation problem in single-leg air cargo revenue management. We assume that each cargo booking request is endowed with a random weight, volume and profit rate and propose a Markovian model for the booking request/acceptance/rejection process. The decision on whether to accept the booking request or to reserve the capacity for future bookings follows a bid-price control policy. In particular, a cargo will be accepted only when the revenue from accepting it exceeds the opportunity cost, which is calculated based on bid prices. Optimal solutions are derived by maximizing a reward function of a Markov chain. Numerical comparisons between the proposed approach and two existing static single-leg air cargo capacity allocation policies are presented. © 2009 Elsevier B.V. All rights reserved.
Mon, 01 Feb 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/543302010-02-01T00:00:00Z