Anevolutionaryapproachtoincorporatingintradepartmental¯ow intofacilitiesdesign B.A.Norman a, * ,A.E.Smith b ,E.Yildirim a ,W.Tharmmaphornphilas a a Department of Industrial Engineering, University of Pittsburgh, 1048 Benedum Hall, Pittsburgh, PA 15261, USA b Department of Industrial and Systems Engineering, Auburn University, 207 Dunstan Hall, Auburn, AL 36849-5346, USA Accepted17October2000 Abstract Minimizingmaterialtransportationisanimportantdesignobjectformanyfacilities.Intraditionalfacilitydesign,departmentsandwork centershavebeenlocatedbasedoninterdepartmental¯owpatterns.Weintroduceamethodologythatextendstheplanningprocesstoalso considerintradepartmental¯owpatterns.Amathprogrammingapproachisdevelopedthatusesanobjectivefunctionandconstraintsthat speci®callyaddressesboththeintradepartmentalandtheinterdepartmentalmaterial¯owstogether.Themathprogrammingapproachcanbe usedtosolvesmallproblemsbutitisdif®culttoscalethismethodtoproblemswithrealisticsizes.Therefore,wedeviseanevolutionary optimizationmethodologyforthissameproblem.Theevolutionarymethodcanreadilysolvebothlargeandsmallproblems.Theeffec- tivenessoftheevolutionaryapproachisdemonstratedonasuiteoftestproblems. q 2001ElsevierScienceLtd.Allrightsreserved. Keywords:Facilitydesign;Material¯ow;Geneticalgorithms;Optimization 1. Introduction Facility design problems generally involve the partition ofabuildingintodepartmentsworkcentersorcells)along with a material ¯ow structure and a material handling system to link the departments. The primary objective of thedesignproblemistominimizethecostsassociatedwith production and materials movement within the facility. Such problems occur in many organizations, including manufacturing cell layout, hospital layout, semiconductor manufacturing and service center layout. They also occur inenvironmentalmanagementofforests,wetlands,etc.[1]. Byanymonetarymeasure,facilitiesdesignisanimportant problemandonethathasassumedevengreaterimportance asmanufacturersstrivetobecomemoreagileandrespon- sive[2].ForUSmanufacturers,between20and50%oftotal operating expenses are spent on material handling and an appropriate facilities design can reduce these costs by at least 10±30% [3]. Dr James A. Tompkins, a seminal researcher in the ®eld, wrote in the August 1997 issue of IIE Solutions,ªSince1955,approximately8percentofthe U.S. GNP has been spent annually on new facilities. In addition, existing facilities must be continually modi- ®ed¼These issues represent more than $250 billion per year attributed to the design of facility systems, layouts, handlingsystems,andfacilitieslocations¼º[2]. An important aspect of facilities design is locating the input/output I/O) points also called pickup and delivery points)foreachdepartmentwithinafacility.Thisisgener- ally done by considering only the ¯ows coming into and going out of each department and locating a speci®ed numberofI/Osperdepartmentusuallyoneandusuallya combined input and output point). Flows between depart- mentsaresigni®cantinfacilitiesthatoperateasjobshops andalsoinfacilitiesthatutilizemanufacturingcellsifthere is¯owbetweencellsorifthelayoutisahybridhavingboth jobshopandcellularmanufacturingfeatures.However,how material¯owswithinadepartmentcanbeequallyimportant indeterminingIandOsites.Infact,therearecertainmanu- facturing methods and production methodologies that demand a certain ¯ow pattern within the department and these strongly affect the proper placement of I/Os. In this paper, we incorporate the manner of ¯ow of material within departmentswiththe¯ows between departments to optimallylocateI/Opoints. Speci®cally, we consider designs where there are both separate input I) locations and output O) locations and where there are combined I and O locations. Consider departments E, G and N in Fig. 1 where each exhibits a commontypeofintradepartmental¯owpattern.Department AdvancesinEngineeringSoftware322001)443±453 0965-9978/01/$-seefrontmatter q 2001ElsevierScienceLtd.Allrightsreserved. PII:S0965-997800)00106-X www.elsevier.com/locate/advengsoft * Correspondingauthor.Tel.: 11-412-624-9841;fax: 11-412-624-9831. E-mail addresses: banorman@engrng.pitt.eduB.A.Norman), aesmith@eng.auburn.eduA.E.Smith).