Evaluation of optimisation techniques in the design of composite pipelines A.M. Harte a,* , J.F. McNamara b , I. Roddy c a Department of Civil Engineering, NUI, Galway, Ireland b Department of Mechanical Engineering, NUI, Galway, Ireland c MCS International, Lismoyle House, Merchants Road, Galway, Ireland Abstract The optimisation of design parameters associated with glass-reinforced epoxy pipelines for use in gas distribution networks is investigated. Maximum operating pressures are set at 70 bar with a factor of safety on burst pressures of 4.5. The optimisation procedures are extensively automated whereby iterative ®nite element solutions are executed under the control of a software suite containing information on the optimisation parameters, objective functions and constraints. As no optimisation algorithm is suitable for all parameters a variety of mathematical techniques are available, and these are extensively evaluated with respect to the design of a composite pipeline. The major parameters investigated are pipeline layer thicknesses and winding angles. Four optimisation procedures are extensively tested and evaluated and particular problems with parameters such as winding angles are exposed. Recommendations on preferred approaches to the application of optimisation techniques in the design of composite pipelines are advanced. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Optimisation; Composite; Pipeline 1. Introduction The overall problem addressed in this paper is the opti- misation of glass-reinforced epoxy GRE) pipelines for use ingasdistributionnetworks.Theinnovativeaspectistheuse of GRE at the relatively high operating pressure of 70 bar with a safety factor of 4.5. A feature of the optimisation procedure is that it is extensively automated such that a designerisnotrequiredtobeanexpertinthe®eldinorderto applyit.Theoptimisationroutinesandcontrolsareheldina softwarepackagenamedBOSS[1]whichinterfacesdirectly with a general purpose, commercial ®nite element code called SAMCEF [2]. Solution parameters, objective func- tions and constraints are de®ned in BOSS and successive ®niteelementsolutionsareautomaticallyiterateduponuntil the optimum solution is achieved. A major dif®culty with such optimisation procedures is that no one method is suitable for all optimisation para- meters and, therefore, a variety of mathematical techniques are available under the BOSS/SAMCEF system. A contri- bution of this paper is the evaluation of these methods and theirperformancewithrespecttocompositepipelinedesign. Particular parameters addressed here are pipe layer thick- nesses and winding angles. Inthefollowingsectionsthecandidatepipelinegeometry and material properties are outlined, the design and opti- misationproceduresaredescribedandnumericalresultsare presentedfortherespectiveapproaches.Finally,recommen- dations on the utility of the various optimisation techniques for the pipeline design problems considered are presented. 2. Pipeline description and properties The candidate pipeline has a ®xed internal diameter of 101 mm due to ¯ow considerations and is ®lament wound usinganumberoflayers;forthepurposeoftheoptimisation the number of layers is taken as 4. The material constants andlimitstressesfortheGREcompositearelistedinTable1. ThepipelineloadsaregiveninTable2andareconsistent with a buried gas line. The factor of safety of 4.5 on the 70 bar operating pressure accounts for the degradation of the mechanical properties over a projected lifetime of 20 years. The axial force of 254.2 kN speci®ed is due to the endcap effect. Aschematicofthe®niteelementmodelforthepipelineis shown in Fig. 1 where four-noded axisymmetric elements areusedwithoneelementforeachofthefourlayersacross the thickness of the pipe. It is only necessary to use one element along the pipe axis direction so that a relatively Journal of Materials Processing Technology 118 2001) 478±484 * Corresponding author. 0924-0136/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII:S0924-013601)00989-X