Computational & Technology Resources an online resource for computational,engineering & technology publications not logged in - login Civil-Comp ProceedingsISSN 1759-3433 CCP: 73PROCEEDINGS OF THE EIGHTH INTERNATIONAL CONFERENCE ON CIVIL AND STRUCTURAL ENGINEERING COMPUTING Edited by: B.H.V. Topping Paper 101Structural Optimisation of an Orthotropic Plate D. TranFaculty of Engineering and Science, Victoria University of Technology, Melbourne, Australia doi:10.4203/ccp.73.101 Full Bibliographic Reference for this paper D. Tran, "Structural Optimisation of an Orthotropic Plate", in B.H.V. Topping, (Editor), "Proceedings of the Eighth International Conference on Civil and Structural Engineering Computing", Civil-Comp Press, Stirlingshire, UK, Paper 101, 2001. doi:10.4203/ccp.73.101 Keywords: structural optimisation, finite element modelling, orthotropic plate, weight minimization, finite element simulation. Summary Structural elements in the form of orthotropic plates are often employed in many engineering structures, for example in superstructure of bridge and ship structures. This paper investigates the optimisation problem of minimizing weight of an orthotropic plate that consists of a thin plate stiffened by stiffeners arranged symmetrically in two orthogonal directions, such that the maximum Mises stress in the whole structure does not exceed a specified value. The design variables are the thickness of the plate and stiffeners, the positions of stiffeners and depths of stiffeners. It was shown that the relationship between the objective function and constraint variable with design variables is very complex resulting in a great number of local minima, often in the neighbourhood of the global minimum. This fact highlights the danger of getting bogged down in a local minimum during the course of an optimisation algorithm. The optimisation problem of minimizing weight of these orthotropic plates subject to a design stress is basically a sizing optimisation problem. Three methods were used: Subproblem Approximation (SAM), First Order (FOM) and Finite Element Simulation of Durelli's method (FESD). The first two are available in FEM software ANSYS 5.7; the third method, FESD, developed by the author, as a shape optimisation method is adapted into this sizing optimisation problem. SAM and FOM are simple to use, however due to the existence of many local minima, these methods take a long time to converge, and usually converge to a local minimum, in spite of efforts to use various techniques like random design or a global sweep run so as not to overlook the global minimum. FESD used the concept of iterative simulated removing material where the structure is under-stressed and simultaneous adding material where over-stressed, can be adapted to this problem. In the course of an optimisation loop, the FESD algorithm solves the current FEM model, monitor where the over-stressed and under-stressed regions of the structures are, identify the associated design variables and then change the design variables in appropriate direction. It was found that the bottom-up solid modelling method combined with parametric design language of ANSYS 5.7 were suitable for the FESD algorithm. It was found that SAM and FOM are less effective than FESD, in terms of number of iterations to convergence as well as the optimum value of the objective function. References 1 British Standard, "Gully tops and manhole tops for vehicular and Pedestrian areas-Design requirements, type testing, marking, quality control, BS EN124: 1994", BSI, 1994. 2 B. Hassani and E. Hinton, "Homogenization and Structural Topology Optimization, Theory, Practice and Software", Springer, London, UK, 1998. 3 A.A. Seireg and J. Rodriguez, (1997), "Optimizing the Shape of Mechanical Elements and Structures", Marcel Dekker, Inc, New York, USA, 1997. 4 R.T. Haftka and Z Gurdal, "Elements of Structural Optimization", Kluwer Academic Publishers, Dordrecht, The Netherlands, 1992. 5 D. Tran and V. Nguyen, "Optimal hole profile in a finite plate under uniaxial stress by finite element simulation of Durelli's photoelastic stress minimisation method", Int. J. of Finite Elements in Analysis and Design, 32, 1-20, 1999. doi:10.1016/S0168-874X(98)00072-9 6 V. Nguyen and D. Tran, "FESD: Finite Element Simulation of Durelli's Method of Photoelastic Stress Minimization", in " Identification, Control and Optimisation of Engineering Structures", G. De Roeck and B.H.V. Topping (editors), Civil-Comp Press, Edinburgh, UK, 2000. doi:10.4203/ccp.72.5.2 7 A.J. Durelli and K. Rajaiah, "Optimum Hole Shapes in Finite Plates under Uniaxial Load", Journal of Applied Mechanics, 46, 691-695, 1979. doi:10.1002/nme.1620140109 8 E. Hinton, E. and J. Sienz, "Fully Stressed Topological Design of Structures Using an Evolutionary Procedure", Engineering Computation, 12, 229-244, 1995. doi:10.1108/02644409510799578 9 A.E. Tekaya and A. Guneri, (1996), Shape optimization with the biological growth method: a parameter study, Engineering computations, 13, 8, 4-17, 1996. doi:10.1108/02644409610152989 10 Y.M. Xie and G.P. Steven, "A Simple Evolutionary Procedure for Structural Optimization", Computers & Structures, 49 (5), 885-896, 1993. doi:10.1016/0045-7949(93)90035-C 11 L.J. Wheeler, "On the Role of Constant Stress Surfaces in the Problem of Minimizing Elastic Stress Concentration", Int. J. of Solids and Structures, 12, 779-789, 1976. doi:10.1016/0020-7683(76)90042-1 12 E. Schnack, "An Optimization Procedure for Stress Concentrations by Finite Element Technique", Int. J. for Num Methods in Eng, 14, 1979, 115- 124, 1979. doi:10.1002/nme.1620140109 13 N.V. Bainichuk, "Problems and Methods of Optimal Structural Design", Plenum Press, New York, USA, 1983. purchase the full-text of this paper (price £20) Back to top ©Civil-Comp Limited 2020 - terms & conditions