3002

127 دكتري

دكتري

﴿طراحي كاربردي﴾

اصفهان: دانشگاه صنعتي اصفهان، دانشكده مكانيك

1384

هيجده، 159، [II]ص.: مصور، جدول، شكل، نمودار

ص. ع. به فارسي و انگليسي

محمود فرزين، حميد هاشم الحسيني

سعيد ضيايي راد، بهزاد سلطاني

محمود سليمي، بيژن برومند، رضا نقدآبادي، احمد عاصم پور

1395/12/10

كتابنامه

مهندسي مكانيك

ID127 دكتري

به فارسي و انگليسي: قابل رويت در نسخه ديجيتالي

Abstract The objective of this thesis is to study the applications of meshless methods in engineering problems and to extend the scope of these methods to the field of metalforming processes Despite the remarkable progresses achieved by meshless methods invarious fields of science and engineering their applications in metal forming are verylimited and undeveloped One of the purposes of the present work is to introduce a simple and effective finite point approach in order to determine hydrostatic pressures In the analyses of metalforming processes by the flow formulation the pressure field whether obtained fromLagrange formulation or from the penalty equation is not accurate and may exhibitspurious modes A hydrostatic pressure recovery method has been proposed which can beconsidered as a post treatment procedure This method not only improves the precision ofthe obtained hydrostatic pressure field by the flow finite element method but also considerably improves the state of equilibrium The results show that if the deviatC ricstress field is sufficiently precise the hydrostatic pressure field can also be preciselypredicted by the present new hydrostatic pressure recovery method This method isinexpensive since it is a post treatment procedure Another main achievement in this research is related to a new mesh free techniqueentitled Point wise Least Squares Element Free PLSEF method which is based on optimization techniques and the moving least squares MLS approximation By thistechnique nodal displacements or velocities are determined by minimizing an error term in a least squares sense This error term is the summation of errors in the equilibriumequations essential boundary conditions and load boundary conditions The MLSprocedureis employed to approximate field variables and their derivatives The advantagesof this new technique can be summarized as follows Prescribed boundary displacements velocities and loads can be imposed directly and there is no need to use the Lagrange multiplier penalty constant or coupling with the BEM or FEM methods The method does not involve integration therefore there is no need for any background mesh Since no background mesh is needed to perform the numerical integration this new approach can be classified as a truly mesh free method As numerical examples of the proposed scheme a cantilever beam and a Poisson equationhave beenconsidered The numerical results compare very well with analytical solutions In using PLSEF method for derivation of the discretized system equations spatialderivatives of field variables are required in terms of unknown nodal values Hence it isnecessary compute the derivatives of MLS shape functions Another contribution of this toresearchis formulating a new and simple numerical technique for computing the secondand higher order derivatives of field variables The main advantage of this technique is thatwhen writing the second and higher derivatives of field variables only the first derivativesof MLS approximation functions are used In the last section a new method of bulk metal forming simulation is introduced Thistechnique is based on PLSEF method and rigid plastic flow formulation for slightlycompressible materials This work is the first application of PLSEF method in thenonlinear metal forming problems A plane strain upsetting problem has been analyzed bythis technique The results are very encouraging and show the power of this technique forsolving non linear problems The method of PLSEF seemsto have a strong potential in solid mechanics problems dueto the many advantages such as being mesh less integral less and easy imposition ofDirichlet and Numan boundary conditions However this method has been verified by afew examples and its broader applications to solid mechanics problems need furtherinvestigations Further improvements in the efficiency of PLSEF technique are anticipated The directions of these improvements are suggestedin the last part of this work At I J J ii f LJ

محمود فرزين، حميد هاشم الحسيني

سعيد ضيايي راد، بهزاد سلطاني

محمود سليمي، بيژن برومند، رضا نقدآبادي، احمد عاصم پور