摘要:

AbstractA general approach to shape design sensitivity analysis of three‐ and two‐dimensional elastic solid objects is developed using the material derivative‐adjoint variable technique and boundary element method. The formulation of the problem is general and first‐order sensitivities in the form of boundary integrals for the effect of boundary shape variations are derived for an arbitrary performance functional. Second‐order quadrilateral surface elements (for 3‐D problems) and quadratic boundary elements (for 2‐D problems) are employed in the solution of primary and adjoint systems and discretization of the boundary integral expressions for sensitivities. The accuracy of sensitivity information is studied for selected global performance functionals and also for boundary state fields at discrete points. Numerical results are presented to demonstrate the accuracy and efficiency of

ISSN:0029-5981    

DOI:10.1002/nme.1620381702

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe equations of motion of thin‐walled beams with open cross‐section, considering the effects of shear flexibility and rotatory inertia in the stress resultants, as well as variable cross‐sectional properties are presented using a state variables approach. These equations are based on Vlasov's theory of thin‐walled beams, which is modified to include the effects indicated above. The resulting equations are used in the determination of the natural frequencies of an open cross‐section prestressed concrete beam. Comparisons with other formulations are also presented employing the waves dispersion

ISSN:0029-5981    

DOI:10.1002/nme.1620381703

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe performance of finite elements is scrutinized in isochoric and dilatant/contractant plastic flow. Standard displacement based elements, uniformly and selectively integrated elements, and elements with augmented strain rate fields are considered in plane‐strain, axisymmetric and three‐dimensional configurations with particular reference to the kinematic constraint imposed by dilatant/contractant plastic flow. It turns out that findings for isochoric deformations do not necessarily carry over to cases with plastic dilatancy or contraction. For the elements with augmented strain rate fields the danger of spurious mechanisms in ideal plasticity is brought out. A particular strategy which augments only the normal strain rates at the expense of a lesser improvement for the bending behaviour does not suffer from the possibility of spurious modes, while preserving the ability to accommodate dilatant/contractant plastic flow. Illustrative examples on plane‐strain, axisymmetry and three‐dimensional structures are included which support the above f

ISSN:0029-5981    

DOI:10.1002/nme.1620381704

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractWhen the driving joint forces, determined using the inverse dynamics procedure, are applied in the feedforward control of mechanical systems, discrepancies between the specified and the actual motion are observed. In some recent publications, these discrepancies were attributed to the wave phenomenon. It is shown in this investigation that the solution of the inverse dynamics of flexible mechanical systems defines two types of driving forces which can be classified asdriving joint forcesanddriving elastic forces.The driving joint forces which depend on the deformation of the flexible bodies define the torque and the actuator forces which must be applied at the joints. The driving elastic forces are associated with the deformation degrees of freedom, and therefore, there is no gaurantee that an algorithm that ignores these driving elastic forces will converge and achieve the desired solution. It is the objective of this investigation to examine the nature of the driving elastic forces in the solution of the inverse dynamics problem, and demonstrate that the driving elastic forces associated with two different sets of vibration modes which produce the same physical displacements are basically the same and they differ only by a co‐ordinate transformation. The effect of the selection of the deformable body co‐ordinate system on these forces is also examined numerically using a slider crank mechanism with a flexible connecting

ISSN:0029-5981    

DOI:10.1002/nme.1620381705

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe detailed discretization of contact zones with contact stiffness based on real physical characteristics of contact surfaces can produce stiffness terms which induce ill‐conditioning of the global stiffness matrix. Moreover the consistent treatment of frictional behaviour generates non‐symmetric tangent stiffness matrices due to the non‐associativity of the slip phase. Other non‐symmetries are due to the coupling terms and to the dependencies on various parameters that can be involved. To overcome these difficulties almost consistent techniques based on two‐step algorithms have been proposed in the past. Here an augmentation technique is proposed which takes into account micro‐mechanical effects, and permits the symmetrization of the tangent stiffness during frictional

ISSN:0029-5981    

DOI:10.1002/nme.1620381706

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractEquilibrium constraints are used to improve the stress accuracy of existing assumed natural‐co‐ordinate strain (ANS) plate elements. This is accomplished by introducing hierarchical degrees of freedom, which are subsequently eliminated by invoking kinematic consistency and element‐interior homogeneous equilibrium conditions. The resulting element enrichments are completely contained in the strain‐displacement matrix. In addition, the modified displacement shape functions become available for consistent mass and nodal load calculations, a feat not shared by some hybrid‐type elements. The performance of the present element (ANS‐EC) is compared with other plate bending elements. This performance comparison includes convergence studies for both displacements a

ISSN:0029-5981    

DOI:10.1002/nme.1620381707

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractA second‐order shape design sensitivity analysis (DSA) method applicable to the shape change on the loaded boundaries is derived for three‐dimensional linear elastic solids using a continuum method with the material derivative. The continuum method is also used to derive mixed second‐order variations of stress and displacement performance measures with respect to shape design variables and distribution of non‐conservative traction loads, and also with respect to shape design variables and material properties. A shape design acceleration field is defined for the second‐order shape design sensitivity. Both direct differentiation and hybrid methods are presented in this paper. A numerical method, which can be implemented using established finite element analysis (FEA) codes, is developed. The feasibility and accuracy of the proposed second‐order shape DSA method has been demonstrated by solving a structural example‐doubly cu

ISSN:0029-5981    

DOI:10.1002/nme.1620381708

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

ISSN:0029-5981    

DOI:10.1002/nme.1620381709

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

ISSN:0029-5981    

DOI:10.1002/nme.1620381701

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY