摘要:

AbstractStructures presenting kinematical inderterminacy are usually calledmechanisms. This paper is entirely concerned with assemblies which reveal themselves to be mechanisms at a null value of the load. Among them a first distinction is made between infinitesimal and finite ones, the former being characterized by one or several directions of lower (but not zero) stiffness, whereas the latter show at least one finite admissible displacement for which none of the bars undergoes any elongation. Moreover, there exists the possibility to make a further distinction among the infinitesimal mechanisms, according to which is the order of the stiffness along the direction considered above. The way of evaluating this order is to perform a local analysis of the strain energy of the assembly, once the displacement field is parametrized in terms of a suitable parameter. By means of a finite element technique, this analysis can be easily performed through the numerical approach presented in this report.

ISSN:0029-5981    

DOI:10.1002/nme.1620350702

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractAn asymptotic method directly derived from Koiter's theory and suitable for the solution of elastic buckling problems and its natural adaptation to a numerical solution by means of a finite element technique are presented here. The order of the extrapolation of the equilibrium equations has been intentionally kept very low because attention has been entirely devoted to all those features (theoretical definitions, eigenproblem numerical techniques, suitable FEM implementation) which make such an approach competitive with respect to the classic step‐by‐step methods. For plane frames and 3D pin‐jointed trusses, the performances of the algorithm (numerical accuracy and computational cost) are compared with those of Riks' are‐length

ISSN:0029-5981    

DOI:10.1002/nme.1620350703

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThis paper presents a fast numerical algorithm for the implementation of material models for creep into finite element codes. First, an overview of existing algorithms for transient and steady‐state creep is given. Next, a new formulation is presented which reduces the constitutive integration to the solution of a scalar non‐linear algebraic equation. A solution is shown to exist without the need for subincrementation. Details of the numerical algorithm are then discussed. The paper closes with several numerical examples which illustrate the speed, robustness and accuracy of the proposed procedure as implemented in the Lawrence Livermore National Laboratory finite element codes NIKE2D and NIK

ISSN:0029-5981    

DOI:10.1002/nme.1620350704

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractA family ofp‐method plane elasticity elements is derived based on the hybrid Trefftz formulation.1Exact solutions of the Lamé‐Navier equations are used for the intra‐element displacement field together with an independent displacement frame function field along the element boundary. The final unknowns are the parameters of the frame function field consisting of the usual degrees of freedom at corner nodes and an optional number of hierarchic degrees of freedom associated with the mid‐side nodes. Since the element matrices do not involve integration over the element area, the elements have a polygonal contour with an optional number of curved sides. The quadrilateral element has the same external appearance as the conventionalp‐method plane elasticity element.2,3But unlike in the conventionalp‐method approach, suitable special‐purpose Trefftz functions are generally used to handle the singularity and/or stress concentration problems rather than a local mesh refinement. The practical efficiency of the new elements is assessed through a seri

ISSN:0029-5981    

DOI:10.1002/nme.1620350705

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractA new method is presented for evaluating the Cauchy principal value integral and the free term in the three‐dimensional elastic boundary element method. This method expresses the singular integral as the sum of a weakly singular integral and an integrable Cauchy principal value integral. The former can be computed by means of the usual standard Gaussian quadrature after a transformation suggested by Lachat and Watson,10who correctly limited its use only to weakly singular integral. The latter can be calculated by direct integration in the Cauchy principal value sense. This paper also points out some limitations in the use of triangle polar co‐ordinate suggested by Liet al.11and later extended by Zhang and Xu.16The general expression of the free term for a boundary point with arbitrary characteristic surface is also presented. Simple numerical examples which verify the efficiency and accuracy of the present method are gi

ISSN:0029-5981    

DOI:10.1002/nme.1620350706

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractA solution strategy to find the shape and topology of structures that maximize a natural frequency is presented. The methodology is based on a homogenization method and the representation of the shape of the structure as a material property. The problem is formulated as a reinforcement problem in which a given structure is reinforced using a prescribed amount of material. Two dimensional, plane elasticity problems are considered. Examples are presented for illustration.

ISSN:0029-5981    

DOI:10.1002/nme.1620350707

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractModelling of heat conduction processes with phase changes benefits from the application of variable time‐step methods when the behaviour of the moving boundary is not knowna prioiri. Due to convergence and stability constraints only implicit difference equations have been used with these methods. Implicit methods show a significant loss of accuracy and exhibit convergence difficulties when used for relatively slow or rapid moving‐boundary problems. To overcome these problems an improved explicit variable time‐step method which combines the explicit exponential difference equation and a variable time‐step grid network with virtual subspace increments around the moving boundary is presented and tested for both a solidification and a melting problem. A virtual subinterval time‐step elimination technique is incorporated to ensure that stability is automatically maintained for any mesh size. Unlike the implicit variable time‐step methods, the accuracy of the resulting method is not affected by the velocity of the moving boundary. For both test problems numerical results are in better agreement with known analytical solutions than results predicted by other numeri

ISSN:0029-5981    

DOI:10.1002/nme.1620350708

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractFor the analysis of thick laminated composite structures this paper proposes a partial mixed 3‐D element. The variational principle of this new element is obtained by modifying the Hellinger–Reissner principle. The functional of the present stationary principle is constructed by treating three displacements (u, v, w) and two transverse shear stresses (τxz, τyz) as independent of each other. Hence the nodal variables of the present mixed element contain three displacements and two transverse shear stresses. The other stresses (σx, σy, τxy, σz) are computed from the assumed displacement field and nodal displacement field and nodal displacements. The present element can satisfy the requirements of (1)transverse shear stress continuity between laminate layers and (2)boundary conditions of free transverse shear stresses on the top and bottom surfaces. These requirements are violated by conventional displacement finite elements. Since the stiffness matrix of the present element is formulated by combining a displacement model and a mixed model, it is definite, rather than indefinite as for the conventional mixed elements. Also, these two transverse shear stresses are part of the solution variables and are solved directly together with displacements. Examples are presented to demonstrate the accuracy and efficiency of this proposed partial mixed 3‐D element in the analysis of thick laminated composite

ISSN:0029-5981    

DOI:10.1002/nme.1620350709

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

ISSN:0029-5981    

DOI:10.1002/nme.1620350710

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

ISSN:0029-5981    

DOI:10.1002/nme.1620350711

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY