| 1. |
- Christensen, P. W., et al.
(författare)
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Formulation and comparison of algorithms for frictional contact problems
- 1998
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Ingår i: International Journal for Numerical Methods in Engineering. - : John Wiley & Sons. - 0029-5981 .- 1097-0207. ; 42:1, s. 145-173
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents two algorithms for solving the discrete, quasi-static, small-displacement, linear elastic, contact problem with Coulomb friction. The algorithms are adoptions of a Newton method for solving B-differentiable equations and an interior point method for solving smooth, constrained equations. For the application of the former method, the contact problem is formulated as a system of B-differentiable equations involving the projection operator onto sets with simple structure; for the application of the latter method, the contact problem is formulated as a system of smooth equations involving complementarity conditions and with the non-negativity of variables treated as constraints. The two algorithms are numerically tested for two-dimensional problems containing up to 100 contact nodes and up to 100 time increments. Results show that at the present stage of development, the Newton method is superior both in robustness and speed. Additional comparison is made with a commercial finite element code.
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| 2. |
- Kjellmert, Bo
(författare)
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A Chebyshev collocation multidomain method to solve the Reissner-Mindlin equations for the transient response of an anisotropic plate subjected to impact
- 1997
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Ingår i: International Journal for Numerical Methods in Engineering. - 0029-5981 .- 1097-0207. ; 40:20, s. 3689-3702
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Tidskriftsartikel (refereegranskat)abstract
- The transient response of an anisotropic rectangular plate subjected to impact is described through a Chebyshev collocation multidomain discretization of the Reissner-Mindlin plate equations. The trapezoidal rule is used for time-integration. The spatial collocation derivative operators are represented by matrices, and the subdomains are patched by natural and essential conditions. At each time level the resulting governing matrix equation is reduced by two consecutive block Gaussian eliminations, so that an equation for the variables at the subdomain corners has to be solved. Back-substitution gives the variables at all other collocation points. The time history as represented by computed contour plots has been compared with analytical results and with photos produced by holographic interferometry. The agreements are satisfactory.
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| 3. |
- Kjellmert, Bo
(författare)
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A spectral method to solve the equations of linear elasticity for the transient response of a tube subjected to impact
- 1999
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Ingår i: International Journal for Numerical Methods in Engineering. - 0029-5981 .- 1097-0207. ; 45:8, s. 1115-1133
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Tidskriftsartikel (refereegranskat)abstract
- The transient response of a tube subjected to impact is described through Fourier-Galerkin and Chebyshev collocation multidomain discretizations of the equations of linear elasticity. The trapezoidal rule is used for time integration. For each Fourier mode the spatial collocation derivative operators are represented by matrices, and the subdomains are patched by natural and essential conditions. At each time level the resulting governing matrix equation is reduced by two consecutive block Gaussian eliminations, so that an equation for the complex Fourier coefficients at die subdomain corners has to be solved. Back-substitution gives the coefficients at all other collocation points. An inverse discrete Fourier transform generates, at optional time levels, the three components of the displacement field. Through this method the long-term evolution of the field may be calculated, provided the impact time is long enough. The time history as represented by computed contour plots has been compared with photos produced by holographic interferometry. The agreements are satisfactory.
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| 4. |
- Lindgren, Lars-Erik, et al.
(författare)
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Simulation of multipass welding of a thick plate
- 1999
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Ingår i: International Journal for Numerical Methods in Engineering. - 0029-5981 .- 1097-0207. ; 44:9, s. 1301-1316
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Tidskriftsartikel (refereegranskat)abstract
- Multipass butt welding of a very thick steel plate has been performed. Transient temperatures and residual stresses have been measured. The agreement between calculations and experiments is good. Two different approaches, quiet and inactive elements, for modelling multipass welding are compared. The first approach is straightforward to apply in most finite element codes. The inactive element method requires a code that can regenerate the finite element model automatically or otherwise very tedious manual work is necessary as the elements are added to the model when welds are laid. It is shown that both techniques give the same results but the computational effort is reduced by using inactive elements. It also circumvents the problem in the quiet element approach of choosing properties of elements in the model that represent the case when welds are not laid.
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| 5. |
- Svoboda, Ales, et al.
(författare)
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The effective stress function algorithm for pressure‐dependent plasticity applied to hot isostatic pressing
- 1998
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Ingår i: International Journal for Numerical Methods in Engineering. - 0029-5981 .- 1097-0207. ; 43:4, s. 587-606
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Tidskriftsartikel (refereegranskat)abstract
- An algorithm for unconditionally stable and accurate integration of elasto-viscoplastic pressure-dependent constitutive model is presented. Rate form constitutive equations of thermal-elastoviscoplastic type with compressibility take into account the changes in relative density. The algorithm computes the deviatoric and volumetric creep strains by finding the value of the effective stress which satisfies the functional relationship, the effective stress function. Thus, one non-linear scalar equation is solved to find the unknown volumetric and deviatoric components of creep strain tensor. The tangent modulus is evaluated consistent with the integration algorithm. The application of the method to the simulation of hot isostatic pressing of metal powder is shown. The paper presents the solution of the verification problem and comparison with the experimental result.
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| 6. |
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| 7. |
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| 8. |
- Möller, Peter, et al.
(författare)
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On advancing front mesh generation in three dimensions
- 1995
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Ingår i: International Journal for Numerical Methods in Engineering. - : Wiley. - 0029-5981 .- 1097-0207. ; 38:21, s. 3551-3569
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Tidskriftsartikel (refereegranskat)abstract
- This paper deals with some aspects of unstructured mesh generation in three dimensions by the advancing front technique. In particular, the parameters used in the algorithm are characterized, and strategies that may be used to improve robustness are suggested. We also describe a method whereby structured tetrahedral meshes with exceptionally stretched elements adjacent to boundary surfaces may be produced. The suggested method can be combined with the advancing front concept in a natural way.
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| 9. |
- Petersson, Joakim, 1968-, et al.
(författare)
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Slope Constrained Topology Optimizaton
- 1999
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Ingår i: International Journal for Numerical Methods in Engineering. - 0029-5981 .- 1097-0207. ; 41, s. 1417-1438
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Tidskriftsartikel (populärvet., debatt m.m.)
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| 10. |
- Sandberg, Göran
(författare)
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A new strategy for solving fluid-structure problems
- 1995
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Ingår i: International Journal for Numerical Methods in Engineering. - : Wiley. - 1097-0207 .- 0029-5981. ; 38:3, s. 357-370
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Tidskriftsartikel (refereegranskat)abstract
- A scheme for treating unsymmetrical coupled systems is outlined. Such systems occur naturally in connection with fluid-structure interaction, where an acoustic fluid is contained in an elastic structure. The discretization is performed by means of the finite element method, using displacement formulation in the structure and either pressure or displacement potential in the fluid. Based on the eigenvalues of each subdomain some simple steps give a standard eigenvalue problem. It might also be concluded that the unsymmetrical matrices have real eigenvalues.
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