Evangelos Gavalas, Ioannis Pressas and Spyros Papaefthymiou
The purpose of this paper is to compare the performance of implicit and explicit integration schemes for simulating the metal rolling process using commercial software packages…
Abstract
Purpose
The purpose of this paper is to compare the performance of implicit and explicit integration schemes for simulating the metal rolling process using commercial software packages ANSYS™ and LS-DYNA™.
Design/methodology/approach
For the industrial application of finite element method, the time discretization is one of the most important factors that determine the stability and efficiency of the analysis. An iterative approach, which is unconditionally stable in linear analyses, is the obvious choice for a quasi-static problem such as metal rolling. However, this approach may be challenging in achieving convergence with non-linear material behavior and complicated contact conditions. Therefore, a non-iterative method is usually adopted, in order to achieve computational accuracy through very small time steps. Models using both methods were constructed and compared for computational efficiency.
Findings
The results indicate that the explicit method yields higher levels of efficiency compared to the implicit method as model complexity increases. Furthermore, the implicit method displayed instabilities and numerical difficulties in certain load conditions further disfavoring the solver’s performance.
Originality/value
Comparison of the implicit and explicit procedures for time stepping was applied in 3D finite element analysis of the plate rolling process in order to evaluate and quantify the computational efficiency.
Details
Keywords
Nikolaos Athanasopoulos, Evangelos Gavalas and Spyros Papaefthymiou
The purpose of this paper is to present a finite element method (FEM) model that predicts the collapse pressure of the majority of the gas/petroleum pipelines worldwide. More…
Abstract
Purpose
The purpose of this paper is to present a finite element method (FEM) model that predicts the collapse pressure of the majority of the gas/petroleum pipelines worldwide. More specifically, it refers to pipelines with diameter to wall thickness (D/t) ratios between 15 and 45. The model’s results were evaluated on the basis of the DNV-OS-F101 offshore pipeline design code.
Design/methodology/approach
A series of FEM simulations were conducted using a 2D model created in the ANSYS’ software environment considering both the plane strain and the plane stress approach. The corresponding values of the collapse pressure for pipes with different value sets of D/t and ovality were calculated in Python (programming language) according to the DNV equations. Given that the pipeline’s resistance to collapse is governed by geometric imperfections and material properties, amongst others, the influence of other crucial factors, such as ovality, eccentricity, hardening modulus and the chemical composition (pipe’s steel grade) was examined.
Findings
The FE model approaches very closely the DNV calculations. Although the effect of the hardening modulus and pipe’s steel grade, respectively, was found to be insignificant on the pipeline’s collapse, it turned out that the lower the D/t ratio was the bigger the influence of these factors appeared. The D/t ratio does not affect the pipe’s sensitivity in eccentricity, because for a pipe with the same characteristics and eccentricity, but with higher ovality, the decrease in collapse pressure was found to be lower.
Originality/value
A 2D FEM which estimates collapse pressure and simultaneously takes into account the effect of various factors is less time-consuming and costly than the full-scale pipe collapse tests in pressure chambers.