SUMMARYThe dynamic response of submarine pipelines to earthquake-generated vertical seabed motions is examined with the aid of a finite element model. A relaxation algorithm is adopted in order to overcome the problem of unknown dynamic seabed reaction forces. Rotational rigidity is assumed at the boundary points, which are allowed to move vertically in unison with the random seabed oscillations. For the interior nodes, the description of the kinetic energy loss, resulting from pipeline-seabed impact, is approached through the use of a restitution coefficient of 0)5, which represents an intermediate collision mode between a perfectly elastic and an inelastic one. Fundamental system frequencies are determined by the use of support positions obtained from a static analysis of the unilaterally constrained structure. The structural damping matrix is approximately evaluated according to Rayleigh's method. Response spectra to a strong motion vertical acceleration earthquake record provide an initial guideline into the pipeline stability. Peak dynamic and static bending stresses are calculated for a case study involving two submarine pipeline crossings. Complete, partial and lack of pipeline gravel cover is assumed in the analysis. A seabed profile alteration, due to probable soil liquefaction, is furthermore imposed, in order to investigate the subsequent effect upon the dynamic pipeline stresses.1998 John Wiley & Sons, Ltd.
SUMMARYNon-Darcy groundwater flow parameters are identified for three different flow systems. In the first system, which is essentially one-dimensional, the parameters are determined by means of an integral method. A rectangular parametric grid is used for the identification of the non-Darcy friction coefficients in the second system, which is two-dimensional. The parameters in the third system, which involves a hybrid simulation of three-dimensional flow, are optimized by adopting a constrained non-linear programming technique. This technique combines Cauchy's steepest-descent method together with the modeller's subjective judgement of the results at the end of each iterative step. The paper is concluded with a brief description of the additional research which is thought to be necessary before the difficulties of optimizing the non-Darcy flow parameters can be overcome.
SUMMARYA non-linear ®nite element numerical procedure is adopted for predicting the bending stresses developed along highly curved submarine pipelines during the installation process from a laybarge towards an irregular sea¯oor. The problem of partial seabed-pipeline and stinger-pipeline contact is tackled by means of a point iterative calculation approach. The geometric non-linearity embedded in the beam¯exural theory enables major deformations of the submarine line structures to be accurately modelled. Numerical calculations tend to be demanding, especially when large dierences occur between the pipeline and seabed con®gurations. Three structural problems of practical signi®cance provide a suitable application platform for testing the eciency of the mathematical model. A Fortran subroutine implementing the fundamental procedures of the proposed numerical theory is included. #
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.