1,721,030 research outputs found
Analysis of submerged pipelines during installation: influence of the ovalization
No full textOne of the most important problems in deep water pipelaying consists in the analysis of the configuration at the installation stage. In fact it is well known from practical experience that most pipelines are likely to encounter their highest stresses during the laying process.
From a mechanical point of view the problem is one of large displacements and is furthermore complicated by the fact that the length of the suspended span is a priori unknown, as well as some boundary conditions at the seabed touchdown point and at the connection to the laybarge.
In the case of deep waters, additional problems become significant. In fact the curvature of the pipeline during the installation process tends to cause the ovalisation of the cross-section according to the well known von Kàrmàn effect and in turn the consequent reduction of the bending stiffness influences the pipeline axis configuration. Thus the rod equilibrium problem becomes non-linear also in the bending moment-curvature relationship even for a linear elastic material.
The present paper proposes an analytical approach for the calculation of the elastic deflection of submerged pipelines laid with a stinger which takes into account the overall effects of the ovalisation of the cross-section. The analysis is performed by means of a singular perturbation technique and the analytical solution obtained turns out to present some advantages over the finite element method. A practical example is discussed and a comparison with the results obtained by means of a well-known commercial finite element package (ABAQUS v. 5.7) is performed
Is preoperative levosimendan indicated to treat normal left ventricular function and left ventricle outflow obstruction?
No full text[No abstract available
Letter by Guarracino et al Regarding Article, “Direct Myocardial Effects of Levosimendan in Humans With Left Ventricular Dysfunction: Alteration of Force-Frequency and Relaxation-Frequency Relationships”
No full text
On the “relativistic” description of motion of soliton-like defects in elastic media
No full textAn analysis of the manner of establishing a relativistic micro-universe with respect to the motion of soliton-like defects in elastic media is performed. It is demonstrated that the change of variables in the elastic-dynamic equations holding the motion of ascrew dislocation must be complemented by the contraction law for the displacement vector and that a theory based on Lorentz Tstransformations is not the only possible framework for representing the motion of soliton-like defects
Non-linear analysis of pipeline installation
No full textThe paper presents an analytical basis for a very accurate yet extremely rapid analysis of the deformations of a pipe installed in any depth of water. The analysis is suitable for use on a desk-top computer and the speed of solution, 2-7 secs depending on water depth, permits a real-time assessment of the pipeline conditions during installation. The very rapid solution time of the method described here means that it can be used in real-time to monitor the lay-down geometry of a pipeline during installation and therefore can be an aid to minimising the occurrence of spans.
The analysis of a practical case shows the accuracy of the procedure and allows to draw a comparison with a finite element approach
A refined analytical analysis of submerged pipelines in seabed laying
No full textThe paper analyzes the elastic deflection of submerged pipelines laid with a stinger by taking into account the overall effects of the ovalization of the cross section. The analysis is performed by means of a singular perturbation technique and the analytical solution obtained is shown to offer different advantages over the finite element method. Two example demonstrate the effectiveness of the procedure by means of a comparison with results from other less refined analytical solutions and from the commercial finite element code ABAQUS
“Relativistic” characterisation of the energy of soliton-like defects in continuous media
No full textThe foundation of the relativistic behaviour of some classical physical models is investigated. It is shown that, in the case of moving screw dislocations as well as in the continuum Frenkel–Kontorova model (Sine-Gordon equation and generalisations), the value of a particular function associated with the static equilibrium solutions plays a fundamental role in obtaining a fully relativistic behaviour of the energy. Finally, the equivalence between mass and energy and the presence of preferred frames of reference are considered
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