Pipeline-seabed interaction analysis subjected to horizontal cyclic loading

Author(s):  
T Takatani
Author(s):  
Zefeng Zhou ◽  
David J. White ◽  
Conleth D. O’Loughlin

Steel catenary risers (SCRs) are subjected to fatigue in the touchdown zone (TDZ) where the pipe interacts with the seabed. In this zone the seabed is subjected to intermittent episodes of cyclic loading and reconsolidation during long-term operation. Cyclic loading, reconsolidation and maintained load can cause variations in the soil strength and stiffness, which has a significant influence on the fatigue life of the riser in the TDZ. The weakening effect of cyclic loading on soil strength is well recognized throughout design practice, and methodologies for determining the cyclic ‘fatigue’ of clay during undrained cyclic loading are well established (e.g. Andersen et al. 1988; Andersen 2015). However, traditional undrained assessments neglect the effects of drainage and consolidation that inevitably occur in pipe-seabed interaction during long-term operational stages, and can lead to changes in stiffness by a factor of up to 5 or 10. This overlooked effect of consolidation on soil resistance and stiffness can be very important for SCR fatigue analysis. In this paper, a new analytical framework considering these effects has been used to analyze vertical pipe-seabed interaction. This framework is developed using a critical-state concept with effective stresses, and by discretizing the soil domain as a one-dimensional column of soil elements. The model can accurately capture the changing soil resistance and stiffness to account for the effects of remoulding, reconsolidation and maintained load. The framework is used to back-analysis the pipe-soil interaction response during small and large amplitude vertical cycles. The simulation prediction compares well with the measured results from the laboratory (Aubeny et al., 2008), and can accurately capture the observed changes in stiffness of up to a factor of 5.


Author(s):  
Shangmao Ai ◽  
Liping Sun ◽  
Gang Ma

Improving the knowledge about the effect of pipe-seabed-interaction on VIV is quite important for free spanning pipelines, which are often highly nonlinear due to interaction with the seabed. However, the implicit requirement for frequency domain procedures is structural linearity. In this study, a time domain analysis method for nonlinear pipe-seabed-interaction analysis of free spanning pipelines under VIV conditions has been developed. The flow is modeled by a Van-der-Pol wake oscillator developed by Facchinetti et al. And the stall parameter is taken into account in the general form of the VIV amplitude and the response frequency, which can successful model the VIV response amplitude comparing with a constant. After the free spanning pipeline discretized into finite elements, the average acceleration method is chosen to integrate the equations of motion. Three types of pipe-seabed-interaction (linear spring, perfectly plastic nonlinear spring, and tension cut-off nonlinear spring) are considered. The results show that the presented time domain method can capture the non-linear interaction between the pipeline and the seabed at the free span shoulders. And the maximum response amplitude of nonlinear case is lower than the one with linear spring.


2020 ◽  
Vol 21 (5) ◽  
pp. 505
Author(s):  
Yousef Ghaderi Dehkordi ◽  
Ali Pourkamali Anaraki ◽  
Amir Reza Shahani

The prediction of residual stress relaxation is essential to assess the safety of welded components. This paper aims to study the influence of various effective parameters on residual stress relaxation under cyclic loading. In this regard, a 3D finite element modeling is performed to determine the residual stress in welded aluminum plates. The accuracy of this analysis is verified through experiment. To study the plasticity effect on stress relaxation, two plasticity models are implemented: perfect plasticity and combined isotropic-kinematic hardening. Hence, cyclic plasticity characterization of the material is specified by low cycle fatigue tests. It is found that the perfect plasticity leads to greater stress relaxation. In order to propose an accurate model to compute the residual stress relaxation, the Taguchi L18 array with four 3-level factors and one 6-level is employed. Using statistical analysis, the order of factors based on their effect on stress relaxation is determined as mean stress, stress amplitude, initial residual stress, and number of cycles. In addition, the stress relaxation increases with an increase in mean stress and stress amplitude.


Author(s):  
M. G. Koliada ◽  
T. I. Bugayova

The article discusses the history of the development of the problem of using artificial intelligence systems in education and pedagogic. Two directions of its development are shown: “Computational Pedagogic” and “Educational Data Mining”, in which poorly studied aspects of the internal mechanisms of functioning of artificial intelligence systems in this field of activity are revealed. The main task is a problem of interface of a kernel of the system with blocks of pedagogical and thematic databases, as well as with the blocks of pedagogical diagnostics of a student and a teacher. The role of the pedagogical diagnosis as evident reflection of the complex influence of factors and reasons is shown. It provides the intelligent system with operative and reliable information on how various reasons intertwine in the interaction, which of them are dangerous at present, where recession of characteristics of efficiency is planned. All components of the teaching and educational system are subject to diagnosis; without it, it is impossible to own any pedagogical situation optimum. The means in obtaining information about students, as well as the “mechanisms” of work of intelligent systems based on innovative ideas of advanced pedagogical experience in diagnostics of the professionalism of a teacher, are considered. Ways of realization of skill of the teacher on the basis of the ideas developed by the American scientists are shown. Among them, the approaches of researchers D. Rajonz and U. Bronfenbrenner who put at the forefront the teacher’s attitude towards students, their views, intellectual and emotional characteristics are allocated. An assessment of the teacher’s work according to N. Flanders’s system, in the form of the so-called “The Interaction Analysis”, through the mechanism of fixing such elements as: the verbal behavior of the teacher, events at the lesson and their sequence is also proposed. A system for assessing the professionalism of a teacher according to B. O. Smith and M. O. Meux is examined — through the study of the logic of teaching, using logical operations at the lesson. Samples of forms of external communication of the intellectual system with the learning environment are given. It is indicated that the conclusion of the found productive solutions can have the most acceptable and comfortable form both for students and for the teacher in the form of three approaches. The first shows that artificial intelligence in this area can be represented in the form of robotized being in the shape of a person; the second indicates that it is enough to confine oneself only to specially organized input-output systems for targeted transmission of effective methodological recommendations and instructions to both students and teachers; the third demonstrates that life will force one to come up with completely new hybrid forms of interaction between both sides in the form of interactive educational environments, to some extent resembling the educational spaces of virtual reality.


Author(s):  
R. Z. Aminov ◽  
A. N. Bayramov ◽  
M. V. Garievskii

The paper gives the analysis of the problem of the primary current frequency regulation in the power system, as well as the basic requirements for NPP power units under the conditions of involvement in the primary regulation. According to these requirements, the operation of NPPs is associated with unloading and a corresponding decrease in efficiency. In this regard, the combination of nuclear power plants with a hydrogen complex is shown to eliminate the inefficient discharge mode which allows the steam turbine equipment and equipment of the reactor facility to operate in the basic mode at the nominal power level. In addition, conditions are created for the generation and accumulation of hydrogen and oxygen during the day, as well as additionally during the nighttime failure of the electrical load which allows them to be used to generate peak power.  The purpose of the article is to assess the systemic economic effect as a result of the participation of nuclear power plants in combination with the hydrogen complex in the primary control of the current frequency in the power sys-tem, taking into account the resource costs of the main equipment. In this regard, the paper gives the justification of cyclic loading of the main equipment of the hydrogen complex: metal storage tanks of hydrogen and oxygen, compressor units, hydrogen-oxygen combustion chamber of vapor-hydrogen overheating of the working fluid in the steam turbine cycle of a nuclear power plant. The methodological foundations for evaluating the working life of equipment under cyclic loading with the participation in the primary frequency control by the criterion of the growth rate of a fatigue crack are described. For the equipment of the hydrogen complex, the highest intensity of loading is shown to occur in the hydrogen-oxygen combustion chamber due to high thermal stresses.  The system economic effect is estimated and the effect of wear of the main equipment under cyclic loading is shown. Under the conditions of combining NPP power units with a hydrogen complex, the efficiency of primary reg-ulation is shown to depend significantly on: the cost of equipment subjected to cyclic loading; frequency and intensity of cyclic loading; the ratio of the tariff for peak electricity, and the cost of electricity of nuclear power plants.  Based on the developed methodology for assessing the effectiveness of the participation of nuclear power plants with a hydrogen complex in the primary frequency control, taking into account the damage to the equipment, the use of the hydrogen complex is shown to provide a tangible economic effect compared with the option of unloading nuclear power plants with direct participation in frequency control.


PCI Journal ◽  
1998 ◽  
Vol 43 (6) ◽  
pp. 58-71 ◽  
Author(s):  
Rosa M. Vasconez ◽  
Antoine E. Naaman ◽  
James K. Wight

Sign in / Sign up

Export Citation Format

Share Document