Strength Analysis of Adhesive Joints for Riser Pipes in Deep Sea Enviroment Loading

Nowadays, adhesive joints are widely used in riser pipes, which are subjected to many kinds of loadings in deep sea, such as external pressure, internal pressure, tension, torsion, bending, and also a combination of these loadings. Adhesive joints of riser pipes are the most dangerous parts in term of strength, as singular stress fields exist at the end of the interface between the adhesive and the adherends, so it is very important to evaluate the strength of adhesive bonded joints for riser pipes in deep sea environment loadings. In this research, the strength of adhesive joints of riser pipes is studied under external pressure, internal pressure, tension, torsion, bending loadings, and it is found that singular stress fields exist around the end of the interface. The riser pipe under external pressure, internal pressure and tension loading is more prone to break than under bending and torque loading

Integral transform solutions of dynamic response of a clamped–clamped pipe conveying fluid

Analysis of dynamic response of pipe conveying fluid is an important aspect in nuclear power plant design. In the present paper, dynamic response of a clamped–clamped pipe conveying fluid was solved by the generalized integral transform technique (GITT). The governing partial differential equation was transformed into a set of second-order ordinary differential equations which is then numerically solved by making use of the subroutine DIVPAG from IMSL Library. A thorough convergence analysis was performed to yield sets of reference results of the transverse deflection at different time and spanwise position. We found good agreement between the computed natural frequencies at mode 1–3 and those obtained by previous theoretical study. Besides, modal separation analysis was carried out and the influence of mass ratio on deflection and natural frequencies was qualitatively and quantitatively assessed.Indisponível

Multi-objective optimization of semi-submersible platforms based on a support vector machine with grid search optimized mixed kernels surrogate model

Determination of optimal hull configurations in the semi-submersible platform (SEMI) should account for several objectives. These objectives are pertinent to hydrodynamic performances of SEMI under wave action but also total structure cost. They are often contradictory and cannot achieve the minimum simultaneously. Hence, a group of relative optimal and balanced solutions is introduced as optimization results, called Pareto-optimal solutions. This paper presents a surrogate-assisted technique to seek the optimal configuration of SEMI for minimal heave and roll response and the lightest weight. Design variables samples are generated by means of multidimensional Ladin hypercube design, and then these inputs are employed for hydrodynamic simulation to acquire the response data. To determine the relationship between objectives and hull structure size, Support Vector Machine with Grid Search optimized mixed kernels (SVM-GSM) is constructed as a surrogate model, and triple verification in terms of errors and robustness warrants its reliability. Three categories of Pareto optimal solutions are obtained by Non-dominated Sorting Genetic Algorithm II (NSGA-II), which correspond to three optimal goals. For optimization results, a presented comprehensive verification approach integrates frequency -domain analysis (FD), time-domain analysis (TD), convergence analysis, and main factors screening. This combination renders sufficient and reliable validation to optimization results. Results from FD and TD for SEMI indicate that the optimized effect of Pareto solutions is satisfactory. Besides, the main influence factors in design variables for hydrodynamic response are screened and investigated. Finally, the ranking of the influence degree of each variable is obtained and evaluated. The proposed framework in this paper provides a comprehensive validation idea for the construction of the surrogate model and optimization results for SEMI hull structure optimization

Vibrational Responses of an Ultra-Large Cold-Water Pipe for Ocean Thermal Energy Conversion: A Numerical Approach

The transportation of seawater on a grand scale via an ultra-large cold-water pipe situated within the context of ocean thermal energy conversion (OTEC) floating installations inherently presents challenges associated with instability and potential malfunction in the face of demanding operational circumstances. This study endeavors to augment the stability and security of cold-water pipe (CWP) operations by scrutinizing their vibrational attributes across diverse boundary configurations. Initially, we invoke Euler–Bernoulli beam theory to forge the analytical framework and proffer a semi-analytical resolution by utilizing the generalized integral transform technique (GITT). Subsequently, we authenticate the convergence and precision of our proposed approach through comparative analysis with extant theories. Our findings underscore the conspicuous influence of boundary conditions on the convergence of transverse displacement. The influence of internal flow on the transverse displacement and the natural frequency manifests substantial variability under different boundary conditions. Significantly, an escalation in the internal flow velocity triggers a concomitant reduction in the natural frequency, ultimately culminating in instability once the critical velocity threshold is reached. Additionally, the reliance of the transverse displacement and the natural frequency on the clump weight at the bottom is markedly pronounced. Our discoveries propose that pipe stability can be ameliorated by adjusting the clump weight at the bottom. Furthermore, the novel insights obtained through our proposed approach can significantly aid in the early-stage design and analysis of CWP

Selection of deepwater floating oil platform based on grey correlation

To select a suitable floating oil platform for a given deepwater oilfield, a method based on grey-correlation theory was proposed and verified. By analyzing factors that may affect selection of deepwater platform, thirteen main factors were chosen. This article also summed up the statistics on 65 deepwater floating platforms (including tension leg platform, deep-draft column type platform, semi-submersible platform, and floating storage mining and unloading device) performing well in the world. With a deepwater oilfield to be developed as a sample, the application of the method was illustrated: Considering the factor series of the given oilfield to be developed as referent series, the relevance between referent series and factor series of each platform in statistics was calculated with grey-correlation analysis, and the optimal platform was identified as the one that had the highest relevance. Two examples proved the feasibility and reliability of the method. Key words: deepwater oil and gas development, tension leg platform (TLP), deep-draft column type platform (SPAR), semi- submersible platform (SEMI), floating storage mining and unloading device (FPSO), platform selection, grey correlation analysi

Experimental and Numerical Study of Lateral Indentation for Pipe-in-Pipe Structures

Pipe-in-pipe (PIP) flowlines have been widely arranged in offshore oil and gas fields for transportation, to achieve a significant thermal insulation capacity and outstanding resistance to external loads. However, the lateral indentation mechanisms of these multilayer pipelines are more complicated than those of single-layer pipelines. In this paper, the change and deformation laws of lateral indentation in the PIP structure were studied by experimental and numerical methods, and three stages of deformation behavior for PIP during lateral indentation were observed. The effects of the diameter and wall thickness of inner and outer pipes on the relationship between the indentation load and lateral indentation were also studied, which provided a reference for the design and analysis of PIP structures

Test Study on Vortex-Induced Vibration of Deep-Sea Riser under Bidirectional Shear Flow

A model test was carried out to reveal the vortex-induced vibration characteristics of a deep-sea riser under bidirectional shear flow. Bandpass filtering and modal analysis were used to process the test strain data, and the amplitude and frequency response characteristics of the vortex-induced vibration of the riser in the bidirectional shear flow field were obtained. The results of the test data analysis show that the dominant frequency of the vortex-induced vibration of the riser model under bidirectional shear flow is locked in the natural frequency of the riser and does not increase with the increase in flow velocity, that the average resistance coefficient of the riser model has little change under different flow velocities because of the distribution characteristics of the “bidirectional shear” flow field, that there is an extreme value of the shear force in the middle of the riser model, and that the Strouhal number in the transverse direction of the vortex-induced vibration under bidirectional shear flow is less than the recommended value of the current vortex-induced vibration prediction software. The obtained results provide basic data for the prediction of vortex-induced vibration and research into the fatigue analysis method of a riser under an internal wave flow field