Jijun Gu

Parameter determination of double-ellipsoidal heat source model and its application in the multi-pass welding process

The parameters of the heat source model have significant influence on the temperature field and sequentially affect the residual stress field. In this paper, a neural-network programme based on the Levenberg–Marquardt algorithm is developed to predict the parameters of Goldaks double-ellipsoidal heat source model. The analytical solution of the heat conduction equation based on the double-ellipsoidal heat source is obtained by integrating a series of instant point heat sources over the volume of the ellipsoidal heat source. The transient temperature distribution and the sizes of the molten pool are obtained under various welding processes by using the analytical method. Then, a neural-network programme is employed to train and predict the heat source parameters. These results of temperature and molten pool size obtained by the numerical simulation with the predicted heat source parameters are calibrated by the published experimental results. The numerical results show a good agreement with the experimental measurements. Finally, the developed Levenberg–Marquardt neural network is employed to predict the heat source parameters in the multi-pass welding process in the laboratory. By comparing the finite element (FE) numerical results with experimental results, the heat source parameters have been successfully identified in the multi-pass welding process.

A vortex-induced vibration model for the fatigue analysis of a marine drilling riser

ABSTRACT The objective is to propose a quick and accurate vortex-induced vibration (VIV) model to predict the fatigue life of marine drilling risers. The nonlinear wake oscillator model was applied to represent the lift force, which is described by a fourth-order partial differential equation set. Next, we adopted the generalised integral transform technique (GITT) to transform it into second-order ordinary differential equation system, which was solved by the Runge-Kutta method. Validation of the numerical model was implemented and a good agreement was achieved. Next, an S-N curve was adopted to conduct fatigue prediction. The results demonstrate that under the conditions set forth in this paper, an increase in the current and outer diameter could reduce fatigue life, except when the outer diameter reaches a certain value, at which point the tendency is reversed. Moreover, when the top tension coefficient reaches a certain value, the fatigue life tendency is also reversed.

Study on the system design and control method of a semi-active heave compensation system

ABSTRACT The heave compensation system is essential for the installation of subsea equipment. A new semi-active heave compensation system is designed and the control system is analysed, with the aim of solving heave movement problems during deep-water installation. The heave compensation is implemented with a pulley block system and actuated by a compound hydraulic cylinder. The control system can switch between passive compensation mode and semi-active compensation mode. The state-space equations of both modes are set up based on the mechanical and hydraulic system models of the compensation system. With the state-space equations, three control strategies are compared based on the classic Proportion Integration Differentiation (PID) control, and the limitations of PID control are also analysed. In order to avoid defects of the PID controller, the active disturbance rejection control (ADRC) technology is introduced, and a newly developed second-order ADRC controller is applied in the tension control strategy for heave compensation, which results in improved compensation effect.

Dynamic analysis of a fluid-conveying pipe under axial tension and thermal loads

The risers and pipelines are widely used in offshore oil and gas transportation, and they may undergo instabilities and buckling generated by internal fluid and thermal loads. This paper conducted a dynamic analysis of the fluid-conveying pipe under axial tension and thermal loads through the generalised integral transform technique (GITT). The governing partial differential equation (PDE) is converted into ordinary differential equations (ODEs) which are then numerically handled by the subroutine DIVPAG from IMSL Library. An excellent convergence behaviour is demonstrated and the numerical results are verified with previous theoretical study. The influence of the fluid velocity, temperature and axial tension is analysed qualitatively and quantitatively; the results show that the vibration frequency decreases when the fluid velocity and temperature increase or the axial tension decreases, and the critical fluid velocity decreases when the temperature increases or the axial tension decreases. As for the vibration deflection, an increase in both the temperature and the fluid velocity will lead to an increase in maximum deflection, whereas increasing the axial tension will suppress the maximum deflection.

A new partition model for the optimization of subsea cluster manifolds based on the new definition of layout cost

The engineering practicability for the partition optimization of subsea cluster manifolds should be improved to provide a broader insight to subsea engineering designers, considering three connection types of jumpers between subsea wells and cluster manifolds. With the jumpers, pipeline end terminations and infield flowlines, this study describes an optimization method by a new definition of the layout cost of a piecewise function. That is different from the layout cost of the square of Euclidean Distance when the connection types are assumed to be straight flowlines without considerations of the connection facilities. A new practical optimization model of the partition of cluster manifolds at the lowest cost is presented and its core algorithm is developed with a program by MATLAB. Meanwhile, the demonstration of the convergence of the proposed algorithm is conducted. The validity of the model is evaluated by the simulation with a random two-dimensional distribution of 20 subsea wells. With the rapid convergence of the algorithm, 20 subsea wells can be partitioned into corresponding two to seven cluster manifolds and three connection types of jumpers in engineering can be obtained exactly by comparisons. In addition, spared well slots on cluster manifolds can be left for the future tiebacks of subsea wells by changing the types of cluster manifolds.

Dynamic Response of a Fluid-Conveying Riser Subject to Vortex-Induced Vibration: Integral Transform Solution

Analysis of dynamic response of a fluid-conveying riser is an important aspect in subsea production system. In the present paper, dynamic response of a pinned-pinned riser subject to external fluid force was solved by the generalized integral transform technique (GITT). A nonlinear wake oscillator models was used to represent the cross-flow and in-line force acting on the riser, leading to a coupled system of second-order Partial Differential Equations (PDEs). The GITT approach was used to transform the system of PDEs to a system of Ordinary Differential Equations (ODEs), which was numerically solved by using the Adams-Moulton and Gear method (DIVPAG) developed by the International Mathematics and Statistics Library (IMSL). Numerical results were presented for comparison to those given by the numerical and experimental results, allowing a critical evaluation of the technique performance. The influence of conveying fluid velocity and mean top tension were evaluated to show that they should not be negligible in numerical simulation of Vortex-Induced Vibration of a long flexible riser.Copyright