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The development of offshore oil and gas resources is inevitable for a submarine pipe network. Submarine pipeline leakage can easily escalate into a catastrophic event, causing enormous loss of life and property and environmental pollution. Therefore, it is imperative to conduct risk assessments of submarine pipelines. A failure mode and effects analysis (FMEA) is a significant method in risk analysis. However, due to the uncertainty in the risk analysis process, the assessment results may not be sufficiently accurate. In this paper, to evaluate the risk of submarine pipeline with enhanced reliability, an improved FMEA method based on cloud model and extended vlsekriterijumska optimizacija i kompromisno resenje (VIKOR) is proposed. The main contributions of this method are as follows. First, to minimize the associated linguistic uncertainties during the evaluation process, the cloud model theory is used, enabling the fuzziness and randomness to be comprehensively considered. Second, an improved synthetic dynamic weight algorithm, considering the personal status of experts as well as the agreement degree and confidence level of expert comments is proposed to strengthen the knowledge of the experts to minimize incompleteness. Third, an extended two-level risk factor hierarchy of submarine pipeline failure is established to improve the comprehensiveness of risk assessment, meanwhile, an integrated weighting method considering both subjective and objective aspects is utilized to obtain the risk factor weights, which can comprehensively reveal the risk factors’ relative importance. Fourth, the VIKOR method is extended with the cloud model to determine the risk priority of failure modes, which can offer a compromise solution in the context of uncertainty. Furthermore, a case study on a submarine pipeline of the Chengbei oilfield in China is performed to illustrate the applicability of proposed approach. Sensitivity analysis are carried out to observe the robustness of the proposed method. Finally, the comparison between the obtained results and that from pre-existing methods shows that the proposed method is a more accurate and effective method for the risk assessment of a submarine pipeline.

In order to solve the problems of die and tooling manufacturing and assembling for the foil forming, especially for the foil micro forming, high-pressure water jet forming (HPWJF), a new die-less forming process for foil parts is proposed. In the forming process, liquid medium such as water and oil is utilized as a flexible tool to deform the ultrathin foil. In this paper, the computational fluid dynamics (CFD) software Fluent was used to simulate the water jet generation in the water jet nozzle and high-speed water impacting on a rigid surface. And then, the effects of jetting distance on the jetting pressure were obtained. To measure the precise mechanical parameters of copper foils, a digital speckle test method was used to detect the tensile process. Local bulging experiment was conducted for the copper foil with a thickness of 50 μm. When the inlet pressure is 8.5 MPa, the suitable jetting distance is 40 mm for the 50-μm-thick copper foil. In such conditions, the bulging height of the copper foil is 1.20 mm in the experiment. The fluid–solid coupled method by using Fluent and Abaqus was applied to simulate the deformation of the copper foil. The errors between the simulated results and the experimental values are lower than 10 %. Furthermore, both the experiment and simulation for micro stretching of 30-μm-thick copper foil were performed. The cylinder die with a diameter of 3 mm and a height of 1.5 mm is used to form the copper foil. Results show that the copper foil cracks when the jetting distance is 24 mm, and the inlet pressure is 12 MPa. With the increase of the inlet pressure, the drawing depth of the copper foil gradually increases, and the bottom of the cylinder part thins gradually, and the wrinkling of the flange of the cylinder part becomes more and more severe.

The thread and spline synchronous rolling process can form the external threaded and external splined tooth profiles on different parts of component by only one rolling process. However, it is a coupled rolling process where the thread rolling coupling with the spline rolling, and both phase adjusting requirements of dies before rolling for thread rolling and spline rolling should be satisfied in the synchronous rolling process. Thus, the phase adjustment only by rotating die may be difficult to ensure the thread and spline rolling by different dies well connects respectively. In this paper, requirements of phase difference adjustment for dies before thread rolling and before spline rolling have been studied systematically, and the mathematical expressions of phase difference adjustment have been established, and then the requirements of phase difference under different starts of threaded workpiece and die (or teeth of splined workpiece and die) for two and three rolling dies before thread rolling (or spline rolling) have been investigated. Based on these, the ratio S of phase difference between corresponding threaded sections of rolling dies to that between corresponding splined sections of rolling dies was introduced, and the phase characteristic between dies and the method of phase difference adjustment under different parameters in thread and spline synchronous rolling process were systematically researched. The results indicated that: (1) for thread (or spline) rolling process, if the remainder from dividing the starts nw of thread (or teeth Zw of spline) of workpiece by number N of rolling dies is equal to the remainder from dividing the starts nd of thread (or teeth Zd of spline) of rolling die by N, i.e., nw≡nd(mod N) (or Zw≡Zd(mod N)), then the phases of dies before rolling are the same, else there is a phase difference between dies; (2) for thread and spline synchronous rolling process, if the phase difference of splined section between rolling die j (j = 2,…, N) and rolling die 1 is \( {\varphi}_{{\mathrm{s}}_{j1}}=\frac{h}{N}{\theta}_s\left(h=1,\dots, N\right) \) and ratio of phase difference is \( {S}_{j1}=\frac{N}{h}k+1\left(k=0,1,2,3,\dots \right) \), then the die structures of two dies are the same, i.e., the relative phase between threaded and splined sections for two dies are the same, else the die structures of rolling dies j and 1 are different and the phase difference for threaded sections of rolling dies and the phase difference for splined sections of rolling dies are assured by die structure itself.