Xiaojie Tian

Using Bayesian networks in reliability evaluation for subsea blowout preventer control system

The Bayesian network models of redundant systems including parallel system and voting system, taking account of common cause failure and imperfect coverage, are proposed. The Triple Modular Redundancy (TMR) and Double Dual Modular Redundancy (DDMR) control systems for subsea Blowout Preventer (BOP) are presented. By applying the proposed Bayesian network models, the reliability of subsea BOP control systems are evaluated at any given time, and the difference between posterior and prior probabilities of each single component given the system failure is obtained. The effects of coverage factor of redundant subsystem and failure rate of single component on reliability of systems are also researched. The results show that the DDMR control system has a little higher reliability than TMR system. To improve the reliability of subsea BOP control systems, the component failure rates of Ethernet switch (ES), programmable logic controller (PLC) and personal computer (PC) should be reduced for TMR system, whereas the failure rates of ES and PC should be reduced for DDMR system. The recovery mechanism of PLC, PC and ES subsystems, and PC and ES subsystems should be paid more attention for TMR and DDMR control systems, respectively.

Application of Bayesian Networks in Quantitative Risk Assessment of Subsea Blowout Preventer Operations

This article proposes a methodology for the application of Bayesian networks in conducting quantitative risk assessment of operations in offshore oil and gas industry. The method involves translating a flow chart of operations into the Bayesian network directly. The proposed methodology consists of five steps. First, the flow chart is translated into a Bayesian network. Second, the influencing factors of the network nodes are classified. Third, the Bayesian network for each factor is established. Fourth, the entire Bayesian network model is established. Lastly, the Bayesian network model is analyzed. Subsequently, five categories of influencing factors, namely, human, hardware, software, mechanical, and hydraulic, are modeled and then added to the main Bayesian network. The methodology is demonstrated through the evaluation of a case study that shows the probability of failure on demand in closing subsea ram blowout preventer operations. The results show that mechanical and hydraulic factors have the most important effects on operation safety. Software and hardware factors have almost no influence, whereas human factors are in between. The results of the sensitivity analysis agree with the findings of the quantitative analysis. The three-axiom-based analysis partially validates the correctness and rationality of the proposed Bayesian network model.

Development of an automatic subsea blowout preventer stack control system using PLC based SCADA.

An extremely reliable remote control system for subsea blowout preventer stack is developed based on the off-the-shelf triple modular redundancy system. To meet a high reliability requirement, various redundancy techniques such as controller redundancy, bus redundancy and network redundancy are used to design the system hardware architecture. The control logic, human-machine interface graphical design and redundant databases are developed by using the off-the-shelf software. A series of experiments were performed in laboratory to test the subsea blowout preventer stack control system. The results showed that the tested subsea blowout preventer functions could be executed successfully. For the faults of programmable logic controllers, discrete input groups and analog input groups, the control system could give correct alarms in the human-machine interface.

Experimental Characterization of Sinking Electrical Discharge Machining Using Water in Oil Emulsion as Dielectric

Electrical discharge machining (EDM) has been wildly used in the modern manufacture industry due to its advantage over the traditional manufacture method of some hard-to-cut materials. However, compared with the traditional manufacture method, the EDM process was inefficient and environmentally hazardous due to the decomposition of the dielectrics, especially in the case of sinking EDM which used oil-based dielectric. In order to improve the EDM performance, and for the other hand, alleviate the environmental impact of the process, a new type of dielectric, water in oil (W/O) emulsion was proposed as the working fluid. This work presents a systematical study on the performance of this new type dielectric based on the orthogonal and additional single factor experiments. Statistical analysis of the results show that discharge current (I) and water content of the emulsion significantly influence the machining performance of sinking EDM. The study also analyzed the influence of the emulsion temperature and flushing condition on its EDM performance. It was observed that both MRR and EWR decrease with increasing temperature of the emulsion. Experiments results indicated that W/O emulsion can be used as the working fluid of sinking EDM and alleviated the environmental impact of the process.

Optimization of Submersible Solenoid Valves for Subsea Blowout Preventers

An analytical optimization approach of the submersible solenoid valve constrained in a specific small volume is presented. In order to maximum the electromagnetic force, thermal model and electromagnetic model are constructed, and five radial dimensions are optimized when the main limiting quantity is the maximum allowed temperature. A numerical optimization calculation is performed in order to verify the proposed analytical approach. The optimal solution of the numerical calculation is compared with the solution of the analytical approach, which shows a good agreement between the two methods. A thermal analysis of the optimal submersible solenoid valve based on AYSYS is also performed to verify the thermal model. A comparative study between the experimental and simulated static characteristics of the optimal submersible solenoid valve is also performed. The results show that the proposed analytical approach is correct.

Experimental study of galvanic corrosion behaviour of carbon fibre composite coupled to aluminium in artificial seawater

Abstract The galvanic corrosion behaviours of carbon fibre composite coupled to aluminium are studied when the galvanic couple is just immersed in artificial seawater or connected to a closed electric circuit. The effects of grinding condition, concentration of artificial seawater, applied torque, applied current and experimental time are studied. The roughness average, weight gain of carbon fibre composite and weight loss of aluminium are investigated as a function of the above variables. The results show that the applied current can accelerate the galvanic corrosion greatly. With improving grinding condition and increasing applied torque, the roughness average, weight gain of carbon fibre specimen and weight loss of aluminium specimen increase, reach maximum and then decrease. With increasing concentration of artificial seawater, applied current and experimental time, these measured values increase. Corroded surface morphology is also investigated using scanning electron microscopy.

Application of Petri nets to performance evaluation of subsea blowout preventer system

This paper presents an application of deterministic and stochastic Petri nets (DSPN) to evaluate the performance of subsea blowout preventer (BOP) system. The overall subsea BOP system is comprised of five mechanical subsystems and five electrical subsystems, which can be viewed as a series-parallel system. In regard to common cause failures, TimeNET 4.0 toolkit is utilized to develop and analyze the DSPN models. Availability and reliability of the subsea BOP system and its subsystems are obtained. Besides, the effects of failure rate and repair time of each component on system performance are researched.

Carbon Fiber in Micro–Electric Discharge Machining

Micro-electric discharge machining (micro-EDM) has become an important issue in the fabrication of microcomponents, especially after the development of the wire electro discharge grinding (WEDG) technology. However, the fabrication of microelectrodes through the WEDG technology is very complicated and time consuming, which limits the extensive industrial application of micro-EDM. This article reports the feasibility of utilizing carbon fiber as the electrode in micro-EDM. A novel chucking method and device are developed to chunk the extremely slender carbon fiber. The experiment results show that carbon fiber is a promising material in micro-EDM.

Sensitivity thermal analysis of electrical discharge machining process based on probabilistic design system

The probabilistic design system is introduced for the sensitivity analysis to analyze the effects of machining parameters during electrical discharge machining process. An axisymmetric finite element thermal model is presented to investigate the electrical discharge machining process. By comparing the discharge crater geometry for the finite element method results and experiment results under different conditions, the deterministic thermal model is proved to be validated. Monte Carlo simulation method and response surface method are both used in the sensitivity analysis. Parameters of discharge voltage, peak current, pulse-on time and discharge channel radius are selected as the design variables. The sensitivity analysis results meet the confidence limit of 0.95. It is concluded that the discharge voltage and peak current have significant influences on the electrical discharge machining process, whereas the pulse-on time and discharge channel radius have little influence. Moreover, the increase in discharge channel radius can reduce the material removal rate. The increase in other parameters can increase the material removal rate.

Design of Three-axis ED Milling Machine Based on the PMAC Motion Card

This paper presents a new three-axis ED milling machine, which is based on the PMAC motion card. The machine is composed of the motion system, the control system, the working fluid supplying system and the EDM pulse generator. First, the motion system , the working fluid supplying system, the hardware of the control system, and the EDM pulse generator have been built, then the software system of the industrial computer has been developed based on the Visual Basic 6.0 in order to control the machine and monitor the status of the machine. Using the PMAC motion card, the servo control program, the decoding program and the PLC program have been programmed. The software system of the EDM pulse generator is implemented based on a good real time operating system called μC/OS-II, and the software system is composed of three main tasks, namely the data processing task, the communication task and the monitoring task. The milling experiments have been carried out on the ED milling machine based on the PMAC motion card, and the results show that the ED milling machine is steady and reliable when milling with three-axis.