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Long-distance gas pipelines are the most common means of transporting natural gas resources. However, the propagation of longitudinal ductile fractures in gas pipelines can result in catastrophic accidents, which must be avoided as much as possible. Crack arrestors can prevent or at least limit the rapid spread of longitudinal cracks by constraining the outwall of pipelines. Carbon fiber-reinforced composite material is one of the best candidates for crack arrestors because of its excellent strength and toughness. However, due to the significant variations in composite material performance, clear design criteria for determining the size of crack arrestors have not yet been developed. This paper presents a comprehensive design procedure for determining the geometrical parameters of composite material crack arrestors based on a finite element model of dynamic pipeline fractures under crack arrestor constraints. Pipeline crack propagation is accomplished using the cohesive zone model, and composite material failure is defined by Hashin criteria. A series of numerical simulations are conducted to assess the ability of crack arrestors to stop a growing crack in a gas pipeline. Ultimately, the minimum wall thickness and axial length of the effective crack arrestor are determined. The proposed design procedure enables the numerical design of composite material crack arrestors and supports safe pipeline operation. • The proposal of a numerical design procedure for composite crack arrestors. • Establishing a numerical model of pipeline fracture under arrestor's constraints. • Evaluating the performance of crack arrestors in arresting pipeline cracks. • The determination of the composite arrestors' geometrical parameters. [ABSTRACT FROM AUTHOR]

A reluctance lead screw (RLS) is proposed in this paper which consists of a rotor and a translator, forming a magnetic device that is able to transfer low-speed linear motion into high-speed rotational motion. Permanent magnets (PMs) are only installed in the rotor, making it more suitable for long-stroke applications. The design aspects are assessed by finite element analysis (FEA) and the performance is evaluated. In addition, the thrust force per magnet volume is presented for evaluating the utilization rate of the PMs. The simulation results show that RLS has an advantage in terms of the PM utilization rate. A new method for realizing spiral magnets has also been developed which can not only reduce the manufacturing difficulties, but also ease the installation work. Finally, based on the simulations and analyses, two RLS prototypes designed for wave energy converters (WECs) are presented to show the potential applications of this novel topology. [ABSTRACT FROM AUTHOR]

• A dynamic fracture finite element model of the buried gas pipeline is established to simulate the actual fracture process incorporating external soil constraints and inner gas decompression. • The fracture velocity and crack tip opening angle are calculated using this model, and the effects of internal pipeline pressure and the soil spring stiffness outside the pipe are studied. A long-distance natural gas transmission pipeline is the primary solution for natural gas resource distribution. In fact, the longitudinal crack propagation of gas transmission pipelines has always been a concern of the natural gas industry. Because it will cause disastrous accidents once the ductile crack in the pipeline propagates rapidly. Most natural gas transmission pipelines are buried underground to improve the safety of pipeline operation as the backfill soil can absorb energy during the fracture process and restrain the displacements of the flaps. Fracture control is a fundamental requirement for the safe operation of underground pipelines. In this study, the dynamic fracture finite element model of the buried gas pipeline is developed to simulate the actual fracture process instead of the costly full-scale burst experiments. The finite element model incorporates different external soil constraints and internal gas decompression behaviors during pipe rupture in which soil constraints are represented by discrete soil springs, and a user-defined subroutine realizes the gas decompression behavior. The explicit dynamic analysis is employed to simulate the high-speed dynamic fracture process of the pipeline, and the crack propagation is simulated by using the cohesive zone model. Finally, the crack propagation velocity is calculated by this model, and the influence of different internal pressures on the fracture velocity is studied; the crack tip opening angle (CTOA) is predicted, and the effect of soil spring stiffness on CTOA is evaluated. [ABSTRACT FROM AUTHOR]