Jinyang Zheng

Finite Element Analysis of Buried Polyethylene Pipe Subjected to Seismic Landslide

Polyethylene (PE) pipes are widely used in natural gas transportation systems in urban areas nowadays. As landslide caused by earthquake would cause destructive damage to buried pipes, increasing attention is attracted to the safety of buried PE pipes under seismic load. In this paper, the deformation behavior of PE pipe subjected to seismic landslide was investigated and a related failure criterion due to yielding was proposed. Based on extensive uniaxial tensile tests, a rate-dependent constitutive model of PE was applied to simulate the mechanical behavior of PE pipes. The extended Drucker-Prager model was used for surrounding soil. In our proposed finite element model, a quartic polynomial bending deflection displacement normal to the pipeline was loaded along the axial direction of PE pipe. The numerical simulation results revealed that the main failure mode of buried PE pipe subjected to seismic landslide shifted from bending deformation to ovalization deformation with increasing bending deflection. On the basis of deformation behavior analysis, failure criterion curves were put forward, which depicts the maximum relative deflection of the pipe cross-section, and the maximum displacement of the pipe versus pipe length subjected to seismic landslide. The results may be referable for design and safety assessment of PE pipes due to seismic landslide. [DOI: 10.1115/1.4026148]

Numerical Simulation of Blast Loadings on a Thick-Walled Cylindrical Vessel

Determining blast loadings on an explosion containment vessel (ECV) is the foundation to design the ECV. Explosion of TNT centrally located in a thick-walled cylindrical vessel and its impact on the cylinder was simulated using the explicit finite element code LS-DYNA. Blast loadings on the cylinder computed are in good agreement with the corresponding experimental results. Then wall thickness and yield stress of the cylinder were changed in the following simulation to investigate effect of shell deformation on blast loadings. It is revealed that shell deformation during the primary pulses of blast loadings is so slight that it has little influence on the blast loadings. Though the deformation may increase greatly after the primary pulses, the dynamic response of an ECV is mainly affected by the primary pulses. Therefore, decoupled analyses are appropriate, in which the shell of an ECV is treated as a rigid wall when determining blast loadings on it.© 2007 ASME

Safety Investigation of Buried Polyethylene Pipe Subject to Seismic Landslide

As polyethylene (PE) pipes are widely used in the gas transportation system nowadays, increasing attention is attached to the safety of buried PE pipe under seismic load. In this paper, the related failure criterion is proposed and mechanical behavior of PE pipe subject to seismic landslide is investigated. Based on extensive tensile tests, an appropriate constitutive model of PE is selected and the parameters are estimated to simulate mechanical behavior of PE pipes using finite element method. The pipe is assumed to be loaded with a quartic polynomial bending deflection displacement along the axial direction and the soil acts linear elastic. From the numerical simulation results, it is concluded that cross-section deformation is the governing failure mode of buried PE pipe subject to seismic landslide and the critical pipe deflection is about 0.048. Failure criterion curves of seismic landslide are put forward with the combination of failure criterion and engineering practice. The proposed failure criterion curves serve as a foundation available not only for the safety design and assessment also for engineering acceptance criterion of the failure of PE pipe due to seismic landslide.Copyright

Effects of Structural Perturbations on Strain Growth in Containment Vessels

Strain growth is a phenomenon observed in the elastic response of containment vessels subjected to internal blast loading. The local dynamic response of a containment vessel may become larger in a later stage than its response in the initial breathing mode response stage. It has been reported in our previous study that bending modes may be excited after several cycles of breathing mode vibration, due to the dynamic instability in cylindrical and spherical shells without structural perturbations. The nonlinear modal coupling between the breathing mode and the excited bending mode is one of the causes for the strain growth observed in containment vessels. In this study, we demonstrate that, due to the existence of structural perturbations, various vibration modes may be excited in containment vessels in earlier response stage before the occurrence of nonlinear modal coupling. The linear superposition of the breathing mode and the vibration modes excited by structural perturbations may cause larger response than the pure breathing mode response, which is a different strain growth mechanism from the nonlinear modal coupling. In the later response stage when the nonlinear modal coupling happens, not only the breathing mode, but also the vibration modes excited by structural perturbations will interact nonlinearly with the bending modes excited by dynamic unstable vibration. Dynamic nonlinear finite element program, LS-DYNA, is employed to understand the effects of structural perturbations on strain growth in containment vessels subjected to internal blast loading.

Effects of wall temperature on the heat and mass transfer in microchannels using the DSMC method

Micro-electro-mechanical systems (MEMS) and nano-electro-mechanical systems (NEMS) have become the research focuses which attract a great deal of attention in recent years. The fluidic and thermal behaviors are usually different from those of the macro devices. In this paper, the heat and mass transfer characteristics of the rarefied nitrogen gas flows in microchannels are investigated using DSMC method. In order to study the effects of the wall temperature (Tw) on the mass flux and wall heat flux in the microchannels, the temperature of the incoming gas flow (T∞) is set constant at 300 K, and the wall temperature varies from 200 K to 800 K. For all of the simulated cases, majority of wall heat flux stays within the channel entrance region and drops to nearly zero when it reaches the middle region of the channel. When Tw ≪ T∞, with the restriction of the pressure driven condition and continuity of pressure, the number density of the flow has to decrease along the flow direction eventually after a short increase at the entrance region. When Tw ≫ T∞, the number density of the flow drops rapidly near the inlet, and the temperature of the gas flow increases. As the Tw increases, the flow becomes more rarefied, the mass flux decreases, and the resistance at the entrance region increases. Furthermore, when Tw ≫ T∞, sudden jump in heat transfer flux and temperature are observed at the exit region of the channel.

Improving DSMC with New Pressure Boundary Conditions for Heat and Mass Transfer of Microchannel Flows

A new treatment of pressure boundary conditions for the DSMC method is proposed for flow prediction in microchannels. Validity and accuracy of the new method are verified by comparing to the analytical solutions of the micro-Poiseuille flow under slip condition. The new method shows better convergence compared with previous boundary treatments. This advantage becomes more remarkable as the geometry of the microchannel becomes more complex. A study on a microchannel with sudden expansion is demonstrated using the new DSMC method. Wall temperature in the expanded region of the microchannel independently varies from 200 to 800 K to study the effects on the pressure distribution, velocity, mass flow rate, and heat flux of the microchannel flow. The results show that the wall temperature in the expanded region significantly affects the microchannel flow. Some unique phenomena are observed to be quite different from those of the macroscopic flow and the mechanism of these interesting phenomena is discussed.

Safety Assessment of Cold Welding Defect in Electro-Fusion Joint of Polyethylene Pipe

Cold welding defect is the most common defect in electro-fusion (EF) joint for connecting polyethylene (PE) pipe. In our previous study [1], the cold welding defect is successfully inspected by an eigen-line method based on phased array ultrasonic testing technology. However, limited research has been reported on the acceptance criterion of cold welding defect in EF joint. In this paper, the bonding strength of EF joint is measured using a peeling test. The bonding energy of welding interface is calculated both by phenomenological model and deformation energy analysis method. EF joints with different degrees of cold welding are made and used for peeling tests. The results show that the bonding energy of fused interface rises rapidly after bonding and then goes through a plateau region. The starting point of the plateau region in the bonding energy versus welding time curve is regarded as the minimum required welding time of EF joint. Based on bilinear fitting, the acceptance criterion of cold welding defect is proposed.

Formation Mechanism of the Eigen-line in Electrofusion Joints of Polyethylene Pipes

Cold welding is the most dangerous defect in the electrofusion joint of polyethylene (PE) pipes. A proprietary method was developed to detect the degree of cold welding by using an Eigen-line, which was discovered in our previous study. To understand when, where, and how the Eigen-line would appear, the forming mechanism was investigated in this paper. Three factors, i.e., micro-air-bubbles, difference of acoustic impendence of PE in the melted and unmelted region, and small-crowded crystals in the region of the interface of melted and unmelted region, may cause the appearance of the Eigen-line. It was found that the number of Eigen-lines was the same as that of welding times when rewelded with decreasing welding time, and only one Eigen-line could be observed when rewelded with increasing welding time. The result showed that small-crowded crystals in the region of the interface of melted and unmelted region may be the dominating factor. This was then verified by the temperature analysis and differential DSC tests, and the forming process of the small-crowded crystals was discussed in detail.

Buckling Analysis of Plastic Pipe Reinforced by Cross-Winding Steel Wire Under Bending

A plastic pipe reinforced by cross helically wound steel wires (PSP) has been developed rapidly in China as a new type of metal-plastics composite pipes. To deeply understand the mechanical properties of PSPs under pure bending, a four-layer analytical model is proposed based on Donnel theory. Additionally, a 3D finite element model (FEM) of PSPs under bending using an eigenvalue method is present. Good agreement between the theoretical results and finite element results is obtained, which shows that the proposed FEM can predict the buckling moments of PSPs. Further, A FEM of the PSP under bending is preformed by using the geometrically nonlinear finite element analysis (FEA). The buckling load is found by searching a bifurcation point on the geometrically nonlinear deformation path and the corresponding buckling mode is obtained from the eigenvalue analysis. Finally, the influence of the pipe lengths, design parameters and initial flaws on the buckling moment is analyzed using nonlinear FEA.Copyright

A Method of Automatic Defect Recognition for Phased Array Ultrasonic Inspection of Polythene Electro-Fusion Joints

Defect classification is the basis of defect safety assessment because defects of different types can lead to failure in different forms. However, the identification of defect type has long been a critical issue in ultrasonic inspection. Wave acoustic was applied in this study to investigate the sound scattering of metal wires in polyethylene (PE), which provided theoretical support for ultrasonic feature extraction. A method of defect recognition for PE electro-fusion (EF) joints was proposed based on pattern recognition of ultrasonic inspection images. According to location, shape, signal intensity, and cluster conditions, typical defects of EF joints of PE pipes were distinguished and identified in phased array ultrasonic images. Furthermore, an automatic defect recognition software was designed based on the proposed approach; the software was improved and verified through defect inspection and identification experiments. Results showed that accuracy can reach 80% for joints with complex defects and 100% for those with single defects.Copyright