Stress and Fracture Strength Analysis for Three-Way Pipes

Three-way pipes, T and Y pipes, are very important connecting components in pipeline systems, their strength are related to the safety of pipelines. In the case that crack is not detected in the three-way pipe, ANSYS finite element program version 5.6 is applied to study the stress distribution of the three-way pipe and to obtain the optimum fillet radius in the crotch region of the two pipes. The reasonable intersection angle of the two pipes is also obtained. In the case that a surface crack is detected in the three-way pipe, the maximum stress intensity factor (SIF) near the front of the surface crack is studied.

AN EIGENVALUE METHOD ON GROUP DECISION

In this paper. a new group decision eigenvalue method abbreviated as GEM isproposed. It overcomes the non-consistence of judgement matrix and will open up anew route for the selection of experts in the decision system.

Analysis of dynamic features in intersecting pedestrian flows

This paper focuses on the simulation analysis of stripe formation and dynamic features of intersecting pedestrian flows.The intersecting flows consist of two streams of pedestrians and each pedestrian stream has a desired walking direction.The model adopted in the simulations is the social force model, which can reproduce the self-organization phenomena successfully. Three scenarios of different cross angles are established. The simulations confirm the empirical observations that there is a stripe formation when two streams of pedestrians intersect and the direction of the stripes is perpendicular to the sum of the directional vectors of the two streams. It can be concluded from the numerical simulation results that smaller cross angle results in higher mean speed and lower level of speed fluctuation. Moreover, the detailed pictures of pedestrians＇ moving behavior at intersections are given as well.

Numerical simulation of effect of various parameters on atomization in an annular slit atomizer

As the width-thickness ratio of the discrete nozzle atomizer’s discrete hole greatly influences the loss of atomizing gas flow rate,the discrete nozzle atomizer was transformed into an annular slit atomizer with the same total nozzle outlet area.A numerical simulation study on the effect of various parameters on the atomization in the annular slit atomizer was carried out by coupling both the large eddy simulation(LES)and volume of fluid(VOF)model,which is based on the applicability of LES in capturing the breakup behavior of transient liquid droplets and the advantage of VOF method in directly capturing the phase interface.The simulation results showed that the increase in the atomization pressure makes the gas gain higher momentum,while the increase in the nozzle intersection angle decreases the distance between the nozzle exit and the computational domain axis.The increase in these two variables results in enhancing the gas-liquid interaction in the primary atomization zone and the formation of more aluminum droplets simultaneously.It is considered that the atomization effect becomes better when atomization pressure is 2.5 MPa,and the nozzle intersection angle is 60°.Industrial tests showed that the aluminum powder prepared by the optimized annular slit atomizer has a finer mean particle size and a higher yield of fine powder.The numerical simulation results agree well with the industrial test data of the powder particle size.

Centrifuge modeling of tunneling-induced ground surface settlement in sand

Stress changes in the soil induced by tunnel excavation may cause excessive ground settlement.However,high-quality experimental data on ground settlement due to tunnel excavation are limited.In this study,centrifuge tests are conducted to investigate the threedimensional ground surface settlement,considering different intersection angles and cover-to-tunnel diameter ratios.The results indicate that the major influence zone along the longitudinal direction on the ground surface settlement is±1.25D,where D is the tunnel diameter.When the monitoring section is perpendicular to the tunneling direction,the transverse ground settlement due to the tunnel excavation is symmetrical with respect to the tunnel centerline.In contrast,an asymmetric ground settlement profile is observed when the monitoring section intersects the tunneling direction at an angle of 60.Applying a Gaussian curve to fit the ground surface settlement curve,the width parameter,K(i.e.,the distance between the tunnel centerline and the inflection point of the settlement trough to the tunnel burial depth),varies from 0.33 to 0.39.The ground surface settlement induced by twin tunnel excavation can be captured reasonably by superimposing two identical Gaussian curves.When the cover to tunnel diameter ratios(C/D)are 1.5 and 2.7,the maximum ground surface settlements are 0.67%of D and 0.35%of D,respectively.It is clear that the maximum ground surface settlement decreases with an increase in the C/D ratio.