Blunden, BG & Indraratna, B 2000, 'Evaluation of surface and groundwater management strategies for drained sulfidic soil using numerical simulation models', Soil Research, vol. 38, no. 3, pp. 569-569.
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The effective management of acid sulfate soils is a major issue for manycoastal regions in Australia. Simulations were conducted to evaluate 4different water management strategies that could be applied to agriculturalland on the south coast of New South Wales, Australia, to minimise acidgeneration from acid sulfate soils. The water management strategies arecompared with the existing extensively drained situation which generates anddischarges large quantities of acidic pyrite oxidation products. The 4 watermanagement strategies include elevated drain water levels using a weir, 25 mmirrigation on a 7- or 14-day cycle, and elevated drain water levels withirrigation. All of these strategies were designed to minimise the generationof acid by reducing the transport of oxygen to the sulfidic soil. Simulationswere conducted for weather and site conditions experienced during a 12-monthperiod starting in July 1997.Model simulations showed that maintenance of elevated drain water levels usinga weir in the drain significantly reduced the amount of acid generated by75% and 57%, at 10 and 90 m distance from the drain,respectively, by comparison with the existing drained state. The addition of25 mm irrigation on a 14-day cycle to the weir simulation reduced theoxidation of pyrite by a further 1–2%. Application of irrigationonly on a 7-day cycle also reduced the acid generated by 89% and94% at 10 and 90 m distance from the drain, respectively, by comparisonwith the existing drained state. Irrigation on a 14-day cycle was not assuccessful in reducing pyrite oxidation as either the 7-day irrigation or weirstrategies. Evaluation of the 4 water management options showed thatsignificant improvements can be made with respect to the amount of acidgenerated by relatively simple and cost-effective land management practices.
Gadad, A 2000, 'Synthesis and antibacterial activity of some 5-guanylhydrazone/thiocyanato-6-arylimidazo[2,1-b]-1,3,4-thiadiazole-2-sulfonamide derivatives†', European Journal of Medicinal Chemistry, vol. 35, no. 9, pp. 853-857.
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Indraratna, B & Redana, IW 2000, 'Numerical modeling of vertical drains with smear and well resistance installed in soft clay', Canadian Geotechnical Journal, vol. 37, no. 1, pp. 132-145.
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Indraratna, B & Redana, IW 2000, 'Numerical modeling of vertical drains with smear and well resistance installed in soft clay', Canadian Geotechnical Journal, vol. 37, no. 1, pp. 132-145.
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This study describes the behavior of embankments stabilized with prefabricated vertical drains installed in soft clay foundations, based on several fully instrumented case histories selected from Thailand and Malaysia. A multidrain analysis is conducted based on an equivalent, plane strain model developed by the authors. The deformation of soft clay beneath an embankment (i.e., along and away from the centerline) is predicted and compared with the available field measurements. The effects of both smear and well resistance are incorporated in the analytical formulation, which is used in conjunction with the modified Cam-clay theory. It is demonstrated that the installation of vertical drains significantly increases the rate of settlement, improves the dissipation of pore-water pressure, and decreases the lateral deformation of the soft clay foundation. To obtain better predictions, especially of pore pressures and lateral displacements, the equivalent discharge capacity of the drains needs to be modeled appropriately. The inclusion of the effects of smear and well resistance in the analysis of vertical drains improves the accuracy of predictions significantly, in comparison with the field measurements.Key words: clay, consolidation, embankment, finite element method, settlement, smear zone, vertical drain.
Indraratna, B, Nemcik, JA & Gale, WJ 2000, 'Review and interpretation of primary floor failure mechanism at a longwall coal mining face based on numerical analysis', Géotechnique, vol. 50, no. 5, pp. 547-557.
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This paper describes the conceptual model of primary rock failure mechanisms in the floor ahead of the longwall coal mining face based on underground observations and numerical modelling. During longwall mining, the stress fields and displacements of strata are constantly changing. High stress concentrations ahead of the longwall face can initiate fractures in the rock floor that can, under unfavourable stress conditions, develop into secondary floor failure, where large displacements of strata can occur. Severely broken floor strata or floor heave can seriously interfere with mining operations. Underground observations indicate that the sub-vertical shear fractures and the shear failure along the bedding planes in stratified rock are the most common fracture types observed in the rock floor below the longwall face. To explain how these fractures occur, basic principles of rock failure mechanism are applied to an overstressed rock subject to stress concentrations typically found at the longwall face. The computational simulation of the progressive longwall mining operations was undertaken in stratified rock to model complex stress distributions ahead of the longwall face and to simulate the rock failure in the mining floor. The model indicates that the shear fractures and the bedding plane failure dominate the floor failure ahead of the moving longwall face, as was observed underground.
Ji, JC & Hansen, CH 2000, 'Non-linear response of a post-buckled beam subjected to a harmonic axial excitation', JOURNAL OF SOUND AND VIBRATION, vol. 237, no. 2, pp. 303-318.
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An experimental investigation of the non-linear response of a clamped-sliding postbuckled beam subjected to a harmonic axial load is presented. Two types of resonances are considered: fundamental and subharmonic. The data demonstrate several non-linear phenomena including period-doubling sequence bifurcation, period-three, and chaotic motion. In addition, the effect of damping on the dynamic instability of the post-buckled beam is investigated. The regions of instability and chaotic response are shown for different damping levels. The resulting locus of instability of the periodic solutions in the amplitude-frequency parameter space provides valuable information on the overall dynamic behavior of the system. The qualitative changes can be observed when either the frequency or the amplitude of excitation is varied across a bifurcation curve. The measured data are illustrated through time histories, phase plots, Fourier spectra, and Poincare sections.
Ji, JC & Yu, L 2000, 'Drop dynamics of a high-speed unbalanced rotor in active magnetic bearing machinery', MECHANICS OF STRUCTURES AND MACHINES, vol. 28, no. 2-3, pp. 185-200.
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The transient nonlinear dynamics of a high-speed unbalanced rigid rotor dropping onto rigid sliding bearings is investigated. The equations of motion are formulated and solved numerically to examine dynamics of the rotor for different regimes of the touchdown process. The contribution of parameters such as unbalance, air gap, coefficient of friction, and coefficient of restitution to drop dynamics of the rotor are examined. When the unbalance is small, the resulting motion is also small. As the level of unbalance increases, the motion of the rotor becomes larger, so there is potential for damage to the rotor and the backup bearings. The orbits of the rotor in the backup bearings after the rotor drops, velocities, and power loss during sliding-whirling stages are presented for various initial conditions and system parameters. Finally, based on simulation results, some design guidelines and suggestions are given.
Ji, JC, Yu, L & Leung, AYT 2000, 'Bifurcation behavior of a rotor supported by active magnetic bearings', JOURNAL OF SOUND AND VIBRATION, vol. 235, no. 1, pp. 133-151.
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The non-linear dynamics of a rigid rotor levitated by active magnetic bearings is investigated. The vibrations in the horizontal and vertical directions are analyzed on the center manifold near the double-zero degenerate point by using normal-form method. The resulting normal forms in the horizontal and vertical directions are different due to the effect of rotor weight. It is shown that the vibratory behavior in the vertical direction can be reduced on the center manifold to the Bogdanov-Takens form. For the autonomous case, there exist saddle-node bifurcation and Hopf bifurcation for local analysis, and a saddle-connection bifurcation for global analysis. For non-autonomous case, the Melnikov technique is used to determine the critical parameter at which the homoclinic orbits intersect transversally. For the vibrations in the horizontal direction, the essential non-linear terms of the truncated normal form are third order. The behaviors of zero solutions are given. Finally, numerical simulations are performed to verify the analytical predictions.
Khalili, N, Khabbaz, MH & Valliappan, S 2000, 'An effective stress based numerical model for hydro-mechanical analysis in unsaturated porous media', Computational Mechanics, vol. 26, no. 2, pp. 174-184.
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Nemcik, JA 2000, 'Floor failure analysis at a longwall mining face based on the multiple sliding block model', Geotechnical and Geological Engineering, vol. 18, no. 3, pp. 175-192.
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This paper presents an analytical model of a floor failure at a longwall coal mining face based on the multiple sliding block model. During longwall mining, stresses and displacements of strata are constantly changing. High stress concentrations at the coal face can exceed the rock strength and initiate fractures in the strata that can, under unfavourable conditions, lead to large floor displacements and disruption of mining operations. Underground observations of the rock floor and the computational modelling of the longwall face indicate that two types of fracture dominate floor failure. Extensive lateral fracturing often develops along the numerous weak bedding planes that are typically present in the sedimentary strata while sub-vertical fractures form in response to changing stress abutments ahead of the longwall coal face. The fractures that initially develop ahead of the longwall face are subject to a "secondary" movement when exposed ahead of the longwall supports. In response to the stress relief as the coal is mined from above. Strata move towards the opening and bending of the floor occurs. If fractures in the floor exist, the floor blocks will displace in response to the floor movement and interact at the fractured surfaces. This analysis attempts to explain how the stress distribution develops within the broken floor during an active movement of floor strata leading to high stress concentrations at the floor level. The analytical formulation in this paper is supplemented by numerical modelling, and results are presented to verify that the analytical solutions are in accordance with the numerical predictions.
Pradhan, B & Kumar, S 2000, 'Finite Element Analysis of Low-Velocity Impact Damage in Composite Laminates', Journal of Reinforced Plastics and Composites, vol. 19, no. 4, pp. 322-339.
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This paper investigates the low-velocity impact behaviour and impact-induced damages in graphite/epoxy composite laminates. A three-dimensional finite element and transient dynamic analysis is performed to calculate the time-varying displacements, forces, strains and stresses throughout the laminate resulting from transverse impact. A layered version of an eight-noded isoparametric brick element with incompatible modes is used to model the laminate. Transient dynamic equilibrium equation is integrated step-by-step with respect to time using Newmark direct time integration method. Modified Hertzian contact law is used to model the local contact behaviour. Appropriate three-dimensional failure criteria are used for predicting the occurrence of matrix cracking and the extent of delamination after impact.
PRADHAN, B & KUMAR, S 2000, 'Finite Element Analysis of Low-Velocity Impact Damage in Composite Laminates', Journal of Reinforced Plastics and Composites, vol. 19, no. 4, pp. 322-339.
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Sheng, D & Smith, DW 2000, 'Numerical modelling of competitive components transport with non-linear adsorption', International Journal for Numerical and Analytical Methods in Geomechanics, vol. 24, no. 1, pp. 47-71.
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Sheng, D, Sloan, SW & Yu, HS 2000, 'Aspects of finite element implementation of critical state models', Computational Mechanics, vol. 26, no. 2, pp. 185-196.
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Sloan, SW, Sheng, D & Abbo, AJ 2000, 'Accelerated initial stiffness schemes for elastoplasticity', International Journal for Numerical and Analytical Methods in Geomechanics, vol. 24, no. 6, pp. 579-599.
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Zhang, XP, Wang, CH, Li, JC, Mai, YW & Ye, L 2000, 'A Combined Model of Short Crack Closure Accounting for Both Plasticity and Roughness Induced Crack Closures', Key Engineering Materials, vol. 183-187, pp. 217-222.
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Zhang, XP, Wang, CH, Li, JC, Mai, YW & Ye, L 2000, 'Combined model of short crack closure accounting for both plasticity and roughness induced crack closures', Key Engineering Materials, vol. 183.
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A new model combining both plasticity-induced and surface roughness-induced crack closures is proposed to describe short fatigue crack growth. The numerical results obtained using this model agree well with the analytical predictions of Budiansky-Hutchinson and are reasonably close to the experimental data.
