Description:
Real-time solution of the Discrete Element Method is a computational challenge that is hardly achievable on standard PCs, especially when a large number of triangular shaped particles are involved. This paper presents a scalable architecture, including a domain decomposition technique, of a GPU accelerator for the two-dimensional Discrete Element Method for triangular shaped particles. This approach achieved a speed up of about 140 times as a single core and about 80 after domain decomposition on a consumer level GPU compared to a similar algorithm run on a fast desktop PC.
Description:
It is not uncommon for conventional ballasted railway track systems to have unsupported sleepers due the uneven settlement of the ballast or subgrade. In order to investigate the possible implications of unsupported sleepers, this paper describes the development of a dynamic finite element model which includes wheel/rail friction. The developed model was used to investigate the behavior of a section of existing track on the ballasted Shuohuang heavy haul railway line in China. The investigation showed that the maximum displacement of the rails and sleepers increases significantly with the number of consecutive unsupported sleepers. Furthermore, the magnitude of the displacement between an unsupported sleeper and the ballast is likely to greatly exacerbate ballast/sleeper attrition and reduce the fatigue life of the hanging sleeper. An increase in the number of unsupported sleepers amplifies these effects. In addition, it was found that the sleepers adjacent to unsupported ones carry an additional load resulting potentially in their increased wear and additional damage to the substructure. To better understand the wider implications of the presence of unsupported sleepers on track performance, the stability, safety (in terms of derailment) and potential for rail and substructure damage were computed as a function of the number of unsupported sleepers (one to four) and compared with specifications. The results showed that the number of unsupported sleepers has a significant adverse impact on all four measures. However, while the effects on stability, safety and rail damage were within the limits suggested in specifications, even when four sleepers were modeled, the potential for substructure failure within a typical design life of the railway system was identified.
Description:
In this study, based on the dynamic Biot’s theory “u-p” approximation, a 3D finite element method (FEM) numerical soil model is developed, in which the Generalized Newmark-method is adopted to determine the time integration. The developed 3D FEM soil model is a part of the coupled model PORO-WSSI 3D for 3D wave-seabed-marine structures interaction problem, and is validated by the analytical solution proposed by Wang (2000) for a laterally infinite seabed loaded by a uniform force. By adopting the developed 3D soil model, the consolidation of seabed under a caisson breakwater and hydrostatic pressure is investigated. The numerical results show that the caisson breakwater built on seabed has very significant effect on the stresses/displacements fields in the seabed foundation after the transient deformation and primary consolidation are completed. The parametric study indicates that the Young’s modulus E of seabed is the most important parameter to affect the settlement of breakwater, and the displacement fields in seabed foundation. Taking the consolidation status as the initial condition, the interaction between ocean wave, caisson breakwater and seabed foundation is briefly investigated. The 3D ocean wave is determined by solving the Navier-Stokes equations with finite volume method (FVM). The numerical results indicate that there is intensive interaction between ocean wave, caisson breakwater and seabed foundation; and the breakwater indeed can effectively block the wave energy propagating to the coastline.
Description:
This paper investigates the seismic response of lightweight acceleration-sensitive non-structural components (NSCs) mounted on irregular reinforced concrete (RC) primary structures (P-structures) using non-linear dynamic finite element (FE) analysis. The aim of this paper is to study the influence of NSC to P-structure vibration period ratio, peak ground acceleration, NSC to P-structure height ratio, and P-structure torsional behaviour on the seismic response of the NSCs. Representative constitutive models were used to simulate the behaviour of the RC P-structures. The NSCs were modelled as vertical cantilevers fixed at their bases with masses on the free ends and varying lengths so as to match the frequencies of the P-structures. Full dynamic interaction is considered between the NSCs and P-structures. A set of 21 natural and artificial earthquake records were used to evaluate the seismic response of the NSCs. The numerical results indicate that the behaviour of the NSCs is significantly influenced by the investigated parameters. Comparison between the FE results and Eurocode (EC8) predictions suggests that EC8 underestimates the response of NSCs mounted on the flexible sides of irregular RC P-structures when the fundamental periods and heights of the NSCs match those of the P-structures. The perceived cause of this discrepancy is that EC8 does not take into account the amplification in the dynamic response of NSCs induced by the torsional behaviour of RC P-structures.
Description:
Cold-formed steel (CFS) sections are commonly used in modern roof construction. Most purlin members are of thin-walled open cross section. They are usually subjected to roof loading at the top flange in either an upward or a downward direction. The load application points, where the sheeting/purlin connections are located, are often eccentric to the shear centre, and thus inevitably generate a torsional moment that will induce twisting and/or warping deformations in addition to bending deflection. This type of complexity associated with the loading conditions will be exacerbated by the occurrence of single- or mixed-mode buckling (e.g. overall, distortional and local buckling) due to compression flanges tending to move sideways. The connections between purlin and roof sheeting provide a restraining effect on purlin members by preventing such lateral and twisting movements, and thus have a beneficial effect on their load-carrying capacity. In design practice, this effect should be taken into account from a design-efficiency perspective. To this end, a key step is to quantify the rotational restraint stiffness by using an engineering-orientated model. This paper firstly reports a series of torsional restraint tests (F-tests) for both sigma and zed sections. Two loading directions were examined by adjusting the purlin fixing direction. The rotational angles between the connected flange and sheeting were recorded at each loading step, from which the moment–rotation curves were produced and presented for each test case. A linear relationship has been observed for the moment–rotation relationship from all test specimens. Secondly, a hand calculation model for calculating the rotational stiffness at each connection was developed. In that model, the rotation was deemed to be primarily caused by the localised deformation of the roof sheeting and the distortional deformation of the purlin flange. The rotation caused by the separation of connection was found to be negligible. The model was validated by the experimental test results and an example was presented to demonstrate the application of the model proposed. The rotational stiffness calculated by this model can be used to evaluate the input parameters required for numerical modelling of purlin–sheeting interaction.
Description:
In the practice of engineering, breaking wave is much more dangerous for the stability of composite breakwater built on porous seabed than non-breaking wave in offshore area. In previous investigations or design codes, the empirical formulations generally were adopted to estimate the wave impact acting on the lateral side of caisson. The interaction between breaking wave, seabed foundation and composite breakwater is not taken into consideration. In this study, adopting the integrated numerical model PORO-WSSI 2D developed by (Ye, 2012a) and (Jeng et al., 2013), the interaction mechanism between breaking wave, seabed foundation and composite breakwater is investigated numerically. In PORO-WSSI 2D,the Volume-Averaged Reynolds Averaged Navier–Stokes (VARANS) equations govern the wave motion and the porous flow in seabed foundation and in rubble mound; and the dynamic Biot's equations (known as “u-p” approximation) govern the dynamic behaviors of seabed foundation and composite breakwater under breaking wave loading. Numerical analysis indicates that the turbulent energy of breaking wave is significant, and the wave impact on caisson applied by breaking wave is much greater than non-breaking wave. The composite breakwater and its seabed foundation respond to the breaking wave loading intensively. The maximum horizontal vibration magnitude of the composite breakwater is up to 5 mm; the maximum liquefaction depth in the seabed in front of the composite breakwater reaches up to 1.2 to 1.6 m. The parametric study shows that the permeability and saturation of seabed, wave height are three dominant factors for the wave-induced liquefaction in seabed foundatio
Description:
The WHO classification subdivides large granular lymphocytic leukemias (LGLLs) into two subtypes, T and natural killer (NK) LGLLs, with distinct immunophenotypes and clinical presentations.1 Although arising from a common progenitor cell, NK cells are bone marrow–derived innate immune cells capable of cytokine production and cytotoxicity, and T cells are thymic-derived, antigen-specific lymphocytes that express a T-cell receptor (TCR).2 Natural killer T (NKT) cells, a subset of T cells, express NK-associated antigens such as CD16, CD56, and CD57, in addition to a CD1d-restricted, semi-invariant TCR.3 The point at which NKT cells branch from other TCR rearranged cells is not clearly defined. However, this is believed to be mediated through CD1d thymic-dependant signaling in CD4 CD8 double-positive thymocyte precursors.4,5 NK LGLL has a CD3−, CD8+, CD16+, CD56+ phenotype, with variable expression of CD57. It presents in teenagers and young adults with “B” symptoms, lymphadenopathy, hepatosplenomegaly, lymphocytosis, anemia, and thrombocytopenia and typically follows an aggressive clinical course.6 T-cell LGLLs are CD3+, CD8+, CD16+ with a clonal TCR rearrangement and defective Fas (CD95) -mediated apoptosis.7,8 Median age of onset is 55 years, presenting with splenomegaly, neutropenia, and recurrent infections. It is associated with rheumatoid arthritis and follows an indolent and protracted clinical course.9 We describe the case of a teenage patient with T-cell LGLL, who despite having a CD56 immunophenotype, initially showed an aggressive clinical course more in keeping with an NKT leukemia. We discuss the reasoning behind his conservative management and the observed changes in lymphocyte count and serum cytokine/chemokine levels over an 18-month period. There have been no reported cases of an initially aggressive presentation with subsequent spontaneous regression.
Description:
This paper presents a numerical study of soil fluidisation induced by local leakage from a buried pipe using the coupled discrete element and lattice Boltzmann approach (DEM–LBM). The behaviour of the system is studied using different flow rates and initial bed heights. The excess pore pressure distribution and the soil behaviour due to a localised leak are investigated and compared with previous experimental findings. The comparison indicates that DEM–LBM is capable of capturing the leakage–soil interaction at the particle scale. Moreover, as the flow distribution is found to be one-dimensional in the radial direction rather than one-dimensional in the vertical direction, an extension to the Ergun flow equation is derived and the numerically measured fluidising pressure shows good agreement with this analytical solution. In addition, as indicated by the numerical results and the derived analytical solution, the relationship between fluidising pressure and pipe buried depth as well as leak size is also established. The simulation results suggest that DEM–LBM is a promising tool to carry out further studies into the internal fluidisation phenomenon.
Description:
Chinese Railways is seeking to increase the capacity of many of its heavy haul railway lines by increasing their utilization and at the same time increasing axle loads from 250 to 300 kN. These projected increases in railway traffic may result in accelerated deterioration of the railway network. A vulnerable part of the network, are bridge–embankment transition zones which frequently experience high degradation rates. To investigate the possible implications of the forecasted increases in railway traffic on these structure, a study was carried out which consisted of instrumenting a transition zone to measure accelerations under existing loads and building a three-dimensional finite element dynamic model of the bridge–embankment transition to predict the effects of the anticipated future traffic. The results of the study indicated that commonly used measures of stability, safety and substructure damage would remain within specified limits, despite the projected increases in axle load. However, excessive wear of the wheel and or rail may occur.
Description:
This paper investigates the structural behavior of uncorroded as well as corroded RC T-beams strengthened in shear with either externally bonded (EB) carbon fiber-reinforced polymer (CFRP) sheets or embedded CFRP rods. Nine tests were carried out on RC T-beams having an effective depth of 295 mm and a shear span to effective depth ratio of 3.05. The investigated parameters are the shear link corrosion level (uncorroded, 7% corroded, or 12% corroded) and type of CFRP strengthening system (EB CFRP sheets or embedded CFRP rods). The unstrengthened beams with shear link corrosion levels of 7 and 12% had shear strengths that were 11 and 14%, respectively, less than the shear strength of the uncorroded unstrengthened beam. Both the embedded CFRP rods and EB CFRP sheets were effective in enhancing the shear strength of tested beams but the effectiveness of both strengthening systems decreased with increasing shear link corrosion level. The shear strength enhancement provided by the embedded CFRP rods and EB CFRP sheets decreased from 19 and 15%, respectively, to 12 and 11%, respectively, with an increase in shear link corrosion level from 7 to 12%. Corrosion of the shear links did not have a significant effect on the beam stiffness. Premature debonding limited the effectiveness of the EB CFRP sheets whereas the embedded CFRP rods did not exhibit signs of debonding and therefore showed higher effectiveness.
Description:
This paper investigates the structural behavior of uncorroded as well as corroded RC T-beams strengthened in shear with either externally bonded (EB) carbon fiber-reinforced polymer (CFRP) sheets or embedded CFRP rods. Nine tests were carried out on RC T-beams having an effective depth of 295 mm and a shear span to effective depth ratio of 3.05. The investigated parameters are the shear link corrosion level (uncorroded, 7% corroded, or 12% corroded) and type of CFRP strengthening system (EB CFRP sheets or embedded CFRP rods). The unstrengthened beams with shear link corrosion levels of 7 and 12% had shear strengths that were 11 and 14%, respectively, less than the shear strength of the uncorroded unstrengthened beam. Both the embedded CFRP rods and EB CFRP sheets were effective in enhancing the shear strength of tested beams but the effectiveness of both strengthening systems decreased with increasing shear link corrosion level. The shear strength enhancement provided by the embedded CFRP rods and EB CFRP sheets decreased from 19 and 15%, respectively, to 12 and 11%, respectively, with an increase in shear link corrosion level from 7 to 12%. Corrosion of the shear links did not have a significant effect on the beam stiffness. Premature debonding limited the effectiveness of the EB CFRP sheets whereas the embedded CFRP rods did not exhibit signs of debonding and therefore showed higher effectiveness.