Frictional contact algorithms in SPH for the simulation of soil–structure interaction

Simulation of frictional contact between soils and rigid or deformable structure in the framework of smoothed particle hydrodynamics (SPH) is presented in this study. Two algorithms are implemented into the SPH code to describe contact behavior, where the contact forces are calculated using the law of conservation of momentum based on ideal plastic collision or using the criteria of partial penetrating. In both algorithms, the problem of boundary deficiency inherited from SPH is properly handled so that the particles located at contact boundary can have precise acceleration, which is critical for contact detection. And the movement and rotation of the rigid structure are taken into account so that it is easy to simulate the process of pile driving or movement of a retaining wall in geotechnical engineering analysis. Furthermore, the capability of modeling deformability of a structure during frictional contact simulations broadens the fields of SPH application. In contrast to previous work dealing with contact in SPH, which usually use particle‐to‐particle contact or ignoring sliding between particles and solid structure, the method proposed here is more efficient and accurate, and it is suitable to simulate interaction between soft materials and rigid or deformable structures, which are very common in geotechnical engineering. A number of numerical tests are carried out to verify the accuracy and stability of the proposed algorithms, and their results are compared with analytical solutions or results from finite element method analysis. Good agreement obtained from these comparisons suggests that the proposed algorithms are robust and can be applied to extend the capability of SPH in solving geotechnical problems. Copyright © 2013 John Wiley & Sons, Ltd.     

Viscoelastic functionally graded finite element method with recursive time integration and applications to flexible pavements

The finite‐element (FE) method is used for modeling geotechnical and pavement structures exhibiting significant non‐homogeneity. Property gradients generated due to non‐homogeneous distributions of moisture is one such example for geotechnical materials. Aging and temperature‐induced property gradients are common sources of non‐homogeneity for asphalt pavements. Investigation of time‐dependent behavior combined with functionally graded property gradation can be accomplished by means of the non‐homogeneous viscoelastic analysis procedure. This paper describes the development of a generalized isoparametric FE formulation to capture property gradients within elements, and a recursive formulation for solution of hereditary integral equations. The formulation is verified by comparison with analytical and numerical solutions. Two application examples are presented: the first describes stationary crack‐tip fields for viscoelastic functionally graded materials, and the second example demonstrates the application of the proposed procedures for efficient and accurate simulations of interfaces between layers of flexible pavement. Copyright © 2011 John Wiley & Sons, Ltd.     

Evaluation of physical, chemical and microbiological parameters of water quality in the Harris Neck estuarine marshes along the Georgia coast

Analysis of the physical, chemical and biological parameters assessing water quality in Harris Neck estuary indicated that the average dissolved oxygen level was 8.6 mg/L, it maintained moderate levels of total dissolved nitrogen (2.7-4.6 mg/L) and total dissolved phosphorous (<0.05 mg/L), chlorophyll a was above 5.0 μg/L and it is contaminated with low levels of fecal bacteria. Bifidobacterium adolescentis, a putative marker of human fecal pollution, was detected once at stations 3 and 5. Overall the Harris Neck water quality analyses indicated a relatively pristine and a healthy functioning marine environment.     

Impact of rainstorm-triggered landslides on high turbidity in a mountain reservoir

Typhoon-triggered landslides deliver huge amounts of sediment to the upstream channel of the Shihmen Reservoir in northern Taiwan. Observation data regarding landsliding, sediment discharge and water turbidity following five major typhoon events from 1985 to 2006 demonstrated that each time water turbidity in the reservoir area rapidly increased up to ten-fold from the river catchment drainage, and the weight of landslide debris exceeded total sediment discharge five-fold. The fact that huge amounts of landslide debris still remained on upstream slopes and water turbidity suddenly increased in the reservoir area but not in upstream channel implied that the increasing water turbidity in the Shihmen Reservoir was indirectly related to the large landslides occurring in the upstream catchment. The main cause of high turbidity in the reservoir area was that, during a typhoon event, high water discharge flowing into the reservoir scoured the fine fraction sediment at the bottom of the reservoir and formed hyperpycanl flow with high turbidity, which then ascended to contaminate the reservoir surface water.     

Location Intelligence: An Innovative Approach to Business Location Decision‐making

As one of the leading ‘world cities’, London is particularly reliant on sources of foreign direct investment (FDI). In the face of increasing global competition and a difficult economic climate, the capital must compete effectively to encourage and support such investors. Through a collaborative study with London's official FDI promotion agency, Think London, the need for a coherent framework for data, methodologies and tools to inform business location decision‐making became apparent. This article discusses the development of a rich environment to explore, compare and rank London's business neighbourhoods. This is achieved through the development and evaluation of a model for location‐based decision support. First, we discuss the development of a geo‐business classification for London which draws upon methods and practices common in geodemographic neighbourhood classification. A geo‐business classification is developed, encapsulating relevant location variables using Principal Components Analysis into a set of composite area profiles. Second, we discuss the implementation of an appropriate Multi‐Criteria Decision Making methodology, in this case Analytical Hierarchy Process (AHP), enabling the aggregation of the geo‐business classification and decision‐makers' preferences into discrete decision alternatives. Finally, we present the results of the integration of both data and model through the development and evaluation of a web‐based prototype.     

The SOLAS air-sea gas exchange experiment (SAGE) 2004

The SOLAS air-sea gas exchange experiment (SAGE) was a multiple-objective study investigating gas-transfer processes and the influence of iron fertilisation on biologically driven gas exchange in high-nitrate low-silicic acid low-chlorophyll (HNLSiLC) Sub-Antarctic waters characteristic of the expansive subpolar zone of the southern oceans. This paper provides a general introduction and summary of the main experimental findings. The release site was selected from a pre-voyage desktop study of environmental parameters to be in the south-west Bounty Trough (46.5°S 172.5°E) to the south-east of New Zealand and the experiment was conducted between mid-March and mid-April 2004. In common with other mesoscale iron addition experiments (FeAX’s), SAGE was designed as a Lagrangian study, quantifying key biological and physical drivers influencing the air-sea gas exchange processes of CO₂, DMS and other biogenic gases associated with an iron-induced phytoplankton bloom. A dual tracer SF₆/³He release enabled quantification of both the lateral evolution of a labelled volume (patch) of ocean and the air-sea tracer exchange at tenths of kilometer scale, in conjunction with the iron fertilisation. Estimates from the dual-tracer experiment found a quadratic dependency of the gas exchange coefficient on windspeed that is widely applicable and describe air-sea gas exchange in strong wind regimes. Within the patch, local and micrometeorological gas exchange process studies (100 m scale) and physical variables such as near-surface turbulence, temperature microstructure at the interface, wave properties and windspeed were quantified to further assist the development of gas exchange models for high-wind environments.There was a significant increase in the photosynthetic competence (F_v/F_m) of resident phytoplankton within the first day following iron addition, but in contrast to other FeAX’s, rates of net primary production and column-integrated chlorophyll a concentrations had only doubled relative to the unfertilised surrounding waters by the end of the experiment. After 15 days and four iron additions totalling 1.1 ton Fe²⁺, this was a very modest response compared to other mesoscale iron enrichment experiments. An investigation of the factors limiting bloom development considered co-limitation by light and other nutrients, the phytoplankton seed-stock and grazing regulation. Whilst incident light levels and the initial Si:N ratio were the lowest recorded in all FeAXs to date, there was only a small seed-stock of diatoms (less than 1% of biomass) and the main response to iron addition was by the picophytoplankton. A high rate of dilution of the fertilised patch relative to phytoplankton growth rate, the greater than expected depth of the surface mixed layer and microzooplankton grazing were all considered as factors that prevented significant biomass accumulation. In line with the limited response, the enhanced biological draw-down of pCO₂ was small and masked by a general increase in pCO₂ due to mixing with higher pCO₂ waters. The DMS precursor DMSP was kept in check through grazing activity and in contrast to most FeAX’s dissolved dimethylsulfide (DMS) concentration declined through the experiment. SAGE is an important low-end member in the range of responses to iron addition in FeAX’s. In the context of iron fertilisation as a geoengineering tool for atmospheric CO₂ removal, SAGE has clearly demonstrated that a significant proportion of the low iron ocean may not produce a phytoplankton bloom in response to iron addition.     

River drainage reorientation during placer gold accumulation, southern New Zealand

Many alluvial placer deposits around the world occur in river systems that have been affected by tectonic events, causing drainage reorientation and severance of links between placers and their sources. This study documents tectonic rejuvenation of topography in the Otago giant placer goldfield, New Zealand, which has resulted in numerous river capture and drainage reorientation events. These events have induced changes to gold transport directions and numerous stages of separation of detrital gold from primary sources. Goldfield-wide reconstructions of drainage patterns through time are as yet only possible for Miocene–Recent, and numerous earlier drainage changes back to Cretaceous primary orogenic mineralisation are probable. Variations in basement lithologies permit auriferous gravel provenance determinations, facilitating paleodrainage pattern reconstruction and documentation of river capture events. River capture events and timing of these events for gold-bearing paleodrainages have also been documented using genetic divergences of populations of freshwater galaxiid fish that were isolated by drainage reorientation. Gold-bearing quartz pebble conglomerates had a southeastward drainage in the Miocene. This was disrupted in the Pliocene by mountain range uplift and gold placer recycling, with deposition of lithic conglomerates containing only minor gold placers. The most dramatic changes in gold transport directions occurred through the Quaternary, as antiformal ranges grew across the pre-existing drainages. Miocene and Pliocene placers were recycled with numerous local (1–10 km scale) changes in river directions and numerous capture events. Large axial rivers were segmented into a more complex drainage pattern, and on-going river capture resulted in growth of the main Clutha River catchment at the expense of neighbouring catchments. The most productive placers developed in the Clutha River in late Quaternary when increased discharge from captured mountain catchments enhanced gold transport and concentration. Similar river drainage reorientation has occurred in other placer fields around the world, but the lack of preserved evidence inhibits documentation of most such changes.     

Observations of Hipparcos short-period red giant stars

Optical UBV(RI) _C and infrared JHK photometry is presented of a small sample of giant stars with short periods in the Hipparcos catalogue. Observations were limited, but were sufficient to rule out most of the Hipparcos periods. Radial velocity measurement were also made for a few stars, over six successive nights. Low-level variability was detected in a few stars. It is argued that in most cases the brightness variations are primarily due to temperature changes. These findings show that high-overtone pulsations in M giant stars occur, if at all, in a far more limited number of stars than proposed in the authors' previous discussion of the Hipparcos data alone.