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The smoothed particle hydrodynamics (SPH) method is extended and tested for the numerical simulation of transient viscoelastic free surface flows. The basic equations governing the free surface flow of an Oldroyd-B fluid are considered and approximated by SPH. In particular, a drop of an Oldroyd-B fluid impacting a rigid plate is simulated. Results for a Newtonian fluid are also presented for comparison. It is found that the original SPH method, which has been successfully applied to the simulation of transient viscoelastic flows in bounded domains (such as the start-up flow between parallel plates), is unable to simulate the viscoelastic free surface flow considered here because of the so-called tensile instability. This instability leads to unrealistic fracture and particle clustering in fluid stretching and may eventually result in complete blowup of the simulation. Recent works have shown that in simulations of elastic solids the tensile instability can be removed by an artificial stress. Here we show that the same idea also works for viscoelastic fluids provided that the constant parameter entering in the definition of the artificial stress is properly chosen. Numerical results obtained are in good agreement with those simulated by a finite difference technique.

In this paper we present two enhanced variants of the smoothed particle hydrodynamics (SPH) method for the numerical simulation of free surface flows of viscous fluids. Improvements are achieved by deriving a new set of general discrete SPH-like equations under an energy-based framework and applying a corrected (high-order) or coupled particle approximation scheme for function derivatives. By doing so, we ensure that the enhanced variants retain the conservative nature of SPH which is important for the stability of long-term simulations. Among various corrected approximations, we here implement the one obtained by the so-called finite particle method (FPM) within the framework to produce a higher-order SPH method which conserves both linear and angular momentums. In order to improve the efficiency of the higher-order variant, a coupled approach with the idea of using the SPH approximation for the interior particles and the FPM approximation for the exterior particles is also proposed and tested in this paper. Three prototype tests concerning free deformation of a viscous fluid patch with free surface are presented with comparisons between different methods to demonstrate the performance of the two proposed methods. Numerical results show that both the higher-order version using FPM and the coupled version using FPM/SPH outperform the original version of SPH in respect of accuracy and stability.

Elevated in-stream temperature has led to a surge in the occurrence of parasitic intrusion proliferative kidney disease and has resulted in fish kills throughout Switzerland's waterways. Data from distributed temperature sensing (DTS) in-stream measurements for three cloud-free days in August 2007 over a 1260 m stretch of the Boiron de Morges River in southwest Switzerland were used to calibrate and validate a physically based one-dimensional stream temperature model. Stream temperature response to three distinct riparian conditions were then modeled: open, in-stream reeds, and forest cover. Simulation predicted a mean peak stream temperature increase of 0.7°C if current vegetation was removed, an increase of 0.1°C if dense reeds covered the entire stream reach, and a decrease of 1.2°C if a mature riparian forest covered the entire reach. Understanding that full vegetation canopy cover is the optimal riparian management option for limiting stream temperature, in-stream reeds, which require no riparian setaside and grow very quickly, appear to provide substantial thermal control, potentially useful for land-use management.

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Thanks to a sophisticated transient hydrogeological modelling allowing the determination of the pore pressure fields in La Frasse landslide mass during a crisis, it has been possible to model the mechanical behaviour of the slide and obtain results that prove to be similar to the monitored data, in terms of peak velocity, distribution of velocity with time and space and total displacements. Such results are reached only when appropriate constitutive modelling laws are used, and when geotechnical tests supply all the required parameters. The main results concern the potential effect of a drainage system during a crisis, like the one experienced in 1994. It can include vertical boreholes equipped with pumps or drains drilled from a gallery. The draining system reduces horizontal displacements down to 5% of the values modelled during the crisis. This effect, which appears to extend over a large width, will be even more significant if the boreholes discharge the drained water into the gallery, due to its extension in the presently stabilised landslide mass below the active zone. The modelling tools developed for La Frasse landslide thus provide all the necessary information to optimise the drainage scheme.

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