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This paper makes a contribution to the field of positive displacement piston machines by presenting an approach that models the piston/cylinder interface, taking into account thermal effects and surface asperity contact. The pressure distribution in the interface is evaluated using the universal mixed thermal Reynolds equation, while the temperature distribution is determined using a simplified formulation of the conservation of energy. The rigid body motion and elasto-hydrodynamic effects of the piston and block bodies are described by Newton's second law and an influence matrix method, respectively. A coupled formulation for the heat transfer problem is used to describe the temperature distribution in the piston and block bodies. The effect of heat dissipation due to asperity contact is considered by incorporating an experimentally determined asperity friction coefficient. The proposed modeling approach is then validated by comparing it with experimentally measured temperature distribution in the block, and the error between the simulation and experiments is found to be less than 6%. The paper emphasizes the importance of considering thermal effects in such an interface and highlights the potential applications of the model. [ABSTRACT FROM AUTHOR]

The study of the interaction of mud-flows with obstacles is important to define inundation zones in urban areas and to design the possible structural countermeasures. The paper numerically investigates the impact of a mud-flow on rigid obstacles to evaluate the force acting on them using two different depth-integrated theoretical models, Single-Phase Model (SPM) and Two-Phase Model (TPM), to compare their performance and limits. In the first one the water-sediment mixture is represented as a homogeneous continuum described by a shear-thinning power-law rheology. Alternatively, the two-phase model proposed by Di Cristo et al in 2016 is used, which separately accounts for the liquid and solid phases. The considered test cases are represented by a 1D landslide flowing on a steep slope impacting on a rigid wall and a 2D mud dam-break flowing on a horizontal bottom in presence of single and multiple rigid obstacles. In the 1D test case, characterized by a very steep slope, the Two-Phase Model predicts the separation between the two phases with a significant longitudinal variation of the solid concentration. In this case the results indicate appreciable differences between the two models in the estimation of both the wave celerity and the magnitude of the impact, with an overestimation of the peak force when using the Single-Phase Model. In the 2D test-cases, where the liquid and solid phases remain mixed, even if the flow fields predicted by the two models present some differences, the essential features of the interaction with the obstacles, along with the maximum impact force, are comparable. [ABSTRACT FROM AUTHOR]

This study illustrates a novel numerical approach for investigating the complex physics involved in radial piston pump (rotating cam type) operation. This approach is based on a fully-coupled model that combines the evaluation of the main flow through the unit, realized by the pistons’ displacement, with the simulation of the internal lubricating interfaces, given by the piston-cylinder interface and the cam-piston interface. These interfaces represent the main source of power dissipation due to leakages and shear. The comprehensive multi-domain simulation tool presented in this paper incorporates a robust fluid-structure interaction based numerical model for the piston-cylinder lubricating interface as well as a model for the lubricant flow in the cam-piston interface. Since the approach used for piston-cylinder interface was previously presented by the authors, in this work particular emphasis is given to the description of the elastohydrodynamic lubrication model for the cam-piston interface. The overall coupling between these models enables an accurate estimation of the piston micro-motion that is critical to analyzing fluid flow in the lubricating gaps during pump operation. Results are shown with reference to a pump with four pistons designed to reach pressures up to 2500 bar. For this unit, the outer race of the cam—which is in contact with multiple pistons during pump operation—is unconstrained in its rotation, and it undergoes a complex motion due to which experimental measurements of its angular velocity were performed. The results from the study confirm the utility of the numerical model as an effective tool for modeling radial piston machines. [ABSTRACT FROM AUTHOR]

In this study, we determined the metal (Zn, Pb and Hg) contents in epigean and hypogean organs of Pistacia lentiscus L., a Mediterranean native plant grown on heavy metal-rich soils of Iglesiente (southwestern Sardinia, Italy), in view of its perspective use for revegetation and phytostabilization of mine waste piles. Plant samples were collected from four different areas in the district. Metal contents in the different plant tissues are roughly dependent on their total and mobile (diethylene triamine penta acetic acid (DTPA)-extractable) contents in soil and are shown in the following ranges: 48-628 mg kg (Zn), 2-354 mg kg (Pb) and 13-530 μg kg (Hg) and usually decrease in the following order: roots > stems > leaves; the apparent exception for Hg, with an order of leaves > stems, is ascribed to foliar absorption of this element. The biological concentration factors are consistently low (≤0.05) for all metals and support the concept that the strategy of metal tolerance of P. lentiscus is based on exclusion. These results are consistent with most previous literature data, confirming that P. lentiscus is well suited for revegetation actions and could decrease metal mobility through the soil stabilization strategy. [ABSTRACT FROM AUTHOR]

In the present paper the stability of gradually varying mud-flows in wide open channel is analyzed. The governing equations derive from a Saint-Venant-like approach with a Herschel & Bulkley model for the fluid rheology. In order to define the stability of a given initial accelerating or decelerating flow depth profile, the spatial evolution of a wavefront is analyzed. A stability criterion based on the linearized flow model is introduced, showing that the streamwise non-uniformity of the flow substantially influences the stability limits. A positive flow depth slope induces a stabilization while a negative one determines a destabilizing effect. The dependency of the linear stability on the values of rheological parameters is deeply discussed. A non-linear analysis of the wavefront propagation, along with the full non-linear solution of the problem, has been carried out to confirm the role played by the initial profile on the flow stability. The results of the presented study may be useful for engineering applications in order to prevent or to inhibit roll-waves formation in subcritical flows of a Herschel & Bulkley fluid. [ABSTRACT FROM AUTHOR]

Simplified wave models - such as kinematic, diffusion and quasi-steady - are widely employed as a convenient replacement of the full dynamic one in the analysis of unsteady open-channel flows, and especially for flood routing. While their use may guarantee a significant reduction of the computational effort, it is mandatory to define the conditions in which they may be confidently applied. The present paper investigates the applicability conditions of the kinematic, diffusion and quasisteady dynamic shallow wave models for mud flows of power-law fluids. The power-law model describes in an adequate and convenient way fluids that at low shear rates fluids do not posses yield stress, such as clay or kaolin suspensions, which are frequently encountered in Chinese rivers. In the framework of a linear analysis, the propagation characteristics of a periodic perturbation of an initial steady uniform flow predicted by the simplified models are compared with those of the full dynamic one. Based on this comparison, applicability criteria for the different wave approximations for mud flood of power-law fluids are derived. The presented results provide guidelines for selecting the appropriate approximation for a given flow problem, and therefore they may represent a useful tool for engineering predictions. [ABSTRACT FROM AUTHOR]

The occurrence of roll-waves in mud-flows is investigated based on the formulation of the marginal stability threshold of a linearized onedimensional viscoplastic (shear-thinning) flow model. Since for this kind of non-Newtonian rheological models this threshold may occur in a hypocritical flow, the downstream boundary condition may have a nonnegligible effect on the spatial growth/decay of the perturbation. The paper presents the solution of the 1D linearized flow of a Herschel and Bulkley fluid in a channel of finite length, in the neighbourhood of a hypocritical base uniform flow. Both linearly stable and unstable conditions are considered. The analytical solution is found applying the Laplace transform method and obtaining the first-order analytical expressions of the upstream and downstream channel response functions in the time domain. The effects of both the yield stress and the rheological law exponent are discussed, recovering as particular cases both power-law and Bingham fluids. The theoretical achievements may be used to extend semi-empirical criteria commonly employed for predicting roll waves occurrence in clear water even to mud-flows. [ABSTRACT FROM AUTHOR]

In the present paper, an analytical expression of the Green's function of linearized Saint-Venant equations (LSVEs) for shallow water waves is provided and applied to analyse the propagation of a perturbation superposed to a uniform flow. Independently of the kinematic character of the base flow, i.e., subcritical or supercritical uniform flow, the effects of a non-uniform vertical velocity profile and a non-constant resistance coefficient are accounted for. The use of the Darcy-Weisbach friction law allows a unified treatment of both laminar and turbulent conditions. The influence on the wave evolution of the wall roughness and the fluid viscosity are finally discussed, showing that in turbulent regime the assumption of constant friction coefficient may lead to an underestimation of both amplification and damping factors on the wave fronts, especially at low Reynolds numbers. This conclusion has to be accounted for, particularly in describing hyper-concentrated suspensions or other kinds of Newtonian mixtures, for which the high values of the kinematic viscosity may lead to relatively low Reynolds numbers. [ABSTRACT FROM AUTHOR]

GRIDA3 (Shared Resources Manager for Environmental Data Analysis and Applications) is a multidisciplinary project designed to deliver an integrated system to forge solutions to some environmental challenges such as the constant increase of polluted sites, the sustainability of natural resources usage and the forecast of extreme meteorological events. The GRIDA3 portal is mainly based on Web 2.0 technologies and EnginFrame framework. The portal, now at an advanced stage of development, provides end-users with intuitive Web-interfaces and tools that simplify job submission to the underneath computing resources. The framework manages the user authentication and authorization, then controls the action and job execution into the grid computing environment, collects the results and transforms them into an useful format on the client side. The GRIDA3 Portal framework will provide a problem-solving platform allowing, through appropriate access policies, the integration and the sharing of skills, resources and tools located at multiple sites across federated domains. [ABSTRACT FROM AUTHOR]