A flow-dependent estimation of constriction size distribution in gap-graded soils: an integrated statistical approach

2022 ◽  
Vol 12 (1) ◽  
pp. 1-25
S.M. Dassanayake ◽  
A. Mousa

The clogging-unclogging process in gap-graded soils is a result of the migration of seepage-driven fines, which subsequently induces measurable changes in the local hydraulic gradients. This process can be temporally observed in the variations of Darcy's hydraulic conductivity (K). The current study proposes an integrated statistical Monte Carlo approach combining the discrete element method and 2D computational fluid dynamics simulations to estimate the flow-dependent constriction size distribution (CSD) for a gap-graded soil. The computational inferences were supported with experimental results using an internally stable soil, which was subjected to one-dimensional flow stimulating desired hydraulic loadings: a hydraulic gradient lower than the critical gradient applied as a multi-staged loading pattern. The 35th percentile size of the flow-dependent CSD (Dc35) for both internally stable and unstable gap-graded soils becomes approximately equal to Dc35 at steady-state. However, a greater variation of larger constrictions persists for the unstable soils. This pilot study has shown the applicability of the proposed method to estimate flow-dependent CSD for a wide range of experimentally observed K values.

2014 ◽  
Vol 18 (3) ◽  
pp. 1029-1040 ◽  
Jasmina Bogdanovic-Jovanovic ◽  
Dragica Milenkovic ◽  
Dragan Svrkota ◽  
Bozidar Bogdanovic ◽  
Zivan Spasic

As the global demand for energy grows, numerous studies in the field of energy efficiency are stimulated, and one of them is certainly the use of pumps in turbine operating mode. In order to reduce time necessary to determine pump characteristic in turbine operating mode problem was studied by computational fluid dynamics approach. The paper describes various problems faced during modeling (pump and turbine mode) and the approaches used to resolve the problems. Since in the majority of applications, the turbine is a pump running in reverse, many attempts have been made to predict the turbine performance from the known pump performance, but only for best efficiency point. This approach does not provide reliable data for the design of the system with maximum energy efficiency and does not allow the determination of the head for a wide range of flow rates. This paper presents an example of centrifugal norm pump operating in both (pump and turbine) regime and comparison of experimentally obtained results and computational fluid dynamics simulations.

2021 ◽  
Vol 24 (1) ◽  
T. van Druenen ◽  
B. Blocken

AbstractSome teams aiming for victory in a mountain stage in cycling take control in the uphill sections of the stage. While drafting, the team imposes a high speed at the front of the peloton defending their team leader from opponent’s attacks. Drafting is a well-known strategy on flat or descending sections and has been studied before in this context. However, there are no systematic and extensive studies in the scientific literature on the aerodynamic effect of uphill drafting. Some studies even suggested that for gradients above 7.2% the speeds drop to 17 km/h and the air resistance can be neglected. In this paper, uphill drafting is analyzed and quantified by means of drag reductions and power reductions obtained by computational fluid dynamics simulations validated with wind tunnel measurements. It is shown that even for gradients above 7.2%, drafting can yield substantial benefits. Drafting allows cyclists to save over 7% of power on a slope of 7.5% at a speed of 6 m/s. At a speed of 8 m/s, this reduction can exceed 16%. Sensitivity analyses indicate that significant power savings can be achieved, also with varying bicycle, cyclist, road and environmental characteristics.

Materials ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2041
Eva C. Silva ◽  
Álvaro M. Sampaio ◽  
António J. Pontes

This study shows the performance of heat sinks (HS) with different designs under forced convection, varying geometric and boundary parameters, via computational fluid dynamics simulations. Initially, a complete and detailed analysis of the thermal performance of various conventional HS designs was taken. Afterwards, HS designs were modified following some additive manufacturing approaches. The HS performance was compared by measuring their temperatures and pressure drop after 15 s. Smaller diameters/thicknesses and larger fins/pins spacing provided better results. For fins HS, the use of radial fins, with an inverted trapezoidal shape and with larger holes was advantageous. Regarding pins HS, the best option contemplated circular pins in combination with frontal holes in their structure. Additionally, lattice HS, only possible to be produced by additive manufacturing, was also studied. Lower temperatures were obtained with a hexagon unit cell. Lastly, a comparison between the best HS in each category showed a lower thermal resistance for lattice HS. Despite the increase of at least 38% in pressure drop, a consequence of its frontal area, the temperature was 26% and 56% lower when compared to conventional pins and fins HS, respectively, and 9% and 28% lower when compared to the best pins and best fins of this study.

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