Search Results (13)

Non-Newtonian mud and debris flows include a wide range of physical processes depending on the setting, concentration, and soil properties. Numerical modelers have developed a variety of non-Newtonian algorithms to simulate this range of physical processes. However, the assumptions and limitations in any given model or software package can be difficult to replicate. This diversity in the physical processes and algorithmic approach to non-Newtonian numerical modeling makes a modular computation library approach advantageous. A computational library consolidates the algorithms for each process. This work presents a flexible numerical library framework (DebrisLib) that has a diverse range of software implemented to simulate geophysical flows using steady flow, kinematic wave, diffusion wave, and shallow-water models with finite difference, finite element, and finite volume computational schemes. DebrisLib includes a variety of non-Newtonian closures that predict a range of geophysical flow conditions and modular code designed to operate with any Newtonian parent-code architecture. This paper presents the DebriLib algorithms and framework and laboratory validation simulation. The simulations demonstrate the utility of the algorithms and the value of the library architecture by calling it from different modeling frameworks developed by the US Army Corps of Engineers (USACE). We present results with the one-dimensional (1D) and two-dimensional (2D) Hydrologic Engineering Center River Analysis System (HEC-RAS) and the 2D Adaptive Hydraulics (AdH) numerical models, each calling the same library. Full article

With the increasing construction of engineering structures on soft soils, accurately assessing their consolidation behavior has become crucial. To address this, Terzaghi’s one-dimensional consolidation model was revisited. The elastic behavior of soil skeleton was modified by incorporating viscous effects using the fractional derivative Merchant model (FDMM), while the linear Darcy’s law governing flux–pressure relations was extended by introducing time memory formalism through the fractional derivative Darcy model (FDDM). The governing equation is derived by incorporating the resulting constitutive behavior of both the soil skeleton and water flow into the Terzaghi’s formulation of the poroelasticity problem. The proposed rheological consolidation model is solved by a forward time-centered space scheme (FTCS). After verifying the numerical procedure with published data, the influence of parameters on both the average degree of settlement and the pressure was comprehensively studied. Full article

The natural gas hydrate reservoir in the sea area is shallowly buried and mainly composed of silty silt. The reservoir sediment is weakly consolidated and has fine particles, which shows a higher sand production risk and needs sand control. However, the fine silt particles can easily cause blockages in the sand control medium, so the balance between sand control efficiency and gas production should be considered. At present, there is a lack of reasonable and effective measures to prevent pore blockage in the sand control medium. In this study, the influence of the formation of sand on the blockage in sand-retaining mediums under the condition of gas–water mixed flow is discussed, and the plugging process is analyzed. The results show that: (1) Although the ceramic particles have high sphericity and regular shape, they can form higher porosity and permeability, but the finer ceramic particles will also cause blockages in the muddy silt and reduce productivity. (2) The experimental results of different ceramide filling schemes show that Saucier’s empirical criteria are not suitable for hydrate reservoir development and cannot be directly used for reference. In order to balance the problem of sand control and productivity in the development of the hydrate reservoir, it is recommended to use a 40 × 70 mesh ceramide as the critical optimal condition. The experimental results of this paper have important guiding significance for the development of pre-filled sand control screens and the formulation and optimization of sand control schemes. Full article

In China, groundwater loss caused by underground coal mining is becoming increasingly serious. The key to groundwater restoration is to repair mining-induced water-conducting fractures (WCFs) in the overlying strata. In this study, the adsorption–consolidation sealing characteristics of chemical precipitates were used to conduct permeability reduction (PR) experiments, including adding mixed CaCO₃ and Fe(OH)₃ to a sandstone specimen with a single fracture at room temperature. An aqueous solution of Na₂CO₃ was used as the simulated groundwater, and a solution of mixed CaCl₂ and FeCl₂ was used as the repair reagent to simulate the water seepage conditions of a fractured rock mass. The two aqueous solutions were simultaneously injected into a single-fractured rock specimen at a constant flow rate. The experimental results show that the Fe(OH)₃ colloid encapsulated CaCO₃ crystals in a mixed precipitate, reducing the overall structural stability of the mixed precipitate and restricting repair and PR efficiency. However, the Fe(OH)₃ precipitate had better PR efficiency in the initial stage of the experiment. Therefore, a better scheme was put forward to repair the WCF, utilizing a mixed Fe(OH)₃ and CaCO₃ precipitate with a molar ratio close to 1:4 in the early stage and a single CaCO₃ precipitate in the later stage. Full article

The Gully Consolidation and Highland Protection (GCHP) project is an important governance measure for controlling source erosion and reducing soil erosion in the Loess Plateau, which has been explored and developed continuously in recent decades. However, there is no international precedent for research on the implementation effect of the GCHP project, and it is still relatively weak. In order to quantify the erosion of a small watershed under the construction of a gully head landfill, this study selected Yangjiagou (YJG) as the research area. The spatial analysis function of ArcGIS was used to process DEM and soil type data, the GeoWEPP model was used to simulate soil erosion, and the changes of runoff and sediment yield before and after gully head landfill were analyzed. The results showed that compared with the simulated original soil erosion amount, the annual runoff decreased by 13.13%, and the sediment yield decreased by 37.61% after gully head landfill, indicating that the GCHP project positively influenced soil erosion control. After the gully head landfill measures are taken, the flow path becomes shorter, so the flow scour capacity is weakened. Soil and water control is very effective in the short term, but if long-term maintenance is not carried out, the intensity of soil and water loss is likely to be aggravated. This study provides an effective verification method for the feasibility of a soil loss control scheme on the Loess Plateau and provides a reference for promoting ecological priority and efficient management in the Loess gully area. Ultimately, it will serve the ecological protection and high-quality development of the Yellow River Basin. Full article

Marine natural gas hydrate (NGH) can mainly be found in argillaceous fine-silt reservoirs, and is characterized by weak consolidation and low permeability. Sand production is likely to occur during the NGH production process, and fine-silt particles can easily plug the sand-control media. In view of this, experiments were conducted to assess the influence of the formation sand on the sand retention media in gravel-packed layers under gas–water mixed flow, and the plugging process was analyzed. The results show that following conclusions. (1) The quartz-sand- and ceramic-particle-packed layers show the same plugging trend, and an identical plugging law. The process can be divided into three stages: the beginning, intensified, and balanced stages of plugging. (2) The liquid discharge is a key factor influencing the plugging of gravel-packed layers during NGH exploitation by depressurization. As the discharge increases, plugging occurs in all quartz-sand packing schemes, while the ceramic-particle packing scheme still yields a high gas-flow rate. Therefore, quartz sand is not recommended as the packing medium during NGH exploitation, and the grain-size range of ceramic particles should be further optimized. (3) Due to the high mud content of NGH reservoirs, a mud cake is likely to form on the surface of the packing media, which intensifies the bridge plugging of the packed layer. These experiment results provide an important reference for the formulation and selection of sand-control schemes. Full article

The non-unique critical state represents the distance between the critical state line (CSL) and the isotropic consolidation line (ICL) that significantly varies with stress paths and particle size distribution of soils. A structural bounding surface plasticity model with spacing ratio r (SBSP-R model) was implemented using an explicit algorithm. However, the explicit algorithm did not well capture the non-unique critical state of soils with a large spacing ratio r, which prevented the soil mechanics research on non-unique critical state via finite element analysis. To overcome the limitation, the implicit algorithm of the SBSP-R model is formulated, and it mainly includes elastic prediction and plastic correction. The plastic correction is realized using the Newton–Simpson scheme with a controlling equation set related to consistency condition, plastic flow, hardening parameter, structural bounding surface, plastic modulus, and mapping rule. Case studies indicate that the implicit algorithm of the SBSP-R model is right and stable in predicting non-unique critical states. Comparisons between predicted and tested results indicate that the implicit algorithm of the SBSP-R model not only captures the critical state, stress-strain, and stress paths of various soils but also shows higher computational accuracy and efficiency compared with the previous explicit algorithm. These results indicate that the formulated implicit algorithm of the SBSP-R model is an alternative approach to the previous explicit algorithm. Full article

The efficiency increase that distributed propulsion could deliver for future hybrid-electric aircraft is in line with the urgent demand for higher aerodynamic performances and a lower environmental impact. Several consolidated proprietary tools (not always available) are developed worldwide for distributed propulsion simulation. Therefore, prediction and comparisons of propeller performances, with computational fluid dynamic codes featuring different implementation of solvers, numerical schemes, and turbulence models, is of interest to a wider audience of research end-users. In this framework, the paper presents a cross-comparison study among different CFD solvers, the SU2 Multiphysics Simulation and Design Software, the CIRA proprietary flow solver UZEN, and the commercial ANSYS-FLUENT code, for the simulation of a wing section with a tractor propeller at different flow attitudes. The propeller is modelled as an actuator disk according to the general momentum theory and is accounted for in the flow solvers as a boundary condition, for the momentum and energy equations. In this study, a propeller with a fixed advance ratio $J=0.63$ is considered, while propeller performances are assumed variable along with the radius. To perform the comparisons among the solvers, an in-house procedure, which provides the input thrust and torque distributions in a unified format among the three solvers, is developed. Steady RANS simulations are performed at $R{e}_{\infty }=1.7\times {10}^6$ and $M_{\infty }=0.11$, for the flowfield of an isolated propeller. Successively, a wing section with a fixed forward-mounted propeller configuration with no nacelle, is studied at $\alpha =0^{\circ },4^{\circ },$ and $8^{\circ }$ angles of attack. The comparisons in terms of the lift coefficient show a good agreement among the three flow solvers both in power-off and power-on conditions. Simulations also evidenced the strong stability preserving property of upwind schemes, applied to propeller simulation at low-Mach number. Some discrepancies in the drag coefficient are observed and related to different levels of numerical diffusion between the three codes, which affects the downstream wake. Differences in flow properties in near disk region are observed and explained considering the different hub implementations. Full article

Middleboxes are critical components in today’s networks. Due to the variety of network/security policies and the limitations of routing protocols, middleboxes are installed in multiple physical locations to face high traffic with few considerations for efficiency. Reducing the number of deployed middleboxes would reduce capital and operation costs. Moreover, some flows prefer to bypass one or more in-path middlebox where they provide useless services, such as payload compression for multimedia streams. These challenges can be partially tackled by network function virtualization (NFV) schemes with the costs of performance reduction and replacement expenses. Given the rapid growth and the wide adoption of software-defined networking solutions and the recent advances in managing middleboxes’ configuration, the consolidation of middleboxes is becoming easier than before. We designed and evaluated SALMA, a new pre-NFV practical solution that systematically recreates the infrastructure of middleboxes by proposing the Integrated Middleboxes Subnets scheme. In this work, we attempted to reduce the number of installed middleboxes by implementing horizontal integration of middleboxes’ functions, such as every pair of middleboxes being integrated into a dedicated hardware box. We support the motivation for creating SALMA with a practical survey of in-production middleboxes from 30 enterprises. Our solution addresses key challenges of middleboxes, including cost, utilization, flexibility, and load balancing. SALMA’s performance has been evaluated experimentally as well. Full article

Vacuum preloading combined with prefabricated vertical drains (PVDs) has the potential to improve the soft sediments under water, however, its development is partly limited by the unclear understanding of the mechanism. This paper aims to extend the comprehension of the influential mechanism of overlapping water in the scenario of underwater vacuum preloading with PVDs. The systematic investigations were conducted by small strain finite element drained analyses, with the separated analysis schemes considering suction-induced consolidation, seepage and their combination. The development of settlement in the improved soil region and the evolution of seepage flow from the overlapping water through the non-improved soil region into improved zone are examined in terms of the build-up of excess pore pressure. Based on the results of numerical analyses, a theoretical approach was set out. It was capable to estimate the time-dependent non-uniform settlement along the improved soil surface in response to the combined effects of suction-induced consolidation and seepage. The difference of underwater and onshore vacuum preloading with PVDs is discussed with some practical implication and suggestion provided. Full article

Carbon capture, utilization, and storage (CCUS) describes a set of technically viable processes to separate carbon dioxide (CO₂) from industrial byproduct streams and inject it into deep geologic formations for long-term storage. Legacy wells located within the spatial domain of new injection and production activities represent potential pathways for fluids (i.e., CO₂ and aqueous phase) to leak through compromised components (e.g., through fractures or micro-annulus pathways). The finite element (FE) method is a well-established numerical approach to simulate the coupling between multi-phase fluid flow and solid phase deformation interactions that occur in a compromised well system. We assumed the spatial domain consists of a three-phases system: a solid, liquid, and gas phase. For flow in the two fluids phases, we considered two sets of primary variables: the first considering capillary pressure and gas pressure (PP) scheme, and the second considering liquid pressure and gas saturation (PS) scheme. Fluid phases were coupled with the solid phase using the full coupling (i.e., monolithic coupling) and iterative coupling (i.e., sequential coupling) approaches. The challenge of achieving numerical stability in the coupled formulation in heterogeneous media was addressed using the mass lumping and the upwinding techniques. Numerical results were compared with three benchmark problems to assess the performance of coupled FE solutions: 1D Terzaghi’s consolidation, Liakopoulos experiments, and the Kueper and Frind experiments. We found good agreement between our results and the three benchmark problems. For the Kueper and Frind test, the PP scheme successfully captured the observed experimental response of the non-aqueous phase infiltration, in contrast to the PS scheme. These exercises demonstrate the importance of fluid phase primary variable selection for heterogeneous porous media. We then applied the developed model to the hypothetical case of leakage along a compromised well representing a heterogeneous media. Considering the mass lumping and the upwinding techniques, both the monotonic and the sequential coupling provided identical results, but mass lumping was needed to avoid numerical instabilities in the sequential coupling. Additionally, in the monolithic coupling, the magnitude of primary variables in the coupled solution without mass lumping and the upwinding is higher, which is essential for the risk-based analyses. Full article

This paper presents effective and efficient solutions for components of urban logistics. The specificity of such logistics and the multiple limitations led to particular solutions. However, they all share one common feature—the flow consolidation in different variants. This study considers the flow consolidation at the boundary of urban congested areas, through horizontal collaboration between logistic platforms. This way, the urban distribution centers (UDCs) receive all the goods according to the orders addressed to each producer (or group in case of “on-going consolidations”). Deliveries are addressed to a single logistic platform. Thus, the flow consolidation is achieved. Each logistic platform receives part of the consumer goods intended for commercialization, but through collaboration between them (freight exchanges), all the warehouses of the producers have all the ordered goods. Dedicated management of logistics platforms and warehouses within each UDC ensures the confidentiality of distributor data. Three scenarios are presented concerning the same pattern of flow addressed to each UDC. These scenarios differ by the accessibility of the logistics platforms and by the connection between them (due to infrastructure development). The methodology of choosing the variants for composing the flow sent from each logistics platform considered the minimization of transfer times to UDC warehouses. Synthetic indicators allow for comparison between the analyzed scenarios. Full article

Wildfires are one of the most prominent risks for Mediterranean forests, reducing the flow of ecosystem services and representing a hazard for infrastructure and human lives. Several wildfire prevention programs in southern Europe are currently incorporating extensive livestock grazers in fire prevention activities to reduce the high costs of mechanical clearance. Among these the Andalusian network of grazed fuel breaks, the so-called RAPCA program, stands out for its dimension and stability over time. RAPCA currently works with 220 local shepherds who, with their guided flocks maintain low biomass levels in almost 6000 ha of fuel breaks in public forests to meet fire prevention standards. This work analyses the institutional design and performance of the RAPCA payment scheme under a payment for environmental services (PES) framework. Results show effectiveness of the payment scheme while efficiency is achieved through savings relative to the mainstream mechanized biomass removal, as well as through reduced information asymmetry. High-level and stable political commitment has been crucial for the emergence and consolidation of RAPCA. Moreover, key intermediaries and sound monitoring practices increased levels of trust amongst involved actors. Beneficial side-effects include social recognition of shepherds’ activities and reduction of their friction with forest managers. Full article