scholarly journals Numerical study of a desaturation process by air injection in sandy soil

2021 ◽  
Vol 337 ◽  
pp. 02004
Author(s):  
Sebastian Sepulveda-Cano ◽  
Edwin F. Garcia-Aristizabal ◽  
Carlos A. Vega-Posada
Keyword(s):  
Numerical Study ◽  
Characteristic Curve ◽  
Cyclic Strength ◽  
Air Injection ◽  
Coarse Grained ◽  
Free Form ◽  
Void Space ◽  
Injection Wells ◽  
Sandy Deposit ◽  
Desaturation Process

This work aims to numerically study the desaturation process in a coarse-grained sandy deposit by means of air injection. It is well-known that the soil cyclic strength to liquefaction of a saturated, sandy deposit is positively affected by the presence of gas in the void space in either a dissolved or a free form. A numerical study is performed to investigate some of the factors affecting the desaturation advance and controlling the soil desaturation process by air injection. Among these factors are: a) soil-water characteristic curve and intrinsic permeability (hydraulic parameters), b) injection time, and c) standard approach to two injection wells placement. Only the standard mechanisms of biphasic flow are investigated (i.e., incompressible and isothermal biphasic flow in an isotropic homogeneous porous media with capillary effects).

scholarly journals Numerical Study of the Dynamic Compaction Process considering the Phenomenon of Particle Breakage

2018 ◽  
Vol 2018 ◽  
pp. 1-10 ◽  
Author(s):  
Xi Li ◽  
Jing Li ◽  
Xinyan Ma ◽  
Jidong Teng ◽  
Sheng Zhang
Keyword(s):  
Numerical Study ◽  
High Energy ◽  
Particle Breakage ◽  
Dynamic Compaction ◽  
Coarse Grained ◽  
Impact Stress ◽  
Logarithmic Curve ◽  
Before And After ◽  
Soil Foundation ◽  
Overlapping Method

Dynamic compaction (DC) is commonly used to strengthen the coarse grained soil foundation, where particle breakage of coarse soils is unavoidable under high-energy impacts. In this paper, a novel method of modeling DC progress was developed, which can realize particle breakage by impact stress. A particle failure criterion of critical stress is first employed. The “population balance” between particles before and after crushing is guaranteed by the overlapping method. The performance of the DC model is successfully validated against literature data. A series of DC tests were then carried out. The effect of particle breakage on key parameters of DC including crater depth and impact stress was discussed. Besides, it is observed that the relationship between breakage amount and tamping times can be expressed by a logarithmic curve. The present method will contribute to a better understanding of DC and benefit further research on the macro-micro mechanism of DC.

Numerical Assessment of Fan-Ducting Coupling for Gas Turbine Ventilation Systems

2015 ◽  
Author(s):  
Alessandro Corsini ◽  
Giovanni Delibra ◽  
Stefano Minotti ◽  
Stefano Rossin
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Static Pressure ◽  
Numerical Study ◽  
Characteristic Curve ◽  
Ventilation System ◽  
Maximum Pressure ◽  
Term Operation ◽  
Axial Fans ◽  
Pressure Discontinuity

Gas turbines enclosures entail a high number of auxiliary systems which must be preserved from heat, ensuring therefore the long term operation of the internal instrumentation and of the data acquisition system. A dedicated ventilation system is designed to keep the enclosure environment sufficiently cool and dilute any gas coming from potential internal leakage to limiting explosion risks. These systems are equipped with axial fans, usually fed with air coming from the filter house which provides air to the gas turbine combustion system, through dedicated filters. The axial fans are embedded in a ducting system which discharges fresh air inside the enclosure where the gas turbine is housed. As the operations of the gas turbine need to be guaranteed in the event of fan failure, a backup redundant system is located in a duct parallel to the main one. One of the main requirements of a ventilation fan is the reliability over the years as the gas turbine can be installed in remote areas or unmanned offshore platforms with limited accessibility for unplanned maintenance. For such reasons, the robustness of the ventilation system and a proper understanding of coupling phenomena with the axial fan is a key aspect to be addressed when designing a gas-turbine system. Here a numerical study of a ventilation system carried out with RANS and LES based methodologies will be presented where the presence of the fan is synthetized by means of static pressure discontinuity. Different operations of the fans are investigated by means of RANS in order to compare the different operating points, corresponding to 1) clean and 2) dirty filters operations, 3) minimum and 4) maximum pressure at the discharge section. Large Eddy Simulations of the same duct were carried out in the maximum loading condition for the fan to investigate the unsteady response of the system and validate its correct arrangement. All the simulations were carried out using OpenFOAM, a finite volume open source code for CFD analysis, treating the filters as a porous medium and the fan as a static pressure discontinuity according to the manufacturer’s characteristic curve. RANS modelling was based on the cubic k-ε model of Lien et al. while sub-grid scale modelling in LES was based on the 1 equation model of Davidson. Computations highlighted that the ventilation system was able to work in similarity for flow rates between 15 m3/s and 23.2 m3/s and that the flow conditions onto the fan suggest that the aerodynamic stress on the device could be reduced introducing in the duct flow straighteners or inlet guided vanes.

The effects of step inclination and air injection on the water flow in a stepped spillway: A numerical study

2017 ◽  
Vol 29 (2) ◽  
pp. 322-331 ◽  
Author(s):  
Khadidja Kherbache ◽  
Xavier Chesneau ◽  
Belkacem Zeghmati ◽  
Stéphane Abide ◽  
Saâdia Benmamar
Keyword(s):  
Water Flow ◽  
Numerical Study ◽  
Air Injection ◽  
Stepped Spillway

scholarly journals Numerical Study of Pump-Turbine Instabilities Under Pumping Mode Off-Design Conditions

2015 ◽  
Author(s):  
Uroš Ješe ◽  
Regiane Fortes-Patella ◽  
Matevž Dular
Keyword(s):  
Power Plants ◽  
Numerical Study ◽  
Guide Vane ◽  
Characteristic Curve ◽  
Rotating Stall ◽  
Electrical Network ◽  
Pump Turbine ◽  
Wide Range ◽  
Pumping Mode ◽  
And Performance

Pumped storage power plants, using reversible pump-turbines, are a great solution to maintain the stability of an electrical network. The continuous operating area of reversible pump-turbines machines is usually delimited by cavitation or a hydraulic instability called hump phenomena at part load. If the machine operates under these off-design conditions, it might be exposed to vibrations and performance losses. The paper focuses on the numerical analysis of the pumping mode regime and pays special attention to the prediction of the hump shaped characteristic curve and associated rotating stall. The investigations were made on a high head pump-turbine design (nq=27) at model scale for four different guide vane opening angles and a wide range of flow rates. Numerical simulations were performed and analyzed in LEGI and were compared to the global experimental data, provided by Alstom Hydro.

Adjoint-Based Optimization of a Modern Jet-Engine Fan Blade

2020 ◽  
Author(s):  
Andrea Giugno ◽  
Shahrokh Shahpar ◽  
Alberto Traverso
Keyword(s):  
Design Space ◽  
Characteristic Curve ◽  
Free Form ◽  
Design Parameters ◽  
Jet Engine ◽  
Discrete Adjoint ◽  
Active Design ◽  
Fan Blade ◽  
Adjoint Gradient ◽  
Real Test

Abstract A Multi-point Approximation Method (MAM) coupled with adjoint is presented to increase the efficiency of a modern jet-engine fan blade. The study performed makes use of Rolls-Royce in-house suite of codes and its discrete adjoint capability. The adjoint gradient is used along with MAM to create a Design Of Experiment to enhance the optimization process. A generalized Free-Form Deformation (FFD) technique is used to parametrize the geometry, creating a design space of 180 parameters. The resulting optimum blade at design conditions is then evaluated at off-design conditions to produce the characteristic curve, which is compared with real test data. Finally, a preliminary Active Design Subspace (ADS) representing the fan efficiency is created to evaluate the robustness of the objective function in respect to the most significant design parameters. The ADS allows to collapse a large design space of the order of hundreds parameters to the few most important variables, measuring their contribution. This map is valuable in many respects to the fan designers and manufacture engineers to identify any ridges where the performance may deteriorate rapidly, hence a more robust part of the design space can easily be visualized and identified.

Experimental and numerical study on the performance of new prefabricated connections for free-form grid structures

Structures ◽  
2022 ◽  
Vol 36 ◽  
pp. 1050-1067
Author(s):  
Guan Quan ◽  
Jiafeng Qi ◽  
Hui Wu ◽  
Jun Ye ◽  
Boqing Gao ◽  
...  
Keyword(s):  
Numerical Study ◽  
Free Form

The Application of Vapour Equlibrium Technique in Water Retention Study of Fine Grained Tailings

2013 ◽  
Vol 838-841 ◽  
pp. 1785-1790
Author(s):  
Qing Hua Jiang ◽  
Chen Xiang Yu
Keyword(s):  
Water Retention ◽  
Characteristic Curve ◽  
Size Composition ◽  
Engineering Properties ◽  
Coarse Grained ◽  
Dry Density ◽  
Soil Suction ◽  
Fine Grained ◽  
Theoretical Support ◽  
Tailing Dam

As a problematic material, fine grained tailings have many particular engineering characteristics and seriously affect the safety and stability of the tailing dam body. These engineering properties are closely related to moisture migration and soil suction under different water content. This article chose fine grained tailings of Li Tie Lan Ting tailings dam in Zhejiang province as an example, and measured the soil water characteristic curve (SWCC) of fine grained tailings with different partical size composition and dry density using vapour equilibrium technique. Efforts have also been made to demonstrate the influences of soil type, dry density on water retention. The study result shows that particle-size composition has a significant impact on SWCCs of the tailings. Finer grained samples have lower water loss rate and higher water-holding capacity than coarse grained samples in the same suction state. Contrary with low suction stage, dry density has negligible influence on the soil suction, and parameters effect SWCCs at high suction stage. The research results may provide a theoretical support and a beneficial reference for further research of fine grained tailingss engineering properties.

Numerical Study on Airfoil Diversion Technology Used in Saving Energy by Air Injection on Large Ship

2013 ◽  
Vol 353-356 ◽  
pp. 3341-3344 ◽  
Author(s):  
Ye Qing ◽  
Wen Cai Dong ◽  
Yong Peng Ou
Keyword(s):  
Power Consumption ◽  
Numerical Method ◽  
Numerical Study ◽  
Attack Angle ◽  
Air Injection ◽  
Plate Surface ◽  
Saving Energy ◽  
Large Ship ◽  
Air Lubrication

The power consumption is too large when the method saving energy by air injection is used on large ship because of the deep draft. The feasibility and some key matters of the implication of airfoil diversion technology on air lubrication ,such as the attack angle, the distance from the airfoil to the plate and the position of the air injection, was investigate by a numerical method. The result shows that the pressure of the air injection entrance is significantly decreased by setting an airfoil at the air injection entrance reasonably, the pressure of the plate surface declines when the distance from the plate to the airfoil is decreasing and the attack angle is increasing, however, the resistance became larger. For the airfoil 2032cjc we investigated in this paper, when d/C=0.3, the attack angle range from 6°~8°,the pressure reduces comparative large and the resistance increases small. The best position for air injection is determined by the position and attack angle of the airfoil.

scholarly journals An Accurate Estimate of the Free Energy and Phase Diagram of All-DNA Bulk Fluids

2018 ◽  
Author(s):  
Emanuele Locatelli ◽  
Lorenzo Rovigatti
Keyword(s):  
Phase Diagram ◽  
Free Energy ◽  
Large Scale ◽  
Nearest Neighbor ◽  
Numerical Study ◽  
Thermodynamic Description ◽  
Numerical Approach ◽  
Quantitative Agreement ◽  
State Theory ◽  
Coarse Grained

We present a numerical study in which large-scale bulk simulations of self-assembled DNA constructs have been carried out with a realistic coarse-grained model. The investigation aims at obtaining a precise, albeit numerically demanding, estimate of the free energy for such systems. We then, in turn, use these accurate results to validate a recently proposed theoretical approach that builds on a liquid-state theory, the Wertheim theory, to compute the phase diagram of all-DNA fluids. This hybrid theoretical/numerical approach, based on the lowest order virial expansion and a nearest-neighbor DNA model, can provide, in an undemanding way, a thermodynamic description of DNA associating fluids that is in semi-quantitative agreement with experiments. We show that the predictions of such scheme are as accurate as the ones obtained with more sophisticated methods. We also demonstrate the flexibility of the approach by incorporating non-trivial additional contributions that go beyond the nearest-neighbor model to compute the DNA hybridization free energy.

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