The factors affecting chemical use in aquaculture in the Central Coast Region of Vietnam

Using the econometric approach of Ordinary Least Squares, this study has identified the key factors affecting the use of inorganic chemicals in coastal aquaculture in South Central Vietnam. These factors included the amount of training and support policies for extensions and the level of participation by cooperative groups in aquaculture activities. The greatest impact factor to the use of inorganic chemicals in aquaculture was “Fishery Extension Support Policy Group” by −0.747. This value means that if the remaining variables do not change and this variable increased by one unit (meaning that an increasing in support including capital, machinery, the consultants, seed for aquaculture farmers), the use of chemicals in aquaculture sector will decrease 0.747 units. In contrast, the level of “participation in cooperative groups” in aquaculture in Vietnam was directly proportional, extended to the use of inorganic chemicals with a coefficient by 0.706. This result suggests that households participating in “cooperative group” aquaculture will tend to use more 70.6% inorganic chemicals than non-participating households. This suggests the need for corresponding policies to limit the usage of inorganic chemicals and antibiotics in aquaculture in the region in order to achieve the development goals of green growth and sustainability

Modeling submerged granular flow across multiple regimes using the Eulerian-Eulerian approach with shear-induced volumetric behavior

The behavior of submerged granular flow is strongly dependent on the solid volume fraction and the viscosity discontinuity over a wide range of flow regimes. To obtain a general description of this type of flow, this study proposes a new model to compute solid effective stresses of submerged granular materials across multiple flow regimes. Here, based on the critical state soil mechanics framework, a new equation is proposed to describe the evolution of elastic reference of materials caused by elastoplastic deformation. The evolution of elastic reference subsequently informs the development of static pressure, and together with the dynamic pressure computed using a well-established blended model, resulting in a new approach to compute the solid pressure induced by both dynamic and static effects. The proposed model is then implemented in the Eulerian–Eulerian approach using the finite volume method to simulate the collapses of submerged granular columns, covering different flow regimes from quasi-static to viscous depositions. Simulation results agreeing well with experimental and numerical data in the literature are a testament to the performance of a well-developed constitutive law. In addition, the simulation results comprehensibly demonstrate the important role of interstitial fluid flow as well as the initial solid volume fraction in the collapsing process across different flow regimes with different packing densities. Furthermore, the effects of initial volume fraction, fluid pressure, and phase interaction forces on the flow responses are also discussed.Quoc T. Phan, Ha H. Bui, and Giang D. Nguye

Strain localization in the standard triaxial tests of granular materials: Insights into meso- and macro-scale behaviours

First published: 09 January 2024The standard triaxial tests cease to be valid as material tests since the homogeneity of the granular mass is lost when localized failures such as shear bands occur requiring a different approach to interpreting and analyzing material responses at the meso scale from the macro behaviour. This study sheds light on the above issue by analyzing the standard triaxial tests of the granular specimens undergoing localized failure at different scales using DEM. For the first time, the behaviour of material inside and outside of the shear band as well as the entire sample are quantitatively quantified through DEM simulations. The results enable confirmation of various theoretical hypotheses and experimental observations on the localized failure in granular materials. For example, by quantifying the inter‐particle contact forces of materials inside and outside the shear band zone, it is confirmed that the material outside the localization band undergoes inelastic unloading beyond the bifurcation point, while those inside the localization band experience inelastic shearing to reach the critical state. Moreover, the analysis in this study suggests that if the volume of the localization zone can be precisely measured from the experiment, the mesoscale constitutive responses that truly represent the inelastic behaviour can be quantified. This gives rise to a more appropriate method to obtain inelastic constitutive responses of granular materials from specimens undergoing localized failure in triaxial tests.Quoc T. Phan, Ha H. Bui, Giang D. Nguyen, François Nico

Effect of particle rolling resistance on drained and undrained behaviour of silty sand

Published: 04 January 2021This paper explores the effect of particle rolling resistance on the mechanical behaviour of silty sand under various shearing conditions. The elastic–plastic spring–dashpot rolling resistance model was employed, and drained and undrained triaxial tests were conducted on silty sand with various fines contents and rolling resistance. It was found that the rolling resistance of fines contents had a strong impact on the critical state, peak state, phase transformation state as well as zero-dilatancy state of silty sands. Moreover, depending on the correlation between rolling resistance of coarse and fine particles, fines can positively or negatively contribute to the overall structure of silty sand. Increasing the rolling resistance of fines enhances the liquefaction resistance of silty sands. Thus, the presence of fines of high rolling resistance in the sand can result in a marked decrease in collapsibility or liquefaction susceptibility compared with the presence of fines of lower rolling resistance.Quoc T. Phan, Ha H. Bui, Giang D. Nguyen and Abdelmalek Bouazz