Fabric anisotropy has a significant influence on the mechanical behavior of sand. An anisotropic plasticity model incorporating fabric evolution is formulated in this study. Information on the overall stress–strain relationship and micromechanical fabric states from DEM numerical tests is used in the development of the constitutive model, overcoming the difficulties of fabric measurement in physical tests. The framework of the model and its formulations for fabric evolution, plasticity, and dilatancy enables it to capture the strength, shear modulus, and dilatancy of sand under both monotonic and cyclic loading. The model is validated against DEM numerical tests and physical laboratory tests on samples with different initial fabric, showing good agreement between the simulation and test results for the anisotropic stress–strain behavior of sand. The use of DEM test data also allows for the validation of the model on the micromechanical fabric level, showing that the model can reproduce the fabric evolution and its influence on key constitutive features reasonably well. The model is further applied to analyze the liquefaction behavior of sand, exhibiting the significant influence of fabric anisotropy on both liquefaction resistance and postliquefaction shear deformation.

To overcome the disadvantage of large suction requirements, the suction control for drag reduction is optimized. Computational fluid dynamics (CFD), in conjunction with multi-island genetic algorithm (MIGA), is employed to achieve the optimization. An E387 airfoil is employed as the physical model. The suction location and mass flux of a slot are set as the design parameters. The goal is to minimize both the airfoil drag and suction requirement by identifying the optimal suction location on the upper airfoil surface. The effects of different numbers of suction slots were investigated. Results show that the suction control for drag reduction could be optimized using MIGA. For a single-suction slot, the reduction in airfoil drag is up to 8.3%, and the mass flux of a slot reaches the lower limit of the optimization interval. The increase in suction slot number results in a better drag reduction effect, which is accompanied by larger suction requirement and slower convergence. The main reason for airfoil drag reduction is the decrease in the pressure drag.

The relationship between dilatancy and anisotropy is a fundamental aspect of anisotropic behavior of granular materials. Existing test data directly investigating this relationship are scarce and conflicting. Discrete element biaxial and triaxial numerical tests on idealized granular materials in both two-dimensional (2D) and three-dimensional (3D) are conducted in this study to acquire high quality stress, strain, dilatancy, and fabric data for various anisotropic samples, which are utilized to analyze the dependency of dilatancy ratio on fabric anisotropy. The test results indicate that the dilatancy ratio is not only dependent on the initial fabric anisotropy, but is also influenced by the evolution of fabric, especially the contact normal fabric. At low deviatoric stress ratio under biaxial and triaxial loading, difference in initial fabric anisotropy of granular materials can lead to distinctly different dilatancy ratios. As loading continues, the deviatoric stress ratio, void ratio, and fabric of granular materials evolve toward the unique critical state, causing the dilatancy ratio to converge irrespective of its initial value. The anisotropic critical state theory (ACST) is shown to be capable of providing a framework for quantitative mathematical depiction of the dependency of dilatancy ratio on fabric anisotropy.

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