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Wear occurs at most solid surfaces that come in contact with other solid surfaces. While biological surfaces and tissues usually have the ability to repair minor wear damage, engineered self-healing materials only started to emerge recently. An example of a smart self-healing material is the material with imbedded microcapsules or microtubes, which rupture during crack propagation and release a healing agent that repairs the crack. Self-healing mechanisms are hierarchical in the sense that they involve interactions with different characteristic scale lengths. While traditional models of self-healing require equations with many degrees of freedom, taking into account the hierarchical organization allows us to reduce the number of equations to a few degrees of freedom. We discuss the conditions under which the self-healing occurs and provide a general theoretical framework and criteria for self-healing using the concept of multiscale organization of entropy and non-equilibrium thermodynamics. The example of a self-healed Al alloy reinforced with microtubes filled with Sn60Pb40 solder is discussed as a case study.

A numerical study is made of the characteristics of turbulent submerged axisymmetric incompressible jets impinging on a flat plate and flowing into an axisymmetric cavity. The purpose of the study is to obtain a better understanding of the behavior of a fluid jet used to cut solid materials. In the computations a hybrid finite difference method is used to solve the full Navier-Stokes equations for an incompressible submerged jet with the k ∼ ε turbulence model. All computed results are compared with experimental data reported in the literature. For the case of the jet impinging on a flat plate, the computations are made for nozzle-to-plate distances ranging from 2 to 40 nozzle diameters. For the jet flowing into an axisymmetric cavity, computations are made for cavity depths ranging from 0 to 60 nozzle diameters. The use of the k ∼ ε turbulence model results in good predictions of the velocity, pressure, and skin friction distributions. The near-wall models for the kinetic energy and turbulent shear stress give good predictions of the skin friction coefficients.

Wind energy is a well proven and cost-effective technology and expected to be a promising technology in which industry responds to the environmental targets—so becoming an important source of power generation in years to come. This paper focuses on the current status of wind energy and more advanced subjects needed to understand the current technology in the wind power engineering.