**Preface to "Selected Papers from the ICEUBI2019 – International Congress on Engineering – Engineering for Evolution"**

This *Energies* Special Issue Book "Elected Papers from the ICEUBI2019 – International Congress on Engineering – Engineering for Evolution" comprises six papers that are the latest advances in basic and application research in the field of engineering, specifically covering areas of aeronautics, electrotechnics and mechanics. The accepted papers illustrate the highly innovative and informative venue for essential and advanced scientific and engineering research in those fields. Magalhaes ˜ et al. propose a Reynolds averaged Navier–Stokes (RANS) computational method following an incompressible but a variable density approach by to the study of supercritical nitrogen mixing layers, in which the performances of several turbulence models are compared in conjunction with a high accuracy multi-parameter equation of state. In addition, a suitable methodology to describe transport properties accounting for dense fluid corrections is applied. The results are discussed and validated against experimental data. Considerations about the applicability of the tested turbulence models in supercritical simulations are given based on the results and each model's structural nature. Camacho et al. present the computational study of the influence of the Reynolds number, frequency, and amplitude of the oscillatory movement of a NACA0012 airfoil in the aerodynamic performance. The thrust and power coefficients are obtained, which together are used to calculate the propulsive efficiency. The simulations were performed using ANSYS Fluent with a RANS approach for Reynolds numbers between 8500 and 34,000, reduced frequencies between 1 and 5, and Strouhal numbers from 0.1 to 0.4. The aerodynamic parameters and their interaction are explored and discussed. Alves et al. give a brief overview of aviation performance trends since the past century. Comparison examples between aircrafts designed in different paradigms are presented. Cruising speed trends and other performance parameters are discussed, looking at different periods and circumstances. The use of aircraft propellers as a reborn propulsive device and its role in aviation progress, even for commercial aviation, is discussed. New playgrounds for propeller innovation like the electric VTOL aircraft aimed for urban mobility are presented. Faria et al. propose a new method for the simultaneous determination of the optimal control parameters of proportional resonant controllers and the optimal design of the output filter of a grid-tied three-phase inverter, based on the grey wolf optimization (GWO) algorithm. The proposed optimization methodology is validated, by using two output filter topologies with series and complex passive damping methods. Bento et al. propose a novel Lagrangian multiplier update adaptative algorithm to automatically adjust the step-size used to update Lagrange multipliers. This new adaptative step-size update is a crucial stage when employing Lagrangian relaxation to solve the hydro-thermal coordination problem in a conventional electrical power generation system. This coordination problem is intrinsically complex, with a large-scale and constrained in nature; thus, the feasibility of a direct approach is reduced. Hence, Lagrangian relaxation, a decomposition method, is a consolidated choice to "simplify" the problem by deriving and solving the associated dual problem. A results comparison is made against two traditionally employed step-size update heuristics, using two real hydrothermal scenarios derived from the Portuguese power system. Santos et al., knowing the unique and growing importance of water, propose a new index, total water impact (TWI), which allows a holistic comparison of the impact of water use on water, air and evaporative condensation climate systems. Energy demand growing for air conditioning comes from a combination of rising temperatures, rising population and economic growth. This increase in energy will directly impact water consumption, either to directly cool the condenser of equipment or to serve indirectly as a basis for energy sources. The proposed index provides a new insight about energy consumption and ultimately, about sustainability. To conclude, the Special Issue editors would like to thank those who have contributed to this book for their high-quality submissions. We would also like to thank those who performed reviews of the manuscripts and their valuable feedback.

> **Maria do Ros ´ario Alves Calado, Jorge Miguel dos Reis Silva** *Editors*
