Seong-Jin Kwon

Overtaking maneuvers can induce significant changes in the airflow field between vehicles, potentially compromising the stability and safety of the overtaken vehicle. This study investigates the aerodynamic characteristics during overtaking in a platoon of vehicles using the 1:2.5 DrivAer fastback model as the subject of analysis. To simulate the external flow during overtaking within a vehicle platoon, the Reynolds-Averaged Navier–Stokes (RANS) equations are employed under steady-state, incompressible flow assumptions. A baseline simulation is first performed for a single vehicle, and the results are validated against experimental data to ensure the reliability of the numerical method. The simulation is subsequently extended to a two-vehicle platoon configuration with a longitudinal spacing of half a vehicle length. Under steady platoon driving conditions, no significant lateral aerodynamic disturbances are observed between adjacent vehicles, and a two-vehicle platoon is subjected to relatively small lateral forces. However, during the overtaking process, notable variations in aerodynamic forces and moments occur. In particular, the lateral force coefficient and yaw moment coefficient of two-vehicle platoons reach their peak values at about two vehicle lengths ahead of the critical overtaking position. Furthermore, during the overtaking maneuver, the aerodynamic characteristics of the overtaken vehicle exhibit continuous fluctuations. The resulting variations in the lateral force coefficient and cornering stiffness have a sustained impact on vehicle handling stability, providing crucial insights for enhancing vehicle maneuverability.

The synthesis of lithium lead borosilicate bismuth vanadate glasses with varying Tl₂O₃ concentrations (between 0 to 5.0 mol %) was achieved through the implementation of the melt quenching technique. A comprehensive analysis has been conducted to examine the electrical and dielectric properties over a broad spectrum of frequencies (10²–10⁶ Hz) and temperatures (303–573 K). According to the findings of conductivity studies, mixed conduction (both electronic and ionic) occurs in the produced glasses. As the concentration of Tl₂O₃ increases in the base glass, the dielectric properties, including dielectric loss, dielectric constant, and ac conduction, exhibit a decreasing trend. An increasing number of V⁵⁺ ions has been identified as being involved in the formation of networks near crystal structures of VO₅. The quantitative study of ac conductivity and dielectric property data revealed that increasing the concentration of Tl₂O₃ in the glass network increases the insulating character of the glass. In the glass structure, the migration of thallium ions to tetrahedral coordination from octahedral coordination occurs, accompanied by a de-clustering effect of these ions.

In this study, PbO–GeO₂ glasses were melt-quenched at different nickel oxide concentrations. XRD and DSC techniques were characterized whether the samples are glass or crystalline materials. IR, Raman, and optical absorption techniques are used to obtain structural details. The IR spectra have revealed that the glass network contained conventional structural units GeO₄ and GeO₆. The Ni²⁺ ion octahedral transition exhibited luminescence spectra in the region of 1200–1500 nm; it is due to ³T₂ (3F) → ³A₂(3F) transition. The glasses containing the highest concentration of NiO have been found to have high values of luminescence efficiency and the cross-section. The dielectric characteristics, such as the dielectric constant, loss, and a.c. conductivity (σ_ac), were analyzed across extensive frequency and temperature ranges, with a specific emphasis on the nickel oxide concentration. Analyzing optical absorption and dielectric properties of the samples, it has been found that nickel ions’ majority occur in tetrahedral sites. It is proved that the dielectric constant and loss values are highest for the sample N₁₀ and ac conductivity due to dipoles being lowest for the sample N₁₀. It is revealed that the glasses are highly conducting due to the modifying action of Ni²⁺ ions so these glasses are suitable for solid electrolyte uses besides their optical applications in NLO devices.