The application of micro components in various fields such as biomedical, medical, automobile, electronics, automobile and aviation significantly improved. To manufacture the micro components, different techniques exist in the non-traditional machining process. In those techniques, electrochemical micromachining (ECMM) exhibits a unique machining nature, such as no tool wear, non-contact machining process, residual stress, and heat-affected zone. Hence, in this study, micro holes were fabricated on the copper work material. The sodium nitrate (NaNO₃) electrolyte is considered for the experiments. During the experiments, magnetic fields strength along with UV rays are applied to the electrolyte. The L₁₈ orthogonal array (OA) experimental design is planned with electrolyte concentration (EC), machining voltage (MV), duty cycle (DC) and electrolyte temperature (ET). The optimization techniques such as similarity to ideal solution (TOPSIS), VlseKriterijumska Optimizacija I Kompromisno Resenje (VIKOR) and grey relational analysis (GRA) were employed to find the optimal parameter combinations. The entropy weight method is used to assess the weight of responses such as MR and OC. The optimal combination using TOPSIS, VIKOR and GRA methods shows the same results for the experimental runs 8, 9 and 7, and the best optimal parameter combination is 28 g/l EC, 11 V MV, 85 % DC and 37°C ET. Based on the analysis of variance (ANOVA) results, electrolyte concentration plays a significant role by contributing 86 % to machining performance. The second and least contributions are DC (3.86 %) and ET (1.74 %) respectively on the performance. Furthermore, scanning electron microscope (SEM) images analyses are carried out to understand the effect of magnetic field and heated electrolyte on the work material.

Diagnostic methodologies are of fundamental importance for operational strategies of electrical devices, both in the power grid and in industrial applications. This paper reports about a novel approach based on partial discharge analysis applied to high voltage electrical insulation. Especially dynamics of charges deposited by partial discharges is explored applying a chopped sequence. The applications refer to microvoids occurring inside solid insulating systems or at the interfaces, such as delaminations at the electrodes. The experiments were carried out on embedded voids having distinctive wall dielectric materials. The underlying physical phenomena of post discharge charge transport are analyzed. The assessment is performed using phase-resolved partial discharge patterns acquired applying a chopped sequence. The chopped partial discharge (CPD) method provides quantitative insight into post discharge charge decay processes due to deposited and accumulated charges fluctuations. The assessment indicator is based on comparing partial discharge inception angle between chopped sequence and continuous run. The experiments have shown that materials with distinctive surface conductivity revealed adequately different charge decay time dynamics. The detailed analysis yields time constant of walls charge decay for insulating paper equal to 12 ms and cross-linked polyethylene 407 ms. The CPD method may be further used to investigate streamer physics inside bounded cavities in the form of voids. The presented method provides a quantitative approach for charge non-invasive decay assessment and offers high potential in future diagnostics applications.

The following paper presents wind tunnel investigation of aerodynamic characteristics of hovering propellers. This propulsion system may be applied on a lightweight Quad Plane VTOL (Vertical Take-Off and Landing) UAV (Unmanned Aerial Vehicle). A Quad Plane is a configuration consisting of a quadcopter design combined with a conventional twin-boom airplane. This kind of design should therefore incorporate the advantages of both types of vehicles in terms of agility and long endurance. However, those benefits may come with a cost of worse performance and higher energy consumption. The characteristics of a fixed-wing aircraft and propellers in axial inflow are well documented, less attention is put to non-axial flow cases. VTOL propellers of a hybrid UAV are subject to a multitude of conditions – various inflow speeds and angles, changing RPMs, interference between propellers and between nearby aerodynamic structures. The tested system presented in this article consists of four electric motors with two coaxial pairs of propellers mounted on one of the fuselage beams. Such a configuration is often chosen by designers of small and medium hybrid UAVs. There is a need for studies of clean, efficient ways of transporting, and this article can aid future designers of a new type of electric UAVs.