Acta Universitatis Sapientiae Electrical and Mechanical Engineering
Latest Publications

Abstract The actual energy situation and the significant energy demand of agricultural production require the exploration and analysis of the general laws of the main processes in the field of energy, which is part of the borderline between the technical sciences and the agricultural sciences. Tillage machines change the physical properties of the soil, but at the same time the mechanical properties of the soil react to the implement. One of the basic works of seedbed preparation is harrowing. In this work we study the kinematics and dynamics of the active rotary harrow implements, taking into account the cutting resistance of the soil. The results obtained with the developed modeling methods, give reliable approximations to the experienced tilling processes.

Abstract 5G cellular networks have introduced a completely novel air interface called New Radio (NR). This technology delivers numerous benefits compared to previous generations, including significantly higher peak data rates. However, due to the propagation properties of the frequencies used in NR, the volatility of the available downlink capacity also increases. In this paper, we study two TCP congestion control algorithms which are designed to be able to quickly utilize sudden increases in available capacity. We present an implementation of TCP SIAD in the ns-3 open source network simulator and compare its performance with TCP BBR using the mmWave module of the simulator.

Abstract The paper presents the energy loss minimization of a hybrid energy storage system used in an electric vehicle, composed by a battery and a supercapacitor. The optimization is carried out by searching the optimal power sharing between the energy storage devices. The power sharing factor is defined as a discrete time variable, with constant values during each subdivision of the driving cycle. The elements of the optimal solution vector are the power sharing factors and the time instants that define the subdivisions. The particle swarm optimization algorithms have been validated using the Rastrigin test function, and three versions of the boundary behaviour have been compared in case of the constrained optimization. The algorithms have been tested for the energy loss minimization in case of a simple driving cycle, and their performance has been assessed by statistical analysis for different swarm sizes.

Abstract The paper presents a study regarding the implementation of two representative grid synchronization methods, intended to be used in the control structure of a three phase switch mode voltage rectifier. The methods considered are the Synchronous Reference Frame Phase Locked Loop (SRF PLL) and the Double Synchronous Frame Phase Locked Loop (DSRF PLL), respectively. These synchronization methods have been compared on a real time development system type dSpace 1104 from the point of view of their performance in case of an unbalanced mains voltage system. Finally, the influence of the chosen grid synchronization method on the performance of a synchronous reference frame controlled three-phase switch mode voltage rectifier is studied by simulation, and better results are demonstrated to be provided by the use of the DSRF PLL.

Abstract The presence of the lubricant POE 68 in the refrigeration system changes the thermophysical properties of the refrigerant, which significantly affects the heat transfer and the hydraulic processes. The purpose of this research is to investigate the thermodynamic properties of the R152a, R125, R134a and R123 refrigerant and POE 68 lubricant mixtures at different temperatures from 233,15 to 313,15 K. There have been investigated the values of the densities and kinematic viscosities of the mixtures at different concentrations (100%, 90%, 80%). Finally, it was found that, the density and kinematic viscosity of the R123/POE 68 mixture were most affected by the change of the concentration.

Abstract The aim of this work was to investigate the effect of processing parameters of the electrospinning method on the resulting poly (vinylidene fluoride) (PVDF) fiber diameter. A three factorial Box-Behnken experimental design was employed to study the influence of applied voltage, the capillary-to-collector distance and the applied flow rate on the resulting fiber diameter. We successfully prepared bead-free PVDF nanofibers with fiber diameters ranging from 510-1300 nm. The experimental design analysis did not show significant influence of the studied process parameters under the used boundary conditions on the fiber diameter, thus indicating the robustness of the process.

Abstract Majority of the optimal control techniques can only be applied successfully if the model of the controlled process is known and it is linear. If the system model is nonlinear, then this nonlinear model can be approximated with different simple, linear models. However, these models are valid only in the neighbourhood of the operating points. The success of the control algorithms is highly dependent on the used linearization methods. The aim of the paper is to compare different optimal control algorithms and linearization methods. The presented optimal control algorithms have been also tested in constrained and unconstrained versions.

Abstract In this paper we discuss some image processing methods that can be used for motion recognition of human body parts such as hands or arms in order to interact with robots. This interaction is usually associated to gesture-based control. The considered image processing methods have been experienced for feature recognition in applications involving human robot interaction. They are namely: Sequential Similarity Detection Algorithm (SSDA), an appearance-based approach that uses image databases to model objects, and Kanade-Lucas-Tomasi (KLT) algorithm which is usually used for feature tracking. We illustrate the gesture-based interaction by using KLT algorithm. We discuss the adaptation of each of these methods to the context of gesture-based robot interaction and some of their related issues.

Abstract This paper presents a study regarding the gear hob’s rake face grinding possibilities and its consequences. A simple theoretical lined surface is considered. The mathematical model of the reciprocate meshing of surfaces was applied. It was proven that the proposed form of the rake face cannot be obtained because an undercut of inacceptable extent occurs. It is also proven and sustained by CAD modeling that using a simplified, flat grinding disk, the undercut is avoided, but the phenomenon of transection appears.

AbstractSpecies separation in heterogeneous porous media is a field of interest of many industrial activities. In our investigation, the effect of a single discrete fracture on the thermosolutal convection coupled with the Soret effect have been analyzed. The main results show that the fracture can greatly affect the behavior of the thermogravitational flow and might play a positive role to the separation caused by the Soret effect. Furthermore, the fracture tilted to the cold wall causes a large separation compared to the one tilted to the hot wall with the same angle. Therefore, the separation process could be greatly improved.