Proceedings of the Technical University of Sofia

Abstract: The evolution of automotive Electrical/Electronics (E/E) architectures has undergone a huge technological improvement such as aeronautics, railway architectures. These changes are started from simple mechanically focused systems to complex, software-driven platforms. This study examines the comparison study of E/E architectures of automotives on many aspects from past, distributed Electric and Electronics Architectures to present, zonal centralized architectures across the harness complexity, electronic control units’ functional capabilities/complexities and their numbers in vehicles, cost-efficiency of E/E Architectures, design philosophies. As a plus, this study includes the technologies that lights the future. Moreover, the research examines the shift from distributed E/E Architectures and domain-centralized designs to new zonal and software-defined models, starting with early distributed systems that had discrete ECUs and little integration. This transition reflects the automotive industry's broader move toward software-defined vehicles, where functionality is increasingly determined by software rather than hardware. All these systems will be explained with their advantages and disadvantages.

Abstract: Systematic components of measurement errors that are non-random in nature can lead to a significant decrease in the efficiency of the estimation process. This case occurs, in particular, in inertial navigation systems. Due to the bias in measurements, the Kalman filter estimates will be biased. This study proposes a new discrete Kalman filter that takes into account unknown systematic measurement errors. In this case, the filtering algorithm estimates the differences between two successive states. The differences between two successive measurements are used as measurements, as a result of which the systematic measurement errors mutually exclude each other. Corresponding expressions for estimating the state, the variance of the estimation errors, and the gain coefficient of the difference filter are derived. The proposed filter significantly improves the quality of estimation in the presence of constant or slowly changing offsets in measurements. Theoretical studies and computer simulations are carried out for a one-dimensional dynamic system.

Abstract: The growing reliance on unmanned systems – ranging from aerial and ground vehicles to surface and underwater platforms—demands highly adaptable, secure, and efficient communication solutions. Traditional hardware-based radios often lack the flexibility required to operate in complex and dynamic spectrum environments. Software Defined Radios (SDRs) provide a transformative approach by enabling communication protocols and signal processing tasks to be implemented in software, allowing real-time reconfiguration, multi-band operation, and seamless interoperability across domains. This paper explores the integration of SDRs in various types of unmanned systems, highlighting their advantages in terms of spectrum agility, resilience to interference, and support for mission-specific waveforms. Use cases are discussed across domains such as UAV swarming, autonomous ground vehicles, maritime surveillance, and underwater exploration. Key technical challenges—including size, weight, and power (SWaP) constraints, processing latency, and security considerations—are analyzed. By enabling flexible and intelligent communication capabilities, SDRs are set to become a critical enabler for the next generation of autonomous and connected unmanned systems.

Abstract: The demand for lightweight and high-performance components in the aerospace sector has driven the adoption of Additive Manufacturing technologies. Among several materials, polyamide 12 reinforced with carbon fibers (PA12-CF) offers a promising balance of mechanical strength, thermal stability, and printability, making it suitable for flight-ready components. This study investigates the structural performance of 3D-printed PA12-CF fins for rocket applications through a combination of experimental characterization and analytical modeling. Tensile, fatigue, and dynamic mechanical analysis tests were performed to establish the static and dynamic properties of the material. Modal and vibrational simulations, based on beam theory, were conducted to predict bending and torsional frequencies and to evaluate potential resonance with aerodynamic vortex shedding. Results show that PA12-CF provides superior stiffness and fatigue resistance compared to standard AM polymers, while dynamic analysis identifies critical frequency ranges requiring careful attention. Estimated vibration intensities indicate significant but manageable accelerations during flight. The study proposes that PA12-CF is a suitable material for aerospace-grade AM in laboratory scale, with future validation recommended through finite element analysis, computational fluid dynamics, and flight testing.

Abstract: This paper presents a real-time roll stabilization control system that employs actuation system consisting of a brushless motor with a mounted propeller and a dedicated electronic speed controller (ESC) and an inertial measurement unit (IMU) integrated with an ESP32 microcontroller platform. The system utilizes a low- pass filtering for obtaining accurate gyroscope data, a complementary filter for sensor data fusion, a proportional-integral-derivative (PID) control algorithm with parameter tuning in real-time as well as telemetry readings for monitoring performance and crucial data such as revolutions per minute (RPM). One test was conducted throughout the process which exploits the ESP32 microcontroller as the main platform for collecting and monitoring data as well as controlling the system. The results of the experiment are satisfactory due to demonstrated good roll angle stabilization, done with a relatively quick response time, which allowed us to continue to the next phase of the experiment, where MATLAB would be used for computation and control while the ESP32 would be utilized as a pure data bridge. When all of the work is done and backed with acceptable test results this stand can be used for applications including but not limited to teaching and integrating artificial intelligence (AI) agents for autopilots.

Abstract: The paper presents the results of a student project to study the aerodynamic characteristics of two common types of wingtip devices in the wind tunnel of the National Center for Mechatronics and Clean Technologies (NCMCT). The wingtip devices examined were canted winglet and wingtip fence. As a baseline configuration the wing without wingtip device was used. The tests were conducted at airspeeds of 12 m/s corresponding to Reynolds number of approximately 10000. The results correspond well to the theoretical expectations and prove the advantage of canted winglet over the other configurations. The results can be used in the future for the purpose of adjusting and validating CFD models of wingtip devices for low-speed small unmanned airplanes.

Abstract: A surface model of the variation in operating costs of freight block trains with constant number of wagons in the composition has been presented in the report. The results refer to the movement of freight trains with a constant composition between the initial train-forming and final for the train railway station. The study has been conducted for freight trains running on domestic rail lines in the Republic of Bulgaria. The model takes into account the costs for preparing and operating a freight train, related to: the charges for use of railway infrastructure; the costs of using electric locomotives; the costs of electricity for traction power; the costs of paying the labour of locomotive`s drivers and the costs related to the activities of preparing and check the train and load at the initial and final railway stations. The study has been carried out for freight block trains with a gross mass varying between 400 and 2,200 tons and for train route length varying between 100 and 500 km. The two parameters – the route length and gross mass – form the polygon of the graphical surface model. The results have been presented through the direct relative operating costs related to three widely used in railway transport parameters - the transportation work performed, travelled wagon-kilometres and number of wagons transported by train. The results of the study show, for the conditions it has been conducted, that the relative costs of the trains vary according to the different parameters respectively into intervals 10.31÷43.66 Euro per 1000 gross tkm, 0.61÷1.43 Euro per a wagon kilometre and 87.32÷518.52 Euro per a transported wagon by the train.

Abstract: Настоящото изследване представя количествена оценка на газовите емисии от въздухоплавателни средства по време на стандартния цикъл на излитане и кацане (LTO) на летище „Васил Левски“за 2023 година. Прилага се методологията, разработена от Международната организация за гражданска авиация (ICAO), която обхваща четирите основни фази на LTO цикъла: рулиране, излитане, набор на височина и заход за кацане. Анализът се фокусира върху най-често използваните типове въздухоплавателни средства, опериращи на летището. Оперативните данни за 2023 г. са предоставени от оператора на летище Васил Левски- София "SOF Connect. С използването на емисионният индекс за всеки газов замърсител и оперативните данни са изчислени емисиите на азотни окиси (NOₓ), неизгорели въглеводороди (HC) и въглероден окис (CO). Целта на изследването е да предостави надеждна основа за бъдещи мерки, насочени към намаляване на екологичното въздействие на авиацията на местно ниво.

Abstract: The study presents the development of computational models for the support component of the drawbar device used in railway wagons. The aim is to create reliable finite element method (FEM) models that replicate the real operational behavior of the support plate under static and dynamic loads. The methodology includes an analysis of relevant European and international standards (EN 15566, UIC 520, UIC 826, TSI), identification of load cases for drawbar systems with nominal forces of 1.0, 1.2 and 1.5 MN, and evaluation of material fatigue using Miner’s rule and the Goodman criterion. Numerical simulations were carried out in ANSYS Workbench™ and DesignLife™, and material properties of ductile cast iron GJS 600-3 were applied. The obtained results indicate that the developed models realistically describe the stress-strain state of the support element and predict reliable fatigue performance for the required 30-year service life.

Abstract: A significant problem in the operation of long freight trains is the occurrence of excessively large forces in the couplers of the railway rolling stock. These forces are the subject of research by various authors around the world, mainly from countries where the use of long-length trains is typical. This report studies the existing methods for studying the longitudinal dynamics of trains with a focus on studies related to their braking. For this purpose, the main types of braking systems used in railway transport are analyzed first of all and accordingly their influence on longitudinal forces. The various factors influencing the forces that arise in the longitudinal direction are systematized and an in-depth study of the existing methods for their study is done.

Abstract: Vehicles are a serious source of air pollution, especially in urban areas. Real Driving Emissions (RDE) testing procedures have been introduced in the EU to determine emissions from cars during on-road operation. This study presents a method for determining emissions from a car under different driving modes using a dynamometer. The measuring equipment and testing methodology are presented. A number of experiments have been conducted to determine average emissions. The presented method can be used as an additional procedure to annual technical inspections and as a complement to real road conditions for a more accurate and correct determination of harmful substances emitted into the atmosphere.

Abstract: This paper explorers the algorithms and real-time deployments for smart traffic lights from 2015–2025. It introduces a taxonomy of control paradigms (centralized optimization, decentralized heuristics, max-pressure, model predictive control) and learning methods, with emphasis on single- and multi-agent reinforcement learning. It compares coordination strategies across intersections, simulation-to-reality transfer and federated training workflows, and multiobjective formulations balancing delay, emissions, safety, and priority for public transport and emergency services. Evidence from pilots and city-scale platforms is compiled to quantify travel-time and throughput gains. A benchmarking map classifies approaches by data, optimization strategy, and maturity of adoption, exposing gaps in generalization, rare-event resilience, and interpretability. The paper closes with guidance on hybrid edge–cloud architectures, standardized interfaces, and reproducible evaluation protocols covering heterogeneous networks and operating conditions.

Abstract: The growing global scarcity of raw materials, combined with the rising economic costs of manufacturing, has increasingly directed research and industrial efforts toward the development of innovative products designed with improved material efficiency. These efforts typically focus on minimizing material consumption, adopting more cost-effective and energy-efficient production technologies, and reducing reliance on manual labor through automation. Such strategies not only contribute to lowering the overall production cost of components but also support improvements in operational efficiency, for instance by enabling even slight increases in the payload capacity of railway freight transport. Nevertheless, optimization of this kind must not come at the expense of safety. On the contrary, the requirements imposed on newly manufactured components in the railway sector have become progressively more stringent, reflecting both regulatory demands and the expectations of operational reliability. In the present study, a draw gear support designed in accordance with EN 15566 was investigated. A topology optimization procedure was carried out to reduce the mass of the component, followed by a stress–strain analysis and a fatigue assessment to evaluate its structural performance and durability.

Abstract: This article presents the results of a study of the soundproofing characteristics of three types of doors – glass, fire-resistant /with mineral wool filling/ and wooden /plywood filled with wooden profiles/. Unlike standard laboratory tests, the aim of the study is to measure the real soundproofing of doors in the conditions of their final operating environment, i.e. at the installa-tion site. The measurements were carried out in several rooms with different functions, using precise devices for determining the sound pressure level. The results of the study were analyzed. The results show that despite the different construction, both types of doors demonstrate limited soundproofing capabilities, especially at low and medium frequencies. The conclusions drawn emphasize the need to take additional measures or alternative solutions when it is necessary to ensure a high value of the soundproofing characteristics of the doors used.