machinery
Not a member yet
8395 research outputs found
Sort by
INACCURACY ANALYSIS OF CHEBYSHEV’S MECHANISM
No full textConverting rotary motion into rectilinear motion can be very useful in mechanical applications. This type of conversion is mostly achieved using specific types of joints. However, it can be convenient to use mechanisms that can convert rotary motion into rectilinear motion for a specific engineering purpose. The mechanisms with this possibility are called Straight-line generators. The mechanism described in this paper is part of this group, and it is called Chebyshev's mechanism. Chebyshev's mechanism consists of four connected links with proportional dimensions. It is important to point out that this mechanism and most mechanisms from the Straight-line generators group do not generate the perfect straight line. The generated line is an approximate straight line with a changeable deviation from the perfect straight line. This paper shows how the parameters of the mechanism impact the deviation, how the generated line can be described, and what the generated line specifics are.Editor: Dr Boris Dumnić, full professor, dean
Technical treatment and design: Dr Đorđe Vukelić, full professor
Dr Milana Ilić Mićunović, assistant professor
MSc Aleksandar Milošević, assistan
Control and physical intelligence
No full textChapter 5 focuses on biological and synthetic control/intelligence. This chapter of the 2nd edition includes discussion of deep learning, do-it-yourself (DIY) robotic projects, popular microcontrollers, contributed by Marko Popovic as well as material contributed by new co-author Mihailo Lazarevic on fractional PID control approach. All these are quite relevant in the context of biomechatronics research
CARNOT BATTERY BASED ON PUMPED THERMAL ENERGY STORAGE WITH REGENERATIVE PEBBLE BED AND STEAM ACCUMULATOR
No full textA novel design of the Carnot battery is proposed based on the thermodynamic cycle consisting of water heating and boiling by heat pumps, steam superheating by compression, high-temperature thermal energy storage in the pebble-bed regenerative porous structure, steam accumulation in the pressurized steam accumulator vessel and steam turbine expansion. The heat pumps and steam compressors are powered by the electricity surplus production from intermittent renewable power sources – solar power plants and wind turbines. The heat pumps are based on the CO2 supercritical cycle, which provides fresh steam generation with a sufficiently high temperature to serve as the input for subsequent compression to a superheated state. The heat is stored in two types of storage devices: steam generators and pebble beds. Steam accumulators enable efficient, cheap and high-capacity thermal energy storage due to the water latent heat of condensation and evaporation, which inherently provides high capacity of thermal energy storage per unit mass and volume of accumulator. The steam accumulator charging and discharging is performed under the sliding pressure and thermal non-equilibrium between the liquid and steam phases in the accumulator vessel. The consequences of such transient behaviour on the Carnot battery operational conditions are evaluated. The porous pebble beds store and release heat at elevated temperature, which provides a superheated steam at the steam turbine inlet. Namely, the pebble beds are alternately heated by the superheated fresh steam and cooled by the saturated steam from the steam accumulator, which is superheated in the pebble bed before entering the steam turbine. The design of the storage facility is based mainly on the equipment confirmed as mature technology in engineering practice. Evaluated are the cycle operational parameters, equipment dimensions and capacities, as well as the roundtrip thermodynamic efficiency of the charging and discharging cycle
HYBRID KINEMATIC MACHINE TOOLS
No full textZnačajan pravac za inovacije i razvoj novih mašina alatki je razvoj mašina alatki sa hibridnom kinematikom (MHK) koja ima odgovarajuće prednosti serijskog i paralelnog mehanizma. Ovaj rad razmatra i daje pregled razvijenih domaćih konfiguracija mašina sa hibridnom kinematikom. U radu su prikazane originalne konfiguracije mašina na Mašinskom fakultetu Univerziteta u Beogradu i Fakultetu tehničkih nauka Univerziteta u Novom Sadu.Significant direction for the innovation and development of new machine tool is a developing a hybrid kinematic machine (HKM) which have the respective advantages of serial and parallel mechanism. This paper considers the developed domestic configurations of HKM. The paper presents the developed original HKM configurations in University of Belgrade Faculty of Mechanical Engineering and Faculty of Technical Science University of Novi Sad
Analysis of failures of power pack of diesel hydraulic multiple unit series 711
No full textThe passenger diesel-hydraulic train series DMU 711 is one of the newer trains in Serbia, owned by “Srbija voz”. The train consists of two coaches. Each coach is equipped with one driving bogie powered by a diesel engine coupled with a hydraulic transmission and one free bogie. Diesel engines, hydraulic transmissions, cooling and heating systems, and many other pieces of equipment and devices were placed in one assembly - a power pack. During operation, the owner noticed that the train was often out of service because of failures in the power pack. The main reason for the failure of the power pack is overheating. Radiators, as a part of the cooling and heating system, were placed along one side of the power packs. During the inspection, it was observed that the radiators are heavily contaminated with vegetation, dust, and debris picked up during operation. The maximum designed speed of the train is 120 kilometres per hour, but most often running speed is significantly lower. The owner informed the producer that DMU has had problems with overheating from the start of service. Analysis of the train behaviour in different weather conditions and seasons, over the years, gave a clearer image of the overheating problem. The most common problem caused is the low running speed in combination with dust, grass, and other dirt that trains collect in the cooling radiators. This leads to radiator clogging, decreasing cooling capacity, and therefore overheating. When the operating temperature of the diesel motor exceeds the limit value, the safety system of the power pack is activated, causing it to shut down. Next to the mentioned problem, one more is directed to the common cooling-heating system for the power pack and passenger area, which is obvious under-dimension, especially for the summer days. Considering the reasons for the power pack frequently malfunctioning, one of the solutions for resolving the problem is the separation of a cooling-heating system for the power pack and passenger area. Additionally, analyses showed that displacement of the cooling system on the roof is an even better solution, to exclude dirt impact and improve airflow and cooling. Both solutions can be implemented during regular repair or modernization of DMU. Additional analyses will be conducted after the owner provides source documentation from the producer. Finally, the possibility of replacing the power pack with one of the improved generations installed in the newer DMU 711 should be explored for efficiency, although it may not necessarily be the most cost-effective solution
Comparative analysis of ABS materials mechanical properties
No full textAdditive Manufacturing (AM) has shown rapid development during the last decades. More commonly known as 3D printing, this technology offers significant benefits for the fabrication of physical models with complex geometries. This technology started as a valuable tool for prototyping purposes but is considered for general manufacturing due to the production cycle shortening and less (if none) material waste. Out of seven possible AM technologies, this research covers three of them, namely: Fused Deposition Modeling (FDM), Stereolithography (SLA), and Digital Light Processing (DLP). Although, ABS thermoplastic material is a thoroughly researched AM material, a new resin material also called ABS is an interesting object for research. Hence, the aim of this paper is to acquire the tensile properties of this material and to compare them to the “original” ABS thermoplastic material
Tensile strength and stiffness properties of additively manufactured PET-G polymer-based composite plates reinforced with different weight fractions of short carbon fibers
No full textTensile properties of composite thin-plate specimens additively manufactured from two commercially available filaments composed of PET-G polymer loaded with 15 wt% and 30 wt% of short carbon fibers (SCF) are experimentally determined, together with neat PET-G specimens tested for comparison. Relatively high overall average values of ultimate tensile strength were obtained for the SCF reinforced specimens (61.6 MPa and 52.2 MPa, respectively for specimens with 15 % and 30 % of SCF), compared to the value obtained for neat PET-G specimens (43.9 MPa). Similarly, the average value of modulus of elasticity for 15 % SCF specimens (5990 MPa) was higher than the value obtained for the ones with 30 % of SCF (4752 MPa), again both being higher than the value reached with neat polymer (1694 MPa). Scanning electron microscopy (SEM) was used to analyze specimens’ fracture surfaces. SEM images of 30 % SCF specimens revealed higher presence of voids compared to 15 % SCF specimens
A comprehensive review of Maritime Bibliometric Studies (2014–2024)
No full textA significant number of Maritime Bibliometric Studies (MBSs) have been published over the past years. The present research aims to evaluate a large amount of the relevant literature to characterize Maritime Industry Areas (MIAs). A bibliometric analysis of MBSs is conducted to evaluate important MBSs. The performed analysis examines the main features of each MBS, relationships between them, and their impact on the development of MIAs. A unique approach is developed based on a bibliometric methodology to study previously published MBSs through the performance analysis, trend analysis, statistical analysis, bibliographic coupling analysis, word clouds analysis, and conceptual thematic map analysis. To provide a high level of accuracy and reliability of mapping and analysis, various bibliometric software tools are used. The visibility and readability of the obtained results aim to establish the new pathways for bibliometric studies that could be easily applied to a broad spectrum of research areas. The outcomes of the conducted analysis confirm that MBSs present very accumulative research paths in MIAs with a continuous change in dynamics that well characterize this research domain and highlight the conceptual structure of MIAs. The findings showcase journal and publication trends, identified research topics and sub-topics, the main study attributes, and the most influential MBSs with the highest scholarly impact. Some interesting future research directions that can be explored for MBSs in the following years are comprehensively described. Last but not least, the important role of bibliometric methods for evaluation of the existing and future studies related to MIA applications is discussed in detail as well
DEVELOPMENT OF EXOSKELETON FOR HANDHELD POWERTOOLS
No full textHandheld power tools, such as electric drills and electric screwdrivers, are widely used today. They are applied in households, the furniture industry, the automotive industry, and even in construction and interior design. Major companies that produce handheld power tools (e.g., BOSCH, MAKITA, BLACK&DECKER, STIHL, HILTI) invest significant material and financial resources in improving existing products and developing new ones to outperform the competition in the international market and achieve greater profit. One way to overcome existing problems in the use of handheld power tools is to develop and design external systems for their easier use and control – exoskeletons. This is precisely the goal of the prototype developed at the Faculty of Mechanical Engineering, University of Belgrade, within the proof-of-concept project funded by the Innovation Fund of the Republic of Serbia. It has been observed that almost all handheld power tools available on the market require the use of both hands during operation, demand significant physical strength from the user, and generate substantial vibrations that are transmitted to the user, making the use of handheld power tools even more challenging. To overcome these problems, the primary function of the developed exoskeleton has been broken down into elementary functions, for which appropriate actuators have been defined, followed by the development of several alternative solutions, from which the best was further developed into a functional prototype with multiple benefits for the user. The developed exoskeleton transfers the loads typically handled by the user's second hand to the forearm of the first hand using a lever system, preventing wrist overload while maintaining precise control and handling of the tool. This allows the user's second hand to remain free for other tasks, such as holding the workpiece. Additional force in the tool's direction is provided by the exoskeleton being supported on the user's upper arm, utilizing body mass along with the biceps and other arm muscles during operation. Vibrations from the tool are minimized by incorporating a vibro-elastic element in the exoskeleton, significantly reducing vibration transfer to the user. Additionally, the handheld power tool can be used in various positions – above the head, downwards (towards the floor), at shoulder, or waist level. Also, during the development of the exoskeleton, special attention has been paid to the safety of the user, so the handheld power tool is connected to the exoskeleton by a detachable joint, allowing the tool to be quickly discarded if necessary. It is important to note that during the development of the exoskeleton, all guidelines of the German association VDI were applied, significantly accelerating the product development process, along with the use of available rapid prototyping and 3D printing technologies. Finally, all solutions presented have been submitted for patent protection, with registration currently underway (patent application no. 2024/0025)
