Machinery - Repository of the Faculty of Mechanical Engineering, University of Belgrade
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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
ENHANCING INDUSTRIAL WATER MANAGEMENT: INNOVATIONS IN WASTEWATER RECYCLING
No full textWater treatment is the process of raising water quality so that it can be used for drinking, industrial activities, irrigation, and other uses. There are several physical, chemical, and biological procedures used to remove contaminants from water. This paper examines cutting-edge techniques for recycling wastewater in commercial buildings to reduce water usage. Industrial facilities face challenges in managing water resources sustainably and minimizing their negative environmental impact due to the growing global demand for water and the implementation of more stringent environmental standards. Various wastewater recycling methods are analyzed, such as biological treatments, membrane processes, advanced oxidation techniques, and the incorporation of renewable energy sources. The effectiveness, long-term viability, and environmental impacts of diverse recycling techniques are investigated by examining case studies from various industrial sectors. The research findings highlight the benefits and drawbacks of each approach, providing best practices and ways to implement them in industrial facilities. This paper aims to show improvements in industrial water treatment procedures to accomplish the objectives of sustainable development and water resource protection
Fractional order time delayed acceleration feedback control of inverted pendulum system
No full textThe issue of human balancing in the sagittal plane using fractional order time delayed acceleration feedback is studied in this contribution. The problem of asymptotic stability of closed-loop fractional order neutral time delay system is solved by applying the D-decomposition approach. Stability regions in the control parameters space are determined using this method. Special attention was focused on the consideration of the influence of the time delay on the asymptotic stability of the system. Finally, simulation results are presented to illustrate the superiority and effectiveness of the proposed method
Cavitation erosion of samples based on cordierite-talc ceramics
No full textIn the paper, the cavitation resistance of cordierite samples with the addition of 10%, 15% and 20% talc, sintered at 1200ºC, was investigated. The ultrasonic vibration method with a stationary sample according to the ASTM G32 standard was applied. The formation and development of damage to the surface of the samples was monitored using a scanning electron microscope and the level of damage to the surface of the samples was quantified using image analysis. The change in the mass of the samples as a function of the cavitation time was monitored to determine the cavitation rate. By measuring the mass loss and morphological analysis of the pits formed on the surface of the sintered samples of the cordierite-talc ceramics, the mechanism of degradation and resistance to the effect of cavitation was monitored. The obtained results were compared with the results of earlier tests of cavitation resistance of sintered cordierite samples. The addition of talc in the mixture with cordierite significantly improved cavitation resistance of the sintered material compared to sintered pure cordierite. The tests were done to see the potential application of this material in hydrodynamic conditions, especially because of the strong corrosion resistance of these refractory materials
DIRECT AND INVERSE KINEMATICS FOR 6DOF ROBOT BASED ON SCREW THEORY
No full textIn the modern age, robotics is gaining an ever-increasing role in shaping modern life, hence
why innovations are increasingly more directed towards this interdisciplinary scientific field.
The structure of a robot is complex and with a plethora of different ways to construct and
control it, here we provide an elegant geometric approach for achieving the desired task by
using screw theory [1]. As proved by the Chasles-Mozzi theorem, all motion can be obtained by a rotation around
a fixed screw axis and a translation along the same which lends itself naturally to the
representation of motion by screws. This is attained by an exponential coordinate
representation where given a screw axis and an angle we may find a matrix defining our motion
from a given coordinate frame. But why stop there? Not only motion, spatial velocities and
forces are defined within screw theory as twists and wrenches that act on inertial coordinate
frames attached that are instantaneously coincident to a fixed or even possibly moving frame.
However, unlike other ways of describing a robot's motion such as the Denavit-Hartenberg
method which has an excessive amount of coordinate frames, or the use of Euler angles (in
combination with position vectors) which have singularities at points, screw theory uses a less
cumbersome mathematical apparatus and uses implicit representations thereby avoiding
singularities. The mathematical foundation of screw theory lies on the foundation of the SO(3)
and SE(3) Lie groups and their algebras so(3) and se(3) which represent rigid body rotations
and motions in three-dimensional space respectively.
By far, the largest part of screw theory is rooted in linear algebra which ties in nicely to
implementation in practice. Everything described in this paper will be implemented using
Python and the Robot Operating System (ROS) on a six-degree-of-freedom robot manipulator
Niryo One. In Fig. 1(a) we have the basic geometric description of the Niryo One robot where
we have the position of each joint and its direction of rotation. Next, we define a fixed space
frame at the bottom of the robot and a moving body frame at the end-effector. Putting this all
together we have a kinematic diagram.
In robot kinematics, we use the Product of Exponentials to determine the forward kinematics
of a robot-given a set of joint angles, find the representation of the end-effector. While this is
straightforward, a more interesting problem which has garnered a lot of interest and is being
actively researched is the inverse kinematics-given a representation of the end-effector, find
the joint angles that correspond to it. There are two main ways of solving this problem,
analytically and numerically, both of which have their advantages and drawbacks. The Paden-
Kahan subproblems [2] seek to break apart the inverse kinematics into subproblems that have
a known analytical solution. On the other hand, fundamental to numerical nonlinear rootfinding
is the Newton-Raphson method which can find approximate solutions within a given
tolerance. But analytical solutions, if they exist, may not always have a closed-form solution
or their computation may be quite involved. The numerical approach, while usually efficient
and precise to a practically arbitrary degree, may not always converge with a given initial value.
Here we suggest a synergetic approach for robots that do not yield to Paden-Kahan
subproblems by a slight amount. It involves finding an approximate analytical solution using
the Paden-Kahan subproblems and using that as an initial value for the Newton-Raphson
method
Influence of build orientation and different printing angles on impact toughness of carbon-reinforced PET-G FDM material
No full textCarbon-reinforced polyethylene terephthalate glycol (PET-G) material is used in additive manufacturing (AM) for the production of moderately loaded polyester-based parts. Scientific papers show that the mechanical properties of additively manufactured specimens are substantially influenced by their build orientation and printing direction angle. This paper explores the additional influence of short carbon fibers on the impact toughness of composite specimens. In this study, low-energy instrumented Charpy test was used as an experimental method for evaluating the impact behavior of material. Experimental evaluation of impact toughness in the case of AM composite specimens fabricated with different build orientations and printing angles was performed. The impact tests were carried out on 5 specimens per batch (a total of 30 specimens). The obtained results from an instrumented pendulum were compared between different specimen groups to have an insight into the influence of build orientation and printing angle on short carbon fiber reinforced PET-G material. It was confirmed that different build orientations and printing direction angles (0° and 90°) strongly influence the final mechanical properties of this material
THE SIMULATION OF MACHINING FREE-FORM SURFACES ON A MILLING MACHINE WITH A HORIZONTAL ROTARY AXIS
No full textU okviru ovog rada je prikazana je simulacija procesa obrade skulptorskih površina na mašinama sa horizontalnom obrtnom osom. Predmet ovog rada je četvoroosna glodalica LOLA VMC4 iz klase mašina MultiProDesk, strukture A'Y'OXZ. Za potrebe programiranja ove mašine, razvijen je postprocesor baziran na jednačinama inverzne kinematike. Deo za koji se definiše obrada je deo kompleksne geometrije koji služi kako bi se verifikovala obrada složenih površina na razmatranoj mašini, kao i mogućnost softvera za postprocesiranje za proračun putanje alata pri obradi kompleksnih površina. Za generisanje početne putanje alata korišćen je CAD/CAM softverski paket PTC Creo Parametric. Obrada dela je izvršena u okviru virtuelnog tehnološkog okruženja u softverskom paketu Vericut.This paper presents a simulation of machining a part with a complex, freeform surface on a milling machine with a horizontal rotary axis. The machine on which this simulation is based is the four-axis milling machine with a horizontal rotary axis and the kinematic structure A'Y'OXZ, LOLA VMC4 from the machine class MultiProDesk. A custom-made postprocessor with integrated machine kinematics was used to generate the toolpath for this machine. The test piece was chosen with specific free-form surfaces intended to evaluate the performance of the machining system and
the postprocessing program under various operational scenarios The initial toolpath was defined using the CAD/CAM software PTC Creo Parametric. The virtual machining of the said part was done in a virtual machining environment using the Vericut software.Za izdavača: Dekan, dr Vladimir Popović, red. prof.
Tehnički urednici:
Prof. dr Saša Živanović, Doc. dr Miloš Pjević , Doc. dr Dušan Nedeljković, Lazar Matijašević, mast. inž. maš.
Štampa: Planeta prin
Comparison of Numerical Simulation Results and Experimental Measurements of Swirling Flow in the Pipe behind the Axial Fan Impeller
No full textThis is an extended abstract on two pages, published in the Booklet of Abstracts, 2nd International Conference on Mathematical Modelling in Mechanics and Engineering, Ed.: I. Atanasovska, Mathematical Institute of the Serbian Academy of Sciences and Arts, Belgrade, Serbia
Simulation of parallel kinematic machine with specific solutions of the passive translatory joint
No full textThe paper discusses ideas for the development of new 3-axis parallel kinematic machines, which have one dominant elongated axis, with the application of specific solutions for a passive translatory joint, which uses mechanisms that generate a straight line, such as the Chebyshev's mechanism.For publisher: PhD Saša Prodanović, associate professor
Editors: PhD Biljana Marković, full professor, PhD Miroslav Milutinović, full professor ,PhD Davor Milić, assitant professo
Horizontal Boring Mill Machine Feedrate Revitalization with DC Converter and PLC
No full textThis paper presents the revitalization of the feedrate system of the Stankoimport 2620B horizontal boring mill machine using a PLC controller and a DC converter with special reference to the way of adjusting the speed and current loop parameters of the converter using Matlab and OPC server. Using Matlab, a model of auxiliary movement was created and simulated. The simulation model was taken as a reference and connected to the PLC and the DC converter using the OPC server, and based on the comparison of the response difference between the simulation model and the real system, the parameters of the PI controller of the DC converter were tuned. Revitalization and reconstruction was carried out using modern components for the regulation of auxiliary movement. During the reconstruction, the components were integrated into the old system, which represents a special challenge, because the control system dating from 1970 was combined with the new control system. New electrical documentation was designed, software for the PLC controller was developed and written. After revitalization, testing was carried out in real conditions in metal machining and functionality was proven