Cybersecurity issues in motion control – an overview of challenges

The fourth industrial revolution known as Industry 4.0 brings digitalization of manufacturing processes to a new level through ubiquitous interconnection and real-time information flow between information technologies (IT) and operational technologies (OT) as parts of Industrial Control Systems (ICS). This information flow is not limited to but expands beyond factory walls enabling manufacturing systems to adapt quickly and efficiently to changing customer demands and diversified products. The adaptation is carried out through physical and/or functional reconfiguration of manufacturing systems where Industrial Internet of Things (IIoT) based on Cyber-Physical Systems (CPS) represents the key technical enabler. These changes result in a transition from centralized to distributed control systems architecture where the whole control task is achieved through intensive cooperation between smart devices (e.g., sensors and actuators) with integrated communication and computation capabilities. However, introducing IIoT in ICS brings about new cybersecurity issues due to increased communication between system elements and connection to the global network, making ICS vulnerable to different cyber-attacks with potentially catastrophic consequences. Recently, the research in ICS cybersecurity has intensified leading to significant results for continuous time and discrete events-controlled systems. However, cybersecurity issues in motion control systems that are frequently employed in different manufacturing resources such as machine tools and industrial robots were not sufficiently explored. This work provides an overview of the cybersecurity related challenges in motion control tasks

Influence of Raster Angle on Tensile Properties of FDM Additively Manufactured Plates made from Carbon Reinforced PET-G Material

Tensile properties of thin plate specimens made from short carbon fiber reinforced PET-G material are experimentally evaluated for various raster angles (printing directions). In additive manufacturing (AM), raster angle is recognized as one of the key printing parameters which strongly influences the strength and stiffness of the final part. The relatively high average value of ultimate tensile strength was obtained for specimens printed with the 0° raster angle, compared to the value obtained for specimens printed with the 90° raster angle - 52.2 MPa and 25.4 MPa, respectively. Similarly, noticeably higher average value of modulus of elasticity was obtained for specimens printed with the 0° raster angle, compared to the value obtained for specimens printed with the 90° raster angle - 4752 MPa and 1569 MPa, respectively. Scanning electron microscopy (SEM) was used for analysis of specimens’ fracture surfaces. SEM images revealed considerable volume fraction of voids (porosity). Тhe porosity, together with weak bonding between two adjacent rasters, could be one of key factors for poor tensile properties of samples printed with rasters perpendicular to direction of load application (90° raster angle

LOAD-CARRYING CAPACITY OF SHEAR-LOADED BOLTED JOINTS

Bolted joints are the most common and primary form of joints in most machines. The directions of research in this area mostly relate to strength, stiffness, load-carrying capacity, causes of failure, temperature influences etc. Fitted and clamped group bolted joints shear-loaded with torque are analyzed in this paper. A comparative analysis of their load-carrying capacity was performed. When the factor of safety (FOS) ratio of fitted and clamped bolts was determined, the geometric characteristics were varied so that this ratio was reduced, i.e. their load-carrying capacities became close. The carried-out research aims to provide the constructor with relevant data for the selection and application of the appropriate type of bolted joint. Using an analytical research method, the nominal thread diameter of the bolts, the number of bolts in a group joint, and the pitch diameter on which the bolts are mounted were varied. Useful practical results have been obtained, based on which the designer can make a choice of the appropriate type of shear-loaded bolted joint (fitted or clamped) and combine different influence parameters of the group joint (number of bolts and pitch diameter) to achieve the same load-carrying capacity or, in the case of different load-carrying capacity, to know in what relation would be their FOS

The preformances of air cooled heat exchangers with water spraying

Ваздушни хладњаци се у термотехници и процесној техници често примењују уусловима када су температуре амбијенталног ваздуха јако високе и знатно више одтемпература усвојених у прорачунима, па није могуће одвести прорачунску количинутоплоте. Потребна топлотна снага се у таквим случајевима може достићи ако се околниваздух орошава (влажи) распршивањем воде на улазу у апарат, јер се тиме снижаватемпература ваздуха, па се температурна разлика повећава, као и размењена количинатоплоте. Појава слоја влаге на размењивачу топлоте кључно мења топлотне и струјнеперформансе оваквих апарата.Детаљнија анализа расположиве литературе показала је да радови у којима сеистражује проблематика размене топлоте и супстанције на површини оребреногразмењивача топлоте са напрскавањем воде нису бројни, те се доводи у питањемогућност реалне примене података доступних у литератури за потребе инжењерскихпрорачуна при експлоатацији оваквих апарата, односно коју методологију прорачунакоефицијената прелаза топлоте и влаге препоручити као релевантну у одређенимусловима.У овој докторској дисертацији испитивани су различити режими рада ваздушниххладњака са оребреним цевима при њиховом напрскавању водом на улазу у апарат.Експериментална истраживања рада предметних размењивача топлоте су спроведена насамостално пројектованој инсталацији, која је направљена и монтирана у оквирутоплотне подстанице Машинског факултета у Београду. Развој физичког и прорачунскогмодела, заснованог на истовременом транспорту топлоте и супстанције, битан је заодређивање и прорачун релевантних параметара рада размењивача топлоте. Применомтеорије сличности, уз одговарајуће статистичке методе, одређене су меродавнекритеријумске зависности за израчунавање пада притиска, као и коефицијената прелазатоплоте и супстанције, тј. одређени су изрази погодни за инжењерску праксу.Ова докторска дисертација представља наставак истраживања проблемапроналажења поуздане прорачунске процедуре за одређивање коефицијената прелазатоплоте, супстанције и трења за широк опсег Рејнолдсових бројева и различитегеометријске карактеристике цевних размењивача топлоте са оребрењем који сеиспитују на Машинском факултету у Београду.In HVAC&R and process engineering, air coolers are often used in the conditions whenambient air temperatures are very high and significantly higher than the temperatures acceptedin the calculations, and hence it is not possible to remove the calculated amount of heat. Inthese cases, the required heat can be reached if the surrounding air is humidified by sprayingwater at the entrance to the apparatus, because this lowers the air temperature, so thetemperature difference increases, as well as the amount of exchanged heat. The appearance ofa layer of moisture on the heat exchanger crucially changes the thermal performance and flowpattern of such apparatus.A more detailed analysis of the available literature shows that the papers whichinvestigate the problem of heat and substance exchange on the surface of the finned heatexchanger with water spraying are not numerous. Hence, the possibility of real application ofdata available in the literature is questionable when it comes to engineering calculations inexploitation of these apparatus, as well as to recommending relevant methodology forcalculating the coefficients of heat and mass transfer in certain conditions.This doctoral dissertation examines different operating regimes of air coolers with finnedtubes during their spraying with water at the entrance to the apparatus. Experimental researchon the operation of these heat exchangers was conducted on a self-designed installation, whichwas made and installed within the heating substation of the Faculty of Mechanical Engineeringin Belgrade. The deployment of a physical and computational model, based on thesimultaneous transport of heat and substance, is important for determining and calculating therelevant operating parameters of heat exchangers. Applying the theory of similarity, along withthe appropriate statistical methods, the relevant criteria equations for the calculation of pressuredrop were determined, as well as the coefficients of heat and mass transfer, i.e. certainequations suitable for engineering practice.This doctoral dissertation is a continuation of research on the problem of finding areliable calculation procedure for determining the coefficients of heat and mass transfer andthe coefficient of friction for a wide range of Reynolds numbers and different geometriccharacteristics of tubular heat exchangers with fins that are tested at the Faculty of MechanicalEngineering in Belgrade

A novel method for calculation of the CO2 concentration impact on correlation between thermal comfort and human body exergy consumption

The majority of studies dealing with the correlation between human body exergy consumption and thermal comfort use adopted, constant values of metabolic rate for appropriate activity level. Taking into account correlations between metabolic rate and the occupant’s exhaled CO2 volumetric flow rate, this study proposes a novel method for the calculation of metabolic rate using measured CO2 concentration in the indoor air. Using measured values of the air and radiant temperature, relative humidity and air velocity, and calculated values of metabolic rate, the human body exergy consumption rate and corresponding Predicted Mean Vote (PMV) are calculated. Moreover, a novel polynomial relation between them is proposed. Results show that metabolic rate values vary in the range of 0.97 to 1.54 met which leads to significantly wider range of PMV and human body exergy consumption rate comparing to the assumed value of 1.2 met for sedentary school activity. According to the obtained relation, the minimal value of the human body exergy consumption rate occurs for PMV = − 0.02. Results of this study imply that treating CO2 concentration as variable does have an impact on the thermal comfort assessment, providing enhanced correlations between thermal comfort and human body exergy consumption rate

Enstrophy Study of the Turbulent Swirling Flow in Pipe

Turbulent swirling flow is characterized by significant vortex fluctuations, intensive diffusion processes and energy cascade transfer from larger to smaller vortices over a continuous spectrum of wave numbers. The dissipation of the kinetic energy of turbulence occurs in the smallest vortices, because in these areas, both the velocity gradients and the deformation velocities are the largest. In this paper is analyzed turbulent swirling flow in pipe, generated by the axial fan impellers for three various blade angles (22°, 26° and 30°). Vorticity, enstrophy and lambda 2 values are calculated in order to study the structure of the generated turbulent swirling flows. Axial fan impeller operates in the region of lower flow rates, and it is shown that blade angle doesn’t influence much on the integral flow parameters, as well as on the enstrophy distribution. It is, also, shown that the dissipation of the kinetic energy of turbulence is associated with the vorticity fluctuations, i.e. with turbulent fluctuating enstrophy. All these distributions are obtained by use of the high speed particle image velocimetry data and provided velocity fields. Enstrophy is directly related to the kinetic energy, i.e. it corresponds to dissipation effects in this flow. It has maximum in small vortices, i.e. in shear layer, that surrounds vortex core region, where the process of turbulence kinetic energy dissipation occurs

Reinforcement Learning-based Collision Avoidance for UAV

One of the significant aspects for enabling the intelligent behavior to the Unmanned Aerial Vehicles (UAVs) is by providing an algorithm for navigation through the dynamic and unseen environment. Therefore, to be autonomous, they need sensors to perceive their surroundings and utilize gathered information to decide which action to take. Having that in mind, in this paper, the authors designed the system for obstacle avoidance and also investigate the elements of the Markov decision process and their influence on each other. The flying mobile robot used within the considered problem is quadrotor type and has an integrated Lidar sensor which is utilized to detect obstacles. The sequential decision-making model based on Q-learning is trained within the MATLAB Simulink environment. The simulation results demonstrate that the UAV can navigate through the environment in most algorithm runs without colliding with surrounding obstacles

A bibliometric analysis and assessment of container terminal operations research

Purpose – The paper undertakes a bibliometric analysis and assessment of journal publications in the field of container terminal operations research (CTOR), in an attempt to identify high-impact papers (HIPs) published in Science Citation Index/Social Science Citation Index (SCI/SSCI) journals ofCTORsubject category from1973 to 2020. Design/methodology/approach –Astructured approach for identifying the HIPs is developed based on the utilization of bibliometric and network analyses. Findings – The CTOR papers are assessed in terms of publication outputs, distribution of outputs in SCI/SSCI journals, authorship, institutions and countries, as well as citation life cycles of papers with the highest total citations since their publication until the year 2020. The results show that between 1989 and 2015, there were 82 HIPs in the field of CTOR, which have been cited at least 200 times, with more than 50% of these citations allocated in the second part of paper citation life cycle according to the database of Google Scholar. Practical implications – The practical implication of the aforementioned reviewing and assessing journal publications of CTOR is that it offers the ability to reveal the tone of its development through addressing main characteristics of the relevant HIPs as determined by the highly cited papers in this field of research. Originality/value – This paper offers a unique analysis and assessment in the field of CTOR by identifying the relevant HIPs and their associated scientific actors (authors, institutions and countries), thus facilitating the future research effort in the field of CTOR

On Some Novel Fixed Point Results for Generalized F-Contractions in b-Metric-Like Spaces with Application

The focus of our work is on the most recent results in fixed point theory related to contractive mappings.We describe variants of (s, q, φ, F)-contractions that expand, supplement and unify an important work widely discussed in the literature, based on existing classes of interpolative and F-contractions. In particular, a large class of contractions in terms of s, q, φ and F for both linear and nonlinear contractions are defined in the framework of b-metric-like spaces. The main result in our paper is that (s, q, φ, F)-g-weak contractions have a fixed point in b-metric-like spaces if function F or the specified contraction is continuous. As an application of our results, we have shown the existence and uniqueness of solutions of some classes of nonlinear integral equations

EXCAVATOR’S AND BULLDOZER’S DOWNTIME COMPARISON AND RISK MANAGEMENT: PRELIMINARY STUDY

Risk management of engineering systems is of vital importance, but very often there is no enough data to quantitatively evaluate risk and accordingly create risk management strategy. Proper maintenance of excavators and bulldozers maximizes fuel efficiency and reduces operating costs, as well as reduces equipment failure and enhances safety. Accordingly, previous research opens avenue to analyze these two machinery types when working in mining industry. This paper aims to create statistical comparisons on data collected about excavators’ and bulldozers’ as technological failure/stoppage, electrical failure/stoppage, mechanical failure/stoppage, misuse, organizational failure/stoppage and external cause of failure/stoppage. After performing descriptive statistics, hypothesis testing has not found significant differences between technological failures/stoppages of excavators vs. bulldozers, mechanical failures/stoppages between already mentioned machines or theirs hazard degrees or total downtimes. Further research focus should be directed to the sample enlargement and further analysis, which is expected to prove preliminary results