Simulacija širenja prsline u titanijumskim mini dentalnim implantima (MDI)

Developments in mini dental implants (MDI) manufacturing are aimed at making them more biocompatible and, at the same time, lighter, more durable and simultaneously safer than the existing implants. But, occasionally, during installation the failure of MDI may occur or cracks may appear, which could lead to the later failure of MDI. In order to understand and assess crack growth in titanium MDI, Finite Element (FE) software packages ANSYS v13 and FRANC3D v5 have been used. Using FRANC3D software different crack sizes and shapes have been modeled and simulations of crack propagations in three-dimensional model of MDI have been performed. Based on simulation results, the approximate fatigue life of damaged MDI was calculated.Unapređenja u proizvodnji mini dentalnih implantata (MDI) su uglavnom usmerena ka povećanju njihove biokompatibilnosti i, u isto vreme, izdržljivosti i bezbednosti, ali i ka smanjenju njihovih dimenzija u odnosu na postojeće implantate. Međutim, tokom ugradnje MDI-a može doći do njegovog loma ili nastanka prsline koja kasnije može prouzrokovati lom. Da bi se analiziralo širenje prsline u titanijumskom MDI-u, korišćeni su softveri za primenu metode konačnih elemenata (MKE) ANSYS v13 i FRANC3D v5. Korišćenjem FRANC3D programa izmodelirane su prsline različitih veličina i oblika na 3D geometriji MDI-a i izvršeno je simuliranje njihovog širenja. Na osnovu rezultata simulacije izračunat je približan zamorni vek oštećenog MDI-a

Air traffic modernization and control: ADS-B system implementation update 2022: A review

Automatic Dependent Surveillance-Broadcast (ADS-B) is a multiparameter surveillance system designed to improve key segments of air traffic: enabling real-time surveillance, raising safety and efficiency levels, and improving flight information and weather services. ADS-B consists of two subsystems, ADS-B Out and ADS-B In. Although only a complete system, ADS-B In/Out provides numerous benefits (additional situational awareness, more efficient oceanic routing, etc.) FAA and EASA only require ADS-B Out (by January and June 2020, respectively), whereby ADS-B In remains optional. Because of its many advantages, ADS-B In/Out will be popular, but there are some weaknesses, which are primarily related to its cyber vulnerabilities due to insufficient authentication and encryption in the applied protocol. In this paper, an overview of the ADS-B system is presented as an aid to understanding the security problems and the different ways of potential attack. In addition, this review deals with the current state of ADS-B deployment and its future perspective and challenges

Aerodynamic airfoil at critical angles of attack / Аэродинамические характеристики крыла при критическом угле атаки / Aerodinamičke karakteristike aeroprofila pri kritičnim napadnim uglovima

Aircraft construction experts must not neglect the behavior of aircraft in extreme or closely extreme flight conditions, such as flights at critical angles of attack, where a normal flight can be easily converted into a stall. This paper highlights the essential factors that influence the behavior of aircraft in flight at critical angles of attack. Based on the available experimental results and estimations, the performances of airfoils were analysed depending on air flow conditions (categorized according to Mach and Reynolds numbers), airfoil shapes, dynamics of the transition of angles of attack, description of the flow around airfoils with increasing the angle of attack upon reaching a critical value, and the effect of roughness of airfoil surfaces at critical angles of attack. The paper gives a physical interpretation of a lift decrease and a stall. It minutely describes the origin of flow separation and categorizes airfoil sections by type of separation and their behavior during the flow at the critical angle of attack. Based on modern aerodynamics, this paper aims to show and explain the issues and the most important characteristics of the flow past the body at critical angles of attack and give practical recommendations for airfoil design. As such, it may be of interest to pilots and engineers as well as to educational and research institutions. / При разработке летательных аппаратов неследует пренебрегать фактором возникновения чрезвычайных ситуаций, а также условиями близкими критическим, так как при критическом угле атаки, обычный полет может перейти в аварийный режим. В данной работе приведены важные факторы, влияющие на состояние крыла в течение полета при критическом угле атаки. На основании доступных испытательных результатов и расчетов, произведен анализ поведения крыла в зависимости от условий обтекания (в соответствии с классификацией чисел Маха и Рейнольдса), формы крыла, динамики угла атаки. В работе также описано обтекание крыла при критическом увеличении угла атаки, и влияние неровностей на поверхности крыла в подобных условиях. В данной работе также представлены физические параметры критического режима полета, в т.ч. снижения подъемной силы и сваливания. Подробно описан процесс обтекания крыла с отрывом потока и выполнена классификация типов профелей с учетом срыва струи и поведения крыла в критическом режиме полета. Цель работы заключается в выявлении наиболее значимых характеристик обтекания крыла при критическом угле атаки и анализе, проведенного на основах современной аэродинамики, в результате которых предлагается практическая рекомендация для выбора аэродинамического профиля. Результаты данной работы могут представлять интерес как для летчиков и инженеров, так и для образовательных и исследовательских учреждений. / Prilikom konstrukcije vazduhoplova ne sme se zanemariti ponašanje letelice u ekstremnim, odnosno blisko ekstremnim uslovima leta, kakav je let pri kritičnim napadnim uglovima, gde se normalan let može lako preobratiti u prevučen let. U ovom radu naglašeni su bitni činioci koji utiču na ponašanje aeroprofila u letu pri kritičnim napadnim uglovima. Na osnovu dostupnih eksperimentalnih rezultata i proračuna izvršena je analiza ponašanja aeroprofila u zavisnosti od uslova strujanja (kategorisanih prema Mahovom i Rejnoldsovom broju), oblika aeroprofila, dinamike priraštaja napadnog ugla, opstrujavanja aeroprofila sa povećanjem napadnog ugla nakon dostizanja kritične vrednosti, kao i uticaja površinskih neravnina aeroprofila pri kritičnim napadnim uglovima. Prikazano je i fizičko tumačenje pada uzgona i pojave prevučenog leta. Detaljno je opisan nastanak otcepljenja strujanja oko aeroprofila i izvršena kategorizacija aeroprofila prema tipu otcepljenja i njegovom ponašanju pri kritičnim napadnim uglovima opstrujavanja. Cilj ovog rada jeste da na savremenim osnovama aerodinamike prikaže i obrazloži problematiku i najznačajnije osobenosti opstrujavanja aeroprofila pri kritičnim napadnim uglovima, da dâ praktične preporuke prilikom izbora aeroprofila, a može biti koristan i pilotima, inženjerima i istraživačima

Single rotor helicopter parasite drag estimation in the preliminary design stage

This paper presents the methodology for the rapid estimation of the single rotor helicopter parasite drag in the forward flight in the preliminary design phase. The aerodynamic drag of fuselage, main rotor hub, landing gear and the other, non-rotating defective surfaces contribute with more than 50% of the total power required for the forward flight at higher cruising speeds and therefore requires a more approximate determination in the design stages before the prototype development. The parasite drag determination is based on the evaluation of the basic value of The Equivalent Parasite Drag Flat Plate Area and its changes depending on the fuselage angle of attack. Plenty of the statistical indicators, aerotunnel tests results and the recent CFD investigations were taken into consideration during the process of developing and testing this methodology

Numerical Simulation of Crack Propagation in Seven-Wire Strand

This paper discusses certain aspects of numerical simulation of crack propagation in wire ropes subjected to axial loading, with the aim to explore and to demonstrate the capacity, performances and difficulties of crack propagation modeling by usage of numerical computational methods in such complex structures. For this purpose, the finite element method (FEM) was used, and 3D numerical analyses were performed in Ansys Workbench software. In order to validate and verify performed numerical modeling, crack growth rate based on calculated stress intensity factors (SIFs) along the crack fronts was obtained for the model for which experimental results could be found in the available literature. Finally, using the advanced modeling techniques, the parametric 3D model of seven-wire strand was analyzed. Conducted analysis showed that FEM could be a powerful tool for fatigue life predictions in order to reduce the need for experiments, which are still the only successful method for fatigue life estimation of wire ropes. © Springer Nature Switzerland AG 2020.In: Mitrovic N., Milosevic M., Mladenovic G. (eds) Computational and Experimental Approaches in Materials Science and Engineering. CNNTech 2018. Lecture Notes in Networks and Systems, vol 90. Springer, Cha