A note on the damped vibrating systems

The presence of pure imaginary eigenvalues of the partially damped vibrating systems is treated. The number of such eigenvalues is determined using the rank of a matrix which is directly related to the system matrices

Identification of parameters of diesel engine crankshaft equivalent dynamic-torsion system based on crankshaft variable angular velocity

Trenutna ugaona brzina motora SUS se najčešće koristi za analizu radnih procesa u cilindrima motora, pošto takve informacije u njoj dominiraju. Kod većih motora elastične deformacije kolenastog vratila usled torzionih oscilacija ostavljaju mnogo dublji trag na trenutnu ugaonu brzinu nego što je to slučaj kod manjih, ne mnogo opterećenih motora. Sa stanovištva torzionih oscilacije, dve najvažnije informacije procenjene sa velikom tačnošću, mogu se dobiti jednostavnom harmonijskom analizom trenutne ugaone brzine kolenastog vratila. To su informacije o vrednostima sopstvenih frekvencija oscilovanja i potencijalno kritičnim brojevima obrtaja. Dalji proračuni vezani za probleme torzionog oscilovanja dinamičkog sistema sa motorom kao njegovim delom, zasnivaju se na idealizaciji i uvođenju ekvivalentnog dinamičkotorzionog sistema (EDTS). Parametri EDTS koje je potrebno definisati su inercijalne mase, torzione krutosti i koeficijenti unutrašnjeg i spoljašnjeg prigušenja. Pored toga, potrebno je poznavati momente koji pobuđuju kretanja (uključujući i torzione oscilacije) pojedinih inercijalnih masa dinamičkog sistemu. Za ovakav sistem se mogu postaviti diferencijalne jednačine sa ciljem da opišu kretanja svake inercijalne mase. Ni za jedan od nabrojanih parametara EDTS se ne može tvrditi da je prethodno relativno tačno procenjen, pošto postoje metode koje obezbeđuju samo njihovu orijentacionu procenu. U ovom radu je prikazan postupak identifikacije parametara EDTS na primeru dizelmotora sa dvanaest cilindara u V gradnji, primenom optimizacione metode Markvarta (Marquardt) baziranoj na minimizaciji sume kvadrata razlika izmerene i modelirane trenutne ugaone brzine kolenasatog vratila. Koeficijenti unutrašnjeg prigušenja su poslužili da se proceni ukupni srednji moment trenja u motoru. Momenti gasnih sila su procenjeni na osnovu izmerenih pritisaka u dva cilindra na suprotnim stranama ispitivanog motora. Na ovom primeru se jasno pokazalo da je pretpostavka o ujednačenosti radnih procesa po cilindrima ključni faktor koji utiče na odstupanja izmerene i modelirane trenutne ugaone brzine kolenastog vratila. Procenom pobudnih momenata inercijalnih sila na osnovu razvijene procedure određivanja promenljivog momenta inercije složenog krivajnog mehanizma ispitivanog motora, isključena je mogućnost da se sa te strane unese greška u proračun. Dodatno, momenti koji se od kolenastog vratila oduzimaju za pogon značajnijih podsistema motora su kombinacijom matematičkog modeliranja i neposrednog merenja procenjeni u ugaonom domenu kolenastog vratila i direktno ugrađeni u matematički model. Razvijeni modeli i postupci su iskorišćeni za procenu nivoa torzionih oscilacija u ispitivanom dinamičkom sistemu i mehničkog stepena korisnosti motora.The current angular velocity of IC engines is most commonly used to analyze the work processes in engine cylinders, since such information dominate in it. In larger engines, the crankshaft elastic deformations, due to torsional vibrations, leave a much deeper mark on the current angular velocity than in the case of smaller engines which are not heavily stressed. From the viewpoint of torsional oscillations, the two most important information, estimated with high accuracy, can be obtained by simple harmonic analysis of the crankshaft current angular velocity. Those are information about the values of natural oscillation frequencies and potentially critical rpm. Further calculations related to the problems of torsional oscillation of a dynamical system with an engine as its part, are based on idealization and introduction of an equivalent dynamic-torsional system (EDTS). The EDTS parameters which must be defined are the inertial masses, the torsion stiffnesses and the coefficients of internal and external damping. In addition, it is necessary to know the moments that cause motions (including torsional oscillations) of individual inertial masses of the dynamic system. Differential equations can be set up for such a system in order to describe the motion of each inertial mass. For none of the EDTS parameters mentioned above can be said that it was previously estimated with relative accuracy, since there are only methods that provide their approximate estimation. This paper presents a procedure to identify the parameters of the EDTS, on the example of diesel engine with twelve cylinders in V layout, by applying the Marquardt optimization method based on the minimization of the squares sum of the differences between the measured and modeled current angular velocity of the crankshaft. Internal damping coefficients were used to estimate the total mean friction moment in the engine. Moments of gas forces are estimated based on the measured pressures in two cylinders on opposite sides of the tested engine. This example clearly shows that the assumption of work processes uniformity per cylinders is the key factor that affects the deviations of the measured and modeled current angular velocity of the crankshaft. By evaluating the excitation moments of inertial forces on the basis of developed procedure for determining the variable moment of inertia of the complex crank mechanism of the tested engine, any possibility of introducing an error in the calculus from this side was excluded. In addition, by combining the mathematical modeling and direct measurements, the moments taken from the crankshaft to drive the engine major subsystems are estimated in the crankshaft angular domain and incorporated directly into the mathematical model. The developed models and procedures were used to estimate the level of torsional oscillations in the tested dynamic system and engine mechanical efficiency

Miscibility of Poly(Vinyl Chloride) with Poly(Ethylene Oxide) of Different Molecular Weights

In this work, five different techniques: dilute solution viscometry, differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), Fourier transform infrared spectroscopy (FT-IR), and scanning electronic microscopy (SEM) were employed in order to evaluate interactions of amorphous poly(vinyl chloride) (PVC) and semi-crystalline poly(ethylene oxide) (PEO) in solution and solid state. The results varied significantly from one experimental technique to another. The positive interactions between the investigated polymers were found over the whole composition range only in solution. However, in the solid state, by DSC and DMA analysis, the positive interactions were found only at elevated PVC content, while FT-IR and SEM analysis could not confirm interactions between the investigated polymers

Radiocarbon dating the 3rd millennium BC in the central Balkans: a re-examination of the Early Bronze Age sequence

Long-standing archaeological narratives suggest that the 3rd millennium cal BC is a key period in Mediterranean and European prehistory, characterised by the development of extensive interaction networks. In the Balkans for instance, the identification of such interactions relies solely upon typological arguments associated with conflicting local terminologies. Through a combination of 25 new radiocarbon dates and re-examination of the existing documentation, this paper defines the absolute chronology for groups which were previously only broadly framed into the 3rd millennium BC central Balkans (modern-day Serbia and North Macedonia). These absolute dates allow us to establish with greater clarity the chronological relations between different cultural groups that represent the main cultural units of the central Balkans sequence for the 3rd millennium cal BC: Coțofeni-Kostolac, Bubanj-Hum II, Belotić-Bela Crkva, Armenochori, and Bubanj Hum III. When comparing together the chronologies for material culture, funerary treatment of the body funerary architecture, there are no easily discernable patterns. We observe instead a complex mix of traits criss-crossing over a wide area encompassing the Pannonian basin, the central Balkans and the Greek peninsula

Research of combustion in older generation spark-ignition engines in the condition of use leaded and unleaded petrol

This paper analyzes the potential problems in the exploitation of the older generation of spark-ignition engines with higher octane number of petrol (unleaded petrol BMB 95) than required (leaded petrol MB 86). Within the experimental tests on two different engines (STEYR-PUCH model 712 and GAZ 41) by applying piezoelectric pressure sensors integrated with the engine spark plugs, acceleration sensors (accelerometers) and special electronic block connected with distributor, show that the cumulative first and second theoretical phase of combustion when petrol of higher octane number (BMB 95) is used lasts slightly longer than when the low-octane petrol MB 86 is used. For new petrol (BMB 95) higher optimal angles of pre-ignition have been determined by which better performances of the engine are achieved without a danger of the combustion with detonation (also called knocking)

Bioremediation of groundwater contaminated with petroleum hydrocarbons applied at a site in Belgrade (Serbia)

Due to their extensive use, petroleum hydrocarbons are among the most common groundwater contaminants. Compared to the traditional methods of physical pumping of contamination from the aquifer and subsequent treatment (i.e., pump and treat), bioremediation is an economically cost-effective technology. The aim of this remediation approach is to transform biologically contaminants, most often by microbiological activity, into non-toxic compounds. More precisely, it is an active remediation process that involves biostimulation (increase of aquifer oxygenation, addition of nutrients) and/or bioaugmentation (injection of a concentrated and specialized population of microorganisms). Using both biostimulation and bioaugmentation, enhanced in situ groundwater bioremediation was applied at a hydrocarbon-contaminated site in Belgrade. The bioremediation treatment, applied over twelve months, was highly efficient in reducing the concentrations of total petroleum hydrocarbon (TPH) to acceptable levels. The concentration of TPH in the piezometer P-5 was reduced by 98.55 %, in the piezometer P-6 by 98.30 % and in the piezometer P-7 by 98.09 %. These results provided strong evidence on the potential of this remediation approach to overcome site-limiting factors and enhance microbiological activity in order to reduce groundwater contamination. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. III 43004

Research of combustion in older generation spark-ignition engines in the condition of use leaded and unleaded petrol

This paper analyzes the potential problems in the exploitation of the older generation of spark-ignition engines with higher octane number of petrol (unleaded petrol BMB 95) than required (leaded petrol MB 86). Within the experimental tests on two different engines (STEYR-PUCH model 712 and GAZ 41) by applying piezoelectric pressure sensors integrated with the engine spark plugs, acceleration sensors and special electronic block connected with distributor, show that the cumulative first and second theoretical phase of combustion when petrol of higher octane number (BMB 95) is used lasts slightly longer than when the low-octane petrol MB 86 is used. For new petrol (BMB 95) higher optimal angles of pre-ignition have been determined by which better performances of the engine are achieved without a danger of the combustion with detonation (also called knocking)