Stress distribution as a cause of industrial steel chimney root section failure

Ovaj rad razmatra iniciranje otkaza korene sekcije industrijskog čeličnog dimnjaka visine 60 m. Prsline nastale u čeličnoj strukturi spoljašnjeg plašta dimnjaka značajno su uticale na integritet strukture. Izvršena je analitička i numerička analiza pojave prslina. Analiza metodom konačnih elemenata ukazala je na postojanje zona sa visokom koncentracijom napona. Identifikovane zone poklopile su se sa mestima na kojima je došlo do iniciranja prslina. Rezultati analize razjasnili su uzroke otkaza i omogućili izradu programa sanacije i dalje mere održavanja dimnjaka.This paper has studied failure initiation of the root section of 60 m tall industrial steel chimney. Cracks that occurred in steel wall of the wind shield have significantly influenced integrity of the structure. Analytical and numerical analysis of failure occurrence was performed. Location of extreme stress values in the steel structure were identified numerically by finite element method. Identified locations coincided with the location of the cracks initiation. The results of analysis identified causes of the failure initiation and allowed expression of the recommendation for root redesign and further maintenance procedures

Stress distribution as a cause of industrial steel chimney root section failure

Ovaj rad razmatra iniciranje otkaza korene sekcije industrijskog čeličnog dimnjaka visine 60 m. Prsline nastale u čeličnoj strukturi spoljašnjeg plašta dimnjaka značajno su uticale na integritet strukture. Izvršena je analitička i numerička analiza pojave prslina. Analiza metodom konačnih elemenata ukazala je na postojanje zona sa visokom koncentracijom napona. Identifikovane zone poklopile su se sa mestima na kojima je došlo do iniciranja prslina. Rezultati analize razjasnili su uzroke otkaza i omogućili izradu programa sanacije i dalje mere održavanja dimnjaka.This paper has studied failure initiation of the root section of 60 m tall industrial steel chimney. Cracks that occurred in steel wall of the wind shield have significantly influenced integrity of the structure. Analytical and numerical analysis of failure occurrence was performed. Location of extreme stress values in the steel structure were identified numerically by finite element method. Identified locations coincided with the location of the cracks initiation. The results of analysis identified causes of the failure initiation and allowed expression of the recommendation for root redesign and further maintenance procedures

Measurement and analysis of vibrations on the helicopter structure in order to detect defects of operating elements

U radu je prezentovan praktičan primer merenja i analize vibracija na helikopterskoj strukturi sa ciljem da se otkriju potencijalna oštećenja radnih elemenata. Sveobuhvatna metodologija merenja vibracija je predstavljena u ovom članku i sprovedena sa ciljem da se utvrdi ispravan rad rotirajućih komponenata. Poseban osvrt je dat na analizi uzdužnih i vertikalnih vibracija trupa helikoptera u frekventnom domenu za različite profile leta. Merenje i analiza vibracija na određenim lokacijama helikopterske strukture, rezultiralo je blagovremenim tehničkim pregledom odgovarajuće komponente i otkrivanjem njenog površinskog oštećenja. Praktična upotreba predložene metodologije merenja i analize je moguće implementirati na više vrsta letelica u cilju produženja životnog veka.A practical example of the measurement and analysis of vibrations on helicopter structures in order to detect defects on operating elements is presented in this paper. A comprehensive methodology of vibration testing is presented in this article and implemented in order to determine the correct operation of rotating components. A particular attention is given to the analysis of longitudinal and vertical vibrations on the helicopter fuselage in the frequency domain for different flight profiles. The vibration measurement and analysis on specific locations on a helicopter structure resulted in a timely technical review of a relevant component and a disclosure of the damage on its surface. The proposed methodology of measurement and analysis can be implemented on different types of aircraft in order to extend their life expectancy.

Measurement and analysis of vibrations on the helicopter structure in order to detect defects of operating elements

U radu je prezentovan praktičan primer merenja i analize vibracija na helikopterskoj strukturi sa ciljem da se otkriju potencijalna oštećenja radnih elemenata. Sveobuhvatna metodologija merenja vibracija je predstavljena u ovom članku i sprovedena sa ciljem da se utvrdi ispravan rad rotirajućih komponenata. Poseban osvrt je dat na analizi uzdužnih i vertikalnih vibracija trupa helikoptera u frekventnom domenu za različite profile leta. Merenje i analiza vibracija na određenim lokacijama helikopterske strukture, rezultiralo je blagovremenim tehničkim pregledom odgovarajuće komponente i otkrivanjem njenog površinskog oštećenja. Praktična upotreba predložene metodologije merenja i analize je moguće implementirati na više vrsta letelica u cilju produženja životnog veka.A practical example of the measurement and analysis of vibrations on helicopter structures in order to detect defects on operating elements is presented in this paper. A comprehensive methodology of vibration testing is presented in this article and implemented in order to determine the correct operation of rotating components. A particular attention is given to the analysis of longitudinal and vertical vibrations on the helicopter fuselage in the frequency domain for different flight profiles. The vibration measurement and analysis on specific locations on a helicopter structure resulted in a timely technical review of a relevant component and a disclosure of the damage on its surface. The proposed methodology of measurement and analysis can be implemented on different types of aircraft in order to extend their life expectancy.

Review of the current wind energy technologies and global market

U radu je dat pregled modernih vetroenergetskih tehnologija i trendova razvoja tržišta. Ukratko su opisani osnovni principi koverzije energije vetra u električnu energiju sa kratkim osvrtom na moderne konstrukcije podsklopova kao što su lopatice vetroturbina i agregati. Izvršen je pregled stanja vetroenergetike u svetu u cilju dobijanja predstave o budućem razvoju tržišta. Najrazvijenije države u pogledu iskorišćenja energije vetra, kao što su Danska, Nemačka, Španija i SAD identifikovane su kao glavni pokretači daljeg napredovanja vetroenergetike. Nakon dugog vođstva Evropske Unije u pogledu izgradnje vetroenergetskih kapaciteta na godišnjem nivou, Kina i SAD su preuzele vodeće pozicije u poslednjih nekoliko godina. Troškovi proizvodnje električne energije korišćenjem energije vetra su posle postepenog opadanja do 2005. godine zabeležile blagi rast usled visoke tražnje i viših cena repromaterijala. Procenjeno je da će troškovi proizvodnje električne energije iz energije vetra u budućnosti imati trend opadanja. U narednim godinama predviđa se stabilan rast vetroenergetskih kapaciteta, uz očekivanja da će sadašnji instalisani kapaciteti u svetu od oko 200 GW porasti do skoro 1 TW do 2020. godine.The modern wind energy technologies and recent global wind energy market trends are reviewed in the paper. Basic principles of conversion of wind energy to electricity are described with brief overview of the state-of-the-art technologies for subassemblies such as wind turbine blades and drive trains. Global wind energy market was reviewed in order to attain notion of wind power market developments in the future. The most developed countries in terms of wind energy utilization such as Denmark, Germany, Spain and USA were identified as the key drivers of wind energy technology advances. After the long leadership of European Union in built annual wind power capacities, China and USA have overtook leading positions for the last several years. Wind energy costs per unit of electricity produced after gradual decrease until 2005 have recorded slight increase until the present due to high demand and higher raw materials price. It was predicted that the trend of the wind energy cost will decrease in the future. Steady growth of wind energy capacities was predicted in the next years, with forecast that present global installed capacities of nearly 200 GW should grow to almost one terawatt by the 2020

Multi-objective fuzzy optimization of sizing and location of piezoelectric actuators and sensors

Ovaj rad predstavlja višeciljnu fazi optimizaciju veličine i položaja piezoelektričnih aktuatora i senzora na tankozidu kompozitnu gredu za aktivno upravljanje vibracija koristeći stepen upravljivosti (DC) kontrolisanih modova kao kriterijum optimizacije. Proces optimizacije je izvršen uz ograničenje promene prvobitnih dinamičkih karakteristika, uključujući ograničenje u porastu mase, upotrebljavajući ili zanemarujući ograničenja stepena upravljivosti rezidualnih modova za redukciju 'spillover' efekta. Pseudociljne funkcije izvedene na bazi teorije fazi skupova na jedinstven način definišu globalne funkcije cilja eliminišući upotrebu kaznenih funkcija. Problem je definisan upotrebom metode konačnih elemenata bazirane na 'TSD' teoriji. 'Particle Swarm' optimizacija je upotrebljena za nalaženje optimalne konfiguracije. Nekoliko numeričkih primera je prikazano za slučaj konzole.This paper presents the multi-objective fuzzy optimization of sizing and location of piezoelectric actuators and sensors on the thin-walled composite beam for active vibration control, using the degree of controllability (DC) for controlled modes as optimization criteria. The optimization process is performed constraining the original dynamics properties change including the limitation of increase of the mass, using or neglecting the limitation in degrees of controllability for residual modes for reduction spillover effect. Pseudogoal functions derived on the fuzzy set theory gives a unique expression for global objective functions eliminating the use of penalty functions. The problem is formulated using the finite element method based on the third-order shear deformation theory. The particle swarm optimization technique is used to find optimal configuration. Several numerical examples are presented for the cantilever beam

Two-dimensional numerical analysis of active flow control by steady blowing along foil suction side by different urans turbulence models

The effects of active separation control by steady blowing jets were investigated numerically on three different examples: subsonic flow past Aerospatiale A airfoil at 13 degrees angle-of-attack, transonic flow past NACA 0012 airfoil at 4 degrees angle-of attack, and transonic flow in linear compressor/turbine cascade. Performed analyses are two-dimensional, flow is turbulent (or transitional) while fluid is viscous and compressible. Jets are positioned along the suction sides of the foils, the first one being located just upstream of the separation point, and modeled by source terms added to flow equations. Several different jet diameters and intensities are investigated. As the choice of turbulence model affects the final solution of Reynolds equations, turbulence is modeled by four different models: Spalart-Allmaras, realizable k-epsilon, k-omega SST, and gamma-Re-theta, and a comparison of obtained results is performed. Goals of the study include definition of an adequate numerical setting that enables sufficiently correct simulation of the problems in question as well as evaluation of the possible increase in aerodynamic performances. Lift coefficients, lift-to-drag ratios or relative pressure differences are improved for all controlled cases

Multi-objective fuzzy optimization of sizing and location of piezoelectric actuators and sensors for vibration control based on the particle swarm optimization technique: Part 2: Numerical analysis

Ovo je drugi deo istraživanja višeciljne fazi optimizacije veličine i položaja piezoelektričnih aktuatora i senzora na tankozidnoj kompozitnoj gredi. Prvi rad je fokusiran na teorijskom modelu optimizacione tehnike za optimalno dimenzionisanje i postavljanje piezoelektičnih aktuatora i senzora na pametnu strukturu za aktivno upravljanje vibracijama. U ovom delu, biće prikazana numerička analiza predstavljene optimizacione tehnike za kompozitnu konzolu sa i bez ograničenja u pogledu stepena upravljivosti za rezidualne modove.This is the second part of a two-paper research of the multi-objective fuzzy optimization of sizing and location of the collocated piezoelectric actuators and sensors on the thin-walled composite beam. The first paper is focussed on the theoretical model of a optimization techique for optimal sizing and location of piezoelectric actuators and sensors on a smart structure for active vibration control. In this part, the numerical analysis of the presented optimization technique will be presented for the cantilever composite beam with and without limitations in degrees of controllability (DCs) for residual modes

Multi-objective fuzzy optimization of sizing and location of piezoelectric actuators and sensors for vibration control based on the particle swarm optimization technique: Part 2: Numerical analysis

Ovo je drugi deo istraživanja višeciljne fazi optimizacije veličine i položaja piezoelektričnih aktuatora i senzora na tankozidnoj kompozitnoj gredi. Prvi rad je fokusiran na teorijskom modelu optimizacione tehnike za optimalno dimenzionisanje i postavljanje piezoelektičnih aktuatora i senzora na pametnu strukturu za aktivno upravljanje vibracijama. U ovom delu, biće prikazana numerička analiza predstavljene optimizacione tehnike za kompozitnu konzolu sa i bez ograničenja u pogledu stepena upravljivosti za rezidualne modove.This is the second part of a two-paper research of the multi-objective fuzzy optimization of sizing and location of the collocated piezoelectric actuators and sensors on the thin-walled composite beam. The first paper is focussed on the theoretical model of a optimization techique for optimal sizing and location of piezoelectric actuators and sensors on a smart structure for active vibration control. In this part, the numerical analysis of the presented optimization technique will be presented for the cantilever composite beam with and without limitations in degrees of controllability (DCs) for residual modes

Aerodynamic characteristics of high speed train under turbulent cross winds: A numerical investigation using unsteady-RANS method

Usled trenda povećanja brzina i smanjenja mase modernih vozova velikih brzina neophodno je razmatrati dejstvo jakih bočnih vetrova na njihovu aerodinamiku. Jaki bočni vetrovi mogu uticati na stabilnost ovih vozova usled povećanja aerodinamičke sile i momenta. U ovoj analizi sprovedene su numeričke simulacije turbulentnih bočnih vetrova koji duvaju preko prvog i poslednjeg vagona brzog voza ICE-2 pri različitim uglovima skretanja. Problemi stabilnosti voza su blisko vezani za strujno polje oko voza. Okolni fluid smatran je nestišljivim, a strujno polje oko voza dobijeno je rešavanjem nestacionarnih Rejnoldsovih jednačina (RANS) u kombinaciji sa realizable k-epsilon turbulentnim modelom. Aerodinamički koeficijenti važni za ovu analizu, koeficijent sile klizanja i momenta skretanja, izračunati su za uglove skretanja u opsegu od -30° do 60° i upoređeni sa rezultatima dobijenim u aerotunelu. Kvalitativna analiza zavisnosti strujnih struktura od ugla skretanja je takođe sprovedena i prikazana.Increasing velocity combined with reduced mass of modern high speed trains poses the question of influence of strong cross winds on its aerodynamics. Strong cross winds may affect the running stability of high speed trains via the amplified aerodynamic forces and moments. In this study, simulations of turbulent cross wind flows over the leading and end car of ICE-2 high speed train have been performed at different yaw angles The train aerodynamic problems are closely associated with the flows occurring around train. The flow around the train has been considered as incompressible and was obtained by solving the incompressible form of the unsteady Reynolds-Averaged Navier-Stokes (RANS) equations combined with the realizable k-epsilon turbulence model. Important aerodynamic coefficients such as the side force and rolling moment coefficients have been calculated for yaw angles ranging from -30° to 60° and compared to results obtained from wind tunnel tests. The dependence of the flow structure on yaw angle has also been presented