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Influence of defects on limit loads and integrity of the pipeline at hydropower plant 'Pirot'
Get PDFTopic of this work is the integrity assessment of the pipeline section from hydropower plant Pirot. Crack-like defect size, maximum depth, is determined based on non-destructive evaluation - the largest crack depth is taken as the initial value for load carrying capacity estimation. Also, the crack dimensions (both length and depth) are varied. Limit pressure values are determined from 3D and 2D models of pipes with axial cracks on external surface. The influence of tensile loading on the load carrying capacity of the pipes with circumferential cracks is also examined. Integrity of pipes with both types of defects (axial and circumferential) is assessed through application of FAD diagrams
Numerical model of fluid-structure interaction for water tower analysis of vibrations
Get PDFThis paper deals with the aspects of vibration analysis of 3D numerical water tower models with the explicitly generated 3D finite element (FE) solid fluid model that simulates the fluid-structure interaction (FSI). The development and implementation of the 3D FE solid fluid model in modelling and analysing the system response is extremely important, both in terms of determining the impulsive and convective hydrodynamic pressure, and in terms of overall sizing of the water tower. Vibration of the water tower is calculated based on the analysis of its eigenvibrations, analysis of eigenvibrations occurring when charging and discharging the water tower reservoir (SFA - Staged Fluid Analysis), Steady-State Analysis (SSA) in the frequency domain and the analysis of the system response in the time domain (THA - Time History Analysis), followed by the transformation of the frequency domain response using the Fast Fourier Transform (FFT). The analysis of eigenvalues using the Ritz vectors (Ritz analysis) and the Power Spectral Density Analysis (PSDA) are carried out as the means of additional control and with the purpose of identifying vibration periods. The system's stiffness matrix and mass matrix are corrected using the 3D FE solid fluid model for analysing the water tower vibrations. Effects of the system's increasing vibration period are determined for the partially charged reinforced concrete (RC) water tower reservoir, given the strong action of the fluid mass that is excited for convective hydrodynamic action (sloshing) due to the water tower dimensions and the amount of fluid contained in the reservoir in this case
Repair of shaft and ventilation ring vanes damages of the generator of the hydroelectric generating set at the hydro power plant
Get PDFHydro power plant ’Pirot’, which was built in 1990, is
an accumulation-derivative power plant, which consists of 2
above-ground vertical hydroelectric generating sets that contain
Francis turbines with nominal power of 41,5 MW, manufactured
in Czech Republic, a tunnel and a sunken pipeline with overall
length of 2.030 m and diameter that ranges from 3.000 to
3.500 mm. Pipeline, made of 22 mm thick pipes, has been
designed and built without anchor blocks at curvatures, which is
a rarity elsewhere. Maximum pressure of 2.5 MPa occurs in front
of the turbine cover. This paper contains the analysis of the state
of the generator shaft on which the mechanical damages were detected, as well as the analysis of the state of vanes of the upper
and lower ventilation ring designed for air cooling of the
generator rotor where corrosion, erosion and, most of all,
cavitation damages were detected, based on results of nondestructive
testing (visual testing, penetrant testing, ultrasonic
testing). Procedures for the rehabilitation of damaged
components without disassembling them were defined. The
execution of these procedures helped in saving approximately
100.000 €. Taking into account the period of time necessary to
perform complete disassembling of components, as well as the
period of time needed to perform reassembling, which is directly
linked with the amount of energy the hydroelectric generating set
A2 would produce during that period, the overall save would
mount up to approximately 500.000 €
Failure analysis of ATR 72 tow bar–opportunity for re-design for inspection
No full textThe safe towing of aircraft is an important part in aviation security. Failures during the towing and parking
related operations are not so rare due to bad working circumstance, human error, etc. Tow bars are simple
but very important elements, for towing aircrafts on airports all over the world. This paper describes
failure analysis of accident during towing of regional ATR 72 aircraft. During towing of ATR 72 aircraft
sudden fracture of shear pins caused that tow tractor goes into one and airplane ATR 72 into other
direction. As a result, the airplane crashed on the empty tanker truck and severely deformed nose in this
ground damage incident. Design of failed tow bar key elements and of susceptibility to corrosion was
discussed in this paper. Failure analysis unveil the several key elements that lead to fracture of shear pins: outdated design of tow
bar, improper maintenance and non-regular towing of aircraft. Combination of reduction of load capacity
of shear pins induced by corrosion and impulse overloading caused premature fracture of the shear pins.and damage of ATR 72 aircraft. As a result of presented analysis the remedy was initiative for detail
inspection of existing tow bars and redesign or purchasing the new ones. The results are presented
Uticaj različitih tipova pragova na zvučnu izolaciju vrata
No full textU savremenoj građevinskoj praksi interesantno je da se poslednjih godina teži
izbacivanju klasičnih fiksnih pragova i upotrebi tzv. padajućih pragova kod izvedbe vrata.
Prilikom projektovanja arhitekte u poslednje vreme u većini slučajeva projektuju ulazna vrata u
hotelske sobe bez fiksnog praga, iz estetskih prohteva, ali prvenstveno zbog činjenice da fiksni
prag smeta pri svakodnevnoj upotrebi prtljaga sa točkovima pri ulasku i izlasku iz hotelske
sobe. U radu su prikazani rezultati serije laboratorijskih merenja izolacije od vazdušnog zvuka
jednog tipa ulaznih vrata sa varijacijama padajućih pragova i fiksnog praga. Ispitivanja su
izvršena u skladu sa serijom standarda za laboratorijska ispitivanja izolacije od vazdušnog
zvuka u građevinarstvu, SRPS EN ISO 10140
Primena mehanički aktivirane kaolinske gline u cementnim kompozitima / reparaturnim malterima
No full textKorisnik tehničkog rešenja: Maxima d.o.o., Dragiše Mišovića 16, 32240 Lučani
godina početka primene tehničkog rešenja: 2020. god;
Verifikacija tehničkog rešenja od strane Matičnog naučnog odbora za saobraćaj, urbanizam i građevinarstvo sprovedena je na sednici održanoj 29.12.2020. godin
Finite element model for stress state analysis of deep groove ball bearings with defects
Get PDFIn the framework of Industry 4.0, new specific or improved methods for
monitoring and prediction of operational conditions of machine elements are required.
Ball bearings are among the elements with high impact on safety and reliability of
mechanical systems operation. Hence, the development of accurate methods for their
working conditions monitoring is one of the important tasks within this framework. In
this paper, the development of 3D Finite Element Model for deep groove ball bearings
with defects on ring races is described in detail and its place in the new monitoring
methods is discussed. Special attention is paid to the modeling of contact finite
elements and selection of FEA parameters for fast and secure convergence during
non-linear calculations. The stress analysis of contact zones with defects and influence
of variable defect dimensions are presented, also
Tie-rods of the bucket wheel excavator slewing superstructure: A study of the eye plate stress state
No full textTie-rods of the bucket wheel and counterweight booms are vital parts of the bucket wheel excavator slewing superstructure. This paper is dedicated to the problem of identifying the stress state of the critical cross-section ('net section') of the eye plates on these tie-rods. It presents the results of the experimental and numerical investigations carried out on the eyebar model. The results show the appearance of a plastic deformation in the zone near the contour of the hole even when the eye is subjected to the loads within the range of the permissible loads prescribed by the standard DIN 22261-2. Plastification in the eye net section occurs across the full thickness of the plate, but it does not jeopardize the integrity of the structure. The stress value in the eye net section, calculated in accordance with the standard DIN 22261-2, is significantly lower than the actual stress values around the hole and serves only as a comparative value for the static strength proof for the eye
Laboratorijski razvijena metoda za određivanje glavnih elemenata i elemenata u tragovima u uzorcima cementnih veziva pomoću energetsko disperzivne rendgensko fluorescentne (ED-XRF) tehnike
No full textKorisnik/naručilac: Institut za ispitivanjematerijala a.d. Beograd, Centralna laboratorija za ispitivanje materijala, Laboratoriji za veziva, hemiju i maltere u okviru Centra za materijal
Remote Modification of Bidentate Phosphane Ligands Controlling the Photonic Properties in Their Complexes: Enhanced Performance of [Cu(RN-xantphos)(N^N)][PF6] in Light-Emitting Electrochemical Cells
No full textA series of copper(I) complexes of the type [Cu(HN-xantphos)(N^N)][PF6] and
[Cu(BnN-xantphos)(N^N)][PF6], in which N^N = bpy, Mebpy, and Me2bpy,
HN-xantphos = 4,6-bis(diphenylphosphanyl)-10H-phenoxazine and BnNxantphos
= 10-benzyl-4,6-bis(diphenylphosphanyl)-10H-phenoxazine is
described. The single crystal structures of [Cu(HN-xantphos)(Mebpy)][PF6]
and [Cu(BnN-xantphos)(Me2bpy)][PF6] confirm the presence of N^N and P^P
chelating ligands with the copper(I) atoms in distorted coordination environments.
Solution electrochemical and photophysical properties of the BnNxantphos-
containing compounds (for which the highest-occupied molecular
orbital is located on the phenoxazine moiety) are reported. The first oxidation
of [Cu(BnN-xantphos)(N^N)][PF6] occurs on the BnN-xantphos ligand. Timedependent
density functional theory (TD-DFT) calculations have been used to
analyze the solution absorption spectra of the [Cu(BnN-xantphos)(N^N)][PF6]
compounds. In the solid-state, the compounds show photoluminescence in
the range 518–555 nm for [Cu(HN-xantphos)(N^N)][PF6] and 520–575 nm for
[Cu(BnN-xantphos)(N^N)][PF6] with a blue-shift on going from bpy to Mebpy
to Me2bpy. [Cu(BnN-xantphos)(Me2bpy)][PF6] exhibits a solid-state photoluminescence
quantum yield of 55% with an excited state lifetime of 17.4 μs.
Bright light-emitting electrochemical cells are obtained using this complex,
and it is shown that the electroluminescence quantum yield can be enhanced
by using less conducting hole injection layers