Electric power frequency and nuclear safety - Subsynchronous Resonance case study

Andrija Volkanovski,Andrej Prosek 한국원자력학회 2019 Nuclear Engineering and Technology Vol.51 No.4

The increase of the alternate current frequency results in increased rotational speed of the electricalmotors and connected pumps. The consequence for the reactor coolant pumps is increased flow inprimary coolant system. Increase of the current frequency can be initiated by the subsynchronousresonance phenomenon (SSR). This paper analyses the implications of the SSR and consequential increase of the frequency on thenuclear power plant safety. The Simulink MATLAB® model of the steam turbine and governor system andRELAP5 computer code of the pressurized water reactor are used in the analysis. The SSR results in fast increase of reactor coolant pumps speed and flow in the primary coolant system. The turbine trip value is reached in short time following SSR. The increase of flow of reactor coolantpumps results in increase of heat removal from reactor core. This results in positive reactivity insertionwith reactor power increase of 0.5% before reactor trip is initiated by the turbine trip. The main parametersof the plant did not exceed the values of reactor trip set points. The pressure drop over reactorcore is small discarding the possibility of core barrel lift

Hybrid infrared-visible multiview correlation to study damage in a woven composite complex-shaped specimen

Andrija Zaplatic,Zvonimir Tomicevic,Xuyang Chang,Ivica Skozrit,Stephane Roux,Francois Hild Techno-Press 2023 Coupled systems mechanics Vol.12 No.5

In this study, a cyclic tensile test on a notched butterfly specimen made of woven glass fiber composite was performed on a modified Arcan fixture. During the mechanical test, the sample was monitored with a hybrid stereoscopic system comprised of two visible lights and one infrared camera. The visible light cameras were employed for kinematic measurements using a finite-element-based multiview correlation technique. A semi-hybrid correlation approach was followed, providing Lagrangian temperature fields of the Region of Interest. Due to the complex composite architecture and specimen shape, localized shearing was observed during the tensile loading. Furthermore, asymmetrical damage developed around the notches as revealed by localized strains and thermal hot spots.

Identifiability of Ludwik's law parameters depending on the sample geometry via inverse identification procedure

Zaplatic, Andrija,Tomicevic, Zvonimir,Cakmak, Damjan,Hild, Francois Techno-Press 2022 Coupled systems mechanics Vol.11 No.2

The accurate prediction of elastoplasticity under prescribed workloads is essential in the optimization of engineering structures. Mechanical experiments are carried out with the goal of obtaining reliable sets of material parameters for a chosen constitutive law via inverse identification. In this work, two sample geometries made of high strength steel plates were evaluated to determine the optimal configuration for the identification of Ludwik's nonlinear isotropic hardening law. Finite element model updating(FEMU) was used to calibrate the material parameters. FEMU computes the parameter changes based on the Hessian matrix, and the sensitivity fields that report changes of computed fields with respect to material parameter changes. A sensitivity analysis was performed to determine the influence of the sample geometry on parameter identifiability. It was concluded that the sample with thinned gauge region with a large curvature radius provided more reliable material parameters.

Xylella fastidiosa in Europe: From the Introduction to the Current Status

Vojislav Trkulja(Vojislav Trkulja ),Andrija Tomić(Andrija Tomić ),Renata Iličić(Renata Iličić ),Miloš Nožinić(Miloš Nožinić ),Tatjana Popović Milovanović(Tatjana Popović Milovanović ) 한국식물병리학회 2022 Plant Pathology Journal Vol.38 No.6

Xylella fastidiosa is xylem-limited bacterium capable of infecting a wide range of host plants, resulting in Pierce's disease in grapevine, citrus variegated chlorosis, olive quick decline syndrome, peach phony disease, plum leaf scald, alfalfa dwarf, margin necrosis and leaf scorch affecting oleander, coffee, almond, pecan, mulberry, red maple, oak, and other types of cultivated and ornamental plants and forest trees. In the European Union, X. fastidiosa is listed as a quarantine organism. Since its first outbreak in the Apulia region of southern Italy in 2013 where it caused devastating disease on Olea europaea (called olive leaf scorch and quick decline), X. fastidiosa continued to spread and successfully established in some European countries (Corsica and PACA in France, Balearic Islands, Madrid and Comunitat Valenciana in Spain, and Porto in Portugal). The most recent data for Europe indicates that X. fastidiosa is present on 174 hosts, 25 of which were newly identified in 2021 (with further five hosts discovered in other parts of the world in the same year). From the six reported subspecies of X. fastidiosa worldwide, four have been recorded in European countries (fastidiosa, multiplex, pauca, and sandyi). Currently confirmed X. fastidiosa vector species are Philaenus spumarius, Neophilaenus campestris, and Philaenus italosignus, whereby only P. spumarius (which has been identified as the key vector in Apulia, Italy) is also present in Americas. X. fastidiosa control is currently based on pathogen-free propagation plant material, eradication, territory demarcation, and vector control, as well as use of resistant plant cultivars and bactericidal treatments.

Stressed Skin Design Versus Braced Frame Design Through Efficient Numerical Modelling

Todor Vacev,Andrija Zorić,Miloš Milić,Stepa Paunović,Ivan Nešović 한국강구조학회 2020 International Journal of Steel Structures Vol.20 No.4

Steel frame structures are traditionally designed with bracings that stabilize the main bearing structure. Another approach is to apply the “stressed skin design” where the cladding structure takes the role of the bracings. In this research, the two approaches were analysed and compared in order to fi nd advantages of any. A typical steel frame structure was chosen, and for the cladding, trapezoidal sheet metal was selected. Optional bracings were also considered. All static analyses were done using the fi nite element method (FEM) and ANSYS Workbench software, including geometric and material nonlinearity. The structure was loaded perpendicularly to its gable, thus simulating typical wind action. Number of fasteners connecting the cladding and the frame is crucial for the “stressed skin design” concept, so this parameter was varied through the analysis. The stiff ness of the fastener devices was simulated in two ways: (1) simplifi ed, by merging of the adjacent nodes of the cladding and the frame, and (2) more accurately, using special joint elements with prescribed stiff ness. Obtained stresses and deformations were compared, and they showed obvious advantages of the “stressed skin design” over braced frame design, both in structural, and in economical aspect. In addition, important practical guidelines for the “stressed skin design” using FEM were proposed.

Analysis of Stressed Skin Behaviour of a Steel Façade Frame Under Varying Structural Conditions

Todor Vacev,Andrija Zorić,Slobodan Ranković,Miloš Milić,Stepa Paunović,Ivan Nešović 한국강구조학회 2021 International Journal of Steel Structures Vol.21 No.1

Steel structures are traditionally designed neglecting the in-plane bearing capacity of the cladding. However, the cladding can act in coordination with the main structure, behaving as a diaphragm and contributing to its spatial stability, enabling the so-called stressed skin concept design . The subject of this paper was an analysis of behaviour of a sample steel frame cladded with corrugated sheet metal, and connected to each other by self-tapping screws. Various conditions regarding the set and the number of fastening devices, as well as method of numerical modelling of fasteners, type of the corrugated sheet metal, and overall dimensions of the frame were analysed using FEM and ANSYS workbench software, including geometric and material nonlinearity. Results can serve as useful and reliable design guidelines, and as an argument for further propagation of the stressed skin concept design as a rational design approach for steel structures.

Aerodynamic characteristics of two slipstreaming race cars

Ivo Džijan,Aleksandar Pašić,Andrija Buljac,Hrvoje Kozmar 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.1

A computational model was developed to study aerodynamic forces acting on two closed-wheel race cars in the slipstreaming (drafting) arrangement, i.e., when the cars are characterized by the same driving speed and situated one directly behind the other one. A particular focus was on the influence of a distance between the two cars on flow characteristics and aerodynamic loads experienced by the cars. Computational fluid dynamics (CFD) simulations were performed for a steady viscous fluid flow using the realizable k-ε turbulence model and non-equilibrium wall functions. The results indicate some important findings. The leading car experiences the smaller drag force coefficient for all studied distances when compared to the single car case. For larger distances between the cars, the drag force coefficient of the trailing car is generally larger than for a single car due to a complex turbulent wake flow of the leading car (drag bubble) that impinges the trailing car. The drag force coefficient of the trailing car decreases when decreasing a distance from the leading car. The modifications of the lift force coefficient are more pronounced for the trailing car as there is a decrease in the negative lift force (downforce). The downforce coefficient is significantly smaller for the trailing car than for the single car configuration at all studied distances. A slight decrease in the downforce coefficient is present for the leading car as well.

Correlation of Gley Soils Classified According to the Croatian Soil Classification with the Wrb

Stjepan Husnjak,Vedran Rubinic,Andrija Spoljar,Boris Vrbek 한국토양비료학회 2014 한국토양비료학회 학술발표회 초록집 Vol.2014 No.6

AERODYNAMIC DESIGN OF A SOLAR ROAD VEHICLE

Ljubomir Majdandžić,Dalibor Buljić,Andrija Buljac,Hrvoje Kozmar 한국자동차공학회 2018 International journal of automotive technology Vol.19 No.6

Solar road vehicles have very specific design requirements. This makes their aerodynamic characteristics quite different from classic sedan vehicles. In the present study, the computational model of a typical solar road vehicle was developed to investigate its aerodynamic forces and flow characteristics. Computations were performed assuming the steady viscous flow and using the Reynolds-averaged Navier Stokes equations along with the k-ω turbulence model. The obtained results indicate some important findings that are commonly not present for classic sedan vehicles. In particular, a contribution of the viscous drag force to the overall drag force is considerably larger (41 %) than it is the case for the standard passenger road vehicles, where the form drag force dominates over the viscous drag force. Surface pressure distribution patterns indicate a favorable aerodynamic design of this vehicle. In particular, larger pressure coefficients on the top of the vehicle body as compared to the bottom surface contribute to increasing a downforce and thus the vehicle traction. The airfoil-shaped crosssection of the designed cockpit canopy has favorable properties with respect to reduction of the aerodynamic drag force.

Influence of Support Conditions on Single-Span Profiled Sheet Metal Strength Through Nonlinear FEM Analysis

Todor Vacev,Ivan Nešović,Miloš Milić,Andrija Zorić,Stepa Paunović 한국강구조학회 2020 International Journal of Steel Structures Vol.20 No.4

Profi led sheets are widely used in modern steel structures, either as cladding or as casing in composite structures. Strength calculation of such structures is a crucial design issue, and it represents a complex task because one must deal with thinwalled structures that have complicated cross-section shape. Manufacturers of these structural elements provide data about its strength, mostly based on experimental testing. However, catalogues provide little data about the supporting conditions at the ends that may have infl uence on structural strength. In this research, the fi nite element method analysis with geometrical and material nonlinearity and contact analysis in the support zones was applied for the strength calculation of a profi led steel sheet with very high depth. The analysis encompassed determination of the ultimate limit strength and serviceability limit strength with limited defl ection. All analyses were conducted for surface load applied over the area of one sheet. Thereat, infl uence of several factors related to support conditions was considered: friction on the supports, support width, and number of fasteners. Failure mechanisms were also analysed. Obtained results were compared with other sources and methods, like analytical solution, manufacturer’s software, and catalogue data. Results of the research showed that behaviour and strength of those elements depend to the great extent on end support detailing, which cannot be encompassed by classical calculation methods and linear analysis. Signifi cance of the support conditions was proven, and attention was paid on absence of such data in published catalogues.