38 research outputs found
Estimation of the eddy thermal conductivity for lake Botonega
This paper presents a part of a computer model that is suitable for limited temperature prediction and its application for Lake Botonega, which is located in Istria, Croatia. The main assumption of this study is that the heat transfer can be described by the eddy diffusivity model to formulate the model of the heating and cooling of a lake using a series of water and air temperature measurements. The coefficient of thermal diffusion, which is a function of the lake depth, is determined using the inverse model of eddy thermal diffusivity. The inverse model is linearized using the finite element approach. The model of lake thermal diffusivity consists of a conductive part and a radiative part, with the latter part being replaced with the heat flux on the boundary. The model parameters are calculated in two stepsāa predictor step and a corrector stepāand the coefficient of conduction is calculated instead of the diffusion. The estimated parameters are intended for inclusion in a simple three-dimensional thermal model, which provides the lake temperature prediction that is based on previous temperature measurements, as demonstrated in the examples
Analysis of two time-delayed sliding pendulums
In this paper a model of two pendulums sliding
along an elastic cable is presented. There is a time
delay between them, so the problem has been
divided into two phases in which systems of
ordinary differential equations are solved. In phase
one there is only one mass and the solution at the
end gives the initial conditions for phase two. In
phase two, the second mass is added and a system
of six differential equations with six unknowns with
initial conditions is derived. The validation of the
model is shown in an example of a zip line structure
in Croatia. Three cases are studied ā when
resistance is introduced when pendulums are in
antiphase and when the second mass reaches the
first mass
OdreÄivanje dinamiÄkog modula elastiÄnosti betona upotrebom impulsnog ÄekiÄa
Experimental determination of dynamic modulus of elasticity of fiber-reinforced concrete (FRC) by using impact hammer is based on measuring resonant frequencies of flexural vibrations in prismatic specimens. The natural frequencies are determined as resonant peaks from frequency response function (FRF), which is obtained by measuring the excitation and response function. The determination of the natural frequencies in this way represents an improvement over standardized test methods. The dynamic modulus of elasticity is determined using fundamental resonant frequency according to relations given in standards. The results are compared to the modulus of elasticity obtained by correlation with compression strength.Eksperimentalno ispitivanje dinamiÄkog modula elastiÄnosti mikroarmiranog betona (MAB) je provedeno koriÅ”tenjem impulsnog ÄekiÄa na osnovu mjerenja rezonantnih frekvencija savojnih vibracija na prizmatiÄnim uzorcima. Vlastite frekvencije su odreÄene kao rezonantni vrhovi funkcije frekventnog odgovora dobivene na osnovu mjerenja funkcije pobude i odgovora. Ovaj naÄin odreÄivanja vlastitih frekvencija predstavlja poboljÅ”anje u odnosu na standardizirane naÄine mjerenja primjenom rezonantne metode. ProraÄun dinamiÄkog modula elastiÄnosti proveden je koriÅ”tenjem prve vlastite frekvencije prema izrazima danim u standardima. Rezultati su usporeÄeni s modulom elastiÄnosti dobivenim iz korelacije s tlaÄnom ÄvrstoÄom
Some numerical procedures for solving reservoir leakage difficulties
Opisuje se odreÄivanje visine vode u akumulaciji poznatog obujma, u koju ulazi poznata koliÄina vode, a izlaz vode je moguÄ preko preljeva ili na neki drugi naÄin. Za razliku od metoda koje se baziraju na integralnoj formulaciji ravnoteže masa autori razvijaju diferencijalnu formulaciju problema. Pri tome se uvodi novi parametar āderivacija funkcije kapaciteta akumulacijeā. Usporedba dvaju pristupa pokazuje da je diferencijalna formulacija jednostavnija i toÄnija u primjeni.The authors describe procedures for determining the level of water in the water storage reservoir of known volume, to which a known quantity of water is supplied, and from which the water can be evacuated via an overflow or in some other way. Unlike methods that are based on an integral formulation of mass balance, the authors have developed a differential formulation of the problem. At that, they have introduced a novel parameter "storage capacity function derivative". The comparison of these two approaches reveals that the differential formulation is simpler and more accurate in practical use
Flux determination using finite elements: global vs. local calculation
Metoda konaÄnih razlika nije prikladna za odreÄivanje gustoÄe toka polja izraÄunatog metodom konaÄnih elemenata. NaÄinjena je nova metoda za raÄunanje gustoÄe toka koja se temelji na slaboj formulaciji i prikladna je za upotrebu s konaÄnim elementima. Prikazana je matriÄna formulacija za lokalnu i globalnu primjenu u metodi konaÄnih elemenata. Dodatna prednost metode je da se Neumann-ov rubni uvjet lako može ugraditi u formulaciju konaÄnih elemenata kojom se opisuje nelinearni problem rjeÅ”avanja polja. Na jedno- i dvo- dimenzionalnim primjerima prikazuje se usporedba rjeÅ”enja metodom konaÄnih razlika, Pade-ove derivacije i nove metode s konaÄnim elementima.Finite difference procedures for flux determination are not well suited for application to field results obtained from finite element calculations. A novel method for flux calculation has been derived. This method is based on the weak formulation and is suitable for use with finite elements. A matrix formulation for local and global application to finite element formulations is presented. An additional benefit of the method is that Neumann boundary conditions can be easily incorporated in the finite element formulation of the nonlinear field problem. A comparison between the finite difference, Pade derivative and novel finite element procedures is demonstrated through one- and two-dimensional examples
Determination of flow resistance coefficient
U cilju odreÄivanja koeficijenta otpora teÄenju provedena su mjerenja geometrijskih i hidrauliÄkih veliÄina na viÅ”e presjeka duž odvodnog kanala Botonega. NaÄinjen je program za raÄunalo u programskom okruženju MathCad za jednodimenzijski model teÄenja rjeÅ”avanjem jednadžbe kontinuiteta i energijske jednadžbe uz opis otpora teÄenju preko Manningove jednadžbe. Dobivene su vrijednosti Manningovog koeficijenta hrapavosti za razliÄite protoke i usporeÄene s podacima iz literature.Geometric and hydraulic measurements were made on several sections along the Botonega drainage channel in order to determine the flow resistance coefficient. A MathCad based computer program was developed for one-dimensional flow modelling purposes, and this through resolution of continuity and energy equations, while the Manning equation was used to describe flow resistance. The Manning\u27s roughness coefficient values for various flow rates were obtained and compared with literature data
Analysis of chloride penetration into the reinforced-concrete pier
U radu je prikazan 1D i 2D proraÄun prodora klorida u ab stup proveden na domeni popreÄnog presjeka stupa KrÄkog mosta primjenom MKR, te je odreÄeno vrijeme koje je potrebno da koncentracija klorida neposredno uz armaturu dosegne kritiÄnu vrijednost. Usporedbom dobivenih rezultata, može se zakljuÄiti da prodor klorida iz dva smjera uzrokuje veÄu koncentraciju klorida uz armaturu u kutnoj zoni konstrukcijskog elementa, od koncentracije predviÄene modelom 1D, za isto razdoblje.1D and 2D analysis of chloride penetration into the reinforced-concrete pier, conducted in the cross-section of a Krk Bridge pier, and based on the finite-difference method, is presented in the paper. The time the chloride concentration next to reinforcement requires to reach the critical value is defined. In can be concluded, by comparison of results obtained in the analysis, that chloride penetration from two directions causes greater concentration of chloride next to reinforcement in the corner zone of structural elements, when compared to concentration anticipated by the 1D model, for the same period of analysis
Analysis of the torrential-watercourse wall exposed to thermal action
Razmatra se djelovanje toplinskog optereÄenja na zid bujiÄnog vodotoka u MoÅ”ÄeniÄkoj Dragi. Modeliran je dio zida na kojem su se pojavile pukotine te je proraÄunan kao model dvodimenzionalnog Å”tapa u ravnini. Temperaturno optereÄenje izaziva naprezanja veÄa od dopuÅ”tenih za zadanu marku betona pa su se pojavile pukotine. Rezultati mjerenja pukotina usporeÄeni su s izraÄunatim pomacima. VeliÄine pomaka upuÄuju na dilatacije koje nisu izvedene, a potrebne su da zid ne bi pucao.The thermal load imposed on a torrential-watercourse wall in MoÅ”ÄeniÄka Draga is considered. The part of the wall affected by cracking was modelled and analyzed as a two-dimensional member in the plane. The temperature load leads to stress values greater than those allowed for the concrete type used, which results in the formation of cracks. Cracking measurement results are compared with calculated displacements. The displacement values show that expansion joints, not anticipated in this case, were in fact necessary to prevent wall cracking