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 steps—a predictor step and a corrector step—and 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 – when resistance is introduced when pendulums are in antiphase and when the second mass reaches the first mass

Određivanje dinamičkog modula elastičnosti betona upotrebom impulsnog čekića

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 dinamičkog modula elastičnosti mikroarmiranog betona (MAB) je provedeno korištenjem impulsnog čekića na osnovu mjerenja rezonantnih frekvencija savojnih vibracija na prizmatičnim uzorcima. Vlastite frekvencije su određene kao rezonantni vrhovi funkcije frekventnog odgovora dobivene na osnovu mjerenja funkcije pobude i odgovora. Ovaj način određivanja vlastitih frekvencija predstavlja poboljšanje u odnosu na standardizirane načine mjerenja primjenom rezonantne metode. Proračun dinamičkog modula elastičnosti proveden je korištenjem prve vlastite frekvencije prema izrazima danim u standardima. Rezultati su uspoređeni s modulom elastičnosti dobivenim iz korelacije s tlačnom čvrstoćom

Some numerical procedures for solving reservoir leakage difficulties

Opisuje se određivanje visine vode u akumulaciji poznatog obujma, u koju ulazi poznata količina vode, a izlaz vode je moguć preko preljeva ili na neki drugi način. Za razliku od metoda koje se baziraju na integralnoj formulaciji ravnoteže masa autori razvijaju diferencijalnu formulaciju problema. Pri tome se uvodi novi parametar „derivacija funkcije kapaciteta akumulacije“. Usporedba dvaju pristupa pokazuje da je diferencijalna formulacija jednostavnija i točnija 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 konačnih razlika nije prikladna za određivanje gustoće toka polja izračunatog metodom konačnih elemenata. Načinjena je nova metoda za računanje gustoće toka koja se temelji na slaboj formulaciji i prikladna je za upotrebu s konačnim elementima. Prikazana je matrična formulacija za lokalnu i globalnu primjenu u metodi konačnih elemenata. Dodatna prednost metode je da se Neumann-ov rubni uvjet lako može ugraditi u formulaciju konačnih elemenata kojom se opisuje nelinearni problem rješavanja polja. Na jedno- i dvo- dimenzionalnim primjerima prikazuje se usporedba rješenja metodom konačnih razlika, Pade-ove derivacije i nove metode s konačnim 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

Some numerical procedures for solving reservoir leakage difficulties

Opisuje se određivanje visine vode u akumulaciji poznatog obujma, u koju ulazi poznata količina vode, a izlaz vode je moguć preko preljeva ili na neki drugi način. Za razliku od metoda koje se baziraju na integralnoj formulaciji ravnoteže masa autori razvijaju diferencijalnu formulaciju problema. Pri tome se uvodi novi parametar „derivacija funkcije kapaciteta akumulacije“. Usporedba dvaju pristupa pokazuje da je diferencijalna formulacija jednostavnija i točnija 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

Determination of flow resistance coefficient

U cilju određivanja koeficijenta otpora tečenju provedena su mjerenja geometrijskih i hidrauličkih veličina na više presjeka duž odvodnog kanala Botonega. Načinjen je program za računalo u programskom okruženju MathCad za jednodimenzijski model tečenja rješavanjem jednadžbe kontinuiteta i energijske jednadžbe uz opis otpora tečenju preko Manningove jednadžbe. Dobivene su vrijednosti Manningovog koeficijenta hrapavosti za različite protoke i uspoređene 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 proračun prodora klorida u ab stup proveden na domeni poprečnog presjeka stupa Krčkog mosta primjenom MKR, te je određeno vrijeme koje je potrebno da koncentracija klorida neposredno uz armaturu dosegne kritičnu vrijednost. Usporedbom dobivenih rezultata, može se zaključiti da prodor klorida iz dva smjera uzrokuje veću koncentraciju klorida uz armaturu u kutnoj zoni konstrukcijskog elementa, od koncentracije predviđene 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 opterećenja na zid bujičnog vodotoka u Mošćeničkoj Dragi. Modeliran je dio zida na kojem su se pojavile pukotine te je proračunan kao model dvodimenzionalnog štapa u ravnini. Temperaturno opterećenje izaziva naprezanja veća od dopuštenih za zadanu marku betona pa su se pojavile pukotine. Rezultati mjerenja pukotina uspoređeni su s izračunatim pomacima. Veličine pomaka upućuju na dilatacije koje nisu izvedene, a potrebne su da zid ne bi pucao.The thermal load imposed on a torrential-watercourse wall in Mošćenička 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