Weather Downtime Assesment for Complex Offshore Projects

Analysis of the expected downtime in complex offshore operations is performed with metocean analysis of the area of interest which is then compared to the operative limits defined by installation analyses. The metocean conditions are commonly represented by seastate hindcast time series. On the other end, the operative limits can be defined as maximum allowable sea state, as well as the maximum allowable vessel motion. This paper presents the methodology to evaluate the operative weather downtime based on classical operative sea state limit

Tension splines with application on image resampling

Digital raster images often need to be represented in higher and lower resolutions. Resampling of digital images is an essential part of image processing. Most efficient and sufficiently accurate image resampling techniques can produce spurious oscillations near sharp transitions of color. To improve that, we introduce tension splines applied dimension by dimension. The presented tension spline procedure provides an elegant solution to the image resampling by constructing a smooth approximation with sharp non-oscillatory resolution of discontinuities. The numerical results on real digital images are given to show effectiveness of the proposed algorithm

Tension splines with application on image resampling

Digital raster images often need to be represented in higher and lower resolutions. Resampling of digital images is an essential part of image processing. Most efficient and sufficiently accurate image resampling techniques can produce spurious oscillations near sharp transitions of color. To improve that, we introduce tension splines applied dimension by dimension. The presented tension spline procedure provides an elegant solution to the image resampling by constructing a smooth approximation with sharp non-oscillatory resolution of discontinuities. The numerical results on real digital images are given to show effectiveness of the proposed algorithm

Comparison of numerical flow models based on a dam failure example

Uspoređeni su i vrednovani numerički 2D model plitkih voda obrađen softverom Stripp12 i 3D Navier-Stoksov model dvofaznog strujanja sa slobodnom površinom obrađen softverom Fluent. Kao test-primjer upotrijebljen je standardni laboratorijski eksperiment rušenja brane definiran u sklopu međunarodnog CADAM projekta. Analiza dobivenih rezultata pokazuje da rušenja oba modela daju visoku točnost rezultata, s time da se 3D model strujanja sa slobodnom površinom pokazuju točnijim.The numerical 2D shallow water model developed using the Stripp 12 software, and the 3D Navier- Stokes two-phase free-surface flow model based on the Fluent software, are compared and evaluated. The standard laboratory dam collapse experiment, defined in the scope of the international CADAM project, was used as a test example. The analysis of results shows that highly accurate failure results have been obtained for both models, although the 3D free surface flow model has proven to be more accurate

Numerical simulations of hydraulic transients in hydropower plant Jajce II

Hydraulic transients in hydropower plant Jajce II (Bosnia and Herzegovina) were simulated with 1D unsteady pipe flow model. High accuracy of the model was accomplished with the use of non-conservative formulation of an unsteady pipe flow model incorporating a modified instantaneous acceleration-based unsteady friction model and second order flux limited numerical scheme. In order to apply the model, complex dual surge tank geometry needed to be represented with a unified surge tank. The numerical model was validated against the measured data on three simulation scenarios, defined with different turbine discharge reductions. Simulation results show a very good agreement between the computed and measured piezometric heads, both in amplitude and frequency of the oscillation

Numerical simulations of hydraulic transients in PHPP Fužine

U radu su provedene numeričke simulacije hidrauličkih tranzijenata u sustavu crpne hidroelektrane (CHE) Fužine pomoću nestacionarnog 1D modela strujanja pod tlakom u cijevi. Primjenom nekonzervativne formulacije modela nestacionarnog strujanja tekućine u cijevi pod tlakom i fluks-limitirane numeričke metode drugog reda postignuta je zadovoljavajuća točnost modela. Dobiveni numerički rezultati su pokazali dobro slaganje s izmjerenim podacima promatranog sustava.Hydraulic transients in pumping hydroelectric power plant (PHPP) Fužine were simulated with 1D unsteady pipe flow model. High accuracy of the model was accomplished with the use of nonconservative formulation of unsteady pipe flow model incorporating unsteady friction model and second order flux limited numerical scheme. Simulation results show very good agreement between the computed and measured piezometric heads, both in amplitude and frequency of the oscillation

Comparison of numerical flow models based on a dam failure example

Uspoređeni su i vrednovani numerički 2D model plitkih voda obrađen softverom Stripp12 i 3D Navier-Stoksov model dvofaznog strujanja sa slobodnom površinom obrađen softverom Fluent. Kao test-primjer upotrijebljen je standardni laboratorijski eksperiment rušenja brane definiran u sklopu međunarodnog CADAM projekta. Analiza dobivenih rezultata pokazuje da rušenja oba modela daju visoku točnost rezultata, s time da se 3D model strujanja sa slobodnom površinom pokazuju točnijim.The numerical 2D shallow water model developed using the Stripp 12 software, and the 3D Navier- Stokes two-phase free-surface flow model based on the Fluent software, are compared and evaluated. The standard laboratory dam collapse experiment, defined in the scope of the international CADAM project, was used as a test example. The analysis of results shows that highly accurate failure results have been obtained for both models, although the 3D free surface flow model has proven to be more accurate

Numerical simulations of hydraulic transients in pipelines with application to hydroelectric power plants

U radu je opisano nestacionarno strujanje fluida u cijevima s fizikalnog, matematičkog i numeričkog gledišta, te primjena modela nekompresibilnog strujanja fluida. U prvom dijelu rada izložene su fizikalne osnove strujanja fluida u cijevima. Definirani su matematički modeli strujanja tekućine u cijevima, tj. Allievijev model strujanja tekućine proširen s K modelom nestacionarnog trenja. U središnjem dijelu rada opisane su upwind numeričke metode, s naglaskom na Q-sheme, fluks limitirane i esencijalno neoscilirajuće (ENO i WENO ) numeričke sheme, kao i implementacija navedenih numeričkih metoda na opisane matematičke modele nestacionarnog strujanja tekućine u cijevima što predstavlja proširenje na dosad opisanu primjenu numeričkog modela tog tipa. Konačno, provjera matematičkog i numeričkog modela za jednodimenzionalno strujanje tekućine je izvršena rezultatima dobivenim iz laboratorijskih testova kao i na realnim primjerima nestacionarnog strujanja hidroeletrani Jordan i HE Rijeka

Numerical Simulation of Hydraulic Transients in Rijeka HPP

In this work a new approach considering numerical modelling of waterhammer dissipation and attenuation is proposed. The classical Allievi liquid flow model has been extended with the Brunone unsteady friction model which includes separation of the local and convective unsteady friction factor. A widely-adopted approach in solving this model is treatment of the unsteady friction term as a classical source term, while the authors propose a non-conservative formulation, due to the existence of a non-conservative source term. The second order flux limited scheme is applied to the proposed formulation and is applied to simulations of transient flow in Rijeka HPP