Pregled pučinskih obnovljivih izvora energije

Smanjenje rezervi fosilnih goriva u svijetu, kao i rastuća svijest o ljudskom utjecaju na klimatske promjene značajno su doprinjeli razvoju različitih tehnologija obnovljivih izvora energije. Iznimno veliki i gotovo neupotrebljeni energetski potencijali energije vjetra, valova, mjenskih i oceanskih struja, termalne energije i gradijenta saliniteta mogu se uspješno koristiti pomoću različitih uređaja pučinskih obnovljivih izvora energije. Primjenom najnovijih saznanja u razvoju pučinske tehnologije može se uspješno i ekološki zadovoljiti rastuća potreba za energetskim resursima. Ovaj rad predstavlja pregled potencijala pučinskih obnovljivih izvora energije, različitih tehnologija, trenutačne primjene, troškova izgradnje i glavnih društvenih utjecajnih faktora

An analytical solution to free rectangular plate natural vibrations by beam modes – ordinary and missing plate modes

Relatively simple analytical procedures for the estimation of natural frequencies of free thin rectangular plates, based on the Rayleigh quotient and the Rayleigh-Ritz method, are presented. First, natural modes are assumed in the usual form as products of beam natural modes in the longitudinal and transverse directions, satisfying the grillage boundary conditions. Based on a detailed FEM analysis, the missing of some natural modes, defined as a sum and a difference of the cross products of beam modes, is noted. The frequencies of these modes are very similar and identical in some special cases, manifesting in such a way a double frequency phenomenon. These families of natural mode shapes form a complete natural frequency spectrum of a free rectangular plate as a novelty. The reliable approximation of natural modes enables the application of the Rayleigh quotient for the estimation of higher natural frequencies. The application of the developed procedure is illustrated by the case of a free thin square plate. The obtained results are compared with those determined by FEM and also with rigorous ones from the relevant literature based on the Rayleigh-Ritz method. The achieved accuracy is acceptable from the engineering point of view. Furthermore, the same problem is solved by the Rayleigh-Ritz method using approximate natural modes as mathematical ones. Direct and iterative procedures are presented. A small number of mathematical modes and iteration steps are sufficient to achieve reliable results

Some Aspects of Mega-Floating Airport Design and Production

Mega-Floating Airports (MFA) are unique and complex offshore transport system components that emerged as a consequence of tremendous land price increase in the vicinity of very large coastal cities. An overview of MFAs design and production aspects is presented within this paper including design concept, model tests and full scale measurement, air transport analysis, infrastructure, main particulars and structure, wave breaker, hydroelastic analysis due to wave load and airplane moving mass, mooring analysis, production technology and environmental aspects. MFA dynamic response due to airplane load is emphasized as the most challenging problem. Theoretical outline as well as a realistic illustrative numerical example are presented

Hidroelastični odziv velikog kontejnerskog broda

Veliki kontejnerski brodovi su relativno elastični i brzi, pa su njihove prirodne frekvencije bliske susretnim frekvencijama. Za pouzdanije projektiranje takvih brodova potrebno je koristiti hidroelastične proračunske modele koji omogućuju vjerodostojnije modeliranje distribucije opterećenja i istovremeno uzimanje u obzir gibanja i elastičnih deformacija brodske konstrukcije. U ovom radu prikazane su teorijske osnove strukturnog, hidrodinamičkog i hidrostatičkog modela čijim spajanjem nastaje hidroelastični model. Razvijeni postupak temelji se na kombiniranju strukturnog 1D grednog modela konačnih elemenata i 3D hidrodinamičkog modela, što ga čini iznimno pogodnim za preliminarnu fazu osnivanja. Ukratko su opisani računalni programi izrađeni za potrebe hidroelastične analize, te je provedena analiza hidroelastičnog odziva velikog kontejnerskog broda nosivosti 7800 TEU. Valjanost 1D MKE modela provjerena je koreliranjem prirodnih frekvencija i oblika vibriranja s rezultatima 3D MKE analize. Rezultati su uspoređeni s rezultatima analize odziva krutog broda na valovima

Neki aspekti projektiranja i gradnje velikih plutajućih aerodroma

Iznimno veliko povećanje cijene zemlje u blizini velikih obalnih gradova rezultiralo je pojavom velikih plutajućih aerodroma koji predstavljaju jedinstvenu i složenu pučinsku komponentu transportnog sustava. Pregled projektnih i proizvodnih aspekata velikih plutajućih aerodroma u ovom radu uključuje projektni koncept, modelska ispitivanja i mjerenja u naravi, valobran, hidroelastičnu analizu uslijed valnog opterećenja te uzlijetanja i slijetanja zrakoplova, analizu sidrenja, tehnologiju gradnje i utjecaj na okoliš. Dinamički odziv strukture na opterećenje uslijed gibanja zrakoplova je istaknut kao iznimno zahtjevan problem. Teorijski pregled ilustriran je jednim numeričkim primjerom iz prakse

Static and dynamic rectangular finite elements for plate vibration analysis

Nowadays dynamic finite elements with frequency dependent unified stiffness matrix are considered in order to reduce finite element mesh density, and, consequently, system of algebraic equations in eigenvalue formulation. In this paper, an attempt to develop a 4-noded rectangular finite element for thin plate bending is presented. Since there is no simple general analytical solution of plate vibrations for arbitrary boundary conditions, dynamic shape functions are assumed as products of beam shape functions in longitudinal and transverse direction. Dynamic finite element with frequency dependent stiffness and mass matrix is derived by energy approach. Convergence of results is checked and it is found that such finite element formulation is not suitable for wider use. Therefore, strip finite element for vibration analysis of rectangular plate with simply supported two opposite edges is developed, which gives exact results. Application of both finite elements is illustrated by several numerical examples