Resonance in Ploče Harbor (Adriatic Sea)

In this paper, we extract and validate high-frequency oscillations in the port of Ploče, based on sea level data from one year (March 2002-March 2003) measured at a tide gauge in the harbor. Frequency was analyzed by applying stationary (spectral) and non-stationary (wavelet and filtering) analyses of the data to extract temporal characteristics of the fundamental seiches with a period of 30 min. Seiches are pertinent throughout the year, but their maximum amplitude doubles (up to 25 cm) during the summer. Modeling studies showed that seiches are primarily a result of incoming waves from the open sea, generated by resonant coupling with air pressure traveling waves. In contrast, direct wind forcing has a minor influence on seiche generation. Seiches endanger ferries and small moored boats as well as large cargo ships in harbors where strong currents (greater than 50 cm s-1) appear during extreme events

Research, processing and analysis of exploitation reliability results of high-speed radial diesel engine

This paper presents the research on reliability of high-speed radial marine diesel engine Zvijezda M 504 B2 based on experimental data of malfunctions on the engine and time required for repair. Exploitation reliability and failure intensity were calculated from operational data collected from the engine log book. Results were tested by computer program to determine the relevance of the obtained results. Mathematically calculated reliability model of high-speed radial marine diesel engine Zvijezda M 504 B2 showed continuous increasing function of the intensity of failure and the fact that the reliability of the engine can be reliably approximated by Weibull distribution. Based on the obtained results it has been shown that this distribution, regardless of its complexity, should be used in practice when calculating reliability of engines with similar constant and growing malfunction’s intensity. The conclusion is that proposed distribution enables a better depiction of the observed technical system and the impact of aging of components on the system reliability

Sažetak

This paper presents a new numerical model for the analysis of beam type structures. The model uses two-noded rotation free finite elements and takes into account material non-linearity, finite displacements, finite rotations and finite strains. The presented numerical model has been implemented into the open source ‘Yfdem’, which is based on the Combined Finite Discrete Element Method. The performance of the new numerical model was demonstrated on simple benchmark tests, by a comparison with known experimental and analytical results.U ovom radu prezentiran je novi numerički model za analizu grednih konstrukcija. Model koristi dvočvorne konačne elemente sa translacijskim stupnjevima slobode u svakom čvoru i pri tome uzima u obzir materijalnu nelinearnost, velike pomake, velike rotacije i velike deformacije. Prezentirani numerički model je implementiran u numerički paket ‘Yfdem’ koji se bazira na kombiniranoj metodi konačnih i diskretnih elemenata. Prednosti novog numeričkog modela demonstrirane su na jednostavnim primjerima usporedbom rezultata s poznatim analitičkim i eksperimentalnim rješenjima iz literature

Istočna obala srednjeg Jadrana i tokovi rijeka Cetine i Neretve za vrijeme posljednjeg glacijalnog maksimuma

he paper documents the use of a Digital Elevation Model (DEM) method to reconstruct paleo-channels and the paleo-coastline during the Last Glacial Maximum (LGM) in the Central Eastern Adriatic area. We focused on the paleo-coastline and paleo-channels of the Neretva and the Cetina rivers, which were estimated from the 15’’ bathymetry available for the Adriatic Sea. While being aware of the limitations of the method and the resolution of the bathymetry grid, we successfully reproduced the paleo-channels of both rivers. Results for the Cetina River indicate the presence of depressions that were filled with water along its flow. The configurations of existing seabeds in the vicinity of the Cetina and Neretva River mouths indicate morphologies, similar to river mouths. The vertical profiles suggest that during the LGM the sea level was about 115 m lower than today. The total length of the Neretva riverbed was longer for about 136 km than today, and the Cetina River was approximately 154 km longer.U ovom radu prikazana je rekonstrukcija istočne obale srednjeg Jadrana i tokova rijeka Cetine i Neretve za vrijeme posljednjeg glacijalnog maksimuma. Rekonstrukcija je izvršena korištenjem digitalnog modela reljefa Jadranskog mora rezolucije 15’’. Prilikom razmatranja rezultata rekonstrukcije, potrebno je uzeti u obzir ograničenja proizašla iz rezolucije modela reljefa, te ograničenja same metode. Rekonstruirani tok rijeke Cetine upućuje da su na više mjesta postojale depresije ispunjene vodom. Oblik dna u blizini tadašnjih ušća Neretve i Cetine podsjeća na nanose koje rijeke donose svojim ulijevanjem u more. Iz vertikalnog profila dna u blizini ušća proizlazi da je u doba zadnjeg glacijalnog maksimuma razina mora bila na današnjoj dubini od oko 115 m. Prema rekonstrukciji, duljina toka rijeke Neretve bila je tada duža za 136 km, a duljina toka rijeke Cetine je bila duža za 154 km

Lake-land breezes over a small elongated lake (Kozjak, Plitvice Lakes, Croatia)

Temperatura malog duguljastog jezera (2,3 km × 0,1–0,6 km; maksimalna dubina od 46 m) smještenog u brdsko-planinskom području mjerena je tijekom tri razdoblja od srpnja do rujna u blizini jezerske površine (dubina od 0,2 m). Istovremeno su u blizini jezera mjerene standardne meteorološke varijable. Na temelju atmosferskih i jezerskih uvjeta definirani su kriteriji za detekciju dana s perzistentnim povjetarcem (LLB). Rezultati su pokazali da se u 17,7% ispitanih dana nad jezerom uspostavljao povjetarac. Svi ti dani bili su popraćeni s povišenom energijom u normaliziranom valićnom spektru brzine vjetra pri periodu od 24 sata. Dnevni povjetarac s jezera najčešće je zbog okolne topografije bio kanaliziran u smjeru glavne osi jezera. Sukladno tome, dnevno anticiklonalno zakretanje vjetra bilo je poremećeno. Međutim, noću je bila izražena rotacija vjetra u smjeru kazaljke na satu. Nadalje, rezultati su pokazali jasnu vezu između jačine povjetarca i razlike temperature zraka nad tlom i nad jezerom.The temperature of a small elongated lake (2.3 km by 0.1-0.6 km; maximum depth of 46 m) located in a mountaneous area was measured during July-September period over three years (2018-2020) at the depth close to the lake surface (0.2 m). Concurrent standard meteorological variables were measured in the vicinity of the lake. Criteria based on atmospheric and lake conditions were defined to detect the days with persistent lake-land breeze (LLB) events. The results showed that 17.7% of the investigated days were associated with LLB events. These days were accompanied by elevated energy in the normalized wavelet spectra for the wind speed at period of 24 hours. Daytime onshore lake breezes were mainly channeled in the along-lake direction due to the surrounding topography. Accordingly, during the daytime, diurnal wind veering was distorted. However, during the nighttime, a clear clockwise wind rotation was present. In addition, the results exhibited a clear relationship between the lake-land temperature difference and the strength of the LLBs