Strength modelling of orthotropic ship structure panels by equivalent unstiffened plates

Проблеми понашања оребрених плоча (панела), као основних јединица бродских конструкција представљају једну од најзначајнијих истраживачких тема из области чврстоће бродских консктрукција. У овом раду оребрене плоче моделиране су неоребреним плочама, са циљем да се одзиви и једне и д руге у ш то в ећој м ери п одударају. У т у с врху р азвијена ј е процедура (метода еквиваленције) којом се за сваку оребрену плочу могу прорачунати параметри еластичности неоребрене плоче, тако да маскимални угиби и напони, у обе плоче, буду једнаки. Ово подразумева и дефинисање еквивалентног коначног елемента плоче који у својој матрици крутости, хомогенизује особине плоче и укрућења. Развијени математички алгоритам узима у обзир употребу теорије ортоторпних плоча и методе коначних елемената. С о бзиром д а ј е т руп б рoда састављен од великог броја оребрених плоча, сврха моделирања чврстоће еквивалентним плочама свакако је формирање нумеричког модела бродске конструкције са редукованим бројем елемената и степени слободе. Овај модел, за разлику од конвецнионалног, не поседује укрућења, само еквивалентне неоребрене плоче. Поређењем конкретног нумеричког модела трупа брода састављеног од конвенционалних коначних елемената и оног од нових, еквивалетних елемената, добијена је јаснија слика о примени, предностима и манама развијене методе. Циљ рада је да се употребом методе еквиваленције, поједностави структурно моделирање великих нумеричких модела бродске конкстуркције, без значајнијих губитака у квалитету анализе, односно одређеним померањима и напонима у констуркцији. Такође је урађена и серија мерења на конкретним моделима оребрених плоча да би се утврдила генерална разлика у одзивима реалне консктрукције у односу на одзив добијен применом методе коначних елемената, имајући у виду да се ова нумеричка метода користи у оквиру методе еквиваленције.One of the most important research topic in the field of ship strength analysis is the problem of structural behavior of stiffened plates (panels), as the basic units of ship structures. In this paper, stiffened plates are modeled as unstiffened ones, with the purpose to achieve the compliance in their structural response, as much as possible. Therefore, the procedure (equivalence method) is developed in order to obtain elasticity parameters of unsiffened plates so that maximum displacements and stresses would be the same in both plates. Furthermore, an equivalent finite element is defined. This element has stiffness matrix that homogenize the mechanical prorerties of both plate and stiffener. Developed mathematical algorithm takes into account application of orthotropic plate theory and finite element method. Considering that ship hull consists of large number of stiffened plates, the goal of equivalent plate strength modeling is to form a numerical model of ship structure with a reduced number of elements and degrees of freedom. This model, apart from convencional one, does not have stiffeners, just equivalent unstiffened plates. Comparing the specific numerical model of ship structure that consists of conventional finite elements and one that consists of new, equivalent elements, one can get more clear view on application, advanteges and disadvantages of developed method. The goal of this thesis is to simplify structural modelling of large numerical models of ship strucutures, without any significant loss in quality of the analysis, namely resulting displacements and stresses. Furthermore, a series of measurements is performed on specific models of stiffened plates in order to achieve general comparison of the structural response of real structure as opposed to numerically modeled one, especially having in mind that finite element method is incportporeted in equivalence method

Characteristics of Mortar from the Archeological site Caričin Grad

The paper presents research of mortar from the archeological site Caričin Grad. Caričin Grad is an early Byzantine site located near Leskovac, Serbia. It is of extreme importance for the study of early Medieval architecture. The town covers the area of around 7 ha. In town planning terms, it consists of Acropolis, Middle, and Lower tow, each with its system of ramparts and the structures leaning on them. There is a large number of sacred buildings, Baths, public and private buildings, well developed water supply and sewerage system provide evidence of the town’s importance. Mortar was sampled from the buildings surrounding the circular square of the Middle town, from the structures north of Acropolis, gate between the Middle and Lower town, east gate of the Lower city as well as the aqueduct structure. Mortars were analyzed with the goal of obtaining information about morphological, mineralogical, chemical and basic physical properties of mortar. For analysis of these properties, optical microscopy was used and scanning electronic microscope. Depending on the location sampled mortars, there are differences of individual properties of mortar. The optical examination of macroscopic appearance of mortar samples indicated that those are limestone mortars. The aggregate grains detected are river and crushed limestone aggregate and fine pieces of bricks

Fractals applications on fractured archeological samples reconstruction

The civil engineering materials in the whole existing civilization have many characteristics which do not depend of past historical period, but, there is forever and everywhere fractal characteristic of structures morphology. Many archeological sources which are very rich with samples from prehistorical periods, ancient Greece, Roman and Vestian period, Slovenes and later, are existing in Balkan and South-East Europe. These sources and samples are very important for our civilization evaluation. Sometimes or even often, we fined archeological samples which are fractured and damaged. In such situation, it is very important to reconstruct some of these parts. We developed quite new method based on fractals analysis and characterization which is an excellent tool for reconstruction the archeological and heritage samples. In these paper, we successfully presented this application and opened new perspectives for research in this area

Copmarative analysis of mortars from the archeological sites Gamzigrad (Romuliana) and Caričin Grad for the purpose of making compatible repair mortars

The paper presents a comparative analysis of mortars found at two significant archeological sites in Serbia. Specifically, those are Gamzigrad (Romuliana) near Zajecar and the archeological site Caricin Grad near Leskovac. In the previous papers, we dealst with the characterization of mortars from both sites. It was the first examination of mortars from both locations. The comparative analysis of mortars was performed based on the data obtained by testing physical-mechanical properties such as: water absorption, porosity, gravity and specific mass. Mineralogical composition (both quantitative and qualitative) was obtained based on XRD / XRF and SEM/EDS analyses. The comparative analyses of the mortar obtained from the mentioned archeological sites indicated that mortars from both locations contained grains of river aggregate, crushed limestone aggregate and crushed masonry bricks. The share percentage varied. Regarding the binder, the mortar from the Gamzigrad (Romuliana) site had limestone used for the binder, while the mortar from the Caricin Grad site had clay and powdered masonry bricks. The obtained results of mortar analysis pave the way for further research with an aim of making repair mortars

Characteristics of Mortar from fhe Archeolical Site Romuliana – Gamzigrad

Felix Romuliana is a palace erected during the rain and after the design of the Emperor Gaius Valerius Galerius Maximianus. It belongs to the category of monuments of Roman court architecture which is associated with the time of Tetrarchy. During the archeological excavations, two fortification systems were discovered, they younger outer system with twenty polygonal massive towers, and an older inner system with sixteen towers of quadragonal and octagonal towers flanking the gates. The younger outer fortification is polygonal. The communication east-west connecting two gates divides interior space into two entities. Systemic archeological research last since 1953 by probing the northwest part of the inner space. Conservation works run simultaneously with the excavations. Mortar samples were taken from the towers XI and XII of the old fortification, as well as from the tower 15 and the part of the rampart between towers 1 and 3 of the younger fortification. Mortars were analyzed with the goal of obtaining information about morphological, mineralogical, chemical and basic physical properties of mortar. For analysis of these properties, optical microscopy and scanning electronic microscope were used. Depending on the location sampled mortars, there are differences of individual properties of mortar. The optical examination of macroscopic appearance of mortar samples indicated that those are limestone binder mortars. Aggregae grains are both river and stone aggregate. Mortar porsity differs depending on the location where samples were taken

Screening of pectinase-producing Aspergillus spp. for use in strawberry juice clarification

U ovom radu urađen je skrining sojeva Aspergillus spp. koji proizvode pektinaze fermentacijom u tečnom medijumu, a koje su efikasne u izbistravanju soka od jagode. Endo-pektinaze su detektovane difuzionim testom, a ukupna pektinazna aktivnost određena je DNS metodom. Izbistravanje soka nakon tretmana pektinazama određeno je merenjem transmitancije na 660 nm, a povećanje prinosa soka izmereno je centrifugiranjem. Dobijeni rezultati su pokazali da su ove pektinaze visokoefikasne za tretman soka od jagode u poređenju sa komercijalnim pektinaznim preparatom Lafase Fruit.In this work, the screening of Aspergillus spp which produce pectinases by fermentation in a liquid medium was performed, as pectinases are effective in clarifying strawberry juice. Endo-pectinases were detected by the diffusion assay, and total pectinase activity was determined by the DNS method. The clarification of juice after pectinase treatment was determined by measuring the transmission at 660 nm, and an increase in juice yield was measured by centrifugation. The results obtained showed that these pectinases are very effective for the treatment of strawberry juice in comparison with the commercial pectinase preparation Lafase Fruit.59th Meeting of the Serbian Chemical Society; June 1-2, 2023, Novi Sad, Serbi

Ventilatory lung function in workers in the tobacco industry

U cilju odgovora na pitanje u kojoj su meri profesionalne nokse registrovane u duvanskoj industriji mogle uticati na stanje ventilacije pluća eksponiranih radnika sprovedena su ispitivanja u radnoj sredini i na radnicima. U radnoj sredini je izvršena analiza tehnološkog procesa rada, rezultata mikroklimatskih merenja, hemijskih štetnosti i zaprašenosti. Ispitivanje ventilacije pluća sprovedeno je na 95 radnika eksponirane grupe i 129 radnika kontrolne grupe. Rezultati analize radne sredine ukazuju na prisustvo duvanske prašine iznad maksimalno dopuštenih koncentracija. lspitivanja ventilacije pluća eksponiranih radnika su pokazala statistički značajno sniženje vrednosti nekih primenjenih testova kod nepušača ove grupe u odnosu na nepušače kontrolne grupe, što objašnjavamo delovanjem navedenih noksi na radnom mestu.A study was carried out to determine respiratory hazards to workers in tobacco manufacture. The investigations at the workplace included analysis of the work technology and measurements of chemical pollutants and dust concentrations in the work rooms. Ventilatory lung function tests were performed in 95 workers exposed to tobacco dust and in 129 control workers. Results of workplace analysis showed the presence of tobacco dust levels exceeding the maximum permissible concentrations. The values of some lung function tests for exposed workers non-smokers were significantly lower than for control workers non-smokers. They could be attributed to the effect of occupational noxae on the respiratory system

The use of nanoparticles to improve the analytical capabilities of LIBS for solution sample analysis

Laser-induced breakdown spectroscopy (LIBS) is a diagnostic technique based on optical emission spectroscopy, suitable for rapid, in situ, and multi-element analysis of all sample types. LIBS has demonstrated its greatest potential in the analysis of solids, both conducting and nonconducting. However, when it comes to quantitative LIBS analysis of liquids, there are still some drawbacks that limit its applicability, such as poor repeatability and low sensitivity. To some extent LIBS performance may be improved if directly performing LIBS on the solution is avoided by converting the liquid into a solid phase. Another recently proposed method to resolve the difficulties in LIBS analysis of liquid samples is the application of Nanoparticle - Enhanced LIBS (NELIBS) [1,2]. The aim of the present work was to examine the effect of copper oxide nanoparticles (NPs) on the analytical capabilities of LIBS analysis of lead in aqueous solutions. The apparatus for NELIBS experiments comprises a laser source, a spectrograph (F=850 mm, grating 1800 groves/mm, F/11) coupled with a CCD, and the focusing and collecting optics, i.e. the same as used in conventional LIBS. A double pulse Q-switched Nd:YAG laser at 1064 nm, pulse duration 10 ns, pulse energy 50 mJ, interpulse delay 1 μs was used. The spectra were registered in a time-integrated mode (integration time 1 ms). A glass plate was chosen as the substrate to ensure there is no interference between NPs and the substrate. The first type of samples was prepared by drying a droplet of a Pb solution (10 μl, concentration 100 ppm) on the glass substrate. The second type was prepared by drying a droplet of the copper oxide colloidal solution on the glass, prior to the deposition of the analyte solution. Three sets of the LIBS spectra were acquired; spectra of glass with deposited CuO NPs, of glass with deposited sample solution of Pb, and of the glass with deposited NPs of CuO and the sample solution of Pb. The spectra were obtained in the 395-415 nm spectral range. Only in the third case, intense Pb lines appeared in the spectrum. Estimation of the limit of detection (LOD) for the resonance Pb line at 405.78 nm, without additional optimization of the measurement parameters, gave a value of 3.6 ppm. Regarding the fact that without the addition of the NPs layer no analyte signal was obtained, it can be concluded that the enhancement of the lead emission line intensity is caused by the presence of the NPs, i.e. by the lower plasma formation threshold and more efficient atomization of the analyte deposited on the NP layer. The main benefits of using NELIBS for the analysis of solutions lie in its simplicity, speed, the small amount of solution needed (few microliters), and the ability to analyze very dense or slurry samples.VII International School and Conference on Photonics : PHOTONICA2019 : Abstracts of Tutorial, Keynote, Invited Lectures, Progress Reports and Contributed Papers; August 26-30; Belgrad

Remediation of arsenic contaminated water by a novel carboxymethyl cellulose bentonite adsorbent

Suitability of bentonite clay modified with sodium carboxymethyl cellulose (Na-CMC) for the removal of arsenic(III) ions from aqueous solution was tested in batch adsorption studies and complemented by theoretical modeling with Langmuir, Freundlich and Temkin isotherm models. The effects of various factors, such as the initial adsorbate concentrations, pH, and temperature of the solutions were investigated in series of experiments. FTIR analysis was used to detect functional groups typical for cellulose and bentonite. Scanning electron microscope was used to analyze the surface morphology of the composites. It was established that the removal process was fast in the beginning and adsorption equilibrium was attained in around 20 minutes with good fittings to both Langmuir and Freundlich model. Maximum adsorption capacity (Q max ) obtained from experiments was 9.4 mg/g. No influence of solution pH and temperature on the sorption was noticed. The series of conducted experiments showed that synthesized composites are suitable for the removal of arsenic from wastewaters by adsorption as efficient and low-cost technique. © 2019, ALÖKI Kft., Budapest, Hungary

Occupational exposure in a metal industry and ventilatory lung function

U cilju odgovora na pitanje u kojoj su meri profesionalne nokse registrovane u metaloprerađivačkoj industriji (MIN) mogle uticati na stanje ventilacije pluća eksponiranih radnika sprovedena su ispitivanja u radnoj sredini 1 na radnicima. U radnoj sredini je izvršena analiza tehnološkog procesa rada, rezultata mikroklimatskih merenja, hemijskih štetnosti i zaprašenosti. Ispitivanje ventilacije pluća sprovedeno je na radnicima eksponirane grupe (129) i radnika kontrolne grupe (129). Rezultati analize radne sredine ukazuju na prisustvo sledečih respiratornih noksi iznad MDK: mineralne prašina (SiO2 do 10%) aerosoli i boje, toluol i vajšpirit, Osim ovih noksi nađene su i druge kao što su: aceton, CO, C02, nafta, S02, FeO i ZnO, ali su njihove vrednosti ispod dozvoljenih koncentracija. Ispitivanja ventilacije pluća eksponiranih radnika su pokazala statistički značajno sniženje vrednosti ispitivanih testova kod ove grupe u odnosu na kontrolnu grupu, što objašnjavamo delovanjem navedenih noksi na radnom mestu.A study was carried in a metal processing industry with the aim to analyse the relationship between occupational exposure and lung functions. Measurements in the working environment showed the presence of the following respiratory noxae exceeding MAC values: mineral dust (Si02 up to 10%), aerosols, dyes, toluol and white-spirit. The concentrations of acetone, CO, CO2, oil, SO2, FeO and ZnO, which were also determined, did not exceed permissibile concentrations. Lung function tests were performed in two groups of workers- 129 exposed and 129 control ones. The test values were significantly lower in the exposed group of workers than in controls. This is explained by the effect of the occupational noxae present