Finite-Discrete Element Method for Static and Dynamic Analysis of Thin Arch and Shell Structures : Doctoral Thesis

U ovom radu su u okviru metode konačno-diskretnih elemenata razvijeni novi numerički modeli za simulaciju ponašanja tankih grednih i lučnih elemenata, te tankih konstrukcija ploča i ljusaka izloženih statičkom i dinamičkom opterećenju. Prikazane su do sada uvriježene metode proračuna predmetnih konstrukcija te njihove prednosti i nedostaci. Također, prikazane su osnove kombinirane metode konačno-diskretnih elemenata i razlozi njezinog odabira. Motivacija se nalazila na razvoju preciznih, robusnih i numerički povoljnih modela. Numerički model za analizu tankih grednih i lučnih konstrukcija koristi ravne dvočvorne elemente oslobođene rotacije, i u obzir uzima linearno elastično ponašanje materijala, konačne pomake, konačne rotacije i male deformacije. U radu su detaljno opisani mehanizmi prijenosa uzdužne i savojne krutosti kod grednih konačnih elemenata. Model je implementiran u postojeći open-source program Yfdem, temeljen na kombiniranoj metodi konačno-diskretnih elemenata. U sklopu rada provedena je verifikacija predloženog modela, te prikazana njegova primjena u seizmičkoj analizi lučnih konstrukcija. Također, razvijen je novi numerički model za analizu tankih ploča i ljusaka. Model za ploče i ljuske koristi ravne tročvorne trokutaste elemente oslobođene rotacije i u obzir uzima linearno elastično ponašanje materijala, konačne pomake, konačne rotacije i male deformacije. U radu su detaljno opisani mehanizmi prijenosa membranske i savojne krutosti kod trokutastih konačnih elemenata. Model je implementiran u postojeći opensource program Yfdem. U sklopu rada provedena je verifikacija predloženog modela, te je prikazana njegova primjena na tipske problema stabilnosti ploča i ljusaka. Predložene su daljnje smjernice za nadogradnju razvijenog programa u smjeru interakcije i matelijarne nelinearnosti.This thesis presents new numerical models for analysis of thin beam and arch structures and thin plate and shell structures based on the combined finite-discrete element method (FDEM). The new models perform quasistatic and dynamic analysis. The thesis also presents an overview of the established numerical tools for the analysis of arch and shell structures, together with their strengths and disadvantages. The bases of the combined finite-element method and its strengths are also presented. The main motivation was the development of precise, robust and computationally efficient numerical models. The model for the analysis of thin beam and arch structures uses straight two-noded rotation free finite elements, and takes into account linear-elastic material behaviour, finite displacement, finite rotations and small strains. The thesis describes axial and bending carrying mechanisms of a beam finite element in detail. The presented model is implemented into the open source FDEM package ‘Yfdem’. Performance of the new numerical model is demonstrated on simple benchmark tests by a comparison with known analytical and numerical results. Its application for the seismic analysis of arch structures is presented. This thesis also presents a new numerical model for analysis of thin plate and shell structures. The model uses three-noded triangular finite elements, and takes into account linear-elastic material behaviour, finite rotations, finite displacements and small strains. The thesis describes membrane and bending carrying mechanisms for triangular finite element in detail. The model is implemented into the open source FDEM package ‘Yfdem’. Performance of the new numerical model was demonstrated on simple benchmark tests by comparing it with the known analytical and numerical results. Its application in typical problems of stability of plate and shell structures is presented. Directions for further development and upgrade of the model in performing contact interaction and material nonlinearity are given

A New Algorithm for Dynamic Analysis of Thin Plates in the Combined Finite-Discrete Element Method

This paper presents a new numerical algorithm for a dynamic analysis of thin plate structures based on the combined finite-discrete element method (FDEM). A nonlinear analysis of thin plates subjected to static or dynamic load has been provided. The model uses 3-noded triangular finite elements and is implemented in the open source FDEM package - Yfdem. The performance of the new model on simple benchmark tests is presented

In Vivo and In Vitro Virulence Analysis of Four Genetically Distinct Toxoplasma gondii Lineage III Isolates

Toxoplasma gondii archetypes II and III are mildly virulent, yet virulence of variant strains is largely unknown. While lineage II dominates in humans in Europe, lineage III strains are present in various intermediate hosts. In Serbia, lineage III represents 24% of the population structure and occurs most frequently in domestic animals, implying a significant presence in the human food web. In this study, the virulence of four genetically distinct lineage III variants was assessed in vivo and in vitro. In vivo, two strains were shown to be intermediately virulent and two mildly virulent, with cumulative mortalities of 69.4%, 38.8%, 10.7%, and 6.8%, respectively. The strain with the highest mortality has previously been isolated in Europe and may be endemic; the strain with the lowest mortality matches ToxoDB#54, while the remaining two represent novel genotypes. Identical alleles were detected at ROP5, ROP16, ROP18, and GRA15. A set of in vitro analyses revealed proliferation and plaque formation as virulence factors. Higher levels of expression of ENO2 in intermediately virulent strains point to enhanced metabolism as the underlying mechanism. The results suggest that metabolic attenuation, and possibly stage conversion, may be delayed in virulent strains

Toxoplasma gondii genotypes circulating in domestic pigs in Serbia

Consumption of undercooked or raw pork is considered a significant risk factor for human infection with Toxoplasma gondii. In this study, we investigated the genetic structure of 18 T. gondii strains obtained from slaughter pigs from Northern Serbia (mainly Vojvodina). The examined samples originated from eight pigs from large commercial farms, six backyard pigs and four free-range Mangalica pigs, all found to be positive for either viable T. gondii or T. gondii DNA. Genotyping was attempted from both pig tissues and mouse brains from the bioassays using a multiplex multilocus nested polymerase chain reaction-restriction fragment length polymorphism (Mn-PCR-RFLP) method with seven markers (GRA6,.lt. SAG2, PK-1, BTUB, C22-8, CS3 and Apico). Identification was achieved for nine T. gondii isolates. Seven isolates were classified as type II and two as type III. These results are consistent with previous studies on animal isolates from Serbia as well as with previous reports that type III is more frequently found in samples from Southern Europe than in those from other parts of the continent

Multiplicative Decomposition Based FDEM Model for Membrane Structures

A finite strain large displacement model for membrane structures based on the combined finite-discrete element method (FDEM) has been developed. The model is implemented in the open source FDEM package - Yfdem. The paper also presents benchmark tests and numerical results

Stabilnost napitka od maslinovog lista ovisno o skladištenju na različitim temperaturama

In the olive oil production, olive leaves mostly often remain insufficiently used and represent waste, although many studies showed its anticancer, antiinflammatory and antimicrobial properties due to abundance of polyphenols, which makes olive leaves potential ingredient for functional food production. Also, olive leaf drink due to it valuable composition represents functional drink itself. But, functional properties can reduce due to polyphenols degradation, especially during storage. Hence, this research aimed to investigate the stability of olive leaf drink during nine weeks storage at different temperatures (8, 22 and 32 °C). Influence of storage time and storage temperature was monitored by analysis of total phenols, antioxidant capacity by DPPH, color parameters (L*, a*, b*, , BI) and sensory properties of olive leaf drink samples. Obtained results showed that total phenols slightly decreased during storage, being most stabile on 8 °C. Antioxidant capacity showed approximately similar trend. Color of all samples darkened by the storage with increase rate of L*, and BI related to temperature increase. Major color changes were observed by the storage ending at 32 °C. Sensory analysis confirmed change of olive leaf drink color, where yellowness decreased as brownness increased by the storage time and temperature. Odor and flavor decreased with time and at higher storage temperatures. Intensity of drink\u27s main taste attributes (astringent and bitter taste) decreased by storage time, especially on higher temperatures, resulting with higher scored harmony taste. Obtained results showed good stability of olive leaf drink, suggesting its potential as a functional product or semi-product.U proizvodnji maslinovog ulja, maslinovo lišće najčešće ostaje nedovoljno upotrebljeno i predstavlja otpad, iako su mnoge studije pokazale njegova antikancerogena, protuupalna i antimikrobna svojstva zbog obilja polifenola, što ga čini potencijalnim sastojkom za proizvodnju funkcionalne hrane. Također, napitak od maslinovog lista predstavlja samostalno funkcionalno piće zbog njegovog vrijednog sastava. No, funkcionalna svojstva se, osobito tijekom skladištenja, mogu smanjiti zbog degradacije polifenola. Stoga je ovo istraživanje imalo za cilj istražiti stabilnost napitka od maslinovog lista tijekom devet tjedana skladištenja na različitim temperaturama (8, 22 i 32 °C). Utjecaj vremena i temperature skladištenja ispitan je određivanjem ukupnih fenola, antioksidacijskog kapaciteta DPPH metodom, parametara boje (L*, a*, b*, , BI) i senzorskih svojstava napitka od maslinovog lista. Dobiveni rezultati pokazali su da se ukupni fenoli tijekom skladištenja neznatno smanjuju, pokazujući najveću stabilnost na 8 °C. Antioksidacijski kapacitet pokazao je približno isti trend. Boja svih uzoraka je skladištenjem potamnila uz porast L*, i BI povećanjem temperature. Najveće promjene boje zabilježene su na 32 °C krajem skladištenja. Senzorska analiza potvrdila je promjenu boje napitka od maslinovog lista smanjenjem žute te povećanjem smeđe boje s vremenom i temperaturom skladištenja. Miris i aroma su se s vremenom i na višoj temperaturi smanjili. Intenzitet glavnih svojstava okusa napitka (trpak i gorak okus) se za vijeme skladištenja smanjio, osobito na višim temperaturama, što je rezultiralo više ocijenjenom harmoničnosti okusa. Dobiveni rezultati pokazali su dobru stabilnost napitka od maslinovog lista ukazujući na njegov potencijal kao funkcionalnog proizvoda ili poluproizvoda

The Influence of Processing on Physico-chemical Parameters, Phenolics, Antioxidant Activity and Sensory Attributes of Elderberry (Sambucus nigra L.) Fruit Wine

Production of elderberry fruit wine in Croatia is very limited and primarily conducted in small family farms, so the aim of this research was to determine the quality parameters of elderberry fruit and elderberry fruit wine as the fi nal product. Six types of elderberry fruit wines (A, B, C, D, E and F) were produced with addition of different amounts of sugar (0, 0.5, 1, 1.5, 1.5 and 0.5 kg per 4 kg of elderberry fruit) and water (wines C, D, E). Quality of wines was evaluated using physico-chemical analysis, determination of phenolic compounds (total phenols, total flavonoids, hydrolised tannins and anthocyanins), antioxidant activity and sensory evaluation. According to the amount of total sugar after the fermentation, wines A, B, C and F can be considered as dry wines while wines D and E can be categorized as semi-dry wines. Total acidity in all wines was higher when compared to fresh elderberry fruit. Fresh elderberry fruit as well as wines had high concentration of phenolic compound with anthocyanins in the highest extent, although the winemaking process decreased the amount of phenolics. Both elderberry fruit and wine show high antioxidant activity and present a rich source of biologically active compounds. Consumers found the wine with high sugar amount and low acidity to be the most acceptable

The Influence of Processing on Physico-chemical Parameters, Phenolics, Antioxidant Activity and Sensory Attributes of Elderberry (Sambucus nigra L.) Fruit Wine

Production of elderberry fruit wine in Croatia is very limited and primarily conducted in small family farms, so the aim of this research was to determine the quality parameters of elderberry fruit and elderberry fruit wine as the fi nal product. Six types of elderberry fruit wines (A, B, C, D, E and F) were produced with addition of different amounts of sugar (0, 0.5, 1, 1.5, 1.5 and 0.5 kg per 4 kg of elderberry fruit) and water (wines C, D, E). Quality of wines was evaluated using physico-chemical analysis, determination of phenolic compounds (total phenols, total flavonoids, hydrolised tannins and anthocyanins), antioxidant activity and sensory evaluation. According to the amount of total sugar after the fermentation, wines A, B, C and F can be considered as dry wines while wines D and E can be categorized as semi-dry wines. Total acidity in all wines was higher when compared to fresh elderberry fruit. Fresh elderberry fruit as well as wines had high concentration of phenolic compound with anthocyanins in the highest extent, although the winemaking process decreased the amount of phenolics. Both elderberry fruit and wine show high antioxidant activity and present a rich source of biologically active compounds. Consumers found the wine with high sugar amount and low acidity to be the most acceptable

Total Phenolics and Antioxidant Capacity Assays of Selected Fruits

The biologically active compounds, especially fruit phenolics, are responsible for reduced risk of developing chronic diseases (cardiovascular disease, cancer, diabetes, etc.), due to their antioxidant activities. Th is study summarized some chemical principles of antioxidant capacity assays and the antioxidant capacity of selected fruit varieties (strawberry, sour cherry, cornelian cherry, blackthorn). We determined the contents of total phenolics (TPC), total flavonoids (TF), total non-flavonoids (TNF) and total anthocyanins (TA) in selected fruits. The content of TPC, TF and TNF in fruits was analyzed by Folin-Ciocalteu colorimetric method, while the TA content of extracts was determined by bisulphite bleaching method. Total antioxidant capacity (TAC) of selected fruits were analyzed using 2,2-azinobis(3-ethylbenzothiazoline- 6-sulfonic acid) radical cation (ABTS), 2,2-diphenil-1-picrylhydrazyl radical scavenging capacity (DPPH), ferric ion reducing antioxidant power (FRAP) and oxygen radical absorbance capacity (ORAC). Cornelian cherry had the highest content of TPC, while sour cherry cv. Marasca had the highest content of TA. TAC was the highest in cornelian cherry fruits and decreased in other fruits as follow: sour cherry, blackthorn and strawberry. The fruit extracts had different TAC in relation to the method applied, and the different TAC of fruits can be ascribed to their TPC, TF, TNF or TA content. There was a direct correlation between the TAC determined using DPPH and ORAC methods and the TA content of fruit extracts. Using FRAP method correlation was weaker, but using ABTS method correlation was not observed. The ripping correlation between TF or TNF and TAC was observed using ABTS and ORAC methods