On Prediction of 3d Stress State in Elastic Shell by Higher-order Shell Formulations

In this work we study the accuracy of modem higher-order shell finite element formulations in computation of 3d stress state in elastic shells. In that sense we compare three higher-order shell models: (i) with seven dislacement-like kinematic parameters, and (ii, iii) with six displacement-like kinematic parameters plus one strain-like kinematic parameter introduced by two different versions of enhanced assumed strain (EAS) concept. The finite element approximations of all shell models are based on 4-node quadrilateral elements. Geometrically nonlinear and consistently linearized forms of considered formulations are given. Several numerical examples are presented, where computed stresses are compared with analytical solutions. It was found that through-the-thickness variation of some (non-dominant) stress tensor components, including through-the-thickness normal stress, may be computed very inaccurately. The reliable representation for those stresses can be interpreted only if the ``layer-wise'' averaging or the through-the-thickness averaging is performed

Model adaptivity for finite element analysis of thin or thick plates based on equilibrated boundary stress resultants

Purpose – The purpose of this paper is to address error-controlled adaptive finite element (FE) method for thin and thick plates. A procedure is presented for determining the most suitable plate model (among available hierarchical plate models) for each particular FE of the selected mesh, that is provided as the final output of the mesh adaptivity procedure. \ud \ud Design/methodology/approach – The model adaptivity procedure can be seen as an appropriate extension to model adaptivity for linear elastic plates of so-called equilibrated boundary traction approach error estimates, previously proposed for 2D/3D linear elasticity. Model error indicator is based on a posteriori element-wise computation of improved (continuous) equilibrated boundary stress resultants, and on a set of hierarchical plate models. The paper illustrates the details of proposed model adaptivity procedure for choosing between two most frequently used plate models: the one of Kirchhoff and the other of Reissner-Mindlin. The implementation details are provided for a particular case of the discrete Kirchhoff quadrilateral four-node plate FE and the corresponding Reissner-Mindlin quadrilateral with the same number of nodes. The key feature for those elements that they both provide the same quality of the discretization space (and thus the same discretization error) is the one which justifies uncoupling of the proposed model adaptivity from the mesh adaptivity. \ud \ud Findings – Several numerical examples are presented in order to illustrate a very satisfying performance of the proposed methodology in guiding the final choice of the optimal model and mesh in analysis of complex plate structures. \ud \ud Originality/value – The paper confirms that one can make an automatic selection of the most appropriate plate model for thin and thick plates on the basis of proposed model adaptivity procedure.\u

Adaptive modeling of plate structures

V disertaciji se ukvarjamo z različnimi vidiki modeliranja ploskovnih konstrukcij s končnimi elementi. Modeliranje plošč je nekoliko specifično in je zaradi kompleksnosti in pojavov, ki jih opisuje, bistveno prispevalo k razvoju same metode končnih elementov. Danes je na voljo več uveljavljenih modelov plošč in pripadajočih končnih elementov, ki uporabniku nudijo široko množico možnosti, iz katere lahko izbira. Prav široka možnost izbire predstavlja tudi največjo težavo, saj je težje določiti, kateri model je primernejši in tudi, katera mreža končnih elementov je za dan problem optimalna. Glavni cilj disertacije je raziskati ključne korake v procesu prilagodljivega modeliranja plošč, ki omogoča samodejno določitev optimalnega modela za dan problem. Ker je prilagodljivo modeliranje odvisno od zanesljivih ocen napak, je večji del disertacije posvečen metodam za izračun diskretizacijske in modelske napake. Na praktičnih primerih smo preučili nekaj najbolj uveljavljenih metod za oceno napake. V nasprotju z ocenami napake diskretizacije, je modelsko napako mnogo težje določiti. Posebna pozornost je bila zato namenjena metodi uravnoteženja rezidualov, ki ima potencial tudi na področju ocene modelske napake. V tem smislu to delo predstavlja pomemben prispevek k področju računanja modelske napake za plošče. Koncept prilagodljivega modeliranja ploskovnih konstrukcij je bil preskušen na hierarhični družini končnih elementov za plošče - od tankih plošč do modelov višjega reda, ki upoštevajo deformacije po debelini. Ravno dobro vzpostavljena hierarhija v družini končnih elementov se je pokazala za ključno pri zanesljivi oceni modelske napake. Prilagodljivo modeliranje ploskovnih konstrukcije je bilo preskušeno na nekaj zahtevnejših primerih. Območje je bilo najprej modeliranjo z najbolj grobim modelom na sorazmerno redki mreži. Z uporabo informacije o napaki začetnega izračuna je bil zgrajen nov model. Primerjava izračuna na novem modelu z začetnim računom je pokazala, da je predlagan način prilagodljivega modeliranja sposoben nadzorovati porazdelitev napake, kakor tudi zajeti vse pomembnejše po- jave, ki so značilni za modeliranje plošč.The thesis deals with adaptive finite element modeling of plate structures. The finite element modeling of plates has grown to a mature research topic, which has contributed significantly to the development of the finite element method for structural analysis due to its complexity and inherently specific issues. At present, several validated plate models and corresponding families of working and efficient finite elements are available, offering a sound basis for an engineer to choose from. In our opinion, the main problems in the finite modeling of plates are nowadays related to the adaptive modeling. Adaptive modeling should reach much beyond standard discretization (finite element mesh) error estimates and related mesh (discretization) adaptivity. It should also include model error estimates and model adaptivity, which should provide the most appropriate mathematical model for a specific region of a structure. Thus in this work we study adaptive modeling for the case of plates. The primary goal of the thesis is to provide some answers to the questions related to the key steps in the process of adaptive modeling of plates. Since the adaptivity depends on reliable error estimates, a large part of the thesis is related to the derivation of computational procedures for discretization error estimates as well as model error estimates. A practical comparison of some of the established discretization error estimates is made. Special attention is paid to what is called equilibrated residuum method, which has a potential to be used both for discretization error and model error estimates. It should be emphasized that the model error estimates are quite hard to obtain, in contrast to the discretization error estimates. The concept of model adaptivity for plates is in this work implemented on the basis of equilibrated residuum method and hierarchic family of plate finite element models. The finite elements used in the thesis range from thin plate finite elements to thick plate finite elements. The latter are based on a newly derived higher order plate theory, which includes through the thickness stretching. The model error is estimated by local element-wise compu- tations. As all the finite elements, representing the chosen plate mathematical models, are re-derived in order to share the same interpolation bases, the difference between the local com- putations can be attributed mainly to the model error. This choice of finite elements enables effective computation of the model error estimate and improves the robustness of the adaptive modeling. Thus the discretization error can be computed by an independent procedure. Many numerical examples are provided as an illustration of performance of the derived plate elements, the derived discretization error procedures and the derived modeling error procedure. Since the basic goal of modeling in engineering is to produce an effective model, which will produce the most accurate results with the minimum input data, the need for the adaptive modeling will always be present. In this view, the present work is a contribution to the final goal of the finite element modeling of plate structures: a fully automatic adaptive procedure for the construction of an optimal computational model (an optimal finite element mesh and an optimal choice of a plate model for each element of the mesh) for a given plate structure. vii

On the electrostatics of DNA in chromatin

We examine the interaction between DNA molecules immersed in an aqueous solution of oppositely charged, trivalent spermidine molecules. The DNA molecules are modeled as planar, likecharged surfaces immersed in an aqueous solution of multivalent, rod-like ions consisting of rigidly bonded point charges. An approximate field theory is used to determine the properties of this system from the weak to the intermediate through to the strong coupling regimes. In the weak coupling limit, the interaction between the charged surfaces is only repulsive, whereas in the intermediate coupling regime, the rod-like ions with spatial charge distribution can induce attractive force between the charged surfaces. In the strong coupling limit, the inter-ionic charge correlations induce attractive interaction at short separations between the surfaces. This theoretical study can give new insights in the problem of interaction between DNA molecules mediated by trivalent spermidine molecules

A field theoretic approach to the electric interfacial layer : mixture of trivalent rod-like and monovalent point-like ions between charged walls

In this paper, we study the interaction between charged macroions (surfaces) immersed in a solution of oppositely charged, rod-like counterions and point-like co-ions. The system is modeled by a field theoretic approach, which was extended to treat mixtures of rod- and point-like ions. The theory is applicable from the weak to the intermediate through to the strong coupling regimes. In the weak coupling limit, the force between the charged surfaces are only repulsive. In the intermediate coupling regime, the rod-like ions can induce attractive force between the charged surfaces. In the strong coupling limit, the inter-ionic charge correlations dominate the attractive forces at short separations between the charged surfaces

Twelve years (2005-2017) of scientific and professional work in the field of stored products pests protection in Slovenia: Poster

Scientific and professional work in the field of stored products pests protection in Slovenia began in 2005, when we tested the efficacy of entomopathogenic nematodes against the granary weevil (Sitophilus granarius) and the sawtoothed grain beetle (Oryzaephilus surinamensis) adults under laboratory conditions. In 2007, we participated as partners in the project SEE-ERA.NET “Development of a non-toxic, ecologically compatible, natural-resource based insecticide from diatomaceous earth deposits of South Eastern Europe to control storedgrain insects pests” (coordinated by C. Athanassiou), and we thus became acquainted with the research work in the field of investigation the efficacy of diatomaceous earth in controlling beetles from the Sitophilus genus. We have continued the research of different aspects of diatomaceous earth (the influence of geochemical composition and abiotic factors on its efficiency, the effects of individual and combined application, the effects on various harmful insect pests, etc.). In search for comparable substances to diatomaceous earth (regarding the efficacy), we have studied insecticidal effects of quartz sand and entomopathogenic nematodes from Slovenia, plant powders and essential oils on various harmful beetles. In the recent years, our research work has been mainly dedicated to studying the efficacy of wood ash and zeolites as natural insecticides, which have demonstrated sufficient efficiency in suppressing Sitophilus beetles. In the same period, we studied the seasonal dynamics of the Indian mealmoth (Plodia interpunctella), the Mediterranean flour moth (Ephestia kuehniella) and the Angoumois grain moth (Sitotroga cerealella) in cereal stores, where we were also searching for possible indigenious natural enemies of stored product insects pests. We have confirmed the occurrence of two parasitoids, Anisopteromalus calandrae and Dibrachys microgastri. In 2017, we have organized the 11th Conference of the IOBC/wprs Working Group on Integrated Protection of Stored Products (Ljubljana, 3-5 July), which was attended by 136 participants from 25 countries. We also transfer knowledge to Slovenian agricultural specialists about the harmfulness and possible ways of controlling stored products insects pests. In 2014, we have organized a workshop on this topic (“From Technological Maturity to Storing of Cereals and Legumes“). In 2015, we have hosted C. Athanassiou as an invited lecturer at the 12th Slovenian Conference on Plant Protection with international participation in Ptuj. In recent years, we have been working with experts from other countries with the aim of studying the efficacy of environmentally acceptable insecticides (spinosad, spinetoram) and the influence of cereal production technologies on grains’ susceptibility to attack by Sitophilus beetles. Furthermore, we participate in the research regarding the efficiency of new formulations of insecticidal preparations. The paper presents the chronology of activities in this area of our work.Scientific and professional work in the field of stored products pests protection in Slovenia began in 2005, when we tested the efficacy of entomopathogenic nematodes against the granary weevil (Sitophilus granarius) and the sawtoothed grain beetle (Oryzaephilus surinamensis) adults under laboratory conditions. In 2007, we participated as partners in the project SEE-ERA.NET “Development of a non-toxic, ecologically compatible, natural-resource based insecticide from diatomaceous earth deposits of South Eastern Europe to control storedgrain insects pests” (coordinated by C. Athanassiou), and we thus became acquainted with the research work in the field of investigation the efficacy of diatomaceous earth in controlling beetles from the Sitophilus genus. We have continued the research of different aspects of diatomaceous earth (the influence of geochemical composition and abiotic factors on its efficiency, the effects of individual and combined application, the effects on various harmful insect pests, etc.). In search for comparable substances to diatomaceous earth (regarding the efficacy), we have studied insecticidal effects of quartz sand and entomopathogenic nematodes from Slovenia, plant powders and essential oils on various harmful beetles. In the recent years, our research work has been mainly dedicated to studying the efficacy of wood ash and zeolites as natural insecticides, which have demonstrated sufficient efficiency in suppressing Sitophilus beetles. In the same period, we studied the seasonal dynamics of the Indian mealmoth (Plodia interpunctella), the Mediterranean flour moth (Ephestia kuehniella) and the Angoumois grain moth (Sitotroga cerealella) in cereal stores, where we were also searching for possible indigenious natural enemies of stored product insects pests. We have confirmed the occurrence of two parasitoids, Anisopteromalus calandrae and Dibrachys microgastri. In 2017, we have organized the 11th Conference of the IOBC/wprs Working Group on Integrated Protection of Stored Products (Ljubljana, 3-5 July), which was attended by 136 participants from 25 countries. We also transfer knowledge to Slovenian agricultural specialists about the harmfulness and possible ways of controlling stored products insects pests. In 2014, we have organized a workshop on this topic (“From Technological Maturity to Storing of Cereals and Legumes“). In 2015, we have hosted C. Athanassiou as an invited lecturer at the 12th Slovenian Conference on Plant Protection with international participation in Ptuj. In recent years, we have been working with experts from other countries with the aim of studying the efficacy of environmentally acceptable insecticides (spinosad, spinetoram) and the influence of cereal production technologies on grains’ susceptibility to attack by Sitophilus beetles. Furthermore, we participate in the research regarding the efficiency of new formulations of insecticidal preparations. The paper presents the chronology of activities in this area of our work

Social Enterprise Law: A Theoretical And Comparative Perspective

This article analyzes social enterprise from a theoretical and comparative perspective. Social enterprises are distinct from nonprofits because they have equity-holders; they are distinct from socially minded for-profits because their mission is sacrosanct. We set out a regulatory template to support entities with this unique hybrid character. Only companies that commit to a mission-centric purpose, and adopt transparency and accountability mechanisms that police faithfulness to this commitment, would be entitled to call themselves “social enterprises.” This narrowly tailored regulatory structure would allow these firms to stand out and attract likeminded consumers and investors. Neither the US nor the EU offers something like this. Social enterprises in the US may form as benefit corporations and obtain the related B Corp certification. These mechanisms, while laudable, fall short because they group socially minded firms and social enterprises together despite the important distinction between the two. Such conflation is not a problem in the EU. A number of EU countries have specific social-enterprise regulations. But the rules vary greatly. They also tend to define social enterprise too narrowly, fail to mandate appropriate governance structures, and lack transparency mandates. A proposed EU-wide rule would help harmonize the area, but it is too reliant on country-level rules to have a significant impact. Social enterprises on both continents would benefit from new rules that appreciate their unique role in the economy and hold them to their principles

About Previous Investigations Regarding the Role of Glucosinolates in Controlling Brassica Insect Pests in Slovenia

The chapter presents previous field and laboratory investigations of cabbage flea beetles (Phyllotreta spp.) and cabbage stink bugs (Eurydema spp.) interactions with different Brassica crops in Slovenia. The special emphasis is given to an influence of different glucosinolates on injuries caused by mentioned economically important two genera of insect pests. In the study, we found out that the content of glucosinolates differs between different Brassica species, as well as between individual plant organs of the same species. The content of glucosinolates is conditioned also by environmental influences. Among the analysed glucosinolates, glucobrassicin was presented in all plant species. In almost all plant species, it inhibited the feeding of cabbage flea beetles, except in oil rape, where it had stimulative effects. We have established that the influence of individual glucosinolate on Phyllotreta spp. and Eurydema spp. is not identical as it differs between individual plant species. Because of the variability of glucosinolates as well as different preferences of the studied groups of harmful pests in regard to the plant species, one of the options for diminishing the damage caused by cabbage stink bugs and cabbage flea beetles is the use of mixed Brassica crops for trapping the pests in the growing season. In the future, glucosinolates should be employed to a greater extent in environmentally acceptable ways of food production, one of which is also the use of trap crops in order to reduce harmful effects of cabbage stink bugs