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Gdańsk University of Technology

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  • Numerical Study on Seismic Response of a High-Rise RC Irregular Residential Building Considering Soil-Structure Interaction
    • Tomasz Falborski
    2020

    The objective of the present study is to investigate the importance of soilstructure interaction effects on the seismic response of a high-rise irregular reinforced-concrete residential building. In order to conduct this research, a detailed three-dimensional structure model was subjected to various earthquake excitations, also including a strong mining tremor. Soil-foundation flexibility was represented using the spring-based solutions, incorporating foundation springs and dashpots. For each soil type analyzed in this study, the foundation stiffness was calculated using the static stiffness, embedment correction factors, and dynamic stiffness modifiers. The influence of diverse soil conditions (represented by their average effective profile velocities and shear moduli) on the dynamic characteristics (e.g. fundamental vibration period) and seismic response (e.g. peak lateral accelerations) of the structure model was investigated and discussed. The numerical analysis results clearly demonstrate that the seismic performance of the building to the strong earthquake shaking can be significantly affected by the soil-structure interaction effects.

  • O analizach kratownicy ze ściskanym pasem dolnym
    • Marcin Krajewski
    2020 Inżynieria i Budownictwo

    Praca poświęcona jest analizom stateczności kratownicy poddanej obciążeniu skierowanemu pionowo ku górze. Przedstawione zostały badania wpływu stężeń usytuowanych w pasie górnym na nośność wyboczeniową konstrukcji. Przedstawiony został model zastępczy kratownicy w formie ściskanego pasa dolnego na podłożu sprężystym. Analizie poddano również wpływ sztywności skrętnej podpór skrajnych na wartość obciążenia krytycznego.

  • O historii i działalności Katedry Konstrukcji Metalowych Politechniki Gdańskiej
    • Piotr Iwicki
    2020 Full text Inżynieria i Budownictwo

    W artykule przedstawiono prowadzone w Katedrze Konstrukcji Metalowych badania naukowe, współpracę z przemysłem i działalność dydaktyczną od czasu jej powstania w 1945 r. po dzień dzisiejszy.

  • O nadjeżdżającej rewolucji w transporcie
    • Paweł Gora
    2020 Full text Pismo PG

    1,3 miliona – tyle osób rocznie na świecie ginie w wypadkach drogowych. Ponad 20 milionów zostaje rannych! 4 miliardy złotych – prawie tyle rocznie tracą kierowcy w 7 największych miastach w Polsce z powodu korków (a są to jedynie szacowane koszty straconego czasu i paliwa, bez uwzględnienia np. negatywnego wpływu na środowisko). Czy możemy coś z tym zrobić?

  • O średniowiecznej architekturze zakonów żebraczych w Chełmnie. Na marginesie tomu pierwszego "Księgi klasztorów ziemi chełmińskiej w średniowieczu"
    • Piotr Samól
    2020 Full text Zapiski Historyczne. Poświęcone Historii Pomorza i Krajów Bałtyckich

    Celem artykułu było przedstawienie wyników wieloletnich badań autora nad architekturą zakonów żebraczych w Chełmnie i polemika z ustaleniami najnowszej publikacji na ten temat. Autor, historyk architektury, prowadził kwerendy archiwalne i badania terenowe w Chełmnie od 2010 r. zbierając obszerny materiał źródłowy o kościołach świętych Piotra i Pawła (dominikanów) oraz świętych Mikołaja i Jakuba (franciszkanów). Na jego podstawie podjął polemikę z ustaleniami najnowszej monografii dotyczącej budownictwa klasztornego na ziemi chełmińskiej autorstwa Moniki Jakubek-Raczkowskiej, Juliusza Raczkowskiego i Piotr Olińskiego. Artykuł został podzielony na cztery części. W pierwszej z nich omówiono konieczność sprzężenia metod historycznych i architektonicznych, które pozwalają traktować zabytek jak źródło historyczne. Wskazano na niewykorzystane dotychczas źródła z archiwów polskich i niemieckich, które pozwalają doprecyzować historię budowlana założeń zakonów żebraczych w Chełmnie. Druga część dotyczy różnic w ustaleniach na temat kościoła dominikańskiego. Autor odnosi się w niej do podnoszonych w „Księdze klasztorów ziemi chełmińskiej w średniowieczu” wątpliwości, co do interpretacji wyników jego badań z 2014 r. Krótki przegląd stanu badań zestawiono z analizowanymi śladami materialnymi (wynikami badań architektonicznych), co pozwoliło falsyfikować wiele formułowanych w przeszłości hipotez na temat jego rozwoju przestrzennego. W trzeciej części omówiono możliwości rekonstrukcji układu przestrzennego średniowiecznego klasztoru predykantów oraz podstawowe fazy przebudowy w okresie nowożytnym, które poprzedziły rozbiórkę w latach trzydziestych XIX w. Ustalenia te są szczególnie ważne dla prowadzonych w przyszłości badań archeologicznych. Odstąpiono od przedstawienia historii budowlanej całego kościoła świętych Mikołaja i Jakuba, ponieważ jego złożona materia jest przedmiotem osobnego opracowania monograficznego. Ostatnia, czwarta część zawiera uwagi na temat lektoriów w świątyniach dominikanów i franciszkanów w Chełmnie. Ważnym elementem jest przedstawiona autorska dokumentacja śladów architektonicznych, pominięta w dotychczasowej literaturze przedmiotu. Opisane wyżej badania historyczne i architektoniczne skłaniają do refleksji nad metodą badań obiektów historycznych, które wymagają dobrego rozpoznania źródeł – zarówno pisanych, jak i architektonicznych. Ustalenia mają zastosowanie nie tylko w historii architektury, ale i dyscyplinach pokrewnych.

  • O wymiarowaniu kształtowników giętych na zimno według eurokodów i norm amerykańskich.
    • Patryk Deniziak
    2020 Full text Inżynieria i Budownictwo

    Nośne konstrukcje z kształtowników giętych na zimno były wykorzystywane w przemyśle lotniczym i motoryzacyjnym od początku XX w. W obiektach budowlanych początkowo pełniły one rolę elementów konstrukcyjnych drugorzędnych, takich jak ościeżnice czy elementy ścian działowych. Obecnie są stosowane również jako główne elementy nośne w halach przemysłowych (słupy, wiązary, konstrukcje wsporcze dźwignic). Pręty cienkościenne, ze względu na dużą smukłość ścianek, są wrażliwe na zjawisko utraty stateczności. W niniejszym artykule przedstawiono główne założenia i różnice pomiędzy dwiema metodami wymiarowania prętów cienkościennych: metoda amerykańska oraz europejska.

  • Obraz olejny, 100x180 cm, Bez tytułu
    • Jan Buczkowski
    2020

    Prezentacja obrazu na wystawie w Centrum Sztuki Współczesnej Łaźnia w Gdańsku

  • Obtaining and Characterization of the PLA/Chitosan Foams with Antimicrobial Properties Achieved by the Emulsification Combined with the Dissolution of Chitosan by CO2 Saturation
    • Szymon Mania
    • Karolina Partyka
    • Joanna Pilch
    • Ewa Augustin
    • Mateusz Cieślik
    • Jacek Ryl
    • Jia-Rong Jinn
    • Ya-Jane Wang
    • Anna Michałowska
    • Robert Tylingo
    2020 Full text

    A new method of obtaining functional foam material has been proposed. The materials were created by mixing the poly lactic acid (PLA) solution in chloroform, chitosan (CS) dissolved in water saturated with CO2 and polyethylene glycol (PEG), and freeze-dried for removal of the solvents. The composite foams were characterized for their structural (SEM, FT-IR, density, porosity), thermal (DSC), functional (hardness, elasticity, swelling capacity, solubility), and biological (antimicrobial and cytotoxic) properties. Chitosan in the composites was a component for obtaining their foamed form with 7.4 to 22.7 times lower density compared to the neat PLA and high porosity also confirmed by the SEM. The foams had a hardness in the range of 70–440 kPa. The FT-IR analysis confirmed no new chemical bonds between the sponge ingredients. Other results showed low sorption capacity (2.5–7.2 g/g) and solubility of materials (less than 0.2%). The obtained foams had the lower Tg value and improved ability of crystallization compared to neat PLA. The addition of chitosan provides the bacteriostatic and bactericidal properties against Escherichia coli and Staphylococcus aureus. Biocompatibility studies have shown that the materials obtained are not cytotoxic to the L929 cell line

  • Occurrences, sources, and transport of organochlorine pesticides in the aquatic environment of Antarctica
    • Joanna Potapowicz
    • Dimitra Lambropoulou
    • Christina Nannou
    • Krystyna Kozioł
    • Żaneta Polkowska
    2020 Full text SCIENCE OF THE TOTAL ENVIRONMENT

    We review information on the concentration levels of organochlorine pesticides in the abiotic aquatic environment (in seawater, sea ice, surface freshwater, snow, firn, and glacial ice) and the organisms inhabiting those, in Antarctica. Particular attention is given to the environmental fate of these pollutants, which modifies their impact on the organisms living in the Antarctic. OCPs have been delivered to the Antarctic environment mainly via long-range transport from inhabited areas, and due to their long accumulation they are sometimes reemitted from melting cryosphere. Since climate change is forecasted to intensify, the release of anthropogenic pollutants from increased seasonal thaw may prove its importance for the future state of this unspoiled environment. However, the limited estimations of the OCPs storage magnitude in the Antarctic cryosphere are relatively crude and may err significantly towards higher values. The OCPs are already present in different types of animal tissues at every trophic level, where they may cause negative effects such as reproductive disorders, decreased survival rates, and an increased parasitic load. Therefore, it is important to continuously monitor OCP concentrations in various elements of the Antarctic environment and the fate of these pollutants, taking into account their global and local sources, including the remobilization from frozen state.

  • Ocena jakości superkondensatorów wybranymi metodami, wykorzystując zjawiska losowe i badania rozkładu temperatury
    • Stanisław Galla
    • Arkadiusz Szewczyk
    • Janusz Smulko
    2020 Full text Przegląd Elektrotechniczny

    W artykule przedstawiono metody analizy jakości wykonania próbek superkondensatorów na podstawie pomiarów szumów generowanych w ich strukturach oraz rozkładów temperatury na ich powierzchni. Prezentowane metody zostały porównane z obecnie stosowanymi parametrami oceny jakości tych elementów. Wyniki uzasadniają wprowadzenie dodatkowych parametrów, pozwalających oceniać jakość superkondensatorów.

  • Ocena klimatu akustycznego w przestrzeni pasażerskiej elektrycznego zespołu trakcyjnego serii EN57
    • Roksana Licow
    • Dominika Szabłowska
    2020 Full text Pojazdy Szynowe

    W pracy przedstawiono wyniki badań poziomów dźwięku w przestrzeni pasażerskiej elektrycznego zespołu trakcyjnego (EZT) serii EN57 podczas postoju, rozruchu, jazdy oraz hamowania. Badania przeprowadzono na podstawie autorskiej metodyki badawczej bazując na normie PNEN ISO 3381:Kolejnictwo. Akustyka. Pomiar hałasu wewnątrz pojazdów szynowych. Badania przeprowadzono na linii kolejowej nr 250 od przystanku Gdańsk Śródmieście do stacji Rumia. Celem badań była ocena klimatu akustycznego w przestrzeni pasażerskiej elektrycznego zespołu trakcyjnego serii EN57, trójmiejskiej szybkiej kolei miejskiej linii S2 Gdańsk Śródmieście – Rumia. Wyniki przeprowadzonej analizy wskazały na miejsca potencjalnie zagrożone wyższymi poziomami dźwięków niż pozostałe oraz wpływ tych poziomów dźwięku na pasażerów korzystających z transportu publicznego jakim jest EZT serii EN57 w Trójmieście.

  • Ocena komfortu pieszego na kładkach. Case study
    • Anna Banaś
    2020 Full text Builder

    Trend w projektowaniu nowych kładek dla pieszych wymaga, aby były one coraz bardziej „wyszukane” i lekkie. Bardzo często jednak z tego powodu obiekty te mają pierwszą częstotliwość giętną pomostu zbliżoną do wymuszenia chodem pieszego. W niniejszej pracy przedstawiono trzy konstrukcje kładek dla pieszych. Każda z nich znalazła się w innej grupie narażenia na wystąpienie drgań rezonansowych, z uwagi na pierwszą częstotliwość drgań giętnych pomostu. Przeprowadzone badania pokazały, że kładka nad drogą S8, która znajdowała się w wysokiej grupie ryzyka, bez względu na sposób wymuszenia spełnia najwyższy poziom komfortu. W przypadku kładki w Bydgoszczy, która znalazła się w średniej grupie ryzyka poziomy przyspieszeń były znacznie większe. Przy wymuszeniach synchronicznych zapewniały często tylko minimalny komfort jej użytkownikom. W przypadku kładki w Gdyni, mimo stosunkowo wysokiej wartości częstotliwości drgań własnych i niskiego ryzyka wystąpienia rezonansu, nawet dla bardzo małych grup pieszych przyspieszenia były na bardzo wysokim poziomie. Kładka w normalnych warunkach eksploatacji zapewnia minimalny komfort użytkownikom. Przy wymuszeniach synchronicznych poziom komfortu jest już jednak nieakceptowalny. Przeprowadzone analizy i badania pokazują, że jednym z kluczowych elementów etapu projektowania jest analiza dynamiczna.

  • Ocena stopnia denaturacji oraz zawartości hydroksyproliny w kosmetycznej bazie kolagenowej.
    • Szymon Mania
    2020

    W ramach zadania wykonano pomiary oraz opracowano wyniki dotyczące określenia temperatury denaturacji oraz zawartości hydroksyproliny w bazie kolagenowej.

  • Ocena zagrożenia korozyjnego zbiorników na terenie modernizowanego Terminala Paliw LOTOS w Piotrkowie Trybunalskim.
    • Krzysztof Żakowski
    • Kazimierz Darowicki
    • Łukasz Gaweł
    • Tadeusz Sonneck
    2020

    Zbadano zagrożenie korozyjne nowo budowanych zbiorników na terenie modernizowanego terminala paliw. Oceny dokonano na podstawie badań agresywności korozyjnej pobranych próbek gruntu oraz wykonanych pomiarów terenowych. Uzyskane wyniki będą wykorzystane przy projektowaniu systemu ochrony katodowej nowych zbiorników podziemnych.

  • Od postawy prozdrowotnej w stoczni jachtowej do ograniczania zagrożeń na stanowisku pracy formierza-laminiarza
    • Anna Dembicka
    • Katarzyna Mołas
    2020 Full text Problemy Jakości

    Tematyka zdrowia i bezpieczeństwa pracowników, coraz częściej popularyzowana w świecie biznesu, nadal stanowi dość mało rozpoznany obszar działalności polskich przedsiębiorstw. Niniejszy artykuł porusza ważką kwestię promocji zdrowia w miejscu pracy jako czynnika zwiększającego efektywność pracy oraz jego wpływ na osiąganie wysokiej jakości produktu. Publikacja omawia znaczenie postawy prozdrowotnej i sposobów jej kształtowania w przemyśle jachtowym na przykładzie pracy formierza-laminiarza. Uszczegółowionej analizie poddana zostaje kwestia zmniejszania uciążliwości i szkodliwości czynników występujących podczas naprawy błędów powstających w procesie laminowania jachtu. Artykuł wieńczą propozycje możliwych do wdrożenia aktywności prozdrowotnych zarówno w pracy, jak i poza miejscem pracy. Publikacja wchodzi w skład cyklu prezentującego różne aspekty zarządzania procesowego w przemyśle stoczni jachtowych. Artykuł koncentruje się na procesie zarządzania kapitałem ludzkim w świetle orientacji prozdrowotnej.

  • Oddziaływanie elektronów z wybranymi prekursorami metalicznych i półprzewodnikowych nanostruktur wytwarzanych za pomocą skupionych wiązek elektronowych
    • Sylwia Stefanowska-Tur
    2020 Full text

    Praca poświęcona jest oddziaływaniom elektronów z prostymi prekursorami metody FEBID. W szczególności wyznaczono oraz przeanalizowano całkowite przekroje czynne na rozpraszanie elektronów funkcji energii dla wybranych cząsteczek: SnCl4, TiCl4, C(CH3)4, Si(CH3)4 oraz Ge(CH3)4, C5H6. W ramach pracy badano korelacje pomiędzy wartościami całkowitych przekrojów czynnych, a wybranymi fizykochemicznymi wielkościami charakteryzującymi badane związki, takimi jak statyczna dipolowa polaryzowalność elektryczna oraz elektryczny moment dipolowy. Szczególną uwagę zwrócono na wpływ metylacji, w tetraedrycznych związkach węgla, krzemu i germanu, na efektywność procesu rozpraszania elektronów. Zbadano wpływ zmiany zarówno atomu centralnego, jak i zamiany atomów zewnętrznych w cząsteczce tetraedrycznej, na zależność energetyczną całkowitego przekroju czynnego. Przeprowadzone badania przyczyniają się do lepszego zrozumienia oddziaływania elektronów z cząsteczkami zawierającymi atomy C, Si, Ge, Sn oraz Ti.

  • Oko, obraz olejny na płótnie
    • Krzysztof Wróblewski
    2020

    Krzysztof Wróblewski w 1992 roku rozpoczął komponowanie symetrycznych obrazów składających się z realistycznych i abstrakcyjnych powierzchni. Połowę obrazu stanowią zawsze układy trójkątów. Relacje pomiędzy realizmem i abstrakcją oraz współzależność malarstwa i fotografii są kluczowymi zagadnieniami w jego twórczości. Jego prace często tworzą cykle tematyczne. Obraz pt. Oko prezentowany na 11. Charytatywnej Aukcji Sztuki Współczesnej Aperio należy do jednego z tych cyklów i jest charakterystyczny dla twórczości artysty.

  • Określenie przyczyn korozji śrub napędowych ORP Drużno.
    • Krzysztof Żakowski
    • Stefan Krakowiak
    2020

    Przedmiotem ekspertyzy było określenie przyczyn korozji śrub napędowych na okręcie ORP Drużno oraz wskazanie zaleceń odnośnie ograniczenia czynników powodujących ich korozję.

  • On Applications of Elements Modelled by Fractional Derivatives in Circuit Theory
    • Jacek Gulgowski
    • Tomasz Stefański
    • Damian Trofimowicz
    2020 Full text ENERGIES

    In this paper, concepts of fractional-order (FO) derivatives are reviewed and discussed with regard to element models applied in the circuit theory. The properties of FO derivatives required for the circuit-level modeling are formulated. Potential problems related to the generalization of transmission-line equations with the use of FO derivatives are presented. It is demonstrated that some formulations of FO derivatives have limited applicability in the circuit theory. Out of the most popular approaches considered in this paper, only the Grünwald–Letnikov and Marchaud definitions (which are actually equivalent) satisfy the semigroup property and are naturally representable in the phasor domain. The generalization of this concept, i.e., the two-sided fractional Ortigueira–Machado derivative, satisfies the semigroup property, but its phasor representation is less natural. Other ideas (including the Riemann–Liouville and Caputo derivatives—with a finite or an infinite base point) seem to have limited applicability.

  • On Applications of Fractional Derivatives in Circuit Theory
    • Jacek Gulgowski
    • Tomasz Stefański
    2020

    In this paper, concepts of fractional-order (FO) derivatives are discussed from the point of view of applications in the circuit theory. The properties of FO derivatives required for the circuit-level modelling are formulated. Potential problems related to the generalization of transmission line equations with the use of FO derivatives are presented. It is demonstrated that some of formulations of the FO derivatives have limited applicability in the circuit theory. That is, the Riemann-Liouville and Caputo derivatives with finite base point have a limited applicability whereas the Grünwald-Letnikov and Marchaud derivatives lead to reasonable results of the circuit-level modelling.

  • On Applications of Fractional Derivatives in Electromagnetic Theory
    • Jacek Gulgowski
    • Tomasz Stefański
    2020 Full text

    In this paper, concepts of fractional-order (FO) derivatives are analysed from the point of view of applications in the electromagnetic theory. The mathematical problems related to the FO generalization of Maxwell's equations are investigated. The most popular formulations of the fractional derivatives, i.e., Riemann-Liouville, Caputo, Grünwald-Letnikov and Marchaud definitions, are considered. Properties of these derivatives are evaluated. It is demonstrated that some of formulations of the FO derivatives have limited applicability in the electromagnetic theory. That is, the Riemann-Liouville and Caputo derivatives with finite base point have a limited applicability whereas the Grünwald-Letnikov and Marchaud derivatives lead to reasonable generalizations of Maxwell's equations.

  • On coertia and inertia in aspects of Natanson’s nonlinear extended thermodynamics
    • Janusz Badur
    • Paweł Ziółkowski
    • Tomasz Kowalczyk
    • Sylwia Gotzman
    • Daniel Sławiński
    • Tomasz Ochrymiuk
    • Marcin Daniel Lemański
    • Rafał Hyrzyński
    • Bartosz Kraszewski
    • Mateusz Bryk
    • Michał Stajnke
    • Piotr Józef Ziółkowski
    2020 Full text

    In this article, the previously underrepresented contributions of Natanson to the field of thermodynamics have been presented. In order to identify a source of irreversibility at Nature, Natanson introduced the concept of Coertia, which is similar to inertia. Natanson’s Coertia is a fundamental property of space that is responsible for every irreversible phenomena in matter, as well as in the electromagnetic and gravitational fields. We focus on the mathematical reconstruction of a few of his principal ideas that until now have been neglected by the literature. To set these ideas in proper epistemological order, we thought it would be valuable to first revalue and reconstruct some missing parts of the proceedings process by Ladislavus Natanson constructed their thermodynamics. We also aimed to present Natanson’s achievements against the background of modern continuum mechanics, exemplifying old but still relevant approaches. We propose that Natanson’s ideas were ahead of their time by about one century. Give that scientist was educated in the scientific royal way: chemistry, through mechanic of solid and fluid, thermodynamics, electro-chemistry, electrodynamics, early quantum and relativistic mechanics, we can closely compare their conceptions and solutions. Natanson was in strong opposition with Newtonian mechanisms, the Maupertuis least action principle formed the basis of his activities, which they were developing as a sum of elementary quantum actions.

  • On Computationally-Efficient Reference Design Acquisition for Reduced-Cost Constrained Modeling and Re-Design of Compact Microwave Passives
    • Sławomir Kozieł
    • Anna Pietrenko-Dąbrowska
    2020 Full text IEEE Access

    Full-wave electromagnetic (EM) analysis has been playing a major role in the design of microwave components for the last few decades. In particular, EM tools allow for accurate evaluation of electrical performance of miniaturized structures where strong cross-coupling effects cannot be adequately quantified using equivalent network models. However, EM-based design procedures (parametric optimization, statistical analysis) generate considerable computational expenses. These can be mitigated using fast surrogate models, yet their construction is hindered by the curse of dimensionality but also the utility requirements: a practically useful model needs to cover sufficiently broad ranges of geometry/material parameters as well as operating conditions. The recently proposed constrained modeling methods—both forward and inverse—work around the above issues by setting up the surrogate only in the relevant regions of the parameter space, i.e., containing designs that are of high quality with respect to the assumed performance measures. The model domain is established using pre-optimized sets of reference points. The high cost of generating such designs may significantly diminish the computational savings achieved by operating in confined domains. This paper discusses a technique for fast reference design acquisition, involving inverse gradients, and expedited local refinement aided by the response feature technology. The presented approach is validated using a branch-line coupler and miniaturized rat-race coupler. It is also demonstrated to considerably reduce the cost of constructing performance-driven surrogates as well as setting up efficient procedures for fast geometry scaling of microwave components.

  • On description of periodic magnetosonic perturbations in a quasi-isentropic plasma with mechanical and thermal losses and electrical resistivity
    • Anna Perelomova
    2020 Full text PHYSICS OF PLASMAS

    Magnetosonic periodic perturbations in a uniform and infinite plasma model are considered. Damping due to compressional viscosity, electrical resistivity, and thermal conduction are taken into account, as well as some heating–cooling function, which may destroy the isentropicity of wave perturbations. The wave vector forms arbitrary angle h with the equilibrium straight magnetic field, and all perturbations are functions of time and longitudinal coordinate. Variable h and plasma- b bring essential difficulties in the description of magnetosonic perturbations, which may be fast or slow. Wave damping of each kind depends differently on h and plasma- b . Longitudinal velocity, which is periodic at any distance from an exciter, is analytically constructed. It approximates the exact solution with satisfactory accuracy.

  • On design and analysis of flow characteristics of the last stage of gas-steam turbine
    • Stanisław Głuch
    • Paweł Ziółkowski
    • Łukasz Witanowski
    • Michał Stjanke
    • Piotr Józef Ziółkowski
    • Janusz Badur
    2020 Full text

    Research regarding blade design and analysis of flow have been conducted for over a century. Meanwhile new concepts and design approaches were created and improved. Advancements in information technologies allowed to introduce computational fluid dynamics (CFD) and computational flow mechanics (CFM). Currently a combination of mentioned methods is used for design of turbine blades. These methods enabled us to improve flow efficiency and strength of turbine blades. This paper relates to a new type turbine which is in the phase of theoretical analysis, because the working fluid is a mixture of steam and gas generated in wet combustion chamber. Conception of this cycle and thermodynamic calculations are presented in previous papers, therefore the main aim of this article is design and analysis of flow characteristics of the last stage of gas-steam turbine. When creating the spatial model, the atlas of profiles of reaction turbine steps was used. In this paper results of CFD calculations of twisting of the last stage are presented. Blades geometry and the computational mesh are also presented. Triangles of velocity for selected dividing sections are presented. It is worth noting that the velocity along the pitch diameter varies greatly. Near the root it shows an action triangle, on the other hand, near the tip it presents a reaction type of triangle. Velocity fields and pressure fields show the flow characteristics of the last stage of gas-steam turbine. The net efficiency of the cycle is estimated as 54.35% regarding to enthalpy drop, however, the net efficiency taking into account the mechanical power determined from the stage theory is equal 52.61%.

  • On DoA estimation for rotating arrays using stochastic maximum likelihood approach
    • Michał Meller
    • Kamil Stawiarski
    2020 Full text IEEE TRANSACTIONS ON SIGNAL PROCESSING

    The flexibility needed to construct DoA estimators that can be used with rotating arrays subject to rapid variations of the signal frequency is offered by the stochastic maximum likelihood approach. Using a combination of analytic methods and Monte Carlo simulations, we show that for low and moderate source correlations the stochastic maximum likelihood estimator that assumes noncorrelated sources has accuracy comparable to the estimator that includes the correlation coefficient as one of the parameters. We propose several fast approximations of the stochastic maximum likelihood estimator and compare their accuracy with the Cramer-Rao lower bound. We also discuss the model order selection problem for the binary- and multiple-hypotheses cases.

  • On Dynamic Extension of a Local Material Symmetry Group for Micropolar Media
    • Victor Eremeev
    • Violetta Konopińska-Zmysłowska
    2020 Full text Symmetry-Basel

    For micropolar media we present a new definition of the local material symmetry group considering invariant properties of the both kinetic energy and strain energy density under changes of a reference placement. Unlike simple (Cauchy) materials, micropolar media can be characterized through two kinematically independent fields, that are translation vector and orthogonal microrotation tensor. In other words, in micropolar continua we have six degrees of freedom (DOF) that are three DOFs for translations and three DOFs for rotations. So the corresponding kinetic energy density nontrivially depends on linear and angular velocity. Here we define the local material symmetry group as a set of ordered triples of tensors which keep both kinetic energy density and strain energy density unchanged during the related change of a reference placement. The triples were obtained using transformation rules of strain measures and microinertia tensors under replacement of a reference placement. From the physical point of view, the local material symmetry group consists of such density-preserving transformations of a reference placement, that cannot be experimentally detected. So the constitutive relations become invariant under such transformations. Knowing a priori a material’s symmetry, one can establish a simplified form of constitutive relations. In particular, the number of independent arguments in constitutive relations could be significantly reduced.

  • On Effective Bending Stiffness of a Laminate Nanoplate Considering Steigmann–Ogden Surface Elasticity
    • Victor Eremeev
    • Tomasz Wiczenbach
    2020 Full text Applied Sciences-Basel

    As at the nanoscale the surface-to-volume ratio may be comparable with any characteristic length, while the material properties may essentially depend on surface/interface energy properties. In order to get effective material properties at the nanoscale, one can use various generalized models of continuum. In particular, within the framework of continuum mechanics, the surface elasticity is applied to the modelling of surface-related phenomena. In this paper, we derive an expression for the effective bending stiffness of a laminate plate, considering the Steigmann–Ogden surface elasticity. To this end, we consider plane bending deformations and utilize the through-the-thickness integration procedure. As a result, the calculated elastic bending stiffness depends on lamina thickness and on bulk and surface elastic moduli. The obtained expression could be useful for the description of the bending of multilayered thin films.

  • On homotopies of morphisms and admissible mappings
    • Zdzisław Dzedzej
    • Tomasz Gzella
    2020 Full text Journal of Fixed Point Theory and Applications

    The notion of homotopy in the category of morphisms introduced by G´orniewicz and Granas is proved to be equivalence relation which was not clear for years. Some simple properties are proved and a coincidence point index is described.

  • On Inadequacy of Sequential Design of Experiments for Performance-Driven Surrogate Modeling of Antenna Input Characteristics
    • Anna Pietrenko-Dąbrowska
    • Sławomir Kozieł
    2020 Full text IEEE Access

    Design of contemporary antennas necessarily involves electromagnetic (EM) simulation tools. Their employment is imperative to ensure evaluation reliability but also to carry out the design process itself, especially, the adjustment of antenna dimensions. For the latter, traditionally used parameter sweeping is more and more often replaced by rigorous numerical optimization, which entails considerable computational expenses, sometimes prohibitive. A potentially attractive way of expediting the simulation-based design procedures is the replacement of expensive EM analysis by fast surrogate models (or metamodels). Unfortunately, due to the curse of dimensionality and considerable nonlinearity of antenna characteristics, applicability of conventional modeling methods is limited to structures described by small numbers of parameters within narrow ranges thereof. A recently proposed nested kriging technique works around these issues by allocating the surrogate model domain within the regions containing designs that are of high quality with respect to the selected performance figures. This paper investigates whether sequential design of experiments (DoE) is capable of enhancing the modeling accuracy over one-shot space-filling data sampling originally implemented in the nested kriging framework. Numerical verification carried out for two microstrip antennas indicates that no noticeable benefits can be achieved, which contradicts the common-sense expectations. This result can be explained by a particular geometry of the confined domain of the performance-driven surrogate. As this set consists of nearly-optimum designs, the average nonlinearity of the antenna responses therein is almost location independent, therefore optimum training data allocation should be close to uniform. This is indeed corroborated by our experiments.

  • On instabilities and post-buckling of piezomagnetic and flexomagnetic nanostructures
    • Mohammad Malikan
    • Nikolay S. Uglov
    • Victor Eremeev
    2020 Full text INTERNATIONAL JOURNAL OF ENGINEERING SCIENCE

    We focus on the mechanical strength of piezomagnetic beam-like nanosize sensors during post-buckling. An effective flexomagnetic property is also taken into account. The modelled sensor is selected to be a Euler-Bernoulli type beam. Long-range interactions between atoms result in a mathematical model based on the nonlocal strain gradient elasticity approach (NSGT). Due to possible large deformations within a post-buckling phenomenon, the resultant equations are essentially nonlinear. We establish the results using an analytical approach, including a variety of boundary conditions. We visualize the effective response of the designed sensor for several key components. It was obtained that the flexomagnetic effect is meaningful for less flexible boundary conditions. Besides, it was found that the failure originated from post-buckling occurs sooner if the numerical amounts of nonlocal parameter and the strain gradient one are respectively so small and exceedingly large.

  • On Nonlinear Bending Study of a Piezo-Flexomagnetic Nanobeam Based on an Analytical-Numerical Solution
    • Mohammad Malikan
    • Victor Eremeev
    2020 Full text Nanomaterials

    Among various magneto-elastic phenomena, flexomagnetic (FM) coupling can be defined as a dependence between strain gradient and magnetic polarization and, contrariwise, elastic strain and magnetic field gradient. This feature is a higher-order one than piezomagnetic, which is the magnetic response to strain. At the nanoscale, where large strain gradients are expected, the FM effect is significant and could be even dominant. In this article, we develop a model of a simultaneously coupled piezomagnetic–flexomagnetic nanosized Euler–Bernoulli beam and solve the corresponding problems. In order to evaluate the FM on the nanoscale, the well-known nonlocal model of strain gradient (NSGT) is implemented, by which the nanosize beam can be transferred into a continuum framework. To access the equations of nonlinear bending, we use the variational formulation. Converting the nonlinear system of differential equations into algebraic ones makes the solution simpler. This is performed by the Galerkin weighted residual method (GWRM) for three conditions of ends, that is to say clamp, free, and pinned (simply supported). Then, the system of nonlinear algebraic equations is solved on the basis of the Newton–Raphson iteration technique (NRT) which brings about numerical values of nonlinear deflections. We discovered that the FM effect causes the reduction in deflections in the piezo-flexomagnetic nanobeam.

  • On Radar DoA Estimation and Tilted Rotating Electronically Scanned Arrays
    • Michał Meller
    • Kamil Stawiarski
    2020 Full text

    We consider DoA estimation in a monopulse radar system employing a tilted rotating array. We investigate the case of nonzero steering angles, in which case the mapping between the target’s azimuth and elevation in the global coordinate system and their counterparts in the array local coordinate system becomes increasingly nonlinear and coupled. Since estimating the azimuth using coherently integrated signals might be difficult because of strong modulation in the difference signal induced by the rotation of the antenna, we develop an iterative approach that alternates between estimating the elevation using coherently integrated signals and estimating the azimuth using unfiltered signals. We also develop a simplified version of the scheme, which employs only one iteration and forms the final estimates by applying simple corrections to results of the first iteration.

  • On rotational instability within the nonlinear six-parameter shell theory
    • Jacek Chróścielewski
    • Francesco Dell’isola
    • Victor Eremeyev
    • Agnieszka Sabik
    2020 INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES

    Within the six-parameter nonlinear shell theory we analyzed the in-plane rotational instability which oc- curs under in-plane tensile loading. For plane deformations the considered shell model coincides up to notations with the geometrically nonlinear Cosserat continuum under plane stress conditions. So we con- sidered here both large translations and rotations. The constitutive relations contain some additional mi- cropolar parameters with so-called coupling factor that relates Cosserat shear modulus with the Cauchy shear modulus. The discussed instability relates to the bifurcation from the static solution without rota- tions to solution with non-zero rotations. So we call it rotational instability. We present an elementary discrete model which captures the rotational instability phenomenon and the results of numerical anal- ysis within the shell model. The dependence of the bifurcation condition on the micropolar material parameters is discussed.

  • On Solvability of Boundary Value Problems for Elastic Micropolar Shells with Rigid Inclusions
    • Victor Eremeev
    • Leonid Lebedev
    2020 Mechanics of Solids

    In the framework of the linear theory of micropolar shells, existence and uniqueness theorems for weak solutions of boundary value problems describing small deformations of elastic micropolar shells connected to a system of absolutely rigid bodies are proved. The definition of a weak solution is based on the principle of virial movements. A feature of this problem is non-standard boundary conditions at the interface between the shell and solids.

  • On stress singularity near the tip of a crack with surface stresses
    • Nikolai Gorbushin
    • Victor Eremeev
    • Gennady Mishuris
    2020 Full text INTERNATIONAL JOURNAL OF ENGINEERING SCIENCE

    In the framework of the simplified linear Gurtin–Murdoch surface elasticity we discuss a singularity of stresses and displacements in the vicinity of a mode III crack. We show that inhomogeneity in surface elastic properties may significantly affect the solution and to change the order of singularity. We also demonstrate that implicitly or explicitly assumed symmetry of the problem may also lead to changes in solutions. Considering various loading and symmetry conditions we show that the stresses may have logarithmic or square root singularity or be bounded in the vicinity of a crack tip.

  • On Surface Kinetic Constitutive Relations
    • Victor Eremeev
    • Leonid Lebedev
    2020

    In the framework of the strain gradient surface elasticity we discuss a consistent form of surface kinetic energy. This kinetic constitutive equation completes the statement of initial–boundary value problems. The proposed surface kinetic energy density is the most general function consistent with the constitutive relations in bulk. As the surface strain energy depends on the surface deformation gradient and its gradient, the kinetic energy is a quadratic function of the velocity and its surface gradient.

  • On the connected and weakly convex domination numbers
    • Magdalena Lemańska
    • Magda Dettlaff
    • Dorota Osula
    • Maria Jose Souto Salorio
    2020 Full text Journal of Combinatorial Mathematics and Combinatorial Computing

    In this paper we study relations between connected and weakly convex domination numbers. We show that in general the difference between these numbers can be arbitrarily large and we focus on the graphs for which a weakly convex domination number equals a connected domination number. We also study the influence of the edge removing on the weakly convex domination number, in particular we show that a weakly convex domination number is an interpolating function.

  • On the Consumption of Multimedia Content Using Mobile Devices: a Year to Year User Case Study
    • Przemysław Falkowski-Gilski
    2020 Full text Archives of Acoustics

    In the early days, consumption of multimedia content related with audio signals was only possible in a stationary manner. The music player was located at home, with a necessary physical drive. An alternative way for an individual was to attend a live performance at a concert hall or host a private concert at home. To sum up, audio-visual effects were only reserved for a narrow group of recipients. Today, thanks to portable players, vision and sound is at last available for everyone. Finally, thanks to multimedia streaming platforms, every music piece or video, e.g. from one’s favourite artist or band, can be viewed anytime and everywhere. The background or status of an individual is no longer an issue. Each person who is connected to the global network can have access to the same resources. This paper is focused on the consumption of multimedia content using mobile devices. It describes a year to year user case study carried out between 2015 and 2019, and describes the development of current trends related with the expectations of modern users. The goal of this study is to aid policymakers, as well as providers, when it comes to designing and evaluating systems and services.

  • On the Correlation of Lignocellulosic Filler Composition with the Performance Properties of Poly(ε-Caprolactone) Based Biocomposites
    • Aleksander Hejna
    • Mohamed Sulyman
    • Marta Przybysz-Romatowska
    • Mohammad Saeb
    • Marek Klein
    • Krzysztof Formela
    2020 Full text Waste and Biomass Valorization

    In this work, three types of agricultural waste: olive stones (OS), date seed (DS) and wheat bran (WB) were applied as potential lignocellulosic fillers in poly(ε-caprolactone) (PCL) based biocomposites. Differences in composites’ performance were related to the higher content of proteins, noted for WB comparing to other fillers applied, which enhanced plasticization of PCL matrix. The mechanical properties of biocomposites were significantly affected by the agricultural waste fillers. Use of WB caused an obvious, even 25% decrease of tensile strength and hardness, which could be explained on account of glass transition temperature depletion and weaker matrix–filler interfacial interactions. Such phenomenon also increased water uptake of PCL/WB composites by more than 100%, while for PCL/OS and PCL/DS systems only for about 50%. Thermogravimetric analysis revealed that all investigated composites can be effectively processed without thermal decomposition. Generally, the outcome of this work demonstrated that OS, DS, and WB could be applied as promising lignocellulosic fillers used in manufacturing of high-performance polymer biocomposites.

  • On the Dynamics of a Visco–Piezo–Flexoelectric Nanobeam
    • Mohammad Malikan
    • Victor Eremeev
    2020 Full text Symmetry-Basel

    The fundamental motivation of this research is to investigate the effect of flexoelectricity on a piezoelectric nanobeam for the first time involving internal viscoelasticity. To date, the effect of flexoelectricity on the mechanical behavior of nanobeams has been investigated extensively under various physical and environmental conditions. However, this effect as an internal property of materials has not been studied when the nanobeams include an internal damping feature. To this end, a closed-circuit condition is considered taking converse piezo–flexoelectric behavior. The kinematic displacement of the classical beam using Lagrangian strains, also applying Hamilton’s principle, creates the needed frequency equation. The natural frequencies are measured in nanoscale by the available nonlocal strain gradient elasticity model. The linear Kelvin–Voigt viscoelastic model here defines the inner viscoelastic coupling. An analytical solution technique determines the values of the numerical frequencies. The best findings show that the viscoelastic coupling can directly affect the flexoelectricity property of the material.

  • On the effective properties of foams in the framework of the couple stress theory
    • Andrzej Skrzat
    • Victor Eremeev
    2020 Full text CONTINUUM MECHANICS AND THERMODYNAMICS

    In the framework of the couple stress theory, we discuss the effective elastic properties of a metal open-cell foam. In this theory, we have the couple stress tensor, but the microrotations are fully described by displacements. To this end, we performed calculations for a representative volume element which give the matrices of elastic moduli relating stress and stress tensors with strain and microcurvature tensors.

  • On the electronic structure of methyl butyrate and methyl valerate
    • Małgorzata Śmiałek-Telega
    • Denis Duflot
    • Nykola C. Jones
    • Søren Hoffmann
    • Lucia Zuin
    • Michael MacDonald
    • Nigel J. Mason
    • Paulo Limão-Vieira
    2020 Full text EUROPEAN PHYSICAL JOURNAL D

    We present novel results of the analysis of the electronic structure of two aliphatic esters: methyl butyrate and methyl valerate. High-resolution photoabsorption spectra were collected and analyzed over the energy range 4.0–10.8 eV and showed for both the molecules not only a clear band of the HOMO to LUMO transition, but also vibronic structure associated with the first Rydberg-valence transition. Photoelectron spectra recorded from 9 to over 28 eV revealed many ionization states with the first adiabatic ionization energies found to be 9.977 eV and 9.959 eV for methyl butyrate and methyl valerate, respectively. Ab initio calculations have been performed in order to help assign the photoabsorption and photoelectron features. Photolysis life times in the atmosphere were calculated revealing that photolysis is not competitive over hydroxyl radical scavenging in the process of removal of these esters from the atmosphere.

  • On the Existence of Homoclinic Type Solutions of a Class of Inhomogenous Second Order Hamiltonian Systems
    • Jakub Ciesielski
    • Joanna Janczewska
    • Nils Waterstraat
    2020 Full text Journal of Dynamics and Differential Equations

    We show the existence of homoclinic type solutions of a class of inhomogenous second order Hamiltonian systems, where a C1-smooth potential satisfies a relaxed superquadratic growth condition, its gradient is bounded in the time variable, and a forcing term is sufficiently small in the space of square integrable functions. The idea of our proof is to approximate the original system by time-periodic ones, with larger and larger time-periods. We prove that the latter systems admit periodic solutions of mountain-pass type, and obtain homoclinic type solutions of the original system from them by passing to the limit (in the topology of almost uniform convergence) when the periods go to infinity.

  • On the geometrically nonlinear vibration of a piezo-flexomagnetic nanotube
    • Mohammad Malikan
    • Victor Eremeev
    2020 Full text MATHEMATICAL METHODS IN THE APPLIED SCIENCES

    In order to describe the behavior of thin elements used in MEMS and NEMS, it is essential to study a nonlinear free vibration of nanotubes under complicated external fields such as magnetic environment. In this regard, the magnetic force applied to the conductive nanotube with piezo-flexomagnetic elastic wall is considered. By the inclusion of Euler-Bernoulli beam and using Hamilton’s principle, the equations governing the system are extracted. More importantly, a principal effect existed in a nonlinear behavior such as axial inertia is thoroughly analyzed which is not commonly investigated. We then consider the effects of nanoscale size using the nonlocal theory of strain gradient (NSGT). Hereafter, the frequencies are solved as semi-analytical solutions on the basis of Rayleigh-Ritz method. The piezo-flexomagnetic nanotube (PF-NT) is calculated with different boundary conditions. In order to validate, the results attained from the present solution have been compared with those available in the open literature. We realized that the nonlinear frequency analysis is so significant when a nanotube has fewer degrees of freedom at both ends, and its length is long.

  • On the non-linear dynamics of torus-shaped and cylindrical shell structures
    • Shahriar Dastjerdi
    • Bekir Akgöz
    • Ömer Civalek
    • Mohammad Malikan
    • Victor Eremeev
    2020 Full text INTERNATIONAL JOURNAL OF ENGINEERING SCIENCE

    In this study, the non-linear dynamic analysis of torus-shaped and cylindrical shell-like structures has been studied. The applied material is assumed as the functionally graded material (FGM). The structures are considered to be used for important machines such as wind turbines. The effects of some environmental factors on the analysis like temperature and humidity have been considered. The strain field has been calculated in general form and in continue the dynamic governing equations of torus structure have been derived based on the first-order shear deformation theory. The rotation around two independent axes in the torus coordinate system is considered and time-dependent equations are solved using SAPM semi-analytical method. The stresses and deformations generated in the torus and cylindrical shaped structures are plotted. The rotation of structures has been attended due to some transportation purposes. The effect of internal pressures as well as rotational speed at torus and cylindrical structures has been investigated in several numerical diagrams. The results are presented in the form of graphs that consider the rotational effects, loading, thermal and humid (hygro-thermal) environments, and size of the structures. This research can provide scientific perspectives to researchers who will examine the dynamic analysis of torus and cylindrical shaped structures.

  • On the plastic buckling of curved carbon nanotubes
    • Mohammad Malikan
    2020 Full text Theoretical and Applied Mechanics Letters

    This research, for the first time, predicts theoretically static stability response of a curved carbon nanotube (CCNT) under an elastoplastic behavior with several boundary conditions. The CCNT is exposed to axial compressive loads. The equilibrium equations are extracted regarding the Euler–Bernoulli displacement field by means of the principle of minimizing total potential energy. The elastoplastic stress-strain is concerned with Ramberg–Osgood law on the basis of deformation and flow theories of plasticity. To seize the nano-mechanical behavior of the CCNT, the nonlocal strain gradient elasticity theory is taken into account. The obtained differential equations are solved using the Rayleigh–Ritz method based on a new admissible shape function which is able to analyze stability problems. To authorize the solution, some comparisons are illustrated which show a very good agreement with the published works. Conclusively, the best findings confirm that a plastic analysis is crucial in predicting the mechanical strength of CCNTs.

  • On the preestimation technique and its application to identification of nonstationary systems
    • Maciej Niedźwiecki
    • Artur Gańcza
    • Marcin Ciołek
    2020

    The problem of noncausal identification of a nonstationary stochastic FIR (finite impulse response) sys- tem is reformulated, and solved, as a problem of smoothing of preestimated parameter trajectories. Three approaches to preestimation are critically analyzed and compared. It is shown that optimization of the smoothing operation can be performed adaptively using the parallel estimation technique. The new approach is computationally attractive and yields estimation results that are comparable or better than those provided by the state-of-the-art local basis function approach and the multi- resolution wavelet approach.

  • On the Usefulness of the Generalised Additive Model for Mean Path Loss Estimation in Body Area Networks
    • Michał Laskowski
    • Sławomir Ambroziak
    • Luis M. Correia
    • Krzysztof Świder
    2020 Full text IEEE Access

    In this article, the usefulness of the Generalised Additive Model for mean path loss estimation in Body Area Networks is investigated. The research concerns a narrow-band indoor off-body network operating at 2.45 GHz, being based on measurements performed with four different users. The mean path loss is modelled as a sum of four components that depend on path length, antenna orientation angle, absolute difference between transmitting and receiving antenna heights and relative polarisation of both antennas. It is proved that the Generalised Additive Model allows for mean path loss estimation with a higher accuracy in comparison with Linear Regression. The obtained mean error is 0 dB, the root mean square error is 5.52 dB and the adjusted coefficient of determination is 61.2%.

  • On the well posedness of static boundary value problem within the linear dilatational strain gradient elasticity
    • Victor Eremeev
    • Sergey Lurie
    • Yury Solyaev
    • Francesco dell'Isola
    2020 Full text ZEITSCHRIFT FUR ANGEWANDTE MATHEMATIK UND PHYSIK

    In this paper, it is proven an existence and uniqueness theorem for weak solutions of the equilibrium problem for linear isotropic dilatational strain gradient elasticity. Considered elastic bodies have as deformation energy the classical one due to Lamé but augmented with an additive term that depends on the norm of the gradient of dilatation: only one extra second gradient elastic coefficient is introduced. The studied class of solids is therefore related to Korteweg or Cahn–Hilliard fluids. The postulated energy naturally induces the space in which the aforementioned well-posedness result can be formulated. In this energy space, the introduced norm does involve the linear combination of some specific higher-order derivatives only: it is, in fact, a particular example of anisotropic Sobolev space. It is also proven that aforementioned weak solutions belongs to the space H1(div,V), i.e. the space of H1 functions whose divergence belongs to H1. The proposed mathematical frame is essential to conceptually base, on solid grounds, the numerical integration schemes required to investigate the properties of dilatational strain gradient elastic bodies. Their energy, as studied in the present paper, has manifold interests. Mathematically speaking, its singularity causes interesting mathematical difficulties whose overcoming leads to an increased understanding of the theory of second gradient continua. On the other hand, from the mechanical point of view, it gives an example of energy for a second gradient continuum which can sustain externally applied surface forces and double forces but cannot sustain externally applied surface couples. In this way, it is proven that couple stress continua, introduced by Toupin, represent only a particular case of the more general class of second gradient continua. Moreover, it is easily checked that for dilatational strain gradient continua, balance of force and balance of torques (or couples) are not enough to characterise equilibrium: to this aim, externally applied surface double forces must also be specified. As a consequence, the postulation scheme based on variational principles seems more suitable to study second gradient continua. It has to be remarked finally that dilatational strain gradient seems suitable to model the experimentally observed behaviour of some material used in 3D printing process.