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    Wyświetlanie 1-9 z 9
    Tytuł:
    Failure criterion for brick masonry: a micro-mechanics approach
    Autorzy:
    Kawa, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/178604.pdf
    Data publikacji:
    2014
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    strength anisotropy
    micromechanics
    masonry microstructure
    masonry
    failure criterion
    Opis:
    The paper deals with the formulation of failure criterion for an in-plane loaded masonry. Using micro-mechanics approach the strength estimation for masonry microstructure with constituents obeying the Drucker–Prager criterion is determined numerically. The procedure invokes lower bound analysis: for assumed stress fields constructed within masonry periodic cell critical load is obtained as a solution of constrained optimization problem. The analysis is carried out for many different loading conditions at different orientations of bed joints. The performance of the approach is verified against solutions obtained for corresponding layered and block microstructures, which provides the upper and lower strength bounds for masonry microstructure, respectively. Subsequently, a phenomenological anisotropic strength criterion for masonry microstructure is proposed. The criterion has a form of conjunction of Jaeger critical plane condition and Tsai-Wu criterion. The model proposed is identified based on the fitting of numerical results obtained from the microstructural analysis. Identified criterion is then verified against results obtained for different loading orientations. It appears that strength of masonry microstructure can be satisfactorily described by the criterion proposed.
    Źródło:
    Studia Geotechnica et Mechanica; 2014, 36, 3; 37-48
    0137-6365
    2083-831X
    Pojawia się w:
    Studia Geotechnica et Mechanica
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Differential protection with better stabilization for external faults
    Zabezpieczenie różnicowe z lepszą stabilizacją dla zwarć zewnętrznych
    Autorzy:
    Solak, K.
    Rebizant, W.
    Powiązania:
    https://bibliotekanauki.pl/articles/410581.pdf
    Data publikacji:
    2011
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    current differential criterion
    current transformer
    fuzzy logic
    saturation
    Opis:
    This paper presents a new differential protection scheme for transmission lines with application of fuzzy signal processing and support of phase comparison criterion. Traditional differential relays may have problems with proper classification of external faults with CT saturation. Better protection stabilization for such cases is obtained with support of fuzzy signal processing. In proposed solution the input signals as well as the standard percentage characteristic are fuzzified. The performance of presented fuzzy protection scheme has been tested with the signals generated with use of EMTP-ATP program and compared to the traditional solution.
    W artykule zaprezentowano nowe zabezpieczenie różnicowe, w którym zastosowano rozmyte przetwarzanie sygnałów oraz dodatkowe kryterium porównawczo-fazowe. Proponowane zabezpieczenie jest bardziej odporne na zwarcia zewnętrzne z nasyceniem przekładników prądowych, co potwierdziły przeprowadzone testy. Proponowany algorytm testowany był na sygnałach pochodzących z symulacji w EMTP-ATP, a wyniki porównano ze standardowym przekaźnikiem różnicowym.
    Źródło:
    Present Problems of Power System Control; 2011, 1; 39-48
    2084-2201
    Pojawia się w:
    Present Problems of Power System Control
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Identification of anisotropic criteria for stratified soil based on triaxial tests results
    Autorzy:
    Tankiewicz, M.
    Kawa, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/178919.pdf
    Data publikacji:
    2017
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    strength
    anisotropy
    varved clay
    Pariseau criterion
    weakness plane
    Opis:
    The paper presents the identification methodology of anisotropic criteria based on triaxial test results. The considered material is varved clay – a sedimentary soil occurring in central Poland which is characterized by the so-called “layered microstructure”. The strength examination outcomes were identified by standard triaxial tests. The results include the estimated peak strength obtained for a wide range of orientations and confining pressures. Two models were chosen as potentially adequate for the description of the tested material, namely Pariseau and its conjunction with the Jaeger weakness plane. Material constants were obtained by fitting the model to the experimental results. The identification procedure is based on the least squares method. The optimal values of parameters are searched for between specified bounds by sequentially decreasing the distance between points and reducing the length of the searched range. For both considered models the optimal parameters have been obtained. The comparison of theoretical and experimental results as well as the assessment of the suitability of selected criteria for the specified range of confining pressures are presented.
    Źródło:
    Studia Geotechnica et Mechanica; 2017, 39, 3; 59-65
    0137-6365
    2083-831X
    Pojawia się w:
    Studia Geotechnica et Mechanica
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Effect of increasing mining rate on longwall coal mining – Western Donbass case study
    Autorzy:
    Sdvyzhkova, O.
    Patyńska, R.
    Powiązania:
    https://bibliotekanauki.pl/articles/178393.pdf
    Data publikacji:
    2016
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    rock
    stress-strain state
    mining rate
    failure criterion
    roof collapse
    Opis:
    This paper presents the problems associated with the rapid change of the rock stress-strain state in terms of increasing the rate of coal mining. Parameters of the roof collapse are determined depending on the rate of a longwall advancing under conditions of poor rocks. Statistical data are processed to obtain a general trend concerning the mining rate impact on the roof collapse. The statistical strength theory is applied to explain the increase in mined-out space and the size of hanging roof behind a coal face. Numerical simulation is carried out to determine a critical size of mined-out space that provokes a roof collapse. The area of yielded rocks is outlined using the criterion developed taking into account the rate of longwall advancing. A general regularity is obtained to determine the roof collapse parameters. The developed technics gives a possibility to predict the moment of general roof collapse at the initial stage of longwalling to prevent the negative effect of the rapid stress redistribution provoking joints propagation and intensive gas release. The estimation of the rock stress-strain state considering the rate of mining operations can be useful for tasks related to a new technology implementation. The statistical strength theory and failure criterion applied together provides adequate planning of mining activities and the assessment of natural hazards.
    Źródło:
    Studia Geotechnica et Mechanica; 2016, 38, 1; 91-98
    0137-6365
    2083-831X
    Pojawia się w:
    Studia Geotechnica et Mechanica
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Analysis of the Collapse Gradient of Deep Water Horizontal Wellbore and the Effects of Mud Chemical Activity and Variation in Water Depth
    Autorzy:
    Dosunmu, Adewale
    Nwonodi, Roland I.
    Ekeinde, Evelyn
    Powiązania:
    https://bibliotekanauki.pl/articles/1845117.pdf
    Data publikacji:
    2020
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    Mogi-Coulomb criterion
    collapse gradient
    horizontal well
    deep water
    chemical activity
    Opis:
    Wellbore collapse is an instability-event that occurs at low mud density and leads to unfavorable economic project, reaching billions of US dollars. Thus, it is important to accurately determine its value, especially in deepwater horizontal wellbores. The main reasons for nontrivial problems with such wellbores are evident: the shale encountered are anisotropic in nature and possess planes of weakness; they react with water-based mud, generate osmotic stresses, swell, and fall unto the wellbore bottom, thereby increasing the non-productive time. To this end, salts are added to reduce the collapse tendency, but it is not currently known what amount of salt addition maintains stability, and does not lead to wellbore fracture; in deepwater, the current trend in global warming means there is a future concern to the industry. As the climate temperature increases, more ice melts from the polar region, the seawater expands and the sea level rises. How to incorporate the corresponding effect on collapse gradient is scarcely known. This study captures the major concerns stated above into wellbore stability analysis. Following the classical approach for geomechanical analysis, Mogi-Coulomb criterion was combined with a constitutive stress equation comprising contributions from mechanical and osmotic potentials of mud and shale. A sophisticated industry model was used to consider the deepwater effect. The results show significant reduction in collapse gradient as the water depth increases, also, larger difference between the mud and shale chemical activities represents higher complexities in the wellbore. In addition, the reduction in the chemical activities of mud limited to 37.5% of the initial value can be practically safe.
    Źródło:
    Studia Geotechnica et Mechanica; 2020, 42, 3; 232-241
    0137-6365
    2083-831X
    Pojawia się w:
    Studia Geotechnica et Mechanica
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Three-dimensional biomechanical modeling and simulation of trephine cutting cornea for keratoplasty
    Autorzy:
    Su, P.
    Lu, D.
    Deng, S.
    Zhang, L.
    Hao, Y.
    Yang, Y.
    Powiązania:
    https://bibliotekanauki.pl/articles/307486.pdf
    Data publikacji:
    2018
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    rogówka
    biomechanika
    kryterium wytężeniowe
    FEM
    cornea
    biomechanics
    failure criterion
    finite element simulation
    Opis:
    Trephination is one of the basic operations of keratoplasty, and the biomechanical mechanism of the operation can be revealed based on three-dimensional modeling and simulation of trephine cutting cornea. Methods: Based on the analysis of the physical and biomechanical characteristics of corneal trephination, a three-dimensional numerical model of corneal trephination is built, where the cornea can be simplified to two layers structure including stroma and epithelium, and the trephine cuts the cornea under the vertical motion load and the rotational motion load. A three-dimensional failure criterion of corneal material is proposed based on the yield strength theory. On this basis, trephination simulation is carried out, and the units of corneal material are removed from the model when they meet the defined failure criterion. Results: Under the given parameters including the velocity, the angle and the angular velocity, the trephine force curves, include the linear cutting force and the rotary cutting force are obtained, and show the change of the forces with displacement during the process of trephination simulation. The maps of the equivalent stress show the destruction and deformation of the cornea. Then, the experiment of robotic trephination is carried out under the same parameters and the effectiveness of the simulation is evaluated. Conclusions: Based on mechanics theory and finite element method, the process of trephine cutting cornea has been reproduced, and the interaction mechanism is revealed, which lays the foundation for the development of real-time simulation and virtual system of the corneal surgery.
    Źródło:
    Acta of Bioengineering and Biomechanics; 2018, 20, 2; 23-33
    1509-409X
    2450-6303
    Pojawia się w:
    Acta of Bioengineering and Biomechanics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Scenario planning as a new application area for TOPSIS
    Autorzy:
    Gaspars-Wieloch, Helena
    Powiązania:
    https://bibliotekanauki.pl/articles/27315335.pdf
    Data publikacji:
    2023
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    TOPSIS
    scenario planning
    uncertainty
    certainty
    one-criterion decision-making
    multi-criteria decision-making
    rankings
    Opis:
    TOPSIS is a well-known approach applied to multi-criteria decision-making under certainty (M-DMC). However, recently, some analogies between this domain and scenario-based one-criterion decision-making under uncertainty (1-DMU) have been revealed in the literature. Thus, the similarities aforementioned give the possibility to adjust TOPSIS to another area. The goal of the paper is to create a new method for problems with non-deterministic parameters on the basis of TOPSIS ideas. In the suggested approach criteria weights (declared within TOPSIS) are replaced by subjective chances of occurrence which are estimated for each scenario. The novel method has an advantage over existing classical decision rules designed for 1-criterion decision-making under uncertainty since within this procedure each payoff connected with a given option is compared with the positive and negative-ideal solutions.
    Źródło:
    Operations Research and Decisions; 2023, 33, 2; 23--34
    2081-8858
    2391-6060
    Pojawia się w:
    Operations Research and Decisions
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Evaluation of the impact of hydrostatic pressure and Lode angle on the strength of the rock mass based on the Hoek–Brown criterion
    Autorzy:
    Marczak, H.
    Powiązania:
    https://bibliotekanauki.pl/articles/178623.pdf
    Data publikacji:
    2015
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    generalized Hoek–Brown failure criterion
    equivalent cohesion
    equivalent friction angle
    global strength
    invariant stress
    Opis:
    Determination of the global uniaxial compressive strength of rock mass on the basis of the Hoek–Brown failure criterion requires knowledge of the strength parameters: cohesion and the angle of internal friction. In the conventional method for the determination of these parameters given by Balmer, they are expressed by the minimum principal stress. Thus, this method does not allow for the assessment of an impact of hydrostatic pressure and stress path on the value of cohesion, friction angle and global uniaxial compression of rock mass. This problem can be eliminated by using the Hoek–Brown criterion expressed by the invariants of the stress state. The influence of hydrostatic pressure and the Lode angle on the strength parameters of the rock mass was analysed.
    Źródło:
    Studia Geotechnica et Mechanica; 2015, 37, 2; 85-91
    0137-6365
    2083-831X
    Pojawia się w:
    Studia Geotechnica et Mechanica
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    The probability of traumatic brain injuries based on tissue-level reliability analysis
    Autorzy:
    Hazay, Máté
    Bojtár, Imre
    Powiązania:
    https://bibliotekanauki.pl/articles/306651.pdf
    Data publikacji:
    2019
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    analiza niezawodności
    kryterium urazu głowy
    HIC
    ryzyko obrażeń
    traumatic brain injuries
    finite element simulations
    reliability analysis
    Head Injury Criterion
    injury risk curves
    Opis:
    Motor vehicle crashes are one of the leading causes of traumatic brain injuries. Restraint systems of cars are evaluated by crash tests based on human tolerance data, however, the reliability of data currently used has been questioned several times in the literature due to the neglect of certain types of effects, injury types and uncertainties. Our main goal was to re-evaluate the currently applied risk curve by taking the previously neglected effects into account. Methods: In this paper, the probability of traumatic brain injury was determined by reliability analysis where different types of uncertainties are taken into account. The tissue-level response of the human brain in the case of frontal crashes was calculated by finite element analyses and the injury probability is determined by Monte Carlo simulations. Sensitivity analysis was also performed to identify which effects have considerable contribution to the injury risk. Results: Our results indicate a significantly larger injury risk than it is predicted by current safety standards. Accordingly, a new risk curve was constructed which follows a lognormal distribution with the following parameters: μLN = 6.5445 and LN = 1.1993. Sensitivity analysis confirmed that this difference primarily can be attributed to the rotational effects and tissue-level uncertainties. Conclusions: Results of the tissue-level reliability analysis enhance the belief that rotational effects are the primary cause of brain injuries. Accordingly, the use of a solely translational acceleration based injury metric contains several uncertainties which can lead to relatively high injury probabilities even if relatively small translational effects occur.
    Źródło:
    Acta of Bioengineering and Biomechanics; 2019, 21, 1; 141-152
    1509-409X
    2450-6303
    Pojawia się w:
    Acta of Bioengineering and Biomechanics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
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