prof. dr hab. inż. Wojciech Witkowski
Zatrudnienie
- Profesor w Katedra Wytrzymałości Materiałów
Publikacje
Filtry
wszystkich: 96
Katalog Publikacji
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Modeling of Composite Shells in 6-Parameter Nonlinear Theory with Drilling Degree of Freedom
PublikacjaWithin the framework of a 6-parameter nonlinear shell theory, with strain measures of Cosserat type, constitutive relations are proposed for thin elastic composite shells. The material law is expressed in terms of five engineering constants of classical anisotropic continuum plus an additional parameter accounting for drilling stiffness. The theory allows for unlimited displacements and rotations. A number of examples are presented...
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Geometrically nonlinear FEM analysis of FGM shells based on neutral physical surface approach in 6-parameter shell theory
PublikacjaThe paper presents the formulation of the elastic constitutive law for functionally graded materials (FGM) on the grounds of nonlinear 6-parameter shell theory with the 6th parameter being the drilling degree of freedom. The material law is derived by through-the-thickness integration of the Cosserat plane stress equations. The constitutive equations are formulated with respect to the neutral physical surface. The influence of...
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Influence of meniscus shape in the cross sectional plane on the knee contact mechanics
PublikacjaWe present a three dimensional finite element analysis of stress distribution and menisci deformation in the human knee joint. The study is based on the Open Knee model with the geometry of the lateral meniscus which shows some degenerative disorders. The nonlinear analysis of the knee joint under compressive axial load is performed. We present results for intact knee, knee with partial and complete radial posterior meniscus root...
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Nonlinear FEM 2D failure onset prediction of composite shells based on 6-parameter shell theory
PublikacjaWithin the framework of the nonlinear 6-parameter shell theory with the drilling rotation and asymmetric stress measures, the modifications of Tsai-Wu and Hashin laminate failure initiation criteria are proposed. These improvements enable to perform first ply failure estimations taking into account the non-symmetric stress measures. In order to check the validity of the proposed criteria, finite element analyses are performed with...
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On some properties of 2d spectral finite elements in problems of wave propagation
PublikacjaW pracy przedstawiono sformułowanie dwuwymiarowych elementów spektralnych stosowanych w symulacji propagacji fal prowadzonych. Zbadano własności tych elementów pod kątem występowania form pasożytniczych, odporności na dystorsję siatki oraz zbadano wpływ kształtu elementu na krzywe dyspersji
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Elastoplastic nonlinear FEM analysis of FGM shells of Cosserat type
PublikacjaThe paper is a continuation of [1] where the formulation of the elastic constitutive law for functionally graded materials (FGM) on the grounds of nonlinear 6-parameter shell theory with the 6th parameter (the drilling degree of freedom) was presented. Here the formulation is extended to the elasto-plastic range. The material law is based on Cosserat plasticity and employs the well-known Tamura-Tomota-Ozawa (TTO) [2] mixture...
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On some constitutive equations for micropolar plates
PublikacjaW pracy porównano równania konstytutywne dla płyt podane przez Altenbacha i Eremeyeva. Na podstawie ich wyprowadzeń określono zakres zmienności współczynnika momentów owinięcia i jego możliwy wpływ na wyniki otrzymane w rozwiązaniach MES w zakresie liniowym
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Experimental and numerical analysis of the modified TB32 crash tests of the cable barrier system
PublikacjaRoad restraint systems, including safety barriers, are one of the means used to improve road safety. Currently, they can be allowed to general use after passing the specific crash tests. However, it is always important and desirable to evaluate their performance under various realistic conditions, which can happen on the roads. In this study, the behaviour of the cable barrier system in impact conditions different than assumed...
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Geometrically nonlinear FEM analysis of 6-parameter resultant shell theory based on 2-D Cosserat constitutive model
PublikacjaWe develop the elastic constitutive law for the resultant statically and kinematically exact, nonlinear, 6-parameter shell theory. The Cosserat plane stress equations are integrated through-the- thickness under assumption of the Reissner-Mindlin kinematics. The resulting constitutive equations for stress resultant and couple resultants are expressed in terms of two micropolar constants: the micropolar modulus Gc and the micropolar...
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Discrepancies of energy values in dynamics of three intersecting plates
PublikacjaW pracy analizuje się lot konstrukcji powłokowej złożonej z trzech przecinających się powłok. Obciążeniem jest przestrzenny układ sił o zadanym trójkątnym przebiegu w czasie. Po ustaniu obciążenia powłoka doświadcza swobodnego lotu. Celem pracy jest dyskusja różnic wartości energii całkowitej układu w locie swobodnym jakie znane są w literaturze przedmiotu. W pracy przedstawiono także przykład weryfikujący zastosowane algorytmy...
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Fem analysis of cosserat plates and shells based on some constitutive relations
PublikacjaPrzeprowadzono studium doboru mikropolarnych współczynników konstytutywnych w pewnym modelu płyty Cosseratów. Wyznaczono ograniczenia na ich wartości i przeprowadzono parametryczną analizę wpływu tych współczynników na geometrycznie nieliniowe deformacje powłok z ortogonalnymi przecięciami płatów.
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The Influence of Articular Cartilage Thickness Reduction on Meniscus Biomechanics
PublikacjaObjective Evaluation of the biomechanical interaction between meniscus and cartilage in medial compartment knee osteoarthritis. Methods The finite element method was used to simulate knee joint contact mechanics. Three knee models were created on the basis of knee geometry from the Open Knee project. We reduced the thickness of medial cartilages in the intact knee model by approximately 50% to obtain a medial knee osteoarthritis...
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The influence of a change in the meniscus cross-sectional shape on the medio-lateral translation of the knee joint and meniscal extrusion
PublikacjaObjective The purpose of this study was to evaluate the influence of a change in the meniscus cross sectional shape on its position and on the biomechanics of a knee joint. Methods One main finite element model of a left knee joint was created on the basis of MRI images. The model consisted of bones, articular cartilages, menisci and ligaments. Eight variants of this model with an increased or decreased meniscus height were then...
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Elastoplastic law of Cosserat type in shell theory with drilling rotation
PublikacjaWithin the framework of six-parameter non-linear shell theory, with strain measures of the Cosserat type, we develop small-strain J2-type elastoplastic constitutive relations. The relations are obtained from the Cosserat plane stress relations assumed in each shell layer, by through-the-thickness integration employing the first-order shear theory. The formulation allows for unlimited translations and rotations. The constitutive...
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Curb-to-Barrier Face Distance Variation an a TB51 Bridge Barrier Crash Test Simulation
PublikacjaThis paper addresses the problem of road safety regarding barrier placement as relative to the curb. A short summary of existing regulations is presented. Numerical simulations using the explicit finite element system Ls- Dyna are shown. In the analysis, variable distance between the barrier and the curb is assumed. The obtained result reveals that the distance has little impact on the working width of the barrier.
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2-D constitutive equations for orthotropic Cosserat type laminated shells in finite element analysis
PublikacjaWe propose 2-D Cosserat type orthotropic constitutive equations for laminated shells for the purpose of initial failure estimation in a laminate layer. We use nonlinear 6-parameter shell theory with asymmetric membrane strain measures and Cosserat kinematics as the framework. This theory is specially dedicated to the analysis of irregular shells, inter alia, with orthogonal intersections, since it takes into account the drilling...
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Numerical studies on the influence of selected construction features and road conditions on the performance of road cable barriers
PublikacjaCable barriers are commonly used on Polish roads, including motorways and local roads. Their main elements are pre-stressed wire ropes, which are usually anchored at two ends in concrete blocks buried in the soil. In this work numerical studies concerning the influence of selected construction features and parameters of the vehicle motion on the performance of cable barriers were performed. Numerical simulations are a useful tool...
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Numerical Analysis of TB32 Crash Tests for 4-cable Guardrail Barrier System Installed on the Horizontal Convex Curves of Road
PublikacjaHorizontal curves are one of the elements of road infrastructure where statistically a relatively high number of accidents have been reported. In the last ten years in Poland approx. 10% of all road accidents happened on horizontal curves of roads and was responsible for approx. 14% of all fatalities on Polish roads. Thus, this issue is important and requires extensive research and proper road safety treatments. One possible measure...
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High meniscal slope angle as a risk factor for meniscal allograft extrusion
PublikacjaA meniscal graft extrusion is still an unresolved problem that affects most patients after a meniscal transplantation. Despite the advances in surgical techniques, together with the improved methods for a meniscal allograft sizing, success is only observed in up to 75% of patients after they experience a meniscal allograft transplantation. Because a meniscal extrusion is associated with a cartilage deterioration and the progression...
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Robust four-node elements based on Hu–Washizu principle for nonlinear analysis of Cosserat shells
PublikacjaMixed 4-node shell elements with the drilling rotation and Cosserat-type strain measures based onthe three-field Hu–Washizu principle are proposed. In the formulation, apart from displacement and rotationfields, both strain and stress resultant fields are treated as independent. The elements are derived in the frame-work of a general nonlinear 6-parameter shell theory dedicated to the analysis of multifold irregular shells.The...
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Numerical methods for the assessment of bridge safety barriers
PublikacjaThe paper presents a numerical study of the bus crash test for bridge safety barriers. The analysis is conducted with the use of explicit code LS-DYNA. The problem of hourglass effect in shell elements is discussed. The simulations of bus impact against the barrier show that the analyzed barrier withstands the impact forces and restrains the bus trajectory to the bridge road.
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Influence of the femoral offset on the muscles passive resistance in total hip arthroplasty
PublikacjaBackground Soft tissue tension is treated as a crucial factor influencing the post-THA dislocation. The femoral offset is regarded as one of the major parameters responsible for the stabilization of the prosthesis. It is unclear which soft tissue is mostly affected by the offset changes. Methods A finite element model of the hip was created. The model comprised muscles, bones, a stem, the acetabular component and a liner. The muscles...
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The role of numerical tests in assessing road restraint system functionality
PublikacjaKey to understanding the needs and building road infrastructure management tools to prevent and mitigate run-off-road accidents is to identify hazards and their sources which are a result of wrong design, construction, and installation of road restraint systems. Building such tools requires advanced studies with field tests, simulations and models to demonstrate the effects of selected parameters on road user safety. The research...
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Damage detection of a T-shaped panel by wave propagation analysis in the plane stress
PublikacjaW pracy zaprezentowano podejście obliczeniowe do analizy propagacji fal w płaskim stanie naprężenia. Problem brzegowo-początkowy podlega przestrzennej aproksymacji z użyciem wielowęzłowych, izoparametrycznych, czworobocznych elementów klasy C0. Macierze elementowe są całkowane numerycznie za pomocą kwadratury Gauss-Legendre-Lobatto. Aproksymację w dziedzinie czasu wykonano za pomocą algorytmu Newmarka. Symulacje numeryczne przeprowadzono...
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A novel formulation of 3D spectral element for wave propagation in reinforced concrete
PublikacjaThe paper deals with numerical simulations of wave propagation in reinforced concrete for damage detection purposes. A novel formulation of a 3D spectral element was proposed. The reinforcement modelled as the truss spectral element was embedded in the 3D solid spectral finite element. Numerical simulations have been conducted on cuboid concrete specimens reinforced with two steel bars. Different degradation models were considered...
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Biomechanics of Lumbar Spine Injury in Road Barrier Collision–Finite Element Study
PublikacjaLiterature and field data from CIREN database have shown that lumbar spine injuries occur during car crashes. There are multiple hypotheses regarding how they occur; however, there is no biomechanical explanation for these injuries during collisions with road safety barriers (RSBs). Therefore, the objective of this study was to investigate the mechanics of vertebral fractures during car collisions with concrete RSBs. The finite...
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Examination of selected failure criteria with asymmetric shear stresses in the collapse analysis of laminated shells
PublikacjaThe paper is concerned with failure analysis of composite shells performed with the usage of the nonlinear 6‐parameter shell theory with drilling rotation degree of freedom. This special theory embodies naturally unlim-ited translations and rotations and is suitable for analysis of irregular shells for instance with various, partic-ularly orthogonal, intersections. The presence of the drilling rotation is inherently accompanied...
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On the validation of the LS-DYNA Geo Metro numerical model
PublikacjaThe paper presents experiences gained during work with numerical model of Geo Metro vehicle used for simulations of crash tests with road safety barriers. Attention is drawn to the subject of tire/wheel breakage during collision events. Some methods for improvement of the model are presented in the paper. Several results for the normative vehicle numerical tests are introduced. Simulations were carried out using LS-DYNA finite...
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On the influence of the acceleration recording time on the calculation of impact severity indexes
PublikacjaThe paper concerns with the analysis of normative requirements pertaining to experimental setup of a crash test and its numerical modelling. An overview of parameters describing the collision of a vehicle with a road restraining system is presented. A short description of a concrete road safety barrier is presented. A brief description of numerical modelling procedures for crash tests is given as well. The parametric influence...
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Analysis of passenger car crash with a cable barrier installed with anti-glare screens on a horizontal convex road curve with 400 m radius
PublikacjaHigh-tension cable barriers have been used on roads for a relatively short period compared with other types of road barriers. Hence, there remains a need for further research on various crash scenarios. An important issue is the performance of a cable barrier on a road curve, particularly when a vehicle impacts the convex side of the barrier. To address this issue, the analysis in this study considers a system of anti-glare screens...
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Medially positioned plate in first metatarsophalangeal joint arthrodesis
PublikacjaObjective The purpose of this study was to biomechanically compare the stability of first metatarsophalangeal (MTP1) joint arthrodesis with dorsally and medially positioned plates. Methods A physical model of the MTP1 joint consists of printed synthetic bones, a titanium locking plate and screws. In the experiments, samples with dorsally and medially positioned plates were subjected to loading of ground load character in a universal...
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On analysis of double-impact test of 1500-kg vehicle into w-beam guardrail system
PublikacjaEvery day on roads many scenarios of accidents may occur. One of the measures to minimize their consequences is road safety barriers. Finite Element analyses are being increasingly used to support the physical testing of these devices. The paper addresses the issue of a secondary impact into the previously damaged w-beam guardrail system. This situation belongs to one of the most dangerous which can happen on roads and may cause...
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The influence of position of the post or its absence on the performance of the cable barrier system
PublikacjaRoad safety barriers are used to increase safety in potentially dangerous places on the roads. They are designed and installed on the roads to prevent any vehicle from getting outside the travelled way or from entering the opposite lane of the road. Barriers, which are used on European roads, have to undergo full scale crash tests according to the EN 1317 standards. Nowadays as a supplement to real crash tests, numerical simulations...
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Development and validation of lumbar spine finite element model
PublikacjaThe functional biomechanics of the lumbar spine have been better understood by finite element method (FEM) simulations. However, there are still areas where the behavior of soft tissues can be better modeled or described in a different way. The purpose of this research is to develop and validate a lumbar spine section intended for biomechanical research. A FE model of the 50th percentile adult male (AM) Total Human Model for Safety...
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Failure Analysis of footbridge made of composite materials
PublikacjaFinite element method analysis of a pedestrian footbridge made of sandwich material is presented. The internal structure of the material is modelled as a structural shell assuming the Equivalent Single Layer approach (ESL). Two FEM commercial codes are employed. The response of the structure is studied in order to determine the load level that activates Hashin and Tsai-Wu failure criteria. Some practical aspects of designing footbridges...
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Speed estimation of a car at impact with a W-beam guardrail using numerical simulations and machine learning
PublikacjaThis paper aimed at developing a new method of estimating the impact speed of a passenger car at the moment of a crash into a W-beam road safety barrier. The determination of such a speed based on the accident outcomes is demanding, because often there is no access to full accident data. However, accurate determination of the impact speed is one of the key elements in the reconstruction of road accidents. A machine learning algorithm...
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Symulacje numeryczne stalowej bariery ochronnej na łuku drogi
PublikacjaW pracy wymieniono pewne czynniki związane z bezpieczeństwem ruchu drogowego, wskazując łuki poziome dróg jako miejsca, gdzie występuje istotna liczba groźnych w skutkach wypadków. W części pracy obejmującej symulacje numeryczne, zrealizowano serię badań spełniających warunki testu zderzeniowego TB11 ze zmiennym promieniem bariery. Oszacowano wpływ zróżnicowania geometrii na parametry bezpieczeństwa.
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The effects of vehicle restraint systems on road safety
PublikacjaKey to understanding the needs and tools of road infrastructure management for preventing run-off-road crashes or minimising their consequences, is to identify the hazads and sources of hazards caused by wrong or improper use of road safety devices and identify errors in the desifn, structure, construction and operation of road safety devices. Studying such an extended scope of the problem required fieldwork and surveys with road...
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On implementation of fibrous connective tissues’ damage in Abaqus software
PublikacjaConnective fibrous tissues, such as tendons and ligaments, in humans and animals exhibit hyperelastic behaviour. The constitution of the material of these tissues is anisotropic due to the presence of the collagen fibres, where one family of fibres is the typical case. Traumatic events and/or aging may sometimes lead to the damage of the tissue. The study of motion of affected joints or limbs is usually not permitted in vivo. This...
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Analiza drgań kładki kompozytowej wywołanych działaniem wiatru
PublikacjaW pracy omówiono sposób przeprowadzenia uproszczonej, numerycznej analizy drgań kładki kompozytowej wywołanych działaniem wiatru. Rozważaniom poddano swobodnie podpartą konstrukcję o rozpiętości 16m i przekroju w kształcie litery U. W pierwszej kolejności, przeprowadzono dwuwymiarową analizę opływu niepodatnego kształtu przekroju w poziomym strumieniu wiatru o prędkości 10m/s. Obliczenia numeryczne przeprowadzono programem ANSYS...
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Analiza drgań kładki kompozytowej wywołanych działaniem wiatru
PublikacjaW pracy omówiono sposób przeprowadzenia uproszczonej, numerycznej analizy drgań kładki kompozytowej wywołanych działaniem wiatru. Rozważaniom poddano swobodnie podpartą konstrukcję o rozpiętości 16 m i przekroju w kształcie litery U. W pierwszej kolejności przeprowadzono dwuwymiarową analizę opływu niepodatnego kształtu przekroju kładki w poziomym strumieniu wiatru o prędkości 10 m/s. Obliczenia numeryczne przeprowadzono programem...
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Mixed 4-node shell element with assumed strain and stress in 6-parameter theory
PublikacjaWe propose a mixed hybrid 4-node shell elements based on Hu-Washizu principle. Apart from displacements both strains and stress fields are treated as independent fields. The element is derived in the framework of a general nonlinear 6-field shell theory with drilling rotation which is dedicated to the analysis of multifold irregular shells with intersections. The novelty of the presented results stems from the fact that the measures...
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Recent Achievements in Constitutive Equations of Laminates and Functionally Graded Structures Formulated in the Resultant Nonlinear Shell Theory
PublikacjaThe development of constitutive equations formulated in the resultant nonlinear shell theory is presented. The specific features of the present shell theory are drilling rotation naturally included in the formulation and asymmetric measures of strains and stress resultants. The special attention in the chapter is given to recent achievements: progressive failure analysis of laminated shells and elastoplastic constitutive relation...
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Mixed 4-node shell element with assumed strain and stress in 6-parameter theory
PublikacjaWe propose a mixed hybrid 4-node shell elements based on Hu-Washizu principle. Apart from displacements both strains and stress fields are treated as independent fields. The element is derived in the framework of a general nonlinear 6-field shell theory with drilling rotation which is dedicated to the analysis of multifold irregular shells with intersections. The novelty of the presented results stems from the fact that the measures...
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Simple model of rain wind induced vibrations of stayed cables.
PublikacjaAnalizowano prosty, liniowy model drgań kabli mostów wantowych pod obciążeniem wiatrem i deszczem. Zakłada się, iż częstotliwość ruchu górnej kropli po powierzchni kabla i częstotliwość kabla są równe oraz iż amplituda ruchu kropli dla danej prędkości wiatru są stałe. Otrzymane rezultaty są porównane z istniejącymi w literaturze wynikami badań eksperymentalnych. Podaje się analityczne związki służące do oszacowania tłumienia...
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Modelowanie drgań kabli wywołanych działaniem wiatru i deszczu
PublikacjaW referacie zaproponowano prosty, liniowy model drgań kabli mostów wantowych obciążonych wiatrem i deszczem. Założono, iż częstotliwość ruchu górnej kropli po powierzchni kabla i częstotliwość kabla są równe oraz iż amplituda ruchu kropli dla danej prędkości wiatru są stałe. Otrzymane rezultaty porównano z istniejącymi w literaturze wynikami badań eksperymentalnych. Podano analityczne związki służące do oszacowania tłumienia aerodynamicznego...
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Badania systemów powstrzymujących pojazd przed wypadnięciem z drogi - cz. II
PublikacjaW artykule zaprezentowana została tematyka systemów powstrzymujących pojazd przed wypadnięciem z drogi. Podczas codziennego użytkowania dróg występuje szereg zagrożeń, które wpływają na bezpieczeństwo. Badanie, identyfikacja i klasyfikacja zagrożeń stanowią istotny element utrzymania dróg. Artykuł stanowi drugą część podjętej problematyki. Pierwsza została opublikowana w magazynie Mosty nr 3-4/19 str. 66-68.
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Torsional buckling paradox - extended studies.
PublikacjaAnalizowano wyboczenie skrętne pręta cienkościennego o dwuteowym przekroju poprzecznym ze zmienną szerokością półek. Wykazano, że siła krytyczna wyboczenia skrętnego może przekraczać granice wyznaczone przez siły odpowiadające prętom o stałych ekstremalnych szerokościach półek. Ten paradoksalny wynik uzyskano w ramach teorii prętów cienkościennych o przekroju nieodkształcalnym. Przeanalizowano siłę krytyczną wyboczenia skrętnego...
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Efektywny 4-węzłowy element skończony o wzbogaconym polu odkształceń w nieliniowej 6-parametrowej teorii powłok.**2005, 144 s. 85 rys. 20 tab. bibliogr. 127 poz. maszyn.
PublikacjaCelem rozprawy doktorskiej było opracowanie efektywnego elementu skończonego, bazującego na technice wzbogaconych odkształceń w nieliniowej 6-parametrowej teorii powłok.Omówiono podstawy mechaniki powłok oraz działania na grupie obrotów SO(3).Wprowadzono i zlinearyzowano zmodyfikowaną zasadę wariacyjną Hu-Washizu.Omówiono techniki interpolacji i akumulacji pol niewiadomych z uwzględnieniem grupy obrotów SO(3).Omówiono koncepcję...
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Dynamics based on six-field theory of shells in the context of energy-conserving scheme
PublikacjaPraca dotyczy zaproponowanego algorytmu zachowującego energię w całkowaniu równań ruchu powłok sprężystych sformułowanych w ramach teorii sześcioparametrowej. Zawiera podstawowe założenia konieczne do formułowania schematów i podstawowe testy numeryczne. Aproksymacja przestrzenna zagadnienia oparta jest o Metodę Elementów Skończonych zaś aproksymacja w czasie wykorzystuje regułę punktu środkowego. Przykłady analizy dynamicznej...
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