Zpět na hlavní stránku Semináře ÚT
| Úterý 18. prosince 2018, 11:00, posluchárna B | |
Active grids as a tool for turbulence and wind energy studies |
|
| Jason Hearst, Department of Energy and Process Engineering, Faculty of Engineering, Norwegian University of Science and Technology, Trondheim, Norway | |
|
Abstract: Traditional wind tunnel testing has been limited by our ability to accurately control the incoming flow conditions. While a wind tunnel offers simple control of the Reynolds number (velocity), conducting measurements in different turbulent flows is significantly more challenging due to severe limitations on our ability to produce bespoke turbulent shear flows in a wind tunnel. Over the last quarter-century, active grids have become popular tools to overcome this limitation. An active grid is a motorized device placed at the inlet of a wind tunnel that produces a transient blockage. By controlling the time variation of this blockage, a user can exert some degree of control authority over the incoming turbulence conditions. It will be demonstrated that using this methodology, the turbulence intensity and the mean shear can be adjusted independently, offering unprecedented control authority over the experimental turbulence conditions. The application of this approach to wind energy will then be illustrated via particle image velocimetry measurements of the near-field of a model horizontal axis wind turbine. This will be compared to simpler measurements of a vertical axis wind turbine in more basic turbulent flows produced by conventional meshes. Ultimately, increasing turbulence intensity is shown to mitigate Reynolds number effects, and impact wake recovery.
|
|
| Středa 5. prosince 2018, 10:00, posluchárna B | |
Využití FEM pro virtuální zajištění funkčnostipři vývoji karoserie vozu ve Škoda auto a.s. |
|
| Ing. Jan Korouš, Ph.D., ŠKODA AUTO a.s. | |
|
Metoda konečných prvků (FEM) je již řadu let nedílnou součástí všech fází procesu vývoje vozu, karoserie a jejích komponent ve ŠKODA AUTO a.s. V počátečních fázích vývoje nahrazuje a simuluje reálné zkoušky a umožňuje prověřit velké množství konstrukčních variant, které musí splňovat mnoho často protichůdných požadavků. Neustále rostoucí kapacita výpočetních clusterů umožňuje díky paralelizaci nejen zvládnout permanentně zvyšující se počet výpočtů, ale taktéž popsat chování virtuálního modelu stále ve větších detailech. Přednáška přestaví filozofii použití (FEM) při dimenzování karosérie vozu a přehled portfolia výpočtů, které pokrývají nejen statické zátěžné stavy, ale především velké množství crash testů, kterým jsou dnes moderní vozy podrobovány. Zmíněny budou základní metodiky modelování, ale i současné trendy pro popsání procesů odehrávajících ve struktuře
vozu při dynamických nárazových testech, které souvisí např. s porušováním materiálů. |
|
| Cyklus přednášek: Úterý 6. listopadu 2018, 14:00, posluchárna B Středa 7. listopadu 2018, 14:00, posluchárna B Pátek 9. listopadu 2018, 14:00, posluchárna B |
|
Lecture series on Computational Plasticity |
|
| Prof. Nikolaos Aravas, University of Thessaly, Greece | |
|
Prof. Nikolaos Aravas is a world-recognized specialist in the field of Computational Mechanics of Materials. His almost 33-years academic career has been associated with the University of Thessaly in Greece and the University of Pennsylvania. Prof. N. Aravas has made significant contributions in the fields of computational plasticity, non-linear fracture mechanics, strain-gradient elasticity theories, and modelling of mechanical behaviour of human tissue. His current research interests include non-linear homogenization theories for multi-phase media and the analysis of electromechanical problems including piezoelectricity and flexo-electricity.
Lecture 1General form of elastoplastic constitutive equations. Rate-dependent versus rate-independent models. The elastoplastic boundary value problem. The weak formulation of the problem.
Lecture 2Finite element formulations. Methods of solution of non-linear finite element problems. Consistent linearization. Algorithms for the numerical integration of general elastoplastic models. Backward versus forward Euler methods.
Lecture 3Applications: von Mises plasticity, pressure-dependent plasticity, the Gurson model, general isotropic plasticity, J3-dependence, kinematic hardening, rate-dependent models, implementation in general purpose commercial finite element codes, e.g., ABAQUS.
|
|
| Středa 7. listopadu 2018, 10:00, posluchárna B | |
Evropa bez USA – nejen v energetice |
|
| Václav Bartuška, zvláštní vyslanec ČR pro otázky energetické bezpečnosti, MZV ČR | |
|
Největším zlomem v „klasické“ energetice posledních desetiletí je nástup nových metod těžby (fracking) v USA. V minulé dekádě se USA z dovozce zemního plynu staly vývozcem; v této dekádě se totéž odehrává v ropě. Trend dále pokračuje: podle odhadů International Energy Agency (IEA) má v příštích třech letech plných 80 % nové těžby ropy na světě pocházet z USA. Jak se projevuje tato změna ve vzájemném vztahu Evropy a USA?
|
|
| Středa 7. listopadu 2018, 10:30, posluchárna B | |
New role of silicon thin films in advanced photovoltaics |
|
| Antonín Fejfar, Fyzikální ústav AV ČR | |
|
Currently photovoltaics is becoming an established industrial field with the global installed capacity over 400 GWp, with perspective of reaching the terawatt installed capacity within the following decade. The field is dominated by silicon wafer based cells which reached the unforseen low system prices. The advantages of silicon thin film based photovoltaics of lower consumption of semiconductors and shorter energy payback time was not sufficient to overcome the disadvantage of lower efficiencies (record is 14 % for Si thin films is about half of the best Si wafer based cell). The most recent record efficiencies are due to the combination of the two technologies: the interdigitated back contacted silicon heterojunction based cells reached 26.7 % efficiency by combining high quality wafer with very thin silicon films for preparing passivating selective contacts. In another parallel development silicon thin films make part of silicon nanowire based solar cells which unite the concept of geometrically thin – optically thick films with simple manufacturing. In our group we have contributed to the field by developing optical profilometry for nanometer thin films based on Raman spectroscopy, microscopic methods for characterizing the local properties of the silicon nanostructures or for exploring photovoltaic materials and we explore new ways of junction engineering by inserting 2D materials or self-assembled dipolar molecule monolayers.
|
|
| Středa 3. října 2018, 10:00, posluchárna B | |
The development of Fuel Cell & Energy Storage technologies in ITRI – Status and Prospective |
|
| Wen-Sheng Chang, Director, Division of Energy Storage Technology, Green Energy and Environment Research Laboratories, ITRI | |
With the advantages of high efficiency, distributed, and environmental protection, fuel cell industries have been booming in recent years and the market for electric vehicles and power stations are continuously growing. With the support and demonstration by the government, Taiwan stationary power generation has successful popularized. Not only certain key technologies and related industrial chains have been established, industries also try to expand the overseas markets. In addition to promote the distributed power sources, fuel cell can be used with renewable energy as a fuel storage option. Energy storage is one of the major focuses as the infrastructure of green energy for government in the green energy industry. It is also considered as one of the solutions to the problem caused by high penetration rate of renewable energy. In response to the 20% development goal of renewable energy in 2025, utilization of energy storage technology to strengthen the renewable energy is expected. Energy storage can stabilize intermittent power output of renewable energy, eliminates transient fluctuation of grid power, and improves reliability of power grid. ITRI has devoted to developing core technologies of PEMFC, Aluminum ion battery, Vanadium Redox flow battery for distributed energy supply and storage. Hoping that this meeting achieves strengthen cooperation between ITRI and CAS and jointly creates innovative research and application on the hydrogen energy and energy storage area. |
|
| Středa 3. října 2018, 10:40, posluchárna B | |
Nanoparticle synthesis by spark discharge |
|
| Tomáš Němec, Institute of Thermomechanics of the Czech Academy of Sciences, Prague | |
Nanoparticle synthesis in the gas phase is advantageous for certain applications. It is typically a continuous process that offers high purity of product nanomaterials, reduced waste formation, and straightforward scale-up possibilities. Cooling of the gaseous systems can be well controlled and therefore, the morphology and size distribution of the nanoparticles can be tailored to specific applications. Also, nanoalloys can be generated by this technique. We constructed a spark discharge generator, which achieves nanoparticle production rate of tens of miligrams per hour. This production rate allows us to generate enough material for sample analysis, but also represents usable amounts of nanopowders for various applications. Our target application is the use of platinum-based nanomaterials as catalysts in hydrogen fuel cells. We synthesized nanoparticles from platinum, iridium, tungsten, and characterized the materials by TEM and XRD techniques. |
|
| Čtvrtek 7. listopadu 2018, 10:00, posluchárna B | |
New role of silicon thin films in advanced photovoltaics |
|
| Antonín Fejfar, Institute of Physics of the Czech Academy of Sciences, Prague | |
|
|
| Čtvrtek 6. září 2018, 10:00, posluchárna B | |
Predicting low and high friction in rotating mechanisms |
|
| Juan Carlos Jauregui, Universidad Autonoma de Queretaro, Mexico | |
|
|
| Pátek 22. června 2018 od 12:00, posluchárna B | |
A nonlinear continuum theory of finite deformations of elastoplastic media |
|
| Doc. Ing. Ladislav Écsi, PhD., Faculty of Mechanical Engineering, Slovak University of Technology in Bratislava | |
| Contemporary flow plasticity theories in finite-strain elasto-plasticity are either based on an additive decomposition of a strain rate tensor into an elastic part and a plastic part, or on a multiplicative decomposition of the deformation gradient tensor into an elastic part and a plastic part. While the former theories are considered to be ad hoc extensions of small-strain flow plasticity theories into the area of finite deformations to cover large displacements, but small strains in the material of the deforming body, the latter are now generally accepted as true finite-strain flow plasticity theories. Unfortunately, none of the theories entirely satisfies the requirements of thermodynamic consistency, and as a result, the material models and their analysis results, when used in numerical analyses, are dependent on the description and the particularities of the material model formulation. Recently a nonlinear continuum mechanical theory of finite deformations of elastoplastic media has been developed, which allows for the development of objective and thermodynamically consistent material models. This means that the plastic flow, including ‘normality rules’ can be described in a thermodynamically consistent manner in terms of different stress measures and strain rates or their objective derivatives, which are conjugate with respect to the mechanical power, using various instances of the yield surface defined in the above stress spaces. A few results of the modified hypoelastoplastic and hyper-elastoplastic material models based on the aforementioned nonlinear continuum mechanical theory will be presented and discussed. |
|
| Středa 6. června 2018, 11:00, posluchárna B | |
IMPLEMENTATION AND APPLICATIONS OF A GENERAL MODEL FOR VARIOUS CONTACTS WITH ADHESION AND/OR FRICTION |
|
| Doc. Ing. ROMAN VODIČKA, PhD., Faculty of Civil Engineering, Technical University of Kosice | |
| A general model covering a large variety of adhesive or cohesive contact interfaces with friction between visco-elastic bodies is presented. A semi-implicit time discretisation advantageously decouples the solved system and, after a spatial discretisation, it enables an efficient numerical implementation by the boundary element method. The model is illustrated by various examples documenting its wide applicability. | |
| Pátek 1. června 2018 od 10:00, posluchárna B | |
Developments in Fluid-Structure Interaction Modeling and Analysis |
|
| Prof. K. C. Park, Center for Aerospace Structures and Department of Aerospace Engineering Sciences University of Colorado, Boulder | |
| The talk offers some recent developments in modeling, analysis and some applications of external and internal fluid-structure interaction (FSI) problems, largely based on the speaker’s experience. We begin by reviewing classical internal flow characterizing sloshing and its interaction with the liquid containers. We then introduce the origin of a staggered solution procedures to tackle external FSI solution tracing back to the 1970s. We introduce a modern continuum mechanics-based formulation of incompressible and/or nearly incompressible flows interacting structures. Finally, we discuss some improvements in approximate modeling of external acoustic-structure interaction problems by the boundary element method and its computational performance. | |
| Úterý 10. 4. 2018, 13:00, posluchárna B | |
Behaviour of brittle materials under dynamic loading. |
|
| Jaroslav Buchar a Jan Trnka, Ústav termomechaniky AV ČR, v. v. i. | |
| The lecture deals with some achievement on description of brittle materials behavior at highstrain-rate loadings such as: air blast loading or percussive drilling of rocks, ballistic impact against ceramic armour or transparent windshields, plastic explosives used to damage or destroy concrete structures, soft or hard impacts against concrete structures and many others in civil and military applications. The most popular dynamic testing techniques used for this which are based on the use of split Hopkinson pressure bar methodologies and/or plate impact testing methods are briefly described. The influence of the strain rate on the material strength is discussed. Some constitutive equations are presented. Some of them are used in the numerical simulation of some ballistic loading of ceramics. |
|
| Středa 28. 3. 2018, 11:00, posluchárna B | |
Finite Fracture Mechanics and its Applications to Composite Materials |
|
| Vladislav Mantič, Department of Continuum Mechanics and Structural Analysis, School of Engineering, University of Seville, Spain | |
| The basic assumption of Finite Fracture Mechanics (FFM) is to allow crack growth by (possibly) finite steps, in opposite to the hypothesis of crack growth by infinitesimal steps adopted in classical Linear Elastic Fracture Mechanics (LEFM). The coupled (stress and energy) criterion of FFM introduced by D. Leguillon (2002) requires that both stress and energy conditions are simultaneously fulfilled for such a finite crack advance. A quite general formulation of the coupled criterion of FFM leading to an optimization problem is introduced. Several examples of applications of this coupled criterion to the prediction of damage initiation in form of cracks at micro- and meso-scale in composites are presented. | |
| Středa 28. 3. 2018, 14:00, posluchárna B | |
Brief introduction to optimization and topology optimization |
|
| Dr. Paulo Salvador Britto Nigro, Software Developer and Researcher of Virtual.PYXIS optimization, São Paulo, Brazil | |
The lecture will address the following topics in Topology Optimization (OT):
Dr Paulo Salvador Britto Nigro is a Software Developer skilled in Numerical Simulation applied to |
|
| Středa 28. 3. 2018, 10:00, posluchárna B | |
Micromechanics of Martensitic Laminates |
|
| Doc. Ing. Hanuš SEINER, Ph.D., Institute of Thermomechanics, Czech Academy of Sciences / Visiting Fulbright Scholar at the University of Minnesota, Minneapolis, USA | |
| The talk will summarize the main theoretical aspects of mechanics of geometrically ordered microstructures appearing in single crystals of shape memory alloys, called martensitic laminates. It will be shown that the formation of the laminates can be explained based on the concept of non-linear elasticity and energy-minimizing sequences. The applicability of this theoretical framework will be illustrated on two technologically important examples: i) branched laminates at the phase interfaces; ii) highly mobile laminate-laminate interfaces in the ferromagnetic shape memory alloys. For both cases, explicit constructions of energy upper-bounds will be shown, and the implications of the theoretical findings for designing of new alloys with advanced functionalities will be discussed. The development of these upper-bounds and the exploration of their properties are the main subjects of the current speaker’s research at the University of Minnesota, done in collaboration with prof. R.D. James and his research group. |
|
| Středa 7. 3. 2018, 10:00, posluchárna B | |
Catch the yield surface, experimentally, theoretically, and computationally |
|
| Dr. Li-Wei Liu, Department of Civil Engineering, National Taiwan University, Taipei 10617, Taiwan / Institute of Thermomechanics of CAS, v. v. i., Prague |
|
| The yield surface of a material is the boundary of the elastic region where every stress point inside the region result from the elastic response of the material. The experimental evidence shows that the yield surface changes position, size, shape, and orientation during the material undergoing the plastic loading which results in the permanent deformation. Based on the experimental observation, the modelling of the yield surface evolution is a key point to completely simulate the plastic behavior of the material. Most experiments of yield surface detection were conducted in the two-dimensional space (axial-torsional or bi-axial). Due to the complete stress space is six dimensional, detecting the yield surface in the space whose dimension is more than two can collect more detail of the yield surface evolution. For the experiment of yield surface detection, the determination of yield point underpins the accuracy of the geometry of the yield surface. Nowadays, test machines used for the experiments of yield surface detection are usually servo-controlled hydraulic system, hence the scatter of data should be taking into account in the determination of yield point. To this end, an automated yield stress determination based on the Weibull distribution is introduced. After conducting the experiment in the axial-torsional-hoop stress space, yield points are obtained according to the yield-stress determination and designed probing paths. To further capture the global information from these yield points and observe the evolution of yield surface during different pre-loading paths, a convex-closed-cubic polynomial, which is capable of description of the yield surface evolution, including translation, expansion/ contraction, rotation, affine deformation, and distortion in the three dimensional space, is proposed and the corresponding three-stage estimation for parameters of the polynomial is developed. This polynomial enable us to observe the yield surface evolution from the three dimensional point of view and it can also be a candidate of potential yield functions. Furthermore, the computation of elastoplastic models needs more attention to the special mathematical structure of the model containing ordinary differential equations, algebraic equations, and inequalities. Exploring the underlying structure of elastoplastic models shows part of them possesses internal symmetry that is the pseudo-sphere of real pseudo-Euclidean space Rp,q on which the proper orthochronous pseudo-orthogonal group SOo(p,q), a sub group of the Lie group, leaves acts. Based on the internal symmetry, a return-free integration is developed and it keeps the computed stress point on the yield surface automatically and exactly without any extra enforcement during the plastic deformation. | |
| 15. 2. 2018, 14:00, posluchárna B | |
Complementary near field technique for assessment of materials with added value |
|
| Dr. Adriana Savin, Head of Nondestructive Testing Department, National Institute of Research and Development for Technical Physics, Iasi, Rumunsko | |
| The National Institute of Research and Development for Technical Physics (NIRDTP) is a part of the national institutes R&D network coordinated by the Ministry of Research and Innovation - National Authority for Scientific Research and Innovation. Institute performs basic and applied research in the field of advanced materials with novel structures and properties, devices (i.e., sensors, transducers, actuators, measuring systems) based on advanced materials, new preparation methods and characterisation techniques, including non-destructive evaluation and magnetometry, electrical and magnetic separation, and devices for applications in engineering, healthcare, and biotechnology.
Nondestructive Testing Department (NDT) performs theoretical and applicative research in the field of electromagnetic testing of cylindrical and plate products including composite materials; calculation of the fields scattered by material discontinuities located at different areas of the multilayered medium by solving the forward problems; theoretical optimization of the operation of different types of sensors. Department also performs ultrasonic testing, development of specific methods for ultrasonic signal processing with FFT, digital filtering, neuro-fuzzy networks, development of the algorithms for defects localization and automaticclassification of flaws. In this lecture, a new possibility of using sensor with metamaterial lens for the nondestructive evaluation of metallic strip gratings and carbon fiber reinforced plastics will be presented. The sensor has enhanced spatial resolution due to the apparition of evanescent waves in the space between strips and between carbon fibers respectively, during the excitation by transversal electromagnetic field polarized along z-axis. The evanescent waves can be manipulated by a lens made from two conical Swiss rolls that act as a field concentrator. The detection has spatial resolution better than λ/2000. |
|
| 25. 1. 2018, 14:00 posluchárna B | |
Evolution and Verification of a Kinematic Hypothesis
|
|
| Prof. Herbert A. Mang, Institute for Mechanics of Materials and Structures, Vienna University of Technology | |
| Splitting of the strain energy into its “non-membrane” and membrane percentage provides insight into the load-carrying mechanism of structures, subjected to proportional loading. It may be useful, for example, for sensitivity analysis of the initial post-buckling behavior of beams, arches, plates, and shells, and assemblies of such structures. The task of this work is to determine this percentage without computing insignificant numbers such as the values of the strain energy and its membrane part. It is hypothesized that this percentage is proportional to the acceleration of a fictitious particle, moving along a curve on the unit sphere. The curve is described by the vertex of the normalized “fundamental eigenvector” of the so-called “consistently linearized eigenvalue problem”. The proportionality factor is obtained from the initial condition for the “non-membrane” percentage of the strain energy, hypothesized as twice the initial velocity of the particle. The lower bound of this factor signals the constancy of this percentage with increasing load, whereas the upper bound indicates a monotonic increase or decrease up to its ab initio predictable value at a stability limit or to an unphysical asymptotic limiting value. The proof of the universal validity of the two hypotheses begins with their verification for the special cases of a membrane stress state and pure bending. The assertion that this is a sufficient condition for the universal validity of these hypotheses is subsequently verified for an example with a monotonically increasing “non-membrane” percentage of the strain energy. It is finally confirmed by an indirect proof of their validity for a non-monotonic course of this percentage. A by-product of this work are conditions for extreme values of the stiffness of structures, subjected to proportional loading. | |
Zpět na hlavní stránku Semináře ÚT
© 2008 – 2018 Ústav termomechaniky AV ČR, v. v. i. 
