bluuebunny/crossref_metadata_2025 huggingface dataset:
Experiments with Externally Prestressed Continuous Composite Girders
Authors: Safan M. , Kohoutková A.
Published: March 2021

Steel-concrete composite girders have attractive potentials when applied in bridge construction. The serviceability performance of continuous composite girders is becoming more and more a deterministic parameter in the design of this type of structures. An effective method for improving this performance is to apply prestressing to control or completely eliminate concrete deck cracking caused by static and time dependent actions. Little literature has been found addressing the experimental analysis of continuous girders prestressed by means of external deviated tendons. The current research aims to investigate the behavior of a double-span steel composite beam externally prestressed by means of continuous tendons in terms of cracking characteristics, load deflection response, and load carrying capacity. The efficiency of prestressing is evaluated by comparing the results to those of a non-prestressed beam with similar cross sections and spans.
Genetic Algorithm Optimisation of a Ship Navigation System
Authors: Alfaro-Cid E. , McGookin E. W. , Murray-Smith D. J.
Published: March 2021

The optimisation of the PID controllers' gains for separate propulsion and heading control systems of CyberShip I, a scale model of an oil platform supply ship, using Genetic Algorithms is considered. During the initial design process both PID controllers have been manually tuned to improve their performance. However this tuning approach is a tedious and time consuming process. A solution to this problem is the use of optimisation techniques based on Genetic Algorithms to optimise the controllers' gain values. This investigation has been carried out through computer-generated simulations based on a non-linear hydrodynamic model of CyberShip I.
Conceptual Design of a Hydraulic Valve Train System
Authors: Pohl J. , Warell A. , Krus P. , Palmberg J.-O.
Published: March 2021

Variable valve train systems have been brought into focus during recent years as a means to decrease fuel consumption in tomorrow's combustion engines. In this paper an integrated approach, called simulation driven experiments, is utilised in order to aid the development of such highly dynamic systems. Through the use of systematic design methodology, a number of feasible concepts are developed. Critical components are subsequently identified using simulation. In this approach, component behaviour is simulated and validated by measurements on prototype components. These models are unified with complete system models of hydraulically actuated valve trains. In the case of the valve trains systems studied here component models could be validated using comparably simple test set-ups. These models enable the determination of non-critical design parameters in an optimal sense. This results in a number of optimised concepts facilitating an impartial functional concept selection.
Control System Design Based on a Universal First Order Model with Time Delays
Authors: Vyhlídal T. , Zítek P.
Published: March 2021

An original modelling approach for SISO systems is presented, based on a first order model with more than one delay in its structure. By means of this model it is possible truly to hit off the properties of systems which are conventionally described by higher order models. The identification method making use of a relay feedback test combined with transient responses of the system has proved to be suitable for assessing the model parameters. With respect to its plain structure the model is well suited to be applied in the framework of an internal model control scheme (IMC). The resultant control algorithm with only one optional parameter is very simple and can easily be implemented, for example by means of a programmable controller (PLC).
Stress Distribution in a Coal Seam before and after Bump Initiation
Authors: Vacek J.
Published: March 2021

This paper deals with to the behaviour of open rock that occurs, for example, during longwall mining in coal mines, in deep tunnel, or shaft excavation.Longwall instability leads to extrusion of rock mass into an open space. This effect is mostly referred to as a bump, or a rock burst. For bumps to occur, the rock has to possess certain particular rock burst properties leading to accumulation of energy and the potential to release this energy. Such materials may be brittle, or the bumps may arise at the interfacial zones of two parts of the rock, that have principally different material properties.The solution is based on experimental and mathematical modelling. These two methods have to allow the problem to be studied on the basis of three presumptions: – the solution must be time dependent – the solution must allow the creation of crack in the rock mass – the solution must allow an extrusion of rock into an open space (bump effect)
Credibility of Design Procedures
Authors: Marková J. , Holický M.
Published: March 2021

Theory of structural reliability enables comprehensive analysis of structural elements with respect to various limit states, and provides valuable insights into the methodology of applied standards. In addition to reliability analysis of the structural element, a new concept of the credibility of theoretical models used to calculate the design value of basic variables is introduced. The presented example of structural verification for limit states of cracking shows that the credibility of commonly applied formulas and reliability of a reinforced concrete slab have a great scatter and are in some cases inadequate.
Power Input of High-Speed Rotary Impellers
Authors: Beshay K. R. , Kratěna J. , Fořt I. , Brůha O.
Published: March 2021

This paper presents the results of an experimental investigation of the power input of pitched blade impellers and standard Rushton turbine impellers in a cylindrical vessel provided with four radial baffles at its wall under a turbulent regime of flow of an agitated liquid. The influence of the geometry of the pitched blade impellers (pitch angle, number of blades) and the off-bottom impeller clearance of both high-speed impellers tested on the impeller power input is determined in two sizes of the cylindrical vessel (0.3 m and 0.8 m diameter of vessel). A strain gauge torquemeter is used in the small vessel and a phase shift mechanical torquemeter is used in the large vessel. All results of the experiments correspond to the condition that the Reynolds number modified for the impeller exceeds ten thousand. The results of this study show that the significant influence of the separating disk thickness of the turbine impeller corresponds fairly well to the empirical equations presented in the literature. Both the influence of the number of impeller blades and the blade pitch angle of the pitched blade impeller were expressed quantitatively by means of the power dependence of the recently published correlations: the higher the pitch angle and the number of blades, the higher the values of the impeller power input. Finally, it follows from results of this study that the impeller off-bottom clearance has a weak influence on the power input of the Rushton turbine impeller, but with decreasing impeller off-bottom clearance the power input of the pitched blade impeller increases significantly.
Stellar Image Interpretation System using Artificial Neural Networks: Unipolar Function Case
Authors: Younis F. I. , Alawy A. El-Bassuny , Šimák B. , Ella M. S. , Madkour M. A.
Published: March 2021

An artificial neural network based system for interpreting astronomical images has been developed. The system is based on feed-forward Artificial Neural Networks (ANNs) with error back-propagation learning. Knowledge about images of stars, cosmic ray events and noise found in images is used to prepare two sets of input patterns to train and test our approach. The system has been developed and implemented to scan astronomical digital images in order to segregate stellar images from other entities. It has been coded in C language for users of personal computers. An astronomical image of a star cluster from other objects is undertaken as a test case. The obtained results are found to be in very good agreement with those derived from the DAOPHOTII package, which is widely used in the astronomical community. It is proved that our system is simpler, much faster and more reliable. Moreover, no prior knowledge, or initial data from the frame to be analysed is required.
Modeling Nonlinear Systems by a Fuzzy Logic Neural Network Using Genetic Algorithms
Authors: Attia Abdel-Fattah , Horáček P.
Published: March 2021

The main aim of this work is to optimize the parameters of the constrained membership function of the Fuzzy Logic Neural Network (FLNN). The constraints may be an indirect definition of the search ranges for every membership shape forming parameter based on 2nd order fuzzy set specifications. A particular method widely applicable in solving global optimization problems is introduced. This approach uses a Linear Adapted Genetic Algorithm (LAGA) to optimize the FLNN parameters. In this paper the derivation of a 2nd order fuzzy set is performed for a membership function of Gaussian shape, which is assumed for the neuro-fuzzy approach. The explanation of the optimization method is presented in detail on the basis of two examples.
Thermal Comfort and Optimum Humidity Part 1
Authors: Jokl M. V.
Published: March 2021

The hydrothermal microclimate is the main component in indoor comfort. The optimum hydrothermal level can be ensured by suitable changes in the sources of heat and water vapor within the building, changes in the environment (the interior of the building) and in the people exposed to the conditions inside the building. A change in the heat source and the source of water vapor involves improving the heat - insulating properties and the air permeability of the peripheral walls and especially of the windows. The change in the environment will bring human bodies into balance with the environment. This can be expressed in terms of an optimum or at least an acceptable globe temperature, an adequate proportion of radiant heat within the total amount of heat from the environment (defined by the difference between air and wall temperature), uniform cooling of the human body by the environment, defined a) by the acceptable temperature difference between head and ankles, b) by acceptable temperature variations during a shift (location unchanged), or during movement from one location to another without a change of clothing. Finally, a moisture balance between man and the environment is necessary (defined by acceptable relative air humidity). A change for human beings means a change of clothes which, of course, is limited by social acceptance in summer and by inconvenient heaviness in winter. The principles of optimum heating and cooling, humidification and dehumidification are presented in this paper.Hydrothermal comfort in an environment depends on heat and humidity flows (heat and water vapors), occurring in a given space in a building interior and affecting the total state of the human organism.
Non-isothermal Diffusion of Water Vapour in Porous Building Materials
Authors: Ficker T. , Podešvová Z.
Published: March 2021

Non-isothermal diffusion is analysed using Fick's laws. The exact relations for non-isothermal diffusion flux and partial pressure profiles in porous building materials are derived and discussed.
Pumping Efficiency of Screw Agitators in a Tube
Authors: Rieger F.
Published: March 2021

Most information on pumping efficiency that is available in the literature is limited to the turbulent region (centrifugal pumps). The aim of this paper is to show the effect of the Reynolds number on the pumping efficiency of screw agitators for a wide range of Reynolds number values from creeping to the turbulent flow region. The dependence of pumping efficiency on Reynolds number extends our knowledge about the efficiency of classical impeller pumps restricted usually to the turbulent region.
Formation of Haloforms during Chlorination of Natural Waters
Authors: Grünwald A. , Šťastný B. , Slavíčková K. , Slavíček M.
Published: March 2021

Recent drinking water regulations have lowered the standards for disinfection by-products and have added new disinfection by-products for regulation. Natural organic matter (NOM), mainly humic compounds, plays a major role in the formation of undesirable organic by-products following disinfection of drinking water. Many disinfection by-products have adverse carcinogenic or mutagenic effects on human health. This paper deals with the formation potencial of disinfection by-products in water samples taken from different places in the Flaje catchment.
The Danger of Toxic Substances
Authors: Jokl M. V.
Published: March 2021

Toxic (harmful) gases enter building interiors partly from outdoors (sulfur oxides, nitrogen oxides, carbon monoxide, ozone, smog and acid rains), partly originate indoors - as a result of human activity (carbon monoxide, tobacco smoke, nitrogen oxides, ozone, hydrocarbons) and also emanate from building materials (formaldehyde, volatile organic compounds). The human organism is most often exposed to cigarette smoke (especially nonsmokers are endangered, as cigarette smoke devastes the pulmonary and cardiovasculary system) and to smog entering from outdoors, paradoxically during sunny weather. Preventing toxic production is the most effective measure, e.g., by coaxing to coax smokers out of "civilized" areas, by using energy rationally (i.e., conserving energy), to turn to pure fuels and to increase energy production by non-combustion technologies. Besides ventilation and air filtration, the toxic gases can be removed to a remarkable extent by plants (by which decay the substances into nontoxic gases), and by air ionization. Review article.
Using the Correlation Function in Ultrasonic Non-destructive Testing
Authors: Kreidl M. , Houfek P.
Published: March 2021

This paper deals with ultrasonic signal de-noising by means of correlation. It is commonly known that the cross-correlation function shows the statistical dependence between two signals. In ultrasonic inspection, the measured signal is taken as the first signal. The most important aspect of this method is the choice of the second signal. Various types of the second signals can be tried.
Non Linear Modelling and Control of Hydraulic Actuators
Authors: Šulc B. , Jan J. A.
Published: March 2021

This paper deals with non-linear modelling and control of a differential hydraulic actuator. The nonlinear state space equations are derived from basic physical laws. They are more powerful than the transfer function in the case of linear models, and they allow the application of an object oriented approach in simulation programs. The effects of all friction forces (static, Coulomb and viscous) have been modelled, and many phenomena that are usually neglected are taken into account, e.g., the static term of friction, the leakage between the two chambers and external space. Proportional Differential (PD) and Fuzzy Logic Controllers (FLC) have been applied in order to make a comparison by means of simulation. Simulation is performed using Matlab/Simulink, and some of the results are compared graphically. FLC is tuned in a such way that it produces a constant control signal close to its maximum (or minimum), where possible. In the case of PD control the occurrence of peaks cannot be avoided. These peaks produce a very high velocity that oversteps the allowed values.
A Comparison of Acoustic Field Measurement by a Microphone and by an Optical Interferometric Probe
Authors: Bálek R. , Šlegrová Z.
Published: March 2021

The objective of this work is to show that our optical method for measuring acoustic pressure is in some way superior to measurement using a microphone. Measurement of the integral acoustic pressure in the air by a laser interferometric probe is compared with measurement using a microphone. We determined the particular harmonic components in the acoustic field in the case of relatively high acoustic power in the ultrasonic frequency range.
Propagation of Quasi-plane Nonlinear Waves in Tubes
Authors: Koníček P. , Bednařík M. , Červenka M.
Published: March 2021

This paper deals with possibilities of using the generalized Burgers equation and the KZK equation to describe nonlinear waves in circular ducts. A new method for calculating of diffraction effects taking into account boundary layer effects is described. The results of numerical solutions of the model equations are compared. Finally, the limits of validity of the used model equations are discussed with respect to boundary conditions and the radius of the circular duct. The limits of applicability of the KZK equation and the GBE equation for describing nonlinear waves in tubes are discussed.
Certain Discrete Element Methods in Problems of Fracture Mechanics
Authors: Procházka P. P. , Kugblenu M. G.
Published: March 2021

In this paper two discrete element methods (DEM) are discussed. The free hexagon element method is considered a powerful discrete element method, which is broadly used in mechanics of granular media. It substitutes the methods for solving continuum problems. The great disadvantage of classical DEM, such as the particle flow code (material properties are characterized by spring stiffness), is that they have to be fed with material properties provided from laboratory tests (Young's modulus, Poisson's ratio, etc.). The problem consists in the fact that the material properties of continuum methods (FEM, BEM) are not mutually consistent with DEM. This is why we utilize the principal idea of DEM, but cover the continuum by hexagonal elastic, or elastic-plastic, elements. In order to complete the study, another one DEM is discussed. The second method starts with the classical particle flow code (PFC - which uses dynamic equilibrium), but applies static equilibrium. The second method is called the static particle flow code (SPFC). The numerical experience and comparison numerical with experimental results from scaled models are discussed in forthcoming paper by both authors.
Application of Discrete Element Methods to the Problem of Rock Bumps
Authors: Procházka P. P. , Kugblenu M. G.
Published: March 2021

This paper is a continuation of a previous paper by the authors. Applications of two discrete element methods (DEM) to several fields of geotechnics are discussed. The free hexagon element method is considered a powerful discrete element method, and is widely used in mechanics of granular media. It substitutes the methods for solving continuum problems. In order to complete the study, other discrete element methods are discussed. The second method starts with the classical particle flow code (PFC, which uses dynamic equilibrium), but we apply static equilibrium in our case. The second method is called the static particle flow code (SPFC). The numerical experiences and comparison with experimental results from scaled models are discussed.
Measuring the Process Parameters of the IBAD Method
Authors: Zoriy M. , Černý F. , Palamarchuk D. , Konvičková S. , Hüttel I.
Published: March 2021

Chromium nitride films are known as good protective layers for against both corrosion and wear. These coatings have been studied in detail during recent years. Their protective capability strongly depends on the deposition conditions. A modern method for preparing chromium nitride is the IBAD (Ion Beam Assisted Deposition) method. The main parameter determining the composition and properties of the films prepared by the IBAD method is the arrival ratio of impinging nitrogen ions to chromium atoms. In order to calibrate the ion beam XY-mechanical scanner with a Faraday cup, a detector was designed and constructed. By mathematical processing of the data, the flux of the nitrogen atoms was found. To obtain the flux of the chromium atoms the RBS and Talystep methods were used. Now, on the basis of this data, we can perform CrNx, coatings with controlled composition and properties.
Aerodynamic Design and Experimental Investigation of the Sailplane Wing Tip Devices
Authors: Anderle P. , Smrček L. , Coton F. N.
Published: March 2021

This paper describes an experimental set-up for the investigation of wing tip devices developed as part of a study into the velocity and vorticity distributions in the flow field behind winglets, using hot-wire anemometry. In this study, effort was focused on gaining a greater understanding of what happens in the region where the winglet joins the wing. The measurements were performed in the Handley-Page wind tunnel of the Department of Aerospace Engineering at the University of Glasgow. In order to carry out measurements with the hot-wire anemometry system, a new traverse mechanism was designed and manufactured. This traverse mechanism was integrated with the other test instrumentation to create a complete measurement chain. The complete system allows fully automated hot wire measurements to be made over a defined area using programmable test parameters.
Modeling the Aerodynamics and Performances of a Historic Airplane: the Spanish
Authors: González-Betes A. , Martínez-Val R.
Published: March 2021

The process of modeling the aerodynamics and performances of a historic airplane is very similar to the conceptual and preliminary design phases of a new plane, with the advantage of knowing the configuration and that the airplane was airworthy; thus it is unnecessary to outline and assess many different alternatives. However, the drag polar, the real performances, stability features, etc, are still unknown. For various reasons (in particular because of two World Wars, or the Civil War in the Spanish case) most details of many historical airplanes have been lost.In the present research work, the situation is as follows. In June 1933 the "Cuatro Vientos", a Spanish-built Bréguet XIX Super TR, flew non-stop from Seville to Cuba; a distance of 7500 km (about 4100 nautical miles) in around 40 hours. A few days later, in a far less complicated stage between Havana and Mexico, the airplane was lost with its occupants to a storm in the Yucatan peninsula.The modeling considered in this paper starts by addressing the aerodynamic modifications introduced in the airplane for the extremely long flight. Then, with the help of old and present day aerodynamic data and methods the drag polar is estimated. The available engine data is completed and extrapolated to obtain information on power and fuel consumption. Finally, all this data is integrated to provide a reliable and technically sound reproduction of the Seville-Cuba flight.
A Magnetic Resonance Measurement Technique for Rapidly Switched Gradient Magnetic Fields in a Magnetic Resonance Tomograph
Authors: Bartušek K. , Gescheidtová E.
Published: March 2021

This paper describes a method for measuring of the gradient magnetic field in Nuclear Magnetic Resonance (NMR) tomography, which is one of the modern medical diagnostic methods. A very important prerequisite for high quality imaging is a gradient magnetic field in the instrument with exactly defined properties. Nuclear magnetic resonance enables us to measure the pulse gradient magnetic field characteristics with high accuracy. These interesting precise methods were designed, realised, and tested at the Institute of Scientific Instruments (ISI) of the Academy of Sciences of the Czech Republic. The first of them was the Instantaneous Frequency (IF) method, which was developed into the Instantaneous Frequency of Spin Echo (IFSE) and the Instantaneous Frequency of Spin Echo Series (IFSES) methods. The above named methods are described in this paper and their a comparison is also presented.
On Planning and Managing the Preservation of Historical Buildings
Authors: Jarský Č.
Published: March 2021

The process of preserving and reconstructing historical buildings poses several specific questions and raises problems which must be solved in the planning and management stage of the building process - from questions of architectural and art-historical significance, via the future purpose of use of the building, links to the surrounding buildings, environmental questions, questions of cost, time analysis, and quality assurance problems. Many of these problems can be solved with the help of a computer model of the course of the rehabilitation and reconstruction of the building created by a construction technology network diagram. The CONTEC integrated project planning, management and quality control system based on these diagrams has been used for bidding, planning and managing the reconstruction process of several significant historical buildings in Prague and other cities.
Modal Logic - a Tool for Design Process Formalisation
Authors: Jelínek I.
Published: March 2021

In this paper we show the possibility to formalize the design process by means of one type of non-standard logic - modal logic [1]. The type chosen for this study is modal logic S4. The reason for this choice is the ability of this formalism to describe modeling of the individual discrete steps of design, respecting necessity or possibility types of design knowledge.
Numerical Simulation of Stresses in Thin-rimmed Spur Gears with Keyway
Authors: Brůžek B. , Leidich E.
Published: March 2021

This paper contains an investigation of the key on a stress distribution in a thin-rimmed spur gear. A stress analysis was carried out by means of the Finite Element Method (FEM). The 2D-FE analysis has helped to find the influence of turning the gearing towards the keyway on the stress in the loaded root of the tooth and in the keyway. 2D and 3D numerical analysis has been used to find mutual influence of every single notch (root of tooth and keyway), influence of thickness of the hub, length of the key and the form of loading. Verification has been carried out through experimental method.
Concurrent Design of Railway Vehicles by Simulation Model Reuse
Authors: Valášek M. , Steinbauer P. , Kolář J. , Dvořák J.
Published: March 2021

This paper describes a concurrent design approach to railway vehicle design. Current railway vehicles use many different concepts that are combined into the final design concept. The design support for such systems is based on reusing components from previous design cases. The key part of the railway vehicle design concept is its simulation model. Therefore the support is based on support for reuse of previous simulation models. The simulation models of different railway component concepts are stored using the methodology from the EU CLOCKWORK project. The new concept usually combines stored components.
Optimization of Flapping Airfoils for Maximum Thrust and Propulsive Efficiency
Authors: Tuncer I. H. , Kay M.
Published: March 2021

A numerical optimization algorithm based on the steepest decent along the variation of the optimization function is implemented for maximizing the thrust and/or propulsive efficiency of a single flapping airfoil. Unsteady, low speed laminar flows are computed using a Navier-Stokes solver on moving overset grids. The flapping motion of the airfoil is described by a combined sinusoidal plunge and pitching motion. Optimization parameters are taken to be the amplitudes of the plunge and pitching motions, and the phase shift between them. Computations are performed in parallel in a work station cluster. The numerical simulations show that high thrust values may be obtained at the expense of reduced efficiency. For high efficiency in thrust generation, the induced angle of attack of the airfoil is reduced and large scale vortex formations at the leading edge are prevented.
The Psychological Image of Realistic Physical Quantities. The Psychological Speed of Aging
Authors: Végh L.
Published: March 2021

The article is dealing with psychological images of real physical quantities, such as time, length, etc. and with their interrelationship in general and in the scientific field in particular. It has been shown that the importance of the above is reflected by the possibility to influence or reshape, within certain limits, positively or negatively, the psychological images of real values, so as to meet the outlined or desired expectation. As shown, one of the possible practical application of the above phenomenon is the possibility to positively influence the speed of aging.This problem has been demonstrated in the article analytically, as well as graphically.
Knowledge Support of Simulation Model Reuse
Authors: Valášek M. , Steinbauer P. , Šika Z. , Zdráhal Z.
Published: March 2021

This describes the knowledge support for engineering design based on virtual modelling and simulation. These are the results of the EC Clockwork project. A typical and important step in the development of a simulation model is the phase of reusing. Virtual modelling and simulation often use the components of previous models. The usual problem is that the only remaining part of the previous simulation models is the model itself. However, a large amount of knowledge and intermediate models have been used, developed and then lost. A special methodology and special tools have therefore been developed on support of storing, retrieving and reusing the knowledge from previous simulation models. The knowledge support includes informal knowledge, formal knowledge and intermediate engineering models. This paper describes the overall methodology and tools, using the example of developing a simulation model of Trijoint, a new machine tool.
A coding and On-Line Transmitting System
Authors: Zagursky V. , Zarumba I. , Riekstinsh A.
Published: March 2021

A distributed data acquisition system is proposed. It provides parallel and simultaneous coding and on-line transmission of signals. This system has higher accuracy of measurements and performance in sampling and transmission than known analogs.
Response of a Light Aircraft Under Gust Loads
Authors: Chudý P.
Published: March 2021

This project presents work performed by the Institute of Aerospace Engineering, Brno University of Technology. The primary purpose of this work was to estimate the aeroelastic response of a light aircraft under gust loads. In the past, the gust response has been investigated using the Pratt - Walker formula. This formula is derived from the response of a rigid airplane to a discrete gust. However, the Pratt-Walker formula does not capture either the stochastic nature of continuous turbulence or the effects of structural flexibility. The analysis described here was performed using the advanced FEM software package MSC Nastran.
Finite Element Modelling of Mechanical Phenomena Connected to the Technological Process of Continuous Casting of Steel
Authors: Heger J.
Published: March 2021

A finite element method algorithm is presented that enables numerical simulation of real phenomena that take place during an industrial process of continuous casting of steel. The algorithm takes into account all known kinds of nonlinearities: material nonlinearity connected to the nonlinear temperature dependence of material properties, large deformations from the process of material forming and contacts between the slab and rollers of the strand. Received results describe the sensitivity of the product to crack initiation, not only during the process of continuous casting itself but also in the finished and cooled slab.
Superior Properties of Ultra-fine-grained Steels
Authors: Leinonen J. I.
Published: March 2021

A description of the improved mechanical properties obtained in ultra-fine-grained steels up to now will be presented in this paper, and some potential applications of these new generation steels will be described. In addition, the principle and implementation of a novel hot rolling process developed by the author will be introduced. This novel Thermomechanical Nonrecrystallisation Control Process (TNCP) has been shown to give an ultra-fine ferrite (uff) structure with grain sizes of 2 to 3mm in various test steels, thus resulting in super-toughness. Charpy V impact test results suggest that some of these steels could still be tough at temperatures lower than -100 °C. This novel process, TNCP, is one potential candidate for the commercial production of superior ultra-fine-grained steels in the future.
Explicit Time Integrators for Nonlinear Dynamics Derived from the Midpoint Rule
Authors: Krysl P.
Published: March 2021

We address the design of time integrators for mechanical systems that are explicit in the forcing evaluations. Our starting point is the midpoint rule, either in the classical form for the vector space setting, or in the Lie form for the rotation group. By introducing discrete, concentrated impulses we can approximate the forcing impressed upon the system over the time step, and thus arrive at first-order integrators. These can then be composed to yield a second order integrator with very desirable properties: symplecticity and momentum conservation.
Experimental Analysis of Sandstone and Travertine
Authors: Doležel T. , Drdácký M. , Konvalinka P. , Kopecký L.
Published: March 2021

Sandstone and travertine are sedimentary rocks. The former is clastic, while the latter is sourced by chemical precipitation from hot springs. Their applications in civil engineering structures are mostly influenced by the ability to carry compression loading. A three-point bending experiment is usually used to determine material characteristics. However it does not correspond very well to applicatiosn in structures. For this reason we used a uniaxial compression test to obtain the modulus of elasticity and the stress-strain diagram. To obtain detailed information about the crystalline structure of sandstone and travertine a microscopic analysis wascarried out, using optical microscopy and an EDAX multichannel spectrometer for elementary microanalysis.
Efficient Analytical Model for Calculation of the Influence Zone inside the Subsoil below Foundations Slabs
Authors: Kuklík P. , Kopáčková M.
Published: March 2021

This paper presents analytical approaches for evaluating the depth of the influence zone. The model focuses on variations in the ground water table. Referring to [6], the term influence zone is assigned to the region where the load has a substantial influence on the deformation of the soil skeleton. The first approach relies on an analytical solution based on an analysis of the Westergard subspace, assuming an elastic material response. This idea is accompanied by the effect of water pressure on the effective (skeleton) stress state. The approach provides any extremely efficient estimate of the depth of the influence zone. The proposed analytical solution is verified against the finite element analysis, assuming that the material response is driven by the modified Cam clay model. The predicted analytical result is found to be in a good agreement with the numerical solution derived with the help of the ADINA 8.1 general-purpose finite element code. The presented results further suggest that this analytical procedure can be applied to solve the interaction problem of the slab and the subsoil and its progress in the structural process, namely by varying the ground water table.
A Shear Lag Analysis for Composite Box Girders with Deformable Connectors
Authors: Křístek V.
Published: March 2021

A method is proposed for shear lag analysis which can be applied to steel-concrete composite box girders. The proposed method uses harmonic analysis and allows the determination of shear lag effects from simple calculations so that the method is regarded as a design aid. The character of the method can illustrate the influence of certain key parameters upon the extent of the shear lag effect.
A New Methodology to Establish Upper Bounds on Open-Cell Foams Homogenized Properties
Authors: Dimitrovová Z.
Published: March 2021

The methodology for determining the upper bounds on the homogenized linear elastic properties of cellular solids, described for the two-dimensional case in Dimitrovová and Faria (1999), is extended to three-dimensional open-cell foams. Besides the upper bounds, the methodology provides necessary and sufficient conditions on optimal media. These conditions are written in terms of generalized internal forces and geometrical parameters. In some cases dependence on internal forces can be replaced by geometrical expressions. In such cases, the optimality of some medium under consideration can be verified directly from the microstructure, without any additional calculation. Some of the bounds derived in this paper are published for the first time, along with a proof of their optimality.
On Adequacy of Two-point Averaging Schemes for Composites with Nonlinear Viscoelastic Phases
Authors: Zeman J. , Valenta R. , Šejnoha M.
Published: March 2021

Finite element simulations on fibrous composites with nonlinear viscoelastic response of the matrix phase are performed to explain why so called two-point averaging schemes may fail to deliver a realistic macroscopic response. Nevertheless, the potential of two-point averaging schemes (the overall response estimated in terms of localized averages of a two-phase composite medium) has been put forward in number of studies either in its original format or modified to overcome the inherited stiffness of classical ”elastic” localization rules. However, when the material model and geometry of the microstructure promote the formation of shear bands, none of the existing two-point averaging schemes will provide an adequate macroscopic response, since they all fail to capture the above phenomenon. Several examples are presented here to support this statement.
Deformation Stress State of Elastic Bodies
Authors: Skokánek J.
Published: March 2021

The theory of the deformation stress state is based on the actual corpuscular structure of matter characterized in terms of mechanics by the fact that an increase in the distance of two adjacent atoms is accompanied by the origin of an attractive force and a reduction in their distance by the origin of a repulsive force. These forces differ significantly from the classical internal forces, which are the forces of the mechanics of perfectly solid bodies. These express the equilibrium of forces with reference to the given area within the loaded body, and have no direct deformation effect. This paper defines the quantities of the deformation stress state – the deformation force and the deformation stress – the direct manifestation of which is a deformation. The author introduces the term of deformation stress state theory (DSS theory) to the field of the theory of elasticity dealing with the stress state of deformable bodies. The quantities and the equations of this theory also form the basis for the formulation of the theory of failure, which makes it possible to determine reliably the safety margin and the strength of a multiaxially loaded body from the stress state described by the static quantities (stress tensor) and uniaxial strength.
Influence of Ring Stiffeners on a Steel Cylindrical Shell
Authors: Lemák D. , Studnička J.
Published: March 2021

Shell structures are usually formed from concrete, steel and nowadays also from many others materials. Steel is typically used in the structures of chimneys, reservoirs, silos, pipelines, etc. Unlike concrete shells, steel shells are regularly stiffened with the help of longitudinal and/or ring stiffeners.The authors of this paper investigated steel cylindrical shells and their stiffening with the use of ring stiffeners. The more complete the stiffening, the more closely the shell will act to beam theory, and the calculations will be much easier. However, this would make realization of the structure more expensive and more laborious. The target of the study is to find the limits of ring stiffeners for cylindrical shells. Adequate stiffeners will eliminate semi-bending action of the shells in such way that the shell structures can be analyzed with the use of numerical models of the struts (e.g., by beam theory) without significant divergences from reality. Recommendations are made for the design of ring stiffeners, especially for the distances between stiffeners and for their bending stiffness.
Realization of Logical Circuits with Majority Logical Function as Symmetrical Function
Authors: Bokr J. , Jáneš V.
Published: March 2021

The paper deals with the “production” and design of symmetrical functions, particularly aimed at the design of circuits with majority elements, which lead to interesting solutions of logical structures. The solutions are presented in several examples, which show the applicability of the procedures to the design of FPGA morphology on chips.
Solving Inverse Kinematics – A New Approach to the Extended Jacobian Technique
Authors: Šoch M. , Lórencz R.
Published: March 2021

This paper presents a brief summary of current numerical algorithms for solving the Inverse Kinematics problem. Then a new approach based on the Extended Jacobian technique is compared with the current Jacobian Inversion method. The presented method is intended for use in the field of computer graphics for animation of articulated structures.
Trivial Logic Arrays
Authors: Bokr J. , Jáneš V.
Published: March 2021

This paper deals with matrix modelling of trivial logic arrays (PLA, PAL, ROM) and the design of the above array as structural models of static and dynamic logic objects.
Cost-Effective Architectures for RC5 Brute Force Cracking
Authors: Buček J. , Hlaváč J. , Matušková M. , Lórencz R.
Published: March 2021

In this paper, we discuss the options for brute-force cracking of the RC5 block cipher, that is, for revealing the unknown secret key, given a sample ciphertext and a portion of the corresponding plaintext. First, we summarize the methods employed by the current cracking efforts. Then, we present two hardware architectures for finding the secret key using the “brute force” method. We implement the hardware in FPGA and ASIC and, based on the results, we discuss the cost and time needed to crack the cipher using today’s technology and suggest a minimum key length that can be considered secure.
Elicitation of Preference Structure in Engineering Design
Authors: Tan J. K.
Published: March 2021

Engineering design processes, which inherently involve multiple, often conflicting criteria, can be broadly classified into synthesis and analysis processes. Multiple Criteria Decision Making addresses synthesis and analysis processes through multiple objective optimisation to generate sets of efficient design solutions (i.e. on Pareto surfaces) and multiple attribute decision making to analyse and select the most preferred design solution(s). MCDM, therefore, has been widely used in all fields of engineering design; for example it has been applied to such diverse areas as naval battle ships criteria analysis/selection and product appearance design. Given a list of design alternatives with multiple conflicting criteria, preferences often determine the final selection of a particular set of design alternative(s). Preferences may also be used to drive the design/design optimisation processes. Various methods have been proposed to model preference structure, for example simple weights, multiple attribute utility theory, pairwise comparison, etc. Preference structure is often non-linear, discontinuous and complex. An Artificial Neural Network (ANN) learning-based preference elicitation method is presented in this paper. ANNs efficiently model the non-linearity, complexity and discontinuity nature of any given preference structure. A case study is presented to illustrate the learning-based approach to preference structure elicitation.
Towards Integration of CAx Systems and a Multiple-View Product Modeller in Mechanical Design
Authors: Song H. , Eynard B. , Lafon P. , Roucoules L.
Published: March 2021

This paper deals with the development of an integration framework and its implementation for the connexion of CAx systems and multiple-view product modelling. The integration framework is presented regarding its conceptual level and the implementation level is described currently with the connexion of a functional modeller, a multiple-view product modeller, an optimisation module and a CAD system. The integration between the multiple-view product modeller and CATIA V5 based on the STEP standard is described in detail. Finally, the presented works are discussed and future research developments are suggested.
Finite Element Modelling of Cold Formed Stainless Steel Columns
Authors: Macdonald M. , Rhodes J.
Published: March 2021

This paper describes the results obtained from a finite element investigation into the load capacity of column members of lipped channel cross-section, cold formed from Type 304 stainless steel, subjected to concentric and eccentric compression loading. The main aims of this investigation were to determine the effects which the non-linearity of the stress-strain behaviour of the material would have on the column behaviour under concentric or eccentric loading. Stress-strain curves derived from tests and design codes are incorporated into non-linear finite element analyses of eccentrically loaded columns and the results obtained are compared with those obtained on the basis of experiments on stainless steel channel columns with the same properties and dimensions. Comparisons of the finite element results and the test results are also made with existing design specifications and conclusions are drawn on the basis of the comparisons.
Properties and Performance of a New Compact HF Aerial Design for Multi-Band Operation
Authors: Telfer D. , Spencer J.
Published: March 2021

This work is an extension to that of Telfer and Austin [1] in that here a balanced feed embodiment of an inwardly-inclined folded dual monopole aerial is presented and discussed in terms of its improved performance over the original configuration. This includes greater control of the stability of the far-field (FF) lobe pattern with operating frequency, and a considerably extended frequency range (3:1 ratio) over which Near Vertical Incidence Skywave (NVIS) propagation in the high frequency (HF) bands can be exploited. Furthermore, the FF lobe patterns at frequencies >2× the fundamental design frequency are such that advantage can be taken of conventional non-NVIS horizontal propagation at those frequencies using the same aerial. At the fundamental frequency, compactness of design and robustness of its NVIS FF pattern to orientation make the novel balanced aerial design a convenient replacement for a full-length low dipole in cluttered environments. The paper also presents a vehicle-mounted version for medium range operation within HF skip distances. Applications highlighted include stations for remote monitoring of environmental measurements in difficult or hostile terrain.
Ontologies and Formation Spaces for Conceptual ReDesign of Systems
Authors: Bíla J. , Tlapák M.
Published: March 2021

This paper discusses ontologies, methods for developing them and languages for representing them. A special ontology for computational support of the Conceptual ReDesign Process (CRDP) is introduced with a simple illustrative example of an application. The ontology denoted as Global context (GLB) combines features of general semantic networks and features of UML language. The ontology is task-oriented and domain-oriented, and contains three basic strata – GLBExpl(stratum of Explanation), GLBFAct (stratum of Fields of Activities) and GLBEnv (stratum of Environment), with their sub-strata. The ontology has been developed to represent functions of systems and their components in CRDP. The main difference between this ontology and ontologies which have been developed to identify functions (the semantic details in those ontologies must be as deep as possible) is in the style of the description of the functions. In the proposed ontology, Formation Spaces were used as lower semantic categories the semantic deepness of which is variable and depends on the actual solution approach of a specialised Conceptual Designer.