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Showing papers in "Bulletin of The Polish Academy of Sciences-technical Sciences in 2013"


Journal ArticleDOI
TL;DR: In this paper, the effects of high temperature on concrete have been investigated, including changes taking place in cement paste, aggregates, as well as the interaction of these two constituents, that result in changes of mechanical and physical characteristics of concrete.
Abstract: The paper presents the impact of high temperature on cement concrete. The presented data have been selected both from the author's most recent research and the published literature in order to provide a brief outline of the subject. The effect of a high temperature on concrete covers changes taking place in cement paste, aggregates, as well as the interaction of these two constituents, that result in changes of mechanical and physical characteristics of concrete. This paper presents the effects of a high temperature on selected physical properties of concrete, including colour change, thermal strain, thermal strains under load, and transient thermal strains. In addition, changes to mechanical properties are discussed: stress-strain relationship, compressive strength, and modulus of elasticity. Moreover, the phenomenon of explosive spalling and the main factors that affect its extent are analysed in light of the most recent research. Interest in the behaviour of concrete at a high temperature mainly results from the many cases of fires taking place in buildings, high-rise buildings, tunnels, and drilling platform structures. During a fire, the temperature may reach up to 1100 ◦ C in buildings and even up to 1350 ◦ C in tunnels, lead- ing to severe damage in a concrete structure (1). However, in some special cases, even much lower temperature, may cause explosive destruction of concrete, thus endangering the bear- ing capacity of the concrete element. Nevertheless, concrete is considered a construction material that satisfactorily preserves its properties at high temperature. Owing to concrete's fairly low coefficient of thermal conductivity, the movement of heat through concrete is slow, and thus reinforced steel, which is sensitive to high temperature, is protected for a relatively long period of time. When concrete is heated under conditions of fire, the increase in temperature in the deeper layers of the ma- terial is progressive, but because this process is slow, signifi- cant temperature gradients are produced between the concrete member's surface and core inducing additional damage to the element. Fundamental issues related to the impact of high temperature on concrete involve identification of the complex changes that take place in concrete while heated. This con- cerns both the physical and chemical changes taking place in the cement matrix, as well as the phenomena involved in mass movement (gases and liquids). The analysis is complicated due to the fact that cement concrete is a composite consisting of two substantially different constituents: cement paste and aggregates. The effects of the various changes taking place in heated concrete are the alterations of its physical, thermal, and mechanical properties. Research has demonstrated (1, 2), that changes in the strength of concrete as a function of tem- perature are related to, inter alia, concrete composition the type of aggregate used, the water/cement ratio, the presence of pozzolana additives, etc. Important factors are also the rate of heating and the time of concrete exposure to high tempera- ture. The increase in temperature results in water evaporation, C-S-H gel dehydration, calcium hydroxide and calcium alu- minates decomposition, etc. Along with the increase in tem- perature, changes in the aggregate take place. Due to those changes, concrete strength and modulus of elasticity gradu- ally decreases, and when the temperature exceeds ca. 300 ◦ C, the decline in strength becomes more rapid. When the 500 ◦ C threshold is passed, the compressive strength of concrete usu- ally drops by 50% to 60%, and the concrete is considered fully damaged. The Eurocode method of calculating the load- bearing capacity of reinforced concrete members subjected to a fire is based on this assumption. In the 500 ◦ C isotherm method, sections of concrete surface where the temperature had exceeded 500 ◦ C are omitted from the calculations (3).

318 citations


Journal ArticleDOI
TL;DR: Controllability is a qualitative property of dynamical control systems and is of particular importance in control theory as discussed by the authors, and controllability plays an essential role in the development of modern mathematical control theory.
Abstract: The main objective of this article is to review the major progress that has been made on controllability of dynamical systems over the past number of years. Controllability is one of the fundamental concepts in the mathematical control theory. This is a qualitative property of dynamical control systems and is of particular importance in control theory. A systematic study of controllability was started at the beginning of sixties in the last century, when the theory of controllability based on the description in the form of state space for both time-invariant and time-varying linear control systems was worked out. Roughly speaking, controllability generally means, that it is possible to steer a dynamical control system from an arbitrary initial state to an arbitrary final state using the set of admissible controls. It should be mentioned, that in the literature there are many different definitions of controllability, which strongly depend on a class of dynamical control systems and on the other hand on the form of admissible controls. Controllability problems for different types of dynamical systems require the application of numerous mathematical concepts and methods taken directly from differential geometry, functional analysis, topology, matrix analysis and theory of ordinary and partial differential equations and theory of difference equations. In the paper we use mainly state-space models of dynamical systems, which provide a robust and universal method for studying controllability of various classes of systems. Controllability plays an essential role in the development of modern mathematical control theory. There are various important relationships between controllability, stability and stabilizability of linear both finite-dimensional and infinite-dimensional control systems. Controllability is also strongly related to the theory of realization and so called minimal realization and canonical forms for linear time-invariant control systems such as the Kalmam canonical form, the Jordan canonical form or the Luenberger canonical form. It should be mentioned, that for many dynamical systems there exists a formal duality between the concepts of controllability and observability. Moreover, controllability is strongly connected with the minimum energy control problem for many classes of linear finite dimensional, infinite dimensional dynamical systems, and delayed systems both deterministic and stochastic. Finally, it is well known, that controllability concept has many important applications not only in control theory and systems theory, but also in such areas as industrial and chemical process control, reactor control, control of electric bulk power systems, aerospce engineering and recently in quantum systems theory.

122 citations


Journal ArticleDOI
TL;DR: In this paper, mathematical models of the supercapacitors are investigated based on electrical circuits in the form of RC ladder networks and the dynamic behavior of the circuit is described using fractional-order differential equations and its properties are analyzed.
Abstract: Abstract. In the paper, mathematical models of the supercapacitors are investigated. The models are based on electrical circuits in the form of RC ladder networks. The elementary cell of the network may consist of resistances and capacitances that are connected in series or parallel. The dynamic behavior of the circuit is described using fractional-order differential equations and its properties are analyzed. The identification procedure with quadratic performance index is performed in time domain to identify the parameters of the supercapacitor models. The results of numerical simulations are compared with the results measured experimentally in the physical system. In addition, an example from the automotive industry is used for an experimental evaluation of the theoretical analysis and to present a perspective on the applicability of the approach for other industrial projects.

90 citations


Journal ArticleDOI
TL;DR: This paper presents an application of the grid convergence index (GCI) concept based on the Richardson extrapolation to a selected simple problem of a cantilever beam loaded with vertical forces at the tip end, and the results differ for different FE formulations.
Abstract: This paper presents an application of the grid convergence index (GCI) concept based on the Richardson extrapolation to a selected simple problem of a cantilever beam loaded with vertical forces at the tip end. The GCI method, popular in computational fluid dynamics, has been recently recommended for finite element (FE) applications in solid and structural mechanics. Based on the results obtained usually for three meshes, the GCI method enables one to determine, in an objective manner, the order of convergence to estimate the asymptotic solution and the bounds for discretization error. The example shows that the characteristics of the convergence depend on the selection of the quantity of interest, which can be local or a global functional such as the deflection considered here. The results differ for different FE formulations, and the difference is bigger when the nonlinearities (e.g., due to plastic response) are taken into account.

65 citations


Journal ArticleDOI
TL;DR: In this article, a series of new results on the asymptotic stability of discrete-time fractional difference state space systems and their finite-memory approximations are presented.
Abstract: This paper presents a series of new results on the asymptotic stability of discrete-time fractional difference (FD) state space systems and their finite-memory approximations called finite FD (FFD) and normalized FFD (NFFD) systems. In Part I, new, general, necessary and sufficient stability conditions are introduced in a unified form for FD/FFD/NFFD-based systems. In Part II, an original, simple, analytical stability criterion is offered for FD-based systems, and the result is used to develop simple, efficient, numerical procedures for testing the asymptotic stability for FFD-based and, in particular, NFFD-based systems. Consequently, the so-called f -poles and f -zeros are introduced for FD-based system and their closed-loop stability implications are discussed.

62 citations


Journal ArticleDOI
TL;DR: In this article, the stability analysis for switched linear systems under arbitrary switching is reviewed, and necessary and sufficient conditions for asymptotic stability are highlighted. And the controllability results are reviewed.
Abstract: The study of properties of switched and hybrid systems gives rise to a number of interesting and challenging mathematical problems. This paper aims to briefly survey recent results on stability and controllability of switched linear systems. First, the stability analysis for switched systems is reviewed. We focus on the stability analysis for switched linear systems under arbitrary switching, and we highlight necessary and sufficient conditions for asymptotic stability. After that, we review the controllability results.

58 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of substrate roughness and superficial microcraking upon adhesion of repair systems using concrete surface engineering approach is analyzed. And the results obtained confirm also that Concrete Surface Engineering, as a scientific concept, will definitely contribute to shed more light on how to optimize repair bond, taking into account interactions between the materials at different observation scales.
Abstract: The objective of the paper is to analyze the effect of substrate roughness and superficial microcraking upon adhesion of repair systems using concrete surface engineering approach. The results presented in this paper have been obtained within the framework of research projects performed to develop a better understanding of the factors affecting the adhesion of repair materials through a surface engineering approach. Based on the results of investigations, the authors showed that the durability and quality of concrete repairs depend to a large degree on the characteristics of the substrate. Mechanical preparation and profiling of the concrete surface to be repaired has to be balanced with potential co-lateral effects such as superficial cracking, too often induced as a result of inappropriate concrete removal method selection, and the loss of benefits due to better mechanical anchorage. The results obtained confirm also that Concrete Surface Engineering, as a scientific concept, will definitely contribute to shed more light on how to optimize repair bond, taking into account interactions between the materials at different observation scales.

54 citations


Journal ArticleDOI
TL;DR: In this paper, the problems of practical stability and asymptotic stability of fractional discrete-time linear systems are addressed in terms of eigenvalues of the state matrix of the system.
Abstract: In the paper the problems of practical stability and asymptotic stability of fractional discrete-time linear systems are addressed. Necessary and sufficient conditions for practical stability and for asymptotic stability are established. The conditions are given in terms of eigenvalues of the state matrix of the system. In particular, it is shown that (similarly as in the case of fractional continuous-time linear systems) in the complex plane exists such a region, that location of all eigenvalues of the state matrix in this region is necessary and sufficient for asymptotic stability. The parametric description of boundary of this region is given. Moreover, it is shown that Schur stability of the state matrix (all eigenvalues have absolute values less than 1) is not necessary nor sufficient for asymptotic stability of the fractional discrete-time system. The considerations are illustrated by numerical examples.

53 citations



Journal ArticleDOI
TL;DR: In this article, an analysis of a mathematical model of the human arm dynamics in terms of observability is presented, based on the two-link manipulator moving horizontally and vertically.
Abstract: The paper presents an analysis of a mathematical model of the human arm dynamics in terms of observability. The purpose of the performed experiments is the selection of an observer for the possibility of arm tracking. The arm model is based on the two-link manipulator moving horizontally and vertically. For the study a model was linearized and the model part responsible for the work of human muscles was omitted. The experimental part involved simulated measurements of the motion parameters that imitate real-IMU (Inertial Measurement Unit) measurements. Finally, the simulation results using the observer in the form of a Kalman filter and the particle filter have been presented.

44 citations


Journal ArticleDOI
TL;DR: In this article, a numerical model based on FEAP 7.5 in 3D space has been used to evaluate the influence of porosity on the thermal properties (thermal conductivity) of the composite.
Abstract: Copper-based composites could be widely used in automotive, electronic or electrical industry due to their very promising thermal properties. In the present paper, Cu-AlN metal matrix composites with ceramic volume fractions between 0.1 and 0.4 were fabricated by hot pressing method in vacuum. Dependence of the coefficient of thermal expansion (CTE) and the thermal conductivity (TC) on the chemical composition of composites has been investigated. The measured values of the thermal expansion coefficient have been compared with the analytical models' predictions. A numerical model based on FEAP 7.5 in 3D space has been used to evaluate the influence of the porosity on the thermal properties (thermal conductivity) of the composite. A fairly good correlation between the FEM results and the experimental measurements has been obtained.

Journal ArticleDOI
TL;DR: A stochastic model for a class of population-based global optimization meta-heuristics, that generalizes existing models in the following ways, and is mainly devoted to study memetic algorithms.
Abstract: The paper introduces a stochastic model for a class of population-based global optimization meta-heuristics, that generalizes existing models in the following ways. First of all, an individual becomes an active software agent characterized by the constant genotype and the meme that may change during the optimization process. Second, the model embraces the asynchronous processing of agent’s actions. Third, we consider a vast variety of possible actions that include the conventional mixing operations (e.g. mutation, cloning, crossover) as well as migrations among demes and local optimization methods. Despite the fact that the model fits many popular algorithms and strategies (e.g. genetic algorithms with tournament selection) it is mainly devoted to study memetic algorithms. The model is composed of two parts: EMAS architecture (data structures and management strategies) allowing to define the space of states and the framework for stochastic agent actions and the stationary Markov chain described in terms of this architecture. The probability transition function has been obtained and the Markov kernels for sample actions have been computed. The obtained theoretical results are helpful for studying metaheuristics conforming to the EMAS architecture. The designed synchronization allows the safe, coarse-grained parallel implementation and its effective, sub-optimal scheduling in a distributed computer environment. The proved strong ergodicity of the finite state Markov chain results in the asymptotic stochastic guarantee of success, which in turn imposes the liveness of a studied metaheuristic. The Markov chain delivers the sampling measure at an arbitrary step of computations, which allows further asymptotic studies, e.g. on various kinds of the stochastic convergence.

Journal ArticleDOI
TL;DR: In this paper, 3D viscoelasticplastic models of asphalt aggregate-mixes are proposed based on a generalized macroscopic theory taking into account the effect of pressure-dependency on yielding.
Abstract: . The procedure of the formulation of constitutive equations for asphalt-aggregate mixes is based very often on rheological schemescomposed of classical elastic, plastic and viscous elements. The parameters of these schemes can be obtained based on laboratory experiments.In order to obtain better curve fitting results one can use non-classical viscoelastic elements described by fractional derivatives. In this paperwe present the characteristics of the fractional viscoelastic Huet-Sayegh model as well as the characteristics of an original simplified fractionalmodel. The results have been obtained using algorithms of numerical calculation of inverse Laplace transforms. Then the proposal of anoriginal rheological model including plasticity has been given. The non-linear differential constitutive relationships of such a model arepresented in the paper. The results of computer simulations are also visualized. Finally, 3D viscoelasticplastic models of asphalt aggregate-mixes are proposed. The models are based on a generalized macroscopic theory taking into account the effect of pressure-dependency onyielding.

Journal ArticleDOI
TL;DR: In this paper, the authors deal with information concerning properties and technology of a new generation cementitious composite i.e. Reactive Powder Concretes (RPC), which show both outstanding durability and mechanical properties.
Abstract: The paper deals with information concerning properties and technology of a new generation cementitious composite i.e. Ultra-High Performance Concrete. High performance here means both high strength and high durability under the influence of environmental factors. This group of composites is mainly represented by Reactive Powder Concretes (RPC), which show both outstanding durability and mechanical properties. Characteristic features of RPC are mainly due to the very low water-cement ratio, which involves application of superplasticizer, significant reduction of aggregate grains size as well as hydrothermal treatment. In the first part of the paper selected properties of RPC are compared to ordinary concrete and to other groups of new generation concrete. Moreover, fundamental technological factors influencing properties of RPC are described as well. The second part deals with the RPC developed at Cracow University of Technology. The presented test results are mainly focused on the influence of steel fibres content on mechanical properties of reactive powder concrete and hydrothermal treatment on composites microstructure. The quantitative and qualitative evaluation of this relationship expand the knowledge of the UHPC technology. Finally, the third part presents the most significant and newest structures which have been erected with the use of RPC.

Journal ArticleDOI
TL;DR: In this article, the controllability problem of a nonlinear fractional order discrete-time system is solved using the Riemann-Liouville, Caputo and Grünwald-Letnikov fractional-order difference operators.
Abstract: The Riemann-Liouville, Caputo and Grünwald-Letnikov fractional order difference operators are discussed and used to state and solve the controllability problem of a nonlinear fractional order discrete-time system. It is shown that independently of the type of fractional order difference, such a system is locally controllable in q steps if its linear approximation is globally controllable in q steps.

Journal ArticleDOI
TL;DR: In this article, an idea of predicting durability of concrete structures with steel reinforcement under conditions of chloride and carbonation corrosion risk is presented, and mechanisms of destruction due to steel corrosion in such conditions are shown.
Abstract: The paper presents an idea of predicting durability of concrete structures with steel reinforcement under conditions of chloride and carbonation corrosion risk. Mechanisms of destruction due to steel corrosion in such conditions are shown. The recently elaborated model of carbonation and general model of chloride diffusion have been discussed. An algorithm of the rest service life time prognosis has been shown and options of its main stages realization have been done. An example of durability prognosis for pre-stressed hollow-core floor slab with upper layer of concrete and epoxy-resin coating has been given. This example confirms the usefulness of the described prognosis method and demonstrates its helpfulness in a structure management according to the standards of EN 1504 series.

Journal ArticleDOI
TL;DR: This article presents the procedure of identification radar emitter sources with the trace distinctive features of original signal with the use of fractal features, and the method analysing properties of the measurement function caused the extraction of two additional distinctive features.
Abstract: . This article presents the procedure of identification radar emitter sources with the trace distinctive features of original signalwith the use of fractal features. It is a specific kind of identification called Specific Emitter Identification , where as a result of usingtransformations, which change measure points, a transformation attractor was received. The use of linear regression and the Lagrangepolynomial interpolation resulted in the estimation of the measurement function. The method analysing properties of the measurementfunction which has been suggested by the authors caused the extraction of two additional distinctive features. These features extended thevector of basic radar signals’ parameters. The extended vector of radar signals’ features made it possible to identify the copy of radar emittersource. Key words: fractal feature, pattern of radar, signal processing, Specific Emitter Identification (SEI). 1. Introduction The word “fractal” was introduced and popularized by BenoitMandelbrot in the book The Fractal Geometry of Nature [1].This term concerns a wide range of example geometric ob-jects such as Cantor set [2], Helge’a von Koch curve [3],Sierpinski carpet [4], Julia Mandelbrot’s sets and many more.In her early works Mandelbrot describes fractals using threebasic properties i.e. defined by the recursive relation and notby a formula, having the self-similarity feature (a part is sim-ilar to the entire object) and their dimension is not an integer.However, it has to be said that the properties of fractals can-not be a base for an accurate mathematical definition as thesame objects may be defined in different ways. The term “re-cursive” is also one of many others as some “typical fractal”may be defined in an algebraic way. A good example of it isthe Cantor set. The self-similarity feature is also difficult todefine especially while taking into account the fact that thesimplest geometric objects have this feature. One should focusits attention on the dimension of geometric object especiallywhen it is difficult to define it by an integer. Therefore, oneof the most common number characteristics of fractals is thedimension. At the same time examples of sets such as Cantorset, Peano curves [5] and Hilbert curves [6] resulted in a newdefinition of dimension [7]. Also Hausdorffdimension [8] andthe definition of Menger topological dimension [9] have a di-rect influence on the Mandelbrot definition. The researchersof the field of science often use the definition of dimensionby Minkowski [10], which is also called a

Journal ArticleDOI
TL;DR: The paper presents a concept and a structure of the system that has been created, comparing it with similar devices that have already existed, and some connections and areas where the subunits merge.
Abstract: Mechatronics is nowadays a dominating concept in design of various kinds of systems and technical devices. High speeds of data processing by control units of mechatronic systems, as well as high dynamics of their actuators allow the systems to be applied in wider fields. This refers to the medicine as well, especially while making attempts to replace lost human motor abilities by means of robots aiding the man. These devices can be divided into three groups: exoskeletons designed to strengthen the natural force of human muscles, orthotic robots that restore lost or weakened functions of human limbs, and prosthetic robots replacing an amputated limb. The first and the third group are known quite well, whereas the orthotic robots are at an initial phase of their development. The authors have worked on a device for aiding the motion of disabled people suffering from paresis of the lower limbs. The paper presents a concept and a structure of the system that has been created, comparing it with similar devices that have already existed. There are indicated some connections and areas where the subunits merge, as well as the rules of their working with the user.

Journal ArticleDOI
TL;DR: In this article, the authors evaluated the ability to self-repair of a cement composite modified with epoxy resin without a hardener, and the results of the investigation have confirmed the possibility of selfrepairing of the composite.
Abstract: Self-repairing means ability to the total or partial recovering of the properties which were worsened as a consequence of damage of the material. The subject of the paper is evaluation of ability to self-repair of a cement composite modified with epoxy resin without a hardener. The methodology of investigation of self-repairing building materials, developed by the authors, has been described, with controllable enforcing of the limited weakening of the material. Also, the self-repair degree has been defined as the measure of self-repairing ability of the building composites. The material model of the epoxy-cement composite has been developed on the basis of the tests results. The material optimization of the composite towards the maximum self-repairing ability has also been carried out. The results of investigation have confirmed the possibility of self-repairing of the cement composite modified with the epoxy resin without hardener. The conclusion and further research needs in the range of the self-repairing epoxy-cement composites have been pointed out.

Journal ArticleDOI
TL;DR: In this paper, a parametric study of Split Hopkinson pressure bar (SHPB) is presented, where LS-Dyna code with a quasi-optimization process carried out using LS-Opt software is used to obtain the pulse peak shape.
Abstract: . High strain rate experimental tests are essential in a development process of materials under strongly dynamic conditions. Forsuch a dynamic loading the Split Hopkinson Pressure Bar (SHPB) has been widely used to investigate dynamic behaviour of variousmaterials. It was found that for different materials various shapes of a generated wave are desired. This paper presents a parametric studyof Split Hopkinson Pressure Bar in order to find striker’s design variables, which influence the pulse peak shape in the incident bar. Withexperimental data given it was possible to verify the developed numerical model, which was used for presented investigations. Dynamicnumerical simulations were performed using explicit LS-Dyna code with a quasi-optimization process carried out using LS-Opt software inorder to find striker’s design variables, which influence the pulse peak shape. Key words: Split Hopkinson Pressure Bar, pulse shape, numerical studies, parametric study. 1. Introduction The Hopkinson bar with all its versions is widely used toquantify the dynamic behaviour of solid materials at highstrain rates within the range of 10

Journal ArticleDOI
TL;DR: In this article, the problem of compensator placement and sizing in electrical networks has been analyzed and a few objective functions have been proposed for this optimization problem, which may lead to suboptimal solutions and in fact a function reflecting the relation between the compensator size and its price must be incorporated into objective functions.
Abstract: The significant problem of compensator placement and sizing in electrical networks has been analyzed in the paper. The compensation is usually realized by means of passive or active power filters. The former solution is widely used mainly because of the economical reasons, but the latter one becomes more and more popular as the number of nonlinear loads increases. Regardless of the compensator type the most important goal consists in voltage and current distortion drop below levels imposed by standards. Nevertheless, the desired effects should be achieved with the minimum cost. So far a few objective functions have been proposed for this optimization problem. It is claimed that minimization of the compensator currents leads also to the minimum costs. This paper shows that such simplified approach could lead to suboptimal solutions and in fact a function g(·) reflecting the relation between the compensator size and its price must be incorporated into objective functions. Moreover, in this case it is very easy to compare solutions obtained using compensators offered by different suppliers – it is enough to change the function g(·). Theoretical considerations have been illustrated by an example of active power filter allocation and sizing.


Journal ArticleDOI
TL;DR: In this paper, the minimum energy control problem for the fractional positive continuous-time linear systems is formulated and solved, and sufficient conditions for the existence of solution to the problem are established.
Abstract: The minimum energy control problem for the fractional positive continuous-time linear systems is formulated and solved. Sufficient conditions for the existence of solution to the problem are established. A procedure for solving of the problem is proposed and illustrated by numerical examples.

Journal ArticleDOI
TL;DR: In this article, the authors presented an analysis of the power transfer between two DC circuits by use a single phase galvanically isolated dual active bridge (DAB) and the analytical description of instantaneous values of the currents in both DC and in AC circuits of the DAB is done.
Abstract: This paper presents an analysis of the power transfer between two DC circuit by use a single phase galvanically isolated dual active bridge – DAB. The analytical description of instantaneous values of the currents in both DC and in AC circuits of the DAB is done. The influence of the dead time as well as voltage drops across the transistors and diodes of the bridges is examined. The different relations between voltages of the DC circuits coupled through DAB and various phase shift ratios are considered. The analytical relations describing the average values of the currents in DC circuits are derived. These currents can be used to predict the power in both DC circuits and power losses generated in semiconductor devices of the converter. It is assumed that the voltage drops across these devices in conduction states are constant. The calculation of the transferred power as well as power losses and energy efficiency for the DAB converter power rated 5600 VA which is used to energy transfer between DC circuits 280 V and 51 V±20% is presented. The proposed relations and calculation results can be useful for preliminary evaluation of power losses generated in semiconductor devices and for design of the cooling system. Due to the high switching frequency of 100 kHz, the phase shift modulation for the control of DAB is used. To validate the theoretical investigations a few experimental results are presented.

Journal ArticleDOI
TL;DR: In this paper, the polycaprolactone/gelatin (PCL/Gt) blends were analyzed in terms of their miscibility, and changes in the PCL spherulitic structure with Gt content were investigated by a polarizing-interference microscope.
Abstract: Synthetic and natural polymers blends represent a new brand of materials with application in wound healing, scaffolds or drug delivery systems. Polycaprolactone/gelatin (PCL/Gt) blends were analyzed in terms of their miscibility. The PCL structure was investigated as a function of Gt content. Changes in the PCL spherulitic structure with Gt content were investigated by a polarizing-interference microscope. The analysis of the glass transition temperature (Tg) of both components as a function of PCL/Gt ratio by differential scanning calorimetry indicates that the system of polycaprolactone/gelatin belongs to a type of s.c. compatible system, being intermediate between miscible and immiscible systems. There is possibility of very limited miscibility of both components. Supplementary wide angle X-ray scattering results are presented.


Journal ArticleDOI
TL;DR: In this paper, the authors presented a hybrid (hydro-numerical) circulatory model built to be used as a complementary tool for clinical purposes, which was developed at the Institute of Biocybernetics and Biomedical Engineering - Polish Academy of Sciences (Poland).
Abstract: The paper presents a hybrid (hydro-numerical) circulatory model built to be used as a complementary tool for clinical purposes. It was developed at the Institute of Biocybernetics and Biomedical Engineering – Polish Academy of Sciences (Poland) in co-operation with the Institute of Clinical Physiology – National Council of Research (Italy). Main advantages of the model are: 1) high accuracy and repeatability of parameters setting, characteristic of numerical solutions, 2) maximum flexibility achieved by implementing the largest possible number of the model’s elements in the numerical way, 3) ability to test mechanical heart assist devices provided by special computer applications; in the model two physically different signal environments – numerical and hydraulic – are connected by special impedance transformers interfacing physical and numerical parts of the model; 4) eliminating flowmeters, as the voltage controlled flow sources embedded in the system provide information on flows. In vitro tests were performed to evaluate the circulatory model: a) modelling and simulation of physiological and pathological states parameters vs. left ventricular end-systolic elastance (Emax l) and rest volume (V ol) variations, b) testing the effect of LVAD counterpulsation on circulatory hemodynamics and ventricular energetics; it resulted in the increase of total cardiac output (COLV tot) from pathological value 3.8 to 5.4 l·min, mean aortic pressure mPas from 67.8 to 96.1 mmHg and in the decrease of left atrial pressure mPla from 15.7 to 7.7 mmHg and External Work nEW by 37.5%. The model was verified based on literature data.

Journal ArticleDOI
TL;DR: In this paper, an experimental verification of sensorless control of permanent magnet synchronous motors using Kalman filters is presented, which uses only the measurement of the motor current for on-line estimation of speed, rotor position and load torque reconstruction.
Abstract: This paper describes a study and the experimental verification of sensorless control of permanent magnet synchronous motors using Kalman filters. There are proposed two structures, extended and unscented Kalman filters, which use only the measurement of the motor current for on-line estimation of speed, rotor position and load torque reconstruction. The Kalman filter is an optimal state estimator and is usually applied to a dynamic system that involves a random noise environment. These structures are described in detail, starting with the selection of the variables state vector, the filters structure, and ending with in-depth laboratory tests. It has become possible, without using position and torque sensors, to apply these control structures as a cost-effective solution. Experimental results confirm the validity of the proposed estimation techniques.

Journal ArticleDOI
TL;DR: In this article, large-signal and small-Signal averaged models of basic switch-mode DC-DC power converters: BUCK (stepdown) and BOOS T (step-up) are derived with the separation of variables approach and have the form of equivalent circuits, suitable for a circuit simulation.
Abstract: Large-signal and small-signal averaged models of basic switch-mode DC-DC power converters: BUCK (step-down) and BOOS T (step-up) are presented. Models are derived with the separation of variables approach and have the form of equivalent circuits, suitable for a circuit simulation. Apart from equivalent circuits, small-signal transmittances of converters for CCM and DCM modes are discussed. Parasitic resistances of all components of converters are taken into account. A few examples of simulations and measurement results of selected converter characteristics are also presented. It is shown, that neglecting parasitic resistances (often met in works of other authors) may lead to serious errors in an averaged description of converters.

Journal ArticleDOI
TL;DR: In this paper, a method of modeling the residual stresses induced during thermal deposition of coatings was described, where the simulation was performed in two stages, the first dynamic stage simulated the impacts of the individual particles of the coating material onto the substrate, and the next static stage included a non-linear thermo-mechanical analysis intended for simulating the process of layer-by-layer deposition, with a specified thickness, and then cooling the entire system to the ambient temperature.
Abstract: There is described a method of modeling by the finite element method the residual stresses induced during thermal deposition of coatings. The simulation was performed in two stages. The first dynamic stage simulated the impacts of the individual particles of the coating material onto the substrate, and the next static stage included a non-linear thermo-mechanical analysis intended for simulating the process of layer-by-layer deposition of the coating, with a specified thickness, and then cooling the entire system to the ambient temperature. In the computations, the samples were assumed to be cylindrical in shape and composed of an Al2O3 substrate and a titanium coating (with three different thicknesses) deposited using the detonation method. The correctness of the numerical model was verified experimentally by measuring the deflections of a real Ti coating/Al2O3 substrate sample with the Ti coating detonation-sprayed on the ceramic substrate, after cooling it to the ambient temperature. The experimental results appeared to be in good agreement with those obtained by the numerical computations.