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Number of results: 213
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Abstract

The subject of the numerical investigation is an ellipsoidal head with a central (axis-symmetrical) nozzle. The nozzle is loaded by axial load force. The ellipsoidal head is under axial-symmetrical compression load. The numerical FEM model is elaborated. The calculation will provide the critical loads and equilibrium paths for the sample head.. The investigation will measure the influence of the diameter of the nozzle on the critical state of the ellipsoidal head.

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Authors and Affiliations

P. Jasion
K. Magnucki
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Abstract

The basic element of a project organizing construction works is a schedule. The preparation of the data necessary to specify the timings of the construction completion as indicated in the schedule involves information that is uncertain and hard to quantify. The article presents the methods of building a schedule which includes a fuzzy amount of labour, time standards and number of workers. The proposed procedure allows determining the real deadline for project completion, taking into account variable factors affecting the duration of the individual works.

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Authors and Affiliations

E. Plebankiewicz
P. Karcińska
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Abstract

The paper present the concept of stability assessing the of solutions which are construction schedules. Rank have been obtained through the use of task scheduling rules and the application of the KASS software. The aim of the work is the choice of the equivalent solution in terms of the total time of the project. The selected solution optimization task should be characterized by the highest resistance to harmful environmental risk factors. To asses the stability of schedule simulation technique was used.

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Authors and Affiliations

M. Krzemiński
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Abstract

To guarantee a durable pavement construction that only needs a little care, it is crucial to manage problematic soil conditions properly and prepare the foundation. Some organizations remove soils since they have realized they do not function as well as other materials (for example, a state specification dictating that frost susceptible loess could not be present in the frost penetration zone). Nevertheless, there are more advantageous or desirable courses of action than this (e.g., excavation might create a disturbance, plus additional issues of disposal and removal). The subgrade conditions described in the preceding section may be improved by stabilization, offering an alternative solution. It is impossible to overstate the importance of ensuring a homogeneous soil profile in terms of density, moisture content, and textural categorization in the top section of the subgrade. Thru soil sub-cutting or other stabilizing methods, this consistency may be attained. Additionally, stabilization may be utilized to prevent swelling in expansive materials, create a weather-resistant work platform, enhance soil workability, and limit issues with frost heave. Alternative stabilizing techniques will be discussed in this part, and advice for choosing the best technique will be adequately provided. The current review paper aims to identify bridge issues related to soft soil and takes two ways of soft soil stabilization: chemical and mechanical. The finding of both methods show that the compressive strength and settlement have been improved after using waste materials; therefore, using waste materials as a cement replacement is considered one of the expansive utilized methods in most construction applications and bridges of that applications.
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Authors and Affiliations

Mayadah W. Falah
1 2
Haitham Muteb
2

  1. Building and Construction Engineering Technology Department, Al-Mustaqbal University,Hillah 51001, Iraq
  2. Department of Civil Engineering, College of Engineering/University of Babylon, Babylon, 51001
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Abstract

This paper proposes a power system stabilizer (PSS) with optimal controller parameters for damping low-frequency power oscillations in the power system. A novel meta-heuristic, weighted grey wolf optimizer (WGWO) has been proposed, it is a variant of the grey wolf optimizer (GWO). The proposed WGWO algorithm has been executed in the selection of controller parameters of a PSS in a multi-area power system. A two-area fourmachine test system has been considered for the performance evaluation of an optimally tuned PSS. A multi-objective function based on system eigenvalues has been minimized for obtained optimal controller parameters. The damping characteristics and eigenvalue location in the proposed approach have been compared with the other state-of-the-art methods, which illustrates the effectiveness of the proposed approach.
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Authors and Affiliations

Murali Krishna Gude
1
ORCID: ORCID
Umme Salma Salma
1
ORCID: ORCID

  1. Gandhi Institute of Technology and Management (GITAM), Visakhapatnam, India
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Abstract

Dynamic stability analysis of the World Class Glider PW-5 has been presented. Glider was assumed to be a rigid body of three degrees of freedom - two linear displacements and one rotation - all in the plane of symmetry. Responses of the glider due to gust and deflection of elevator have been determined. The Laplace transform has been applied to convert the differential equations into algebraic ones. The transformed algebraic equations, after a number of manipulations have been solved for the output variables. Partial-fraction expansions have been performed to obtain the inverse Laplace transforms from the Laplace transform table. Although some restricting assumptions have been made (rigid body, small disturbances) the presented results are original and have not been presented before. The airworthiness regulations (JAR, FAR) do not require performing dynamic analysis in order the glider to be granted a Certificate of Airworthiness by the national aviation authority. To certificate the glider it is sufficient to prove static stability by means of in-flight tests. Flying qualities are qualitatively estimated basing on subjective opinions of the test pilots
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Authors and Affiliations

Zdobysław Goraj
Adam Przekop
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Abstract

Low voltage microgrids are autonomous subsystems, in which generation, storage and power and electrical energy consumption appear. In the paper the main attention has been paid to the voltage stability issue in low voltage microgrid for different variants of its operation. In the introduction a notion of microgrid has been presented, and also the issue of influence of active and reactive power balance on node voltage level has been described. Then description of voltage stability issue has been presented. The conditions of voltage stability and indicators used to determine voltage stability margin in the microgrid have been described. Description of the low voltage test microgrid, as well as research methodology along with definition of considered variants of its operation have been presented further. The results of exemplary calculations carried out for the daily changes in node load of the active and reactive power, i.e. the voltage and the voltage stability margin indexes in nodes have been presented. Furthermore, the changes of voltage stability margin indexes depending on the variant of the microgrid operation have been presented. Summary and formulation of conclusions related to the issue of voltage stability in microgrids have been included at the end of the paper.
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Authors and Affiliations

Mirosław Parol
Łukasz Rokicki
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Abstract

A new concept (notion) of the practical stability of positive fractional discrete-time linear systems is introduced. Necessary and sufficient conditions for the practical stability of the positive fractional systems are established. It is shown that the positive fractional systems are practically unstable if corresponding standard positive fractional systems are asymptotically unstable.

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Authors and Affiliations

T. Kaczorek
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Abstract

The study deals with stability and dynamic problems in bar structures using a probabilistic approach. Structural design parameters are defined as deterministic values and also as random variables, which are not correlated. The criterion of structural failure is expressed by the condition of non-exceeding the admissible load multiplier and condition of non-exceeding the admissible vertical displacement. The Hasofer-Lind index was used as a reliability measure. The primary research tool is the FORM method. In order to verify the correctness of the calculations Monte Carlo and Importance Sampling methods were used. The sensitivity of the reliability index to the random variables was defined. The limit state function is not an explicit function of random variables. This dependence was determined using a numerical procedure, e.g. the finite element methods. The paper aims to present the communication between the STAND reliability analysis program and the KRATA and MES3D external FE programs.

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Authors and Affiliations

A. Dudzik
U. Radoń
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Abstract

The main focus of the paper is on the asymptotic behaviour of linear discrete-time positive systems. Emphasis is on highlighting the relationship between asymptotic stability and the structure of the system, and to expose the relationship between null-controllability and asymptotic stability. Results are presented for both time-invariant and time-variant systems.

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Authors and Affiliations

G. James
V. Rumchev
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Abstract

This paper discusses contemporary transformations in the way work is organised and the consequences for the stability of careers and biographies. It debates the widely held belief that organised and predictable life-course paths (including professional careers) have ceased to exist and that work itself has lost its stabilising quality. Biographical data collected among Polish employees of transnational corporations within the project “Poles in the World of Late Capitalism” proves that even though transnational corporations are widely criticised for propelling neoliberal tendencies in the global economy, they provide a means of protecting their employees against today’s uncertainty and occupational risk. Three empirical cases are presented to show how work in a transnational corporation may contribute to achieving and maintaining stability for persons who have had troublesome experiences of working in other sectors of the labour market.

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Authors and Affiliations

Marcin Gońda
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Abstract

In the paper, the application of multi-criteria optimization of the parameters of PSS3B system stabilizers to damping electromechanical swings in an extended power system (PS) is presented. The calculations of the power system stabilizer (PSS) parameters were divided into two stages. In the first stage, single-machine systems, generating unit – infinite bus, of generating units critical for the angular stability of the PS were analyzed. Time constants and preliminary values of the PSS gains were calculated. In the second stage, the main one, the main gains on which the effectiveness of operation of PSSs depends the most were calculated by multi-criteria optimization of the extended PS. The calculations were carried out in several variants: for two-dimensional objective functions and the six-dimensional objective function. In multi-criteria optimization, the solution is not one set of PSS parameters, but a set of sets of these parameters, i.e. a set of compromises that were determined for each analyzed case. Additionally, for the six-dimensional compromise set, projections of this set on the planes connected with the quantities of individual generating units and the boundary of these projections on these planes were determined. A genetic algorithm adapted to multi-criteria issues was used to minimize the multivariate objective function. Sample calculations were made for the model of the National (Polish) Power System taking into account 57 selected generating units operating in high and extra high voltage networks (220 and 400 kV). The presented calculations show that the applied multi-criteria optimization of the PSS3B stabilizer parameters allows effectively damping electromechanical swings withoutworsening the voltagewaveforms of generating units in the extended PS.
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Authors and Affiliations

Adrian Nocoń
1
ORCID: ORCID
Stefan Paszek
1
ORCID: ORCID
Piotr Pruski
1
ORCID: ORCID

  1. Faculty of Electrical Engineering, Silesian University of Technology, Akademicka 10, 44-100 Gliwice, Poland
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Abstract

New equivalent conditions of the asymptotical stability and stabilization of positive linear dynamical systems are investigated in this paper. The asymptotical stability of the positive linear systems means that there is a solution for linear inequalities systems. New necessary and sufficient conditions for the existence of solutions of the linear inequalities systems as well as the asymptotical stability of the linear dynamical systems are obtained. New conditions for the stabilization of the resultant closed-loop systems to be asymptotically stable and positive are also presented. Both the stability and the stabilization conditions can be easily checked by the so-called I-rank of a matrix and by solving linear programming (LP). The proposed LP has compact form and is ready to be implemented, which can be considered as an improvement of existing LP methods. Numerical examples are provided in the end to show the effectiveness of the proposed method.

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Authors and Affiliations

H. Yang
Y. Hu
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Abstract

We built a logistic regression Early Warning Models (EWM) for banking crises in a panel of 47 countries based on data from 1970-2014 using candidate variables that cover macro and financial market indicators. We find that VIX, a proxy of global risk-premium, has a strong signalling properties and that low VIX (low price of risk) increases likelihood of crisis. It does not only mean that stability leads to instability, but that this tends to be a global rather than a domestic phenomenon. We also find that particularly high contribution of financial sector to GDP growth often precedes crises, suggesting that such instances are primarily driven by excessive risk taking by financial sector and may not necessarily be sustainable. Other variables that feature prominently include credit and residential prices. Models using multiple variable clearly outperform single variable models, with probability of correct signal extraction exceeding 0.9. Our setting includes country-specific information without using country-specific effects in a regression, which allows for direct application of EWM we obtain to any country, including these that have not experienced a banking crisis.
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Authors and Affiliations

Piotr Bańbuła
1
Marcin Pietrzak
2

  1. Narodowy Bank Polski and Warsaw School of Economics
  2. Brown University and Institute of Economics, Polish Academy of Sciences
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Abstract

Accurate understanding of the three-dimensional (3D) morphology of a complex goaf and its relative displacement in space is a precondition to further analyzing the stability of the cavity. In this study, to make an accurate stability analysis of the goaf, laser detection and numerical simulation are used to study the interior space form of goaf and the change characteristics of stress and displacement in goaf. The results of the study show that the BLSS-PE mining 3D laser system as a field detection tool can detect the morphology of the cavity more comprehensively and improve the accuracy of the detection data to a certain extent. Combined with the numerical simulation software analysis, it can be seen that the maximum principal stress in the 818-2# goaf increases after excavation. In addition, the maximum value appears in the top and bottom plates of the goaf, and the minimum stress remains nearly unchanged. The tensile stress appears in the upper and lower plates but is lower than the surrounding rock. The maximum horizontal and vertical displacements of the 818-2# goaf are small. The plastic zone appears in the surrounding rock of the goaf as the mining work progresses, but the area is small. It is concluded that the goaf is relatively stable overall. The research results may provide a strong reference for ground pressure management in mines and comprehensive control of goaves.
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Authors and Affiliations

Gangyou Sun
1
ORCID: ORCID
Yuandi Xia
2
ORCID: ORCID
Qinrong Kang
2
ORCID: ORCID
Weizhong Zhang
2
ORCID: ORCID
Qingzhen Hu
2
ORCID: ORCID
Wei Yuan
2
ORCID: ORCID

  1. The Fourth Research and Design Engineering Corporat ion, China
  2. School of Resources and Safety Engineering, Wuhan Institute of Technology, China
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Abstract

Investments in made ground are a big problem. The present investigation concerns ground derived from limestone treatment waste from SOLVAY soda plants. This waste is deposited in the southern area of Krakow in a reservoir called ‘White Seas’ in an area of approximately 15 ha. Currently, part of the route and tram investment, ‘The Łagiewniki Route’ Currently through the ‘White Seas’ area. The article presents an analysis of a section of this route by a high and steep slope made from made ground. The first stage of the in-situ measurements was to scan the shape of the high slope with the RIEGL VZ-400 terrestrial laser scanner. It was necessary to obtain the shape of the slope for numerical modelling using the FEM method. The point cloud perfectly reflected the shape of the slope with an accuracy of 5 mm. Soil samples (limestone waste) were also collected in the area of the slope for laboratory tests. In order to determine the effective strength parameters of the made ground of the embankment, a series of tests was carried out using triaxial compression apparatus. All triaxial tests were performed in accordance with British Standard 1337 Part 8. Modelling was performed using an FEM finite element method in MIDAS. The analyses also included the variant of irrigation of made ground. The conducted research shows that the high and steep slope made from calcareous waste indicates stability. The irrigated land did not make the high escarpment unstable.
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Authors and Affiliations

Elżbieta Pilecka
1
ORCID: ORCID
Jakub Zięba
2
ORCID: ORCID
Dariusz Szwarkowski
2
ORCID: ORCID

  1. DSc., PhD., Eng., Prof. of CUT, Cracow University of Technology, Faculty of Civil Engineering, ul. Warszawska 24, 31-155 Kraków, Poland
  2. MSc., Eng., Cracow University of Technology, Faculty of Civil Engineering, ul. Warszawska 24, 31-155 Kraków, Poland
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Abstract

This paper deals with the problem of stabilization by an estimated state feedback for a family of nonlinear time-delay Takagi-Sugeno fuzzy parameterized systems. The delay is supposed to be constant where the parameter-dependent controls laws are used to compensate the nonlinearities which are formulated in terms of linear matrix inequalities (LMIs). Based on the Lyapunov- Krasovskii functionals, global exponential stability of the closed-loop systems is achieved. The controller and observer gains are able to be separately designed even in the presence of modeling uncertainty and state delay. Finally, a numerical example is given to show the applicability of the main result.
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Authors and Affiliations

Nizar Hadj Taieb
1
Mohamed Ali Hammami
2
François Delmotte
3

  1. University of Sfax, IPEIS Sfax, Tunisia
  2. University of Sfax, Faculty of Sciences of Sfax, Tunisia
  3. University of Artois, Bethune, France
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Abstract

This paper presents non-linear mathematical model of a computer network with a part of wireless network. The article contains an analysis of the stability of the network based on TCP-DCR, which is a modification of the traditional TCP. Block diagram of the network model was converted to a form in order to investigate the D-stability using the method of the space of uncertain parameters. Robust D-stability is calculated for constant delays values.
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Authors and Affiliations

Jerzy Klamka
Jolanta Tańcula
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Abstract

In deformation analyses, it is important to find a stable reference frame and therefore the stability of the possible reference points must be controlled. There are several methods to test such stability. The paper’s objective is to examine one of such methods, namely the method based on application of R-estimation, for its sensitivity to gross errors. The method in question applies three robust estimators, however, it is not robust itself. The robustness of the method depends on the number of unstable points (the fewer unstable points there are, the more robust is the proposed method). Such property makes it important to know how the estimates applied and the strategy itself respond to a gross error. The empirical influence functions (EIF) can provide necessary information and help to understand the response of the strategy for a gross error. The paper presents examples of EIFs of the estimates, their application in the strategy and describes how important and useful is such knowledge in practice.
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Authors and Affiliations

Robert Duchnowski
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Abstract

This paper addresses the state-variable stabilising control of the power system using such series FACTS devices as TCPAR installed in the tie-line connecting control areas in an interconnected power system. This stabilising control is activated in the transient state and is supplementary with respect to the main steady-state control designed for power flow regulation. Stabilising control laws, proposed in this paper, have been derived for a linear multi-machine system model using direct Lyapunov method with the aim to maximise the rate of energy dissipation during power swings and therefore maximisation their damping. The proposed control strategy is executed by a multi-loop controller with frequency deviations in all control areas used as the input signals. Validity of the proposed state-variable control has been confirmed by modal analysis and by computer simulation for a multi-machine test system.
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Authors and Affiliations

Łukasz Nogal
Jan Machowski
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Abstract

The analysis of the positivity and stability of linear electrical circuits by the use of state-feedbacks is addressed. Generalized Frobenius matrices are proposed and their properties are investigated. It is shown that if the state matrix of an electrical circuit has generalized Frobenius form then the closed-loop system matrix is not positive and asymptotically stable. Different cases of modification of the positivity and stability of linear electrical circuits by state-feedbacks are discussed and necessary conditions for the existence of solutions to the problem are established.

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Authors and Affiliations

Tadeusz Kaczorek
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Abstract

Extracellular laccase produced by the wood-rotting fungus Cerrena unicolor was immobilised covalently on the mesostructured siliceous foam (MCF) and three hexagonally ordered mesoporous silicas (SBA-15) with different pore sizes. The enzyme was attached covalently via glutaraldehyde (GLA) or by simple adsorption and additionally crosslinked with GLA. The experiments indicated that laccase bound by covalent attachment remains very active and stable. The best biocatalysts were MCF and SBA-15 with Si-F moieties on their surface. Thermal inactivation of immobilised and native laccase at 80°C showed a biphasic-type activity decay, that could be modelled with 3- parameter isoenzyme model. It appeared that immobilisation did not significantly change the mechanism of activity loss but stabilised a fraction of a stable isoform. Examination of time needed for 90% initial activity loss revealed that immobilisation prolonged that time from 8 min (native enzyme) up to 155 min (SBA-15SF).

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Authors and Affiliations

Jolanta Bryjak
Katarzyna Szymańska
Andrzej B. Jarzębski
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Abstract

Stability of silver nanoparticles strongly influences the potential of their application. The literature shows wide possibilities of nanoparticles preparation, which has significantly impact on their properties. Therefore, the improvement of AgNPs preparation plays a key role in the case of their practical use. The pH values of the environment are one of the important factors, which directly influences stability of AgNPs. We present a comparing study of the silver nanoparticles prepared by „bottom-up“ methods over by chemical synthesis and biosynthesis using AgNO3 (0.29 mM) solution. For the biosynthesis of the silver nanoparticles, the green freshwater algae Parachlorella kessleri and Citrus limon extracts were used as reducing and stabilizing agents. Chemically synthesized AgNPs were performed using sodium citrate (0.5%) as a capping agent and 0.01% gelatine as a reducing agent. The formation and long term stability of those silver nanoparticles synthesized either biologically and chemically were clearly observed by solution colour changes and confirmed by UV-vis spectroscopy. The pH values of formed nanoparticle solutions were 3 and 5.8 for biosynthesized AgNPs using extract of Citrus limon and Parachlorella kessleri, respectively and 7.2 for chemically prepared AgNPs solution using citrate. The SEM as a surface imaging method was used for the characterization of nanoparticle shapes, size distribution and also for resolving different particle sizes. These micrographs confirmed the presence of dispersed and aggregated AgNPs with various shapes and sizes.
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Authors and Affiliations

O. Velgosová
A. Mražíková
J. Kavuličová
M. Matvija
E. Čižmárová
J. Willner

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