Wyniki wyszukiwania - BazTech

1

When to Trust AI: Advances and Challenges for Certification of Neural Networks

Kwiatkowska Marta, Zhang Xiyue

Annals of Computer Science and Information Systems

|

2023

|

Vol. 35

25--37

EN

Artificial intelligence (AI) has been advancing at a fast pace and it is now poised for deployment in a wide range of applications, such as autonomous systems, medical diagnosis and natural language processing. Early adoption of AI technology for real-world applications has not been without problems, particularly for neural networks, which may be unstable and susceptible to adversarial examples. In the longer term, appropriate safety assurance techniques need to be developed to reduce potential harm due to avoidable system failures and ensure trustworthiness. Focusing on certification and explainability, this paper provides an overview of techniques that have been developed to ensure safety of AI decisions and discusses future challenges.

2

Spectral response of stationary jack-up platforms loaded by sea waves and wind using perturbation method

Rozmarynowski Bogdan, Jesien Wojciech

Polish Maritime Research

|

2021

|

nr 4

53--62

EN

The paper addresses non-linear vibrations of offshore jack-up drilling platforms loaded by sea waves and wind in their stationary condition using the perturbation method. Non-linearity of dynamic equations of motion for fixed offshore platforms yields from two factors. The first is load excitation generating non-linear velocity coupling in a dynamic system. This coupling is inherent in the modified Morison equation, involving the excitation function in the form of the sum of the inertial and velocity forces of sea waves, taking into account relative wave–structure kinematics. Moreover, the wind acting on the exciting side causes similar effects. The second source is the subsoil‒structure interaction problem, modelled by a system of springs and dashpots that yields stochastic non-linearity of the dynamic system. The matrix equations of structural motion in FEM terms are set up. The perturbation method is adopted to determine the mechanical response of the system, making it possible to determine response spectra of the first and the second approximations for displacements and internal forces of the platform. The paper is the continuation of research detailed in the paper [1]. It is assumed, that the fluctuation parts of the dynamic loading forces are in line with the direction of sea wave propagation. Sea current and lift forces effects are neglected in this study. A numerical example refers to structural data of the Baltic drilling platform in the stationary configuration, i.e. when three legs support the deck above the seawater level.

3

Review on relationship between the universality class of the Kardar-Parisi-Zhang equation and the ballistic deposition model

Sayfidinov Okhunjon, Bognar Gabriella

International Journal of Applied Mechanics and Engineering

|

2021

|

Vol. 26, no. 4

206--216

EN

We have analysed the research findings on the universality class and discussed the connection between the Kardar-Parisi-Zhang (KPZ) universality class and the ballistic deposition model in microscopic rules. In one dimension and 1+1 dimensions deviations are not important in the presence of noise. At the same time, they are very relevant for higher dimensions or deterministic evolution. Mostly, in the analyses a correction scale higher than 1280 has not been studied yet. Therefore, the growth of the interface for finite system size [...] value predicted by the KPZ universality class is still predominant. Also, values of [...] obtained from literature are consistent with the expected KPZ values of [...] connection between the ballistic deposition and the KPZ equation through the limiting procedure and by applying the perturbation method was also presented.

4

Vibration of a composite elastic beam on an inhomogeneous elastic foundation

Sahin Onur

Journal of Applied Mathematics and Computational Mechanics

|

2020

|

Vol. 19, nr 2

107--119

EN

The lowest vibration modes of a composite beam resting on an inhomogeneous elastic foundation in the case of a clamped-free boundary condition are investigated. It is observed that the relation between the frequency and foundation constant has an effect on the valid solution of the problem. An asymptotic procedure is employed to derive the eigenfrequencies as well as the eigenforms revealing that only under certain conditions on the ratios of material parameters. Numerical illustrations are presented to confirm that the obtained asymptotic frequencies agree well with the exact frequencies in the lowest frequency range. Comparisons of asymptotic and exact displacements are also presented and a remarkable agreement is observed for high-contrast beam components.

5

Transient heat and mass transfer of hydromagnetic effects on the flow past a porous medium with movable vertical permeablesheet

Okedoye A. M., Salawu S. O.

International Journal of Applied Mechanics and Engineering

|

2020

|

Vol. 25, no. 4

175--190

EN

An unsteady flow of heat and species transport through a porous medium in an infinite movable vertical permeable flat surface is considered. The hydromagnetic chemical reactive fluid flow is stimulated by the thermal and solutant convection, and propelled by the movement of the surface. The formulated nonlinear flow equations in time space are solved analytically by asymptotic expansions to obtain solutions for the flow momentum, energy and chemical concentration for various thermo-physical parameters. The existence of flow characteristic is defined with the assistance of the flow parameters. In the study, the impact of some pertinent flow terms is reported and discussed. The study revealed that the species boundary layer increases with a generative chemical reaction and decreases with a destructive chemical reaction. Also, arise in the generative species reaction term reduces the flow momentum for the cooling surface. The impact of other flow governing parameters is displayed graphically as well as the fluid wall friction, wall energy and species gradients. The results of this study are important in chemical thermal engineering for monitoring processes to avoid solution blow up.

6

Infinitely many solutions for some nonlinear supercritical problems with break of symmetry

Candela Anna Maria, Salvatore Addolorata

Opuscula Mathematica

|

2019

|

Vol. 39, no. 2

175--194

EN

In this paper, we prove the existence of infinitely many weak bounded solutions of the nonlinear elliptic problem [formula], where [formula] is an open bounded domain, N ≥ 3, and [formula] are given functions, with[formula], such that A(x, •, •) is even and g(x, •) is odd. To this aim, we use variational arguments and the Rabinowitz's perturbation method which is adapted to our setting and exploits a weak version of the Cerami-Palais-Smale condition. Furthermore, if [formula] grows fast enough with respect to t, then the nonlinear term related to g(x,t) may have also a supercritical growth.

7

Measurements of the angular and linear displacements of steered wheel

Wach K.

Technical Transactions

|

2018

|

Vol. 115, iss. 2

219--227

EN

This paper concerns the use of a prototype measuring instrument for conducting measurements of the linear and angular displacements of a steered wheel in relation to the car body. The theoretical principles of the measurement are presented, as are the notation method and a solution to the system of equations of the geometric constraints of the instrument’s mechanism. In the research section, the manner in which the measurements were conducted is discussed and sample results are described. A preliminary analysis of the results is performed in the summary section.

PL

Praca dotyczy pomiarów przemieszczenia i orientacji koła kierowanego względem nadwozia pojazdu wykonanych za pomocą prototypowego przyrządu pomiarowego. Przedstawione zostały teoretyczne podstawy pomiaru, jak również sposób zapisu i rozwiązywania układu równań więzów geometrycznych mechanizmu przedmiotowego przyrządu. W części badawczej omówiono sposób przeprowadzania pomiarów oraz przedstawiono przykładowe wyniki. W podsumowaniu została dokonana ich wstępna ocena i analiza.

8

On problems of heat and mass transfer in concrete structures

Kowalik M., Poński M.

Zeszyty Naukowe Politechniki Częstochowskiej. Budownictwo

|

2016

|

Z. 22 (172)

171-183

EN

A stochastic finite difference approach based on stochastic finite elements is proposed for heat and mass transfer modeling. Porous structure with random material properties is investigated. The theoretical formulation of the problem is described. A system of partial differential equations is obtained and solved for first two probabilistic moments of the random temperature field. Example of stochastic thermal analysis in concrete structure with random material parameters are given.

PL

W artykule zastosowano metodę stochastycznych różnic skończonych do analizy problemów przepływu ciepła i ruchu wilgoci. Przedstawiono sformułowanie teoretyczne problemu. Badano porowatą strukturę z losowymi parametrami materiałowymi. Do rozwiązania zagadnienia zastosowano metodę perturbacyjną.

9

Natural frequencies of layered elongated cylindrical panels for geometrically nonlinear deformation at discrete consideration of components

Marchuk M., Goriachko T., Pakosh V.

Vibrations in Physical Systems

|

2016

|

Vol. 27

255--264

EN

The proposed and verified the technique of finding a finite number of first natural frequencies for geometrically nonlinear vibrations of layered elongated cylindrical panels at discrete consideration of components. The influence of the radius of curvature on the natural frequencies of three- and five-layered panels is investigated. The dependence between the volume of filler three-layer panels and the lowest natural frequency has been established.

10

Coupled lateral-torsional vibrations of a symmetric rotor

Chiliński B., Pakowski R., Stanik Z.

Journal of KONES

|

2016

|

Vol. 23, No. 4

41--47

EN

The paper presents a cross-sectional analysis of dynamics of rotating systems with different characteristics, starting from the search for solutions in an analytical way, and ending with the numerical attempt to verify the results. There is presented a problem of bending and torsional vibrations in rotational systems, using possibly the simplest model of the phenomenon. It is a heavy disk embedded on the deformable massless shaft. The rotor is symmetric and it is assumed that stiffness can be nonlinear. The analysis of vibrations occurring in rotors is made with the use of this model. This is followed by a preliminary discussion on the problem and the conclusions of the pilot studies. There are presented basic problems related to the phenomenon of lateral-torsional coupling in rotational systems with an emphasis on critical states. Formulation of the problem is the conclusion of preliminary part of the paper. Next, there are discussed the selected methods currently used to solve such problems, together with a discussion of their application in this case. In addition, there is discussed a problem of numerical or analytical character of obtained results and the range of using methods in modelling, designing and experimental studies. The next part of the paper focuses on the solution of the model presented in the introduction, using the following analytical or numerical methods: Krylov-Bogolubov, Adams and Runge-Kutta methods. There are presented assumptions, simplifications of the model, technical details of searching for solutions and the results together with a discussion of their correctness. The results, which were obtained from analysis, are polyharmonic. Due to this fact, the spectra of each solution were presented. These aspects are discussed in the context of the solving methods and motion analysis for rotor systems. The whole paper is summarized with a discussion of the results and their confrontation with reality.

11

Wyznaczanie orientacji głównych osi obrotu przegubów metalowo-gumowych wielowahaczowego zawieszenia kół kierowanych

Struski J., Kowalski M.

Logistyka

|

2015

|

nr 4

5830--5839, CD 2

PL

Równania więzów geometrycznych nakładających ograniczenia na ruch względny poszczególnych członów mechanizmu wielowahaczowego zawieszenia kół kierowanych rozwiązano za pomocą metody perturbacji. Rozwiązania tych równań wykorzystano do sporządzenia charakterystyk współrzędnych środka wybranego przegubu kulowego, łączącego wahacz ze zwrotnicą koła. Przekroje tych charakterystyk dla różnych ugięć zawieszenia wykorzystano do wyznaczenia kątów orientacji głównych osi obrotu przegubów metalowo-gumowych w układzie współrzędnych {N}.

EN

The equations of geometric constraints impose restrictions on the relative motion of individual members multilink suspension mechanism steered wheels solved by a perturbation method. Solutions to these equations were used to prepare the characteristics of the center coordinates of the ball joint, connecting to a switch rocker wheels. Sections of these characteristics for various suspension deflection angles were used to determine the orientation of the major axis of rotation of metal-rubber joints in the coordinate system {N}.

12

Some reliability issues of the corrugated i-beam girder

Sokołowski D, Kamiński M.

Engineering Transactions

|

2015

|

Vol. 63, iss. 3

297--315

EN

The main aim of this paper is reliability analysis of the corrugated-web I-girder carried out to verify its susceptibility to the random corrosion of the web and to make a comparison of the results of the first and of the second order reliability analysis. The methodology implemented in the study is based on the stochastic finite element method related to the generalized stochastic perturbation technique, where a discretization of the entire structure is carried out with four-node quadrilateral shell finite elements. This is numerically implemented using the FEM engineering system ROBOT and computer algebra system MAPLE, where all probabilistic procedures are programmed. The perturbation-based results are compared with these coming from the Monte-Carlo simulation and with an analytical solution obtained via symbolic integration carried out in MAPLE also. The indices of reliability are determined for the maximum deflections of the beam as the function of an input coefficient of variation of the web’s thickness whose meaning is the extent of a corrosion process.

13

Axisymmetric steady temperature field in FGM cylindrical shells with temperature-dependent heat conductivity and arbitrary linear boundary conditions

Moosaie A.

Archives of Mechanics

|

2015

|

Vol. 67, nr 3

233--251

EN

An approximate analytical solution to the axisymmetric heat conduction equation for a hollow cylinder made of functionally graded material with temperature-dependent heat conductivity is presented. General linear boundary conditions are considered. The Poincaré method for regular perturbation problems is employed to obtain an analytical closed-form approximate solution for the temperature field. The hierarchical asymptotic problems are solved up to the second-order approximation. A numerical example is worked out, i.e., the one-dimensional heat conduction in the radial direction with prescribed temperatures at the boundaries. The approximate temperature profiles are compared with a numerical solution of the full nonlinear problem which provides the reference “exact” solution. A good agreement between the approximate and reference solutions is established. The convergence of the asymptotic series as well as the properties of the temperature field are studied.

14

Geometrically nonlinear free transversal vibrations of thin-walled elongated panels with arbitrary generatrix

Marchuk M., Goriachko T., Pakosh V.

Vibrations in Physical Systems

|

2014

|

Vol. 26

153--160

EN

The algorithm for finding a finite number of the first values of natural frequencies and forms of geometrically nonlinear free transverse vibrations of thin-walled elongated panels with arbitrary generatrix is proposed and verified. Under normal coordinate quadratic the approximation of displacements is used. Along the tangential coordinates used one-dimensional finite elements. The discrete variation problem is built. For its solving the perturbation method is applied. The numerical results are compared with previously obtained by other authors.

15

The Design of MPPT Controller in Photovoltaic System

Che Y., Zhang W., Li W.

Przegląd Elektrotechniczny

|

2013

|

R. 89, nr 3b

71--73

EN

In photovoltaic power system, the maximum power point changes under different circumstances, so it is meaningful to track the unique point to provide maximum power for the load. In this paper, we designed the main circuit and control circuit of the maximum power point tracking controller. This controller uses the observation and perturbation method to achieve the maximum power point tracking. At last we tested the efficiency of the controller, the experimental result demonstrates that the system tracks the maximum power point rapidly, works safely and reliably.

PL

W artykule przedstawiono projekt elektronicznego sterownika do śledzenia punktu mocy maksymalnej. Budowę urządzenia oparto na teorii obserwacji i perturbacji. Zawarte wyniki eksperymentalne potwierdzają skuteczność śledzenia i szybkość reakcji na zmiany w systemie PV.

16

Effect of vertical vibrations on the onset of binary convection

Swamy M. S.

International Journal of Applied Mechanics and Engineering

|

2013

|

Vol. 18, no. 3

899--910

EN

In the present work the linear stability analysis of double diffusive convection in a binary fluid layer is performed. The major intention of this study is to investigate the influence of time-periodic vertical vibrations on the onset threshold. A regular perturbation method is used to compute the critical Rayleigh number and wave number. A closed form expression for the shift in the critical Rayleigh number is calculated as a function of frequency of modulation, the solute Rayleigh number, Lewis number, and Prandtl number. These parameters are found to have a significant influence on the onset criterion; therefore the effective control of convection is achieved by proper tuning of these parameters. Vertical vibrations are found to enhance the stability of a binary fluid layer heated and salted from below. The results of this study are useful in the areas of crystal growth in micro-gravity conditions and also in material processing industries where vertical vibrations are involved.

17

Analiza kinematyki czterowahaczowego zawieszenia kół kierowanych za pomocą układów równań więzów geometrycznych o różnej strukturze

Struski J., Kowalski M. S.

Czasopismo Techniczne. Mechanika

|

2012

|

R. 109, z. 3-M

9--18

PL

W badaniach właściwości kinematycznych i dynamicznych złożonych układów mechanicznych wykorzystywane są wyniki eksperymentów numerycznych. Wymagana jest minimalizacja czasu rozwiązywania różnych zagadnień z tego zakresu. W opracowaniu wykazano, że spełnienie tego warunku jest możliwe przez zmianę struktury więzów geometrycznych mechanizmu wielowahaczowego zawieszenia kół.

EN

In research of the kinematic and dynamic properties of compound mechanical set-ups, results of numerical experiments are used. It is required to minimize the calculation time of various problems in the domain. In the current paper it is demonstrated, that fulfilling of this demand is possible by the change of the geometrical constraint’s structure of the multi-link wheel suspension system.

18

Reliability modeling in some elastic stability problems via the generalized stochastic finite element method

Kamiński M., Świta P.

Archives of Civil Engineering

|

2011

|

Vol. 57, nr 3

275-295

EN

The main idea of this work is to demonstrate an application of the generalized perturbation-based Stochastic Finite Element Method for a determination of the reliability indicators concerning elastic stability for a certain spectrum of the civil engineering structures. The reliability indicator is provided after the Eurocode according to the First Order Reliability Method, and computed using the higher order Taylor expansions with random coefficients. Computational implementation provided by the hybrid usage of the FEM system ROBOT and the computer algebra system MAPLE enables for reliability analysis of the critical forces in the most popular civil engineering structures like simple Euler beam, 2 and 3D single and multi-span steel frames, as well as polyethylene underground cylindrical shell. A contrast of the perturbation-based numerical approach with the Monte-Carlo simulation technique for the entire variability of the input random dispersion included into the Euler problem demonstrates the probabilistic efficiency of the perturbation method proposed.

PL

Zasadniczym problemem omawianym w tej pracy jest zastosowanie Uogólnionej Stochastycznej Metody Elementów Skończonych opartych na metodzie perturbacji stochastycznej do wyznaczania wskaźników niezawodności w przypadku stateczności konstrukcji budowlanych pracujących w zakresie sprężystym. Wskaźnik niezawodności jest modelowany zgodnie z definicją podaną w normie Eurokod odpowiednią dla analizy niezawodności pierwszego rzędu, a obliczony dzięki zastosowaniu rozwinięcia wszystkich funkcji stanu w szereg Taylora ze współczynnikami z uwzględnieniem wyrazów wyższego rzędu. Procedura obliczeniowa jest oparta na jednoczesnym zastosowaniu programu Metody Elementów Skończonych ROBOT oraz systemu algebry komputerowej MAPLE i jest wykorzystana do analizy obciążeń krytycznych w popularnych konstrukcjach inżynierskich takich jak pręt Eulera, dwu i trójwymiarowe modele jedno- i wieloprzęsłowej ramy stalowej, jak również polietylenowy zbiornik podziemny o kształcie cylindrycznym. Porównanie metody perturbacji stochastycznej z techniką symulacji Monte-Carlo w całym zakresie losowej zmienności wykorzystywanych parametrów wejściowych na przykładzie zagadnienia Eulera pokazuje efektywność i ograniczenia zastosowanej metody perturbacji.

19

Flow and heat transfer of Poiseuille-Couette flow in an inclined channel for composite porous medium

Umavathi J. C., Kumar J. P., Sridhar K. S. R.

International Journal of Applied Mechanics and Engineering

|

2010

|

Vol. 15, no 1

249-266

EN

An analysis of the Poiseuille-Couette flow in an inclined channel in a composite porous medium is presented. The flow is modeled using the Darcy-Lapwood-Brinkman equation. The viscous and Darcy dissipation terms are included in the energy equation. The coupled nonlinear equations are solved analytically using the regular perturbation method and numerically using the finite difference method. The effects of various parameters such as the porous parameter, inclination angle, Grashof number, ratios of heights, viscosities and thermal conductivities are discussed.

20

Hartmann two-fluid Poiseuille-Couette flow in an inclined channel

Umavathi J. C., Sridhar K. S. R.

International Journal of Applied Mechanics and Engineering

|

2009

|

Vol. 14, no 2

539-557

EN

A numerical and analytical study of a two fluid magnetohydrodynamic Poiseuille-Couette flow in an inclined channel is investigated. The fluids in both the regions are incompressible, electrically conducting and the transport properties are assumed to be constant. The channel walls are assumed to be electrically insulating. Separate solutions for each fluid are obtained and these solutions are matched at the interface using suitable matching conditions. The governing equations of motion are solved analytically and are valid for small Eckert numbers and numerically valid for large . Solutions for large show a marked change on the velocity and temperature profiles. The results are presented graphically for various Hartmann number, Grashof number, angle of inclination and also for various ratios. It is found that the flow can be controlled effectively by a suitable choice of values of ratios of electrical conductivities, widths, viscosities and thermal conductivities.