Wyniki wyszukiwania - BazTech

1

Effects of non-classical boundary conditions on the free vibration response of a cantilever Euler-Bernoulli beams

Afras Abderrachid, El Ghoulbzouri Abdelouafi

Diagnostyka

|

2023

|

Vol. 24, No. 1

art. no. 2023107

EN

In this article, the problem of the free vibration behavior of a cantilever Euler-Bernoulli beam with various non-classical boundary conditions, such as rotational, translational spring, and attached mass is investigated. For describing the differential equation of the system. An analytical procedure is proposed firstly, and a numerical method based on the differential transform method DTM is developed in order to validate the obtained results. A parametric study for various degenerate cases is presented with the aim to analyze the influence of rotational stiffness, vertical stiffness, and mass ratio on the free vibration response of the beam, particularly on its modal characteristics. The results show that the non-classical boundary conditions significantly affect the natural frequency and mode shapes of the studied beam system in comparison to the case of a classical boundary conditions such as Simply supported, clamped-clamped, etc. The comparison between the obtained results based on the proposed analytical solution and numerical scheme, and those available in the literature shows an excellent agreement.

2

Defining the computational domain and boundary conditions for fluid flow in a mining excavation

Janus Jakub, Krawczyk Jerzy

Archives of Mining Sciences

|

2023

|

Vol. 68, no. 3

425--441

EN

For underground mine workings, the shape of the computational domain may be difficult to define. Historically, the geometry models of mine drifts were not accurate representations of the object but rather a simplified approximation. To fully understand a phenomenon and save time on computations, simplification is often required. Nevertheless, in some situations, a detailed depiction of the geometry of the object may be necessary to obtain adequate simulation results. Laser Scanning enables the generation of 3D digital models with precision beyond the needs of applicable CFD models. Images composed of millions of points must be processed to obtain geometry suitable for computational mesh generation. A section of an underground mine excavation has been selected as an example of such transformation. Defining appropriate boundary conditions, especially the inlet velocity profile, is a challenging issue. Difficult environmental conditions in underground workings exclude the application of the most efficient and precise methods of velocity field measurements. Two attempts to define the inlet velocity profile have been compared. The first one used a sequence of simulations starting from a flat profile of a magnitude equal to the average velocity. The second one was based on the sixteen-point simultaneous velocity measurement, which gave consistency with measurement results within the range of applied velocity measurement method uncertainty. The article introduces a novel methodology that allows for more accurate replication of the mine excavation under study and the attainment of an appropriate inlet velocity profile, validated by a satisfactory correspondence between simulation outcomes and field measurements. The method involves analysing laser-scanned data of a mine excavation, conducting multi-point velocity measurements at specific cross-sections of the excavation that are unique to mining conditions, and utilising the k-ω SST turbulence model that has been validated for similar ventilation problems in mines.

3

A modified Fourier-Ritz method for free vibration of rectangular plates with elastic constrains

Wu Tao, Chen Zhao Bo, Qu Jian Jun

Journal of Theoretical and Applied Mechanics

|

2022

|

Vol. 60 nr 1

77--89

EN

In this paper, a modified Fourier-Ritz method is used to study free vibration of a rectangular plate with a set of simply supported opposite sides and another set of arbitrary elastic constraints. The influence of different elastic constraint stiffness values on the modal response of the rectangular plate is also analyzed. In order to avoid that the displacement function of the rectangular plate calculated by the traditional method and its derivative may be discontinuous or non-derivable at the boundary, the displacement function is expressed in the form of the sum of standard cosine series and a periodic polynomial function. Compared with the sine series expansion, the convergence of the result is enhanced. Several sets of numerical examples with different boundary conditions are given in the article, the data shows that the results calculated by this method have good accuracy and fast convergence. In addition, this paper also analyzes the boundary conditions and discusses the influence of different spring stiffness values on the setting of boundary conditions. The results can be applied to the setting of general boundary conditions and the study of vibration control of rectangular plates.

4

Interception of a hypersonic vehicle by low-speed interceptors: novel perspectives and cost optimisation

Liu Shuangxi, Liu Shijun, Yan Binbin, Zhang Tong, Zhang Xu, Yan Jie

Bulletin of the Polish Academy of Sciences. Technical Sciences

|

2022

|

Vol. 70, nr 6

art. no. e143537

EN

The conditions for accurately intercepting hypersonic vehicles by low-speed interceptors in the terminal guidance process are examined, considering the general form of a guidance scheme. First, based on the concept of the engagement geometry, three interception scenarios are established considering different manoeuvring configurations of the interceptors and hypersonic vehicle. Second, the boundary conditions for intercepting hypersonic vehicles (with speeds higher than those of the interceptors) are specified for the three scenarios, considering several factors: the speed, path angle, line-of-sight angle, and available overload of the interceptor; path angle and manoeuvrability of the hypersonic vehicle; and relative distance between the interceptor and vehicle. A series of simulations are performed to clarify the influence of each factor on the interception performance in the three interception scenarios. The challenges associated with accurately intercepting hypersonic vehicles by low-speed interceptors are summarised, and several recommendations for designing guidance laws are presented.

5

Features of residual service life determination for high pressure rotors of K-200-130 and K-1000-60/3000 turbines

Nikulenkova Tetyana, Nikulenkov Anatolii

Journal of New Technologies in Environmental Science

|

2021

|

Vol. 5, nr 1

34--39

EN

So far, certain approaches have been developed to extension of service life of equipment in the different stages of metal physical exhaustion. The possibility of defining operating conditions of plant equipment beyond the fleet service life becomes even more relevant with increased operating time. The service life is determined as an individual one and is assigned based on the results of individual an inspection of a separate element or the largest group of single-type equipment elements of the considered plant. The fleet service life being reached is followed by diagnostics of specific units of power installations and analysis of their operation, measurement of actual dimensions of components, examination of structure, properties and damage accumulation in the metal, non-destructive testing and estimate of stress strain state and residual service life of the component. The results of performed studies are used to determine an individual service life of each element of energy equipment.

6

Thermal behavior of hollow and solid steel beamswith different boundary conditions

Daud Harbi A., Daud Sultan A., Al-Azzawi Adel A.

Computer Assisted Methods in Engineering and Science

|

2021

|

Vol. 28, no. 3

171--191

EN

The thermal behavior of hollow steel structural members due to the temperature increasehas not been investigated and discussed in many design codes. This work presents a studyof the hollow and solid steel beams’ carrying capacity under elevated temperatures. Thematerial properties of such beams decline under the temperature expected to increasethe moments on the beams. The finite difference technique is selected first to analyze theproblem. The solved problems cover beams under concentrated point load levels with dif-ferent end conditions such as cantilever, pin roller, and both ends fixed. The beam response(deflection, bending moment, and normal force) is examined. The finite element analysiswas conducted using the DIANA FEA software to study the same problem incorporatingmaterial and geometric nonlinearities. It was found that both finite difference and finiteelement analysis solved the problem accurately when the temperature was under 500C.It was also found that when the temperature was applied to the beam bottom face thedeflection was smaller than when the temperature was applied to the side faces only andthe whole section.

7

Experimental and numerical investigations of ultimate strength of imperfect stiffened plates of different slenderness

Woloszyk Krzysztof, Garbatov Yordan, Kowalski Jakub, Samson Leszek

Polish Maritime Research

|

2020

|

nr 4

120--129

EN

The objective of this study is to analyse the behaviour of compressed stiffened plates of different slenderness using experimental and numerical methods. The presented results are part of a long-term project to investigate the ultimate strength of geometrically imperfect structures subjected to different degradation phenomena, including corrosion degradation and locked cracks. Several specimens were subjected to a uniaxial compressive force, and the most important quantities related to the structural behaviour were captured and analysed. A finite element model, accounting for material and geometrical nonlinearities and initial geometrical imperfections, was developed using the commercial software ANSYS. The residual welding-induced stresses were measured in the middle cross-section for two specimens. The initial imperfection was identified by employing a close-range photogrammetry approach. It was concluded that the numerical analyses, based on the finite element model, predict the ultimate strength of stiffened plates accurately, although some deviations were also observed. The detailed analysis with the indication of possible uncertainty is presented, and several conclusions are derived.

8

Influence of marine main engine foundations on the results of vibration calculations

Murawski Lech

Journal of KONES

|

2019

|

Vol. 26, No. 1

95--101

EN

The article presents an influence of foundations of slow-speed main engine body on the results of numerical analysis of the engine dynamic stiffnesses and thermal deformations. The engine body is much stiffer than its foundation pads and ship hull (double bottom) – boundary conditions of the engine. Especially for the high power, marine engines, the correct model of the boundary conditions plays a key role during the analyses. Therefore, modelling method of engine foundation (boundary conditions) of that kind of model is essential during the analyses. During shaft line alignment and crankshaft springing analyses, knowledge of dynamic stiffnesses characteristics and thermal displacements of radial (main) bearings is significant. Those data of marine main engine body are difficult to estimate because of lack of available documentation and complicated shape of the engine and ship hull. The article presents the methodology of the characteristics determination of the marine engine’s body as well as the example of computations for a MAN B&W K98MC type engine (power: 40000 kW, revolutions: 94 rpm) mounted on a 3000 TEU (twenty-foot container equivalent unit) container ship (length: 250 m). Numerical analyses were performed with usage of Nastran software based on Finite Element Method. The FEM model of the engine body comprised over 800 thousand degree of freedom.

9

On nonlinear neutral Liouville-Caputo-type fractional differential equations with Riemann-Liouville integral boundary conditions

Ahmad Bashir, Ntouyas Sotiris K., Alsaedi Ahmed

Journal of Applied Analysis

|

2019

|

Vol. 25, nr 2

119--130

EN

This paper studies neutral Liouville-Caputo-type fractional differential equations and inclusions supplemented with nonlocal Riemann-Liouville-type integral boundary conditions. Sadovskii’s fixed point theorem is applied to establish the existence result for the single-valued case, while the multivalued case is investigated by using nonlinear alternative for contractive maps. Examples are constructed to illustrate the main results. The case of nonlinear nonlocal boundary conditions is also discussed.

10

Impact of Boundary Conditions on Acoustic Excitation of Entropy Perturbations in a Bounded Volume of Newtonian Gas

Perelomova Anna

Archives of Acoustics

|

2019

|

Vol. 44, No. 2

321--328

EN

Excitation of the entropy mode in the field of intense sound, that is, acoustic heating, is theoretically considered in this work. The dynamic equation for an excess density which specifies the entropy mode, has been obtained by means of the method of projections. It takes the form of the diffusion equation with an acoustic driving force which is quadratically nonlinear in the leading order. The diffusion coefficient is proportional to the thermal conduction, and the acoustic force is proportional to the total attenuation. Theoretical description of instantaneous heating allows to take into account aperiodic and impulsie sounds. Acoustic heating in a half-space and in a planar resonator is discussed. The aim of this study is to evaluate acoustic heating and determine the contribution of thermal conduction and mechanical viscosity in different boundary problems. The conclusions are drawn for the Dirichlet and Neumann boundary conditions. The instantaneous dynamic equation for variations in temperature, which specifies the entropy mode, is solved analytically for some types of acoustic exciters. The results show variation in temperature as a function of time and distance from the boundary for different boundary conditions.

11

Motion of a particle with stick-slip boundary conditions towards a flat interface: hard wall or free surface

Ekiel-Jeżewska M., Wajnryb E.

Physicochemical Problems of Mineral Processing

|

2018

|

Vol. 54, iss. 1

203--209

EN

Motion of a particle with stick-slip boundary conditions towards a hard wall or free surface is investigated in the range of Reynolds numbers much smaller than unity, based on the multipole expansion of the Stokes equations. The slip parameter can be interpreted as a measure of a solid particle roughness or as the effect of a surfactant on the motion of a small spherical non-deformable bubble. The particle friction coefficient is evaluated as a function of the distance from its center to the wall, based on the inverse power series expansion, and the results are used to derive explicit lubrication expressions for the friction coefficient, in a wide range of the slip parameters. It is pointed out that for a very small thickness of the fluid film, the lubrication expressions are more accurate than the series expansion. The drainage time is calculated and analyzed, and estimated in terms of explicit lubrication expressions.

12

To the question of a logarithmic velocity profile correspondence with the experimental data

Zaryankin A. E.

Mechanics and Mechanical Engineering

|

2018

|

Vol. 22, nr 2

637--647

EN

The methodology of obtaining a logarithmic velocity profile describing the velocity distribution in the cross section of the boundary layer, which is based on the well-known equation of L. Prandtl, based on its semi-empirical turbulence theory, is considered. It is shown that the logarithmic velocity profile obtained in this way does not satisfy any boundary condition arising from the classical definition of such concept as the boundary layer. The perfect coincidence of this velocity profile with the experimental data of Nikuradze demonstrated in the world scientific literature is a consequence of making these profiles not in a fixed, but in a floating coordinate system. When rebuilding the velocity profiles obtained at different Reynolds numbers, all the profiles lose their versatility and do not coincide with the actual velocity profiles in cylindrical pipes.

13

Calculation method for plates with discrete variable thickness under uniform loading or hydrostatic pressure

Aryassov G., Gornostajev D., Penkov I.

International Journal of Applied Mechanics and Engineering

|

2018

|

Vol. 23, no. 4

835--853

EN

The article proposes a new analytical method for the calculation of plates with constant and variable rigidity parameters. This method renders it possible to decrease the weight of the plates working under hydrostatic pressure by using variable thicknesses. Firs, a short overview of existing calculation methods and their results are compared. It is shown that all existing methods depend on boundary conditions. Then is given the theory of the proposed calculation method is described and calculations for plates with constant and variable thickness worked under uniformly loaded forces and hydrostatic pressure are made. The results are compared to the FEM calculations and experimental results obtained by a tensile test machine and special equipment. Calculation results obtained by the proposed analytical method and FEM results are very close. Deviations are not more than 11%. Deviations between theoretical calculations and experimental results depend on loading type and design of the test specimens but maximum values are not more than 17%. The proposed calculation method does not depend on the boundary conditions and can be used for plate calculations. Especially for plates with difficult design and complex loading.

14

Numerical creep analysis of FGM rotating disc with GDQ method

Zharfi H., Toussi H. E.

Journal of Theoretical and Applied Mechanics

|

2017

|

Vol. 55 nr 1

331--341

EN

Rotating discs are the vital part of many kinds of machineries. Usually, they are operating at relatively high angular velocity and temperature conditions. Accordingly, in practice, the creep analysis is an essential necessity in the study of rotating discs. In this paper, the time dependent creep analysis of a thin Functionally Graded Material (FGM) rotating disc investigated using the Generalized Differential Quadrature (GDQ) method. Creep is described with Sherby’s constitutive model. Secondary creep governing equations are derived and solved for a disc with two various boundary conditions and with linear distribution of SiC particles in pure Aluminum matrix. Since the creep rates are a function of stresses, time and temperature, there is not a closed form solution to these equations. Using a solution algorithm and the GDQ method, a solution procedure for these nonlinear equations is presented. Comparison of the results with other existing creep studies in literature reveals the robustness, precision and high efficiency beside rapid convergence of the present approach.

15

Identification of material model for Finite Element Modelling of quenching process

Michalik K., Banaś K., Bzowski K., Rauch Ł., Cybułka P.

Hutnik, Wiadomości Hutnicze

|

2017

|

Vol. 84, nr 4

146--149

EN

The paper concerns modelling of quenching process using the finite element method. The special emphasis is put on finding the proper material characteristics, in particular for heat transfer coefficient on solid-fluid contact boundary and heat conduction for fluid, in case of highly complex flow close to the solid-fluid boundary. Only heat transfer and fluid flow are considered with solid phase mechanical behaviour neglected. The paper presents an approximate numerical model of the process and technical means by which its implementation is realised. The included numerical examples show how the obtained model allows for fast approximate simulations of quenching.

PL

W pracy analizowany jest przypadek modelowania - za pomocą metody elementów skończonych - hartowania z wykorzystaniem oleju jako czynnika chłodzącego, w którym dochodzi do kontaktu ciała stałego i płynu w temperaturach przekraczających temperatury wrzenia oleju. Praca przedstawia techniczne aspekty realizacji numerycznej w ramach własnego oprogramowania do symulacji MES [5], ze szczególnym uwzględnieniem empirycznego doboru własności materiałowych. Wyniki wskazują, że warunki brzegowe na granicy ciała stałego z płynem z eksperymentalnymi wartościami współczynnika przenikania ciepła pozwalają na bardziej dokładne modelowanie przepływu ciepła w procesie hartowania metalu w oleju.

16

Problem odnowy rumowiska wleczonego poniżej zapór. Ocena możliwości sztucznego uzupełniania rumowiska poniżej stopnia wodnego we Włocławku

Habel M., Babiński Z., Szatten D.

Gospodarka Wodna

|

2017

|

Nr 11

360--363

PL

Artykuł stanowi pierwszą część z cyklu poświęconego projektowi sztucznego uzupełniania rumowiska wleczonego w odcinkach, gdzie występuje jego deficyt. Podjęto próbę wyznaczenia warunków brzegowych dla trwałego ustabilizowania procesów erozyjno-akumulacyjnych koryta dolnej Wisły. Ustalono, że powstanie sztucznego zbiornika wodnego skutkuje zmianą reżimu hydrologicznego rzeki, w tym następuje ograniczenie przepływu rumowiska rzecznego. Przeciętna roczna wielkość transportu osadów piaszczysto-żwirowych na dolnej Wiśle to ok. 2,2 mln ton i tyle jego dociera do cofki zbiornika włocławskiego. Deficyt w transporcie rumowiska poniżej zapory jest uzupełniany w wyniku erozji wgłębnej, często też bocznej, jednak tylko do przeciętnej rocznej wartości 1,1 mln ton. Wskazuje to na fakt, że Wisła samodzielnie nie jest w stanie odbudować transportu swoich osadów. W rezultacie rozważań proponuje się potrzebę „dokarmiania” koryta osadami piaszczysto-żwirowymi w odcinku erozyjnym w ilości mniejszej niż 0,5 mln ton rocznie.

EN

The article is the first of a cycle devoted to the project of artificial reconstruction of the bed load in sections where its shortage occurs. It attempts to determine the framework conditions for permanent stabilization of the erosion and accumulation processes in the Lower Vistula riverbed. It was found that creation of an artificial reservoir results in modification of the river’s hydrological regime, including limitation of the bed load flow. The average annual value of the sand and gravel deposits transport in Lower Vistula amounts to approx. 2.2 million tons and this is the amount that reaches the backwater part of the Włocławek reservoir. The deficit in the bed load transport downstream of the dam is completed mainly as a result of bottom erosion and, frequently, lateral erosion, but no more than to the average annual value of 1.1 million tons. It indicates that Vistula is not able to autonomously recreate the transport of its deposits. As a result of these considerations, the authors propose to “feed” the riverbed with sand and gravel deposits in the erosion section, in the amount of not less than 0.5 million tons per year.

17

Influence of the transverse inhomogeneity on the nonlinear post-buckling path of compressed FG cylindrical panels

Lykhachova O., Kołakowski Z.

Engineering Transactions

|

2017

|

Vol. 65, iss. 4

563--577

EN

In this paper, nonlinear stability of axially compressed cylindrical panels simply supported according to two types of boundary conditions (with possible or limited circumferential displacements of unloaded sides) is presented. Panels made of functionally graded materials (FGMs) of two constituents (metallic and ceramic phases) are treated as multi-layered composite structures with transverse inhomogeneity. Volume fractions of ceramics and metal distribution throughout the layer thickness are described by a simple power law. The influence of the transverse inhomogeneity of FGM panels on unsymmetrical stable post-buckling paths is shown. Special attention is paid to effect of the imperfection sign on post-buckling paths of investigated FGM panels. Some validations of the finite element analysis are discussed for isotropic panels compressed according to two (force and kinematic) loading schemes.

18

Practical method for analysis of orthogonal plates with consideration of specific model of design diagram, boundary conditions and loading

Kipiani G., Kakhidze R., Touda M., Rekhviashvili G., Chorkhauli N.

Zeszyty Naukowe Politechniki Częstochowskiej. Budownictwo

|

2016

|

Z. 22 (172)

128-134

EN

Is stated practical method for analysis of orthogonal plates with consideration of specific model of design diagram, boundary conditions and loading. For illustration of offered method are considered specific examples: applied in the center pinning on all four sides plate, when is constant, all four sides of plate are rigidly attached and on them is applied uniformly distributed constant loading.

PL

W artykule przedstawiono metodę analizy ortogonalnych płyt, która ma zastosowanie praktyczne. Metoda projektowania polega na analizie schematu statycznego, warunków brzegowych i obciążeń. W celu zilustrowania metody przedstawiono przykłady obliczeniowe. Pierwszy dotyczy płyty opartej swobodnie na wszystkich czterech krawędziach, obciążonej siłą skupioną pośrodku, natomiast drugi dotyczy płyty zamocowanej sztywno oraz obciążonej obciążeniem równomiernie rozłożonym.

19

The effect of fuel injection advance angle on temperature state of diesel engine piston

Aryan R., Pylyov V.

Zeszyty Naukowe Instytutu Pojazdów / Politechnika Warszawska

|

2016

|

z. 4/108

77--86

EN

It was proven that fuel injection advance angle has an effect on temperature state of diesel engine piston. This effect is significant and commensurable with the piston oil cooling effect. The methodology for determining boundary conditions of piston heat exchange that considers fuel injection advance angle was developed. Empiric dependency of heat transfer in piston CC from diesel power and fuel injection advance angle is offered. The results of temperature state of diesel piston 4ЧН12/14 are represented at different engine boost levels, fuel injection advance angle and structure oil-cooling methods.

PL

Wykazano, że stan cieplny tłoka zależy od kąta wyprzedzenia wtrysku oleju napędowego. Efekt ten jest istotny i współmierny z efektem chłodzenia tłoków olejem smarującym. W pracy przedstawiono empiryczną zależność przewodzenia ciepła w komorze spalania tłoka silnika o zapłonie samoczynnym od kąta wyprzedzenia wtrysku paliwa. Artykuł zawiera również wyniki badań stanu cieplnego tłoka silnika o zapłonie samoczynnym 4ChN12/14 dla różnych wartości obciążenia, kąta wyprzedzenia wtrysku paliwa i konstrukcji systemu chłodzenia olejem.

20

Analysis of the processes of heat exchange on infrared heater surface

Zhelykh V., Ulewicz M., Spodyniuk N., Shapoval S., Shepitchak V.

Diagnostyka

|

2016

|

Vol. 17, No. 3

81--85

EN

The article deals with the research results of temperature distribution on infrared heater surface. Mathematical model of the process of heat exchange on infrared heater surface was developed. The experimental measurements have been carried out and the data of the temperature on infrared heater surface have been obtained for verification the reliability of the results of theoretical studies. The results of the studies showed that the temperature gradient of the area of heater changed no more than 4.5°C.