Theoretical and Applied Mechanics Research Papers (original) (raw)

2025, STRUCTURES

The article presents the closed-form analytical design formulas for maximal deflections as well as for extremal stresses in adherends and maximal shear stress in the adhesive layer for adhesively bonded composite beams. Nine load and support layouts are considered. Applicability of the proposed formulas is validated with the experimental results reported in the literature [1-12] regarding 60 specimens of 36 types of adhesively bonded beams. Additionally, 36 linear Finite Element models were analyzed in order to compare the numerical simulations with theoretical predictions and recorded experimental data. The relative error of theoretical estimates with respect to FEA results in the majority of cases was within 0-30 %. The proposed formulas were also compared with predictions of the commonly used γ-method-it was found that both approaches provide nearly the same estimates. Relative error of theoretical estimates was analyzed with the use of the similarity theory. It may be conjectured that the proposed formulas provide the best estimates for beams with stiff adherends and relatively flexible adhesives, with the thickness of the bondline t equal 1 %-10 % of the height of the smaller adherend.

2025, IJETT Journal

In this paper, an experimental study was conducted on a gear mechanism with eccentricity anomalies, emphasising advanced time-frequency domain methods to improve the diagnosis. Vibrations captured under various operating conditions were examined using RPM-frequency mapping, Short-Time Fourier transform (STFT), 3D waterfall FFT, and 3D Time-Frequency analysis. These techniques allowed for more accurate detection of eccentricity signs, including its impact on the interaction between gears and transmission performance. The results showed that elaborate phenomena such as intense modulation and nonlinear behaviors complicate accurate fault detection using traditional methods based solely on time and frequency domain. However, the multidimensional method adopted here allows for highlighting localised signal indicators that are directly associated with transmission disturbances due to eccentricity. This work, therefore, highlights the need to apply time-frequency methods to monitor the condition of gears and optimize their maintenance more effectively.

2025, IJETT Journal

This paper employs a nine-degree-of-freedom dynamic model, considering torsional and lateral motions, to analyse the dynamic characteristics of a two-stage spur gear system. The model incorporates gear eccentricity faults and dynamic transmission errors by establishing a mesh stiffness model. The differential vibration equations for the spur gear system are derived using the Lagrangian method. Numerical simulations are conducted using a combination of the Short-Term Fourier Transform (STFT), 3D Waterfall FFT (Fast Fourier Transform), and RPM-frequency mapping technique under various operating scenarios. Analysing the responses imposed by the system under both regular and chaotic vibrations reveals that gear eccentricity faults significantly impact the system's performance. The frequency content changes over time and 3D plots provide a more detailed frequency-RPM representation, allowing the detection of transient faults in gears compared to the time domain and frequency domain. Theoretical analysis confirms the effectiveness of the STFT and 3D Waterfall FFT-based frequency-RPM transmission error detection approach.

2025, Journal of Engineering Mathematics

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

2025, IOP Conference Series: Earth and Environmental Science

Tip-clearance cavitation is one of the most aggressive and widespread forms of cavitation in hydraulic machinery that occurs due to liquid leaking through narrow gaps between tips or end faces of blades/vanes and a stator wall. The research is aimed at the study of a passive control of tip-leakage flow and tip-clearance cavitation by modifying the gap geometry. The test object was a NACA0022-34 hydrofoil with a 100 mm chord that was equipped with a double-sided axis of rotation. The gap geometry was changed by mounting side plates with different end surfaces (flat and grooved) to the hydrofoil end face. We used high-speed imaging to analyze the temporal and spatial cavity evolution simultaneously on the foil suction side and inside the clearance using three cameras. The implemented control method was shown to allow an effective management of the tip-leakage flow and tip-clearance cavitation, especially at higher angles of attack. The modified end plate makes the tip-leakage flow les...

2025, International Journal of Multiphase Flow

We report on the experimental investigation of cavitating flow control over a 2D model of guide vanes of a Francis turbine by means of a continuous tangential injection of liquid along the foil surface. The generated wall jet, providing supplementary mass and momentum, issues from a nozzle chamber inside the hydrofoil through a spanwise slot channel on its upper surface. High-speed imaging was used to distinguish cavity flow regimes, study the spatial patterns and time dynamics of partial cavities, as well as to evaluate the characteristic integral parameters of cavitation. Time-resolved LIF visualization of the jet discharging from the nozzle was employed to check if the generated wall jet is stable and spanwise uniform. Hydroacoustic measurements were performed by a hydrophone to estimate how the amplitudes and frequencies of pressure pulsations associated with cavity oscillations change with the injection rate. A PIV technique was utilized to measure the mean velocity, its fluctuations and the dominant turbulent shear stress component, which were all compared for different flow conditions and with the results for the unmodified (standard) foil. The effect of injection rate on cavitation and flow dynamics was examined for three attack angles, 0, 3 and 9 degrees, and a range of cavitation numbers corresponding to different regimes. The low-speed injection was shown to lead to an intensification of turbulent fluctuations in the boundary layer and shrinking of the attached cavity length by up to 25% compared to the case without injection. The injection with a high velocity, in turn, causes a rise of the local flow velocity and a reduction of turbulent fluctuations near the wall, which, consequently, increases the foil hydrodynamic quality at a relatively low energy consumption for generation of the wall jet. However, in this case the vapor cavity becomes longer. Thus, the low-speed injection turns out to be effective to mitigate cavitation but the injection at a high velocity is more preferable from the standpoint of the flow hydrodynamics. In the whole, the implemented control method showed to be quite an efficient tool to manipulate cavitation and hydrodynamic structure of the flow and, thereby, under certain conditions, to suppress the cavitation-caused instabilities.

2025, Journal of Visualization

High-speed imaging of cavitation regimes on a roundleading-edge flat plate and NACA0015 hydrofoil

2025, Marine Navigation and Safety of Sea Transportation

According to some authors it is estimated that around 80% of accidents at sea are caused by human and organizational errors (HOE). In order to gain knowledge of phenomena that occur during ship operations, a decision was made to design and build a test site for carrying out model-based investigations of ships, including in situations of hazard to buoyancy. The model-based investigations are used as the basic and universal method for forecasting ship dynamic properties. The results of initial research on the dynamic impact of air flow on an 888 project type ship model are presented in the elaboration. The research has been executed at a test stand located in the Polish Naval Academy. The experimental results have been compared with theoretical calculations for angle of dynamic heel. Input parameters for the tests and calculations have been defined in accordance with recommendations of the Polish Register of Shipping (PRS) and International Maritime Organization (IMO) (IMO Instruments).

2025, arXiv (Cornell University)

The ability to change a surface's profile allows biological systems to effectively manipulate and blend into their surroundings. Current surface morphing techniques rely either on having a small number of fixed states or on directly driving the entire system. We discovered a subset of scale-independent auxetic metamaterials have a state trajectory with a star-graph structure. At the central node, small nudges can move the material between trajectories, allowing us to locally shift Poisson's ratio, causing the material to take on different shapes under loading. While the number of possible shapes grows exponentially with the size of the material, the probability of finding one at random is vanishingly small. By actively guiding the material through the node points, we produce a reprogrammable surface that does not require inputs to maintain shape and can display arbitrary 2D information and take on complex 3D shapes. Our work opens new opportunities in micro devices, tactile displays, manufacturing, and robotic systems. In the natural world, rapid shifts in texture allows animals such as frogs, cuttlefish, and octopi to blend into their surroundings 1- 3 , and in our own fingertips, the wrinkling of skin improves our ability to grip objects underwater 4 . Current morphing surfaces rely either on individual actuators to drive and maintain system states, making them large, inefficient, and difficult to build [5][6][7][8] , or they must be programmed at construction, limiting the range of accessible states for a single structure [9][10][11] . Despite the utility found by nature, the ability to produce varied and passively stable surface changes in mechanical devices on demand has eluded us. We have developed reprogrammable metamaterials that can generate arbitrary surface profiles and be rewritten after fabrication to utilize kinematic singularities and a star-graph state trajectory structure. These metamaterials have a transition state where small inputs can cause the system to have significantly different responses to global loading. We use this to program both global and spatially varying Poisson's ratio, program edge profiles, display 2d information and make fully developable surfaces. Our results demonstrate how the structure of the state space of a mechanical metamaterial can be used produce writable and stable constructs that change shape and mechanical properties. Figure 1 | Reprogrammable Star Graph Configuration. A) A single compliant 4-bar unit cell (top) and 3D printed blockers for constraining the deformation of the cell (bottom). B) An 𝐴 × 𝐵 lattice with 𝐴 = 6 and 𝐵 = 4 vertical linkages can transition into 6642 different valid configurations, matching a star graph structure (SM). C) A single 2 × 2 linkage unit cell can be reprogrammed to 4 cell types (6 including mirrors), each with different mechanical properties. D) Encoding different unit cells throughout a structure enables complex deformations of a 3D printed lattice.

2025, Journal of Theoretical and Applied Mechanics

Application of the linear six-parameter shell theory to the analysis of orthotropic tensegrity plate-like structures is proposed in the paper. A continuum model of a tensegrity plate with the self-stress state included is used. The tensegrity module, which is based on 4-strut expanded octahedron modules with additional connecting cables is proposed as an example. Different planes of support of the structures are taken into account and thus different reference surfaces of the plate model are considered. The self-stress state and some geometrical parameters are introduced for parametric analysis.

2025, Journal of Theoretical and Applied Mechanics

The paper contains a proposal of a new model for the stress-life curve. The new model reflects the nature of the stress curve occurring under current conditions, which means its shape of an inclined letter S. It can be used for both low and high cycle fatigue. Verification of the proposed model was performed on experimental results of ten various materials from three main types that are low-alloy, high-alloy and non-alloy steels.

2025, Journal of Theoretical and Applied Mechanics

This paper proposes a model for estimating fatigue life under multiaxial stress states, based on critical plane concepts, taking into account the effect of mean shear stress. The fatigue life test results calculated on the basis of the proposed model are compared to the experimental ones related to 2017A-T4 and 6082-T6 aluminium alloy, S355J0 alloy steel under constant-amplitude bending, torsion and proportional combinations of bending and torsion; Ti-6Al-4V alloy under tension-compression, torsion and combination tension-compression -torsion. For the results obtained, statistical analysis is performed by comparing the calculation results proposed by Findley and Dang Van criteria with the experimental data.

2025

Two-phase induction machine dynamic model in a coordinate system which rotates at synchronous speed and one-mass dynamic model of mechanism driven in relative units describing transient processes when starting an induction machine in case of constant load conditions are developed.The influence of equivalent circuit parameters of induction machine and mechanism parameters on impact currents and torques and starting time of common used induction machines is studied by means of design of experiment method.

2025

effects of time-dependent dissipation on the basins of

2025

In this work, it is shown the results concerning to the natural frequencies and damping coefficient obtained in case of a rectangular plate made of polymeric composite material reinforced both with glass woven fabric and recycled rubber. The first of all, the material structure is described (number of the reinforcement layers, the fiber volume fraction, the rubber content). Then, the Bruel  Kjaer equipment and the advanced method used for the determination of the natural frequencies are presented. The change of the damping coefficient with respect to the natural frequencies is graphically shown. This results was recorded during four tests.

2025

In the paper a mathematical-physical model, results of computer simulation of the propelling of metal fragments by pressure of detonation products and their catching by the protective casing made of a quasiaramide fabric have been presented. The impact on the protective casing due to shock waves generated by the explosion has been examined. Depending on the nature of the issue, the 2D free particles or 1D Lagrange method has been used in the computer simulation.

2025, Journal of Engineering Research_Libya

In light of the increasing global demand for energy, this study explores the potential of small scale (domestic) wind turbines for generating energy domestically. Focusing on airfoils, which are the main elements of wind turbine blades, the research examines the performance of two different designs: NREL S826 and NACA 2412. For this purpose, two-dimensional numerical model was created for each airfoil. The models utilised a C-type grid and incorporated mesh generation with boundary inflation for accurate representation. The Spalart–Allmaras turbulence model was employed to examine the intricate dynamics of flow surrounding the airfoils and to guarantee the precision of the developed numerical model, the outcomes were contrasted with verified experimental data. The current research involved an in-depth examination of pressure and velocity distributions over the airfoils at different wind speeds (5.5 m/s, 7 m/s, 8.3 m/s, and 9.7 m/s) and angles of attack (0°, 2°, 4°, 6°, 8°, 10°, 12°, 14°, and 16°). One of the critical aspects of this study encompasses comparing the lift coefficient and the lift force generated by each airfoil under the diverse operating conditions that were considered. The findings revealed that for the angle of attack ranging from12° to 14°, both airfoils achieved their optimal lift performance. Interestingly, the NREL S826 airfoil demonstrated a slight preference within this optimal range. At the highest wind speed (9.7 m/s), the NREL S826 achieved a maximum lift coefficient of 4.9176 at an angle of attack of 14°, exceeding the NACA 2412's maximum of 3.6878 at 12° at the same wind speed.

2025

Problem on mathematical modeling of a plane film flow affected by alternating electromagnetic field (running horizontal EM wave) is considered. The parametric excitation and suppression of oscillations on a film surface at the essential inertia forces are studied using the developed model and computer simulation. In a linear approach some interesting new phenomena of the electromagnetic wave spreading in a plane film flow and its impact on excitation and suppression of oscillations on a film surface are investigated. Key-Words: Plane, Film, Flow, Electromagnetic, Horizontal, Wave, Instability, Excitation, Suppression 1 Oscillations in the plane film flow Earlier investigated impact of the vertical electromagnetic wave on surface waves on the plane film flow spreading on a solid plate has shown the features of the system (see Fig.1 and Fig.2) [1-3]. Fig.1 Configuration of the induced electric current from vertical EM wave in a plane film flow Fig.2 Creation of the plane film flow: 00...

2025

The specific granulation problem is presented, which has concern to the controlled liquid metal jet and film flows for a production of the uniform by size and form particles (granules) cooled with a high rate, to be amorphous or close to the amorphous materials. Basics of the developed theory of the controlled jet and film flow disintegration with further rapid cooling of the drops after disintegration of film flow are presented together with the new patented granulation devices developed and tested. The original methods and devices can be used for production of the amorphous granules in a wide range of the given sizes, with a very narrow (plusminus 50%) deviation in size Keywords—Film flow, disintegration, drops, high cooling rate, granulation, amorphous material. I. THE FINE PRECISE METALS’ GRANULATION In a contrast to the known works by amorphous materials and granulation of the metals and alloys, we deal with a granulation of the middle-temperature metals (Cu, Al, Pb, Mg, etc.),...

2025

The new technological decisions, some concrete designs are presented and discussed, and the information on their efficiency and practical tests is supplied. These granulation technologies and devices were done for amorphous materials’ production in the newly created machines with parametric film flow decay and highly intensive particles’ cooling methods based on the idea of particles’ passing through the system of the nitrogen liquid film flows. Key-Words: Parametric, Wave, Excitation, Granulation, Control, Film Flow, Cooling, Nitrogen,Amorphous 1 Vitality of the problem Vitality of problem is due to intensive development of the new technologies, creation of the devices of high efficiency and profitability based on the use of parametrically controlled oscillations, as well as based on stability of a system impossible in absence of effective suppression of the oscillations. The methods based on use of the strong (resonant) effects allowing developing the new energyand resource-saving...

2025, arXiv: Applied Physics

The problem of granulation is very bright by the granulated materials, as well as by their application. In the paper, some history of the granulation problem during over century and modern applications of the metallic granulates and amorphous materials are given at the beginning. Then the specific own granulation problem is presented, which has concern to the controlled liquid metal jet and film flows for a production of the uniform by size and form particles (granules) cooled with a high rate, to be amorphous or close to the amorphous materials. Such granules of the given size and form are needed for the new material science. The basics of developed theory of the controlled jet and film flow disintegration with further rapid cooling of the drops obtained after flow disintegration are presented together with the new patented granulation devices. The developed methods and devices can be used for production of the amorphous or close to amorphous granules in a wide range of the given s...

2025

The approximate mathematical model for a cooling of the particle in a volatile liquid is developed and analyzed. Despite the precise model is complex and requires the solution of the nonstationary two-phase flow equations with the conjugated heat transfer boundary problem for the particle, vapor, and liquid cooling pool, the considered simple model may be of interest. Vapor is permanently produced and removed from the coolant’s pool. Analysis of the model obtained resulted in some correlations for the three main parameters of the cooling process, which may be used for estimation of the particle’s cooling.

2025, arXiv: Fluid Dynamics

The results by development of physical, mathematical and numerical models for parametric excitation and suppression of oscillations on the interfaces separating continuous media, for carrying out computing, physical and natural experiments by revealing the new phenomena and parametric effects, and for their use in improvement the existing and creation the perspective highly efficient technological processes are presented. Scientific novelty of this work consists in development of the theory and applications of parametric excitation and suppression of oscillations on the boundaries of continua on the samples of three tasks classes: flat and radial spreading film flows of viscous incompressible liquids, conductive as well as non-conductive ones; surfaces of phase transition from a liquid state into a solid one; and heterogeneous granular media. The external actions considered are: alternating electromagnetic, vibration, acoustic and thermal fields. Along with linear the non-linear par...

2025, arXiv: Applied Physics

The approximate mathematical model for a cooling of the particle in a volatile liquid is developed and analyzed. Despite the precise model is complex and requires the solution of the nonstationary two-phase flow equations with the conjugated heat transfer boundary problem for the particle, vapor, and liquid cooling pool, the considered simple model may be of interest. Vapor is permanently produced and removed from the coolant pool. Analysis of the model obtained resulted in some correlations for the three main parameters of the cooling process, which may be used for estimation of the particle cooling.

2025

The 2-D model of a non-stationary, non-isothermal steam (gas) filtration through a monospherical particle layer with internal heat generation is considered and analyzed with the particular emphasis on the non-thermal steam/particles local equilibrium. The real non-linear properties of the steam (gas) and particles, as well as the influence of the impermeable medium surrounding the permable layer are taken into account. Boundary-value problem for the complex multiphase system of the steam (gas) flow and the layer of particles is formulated both in the dimension and then in dimensionless forms and both are discussed. The thermal hydraulic problem is solved numerically using the effective finite-difference fractional timestep method earlier develod by one of the authors. It is shown that some initial thermodynamic perturbations in the system, which are always present in such kind of systems, may cause the phenomenon of local abnormal steam heating (mainly due to non-linear heat conductivity of the steam having power-law character by temperature). This phenomenon was first revealed for such non-linear boundaryvalue problems in a modeling of geothermal systems 25 years ago. Then it was revealed for the severe accidents scenario both theoretically and experimentally. The phenomenon of local abnormal heating may cause some temperature escalation in a specific spatial region of the system, which is of paramount interest for many modern industrial and natural processes because it differs dramatically from the linear case, which is conventionally considered in a similar systems without taking into account the real non-linear processes.

2025

Theoretical research of the problems on boundary control of phase transition is conducted by creation of physical and mathematical models of the corresponding physical phenomena. The models are constructed, whenever possible, simple but reflecting main features of the studied phenomena. Complex mathematical models for the most general cases are realized on computer. So, in a task about stabilization of a garnissage the regions of system’s instability are calculated on computer in a wide range of the varied parameters, and the values of coefficient of feedback control for the regulator intended for suppression of unstable modes of the boundaries’ oscillations are defined. In a view of complexity of the considered magnetohydrodynamic and thermal phenomena the most influential factors are considered, which have a principal importance in the studied systems. The constructed physical and mathematical models may be useful in further developments for the solution of more complex practical ...

2025, Journal of Theoretical and Applied Mechanics

2025

This paper investigates four different boundary conditions for the upstream reservoir boundary for dam-reservoir interaction problems. Accurate numerical modelling of the reservoir hydrodynamic pressures on dams is used as a means of assessment of the different boundary conditions. The reservoir is modelled with two-dimensional plane-strain displacement-based isoparametric solid finite elements. The study considers stiff dams with vertical upstream faces under ramp and harmonic acceleration loads. The numerical results were compared and found to be in good agreement with available closed-form solutions. The same approach may be used in analyses of other waterfront structures such as quay walls.

2025

2025, Journal of Theoretical and Applied Mechanics

W pracy wyprowadzono stowarzyszone równania cał kowe dla równania H elmholtza i pokazano ich zastosowania do rozwią zywani a zagadnień odwrotnych przewód* nictwa cieplnego. Przez zagadnienia odwrotne rozumie się przy tym zagadnienia wyznaczania strumienia ciepł a lub temperatury na brzegu i wewną tr z pewnego obszaru D a E"\ m = 1,2, 3, na podstawie tzw. wewnę trznyc h odpowiedzi temperaturowych lub strumieniowych, . Z tego typu problemami moż n a się spotkać w wielu dziedzinach techniki; doczekał y się one także dosyć bogatej literatury (por. [8, 9, 10]). W niniejszej pracy omówiono trzy typy jednowamiarowych zagadnień odwrotnych, a mianowicie zagadnienia dotyczą c e warstwy pł askiej, kuli i warstwy kulistej oraz walca i warstwy walcowej. D o rozwią zywani a tych zagadnień zastosowano równania cał kowe wyprowadzone w pracy [1], Równania te w wymienionych przypadkach moż n a był o rozwią za ć w postaci zamknię tej , co pozwolił o otrzymać wzory rekurencyjne okreś lają c e pewne ukł ady funkcji, które stanowią przybliż on e rozwią zani a tych zagadnień. Analiza tych wzorów doprowadził a do interesują cyc h wniosków dotyczą cyc h wpł ywu bł ę d u danych na wyniki obliczeń. Wnioski te znalazł y swoje potwierdzenie w przykł adach liczbowych. gdzie x eQ\ 8Q*, t e T, zaś n(x*) jest normalną zewnę trzn ą do 3Q*. N iech funkcja ® 0 (x), x eQ, opisuje począ tkow y rozkł ad temperatury w obszarze Q, tzn.

2025, Journal of Theoretical and Applied Mechanics

Równanie falowe jest w literaturze naukowej chyba najbardziej znanym równaniem. Rozwią zanie tego równania w przypadku jednowymiarowym, gdy x e (a, b), gdzie a i b są liczbami skoń czonymi , bą dź są równe nieskoń czonoś ci , są powszechnie znane i opisane (por. [1, 2, 3] i in.). Mał o natomiast spotyka się w literaturze rozwią zań tzw. zagadnień odwrotnych dla równania falowego. Warto tu nadmienić, że samo okreś leni e "zagadnienie odwrotne" jest dosyć niejednoznaczne. I tak np. szkoł a radziecka rozumie pod tym hasł em zagadnienia wyznaczania nieznanych, stał ych lub zmiennych współ czynników równań róż niczkowych , , bą dź funkcji ź ródł a [21, 5] przy znanym rozwią zaniu tych równań, bą dź też problem wyznaczania rozwią zania zagadnienia dynamicznego dla t < t 0 przy znanym rozwią zaniu w chwili / = tę , [6]. D la odmiany szkoł a amerykań sk a uż yw a tego okreś leni a w przypadku zagadnień dynamicznych, w których na podstawie znajomoś c i rozwią zania równania róż niczkoweg o jako funkcji czasu w pewnych punktach obszaru okreś lonoś c i tego rozwiązania, poszukuje się warunków brzegowych, które powodują taką .wł aś ni e zmienność w czasie rozwią zania w tych punktach (por. [12, 13, 14, 15] i in.). Moż n a zatem z grubsza podzielić zagadnienia odwrotne na zagadnienia identyfikacji funkcji ź ródł a, zagadnienia identyfikacji współ czynników, zagadnienia odtwarzania historii procesu oraz zagadnienia identyfikacji obcią ż e ń brzegu obszaru. Zwykł e zagadnienia brzegowo-począ tkowe nazywane są -w odróż nieni u od wspomnianych wyż e j -zagadnieniami prostymi lub bezpoś rednimi . Rozważ ani a na temat zagadnień odwrotnych dla równania falowego spotyka się w literaturze radzieckiej, (np. 21]), są to jednakże gł ównie zagadnienia identyfikacji współ czynników lub funkcji ź ródł a bą dź zagadnienia odtwarzania historii procesu. N atomiast brak jest prac traktują cych o identyfikacji obcią ż e ń brzegu obszaru, w którym rozważa się zagadnienie propagacji fal. O takim wł aś ni e zagadnieniu traktuje niniejsza praca. • Problem identyfikacji dynamicznych obcią ż e ń brzegu sprowadza się w niniejszej pracy do zagadnienia rozwią zania równań cał kowych pierwszego rodzaju, typu. splotowego, . Zagadnienia tego typu należą do tzw. zagadnień ź l e postawionych, . W pracy pokazany jest sposób rozwią zania tego typu zagadnienia w przypadku równania falowego.

2025, Journal of Theoretical and Applied Mechanics

Identyfikacja obcią ż e ń termicznych na powierzchniach warstwy pł askiej na podstawie pewnych danych termicznych lub mechanicznych pochodzą cych z punktów wewnę trznych warstwy, przy -jednocześ ni e -znanych warunkach mechanicznych na obu powierzchniach warstwy i warunkach począ tkowych jest problemem, zaliczanym do tzw. zagadnień odwrotnych pól temperatur, . Podobne problemy był y rozważ an e na gruncie teorii wymiany ciepł a, [2, 3, 4 i in.], a także na gruncie teorii naprę ż e ń cieplnych, . W niniejszej pracy problem identyfikacji strumienia ciepł a i temperatury otoczenia rozważ an y jest na gruncie termosprę ż ystoś ci , przy zał oż eniu , iż w równaniach ruchu pomijalnie mał y jest czł on inercyjny. Poszczególne prace, traktują ce o zagadnieniach odwrotnych pól temperatur róż ni ą się , czę sto dość znacznie, tak-w podejś ciac h do problemu, jak i w rozumieniu samego poję cia "zagadnienie odwrotne". Szersze uwagi dotyczą ce tego tematu moż n a znaleźć w pracy . Metoda badawcza, oparta na zagadnieniach odwrotnych, która ł ą czy ze sobą pomiary, aparat matematyczny oraz inż ynierski e wyczucie, jest czę sto jedyną , umoż liwiają c ą określenie obcią ż e ń termicznych brzegu ciał a, na którym to brzegu umieszczenie czujników jest niemoż liw e bą dź niewskazane (np. ś cian a komory spalania silnika spalinowego, wewnę trzne ś cian y silnika odrzutowego, powierzchnie ł opatek turbin, wewnę trzna ś cian a lufy itp.). Identyfikacja strumienia ciepł a na powierzchni odgrywa istotną rolę tam, gdzie należy okreś li ć ilość ciepł a pochł anianego czy odprowadzanego z oś rodka , a wię c np. w procesach stygnię cia odlewu, czy też równomiernego nagrzewania lub chł odzenia. Tam, gdzie mogą wystę pować duże gradienty temperatury, oprócz efektów czysto termicznych pojawiają się także efekty termomechaniczne, których wielkość może być nie do pominię cia podczas rozważ a ń dotyczą cych takiego wł aś ni e procesu termosprę ż ystego . Ponieważ okreś lon e obcią ż eni a termiczne brzegów wywoł ują w ciele termosprę ż ysty m okreś lon e reakcje typu termicznego i mechanicznego, wię c moż n a pokusić się o rozważ eni e zagadnienia, w którym dane są przebiegi pewnych wielkoś c i termicznych lub mechanicznych w punktach wewnę trznych ciał a (tzw. wewnę trzne odpowiedzi, w skrócie WO), a wielkoś ciam i identyfikowanymi są przyczyny np. typu termicznego, które je wywoł ał y, czyli termiczne warunki brzegowe. Przy tak postawionym zagadnieniu trzeba wszakże wiedzieć, jakiego typu warunki termiczne należy przyją ć na brzegach, na których się je identyfikuje. W niniejszej

2025

The paper presents results of numerical calculations conducted in order to define the heat transfer coefficient in flow boiling in a vertical minichannel with one side made of a heating foil with liquid crystals. During the experiment, we measured the local temperature of the foil, inlet and outlet liquid temperature and pressure, current and voltage drop of the electric power supplied to the heater. Local measurements of foil temperature were approximated with a linear combination of the Trefftz functions. The known temperature measurement errors allowed application of the adjustment calculus. The foil temperature distribution was determined by the FEM combined with the Trefftz functions. Local heat transfer coefficients between the foil and the boiling fluid were calculated from the third-kind condition.

2025

On the limitations of linear beams for the problems of moving mass-beam interaction using a meshfree method

2025, Journal of Theoretical and Applied Mechanics

The paper presents a combined graphical and analytical method of determination of two structural parameters of a permeable medium: permeability and tortuosity. The method is based on a two-phase model of permeable material and uses... more

2025, Journal of Theoretical and Applied Mechanics

Academician Yachko Ivanov turned 90 in September 2022. We are pleased to present a short interview with the jubilee outlining the basic achievements of his remarkable scientific carrier.

2025, Journal of Theoretical and Applied Mechanics

In this research, a mathematical model is derived to enable analytical determination of effective ultimate forces in the process of plasticization of the surface layer of wood. The experimentally determined thermo-mechanical properties of the material subjected to the process of plasticization are used in defining the structure of the model. The analysis of plastic strain in the layer in consideration is based on a generalised model of an ideally rigid-plastic medium, including certain modifications. Considering the anisotropic properties of wood, the Azzi-Tsai-Hill (ATH) strength criterion is applied which takes into account variation in the response of the loaded material depending on the direction. The article presents also results of FEM analysis of the same process of hot rolling of wood.

2025

In the paper, we introduce information on limitations of the Finite Element Method in acoustic analysis. Difficulties that appear in acoustic analysis are mainly caused by the form of shape functions and sensitivities to boundaries, so we start with a short description of mathematical background. The propositions how to overcome and simplify those disadvantages are summarized and illustrated with a real application.

2025

The paper describes various aspects of numerical modeling of biomecha-nical problems by the finite element method. The authors would like to present what they mean by the numerical complexity of modeling of bio-mechanical problems. The attention is focused on numerical simulation of dental implants and human lumbar spine motion segment (L4-L5). In both cases, acquisition and creation of geometry, number of DOFs, combining different types of elements, properties of the material, con-tact definitions, loads and boundary conditions are difficult tasks. The acquisition of geometric data of living body parts can be realized only by using noninvasive techniques like NMR or CT. The processing of these data requires specialized software and methods. The methodologies of defining mechanical parameters of human tissues are usually inaccura-te and have to be used in practice on living people very carefully. The constitutive data in literature are usually grossly inconsistent. In nume-rical sim...

2025, Journal of Theoretical and Applied Mechanics

The analytical solution of steady-state asymmetric thermo-electro-mechanical loads of a hollow thick infinite cylinder made of porous piezoelectric materials (2D-PPMs) based on two-dimensional equations of thermoelasticity is considered. The general form of thermal and mechanical boundary conditions is considered on the inside and outside surfaces. A direct method is used to solve the heat conduction equation and the non-homogenous system of partial differential Navier equations using the complex Fourier series and the powerexponential law functions method. The material properties are assumed to depend on the radial and circumferential variable and are expressed as power-exponential law functions along the radial and circumferential direction.

2025, Journal of Theoretical and Applied Mechanics

Multilayer structures allow obtaining good performance in acoustic insulation to eliminate unwanted noise in the medium and high frequencies in many applications such as building and transport industry. In this paper, the sound transmission of multilayer systems is studied using the Transfer Matrix Method (TMM). The studied multi-layered panels include elastic, viscoelastic and porous materials. Several configurations of multilayer systems are studied, and their corresponding transmission loss T L is computed. Also, the effects of porous material characteristics are studied to evaluate the impact of each parameter.

2025

is a Project Design En gineer with Mechanical Te chnology Incorporated, a high technology engineering/ consulting firm. In this position, he is re sponsible for performing analytical studies, troubleshooting, and design audits in the areas of rotordynamics, fluid-film lubrica tion, and hydraulics for various customers within the turbomachinery industry. Prior to joining MTI in I 995, he spent 12 years in the aerospace industry designing and analyzing pumps, valves, controls, and electromechanical compo nents for gas turbine engines. His fields of expertise include rotordynamics, journal bearings, incompressible and compressible flow, computational fluid dynamic;s, stress analysis, finite element analysis, dynamic simulations, and mechanical design. He holds B.S. and M.S. degrees (Mechanical Engineering) from Rensselaer Polytechnic Institute. He is a member of ASME.

2025

One of the foremost concerns facing turbomachinery users today is that of torsional vibration. In contrast to lateral vibration problems, torsional failures are especially heinous since the first symptom of a problem is often a broken shaft, gear tooth, or coupling. The difficulty of detecting incipient failures in the field makes the performance of a thorough torsional vibration analysis an essential component of the turbomachinery design process. The authors' purpose is to provide users with a practical design procedure that can be used to ensure that their systems will not 189 encounter major difficulties in the field. It has been the authors' experience that most turbomachinery users encounter little difficulty in determining their machine's natural frequencies due to the large number of resources available in that area. However, problems often arise when they must translate this information into an accurate prediction of whether or not their design will experience t...

2025, Journal of Theoretical and Applied Mechanics

The onset of convective instability is analysed in a rotating multicomponent fluid layer in which density depends on n stratifying agents (one of them is heat) having different diffusivities. Two problems have been analysed mathematically. In the first problem, a sufficient condition is derived for the validity of the principle of the exchange of stabilities. Further, when the complement of this condition holds good, oscillatory motions of neutral or growing amplitude can exist, and thus it is important to derive upper bounds for the complex growth rate of such motions when at least one of the bounding surfaces is rigid so that exact solutions of the problem in closed form are not obtainable. Thus, as the second problem, bounds for the complex growth rates are also obtained. Above results are uniformly valid for quite general nature of the bounding surfaces.

2025, http://resolver. caltech. edu/ …

Paper contain results o f development of approximate methods and analysis of possibilities of flows and motion predictions for high speed movement prolate mainly axisymmetric bodies in water with supercavitation. Investigations are based on known approximation of the Slender Body Theory (SBT) and application of Matched Asymptotic Expansions Method (MAEM), integral conservation laws , heuristic models and another approaches. Alike consideration give the possibility to analyze the number of key problems as whole from united point of view. With account of two the most important ranges of speeds: moderate high speeds and very high speeds in the range of Mach Number M ~0.5-2 and over it is applied accordingly two base models: of ideal incompressible fluid and izentropically compressible fluids. Every of this characteristic cases correspond different cases of applications and accordingly developed parts of the theory. The problems of development of the methods for prediction of steady and unsteady prolate supercavities for given pressure and cavities with gas injection are analyzed with account of base perturbations factors. Possibilities and state of problem of prediction supercavitation for very high speeds with account of compressibility effects are considered. Peculiarities and possibilities of predictions movement trajectory of supercavitating bodies are analyzed and influence of hydro elastic effects under motion. are investigated