Hasil untuk "Mechanics of engineering. Applied mechanics"

Musil Miloš, Gašparovič Luboš, Úradníček Juraj et al.

This article presents a novel procedure for detecting and locating damage caused by a loose bolted joint in a modular plate structure. The primary aim of this work is to locate the loose joint with minimum measured points and without precise tune of computational model. The proposed method is based on correlating patterns of modal property changes using simulated and measured data. These patterns combine the relative shifts in natural frequencies and the norms of relative changes in mode shapes, derived from a pre-computed database of finite element method (FEM) simulations for various potential damage scenarios. The experimental validation demonstrates that the procedure can effectively and accurately locate the position of a loose joint using only five accelerometers, despite using an untuned FEM model for prediction.

Bouazizi Maher, Soula Mohamed, Ben Rhouma Amir

Woven laminate composites are extensively used in various industries, especially in yacht manufacturing, where a comprehensive understanding of their elastic mechanical properties, failure mechanisms, and the effects of layer stacking in E-glass/polyester composites is essential. A combined experimental and numerical approach was employed to investigate these aspects. Tensile and three-point bending tests were performed to assess the elastic mechanical properties of woven specimens, and optical microscopy was used to analyze fracture surfaces and identify failure mechanisms. For numerical analysis, a two-step homogenization method was applied. The numerical model was validated by comparing its results with experimental data.

Artem Alexandrov, Alexey Glutsyuk, Alexander Gorsky

In this study, we discuss the Prufer transform that connects the dynamical system on the torus and the Hill equation, which is interpreted as either the equation of motion for the parametric oscillator or the Schrodinger equation with periodic potential. The structure of phase-locking domains in the dynamical system on torus is mapped into the band-gap structure of the Hill equation. For the parametric oscillator, we provide the relation between the non-adiabatic Hannay angle and the Poincare rotation number of the corresponding dynamical system. In terms of quantum mechanics, the integer rotation number is connected to the quantization number via the Milne quantization approach and exact WKB. Using recent results concerning the exact WKB approach in quantum mechanics, we discuss the possible non-perturbative effects in the dynamical systems on the torus and for parametric oscillator. The semiclassical WKB is interpreted in the framework of a slow-fast dynamical system. The link between the classification of the coadjoint Virasoro orbits and the Hill equation yields a classification of the phase-locking domains in the parameter space in terms of the classification of Virasoro orbits. Our picture is supported by numerical simulations for the model of the Josephson junction and Mathieu equation.

Jahangir Alam, Ghulam Murtaza, Efstratios E. Tzirtzilakis et al.

The flow and heat transfer of a steady, viscous biomagnetic fluid containing magnetic particles caused by the swirling and stretching motion of a three-dimensional cylinder has been investigated numerically in this study. Because fluid and particle rotation are different, a magnetic field is applied in both radial and tangential directions to counteract the effects of rotational viscosity in the flow domain. Partial differential equations are used to represent the governing three-dimensional modeled equations. With the aid of customary similarity transformations, this system of partial differential equations is transformed into a set of ordinary differential equations. They are then numerically resolved utilizing a common finite differences technique that includes iterative processing and the manipulation of tridiagonal matrices. Graphs are used to depict the physical effects of imperative parameters on the swirling velocity, temperature distributions, skin friction coefficient, and the rate of heat transfer. For higher values of the ferromagnetic interaction parameter, it is discovered that the axial velocity increases, whereas temperature and tangential velocity drop. With rising levels of the ferromagnetic interaction parameter, the size of the axial skin friction coefficient and the rate of heat transfer are both accelerated. In some limited circumstances, a comparison with previously published work is also handled and found to be acceptably accurate.

Mostafa A. Rushdi, Shigeo Yoshida, Koichi Watanabe et al.

Wind–solar towers are a relatively new method of capturing renewable energy from solar and wind power. Solar radiation is collected and heated air is forced to move through the tower. The thermal updraft propels a wind turbine to generate electricity. Furthermore, the top of the tower’s vortex generators produces a pressure differential, which intensifies the updraft. Data were gathered from a wind–solar tower system prototype developed and established at Kyushu University in Japan. Aiming to predict the power output of the system, while knowing a set of features, the data were evaluated and utilized to build a regression model. Sensitivity analysis guided the feature selection process. Several machine learning models were utilized in this study, and the most appropriate model was chosen based on prediction quality and temporal criteria. We started with a simple linear regression model but it was inaccurate. By adding some non-linearity through using polynomial regression of the second order, the accuracy increased considerably sufficiently. Moreover, deep neural networks were trained and tested to enhance the power prediction performance. These networks performed very well, having the most powerful prediction capabilities, with a coefficient of determination <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msup><mi>R</mi><mn>2</mn></msup><mo>=</mo><mn>0.99734</mn></mrow></semantics></math></inline-formula> after hyper-parameter tuning. A 1-D convolutional neural network achieved less accuracy with <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msup><mi>R</mi><mn>2</mn></msup><mo>=</mo><mn>0.99647</mn></mrow></semantics></math></inline-formula>, but is still considered a competitive model. A reduced model was introduced trading off some accuracy (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msup><mi>R</mi><mn>2</mn></msup><mo>=</mo><mn>0.9916</mn></mrow></semantics></math></inline-formula>) for significantly reduced data collection requirements and effort.

Eduard C. Groen, Kazi Rezoanur Rahman, Nikita Narsinghani et al.

The farming domain has seen a tremendous shift towards digital solutions. However, capturing farmers' requirements regarding Digital Farming (DF) technology remains a difficult task due to domain-specific challenges. Farmers form a diverse and international crowd of practitioners who use a common pool of agricultural products and services, which means we can consider the possibility of applying Crowd-based Requirements Engineering (CrowdRE) for DF: CrowdRE4DF. We found that online user feedback in this domain is limited, necessitating a way of capturing user feedback from farmers in situ. Our solution, the Farmers' Voice application, uses speech-to-text, Machine Learning (ML), and Web 2.0 technology. A preliminary evaluation with five farmers showed good technology acceptance, and accurate transcription and ML analysis even in noisy farm settings. Our findings help to drive the development of DF technology through in-situ requirements elicitation.

Jiang Chunlei

The research starts with the treatment of the multiscale transmission problem and establishes the electromagnetic solidification transmission coupling mathematical model based on the indirect coupling method. It uses the three-dimensional magnetic field finite element theory to establish a three-dimensional crucible structure continuous casting model built on the electromagnetic solidification transmission coupling mathematical model. This model is used to optimize the parameters of the composite crucible structure and to simulate electromagnetic transmission and braking phenomena. The results show that the L-shaped static magnetic field has a more potent inhibition and a guidance effect on melt circulation. The braking effect of the actual magnetic field on the downward impact is worse. Under the influence of an L-shaped magnetic field, the flow velocity of the melt is better, and the flow state distribution is more smooth and uniform. The computational efficiency test results show that the conversion calculation time of the method designed in this study is 18.03 min. The total calculation time is 680.48 min, which is superior to traditional methods. It proves that this model can accurately analyze the magnetic field coupling problem and at the same time ensure the superiority of its computing efficiency.

Mário j. de Oliveira

We show that the dynamics of a quantum system can be represented by the dynamics of an underlying classical systems obeying the Hamilton equations of motion. This is achieved by transforming the phase space of dimension $2n$ into a Hilbert space of dimension $n$ which is obtained by a peculiar canonical transformation that changes a pair of real canonical variables into a pair of complex canonical variables which are complex conjugate of each other. The probabilistic character of quantum mechanics is devised by treating the wave function as a stochastic variable. The dynamics of the underlying system is chosen so as to preserve the norm of the state vector.

Mahmoud Sesa, Hagen Holthusen, Lukas Lamm et al.

The development of tissue-engineered cardiovascular implants can improve the lives of large segments of our society who suffer from cardiovascular diseases. Regenerative tissues are fabricated using a process called tissue maturation. Furthermore, it is highly challenging to produce cardiovascular regenerative implants with sufficient mechanical strength to withstand the loading conditions within the human body. Therefore, biohybrid implants for which the regenerative tissue is reinforced by standard reinforcement material (e.g. textile or 3d printed scaffold) can be an interesting solution. In silico models can significantly contribute to characterizing, designing, and optimizing biohybrid implants. The first step towards this goal is to develop a computational model for the maturation process of tissue-engineered implants. This paper focuses on the mechanical modeling of textile-reinforced tissue-engineered cardiovascular implants. First, we propose an energy-based approach to compute the collagen evolution during the maturation process. Then, we apply the concept of structural tensors to model the anisotropic behavior of the extracellular matrix and the textile scaffold. Next, the newly developed material model is embedded into a special solid-shell finite element formulation with reduced integration. Finally, we use our framework to compute two structural problems: a pressurized shell construct and a tubular-shaped heart valve. The results show the ability of the model to predict collagen growth in response to the boundary conditions applied during the maturation process. Consequently, we can predict the implant's mechanical response, such as the deformation and stresses of the implant.

Mahdi Saadatfar

In this article, temperature and moisture distributions in a finite-length hollow cylinder made of functionally graded material (FGM) under transient coupled hygrothermal condition was presented. The coupled equations of heat conduction and moisture diffusion were solved employing the Fourier series expansion method along the longitudinal direction, the differential quadrature method (DQM) along the radial direction, and the Newmark method for the time domain. Finally, the history of temperature and moisture potentials was obtained. The effect of coupled and uncoupled hygrothermal loading, grading index, and hygrothermal boundary conditions was illustrated in numerical examples. Results show that the difference between the coupled model and uncoupled model is more obvious in the moisture rather than the temperature. Also, the negative grading index increases the temperature and moisture. While the effect of the positive grading index is vice versa. Moreover, to have a more accurate analysis of the transient hygrothermal process, it is important to employ the coupled model.

E. Hosseini

Retraction Notice: JMES editorial team takes integrity matters seriously and would not allow any manipulation of scientific articles. We would like to apologise to JMES readers for any inconvenience caused by this retraction. Please contact editor in chief for more info.

S. Shashi Prabha Gogate, Ramesh Kudenatti

The magnetohydrodynamic flow of a viscous fluid over a constant wedge in three- dimensional boundary-layer has been analyzed both numerically and asymptotically. The magnetic field is applied normal to the flow. The mainstream flows aligned with wedge surface are assumed to be proportional to the power of the coordinate distances. The system is described using three-dimensional MHD boundary-layer equations which are converted to couple nonlinear ordinary differential equations using similarity transformations. The resulting equations are solved numerically using the Keller-box method which is second-order accurate and asymptotically for far-field behavior. Both numerical and asymptotic solutions give good agreement in predicting the velocity behaviors and wall shear stresses. The effects of Hartmann number, pressure gradient and shear-to- strain-rate on the velocity fields are studied. Particularly, it is shown that the solutions of three-dimensional boundary-layer for variable pressure gradient exist, its effects are important on the boundary-layer flow. Results show that there are new families of solutions for some range of shear-to-strain-rate and there exists a threshold value of it beyond which no solutions exist. For some range of parameters, there is a reverse flow at which our boundary-layer assumptions are no longer valid. Various results for the velocity profiles, wall-shear stresses and displacement thicknesses are also obtained. The physical mechanisms behind these results are discussed.

C. Rajendran, M. Vinoth Kumar, Tushar Sonar et al.

Friction stir welding (FSW) was employed to join 10 mm thick AA2024-T6 aluminium alloy plates to overcome the fusion welding related problems such as grain coarsening in fusion zone, heat affected zone (HAZ) softening, lower joint efficiency and premature joint failure. The center cracked test (CCT) specimens were used to evaluate the fatigue crack growth rate of the welded joints. The microstructural features of joint were characterized using optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The fractured surfaces of CCT specimens were analyzed using scanning electron microscopy. Results showed that the FSW joints exhibit lower fatigue strength than the parent metal due to the dissolution of second phase strengthening precipitates. The post weld heat treatment (PWHT) specifically solution treatment (ST), artificial ageing (AA), solution treatment and ageing (STA) were employed to improve the fatigue properties of FSW joints. It was observed that the STA treated FSW joint exhibit higher fatigue life than the ST and AA treated joints. It is attributed to the precipitation of second phase strengthening precipitates in welded joint after STA.

Fuwei Yang, Bai Song Center for Nano, Micro Mechanics et al.

Active control of heat flow is of both fundamental and applied interest in thermal management and energy conversion. Here, we present a fluctuational electrodynamic study of thermal radiation between twisted bilayer graphene (TBLG), motivated by its unusual and highly tunable plasmonic properties. We show that near-field heat flow can vary by more than 10-fold over only a few degrees of twist, and identify special angles leading to heat flow extrema. These special angles are dictated by the Drude weight in the intraband optical conductivity of TBLG, and are roughly linear with the chemical potential. Further, we observe multiband thermal transport due to the increasing role of interband transitions as the twist angle decreases, in analogy to monolayer graphene in a magnetic field. Our findings are understood via the surface plasmons in TBLG, and highlight its potential for manipulating radiative heat flow.

Silvia Barbi, Francesco Barbieri, Alessandro Bertacchini et al.

This study aims to optimize the conditions for “Genovese” basil (<i>Ocimum Basilicum</i>) germination and growth in an indoor environment suitable for horticulture through a synergic effect of light and fertilizers addition. In fact, several studies determined that specific light conditions are capable of enhancing basil growth, but this effect is highly dependent on the environmental conditions. In this study, the effect of different light sources was determined employing a soil with a negligible amount of fertilizer, demonstrating substantial improvement when light-emitting diode (LED) lights (hyper red and deep blue in different combinations) were applied with respect to daylight (Plants height: +30%, Total fresh mass: +50%). Thereafter, a design of experiment approach has been implemented to calculate the specific combination of LED lights and fertilizer useful to optimize the basil growth. A controlled-release fertilizer based on nitrogen, phosphorus, and potassium (NPK) derived from agro-residues was compared with a soil enriched in macronutrients. The results demonstrate significant improvements for the growth parameters with the employment of the controlled-release NPK with respect to enriched soil combined with a ratio of hyper red and deep blue LED light equal to 1:3 (Total fresh mass: +100%, Leaves number: +20%).

Ashkan Shekaari, Mahmoud Jafari

The perturbative approach was adopted to develop a temperature-dependent version of non-relativistic quantum mechanics in the limit of low-enough temperatures. A generalized, self-consistent Hamiltonian was therefore constructed for an arbitrary quantum-mechanical system in a way that the ground-state Hamiltonian turned out to be just a limiting case at absolute zero. The weak-coupling term connecting the system of interest and its immediate environment was accordingly treated as the perturbation. Applying the obtained generalized Hamiltonian to some typical quantum systems with exact zero-temperature solutions, including the free particle in a box, the free particle in vacuum, and the harmonic oscillator, up to the first order of self-consistency, therefore corrected their associated Hamiltonians, energy spectrums, and wavefunctions to be consistent with the low-temperature limit. Further investigation revealed some kind of quantum tunneling effect by a residual probability for the free particle in a box, as a chief consequence of thermally coupling to the reservoir. The possible effects of thermal environment on the main properties of the wavefunctions were also thoroughly examined and discussed.

Waleed T. Rashid

The aim of this study is to studding the effect of addition of alumina and fly ash with the particles size 106µm and different weight rations (2:2, 2:4, 4:2) to aluminium-magnesium-silicon alloy on microstructure, mechanical properties, corrosion resistance, and wear. The vortex technique was used to prepare the composite material. The microscopic structure was also examined using optical microscopy and mechanical tests (hardness, tensile strength, yield strength and elongation) and wear test. The results showed that the composite material the containing (2% fly ash and 4% alumina) had the highest tensile strength (119 Mpa), yield strength (76 Mpa) and hardness (89 kg \ mm2), while it has the lowest ductility (5.3%). It was also found to have the lowest wear rate (1.8* 10-6gm \ cm) and the highest corrosion resistance.

I. S. Othman, M. A. F. M. M. Azam, M. F. A. Bakar et al.

The main purpose of this research is to investigate the effect of various ball milling duration on the surface morphology, hardness and wear properties of nickel- quarry dust (Ni-QD) composite coating on aluminium alloy 6061 (AA6061) substrate. Ni-QD composite coatings were deposited on zincated AA6061 substrate by using electrodeposition technique. The quarry dust particles were prepared by ball milling process at 5, 10, 15 and 20 hours. Later, the quarry dust particles were added to nickel citrate bath at 50 g/l for electrodeposition of Ni-QD composite coating. The electrodeposition process was carried out for 1 hour at 40º C, under the current density of 3 A/dm2. X-ray Fluorescence (XRF), X-ray Diffraction (XRD) and scanning electron microscope (SEM) analyses were carried out in order to investigate the influence of ball milling duration on the prepared quarry dust as well as the produced composite coating. In addition, microhardness and wear testing of Ni-QD composite coatings were also performed in this study. The microhardness values of the nickel composite coatings using ball milled quarry dust are higher than using crushed quarry dust. The microhardness values for all nickel composite coatings produced from crushed and ball milled quarry dust increases from 190.6 to 282.2. The increase in microhardness values is due to the high density of quarry dust in the electrolyte. The damage of the wear scar was improved, as the ball milling duration increases from 0 to 20 hours.

Chi-Chun Zhou, Wu-Sheng Dai

The main aim of this paper is twofold: (1) Suggesting a statistical mechanical approach to the calculation of the generating function of restricted integer partition functions which count the number of partitions --- a way of writing an integer as a sum of other integers under certain restrictions. In this approach, the generating function of restricted integer partition functions is constructed from the canonical partition functions of various quantum gases. (2) Introducing a new type of restricted integer partition functions corresponding to general statistics which is a generalization of Gentile statistics in statistical mechanics; many kinds of restricted integer partition functions are special cases of this restricted integer partition function. Moreover, with statistical mechanics as a bridge, we reveals a mathematical fact: the generating function of restricted integer partition function is just the symmetric function which is a class of functions being invariant under the action of permutation groups. Using the approach, we provide some expressions of restricted integer partition functions as examples.

Lucas Gren

Background. There are some publications in software engineering research that aim at guiding researchers in assessing validity threats to their studies. Still, many researchers fail to address many aspects of validity that are essential to quantitative research on human factors. Goal. This paper has the goal of triggering a change of mindset in what types of studies are the most valuable to the behavioral software engineering field, and also provide more details of what construct validity is. Method. The approach is based on psychological test theory and draws upon methods used in psychology in relation to construct validity. Results. In this paper, I suggest a different approach to validity threats than what is commonplace in behavioral software engineering research. Conclusions. While this paper focuses on behavioral software engineering, I believe other types of software engineering research might also benefit from an increased focus on construct validity.