Manuel A. González-Fernández, Ignacio Pérez-Rey, Fei Song
et al.
Strain measurements during uniaxial compressive strength (UCS) testing and their subsequent interpretation to obtain elastic parameters are relatively straightforward for most rocks. However, for slates, which are foliated metamorphic rocks characterized by significant anisotropy, the dependence of elastic properties on the orientation of foliation complicates the measurement and interpretation of strain data. In this study, a series of wave propagation velocity tests and UCS tests are conducted on cylindrical and prismatic slate specimens to gain a better understanding of how to obtain and process deformability and strength results. Wave propagation velocity results demonstrate an increase with the dip of foliation planes crossed, which is consistent with previous studies. Based on UCS test results, two methodologies are considered for obtaining transversely isotropic deformability parameters: the least-squares method and the recently proposed generalized reduction gradient (GRG) algorithm. Their performance is assessed in the context of potentially variable and limited amounts of data. GRG algorithms provide an enhanced analysis technique for estimating anisotropic elastic properties when dealing with limited or heterogeneous laboratory test data. Different strength models have also been considered, including the classic Jaeger's weakness plane (JPW) and its subsequent modification, i.e. 2HBJPW. The 2HBJPW approach has proven to be more consistent with the obtained results and enhances the representation of the strength properties of slates. Additionally, a finite element method (FEM) numerical approach is employed to compare results with analytical and experimental ones, demonstrating a good match, thereby offering calibrated inputs for rock engineering applications.
Engineering geology. Rock mechanics. Soil mechanics. Underground construction
Jorge Pérez-Contreras, Rodrigo Villaseca-Vicuña, Esteban Aedo-Muñoz
et al.
<b>Background/Objectives:</b> To compare the external load (EL) of elite youth soccer players during official international matches between age categories and playing positions. <b>Methods</b>: The sample consisted of 42 elite youth soccer players categorized by age categories, U-15, U-17 and U-20 and playing positions: central defender (CD); fullback (FB); midfielder (MF); wide attacker (WA) and striker (ST). The Vector X7 (Catapult Sports) device was used for collecting the following EL variables: total distance traveled (TD), player load (PL) and distance traveled per velocity band 0 to 7 km/h (D7); 7 to 13 km/h (D13); 13 to 19 km/h (D19); 19 to 23 km/h (D23) and >23 km/h (HSR). Linear mixed-effect models were applied to analyze the differences. <b>Results</b>: Large differences were found between positions (<i>p</i> < 0.01) in TD (η<sup>2</sup>p = 0.48), PL (η<sup>2</sup>p = 0.30), D19 (η<sup>2</sup>p = 0.44), D23 (η<sup>2</sup>p = 0.68) and HSR (η<sup>2</sup>p = 0.53). Large differences were found according to category between U-15 and U-17 in TD (<i>p</i> = 0.006 and η<sup>2</sup>p = 0.25) and D13 (<i>p</i> = 0.003 and η<sup>2</sup>p = 0.27). Large interaction effects were found in DT (<i>p</i> = 0.014 and η<sup>2</sup>p = 0.44) and D23 (<i>p</i> = 0.002 and η<sup>2</sup>p = 0.51). <b>Conclusions:</b> This study concludes that there are differences in EL in official matches in elite youth players between age categories and playing position. These differences can be applied in practice to design individualized training by playing position and to monitor EL during microcycles.
Mechanics of engineering. Applied mechanics, Descriptive and experimental mechanics
The growth of the thermally grown oxide (TGO), formed during the oxidation of thermal barrier coatings (TBCs) in advanced gas turbine engines, exhibits a pronounced size effect as the thickness approaches its grain size. Addressing the gap in current coupling theories for capturing scale-dependent oxidation behavior, this study further develops an enhanced theoretical framework that integrates large deformation mechanical-thermal-chemical coupling, incorporating strain gradient effects. By utilizing the Green strain as an independent field variable, numerical solutions were obtained using a mixed finite element method. The growth kinetics of the TGO are investigated under isothermal conditions. Numerical results indicate that the strain gradient effect increases the compressive stress within the TGO growth region by 77.8 % and promotes a more uniform stress distribution with increasing scale parameters. Consequently, the growth rate and non-uniform expansion of the TGO are substantially mitigated, as the stress-induced inhibition effect is more effectively utilized. With suppressed non-uniform expansion of the TGO, the susceptibility of the coating to surface wrinkling diminishes with larger scale parameters. This research is instrumental in elucidating the oxidation dynamics of TBCs.
Mechanics of engineering. Applied mechanics, Technology
Multidirectional torsional hysteretic damper is a new type of damper that can be used to isolate and dissipate seismic effects on a structure. It can be designed to have a controllable post-elastic stiffness and exhibit high levels of damping as well as stable cyclic response. In this article, while offering a simplified numerical relationship for force-displacement response of the damper, the structure that is fitted with this innovative type of damper is optimized using the harmony search optimization procedure with discrete design variables. Numerical experiments show that the harmony search methodology can determine the damper parameters with high computational efficiency and outperform genetic algorithm and simulated annealing procedure in this regard.
Paweł Lipowicz, Marta Borowska, Agnieszka Dardzińska-Głębocka
Computed tomography (CT) is one of the fundamental imaging modalities used in medicine, allowing for the acquisition of accurate cross-sectional images of internal body tissues. However, during the acquisition and reconstruction process, various artifacts can arise, and one of them is ring artifacts. These artifacts result from the inherent limitations of CT scanner components and the properties of the scanned material, such as detector defects, non-uniform distribution of radiation from the source, or the presence of metallic elements within the scanning region. The purpose of this study was to identify and reduce ring artifacts in tomographic images using image decomposition and average filtering methods. In this study, tests were conducted on the effectiveness of identifying ring artifacts using wavelet decomposition methods for images. The test was performed on a Shepp–Logan phantom with implemented artifacts of different intensity levels. The analysis was performed using different wavelet families, and linear approximation methods were used to filter the image in the identified areas. Additional filtering was performed using moving average methods and empirical mode decomposition (EMD) techniques. Image comparison methods, i.e., RMSE, SSIM and MS-SSIM, were used to evaluate performance. The results of this study showed a significant improvement in the quality of tomographic phantom images. The authors obtained more than 50% improvement in image quality with reference to the image without any filtration. The different wavelet families had different efficiencies with relation to the identification of the induction regions of ring artifacts. The Haar wavelet and Coiflet 1 showed the best performance in identifying artifact induction regions, with comparative RMSE values for these wavelets of 0.1477 for Haar and 0.1469 for Coiflet 1. The applied additional moving average filtering and EMD permitted us to improve image quality, which is confirmed by the results of the image comparison. The obtained results allow us to assess how the used methods affect the reduction in ring artifacts in phantom images with induced artifacts.
Abstract The uniaxial compressive strength (UCS) of rock is an important geotechnical parameter for engineering applications. However, how to determine the UCS simply and accurately has drawn the attentions of may researchers. To date, different kinds of indirect methods have been invented to determine the UCS of rocks, and among these methods, estimation of the UCS based on the Schmidt hammer rebound value (Hr) was commonly adopted. In this paper, an insightful analysis of the literature related to UCS estimation using the Schmidt hammer test was conducted, and three stages for the development of UCS estimation using Hr were classified. The drawbacks and merits of different kinds of techniques were analyzed in detail. Then, a data set containing the data for different rock types was collected from references, and to obtain an objective empirical formula, the simulated annealing-gene expression programming (SA-GEP) method was employed to establish the correlation between UCS and Hr. Based on the calculation results, the L-type Schmidt hammer was suggested for use in UCS estimation, and the corresponding empirical formula was established. To confirm validity of the empirical formula, the Schmidt hammer tests and uniaxial compressive tests were conducted separately, the experimental results were in a good agreement with the proposed empirical formula, implying that the proposed empirical formula can be applied in engineering practice.
M. Belarbi, Li Li, Mohammed Sid Ahmed Houari
et al.
This work studies the size-dependent free vibration response of functionally graded (FG) nanoplates using a layerwise theory. The proposed model supposes not only a higher-order displacement field for the core but also the first-order displacement field for the two face sheets, thereby maintaining an interlaminar displacement continuity among layers. Unlike the conventional layerwise models, the number of variables is kept fixed and does not increase for an increased number of layers. This is a very important feature compared to conventional layerwise models and facilitates significantly the engineering analyses. The material properties of the FG nanoplate are graded continuously through the thickness direction in accordance with a power-law function. The Eringen’s nonlocal elasticity theory is here adopted to relax the continuum axiom required in classical continuum mechanics and hence hopeful to capture the small size effects of naturally discrete nanoplates. The equations of motion of the problem are obtained via a classical Hamilton’s principle. The present layerwise model is implemented with a computationally efficient C0- continuous isoparametric serendipity elements and applied to solve a large-scale discrete numerical problem. The robustness and reliability of the developed finite element model are demonstrated by a comparative evaluation of results against predictions from literature. The comparative studies show that the proposed finite element model is: (a) free of shear locking, (b) accurate with a fast rate convergence for both thin and thick FG nanoplates, and (c) excellent in terms of numerical stability. Moreover, a detailed parametric analysis checks for the sensitivity of the vibration response of FG nanoplates to the aspect ratio, length-to-thickness ratio, nonlocal parameter, boundary conditions, power-law index, and modes shapes. Referential results are also reported, for the first time, for natural frequencies of FGM nanoplates which will serve as benchmarks for further computational investigations.
Solution representations are available for several differential equations. For elasticity problems some of the solution representations are considered in this paper. The solution representations can be used for a systematic construction of Trefftz functions for the derivation of Trefftz-type finite elements. For the example of a thick plate a set of Trefftz functions is presented.
Computer engineering. Computer hardware, Mechanics of engineering. Applied mechanics
An analysis of the ship stability requires computer simulations of the ship motions leading to its capsizing. The large amplitudes of roll motion of the ship are connected with phenomena of immersing of ship deck into water. These phenomena require to take into account additional moments connected with water on a deck. The paper presents a new method (1994) of calculating these additional moments. An approximate and simple calculation of the additional moments is based on the second principle of dynamics applied to an element of a water running off the deck. The additional moments applied in numerical simulations of the ship motions, change significantly the roll motion. The paper presents results obtained from computer simulations. Some of the results are compared with the results of an experiment done with the ship model.
Computer engineering. Computer hardware, Mechanics of engineering. Applied mechanics
Sadjad Arzash, Anupama Gannavarapu, Fred C. MacKintosh
At zero temperature, spring networks with connectivity below Maxwell's isostatic threshold undergo a mechanical phase transition from a floppy state at small strains to a rigid state for applied shear strain above a critical strain threshold. Disordered networks in the floppy mechanical regime can be stabilized by entropic effects at finite temperature. We develop a scaling theory based on a real-space renormalization approach for this mechanical phase transition at finite temperature, yielding relationships between various scaling exponents. Using Monte Carlo simulations, we verify these scaling relations and identify anomalous entropic elasticity with sub-linear $T$-dependence in the linear elastic regime. While our results are consistent prior studies of phase behavior near the isostatic point, the present work also makes predictions relevant to the broad class of disordered thermal semiflexible polymer networks for which the connectivity generally lies far below the isostatic threshold.
Tsang and Caves suggested the idea of a quantum-mechanics-free subsystem in 2012. We contend that Sudarshan's viewpoint on Koopman-von Neumann mechanics is realized in the quantum-mechanics-free subsystem. Since quantum-mechanics-free subsystems are being experimentally realized, Koopman-von Neumann mechanics is essentially transformed into an engineering science.
Bringing together contributions on a diverse range of topics, this text explores the relationship between discrete and continuum mechanics as a tool to model new and complex metamaterials. Providing a comprehensive bibliography and historical review of the field, it covers mechanical, acoustic, and pantographic metamaterials, discusses naive model theory and Lagrangian discrete models, and their applications, and presents methods for pantographic structures and variational methods for multidisciplinary modeling and computation. The relationship between discrete and continuous models is discussed from both mathematical and engineering viewpoints, making the text ideal for those interested in the foundation of mechanics and computational applications, and innovative viewpoints on the use of discrete systems to model metamaterials are presented for those who want to go deeper into the field. An ideal text for graduate students and researchers interested in continuum approaches to the study of modern materials, in mechanical engineering, civil engineering, applied mathematics, physics, and materials science.
Combined turbulent wall and offset jets with and without the presence of a parallel co-flow stream are investigated using the k-ω turbulence model. We focus on the effects of co-flow velocity on the locations of various characteristic points formed owing to the interaction of wall and offset jets in the dual jet flow. The inlet Reynolds number is taken as 15,000 and the offset ratio is varied from 5 to 11. At low offset ratios, the co-flow velocity effect remains almost negligible. With the progressive increase in co-flow velocity, the characteristic points are gradually relocated towards the further downstream direction with a transverse movement away from the bottom wall whose effect is weakened with the increase in co-flow velocity. Furthermore, regression analysis shows power law and linear correlations of the longitudinal and transverse coordinates of characteristic points with the co-flow velocity and the offset ratio.
Nuguzhinov Zhmagul, Khabidolda Omirkhan, Bakirov Zhetpisbai
et al.
The work is devoted to determining the stress parameters of flexible reinforced concrete beams with cracks. The problem is solved using LIRA-SAPR using beam finite elements, taking into account the nonlinear relationship between deformation and stress in concrete. In the course of solution, a step-by-step loading method is used with the use of an iterative process at each step. To obtain the dependence of the stress parameters on varied factors, a rational planning matrix for a multifactor computer simulation was compiled to determine the stress parameters in bent rectangular reinforced concrete beams with a crack. According to this plan, computer simulations were conducted for concrete beams of C20/25 and B32/40 class. The obtained dependences enable to evaluate the operability of the considered structural elements for both groups of limiting states. They can be used to determine the parameters of fracture mechanics and evaluate the crack resistance of a beam.
Abhinav Singhal, Juhi Baroi, Mafruza Sultana
et al.
This article presents the study of wave mechanics in a multiferroic structure having imperfection in the structure’s interface. This article reflects the study of shear horizontal (SH) wave propagation in a layered cylindrical structure consisting of thin layers of different materials (reinforced material and piezomagnetic material) with an imperfect interface. The interface considered between both materials is mechanically imperfect. Dispersion relations are achieved analytically. Distinct graphs are drawn (numerically) to exhibit the influence of parameters like rotation, initial stress, and mechanically imperfect parameters on phase velocity. Numerical results are drawn analytically and explained for each affecting distinct parameters for materials and interface. Parametric results on the phase velocities yield a significant conclusion of which some are: (a) Performance of Piezo with reinforcement material have an influential impact on wave velocity. (b) The mechanical imperfection affects the significantly on wave velocity (c) The Reinforcement/PM stiffening can monotonically up the velocity of phase velocity.
Armin Norouzi, Saeid Shahpouri, David Gordon
et al.
Machine learning (ML) and a nonlinear model predictive controller (NMPC) are used in this paper to minimize the emissions and fuel consumption of a compression ignition engine. In this work machine learning is applied in two methods. In the first application, ML is used to identify a model for implementation in model predictive control optimization problems. In the second application, ML is used as a replacement of the NMPC where the ML controller learns the optimal control action by imitating or mimicking the behavior of the model predictive controller. In this study, a deep recurrent neural network including long-short term memory (LSTM) layers are used to model the emissions and performance of an industrial 4.5 liter 4-cylinder Cummins diesel engine. This model is then used for model predictive controller implementation. Then, a deep learning scheme is deployed to clone the behavior of the developed controller. In the LSTM integration, a novel scheme is used by augmenting hidden and cell states of the network in an NMPC optimization problem. The developed LSTM-NMPC and the imitative NMPC are compared with the Cummins calibrated Engine Control Unit (ECU) model in an experimentally validated engine simulation platform. Results show a significant reduction in Nitrogen Oxides (\nox) emissions and a slight decrease in the injected fuel quantity while maintaining the same load. In addition, the imitative NMPC has a similar performance as the NMPC but with a two orders of magnitude reduction of the computation time.