Hasil untuk "Descriptive and experimental mechanics"

Jullyanne Silva, Tiago Atalaia, João Abrantes et al.

According to the World Health Organization, one-third of elderly people aged 65 or over fall annually, and this number increases after 70. Several gait biomechanical parameters were associated with a history of falls. This study aimed to conduct a systematic review to identify and describe the gait biomechanical parameters related to falls in the elderly. MEDLINE Complete, Cochrane, Web of Science, and CINAHL Complete were searched for articles on 22 November 2023, using the following search sentence: (gait) AND (fall*) AND ((elder*) OR (old*) OR (senior*)) AND ((kinematic*) OR (kinetic*) OR (biomechanic*) OR (electromyogram*) OR (emg) OR (motion analysis*) OR (plantar pressure)). This search identified 13,988 studies. From these, 96 were selected. Gait speed, stride/step length, and double support phase are gait biomechanical parameters that differentiate fallers from non-fallers. Fallers also tended to exhibit higher variability in gait biomechanical parameters, namely the minimum foot/toe clearance variability. Although the studies were scarce, differences between fallers and non-fallers were found regarding lower limb muscular activity and joint biomechanics. Due to the scarce literature and contradictory results among studies, it is complex to draw clear conclusions for parameters related to postural stability. Minimum foot/toe clearance, step width, and knee kinematics did not differentiate fallers from non-fallers.

Jordi Arboix-Alió, Guillem Trabal, Bernat Buscà et al.

This study aimed to investigate the influence of stick grasping on the performance of elite youth rink hockey players in 10 m linear sprints and 180° change of direction (COD) tasks. Forty-nine rink hockey players (age = 18.40 ± 2.12 year; body mass = 73.52 ± 6.02 kg; height = 1.82 ± 0.07 m; BMI = 23.61 ± 1.69; sports experience = 6.42 ± 1.41 years; 4.89 ± 0.68 years’ post-peak height velocity) participated in this cross-sectional study. Measurements included 10 m sprint time and COD 180° performance with and without stick grasping. Results revealed non-significant differences when carrying a stick in the 10 m linear sprint (1.90 s ± 0.08 with stick vs. 1.89 s ± 0.08 without stick; <i>p</i> = 0.71; <i>d</i> = 0.05), neither did COD 180° for the left limb (2.75s ± 0.11 with stick vs. 2.76 s ± 0.11 without stick; <i>p</i> = 0.91; <i>d</i> = 0.02). However, for the right limb, significantly better performance in COD 180° was found when players held the stick (2.72 s ± 0.11 with stick vs. 2.75 s ± 0.09 without stick; <i>p</i> = 0.03; <i>d</i> = 0.32). These findings imply that the distinctive biomechanics and requirements of rink hockey, especially the lateral movements inherent in skating, might alleviate the negative impacts associated with implement grasping observed in other sports. This study highlights that stick grasping did not hinder COD ability and may even have a facilitating effect on certain movements, emphasizing the importance of considering sport-specific biomechanics in rink hockey performance analysis.

Muner M. Abou Hasan, Ethar A. A. Ahmed, Ahmed F. Ghaleb et al.

An efficient numerical approach based on weighted-average finite differences is used to solve the Newtonian plane Couette flow with wall slip, obeying a dynamic slip law that generalizes the Navier slip law with the inclusion of a relaxation term. Slip is exhibited only along the fixed lower plate, and the motion is triggered by the motion of the upper plate. Three different cases are considered for the motion of the moving plate, i.e., constant speed, oscillating speed, and a single-period sinusoidal speed. The velocity and the volumetric flow rate are calculated in all cases and comparisons are made with the results of other methods and available results in the literature. The numerical outcomes confirm the damping with time and the lagging effects arising from the Navier and dynamic wall slip conditions and demonstrate the hysteretic behavior of the slip velocity in following the harmonic boundary motion.

Jacinto Ulloa, Laurent Stainier, Michael Ortiz et al.

This paper explores the role of generalized continuum mechanics, and the feasibility of model-free data-driven computing approaches thereof, in solids undergoing failure by strain localization. Specifically, we set forth a methodology for capturing material instabilities using data-driven mechanics without prior information regarding the failure mode. We show numerically that, in problems involving strain localization, the standard data-driven framework for Cauchy/Boltzmann continua fails to capture the length scale of the material, as expected. We address this shortcoming by formulating a generalized data-driven framework for micromorphic continua that effectively captures both stiffness and length-scale information, as encoded in the material data, in a model-free manner. These properties are exhibited systematically in a one-dimensional softening bar problem and further verified through selected plane-strain problems.

Georgi Djambazov

The numerically simulated method of using electromagnetic field from an alternating current is a patented method to create in liquid metal, under the conditions of resonance, acoustic waves of sufficient strength to cause cavitation and implosion of gas bubbles, leading to beneficial degassing and grain refinement. The modelling stages of electromagnetics are described below along with acoustics in liquids, bubble dynamics, and their interactions. Sample results are presented for a cylindrical container with liquid aluminium surrounded by an induction coil. The possibility of establishing acoustic resonance and sustaining the bubble oscillation at a useful level is demonstrated. Limitations of the time-dependent approach to this multi-physics modelling problem are also discussed.

Tuck C. Choy

Heisenberg's breakthrough in his July 1925 paper that set in motion the development of Quantum Mechanics through subsequent papers by Born, Jordan, Heisenberg and also Dirac (from 1925 to 1927) is reexamined through a modern lens. In this paper, we shall discuss some new perspectives on (i) what could be the guiding intuitions for his discoveries and (ii) the origin of the Born-Jordan-Heisenberg canonical quantization rule. From this vantage point we may get an insight into Einstein's Quantum Riddle (Lande1974,Sommerfeld1918,Born1926) and a possible glimpse of what might come next after the last 100 years of Heisenberg's quantum mechanics.

Toshihiro Takahashi, Takaaki Tateishi, Michiaki Tatsubori

Semantic text similarity plays an important role in software engineering tasks in which engineers are requested to clarify the semantics of descriptive labels (e.g., business terms, table column names) that are often consists of too short or too generic words and appears in their IT systems. We formulate this type of problem as a task of matching descriptive labels to glossary descriptions. We then propose a framework to leverage an existing semantic text similarity measurement (STS) and augment it using semantic label enrichment and set-based collective contextualization where the former is a method to retrieve sentences relevant to a given label and the latter is a method to compute similarity between two contexts each of which is derived from a set of texts (e.g., column names in the same table). We performed an experiment on two datasets derived from publicly available data sources. The result indicated that the proposed methods helped the underlying STS correctly match more descriptive labels with the descriptions.

Andrey Kozelkov, Elena Tyatyushkina, Vadim Kurulin et al.

This paper considers turbulence effects on tsunami runup on the shore in tsunami simulations using the system of three-dimensional Navier–Stokes equations. The turbulence effects in tsunami propagation and runup are studied by solving the problem of a wave propagating in a nonuniform-bottom pool and collapsing with a barrier. To solve this problem, we used the turbulence model, RANS SST (Reynolds-averaged Navier–Stokes shear stress transport). We compared the wave profiles at different times during wave propagation, runup, and collapse. To quantify the turbulence effects, we also compared the forces acting on the basin bottom. We demonstrated that the turbulence had almost no effect on the shape of the wave and the way of its propagation (except collapse). However, turbulence effects during the runup and collapse became noticeable and could boost the flow (increasing the pressure force and the total force) by up to 25 percent.

Achilles Bergne, Guido Baardink, Evripides G Loukaides et al.

Mechanical metamaterials are structures designed to exhibit an exotic response, such as topological soft modes at a surface. Here we explore single-material 3D prints of these topological structures by translating a ball-and-spring model into a physical prototype. By uniaxially compressing the 3D-printed solid having marginal rigidity, we observe that the surfaces are consistently softer than the bulk. However, we also find that either of two opposite surfaces can be the softest, in contrast to the topologically robust predictions of the linear model. Finite-element simulations allow us to bridge this gap. We explore how the printing geometry and deformation amplitude could affect surface softness. For small strains, we find qualitative agreement with the ball-and-spring model but, surprisingly, nonlinear deformations can select which side is softest. Our work contextualizes the predictions of topological mechanics for real 3D materials and their potential for cushioning applications.

Khairani Syahfitri, M. Mulyono, P. Siagian et al.

This study aims to: (1) analyze the differences in mathematical dispositions between students who are given a contextual learning model assisted by Geogebra and students who are given a model of cooperatif learning assisted by Geogebra at SMK Harapan Mekar 1 Medan, (2) analyze the interaction between learning and early mathematics ability (high, moderate, low) students towards improving students' mathematical communication skills at SMK Harapan Mekar 1 Medan, (3) analyzing the interaction between learning and the initial mathematics ability (high, medium, low) of students towards improving the mathematical disposition of students at SMK Harapan Mekar 1 Medan. The population of this study were all students of SMK Harapan Mekar 1 Medan in class X majoring in Automotive Mechanics and Computer Engineering. Samples were taken randomly from 6 classes, Students were selected as a sample of 2 classes, namely class X-2 as the experimental class I which was given the contextual learning model assisted by Geogebra and class X-3 as the experimental class 2 which was given the cooperative learning model assisted by Geogebra, with a total of 64 students. Data were analyzed using descriptive statistical analysis through two-way analysis. The results of this study indicate that: (1) There are differences in mathematical communication skills between students who are given a contextual learning model assisted by Geogebra and students who are given a cooperative learning model, (2) there are differences in mathematical disposition between students who are given a contextual learning model assisted by Geogebra and students who given a cooperative learning by Geogebra.

Pushpender Kumar Gangwar and Rajesh Kumar Verma

Shock waves in solids represent a critical area of high-strain-rate mechanics, encompassing elastic-plastic deformation, phase transitions, spallation, and high-pressure equation-of-state (EOS) studies. This review synthesizes fundamental physics, theoretical models, experimental techniques, and engineering applications of shock wave propagation in condensed matter. Key concepts such as the Hugoniot Elastic Limit (HEL), Rankine-Hugoniot relations, and elastic-plastic wave structure are discussed. Experimental methods (plate impact, explosive loading) and numerical approaches are evaluated. The review highlights the influence of material microstructure, viscosity, and strength on shock structure and decay. Applications in armor design, planetary impact cratering, and material synthesis are summarized.

Valerio Bonometti, Mathieu J. Ruiz, Anders Drachen et al.

Incentive salience attribution can be understood as a psychobiological mechanism ascribing relevance to potentially rewarding objects and actions. Despite being an important component of the motivational process guiding our everyday behaviour its study in naturalistic contexts is not straightforward. Here we propose a methodology based on artificial neural networks (ANNs) for approximating latent states produced by this process in situations where large volumes of behavioural data are available but no experimental control is possible. Leveraging knowledge derived from theoretical and computational accounts of incentive salience attribution we designed an ANN for estimating duration and intensity of future interactions between individuals and a series of video games in a large-scale ( N > 3 × 10^6) longitudinal dataset. We found video games to be the ideal context for developing such methodology due to their reliance on reward mechanics and their ability to provide ecologically robust behavioural measures at scale. When compared to competing approaches our methodology produces representations that are better suited for predicting the intensity future behaviour and approximating some functional properties of attributed incentive salience. We discuss our findings with reference to the adopted theoretical and computational frameworks and suggest how our methodology could be an initial step for estimating attributed incentive salience in large-scale behavioural studies.

A. Swandi, B. D. Amin, S. Viridi et al.

Technology-Enabled Active Learning Simulations (TEALSim) is a pedagogic innovation in learning by utilizing multimedia in the form of interactive simulations through active learning. In Indonesia, the use of TEALSim is still very poor. This study aims to identify the influence of the use of TEALSim in the learning of material physics of particle wave dualism at Makassar State University. This research is a quasi experiment using Nonequivalent Control Group Design. Data sources were obtained from the final test in the form of the Force Concept Inventory (FCI) and the Mechanics Baseline Test (MBT). The sample is two classes who programed introductory courses in quantum physics in the physics department of Makassar State University. The first is physics education class B with 25 students as experiment class and the second is physics education class C with 30 students. Data analysis is done descriptively and inferentially. Based on the results of data analysis, it was obtained information that there were significant differences between the FCI test results of the experimental class and the control class, whereas there were no significant differences in the results of the MBT test for both classes. It can be concluded that there needs to be another method in the use of TEALSim in order to be able to improve conceptual understanding, analytical skills, and mathematical skills

S. Andal, Prerna Singh, Sukriti Mondal et al.

Carlo Cravero, Andrea Ottonello

In the last three decades computer simulation tools have achieved wide spread use in the design and analysis of engineering devices. This has shortened the overall product design cycle (physical experiments may be impossible during early design stages) and it has also provided better understanding of the operating behavior of the systems under investigation. As a consequence numerical simulation have led to a reduction of physical prototyping and to lower costs for manufacturing production chains. Despite this success, it remains difficult to provide objective confidence levels in quantitative information derived from numerical predictions. The complexity arises from the amount of uncertainties related to the inputs of any computation attempting to represent a physical system. This paper focuses on geometrical sources of uncertainty in the field of CFD applied to twin scroll radial turbines. In particular it has been investigated the effect of uncertainties on tip clearance values at rotor blade leading edge and trailing edge on selected turbine performance parameters. The analysis shows the use of the Surrogate-based uncertainty quantification technique that has been setup by the authors in the Dakota^® environment. The polynomial chaos expansion method has been applied to the same case. The comparison of the results coming from the different approaches and the discussion of the pros and cons related to each technique lead to interesting conclusions, which are proposed as guidelines for future UQ applications on the theme of CFD applied to radial turbines.

Dimitrios Konispoliatis, Spyridon Mavrakos

This paper presents a numerical and experimental investigation of the second-order steady horizontal and vertical drift forces acting on cylindrical bodies in regular waves. The examined bodies are either kept restrained in front of a vertical breakwater or are considered free- floating when alone in the wave field. Two principally different approaches for mean drift forces determination are described: the momentum conservation principle and the direct integration of all pressure contributions upon the instantaneous wetted surface of the bodies, whereas, for the solution of the associated diffraction and motion radiation problems, analytical and panel methodologies are applied. The hydrodynamic interaction phenomenon between the bodies and the adjacent breakwater are taken into account by using the method of images. Theoretical and numerical results, concerning the horizontal and the vertical drift forces, are presented and compared with each other. Furthermore, additional comparisons are made with experimental data obtained during an experimental campaign at French research institute for exploitation of the sea (IFREMER), in France.

Vahid Ebrahimpour Ahmadi, Akam Aboubakri, Abdolali Khalili Sadaghiani et al.

Flow boiling is one of the most effective phase-change heat transfer mechanisms and is strongly dependent on surface properties. The surface wettability is a crucial parameter, which has a considerable effect on the heat transfer performance, particularly in flow boiling. The contact angle determines the number of nucleation sites as well as bubble dynamics and flow patterns. This study introduces three new generation mixed wettability surfaces and compares them with a wholly hydrophobic surface reference sample, in flow boiling in a high aspect ratio microchannel. The mixed wettability substrates have five regions as fully Al₂O₃, (hydrophobic zone) region, three different patterned configurations with various A* values, and fully SiO₂ (hydrophilic zone) region, where A* is defined as A _Al2O3/A _total (hydrophobicity ratio). Boiling heat transfer results were obtained for each surface at various wall heat fluxes and three different mass fluxes. According to the obtained results, significant enhancements in heat transfer (by up to 56.7%) could be obtained with biphilic surfaces compared to the reference sample (hydrophobic surface). Performed flow visualization proves that the tested biphilic surfaces enhance heat transfer by reducing the bubbly flow regime and extending the slug regime.

Koushik Viswanathan, Shwetabh Yadav, Dinakar Sagapuram

Shear banding is a material instability in large strain plastic deformation of solids, where otherwise homogeneous flow becomes localized in narrow micrometer-scale bands. Shear bands have broad implications for materials processing and failure under dynamic loading in a wide variety of material systems ranging from metals to rocks. This year marks 75 years since the publication of Zener and Hollomon's pioneering work on shear bands which is widely credited with drawing the attention of the mechanics community to shear bands and related localization phenomena. There has since been significant experimental and theoretical investigation into the onset of shear banding. Yet, given the extremely small length and time scales associated with band development, several challenges persist in studying the evolution of single bands. Recent full-field displacement measurements, coupled with numerical modeling, have only begun to ameliorate this problem. This article summarizes our present understanding of plastic flow dynamics around single shear bands and the subsequent transition to fracture, with special applications to materials processing. We begin with a semi-historical look at some of Zener's early ideas on shear bands and discuss recent advances in experimental methods for mapping localized flow during band formation, including direct \emph{in situ} imaging as well as \emph{ex situ}/post-mortem analyses. Classical theories are revisited in the light of recently published experimental data. Shear bands exhibit a wealth of complex flow characteristics that bear striking resemblance to boundary layer phenomena in fluid flows. It is hoped that these will help further our understanding of shear band dynamics, the subsequent transition to fracture, and lead to practical `control' strategies for suppressing shear band-driven failures in processing applications.

Alejandro Hnilo

Here it is shown that the simplest description of Bell's experiment according to the canon of von Neumann's theory of measurement explicitly assumes the (Quantum Mechanics-language equivalent of the classical) condition of Locality. This result is complementary to a recently published one demonstrating that non-Locality is necessary to describe said experiment within the framework of classical hidden variables theories, but that it is unnecessary to describe it within the framework of Quantum Mechanics. Summing up these and other related results, it is concluded that, within the framework of Quantum Mechanics, there is absolutely no reason to believe in the existence of non-Local effects. In addition to its foundational significance, this conclusion has practical impact in the fields of quantum-certified and device-independent randomness generation and on the security of Quantum Key Distribution schemes using entangled states.

D. Riccobelli, G. Noselli, M. Arroyo et al.

In this work, we study the mechanics of metamaterial sheets inspired by the pellicle of Euglenids. They are composed of interlocking elastic rods which can freely slide along their edges. We characterize the kinematics and the mechanics of these structures using the special Cosserat theory of rods and by assuming axisymmetric deformations of the tubular assembly. Through an asymptotic expansion, we investigate both structures that comprise a discrete number of rods and the limit case of a sheet composed by infinitely many rods. We apply our theoretical framework to investigate the stability of these structures in the presence of an axial load. Through a linear analysis, we compute the critical buckling force for both the discrete and the continuous case. For the latter, we also perform a numerical post-buckling analysis, studying the non-linear evolution of the bifurcation through finite elements simulations.