Hasil untuk "Descriptive and experimental mechanics"

Yuto Tanaka, Yoshiaki Ono, Yosuke Tomita

<b>Background/Objective:</b> Postural stability and motor coordination require precise regulation of agonist and antagonist muscle activities. Jaw clenching modulates neuromuscular control during static and reactive postural tasks. However, its effects on dynamic voluntary movement remain unclear. This pilot study aimed to investigate the effects of jaw clenching on muscle activity and kinematics during repetitive single-leg sit-to-stand task performance. <b>Methods:</b> Eleven healthy adults (age: 21.2 ± 0.4 years; 6 males and 5 females; height: 167.9 ± 9.6 cm; body weight: 59.7 ± 8.1 kg) performed repetitive single-leg sit-to-stand tasks for 30 s under jaw-clenching and control conditions. Electromyography (EMG) signals from eight muscles and kinematic data from 16 inertial measurement unit sensors were analyzed, focusing on the seat-off phase. <b>Results:</b> Jaw clenching resulted in a significantly lower success rate than the control condition (success rate: 0.96 ± 0.13 vs. 0.78 ± 0.29, <i>p</i> = 0.047). Under the jaw clenching condition, failed trials exhibited higher medial gastrocnemius and masseter EMG activity (<i>p</i> < 0.001), lower erector spinae longus EMG activity (<i>p</i> < 0.001), and altered kinematics, including increased trunk yaw and roll angles (<i>p</i> < 0.001). Jaw clenching increased the coactivation of the gastrocnemius and tibialis anterior muscles (<i>p</i> < 0.001), disrupting the reciprocal muscle patterns critical for task performance. <b>Conclusions:</b> These findings suggest that jaw clenching may reduce task performance by altering neuromuscular coordination during dynamic postural tasks.

Yadong Han, Bingfu Han, Ming Liu et al.

Cavitating flows are of great interest in the fields of hydraulic machineries, which can significantly affect mechanical performance and safety. Despite various efforts being dedicated to figuring out the interaction between flow and cavitation fields, their correlation has not been clearly addressed. To this end, in this study, a convolutional neural network, U-Net, was adopted to build a model that can predict the vapor volume fraction from velocity fields. Large eddy simulations of cavitating flows around a Clark-Y hydrofoil were conducted, and the simulated snapshots with velocity and vapor volume fraction were adopted as a dataset for training the network. The predicted vapor volume fraction shows good agreement with the referred simulation results, with a <i>L</i>₁ deviation lower than 2 × 10⁻⁴, considering all the snapshots. The comparable <i>L</i>₁ deviation between the training and validation datasets suggests the existence of a strong correlation between velocity and cavitation fields. The cavitation–velocity interaction derived from using U-Net suggests that the location with zero velocity indicates the interior part of attached and cloud cavitations, and the local vortical velocity fields usually suggest the existence of cavitation shedding.

Dimitrios Mathioulakis, Nikolaos Vasilikos, Panagiotis Kapiris et al.

The aerodynamic loading of four as well as of six tilted flat plates-panels arranged in tandem and in close proximity to the ground is examined through force and pressure measurements. In the four-plate set up, conducted in an open-circuit wind tunnel, a movable floor is used to vary the ground clearance, and a one-component force balance is employed to measure the drag coefficient Cd of each plate for tilt angles 10° to 90° and for two head-on wind directions, 0° and 180°. An increase in the ground clearance from 20% to 60% of the plates’ chord length, results in a Cd increase of over 40% in the downstream plates, and up to 20% in the leading one. For tilt angles below 40°, the drag on the first plate is up to 25% higher under the 180° wind direction compared to the opposite direction. Pressure distributions are also presented on a series of six much larger plates, examined in a closed-circuit wind tunnel at tilt angles ±30°. While the windward surfaces exhibit relatively uniform pressure distributions, regions of low pressure develop on their suction side, near the plates’ tips leading edge, tending to become uniform streamwise.

Muhammad Waqas Zaffar, Ishtiaq Haasan, Abdul Razzaq Ghumman

Hydraulic structures, such as barrages, play an important role in the sustainable development of several regions worldwide. The aim of this novel study is to identify the critical hydraulic parameters (CHPs) of Taunsa Barrage, built on the Indus River. These CHPs, including free surface profiles, flow depths, Froude number, velocity profiles, energy dissipation and turbulence kinetic energy, were investigated using simulation via FLOW-3D numerical models. Incompressible Reynolds-averaged Navier–Stokes (RANS) equations on each computational cell were solved using the numerical methods available in FLOW-3D. The simulation results indicated that the locations of hydraulic jumps (HJs) were lower than that were reported in the previous one-dimensional study. Similarly, the distances of the HJs from the downstream toe of the glacis were reached at 2.97 m and 6 m at 129.10 m and 130.30 m tailwater levels, respectively, which deviated from the previous studies. In higher tailwater, the sequent depth ratio also deviated from the previous data. The maximum turbulent kinetic energies were observed in the developing regions of HJs, which were found to be decreased as the distance from the HJ was increased. The results of this research will be highly useful for engineers working in the field of design of hydraulic structures.

Giuseppe Procopio, Massimiliano Giona

This article develops a modal expansion (in terms of functions exponentially decaying with time) of the force acting on a micrometric particle and stemming from fluid inertial effects (usually referred to as the Basset force) deriving from the application of the time-dependent Stokes equation to model fluid–particle interactions. One of the main results is that viscoelastic effects induce the regularization of the inertial memory kernels at <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>t</mi><mo>=</mo><mn>0</mn></mrow></semantics></math></inline-formula>, eliminating the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mn>1</mn><mo>/</mo><msqrt><mi>t</mi></msqrt></mrow></semantics></math></inline-formula>-singularity characterizing Newtonian fluids. The physical origin of this regularization stems from the finite propagation velocity of the internal shear stresses characterizing viscoelastic constitutive equations. The analytical expression for the fluid inertial kernel is derived for a Maxwell fluid, and a general method is proposed to obtain accurate approximations of it for generic complex viscoelastic fluids, characterized by a spectrum of relaxation times.

Sadegh Pourghasemi Hanza, Hamed Ghafarirad

In this study, an inhomogeneous Cosserat rod theory is introduced and compared to the conventional homogeneous rod for modeling soft manipulators. The inhomogeneity is addressed by considering the pressure actuation as part of the rod's constitutive laws, resulting in shifting the neutral axis. This shift is investigated for a soft manipulator with three parallel fiber-reinforced actuators. Furthermore, a fiber-reinforced actuator is modeled using nonlinear continuum mechanics to extract the effect of radial pressure on axial deformation and is combined with Cosserat model. Finally, several numerical methods are employed to solve the proposed model and validated by a series of experiments.

Jakub A. Kochanowski, Bobby Carroll, Merrill E. Asp et al.

Bacteria build multicellular communities termed biofilms, which are often encased in a self-secreted extracellular matrix that gives the community mechanical strength and protection against harsh chemicals. How bacteria assemble distinct multicellular structures in response to different environmental conditions remains incompletely understood. Here, we investigated the connection between bacteria colony mechanics and the colony growth substrate by measuring the oscillatory shear and compressive rheology of bacteria colonies grown on agar substrates. We found that bacteria colonies modify their own mechanical properties in response to shear and uniaxial compression with the increasing agar concentration of their growth substrate. These findings highlight that mechanical interactions between bacteria and their microenvironment are an important element in bacteria colony development, which can aid in developing strategies to disrupt or reduce biofilm growth.

B. Rae, M. Hrabia, V. Baggiolini et al.

The CERN fixed target experimental areas are composed of more than 8 km of beam lines with around 800 devices used to define and monitor the beam parameters. Each year more than 140 groups of users come to perform experiments in these areas, with a need to control and access the data from these devices. The software to allow this therefore has to be simple and robust, and be able to control and read out all types of beam devices. This contribution describes the functionality of the beam line control system, CESAR, and its evolution. This includes all the features that can be used by the beam line physicists, operators, and device experts that work in the experimental areas. It also underlines the flexibility that the software provides to the experimental users for control of their beam line, allowing them to manage this in a very easy and independent way. This contribution also covers the on-going work of providing MAD-X support to CESAR to achieve an easier way of integrating beam optics. An overview of the on-going software migration of the Experimental Areas is also given.

Ángel Salvatierra Melgar, C. Luy-Montejo, Segundo Sigifredo Pérez Saavedra et al.

In the framework of continuous improvement of university education, the corresponding bodies are attentive to the good practices detached by the agents that comprise them. In this study, gamification in the mathematics learning process is described from the perspective of 286 students identified by non-probabilistic intentional sampling. Under these arguments, the methodology of the study is non-experimental, descriptive ex-post-facto level; the data for the analysis were collected in two stages: first moment in an instantaneous way to be able to perceive directly the gamification in the learning of mathematics through the Mentimenter tool; in second moment, the questionnaire was applied with 33 items composed of three dimensions: dynamics, mechanics and component from the contributions of Kevin Werbach. The results attributed to the study show that gamification, from the student's perspective, is a dynamic tool for the learning of previous concepts of Basic Mathematics and Mathematical Complements in the first academic semesters; in addition, the teacher plays the role of facilitator and the student responsibly manages his space and learning environment.

Bernhard Ćosić, Dominik Waßmer, Franklin Genin

Fluidic oscillators have proven their capabilities and advantages in terms of the generation of oscillating jets without moving parts for many years, mainly in experimental studies. In this paper, the design, development, and integration of fluidic atomizers into the liquid-fuel system of the dual-fuel low NO_X Advanced Can Combustion (ACC) system of the MAN Gas Turbines (MGT) are presented. The two-stage system comprises a pressure-swirl nozzle as a pilot stage and an assembly of four main premixed nozzles, based on fluidic technology. The design and the features of the pilot nozzle are briefly presented, whereas the focus lies on the functionality and layout of the fluidic nozzles. The complete integration, validation, and verification of this innovative liquid-fuel injection unit are presented. The final system features fast fuel-switchovers, low complexity, high reliability, and dry low emissions in liquid-fuel operation.

Dmytro Mishchuk, Yevhen Mishchuk, Ievgenii Gorbatyuk

Задачі оптимізації режимів руху механічних систем, зокрема роботів та маніпуляторів, є актуальною в контексті сучасного розвитку суспільства та машинобудування. Роботи і маніпулятори здатні автономно виконувати складні задачі по заданих програмах керування, що значно знижує вартість виконуваних ними робіт. Алгоритми оптимальних переміщень складових елементів роботів і маніпуляторів дозволяють реалізовувати складні траєкторії переміщень їхніх робочих органів з прогнозованими енерговитратами, точністю позиціювання, швидкодією. Пошук оптимальних режимів руху є складною і не однозначною задачею, що вимагає точного формулювання функції оптимізації, рівнянь обмежень та методів визначення оптимальних законів, які б задовольняли критерії поставленої оптимізаційної задачі. Одним із шляхів вирішення таких складних задач є евристичні методи перебору варіантів розв’язку на обмеженій площині, зокрема одним з таких є методів рою частинок.  В даному досліджені проаналізовано класичний метод рою частинок для пошуку оптимального режиму руху стріли маніпулятора за однієї з узагальнених координат. Цільовою функцією оптимізації вибрано «енергію» прискорень механічної системи, а пошук оптимального закону переміщення здійснюється із застосуванням полінома четвертого порядку. Проведене теоретичне дослідження показало, що метод рою частинок може бути застосований для пошуку оптимальних законів руху, проте при роботі з даним методом необхідно модернізувати алгоритм визначення його складових, зокрема швидкості переміщення частинок та їх корегувальних коефіцієнтів. При визначенні оптимальних законів руху маніпулятора методом рою в даному дослідженні застосовується підхід, де прийнято, що час є дискретним, а значення цільової функції визначалося лише в прийнятих точках дискретизації часу.

Susumu Osaki, Kosuke Hayashi, Hidehito Kimura et al.

Lattice Boltzmann simulations and a velocity measurement of flows in a cerebral aneurysm reconstructed from MRA (magnetic resonance angiography) images of an actual aneurysm were carried out and the numerical results obtained using the bounce-back schemes were compared with the experimental data to discuss the effects of the numerical treatment of the no-slip boundary condition of the complex boundary shape of the aneurysm on the predictions. The conclusions obtained are as follows: (1) measured data of the velocity in the aneurysm model useful for validation of numerical methods were obtained, (2) the numerical stability of the quadratic interpolated bounce-back scheme (QBB) in the flow simulation of the cerebral aneurysm is lower than those of the half-way bounce-back (HBB) and the linearly interpolated bounce-back (LBB) schemes, (3) the flow structures predicted using HBB and LBB are comparable and agree well with the experimental data, and (4) the fluctuations of the wall shear stress (WSS), i.e., the oscillatory shear index (OSI), can be well predicted even with the jaggy wall representation of HBB, whereas the magnitude of WSS predicted with HBB tends to be smaller than that with LBB.

Lorenzo Fusi, Andrea Ballotti

In this paper, we studied the squeeze flow between circular disks of a new class of fluids defined by an implicit relation referred to as stress power law fluids. The constitutive response of these fluids was written expressing the symmetric part of the velocity gradient as a tensorial function of the Cauchy stress. We assumed that the aspect ratio between the gap separating the disks and the radius was small so that a lubrication expansion could be adopted. We wrote the general problem and looked for a solution that could be written in terms of the small aspect ratio parameter. We obtained a sequence of problems that could be solved iteratively at each order, and we focused on the leading and first order, deriving explicit expressions for the velocity field, stress, and pressure.

Hanifa Aziz, Faiza Abrar, S. Gul et al.

Background: Advanced ventilation technologies require critical nursing management to facilitate patientcare. The nursing workforce in the intensive care units (ICUs) should have basic knowledge and understanding of the ventilator and its mechanics to recognise adverse events and improve the care quality. Methods: A pre-experimental study using an educational intervention was conducted in the ICUs at a tertiary care hospital, was conducted to assess the baseline knowledge of nursing staff about ventilator mechanics and respiratory physiology, and to identify the effectiveness of the module and teaching sessions on their knowledge score. A self-administered and structured questionnaire was used to collect data. A self-developed educational module was used as an intervention. Descriptive analysis was reported for demographic characteristics; paired t-test was conducted to identify difference in mean scores before and after intervention; and stratified analysis was also performed. Results: The knowledge scores significantly increased at 95% CI (P-value = 0.00) after conducting the intervention. The mean post-test score was significantly higher with a difference of 7.77 (P-value < 0.05). Conclusion: Nursing knowledge regarding ventilator mechanics becomes important to ensure safe and quality nursing care. Continuous professional nursing education is important to improve nursing knowledge and quality patientcare.

Vasil Penchev

The paper follows the track of a previous paper “Natural cybernetics of time” in relation to history in a research of the ways to be mathematized regardless of being a descriptive humanitarian science withal investigating unique events and thus rejecting any repeatability. The pathway of classical experimental science to be mathematized gradually and smoothly by more and more relevant mathematical models seems to be inapplicable. Anyway quantum mechanics suggests another pathway for mathematization; considering the historical reality as dual or “complimentary” to its model. The historical reality by itself can be seen as mathematical if one considers it in Hegel’s manner as a specific interpretation of the totality being in a permanent self-movement due to being just the totality, i.e. by means of the “speculative dialectics” of history, however realized as a theory both mathematical and empirical and thus falsifiable as by logical contradictions within itself as emprical discrepancies to facts. Not less, a Husserlian kind of “historical phenomenology” is possible along with Hegel’s historical dialectics sharing the postulate of the totality (and thus, that of transcendentalism). One would be to suggest the transcendental counterpart: an “eternal”, i.e. atemporal and aspatial history to the usual, descriptive temporal history, and equating the real course of history as with its alternative, actually happened branches of the regions of the world as with only imaginable, counterfactual histories. That universal and transcendental history is properly mathematical by itself, even in a neo-Pythagorean model. It is only represented on the temporal screen of the standard historiography as a discrete series of unique events. An analogy to the readings of the apparatus in quantum mechanics can be useful. Even more, that analogy is considered rigorously and logically as implied by the mathematical transcendental history and sharing with it the same quantity of information as an invariant to all possible alternative or counterfactual histories. One can involve the hypothetical external viewpoint to history (as if outside of history or from “God’s viewpoint to it), to which all alternative or counterfactual histories can be granted as a class of equivalence sharing the same information (i.e. the number choices, but realized in different sequence or adding redundant ones in each branch) being similar and even mathematically isomorphic to Feynman trajectories in quantum mechanics. Particularly, a fundamental law of mathematical history, the law of least choice of the real historical pathway is deducible from the same approach. Its counterpart in physics is the well-known and confirmed law of least action as far as the quantity of action corresponds equivocally to the quantity of information or that of number elementary historical choices.

Syahban Mada Ali, Nurul Hasanah

V. Romanov, А РомановВ., P. Taranenko et al.

The quantitative estimates of the flow rate (or density) of the flowing fluid obtained by the measurements using the industrial Coriolis flowmeters are made by using the laboratory experiments previously performed with the exemplary sensor. In this case we face two limitations, such as the unavailability of the facilities because of intense laboratory schedules and little time to upgrade the sensor oscillatory system. So we suggest using the virtual prototyping approaches as an alternative to the descriptive approaches. One of the fundamental problems of creating a virtual prototype of the Coriolis flowmeter is to separate the main parameter measured by the flowmeter (the phase shift) into the parts connected to the gyroscopic and dissipative forces. To solve this problem, we need to identify the dissipative forces model of the flowmeter oscillatory system. The article discusses the experimental results determining the dissipative properties of the mechanical oscillatory system of one of the commercially available Coriolis flowmeter samples. The algorithm identifying the model of the dissipative properties of the flowmeter oscillatory system is based on studying the nonlinearity degree of the envelope of the vibrogram of free damped oscillations. The experiments were carried out at the pouring stand of the Center for Experimental Mechanics of the South Ural State University, which allows controlling the speed and phase composition of the fluid flowing through the flowmeter. The article describes the processing algorithms for vibrograms of the damped oscillations, which make it possible to isolate the contribution into the dissipated energy from the dry (Coulomb model), the linear viscous (Rayleigh model) and quadratic viscous friction. The pronounced dependence of the vibrational system dissipation of the Coriolis flowmeter on the features of the fluid flow (velocity, mode: continuous, slug) was experimentally proven, the solutions of identifying the model of the dissipative forces are presented. The identification algorithm for the model of the dissipative properties of the flowmeter oscillatory system is based on studying the nonlinearity degree of the envelope of the vibrogram of the free damped oscillations. The use of the pouring stand made it possible to control the speed and phase composition of the fluid flowing through the flowmeter. The article describes the processing algorithms for the vibrograms of the damped oscillations by isolating the contribution into the dissipated energy from the dry (Coulomb model), linear viscous (Rayleigh model) and quadratic viscous friction. The pronounced dependence of the dissipation of the vibrational system of the Coriolis flowmeter on the features of the fluid flow (velocity, mode: continuous, slug) was experimentally proved, and the results of identifying the model of the dissipative forces are presented. The experiments included water acts as a fluid medium and air acts as a dispersed phase.

Wondwosen Tesfamichael

Rafael Bardera, Ángel Rodríguez-Sevillano, Adelaida García-Magariño

A wind tunnel tests campaign has been conducted to investigate the aerodynamic flow around a wing morphing to be used in a micro air vehicle. Non-intrusive whole field measurements were obtained by using PIV, in order to compare the velocity and turbulence intensity maps for the modified and the original version of an adaptive wing designed to be used in a micro air vehicle. Four sections and six angles of attack have been tested. Due to the low aspect ratio of the wing and the low Reynold number tested of 6.4 × 10⁴, the influence of the 3D effects has been proved to be important. At high angles of attack, the modified model prevented the detachment of the stream, increased the lift of the wing and reduced the turbulence intensity level on the upper surface of the airfoil and in the wake.

Mario A. Ciampini, Álvaro Cuevas, Paolo Mataloni et al.

We show an experimental procedure to certify the classical capacity for noisy qubit channels. The method makes use of a fixed bipartite entangled state, where the system qubit is sent to the channel input and the set of local measurements $σ_{x}\otimesσ_{x}$, $σ_{y}\otimesσ_{y}$ and $σ_{z}\otimesσ_{z}$ is performed at the channel output and the ancilla qubit, thus without resorting to full quantum process tomography. The witness to the classical capacity is then achieved by reconstructing sets of conditional probabilities, noise deconvolution, and classical optimization of the pertaining mutual information. The performance of the method to provide lower bounds to the classical capacity is tested by a two-photon polarization entangled state in Pauli channels and amplitude damping channels. The measured lower bounds to the channels are in high agreement with the simulated data, which take into account both the experimental entanglement fidelity $F=0.979\pm 0.011$ of the input state and the systematic experimental imperfections.