Hasil untuk "Descriptive and experimental mechanics"

Saeed Tourchi

This paper synthesizes nearly a decade of research on the coupled thermo-hydro-mechanical (THM) behavior of clays and argillaceous rocks. Drawing from experimental observations, numerical model development, and field-scale simulations, it presents a consolidated view of soil-structure interaction under thermal loading, desiccation cracking, and long-term excavation impacts. Key findings are drawn from constitutive modeling, in situ tests, and energy geostructure applications, offering a practical THM framework for nuclear waste repositories and climate-resilient infrastructure.

Nicola Andretta, Antonio Rossetti, Alarico Macor

The IC2OC transmission is a continuous transmission whose layout can change from simple IC to simple OC configuration and vice versa. It was proposed to cover a wider range of vehicle speeds without adding gears. Its sizing can lead to higher efficiencies than those of the IC and OC layouts. Therefore, this work deals with the sizing methodologies of this transmission. Two methodologies are proposed and discussed: the first uses the functional and constitutive equations of the transmission; the second is based on a mathematical programming problem. Both methodologies start from the choice of the full mechanical point speeds. The comparison between the two methods is carried out on the transmission of a commercially available 230 kW reach stacker. The comparison shows that the functional method, leaner and faster, can provide results very close to those obtained with the heavy and time-consuming optimization, provided that the values of the two full mechanical point speeds are the optimal ones for the two basic transmissions taken individually.

Annalisa Quaini, Omer San, Alessandro Veneziani et al.

Reduced-order models (ROMs) have achieved a lot of success in reducing the computational cost of traditional numerical methods across many disciplines. In fluid dynamics, ROMs have been successful in providing efficient and relatively accurate solutions for the numerical simulation of laminar flows. For convection-dominated (e.g., turbulent) flows, however, standard ROMs generally yield inaccurate results, usually affected by spurious oscillations. Thus, ROMs are usually equipped with numerical stabilization or closure models in order to account for the effect of the discarded modes. The literature on ROM closures and stabilizations is large and growing fast. In this paper, instead of reviewing all the ROM closures and stabilizations, we took a more modest step and focused on one particular type of ROM closure and stabilization that is inspired by large eddy simulation (LES), a classical strategy in computational fluid dynamics (CFD). These ROMs, which we call LES-ROMs, are extremely easy to implement, very efficient, and accurate. Indeed, LES-ROMs are modular and generally require minimal modifications to standard (“legacy”) ROM formulations. Furthermore, the computational overhead of these modifications is minimal. Finally, carefully tuned LES-ROMs can accurately capture the average physical quantities of interest in challenging convection-dominated flows in science and engineering applications. LES-ROMs are constructed by leveraging spatial filtering, which is the same principle used to build classical LES models. This ensures a modeling consistency between LES-ROMs and the approaches that generated the data used to train them. It also “bridges” two distinct research fields (LES and ROMs) that have been disconnected until now. This paper is a review of LES-ROMs, with a particular focus on the LES concepts and models that enable the construction of LES-inspired ROMs and the bridging of LES and reduced-order modeling. This paper starts with a description of a versatile LES strategy called evolve–filter–relax (EFR) that has been successfully used as a full-order method for both incompressible and compressible convection-dominated flows. We present evidence of this success. We then show how the EFR strategy, and spatial filtering in general, can be leveraged to construct LES-ROMs (e.g., EFR-ROM). Several applications of LES-ROMs to the numerical simulation of incompressible and compressible convection-dominated flows are presented. Finally, we draw conclusions and outline several research directions and open questions in LES-ROM development. While we do not claim this review to be comprehensive, we certainly hope it serves as a brief and friendly introduction to this exciting research area, which we believe has a lot of potential in the practical numerical simulation of convection-dominated flows in science, engineering, and medicine.

Hong Yuan, Chang-Pu Sun

To address the observation of Max Born (M. Born 1969) that the Newton's second law can emerge from a purely statistical perspective, we derive the evolution equation about the statistical distribution for dilute gas based solely on statistical principles, without invoking Newtonian mechanics, and then obtain the equations of motion for individual particles. Newton's second law for a single particle naturally emerges when the distribution reaches equilibrium. We demonstrate that the magnitude of an external force, traditionally measured by particle acceleration, can be understood as a measure of distribution inhomogeneity. We further show that the entropic force (utilized in current gravity studies) is equivalent to the statistical force and under non-equilibrium conditions, a deviation arises between the entropic force and the Newtonian force. This framework offers a novel perspective distinct from classical Newtonian mechanics and broadens the potential scope of its application.

Daniel Costero, Federico Piscaglia

In computations of unsteady flow problems by the arbitrary Lagrangian–Eulerian (ALE) method, the introduction of the grid velocity in the transport terms of the governing equations is not a sufficient condition for conservativeness if topology changes in the dynamic mesh are present and the number of mesh cells changes. We discuss an extension to second-order time differencing schemes (Implicit Euler and Crank–Nicolson) in the finite volume framework, to achieve second-order time-accuracy of the solution. Numerical experiments are given to illustrate the effectiveness of the presented method.

Dariya Kalyuzhnaya, Evgeniy Sokolov, Anastasia Vasilyeva et al.

The formation of droplets in microchannels (droplet microfluidics) has a large number of applications, such as in micro-dosing and gas meters. This paper considers the dynamics of direct and inverse emulsions based on water, polydimethylsiloxane, and synthetic and mineral oil in microfluidic chips based on two technologies: glass–parafilm–glass sandwich structures and removable scaffold in a silicone compound. It is shown that wettability, roughness and chip wall material; channel thickness; magnetic fluid flow rate; and magnetic field strength affect the size of emulsion droplets formed in a microfluidic chip. The addition of another mechanism for regulating the hydrodynamics of emulsions using a magnetic field opens up new possibilities for the development of promising devices.

Arash Bagheri, Keith Alexander

Background: The aging process contributes to the decline in physical capacity that leads to loss of independence in performing life activities. Immobility and instability are the most significant predictors and indicators of physical disability and dependence. As a result, a variety of assistive devices exist to address immobility and instability in older adults, including walkers, canes, crutches, wheelchairs and handrails. Sit-to-stand (STS) transitions are the most common transitions in daily mobility activities. The ability to perform STS transitions successfully is therefore one of the most important activities to focus attention on. As a result of physical deterioration, older adults will sooner or later be faced with their physical limitations, and in particular, will not be able to provide enough torque at critical body joints to make the STS transition. Aim: This paper suggests employing two-arm assistance using two handles located symmetrically in the body’s sagittal plane. During the aging process, people are faced with varying levels of muscle deterioration and body constraints and consequently require different levels of assistance to complete the transition successfully. This paper aims to develop a tool to find the optimum handle location for people based on their body constraints to reduce knee torque (identified as the critical joint in the STS transition). These findings are also used to measure the effects of assistive device handle position on the biomechanics of the two-arm assisted STS transition. Methods: For this purpose, a theoretical tool was developed by integrating human body kinetics with a multi-objective genetic algorithm to find the optimum hand force required at the seat-off point for a set of potential handle locations. The tool was set to achieve the minimum knee torque within the defined body constraints and assumptions. In line with the physics of the STS transition, the “seat-off point”, when subjects lose their seat support, was chosen as the most challenging point of the task. This was coupled with the “nose over toes” posture recommended to older adults by occupational therapists. Results and Discussion: The schematic of the developed tool shows that the best handle locations requiring the minimum torques at the body joints are positioned in handle zone 2, where the handles are placed vertically above the knee and below the hip joints and horizontally located ahead of the hip and behind the knee joints. Within this handle zone, both components of the hand forces (vertical downward and horizontal backward) provide assisting torque to all the body joints and consequently reduce the torques required at body joints.

Ngo Minh Tuan, Tran The Long, Tran Bao Ngoc

Lubrication and cooling in hard machining is an urgent and growing concern. The use of a suitable cooling lubrication condition is a crucial factor and has a great influence on the machining efficiency and the machined surface quality in hard machining. Among the proposed technological solutions, minimum quantity lubrication (MQL) using nano-cutting oils is a novel solution and its effectiveness has been proven for hard turning. This work aims to investigate the influence of MQL technological parameters using MoS₂ nano-cutting oil including nanoparticle concentration, air pressure, and air flow rate on surface roughness and the resultant cutting force in hard turning using CBN inserts. Box-Behnken optimal experimental design and ANOVA analysis were used to study the influence of the input parameters and determine the optimal values. The results present the influence of the survey parameters and provide technological guides for specific objective functions for further sustainable studies on MQL hard turning using nano-cutting oil.

Pedro Vayssière Brandão, Michele Celli, Antonio Barletta et al.

The present work analyzes the thermal instability of mixed convection in a horizontal porous channel that is saturated by a shear-thinning fluid following Ellis’ rheology. The fluid layer is heated from below by a constant heat flux and cooled from above by the same heat flux. The instability of such a system is investigated by means of a small-disturbances analysis and the resulting eigenvalue problem is solved numerically by means of a shooting method. It is demonstrated that the most unstable modes on the instability threshold are those with infinite wavelength and an analytical expression for such conditions is derived from an asymptotic analysis. Results show that the non-Newtonian character of the fluid has a destabilizing role.

Christophe Bouvet, B. Vieille, J-D. Pujols-Gonzalez

This study was aimed at investigating the influence of initial notch orientation on the translaminar fracture of woven-ply hybrid fibers reinforced thermoplastic polyether ether ketone (PEEK) laminates. This work is based on the experimental characterization of translaminar fracture of Single-edge-notch bending (SENB) specimens with two initial notches (0{\textdegree} and 45{\textdegree}). Such geometry results in a complex stress state within the laminates plies as well as simultaneous tension/compression failures. A digital image analysis technique has been implemented to monitor the crack initiation and growth during mechanical loading. To better understand the role played by the initial notch orientation as well as the plies orientation contribution to fracture behavior, a specific Finite Element mesoscale modelling was built to account for the deformation mechanisms (namely local plasticity) and the different damage behaviours (fiber breakage in tension and compression, kinking/crushing in compression, delamination) occurring within the plies of quasi-isotropic laminates. Linear elastic fracture mechanics concepts have been applied to quantify the critical translaminar fracture toughness (about 40 kJ/m${}^2$ in both cases). Finally, the G-R curves were computed from the compliance method to investigate the influence of the initial notch orientation on the evolution of the fracture energy.

Nadia Kianvashrad, Doyle Knight

The recent revival of interest in developing new hypersonic vehicles brings attention to the need for accurate prediction of hypersonic flows by computational methods. One of the challenges is prediction of aerothermodynamic loading over the surface of the vehicles. Reynolds Average Navier-Stokes (RANS) methods have not shown consistent accuracy in prediction of such flows. Therefore, new methods including Large Eddy Simulations (LES) should be investigated. In this paper, the LES method is used for prediction of the boundary layer over a flat plate. A new recycling-rescaling method is tested. The method uses total enthalpy and static pressure along with the velocity components to produce the best results for the Law of the Wall, turbulent statistics and turbulent Prandtl number.

Matthew Aultman, Rodrigo Auza-Gutierrez, Kevin Disotell et al.

Lattice Boltzmann method (LBM) simulations were performed to capture the long-period dynamics within the wake of a realistic DrivAer fastback model with stationary and rotating wheels. The simulations showed that the wake developed as a low-pressure torus regardless of whether the wheels were rotating. This torus shrank in size on the base in the case of rotating wheels, leading to a reduction in the low-pressure footprint on the base, and consequently a <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mn>7</mn><mo>%</mo></mrow></semantics></math></inline-formula> decrease in the total vehicle drag in comparison to the stationary wheels case. Furthermore, the lateral vortex shedding experienced a long-period switching associated with the bi-stability in both the stationary and rotating wheels cases. This bi-stability contributed to low-frequency side force oscillations (<1 Hz) in alignment with the peak motion-sickness-inducing frequency (0.2 Hz).

Gino Perrotta, Frank E. Fish, Danielle S. Adams et al.

California sea lions are among the most agile of swimming mammals. Most marine mammals swim with their hind appendages—flippers or flukes, depending on the species—whereas sea lions use their foreflippers for propulsion and maneuvering. The sea lion’s propulsive stroke generates thrust by forming a jet between the flippers and the body and by dragging a starting vortex along the suction side of the flipper. Prior experiments using robotic flippers have shown these mechanisms to be possible, but no flow measurements around live sea lions previously existed with which to compare. In this study, the flow structures around swimming sea lions were observed using an adaptation of particle imaging velocimetry. To accommodate the animals, it was necessary to use bubbles as seed particles and sunlight for illumination. Three trained adult California sea lions were guided to swim through an approximately planar sheet of bubbles in a total of 173 repetitions. The captured videos were used to calculate bubble velocities, which were processed to isolate and inspect the flow velocities caused by the swimming sea lion. The methodology will be discussed, and measured flow velocities will be presented.

Kevin Leung, Noah B. Schorr, Matthew Mayer et al.

Graphite fluoride (CFx) cathodes coupled with lithium anodes yield one of the highest theoretical energy densities (>860 Wh/g) among primary batteries. In practice, the observed discharge voltage (~2.5 V) is significantly lower than thermodynamic limits (>4.5 V), the discharge rate is low, and so far Li/CFx has only been used in primary batteries. Understanding the discharge mechanism at atomic length scales will improve practical CFx energy density, rate capability, and rechargeability. So far, purely experimental techniques have not identified the correct discharge mechanism or explained the discharge voltage. We apply Density Functional Theory calculations to demonstrate that a CFx-edge propagation discharge mechanism based on lithium insertion at the CF/C boundary in partially discharged CFx exhibits a voltage range of 2.5 to 2.9 V -- depending on whether solvent molecules are involved. The voltages and solvent dependence agrees with our discharge and galvanostatic intermittent titration technique measurements. The predicted discharge kinetics are consistent with CFx operations. Finally, we predict Li/CFx rechargeability under the application of high potentials, along a charging pathway different from that of discharge. Our work represents a general, quasi-kinetic framework to understand the discharge of conversion cathodes, circumventing the widely used phase diagram approach which most likely does not apply to Li/CFx because equilibrium conditions are not attained in this system.

Hiroki Oshiyama, Naokazu Shibata, Sei Suzuki

We study the Kibble-Zurek mechanism in the transverse Ising chain coupled to a dissipative boson bath, making use of a new numerical method with the infinite time evolving block decimation combined with the discrete-time path integral. We first show the ground-state phase diagram and confirm that a quantum phase transition takes place in the presence of the system-bath coupling. Then we present the time dependence of the energy expectation value of the spin Hamiltonian and the scaling of the kink density with respect to the time period over which the spin Hamiltonian crosses a quantum phase transition. The energy of spins starts to grow from the energy at the ground state of the full system near a quantum phase transition. The kink density decays as a power law with respect to the time period. These results confirm that the Kibble-Zurek mechanism happens. We discuss the exponent for the decay of the kink density in comparison with a theoretical result with the quantum Monte-Carlo simulation. A comparison to an experimental study is also briefly mentioned.

Victor Buendía, Pablo Villegas, Serena di Santo et al.

The cortex exhibits self-sustained highly-irregular activity even under resting conditions, whose origin and function need to be fully understood. It is believed that this can be described as an "asynchronous state" stemming from the balance between excitation and inhibition, with important consequences for information-processing, though a competing hypothesis claims it stems from critical dynamics. By analyzing a parsimonious neural-network model with excitatory and inhibitory interactions, we elucidate a noise-induced mechanism called "Jensen's force" responsible for the emergence of a novel phase of arbitrarily-low but self-sustained activity, which reproduces all the experimental features of asynchronous states. The simplicity of our framework allows for a deep understanding of asynchronous states from a broad statistical-mechanics perspective and of the phase transitions to other standard phases it exhibits, opening the door to reconcile, asynchronous-state and critical-state hypotheses. We argue that Jensen's forces are measurable experimentally and might be relevant in contexts beyond neuroscience.

Tran Thi Thom, Nguyen Dinh Kien

Free vibration analysis of two-directional functionally graded material (2-D FGM) beams in thermal environment based on a new third-order shear deformation theory is presented. The material properties are assumed to be graded in both the thickness and longitudinal directions by a power law distribution, and they are considered to be temperature-dependent. Equations of motion, in which the shear rotation rather than the cross-sectional rotation is considered to be an independent variable, are constructed from Hamilton's principle. A finite element formulation is derived and employed to compute the vibration characteristics of the beams. The numerical results reveal that the developed formulation is accurate, and it is capable to give accurate natural frequencies by using a small number of elements. A parametric study is carried out to highlight the effects of material composition, temperature rise on the vibration characteristics of the beams.

A. A. Gubaidullin, N. G. Musakaev, Duong Ngoc Hai et al.

In this work the mathematical model is constructed and the features of the injection of warm carbon dioxide (with the temperature higher than the initial reservoir temperature) into the porous reservoir initially saturated with methane gas and water are investigated. Self-similar solutions of the one-dimensional problem describing the distributions of the main parameters in the reservoir are constructed. The effect of the parameters of the injected carbon dioxide and the reservoir on the intensity of the CO2hydrate formation is analyzed.

Li-Chun Zhang

We examine the conditions under which descriptive inference can be based directly on the observed distribution in a non-probability sample, under both the super-population and quasi-randomisation modelling approaches. Review of existing estimation methods reveals that the traditional formulation of these conditions may be inadequate due to potential issues of under-coverage or heterogeneous mean beyond the assumed model. We formulate unifying conditions that are applicable to both type of modelling approaches. The difficulties of empirically validating the required conditions are discussed, as well as valid inference approaches using supplementary probability sampling. The key message is that probability sampling may still be necessary in some situations, in order to ensure the validity of descriptive inference, but it can be much less resource-demanding provided the presence of a big non-probability sample.

Anush Tserunyan

We give a descriptive construction of trees for multi-ended graphs, which yields yet another proof of Stallings' theorem on ends of groups. Even though our proof is, in principle, not very different from already existing proofs and it draws ideas from a paper of Krön, it is written in a way that easily adapts to the setting of countable Borel equivalence relations, leading to a free decomposition result and a sufficient condition for treeability.