Hasil untuk "Descriptive and experimental mechanics"

James R. Jowsey, G. Gregory Haff, Paul Comfort et al.

Background: CrossFit^® aims to be equitable between both males and female athletes, supporting equal representation and equal prize money at international events. However, to date, limited information is known on CrossFit^® athletes’ performance in the countermovement jump (CMJ), countermovement rebound jump (CMR-J), and isometric mid-thigh pull (IMTP) when assessed using force plates, and if there are any differences between sexes. Therefore, the purpose of the present study was to observe whether any sex-based differences and relationships exist between performance within these assessments. Methods: A total of CrossFit athletes (43 male = 32.8 ± 9.0 years; height 1.78 ± 0.06 m; mass = 92.4 ± 10.6 kg; and 31 female = 31.0 ± 7.6 years, height = 1.64 ± 0.05 m; mass = 68.8 ± 6.0 kg) completed three trials of CMJ, CMR-J and IMTP using portable dual-system force-plate sampling at 1000 Hz. Results: Moderate–large relationships were observed between CMJ, CMR-J and IMTP outcome measures (<i>r</i> = 0.396–0.809, <i>p</i> < 0.001). Males demonstrated small to moderately greater performance outcomes than females for CMJ height (males = 0.35 ± 0.08 m; females 0.30 ± 0.06 m, <i>d</i> = 0.73), CMR-J height (males = 0.32 ± 0.08 m; females = 0.30 ± 0.06 m, <i>d</i> = 0.39) and IMTP peak net force (males = 30.62 ± 10.01 N·kg⁻¹; females = 27.49 ± 6.44 N·kg⁻¹, <i>d</i> = 0.29). Conclusions: Maximal relative strength in CrossFit^® athletes should be seen as imperative in both male and female athletes due to the meaningful relationship in ballistic and plyometric ability. Moreover, previous relationships with CrossFit^® performance and the injury risk reduction benefits of improving strength provide further support. The descriptive data presented could be used by CrossFit^® coaches to assess and compare the current performance of their own athletes in a battery of tests examining CMJ, CMR-J and IMTP, while also facilitating decisions upon prescription within training and competition.

Haozhe Jin, Haotian Xu, Jiongming Zhang et al.

High-performance control valves are essential components in power plants. High-parameter control valves are specialized valves for controlling high-pressure, high-flow, high-temperature, and highly corrosive media. Control valve performance is critical for the stable operation of power plants. The multi-stage counter-flow passage is a common structure in pressure-reducing control valves, effectively mitigating cavitation and erosion on the valve walls. However, in practice, vibration issues in multi-stage passage valves are particularly pronounced. This study employs FSI (fluid–structure interaction) to simulate the vibration characteristics of multi-stage passages. Flow field data for the multi-stage passage are obtained through FLUENT software. A time-frequency analysis of the lift coefficient in the multi-stage passage flow field was performed. The vibration characteristics of the valve core’s inlet and outlet surfaces were studied using Transient Structural software. The results show that when high-pressure fluid passes through the valve core’s passage, it undergoes buffering, steering, and rotating motions, leading to a gradual pressure drop and generating resistance and lift. These phenomena are primarily caused by vortex shedding in the flow field, with the dominant frequency observed to be approximately 5400 Hz. Additionally, as the valve core progresses through the P1 phase at the inlet and the P2 phase at the outlet, the vibration intensity gradually decreases, reaching a minimum in the sixth phase, before increasing and peaking in the final stage. Analysis of the flow field characteristics within the valve core passage reveals the significant impact of vortex shedding on the valve core’s vibration and lift. Phase analysis of the valve core’s vibration intensity further clarifies its behavioral changes at different operational stages. These findings help optimize the design of multi-stage buffering valve cores, improving their performance and stability.

E. Poisson

Deepa Raj Mopuru, Nishanth Dongari, Srihari Payyavula

Micro-nozzles are essential for enabling precise satellite attitude control and orbital maneuvers. Accurate prediction of performance parameters, including thrust and specific impulse, is critical, necessitating careful design of these nozzles. Given the high Knudsen numbers associated with micro-nozzle flows, rarefied gas dynamics often dominate, and conventional computational fluid dynamics (CFD) methods fail to capture accurate flow expansion behavior. The Direct Simulation Monte Carlo (DSMC) method, developed by Bird, is widely used for modeling rarefied flows; however, it has been primarily implemented on platforms like OpenFOAM and FORTRAN, with limited exploration in MATLAB. This study presents the development of a viscosity-based DSMC (μDSMC) simulation framework in MATLAB for analyzing rarefied gas expansion through micro-nozzles. Key boundary conditions, including upstream and downstream pressure conditions and thermal wall treatments with diffuse reflection, are incorporated into the code. The μDSMC results are validated against traditional DSMC outcomes, showing strong agreement. Grid convergence studies indicate that the radial grid size must be less than one-third of the mean free path, with a more relaxed requirement on axial grid size. Flow characteristics within micro-nozzles are evaluated across varying ambient pressures and gas species in terms of the back pressure ratio, effective exit flow ratio, and exit flow velocity. Studies indicated that a minimum back pressure ratio is required, beyond which the effective nozzle flow expansion is achieved. Parametric analysis further suggests that gases with lower molecular weights are preferable for achieving optimal expansion in micro-nozzles under low ambient pressures.

J. D. Clayton

A continuum mechanical theory with foundations in generalized Finsler geometry describes the complex anisotropic behavior of skin. A fiber bundle approach, encompassing total spaces with assigned linear and nonlinear connections, geometrically characterizes evolving configurations of a deformable body with the microstructure. An internal state vector is introduced on each configuration, describing subscale physics. A generalized Finsler metric depends on the position and the state vector, where the latter dependence allows for both the direction (i.e., as in Finsler geometry) and magnitude. Equilibrium equations are derived using a variational method, extending concepts of finite-strain hyperelasticity coupled to phase-field mechanics to generalized Finsler space. For application to skin tearing, state vector components represent microscopic damage processes (e.g., fiber rearrangements and ruptures) in different directions with respect to intrinsic orientations (e.g., parallel or perpendicular to Langer’s lines). Nonlinear potentials, motivated from soft-tissue mechanics and phase-field fracture theories, are assigned with orthotropic material symmetry pertinent to properties of skin. Governing equations are derived for one- and two-dimensional base manifolds. Analytical solutions capture experimental force-stretch data, toughness, and observations on evolving microstructure, in a more geometrically and physically descriptive way than prior phenomenological models.

H. S. Gandhi

The application of stainless-steel wire is still the "standard of care" and is believed to be the "gold standard" after trans-sternal thoracotomy. To overcome postoperative instability and surgical wound infection there had been the development of a variety of circumferential, Hemi-circular, and surface on-lay implant designs to enhance bone healing of the sternum particularly in compromised patients. This fundamental descriptive theoretical research study probes into biology and effects of mechanical environment on fracture healing in general and various types of ossifications that may occur during healing of the sternum. Following surgical anatomy of the sternum, the biology of fracture (osteotomy) healing, an update on the conventional and newer biomaterials, and role of 3D printing in custom additive manufacturing of the surgical implants have been discussed in detail. There is discussion on design principles and structural optimization in-line with patient-specific and patient-appropriate osteosynthesis. In support, the Teorija Rezhenija Izobretatelskikh Zadatch engineering principles have been applied to improve implant design in the face of the current strategies to relieve some of the recalcitrant deficiencies underlying the mechanics of the most favored implant for the reconstruction of the sternum. Several scientific domains of the engineering design principles and fracture healing processes have been connected leading to four newly conceptualized prototype designs for the reconstruction of the sternum. In conclusion, despite increased knowledge of the fracture healing process there are limited means to mitigate the adverse mechanical environment experienced by the healing sternum. There are uncertainties how to transfer the well-known facts of tissue strain during healing from the experimental platform to the operating table at the time of fracture fixation and reconstruction of the sternum for its optimal healing.

Maria Sabrina Souza, Andrews Souza, Violeta Carvalho et al.

Intracranial aneurysms (IA) are dilations of the cerebral arteries and, in most cases, have no symptoms. However, it is a very serious pathology, with a high mortality rate after rupture. Several studies have been focused only on the hemodynamics of the flow within the IA. However, besides the effect of the flow, the development and rupture of the IA are also associated with a combination of other factors such as the wall mechanical behavior. Thus, the objective of this work was to analyze, in addition to the flow behavior, the biomechanical behavior of the aneurysm wall. For this, CFD simulations were performed for different Reynolds numbers (1, 100, 500 and 1000) and for two different rheological models (Newtonian and Carreau). Subsequently, the pressure values of the fluid simulations were exported to the structural simulations in order to qualitatively observe the deformations, strains, normal stresses and shear stress generated in the channel wall. For the structural simulations, a hyperelastic constitutive model (5-parameter Mooney–Rivlin) was used. The results show that with the increase in the Reynolds number (Re), the recirculation phenomenon is more pronounced, which is not seen for Re = 1. The higher the Re, the higher the strain, displacement, normal and shear stresses values.

Minori Shirota, Masaki Kato, Ai Ishio

The rim breakup of an impacting drop is experimentally investigated by comparing the impacts on superheated and superhydrophobic surfaces. The objective of the present study is to experimentally examine whether the <i>Bo</i> = 1 criteria holds for the rim breakups of drops impacting on the surfaces. A transparent sapphire plate was heated to achieve the Leidenfrost impact, which enables us to observe with a high-speed camera from below. The characteristics of the rim breakup were evaluated quantitatively using a particle tracking velocimetry method for both the rim and the drops generated. As a result, we clarified that <i>Bo</i> of the rim increases in the spreading phase and marks the highest value of 0.5 on a superheated surface, which is smaller than that on a pillar, where <i>Bo</i> ≈ 1. On a superhydrophobic surface, the highest <i>Bo</i> was 1.2, which is smaller than that on a wettable solid surface, 2.5, but close to the value on a pillar. We also revealed that diameters of generated drops collapse on a master curve when plotted as a function of pinch-off time for both the impacts on superheated and superhydrophobic surfaces.

Gabriel Nastac, Abdelkader Frendi

Characterization of unsteady loads is critical for the development of control systems for next-generation air vehicles. Both Direct Numerical Simulation (DNS) and Large Eddy Simulation (LES) methods are prohibitively expensive, and existing Reynolds-Averaged Navier-Stokes (RANS) approaches have been shown to be inadequate in predicting both mean and unsteady loads. In recent years, scale-resolving methods, such as Partially Averaged Navier-Stokes (PANS) and Detached Eddy Simulation (DES), have been gaining acceptance and filling the gap between RANS and LES. In this study, we focus on a new variant of the PANS method, namely blended PANS or BPANS, which was shown to perform well in the incompressible regime for both wall-bounded and free shear flows. In this paper, we extend BPANS to compressible supersonic flows by adding a compressibility correction, leading to a new model called BPANS CC. The new model is tested using a well-known supersonic mixing layer case, and the results show good agreement with experimental data. The model is then used on a complex supersonic retropropulsion case and the results are in good agreement with experimental data.

Jendrian Riedel

M. Pellegrini, G. Hedenstierna, A. Larsson et al.

Background Potentially harmful lung overstretch can follow intraparenchymal gas redistribution during mechanical ventilation. We hypothesized that inspiratory efforts characterizing spontaneous breathing, positive end-expiratory pressure (PEEP), and high inspiratory resistances influence inspiratory intraparenchymal gas redistribution. Methods This was an experimental study conducted on a swine model of mild acute respiratory distress syndrome. Dynamic computed tomography and respiratory mechanics were simultaneously acquired at different PEEP levels and external resistances, during both spontaneous breathing and controlled mechanical ventilation. Images were collected at two cranial–caudal levels. Delta-volume images (ΔVOLs) were obtained subtracting pairs of consecutive inspiratory images. The first three ΔVOLs, acquired for each analyzed breath, were used for the analysis of inspiratory pendelluft defined as intraparenchymal gas redistribution before the start of inspiratory flow at the airway opening. The following ΔVOLs were used for the analysis of gas redistribution during ongoing inspiratory flow at the airway opening. Results During the first flow-independent phase of inspiration, the pendelluft of gas was observed only during spontaneous breathing and along the cranial-to-caudal and nondependent-to-dependent directions. The pendelluft was reduced by high PEEP (p < 0.04 comparing PEEP 15 and PEEP 0 cm H2O) and low external resistances (p < 0.04 comparing high and low external resistance). During the flow-dependent phase of inspiration, two patterns were identified: (1) gas displacing characterized by large gas redistribution areas; (2) gas scattering characterized by small, numerous areas of gas redistribution. Gas displacing was observed at low PEEP, high external resistances, and it characterized controlled mechanical ventilation (p < 0.01, comparing high and low PEEP during controlled mechanical ventilation). Conclusions Low PEEP and high external resistances favored inspiratory pendelluft. During the flow-dependent phase of the inspiration, controlled mechanical ventilation and low PEEP and high external resistances favored larger phenomena of intraparenchymal gas redistribution (gas displacing) endangering lung stability.

J. Retamal, L. Damiani, R. Basoalto et al.

Using protective mechanical ventilation strategies with low tidal volume is usually accompanied by an increment of respiratory rate to maintain adequate alveolar ventilation. However, there is no robust data that support the safety of a high respiratory rate concerning ventilator‐induced lung injury. Several experimental animal studies have explored the effects of respiratory rate over lung physiology, using a wide range of frequencies and different models. Clinical evidence is scarce and restricted to the physiological impact of increased respiratory rate. Undoubtedly, the respiratory rate can influence respiratory mechanics in various ways as a factor of multiplication of the power of ventilation, and gas exchange, and also on alveolar dynamics. In this narrative review, we present our point of view over the main experimental and clinical evidence available regarding the effect of respiratory rate on ventilator‐induced lung injury development.

M. Mohammadi, Z. Khoshneshin, N. Mohammadhasani

Antonino Drago

I review the various algebraic foundations of quantum mechanics. They have been suggested since the birth of this theory till up to last year. They are the following ones: Heisenberg-Born-Jordan (1925), Weyl (1928), Dirac (1930), von Neumann (1936), Segal (1947), T.F. Jordan (1986), Morchio and Strocchi (2009) and Buchholz and Fregenhagen (2019). Three cases are stressed: 1) the misinterpretation of Dirac foundation; 2) von Neumann conversion from the analytic approach of Hilbert space to the algebraic approach of the rings of operators; 3) the recent foundation of quantum mechanics upon the algebra of perturbation Lagrangians. Moreover, historical considerations on the go-and-stop path performed by the algebraic approach in the history of QM are offered. The level of formalism has increased from the mere introduction of matrices till up to group theory and C*-algebras. But there was no progress in approaching closer the foundations of physics; therefore the problem of discovering an algebraic formulation of QM organized as a problem-based theory and making use of no more than constructive mathematics is open.

R. Calvert, M. L. McAllister, C. Whittaker et al.

Periodic water waves generate Stokes drift as manifest from the orbits of Lagrangian particles not fully closing. Stokes drift can contribute to the transport of floating marine litter, including plastic. Previously, marine litter objects have been considered to be perfect Lagrangian tracers, travelling with the Stokes drift of the waves. However, floating marine litter objects have large ranges of sizes and densities, which potentially result in different rates of transport by waves due to the non-Lagrangian behaviour of the objects. Through a combination of theory and experiments for idealised spherical objects in deep-water waves, we show that different objects are transported at different rates depending on their size and density, and that larger buoyant objects can have increased drift compared with Lagrangian tracers. We show that the mechanism for the increased drift observed in our experiments comprises the variable submergence and the corresponding dynamic buoyancy force components in a direction perpendicular to the local water surface. This leads to an amplification of the drift of these objects compared to the Stokes drift when averaged over the wave cycle. Using an expansion in wave steepness, we derive a closed-form approximation for this increased drift, which can be included in ocean-scale models of marine litter transport.

Lucie Bordois, Jonas Nycander, Alexandre Paci

We hereby present two different spectral methods for calculating the density anomaly and the vertical energy flux from synthetic Schlieren data, for a periodic field of linear internal waves (IW) in a density-stratified fluid with a uniform buoyancy frequency. The two approaches operate under different assumptions. The first method (hereafter Mxzt) relies on the assumption of a perfectly periodic IW field in the three dimensions (<i>x</i>, <i>z</i>, <i>t</i>), whereas the second method (hereafter MxtUp) assumes that the IW field is periodic in x and t and composed solely of wave components with downward phase velocity. The two methods have been applied to synthetic Schlieren data collected in the CNRM large stratified water flume. Both methods succeed in reconstructing the density anomaly field. We identify and quantify the source of errors of both methods. A new method mixing the two approaches and combining their respective advantages is then proposed for the upward energy flux. The work presented in this article opens new perspectives for density and energy flux estimates from laboratory experiments data.

Hongliang Qi, Junxing Zheng, Chenguang Zhang

This research explores the effects of different spans of two columns of tandem piers on the characteristics of x-velocity near the river bed based on computational fluid dynamics (CFD) simulations. With a span shorter than 27.5D (D is the diameter of piers), the shape and the lateral range of the x-velocity increases with the increase of distance downwards the x-direction. For the area between the tandem piers and the wall, the <i>V_Ri/V_R</i>₁ (the ratio of the x-velocity at the <i>i</i>-th row to the x-velocity of the first row in each model) near the wall increases up to 1.26. For the area between the two columns of tandem piers, the profile of <i>V_Ri/V_R</i>₁ changes from a &#8220;&cap;-shape&#8221; to an &#8220;M-shape&#8221; in each model. <i>R_AVC</i> (average velocity change ratio) of different spans increases gradually and tends to be stable with the increases of the span. The largest <i>R_AVC</i> is about &#8722;17.66% with a span of 0.52 m. The <i>R_MV</i> (the ratio of the maximum x-velocity among piers in each row in different models to the maximum x-velocity of the two piers arranged side by side) of piers in the first row of different models is around 0.95. The <i>R_MV</i> becomes 0.82 at the second pier in each model when the span is shorter than 27.5D, and increases to 0.91 if the span is longer than 27.5D. If the span is longer than 27.5D, the <i>R_MV</i> of different piers are close to each other from the 2nd pier to the last one.

Emily M. Stump, Courtney L. White, Gina Passante et al.

Measurement uncertainty and experimental error are important concepts taught in undergraduate physics laboratories. Although student ideas about error and uncertainty in introductory classical mechanics lab experiments have been studied extensively, there is relatively limited research on student thinking about experimental measurement uncertainty in quantum mechanics. In this work, we used semi-structured interviews to study advanced physics students' interpretations of fictitious data distributions from two common undergraduate laboratory experiments in quantum mechanics and one in classical mechanics. To analyze these interpretations, we developed a coding scheme that classifies student responses based on what factors they believe create uncertainty and differentiates between different types of uncertainty (e.g. imprecision, inaccuracy). We found that participants in our study expressed a variety of ideas about measurement uncertainty that varied with the context (classical/quantum) and the type of uncertainty.

Lorenzo Fusi, Angiolo Farina, Fabio Rosso et al.

In this paper, we study the pressure-driven thin film flow of an inhomogeneous incompressible fluid in which its viscosity depends on the density. The constitutive response of this class of fluids can be derived using a thermodynamical framework put into place to describe the dissipative response of materials where the materials&#8217; stored energy depends on the gradient of the density (Mechanics of Materials, 2006, 38, pp. 233&#8315;242). Assuming a small aspect ratio for the channel, we use the lubrication approximation and focus on the leading order problem. We show the mathematical problem reduce to a nonlinear first order partial differential equation (PDE) for the density in which the coefficients are integral operators. The problem is solved numerically and plots that describe the evolution of the density in the fluid domain are displayed. We also show that it was possible to determine an analytical solution of the problem when the boundary data are small perturbations of the homogeneous case. Finally, we use such an analytical solution to validate the numerical scheme.

Vuong Thi My Hanh, Le Hoai Chau, Vu Lam Dong et al.

Numerical finite element simulations on the homogenization problem for large samples of particular 2D hexagonal-shape-geometry random orientation aggregates from the base crystals of orthorhombic symmetry have been performed. At sufficiently large random-aggregate samples, the scatter intervals of the macroscopic 2D bulk and shear elastic moduli converge toward the Voigt-Reuss-Hill bounds, and then our recently constructed theoretical estimates, which have been specified for the aggregates.