Symmetric Force Research Articles

Simulation analysis of the internal flow field in single screw compressor using local re-meshing method

Abstract The single screw compressor (SSC) is considered an excellent competitor to the twin screw compressor due to its symmetrical structure and balanced gas forces on the screw rotor. To enhance the performance of SSC, it is crucial to have a thorough understanding of the internal flow field, particularly in the leakage channels. Nevertheless, the vertical relationship between the star wheel axis and the screw axis leads to mesh distortion, which presents technical challenges for mesh division in CFD simulations. In this paper, the method of local re-meshing is employed to simulate the comprehensive flow field using the Forte software. The mesh is regenerated near the motion boundary, while the mesh in the remaining areas remains unchanged. The pressure and temperature distribution of the internal flow field of the compressor are obtained, as well as its variation during operation. The results indicate a noticeable pressure gradient change in the leakage gap. The pressure and temperature of gas gradually increase along the axis direction of the screw, reaching the maximum value in the exhaust channel. The research can provide support for the future optimization design of the SSC.

α effect in three-dimensional vortex of conducting rotating liquid.

We study one-point statistics of helical turbulent pulsations in the background of a three-dimensional large-scale vortex in a rotating fluid. Assuming that the helical flow is created by a statistically axially symmetric random force with broken mirror symmetry, we analytically calculate the velocity-vorticity mean including its magnitude and the anisotropy. For electrically conducting liquid, we examine the α-effect in the system. The found elements of the α-matrix strongly depend on the relation between Rossby Ro and magnetic Prandtl Pr_{m} numbers in the considered region Ro≪1,Pr_{m}≪1. We establish a criterion for the numbers when the α-effect leads to instability of large-scale magnetic field.

Jet mixing optimization using a flexible nozzle, distributed actuators, and machine learning

In this paper, we introduce the first jet nozzle allowing simultaneous shape variation and distributed active control, termed “Smart Nozzle” in the sequel. Our Smart Nozzle manipulates the jet with an adjustable flexible shape via 12 equidistant stepper motors and 12 equidistantly placed inward-pointing minijets. The mixing performance is evaluated with a 7 × 7 array of Pitot tubes at the end of the potential core. The experimental investigation is carried out in three steps. First, we perform an aerodynamic characterization of the unforced round jet flow. Second, we investigate the mixing performance under five representative nozzle geometries, including round, elliptical, triangular, squared, and hexagonal shapes. The greatest mixing area is achieved with the square shape. Third, the symmetric forcing parameters are optimized for each specified nozzle shape with a machine learning algorithm. The best mixing enhancement for a symmetric active control is obtained by the squared shape, which results in a 1.93-fold mixing area increase as compared to the unforced case. Symmetrically unconstrained forcing achieves a nearly 4.5-fold mixing area increase. The Smart Nozzle demonstrates the feasibility of novel flow control techniques that combine shape variation and active control, leveraging the capabilities of machine learning optimization algorithms.

GAIT CHANGES FOLLOWING CERAMIC-ON-CERAMIC HIP RESURFACING ARTHROPLASTY: A PROSPECTIVE STUDY

A ceramic-on-ceramic hip resurfacing implant (cHRA) was developed and introduced in an MHRA-approved clinical investigation to provide a non metallic alternative hip resurfacing product. This study aimed to examine function and physical activity levels of patients with a cHRA implant using subjective and objective measures both before and 12 months following surgery in comparison with age and gender matched healthy controls.Eighty-two unilateral cHRA patients consented to this study as part of a larger prospective, non-randomised, clinical investigation. In addition to their patient reported outcome measures (PROMs), self- reported measures of physical activity levels and gait analysis were undertaken both pre- operatively (1.5 weeks) and post operatively (52 weeks). This data was then compared to data from a group of 43 age gender and BMI matched group of healthy controls. Kinetics and kinematics were recorded using an instrumented treadmill and 3D Motion Capture. Statistical parametric mapping was used for analysis.cHRA improved the median Harris Hip Score from 63 to 100, Oxford Hip score from 27 to 48 and the MET from 5.7 to 10.3. cHRA improved top walking speed (5.75km vs 7.27km/hr), achieved a more symmetrical ground reaction force profile, (Symmetry Index value: 10.6% vs 0.9%) and increased hip range of motion (ROM) (31.7° vs 45.9°). Postoperative data was not statistically distinguishable from the healthy controls in any domain.This gait study sought to document the function of a novel ceramic hip resurfacing, using those features of gait commonly used to describe the shortcomings of hip arthroplasty. These features were captured before and 12 months following surgery. Preoperatively the gait patterns were typical for OA patients, while at 1 year postoperatively, this selected group of patients had gait patterns that were hard to distinguish from healthy controls despite an extended posterior approach. Applications for regulatory approval have been submitted.

Chiral whispering gallery modes and chirality-dependent symmetric optical force induced by a spin-polarized surface wave of photonic Dirac semimetal.

Dirac degeneracy is a fourfold band crossing point in a three-dimensional momentum space, which possesses Fermi-arc-like surface states, and has extensive application prospects. In this work, we systematically study the exceptional effects of the robust chiral surface wave supported by photonic Dirac semimetal acts on the dielectric particles. Theoretical results show that orthogonal electromagnetic modes and helical or chiral whispering gallery modes (WGMs) of dielectric particles can be efficiently excited by the unidirectional spin-polarized surface wave. More importantly, optical forces exerted by the spin-polarized surface wave exhibit chirality-dependent symmetric behavior and high chiral Q factor with precise size selectivity. Our findings may provide potential applications in the area of chiral microcavity, spin optical devices, and optical manipulations.

A modified dynamic relaxation form-finding method for symmetrical tensegrity structures with group theory and fuzzy clustering

For tensegrity structures, there are many groups of cables and bars with symmetrical structures or similar internal forces. In this paper, an application of a fuzzy clustering algorithm in the context of form-finding processes for symmetric tensegrity structures is proposed. This algorithm aims to automate grouping, optimize form-finding strategies, and expedite convergence. Point sets are generated through the segmentation of structural components, and Hausdorff distance is used to extract spatial features. Following this, fuzzy clustering automatically groups components with geometric symmetry. The resultant clustering matrix facilitates the refinement of form-finding processes, thus reducing the computational load associated with solving the equilibrium matrix for internal forces within tensegrity structures. By clustering components with analogous internal forces, computational efficiency is enhanced. Additionally, this methodology refines numerical form-finding outcomes based on symmetrical attributes, improving form-finding precision.

Al-Jazeera Arabic and Al-Jazeera English headlines on the Russian-Ukrainian conflict: a Hallidayan transitivity analysis

ABSTRACT Research in communication studies has suggested that Al-Jazeera produces different versions of news stories for different audiences. Yet, examining the linguistic means used to create these versions has remained under-researched. Drawing on Fairclough’s three-dimensional model (1992) and Halliday’s transitivity model (1985), this study aims at exploring how Al-Jazeera Arabic (AJA) and Al-Jazeera English (AJE) discursively represented the participants involved in the 2022 Russo-Ukrainian conflict in headlines. The analysis of transitivity patterns in AJA and AJE headlines reveals both similar and different representations of the conflict. Although they avoided negative labeling of the Russian government, both channels ascribed conflict escalation to it, highlighting civilians suffering and protesting. Nevertheless, while AJE emphasized the Ukrainian government vulnerability, AJA presented the conflict as a confrontation between two symmetrical forces. Similarities are attributed to organizational and social institutional forces, while differences result from different editorial policies and audience preferences. As discursive and social practices, the headlines contribute to shaping audience perceptions of the conflict, with AJA challenging the prevailing western narrative of the conflict while AJE reinforcing it.

The fluidic pinball with symmetric forcing displays steady, periodic, quasi-periodic, and chaotic dynamics

The fluidic pinball with symmetric forcing displays steady, periodic, quasi-periodic, and chaotic dynamics

Mechanical Janus lattice with plug-switch orientation

In recent years, materials with asymmetric mechanical response properties (mechanical Janus materials) have been found possess numerous potential applications, i.e. shock absorption and vibration isolation. In this study, we propose a novel mechanical Janus lattice whose asymmetric mechanical response can be switched in orientation by a plug. Through finite element analysis and experimental verification, this lattice exhibits asymmetric displacement responses to symmetric forces. Furthermore, with such a plug structure inside, individual lattices can switch the orientation of asymmetry and thus achieve reprogrammable design of a mechanical structure with chained lattices. The reprogrammable asymmetry of this material will offer multiple functions in design of mechanical metamaterials

О корректности размера позитрония

It is noted that initially the minimum size of the hydrogen atom was determined by the semiclassical method, which is still widely used today. When calculating the minimum size of a positronium atom, the method tested on the hydrogen atom was not used. Instead, in the formula for the radius, the mass was replaced by the reduced mass of positronium. There would be nothing wrong with this if the above “hydrogen” method gave the same result. However, it is not. The difference between the formula for positronium and the “hydrogen” formula is the coefficient “2”, due to the fact that the positive charge is not in the center of mass. In the literature, the minimum size of a positronium atom (Bohr radius of positronium) was determined in accordance with the two-body problem method. In the particular case under consideration, the method of the two-body problem is redundant and can be successfully replaced by solving the problem of the motion of one of the bodies. This allows you to obtain more visual and obvious solutions without excessive formalism with the reduced mass and displacement vector. The doubly refined value of the positronium radius was determined using the semiclassical method. However, positronium is a quantum object. Therefore, a quantum mechanical consideration is also presented. The textbook solutions are taken as a basis. The solution to the problem of two particles is found in the form of an equivalent solution for one of the particles moving relative to a stationary center of mass, especially since there is a reliable quantum mechanical solution for the case of a spherically symmetric force field, which assumes a stationary center of force. The latter is especially important, since the mobility of the force center (electric charge) can lead to radiation and, consequently, a change in the energy balance. It has been established that the calculated minimum radius of positronium (the distance from its center of mass at which the probability of finding an electron/positron is maximum) is equal to four, and not two Bohr radii of hydrogen, as indicated in the literature. In this case, the semiclassical and quantum solutions do not contradict each other.

Design of a two-stage compliant asymmetric piezoelectrically actuated microgripper with parasitic motion compensation

The parasitic motion of microgripper jaws affect clamping accuracy. The parallelogram mechanism (PM) is often used as the last-stage of the multi-stage amplification mechanisms (AMs) because of its parallel clamping characteristics. However, the PM traditionally used in multi-stage AMs is asymmetrically stressed, which will affect its parallel clamping accuracy. Based on this, a PM with symmetrical forces is designed. The paper addresses the issue of parasitic motion in microgripper jaws and its impact on clamping accuracy, which is a relevant concern in micro-scale manipulation systems. The design of a symmetrically stressed PM for use in a two-stage asymmetric microgripper is a novel contribution to the field. Based on the minimum potential energy principle and the Castigliano's second theorem, the mechanical modeling of the mechanism's parasitic displacement, magnification and parallel clamping accuracy is carried out. Comparing the mechanical model, finite element analysis (FEA) and experimental measurement results, the values given by the three different methods are close. The method given in this paper to improve the clamping accuracy of the mechanism is also applicable to similar compliant mechanisms.

Internal shear layers in librating spherical shells: the case of attractors

Following our previous work on periodic ray paths (He et al., J. Fluid Mech., vol. 939, 2022, A3), we study asymptotically and numerically the structure of internal shear layers for very small Ekman numbers in a three-dimensional spherical shell and in a two-dimensional cylindrical annulus when the rays converge towards an attractor. We first show that the asymptotic solution obtained by propagating the self-similar solution generated at the critical latitude on the librating inner core describes the main features of the numerical solution. The internal shear layer structure and the scaling for its width and velocity amplitude in $E^{1/3}$ and $E^{1/12}$ , respectively, are recovered. The amplitude of the asymptotic solution is shown to decrease to $E^{1/6}$ when it reaches the attractor, as is also observed numerically. However, some discrepancies are observed close to the particular attractors along which the phase of the wave beam remains constant. Another asymptotic solution close to those attractors is then constructed using the model of Ogilvie (J. Fluid Mech., vol. 543, 2005, pp. 19–44). The solution obtained for the velocity has an $O(E^{1/6})$ amplitude, but a self-similar structure different from the critical-latitude solution. It also depends on the Ekman pumping at the contact points of the attractor with the boundaries. We demonstrate that it reproduces correctly the numerical solution. Surprisingly, the numerical solution close to an attractor with phase shift (that is, an attractor touching the axis in three or two dimensions with a symmetric forcing) is also found to be $O(E^{1/6})$ , but its amplitude is much weaker. However, its asymptotic structure remains a mystery.

Changes in the distribution of occlusal forces in the course of the orthodontic retention phase : Aprospective cohort study.

Aim of the present study was to assess the relative distribution of occlusal forces after orthodontic treatment and during the first 3months of the retention phase using acomputerized occlusal analysis system (T-Scan, Tekscan Inc., Norwood, MA, USA). A total of 52patients were included in this prospective cohort study and underwent analysis of occlusal forces on the level of tooth, jaw-half, and -quadrant during a3-month period. Furthermore, differences between three retention protocols (groupI: removable appliances in both jaws; groupII: fixed 3-3 lingual retainers in both jaws; groupIII: removable appliance in the maxilla and fixed 3-3 lingual retainer in mandible) were assessed with Wilcoxon signed-rank tests at 5%. Directly after debonding, measured forces distribution were similar to published references for untreated samples. In the following, no significant difference was found between retention protocolsII andIII with regard to the asymmetry of the anterior occlusal forces. Both groups maintained an asymmetric force distribution in the anterior segment during the study period. There was also no difference between groupsII andIII in the distribution of occlusal forces for the posterior segments. Both retention concepts kept the symmetrical distribution of occlusal forces stable over the observation period. The retention concept of groupI demonstrated asymmetrical distribution of occlusal forces in the anterior segment after debonding and this remained stable during the 3‑month period. In the posterior segment, no improvement of the initially asymmetric masticatory force distribution could be observed. All three studied retention protocols showed stability in retaining their original symmetrical or asymmetrical occlusal force distribution posteriorly/anteriorly during the 3‑month observation period. Therefore, an even distribution of occlusal forces should be the aim of the finishing phase, as no relative benefit of any single retention scheme in terms of post-debond improvement during the retention phase was seen.

Temperature anomalies of oscillating diffusion in ac-driven periodic systems.

We analyze the impact of temperature on the diffusion coefficient of an inertial Brownian particle moving in a symmetric periodic potential and driven by a symmetric time-periodic force. Recent studies have revealed the low-friction regime in which the diffusion coefficient shows giant damped quasiperiodic oscillations as a function of the amplitude of the time-periodic force [I. G. Marchenko et al., Chaos 32, 113106 (2022)1054-150010.1063/5.0117902]. We find out that when temperature grows the diffusion coefficient increases at its minima; however, it decreases at the maxima within a finite temperature window. This curious behavior is explained in terms of the deterministic dynamics perturbed by thermal fluctuations and mean residence time of the particle in the locked and running trajectories. We demonstrate that temperature dependence of the diffusion coefficient can be accurately reconstructed from the stationary probability to occupy the running trajectories.

The Matsuno–Gill model on the sphere

We extend the Matsuno–Gill model, originally developed on the equatorial $\beta$ -plane, to the surface of the sphere. While on the $\beta$ -plane the non-dimensional model contains a single parameter, the damping rate $\gamma$ , on a sphere the model contains a second parameter, the rotation rate $\epsilon ^{1/2}$ (Lamb number). By considering the different combinations of damping and rotation, we are able to characterize the solutions over the $(\gamma, \epsilon ^{1/2})$ plane. We find that the $\beta$ -plane approximation is accurate only for fast rotation rates, where gravity waves traverse a fraction of the sphere's diameter in one rotation period. The particular solutions studied by Matsuno and Gill are accurate only for fast rotation and moderate damping rates, where the relaxation time is comparable to the time on which gravity waves traverse the sphere's diameter. Other regions of the parameter space can be described by different approximations, including radiative relaxation, geostrophic, weak temperature gradient and non-rotating approximations. The effect of the additional parameter introduced by the sphere is to alter the eigenmodes of the free system. Thus, unlike the solutions obtained by Matsuno and Gill, where the long-term response to a symmetric forcing consists solely of Kelvin and Rossby waves, the response on the sphere includes other waves as well, depending on the combination of $\gamma$ and $\epsilon ^{1/2}$ . The particular solutions studied by Matsuno and Gill apply to Earth's oceans, while the more general $\beta$ -plane solutions are only somewhat relevant to Earth's troposphere. In Earth's stratosphere, Venus and Titan, only the spherical solutions apply.

Theoretical fracture analysis of double cantilever microbeam using two-phase local/nonlocal integral models with discontinuity

A mathematical approach is proposed to apply strain-driven (εD) and stress-driven (σD) two-phase local/nonlocal integral models (TPNIMs) with discontinuity of variable fields. The equivalently differential form together with constitutive boundary conditions and constitutive continuity conditions is derived explicitly. Compare to constitutive boundary conditions, constitutive continuity conditions have one more integral item, and the discontinuity plays no role on differential constitutive relation and constitutive boundary conditions. εD- and σD-TPNIMs are applied to formulate the Mode I and II fracture problem of double cantilever Euler-Bernoulli microbeams subjected symmetric and anti-symmetrical end moment and force loads. It is found that constitutive continuity conditions play no role on Mode I fracture problem since that the flexible deformation disappears for intact microbeam under symmetry loads. The bending deflections under different loads are solved analytically, and the energy release rate (ERR) and stress intensity factor (SIF) are derived explicitly. On the basis of the superposition principle, SIF for edge-cracked Euler-Bernoulli microbeams subjected generally end moment and force can be calculated. The influence of nonlocal parameters and the intact microbeam length on the size-dependent fracture behavior is investigated numerically. The obtained results can explain the superior fracture performance of nanomaterials.

Nonreciprocal slow or fast light in anti- PT -symmetric optomechanics

Non-Hermitian systems with anti-parity-time ($\mathcal{APT}$) symmetry have revealed rich physics beyond conventional systems. Here, we study optomechanics in an $\mathcal{APT}$-symmetric spinning resonator and show that, by tuning the rotating speed to approach the exceptional point (EP) or the non-Hermitian spectral degeneracy, nonreciprocal light transmission with a high isolation ratio can be realized. Accompanying this process, nonreciprocal group delay or advance is also identified in the vicinity of EP. Our work sheds new light on manipulating laser propagation with optomechanical EP devices and, in a broader view, can be extended to explore a wide range of $\mathcal{APT}$-symmetric effects, such as $\mathcal{APT}$-symmetric phonon lasers, $\mathcal{APT}$-symmetric topological effects, and $\mathcal{APT}$-symmetric force sensing or accelerator.

Static Analysis of Wooden Beams Strengthened with FRCM-PBO Composite in Bending

The article presents an analysis of the static work of bent solid-wood beams reinforced with FRCM-PBO (fiber-reinforced cementitious matrix-p-phenylene benzobis oxazole) composite. In order to ensure better adhesion of the FRCM-PBO composite to the wooden beam, a layer of mineral resin and quartz sand was applied between the composite and the wooden beam. Ten wooden pine beams with dimensions of 80 × 80 × 1600 mm were used for the tests. Five wooden beams, unreinforced, were used as referenced elements and another five were reinforced with FRCM-PBO composite. The tested samples were subjected to a four-point bending test in which the static scheme of a simply supported beam subjected to two symmetrical concentrated forces was used. The main purpose of the experiment was to estimate the load capacity, the flexural modulus and the maximum bending stress. The time needed to destroy the element and the deflection were also measured. The tests were carried out based on the PN-EN 408: 2010 + A1 standard. The material used for the study was also characterized. The methodology and assumptions adopted in the study were presented. The tests confirmed a significant increase in destructive force by 141.46%, maximum bending stress by 118.9%, modulus of elasticity by 18.32%, time needed to destroy the sample by 106.56% and deflection by 115.58% compared to the reference beams. The unusual method of wood reinforcement presented in the article can be considered as innovative, characterized not only by a significant load capacity margin exceeding 141%, but also by simplicity of application.

Three Different Fixation Modalities following Mandibular Setback Surgery with Sagittal Split Ramus Osteotomy: A Comparative Study using Three-dimensional Finite Elements Analysis.

The provision of sufficient stability after maxillofacial surgery is essential for the reduction of complications and disease recurrence. The stabilization of osteotomized pieces results in rapid restoration of normal masticatory function, reduction of skeletal relapse, and uneventful healing at the osteotomy site. We aimed to compare qualitatively stress distribution patterns over a virtual mandible model after bilateral sagittal split osteotomy (BSSO) bridged with three different intraoral fixation techniques. This study was conducted in the Oral and Maxillofacial Surgery Department of Mashhad School of Dentistry, Mashhad, Iran, from March 2021-March 2022. The mandible computed tomography scan of a healthy adult was used to generate a 3D model; thereafter, BSSO with a 3mm setback was simulated. The three following fixation techniques were applied to the model: 1) two bicortical screws, 2) three bicortical screws, and 3) a miniplate. The bilateral second premolars and first molars were placed under mechanical loads of 75, 135, and 600N in order to simulate symmetric occlusal forces. Finite element analysis (FEA) was carried out in Ansys software, and the mechanical strain, stress, and displacement calculations were recorded. The FEA contours revealed that stress was mainly concentrated in the fixation units. Although bicortical screws presented better rigidity than miniplates, they were associated with higher stress and displacement readings. Miniplate fixation demonstrated the most favorable biomechanical performance, followed by fixation with two and three bicortical screws, respectively. Intraoral fixation with miniplates in combination with monocortical screws can serve as an appropriate fixation arrangement and treatment option for skeletal stabilization after BSSO setback surgery.

Existence of Global and Local Mild Solution for the Fractional Navier–Stokes Equations

Navier–Stokes equations (NS-equations) are applied extensively for the study of various waves phenomena where the symmetries are involved. In this paper, we discuss the NS-equations with the time-fractional derivative of order β∈(0,1). In fractional media, these equations can be utilized to recreate anomalous diffusion equations which can be used to construct symmetries. We examine the initial value problem involving the symmetric Stokes operator and gravitational force utilizing the Caputo fractional derivative. Additionally, we demonstrate the global and local mild solutions in Hα,p. We also demonstrate the regularity of classical solutions in such circumstances. An example is presented to demonstrate the reliability of our findings.