Search

Thin-walled plates are extensively used in the aerospace industry due to their lightweight properties. However, their low rigidity makes them susceptible to deformation and chatter during traditional machining processes, which increases machining complexity and reduces both quality and efficiency. Therefore, this paper proposes an electrochemical machining method involving the use of a rotating body with complex structured windows as the cathode, enabling pure rolling motion on the workpiece surface. Through the action of an electrolyte and an external power supply, the material is removed from the machined surface layer by layer in the form of ions, thus facilitating the manufacture of complex thin-walled plates. Based on the principles of this method, a kinematics model was established to determine the relative position relationship between the cathode and anode during machining. Additionally, an electric field model and a material dissolution model were established to analyze the electric potential distribution and simulate the process of material removal. The simulation results indicate that the trajectory of the cathode windows forms a "V" shape, with the taper angle being independent of the window angle, but decreasing as the cathode diameter increases. Furthermore, it was observed that the use of an insulation coating can effectively reduce stray corrosion on convex structures of the workpiece surface. Based on these simulation results, electrochemical machining experiments were conducted on nickel-based GH4169 plates measuring 600 × 96 mm with a thickness of 3 mm. The results demonstrate that the average thickness of machined workpieces is 1.1 mm, with a thickness error of 0.12 mm. Meanwhile, the surface roughness Ra is 0.778 μm, with a material removal rate reaching 1.01 cm3/min (8271.9 mg/min). Therefore, electrochemical machining proves to be an effective method for manufacturing thin-walled plates. [ABSTRACT FROM AUTHOR]

Mixed convection flows across the revolving bodies have eminent applications in science and technology, such as fibre coating, polymer deposition, centrifugal blood pumps, rotatory machinery, and so forth. In the current work, magnetohydrodynamic (MHD) flow and heat transfer characteristics of Casson hybrid nanofluid (Ag/MgO as nanoparticles) over the rotating sphere at the stagnation zone are being studied. Moreover, an analysis of heat transmission is conducted by considering the influence of thermal radiation, temperature‐dependent thermal conductivity, magnetic field, and viscous dissipation. The relevant partial differential equations are reformed into ordinary differential equations by appropriate transformations, which are solved using the successive linearization method (SLM). The thermal field, velocity components in x and z directions, heat transfer rate, and skin friction coefficient are computed for various physical quantities like rotation parameter mixed convection parameter, radiation parameter, Eckert number, Casson parameter, magnetic parameter, variable thermal conductivity parameter, and so forth. The current findings align well with the literature in a limiting sense. Thermal enhancement in hybrid nanofluid is observed for the viscous dissipation parameter (Ec), thermal conductivity parameter (ε), and radiation parameter (Rd). The degree of heat transfer rises from 12.8% to 20% when the Casson parameter's value (β0) increases. Also, a decrease of approximately 33% is depicted between the peak values of the velocity magnitude with an increase in rotation parameter. [ABSTRACT FROM AUTHOR]

Triboelectric nanogenerators, known as TENGs, offer great potential as versatile energy harvesting devices. In recent years, there has been a rise in TENG designs that prioritize compatibility with sustainable biomaterials, leading to new possibilities in green technology. The novelty of this work lies in its pioneering exploration of utilizing sustainable biomaterials, particularly coconut husk, within the field of Tribo-electric nanogenerators (TENGs). This study focuses on evaluating and characterizing coconut husk as TENG material considering factors such as rotational speed, vane count, and coarseness, all of which influence the output potential of the B-TENG. The BTENG model employed in this research operates on a rotational sliding mode, featuring a biobased material layer of coconut husk, a layer of PTFE, and copper as electrodes. The B-TENG has a diameter of 100 mm with varying vane configurations (3-vane, 4-vane, and 5-vane). The sliding mode demonstrated impressive versatility, yielding output voltages spanning from 0.73 V to 4.0 V across rotational speeds of 200 RPM to 1400 RPM. Remarkably, the 5-vane fine-grained coconut husks achieved a maximum power of 121.10 mW at 10 Ohm and a power density of 3.84 mW/cm². This research carries global significance, contributing to the advancement of energy harvesting technology. Its applications range from harnessing the motion of human bodies to rotating machineries in any industry. [ABSTRACT FROM AUTHOR]

This model consists of a porous spherical body rotating in an incompressible conducting fluid in the existence of a toroidal magnetic field. The toroidal field is generated by an electric dipole along the axis of symmetry. The model is split into two parts—the clear fluid region and the porous sphere. The clear fluid area is driven by the momentum equation and the permeable sphere region is driven by the Brinkman equation. The study is being done for the scenario where the impact of viscous force is much more than inertia force. The expression is found for fluid velocity and stream function by the superposition method. The results depict the impact of rotational parameters and the Darcy number on separation parameter. It is shown that the separation is low for the highly permeable sphere. [ABSTRACT FROM AUTHOR]

Equations of a heavy rotating body with one fixed point can be deduced starting from a variational problem with holonomic constraints. When applying this formalism to the particular case of a Lagrange top, in the formulation with a diagonal inertia tensor the potential energy has a more complicated form as compared with that assumed in the literature on dynamics of a rigid body. This implies the corresponding improvements in equations of motion. Therefore, we revised this case, presenting several examples of analytical solutions to the improved equations. The case of precession without nutation has a surprisingly rich relationship between the rotation and precession rates, which is discussed in detail. [ABSTRACT FROM AUTHOR]

AbstractAiming at the problems of high environmental vibration frequency, low output power and short life of the energy harvesters, a noncontact magnetically coupled piezo-electromagnetic rotary energy harvester is proposed in this paper. It consists of a base, a top cover, a rotating body, a cantilever beam, a permanent magnet, a coil, a hollow tube and a clamp. The novel hybrid harvester can produce both piezoelectric and electromagnetic energy at the same time, and in addition, it can efficiently generate electricity at low ambient vibration. Moreover, the piezoelectric material is protected from direct collision by noncontact magnetic coupling excitation. In order to conduct a comprehensive study on the performance of the piezoelectric-electromagnetic rotary energy harvester, we set up a rotating test platform to carry out systematic test verification, and to determine the distance between the permanent magnet and the rotating body and the number of permanent magnets on the rotating body. The test results show that when four permanent magnets are uniformly pasted on the rotating body and the rotating speed is 775 r/min, the piezoelectric and electromagnetic output power are 3.4 mW and 2.69 mW, respectively, and the total hybrid output power is 6.09 mW. [ABSTRACT FROM AUTHOR]

Due to the fact that most ceramic products formed by drawing embryos can be geometrically viewed as rotating bodies generated by the rotation of their profile curves, the design of these ceramic products can focus on the description of profile curves. A scheme for describing profile curves of ceramic products using the quasi-cubic uniform B-spline is proposed. Different shapes of C² profile curves can be obtained by modifying the control points or local parameters of the quasi-cubic uniform B-spline, thereby meeting the practicality and personality of ceramic product design. Furthermore, a method for determining the optimal local parameters in the quasi-cubic uniform B-spline using energy minimization is presented. The proposed method can generate smooth profile curves of ceramic products, thereby meeting the aesthetics of ceramic product design. [ABSTRACT FROM AUTHOR]

We study the motion of tiny heavy inertial particles advected by a two-dimensional inviscid fluid flow, composed of N identical point vortices regularly placed on a ring and rotating as a solid body, therefore forming a vortex crystal. In the limit of weak particle inertia, we show asymptotically that, in the reference frame of the crystal, inertial particles have N asymptotically stable equilibrium positions located outside the crystal, in agreement with numerical observations by Ravichandran et al. ["Clustering of heavy particles in vortical flows: A selective review," Sādhanā 42, 597–605 (2017)]. In addition to these "satellite" attracting points, we observe that for N ≥ 3 , the center of the ring, though degenerate, is a stable equilibrium position for inertial particles. This creates a kind of cage formed by vortices, where inclusions slowly drift toward the center under the effect of the surrounding vortices. The central attracting point is observed to persist even at larger Stokes numbers, in contrast with the satellite attracting points that vanish when the Stokes number is above some critical value. [ABSTRACT FROM AUTHOR]

Due to perturbation forces and control forces, trajectories of spacecraft around the Earth are usually non-Keplerian orbits, which may result in a gyroscopic effect. To meet the complex demands of space operations in the future, the trajectory prediction of spacecraft under the influence of the gyroscopic effect generated during non-Keplerian motion needs to be studied in depth. The paper investigated the trajectory of spacecraft under the gyroscopic effect generated during non-Keplerian motion. Firstly, according to the similarity between the spacecraft precession motion and the gyroscopic precession, as well as the definition of the "gyroscopic effect" of high-speed rotating bodies, the "gyroscopic effect" generated during the non-Keplerian motion of spacecraft around the earth was defined. Then, taking a continuous radial thrust orbit as an example, the dynamics equations of spacecraft under the influence of gyroscopic effect were deduced. Through theoretical analysis and numerical simulation, the trajectory of spacecraft under the influence of the gyroscopic effect generated during non-Keplerian motion was investigated. Finally, the paper simulated the examples and tested the performance of the proposed method. Simulation results show that a large gyroscopic moment may be generated in some non-Keplerian motion of the spacecraft. The greater the rotational angular velocity of the orbital plane, the greater the gyroscopic moment. Due to the gyroscopic effect, there is a significant deviation in the orbit and the orbital elements compared to those without considering the gyroscopic effect, which indicates that the influence of the gyroscopic effect generated during non-Keplerian motion on the orbit of the spacecraft cannot be ignored. It can be seen from the simulation results that the gyroscopic effect has a significant influence on the trajectory of spacecraft. In some special cases, the gyroscopic effect can be utilized reasonably to save fuel and realize low-energy orbit maneuver control technology in actual space missions; but the control should be considered for the spacecraft to bring it back to the desired orbit in most cases. It is necessary to study the trajectory of spacecraft under the influence of gyroscopic effect. The method and conclusions proposed can provide a theoretical reference for spacecraft trajectory prediction and future large-scale fast orbital maneuvers to meet the needs of complex space operations. [ABSTRACT FROM AUTHOR]

A method for studying the secular evolution and stabilization of the shape of rings in small celestial bodies that do not have shepherd satellites is developed. A model of a compound ring consisting of two close, generally non-coplanar elliptical Gaussian rings is constructed. The self-gravitation of the ring is taken into account through the mutual gravitational energy of the boundary rings Wmut. The function Wmut is presented as a series with an accuracy of up to the 4th power of small eccentricities and mutual inclination of the rings. The secular evolution of a compound ring is described by differential equations in special (collective) variables. For rings without a central body (problem 1), a closed system of eight differential equations is obtained using the mutual energy function. The evolution of rings in the azimuthally averaged potential of a rotating triaxial body is also studied (problem 2), for which a second system of eight differential equations is derived. In both problems, besides the general case, two particular ones are considered: (i) the case of coplanar elliptical rings, and (ii) the case of circular rings with a tilt. The theory is applied to study the recently discovered ring of dwarf planet Haumea. It is shown that without taking into account self-gravity, the nodal precession time of the Haumea ring is equal to TΩ = 12.9 ± 0.7d but taking into account the self-gravity of the ring can reduce this period. It is established that self-gravity does indeed contribute to the preservation of the ring shape without invoking the hypothesis of shepherd satellites. Criteria for the preservation of the ring shape are obtained, which made it possible to estimate the interval for the ratio of the ring mass to the mass of Haumea 10–4 < m/M < 10–3. Taking into account the optical thickness of the ring τ ≈ 0.5, it is shown that the Haumea ring with a mass m/M ≈ (1–2) × 10–4 can consist of ice particles with a size of m. [ABSTRACT FROM AUTHOR]

It is often noted that the Earth is slightly oblate rather than spherical, but the calculation of the Earth's eccentricity can be challenging. Here, we calculate it by minimizing the sum of the Earth's gravitational potential energy and its centrifugal potential energy. The Earth's gravitational potential energy can be derived with the help of the Green's function of the Laplace operator in oblate spheroidal coordinates. Under the assumption of a homogeneous planet, we obtain an analytic relationship for the Earth's eccentricity that was first derived by Maclaurin in 1742 and is about 13 percent larger than the observed value. Better agreement with observation is obtained by assuming that the Earth's core is about twice the density of the mantle, which reduces the Earth's moment of inertia. This exercise can provide practice in analyzing gravitational systems in spheroidal coordinates; the problem may also be relevant for other gravitating and rotating bodies, such as stars and galaxies. Editor's note: This short paper presents a new derivation of the Earth's eccentricity using the minimization of the Earth's total energy that includes both the gravitational and the centrifugal energies. It employs the Green's function of the Laplace operator, a mathematical tool that is commonly used, for instance in electrostatics. Appropriate for advanced undergraduate mechanics courses or for illustrating the utility of Green's functions. [ABSTRACT FROM AUTHOR]

In 1971, Zel'dovich predicted the amplification of electromagnetic (EM) waves scattered by a rotating metallic cylinder, gaining mechanical rotational energy from the body. This phenomenon was believed to be unobservable with electromagnetic fields due to technological difficulties in meeting the condition of amplification that is, the cylinder must rotate faster than the frequency of the incoming radiation. Here, we measure the amplification of an electromagnetic field, generated by a toroid LC-circuit, scattered by an aluminium cylinder spinning in the toroid gap. We show that when the Zel'dovich condition is met, the resistance induced by the cylinder becomes negative implying amplification of the incoming EM fields. These results reveal the connection between the concept of induction generators and the physics of this fundamental physics effect and open new prospects towards testing the Zel'dovich mechanism in the quantum regime, as well as related quantum friction effects. The Authors measure the amplification of electromagnetic waves scattered by a rotating metallic cylinder, gaining mechanical rotational energy from the body, as predicted by Zel'dovich in 1971. [ABSTRACT FROM AUTHOR]

This study explores the dynamical rotary motion of a charged axisymmetric spinning rigid body (RB) under the effect of a gyrostatic moment (GM). The influence of transverse and invariable body fixed torques (IBFTs), and an electromagnetic force field, is also considered. Euler's equations of motion (EOM) are utilized to derive the regulating system of motion for the problem in a suitable formulation. Due to the lack of torque exerted along the spin axis and the nearly symmetrical nature of the RB, the spin rate is nearly unchanged. Assuming slight angular deviations of the spin axis relative to a fixed direction in space, it is possible to derive approximate analytical solutions (AS) in closed form for the attitude, translational, and rotational movements. These concise solutions that are expressed in complex form are highly effective in analyzing the maneuvers performed by spinning RBs. The study focuses on deriving the AS for various variables including angular velocities, Euler's angles, angular momentum, transverse displacements, transverse velocities, axial displacement, and axial velocity. The graphical simulation of the subsequently obtained solutions is presented to show their precision. Furthermore, the positive impacts that alterations in the body's parameters have on the motion's behavior are presented graphically. The corresponding phase plane curves, highlighting the influence of different values in relation to the electromagnetic force field, the GM, and the IBFTs are drawn to analyze the stability of the body's motion. This study has a significant role in various scientific and engineering disciplines. Its importance lies in its ability to optimize mechanical systems, explain celestial motion, and enhance spacecraft performance. [ABSTRACT FROM AUTHOR]

This paper applies fractional calculus to a practical example in fluid mechanics, illustrating its impact beyond traditional integer order calculus. We focus on the classic problem of a rigid body rotating within a uniformly rotating container, which generates a liquid vortex from an undisturbed initial state. Our aim is to compare the time evolutions of the physical system in fractional and integer order models by examining the torque transmission from the rotating body to the surrounding liquid. This is achieved through closed-form, time-developing solutions expressed in terms of Mittag–Leffler and Bessel functions. Analysis reveals that the rotational velocity and, consequently, the vortex structure of the liquid are influenced by three distinct time zones that differ between integer and noninteger models. Anomalous diffusion, favoring noninteger fractions, dominates at early times but gradually gives way to the integer derivative model behavior as time progresses through a transitional regime. Our derived vortex formula clearly demonstrates how the liquid vortex is regulated in time for each considered fractional model. [ABSTRACT FROM AUTHOR]

This study investigates the impact of yaw conditions on the aerodynamic performance and flow field of three high-performance vehicle model configurations by means of wind tunnel testing and unsteady Reynolds-Averaged Navier–Stokes-based computational fluid dynamics simulations. While yaw effects on automotive vehicles have been explored, the effects on far more complex flow fields of high-performance vehicles remain insufficiently researched. This paper reveals that yaw conditions have a significant negative influence both downforce and drag performance. Spoiler and rear wing devices enhance downforce but increase the vehicle's sensitivity to yaw. Furthermore, yaw conditions significantly alter vortex structures and local flow velocities, affecting downstream flow behavior. Surface pressure measurements on the slant confirm these findings and highlight notable yaw effects and upstream effects from spoiler and rear wing devices. Wake analyses through total pressure measurements show that yaw induces a substantial deviation from straight-line wake characteristics, which become dominated by an inboard rotating vehicle body vortex. Overall, this research enhances the understanding of the effects of yaw conditions on high-performance vehicle aerodynamics and provides valuable data for future vehicle aerodynamics research in real-world operating conditions. [ABSTRACT FROM AUTHOR]

Bearings are pivotal components in mechanical systems, providing crucial support to rotating bodies. However, traditional bearings are susceptible to failure caused by friction and wear. This vulnerability is particularly pronounced in scenarios involving ultrahigh speeds and extreme conditions, necessitating the minimization of bearing losses and the enhancement of performance. Magnetic bearings, distinguished by their frictionless operation, absence of lubrication requirements, and high-speed capabilities, offer a promising solution to mitigate bearing failure attributable to friction. Nevertheless, a comprehensive review of magnetic bearings, encompassing their structural attributes, modeling mechanisms, and control strategies, is currently lacking in the literature. This paper aims to address this gap by conducting an exhaustive literature review on magnetic bearings. The objective is to provide scientists with a profound understanding of the structural characteristics, operational mechanisms, control performance, and future development trajectories of this technology. The paper begins by categorizing various magnetic bearings and conducting an in-depth analysis of their properties and characteristics, focusing on their magnetic circuit structures. Subsequently, it delves into the working principles and performance of mathematical models for magnetic bearings with different configurations, outlining the modeling procedures and optimization approaches. Additionally, the paper highlights the impact of control strategies on the performance of magnetic bearings. Modern control theory has demonstrated a remarkable 50% improvement in position accuracy and adjustment time compared to traditional PID control. Finally, the paper offers a glimpse into the future of magnetic bearing design, modeling mechanisms, and control strategies, presenting prospective directions for further advancements in this field. [ABSTRACT FROM AUTHOR]

Since the middle of the 20th century, an understanding of the diversity of the natural magnetohydrodynamic phenomena surrounding us has begun to emerge. Magnetohydrodynamic nature manifests itself in such seemingly heterogeneous processes as the flow of water in the world's oceans, the movements of Earth's liquid core, the dynamics of the solar magnetosphere and galactic electromagnetic fields. Their close relationship and multifaceted influence on human life are becoming more and more clearly revealed. The study of these phenomena requires the development of theory both fundamental and analytical, unifying a wide range of phenomena, and specialized areas that describe specific processes. The theory of translational fluid motion is well developed, but for most natural phenomena, this condition leads to a rather limited model. The fluid motion in the cavity of a rotating body such that the Coriolis forces are significant has been studied much less. A distinctive feature of the problems under consideration is their significant nonlinearity, (i.e., the absence of a linear approximation that allows one to obtain nontrivial useful results). From this point of view, the studies presented here were selected. This review presents studies on the movements of ideal and viscous fluids without taking into account electromagnetic phenomena (non-conducting, non-magnetic fluid) and while taking them into account (conducting fluid). Much attention is payed to the macroscopic movements of sea water (conducting liquid) located in Earth's magnetic field, which spawns electric currents and, as a result, an induced magnetic field. Exploring the processes of generating magnetic fields in the moving turbulent flows of conducting fluid in the frame of dynamic systems with distributed parameters allows better understanding of the origin of cosmic magnetic fields (those of planets, stars, and galaxies). Various approaches are presented for rotational and librational movements. In particular, an analytical solution of three-dimensional unsteady magnetohydrodynamic equations for problems in a plane-parallel configuration is presented. [ABSTRACT FROM AUTHOR]

The control of angular velocities in the fixed-axis rotation of rigid bodies is crucial for ensuring the safety and functionality of civil structures and mechanical systems. In this research, a novel enhanced torsional eddy current damper (ETECD) is proposed to effectively control the angular velocities of rigid bodies within confined installation spaces. At first, an estimation approach is developed to determine the damping coefficient of the eddy current damper (ECD) within limited installation space. Furthermore, we utilize a gearbox to enhance the damping performance of the ECD in confined spaces. To establish the framework for the design of the proposed ETECD, the motion equation and solution of the rotating body are derived. By analytically presenting the approximate solution for the responses of a rotating body with a torsional viscous damper, the required range of the torsional damping coefficient is derived. This range ensures compliance to velocity restrictions under linearly angle-related torques, guiding the design of the ETECD. The ETECD, comprising two cylindrical torsional eddy current dampers (ECDs) and a motion-amplified gearbox, is designed and tested for a rotating body. Numerical examples and experimental tests are carried out to validate the performance of the proposed ETECD. The calculated damping coefficients and predicted control performance in the numerical examples agree well with the experimental results. Notably, under the minimum and maximum torques, the terminal angular velocity (TAV) of the rotating body can be significantly reduced by 70.76% and 58.99%, respectively. The proposed work emphasizes the potential of the ETECD as an effective and economic method in reducing angular velocities for rotating bodies. [ABSTRACT FROM AUTHOR]

The theory of nested figures of equilibrium, expanded in Papers I and II, is investigated in the limit where the number of layers of the rotating body is infinite, enabling to reach full heterogeneity. In the asymptotic process, the discrete set of equations becomes a differential equation for the rotation rate. In the special case of rigid rotation (from centre to surface), we are led to an integro-differential equation (IDE) linking the ellipticity of isopycnic surfaces to the equatorial mass-density profile. In contrast with most studies, these equations are not restricted to small flattenings, but are valid for fast rotators as well. We use numerical solutions obtained from the self-consistent-field method to validate this approach. At small ellipticities (slow rotation), we fully recover Clairaut's equation. Comparisons with Chandrasekhar's perturbative approach and with Roberts' work based on virial equations are successful. We derive a criterion to characterize the transition from slow to fast rotators. The treatment of heterogeneous structures containing mass-density jumps is proposed through a modified IDE. [ABSTRACT FROM AUTHOR]

Maintenance strategy selection is an important step in maintenance management, which is the basis for implementing maintenance optimization and formulating specific maintenance schemes. This paper takes the meta-action unit (MU) as the research object, considers the randomness and fuzziness of expert evaluation and the interaction between evaluation criteria in the selection process of maintenance strategy, and proposes a maintenance strategy selection method based on cloud DEMATEL-ANP. Firstly, DEMATEL based on cloud model is used to establish the interaction model between the main criteria, determine the weighted cloud weight of the super matrix and the inner dependencies of the sub-criteria under the same main criteria. Then, the cloud-ANP model is used to determine the outer dependencies relationship and construct the cloud super matrix, so as to obtain the cloud weight of each evaluation criteria in maintenance strategy selection. By using the subjective and objective weighting method, the evaluation of different experts on different maintenance strategy criteria is integrated, and the priority of alternative maintenance strategies of MU is obtained. Finally, different methods are used to sort and compare the alternative maintenance strategies of the rotating body rotation MU of the CNC turntable, which verifies the scientificity and effectiveness of the maintenance strategy selection method based on cloud DEMATEL-ANP are verified. [ABSTRACT FROM AUTHOR]

In this paper, we present neural networks learning mechanical systems that are both symplectic (for instance particle mechanics) and non-symplectic (for instance rotating rigid body). Mechanical systems have Hamiltonian evolution, which consists of two building blocks: a Poisson bracket and an energy functional. We feed a set of snapshots of a Hamiltonian system to our neural network models which then find both the two building blocks. In particular, the models distinguish between symplectic systems (with non-degenerate Poisson brackets) and non-symplectic systems (degenerate brackets). In contrast with earlier works, our approach does not assume any further a priori information about the dynamics except its Hamiltonianity, and it returns Poisson brackets that satisfy Jacobi identity. Finally, the models indicate whether a system of equations is Hamiltonian or not. [ABSTRACT FROM AUTHOR]

The heterogeneity of the small body population complicates the prediction of small body properties before the spacecraft's arrival. In the context of autonomous small body exploration, it is crucial to develop algorithms that estimate the small body characteristics before orbit insertion and close proximity operations. This paper develops a vision-based estimation of the small-body rotational state (i.e., the center of rotation and rotation axis direction) during the approach phase. In this mission phase, the spacecraft observes the rotating celestial body and tracks features in images. As feature tracks are the projection of the landmarks' circular movement, the possible rotation axes are computed. Then, the rotation axis solution is chosen among the possible candidates by exploiting feature motion and a heuristic approach. Finally, the center of rotation is estimated from the center of brightness. The algorithm is tested on more than 800 test cases with two different asteroids (i.e., Bennu and Itokawa), three different lighting conditions, and more than 100 different rotation axis orientations. Each test case is composed of about 250 synthetic images of the asteroid which are used to track features and determine the rotational state. Results show that the error between the true rotation axis and its estimation is below 10 ° for 80% of the considered test cases, implying that the proposed algorithm is a suitable method for autonomous small body characterization. • Small bodies have heterogeneous characteristics complexifying mission design and operations. • The small body properties are hard to predict before the encounter. • Vision-based techniques enables autonomous estimation of the small-body rotational state. • The proposed method estimates the small-body rotational state from images. • The proposed method is tested on numerical simulations with different observational geometries. [ABSTRACT FROM AUTHOR]

The repeatable and determinate pattern of asymmetric vortices at a regular state can be obtained by manually setting an artificial micro-perturbation (AMP) on the nose tip of a pointed-nosed slender body at a high angle of attack (AoA). Wind tunnel experiments and numerical simulations were conducted to investigate the predominant role of AMP in an asymmetric flow at α = 50°. The bi-stable asymmetric flow structures are presented when AMP rotates around the body axis. Thus, the corresponding side force acting on the slender body is shown as a square wave with two periods. The shear layer separation is presented as the separation lines to investigate the bi-stable asymmetry induced by the AMP. Results show that the AMP restricts the flow separation on the same side of the model with itself when it is located at windward. The separation location on the same side of the AMP moves to the leeward of the model (or the separation angle on the same side of the AMP increases); hence, the vortex rolls up from this side later than the other side. When the AMP is located at leeward of the slender body, it promotes the separation of flow on the same side of the model with itself. Thus, the separation location on the same side of the AMP moves to the windward of the model (or the separation angle on the same side of the AMP decreases) and the vortex rolls up from this side earlier the other side. [ABSTRACT FROM AUTHOR]

To swim through a viscous fluid, a flagellated bacterium must overcome the fluid drag on its body by rotating a flagellum or a bundle of multiple flagella. Because the drag increases with the size of bacteria, it is expected theoretically that the swimming speed of a bacterium inversely correlates with its body length. Nevertheless, despite extensive research, the fundamental size-speed relation of flagellated bacteria remains unclear with different experiments reporting conflicting results. Here, by critically reviewing the existing evidence and synergizing our own experiments of large sample sizes, hydrodynamic modeling, and simulations, we demonstrate that the average swimming speed of Escherichia coli, a premier model of peritrichous bacteria, is independent of their body length. Our quantitative analysis shows that such a counterintuitive relation is the consequence of the collective flagellar dynamics dictated by the linear correlation between the body length and the number of flagella of bacteria. Notably, our study reveals how bacteria utilize the increasing number of flagella to regulate the flagellar motor load. The collective load sharing among multiple flagella results in a lower load on each flagellar motor and therefore faster flagellar rotation, which compensates for the higher fluid drag on the longer bodies of bacteria. Without this balancing mechanism, the swimming speed of monotrichous bacteria generically decreases with increasing body length, a feature limiting the size variation of the bacteria. Altogether, our study resolves a long-standing controversy over the size-speed relation of flagellated bacteria and provides insights into the functional benefit of multiflagellarity in bacteria. [ABSTRACT FROM AUTHOR]

This paper presents for the first time two types of metamaterials based on the fragmentation–reconstitution of rotating units in order to produce Poisson's ratio discontinuity at the original state. For both metamaterials, each rotating unit takes the form of a rhombus that comprises eight sub-units. During on-axis stretching, each rhombus fragments into eight rotating sub-units. When the prescribed strain is reversed, these eight sub-units reconstitute back into a single rotating rhombus such that they rotate as a rigid body. Using geometrical construction, the incremental Poisson's ratio was established at the original state. In the case of large deformation, the finite Poisson's ratio was formulated in conjunction with the maximum allowable rotations for full stretching along both axes and for full compression. The family of on-axes Poisson's ratio versus rotational angles for various shape descriptors displays a fork-shaped distribution with discontinuity at the original state. Two major distinguishing factors of these metamaterials—property discontinuity at the original state with constant and variable Poisson's ratio under compression and tension, respectively—allow them to function in ways that cannot be fully performed by conventional materials or even by auxetic materials and metamaterials. [ABSTRACT FROM AUTHOR]

In this article, we study the stationary motion of an incompressible Navier–Stokes flow past a rotating body R 3 \ Ω , which is also translating about the x 1 -axis with nonzero constant velocity - k e 1 . Assume that the body rotates with a constant angular velocity ω = | ω | e 1 and the external body force is given by f = div F . Our main purpose is to prove the existence of a weak solution u satisfying ∇ u ∈ L r (Ω) for arbitrary large F ∈ L r (Ω) , 3 / 2 ≤ r ≤ 2 , provided that the flux of u b is sufficiently small with respect to the viscosity ν . This is obtained by the regularity result that mainly use localization procedure. In the end, we also present an optimal existence theorem for strong and very weak solutions. [ABSTRACT FROM AUTHOR]

Copyright of Ordnance Industry Automation is the property of Editorial Board for Ordnance Industry Automation and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The work is devoted to developing a mechanism for returning the mechanical energy expended during braking of the vehicle, lost during transmission to the body and proportional to the loss of volume of the combustible engine. The withdrawal of mechanical energy from the wheel braking system is carried out by a cable having a connection with an additional element between the body and the rotating wheels. This element is an additional weight, which increases the wheel system in insignificant volume and weight - only a few %. The other end of the cable is connected to a special mechanical energy storage spring. The mechanical pulling force of the cable compresses the spring system of the special design and accumulates mechanical energy in a volume of approximately 60–70% of the braking energy. The same end of the cable is also connected to the freewheel clutch and the return spring. After the mechanical energy has been transferred, the cable and the brake disc (additional element) are freely returned to their original position by a return spring. The mechanical energy accumulator is constructed of springs made of good quality steel. It is possible to create a design that stores the energy of all four wheels of the vehicle with a single spring. For the design investigated in the work, a carbon steel spring was selected using the characteristics of this steel. The electric generator installed in the structure, mechanically connected with the mechanical energy accumulator, converts mechanical energy into electrical energy by rotation of the rotor under the action of spring forces. Electricity from the electric generator is directed for collection in the battery banks. [ABSTRACT FROM AUTHOR]

The operation of submerged rotating machines, such as marine current or tidal turbines, can present deleterious fluid phenomena that may provoke extreme structural vibrations. To predict their dynamic responses, it is necessary to know the added modal coefficients of their runners under a whirling motion. For that purpose, a bespoke test rig was designed to investigate the added modal coefficients of a submerged cylinder, which could rotate at different speeds both in air and completely submerged in water inside a cylindrical tank. First, the modes of vibration were experimentally measured by exciting the cylinder with a push-release method during steady tests or with ramps in rotating speed during transient tests. The calculated natural frequencies and damping ratios were then used in a mathematical model of the dynamic system to calculate the added modal coefficients. During steady tests, the natural frequencies and damping ratios of the whirling modes changed significantly as a function of the rotating speed. Additionally, a whirling mode was observed to change its direction at a given rotating speed. During transient tests, rotating speed ramps with high accelerations were found to present lower lock-in amplitude and frequencies. Moreover, fast downward ramps presented lock-in amplitudes four times higher than fast upward ramps. Consequently, the added modal coefficients changed accordingly as a function of the rotating speed, ramp acceleration, and ramp direction. For these reasons, it was confirmed that the modal responses of submerged rotating bodies must be calculated for each operational rotating speed, even at low velocities, and for each transient event in order to precisely predict their vibration behaviors. [ABSTRACT FROM AUTHOR]

The extraction of oil from oilseed material by mechanical pressing is carried out in special machines called mechanical presses. The press's primary component sections are the transmission, press bearings, feed area, press chamber, screw, and barrel output. The screw plays a crucial role in a press's operation. A rotating helical body (screw) inside a cylinder-shaped enclosed space produces the pressing force (pressing chamber) in mechanical presses. In this article, we have designed the screw of an oil press to obtain oil from grape seeds. To make the 3D model, we used SolidWorks software, after which we also simulated the model under stress conditions. In the first phase, the behavior of the 3D model will besimulated for the screw with which a small press is equipped, a model most often used in farms for obtaining oil. Later we also simulated a screw model with a larger pitch to observe the differences in behavior between them. In this paper, we show whether the different pitch of the screw press models influences their degree of erosion and fatigue. [ABSTRACT FROM AUTHOR]

Many high-performance fluid dynamic models do not consider fluids in a rotating environment and often require a significant amount of computational time. The current study proposes a novel parameter-based field reconstruction convolutional neural network (PFR-CNN) approach to model the solute concentration field in rotationally influenced fluids. A new three-dimensional (3D) numerical solver, TwoLiquidMixingCoriolisFoam, was implemented within the framework of OpenFOAM to simulate effluents subjected to the influence of rotation. Subsequently, the developed numerical solver was employed to conduct numerical experiments to generate numerical data. A PFR-CNN was designed to predict the concentration fields of neutrally buoyant effluents in rotating water bodies based on the Froude number (Fr) and Rossby number (Ro). The proposed PFR-CNN was trained and validated with a train-validation dataset. The predicted concentration fields for two additional tests demonstrated the good performance of the proposed approach, and the algorithm performed better than traditional approaches. This study offers a new 3D numerical solver, and a novel PFR-CNN approach can predict solute transport subjected to the effects of rotation in few seconds, and the PFR-CNN can significantly reduce the computational costs. The study can significantly advance the ability to model flow and solute transport processes, and the proposed CNN-based approach can potentially be employed to predict the spatial distribution of any physical variable in the lentic, ocean, and earth system. [ABSTRACT FROM AUTHOR]

Small-scale robots hold great potential for targeted cargo delivery in minimally invasive medicine. However, current robots often face challenges in locomoting efficiently on slippery biological tissue surfaces, especially when loaded with heavy cargo. Here, we report a magnetic millirobot that can walk on rough and slippery biological tissues by anchoring itself on the soft tissue surface alternatingly with two feet and reciprocally rotating the body to move forward. We experimentally studied the locomotion, validated it with numerical simulations, and optimized the actuation parameters to fit various terrains and loading conditions. Furthermore, we developed a permanent magnet set-up to enable wireless actuation within a human-scale volume that allows precise control of the millirobot to follow complex trajectories, climb vertical walls, and carry cargo up to four times its own weight. Upon reaching the target location, it performs a deployment sequence to release the liquid drug into tissues. The robust gait of our millirobot on rough biological terrains, combined with its heavy load capacity, makes it a versatile and effective miniaturized vehicle for targeted cargo delivery. [ABSTRACT FROM AUTHOR]

Ectoparasitic cookiecutter sharks (Chondrichthyes: Squaliformes: Dalatiidae; Isistius) share common features for jaw and teeth structure, in particular, robust lower jaws and dignathic heterodonty (upper teeth crowns are more slender and shorter than the broader and longer lower teeth crowns). The jaws and teeth are well suited for feeding by excising a nearly symmetrical oval-flesh bite plug from a variety of prey species including marine mammals, fishes, and squids. There is considerable speculation regarding cookiecutter shark bite dynamics given that natural feeding behavior has not been observed. To elucidate cookiecutter shark bite dynamics, bites were experimentally simulated for the two cookiecutter shark species; the Cookiecutter Shark, Isistius brasiliensis (Quoy JRC, Gaimard, P (1824) Zoologie (3) Imprimerie royale) and the Largetooth Cookiecutter Shark, Isistius plutodus (Garrick JAF, Springer S (1964) Isistius plutodus, a new squaloid shark from the Gulf of Mexico. Copeia 678–682), using three-dimensional printed models of jaws with teeth. Bite simulations were conducted at standardized jaw bite-gape angles and ballistic gelatin was used to approximate prey flesh, from which aspect ratio analysis of bite wound geometrics was used to determine bite wound morphometrics for each species. The simulated bite experiment also was useful for assessing factors that potentially affect cookiecutter shark total length estimates when based on natural bite geometrics. In addition, the mechanics of producing experimental bites provide new insights related to the necessity for cookiecutter sharks to rotate their body to create nearly symmetrical oval bite wounds. [ABSTRACT FROM AUTHOR]

Laser Doppler vibrometry is actively used in experimental studies because of its noncontact measurement technique. When using a stationary laser to measure the vibrations of rotating bodies and Fourier transform to process the results of such measurements, a problem arises, associated with a decrease in the frequency resolution of the spectra with increasing rotation rate of the body. As a result, at sufficiently high rotation rates, closely spaced discrete components may cease to be resolved. This paper proposes a method for solving such a problem using the least squares method. The operability of this processing method has been demonstrated on experimental data. [ABSTRACT FROM AUTHOR]

Copyright of Advances in New & Renewable Energy is the property of Editorial Office of Advances in New & Renewable Energy and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Coal Geology & Exploration is the property of Xian Research Institute of China Coal Research Institute and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Microelectromechanical system (MEMS) devices have gained tremendous attention in the field of smart electronics applications. A MEMS vibrating gyroscope is a rotational inertial sensor that is exhaustively used in many applications, from GPS, household, smart appliances, and space applications. The reliability of MEMS devices for space applications is a big concern. The devices need to be robust in harsh environments. This paper reports a double-ring MEMS vibrating ring gyroscope with sixteen worm-shaped support springs. The inclusion of the two rings with sixteen worm-shaped springs enhances the sensitivity of the gyroscope. The design symmetry and the worm-shaped springs increase the robustness, mode matching, and gyroscopic sensitivity against harsh environments. The design modeling of the gyroscope is investigated using the ANSYSTM software. The design of the vibrating ring gyroscope incorporates two 10 µm thick rings with an outer ring radius of 1000 µm and an inner ring radius of 750 µm. Both rings are attached with sixteen worm-shaped springs, and a centrally placed anchor supports the whole structure with a radius of 260 µm. The proposed gyroscope operates in two identical wine glass modes. The first targeted resonant mode was recorded at 29.07 kHz, and the second mode of the same shape was recorded at 29.35 kHz. There is a low-mode mismatch of 0.38 kHz observed between the two resonant frequencies, which can be resolved with tuning electrodes. The initial modeling results show a good prospect for the design of a vibrating gyroscope for space applications. [ABSTRACT FROM AUTHOR]

This article from Weatherwise features two photographs of unique weather phenomena. The first photo captures a supercell thunderstorm, known for its large size and intense rotation. The photographer positioned himself several miles away to capture the storm's towering cloud, anvil, wall cloud, and tornado. The second photo showcases a night sky in the Rocky Mountains, with stars, the Milky Way, and faint red and green bands of light caused by gravity waves. The photographer also captured periodic blue-white flashes of light, possibly from a distant thunderstorm. The article highlights the beauty and complexity of these natural events and acknowledges that there is still much to learn about them. [Extracted from the article]

In this paper, we obtain the metric of the space-time generated by a charged and rotating gravitational body surrounded by a loud of strings, namely, the Kerr–Newman black hole space-time with the addition of a cloud of strings. In this background, we find the radial solutions of the Dirac equation for massive particles and show that they are given in terms of the Generalized Heun functions. The dependence of these solutions on the parameter that codifies the presence of the cloud of strings is pointed out. [ABSTRACT FROM AUTHOR]

Copyright of China Sciencepaper is the property of China Sciencepaper and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Ocean vortices are an important regional agent of water transport and cross‐frontal exchange. This study is a first attempt to compare statistics of 3D properties of mesoscale eddies over the Norwegian and Greenland Seas. Results suggest that eddies in the central Greenland Sea are less intense, have smaller vertical extent and much smaller heat anomalies in their cores compared to eddies in the Lofoten Basin of the Norwegian Sea. In addition, these results suggest a relatively small inter‐basin eddy exchange. The large‐scale pattern of eddy translations shows that eddies cyclonically skirt the Norwegian‐Greenland region. There is also a regional cyclonic pattern in the Lofoten Basin with a consistent signature of eddy merger in the northern part of the basin. We confirm that eddies generated from the Norwegian Atlantic Slope Current (NwASC) have a significant effect on the amount of heat the NwASC brings to the Arctic. The heat lost from the NwASC between the Svinoy and Sorkapp sections associated with the westward eddy heat transport translates to 70 ± 23 TW, 90% of which occurs in the Lofoten Basin. This accounts to 35% of the heat advected by the NwASC across the Svinoy section and is comparable with the heat loss in the Barents Sea. Interannual variability of the heat flux due to a change in the number of generated eddies is relatively small (∼10 TW). Nevertheless, our estimates suggest that, by varying temperature of their cores, the generated eddies can effectively damp temperature anomalies that propagate north along the NwASC. Plain Language Summary: Mesoscale eddies in the ocean are large rotating water bodies with typical radii between 10 and 100 km and vertical extents of a few hundred meters. These eddies can be an important regional agent of water transport and cross‐frontal exchange. In this study we found that eddies in the Norwegian Sea have notably larger vertical extent, rotating velocity and intensity of thermohaline anomalies in their cores compared to those in the Greenland Sea. This suggests the predominantly local origin of eddies in each of the basins and a small inter‐basin exchange. All eddies move counterclockwise around the Norwegian‐Greenland region. Counterclockwise eddy translations are also registered in the Lofoten Basin. Propagating away from their generation regions (the continental margin of Lofoten Islands and western Spitsbergen) eddies merge and, on average, become bigger. In the Norwegian Sea, eddies extract about 70 TW of heat from the Norwegian Atlantic Slope Current, which reduces the northward heat transport of the current by one third and is comparable with the amount of heat extracted into the Barens. This eddy heat transport can effectively damp water temperature anomalies propagating along the current from the mid‐latitudes North Atlantic into the Arctic. Key Points: Eddies in the Greenland and Norwegian Seas show clear differences in intensity of thermohaline and dynamic anomalies of their coresThe westward eddy heat transport accounts for about one third of heat loss from the Norwegian Atlantic Slope Current (NwASC)Eddy heat flux can effectively damp temperature anomalies as they propagate north along the NwASC [ABSTRACT FROM AUTHOR]

Vector displacements expressed in spherical coordinates are proposed. They correspond to electromagnetic fields in vacuum that globally rotate about an axis and display many circular patterns on the surface of a ball. The fields satisfy the set of Maxwell's equations, and some connections with magnetohydrodynamics can also be established. The solutions are extended with continuity outside the ball. In order to avoid peripheral velocities of arbitrary magnitude, as it may happen for a rigid rotating body, they are organized to form successive encapsulated shells, with substructures recalling ball‐bearing assemblies. A recipe for the construction of these solutions is provided by playing with the eigenfunctions of the vector Laplace operator. Some applications relative to astronomy are finally discussed. [ABSTRACT FROM AUTHOR]

Many recent studies show that the performance of Savonius turbines can be considerably increased by using wind deflectors. Axisymmetric deflectors are particularly interesting; they concentrate the wind flow in all directions. This study aims to aerodynamically optimize the truncated cone deflector shape through transient 3D CFD simulations using sliding mesh techniques. To reduce the mesh size and thus the simulation time, symmetrical boundary conditions were applied to rotating body faces. A mesh grid sensitivity study was conducted to define the optimum mesh size. Additionally, hybrid numerical approaches combining coupled and SIMPLE solvers were particularly influential in reducing computational time. Concave- and convex-arced-shaped faces deflectors were compared to the original truncated cone deflector, showing an increase in the performance for the convex type and a decrease for the concave one. Then, eight cases involving convex spline shape deflectors were simulated. All these deflectors had an equal volume to the original truncated cone deflector. One of the cases showed a 20% average increase in the performance over the original deflector. This result shows the importance of the geometrical shapes in the design of axisymmetric deflectors. [ABSTRACT FROM AUTHOR]