Spiral Motion Research Articles

Dynamics of freely falling perforated disks

The dynamics of free-falling perforated disks within the moderate Reynolds number Rem regime (700<Rem<1400) are experimentally investigated in this paper, including translation and rotation dynamics. Four falling styles are analyzed, including spiral motion, Hula-Hoop motion, helical precession motion and spiral irregular motion. In contrast to spiral irregular motion, we group the other three motions as regular motions. The relative contribution of different dynamical effects (impulsive effect, Magnus effect and viscous effect respectively) is quantitatively determined. The contribution of impulsive effect is commonly ignorable during the descent, and Magnus effect plays a crucial role in horizontal oscillations. Vortex loads always dominate this dynamical process, and balance the gravity along the vertical direction. In the Frenet–Serret coordinate system, the contribution resulting from Magnus effect is relatively small to that of vorticity-induced fluid force. Hence, an alternative way to model this involved system is presented, which is based on the extended Kelvin-Kirchhoff equations. A Fast Fourier Transform (FFT) is performed on total hydrodynamics forces FHx and FHy. For regular motions with the dimensionless inertia ratio I∗≤1×10−3, sub-harmonic force components are identified in the frequency domain. However, the frequency ratio of high-frequency components and the dominant peak is no longer integer in spiral irregular motion. The azimuth distribution of angular velocity is counted in the Frenet–Serret coordinate system. For spiral irregular motion with the dimensionless inertia ratio I∗>1×10−3, no preferential alignment is observed and its distribution scatters, while those of regular motions are rather concentrated. The probability density functions (PDFs) of angular velocity components in spiral and Hula-Hoop motions share similar distributions, which indicates angular dynamics may decouple from translation dynamics in high Reynolds number regime under certain circumstances.

A companion in V1247 Ori supported by motion in the pattern of the spiral arm

While nearly two dozen spiral arms have been detected from planet-forming disks in near-infrared scattered light, none of their substellar drivers has been confirmed. By observing spiral systems in at least two epochs spanning multiple years and measuring the motion of the spirals, we can distinguish what causes the spirals and locate the orbits of the driving planets if the spirals are triggered by them. Upon a recent validation of this approach using the comotion between a stellar companion and a spiral, we obtained a second-epoch observation for the spiral system in the disk of V1247 Ori in the H-band polarized scattered light using Very Large Telescope (VLT), SPHERE, and IRDIS. By combining our observations with archival IRDIS data, we established a 4.8 yr timeline to constrain the spiral motion of V1247 Ori. We obtained a pattern speed of 0°.40 ± 0°.10 yr−1 for the northeast spiral. This corresponds to an orbital period of 900 ± 220 yr, and the semimajor axis of the hidden planetary driver therefore is 118 ± 20 au for a 2.0 ± 0.1 M⊙ central star. The location agrees with the gap in ALMA dust-continuum observations, which provides joint support for the hypothesis that a companion drives the scattered-light spirals while carving a millimeter gap. With an angular separation of 0″​​.29 ± 0″​​.05, this hidden companion is an ideal target for JWST imaging.

Multi-Physics Field Computation for Microwave Heating of Multi-Mobile Components Based on Transformation Optics and Implicit Function

This paper proposed a method based on transformation optics, implicit function, and level set methods to solve the challenge of multi-physics simulation of a microwave heating cavity with two different motion modes. A 3D computation model with a rotating turntable, a lifting support rod, and a sample is proposed as a detailed demonstration. Based on the theory of transformation optics, the rotating turntable is surrounded by two circles with a time-varying, inhomogeneous and anisotropy medium, and the electric field in the moving region is rotated by controlling the two mediums. The implicit function and level set methods compute the lifting motion by setting the properties of the lifting region as a function of space and time. The correctness of the proposed method is verified by comparing the proposed method’s results with the discrete position’s results, and then its accuracy is further verified by experiment. Subsequently, compared with the implicit function and level set methods only, the proposed method is more accurate. Finally, the effects of lifting motion, rotating motion and lifting motion (i.e., spiral motion) on microwave heating uniformity and heating efficiency were analyzed, respectively.

A numerical analysis of fluid flow and heat transfer between two rotating disks with induced porous medium

In this article, fluid flow between rotating disks is a fundamental topic in fluid dynamics and has various practical applications in engineering and technology. The primary motivation for studying fluid flow between two rotating disk includes its applications in heat exchanger design, generating energy, designing aircraft components like helicopter blades, propellers, wind turbine rotors, fluid pumping, stirring, etc. Authors have considered radially stretching and rotating disks simultaneously under the spiraling motion of a couple stress fluid. This type of motion is developed by radial stretching in addition to the disk’s uniform rotation. This study gives information about the effect of various physical parameters on radial, tangential velocities, and temperature profiles. The similarity transformation resulted in coupled nonlinear ordinary differential equations from the constitutive flow rules of nonlinear partial differential equations. For getting numerical solutions, the authors have used the in-build NDSolve command in MATHEMATICA software, which uses the finite difference method for discretizing and solving differential equations. The outcomes of the above study depict how the fluid flow pattern between the rotating disks is affected by Darcy’s parameter, and other parameters, like Prandtl number, rotation parameter, stretching parameter, couple stress parameter, etc. on the flow, have been thoroughly analyzed, with the physical relevance illustrated. Radial and tangential velocity profiles decrease whenever the Darcy parameter increases. An increase in rotation parameter enhances the radial and tangential velocity due to rotation of the disks.

Anti-Disturbance Path-Following Control for Snake Robots With Spiral Motion

Three-dimensional spiral gait enables a snake robot to climb over obstacles, cross caves, and adapt to complex environments. This paper reports an anti-disturbance path-following control method for a snake robot with a spiral gait. This method reduces the deviation of the robot's position in following the ideal path by estimating the time-varying parameters, the external disturbances, and the viscous friction coefficients. The estimations are used to compensate for the control inputs of the system, which can improve the adaptability of the robot to the environment. Then, the attitude and position errors can rapidly converge to the origin. An appropriate Lyapunov function is adopted to explore the stability of following errors. Experimental results show that the proposed method can accelerate the convergence rate of errors, reduce the fluctuation peak, and improve the following stability of snake robots.

Lagrangian investigation of the interface dynamics in single-mode Rayleigh–Taylor instability

We apply Lagrangian particle tracking to the two-dimensional single-mode Rayleigh–Taylor (RT) instability to study the dynamical evolution of fluid interface. At the onset of the nonlinear RT stage, we select three ensembles of tracer particles located at the bubble tip, at the spike tip, and inside the spiral of the mushroom structure, which cover most of the interfacial region as the instability develops. Conditional statistics performed on the three sets of particles and over different RT evolution stages, such as the trajectory curvature, velocity, and acceleration, reveals the temporal and spatial flow patterns characterizing the single-mode RT growth. The probability density functions of tracer particle velocity and trajectory curvature exhibit scalings compatible with local flow topology, such as the swirling motion of the spiral particles. Large-scale anisotropy of RT interfacial flows, measured by the ratio of horizontal to vertical kinetic energy, also varies for different particle ensembles arising from the differing evolution patterns of the particle acceleration. In addition, we provide direct evidence to connect the RT bubble re-acceleration to its interaction with the transported fluid from the spike side, due to the shear driven Kelvin–Helmholtz instability. Furthermore, we reveal that the secondary RT instability inside the spiral, which destabilizes the spiraling motion and induces complex flow structures, is generated by the centrifugal acceleration.

Behavioural and Histopathological Changes Associated With Urea Toxicity in Fingerlings of Rohu,&lt;I&gt; Labeo rohita&lt;/I&gt;

Fingerlings of rohu, Labeo rohita weighing 8.52±2.54 g and a mean body length of 6.11±2.52 cm were used for acute and chronic toxicity tests. The LC50 value was determined as 124.59 mg/l at 96 hours. Clinical signs and symptoms of the test organisms were recorded. Behavioural changes included vigorous caudal fin movement, hyperexcitability and spiral movement with head downward. The moribund fish floated upside down at the surface, often sinking passively to the bottom. Further, the fingerlings were exposed to sublethal concentration of 96 hours 1/10th and 1/50th LC50 over 45 days. The organ tissue, viz., skin, muscle, gill, liver, kidney, brain and heart were examined for histopathological study and the changes are described and discussed.

An acoustically controlled helical microrobot.

As a next-generation toolkit, microrobots can transform a wide range of fields, including micromanufacturing, electronics, microfluidics, tissue engineering, and medicine. While still in their infancy, acoustically actuated microrobots are becoming increasingly attractive. However, the interaction of acoustics with microstructure geometry is poorly understood, and its study is necessary for developing next-generation acoustically powered microrobots. We present an acoustically driven helical microrobot with a length of 350 μm and a diameter of 100 μm that is capable of locomotion using a fin-like double-helix microstructure. This microrobot responds to sound stimuli at ~12 to 19 kHz and mimics the spiral motion of natural microswimmers such as spirochetes. The asymmetric double helix interacts with the incident acoustic field, inducing a propulsion torque that causes the microrobot to rotate around its long axis. Moreover, our microrobot has the unique feature of its directionality being switchable by simply tuning the acoustic frequency. We demonstrate this locomotion in 2D and 3D artificial vasculatures using a single sound source.

Integrated Dynamics of Space Rigid-Flex Combination System with Time-Varying Configuration

Dual numbers were applied to the dynamics of a rigid-flexible combination system (RFCS) with time-varying configuration in this paper. The six-dimensional spinor form of the motion of flexible modules, including the dual vector, dual momentum, dual inertia operator, dual coupling coefficient operator, and dual-modal coordinates, was derived using the dual numbers that could represent spiral motion in a compact form. On this basis, the integrated dynamic model of a rigid-flexible combination system with a time-varying configuration was proposed. And then, the relative dynamics equations between two rigid-flexible combination systems which both have time-varying configuration were provided. An on-orbit assembly mission of flexible modules transported and operated by free-flying space robots (FFSRs) is presented as an exemplary application of relative dynamics. Simulation results illustrate the complex coupling effects on the relative motion between two rigid-flex combination systems with time-varying configuration.

Accumulation and Cross-Shelf Transport of Coastal Waters by Submesoscale Cyclones in the Black Sea

High- and medium-resolution satellite optical imagery show that submesoscale cyclonic eddies (SCEs) trap coastal waters and induce their rapid cross-shelf transport. Due to the presence of a rigid boundary, the convergence is observed in the coastal part of SCEs. It causes accumulation of suspended matter, which spins inward in a spiral motion toward the SCE core. Small SCEs with a radius of 1–10 km transport waters with local anomalies in the concentration of chlorophyll, total suspended matter and temperature to a distance of up to 150 km and are observed for more than 10 days. Lagrangian calculations based on realistic NEMO numerical model are used to estimate the fate of the coastal waters in such SCEs. The eddy entrains the largest number of particles during its separation from the coast when its vorticity reaches the maximum. Then, the SCE weakens, which is accompanied by the flattening of initially risen isopycnals and deepening of the trapped coastal waters. The described mechanism shows that coastal SCEs may cause intense short-period cross-shelf transport of the biological and chemical characteristics, and is another process affecting the functioning of the marine ecosystems.

Numerical study on circumferential nonuniform characteristics of flow and heat transfer on double-side heating once-through steam generator with helical tubes

In this paper, double-side heating once-through steam generator with helical tubes as the prototype to establish its two-fluid Euler numerical model and verified through the Becker experiment. The results show that the two-phase fluid in the crescent-shaped passage moves spirally, and the two-phase flow velocity fluctuates along the Z-axis with a slip ratio greater than 1.0. The spiral motion results in greater centrifugal strength of the vapor phase than the liquid phase, the high centrifugal strength of the vapor phase results in a higher vapor phase volume fraction on the outer wall, which makes the position of the beginning of dryout and the position of the total dryout of the outer wall is advanced. The liquid phase volume fraction is highest on the narrow side inner wall and lowest on the wide side inner wall, so the inner wall dryout appears first and total dryout last. The circumferential non-uniformity results in a spiral band of vapor content and temperature distribution.

An Argument Against Weiism: A Nietzschean and Philosophical Posthumanist Reading of Ira Levin’s This Perfect Day

ABSTRACT In this paper, I set out to argue in favour of a philosophical posthumanist and Nietzschean reading of Ira Levin’s This Perfect Day while demonstrating how transhumanism isunbefitting of being called a Nietzschean theory. I will do this by establishing Chip, the protagonist, as a posthuman and being on the path of the ‘Overhuman’ whereas Wei, the antagonist, will be illustrated as Chip’s intended counterpart the Last Human. Through explaining ‘Transhumansim’ and connecting the field to Wei, I will showcase a new way of reading transhumanist ideology, namely ‘Weiism’. The polar opposite in characters of ‘Overhuman’ and ‘Last Human’ will argue in favour of the Nietzschean paradoxical, as part of philosophical posthumanism. Amor fati and the eternal recurrence become posthumanist narrative tools through their weaving into the posthuman narrative of Chip. My argument is that by making philosophical posthumanism more existentialist in nature, it becomes simpler to argue against nihilistic and totalitarian tendencies of worshipping technology. Finally, it is the spiralling motion forward as a mix between the Nietzschean, eternally cyclical re-inventing of oneself and the posthumanist consideration for the future which makes for a literary combination of the two fields of study.

Hydrodynamics of an odd active surfer in a chiral fluid

We theoretically and computationally study the low-Reynolds-number hydrodynamics of a linear active microswimmer surfing on a compressible thin fluid layer characterized by an odd viscosity. Since the underlying three-dimensional fluid is assumed to be very thin compared to any lateral size of the fluid layer, the model is effectively two-dimensional. In the limit of small odd viscosity compared to the even viscosities of the fluid layer, we obtain analytical expressions for the self-induced flow field, which includes non-reciprocal components due to the odd viscosity. On this basis, we fully analyze the behavior of a single linear swimmer, finding that it follows a circular path, the radius of which is, to leading order, inversely proportional to the magnitude of the odd viscosity. In addition, we show that a pair of swimmers exhibits a wealth of two-body dynamics that depends on the initial relative orientation angles as well as on the propulsion mechanism adopted by each swimmer. In particular, the pusher–pusher and pusher–puller-type swimmer pairs exhibit a generic spiral motion, while the puller–puller pair is found to either co-rotate in the steady state along a circular trajectory or exhibit a more complex chaotic behavior resulting from the interplay between hydrodynamic and steric interactions. Our theoretical predictions may pave the way toward a better understanding of active transport in active chiral fluids with odd viscosity, and may find potential applications in the quantitative microrheological characterization of odd-viscous fluids.

Publisher Erratum to: A Three-Dimensional Multiphase Simulation of the Fiber Spiral Motion Under a Melt-Blowing Swirl Die

Publisher Erratum to: A Three-Dimensional Multiphase Simulation of the Fiber Spiral Motion Under a Melt-Blowing Swirl Die

Molecular choreography of primer synthesis by the eukaryotic Pol α-primase

The eukaryotic polymerase α (Pol α) synthesizes an RNA-DNA hybrid primer of 20–30 nucleotides. Pol α is composed of Pol1, Pol12, Primase 1 (Pri1), and Pri2. Pol1 and Pri1 contain the DNA polymerase and RNA primase activities, respectively. It has been unclear how Pol α hands over an RNA primer from Pri1 to Pol1 for DNA primer extension, and how the primer length is defined. Here we report the cryo-EM analysis of yeast Pol α in the apo, primer initiation, primer elongation, RNA primer hand-off from Pri1 to Pol1, and DNA extension states, revealing a series of very large movements. We reveal a critical point at which Pol1-core moves to take over the 3’-end of the RNA from Pri1. DNA extension is limited by a spiral motion of Pol1-core. Since both Pri1 and Pol1-core are flexibly attached to a stable platform, primer growth produces stress that limits the primer length.

Dynamics modeling and typical motion performance analysis for a multi-joint autonomous underwater vehicle

This paper addresses the dynamics modeling and typical motion analysis of a highly-maneuverable multi-joint autonomous underwater vehicle (MJ-AUV) for deep-sea exploration. A generalized recursive dynamics modeling method is proposed based on the Newton-Euler dynamics equation and its derivation process is provided. The kinematic model is established through the screw theory and the product of exponentials (PoE) formula. A detailed dynamics model is obtained by analyzing the force states of the MJ-AUV and computing the hydrodynamic coefficients based on the computational fluid dynamics (CFD) approach. Three typical motion modes, i.e., spiral, vertical profile, and cruise motion, are selected to investigate the motion performance of the MJ-AUV via simulations and sea/lake experiments based on the detailed dynamics model. The experimental and simulation results demonstrate that the MJ-AUV has good maneuverability and can resist external disturbances, which validate the effectiveness of the proposed dynamics model.

A Genetic Algorithm (GA) and Swarm-Based Binary Decision Diagram (BDD) Reordering Optimizer Reinforced With Recent Operators

The use of Binary Decision Diagrams (BDDs) has proliferated in numerous fields. When a system criterion is formulated in form of a Boolean function, its BDD is constructed. Each node in the BDD is further mapped into another form to be exploited in the system analysis. However, the cost of the resultant mapping form is directly related to the BDD size which can be effectively reduced through applying proper variable reordering followed by applying reduction rules that preserve the fidelity of the BDD in correctly representing the input Boolean function. Although several algorithms have been proposed in the literature to find the optimal order of variables in the BDD, the scalability of such algorithms is a serious barrier when it comes to complex systems with exponential explosion in the possible number of orders in the search space. Furthermore, solely exploring the search space in BDD reordering is not sufficient since better permutations might be obtained with slight tuning of the candidate solutions. Thus, a sufficient degree of equilibrium between exploration and exploitation should be preserved during the evolution of the reordering algorithm. In this paper, we propose a BDD optimizer driven by either Genetic Algorithm (GA) or swarm engines. The proposed GA-based BDD reordering optimizer iteratively processes an essentially large population with a randomized mixing of low destructive crossover/mutation operators. The proposed swarm-based optimizer, on the other hand, maps a vector of real numbers into a permutation to further construct its companion BDD. The generation of the next vector is guided by recent parameter and parameter-less swarm algorithms that are armed with effective mechanisms to simultaneously conduct exploration and exploitation. Experimental results show that our proposed optimizer effectively reduces the resultant BDD size for input Boolean functions with almost linear computational complexity. Furthermore, it has been found that exploiting recent swarm optimizers with spiral movement in BDD reordering problem can outperform GA for large scale Boolean functions. Finally, as a real-world application, our proposed algorithm is applied to reversible logic synthesis to show the achieved reduction in the Quantum Cost (QC) associated with BDD-based synthesis.

Characteristics and Mechanisms of the Zigzag and Spiral Movement of Rising Bubbles in Still Water

When a bubble rises freely in still water, it often moves along a zigzag or spiral trajectory. In order to explore the mechanism of this movement, an experiment was conducted to record the changes in the movement trajectory and bubble shape. The results show that this movement can be explained by the swing of trailing vortices and the change in vorticity. There is asymmetric shedding of the trailing vortices. The change in bubble velocity caused by the shedding of the bubble trailing vortices will lead to an asymmetric change in the vorticity of the trailing vortices. Two factors lead to an asymmetric change in the drag force of the trailing vortices on both sides of the bubble, resulting in the zigzag trajectory. Only when the aspect ratio λ reaches 2.0 will the bubble move along the zigzag. The trailing vortices moving in two orthogonal directions will lead to a spiral trajectory. The movement of the trailing vortices not only changes the trajectory of the bubble but also changes its shape. The effect of the trailing vortices on the bubble can be equivalent to a low-pressure area around a bubble. When a bubble moves along a zigzag trajectory, the low-pressure area at the trailing of a bubble swings back and forth in a plane, and the bubble is flatter. When moving along a spiral trajectory, the low-pressure area rotates around the trailing of the bubble and becomes more spherical. Compared with a zigzag trajectory, a bubble has a higher velocity and lower frequency when moving along a spiral trajectory.

Gravitational-wave signature of core-collapse supernovae

We calculate the gravitational-wave (GW) signatures of detailed 3D core-collapse supernova simulations spanning a range of massive stars. Most of the simulations are carried out to times late enough to capture more than 95% of the total GW emission. We find that the f/g-mode and f-mode of proto-neutron star oscillations carry away most of the GW power. The f-mode frequency inexorably rises as the proto-neutron star (PNS) core shrinks. We demonstrate that the GW emission is excited mostly by accretion plumes onto the PNS that energize modal oscillations and also high-frequency (``haze") emission correlated with the phase of violent accretion. The duration of the major phase of emission varies with exploding progenitor and there is a strong correlation between the total GW energy radiated and the compactness of the progenitor. Moreover, the total GW emissions vary by as much as three orders of magnitude from star to star. For black-hole formation, the GW signal tapers off slowly and does not manifest the haze seen for the exploding models. For such failed models, we also witness the emergence of a spiral shock motion that modulates the GW emission at a frequency near $\sim$100 Hertz that slowly increases as the stalled shock sinks. We find significant angular anisotropy of both the high- and low-frequency (memory) GW emissions, though the latter have very little power.

Chromatic confocal sensor-based on-machine measurement for microstructured optical surfaces featuring a self-aligned spiral center.

Chromatic confocal sensor-based on-machine measurement is effective for identifying and compensating for form errors of the ultra-precisely machined components. In this study, an on-machine measurement system was developed for an ultra-precision diamond turning machine to generate microstructured optical surfaces, for which the sensor probe adopts a uniform spiral scanning motion. To avoid the tedious spiral center alignment, a self-alignment method was proposed without additional equipment or artefact, which identified the deviation of the optical axis to the spindle axis by matching the measured surface points and the designed surface. The feasibility of the proposed method was demonstrated by numerical simulation with full consideration of noises and system dynamics. Practically, taking a typical microstructured surface as an example, the on-machine measured points were reconstructed after calibrating the alignment deviation, which was then verified by off-machine white light interferometry measurement. Avoiding tedious operations and special artefacts may significantly simplify the on-machine measurement process, thereby greatly improving the efficiency and flexibility for the measurement.