Vertical Oscillations Research Articles

Buoyancy response of a disc to an embedded planet: a cross-code comparison at high resolution

ABSTRACT In radiatively inefficient, laminar protoplanetary discs, embedded planets can excite a buoyancy response as gas gets deflected vertically near the planet. This results in vertical oscillations that drive a vortensity growth in the planet’s corotating region, speeding up inward migration in the type-I regime. We present a comparison between pluto/idefix and fargo3D using 3D, inviscid, adiabatic numerical simulations of planet–disc interaction that feature the buoyancy response of the disc, and show that pluto/idefix struggle to resolve higher-order modes of the buoyancy-related oscillations, weakening vortensity growth, and the associated torque. We interpret this as a drawback of total-energy-conserving finite-volume schemes. Our results indicate that a very high resolution or high-order scheme is required in shock-capturing codes in order to adequately capture this effect.

Dynamic Responses of 8-DoF Vehicle with Active Suspension: Fuzzy-PID Control

The driving smoothness of vehicles is heavily influenced by their suspension system, and implementing active suspension control can effectively minimize the vibration movement of the vehicle and ensure a comfortable driving experience. An 8-DoF active suspension model of the full vehicle is established, and a fuzzy-PID controller is designed to autonomously regulate the parameters of the PID controller. Using the MATLAB/Simulink environment, a simulation model for suspension is created, and the vibration characteristics of passive, PID control, and fuzzy-PID control suspensions are compared with the help of the continuous crossing road hump model and C-level road model as road inputs. The results show that the utilization of fuzzy-PID control considerably diminishes the vertical, pitch, and roll oscillations of the suspension body and modifies the suspension dynamic deflection and tire dynamic load in contrast to the other two scenarios, thus enhancing ride comfort. Fuzzy-PID control led to a decrease of approximately 40% in acceleration, 25% in suspension workspace, and 30% in tire deflection compared to passive suspension. In addition, the reduction in acceleration is about 20%, the reduction in suspension workspace is approximately 10%, and the reduction in tire deflection is about 15% compared to the PID control suspension system.

On Splitting of Separatrices Corresponding to the Working Mode of the Watt Regulator

The nonlinear problem of the Watt regulator dynamics is investigated. It is assumed to be installed on a machine that performs the specific harmonic oscillations of small amplitude along the vertical. Viscous friction forces is believed to arise in the hinges of the regulator, and these forces are small. In the main operating mode of the regulator, its rods, carrying massive weights, are deflected from the downward vertical by a constant acute angle. If friction and vertical oscillations of the machine are neglected, then we obtain an approximate problem in which the dynamics of the regulator is described by an autonomous Hamiltonian system with one degree of freedom. On the phase portrait of the approximate problem, the operating mode corresponds to a singular point of the center type. The trajectories surrounding this point lie inside the separatrix, which is a homoclinic doubly asymptotic trajectory that passes through the equilibrium position corresponding to the vertical position of the rods with weights. In the phase portrait, this position corresponds to a saddle singular point. The Melnikov method is used to obtain the splitting condition for the unperturbed separatrix in the complete perturbed problem, taking into account dissipation in the hinges and vertical vibrations of the machine.

Biomechanical analysis of running: correlation between main frontal findings and foot and ankle injuries in amateur runners

To correlate the most prevalent ankle and foot injuries in amateur runners with the biomechanical analysis of running, considering the patterns of frontal analysis evaluated in a private orthopedic and physical therapy service. Retrospective analysis of 56 medical records of amateur runners with ankle and foot complaints who underwent biomechanical assessment of running in an Orthopedics and Physical Therapy clinic in 2017 and 2018. Lesions found: Shin splints (26.78%); plantar fasciitis (21.42%); Achilles tendinopathy (21.42%); Tibial Stress Syndrome (8.92%); lower limb stress fractures (5.35%); posterior tibial tendonitis (5.35%); peroneal tendinopathy and ankle sprain (7.14%); talar chondral lesion (1.78%) and Morton’s neuroma (1.78%). The biomechanical analysis showed that the most common findings were valgus knees, with 43 cases (76.78%), followed by pelvic drop and center of mass vertical oscillation, with 40 cases each (71.42%) and hamstring retraction, with 37 cases (66.07%). Among the least prevalent, varus knees and supinated foot stand out, with two cases each (3.57%) and medial or lateral heel whip (5.35%, 3 cases). The most prevalent findings were valgus knee, pelvic drop, center of mass vertical oscillation, and hamstring retraction. Among the least present, stand out the varus knees, the supinated foot and the medial or lateral heel whip.

Scattering of Long Waves by Freely Oscillating Submerged Plates

Abstract We consider a horizontal, submerged plate in shallow water that is allowed to oscillate in the vertical direction due to the wave loads. The plate is attached to a linear spring and damper to control the oscillations. The focus of the study is on the transformation of the wave field by the submerged oscillating plate. To estimate energy scattering, wave reflection and transmission coefficients are determined from four wave gauges: two placed upwave and two placed downwave of the oscillating plate. The flow is governed by the nonlinear level I Green–Naghdi (GN) equations, coupled with the equations of the vertical oscillations of the plate. Time series of water surface elevation recorded at gauges upwave and downwave of the plate obtained by the GN model are compared with the available laboratory experiments and other data, and very good agreement is observed. Wave reflection and transmission coefficients are then determined for a range of involved parameters, including wave conditions (wavelength and wave height), initial submergence depth of the plate, plate length, and the spring-damper system attached to the plate. It is found that a submerged oscillating plate can have a remarkable effect on the wave field and that nonlinearity plays an important role in this wave–structure interaction problem. Discussion is provided on how the wave reflection and transmission coefficients vary with the wave conditions, plate characteristics, initial submergence depth, and spring-damper system properties.

Simulation Modeling of an Inhomogeneous Medium, in Particular: Round, Triangular, Square Shapes

The article analyzes and develops an algorithm for the operation of the powder backfill process using vibration oscillations. The results of the study make it possible to predict the main properties of particles of any shape. The developed computer simulation model also provides for the superposition of horizontal and vertical oscillations. It should be noted that the difference between them is that the main one for the implementation of horizontal oscillations is the X - coordinate, and for vertical ones – the Y - coordinate. It is also important that the model algorithm provides for simultaneous application of vibration oscillations, which makes it possible to study the influence of the history of the backfill process. It should also be noted that in this scientific study, a number of experiments were conducted, the change in porosity during the imposition of oscillations was studied, and graphs of the obtained experimental dependences were constructed. Porosity from the main parameters of the bunker, in particular: width and height, is also studied. The obtained results made it possible to record the optimal porosity of the backfill with a reliable deviation error (± 1%).

Upwellings and Downwellings Caused by Mesoscale Water Dynamics in the Coastal Zone of Northeastern Black Sea

The paper analyzes quasiperiodic upwellings and downwellings on the shelf and upper part of continental slope of the northeastern Black Sea. It is shown that these processes are related to changes in intensity and direction of alongshore current and the following geostrophic adjustment of the density field. The source of such changes is the meandering of the Black Sea Rim Current (RC). It leads to a quasiperiodic change in direction of the alongshore current, from northwestern (cyclonic RC meander) to southeastern (anticyclonic RC meander, or eddy). These cycles, or phases, have an average duration of about 10 days. During the northwestern phase, the permanent Black Sea pycnohalocline (hereafter pycnocline) and seasonal thermocline descend, their thickness increases, and so does the thickness of the upper mixed layer (UML). During the southeastern phase, both the pycnocline and seasonal thermocline ascend and become thinner, along with the UML, which also becomes thinner. In both phases, isopycnals in the pycnocline and isotherms in the thermocline demonstrate quasi-in-phase vertical oscillations, which have a good correlation with the speed and direction of the alongshore current. These correlations allow estimation of the magnitude of upwellings and downwellings in the shelf–slope area of the northeastern Black Sea using data series of current velocity profiles.

РОЗРОБКА НОВОЇ МЕТОДИКИ ЕКСПЕРИМЕНТАЛЬНИХ ДОСЛІДЖЕНЬ ІНТЕНСИВНОСТІ КОЛИВАЛЬНИХ ПРОЦЕСІВ МАШИННО-ТРАКТОРНИХ АГРЕГАТІВ

An important operational indicator of agricultural machine-tractor units is the smoothness of movement, which significantly affects the traction and dynamic performance of their work, productivity, agronomic qualities of the operation, traffic safety, durability and efficiency. As a rule, it is evaluated by the influence of oscillations (translational vertical, transverse, angular longitudinal, etc.), on these indicators, as well as on the physical condition and health of operators who control these units in real production conditions. This article presents an improved method and results of experimental assessment of the smoothness of the movement of the modular agricultural unit, which moves in the footsteps of a constant technological track. Studies of the smoothness of the modular unit showed that the graphs of normalized correlation functions of vertical oscillations of the modular agricultural tool developed by us in its motion in the wake of a constant techno-logical track is characterized by a function containing along with random components harmonic, which are expressed by attenuating periodic oscillations. The range of frequencies of oscillations of the frame of the agricultural tool is concentrated in the range from 0 tо 20 s−1, which is consistent with the frequency range 0…0.3 s−1 in which the variances of oscillations of inequalities of a profile of traces of a technological track are concentrated. Studies have confirmed the effectiveness of the method of estimating the intensity of vertical oscillations of the agricultural unit measuring and recording system based on a tablet computer with Android operating system with built-in accelerometer sensors and Accelerometer Meter application. The developed technique of mathematical modelling and experimental determination of vertical oscillations of the machine-tractor unit can be used in the study of the dynamics of other agricultural machines and units.

Charged particles and quasiperiodic oscillations around magnetized Schwarzschild black holes

We study the motion of charged particles around Schwarzschild black holes immersed in external (i) asymptotically uniform, (ii) dipolar, and (iii) parabolic-like magnetic fields. The effect of the different magnetic-field configurations on the position of innermost stable circular orbits (ISCOs) for test-charged particles is analyzed. Furthermore, we investigated frequencies of radial and vertical oscillations of the charged particles along their stable circular orbits together with the Keplerian one. As an astrophysical application, we explore quasiperiodic oscillations (QPOs) observed in microquasars sourced by black hole candidates in the frame of the relativistic precession (RP) model. In order to obtain constraints on the values of the magnetic parameter and black hole mass for the microquasars GRO J1655-40 and GRS 1915-105, we use the method so-called chi ^2 in the Bayesian approach. Also, we get constraints on the magnetic field around the black hole in the microquasars by treating electrons and protons as oscillating test-charged particles in the accretion disc. Our performed analyses show that the masses of black hole candidates in the above-mentioned objects and magnetic parameters are different for the uniform and dipolar magnetic field configurations. However, no constraints on the magnetic field and black hole masses are obtained in the case of a parabolic magnetic field configuration. The obtained results on the black hole masses are compared with the measurements in independent astrophysical observations of these black hole masses.

Observed nonlinear site amplification of vertical ground motion in Taiwan

The objective of this study is to evaluate the possible reason for the observed nonlinear site amplification (NSA) of vertical ground motions in Taiwan. First, we observe that NSA generally occurs simultaneously in both the horizontal and vertical components of a ground-motion record and that the NSA levels are similar between these components. We also observe that most vertical peak ground acceleration (PGA) and vertical peak oscillator spectral acceleration (SA) responses for different periods occur during the shear wave (S-wave) window after S-wave arrival. The differences in the source, path, and site effects on PGA and SA responses occurring during the pressure wave (P-wave) and S-wave windows are evaluated individually through a regression analysis. We determine that NSA is observed only when PGA and SA responses occur during the S-wave window. This evidence demonstrates that the observed NSA of vertical ground motions in Taiwan may result from the hysteresis of the soil layer subjected to S-waves. This study provides physical evidence for the observed NSA of vertical ground motions in Taiwan.

Evaluation of Effectiveness of Application of Horizontal Inertial Barriers to Reduce Vibrations Propagating in Ground Environment

The paper presents calculations of vibrations of the soil mass when a horizontal inertial barrier in the form of a rectangular concrete slab buried in the ground is placed on the propagation path of vibrations. The damping effect of a surface wave upon its contact with an inertial plate is associated with its reflection, refraction and partial absorption. Theoretical studies have been carried out using the finite element method. The ground medium has been considered as an elastic inertial array bounded by non-reflecting boundaries. Various variants of the geometry of the inertial plate and its spatial arrangement on the surface of the soil medium between the vibration source and the considered point behind the barrier are modeled. The effectiveness of each variant of vibration isolation has been quantified by the value showing how many times the speed of vertical oscillations of the ground behind the barrier decreases compared to the free propagation of surface waves. It is shown that an intensive decrease in vertical displacements occurs starting from the side face of the inertial plate. Here, the amplitude of vertical oscillations decreases by 9,8 times for a concrete slab 15 m long, and by 4,2 times for a 3-meter slab. At a distance of 22 m from the point of application of the dynamic load, the amplitudes decrease by factors of 5.48 and 2.95, respectively, for slabs of 15 and 3 m width. This method of reducing vibro-dynamic effects has a simple design and can be used in cramped conditions of urban development to protect existing and planned buildings and structures.

Vehicular Visible Light Communication With Low Beam Transmitters in the Presence of Vertical Oscillation

The availability of light-emitting diodes (LEDs) in vehicle exteriors makes possible the use of visible light communication (VLC) as a vehicle-to-vehicle (V2V) wireless connectivity solution. Although high beam headlights offer higher illumination levels and further communication distances compared to low beam headlights, regulations restrict high beam utilization in many driving cases. These restrictions make low beam headlights a more suitable candidate for vehicular VLC systems. In this paper, we consider two heavy vehicles (e.g., trucks) on a road following each other. Low beam headlights of the follower truck act as wireless transmitters and the lead truck is equipped with a photodetector at its back. We first propose an accurate path loss model based on experimental measurements. The proposed model takes into account the presence of lateral shift between the trucks as well as the fact that headlamps and photodetector can be placed at different heights. Furthermore, we model the truck vertical oscillation experimentally at different speeds. Utilizing these models, we derive a bit error rate (BER) expression for VLC-based truck-to-truck communication system and investigate the effect of several system and channel parameters on the performance. In an attempt to mitigate the degrading effects of the vertical oscillation, we further investigate the proper selection of photodetector location in order to minimize the error rate performance.

MATHEMATICAL MODELS, NUMERICAL METHODS AND RESULTS OF STUDY OF TRANSSONIC FLOW AROUND PROFILES OF BLADE SYSTEMS

The aerodynamic characteristics of blade profiles in a transonic flow of an ideal gas are considered, which are obtained on the basis of the numerical solution of the system of gas dynamics equations (laws of conservation) in integral form. The solution is found by stabilizing over time, which avoids complications in the numerical method for a stationary system of variable-type equations with unknown lines of change from elliptic to hyperbolic and vice versa. The peculiarities of the position of the shock wave (jump) depending on the algorithm for calculating the parameter values on the faces of the cells of the difference grid in the finite-volume algorithm are pointed out. The calculation of numerical flows on the faces of the volume is based on the solution of the problem of the decay of an arbitrary discontinuity of parameters on them in a one-dimensional direction along the normal to the face. The choice of the working difference scheme is based on the indicators of accuracy (order of approximation) and complexity (explicit and implicit) of transition to the next time layer. The development of difference schemes of a higher order of approximation allows to obtain more detailed information about gas-dynamic flows on real grids, which was unattainable when using schemes of the first order of accuracy with high scheme (approximation) viscosity and inconsistency of the propagation of disturbances on a heterogeneous background of parameter values (dispersion calculation effects). The results of calculations using S.K. Godunov's scheme of a higher order of approximation, aerodynamic characteristics of the rigid profile and their comparison with experimental data are given. The characteristics of a profile that performs incoherent angular and vertical oscillations according to a given law are studied.

Effects of finite depth and surface tension on the linear and weakly non-linear stability of Faraday waves in Hele-Shaw cell

A linear and a non-linear analysis are carried out for the instability of the free surface of a liquid layer contained in a Hele-Shaw cell subjected to periodic vertical oscillation. The linear stability analysis shows that for certain ranges of the oscillation frequency, the depth of the liquid layer and the surface tension can have a substantial effect on the selection of the wavenumbers and on the critical forcing amplitude. This results in a new dispersion relation, relating the critical wavenumber and the frequency of oscillation, which is in excellent agreement with recent experimental results by Li et al (2018 Phys. Fluids 30 102103). On the other hand, for low frequencies, the thresholds can be either harmonic or subharmonic with the existence of a series of bicritical points where these two types of thresholds can coexist. Weakly nonlinear analysis is performed in the vicinity of the first subharmonic resonance that occurs in the high frequency limit. Thus, using the multiscale technique, for low dissipation and forcing, we derive a free surface amplitude equation, involving a new nonlinear term coefficient, χ, that includes finite depth and surface tension. For infinite depth, Rajchenbach et al (2011 Phys. Rev. Lett. 107 024502), and Li et al (2019 J. Fluid Mech. 871 694–716) showed that hysteresis can only occur if the response frequency is lower than the natural frequency. However in the present work, it turns out that the coefficient χ can be either positive or negative depending on the depth and surface tension of the fluid. Thus, if χ is positive, hysteresis is found when the response frequency is greater than the natural frequency. Furthermore, the infinite depth approximation, where the short wavelengths dominate, is valid when the depth and wavenumber satisfy kh > 5, whereas for kh < 5, where long wavelengths dominate, the finite depth should be considered.

The wavedrifter: a low-cost IMU-based Lagrangian drifter to observe steepening and overturning of surface gravity waves and the transition to turbulence

ABSTRACT Waves and wave breaking are important to many deep and shallow water processes. We describe the wavedrifter, an in situ water-following inertial measurement unit (IMU)-based drifter that measures wave steepening and overturning kinematics, and the subsequent transition to turbulence. The wavedrifter has 5 cm diameter, 77 g mass, and 0.84 saltwater specific gravity. GPS provides time synchronization. MATLAB’s Attitude, Heading, Reference System (AHRS) library provides wavedrifter orientation. Laboratory experiments quantify the wavedrifter vertical oscillation mode, water following properties, and ability to reproduce wave spectra for small, f = 1.5 Hz waves. The wavedrifter observed wave overturning and the transition to turbulence at the Surf Ranch wave basin. Synchronized video observations provide context. The upper-back of the overturn had large ( ≈ 4 g ) accelerations and 14 g acceleration magnitude occurs with the impact of the overturning jet. Trajectories reveal the Lagrangian structure of the overturn and subsurface vortex. Although it has limitations, the wavedrifter is a powerful in situ tool to probe wave processes.

Validation and enhancement of a vocal fold medial surface 3D reconstruction approach for in-vivo application

In laryngeal research, studying the vertical vocal fold oscillation component is often disregarded. However, vocal fold oscillation by its nature is a three-dimensional process. In the past, we have developed an in-vivo experimental protocol to reconstruct the full, three-dimensional vocal fold vibration. The goal of this study is to validate this 3D reconstruction method. We present an in-vivo canine hemilarynx setup using high-speed video recording and a right-angle prism for 3D reconstruction of vocal fold medial surface vibrations. The 3D surface is reconstructed from the split image provided by the prism. For validation, reconstruction error was calculated for objects located at a distance of up to 15 mm away from the prism. The influence of camera angle, changing calibrated volume, and calibration errors were determined. Overall average 3D reconstruction error is low and does not exceed 0.12 mm at 5 mm distance from the prism. Influence of a moderate (5°) and large (10°) deviation in camera angle led to a slight increase in error to 0.16 mm and 0.17 mm, respectively. This procedure is robust towards changes in calibration volume and small calibration errors. This makes this 3D reconstruction approach a useful tool for the reconstruction of accessible and moving tissue surfaces.

A Comprehensive Perturbative Formalism for Phase Mixing in Perturbed Disks. II. Phase Spirals in an Inhomogeneous Disk Galaxy with a Nonresponsive Dark Matter Halo

We develop a linear perturbative formalism to compute the response of an inhomogeneous stellar disk embedded in a nonresponsive dark matter (DM) halo to various perturbations like bars, spiral arms, and encounters with satellite galaxies. Without self-gravity to reinforce it, the response of a Fourier mode phase mixes away due to an intrinsic spread in the vertical (Ω z ), radial (Ω r ), and azimuthal (Ω ϕ ) frequencies, triggering local phase-space spirals. The detailed galactic potential dictates the shape of phase spirals: phase mixing occurs more slowly and thus phase spirals are more loosely wound in the outer disk and in the presence of an ambient DM halo. Collisional diffusion due to scattering of stars by structures like giant molecular clouds causes superexponential damping of the phase spiral amplitude. The z–v z phase spiral is one-armed (two-armed) for vertically antisymmetric (symmetric) bending (breathing) modes. Only transient perturbations with timescales (τ P) comparable to the vertical oscillation period (τ z ∼ 1/Ω z ) can trigger vertical phase spirals. Each (n, l, m) mode of the response to impulsive (τ P < τ = 1/(nΩ z + lΩ r + mΩ ϕ )) perturbations is power-law (∼τ P/τ) suppressed, but that to adiabatic (τ P > τ) perturbations is exponentially weak () except for resonant (τ → ∞ ) modes. Slower (τ P > τ z ) perturbations, e.g., distant encounters with satellite galaxies, induce stronger bending modes. Sagittarius (Sgr) dominates the solar neighborhood response of the Milky Way (MW) disk to satellite encounters. Thus, if the Gaia phase spiral was triggered by a MW satellite, Sgr is the leading contender. However, the survival of the phase spiral against collisional damping necessitates an impact ∼0.6–0.7 Gyr ago.

Аналитический анализ виброзащитной системы человека-оператора

The task of mathematical description and study of vibration isolation systems for seats of mobile machine operators is relevant, since operators of many construction, road and other mobile machines are exposed to significant vibration effects. An original analytical solution was proposed for the differential equation of forced oscillations of a linear oscillator with kinematic excitation, which describes the vertical oscillations of the seat with the operator, for given sinusoidal oscillations of the seat base. Analytical differentiation in time of the expression for the absolute displacement of the vibration-protected mass of the seat with the operator made it possible to obtain an analytical expression for the absolute velocity of the mass, the simplification of which made it possible to obtain a compact expression for the first and then the zero derivative of the absolute coordinate in the steady state oscillation mode. From the expression for the absolute displacement of the vibration-protected mass using a trigonometric transformation, an analytical expression for its amplitude was obtained, from which, in turn, an analytical expression for the transmission coefficient of the vibration protection system was obtained. The equation based on the analytical expression of the derivative of the transfer coefficient with respect to the circular frequency was solved analytically, which made it possible to obtain analytical expressions for the resonant amplitude of absolute displacements and the transfer coefficient. Examples of functional dependencies obtained using the derived analytical expressions are given. The obtained analytical expressions make it possible to conduct studies of vibration protection systems of seats with maximum accuracy.

Research of features of oscillating process’ behavior in the nonlinear system of individual traction drive of an electrobus

BACKGROUND: When a vehicle is in motion, self-oscillations which properties are dependent on slip rate in a contact patch may occur in the area of tire interaction with ground surface. Oscillations frequency will vary in dependence with value of wheel slip relative to ground surface. Soft self-oscillations are excited by variable set of initial conditions at full slip in traction and driven wheel rolling modes as well as in mixed braking mode with partial slip. Hard mode of self-oscillations occurs at full wheel slip in braking mode. These processes have a negative impact on the processes in electric drive and mechanical drivetrain reducing their efficiency and may cause damage of components. Oscillations in the system are excited by interaction forces of an elastic tire with ground surface featuring vertical oscillations due to elastic behavior of its interaction with road unevenness. AIMS: Research of features of oscillating process behavior in the nonlinear system of individual traction drive of an electrobus. METHODS: Simulation of self-oscillation excitation processes in the area of contact interaction of a wheel and road was carried out in the MATLAB/Simulink software package. RESULTS: The article features the results of simulation and experimental studies of self-oscillation excitation processes of the KAMAZ 6282 electrobus moving on asphalt-concrete surface. It was found that vertical wheel displacement when moving through unevenness lead to oscillating behavior of vertical reaction forces in contact patches and, as a consequence, to oscillating behavior of longitudinal reaction forces, torque and rotation velocity of the shaft of the traction electric motor of the individual drive. It was defined that tire oscillation frequency is 67 Hz that coincides with electric motor shaft rotation oscillation frequency and this value is the same for both experiment and simulation. CONCLUSIONS: Practical value of the study lies in ability of using the study results at development of self-oscillation processes exclusion algorithms as a part of vehicle control system.

Teaching Video NeuroImage: Pendular Vertical Oscillations in a Young Adult With a Pontine Hemorrhage.

Teaching Video NeuroImage: Pendular Vertical Oscillations in a Young Adult With a Pontine Hemorrhage.