Vertical Oscillations Research Articles

Structural and dynamical behavior of a vibrated granular system of hard-cubes

We study experimentally and by molecular dynamics simulations a quasi-two-dimensional granular system of cubic particles, confined in a squared box and kept in a dynamic steady state via vertical oscillations. First, we compared the dynamics of a single spherical bead and a cube. Remarkably, the trajectory of the cube shows characteristics of Brownian motion induced by the particle geometry, i.e. an erratic path generated by the collisions of the vertexes and edges of the cube with the vibrated plate; in contrast to the more predicted ballistic motion of a spherical bead. Upon the addition of more cubic particles to the system, the erratic motion is enhanced by multiple collisions, leading to a rich collective behavior. As the number of particles is increased, for instance, both the radial distribution function and the mean square displacement exhibit the qualitative features of the gas, liquid and crystalline-solid phases observed in thermally driven colloidal systems. The results obtained with experiments and simulations are in good agreement and, combined, suggest that a vibrated system of granular cubic particles provides a macroscopic ideal model of Brownian motion.

Hydrodynamic Response of a Large-Scale Mariculture Ship Based on Potential Flow Theory

The marine fishery will be the main form of the marine economy in the future. Simulating a hydrodynamic response under normal and extreme working conditions is the main means of structural analysis and design of a mariculture ship. In this paper, a simulation methodology is proposed based on potential flow theory, focusing on a semi-submersible large-scale mariculture ship with a rigid frame. Abaqus/Aqua 2020 software is used to establish a full-scale dynamic analysis model of the fishery. In the simulation, a nonlinear implicit integration method is applied, and the non-deterministic boundary conditions of the floating body are optimized using dynamic equilibrium principles. By varying the wave and flow conditions, the variations in mooring forces, vibration amplitudes, and average vibration values are analyzed. Furthermore, the dynamic changes in the overall spatial displacements of the fishery, characteristics of longitudinal and vertical oscillations, and mid-span deflections are analyzed. It is concluded that the mooring force is linearly correlated with the flow velocity, that a higher wave increases the longitudinal oscillation amplitude, and that a longer wave period leads to higher mooring forces and longitudinal heaving amplitude. These dynamic response and displacement results of the mariculture ship are expected to provide a basis for its design and safety assessment.

Valence and Rydberg excitations of 3-fluorotoluene in the 4.4–10.8 eV photoabsorption energy region

The absolute photoabsorption cross sections for 3-fluorotoluene in the 4.4–10.8 eV energy-range were obtained for the first-time using a synchrotron radiation light source. New theoretical calculations, providing vertical excitation energies and oscillator strengths, were performed at the time-dependent density functional theory and the equation-of-motion coupled cluster method restricted to single and double excitations to qualitatively support the experimental data. The electronic transitions discernible in the photoabsorption spectrum have been assigned to valence, mixed valence-Rydberg and Rydberg transitions. Additionally, a comprehensive assignment of the vibronic structure was performed with the main contribution of C–H in plane bending mode progressions dictating the spectroscopy of the lowest-lying absorption band. From the absolute photoabsorption cross sections, the photolysis lifetimes of 3-fluorotoluene in the Earth's atmosphere were also obtained.

Reference Values and Determinants of Spatiotemporal and Kinetic Variables in Recreational Runners.

Identifying atypical lower limb biomechanics may help prevent the occurrence or recurrence of running-related injuries. No reference values for spatiotemporal or kinetic variables in healthy recreational runners are available in the scientific literature to support clinical management. To (1) present speed- and sex-stratified reference values for spatiotemporal and kinetic variables in healthy adult recreational runners; (2) identify the determinants of these biomechanical variables; and (3) develop reference regression equations that can be used as a guide in a clinical context. Descriptive laboratory study. This study involved 860 healthy recreational runners (age, 19-65 years [38.5% women]) tested on an instrumented treadmill at their preferred running speed in randomly allocated, standardized running shoes with either hard or soft cushioning. Twelve common spatiotemporal and kinetic variables-including contact time, flight time, duty factor, vertical oscillation, step cadence, step length, vertical impact peak (VIP), time to VIP, vertical average loading rate, vertical stiffness, peak vertical ground-reaction force (GRF), and peak braking force-were derived from GRF recordings. Reference values for each biomechanical variable were calculated using descriptive statistics and stratified by sex and running speed category (≤7, 8, 9, 10, 11, 12, 13, 14, and ≥15 km/h). Correlations and multiple regression analyses were performed to identify potential determinants independently associated with each biomechanical variable and generate reference equations. The mean running speed was 10.5 ± 1.3 km/h and 9 ± 1.1 km/h in men and women, respectively. While all potential predictors were significantly correlated with many of the 12 biomechanical variables, only running speed showed high correlations (r > 0.7). The adjusted R2 of the multiple regression equations ranged from 0.19 to 0.88. This study provides reference values and equations that may guide clinicians and researchers in interpreting spatiotemporal and kinetic variables in recreational runners. The reference values can be used as targets for clinicians working with recreational runners in cases where there is a clinical suspicion of a causal relationship between atypical biomechanics and running-related injury.

Prediction of instantaneous perceived effort during outdoor running using accelerometry and machine learning.

The rate of perceived effort (RPE) is a subjective scale widely used for defining training loads. However, the subjective nature of the metric might lead to an inaccurate representation of the imposed metabolic/mechanical exercise demands. Therefore, this study aimed to predict the rate of perceived exertions during running using biomechanical parameters extracted from a commercially available running smartwatch. Forty-three recreational runners performed a simulated 5-km race on a track, providing their RPE from a Borg scale (6-20) every 400 m. Running distance, heart rate, foot contact time, cadence, stride length, and vertical oscillation were extracted from a running smartwatch (Garmin 735XT). Machine learning regression models were trained to predict the RPE at every 5 s of the 5-km race using subject-independent (leave-one-out), as well as a subject-dependent regression method. The subject-dependent method was tested using 5%, 10%, or 20% of the runner's data in the training set while using the remaining data for testing. The average root-mean-square error (RMSE) in predicting the RPE using the subject-independent method was 1.8 ± 0.8 RPE points (range 0.6-4.1; relative RMSE ~ 12 ± 6%) across the entire 5-km race. However, the error from subject-dependent models was reduced to 1.00 ± 0.31, 0.66 ± 0.20 and 0.45 ± 0.13 RPE points when using 5%, 10%, and 20% of data for training, respectively (average relative RMSE < 7%). All types of predictions underestimated the maximal RPE in ~ 1 RPE point. These results suggest that the data accessible from commercial smartwatches can be used to predict perceived exertion, opening new venues to improve training workload monitoring.

Charged particles motion and quasiperiodic oscillation in Simpson–Visser spacetime in the presence of external magnetic fields

The present work is devoted to the study of the dynamics of charged particles around Simpson–Visser black holes (with the length parameter lle 2) and wormholes (l>2) immersed in an external asymptotically uniform magnetic field. To do this, first, we solve the Maxwell equation for 4-potentials of the electromagnetic field and show that the difference between the numerical solution and Wald’s solution is small enough to neglect it, which may allow us to use the solution obtained by Wald. We also study fundamental frequencies of in the vertical and radial oscillations of charged particles around circular stable orbits around the magnetized black hole. The effects of the magnetic interaction and length parameters on the fundamental frequencies. We investigate the quasiperiodic oscillations (QPOs) around the black hole in relativistic precession and epicyclic resonance models. It is also shown that the combined effects of magnetic interaction for negatively charged particles and length parameters can mimic the spacetime effects of the Schwarzschild black hole compensating for their effects, as well as the spin of rotating Kerr black holes. The distance between an orbit where a QPO is generated with the ratio of upper and lower frequencies 3: 2 and innermost stable circular orbits is also studied. It is found that the QPO orbits are very close to ISCO in the RP model at l<2. This implies that the obtained result helps to determine the ISCO around black holes. We also study the applications of observed QPOs around stellar-mass black holes in microquasars and supermassive black holes.

Stability of Vertical Rotations of an Axisymmetric Ellipsoid on a Vibrating Plane

In this paper, we address the problem of an ellipsoid with axisymmetric mass distribution rolling on a horizontal absolutely rough plane under the assumption that the supporting plane performs periodic vertical oscillations. In the general case, the problem reduces to a system with one and a half degrees of freedom. In this paper, instead of considering exact equations, we use a vibrational potential that describes approximately the dynamics of a rigid body on a vibrating plane. Since the vibrational potential is invariant under rotation about the vertical, the resulting problem with the additional potential is integrable. For this problem, we analyze the influence of vibrations on the linear stability of vertical rotations of the ellipsoid.

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.