Attitude-pendulum-sloshing coupled dynamics of quadrotors slung liquid containers

Quadrotors suspended water containers may be used for fire-fighting services. Unfortunately, the complicated dynamics in this type of system degrade the flight safety because of coupling effects among the quadrotor attitude, container swing, and liquid sloshing. However, few effects have been directed at the attitude-pendulum-sloshing dynamics in this type of aerial cranes. A novel planar model of a quadrotor carrying a liquid tank under dual-hoist mechanisms is presented. The model includes vehicle-attitude dynamics, load-swing dynamics, and fluid-sloshing dynamics. Resulting from the model, a new method is proposed to control coupled oscillations among the vehicle attitude, load swing, and fluid sloshing. Numerous simulations on the nonlinear model demonstrate that the control method can reduce the undesirable oscillations, stabilize the quadrotor’s attitude, and reject the external disturbances. The theoretical findings may also extend to the three-dimensional dynamics of quadrotors slung liquid tanks, and other types of aerial vehicles transporting liquid containers including helicopters or tiltrotors.

Wilberforce pendulum: modelling linearly damped coupled oscillations of a spring-mass system

The Wilberforce pendulum is a coupled spring-mass system, where a mass with adjustable moment of inertia is suspended from a helical spring. Energy is converted between the translational and torsional modes, and this energy conversion is most clearly observed at resonance, which occurs when the damped natural frequencies of the two oscillation modes are equal. A theoretical model—with energy losses due to viscous damping accounted for—was formulated using the Lagrangian formalism to predict the pendulum mass’ trajectory. Theoretical predictions were compared with experimental data, showing good agreement. Fourier analysis of both theoretical predictions and experimental data further corroborate the validity of our quantitative model. The dependence of oscillation features like beat frequency and maximum conversion amplitude on relevant parameters such as the initial vertical displacement, initial angular displacement and moment of inertia was also investigated and experimentally verified.

Mud Motor PDM Dynamics: An Analytical Model

In a fast drilling environment, suchas shale drilling, refining advanced technologies for preventing downhole toolfailures is paramount. Challenges are still very much associated with complex bottom-hole assemblies and the vibration of the drill string when used with a downhole mud motor. The mud positive displacement motor with various lobe configurations and designs becomes an additional excitation source of vibration. Further, it affects the transient behavior of the performance mud motor. Unbalanced force exists because the center ofmass of the motor rotor does not coincide with the axis of rotation.Further, the vector of full acceleration of the center of the rotor can be decomposed into two perpendicular projections—tangent and normal—which aretaken into account and integrated intothe full drill string forced frequency modelas force and displacement at the motorlocation. The paper includes two models, first one to predict the critical speeds and the second one to see the transient behavior of the downhole parameters when the mud motor is used.The model also considers the effect of the stringspeed. The unbalanced force is more pronounced at the lower pair or lobe configuration as compared to the higher pairlobe configuration because of the larger eccentricity. The unbalance is modeled in terms of an equivalent mass of therotor with the eccentricity of the rotor. Also, the analysis provides an estimation of relative bending stresses, shear forces, lateral displacements and transient bit rpm, bit torque, and weightone bit for the assembly used. Based onthe study, severe vibrations causing potentially damaging operating conditionswhen transient downhole forcing parametersare used for the vibration model.It has been found that when a mud motor isused using static forcing parameters may not provide the conservative estimation of the critical speeds as opposed totransient parameters. This is because coupled oscillations fundamentally can create new dynamic phenomena, which cannot be predicted from the characteristics of isolated elements of the drilling system.

Specifics of Construction of Measuring Transducers with Logometric Output Based on Interconnected Piezoresonators

The paper presents the results of simulation modeling of measuring devices. The simulation modeling is based on the use of coupled oscillations in systems with two degrees of freedom. Methods of controlling the parameters of the oscillatory system of the converter based on interconnected piezoresonators are considered. A comparative assessment of the metrological characteristics of possible variants of piezoresoanase sensors with logometric (differential) output is conducted. It is shown that when the Q-factor of the oscillatory system of the primary converter is affected, a higher sensitivity of the measuring process is provided by the control of the active resistance of the coupling element replacement circuit between the resonators. In this case, it is proposed to use the ratio of the oscillation amplitudes of one of the interconnected resonators measured at the frequencies of common-mode and antiphase oscillations in the system as the output signal of the sensor. When the frequency-setting parameters of the converter are affected, it is recommended to use the ratio of the oscillation amplitudes of two interconnected piezoresonators measured at one of the normal frequencies of synchronized oscillations in the system to generate the output signal. There are several advantages of measuring devices of this type, such as high sensitivity, simplicity of design, low cost, manufacturability, and operational applicability for harsh conditions.

Coupled oscillations enable rapid temporal recalibration to audiovisual asynchrony

The brain naturally resolves the challenge of integrating auditory and visual signals produced by the same event despite different physical propagation speeds and neural processing latencies. Temporal recalibration manifests in human perception to realign incoming signals across the senses. Recent behavioral studies show it is a fast-acting phenomenon, relying on the most recent exposure to audiovisual asynchrony. Here we show that the physiological mechanism of rapid, context-dependent recalibration builds on interdependent pre-stimulus cortical rhythms in sensory brain regions. Using magnetoencephalography, we demonstrate that individual recalibration behavior is related to subject-specific properties of fast oscillations (>35 Hz) nested within a slower alpha rhythm (8–12 Hz) in auditory cortex. We also show that the asynchrony of a previously presented audiovisual stimulus pair alters the preferred coupling phase of these fast oscillations along the alpha cycle, with a resulting phase-shift amounting to the temporal recalibration observed behaviorally. These findings suggest that cross-frequency coupled oscillations contribute to forming unified percepts across senses.

Совместное влияние магнитного поля и спин-поляризованного тока на связанную динамику магнитных вихрей в спин-трансферном наноосцилляторе

The joint effect of the spin polarized current and an external magnetic field on the dynamics of magnetization in vortex spin-transfer nano-oscillators with a diameter of 400 nm is investigated. For the numerical calculation of the coupled dynamics of magnetic vortices, the SpinPM software package for micromagnetic modeling was used. The dependence of the frequency of stationary coupled oscillations of vortices on the magnitude of the magnetic field, which determines the operating frequency range of a tunable vortex spin-transfer nano-oscillator.

Fine details of crystal structure and atomic vibrations in YbB12 with a metal–insulator transition

The crystal structure of single-crystal Kondo insulator YbB12 was studied at nine temperatures in the range 85–293 K based on X-ray diffraction data. Very weak Jahn–Teller distortions of the cubic lattice were detected at all temperatures, but did not require a revision of the structural model. Heat capacity and electrical conductivity of YbB12 single crystals were studied in the temperature range 1.9–300 K. It is found that both the structural parameters and the indicated physical properties have some specific features in the temperature range 120–160 K. The unit cell of YbB12 contracts when cooled below 160 K and expands at around 120 K. The temperature dependences of the equivalent atomic displacement parameters U eq(T) are no longer monotonic around 140 K and should be modeled by two Einstein curves for Yb and two Debye curves for boron atoms above and below this temperature. As follows from the temperature behavior of the specific heat, coupled oscillations of Yb ions in a double-well potential lead to the appearance of a charge gap in the density of states and gradual deterioration in conductive properties of the crystal below 150 K. This metal–insulator phase transition is accompanied by a kink in the U eq(T) curves and changes in the unit-cell values.