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It is showed the possibility of contactless excitation of transverse oscillations in quartz optical microfibers (fiber microguides) due to their diamagnetic properties. The microguides are made from standard optical fibers by chemical etching and thermal drawing in an electric discharge arc. Dependences were found of resonance frequencies and Q factors of transverse oscillation modes of microguides on the ambient air density in a wide range of values corresponding to a pressure of 5 to 10 5 Pa. Laser excitation of transverse oscillations in microguides was implemented and possible mechanisms of this excitation are discussed. It was found that in vacuum the resonance frequencies of transverse oscillations in microguides under laser excitation conditions are noticeably higher than in the case of magnetic force excitation of oscillations. The magnetic force excitation of microguide oscillations is shown to be possible at significant distances (~1 mm) between a microguide and the source of inhomogeneous magnetic field. These findings can serve as a basis for the development of new types of optical fiber modulators controlled by magnetic field and/or laser radiation and for the design of resonant optical fiber optic sensors with sensitive elements, based on optical microfibers.

We consider the inverse problem of simultaneous determination of two coefficients in the model of small transverse oscillations of a homogeneous bounded string, on whose one end an elastic force acts, and whose other end is not fixed. The oscillation process is modeled by a non-homogeneous equation of hyperbolic type, with the non-homogeneity in the equation represented by multipliers depending on different arguments. The specified values of the solution of the direct problem at the free end of the string constitute some additional information for solving the inverse problem. In this context, within the framework of posing the inverse problem, it is required to define the function in the boundary condition of the third kind as well as the functional multiplier in the non-homogeneity of the equation. The paper establishes conditions for solvability of the inverse problem, some properties of its solution, and proposes an algorithm for numerical approximation of the solution

The article covers the technology of computer modeling of technological processes on example of the research of transverse oscillations of the thread in weaving process. During the formation of the fabric, various dynamic processes took place, including fluctuations in the threads. As an example, the longitudinal oscillations and tension of the threads in the process of surf on a loom are considered. The program and the results of the calculation are given using the software package “Mathcad”.

Bolts are widely used in transmission lines and are key connecting parts of transmission lines. Transmission lines have been affected by the natural environment for a long time, and bolts are prone to frequent vibration leading to loosening or falling off. Bolt loosening endangers the safe and stable operation of transmission lines. This paper analyses the loosening mechanism of the transmission line screw connection, carries out the transverse vibration contrast test of the common bolt anti-loosening measures, and develops the integrated self-locking double nut for the hidden danger of the transmission line bolt loosening, which has good anti-loosening performance, convenient installation, and the conditions for engineering popularization and application.

Most notes of a piano are fitted with two or three strings that, in normal playing conditions, are simultaneously struck by the hammer. In grand pianos, the una corda pedal offers alternative musical effects, notably a softer and duller tonal quality. This pedal’s operation is linked to a lever system that displaces the action to one side causing the hammer to hit only one-out-of-two or two-out-of-three strings, thereby altering the sound. Meanwhile, the other strings of the same note undergo sympathetic vibration, owing to their structural connection through the bridge. This paper introduces a dynamic model that replicates the effects of the una corda pedal. It consists of a state-space scheme, serving as a framework to couple the dynamic behaviour of the various components. Stiff-string models describe the strings’ vibration in three dimensions while a reduced modal model captures the dynamics of the soundboard. Results show how the string vibration and the force transmitted to the soundboard are affected by applying hammer excitation to individual or multiple strings. When all strings are struck, the transverse vibration shows beating. This effect is audible and evidenced in the spectrograms, where the amplitude of partials oscillates over time. In the una corda case, the force exerted on the bridge by the passive string increases initially with time, and its contribution to the overall transmitted force is smaller. However, there is no beating, the decay is more even, and the spectrograms do not show irregularities over time.

The focus of this work is to dissect the physical mechanisms that drive and sustain flow-induced, transverse vibrations of cylinders. The influence of different mechanisms is quantified by using a method to partition the fluid dynamic force on the cylinder into distinct, physically relevant components. In conjunction with this force partitioning, calculations of the energy extracted by the oscillating body from the flow are used to make a direct connection between the phenomena responsible for force generation and their effect on driving flow-induced oscillations. These tools are demonstrated in a study of the effect of cylinder shape on flow-induced vibrations. Relatively small increases in cylinder aspect ratio are found to have a significant influence on the amplitude of oscillation, resulting in a large drop in oscillation amplitude at reduced velocities that correspond to the upper range of the synchronization regime. By mapping out the energy transfer between the fluid and structure as a function of aspect ratio, we identify the existence of a low-amplitude stationary state as the cause of the drop in amplitude. Partitioning the fluid dynamic forces on cylinders of varying aspect ratio then allows us to uncover the physical mechanisms behind the appearance of the underlying bifurcation. The analysis also suggests that while vortex shedding in the wake is necessary to initiate oscillations, it is the vorticity associated with the boundary layer over the cylinder that is responsible for the sustenance of flow-induced vibrations.

The purpose of this work is to numerically visualize the flow past forced oscillating square cylinder and investigate the effect of corner radius on flow induced forces. The finite volume code was applied to simulate the two dimensional flow past forced oscillating square cylinder with different radius to diameter ratios, (R/D = 0 referring to a square cylinder with sharp edges and R/D = 0.5 as a circular cylinder). The near wake of a square section cylinder with an increment of R/D = 0.1 was studied as the body undergoes a complete oscillatory cycle at lock-in condition, F = fe / fs = 1 (where fe is the excitation frequency and fs is the vortex shedding frequency for the stationary cylinder). The computational model was validated for flow past oscillating cylinder with R/D = 0.5 at frequency ratios F = 0.5, 1.0 and 1.50, using as the lock-in and lock-out limits and the results shown good agreement. It was observed that computed value of Strouhal Number is nearly same for both stationary and oscillation case and a similar trend was observed, as R/D ratio increases. However, the results obtained from oscillation cylinder cases show the significant increase in root mean square value of lift coefficient (CL,RMS) and mean drag coefficient (CD) as compared to the stationary cylinder. Finally, It was found that the percentage increase of CL,RMS is higher than CD in force oscillating condition for R/D = 0, whereas both values decreases with the increase of R/D.

Mutual conversion of various kinds of magnetohydrodynamic (MHD) waves can have profound impacts on wave propagation, energy transfer, and heating of the solar chromosphere and corona. Mode conversion occurs when an MHD wave travels through a region where the Alfvén and sound speeds are equal (e.g., a 3D magnetic null point). Here we report the direct extreme ultraviolet (EUV) imaging of mode conversion from a fast-mode to a slow-mode MHD wave near a 3D null point using Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) observations. An incident fast EUV wavefront associated with an adjacent eruptive flare propagates laterally through a neighboring pseudostreamer. Shortly after the passage of the fast EUV wave through the null point, a slow-mode wave appears near the null that propagates upward along the open structures and simultaneously downward along the separatrix encompassing the fan loops of the pseudostreamer base. These observations suggest the existence of mode conversion near 3D nulls in the solar corona, as predicted by theory and MHD simulations. Moreover, we observe decaying transverse oscillations in both the open and closed structures of the pseudostreamer, along with quasiperiodic type III radio bursts indicative of repetitive episodes of electron acceleration.

The flow-induced oscillation of a transversely clamped buckled flexible filament in a uniform flow was explored using the penalty immersed boundary method. Both inverted and conventional configurations were analysed. The effects of bending rigidity, filament length and Reynolds number were examined. As these parameters were varied, four distinct modes were identified: conventional transverse oscillation mode, deflected oscillation mode, inverted transverse oscillation mode and structurally steady mode. The filament exhibited a 2S wake pattern under the conventional transverse oscillation mode and the small-amplitude inverted transverse oscillation mode, a P wake pattern under the deflected oscillation mode and a 2S + 2P wake pattern for the large-amplitude inverted transverse oscillation mode. Irrespective of their initial conditions, all of the filaments converged to the conventional transverse oscillation mode under low bending rigidity. Multistability was observed in the transversely clamped buckled flexible filament under moderate bending rigidity. The deflection in the oscillation mode increased with increasing filament length. The inverted buckled filament was sensitive to the Reynolds number, unlike the conventional buckled filament. The transverse oscillation mode demonstrated superior energy-harvesting performance.

Direct laser acceleration of electrons during a high-energy, picosecond laser interaction with an underdense plasma has been demonstrated to be substantially enhanced by controlling the laser focusing geometry. Experiments using the OMEGA EP facility measured electrons accelerated to maximum energies exceeding 120 times the ponderomotive energy under certain laser focusing, pulse energy, and plasma density conditions. Two-dimensional particle-in-cell simulations show that the laser focusing conditions alter the laser field evolution, channel fields generation, and electron oscillation, all of which contribute to the final electron energies. The optimal laser focusing condition occurs when the transverse oscillation amplitude of the accelerated electron in the channel fields matches the laser beam width, resulting in efficient energy gain. Through this observation, a simple model was developed to calculate the optimal laser focal spot size in more general conditions and is validated by experimental data.