PARAMETER ESTIMATION FOR OSCILLATORY SYSTEMS

Simple harmonic motion was investigated of a rotational oscillating system. The effect of dumping and forcing on motion of the system was examined and measurements were taken. Resonance in a oscillating system was investigated and quality factor of the dumping system was measured at different damping forces using three different methods. Resonance curves were constructed at two different damping forces. A probabilistic model was built and system parameters were estimated from the resonance curves using Stan sampling platform. The quality factor of the oscillating system when the additional dumping was turned off was estimated to be $Q = \num{71 \pm 1}$ and natural frequency $\omega_0 = \num{3.105 \pm 0.008}\, \si{\per\second}$.

Nonlinear Dynamic Analysis of the Cutting Process of a Nonextensible Composite Boring Bar

A nonlinear dynamic analysis of the cutting process of a nonextensible composite cutting bar is presented. The cutting bar is simplified as a cantilever with plane bending. The nonlinearity is mainly originated from the nonextensible assumption, and the material of cutting bar is assumed to be viscoelastic composite, which is described by the Kelvin–Voigt equation. The motion equation of nonlinear chatter of the cutting system is derived based on the Hamilton principle. The partial differential equation of motion is discretized using the Galerkin method to obtain a 1-dof nonlinear ordinary differential equation in a generalized coordinate system. The steady forced response of the cutting system under periodically varying cutting force is approximately solved by the multiscale method. Meanwhile, the effects of parameters such as the geometry of the cutting bar (including length and diameter), damping, the cutting coefficient, the cutting depth, the number of the cutting teeth, the amplitude of the cutting force, and the ply angle on nonlinear lobes and primary resonance curves during the cutting process are investigated using numerical calculations. The results demonstrate that the critical cutting depth is inversely proportional to the aspect ratio of the cutting bar and the cutting force coefficient. Meanwhile, the chatter stability in the milling process can be significantly enhanced by increasing the structural damping. The peak of the primary resonance curve is bent toward the right side. Due to the cubic nonlinearity in the cutting system, primary resonance curves show the characteristics of typical Duffing’s vibrator with hard spring, and jump and multivalue regions appear.

Improved Determination of Q Quality Factor and Resonance Frequency in Sensors Based on the Magnetoelastic Resonance Through the Fitting to Analytical Expressions

The resonance quality factor Q is a key parameter that describes the performance of magnetoelastic sensors. Its value can be easily quantified from the width and the peak position of the resonance curve but, when the resonance signals are small, for instance when a lot of damping is present (low quality factor), this and other simple methods to determine this parameter are highly inaccurate. In these cases, numerical fittings of the resonance curves allow to accurately obtain the value of the quality factor. We present a study of the use of different expressions to numerically fit the resonance curves of a magnetoelastic sensor that is designed to monitor the precipitation reaction of calcium oxalate. The study compares the performance of both fittings and the equivalence of the parameters obtained in each of them. Through these numerical fittings, the evolution of the different parameters that define the resonance curve of these sensors is studied, and their accuracy in determining the quality factor is compared.

Determination of the anisotropy fields of polycrystalline hexaferrites by FMR

We propose the method for calculating the ferromagnetic resonance curves of polycrystalline hexaferrites with anisotropy of the easy magnetization plane. The results of the experimental studies of the magnetocrystalline anisotropy fields and the magnetomechanical ratios of hexaferrites Ba3Co1.5+xTixFe245–2xO41 (0.0 ≤ x ≤ 1.0) and Ba3Co2.5–x ZnxTi0.5 Fe23O41 (0.0 ≤ x ≤ 1.2) systems at room temperature are presented.

Propagation of Current Waves along Randomly Located Multiconductor Transmission Lines inside a Rectangular Resonator

Propagation of current waves along randomly located multiconductor transmission lines inside a rectangular resonator is investigated. Two different line configurations are considered: parallel wires and perpendicular lines. The analytical solutions for both types of lines are obtained, using the method of symmetrical lines inside the resonator. Computer realization of this method allows it to obtain a fast solution. Therefore, it becomes possible to investigate statistical properties of induced currents. It could be shown that the mutual coupling of the currents in the wires is strong when the frequency is near resonances in the system “cavity and wires” and relatively small far from these resonances. Stochastization leads to a broadening of the resonance curves.