Oscillation Method Research Articles

Study on the influence of TiO2 nanoparticles on the breakdown voltage of transformer oil under severe cold conditions.

The modified nanoparticles can significantly improve the insulation characteristics of transformer oil. Currently, there is a lack of research on the actual motion state of particles in nanofluid to further understand the micro-mechanism of nanoparticles improving the insulation characteristics of transformer oil. In this study, the nanofluid containing 0.01g/L of TiO2 with a particle size of 20nm is prepared using the thermal oscillation method. Breakdown voltage tests are carried out. The experimental test results show that adding nanoparticles can significantly reduce the breakdown probability of transformer oil. The more the water content, the less the enhancement effect of the nanofluid on breakdown voltage. The higher the temperature, the stronger the enhancement effect of the nanofluid on breakdown voltage. Finally, the polarization process of nanoparticles and the trajectory of charged particles in the transformer oil under different electric fields are simulated using COMSOL to further analyze the influence mechanism of nanoparticles on the insulation characteristics of transformer oil. The simulation results show that under the action of the electric field, nanoparticles polarize and generate charge shallow traps to adsorb electrons, reducing the high-speed free charges in the oil, and indirectly increasing the breakdown voltage.

Squirt flow in a tight sandstone: an interlaboratory study

SUMMARY In the spirit of interlaboratory benchmarking of related techniques, we have re-examined the seismic-frequency mechanical properties of a low-porosity Wilkeson sandstone specimen tested in axial stress oscillation under water-saturated conditions by Pimienta et al. The same specimen has been newly tested at periods of 1–1000 s under dry and argon-, water- and glycerine-saturated conditions by torsional and flexural oscillation methods, allowing direct measurement of the shear modulus G and Young's modulus E and associated strain-energy dissipations. The results show a steady increase of G and E for the dry specimen with increasing pressure, indicative of progressive closure of the compliant intergranular contacts. Under argon- and water-saturated conditions, the measured moduli differ only marginally from those for dry conditions, without any significant stiffening or dispersion, suggesting that such measurements probe the saturated-isobaric regime. In marked contrast, glycerine saturation results in substantially higher and frequency-dependent moduli, along with frequency-dependent dissipation. We attribute this behaviour to the squirt flow transition with decreasing frequency from the saturated-isolated to the saturated-isobaric regime, modelled with a log-normal distribution of relaxation times (broader than the Debye peak of the standard anelastic solid) superimposed upon a monotonically frequency-dependent background. Although there are differences in detail, these findings corroborate those of Pimienta et al. for the same material tested in axial stress oscillation to higher frequencies under water-saturated conditions. Taken together, the two studies thus provide robust support for theoretical models of squirt flow dispersion and dissipation, occurring at frequencies between those of conventional ultrasonic wave-propagation laboratory methods and those of seismic exploration of the shallow crust.

Algorithm performance study pulse suppression of auto-oscillation phenomena in the electromechanical system of the electric traction drive in braking mode electric traction drive system in braking mode by methods of simulation modeling

Research relevance. Modes accompanied by increased sliding of a wheel with negative viscous friction, characterized by reduction of friction force at growth of sliding speed, can arise at the movement of the vehicle. In these cases, a loss of stability may occur, resulting in the excitation of auto-oscillation phenomena in the electromechanical system (road-wheel-mechanical drive-electric motor). The emergence of this process sharply increases the dynamic load of the system, which can lead to its failure or breakdown. As a consequence, the development of suppression methods of auto-oscillation phenomena is considered to be an urgent task.Purpose of the research. Verification of operability and efficiency of the suppression method of auto oscillations in the electromechanical system of wheel drive during braking of the vehicle.Materials and Methods. With the help of Lyapunov’ function analysis for the electromechanical system of wheel drive the suppression method of auto oscillation phenomena is substantiated. The study of the algorithm performance has been carried out with the use of MATLAB Simulink program complex.Research results. The operability and efficiency of the algorithm is proved by methods of simulation mathematical modeling, which allows its further use in the development of traffic control systems. In case of braking of the vehicle equipped with antilock braking system with the function of suppression of auto oscillations on a slippery support base the reduction of amplitudes oscillation of angular velocities of wheels by 80% and braking moments by 96% is observed. When this vehicle is braked on a high adhesion base, the amplitudes are reduced by 98% in angular velocities and 81% in torques. In simulation modeling of vehicle braking dynamics on a support base with low adhesion properties it has also been shown that in these cases the evasive maneuver can be performed, which indicates on the increase in controllability and active safety of the vehicle.Conclusion. The practical value of the study lies in the possibility of using the developed algorithm for suppressing auto oscillations in practical application as part of vehicle control systems. The developed algorithm can be used on vehicles of different classes equipped with individual traction electric drive of driving wheels.

Origin Analysis and Mitigation Method of Voltage Oscillation Occurred Inside the Winding of Medium-Voltage Medium-Frequency Transformer

Origin Analysis and Mitigation Method of Voltage Oscillation Occurred Inside the Winding of Medium-Voltage Medium-Frequency Transformer

Non-Contact Thermophysical Property Measurements of High-Temperature Corium Through Aerodynamic Levitation

The thermophysical properties of corium are critical for improving the predictive accuracy of severe accident analysis codes. However, due to the high melting temperature and high volatility of corium, thermophysical property measurements are extremely challenging, resulting in a significant lack of data. This study presents a non-contact measurement facility based on the aerodynamic levitation technique, enabling the measurement of the density, surface tension, and viscosity of corium components at temperatures exceeding 3000 K. Density is measured based on the axisymmetric ellipsoid assumption of levitated drops, while the surface tension and viscosity are determined using the drop oscillation method. Experimental results for key corium components, including ZrO2 and a UO2-ZrO2 mixture, are presented, addressing data gaps in the thermophysical properties of UO2-containing materials.

Improved Oscillation Method for High-Frequency Magnetic Core Loss Measurement

Improved Oscillation Method for High-Frequency Magnetic Core Loss Measurement

Novel electromagnetic oscillation method for uniform grain refinement and mechanical properties enhancement of flat-shaped aerospace components

Novel electromagnetic oscillation method for uniform grain refinement and mechanical properties enhancement of flat-shaped aerospace components

Experimental observation of moduli dispersion and attenuation at seismic frequencies in saturated tight rock: effect of microstructure and fluid viscosity

SUMMARY The frequency-dependent elastic properties of fully saturated rocks are notably influenced by fluid pressure diffusion at the microscopic scale. Our experimental evaluation, utilizing forced oscillation and ultrasonic transmission methods under varying effective pressures (${P_{{\rm{eff}}}} = [ {1 - 20} ]$ MPa) and temperatures ($T = [ {{3^{\rm{\circ\!}}}{\rm{C}},{\rm{\,\,}}{{10}^{\rm{\circ\!}}}{\rm{C}},{\rm{\,\,}}{{23}^{\rm{\circ\!}}}{\rm{C}}} ]$), provides critical insights into how rock microheterogeneity and pore fluid viscosity affect elastic dispersion and attenuation at frequencies of $f = [ {1 - 300,{\rm{\,\,}}{{10}^6}} ]$ Hz. We employed a sandstone rock sample with $8.2\,\,\mathrm{ per}\,\,\textrm{cent}$ porosity and conducted measurements using three different fluids: N2, brine and glycerine. In its dry state, our chosen rock exhibits frequency independent elastic moduli at measured effective pressures due to the absence of fluid flow, resulting in negligible deviations in local measurements at different locations. However, this uniform response changes markedly when the rock is saturated with fluids. Gassmann's predictions agree with the measured undrained elastic moduli. Under fluid-saturated conditions, rock's elastic moduli increase with frequency, revealing significant differences depending on measurement positions. This variation suggests that differentiation in elastic properties is amplified during wet measurements, particularly at seismic frequencies. Our modelling indicates that the dominant mechanism is squirt flow, arising from microscopic compressibility heterogeneities within the rock frame and saturating fluid. As the viscosity of the saturating fluid decreases with rising temperature, the magnitude of attenuation peaks diminishes, while their frequency spread widens. This behaviour aligns with predictions from the squirt flow model, which considers the microstructure and varied pore types within the rock. Consequently, the observed frequency dependence in elastic moduli is primarily attributed to fluid flow processes driven by microheterogeneity, which are highly sensitive to small variations in the rock's microstructures. In microstructurally complex regions, it is evident that assuming isotropic and homogeneous conditions for forced axial oscillation measurements can introduce errors. The inherent heterogeneity of the rock must be taken into account to accurately interpret the frequency dependence of elastic moduli. This is especially relevant for applications in geophysical hydrocarbon exploration and seismic monitoring of reservoir geomechanical integrity during CO2 geo-sequestration.

Regular Quaternion Equations of the Spatial Hill Problem in Kustaanheimo–Stiefel Variables and Quaternion Osculating Elements

Regular quaternion equations of the spatial Hill problem (a variant of the limited three-body problem (Sun, Earth, Moon (or another low-mass moving cosmic body under study)) are obtained, when the distance between two bodies with finite masses is considered very large, in four-dimensional Kustaanheimo-Stiefel variables (KS-variables) within the framework of the elliptical and circular spatial bounded three-body problem, as well as the regular quaternion equations of the planar Hill problem in two-dimensional Levi-Civita variables. In these equations, the variables are KS-variables or Levi-Civita variables and the energy of relative motion of the body under study, or a variable that converts for the circular Hill problem into a constant of motion of this body (the Jacobi integration constant), as well as the planetocentric distance of the Sun and real time associated with a new independent variable by the Sundman differential transformation of time or other more complex differential ratio. These equations are supplemented by the equation of the Earth’s orbit in polar coordinates and the equation for the true anomaly characterizing the Earth’s position in the orbit. The first integral of the obtained equations in KS-variables in the case of a circular problem is established. Another first partial integral in the general case is a bilinear relation connecting KS-variables and their first derivatives. Three new forms of regular equations of the spatial Hill problem in quaternion osculating elements (slowly changing quaternion variables) are proposed. The proposed regular quaternion equations have an oscillatory form or the form of equations with slowly changing variables, which makes it possible to effectively use analytical and numerical methods of oscillation theory and methods of nonlinear mechanics in the study of the Hill problem.

Core‐shell Structured Nano CuO@CER Composites for the Photoelectrocatalytic Degradation of Methylene Blue

AbstractThe composite material of nano CuO loaded on ion exchange resin (CuO@CER) as the carrier was prepared successfully by constant temperature oscillation and hydrothermal synthesis methods. It was applied to the photoelectrocatalytic degradation of methylene blue (MB) as an organic pollutant, and further to explore the optimal conditions for CuO@CER photoelectrocatalytic degradation of MB. The results showed that the composite material had a typical core‐shell structure, and the nano CuO loaded on the ion exchange resin had good crystallinity and high purity. CuO@CER exhibited excellent photocatalytic and photoelectrocatalytic performance towards MB, with degradation rates of 92.02% and 95.20% in 70 min under their respective optimal reaction conditions. Furthermore, the photoelectrocatalytic stability of CuO@CER was good relatively, and the degradation rates of MB exceeded 96% after 5 cycles of photoelectrocatalytic experiments. Free radical quenching experiments indicated that superoxide radicals were the main active groups during the photoelectrocatalysis. Additionally, the mechanism of photocatalytic degradation for MB under the electric field was briefly analyzed. This study will provide technical support for the photoelectrocatalytic degradation of organic dye wastewater.

Fast and Robust Noise Background Modeling and Quasiperiodic Oscillation Detection for Astronomical Time Series

Spectrum with confidence levels is a commonly used method for quasiperiodic oscillation (QPO) detection, but it is prone to yield false positives for two reasons: poor choice and/or biased modeling of the null hypothesis (or noise background). Motivated by this, we propose a new time-domain maximum-likelihood estimation method, which can quickly and accurately estimate the noise background free from background trends, spectra peaks, and even QPOs. Our method provides a wide range of candidate stochastic models (e.g., conventional first-order autoregressive, power law, generalized Gauss–Markov, Matérn, and damped random walk), some of which have not been considered previously. Some pitfalls (e.g., detrending) in previous QPO detections are also correctly processed to minimize the false detections. Along with the multitaper method and wavelet, we revisit QPO detection in the X-ray emission from the active galaxies RE J10341+396 and 1H 0707-495, and point out why the significance levels of the QPO at ∼2.6 × 10−4 Hz would be different in previous detections and reduced if the whole observation duration is considered. Our algorithm can be easily extended to other branches of astrophysics and beyond.

Pressure oscillation and suppression method of large-aspect-ratio solid rocket motors

Pressure oscillation and suppression method of large-aspect-ratio solid rocket motors

Role of Impulse Oscillometry (IOS) Together with Diffusing Capacity of the Lungs for Carbon Monoxide (DLCO) and High-Resolution Computed Tomography for the Chest in Early Diagnosis of Interstitial Lung Disease in Patients with Connective Tissue Diseases

Abstract Background Connective Tissue Diseases (CTDs) are systemic autoimmune conditions characterized by frequent lung involvement. Interstitial lung disease (ILD) is a severe pulmonary complication in CTD and associated with significant increased morbidity and mortality, so early detection of ILD is essential. Aim of the Work To find the best modality for early diagnosis of interstitial lung disease in patients with connective tissue disorders by using DLCO, impulse oscillometry and HRCT chest. Patients and Methods This observational, analytical and cross sectional study was conducted upon 60 patients whom were diagnosed as connective tissue disease during the period from march 2022 to march 2023 who were admitted to chest and rheumatology department or outpatient clinics visitors, to Ain Shams University Hospitals. Results regarding our results, there was high statistical significance between DLCO and IOS (Best x5). Sensitivity and specificity of Diffusion lung of CO2; DLCO score in prediction of outcome in CT Chest Findings showing significance in DLCO score; p = 0.024 with CI ranged between 53.9-81.4% and sensitivity 67.6%. Sensitivity and specificity of the impulse oscillation method; R5, R20,and Best-X5 score in prediction of outcome in CT Chest Findings. Showing no significance in all with sensitivity 50.2%, 46.1%, 43.4% and 57.5% respectively Conclusion ILD should always be considered in patients with CTD. Diagnosis of CTD-ILD is challenging so Early diagnosis of ILD using DLCO, HRCT chest or by using IOS is important as it could affect therapy plans.

Control of deposits on pipeline systems by the method of free oscillations

RELEVANCE. There are a large number of heat exchangers in operation enterprises that operate under various temperature conditions. Steam, hot water, heated products of oil refining and other industries, which may contain oxides of iron, aluminum, calcium sulfate silicates, etc., are used as a heating agent. The efficiency of the heat exchange equipment depends on the condition of the heating surfaces. Contamination of these surfaces with various deposits dramatically reduces the heat transfer coefficient, which leads to a significant increase in heat consumption. The nature of the deposits depends on the properties of the heating agent and the heated medium.THE PURPOSE. The purpose is to assess the possibility of controlling deposits on the surfaces of heat exchange equipment by the free oscillation method. The presence of deposits changes the mass of structures and, consequently, the natural frequencies of vibrations, the analysis of which can determine not only the presence and thickness of deposits, as well as their appearance.METHODS. The paper shows the results of experimental studies conducted using a hardware and software package and calculations of natural vibrations of the surfaces of heat exchange equipment in the ANSYS software package to identify their dependence on the thickness and density of deposits. A plate, a pipe, and a pressurized pipe were modeled as heat transfer surfaces.RESULTS. The results obtained experimentally and computationally coincided, and it was concluded that the free oscillation method makes it possible to determine not only the presence of deposits on heat exchange surfaces, but their thickness and appearance.CONCLUSION. The free oscillation method can detect deposits in a timely manner and monitor their condition, which in turn will, reduce overall operating costs, increase energy efficiency and extend service life.

Control Method for Ultra-Low Frequency Oscillation and Frequency Control Performance in Hydro–Wind Power Sending System

In a hydropower-dominated power grid, the primary frequency regulation (PFR) capability of hydropower units is typically compromised to suppress ultra-low frequency oscillations (ULFOs). However, as renewable wind power is further integrated, a practicable solution to damp ULFOs has emerged, which is to adjust the frequency control parameters of wind turbine (WT) units. Driven by the goals of overall damping enhancement and ULFO suppression, this paper first establishes an extended unified frequency model (EUFM) of a hydro–wind power sending system. Based on EUFM, the damping torque of the hydro–wind power sending system is derived, and the specific impact of WT control parameters on ULFOs and PFR characteristics is investigated. Then, a novel optimization objective function considering damping in the ultra-low frequency band and PFR is formulated and solved using an intelligence algorithm. By optimizing the parameters of the WT to suppress ULFOs, the PFR capability of hydropower units can be released. Finally, simulation results verify that the optimized WT parameters can simultaneously address the ULFO problem and guarantee PFR performance, thereby enhancing the frequency dynamic stability of the sending system.

Interval estimation of dynamic liquid level of sucker-rod pumping systems based on dynamometer card

Interval estimation of dynamic liquid level of sucker-rod pumping systems based on dynamometer card

Deep Eutectic Solvent + Water System in Carbon Dioxide Absorption.

In the present work, deep eutectic solvents (DESs) were synthesized in a one-step process by heating the hydrogen bond acceptors (HBAs) tetrabutylammonium bromide and tetrabutylphosphonium bromide, along with two hydrogen bond donors (HBDs) ethanolamine and N-methyldiethanolamine, which were mixed in certain molar ratios. This mixture was then mixed with water to form a DES + water system. The densities of the prepared DES + water systems were successfully measured using the U-tube oscillation method under atmospheric pressure over a temperature range of 293.15-363.15 K. The CO2 trapping capacity of the DES + water systems was investigated using the isovolumetric saturation technique at pressures ranging from 0.1 MPa to 1 MPa and temperatures ranging from 303.15 K to 323.15 K. A semi-empirical model was employed to fit the experimental CO2 solubility data, and the deviations between the experimental and fitted values were calculated. At a temperature of 303.15 K and a pressure of 100 kPa, the CO2 solubilities in the DES + water systems of TBAB and MEA, with molar ratios of 1:8, 1:9, and 1:10, were measured to be 0.1430 g/g, 0.1479 g/g, and 0.1540 g/g, respectively. Finally, it was concluded that the DES + water systems had a superior CO2 capture capacity compared to the 30% aqueous monoethanolamine solution commonly used in industry, indicating the potential of DES + water systems for CO2 capture.

Viscosity of Al–Ni–Co–Nd(Sm) glass-forming melts at high temperatures

Obtaining amorphous alloys with good mechanical and anticorrosion properties is an important problem of modern condensed matter physics. Since the preparation of amorphous alloys involves casting them from liquid state, information on the properties of the melts is needed. Viscosity is one of the most informative structure-sensitive property of melts. In this paper viscosity of some glass-forming Al–Ni–Co–Nd(Sm) melts with different ratio of transition metals was studied using damped oscillation method in a wide temperature range up to 1550 K. Activation energies of the viscous flow were calculated from the experimental data. The hysteresis of viscosity temperature dependences during heating and subsequent cooling was found. It can be associated with a melt transition to a more homogeneous state. The repeated heating and cooling of the melts without crystallization lead to Arrhenius type of viscosity temperature dependences.

Experimental study on dynamic adsorption properties of methylene blue onto coal-based activated carbon using a hydrocyclone

Experimental study on dynamic adsorption properties of methylene blue onto coal-based activated carbon using a hydrocyclone

On the Homotopy-First Integral Method for Non-conservative Oscillators

This paper presents a ready-to-use formula for determining the number and approximate location of periodic orbits in second-order Lienard systems. As a result of the exact closed-form derived in [16], in which an ordinary differential equation (ODE) must be solved to determine the existence and location of periodic orbits for general non-conservative oscillators, a homotopy functional is defined for Lienard-type systems. This provides a closed-form and ready-to-use polynomial formula with roots as an approximation of the periodic orbit's amplitude. In addition, some examples are analyzed, along with conclusions and future plans.