Forced Oscillation Research Articles

ИНЕРЦИОННЫЕ СВОЙСТВА ДИСПЕРСНОГО МАТЕРИАЛА В РЕЖИМЕ ВЫНУЖДЕННЫХ КОЛЕБАНИЙ

It is noted that the modes of forced and natural oscillations are taken into account to calculate strength of structural elements of transport vehicles and mechanisms. In this regard, the dynamic properties of the transported cargo are considered, and they are significantly different for solid and disperse materials. 
 The study objective is to define the dynamic properties of a disperse material under harmonic vibrations. The research method is to present the status of the system under study in the form of a combination of its diametrically opposite maximum statuses. A common example of such a representation is the composition of a dry construction mixture – a combination of sand and cement (100% sand in the mixture is one maximum status, 100% cement is the diametrically opposite maximum status). A disperse material located on a platform performing harmonic oscillations is considered. To assess the instability (or stability) of the disperse material relative to the platform, a dimensionless quantity ξ is introduced. The main problem in determining the dynamic properties of a disperse material is the impossibility of calculating the average coefficient of dynamic friction, since its value is influenced by the interaction of dispersed particles with each other in the entire mass of the material, and not only with the surface of the platform. The description of the dynamic status of a disperse material as a composition of its unstable and stable statuses provides the key to solving this and similar problems. The opposite maximum statuses of the system under study may be comparable and incomparable in terms of quantitative assessment.
 The subject of the study are systems with equal maximum statuses. This method is universal and applicable to a wide variety of systems with different statuses and parameters.

Primordial-tensor-induced stochastic gravitational waves

Cosmological stochastic gravitational waves (GWs) induced by a spectator field are usually expected to have an amplitude very small compared with those generated by the curvature perturbation, or equivalently by a field dominating the universe. On the contrary to this expectation, we show that a spectator field that provides a tensor perturbation, on top of the metric tensor perturbation, can generate a significant amount of GWs. The amplitude and frequency of the generated GWs may lie within the sensitivity range of future GW detectors. In particular, if the sound velocities of the two tensor perturbations coincide, the induced GW amplitude may become very large due to resonance by forced oscillation, even in the limit of small coupling between them. A distinct feature of this scenario is that, since tensor modes can hardly lead to the formation of primordial black holes (PBHs), we expect no presence of PBHs, in contrast to the usual scalar-induced case, in which the detection of strong enough induced GWs suggests the existence of PBHs.

The oscillating Fischer-Tropsch reaction.

The mechanistic steps that underlie the formation of higher hydrocarbons in catalytic carbon monoxide (CO) hydrogenation at atmospheric pressure over cobalt-based catalysts (Fischer-Tropsch synthesis) have remained poorly understood. We reveal nonisothermal rate-and-selectivity oscillations that are self-sustained over extended periods of time (>24 hours) for a cobalt/cerium oxide catalyst with an atomic ratio of cobalt to cerium of 2:1 (Co2Ce1) at 220°C and equal partial pressures of the reactants. A microkinetic mechanism was used to generate rate-and-selectivity oscillations through forced temperature oscillations. Experimental and theoretical oscillations were in good agreement over an extended range of reactant pressure ratios. Additionally, phase portraits for hydrocarbon production were constructed that support the thermokinetic origin of our rate-and-selectivity oscillations.

A study to detect early lung function deterioration using forced oscillation technique in smokers

A study to detect early lung function deterioration using forced oscillation technique in smokers

Numerical Study of Circular-Cylinder Disturbance Generators with Rigid Splitter Plates

This paper describes the numerical study of oscillating circular cylinders with rigid splitter plates of different lengths. These geometries may be used as disturbance generators for the study of unsteady airfoils and wings operating in highly vortical flowfields. It has been shown that cylinders undergoing forced rotational oscillations at their natural shedding frequency can produce wakes with minimal deviation in cycle-to-cycle vortex strength and position. Adding a splitter plate allows these deviations to be reduced even further. We present cases for oscillating cylinders having splitter-plate lengths up to at a Reynolds number of 7600. Frequencies are maintained at the natural shedding frequency, and a rotational amplitude of 45 deg is used. Numerical simulations are performed using a two-dimensional unsteady Reynolds-averaged Navier–Stokes (RANS) code. Results are presented in the form of vorticity contours and cycle-averaged velocity profiles, as well as the dominant frequencies of cylinder lift force and downstream velocity angles. The results show that splitter-plate lengths shorter than adversely affect the ability to generate a coherent vortex wake due to shear layer roll-up near the trailing edge of the plate. Splitter plates longer than produced a reverse von Kármán wake with consistent cycle-to-cycle vortex shedding.

ABOUT THE CHOICE OF DIFFERENT STEPS OF MILLING CUTTERS FOR METAL PROCESSING

The article discusses the technology of choosing the different steps of milling cutters for processing metal products. The existing methods of designing multistep milling cutters aimed at reducing the probability of resonant during milling are analyzed. A new method of designing milling cutters with non-repeating steps and a addition to it, providing a reduction of their imbalance, is proposed. A study of the frequencies of forced oscillations during milling is carried out using examples of milling cutters developed by the proposed method.

Experimental evaluation of a solid oxide fuel cell system exposed to inclinations and accelerations by ship motions

Solid Oxide Fuel Cell (SOFC) systems have the potential to reduce emissions from seagoing vessels. However, it is unknown whether ship motions influence the system’s operation. In this research, a 1.5 kW SOFC module is operated on an inclination platform that emulates ship motions, to evaluate the influence of static and dynamic inclinations on the system’s safety, operation, and lifetime. The test campaign consists of a static inclination test, a dynamic test, a degradation test, and a high acceleration test. There were no interruptions in the power supply during the different tests, and no detectable gas leakages or safety hazards. Although the SOFC does not fail in any test condition, dynamic inclinations result in forced oscillations in the fuel regulation, which propagate through the system by different feedback loops in the control architecture, leading to significant deviations in the operational parameters of the system. Additionally, for motion periods from 16 to 26 s, reoccurring exceedance of the fuel utilisation results in a gradual reduction of the power supply. Several enhancements are recommended to improve the design of SOFCs and marine fuel cell regulations to ensure their safe operation on ships.

CSF-to-blood toxins clearance is modulated by breathing through cranio-spinal CSF oscillation.

Clearance of brain toxins occurs during sleep, although the mechanism remains unknown. Previous studies implied that the intracranial aqueductal cerebrospinal fluid (CSF) oscillations are involved, but no mechanism was suggested. The rationale for focusing on the aqueductal CSF oscillations is unclear. This study focuses on the cranio-spinal CSF oscillation and the factors that modulate this flow. We propose a mechanism where increased cranio-spinal CSF movements enhance CSF-to-blood metabolic waste clearance through the spinal CSF re-absorption sites. A recent study demonstrating that disturbed sleep impairs CSF-to-blood but not brain-to-CSF clearance, supports the fundamentals of our proposed mechanism. Eight healthy subjects underwent phase-contrast magnetic resonance imaging to quantify the effect of respiration on the cranio-spinal CSF oscillations. Maximal CSF volume displaced from the cranium to the spinal canal during each respiration and cardiac cycle were derived as measures of cranio-spinal CSF mixing level. Transition from normal to slow and abdominal breathing resulted in a 56% increase in the maximal displaced CSF volume. Maximal change in the arterial-venous blood volume, which is the driving force of the CSF oscillations, was increased by 41% during slow abdominal breathing. Cranio-spinal CSF oscillations are driven by the momentary difference between arterial inflow and venous outflow. Breathing modulates the CSF oscillation through changes in the venous outflow. The amount of toxins being transferred to the spinal canal during each respiratory cycle is significantly increased during slow and deeper abdominal breathing, which explains enhanced CSF-to-blood toxins clearance during slow-wave sleep and poor clearance during disrupted sleep.

Slicing of a soft solid.

Cutting of soft materials is a complex problem, which is still not well understood at the fundamental level, especially for soft materials. The cutting process we consider is slicing, which starts with indentation, followed by sliding of a knife on the material to be cut. Here, we describe cutting experiments on PDMS elastomers with three different moduli. Our experiments reveal typical stages of this cutting process, starting with indentation and ending at steady state cutting. The process starts with a pre-cutting phase in which the blade does not slip grossly relative to the solid to be cut, and deformation is mostly elastic. Slip of the blade initiates suddenly and is often accompanied by initiation of cutting. Cutting is relatively smooth in the next stage, which requires a continuous increase in shear force. For soft PDMS, this smooth cutting stage is followed by one in which folds or creases form on the cutting surface. The corresponding shear force response is no longer smooth as "steady" sliding occurs in a stick-slip fashion with oscillatory forces. The average shear force reaches a plateau and no longer increases with shear displacement. Experimental observations of the various cutting stages are interpreted quantitatively.

A graphics processing unit-based computational framework for impact failure of automotive coatings

This paper is the first one to develop a graphics process unit-based computational framework to accelerate impact failure simulations of automotive coatings, which require a considerable computational cost. Such an efficient computational framework considers both intra- and inter-laminar failures, including a multi-mechanism damage model for polymer-ply fracture and a discontinuous Galerkin/cohesive zone model for coating delamination. The cohesive zone model is implemented as a contact algorithm with a cohesive constitutive law, hence maintaining the ability to simulate delamination problems under large deformation. Additionally, a parallel contact algorithm for the cohesive zone model is developed with the simultaneous elimination of bitwise non-reproducibility and unphysical force oscillations occurring when Gauss points transition between segments. After verification via numerical examples, this framework is applied to the impact failure of multi-layered automotive coatings, where experimental failure patterns of the coating are well reproduced. Through parallel computing, a speedup of up to 119.7 times in terms of wall clock time is gained.

Separation of interacting active particles in an asymmetric channel.

We study the diffusive behavior of interacting active particles (self-propelled) with mass m in an asymmetric channel. The particles are subjected to an external oscillatory force along the length of the channel. In this setup, particles may exhibit rectification. In the absence of interaction, the mean velocity 〈v〉 of the particles shows a maximum at moderate m values. It means that particles of moderate m have higher velocities than the others. However, by incorporating short-range interaction between the particles, 〈v〉 exhibits an additional peak at lower m values, indicating that particles of lower and moderate m can be separated simultaneously from the rest. Furthermore, by tuning the interaction strength, the self-propelled velocity, and the parameters of the oscillatory force, one can selectively separate the particles of lower m, moderate m, or both. Empirical relations for estimating the optimal mass as a function of these parameters are proposed. These findings are beneficial for separating the particles of selective m from the rest of the particles.

A critical evaluation of decadal solar cycle imprints in the MiKlip historical ensemble simulations

Abstract. Studies concerning solar–terrestrial connections over the last decades claim to have found evidence that the quasi-decadal solar cycle can have an influence on the dynamics in the middle atmosphere in the Northern Hemisphere (NH) during the winter season. It has been argued that feedbacks between the intensity of the UV part of the solar spectrum and low-latitude stratospheric ozone may produce anomalies in meridional temperature gradients which have the potential to alter the zonal-mean flow in middle to high latitudes. Interactions between the zonal wind and planetary waves can lead to a downward propagation of the anomalies, produced in the middle atmosphere, down to the troposphere. More recently, it has been proposed that top-down-initiated decadal solar signals might modulate surface climate and synchronize the North Atlantic Oscillation. A realistic representation of the solar cycle in climate models was suggested to significantly enhance decadal prediction skill. These conclusions have been debated controversial since then due to the lack of realistic decadal prediction model setups and more extensive analysis. In this paper we aim for an objective and improved evaluation of possible solar imprints from the middle atmosphere to the surface and with that from head to toe. Thus, we analyze model output from historical ensemble simulations conducted with the state-of-the-art Max Planck Institute for Meteorology Earth System Model in high-resolution configuration (MPI-ESM-HR). The target of these simulations was to isolate the most crucial model physics to foster basic research on decadal climate prediction and to develop an operational ensemble decadal prediction system within the “Mittelfristige Klimaprognose” (MiKlip) framework. Based on correlations and multiple linear regression analysis we show that the MPI-ESM-HR simulates a realistic, statistically significant and robust shortwave heating rate and temperature response at the tropical stratopause, in good agreement with existing studies. However, the dynamical response to this initial radiative signal in the NH during the boreal winter season is weak. We find a slight strengthening of the polar vortex in midwinter during solar maximum conditions in the ensemble mean, which is consistent with the so-called “top-down” mechanism. The individual ensemble members, however, show a large spread in the dynamical response with opposite signs in response to the solar cycle, which might be a result of the large overall internal variability compensating for rather small solar imprints. We also analyze the possible surface responses to the 11-year solar cycle and review the proposed synchronization between the solar forcing and the North Atlantic Oscillation. We find that the simulated westerly wind anomalies in the lower troposphere, as well as the anomalies in the mean sea level pressure, are most likely independent from the timing of the solar signal in the middle atmosphere and the alleged top-down influences. The pattern rather reflects the decadal internal variability in the troposphere, mimicking positive and negative phases of the Arctic and North Atlantic oscillations throughout the year sporadically, which is then assigned to the solar predictor time series without any plausible physical connection and sound solar contribution. Finally, by applying lead–lag correlations, we find that the proposed synchronization between the solar cycle and the decadal component of the North Atlantic Oscillation might rather be a statistical artifact, affected for example by the internal decadal variability in the ocean, than a plausible physical connection between the UV solar forcing and quasi-decadal variations in the troposphere.

DETERMINATION OF THE FREQUENCY OF NATURAL OSCILLATIONS OF THE ELEMENTS OF THE MECHANICAL SYSTEM OF THE MOTOR CARRIAGE ROLLING STOCK

The article is devoted to highlighting the peculiarities of determining the frequencies of natural oscillations of the elements of the mechanical system of modern rolling stock. A significant volume of passenger transportation in suburban traffic on railway networks of Ukraine is carried out by the operating fleet of rolling stock, most of which are operated overtime. Taking into account the relatively slow pace of renewal of Ukrzaliznytsia's rolling stock fleet, scientific research aimed at maintaining a high level of technical and economic indicators of electric trains in operation becomes especially important. Therefore, research aimed at improving performance indicators of structural elements of rolling stock should be considered relevant. As one of the most responsible units of the mechanical system of modern rolling stock, the crew part can be singled out, which includes a traction electric drive, during the operation of which the phenomenon of jolts is observed in some modes of operation. Such a phenomenon is observed in resonant modes of operation, that is, the coincidence of the frequencies of natural and forced oscillations, which negatively affects the reliability and durability of the mechanical system as a whole. Therefore, the task of identifying resonant frequencies and eliminating the manifestation of the negative phenomenon of resonance arises. One of the possible ways to solve the given problem is to adjust the operation of the traction drive mechanism in non-resonant modes, which in turn requires research on the torsional oscillations of the mechanical drive system. The article presents an approach using geometric models of the design elements of the traction drive of electric trains, the corresponding mathematical model, and the results of modeling the shape of the frequency of natural oscillations of the traction drive of an electric train. Based on the results of the calculations, it was determined that the form of natural oscillation frequencies of the considered mechanical system has a two-node character. The proposed approach is based on the use of a tabular form of calculation of recurrent formulas. Based on the results of the research, recommendations are given for the further use of the obtained results. Keywords: motor-wagon rolling stock, electric train, traction drive, self-oscillations.

Forced oscillation management in a microgrid with distributed converter-based resources using hierarchical deep-learning neural network

In future microgrids (MGs), increasing penetration of distributed converter-based resources (DCRs) has inevitably resulted in the problem of inertia scarcity. The interaction, combination, and/or resonance among converter control loops of DCRs, forced inputs, grid parameters, parasitic elements in networks, and system dominant modes can lead to major forced oscillations (FOs). Previous research works mostly focused the problem of FOs on large-scale power systems. However, the effects of FOs in MGs may be more severe than large-scale power systems due to the lower system inertia. With different characteristics of each DCR, conventional FO management methods applied in large-scale power systems may be ineffective. In this paper, a unified AI-framework named hierarchical deep-learning neural network (HiDeNN) is proposed to effectively handle the FOs in a MG with DCRs. To properly managing the FOs, the HiDeNN is divided into three levels for FO detection, identification, and mitigation, respectively. By considering big data produced from DCRs, the HiDeNN is used to solve complicated FO management problems with a low computational demand. By comparison to conventional FO management methods, performances of the proposed HiDeNN are verified in the modified IEEE 13-node feeder with DCRs under various operating points and FO conditions.

Low-frequency laboratory measurements of the elastic properties of solids using a distributed acoustic sensing system

In recent decades, low-frequency (LF) experiments based on the forced-oscillation (FO) method have become common practice in many rock physics laboratories for measuring the elastic and anelastic properties of rocks. However, the use of the electronic displacement sensors in traditional acquisition systems of FO devices such as conventional capacitive transducers or strain gauges seriously limits both the efficiency and productivity of LF measurements, and, due to the limited contact area of the displacement sensors with a sample under test, increases the requirements for sample homogeneity. In this paper, we present the first results obtained in the development of a new laboratory method elaborated to measure the elastic properties of solids. The method is a further development of the FO method where traditional data acquisition is replaced by acquisition based on fiber-optic distributed acoustic sensing (DAS) technology. The new method was tested in a laboratory study using two FO setups designed for measurements under uniaxial and confining pressures. The study was carried out on a sample made from polymethyl methacrylate (PMMA) and an aluminium standard, first under uniaxial pressure at FO frequencies of 1, 10, 30, 60 and 100 Hz, and then under confining pressure at an FO frequency of 1 Hz. Both uniaxial and confining pressures were equal to 10 MPa, and the strain in the PMMA sample in all measurements did not exceed 4 × 10-8. The performance of DAS acquisition was compared with the measurements conducted at a strain of 1 × 10-6 using the traditional FO method based on the use of semiconductor strain gauges and the ultrasonic method. The results of the DAS measurements are in good agreement with the FO measurements carried out using semiconductor strain gauges and with the literature data.

Autonomous Pulse Frequency Modulation for Wireless Battery Charging With Zero-Voltage Switching

This paper proposes an autonomous pulse frequency modulation (APFM) scheme for wireless battery charging in which the self-excited oscillating (SEO) wireless power transfer (WPT) system can offer output power regulation with reliable zero-voltage switching (ZVS). The key is to utilize the self-excited oscillation feature to adjust the WPT operating frequency autonomously so as to deliver more power in the strong coupling region than the traditional forced-oscillating (FO) WPT system while the transmission efficiency can maintain at a high level. In the weak coupling region, the system becomes equivalent to the FO-WPT system. The pulse frequency modulation enables the system to adjust the output power by changing its duty ratio. Besides, reliable ZVS is achieved by extracting and processing the current signal at the primary side. Both theoretical analysis and experimental verification are provided to support the feasibility of the proposed APFM for SEO-WPT system.

Theoretical Investigation on the Connections Between Loop Impedance-Based Criterion and State-Space-Based Method

The loop impedance-based criterion (LIC) is a practical approach for studying the sub-synchronous oscillation (SSO) instability induced by converter-interfaced wind turbine generators (WTGs) via checking whether the resistance is positive or not. However, few existing works have discussed the background mathematical theory of such criterion. In this paper, a theoretical impedance solving method is raised based on a forced oscillation analysis method, which is efficient to obtain accurate impedance and can connects the state-space function, eigenvector and impedance inherently. Therefore, the applicability of LIC can be revealed in different stability regions from the viewpoint of the strict eigen-analysis based method (EBM). The general LIC stability criteria is then derived, and the conditions where LIC may cause misjudgment are discussed. Cases considering different operating scenarios are conducted to verify the proposed impedance calculation method and illustrate the connections and differences between LIC and EBM.

SOME SOLUTION FOR FORCED OSCILLATIONS OF BEAM SYSTEMS WITH DISTRIBUTED PARAMETERS

Methods for determining response of the beam with distributed parameters to harmonic external loads are considered. The main attention is paid to the method of decomposition of displacements by modes of oscillations. The features of the method are described for beams without damping, with external and internal damping. For specific examples, a complete calculation of the steady-state forced oscillations is carried out. The frequency dependence of generalized coordinates and phase parameters are obtained and investigated in a wide frequency range of external dynamic action.

Nebulized caffeine alleviates airway hyperresponsiveness in a murine asthma model.

The clinical definition of "difficult asthma" has expanded recently to include an ever-growing subset of patients with symptoms that cannot be controlled by conventional means, forcing the medical community to develop innovative therapeutics. Beneficial effects of coffee for subjects with asthma, primarily the effect of methylxanthine components, have long been described. Methylxanthines, including theophylline and caffeine, inhibit phosphodiesterases and downstream cAMP signaling to prevent mast cell degranulation while promoting immunomodulation (Peleman RA, Kips JC, Pauwels RA. Clin Exp Allergy 28: 53-56, 1998; Deshpande DA, Wang WCH, McIlmoyle EL, Robinett KS, Schillinger RM, An SS, Sham JSK, Liggett SB. Nat Med 16: 1299-1304, 2010). Caffeine is also a bitter taste receptor agonist, binding to taste-sensing type 2 receptors (TAS2R) before releasing calcium to hyperpolarize airway smooth muscle membranes, inducing bronchodilation (Workman AD, Palmer JN, Adappa ND, Cohen NA. Curr Allergy Asthma Rep 15: 72, 2015; Devillier P, Naline E, Grassin-Delyle S. Pharmacol Ther 155: 11-21, 2015). Theophylline is conventionally used to treat asthma, whereas, according to the literature, the dosage required for orally administered caffeine has yielded modest improvement (Alfaro TM, Monteiro RA, Cunha RA, Cordeiro CR. Clin Respir J 12: 1283-1294, 2018). We sought to determine whether aerosolization of ultrafine caffeine particles (2.5-4 μm) directly to the lungs of susceptible A/J mice challenged with methacholine would improve pulmonary function via forced oscillation technique. In addition, we assessed whether nebulization of caffeine leads to changes in lung pathophysiology and bronchoalveolar lavage cell profiles. We found that mice that received aerosolized caffeine had statistically significant decreases in maximum airway resistance [6.3 vs. 3.9 cmH2O·s/mL at 62.5 mg/mL caffeine; confidence interval (CI) = -4.3, -0.4; P = 0.02] and significant delays in the time required to reach maximum resistance compared with that of controls (64.7 vs. 172.1 sec at 62.5 mg/mL caffeine, CI = 96.0, 118.9; P < 0.0001). Nebulized caffeine yielded a consistent effect on airway hyperresponsiveness at a range of doses without evidence of significant pathology relative to vehicle control.NEW & NOTEWORTHY For decades, coffee has been shown to improve symptoms in patients with asthma. One component, theophylline, is conventionally used to treat asthma, whereas the dosage required for orally administered caffeine has yielded modest improvement. We sought to determine whether aerosolization of caffeine directly to the lungs of susceptible A/J mice challenged with methacholine would alter pulmonary function via forced oscillation technique. We found nebulized caffeine yielded a consistent improvement on murine AHR.

An analytical frequency‐domain model of aerodynamic mass and damping of floating wind turbines

AbstractThe fore‐aft motion of the rotor‐nacelle assembly (RNA) of a rotating floating wind turbine (FWT) can cause an oscillation in aerodynamic thrust, which may be equivalently treated as frequency‐dependent aerodynamic mass and damping effects. In this study, an explicit frequency‐domain analytical model is proposed to calculate the equivalent aerodynamic mass and damping of FWTs, with proper linearization of control system. Assuming that an FWT operates under steady wind conditions and a forced oscillation is exerted at the RNA along the wind direction, the thrust fluctuations are equivalently represented by the force and moment acting on the nacelle instead of pure aerodynamic loads. Based on the thrust oscillation expression, equivalent aerodynamic mass and damping are derived analytically. After verifying the model by numerical comparison, it is used to demonstrate equivalent aerodynamic mass and damping of three wind turbines (5–15 MW). Effects of wind turbine up‐scaling and controller dynamics are addressed. Results show that equivalent aerodynamic mass and damping present a nonlinear characteristic with oscillation frequency in the below‐rated region, while the relationship is close to linear for higher wind speeds. The effect of wind turbine up‐scaling has a visible impact on equivalent aerodynamic mass and damping, especially at near‐rated wind speed. Controller gains affect equivalent aerodynamic mass and damping and should be tuned reasonably in the controller design for FWTs. Outcomes of our study can be used to establish a frequency‐domain coupled model of FWTs and are beneficial for conceptual design and parameter optimization of the platform of FWTs.