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The use of active inceptor systems allows for control of the aircraft even following mechanical failures within the control inceptor. For the specific case of isometric failure, whereby the inceptor "freezes" in position, a virtual force-displacement model is used to continue to provide control input. Testing on DLR's experimental helicopter (active control technology/flying helicopter simulator) has shown the potential to encounter pilot-induced oscillation (PIO) tendencies when flying using this mode. This paper presents results from a simulation campaign undertaken to determine whether PIOs could be exposed through this use of control and/or the resultant severity. The results show that isometric failure caused severe PIOs. Unacceptable failure characteristics were reported by all four pilots. PIO incipience was predicted through the use of offline tools. It is recommended that specific PIO investigations be undertaken during the evaluation of active inceptor failure modes.

This article deals with the problem of describing the fields of vibration in string lattices with triangular (centered hexagonal) cells. The problems of this kind have not been adequately studied despite the fact that the required models find application in the dynamic analysis of various machines and structures as well as in crystallography and materials science. Equations of motion are provided. Problems of propagation of sinusoidal waves and induced oscillations under a random broadband force action are considered.

The paper is devoted to preventing oscillations in the angular motion of piloted aircraft by the pseudo-linear correcting device. The prime cause of this event is the unfavorable interaction between the pilot and the vehicle or the so-called pilot-induced oscillations. In this connection, it becomes necessary to consider the human influence on the piloting process to preserve the formation.

Passive turbulence control (PTC) is being used in the Marine Renewable Energy Laboratory (MRELab) of the University of Michigan to enhance flow induced oscillations (FIO) of cylinders in the VIVACE (Vortex Induced Vibration for Aquatic Clean Energy) Converter. Large PTC triggers VIV and galloping at lower flow speeds for energy harvesting. Currently, FIO of cylinders with large PTC for high Re has received limited attention and, particularly, the effect of variable PTC height on FIO of cylinders. The vast majority of ocean currents, rivers, and tides are too slow for Marine Hydro Kinetic (MHK) energy technologies to harness it. In order to enhance FIO and to initiate galloping earlier, a circular cylinder is geometrically modified using straight strips placed on the cylinder surface symmetrically PTC strips on the cylinder effectively change the flow properties. In the present study, the FIO of a single-cylinder with large PTC, on end linear-springs, is modelled and simulated using a Fluid-Structure Interaction (FSI) code. Results are verified by corresponding experimental data. Results show that VIV onset occurs at lower Re for large-PTC cylinder in comparison with lower-PTC cylinder. Contrary to smooth cylinders for which the amplitude ratio is small in the transition region between VIV and galloping, application of large PTC leads to high amplitude response in the transition region. The mechanism behind this observation is the further departure of the geometry from the smooth circular cylinder. The latter does not exhibit galloping due to flow and geometric symmetry in all directions. Moreover, in the galloping region, the amplitude ratio increases with the height of PTC. Earlier onset of galloping and enhancement of geometric asymmetry support this observation as well.

�� 2019 The Authors. Biotechnology and Bioengineering published by Wiley Periodicals, Inc. The influence of process strategies on the dynamics of cell population heterogeneities in mammalian cell culture is still not well understood. We recently found that the progression of cells through the cell cycle causes metabolic regulations with variable productivities in antibody-producing Chimese hamster ovary (CHO) cells. On the other hand, it is so far unknown how bulk cultivation conditions, for example, variable nutrient concentrations depending on process strategies, can influence cell cycle-derived population dynamics. In this study, process-induced cell cycle synchronization was assessed in repeated-batch and fed-batch cultures. An automated flow cytometry set-up was developed to measure the cell cycle distribution online, using antibody-producing CHO DP-12 cells transduced with the cell cycle-specific fluorescent ubiquitination-based cell cycle indicator (FUCCI) system. On the basis of the population-resolved model, feeding-induced partial self-synchronization was predicted and the results were evaluated experimentally. In the repeated-batch culture, stable cell cycle oscillations were confirmed with an oscillating G1 phase distribution between 41% and 72%. Furthermore, oscillations of the cell cycle distribution were simulated and determined in a (bolus) fed-batch process with up to 25 �� 106 cells/ml. The cell cycle synchronization arose with pulse feeding only and ceased with continuous feeding. Both simulated and observed oscillations occurred at higher frequencies than those observable based on regular (e.g., daily) sample analysis, thus demonstrating the need for high-frequency online cell cycle analysis. In summary, we showed how experimental methods combined with simulations enable the improved assessment of the effects of process strategies on the dynamics of cell cycle-dependent population heterogeneities. This provides a novel approach to understand cell cycle regulations, control cell population dynamics, avoid inadvertently induced oscillations of cell cycle distributions and thus to improve process stability and efficiency.

We investigate Bragg-induced oscillations in complex non-PT periodic structures, that is, a periodic medium with gain and loss and not necessarily symmetric under the combined action of parity and time reversal operations. We compare our analytic results based on the expansion of the optical field in Bragg-resonant plane waves with a direct numerical integration of the paraxial wave equation beyond the shallow potential approximation and using a wide Gaussian beam as initial condition. In particular, we study under which conditions a mode trapping phenomenon may still be observed and to inspect how the energy exchange between the spectral modes takes place during propagation in this more general class of asymmetric complex potentials.

The advent of fly-by-wire technology brought many advantages to aircraft design, but also increased the number of occurrences of the undesirable pilot-induced oscillation phenomena. To analyze such...

Induced oscillations in the electromechanical worm-gear drives of rotary-type manufacturing machines are investigated. Using two design models, viz., a model with rigid linkages and a model that accounts for elastic linkages, natural frequencies have been determined and amplitude-frequency characteristics have been constructed. An asynchronous drive motor is described by the dynamic characteristic. A comparison of the results calculated using two models has established the range of the initial parameters within which the dependences can be used that were obtained from the simplest design model with rigid linkages. This will allow considerable simplification and reduction in the time of synthesizing the drive under consideration.

In a study on one patient during hemodialysis, we used near-infrared spectroscopy (NIRS) to measure coherent oscillations of cerebral concentrations of oxyhemoglobin ([HbO2]), deoxyhemoglobin ([Hb]), and total-hemoglobin ([HbT]) induced by systemic oscillations in mean arterial pressure (MAP) at a frequency of 0.07 Hz. During hemodialysis, we observed that the phase of [Hb] versus [HbO2] becomes less negative, whereas the phase of [HbT] versus MAP becomes more negative. By applying a quantitative hemodynamic model, we assign these phase changes to an increase in venous blood transit time and a less effective cerebral autoregulation during the hemodialysis process.

This paper is concerned with the robustness of the sustained oscillations predicted by an epidemic ODE model defined on contact networks. The model incorporates the spread of awareness among individuals and, moreover, a small inflow of imported cases. These cases prevent stochastic extinctions when we simulate the epidemics and, hence, they allow to check whether the average dynamics for the fraction of infected individuals are accurately predicted by the ODE model. Stochastic simulations confirm the existence of sustained oscillations for different types of random networks, with a sharp transition from a non-oscillatory asymptotic regime to a periodic one as the alerting rate of susceptible individuals increases from very small values. This abrupt transition to periodic epidemics of high amplitude is quite accurately predicted by the Hopf-bifurcation curve computed from the ODE model using the alerting rate and the infection transmission rate for aware individuals as tuning parameters., Comment: 17 pages, 11 figures

Numerical simulation of self-induced pitch oscillations of a segmental-conical body at Mach number M = 2.0 is performed using the mathematical model of the pitching moment, which includes an ordinary linear differential equation of the first order. The parameters of the mathematical model were determined from the condition of the best agreement between the calculated and experimental transient processes pitch angle in time. Numerical modeling of self-induced oscillations was also carried out using the time-lag hypothesis and concepts of aerodynamic derivatives. It is shown that the proposed mathematical model is not only satisfactory describes the experimental transient process like the other two, but also explains the known experimental effects.

Dry friction can be a cause of undesired self-excited oscillations. One way to suppress this underlying mechanism is the superposition of high-frequency vibrations whereby the effective friction characteristics is changed and a quasi-equilibrium can be stabilized. This damping effect is analyzed in detail for single-degree-of-freedom systems [1] and experiments and simulations show a good accordance [2]. In this work, the analytical approach from [1] is used to analyze the stabilizing effect of superposed oscillations for a two-degree-of-freedom system subject to friction.

Eclipsing binary stars are rare and extremely valuable astrophysical laboratories that make possible precise determination of fundamental stellar parameters. Investigation of early-type chemically peculiar stars in eclipsing binaries provides important information for understanding the origin and evolutionary context of their anomalous surface chemistry. In this study we discuss observations of eclipse variability in six mercury-manganese (HgMn) stars monitored by the TESS satellite. These discoveries double the number of known eclipsing HgMn stars and yield several interesting objects requiring further study. In particular, we confirm eclipses in HD 72208, thereby establishing this object as the longest-period eclipsing HgMn star. Among five other eclipsing binaries, reported here for the first time, HD 36892 and HD 53004 stand out as eccentric systems showing heartbeat variability in addition to eclipses. The latter object has the highest eccentricity among eclipsing HgMn stars and also exhibits tidally induced oscillations. Finally, we find evidence that HD 55776 may be orbited by a white dwarf companion., Comment: 5 pages, 5 figures; accepted for publication in MNRAS

Flow Induced Oscillations (FIO) of tandem cylinders can be enhanced to harness hydrokinetic energy by varying the system parameters. In general, the Converter consists of two mass–spring–damper oscillators subjected to transverse FIOs and specifically Vortex Induced Vibrations and galloping. These FIOs are strongly influenced by variations of the inflow velocity, damping, stiffness, mass and in-flow center-to-center spacing L between two tandem cylinders. In turn, those influence the harnessed power and efficiency of the Converter. In previous experiments, the interactions between the cylinders were proven to be beneficial for the synergy of the cylinders. In this paper, modeling of tandem-cylinder converters is studied considering the Converter parameters, aiming at enhancing the cylinder synergy resulting in increased harnessed power by using a backpropagation (BP) neural network. The main conclusions are: (1) The surrogate model is constructed by a BP network using the experimental data to reduce excessive experimentation or computational inaccuracy. The harnessed power at different flow velocities is computed by the present model and is found to be consistent with experimental results not included in the modeling. (2) Increasing the damping ratio (0.20–0.30) of two tandem cylinders is conducive to improve the power efficiency, but has little effect on power harvesting. (3) In galloping, the harnessed power and its corresponding efficiency for the case of L/D = 1.57 perform at a higher level than that of bigger spacing ratios.

Based on the drive signals of a milling center, process forces can be reconstructed. Therefore, a novel approach is presented to reconstruct the process forces with a long short-term memory neural network (LSTM) using drive signals as an input. The LSTM is evaluated and compared to a model-based approach. The latter compensates nonlinearities and disturbances such as friction and inertia. For training of the LSTM, multiple milling processes are considered to enhance the generalizability. Training data is generated by recording drive signals and process forces measured by a dynamometer. The LSTM is then evaluated using a test set, which comprises new process parameters. It is shown that the LSTM has a lower root mean square error (RMSE) in comparison to the model-based approach. Especially, when changing the feed motion direction during milling, the neural network clearly outperforms the model-based approach. Nevertheless, there are processes, where the LSTM induced oscillations, which do not correspond to the measured forces. © 2020 MDPI Multidisciplinary Digital Publishing Institute. All rights reserved.

Neural activity is organized at multiple scales, ranging from the cellular to the whole brain level. Connecting neural dynamics at different scales is important for understanding brain pathology. Neurological diseases and disorders arise from interactions between factors that are expressed in multiple scales. Here, we suggest a new way to link microscopic and macroscopic dynamics through combinations of computational models. This exploits results from statistical decision theory and Bayesian inference. To validate our approach, we used two independent MEG datasets. In both, we found that variability in visually induced oscillations recorded from different people in simple visual perception tasks resulted from differences in the level of inhibition specific to deep cortical layers. This suggests differences in feedback to sensory areas and each subject’s hypotheses about sensations due to differences in their prior experience. Our approach provides a new link between non-invasive brain imaging data, laminar dynamics and top-down control., Pinotsis and Miller present a simplified neural mass model for estimating the laminar dynamics that contribute to non-invasively recorded time frequency data. Using two independent MEG datasets, they give evidence for deep cortical layers contributing to inter-individual variability in visually induced oscillations. Their study links non-invasive brain imaging data, laminar dynamics and top-down control.

The Open-Loop Onset Point (OLOP) criterion has, for many years, been successfully used as a method to predict quasi-non-linear pilot-induced oscillations (PIOs) for fixed-wing aircraft. Only limited research has been conducted using the criterion for prediction of PIOs occurring in rotorcraft. This paper details a study to extend the application of OLOP to rotorcraft, using the combination of control inputs appropriate for the task and a suitable pilot model. Results are compared between pilot subjective opinion and OLOP predictions, from tests performed in a ground-based simulation facility. Using ‘task-specific’ application of OLOP, results obtained in the investigation are encouraging, whereby the objective predictions reflect subjective pilot assessment. From results obtained, a modified boundary is presented.

Summary Modelling the dynamic fluid behaviour of Low Salinity Water Flooding (LSWF) at the reservoir scale is a challenge which requires a coarse grid enable prediction in a feasible timescale. However, evidence shows that using low resolution models will result in a considerable mismatch compared with an equivalent fine scale model with the potential of strong numerically induced oscillations. This work examines two new upscaling methods in a heterogenous reservoir where viscous crossflow takes place to improve the precision of predictions. We apply two approaches to upscaling of the flow to improve precision. In the first upscaling method, we shift the effective salinity range for the coarse model based on algorithms that we have developed to correct for numerical dispersion. The second upscaling method uses appropriate pseudo relative permeability curves that we derive. The shape of this new set of relative permeability is designed based on a modified fractional flow analysis of LSWF that we have developed and captures the relationship between dispersion and the waterfront velocities. This approach removes the need for explicit simulation of salinity transport. We applied these approaches in layered models and for permeability distributed as a correlated random field. Upscaling by shifting the effective salinity range of the coarse model gave a good match to the fine case scenario, while considerable mismatch was observed for traditional upscaling of the absolute permeability only using averaging methods. For highly coarsened models, this method of upscaling reduces the oscillations appear, but they can be apparent. On the other hand, upscaling by using a single (pseudo) relative permeability produced more robust results with a very promising match to the fine scale scenario. These methods of upscaling showed promising results where they were used to upscale fully communicating and non-communicating layers as well as models with randomly correlated permeability. Unlike documented methods in literate, these newly derived methods take into account the crucial effect of numerical dispersion and effective concentration on fluid dynamic using mathematical tools. These methods could be applied for other models where the phase mobilities change as a result of an injected solute, such as surfactant flooding and alkaline flooding. Usually these models use two sets of relative permeability and switch from one to another as a function of the concentration of the solute.

Spontaneous oscillations induced by time delays are observed in many real-world systems. Phase reduction theory for limit-cycle oscillators described by delay-differential equations (DDEs) has been developed to analyze their synchronization properties, but it is applicable only when the perturbation applied to the oscillator is sufficiently weak. In this study, we formulate a nonlinear phase-amplitude reduction theory for limit-cycle oscillators described by DDEs on the basis of the Floquet theorem, which is applicable when the oscillator is subjected to perturbations of moderate intensity. We propose a numerical method to evaluate the leading Floquet eigenvalues, eigenfunctions, and adjoint eigenfunctions necessary for the reduction and derive a set of low-dimensional nonlinear phase-amplitude equations approximately describing the oscillator dynamics. By analyzing an analytically tractable oscillator model with a cubic nonlinearity, we show that the asymptotic phase of the oscillator state in an infinite-dimensional state space can be approximately evaluated and non-trivial bistability of the oscillation amplitude caused by moderately strong periodic perturbations can be predicted on the basis of the derived phase-amplitude equations. We further analyze a model of gene-regulatory oscillator and illustrate that the reduced equations can elucidate the mechanism of its complex dynamics under non-weak perturbations, which may be relevant to real physiological phenomena such as circadian rhythm sleep disorders.

In ecological modeling, seasonality can be represented as an alternation between environmental conditions. We consider a switching strategy that alternates between two undesirable dynamics and find that they can yield a desirable periodic behavior in the case of the Beverton–Holt, Ricker, and modified Ricker maps, which have been extensively used to model ecological populations. For the Ricker and modified Ricker models, we observe coexistence of attractors, which, under the same conditions, define basin of attractions, and the final dynamic behavior depends on the initial conditions.

This paper explores the concept of dual-stage actuators in order to reduce the errors generated by output quantization in motion systems. Oscillations are induced upon the quantized actuator such that its trajectory is reconstructible by a model-free estimator. Based on the nature of these oscillations and on intermittent measurements that indicate when the output crossed from one quantization region to another, the exact value of the actuator output is computed. The micro actuator is then used to compensate the error generated by these oscillations and achieve an improved steady-state response. Simulation results show a promising perspective for the proposed approach.

The paper is devoted to such an important problem of piloted aircraft control as an unfavorable aircraft-pilot coupling. Mainly, the so-called Pilot-Induced Oscillations, i.e., long uncontrolled irregular oscillations which may happen due to the controlling surface magnitude and rate limitations when pilot attempts to control the aircraft with the high rate and accuracy. The simulation and in-flight test results of several PIO events are described, and the literature overview of the PIO prevention method is given.

Collisions between structures due to seismic oscillations have been reported many times in literature as a common case of damage. Further it is quite usual seismically induced oscillations of a structure in a city center block of buildings to be partly restrained in lateral displacements and therefore torsional behavior to be introduced in the structure. Two different types of structural interaction may be defined: (a) Diaphragm-to-diaphragm collisions (Type A). (b) The floor levels of the two structures are different. Consequently during the seismic oscillations the diaphragms of the first one impact the columns of the other (Τype B or interstory pounding). In this work the cases of an 8-story reinforced concrete building that suffers pounding with an adjacent structure that has 1, 2, 3, 4, 5, 6, 7 or 8 stories are studied. Pounding occurs only in one (Case 1) or in two (Case 2) columns of the structures and since the other columns are free to move without restrictions a torsional behavior is introduced (asymmetric pounding). Moreover in Type B interaction these columns of the 8-story frame structure undergo impacts at a height equal to 2/3 of their deformable length from the diaphragms of the other structure. The influence of an initial distance between the two interacting structures on the torsion effect is investigated too. Nonlinear seismic step-by-step analyses are performed. More than two hundred pounding cases with torsional effect each one for three natural seismic excitations are studied. Results in terms of shear and ductility demands of the columns are presented and commented. Both types A and B yielded high torsional structural rotation. In interaction Type B it can be deduced from the cases under examination that the column that is endured the impact from the top floor of the other structure develops high shear demands that exceed the available capacity many times during the step-by-step seismic analysis. Moreover high ductility demands have been observed for this column. Finally it is concluded that for buildings that may undergo asymmetric pounding not taking it into account may lead under certain conditions to non-secure design or even critical situations.

Background Capnography has been proposed as a method for monitoring the ventilation rate during cardiopulmonary resuscitation (CPR). A high incidence (above 70%) of capnograms distorted by chest compression induced oscillations has been previously reported in out-of-hospital (OOH) CPR. The aim of the study was to better characterize the chest compression artefact and to evaluate its influence on the performance of a capnogram-based ventilation detector during OOH CPR. Methods Data from the MRx monitor–defibrillator were extracted from OOH cardiac arrest episodes. For each episode, presence of chest compression artefact was annotated in the capnogram. Concurrent compression depth and transthoracic impedance signals were used to identify chest compressions and to annotate ventilations, respectively. We designed a capnogram-based ventilation detection algorithm and tested its performance with clean and distorted episodes. Results Data were collected from 232 episodes comprising 52 654 ventilations, with a mean (±SD) of 227 (±118) per episode. Overall, 42% of the capnograms were distorted. Presence of chest compression artefact degraded algorithm performance in terms of ventilation detection, estimation of ventilation rate, and the ability to detect hyperventilation. Conclusion Capnogram-based ventilation detection during CPR using our algorithm was compromised by the presence of chest compression artefact. In particular, artefact spanning from the plateau to the baseline strongly degraded ventilation detection, and caused a high number of false hyperventilation alarms. Further research is needed to reduce the impact of chest compression artefact on capnographic ventilation monitoring.

In the current study, we investigated the effects of short-term visual deprivation (2 h) on a haptic recognition memory task with familiar objects. Behavioral data, as well as event-related potentials (ERPs) and induced event-related oscillations (EROs) were analyzed. At the behavioral level, deprived participants showed speeded reaction times to new stimuli. Analyses of ERPs indicated that starting from 1000 ms the recognition of old objects elicited enhanced positive amplitudes only for the visually deprived group. Visual deprivation also influenced EROs. In this sense, we observed reduced power in the lower-1 alpha band for the processing of new compared to old stimuli between 500 and 750 ms. Overall, our data showed improved haptic recognition memory after a short period of visual deprivation. These effects were thought to reflect a compensatory mechanism that might have developed as an adaptive strategy for dealing with the environment when visual information is not available.

Aerodynamic and structural nonlinearities of aeroelastic systems control different aspects of their limit cycle oscillations and bifurcations. One strong nonlinear unsteady aerodynamic effect that results in self-induced oscillations of airfoils is the dynamic stall. So, the concept of power extraction from stall-induced oscillations of a pitching airfoil is investigated. Experiments are performed to explore and enhance the conversion of the oscillations of a NACA0012 airfoil that is restrained elastically in pitching to electrical power. Wind tunnel tests are performed on an airfoil model connected to a DC electric motor to harvest the energy. The effects of varying the position of the axle, which defines the elastic axis, are investigated. Bifurcation diagrams as the air speed is increased and average power estimates for different experimental conditions are used to analyze the power extraction features. The results show an aerodynamic efficiency of about 40% indicating that an airfoil oscillating under the effects of dynamic stall is an adequate platform for energy harvesting.

A long-term sea level series were analyzed, recorded at 12 coastal tide gauges located on the coast of the Sea of Okhotsk and the Pacific coast of the Kuril Islands and Kamchatka. Estimates for the maximum heights of the tidal level, storm surges, and tsunamis were obtained separately, as well as for the rare recurrence of the total sea level height with the probability of these individual components superposition. The maximum total height of the sea level without a tsunami were obtained for the Magadan station, where the main factor is anomalously large tides, as well as for Iturup and Matua islands, where the highest storm surges were recorded. The minimum values were obtained for Ust’-Kamchatsk and Malokuril’sk (Shikotan Island) on different flanks of the study area. When a tsunami is included, the maximum values of possible total sea level rises were observed on the Pacific coast of the Kuril Ridge and the influence of tides and meteorologically induced oscillations are small. On the east coast of Kamchatka adjacent to the considered closed area, the role of tsunamis is much smaller. At the Kuril’sk station, where the height of the largest tsunami (Chilean, May 1960) was about a half the strongest surge height, the contribution of the tsunami scarcely affected the resulting estimates. As a rule, the contribution of a tsunami becomes significant at other stations on the coast of the Sea of Okhotsk with a recurrence period of 100 years.

Spurious induced oscillations have been one of the fundamental problem associated with numerical approximation of the solution of hyperbolic conservation laws. In this note, using notion of data dependent stability, generic three point schemes for scalar case are analysed to show that the induced oscillations depend on initial data too. Further, it is concluded that it is not possible to have an initial data independent, ’uniformly’ non-oscillatory three point fixed stencil scheme irrespective of its accuracy.

Non-linear time series analysis based methods are a popular choice for industrial control loop data analysis. In this paper a delay vector variance (DVV) based approach is presented to analyze the source of oscillations in an industrial control loop. The method is capable of differentiating between the linear and non-linear causes of oscillations and can also help in isolating the source of non-linearity. The automatic determination of embedding dimensions is augmented with the DVV analysis to make it more robust and reliable. The efficacy of the proposed method is established using simulation as well as industrial case studies.

Inverted pendulum models are commonly used to study the bio-mechanics of biped walkers. In its simplest form, the inverted pendulum consists of a point mass attached to two straight mass-less legs. Most works constrain the motion of the mass to the sagittal plane, i.e. the plane perpendicular to the ground that contains the direction toward the biped is walking. In this article, we remove this constrain to study the oscillations, the mass experiences in the direction perpendicular to the sagittal plane as the biped walks. While small, these lateral oscillations are unavoidable and of importance in the understanding of balance and stability of walkers, as well as walkers induced oscillations in pedestrian bridges.