Coherent Disturbances Research Articles

Phase-locked measurements of linear and weakly nonlinear interfacial waves in a stratified turbulent gas–liquid pipe flow

The present work reports an experimental characterization of linear and weakly nonlinear interfacial waves in a stratified air–water horizontal pipe flow. An oscillating paddle was employed to generate controlled waves at the liquid interface. The driving signal of the oscillating paddle was controlled and synchronized with image acquisitions, enabling phase-locked measurements and the application of ensemble averaging techniques. Velocity field measurements in the liquid and gas phases were performed simultaneously using an off-axis particle image velocimetry setup and shadowgraphy. The combined techniques allowed us to extract the coherent part of flow fluctuations related to the excited waves. This was done for a range of flow rates and wave frequencies. The selected conditions are close to the transition from stratified to slug/plug flow regimes. In the presence of linear waves, the coherent disturbances in both phases were weakly dependent on near-wall disturbances. Flow changes in the presence of weakly nonlinear waves were also investigated. In these cases, noticeable modifications in the mean flow and in turbulence distribution were observed near the interface, whereas close to the wall, the flow was weakly affected. This investigation follows the work of Farias et al. [“Characterization of interfacial waves in stratified turbulent gas-liquid pipe flow using Particle Image Velocimetry and controlled disturbances,” Int. J. Multiphhase Flow 161, 104381 (2023)], where the threshold for linear and weakly nonlinear waves was studied. Here, a clear comparison between wave-induced disturbances in linear and weakly nonlinear regimes is reported in the literature for the first time for stratified turbulent gas–liquid pipe flows. The methodology proposed is relatively simple and can contribute to describe wave-related phenomena in stratified pipe flows.

Model predictive control for robust quantum state preparation

A critical engineering challenge in quantum technology is the accurate control of quantum dynamics. Model-based methods for optimal control have been shown to be highly effective when theory and experiment closely match. Consequently, realizing high-fidelity quantum processes with model-based control requires careful device characterization. In quantum processors based on cold atoms, the Hamiltonian can be well-characterized. For superconducting qubits operating at milli-Kelvin temperatures, the Hamiltonian is not as well-characterized. Unaccounted for physics (i.e., mode discrepancy), coherent disturbances, and increased noise compromise traditional model-based control. This work introduces model predictive control (MPC) for quantum control applications. MPC is a closed-loop optimization framework that (i) inherits a natural degree of disturbance rejection by incorporating measurement feedback, (ii) utilizes finite-horizon model-based optimizations to control complex multi-input, multi-output dynamical systems under state and input constraints, and (iii) is flexible enough to develop synergistically alongside other modern control strategies. We show how MPC can be used to generate practical optimized control sequences in representative examples of quantum state preparation. Specifically, we demonstrate for a qubit, a weakly-anharmonic qubit, and a system undergoing crosstalk, that MPC can realize successful model-based control even when the model is inadequate. These examples showcase why MPC is an important addition to the quantum engineering control suite.

Coherence of digital processing of current and voltage signals at decimation for power systems with a large share of renewable power stations

The high energy and environmental performance of renewable power stations (RPS) contributes to their widespread introduction in many countries. A trend towards decentralization of generating capacities and an increase in the share of RPS in their structure brings about the multifactorial features that affect the reliability of power systems. These factors can result in a failure and unnecessary or false operation of intelligent digital devices and systems that perform the protection and automatic control functions. Digital substations using the IEC 61850 protocol to exchange instantaneous values of analog signals employ merging units (MUs) for digital processing of current and voltage. MUs use down-sampling, i.e., decimation, to reduce the number of calculations and meet other purposes. The paper presents findings of an analysis of the digital processing effects associated with the disturbance of coherence of current and voltage signals during decimation. Failure to comply with the coherence requirements during decimation leads to significant errors in the estimates of signal parameters. The extent to which the sinusoidality of signals is distorted due to incoherence can be determined using a normalized cross-correlation coefficient. Simulation results have shown that incoherent sampling enhances the distorting effect for the signals containing high-frequency harmonics and interharmonics. Coherence of digital signal processing after decimation can be ensured by preliminary digital filtering. Superposition of noise components does not affect much the estimations of signal amplitudes during decimation, which are within the allowable error. Coherence of digital processing of current and voltage signals during decimation contributes to the reliable operation of power systems with a large share of RPS, first of all solar photovoltaic and wind power stations.

Supersonic cylinder wake dynamics

The supersonic wake of a circular cylinder in Mach 3 flow was studied through high-speed, focussing schlieren photography. The mean and unsteady behaviour of the separated shear layers, the reattachment process, the recompression wave and the early wake are analysed, and discussed in detail. The fluctuations in the wake are stronger and more coherent than those within the approaching shear layers and the recirculation region. The recompression of the shear layers energises the finer scales in the flow which leads to a departure from a $-$ 1 spectral roll-off observed in the schlieren spectra further upstream. The recompression wave exhibits low-frequency unsteadiness and a ripple-type motion which occurs as it is perturbed by shocklets radiating from the coherent structures in the wake. The wake consists of coherent disturbances with the same characteristic frequency as that for an incompressible flow over a cylinder; however, this instability is suppressed as the wake accelerates, presumably due to increasing compressibility. The primary instability of the wake flow has a characteristic frequency nearly twice that of its incompressible counterpart and it is shown to be driven by the presence of aeroacoustic resonance in the wake. It is also shown that the resonance, which leads to the formation of broadband standing waves in the wake, is the result of an interaction between the wake instabilities and upstream propagating acoustic waves in the wake. The acoustic waves originate upstream of the reattachment region and are believed to be generated by the unsteady separation on the cylinder surface.

Phenomenological model of disturbance waves in annular two-phase flow

A new, phenomenological, model of disturbance waves in annular two-phase flow is presented. The model builds upon the three-field (gas, drops and film) one-dimensional model of annular two-phase flow by considering the disturbance waves as an additional fluid field, traveling over a thin liquid base film, along with its own mass, momentum and energy conservation equations. The waves are modeled as fluid particles characterized by basic macroscopic parameters such as the wave shape factor (amplitude/width) and the wave number density (spatial frequency of waves). Phase change is considered and relevant closure models are developed for the field mass and momentum exchange rates (drop entrainment/deposition and waves/base film interactions). A Boltzmann transport equation of wave number density is introduced to model the hydrodynamic non-equilibrium effects related to the wave creation, merging and splitting processes, characteristic of developing annular two-phase flows (due to e.g., inlet effect, phase change, geometrical change or transient). Finally, the base film mass and wave number density sink and source rates are modeled using a relaxation time approximation. The new model is motivated and fully documented in this paper and has been implemented in the latest version of the transient sub-channel analysis code MEFISTO-T. While the proposed model framework is generic for coherent disturbance waves, the required wave characteristic correlations are specifically developed and calibrated using high pressure steam/water experiments under equilibrium conditions relevant of Boiling Water Reactor operation. The model relaxation times are then estimated by comparing the model predictions against measured wave parameters downstream various flow perturbations (evaporation and film suction), along the channel recovery length toward equilibrium. For all considered experiments, the model predicts the averaged wave and base film parameters typically within +/-20% and is able to capture the axial development of disturbance wave characteristics. The consideration of non-equilibrium effects is found fundamental to the accurate simulation of axially developing annular two-phase flows.

Potential Amplification Mechanism of Rotor–Stator-Interaction Noise via Spiral-Poiseuille-Flow Instability

This study investigates the instabilities of the interstage flow between a rotor and a stator in turbomachinery and evaluates their impact on the fan noise. By viewing the interstage flow as the so-called spiral-Poiseuille flow, linear stability analysis of the incompressible Navier–Stokes equations reveals two distinct instability regimes at the Reynolds numbers up to : The first mode excites disturbances over wide frequencies, including the rotor speed, and forms wavepacket-like structures above the outer-wall boundary layer. The second mode evolves inside the outer-wall boundary layer with slower velocity and possesses much smaller axial wavenumbers. We extract these modes using an approach analogous to dynamic mode decomposition from a database of our improved–delayed–detached eddy simulation solving NASA’s turbofan-rig test at low speed. The dynamic mode decomposition technique successfully visualizes these two instability modes even at , and their dispersion relations approximately agree with the characteristics predicted by the linear stability analysis. These analyses suggest that the instabilities amplify coherent disturbances in the rotor wakes and vortices near the tip until they interact with the stator; moreover, coherent structures associated with the second instability may act as stationary objects, possibly resulting in an additional fan-noise source.

Transverse mode analysis for free-space laser beams using Bayesian analysis.

Reliable and rapid assessment of the transverse mode quality of a free-space laser beam has a wide range of applications in laser development, research, and utilization. It has become even more important with recent advances in developing orbital angular momentum photon beams across a broad spectral region. In this work, a general modal analysis method for a free-space multimode laser beam has been developed based on Bayesian analysis. After transforming mode decomposition into a linear system problem, a Gaussian probabilistic model is used to find a closed-form solution. The method is found to be robust with the presence of Gaussian noise. Prior knowledge about the mode content can be incorporated into the method to improve the solution for situations when coherent disturbances or contamination are present in the laser beam. This method can be used to analyze the mode content for laser beams in different bases, such as Hermite-Gaussian (HG) modes and Laguerre-Gaussian (LG) modes. Three applications of this method are presented: a detailed modal analysis of the beam image from the incoherent intensity addition of HG modes and two examples of mode decomposition using the complex wavefront from the coherent superposition of HG and LG modes. The feasibility of this method is demonstrated using various simulation results. Based on digital images of a laser beam recorded without complex wavelength-limiting optics, in principle, this method can be used in a wide wavelength range from infrared to ultraviolet, and possibly x ray.

Is Fresh Frozen Plasma Still Necessary for Management of Acute Traumatic Coagulopathy?

Massive blood loss secondary to major trauma is a leading cause of death worldwide. In recent years, multiple different strategies have evolved to counteract this life-threatening condition. In this review, we will review our understanding of trauma-induced coagulopathy and summarize current clinical transfusion regimes utilized in military and civilian settings. We will review currently available blood products used to rectify the coherent disturbances of haemostasis by outlining the characteristics of the different products. Current evidence suggests that fresh frozen plasma and fibrinogen components play a fundamental role in trauma resuscitation with recent studies suggesting pre-hospital plasma and fibrinogen administration might also be beneficial in counteracting trauma-induced coagulopathy. Based on experience out of combat zones, whole blood transfusion might experience a renaissance in the future. Multiple different plasma-based products are available to treat and prevent trauma-induced coagulation disturbances. As randomized controlled trials in trauma population are difficult to conduct, most of the evidence is currently based on relatively small studies. While the overarching result of our review suggests the early use of plasma and fibrinogen products in combination with packed red blood cells will prevent trauma-induced coagulopathy, large, multi-centre studies are warranted to evaluate the long-term effects on patients’ outcome.

Circadian rhythms in innate immunity and stress responses.

Circadian clocks are a common feature of life on our planet, allowing physiology and behaviour to be adapted to recurrent environmental fluctuation. There is now compelling evidence that disturbance of circadian coherence can severely undermine mental and physical health, as well as exacerbate pre-existing pathology. Common molecular design principles underpin the generation of cellular circadian rhythms across the kingdoms, and in animals, the genetic components are extremely well conserved. In mammals, the circadian timing mechanism is present in most cell types and establishes local cycles of gene expression and metabolic activity. These distributed tissue clocks are normally synchronized by a central pacemaker, the suprachiasmatic nuclei (SCN), located in the hypothalamus. Nevertheless, most clocks of the body remain responsive to non-SCN-derived hormonal and metabolic cues (for example, re-alignment of liver clocks to altered meal patterning). It has been demonstrated that the clock is an influential regulator of energy metabolism, allowing key pathways to be tuned across the 24-hr cycle as metabolic requirements fluctuate. Furthermore, clock components, including Cryptochrome and Rev-Erb proteins, have been identified as essential modulators of the innate immune system and inflammatory responses. Studies have also revealed that these proteins regulate glucocorticoid receptor function, a major drug target and crucial regulator of inflammation and metabolism.

Nonlinear flame response dependencies of a V-flame subjected to harmonic forcing and turbulence

We study the dependence of the flame sheet response of an open V-flame when subjected to simultaneous but independently controlled – (1) narrowband, coherent disturbances, (2) mean flow velocity, and (3) turbulent broadband disturbances. We re-examine the data presented in Humphrey et al. (2018). Flame edge and flow field were obtained from Mie scattering images and PIV vector fields, respectively. We determine the flame sheet response, which allows us to understand the effects of kinematic restoration on the local and global flame dynamics. We find some highly nonlinear behaviors in the flame sheet response, which have not been reported previously. In particular, we observe (1) oscillations in the rise and peak region of the flame response, and (2) early onset of the nonlinear coupling between narrowband and broadband disturbances, resulting in oscillatory decay immediately downstream of the flame holder region. The spatial oscillations seen in the flame response arise only when unalike disturbances such as vortical and flame wrinkle disturbances have a comparable wavelength and, thus, interfere. We then find that higher nominal velocity and turbulent intensities increase asymmetry in the flame response, and subsequently affect the local and global heat release response (HRR). We analytically calculate HRR from flame sheet response. We find that there is a monotonic increase in the response with increasing flame length for lower nominal velocities, possibly due to higher flame symmetry. Moreover, the HRR calculated from flame sheet response captures the effect of kinematic restoration very well. Notably, there is a decrease in HRR with increasing turbulence intensity due to enhanced smoothing from kinematic restoration at higher turbulence levels. We further find that the flame response dependence on harmonic forcing manifest in the low-pass filter characteristics of the global HRR response.

Self-consistent triple decomposition of the turbulent flow over a backward-facing step under finite amplitude harmonic forcing.

We investigate the saturation of harmonically forced disturbances in the turbulent flow over a backward-facing step subjected to a finite amplitude forcing. The analysis relies on a triple decomposition of the unsteady flow into mean, coherent and incoherent components. The coherent-incoherent interaction is lumped into a Reynolds averaged Navier-Stokes (RANS) eddy viscosity model, and the mean-coherent interaction is analysed via a semi-linear resolvent analysis building on the laminar approach by Mantič-Lugo & Gallaire (2016 J.Fluid Mech. 793, 777-797. (doi:10.1017/jfm.2016.109)). This provides a self-consistent modelling of the interaction between all three components, in the sense that the coherent perturbation structures selected by the resolvent analysis are those whose Reynolds stresses force the mean flow in such a way that the mean flow generates exactly the aforementioned perturbations, while also accounting for the effect of the incoherent scale. The model does not require any input from numerical or experimental data, and accurately predicts the saturation of the forced coherent disturbances, as established from comparison to time-averages of unsteady RANS simulation data.

Strain–curvature coupling in harmonically excited, turbulent premixed flames

Abstract Premixed flames in turbulent, shear flows are disturbed by a superposition of broadband, turbulent fluctuations, and coherent disturbances originating from acoustic disturbances and/or hydrodynamic instabilities. Prior studies have shown nonlinear interactions between such coherent and stochastic disturbances on the flame. This paper investigates the effect of these interactions on the correlation between tangential flame stretch and curvature, an important quantity in turbulent premixed flame physics. High speed particle image velocimetry is used to measure the flow field in an experimental facility where harmonic wrinkles are introduced into a premixed flame that is subjected to varying turbulence intensities, while Mie scattering images are used to extract flame edges. Results show a clear correlation between phase-averaged tangential flame stretch and flame curvature. The magnitude of the fluctuations in both of these quantities decreases with increase in turbulence intensity, even while their overall correlation remains strong. Results from a linearized analysis of the perturbation of the approach flow by a curved, laminar flame are shown to capture the key features of the experimental data. These results suggest that the phase-averaged tangential stretch-curvature correlation is due to gas expansion effects, causing divergence of the approach flow in regions of positive flame curvature, the same mechanism that is responsible for the Darrieus–Landau instability. This result shows that turbulent flames in shear flows with large scale coherent structures, are subjected to not only mean strain, but also coherent modulations in strain rate.

Trade-off relation for coherence and disturbance

Quantum measurements necessarily disturb the state of physical system. Once we perform a complete measurement, the system undergoes decoherence and loses its coherence. If there is no disturbance, the state retains all of its coherence. It is therefore natural to ask if there is trade-off between disturbance caused to a state and its coherence. We present a coherence disturbance complementarity relation using the relative entropy of coherence. For bipartite states we prove a complementarity relation between the quantum coherence, entanglement and disturbance. Similar relation also holds for quantum coherence, quantum discord and disturbance for a bipartite state. We illustrate the trade-off between the coherence and the disturbance for single qubit state for various quantum channels.

Scrutiny of buffet mechanisms in transonic flow

PurposeThis paper aims to show results of numerical simulations of transonic flow around a supercritical airfoil at chord Reynolds number Rec = 3 × 106, with the aim of elucidating the mechanisms responsible for large-scale shock oscillations, namely, transonic buffet.Design/methodology/approachUnsteady Reynolds-averaged Navier–Stokes simulations and detached-eddy simulations provide a preliminary buffet map, while a high fidelity implicit large-eddy simulation with an upstream laminar boundary layer is used to ascertain the physical feasibility of the various buffet mechanisms. Numerical experiments with unsteady RANS highlight the role of waves travelling on pressure side in the buffet mechanism. Estimates of the propagation velocities of coherent disturbances and of acoustic waves are obtained, to check the validity of popular mechanisms based on acoustic feedback from the trailing edge.FindingsUnsteady RANS numerical experiments demonstrate that the pressure side of the airfoil plays a marginal role in the buffet mechanism. Implicit LES data show that the only plausible self-sustaining mechanism involves waves scattered from the trailing edge and penetrating the sonic region from above the suction side shock. An interesting side result of this study is that buffet appears to be more intense in the case that the boundary layer state upstream of the shock is turbulent, rather than laminar.Originality/valueThe results of the study will be of interest to any researcher involved with transonic buffet.

Propagation of fully coherent and partially coherent complex scalar fields in aberration space

We consider the propagation of both fully coherent and partially coherent complex scalar fields, through linear shift-invariant imaging systems. The state of such imaging systems is characterized by a countable infinity of aberration coefficients, the values for which can be viewed as coordinates for an infinity of orthogonal axes that span the "aberration space" into which the output propagates. For fully coherent complex scalar disturbances, we study the propagation of the field through the imaging system, while for partially coherent disturbances it is the two-point correlation functions whose propagation we study. For both systems we write down generalized propagators in both real and Fourier space, differential equations for evolution through aberration space, transport equations, and Hamilton-Jacobi equations. A generalized form of the Wolf equations is an important special case of our formalism.

The infant disorganised attachment classification: “Patterning within the disturbance of coherence”

Since its introduction by Main and Solomon in 1990, the infant disorganised attachment classification has functioned as a predictor of mental health in developmental psychology research. It has also been used by practitioners as an indicator of inadequate parenting and developmental risk, at times with greater confidence than research would support. Although attachment disorganisation takes many forms, it is generally understood to reflect a child's experience of being repeatedly alarmed by their parent's behaviour. In this paper we analyse how the infant disorganised attachment classification has been stabilised and interpreted, reporting results from archival study, ethnographic observations at four training institutes for coding disorganised attachment, interviews with researchers, certified coders and clinicians, and focus groups with child welfare practitioners. Our analysis points to the role of power/knowledge disjunctures in hindering communication between key groups: Main and Solomon and their readers; the oral culture of coders and the written culture of published papers; the research community and practitioners. We highlight how understandings of disorganised attachment have been magnetised by a simplified image of a child fearful of his or her own parent.

New veto for continuous gravitational wave searches

We present a new veto procedure to distinguish between continuous gravitational wave (CW) signals and the detector artifacts that can mimic their behavior. The veto procedure exploits the fact that a long-lasting coherent disturbance is less likely than a real signal to exhibit a Doppler modulation of astrophysical origin. Therefore, in the presence of an outlier from a search, we perform a multi-step search around the frequency of the outlier with the Doppler modulation turned off (DM-off), and compare these results with the results from the original (DM-on) search. If the results from the DM-off search are more significant than those from the DM-on search, the outlier is most likely due to an artifact rather than a signal. We tune the veto procedure so that it has a very low false dismissal rate. With this veto, we are able to identify as coherent disturbances >99.9% of the 6349 candidates from the recent all-sky low-frequency Einstein@Home search on the data from the Advanced LIGO O1 observing run [1]. We present the details of each identified disturbance in the Appendix.

Enhanced quantitative phase imaging in self-interference digital holographic microscopy using an electrically focus tunable lens.

Self-interference digital holographic microscopy (DHM) has been found particular suitable for simplified quantitative phase imaging of living cells. However, a main drawback of the self-interference DHM principle are scattering patterns that are induced by the coherent nature of the laser light which affect the resolution for detection of optical path length changes. We present a simple and efficient technique for the reduction of coherent disturbances in quantitative phase images. Therefore, amplitude and phase of the sample illumination are modulated by an electrically focus tunable lens. The proposed method is in particular convenient with the self-interference DHM concept. Results from the characterization of the method show that a reduction of coherence induced disturbances up to 70 percent can be achieved. Finally, the performance for enhanced quantitative imaging of living cells is demonstrated.

Storm tracks in the Southern Hemisphere subtropical oceans

AbstractOcean storm tracks have previously been associated with the midlatitude western boundary currents (WBCs) and the Antarctic Circumpolar Current (ACC). Here we identify and examine large‐scale baroclinically unstable waves occurring within waveguides associated with potential density gradients in the subtropical regions of the Southern Hemisphere (SH) oceans where the trade winds and westerlies meet and at depths associated with mode water formation. In contrast to the Northern Hemisphere subtropics, the SH pathways are more extensive allowing large‐scale coherent disturbances to communicate information westward from the midlatitudes to the subtropics (South Pacific Ocean) and from the subtropics to the tropics (Indian Ocean). Particular consideration is given to the subtropical South Pacific Ocean as this is a region where resonant interactions between large‐scale Rossby waves and significant topographic features have been reported to occur. Using an ocean general circulation model and a simple potential energy transfer diagnostic, we identify the relevant nonlinearly modified structures comparing their propagation characteristics to planetary Rossby waves calculated using a shallow water model. Although at first appearance baroclinic disturbances resemble planetary Rossby waves, we show they are inherently nonlinear, multiscale and are amplified where topography occurs. The location of the disturbances coincides with regions of high variability in sea surface height observed in satellite altimetry and their speeds closely match the large‐scale coherent westward propagating structures described in the observational literature. Our study provides evidence that, in addition to the midlatitude WBCs and the ACC, significant ocean storm tracks are also manifest in the SH subtropics.

Performance of active feedforward control systems in non-ideal, synthesized diffuse sound fields.

The acoustic performance of passive or active panel structures is usually tested in sound transmission loss facilities. A reverberant sending room, equipped with one or a number of independent sound sources, is used to generate a diffuse sound field excitation which acts as a disturbance source on the structure under investigation. The spatial correlation and coherence of such a synthesized non-ideal diffuse-sound-field excitation, however, might deviate significantly from the ideal case. This has consequences for the operation of an active feedforward control system which heavily relies on the acquisition of coherent disturbance source information. This work, therefore, evaluates the spatial correlation and coherence of ideal and non-ideal diffuse sound fields and considers the implications on the performance of a feedforward control system. The system under consideration is an aircraft-typical double panel system, equipped with an active sidewall panel (lining), which is realized in a transmission loss facility. Experimental results for different numbers of sound sources in the reverberation room are compared to simulation results of a comparable generic double panel system excited by an ideal diffuse sound field. It is shown that the number of statistically independent noise sources acting on the primary structure of the double panel system depends not only on the type of diffuse sound field but also on the sample lengths of the processed signals. The experimental results show that the number of reference sensors required for a defined control performance exhibits an inverse relationship to control filter length.