Sinusoidal Perturbation Research Articles

Modified honeycomb cores for enhancing the durability of sandwich structures under low-velocity impact

Honeycomb cores are essential components of composite sandwich structures, and enhancing their ability to withstand out-of-plane loads can improve the resilience of sandwich structures under low-velocity transverse impacts. Therefore, this study computationally investigates the potential for improving the out-of-plane strength of honeycomb cores by superposing periodic sinusoidal perturbations to their cell walls. Such perturbations have been used to enhance the acoustic properties of honeycomb cores. Results demonstrated that introducing these perturbations can improve the strength of honeycomb cores under localized out-of-plane loadings resembling colliding with small objects at low impact speeds. Superposed perturbations increased the out-of-plane strength by a maximum of 28.5 % and eliminated the post-buckling softening behavior. Moreover, they increased the toughness, represented by the area under the force-displacement curve, under localized out-of-plane loads by a maximum of 56.7%. The perturbed honeycomb cores showed more sensitivity to the frequency of the superposed perturbations than their magnitude.

Rapid Normal Stress Oscillations Cause Weakening and Anelastic Dilation in Gouge‐Bearing Faults

AbstractFault normal stress (σn) changes dynamically during earthquakes. However, the impact of these changes on fault strength is poorly understood. We explore the effects of rapidly varying σn by conducting rotary‐shear experiments on simulated fault gouges at 1 μm/s, under well‐drained, hydrothermal conditions. Our results show both elastic and anelastic (time‐dependent but recoverable) changes in gouge layer thickness in response to step changes and sinusoidal oscillations in σn. In particular, we observe dilation associated with marked weakening during ongoing σn‐oscillations at frequencies >0.1 Hz. Moreover, recovery of shear stress after such oscillations is accompanied by transient (anelastic) compaction. We propose a microphysically based friction model that explains most of the observations made, including the effects of temperature and step versus sinusoidal perturbation modes. Our results highlight that σn‐oscillations above a specific frequency threshold, controlled by the loading regime and frictional properties of the fault, may enhance seismic hazards.

Sensorimotor adaptation impedes perturbation detection in grasping.

Humans achieve skilled actions by continuously correcting for motor errors or perceptual misjudgments, a process called sensorimotor adaptation. This can occur with the actor both detecting (explicitly) and not detecting the error (implicitly). We investigated how the magnitude of a perturbation and the corresponding error signal each contribute to the detection of a size perturbation during interaction with real-world objects. Participants grasped cuboids of different lengths in a mirror-setup allowing us to present different sizes for seen and felt cuboids, respectively. Visuo-haptic size mismatches (perturbations) were introduced either abruptly or followed a sinusoidal schedule. These schedules dissociated the error signal from the visuo-haptic mismatch: Participants could fully adapt their grip and reduce the error when a perturbation was introduced abruptly and then stayed the same, but not with a constantly changing sinusoidal perturbation. We compared participants' performance in a two-alternative forced choice (2AFC) task where participants judged these mismatches, and modelled error-correction in grasping movements by looking at changes in maximum grip apertures, measured using motion tracking. We found similar mismatch-detection performance with sinusoidal perturbation schedules and the first trial after an abrupt change, but decreasing performance over further trials for the latter. This is consistent with the idea that reduced error signals following adaptation make it harder to detect perturbations. Error-correction parameters indicated stronger error-correction in abruptly introduced perturbations. However, we saw no correlation between error-correction and overall mismatch-detection performance. This emphasizes the distinct contributions of the perturbation magnitude and the error signal in helping participants detect sensory perturbations.

A High-Speed Multichannel Electrochemical Impedance Spectroscopy System Using Broadband Multi-Sine Binary Perturbation for Retired Li-Ion Batteries of Electric Vehicles

Retired electric vehicle (EV) batteries are reused in second-life energy storage applications. However, the overall performance of repurposed energy storage systems (ESSs) is limited by the variability in the individual batteries used. Therefore, battery grading is required for the optimal performance of ESSs. Electrochemical impedance spectroscopy (EIS)-based evaluation of battery aging is a promising way to grade lithium-ion batteries. However, it is not practical to measure the impedance of mass-retired batteries due to their high complexity and slowness. In this paper, a broadband multi-sine binary signal (MSBS) perturbation integrated with a multichannel EIS system is presented to measure the impedance spectra for the high-speed aging evaluation of lithium-ion batteries or modules. The measurement speed is multiple times higher than that of the conventional EIS. The broadband MSBS is validated with a reference sinusoidal sweep perturbation, and the corresponding root-mean-square error (RMSE) analysis is performed. Moreover, the accuracy of the presented multichannel EIS system is validated by impedance spectra measurements of Samsung INR18650-29E batteries and compared with those measured using a commercial EIS instrument. A chi-squared error under 0.641% is obtained for all channels. The non-linearity of batteries has a significant impact on the quality of impedance spectra. Therefore, Kronig–Kramer (KK) transform validation is also performed.

Experimental study on the damage characteristics of cyclic disturbance and acoustic emission characteristics of different types of sandstones under high stress in deep mines

AbstractThree sandstone specimens common in rock engineering were selected to study the differences in the mechanical properties of rocks with different lithologies. The development and expansion of the internal cracks in the specimens were observed by combining the simulation system with the acoustic emission system. Through the combination of dynamic and static stresses, the deformation and damage of rocks under deep rock excavation and blasting were simulated. As the results show, the acoustic emission events of specimens with different lithologies under combined static and dynamic cyclic loading can be roughly divided into three phases: weakening, stabilizing, and surging periods. In addition, the acoustic emission characteristics of specimens with different lithologies show general consistency in different compression phases. The degree of fragmentation of specimens increases with the applied stress level; therefore, the stress level is one of the important factors influencing the damage pattern of specimens. The acoustic emission system was used to simulate the deformation and damage of rocks subjected to deep rock body excavation and engineering blasting. Cyclic dynamic perturbations under sinusoidal waves with a frequency of 5 Hz, a loading rate of 0.1 mm/min, a cyclic amplitude of 5 MPa, and a loading rate of 0.1 mm/min were applied to the three rock samples during the experiments. Among them, the fine‐grained sandstones are the most sensitive to the sinusoidal cyclic perturbation, followed by the muddy siltstone and the medium‐grained sandstones. On this basis, the acoustic emission energy release characteristics were analyzed, and the waveform characteristics in the damage evolution of the specimen under dynamic perturbation were studied by extracting the key points and searching for the main frequency eigenvalues.

Development of real-time density feedback control on MAST-U in L-mode

In this paper we report on the development and demonstration of density feedback control for MAST-U. Sinusoidal perturbations are used to measure the frequency response from a deuterium gas valve (actuator) to line-integrated core electron density measured by the interferometer (sensor). In the frequency range relevant for control design, only two system-identification experiments were needed to regress a first-order dynamic model. This control-oriented model informs the offline design of a proportional integral controller with the established loop-shaping controller design method. After offline verification of the controller implementation, control is demonstrated by experimentally tracking a staircase reference for the line-integrated electron density. This paper demonstrates the efficiency of controller design using system-identification and loop-shaping, providing reliable density control for MAST-U.

Flexural response of sandwich structures comprising topologically perturbed cores

Enhancing the flexural stiffness of sandwich structures comprising honeycomb cores through perturbing their cellular cores is explored computationally in this work. In-plane sinusoidal perturbations are imposed on the ligaments of hexagonal cores to increase their second moment of inertia and flexural load-carrying capacity. The sensitivity of sandwich structures’ flexural strength, peak load and specific energy absorption to the imposed perturbation is investigated. Introduced perturbations are controlled through their amplitude and frequency. Results show that increasing the perturbation frequency and amplitude generally increases the flexural stiffness and peak loads of sandwich structures with perturbed cores without compromising their lightweight properties. However, low frequencies and amplitudes had a negligible effect on the sandwich structures’ mechanical properties.

Impact of image registration errors on the quality of hyperspectral images in imaging static Fourier transform spectrometry

Imaging static Fourier transform spectrometry (isFTS) is used for pushbroom airborne or spaceborne hyperspectral remote sensing. In isFTS, a static two-wave interferometer imprints linear interference fringes over the image of the scene, so that the spectral information is multiplexed over several instantaneous images, and numerical reconstruction is needed to recover the full spectrum for each pixel. The image registration step is crucial since insufficient accuracy leads to artefacts on the images and the estimated spectra. In order to investigate these artifacts, we performed a theoretical study and designed a simulation program. We established that registration errors create crenellated spatial patterns, the magnitude of which depends on the radiance gradient of the scene, the amplitude of the registration error, and the wavelength. In the case of sinusoidal perturbations, which may correspond for instance to mechanical vibrations of the carrier, we established that spurious peaks appear on the spectrum, similarly to what happens in dynamic FTS, but with spatial patterns specific to static interferometers.

Implementation and optimization of perturbation currents for vehicular proton exchange membrane fuel cells online electrochemical impedance spectroscopy measurements

AbstractThis paper presents an implementation method of perturbation currents for vehicular proton exchange membrane fuel cell (PEMFC) online electrochemical impedance spectroscopy (EIS) measurements. The topology of the parallel dual‐boost DC/DC converter system for the EIS measurement is presented. The DCdc and DCac modules in the converter system implement the DC current and the sinusoidal EIS perturbation current independently. Simulation results show that the proposed perturbation current generation method can be implemented efficiently. In the frequency domain, the current of DCdc couples to the perturbation current of DCac, leading to a reduction in the accuracy of the current amplitude after superposition. The mechanism of current amplitude reduction after superposition is discussed. Feed‐forward compensation and fuzzy compensation optimization are proposed for the DCdc current control. Both compensation algorithms achieve excellent results. A comprehensive framework for evaluating the compensation effect is presented. The evaluation results show that feed‐forward compensation has a better advantage in solving the above problems due to its simplicity and less impact on hardware control. Experimental results show that with the optimization algorithm, the input perturbation current increases from 6% to 83% of the theoretical value.

Wavy Ice Patterns as a Result of Morphological Instability of an Ice–Water Interface with Allowance for the Convective–Conductive Heat Transfer Mechanism

In this research, the wavy ice patterns that form due to the evolution of morphological perturbations on the water–ice phase transition interface in the presence of a fluid flow are studied. The mathematical model of heat transport from a relatively warm fluid to a cold wall includes the mechanism of convective–conductive heat transfer in liquid and small sinusoidal perturbations of the water–ice interface. The analytical solutions describing the main state with a flat phase interface as well as its small morphological perturbations are derived. Namely, the migration velocity of perturbations and the dispersion relation are found. We show that the amplification rate of morphological perturbations changes its sign with variation of the wavenumber. This confirms the existence of two different crystallization regimes with (i) a stable (flat) interfacial boundary and (ii) a wavy interfacial boundary. The maximum of the amplification rate representing the most dangerous (quickly growing) perturbations is found. The theory is in agreement with experimental data.

Investigating the Nature of Plasma Oscillations in Cold Plasma

Plasma oscillations are one of the important phenomena in plasma. The research in the field of plasma oscillation has a long history for more than six decades. The cold plasma is one in which electron temperature is very large but the neutral atoms are at room temperature. This study aims to obtain electron number density, electric field and velocity profile in cold plasma. Analytical method has been used to conduct this study. Fluid equations were solved to get the solution for number density, electric field and velocity of electron. To get the solution, first fluid equations are transferred to Lagrangian co-ordinates, where equations become linear and expression for respective parameter was obtained. A sinusoidal perturbation was taken as an initial condition and solution for number density; electric field and velocity were obtained. Value of perturbation was varied and corresponding waveforms were achieved and analyzed. As the perturbation increases the wave amplitude also increased. It is found that as the perturbation value is there is wave breaking in number density profile. Unlike in the number density, no such wave breaking is obtained for electric field and velocity profile. However the amplitude of waveform of electric field and velocity profile found to increases with increase in perturbation level.

Pain alleviation improves balance control and muscular coordination of lower limbs in patients with chronic ankle instability during sinusoidal perturbations

BackgroundIt is well established that individuals with chronic ankle instability manifest deficits in balance control and muscle activation. Given the prevalence of pain as a prominent symptom in this population, there is a need for in-depth investigation of its role in contributing to these impairments. MethodsA Stewart platform was used to generate translational sinusoidal perturbations in the antero-posterior direction. Eighteen individuals with chronic ankle instability and concurrent ankle pain were recruited. They were instructed to assume a central stance on the support surface with open eyes both before and 30 min after local analgesia. Data of center of pressure and electromyography of the tibialis anterior and medial gastrocnemius were recorded. Statistical analysis was performed to make comparisons pre- and post-analgesia using two-tailed paired t-test for the continuous variables. FindingsPain intensity was significantly decreased after local anesthetic injections. Antero-posterior center of pressure parameters significantly decreased following the injection. Also, there was an increase in the regularity of the center of pressure pattern. The electromyographic pattern of the tibialis anterior and medial gastrocnemius exhibited various activation patterns. After pain alleviation, the characteristic electromyographic response of the tibialis anterior and medial gastrocnemius was reciprocal contraction and relaxation that corresponded with the sinusoidal pattern of the perturbations. InterpretationIndividuals who had chronic ankle instability and ankle pain demonstrated impaired balance control during sinusoidal perturbations. Mitigating pain improved their balance performance, evident in the center of pressure pattern and the coordination of lower limb muscles.

Disturbance growth and its effect on convection in a buoyancy-driven vertical channel with one heated wall

Three-dimensional buoyancy-driven flow in a vertical channel with one heated wall that resembles a solar chimney is studied employing direct numerical simulation in order to capture the instability and disturbance growth in this flow. The aspect ratio of the simulated channel is 20, and the Grashof number is 6.1×1010. Linearly-unstable sinusoidal perturbations are individually applied to the pressure, velocity, and temperature fields at the entrance of the channel. It is shown that the imposed perturbations grow in time and change the characteristics of the flow from a laminar to a transitional character with a range of active scales of flow disturbances. Two dominant vortical structures identified in the transitional flow consist of two-dimensional spanwise and three-dimensional predominantly streamwise vortices, both growing spatially near the heated wall as the flow rises. For the ranges studied, both vortical structures appear to be independent of the amplitude or the type of the introduced perturbations. Budgets of the fluctuation kinetic energy show that buoyancy plays the main role in producing the fluctuating energy, although the role of shear production becomes more important as the flow rises along the channel. The effect of the disturbance growth on bulk convection in the solar chimney is to increase the friction coefficient, lowering the flow rate by 14% compared to a laminar condition. Moreover, the turbulent Prandtl number diverges significantly from unity near the heated wall, suggesting that the assumption of near-unity turbulent Prandtl number that is commonly made in Reynolds-averaged Navier–Stokes simulations of solar chimneys may lead to inaccurate predictions.

Relationship between wake and cylinder dynamics for a cylinder undergoing modulated vortex-induced vibrations

Vortex-induced vibrations (VIV) in the initial branch are investigated for a 2-degree-of-freedom circular cylinder placed near a plane boundary (Re=UDν=200, where U is the inflow average streamwise velocity, D is the cylinder diameter, and ν is the kinematic viscosity) with imposed sinusoidal perturbations of the free stream at resonant, 2fo, and near-resonant conditions, 2.2fo (fo is the natural shedding frequency). The cylinder exhibits a quasi-periodic response, which challenges the comprehension of its relationship with the wake dynamics obtained through conventional VIV models. The total force acting on the cylinder is decomposed into a vortex-induced force, FV, linearly coupled to VIV, and a force induced by the effective mass of the cylinder, FS, which is non-linearly coupled to VIV. The proposed semi-empirical model reveals that the time-varying nature of the effective mass in FS drives the non-linear response. The model's physical consistency is verified against simulation results. While focusing on VIV in the initial branch, the validity of the proposed model is expected to extend to other branches of response, offering a promising avenue for developing a robust predictive model for VIV under various flow conditions.

First-of-Its-Kind Frequency Enhancement Methodology Based on an Optimized Combination of FLC and TFOIDFF Controllers Evaluated on EVs, SMES, and UPFC-Integrated Smart Grid

The most recent advancements in renewable energy resources, as well as their broad acceptance in power sectors, have created substantial operational, security, and management concerns. As a result of the continual decrease in power system inertia, it is critical to maintain the normal operating frequency and reduce tie-line power changes. The preceding issues sparked this research, which proposes the Fuzzy Tilted Fractional Order Integral Derivative with Fractional Filter (FTFOIDFF), a unique load frequency controller. The FTFOIDFF controller described here combines the benefits of tilt, fuzzy logic, FOPID, and fractional filter controllers. Furthermore, the prairie dog optimizer (PDO), a newly developed metaheuristic optimization approach, is shown to efficiently tune the suggested controller settings as well as the forms of the fuzzy logic membership functions in the two-area hybrid power grid investigated in this paper. When the PDO results are compared to those of the Seagull Optimization Algorithm, the Runge Kutta optimizer, and the Chaos Game Optimizer for the same hybrid power system, PDO prevails. The system model incorporates physical constraints such as communication time delays and generation rate constraints. In addition, a unified power flow controller (UPFC) is put in the tie-line, and SMES units have been planned in both regions. Furthermore, the contribution of electric vehicles (EVs) is considered in both sections. The proposed PDO-based FTFOIDFF controller outperformed many PDO-based traditional (such as proportional integral derivative (PID), proportional integral derivative acceleration (PIDA), and TFOIDFF) and intelligent (such as Fuzzy PID and Fuzzy PIDA) controllers from the literature. The suggested PDO-based FTFOIDFF controller has excellent performance due to the usage of various load patterns such as step load perturbation, multi-step load perturbation, random load perturbation, random sinusoidal load perturbation, and pulse load perturbation. Furthermore, a variety of scenarios have been implemented to demonstrate the advantageous effects that SMES, UPFC, and EV units have on the overall performance of the system. The sensitivity of a system is ascertained by modifying its parameters from their standard configurations. According to the simulation results, the suggested PDO-based FTFOIDFF controller can improve system stability despite the multiple difficult conditions indicated previously. According to the MATLAB/Simulink data, the proposed method decreased the total fitness function to 0.0875, representing a 97.35% improvement over PID, 95.84% improvement over PIDA, 92.45% improvement over TFOIDFF, 83.43% improvement over Fuzzy PID, and 37.9% improvement over Fuzzy PIDA.

Adiabatic collapse of non-homogeneous self-gravitating gas cloud

In this letter, we find the critical mass of a self-gravitating, spherically symmetric gas cloud, above which the fluid, within the bubble, collapses. Our analysis departs from a non-homogeneous equilibrium density, satisfying the Boltzmann relation. A time scale is defined in terms of the adiabatic index of the gas. Subsequently, a sinusoidal perturbation around equilibrium is regarded, thereby leading to a dispersion relation of frequency with wavelength, which does not depend on geometrical curvature effects. Such a formulation clearly justifies that the collapse occurs much faster than predicted by the well-known Jeans approach. The equilibrium profiles of the density, gravitational field, and potential are obtained as functions of the spherical radius coordinate at marginal instability. Since our theory captures the essential physics of gravitational collapse, it can be used as the starting point for several advancements in galactic dynamics.

Intracycle Control Sensitivity of Cross-Flow Turbines

Intracycle control for cross-flow turbines employs sinusoidal perturbations in rotational speed to affect turbine power output and loads. This technique is explored for one- and two-bladed turbines with experiments that combine performance measurements with in-rotor flow-field measurements using non-intrusive particle image velocimetry. Performance enhancement is demonstrated for a wide range of control parameters but is found to be more sensitive to the sinusoidal phase offset than amplitude. Optimal performance is observed under conditions which maintain constant nominal blade angle of attack and consistently high blade-relative velocities once the static stall angle is exceeded during the power stroke. This maintains high lift and delays vortex separation. Perhaps most significantly, kinematics are also identified which decrease peak turbine loading by 12% while still producing marginally higher power output, highlighting the utility of intracycle control for load mitigation. The range of control parameters that produce these beneficial loading properties is relatively narrow and flow-fields are similar to operation at a constant rotation rate. We hypothesize that reductions in maximum loading are achieved by smoothing the changes in angle of attack and blade relative velocity profiles throughout the cycle.

A Method for Estimating Global Subgrid‐Scale Orographic Gravity‐Wave Temperature Perturbations in Chemistry‐Climate Models

AbstractMany chemical processes depend non‐linearly on temperature. Gravity‐wave‐induced temperature perturbations have been shown to affect atmospheric chemistry, but accounting for this process in chemistry‐climate models has been a challenge because many gravity waves have scales smaller than the typical model resolution. Here, we present a method to account for subgrid‐scale orographic gravity‐wave‐induced temperature perturbations on the global scale for the Whole Atmosphere Community Climate Model. Temperature perturbation amplitudes consistent with the model's subgrid‐scale gravity wave parameterization are derived and then used as a sinusoidal temperature perturbation in the model's chemistry solver. Because of limitations in the parameterization, we explore scaling of between 0.6 and 1 based on comparisons to altitude‐dependent distributions of satellite and reanalysis data, where we discuss uncertainties. We probe the impact on the chemistry from the grid‐point to global scales, and show that the parameterization is able to represent mountain wave events as reported by previous literature. The gravity waves for example, lead to increased surface area densities of stratospheric aerosols. This increases chlorine activation, with impacts on the associated chemical composition. We obtain large local changes in some chemical species (e.g., active chlorine, NOx, N2O5) which are likely to be important for comparisons to airborne or satellite observations, but the changes to ozone loss are more modest. This approach enables the chemistry‐climate modeling community to account for subgrid‐scale gravity wave temperature perturbations interactively, consistent with the internal parameterizations and are expected to yield more realistic interactions and better representation of the chemistry.

Machine learning assisted approach to design lattice materials with prescribed band gap characteristics

An artificial intelligence-assisted design framework for designing lattice materials with prescribed band gap characteristics in the range of 0–1000 kHz is proposed. The framework utilizes the double-walled hexagonal lattice which exhibits limited and narrow band gaps. The band gap characteristics of the double-walled hexagonal lattice are enhanced by increasing their number and width by imposing sinusoidal periodic perturbations on the lattice's cell walls. The imposed perturbations are controlled through their frequency and amplitude. A wide range of frequencies and amplitudes are considered to realize perturbed lattices with band gaps that cover the entire frequency range between 0 and 1000 kHz. The band gaps of each perturbed lattice over a range of porosities are obtained using finite element analysis. Machine learning, namely parallel multilayer neural networks, is used to model the relationship between porosity, perturbation amplitude and frequency on one side and band gap characteristics on the other. Results show that the proposed neural networks can predict the band gap characteristics with an average accuracy that exceeds 80%. The proposed neural networks are used to invert the topology-band gap relationship and determine the lattice parameters needed to provide a prescribed band gap characteristic. Based on the achieved accuracy of the proposed neural networks, the neural networks are used in the design framework to identify a few candidate solutions which are subsequently filtered using finite element analysis. The proposed framework promises to significantly minimize the time-consuming iterations associated with designing lattices with prescribed band gap behavior. Finally, a case study is used to demonstrate the application of the proposed framework to design a lattice material with a band gap between 575 and 625 kHz.

Response of a novel denitrifying phosphorus removal (AAO-BCO) system to sinusoidal flow perturbation of municipal sewage: Adaptability, tolerance and improvement

To date, studies on the effect of sewage disturbances on treatment facilities were based on fixed-length flow variations, which are incapable of imitating the actual dynamic flow characteristics of municipal sewage. Here, an innovative dynamic influent disturbance control system is established in this study and applied in a novel denitrifying phosphorus removal (anaerobic anoxic oxic-biological contact oxidation, AAO-BCO) system to simulate seasonal and diurnal sewage fluctuations in laboratory-scale experiments. The results showed that, under sinusoidal influent flow perturbation, the effluent pollutant content followed a relatively gentle sinusoidal trend and did not always result in desired level of pollutant removal. The ability of the system to cope with sinusoidal flow variations was susceptible to the amplitude of diurnal sewage fluctuation, while stronger tolerance capacity was observed to seasonal and momentary increase in wastewater flowrate. There was also a discrepancy in the system buffering capacity towards various pollutants removal (COD > TIN > PO43−), which may be attributed to wide fluctuations in PO43−/NO3− and different decrease in metabolic activity of denitrifying phosphorus removal (DPR) sludge caused by extreme hydraulic retention times. To improve the robustness and stability of the DPR system, a regulating strategy was proposed to alleviate the biomass reduction and uncoordinated PO43−/NO3−.