Resonance Amplitude Research Articles

Influence of bottom slope on gap resonance behavior between fixed body and back wall in close proximity

Narrow gap resonances ubiquitously presenting in coastal and offshore engineering domain may provoke unexpected structure damages and threaten operation safety, especially those occurring between floating bodies and vertical walls. While most of the existing studies assume a flat bottom, effects of the real-world sloping bottom are still unclarified and may probably change gap resonance behavior. By combining the advantages of CFD based model and modified potential flow model, this study focuses on variations of gap resonance height with the presence of a sloping bottom and the capacity of potential flow model with artificial damping method in predicting resonant patterns. For the incident wave heights from minimal ones to relatively larger ones, empirical relationship between gap resonance amplitude and incident wave amplitude is re-examined and found to be similar to that obtained from a flat bottom but with geometry-specific parameters. The potential flow model is interestingly revealed to possibly perform even better in dealing with larger incident wave amplitude and steeper bottom slope once the damping term is well-tuned. Origin of the better performance is qualitatively found to be related to the turbulence patterns inside the fluid domain beneath the narrow gap.

A study of the sign reversal from a transmission peak to an absorption dip in a V-type system using the D1 and D2 lines of 87Rb in the presence of a buffer gas

In this work, we have investigated the transmission peak and absorption dip in the Doppler broadened V-type system using the D1 and D2 lines of 87Rb atoms in the presence of nitrogen buffer gas. The effects of the probe power variations at a fixed pump power on these resonances are examined both experimentally and theoretically. We have explored the fact that the transmission peak essentially turns into an absorption dip when the probe power is stronger than the pump power. Moreover, the theoretical model of a five-level V-type system is found to be sufficient to support the experimental outcomes when the effect of collision due to the presence of buffer gas is included in the theoretical model. We have also shown the variation of the resonance amplitude and population distribution in the upper level (|5〉) with increasing probe power.

H‐polarized plane wave diffraction by a slotted cylinder with different surface impedances: Solution by the analytical—Numerical approach

The study investigates the H-polarized plane wave diffraction by a slotted cylinder with different surface impedances employing an analytical-numerical approach. The solution is obtained by expressing the current distribution on the obstacle with Gegenbauer polynomials considering the edge conditions. To obtain the field and current distribution on the surface, the Leontovich boundary condition on each side of the slotted cylinder is employed. The results are compared with Dirichlet and Neumann boundary condition cases obtained previously. It is observed that the resonant field amplitudes and the location at the resonances strongly depend on the impedance values.

On-Surface Synthesis and Spectroscopy of Aluminum Phthalocyanine on Superconducting Lead.

Large ordered islands of aluminum phthalocyanine (AlPc) molecules, which are unstable in air, are synthesized from ClAlPc on Pb(100) via dechlorination. Low-temperature scanning tunneling microscopy reveals that isolated AlPc molecules lose their spin moment on superconducting Pb(100). Molecular magnetism, which is detected via Yu-Shiba-Rusinov (YSR) resonances, may be restored by surrounding a molecule with an array of neighbor molecules in artificial arrays or in a self-assembled monolayer. Unlike phthalocyanine (H2Pc) or lead phthalocyanine (PbPc) monolayers, where the YSR energy was found to depend strongly on the detailed configuration of the neighboring molecules, we find a similar magnetic moment on every second molecule for AlPc. In addition, YSR resonances lead to unusually high conductance peaks that are due to vibrational excitations. Twelve vibrational modes are resolved and discussed with respect to similar results from PbPc. The enhancement of the inelastic transitions is tentatively attributed to the large amplitude of the YSR resonances and the long lifetime of electrons in the molecular bound state. By assembling neighboring molecules into configurations that differ from those of the monolayer, the YSR energy may be fine-tuned, and a simple spin-state switching device is constructed.

Numerical Investigation on Temporal Evolution Behavior for Triad Resonant Interaction Induced by Steady Free-Surface Flow over Rippled Bottoms

Investigating the wave hydrodynamics of free-surface flow over rippled bottoms is a continuing concern due to the existence of submarine multiple sandbars and ambient flow in coastal and estuarial areas. More attention to free-surface wave stimulation has been received from the perspective of resonant wave-wave interaction, which is an intensive way for wave energy transfer and a potential way for wave component generation. However, the basic behavior of the triad resonant interaction of this problem is still limited and unclear. In this study, the triad resonant interaction induced by steady free-surface flow over rippled bottoms is numerically investigated by means of the High-Order Spectral (HOS) method. By considering the interactions among free-surface waves, ambient current, and rippled bottoms, the numerical model is applied for this situation based on Zakharov equation with ambient flow term. The temporal evolution of the triad resonant wave amplitude has been numerically investigated and compared well with multiple-scale expansion perturbation theory. Specifically, the temporal evolution behaviors of all six triad resonant wave components are confirmed by both numerical simulation and nonlinear perturbation analysis.

Synthetical vibration reduction of the nonlinear acoustic metamaterial honeycomb sandwich plate

Light-weight and high-stiffness honeycomb sandwich plates are widely used in high- speed vehicles. Suppressing their low-frequency and broadband vibration is significant for improving safety and reducing noise, but remains challenging with limited mass cost. Bandgaps and chaotic band in nonlinear acoustic metamaterials (NAMs) offer an effective way for vibration reduction. This paper conceives a NAM sandwich plate and studies its vibration reduction properties based on numerical and experimental methods. We establish its nonlinear finite element model based on the equivalent homogeneous model and experiments. The influences of the resonator distribution, nonlinear stiffness, resonant frequencies, mass, amplitude and structural plate parameters on its vibration are thoroughly analyzed to achieve the best performance. Then, we manufacture an optimized NAM plate and experimentally demonstrate that all resonances of the high-stiffness NAM plate below 800 Hz are greatly reduced with only 17.7 % attached mass; particularly, the first low-frequency resonance at 93 Hz is reduced by 20 dB. This shows that the NAM strategy can robustly and effectively suppress the low-frequency and broadband vibration of the light-weight and high-stiffness plates with small mass cost, a synthetical performance desired for broad potential applications. The models, regularities, designs and experiments can also enlighten more studies on relate topics.

Lateral Dynamic Response of Offshore Pipe Piles Considering Effect of Superstructure

The dynamic characteristics of pipe piles are of considerable importance for the dynamic foundation design of offshore wind turbines. In this study, we develop an analytical model for the lateral vibration of offshore pipe piles with consideration of the inertia effect and axial loading from the superstructure. A coupled dynamic saturated soil–pile interaction model is established based on Biot’s poroelastic theory and Euler–Bernoulli theory. The potential function, operator decomposition method, variable separation method and matrix transfer method are introduced herein to obtain the lateral force of the inner and outer soil acting on the pile shaft. Then, the analytical solution of the pile dynamic impedance in the frequency domain is derived by employing the soil–pile continuous deformation conditions and the boundary conditions of the pile. The rationality and accuracy of the presented solution have were by comparing its results with those predicted by existing solutions. The influence of superstructure, pile geometry and soil plug height on the lateral dynamic impedance and natural frequency of pipe piles was thoroughly investigated based on the theoretical model. The main findings can be summarized as: (1) The dynamic stiffness of piles will be remarkably underestimated if the inertia effect of the superstructure is not accounted for. (2) The vertical load of the superstructure is main factor affecting the natural frequency, whereas the inertia effect of the superstructure will enlarge the resonance amplitude. (3) The overall lateral dynamic impedance and first-order natural frequency of the pile increase significantly with the soil plug height.

Vibration Reduction of a Timoshenko Beam with Multiple Parallel Nonlinear Energy Sinks

A nonlinear energy sink is a promising device to reduce structural vibrations. In this work, the vibration reduction performances of multiple parallel nonlinear energy sinks attached to a short beam are investigated based on the Timoshenko beam theory. The dynamic equations of a vibration reduction system subjected to a harmonic excitation are established. The frequency responses are analyzed based on Galerkin discretization and the harmonic balance method, and the accuracy is verified by the Runge–Kutta method. An optimization method based on the genetic algorithm is proposed for the number, location, and cubic stiffness of the nonlinear energy sinks. The study reveals that, with the same total mass, multiple parallel nonlinear energy sinks can achieve a larger vibration reduction ratio than a single nonlinear energy sink. The parameter influences of the nonlinear energy sinks are revealed, and unstable responses with large cubic stiffness are presented. The optimal locations of the multiple parallel nonlinear energy sinks are related to low-order modal shapes. A larger reduction ratio on the resonant amplitude can be achieved compared to a uniform distribution of the nonlinear energy sinks. The optimal locations and cubic stiffness are related to the number of nonlinear energy sinks. In the studied case, the optimal number of nonlinear energy sinks was two.

Mode Transitions and Thickness Measurements During Deposition of Nanoscale TiO2 Coatings on Tilted Fiber Bragg Gratings

The mode transition is a phenomenon observed in thin film coated long period fiber gratings (LPGs) and single-mode multimode single-mode (SMS) fibers for certain values of the coating thickness and refractive index, resulting in increased sensitivity for sensing applications. It is shown here that mode transitions occur simultaneously for a large number of mode resonances in the transmission spectra of tilted fiber Bragg gratings (TFBG) measured during the deposition of ∼350 nm thick TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> coatings by Atomic Layer Deposition (ALD). In TFBGs, the mode transition shows up as an acceleration of the resonance wavelength shift vs thickness, but without fading of the resonance amplitude. Furthermore, the results show that the mode transition for cladding modes with predominantly “TE” polarization at the cladding boundary is significantly sharper than that of predominantly “TM” polarized modes and that it occurs at a smaller coating thickness (<100 nm vs >200 nm). Finally, using a separately determined coating refractive index (2.14, by ellipsometry on witness flats deposited simultaneously) and simulations of the resonance shifts of the TFBG with coating thickness, it is demonstrated that a TFBG connected to a spectral interrogation system can be used to measure the growth of a coating on the surface of the fiber in real time.

Flow Estimation by Flow Induced Vibration of Bluff Bodies

The study confirms the feasibility of using information from flow-induced vibration generated by bluff bodies for measurement of flow. The proposed methodology is based on experiments conducted for recording acceleration signals from vibration sensors embedded along with bluff bodies in cross flow. The studies were undertaken in a wide Reynolds number range of 4700 to 5.655x105, with five different geometries of bluff bodies for shape optimization. Resonance and vortex shedding frequencies of samples are determined experimentally. The recorded acceleration signals are analysed using three different techniques such as frequency shift method, resonance amplitude method and overall acceleration estimation method. In this, the frequency shift method shows correlation at low flow velocities. In the resonance amplitude method and overall acceleration method, acceleration levels show a cubic relation with the flow rate. In the resonance amplitude method, obtained R2 values are from 0.93 to 0.99. Overall acceleration estimation method has shown better correlation with flow rate and its R2 values were above 0.99. The study confirms that application of all three methods together yields reasonably good estimation for a wide range of flow.

Site effect estimation for shallow engineering bedrock using microtremor HVSR method and geotechnical borehole data, Riyadh city, Saudi Arabia

The estimation of local site response and geotechnical properties of near-surface deposits becomes essential for improving the building codes especially in big cities as Riyadh. This study aims to estimate the site response parameters in the northern expansion zone of Riyadh city. Microtremor measurements were recorded at 45 sites at the study area, north of Riyadh, and the resonance frequency and amplification factor were calculated using the H/V spectral ratio approach. The microtremor data has been processed using geopsy software to get the H/V curve and get the value of the resonance frequency (fo) and amplitude (Ao). The values of the resonance frequency span from 0.79 to 45 Hz, while the amplification factor ranges from 1.22 to 8.5, indicating the presence of foundation bedrocks at various levels with varying soil thickness. Moreover, the N60 parameter was calculated to correct the SPT-N uncorrected field readings in order to estimate the shear wave velocity parameter down to 30 m depth (Vs30). The computed shear wave velocity for a depth of 30 m (Vs30) ranges from 210 to 630 m/s. Accordingly, the soil at the studied area can be divided into two site soil classes C and D according to the National Earthquake Hazard Reduction Program (NEHRP). The findings of this study should be considered as part of the development of the Saudi Building Code for Riyadh City.

Improving magnitude and phase comparison metrics for frequency response functions using cross-correlation and log-frequency shifting

This paper provides a new method for matching dominant features of Frequency Response Functions (FRFs). In particular, this paper proposes a slicing and shifting method where the key features (in this case, resonant amplitudes) of a baseline FRF are compared with a similar FRF using cross-correlation and a Log-Frequency Shift (LFS). The goal is to provide an alternative to classic point-to-point methods for FRF comparison and instead to match the dominant features of two FRFs in a way similar to visual inspection. This enables existing FRF comparison metrics to then be applied with greater fidelity. Additionally, this paper introduces the Phase Similarity Metric (PSM) for comparing phases of two FRFs and illustrates the improvement of using LFS for phase comparisons as well. This paper uses a cantilever beam experiment in multiple configurations to provide a benchmark case for FRF comparison improvements.

Actively tunable toroidal dipole resonance in hybrid terahertz metal-graphene metamaterials

The toroidal dipole is a localized electromagnetic excitation induced by a reversely distributed circulating current. The magnetic fields with opposite directions are connected end to end to form a closed circular magnetic field, and a toroidal dipole with non-radiative electric field characteristics is obtained. However, active manipulation of the toroidal resonance has remained largely unexplored due to the scarcity of compact tunable elements so far. Here, we propose a planar terahertz metamaterial composed of an asymmetric metallic double splits ring resonator, which can excite a toroidal dipole resonance. To active control the toroidal dipole resonance, the monolayer graphene is integrated with the metamaterial. By changing Fermi energy of graphene, the transmission amplitude of the toroidal dipole resonance is actively modulated and finally switched into a electric resonance or magnetic resonance. Therefore, switching between the non-radiation and the high-radiation, as well as active modulation of the toroidal dipole have potential application prospects in the design of filters, high-sensitivity sensors, and modulators.

Study of EIT line shape in optically thin and thick media using 87Rb D1 and D2 lines: theory and experiment

In this work, we have presented the variation of the amplitude of electromagnetically induced transparency (EIT) resonances with the density of the atom in a V-type system using 87Rb D1 and D2 lines both theoretically and experimentally. Up to the value of atomic density 18.1 × 1010 cm−3, the amplitude of the EIT resonance gradually increases with the increase of atomic density and then it decreases with the increase of the density of the atom. We have also found the radiation trapping effect in this experiment. We observe the effect of the atomic density on the electromagnetically induced transparency when the systems act as a thin optical media as well as thick optical media. We have found that the amplitude of EIT also depends on pump laser Rabi frequency. Numerical simulations are agreed well with the experimental observations.

Application of ray methods to one-dimensional site response of inhomogeneous soil deposits

The technique referred as ray approximation treats wave propagation in a heterogeneous medium at the infinitely small wavelength limit. This classic simplification allows useful approximate analytical results to be obtained in cases where complete description of the waveform behaviour is virtually unattainable, hence its wide use in physics. In seismology, this approximation has been widely applied. This paper presents an application in one-dimensional site response (1DSR) analysis: it is used herein, first to explain and elucidate the generality of some previous observations as to the use of the harmonic mean of a shear-wave velocity profile to represent the global behaviour of a site; and second to partially settle an open question in 1DSR, namely ‘What are the equivalent homogeneous properties that yield the same response, in terms of natural frequencies and resonance amplitude, for a given inhomogeneous site?’, providing a few assumptions are met – chiefly, that excitations of sufficiently high frequency are considered.

Traveling wave resonance analysis of flexible spur gear system with angular misalignment

The aero-engine spur gear system is often designed as thin rim structure due to lightweight consideration, which leads to traveling wave resonance phenomenon when spur gear system has angular misalignment during operation. This paper mainly analyzes traveling wave resonance phenomenon of aero-engine angular misalignment thin rim spur gear system. Time-varying mesh stiffness (TVMS) of spur gear system is calculated by loaded tooth contact analysis (LTCA) method, angular misalignment is introduced into spur gear system, and axial component of TVMS is obtained by the projection method. Flexible gear foundations are simulated by 8-node shell element and rotational shafts are simulated by Timoshenko beam element, combined with axial stiffness, the dynamic model of flexible spur gear system is established. Simulation results are compared with the references and finite element (FE) model, which proves the accuracy of the proposed method. The analysis results of angular misalignment spur gear system traveling wave resonance phenomenon show that during the operation of spur gear system, angular misalignment produces axial excitation, which excite nodal diameter vibration of gear foundations, and traveling wave resonance phenomenon appears at nodal diameter vibration resonance speed. The effects of misalignment angle, web thickness and gear torque on spur gear system traveling wave resonance amplitude and resonance speed are discussed. The research of aero-engine angular misalignment spur gear system provides theoretical basis for structural design and fault diagnosis of aero-engine gear systems.

A Room-Temperature Ferroelectric Resonant Tunneling Diode.

Resonant tunneling is a quantum-mechanical effect in which electron transport is controlled by the discrete energy levels within a quantum-well (QW) structure. A ferroelectric resonant tunneling diode (RTD) exploits the switchable electric polarization state of the QW barrier to tune the device resistance. Here, the discovery of robust room-temperature ferroelectric-modulated resonant tunneling and negative differential resistance (NDR) behaviors in all-perovskite-oxide BaTiO3 /SrRuO3 /BaTiO3 QW structures is reported. The resonant current amplitude and voltage are tunable by the switchable polarization of the BaTiO3 ferroelectric with the NDR ratio modulated by ≈3 orders of magnitude and an OFF/ON resistance ratio exceeding a factor of 2×104 . The observed NDR effect is explained an energy bandgap between Ru-t2g and Ru-eg orbitals driven by electron-electron correlations, as follows from density functional theory calculations. This study paves the way for ferroelectric-based quantum-tunneling devices in future oxide electronics.

Characterization of LCR Parallel-Type Electromagnetic Shunt Damper for Superconducting Magnetic Levitation

This study investigated the effect of electromagnetic shunt dampers on the resonance amplitude reduction in a superconducting magnetic levitation system. There are two types of electromagnetic shunt dampers, series type and parallel type, depending on the configuration of the electric circuit, and their damping characteristics may differ depending on the external resistance value in the circuit. In this study, after discussing the vibration-suppression effects of both types according to the governing equations, vibration experiments were conducted using both dampers with different resistance values. As a result, it was confirmed that, for the larger resistance value, the amplitude reduction effect is smaller in the series-type damper, while it remained high in the parallel type. We also performed numerical integrations, including the nonlinearity of magnetic force in the superconducting magnetic levitation system. As a result, it was numerically confirmed that the parallel-type damper can also be expected to reduce amplitude at a resonance caused by nonlinearity.

Neutrino-induced single pion production and the reanalyzed bubble chamber data

In this work we report the calculation of the charged current total and differential cross sections for weak pion production with neutrinos and antineutrinos, with the final pion-nucleon pair invariant mass ${W}_{\ensuremath{\pi}N}\ensuremath{\lesssim}2\text{ }\text{ }\mathrm{GeV}$. Our results are compared with the recent reanalyzed data from the old bubble chamber experiments, that solved the discrepancy between the Argonne National Laboratory and Brookhaven National Laboratory data. We implement a model previously tested for the cuts ${W}_{\ensuremath{\pi}N}&lt;1.4$, 1.6 GeV, which explicitly includes resonances in the first and second resonance regions within different approaches for the resonances self-energy and $\frac{3}{2}$ vertexes and propagators, a fact not usually analyzed. Our model leans on consistently effective Lagrangians that generate resonant amplitudes together with nonresonant and resonant backgrounds. Effects of hadrons' finite extension and more energetic resonances correspond to the emitted pion-nucleon invariant mass in the $1.6&lt;{W}_{\ensuremath{\pi}N}&lt;2\text{ }\text{ }\mathrm{GeV}$ region are taking into account using appropriate form factors in consistency with previous results on neutral current pion production calculations. Our results reproduce well the reanalyzed data without cuts and are compared with other models.

Bragg–Cherenkov resonance and polaron-like decoupling of the Wigner solid on superfluid helium

Nonlinear polaron-like dynamics of the two-dimensional Wigner solid (WS) on superfluid 4He are theoretically analyzed in different models and transport regimes for their similarities and distinctions. The Bragg-Cherenkov (BC) resonant excitation of surface waves and WS decoupling from surface dimples were usually considered in terms of a dc transport model. At the same time, field-velocity characteristics of the WS are measured under ac conditions and presented for time-averaged quantities. Here the nonlinear equation of motion of the WS coupled to surface dimples is studied for ac conditions using two different approaches based on fixing the driving field or the output current. Both approaches are shown to give similar results for the first harmonics of major transport properties. In the ac theory, the BC resonances for dimple inertia and the momentum relaxation rate have asymmetrical shapes, which is in contrast with the results of dc models. Even a quite low driving frequency is shown to affect the amplitude of the BC resonance and decoupling of the WS. Above the BC threshold, the effective mass of surface dimples as a function of the velocity amplitude strongly oscillates indicating multiple recoupling processes.