An official website of the United States government
Abstract Incorporating wave energy converters (WECs) into existing oceanographic instrument systems and offshore floating platforms can not only enhance the performance of these applications but reduce operational expenses. This article studies a system integrating a floater WEC with a floating spar platform via the inerter pendulum vibration absorber with a power take-off (IPVA-PTO) mechanism, with a focus on random wave excitation. Experiments and simulations performed on a simplified system in which the WEC is held fixed and radiation damping is absent reveal that the power spectral density (PSD) of the system consists of odd-order superharmonics when the peak frequency of wave excitation is equal to the natural frequency of the system. It is found that the odd-order superharmonics are created by the IPVA and have a strong correlation with an enhancement in power output. Simulations without the aforementioned simplifications confirm the odd-order superharmonics and the correlation, and demonstrate an improvement in the capture width ratio (CWR) of 161.4% at resonance without compromising the response amplitude operator (RAO) of the spar, in comparison with a linear benchmark with optimal electrical damping.
more »
« less
Navier-Stokes-based modeling of the clarinet
Results are presented from a modeling study of the clarinet in which the air flow through the instrument is calculated using the Navier-Stokes equations. The reed is modeled as an Euler-Bernoulli beam with damping whose motion is driven by the pressure in the mouthpiece. Damping of the reed due to its contact with the lip is studied and shown to be crucial to achieve oscillations in which the reed vibrates at the lowest resonant frequency of the instrument, producing sound at that frequency. This finding is consistent with previous studies in which a clarinet is excited with an artificial blowing machine.
more »
« less
- PAR ID:
- 10190883
- Date Published:
- Journal Name:
- Proceedings of the International Symposium on Musical and Room Acoustics, Detmold, Germany
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Articular cartilage is a thin layer of a solid matrix swollen by fluid, and it protects joints from damage via poroviscoelastic damping. Our previous experimental and simulation studies showed that cartilage-like poroviscoelastic damping could widen the range of damping methods in a low-frequency range (<100 Hz). Thus, the current study aimed to realize cartilage-like damping capacity by single- and two-indenter–foam poroviscoelastic dampers in a low-frequency range. Multiple single-indenter–foam dampers were designed by combining foam sheets with different pore diameters and indenters with different radii. Their damping capacity was investigated by dynamic mechanical analysis in a frequency range of 0.5–100 Hz. Single-indenter–foam dampers delivered peak damping frequencies that depended on the foam’s pore diameter and characteristic diffusion length (contact radii). Those dampers maximize the damping capacity at the desired frequency (narrowband performance). A mechanical model combined with simple scaling laws was shown to relate poroelasticity to the peak damping frequencies reasonably well. Finally, combinations of single-indenter–foam dampers were optimized to obtain a two-indenter–foam damper that delivered nearly rate-independent damping capacity within 0.5–100 Hz (broadband performance). These findings suggested that cartilage-like poroviscoelastic dampers can be an effective mean of passive damping for narrowband and broadband applications.more » « less
-
This research explores the inherent vulnerability of nonlinear vehicle platoons characterized by the oscillatory behavior triggered by external perturbations. The perturbation exerted on the vehicle platoon is regarded as an external force on an object. Following the mechanical vibration analysis in mechanics, this research proposes a vibration-theoretic approach that advances our understanding of platoon vulnerability from two aspects. First, the proposed approach introduces damping intensity to characterize vehicular platoon vulnerability, which divides platoon oscillations into two types, i.e., underdamped and overdamped. The damping intensity measures the platoon’s recovery strength in responding to perturbations. Second, the proposed approach can obtain the resonance frequency of a nonlinear vehicle platoon, where resonance amplifies platoon oscillation magnitude when the external perturbation frequency equals the platoon’s damping oscillation frequency. The main contribution of this research lies in the analytical derivation of the closed-form formulas of damping intensity and resonance frequency. In particular, the proposed approach formulates platoon dynamics under perturbation as a second-order non-homogeneous ordinary differential equation, enabling rigorous derivations and analyses for platoons with complicated nonlinear car-following behaviors. Through simulations built on real-world data, this paper demonstrates that an overdamped vehicle platoon is more robust against perturbations, and an underdamped platoon can be destabilized easily by exerting a perturbation at the platoon’s resonance frequency. The theoretical derivations and simulation results shed light on the design of reliable platooning control, either for human-driven or automated vehicles, to suppress the adverse effects of oscillations.more » « less
-
Ferromagnetic resonance force microscopy (FMRFM) is a powerful scanned probe technique that uses sub-micrometer-scale, spatially localized standing spin wave modes (LMs) to perform local ferromagnetic resonance (FMR) measurements. Here, we show the spatially resolved imaging of Gilbert damping in a ferromagnetic material (FM) using FMRFM. Typically damping is measured from the FMR linewidth. We demonstrate an approach to image the spatial variation of Gilbert damping utilizing the LM resonance peak height to measure the LM resonance cone angle. This approach enables determination of damping through field-swept FMRFM at a single excitation frequency. The extreme force sensitivity of ∼2 fN at room temperature can resolve changes of Gilbert damping as small as ∼2×10−4 at 2 GHz, corresponding to ∼0.16 Oe in FMR linewidth resolution. This high sensitivity, high spatial resolution, and single frequency imaging of Gilbert damping creates the opportunity to study spin interactions at the interface between an insulating FM and a small volume of nonmagnetic material such as atomically thin two-dimensional materials.more » « less
-
The presence and nature of low-frequency (0.1–10 mHz) Alfvénic waves in the corona have been established over the past decade, with many of these results coming from coronagraphic observations of the infrared Fexiiiline. The Cryo-NIRSP instrument situated at DKIST has recently begun acquiring science-quality data of the same Fexiiiline, with at least a factor of 9 improvement in spatial resolution, a factor of 30 increase in temporal resolution, and an increase in signal-to-noise ratio, when compared to the majority of previously available data. Here we present an analysis of 1 s cadence sit-and-stare data from Cryo-NIRSP, examining the Doppler velocity fluctuations associated with the Fexiii1074 nm coronal line. We are able to confirm previous results of Alfvénic waves in the corona and explore a new frequency regime. The data reveal that the power-law behavior of the Doppler velocity power spectrum extends to higher frequencies. This result appears to challenge some models of photospheric-driven Alfvénic waves that predict a lack of high-frequency wave power in the corona owing to strong chromospheric damping. Moreover, the high-frequency waves do not transport as much energy as their low-frequency counterparts, with less time-averaged energy per frequency interval. We are also able to confirm the incompressible nature of the fluctuations with little coherence between the line amplitude and Doppler velocity time series.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Conference Paper:
- The DOI is not currently available.
