High Velocity Amplitude Research Articles

The damage-based inelastic displacement ratio for performance-based design of fully self-centering systems under pulse-like near-fault earthquake ground motions

In this investigation, the damage-based inelastic displacement ratio (IDR) for fully self-centering (SC) systems with flag-shaped hysteresis behavior is determined under pulse-like earthquake ground motions to use in performance-based design theory. Pulsive earthquakes are known as dangerous natural phenomena due to the location of structures in the vicinity of the fault with forward-directivity and high-velocity amplitude features, which expose the system to high risk. Before this, the IDRs were obtained based on constant-ductility and strength reduction factor intensities for designing new and evaluating existing structures with SC behavior. However, the issue could be extended to an energy-based theory using the Park-Ang damage model as a popular index among researchers, with the ability to consider record amplitude, frequency content, and duration. Therefore, the damage-based IDR was determined under 252 pulse-like records with 126 pairs at four damage levels, 30 periods of vibration, four ultimate ductility factors (µu), four stiffness hardening ratios (α), and three dissipative energy factors (βn) by conducting comprehensive nonlinear dynamic analysis. Then, the influence of the mentioned parameters on obtained IDRs is evaluated to propose a robust equation for estimating target displacement in these systems. Statistical results illustrate that the approximate equation based on normalizing the structural period to the predominated period can predict the target displacement compared to achieved ones from direct time-history analysis, where the difference between estimated and mean target displacements is below 15%.

The closest extremely low-mass white dwarf to the Sun

ABSTRACT We present the orbit and properties of 2MASS J050051.85−093054.9, establishing it as the closest (d ≈ 71 pc) extremely low-mass white dwarf to the Sun. We find that this star is hydrogen rich with $T_\textrm {eff}\approx 10\, 500$ K, log g ≈ 5.9, and, following evolutionary models, has a mass of ≈0.17 M⊙. Independent analysis of radial velocity and Transiting Exoplanet Survey Satellite(TESS) photometric time series reveals an orbital period of ≈9.5 h. Its high velocity amplitude ($K\approx 144~\textrm {km}\, \textrm {s}^{-1}$) produces a measurable Doppler beaming effect in the TESSlight curve with an amplitude of 1 mmag. The unseen companion is most likely a faint white dwarf. J0500−0930 belongs to a class of post-common envelope systems that will most likely merge through unstable mass transfer and in specific circumstances lead to Type Ia supernova explosions.

Effects of Acoustic Excitation on the Combustion Instability of Hydrogen-Methane Lean Premixed Swirling Flames.

Lean premixed flames are useful for low nitrogen oxide (NOx) emissions but more prone to induce combustion instability in gas turbines. Combustion instability of a lean premixed swirling flame (LPSF) with hydrogen–methane was investigated experimentally. The effects of hydrogen addition on combustion instability with equivalence ratios 0.75–1 were investigated with acoustic frequencies (90–240 Hz) and acoustic amplitudes (the ratio of velocity fluctuation to an average velocity of 0–0.5), respectively, which are characterized by the gain and phase of the flame describing function (FDF). The evolution of vortex and the flame morphologies were observed by the particle image velocimetry (PIV), intensified charge-coupled device (ICCD), photomultiplier tube (PMT), and Cassegrain optical systems. The global and local heat release fluctuations of the LPSF were shown by CH*/OH* chemiluminescence and temperature measurements. Results show that the FDF features maximum and minimum gain values in the acoustic frequency range of 90–240 Hz and reaches local maximum peaks at 110 and 180 Hz and local minimum peaks at 160 Hz. It can also be observed that varying velocity amplitudes (0–0.5) have greater effects on the gain and phase of FDF than changing equivalence ratios (0.75–1) for lean swirling flames. Higher velocity amplitudes more effectively intensified the compression of the flame length, which enhanced the mixing of the high-burning gas and the unburned gas, and then heat release fluctuations increased. However, it is more interesting that the effects of hydrogen addition on the combustion instability of the LPSF show a completely opposite phenomenon due to acoustic frequency under all experimental conditions. The FDFs were compared at typical frequencies of 140 and 180 Hz, and it was found that combustion instability enhanced with increasing hydrogen content at 140 Hz while weakened at 180 Hz. The flow field of PIV images shows that it is related to the location and development of vortices in the flame with varying acoustic frequencies. The intensity of OH*/CH* chemiluminescence, local temperature, and heat release rate show the same changing trend with the flame morphology for two acoustic parameters with the increasing hydrogen content in the LPSF. This directly affects the compression and curvature of the LPSF and thereby changes the mixture and temperature of the combustible gas, which influence the heat release fluctuation of the LPSF.

A Dynamic Model for Vibration Studies of Deep Groove Ball Bearings Considering Single and Multiple Defects in Races

A dynamic model is reported herein for the study of vibrations of deep groove ball bearings having single and multiple defects on surfaces of inner and outer races. Masses of shaft, housing, races, and balls are considered in the modeling. The coupled solution of governing equations of motions is obtained using Runge–Kutta method. The model provides the vibrations of shaft, balls, and housing in time and frequency domains. Computed results from the model are validated with experimental results, which are generated using healthy and defective deep groove ball bearings. Characteristic defect frequencies and its harmonics are broadly investigated using both theoretical and experimental results. Comparison of vibration spectra for the cases having single and two defects on races reveals relatively higher velocity amplitudes with two defects. Good correlations between theoretical and experimental results are observed. Authors believe that this dynamic model can be used with confidence for the study and prediction of vibrations of healthy and defective deep groove ball bearings.

Pulsating Jet Impingement Heat Transfer Enhancement

This article presents results from a numerical study of pulsating jet impingement heat transfer. The motivation is to seek conditions offering a significant enhancement compared to steady flow impingement drying. The CFD software package FLUENT was used for simulating slot-type pulsating jet impingement flows with confinement. The parameter study included velocity amplitude ratio, mean jet velocity, and pulsation frequency. The distance from nozzle exit to surface was three times the hydraulic diameter of the nozzle. The Reynolds number based on the nozzle hydraulic diameter and jet temperature was 2,460 with a mean jet velocity of 30 m/s, which is the base case of the numerical experiments. Results showed that time-averaged surface heat transfer increased with increasing velocity amplitude for the same mean jet velocity. Large velocity amplitudes helped enhance heat transfer by two mechanisms: high jet velocity during the positive cycle and strong recirculating flows during the negative cycle. For the cases with different mean jet velocities but the same maximum velocity, time-averaged surface heat flux decreased with decreasing mean jet velocity. As for the effects of pulsation frequency, with high-velocity amplitude ratio, time-averaged surface heat fluxes were at the same level regardless of frequency. However, at low-velocity amplitude ratio, high frequency caused stronger recirculating flows resulting in greater heat transfer compared to the cases with a lower frequency.

High-eccentricity planets from the Anglo-Australian Planet Search

We report Doppler measurements of the stars HD187085 and HD20782 which indicate two high eccentricity low-mass companions to the stars. We find HD187085 has a Jupiter-mass companion with a ~1000d orbit. Our formal `best fit' solution suggests an eccentricity of 0.47, however, it does not sample the periastron passage of the companion and we find that orbital solutions with eccentricities between 0.1 and 0.8 give only slightly poorer fits (based on RMS and chi^2) and are thus plausible. Observations made during periastron passage in 2007 June should allow for the reliable determination of the orbital eccentricity for the companion to HD187085. Our dataset for HD20782 does sample periastron and so the orbit for its companion can be more reliably determined. We find the companion to HD20782 has M sin i=1.77+/-0.22M_JUP, an orbital period of 595.86+/-0.03d and an orbit with an eccentricity of 0.92+/-0.03. The detection of such high-eccentricity (and relatively low velocity amplitude) exoplanets appears to be facilitated by the long-term precision of the Anglo-Australian Planet Search. Looking at exoplanet detections as a whole, we find that those with higher eccentricity seem to have relatively higher velocity amplitudes indicating higher mass planets and/or an observational bias against the detection of high eccentricity systems.

Plane Couette flow of viscoplastic materials along a slippery vibrating wall

This study looks at the influence of slip at the wall on plane Couette flows of viscous and yield stress fluids with ultrasonic wall motion. These fluids are used in coating processes. A constant speed V at one wall creates the flow, and vibrations and slip take place at the other wall. Isothermal conditions and arbitrary (longitudinal or transverse) vibrations are considered, with negligible vibrational inertia. For the Bingham model, due to its nonlinearity, whatever the vibration direction and the wall slipperiness, significant decreases occur in the average stress as soon as moderate values of the dimensionless vibration velocity amplitude are involved. Such effects are associated with adherent or slippery walls, even with linear friction laws. They do not occur with linear viscous (Newtonian) models. Average stress reductions can reach nearly 100% for very high Oldroyd numbers, i.e. for stress values without vibration close to the yield limit. Slip velocity also decreases. The cost in terms of the power dissipated remains relatively less than in the Newtonian case, and may contribute to a change in the temperature field. Even when the flow without vibration is a pure slip one, large enough amplitude vibrations, either longitudinal or transverse, applied at the wall can reduce the average shear stress and slip velocity, giving rise to an average axial shear flow. Hence vibrations of moderate or high-velocity amplitude applied to adherent or slippery walls enhance plane Couette flow rates for viscoplastic materials. With moderate values of this amplitude, longitudinal vibrations may be 1.5–2 times more efficient than transverse vibrations with an equivalent cost. However, if for technological reasons transverse vibrations have to be preferred, they can also produce significant results. In any case, coating flows should benefit from an adequate application of ultrasound at the wall.

Periodic Motion along a Solar Filament Initiated by a Subflare

A type of mass motion in solar filaments, not previously reported, is studied with high-cadence (1 minute) Hα observations made at the Big Bear Solar Observatory on 2001 October 24. This oscillatory motion is along the filament and extends over a long distance (~1.4 × 105 km) with a period of ~80 minutes and a very high velocity amplitude of ~92 km s-1. Another significant property of this oscillation is that it is triggered by a subflare that occurred near its footpoint. The oscillation completes three cycles before it damps out over a timescale of ~210 minutes. We mainly discuss whether this oscillation is an extreme form of the recently discovered counterstreaming flows in filaments or is a form of the large-amplitude filament oscillations (known as a winking filament) discovered a half-century ago.

A dispersion relation in the atomic rearrangement high-velocity amplitude

It is pointed out that the second Born amplitude, which dominates in 1s-1s electron capture at high collision velocity, upsilon , obeys to order (1/ upsilon ) a dispersion relation in the square of the momentum transfer, lambda . Consequently contributions to the Thomas peak from off-energy-shell (virtual) intermediate states may be expressed as an integral over the on-shell (real) intermediate state contributions, and vice versa.