Coupling Between Alfvén Wave and Kelvin–Helmholtz Waves in the Low Latitude Boundary Layer

The Kelvin–Helmholtz (KH) instability of magnetohydrodynamic surface waves at the low latitude boundary layer is examined using both an eigenfrequency analysis and a time-dependent wave simulation. The analysis includes the effects of sheared flow and Alfvén velocity gradient. When the magnetosheath flows are perpendicular to the ambient magnetic field direction, unstable KH waves that propagate obliquely to the sheared flow direction occur at the sheared flow surface when the Alfvén Mach number is higher than an instability threshold. Including a shear transition layer between the magnetosphere and magnetosheath leads to secondary KH waves (driven by the sheared flow) that are coupled to the resonant surface Alfvén wave. There are remarkable differences between the primary and the secondary KH waves, including wave frequency, the growth rate, and the ratio between the transverse and compressional components. The secondary KH wave energy is concentrated near the shear Alfvén wave frequency at the magnetosheath with a lower frequency than the primary KH waves. Although the growth rate of the secondary KH waves is lower than the primary KH waves, the threshold condition is lower, so it is expected that these types of waves will dominate at a lower Mach number. Because the transverse component of the secondary KH waves is stronger than that of the primary KH waves, more efficient wave energy transfer from the boundary layer to the inner magnetosphere is also predicted.

Wave propagation analysis of magnetic nanotubes conveying nanoflow

According to the nonlocal strain gradient theory, wave propagation in magnetic nanotubes conveying magnetic nanoflow under longitudinal magnetic field is inspected. The nonlocal strain gradient Timoshenko beam model is coupled with magnetic nanoflow considering slip boundary condition to model fluid structure interaction. By applying Hamilton’s principle, the size-dependent governing equations of motion have been obtained. Calculation of the wave frequency as well as phase velocity has been carried out based on the harmonic solution. The influences of strain gradient length scale, nonlocal parameter, Knudsen number, longitudinal magnetic field and magnetic nanoflow on nanotubes’ wave propagation behavior have been examined. According to analytical results, the magnetic intensity related to the longitudinal magnetic field contributes significantly to increasing nanotubes’ wave frequency as well as phase velocity. Besides, the magnetic nanotubes conveying magnetic nanoflow predict the highest phase velocity and wave frequency. Also, the wave frequency decrease when the nonlocal parameter increases or the strain gradient length scale decreases. Moreover, an increase in fluid velocity reduces the wave frequency and phase velocity. Article highlights The nonlocal strain gradient Timoshenko beam model is considered. Wave propagation in magnetic nanotubes conveying magnetic nanoflow is studied. Longitudinal magnetic field and magnetic nanoflow with considering slip boundary condition is inspected. Wave frequency decrease when the nonlocal parameter increases or the strain gradient length scale decreases. Increase in fluid velocity reduces the wave frequency and phase velocity.

Experimental Study on Operation Performance of Two-Body Wave Energy Generator

The two-body oscillating type wave energy converter (WEC) is a hot research topic at present. A two-body device with damping disc was taken as the test model in this paper. The two bodies were connected by a hydraulic piston cylinder to realize the relative motion energy conversion. Physical experiments were carried out in a wave-making flume to study the operation performance. The effects of wave elements and load on the hydrodynamic characteristics and capture width ratio (CWR) of the model were analysed respectively. The results showed that wave frequency and external load were the main factors affecting the motion response and energy conversion of the device. With the increase of wave frequency and external load, the response amplitude operator (RAO) and the capture width ratio both increase first and then decrease. Wave height has little effect on system characteristics. There exists a best-matching wave period condition, and the optimal motion response and energy conversion are obtained.

An Improved Numerical Fit to the Peak Harmonic Gravitational Wave Frequency Emitted by an Eccentric Binary

I present a numerical fit to the peak harmonic gravitational wave frequency emitted by an eccentric binary system in the post-Newtonian approximation. This fit significantly improves upon a previous commonly-used fit in population synthesis studies, in particular for eccentricities ≲0.8.