Experimental study on drag coefficient of flexible vegetation under non-breaking waves

Laboratory experiments of wave propagation over rigid and flexible vegetation fields, with the same configurations, were conducted to understand the effect of vegetation flexibility on the drag coefficient (C_D). The direct method and the least squares method (LSM), based on force and flow measurements, are applied to calculate the...

Damage Classification of a Bolted Connection using Guided Waves and Explainable Artificial Intelligence

With the improvements in computational power and advances in chip and sensor technology, the applications of machine learning (ML) technologies in structural health monitoring (SHM) are increasing rapidly. Compared with traditional methods, deep learning based SHM (Deep SHM) methods are more efficient and have a higher accuracy. However, due...

Cavity magnonics

Cavity magnonics deals with the interaction of magnons — elementary excitations in magnetic materials — and confined electromagnetic fields. We introduce the basic physics and review the experimental and theoretical progress of this young field that is gearing up for integration in future quantum technologies. Much of its appeal is derived...

Wave Breaking Induced by Opposing Currents in Submerged Vegetation Canopies

Wave height attenuation in vegetation canopies is often all attributed to the drag force exerted by vegetation, whereas other potential dissipation process is often neglected. Previous studies without vegetation have found that opposing currents can induce wave breaking and greatly increase dissipation. It is not clear if similar process may...

Unsteady mechanisms in shock wave and boundary layer interactions over a forward-facing step

The flow over a forward-facing〉 step (FFS) at Ma_∞ = 1.7 and Re_δ0 = 1.3718 × 10⁴ is investigated by well-resolved large-eddy simulation. To investigate effects of upstream flow structures and turbulence on the low-frequency dynamics of the shock wave/boundary layer interaction (SWBLI), two cases are considered:...

Low-frequency unsteadiness mechanisms in shock wave/turbulent boundary layer interactions over a backward-facing step

The low-frequency unsteady motions behind a backward-facing step (BFS) in a turbulent flow at and are investigated using a well-resolved large-eddy simulation. The instantaneous flow field illustrates the unsteady phenomena of the shock wave/boundary layer interaction (SWBLI) system, including vortex shedding in the shear layer, the flapping...

Dynamics of a supersonic flow over a backward/forward-facing step

The backward/forward-facing step (BFS/FFS) is one of the canonical geometries in aerospace engineering applications, the flow field over which has attracted extensive attention in the past decades. In a supersonic flow, laminar-to-turbulent transition and shock wave/boundary layer interaction (SWBLI) can occur over these configurations, which...

Non-hydrostatic modeling of drag, inertia and porous effects in wave propagation over dense vegetation fields

A new wave-vegetation model is implemented in an open-source code, SWASH (Simulating WAves till SHore). The governing equations are the nonlinear shallow water equations, including non-hydrostatic pressure. Besides the commonly considered drag force induced by vertical vegetation cylinders, drag force induced by horizontal vegetation cylinders...

Deriving vegetation drag coefficients in combined wave-current flows by calibration and direct measurement methods

Coastal vegetation is efficient in damping incident waves even in storm events, thus providing valuable protections to coastal communities. However, large uncertainties lie in determining vegetation drag coefficients (C_D), which are directly related to the wave damping capacity of a certain vegetated area. One major uncertainty is...

Tidal flat landscape formation and evolution

Tidal flat landscape formation and evolution are closely related to the biotic and abiotic processes that take place in the intertidal environments. Extensive studies have been carried out on the relevant agents such as hydrodynamics, sediment transport and the related ecosystem (vegetation and benthic communities) dynamics. However, the...

Beam and phase distributions of a terahertz quantum cascade wire laser

We report on both measurements and simulations of the beam profile and wavefront of a single-mode, 3.5?THz quantum cascade wire laser, incorporating a lateral corrugated metal-metal waveguide, 3rd-order distributed feedback grating. The intrinsic wavefront was measured by using a Hartmann wavefront sensor (HWS) without any optical components...

Hot electron bolometer heterodyne receiver with a 4.7-THz quantum cascade laser as a local oscillator

We report on a heterodyne receiver designed to observe the astrophysically important neutral atomic oxygen [OI] line at 4.7448?THz. The local oscillator is a third-order distributed feedback quantum cascade laser operating in continuous wave mode at 4.741?THz. A quasi-optical, superconducting NbN hot electron bolometer is used as the mixer. We...

Frequency and amplitude stabilized terahertz quantum cascade laser as local oscillator

We demonstrate an experimental scheme to simultaneously stabilize the frequency and amplitude of a 3.5 THz third-order distributed feedback quantum cascade laser as a local oscillator. The frequency stabilization has been realized using a methanol absorption line, a power detector, and a proportional-integral-derivative (PID) loop. The amplitude...

Terahertz heterodyne spectrometer using a quantum cascade laser

A terahertz (THz) heterodyne spectrometer is demonstrated based on a quantum cascade laser (QCL) as a local oscillator (LO) and an NbN hot electron bolometer as a mixer, and it is used to measure high-resolution molecular spectral lines of methanol (CH3OH) between 2.913–2.918 THz. The spectral lines are taken from a gas cell containing methanol...

Phase locking and spectral linewidth of a two-mode terahertz quantum cascade laser

We have studied the phase locking and spectral linewidth of an ? 2.7?THz quantum cascade laser by mixing its two lateral lasing modes. The beat signal at about 8?GHz is compared with a microwave reference by applying conventional phase lock loop circuitry with feedback to the laser bias current. Phase locking has been demonstrated, resulting in...

Beam patterns of terahertz quantum cascade lasers with subwavelength cavity dimensions

The need to reach single-mode lasing and minimize at the same time the electrical dissipation of cryogenically operated terahertz quantum cascade lasers may result in small and subwavelength cavity dimensions. To assess the influence of such dimensions on the shape of the laser emission, we have measured the beam pattern of two metal-metal...

Terahertz heterodyne receiver based on a quantum cascade laser and a superconducting bolometer

We report the first demonstration of an all solid-state heterodyne receiver that can be used for high-resolution spectroscopy above 2?THz suitable for space-based observatories. The receiver uses a NbN superconducting hot-electron bolometer as mixer and a quantum cascade laser operating at 2.8?THz as local oscillator. We measure a double...