EXPERIMENTAL INVESTIGATION INTO THE EFFECTS OF REDUCED VERTICAL CENTRE OF GRAVITY OF AN ARTICULATED CONCRETE MATTRESS IN CURRENT FLOW

An articulated concrete mattress model has been utilised to investigate the effects of reduced vertical centre of gravity on the stability of a 400 series block. Experimental testing was conducted at the AMC CWC, Beauty Point. To determine the effects that a reduced centre of gravity has on stability, the 3 by 3 articulated concrete mattress model was subject to pure uniform current flow. The subsequent forces were analysed with a six degree of freedom underwater force sensor. In order to gain a range of real world scenarios, the experimental model was tested at six flow angles ranging from -15 degrees through to 60 degrees, at 15 degree increments. Additionally, five fluid velocities starting at 0.6 m/s through to 1.4 m/s, at 0.2 m/s increments were investigated. These results explain how the inversion of a 400 series block increases its hydrodynamic coefficients and subsequently decreases its stability performance in current flow. Ultimately, this study provides experimental information for the installation of 400 series articulated concrete mattresses in the inverted orientation.

Numerical Modeling of the Wave-Plate-Current Interaction by the Boundary Element Method

The aim of this work is to propose a numerical study of the interaction of a wave-horizontal plate fixed and completely immersed in a flat-bottomed tank with a uniform current flowing in the same direction as the incident wave. We investigate in particular the effect of the plate at minimizing the impact of the wave on the coast of beaches by studying the free surface elevation and the reflection coefficient, as well as the influence of the various geometrical parameters on the latter, taking into account the presence of the current. The numerical method used in this study is the boundary element method (BEM), and the results obtained will be confronted with experimental and analytical data existing in the literature.

Understanding composite negative differential resistance in niobium oxide memristors

Volatile memristors, or threshold switching devices, exhibit a diverse range of negative differential resistance (NDR) characteristics under current-controlled operation and understanding the origin of these responses is of great importance for exploring their potential as nano-scale oscillators for neuromorphic computing. Here we use a developed two-zone, parallel memristor model of NDR to undertake a systematic analysis of NDR modes in two-terminal metal-oxide-metal devices. The model assumes that the non-uniform current distribution associated with filamentary conduction can be represented by a high current density core and a lower current-density shell where the core is assumed to have a memristive response due to Poole-Frenkel conduction and the shell is represented by either a fixed resistor or a second memristive region. The detail analysis of the electrical circuits is undertaken using a lumped-element thermal model of the core-shell structure, and is shown to reproduce continuous and discontinuous NDR responses, as well as more complex compound behaviour. Finally, an interesting double-window oscillation behaviour is predicted and experimentally verified for a device with compound NDR behaviour. These results clearly identify the origin of different NDR responses and provide a strong basis for designing devices with complex NDR characteristics.

Noise Improvement of a-Si Microbolometers by the Post-Metal Annealing Process

To realize high-resolution thermal images with high quality, it is essential to improve the noise characteristics of the widely adopted uncooled microbolometers. In this work, we applied the post-metal annealing (PMA) process under the condition of deuterium forming gas, at 10 atm and 300 °C for 30 min, to reduce the noise level of amorphous-Si microbolometers. Here, the DC and temperature coefficient of resistance (TCR) measurements of the devices as well as 1/f noise analysis were performed before and after the PMA treatment, while changing the width of the resistance layer of the microbolometers with 35 μm or 12 μm pixel. As a result, the microbolometers treated by the PMA process show the decrease in resistance by about 60% and the increase in TCR value up to 48.2% at 10 Hz, as compared to the reference device. Moreover, it is observed that the noise characteristics are improved in inverse proportion to the width of the resistance layer. This improvement is attributed to the cured poly-silicon grain boundary through the hydrogen passivation by heat and deuterium atoms applied during the PMA, which leads to the uniform current path inside the pixel.

Three-dimensional interaction between uniform current and a submerged horizontal cylinder in an ice-covered channel

The problem of interaction of a uniform current with a submerged horizontal circular cylinder in an ice-covered channel is considered. The fluid flow is described by linearized velocity potential theory and the ice sheet is treated as a thin elastic plate. The potential due to a source or the Green function satisfying all boundary conditions apart from that on the body surface is first derived. This can be used to derive the boundary integral equation for a body of arbitrary shape. It can also be used to obtain the solution due to multipoles by differentiating the Green function with its position directly. For a transverse circular cylinder, through distributing multipoles along its centre line, the velocity potential can be written in an infinite series with unknown coefficients, which can be determined from the impermeable condition on a body surface. A major feature here is that different from the free surface problem, or a channel without the ice sheet cover, this problem is fully three-dimensional because of the constraints along the intersection of the ice sheet with the channel wall. It has been also confirmed that there is an infinite number of critical speeds. Whenever the current speed passes a critical value, the force on the body and wave pattern change rapidly, and two more wave components are generated at the far-field. Extensive results are provided for hydroelastic waves and hydrodynamic forces when the ice sheet is under different edge conditions, and the insight of their physical features is discussed.

Drift of elastic floating ice sheets by waves and current, part I: single sheet

The drift motion of a freely floating deformable ice sheet in shallow water subjected to incident nonlinear waves and uniform current is studied by use of the Green–Naghdi theory for the fluid motion and the thin plate theory for an elastic sheet. The nonlinear wave- and current-induced forces are obtained by integrating the hydrodynamic pressure around the body. The oscillations and translational motion of the sheet are then determined by substituting the flow-induced forces into the equation of motion of the body. The resulting governing equations, boundary and matching conditions are solved in two dimensions with a finite difference technique. The surge and drift motions of the sheet are analysed in a broad range of body parameters and various wave-current conditions. It is demonstrated that wavelength to sheet length ratio plays an important role in the drift response of the floating sheet, while the sheet mass and rigidity have comparatively less impact. It is also observed that while the presence of the ambient current changes the drift speed significantly (almost linearly), it has little to no effect on its oscillations. However, under the same ambient current, the drift speed changes remarkably by the wave period (or wavelength).

WAYS TO INCREASE THE LIGHTNING PROTECTION OF CARBON FIBER PLASTICS

Based on the previously conducted analytical study of the destruction of conducting composites by lightning currents, methods for increasing their lightning resistance are considered. To substantiate these methods, an analysis of the current distribution at different ratios of transverse and longitudinal resistivity was carried out. One of the methods using conductive additives in the composition of the binder material allows you to influence the anisotropy of the conductive medium of carbon fiber. The parameters of the range of the degree of anisotropy of carbon fiber are proposed to achieve uniform current spreading and reduce the radius of destruction of the composite by lightning currents. The formula for the fracture radius in the absence of anisotropy is obtained and estimated calculations are performed. The method of reinforcing carbon fiber with thin wires to increase its lightning resistance is considered. Calculated expressions are found for estimating the weight, the number of delays per unit area, and the absence of overheating. Comparisons of weight characteristics for various reinforcing materials are carried out and a conclusion is made on their effectiveness. The advantages and disadvantages of this method of protection are considered. The third way to increase the lightning resistance of the composite suggests using a carbon fiber material with a woven structure as a protective coating. This protection reduces the energy release in the material and the size of the damage. It is concluded that it is necessary to control the lightning protection parameters and choose a coating with the required characteristics. The principles and criteria of lightning protection for real carbon fiber plastics will be considered in subsequent works.