Generation of Localised Vertical Streams in Unstable Stratified Atmosphere

A new model of axially symmetric concentrated vortex generation was developed herein. In this work, the solution of a nonlinear equation for internal gravity waves in an unstable stratified atmosphere was obtained and analysed in the framework of ideal hydrodynamics. The related expressions for the velocities in the inner and outer regions of the vortex were described by Bessel functions and modified zeroth-order Bessel functions. The proposed new nonlinear analytical model allows the study of the structure and dynamics of vortices in the radial region. The formation of jets (i.e., structures elongated in the vertical direction with finite components of the poloidal (radial and vertical) velocities that grow exponentially in time in an unstable stratified atmosphere) was also analysed. The characteristic growth time was determined by the inverse growth rate of instability. It is shown that a seed vertical vorticity component may be responsible for the formation of vortices with a finite azimuthal velocity.

Nonlinear Analytical Model of Localized Sub-THz and THz Rectifications in FET Power Detectors

<div>A nonlinear analytical model for THz FET power detectors based on their distributed RC network is presented. This empirical model works well for both drain-unbiased and drain-biased THz FET responses. The physics-based analysis reveals that localized THz rectifications in long channel transistors may be mathematically expressed in the same way as regular RF frequency rectifications of a single lumped device. However, the one lumped FET model can’t work properly at THz frequencies without correct definitions of THz signals on its terminals and independently considers localized rectifications on the source and drain sides. An improved compact one lumped THz FET power detector model with additional Schottky diodes at the source and drain terminals is presented. THz FET detector can also perform a simultaneous self-amplification (active rectification) of the localized THz rectified dc signal when operates in the saturation regime beyond its unity gain frequency. A novel analytical expression for the localized THz dc rectified response is developed for FETs operating in the saturation regime. The presented physics-based model agrees excellently with the measured experimental results of GaAs HEMT transistors at 1.6THz under arbitrary biasing conditions. Many novel electronic designs can be implemented for Millimeter-wave and THz technologies based on the physical FET's nonlinear nature in this frequency range</div>

Nonlinear Analytical Model of Localized Sub-THz and THz Rectifications in FET Power Detectors

<div>A nonlinear analytical model for THz FET power detectors based on their distributed RC network is presented. This empirical model works well for both drain-unbiased and drain-biased THz FET responses. The physics-based analysis reveals that localized THz rectifications in long channel transistors may be mathematically expressed in the same way as regular RF frequency rectifications of a single lumped device. However, the one lumped FET model can’t work properly at THz frequencies without correct definitions of THz signals on its terminals and independently considers localized rectifications on the source and drain sides. An improved compact one lumped THz FET power detector model with additional Schottky diodes at the source and drain terminals is presented. THz FET detector can also perform a simultaneous self-amplification (active rectification) of the localized THz rectified dc signal when operates in the saturation regime beyond its unity gain frequency. A novel analytical expression for the localized THz dc rectified response is developed for FETs operating in the saturation regime. The presented physics-based model agrees excellently with the measured experimental results of GaAs HEMT transistors at 1.6THz under arbitrary biasing conditions. Many novel electronic designs can be implemented for Millimeter-wave and THz technologies based on the physical FET's nonlinear nature in this frequency range</div>

Nonlinear analytical modelling of flat and hyperbolic paraboloidal panels under shear

The hyperbolic paraboloid (hypar) form has been widely used in long-span roof structures and is the subject of much research under out-of-plane loading. However, the behaviour of hypars under in-plane loading has been less keenly studied, and there is no suitable guidance for their design in current codes of practice. A nonlinear analytical model treating the hypar as a deliberate imperfection applied to a flat plate is presented. A Rayleigh–Ritz formulation using appropriate shape functions is developed and the resulting equations are solved using numerical continuation techniques. The results are verified with nonlinear finite-element models, showing good correlation across a range of thicknesses and degrees of initial curvature. Key modal contributions that influence the behaviour of the hypar are identified, providing insight into the nonlinear behaviour of hypars subject to in-plane shear. The main differences in behaviour between the flat plate and the hypar panel are shown to be most prevalent in the early stages of loading, where the influence of the initial geometry is at its greatest.

Dynamics of Single-Action Pneumatic Actuators

The asymmetry in the dynamics of an electro-pneumatic actuating device consisting of an electro-pneumatic transducer and a single-action pneumatic actuator was unexpectedly found experimentally. This asymmetry manifests in response to large step excitations. The dynamic asymmetry effect is understood as a change in the shape of the response of an actuator depending on the direction of the actuators stem movement. The questions appears: How to explain this effect? Does this phenomenon reflect thermodynamic air processes? Is it connected with air-to-mechanical energy conversion? Together, six working hypotheses explaining this effect were formulated. The asymmetry was studied in detail using analytical and simulation modeling, as well as experimental research. In this respect, a nonlinear analytical model was developed, tuned, and later solved using simulations. The simulation model was verified based on the experiment data. In addition, the problem of the efficiency in the energy conversion of a single-action actuator was discussed and, in result, the maximum theoretical energy efficiency was determined. Subsequently, all six working hypotheses were verified. Finally, the hypothesis explaining asymmetry as an effect of the different thermodynamic air processes in both actuator&rsquo;s stem travel directions was confirmed.

Design and Bench Tests of a Smart Railroad Tie for Energy Harvesting

This paper presents the design, modeling and bench testing of a smart railroad tie for energy harvesting from the motion of railway track. The system is intended for applications that require trackside power in remote locations, such as wayside electrical devices and safety equipment, signal lights, crossing gates, wireless communication, as well as rail health monitoring systems. The smart tie, which is designed to have similar dimensions to a conventional railroad tie, is installed in the same manner as a standard tie on the track. In particular, the mechanical energy harvesting module and its corresponding power management unit can be both embedded inside a composite, concrete or wooden tie, in order to shield the components from the harsh environment and protect the system against any potential theft or vandalism. Different from other railway track harvesters that typically harvest energy from bidirectional track deflections, the proposed smart tie only harvests the kinetic energy of the track when the wheels push it downwards, which resolves the preload and installation challenges of bidirectional harvesting and increases the overall system reliability. A nonlinear analytical model is developed to analyze the dynamic characteristic of the system and the simulation is conducted to predict the performance. Bench tests are subsequently carried out under both harmonic and recorded tie displacement inputs to validate the model and assess the harvesting performance. During the bench tests, the generator shaft was observed to start rotation at 0.1 mm vibration amplitude, indicating that the overall prototype has a relatively small backlash. In-lab test results indicate that an average power of 26.1–42.2W on 4 Ohms and 2 Ohms external loads were achieved under simulated tie movement recorded from a service track.