Large Flare Angle Research Articles

Numerical investigations on seakeeping and added resistance in head waves based on nonlinear potential flow methods

A fully nonlinear potential flow (FNPF) method and a body-exact (BE) method based on the time-domain desingularized-Rankine panel (DRP) method have been developed to compute the motion responses and added resistance for ships traveling in regular head waves. In the present methods, the disturbed wave potential is separated from the incident potential, and the boundary value problem (BVP) for the disturbed potential is established in each method. To validate the present FNPF and BE methods, different hull forms are adopted, including two Wigley hulls and the S-175 containership. The results of radiation, diffraction, and free motion simulations are presented and systematically compared with the experimental data and linear solutions using the double-body (DB) and Neumann–Kelvin (NK) methods. Through comparison, we demonstrate that the present FNPF method can accurately predict the motion responses and added resistance of ships. For the ships with large flare angles, the FNPF and BE methods give better predictions of peak motion responses than those using DB and NK. In addition, the FNPF method can well predict the added resistance, and has significant advantages over the other numerical methods at high forward speed (Fn=0.3). The analyses also confirm that, compared with the heave and pitch motions, the added resistance and the total wave elevations are more sensitive to the incident wave amplitude. The dimensionless added resistance decreases with the increase of incident wave amplitude, which is mainly driven by the total wave elevations along the waterline in the bow region. As the incident wave amplitude increases, the 1st harmonic amplitudes of the heave and pitch motions and the total wave elevations in the bow region decrease, while the 2nd harmonic amplitudes increase.

A generalized weak-scatterer approximation for nonlinear wave–structure interaction in marine hydrodynamics

In this paper, a generalized weak-scatterer (GWS) approximation is proposed for solving nonlinear wave–structure interaction problems. In contrast to the original weak-scatterer (OWS) theory, where the approximated free surface boundary conditions (FSBCs) are Taylor-expanded in the vertical direction from the incident wave surface, we apply Taylor series expansion in an arbitrary direction which, in particular, is tangential to the boundary of the floating structure close to the waterline. This leads to generalized kinematic and dynamic FSBCs for the radiated and scattered waves, along with corresponding expressions of the wave loads. Accordingly, an Arbitrary Lagrangian–Eulerian (ALE) approach is adopted to track the free-surface properties. The new GWS method is more consistent than the OWS model in that the wave markers do not separate from the body surface at the waterline for structures with flare. An Immersed-Boundary Adaptive Harmonic Polynomial Cell (IB-AHPC) method is implemented to solve the corresponding boundary value problems (BVPs) for both the velocity potential and the Lagrangian acceleration potential at each time step. The new formulation introduces additional convective terms in the FSBCs, making them similar to the seakeeping problems for ships with forward speed, and this requires special treatment to avoid instability in the time-domain simulations. Based on a matrix-based eigenvalue stability analysis, we illustrate that stable solutions can be achieved by introducing an upwind-biased scheme to discretize the convective terms in the kinematic FSBC. The proposed model is verified by three wave diffraction problems in regular waves, including a submerged circular cylinder, a rounded-corner rectangular ship section, and a trapezoidal section with a large flare angle.

A Compact Wideband High-Gain Metasurface-Lens-Corrected Conical Horn Antenna

In this letter, a compact wideband high-gain metasurface-lens-corrected conical horn (meta-horn) antenna is developed. A metasurface lens that has a thickness of less than 0.1 λ is developed to provide wideband transmission phase compensation with high transmission efficiency. The ultrathin lens is then used to develop a wideband high-gain horn antenna that has a shorter horn length and a large flare angle, resulting in a compact horn structure that is easy to be fabricated and mounted, and at a low cost. Simulations and experiments were conducted to demonstrate the effectiveness of the design. Measured results show that the meta-horn has a peak gain of 24.2 dBi and a 3 dB gain bandwidth of over 26%.

Broadband compact smooth horn with flat‐top radiation pattern

A broadband compact smooth horn with flat-top radiation pattern is presented in this Letter. Using a large flare angle, the whole length of the horn is reduced to 1.875λc (λc is the wavelength of 95 GHz) and the TE21 mode and higher order electromagnetic modes can be excited to exhibit flat-top radiation performance. The measured radiation pattern of the presented horn can achieve <1 dB amplitude ripple in a beam width range of ±10° at 85–105 GHz (21%) where the reflection coefficient is below −22 dB. It indicates that the broadband compact smooth horn with flat-top radiation pattern can be applied in wireless communication and reflector systems in the millimetre-wave band.

In brief

PAGE 131 The quality control of manufactured glass containers is of paramount importance to industry due to their cost effectiveness. A collaboration of researchers from Canada and China have designed a practical inspection system based on deep learning networks to inspect the containers with greater speed and accuracy, demonstrating the continued wide-ranging applications of deep learning methods. PAGE 119 A compact smooth horn antenna with a flat-top radiation pattern has been presented by researchers from China and the UK. The antenna is made compact using a large flare angle to reduce its length with the resulting radiation pattern achieving low amplitude ripple in its intended beamwidth range. The design has applications in the mm-wave band. Samples of acquired images of glass containers. PAGE 149 Researchers in China have analysed the characteristics of streamlined ballistic targets, as these reflect real life projectiles better than current investigations with cone and blunt-nosed shaped targets. The analysis is verified using electromagnetic calculation and simulation. Image of the compact smooth horn. PAGE 144 A team of researchers from France report an Indium-Arsenide (InAs) based quantum cascade laser (QCL) operating close to 25 micrometres with thick n-doped cladding layers used for optical confinement. The device operated up to 240 K and exhibited the best performance in threshold current density for all QCLs emitting above 20 micrometres. Micro-motion model of ballistic target. PAGE 153 Planetary bodies can be investigated with orbital radar sounders with the chosen high frequency signals allowing high penetration but being subject to electromagnetic interference. The proposed model seeks to suppress this interference to improve the resolution in the received signals and presents results from the Mars Advanced Rover Sounding. Laser waveguide cross section. Data frame comparison.

High Gain Conical Beam Antenna Array Exploiting Grating Lobes

The alternative solution is presented for single- and multi-ring arrays with a high-gain and wide elevation coverage conical beam. Effects of ring radii, number of elements, beam switching and multi-ring operation are analyzed using array theory. Gain enhancement at the large flare angle is obtained by using grating lobes of the array factor with conical pattern elements. The switching technology is employed to improve pattern ripple in azimuthal plane and to exploit the grating lobes for achieving high gain. Excitations of all the elements are in phase. A prototype of a single-ring array with 13 elements has been fabricated and measured. Three sub-arrays each composed of four elements are arranged on the ring and the other single element is located at the center. Measured results show that elevation beam coverage is from 20° to 55° and the maximum radiation gain is 9 dBi at 48° elevation at 12.5 GHz.

Smooth-Walled Light-Weight Ka-Band Shaped Horn Antennas in Metallized Foam

Several smooth-walled axis-symmetrical dielectric-loaded horn antennas with large flare angles have been designed and characterized in Ka-band. They have been optimized using an in-house CAD tool based on the BoR-FDTD technique and genetic algorithms. Two antenna configurations have been compared: in the first case, only the metallic profile of the horn is shaped and the radiating aperture remains flat, whereas in the second one, the shapes of the horn profile and the aperture are simultaneously optimized. The impact of both techniques in terms of antenna size and performance is discussed. An original fabrication process (metallized foam) has been developed to produce monolithic prototypes. Two prototypes with optimized shapes have been fabricated, and their main characteristics (radiation characteristics, bandwidth, compactness, weight) are compared to those of a standard conical horn used as a reference (same flare angle, same diameter, but without shaped profile). Our results show that the proposed design and fabrication procedures enable us to produce reduced-size horns with high radiation efficiency; the total loss, including the transition loss, is lower than 1 dB in average around 29.5 GHz.

Optimization of Reduced-Size Smooth-Walled Conical Horns Using BoR-FDTD and Genetic Algorithm

An accurate optimization tool has been developed to design arbitrarily-shaped axis-symmetrical devices. It is based on the combination between a genetic algorithm (GA) and a finite-difference time-domain (FDTD) solver formulated in a cylindrical coordinate system. For validation purposes, this tool is applied to design several smooth-walled compact conical horns with a large flare angle (90°) in the 60-GHz band. The unavoidable phase distortions appearing in the horn aperture are compensated by loading the horn mouth with thin shaped dielectric lenses made in Rexolite. Based on these test cases, several synthesis strategies are discussed and compared in order to select the best antenna prototype among those synthesized. A scaled version of this prototype has been fabricated to operate around 29.5 GHz. The numerical and experimental results are in excellent agreement. Horn size reduction rates up to 80% have been reached.

Design and numerical simulation of miniaturised COBRA lens horn

Proposed is a novel miniaturisation method of a coaxial beam-rotating antenna (COBRA) lens horn for high power application. Generally, a miniaturised horn increases the phase error at the aperture because of large flare angle which causes gain decrease. However, since the proposed COBRA lens horn compensates phase error with a modified COBRA lens, radiation characteristics such as gain and radiation pattern of the miniaturised COBRA lens horn are similar to the conventional one while the length of the horn is reduced by more than 50%.

Resistively loaded antennas for ground-penetrating radar: A modeling approach

The design of surface ground-penetrating radar (GPR) antennas is inherently difficult, primarily because the presence of the air-soil interface greatly complicates both analytic and laboratory-based approaches aimed at characterizing the antennas. Versatile numerical simulation techniques capable of describing the key physical principles governing GPR antenna radiation offer new solutions to this problem. We use a finite-difference time-domain (FDTD) solution of Maxwell's equations in three dimensions to explore the radiation characteristics of various bow-tie antennas (including quasi-linear antennas) operating in different environments. The antenna panels are either modeled as having an infinite conductivity [i.e., a perfect electrical conductor (PEC)], a constant finite conductivity, or a Wu-King finite-conductivity profile. Finite conductivities are accommodated through a subcell extension of the classical FDTD approach, with the model space surrounded by highly efficient generalized perfectly matched layer (GPML) absorbing boundary conditions. Our results show that input impedances, radiated waveforms, and radiation patterns of bow-tie antennas with Wu-King conductivity profiles are largely invariant when placed in free space or above diverse half-space earth models. By comparison, antennas with PEC or constant finite-conductivity panels have variable characteristics that depend somewhat on their operating environment. Quasi-linear antenna designs tend to be less sensitive in this respect, and hence may be suitable for a somewhat larger variety of soil conditions than planar bow-tie antennas characterized by large flare angles. Antennas with constant finite-conductivity panels are considerably more robust (i.e., less sensitive to their environment) than their PEC analogs because the loss resistance is increased, and the range over which a significant amount of current flow occurs is decreased when the antenna panels are resistively loaded. For the extreme case of Wu-King conductivity profiles, the current in the antenna panels approaches that of a quasi-infinitesimal electric dipole. This is shown by the surface-charge distributions on the various antennas and by the corresponding energy radiation patterns. Unfortunately, the favorable characteristics of the latter antennas are counterbalanced by markedly lower radiation efficiency. For the antenna designs considered in this study, we found that the peak energy radiated into earth models from bow-tie antennas with Wu-King conductivity profiles is about one order of magnitude lower than for antennas with PEC terminals.

Compact Low-Cross-Polarization Horn Antennas With Serpentine-Shaped Taper

A compact horn with low cross polarization component less than -35 dB over 5% frequency bandwidth has been obtained by optimizing the taper configuration. To reduce the gain loss caused by spherical wavefront in a short length horn with a large flare angle, a serpentine-shaped taper successfully generates five higher-order modes. Such a taper configuration is represented by varying lengths of various uniform waveguides in stepwise approximation, while keeping the dimension of each step discontinuity constant. As a result, the computational time for obtaining the proposed horn is greatly reduced because scattering matrices of the step discontinuities are pre-calculated before the optimization. The verification of its high performance has been performed numerically and experimentally.

Cable Erection Test at Splay Band for Spatial Suspension Bridge

The Yongjong Grand Bridge includes a self-anchored suspension bridge with inclined cable planes. The bridge uses splay bands (cable collars) to flare the main cables at the anchorage, which is located at the end of a stiffening truss. During cable erection, some of the wires at the splay band were expected to experience lateral displacement and/or lift phenomena because of the large flare angles at the splay band. Mockup cable erection tests at the anchorage were carried out to find the degree of displacement of the wires and to determine appropriate measures to deal with these problems. Through these tests, methods to arrange wires at the splay bands were devised and tried, and the selected method was successfully used for the actual bridge.

Investigations on directivity improvement of wide flare angle conical horns using inserted metallic discs

A simple and low cost method to enhance gain of wide angle conical horns is described. The method consists of inserting disc(s) inside the horn at particular axial locations. Investigations realised by simulation and measurements are reported for different flare angle horns as a function of different geometrical parameters and frequency. The study shows that aperture efficiency enhancement can be achieved for large flare angle horns using this concept, thus resulting in an increase of the directivity. The insertion of discs influences the impedance match. However, since the objective is to study the directivity enhancement, the mismatch losses are removed from experimental data. In practice, the horn design can incorporate a matching network to eliminate the problem.

High-gain step-profiled integrated diagonal horn-antennas

Dipole-excited integrated horn antennas are limited by their large flare angle of 70 degrees , which is inherent in the anisotropic etching process of

Computer Analysis of Gradually Tapered Waveguide with Arbitrary Cross Sections (Short Papers)

This short paper presents a general computer analysis of gradually tapered waveguide with arbitrarily shaped cross sectious. The technique combines coupled-mode theory with numerical methods for solving the uniform waveguide problem. The coupling coefficients are computed by using eigenvalues and eigenfunctions obtained numerically. The mode amplitudes are obtained either by numerical solution of a set of differential equations or from a closed-form solution. The applicability of this technique is illustrated by the analysis and measurement of two transitions. It is shown that theoretical prediction of coupled-mode amplitudes is reliable for gradual tapers where the flare angle is small. For large flare angles, more rigorous coupled-mode theory has to be employed.

Transition section spurious mode program

A transition section spurious mode program is presented to calculate the magnitude and phase of propagating modes in H-plane waveguide transition sections with large flare angles. This program is based on a full wave analysis which employs local radial waveguide modes. This program is particularly suitable when some of the waveguide modes change from propagating to evanescent modes in the transition sections.

Radiation of conical horns excited in higher-order modes

Theoretical investigations carried out for the far-field-radiation-pattern prediction of conical horns excited in the spherical TMmn and TEmn modes are applied on the radiation-pattern analysis of TM01 and TE01 modes. The results, valid even for conical horns with large flare angles, provide an optimum horn design for a maximum gain slope near the boresight axis.

H-plane multimode waveguide transition sections with large flare angles: radial and rectangular modal analyses

Waveguide transition sections that connect standard single-propagating-mode waveguides to multimode waveguides are designed using a quasioptical approach, as well as fullwave techniques based on both radial and rectangular modal analyses. The three different approaches to the problem result in the derivation of the coupled wave equations for the wave amplitudes, which are solved numerically using an iterative method as well as the Runge-Kutta method. These numerical solutions are compared with experimental results. The advantages and disadvantages of the different approaches are discussed in detail. The quasioptical approach is found to be very suitable for transition sections with small flare angles. For transition sections with large flare angles, the fullwave solutions must be used. It is shown that the radial modal analysis is here more efficient.

Radiation from conical horns with large flare angles

Radiation patterns of conical horns with large flare angles excited in the TE_{11} mode are calculated from a simple solution for horn modes using the vector diffraction formula. Radiation patterns are expressed in closed form when the half-flare angle is less than 30\deg . Patterns obtained by experiment show close agreement with calculated results.

Wave Scattering in Nonuniform Waveguides with Large Flare Angles and Near Cutoff

A set of coupled first-order differential equations for the wave amplitudes in nonuniform waveguides is developed. The coupling coefficients are regarded as differentiaI transmission and reflection scattering coefficients between two adjacent elementary radial waveguide sections. The analysis is an extension of an earlier quasi-optical solution. This set of coupled equations is compared with the familiar generalized telegraphist's equations which may be derived by considering the nonuniform waveguide to consist of elementary rectangular waveguide sections. The equations for the wave amplitudes derived in this paper are less coupled than the commonly used telegraphist's equations, and they may also be applied to waveguides with large flare angles and in regions at which the waveguide modes are at their respective cutoff cross sections.