Coaxial Square Research Articles

Aerodynamic analysis of rotor-to-rotor interactions in different octocopter configurations

Rotor-to-rotor interaction among neighboring rotors of a multirotor has great significance for aerodynamically efficient multirotor design. Current research is conducted to analyze aerodynamic performance of different octocopter configurations amid hover and forward flight. Conventional and coaxial configurations are studied and a hybrid configuration is also proposed to rectify the disadvantages associated with the earlier two. Comparison is carried out for the aforementioned configurations along with comparison of coaxial and hybrid octocopters with bigger diameter rotors in the same confined space for high thrust requirement missions. Vertical spacing of coaxial configuration is also studied. Virtual Blade Method (VBM) is considered herein due to its great computational efficiency. The results show that there are 11.89% and 14.22% loss in thrust for coaxial octocopter compared to conventional and hybrid configurations with normal size rotors and 15.61% loss compared to hybrid configuration with bigger rotors in hover, whereas coaxial square configuration performs the worst in forward flight with a lift loss of 9.1%, 14.77% and 18.8% compared to coaxial diamond, conventional and hybrid configurations with normal size rotors and 9.96% and 17.82% loss compared to coaxial diamond and hybrid configurations with bigger rotors. Combined FM shows that hybrid configuration outperforms other octocopter configurations in overall aerodynamic performance.

Effect of Nonlinear Magnetic Forces on Transverse Galloping Dynamics of Square Cylinders

Under the influence of cross-fluid flow, a cylinder of a square cross-section may gallop. Galloping is a self-excited vibration mode that can be utilized for low-power harvesting applications. The harvested power depends on several factors, including upstream flow velocity and system dynamics. This study explores the potential of magnetically-induced nonlinear stiffness to improve the power output of galloping-based energy harvesters. In this experimental study, the vibration response of a square rod with a mass ratio of 10 is investigated at a Reynolds number of 200. The vibration behavior of two identical coaxial square rods with magnetic monopoles at opposite ends is analyzed. Results reveal that the magnets’ configuration and strength significantly affect vibration amplitude and the critical flow velocity necessary for the onset of galloping.

Development and Optimization of Micro‐Nanotopographical Platforms for Surface Enhanced Raman Scattering Biomolecular Detection

AbstractTopologically designed micro‐ and nanostructured surface‐enhanced Raman scattering (SERS) substrates propel the advancements of innovative applications, including environmental and forensic point‐of‐care miniaturised devices via enhancing the localised electric fields for accurate analyte sensing. Herein, a method for designing, optimising and fabricating fine‐tuneable concentric hexagonal, triangular and rectangular SERS‐active micronano‐substrates is developed, with each unit yielding significant enhancement. Numerical simulations of the 3D near‐field electric field guided the optimal design process. While the coaxial SERS substrates consistently outperformed their solid counterparts, the hexagonal micro‐nano topologies exhibited ×21 higher signal than coaxial square arrays and a 12‐15‐fold increase over the triangle structures. Alternation of the topological designs from square to triangle lattice yielded more uniform plasmonic modes propagating along the 60°‐directions with various resonance modes playing key roles in light reflectance. This enables the engineering of platforms with tailor‐enhanced signals by changing the arrangement of micro‐nano patterned coaxial arrays. The fabricated SERS substrates are validated by detecting traumatic brain injury biomarkers, effectively yielding the characteristic fingerprint spectra of each neuro‐molecule. The straightforward development of sub‐micrometre tuneable SERS‐active architectures enables anelegant route for high‐throughput biochemical sensing, laying a platform for amplified bimolecular detection of disease biomarkers and integration in bioanalytical systems.

Influence of magnetically-induced nonlinear added stiffness on the lift galloping of square cylinders at low Reynolds number

A square cylinder may gallop if subjected to fluid flow, experiencing a self-excited vibration mode that can harvest energy for low-power applications. The harvested power is typically low and depends on the upstream flow velocity and system dynamic parameters. In this study, the influence of nonlinear stiffness induced by two repulsive magnetic poles on the galloping response of square rods is investigated at a mass ratio of 10 and a Reynolds number of 200. The vibration response of two identical coaxial square rods with magnetic poles attached to their opposite ends is analyzed. Two simplified configurations are selected to model the magnetic forces: a pair of identical monopoles and a pair of identical dipoles. Results show that the magnet configuration and strength significantly affect the vibration amplitude and the onset flow velocity. A weak magnetic force can enhance vibration and reduce onset flow velocity, while a stronger pair of dipoles may push the bistable system to a state of low-amplitude vibration with a mean displacement. The influence of magnets in this configuration has potential as a control technique for energy harvesting applications.

Effect of terahertz laser field on anisotropic optical absorption and refractive index changes of coaxial square quantum well wires

The influence of terahertz laser field on nonlinear anisotropic optical properties, such as optical absorption and refractive index changes is studied. By solving the Schrödinger equation of the system in the framework of effective mass with the Kramers–Henneberger (KH) transformation, the eigenfunctions and energy eigenvalues of the system are obtained. The optical absorption and refractive index changes are deduced by the compact density matrix form and the scheme of iterative method. The results show that the polarization angle and intensity of terahertz laser field have a strongly influence on the peak of optical absorption and refractive index change in different directions respectively.

Effect of Rayleigh Number on Internal Eccentricity in a Heated Horizontal Elliptical Cylinder to its Coaxial Square Enclosure

This paper deals with numerical investigation of a natural convective flow in a horizontal annular space between a heated square inner cylinder and a cold elliptical outer cylinder with a Newtonian fluid. Uniform temperatures are imposed along walls of the enclosure. The governing equations of the problem were solved numerically by the commercial code Fluent, based on the finite volume method and the Boussinesq approximation. The effects of Geometry Ratio GR and Rayleigh numbers on fluid flow and heat transfer performance are investigated. The Rayleigh number is varied from 10<sup>3</sup> to 10<sup>6</sup>. Throughout the study the relevant results are presented in terms of isotherms, and streamlines. From the results, we found that the increase in the Geometry Ratio B leads to an increase of the heat transfer coefficient. The heat transfer rate in the annulus is translated in terms of the average Nusselt numbers along the enclosure’s sides. Tecplot 7 program was used to plot the curves which cleared these relations and isotherms and streamlines which illustrate the behavior of air through the channel and its variation with other parameters. The results for the streamlines, isotherms, local and average Nusselt numbers average Nusselt numbers are compared with previous works and show good agreement.

Radiation View Factor from Rectangular Plate to Coaxial Disk: A Model Correlation

A robust correlation is proposed for calculation of radiation view factor (VF) from a rectangular plate to a coaxially-parallel round disk. It is nearly impossible to develop an exact, closed-form VF formula for this basic configuration. It seems that at present there are only two relevant studies that report generalized results for VF between: (a) disk and coaxial square; and (b) finite rectangle and coaxial disk. A well-known online catalog of radiation VFs documents only the latter. Contemporary heat transfer textbooks or handbooks lack ready-to-use tools to estimate VF for this arrangement. The available prescriptions for this configuration have some limitations. Therefore, an alternative VF calculation tool is desirable. In this paper, a single VF correlation is developed for use over a wide range of plate and disk sizes. Compared to the existing correlations, this generalized model correlation offers a smaller margin of error in its predicted VF-values. The proposed tool can also be used for VF calculations when a rectangular plate and a parallel circular disk are non-coaxial.

Natural convective heat transfer from a heated horizontal elliptical cylinder to its coaxial square enclosure

Natural convective heat transfer from a heated horizontal elliptical cylinder to its coaxial square enclosure

Scalar transport in the near field between two coaxial square air jets

The scalar transport in the near field of two square coaxial free air jet flow has been experimentally investigated. In order to study the entrainment and mixing processes taking place between the two jets, heat was used as a scalar. A triple sensor probe was used consisting of an X-wire probe for the point measurement of two velocity components and a single cold wire probe, for the simultaneous recording of instantaneous temperature. From the velocity and temperature signals the momentum and heat flux components were calculated. Eddy diffusivities of heat and momentum were directly evaluated from the experimental data. These diffusivities for all streamwise positions reach a maximum in the interaction region between the two jets; the maximum values increase with the downstream distance in the near field. The quadrant splitting technique applied to turbulent fluxes of momentum and the scalar revealed that the positive contributions to these transport terms are much larger than the negative ones. The quadrant splitting data confirmed that the flow is dominated by large scale coherent structures, which are intermittent in character and permitted the association of the scalar transport with vortical structures occurring in the near field of the coaxial jet flow. A proposed simplified mechanistic flow picture, which shows the passage of a vortex series through the mixing layer in the near field of the jets, is in agreement with the dominant characteristics of the flow.

TASEP on parallel tracks: Effects of mobile bottlenecks in fixed segments

We study the flux of totally asymmetric simple exclusion processes (TASEPs) on a twin co-axial square tracks. In this biologically motivated model the particles in each track act as mobile bottlenecks against the movement of the particles in the other although the particles are not allowed to move out of their respective tracks. So far as the outer track is concerned, the particles on the inner track act as bottlenecks only over a set of fixed segments of the outer track, in contrast to site-associated and particle-associated quenched randomness in the earlier models of disordered TASEP. In a special limiting situation the movement of particles in the outer track mimic a TASEP with a “point-like” immobile (i.e., quenched) defect where phase segregation of the particles is known to take place. The length of the inner track as well as the strength and number density of the mobile bottlenecks moving on it are the control parameters that determine the nature of spatio-temporal organization of particles on the outer track. Variation of these control parameters allows variation of the width of the phase-coexistence region on the flux–density plane of the outer track. Some of these phenomena are likely to survive even in the future extensions intended for studying traffic-like collective phenomena of polymerase motors on double-stranded DNA.

Simulation and Measurements of Electric and Magnetic Fields of an RFID Loop Antenna Anti-Theft Gate System

The radiation of RFID anti-theft gate system based on two parallel coaxial square loop antennas has been analyzed.The system was simulated in FEKO and near electric andmagnetic fields have been calculated. A physical model of thesystem was realized and near magnetic field was measured.Measurement results were found to be in excellent agreementwith the simulation. The obtained simulation and measurementresults have been compared to the exposure limits given asreference levels in the ICNIRP guidelines. No violation of limitshas been shown, regarding both occupational and publicexposure.

Phaselike resonance behavior in optical transmission of sandwich coaxial square ring arrays

We studied the optical transmission through sandwich coaxial square ring arrays experimentally and theoretically. The hybridized mode of the localized surface-plasmons and surface-plasmon polaritons has been observed. This hybridized mode resembles the phase resonance mode in a compound grating structure and can be named as phaselike resonance mode. For the 0-phase resonance mode, energy can tunnel through the sample due to coherent constructive interference, forming a peak in the transmission spectrum. For the π-phase resonance mode, a dip appears instead. When the incident angle is increased, the π-phase resonance mode is split into two branches, one is redshifted while the other blueshifted.

Enhancing the light transmission of plasmonic metamaterials through polygonal aperture arrays

While plasmonic metamaterials find numerous applications in the field of nanophotonic devices, a device may work as a normal or plasmonic device, depending on whether it operates at the resonance mode. In this paper, the extraordinary light transmission through coaxial polygonal aperture arrays, including circle, hexagon, square, and triangle geometries, is studied using FDTD simulation. Circular, hexagonal and squared aperture arrays have similar high transmission rate, while triangular aperture array has considerably lower transmission rate. It is found that the transmission peaks reflect the resonance modes propagating along the direction of neighboring apertures. We hence rearrange the apertures from square lattice to triangle lattice to obtain a uniform resonance mode along the neighboring apertures. This leads to enhanced light transmission. The study gains understanding of new properties of the metamaterials based on plasmonic resonance.

The electronic properties of a coaxial square GaAs/Al xGa 1−xAs quantum well wire in an electric field

The binding energy of a hydrogenic impurity in a coaxial square quantum well wire (QWW) system is investigated as a function of the barrier thickness for two different impurity positions under the electric fields. Within the effective mass approximation, the ground state energy in the presence of an external electric field applied perpendicular to the symmetry axis of the wire system is calculated using the finite difference method. Then, the ground state binding energy of a hydrogenic impurity is found employing a variational method. It is found that the binding energy in critical barrier thickness shows an increase or decrease depending on the impurity position and electric field strength.

Measurements in the Near Field of a Confined Coaxial Square Jet

The near field of a confined coaxial square jet configuration has been investigated using a two-component laser Doppler anemometer. Measurements at velocity ratios (γ u = U o /U i ) 0.5, 1.0, and 2.0 with a fixed mean velocity (0.7 m/s) for the inner stream were obtained. Reynolds numbers based on the average velocity of the two coflowing streams U M and the jet equivalent diameter D e were ranged from 1.53 x 10 4 to 4.2 × 10 4 . The streamwise vortices generated at the corners of the inner square nozzles had affected the downstream flow development considerably. The spreading rate at γ u = 0.5 was found to be the highest among the three cases investigated and that for respective cases were also higher than their circular counterparts under similar flow conditions. Self-similarity can be attained and is in the order of γ u =0.5, 1.0, and 2.0. The difference can be attributed to the relative strength as well as the sense of rotation for the corner streamwise vortices generated by the inner jet. The downstream developments for various velocity components are presented. Finally, the flow structure at different velocity ratios will be briefly discussed via inviscid vortex dynamics

Effect of Delta Tabs on Axis Switching of a Coaxial Square Jet

The effects of delta tabs in the near field of a coaxial square jet have been studied experimentally using a laser Doppler anemometer. The tabs are added to the centers of the four sidewalls of the inner nozzle trailing edge, with the tip of each tab tilted into the inner jet, that is, θ = 45 deg, or into the outer jet, that is, θ = -45 deg. For each tab orientation, three velocity ratios have been considered: γ u = 0, 0.5, and 1.0 for θ = 45 deg and γ u = 1.0, 2.0, and oo for θ = -45 deg. The results illustrate that tabs increase the mixing between the inner jet and outer jet and may promote or suppress the phenomenon of axis switching, depending on the orientation of the tabs. Axis switching is defined as follows: As a noncircular (here square) jet spreads, its cross-section may evolve from the initial shape similar to that the jet exit, to have its axis rotated some angle at some downstream location. In the case of θ =45 deg, the cross-sectional shape of the inner mixing layers is bifurcated into a four-finger structure, which tends to suppress the onset of axis switching. When θ = -45 deg, it exhibits an eightfold mode, and a rapid axis-switching occurs in the near-field. The effect of tabs is briefly discussed using inviscid vortex dynamics.

On thermal convection between two coaxial square containers inclined by 45°

This paper is concerned with flow visualization, velocity, streakline, and heat transfer measurements on thermal convection between two coaxial square containers inclined by 45°. It is found that there is no critical Rayleigh number (Ra)c for the onset of thermal convection in the test section. There appear two great circulations, which are symmetrical with respect to the diagonal vertical plane of the two coaxial square containers, and enhance the heat transfer significantly.

On thermal convection between two coaxial square containers inclined by forty five degrees

This paper is concerned with flow visualization, velocity, streakline, and heat transfer measurements on thermal convection between two coaxial square containers inclined by forty five degrees. It is found that there is no critical Rayleigh number for the onset of thermal convection in the test section. There appear two great circulations, which are symmetrical with respect to the diagonal vertical plane of the two coaxial square containers.

Forces and torques between two square current loops

We derive closed-form expressions for the magnetic forces and torques between two coaxial square current loops as a function of their relative tilt angle. These expressions involve simple numerical integrations. An analytic expression for the torsion constant at zero tilt angle is derived for loop filaments and for loops of finite axial extent.

Thermal convection between two coaxial horizontal square containers

This paper is concerned with experiments on thermal convection between two coaxial square containers. It is found that there exists a critical Rayleigh number (Ra)c of 1660 approximately for the onset of the thermal convection in top-test section. The vertical velocity distributions at the middle height of left side-test section agree with the classical theory well. The width of the present convection roll in top-test section is of the same order as the height. The reason why the convection rolls or fluid mass in top-test section are transported to the right- or left-direction is discussed and attributed to a new mechanism of mass transport, consisting of three-stages broadly, viz., (a) extension-stage, (b) splitting-stage, and (c) birth-stage.