Circular Disk Research Articles

Deep learning-based circular disk type radar target detection in complex environment

Target identification is one of the most popular radar uses in real life. Target identification is a classifier that analyzes whether a signal contains an echo from a target (target-present) or is merely noise (target-absent). Deep learning techniques are a popular topic in classification, and they have evinced to be effective in a range of applications. In this paper, a 64 layers Circular Disk type RADAR Target Detection (CDRTD) model is proposed based on Transfer Learning using the SqueezeNet architecture of Convolutional Neural Network (CNN) that functions directly with processed radar target return eco signal and minimize the requirement of conventional laborious radar signal processing. Further, the proposed 64 layers SqueezeNet-based CNN CDRTD model was then implemented to identify circular disk type targets in complex environment. Finally, the target return eco data was tested to identify the circular disk type radar target in complex environments. We further analyzed target detection probability, false alarm rate, precision, recall, F1 in a complex environment and compared it with the ideal case. We found that our proposed CDRTD model can classify 83.3% of the test samples correctly with an overall accuracy of 94.59% in a noisy and cluttered environment whereas 100% of the test samples are classified correctly with an overall accuracy of 100% in an ideal environment.

On cavitation in the radial flow of a thin lubricating film between two overlying disks

This study is focused on the characterization and modeling of aviation fuel cavitation physics in radial flow in a thin layer between two disks—a geometry highly relevant to aviation fuel pump systems. This involves a lower circular disk with a centrally located fuel injection port and a matching disk resting on top of the lower disk. In the described experiments, we have quantified and compared cavitating disk behavior for distilled water and JP-5 fuel at various inlet supply pressures via high-speed imaging and radial pressure measurements. High-speed imaging data were used to quantify the radial collapse location of cavitation voids. An enhanced gradient shadowgraphy method was employed to obtain the spatial–temporal evolution of propagating bubbly shock waves. This technique revealed unsteady shock waves propagating in a spiral motion in JP-5 fuel, while a standing bubbly shock was observed in water. In our modeling efforts, the Rayleigh–Plesset equation was adapted to a spatial form in order to predict the radial location of cavitation bubble collapse. Further work incorporated the spatial Rayleigh–Plesset equation into the barotropic model that has been used previously for cavitating nozzle flows and generalized it to radial flow geometry in order to reproduce radial pressure profiles obtained from the experiment. The model predictions of the radial location of bubble collapse and the radial pressure profiles are shown to be in excellent agreement with the experiments. This approach will be valuable for predicting aviation fuel cavitation in complex fuel system geometries.

Floating hydroelastic circular plate in regular and irregular waves

An understanding of the hydroelastic response of a flexible circular plate to water waves is relevant to many problems in ocean engineering ranging from offshore wave energy converters and solar wind devices to very large floating structures such as floating airports and ice sheets. This paper describes results from physical model tests undertaken in the COAST laboratory at the University of Plymouth. Response amplitude operators (RAOs) of a floating flexible circular disk are determined for incident monochromatic and irregular wave trains, the latter defined by JONSWAP spectra. Free-surface displacements are measured using wave gauges, and the plate motion recorded using a QUALISYS® motion tracking system. Different basin depths and plate thicknesses are considered in order to quantify the effects of water depth and flexural plate rigidity on the overall dynamic behaviour of the circular disk. We present synchronous and subharmonic nonlinear responses for monochromatic waves, and displacement spectra for irregular waves. The measured wave hydrodynamics and disk hydroelastic responses match theoretical predictions based on linear potential flow theory.

Design and Fabrication of Compact, Multiband, High Gain, High Isolation, Metamaterial-Based MIMO Antennas for Wireless Communication Systems

We proposed a novel approach based on a complementary split-ring resonator metamaterial in a two-port MIMO antenna, giving high gain, multiband results with miniature size. We have also analyzed a circular disk metasurface design. The designs are also defected using ground structure by reducing the width of the ground plane to 8 mm and etching all other parts of the ground plane. The electric length of the proposed design is 0.5λ × 0.35λ × 0.02λ. The design results are also investigated for a different variation of complementary split-ring resonator ring sizes. The inner and outer ring diameters are varied to find the optimized solution for enhanced output performance parameters. Good isolation is also achieved for both bands. The gain and directivity results are also presented. The results are compared for isolation, gain, structure size, and the number of ports. The compact, multiband, high gain and high isolation design can apply to WiMAX, WLAN, and satellite communication applications.

A Numerical Model for Rotational Autofrettage of Disks Based on von Mises Yield Criterion and its Application in Strengthening Flanged Disks Used for Joining High-Pressure Pipelines

In this work, a numerical analysis of the recently proposed rotational autofrettage method for strengthening hollow circular disks is carried out. The analysis of this new process is in nascent stage. Some analyses are available in the literature to study rotational autofrettage based on Tresca yield criterion. However, in general, the von Mises yield criterion closely replicates the yielding behavior of metals. Thus, in this work, the rotational autofrettage of disks is analyzed incorporating von Mises yield criterion. The governing differential equations are obtained for the elastic and plastic deformations in the disk under centrifugal loading based on the assumption of axisymmetric condition and plane stress incorporated in von Mises yield criterion. A numerical scheme is then followed to solve the set of governing differential equations along with the boundary conditions to obtain the stress distribution in an elastic-perfectly plastic disk during loading stage of rotational autofrettage. The residual stress distribution in the disk after unloading of the centrifugal loading are also obtained. The rotationally autofrettaged disk of typical radial dimension is numerically experimented for its different in-service load carrying capacities. Significant improvements are achieved in in-service pressure, radial temperature and centrifugal load carrying capacities in the autofrettaged disk as compared to their non-autofrettaged counterpart. Different numerical results are compared with corresponding solution due to Tresca yield criterion. Further, the present solution of rotational autofrettage is proposed to apply in strengthening industrial standard flanged disks of various dimensions used in connecting high pressure pipelines. It is found that the maximum pressure carrying capacity of flanged disk can be increased up to 77% for wall thickness ratios more than 3.5 by employing rotational autofrettage.

Field-synergy and nanoparticle’s diameter analysis on circular jet impingement using three oxide–water-based nanofluids

The field synergy study is carried out using three oxide nanofluids impinging circular jet on the horizontal circular disc to analyse the synergetic interaction of cooling processes between temperature and flows fields. The h eat transfer effect o f the nanofluid is examined by rising the Reynolds number and the nanoparticle concentration depending on field synergy number. For jet impinged cooling process, the scale of synergy between the nanofluid flow speed and temperature is decayed with the increase of Reynolds number. Hence, it is contributed to a lower heat transfer efficiency of the nanofluid. Whe reas, the scale of synergy between the nanofluid flow speed and temperature can be enhanced by rising the particle concentration. Thus, the heat transfer efficiency of the nanofluid is increased. Analysis showed that Al2O3 nanofluid has the maximum relative field synergy among selected three oxide nanofluids. It is evident that the nanoparticle concentration, nanoparticle material and Reynolds number have significant effect on the heat transfer augmentation. In addition, the study is explored by varying jet-disk spacing. Moreover, the investigation has shown that the reducing heat transfer effect for the materials is Al2O3, CuO and TiO2 subsequently. It is revealed that the heat enhancement is higher for smaller nanoparticle’s diameter (i.e., 20 nm) than bigger nanoparticle’s diameter (i.e., 80 nm) of the same material.

Disk wakes in nonlinear stratification

Nonlinearity of density stratification modulates buoyancy effects. We report results from a body-inclusive large eddy simulation of a wake in nonlinear stratification, specifically for a circular disk at diameter-based Reynolds number ( ${\it Re} $ ) of $5000$ . Five density profiles are considered; the benchmark has linear stratification and the other four have hyperbolic tangent profiles of the same thickness to model a pycnocline. The disk moves inside the central core of the pycnocline in two of those four cases and, in the other two cases with a shifted density profile, the disk moves partially/completely outside the pycnocline. The maximum buoyancy frequency ( $N_{max}$ ) for all the profiles is the same. The first part of the study investigates the centred cases. Non-uniform stratification results in increasing wake turbulence relative to the benchmark owing to reduced suppression of turbulence production as well as wave trapping in the pycnocline. Steady lee waves are also quantified to understand the limitations of linear theory. The second part pays attention to the effect of a relative shift between the pycnocline and the disk. The wake defect velocity decays substantially faster in the cases with a shift and the wake has higher turbulence level. The effect of disk location on the Kelvin wake waves (a family of steady waves within the pycnocline) and its modal form is obtained and explained by solving the Taylor–Goldstein equation. The family of unsteady internal gravity waves that are generated by the wake is also studied and the effect of disk shift is quantified.

Average Surface Temperature Over the Circular Disk Heat Source/Sink Embedded in an Insulating Boundary Plane. Analytic Solution.

Reduction of a Bessel integral solution for the average transient temperature change at the surface of a constant flux thermal source/sink of circular disk aspect embedded in an otherwise insulating plane boundary of a homogeneous, isotropic, and conducting half-space is reported. The analytic solution comprises algebraic expressions of tabulated functions.

Trapping of single diffusing particles by a circular disk on a reflecting flat surface. Absorbing hemisphere approximation.

Recent progress in biophysics (for example, in studies of chemical sensing and spatiotemporal cell-signaling) poses new challenges to statistical theory of trapping of single diffusing particles. Here we deal with one of them, namely, trapping kinetics of single particles diffusing in a half-space bounded by a reflecting flat surface containing an absorbing circular disk. This trapping problem is essentially two-dimensional and the question of the angular dependence of the kinetics on the particle starting point is highly nontrivial. We propose an approximate approach to the problem that replaces the absorbing disk by an absorbing hemisphere of a properly chosen radius. This replacement makes the problem angular-independent and essentially one-dimensional. After the replacement one can find an exact solution for the particle propagator (Green's function) that allows one to completely characterize the kinetics. Extensive testing of the theoretical predictions based on the absorbing hemisphere approximation against three-dimensional Brownian dynamics simulations shows excellent agreement between the analytical and simulation results when the particle starts sufficiently far away from the disk. Our approach fails and the angular dependence of the kinetics is important when the distance of the particle starting point from the disk center is comparable with the disk radius. However, even when the initial distance is only two disk radii, the maximum relative error of the theoretical predictions is about 10%. The relative error rapidly decreases as the initial distance increases.

Experimentation of Evaporation Suppression by Various Plastic Bottles Coverage Area

Evaporation significantly affects the loss of water in reservoir. The effective use of water-surface covering materials for evaporation reduction purpose is commercially performed including plastic spherical and circular shapes. This study initiates to reuse very common polyethylene terephthalate (PET) drinking-water bottles to cover water surface instead. The bottle shape could have a covering percentage ratio as much as 91% equal to a commercial ball or circular disk. The experiment was designed and conducted to prove the reduction of water evaporation rate using five simulated ponds. The testing aspect is the percentage of the coverage area over the water surface. Based on environmental impact concern, the deterioration of PET bottles due to hydrolysis reaction and ultraviolet rays in natural conditions is also investigated. The initial result from the experiment shows that PET bottles have a potential for the evaporation reduction which are a very cost-effective alternative to the existing commercial materials and help support the reuse of plastic waste.

A quasi-two-dimensional fluid experimental apparatus based on tank-in-tank configuration.

The fluid tank is an essential facility for experimental research on fluid mechanics. However, owing to the hydrostatic fluid pressure, a fine uniformity of the narrow channel is difficult to be maintained in a tall narrow-channel tank. To address this issue, we proposed a quasi-two-dimensional fluid experimental apparatus based on a "tank-in-tank" configuration and built with an outer tank and an inner tank. The outer tank was cuboid-shaped and used to load the fluid medium, while the inner tank, consisting of two parallel glass plates, was embedded into the outer tank and served as the experimental channel. The hydrostatic pressure acting on the channel was balanced so that a high level of uniformity was maintained over the whole channel. The available height and width of the channel were 2800 and 1500mm, respectively, while its gap distance could be adaptive from 0 to 120mm. Experimental research on motion characteristics of circular disks falling in the quasi-2D channel was implemented to investigate the effects of the falling environment and disk geometry. Four distinct falling types were observed, and the wake flow fields of the falling disks were visualized. The Reynolds numbers of falling disks ranged from 400 to 63 000 presently. Chaotic motion and regular motion were demarcated at Re ≈ 30 000. An analytical model was established to predict the final average falling velocity and Reynolds number. Finally, potential directions for future research and improvements to the apparatus were suggested.

The Plastic Bag Store (Excerpt)

The Plastic Bag Store (Excerpt)

Towards Haptic-Based Dual-Arm Manipulation

Vision is the main component of current robotics systems that is used for manipulating objects. However, solely relying on vision for hand-object pose tracking faces challenges such as occlusions and objects moving out of view during robotic manipulation. In this work, we show that object kinematics can be inferred from local haptic feedback at the robot-object contact points, combined with robot kinematics information given an initial vision estimate of the object pose. A planar, dual-arm, teleoperated robotic setup was built to manipulate an object with hands shaped like circular discs. The robot hands were built with rubber cladding to allow for rolling contact without slipping. During stable grasping by the dual arm robot, under quasi-static conditions, the surface of the robot hand and object at the contact interface is defined by local geometric constraints. This allows one to define a relation between object orientation and robot hand orientation. With rolling contact, the displacement of the contact point on the object surface and the hand surface must be equal and opposite. This information, coupled with robot kinematics, allows one to compute the displacement of the object from its initial location. The mathematical formulation of the geometric constraints between robot hand and object is detailed. This is followed by the methodology in acquiring data from experiments to compute object kinematics. The sensors used in the experiments, along with calibration procedures, are presented before computing the object kinematics from recorded haptic feedback. Results comparing object kinematics obtained purely from vision and from haptics are presented to validate our method, along with the future ideas for perception via haptic manipulation.

Method to quantify the dynamic near-fault full-field stress evolution associated with rough fault shear deformation based on 3D printed models and photoelastic measurements

Quantifying the dynamic near-fault stress evolution associated with fault shear deformation is crucial for revealing the earthquake nucleation mechanisms of rough faults. However, it is still challenging via traditional methods because of the difficulties in resolving continuously evolved stresses and high stress heterogeneity. In this study, we present a novel method to quantify the dynamic full-field stress evolution using three-dimensional printed models and photoelastic techniques. The dynamic full-field stresses in a circular disc determined by this method and an analytical model are compared to verify the accuracy of the proposed method. A new method to count the fringe orders near the rough fault is proposed to achieve the stress quantification. The full-field principal stress difference in a rough fault model under shear forces is derived. Our findings indicate that the proposed method can significantly improve the efficiency of stress calculation and effectively quantify the dynamic full-field stress near rough faults.

Magneto-thermal–mechanical analysis of functionally graded rotating cylinder and circular disk

Magneto-thermal–mechanical analysis of functionally graded rotating cylinder and circular disk

광대역 특성을 갖는 3층형 소형 모노콘 안테나

In this study, an electrically small 3-stage monocone antenna with wideband characteristics is proposed. The proposed antenna consists of a 3-stage monocone radiator, a circular disk located above the radiator, shorting pins connecting the circular disk and the ground plane, and parasitic structures. The impedance matching characteristics in the high-frequency band are improved by dividing the monocone radiator into three stages. The insertion of a slot in the circular disk improves the mid-frequency band performance. The low-frequency band is expanded by using shorting pins. In addition, by attaching parasitic structures to the ground plane, the impedance-matching characteristics in the mid-frequency band are further improved. The proposed antenna has a −10 dB impedance bandwidth ranging from 0.98 to 11.1 GHz and a monopole-like radiation pattern.

Static Magnetic Shielding of a Perfectly Electric Conducting Circular Disk: Exact Analytical Solution Considering Radius of Emitting Loop

This letter proposes an accurate analytical formulation for the shielding problem of a perfectly electric conducting disk against the static magnetic field of a circular current loop placed coaxially with the disk. The key is to convert this problem into an electric field problem: the circular disk is grounded and is excited by nonuniform line charges distributed on the loop. The latter can be solved through the known Green function. Then, we obtain the accurate solution in integral form for magnetic vector potential at any field point and the accurate analytical solution for the magnetic field on the central axis of the disk. Also, the solution for the magnetic field is extended to the whole space when the loop radius is approaching zero.

Design of low profile, compact, high gain and broadband metasurface-based MIMO antenna for 5G/WiMAX/WLAN applications

ABSTRACT We have presented two-port MIMO antenna designs with low-profile material. Two different MIMO antenna designs are prepared and investigated to observe their effect on the gain, bandwidth, etc. The designs are prepared based on metasurface concepts with one design having a circular ring metasurface design and second having circular disk metasurface design. The designs are showing broadband response covering frequency range of 1.85 GHz to 4.27 GHz. The bandwidth of 2.320 GHz is achieved for this metasurface MIMO antenna design. The gain and directivity results show that highest gain of 5.88 dB and directivity of 6.39 dB are achieved with circular ring metasurface MIMO antenna design. Both metasurface MIMO antenna designs are fabricated, and measured results are also provided to verify the simulation results. The broadband and high gain design are applicable for 5G communication, WiMAX and WLAN applications.

Tuning of oscillation modes by controlling dimensionality of spin structures

Harmonic oscillation of spin structures is a physical phenomenon that offers great potential for applications in nanotechnologies such as nano-oscillators and bio-inspired computing. The effective tuning of oscillations over wide frequency ranges within a single ferromagnetic nanoelement is a prerequisite to realize oscillation-based nanodevices, but it has not been addressed experimentally or theoretically. Here, utilizing a vortex core structure, one of spin structures, we report a drastic change of oscillation modes over the frequency range from MHz to sub-GHz in a 100 nm-thick permalloy circular disk. Oscillation mode was found to considerably depend on the shape and dimension of the vortex core structure and various oscillation modes over a wide range of frequencies appeared with dimensional change in the vortex core structure. This work demonstrates that oscillation modes of the vortex core structure can be effectively tuned and opens a way to apply spin structures to oscillation-based technology.

Axisymmetric torsion problem by a rigid disc of an elastic half-space weakened by an annular crack

This investigation is devoted to an axisymmetric torsion of a circular disc subjected to a half-space, containing an annular crack. The stress–strain state and the stress intensity factors pertaining to the inner and outer crack edges are investigated. The proposed problem is solved by applying the Hankel integral transformation method. The mixed boundary-value problem is reduced to a system of coupled dual and triple integral equations. We developed a new method to solve this system. By using the Gegenbauer formulas, we obtain a system of infinite algebraic equations for getting the unknown functions. The solution is analysed and discussed. Numerical computations are carried out and the results are presented in the form of tables and graphs. Some special cases are considered.