Concave Spherical Surface Research Articles

Triboelectric nanogenerator based on a water droplet spring with a concave spherical surface for harvesting wave energy and detecting pressure

Abstract Triboelectric nanogenerator (TENG) has strong application potential in collecting nano energy and detecting micro motion. In this study, a TENG based on a water droplet spring with a concave spherical surface was proposed. The dispersive-aggregative triboelectric nanogenerator (DA-TENG) added the water droplet to the concave spherical surface which was covered with circular copper foil electrode and polytetrafluoroethylene. External loading/unloading caused water droplet dispersion/aggregation. Therefore, the solid and liquid electrodes could generate voltage by contacting and separating. Meanwhile, DA-TENG design parameters were optimized to find optimal output conditions, including the water droplet volume, the cross-sectional radius of the concave spherical surface, the force area of the elastic membrane, and the excitation frequency of the shaker. In addition, the voltage signal generated by volunteers pressing DA-TENG could show the keyboard usage habits of different people and thus serve as a basis for personnel identification, which suggested DA-TENG could be used as a self-powered pressure detector. Finally, DA-TENG was designed as a harvesting wave energy device. Under a 6 MΩ load, a unit of work could produce a peak current of 1.7 μA and an effective power of 8.82 μW; three units could produce a peak current of 5.3 μA.

Convective heat transfer from a spherical concave surface due to swirling impinging jets issuing from a circular pipe

Impinging jet heat transfer from curved surfaces is available in many industrial applications, such as cooling of gas turbine leading edge and deicing of airplane wing leading edge (heating). Most of the published studies on this topic involve non-swirling jet impingement from flat surfaces. Swirling jets are also used in some applications with the anticipation of heat transfer augmentation. Swirling impinging jet flow characteristics are significantly different from that of the non-swirling jet. However, fundamental studies of swirling jet impingement onto curved surfaces are very limited. As such, flow dynamics and convective heat transfer from a heated concave surface due to swirling impinging jets from a circular nozzle are numerically investigated using the RANS approach and the realizable k-ε turbulence model. Various flow and geometric parameters, such as the jet Reynolds number (Re) in the range of 11,600–35,000; the swirl number (Sw) in the range of 0–2.4; and the jet-to-surface separation distance (H) of 0.5–8 times the nozzle diameter, at a fixed impingement surface curvature (diameter) are studied. The results show that two counter-rotating recirculation zones appear near the target surface for near-field impingement (H ≤ 1) and higher swirl numbers (Sw ≥ 1.2), whereas for far-field impingements (H > 2), they are formed inside and outside of the main jet stream. An intense surface heat transfer zone develops only for near-field impingement in the range 1 ≤ S ≤ 3 at higher swirl numbers, where S is the distance along the impingement surface from the domain axis. More uniform thermal distribution along the curved surface is found for far-field impingement at Sw ≥ 0.8. Whilst the transitional Sw and H for Re = 11,600 are 0.8 and 2 respectively, the transitional Sw and H for Re = 35,000 are 0.8–1.2 and 4, respectively. Maximum heat transfer zones are found to be correlated with strong turbulence. Correlations are developed for the average Nusselt number as a function of the jet Reynolds number, jet exit to impingement surface separation distance, and swirling strength.

A modified dynamic contact angle model applied to double droplet impact curved surface

The microscopic processes involving droplet impact and interaction on spatially curved surfaces remain unclear. In this study, we implement a dynamic contact angle model with adjusted upper and lower limits into a simulation of droplet motion, constructing a three-dimensional numerical model to depict the dynamics and heat transfer characteristics of symmetric double droplets impacting plane, concave, and convex cylindrical, and concave and convex spherical surfaces. The processes of droplet spreading, retraction, rebound, splitting, and heat transfer are elaborated, revealing the role of surface curvature during impact. Our results show that different curvatures significantly affect the flow morphology of the flow dividing line. For the two main curvatures of the surface, the curvature in the direction of droplet arrangement predominates. Positive curvature promotes spreading and repels the liquid phase, while negative curvature promotes agglomeration and attracts the liquid phase. Extreme situations arise when both positive and negative curvatures occur simultaneously. Regarding heat transfer, the overall heat transfer rate is mainly determined by the spread area, and the heat transfer performance of convex surfaces is better than that of plane or concave surfaces. Residual bubbles increase heat transfer inhomogeneity, but different surfaces do not show significant variability. Additionally, the heat flow intensity in the central interaction region has the following relationship with its rebound height and is independent of the overall heat transfer intensity.

Simultaneous Manipulation of the Temporal and Spatial Behaviors of Nanosecond Laser Based on Hybrid Q-Switching

A hybrid Q-switching method based on a special-shaped saturated absorber was proposed for simultaneous manipulation of the temporal and spatial behaviors of a solid-state pulse laser. The temporal–spatial rate equation model of the laser was given and used to optimize the design parameter of the saturated absorber. Best spatial intensity homogenization performance can be expected using an active-passive hybrid Q-switched laser, comprising a Pockels cell and a cylinder Cr:YAG crystal with one end cut as a spherical concave surface. The optimized laser pulse width could be narrowed to 2.39 ns and the laser radial intensity distribution became quasi-super-Gaussian distribution with a radial intensity distribution ratio of 0.91, while that for the Gaussian beam was 0.84. In principle, the laser coherence can be maintained, and the laser spatial intensity distribution can be kept in a long propagation distance.

Bessel acoustic-beam acoustic lens for extending the depth of field of detection in optical-resolution photoacoustic microscopy.

As an important part of optical-resolution photoacoustic microscopy, the acoustic lens is responsible for efficient collection of photoacoustic signals. The spherical focused acoustic lens is commonly used in photoacoustic microscopy because of its efficient detection of the photoacoustic signal in the focus area. However, the narrow depth of field of the spherical focused acoustic lens limits the expansion of the depth of field of the photoacoustic microscopy. To solve this problem, a Bessel acoustic-beam acoustic lens is proposed. The Bessel acoustic-beam acoustic lens replaces the spherical concave surface with a conical concave surface to generate a Bessel acoustic beam with non-diffraction. Using the simulation model of Bessel acoustic-beam acoustic lens constructed by COMSOL Multiphysics, it is verified theoretically that the Bessel acoustic-beam acoustic lens can improve the depth of field of detection by ∼2 times. The Bessel acoustic-beam acoustic lens can further promote the capability of high-speed and large volumetric imaging of optical-resolution photoacoustic microscopy and will be helpful in the acquisition of physiological and pathological processes.

On Finding Determinantal Equations Involving the Coordinates of the Object Point, Point of Incidence, Point of Observation and the Image Point in Cases of Reflection and Refraction

This paper is concerned with the procedure of finding determinantal equations, each of which involves the coordinates of the object point, point of incidence, point of observation, and the image point in cases of reflection and refraction of light. An algorithm has been presented for the said purpose and it has been subsequently employed for the generation of relevant determinantal equations by considering some particular cases of reflection and refraction, based on which the readers will be able to reach the desired goal for all other remaining cases of reflection and refraction. Overall, two sets of such determinantal equations have been found to prevail in the present study. One resulted from handling the following cases: (i) Reflection at a plane reflecting surface, (ii) Refraction at a plane surface of discontinuity regardless of whether light moves from a rarer medium to a denser medium or from a denser medium to a rarer medium. The second one has been found while going through the following cases: (i) Reflection at a concave spherical reflecting surface, (ii) Reflection at a convex spherical reflecting surface, (iii) Refraction at a concave spherical surface of discontinuity regardless of whether light passes from a rarer medium to a denser medium or from a denser medium to a rarer medium, (iv) Refraction at a convex spherical surface of discontinuity regardless of whether light moves from a rarer medium to a denser medium or from a denser medium to a rarer medium

Geometrically nonlinear analysis of friction pendulum systems under tri-directional excitation

A three-dimensional formulation for a mass sliding with friction on a concave spherical surface is presented and used to describe the behavior of friction pendulum systems under extreme tri-directional excitation. The proposed approach accounts for large deformations and includes a procedure for handling the characteristic stop-and-go, or stick-slip, motion of friction-based systems. A set of numerical examples are carried out comparing the results of the proposed formulation with available analytical solutions. Where these are not available, such as in the case of earthquake excitation, the convergence rate of Newton’s method and energy balance plots illustrate the accuracy of the computed solutions. Tri-directional earthquake simulations demonstrate the vulnerability of friction pendulum systems to nearly-periodic, and near-fault, long-period ground motions.

Bioinspired three-dimensional hierarchical micro/nano-structured microdevice for enhanced capture and effective release of circulating tumor cells

The efficient capture and release of the circulating tumor cells (CTCs) are promising for the CTC related cancer diagnosis and subsequent analysis. However, it is a great challenge to isolate and enrich the rare CTCs from the complex peripheral blood sample, which inhibits its broad translating to the clinical applications. Although various papers reported that the nanostructure substrates can improve the capture efficiency of CTCs, few of researches constructed 3D hierarchical micro/nano-structured microdevice to enhance the efficiency of CTC capture and release with a simple manner. Herein, a bio-inspirited 3D epithelial cell adhesion molecule (EpCAM) aptamer modified rose petal derived ZnO microchip (EpCAM-RPD-ZnO-Chip) was designed to realize efficient capture and release of the CTCs. The 3D rough spherical concave surfaces on the EpCAM-RPD-ZnO-Chip guaranteed the maximum contact with the CTCs, thus improving the capture efficiency. Moreover, simple release of CTCs by dissolving ZnO under moderate acidic condition was achieved. The topographical and target molecular recognition cooperatively contributed to highly efficient capture of CTCs. The scanning electron microscope (SEM) image clearly showed that the filopodias and lamellipodias of CTCs stretched and attached to the ZnO nanomaterials. In sum, the proposed 3D EpCAM-RPD-ZnO-Chip is expected to be a promising tool for capture and release of CTCs in clinical trials, which might lay a foundation for downstream analysis and precise drug susceptibility test for the cancer treatment.

ELID Mirror Surface Grinding for Concave Molds by Conductive Elastic Wheel Containing Carbon Black

Elastic grinding wheels have previously been adopted for the development of the mirror surface finishing method for concave spheres. In this study, new conductive elastic grinding wheels, to which electrolytic in-process dressing (ELID) can be applied, are developed; the aim of the study is to address the challenge of maintaining a constant removal rate for rubber bond wheels. When ELID grinding is performed using a non-diene (isobutane isoprene rubber, IIR)-based wheel, a larger removal amount is achieved, and a higher-quality surface is also achieved compared to a diene (acrylonitrile-butadiene rubber, NBR)-based wheel. In addition, to investigate the effect of grinding wheel bond hardness on the removal amount and ground shape accuracy, grinding wheels with various levels of hardness are prepared by controlling the amount of carbon black contained in them, and grinding experiments are conducted. Thus, a larger removal amount is achieved using a harder grinding wheel, but the roughness of the ground surfaces deteriorates. Therefore, in practice, it is necessary to select an appropriate grinding wheel that can achieve both productivity and surface quality. Finally, to obtain a high-quality mirror finish on a concave spherical surface, ELID grinding is performed on the workpieces as is done for spherical lens molds. Thus, high-quality mirror surfaces with roughness Ra < 10 nm were generated. When the work pieces are ground using a grinding wheel of the same radius, excessive removal occurs at the edge of the concave spherical profile, decreasing the form accuracy. Numerical simulation demonstrates that chamfering of the grinding wheel is effective for improving the shape accuracy. The results of this study are expected to contribute to automation and cost reduction in the mirror-finishing process for concave molds.

Impact Pressure Evaluation of Water Jet Peening on Typical Concave Surfaces: Theoretical and Finite Element Analysis

Abstract Water jet peening (WJP), a surface modification technique, can use the impact pressure induced by shock waves to introduce compressive residual stress in the surface of metal parts, thereby improving the fatigue life of metal parts, especially has broad application prospects in strengthening the concave surface area of metal parts. The impact pressure of the concave surface is different compared with the flat surface due to the effects of geometrical factors on the shock wave released. In this work, a mathematical model for calculating the peak pressure in the initial contact area of the concave surface is developed, and the effects of geometric factors (opening angle of V surface α and spherical radius R) and WJP parameters (jet velocity v and jet diameter d) on the peak pressure are analyzed by using finite element simulation models of WJP on concave V-shaped surface, concave spherical surface, V-groove surface, spherical groove surface, and spherical groove surface established with the coupled Eulerian–Lagrangian (CEL) algorithm of abaqus. A mechanism of impact pressure evaluation of the concave surface is developed to explain the peak pressure results obtained from finite element models. The results show that the peak pressure is mainly determined by α and v, while d does not affect the peak pressure for a concave V-shaped or V-groove surface. The peak pressure is mainly determined by R, v, and d for a concave spherical or spherical groove surface.

Direct FEM-Domain Decomposition Using Convex-to-Concave Spherical Ports for Space Applications

This letter proposes the application of a hybrid numerical technique to two cases of interest in the space business: the reallocation of radiators and scatters on satellite platforms; and the analysis of antennas for mobile communications. It is based on the analytical manipulation of the generalized scattering matrix obtained from the finite-element method, when concave and convex spherical surfaces are defined as ports. The technique combines: the power of full-wave resolution, the flexibility and speed of the direct domain decomposition techniques and the application of analytical rotations and translations from the addition theorems for spherical vector waves, while keeping the same accuracy as a complete full-wave method since no model simplifications are considered.

Enhancement heat transfer analysis of supercritical hydrogen fuel in small-scale channels with spherical concave

Thermal protection is a key issue for rocket engines. To effectively protect the combustion chamber wall, this paper mainly proposes a novel enhancement heat transfer device of using a spherical concave surface in a small-scale cooling channel, and numerically analyzes the hydrogen flow and heat transfer characteristics under supercritical conditions. The spherical concaves with a depth-to-diameter ratio of 0.2 (D = 1 mm, H = 0.2 mm) are applied on the inner wall of the regenerative cooling channel. The numerical study results show that the spherical concave can significantly improve cooling capacity, increase convective heat transfer coefficient, and reduce the maximum heat wall temperature. The new structure will be conducive to reducing the influence of the non-uniform temperature distribution caused by single-side heating, resulting in the more uniform temperature distribution and the better enhancing heat transfer capacity. For Re = 42000, the average Nu of the spherical concave channel can be improved by 40%, but the pressure drop only increases 14% than the smooth channel.

Reconfigurable RCS Reduction from Curved Structures Using Plasma Based FSS

The radar cross section (RCS) reduction from curved surfaces using plasma based frequency selective surfaces (FSS) is investigated. A frequency reconfigurable plasma based FSS unit-cell element with target-shaped structure is proposed. The operating frequency of the FSS is governed by the plasma ionization degree (i.e. plasma frequency). zero crossing frequency of the FSS unit-cell has a tuning range extending from 9.6 GHz to 11.3 GHz with an average bandwidth of 1.1 GHz. Planar and curved metallic surfaces are investigated. The curves structures include cylindrical (convex and concave), and spherical (convex and concave) surfaces. Single ionization source is applied at the rare end of the plasma FSS array design is optimized to maintain uniform plasma flow over the metallic surfaces by applying a single ionization source at the rare end of the array. The plasma FSS arrangement with ωp = 9 × 1011 rad/Sec loading a planar sheet reduces the RCS by 23 dB at 10.2 GHz and the (− 5 dB) frequency band of 14.7% for planar plate compared with the unloaded plate case. Different hybrid arrangements are investigated for wideband RCS reduction of 36.4% by superimposing reduction bands of three different plasma frequencies. A 21.5 dB reduction is achieved at 9.8 GHz for FSS arrangements (III). The effect of changing the radii of curvature for convex and concave cylindrical and spherical metallic surfaces is studied at different plasma frequencies. A full-wave analysis of the loaded metallic plates with plasma FSS is used to calculate the backscattered and bistatic RCS for different surfaces.

Study on Analysis of Cutting Mechanism of Ball End Mill for Concave and Convex Spherical Surface Using 3D-CAD

In this paper, cutting mechanism and cutting performance of ball end mill for spherical surface with contour path method is investigated. Ball end mills are used to produce molds, dies and so on. However, the edge shape is complex, so cutting process is not clear. Then, it is not clear effectively using method of the tool based on good cutting performance. Therefore, in this study, the purpose is proposal of high efficient and high accurate cutting method is using 5-axis control machine tool. At first, cutting model assembled by a ball end mill (R8 mm) and a workpiece with convex or concave spherical surface (Workpiece radius 20 mm) is carried out using 3D-CAD (SolidWorks). The pick feed direction which is from bottom to top is defined “Stepped up”, the one which is inverse direction is defined “Stepped down”. In addition, both cutting methods include up milling and down milling, then there are four cutting modes. The radius of tool path for contour path are varied from 14.0 mm to 19.4 mm for convex spherical surface, from 6.5 to 9.2 mm for concave spherical surface. The lead angle of the tool is defined the plus sign when the tool is inclined to the tool feed direction and varied from-45° to 45°. Secondly, the cutting cross-sectional area is calculated by the interference of a rake surface of the tool and an uncut chip volume which can be removed by one cutting operation. Thirdly, cutting experiments are done in order to measure cutting force. Finally, analytical and experimental results are discussed, and then the cutting conditions which are expected good cutting performance are considered.

Dendron and Hyperbranched Polymer Brushes in Good and Poor Solvents.

We present a theory of conformational transition triggered by inferior solvent strength in brushes formed by dendritically branched macromolecules tethered to planar, concave, or convex cylindrical and spherical surfaces. In the regime of linear elasticity for brush-forming dendrons, an analytical strong stretching self-consistent field (SS-SCF) approach provides brush conformational properties as a function of solvent strength. A boxlike model is applied to describe the collapse transition in brushes formed by macromolecules with arbitrary treelike topology, including hyperbranched polymers. We demonstrate that an increase in the degree of branching, that is, an increase in the number of generations or/and functionality of branching points in tethered macromolecules, makes the swelling-to-collapse transition less sharp. A decrease in surface curvature has a similar effect. The numerical Scheutjens-Fleer self-consistent field approach is used to analyze the collapse transition in dendron brushes in the nonlinear stretching regime. It is demonstrated that inferior solvent strength suppresses stratification that is exhibited under good solvent conditions by densely grafted dendron brushes.

Fermat’s principle leading to the generalized vectorial laws of reflection and refraction

This paper discloses the derivation of the generalized vectorial laws of reflection and refraction reported by the author in 2005 on the basis of Fermat’s principle. The cases of plane as well as concave spherical mirrors have been considered for the derivation of the generalized vectorial law of reflection. On the other hand, the derivation of the generalized vectorial law of refraction has been accomplished by considering plane as well as concave spherical surfaces of discontinuity.

Absolute interferometric test for high numerical-aperture spherical concave surfaces: Gravitational effect

Abstract Spherical concave surfaces with high numerical apertures are required in industry for lithography optics at ultraviolet and X-ray wavelengths. Among the systematic errors in these spherical-surface test, the gravitational deformation has not been separated from the other optical aberrations. We utilized a two-surface comparison method to quantify the gravitational deformation in a vertical Fizeau interferometer. Certain aberrations vary with rotation around the optical axis. We averaged the ordinary aberrations and isolated the aberration caused by gravitational deformation. Experimental results show that a 4-in concave surface with an F -number 0.75 reveals to have a gravitational deformation of 7 nm peak-to-valley.

The contact angle for a droplet on homogeneous and spherical concave surfaces

Wetting of droplets on homogeneous and spherical concave rough surfaces is investigated based on thermodynamics. In this study, neglecting the droplet gravity and the thickness of the precursor film of the liquid–vapor interface, the three-phase system is divided into six parts using Gibbs concept of dividing surface. The system Helmholtz free energy is established based on thermodynamics. Supposing the temperature and chemical potential to be constant, a new generalized Young’s equation of the equilibrium contact angle for a spherical droplet on a spherical concave rough surfaces is obtained including the line tension effects. Under certain conditions, this generalized Young’s equation is the same as the Rusanov’s equation.

On finding the correlation between the incident wavefront, reflected (refracted) wavefront and the reflecting surface (surface of discontinuity)

This paper considers the derivation of the relations existing between the incident, reflected (refracted) wavefronts and the reflecting surface (surface of discontinuity) by making use of the most unambiguous generalized vectorial laws of reflection and refraction developed by the author in 2015. The cases of reflection of a plane wavefront by plane as well as convex reflecting surfaces have been considered along with the cases of refraction of a plane wavefront by plane as well as concave spherical surfaces of discontinuity for the derivation of the concerned relations. All the relations offered are being claimed to be novel and the relations derived in cases of reflection (refraction) of a plane wavefront by a plane reflecting surface (plane surface of discontinuity) appear to be the most simple and elegant.

Photodetached electron spectrum of H- near a surface having spherical dent

The detached electron flux and photodetachment cross section are derived using the theoretical imaging method and quantum approach for system comprising of hydrogen negative ion ([Formula: see text]) placed near a surface having spherical dent. The dent is modeled like a spherical concave surface. It is observed that the spherical dent generates additional oscillatory and smooth structure in the detached electron flux and photodetachment cross section, respectively. The radius of curvature, inter-ion surface distance and the dent factor strongly manipulate the results. When the inter-ion surface distance is equal to the focal length of the concave surface, the detached electron flux and photodetachment cross section are not well behaved. The photodetachment cross section is also not well behaved for the inter-ion surface distance equal to the radius of curvature. The focus and center of curvature of the concave surface act as a spherical singularity. This study gives new understanding on the photodetachment of negative ions in the vicinity of concave surfaces.