Initial Incident Angle Research Articles

Establishment of fog droplet distribution model and study on canopy deposition uniformity

In plant protection operations, the distribution of droplets affects the atomization effect. To make the distribution of fog droplets more uniform in the air field, a fog droplet distribution model was established based on a three-dimensional motion model of droplets and the particle size distribution function, combined with a two-dimensional normal distribution function. The effects of the initial incidence angle and the additional wind speed on the distribution of fog droplets were analyzed. The fog droplet distribution was simulated to analyze the droplet distribution in the spatial layer, which was compared with the experimental results. To investigate the impacts of different factors on the atomization distribution, the Lagrangian interpolation method was employed, and the optimal initial incidence angle and external wind speed were found. When the initial angle of incidence was 17°, the slope of the fitted curve was the smallest, with a coefficient of determination of 0.9622 and a relative error of 3.12%. With an additional wind speed of 0.1 m/s, the coefficient of determination was 0.9782, with an average error of 4.61%. The simulation results were consistent with the experimental findings, and the accuracy of the fog droplet distribution model was verified. In summary, this research provides a novel method to improve the uniformity of the droplet distribution, which can provide a theoretical basis for determining the operating parameters.

Numerical research of high-speed oblique water-entry of projectile based on rigid body and fluid-structure interaction model

When a projectile enters the water at high speed, the projectile can suffer a huge impact of water. If a deformation occurs in the structure of the projectile during water-entry, the numerical method based on rigid body model will be limited, while the accuracy and precision of the results can be affected. The two numerical methods of the rigid body and fluid-structure interaction (FSI) model have been built to get the results of the oblique water-entry of the projectile in this paper. Moreover, the numerical results for the given projectile under the same water-entry conditions (initial angle of incidence of θ = 15°, initial angle of attack of α = 5°, initial speed of V = 200m/s ) have been contrasted. The results show that if a small deformation occurs in the body of the projectile during the water-entry, the numerical results of the FSI and the rigid body are different. Further, the small deformation within the limit of flexibility can change the motion attitude and the trajectory of projectile during the water-entry, meanwhile the change can cause the bending of the ballistic and the super-cavity. For the projectile with the structural response, the change in the distribution of the stress concentration area can affect the drag force suffered by projectile.

Defocus Effect Correction for Back Focal Plane Ellipsometry for Antivibration Measurement of Thin Films

Back focal plane (BFP) ellipsometry, which acquires the ellipsometric parameters of reflected light at different incident and azimuthal angles through a high-NA objective lens, has recently shown great potential in industrial film measurement. In on-line metrology cases for film manufacturing, the film vibration, which is caused by equipment vibrations or environmental disturbances, results in defocus blur and distortion of the received BFP images. Thus, subsequently extracted ellipsometric spectra and film parameters significantly deviate from the ground truth values. This paper proposes a cost-effective method for correcting vibration-induced BFP ellipsometric spectral errors. The method relies on an initial incident angle calibration of BFP radii at different defocus positions. Then, corresponding ellipsometric spectral errors are corrected by inserting a calibrated Jones compensation matrix into a system model. During measurement, the defocus position of the vibrational film is first determined. Then, BFP ellipsometric spectral errors, including incident angle mapping distortion and ellipsometric parameter variations, are corrected for a bias-free film analysis using the previous calibration results. Experimental results showed that this method significantly improved measurement accuracy without vibrational defocus compensation, from over 30 nm down to less than 1 nm.

Development and investigation of birefringent Beta-Barium borate for optical angle sensor

A high birefringent beta-barium borate (BBO) plate is proposed for an optical angle sensor in a homodyne interferometer. Simulations show that the angle measurement sensitivity can be improved by reducing a relative refractive index between the BBO plate and the environmental medium. Thus, the BBO plate is immersed in a square glass container filled with grapeseed oil. According to the optimization of an initial incident angle, linear dynamic measurement is achievable in the experiments for both probing wavelengths of 532 nm and 632.8 nm. Finally, the best angular displacement resolution of 1.5 ×10-5° is achievable in angular displacements of 5° by using the probing wavelength of 632.8 nm.

A Universal Method to Eliminate the Effect of Sounding Velocity Errors on Multibeam Sounding Data

The presence of sound velocity errors (SVEs) is common in multibeam sounding. Existing methods are good at eliminating these errors in the area with flatter seabed terrains but are not suitable for deep and complex seabed terrains. Therefore, a universal method is proposed in this paper to eliminate these errors in various depth and terrain areas with a regression model and the equivalent sound speed profile (ESSP). The vertical biases are calculated at these homonymy points of the main survey line and the inner swaths of the auxiliary survey line firstly. Then, a regression model is built by associating the vertical bias with the initial incident angle and travel time, and the regression coefficients are estimated with the help of the partial least squares (PLS) method. On the basis of the determined regression model and ESSP, the effects of sound errors for multibeam sounding data are eliminated. The proposed method was verified by the multibeam sounding data measured in the medium-shallow and deep water areas, and the standard deviations of the absolute values of depth differences (AVDDs) after correction were both about 2 times lower than those before correction.

Dynamic Stall over a Pitching Natural-Laminar-Flow Airfoil

High-fidelity large-eddy simulations are performed to study the unsteady boundary layer sensitivity of a natural-laminar-flow airfoil (NLF-0414) undergoing dynamic stall in comparison to two traditional airfoil sections (NACA 0012 and SD 7003). In this work, the natural-laminar-flow airfoil at and pitches with a constant nondimensional rate of from an initial incidence angle of 4 deg to angles of attack beyond the onset of dynamic stall. It is found that the transition of the NLF-0414’s unsteady boundary layer during the pitchup is much more abrupt than the standard airfoil sections before the formation of the laminar separation bubble. Once the laminar separation bubble is established near the leading edge, the overall dynamic stall process of the NLF-0414 evolves very similarly to that of the SD 7003 and the NACA 0012. Minor differences are observed in the formation of the turbulent separation vortex near the trailing edge and convection of the dynamic stall and shear-layer vortices. The dynamic stall of the NLF-0414 airfoil more closely resembles that of the SD 7003 and the NACA 0012 at reduced Reynolds numbers, suggesting that the extended laminar flow acts to delay Reynolds number effects of traditional airfoil profiles.

Tunable optical bistability at microwave frequency based on 1D sandwich photonic structure consisting of a nonlinear dielectric slab and two magnetized cold plasma layers

In this paper, tunable optical bistability that denotes the relationship between input intensity and output intensity is numerically investigated in the microwave frequency region based on the one-dimensional (1D) sandwich photonic structure consisting of a Kerr-type nonlinear material slab and two magnetized cold plasma layers. Results show that, in the case of TM-polarized electromagnetic wave, width and switching thresholds of the bistability loops are dependent on the working frequency, initial incidence angle, layer thickness, plasma density, and external magnetic field, which should be judiciously selected to obtain a required bistability behavior. Compared to the case of switch-down threshold, the switch-up threshold in the bistability loop is more sensitive to the changes of parameters. Through this study, the suggested 1D sandwich photonic structure is beneficial to the all-optical signal processing.

Influence of pumping effect on axial rotating holes

Rotating holes are widely used in jet engine internal air systems as an important kind of throttling element. The flow characteristics of rotating holes are of great importance in the design of the internal air system. This paper aims to investigate the influence of pumping effect on the flow characteristics of axial rotating holes. Pumping effect refers to the flow phenomenon induced by a rotating plate which characterized by a radial outflow. There are altogether two types of holes considered in the paper: round hole and square hole. A 1/25 (14.4-degree) sector model is used to carry out the numerical investigation using the commercial software ANSYS CFX. In the simulation, the SST turbulent model is used. Meanwhile, a non-rotating method using the relative frame of reference is used. In the non-rotating method, an initial incidence angle is given at the inlet instead of setting the plate to be rotating, thus the pumping effect induced by the rotating plate can be eliminated. The non-rotating method results are compared with the conventional reference frame results to investigate the influence of pumping effect. The results show that due to the influence of the pumping effect-induced radial outflow, the theoretical two-dimensional incidence angle becomes three-dimensional, which has negative effects on the hole discharge coefficient. At the same time, due to a larger circumferential length, square holes will undermine the pumping effect, thus has a higher discharge coefficient than the round holes.

Theoretical research on surface material migration of field constrained abrasive polishing

The current research on the removal mechanism of ultra-precision polishing lacks various microscopic understandings of material removal and the process of surface material migration, which hinders the development of ultra-precision polishing technology, especially field constrained abrasive polishing. In order to clarify effects of abrasives at the atomic level on material removal in the field constrained abrasive polishing, a three-dimensional molecular dynamics model is conducted to study the mechanics of ultra-precision polishing on an aluminum (Al) specimen with a diamond abrasive. In order to simulate the real polishing environment, a double abrasive polishing system is designed. The mechanism of material removal was studied by observing the surface topography, surface damage, and coordination number of the working area during polishing. The influence factors of material removal were also investigated by changing the initial velocity, incidence angle, initial force, and relative position of the double abrasives. The results show that the transverse distance and the longitudinal distance between the double abrasives make a slight difference to the number of phase transformation atoms in the double abrasive polishing system, which is directly proportional to the initial velocity, the initial force, the distance between the specimen and its closest abrasive in the Z direction, and the distance between the double abrasives in the Z direction and inversely proportional to the incident angle of the double abrasives. Finally, it is found that the force on the abrasives is the main factor that determines the removal efficiency of the field constrained abrasive polishing.

On generalized waves reflection in a micropolar thermodiffusion elastic half-space under initial stress and electromagnetic field

We discuss the reflection waves phenomenon in a generalized thermoelastic micropolar half-space under initial stress, electromagnetic field, and diffusion based on two models: Lord-Shulman (LS) and Dual-Phase-Lag (DPL). The governing equations are formulated by considering new parameters as a constitutive equation, equation of motion, diffusion equation, and micropolar equation in the context of two thermoelastic models. Lame potentials are used to separate the equations to dilatational and shear components. So, the characteristic equation indicates to five reflected waves due to the motion, diffusion, micropolar, and thermoelastic effects. The boundary conditions have been applied concerning the mechanical and maxwell stresses, temperature, diffusion, and micropolar. The reflection coefficients ratios are calculated for the general case in the presence of thermodiffusion and microplarity, and the absence of microplarity of the medium. The effect of the initial stress, relaxation times, electromagnetic field, and angle of incidence on the reflection coefficients for thermal wave incidents are displayed graphically to show the physical meaning of the phenomenon. We compare our results which we obtain by using the external parameters effect with other results. The specific loss of energy has been also computed analytically and presented by graph.

Angle- and polarization-dependent reflection and backscattering from FS-LIPSS covered stainless steel surfaces: experimental study

Large double-scale random rough surfaces covered by femtosecond laser-induced periodic structures are produced experimentally. Irradiation circumstance is considered as the main approach for manufacturing various samples. Fabricated surfaces on the steel substrate are full of high spatial frequency ripples which are crossed by deeper grooves. A polarized He–Ne laser beam is utilized to illuminate the complex surfaces and probe their optical features. Intensities of the reflected and backscattered beams at various incident angles (from small values to large amounts) are monitored in this regard. Results show that the linearly polarized probe beam is scattered diffusely and also de-polarized significantly after striking the irradiated surfaces. However, the amounts of de-polarization of the reflected/backscattered lights are dependent on characteristics of the surface as well as the initial polarization and incident angle of the probe beam. Besides, a relation between the optical response and orientation of the samples is also observed. Finally, at last section, discussions concerning the physical phenomena that are playing a role in the optical response of the samples are presented in detail. Our experimental results reveal that photo-ablation with ultrashort laser systems is highly sensitive and fast enough method for fabrication of surfaces with applications in industry and medical fields in which controlled light reflections or backscattering are needed.

Aerodynamic modeling of a flexible flapping-wing micro-air vehicle in the bond graph environment with the aim of assessing the lateral control power

In this paper, an integrated and systematic modeling of all components and subsystems of a flapping bird robot is developed using the bond graph method. The wings kinematic is independently implemented with the aim of evaluating lateral movements of the bird and aerodynamic forces are accurately extracted by assuming quasi-steady theory. In the present dynamic model, the aeroelastic bending behavior of flexible wing of the flapping bird is revealed by the bond graph method. In this regard, three elastic bending modes and one rigid motion mode of the wing are added to the model. In the following, the performance evaluation of the flapping bird and parametric study are carried out around important quantities such as frequency, initial incidence angle, torsional stiffness, and flapping amplitude of the wings, which results in applicable and attractive consequences. As an innovation, the initial classification and presentation of the comparative characteristic curves for generating lateral forces without using an additional control surface and only based on asymmetry in the flapping kinematic using the bond graph approach is done, which is essential to perform lateral-directional maneuvers. Some important correlations are achieved, which are presented in detail in the text. As an example, the relation between lateral force and phase difference between wings is quasi-linear in a variety of velocities. Therefore, this parameter can be used as input in design of lateral control system. On the other hand, the sensitivity of the lateral force to active pitch angle is more than other quantities; as a result, such mechanism can be effectively used in rapid maneuvers. Finally, based on the presented bond graph model, it would be easily possible to study the effects of design variables, mechanical properties, geometric constraints, and specially flapping kinematics on a wide range of functional and performance indices.

Thermal-structural analysis for flexible spacecraft with single or double solar panels: A comparison study

The thermal-structural analysis for a flexible spacecraft with double solar panels is carried out in this paper through a comparison study with spacecraft having a single panel. The solar panels are composed of honeycomb panel and subjected to time-varying thermal loading. Taking into account the coupling effect among attitude motion, structural deformation and thermal loading, the rigid-flexible-thermal coupling dynamic model of the spacecraft is established by using the Hamiltonian Principle. Based on the finite difference method, an explicit algorithm is developed to solve the transient heat conduction problem of the solar panel. The coupled thermal-structural analysis reveals significant differences between the dynamic characteristics of thermally induced vibration of spacecraft with single and double solar panels. The thermally induced dynamic response significantly affects the attitude of spacecraft with a single solar panel, while it hardly affects the attitude of spacecraft with double solar panels. As the maneuver attitude or the initial incident angle of heat flux increase, the thermally induced vibration of spacecraft with a single solar panel changes from stable to unstable and thermal flutter occurs, while that of spacecraft with double solar panels always keeps stable.

Chemical Dynamics Simulations and Scattering Experiments for O2 Collisions with Graphite

Energy transfer in collisions of O2 with a graphite surface was studied by chemical dynamics simulations. The simulations were performed for three collision energies Ei of 2.1, 7.4, and 15 kcal/mol, with the initial incident angle fixed at θi = 45°. Simulations were performed for each Ei at a surface temperature Tsurf = 300 K. For the higher surface temperature of 1177 K, a simulation was only performed for Ei = 15 kcal/mol. The following properties were determined and analyzed for the O2 + graphite collisions: (1) translational energy distributions of the scattered O2; (2) distribution of the final polar and azimuthal angle for the scattered O2; and (3) number of bounces of O2 on the surface before scattering. The average energy transferred to the graphite surface and that remaining in O2 translation, i.e., ⟨ΔEsurf⟩ and ⟨Ef⟩, exhibit a linear dependence with the initial translational energy. For the O2 + graphite scattering, the physisorption/desorption residence time distribution decays exponentially, with an increase in residence time with a decrease in Ei. The rate at which the distribution decreases shows a near-linear dependence with an increase in Ei. For higher collisional energies of 7.4 and 15 kcal/mol, O2 scattering from the surface follows a nearly quasi-trapping desorption process. However, for the lowest collision energy, it mostly follows conventional physisorption/desorption. For all of the scattering conditions considered experimentally, the relationship between the average final translational energy and average scattering angle for the O2 molecules found from the simulations is in excellent agreement with the experimental results. This experimental validation of precise simulation outcomes is important as it indicates that collisional energy-transfer predictions for this system can be reliably used in assessing interfacial energy flow in a variety of technological applications, including high-performance flight systems.

Performance analysis of air-water quantum key distribution with an irregular sea surface

In the air-water quantum key distribution (QKD), the irregular sea surface has some influence on the photon polarization state. The wind is considered as the main factor causing the irregularity, so the model of irregular sea surface based on the wind speed is adopted. The relationships of the quantum bit error rate with the wind speed and the initial incident angle are simulated. Therefore, the maximum secure transmission depth of QKD is confirmed, and the limitation of the wind speed and the initial incident angle is determined. The simulation results show that when the wind speed and the initial incident angle increase, the performance of QKD will fall down. Under the intercept-resend attack condition, the maximum safe transmission depth of QKD is up to 105 m. To realize safe communications in the safe diving depth of submarines (100 m), the initial incident angle is requested to be not exceeding 26°, and with the initial incident angle increased, the limitation of wind speed is decreased.

Thermal-structural analysis for an attitude maneuvering flexible spacecraft under solar radiation

A coupled thermal-structural analysis for an attitude maneuvering spacecraft under solar radiation is conducted and the interaction between the thermally induced vibration and attitude maneuver is studied. The spacecraft consists of a rigid hub and a solar array composed of honeycomb panel. By considering the thermal stress of solar panel, the system's rigid-flexible-thermal coupling dynamic model is established in terms of the Hamiltonian Principle and non-constrained modes. Based on the finite difference method, an explicit recursive algorithm is developed to compute the transient cross-sectional temperature distribution of solar panel which is modeled as a three-layer laminated structure. The coupled thermal-structural analysis reveals that the torque, which can maneuver the spacecraft to the desired attitude in the simulation of rigid-flexible model, cannot accomplish the attitude maneuver mission for a spacecraft under solar radiation even though the desired attitude is small. In the case of large final incident angle of heat flux (the sum of initial incident angle and the maneuver attitude angle), the thermally induced vibration of a spacecraft with small damping may be unstable and the thermal flutter may occur. Moreover, the thermally induced vibration decays with time in the case of large damping.

Experimental investigation of flow-induced vibration of a pitch–plunge NACA 0015 airfoil under deep dynamic stall

The flow-induced vibration of a NACA 0015 airfoil model with pitch and plunge degrees of freedom is investigated in a high-speed wind tunnel using motion sensors, pressure sensors on the airfoil surface and synchronized high-speed Schlieren visualizations of the unsteady flow field at Reynolds numbers Re=180000–570000. Compared to other studies, the model has considerably smaller dimensions (with a chord length of 59.5mm) and operates at higher flow velocities (from 37 to 125m/s). With a relatively low pitch to plunge natural frequency ratio and zero initial incidence angle, the model is highly susceptible to deep dynamic stall instability with the peak-to-peak pitch amplitude reaching up to 90°. The limit cycle response of the system as a function of freestream flow velocity is reported in detail, together with synchronized Schlieren visualizations of the flow field revealing the boundary layer behavior during dynamic stall. With increasing inflow velocity, the plunge amplitude increases dramatically, accompanied also by slight rise in the frequency of oscillation and decrease of the phase lag between pitch and plunge. The pitch amplitude has a maximum at 62m/s and further decreases with increasing flow velocities.

A prism-based non-linear optical readout method for MEMS cantilever arrays

This paper demonstrates the use of a single right-angle prism for the optical readout of micro-electro-mechanical systems (MEMS) cantilever arrays. The non-linear reflectivity arisen from the internal reflection at the right-angle prism’s hypotenuse plane enables the measurement of cantilever deflections. The cantilever arrays used in the experiments are made of electroplated nickel structures and actuated at resonance by an external electro-coil. A laser beam illuminates multiple cantilevers, and then it is partially reflected by the prism. The prism reflectivity changes with the cantilever deflection and modulates the laser intensity at the photodetector. The detection sensitivity of the optical readout system is determined by the initial angle of incidence at the prism’s hypotenuse plane, numerical aperture of the illumination system and the polarization of the laser beam. In this paper, we showed both theoretically and experimentally that self-sustained oscillations of two MEMS cantilevers with simple rectangular geometry is achievable using only one actuator and one photodetector. The gain saturation mechanism for the oscillators was provided by the optical non-linearity in the prism readout, which eliminates the requirement for separate sensing electronics for each cantilever. Based on our analytical and experimental data, we found that the prism incident angle around 41.2° is desirable in the closed-loop system due to high responsivity. Finally, we demonstrated simultaneous self-sustained oscillations of two cantilevers in closed-loop with resonant frequencies in the range 25–30kHz. It was shown that multiple oscillations are obtainable if the cantilever resonant frequencies are separated from each other by at least 3dB bandwidth.

Reflection Characteristics of Oxygen Molecule on Ionomer Surface

The widespread utilization of polymer electrolyte fuel cells for transportation applications such as fuel cell vehicles requires high power density operation. However, as the current density increases, the diffusion polarization, which is attributed to the insufficient mass transport, degrades the cell performance. In particular, the oxygen transport resistance in catalyst layers (CLs) and micro porous layers (MPLs) at the cathode side is one of the major factors of the performance degradation. Therefore, the reduction in the oxygen transport resistance is important for the high power density operation. In the previous research, Kinefuchi et al. have investigated the oxygen diffusion resistance in MPLs and CLs using the direct simulation Monte Carlo (DSMC) method. They reported that the simulation well reproduces the experimental result in MPLs. However, the DSMC results underestimate the oxygen diffusion resistance in CLs. This discrepancy is caused by the drawback to a scattering model of gas molecules on surfaces, which plays a crucial role in DSMC analysis. In these calculations, the same scattering model is used for the scattering of oxygen molecules on surfaces regardless of the presence or absence of ionomer on micro porous carbons. An advanced scattering model that can reproduce the scattering and surface diffusion phenomena on ionomer surface, is required for more accurate analysis of the oxygen transport in CLs. The construction of the model needs the detailed understanding of the gas‒surface interaction. In this study, we have investigated the mechanics of oxygen scattering and surface diffusion on ionomer surface using molecular dynamics simulation. We modeled the solid surface in CLs as an ionomer film covering the carbon layers. The simulation domain was 51.1 × 44.2 × 100 Å3 in size. The ionomer film was composed of water molecules hydronium ions, and perfluorosulfonic acid molecules as typified by Nafion, water molecules, and hydronium ions. Oxygen molecules were directed to the ionomer surface and the trajectory calculations were performed for 20 ps. The initial translational energy and incident angle were the same for all the incident molecules, but the initial position and orientation were given randomly in order to obtain the sufficient statistics. If an oxygen molecule desorbed from the surface and reached the initial height, it was defined to be scattered. Firstly, we have evaluated the energy transfer between oxygen molecules and the ionomer surface by calculating between translational energy before and after the scattering. Oxygen molecules with low incident energy tend to receive energy when they leave the surface after the collisions. Next, we have evaluated the scattering phenomena of oxygen molecules on ionomer surface by examining the energy and angular probability distributions of scattered molecules. The energy distribution depends on the incident energy, and deviates from the distribution given by diffusive scattering model, that the incident molecules are assumed to accommodate completely with the surface. On the other hand, the scattering angle distribution is independent of the incident energy, and well-reproduced by the diffusive scattering model. These results suggest that oxygen molecules do not accommodate completely with the ionomer surface when they are reflected, however they are reflected following the diffusive scattering model because of the corrugation of the ionomer surface.

Reflection of cylindrical converging shock wave over a plane wedge

The cylindrical converging shock reflection over a plane wedge is investigated experimentally and numerically in a specially designed shock tube which converts a planar shock into a cylindrical one. When the converging shock is moving along the wedge, both the shock strength and the incident angle are changing, which provides the possibility for the wave transition. The results show that both regular reflection (RR) and Mach reflection (MR) are found on the wedge with different initial incident angles. The wave transitions from direct Mach reflection (DiMR) to inverse Mach reflection (InMR) and further to transitioned regular reflection (TRR) are observed with appropriate initial incident angles. The instability development in the shear layer and strong vortices formation near the wall are evident, which are ascribed not only to the interaction of two shear layers but also to the shock impact and the shock converging effect. Because of the flow unsteadiness after the converging shock, the detachment criterion provides a good estimation for the RR → MR transition, but fails to predict the DiMR → InMR transition, and MR is found to persist slightly below the mechanical equilibrium condition. A hysteresis process is found in the MR → TRR transition and becomes more apparent as the increase of the initial incident angle due to the shock converging effect.