Extreme Angles Research Articles

Leading edge redesign of dual-peak type variable inlet guide vane and its effect on aerodynamic performance

Recently, a new type airfoil for variable inlet guide vane (VIGV), featuring “dual-peak” surface velocity pattern at high incidence, is proposed and shows wide low-loss operation range. To further improve its performance, this paper researches the influence of leading edge (LE) thickness and shape on the loss level and surface velocity features of the “dual-peak” type airfoil. Firstly, a polynomial-based continuous-curvature leading edge design method was briefly introduced and used in the LE redesign of sample airfoils. Then, steady simulations based on Reynolds-Averaged Navier-Stokes method (RANS), carried out by commercial software CFX after grid independent study, were used to determine the aerodynamic performance, surface velocity distribution and boundary-layer behaviors of all research airfoils. Simulation results indicate that there exists an optimized range of LE relative thickness that can achieve lower airfoil loss level at high incidence condition. For Case 1 ([Formula: see text]) and Case 2 ([Formula: see text]), the optimized LE relative thickness range is [Formula: see text] and [Formula: see text]. The LE shape optimization can further reduce the maximum incidence condition loss coefficient with proportion up to 18% for airfoils with optimal LE thickness. Analysis of flow mechanism indicates that the optimized LE thickness and shape can reduce the suction spike height and subsequent adverse pressure gradient, therefore, decrease the LE separation scale and result in a lower loss coefficient. As an application, a dual peak VIGV with circular LE, presented in previous paper as the optimized VIGV, is redesigned in the LE portion according to the research findings and achieved 0.6 percent improvement in passage-averaged total pressure recovery coefficient [Formula: see text] at extreme high stagger angle point and the low-loss operation range extends with about 5°, which confirms the effectiveness of the research findings in three-dimensional environment.

Nanopatterning of the (001) surface of crystalline Ge by ion irradiation at off-normal incidence: Experiment and simulation

Intricate topographical patterns can form on the surface of crystalline Ge(001) subject to low-energy ion irradiation in the reverse epitaxy regime, i.e., at elevated temperatures which enable dynamic recrystallization. We compare such nanoscale patterns produced by irradiation from varied polar and azimuthal ion incidence angles with corresponding calculated surface topographies. To this end, we propose a continuum equation including both anisotropic erosive and anisotropic diffusive effects. Molecular dynamics simulations provide the coefficients of angle-dependent sputter erosion for the calculations. By merely changing these coefficients accordingly, the experimentally observed surface morphologies can be reproduced, except for extreme ion incidence angles. Angle-dependent sputter erosion is thereby identified as a dominant mechanism in ion-induced pattern formation on crystalline surfaces under irradiation from off-normal incidence angles.

Multi-layer light trapping structures for enhanced solar collection.

Light trapping is a commonly used technique for enhancing the efficiency of solar collection in many photovoltaic (PV) devices. In this paper, we present the design of multi-layer light trapping structures that can potentially be retrofitted, or directly integrated, onto crystalline or amorphous silicon solar panels for enhanced optical collection at normal and extreme angle of incidence. This approach can improve the daily optical collection performance of solar panel with and without internally integrated light trapping structure by up to 7.18% and 159.93%, respectively. These improvements predict an enhancement beyond many research level and commercially deployed light trapping technologies. We further enhance this performance by combining our multi-layer optics with high refractive index materials to achieve a daily optical collection of up to 32.20% beyond leading light trapping structures. Our additive light trapping designs could enable the upgradeability of older PV technologies and can be tailored to optimally operate at unique angular ranges for building exteriors or over a wide range of incidence angle for applications such as unmanned aerial vehicles.

Performance of helical router bit in milling of composite boards

An extreme inclination angle of helical cutting tool edge has been developed in milling of new commercially composite boards. The purpose of this research was to investigate wear resistance, chip formation, surface roughness, and noise level of helical edge router bits in milling composite boards. The composite boards of wood plastic composite, laminated veneer lumber, and strand board were cut by the helical edge router bits (helical angle 15°, 30°, 45°, 60°, and 75°) in a computer numerical control router. The results show that the helical edges provide better wear resistance, smoother surface of machined composite boards, and lower noise emission compared to the conventional edge (0°). Edge wear, surface roughness, and noise level decreased with increasing helix angle of the edge router bits. The differences in structure among the composite boards resulted in the difference in cutting tool wear, chip formation, surface roughness, and noise level phenomenon. The 75° inclination angle of router bit provided the highest wear resistance, better surface of machined composite board, and the lowest noise level.

An accurate and fast iterative scheme for estimating the ship rolling and capsizing in regular waves

A short number of steep breaking waves hitting a ship from the side may affect its dynamic behaviour and to determine extreme roll angles and, eventually, capsizing. This last phenomenon is a challenging task for naval engineers because it is responsible not only for a lot of material damages, but also for human lives. It is therefore not surprising that there have been published many relevant theoretical and experimental studies on heavy rolling and capsizing but the problem is not yet fully resolved. Generally, the ship rolling in beam regular seas could be described by a second-order non-linear differential equation with the roll angle as dependent variable. Non-linearity comes from the restoring and damping moments, which are usually represented by (odd) polynomials of roll angle or of its time derivative. Numerical integrators incorporated in modern software packages (e.g. ode45 in Matlab) encounter efficiency problems for the unbounded solutions associated with capsizing, the running time being extremely high. The alternative is to write a computer software, appropriate to the topic to be solved. In the paper, the roll equation was solved using a simple, fast and accurate iterative scheme based on Taylor expansion. Compared with Runge-Kutta 4th order numerical technique, the used scheme demonstrated not only an excellent agreement of the results, but also a significant reduction of the CPU time. The rapidity of the scheme allowed us to conduct a comprehensive investigation on fractal erosion of safe basins and to represent the normalized integrity curves and the amplitude-frequency response curves for different combinations of wave parameters. The restoring and damping coefficients corresponded to a vehicle ferry model, considered to be either intact or damaged, on the one hand, and with or without bilge keels, on the other.

Comparing methods for estimating leaf area index by multi-angular remote sensing in winter wheat

The reflectance of wheat’s canopy exhibits angular sensitivity, which can influence the accuracy of different methods for its leaf area index (LAI) estimation through multi-angular remote sensing. The primary objective of this study was to assess and compare the ability of various methods for LAI estimation from 13 view zenith angles (VZAs). The four methods included: (1) common hyper-spectral vegetation indices (VIs), (2) optimal two-band combination VIs (i.e., VIs: normalized difference index, simple ratio index, and difference vegetation index), (3) back-propagation neural network (BPNN), and (4) partial least squares regression (PLSR). Our results demonstrated that the red-edge plays a key role in estimating LAI, in that the traditional VIs, optimal two-band VIs, and PLSR including the red-edge band all showed satisfactory performance, with coefficient of determination (R2) > 0.72 in the nadir direction. However, the estimation accuracy of LAI was not positively related with band number, and BPNN gave unsatisfactory results under a larger viewing angle, with R2 ≤ 0.60 for extreme angles. The predictive ability of all four methods declined with an increasing VZA, with reliable LAI estimation near the nadir direction. Importantly, by comparing the four methods, PLSR emerged as superior in both its estimation accuracy and angular insensitivity, with R2 = 0.83 in the nadir direction and ≥ 0.65 for extreme angles. For this reason, we highly recommend it be used with multi-angular remote sensing data, especially in agricultural applications.

Analytic Impulsive Maneuver Sequences for Nominal Safety Ellipse Reconfigurations

This paper presents analytic solutions for three-impulse maneuver sequences that perform safety ellipse resizing and phasing. Safety ellipses are relative motion trajectories that do not require thrusting to ensure a high probability of short-term collision avoidance. Primer vector theory, validated with numerical analysis, is used to derive analytic expressions that relate optimality to properties of the initial and final safety ellipses. This analysis shows that the maneuver sequences are optimal for a range of resizing and phasing scenarios. An analysis is also performed on the passive safety of transfer trajectories that result from incomplete maneuver sequences. It is shown that only phasing scenarios that call for an extreme phase angle change result in potentially unsafe transfer trajectories.

Tensor analyzing power component [formula omitted] of the [formula omitted] process in the photon energy range from 200 to 400 MeV

The tensor analyzing power component, T20, of the γd→→π0d process in the photon energy range from 200 to 400 MeV is investigated. This work is motivated by the most recent and unique measurements from the VEPP-3 electron storage ring at the Budker Institute of Nuclear Physics in Novosibirsk, Russia. We point out a special sensitivity of T20 to the elementary γN→πN amplitude and to the realistic NN potential model adopted for the deuteron wave function at backward pion angles, especially in the region 90°<θ<150°. The estimated results for T20 are compared with the experimental data from VEPP-3 and a satisfactory agreement is obtained at incident photon energies below 375 MeV. At higher photon energies and extreme backward pion angles, the estimated results of T20 considerably underestimate the data.

Optofluidic waveguide bending by thermal diffusion for visible light control.

Optofluidics has inspired many promising optical devices. Among them, waveguide bending is an important element for guiding light. Here, we demonstrated the thermal-diffusion liquids, acting as a natural transformation optical material in an annular structure. Compared with conventional step-index waveguide bending, this thermal one enables real-time tunable visible light bends by extreme angles, with nearly no power loss and intensity distribution. This unique light bending is because gradient refractive-index profiles caused by thermal diffusion meet the requirements by transformation optics. The work demonstrates the thermal diffusion in liquids as a natural technology to realize optofluidic gradient-index designs and has potential for tunable optical systems.

Waveform Capture? All You Need is a Smartphone

HeartWare assist device (HVAD) monitor provides flow and power waveform information which has been shown to respond to changes in physiological loading conditions, cardiac contractility and aortic valve status. Instantaneous point data is recorded every 15 minutes into the controller logfile. Because some phenomena are of short duration or need an immediate intervention (such as suction or tamponade), significant changes may not be captured within the logfile. We present a simple method to capture the displayed waveforms via a smartphone photo followed by re-digitization for data extraction. Waveform recording provides an opportunity for teaching or research. During an interesting event, a photo of the screen of the HVAD monitor is taken. The photographer will take care to capture the border of the waveform screen as reference. The second step is the restitution of parallel lines using the smartphone application TurboScan (picksoft, V.3.0.2). This will use the border of the screen to straighten the whole picture. Loss of quality can happen during this stage if an extreme angle is used. To reconstruct the axis, we feed the picture in WebPlotDigitalizer (Atomeris, V.4.2). Using the built-in VAD-screen scale, the software will output a table of calibrated values corresponding to the flow or power trace. Using an R-script (3.6.1) written within R-studio (V.12.1355), we can reproduce flow and power waveforms identical to that displayed from the HVAD controller with sampling frequency of data up to 100Hz. This can be used as an algorithm input for further waveform analysis (waveform, rhythm, PI) or for illustration purposes. Our illustrative case shows a photo taken during a normal VAD-clinic appointment and reconstituted using our technique. This technique is cheap, easy to use at the bedside or clinic and represents an opportunity to capture interesting waveform events for teaching or illustration purposes or subsequent algorithm development.

Wake steering optimization under uncertainty

Abstract. Turbines in wind power plants experience significant power losses when wakes from upstream turbines affect the energy production of downstream turbines. A promising plant-level control strategy to reduce these losses is wake steering, where upstream turbines are yawed to direct wakes away from downstream turbines. However, there are significant uncertainties in many aspects of the wake steering problem. For example, infield sensors do not give perfect information, and inflow to the plant is complex and difficult to forecast with available information, even over short time periods. Here, we formulate and solve an optimization under uncertainty (OUU) problem for determining optimal plant-level wake steering strategies in the presence of independent uncertainties in the direction, speed, turbulence intensity, and shear of the incoming wind, as well as in turbine yaw positions. The OUU wake steering strategy is first examined for a two-turbine test case to explore the impacts of different types of inflow uncertainties, and it is then demonstrated for a more realistic 11-turbine wind power plant. Of the sources of uncertainty considered, we find that wake steering strategies are most sensitive to uncertainties in the wind speed and direction. When maximizing expected power production, the OUU strategy also tends to favor smaller yaw angles, which have been shown in previous work to reduce turbine loading. Ultimately, the plant-level wake steering strategy formulated using an OUU approach yields 0.48 % more expected annual energy production for the 11-turbine wind plant than a strategy that neglects uncertainty when considering stochastic inputs. Thus, not only does the present OUU strategy produce more power in realistic conditions, but it also reduces risk by prescribing strategies that call for less extreme yaw angles.

Analysis of ZnS and MgF2 layered nanostructures grown by glancing angle deposition for optical design

This study investigated the multilayer growth and properties of ZnS and MgF2 using glancing angle deposition. We used deposition angles of 85°–89° for ZnS and 70°–88° for MgF2 to obtain the structural properties. The film properties primarily followed Tait’s rule with a deposition angle of less than 87° in the vapor flux. However, film growth with a vapor flux angle of 88°–89° followed the tangent rule. Mathematical and cross-sectional scanning electron microscopy examinations found a transition point for the growth mechanisms at 87°, which comes from an extreme angle property for glancing angle deposition. We also performed mathematical derivations for the well-known empirical formula of the tangent rule and its generalized version. To stabilize the interface structure and surface roughness of multilayer structures, film growth at slightly tilted angles is recommended. Based on these results, an optical structure was designed, fabricated, and analyzed for a 550 nm wavelength pass filter on a glass substrate.

Effects of Daily Activities and Position on Kinematics and Contact Mechanics of Dual Mobility Hip Implant.

Dual mobility hip implants have been widely introduced to overcome dislocation in recent years. However, the potential influence of different gaits on kinematics and contact mechanics for dual mobility hip implants is still unclear. Furthermore, a large range of motion coupling with the implant position, especially high inclination or anteversion angle, may result in poor kinematics and contact mechanics. A previously developed dynamic finite element method was adopted in this study to examine the kinematics and corresponding stability of dual mobility hip implants under different gaits coupling with different inclinations or anteversion angles. The results showed only inner relative sliding under knee-bending for dual mobility hip implants under moderate inclination and anteversion angles, whereas an anteversion angle of 25° induced both impingement and consequent relative sliding of the outer articulation. However, the impingement (between the stem neck and the liner inner rim) indeed happened under stair-climbing and sitting-down/stand-up as well as combined movements when inclination and anteversion angles were set as 45° and 0°, respectively, and this finally led to relative sliding at the outer articulation. A high inclination angle did not worsen both the impingement and related outer sliding compared to modest inclination and anteversion angles of the liner, but a high anteversion angle prolonged the period of both the impingement and the outer relative sliding. The extreme motions and high anteversion angles are hardly inevitable, and they indeed lead to motions at both articulations for dual mobility hip implants.

Associations of trochlea morphology and patellofemoral alignment with prevalent radiographic patellofemoral osteoarthritis

To investigate the relation of trochlea morphology and patellofemoral alignment to prevalent radiographic patellofemoral osteoarthritis (PFOA). A within-person knee-matched case-control study was performed. Participants with unilateral radiographic PFOA were selected from the Multicenter Population-based Osteoarthritis Study (MPOA) in three towns in northern China that was approved by Peking University Health Science Center Ethics Committee (2018PHB166-01). Radiographic PFOA, radiographic tibiofemoral OA, sulcus angle, patellofemoral index and patella displacement were assessed using posterio-anterior and skyline views of the knee. We classified sulcus angle, patellofemoral index and patella displacement into quarters and investigated the relation of each of these measures to prevalent radiographic PFOA. Among 451 participants (mean age: 65.2 years, women: 66.8%) with unilateral radiographic PFOA, a reverse J-shaped relationship was observed between sulcus angle and prevalent radiographic PFOA (P=0.039 for quadratic term). Both higher patellofemoral index and patella displacement were associated with higher prevalent radiographic PFOA. Adjusted odds ratios (ORs) of prevalent radiographic PFOA in the highest quarter of patellofemoral index and patella displacement were 4.69 and 3.60 (Pfor trend <0.001), respectively, compared with the lowest quarter of each measurement. A similar relationship was observed between sulcus angle with either prevalent radiographic lateral or medial PFOA. Higher values of patellofemoral index and patella displacement were statistically significantly associated with higher prevalent radiographic lateral (ORs=5.07 and 4.59, respectively), but not medial PFOA (ORs=0.58 and 0.76, respectively). Extreme sulcus angles as well as higher values of patellofemoral index and patella displacement were associated with higher prevalent radiographic PFOA.

Head and neck extension more than 30° may disturb standing balance in healthy older adults

Although there is clinical evidence of postural instability at extreme angles of head extension, the effects of lower angles on balance have been not investigated. This study aimed to investigate the effects of different head and neck extension angles on standing balance in older adults, and to determine the critical angle of instability. Twenty-eight healthy older adults were tested at 0°, 20°, 30° and 40° head and neck extension. The center of pressure (COP) parameters were recorded with a force plate. Significant differences were observed between 30° and 40° compared to 0° in anteroposterior and mediolateral COP displacement and total COP velocity, and between 40° and 0° in mediolateral COP velocity. Head and neck extension at 30° was the critical angle associated with the appearance of instability, and this value should be considered in the ergonomic design of work and living spaces, exercise programming and daily activities in older adults.

A Method for the Prediction of Extreme Ship Responses Using Design-Event Theory and Computational Fluid Dynamics

The design of a naval vessel requires accurate estimation of the extreme loads and motions that it will experience during its lifetime. Operation in large seaways in which the ship-wave interaction is highly nonlinear and transient leads to design events such as maximum internal loads due to global wave bending, local slamming loads, extreme roll, combinations of the global wave bending and local slamming, and many others. In this article, a method is presented that allows for nonlinear analysis to be used to predict events with user-specified rareness. The core of the method combines probability, frequency, and time-domain analyses to generate short time-window sea environments that lead to extreme dynamical events. The Office of Naval Research Tumblehome geometry is analyzed for the extreme roll angle when advancing in stern quartering irregular seas. 1. Introduction The design of a naval vessel requires accurate estimation of extreme loads and motions that it will experience during its lifetime. Specific quantities of interest are the maximum slamming load during wet-deck impact, maximum acceleration at different locations on the vessel, maximum green-water load on the bow structure or helicopter deck, maximum roll angle, or frequency of occurrence of capsize, to name a few. It is important to recognize that a ship lifetime is decades long, and the exposure time in different severe storms over the lifetime is of the order of weeks, if not months. Furthermore, because of the random nature of the sea and, hence, the dynamical response of the ship, the extreme response is also random and should be characterized statistically. This means that a single lifetime realization in a given seaway by either model tests or numerical simulation only gives one sample of the extreme response, and multiple lifetime realizations are required to characterize the extreme response.

Theoretical Modeling and Exact Solution for Extreme Bending Deformation of Hard-Magnetic Soft Beams

Abstract Hard-magnetic soft materials (HMSMs) manufactured by embedding hard-magnetic particles in soft materials belong to a new type of soft active materials. The abilities of fast and complicated transformations of hard-magnetic soft structures provide a promising technology for soft robotics, flexible electronics, and biomedical devices. It is significant to investigate the mechanical behaviors of hard-magnetic soft structures for their better applications. In this work, a hard-magnetic soft beam under an external magnetic field is theoretically modeled and the exact solutions for its mechanical responses are presented. First, the governing equations and boundary conditions are derived based on the principle of minimum potential energy. To solve the derived governing equations analytically, a new polynomial fitting model for hyperelastic materials is proposed for the hard-magnetic soft beam. Then, the exact solutions of a cantilevered hard-magnetic soft beam actuated by a uniform magnetic field in any direction are obtained. The newly derived exact solutions are further verified by comparing current results with those from recent simulations and experiments. For large bending angles up to 90 deg and extreme bending angle up to 180 deg, quite consistent agreement among exact solutions, numerical simulations, and experimental observations can be achieved. Finally, using our theoretical model, the deformation of the hard-magnetic soft beam actuated by magnetic fields in an arbitrary direction with non-zero magnetic declination is explored. When the magnetic actuation is increased from a small level gradually, the hard-magnetic soft beam deflects and it would undergo small, large, and extreme bending deformations in sequence. It is very interesting that, when the magnetic actuation is sufficiently large, the hard-magnetic soft beam is stretched and its centerline tends to align with the external magnetic field direction, implying that the hard-magnetic soft beam undergoes a uniaxial tension. The theoretical modeling and exact solutions for hard-magnetic soft beams are expected to be useful in the analysis and design of soft materials and structures.

An Unbalanced Sinuous Antenna for Near-Surface Polarimetric Ground-Penetrating Radar

Sinuous antennas are capable of producing ultra-wideband radiation with polarization diversity. This capability makes the sinuous antenna an attractive candidate for UWB polarimetric radar applications. Additionally, the ability of the sinuous antenna to be implemented as a planar structure makes it a good fit for close-in sensing applications such as ground-penetrating radar (GPR). In this work, each arm of a four-port sinuous antenna is operated independently to achieve a quasi-monostatic antenna system capable of polarimetry while separating transmit and receive channels-which is often desirable in GPR systems. The quasi-monostatic configuration of the sinuous antenna reduces system size as well as prevents extreme bistatic angles, which may significantly reduce sensitivity when attempting to detect near-surface targets. A prototype four-port sinuous antenna is fabricated and integrated into a GPR testbed. The polarimetric data obtained with the antenna is then used to distinguish between buried target symmetries.

The Influence of Spacecraft Charging on Low‐Energy Ion Measurements Made by RPC‐ICA on Rosetta

AbstractSpacecraft charging is problematic for low‐energy plasma measurements. The charged particles are attracted to or repelled from the charged spacecraft, affecting both the energy and direction of travel of the particles. The Ion Composition Analyzer (RPC‐ICA) on board the Rosetta spacecraft is suffering from this effect. RPC‐ICA was measuring positive ions in the vicinity of comet 67P/Churyumov‐Gerasimenko, covering an energy range of a few eV/q to 40 keV/q. The low‐energy part of the data is, however, heavily distorted by the negatively charged spacecraft. In this study we use the Spacecraft Plasma Interaction Software to model the influence of the spacecraft potential on the ion trajectories and the corresponding distortion of the field of view (FOV) of the instrument. The results show that the measurements are not significantly distorted when the ion energy corresponds to at least twice the spacecraft potential. Below this energy the FOV is often heavily distorted, but the distortion differs between different viewing directions. Generally, ions entering the instrument close to the aperture plane are less affected than those entering with extreme elevation angles.

Excitation of the electric pygmy dipole resonance by inelastic electron scattering⋆

To complete earlier studies of the properties of the electric pygmy dipole resonance (PDR) obtained in various nuclear reactions, the excitation of the 1$^-$ states in $^{140}$Ce by $(e,e')$ scattering for momentum transfers $q=0.1-1.2$~fm$^{-1}$ is calculated within the plane-wave and distorted-wave Born approximations. The excited states of the nucleus are described within the Quasiparticle Random Phase Approximation (QRPA), but also within the Quasiparticle-Phonon Model (QPM) by accounting for the coupling to complex configurations. It is demonstrated that the excitation mechanism of the PDR states in $(e,e')$ reactions is predominantly of transversal nature for scattering angles $\theta_e \approx 90^o-180^o$. Being thus mediated by the convection and spin nuclear currents, the $(e,e')$ like the $(\gamma,\gamma')$ reaction, may provide additional information to the one obtained from Coulomb- and hadronic excitations of the PDR in $(p,p')$, $(\alpha,\alpha')$, and heavy-ion scattering reactions. The calculations predict that the $(e,e')$ cross sections for the strongest individual PDR states are in general about three orders of magnitude smaller as compared to the one of the lowest $2^+_1$ state for the studied kinematics, but that they may become dominant at extreme backward angles.