Ground Effect Research Articles

Physics and Accuracy of Dual-Solver Simulations of Rotors in Ground Effect

To characterize the interactions between rotorcraft and ground obstacles when tackling modern and emerging problems such as shipboard landings and urban air mobility, first-principles computational models offer the ability to perform design and analytical studies while resolving detailed flow features. However, the cost of Navier–Stokes methods with very high resolution is, for the most part, only tractable for research use cases. Conversely, midfidelity potential-based methods are cost-effective but may not capture important physics that occur near the rotor blades. Hybrid approaches that couple Navier–Stokes and potential solvers have recently been developed, which provide the ability to resolve complex physics with a Navier–Stokes solution while employing a potential solver to resolve far-wake effects for which it is well-suited. This research discusses the impact of new improvements to and best practices for the hybrid Navier–Stokes/free-wake solver OVERFLOW-CHARM applied to rotors in ground effect. Predictions of rotor performance and flow features are compared with experimental data for microscale and subscale rotors. Rotor performance is predicted within 6% of a conventional computational fluid dynamics simulation at approximately 20% of the computational cost and predicted flow features correlate well to experimental flow visualization.

Synthesizing coherence loss by atmospheric turbulence in virtual microphone array signals.

Phased microphone array methods are increasingly used to localize and quantify noise sources of aircraft under flight condition. However, beamforming results suffer from loss of image resolution and corruption of sound levels due to atmospheric turbulence causing coherence loss between microphones. A synthesis method is presented that reproduces these effects in a virtual environment. Sound propagation through turbulent atmosphere is described by models by Ostashev and Wilson and by von Kármán turbulence spectra. Spatial coherence is calculated based on the parabolic equation for statistically inhomogeneous, isotropic turbulence. Decorrelation of signals is achieved by time-varying mixing of mutually independent signals with identical PSD based on coherence factors. The concept of auralization is employed to account for propagation delay, geometrical spreading, Doppler effect, air absorption, and ground effect. The application is demonstrated for a virtual 56 m aperture microphone array. The impact of different meteorological conditions on the beamforming and deconvoluted results are presented. For increasing turbulence strength, the results show decreasing sound levels and increasingly blurred images. The proposed method allows us to reproduce the effects of turbulence-induced coherence loss in phased microphone array measurements and to optimize array designs and algorithms in a virtual, controllable environment.

Komparativna računarska analiza NATO 5,56 mm, APM2 7,62 mm i AK-47 7,82 mm metka koji se kreće brzinom od 2,0 maha u neposrednoj blizini zida

Comparative Computational Analysis of NATO 5.56 mm, APM2 7.62 mm and AK-47 7.82 mm Bullet Moving at Mach 2.0 in Close Vicinity to the Wall Various rifles require unique bullets. Each bullet has its capability, speed, and impact on the target. In metropolitan warfare, several bullets are shot close to the solid walls. These near walls affect the pressure distribution over the entire asymmetric bullet. The influence of a reflected shock depends on the angle at which it was reflected and the altitude from the ground to the body of the bullet. The current research emphasizes three bullets of varying diameters used in different types of guns. The first bullet is of NATO 5.56 mm, the second is APM2's 7.62 mm bullet, and the third is a 7.82 mm bullet from an AK-47 rifle. For 2-D steady computations, the supersonic speed of Mach 2 is considered to analyze the flowfield across all three bullets. The heights of the bullet are taken considering the height-to-diameter ratios (h/D ratio) from 0.5 to 3.0. The Mach contour drawn from the numerical simulations is used to analyze the flowfield, and aerodynamic coefficients like lift, drag, and moment are also plotted to analyze the ground effects on the projectile. The comparative analysis showed that the trend of shock wave reflections was similar in the bullets till h/D of 1.5. The APM2 bullet experienced maximum drag, followed by AK-47's 7.82 mm and NATO's 5.56 mm bullet. The 7.82 mm bullet experienced maximum lifting force at h/D = 1.0 due to its larger surface area than the other two ammo. The 7.82 mm bullet experienced a nose-up moment, whereas the other two faced a nose-down moment. As the altitude of the bullets from the ground increased, the ground effect appearing on the bullets reduced. The present comparative analysis research shows that it is suitable to fire an AK-47 bullet from h/D greater than 2.0 and the other two bullets from an altitude greater than or equal to h/D of 3.0.

Ground effect on aerodynamics of the flapping wing in different Reynolds number and flapping amplitude

Ground effect on aerodynamics of the flapping wing in different Reynolds number and flapping amplitude

The Effect of Surface Grinding and Finishing on the Surface Roughness And Flexural Strength of Cubic Zirconia

The Effect of Surface Grinding and Finishing on the Surface Roughness And Flexural Strength of Cubic Zirconia

Experimental Analysis of the Flow over a Wing under Ground and Down Force Effects

Experimental Analysis of the Flow over a Wing under Ground and Down Force Effects

Airflow-based odometry for MAVs using thermal anemometers

This article concerns airflow-based odometry for estimating MAV flight speed from airflow measurements provided by a set of thermal anemometers. Our approach relies on a Gated Recurrent Unit (GRU) based deep learning approach to extract deep features from noisy and turbulent measurement signals of triaxial thermal anemometers, in order to establish the underlying mapping between the airflow measurement and the flight speed. The proposed solution is validated on a multi-rotor MAV. The results show that the GRU-based model can effectively extract noise features and perform denoising, and compensate for induced velocity effects along the propellers’ rotation axis. As a consequence, robust prediction of the flight speed is performed, including during takeoff and landing that induce ground effects and strong variations of vertical airflow.

The effects of dry grinding and wet grinding on synthesizing iodosodalite

How to dispose of radioactive iodine waste in a green and safe way has become a hot spot for research institutions around the world. In this study, we mainly compare the effects of wet grinding - hydrolysis transformation - sintering (wet grinding) and dry grinding - cold pressing - sintering (dry grinding) on the synthesis of iodosodalite. The analysis results show that the particle size of 4A zeolite treated by wet grinding for 2.5 ​h is approximately 5.5 ​μm. The results of in situ XRD, infrared spectroscopy, and in situ Raman show that the effect of wet grinding and refining treatment is more obvious for iodosodalite synthesis at 900 ​°C. TEM-EDS shows that the morphology of iodosodalite prepared by the wet method is more intact. Based on the above results, it is demonstrated that the wet milling treatment method is more favorable for the synthesis of iodosodalite.

Effect of low temperature grinding on phytochemicals profile of fenugreek seed powder

The grinding of spices at ambient temperature causes the loss of valuable heat-sensitive constituents. While higher investment and maintenance of cryogenic grinding make it prohibitive for small-scale industries. So, the present study was carried out to check the effects of low-temperature grinding on various phytochemicals of ground powder of fenugreek seeds. Water at ambient temperature, chilled water and coolant were circulated around the grinding chamber to lower the grinding temperature. Additionally, fenugreek seeds were fed at ambient and low temperatures (-100C). The temperature inside the grinding chamber at the end of grinding for three kg of fenugreek seeds ranged from 91.330C–53.330C for different treatments. A fall in grinding temperature resulted in the retention of a higher quantity of total phenol (7.71 mg g-1), total flavonoid (12.08 mg quercetin equivalent/g extract), antioxidant activity (21.29%) and volatile components in powder of fenugreek seeds ground by coolant circulation with low-temperature feed.

The Effect of Earthing Mat on Stress-Induced Anxiety-like Behavior and Neuroendocrine Changes in the Rat.

Grounding is a therapeutic technique that involves doing activities that "ground" or electrically reconnect us to the earth. The physiological effects of grounding have been reported from a variety of perspectives such as sleep or pain. However, its anti-stress efficacy is relatively unknown. The present study investigated the stress-related behavioral effects of earthing mat and its neurohormonal mechanisms in the Sprague-Dawley male rat. Rats were randomly divided into four groups: the naïve normal (Normal), the 21 days immobilization stressed (Control), the 21 days stressed + earthing mat for 7 days (A7) or 21 days (A21) group. The depressive-and anxiety like behaviors were measured by forced swimming test (FST), tail suspension test (TST) and elevated plus maze (EPM). Using immunohistochemistry, the expression of corticotrophin-releasing factor (CRF) and c-Fos immunoreactivity were analyzed in the brain. In the EPM, time spent in the open arm of the earthing mat groups was significantly increased compared to the Control group (p < 0.001), even though there were without effects among groups in the FST and TST. The expression of CRF immunoreactive neurons in the earthing mat group was markedly decreased compared to the Control group. Overall, the earthing mat reduced stress-induced behavioral changes and expression of c-Fos and CRF immunoreactivity in the brain. These results suggest that the earthing mat may have the potential to improve stress-related responses via the regulation of the corticotrophinergic system.

Lift Computation Through Crossflow Measurement Behind a Rectangular Semiwing in Ground Effect

Abstract The lift force of a rectangular semiwing in stationary ground effect was computed based on the spanwise circulation distribution inferred from wake crossflow measurement and was compared with the direct force balance data at Re = 2.48 × 105. The lift calculated was found to be in good agreement with the force-balance measurement for ground distances h larger than 10% of the airfoil chord c. In close ground proximity (h/c ≤ 10%), a large discrepancy however existed due to the appearance of a multiple vortex system consisting of a tip vortex, a corotating ground vortex, and a counter-rotating secondary vortex. The counter-rotating secondary vortex offset the vorticity of the tip vortex. By considering its contribution additive, the discrepancy observed between the lift forces computed and measured with the force balance in close ground proximity became marginal. The impact of ground effect on lift-induced drag was also discussed.

Effects of traditional grinding and superfine grinding technologies on the properties and volatile components of Protaetia brevitarsis larvae powder

Particle size is an important indicator for determining the quality of products in the field of functional food. However, for edible insects, which will be important resources in the future, there is little information about the impact of particle size. In this study, traditional grinding technology and superfine grinding technology with additives were used to obtain six Protaetia brevitarsis powders, and the differences in physicochemical properties, powder properties and volatile components were determined. The results illustrated that superfine grinding technology could significantly increase the protein and total phenolic content (TPC) and improve the powder properties (including the bulk density, tap density, angle of repose, angle of slide, water holding capacity (WHC), and crystallinity index (CI)). Moreover, a total of 80 volatile components were preliminarily identified from the six P. brevitarsis powders, among which the type and relative content of volatile components in superfine grinding technology combined with 4 g/100 g additives (PBP4%) were the most abundant. In conclusion, superfine grinding technology can change the properties of the powder, which is related to the particle size. The results have a certain reference value for the development of superfine powder products of P. brevitarsis in functional foods.

HIL Flight Simulator for VTOL-UAV Pilot Training Using X-Plane

With the increasing popularity of vertical take-off and landing unmanned aerial vehicles (VTOL UAVs), a new problem arises: pilot training. Most conventional pilot training simulators are designed for full-scale aircrafts, while most UAV simulators are just focused on conceptual testing and design validation. The X-Plane flight simulator was extended to include new functionalities such as complex wind dynamics, ground effect, and accurate real-time weather. A commercial HIL flight controller was coupled with a VTOL convertiplane UAV model to provide realistic flight control. A real flight case scenario was tested in simulation to show the importance of including an accurate wind model. The result is a complete simulation environment that has been successfully deployed for pilot training of the Marvin aircraft manufactured by FuVeX.

Manyetik Anomali Yöntemi Kullanılarak Düşük Maliyetli Mayın Dedektörü Tasarımı

Buried mines pose great dangers to humans and animals around the world, which means thousands of people die each year from buried mines. Detecting and destroying these mines without harming people is an important issue. Today, these landmines are detected using different methods such as Ground Effect Radar, Electromagnetic induction, Infrared and Nuclear Quadrupole Resonance and active sensors are generally used in most of these methods. Although active sensor-based landmine detectors are often used for performance reasons, they can cause unintentional landmine explosions because they operate with transmitted and reflected signals. On the other hand, there is no such obstacle that can perform better in passive sensor-based landmine detectors depending on the design criteria. Therefore, in this study, a prototype design including passive sensor with magnetic anomaly method has been developed and shown. For the performance analysis of this detector, real landmines are used and the designed system is tested with different distance values in different soil types. The results show that the prototype produced successfully detects different types of landmines, is assertive in its lightness and only 1750 grams with its battery, providing sensitivity as well as advantages such as ease of use and low cost. It also shows the feature of being the first handheld landmine detector based on magnetic anomaly.

Effect of Partial Ground and Partial Ceiling on Propeller Performance

Finite extent flat obstacles behind a propeller (“partial ground”) and ahead of the propeller (“partial ceiling”) were examined experimentally for a small-scale fixed-pitch propeller in hover. Cases included circular and annular plates, which can be summed up or superimposed. Near-surface smoke and flow visualization show a projected time-averaged streamline on the ground plate, dividing a swirling flow inboard and a radial flow outboard. The flow pattern was juxtaposed with pressure data on the ground plate. Changes in propeller thrust and power due to ground/ceiling effect were measured by a force balance and correlated with flow visualization. For a plate of diameter equal to that of the propeller, ground effect on thrust and power was comparable to that of an “infinite” plate, while the flowfield also resembles that of the infinite plate. For a plate of less than half of the propeller diameter, ground or ceiling effect was found to be negligible. Thrust and power effects for circular and respective annular plates were superimposed to determine whether the increase in thrust or decrease in power required is itself additive to the respective effects seen with the constituent obstacles. For ceiling effect, this holds but less so for ground effect. A curve fit to thrust and power data resulted in a predictive model accurate to within 6%.

Comparative Analysis of the Self-Propelled Locomotion of a Pitching Airfoil near the Flat and Wavy Ground.

In this paper, a pitching airfoil near flat and wavy ground is studied by numerical simulations. The kinematic features of the airfoil and the flow field around it are analyzed to reveal unsteady vorticity dynamics of the self-propelled airfoil in ground effect. The optimal pitching periods at different initial heights above flat ground are obtained, which make the pitching airfoil achieve the maximum lift-to-drag ratio. Compared with flat ground, at the same initial height, the optimal pitching periods vary with the shape of ground. The structure and the strength of the wake vortices shedding from the airfoil are adjusted by the wavelength of ground. This leads to the changes of amplitude and occurrence times of the peak and valley of lift and drag force. The results obtained in this study can provide some inspiration for the design of underwater vehicles in the ground effect.

Antioxidant and anticancer properties of nano and fermented-nano powders of wheat and rice by-products

In this study, nano and fermented-nano powders of wheat and rice by-products were prepared by superfine grinding of raw and solid-state fermented materials. Effects of fermentation and superfine grinding on phytochemical content, phenolic acids profile as well as antioxidant and anticancer activity were investigated. The results revealed that, phenolic contents of fermented-nano wheat bran (FNWB), fermented-nano wheat germ (FNWG) and fermented-nano rice bran (FNRB) increased by 40.5, 59.2 and 27.9%, respectively compared to their raw samples. The free, conjugated and bound forms of most identified phenolic acids apparently increased. Also, the antioxidant activity of nano and fermented-nano forms significantly increased compared to its raw materials. The anticancer activity of nano and fermented-nano materials against human colon cancer cell line (HCT 116) increased compared to its raw materials. Nano rice bran (NRB) extract was the most effective one with IC50 value of 4.10 mg/mL under the investigated condition. The obtained results indicated that superfine grinding and solid-state fermentation could change the rigid microstructure and liberate bioactive compounds, which enhanced their bio-accessibility and bioavailability to improve bran functionality and usability.

Research on the Effects of Two-Sided Ground Surcharge/Unloading on Existing Shield Tunnels

For the effect of two-sided sudden surcharge/unloading on existing shield tunnels, an indoor dimensional reduction model test was conducted at a scale of 1:15.5, measuring the ground settlement, lateral convergence of the shield tunnel, and additional surrounding pressure after changing the location and soil quality of surcharge/unloading, and an analysis was carried out. The results showed that the location of the maximum transverse convergence value of the existing shield tunnel is related to the position of the surcharge; when surcharging on both sides of the tunnel, as the position of the left surcharge’s offset increases from 0.2 m to 0.6 m, the transverse convergence value of the tunnel first increases and then becomes smaller; the ground settlement value of each measurement point in the unloading process also increases and then becomes smaller. The settlement value of each measurement point first increases and then decreases, and the alleviation effect of unloading on ground settlement is not obvious; after surcharge on one side of the tunnel, if the other side continues to surcharge, it will lead to a continued increase in the surrounding pressure. Unloading can effectively reduce the additional surrounding pressure of the tunnel, but the additional surrounding pressure cannot be immediately and completely eliminated; compared with dry sand, the maximum value of lateral convergence of the tunnel in wet sand is significantly decreased, and the peak value of ground settlement on both sides is not significant; when both sides are surcharged to 172 kg, the additional soil pressure of the tunnel’s subsoil shows three peaks, one of which occurs at measurement point 4 at the bottom of the tunnel, which may be due to the occurrence of stress concentration at the location.

Static aeroelastic instability analysis of an inverted plate in ground effect and comparison with a wind-tunnel test

This paper visits the static instability of an inverted cantilevered plate in axial flow with the ground effect. This plate model is clamped at the trailing edge, and its leading-edge is allowed to move freely. A theoretical analysis strategy and corresponding convergent numerical solutions are reported and compared with a wind-tunnel experiment. In theory, we try a new way to study such an instability problem. We derive the instability equation by operator theory in state-space formulation and model such an instability problem as a mathematical function approximation problem. Glauert’s expansion and the least square method are applied for the numerical solutions of vorticity in ground effect using the mirror image method. The unknown function of the plate slope is expanded as a series of essential polynomial functions based on the Weierstrass theorem, and the least square method is applied for its numerical solutions. The experimental study develops a multi-point contact method using a control rod to preload the tested plate with a slight static deformation close to its natural modal shape. The contact state change between the initially deformed tested plate and the control rod is reflected by the evolution of the voltage output of a designed circuit. A criterion for determining the critical condition of plate instability is established based on such voltage change, and it has a better anti-interference ability to the flow. Results show that the present theoretical analysis agrees well with the experiment and other archived theories. The critical plate slopes (i.e., the plate instability modes) are not dependent on the ground confinement. This conclusion allows us to establish an analytical approximation between the critical dynamic pressure and the ground confinement. The present study and results can successfully predict the plate instability in the ground effect.

Safety Control for Quadrotor UAV Against Ground Effect and Blade Damage

This article proposes a safety control scheme for quadrotor unmanned aerial vehicle (UAV) to counteract ground effect and blade damage. The impacts of ground effect and blade damage are quantitatively analyzed in the established model. The proposed safety control scheme consists of position and attitude loops. Specifically, a proportional and derivative controller is designed as a baseline control with acceleration feedforward in the position loop. A disturbance observer (DO) using the measured Euler angles is exploited to estimate the lumped disturbance forces. The developed DO can effectively mitigate the estimation deviation caused by the angle tracking error. Subsequently, differential flatness theory is used to obtain the Euler angle references and the derivatives. In the attitude loop, sliding mode control and fixed-time sliding mode observer (SMO) are integrated to deal with ground effect and blade damage promptly. To demonstrate the effectiveness of the proposed safety control scheme, flight experiments are carried out, where the quadrotor UAV flies close to the rugged ground in the presence of blade damage.