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This study investigates the influence of atmospheric stability and ground effects on wind turbine wake recovery, challenging the conventional linear relationship between turbulence intensity and wake expansion coefficient. Through comprehensive field measurements and numerical simulations, we demonstrate that the linear wake expansion assumption is invalid at far-wake locations under high turbulence conditions, primarily due to ground effects. We propose a novel nonlinear wake expansion model that incorporates both atmospheric stability and ground effects by introducing a logarithmic relationship between the wake expansion coefficient and turbulence intensity. Validation results reveal the superior prediction accuracy of the proposed model compared to typical engineering wake models, with root mean square errors of wake wind speed predictions ranging from 0.04 to 0.063. The proposed model offers significant potential for optimizing wind farm layouts and enhancing overall wind energy production efficiency. [ABSTRACT FROM AUTHOR]

Near-ground flight is an important state of microducted fan aircraft. To explore the ground effects on the aerodynamic performance of microducted fan systems in near-ground hovering, a full three-dimensional (3D) numerical simulation methodology, which was validated by current experiments, is established in this paper. First, the hovering performance of ducted fan systems without ground effects was studied. Taking the system without ground effects as the reference, the ground effects due to altitude and slope were calculated and analyzed. The simulation results revealed that compared with the results of the current experiments, the maximum prediction error of 6% is reached when the induced power is 30 W. This indicates that the simulation methodology can work effectively. Moreover, a comparison of the performance of the system without ground effects revealed that ground effects can be ignored when the system altitude is greater than the duct length. In contrast, when the system altitude is within the duct length, the mass flow rate can greatly decrease with decreasing system altitude. This is because the blocking effect from the ground becomes significant. Additionally, the ground slope makes the flow field of the ducted fan system asymmetric. Globally, the system is not as sensitive to ground slopes within 18° because the ground effects for both sides of the ducted system are balanced to a certain extent. A side away from the ground can enhance the aerodynamic performance of the system. However, the other side close to the ground weakens the system performance. The mass flow and thrust performance can increase slightly when the slope is less than 12°, and the system behavior tends to stabilize when the slope is greater than 12°. Practical Applications: When microducted aircrafts are used to perform tasks, such as taking photos and ground detection, they are usually flown close to the ground, and alternate hovering with and without ground effects is frequently conducted. Thus, problems related to the aerodynamic interference between the terrain and the fuselage and between the fuselage and the rotor can occur. As shown in this study, the aerodynamic performance of ducted fan systems is affected by ground effects when ducted systems operate at an altitude of one times the duct length. In addition, at an altitude of 0.5 times the duct length, the thrust of the duct system increases with increasing slope within 18°. When the slope is greater than 12°, the influence of the slope from the left and right sides at the duct outlet is almost balanced. In general, the system altitude, ground slope and their effects on system performance need to be considered during the design process. The results can provide a design benchmark and optimization directions for designers, thereby reducing environmental constraints on ducted aircrafts and cost and improving the reliability. [ABSTRACT FROM AUTHOR]

Investigation of ground effects on Unmanned Aerial Vehicle (UAV) are limited. The UAV's ground effect on the water surface and irregular surfaces has not been studied well. The principal objective of this research is to apply numerical solutions to investigate the flow physics and aerodynamic characteristics of selected NACA4412 airfoil for different h/c and surface roughness conditions in the ground effect scenario. The k-ω turbulence model and compressible RANS equations are solved using the Finite Volume Method (FVM). The simulated data is authenticated with the reference data and compared with the DATCOM data. The results express that the lift coefficient variations for various surface roughness are affected by the h/c proportion. The drag coefficient for various roughness has the same pattern for different ratios and almost has the same difference from high to lower values. The result shows that the DATCOM code cannot predict the aerodynamic characteristics with ground effects. [ABSTRACT FROM AUTHOR]

Unmanned aerial vehicles (UAVs) are extensively employed in civilian and military applications because of their excellent maneuverability. Achieving fully autonomous quadrotor flight and precision landing on a wireless charging station in the presence of wind disturbance has become a crucial research topic. This paper presents a composite control technique for UAV altitude and attitude tracking in harsh environments, i.e., wind disturbance. A composite controller was developed based on nonlinear disturbance observer (NDOB) control theory to allow the UAV to land in the presence of random external wind disturbances and ground effects. The NDOB estimated the unknown wind disturbance, and the estimation was fed into the derivative sliding mode nonlinear disturbance observer-based control (DSMNDOBC), allowing the UAV to perform autonomous precision landing. Two loop designs were applied: the inner loop for stabilization and the outer loop for altitude tracking. The quadrotor model dynamics and the proposed controller, DSMNDOBC, were simulated employing MATLAB/Simulink®, and the results were compared with the one obtained by the proportional derivative (PD) controller and the sliding mode controller (SMC). The simulation results indicated that the DSMNDOBC has superior altitude and attitude control compared to the PD and SMC controllers and better disturbance estimation and attenuation performance. [ABSTRACT FROM AUTHOR]

The main objective of this study is to investigate the impact of ground effects on the aerodynamic coefficients of a delta wing aircraft model. Since the flow on the delta wing exhibits vortical flow inherently, it is crucial to examine the influence of ground effects under these conditions. An experimental study was conducted to enhance understanding of the aerodynamic behavior of an aircraft model incorporating a delta wing-body-vertical tail. Experiments were conducted in a subsonic wind tunnel with a test section measuring 2.8m x 2.2 m. Measurements were taken using a sting type balance to determine the aerodynamic forces and moments. All experimental tests were performed at a Reynolds number of 1.5 x 106, with the specific aim of examining and identifying the influence of the ground on aerodynamic coefficients. To investigate how ground effect affects the aerodynamic performance of the model, a fixed plate with an adjustable height was placed underneath it. The distance between the model and the ground was varied, and resulting data indicated that increased proximity to the ground improved longitudinal static stability. The results revealed that the presence of the ground plane resulted in a 6% increase in the maximum lift coefficient. Meanwhile, the lift increases around 25% due to ground effects at an angle of attack of 14° as it approaches the ground. The lift coefficient was enhanced across all angles of attack, while the induced drag coefficient decreased, resulting in an overall increase in aerodynamic efficiency. The lift curve slope saw a 16.9% increase when the model's height from the ground plane was less than half of the wing span. As the height decreased further, the aerodynamic center shifted backward, leading to an increase in longitudinal static stability. The rolling moment and yawing moment coefficients becomes unstable at angles of attack above 30°. [ABSTRACT FROM AUTHOR]

This study investigates the influence of atmospheric stability and ground effects on wind turbine wake recovery, challenging the conventional linear relationship between turbulence intensity and wake expansion coefficient. Through comprehensive field measurements and numerical simulations, we demonstrate that the linear wake expansion assumption is invalid at far-wake locations under high turbulence conditions, primarily due to ground effects. We propose a novel nonlinear wake expansion model that incorporates both atmospheric stability and ground effects by introducing a logarithmic relationship between the wake expansion coefficient and turbulence intensity. Validation results reveal the superior prediction accuracy of the proposed model compared to typical engineering wake models, with root mean square errors of wake wind speed predictions ranging from 0.04 to 0.063. The proposed model offers significant potential for optimizing wind farm layouts and enhancing overall wind energy production efficiency.

The main objective of this study is to investigate the impact of ground effects on the aerodynamic coefficients of a delta wing aircraft model. Since the flow on the delta wing exhibits vortical flow inherently, it is crucial to examine the influence of ground effects under these conditions. An experimental study was conducted to enhance understanding of the aerodynamic behavior of an aircraft model incorporating a delta wing-body-vertical tail. Experiments were conducted in a subsonic wind tunnel with a test section measuring 2.8 m × 2.2 m. Measurements were taken using a sting type balance to determine the aerodynamic forces and moments. All experimental tests were performed at a Reynolds number of 1.5 × 106, with the specific aim of examining and identifying the influence of the ground on aerodynamic coefficients. To investigate how ground effect affects the aerodynamic performance of the model, a fixed plate with an adjustable height was placed underneath it. The distance between the model and the ground was varied, and resulting data indicated that increased proximity to the ground improved longitudinal static stability. The results revealed that the presence of the ground plane resulted in a 6% increase in the maximum lift coefficient. Meanwhile, the lift increases around 25% due to ground effects at an angle of attack of 14° as it approaches the ground. The lift coefficient was enhanced across all angles of attack, while the induced drag coefficient decreased, resulting in an overall increase in aerodynamic efficiency. The lift curve slope saw a 16.9% increase when the model’s height from the ground plane was less than half of the wing span. As the height decreased further, the aerodynamic center shifted backward, leading to an increase in longitudinal static stability. The rolling moment and yawing moment coefficients becomes unstable at angles of attack above 30°.

Unmanned aerial vehicles (UAVs) are extensively employed in civilian and military applications because of their excellent maneuverability. Achieving fully autonomous quadrotor flight and precision landing on a wireless charging station in the presence of wind disturbance has become a crucial research topic. This paper presents a composite control technique for UAV altitude and attitude tracking in harsh environments, i.e., wind disturbance. A composite controller was developed based on nonlinear disturbance observer (NDOB) control theory to allow the UAV to land in the presence of random external wind disturbances and ground effects. The NDOB estimated the unknown wind disturbance, and the estimation was fed into the derivative sliding mode nonlinear disturbance observer-based control (DSMNDOBC), allowing the UAV to perform autonomous precision landing. Two loop designs were applied: the inner loop for stabilization and the outer loop for altitude tracking. The quadrotor model dynamics and the proposed controller, DSMNDOBC, were simulated employing MATLAB/Simulink®, and the results were compared with the one obtained by the proportional derivative (PD) controller and the sliding mode controller (SMC). The simulation results indicated that the DSMNDOBC has superior altitude and attitude control compared to the PD and SMC controllers and better disturbance estimation and attenuation performance.

Modeling atmospheric dispersion of flammable and toxic gases is very common in the industry. There is a large spectrum of different models, from Gaussian, Integral, up to computational fluid dynamics (CFD) models. However, these simple engineering models (Gaussian, Integral) do not always correctly estimate the dispersion of gases with a density higher than air. The purpose of this paper is to present an alternative/new model Ventjet dedicated to the atmospheric dispersion of various gases, including light gases (hydrogen, methane, etc.), neutral gases (nitrogen, oxygen), and heavy gases (CO2, LNG, etc.). Ventjet takes into account various weather condition profiles, namely neutral D and stable F. The effect of the ground is also integrated into Ventjet. Ventjet can be used for various releases, including vertical, angled, and even into the wind. Ventjet has been broadly validated versus multiple measurements from wind tunnel and field experiments, as well as CFD simulations. [ABSTRACT FROM AUTHOR]

Ground effects on arc-shaped conformal dielectric resonator antennas (DRAs) working in the TE11δz mode are investigated and utilized to attain various radiation performances. Manipulation of directivity patterns are achieved with the help of the three-dimensional curved metal ground. The backlobe, beamwidth, broadside gain, backscattering, and cross-polarization level of the antenna are all readily controllable. The geometric theory of diffraction is applied to provide an intuitional explanation for the radiation changes. Detailed analysis is then conducted from the perspective of ground current. It is found that the current distribution is affected by configurations of both the arc DRA and ground plane. Based on this, analytical methods are developed to calculate the ground effects exclusively for conformal arc-shaped DRAs. Next, the design theory of arc DRAs with curved ground is proposed. To demonstrate it, two conformal DRAs owning directional and wide beams, respectively, are designed as paradigms. At last, a prototype is fabricated and measured for validation.

The significant influence of the ground on the hypervelocity jet flow as well as the stability of the projectile cannot be discarded due to the intensity and the wide influence range. The present study examines two three-dimensional simulation models, one with the ground effects included and the other without, based on FLUENT software, using the finite volume method (FVM). The simulation models couple the FVM model with a standard k-ε turbulence model and unstructured dynamic grid based on the Local Remeshing method. An intermediate ballistic model and the six-degrees-of-freedom model are also utilized. For the 300-caliber 1730 m/s countermass propelling gun, two different flow phenomena, with and without the ground effects, were examined. The simulation results indicate that the effect of the ground surface on the jet flow and the projectile emerged gradually at 1.5 ms. The hypervelocity muzzle shock wave was reflected off the ground, creating a new shock-wave phenomenon in the opposite direction. The wave system interacted with the muzzle shock wave so that the pressure in the lower half of the domain was significantly higher than that in the upper half. This phenomenon produced a complete shock-wave surface. Shock waves at the ground produced a vortex, which gradually expanded and developed. The wavefront, which was formed by the ground reflection, led to a new wavefront, producing vortices at the wavefront and propagated towards the front and rear of the main shock wave. The hypervelocity jet flow twisted and generated a more complex wave system. The distorted gas jet caused the projectile to be disturbed, and the lift and torque were influenced so that the parameters such as the angular velocity of the rotation were changed.

This article studies nonlinear system identification of a small scale and flybar-free unmanned helicopter, the Trex450 chopper, built using commercial off-the-shelf components. We employ the real-time input–output data, obtained from human-controlled flight tests, operating the aircraft under severe ground effects during the vertical flight maneuvers. We highlight the efficacy of the entropy fuzzy system identification method with respect to the performance of several well-known nonlinear system identification techniques (i.e., a Takagi–Sugeno Fuzzy system, an adaptive neuro-fuzzy inference system (ANFIS), and a nonlinear autoregressive with exogenous (NARX) model) as our benchmarks. Our research confirms the benefits of the entropy fuzzy identification technique. Despite being nonlinear, the proposed fuzzy model is relatively simple, transparent, and highly accurate to represent the complex non-linear dynamic behaviors of our unmanned helicopter under severe ground effects. Another major advantage of the proposed system identification technique is its ability to avoid overfitting, an essential requirement in modeling. Overall, the fuzzy system is also capable of achieving a delicate balance between maximizing the accuracy while minimizing the complexity of the acquired model. [ABSTRACT FROM AUTHOR]

This research has provided the results for a static test of a conceptual advanced jet trainer (CAJT) aircraft in a low-speed wind tunnel within take-off and landing angle of attack limits. Test data includes longitudinal aerodynamic properties in take-off and landing phases. The analysis includes characteristics for lift and longitudinal stability, horizontal tail effectiveness, and studying the ground effect on the longitudinal aerodynamic properties. The tests have a Reynolds number of more than 1 million. Experiments were conducted in a low-speed, closed-circuit wind tunnel with a test section of 2.2 m width and 2.8 m height. The tests consist of measuring aerodynamic forces and moments using the six-component balance for strain metering. The slope of lift coefficient curve, lift coefficient value, and maximum aerodynamic efficiency value increase due to the presence of the ground. Also, the total aerodynamic center location moves backward as a result of the presence of the ground. It was observed by comparing the data for ground effect with those for out-of-ground effect that ground proximity significantly increases horizontal tail effectiveness as a component of pitching moment control. [ABSTRACT FROM AUTHOR]

A severe rainfall event occurred in southern Calabria between 29 October and 2 November 2015, causing two deaths and serious damage to transport infrastructure. Widespread slope erosion and thousands of shallow landslides were triggered on the slopes, combined with flooding and transport of debris along the streams. Rains recorded by the regional gauge network and the national radar monitoring system were analysed by means of Kriging techniques. Ground effects were surveyed in the field, and mapped using post-event air photos taken along the coastal sector. Shallow landslides, soil erosion (including sheet, rill, and gully erosion), flooding, lateral erosion, and debris deposition along streambeds, overflow on lateral slopes, and fan deposition at the mouths of the streams were mapped at 1:60,000 scale. Isohyets of the rainfall event – in terms of cumulative maxima over 24 h – are also shown on the Main Map. In Annex A, a list of notices of processes and/or damage, arranged by municipalities, with coordinates, types of ground effect, and synthetic descriptions, is also provided.

The present study investigated the ground effects on the VIV of a closed box girder based on wind tunnel tests and numerical methods. First, we presented a vibration measurement system for wind-tunnel test to simulate ground effects on the bridge girder. Second, we investigated the Strouhal number (St), the VIV lock-in phenomena over a range of wind velocities, and the maximum VIV amplitudes and their change laws in correlation with the height from the ground in two different ground conditions. The outcomes showed the following: that a low height from the ground can lead to high St numbers; that ground effects did not change the width of VIV lock-in range, but did impel VIVs to occur earlier in the uniform flow field; and that the maximum VIV amplitudes was reduced and the VIV lock-in range narrowed in the turbulent flow field. Finally, we conducted the numerical simulation method to study the ground effect mechanism on VIVs. The numerical results showed that the periodic vortex shedding will generate periodic forces on the structure, which leads to the occurrence of VIVs. Ground effects can speed up vortex shifting, whereas aerodynamic forces on the deck are weakened. [ABSTRACT FROM AUTHOR]

Abstract The aerodynamic loads that the bridge deck experiences as a result of interactions with the ground are not well studied when bridges are constructed at low heights from the ground. Flutter stability is the primary goal in the modern bridge wind-resistant design. Therefore, it is necessary to investigate the ground effects on the flutter stability and its influence mechanism. The present study investigated the ground effects on the flutter stability of a closed box girder based on wind tunnel tests and numerical simulations method. First, we presented a vibration measurement system for wind-tunnel test to simulate static ground effects on the bridge girder. Second, we investigated the system torsional damping ratios, the flutter derivatives, and the flutter critical wind speeds and their variation laws correlated with the heights from the ground in two flow fields (two different ground conditions) through a series of wind tunnel tests. The outcomes showed the following: that there is an approximate linear relationship between the height from the ground and the flutter critical wind speed in the uniform flow field, but this does not appear in the turbulent flow field; that the flutter critical wind speed dramatically decreases when the height from the ground is reduced in the uniform flow field; that the ground effects increase the absolute values of H* 3 and A* 1 , thus resulting in faster growth in negative aerodynamic damping induced by the coupling effects of the torsional and heaving motions; and that the flutter derivative A* 2 shows a tendency from negative to positive and ground effects make this tendency occur in advance at + 3 °wind attack angle. Finally, we applied the numerical simulations method to study the ground effect mechanism on the flutter stability. The calculated flutter critical wind speeds are in agreement with test results. The numerical results showed that existence of ground boundary layer generally reduces the flow speed in the region between the deck and the ground and increases both the positive pressure on the stagnation point of the lower surface and the local negative pressure on the upper surface. As a result, the positive and negative pressure increase as the height from the ground decreases, leading to large aerodynamic forces on the section, the flutter critical wind speed consequently decreases. Highlights • Flutter critical wind speed decreases as the deck comes closer to the smooth ground. • Ground effects increase the absolute values of H* 3 and A* 1. • Ground effects results in faster growth in negative aerodynamic damping ratio. • The positive and negative pressure increase as the height from the ground decreases. • Ground effects negatively influence the flutter stability of the closed box girder. [ABSTRACT FROM AUTHOR]

The significant influence of the ground on the hypervelocity jet flow as well as the stability of the projectile cannot be discarded due to the intensity and the wide influence range. The present study examines two three-dimensional simulation models, one with the ground effects included and the other without, based on FLUENT software, using the finite volume method (FVM). The simulation models couple the FVM model with a standard k-ε turbulence model and unstructured dynamic grid based on the Local Remeshing method. An intermediate ballistic model and the six-degrees-of-freedom model are also utilized. For the 300-caliber 1730 m/s countermass propelling gun, two different flow phenomena, with and without the ground effects, were examined. The simulation results indicate that the effect of the ground surface on the jet flow and the projectile emerged gradually at 1.5 ms. The hypervelocity muzzle shock wave was reflected off the ground, creating a new shock-wave phenomenon in the opposite direction. The wave system interacted with the muzzle shock wave so that the pressure in the lower half of the domain was significantly higher than that in the upper half. This phenomenon produced a complete shock-wave surface. Shock waves at the ground produced a vortex, which gradually expanded and developed. The wavefront, which was formed by the ground reflection, led to a new wavefront, producing vortices at the wavefront and propagated towards the front and rear of the main shock wave. The hypervelocity jet flow twisted and generated a more complex wave system. The distorted gas jet caused the projectile to be disturbed, and the lift and torque were influenced so that the parameters such as the angular velocity of the rotation were changed. [ABSTRACT FROM AUTHOR]

This brief note aims to describe the history, from its early original idea, of the new macroseismic scale: The Environmental Seismic Intensity Scale 2007 (ESI 2007). It can be used together with other existing scales or alone when needed for measuring the intensity of an earthquake on the basis of the primary and secondary effects of a seismic event on the natural environment. These effects could be the major sources of earthquake hazards, as recently proved. This note also aims to contribute to the understanding of processes that induced the researcher to develop an idea, to pursue it, and bring it to its end, first through the help of valuable Italian researchers and then through the constructive exchange of ideas with researchers of different cultural backgrounds operating almost everywhere in the world. This note is sponsored and approved by the International Union for Quaternary Research (INQUA), and the Environmental Seismic Intensity scale (ESI-07) was published in 2007 after a revision process of about eight years.

On 15th November 2017, the Pohang earthquake (Mw 5.4) had strong ground shaking that caused severe liquefaction and lateral spreading across the Heunghae Basin, around Pohang city, South Korea. Such liquefaction is a rare phenomenon during small or moderate earthquakes (MW < 5.5). There are only a few examples around the globe, but more so in the Korean Peninsula. In this paper, we present the results of a systematic survey of the secondary ground effects—i.e., soil liquefaction and ground cracks—developed during the earthquake. Most of the liquefaction sites are clustered near the epicenter and close to the Heunghae fault. Based on the geology, tectonic setting, distribution, and clustering of the sand boils along the southern part of the Heunghae Basin, we propose a geological model, suggesting that the Heunghae fault may have acted as a barrier to the propagation of seismic waves. Other factors like the mountain basin effect and/or amplification of seismic waves by a blind thrust fault could play an important role. Liquefaction phenomenon associated with the 2017 Pohang earthquake emphasizes that there is an urgent need of liquefaction potential mapping for the Pohang city and other areas with a similar geological setting. In areas underlain by extensive unconsolidated basin fill sediments—where the records of past earthquakes are exiguous or indistinct and there is poor implementation of building codes—future earthquakes of similar or larger magnitude as the Pohang earthquake are likely to occur again. Therefore, this represents a hazard that may cause significant societal and economic threats in the future.

When bridges are constructed with lower heights from the ground, the fonned channel between the deck and the ground will inevitably hinder or accelerate the air flow. This in turn will have an impact on the aerodynamic forces on the deck, which may result in unexpected wind-induced responses of bridges. This phenomenon can be referred to "ground effects." So far, no systematic studies into ground effects on the wind-induced responses of closed box girders have been perforated. In this paper, wind tunnel tests have been adopted to study the ground effects on the aerodynamic force coefficients and the wind-induced responses of a closed box girder. In correlation with the heights from the ground in two ground roughness, the aerodynamic force coefficients, the Strouhal number (S,), the vortex-induced vibration (VIV) lock-in phenomena over a range of wind velocities, the VIV maximum amplitudes, the system torsional damping ratio, the flutter derivatives, the critical flutter wind speeds and their variation laws correlated with the heights from the ground of a closed box girder have been presented through wind tunnel tests. The outcomes show that the ground effects make the vortex-induced phenomena occur in advance and adversely affect the flutter stability. [ABSTRACT FROM AUTHOR]

Utilizing the body surface as the signal transmission medium, capacitive coupling human body communication (CC-HBC) can achieve a much higher energy efficiency than conventional wireless communications in future wireless body area network (WBAN) applications. Under the CC-HBC scheme, the body surface serves as the forward signal path, whereas the backward path is formed by the capacitive coupling between the ground electrodes (GEs) of transmitter (TX) and receiver (RX). So the type of communication benefits from a low forward loss, while the backward loss depending on the GE coupling strength dominates the total transmission loss. However, none of the previous works have shown a complete research on the effects of GEs. In this paper, all kinds of GE effects on CC-HBC are investigated by both finite element method (FEM) analysis and human body measurement. We set the TX GE and RX GE at different heights, separation distances, and dimensions to study the corresponding influence on the overall signal transmission path loss. In addition, we also investigate the effects of GEs with different shapes and different TX-to-RX relative angles. Based on all the investigations, an analytical model is derived to evaluate the GE related variations of channel loss in CC-HBC. [ABSTRACT FROM PUBLISHER]

Numerical calculations, scale model experiments and real-life implementations have shown that the insertion of a closely spaced array of low parallel walls of finite dimension beside a road is potentially useful for road traffic noise abatement. However, previous studies did not consider atmospheric effects. In this work, numerical techniques have been used to predict the sound reduction provided by a low parallel wall structure, subject to wind and temperature related atmospheric effects. Three full-wave prediction schemes show very good agreement when looking at the insertion loss of a low 6 m wide parallel wall structure, consisting of 24 regularly spaced 0.2-m high rigid walls. Meteorological effects are predicted not to deteriorate the insertion loss (relative to rigid flat ground) of the parallel wall array in the low frequency range. However, at high sound frequencies the insertion loss is strongly reduced by downward refraction at a distance of 50 m in case of strong wind. Consequently, overall A-weighted road traffic noise insertion loss will be significantly lower during wind episodes. Although weak turbulence does not alter the energy time-averaged insertion losses, strong turbulence reduces the noise shielding in the high frequency range also. As with conventional noise walls, when considering use of low parallel wall structures for noise reduction outdoors, even at short distances, atmospheric effects should be considered. [ABSTRACT FROM AUTHOR]

A severe rainfall event occurred in southern Calabria between 29 October and 2 November 2015, causing two deaths and serious damage to transport infrastructure. Widespread slope erosion and thousands of shallow landslides were triggered on the slopes, combined with flooding and transport of debris along the streams. Rains recorded by the regional gauge network and the national radar monitoring system were analysed by means of Kriging techniques. Ground effects were surveyed in the field, and mapped using post-event air photos taken along the coastal sector. Shallow landslides, soil erosion (including sheet, rill, and gully erosion), flooding, lateral erosion, and debris deposition along streambeds, overflow on lateral slopes, and fan deposition at the mouths of the streams were mapped at 1:60,000 scale. Isohyets of the rainfall event – in terms of cumulative maxima over 24 h – are also shown on theMain Map. In Annex A, a list of notices of processes and/or damage, arranged by municipalities, with coordinates, types of ground effect, and synthetic descriptions, is also provided. [ABSTRACT FROM PUBLISHER]

Accurate knowledge of the per-unit length impedance of power cables is necessary to correctly predict electromagnetic transients in power systems. In particular, skin, proximity and ground return effects must be properly estimated. In many applications, the medium that surrounds the cable is not uniform and can consist of multiple layers of different conductivity, such as dry and wet soil, water, or air. We introduce a multilayer ground model for the recently proposed MoM-SO method, suitable to accurately predict ground return effects in such scenarios. The proposed technique precisely accounts for skin, proximity, ground, and tunnel effects, and is applicable to a variety of cable configurations, including underground and submarine cables. Numerical results show that the proposed method is more accurate than analytic formulas typically employed for transient analyses, and delivers an accuracy comparable to the finite-element method (FEM). With respect to FEM, however, MoM-SO is over 1000 times faster, and can calculate the impedance of a submarine cable inside a three-layer medium in 0.10 s per frequency point. [ABSTRACT FROM AUTHOR]

The availability of accurate and broadband models for underground and submarine cable systems is of paramount importance for the correct prediction of electromagnetic transients in power grids. Recently, we proposed the MoM-SO method for extracting the series impedance of power cables while accounting for the skin and proximity effects in the conductors. In this paper, we extend the method to include ground return effects and to handle cables placed inside a tunnel. Numerical tests show that the proposed method is more accurate than widely used analytic formulas, and is much faster than existing proximity-aware approaches, such as finite elements. For a three-phase cable system in a tunnel, the proposed method requires only 0.3 s of CPU time per frequency point, against the 8.3 min taken by finite elements, for a speed up beyond 1000 X. [ABSTRACT FROM PUBLISHER]

In this paper, the unconfined and semi-confined condensed phase explosions of TNT will be studied using large eddy simulations based on the unsteady, compressible, reacting, multi-species Navier-Stokes equations to gain further understanding of the physical processes involved in a condensed phase explosion and the effect of confinement on the physical processes involved. The analysis of the mixing and afterburning of TNT explosions in free air (unconfined) and near the ground (semi-confined) indicates that the combustion region of detonation products and air is determined by the vorticity patterns, which are induced by the Richtmeyer-Meshkov instabilities that arise during the explosion. When the explosive is detonated in the vicinity of a surface, the surface affects the shock propagation by creating complex shock systems, thereby changing the orientation of the vorticity, giving the afterburning a mushroom shape, and increasing performance of an explosive charge by prolonging the existence of the mixing layer and thereby the afterburning. [ABSTRACT FROM AUTHOR]

Abstract: The objective of this paper is to provide an investigation, using large eddy simulations, into the dispersion of aircraft jets in co-flowing take-off conditions. Before carrying out such study, simple turbulent plane free and wall jet simulations are carried out to validate the computational models and to assess the impact of the presence of the solid boundary on the flow and dispersion properties. The current study represents a step towards a better understanding of the source dynamics behind an airplane jet engine during the take-off and landing phases. The information provided from these simulations can be used for future improvements of existing dispersion models. [Copyright &y& Elsevier]

A recently presented fully probe-corrected near-field far-field transformation employing plane wave expansion and diagonal translation operators enables near-field far-field transformation for arbitrary measurement contours and arbitrary antennas. A multilevel extension, inspired by the multilevel fast multipole method, is presented that is suitable for the efficient transformation of electrically large antennas with a size of tens or even hundreds of wavelengths. The measurement points are grouped in a multilevel fashion and translations are carried out to the box centers on the highest level only. The plane waves are processed through the different levels to the measurement points using a disaggregation and anterpolation procedure resulting in a reduced overall complexity. In the second part of this paper, the influence of perfectly conducting ground planes and dielectric halfspaces, as an approximation for ground effects in a real measurement setup, is investigated. As such ground reflected waves are assumed, which propagate from the investigated antenna to the field probe and add to the direct wave contributions. The far-field conditions required for these assumptions are achieved by a source box grouping scheme. By this extension ground effects are directly considered within the near-field far-field transformation. Transformation results using simulated and measured near-field data are shown. [ABSTRACT FROM AUTHOR]

Propagation equation of magnetostatic waves in an arbitrarily magnetized yttrium-iron-garnet/gadoliniumgallium-garnet waveguide coated with perfect metal planes is obtained using the method of the surface magnetic permeability. And ground effects on magnetooptic Bragg cells are investigated with the magnetooptic coupled-mode theory. Theoretical analysis indicates that, diffraction efficiency of guided optical waves can be improved by adjusting the spacing of the metal plane from the ferrite film, and ground effects on the diffraction efficiency will be enhanced using an appropriately tilted bias magnetic field. In the metal clad waveguide system, the magnetostatic wave frequency at which the diffraction efficiency peak is obtained corresponds to the "zero-dispersion" point. Performance of RF spectrum analyzers in this system can also be improved by comparing with the case of the sandwich waveguide. Therefore, magnetooptic Bragg cells with the metal clad waveguide are potential applications to the microwave communication and optical signal processing. [ABSTRACT FROM AUTHOR]

Abstract: As the electromagnetic fields propagate over finitely conducting ground, selective attenuation of the high frequencies takes place. As a result, the signatures of broad-band electromagnetic radiation fields generated by lightning flashes change as they propagate over such ground. In addition to being a function of the electrical parameters of the ground over which the electromagnetic fields propagate, these propagation effects depend on the height of their source above ground level. This makes the propagation effects on radiation fields from cloud flashes differ from those on the radiation fields generated by return strokes in ground flashes. In this paper the propagation effects on radiation field pulses of cloud flashes are illustrated and it is shown that these effects are not as severe as those of return strokes in ground flashes. [Copyright &y& Elsevier]

Abstract: The flow induced by a finite disc rotating near horizontal ground is considered, including the effects of an underbody. This paper concentrates on determining the shape of the free layer beyond the rim of the disc which is horizontal in the absence of the underbody and ground but forced to deform to ensure that conditions across the layer are satisfied when the underbody or ground is added. The far-field behaviour, the inviscid flow produced by a nominally infinite disc near the ground and the global solution for small ground clearances are considered analytically, and the full problem is posed as an integral problem. This is then solved numerically and analytically. Results are presented for various heights of the disc above the ground and for discs with an axisymmetric underbody present. A universal form is found for the farfield shape (which is controlled by entrainment into the free layer) but both the underbody and the ground effects are found to increase very significantly for reduced clearances. [Copyright &y& Elsevier]

Abstract: The Eastern Betic Shear Zone (EBSZ) in the Betic Cordillera (southern Spain) accommodates part of the Neogene and Quaternary shortening between the Iberian and the African plates. Although the EBSZ is characterised by shallow low to moderate magnitude instrumental seismicity, it seems to be the source of several historical catastrophic events with MSK intensities ranging from VII to X. Despite the fact that it crosses a densely populated area, the seismogenic behaviour of the EBSZ is still poorly understood. The EBSZ is mainly formed by a set of NE–SW-trending left-lateral strike-slip faults, including the Alhama de Murcia and Albox faults. This paper presents a palaeoseismological study of the eastern Albox fault based on surface and trenching observations. This fault ruptures the surface and is probably seismogenic, with short-term slip-rates ranging from 0.01 to 0.4mm/a. Ground effects of at least two paleoearthquakes were detected: the first one took place not long before 660 years A.D. with an estimated maximum Mw of 6.5±0.1, whereas the second one occurred between 650 a.d. and the XVIII century. The latter produced only a centimetric offset and was not regarded as characteristic. The elapsed time is, therefore, ca. 660 years. The distribution of the long-term cumulative and the short-term ground effects suggest an eastwards migration of the fault tip. [Copyright &y& Elsevier]

In this paper, the convergence behaviour of the method of auxiliary sources (MAS) is studied in cases of simple three-dimensional (3D) problems with open regions. For the assessment of the convergence behaviour in such cases in a general manner, the cases considered herein consist in elemental electric dipoles radiating in the close proximity to a planar dissipative ground. Both vertically and horizontally oriented dipoles with respect to the ground plane are examined. The aim of the study is to investigate the interrelation between the auxiliary sources locations and the resultant field continuity errors. For this, the dependence of the boundary conditions errors on the number and spacing of the auxiliary sources is exhibited and general rules regarding their behaviour are extracted. Moreover, the influence of these errors on quantities of interest is examined. Finally, a few concluding remarks are outlined and their possible utilization in cases of more composite 3D problems is discussed. Copyright © 2004 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper, the convergence properties of the method of auxiliary sources (MAS) when applied to two-dimensional (2D) problems with open boundaries are studied. Although such problems have been examined in the past, the relation of the solution errors with the sources' locations has not been reported in detail. Herein, the convergence behavior in the case of a single infinite wire above a flat ground is thoroughly examined. The dependence of the boundary-condition errors on the number and spacing of the auxiliary sources is illustrated and general rules that govern their behavior are extracted. Finally, a few concluding remarks are outlined and their utilization for the advancement of the MAS is briefly discussed. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 39: 518–522, 2003 [ABSTRACT FROM AUTHOR]

Moderate to strong crustal earthquakes are generally accompanied by a distinctivepattern of coseismic geological phenomena, ranging from surface faulting to groundcracks, landslides, liquefaction/compaction, which leave a permanent mark in thelandscape. Therefore, the repetition of surface faulting earthquakes over a geologictime interval determines a characteristic morphology closely related to seismic potential. To support this statement, the areal distribution and dimensions of effects of recent historical earthquakes in the Southern Apennines are being investigated in detail. This paper presents results concerning the 26 July 1805 earthquake in the Molise region, (I = X MCS, M = 6.8), and the 23 November 1980 earthquake in the Campania and Basilicata regions (I = X MSK, Ms = 6.9). Landslide data are also compared with two other historical earthquakes in the same region with similar macroseismic intensity. The number of significant effects (either ground deformation or hydrological anomalies) versus their minimum distance from the causative fault have been statistically analyzed, finding characteristic relationships. In particular, the decay of the number of landslides with distance from fault follows an exponential law, whereas it shows almost a rectilinear trend for liquefaction and hydrological anomalies. Most effects fall within the macroseismic area, landslides within intensity V to VI, liquefaction effects within VI and hydrologicalanomalies within IV MCS/MSK, hence at much larger distances. A possible correlation between maximum distance of effects and length of the reactivated fault zone is also noted. Maximum distances fit the envelope curves for Intensity and Magnitude based on worldwide data. These results suggest that a careful examination of coseismic geological effects can be important for a proper estimation of earthquake parameters and vulnerability of the natural environment for seismic hazard evaluation purposes. [ABSTRACT FROM AUTHOR]

Cylinders and flat plates are important models for studying flow separation. If a surface is in free flow on the upper and lower surfaces, vortices of equal strength are formed in the opposite direction, and this symmetry causes the average force oscillations to be zero, but when the surface approaches the surface-ground, this symmetry disappears. In other words, in addition to several factors such as boundary layer formation and object geometry, altitude also affects the flow field, known as the ground effect phenomenon. In the present work, the behavior and structure of fluid flow around a plate in and out of the boundary layer of the ground are investigated using a finite volume method. After ensuring the desired numerical solution method, the effects of applying the plasma actuator to control the flow structure behind a plate in ground effect is investigated. The plate is placed on the boundary layer zone with the attack angle of 20 degrees. It is found that the separated flow is dependent on the distance between plate and ground. Specifically, turning on the plasma actuator leads to a significant reduction in the separation zone behind the plates. [ABSTRACT FROM AUTHOR]