Source Height Research Articles

A parametric study of long-range atmospheric sound propagation using Bellhop Ray-tracing Model

In the context of research on the measurement of long-range attenuation of noise from terrestrial sound sources, a parametric study of atmospheric sound propagation channel characteristics as a function of source height, ground characteristics and meteorological conditions is presented. The study relies on ray tracing. The Bellhop ray-tracing model which is well known in underwater acoustics has been used here. In this paper, the accuracy of Bellhop's predictions in the atmosphere is first addressed by comparison with published benchmarks cases by Attenborough et al and results from Salomon's ray model. No significant discrepancy was noticed with respect to these references. The second part of the paper presents a parametric study for source heights ranging from 0.05 m to 200 m, a grid of receivers at ranges between 200m and 2 km from the source and between 2 and 50 m height. A homogeneous flat absorbing ground described by a complex reflection factor is assumed. For the atmospheric conditions, a subset of the WiSi classification was considered. The results are analyzed from the point of view of the receiver and discussed in terms of attenuation, number of arrivals and number of reflections from the ground.

Estimating Polar Cap Density and Medium‐Frequency Burst Source Heights Using 2fce Roar Radio Emissions

AbstractCompeting theories exist for the generation mechanism of auroral medium‐frequency burst (MFB). In an effort to constrain MFB source heights, this study analyzes 33 events in which MFB and auroral 2fce roar co‐occurred at Sondrestrom, Greenland. Using measurements from an array of receiving antennas, direction‐of‐arrival calculations indicate that in a given co‐occurrence, the elevation angle of MFB typically is higher than that of roar. Ray tracing is used to determine source heights of the MFB signals. Density profiles are obtained from the International Reference Ionosphere (IRI) and shifted in magnitude until each event's roar signals originate at heights where the frequency‐matching condition for 2fce roar generation is satisfied. This shifting method is validated using density measurements from the Sondrestrom incoherent scatter radar (ISR) facility for the two events with available ISR data. After shifting, ray tracing demonstrates that in 25 of the 33 events, burst originates at a height of about 200 km, lower than the typical altitude of peak electron density. However, ISR measurements show that the density profile is enhanced at low altitudes while MFB is observed, peaking in the E region rather than the F region. This finding implies that the MFB sources at 200 km are on the topside of the density peak, in a region of downward pointing density gradient, in qualitative agreement with the mechanism of MFB generation by Langmuir waves in the topside ionosphere. These results also suggest a new method of estimating density in the polar cap using roar signals to calibrate IRI profiles.

The acoustics of the “clapping circle” at Purdue University

The unusual acoustical properties of a particular landscape architecture feature of Academy Park on the Purdue University campus have been the subject of speculation for years. The feature, known informally as the “clapping circle,” consists of sixty-six concentric rings of stone tiles. When someone claps while standing at the middle of the circle, they hear a high-pitched squeak immediately afterwards. Experiments were conducted by the Purdue student chapters of the Acoustical Society of America and the Audio Engineering Society to characterize this effect. The response to a clap played from an omnidirectional speaker placed at the center of the circle was recorded using a microphone positioned above the loudspeaker. Spectrograms of the recorded responses revealed the squeak to consist of a descending tone at around 1500 Hz, and its harmonics. This tone disappeared from the spectrogram when the tile rings were covered with absorbing blankets. A mathematical model based on scattering from the gaps between the tile rings reproduced the descending frequency of the squeak, and reproduced the effect of the source and receiver height on the rate of change of frequency. Thus, it was concluded that the squeak is an example of repetition pitch produced by the tile formation.

The 2017 September 6 Flare: Radio Bursts and Pulsations in the 22–5000 MHz Range and Associated Phenomena

Abstract For the 2017 September 6 flare (SOL2017-Sep-06T11:53) we present not only unusual radio bursts but also their interesting time association with the other flare phenomena observed in extreme ultraviolet (EUV), white-light, X-ray, and γ-ray emissions. Using our new method based on wavelets we found quasi-periodic pulsations (QPPs) in several locations of the whole time–frequency domain of the analyzed radio spectrum (11:55–12:07 UT and 22–5000 MHz). Among them the drifting QPPs are new and the most interesting, especially a bidirectional QPP at the time of the hard X-ray and γ-ray peaks and a sunquake start. In the pre-impulsive phase we show an unusual drifting pulsation structure (DPS) in association with the EUV brightenings caused by the interaction of magnetic ropes. In the flare impulsive phase we found an exceptional radio burst drifting from 5000 to 800 MHz. In connection with this drifting burst, we show a U burst at about the onset time of an EUV writhed structure and a drifting radio burst as a signature of a shock wave at high frequencies (1050–1350 MHz). In the peak flare phase we found an indication of an additional energy-release process located at higher altitudes in the solar atmosphere. These phenomena are interpreted considering a rising magnetic rope, magnetosonic waves, and particle beams. Using a density model we estimated the density, wave velocities, and source heights for the bidirectionally drifting QPPs, the density for the pre-impulsive DPS and U burst, and the density and magnetic field strength for the drifting radio burst.

Low Frequency Noise Analysis of Single Gate Extended Source Tunnel FET

This paper presents the analysis of noise in Single Gate Extended Source TFET (SG-ESTFET) considering the absence and presence of interface trap charges, when the device is subjected to scaling and variation of parameters like device gate length (Lg), extended source length and height, SiGe mole fraction (x), oxide thickness (tox), gate dielectric material, and frequency (f). Furthermore, the influence of variation of dimensionality and material parameters in presence of noise on Drain Current Noise Power Spectral Density (Sid) and Gate Voltage Electron Noise Power Spectral Density (Svgee) are studied for different trap charge conditions. Assuming Gaussian distribution of trap charges at the interface, it is perceived that the effect of noise is more as compared to the case of absence of trap charges. In reference to other FET devices, present paper reports that, the proposed SG-ESTFET device under absence of trap charges, illustrates an improved Sid and Svgee value of 1.4 × 10−29 A2/Hz and 5.21 × 10−16 V2/Hz, respectively whereas under the presence of trap charges, Sid and Svgee value are 6.6 × 10−26 A2/Hz and 8.74 × 10−12 V2/Hz, respectively. Moreover, this study also reports that the generation recombination (G-R) noise is mainly prevailing at low and mid-frequencies in presence of trap charges while diffusion noise is prevailing at high-frequencies. Likewise, the flicker noise is observed to be noteworthy at low and medium-frequencies in absence of trap charges.

Study on the Thermodynamic Properties of Concrete Surface during Microwave Deicing of Airport Pavement.

In the cold belt area, the icing phenomenon often appears on the airport pavement, which affects the safety of aircraft take-off and landing. Microwave deicing technology can effectively solve this practical problem and has many advantages. Taking microwave deicing technology as the research object and the surface temperature of pavement concrete as the index, an open microwave test system has been established in this paper. Based on this system, the temperature distribution, variation rule, and influencing factors of concrete have been studied systematically. The results show that the surface temperature of concrete increases linearly due to microwave action. In addition, during the microwave action, the temperature increase of the concrete surface is centered on the center point and shows a stepwise decreasing trend along the radius. At the same time, the increase of microwave source height leads to the increase of surface temperature distribution uniformity. The surface ice affects the rate of temperature increase of concrete in stages under microwave action, and the surface edge area remains frozen for a certain period of time. The temperature distribution of concrete surface is a decisive factor affecting the degree of ice removal, and the concrete surface will generate residual heat after the microwave action ends. This phenomenon can delay the regression of the temperature distribution of the concrete surface, thus effectively preventing the re-freezing of the ice layer.

Effects of elevated pool fire in a naturally ventilated compartment

This paper presents an experimental analysis of fire behavior due to elevated fuel pan with diesel in a fixed ventilated compartment of size 4 m (height) × 4 m (length) × 4 m (width) having door opening of 2 m (Hd) × 1 m (W). A reasonably large pool size of diameter 0.8 m is used in experiments so that the results may be useful for industrial fire hazard analysis. The variable parameter, taken as fire source height ‘h’ is from the floor that is 0.3 m, 0.6 m, 0.9 m, 1.2 m, 1.5 m and 1.8 m. During experimentation, it is observed that variation in pan height significantly affects the mass loss rate (MLR), heat release rate (HRR), flame behavior, smoke layer height, doorway mass flow and global equivalence ratio (GER). In case of higher elevated fire, HRR decreased drastically, one-fourth of maximum HRR value obtained in case of lower elevation of fire source. Lowest elevated pool fire shows good agreement for MLR and HRR with other experiment performed in an open space, i.e., well ventilated condition. For a significant elevated fire, the average fuel mass loss rate, flame temperature, smoke layer height, doorway mass flow rate and exit velocity were lower. With respect to above parameters, fire scenario inside the compartment seems to be less hazardous in case of higher elevated fire. A completely different trend has been found for the variation of GER with respect to MLR in current study.

Interactive effects of large- and local-scale environmental gradients on phenotypic differentiation.

Intraspecific differentiation across a steep environmental gradient depends on the relative influences of evolutionary, organismal, and environmental processes. But steep environmental gradients may be nested within larger-scale, regional conditions that could influence these processes at the local scale. Therefore, we hypothesized that phenotypic differentiation along a steep environmental gradient would vary among regions. To test this hypothesis, we conducted a reciprocal transplant experiment on rocky intertidal shores, a habitat characterized by gradients in abiotic and biotic stress, in three regions of the Gulf of Maine. We used the ubiquitous and ecologically important rockweed species Fucus vesiculosus to quantify differentiation in growth, tissue nitrogen, and nitrogen productivity between upper and lower intertidal individuals. We found that phenotypic differentiation between tide heights varied among traits and regions. Although tissue nitrogen did not vary among any treatment combinations, growth and nitrogen productivity response were region specific. A strong effect of transplant height was found in all regions; however, an effect of home (source) height was only detectable in the central Gulf of Maine. Our study reveals that intraspecific responses to steep environmental gradients vary among populations, but the mechanisms underlying these patterns remain unknown. Given the roles that rockweeds play as food and habitat, these in situ patterns of growth and nitrogen productivity could have important community- and ecosystem-level consequences.

Particle dispersion and deposition in displacement ventilation systems combined with floor heating

The aim of this study is to investigate dispersion and deposition characteristics of different particle diameters (0.5–5–10 μm) for a displacement ventilated and floor heated environment, experimentally and numerically. The experiments are performed in a reduced scale model with the operating parameters determined regarding to the similarity. Results are used to validate simulation outputs obtained via Eulerian-Lagrangian method. Three different outlet opening configurations and particle source heights are considered. Results are compared in terms of air change efficiency (ACE), average concentration of the room and the breathing height, contaminant removal effectiveness (CRE) and deposition fraction. It is disclosed that contaminant distribution is highly related with the outlet opening configuration and particle source position. Moreover, it is figured out that for the best ventilation strategy with the operating parameters to be determined, related performance indices and area of concern to be protected from particles must be well defined.

Wind-tunnel measurements and LES simulations of air pollutant dispersion caused by fire-induced buoyancy plume inside two parallel street canyons

A physical model consisting of two parallel street canyons with the fire room located in the windward side of the first street canyon was established. Large eddy simulation (LES) was employed to investigate the effects of air pollutant dispersion caused by the fire-induced buoyancy plume on the indoor and outdoor air quality. The effect of thermal buoyancy was firstly taken into account by burning the smoke cakes in wind-tunnel experiments under different Fr (Froude number) cases. Results show that the diffusion characteristics of smoke plume, temperature and velocity distributions by wind-tunnel measurements agreed well with the numerical models. According to the smoke soot’s effects on two street canyons, the dispersion of fire pollutants can be divided into three regimes. There exist two critical Fr, Frcrit,1=0.313 and Frcrit,2=0.389, at which the smoke plume begins to influence the 1st and 2nd street canyons, respectively. Moreover, the region areas of w < 0 (vertical velocity) can indirectly represent the concentration distribution of pollutants, and the temperature distribution is closely proportional to the distribution of pollutant (smoke plume, CO2 and CO) concentration, that is, where the plume concentration is high, the temperature is high. The quantitative formulas between Ucrit (Ucrit,1 and Ucrit,2) and the reference height (Zref) of the fire source at different floors were further confirmed. This study provides a new idea for visualizing the diffusion characteristics of fire pollutants, and is helpful for dealing with the building fire, personnel evacuation and emergency escape.

An Alternative Approach for High Uniformity Distribution of Indoor Lighting LED

A high accurately theoretical analysis for high uniformity illumination distribution on the ceiling of indoor lighting LED system based on the super-positions is proposed and performed. Starting from the non-uniform illumination distribution of two LED sources, the dependences of the uniformity ratio on the height of the LED source and the length of the ceiling are investigated. The low intensity in the region near the side-wall can be avoided by rotating the LED source with a small angle, but the low uniformity illumination distribution at the center of the ceiling still exists. The aim of this work proposes the alternative design and approach for several configurations and demonstrates that can be obtained high uniform illumination distribution. The redistributed factor of the illumination through the lens is also considered and calculated. The investigation of this work will be a general guideline for designing the high uniform LED indoor lighting systems as well as being valuable materials for the LED lighting manufacturing industry.

Likelihood maximisation techniques for ranging gunfire over grassland

A study into acoustic parameter inversion in the presence of a non-moving, homogeneous atmosphere and grassland impedance ground is carried out using methods of likelihood maximisation. Measured frequency-dependent sound pressure level and power spectra for a blank firing pistol are used to generate simulated data with added Gaussian error to represent variations usually present in real life experiments. Inference is carried out using maximum likelihood estimation (MLE) and maximum a priori (MAP) where model parameters are either given as known or restricted to some uncertain distribution bounded by realistic conditions. The quality of inference is assessed visually and statistically as the error between the true and inferred predictions for a given propagation range. Application of a prior (MAP) greatly improves inference accuracy compared to the sole maximisation of the likelihood function (MLE). It is shown that the use of a single octave band frequency window does not improve the quality of inference, whereas combinations of several low frequency octave bands do. Exact quantification of the true values of the ground and source height are seemingly less important as range increases beyond 500m. Although the techniques presented in this paper are for military/security applications, they are readily applicable to other acoustical problems, e.g. source characterisation in engineering noise control. The methods adopted are likely to benefit from higher-dimensional models, i.e. inhomogeneous atmospheres, complex terrain or urban environments.

Design of the controller module of mobile carrier radioactive source

A control module for mobile carrier radioactive source has been designed. Mobile carrier radioactive source is a tool used to carry out testing for radiation characteristics both statically and dynamically and to conduct calibration on the Radiation Portal Monitor according to the requirements of SNI IEC 62244-2016. The control module is designed to meet the that requirements, it can set a carrier speed of at least 8 km/h, it can adjust the height of the radioactive source between 1 m and 2.5 m, it has automatic forward and backward direction mode. Furthermore, the mobile carrier can be controlled remotely for personnel tester safety. The control module can stop the mobile carrier suddenly when an emergency occurs. The mobile carrier uses a portable power supply so that it can move freely and easily shifted. To meet these requirements, the driving power of the carrier a motor of 24-volt dc with 250 watts. The radioactive source uses a driving power of 12-volt dc motor with a minimum lift power of 5 kg. The control module designed uses a microcontroller with an android application-based interface that is connected by wireless. In the android application there are virtual numbers and input buttons to give commands to the control module. The application can also receive carrier speed information and the height of the radioactive source. To break the power of driving motor of carrier and the driving power of the lifter of the radioactive source, the mobile carrier uses two-level relays, namely low current conductivity relays and relays with high current conductivity. Next in order to move forward and backward automatically, at each end of the carrier is equipped with a limit switch. The button and top position barriers on the radioactive source lifter use a limit switch.

Sound propagation over underlying surface

The features of noise emission, when its source is located above the underlying (reflecting) surface, have been considered. The main factor determining the pattern of sound pressure distribution in space is the interference between sound waves incident on this surface and reflected from it. The influence of the height of the noise source above the underlying surface, as well as the acoustic characteristics of this surface, on this process has been analyzed.

Research on Fire Behavior of Ship Engine Room

Due to the need for high performance and reduced commercial cost of ownership, and due to many outstanding advantages such as high strength and light weight, steel has been widely used in engineering practice. In the case of fire, in order to prevent and protect these structures, it is the key issue to study the fire behavior environment. The engine room is also the source of power for ships. It is a high-risk area with frequent fires. Therefore, this paper mainly uses FDS to conduct numerical simulation research through a scaled-down engine room with a size of 3m×3m×3.5m. The change of temperature, pressure and smoke movement in the closed cabin with time at a fire source height of 1.5m is studied. The research shows that the fire behavior inside the closed cabin conforms to the two-zone model, and the fire suppression method of the closed fire has its significant advantages, And looked for the best time to reopen the cabin and the location of subsequent repair structures.

Morphology of traces of large blood drops on a snow-covered surface with different bleeding source height

Aim is to study morphology of the traces of a large drop of blood formed on snow-covered surface when it falls from different heights. In the experiment, we studied the morphology of blood drop traces fallen from 20, 50 and 100 cm on a just settled dry snow cover in a moderately frosty environment (-8 °C) Dropping from a height of up to 20 cm, a blood drop formed a cylindrical channel in the snow cover and spread out to form a disc-shaped element. However if the bleeding source was located at a 50 and 100 cm distance, an element close to a ball, consisting of blood crystals and ice was formed in the final section of the cylindrical channel. Morphology of the trace in freshly settled dry snow is due to the realization of the kinetic energy of a falling drop on the one hand, and the cooling of blood and crystallization on the other. Data obtained may be used to identify and describe traces of blood found on the scene in the street in the winter.

Perception of azimuth angle of sound source located at high elevation angle: Effective distance of auditory guide signal

In Japan, auditory guide signals are commonly installed in public spaces to lead visually handicapped pedestrians to their destinations. The sound sources of the signals are usually installed at high places on walls. In other words, the sound sources have not only an azimuth angle but also an elevation angle when viewed from the users. In the present study, under the hypothesis that the horizontal localization error increases with increasing elevation angle of the sound source, a sound localization test allowing head movement was performed to clarify the upper limit of the elevation angle. The results of the test were consistent with the hypothesis and indicated that the upper limit of the elevation angle was 65° within the range of the signal used in the present study and the assumption that the correct discrimination of eight directions is sufficiently accurate in the application of auditory guide signals. Furthermore, the effective distance of auditory guide signals, that is, the closest distance that users can approach to the destination using the signals was studied on the basis of the results of the present study. As a result, it was found that the effective distance of auditory guide signals does not exceed 1 m, in other words, the signals work effectively in the range horizontally farther than 1 m, when the height of the sound source is less than 3 m.

Design and Analysis of Dual Source Vertical Tunnel Field Effect Transistor for High Performance

An optimally designed Dual Source Vertical Tunnel Field Effect Transistors is proposed and investigated using technology computer aided design simulation. The vertical tunnel FET have dispersal of source channel drain in the vertical direction which will enhance the scalability of the simulated device. The benefit of the TFET is switching mechanism which is done by quantum tunnelling method through a barrier instead of thermionic emission over the barrier as that of conventional MOSFETs. The key of this paper, we have developed two-dimensional model of single drain with dual source n-type vertical tunnel field effect transistor. Further introduction to an ultra-thin channel among the drain and gate region will makes aggressive improvement in the numerical simulations of minimum threshold voltage (VT) of 0.15 V and average subthreshold slope of 3.47 mV/decade. The variation effect in the channel thickness, source height, drain doping, source doping, temperature and work function has been simulated and examined by 2D silvaco TCAD tool. High ON current and low OFF current is recorded as 1.74 × 10−4 A/µm and 6.92 × 10−13 A/µm respectively with ION/IOFF current ratio in order of 108 to 109.

Acoustic Emissions from Wind Turbine Blades

Research on broadband aerodynamic noise from wind turbine blades is becoming important in several countries. In this work, computer simulation of acoustic emissions from wind turbine blades are predicted using quasi empirical model for a three-bladed horizontal axis 3 MW turbine with blade length ~47 m. Sound power levels are investigated for source and receiver height of 80 m and 2 m above ground and located at a distance equal to total turbine height. The results are validated using existing experimental data for Siemens SWT-2.3 MW turbine having blade length of 47 m, as well as with 2.5 MW turbine. Aerofoil self-noise mechanisms are discussed in present work and results are demonstrated for wind speed of 8 m/s. Overall sound power levels for 3 MW turbine showed good agreements with the existing experiment data obtained for SWT-2.3 MW turbine. Noise map of single source sound power level, dBA of an isolated blade segment located at 75 %R for single blade is illustrated for wind speed of 8 m/s. The results demonstrated that most of the noise production occurred from outboard section of blade and for blade azimuth positions between 80° and 170°.

Multiple-relaxation-time lattice Boltzmann simulation of natural convection with multiple heat sources in a rectangular cavity

Natural convection and heat transfer in a square cavity with multiple heat sources was investigated through a multiple-relaxation-time (MRT) collision model and lattice Boltzmann method (LBM) in the current work. The MRT-LBM model was verified by a former experiment and numerical findings with different Ra numbers from 103 to 105, which proved the MRT-LBM model is effective to handle the flow and transfer. The heat transfer that developed inside the cavity was analyzed under different width, height, and lateral offset of heat source in this paper. Moreover, the change of spacing between two symmetrically distributed heat sources was discussed. The results showed that the heat exchange efficiency was augmented by increasing width, height, and spacing of the heater, but it was reduced by increasing lateral offset. Specifically, the Nusselt number of the upper wall decreased by increasing height of heat source, and the left and right walls showed better heat exchange efficiency by increasing height. Additionally, the lateral position had a notable influence on the left wall surface of the heat source, and the optimum heat exchange efficiency of the heat source’s left wall existed in the condition of small lateral offset.