Waves In Air Research Articles

LOADS ON SUBMERGED WALLS OF PROTECTIVE STRUCTURES

The intensification of military operations on the territory of Ukraine, which are accompanied by missile attacks and bombing of territories, requires the use of reliable protective structures. Modern codes require the provision of each new building with storage facilities that guarantee the safety of life and health of citizens, so the correct determination of all loads on the structural elements of protective structures is an urgent issue. Taking into acoount the fact that the previous codes were somewhat outdated and had limited access for a long time, a significant event was the adoption in 2023 of new codes for the design of protective structures of civil defence. The main requirements and recommendations of SBC B.2.2-5:20023 were taken into account when conducting research on determining the loads on buried walls of bomb shelters. Such structures, as we know, perceive a constant load from the lateral pressure of the soil, which during an explosion is supplemented by an episodic load from the action of an air wave. Modern specialized literature contains rather limited information on scientific research and development in the field of design of protective structures. An actual issue is also the study of the influence of determining factors on the intensity of the load on the walls of buried protective structures and the possibility of its adjustment in order to reduce it. Taking into account the nature of the distribution of loads on the underground walls of bomb shelters, a dependence was obtained to determine the resulting active pressure and quasi-static load caused by the action of an air wave. The pressures from the soil and the blast wave at different orientations of the contact wall and for different types of soil environment were studied. The loads in contact of a smooth and rough wall with sandy, sandy and loamy soils with different indicators of physical and mechanical characteristics were considered. The obtained results indicate a significant influence of the geometric parameters of the wall and the features of the contact soil on the resulting pressure, which can vary depending on the studied factors by 10-20%, which indicates the possibility of reducing the load on protective structures, operating with the considered indicators.

Sentiment Analysis of BMKG Weather Information Service Using K-Nearest Neighbor Method

The Meteorology, Climatology, and Geophysics Agency (BMKG) is a government institution that provides information related to air quality, climate, dry days, satellite imagery, wave forecasts, wind forecasts, and fire potential. This information is disseminated not only through BMKG's official website but also via the social media platform X, making it easier for the public to access up-to-date information. This study aims to classify user sentiment towards the weather information services provided by BMKG using the K-Nearest Neighbor (KNN) method. Data was collected through a web crawling technique, resulting in 1,031 data points analyzed in this research. The data processing stages included Pre-Processing and sentiment calculation using Vader's Sentiment and Random Forest. The classification results using the KNN algorithm showed an accuracy rate of 96%, with an average precision of 96%, an average recall of 96%, and an average f-measure of 96%. These findings indicate that the KNN model can effectively classify user sentiment towards BMKG's services.

Study on the Effects of Inflow Parameters on the Auto-Initiation of Hydrogen-Rich Gas Rotating Detonation

ABSTRACT To obtain a comprehensive understanding of the auto-initiation characteristics of rotating detonation with the high-temperature hydrogen-rich gas. The experiment was carried out with hydrogen-rich gas as fuel and ambient temperature air as oxidant. The high-temperature hydrogen-rich gas was a kind of fuel-rich gas produced by the pre-combustion of hydrogen and oxygen. The effects of inflow parameters such as air mass flow rate, hydrogen mass flow rate, and hydrogen-rich gas temperature on the auto-initiation delay time and velocity of rotating detonation waves (RDWs) were experimentally studied. The experimental results showed that when the hydrogen and air mass flow rates were 6.3 ~ 17.4 g/s and 314 ~ 610 g/s, respectively, auto-initiation could be successfully achieved and a stable RDW could be formed. As the hydrogen and air mass flow rates increased, the auto-initiation delay times decreased from 40 to 5 ms and from 45 to 19 ms, respectively. When the temperature of the hydrogen-rich gas increased from 460 to 690 K, the auto-initiation delay time decreased from 100 to 10 ms, the RDW velocity decreased from 1368.5 to 1231 m/s. Hydrogen-rich gas has a high temperature, which is easy to cause the non-detonative combustion ahead of the wave of air and hydrogen-rich gas in the RDC, which consumes part of the fuel and resulting in a decrease in the RDW velocity.

Fluctuating pressure gradients and corrugated surfaces effects on wind turbines power output

This paper investigates the effect of corrugated surfaces on the wind turbines power output for both laminar and turbulent flows. Conservation principles including continuity and momentum equations, wind turbine power equations, and the corrugated surface equation have been implemented to build up a theoretical model then which has been solved using MATLAB. This model simulates wind turbines power output and analyzes several case studies implementing different parameters such as air pressure wave amplitude (Po), air wave fluctuation frequency (n), and wind layer turbulence (b). Also, different complex terrains in two main scenarios representing two different positions (X) of the wind turbine are analyzed. This analysis indicates the importance of wind turbines micro siting. In addition, it is found that increasing the pressure ratio increased wind turbine power output, while increasing the frequency decreased the power ratio of the wind turbines for both laminar and turbulent flow conditions. Increasing turbulence for the turbulent model increased the power ratio.

Effect of Amplitude and Frequency on the Speed of Sound Waves in Air and Water Using PhET Simulation

Sound waves can occur not only in solid medium but also in air and water mediums. The effect of amplitude and frequency on the speed of sound waves differs between air and water mediums. The speed of sound waves cannot be seen with the naked eye. A virtual lab is needed to determine the speed of sound wave propagation. The purpose of this study is to determine the effect of amplitude and frequency on the speed of sound waves in air and water medium. The research method used is a quantitative method by conducting experiments online using the PhET application. PhET is used because it can carry out interactive simulations to facilitate research that cannot be done in real terms, but must make use of an effective virtual lab. The results obtained, namely in the medium of air and water, it is proven that the amplitude and frequency are directly proportional to the speed of sound wave propagation. In conclusion, sound waves travel faster in the water medium than in the air medium. Sound waves travel faster in the water medium because in liquid the particles are closer together than in the air medium, so sound waves will travel faster.

Study on Dynamic Response Characteristics of Offshore Floating Wind Turbine Pitch System

Due to its special working conditions, offshore wind turbine will bear large direct and indirect loads under the combined action of air flow and wave flow. In this paper, a variable pitch system composed of variablepitch motorand variable pitch bearing is improved, and the characteristics of system's bending moment, torque, vibration and other physical quantities under the action of multiple physical loads are verified, and the mechanical response characteristics of floating wind turbine under the control of unified variable pitch and independent variable pitch are studied under the running conditions at sea. The results show that mechanical structure of uniform pitch is compared with that of independent pitch, the independent variable pitch structure can effectively reduce the mean oscillation value of wind turbine tower in the parallel direction of air flow by optimizing control strategy, and reduce the thrust at the hub of wind turbine and the bending moment at the root of tower, but increase the vibration frequency and fatigue load of offshore wind turbine tower along parallel direction of air flow. Reduce the fatigue life of equipment. The research results can be used as a reference to reduce the variable pitch control and vibration suppression of offshore wind turbines and improve the reliability of wind turbines.

Animal behavior: Mosquitos ride the wave

Some insects have a frustrating knack for avoiding a swatter. A new study shows that mosquitos not only evade the visual image of the looming threat, they also surf the wave of air the swatter creates.

Quantifying the Ocean Coupling of Air Waves, and Why DART Data Reporting Can Be Deceptive

Quantifying the Ocean Coupling of Air Waves, and Why DART Data Reporting Can Be Deceptive

Noise Reduction System Using Passive Bandpass Noise Filter on Podcast Microphone

The general properties of waves are refraction, reflection, bending (diffraction), interference and polarization. Sound is a form of wave and is in accordance with the law of wave refraction where waves coming from a less dense medium to a denser medium will be refracted closer to the normal line or vice versa. Sound waves easily experience diffraction because sound waves in air have wavelengths of around several centimeters to several meters. Then basically every room, whether you feel it or not, will always have sound. This is inversely proportional to light which has a wavelength of around 500 mm. Therefore, an interference reduction system using a passive bandpass interference filter on the podcast microphone is necessary to reduce interference. Test results carried out by filters used to reduce noise using Passive Band Pass. the waveform is still the original spectrum at 0 Hz – 120 Hz, the original sound conditions and does not cause interference, but interference occurs and filtering Category (Noise %) 10 – 40 low - 98 – 99 high.

Реч и речезнание – предмет и опит за описание на науката

Speech as a gift of nature acquired by homo sapiens (‘wise man’ in Latin) in the process of communicative interaction is an indisputable phenomenon of paramount importance, which in turn justifies the interest of scientists in this type of homo loquens’ (speaking man) activity as a behavioral manifestation of personality. Oral speech offers a vast amount of information for describing communication since it signals discrete sequences of ‘digital’ information on the one hand, while providing additional ‘analogue’ information about the speaking person, on the other. This means that everyday speech in its real use contains speech features related to various speakers who take part in the process of communication. Speech is the material substance which explicates the concrete representation of discourse as it happens in real time, and exists as discourse special dimension in relation to human mind. Human speech can be characterised as a complex set of elements of prosody, which could be divided into the following main groups related to the sound and its time, pitch, force and timbre. The acoustic and perceptual-auditory continuity of speech has become a cornerstone for describing the process of speech in time when solving many practical tasks, since the sounding oral message represents a continuous flow of air waves separated by pauses. The wave-like nature of speech makes it possible to recognise in the structure of the spoken message simultaneous components, just like in a musical cord one can recognise the simultaneous tones of which it is composed. Therefore, the task of developing a special separate research area, called speech science, becomes logical and necessary.

Stretchable, stable, and structural color reversible enabled by mesoscopic regulation and design for flexible photonic crystal mechanical sensors

This paper reports a flexible mechanical sensor developed by combining an opal photonic crystal and a flexible medium through UV curing technology. Under the action of external force, the deformation of the flexible medium causes the change of the photonic crystal lattice constant, which leads to the displacement of the reflection peaks, thus realizing the detection of the deformation of the film. The flexible medium is mixed by photoinitiators and polymer monomers, and its mechanical properties are directly related to the mass fraction of photoinitiators and polymer monomers. The results show that the film can reach a maximum strain of about 180% when the mass fraction of photoinitiator is 3% and the volume ratio of the polymer functional monomers is 8:2. In addition, for the responsiveness test of the sensor under tensile, the results show that at 0%, 26%, and 78% of tensile strain, its structural color is blue-shifted sequentially, and its spectral peaks are 668 nm, 535 nm, and 488 nm, respectively. Finally, the sensor is applied to the detection of acoustic waves in air, and it is found that its spectral response peaks can be obtained for acoustic waves of different frequencies (250–650 Hz), and a spectral peak at 500 Hz. This flexible photon sensor has the potential to match the acoustic resistance of water. It will greatly expand the response research of ocean exploration in the low frequency range.

Turbulent free-surface in self-aerated flows: superposition of entrapped and entrained air

The characterisation and the modelling of air concentration distributions in self-aerated free-surface flows has been subject to sustained research interest since the 1970s. Recently, a novel two-state formulation of the structure of a self-aerated flow was proposed by Kramer & Valero (J. Fluid Mech., vol. 966, 2023, A37), which physically explains the air concentration through the weak interaction of two canonical flow momentum layers, comprising a turbulent boundary layer and a turbulent wavy layer (TWL). The TWL was modelled using a Gaussian error function, assuming that the most dominant contribution are wave troughs. Here, it is shown that air bubbles form an integral part of the TWL, and its formulation is expanded by adopting a superposition principle of entrapped air (waves) and entrained air (bubbles). Combining the superposition principle with the two-state formulation, an expression for the depth-averaged (mean) air concentration is derived, which allows us to quantify the contribution of different physical mechanisms to the mean air concentration. Overall, the presented concepts help to uncover new flow physics, thereby contributing fundamentally to our understanding of self-aerated flows.

Experimental and computer study of the mechanism and identification of conditions for energy-efficient removal of moisture from materials under ultrasonic exposure.

The article is devoted to investigation of energy-efficient moisture removal from capillary-porous materials. Moisture is removed by dispersion at collapse of cylindrical cavitation bubbles, formed by ultrasonic vibrations in the capillaries of the material. Mathematical model, which allowed to investigate the mechanism of moisture dispersion, has been developed. Necessity of realization of cavitation bubble full life cycle in capillary (slow growth, rapid expansion with deformation, collapse) was found. An optimal range of sound pressure levels from 150 dB ("critical level" at which dispersion of water from capillary starts) up to 170 dB (dispersion productivity growth stops due to cavitation bubbles reaching maximum size equal to diameter of capillary) was determined. It is shown that the size of the dewatered sample for maximum drying efficiency should correspond to the ultrasonic wavelength in air. Ultrasonic dispersion of liquid during drying was confirmed experimentally. It is found that for significant reduction of drying time (up to 50% and more) it is necessary to affect in the range of 165-170 dB. And the materials to be dried must be placed as particles or layers having dimensions or thicknesses corresponding to the length of the ultrasonic wave in air. The implementation of ultrasonic drying, on the example of food products (beets) provided a reduction in drying time of 1.9 times, while reducing energy costs by 1.7 times in comparison with convective drying.

Heat Waves Analysis of 2023 Summer in Eastern Part of Romania and Atmospheric Instability Events Which Succeeded Between Them

Abstract The purpose of this paper is a general climatic characterization of the 2023 summer in the region of Moldavia, in eastern part of Romania, but with focus on the analysis of the context in which the most intense tropical air advections occurred in this region. The most significant and lasting tropical air waves were in July and August. From a thermal point of view, June had only one interval in which the maximum temperatures exceeded, for 3 consecutive days, the threshold of 30ºC (between 22nd and 24th of June). Instead, in July there were three intervals in which the maximum temperature exceeded this threshold, for more than 3 days in a row (between 01st - 06th, 15th - 22nd, 24th - 26th of July), and August had the longest such intervals (between 03rd – 06th, 13th – 29th of August). Also, in August, there were four consecutive days with maximum temperatures that exceeded the heat wave threshold (26th -29th of August). Without achieving new absolute temperature records (the highest maximum temperature in this interval being 39˚C at the Iași meteorological station, on August 28th), the last heat wave was notable in terms of duration of manifestation. Considering the definition given by the World Meteorological Organization (WMO) in 2020, according to which heat waves are considered those periods of time that are unusually warm in relation to multi-year averages and that last more than 2 consecutive days, we can frame the tropical air advection of July and August in the category of heat waves.

Cyclic Impact Test with the Hopkinson Bar: Application to Granite

A laboratory scale cyclic impact loading test was developed by modifying a Hopkinson Bar test setup. The modifications involve placing a special shank piece between the striker and the rest of the setup. The shank transmits the impact loading and enables the use of compressed air for rapid reloading of the striker. The short shank is in direct contact with the specimen, i.e., there is no long input bar. With this configuration residual wave motion and reloading of the specimen is avoided. Behind the striker an output bar and momentum trap bar are placed for specimen loading measurement and removal of the wave motion in the system, respectively. The trap bar is stopped by a pneumatic actuator, which also resets the bars and the specimen before the next impact loading. The compressed air flow driving the striker is controlled by high-speed electropneumatic valves connected to a control unit and operated in simple open-loop control. Numerical simulations of both the striker motion by compressed air and dynamic loading wave propagation during impact were used in the design phase as well as setting up the test parameters. The test setup is able to produce stable cyclic impact loading at a frequency of up to 10 impacts per second with striker velocity up to 9 m/s. The feasibility of the test method is demonstrated by providing data from cyclic Brazilian disc experiments on Balmoral Red granite at both impact and quasi-static cyclic loading.

Ventilating noise barrier with slow wave propagation metamaterial

There has been rapid development of acoustic metamaterials over the past decades, which provide more flexible and effective alternatives to conventional acoustic applications in the field of noise insulation. Recent approaches resolve the conflict between noise insulation and ventilation with partially open meta-structures. Such a binary design eliminates the monopolar and dipolar modes, leading to a total reflection boundary. It holds huge potential in practical scenarios. More simple structures and a broader operating bandwidth are highly desirable to enhance its applicability. This work adopts a binary structure to tune the surface response: open areas with air and slow wave propagation layers with helical-structured metamaterial. These two phases alternate along the radial direction, forming a concentrically layered ventilating insulator. The numerically optimized metamaterial performs efficiently in a wide frequency band and has been validated through experiments.

An Experimental Study of GPR Near-Field Problem in Depth Ranging of Buried Objects

We evaluate the often neglected ranging (or cover depth) error of an object located within the Fresnel Region (or called radiating near-field) and reactive near-field region in ground penetrating radar (GPR). The experiments were conducted in concrete specimens with various rebar cover depths from 10 to 80 mm, which imitates any object imaged by GPR from reactive near-field, Fresnel region to far-field region. Velocities of each individual data point of the hyperbolic reflections of the embedded reinforcement in radargram are calculated by developed algorithms based on common offset antenna and multiple trilaterated ray paths. Two different velocity algorithms, based on semi- and full-trilaterated ray paths, were applied to estimate the wave travelling velocity as a prerequisite of cover depth measurement. The algorithms were firstly validated using a high-frequency 2-GHz antenna to verify the travelling speed of radar waves in air, which is equal to the speed of light. Then, the same antenna was used to estimate the cover depth by measuring the time of flight and velocity based on the two velocity algorithms. The results reveal that the ranging accuracy is highly in doubt in reactive near-field and Fresnel regions but is largely improved when the object locates in far-field region where GPR wave propagation becomes plane-type. The measurements, riding on accurate modelling of ray-path’s trilateration models, provide evidence that the normal linear scale of GPR time-to-depth conversion overlooks the effects of near-field/Fresnel region. We therefore suggest that the GPR near-field/Fresnel region and far-field boundary must be taken into account before any attempt of time-to-depth conversion and depth estimation of objects by GPR are carried out.

Експертна оцінка критеріїв вибору методів знешкодження зарядів виведених з експлуатації твердопаливних ракет

The subject of study in this article is the processes that occur during the disposal of solid fuel rockets, methods of disposal, and criteria for choosing an effective method of disposal. This study identified the most significant criteria that determine the choice of an effective method for the disposal of decommissioned solid-fuel rocket charges. The task: to consider the risks of the man-made impact of the process of disposal of solid-fuel intercontinental ballistic missiles on the environment, associated with the emission of harmful substances into the atmosphere, the scattering of fragments, the occurrence of shock air, and seismic and soliton waves; analyze the advantages and disadvantages of existing methods of destruction and use of solid propellant charges of rocket engines; expertly evaluate the criteria for the selection of disposal methods; and a priori ranking of criteria. The method of a priori ranking was chosen as the method of solving the given problem. The following results were obtained. The degree of consistency of the experts’ conclusions was assessed using the concordance coefficient. The hypothesis regarding the significance of the concordance coefficient was tested on the basis of a comparison of the calculated value of the concordance coefficient with the tabulated value at the given values of the significance level and the number of degrees of freedom. The most significant factors that should be taken into account when choosing a disposal method are identified (economic efficiency; the possibility of reusing the fuel that is removed; manufacturability; the probability of emergency situations during the implementation of the method; environmental safety; energy intensity), and factors that can be excluded from further analysis (the need for additional special systems, the degree of mastery of the method). Conclusions. The scientific novelty of the obtained results is as follows: the formalization and mathematical processing of a priori data on the subject of research was conducted, and a comparative assessment of the degree of influence of various criteria on known and promising methods of disposal of solid rocket fuel charges is given. According to the preliminary evaluation, the set of significant selection criteria is most fully met by the cryogenic washing method, the application of which allows the use of solid fuel and crushed substances extracted from solid fuel charges to improve the characteristics of modern detonation engines, to improve the characteristics of the technological processes of applying special refractory coatings, and to organize highly efficient combustion processes in the detonation mode of fuel with the production of thermal and electrical energy.

Acousto-optic modulation of gigawatt-scale laser pulses in ambient air

Control over the intensity, shape, direction and phase of coherent light is essential in numerous fields, from gravitational wave astronomy, quantum metrology and ultrafast sciences to semiconductor fabrication. Modern photonics, however, can involve parameter regimes where the wavelength or high optical powers involved restrict control due to absorption, light-induced damage or optical nonlinearity in solid media. Here we propose to circumvent these constraints using gaseous media tailored by high-intensity ultrasound waves. We demonstrate an implementation of this approach by efficiently deflecting ultrashort laser pulses using ultrasound waves in ambient air, without the use of transmissive solid media. At optical peak powers of 20 GW, exceeding previous limits of solid-based acousto-optic modulation by about three orders of magnitude, we reach a deflection efficiency greater than 50% while preserving excellent beam quality. Our approach is not limited to laser pulse deflection; gas-phase photonic schemes controlled by sonic waves could potentially be useful for realizing a new class of optical elements such as lenses or waveguides, which are effectively invulnerable against damage and can operate in new spectral regions.

Single-shot ultrafast dual-view imaging of shock waves in parallel laser processing

Single-shot ultrafast optical imaging has revealed various non-repetitive processes, but it has conventionally provided only single-view measurements. Here, we demonstrate a single-shot ultrafast dual-view imaging technique by monitoring shock waves in laser processing of glass using single or parallelized excitation pulses. We visualize the spatiotemporal evolution of shock waves in air at 0.5 Gfps with five frames in both top and side views, indicating the velocity anisotropy and interaction of shock waves. Our technique can contribute to a comprehensive understanding not only of shock wave dynamics but also of other spatially complex ultrafast phenomena including laser-induced plasma and electrical discharge.