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Abstract

The complexity of flow conditions at junctions amplifies significantly with supercritical flow. It is a pronounced three-dimensional two-phased flow phenomenon, where standing waves with non-stationary water surface are formed. To analyse the hydrodynamic conditions at an asymmetric right-angled junction with incoming supercritical flows at Froude numbers between 2 and 12, an experimental approach was used. For a phenomenological determination of the relations between the integral parameters of incoming flows and the characteristics of standing waves at the junction area, water surface topographies for 168 scenarios at the junction were measured using non-intrusive measurement techniques. The new, phenomenologically derived equations allow for determination of location, height and extent of the main standing waves at the junction. Research results give important information on the processes and their magnitude for engineering applications.

Abstract

The article shows the relevance of the application of discrete models of rod structures of radio-electronic means (REM) for the study of their behaviour under transient loading. A discrete model of the propagation of harmonic waves in the rod and the study of standing waves are proposed. Computational experiments using the proposed model are conducted. The results show that the model accurately reflects qualitative dynamics of the physical processes in the elastic rod while the waves of elastic deformations are passing through. The proposed models are used for software implementations of systems of mechanical simulation of the behaviour of rod structures.

Abstract

The objective of E-shaped patch antenna with hexagonal slot is to operate in the ISM band for different kind of applications, such as WLAN, GPS, and various modern wireless systems. The posit antenna is designed using FR4 substrate having a dielectric constant of 4.4 with a thickness of 1.6 mm. Probe feed technique is used for this antenna design. A parametric study was included to determine the effect of design approaches and the antenna performance. The realization of the designed antenna was analyzed in term of boost (gain), return loss, and radiation pattern. The design was upsurged to confirm the best achievable result. This antenna resonates at three different frequencies at 1.6 GHz, 3.24 GHz, and 5.6 GHz with a reflection coefficient less than -10 dB and VSWR<2.

Abstract

A novel wool absorption board was prepared by using a traditional non-woven technique with coarse wools as the main raw material mixed with heat binding fibers. By using the transfer-function method and standing wave tube method, the sound absorption properties of wool boards in a frequency range of 250-6300 Hz were studied by changing the thickness, density, and cavity depth. Results indicated that wool boards exhibited excellent sound absorption properties, which at high frequencies were better than that at low frequencies. With increasing thickness, the sound absorption coefficients of wool boards increased at low frequencies and fluctuated at high frequencies. However, the sound absorption coefficients changed insignificantly and then improved at high frequencies with increasing density. With increasing cavity depth, the sound absorption coefficients of wool boards increased significantly at low frequencies and decreased slightly at high frequencies.

Abstract

In this paper a theoretical model of Tesla coil operation is proposed. Tesla coil is described as a long line with distributed parameters in a single-wire form, where the line voltage is measured across electrically neutral space. By applying the principle of equivalence of single-wire and two-wire schemes an equivalent two-wire scheme can be found for a single-wire scheme and the already known long line theory can be applied to the Tesla coil. A new method of multiple reflections is developed to characterize a signal in a long line. Formulas for calculation of voltage in Tesla coil by coordinate and calculation of resonance frequencies are proposed. The theoretical calculations are verified experimentally. Resonance frequencies of Tesla coil are measured and voltage standing wave characteristics are obtained for different output capacities in the single-wire mode. Wave resistance and phase coefficient of Tesla coil is obtained. Experimental measurements show good compliance with the proposed theory. The formulas obtained in this paper are also usable for a regular two-wire long line with distributed parameters.

Abstract

Results from experimental investigation on flame propagation in a pipeline filled with gaseous combustible mixture consisted of hydrogen, methane or 20% hydrogen-methane is presented in the article. The mixture was prepared in separate cylinders and premixed before filling the pipeline. The tests were conducted under various relative equivalence ratio – lambda from 1.0 to 3.0 at pressure of 1 bar and temperature of 25ºC. Hydrogen and methane were selected because these gases are main combustible fractions in several gaseous engine fuels (e.g. natural gas, syngas, biogas). Additionally, the mixture 20% hydrogen and methane, as potential engine fuel, was also under investigation. Flame front was detected with aid of IR photodetectors. Hence, the flame speed was resulted from distance divided by time. As observed, the flame propagation speed was over 100 m/s for both hydrogen and methane premixed mixtures. It was several times higher if compared with the laminar flame speed for these gases. It can be explained by additional acoustic effects (standing waves) taking place inside the pipeline. Results from this investigation can be useful in design and construction of the gas feeding system in the gas fuelled internal combustion engine.

Abstract

In this paper, a micro-strip fed slot antenna array for application in the 2.4GHz industrial, scientific and medical(ISM) band is implemented using the Ansoft HFSS software. Standard formulas are used to calculate different antenna parameters. The proposed antenna is designed to work at 2.4GHz frequency band. A half power beam width(HPBW) of 57°. A bandwidth of around 7.7% is attained. This may have been brought about by poor impedance matching and a high level of surface waves. A way of improving the bandwidth would have been to use proximity coupling feeding method which offers the highest bandwidth and is somewhat easy to model and has low spurious radiation. However, its fabrication would have been more difficult. A directivity of 2.01 dB is achieved. This is a fairly high though directivity increase could have been studied through use of different substrate material and thickness. Adjusting length and width of narrow slot loop antenna will influence on the resonance frequency and bandwidth. By using HFSS software, the characteristics of antenna are investigated and analyzed, including voltage standing wave ratio (VSWR), return loss and far field radiation patterns.

References [1] ISO 10534-2, 1998, Acoustic – Determination of sound absorption coefficient and impedance in impedance tubes – Part 2: Transfer-function method. [2] http://www.scs-controlsys.com/systems/pdf/SCS-MT-PRO-KIT-ABSORPTION.pdf , G. Amadasi, Kundt Tube Acoustic Absorption and Transmission Loss [Online]. [Accessed: 01-2019] [3] BOROŠOVÁ, L., BADIDA, M., BARTKO, L. 2014. Impedance tube as a tool for measuring and evaluation acoustical noise descriptors. Transfer inovácií (Innovation transfer) , 30. ISSN 1337-7094 [4] http://www.angelofarina.it/Public/Standing-Wave

.11.2013 Grimberg, R., Savin A., Steigmann R., Eftimie N., Stanciu M.D, A method to determine the debonding zones in multilayers wood materials, in Proceedings of the 8th International Conference Wood Science and Engineering in the Third Millennium” ICWSE2011, November 3-5, 2011, pp.403 Hong. Zhou, Guangsu. Huang, Xirong. Chen et al, (2004), Chemical Progress, Vol.16, n.3, 450-456, (In Chinese) ISO 10534-1:1996 Acoustics - Determination of sound absorption coefficient and impedance in impedance tubes - Part 1: Method using standing wave ratio. Ming Ma, Yuan Bai, Xiaoming Qian

., Jachowski J., Ship’s ballast tanks size and dimensions review for the purpose of model research into the liquid sloshing phenomenon, Scientific Journals of Maritime University of Szczecin 29(101) pp. 88-94, Szczecin 2012. [10] Zeineb S., Chokri M., Zouhaier H., Khlifa M., Standing wave induced by free liquid sloshing in rectangular tank, Proceedings of the International Renewable Energy Congress, Sousse, Tunisia, November 5-7, 2010.