Revisiting the Difference between Traveling-wave and Standing-wave Thermoacoustic Engines - A Simple Analytical Model for the Standing-wave One

Kyuichi Yasui,Teruyuki Kozuka,Masaki Yasuoka,Kazumi Kato 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.67 No.10

There are two major categories in a thermoacoustic prime-mover. One is the traveling-wave type and the other is the standing-wave type. A simple analytical model of a standing-wave thermoacoustic prime-mover is proposed at relatively low heat-flux for a stack much shorter than the acoustic wavelength, which approximately describes the Brayton cycle. Numerical simulations of Rott’s equations have revealed that the work flow (acoustic power) increases by increasing of the amplitude of the particle velocity (|U|) for the traveling-wave type and by increasing cos for the standing-wave type, where is the phase difference between the particle velocity and the acoustic pressure. In other words, the standing-wave type is a phase-dominant type while the traveling-wave type is an amplitude-dominant one. The ratio of the absolute value of the traveling-wave component (|U|cos) to that of the standing-wave component (|U|sin) of any thermoacoustic engine roughly equals the ratio of the absolute value of the increasing rate of |U| to that of cos. The different mechanism between the traveling-wave and the standing-wave type is discussed regarding the dependence of the energy efficiency on the acoustic impedance of a stack as well as that on !, where ! is the angular frequency of an acoustic wave and is the thermal relaxation time. While the energy efficiency of the traveling-wave type at the optimal ! is much higher than that of the standing-wave type, the energy efficiency of the standing-wave type is higher than that of the traveling-wave type at much higher ! under a fixed temperature difference between the cold and the hot ends of the stack.

Traveling-wave antenna for the current drive using the fast wave in the lower hybrid-frequency range in the Versatile Experiment Spherical Torus (VEST)

Lee, Hyunwoo,Kim, Sunho,Jung, Seungho,Jo, Jonggab,Lee, Hyunyoung,Hwang, Yongseok,Lee, Byungje Elsevier 2018 Fusion engineering and design Vol.136 No.2

<P><B>Abstract</B></P> <P>An antenna using the fast wave in the lower hybrid-resonance frequency range is proposed for the significant attainment of the heating and current-drive efficiencies. For the operational stability regarding the change of the plasma load, the proposed antenna is designed as the combline-structure traveling-wave antenna. It consists of two tapered coaxial cables, two exciting straps of the folded-monopole structure, 12 radiating straps, 11 field isolators, and the Faraday shield. Regarding the vacuum load, the simulated and measured results show the wide impedance bandwidth (45 MHz, VSWR < 2) of the proposed antenna in conjunction with the traveling-wave-antenna structure and the folded-monopole exciting strap. Regarding the plasma load, the simulated results show that the proposed antenna provides the impedance bandwidth (35 MHz, VSWR < 2), and the fast wave is coupled with an input power from 51.5 − 90%. The measured and simulated coupling efficiencies are highly compatible in the Versatile Experiment Spherical Torus (VEST). According to the frequency-range changes, the simulated-variable range of the parallel refractive index (n<SUB>||</SUB>) is from 3 − 4.5 in the operational frequency band of 475–510 MHz.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The development of an efficient external-current-drive device is required. </LI> <LI> The Lower Hybrid Fast Wave can propagate into central region in higher-density plasma. </LI> <LI> The combline-type traveling-wave antenna (TWA) is proposed for the heating and current-drive efficiencies. </LI> <LI> The coupling research between the antenna and simulated plasma model is carried out. </LI> <LI> The simulation and experiment results are compared regarding the coupling efficiency. </LI> </UL> </P>

Thermo-hydraulic performance of nanofluids in a bionic fractal microchannel heat sink with traveling-wave fins

Cong Qi,Liang Sun,Yuxing Wang,Chengchao Wang,Genglin Chen 한국화학공학회 2021 Korean Journal of Chemical Engineering Vol.38 No.8

Aiming at high working power and heat dissipation of electronic components, this study developed a novel bionic fractal microchannel heat sink with traveling-wave fins based on fractal theory and disk-like tree-like structure. -Al2O3-water nanofluid was chosen as the working fluid instead of water in the microchannel heat sink. Thermohydraulic performance of nanofluids in the bionic fractal microchannel heat sink with traveling-wave fins was simulated numerically, and its comprehensive performance was studied. The main control parameters of this study include the depths of the traveling wave structure (h=0.00005 m, 0.00010m, 0.00015 m, 0.00020 m, 0.00025 m), the eccentricity ratios of the traveling wave structure (e=0, 0.1, 0.2, 0.3, 0.4) and Reynolds numbers (Re=200-1,000). Results indicate that the surface temperature of the microchannel heat sink decreases with Reynolds number and depth of traveling wave structure. The use of traveling ribs at fractal corners can convert the inhomogeneous flow caused by the fractal effect into a stable horizontal channel flow more efficiently, while the temperature uniformity increases with depth and eccentricity ratio. Results also show that the traveling wave structure has the best overall performance when the eccentricity ratio of the traveling wave structure is 0.1 or 0.2, and the depth is 0.00020 m or 0.00025 m.

Aerodynamic drag reduction based on static traveling wave structure

Xingjun Hu,Zewei Wang,Jiuchao Li,Guo Yu,Jingyu Wang,Wei Lan,Jinglong Zhang,Pengzhan Ma 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.5

To explore the influence of the traveling wave parameters on the aerodynamic characteristics of Ahmed models, the geometric model of the traveling wave wall is used as the study object, and the influence of the traveling wave geometric parameters on aerodynamic drag is studied by numerical simulation. A cosine-type traveling wave digital model is established on the basis of Ahmed’s original model. Results show that the static traveling wave structure can play a good role in reducing drag under some driving conditions. The traveling wave’s drag reduction characteristics are affected by the layout position, depth, wavelength, and other related parameters and more affected by driving speed. Finally, a group of working conditions with good drag reduction effects is selected, and the principle of drag reduction by using static traveling wave structure is explained qualitatively and quantitatively through velocity field, shear stress, and pressure field.

On traveling wave solutions of the θ-equation of dispersive type

Ha, T.G.,Liu, H. Academic Press 2015 Journal of mathematical analysis and applications Vol.421 No.1

Traveling wave solutions to a class of dispersive models,u<SUB>t</SUB>-u<SUB>txx</SUB>+uu<SUB>x</SUB>=θuu<SUB>xxx</SUB>+(1-θ)u<SUB>x</SUB>u<SUB>xx</SUB>, are investigated in terms of the parameter θ, including two integrable equations, the Camassa-Holm equation, θ=1/3, and the Degasperis-Procesi equation, θ=¼, as special models. It was proved in H. Liu and Z. Yin (2011) [39] that when ½<θ@?1 smooth solutions persist for all time, and when 0@?θ@?12, strong solutions of the θ-equation may blow up in finite time, yielding rich traveling wave patterns. This work therefore restricts to only the range θ@?[0,½]. It is shown that when θ=0, only periodic travel wave is permissible, and when θ=½ traveling waves may be solitary, periodic or kink-like waves. For 0<θ<½, traveling waves such as periodic, solitary, peakon, peaked periodic, cusped periodic, or cusped soliton are all permissible.

Diffusive and inviscid traveling waves of the Fisher equation and nonuniqueness of wave speed

Hilhorst, D.,Kim, Y.J. Pergamon Press ; Elsevier Science Ltd 2016 APPLIED MATHEMATICS LETTERS Vol.60 No.-

<P>In this paper we present an intuitive explanation for the non-uniqueness of the traveling wave speed in the Fisher equation, showing a similar non-uniqueness property in the case of inviscid traveling waves. More precisely, we prove that traveling waves of the Fisher equation with wave speed c > 0 converge to the inviscid traveling wave with speed. c > 0 as the diffusion vanishes. A complete diagram that shows the relation between the diffusive and inviscid traveling waves is given in this paper. (c) 2016 Elsevier Ltd. All rights reserved.</P>

마이크로파 feedline을 고려한 진행파형 광변조기의 특성 분석

구민주,옥성해,윤영설,문연태,김도균,최영완 대한전자공학회 2004 電子工學會論文誌-SD (Semiconductor and devices) Vol.41 No.4

본 논문에서는 마이크로파 feedline을 포함하고, 광도파관과 마이크로파 feedline간의 임피던스 부정합을 고려하여 전계 흡수광변조기(traveling-wave electro-absorption modulator, TW-EAM)의 마이크로파 특성을 분석하였다. Co-planar waveguide(CPW)와 microstrip의 하이브리드 구조를 가지는 광도파관 부분은 등가회로를 통해 모델링 하였으며, 등가회로의 인덕턴스(L)와 커패시턴스 (C)는 3차원 FDTD를 기반으로 한 수식화를 통하여 구하였다. CPW 구조의 마이크로파 feedline은 모멘텀방식을 이용해 분석하였다. 이와 같은 분석을 통해 TW-EAM의 특성을 보다 정확하게 분석 할 수 있음을 제시한다. In this paper, we analyze the microwave characteristics of traveling-wave electro-absorption modulator (TW-EAM) considering the microwave feedline and the impedance mismatch. The TW-EAM is analyzed by using the equivalent circuit model. The capacitance and the inductance of the equivalent circuit are evaluated by using 3-dimensional finite difference time domain (FDTD) method, while the microwave feedline is analyzed by momentum method. In a viewpoint of microwave characteristics, we present the effect of the structure and the length of microwave feedline.

TRAVELING WAVE SOLUTIONS FOR HIGHER DIMENSIONAL NONLINEAR EVOLUTION EQUATIONS USING THE $(\frac{G'}{G})$- EXPANSION METHOD

Zayed, E.M.E. The Korean Society for Computational and Applied M 2010 Journal of applied mathematics & informatics Vol.28 No.1

In the present paper, we construct the traveling wave solutions involving parameters of nonlinear evolution equations in the mathematical physics via the (3+1)- dimensional potential- YTSF equation, the (3+1)- dimensional generalized shallow water equation, the (3+1)- dimensional Kadomtsev- Petviashvili equation, the (3+1)- dimensional modified KdV-Zakharov- Kuznetsev equation and the (3+1)- dimensional Jimbo-Miwa equation by using a simple method which is called the ($\frac{G'}{G}$)- expansion method, where $G\;=\;G(\xi)$ satisfies a second order linear ordinary differential equation. When the parameters are taken special values, the solitary waves are derived from the travelling waves. The travelling wave solutions are expressed by hyperbolic, trigonometric and rational functions.

Study on Traveling-wave Differential Protection for Series Compensated Line

Chen, Fu-Feng,Qian, Guo-Ming,Wang, Fan The Korean Institute of Electrical Engineers 2011 The Journal of International Council on Electrical Vol.1 No.3

The problem appears when traveling-wave differential protection was used to series compensated transmission line. Although the impedance uniformity of transmission line is broken by the f ixed compensated capacitor (FSC), the line between the relay location and FSC is uniform transmission line. The traveling-wave equation is applicable in the transmission line between relay location and FSC. Based on the previous analysis, an advanced traveling-wave differential protection was proposed for series compensated transmission line and also the method to calculate the differential current of fault phase and healthy phase are extended. When external fault or internal fault on FSC mounting point occurs, in principle, this method can completely eliminate the influence of capacitor current, which satisfies the requirement of sensitivity and security. Elector-Magnetic Transient Program (EMTP) simulations demonstrated it.

Modelling and Optimal Design of a Ring-type Structure for the Generation of a Traveling Wave

Liu, Xinchang,Civet, Yoan,Perriard, Yves Journal of International Conference on Electrical 2014 Journal of international Conference on Electrical Vol.3 No.1

Traveling wave generation in a ring type stator has been studied. The basic working principle to create traveling wave has been modelled by the superposition of two orthogonal standing waves. Theoretical analysis shows that the length to radius ratio affects the frequency gap between two pseudo orthogonal modes used to create traveling wave. FEM simulation is then discussed and applied to validate the analytical model. At last, a possible optimal solution is reported with FEM verification.