Wave Fan Research Articles

An Analysis of Commercial Communication Paths of Korean Pop Idols in the Context of New Media

With the development of new media, K-pop has successfully realized cross-cultural communication. Some researchers have analyzed the Korean wave fan groups and the marketing strategies of the Korean wave, but they still lack a correct understanding of the current situation of the commercialization of Korean wave idols and the potential problems. Therefore, through literature analysis, case analysis, and comparative analysis, this paper explores the commercial communication path of Korean pop idols in the context of new media. Finally, the study found that the lack of self-awareness of Korean idols, the politicization of idols, and cultural strategies formulated by the government are the leading causes of the problem. Therefore, people should set up their independent values and judgment in daily contact with Korean Wave culture, and the media should also play a good role in checking and supervising communication to promote positive cultural exchanges between China and South Korea.

Study on the separation in the shock wave/boundary layer interaction induced by a curved fin

The effect of an isentropic compression wave fan on shock wave/turbulent boundary layer interaction induced by a curved fin is studied by the nanoparticle-based planar laser scattering method, oil flow method, and numerical method. The curved fin consists of two parts: A curved surface generating an isentropic compression fan and a planar surface ensuring the compression fan focuses into a swept shock wave. The flowfield is compared with the three-dimensional separation flowfield induced by a planar fin with the same deflection angle. The results show that the compression fan can compress the turbulent boundary layer without separation, while the focused swept shock wave drives the whole turbulent boundary layer to separate. The flat plate turbulent boundary layer beside the fin is mainly rolled into the separation vortex. The focused swept shock wave adjusts the separation zone to be quasi-conical, suggesting that the quasi-conical separation is the nature of the flowfield in which a turbulent boundary layer interacts with a swept shock wave. The isentropic compression part of the curved fin can prevent the secondary separation of the planar swept shock wave/turbulent boundary layer interaction by changing the attachment process. Based on the focus point of the compression wave fan, the equivalent apex of the curved fin is proposed. The area and intensity of the separation vortex induced by the curved fin are nearly linear as those in the planar fin interaction flowfield. However, the area of the separation vortex induced by the curved fin is larger. The intensity growth of the vortex caused by the curved fin is slower than that of the planar fin.

Dafermos regularization and viscous wave fan profiles for Riemann solutions of Burger's equation

We consider self-similar solutions of the Dafermos regularization of Burger's equation that represent viscous wave fan profiles for Riemann solutions. Two important features of the governing dynamical system are revealed: (ⅰ) the existence of a first integral, and (ⅱ) explicit formulas for a normally hyperbolic invariant curve that is a perturbation of the curve of turning points, and for its stable and unstable manifolds. Using (ⅰ) and (ⅱ), we obtain a detailed and explicit description of these self-similar solutions.

K-Pop Business: Prospects and Challenges for Entrepreneurs in Indonesia

The purpose of this research is to find out how K-Pop popularity is turned into a business for entrepreneur in Indonesia. Nowadays people are crazy about Hallyu or Korean Wave, including the K-dramas and K-pop, South Korean music. The market size of the South Korean entertainment is getting bigger and there are over 100 million members of Korean Wave fan clubs in many countries around the world in 2021. The research method was qualitative methods, with data collection techniques through literature studies The results showed that the K-Pop business in Indonesia opens many opportunities for entrepreneurs in developing business by utilizing the popularity of K-Pop. The hype around K-Pop bands and other celebrities has led many fans to spend a lot of money on their idol merchandise. Though the pandemic of Covid-19 has affected the economy, but the popularity of Korean Wave is growing in Indonesia. Many young entrepreneurs are starting small Hallyu businesses by utilizing social media and e-commerce. Although it is economically valuable, there are challenges faced by the entrepreneurs, namely intellectual property rights.

The adiabatic exponent limits of Riemann solutions for the extended macroscopic production model

The exact Riemann solutions for the extended macroscopic production model with an adiabatic exponent are constructed in perfectly explicit forms. The asymptotic limit of Riemann solution consisting of 1-shock wave and 2-contact discontinuity tends to a delta shock solution for the pressureless gas dynamics model under the special over-compressive entropy condition as the adiabatic exponent drops to one. In contrast, the asymptotic limit of Riemann solution composed of 1-rarefaction wave and 2-contact discontinuity tends to the vacuum solution surrounded by two contact discontinuities by letting the adiabatic exponent tend to one, in which the state in the interior of the 1-rarefaction wave fan is developed into vacuum. The intrinsic phenomena of concentration and cavitation are identified and investigated carefully during this limiting process, which displays more complicated and completely different behavior compared with previous literature. In addition, some representative numerical calculations are also provided, which are in well agreement with our theoretical results.

Airflow disturbance induced by coal mine outburst shock waves: A case study of a gas outburst disaster in China

We explore the magnitude of airflow disturbance in mine roadways induced by gas outburst shock waves. Outburst shock wave propagation in the near-field of the outburst source is established and simulated in three dimensions using FLUENT. The effects in connected but distal roadways are represented by a simplified one-dimensional network model and solved by Flowmaster. A Mesh-based Parallel Code Coupling Interface (MPCCI) is applied to couple the three-dimensional (near source) model and the one-dimensional (distal) model. The coupled model is verified by theoretical analysis and against observations from a coal and gas outburst incident comprising 2887 tonnes of coal that occurred in the Jiulishan coal mine, China and general characteristics of outburst events explored. Simulations demonstrate that airflow disturbance induced by outburst shock waves in the coal mine is principally controlled by the shock wave overpressure and fan pressure provided by the main fan. Of these, the shock wave overpressure exerts the dominant impact. The larger the shock-wave overpressure, the more rapid the decrease of airflow in the roadway branches and the larger the ultimate airflow decrease. Furthermore, the arrival time of the minimum air flow rate is delayed. When the fan pressure is large, the ability to resist airflow disturbance is enhanced and the area subject to countercurrent flow is reduced. The initial air flow rate and the restored air flow rate show less correlation with the shock wave overpressures. However, they are both significantly affected by the pressure of the main fan. This work presents a novel approach for the study of airflow disturbance in underground ventilation networks in coal mines caused by coal and gas outbursts and provides guidance for the design of outburst prevention facilities.

Weak shock reflection in channel flows for dense gases

The canonical problem of transonic dense gas flows past two-dimensional compression/expansion ramps has recently been investigated by Kluwick & Cox (J. Fluid Mech., vol. 848, 2018, pp. 756–787). Their results are for unconfined flows and have to be supplemented with solutions of another canonical problem dealing with the reflection of disturbances from an opposing wall to finally provide a realistic picture of flows in confined geometries of practical importance. Shock reflection in dense gases for transonic flows is the problem addressed in this paper. Analytical results are presented in terms of similarity parameters associated with the fundamental derivative of gas dynamics$(\unicode[STIX]{x1D6E4})$, its derivative with respect to the density at constant entropy$(\unicode[STIX]{x1D6EC})$and the Mach number$(M)$of the upstream flow. The richer complexity of flows scenarios possible beyond classical shock reflection is demonstrated. For example: incident shocks close to normal incidence on a reflecting boundary can lead to a compound shock–wave fan reflected flow or a pure wave fan flow as well as classical flow where a compressive reflected shock attached to the reflecting boundary is observed. With incident shock angles sufficiently away from normal incidence regular reflection becomes impossible and so-called irregular reflection occurs involving a detached reflection point where an incident shock, reflected shock and a Mach stem shock which remains connected to the boundary all intersect. This triple point intersection which also includes a wave fan is known as Guderley reflection. This classical result is demonstrated to carry over to the case of dense gases. It is then finally shown that the Mach stem formed may disintegrate into a compound shock–wave fan structure generating an additional secondary upstream shock. The aim of the present study is to provide insight into flows realised, for example, in wind tunnel experiments where evidence for non-classical gas dynamic effects such as rarefaction shocks is looked for. These have been predicted theoretically by the seminal work of Thompson (Phys. Fluids, vol. 14 (9), 1971, pp. 1843–1849) but have withstood experimental detection in shock tubes so far, due to, among others, difficulties to establish purely one-dimensional flows.

Effects of Feeding Pressures on the Flowfield Structures of Supersonic Film Cooling

Schlieren and shadowgraph visualizations of flowfields in a typical configuration of supersonic film cooling in a backward-facing slot were conducted in a Mach 2.95 continuous-suction wind tunnel, with the film gas tangentially ejected through a half-Laval nozzle of Mach 1.5. The flowfields after the step without and with the injection of film coolant were measured in the paper, including the coolant delivery pressures in the matched and unmatched conditions with the mainstream, respectively. The effects of the different injecting pressures of film coolant on the flowfields in these conditions were also analyzed. A clear visual image of the flowfields of supersonic film cooling in a backward-facing step was obtained, and the characteristics of the flowfields near the step were described. The results confirmed that the feeding pressure of film gas affected the flowfields after the step, especially the shock wave emanating from the upper tip of the lip and the shock wave and expansion fan from the lower tip of the lip. This work aided the verification of numerical simulation results and the in-depth understanding of the flowfields of supersonic film cooling near the backward-facing step.

Stability of Nonlinear Wave Patterns to the Bipolar Vlasov–Poisson–Boltzmann System

The main purpose of the present paper is to investigate the nonlinear stability of viscous shock waves and rarefaction wave for bipolar Vlasov-Poisson-Boltzmann (VPB) system. To this end, motivated by the micro-macro decomposition to the Boltzmann equation in [21, 23], we first set up a new micro-macro decomposition around the local Maxwellian related to the bipolar VPB system and give a unified framework to study the nonlinear stability of the basic wave patterns to the system. Then, as the applications of this new decomposition, the time-asymptotic stability of the two typical nonlinear wave patterns, viscous shock waves and rarefaction wave, are proved for the 1D bipolar Vlasov-Poisson-Boltzmann system. More precisely, it is first proved that the linear superposition of two Boltzmann shock profiles in the first and third characteristic fields is nonlinearly stable to the 1D bipolar VPB system up to some suitable shifts without the zero macroscopic mass conditions on the initial perturbations. Then the time-asymptotic stability of rarefaction wave fan to compressible Euler equations is proved to 1D bipolar VPB system. These two results are concerned with the nonlinear stability of wave patterns for Boltzmann equation coupled with additional (electric) forces, which together with spectral analysis made in [18] sheds light on understanding the complicated dynamic behaviors around the wave patterns in the transportation of charged particles under the binary collisions, mutual interactions, and the effect of the electrostatic potential forces.

New interaction estimates for the Baiti-Jenssen system

We establish new interaction estimates for a system introduced by Baiti and Jenssen. These estimates are pivotal to the analysis of the wave front-tracking approximation. In a companion paper we use them to construct a counter-example which shows that Schaeffer's Regularity Theorem for scalar conservation laws does not extend to systems. The counter-example we construct shows, furthermore, that a wave-pattern containing infinitely many shocks can be robust with respect to perturbations of the initial data. The proof of the interaction estimates is based on the explicit computation of the wave fan curves and on a perturbation argument.

Size and shape of the distant magnetotail

AbstractWe employ a global magnetohydrodynamic model to study the effects of the interplanetary magnetic field (IMF) strength and direction upon the cross section of the magnetotail at lunar distances. The anisotropic pressure of draped magnetosheath magnetic field lines and the inclusion of a reconnection‐generated standing slow mode wave fan bounded by a rotational discontinuity within the definition of the magnetotail result in cross sections elongated in the direction parallel to the component of the IMF in the plane perpendicular to the Sun‐Earth line. Tilted cross‐tail plasma sheets separate the northern and southern lobes within these cross sections. Greater fast‐mode speeds perpendicular than parallel to the draped magnetosheath magnetic field lines result in greater distances to the bow shock in the direction perpendicular than parallel to the component of the IMF in the plane transverse to the Sun‐Earth line. The magnetotail cross section responds rapidly to variations in the IMF orientation. The rotational discontinuity associated with newly reconnected magnetic field lines requires no more than the magnetosheath convection time to appear at any distance downstream, and further adjustments of the cross section in response to the anisotropic pressures of the draped magnetic field lines require no more than 10–20 min. Consequently, for typical ecliptic IMF orientations and strengths, the magnetotail cross section is oblate, while the bow shock is prolate.

Experimental investigation of interactions between laminar or turbulent boundary layer and shock wave

Investigation on the interactions between laminar or turbulent layer and shock wave is performed in a Mach 3.4 supersonic wind tunnel, based on nanoparticle-tracer based planar laser scattering (NPLS) system and supersonic particle image velocimetry (PIV) system. The model geometry in this experiment is composed of two flats with different positions in the test section which can provide the flat with different kinds of boundary layer, and a shock wave generator–a 12° wedge. Boundary layer separation/attachment, induced suppression waves, induced shock wave and expansion fan were clearly presented by NPLS images, velocity field and vorticity field were given by PIV results. Instantaneous flow structures and temporal evolution of two different flow conditions were analysised and compared according to both NPLS and PIV results. The experimental results show that: the separation zone in the turbulent boundary layer is long and narrow, but it’s quite different in the turbulent boundary layer where it is oval-shaped; upstream of the oblique shock wave, a serious of suppression waves can be observed outside of the laminar boundary layer and they will focus into a unsteady induced shock wave, but in contrast, only a focused shock wave can be found outside of the turbulent boundary layer and it’s quite stable; the expansion fan downstream of the oblique shock wave is small in the laminar boundary layer, leading to a sufficient acceleration of the flow, and the attachment shock wave behind the expansion fan is extremely weak, however it is a totally different condition in the turbulent boundary layer with a wide expansion fan and a strong attachment shock wave.

Singular Limiting Induced from Continuum Solutions and the Problem of Dynamic Cavitation

In the works of Pericak-Spector and Spector (Arch Rational Mech Anal. 101:293–317, 1988, Proc. Royal Soc. Edinburgh Sect A 127:837–857, 1997) a class of self-similar solutions are constructed for the equations of radial isotropic elastodynamics that describe cavitating solutions. Cavitating solutions decrease the total mechanical energy and provide a striking example of non-uniqueness of entropy weak solutions (for polyconvex energies) due to point-singularities at the cavity. To resolve this paradox, we introduce the concept of singular limiting induced from continuum solution (or slic-solution), according to which a discontinuous motion is a slic-solution if its averages form a family of smooth approximate solutions to the problem. It turns out that there is an energetic cost for creating the cavity, which is captured by the notion of slic-solution but neglected by the usual entropic weak solutions. Once this cost is accounted for, the total mechanical energy of the cavitating solution is in fact larger than that of the homogeneously deformed state. We also apply the notion of slic-solutions to a one-dimensional example describing the onset of fracture, and to gas dynamics in Langrangean coordinates with Riemann data inducing vacuum in the wave fan.

Flow visualization of supersonic laminar flow over a backward-facing step via NPLS

An experimental study on a supersonic laminar flow over a backward-facing step of 5 mm height was undertaken in a low-noise indraft wind tunnel. To investigate the fine structures of Ma = 3.0 and 3.8 laminar flow over a backward-facing step, nanotracer planar laser scattering was adopted for flow visualization. Flow structures, including supersonic laminar boundary layer, separation, reattachment, redeveloping turbulent boundary layer, expansion wave fan and reattachment shock, were revealed in the transient flow fields. In the Ma = 3.0 BFS (backward-facing step) flow, by measuring four typical regions, it could be found that the emergence of weak shock waves was related to the K–H (Kelvin–Helmholtz) vortex which appeared in the free shear layer and that the convergence of these waves into a reattachment shock was distinct. Based on large numbers of measurements, the structure of time-averaging flow field could be gained. Reattachment occurred at the location downstream from the step, about 7–7.5 h distance. After reattachment, the recovery boundary layer developed into turbulence quickly and its thickness increased at an angle of 4.6°. At the location of X = 14h, the redeveloping boundary layer was about ten times thicker than its original thickness, but it still had not changed into fully developed turbulence. However, in the Ma = 3.8 flow, the emergence of weak shock waves could be seen seldom, due to the decrease of expansion. The reattachment point was thought to be near X = 15h according to the averaging result. The reattachment shock was not legible, which meant the expansion and compression effects were not intensive.

An experimental study on fine structures of supersonic laminar/turbulent flow over a backward-facing step based on NPLS

Fine structures of supersonic flow over a 5 mm high backward facing step (BFS), including expansion wave fan, reattachment shock, supersonic boundary layer were measured in a Ma=3.0 low-noise indraft wind tunnel. By varying the superficial roughness of the wall upstream from the step, supersonic laminar flow and supersonic turbulent flow could be formed over a BFS. Measurements on the spatiotemporal features of the holistic flow field and the fine structures in four typical regions were carried out using NPLS (nano-based planar laser scattering). Flow structures, including expansion wave fan, reattachment shock, supersonic boundary layer and its separation, reattachment and redevelopment are revealed by measuring the holistic structure of the transient flow field. Comparing the two time-averaged flow fields with each other, it is apparent that supersonic turbulent flow over a BFS (STF-BFS) has a larger expansion angle and a shorter recirculation region, and its redeveloped boundary layer increases at a smaller obliquity while the angle of reattachment shock is the same for the supersonic laminar flow over a BFS (SLF-BFS). With regard to time-evolution features, the K-H vortices in the SLF-BFS suffers from shearing, expansion, reattachment and three-dimensional effects while in the STF-BFS large-scale structures are affected by the incline and distortion at the reattachment point due to expansion, viscosity and reverse-pressure. Studies on local regions indicate that in the SLF-BFS, the emergence of compression waves which distinctly converge into a reattachment shock is due to the local convective Mach number and the inducement of K-H vortices in the free shear layer. Nevertheless, in the STF-BFS, compression waves and K-H vortices are barely evident, and the formation of a reattachment shock is related to the wall compressive effect.

Propagation and quenching in a reactive Burgers–Boussinesq system

We investigate the qualitative behaviour of solutions of a Burgers–Boussinesq system—a reaction–diffusion equation coupled via gravity to a Burgers equation—by a combination of numerical, asymptotic and mathematical techniques. Numerical simulations suggest that when the gravity ρ is small the solutions decompose into a travelling wave and an accelerated shock wave moving in opposite directions. There exists ρcr1 so that, when ρ > ρcr1, this structure changes drastically, and the solutions become more complicated. The solutions are composed of three elementary pieces: a wave fan, a combustion travelling wave and an accelerating shock, the whole structure travelling in the same direction. There exists ρcr2 so that when ρ > ρcr2, the wave fan catches up with the accelerating shock wave and the solution is quenched, no matter how large the support of the initial temperature. We prove that the three building blocks (wave fans, combustion travelling waves and shocks) exist and we construct asymptotic solutions made up of these three elementary pieces. We finally prove, in a mathematically rigorous way, a quenching result irrespective of the size of the region where the temperature was above ignition—a major difference from what happens in advection–reaction–diffusion equations where an incompressible flow is imposed.

Numerical study on backward-forward double-detonation driver for high enthalpy shock tubes

A numerical investigation on the performance of abackward-forward double-detonation driver for high enthalpy shock tubes wasconducted by solving one-dimensional Euler equations with the DispersionControlled Dissipative (DCD) scheme. The modified two-step chemical reactionmodel was applied to describe chemical reactions of the oxygen-hydrogenmixture. The numerical results indicate that if the initial pressure ratioof the auxiliary driver section to the primary driver section is less thanthe critical value as was estimated under the condition of no Taylorexpansion waves in the driver, Taylor expansion wave is still observablewith a smaller angle of the expansion wave fan; if the initial pressure ratiois set to be equal to the critical value, Taylor expansion waves disappearand the incident shock wave does not attenuate in the driven section; if theinitial pressure ratio is taken to be larger than the critical value, notonly Taylor expansion waves disappear, but also an over-driven detonationwave develops in the detonation driver and can increase further the drivingpressure.

Shock boundary layer interactions in dense gases

AbstractThe concept of triple deck theory is applied to study laminar interacting boundary layers of dense gases in external purely supersonic flow. An impinging shock is generated at distances which are large compared to the upper deck thickness. As predicted by weakly nonlinear theory such a discontinuity may disintegrate into a sonic shock and an associated wave fan depending on its amplitude and the magnitude of the so called fundamental derivative. Incoming and outgoing waves are computed analytically by means of the method of multiple scales taking into account that mutual interaction effects between them are restricted to the linear upper deck region. The lower deck problem is solved numerically. The results show that it is possible to reduce the size of the separation bubble or even to avoid the occurrence of flow separation by choosing an optimal thermodynamic state. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Multiple viscous wave fan profiles for Riemann solutions of hyperbolic systems of conservation laws

For a system of hyperbolic conservation laws in onespace dimension, we study the viscous wave fan admissibility ofRiemann solutions. In particular, we show that structurallyunstable Riemann solutions with compressive and overcompressiveviscous shocks, and with constant portions crossing thehypersurfaces of eigenvalues admit viscous wave fan profiles. Themain tool used in the study is the center manifold theorem forinvariant sets and the exchange lemmas for singular perturbationproblems.

Evolution of Artificial Perturbations in the Boundary Layer on a Plate and in Its Wake at Supersonic Free-Stream Velocity

The evolution of artificial perturbations in the boundary layer on the flat section of a plate, on the backward-facing wedge behind the rarefaction wave fan, and in the wake is studied experimentally at the Mach number M∞=2.