Wave Expansion Research Articles

Components and anisotropy of 3D QFP waves during the early solar eruption

Abstract The propagation of disturbances in the solar atmosphere is inherently three-dimensional (3D), yet comprehensive studies on the spatial structure and dynamics of 3D wavefronts are scarce. Here we conduct high-resolution 3D numerical simulations to investigate filament eruptions, focusing particularly on the 3D structure and genesis of EUV waves. Our results demonstrate that the EUV wavefront forms a dome-like configuration subdivided into three distinct zones. The foremost zone, preceding the flux rope, consists of fast-mode shock waves that heat the adjacent plasma. Adjacent to either side of the flux rope, the second zone contains expansion waves that cool the nearby plasma. The third zone, at the juncture of the first two, exhibits minimal disturbances. This anisotropic structure of the wavefront stems from the configuration and dynamics of the flux rope, which acts as a 3D piston during eruptions—compressing the plasma ahead to generate fast-mode shocks and evacuating the plasma behind to induce expansion waves. This dynamic results in the observed anisotropic wavefront. Additionally, with synthetic EUV images from simulation data, the EUV waves are observable in Atmospheric Imaging Assembly 193 and 211 $\AA$, which are identified as the fast-mode shocks. The detection of EUV waves varies with the observational perspective: the face-on view reveals EUV waves from the lower to the higher corona, whereas an edge-on view uncovers these waves only in the higher corona.

Mathematical Models on Mechanics of Biofluids

In this work, we study the mathematical models of flows for some biofluids. In biomechanics, peristaltic flow plays an important role in which the motion generated in the fluid contained in a distensible tube when a progressive wave of area contraction and expansion travels along the wall of the tube. We consider the effect of elasticity of the tube wall in the flow through the progressive wave travelling along its length without its direct calculation. Since the no – slip condition has used on a moving undulating wall surface, it determines the sinusoidal boundary conditions on the upper and lower wall of the tube. The wide occurrence of peristaltic motion gives its result physiologically from neuro-muscular properties of any tubular smooth muscle.

Numerical simulation of jet interaction flow field of complex configuration based on hybrid grid method

Abstract The supersonic/hypersonic jet interaction flow field includes many fluid phenomena such as shock waves, separation and reattachment of the boundary layer, expansion wave, Mach disk, shear layer, and so on. The complexity of the jet interaction flow field makes it difficult to simulate accurately, and the structured grid method is generally used in engineering applications. However, the structured grid has many shortcomings when dealing with complex configurations, and the traditional hybrid grid method has the problem of insufficient accuracy. In the paper, a structured/unstructured grid algorithmic coupling numerical simulation method is developed. Firstly, the feasibility and accuracy of this method are verified by numerical simulation of the jet interference flow field of cone-cylinder-skirt shape, along with a comparison with the results of the experiment and structural method. Then, the jet interference flow fields of the rudders and the grid fins configuration are simulated to show the efficiency of the method, and the accuracy is further verified. The results show that the hybrid numerical simulation method can save grid generation time and grid quantity to a certain extent when compared with the structural, showing higher accuracy, which provides an accurate and efficient solution to jet interaction problems with complex configurations.

Study on the influence of expansion waves on the reflection type of shock wave in double-wedge configurations

Abstract This paper investigates how variations in the relative positioning between the expansion fan emitted from the triple point in the shock/shock interference on double-wedge geometries in confined spaces and the incidence point of oblique shocks influence the transition of oblique shock reflection types, and understands the roles of expansion waves in inhibiting MR. Predictive analysis through the shock polar line provides critical values for the transition of oblique shock reflection types under the influence of expansion fan effects. The position where the shock/expansion fan undergoes post-oblique reflection on the opposite sidewall can be controlled by adjusting the model’s contraction ratio (H 1/H 2). This study uses the density-based solver blastFOAM in openFOAM to numerically solve the Euler equations, conducting inviscid calculations of shock/shock interactions induced by double wedges in confined spaces with ideal gases. This study compares pressure values in different regions obtained from numerical simulations and examines the reflection types of oblique shocks on opposite sidewalls, confirming the feasibility of shock polar analysis and the accuracy of theoretical predictions.

Mitigation mechanism of porous media hood for the sonic boom emitted from maglev tunnel portals

The micro-pressure waves (MPW) released from maglev tunnel portals can generate audible sonic booms and cause structural resonance in surrounding buildings, posing challenges to developing high-speed maglev trains. This paper proposes a novel porous media hood (PMH) and investigates its mechanism for mitigating the sonic booms emitted from tunnels. The numerical model employs the improved delayed detached eddy simulation turbulence model and overset grid technology, validated against data from moving-model experiments. The influences of the PMH's inherent properties and geometric parameters on MPW, flow field evolution, and aerodynamic loads on the train body were comprehensively discussed. The research demonstrates that PMH effectively dampens the initial wavefront gradient at the entrance and reduces the MPW amplitude by intensifying radiation within its exit vicinity. The porosity of 0.2 facilitates a seamless transition for the streamlined head from the ventilated PMH to the airtight tunnel. Lengthening the PMH enhances its MPW mitigation effect, whereas the impact of PMH thickness is minor. The PMH effectively diminishes the reflection intensity of compression and expansion waves at the tunnel ends, leading to a reduction in the magnitude and changing rate of train aerodynamic loads. This underscores the PMH's potential to enhance passengers' auditory comfort and alleviate issues related to train sway.

Propagation of expansion waves in a heat exchanger within a designated volume of the helioinstallation filler

This article considers a mathematical model of forced bifurcation oscillations of a three-mass chain system, when the measure of its dynamic susceptibility is incommensurable with the measures of forced bifurcation forces. The equivalent medium inside the allocated volume of the filler of the solar installation or filler, or its movement is reversible when turbulence occurs. Distributions of perturbations caused by the internal instability of the pre-central layer after abolishing conditions under a focused shear load in the zones of solidification, crystallization and cooling are obtained. The results of the comparison of the pre-central and central layers are presented.

Does the Colonizing Population Exhibit a Reduced Genetic Diversity and Allele Surfing? A Case Study of the Midday Gerbil (Meriones meridianus Pallas) Expanding Its Range.

Colonizing populations at the leading edge of range expansion are expected to have a reduced genetic diversity and strong genetic structure caused by genetic drift and allele surfing. Until now, few studies have found the genetic signatures of allele surfing in expanding wild populations. Using mtDNA markers, we studied the genetic structure of the population of midday gerbils (Meriones meridianus) expanding their range to the west in Kalmykia (southern Russia) following the new cycle of desertification, re-colonizing areas abandoned in the mid-2010s. In the colonizing population, we found a reduced genetic diversity, the redistribution of haplotype frequencies-in particular, in favor of variants rare in the core population-and strong genetic structure combined with strong differentiation from the core population-patterns suggestive of allele surfing on the wave of expansion. In terms of genetic diversity and spatial structuration, the western edge population sampled in 2008 before its collapse in 2017 occupies the intermediate position between the current colonizing and core population. This suggests that reduced genetic diversity and increased genetic differentiation are general features of marginal populations, enhanced by the founder and allele-surfing effects at the leading edges of expanding ranges.

Nonlinear Seismic Response of Tunnel Structures under Traveling Wave Excitation

Tunnels traditionally regarded as resilient to seismic events have recently garnered significant attention from engineers owing to a rise in incidents of seismic damage. In this paper, the reflection characteristics of the elastic plane wave incident on the free surface are analyzed, and the matrix analysis method SWIM (Seismic Wave Input Method) for the calculation of equivalent nodal loads with artificial truncated boundary conditions for seismic wave oblique incidence is established by using coordinate transformation technology, according to the displacement velocity and stress characteristics of a plane wave. The results show that the oblique incidence method is more effective in reflecting the traveling wave effect, and the “rotational effect” induced by oblique incidence must be considered for P wave and SV wave incidence, including the associated stress and deformation. This effect exhibits markedly distinct rotational phenomenon. In particular, the P wave incidence should be focused on the vault and the inverted arch due to the expansion wave. With the increase of the oblique incidence angle, the structural stress and deformation are rotated to a certain extent, and the values are significantly increased. Simultaneously, the shear action of the SV wave may result in “ovaling” of the tunnel structure, thereby facilitating damage to the arch shoulder and the sidewall components. As the oblique incidence angle, the potentially damaging effects of the “rotational effect” to the vault and the inverted arch, but the numerical value does not change significantly. In addition, in comparison to a circular cross-section, the low-frequency amplification of seismic waves in the surrounding rock and the difference of frequency response function in different parts of the lining are more pronounced. In particular, the dominant frequency characteristics are significant at P wave incidence and the seismic wave signal attenuation tends to be obvious with increasing incidence angle. In contrast, SV waves exhibit more uniform characteristics.

Age-related structural remodelling of the coronary circulation.

While it is broadly accepted that ageing is associated with impairment of coronary microvascular function, little is known about the underlying mechanisms. We investigated age-related changes in coronary microvascular structure in patients with stable angina without epicardial coronary stenoses. In an analysis of the IDEAL registry, a total of 165 vessels without coronary stenosis were interrogated with combined pressure/Doppler guidewires. We calculated diastolic microvascular conductance (DMVC) and backward expansion wave (BEW), and compared them between age tertiles. We calculated the prevalence of CMD, defined by reduced coronary flow reserve (CFR), and the prevalence of low BEW and low DMVC in each group. The three study groups were defined as having 37-53, 54-66, and 67-77 years of age, respectively. Oldest (3rd tertile) patients showed lower hyperemic flow velocity (46.7 ± 14.4 vs. 45.1 ± 12.4 vs. 38.4 ± 11.5 cm s-1, p = 0.019), lower DMVC (1.90 ± 0.71 vs. 1.44 ± 0.56 vs. 1.37 ± 0.67 cm s-1 mmHg-1, p < 0.001) and lower BEW intensity (5.9 [2.9-8.4] vs. 4.8 [2.9-6.8] vs. 4.4 [3.4-6.3] × 106 W m-2 s-1, p = 0.094). Older age was independently associated with lower BEW intensity (B: -0.10, 95% confidence interval [CI]: -0.17 to -0.09, p = 0.021) and DMVC (B: -0.25 95% CI: -0.45 to -0.09, p = 0.027). In patients with CFR < 2.5, the prevalence of BEW intensity and DMVC below the 25th percentile increased with age (25.0% vs. 52.0% vs. 72.7%, p = 0.010). Ageing is independently associated with structural microcirculatory remodeling that is reflected in BEW intensity and DMVC measurements, and with an increased prevalence of structural CMD. These results are important to understand non-obstructive mechanisms of myocardial ischemia in the elderly.

Transient pressure characteristic investigation and performance analysis of a novel three-port gas pressure dividing (GPD) device

The wave-rotor based gas pressure dividing (GPD) is a novel concept to allocate and utilize the pressure energy of gases, presenting significant potential in engineering fields. However, studies about GPD devices are rare, and related mechanism analysis and performance investigations are almost blank. In this study, an experimental platform upon a novel three-port GPD device is established. The transient pressure distribution characteristics in passages of GPD wave rotor are determined experimentally with the customized pressure acquisition system. Besides, the effects of rotation speed, compression ratio (β), and expansion ratio (α) on the pressure dividing performance of the GPD device are systematically examined via experiments and numerical simulations. The results indicate that the interaction of shock waves and expansion waves in passages can enable the medium-pressure gas to divide into high-pressure and low-pressure gases. The rotation speed of 2340 rpm is optimized, determining the greatest gas compression and expansion. The compression ratio increase can improve the compression efficiency and reduce the expansion depth, while the expansion ratio increase can present an opposite regulation. The flow rate efficiency of LP port is decreased with the compression ratio and expansion ratio increase.

Constructos del agua, mercancía y valor

The work revisits certain categories within social sciences to analyze water through two primary lenses. The first lens views water as a social construct, involving various communal, social, and institutional actors. This perspective has historical roots extending back to the liberal era of the early 20th century and continues through the post-war period of 'developmentalism.' During this time, water resources were seen as a public service managed by municipalities, communities, and, following the establishment of the Sistema Nacional de Acueductos y Alcantarillados (SNAA, known as AyA) in 1961, by a centralized state institution. Secondly, the study examines the transition of water from a 'use value' (satisfying a need) to an 'exchange value.' This analysis employs the concept of 'elasticity' of the commodity, representing a kind of expansive long wave embedded in the international political debates of the sixties and seventies. These debates involved various social movements and American business elites, who perceived the concept of 'free enterprise' as under threat. This resulted in 'authoritarian liberalism,' which has had lasting effects. In the present era, a 'total market' logic prevails, where water markets, transnational corporations, and stock market pricing determine the distribution of this resource on the planet through supply and demand laws.

Effect of multi-temperature models on heat transfer and electron behavior in hypersonic flows

In hypersonic computational fluid dynamics, the two-temperature (2-T) model is widely used to simulate thermochemical nonequilibrium. The 2-T model incorporates translational-rotational and electron-electronic-vibrational energies, assuming that the integrated energies have the equivalent temperature. In this study, multi-T models are constructed to accurately predict the effects on heat flux and free electrons due to the separation of energy modes under hypersonic environments. The three-temperature (3-T) model separates the electron-electronic energy from the electron-electronic-vibrational energy of the 2-T model. The 3-T model can accurately predict the distribution and temperature of free electrons by separating the energy of free electrons, which has different characteristics from heavy particles. The four-temperature model treats rotational energy as a nonequilibrium energy mode, distinct from translational-rotational energy. While the rotational temperature reaches equilibrium rapidly at low temperatures, at high-temperature regime rotational temperature shows a relaxation time similar to that of vibrational temperature, which cannot be ignored. To develop multi-T models, electron-vibrational relaxation and translational-rotational relaxation, which are omitted in the 2-T model, are considered. Various flight test and ground facility conditions are analyzed to verify the effects of electron and heat flux under circumstances that include shock, expansion, and shock wave boundary layer interaction. The results of the multi-T models show significant differences in electron temperature and distribution caused by electron-electronic nonequilibrium. Additionally, rotational nonequilibrium increases the shock standoff distance and alters the electron distribution at high altitudes. The heat flux difference across multi-T models is found to be negligible, except in the high degree of ionization condition.

Pinch-off of a regular bubble during the impact of droplets on a liquid pool

A droplet impacting a liquid pool can result in the pinch-off of a regular bubble. In this study, the cavity deformation and regular bubble pinch-off after droplets impacting a liquid pool were experimentally investigated. The results indicate that the phenomenon of regular bubble pinch-off results from the combined effects of cavity expansion and capillary wave propagation. The inertial force, viscous force, and droplet diameter are all crucial to the cavity evolution and the process of regular bubble pinch-off. The cavity depth increases with the droplet's inertial force but does not change with the droplet's viscous force. As the droplet's inertial force increases, the diameter of the regular bubble first increases and then decreases. The diameter of the regular bubble at We = 165 is almost four times that at We = 193. In addition, the peak size of the regular bubble decreases as the liquid viscosity increases, but increases as the droplet diameter increases. These variations in the regular bubble size are explained using a theoretical analysis. Finally, the effects of the inertial and viscous forces on the thresholds between no-bubble and regular-bubble pinch-off regimes are studied. As the Ohnesorge number increases from 1.37 × 10−2 to 2.03 × 10−2, the upper and lower critical Weber numbers for the occurrence of the regular bubble pinch-off can increase by 30 and 25, respectively. The theoretical boundaries of regular bubble pinch-off agree well with the boundaries observed in the experiments.

Controlling sonic rectangular jet with nozzle trailing edge modification

Sonic rectangular jet emanating from a convergent nozzle of aspect ratio 2 with modified trailing edge in the form of triangular extension on its widest side is investigated experimentally at different nozzle pressure ratios corresponding to underexpanded states of sonic jet. To assess the impact of trailing edge modification on jet mixing, the sonic rectangular jet from aspect ratio two plain convergent nozzle (without trailing edge modification) is also studied. The centerline pressure decay results at nozzle pressure ratios 2, 3, 4 and 5 confirm the superiority of modified jet (jet from trailing edge modified nozzle) over plain jet from the mixing point of view. At all the pressure ratios, the modified jet possessed shorter core and weaker shock and expansion waves compared to plain jet, which is an outcome of faster mixing of modified jet with ambient fluid. The enhanced mixing caused the modified jet to decay faster than the plain jet. An appreciable core length reduction of about 32% is noticed at pressure ratio of 5. The modified jet experienced increased spread along major axis than along minor axis owing to the restriction offered by the triangular extension on jet spread along minor axis. Thus, the axis switching was absent in modified jet compared to plain jet switching axes at all pressure ratios. The shadowgraph images confirmed the presence of weaker waves in the modified jet. Also, the images confirmed the absence of Mach disk in the modified jet at pressure ratio of 5 compared to plain jet.

A pyramid-style neural network model with alterable input for reconstruction of physics field on turbine blade surface from various sparse measurements

Data from turbine cascade experiments typically exhibits low spatial–temporal resolution, along with inevitable noise and local data missing. This paper aims to establish a super-resolution model to reconstruct the complete pressure and temperature fields on the blade surface from limited observations, using the deep learning method. Depending on the three-dimensional geometric complexity of the blade, the required cross-sectional data varies, resulting in input data of different sizes. Conventional surrogate models typically confine themselves to a single input format, leading to limited compatibility with diverse inputs. A pyramid-style model with four optional input ports is proposed, designed to accommodate data with different numbers of span-wise sections. Three training strategies have been evaluated, where distributed training has been proven to be more time-effective and flexible while maintaining high prediction precision, compared to holistic and conventional training. Generally, the average relative error over the whole dataset falls below 0.18%, the average peak signal-to-noise ratio exceeds 52 dB, and the average structural similarity index measurement surpasses 0.999. As the number of span-wise sections and the amount of information in the input increase, the overall performance shows a consistent upward trend. Robustness analyses are conducted by applying artificial noises of varying intensities. The results indicate that the model can tolerate noise intensities of up to 5% with a satisfactory reconstruction accuracy. In addition, the model is quite sensitive to the measurement data noises in complex flow regions such as expansion waves, suggesting that more intensive measurements should be targeted to those regions when conducting cascade experiments. The proposed method satisfies the intended objectives and provides an idea for future applications in digital twin platforms.

Vorticity and magnetic dynamo from subsonic expansion waves. II. Dependence on the magnetic Prandtl number, forcing scale, and cooling time

The amplification of astrophysical magnetic fields takes place via dynamo instability in turbulent environments. Vorticity is usually present in any dynamo, but its role is not yet fully understood. This work is an extension of previous research on the effect of an irrotational subsonic forcing on a magnetized medium in the presence of rotation or a differential velocity profile. We aim to explore a wider parameter space in terms of Reynolds numbers, the magnetic Prandtl number, the forcing scale, and the cooling timescale in a Newtonian cooling. We studied the effect of imposing that either the acceleration or the velocity forcing function be curl-free and evaluated the terms responsible for the evolution vorticity. We used direct numerical simulations to solve the fully compressible, resistive magnetohydrodynamic equations with the Pencil Code. We studied both isothermal and non-isothermal regimes and addressed the relative importance of different vorticity source terms. We report no small-scale dynamo for the models that do not include shear. We find a hydro instability, followed by a magnetic one, when a shearing velocity profile is applied. The vorticity production is found to be numerical in the purely irrotational acceleration case. Non-isothermality, rotation, shear, and density-dependent forcing, when included, contribute to increasing the vorticity. As in our previous study, we find that turbulence driven by subsonic expansion waves can amplify the vorticity and magnetic field only in the presence of a background shearing profile. The presence of a cooling function makes the instability occur on a shorter timescale. We estimate critical Reynolds and magnetic Reynolds numbers of 40 and 20, respectively.

Numerical investigation of scramjet inlet models for side spillage reduction

This study introduces and evaluates five models of Mach 7 scramjet inlets designed to reduce side spillage. The baseline model is characterized as a 2D-wedge type inlet without sidewalls. To mitigate interference from expansion waves, an alternative model featuring a converging angle identical to the freestream Mach angle is proposed. Another inlet model presents each ramp's converging angle matched to the local Mach angle of its respective ramp. Subsequently, an inlet model with sidewalls attached to the baseline model is introduced, and an additional inlet model is presented with reduced-height sidewalls. Three-dimensional Reynolds-Averaged Navier-Stokes simulations are conducted for each inlet model, and the performance of the inlets is compared. The mass flow averaged properties at the isolator exit for each inlet model are computed. To evaluate the performance of engines equipped with each inlet model, thrust and specific impulse are determined using thermodynamic cycle analysis. Ultimately, net thrust is calculated by subtracting drag from thrust, and the results are compared. The inlet with converging ramps, which has the largest captured area, indicates the lowest net thrust, amounting to 38% of that of the baseline model. In contrast, the inlet with reduced height sidewalls represents the highest net thrust, which is 3.5 times that of the inlet with converging ramps. These results demonstrate that for scramjet inlet design, using sidewalls to reduce drag is a more effective method for reducing side spillage compared to employing converging ramps with a large captured area.

Expansion wave-reinforced initiation of the oblique detonation wave

Efficient initiation of oblique detonation waves (ODWs) is crucial for optimizing the performance of oblique detonation wave engines. A novel approach is proposed for enhancing ODW initiation through expansion waves in this research. Validation of the expansion wave-reinforced initiation method is conducted via numerical simulations employing multi-species reactive Euler equations and a pressure-dependent reaction mechanism. Results demonstrate a significant reduction in the initiation length of ODWs with the addition of an expansion wave ahead of the wedge, contrasting with the absence of detonation wave initiation on a wedge lacking an expansion wave. A theoretical model, based on expansion wave and shock wave relations, along with constant volume combustion theory, elucidates the underlying mechanism of reinforcement. The model reveals that crossing the expansion wave elevates the fluid's Mach number and locally enlarges the flow deflection angle on the wedge surface, without altering the wedge's structure. Furthermore, post-shock temperature increases and pressure decreases compared to the wedge not encountering an expansion wave. The heightened temperature predominantly triggers ODW initiation, thus reinforcing the process. Theoretical analyses indicate the reinforcement's greater efficacy at lower inflow temperatures and lower inflow Mach numbers, suggesting the expansion wave's suitability for initiation in the early flight stages of an aircraft equipped with oblique detonation wave engines.

The rise of dietary diversity in coral reef fishes.

Diet has been identified as a major driver of reef fish lineage diversification, producing one of the most speciose vertebrate assemblages today. Yet, there is minimal understanding of how, when and why diet itself has evolved. To address this, we used a comprehensive gut content dataset, alongside a recently developed phylogenetic comparative method to assess multivariate prey use across a diverse animal assemblage, coral reef fishes. Specifically, we investigated the diversification, transitions and phylogenetic conservatism of fish diets through evolutionary time. We found two major pulses of diet diversification: one at the end-Cretaceous and one during the Eocene, suggesting that the Cretaceous-Palaeogene mass extinction probably provided the initial ecological landscape for fish diets to diversify. The birth of modern families during the Eocene then provided the foundation for a second wave of dietary expansion. Together, our findings showcase the role of extinction rebound events in shaping the dietary diversity of fishes on present-day coral reefs.

Research on flow and heat transfer characteristics of supersonic film cooling with different hole-configurations

In order to investigates the flow and heat transfer characteristics under supersonic mainstream conditions among three typical film hole-configurations—cylinder hole (CH), fan-shaped hole (FSH), and laidback fan-shaped hole (LFSH), this study conducted numerical simulation using the ANSYS CFX and based on the assumption of compressible flow. The results indicate that the cooling effectiveness of the CH dramatically decreases as the blowing ratio increases, while FSH and LFSH improves. When the supersonic mainstream encounters the coolant, flow structures such as oblique shock waves, expansion waves, and mixing layers et al., will be generated around the film holes, which have an impact on the flow and heat transfer characteristics. Under the conditions of same blowing ratio, the shock wave intensity of LFSH is significantly lower than the other two holes and the kidney vortices formed by the CH develop further along the mainstream direction. While the strength of the kidney vortices formed by the FSH and the LFSH is weaker. Additionally, the LFSH incurred the least total pressure loss from before the shock wave to after the oblique shock wave. Specifically, at a blowing ratio of 0.8, it achieved a reduction of approximately 20% in total pressure loss compared to the CH.