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On 31 March 2007, strong, tsunami-like waves of 1.0–2.5 m were recorded at most tide gauges along the west coast of Korea. The following year, on May 4, unexpected, abnormal waves in the eastern Yellow Sea reached a maximum height of ∼1.3 m. Both events occurred without warning, resulting in severe loss of life and property. Subsequent analysis found that these tsunami-like waves were meteotsunamis generated by air pressure oscillations. Evidence of possible meteotsunamis has been recorded by existing observation systems. However, the lack of understanding of the phenomenon and meteotsunami-specific monitoring system has hindered community preparedness, resulting in severe damage. We utilized existing observation systems (meteorological stations, tide gauges, and radar) during 2018 to develop a real-time meteotsunami monitoring system in the eastern Yellow Sea. This system detects the intensity and propagation of air pressure oscillations to identify potential coastal hazards and prevent damage caused by meteotsunamis. Two air pressure disturbance methods for measuring intensity of air pressure oscillation (a range of pressure changes over a 60 min window vs the rate of pressure change over a 10 min window) were compared, and several test operations were performed during development of the proposed system. The progress and limitations of the current observation and monitoring system were confirmed based on recent monitoring reports of air pressure jumps during the meteotsunamis on 7 April 2019. To address the insufficient lead time of meteotsunami warnings, installation and testing of open-ocean buoys outfitted with pressure sensors commenced in 2019.

The influence of a capillary pressure jump in a porous medium on the equilibrium between its liquid and gas phases, defined by the Peng–Robinson equation of state, was investigated. A numerical analysis of the phase diagrams of a gas–condensate mixture, constructed in gas-pressure and liquid-pressure coordinates for different capillary pressure jumps in the mixture, has been performed. The boundary of the two-phase region of such a mixture was determined as a domain of its existence in the two-phase state. The calculations were not associated with a concrete porous medium, and they were based on the condition of phase equilibrium of such a medium at different capillary pressure jumps in it.

A porous jump model is put forward to predict the breathability of laminated fabrics by utilizing fluent software. To simplify the parameter setting process, the methods of determining the parameters of jump porous model by means of fabric layers are studied. Also, effects of single/multi-layer fabrics and thickness on breathability are analyzed, indicating that fabric breathability reduces with the increase of layers. Multi-layer fabric is simplified into a single layer, and the fabric permeability is calculated by proportion. Moreover, the change curve of fabric layer and face permeability, as well as the equation between the fabric layer and the face permeability are obtained. Then, face permeability and pressure-jump coefficient parameters setting of porous jump model could be integrated into single parameter (i. e. fabric layers), which simplifies the fluent operation process and realizes the prediction of laminated fabric permeability. nema

The surface texture of materials plays a critical role in wettability, turbulence and transport phenomena. In order to design surfaces for these applications, it is desirable to characterise non-smooth and porous materials by their ability to exchange mass and momentum with flowing fluids. While the underlying physics of the tangential (slip) velocity at a fluid–solid interface is well understood, the importance and treatment of normal (transpiration) velocity and normal stress is unclear. We show that, when the slip velocity varies at an interface above the texture, a non-zero transpiration velocity arises from mass conservation. The ability of a given surface texture to accommodate a normal velocity of this kind is quantified by a transpiration length . We further demonstrate that normal momentum transfer gives rise to a pressure jump. For a porous material, the pressure jump can be characterised by so-called resistance coefficients . By solving five Stokes problems, the introduced measures of slip, transpiration and resistance can be determined for any anisotropic non-smooth surface consisting of regularly repeating geometric patterns. The proposed conditions are a subset of the effective boundary conditions derived from formal multi-scale expansion. We validate and demonstrate the physical significance of the effective conditions on two canonical problems – a lid-driven cavity and a turbulent channel flow, both with non-smooth bottom surfaces.

The evaporation process in porous media typically experiences three main periods, among which the first period, named the constant rate period (CRP), performs most efficiently in removing liquid. We aim to prolong the CRP to very low degrees of saturation (S) and increase its evaporation rate by playing with heterogeneity in wettability and pore size. First, we show that a porous medium with a smaller contact angle at the surface and increasing contact angle towards the inside generally dries out faster compared with that with uniform contact angle. Second, a constant contact angle porous medium with smaller/larger pores in the surface/inside part dries out faster than a medium with uniform pore size. The underlying mechanism is the occurrence of a capillary pressure jump at the border between the two layers accompanied by enhanced capillary pumping, increasing/maintaining the interfacial area in the surface pores. Harnessing the potential of this mechanism, we propose an optimized strategy by combining two heterogeneity effects: increasing contact angle and pore size towards the inside. This strategy is found to be robust both for multilayer and larger systems. In this case, a small drying front first penetrates fast towards the inside and then expands, followed by a horizontal drying front moving back layer by layer to the surface. Quantitatively, compared with evaporation from a homogeneously porous medium with uniform contact angle where CRP stops at $S=0.64$, our optimized design can extend the CRP down to $S=0.12$, and decrease five-fold the drying time needed to reach $S=0.05$.

Characterising interfacial and unsaturated flows in heterogeneous porous layers is of both fundamental and practical interest. Under the assumption of vertical gravitational–capillary equilibrium, we present a theoretical model to describe one-dimensional flows in a porous layer with vertical variations in average pore size, porosity, intrinsic permeability and capillary pressure jump between invading and displaced fluids. The model leads to asymptotic solutions for the saturation distribution and outer envelope of the invading fluid, and for the background pressure drop across the porous layer. Eight dimensionless parameters are recognised after appropriate non-dimensionalisation of the governing equations, the influence of which is demonstrated through a series of example calculations. In particular, four asymptotic regimes are identified, representing unconfined sharp-interface flows, confined sharp-interface flows, unconfined unsaturated flows and confined unsaturated flows. Finally, in the context of flow upscaling, analytical solutions are derived for the effective relative permeability curves on the basis of exact solutions of the saturation field and interface shape, shedding light on the subtle influence of competition between injection/pumping and gravitational forces, wetting and capillary effects, viscosity contrast between the invading and displaced fluids and vertical heterogeneity of the porous layer.

We introduce a novel displacement-based material point method for simulating weakly compressible free-surface flows and fluid–structure interaction. To address volumetric locking, we employ a B ¯ / F ¯ -inspired technique, previously developed for solid mechanics. This technique involves projecting the pressure and the dilatational part of the velocity gradient onto a lower-dimensional approximation space, eliminating complexities associated with two-field mixed formulations and operator splitting approaches. Additionally, to mitigate spurious pressure oscillations resulting from the use of a density-dependent equation of state, we enhance the framework with an artificial viscosity term. Finally, we employ higher-order spline background shape functions, resulting in a continuous representation of the velocity gradient and effectively preventing pressure jumps when material points cross element boundaries. Challenging numerical examples are provided to verify and validate our approach, demonstrating results that closely align with existing literature, exhibit reduced pressure oscillations, and are free of volumetric locking issues.

The pre controlled fragment warhead can be applied in certain specific scenarios due to its excellent damage performance and structural integrity. It is widely used in different combat scenarios. In order to obtain the influence of different groove depths on the lethal power performance of warheads, this paper uses numerical simulation methods to establish a finite element model of an annular hollow pre controlled fragment warhead. It carries out numerical simulation calculations on the lethal power performance of the annular hollow pre controlled fragment warhead. The results show that the detonation wave propagation of the annular hollow pre controlled fragment warhead is affected by the cavity sparsity effect, resulting in a secondary pressure jump of 10 9 Pa. The pressure generated by the superposition of spherical waves in the strong direction is about 200% of that in the weak direction. Within a certain range, the axial initial velocity of the pre controlled fragments increases with the deepening of the groove depth. The average initial velocity in the strong direction increases by 22.96% compared to the weak direction. The influence of different groove depths on the circumferential initial velocity of pre controlled fragments near the detonation point is the greatest, followed by the middle part of the warhead, and the influence far from the detonation point is the smallest. The scattering angle of fragments increases first and then decreases with the increase of relative groove depth. When the relative groove depth is 0.5 δ e , the maximum scattering angle of the fragments is 14.6 °. It increases by 35.2%. This study can provide valuable references for the optimization design and damage assessment of related warheads.

The absorption of airborne sound is still a subject of active research, and even more since the emergence of acoustic metamaterials. Although being subwavelength, the screen barriers developed so far cannot absorb more than 50% of an incident wave at very low frequencies (<100 Hz). Here, we explore the design of a subwavelength and broadband absorbing screen based on thermoacoustic energy conversion. The system consists of a porous layer kept at room temperature on one side while the other side is cooled down to a very low temperature using liquid nitrogen. At the absorbing screen, the sound wave experiences both a pressure jump caused by viscous drag, and a velocity jump caused by thermoacoustic energy conversion breaking reciprocity and allowing a one-sided absorption up to 95 % even in the infrasound regime. By overcoming the ordinary low frequency absorption limit, thermoacoustic effects open the door to the design of innovative devices. The control of sound is a common engineering problem and requires the development of new processes to bypass conventional limits. Here, the authors report an efficient, low-frequency, and nonreciprocal absorber based on thermoacoustic effect.

The initial flow past an impulsively started rotating and translating circular cylinder is asymptotically analysed using a Brinkman penalization method on the Navier–Stokes equation. In our previous study (J. Fluid Mech., vol. 929, 2021, A31), the asymptotic solution was obtained within the second approximation with respect to the small parameter, $\\epsilon$, that is of the order of $1 / \\lambda$. Here, $\\lambda$ is the penalization parameter. In addition, the Reynolds number based on the cylinder radius and the translating velocity is assumed to be of the order of $\\epsilon$. The previous study asymptotically analysed the initial flow past an impulsively started translating circular cylinder and investigated the influence of the penalization parameter $\\lambda$ on the drag coefficient. It was concluded that the drag coefficient calculated from the integration of the penalization term exhibits a half-value of the results of Bar-Lev & Yang (J. Fluid Mech., vol. 72, 1975, pp. 625–647) as $\\lambda \\to \\infty$. Furthermore, the derivative of vorticity in the normal direction was found to be discontinuous on the cylinder surface, which is caused by the tangential gradient of the pressure on the cylinder surface. The present study hence aims to investigate the variance on the drag coefficient against the result of Bar-Lev & Yang (1975). First, we investigate the problem of an impulsively started rotating circular cylinder. In this situation, the moment coefficient is independent of the pressure on the cylinder surface so that we can elucidate the role of the pressure to the hydrodynamic coefficients. Then, the problem of an impulsively started rotating and translating circular cylinder is investigated. In this situation, the pressure force induced by the unsteady flow far from the cylinder is found to play a key role on the drag force for the agreement with the result of Bar-Lev & Yang (1975), whereas the variance still exists on the lift force. To resolve the variance, an alternative formula to calculate the hydrodynamic force is derived, assuming that there is the pressure jump between the outside and inside of the cylinder surface. The pressure jump is obtained in this analysis asymptotically. Of particular interest is the fact that this pressure jump can cause the variance on the lift force calculated by the integration of the penalization term.