•Strong nonlinear interactions between one and two underwater explosion bubbles with a free surface are numerically studied.•Numerical method is based on axisymmetrical fully compressible three-phase ...homogeneous model coupled with two interface advection equations.•Numerical and experimental data agree well regarding the shape of bubbles and free surface.•Detailed pressure and velocity contours during the interaction process are obtained and can better reveal the mechanism underlying the dynamics between the bubbles and free surface.•Motion characteristics of the free surface and bubbles are investigated under different non-dimensional standoff parameters.
In this study, strong nonlinear interactions of one and two underwater explosion bubbles with a free surface are numerically studied using an axisymmetrical fully compressible three-phase homogeneous model. The bubble interfaces and free surface are captured by solving two interface advection equations of vapor and air phases. The numerical results are validated via comparisons with the experimental results. The single-bubble case is validated first, and good quantitative and qualitative agreements are achieved. Special features of the interactions, such as jet impact, toroidal bubble, and primary and secondary water spike, are observed in our numerical model. The detailed pressure and velocity contours during the interaction process are obtained and can better reveal the mechanism underlying the bubbles and free surface dynamics. Afterward, the characteristics of the motion of the free surface and the bubbles are investigated considering different non-dimensional standoff parameters. Four distinct patterns of free surface motion are identified. Next, strong interactions between two bubbles and a free surface are simulated. The essential physical phenomena, such as coalesced bubble, annular residual, and bubble splitting, are reproduced well in the representative experiments. Finally, a parametric study reveals the dependence of the center water spike on the interaction between the bubbles and the free surface.
Evolution of strong nonlinear interaction between a spark-genarated underwater explosion bubble with a free surface. Special characteristic motions including jet impact, toroidal bubble, center and secondary free surface spike are well captured with experimental images. Display omitted
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Influence of phase-change on the collapse and rebound stages of spark-generated explosion bubbles was numerically studied.•A reasonable agreement of the bubble radius with the experimental data was ...obtained, particularly at the second cycle.•The condensation process had the highest influence and mainly occurred at the bubble interfaces with a thin boundary layer.•Secondary cavitation regions in the water field induced by rarefaction waves were observed.•The effects of source term by temperature changes on the bubble dynamics were estimated thoroughly.
Influences of phase-change are generally ignored by current numerical models that are used to study spark-generated cavitation bubble dynamics. However, this assumption was limited to predicting bubble behaviors only at the first expansion and collapse stages. In this study, we aimed to explore the phase-change effects on the cavitation bubble dynamics over multiple cycles. A combination of a two-phase homogeneous mixture model and interface-capturing method was adopted to simulate the bubble dynamics. The full compressibility of the water and vapor phases, heat transfer, condensation, and evaporation were involved in our numerical model. Phase-change processes due to pressure changes and temperature changes were evaluated to explore the major influence phenomenon on the bubble dynamics. By comparing with experimental data, a compatible bubble shape and radius evolution under a free-field condition was obtained, particularly at the rebound and collapse stages. Disturbance secondary cavitation regions in the water field induced by rarefaction waves were observed immediately after the second rebound stage. In addition, bubble dynamic behaviors were mainly affected by the condensation phenomenon. The condensation mass transfer rate increases, becomes extremely high at the final collapse stage, and decreases during the rebound stage. Moreover, the condensation phenomenon mainly occurs at the vapor–water bubble interfaces with a thin boundary layer. The evaporation phenomenon occurred purely inside bubbles with a uniform region. Finally, we discuss the effects of phase-change by temperature changes on the cavitation bubble dynamics. In general, these effects were sufficiently small during the first two-cycle bubble oscillations.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Compressible multiphase model based on a geometrical PLIC-VOF based simulation method.•Fully conservative hyperbolic system is solved based on a Riemann solver.•Reconstruction of the Riemann solver ...for oscillation-free behavior near contact discontinuity.•Dynamic behavior of bubble collapses, high-speed jets, and pressure loads.•3D bubble collapse near a free surface and an oblique wall.
The dynamic behavior of bubble collapses, water jets, and pressure loads during the collapse of the bubble near walls and a free surface were numerically investigated via a geometrical volume of fluid (VOF)-based simulation method. The numerical method is based on the compressible Navier–Stokes equations in a conservative form that describe the flow of compressible viscous fluids. The equations are discretized on a general curvilinear grid using an associated Godunov-type numerical scheme, and a reconstruction of a computational finite-volume Riemann solver is introduced for suppression of oscillation near the interface between fluids. The interface was tracked using the VOF reconstruction method. The VOF method is based on a geometrical tool and Lagrangian propagation of the interface reconstructed by a piecewise linear interface calculation (PLIC), resulting in strictly mass-conserving and sharp interface solutions. The numerical procedure was validated for capturing sharp interface and strong shock waves. For the simulation of bubble collapse, grid dependence studies of a spark-generated bubble were studies of both spherical and non-spherical bubbles were conducted. The results showed good agreement between the simulation and experiment of the bubble dynamics during the collapse process. Subsequently, an investigation of a single bubble near a wall with different standoff distances was performed. The pressure loads induced by the jets impacting the walls were calculated and analyzed. Furthermore, a more complex case of bubble collapse near an oblique wall and free surface was simulated. The resulting bubble dynamics with the jets and free surface shape were compared via photographs of the experiments.
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•A simple graphene interdigitated ion selective field effect transistor (ISFET) sensor for detection of carbaryl was developed.•The biosensor based on graphene ISFET structure showed ...a relatively high sensitivity to detect carbaryl as low as 10−8 μg mL−1 with the carbaryl concentration (Ccarbaryl) range of 2.58 × 10−7–2.58 × 10−2 μg mL−1.
Consider advances are being made to develop new technologies capable of fast in-situ tracing of agricultural toxins. In this work, we reported a simple carbaryl sensor with very high sensitivity using graphene interdigitated ion selective field effect transistor (ISFET). The graphene films were first prepared on polycrystalline copper foil by a low-pressure chemical vapor deposition method, and then transferred onto the interdigitated electrodes of ISFETs by a chemical etching technique. The biorecognition is based on the enzymatic inhibition of carbaryl towards urease. As expected, the weaker enzymatic activity of urease in addition of carbaryl would result in the weaker current response. It was demonstrated that the interdigitated ISFET sensor could achieve high sensitivity to detect carbaryl as low as 10−8 μg mL−1 and the current response of the device showed a good linearity against the logarithm of carbaryl concentration Ccarbaryl with a regression equation ΔIds = −0.4 − 0.6 logCcarbaryl (mA) (R2 = 0.99) in the concentration range from 2.58 × 10−7 to 2.58 × 10−2 μg mL−1. In conlusion, such convenient graphene-based ISFET configuration could be advantageously extended for on-line screening of other pesticide and herbicide agents.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Since January 2018, over 53,000 hospitalisations and six deaths due to hand, foot and mouth disease (HFMD) have occurred across Vietnam with most cases from September onward. In a large tertiary ...referral hospital, Ho Chi Minh City, enterovirus A71 subgenogroup C4 was predominant, while B5 was only sporadically detected. The re-emergence of C4 after causing a severe HFMD outbreak with > 200 deaths in 2011-12 among susceptible young children raises concern of another impending severe outbreak.
•Simultaneous thermodynamic and hydrodynamic mechanisms of underwater explosion phenomenon are investigated numerically.•Both bubble dynamics and temperature fields agree well with experimental data ...and analytical solution.•Thermal boundary layer inside spherical and non-spherical collapsing bubble is analyzed in detail.•An approximate linear relation is proposed to describe relationship between thermal parameters and bubble dynamics.
In this study, we numerically investigate the simultaneous thermodynamic and hydrodynamic mechanisms of underwater explosion (UNDEX). Bubble explosion in water at the collapsing stage is extremely violent and becomes extraordinarily hot, exceeding 1,000 K. The evolution of the bubbles and temperature fields are simulated using a fully compressible mixture model. The deformable bubble and the heat transfer of the internal explosive gas are captured with higher accuracy compared with published data. First, a spherical bubble that collapses and rebounds without the effects of gravity is computed to verify the accuracy of the model. The numerical results in terms of the bubble radius and temperature fields are consistent with analytical solutions based on the Rayleigh–Plesset equation. Next, a real 5.2 g trinitrotoluene UNDEX experimental case is simulated, in which the formation of a non-spherical bubble with a non-symmetric thermal boundary layer is analyzed. An excellent agreement between bubble motions and experimental data is obtained. The temperature inside the collapsing bubble increased significantly, reached a maximum value of approximately 2,000 K at its final stage, and then decreased rapidly. In addition, a spatially non-uniform temperature field and a thicker thermal boundary layer along the jet direction at the collapse stage are observed. Furthermore, a case study is conducted to estimate the bubble dynamics of non-isothermal and isothermal cases. Finally, the effects of the initial equilibrium gas temperature and water temperature on the thermodynamic and hydrodynamic mechanisms of UNDEX are investigated in detail. An approximate non-linear relation is proposed to describe the relationship among the important parameters.
Evolution process of bubble shapes and temperature fields of non-spherical bubble generated by 5.2 g TNT in free-field condition Display omitted
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•A improved VOF interface-sharpening method is developed on the general curvilinear grid for two-phase flows.•The dual-time, preconditioning algorithm was employed to solve the Navier–Stokes ...equations.•An evaluation of mass conservation of the present method is performed.•Validated computations for free surface flows are presented.
A three-dimensional volume-of-fluid (VOF) interface-sharpening method is developed on the general curvilinear grid for two-phase incompressible flows. In this method, a VOF discretization scheme is formulated for the advection of a two-fluid interface. To maintain interface sharpness, a treatment is applied by solving an interface-sharpening equation after each advection time step, thereby reducing the numerical diffusion error in the solution of the discretization scheme. To demonstrate the accuracy and capability of the advection scheme, several numerical experiments involving three benchmark tests of pure advection were conducted. The results show that the method can realize a sharp interface reliably and efficiently, and reasonable mass conservation is obtained. For the flow field of viscous incompressible flows, the Navier–Stokes equations are solved by adopting the dual-time preconditioning method. A fully implicit method with a highly efficient lower-upper symmetrical Gauss–Seidel (LU-SGS) algorithm based on a dual-time stepping technique as a sub-iteration scheme is employed to advance the solution in time. To validate the proposed method for computing incompressible free surface flows, a dam-break flow over a dry horizontal bed and the water entry of a hemisphere with one degree of freedom are simulated. Comparisons of the predicted results with the available experimental data are presented herein.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•An unsteady natural cavitating flow around an axisymmetric projectile is numerically studied using fully compressible homogeneous multiphase approach.•Good agreement is obtained regarding the cavity ...structures and dynamics evolution with the experimental data.•Detailed mechanisms of the cavity shedding with periodic cavity–vortex–pressure interaction behaviors are revealed.•The cavity shape tends to be mushier with increasing water temperature under the same reference cavitation number and reynolds number.
Here, an unsteady natural cavitating flow around an axisymmetric projectile is computationally studied using a homogeneous multiphase approach. The numerical models used are based on a dual-time preconditioning method, an interface-capturing scheme, and a modified cavitation model, to capture unsteady cavitation structure behaviors. Full compressibility of two phases and an energy equation are used to determine the effects of temperature on a cavitating flow. First, the experimental data were validated at a cavitation number of σ = 0.435. Both quantitatively and qualitatively good agreements were achieved, including the evolution of the cavity shape, cavity length, and cavity thickness. Then, the key characteristics of an unsteady cavitation structure regarding the cavity growth, re-entrant jet, cavity shedding, and collapse were analyzed. In particular, the mechanism of the re-entrant jet inside the cavity, causing the periodic cavity shedding, was explored. Furthermore, detailed mechanisms of cavity shedding with periodic cavity–vortex–pressure interaction behaviors were analyzed. Finally, the influences of free-stream temperature on the cavitation structure behaviors were carefully investigated. It was found that both the cavity length and thickness increased with the free-stream temperature under the atmospheric pressure condition. The most sensitive effects occurred when the free-stream temperature approached its boiling point. In case of the same reference cavitation number and Reynolds number, the cavity shape tended to be mushier with increasing water temperature.
Evolution of the cavity shape of unsteady natural cavitating flow around an axisymmetric projectile with the cavitation number σ= 0.435. Special characteristic motions including cavity incipient, growth, re-entryre-entrant jet, shedding, and collapse are well captured with experimental images. Display omitted
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Multiple serotypes of enterovirus A cause hand, foot and mouth disease in southern Vietnam.•Clinical characteristics differed slightly between the different pathogen groups.•CV-A6 and CV-A10 emerged ...in Vietnam in 2013–2015.•An unexpected dominance of EV-A71 was found among both inpatients and outpatients.
Hand, foot and mouth disease (HFMD) has been associated with large outbreaks among young children in the Asia-Pacific Region since 1997, including cases of severe illness and death. Severe illness is often associated with enterovirus A71 (EV-A71). Vietnam experienced a large sustained outbreak of 200000 hospitalized cases and over 200 deaths in 2011–12, the large majority occurring in southern Vietnam.
A prospective observational study was conducted in the outpatient clinics, infectious diseases wards, and paediatric intensive care units of the three main referral centres for the treatment of HFMD in southern Vietnam. Demographic data, basic laboratory parameters, and clinical data were recorded, and molecular diagnostic tests were performed.
Between July 2013 and July 2015, a total of 1547 children were enrolled. Four serotypes of enterovirus A (EV-A71, Coxsackievirus (CV) A6, A10, and A16) were responsible for 1005 of 1327 diagnosed cases (75.7%). An unexpected dominance of EV-A71 was found among both inpatients and outpatients, as well as a strong association with severe illness. CV-A6 and CV-A10 emerged in Vietnam during the study period and replaced CV-A16. CV-A10 was associated with different clinical and laboratory characteristics. During admission, 119 children developed a more severe illness. It was found that children with a skin rash showed less progression of severity, but when a rash was present, a macular rash was significantly associated with an increased risk of progression.
This study represents the most comprehensive descriptive HFMD study from Vietnam to date. Co-circulation and replacement of different serotypes has implications for vaccine development and implementation. These findings from a severely affected country add to our understanding of the presentation, progression, and aetiology of HFMD.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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