Strong Shock Waves Research Articles

Molecular dynamics simulation of cancer cell membrane perforated by shockwave induced bubble collapse.

It has been widely accepted that cancer cells are softer than their normal counterparts. This motivates us to propose, as a proof-of-concept, a method for the efficient delivery of therapeutic agents into cancer cells, while normal cells are less affected. The basic idea of this method is to use a water jet generated by the collapse of the bubble under shockwaves to perforate pores in the cell membrane. Given a combination of shockwave and bubble parameters, the cancer membrane is more susceptible to bending, stretching, and perforating than the normal membrane because the bending modulus of the cancer cell membrane is smaller than that of the normal cell membrane. Therefore, the therapeutic agent delivery into cancer cells is easier than in normal cells. Adopting two well-studied models of the normal and cancer membranes, we perform shockwave induced bubble collapse molecular dynamics simulations to investigate the difference in the response of two membranes over a range of shockwave impulse 15-30 mPa s and bubble diameter 4-10nm. The simulation shows that the presence of bubbles is essential for generating a water jet, which is required for perforation; otherwise, pores are not formed. Given a set of shockwave impulse and bubble parameters, the pore area in the cancer membrane is always larger than that in the normal membrane. However, a too strong shockwave and/or too large bubble results in too fast disruption of membranes, and pore areas are similar between two membrane types. The pore closure time in the cancer membrane is slower than that in the normal membrane. The implications of our results for applications in real cells are discussed in some details. Our simulation may be useful for encouraging future experimental work on novel approaches for cancer treatment.

Mesh Adaptation for Simulating Lateral Jet Interaction Flow

Under the condition of supersonic incoming flow, a missile lateral jet flow field has complex flow structures, such as a strong shock wave, an unsteady vortex and flow separation. In order to improve ability to capture complex flow structures in numerical simulation of lateral jets, this paper proposes a combined-grid adaptive method. When combined with finite volume approximation of second-order and h-type adaptive technology, our method was verified by numerical experiments, which shows that wave structure and vortex structure in the jet flow field can be effectively captured at the same time. In comparison of uniformly refined mesh results, it was found that accuracy of computed results and resolution of characteristic flow structures were significantly improved after mesh adaptation. In comparison of the pressure coefficient, it was found that the error between the adaptive mesh and the uniformly refined mesh was smaller, and the maximum errors of the base grid, adaptive grid and uniformly refined grid were 92.1% and 12.3%.

Application of dislocation-based constitutive model into research of dynamic mechanical behavior under shock loading

To understand the plastic deformation mechanism of an FCC metal (pure aluminum) under shock loading and describe its dynamic mechanical behavior accurately, a multiscale constitutive model based on the dislocation substructure is developed, which comprehensively considers the controlling mechanisms of dislocation motion and dislocation evolution. Then, the model is extended to the loading of strong shock waves by incorporating the homogeneous nucleated dislocation within the constitutive framework. The model parameters are successfully determined by the normal plate impact experiments with different thicknesses of specimens. Additionally, shock front perturbation decay experiments are performed using a line velocity interferometer system for any reflector, where the modulated surface of the specimen is subjected to a laser-driven loading. Then, the model is applied to reproduce the perturbation decay of shock fronts in experiments. During the post-process of simulated results, the method based on the pressure gradient is used to determine the amplitude and the location of distributed shock fronts. The extended model shows promise as an effective method to figure out the role of strength (shear response) on the evolution of perturbation amplitude.

Numerical investigation on flow and mixing characteristics of powder fuel under strong shear and shock wave interaction

In this investigation, the mixing process of powder fuel transverse jet and supersonic airflow are discussed. The effects of particle size and induced shock wave on flow and mixing characteristics are also analyzed. The Eulerian-Lagrange method is utilized to simulate the gas-solid two-phase supersonic flow field. This numerical method has been verified using experimental data and simulation data from the open literature. The results reveal that the powder fuel transverse jet interacts violently with the supersonic airflow and forms complex shock wave structures in the flow field. The motion and distribution of particles are affected by their size and the interaction of shock wave/particle. The powder fuel composed of small size particles enhances mixing performance and has less impact on stagnation pressure loss. The existence of induced shock waves leads to part of the particles into the cavity and the stagnation pressure loss is large. With the increase of induced shock wave intensity, the mixing performance of the local region is continuously improved. The case with the inclination angle of 30° owns the best effect with improving the mixing efficiency by 28.33%, but the total pressure loss is increased by 33.88％.

Temperature Stratification Induced Ignition Regimes for Gasoline Surrogates at Engine-Relevant Conditions

ABSTRACT End-gas auto-ignition leading to knocking combustion is one of the major barriers to achieving higher thermal efficiencies in downsized boosted spark-ignition engines. Despite the available framework addressing hotspot-induced ignition (detonation peninsula), a quantitative investigation on hotspot-induced auto-ignition of gasoline surrogates is yet to be done. In particular, the effect of negative temperature coefficient (NTC) chemistry on the distribution of the ignition modes in the detonation peninsula is still missing. Using the established one-dimensional (1D) theoretical and computational framework, the effect of average temperature (including NTC range), initial pressure, and ethanol addition are investigated. Moreover, appearance of NTC chemistry-related events i.e. coolspots, secondary ignition kernels, and off-centered ignition are analyzed using 1D simulations. The results are as follows. 1) NTC chemistry affects the distribution of ignition regimes in detonation peninsula and the dynamics of the front propagation via altering the reactivity gradient. 2) NTC chemistry increases the temperature gradient range associated with the detonation regime. 3) NTC may inhibit detonation development by simultaneously promoting the spontaneous/supersonic ignition modes. 4) An ethanol blend decreases the knock propensity; however, lower ignitability may promote detonation development and the appearance of strong shock waves. 5) Finally, detonation may result in a normal knock at lower initial pressures (20 bar). However, at elevated initial pressures (50 bar), detonation is noted to yield pressure intensities resembling super-knock.

Fluid mechanism analysis on the interaction between natural laminar flow nacelle and wingbody on a transonic aircraft

A transonic natural laminar flow (NLF) nacelle, which is a streamlined fairing used to contain a turbofan engine and mounted under the wing of civil aircraft, can reduce friction drag. Because the fluid mechanism of the interaction between an NLF nacelle and a wingbody is not clear, laminar flow at high Reynolds numbers in the transonic regime is maintained difficultly. In this work, such interaction on a civil aircraft is investigated. Three NLF nacelles with different pressure distribution characteristics and a baseline nacelle with the turbulent flow are examined. These are installed under the wing of a widebody aircraft to investigate the fluid mechanism between a natural laminar flow nacelle and wingbody. The results show that the influence of the wingbody on the fluid characteristics of the nacelle should be considered in the NLF nacelle design. A well-designed isolated NLF nacelle is different from the one that considers the effect of the wingbody. A favorable pressure gradient in the front part of the nacelle is a key factor in drag reduction. An installed NLF nacelle owning a large pressure peak with a weak favorable pressure gradient and a strong shock wave in front of the nacelle is recommended to be applied in civil aircraft.

Stress measurement system for underwater electro-explosive platforms.

As a new method for generating strong underwater shock waves with rapid repetition frequency, the use of underwater electrical-wire explosion (UEWE) to drive insensitive energetic materials has attracted increasing research attention in recent years. Accordingly, equipment based on this new method have been developed. The ability to measure the stress produced by an UEWE on a device plays a very important role in optimizing the device performance. However, in conventional stress measurements, the spatial electromagnetic interference (EMI) produced by the discharge can affect the measurement accuracy or even damage the experimental instruments. In this study, a novel system for measuring stress in a strong electromagnetic field, based on a piezoelectric film and a conditioning circuit, was debugged and evaluated. Shielding was used to eliminate the intense EMI due to the strong electromagnetic field. Our simulation and experimental results demonstrate that the stress generated can be quickly determined by measuring the output voltage of the conditioning circuit. The new system can be used to measure the stress at the fluid-solid interface under a strong electromagnetic field environment.

Technique for Recording the Intensity of the Emission of Gases behind the Front of Strong Shock Waves in the Region of Vacuum Ultraviolet Radiation

Technique for Recording the Intensity of the Emission of Gases behind the Front of Strong Shock Waves in the Region of Vacuum Ultraviolet Radiation

초음파 압력 펄스에 의한 미세기포와 세포 간의 상호작용에 대한 수치적 연구

The collapse of microbubbles using ultrasonic pressure pulses is accompanied by strong shock waves and jets. This phenomenon is an important topic applied to various environmental and medical fields such as surface cleaning, algae removal, cell poration, and drug delivery. However, a numerical model that can capture the strong bubble collapse, liquid jet, and associated deformation of a cell is lacking in the literature. In this work, numerical simulations are performed for the interaction between the spherical bubble and cell under an ultrasonic pulse condition including the effects of bubble collapsing jet and cell deformation. The cell is treated as a compressible liquid and two distance level-set functions are used for the bubble and cell interfaces. The conservation equations of mass and momentum are solved for compressible two-phase flows. The effects of acoustic amplitude and frequency and initial bubble-cell distance are investigated. The results show that cell deformation increases with increasing acoustic amplitude or decreasing frequency, and the distance between the bubble and cell is observed as an important parameter for cell deformation under the same ultrasound conditions. The present work can contribute to a safer and more efficient use of ultrasound in environmental and medical applications.

Sono-sorption versus adsorption for the removal of congo red from aqueous solution using NiFeLDH/Au nanocomposite: Kinetics, thermodynamics, isotherm studies, and optimization of process parameters

As anionic alloy or layered compounds, layered double hydroxides (LDH) have recently attracted much attention due to their excellent adsorption and catalytic properties. In this work, NiFe layered double hydroxide (NiFeLDH) was utilized as a precursor to synthesize NiFeLDH/Au nanocomposites via a simple urea-hydrolyzed hydrothermal process under UV–vis light irradiation. The as-prepared nanomaterials were characterized using XRD, FT-IR, XPS, BET, UV–vis, TEM, and FESEM analysis. The performance of NiFeLDH and NiFeLDH/Au nanocomposites was evaluated in the adsorptive removal of congo red (CR) dye from aqueous media using two methods of adsorption, i.e. liquid phase sorption (MS) and sono-sorption (US). The sono-sorption technique exhibited higher removal efficiency due to the generation of small bubbles, strong shock waves, high-velocity microjets, and diminished thickness of diffusion layers. Furthermore, the NiFeLDH/Au nanocomposite offered much higher performance in CR removal, exhibiting a dye removal efficiency of 95% in 7 minutes of sono-sorption time. The superior performance of the NiFeLDH/Au composite can be assigned to the high specific surface area of the sorbent, better dispersion of Au nanoparticles onto the surface of NiFeLDH materials, and synergistic effects between Au and NiFeLDH. Also, the isothermal evaluation showed that the data of CR adsorption onto fabricated nanohybrids could be well-matched with the Langmuir model indicating uniform surface energies. Moreover, kinetics studies revealed that the best data fitting for CR adsorption can be provided by Ho’s pseudo-second-order kinetics. The thermodynamic study revealed that the adsorption of CR dye onto NiFeLDH/Au was an endothermic and spontaneous process at the investigated temperatures and CR concentrations. Finally, this research suggests a simple method for the synthesis of an LDH-based nano-sorbent capable of almost completely removing organic dyes from aqueous media.

Numerical Simulation and Active Protection of Lightning Discharge Based on Quantum Heuristic Evolutionary Algorithm

Thunder is a discharge phenomenon that often occurs in nature. Due to its physical influences such as strong current, high temperature, strong shock waves, and strong electromagnetic radiation, it has a huge destructive effect instantly, which may bring serious threats to people’s lives and property safety. This study aimed to study the lightning discharge numerical simulation and active protection based on the quantum heuristic evolutionary algorithm and proposed to apply the lightning discharge numerical simulation to the prevention of lightning disasters. This article gives a detailed description of the quantum algorithm, the generation, and harm of lightning discharge. The genetic algorithm is used to optimize the lightning data simulation algorithm, and the optimization process is introduced in detail. In addition, this article conducts related experiments on lightning discharge numerical simulation and active protection. The experimental results show that targeted active protection and effective numerical simulation are important measures to prevent lightning disasters. Active lightning protection measures can reduce lightning by 30%. Losses are caused by disasters.

Underwater Shock Wave Generated by Exploding Wire Ignited Energetic Materials and its Applications in Reservoir Stimulation

The combination of energetic material (EM) and electrical wire explosion (EWE) is an efficient and economical method to generate strong shock waves (SWs). The idea resembles the exploding bridge-wire (EBW) detonator, but in this case, the EWE operates with much higher electrical energy storage, and the EMs of much lower sensitivity can be directly ignited, which provides a practical compromise among limited energy storage, strong SWs, and safe usage of explosives. The hybrid load based on EWE ignited EMs has been successfully applied for reservoir stimulation in exploitation of both conventional and unconventional oil/gas resources. In this brief review, we summarize the EWE characteristics, SW characteristics, ignition mechanism, and engineering applications of this hybrid load, and give suggestions for future research directions.

An improved shock wave capturing method in high Mach numbers

This study describes an improved scheme that can suppress numerical instabilities caused by calculating strong shock waves at high Mach numbers. The current scheme combines a clear detection of shock waves based on a sonic point condition with a hybrid numerical flux used in a dissipative scheme and a low-precision interpolation only near shock waves. This scheme is easily obtained by combining existing schemes often used in hypersonic flows. Its performance in a two-dimensional system is compared to existing schemes using two inviscid flows at Mach numbers 15 and 20. The results show that the scheme outperforms existing schemes in terms of improving accuracy around shock waves. It is also discovered that this scheme can prevent nonphysical numerical oscillations caused by a mismatch between grid and local-shock forms. The significance of the scheme is demonstrated in the interaction field between the normal shock wave and the boundary layer in competition between viscosity and numerical dissipations. Therefore, the current scheme is useful in a high-Mach-number problem.

Motion Capture Technology and Its Applications in Film and Television Animation

In order to improve the production effect of film and television animation, this paper combines motion capture technology to construct a film and television animation production system and proposes a simple correction method to eliminate the instability of animation frames. This method suppresses the occurrence of instability by introducing additional viscosity corresponding to shear waves in the vicinity of strong shock waves. Furthermore, this paper constructs two Riemannian solvers, HLLEC and HLLES, to study the stability of numerical carbuncle problems. In addition, this paper builds a film and television animation production system based on motion capture technology. Through the verification of motion capture and animation production effects, it can be seen that the film and television animation system based on motion capture technology proposed in this paper can effectively promote the improvement of the animation production effect.

Development of a carbuncle-free and low-dissipation Roe-type scheme: Applications to multidimensional Euler flows

The Roe scheme is known to have high resolution but to be afflicted by the notorious shock anomalies (such as the carbuncle phenomena) and the unphysical expansion shocks. This paper aims to develop a new Roe-type scheme which is robust for strong shock waves and low dissipative for contact waves and shear layers. Based on the mechanism analysis of shock instability, a dissipation-controlling strategy is adopted to adjust the entropy wave viscosity and shear wave viscosity of the transverse numerical flux in the numerical shock layer and the robustness of the Roe scheme is thus enhanced. The violation of entropy condition and the problem of expansion shocks are also fixed to broaden the scheme’s application scope. In addition, the THINC reconstruction procedure and a BVD algorithm are implemented to further improve the resolution for contact waves and shear layers. Numerical results of a series of classical one-, two- and three-dimensional test problems fully demonstrate that the proposed new Roe-type scheme has not only better robustness for strong shock waves but also higher resolution for contact waves and shear layers than the original Roe scheme.

Spatially Resolved Observations of Betelgeuse at λ7 mm and λ1.3 cm Just prior to the Great Dimming

We present spatially resolved observations of Betelgeuse (α Orionis) obtained with the Karl G. Jansky Very Large Array at λ ∼ 7 mm (44 GHz) and λ ∼ 1.3 cm (22 GHz) on 2019 August 2, just prior to the onset of the historical optical dimming that occurred between late 2019 and early 2020. Our measurements suggest recent changes in the temperature and density structure of the atmosphere between radii r ∼ 2R⋆ and 3R⋆. At λ7 mm the star is ∼20% dimmer than in previously published observing epochs between 1996 and 2004. We measure a mean gas temperature of T B = 2270 ± 260 K at r ∼ 2.1R⋆, where R ⋆ is the canonical photospheric radius. This is ∼2σ lower than previously reported temperatures at comparable radii and >1200 K lower than predicted by previous semiempirical models of the atmosphere. The measured brightness temperature at r ∼ 2.6R ⋆ (T B = 2580 ± 260 K) is also cooler than expected based on trends in past measurements. The stellar brightness profile in our current measurements appears relatively smooth and symmetric, with no obvious signatures of giant convective cells or other surface features. However, the azimuthally averaged brightness profile is found to be more complex than a uniform elliptical disk. Our observations were obtained approximately 6 weeks before spectroscopic measurements in the ultraviolet revealed evidence of increases in the chromospheric electron density in the southern hemisphere of Betelgeuse, coupled with a large-scale outflow. We discuss possible scenarios linking these events with the observed radio properties of the star, including the passage of a strong shock wave.

Numerical dissipation control of a hybrid large-particle method in vortex instability problems

Current trends in the development of numerical schemes are associated with a decrease in dissipative and dispersion errors, as well as an improvement in the grid convergence of the solution. Achieving the computational properties is not an easy problem since a decrease in scheme viscosity is often associated with an increase in the oscillations of gas dynamic parameters. The paper presents a study of the issues of numerical dissipation control in gas dynamics problems in order to increase the resolution in numerical reproduction of vortex instability at contact boundaries. To solve this problem, a hybrid large-particle method of the second order of approximation in space and time on smooth solutions is used. The method is constructed with splitting by physical processes in two stages: gradient acceleration and deformation of the finite volume of the medium; convective transfer of the medium through its facets. An increase in the order of approximation in time is achieved by a time correction step. The regularization of the numerical solution of problems at the first stage of the method consists in the nonlinear correction of artificial viscosity which, regardless of the grid resolution, tends to zero in the areas of smoothness of the solution. At the stage of convective transport, the reconstruction of fluxes was carried out by an additive combination of central and upwind approximations. A mechanism for regulating the numerical dissipation of the method based on a new parametric limiter of artificial viscosity is proposed. The optimal adjustment of the method by the ratio of dissipative and dispersive properties of the numerical solution is achieved by setting the parameter of the limiting function. The efficiency of the method was tested on two-dimensional demonstrative problems. In one of them, the contact surfaces are twisted into a spiral on which the Kelvin-Helmholtz vortex instability develops. Another task is the classic problem with a double Mach reflection of a strong shock wave. Comparison with modern numerical schemes has shown that the proposed variant of the hybrid large-particle method has a high competitiveness. For example, in the problem with double Mach reflection, the considered version of the method surpasses in terms of vortex resolution the popular WENO (Weighted Essentially Non-Oscillatory) scheme of the fifth order and is comparable to the numerical solution of WENO of the ninth order of approximation. The proposed method can be the basis of a convective block of a numerical scheme when constructing a computational technology for modeling turbulence.

A stochastic particle Fokker–Planck method with nonlinear production terms for a variable hard-sphere gas

The stochastic particle Fokker–Planck (FP) method has been gaining increasing attention in the field of rarefied gas dynamics due to its potential to reduce the computational costs of the direct simulation Monte Carlo method. The FP method approximates the discrete binary collisions of the Boltzmann equation as continuous drift–diffusion phenomena in velocity space. Consistency between the FP method and the Boltzmann equation is achieved by matching production terms. The Maxwell molecular model has been widely used in this process due to the possibility of obtaining closed-form solutions for these production terms. However, it is well known that the Maxwell molecular model has difficulty predicting strong shock waves since it cannot provide accurate relaxation rates for the moments. By contrast, the variable hard-sphere (VHS) molecular model is able to capture the transport properties of real gases better than the Maxwell molecular model. Nonetheless, there have so far been no reports associated with an accurate VHS molecular model for the stochastic particle FP method. In this paper, two different molecular models are developed to describe a monatomic gas interacting through a VHS potential. The proposed VHS molecular models are evaluated using Grad's 13- and 26-moment distribution functions; hence, they are named the G13 and G26 molecular models. The G13 and G26 molecular models include additional nonlinear moments compared with the conventional Maxwell molecular model. A one-dimensional shock wave and two-dimensional hypersonic cylinder flow are considered for validation. The results show that the proposed molecular models perform better than the Maxwell molecular model in predicting supersonic and hypersonic shock waves.

Data structure simulation for the reform of the teaching process of university computer courses

Abstract Initially we applied the same data structure to grid generation, with further research, we found that the overall calculation efficiency of such a design is not high, and it is difficult to maintain. Finally, we designed different data structures based on the different characteristics of the two parts, in the grid generation, more consideration is given to flexibility and maintainability, a method to determine the flux function through the boundary of a triangular mesh is given. This method first obtains the two-dimensional Euler equations in the normal direction of the boundary of the control volume element, in the system of projection equations, the flux along the tangent to the boundary can be regarded as passive convection, therefore, the one-dimensional Riemann problem solver can be directly used to calculate the flux function passing through the boundary of the triangular control unit. This method under various flow conditions, including supersonic pipe flow and subsonic isentropic flow with strong shock waves, all have high precision and good stability.

Experimental Investigation of a Cavitating Water Flow With the Addition of Drag- Reducing Agents

Local reduction of the pressure in a flow field to levels lower than the saturation pressure triggers the production of tiny vaporous bubbles and causes the cavitation phenomenon. Higher pressure reductions significantly increase the cavitation bubbles’ population, which can coalesce and generate large-scale cavitation structures such as cloud cavitation that shed downstream of the flow channel. The chaotic collapse of cavities produces strong shockwaves in regions with a recovered pressure which causes serious erosion on solid surfaces and high levels of noise. Hence, there is a growing interest in cavitation control methods. In this study, drag-reducing polymer additives are utilized as cavitation reducing (CR) agents in a converging-diverging mesoscale nozzle to verify the applicability of these agents in the control of the cavitation process. Analysis of high-speed images of the cavitating flow fields reveals that the viscoelastic flow of a 400 ppm polymer solution reduced the cavitation intensity by nearly 60 % relative to the pure water flow at a similar Reynolds number. Ultra-high-speed imaging of single cavitating bubbles at the inception showed that in a viscoelastic flow, the collapse period of cavities is longer, and their sizes are shrunk at a lower rate relative to their counterparts in the puer water. Particle image velocimetry (PIV) was used to study the near-wall turbulent flow fields at the flow conditions close to the cavitation inception, at different flow locations with non-zero pressure gradients present on the curved surfaces. Preliminary analysis of the results reveals that viscoelasticity alters the near-wall turbulence and distribution of the pressure gradient fluctuations, which might link to the significant reduction of cavitation intensity in polymeric flows.