Rebound Stage Research Articles

Researches on the Dynamics of the Cavitation Bubble Near the Rigid Wall with a Hole

Abstract When cavitation bubbles collapse near the wall, the micro-jet and shock wave causes damage to the surface of hydraulic machineries. In severe cases, this damage may lead to structural harm. This paper focuses on the cavitation bubble evolution process near the rigid wall with a hole by the experiment and numerical simulation. The space-time morphological characteristics of the bubble at distinct stages (the growth stage, the collapse stage and the rebound stage) are described for the situation of γ=0.7. The distribution of the pressure and the velocity fields at different stages are elucidate. At γ=0.7, a shock wave with a maximum value of the pressure approximately to 14MPa is emitted when the bubble collapses. Meanwhile, a micro-jet attaining a maximum velocity of about 129 m/s is created. Notably, the micro-jet induced by the collapse of a bubble near the rigid wall with a hole is away from the wall, which is different from the micro-jet caused by the collapse of a bubble near the rigid wall.

Powder wetting behavior and granule formation mechanism expansion in single-drop granulation

Single-drop granulation is performed under a variety of conditions to characterize the behavior that results from a liquid droplet impacting a powder bed. Drop impact velocity, liquid binder properties, powder bed consolidation status, and primary particle size are all demonstrated to have significant effects on the resulting granule formation mechanism. The process is broken down into a drop impact/drop deformation stage, a drop rebound stage, and a drop imbibition stage. These stages are often in competition with each other to determine the overall drop penetration behavior. Twelve granule formation mechanisms are identified and characterized in this study, in addition to two established granule formation mechanisms that were not observed in this work.

Droplet impact and rebound dynamics on superhydrophobic surfaces

The impact and rebound dynamics of droplets on superhydrophobic surfaces were investigated through numerical analysis employing the phase field method. The influences of contact angle, impact velocity, surface tension, and dynamic viscosity on the fields of pressure and velocity as well as the spreading factor and central height were described comprehensively. The results indicate that there are a series of stages of impingement, spreading, transition, retraction, and rebound in order throughout the life cycle of a droplet. The droplet exhibits distinct pressure and velocity profiles upon impingement stage, with the maximum pressure at the lower center and higher velocities at the upper periphery, spreading around. Velocities are predominantly upward, peaking at the bottom of the droplet during the rebound stage. A larger contact angle, viscosity, surface tension, and lower impact velocity contribute to a reduced maximum spreading factor. Deposition is more likely to occur when the impact velocity, surface tension is lower, and the viscosity is larger. Droplets tend to rebound when the contact angle, impact velocity, and surface tension are larger. Thresholds for impact velocity, surface tension, and viscosity were delineated for droplet rebound. Furthermore, a correlation for predicting the maximum spreading factor of droplets on superhydrophobic surfaces was proposed.

Experimental Investigations on the Cavitation Bubble Dynamics near the Boundary of a Narrow Gap

Cavitation bubbles near narrow gaps widely exist within microfluidic control devices. In the present paper, a laser-induced cavitation bubble is arranged in a narrow gap composed of two parallel plates. The inception position of the bubble is set to be at the same distance from the two plates so that the dynamic behaviors of the bubble are symmetrical. The collapse and rebound dynamics of the bubble near the boundary of a narrow gap are investigated through high-speed photography. The bubble behaviors (e.g., shape deformation, translational movement, and jet characteristics) are analyzed while considering the influence of the dimensionless distance between the bubble and the boundary and the dimensionless gap width. The principal findings include the following: (1) When the dimensionless distance is small, a violent jet towards the gap is generated during the bubble collapse stage, along with a weak counter-jet towards the boundary appearing during the rebound stage. (2) As the dimensionless distance increases, the translational distance of the bubble during the collapse stage initially decreases, then increases, and finally decreases to zero. (3) Within the parameter range considered in this paper, the dimensionless width mainly affects the expansion degree and movement direction of the bubble cloud during its rebound and subsequent stages. The above research findings can provide experimental support for bubble-driven flow control, pumping, and liquid mixing in microfluidic channels.

Research on optimization of basic rail top bending prediction model

Since the basic rail of the switch needs to have a certain bending angle when the train changes direction, top bending is an important link in the production process of the basic rail. The three-point pressure top bending method is simple, flexible and widely used. In this study, the traditional three-point pressure bending is optimized, the influence of the pick width in the model is considered, a corresponding rebound model is established, and the model is applied to the pressure bending process of the basic rail. The bilinear strengthening model of the material was used to construct the bending moment expressions at different positions during the top bending process, and the relationship between the load and bending deflection in the elastic stage and elastic-plastic stage was obtained. The final top bending prediction model was obtained by combining the load-deflection model in the bending stage and the rebound stage. The correctness of the theoretical mathematical model was verified by establishing finite element simulations, and the theoretical calculation results were compared with the experimental results. The results showed that the top bend prediction optimization model established in this study had high feasibility and met the machining accuracy requirements.

Dynamic response of GFRP/Nomex honeycomb sandwich panels subjected to multiple hail impacts – An experimental study

AbstractNowadays, more and more aircraft components are made of composite sandwich structures, and ice impacts are prone to cause internal damage to composite sandwich structures, so it is crucial to study the impact of hail on composite sandwich structures. Since hail impacts may occur several times at a single point, an experimental approach was used to investigate the dynamic response of GFRP/Nomex honeycomb sandwich panels under multiple hail impacts. The dynamic response of the structure was investigated in terms of response rate and deflection‐profile curves using 3D digital image correlation methods, and the effects of impact energy, hail size, and number of impacts on the impact resistance of the honeycomb sandwich structure were explored. The results show that the dynamic response process of sandwich panels can be categorized into the ball‐and‐crown phase, the rebound phase, and the vibration phase. Under the same impact energy, the impact of small‐sized hailstones is more threatening to honeycomb sandwich panels. As the number of impacts increases, the maximum deflection value of the back panel first increases uniformly, and when the layered damage area reaches the threshold value, fiber stripping occurs, and the increment of the maximum deflection value increases significantly.Highlights Since hail impacts may occur several times in real situations, this study conducted multiple impact experiments for one impact site. The dynamic response and damage pattern of the GFRP/Nomex honeycomb sandwich panels under multiple hail impacts were also investigated. The dynamic response process of GFRP/Nomex honeycomb sandwich panels was categorized into three phases: ball‐crown stage, rebound stage, and vibration stage. With the increase of the number of impacts, fiber stripping and fiber break damage began to occur when the layered damage area of the panel reached the threshold value. The honeycomb core has three main failure modes: cell wall folds, cell wall fracture, and cell wall debonding at the TGPW interface. Small‐diameter hails pose a more significant threat of damage to honeycomb sandwich panels at the same impact energy.

Study on the Dynamic Characteristics of Single Cavitation Bubble Motion near the Wall Based on the Keller–Miksis Model

The dynamic model of cavitation bubbles serves as the foundation for the study of all cavitation phenomena. Solving the cavitation bubble dynamics equation can better elucidate the physical principles of bubble dynamics, assisting with the design of hydraulic machinery and fluid control. This paper employs a fourth-order explicit Runge–Kutta numerical method to solve the translational Keller–Miksis model for cavitation bubbles. It analyzes the collapse time, velocity, as well as the motion and force characteristics of bubbles under different wall distances γ values. The results indicate that as the distance between the cavitation bubble and the wall decreases, the cavitation bubble collapse time increases, the displacement of the center of mass and the amplitude of translational velocity of the cavitation bubble increase, and the minimum radius of the cavitation bubble gradually decreases linearly. During the stage when the cavitation bubble collapses to its minimum radius, the Bjerknes force and resistance experienced by the bubble also increase as the distance to the wall decreases. Especially in the cases where γ = 1.3 and 1.5, during the rebound stage of the bubble, the Bjerknes force and resistance increase, causing the bubble to move away from the wall. Meanwhile, this study proposes a radiation pressure coefficient to characterize the radial vibration behavior of cavitation bubbles when analyzing the radiation sound pressure. It is found that the wall distance has a relatively minor effect on the radiation pressure coefficient, providing an important basis for future research on the effects of different scale bubbles and multiple bubbles. The overall idea of this paper is to numerically solve the bubble dynamics equation, explore the characteristics of bubble dynamics, and elucidate the specific manifestations of physical quantities that affect bubble motion. This provides theoretical references for further engineering applications and flow analysis.

The effect of temperature on the pressure energy distribution in the process of near-wall single bubble collapse

At the interface between rotating components and the working medium in fluid machinery, cavitation in the liquid is induced. The temperature of the working medium has a significant influence on the cavitation. However, the effect of temperature on the pressure and pressure energy in the collapse of bubbles cannot be explained accurately. This study established cavitation models containing insoluble gases at different temperatures and iron walls. The Transferable Intermolecular Potential 4 Points-Fluctuating Bonds water model and the Reax force field were selected to study the influence of temperature on pressure energy and pressure in the process of bubble collapse. Employing the model, we examined variations in release pressure and the pressure energy associated with bubble collapse within the system at diverse temperatures. This investigation was conducted by establishing 24 monitoring points. The findings revealed that the near-wall single-bubble collapse process could be delineated into four distinct stages: the precollapse stage, the inertia stage, the rebound stage, and the collapse stage. These four stages manifest on both the pressure curve in the simulation and the curve depicting changes in the cavity area during the experimental phase. The influence of temperature on bubble collapse primarily stemmed from its impact on saturation vapor pressure and viscosity. This influence was observed during the precollapse process, where saturation vapor pressure played a dominant role, and in the collapse stage, where viscosity was predominant.

Numerical Investigation of Cavitation Bubble Jet Dynamics near a Spherical Particle

Synergistic interaction between cavitation bubbles and particles is critical for the operational performance of hydro turbines. The jet dynamics near the wall have been extensively investigated; however, the jet dynamics near the particles are not clear. In the present paper, the bubble jet dynamics near a spherical particle are numerically investigated based on a compressible two-phase flow solver considering the effects of heat transfer and mass transfer between the phases. Furthermore, the effect of the distance between the particle and the initial position of the bubble on the jet characteristics is analyzed in detail. Based on the simulations, three typical cases (i.e., jet during the rebound stage, jet pointing towards the particle, two jets facing each other) of jet behavior are categorized together with the range of dimensionless parameters. As the distance between the particle and the bubble increases, the three cases of jet impacts occur in the rebound stage, in the first period, and in the transition from the first period to the rebound stage, respectively.

Calcium carbonate crystallization process from the mineralization of calcium chloride waste

The distillation waste stream from the ammonia-alkali process contains 90–120 g/L of calcium chloride. Using calcium chloride as raw material to mineralize carbon dioxide can achieve efficient utilization of calcium chloride waste and CO2 emission reduction. This article is based on a two-step synthesis method, using ammonium carbonate and calcium chloride as raw materials to synthesize calcium carbonate. The changes in pH of the mineralized solution with time were investigated under factors such as temperature, ammonium carbonate concentration, feeding method, and retention time. The crystallization mechanism of carbonation process shows that the pH of solution will affect the degree of supersaturation of calcium carbonate, and high supersaturation is conducive to the precipitation of metastable aragonite and vaterite phases. The experimental results showed that when ammonium carbonate was passed into calcium chloride at a rate of 10 mL/min at different temperatures and different ammonium carbonate concentrations, the pH change of the mineralized solution could be divided into three stages: a rapid pH decrease stage (9.5–7), a pH stabilization stage (∼7) and a pH rebound stage (7–8.5). Increasing the temperature is conducive to the formation of submicron calcite type calcium carbonate, changing the concentration of ammonium carbonate, and the crystal phase and size of the product are almost unaffected. If calcium chloride is added to ammonium carbonate, under low calcium ion concentration conditions, calcium carbonate tends to form aragonite phase.

Heterogenous responses of stock markets to covid related news and sentiments: Evidence from the 1st year of pandemic

Covid related news and sentiments had hit the financial market during the initial phase of 2020. The impact of news on the behavior of the asset markets was a long-standing interest of the financial economists. In this paper, we study the impact of the news and sentiments related to covid-19 on the stock returns of United Kingdom (UK) over the period of February 4 – December 7, 2020. Despite a large volume of literature that has investigated how shocks from covid 19 affect stock returns, a stand alone study on the severely affected UK stock market is missing. This is important because market reactions were heterogenous conditioned on the different aggregate variables and UK stock market provides such unique setting as opposed to the other G7 economies. Motivated by this, using time series data, we find that covid-19 daily cases exert a significant negative effect on the stock returns. While, covid-19 daily deaths exert significant and positive impact on stock returns. These findings hold with covid related sentiments indices used, in the 2nd wave data and US policies and equity market volatilities from infectious diseases. The magnitude of effect indicates that the pandemic is not very harmful to the UK stock market. Among the control variables, fake news, and sentiment indices manipulate the market by raising share prices, specifically during fever stage, while government responses index corrects the market by exerting a negative effect in particular in rebound stage. While, investors are very uncertain about the market development. Our results are important for investors, traders and policy makers for trading and risk management purpose.

Training Behaviors and Periodization Outline of Omnivorous, Vegetarian, and Vegan Recreational Runners (Part A)-Results from the NURMI Study (Step 2).

Runners train for long-distance competitions based on underlying motivations, which may be similar to individual dietary motivations (e.g., well-being and performance). Fundamental training differences may arise in recreational runners following different diet types (omnivore, vegetarian, vegan) considering possible motive variations. Following a cross-sectional design, distance runners completed a survey (online), including a thorough assessment of training behaviors with generic training details and periodization specifics in three phases: 1. an intermediary and rebound stage, 2. a main preparatory stage, and 3. a main event stage (tapering or interim event level/s). Kruskal-Wallis and chi-squared tests were used in the statistical analysis. A total of 245 fit recreational runners following omnivore (n = 109), vegetarian (n = 45), and vegan diets (n = 91) were included. Significant differences in the initial running motivation were found across dietary subgroups (p = 0.033) as well as for current motivations (p = 0.038), with vegetarians being the least health motivated (27% and 9%, respectively). No differences in each of the specific periods were found between diet types across the outline (p > 0.05). The present evidence shows that there is a lack of fundamental training differences based on recreational runners following different generic types of diets. The results of the present investigation may be especially relevant for future studies on safety, sustainability, and performance-enhancing dietary practices among athletes.

Effect of dynamic loading conditions on the dynamic performance of MP1 energy-absorbing rockbolts: Insight from laboratory drop test

Energy-absorbing rockbolts have been widely adopted in burst-prone excavation support, and their serviceability is closely related to the frequency and magnitude of seismic events. In this research, the split-tube drop test with varying impact energy was conducted to reproduce the dynamic performance of MP1 rockbolts under a wide range of seismic event magnitudes. The test results showed that the impact process could be subdivided into four distinct stages, i.e. mobilization, strain hardening, plastic flow (ductile), and rebound stage, of which strain hardening and plastic flow are the primary energy absorbing stages. As the impact energy per drop increases from 8.1 to 46.7 kJ, the strain rate of the shank varies between 1.20 and 2.70 s−1, and the average impact load is between 240 and 270 kN, which may be considered as constant. The MP1 rockbolt has a cumulative maximum energy absorption (CMEA) of 31.9–40.0 kJ/m, with an average of 35.0 kJ/m, and the elongation rate is 11.4%–14.7%, with an average of 12.7%, both of which are negatively correlated with the impact energy per drop. Regression analysis shows that energy absorption and shank elongation, as well as momentum input and impact duration, conform to the linear relationship. The complete dynamic capacity envelope of MP1 rockbolts is proposed, which reflects the dynamic bearing capacity, elongation, and distinct stages. This study is helpful to better understand the dynamic characteristics of energy-absorbing rockbolts and assist design engineers in robust reinforcement systems design to mitigate rockburst damage in seismically active underground excavations.

Effects of Different Charging Currents and Temperatures on the Voltage Plateau Behavior of Li-Ion Batteries

Lithium-ion power batteries, which are the foundation of electric cars and are expected to play a significant role in a variety of operating environments and application situations, have major development prospects. In order to obtain the optimal operation range of ternary Li-ion batteries under various current rates and test temperatures, the characteristics of the voltage plateau period (VPP) of batteries in different states are examined by piecewise fitting based on charging and discharging cycle experiments. The findings demonstrate that while charging at current rates of 0.10C, 0.25C, 0.50C, 0.75C, and 1.00C under temperatures of 40 °C, 25 °C, and 10 °C, the battery’s termination voltage changes seamlessly from 3.5–3.75 V, 3.55–3.8 V, 3.6–3.85 V, 3.7–4 V, and 3.85–4.05 V, the growth in surface temperature does not surpass its maximum level, and the charge capacity exceeds 50%. Batteries operate more effectively. When the test temperature is −20 °C, the voltage rebound stage that occurs in the initial period of charging at 0.50C, 0.75C, and 1.00C accounts for the highest charge capacity, close to 70%. The study’s findings can be used as a guide when designing a lithium-ion power battery’s model and control method for an electric vehicle’s energy storage system.

Enhanced horizontal mobility of a coalesced jumping droplet on superhydrophobic surfaces with an asymmetric ridge

Enhancing the horizontal mobility of coalesced droplets on a plane could promote droplet jumping. Here, we achieve enhanced horizontal mobility of a coalesced jumping droplet on superhydrophobic surfaces with an asymmetric ridge and investigate the underlying mechanism through experiment and simulation. Results indicate that the coalesced droplet accelerates during the coalescence-induced jumping stage and gains horizontal velocity during the rebound stage. The nondimensional horizontal velocity can reach 0.47, which is about 2.3 times the jumping velocity on the plane. Depending on the height-to-width ratio of the asymmetric ridge, the ratio of the horizontal velocity to the fallen velocity when the fallen droplet makes contact with the ridge is 0.55–0.75. Furthermore, the coalesced droplet can still obtain considerable horizontal velocity on superhydrophobic surfaces with an asymmetric ridge when the initial droplet radius is unequal. This work provides new insights for improving droplet jumping by surface structure in related fields.

Containment strategy during the COVID-19 pandemic among three Asian low and middle-income countries.

BackgroundCOVID-19 has not been effectively controlled, seriously threatening people’s health and socioeconomic development. This study aims to summarise the successful experiences and lessons in containment strategy learned from Asian Low- and Middle-Income Countries (LMICs) during the COVID-19 pandemic and analyse the effectiveness of their measures to provide lessons for LMICs in general.MethodsThis is a retrospective study on the effectiveness of China, India, and Vietnam’s containment strategies. The objective was to assess the effectiveness of measures taken for COVID-19 and provide lessons for wider LMICs in controlling and preventing the COVID-19 pandemic.ResultsAs of June 16, 2021, the Indian epidemic was in the declining part of the rebound stage, with a total of 21 521.900 cases per million and 276.740 deaths per million – both the highest among the three countries. Entering the normalised prevention and control stage, China stably remained at a total of 63. 615 cases per million and 3.211 deaths per million. Vietnam's number of new cases per million was very low in the first stage and almost stagnant except for cluster epidemics. In May 2021, the number of new cases per million started to rapidly increase, but the total of deaths per million was at the low level of 0.627.ConclusionsA high attention to epidemics at early stages, strict border control measures, and synchronization of government and population on COVID-19 prevention and control opinions and behaviours play important roles in designing containment strategies. In addition, rapid close contact tracing and large-scale nucleic testing are good options for response to cluster epidemics.

Penetration trajectory of rigid projectile in the heterogeneous meso-scale concrete target

For the normal penetration of a symmetrical rigid projectile into a concrete target with coarse aggregates, the lateral deflection may occur under certain conditions depending on geometrical parameters of the projectile, impact velocity and coarse aggregate distribution. In this work, four dimensionless numbers of projectile, that is, impact factor [Formula: see text], length-to-diameter ratio [Formula: see text], nose factor [Formula: see text] and the relative location of mass center [Formula: see text], are employed to study the effects of projectile parameters on the deflection of penetration trajectory. Numerical studies based on three-dimensional (3D) meso-scale concrete model are conducted and the projectile trajectories are obtained under different dimensionless numbers. According to the development of the deflection angle during the rigid projectile penetration into meso-scale concrete, the motion of the projectile can be divided into four stages, that is, initial deflection, rapid change, deflection rebound and final stage. The numerical results show that, for the same meso-scale concrete target, the deflection of the projectile trajectory becomes larger with the increases of [Formula: see text], [Formula: see text] and [Formula: see text], while the deflection angle of projectile decreases with the increase of [Formula: see text].

Drivers and forecasts of multiple waves of the coronavirus disease 2019 pandemic: A systematic analysis based on an interpretable machine learning framework.

Coronavirus disease 2019 (COVID-19) has become a global pandemic and continues to prevail with multiple rebound waves in many countries. The driving factors for the spread of COVID-19 and their quantitative contributions, especially to rebound waves, are not well studied. Multidimensional time-series data, including policy, travel, medical, socioeconomic, environmental, mutant and vaccine-related data, were collected from 39 countries up to 30 June 2021, and an interpretable machine learning framework (XGBoost model with Shapley Additive explanation interpretation) was used to systematically analyze the effect of multiple factors on the spread of COVID-19, using the daily effective reproduction number as an indicator. Based on a model of the pre-vaccine era, policy-related factors were shown to be the main drivers of the spread of COVID-19, with a contribution of 60.81%. In the post-vaccine era, the contribution of policy-related factors decreased to 28.34%, accompanied by an increase in the contribution of travel-related factors, such as domestic flights, and contributions emerged for mutant-related (16.49%) and vaccine-related (7.06%) factors. For single-peak countries, the dominant ones were policy-related factors during both the rising and fading stages, with overall contributions of 33.7% and 37.7%, respectively. For double-peak countries, factors from the rebound stage contributed 45.8% and policy-related factors showed the greatest contribution in both the rebound (32.6%) and fading (25.0%) stages. For multiple-peak countries, the Delta variant, domestic flights (current month) and the daily vaccination population are the three greatest contributors (8.12%, 7.59% and 7.26%, respectively). Forecasting models to predict the rebound risk were built based on these findings, with accuracies of 0.78 and 0.81 for the pre- and post-vaccine eras, respectively. These findings quantitatively demonstrate the systematic drivers of the spread of COVID-19, and the framework proposed in this study will facilitate the targeted prevention and control of the ongoing COVID-19 pandemic.

Thermodynamic effects on single cavitation bubble dynamics under various ambient temperature conditions

Thermodynamic characteristics and their effects on single cavitation bubble dynamics are important to elucidate the physical behaviors of cavitation phenomena. In this study, experimental and numerical methods were utilized to explore the thermodynamic effects on single cavitation bubble dynamics under various ambient temperature conditions. A series of experiments was performed to generate a single cavitation bubble at ambient temperatures between 20 and 80 °C using a laser-induced method and a high-speed camera to observe the dynamic behaviors of bubbles. By increasing the ambient temperature, a nonspherical bubble shape with a jet flow at the bubble rebound stage was observed. Next, the numerical simulation results in terms of the bubble radius and bubble shape were validated with the corresponding experimental data. Generally, the results exhibited reasonable agreement, particularly at the later collapse and rebound stages. Critical hydrodynamic and thermodynamic mechanisms over multiple oscillation stages at different ambient temperatures were analyzed. The bubble behaviors and their intensities were numerically quantified with respect to the bubble radius, collapsing time, internal pressure, internal temperature, and phase transition rate parameters. The results showed that the maximum bubble radius, first minimum bubble radius, and collapsing time increased with an increase in the ambient temperature. Nevertheless, the peak values of the internal pressure and internal temperature decreased with an increase in the ambient temperature. Generally, the bubble collapsed less violently at high temperatures than at low temperatures.

Numerical simulation and analysis of the underwater implosion of spherical hollow ceramic pressure hulls in 11000 m depth

Pressure hulls play an important role in deep-sea underwater vehicles. However, in the ultra-high pressure environment, a highly destructive phenomenon could occur to them which is called implosion. To study the characteristics of the flow field of the underwater implosion of hollow ceramic pressure hulls, the compressible multiphase flow theory, direct numerical simulation, and adaptive mesh refinement are used to numerically simulate the underwater implosion of a single ceramic pressure hull and multiple linearly arranged ceramic pressure hulls. Firstly, the feasibility of the numerical simulation method is verified. Then, the results of the flow field of the underwater implosion of hollow ceramic pressure hulls in 11000 m depth is analyzed. There are the compression-rebound processes of the internal air cavity in the implosion. In the rebound stage, a shock wave that is several times the ambient pressure is generated outside the pressure hull, and the propagation speed is close to the speed of sound. The pressure peak of the shock wave has a negative exponential power function relationship with the distance to the center of the sphere. Finally, it is found that the obvious superimposed effect between spheres exists in the chain-reaction implosion which enhances the implosion shock wave.