Fluid simulation of inductively coupled Ar/O_2 plasmas:Comparisons with experiment

In this work, a two-dimensional fluid model has been employed to study the characteristics of Ar/O2 radio frequency（RF） inductively coupled plasma discharges. The emphasis of this work has been put on the influence of the external parameters（i.e., the RF power, the pressure, and the Ar/O2 gas ratio） on the plasma properties. The numerical results show that the RF power has a significant influence on the amplitude of the plasma density rather than on the spatial distribution.However, the pressure and the Ar/O2 gas ratio affect not only the amplitude of the plasma density, but also the spatial uniformity. Finally, the comparison between the simulation results and the experimental data has been made at different gas pressures and oxygen contents, and a good agreement has been achieved.

Fluid simulation of the effect of a dielectric window with high temperature on plasma parameters in inductively coupled plasma

To maintain the high-density plasma source in inductively coupled plasma(ICP),very high radiofrequency power is often delivered to the antenna,which can heat the dielectric windows near the antenna to high temperature.This high temperature can modulate the plasma characteristics to a large degree.We thus study the effect of dielectric window temperature on plasma parameters in two different ICP structures based on COMSOL software.The distributions of various plasma species are examined at different dielectric window temperatures.The concentration of neutral gas is found to be largely modulated at high dielectric window temperature,which further affects the electron collision probability with neutrals and the electron temperature.However,the electron density profiles are barely affected by the dielectric window temperature,which is mainly concentrated at the center of the reactor due to the fixed power input and pressure.

Fluid simulation of the pulsed bias effect on inductively coupled nitrogen discharges for low-voltage plasma immersion ion implantation

Planar radio frequency inductively coupled plasmas（ICP） are employed for low-voltage ion implantation processes,with capacitive pulse biasing of the substrate for modulation of the ion energy. In this work, a two-dimensional（2D） selfconsistent fluid model has been employed to investigate the influence of the pulsed bias power on the nitrogen plasmas for various bias voltages and pulse frequencies. The results indicate that the plasma density as well as the inductive power density increase significantly when the bias voltage varies from 0 V to-4000 V, due to the heating of the capacitive field caused by the bias power. The N＋fraction increases rapidly to a maximum at the beginning of the power-on time, and then it decreases and reaches the steady state at the end of the glow period. Moreover, it increases with the bias voltage during the power-on time, whereas the N2-＋ fraction exhibits a reverse behavior. When the pulse frequency increases to 25 kHz and40 kHz, the plasma steady state cannot be obtained, and a rapid decrease of the ion density at the substrate surface at the beginning of the glow period is observed.

Effect of radio frequency bias on plasma characteristics of inductively coupled argon discharge based on fluid simulations

t A fluid model is employed to investigate the effect of radio frequency bias on the behavior of an argon inductively coupled plasma(ICP).In particular,the effects of ICP source power,single-frequency bias power,and dual-frequency bias power on the characteristics of ICP are simulated at a fixed pressure of 30 mTorr(1 Torr=1.33322×102 Pa).When the bias frequency is fixed at 27.12 MHz,the two-dimensional(2D)plasma density profile is significantly affected by the bias power at low ICP source power(e.g.,50 W),whereas it is weakly affected by the bias power at higher ICP source power(e.g.,100 W).When dual-frequency(27.12 MHz/2.26 MHz)bias is applied and the sum of bias powers is fixed at 500 W,a pronounced increase in the maximum argon ion density is observed with the increase of the bias power ratio in the absence of ICP source power.As the ratio of 27.12-MHz/2.26-MHz bias power decreases from 500 W/0 W to 0 W/500 W with the ICP source power fixed at 50 W,the plasma density profiles smoothly shifts from edge-high to center-high,and the effect of bias power on the plasma distribution becomes weaker with the bias power ratio decreasing.Besides,the axial ion flux at the substrate surface is characterized by a maximum at the edge of the substrate.When the ICP source power is higher,the 2D plasma density profiles,as well as the spatiotemporal and radial distributions of ion flux at the substrate surface are characterized by a peak in the reactor center,and the distributions of plasma parameters are negligibly affected by the dual-frequency bias power ratio.

An efficient non-iterative smoothed particle hydrodynamics fluid simulation method with variable smoothing length

In classical smoothed particle hydrodynamics(SPH)fluid simulation approaches,the smoothing length of Lagrangian particles is typically constant.One major disadvantage is the lack of adaptiveness,which may compromise accuracy in fluid regions such as splashes and surfaces.Attempts to address this problem used variable smoothing lengths.Yet the existing methods are computationally complex and non-efficient,because the smoothing length is typically calculated using iterative optimization.Here,we propose an efficient non-iterative SPH fluid simulation method with variable smoothing length(VSLSPH).VSLSPH correlates the smoothing length to the density change,and adaptively adjusts the smoothing length of particles with high accuracy and low computational cost,enabling large time steps.Our experimental results demonstrate the advantages of the VSLSPH approach in terms of its simulation accuracy and efficiency.

Adaptive smoothing length method based on weighted average of neighboring particle density for SPH fluid simulation

Background In the smoothed particle hydrodynamics(SPH)fluid simulation method,the smoothing length affects not only the process of neighbor search but also the calculation accuracy of the pressure solver.Therefore,it plays a crucial role in ensuring the accuracy and stability of SPH.Methods In this study,an adaptive SPH fluid simulation method with a variable smoothing length is designed.In this method,the smoothing length is adaptively adjusted according to the ratio of the particle density to the weighted average of the density of the neighboring particles.Additionally,a neighbor search scheme and kernel function scheme are designed to solve the asymmetry problems caused by the variable smoothing length.Results The simulation efficiency of the proposed algorithm is comparable to that of some classical methods,and the variance of the number of neighboring particles is reduced.Thus,the visual effect is more similar to the corresponding physical reality.Conclusions The precision of the interpolation calculation performed in the SPH algorithm is improved using the adaptive-smoothing length scheme;thus,the stability of the algorithm is enhanced,and a larger timestep is possible.

Surface Tension Model Based on Implicit Incompressible Smoothed Particle Hydrodynamics for Fluid Simulation

In order to capture stable and realistic microscopic features of fluid surface, a surface tension and adhesion method based on implicit incompressible SPH （smoothed particle hydrodynamics） is presented in this paper. It gives a steady and fast tension model and can solve the problem of not considering adhesion. Molecular cohesion and surface minimization are considered for surface tension, and adhesion is added to show the microscopic characteristics of the surface. To simulate surface tension and adhesion stably and efficiently, the surface tension and adhesion model is integrated to an implicit incompressible SPH method. The experimental results show that the method can better simulate surface features in a variety of scenarios compared with previous methods and meanwhile ensure stability and efficiency.

A simple approach for bubble modelling from multiphase fluid simulation

This article presents a novel and flexible bubble modelling technique for multi-fluid simulations using a volume fraction representation. By combining the volume fraction data obtained from a primary multi-fluid simulation with simple and efficient secondary bubble simulation, a range of real-world bubble phenomena are captured with a high degree of physical realism, including large bubble deformation,sub-cell bubble motion, bubble stacking over the liquid surface, bubble volume change, dissolving of bubbles,etc. Without any change in the primary multi-fluid simulator, our bubble modelling approach is applicable to any multi-fluid simulator based on the volume fraction representation.

Analysis of parallel multigrid methods in real-time fluid simulation

The multigrid method has been widely used in computational fluid dynamics(CFD)numerical calculations because of its strong convergence.To achieve real-time simulation of a fluid in computer graphics(CG),the operation efficiency is also a significant factor to consider except for operational accuracy.For this problem,we introduced two multigrid cycling schemes,V-Cycle and full multigrid(FMG).Moreover,we have proposed a simple geometric multigrid method(GMG),and compared with the existing wide application of algebraic multigrid(AMG).All the calculations are the solution of parallel computing of GPU in this paper.The results showed that our approaches have improved the algorithm’s computational speed and convergence time,which prominently enhanced the efficiency of the fluid simulation.

Numerical Simulation of the Settling Flux of Biodeposition in a Bay with Cage Culture Through Similarity Theory and a Simplified Pollution Source

The settling flux of biodeposition affects the environmental quality of cage culture areas and determines their environmental carrying capacity.Simple and effective simulation of the settling flux of biodeposition is extremely important for determining the spatial distribution of biodeposition.Theoretically,biodeposition in cage culture areas without specific emission rules can be simplified as point source pollution.Fluent is a fluid simulation software that can simulate the dispersion of particulate matter simply and efficiently.Based on the simplification of pollution sources and bays,the settling flux of biodeposition can be easily and effectively simulated by Fluent fluid software.In the present work,the feasibility of this method was evaluated by simulation of the settling flux of biodeposition in Maniao Bay,Hainan Province,China,and 20 sampling sites were selected for determining the settling fluxes.At sampling sites P1,P2,P3,P4,P5,Z1,Z2,Z3,Z4,A1,A2,A3,A4,B1,B2,C1,C2,C3 and C4,the measured settling fluxes of biodeposition were 26.02,15.78,10.77,58.16,6.57,72.17,12.37,12.11,106.64,150.96,22.59,11.41,18.03,7.90,19.23,7.06,11.84,5.19 and 2.57 g d^(−1)m^(−2),respectively.The simulated settling fluxes of biodeposition at the corresponding sites were 16.03,23.98,8.87,46.90,4.52,104.77,16.03,8.35,180.83,213.06,39.10,17.47,20.98,9.78,23.25,7.84,15.90,6.06 and 1.65 g d^(−1)m^(−2),respectively.There was a positive correlation between the simulated settling fluxes and measured ones(R=0.94,P=2.22×10^(−9)<0.05),which implies that the spatial differentiation of biodeposition flux was well simulated.Moreover,the posterior difference ratio of the simulation was 0.38,and the small error probability was 0.94,which means that the simulated results reached an acceptable level from the perspective of relative error.Thus,if nonpoint source pollution is simplified to point source pollution and open waters are simplified based on similarity theory,the setting flux of biodeposition in the open waters can be simply and effectively simulated by the fluid simulation software Fluent.

Data-driven simulation in fluids animation: A survey

The field of fluid simulation is developing rapidly,and data-driven methods provide many frameworks and techniques for fluid simulation.This paper presents a survey of data-driven methods used in fluid simulation in computer graphics in recent years.First,we provide a brief introduction of physical based fluid simulation methods based on their spatial discretization,including Lagrangian,Eulerian,and hybrid methods.The characteristics of these underlying structures and their inherent connection with data driven methodologies are then analyzed.Subsequently,we review studies pertaining to a wide range of applications,including data-driven solvers,detail enhancement,animation synthesis,fluid control,and differentiable simulation.Finally,we discuss some related issues and potential directions in data-driven fluid simulation.We conclude that the fluid simulation combined with data-driven methods has some advantages,such as higher simulation efficiency,rich details and different pattern styles,compared with traditional methods under the same parameters.It can be seen that the data-driven fluid simulation is feasible and has broad prospects.

Computational fluid dynamics simulation of formaldehyde emission characteristics and its experimental validation in environment chamber

We investigated the effect of supply air rate and temperature on formaldehyde emission characteristics in an environment chamber.A three-dimensional computational fluid dynamics(CFD) chamber model for simulating formaldehyde emission in twelve different cases was developed for obtaining formaldehyde concentration by the area-weighted average method.Laboratory experiments were conducted in an environment chamber to validate the simulation results of twelve different cases and the formaldehyde concentration was measured by continuous sampling.The results show that there was good agreement between the model prediction and the experimental values within 4.3 difference for each case.The CFD simulation results varied in the range from 0.21 mg/m3 to 0.94 mg/m3,and the measuring results in the range from 0.17 mg/m3 to 0.87 mg/m3.The variation trend of formaldehyde concentration with supply air rate and temperature variation for CFD simulation and experiment measuring was consistent.With the existence of steady formaldehyde emission sources,formaldehyde concentration generally increased with the increase of temperature,and it decreased with the increase of air supply rate.We also provided some reasonable suggestions to reduce formaldehyde concentration and to improve indoor air quality for newly decorated rooms.

COMPUTATIONAL FLUID DYNAMICS(CFD) SIMULATIONS OF DRAG REDUCTION WITH PERIODIC MICRO-STRUCTURED WALL

Computational fluid dynamics（CFD） simulations are adopted to investigate rectangular microchannel flows with various periodic micro-structured wall by introducing velocity slip boundary condition at low Reynolds number. The purpose of the current study is to numerically find out the effects of periodic micro-structured wall on the flow resistance in rectangular microchannel with the different spacings between microridges ranging from 15 to 60 pm. The simulative results indicate that pressure drop with different spacing between microridges increases linearly with flow velocity and decreases monotonically with slip velocity; Pressure drop reduction also increases with the spacing between microridges at the same condition of slip velocity and flow velocity. The results of numerical simulation are compared with theoretical predictions and experimental results in the literatures. It is found that there is qualitative agreement between them.

Computational fluid dynamics simulation of gas-liquid two phases flow in 320 m^3 air-blowing mechanical flotation cell using different turbulence models

According to the recently developed single-trough floating machine with the world's largest volume(inflatable mechanical agitation flotation machine with volume of 320 m3) in China, the gas-fluid two-phase flow in flotation cell was simulated using computational fluid dynamics method. It is shown that hexahedral mesh scheme is more suitable for the complex structure of the flotation cell than tetrahedral mesh scheme, and a mesh quality ranging from 0.7 to 1.0 is obtained. Comparative studies of the standard k-ε, k-ω and realizable k-ε turbulence models were carried out. It is indicated that the standard k-ε turbulence model could give a result relatively close to the practice and the liquid phase flow field is well characterized. In addition, two obvious recirculation zones are formed in the mixing zones, and the pressure on the rotor and stator is well characterized. Furthermore, the simulation results using improved standard k-ε turbulence model show that surface tension coefficient of 0.072, drag model of Grace and coefficient of 4, and lift coefficient of 0.001 can be achieved. The research results suggest that gas-fluid two-phase flow in large flotation cell can be well simulated using computational fluid dynamics method.

Numerical simulation of spatial-temporal evolution characteristics of subsurface fluid based on strong body seismogenic model$$$$

Using finite element technique of the plane-strain problem in solid-liquid two-phase medium, we Studied the char acteristics of 'field precursors' and 'focus precursors' of subsurface fluid and their spatial-temporal evolution in case of dip-slip earthquake. The results show that: ① the change of ground fluid is slow and the anomaly is not prominent in the early period which is of elastic accumulation and non-linear; ② dilatancy emerges and anomalyfocus mainly in the source region in the moderate period which is hardening and of local dilatancy. In the period the focus precursors emerge earlier than the field precursors; ③ anomalies spreed continuously in the source area and new regions with big anomaly emerge out of the source region in the middle-short period which is of large scale dilatancy.

Application of Stochastic Fracture Network with Numerical Fluid Flow Simulations to Groundwater Flow Modeling in Fractured Rocks

The continuum approach in fluid flow modeling is generally applied to porous geological media, but has limited applicability to fractured rocks. With the presence of a discrete fracture network relatively sparsely distributed in the matrix, it may be difficult or erroneous to use a porous medium fluid flow model with continuum assumptions to describe the fluid flow in fractured rocks at small or even large field scales. A discrete fracture fluid flow approach incorporating a stochastic fracture network with numerical fluid flow simulations could have the capability of capturing fluid flow behaviors such as inhomogeneity and anisotropy while reflecting the changes of hydraulic features at different scales. Moreover, this approach can be implemented to estimate the size of the representative elementary volume (REV) in order to find out the scales at which a porous medium flow model could be applied, and then to determine the hydraulic conductivity tensor for fractured rocks. The following topics are focused on in this study: (a) conceptual discrete fracture fluid flow modeling incorporating a stochastic fracture network with numerical flow simulations; (b) estimation of REV and hydraulic conductivity tensor for fractured rocks utilizing a stochastic fracture network with numerical fluid flow simulations; (c) investigation of the effect of fracture orientation and density on the hydraulic conductivity and REV by implementing a stochastic fracture network with numerical fluid flow simulations, and (d) fluid flow conceptual models accounting for major and minor fractures in the 2 D or 3 D flow fields incorporating a stochastic fracture network with numerical fluid flow simulations.

Simulation of the plasticizing behavior of composite modified doublebase(CMDB)propellant in grooved calendar based on adaptive grid technology

The frequent occurrence of safety accidents during the calendering process is caused by the flammable and explosive properties of composite modified double-base(CMDB)propellant.Optimization of process parameters with the aid of fluid simulation technology could effectively ensure the safety of the calendering process.To improve the accuracy of the simulation results,material parameters and model structure were corrected based on actual conditions,and adaptive grid technology was applied in the local mesh refinement.In addition,the rheological behavior,motion trajectories and heat transfer mechanisms of CMDB propellant slurry were studied with different gaps,rotational rates and temperatures of two rollers.The results indicated that the refined mesh could significantly improve the contour clarity of boundaries and simulate the characteristics of CMDB propellant slurry reflux movement caused by the convergent flow near the outlet.Compared with the gap,the increased rotational rate of roller could promote the reflux movement and intensify the shear flow of slurry inside the flow region by viscous shear dragging.Meanwhile,under the synergistic effect of contact heat transfer as well as convective heat exchange,heat accumulated near the outlet and diffused along the reflux movement,which led to the countercurrent heat dissipation behavior of CMDB propellant slurry.The plasticizing mechanism of slurry and the safety of calendering under different conditions were explored,which provided theoretical guidance and reference data for the optimization of calendering process conditions.Based on the simulation results,the safety of the CMDB propellant calendering process could be significantly improved with a few tests conducted during a short research and development cycle.

Discontinuity of mode transition and hysteresis in hydrogen inductively coupled plasma via a fluid model

A new type of two-dimensional self-consistent fluid model that couples an equivalent circuit module is used to in- vestigate the mode transition characteristics and hysteresis in hydrogen inductively coupled plasmas at different pressures, by varying the series capacitance of the matching box. The variations of the electron density, temperature, and the circuit electrical properties are presented. As cycling the matching capacitance, at high pressure both the discontinuity and hysteresis appear for the plasma parameters and the transferred impedances of both the inductive and capacitive discharge components, while at low pressure only the discontinuity is seen. The simulations predict that the sheath plays a determi- native role on the presence of discontinuity and hysteresis at high pressure, by influencing the inductive coupling efficiency of applied power. Moreover, the values of the plasma transferred impedances at different pressures are compared, and the larger plasma inductance at low pressure due to less collision frequency, as analyzed, is the reason why the hysteresis is not seen at low pressure, even with a wider sheath. Besides, the behaviors of the coil voltage and current parameters during the mode transitions are investigated. They both increase （decrease） at the E to H （H to E） mode transition, indicating an improved （worsened） inductive power coupling efficiency.

Affine particle-in-cell method for two-phase liquid simulation

Background The interaction of gas and liquid can produce many interesting phenomena,such as bubbles rising from the bottom of the liquid.The simulation of two-phase fluids is a challenging topic in computer graphics.To animate the interaction of a gas and liquid,MultiFLIP samples the two types of particles,and a Euler grid is used to track the interface of the liquid and gas.However,MultiFLIP uses the fluid implicit particle(FLIP)method to interpolate the velocities of particles into the Euler grid,which suffer from additional noise and instability.Methods To solve the problem caused by fluid implicit particles(FLIP),we present a novel velocity transport technique for two individual particles based on the affine particle-in-cell(APIC)method.First,we design a weighed coupling method for interpolating the velocities of liquid and gas particles to the Euler grid such that we can apply the APIC method to the simulation of a two-phase fluid.Second,we introduce a narrowband method to our system because MultiFLIP is a time-consuming approach owing to the large number of particles.Results Experiments show that our method is well integrated with the APIC method and provides a visually credible two-phase fluid animation.Conclusions The proposed method can successfully handle the simulation of a two phase fluid.

Hydroxyapatite Coatings on Titanium Prepared by Electrodeposition in a Modified Simulated Body Fluid

Hydroxyapatite coatings were directly prepared on anodized titanium by electro-deposition method in a modified simulated body fluid.The configuration,structure and bioactivity of the coating were investigated with scanning electron microscopy(SEM),X-ray diffraction analyzer(XRD)and Fourier transform infrared spectros-copy(FTIR)techniques.The results demonstrated that pure and homogeneous hydroxyapatite coating can be obtained without any post-treatment.The prepared coating showed good bioactivity in simulated body fluid(SBF).The time required for a fully covered dense hydroxyapatite coatings was 4 days immersion in SBF.