Numerical Study Of Dynamics Research Articles

A NEW FRACTAL-FRACTIONAL HYBRID MODEL FOR STUDYING CLIMATE CHANGE ON COASTAL ECOSYSTEMS FROM THE MATHEMATICAL POINT OF VIEW

Rapid emissions of green-house gases (GHGs) are causing global warming, which is wreaking havoc on the earth’s climate system. As a result, the coastal ecosystems of the world are on the verge of becoming endangered. We develop a fractal-fractional hybrid model to estimate the influence of rapid emissions of GHGs on the coastal ecosystems and climate changes. The fractal-fractional climate change model is considered for the theoretical and numerical aspects. The theoretical aspect includes the existence and Hyers–Ulam (HU) stability of the solutions while the numerical aspect is based on Lagrange’s interpolation polynomial. Moreover, unique solutions are proved by the Banach contraction principle. Different fractal-fractional orders are considered for the numerical study of dynamics of solutions which prove the importance and accuracy of these hybrid operators.

Numerical study of dynamics of cavitation bubble collapse near oscillating walls

This paper presents a numerical study of the dynamics of an initially spherical bubble collapse near an oscillating rigid wall with a large amplitude; the wall oscillating amplitude is greater than 1% of the initial maximum bubble radius. Numerical simulations were conducted using a compressible two-phase flow model and the volume of fluid (VOF) interphase-sharpening technique on a general curvilinear moving grid. The numerical results for bubbles in the free field and near a wall were computed and compared with published experimental data. To study the effects of the oscillating wall on bubble collapse, a sinusoidal function was used for wall oscillation. The initial bubble conditions were set as a Rayleigh bubble located above the rigid wall at a dimensionless bubble-boundary distance with initial phases of 0° and 180°. During bubble collapse, the interface deformation, jetting behavior, bubble collapse time, and bubble migration were determined. Violent collapse of the bubble, jetting behavior, and shock propagation from the significant effects of the oscillating wall were observed in simulation cases with different wall motions. The effects of the non-dimensional amplitude scale and non-dimensional period timescale were considered with the initial phases in the problem. The trend lines of typical characteristics and critical points of bubble collapse were determined.

A numerical study of dynamics in thin hopper flow and granular jet**Project supported by the National Natural Science Foundation of China (Grant Nos. 11705256 and 11905272), the National Postdoctoral Program for Innovative Talents, China (Grant No. BX201700258), Young Scholar of CAS "Light of West China" Program for Guanghui Yang (Grant No. 2018-98), and the Strategic Priority Research Program of the

The dynamics of granular material discharging from a cuboid but thin hopper, including the hopper flow and granular jet, are investigated via discrete element method (DEM) simulations. The slot width is varied to study its influence on the flow. It is found the flow in the cuboid hopper has similarity with the flow in two-dimensional (2D) hopper. When the slot width is large, the flowrate is higher than the predicted value from Beverloo’s law and the velocity distribution is not Gaussian-like. For granular jet, there is a transition with varying slot width. For large slot width, there is a dense core in the jet and the variations of velocities and density are relatively small. Finally, the availability of continuum model is assessed and the results show that the performance with large slot width is better than that with small slot width.

Numerical study of dynamics of a celt on a horizontal plane with viscous friction

Numerical study of dynamics of a celt on a horizontal plane with viscous friction

Influence of thermal fluctuations on dynamics of charged particles in electromagnetic fields

The numerical study of dynamics of the charged particles in the confined cloud located in a constant electromagnetic field is presented. Calculations are performed for ions with various masses in a wide range of system parameters. For the first time, an influence of thermal fluctuations of particles on their motion in an electromagnetic field is considered. Analytical estimations for the analysis of this effect are proposed.

Contribution to the Experimental and Numerical Dynamic Study of a Turbulent Jet Issued from Lobed Diffuser

In the present work, we are interested to the experimental and numerical study of the free turbulent lobed jet, used in residential heating and air conditioning. The objective of our study is the improvement of the diffusion performance of the ventilation driving air flow, in the occupancy zone. The experiments have been conducted in a room where the dimensions enables a better execution in the conditions of free and hot vertical jet at unfavorable pushing forces. The installation contains a hot air blowing diffuser oriented from top to bottom. The velocities of the flow were measured by a multi-functional thermo-anemometer. The probe is supported by a stem guided vertically and horizontally in order to sweep a maximum space. Experimentally, we measured the axial and radial velocity field. The dynamics field analysis, show that in the potential core region, the dynamic profiles are more spread at the principal plane and this is due to the widening of the lobes’ opening. While, in the transition zone and in the region where the flow is fully developed, these profiles are not influenced by the type of plane and then the jet will be similar to the circular one. Numerically, we used the commercial software Fluent. The obtained numerical results with turbulence method, (RNG k-ε), were in good accordance with the experimental one.

Experimental and numerical study of premixed hydrogen/air flame propagating in a combustion chamber

An experimental and numerical study of dynamics of premixed hydrogen/air flame in a closed explosion vessel is described. High-speed shlieren cinematography and pressure recording are used to elucidate the dynamics of the combustion process in the experiment. A dynamically thickened flame model associated with a detailed reaction mechanism is employed in the numerical simulation to examine the flame-flow interaction and effect of wall friction on the flame dynamics. The shlieren photographs show that the flame develops into a distorted tulip shape after a well-pronounced classical tulip front has been formed. The experimental results reveal that the distorted tulip flame disappears with the primary tulip cusp and the distortions merging into each other, and then a classical tulip is repeated. The combustion dynamics is reasonably reproduced in the numerical simulations, including the variations in flame shape and position, pressure build-up and periodically oscillating behavior. It is found that both the tulip and distorted tulip flames can be created in the simulation with free-slip boundary condition at the walls of the vessel and behave in a manner quite close to that in the experiments. This means that the wall friction could be unimportant for the tulip and distorted tulip formation although the boundary layer formed along the sidewalls has an influence to a certain extent on the flame behavior near the sidewalls. The distorted tulip flame is also observed to be produced in the absence of vortex flow in the numerical simulations. The TF model with a detailed chemical scheme is reliable for investigating the dynamics of distorted tulip flame propagation and its underlying mechanism.

Modeling of the flow structure and heat transfer in a gas-droplet turbulent boundary layer

A numerical study of dynamics and heat/mass transfer in a gas-droplet turbulent boundary layer on a vertical flat plate is carried out. A large number of factors which affect the heat and mass transfer and the structure of thermal and concentration fields in a turbulent boundary layer is analyzed. It is shown that the increase in droplet concentration results in the intensification of heat transfer, as compared with the single-phase air flow. The comparison of this analysis with experimental data shows a qualitative and quantitative agreement between the calculated and experimental data.

Three-dimensional vesicles under shear flow: Numerical study of dynamics and phase diagram

The study of vesicles under flow, a model system for red blood cells (RBCs), is an essential step in understanding various intricate dynamics exhibited by RBCs in vivo and in vitro. Quantitative three-dimensional analyses of vesicles under flow are presented. The regions of parameters to produce tumbling (TB), tank-treating, vacillating-breathing (VB), and even kayaking (or spinning) modes are determined. New qualitative features are found: (i) a significant widening of the VB mode region in parameter space upon increasing shear rate γ and (ii) a robustness of normalized period of TB and VB with γ. Analytical support is also provided. We make a comparison with existing experimental results. In particular, we find that the phase diagram of the various dynamics depends on three dimensionless control parameters, while a recent experimental work reported that only two are sufficient.

Numerical study of dynamics of single bubbles and bubble swarms

A systematic computational study of the dynamics of gas bubbles rising in a viscous liquid is presented. Two-dimensional simulations are carried out. Both the dynamics of single bubbles and small groups of bubbles (bubble swarms) are considered. This is a continuation of our previous studies on the two-bubble coalescence and vortex shedding [A. Smolianski, H. Haario, P. Luukka, Vortex shedding behind a rising bubble and two-bubble coalescence: a numerical approach, Appl. Math. Model. 29 (2005) 615–632]. The proposed numerical method allows us to simulate a wide range of flow regimes, accurately capturing the shape of the deforming interface of the bubble and the surface tension effect, while maintaining the mass conservation. The computed time-evolution of bubble’s position and rise velocity shows a good agreement with the available experimental data. At the same time, the results on the dynamics of bubble interface area, which are, up to our knowledge, presented for the first time, show how much the overall mass transfer would be affected by the interface deformation in the case of the bubble dissolution. Another set of experiments that are of interest for chemical engineers modelling bubbly flows concerns the bubble swarms and their behavior in different bubble-shape regimes. The ellipsoidal and spherical shape regimes are considered to represent, respectively, the coalescing and non-coalescing bubble swarms. The average rise velocities of the bubble swarms are computed and analyzed for both regimes.

A numerical study of dynamics of a temporally evolving swirling jet

Direct numerical simulation (DNS) of a swirling jet near the outlet of a nozzle with axisymmetric and non-axisymmetric disturbances is performed to investigate the dynamic characteristics of the flow. The early (linear) stage of the jet evolution agrees well with the predictions of linear stability theory. In the nonlinear stage, the axisymmetric DNS shows that the interaction between the primary vortex ring and the streamwise columnar vortex creates a secondary vortex structure with opposite azimuthal vorticity near the columnar vortex. Then a vortex pair consisting of the primary and secondary vortices forms and travels radially away from the symmetry axis, causing a rapid increase of the thickness of mixing layer. The non-axisymmetric DNS shows that the streamwise vortex layer developed in the early stage of evolution due to azimuthal instability breakdowns into small eddies under the joint stretch of the axial and azimuthal shear. The results reveal several mechanisms of mixing enhancement by swirl, i.e., the radial motion of vortex ring pairs, the rapid growth of streamwise vorticity, and the creation of three-dimensional small eddies. They are all favorable for fluid entrainment in swirling jets.

Dynamics of a Two-Joint Dolphinlike Propulsion Mechanism. 5th Report. Analysis of a Model of Spring Support for Second Joint.

In this paper, we describes a numerical study of dynamics and efficiency of a two-joint bending propulsion mechanism that is composed of a streamlined body and a caudal fin. First, we extended our analysical model to a model in which the second joint was supported by a spring instead of an actuator by use of an iterative calculation method. Second, we discussed the characteristics of the caudal fin motion and the propulsive efficiency with regard to the variation of the spring constant of the second joint in comparison with the forced motion model so far. It was found that the motion of sufficiently high propulsive efficiency can be attained by spring model with wide variety of spring constant. Finally, we investigated the robustness of the thrust with regard to the temporal variation of the propulsive speed both for the forced motion model so far and for the spring model. It was found that, when the temporal propulsive speed becomes large, the thrust keeps being positive in the spring model although the thrust suddenly decreased to a negative value in the forced motion model. This tendency is especially preferable in the case of propulsion in the ocean.

Dynamics of a Two-Joint Dolphinlike Propulsion Mechanism. (4th Report. Analysis of a Lunate Caudal Fin Model).

This paper describes a numerical study of dynamics and efficiency of a two-joint bending propulsion mechanism that is composed of a streamlined body and a caudal fin. We used the quasivorrtex-lattice-method in order to analyze the lunate caudal fin, comprising the slender body theory for the body. Firstly, we examined the characteristics of the propulsive efficiency of various types of the caudal fins only. It was found that the propulsive efficiency of three dimensional analysis becomes lower than that of two-dimensional analysis and that large swept angle causes reduction of the propulsive efficiency. Next, we investigated the characteristics of the propulsive efficiency of the whole mechanism including the effect of the body. The propulsive efficiency of the whole mechanism exhibited similar tendency to that of caudal fin only, although the propulsive efficiency of the whole mechanism becomes lower than that of caudal fin only, especially at low reduced frequency. Finally, by comparing the calculated results with some observed data of dolphin, it was found that the optimum motion parameters, which gives the highest propulsive efficiency, agree well with the dolphin's motion parameters.

Numerical studies of dynamics and cloud microphysics of the frontal rainbands

A review is given of numerical studies of the dynamics, organization and structure of cloud and precipitation on the mesoscale in various types of atmosphetic fronts. Two- and three-dimensional numerical models were constructed to study the dynamic and microphysical structure of the frontal bands in the winter cloud systems. Numerical investigation of the model equations has been carried out and analyzed for two synoptic situations representing both occluded and warm fronts. A detailed analysis is made of the threedimensional numerical simulation of the evolution of the dynamics and cloud microphysics of three rainbands in an occluded frontal system both in cloud and freecloud atmosphere. For the occluded front, two of the rainbands occurred in the leading portion of the frontal cloud shield and were oriented parallel to the warm front of the system. The third band occurred in the trailing of the cloud shield and had cold frontal orientation. The dynamics, cloud microphysics and precipitation of the band were oscillatory in space and time. The cloudiness may both intensify and weaken the dynamical features in the cloud and in the near-cloud environment depending on the cloud phase. Three rainbands were also found in a warm front in the second case. The highest activity of cloud and precipitation bands was associated with the front's surface.