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Accepted Manuscript , doi: 10.1016/j.taml.2018.06.000
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Abstract:
A numerical simulation is performed to find out a key vortical structure in the laminar-turbulent transition. A low-speed streak is generated inside a laminar boundary layer using an isolated cuboid roughness, aimed at providing an environment unstable to outer disturbances. Then, a short duration jet is issued into the boundary layer. When the jet velocity is low, some vortices appear in the boundary layer, but the transition of the boundary layer does not take place. However, when the jet velocity exceeds a certain threshold, two vortices newly appear above the elongated legs of a V-shaped vortex and only one of them is stretched and survives. After that, vortices are generated one after another around the survived one. By comparing the decayed and the survived vortices, it is found that the difference in their heights is the key characteristic which leads to the transition.
Accepted Manuscript
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Abstract:
An improved smoke-wire flow visualization technique using a large capacitor as the power source was proposed. Electric current discharged from capacitors was used to heat a fine metal wire suspended in the flow field. The oil droplets attached to the wire were vaporized and smoke filaments followed the flow motions. A digital camera was used to record the images of the smoke filaments. The actions of discharging and camera shutter were triggered by signals from a micro-controller to ensure the accurate timing. Clear images of the streaklines were captured at a free-stream velocity up to 12.9 m/s, much higher than the limits of the existing techniques.
Accepted Manuscript , doi: 10.1016/j.taml.2018.06.000
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The spacecraft with multistage solar panels have nonlinear coupling between attitudes of central body and solar panels, especially the rotation of central body is considered in space. The dynamics model is based for dynamics analysis and control, and the multistage solar panels means the dynamics modeling will be very complex. In this research, the Lie group variational integrator method is introduced, and the dynamics model of spacecraft with solar panels that connects together by flexible joints is built. The most obvious character of this method is that the attitudes of central body and solar panels are all described by three-dimensional attitude matrix. The dynamics models of spacecraft with one and three solar panels are established and simulated. The study shows Lie group variational integrator method avoids parameters coupling and effectively reduces difficulty of modeling. The obtained continuous dynamics model based on Lie group is a set of ordinary differential equations and equivalent with traditional dynamics model that offers a basis for the geometry control.
Accepted Manuscript , doi: 10.1016/j.taml.2018.06.008
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Mean sea level rise and climatological wind speed changes occur as part of the ongoing climate change and future projections of both variables are still highly uncertain. Here the Baltic Sea's response in extreme sea levels to perturbations in mean sea level and wind speeds is investigated in a series of simulations with a newly developed storm surge model based on NEMO-Nordic. A simple linear model with only two tunable parameters is found to capture the changes in the return levels extremely well. The response to mean sea level rise is linear and nearly spatially uniform, meaning that a mean sea level rise of 1 m increases the return levels by a equal amount everywhere. The response to wind speed perturbations is more complicated and return levels are found to increase more where they are already high. This behaviour is alarming as it suggests that already flooding prone regions like the Gulf of Finland will be disproportionally adversely affected in a future windier climate.
Accepted Manuscript , doi: 10.1016/j.taml.2018.06.009
[Abstract] (38) [FullText HTML] (23) [PDF 3096KB] (7)
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Head-on collision between two hydroelastic solitary waves propagating at the surface of an incompressible and ideal fluid covered by a thin ice sheet is analytically studied by means of a singular perturbation method. The ice sheet is represented by the Plotnikov-Toland model with the help of the special Cosserat theory of hyperelastic shells and the Kirchhoff-Love plate theory, which yields the nonlinear and conservative expression for the bending forces. The shallow water assumption is taken for the fluid motion with the Boussinesq approximation. The resulting governing equations are solved asymptotically with the aid of the Poincar \begin{document}$\acute{\rm{e}}$\end{document} -Lighthill-Kuo method, and the solutions up to the third order are explicitly presented. It is observed that solitary waves after collision do not change their shapes and amplitudes. The wave profile is symmetric before collision, and it becomes, after collision, unsymmetric and titled backward in the direction of wave propagation. The wave profile significantly reduces due to greater impacts of elastic plate and surface tension. A graphical comparison is presented with published results, and the graphical comparison between linear and nonlinear elastic plate models is also shown as a special case of our study.
Accepted Manuscript
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Abstract:
We study experimentally and theoretically the planar dynamics of purely rolling prisms on a rough ramp, where the rolling motion is interrupted intermittently by edge impacts. The experiments were carried out for prisms made of different materials and having different geometries. We found that the angular velocities of the rolling prisms are material-independent, but they change significantly with their geometry. We modelled the dynamics of edge impacts by considering a so-called detachment front propagating across the contact interface. The detachment front represents the moving boundary between a detached region and a stress region that coexist within the interface plane. The theoretical analysis indicates that the detachment front can be characterized by a scale number, whose value converges to 0.4050 for prisms having large number of edges. A new jump rule for edge impacts is then developed, by which we can accurately reproduce the experimental observations, and explain why the motion of the prism is material-independent.
Accepted Manuscript
[Abstract] (48) [FullText HTML] (29) [PDF 2874KB] (13)
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The specific sign of Reynolds stress in the boundary layer on a flat plate at zero incidence is newly interpreted in present paper based on the theory of vortex-induced vortex. It avoids some problems appeared in a traditional explanation, on the basis of relationship between mean and fluctuating flows due to the transport of momentum. Through the analysis of local flow field in the immediate neighborhood of wall, the characteristics of Reynolds stress are identified through introducing turbulence-induced small-scale streamwise eddies above the flat plate. The positive Reynolds stress is theoretically verified. And such new interpretation illustrates that the generation of Reynolds stress, as well as fluctuating velocity, is intrinsically independent of the mean flow. But its specific sign would be determined by the mean flow due to the inertial forces. Other features, such as the intensity relationship among three components of fluctuating velocity, are also presented.
Accepted Manuscript
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This paper presents a simple nonparametric regression approach to data-driven computing in elasticity. We apply the kernel regression to the material data set, and formulate a system of nonlinear equations solved to obtain a static equilibrium state of an elastic structure. Preliminary numerical experiments illustrate that, compared with existing methods, the proposed method finds a reasonable solution even if data points distribute coarsely in a given material data set.
Accepted Manuscript
[Abstract] (39) [FullText HTML] (21) [PDF 2433KB] (10)
Abstract:
The current structure-preserving theory, including the symplectic method and the multi-symplectic method, pays most attention on the conservative properties of the continuous systems because that the conservative properties of the conservative systems can be formulated in the mathematical form. But, the nonconservative characteristics are the nature of the systems existing in engineering. In this letter, the structure-preserving approach for the infinite dimensional nonconservative systems is proposed based on the generalized multi-symplectic method to broaden the application fields of the current structure-preserving idea. In the numerical examples, two nonconservative factors, including the strong excitation on the string and the impact on the cantilever, are considered respectively. The vibrations of the string and the cantilever are investigated by the structure-preserving approach and the good long-time numerical behaviors as well as the high numerical precision of which are illustrated by the numerical results presented.
Uncorrected proof , doi: 10.1016/j.taml.2018.06.003
[Abstract] (46) [FullText HTML] (32) [PDF 2795KB] (9)
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The dynamic behavior of two-dimensional nanostructures is important to the future application of nano devices. The vibrational behaviors of single-layered hexagonal boron nitride (h-BN) are studied by molecular dynamics simulation and continuum plate model. The bending stiffness and Poisson’s ratios of h-BN along zigzag direction and armchair direction are calculated. H-BN is softer compared with graphene. The continuum plate model can predict the vibration of h-BN with four edge-clamped boundary conditions well. The electric fields in different directions have obvious influence on the vibration of h-BN. The natural frequency of h-BN changes linearly with the electric field intensity along the polarization direction. The natural frequency of h-BN decreases with the increase of electric field intensity along both positive and negative non-polarization direction. While the natural frequency of h-BN increases with the increase of electric field intensity along both positive and negative transverse electric field.
Uncorrected proof , doi: 10.1016/j.taml.2018.06.001
[Abstract] (67) [FullText HTML] (25) [PDF 3879KB] (7)
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The linear and nonlinear dynamic responses of a vibratory ring gyroscope are investigated in this study focusing on the response mechanism of such a vibratory gyroscope. It is found that the nonlinear equations governing the drive and sense directions are coupled through both inertial linear and geometric nonlinear terms. Nonlinear responses are studied based on the full coupled nonlinear dynamic equations. The varying amplitude on the sense direction is analyzed for different input angular rates. The effect of nonlinearity on the ring gyroscope system is performed by comparing the results of nonlinear responses to those of linear responses. The contributions of some parameters to the amplitude responses and gyroscope sensitivity are analyzed, the conclusions of which provide guidelines to improve the sensitivity of the vibratory ring gyroscopes.

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2018, 8(5): 299 -303.   doi: 10.1016/j.taml.2018.05.007
[Abstract] (141) [FullText HTML] (54) [PDF 3697KB] (27)
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The pore configuration in porous medium is assumed to be the randomly distributed cube-like particles which can overlap each other in the periodic cubic domain, and the impact of particle characteristics on the percolation property of these cube-like particle packing systems is analyzed. Firstly, by combining the percolation models and finite-size scaling analysis, three numerical parameters (i.e., percolation transition width \begin{document}$\Delta$\end{document} L, local percolation threshold \begin{document}$\psi$\end{document} c(L), and correlation length exponent \begin{document}$\nu$\end{document} ) for the cube-like particle systems with shape parameter s in [1.0, \begin{document}$+\infty$\end{document} ] are derived successively. Then, based on the relation between the percolation threshold \begin{document}$\psi$\end{document} c in infinite space and the local percolation threshold \begin{document}$\psi$\end{document} c(L), the corresponding \begin{document}$\psi$\end{document} c with s in [1.0, \begin{document}$+\infty$\end{document} ] are further determined. It is shown from the study that the characteristics of cube-like particles have significant influence on the global percolation threshold \begin{document}$\psi$\end{document} c of the particle packing systems. As the parameter s increases from 1.0 to \begin{document}$+\infty$\end{document} , the percolation threshold \begin{document}$\psi$\end{document} c will go down persistently. When the surface of cube-like particles is cubical and spherical, respectively, the minimum and maximum thresholds \begin{document}$\psi$\end{document} c,min and \begin{document}$\psi$\end{document} c,max are obtained.
2018, 8(5): 304 -314.   doi: 10.1016/j.taml.2018.05.005
[Abstract] (75) [FullText HTML] (37) [PDF 4189KB] (4)
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Traffic rule is a key factor affecting traffic flow and safety. We develop our models, including the cellular automata traffic flow model as well as the linear regression one, aiming at calculating traffic flow and evaluating safety conditions with varied traffic rules. Then, we thoroughly investigate four types of paths in a freeway, namely two straight lanes, three straight lanes, ramps, and roundabouts as case studies and discuss the different traffic rules as comparison. The results demonstrate that " Keep-Right-Except-To-Pass” rule is not as effective as the free rule in promoting traffic flow; however, this rule ensures safety for drivers better than the free rule. Additionally, a new traffic rule, which sets different posted speed limits for adjacent lanes, is proposed to promote better traffic flow with safety requirements satisfied. Furthermore, we apply effective rules and alternatives, left driving norms as well as intelligent system as extension and obtain better results. Finally, model’s sensitivity analysis regarding to probability of decelerating and posted speed limits proves the stability of our results.
2018, 8(5): 315 -319.   doi: 10.1016/j.taml.2018.05.002
[Abstract] (105) [FullText HTML] (56) [PDF 2589KB] (10)
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Dropshafts are vertical structures widely used in urban drainage systems and buildings for water transportation. In this paper, a physical model study was conducted to investigate the air entrainment in the dropshaft under various flow regimes with and without air ventilation. Observed from the experiments, the air entrainment mechanisms varied with the water flow regimes in the dropshaft. When there was no water plug formed in the dropshaft, air could be supplied directly from downstream. Once the water plug was formed, while without venting, the air was replenished only from downstream intermittently and then in the form of large air bubble traveling upwards to the airspace at the top; while with venting, air was mainly replenished from the dropshaft top and no large air bubble was observed. The experimental results also showed that the amount of entrained air in the dropshaft with venting was greater than that without venting.
2018, 8(5): 320 -325.   doi: 10.1016/j.taml.2018.05.006
[Abstract] (106) [FullText HTML] (47) [PDF 3252KB] (6)
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The intrinsic physical relationship of vorticity between modes A and B in the three-dimensional wake transition is investigated. Direct numerical simulations for the flow past a square-section cylinder are carried out at Reynolds numbers of 180 and 250, associated with modes A and B, respectively. Based on the analysis of spacial distributions of vorticity in the near wake, characteristics of the vertical vorticity in modes A and B are identified. Moreover, the relationship of three vorticity components with specific signs is summarized into two sign laws, as intrinsic physical relationships between two instability modes. By the theory of vortex-induced vortex, such two sign laws confirm that there are two and only two kinds of vortex-shedding patterns in the near wake, just corresponding to modes A and B. In brief, along the free stream direction, mode A can be described by the parallel shedding vertical vortices with the same sign, while mode B is described by the parallel shedding streamwise vortices with the same sign. Finally, it is found out that the \begin{document}$\Pi$\end{document} -type vortex is a basic kind of vortex structure in both modes A and B.
2018, 8(5): 326 -333.   doi: 10.1016/j.taml.2018.05.003
[Abstract] (76) [FullText HTML] (37) [PDF 2728KB] (7)
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Lattice Boltzmann method is one of the widely used in multiphase fluid flow. However, the two main disadvantages of this method are the instability of numerical calculations due to the large density ratio of two phases and impossibility of the temperature distribution to be fed back into the velocity distribution function when the temperature is simulated. Based on the combination prescribed by Inamuro, the large density ratio two-phase flow model and thermal model makes the density ratio of the model simulation to be increased to 2778:1 by optimizing the interface distribution function of two-phase which improves the accuracy of differential format. The phase transition term is added as source term into the distribution function controlling two phase order parameters to describe the temperature effect on the gas-liquid phase transition. The latent heat generated from the phase change is also added as a source term into the temperature distribution function which simulates the movement of the flow under the common coupling of density, velocity, pressure and temperature. The density and the temperature distribution of single bubble are simulated. Comparison of the simulation results with experimental results indicates a good agreement pointing out the effectiveness of the improved model.
2018, 8(5): 334 -344.   doi: 10.1016/j.taml.2018.05.004
[Abstract] (177) [FullText HTML] (58) [PDF 4235KB] (17)
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A visualized investigation was carried out on the effect of the diverging angle on the bubble motion and interfacial behavior in a Venturi-type bubble generator. It was found two or three large vortexes formed in the diverging section, resulting in strong reentrant jet flow in the front of the bubbles or slugs rushing out of the throat. The jet flow in return bumps into the ongoing bubbles or slugs, leading to strong interaction between the gas and liquid phases. The diverging angle has significant influence on the reentrant flow process and the performance of the bubble generator as well. Increasing the diverging angle results in the reentrant flow moving further forward to the upstream and intensifies the interaction between the two phases. As a consequence, the breakup or collapse of bubbles becomes more violent, whereby finer bubbles are generated. As such, the reentrant flow strongly links to the performance of the Venturi channel taken as a bubble generator, and that a moderate increase in the diverging angle can improve its performance without additional increase in flow resistance like that by increasing liquid flow rate.
2018, 8(5): 351 -354.   doi: 10.1016/j.taml.2018.05.008
[Abstract] (59) [FullText HTML] (40) [PDF 2386KB] (7)
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We solve the local uniaxial tension of an infinite rod in the framework of non-ordinary state-based peridynamics. The singular solutions of stress and displacement are acquired. When the influencing range of the window function approaches zero, these two solutions will return to the solutions of the classical elasticity. The analysis shows that the singularities of the solutions stem from such a feature of the window function that must be represented by a rapidly decreasing function in physics. Contrary to the classical elasticity, the stress solution of peridynamics is smoother than the displacement solution. In addition, a criterion used to select the window function is proposed in this paper.
2018, 8(5): 355 -360.   doi: 10.1016/j.taml.2018.05.001
[Abstract] (78) [FullText HTML] (46) [PDF 3503KB] (3)
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Reaction-diffusion (RD) equation was often used to investigate the pattern dynamics, but telegraph reaction-diffusion (TRD) system was seldom studied. In this paper, the Izhikevich model was modified to explain some biological mechanisms by RD and TRD in neuronal cluster. Then a new condition under which the system loses stability was proposed and the effect of parameters, diffusion, memory and steady state were considered on the process of neuronal spiking. The method presented is a novel approach to investigate the pattern dynamics of biological systems. Finally, simulations are carried out to validate our theoretical results.
2018, 8(5): 345 -350.   doi: 10.1016/j.taml.2018.05.009
[Abstract] (116) [FullText HTML] (37) [PDF 2807KB] (6)
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This letter reports inlet flow disturbance effects on direct numerical simulation of incompressible round jet at Reynolds number 2500. The simulation employs an accurate projection method in which a sixth order biased upwind difference scheme is used for spatial discretization of nonlinear convective terms, with a fourth order central difference scheme used in the discretization of the divergence of intermediate velocity. Carefully identifying reveals that the inlet flow disturbance has some influences on the distribution pattern of mean factor of swirling strength intermittency. With the increase of inlet disturbance magnitude jet core cone slightly shortens, observable differences occur in the centerline velocity and its fluctuations, despite the negligible impacts on the least square fitted centerline velocity decay constant (Bu) and distribution parameter (Ku) for velocity profile in self-similar region.
2018, 8(3): 153-159   doi: 10.1016/j.taml.2018.03.002
[Abstract](288) [FullText HTML](125) [PDF 4354KB](38)
2018, 8(4): 252-256   doi: 10.1016/j.taml.2018.04.006
[Abstract](219) [FullText HTML](112) [PDF 2725KB](37)
2018, 8(4): 245-251   doi: 10.1016/j.taml.2018.04.001
[Abstract](337) [FullText HTML](112) [PDF 2758KB](31)
2018, 8(5): 299-303   doi: 10.1016/j.taml.2018.05.007
[Abstract](141) [FullText HTML](54) [PDF 3697KB](27)
2018, 8(3): 143-146   doi: 10.1016/j.taml.2018.03.006
[Abstract](213) [FullText HTML](124) [PDF 2524KB](23)
2018, 8(3): 147-152   doi: 10.1016/j.taml.2018.03.001
[Abstract](171) [FullText HTML](96) [PDF 3225KB](18)
2018, 8(5): 334-344   doi: 10.1016/j.taml.2018.05.004
[Abstract](177) [FullText HTML](58) [PDF 4235KB](17)
2018, 8(6): 1-6
[Abstract](48) [FullText HTML](29) [PDF 2874KB](13)
2018, 8(4): 272-276   doi: 10.1016/j.taml.2018.04.003
[Abstract](234) [FullText HTML](111) [PDF 2758KB](13)
2018, 8(4): 231-244   doi: 10.1016/j.taml.2018.04.008
[Abstract](221) [FullText HTML](86) [PDF 4064KB](13)