Search results

In FEM computations, the mesh quality improves the accuracy of the approximation solution and reduces the computation time. The dynamic bubble system meshing technique can provide high-quality meshes, but the packing process is time-consuming. This paper aims to improve the running time of the bubble meshing by using the advantages of parallel computing on graphics processing unit (GPU).

This paper is based on the analysis of the processing time on CPU. A massively parallel computing-based CUDA architecture is proposed to improve the bubble displacement and database updating. Constraints linked to hardware considerations are taken into account. Finally, speedup factors are provided on test cases and real scale examples.

The numerical experiences show the efficiency of parallel performance reaches a speedup of 35 compared to the serial implementation.

This contribution is so far limited to two-dimensional (2D) geometries although the extension to three-dimension (3D) is straightforward regarding the meshing technique itself and the GPU implementation. The authors’ works are based on a CUDA environment which is widely used by developers. C\C++ and Java were the programming languages used. Other languages may of course lead to slightly different implementations.

This approach makes it possible to use bubble meshing technique for both initial design and optimization, as excellent meshes can be built in few seconds.

Compared to previous works, this contribution shows that the scalability of the bubble meshing technique needs to solve two key issues: reach a T(N) global cost of the implementation and reach a very fast size map interpolation strategy.

The purpose of this paper is to research the interaction between multiple bubbles and their noise radiation considering the influence of compressibility. The influences of bubble spacing, initial inner pressure, buoyance and phase difference are presented with different bubbles arrangements.

Based on wave equation, the new boundary integral equation considering the compressibility is given by the matching between prophase and anaphase approximation of bubble motion and solved with boundary element method. The time-domain characteristics of noise induced by multiple bubbles are obtained by the moving boundary Kirchhoff integral equation. With the surface discretization and coordinate transformation, the bubbles surface is treated as a moving deformable boundary and noise source, and the integral is implemented on the surface directly.

Numerical results show the manner of jet generation will be affected by the phase difference between bubbles. With the increasing of phase difference, the directive property of noise becomes obvious. With the enlargement of initial inner pressure, the sound pressure will arise at the early stage of expanding, and the increasing of buoyance parameter will reduce the sound pressure after the generation of jet. Since the consideration of compressibility, the oscillation amplitude of bubbles will be weakened.

The paper could provide the reference for the research about the dynamics and noise characteristics of multiple bubbles in compressible fluid. And the new method based on boundary integral equation to simulate the multiple bubbles motion and noise radiation is presented.

The discussion of how to manage air‐quality in a heavily polluted area like Los Angeles (LA), California, in an era of shrinking public budgets and a trend towards deregulation has led to the introduction of a new environmental policy tool: a tradeable emission permit approach (the so called RECLAIM‐program) to reduce SO_x‐ and NO‐emissions from stationary sources was introduced in 1994. This paper is an attempt to analyze and evaluate the first three years of the program, based on the official three year program audit (SCAQMD, 1998) and on a written company survey and personal interviews with experts, as well as administrators active in air quality management in Los Angeles (conducted by the authors between May 1996 and May 1998).

Social network platforms are considered today as a major communication mean. Their success leads to an unprecedented growth of user-generated content; therefore, finding interesting content for a given user has become a major issue. Recommender systems allow these platforms to personalize individual experience and increase user engagement by filtering messages according to user interest and/or neighborhood. Recent research results show, however, that this content personalization might increase the echo chamber effect and create filter bubbles that restrain the diversity of opinions regarding the recommended content.

The purpose of this paper is to present a thorough study of communities on a large Twitter data set that quantifies the effect of recommender systems on users’ behavior by creating filter bubbles. The authors further propose their community-aware model (CAM) that counters the impact of different recommender systems on information consumption.

The authors propose their CAM that counters the impact of different recommender systems on information consumption. The study results show that filter bubbles effects concern up to 10% of users and the proposed model based on the similarities between communities enhance recommendations.

The authors proposed the CAM approach, which relies on similarities between communities to re-rank lists of recommendations to weaken the filter bubble effect for these users.

This article identifies the institutional factors behind both the emergence of a highly vulnerable financial system and the housing bubble that devastated it. The underlying premise is that the financial crisis was a market failure embedded in and caused by an institutional one. The failing institutions were academic, political and regulatory. The article shows how these institutions were fatally undermined, suggesting limits to the rationalization of finance capitalism. The perspective on financial crisis developed here recognizes the pressing need for reform of the financial markets, and also recommends institutional reforms as critical protections against future system failure.

The global financial and economic crisis resulting from the US housing crisis has shown that house prices can have far-reaching consequences for the real economy. For macroprudential supervision, it is, therefore, necessary to identify house price bubbles at an early stage to counteract speculative price developments and to ensure financial market stability. This paper aims to develop an early warning system to signal speculative price bubbles.

The results of explosivity tests are used to identify periods of excessive price increases in 18 industrialized countries. The early warning system is then based on a logit and an ordered logit regression, in which monetary, macroeconomic, regulatory, demographic and private factors are used as explanatory variables.

The empirical results show that monetary developments have the highest explanatory power for the existence of house price bubbles. Further, the study reveals currently emerging house price bubbles in Norway, Sweden and Switzerland.

The results implicate a new global housing boom, particularly in those countries that did not experience a major price correction during the global financial crisis.

The ordered logit model is an advanced approach that offers the advantage of being able to differentiate between different phases of a house price bubble, thereby allowing a multi-level assessment of the risk of speculative excesses in the housing market.

Modern CAD systems facilitate the creation of any surface geometry imaginable, and complex surfaces for free-form grid shells are often represented by a set of Non-Uniform Rational B-Splines surface patches. But it remains an intractable issue how to generate high-quality grids on complex surfaces efficiently. To solve this issue, an automatic triangular mesh generation method is presented, based on bubble dynamics simulation and a modified Delaunay method.

A moderate amount of points are first distributed on a given surface. Next, by regarding the points as elastic bubbles with the same size and introducing the forces acting on bubbles, the motion control equations of bubbles are established. The equilibrium state of the bubble system is found by Verlet algorithm. Then, the Voronoi diagram on the surface is obtained by calculating the intersection between the surface and the three-dimensional (3D) Voronoi diagram of the centers of bubbles. Finally, a triangular mesh, Delaunay triangulation on the surface, is determined based on the dual change of the Voronoi diagram.

This method generates meshes on the surface directly, unlike mapping-based methods, avoiding the mapping distortion. Examples are given to demonstrate the successful execution of this method. The result also illustrates that this method is applicable to various surfaces in high automation level and resultant meshes are highly uniform and well-shaped.

Thus, this method provides the convenience for the geometry design of complex free-form grid structure.

The purpose of this paper is to present numerical investigation of the gas/vapor bubble dynamics under the influence of an ultrasonic field to give a more comprehensive understanding of the phenomenon and present new results

In order to formulate the mathematical model, a set of governing equations for the gas inside the bubble and the liquid surrounding it are used. All hydrodynamics forces acting on the bubble are considered in the typical solution. The systems of equations required to be solved consist of ordinary and partial differential equations, which are both nonlinear and time dependent equations. A fourth order Runge-Kutta method is applied to solve the ordinary differential equations. On the other hand, the finite difference method is employed to solve the partial differential equations and a time-marching technique is applied.

The numerical model which is developed in the current study permits a correct prediction of the bubble behavior and its characteristics in an acoustic field generated at this occasion.

Previous studies considering numerical simulations of an acoustic bubble were performed based on the polytropic approximation or pressure uniformity models of the contents inside the bubble. In this study, an enhanced numerical model is developed to study the acoustic cavitation phenomenon and the enhancement concerns taking into account both the pressure and temperature gradients inside the bubble as well as heat transfer through the bubble surface into account which is very important to obtain the temperature of the liquid surrounding the bubble surface.

This paper aims to develop a numerical method for analysing the time‐dependent conjugate heat and fluid flows inside and around single bubbles rising in a hot liquid.

The procedure combines the moving mesh method for flows in time‐dependent geometries and the zoned calculation algorithm for conjugate viscous flows. A moving axisymmetric boundary‐fitted mesh is used to track the deformable gas‐liquid interface, while conjugate flows in both gas and liquid sides are calculated by a two‐block zoned method. The interfacial stresses are employed to calculate the velocity value and to decide the time‐dependent bubble shape simultaneously. Governing equations for the rising velocity and acceleration of the bubble are derived according to the forces acting on the bubble.

A calculating procedure for time‐dependent conjugate heat and fluid flows inside and around a rising single bubble has been developed. The algorithm has been verified, and can be employed for further analysing heat, mass and momentum transfer phenomena and their relevant mechanisms.

The paper developed a method to obtain high fidelity results for the heat and fluid flow details in the vicinity of a time‐dependent moderately deformable rising bubble; the physically zero‐thickness of a gas‐liquid interface is guaranteed. The governing equations for the time‐dependent rising velocity and acceleration are derived.

Cavitation bubbles cannot be avoided in the hydraulic system. Because of instability of flow and variation of water pressure, the jet often occurs in a bubble collapse. This study aims to accurately predict the shape, velocity and time of the resulting jet, so as to inhibit cavitation erosion.

In the study, a theoretical model of cavitation bubbles in the water has been developed by applying a periodic water film pressure into the Rayleigh–Plesset equation. A fourth-order in time Runge–Kutta scheme is used to obtain an accurate computation of the bubble dynamic characteristics. The behavior of the proposed theory is further simulated in a high-speed photography experiment by using a cavitation bubble test rig. The evolution with time of cavitation bubbles is further obtained.

A comparison with the available experimental results reveals that the bubble evolution with time has a duration of about 0.3T0, that well predicts the expanding and compressing process of cavitation bubbles. The results also show that the initial bubble radius in the water influences the moving velocity of the bubble wall, whereas the perturbation frequency of the water pressure has less effect on the velocity of the bubble wall.

A theoretical model well predicts dynamic characteristics of cavitation bubbles. The bubble evolution with time has a duration of about 0.3T0, Initial bubble radius influences the velocity of bubble wall. Perturbation frequency has less effect on the velocity of bubble wall.