6,687 research outputs found
An improved moving particle semi-implicit method for dam break simulation
Dam break is quite a common and hazard phenomenon in shipbuilding and ocean engineering. The objective of this study is to investigate dam break hydrodynamics with improved Moving Particle Semi-implicit method (MPS). Compared to traditional mesh methods, MPS is feasible to simulate surface flows with large deformation, however, during the simulation, the pressure oscillates violently, due to misjudgment of surface particles as well as particles gathering together. To modify these problems, a new arc method is applied to judge free surface particles, and a collision model is introduced to avoid particles from gathering together. Hydrostatic pressure is simulated by original and improved MPS. The results verify that improved MPS method is more effective. Based on these, dam break model is investigated with improved MPS
Constraining f(R) gravity in solar system, cosmology and binary pulsar systems
The gravity can be cast into the form of a scalar-tensor theory, and
scalar degree of freedom can be suppressed in high-density regions by the
chameleon mechanism. In this article, for the general gravity, using a
scalar-tensor representation with the chameleon mechanism, we calculate the
parameterized post-Newtonian parameters and , the effective
gravitational constant , and the effective cosmological constant
. In addition, for the general gravity, we also
calculate the rate of orbital period decay of the binary system due to
gravitational radiation. Then we apply these results to specific models
(Hu-Sawicki model, Tsujikawa model and Starobinsky model) and derive the
constraints on the model parameters by combining the observations in solar
system, cosmological scales and the binary systems.Comment: LaTex, 19 pages,1 figure, typo corrected. To appear in Physics
Letters
Vibration problem of a spherical tank containing jet propellant: numerical simulations
This document is the final report on the joint research project on vibration problem of a spherical tank containing jet propellant between IHI, Japan and SES, University of Southampton, UK. The background of the project is described. The fundamental principles and numerical method used in numerical simulations are presented. The detailed FEA models for each studied cases are given. The calculation results are presented using tables, curves, figures as well as the attached data files. The available experiment results are listed to compare with the numerical calculations. The calculation results show a fundamental agreement with the experiment results. The numerical analysis confirms that:1)Due to water โ tank interaction, the natural frequencies of the water โ tank system are decreased with the water level increase. For the 25% water level, the natural frequencies, especially heave mode frequency, shows a significant decrease compared with the empty case. However, with continuing increase the filed water more than 25% level, the decrease gradient of the natural frequencies gradually tends to zero. In the 100% water case, the natural frequency of heave mode is about 200 Hz which can not equal zero.2)Considering free surface wave effect produces a lot of sloshing modes of very low frequencies compared with the natural frequencies of the dry tank structure. Therefore, for dynamic response analysis with high frequency excitations, the free surface wave may be neglected. However, to assess loads caused by sloshing modes, the free surface waves have to be considered.3)There exist relative big deformations at the four tank support places in several vibration modes, which may produce a large local stress at support places to cause the product fail in vibration environment. A strengthen local design at the support places is needed.4)The dynamic response results are affected by damping coefficients of all modes used in the dynamic response analysis. The damping coefficients are approximately presented and therefore, the numerical results are good reference for practical designs.The report confirms that the original purpose of this joint research project has well completed by IHI and SES
Boron Nitride Nanosheets for Metal Protection
Although the high impermeability of graphene makes it an excellent barrier to
inhibit metal oxidation and corrosion, graphene can form a galvanic cell with
the underlying metal that promotes corrosion of the metal in the long term.
Boron nitride (BN) nanosheets which have a similar impermeability could be a
better choice as protective barrier, because they are more thermally and
chemically stable than graphene and, more importantly, do not cause galvanic
corrosion due to their electrical insulation. In this study, the performance of
commercially available BN nanosheets grown by chemical vapor deposition as a
protective coating on metal has been investigated. The heating of the copper
foil covered with the BN nanosheet at 250 {\deg}C in air over 100 h results in
dramatically less oxidation than the bare copper foil heated for 2 h under the
same conditions. The electrochemical analyses reveal that the BN nanosheet
coating can increase open circuit potential and possibly reduce oxidation of
the underlying copper foil in sodium chloride solution. These results indicate
that BN nanosheets are a good candidate for oxidation and corrosion protection,
although conductive atomic force microscopy analyses show that the
effectiveness of the protection relies on the quality of BN nanosheets.Comment: With Supporting Informatio
Online-offline activities and game-playing behaviors of avatars in a massive multiplayer online role-playing game
Massive multiplayer online role-playing games (MMORPGs) are very popular in
China, which provides a potential platform for scientific research. We study
the online-offline activities of avatars in an MMORPG to understand their
game-playing behavior. The statistical analysis unveils that the active avatars
can be classified into three types. The avatars of the first type are owned by
game cheaters who go online and offline in preset time intervals with the
online duration distributions dominated by pulses. The second type of avatars
is characterized by a Weibull distribution in the online durations, which is
confirmed by statistical tests. The distributions of online durations of the
remaining individual avatars differ from the above two types and cannot be
described by a simple form. These findings have potential applications in the
game industry.Comment: 6 EPL pages including 10 eps figure
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